WO2017149909A1

WO2017149909A1 - Polarizing plate

Info

Publication number: WO2017149909A1
Application number: PCT/JP2016/088101
Authority: WO
Inventors: 大介濱本
Original assignee: 日東電工株式会社
Priority date: 2016-03-04
Filing date: 2016-12-21
Publication date: 2017-09-08
Also published as: CN108780172B; KR20200022539A; JP6893762B2; JP2017156663A; TW201732332A; CN108780172A; SG11201807351UA; KR102219988B1; TWI645223B; KR20180107221A

Abstract

The present invention provides a polarizing plate that is improved in durability and that can be used as-is in a state where a polarizing film is layered on a resin substrate. This polarizing plate comprises a polyester resin substrate and a polarizing film that is layered on one side of the polyester resin substrate and that has a thickness of 10 µm or less. The degree of crystallinity of the polyester resin substrate as calculated by attenuated total reflection spectrometry is from 0.55 to 0.80, and the boric acid concentration in the polarizing film is from 10 wt% to 20 wt%.

Description

Polarizer

The present invention relates to a polarizing plate.

A method has been proposed in which a polarizing film is obtained by forming a polyvinyl alcohol-based resin layer on a resin substrate and stretching and dyeing the laminate (for example, Patent Document 1). According to such a method, a polarizing film having a small thickness can be obtained, and thus, for example, it has been attracting attention as being able to contribute to the thinning of the image display device.

The polarizing film can be used as it is laminated on the resin substrate (Patent Document 2). However, in such an embodiment, since a crack may occur in the polarizing plate, improvement in durability is required.

JP 2000-338329 A Japanese Patent No. 4997833

The present invention has been made in order to solve the above problems, and its main purpose is a polarizing plate that can be used while the polarizing film is laminated on the resin base material, and has improved durability. It is to provide a polarizing plate.

According to this invention, the polarizing plate which has a polyester-type resin base material and the polarizing film laminated | stacked on the one side of this polyester-type resin base material with a thickness of 10 micrometers or less is provided. In the polarizing plate of the present invention, the crystallinity calculated by the total reflection attenuation spectroscopy (ATR) measurement of the polyester-based resin substrate is 0.55 to 0.80, and the boric acid concentration in the polarizing film Is 10% to 20% by weight.
In one embodiment, the polyester-based resin is polyethylene terephthalate or a copolymer thereof.
In one embodiment, the polarizing film is laminated on one side of the polyester resin base material without an adhesive layer.
In one embodiment, the polarizing plate does not have a protective film on the side of the polarizing film opposite to the side on which the polyester resin substrate is laminated.
In one embodiment, the polarizing plate has an easy-adhesion layer between the polyester resin substrate and the polarizing film.
According to another situation of this invention, the manufacturing method of the said polarizing plate is provided. The production method includes forming a polyvinyl alcohol resin film on a polyester resin base material to produce a laminate, stretching the laminate, dyeing the polyvinyl alcohol resin film, and Crystallizing the polyester resin substrate.

According to the present invention, in a polarizing plate obtained by stretching and dyeing a laminate in which a polyvinyl alcohol-based resin film is formed on a resin substrate, the crystallinity of the resin substrate and boric acid in the polarizing film By adjusting the concentration within a specific range, it is possible to obtain a polarizing plate that can be used while the polarizing film is laminated on the resin base material and is excellent in durability.

(A) And (b) is a schematic sectional drawing of the polarizing plate in one embodiment of this invention, respectively.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Polarizing plate The polarizing plate of the present invention has a polyester resin substrate and a polarizing film having a thickness of 10 μm or less laminated on one side of the polyester resin substrate. Fig.1 (a) is a schematic sectional drawing of the polarizing plate in one Embodiment of this invention. The polarizing plate 10a includes a polyester-based resin base material 11 and a polarizing film 12 stacked in close contact with one surface of the polyester-based resin base material 11 (in other words, without an adhesive layer). FIG.1 (b) is a schematic sectional drawing of the polarizing plate in another embodiment of this invention. The polarizing plate 10 b further includes a protective film 13. The protective film 13 is arrange | positioned on the opposite side to the side by which the polyester-type resin base material 11 of the polarizing film 12 is arrange | positioned. The protective film 13 may be laminated on the polarizing film 12 via an adhesive layer, or may be laminated in close contact (without an adhesive layer). In the polarizing

plates

10a and 10b, the polyester resin substrate 11 can function as a protective film. In the present invention, it is possible to use as a protective film without peeling off the resin base material used during stretching and dyeing in the production process of the polarizing film, and the resin base material (protective film) is provided only on one side of the polarizing film. Even in the configuration of FIG. 1A, the generation of cracks can be suppressed. The polarizing

plates

10a and 10b may have an easy-adhesion layer (not shown) between the polyester resin substrate 11 and the polarizing film 12.

In general, in a polarizing plate obtained by stretching and dyeing a laminate in which a polyvinyl alcohol (hereinafter sometimes referred to as “PVA”) resin film is formed on a resin substrate, relaxation and shrinkage of orientation stress Dimensional changes occur in the resin base material and the PVA resin film due to the generation of stress and the like. At this time, since the amount of dimensional change between the two is different, it is presumed that distortion occurs at the interface and leads to generation of cracks. On the other hand, in this invention, the polyester-type resin base material which has the crystallinity of a specific range is used as a resin base material, and the boric acid density | concentration in a polarizing film is adjusted to a specific range. As a result, in both the absorption axis direction of the polarizing film and the direction orthogonal to the direction, the dimensional change amount of the resin base material and the dimensional change amount of the polarizing film are balanced, so that the distortion is caused at the resin base material / polarizing film interface. It becomes difficult to occur, and the generated distortion is also distributed in both directions. As a result, the occurrence of cracks can be suppressed. In this specification, the “perpendicular direction” includes a case of 90 ° ± 5.0 °, preferably 90 ° ± 3.0 °, more preferably 90 ° ± 1.0 °. is there. The “parallel direction” includes the case of 0 ° ± 5.0 °, preferably 0 ° ± 3.0 °, more preferably 0 ° ± 1.0 °.

A-1. Polarizing film The polarizing film is substantially a PVA resin film in which iodine is adsorbed and oriented. The thickness of the polarizing film is 10 μm or less, preferably 7.5 μm or less, more preferably 5 μm or less. On the other hand, the thickness of the polarizing film is preferably 0.5 μm or more, more preferably 1.5 μm or more. If the thickness is too thin, the optical properties of the obtained polarizing film may be deteriorated. The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizing film is preferably 40.0% or more, more preferably 41.0% or more, and further preferably 42.0% or more. The polarization degree of the polarizing film is preferably 99.8% or more, more preferably 99.9% or more, and further preferably 99.95% or more.

Any appropriate resin can be adopted as the PVA resin for forming the PVA resin film. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. . The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a saponification degree, a polarizing film having excellent durability can be obtained. If the degree of saponification is too high, there is a risk of gelation.

The average degree of polymerization of the PVA resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000 to 10,000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined according to JIS K 6726-1994.

The polarizing film contains boric acid. The boric acid concentration in the polarizing film is 10 to 20% by weight, preferably 12 to 19% by weight. When the boric acid concentration is within the range, the dimensional change rate of the polarizing film in the absorption axis direction and the direction orthogonal to the direction can be made close to the dimensional change rate of the polyester-based resin base material, and the absorption The difference between the dimensional change rate of the polarizing film in the axial direction and the dimensional change rate of the polyester resin substrate is the difference between the dimensional change rate of the polarizing film and the dimensional change rate of the polyester resin substrate in the direction perpendicular to the absorption axis. It can be prevented from becoming too large compared to. The boric acid concentration in the polarizing film is, for example, changing the boric acid concentration in a stretching bath, an insolubilizing bath, a cross-linking bath, etc., and changing the immersion time in these baths, etc. Can be adjusted. The boric acid concentration (% by weight) in the polarizing film can be determined using, for example, a boric acid amount index calculated from total reflection attenuation spectroscopy (ATR) measurement.
(Boric acid amount index) = (Intensity of boric acid peak 665 cm ⁻¹ ) / (Intensity of reference peak 2941 cm ⁻¹ )
(Boric acid concentration) = (Boric acid amount index) × 5.54 + 4.1
Here, both “5.54” and “4.1” are constants obtained by measuring the fluorescent X-ray intensity of a sample having a known boric acid concentration and creating a calibration curve.

A-2. Polyester-based resin base material Examples of the polyester-based resin base material include, for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), isophthalic acid, cyclohexane ring and the like. Copolymerized PET (PET-G) containing other dicarboxylic acids or alicyclic diols, other polyesters, copolymers and blends thereof, and the like can be used. Among these, it is preferable to use PET or copolymerized PET. According to these resins, in an unstretched state, it is amorphous and has excellent stretchability suitable for high-strength stretching, and heat resistance and dimensional stability can be imparted by crystallization by stretching and heating. Furthermore, the heat resistance of the grade which can apply | coat and dry PVA-type resin in an unstretched state is securable.

The glass transition temperature (Tg) of the polyester resin substrate is preferably 170 ° C. or lower. By using such a resin base material, it is possible to sufficiently ensure stretchability while suppressing crystallization of the PVA-based resin film. Considering plasticization of the resin base material with water and good stretching in water, it is more preferably 120 ° C. or lower. In one embodiment, the glass transition temperature of the polyester resin substrate is preferably 60 ° C. or higher. By using such a polyester-based resin base material, the polyester-based resin base material is deformed (for example, generation of irregularities, talmi, wrinkles, etc.) when a coating solution containing a PVA-based resin described later is applied and dried. Etc. can be prevented. Further, the laminate can be stretched at a suitable temperature (eg, about 60 ° C. to 70 ° C.). In another embodiment, a glass transition temperature lower than 60 ° C. may be used as long as the polyester resin base material is not deformed when applying and drying a coating solution containing a PVA resin. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

In one embodiment, the polyester resin base material preferably has a water absorption rate of 0.2% or more, and more preferably 0.3% or more. Such a polyester resin base material absorbs water, and the water can act as a plasticizer to be plasticized. As a result, the stretching stress can be greatly reduced in stretching in water, and the stretchability can be excellent. On the other hand, the water absorption rate of the polyester resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a polyester-based resin base material, it is possible to prevent problems such as a significant decrease in the dimensional stability of the polyester-based resin base material during production and deterioration of the appearance of the resulting laminate. Moreover, it can prevent at the time of extending | stretching in water, or a PVA-type resin film peeling from a polyester-type resin base material. The water absorption is a value determined according to JIS K 7209.

The thickness of the polyester resin base material is preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm.

The degree of crystallinity calculated by measuring total reflection attenuation (ATR) of the polyester resin substrate is 0.55 to 0.80, preferably 0.58 to 0.80, and more preferably 0.60 to 0.8. 75. When the degree of crystallinity of the polyester-based resin substrate is within the above range, the dimensional change rate of the polyester-based resin substrate in the absorption axis direction of the polarizing film and the direction orthogonal to the direction is close to the dimensional change rate of the polarizing film. And the difference between the dimensional change rate of the polarizing film in the direction of the absorption axis and the dimensional change rate of the polyester resin base material is such that the dimensional change rate of the polarizing film in the direction orthogonal to the absorption axis and the polyester resin It can prevent becoming large compared with the difference with the dimensional change rate of a base material. The degree of crystallization of the polyester resin substrate can be adjusted, for example, by changing the heating temperature and / or the heating time for crystallization. In addition, the crystallinity degree of the said polyester-type resin base material is computed based on the following formula | equation.
(Crystallinity) = (Intensity of crystal peak 1340 cm ⁻¹ ) / (Intensity of reference peak 1410 cm ⁻¹ )

A-3. Protective film Examples of the material for forming the protective film include (meth) acrylic resins, cellulose resins such as diacetyl cellulose and triacetyl cellulose, cycloolefin resins, olefin resins such as polypropylene, and polyethylene terephthalate resins. Examples thereof include ester resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. The thickness of the protective film is preferably 10 μm to 100 μm.

A-4. Easy-adhesion layer The easy-adhesion layer may be a layer formed substantially only from the composition for forming an easy-adhesion layer, and the composition for forming an easy-adhesion layer and the material for forming the polarizing film are mixed (compatible). A layer or region that is included). By forming the easy adhesion layer, excellent adhesion can be obtained. The thickness of the easy adhesion layer is preferably about 0.05 μm to 1 μm. The easy adhesion layer can be confirmed, for example, by observing the cross section of the polarizing plate with a scanning electron microscope (SEM). The composition for forming an easily adhesive layer will be described in detail in Section B.

A-5. Adhesive layer The adhesive layer is formed of any suitable adhesive or adhesive. The pressure-sensitive adhesive layer is typically formed of an acrylic pressure-sensitive adhesive. The adhesive layer is typically formed of a vinyl alcohol adhesive.

B. Production method of polarizing plate The production method of the polarizing plate of the present invention typically comprises forming a PVA resin film on a polyester resin substrate to produce a laminate, and stretching the laminate. And dyeing the PVA resin film, and crystallizing the polyester resin substrate.

B-1. Production of Laminate Any appropriate method can be adopted as a method of forming a PVA resin film on a polyester resin substrate. Preferably, a PVA-based resin film is formed by applying a coating liquid containing a PVA-based resin on a polyester-based resin base material and drying it. In one embodiment, an easy-adhesion layer forming composition is applied on a polyester-based resin substrate and dried to form an easy-adhesion layer, and a PVA-based resin film is formed on the easy-adhesion layer To do.

The forming material of the polyester resin base material is as described above. The thickness of the polyester resin substrate (thickness before stretching described later) is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 μm, it may be difficult to form a PVA resin film. If it exceeds 300 μm, for example, in stretching in water, it takes a long time for the polyester-based resin substrate to absorb water, and an excessive load may be required for stretching. Note that the degree of crystallinity calculated by the total reflection attenuation spectroscopy (ATR) measurement of the polyester-based resin substrate when used for the production of the laminate may be, for example, 0.20 to 0.50.

The coating solution is typically a solution obtained by dissolving the PVA resin in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used alone or in combination of two or more. Among these, water is preferable. The concentration of the PVA resin in the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film in close contact with the polyester resin substrate can be formed.

Additives may be added to the coating solution. Examples of the additive include a plasticizer and a surfactant. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the resulting PVA resin film. Moreover, as an additive, an easily bonding component is mentioned, for example. By using the easy-adhesion component, the adhesion between the polyester resin substrate and the PVA resin film can be improved. As a result, for example, problems such as peeling of the PVA-based resin film from the substrate can be suppressed, and dyeing and underwater stretching described later can be performed satisfactorily. As the easily adhesive component, for example, modified PVA such as acetoacetyl-modified PVA is used.

Any appropriate method can be adopted as a coating method of the coating solution. Examples thereof include a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (comma coating method and the like).

The coating / drying temperature of the coating solution is preferably 50 ° C. or higher.

The thickness of the PVA resin film (thickness before stretching described later) is preferably 3 μm to 20 μm.

Before forming the PVA-based resin film, the polyester-based resin substrate may be subjected to a surface treatment (for example, corona treatment), or an easy-adhesion layer-forming composition is applied onto the polyester-based resin substrate (coating) Processing). By performing such a treatment, the adhesion between the polyester-based resin substrate and the PVA-based resin film can be improved. As a result, for example, problems such as peeling of the PVA resin film from the substrate can be suppressed, and dyeing and stretching described below can be performed satisfactorily.

The easy-adhesion layer-forming composition preferably contains a polyvinyl alcohol-based component. Any appropriate PVA-based resin can be used as the polyvinyl alcohol-based component. Specific examples include polyvinyl alcohol and modified polyvinyl alcohol. Examples of the modified polyvinyl alcohol include polyvinyl alcohol modified with an acetoacetyl group, a carboxylic acid group, an acrylic group and / or a urethane group. Among these, acetoacetyl-modified PVA is preferably used. As the acetoacetyl-modified PVA, a polymer having at least a repeating unit represented by the following general formula (I) is preferably used.

In the above formula (I), the ratio of n to l + m + n is preferably 1% to 10%.

The average degree of polymerization of the acetoacetyl-modified PVA is preferably 1000 to 10,000, and preferably 1200 to 5,000. The saponification degree of acetoacetyl-modified PVA is preferably 97 mol% or more. The pH of a 4% by weight aqueous solution of acetoacetyl-modified PVA is preferably 3.5 to 5.5. The average polymerization degree and saponification degree can be determined according to JIS K 6726-1994.

The easy-adhesion layer-forming composition may further contain a polyolefin-based component, a polyester-based component, a polyacrylic-based component, or the like depending on the purpose. Preferably, the easily adhesive layer forming composition further includes a polyolefin-based component.

Any appropriate polyolefin resin can be used as the polyolefin component. Examples of the olefin component that is a main component of the polyolefin resin include olefin hydrocarbons having 2 to 6 carbon atoms such as ethylene, propylene, isobutylene, 1-butene, 1-pentene, and 1-hexene. These may be used alone or in combination of two or more. Among these, olefinic hydrocarbons having 2 to 4 carbon atoms such as ethylene, propylene, isobutylene and 1-butene are preferable, and ethylene is more preferably used.

The proportion of the olefin component in the monomer component constituting the polyolefin resin is preferably 50% by weight to 95% by weight.

The polyolefin-based resin preferably has a carboxyl group and / or an anhydride group thereof. Such a polyolefin resin can be dispersed in water, and an easy-adhesion layer can be formed well. Examples of the monomer component having such a functional group include unsaturated carboxylic acids and anhydrides thereof, half esters and half amides of unsaturated dicarboxylic acids. Specific examples thereof include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid and crotonic acid.

The molecular weight of the polyolefin resin is, for example, 5000 to 80000.

In the composition for forming an easily adhesive layer, the blending ratio of the polyvinyl alcohol component to the polyolefin component (the former: the latter (solid content)) is preferably 5:95 to 60:40, more preferably 20:80 to 50. : 50. When there are too many polyvinyl alcohol-type components, there exists a possibility that adhesiveness may not fully be acquired. Specifically, the peeling force required when peeling the polarizing film from the resin base material may be reduced, and sufficient adhesion may not be obtained. On the other hand, when there are too few polyvinyl alcohol-type components, there exists a possibility that the external appearance of the polarizing plate obtained may be impaired. Specifically, when the easy-adhesion layer is formed, a problem such as white turbidity of the coating film may occur, which may make it difficult to obtain a polarizing plate having an excellent appearance.

The easy-adhesion layer-forming composition is preferably aqueous. The easily adhesive layer forming composition may contain an organic solvent. Examples of the organic solvent include ethanol and isopropanol. The solid content concentration of the easily adhesive layer forming composition is preferably 1.0% by weight to 10% by weight.

Arbitrary appropriate methods can be employ | adopted as a coating method of the composition for easily bonding layer forming. After application of the easy-adhesion layer-forming composition, the coating film can be dried. The drying temperature is, for example, 50 ° C. or higher.

B-2. Stretching Any appropriate method can be adopted as a stretching method of the laminate. Specifically, it may be fixed end stretching (for example, a method using a tenter stretching machine) or free end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Moreover, simultaneous biaxial stretching (for example, a method using a simultaneous biaxial stretching machine) or sequential biaxial stretching may be used. The stretching of the laminate may be performed in one stage or in multiple stages. When performed in multiple stages, the draw ratio (maximum draw ratio) of the laminate described later is the product of the draw ratios of the respective stages.

The stretching treatment may be an underwater stretching method performed by immersing the laminate in a stretching bath, or an air stretching method. In one embodiment, the underwater stretching treatment is performed at least once, and preferably the underwater stretching treatment and the air stretching treatment are combined. According to stretching in water, the polyester resin substrate or PVA resin film can be stretched at a temperature lower than the glass transition temperature (typically about 80 ° C.), and the PVA resin film is crystallized. While suppressing, it can be stretched at a high magnification. As a result, a polarizing film having excellent polarization characteristics can be manufactured.

Any appropriate direction can be selected as the stretching direction of the laminate. In one embodiment, it extends | stretches in the longitudinal direction of an elongate laminated body. Specifically, the laminate is transported in the longitudinal direction and stretched in the transport direction (MD). In another embodiment, it extends | stretches in the width direction of an elongate laminated body. Specifically, the laminate is transported in the longitudinal direction and stretched in a direction (TD) orthogonal to the transport direction (MD).

The stretching temperature of the laminate can be set to any appropriate value depending on the forming material of the polyester resin substrate, the stretching method, and the like. In the case of adopting the air stretching method, the stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the polyester-based resin base material, more preferably the glass transition temperature (Tg) of the polyester-based resin base material + 10 ° C. or higher. Preferably it is Tg + 15 degreeC or more. On the other hand, the stretching temperature of the laminate is preferably 170 ° C. or lower. By stretching at such a temperature, it is possible to suppress rapid crystallization of the PVA-based resin and to suppress defects due to the crystallization (for example, preventing the orientation of the PVA-based resin film due to stretching). it can.

When the underwater stretching method is adopted as the stretching method, the liquid temperature of the stretching bath is preferably 40 ° C. to 85 ° C., more preferably 50 ° C. to 85 ° C. If it is such temperature, it can extend | stretch at high magnification, suppressing melt | dissolution of a PVA-type resin film. Specifically, as described above, the glass transition temperature (Tg) of the polyester-based resin substrate is preferably 60 ° C. or higher in relation to the formation of the PVA-based resin film. In this case, when the stretching temperature is lower than 40 ° C., there is a possibility that the stretching cannot be satisfactorily performed even in consideration of plasticization of the polyester-based resin substrate with water. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin film, and there is a possibility that excellent polarization characteristics cannot be obtained.

When employing an underwater stretching method, it is preferable to stretch the laminate by immersing it in an aqueous boric acid solution (stretching in boric acid in water). By using a boric acid aqueous solution as the stretching bath, the PVA resin film can be provided with rigidity that can withstand the tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid can form a tetrahydroxyborate anion in an aqueous solution and crosslink with a PVA resin by hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin film, the film can be stretched well, and a polarizing film having excellent polarization characteristics can be produced.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight with respect to 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin film can be effectively suppressed, and a polarizing film having higher characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

Preferably, iodide is blended in the stretching bath (boric acid aqueous solution). By blending iodide, elution of iodine adsorbed on the PVA resin film can be suppressed. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Etc. Among these, potassium iodide is preferable. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of water.

The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes. Preferably, the underwater stretching process is performed after the dyeing process.

The draw ratio (maximum draw ratio) of the laminate is preferably 4.0 times or more, more preferably 5.0 times or more with respect to the original length of the laminate. Such a high draw ratio can be achieved, for example, by employing an underwater drawing method (boric acid underwater drawing). In the present specification, the “maximum stretch ratio” refers to a stretch ratio immediately before the laminate is ruptured. Separately, a stretch ratio at which the laminate is ruptured is confirmed, and a value that is 0.2 lower than that value. .

B-3. Dyeing The dyeing of the PVA resin film is typically performed by adsorbing iodine to the PVA resin film. As the adsorption method, for example, a method of immersing a PVA resin film (laminated body) in a staining solution containing iodine, a method of applying the staining solution to the PVA resin film, and applying the staining solution to the PVA resin film The method of spraying etc. are mentioned. Preferably, the PVA resin film (laminate) is immersed in the dyeing solution. This is because iodine can be adsorbed well.

The staining solution is preferably an iodine aqueous solution. The amount of iodine is preferably 0.1 to 0.5 parts by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an iodide to the aqueous iodine solution. Specific examples of the iodide are as described above. The blending amount of iodide is preferably 0.02 to 20 parts by weight, more preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of water. The liquid temperature during dyeing of the dyeing liquid is preferably 20 ° C. to 50 ° C. in order to suppress dissolution of the PVA resin. When the PVA resin film is immersed in the dyeing solution, the immersion time is preferably 5 seconds to 5 minutes in order to ensure the transmittance of the PVA resin film. The staining conditions (concentration, liquid temperature, immersion time) can be set so that the polarization degree or single transmittance of the finally obtained polarizing film is within a predetermined range. In one embodiment, immersion time is set so that the polarization degree of the polarizing film obtained may be 99.98% or more. In another embodiment, the immersion time is set so that the obtained polarizing film has a single transmittance of 40% to 44%.

The staining process can be performed at any appropriate timing. When performing the said underwater extending | stretching, Preferably, it performs before an underwater extending | stretching.

B-4. Crystallization The crystallization of the polyester-based resin substrate is performed, for example, by heating the polyester-based resin substrate (substantially a laminate). Crystallization is preferably performed after dyeing and stretching the PVA resin film.

The heating temperature is typically a temperature that exceeds the glass transition temperature (Tg) of the polyester resin substrate. The heating temperature is preferably 90 ° C. or higher, more preferably 100 ° C. or higher. The heating temperature is preferably 125 ° C. or lower, more preferably 120 ° C. or lower. By heating at such a temperature, a polyester-type resin base material can be made into a desired crystallinity degree. The heating time can be appropriately set according to the heating temperature and the like. The heating time can be, for example, 3 seconds to 2 minutes.

In the above crystallization, it is preferable to perform the crystallization so that the haze value of the polyester-based resin substrate is 2% or less.

B-5. Other treatments In addition to stretching and dyeing, the PVA-based resin film (laminated body) may be appropriately subjected to treatment for forming a polarizing film. Examples of the treatment for forming the polarizing film include insolubilization treatment, crosslinking treatment, washing treatment, and drying treatment. In addition, the frequency | count, order, etc. of these processes are not specifically limited.

The insolubilization treatment is typically performed by immersing a PVA resin film (laminate) in a boric acid aqueous solution. By performing the insolubilization treatment, water resistance can be imparted to the PVA resin film. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20 ° C. to 50 ° C. Preferably, the insolubilization treatment is performed before the above-described underwater stretching or the above-described dyeing treatment.

The cross-linking treatment is typically performed by immersing a PVA resin film (laminate) in an aqueous boric acid solution. By performing the crosslinking treatment, water resistance can be imparted to the PVA resin film. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water. Moreover, when performing a crosslinking process after the said dyeing | staining process, it is preferable to mix | blend an iodide further. By blending iodide, elution of iodine adsorbed on the PVA resin film can be suppressed. The blending amount of iodide is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20 ° C. to 60 ° C. Preferably, the crosslinking treatment is performed before the underwater stretching. In a preferred embodiment, air stretching, dyeing treatment and crosslinking treatment are performed in this order.

The above-described cleaning treatment is typically performed by immersing a PVA resin film (laminated body) in a potassium iodide aqueous solution. The drying temperature in the drying treatment is preferably 30 ° C. to 100 ° C.

As described above, the polarizing plate of the present invention can be obtained by forming a polarizing film on a polyester resin substrate and crystallizing the polyester resin substrate.

C. Application of Polarizing Plate The polarizing plate of the present invention can be mounted on, for example, a liquid crystal display device. In this case, it is preferable that the polarizing film is mounted so as to be disposed closer to the liquid crystal cell than the polyester resin substrate. According to such a structure, the influence which the phase difference which a polyester-type resin base material can have on the image characteristic of the liquid crystal display device obtained can be excluded.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. In addition, the measuring method of each characteristic is as follows. In the following examples and comparative examples, “parts” and “%” represent “parts by weight” and “% by weight”, respectively.
≪Thickness≫
The measurement was performed using a digital micrometer (manufactured by Anritsu Co., Ltd., product name “KC-351C”).
≪Dimension change rate≫
From the polarizing plates obtained in Examples and Comparative Examples, the polarizing film and the resin base material were peeled off by giving a trigger to the end, and the temperature was increased from 30 ° C. to 100 ° C. by 10 ° C. / After the temperature was raised in minutes, the dimensional change rate was further measured when held at 100 ° C. for 60 minutes. In Example 6 with the easy-adhesion layer sandwiched between them, the polarizing film and the resin substrate were isolated in the same procedure from the polarizing plate prepared in the same manner except that the easy-adhesion layer was not formed. The dimensional change of the polarizing film and the resin base material was used.
Dimensional change rate (%) = (Dimension after heat treatment−Dimension before heat treatment) / Dimension before heat treatment × 100
≪Crystallinity≫
The polyester-based resin base materials obtained in the examples and comparative examples were subjected to total reflection attenuation spectroscopy (ATR) using a Fourier transform infrared spectrophotometer (FT-IR) (manufactured by Perkin Elmer, trade name “SPECTRUM2000”). ) The intensity of the crystal peak (1340 cm ⁻¹ ) and the intensity of the reference peak (1410 cm ⁻¹ ) were measured by measurement. The crystallinity was calculated by the following formula from the obtained crystal peak intensity and reference peak intensity.
(Crystallinity) = (Intensity of crystal peak 1340 cm ⁻¹ ) / (Intensity of reference peak 1410 cm ⁻¹ )
≪Glass transition temperature: Tg≫
Measured according to JIS K 7121.
≪Boric acid concentration≫
Using the Fourier transform infrared spectrophotometer (FT-IR) (manufactured by Perkin Elmer, trade name “SPECTRUM2000”) for the polarizing films obtained in Examples and Comparative Examples, total reflection attenuation using polarized light as measurement light The intensity of the boric acid peak (665 cm ⁻¹ ) and the intensity of the reference peak (2941 cm ⁻¹ ) were measured by spectroscopic (ATR) measurement. The boric acid amount index was calculated from the obtained boric acid peak intensity and the reference peak intensity by the following formula, and the boric acid concentration was determined from the calculated boric acid amount index by the following formula.
(Boric acid amount index) = (Intensity of boric acid peak 665 cm ⁻¹ ) / (Intensity of reference peak 2941 cm ⁻¹ )
(Boric acid concentration) = (Boric acid amount index) × 5.54 + 4.1
≪Crack evaluation≫
The polarizing plates obtained in the examples and comparative examples were heated in an oven at 100 ° C. for 240 hours in a state of being bonded to glass through an adhesive so that the polyester resin substrate was on the surface side. The presence or absence of cracks in the polarizing plate after heating was confirmed and evaluated according to the following criteria.
Good: No cracking
Defect: There is a crack

[Example 1]
As the resin substrate, an amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having a long water absorption rate of 0.75% and Tg of 75 ° C. was used.
One side of the resin substrate was subjected to corona treatment, and polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl modification degree 4. An aqueous solution containing 6%, a saponification degree of 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “Gosefimer Z200”) at a ratio of 9: 1 was applied and dried at 25 ° C., and the thickness was 11 μm. A PVA-based resin layer was formed. Thus, a laminate was produced.

The obtained laminate was uniaxially stretched at a free end 1.8 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 120 ° C. (air-assisted stretching).
Next, the laminate was immersed in an insolubilization bath (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Next, it is immersed for 60 seconds in a dyeing bath at 30 ° C. (an iodine aqueous solution obtained by blending 0.2 parts by weight of iodine and 1.5 parts by weight of potassium iodide with respect to 100 parts by weight of water). (Staining treatment).
Subsequently, it was immersed for 30 seconds in a crosslinking bath having a liquid temperature of 30 ° C. (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with respect to 100 parts by weight of water). (Crosslinking treatment).
Thereafter, the laminate is immersed in a boric acid aqueous solution (an aqueous solution obtained by blending 3 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 70 ° C. However, uniaxial stretching was performed in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds so that the total stretching ratio was 5.5 times (in-water stretching).
Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C. (cleaning treatment).

Next, the laminate was put into an oven at 100 ° C. for 30 seconds to crystallize the resin base material.
Thus, a polarizing plate in which a polarizing film having a thickness of 5 μm was laminated on the resin base material was obtained.

[Example 2]
A polarizing plate was obtained in the same manner as in Example 1 except that the laminate was placed in an oven at 110 ° C. for 30 seconds to crystallize the resin substrate.

[Example 3]
A polarizing plate was obtained in the same manner as in Example 1 except that the laminate was placed in an oven at 120 ° C. for 30 seconds to crystallize the resin substrate.

[Example 4]
Example 1 except that the amount of boric acid in the stretching bath during stretching in water was 3.5 parts by weight, and the laminate was put into an oven at 110 ° C. for 30 seconds to crystallize the resin substrate. In the same manner, a polarizing plate was obtained.

[Example 5]
Example 1 except that the amount of boric acid in the stretching bath during stretching in water was 2.5 parts by weight, and the laminate was put into an oven at 110 ° C. for 30 seconds to crystallize the resin substrate. In the same manner, a polarizing plate was obtained.

[Example 6]
The easy adhesion layer was provided on one side of the resin base material by the following method.
One side of the resin base material is subjected to corona treatment, and this corona treatment surface is subjected to acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “Gosefimer Z200”, polymerization degree 1200, saponification degree 99.0 mol. %, Acetoacetyl modification degree 4.6%) and a modified polyolefin resin aqueous dispersion (manufactured by Unitika Ltd., trade name “Arrow Base SE1030N”, solid content concentration 22%) and pure water were mixed. The mixture (solid content concentration 4.0%) was applied so that the thickness after drying was 2000 nm, and dried at 60 ° C. for 3 minutes to form an easy-adhesion layer. Here, the solid content mixing ratio of acetoacetyl-modified PVA and modified polyolefin in the mixed solution was 30:70.
A polarizing plate was obtained in the same manner as in Example 1 except that the surface of the easy-adhesion layer was subjected to corona treatment and a PVA resin layer was formed on the corona-treated surface.

[Comparative Example 1]
A polarizing plate was obtained in the same manner as in Example 1 except that the laminate was placed in an oven at 85 ° C. for 30 seconds to crystallize the resin substrate.

[Comparative Example 2]
Example 1 except that the amount of boric acid in the stretching bath during stretching in water was 4.0 parts by weight, and the laminate was put into an oven at 110 ° C. for 30 seconds to crystallize the resin substrate. In the same manner, a polarizing plate was obtained.

[Comparative Example 3]
A polarizing plate was obtained in the same manner as in Example 1 except that the laminate was put in an oven at 95 ° C. for 30 seconds to crystallize the resin substrate.

Table 1 shows the production conditions of the polarizing plate and the characteristics of the obtained polarizing plate in Examples and Comparative Examples. In the table, MD is the absorption axis direction of the polarizer, and TD is the direction orthogonal to the absorption axis.

As shown in Table 1, in the polarizing plate of the example having the resin base material having a specific crystallinity and the polarizing film satisfying the specific boric acid concentration, occurrence of cracks is suppressed. On the other hand, it can be seen that the polarizing plate of the comparative example is cracked and inferior in durability to the polarizing plate of the example. In addition, the polarizing plate of Example 6 is superior in adhesion between the resin base material and the polarizing film (PVA-based resin layer) as compared to the polarizing plates of other examples or comparative examples. Further, undesired peeling or floating of the polarizing film (PVA resin layer) or the resin base material during processing of the polarizing plate (for example, punching) was suitably prevented.

The reason why the occurrence of cracks in the polarizing plate of the example was suppressed is estimated as follows. That is, in the polarizing plate of the example, the difference between the dimensional change rate of the resin base material and the dimensional change rate of the polarizing film in the MD direction (dimensional change rate of the resin base material−dimensional change rate of the polarizing film) and in the TD direction. The difference between the dimensional change rate of the resin substrate and the dimensional change rate of the polarizing film (the dimensional change rate of the resin base material−the dimensional change rate of the polarizing film) is within 5%, and the dimensional change rate in the TD direction. Difference (absolute value) is close to the difference (absolute value) in the dimensional change rate in the MD direction (within ± 1.5%). Since the polarizing film is oriented in the stretching direction (MD), the mechanical properties tend to be weak in the direction (TD) orthogonal to the stretching direction. Therefore, by making the difference (absolute value) of the dimensional change rate in the TD direction close to the difference (absolute value) of the dimensional change rate in the MD direction, the occurrence of cracks is suppressed without biasing the strain in the TD direction. It is thought.

The polarizing plate of the present invention is suitably used for an image display device, for example.

Claims

A polarizing plate having a polyester resin base material and a polarizing film having a thickness of 10 μm or less laminated on one side of the polyester resin base material,
The degree of crystallinity calculated by total reflection attenuation spectroscopy of the polyester resin substrate is 0.55 to 0.80,
A polarizing plate, wherein the concentration of boric acid in the polarizing film is 10% by weight to 20% by weight.
The polarizing plate according to claim 1, wherein the polyester resin is polyethylene terephthalate or a copolymer thereof.
The polarizing plate according to claim 1 or 2, wherein the polarizing film is laminated on one side of the polyester resin substrate without an adhesive layer.
The polarizing plate according to any one of claims 1 to 3, wherein the polarizing film does not have a protective film on the side opposite to the side on which the polyester resin base material is laminated.
The polarizing plate according to any one of claims 1 to 4, further comprising an easy-adhesion layer between the polyester resin substrate and the polarizing film.
Forming a polyvinyl alcohol resin film on a polyester resin substrate to produce a laminate,
Stretching the laminate,
Dyeing the polyvinyl alcohol resin film; and crystallizing the polyester resin substrate;
The manufacturing method of the polarizing plate in any one of Claim 1 to 5 containing these.