JP2001342447A - Tacky agent for polarizing plate and optical member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tacky agent for polarizing plates excellent in long-term storage property and an optical member using the above tacky agent. SOLUTION: This tacky agent for polarizing plates is an acrylic tacky agent used for attaching polarizing plates and is characterized in that the difference between gel fraction of a tacky agent at initial stage and that of the tacky agent after heating for 500 hr at 80 deg.C is within the range of 5%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylic pressure-sensitive adhesive used for attaching a polarizing plate, and to a polarizing plate adhesive having excellent long-term storage properties, and an optical member using the same.

[0002]

2. Description of the Related Art In a liquid crystal display (LCD), a liquid crystal cell is provided with a polarizing plate, an elliptically polarizing plate, a polarizing plate with an optical compensation film, a polarizing plate with a reflection / semi-transmissive layer, a polarizing plate with a brightness enhancement film, and the like as an adhesive. Are generally laminated via a layer. For the production of such an LCD, a method is employed in which an adhesive is applied to a polarizing plate in advance and then adhered to a liquid crystal cell for the purpose of preventing quality variations and increasing the efficiency of LCD assembly. At that time, as the pressure-sensitive adhesive, an acrylic pressure-sensitive adhesive excellent in optical transparency, exhibiting appropriate adhesive properties such as wettability and cohesiveness, and excellent in weather resistance and heat resistance is widely used. The acrylic adhesive is an adhesive having an acrylic polymer as a base polymer,
Usually, a peroxide is used during polymerization of the acrylic polymer, so that the peroxide or a component derived therefrom remains.

[0003]

However, the physical properties of the pressure-sensitive adhesive change over a long period of time between the time when the acrylic pressure-sensitive adhesive is applied to the polarizing plate and the time when the polarizing plate is adhered, and the adhesive strength is changed. It has been known that the particle size becomes small, and peeling occurs when a durability test is performed after attaching to a night crystal display device. The cause of the change in physical properties of such an adhesive is as follows.
It has not been clarified so far, and there is no effective index for improving long-term storage.

Accordingly, it is an object of the present invention to provide a pressure-sensitive adhesive for a polarizing plate having excellent long-term storage properties and an optical member using the same.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and found that the peroxide component remaining in the acrylic pressure-sensitive adhesive causes a crosslinking reaction to proceed, thereby preserving the pressure-sensitive adhesive for a long time. The inventors have found that the subsequent physical properties change, and have found that the ease of progress of the crosslinking reaction can be accurately grasped by the change in the gel fraction before and after heating, and have completed the present invention.

That is, the pressure-sensitive adhesive for a polarizing plate of the present invention is an acrylic pressure-sensitive adhesive used for attaching a polarizing plate,
After leaving the adhesive at room temperature for one month after coating,
The difference in the gel fraction of the pressure-sensitive adhesive after heating at 0 ° C. for 500 hours is within 5%. Here, the gel fraction, after extracting the dissolved component of the adhesive using a good solvent,
It refers to the percentage of the weight of the insoluble matter (to the initial weight) after only the insoluble matter is removed and the solvent is dried and removed, and can be specifically measured by the method described in Examples.

[0007] In the above, it is preferred that the pressure-sensitive adhesive does not contain a peroxide component.

On the other hand, the optical member of the present invention has an adhesive layer comprising the above-mentioned adhesive for a polarizing plate in at least one layer of a polarizing plate or a laminate including the polarizing plate.

In this case, the polarizing plate or the laminate including the polarizing plate is a polarizing plate, a reflective polarizing plate, a semi-transmissive layer polarizing plate, a polarization separating polarizing plate, or a laminate obtained by laminating a retardation plate and the polarizing plate. It is preferably a body.

According to the pressure-sensitive adhesive for a polarizing plate of the present invention, the difference between the gel fraction of the pressure-sensitive adhesive after standing at room temperature for one month after the application of the pressure-sensitive adhesive and after further heating at 80 ° C. for 500 hours. Is within 5%, and as shown in the results of the examples,
It becomes a pressure-sensitive adhesive for polarizing plates with excellent long-term storage properties. When the difference in the gel fraction exceeds 5%, the progress of the crosslinking reaction increases, and the physical properties of the pressure-sensitive adhesive after long-term storage become poor. In addition, it is left at room temperature for one month after coating in order to stabilize the gel fraction in advance.

When no peroxide component is contained in the pressure-sensitive adhesive,
Providing a polarizing plate pressure-sensitive adhesive that can suppress the progress of the crosslinking reaction due to the peroxide component remaining in the acrylic pressure-sensitive adhesive and keep the difference in the gel fraction within 5% more reliably and has excellent long-term storage properties. Can be.

On the other hand, according to the optical member of the present invention, since the optical member has the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive for a polarizing plate having the above-described effects, the optical member has excellent long-term storage properties.

The polarizing plate or the laminate including the polarizing plate is a polarizing plate, a reflection type polarizing plate, a semi-transmissive layer type polarizing plate, a polarized light separating polarizing plate, or a stacked structure obtained by laminating the polarizing plate and the retardation plate. In this case, these are all adhered to a liquid crystal cell or the like via an adhesive layer, and the problem of long-term storage as described above may occur.
The present invention having the above-described effects is particularly useful.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

The pressure-sensitive adhesive for a polarizing plate of the present invention has a gel fraction of 5% or less after being left at room temperature for one month after coating and after further heating at 80 ° C. for 500 hours. Characteristically, preferably the difference in gel fraction is within 4%. In the present invention, an acrylic pressure-sensitive adhesive having excellent optical transparency, exhibiting appropriate adhesive properties such as wettability and cohesiveness, and having excellent weather resistance and heat resistance is used.

As the acrylic pressure-sensitive adhesive, an alkyl acrylate having an alkyl group having 1 to 9 carbon atoms may be used.
It is preferable to use an acrylic copolymer obtained from a monomer containing 99% by weight. In particular, the content of the alkyl acrylate having 1 to 9 carbon atoms in the alkyl group is 70 to 99% by weight, and the content of the functional monomer having a carboxyl group or / and a hydroxyl group is 1 to 30% by weight. Acrylic copolymers having a weight average molecular weight of 300,000 to 2.4 million are preferred. Such an acrylic copolymer becomes an acrylic pressure-sensitive adhesive having preferable physical properties by being crosslinked with a crosslinking agent.

The above-mentioned acrylic copolymers may be of one kind or two kinds.
70 to 99% by weight of an alkyl acrylate having 1 to 9 carbon atoms in one or more alkyl groups, and 1 to 30% by weight of a functional monomer having one or more carboxyl groups and / or hydroxyl groups. It can be prepared by an appropriate method such as a solution polymerization method, an emulsion polymerization method, or a suspension polymerization method using the above ratios.

At this time, a polymerization initiator is usually used,
In the present invention, in order to keep the difference in the gel fraction before and after heating within the above range, those not using peroxide-based ones such as benzoyl peroxide, acetyl peroxide, lauroyl peroxide, dicumyl peroxide, etc. preferable. Therefore, as the polymerization initiator, it is preferable to use an azo-based initiator such as an azonitrile compound such as azobisisobutyronitrile, a dialkylazo compound or a diarylalkylazo compound, or a disulfide-based initiator.

In order to keep the difference between the gel fractions before and after heating within the above-mentioned range, a peroxide-based polymerization initiator is not used, and a peroxide is used when crosslinking an acrylic copolymer. It is effective to use no system crosslinking agent.

Examples of the alkyl acrylate include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, amyl, and the like.
An alkyl acrylate having a linear or branched alkyl group having 1 to 9 carbon atoms such as a hexyl group, an octyl group, a 2-ethylhexyl group, and an isononyl group is used.

Examples of the functional monomer include carboxyl group-containing compounds having a C = C bond and having 3 to 10 carbon atoms, such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, and maleic anhydride. Or 2-hydroxyethyl acrylate, methacrylic acid 2
A hydroxyl group-containing compound having a C = C bond and having 2 to 10 carbon atoms, such as -hydroxyethyl, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, and allyl alcohol is used.

The functional monomer may contain two or more carboxyl groups or hydroxyl groups, and may contain one or more of both carboxyl groups and hydroxyl groups. Further, a compound containing two or more carboxyl groups may be modified to an anhydride.

The acrylic copolymer which can be preferably used in the present invention has a weight average molecular weight of 300,000 to 24.
Of those having a weight average molecular weight of 350,000 to 250,000, particularly 400,000 to 2.3 million.

The preparation of the acrylic pressure-sensitive adhesive can be carried out, for example, by a method in which a cross-linking agent is added to the liquid containing the acrylic copolymer. As the crosslinking agent to be blended, for example, a polyisocyanate-based crosslinking agent, an epoxy-based crosslinking agent,
Appropriate materials such as a metal chelate crosslinking agent and an amino resin crosslinking agent can be used. The amount of the crosslinking agent used is appropriately determined according to the type of the acrylic copolymer or the crosslinking agent so as to have a predetermined cohesive force. Generally, an acrylic copolymer 100
0.1 to 15 parts by weight, especially 0.2 to 10 parts by weight
Parts by weight, in particular from 0.3 to 5 parts by weight, of crosslinking agent are used.

Examples of the solvent for the acrylic pressure-sensitive adhesive include esters, ketones, aliphatic hydrocarbons and aromatic hydrocarbons, and it is preferable to use the solvent in solution polymerization as it is.

The formation of the pressure-sensitive adhesive layer on the polarizing plate may be performed by an appropriate method such as a coating method or a transfer method of the one provided on the separator. The surface of the pressure-sensitive adhesive layer exposed on the surface is preferably protected by a separator or the like until practical use. The pressure-sensitive adhesive layer may be of a light diffusion type by containing fine particles. The thickness of the pressure-sensitive adhesive layer may be appropriately determined according to the purpose of use, and is generally from 1 to 500.
μm.

The optical member of the present invention has the pressure-sensitive adhesive layer comprising the above-mentioned pressure-sensitive adhesive for a polarizing plate in at least one layer of a polarizing plate or a laminate including the polarizing plate. Examples are shown in FIG. 1 and FIG. In the optical member shown in FIG. 1, a protective film 1 is provided on an upper surface side of an optical material 2 which is a polarizing plate, an adhesive layer 3 is provided on a lower surface side, and a separator 4 is further attached. In the optical member shown in FIG. 2, the optical material 2 shown in FIG.
The protective film 1 is provided on the upper surface side, the adhesive layer 3 is provided on the lower surface side, and the separator 4 is further attached.

The polarizing plate or the laminate including the polarizing plate may be a polarizing plate, a reflective polarizing plate, a semi-transmissive layer polarizing plate, a polarization separating polarizing plate, or a laminate obtained by laminating a retardation plate with the polarizing plate. Is preferred. In the case of a laminate, an appropriate adhesive means such as the pressure-sensitive adhesive layer of the present invention or another pressure-sensitive adhesive layer may be used for the lamination.

Specific examples of the polarizing plate include a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymer-based partially saponified film, and iodine and / or dichroism. Examples thereof include stretched films obtained by adsorbing a dye, and oriented polyene films such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride.

The reflective polarizing plate is provided on the viewing side (display side).
This is for forming a liquid crystal display device or the like of a type that reflects and reflects incident light from the liquid crystal display device, and has an advantage that the incorporation of a light source such as a backlight can be omitted and the thickness of the liquid crystal display device can be easily reduced. . The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is provided on one side of the polarizing plate via a transparent resin layer or the like as necessary. The above-mentioned polarizing plate, in particular, a transparent resin layer provided on one side or both sides of the polarizing film as required can also serve as the protective film 1.

As a specific example of the reflective polarizing plate, a reflective layer is formed by providing a foil or a vapor-deposited film made of a reflective metal such as aluminum on one side of a transparent resin layer such as a protective film or the like which is matted as required. And the like. Further, there may be mentioned, for example, those in which fine particles are contained in the transparent resin layer to form a fine surface unevenness structure, and a reflective layer having a fine unevenness structure is provided thereon. The reflective layer is used in a state where the reflective surface is covered with a transparent resin layer, a polarizing plate, or the like, in order to prevent a decrease in the reflectance due to oxidation, and to maintain the initial reflectance for a long time, and to separately provide a protective layer. Is more preferable.

The reflection layer having the above-mentioned fine uneven structure has an advantage that the incident light is diffused by irregular reflection to prevent directivity and glare, and that unevenness in brightness can be suppressed.
Further, the transparent resin layer containing fine particles also has an advantage that the incident light and the reflected light thereof are diffused when transmitting the light and the unevenness of brightness can be further suppressed. The reflection layer having a fine uneven structure reflecting the fine uneven structure on the surface of the transparent resin layer is formed by, for example, making the metal transparent by an appropriate method such as an evaporation method such as a vacuum evaporation method, an ion plating method, and a sputtering method, and a plating method. It can be carried out by a method of directly attaching to the surface of the resin layer.

For the formation of the protective film or the transparent protective layer, a polymer excellent in transparency, mechanical strength, heat stability, moisture shielding property and the like are preferably used. Examples thereof include polyester resins and acetate resins, polyethersulfone resins and polycarbonate resins, polyamide resins and polyimide resins, polyolefin resins and acrylic resins, or acrylic and urethane resins,
A thermosetting resin such as an acrylic urethane type, an epoxy type, or a silicone type, or an ultraviolet curable type resin may be used.

The transparent protective layer may be formed by an appropriate method such as a method of applying a polymer or a method of laminating a film. The thickness may be determined appropriately. Generally 500μ
m or less, especially 1 to 300 µm, especially 5 to 200 µm. As the fine particles to be contained in the formation of the transparent resin layer having the fine surface unevenness structure, for example, an average particle size of 0.5
20 to 20 μm of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide, and the like, inorganic fine particles which may be conductive, organic fine particles of a crosslinked or uncrosslinked polymer, and the like. Transparent fine particles are used. The amount of the fine particles used is 2 to 25 parts by weight, preferably 5 to 2 parts per 100 parts by weight of the transparent resin.
0 parts by weight are common.

On the other hand, as a specific example of the retardation plate, a multilayer film obtained by stretching a film made of an appropriate polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefin, polyarylate, or polyamide is used. Examples thereof include a refractive film and a liquid crystal polymer alignment film. The retardation plate may be formed by laminating two or more retardation layers and controlling optical characteristics such as retardation.

A laminate of a polarizing plate or a reflective polarizing plate and a retardation plate in an appropriate combination functions as an elliptically polarizing plate or a reflective elliptically polarizing plate. Such elliptically polarizing plates and the like,
(Reflection type) A polarizing plate and a retardation plate can be formed by sequentially and separately laminating them in the manufacturing process of a liquid crystal display device so as to form a combination of a polarizing plate and a retardation plate. In addition, there is an advantage that the manufacturing efficiency of the liquid crystal display device can be improved due to excellent quality stability and laminating workability. Note that a circularly polarizing plate can be used depending on the type of the phase difference plate.

The semi-transmissive layer type polarizing plate is obtained by changing the reflective layer of the reflective type polarizing plate to a semi-transmissive reflective layer. According to this transflective layer type polarizing plate, a reflection mode in which the backlight is turned off under sunlight or the like by disposing a transflective type reflective layer via a polarizing plate on the backlight side of a liquid crystal cell having a backlight. Therefore, the liquid crystal display device can be visually recognized in the transmission mode in which the backlight is turned on at night or in a dark room.

The polarization separating plate has a characteristic of transmitting linearly polarized light having a predetermined polarization axis and reflecting other light, such as a multilayer thin film of a dielectric or a multilayer laminate of thin films having different refractive index anisotropy. As shown, the cholesteric liquid crystal layer, especially the cholesteric liquid crystal polymer oriented film or the one in which the oriented liquid crystal layer is supported on a film substrate, reflects either left-handed or right-handed circularly polarized light to produce other light. Any suitable material such as a material exhibiting transmission characteristics can be used.

Therefore, in the above-mentioned type of polarization separation plate that transmits linearly polarized light having a predetermined polarization axis, the transmitted light is incident on the polarization plate with the polarization axis aligned as it is, so that absorption loss by the polarization plate can be suppressed and efficiently. Can be transmitted. On the other hand, a polarization splitting plate that transmits circularly polarized light, such as a cholesteric liquid crystal layer, can be directly incident on a polarizer.However, from the viewpoint of suppressing absorption loss, the transmitted circularly polarized light is converted to linearly polarized light through a phase difference plate. It is preferable to make the light incident on the polarizing plate. Incidentally, by using a quarter-wave plate as the retardation plate, circularly polarized light can be converted into linearly polarized light.

A retardation plate that functions as a quarter-wave plate in a wide wavelength range such as a visible light region is, for example, a retardation layer that functions as a quarter-wave plate with respect to monochromatic light such as light having a wavelength of 550 nm. , For example, a method of superimposing a retardation layer functioning as a half-wave plate with the retardation layer exhibiting the above retardation characteristic. Therefore, the retardation plate disposed between the polarizing plate and the polarization separating plate may be composed of one or more retardation layers.

In the cholesteric liquid crystal layer, two or three or more cholesteric liquid crystal layers having different reflection wavelengths are combined so as to have an arrangement structure in which circularly polarized light is reflected in a wide wavelength range such as a visible light region. Thus, it is possible to obtain circularly polarized light transmitted in a wide wavelength range.

The layers forming the optical members such as the polarizing plate, the retardation plate, the protective film, the transparent protective layer, and the pressure-sensitive adhesive layer may be made of, for example, salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, cyano compounds, and the like. The ultraviolet absorbing ability can be provided by an appropriate method such as a method of treating with an ultraviolet absorbent such as an acrylate compound or a nickel complex compound.

The optical member of the present invention can be adhered to an appropriate member such as a liquid crystal cell via an adhesive layer. A liquid crystal display having at least one of the above optical members adhered to a liquid crystal cell. It is preferably used for the device.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and the like specifically showing the configuration and effects of the present invention will be described below.

Example 1 100 g of butyl acrylate, 5 g of acrylic acid, and 0.5 g of azobisisobutyronitrile were added to 100 g of ethyl acetate, and polymerized in a flask at 60 ° C. for 8 hours to obtain a polymer solution. 0.5 part by weight of an isocyanate-based crosslinking agent (trade name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to 100 parts by weight of the obtained acrylic polymer to obtain an adhesive syrup.

This adhesive syrup is applied to a 38 μm-thick polyester release film so as to have a thickness of 25 μm after drying, and a polyvinyl alcohol film having a thickness of 80 μm is stretched 5 times in an aqueous iodine solution. Thereafter, the resultant was dried, and bonded to a polarizing plate prepared by bonding cellulose triacetate films on both sides via an adhesive to prepare an optical member.

Comparative Example 1 An optical member was manufactured in the same manner as in Example 1 except that benzoyl peroxide was used instead of azobisisobutyronitrile.

Evaluation Test The gel fraction was measured after the adhesives of Examples and Comparative Examples were allowed to stand at room temperature for one month after coating, and after 500 hours at 80 ° C., and the amount of change before and after heating was measured. (= 50 at 80 ° C
(Gel fraction after leaving for 0 hour-Gel fraction one month after coating)
I asked.

The gel fraction was determined by taking out only the adhesive, weighing it, putting it in ethyl acetate, leaving it at room temperature for one week or more, taking out only the insoluble matter, and removing the solvent contained in the insoluble matter. After being dried and removed, it was weighed and determined by gel fraction = insoluble matter weight / initial weight × 100 (%).

After applying the pressure-sensitive adhesives of Examples and Comparative Examples,
Initial adhesion after leaving at room temperature for 30 days, and after coating,
After standing at room temperature for 24 months, the adhesive strength after long-term storage was measured. The adhesive strength was measured by cutting to a width of 25 mm, pressing the glass plate with a 2 kg rubber roller in a once-in-coming manner, performing autoclave treatment at 50 ° C. and 0.49 MPa for 15 minutes, and then peeling at 90 °. (Pulling speed 3
00 mm / min. 23 ° C).

[0051]

[Table 1] As is clear from the comparison between the examples and the comparative examples, when the pressure-sensitive adhesive does not contain a peroxide component, the change in the gel fraction after heating at 80 ° C. for 500 hours can be kept within 5%. It becomes a pressure-sensitive adhesive excellent in long-term storage property with almost no decrease in adhesive strength after storage.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an optical member of the present invention.

FIG. 2 is a sectional view showing another example of the optical member of the present invention.

[Explanation of symbols]

 2 Optical material (Polarizing plate) 3 Adhesive layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ning Takahashi 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Co., Ltd. No. Nitto Denko F-term (reference) 2H049 BA03 BA04 BA05 BB03 BB33 BB43 BB51 BB62 BC14 BC22 2H091 FA08X FA08Z FA11Z FA14Z FA41Z FB02 FC02 FC03 FC06 FC07 FD06 FD15 GA16 GA17 LA01 4J040 DF05 LA05 GA05 GA07 PA35

Claims (4)

[Claims] An acrylic pressure-sensitive adhesive used for attaching a polarizing plate, wherein the pressure-sensitive adhesive is left at room temperature for one month after coating and further heated at 80 ° C. for 500 hours. Wherein the difference in the gel fraction is within 5%. 2. The pressure-sensitive adhesive for a polarizing plate according to claim 1, wherein the pressure-sensitive adhesive does not contain a peroxide component. 3. An optical member having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive for a polarizing plate according to claim 1 in at least one layer of a polarizing plate or a laminate including the polarizing plate. 4. The polarizing plate or a laminate including the polarizing plate,
4. The optical member according to claim 3, wherein the optical member is a polarizing plate, a reflective polarizing plate, a semi-transmissive layer polarizing plate, a polarized light separating polarizing plate, or a laminate obtained by laminating a retardation plate with the polarizing plate.