JP2006146029A - Transparent protective layer, light diffusion plate for backlight, backlight device and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent protective layer of a light diffusing plate for backlight capable of suppressing yellowing of the light diffusing plate due to light irradiation. <P>SOLUTION: The transparent protective layer comprising acrylic resin composition etc. is stacked on the light source side of the light diffusing plate for backlight. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a transparent protective layer, and more particularly to a transparent protective layer to be arranged on the light source side of a light diffusion plate for a backlight. The transparent protective layer of the present invention can be particularly suitably used as a protective film for a light diffusion plate for a direct type backlight.

  The liquid crystal display device includes, for example, a liquid crystal panel made of TN liquid crystal and a light source (backlight) that emits light from behind the panel, and uses the light from the light source to display a desired image on the front surface of the panel. Form. The backlight is roughly classified into a side type and a direct type according to the arrangement of the light source including a cold cathode tube. Regardless of the type of backlight as described above, any type of liquid crystal display device is required to improve the luminance on the panel by suppressing loss in the light transmission path from the light source to the panel.

  In recent years, in the liquid crystal display device, the demand for a liquid crystal television having a large screen exceeding 15 inches, a display for a PC, and the like has increased dramatically. As such a large flat light emitting device, a direct type backlight is used. The case where is used is increasing. The direct type backlight is constructed by arranging a plurality of lamps (cold cathode tubes) behind the diffuser plate and above the reflecting surface. Since the lamps can be arranged immediately behind the light emitting surface, a large number of lamps are installed. This is because it can be used and it is easy to obtain high luminance and is suitable for increasing the size of high luminance. In addition, the direct type is suitable for increasing the size of the high brightness because the inside of the apparatus has a hollow structure and is light even if the size is increased.

  As described above, the direct type backlight is configured by arranging a plurality of lamps (cold cathode fluorescent lamps) behind a light diffusion plate made of a synthetic resin such as acrylic or polycarbonate and emitting light. A large number of lamps can be used because the lamp can be placed directly behind the surface, and it is easy to obtain high brightness even when the size is increased. In addition, the direct type is suitable for increasing the size of the high brightness because the inside of the apparatus has a hollow structure and is light even if the size is increased.

  Various light diffusing plates used in the direct type backlight have been proposed and put to practical use. Among these, a light diffusion plate for direct-type backlight made of polycarbonate resin for surface-emitting large-sized liquid crystal display devices has been proposed (see Patent Document 1). This light diffusing plate for a direct backlight of a polycarbonate resin for a surface-emitting large-sized liquid crystal display device has little warpage, has excellent surface light-emitting properties, has little luminance unevenness on the light-emitting surface, and is excellent in color tone.

  Moreover, the light diffusing plate which consists of an aromatic polycarbonate resin composition is also proposed (refer patent document 2). This light diffusing plate has high light transmissivity, good light diffusibility, and less unevenness of transmitted light in a minute region.

  However, in these light diffusion plates, the light from the cold-cathode tube or the like is directly irradiated to the light diffusion plate, so that the polycarbonate resin turns yellow, adversely affects the color tone in the color liquid crystal display, decreases the light emission quality, and shortens the life. There was a problem. In addition, when a large direct-type backlight is to be used to ensure high brightness, the display screen is large, so it is necessary to use a large number of lamps. There are problems such as adversely affecting the color tone of the film, decreasing the light emission quality, and shortening the service life.

  On the other hand, a light guide that does not deteriorate due to light from the light source, and a lighting device, that is, a light guide having an ultraviolet absorbing film formed on the light source side of a transparent light guide, and a lighting device have been proposed (Patent Literature). 3). Although this ultraviolet absorbing film shows a certain degree of deterioration suppressing effect, there is no description of the specific amount of titanium oxide. For example, when the amount of titanium oxide is increased, the transparency of the ultraviolet absorbing film is lowered and it is directed to the outside. There was a problem that the amount of emitted light decreased. In addition, when the amount of titanium oxide is reduced, the amount of light radiated to the outside is maintained, but it is difficult to say that it has a sufficient effect for suppressing deterioration of the light guide, and it is further highly transparent and deteriorates. Development of a transparent protective layer having a high suppression effect has been desired.

  On the other hand, various types of transparent protective layers for protecting the substrate have been proposed so far. In particular, the protective layer made of acrylic resin is laminated on the surface of various resin molded products, woodwork products, and metal molded products, taking advantage of its excellent transparency, light resistance, flexibility, and workability. Is being used. Specific examples of the application include skin materials for vehicle interiors, furniture, door materials, window frames, baseboards, bathroom interiors, and other building materials, marking films, high-intensity reflector coating films, and the like. Such a transparent protective layer for protecting a substrate has been used as an outer skin of a molded product or the like so far.

JP 2004-126185 A JP-A-9-281309 JP 2003-272427 A

  The objective of this invention is providing the transparent protective layer of the light diffusing plate for backlights which can suppress the yellowing of the light diffusing plate by irradiation of light.

  In view of the conventional problems as described above, the present inventors have conducted extensive studies on a transparent protective layer for protecting a light diffusing plate to be used in a backlight such as a direct type. It was found that by arranging a transparent protective layer on the light source side of the light diffusing plate to be used in (1), yellowing of the light diffusing plate due to light irradiation can be suppressed, and the present invention has been achieved.

  That is, this invention is a transparent protective layer which should be laminated | stacked on the light source side of the light diffusing plate for backlights.

  The transparent protective layer of this invention is laminated | stacked on the light source side of the light diffusing plate which should be used for backlights, such as a direct type. By laminating the transparent protective layer of the present invention on the light source side of a light diffusing plate used for, for example, a direct type backlight or the like, yellowing of the light diffusing plate due to light irradiated from a light source such as a cold cathode tube is reduced. The liquid crystal display device using this can be improved in color display and quality.

  As described above, since the transparent protective layer of the present invention is laminated on the light source side of the light diffusing plate and suppresses discoloration of the light diffusing plate, a liquid crystal display having a backlight using the same. An apparatus (for example, one having a direct type backlight) can maintain the color tone and light emission quality in color display for a long time.

  According to the aspect in which the total light transmittance of the transparent protective layer of the present invention is 80% or more, the light from the light source is efficiently transmitted when used as the transparent protective layer of the light diffusion plate. The display device further improves the light emission quality.

  According to the aspect in which the tensile elastic modulus when the transparent protective layer of the present invention is independently tested for tensile properties is 500 MPa or more and 3000 MPa or less, wrinkles or the like are difficult to enter when laminated on the light diffusion plate, and the appearance of the light diffusion plate Becomes even better.

  When the multilayer structure polymer used in the transparent protective layer of the present invention is dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion is 0 to 50 per 100 g of the multilayer structure polymer. According to the aspect which is the range, when it is made into a film, the fisheye is reduced and the appearance is good, and the appearance of the light diffusion plate on which the transparent protective layer is laminated is also good.

  Hereinafter, the present invention will be described more specifically.

<Light diffusion plate>
The material of the light diffusing plate on which the transparent protective layer of the present invention is to be laminated is not particularly limited. For example, when the light diffusing plate is made into a sheet, a plate-like body or the like, it is particularly limited as long as it is transparent, has a high light transmittance, a low birefringence, and can be easily laminated with a transparent protective layer. All known ones can be used without any problem. From the viewpoint that the characteristics (for example, yellowing prevention) of the transparent protective layer of the present invention can be suitably exhibited, it is preferable to apply the transparent protective layer to a light diffusing plate for a direct type backlight, but other types Of course, even if it is a light diffusing plate, the characteristic of the transparent protective layer of this invention can be utilized.

  More specifically, examples of the material of the light diffusion plate include methacrylic resin such as polymethyl methacrylate (PMMA), polycarbonate resin, MS resin (methyl methacrylate-styrene resin), polystyrene resin, polyvinyl chloride resin, polyester resin. And cyclic polyolefin resins. Among these, methacrylic resin and polycarbonate resin having high light transmittance can be preferably used as the light diffusion plate.

  In the above-mentioned resin, a transparent resin having light resistance, heat resistance and moisture resistance and having high light diffusibility when used as beads may be contained as required. Specific examples of such bead materials include acrylic resins, styrene resins, polyester resins, melamine resins, silicone resins, urethane resins, epoxy resins, polyethylene resins, nylon resins, norbornene resins, and other synthetic resins such as glass. An inorganic substance is mentioned.

<Lamination method>
The transparent protective layer of the present invention should be laminated on the light source side of a light diffusion plate for backlight (for example, a direct type). The method for laminating the transparent protective layer of the present invention is not particularly limited. The transparent protective layer of the present invention is, for example, known as a coextrusion T die method, a coextrusion method such as a coextrusion lamination method, a film lamination method such as dry lamination, thermal lamination, and a coating method such as coating a resin solution. It can be laminated on the light diffusion plate by appropriately using the method. Of course, any method applicable to the present invention other than these methods can be adopted. Of these, the coextrusion method and the film lamination method are preferred, and the film lamination method is particularly preferred, which can easily obtain a light diffusing plate having a simple and continuous and stable quality. From such a point, the transparent protective layer is preferably a film.

<Material of transparent protective layer>
The transparent protective layer of the present invention is used in the present invention without particular limitation as long as it prevents yellowing of the light diffusion plate due to light irradiated from the light source and does not substantially reduce the light transmitted through the light diffusion plate. be able to. The material is not particularly limited. For example, polyolefin resins such as polyethylene and polypropylene, polystyrene resins, polyvinyl chloride resins, polyvinyl acetate resins, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, norbornene And cyclic polyolefin resins such as polymers having monomers as derivatives thereof, polycarbonate resins, polysulfone resins, polyether sulfone resins, polyarylate resins, polyvinyl alcohol resins, polyurethane resins, polyacrylate resins Synthetic polymers such as acrylic resins such as polymethacrylate resins, and natural polymers such as cellulose resins such as cellulose diacetate and cellulose triacetate can be preferably used. The synthetic polymer may of course be a homopolymer of one kind of monomer, or may be a copolymer obtained by copolymerizing two or more kinds of monomers constituting each of the above resins. From the viewpoint of preventing yellowing of the light diffusion plate, an acrylic resin is particularly preferable.

<Acrylic resin>
The acrylic resin is not particularly limited, but the main raw material is at least one selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate and butyl methacrylate, and acrylic acid having an alkyl group having 1 to 8 carbon atoms as necessary. Examples thereof include a single polymer or a copolymer obtained by using ester, vinyl acetate, vinyl chloride, styrene, acrylonitrile, methacrylonitrile or the like as a copolymerization component. In addition, a multilayer structure polymer as described in JP-B-59-36646, JP-B-62-19309, JP-B-63-20459 and JP-A-63-77963 can be used. .

(Suitable acrylic resin)
A preferred acrylic resin that can be used in the transparent protective layer of the present invention is an acrylic resin containing a rubber-containing polymer mainly composed of acrylic (meth) acrylate. As such a rubber-containing polymer, for example, a multilayer structure polymer (I), a multilayer structure polymer (III), or a rubber-containing polymer (IV) described below is preferably used. Since the transparent protective layer containing these rubber-containing polymers has good light resistance and transparency, it can be suitably used as a protective layer for a light diffusion plate.

[Multilayer structure polymer (I)]
From the center, the multilayer structure polymer (I) is composed of the innermost layer polymer (IA), the first intermediate layer polymer (IB), the second intermediate layer polymer (IC), and the outermost layer polymer ( It is a multilayer structure polymer arranged in the order of ID).

  The innermost layer polymer (IA) includes at least an alkyl methacrylate (I-A1) having an alkyl group having 4 or less carbon atoms, an alkyl acrylate (I-A2) having an alkyl group having 8 or less carbon atoms, an aromatic A polymer obtained by polymerizing a vinyl monomer (I-A3) and a polyfunctional monomer (I-A4) and having a glass transition temperature of 10 ° C. or higher.

  The first intermediate layer polymer (IB) includes at least an alkyl acrylate (I-B1) having an alkyl group having 8 or less carbon atoms, an aromatic vinyl monomer (I-B2), and a polyfunctional monomer. It is a polymer having a glass transition temperature of 0 ° C. or lower, obtained by polymerizing (I-B3) and a graft crossing agent (I-B5).

  The second intermediate layer polymer (IC) is composed of alkyl methacrylate (I-C1) having an alkyl group having 4 or less carbon atoms, alkyl acrylate (I-C2) having an alkyl group having 8 or less carbon atoms, and aromatic vinyl. A polymer obtained by polymerizing a monomer (I-C3) and a graft crossing agent (I-C4), and the outermost layer polymer (ID) is an alkyl having an alkyl group having 4 or less carbon atoms. Glass transition temperature of 50 ° C. or higher obtained by polymerizing methacrylate (I-D1), alkyl acrylate (I-D2) having an alkyl group having 8 or less carbon atoms and aromatic vinyl monomer (I-D3) Is a polymer.

[Multilayer polymer (III)]
The multilayer structure polymer (III) is a multilayer structure polymer arranged in the order of the innermost layer polymer (III-A), the intermediate layer polymer (III-B), and the outermost layer polymer (III-C) from the center. is there.

  This innermost layer polymer (III-A) comprises an alkyl acrylate (III-A1) having an alkyl group having 8 or less carbon atoms, an alkyl methacrylate (III-A2) having an alkyl group having 4 or less carbon atoms, a graft crossing agent ( III-A5) is a polymer having a glass transition temperature lower than the glass transition temperature of the intermediate layer polymer (III-B) described later alone.

  The intermediate layer polymer (III-B) comprises an alkyl acrylate (III-B1) having an alkyl group having 8 or less carbon atoms, an alkyl methacrylate (III-B2) having an alkyl group having 4 or less carbon atoms, and a graft crossing agent ( III-B5), a polymer having a composition different from that of the innermost layer polymer (III-A), and a glass transition temperature in the range of 25 to 100 ° C.

  The outermost layer polymer (III-C) is a polymer having an alkyl methacrylate (III-C1) having an alkyl group having 4 or less carbon atoms, and is a polymer having a glass transition temperature of 60 ° C. or higher.

[Rubber-containing polymer (IV)]
Alkyl acrylate 35-100% by mass, copolymerizable monomer 100% by mass of at least one other copolymerizable vinyl monomer 0-65% by mass, and crosslinkable monomer 0.1-10 Another vinyl copolymerizable with 50 to 100% by mass of alkyl methacrylate in the presence of 100 parts by mass of an elastic copolymer having a structure of one layer or two or more layers obtained by polymerizing a monomer mixture composed of parts by mass It is a rubber-containing polymer having a latex particle diameter of 0.15 to 0.5 μm obtained by polymerizing 10 to 400 parts by mass of at least one monomer consisting of 0 to 50% by mass of a monomer or a mixture thereof. .

(Other suitable acrylic resins)
The acrylic resin that can be suitably used for the transparent protective layer of the present invention includes the above-mentioned multilayer structure polymer and / or rubber-containing polymer, and further a thermoplastic polymer (II) containing, as a main component, alkyl methacrylate as shown below. It may be used as a component. The transparent protective layer containing the thermoplastic polymer (II) has improved fluidity when forming a film, for example, as a transparent protective layer, stability of the film thickness, and further, when the film is laminated on a light diffusion plate In addition, wrinkles and the like are difficult to enter, and transparency is good, which is preferable from the viewpoint of appearance.

  Hereinafter, the preferred embodiments of the multilayer structure polymer (I), the multilayer structure polymer (III), the rubber-containing polymer (IV), and the thermoplastic polymer (II) will be described more specifically.

[Multilayer structure polymer (I)]
The multilayer structure polymer (I) used as the acrylic resin includes the innermost layer polymer (IA), the first intermediate layer polymer (IB), the second intermediate layer polymer (IC), from the center, It is a multilayer structure polymer arrange | positioned in order of outermost layer polymer (ID).

  The innermost layer polymer (IA) includes at least an alkyl methacrylate (I-A1) having an alkyl group having 4 or less carbon atoms, an alkyl acrylate (I-A2) having an alkyl group having 8 or less carbon atoms, and an aromatic vinyl. This is a polymer obtained by polymerizing the monomer (I-A3) and the polyfunctional monomer (I-A4) and having a glass transition temperature of 10 ° C. or higher.

  The first intermediate layer polymer (IB) includes at least an alkyl acrylate (I-B1) having an alkyl group having 8 or less carbon atoms, an aromatic vinyl monomer (I-B2), and a polyfunctional monomer. It is a polymer having a glass transition temperature of 0 ° C. or lower, obtained by polymerizing (I-B3) and a graft crossing agent (I-B5).

  The second intermediate layer polymer (IC) is composed of alkyl methacrylate (I-C1) having an alkyl group having 4 or less carbon atoms, alkyl acrylate (I-C2) having an alkyl group having 8 or less carbon atoms, and aromatic vinyl. A polymer obtained by polymerizing a monomer (I-C3) and a graft crossing agent (I-C4), and the outermost layer polymer (ID) is an alkyl having an alkyl group having 4 or less carbon atoms. Glass transition temperature of 50 ° C. or higher obtained by polymerizing methacrylate (I-D1), alkyl acrylate (I-D2) having an alkyl group having 8 or less carbon atoms and aromatic vinyl monomer (I-D3) Is a polymer.

Furthermore, the following configurations can be used particularly preferably.
(Innermost layer polymer (IA))
The innermost layer polymer (IA) is composed of 30 to 99.7% by mass of an alkyl methacrylate (I-A1) having an alkyl group having 4 or less carbon atoms, and an alkyl acrylate (I-A2) having an alkyl group having 8 or less carbon atoms. ) 0.1-69.8 wt%, aromatic vinyl monomer (I-A3) 0.1-25 wt%, polyfunctional monomer (I-A4) 0.1-10 wt%, and Graft crossover agent (I-A5) 0-5% by mass ((I-A1) + (I-A2) + (I-A3) + (I-A4) + (I-A5) = 100% by mass)) Thus obtained polymer is preferably a polymer having a glass transition temperature (hereinafter referred to as Tg) of 10 ° C. or higher. When Tg is 10 ° C. or higher, the transparency of the transparent protective layer to be obtained tends to be good, which is preferable. The amount of the innermost layer polymer (IA) in the multilayer structure polymer (I) (100% by mass) is 2 to 35% by mass in terms of the transparency of the transparent protective layer obtained by molding. It is preferable.

(First intermediate layer polymer (IB))
1st intermediate | middle layer polymer (IB) is alkyl acrylate (I-B1) 60-99.7 mass% which has a C8 or less alkyl group, Aromatic vinyl monomer (I-B2) 0. 1 to 39.8% by mass, polyfunctional monomer (I-B3) 0.1 to 10% by mass, monomer having copolymerizable double bond (I-B4) 0 to 20% by mass, And graft crossing agent (I-B5) 0.1-5% by mass ((I-B1) + (I-B2) + (I-B3) + (I-B4) + (I-B5)) = 100% by mass ) Is preferably a polymer having a Tg of 0 ° C. or lower. When Tg is 0 ° C. or lower, for example, the film forming stability during film formation, and when the obtained transparent protective layer is laminated on the light diffusion plate, the strength of the transparent protective layer is sufficient so that the transparent protective layer It is preferable because it does not break and tends to improve workability. Moreover, it is preferable that the quantity of the 1st intermediate | middle layer polymer (IB) which occupies for multilayer structure polymer (I) (100 mass%) is 5-60 mass%.

(Second intermediate layer polymer (IC))
The second intermediate layer polymer (IC) is composed of 20 to 89.8% by mass of an alkyl methacrylate (I-C1) having an alkyl group having 4 or less carbon atoms, and an alkyl acrylate having an alkyl group having 8 or less carbon atoms (I -C2) 10-79.8% by mass, aromatic vinyl monomer (I-C3) 0.1-25% by mass, and grafting agent (I-C4) 0.1-5% by mass ((I- C1) + (I−C2) + (I−C3) + (I−C4) = 100 mass%) is preferable. The amount of the second intermediate layer polymer (IC) in the multilayer structure polymer (I) (100% by mass) is preferably 2 to 20% by mass. Moreover, it is preferable that the latex particle diameter in the 2nd intermediate | middle layer polymer (IC) stage in manufacture of multilayer structure polymer (I) is 0.03-0.2 micrometer.

(Outermost layer polymer (ID))
The outermost layer polymer (ID) is composed of 51 to 99.8% by mass of an alkyl methacrylate (I-D1) having an alkyl group having 4 or less carbon atoms, and an alkyl acrylate (I-D2) having an alkyl group having 8 or less carbon atoms. ) 0.1-48.9% by mass, and aromatic vinyl monomer (I-D3) 0.1-25% by mass ((I-D1) + (I-D2) + (I-D3) = 100 The polymer having a Tg of 50 ° C. or higher obtained by polymerizing (mass%) is preferable. A Tg of 50 ° C. or higher is preferred because the resulting transparent protective layer tends to have good heat resistance. Moreover, it is preferable that the quantity of outermost layer polymer (ID) which occupies for multilayer structure polymer (I) (100 mass%) is 10-80 mass% from the heat resistant point of the transparent protective layer obtained. .

(Polymer Tg)
Here, Tg of a polymer can be calculated | required with the following Fox formula, for example in the case of the copolymer which consists of monomer a, b, c ....

1 / Tg = ma / Tga + mb / Tgb + mc / Tgc ...
Tg: Tg [K] of copolymer, ma: mass fraction of monomer a, Tga: Tg [K] of homopolymer obtained from monomer a, mb: mass fraction of monomer b, Tgb: Tg [K] of the homopolymer obtained from the monomer b, mc: Mass fraction of the monomer c, Tgc: Tg [K] of the homopolymer obtained from the monomer c.

(Suitable polymer)
The alkyl methacrylate (I-A1) having an alkyl group having 4 or less carbon atoms constituting the innermost layer polymer (IA) may be either linear or branched, for example, butyl methacrylate, propyl methacrylate, Examples include ethyl methacrylate and methyl methacrylate. These can be used alone or in admixture of two or more. Among them, methyl methacrylate is preferable from the viewpoint of transparency.

  Examples of the alkyl acrylate (I-A2) having an alkyl group having 8 or less carbon atoms include methyl acrylate, ethyl acrylate, butyl acrylate, propyl acrylate, 2-ethylhexyl acrylate, and the like. These can be used alone or in admixture of two or more. Of these, butyl acrylate is preferable from the viewpoint of Tg.

  Examples of the aromatic vinyl monomer (I-A3) include styrene, α-methylstyrene, paramethylstyrene, and the like. These can be used alone or in admixture of two or more. Of these, styrene is preferable from the viewpoint of economy.

  The polyfunctional monomer (I-A4) is a monomer having two or more copolymerizable double bonds in one molecule. Examples of the polyfunctional monomer (I-A4) include alkylene glycol dimethacrylates such as ethylene glycol dimethacrylate, 1,3-butylene dimethacrylate, 1,4-butylene glycol dimethacrylate, and propylene glycol dimethacrylate; Polyvinylbenzene such as divinylbenzene and trivinylbenzene; alkylene glycol diacrylate and the like. These can be used alone or in admixture of two or more. Among these, alkylene glycol dimethacrylate is preferable, and 1,3-butylene glycol dimethacrylate is more preferable.

  The graft crossing agent (I-A5) is a monomer having two or more different copolymerizable double bonds in one molecule. Examples of the graft crossing agent (I-A5) include copolymerizable α, β-unsaturated monocarboxylic acid or dicarboxylic acid allyl ester, methallyl ester, crotyl ester, triallyl cyanurate, triallyl isocyanurate, and the like. Is mentioned. These can be used alone or in admixture of two or more. Of these, allyl methacrylate and triallyl cyanurate are particularly preferable.

  As the alkyl acrylate (I-B1) having an alkyl group having 8 or less carbon atoms constituting the first intermediate layer polymer (IB), the alkyl acrylate represented by (I-A2) may be used alone or in combination of two or more. Can be mixed and used.

  As the aromatic vinyl monomer (I-B2), styrene, α-methylstyrene, paramethylstyrene and the like shown in (I-A3) can be used alone or in admixture of two or more.

  Examples of the polyfunctional monomer (I-B3) include ethylene glycol dimethacrylate, 1,3-butylene dimethacrylate, 1,4-butylene glycol dimethacrylate, and propylene glycol dimethacrylate represented by (I-A4). Alkylene glycol dimethacrylate; polyvinylbenzene such as divinylbenzene and trivinylbenzene; alkylene glycol acrylate and the like can be used alone or in admixture of two or more. Among these, alkylene glycol dimethacrylate is preferable, and 1,3-butylene glycol dimethacrylate is more preferable.

  The monomer (I-B4) having a double bond capable of copolymerization is a monomer other than the above-mentioned monomers and copolymerizable with the above-mentioned monomers. For example, lower alkoxy acrylate , Acrylic monomers such as cyanoethyl acrylate, acrylamide, acrylic acid and methacrylic acid, styrene, acrylic substituted styrene, acrylonitrile, methacrylonitrile and the like. These can be used alone or in admixture of two or more.

  As the graft crossing agent (I-B5), allyl ester, methallyl ester, crotyl ester, triallyl cyanurate of the copolymerizable α, β-unsaturated monocarboxylic acid or dicarboxylic acid shown in (I-A5) And triallyl isocyanurate. These can be used alone or in admixture of two or more. Of these, allyl methacrylate and triallyl cyanurate are particularly preferable.

  As the monomer and graft crossing agent constituting the second intermediate layer polymer (IC) and the outermost layer polymer (ID), the innermost layer polymer (IA) and the first intermediate layer weight The same thing as a unification (IB) is mentioned. These can be used alone or in admixture of two or more.

  The final latex particle size of the multilayer structure polymer (I) is preferably 0.03 to 0.2 μm, more preferably 0.04 to 0.15 μm, and most preferably 0.05 to 0. .1 μm. When the final latex particle size becomes too large, not only the transparency is lowered, but also the transparency may change due to a temperature change. When used as a transparent protective layer such as a light diffusing plate, if the transparency changes due to heat from a light source such as a cold cathode tube, the light emission quality may be degraded. On the other hand, if the particle size becomes too small, for example, when a transparent protective layer is obtained by forming a film, the film is easily cut and the workability deteriorates, or when the obtained transparent protective layer is laminated on the light diffusion plate, A transparent protective layer may be cut off due to insufficient strength of the protective layer, and workability may deteriorate.

(Preferred characteristics)
In the present invention, the acrylic resin used as the protective layer of the light diffusing plate is preferably high in terms of light emission quality when made into a liquid crystal panel and higher in impact resistance in terms of workability. preferable.

  Furthermore, in order to reduce the temperature dependence of the total light transmittance and haze value, the amount of alkyl methacrylate having 4 or less carbon atoms in each layer in the multilayer polymer (I) is reduced by the first intermediate layer polymer (I- From B), the amount of the alkyl methacrylate monotonously increasing toward the second intermediate layer polymer (IC) and the outermost layer polymer (ID) and occupying the first innermost layer polymer (IA) is the first. The amount is preferably larger than the amount occupied in the intermediate layer polymer (IB).

  The aromatic vinyl monomer in each layer (IA), (IB), (IC), and (ID) of the multilayer structure polymer (I) and an alkyl having an alkyl group having 8 or less carbon atoms The mass ratio to the acrylate (aromatic vinyl monomer / alkyl acrylate) is preferably 5/95 to 50/50, more preferably 10/90 to 30/70. As the mass ratio goes away from this range, the transparency decreases, and when used as a protective layer for a light diffusing plate, the light emission quality of a liquid crystal panel using the same tends to decrease.

(Polymer production method)
As a method for producing the multilayer structure polymer (I), a sequential multi-stage polymerization method by an emulsion polymerization method is the most suitable polymerization method. The production of the multilayer structure polymer (I) is not particularly limited. For example, the emulsion polymerization may be carried out by an emulsion suspension polymerization method in which after the emulsion polymerization, the outermost layer polymer is converted into a suspension polymerization system. It can be carried out.

  In addition, although not particularly limited, when the multilayer structure polymer (I) is produced by emulsion polymerization, the monomer mixture that gives the innermost layer polymer (IA) is preliminarily mixed with water and a surfactant. An emulsion is preferably prepared by mixing, supplying this emulsion to the reactor and polymerizing it, and then supplying the monomer mixture constituting each remaining layer to the reactor in order and polymerizing.

(Preferred characteristics)
For example, a multilayer mixture polymer (I) is prepared by supplying an emulsion prepared by mixing a monomer mixture that gives the innermost layer polymer (IA) with water and a surfactant in advance into a reactor and polymerizing it. Is dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion is 0 to 50 per 100 g of the multilayer structure polymer. This is preferable because the appearance is good and the optical properties are good. When a more preferable multilayer structure polymer is dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion is 0-30, more preferably 0-20, per 100 g of the multilayer structure polymer. It is a range.

  In addition, when the multilayer structure polymer is dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion is determined by adding the weighed powder-like multilayer structure polymer in acetone to a concentration of 5% by mass to It can be obtained by dispersing in the range of 10% by mass to prepare a dispersion, and measuring the number of particles having a diameter of 55 μm or more present in the dispersion with a light scattering type particle counter or the like according to JIS B9921. it can.

  Further, when preparing the dispersion, in order to sufficiently permeate acetone between the multilayer structure polymer particles, the multilayer structure polymer is previously superposed with a good solvent for the multilayer structure polymer on a mesh having an opening smaller than 55 μm. A method of preparing a dispersion by dispersing the residue on the mesh in acetone again after sonic cleaning is preferable as a method for measuring the number of particles having a diameter of 55 μm or more present in the accurate dispersion. .

(Surfactant)
As the surfactant used in preparing the emulsion, anionic, cationic and nonionic surfactants can be used, and anionic surfactants are particularly preferable. Examples of the anionic surfactant include rosin soap; potassium oleate, sodium stearate, sodium myristate, sodium N-lauroyl sarcosinate, dipotassium alkenyl succinate; sulfate ester salts such as sodium lauryl sulfate Sulfonic acid salts such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium alkyldiphenyl ether disulfonate; phosphate esters such as polyoxyethylene alkylphenyl ether sodium phosphate; polyoxyethylene alkyl ether phosphate Examples thereof include sodium phosphate salts and the like. Of these, phosphate esters such as polyoxyethylene alkyl ether sodium phosphates are preferable from the viewpoint of ecological protection from endocrine disrupting chemicals, which have become a problem in recent years.

  Preferred specific examples of the surfactant include NC-718 manufactured by Sanyo Chemical Industries, phosphanol LS-529, phosphanol RS-610NA, phosphanol RS-620NA, and phospha Nord-RS-630NA, Phosphanol RS-640NA, Phosphanol RS-650NA, Phosphanol RS-660NA, Latemu P-0404, Latemulu P-0405, Latemulu P-0406, Latemulu P-0407 manufactured by Kao Corporation Is mentioned.

(Preparation method of emulsion)
As a method for preparing an emulsion, a method in which a monomer mixture is charged in water and then a surfactant is added, a method in which a surfactant is charged in water and then a monomer mixture is charged, a monomer For example, a method of charging water after charging a surfactant into the mixture may be used. Among these, the method of charging the surfactant after charging the monomer into water and the method of charging the monomer mixture after charging the surfactant into water are the methods for obtaining the multilayer structure polymer (I). Is preferred.

  Moreover, as a mixing apparatus for preparing an emulsion prepared by mixing the monomer mixture that gives the innermost layer polymer (IA) constituting the multilayer structure polymer (I) with water and a surfactant. These include a stirrer equipped with a stirring blade; various forced emulsifiers such as a homogenizer and a homomixer; a membrane emulsifier.

  The emulsion to be prepared may have either a W / O type or an O / W type dispersion structure, particularly an O / W type in which oil droplets of a monomer mixture are dispersed in water, and the diameter of the oil droplets in the dispersed phase. Is preferably 100 μm or less.

(Polymerization conditions)
The innermost layer polymer (IA), the first intermediate layer polymer (IB), the second intermediate layer polymer (IC), and the outermost layer polymer (I) constituting the multilayer structure polymer (I) As the polymerization initiator used when forming (ID), known ones can be used. As the addition method, a method of adding to one or both of the aqueous phase and the monomer phase can be adopted. Particularly preferred polymerization initiators include peroxides, azo initiators, or redox initiators in which an oxidizing agent / reducing agent is combined. Among these, a redox initiator is more preferable, and a sulfoxylate initiator combined with ferrous sulfate / ethylenediaminetetraacetic acid disodium salt / longalite / hydroperoxide is particularly preferable.

  In particular, an emulsion prepared by mixing the monomer mixture giving the innermost layer polymer (IA) with water and a surfactant is supplied to the reactor and polymerized, and then the first intermediate layer polymer. In the method in which the monomer mixture that gives (IB), the second intermediate layer polymer (IC), and the outermost layer polymer (ID) is sequentially fed to the reactor and polymerized, After heating the aqueous solution containing monoiron, ethylenediaminetetraacetic acid disodium salt and Rongalite to the polymerization temperature, the prepared emulsion is supplied to the reactor for polymerization, and then the first containing a polymerization initiator such as peroxide. A method in which a monomer mixture giving an intermediate layer polymer (IB), a second intermediate layer polymer (IC), and an outermost layer polymer (ID) is sequentially supplied to a reactor and polymerized. The method for obtaining the multilayer structure polymer (I) is most preferable.

  The polymerization temperature during the polymerization varies depending on the type and amount of the polymerization initiator used, but is preferably 40 to 120 ° C, more preferably 60 to 95 ° C.

[Multilayer polymer (III)]
The multilayer structure polymer (III) is a multilayer structure polymer arranged in the order of the innermost layer polymer (III-A), the intermediate layer polymer (III-B), and the outermost layer polymer (III-C) from the center. is there.

  The innermost layer polymer (III-A) is a polymer having units derived from alkyl acrylate (III-A1) having an alkyl group having 1 to 8 carbon atoms and units derived from graft crossing agent (III-A5). is there.

  The intermediate layer polymer (III-B) is a unit derived from an alkyl acrylate (III-B1) having an alkyl group having 1 to 8 carbon atoms, an alkyl methacrylate (III-B2) having an alkyl group having 1 to 4 carbon atoms. It is a polymer having a unit derived from and a unit derived from the graft crossing agent (III-B5) and having a composition different from that of the innermost layer polymer (III-A).

  The outermost layer polymer (III-C) is a polymer having units derived from alkyl methacrylate (III-C1) having an alkyl group having 1 to 4 carbon atoms.

Furthermore, the following composition is preferable.
(Innermost layer polymer (III-A))
The innermost layer polymer (III-A) is composed of 50 to 99.9% by mass of a structural unit derived from an alkyl acrylate (III-A1) having an alkyl group having 1 to 8 carbon atoms, and an alkyl group having 1 to 4 carbon atoms. 0 to 49.9 mass% of structural units derived from alkyl methacrylate (III-A2) having, 0 to 20 mass% of structural units derived from other monomer (III-A3) having a copolymerizable double bond , 0-10% by mass of structural units derived from polyfunctional monomer (III-A4) and 0.1-10% by mass of structural units derived from graft crossing agent (III-A5) ((III-A1) + (III-A2) + (III-A3) + (III-A4) + (III-A5) = 100% by mass).

(Intermediate layer polymer (III-B))
The intermediate layer polymer (III-B) contains 9.9 to 90% by mass of a structural unit derived from an alkyl acrylate (III-B1) having an alkyl group having 1 to 8 carbon atoms and an alkyl group having 1 to 4 carbon atoms. 9.9 to 90% by mass of structural units derived from alkyl methacrylate (III-B2) having, and 0 to 20% by mass of structural units derived from other monomer (III-B3) having a copolymerizable double bond 0 to 10% by mass of a structural unit derived from a polyfunctional monomer (III-B4) and 0.1 to 10% by mass of a structural unit derived from a graft crossing agent (III-B5) ((III-B1) + (III-B2) + (III-B3) + (III-B4) + (III-B5) = 100% by mass) and is a polymer having a composition different from that of the innermost layer polymer (III-A). .

(Outermost layer polymer (III-C))
The outermost layer polymer (III-C) is composed of 80 to 100% by mass of a structural unit derived from an alkyl methacrylate (III-C1) having an alkyl group having 1 to 4 carbon atoms, and an alkyl having an alkyl group having 1 to 8 carbon atoms. 0 to 20% by mass of structural units derived from acrylate (III-C2) and 0 to 20% by mass of structural units derived from other monomer (III-C3) having a copolymerizable double bond ((III − C1) + (III-C2) + (III-C3) = 100% by mass).

(Innermost layer polymer (III-A))
The alkyl acrylate (III-A1) having an alkyl group having 1 to 8 carbon atoms constituting the innermost layer polymer (III-A) may be either linear or branched. Specific examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate and the like. These can be used alone or in admixture of two or more. Of these, n-butyl acrylate is preferred.

  The C1-C4 alkyl methacrylate (III-A2) constituting the innermost layer polymer (III-A) may be either linear or branched. Specific examples thereof include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate and the like. These can be used alone or in admixture of two or more. Of these, methyl methacrylate is preferred.

  Examples of the other monomer (III-A3) having a copolymerizable double bond constituting the innermost layer polymer (III-A) include lower alkoxy acrylate, cyanoethyl acrylate, acrylamide, acrylic acid, methacrylic acid. Acrylic monomers such as acids; styrene, alkyl-substituted styrene, acrylonitrile, methacrylonitrile and the like can be used.

  The polyfunctional monomer (III-A4) constituting the innermost layer polymer (III-A) can be used as necessary. A polyfunctional monomer is defined as a monomer having two or more copolymerizable double bonds in one molecule. Preferable specific examples thereof include alkylene glycol dimethacrylates such as ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, and propylene glycol dimethacrylate. In addition, polyvinylbenzene such as divinylbenzene and trivinylbenzene can be used. Of these, 1,3-butylene glycol dimethacrylate is preferred.

  Also, even when the polyfunctional monomer does not act at all, as long as the grafting agent is present, a fairly stable multilayer structure polymer is obtained. For example, when a hot strength or the like is strictly required, a polyfunctional monomer may be arbitrarily added depending on the purpose of addition.

The graft crossing agent (III-A5) constituting the innermost layer polymer (III-A) is defined as a monomer having two or more different copolymerizable double bonds in one molecule. Specific examples thereof include allyl, methallyl, or crotyl ester of copolymerizable α, β-unsaturated carboxylic acid or dicarboxylic acid. In particular, acrylic acid, methacrylic acid, maleic acid, or acrylic ester of fumaric acid is preferable. Of these, allyl methacrylate is preferable because of its excellent effect. In addition, triallyl cyanurate, triallyl isocyanurate and the like are also effective. In the graft crossing agent (III-A5), the conjugated unsaturated bond of the ester mainly reacts and bonds chemically much faster than the allyl group, methallyl group, or crotyl group. A substantial portion of the allyl, methallyl, or crotyl group works effectively during the polymerization of the next layer polymer to provide a graft bond between adjacent two layers.
The above polymerization may be performed in the presence of a chain transfer agent, if necessary.

  The content of units derived from alkyl acrylate (III-A1) having an alkyl group having 1 to 8 carbon atoms in 100% by mass of all monomer units constituting innermost layer polymer (III-A) is a multilayer structure. From the viewpoint of physical properties such as workability and strength when the polymer (III) is formed into a film, it is 50 to 99.9% by mass, more preferably 55 to 77.9% by mass, most preferably 60 to It is 69.9 mass%.

  The content of units derived from alkyl methacrylate (III-A2) having an alkyl group having 1 to 4 carbon atoms in 100% by mass of all monomer units constituting innermost layer polymer (III-A) is 0 to It is 49.9 mass%, More preferably, it is 20 mass% or more, Most preferably, it is 30 mass% or more. Further, it is more preferably 44.9% by mass or less, and most preferably 39.9% by mass or less.

  The unit derived from another monomer (III-A3) having a copolymerizable double bond in 100% by mass of all monomer units constituting the innermost layer polymer (III-A) is 0-20. It is mass%, More preferably, it is 15 mass% or less.

  The content of units derived from the polyfunctional monomer (III-A4) in 100% by mass of all monomer units constituting the innermost layer polymer (III-A) is 0 to 10% by mass, More preferably, it is 0.1 mass% or more and 6 mass% or less.

  Content of the unit derived from the graft crossing agent (III-A5) in 100% by mass of all monomer units constituting the innermost layer polymer (III-A) is 0.1 to 10% by mass. When the content is 0.1% by mass or more, the obtained multilayer structure polymer can be formed into a film without deteriorating optical properties such as transparency. A content of 10% by mass or less is preferable because sufficient flexibility and toughness can be imparted to the multilayer structure polymer. More preferably, it is 0.5 mass% or more and 2 mass% or less.

  The content of each constituent unit in the innermost layer polymer (III-A) is in the above range, and the properties of the transparent protective layer obtained by molding the multilayer structure polymer (III) such as transparency and strength. It is preferable from the point.

  The Tg of the innermost layer polymer (III-A) alone is an intermediate layer polymer (III-B) described later from the viewpoint of physical properties such as the strength of the transparent protective layer obtained by molding the multilayer structure polymer (III). It is preferably less than a single Tg. More preferably, it is less than 5 degreeC, More preferably, it is 0 degreeC or less, Most preferably, it is -5 degreeC or less.

  The content of the innermost layer polymer (III-A) in the multilayer structure polymer (III) (100% by mass) is in terms of the transparency of the transparent protective layer obtained by molding the multilayer structure polymer (III). 15-50 mass% is preferable, More preferably, it is 15-35 mass% or less. In this case, the multilayer polymer (III) is advantageous in terms of optical properties when used as a transparent protective layer of a light diffusion plate.

  The innermost layer polymer (III-A) may be a single layer, but is preferably composed of two layers. Further, the monomer constitution ratios of the two layers in the innermost layer polymer (III-A) may be the same or different.

  When the innermost layer polymer (III-A) is composed of two layers and the monomer composition ratios of the two layers in the innermost layer polymer (III-A) are different, the Tg of the inner layer (III-A-1) is It may be higher or lower than the Tg of the outer layer (III-A-2).

  From the viewpoint of transparency, the content of the inner layer (III-A-1) in the innermost layer polymer (III-A) (100 mass%) is preferably 1 to 20 mass%, and the outer layer (III-A- The content of 2) is preferably 80 to 99% by mass. The acrylic resin laminated on the light diffusing plate or the like preferably has higher transparency.

  As a preferred multilayer polymer when the innermost layer polymer (III-A) is composed of two layers, the multilayer polymer described in JP-B-62-19309 is exemplified.

(Intermediate layer polymer (III-B))
The alkyl acrylate (III-B1) having an alkyl group having 1 to 8 carbon atoms constituting the intermediate layer polymer (III-B) may be either linear or branched. Specific examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate and the like. These can be used alone or in admixture of two or more. Of these, preferred are methyl acrylate and n-butyl acrylate.

  The alkyl methacrylate (III-B2) having an alkyl group having 1 to 4 carbon atoms constituting the intermediate layer polymer (III-B) may be either linear or branched. Specific examples thereof include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate and the like. These can be used alone or in admixture of two or more. Of these, methyl methacrylate is preferred.

  Examples of the other monomer (III-B3) having a copolymerizable double bond constituting the intermediate layer polymer (III-B) include lower alkoxy acrylate, cyanoethyl acrylate, acrylamide, acrylic acid, methacrylic acid, etc. Acrylic monomers, styrene, alkyl-substituted styrene, acrylonitrile, methacrylonitrile and the like can be used.

  The polyfunctional monomer (III-B4) constituting the intermediate layer polymer (III-B) may be used as necessary. Preferable specific examples thereof include alkylene glycol dimethacrylates such as ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, and propylene glycol dimethacrylate. In addition, polyvinylbenzene such as divinylbenzene and trivinylbenzene can be used. Of these, 1,3-butylene glycol dimethacrylate is preferred.

  Even when the polyfunctional monomer does not act at all, as long as the grafting agent is present, a fairly stable multilayer structure polymer is obtained. For example, when a hot strength or the like is strictly required, a polyfunctional monomer may be arbitrarily added depending on the purpose of addition.

Examples of the graft crossing agent (III-B5) constituting the intermediate layer polymer (III-B) include allyl, methallyl, or crotyl ester of copolymerizable α, β-unsaturated carboxylic acid or dicarboxylic acid. It is done. In particular, acrylic acid, methacrylic acid, maleic acid, or acrylic ester of fumaric acid is preferable. Of these, allyl methacrylate is preferable because of its excellent effect. In addition, triallyl cyanurate, triallyl isocyanurate and the like are also effective. In the graft crossing agent (III-B5), the conjugated unsaturated bond of the ester mainly reacts and chemically bonds much faster than the allyl group, methallyl group, or crotyl group. A substantial portion of the allyl, methallyl, or crotyl group works effectively during the polymerization of the next layer polymer to provide a graft bond between adjacent two layers.
The above polymerization may be performed in the presence of a chain transfer agent, if necessary.

  The content of units derived from alkyl acrylate (III-B1) having an alkyl group having 1 to 8 carbon atoms in 100% by mass of all monomer units constituting the intermediate layer polymer (III-B) is 9. 9-90% by mass. From the viewpoint of the transparency of the transparent protective layer obtained by molding the multilayer structure polymer (III), it is more preferably 19.9% by mass or more, most preferably 29.9% by mass or more. Further, it is more preferably 60% by mass or less, and most preferably 50% by mass or less.

  The content of units derived from alkyl methacrylate (III-B2) having an alkyl group having 1 to 4 carbon atoms in 100% by mass of all monomer units constituting the intermediate layer polymer (III-B) is 9. 9-90% by mass. From the viewpoint of transparency of the transparent protective layer obtained by molding the multilayer structure polymer (III), it is more preferably 39.9% by mass or more, most preferably 49.9% by mass or more. Further, it is more preferably 80% by mass or less, and most preferably 70% by mass or less.

  The content of units derived from another monomer (III-B3) having a copolymerizable double bond in 100% by mass of all monomer units constituting the intermediate layer polymer (III-B) is: It is 0-20 mass%, More preferably, it is 15 mass% or less.

  The content of units derived from the polyfunctional monomer (III-B4) in 100% by mass of all monomer units constituting the intermediate layer polymer (III-B) is 0 to 10% by mass, More preferably, it is 6 mass% or less.

  The content of units derived from the graft crossing agent (III-B5) in 100% by mass of all monomer units constituting the intermediate layer polymer (III-B) is 0.1 to 10% by mass. When the content is 0.1% by mass or more, the obtained multilayer structure polymer (III) can be molded without deteriorating optical properties such as transparency. A content of 10% by mass or less is preferable because sufficient flexibility and toughness can be imparted to the multilayer structure polymer (III). More preferably, it is 0.5 mass% or more and 2 mass% or less.

  The composition of the intermediate layer polymer (III-B) is preferably different from the composition of the innermost layer polymer (III-A). When the compositions of these polymers are different, film properties such as impact resistance when the multilayer structure polymer (III) is formed into a film, transparency, and the like can be satisfied.

  Here, “different composition” as used in the present invention means alkyl acrylate, alkyl methacrylate, other monomers having a copolymerizable double bond, a polyfunctional monomer, and a graft. The type and / or amount of crossover agent is different.

  The Tg of the intermediate layer polymer (III-B) alone is preferably in the range of 5 to 100 ° C. A Tg of 5 ° C. or higher is preferred because the heat resistance, scratch resistance and transparency of the transparent protective layer obtained by molding the multilayer structure polymer (III) are improved. More preferably, it is 10 degreeC or more, Most preferably, it is 15 degreeC or more. Moreover, when Tg is 100 degrees C or less, since the multilayer structure polymer with favorable film forming property is obtained, it is preferable. More preferably, it is 70 degrees C or less, Most preferably, it is 50 degrees C or less.

  Further, although not particularly limited, the content of the intermediate layer polymer (III-B) in the multilayer structure polymer (III) (100% by mass) is preferably 5 to 35% by mass, more preferably It is 20 mass% or less. If it is in this range, a function required as an intermediate layer, for example, transparency can be expressed.

  The alkyl methacrylate (III-C1) having an alkyl group having 1 to 4 carbon atoms constituting the outermost layer polymer (III-C) may be either linear or branched. Specific examples thereof include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate and the like. These can be used alone or in admixture of two or more. Of these, methyl methacrylate is preferred.

  The alkyl acrylate (III-C2) having an alkyl group having 1 to 8 carbon atoms constituting the outermost layer polymer (III-C) may be either linear or branched. Specific examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate and the like. These can be used alone or in admixture of two or more. Of these, preferred are methyl acrylate and n-butyl acrylate.

  Examples of the other monomer (III-C3) having a copolymerizable double bond constituting the outermost layer polymer (III-C) include lower alkoxy acrylate, cyanoethyl acrylate, acrylamide, acrylic acid, methacrylic acid, etc. Acrylic monomers, styrene, alkyl-substituted styrene, acrylonitrile, methacrylonitrile and the like can be used.

  The content of units derived from alkyl methacrylate (III-C1) having an alkyl group having 1 to 4 carbon atoms in 100% by mass of all monomer units constituting outermost layer polymer (III-C) is 80 to 100% by mass, more preferably 85% by mass or more, and most preferably 90% by mass or more.

  The content of units derived from alkyl acrylate (III-C2) having an alkyl group having 1 to 8 carbon atoms in 100% by mass of all monomer units constituting outermost layer polymer (III-C) is 0 to It is 20 mass%, More preferably, it is 1 mass% or more. Further, it is more preferably 15% by mass or less, and most preferably 10% by mass or less.

  The content of units derived from the monomer (III-C3) having a copolymerizable double bond in 100% by mass of all the monomer units constituting the outermost layer polymer (III-C) is 0 to It is 20 mass%, More preferably, it is 15 mass% or less.

  Moreover, although it does not specifically limit, a chain transfer agent can be used at the time of superposition | polymerization of outermost layer polymer (III-C), and the molecular weight of outermost layer polymer (III-C) can be adjusted. This chain transfer agent is preferably selected from those usually used for radical polymerization, and specific examples thereof include alkyl mercaptans having 2 to 20 carbon atoms, mercapto acids, thiophenol, carbon tetrachloride, and the like. These can be used alone or in admixture of two or more. The content of the chain transfer agent is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the monomer ((III-C1) to (III-C3)) of the outermost layer polymer (III-C). . More preferably, it is 0.2 mass part or more, Most preferably, it is 0.3 mass part or more.

  The content of the alkyl acrylate, alkyl methacrylate, other monomer having a copolymerizable double bond, polyfunctional monomer, and graft crossing agent forming the outermost layer polymer (III-C) is as described above. The range is preferable from the viewpoints of moldability and transparency of the transparent protective layer obtained by molding the multilayer structure polymer (III).

  The Tg of the outermost layer polymer (III-C) alone is preferably 60 ° C. or higher. The Tg of 60 ° C. or higher is preferable because a transparent protective layer having good film properties such as heat resistance can be obtained. More preferably, it is 80 degreeC or more, Most preferably, it is 90 degreeC or more.

  Although not particularly limited, the content of the outermost layer polymer (III-C) in the multilayer structure polymer (III) (100% by mass) is preferably 15 to 80% by mass, more preferably in terms of film properties. Is 45 to 80% by mass, most preferably 45 to 70% by mass.

  As a method for producing the multilayer structure polymer (III), a sequential multi-stage polymerization method by an emulsion polymerization method is the most suitable polymerization method as with the multilayer structure polymer (I). The production of the multilayer structure polymer (III) is not particularly limited, and for example, by emulsion suspension polymerization method in which emulsion polymerization is followed by conversion to a suspension polymerization system at the time of polymerization of each outermost layer polymer. It can be carried out.

  Further, although not particularly limited, when the multilayer structure polymer (III) is produced by emulsion polymerization in the same manner as the multilayer structure polymer (I), the single layer polymer (III-A) is obtained. A part or all of the monomer mixture is mixed with water and a surfactant in advance to prepare an emulsion, and after the emulsion is supplied to the reactor and polymerized, the monomer mixture constituting the remaining layers is mixed. A method in which each is sequentially supplied to the reactor and polymerized is preferred.

  An emulsion prepared by previously mixing a monomer mixture that gives the innermost layer polymer (III-A) with water and a surfactant is supplied to the reactor and polymerized to obtain the multilayer structure polymer (III) in acetone. When dispersed in the dispersion, the number of particles having a diameter of 55 μm or more present in the dispersion is 0 to 50 per 100 g of the multilayer structure polymer. Is preferable since the optical properties are improved. When a more preferable multilayer structure polymer is dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion is 0-30, more preferably 0-20, per 100 g of the multilayer structure polymer. It is a range.

  In addition, when the multilayer structure polymer is dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion is determined by adding the weighed powder-like multilayer structure polymer in acetone to a concentration of 5% by mass to It can be obtained by dispersing in the range of 10% by mass to prepare a dispersion, and measuring the number of particles having a diameter of 55 μm or more present in the dispersion with a light scattering type particle counter or the like according to JIS B9921. it can.

  Further, when preparing the dispersion, in order to sufficiently permeate acetone between the multilayer structure polymer particles, the multilayer structure polymer is previously superposed with a good solvent for the multilayer structure polymer on a mesh having an opening smaller than 55 μm. A method of preparing a dispersion by dispersing the residue on the mesh in acetone again after sonic cleaning is preferable as a method for measuring the number of particles having a diameter of 55 μm or more present in the accurate dispersion. .

  As the surfactant used in preparing the emulsion, the same surfactants as used in preparing the emulsion with the multilayer structure polymer (I) can be used.

The method for preparing the emulsion is also preferably the same method as for the multilayer structure polymer (I).
Further, as a mixing apparatus for preparing an emulsion prepared by mixing a monomer mixture that gives the innermost layer polymer (III-A) constituting the multilayer structure polymer (III) with water and a surfactant. Examples thereof include an apparatus used for preparing an emulsion for producing the multilayer structure polymer (I).

  Further, the emulsion to be prepared may have either a W / O type or an O / W type dispersion structure, particularly an O / W type in which oil droplets of a monomer mixture are dispersed in water, and oil droplets in a dispersed phase. The diameter is preferably 100 μm or less.

  Polymerization initiator used in forming the innermost layer polymer (III-A), the intermediate layer polymer (III-B), and the outermost layer polymer (III-C) constituting the multilayer structure polymer (III) As this, a well-known thing can be used. As the addition method, a method of adding to one or both of the aqueous phase and the monomer phase can be adopted. As a particularly preferred polymerization initiator, a peroxide, an azo initiator, or a redox initiator in which an oxidizing agent and a reducing agent are combined is used. Among these, a redox initiator is more preferable, and a sulfoxylate initiator combined with ferrous sulfate / ethylenediaminetetraacetic acid disodium salt / longalite / hydroperoxide is particularly preferable.

  In particular, an emulsion prepared by mixing the monomer mixture giving the innermost layer polymer (III-A) with water and a surfactant is supplied to the reactor and polymerized, and then the intermediate layer polymer (III -B) and the monomer mixture that gives the outermost layer polymer (III-C) are sequentially fed to the reactor, and the polymerization method includes ferrous sulfate, ethylenediaminetetraacetic acid disodium salt, Rongalite After raising the aqueous solution to the polymerization temperature, the prepared emulsion is supplied to the reactor for polymerization, and then the intermediate layer polymer (III-B) containing a polymerization initiator such as peroxide, and the outermost layer polymer A method in which a monomer mixture giving (III-C) is sequentially fed to a reactor and polymerized is the most preferable method for obtaining a multilayer structure polymer (III).

  The polymerization temperature during the polymerization varies depending on the type and amount of the polymerization initiator used, but is preferably 40 to 120 ° C, more preferably 60 to 95 ° C.

  When the multilayer structure polymers (I) and (III) are obtained by emulsion polymerization as described above, a chain transfer agent, other polymerization aids and the like may be used. As the chain transfer agent, known ones can be used, and mercaptans are preferred.

  The multilayer structure polymers (I) and (III) can be produced by recovering the multilayer structure polymer from the polymer latex produced by the above-described method. The method of recovering the multilayer structure polymer from the polymer latex is not particularly limited, and examples thereof include salting out or acid precipitation coagulation, spray drying, freeze drying, and the like, and the powder is recovered in powder form.

[Rubber-containing polymer (IV)]
The rubber-containing polymer (IV) is a component for imparting a film forming property and the like required for forming the transparent protective layer into a film.

  The rubber-containing polymer (IV) comprises 35 to 100% by mass of an alkyl acrylate, 100 parts by mass of a monomer consisting of at least one other copolymerizable monomer (0 to 65% by mass) or a mixture thereof, Alkyl methacrylate 50-100 in the presence of 100 parts by mass of an elastic copolymer having a structure of one layer or two or more layers obtained by polymerizing a monomer mixture consisting of 0.1-10 parts by mass of a polymerizable monomer Latex obtained by polymerizing at least one stage of 10% to 400% by weight of a monomer consisting of 0% to 50% by weight of a vinyl monomer copolymerizable therewith, or a mixture thereof. It is a rubber-containing polymer having a particle size of 0.15 to 0.5 μm.

  As the alkyl methacrylate used here, known alkyl groups having 1 to 8 carbon atoms are used, and among them, butyl acrylate, 2-ethylhexyl acrylate and the like are preferable.

  The alkyl acrylate is preferably used in the range of 35 to 100% by mass. If it is 35% by mass or less, the elongation of the resin composition is insufficient, and it may be difficult to form into a film. A preferable use range is 50 to 90% by mass.

  In obtaining an elastic copolymer, another vinyl monomer that can be copolymerized in a range of 65% by mass or less can be copolymerized. As the vinyl monomer used here, alkyl methacrylates such as methyl methacrylate, butyl methacrylate, and cyclohexyl methacrylate, styrene, acrylonitrile, and the like are preferable, and these can be used alone or in combination of two or more.

  Furthermore, a crosslinkable monomer is used. The crosslinkable monomer to be used is not particularly limited, but is preferably an alkylene glycol such as ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, propylene glycol dimethacrylate and the like. Examples include dimethacrylate, allyl acrylate, allyl methacrylate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, diallyl maleate, trimethylolpropane triacrylate, allyl cinnamate, and these are used alone or in combination. Can be used.

  The crosslinkable monomer is used in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the monomer mixture. When the addition amount is 0.1 parts by mass or less, the amount of the monomer grafted to the elastic copolymer is extremely small, and the moldability in forming a film may be insufficient. The use of 10 parts by mass or more is not particularly problematic, but the effect commensurate with the added amount may not be exhibited. A preferable use range is a range of 0.3 to 7 parts by mass.

  The elastic copolymer can have a structure of one layer or two or more layers. When the structure has two or more layers, the content of the alkyl acrylate as a whole of the elastic copolymer may be 35% by mass or more. For example, in the case of a hard core structure, the content of the first layer alkyl acrylate may be 35% by mass or less.

  As the monomer to be grafted onto the elastic copolymer, 50% by mass or more of alkyl methacrylate is used, and specific examples include methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate and the like. It is done. Further, at least one of the other copolymerizable vinyl monomers is used in an amount of 50% by mass or less, and is not particularly limited. Specifically, alkyl acrylates such as methyl acrylate, butyl acrylate, cyclohexyl acrylate, styrene, acrylonitrile, etc. These can be used, and one kind or a combination of two or more kinds can be used.

  The monomer mixture to be grafted is used in an amount of 10 to 400 parts by weight, preferably 20 to 200 parts by weight, based on 100 parts by weight of the elastic copolymer, and can be polymerized in at least one stage.

  The rubber-containing polymer (IV) in the present invention can be obtained by ordinary emulsion polymerization. In addition, you may use a chain transfer agent, another polymerization adjuvant, etc. at the time of superposition | polymerization. A known chain transfer agent can be used, but mercaptans are preferred.

  Furthermore, the latex particle diameter of the rubber-containing polymer needs to be in the range of 0.15 to 0.5 μm. If it is 0.15 μm or less, the formability when formed into a film may be insufficient. When the thickness is 0.5 μm or more, the production becomes difficult, and the transparency may be deteriorated when the film is formed.

[Thermoplastic polymer (II)]
<Thermoplastic polymer (II)>
The thermoplastic polymer (II) in the present invention is derived from 50 to 100% by mass of a structural unit derived from an alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms, and other vinyl monomers copolymerizable therewith. The polymer has a reduced viscosity (measured at 25 ° C. of 0.1 g of the polymer dissolved in 100 ml of chloroform) of 0.1 l / g or less.

  As the alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms used in the thermoplastic polymer (II), methyl methacrylate is most preferable.

  Examples of other vinyl monomers copolymerizable with alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms used in the thermoplastic polymer (II) include methyl acrylate, ethyl acrylate, butyl acrylate, and propyl acrylate. Alkyl acrylates such as 2-ethylhexyl acrylate; alkyl methacrylates such as butyl methacrylate, propyl methacrylate, ethyl methacrylate and methyl methacrylate; aromatic vinyl compounds such as styrene, α-methyl styrene and paramethyl styrene; acrylonitrile, methacrylonitrile, etc. And vinyl cyanide compounds.

  Further, the reduced viscosity of the thermoplastic polymer (II) is preferably 0.1 l / g or less. When the reduced viscosity exceeds 0.1 l / g, the fluidity may deteriorate and the moldability of the transparent protective layer may deteriorate.

  The polymerization method for obtaining the thermoplastic polymer (II) is not particularly limited, and various methods such as a commonly known suspension polymerization method and emulsion polymerization method are applied.

  The thermoplastic polymer (II) is commercially available as the Dainal BR series manufactured by Mitsubishi Rayon Co., Ltd.

  For example, when an acrylic resin in which the multilayer structure polymer (I) and the thermoplastic polymer (II) are used in the present invention is not particularly limited, 20 to 90 parts by mass of the multilayer structure polymer (I) and the thermoplastic resin are used. It is preferable to use what consists of 80-10 mass parts ((I) + (II) = 100 mass parts) of polymers (II). If the proportion of the multilayer structure polymer (I) is 20 parts by mass or more, the strength of the transparent protective layer tends to be improved, and if it is 90 parts by mass or less, the workability in molding into the transparent protective layer is improved. There is a tendency.

  Moreover, when using the acrylic resin which combined rubber-containing polymer (IV) and thermoplastic resin (II), although it does not specifically limit, rubber-containing polymer (IV) is 22-99. The ratio of the elastic copolymer used in the range of 9 parts by mass and the elastic copolymer contained in the rubber-containing polymer (IV) and the grafted chain in 100 parts by mass of the acrylic resin is 20 parts by mass or more. It is preferable. If the ratio of the crosslinked elastic copolymer contained in the acrylic resin is 20 parts by mass or less, the processability when molding the transparent protective layer tends to be poor. From the viewpoint of workability, the cross-linked elastic copolymer is preferably 30 parts by mass or more in the acrylic resin.

<Additives>
For the transparent protective layer of the present invention, general compounding agents such as stabilizers, lubricants, processing aids, plasticizers, impact aids, foaming agents, fillers, antibacterial agents, antifungal agents are used as necessary. , A release agent, an antistatic agent, and an ultraviolet absorber. In particular, from the viewpoint of protecting the light diffusing plate, it is preferable to add an ultraviolet absorber in order to impart light resistance. The molecular weight of the ultraviolet absorber used is preferably 300 or more, particularly preferably 400 or more. The ultraviolet absorber is not particularly limited, but a benzotriazole type having a molecular weight of 400 or more or a triazine type having a molecular weight of 400 or more can be particularly preferably used. Specific examples of the former include Tinuvin of Ciba Specialty Chemicals Co., Ltd. 234, Adeka Stub LA-31 from Asahi Denka Kogyo Co., Ltd., and specific examples of the latter include Tinuvin 1577 from Ciba Specialty Chemicals.

  Moreover, it is preferable to add the following thermoplastic polymer (V) from the point of film-forming stabilization as a processing aid added when shape | molding the transparent protective layer of this invention in a film form.

(Thermoplastic polymer (V))
The thermoplastic polymer (V) is obtained by polymerizing 50 to 100% by mass of methyl methacrylate and 0 to 50% by mass of another vinyl monomer copolymerizable therewith, and the reduced viscosity ( A polymer obtained by dissolving 0.1 g of a polymer in 100 ml of chloroform and measuring at 25 ° C.) to be 0.2 to 2 l / g, and workability when forming a transparent protective layer into a film, It is a component that shows an important role for chemical resistance. The reduced viscosity of the thermoplastic polymer (V) is important, the preferred reduced viscosity is 0.2 to 1.2 l / g, and the particularly preferred reduced viscosity is 0.2 to 0.8 l / g.

  In the thermoplastic polymer (V), other vinyl monomers copolymerizable with methyl methacrylate include alkyl acrylates having an alkyl group having 1 to 8 carbon atoms and alkyl having an alkyl group having 2 to 4 carbon atoms. Methacrylate, aromatic vinyl compound, vinyl cyanide compound and the like can be mentioned. The alkyl acrylate having an alkyl group having 1 to 8 carbon atoms may be linear or branched. Specific examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and n-octyl. An acrylate etc. are mentioned. The alkyl methacrylate having an alkyl group having 2 to 4 carbon atoms may be either linear or branched, and specific examples thereof include ethyl methacrylate, propyl methacrylate, butyl methacrylate and the like. Examples of the aromatic vinyl compound include styrene, α-substituted styrene, nucleus-substituted styrene and derivatives thereof, for example, α-methylstyrene, chlorostyrene, vinyltoluene and the like. Examples of the vinylcyan compound include acrylonitrile and methacrylonitrile.

(Polymerization conditions, etc.)
Examples of the polymerization initiator used for obtaining the thermoplastic polymer (V) from the above monomers include ordinary inorganic initiators such as persulfates, organic peroxides, and azo compounds. In addition, the above compounds and sulfites, hydrogen sulfites, thiosulfates, first metal salts, sodium formaldehyde sulfoxylate, and the like can be used in combination as redox initiators. Preferred persulfates as the polymerization initiator include sodium persulfate, potassium persulfate, ammonium persulfate and the like. Examples of the organic peroxide include t-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide, and the like.

  Since the molecular weight and molecular weight distribution of the thermoplastic polymer (V) are important factors for the processability imparting effect, an appropriate chain transfer may be performed according to the purpose in producing the thermoplastic polymer (V). Agents can be used.

  The polymerization can be carried out at a temperature equal to or higher than the decomposition temperature of the polymerization initiator under the usual emulsion polymerization conditions, and can be polymerized in one or more stages depending on the purpose. The polymer can usually be recovered in the form of a powder after salting out or acidifying solidification, followed by filtration and washing with water, or by spray drying or freeze drying.

  The thermoplastic polymer (V) is commercially available as Metablene P manufactured by Mitsubishi Rayon Co., Ltd.

  The blending amount of the thermoplastic polymer (V) is an acrylic that is a combination of one or more of the multilayer structure polymer (I), the multilayer structure polymer (III), the rubber-containing polymer (IV), and the thermoplastic polymer (II). 0.1-10 mass parts is preferable with respect to 100 mass parts of resin. When the blending amount of the thermoplastic polymer (V) is less than 0.1 parts by mass, film formation stabilization at the time of molding the transparent protective layer tends to be insufficient. On the other hand, when the compounding quantity of a thermoplastic polymer (V) exceeds 10 mass parts, it exists in the tendency for the melt viscosity at the time of shape | molding a transparent protective layer to a film shape to rise, and for film moldability to fall. Furthermore, the compounding quantity of a preferable thermoplastic polymer (V) is 0.5-5 mass parts.

  The film-forming stability described here means that an acrylic film having a uniform thickness is stably produced.

<Method for producing transparent protective layer>
<Compound>
As an additive method, an acrylic resin that is preferably used for the transparent protective layer of the present invention is supplied to a film-forming machine for forming a film with an acrylic resin, and a compounding agent is added to the acrylic resin in advance. There is a method of kneading and mixing the obtained mixture with various kneaders. Examples of the kneader used in the latter method include ordinary single screw extruders, twin screw extruders, Banbury mixers, roll kneaders, and the like.

<Manufacture of transparent protective layer>
The method for forming the transparent protective layer to be laminated on the light source side of the light diffusion plate of the present invention into a film shape is not particularly limited, but it may be a known melt casting method, T-die method, inflation method or the like. Examples of the method include an extrusion method, and among these, the T-die method is most preferable from the viewpoint of economy.

  Although the thickness of the transparent protective layer laminated | stacked on the light source side of the light diffusing plate of this invention is not specifically limited, From the point of film physical property and workability, it is 10-500 micrometers. When the thickness is from 10 to 500 μm, the film has an appropriate rigidity, so that the laminating property, the secondary workability and the like are easy, and the film forming property is stabilized and the production of the film becomes easy. More preferably, it is 15-200 micrometers, More preferably, it is 30-200 micrometers.

<Transparency>
As for the total light transmittance of the transparent protective layer laminated | stacked on the light source side of the light diffusing plate of this invention, it is preferable that the value when measured by JISK7361-1 is 80% or more. When the total light transmittance of the transparent protective layer is 80% or more, the light from the light source is efficiently transmitted. For example, the light emitting quality of a liquid crystal display device using the light is improved, which is preferable. More preferably, it is 85% or more, more preferably 90% or more.

<Tensile modulus>
The tensile elastic modulus when the transparent protective layer laminated on the light source side of the light diffusing plate of the present invention is tested for tensile properties according to JIS K7127 and JIS K7161 is preferably 500 MPa or more and 3000 MPa or less. When the tensile elastic modulus of the transparent protective layer is 500 MPa or more and 3000 MPa or less, for example, when laminating continuously on a light diffusion plate, there is a tendency that appearance abnormality due to wrinkles is eliminated. Preferably they are 500 MPa or more and 2000 MPa or less, More preferably, they are 700 or more and 1500 MPa or less. Good appearance is the most important light diffusion plate used in liquid crystal display devices.

(Use)
The transparent protective layer of the present invention is laminated on a light diffusing plate, and the light diffusing plate on which this transparent protective layer is laminated has a transparent protective layer disposed on the light source side, and is used as, for example, a light diffusing plate of a direct type backlight. . By disposing a transparent protective layer on the light source side, yellowing of the light diffusing plate by the light source can be suppressed, and the liquid crystal display device using this direct type backlight has long-lasting color tone and light emission quality in color liquid crystal display. Since it can be maintained, the transparent protective layer of the present invention is very useful as a transparent protective layer for a light diffusion plate of a backlight (particularly, a direct type).

The following examples illustrate the invention.
In the examples and comparative examples, “part” represents “part by mass”, and “%” represents “% by mass”. Abbreviations in the reference examples are as follows.

Methyl methacrylate MMA
Methyl acrylate MA
Butyl acrylate BA
Styrene St
Allyl methacrylate AMA
1,3-butylene glycol dimethacrylate 1.3BD
t-Butyl hydroperoxide tBH
Cumene hydroperoxide CHP
n-octyl mercaptan nOM
Emulsifier (1): Sodium mono-n-dodecyloxytetraoxyethylene phosphate [trade name Phosphanol RS-610NA, manufactured by Toho Chemical Co., Ltd.]

  Emulsifier (2): sodium hydroxide partial neutralized product of 40% mono (polyoxyethylene nonylphenyl ether) phosphoric acid and 60% di (polyoxyethylene nonylphenyl ether) phosphoric acid [trade name Phosphanol LO529, Toho Chemical Co., Ltd.]

(Measurement of various physical properties)
In the examples and comparative examples, evaluation of the prepared multilayer structure polymer and rubber-containing polymer and measurement of various physical properties of the transparent protective layer were carried out by the following test methods.

1) Weight average particle diameter of multilayer structure polymer and rubber-containing polymer The polymer latex of the multilayer structure polymer obtained by emulsion polymerization was dynamically measured using a light scattering photometer DLS-700 manufactured by Otsuka Electronics Co., Ltd. It was measured and determined by a light scattering method.

2) Gel content rate of multilayer structure polymer and rubber-containing polymer The weighed multilayer structure polymer was extracted under reflux in an acetone solvent, and this extraction solution was separated by centrifugation. Subsequently, after drying the obtained solid content, mass measurement (mass after extraction) was carried out and it calculated | required with the following formula | equation.

Gel content rate (%) = (mass before extraction (g) −mass after extraction (g)) / mass before extraction (g)
3) Total light transmittance of the transparent protective layer The haze / transmission / reflectometer “HR-100” manufactured by Murakami Color Research Laboratory was used and measured according to JIS K7361-1.
4) Tensile elastic modulus of the transparent protective layer The obtained protective layer was measured under the following conditions using Strograph T manufactured by Toyo Seiki Seisakusho.
Sample size ... Length: 100mm
Width: 15mm
Tensile condition: Between chucks: 50 mm
Tensile speed: 50 mm / min.
5) Light resistance of the light diffusing plate Expose the cold protective tube actual exposure on the transparent protective layer side of the light diffusing plate under the conditions shown below, and the degree of discoloration when the light diffusing plate before and after exposure is placed on white paper. evaluated.

1) Cold cathode tube actual exposure conditions Cold cathode tube φ2.6 lamp Lamp current: 8 mA, 3 in parallel.
Atmospheric temperature: 23 ° C, 50RH%
Lamp-sample surface distance: 1.4mm (design value)
Sample surface temperature: around 50 ° C Exposure period: 6 months ・ Evaluation ○: Almost no discoloration compared to the light diffusion plate before exposure ×: Discoloration compared to the light diffusion plate before exposure

<Production of light diffusion plate>
As a light diffusing plate, a polycarbonate resin having a viscosity average molecular weight of 24,300 obtained from bisphenol A and phosgene, infusible acrylic polymer fine particles (Paraloid EXL-5136, manufactured by Rohm and Haas Company, weight distribution average particle diameter) : 7 μm) is added and mixed, and the thickness is maintained by using a T-die extruder with a vent while maintaining the extruder temperature at 250 to 300 ° C., the die temperature at 260 to 300 ° C., and the vacuum at the vent at 26.6 kPa. A polycarbonate resin light diffusion plate having a width of 2 mm and a width of 1,000 mm was obtained by melt extrusion.

Example 1
<Manufacture of multilayer structure polymer (H-1)>
After charging 8.5 parts of ion-exchanged water into a vessel equipped with a stirrer, a monomer mixture consisting of (I) shown below was charged and stirred and mixed. Next, 1.1 parts of the emulsifier (1) was added to the vessel while stirring, and stirring was continued again for 20 minutes to prepare an emulsified liquid (N-1). The average particle size of the dispersed phase in the obtained emulsion was 10 μm.

  Next, 186.5 parts of ion-exchanged water is placed in a polymerization vessel equipped with a cooler, the temperature is raised to 70 ° C., and the mixture prepared by adding (II) shown below to 5 parts of ion-exchanged water is collected at once. I put it in. Next, the emulsion (N-1) was dropped into the polymerization vessel over 8 minutes while stirring under nitrogen, and then the reaction was continued for 15 minutes to complete the polymerization of the innermost layer polymer (A-1). Subsequently, the monomer mixture consisting of (III) shown below was added in 90 minutes, and then the reaction was continued for 60 minutes to obtain a two-layer crosslinked rubber elastic body containing the crosslinked elastic polymer (B-1). .

  Subsequently, the mixture of (IV) shown below was dropped into the polymerization vessel over 45 minutes, and then the reaction was continued for 60 minutes to form the intermediate layer (D-1).

  Subsequently, after dropping the monomer mixture consisting of (V) into the polymerization vessel over 140 minutes, the reaction is continued for 60 minutes to form the outermost layer polymer (C-1), and the multilayer structure polymer (H- The polymer latex of 1) was obtained.

The weight average particle diameter measured after polymerization was 0.12 μm.
(I) MMA 0.3 part BA 4.5 part 1.3BD 0.2 part AMA 0.05 part CHP 0.025 part

(II) Sodium formaldehyde sulfoxylate 0.2 part Ferrous sulfate 0.0001 part EDTA 0.0003 part

(III) MMA 1.5 parts BA 22.5 parts BD 1.0 part AMA 0.25 parts CHP 0.016 parts

(IV) MMA 6 parts BA 4 parts AMA 0.075 parts CHP 0.0125 parts

(V) MMA 55.2 parts BA 4.8 parts nOM 0.204 parts tBH 0.08 parts

  The polymer latex of the obtained multilayer structure polymer (H-1) is filtered using a vibration type filtration device in which a SUS mesh (average opening 62 μm) is attached to the filter medium, and then an aqueous solution containing 3 parts of calcium acetate. The mixture was salted out, washed with water, separated and recovered, and dried to obtain a powdery multilayer structure polymer (H-1). The gel content of the multilayer structure polymer (H-1) was 60%. Further, when the multilayer structure polymer (H-1) was dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion was 18.

  Next, 100 parts of multilayer structure polymer (H-1), 2.1 parts of “ADK STAB LA-31RG” manufactured by Asahi Denka Co., Ltd. as a compounding agent, “ADK STAB AO-50” 0.1 of Asahi Denka Co., Ltd. Part, "Adekastab LA-57" manufactured by Asahi Denka Co., Ltd. was added and then mixed using a Henschel mixer, and the resulting mixture was heated to 230 ° C (Ikegai Iron Works Co., Ltd.) ) PCM-30) and kneaded to obtain pellets.

  The pellets produced by the above method were dried overnight at 80 ° C., and the dried pellets were supplied to a 40 mmφ non-vent screw type extruder (L / D = 26) equipped with a 300 mm wide T-die to obtain a 50 μm thick pellet. A transparent protective layer was produced. The conditions at that time were a cylinder temperature of 200 ° C. to 240 ° C., a T die temperature of 250 ° C., and a cooling roll temperature of 70 ° C. Further, the obtained transparent protective layer was thermally laminated on the light diffusing plate at 140 ° C. to obtain a light diffusing plate in which the transparent protective layer was laminated.

  Table 1 shows the total light transmittance of the transparent protective layer obtained, the tensile elastic modulus measurement results, and the degree of discoloration after the light diffusion plate exposure test.

Example 2
<Manufacture of multilayer structure polymer (L-1)>
195 parts of ion exchange water was charged into a reaction vessel equipped with a cooler, the temperature was raised to 70 ° C., and a mixture prepared by adding (LL1) shown below to 5 parts of ion exchange water was added all at once. Next, while stirring under nitrogen, a first monomer mixture consisting of (LL2) shown below was dropped into the reaction vessel over 8 minutes, and then the reaction was continued for 15 minutes to produce the innermost polymer (L- 1-A) was obtained. Here, Tg of the innermost layer polymer (L-1-A) was 13 ° C.

  Subsequently, a second monomer mixture consisting of (LL3) shown below is added to the polymerization vessel over 90 minutes, and then the reaction is continued for 60 minutes to contain the first intermediate layer layer containing a crosslinked elastic polymer. The union (L-1-B) was obtained. Here, Tg of the first intermediate layer polymer (L-1-B) was −40 ° C.

  Subsequently, the third monomer mixture (LL4) shown below was dropped into the polymerization vessel over 30 minutes, and then the reaction was continued for 60 minutes to obtain the second intermediate layer polymer (L-1-C). ) Was formed.

  Subsequently, after dripping the 4th monomer mixture which consists of the following (LL5) in a superposition | polymerization container over 130 minutes, reaction is continued for 60 minutes and outermost layer polymer (L-1-D) is made. An acrylic resin latex containing the multilayer structure polymer (L-1) was obtained. Here, Tg of the outermost layer polymer (L-1-D) was 94 ° C. The weight average particle diameter measured after polymerization was 0.09 μm.

  The polymer latex of the obtained multilayer structure polymer (L-1) was filtered in the same manner as in Example 1, and then salted out in an aqueous solution containing 3 parts of calcium acetate, washed and recovered, dried. A powdery multilayer structure polymer (L-1) was obtained. The resulting multilayer structure polymer (L-1) had a gel content of 70%. Further, when the multilayer structure polymer (L-1) was dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion was 8.

(LL1) Sodium formaldehyde sulfoxylate 0.10 parts
Ferrous sulfate 0.0002 parts
EDTA 0.0006 parts

(LL2) MMA 2.3 parts
2.13 parts of BA
St 0.37 parts
1.3BD 0.2 parts
CHP 0.01 parts
Emulsifier (1) 1.3 parts

(LL3) 24.54 parts of BA
St 4.26 parts
1.3BD 1.2 parts
AMA 0.225 parts
CHP 0.03 part

(LL4) MMA 6 parts
3.28 parts of BA
St 0.72 parts
AMA 0.15 parts
CHP 0.02 part

(LL5) MMA 52.25 parts
BA 2.26 parts
St 0.49 parts
nOM 0.193 parts
tBH 0.055 parts Next, 50 parts of a multilayer structure polymer (L-1), 50 parts of Dianal BR-75 (manufactured by Mitsubishi Rayon Co., Ltd., reduced viscosity 0.057 l / g) as a thermoplastic polymer, blended Asahi Denka Co., Ltd. “Adeka Stub LA-31RG” 1.5 parts, Ciba Specialty Chemicals Co., Ltd. “Irganox 1076” 0.1 part, Asahi Denka Co., Ltd. “Adeka Stub LA-57” 0.2 part was added and mixed using a Henschel mixer, and the resulting mixture was supplied to a degassing extruder (PCM-30 manufactured by Ikekai Tekko Co., Ltd.) heated to 230 ° C., kneaded and pelletized Got.

  The pellet produced by the above method was processed in the same manner as in Example 1 to produce a transparent protective layer having a thickness of 75 μm. Moreover, the obtained transparent protective layer was laminated | stacked on the light-diffusion board by the method similar to Example 1, and the light-diffusion board by which the transparent protective layer was laminated | stacked was obtained.

  Table 1 shows the total light transmittance of the transparent protective layer obtained, the tensile elastic modulus measurement results, and the degree of discoloration after the light diffusion plate exposure test.

Example 3
<Production of rubber-containing polymer (I-2)>
Under a nitrogen atmosphere, 244 parts of deionized water was placed in a reaction vessel equipped with a reflux condenser, and the temperature was raised to 80 ° C. Then, (15) shown below was added, and while stirring, 1/15 of the raw material (b) for the innermost polymer inner layer (I-2-A ₁ ) shown below was charged and held for 15 minutes. . Next, the remaining raw material (b) was continuously added at an increase rate of 8% / hour of the monomer component [raw material (b)] with respect to water, and then held for 60 minutes, and the innermost polymer inner layer ( I-2-A ₁ ) latex was obtained. The Tg of the innermost polymer inner layer (I-2-A ₁ ) alone was 24 ° C.

Subsequently, 0.6 parts of sodium formaldehyde sulfoxylate was added to the latex and held for 15 minutes. Then, while stirring at 80 ° C. in a nitrogen atmosphere, the raw material (c) for the innermost polymer outer layer (I-2-A ₂ ) shown below was converted into a monomer component [raw material (c)] for water. After the continuous addition at an increase rate of 4% / hour, the innermost layer polymer outer layer (I-2-A ₂ ) was polymerized by holding for 120 minutes to polymerize the innermost layer polymer (I-2- A latex of A) was obtained. The Tg of the innermost polymer outer layer (I-2-A ₂ ) alone was −38 ° C.

  Subsequently, 0.4 parts of sodium formaldehyde sulfoxylate was added to the latex and held for 15 minutes. Then, while stirring at 80 ° C. in a nitrogen atmosphere, the raw material (d) for the outermost layer polymer (I-2-C) shown below is increased by the monomer component [raw material (d)] with respect to water. After continuously adding at 10% / hour, holding for 60 minutes, the outermost layer polymer (I-2-C) is polymerized to obtain a polymer latex of the rubber-containing polymer (I-2). It was. The Tg of the outermost layer polymer (I-2-C) alone was 99 ° C.

  The weight average particle diameter of the rubber-containing polymer (I-2) measured after the polymerization was 0.28 μm.

(I) Sodium formaldehyde sulfoxylate 0.6 part Ferrous sulfate 0.00012 part EDTA 0.0003 part

(B) MMA 22.0 parts nBA 15.0 parts St 3.0 parts AMA 0.4 parts 1.3BD 0.14 parts tBH 0.18 parts Emulsifier (2) 1.0 parts

(C) nBA 50.0 parts St 10.0 parts AMA 0.4 parts 1.3BD 0.14 parts tBH 0.2 parts Emulsifier (2) 1.0 parts

(D) MMA 57.0 parts MA 3.0 parts nOM 0.3 parts tBH 0.06 parts The polymer latex of the obtained rubber-containing polymer (I-2) was mixed with a mesh made of SUS (average mesh). The mixture is filtered using a vibration type filtration apparatus having an opening of 150 μm), salted out in an aqueous solution containing 3 parts of calcium acetate, washed with water, dried and dried to obtain a powdery rubber-containing polymer (I-2). Obtained. The resulting rubber-containing polymer (I-2) had a gel content of 90%.

  Next, 16 parts of rubber-containing polymer (I-2), 84 parts of Acripet MD (manufactured by Mitsubishi Rayon Co., Ltd., reduced viscosity 0.057 l / g) as a thermoplastic polymer, Asahi Denka Co., Ltd. as a compounding agent "Adeka Stub LA-31RG" 1.0 part manufactured by Asahi Denka Co., Ltd. "Adeka Stub AO-60" 0.1 part, Asahi Denka Co., Ltd. "Adeka Stub LA-67" 0.15 part, Mitsubishi Rayon Co., Ltd. ) 2 parts "Metabrene P-551A" manufactured by Mitsubishi Rayon Co., Ltd. and 0.8 parts "Metbrene L-1000" manufactured by Mitsubishi Rayon Co., Ltd. were mixed using a Henschel mixer, and the resulting mixture was heated to 230 ° C. It supplied to the pneumatic extruder (Ikegai Iron Works Co., Ltd. PCM-30), and knead | mixed, and the pellet was obtained.

  The pellet produced by the above method was processed in the same manner as in Example 1 to produce a transparent protective layer having a thickness of 125 μm. Moreover, the obtained transparent protective layer was laminated | stacked on the light-diffusion board by the method similar to Example 1, and the light-diffusion board by which the transparent protective layer was laminated | stacked was obtained.

  Table 1 shows the total light transmittance of the transparent protective layer obtained, the tensile elastic modulus measurement results, and the degree of discoloration after the light diffusion plate exposure test.

Example 4
<Manufacture of multilayer structure polymer (Y-1)>
After charging 10.8 parts of deionized water in a container equipped with a stirrer, a monomer mixture consisting of (YY1) shown below was charged and stirred and mixed at room temperature. Next, 1.3 parts of emulsifier (1) was added to the vessel while stirring, and stirring was continued again for 20 minutes to prepare an emulsion.

  Next, 139.2 parts of deionized water was put into a polymerization vessel equipped with a condenser, the temperature was raised to 75 ° C., and the mixture prepared by adding (YY2) shown below to 5 parts of ion-exchanged water was added to the mixture. The whole was put into the polymerization vessel. Next, the emulsion was dropped into the polymerization vessel over 8 minutes while stirring under nitrogen, and then the reaction was continued for 15 minutes to complete the polymerization to obtain the innermost layer polymer (Y-1-A1).

  Subsequently, a monomer mixture consisting of (YY3) shown below was dropped into the polymerization vessel over 90 minutes, and then the reaction was continued for 60 minutes to obtain a crosslinked rubber elasticity containing a crosslinked elastic polymer (Y-1-A2). Got the body. Here, the Tg of the innermost layer polymer (Y-1-A1) alone was −48 ° C., and the Tg of the crosslinked elastic polymer (Y-1-A2) alone was −10 ° C.

  Subsequently, a monomer mixture consisting of (YY4) shown below was dropped into the polymerization vessel over 45 minutes, and then the reaction was continued for 60 minutes to form an intermediate layer polymer (Y-1-B). Here, the Tg of the intermediate layer polymer (Y-1-B) alone was 60 ° C.

  Next, after dropping the monomer mixture consisting of (YY5) shown below into the polymerization vessel over 140 minutes, the reaction is continued for 60 minutes to form the outermost layer polymer (Y-1-C), and the multilayer structure A polymer latex of the polymer (III-1) was obtained. Here, the Tg of the outermost layer polymer (Y-1-C) alone was 99 ° C. The weight average particle diameter measured after polymerization was 0.11 μm.

  The polymer latex of the obtained multilayer structure polymer (Y-1) is filtered by the same method as in Example 1, and then salted out in an aqueous solution containing 3.5 parts of calcium acetate, washed with water, recovered and dried. As a result, a powdery multilayer structure polymer (Y-1) was obtained. The resulting multilayer structure polymer (Y-1) had a gel content of 70%. Further, when the multilayer structure polymer (Y-1) was dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion was 20.

(YY1) MMA 0.3 part
4.45 parts of BA
1.3BD 0.2 parts
AMA 0.05 parts
CHP 0.025 part

(YY2) Sodium formaldehyde sulfoxylate 0.20 parts
Ferrous sulfate 0.0001 parts
EDTA 0.0003 parts

(YY3) MMA 9.5 parts
14.25 parts of BA
1.3BD 1.0 part
AMA 0.25 part
CHP 0.016 parts

(YY4) MMA 5.96 parts
MA 3.97 parts
AMA 0.07 parts
CHP 0.0125 part

(YY5) MMA 57 parts
MA 3 parts
nOM 0.264 parts
tBH 0.075 part Next, 75 parts of a multilayer structure polymer (Y-1), 25 parts of Acrypet VH (manufactured by Mitsubishi Rayon Co., Ltd., reduced viscosity 0.059 l / g) as a thermoplastic polymer, as a compounding agent Ciba Specialty Chemicals Co., Ltd. “Irganox 1076” 0.1 part, Ciba Specialty Chemicals Co., Ltd. “Chinubin 234” 1.4 parts, Asahi Denka Co., Ltd. “Adeka Stub LA-67” 0 After adding 3 parts, the mixture was mixed using a Henschel mixer, and the resulting mixture was supplied to a degassing extruder (PCM-30 manufactured by Ikekai Tekko Co., Ltd.) heated to 230 ° C. and kneaded to produce pellets. Obtained.

  The pellet produced by the above method was dried at 80 ° C. for a whole day and night, and processed in the same manner as in Example 1 to produce a transparent protective layer having a thickness of 50 μm. Moreover, the obtained transparent protective layer was laminated | stacked on the light-diffusion board by the method similar to Example 1, and the light-diffusion board by which the transparent protective layer was laminated | stacked was obtained.

  Table 1 shows the total light transmittance of the transparent protective layer obtained, the tensile elastic modulus measurement results, and the degree of discoloration after the light diffusion plate exposure test.

Comparative Example 1
The light diffusion plate without a transparent protective layer was exposed as it was, and the degree of discoloration of the light diffusion plate was observed. The results are shown in Table 1.

From the examples and comparative examples, the following became clear.
Since the light resistance of the light diffusing plate can be improved by laminating the transparent protective layer in Examples 1 to 4 on the light diffusing plate, the transparent protective layer of the present invention has high industrial utility value.

  On the other hand, when the transparent protective layer is not laminated as in Comparative Example 1, the light diffusing plate is discolored by exposure for a short time, and thus the light diffusing plate has a very low industrial utility value.

Claims (4)

  A transparent protective layer laminated on the light source side of the light diffusion plate for backlight.   A light diffusing plate for backlight comprising the transparent protective layer according to claim 1 laminated thereon.   A backlight device comprising a light source disposed on the transparent protective layer side of the backlight light diffusing plate according to claim 2. A liquid crystal display device comprising the backlight device according to claim 3.