JP4740096B2 - Scattering polarizer - Google Patents

Description

  The present invention relates to a scattering polarizer that can be used as a brightness enhancement film, and more specifically, a scattering type having scattering anisotropy that transmits only light in a specific polarization direction and reflects light in other polarization directions. It relates to a polarizer.

  As a configuration example of a liquid crystal display (LCD), as shown in FIG. 1, a glass substrate, a polarizing film, a brightness enhancement film, a diffusion film, a cold cathode tube (backlight unit), and a back surface side (back surface side) of a liquid crystal cell A configuration obtained by sequentially stacking reflection sheets and the like can be exemplified.

  In such a configuration, the polarizing film transmits only light of a specific polarization direction (linearly polarized light) and supplies it to the liquid crystal cell, and absorbs light of other polarization directions. The amount of light supplied decreases and the image becomes dark. Therefore, by arranging a brightness enhancement film on the light source side of the polarizing film as in the above configuration, the amount of light in the polarization direction transmitted by the polarizing film is increased, and the amount of light that can be supplied to the liquid crystal cell is increased. Brightening is done.

  As this kind of brightness enhancement film, a film using a scattering polarizer is known. When a scattering polarizer is used as a brightness enhancement film, if the polarization direction of light passing through the brightness enhancement film matches the polarization direction of light passing through the polarization film, light in the polarization direction absorbed by the polarization film can be obtained. The light is reflected on the light source side by the brightness enhancement film on the near side, and while the reflection and scattering are repeated between the brightness enhancement film and the reflection sheet, the polarization direction of the light changes and passes through the polarization film. As a result, the luminance of the image can be improved.

As such a scattering-type polarizer, for example, as disclosed in Patent Document 1, a polarizer in which films made of a polyester resin or the like are multilayered is known.
In addition, a scattering polarizer is known in which a polymer blend having a phase separation structure composed of two types of polymers having different birefringence is uniaxially stretched. Such a scattering type polarizer has scattering anisotropy in which the degree of scattering of polarized light is different between the stretching direction and the perpendicular direction, and therefore selectively transmits light in a specific polarization direction and light in other polarization directions. Can be selectively reflected or scattered. For example, in Patent Document 2, a sheet in which a second polymer such as polymethyl methacrylate or syndiotactic polystyrene is dispersed in a first polymer made of 2,6-polyethylene naphthalate or the like is stretched. Is disclosed.

Japanese National Patent Publication No. 9-506985 JP 2000-506990 A

  According to the present invention, in a scattering polarizer having a phase-separated structure composed of two types of polymers, it is possible to further improve the luminance by investigating factors that have a negative effect on luminance enhancement and reducing such factors. It is intended to provide a scattering polarizer.

  The present invention is a scattering polarizer having a continuous phase composed of a polyester-based resin (A) and a dispersed phase composed of a polystyrene-based resin (B), wherein the yellowness (YI value) is in the range of −3 to 3. We propose a scattering-type polarizer characterized by being in the inner area.

As a result of earnest research on a scattering polarizer having a continuous phase composed of a polyester-based resin (A) and a dispersed phase composed of a polystyrene-based resin (B), the present inventor has found that the yellowness of the scattering polarizer (hereinafter, The inventors have found that there is a correlation between the brightness improvement rate and the brightness improvement rate (simply referred to as “YI value”), and the present invention has been conceived based on such knowledge.
In a scattering type polarizer having a continuous phase made of a polyester-based resin (A) and a dispersed phase made of a polystyrene-based resin (B), if the YI value is in the range of −3 to 3, for example, a brightness enhancement film As a result, it is possible to further improve the image clarity and further increase the luminance improvement rate.

In the present invention, the form of the scattering polarizer is not particularly limited, and includes a plate form, a sheet form, a film form, a pellet form, and other forms.
In general, the term “sheet” refers to a product that is thin by definition in JIS, and usually has a thickness that is small and flat for the length and width, and “film” generally refers to a length. A thin flat product having an extremely small thickness compared to the width and an arbitrarily limited maximum thickness, usually supplied in the form of a roll (Japanese Industrial Standard JISK6900), but sheets and films. In the present invention, it is not necessary to distinguish between the two, and therefore, in the present invention, the term “film” includes both “sheet” and “sheet”. Shall be included.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail below, but the scope of the present invention is not limited to the embodiments described below.
In this specification, “X to Y” (X and Y are arbitrary numbers) is intended to mean “X or more and Y or less” unless otherwise specified, and simultaneously “greater than X and less than Y”. The intention of “preferably” is also included.

  The scattering polarizer according to the present embodiment (hereinafter referred to as “the present polarizer”) has a continuous phase made of a polyester resin (A) and a dispersed phase made of a polystyrene resin (B). The scattering polarizer is characterized in that the YI value is in the range of −3 to 3.

  The YI value of the present polarizer is preferably in the range of −3 to 3, particularly in the range of −2 to 2. As described above, in a scattering polarizer having a continuous phase made of a polyester resin (A) and a dispersed phase made of a polystyrene resin (B), if the YI value is in the range of −3 to 3, For example, by incorporating it into a liquid crystal display or the like as a brightness enhancement film, the image clarity can be further improved, and the brightness enhancement rate can be further enhanced.

  This polarizer forms the sheet | seat obtained by forming into a sheet form the composition containing the polyester-type resin (A) which comprises a continuous phase, and the polystyrene-type resin (B) which comprises a dispersed phase, for example. It can be obtained by stretching.

At this time, the YI value of the present polarizer is contained in, for example, the main component resin of the composition as a raw material, that is, the type of polyester resin (A) and polystyrene resin (B), the type of compatibilizer, and the sheet. It can be adjusted by the type and amount of impurities, such as crystal nucleating agent (silica) or metal, or by adding a bluing agent, etc., among which polyester resin (A) It is preferable to adjust the YI value of the present polarizer by selecting the YI value of the polystyrene resin (B), particularly the YI value of the polyester resin (A).
Specifically, the YI value of the polyester resin (A) and / or the polystyrene resin (B), particularly the YI value of the polyester resin (A) is in the range of −10 to 10, particularly in the range of −3 to 3. It is preferable to use one that is within. By using such a polyester resin (A) and / or polystyrene resin (B) having a YI value, particularly a polyester resin (A), the YI value of the present polarizer can be effectively adjusted.
Moreover, when polyester-type resin (A) and polystyrene-type resin (B) consist of a mixture, respectively, it is preferable that YI value exists in the range of -10-10 with each resin.

  In this polarizer, examples of the polyester resin (A) that can form a continuous phase include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid, or esters thereof, ethylene glycol, diethylene glycol, 1, 4 -An aliphatic polyester resin obtained by ring-opening polymerization of a lactone, such as an aromatic polyester resin obtained by polycondensation with glycols such as butanediol, neopentyl glycol, 1.4 cyclohexanedimethanol, or poly-ε-caprolactam Polyethylene adipate, polyethylene azelate, polyethylene succinate, polybutylene adipate, polybutylene azelate, polybutylene succinate, polybutylene succinate adipate, polytetramethylene succinate, cyclohexene Aliphatic dicarboxylic acid / cyclohexanedimethanol condensate, etc., aliphatic polyester resin obtained by polymerizing dibasic acid and diol, aliphatic polyester resin obtained by polymerizing hydroxycarboxylic acid such as polylactic acid, polyglycol, etc. Examples include aliphatic polyesters in which part of the ester bonds of the aliphatic polyester, for example, 50% or less of the total ester bonds are replaced with amide bonds, ether bonds, urethane bonds, and the like.

Among them, preferred is a crystalline polyester containing an aromatic molecule such as polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN). it can. Among these, a polymer blend or copolymer (copolymer) comprising a combination of two or more types can be said to be preferable.
Among these, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or a copolymer thereof is particularly preferable.

And it is preferable to select and use those having a YI value in the range of −10 to 10, particularly in the range of −3 to 3, from the above polyester resins.
In the case of polyethylene naphthalate (PEN), for example, Teonex TN8065S (polyethylene naphthalate homopolymer, manufactured by Teijin Chemicals Ltd., intrinsic viscosity 0.71), Teonex TN8065SC (polyethylene naphthalate homopolymer, Teijin Chemical ( Intrinsic viscosity 0.55), Teonex TN8756C (polyethylene naphthalate and polyethylene terephthalate copolymer, Teijin Chemicals Ltd., intrinsic viscosity 0.65) and the like can be mentioned as preferred examples.

On the other hand, the polystyrene resin (B) capable of constituting the dispersed phase is a polymer having styrene and may be a homopolymer or copolymer of styrene monomer or a polymer blend thereof, such as polystyrene, styrene-acrylonitrile. Examples thereof include a copolymer, a styrene- (meth) acrylic acid ester copolymer, and a styrene-maleic anhydride copolymer. Further, examples of the polystyrene include polystyrene having an atactic structure, polystyrene having an isotactic structure, polystyrene having a syndiotactic structure, etc. Among them, polystyrene having an atactic structure (simply “polystyrene” or “polystyrene”). PS ”) and polystyrene having a syndiotactic structure (hereinafter also referred to as“ sPS ”) are preferable, and among them, sPS is particularly preferable.
And it is preferable to select and use those having a YI value in the range of −10 to 10 and particularly in the range of −3 to 3 from the above polystyrene-based resins.

As a preferable combination of the polyester-based resin (A) and the polystyrene-based resin (B), the refractive index in one direction X after stretching is substantially the same among the above resins, that is, the refractive index difference is within 0.05, Preferably, a combination having a refractive index difference in the direction Y perpendicular to the direction X of 0.01 or less is selected and used, for example, a combination having a refractive index difference of 0.1 or more, preferably 0.3 or more. Is preferred. From this viewpoint, polyethylene naphthalate (PEN) and syndiotactic polystyrene (sPS), polyethylene naphthalate (PEN) and polystyrene (PS), polyethylene terephthalate (PET) and syndiotactic polystyrene (sPS), polyethylene terephthalate (PET) A combination of styrene and polystyrene (PS) can be mentioned as a preferred example.
Among these, a combination of a blend of polyethylene naphthalate (PEN) / polyethylene terephthalate (PET) and syndiotactic polystyrene (sPS) is particularly preferable. PEN has a large positive birefringence (Δn = 0.32), sPS has a large negative birefringence (Δn = −0.10), and the refractive index is PEN (1.64)> PET (1.59). ) ≈sPS (1.59). For this reason, when PEN and sPS are blended, when a sea-island structure is formed and stretched, the refractive index difference between PEN and sPS increases in direction X, and the X-direction component of light can be greatly reflected, while direction In Y, the difference in refractive index between PEN and sPS is closer to 0, and the Y-direction component of light can be almost transmitted. By blending an appropriate amount of PET with PEN, the refractive index in the direction Y can be lowered, and the refractive index difference from sPS can be made closer to zero.

  The blending ratio of the polyester-based resin (A) and the polystyrene-based resin (B) is adjusted in a mass ratio of (A) :( B) = 95: 5 to 50:50, particularly 75:25 to 50:50. It is preferable to do this. As the compounding ratio is closer to 50:50, the number of interfaces can be increased. When the proportion of the polystyrene resin (B) is less than 5 parts by mass or exceeds 50 parts by mass, the difference in refractive index between the two components is increased. Tends to be insufficient.

Moreover, you may add additives, such as a compatibilizing agent (C), as needed for the purpose of improving the dispersibility of a dispersed phase.
The compatibilizer (C) can be selected from conventional compatibilizers according to the type of continuous phase and dispersed phase. For example, polycarbonate, ester resin, resin having an epoxy group, resin having an oxazoline ring, Examples thereof include a block copolymer or a graft copolymer comprising at least one resin selected from resins having an azlactone group and at least one resin selected from styrene resins, polyphenylene oxide, and polyamides. Among these, from the viewpoint of improving dispersibility, a resin having an epoxy group or an oxazoline group is particularly preferable, and an epoxy-modified one is particularly preferable.
Commercially available compatibilizers such as “Reseda” (manufactured by Toagosei Co., Ltd.), “Epocross” (manufactured by Nippon Shokubai Co., Ltd.), and “Modiper” (manufactured by Nippon Oil & Fats Co., Ltd.) can also be used. Among these, “reseda” that is epoxy-modified polystyrene and “epocros” that is an oxazoline group-containing polymer are preferable, and “reseda” can be used particularly advantageously.
The blending ratio of the compatibilizer is, for example, 0.1 to 20 parts by mass, preferably 0.2 to 15 parts by mass with respect to 100 parts by mass in total of the polyester resin (A) and the polystyrene resin (B). In particular, the content is preferably 0.2 to 10 parts by mass, more preferably 1 to 10 parts by mass.

(Film forming method)
The composition containing the polyester resin (A) and the polystyrene resin (B) may be melted to form a sheet. For example, the composition is dried, supplied to an extruder, and melted by heating to a temperature equal to or higher than the melting point of the resin. Then, the melted composition may be extruded from the slit-shaped discharge port of the T die and adhered and solidified on a cooling roll to form a cast sheet (unstretched state). However, it is not limited to such a film forming method.

(Stretching method)
The formed sheet is preferably substantially uniaxially stretched. Here, “substantially uniaxial stretching” means stretching performed positively in only one direction. For example, in a process such as film formation, heat treatment, or winding, the direction is different from the one direction. It is intended to include the case where it is naturally stretched. Objectively, this is a case where the stretching ratio in one direction is 4 times or more of the stretching ratio in the direction orthogonal thereto.
By substantially uniaxially stretching in this way, the dispersed phase can be arranged and fixed in a substantially constant direction in the continuous phase, and the anisotropic scattering function can be exhibited. That is, the refractive index in the stretching direction of the polyester resin (A) constituting the continuous phase is remarkably increased, and the refractive index in the non-stretching direction is decreased. In the polystyrene resin (B) constituting the dispersed phase, the refractive index in the stretching direction is significantly decreased, and the refractive index in the non-stretching direction is increased. By uniaxial stretching, the refractive index of the continuous phase and the disperse phase differ greatly in the stretching direction, the direction perpendicular to the stretching direction is almost the same, and polarized light having the same refractive index is almost transmitted. In addition, it is possible to produce a scattering-type polarizing element having a property of scattering polarized light having different refractive indexes.

The stretching method may be any of free-width uniaxial stretching and constant-width uniaxial stretching, and any of stretching method, inter-roll stretching method, roll rolling method, and other methods may be employed.
The stretching temperature is preferably a temperature in the range of about the glass transition temperature (Tg) of the resin to (Tg + 50 ° C.), and particularly preferably 128 ° C. or less. When the stretching temperature is within this range, stretching can be performed stably without breaking during stretching.
The draw ratio is not particularly limited, but for example, it is preferably 4 times or more for TD or MD, preferably 4 to 5 times for TD or MD, and more preferably 4 to 4.5 times for TD or MD.

The stretched sheet is preferably heat-treated to impart heat resistance and dimensional stability. Under the present circumstances, it is preferable that the heat processing temperature shall be 180-230 degreeC, and it is more preferable to set it as 180-200 degreeC. The treatment time required for the heat treatment is preferably 1 second to 5 minutes.
When heat treatment is performed after stretching as described above, it is preferable to use a tenter stretching device capable of performing heat treatment after stretching as the stretching device.

  The thickness of the polarizer is not particularly limited. For example, when used for a brightness enhancement film, the thickness is preferably 100 μm to 250 μm, particularly preferably 100 μm to 200 μm.

(This polarizer)
For example, when the polarizer of the above configuration is measured by laminating it on a backlight unit, the luminance is improved by 1.3 times or more, particularly preferably by 1.4 times or more, compared with the case where the polarizer is not laminated. Can do.
Therefore, the present polarizer is used as a brightness enhancement film, and after adjusting the polarization direction of light passing through the brightness enhancement film and the polarization direction of light passing through the polarization film, for example as shown in FIG. In addition, a glass substrate, a polarizing film, a brightness enhancement film, a diffusion film, a cold-cathode tube (backlight unit), a reflective sheet, etc. are sequentially laminated on the back side (back side) of the liquid crystal cell to form a liquid crystal display (LCD). If comprised, compared with the case where the said brightness improvement film is not laminated | stacked, the brightness | luminance of an image can be improved 1.3 times or more, Most preferably, it is 1.4 times or more.
At this time, if light emitted from a cold cathode tube (backlight) as a light source is represented by light having one polarization direction and light having a polarization direction orthogonal thereto, the light incident on the brightness enhancement film In this case, the polarized light in the non-scattering direction passes through as it is, but the light in the other polarization direction perpendicular to this is reflected to the light source side, and scattering and reflection are repeated between the brightness enhancement film and the reflection sheet to form a brightness enhancement film. If the light is incident again and changed to light having a polarization direction that is not scattered, it passes, otherwise it is reflected again to the light source side, and this is repeated. Thus, since most of the light emitted from the light source can be supplied to the liquid crystal cell before long, the amount of light supplied to the liquid crystal cell can be increased, and the luminance of the image can be improved.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples, and various applications are possible without departing from the technical idea of the present invention.
Here, the take-up (flow) direction of the sheet or film when the sheet or film is manufactured is indicated by MD, and the orthogonal direction thereof is indicated by TD.

(1) Yellowness (YI value)
For yellowness, yellowness (YI value) was measured based on JIS K-7103 using a spectrocolorimeter (“SC-T” manufactured by Suga Test Instruments Co., Ltd.).
The yellowness (YI value) of the raw material resin was measured in the same manner as described above for each of the case where the sheet was formed and the case where it was pelletized. At that time, in the sheet forming, a stretched sheet having a thickness of 130 μm was formed under the same production conditions as in Example 1 described later, and the yellowness (YI value) was measured.

(2) Luminance evaluation A sample unit (brightness enhancement film) and a polarizing film are sequentially laminated and fixed on a backlight unit (Sharp “Aquos” 13-inch, model number: LC-13S4-S), and the screen is separated by 50 cm. The central luminance was measured with a luminance meter (manufactured by Minolta, model: LS-100).
The luminance (reference) when the sample sheet was not incorporated was measured, and the ratio to the luminance was calculated as the luminance improvement rate (see the following formula (1)). The larger this value, the higher the brightness.

  Formula (1): Brightness improvement rate = (luminance when the sample sheet is assembled / luminance before incorporation of the sample sheet)

(3) Chromaticity Evaluation Chromaticity x and y were evaluated using the same optical system as that for luminance evaluation. The chromaticity is defined in JIS K 7103.
In the evaluation, when the sample film is not inserted into the backlight (reference), the difference between x and y is 0.015 or less, and at least the difference between x and y is 0.015 or more. What became became x. The chromaticity when the sample sheet was not incorporated was x = 0.6422 and y = 0.2364.

<Example 1>
Polyethylene naphthalate (PEN, refractive index: 1.64, intrinsic viscosity: 0.71, Tg: 120 ° C., YI of pellet: 0) and polyethylene terephthalate (PET, refractive index: 1.58, Tg: 80 ° C., Epoxy-modified polystyrene obtained by graft polymerization of polystyrene as a compatibilizing agent, YI of pellet 0), syndiotactic polystyrene (sPS, refractive index: 1.59, Tg: 98 ° C., YI of pellet 3). (Epoxy-modified PS-graft-PS, refractive index: 1.58, YI of pellet: 7.5) and PEN: PET: sPS: PS-graft-PS = 50: 10: 40: 2 After being mixed and sufficiently mixed, while being fed by a constant mass feeder, it was extrusion kneaded at a resin temperature of 290 ° C. with a twin screw extruder, cooled and solidified to form a sheet having a thickness of 450 μm.
The obtained sheet was uniaxially stretched 4.5 times to TD at 120 ° C. using a small tenter device (manufactured by Kyoto Machine Co., Ltd.), heat-treated at 180 ° C. for 1 minute, and a sheet-like scattering type polarized light with a thickness of 120 μm. I got a child.

<Example 2>
The type of polyethylene naphthalate is a copolymer of polyethylene naphthalate and polyethylene terephthalate (mass ratio PEN: PET = 95/5 to 90/10, refractive index: 1.63, intrinsic viscosity 0.65, Tg: 118 ° C., A sheet-like scattering polarizer was obtained in the same manner as in Example 1 except that the pellet was changed to YI: 0).

<Comparative Example 1>
Except that the type of polyethylene naphthalate was changed to polyethylene naphthalate (PEN, refractive index: 1.65, intrinsic viscosity 0.95, Tg: 120 ° C., YI of pellet: −15), the same as in Example 1 Thus, a sheet-like scattering polarizer was obtained.

<Comparative example 2>
Except for changing the type of polyethylene naphthalate to polyethylene naphthalate (PEN, refractive index: 1.65, intrinsic viscosity 0.85, Tg: 120 ° C., YI of pellets: 4), the same as in Example 1 A sheet-like scattering polarizer was obtained.

<Comparative Example 3>
Except that the type of polyethylene naphthalate was changed to polyethylene naphthalate (PEN, refractive index: 1.65, intrinsic viscosity 0.65, Tg: 120 ° C., YI of pellet: 13), the same as in Example 1 A sheet-like scattering polarizer was obtained.

<Comparative example 4>
Except that the type of polyethylene naphthalate was changed to polyethylene naphthalate (PEN, refractive index: 1.65, intrinsic viscosity 0.45, Tg: 120 ° C., YI of pellet: 16), the same as in Example 1 A sheet-like scattering polarizer was obtained.

  As is clear from Table 1, the scattering polarizers of Examples 1 and 2 were superior in terms of luminance improvement rate and chromaticity as compared to the scattering polarizers of Comparative Examples 1 to 4. . In particular, the aspect of Example 1 was superior to the aspect of Example 2 in terms of the luminance improvement rate.

It is sectional drawing which showed an example of the general structure of a liquid crystal display (LCD).

Claims (6)

A scattering polarizer having a continuous phase composed of a polyester-based resin (A) and a dispersed phase composed of a polystyrene-based resin (B),
The polyester-based resin (A) is a resin containing polyethylene naphthalate having a pellet-like yellowness (YI value) measured in accordance with JIS K 7103 in the range of −3 to 3 ,
A scattering polarizer characterized in that the yellowness (YI value) of a scattering polarizer at a thickness of 120 μm measured in accordance with JIS K 7103 is in the range of −3 to 3. The yellowness (YI value) of the scattering-type polarizer measured in accordance with JIS K 7103 is determined by measuring the resin temperature of a composition containing a polyester resin (A) and a polystyrene resin (B) using a twin screw extruder. Extruded and kneaded at 290 ° C., cooled and solidified to form a sheet having a thickness of 450 μm, and the obtained sheet was uniaxially 4.5 times TD at 120 ° C. using a small tenter device (manufactured by Kyoto Machine Co., Ltd.). It is a yellowness (YI value) measured according to JIS K 7103 when stretched, heat treated at 180 ° C. for 1 minute, and formed into a sheet having a thickness of 120 μm. The scattering polarizer described. The scattering type polarizer according to claim 1 or 2, wherein the polystyrene resin (B) has a yellowness (YI value) in the range of -10 to 10. It is a scattering polarizer obtained by forming a film containing a polyester resin (A) constituting a continuous phase and a polystyrene resin (B) constituting a dispersed phase, and stretching the obtained sheet. The composition includes 95 to 50 parts by mass of the polyester resin (A) and 5 to 50 parts by mass of the polystyrene resin (B), and is composed of the polyester resin (A) and the polystyrene resin (B). The scattering polarizer according to any one of claims 1 to 3, further comprising 0.2 to 10 parts by mass of a compatibilizer (C) with respect to 100 parts by mass in total. The scattering polarizer according to any one of claims 1 to 4 , wherein a luminance improvement rate is 1.3 or more. The liquid crystal display device including a scattering polarizer according to claim 1.

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