CN111308605B

CN111308605B - Polarizing plate, liquid crystal display device, and organic electroluminescent display device

Info

Publication number: CN111308605B
Application number: CN202010283114.7A
Authority: CN
Inventors: 白石贵志; 吕宜桦
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2015-11-13
Filing date: 2016-11-11
Publication date: 2022-04-22
Anticipated expiration: 2036-11-11
Also published as: JP7407158B2; CN108351461B; TWI751121B; TW202128416A; CN111308604B; CN111308604A; TWI763577B; JP2020181213A; CN108351461A; KR102444055B1; TW201726395A; WO2017082375A1; TW202144172A; CN111308605A; TWI751939B; KR20180084774A; JP2022017257A; JP6743044B2; JPWO2017082375A1; KR20220129673A

Abstract

Polarizing plate, liquid crystal display device and organic electroluminescent display device. The present invention addresses the problem of providing a polarizing plate that is thin and has excellent strength, in which light leakage does not occur even when exposed to high-temperature and high-humidity conditions, and further, appearance defects such as cracking of a polarizing plate are suppressed from occurring in environments in which high and low temperatures are repeated. A polarizing plate comprising a polarizing plate, a protective film and an adhesive layer, wherein when the dimensional change rate of the protective film after 1 hour under a condition of a relative humidity of 5% at 85 ℃ in the direction parallel to the light transmission axis direction of the polarizing plate is referred to as the dimensional change rate of the protective film (85 ℃), and the dimensional change rate of the protective film after 0.5 hour under a condition of a relative humidity of 95% at 30 ℃ in the direction parallel to the light transmission axis direction of the polarizing plate is referred to as the dimensional change rate of the protective film (30 ℃), the absolute value of the difference between the dimensional change rate of the protective film (85 ℃) and the dimensional change rate of the protective film (30 ℃) is 0.02 to 0.50.

Description

Polarizing plate, liquid crystal display device, and organic electroluminescent display device

The present application is a divisional application filed on 2016, 11/h, under the name of 201680065892.0, entitled "polarizing plate, liquid crystal display device, and organic electroluminescent display device".

Technical Field

The present invention relates to a polarizing plate that can be used in various optical applications. Further, the present invention relates to a liquid crystal display device and an organic electroluminescence display device having the polarizing plate.

Background

Polarizing plates are widely used as a supply element of polarized light in display devices such as liquid crystal display devices and as a detection element of polarized light. A polarizing plate obtained by stretching and dyeing a polyvinyl alcohol film is suitably used for such a polarizing plate.

Patent document 1 (jp 2012-145645) discloses a polarizing plate in which the smaller the linear expansion of the protective film as compared with the linear expansion in the transmission axis direction of the polarizer, the less cracks (fractures) in the polarizer. According to patent document 1, a test (thermal shock acceleration test) in which a polarizing plate is simply subjected to a step of raising and lowering the temperature between-40 ℃ and 85 ℃ is carried out, thereby evaluating cracks (cracks) in the polarizing plate. The evaluation based on the linear expansion described in patent document 1 is generally a parameter depending on the temperature.

In recent years, a thin polarizing plate is required, and a polarizer is required to be thin.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2012-145645

Disclosure of Invention

Problems to be solved by the invention

However, the polarizing plate produced by stretching has a problem that cracks (fractures) are easily generated along the stretching axis direction, and for example, if the polarizing plate is exposed to an environment in which rapid temperature changes occur, the polarizing plate fractures, and an optical defect such as a defect in appearance or light leakage may occur. With the recent thinning of polarizing plates, cracks in the polarizer are more likely to occur, and therefore solutions are required.

Further, a polarizing plate including polyvinyl alcohol has low resistance to humidity, and thus is limited in use under humid conditions.

For example, in the invention described in patent document 1, an evaluation based on linear expansion is performed. However, since the evaluation method based on linear expansion is generally expressed by a temperature-dependent parameter, reference 1 does not take any consideration of the relationship between the crack (fracture) of the polarizing plate and humidity.

When the polarizer is thinned in order to satisfy the demand for thinning of the polarizing plate, for example, when a scratch is generated on the surface of the protective film, a crack may be generated in the film-like polarizer.

The invention aims to provide a polarizing plate which does not generate light leakage even if exposed under the conditions of high temperature and high humidity. Further, an object of the present invention is to provide a polarizing plate in which occurrence of appearance defects such as cracks in a polarizing plate is suppressed under an environment where high and low temperatures are repeated.

Means for solving the problems

The present invention includes the following aspects.

[1] A polarizing plate having a polarizer, a protective film and an adhesive layer,

the dimensional change rate of the protective film after 1 hour at 85 ℃ with a relative humidity of 5% was defined as the dimensional change rate of the protective film (85 ℃),

when the dimensional change rate of the protective film after 0.5 hours at 30 ℃ and 95% relative humidity was recorded as the dimensional change rate of the protective film (30 ℃),

the absolute value of the difference between the dimensional change rate (85 ℃) of the protective film and the dimensional change rate (30 ℃) of the protective film is 0.02 to 0.50.

[2] The polarizing plate according to [1], wherein a dimensional change rate of the polarizer after 1 hour under a condition of a relative humidity of 5% at 85 ℃ in a transmission axis direction of the polarizer is defined as a dimensional change rate of the polarizer (85 ℃),

the dimensional change rate of the polarizing plate after 0.5 hours at 30 ℃ and 95% relative humidity in the transmission axis direction of the polarizing plate was defined as the dimensional change rate of the polarizing plate (30 ℃),

the dimensional change rate (8) of the polarizing plate was measuredThe absolute value of the difference between 5 ℃ C. and the dimensional change rate (30 ℃ C.) of the polarizing plate is denoted as F_PZ，

The absolute value of the difference between the dimensional change rate (85 ℃ C.) of the protective film and the dimensional change rate (30 ℃ C.) of the protective film is denoted as F_PF，

Subjecting the above F to_PZMinus the above F_PFThe difference obtained is denoted Δ F_TDAnd is and

ΔF_TDrelative to F_PZRatio of (Δ F)_TD/F_PZ) Is in the range of 0.5 to 0.95.

[3] The polarizing plate according to [1] or [2], wherein the polarizer, the protective film, and the adhesive layer are sequentially stacked.

[4] The polarizing plate according to [1] or [2], wherein the protective film, the polarizer, and the adhesive layer are sequentially stacked.

[5] The polarizing plate according to any one of [1] to [4], wherein the protective film is a transparent resin film containing a cellulose ester resin, a polyester resin, a polycarbonate resin, a (meth) acrylic resin, or a mixture of at least 2 or more of them.

[6] A liquid crystal display device, wherein the polarizing plate according to any one of [1] to [5] is laminated on a liquid crystal cell via the pressure-sensitive adhesive layer.

[7] An organic electroluminescent display device, wherein the polarizing plate according to any one of the above [1] to [5] is laminated on an organic electroluminescent display through the pressure-sensitive adhesive layer.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention provides a polarizing plate which is suppressed in cracks and fractures generated in a polarizer even under high-temperature conditions and high-humidity conditions and has excellent durability. The polarizing plate of the present invention can exhibit good polarization characteristics without causing light leakage, cracks in the polarizing plate, and the like even in an environment where high and low temperatures are repeated, and further, even in an environment where dew condensation occurs. Therefore, the polarizing plate of the present invention can be used under various conditions such as high temperature conditions and high humidity conditions, which have not been conventionally applied, without causing light leakage, cracks, and the like.

Further, according to the present invention, the polarizing plate can be made thin, and even when a flaw is generated on the surface of the protective film, the crack of the polarizing plate can be suppressed. Therefore, the polarizing plate of the present invention is thin and has excellent strength and durability.

Drawings

Fig. 1 (a) is a schematic cross-sectional view showing an example of the layer structure of the polarizing plate according to the present invention, and fig. 1 (b) is a schematic cross-sectional view showing another example of the layer structure of the polarizing plate according to the present invention.

Fig. 2 (a) is a schematic plan view showing the axis angles of the transmission axis and the absorption axis in the polarizing plate having the transmission axis (solid line) in the width direction, and fig. 2 (b) is a schematic plan view showing the axis angles of the transmission axis and the absorption axis in the polarizing plate having the transmission axis (solid line) in the length direction.

Fig. 3 is a schematic cross-sectional view showing an example of the layer structure of the polarizing plate according to the present invention and the glass substrate to which the polarizing plate is bonded.

Detailed Description

Hereinafter, the polarizing plate according to the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

Fig. 1 is a schematic cross-sectional view showing an example of a preferable layer structure in a polarizing plate according to the present invention. In fig. 1 (a), a polarizer 11, a protective film 12, and an adhesive layer 13 are stacked in a polarizing plate 100. Similarly, in fig. 1 (b), a protective film 12, a polarizer 11, and an adhesive layer 13 are stacked in the polarizing plate 100. As described above, in the present invention, the stacking order of the polarizing plate, the protective film, and the adhesive layer is not particularly limited.

The polarizing plate in the present invention is a member having a function of converting light such as natural light into linearly polarized light, and generally has a transmission axis and an absorption axis. The transmission axis direction of such a polarizing plate is understood as a vibration direction of transmitted light when natural light is transmitted in the polarizing plate. On the other hand, the absorption axis of the polarizer is perpendicular to the transmission axis of the polarizer. The polarizing plate may be a stretched film in general, and the absorption axis direction of the polarizing plate coincides with the stretching direction thereof.

In the present invention, the term "direction parallel to the transmission axis direction of the polarizing plate" means a direction parallel or substantially parallel (forming an angle within ± 7 degrees) to the transmission axis direction of the polarizing plate.

In the present invention, the dimensional change rate after 1 hour under the condition of 85 ℃ relative humidity of 5% is measured according to the following formula. The dimensional change rate after 1 hour under the condition of 85 ℃ and 5% relative humidity may be described as a dimensional change rate (85 ℃).

For example, in the present invention, the dimensional change rate of the protective film after 1 hour under the condition of a relative humidity of 5% at 85 ℃ in the direction parallel to the transmission axis direction of the polarizing plate may be described as the dimensional change rate of the protective film (85 ℃).

The dimensional change rate of the polarizing plate after 1 hour under the condition of a relative humidity of 5% at 85 ℃ in the transmission axis direction of the polarizing plate is described as the dimensional change rate (85 ℃).

Hereinafter, for the sake of explanation, the dimensional change rate of the protective film (85 ℃ C.) and the dimensional change rate of the polarizing plate (85 ℃ C.) may be simply referred to as the dimensional change rate (85 ℃ C.).

Dimensional change rate (85 ℃) [ (L0-L85)/L0] × 100

[ wherein L0 represents the film size of the cut film in the direction (longitudinal direction or width direction) parallel to the transmission axis direction of the polarizing plate,

l85 indicates the film size in the direction (longitudinal direction or width direction) parallel to the transmission axis direction of the polarizing plate after 1 hour under the condition of 85 ℃ relative humidity of 5%. ]

For example, when the film was cut and the dimension in the width direction (L0) was measured, the dimension in the width direction of the film was also measured after standing for 1 hour under the condition of a relative humidity of 5% at 85 ℃ (L85) and the dimensional change rate was calculated. Further, when the size (L0) of the protective film obtained by removing the polarizer and the like from the polarizing plate after the polarizing plate was manufactured and measured in the direction parallel to the light transmission axis direction of the polarizer, the protective film was allowed to stand at 85 ℃ under a relative humidity of 5% for 1 hour, and then the size (L85) of the protective film in the direction parallel to the light transmission axis direction of the polarizer was also measured, and the dimensional change rate was calculated.

The dimensional change rate (85 ℃) calculated in this manner can show either a positive value (i.e., shrinkage) or a negative value (i.e., expansion). The protective film having a positive dimensional change rate (85 ℃ C.) is formed, for example, by: a polyolefin resin selected from the group consisting of a chain polyolefin resin and a cyclic polyolefin resin; cellulose ester resins selected from cellulose triacetate and cellulose diacetate, (meth) acrylic resins selected from polymethyl methacrylate resins (PMMA resins) and the like, and the like.

In the same manner as described above, in the present invention, the dimensional change rate after 0.5 hours at 30 ℃ and 95% relative humidity was calculated, and the film whose dimensional change rate (85 ℃) was measured according to the following formula. The dimensional change rate after 0.5 hours at 30 ℃ and 95% relative humidity may be described as a dimensional change rate (30 ℃).

For example, in the present invention, the dimensional change rate of the protective film after 0.5 hours under the condition of 30 ℃ relative humidity of 95% in the direction parallel to the transmission axis direction of the polarizing plate may be described as the dimensional change rate of the protective film (30 ℃). On the other hand, the dimensional change rate after 0.5 hours under the condition of 30 ℃ relative humidity of 95% in the direction parallel to the transmission axis direction of the polarizing plate may be referred to as the dimensional change rate of the polarizing plate (30 ℃).

Hereinafter, for the sake of explanation, the dimensional change rate of the protective film (30 ℃) and the dimensional change rate of the polarizing plate (30 ℃) may be simply referred to as the dimensional change rate (30 ℃).

Dimensional change rate (30 ℃) [ (L030-L30)/L0] × 100

[ wherein L030 is the film size after measuring the dimensional change rate (85 ℃) in the direction (longitudinal direction or width direction) parallel to the transmission axis direction of the polarizing plate,

l30 indicates the film size in the direction (longitudinal direction or width direction) parallel to the transmission axis direction of the polarizing plate after 0.5 hour under the condition of 30 ℃ relative humidity of 95%. ]

For example, L030 can be measured after measuring the dimensional change rate (85 ℃ C.), and leaving at 23 ℃ and 55% humidity for 15 minutes.

The dimensional change rate (30 ℃) calculated in this manner can show either a positive value (i.e., shrinkage) or a negative value (i.e., expansion). The protective film having a positive dimensional change rate (30 ℃) is formed, for example, by: polyolefin resins such as chain polyolefin resins and cyclic polyolefin resins; a polyester resin; such as polyethylene terephthalate.

On the other hand, the protective film having a negative dimensional change rate (30 ℃) is formed, for example, by: cellulose ester resins such as cellulose triacetate and cellulose diacetate, and (meth) acrylic resins such as polymethyl methacrylate resin (PMMA resin).

In the protective film of the present invention, the sign of the dimensional change rate (85 ℃) and the sign of the dimensional change rate (30 ℃) may be the same sign (positive, negative or zero) or different signs at the same time, as long as the absolute value of the difference between the dimensional change rate (85 ℃) and the dimensional change rate (30 ℃) is within the range of the present invention.

In the present invention, the absolute value of the difference between the dimensional change rate (85 ℃) of the protective film and the dimensional change rate (30 ℃) of the protective film is 0.02 to 0.50. The absolute value of the difference between the dimensional change rate (85 ℃) of the protective film and the dimensional change rate (30 ℃) of the protective film is preferably 0.03 to 0.30, and more preferably 0.03 to 0.20.

The polarizing plate of the present invention has an absolute value of the difference in dimensional change rate within the above range, and thus can suppress cracks generated in the polarizer under high-temperature and high-humidity conditions, suppress light leakage, and have excellent durability. In addition, the polarizing plate of the present invention can exhibit good polarization characteristics without light leakage, cracks, and the like even under such an environment that high temperatures and low temperatures are repeated.

Further, the polarizing plate provided with the protective film having such characteristics can reduce the thickness of the polarizer and can suppress cracking of the polarizer even when the surface of the protective film is scratched.

In a preferred embodiment, in the polarizing plate according to the present invention,

the dimensional change rate of the polarizing plate after 1 hour at 85 ℃ with a relative humidity of 5% in the transmission axis direction of the polarizing plate was defined as the dimensional change rate of the polarizing plate (85 ℃),

the absolute value of the difference between the dimensional change rate (85 ℃ C.) of the polarizing plate and the dimensional change rate (30 ℃ C.) of the polarizing plate is denoted as F_PZ，

Subjecting the above F to_PZMinus the above F_PFThe difference obtained is denoted Δ F_TDWhen the temperature of the water is higher than the set temperature,

by Δ F_TD＝F_PZ-F_PFThe table does not show that,

the dimensional change rate can be calculated as described above.

ΔF_TDRelative to F_PZRatio of (Δ F)_TD/F_PZ) Preferably in the range of 0.5 to 0.95. Δ F_TD/F_PZMore preferably 0.55 to 0.95, and still more preferably 0.60 to 0.95.

ΔF_TD/F_PZWhen the amount is more than 0.95, the shrinkage and/or expansion behavior of the protective film is smaller than that of the polyvinyl alcohol film, and the polyvinyl alcohol film may be cracked due to the strain between the polyvinyl alcohol film and the protective film.

By having such a relationship between the polarizer and the protective film, a polarizing plate having excellent durability can be provided in which cracks generated in the polarizer are suppressed under high-temperature conditions and high-humidity conditions. In addition, the polarizing plate of the present invention can exhibit good polarization characteristics without light leakage, cracks, and the like even under such an environment that high temperatures and low temperatures are repeated. Further, the polarizing plate provided with the protective film having such characteristics can reduce the thickness of the polarizer and can suppress cracking of the polarizer even when the surface of the protective film is scratched.

In a preferred embodiment, the polarizing plate of the present invention is a polarizing plate in which a polarizer, a protective film, and an adhesive layer are disposed in this order. In another preferred embodiment, the polarizing plate of the present invention is a polarizing plate in which a protective film, a polarizer, and an adhesive layer are disposed in this order. In a preferred embodiment, the polarizing plate of the present invention and the protective film are bonded to each other via an adhesive layer. The thickness of the adhesive layer is, for example, 0.01 to 5 μm. The adhesive layer may be any known in the art.

For example, as shown in fig. 2, the polarizing plate of the present invention may have an absorption axis and a transmission axis of a polarizer.

For example, (a) of fig. 2 is a schematic plan view showing the axis angles of the transmission axis 11a and the absorption axis 11b in the polarizing plate 100 having the transmission axis 11a of the polarizer in the width direction and the absorption axis 11b of the polarizer in the length direction. Fig. 2 (b) is a schematic plan view showing the axis angles of the transmission axis 11a and the absorption axis 11b in the polarizing plate 100 having the transmission axis 11a of the polarizer in the longitudinal direction and the absorption axis 11b of the polarizer in the width direction.

In a preferred embodiment, as shown in fig. 2 (a), the polarizing plate 100 may have a rectangular outer shape having long sides and short sides, for example. In this case, the light transmission axis 11a of the polarizing plate 100 (polarizer 11) may be parallel or substantially parallel to the short side of the polarizing plate 100 (the angle is within ± 7 degrees). On the other hand, the absorption axis 11b is perpendicular to the transmission axis 11 a.

In another preferred embodiment, as shown in fig. 2 (b), the transmission axis 11a of the polarizing plate 100 (polarizer 11) may be parallel or substantially parallel to the long side of the polarizing plate 100 (the angle is within ± 7 degrees). On the other hand, the absorption axis 11b is perpendicular to the transmission axis 11 a.

[ polarizing plate ]

The polarizing plate may be a product obtained by adsorbing a dichroic dye onto a uniaxially stretched polyvinyl alcohol resin layer and orienting the resin layer. The polarizer can be made thin when the thickness is usually 20 μm or less. In the present invention, a polarizing plate having a thickness of, for example, 10 μm or less, and more preferably 8 μm or less, can be used. The polarizing plate in the present invention generally has a thickness of 2 μm or more.

As the polyvinyl alcohol resin, a polyvinyl acetate resin saponified can be used. Examples of the polyvinyl acetate resin include a copolymer of vinyl acetate and another monomer copolymerizable therewith, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

The saponification degree of the polyvinyl alcohol resin may be in the range of 80 mol% or more, preferably 90 mol% or more, and more preferably 95 mol% or more. The polyvinyl alcohol resin may be a partially modified polyvinyl alcohol, and examples thereof include a polyvinyl alcohol resin prepared by using an olefin such as ethylene or propylene; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; alkyl esters of unsaturated carboxylic acids and acrylamides. The polyvinyl alcohol resin preferably has an average polymerization degree of 100 to 10000, more preferably 1500 to 8000, and further preferably 2000 to 5000.

The polarizing plate can be manufactured, for example, by: the polyvinyl alcohol film is produced by uniaxially stretching an original film made of a polyvinyl alcohol resin, dyeing with a dichroic dye (dyeing treatment), treating with an aqueous boric acid solution (boric acid treatment), washing with water (washing treatment), and finally drying.

The uniaxial stretching of the polyvinyl alcohol resin film may be performed before the dyeing with the dichroic dye, simultaneously with the dyeing with the dichroic dye, or after the dyeing with the dichroic dye. In the case where uniaxial stretching is performed after dyeing with a dichroic dye, the uniaxial stretching may be performed before boric acid treatment or may be performed during boric acid treatment. Further, of course, uniaxial stretching may be performed in these plural stages. In order to conduct uniaxial stretching, stretching may be conducted by passing between rolls having different peripheral speeds, or by nipping with a heat roll. The stretching may be performed in a dry manner by stretching in the air, or may be performed in a wet manner by stretching in a state of being swollen with a solvent. The final draw ratio of the polyvinyl alcohol resin film is usually about 4 to 8.

In the dyeing treatment, the polyvinyl alcohol resin film is dyed with a dichroic dye, and the dichroic dye is adsorbed in the film. The dyeing treatment may be carried out by, for example, immersing the polyvinyl alcohol resin film in an aqueous solution containing a dichroic dye. As the dichroic dye, specifically, iodine or a dichroic dye is used.

When iodine is used as the dichroic dye, a method of immersing a polyvinyl alcohol resin film in an aqueous solution containing iodine and potassium iodide to dye the film is generally employed. The iodine content in the aqueous solution is usually about 0.01 to 0.5 parts by weight relative to 100 parts by weight of water, and the potassium iodide content is usually about 0.5 to 10 parts by weight relative to 100 parts by weight of water. The temperature of the aqueous solution is usually about 20 to 40 ℃, and the time for immersing the aqueous solution is usually about 30 to 300 seconds.

On the other hand, when a dichroic dye is used as the dichroic dye, a method of immersing a polyvinyl alcohol resin film in an aqueous solution containing a water-soluble dichroic dye to dye the resin film is generally employed. The content of the dichroic dye in the aqueous solution is usually 1 × 10 with respect to 100 parts by weight of water^-31X 10 parts by weight^-2About the weight portion. The aqueous solution may contain an inorganic salt such as sodium sulfate. The temperature of the aqueous solution is usually about 20 to 80 ℃, and the time for immersing the aqueous solution is usually about 30 to 300 seconds.

The boric acid treatment is performed by, for example, immersing the dyed polyvinyl alcohol resin film in an aqueous boric acid solution. The content of boric acid in the aqueous boric acid solution is usually about 2 to 15 parts by weight, preferably 5 to 12 parts by weight, based on 100 parts by weight of water. When iodine is used as the dichroic dye, the aqueous boric acid solution preferably contains potassium iodide. The content of potassium iodide in the aqueous boric acid solution is usually about 2 to 20 parts by weight, preferably 5 to 15 parts by weight, based on 100 parts by weight of water. The immersion time of the film in the aqueous boric acid solution is usually about 100 seconds to 1200 seconds, preferably 150 seconds or more, more preferably 200 seconds or more, and preferably 600 seconds or less, more preferably 400 seconds or less. The temperature of the aqueous boric acid solution is usually 50 ℃ or higher, preferably 50 to 85 ℃. In the aqueous boric acid solution, sulfuric acid, hydrochloric acid, acetic acid, ascorbic acid, or the like may be added as a pH adjuster.

The polyvinyl alcohol resin film after the boric acid treatment is usually subjected to a water washing treatment. The water washing treatment is performed by immersing the boric acid-treated polyvinyl alcohol resin film in water. After washing with water, the resultant was dried to obtain a polarizing plate. The temperature of water in the water washing treatment is usually about 5 to 40 ℃, and the immersion time is usually about 2 to 120 seconds. The subsequent drying is usually performed by using a hot air dryer or a far infrared heater. The drying temperature is usually 40-100 deg.C, and the drying time is usually about 120-600 seconds.

[ protective film ]

As described above, in the protective film of the present invention, the absolute value of the difference between the dimensional change rate (85 ℃) of the protective film and the dimensional change rate (30 ℃) of the protective film is 0.02 to 0.50.

The protective film is laminated on at least one surface of the polarizing plate. A protective film (first protective film) may be stacked on one surface of the polarizing plate, and another protective film (second protective film) may be stacked on the other surface. A protective film (first protective film) is preferably stacked on one surface of the polarizing plate. The first protective film and the second protective film may be a single layer, or a plurality of films may be stacked with an adhesive or a bonding agent interposed therebetween.

The protective film (first protective film) and the second protective film may each be a transparent resin film formed of a thermoplastic resin. Examples of the thermoplastic resin include polyolefin resins such as a chain polyolefin resin and a cyclic polyolefin resin exemplified by a polypropylene resin; cellulose ester resins such as cellulose triacetate and cellulose diacetate; polyester resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; a polycarbonate-based resin; a (meth) acrylic resin selected from the group consisting of polymethyl methacrylate resins; or a mixture of at least 2 or more of them, and the like. Further, a copolymer of at least 2 or more monomers constituting the above resin may also be used.

The cyclic polyolefin resin is generally a general term for resins polymerized by using a cyclic olefin as a polymerization unit, and examples thereof include resins described in Japanese patent application laid-open Nos. 1-240517, 3-14882, and 3-122137. Specific examples of the cyclic polyolefin resin include ring-opened (co) polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers (typically random copolymers) of cyclic olefins and linear olefins such as ethylene and propylene, graft polymers obtained by modifying these with unsaturated carboxylic acids or derivatives thereof, and hydrogenated products of these. Among these, norbornene-based resins obtained using norbornene-based monomers such as norbornene and polycyclic norbornene-based monomers are preferably used as the cyclic olefin.

Various products are commercially available as cyclic polyolefin resins. Examples of commercially available products of cyclic polyolefin-based resins include, in terms of trade names, "TOPAS" (registered trademark) produced by TOPAS ADVANCED POLYMERS GmbH and sold by polyplasics co.ltd. in japan, "art" (registered trademark) sold by JSR CORPORATION, "ZEONOR" (registered trademark) and "ZEONEX" (registered trademark) sold by ZEON CORPORATION, and "APEL" (registered trademark) sold by mitsui chemical co.

Further, a commercially available product of the film-formed cyclic polyolefin resin film may be used as the protective film. Examples of commercially available products include "ARTON FILM" (which is a registered trademark of JSR CORPORATION), "Escena" (which is a registered trademark) and "SCA 40" which are sold by SEQUENCE CHEMICAL CO., and "ZEONOR FILM" (which is a registered trademark) which is sold by ZEON CORPORATION, in terms of the trade names.

The cellulose ester resin is usually an ester of cellulose and a fatty acid. Specific examples of the cellulose ester resin include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Further, those obtained by copolymerization of these compounds or those obtained by modifying a part of the hydroxyl groups with other substituents may be used. Among these, cellulose triacetate (triacetyl cellulose: TAC) is particularly preferable. Cellulose triacetate is commercially available in many products, and is advantageous from the viewpoints of availability and cost. Examples of commercially available cellulose triacetate include "FUJITAC (registered trademark) TD 80", "FUJITAC (registered trademark) TD80 UF", "FUJITAC (registered trademark) TD80 UZ", and "FUJITAC (registered trademark) TD40 UZ", KONICA MINOLTA, TAC films "KC 8UX 2M", "KC 2 UA", and "KC 4 UY" manufactured by inc.

Polymethacrylates and polyacrylates (hereinafter, polymethacrylates and polyacrylates are sometimes collectively referred to as (meth) acrylic resins) are readily available from the market.

Examples of the (meth) acrylic resin include homopolymers of alkyl methacrylate or alkyl acrylate, and copolymers of alkyl methacrylate and alkyl acrylate. Specific examples of the alkyl methacrylate include methyl methacrylate, ethyl methacrylate, and propyl methacrylate, and specific examples of the alkyl acrylate include methyl acrylate, ethyl acrylate, and propyl acrylate. As the (meth) acrylic resin, those commercially available as general-purpose (meth) acrylic resins can be used. As the (meth) acrylic resin, a resin called an impact-resistant (meth) acrylic resin can be used.

The (meth) acrylic resin is generally a polymer mainly composed of a methacrylic acid ester. The methacrylic resin may be a homopolymer of 1 kind of methacrylic acid ester, or a copolymer of methacrylic acid ester with other methacrylic acid ester, acrylic acid ester, or the like. Examples of the methacrylic acid ester include alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate, and the number of carbon atoms in the alkyl group is usually about 1 to 4. Furthermore, cyclopentyl methacrylate, cyclohexyl methacrylate, cycloalkyl methacrylate such as methacrylic acid, aryl methacrylate such as phenyl methacrylate, cycloalkyl methacrylate such as cyclohexylmethyl methacrylate, and aralkyl methacrylate such as benzyl methacrylate can also be used.

Examples of the other polymerizable monomers that can constitute the (meth) acrylic resin include acrylic esters and polymerizable monomers other than methacrylic esters and acrylic esters. As the acrylate, alkyl acrylate may be used, and specific examples thereof include: alkyl acrylates having 1 to 8 carbon atoms in the alkyl group, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate. The number of carbon atoms in the alkyl group is preferably 1 to 4. In the (meth) acrylic resin, only 1 kind of acrylate may be used alone, or 2 or more kinds may be used in combination.

Examples of the polymerizable monomer other than the methacrylate and the acrylate include a monofunctional monomer having 1 polymerizable carbon-carbon double bond in the molecule and a polyfunctional monomer having at least 2 polymerizable carbon-carbon double bonds in the molecule, and a monofunctional monomer is preferably used. Specific examples of the monofunctional monomer include: styrene monomers such as styrene, α -methylstyrene, vinyltoluene, halogenated styrene, and hydroxystyrene; cyanoethylenes such as acrylonitrile and methacrylonitrile; unsaturated acids such as acrylic acid, methacrylic acid, maleic anhydride, and itaconic anhydride; maleimides such as N-methylmaleimide, N-cyclohexylmaleimide and N-phenylmaleimide; allyl alcohols such as methallyl alcohol and allyl alcohol; vinyl acetate, vinyl chloride, ethylene, propylene, 4-methyl-1-pentene, 2-hydroxymethyl-1-butene, methyl vinyl ketone, N-vinyl pyrrolidone, N-vinyl carbazole and other monomers.

In addition, specific examples of the polyfunctional monomer include: polyunsaturated carboxylic acid esters of polyhydric alcohols such as ethylene glycol dimethacrylate, butanediol dimethacrylate and trimethylolpropane triacrylate; alkenyl esters of unsaturated carboxylic acids such as allyl acrylate, allyl methacrylate, and allyl cinnamate; polyalkenyl esters of polybasic acids such as diallyl phthalate, diallyl maleate, triallyl cyanurate, triallyl isocyanurate, and the like, and aromatic polyalkenyl compounds such as divinylbenzene, and the like. The polymerizable monomers other than the methacrylic acid ester and the acrylic acid ester may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

The preferred monomer composition of the (meth) acrylic resin is such that the alkyl methacrylate is 50 to 100% by weight, the alkyl acrylate is 0 to 50% by weight, and the other polymerizable monomer is 0 to 50% by weight, more preferably 50 to 99.9% by weight, the alkyl acrylate is 0.1 to 50% by weight, and the other polymerizable monomer is 0 to 49.9% by weight, based on the total monomer amount.

In addition, the (meth) acrylic resin may have a ring structure in the main chain of the polymer in order that the durability of the film may be improved. The ring structure is preferably a heterocyclic structure such as a cyclic acid anhydride structure, a cyclic imide structure, or a lactone ring structure. Specific examples thereof include cyclic acid anhydride structures such as glutaric anhydride structures and succinic anhydride structures; a cyclic imide structure such as a glutarimide structure and a succinimide structure; lactone ring structures such as butyrolactone and valerolactone. The larger the content of the ring structure in the main chain, the higher the glass transition temperature of the (meth) acrylic resin can be made. The cyclic acid anhydride structure and the cyclic imide structure can be introduced by the following method or the like: a method in which a monomer having a cyclic structure such as maleic anhydride or maleimide is copolymerized and introduced; a method of introducing a cyclic acid anhydride structure by dehydration/demethanol condensation after polymerization; a method of introducing a cyclic imide structure by reacting an amino compound, and the like. The resin (polymer) having a lactone ring structure can be obtained by the following method: after a polymer having a hydroxyl group and an ester group in a polymer chain is prepared, the hydroxyl group and the ester group in the obtained polymer are subjected to cyclized condensation by heating in the presence of a catalyst such as an organic phosphorus compound as necessary, thereby forming a lactone ring structure.

The polymer having a hydroxyl group and an ester group in the polymer chain can be obtained by using, as a part of the monomers, (meth) acrylate having a hydroxyl group and an ester group, such as methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, isopropyl 2- (hydroxymethyl) acrylate, n-butyl 2- (hydroxymethyl) acrylate, and tert-butyl 2- (hydroxymethyl) acrylate. A more specific method for producing a polymer having a lactone ring structure is described in, for example, Japanese patent laid-open No. 2007-254726.

The (meth) acrylic resin can be produced by radical polymerization of a monomer composition containing the above-mentioned monomer. The monomer composition may contain a solvent or a polymerization initiator as necessary.

The (meth) acrylic resin may contain other resins than the above-mentioned (meth) acrylic resin. The content of the other resin is preferably 0 to 70% by weight, more preferably 0 to 50% by weight, and still more preferably 0 to 30% by weight. The resin may be, for example, an olefin polymer such as polyethylene, polypropylene, an ethylene-propylene copolymer, poly (4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and chlorinated vinyl resins; styrene polymers such as polystyrene, styrene-methyl methacrylate copolymer, and styrene-acrylonitrile copolymer; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyarylates formed from aromatic diols and aromatic dicarboxylic acids; biodegradable polyesters such as polylactic acid and polybutylene succinate; a polycarbonate; polyamides such as nylon 6, nylon 66, and nylon 610; a polyacetal; polyphenylene ether; polyphenylene sulfide; polyether ether ketone; polyether nitrile; polysulfones; polyether sulfone; polyoxybenzyl ester; polyamideimide, and the like.

The (meth) acrylic resin may contain rubber particles from the viewpoint of improving the impact resistance and film formability of the film. The rubber particles may be particles composed only of a layer exhibiting rubber elasticity, or may be particles having a multilayer structure of a layer exhibiting rubber elasticity and another layer. Examples of the rubber elastomer include olefin-based elastic polymers, diene-based elastic polymers, styrene-diene-based elastic copolymers, acrylic elastic polymers, and the like. Among them, acrylic elastic polymers are preferably used from the viewpoint of light resistance and transparency.

The acrylic elastic polymer may be a polymer mainly composed of an alkyl acrylate, that is, a polymer containing 50% by weight or more of a structural unit derived from an alkyl acrylate based on the total monomer amount. The acrylic elastic polymer may be a homopolymer of an alkyl acrylate, or may be a copolymer containing 50 wt% or more of a structural unit derived from an alkyl acrylate and 50 wt% or less of a structural unit derived from another polymerizable monomer.

As the alkyl acrylate constituting the acrylic elastic polymer, those having 4 to 8 carbon atoms in the alkyl group are generally used. Examples of the other polymerizable monomers include alkyl methacrylates such as methyl methacrylate and ethyl methacrylate; styrene monomers such as styrene and alkylstyrene; monofunctional monomers such as unsaturated nitriles including acrylonitrile and methacrylonitrile, and alkenyl esters of unsaturated carboxylic acids such as allyl (meth) acrylate and methallyl (meth) acrylate; dienyl esters of dibasic acids such as diallyl maleate; and polyfunctional monomers such as unsaturated carboxylic diesters of glycols such as alkylene glycol di (meth) acrylates.

The rubber particles containing an acrylic elastic polymer are preferably particles having a multilayer structure having a layer of an acrylic elastic polymer. Specifically, there may be mentioned: a 2-layer structure having a hard polymer layer mainly composed of alkyl methacrylate on the outer side of the layer of the acrylic elastic polymer; and a 3-layer structure having a hard polymer layer mainly composed of alkyl methacrylate on the inner side of the acrylic elastic polymer layer.

Examples of the monomer composition of the polymer mainly composed of alkyl methacrylate constituting the hard polymer layer formed on the outer side or inner side of the acrylic elastic polymer layer are the same as the monomer composition of the polymer mainly composed of alkyl methacrylate exemplified as the (meth) acrylic resin, and a monomer composition mainly composed of methyl methacrylate is particularly preferably used. Such acrylic rubber elastomer particles having a multilayer structure can be produced by, for example, the method described in Japanese patent publication No. 55-27576.

From the viewpoint of film-forming properties of the (meth) acrylic resin, impact resistance of the film, and sliding properties of the film surface, the average particle diameter of the rubber particles included in the rubber particles up to the rubber elastic layer (the layer of the acrylic elastic polymer) is preferably in the range of 10nm to 350 nm. The average particle diameter is more preferably 30nm or more, further 50nm or more, and further preferably 300nm or less, further 280nm or less.

The average particle diameter of the rubber particles up to the rubber elastic layer (acrylic elastic polymer layer) was measured as follows. That is, when such rubber particles are mixed with a (meth) acrylic resin to prepare a film and the cross section thereof is dyed with an aqueous solution of ruthenium oxide, only the rubber elastomer layer is colored and is observed as a substantially circular shape, and the (meth) acrylic resin as a matrix layer is not dyed. Therefore, from the section of the film obtained by dyeing in this manner, a thin sheet is prepared using a microtome or the like, and is observed with an electron microscope. Then, 100 dyed rubber particles were randomly selected, and the particle diameters (diameters up to the rubber elastic layer) of the respective particles were calculated, and the number average thereof was referred to as the average particle diameter. Since the measurement is performed by such a method, the obtained average particle diameter is a number average particle diameter.

In the case where the outermost layer is a hard polymer mainly composed of methyl methacrylate and the rubber particles in which the rubber elastic layer (layer of acrylic elastic polymer) is embedded are mixed with the matrix (meth) acrylic resin, the outermost layer of the rubber particles is blended with the matrix (meth) acrylic resin. Therefore, when the cross section thereof was stained with ruthenium oxide and observed with an electron microscope, the rubber particles were observed as particles in a state other than the outermost layer. Specifically, in the case of 2-layer structured rubber particles in which the inner layer is an acrylic elastic polymer and the outer layer is a hard polymer mainly composed of methyl methacrylate, the acrylic elastic polymer portion of the inner layer is dyed and observed as particles having a single-layer structure. In the case of 3-layer structured rubber particles in which the innermost layer is a hard polymer mainly composed of methyl methacrylate, the intermediate layer is an acrylic elastic polymer, and the outermost layer is a hard polymer mainly composed of methyl methacrylate, the particles were observed as 2-layer structured particles in which only the acrylic elastic polymer portion of the intermediate layer was dyed without dyeing the particle center portion of the innermost layer.

From the viewpoint of film-forming properties of the (meth) acrylic resin, impact resistance of the film, and sliding properties of the film surface, the rubber particles are preferably blended in a proportion of 3 wt% or more and 60 wt% or less, more preferably 45 wt% or less, and even more preferably 35 wt% or less, based on the total amount of the (meth) acrylic resin constituting the (meth) acrylic resin film. When the rubber elastomer particles are more than 60% by weight, dimensional change of the film becomes large, and heat resistance is lowered. On the other hand, when the rubber elastomer particles are less than 3% by weight, the heat resistance of the film is good, but the film has poor winding properties during film formation, and the productivity may be lowered. In the present invention, when particles having a multilayer structure including a layer exhibiting rubber elasticity and other layers are used as the rubber elastomer particles, the weight of a portion including the layer exhibiting rubber elasticity and the layer inside the layer is defined as the weight of the rubber elastomer particles. For example, when the acrylic rubber elastomer particles having the 3-layer structure are used, the total weight of the acrylic rubber elastic polymer portion in the intermediate layer and the hard polymer portion mainly composed of methyl methacrylate in the innermost layer is defined as the weight of the rubber elastomer particles. When the acrylic rubber elastomer particles having a 3-layer structure are dissolved in acetone, the acrylic rubber elastic polymer portion of the intermediate layer and the hard polymer portion mainly composed of methyl methacrylate of the innermost layer remain as insoluble components, and therefore the weight ratio of the total of the intermediate layer and the innermost layer to the acrylic rubber elastomer particles having a 3-layer structure can be easily determined.

In the case where the (meth) acrylic resin film contains rubber particles, the rubber particle-containing (meth) acrylic resin composition used for producing the film can be obtained by mixing the (meth) acrylic resin and the rubber particles by melt kneading or the like, or alternatively, can be obtained by a method of first producing the rubber particles and polymerizing a monomer composition which becomes a raw material of the (meth) acrylic resin in the presence thereof.

The protective film may contain a common additive, for example, an ultraviolet absorber, an organic dye, a pigment, an inorganic pigment, an antioxidant, an antistatic agent, a surfactant, and the like. Among them, the ultraviolet absorber is preferably used because of its improved weather resistance. Examples of the ultraviolet absorber include 2, 2' -methylenebis [4- (1, 1, 3, 3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol ], 2- (5-methyl-2-hydroxyphenyl) -2H-benzotriazole, 2- [ 2-hydroxy-3, 5-bis (. alpha.,. alpha. -dimethylbenzyl) phenyl ] -2H-benzotriazole, 2- (3, 5-di-tert-butyl-2-hydroxyphenyl) -2H-benzotriazole, 2- (3-tert-butyl-5-methyl-2-hydroxyphenyl) -5-chloro-2H-benzotriazole, 2- (2-tert-butyl-5-methyl-2-hydroxyphenyl) -5-chloro-2H-benzotriazole, and mixtures thereof, Benzotriazole-based ultraviolet absorbers such as 2- (3, 5-di-tert-butyl-2-hydroxyphenyl) -5-chloro-2H-benzotriazole, 2- (3, 5-di-tert-amyl-2-hydroxyphenyl) -2H-benzotriazole, and 2- (2 '-hydroxy-5' -tert-octylphenyl) -2H-benzotriazole; 2-hydroxybenzophenone-based ultraviolet absorbers such as 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octyloxybenzophenone, 2, 4-dihydroxybenzophenone, 2-hydroxy-4-methoxy-4 '-chlorobenzophenone, 2' -dihydroxy-4-methoxybenzophenone, and 2, 2 '-dihydroxy-4, 4' -dimethoxybenzophenone; phenyl salicylate-based ultraviolet absorbers such as p-tert-butylphenyl salicylate and p-octylphenyl salicylate; 2, 4-diphenyl-6- (2-hydroxy-4-methoxyphenyl) -1, 3, 5-triazine, 2, 4-diphenyl-6- (2-hydroxy-4-ethoxyphenyl) -1, 3, 5-triazine, 2, 4-diphenyl- (2-hydroxy-4-propoxyphenyl) -1, 3, 5-triazine, 2, 4-diphenyl- (2-hydroxy-4-butoxyphenyl) -1, 3, 5-triazine, 2, 4-diphenyl-6- (2-hydroxy-4-hexyloxyphenyl) -1, 3, 5-triazine, 2, 4-diphenyl-6- (2-hydroxy-4-octyloxyphenyl) -1, 3, 5-triazine, 2, 4-diphenyl-6- (2-hydroxy-4-dodecyloxyphenyl) -1, 3, 5-triazine, 2, 4-diphenyl-6- (2-hydroxy-4-benzyloxyphenyl) -1, 3, 5-triazine, 2- (2-hydroxy-4- [ 1-octyloxycarbonylethoxy ] phenyl) -4, 6-bis (4-phenylphenyl) -1, 3, 5-triazine, 4-bis [ 2-hydroxy-4-butoxyphenyl ] -6- (2, 4-dibutoxyphenyl) -1, 3, 5-triazine, 2- [4- [ (2-hydroxy-3- (2' -ethyl) hexyloxy ] -2-hydroxyphenyl ] -4, 6-bis (2, 4-dimethylphenyl) -1, 3, 5-triazine, 2- (4, 6-bis (2, 4-dimethylphenyl) -1, 3, 5-triazin-2-yl) -5-hydroxybenzene, 2- [4, 6-bis (2, 4-dimethylphenyl) -1, 3, 5-triazin-2-yl ] -5- (octyloxy) phenol, 2- [2, 6-bis (2, 4-dimethylphenyl) -1, triazine-based ultraviolet absorbers such as 3, 5-triazin-2-yl ] -5-octyloxyphenol, 2- (4, 6-diphenyl-1, 3, 5-triazin-2-yl) -5- [2- (2-ethylhexanoyl) ethoxy ] phenol, and 2,4, 6-tris (2-hydroxy-4-hexyloxy-3-methoxyphenyl) -1, 3, 5-triazine, and 2 or more of these can be used as necessary.

Examples of the ultraviolet absorber that can be used include commercially available triazine-based ultraviolet absorbers such as "Kemisorb 102" (registered trademark) manufactured by CHEMIPRO KASEI corporation, "ADEKA STAB (registered trademark) LA 46", "AEDKA STAB (registered trademark) LAF 70", TINUVIN (registered trademark) 460 "," TINUVIN (registered trademark) 405 "," TINUVIN (registered trademark) 400 ", and" cycloasorb (registered trademark) UV-1164 "(trade names) manufactured by SUN CHEMICAL co. Examples of the benzotriazole-based ultraviolet absorbers include "ADEKA STAB LA 31" and "ADEKA STAB LA 36" manufactured by ADEKA CHEMTEX co.ltd., "sumirorb (registered trademark) 200", "sumirorb (registered trademark) 250", "sumirorb (registered trademark) 300", "sumirorb (registered trademark) 340" and "sumirorb (registered trademark) 350" manufactured by chemico KASEI corporation, "kemiosorb 74" (registered trademark), "kemiosorb 79" (registered trademark) and "Kemisorb 279" (registered trademark), and "TINUVIN (registered trademark) 99-2", "tinnun (registered trademark) 900" and "tinnuvin (registered trademark) 928" (both of which are trade names above) manufactured by BASF corporation. When the ultraviolet absorber is contained in the (meth) acrylic resin film, the amount thereof is usually 0.1% by weight or more, preferably 0.3% by weight or more, and further preferably 3% by weight or less, based on 100% by weight of the (meth) acrylic resin.

For producing the (meth) acrylic resin film, a conventionally known film forming method can be used. The (meth) acrylic resin film may have a multilayer structure, and various conventionally known methods such as a method using a feed block and a method using a multi-manifold mold may be used for the multilayer structure of the (meth) acrylic resin film. Among them, from the viewpoint of obtaining a film having good surface properties, the following method is preferred: for example, a method of laminating the films via a feed block, performing multilayer melt extrusion molding from a T-die, and bringing at least one surface of the obtained laminated film into contact with a roll or a belt to form a film. In particular, from the viewpoint of improving the surface smoothness and surface gloss of the (meth) acrylic resin film, a method of bringing both surfaces of the multilayer film-shaped material obtained by the multilayer melt extrusion molding into contact with a roll surface or a belt surface to form a film is preferable. In the roller or the belt used in this case, the surface of the roller or the surface of the belt in contact with the (meth) acrylic resin is preferably mirror-finished in order to impart smoothness to the surface of the (meth) acrylic resin film.

As for the (meth) acrylic resin film, the film produced in the above manner may be subjected to stretching treatment. Stretching treatment is sometimes required to obtain a film having desired optical and mechanical properties. Examples of the stretching treatment include uniaxial stretching and biaxial stretching. Examples of the stretching direction include a machine flow direction (MD) of an unstretched film, a direction (TD) orthogonal thereto, and a direction oblique to the machine flow direction (MD). The biaxial stretching may be simultaneous biaxial stretching in which the stretching is performed simultaneously in 2 stretching directions, or sequential biaxial stretching in which the stretching is performed in a predetermined direction and then the stretching is performed in the other direction.

The first protective film and the second protective film may be protective films having both optical functions such as a retardation film and a brightness enhancement film as long as they are included in the scope of the present invention. For example, a retardation film to which an arbitrary retardation value is given can be produced by stretching (uniaxial stretching, biaxial stretching, or the like) a transparent resin film formed of the above material, or forming a liquid crystal layer or the like on the film.

The first protective film and the second protective film may have a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer formed on the surface on the side opposite to the polarizing plate. A known method can be used for forming the surface treatment layer on the surface of the protective film.

The first protective film and the second protective film may be the same protective film as each other or different protective films. Examples of the case where the protective film is different include: combinations that differ at least in the kind of thermoplastic resin constituting the protective film; combinations which differ at least in the presence or absence of optical function of the protective film; and a combination of at least different types of surface treatment layers formed on the surface.

The thicknesses of the first protective film and the second protective film are preferably thin from the viewpoint of making the polarizing plate thin, but if too thin, the strength is reduced and the workability is poor. Therefore, the thickness of the first protective film and the second protective film is preferably 5 μm to 90 μm or less, more preferably 60 μm or less, further preferably 50 μm or less, and particularly preferably 30 μm or less.

The protective film (first protective film) can easily obtain the effect of the present application as long as there is an appropriate dimensional change due to water absorption. The transparent resin film is preferably a transparent resin film containing a cellulose ester resin, a polyester resin, a polycarbonate resin, a (meth) acrylic resin, or a mixture of at least 2 kinds of these resins, and more preferably a transparent resin film containing a cellulose ester resin, a (meth) acrylic resin, or a mixture of at least 2 kinds of these resins.

(Binder)

The pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer may be any one selected from conventionally known pressure-sensitive adhesives, and may have such adhesiveness that peeling or the like does not occur in a high-temperature environment, a moist-heat environment, or an environment in which a polarizing plate is exposed to high temperatures and low temperatures repeatedly. Specifically, an acrylic adhesive, a silicone adhesive, a rubber adhesive, and the like are mentioned, and an acrylic adhesive is particularly preferable from the viewpoint of transparency, weather resistance, heat resistance, and processability.

The binder may contain, as necessary, various additives such as a thickener, a plasticizer, a filler made of glass fibers, glass beads, metal powder, other inorganic powder, etc., a pigment, a colorant, a filler, an antioxidant, an ultraviolet absorber, an antistatic agent, a silane coupling agent, etc.

The adhesive layer is generally formed by coating a solution of an adhesive (adhesive) on a release sheet and drying. The release sheet may be coated by roll coating such as reverse coating or gravure coating, spin coating, screen coating, fountain coating, dip coating, spraying, or the like. The release sheet provided with the pressure-sensitive adhesive layer is used by a method of transferring the release sheet. The thickness of the pressure-sensitive adhesive layer is usually about 3 μm to 100 μm, preferably 5 μm to 50 μm.

Preferably, the storage elastic modulus at 23 ℃ of the adhesive layer is preferably 0.01MPa to 1 MPa. If the storage elastic modulus of the pressure-sensitive adhesive layer is less than 0.01MPa, shrinkage of the polarizing plate in a high-temperature test cannot be suppressed, and appearance defects such as peeling tend to easily occur. Further, if the storage elastic modulus of the adhesive layer is more than 1MPa, the adhesive cannot relax the strain generated between the glass and the polarizing plate in the cold-heat impact test, and cracks tend to be easily generated in the polarizing plate.

In a preferred embodiment, the storage elastic modulus of the adhesive layer at 80 ℃ is 0.01MPa to 1 MPa.

A liquid crystal panel can be obtained by bonding a polarizing plate to a liquid crystal cell via an adhesive layer. Further, an organic electroluminescence display device can be obtained by bonding a polarizing plate to an organic electroluminescence display through an adhesive layer. For example, as shown in fig. 3, the liquid crystal panel and the organic electroluminescence display may have a structure including a glass substrate 40, a first adhesive layer 13, a first protective film 12, a polarizing plate 11, a second adhesive layer 23, and a second protective film 22.

The polarizing plate of the present invention can also provide a thin polarizing plate having excellent strength.

Examples

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the examples,% and parts indicating contents or amounts are on a weight basis unless otherwise specified.

[ production of polarizing plate ]

A polyvinyl alcohol film having a thickness of 20 μm (average degree of polymerization: about 2,400, degree of saponification: 99.9 mol% or more) was uniaxially stretched to about 5 times by dry stretching, and further, while being kept in a stretched state, immersed in pure water at 60 ℃ for 1 minute, and then immersed in an aqueous solution having a weight ratio of iodine/potassium iodide/water of 0.05/5/100 at 28 ℃ for 60 seconds. Thereafter, the plate was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 8.5/8.5/100 at 72 ℃ for 300 seconds. Subsequently, the substrate was washed with pure water at 26 ℃ for 20 seconds and then dried at 65 ℃ to obtain a polarizing plate having a thickness of 7 μm in which iodine was adsorbed and oriented in a polyvinyl alcohol film.

[ first adhesive agent ]

A commercially available pressure-sensitive adhesive sheet was used in which an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm was laminated on the release-treated surface of a 38 μm-thick polyethylene terephthalate film (release film) subjected to release treatment. The urethane acrylate oligomer is not blended in the acrylic adhesive. The storage modulus of elasticity of the pressure-sensitive adhesive layer after the release film was removed from the pressure-sensitive adhesive sheet was 0.05MPa at 23 ℃ and 0.04MPa at 80 ℃.

[ second adhesive layer ]

An organic solvent solution obtained by adding a urethane acrylate oligomer and an isocyanate-based crosslinking agent to a copolymer of butyl acrylate and acrylic acid was applied to a release-treated surface of a 38 μm-thick polyethylene terephthalate film (release film) subjected to release treatment by a die coater so that the thickness after drying became 5 μm, and the resulting film was dried to obtain an adhesive sheet having an adhesive layer laminated thereon. The storage modulus of elasticity of the pressure-sensitive adhesive layer after the release film was removed from the pressure-sensitive adhesive sheet was 0.40MPa at 23 ℃ and 0.18MPa at 80 ℃.

[ first protective film-1 ]

A triacetyl cellulose film (thickness 20 μm, in-plane phase difference of 1.2nm at a wavelength of 590nm, and in-thickness phase difference of 1.3nm at a wavelength of 590 nm) manufactured by KONICA MINOLTA, inc.

[ first protective film-2 ]

An unstretched TAC film having a thickness of 25 μm and a trade name of "KC 2 UA" manufactured by KONICA MINOLTA, INC. was used.

[ first protective film-3 ]

A cycloolefin resin film (manufactured by ZEON CORPORATION) having a thickness of 13 μm was used. An in-plane retardation (Re (590)) at a wavelength of 590nm was 0.8nm, a thickness direction retardation (Rth (590)) at a wavelength of 590nm was 3.4nm, a thickness direction retardation (Rth (483)) at a wavelength of 483nm was 3.5nm, and a thickness direction retardation (Rth (755)) at a wavelength of 755nm was 2.8 nm.

[ first protective film-4 ]

A cyclic polyolefin resin FILM having a thickness of 23 μm and having a trade name of "ZEONOR FILM (registered trade name) ZF 14-023" manufactured by ZEON CORPORATION was used.

[ first protective film-5 ]

A triacetyl cellulose FILM (25 KCHC-TC 32 μm thick, manufactured by TOPPAN TOMOEGAWA OPTICAL FILM) having a surface subjected to a hard coating treatment (7 μm thick) was used.

[ first protective film-6 ]

The first protective film-1 was dissolved in 1, 3-dioxolane to be prepared to 12 wt%, and coated on a glass substrate with a bar coater (particle size No. 60) so as to reach a thickness of 10 μm after drying. After drying in an oven at 60 ℃ for 3 minutes, the coating film was peeled off from the glass to obtain a first protective film-6.

[ second protective film ]

A luminance enhancement Film (product name of Advanced Polarized Film, Version 3, manufactured by 3M) having a thickness of 26 μ M was used.

[ preparation of aqueous adhesive ]

To 100 parts of water, 3 parts of carboxyl-modified polyvinyl alcohol (KURARAY co., KL-318 manufactured by LTD) was dissolved, and 1.5 parts of a polyamide epoxy additive (Sumirez Resin (registered trademark) 650(30) manufactured by SUMICA CHEMTEX co., LTD., and an aqueous solution having a solid content of 30%) as a water-soluble epoxy compound was added to the aqueous solution to prepare an aqueous adhesive.

[ preparation of polarizing plate precursor A ]

A first protective film-1 is laminated on one surface of the polarizing plate with an aqueous adhesive interposed therebetween. After the lamination, the first protective film-1 and the polarizing plate were bonded by drying at 80 ℃ for 5 minutes. The second pressure-sensitive adhesive layer laminated on the release film is bonded to the surface of the polarizing plate opposite to the surface to which the first protective film-1 is bonded. The first protective film-1 is bonded to the surface opposite to the surface to which the polarizing plate is bonded, with the first pressure-sensitive adhesive layer stacked on the release film.

The polarizing plates were bonded so that the transmission axis direction of the polarizing plates was parallel to the width direction of the protective film.

In this manner, a polarizing plate precursor a-1 in which a first adhesive layer, a protective film, a polarizer, and a second adhesive layer were sequentially stacked was produced.

Similarly, a polarizing plate precursor manufactured using the first protective film-2 in place of the first protective film-1 is referred to as a polarizing plate precursor a-2. A polarizing plate precursor was produced in the same manner for the other protective films.

[ production of polarizing plate A ]

The release film on the second adhesive layer in the polarizing plate precursor is peeled. The second adhesive layer in the polarizing plate precursor a was laminated with the luminance enhancement film to obtain a polarizing plate a in which the first adhesive layer, the protective film (first protective film), the polarizer, the second adhesive layer, and the luminance enhancement film (second protective film) were sequentially laminated. For example, a polarizing plate manufactured using the first protective film-1 is referred to as a polarizing plate a 1. Similarly, a polarizing plate having such a structure manufactured using the first protective film-2 is referred to as a polarizing plate a 2.

[ production of polarizing plate B ]

A polarizing plate B1 was produced in the same manner as the polarizing plate a1, except that the lamination position of the polarizer and the protective film in the polarizing plate precursor a-1 was changed. The resultant polarizing plate B1 was a polarizing plate in which a first adhesive layer, a polarizer, a protective film (first protective film), a second adhesive layer, and a brightness enhancement film (second protective film) were sequentially laminated.

[ production of polarizing plate C ]

A first protective film-1 is laminated on one surface of the polarizing plate with an aqueous adhesive interposed therebetween. After the lamination, the first protective film and the polarizing plate were bonded by drying at 80 ℃ for 5 minutes. The first pressure-sensitive adhesive layer laminated on the release film was bonded to the surface of the polarizer opposite to the surface to which the first protective film was bonded, and thereafter the release film was peeled off to obtain a polarizing plate C. The obtained polarizing plate was a polarizing plate in which a first adhesive layer, a polarizer, and a protective film (first protective film) were sequentially stacked. In the polarizing plate C, the polarizing plate obtained using the first protective film-1 is referred to as a polarizing plate C1, and the polarizing plate obtained using the first protective film-5 is referred to as a polarizing plate C5, for example.

[ calculation of dimensional Change Rate ]

The difference in dimensional change rate of the protective film was measured by the following method.

In the protective films used in examples and comparative examples, the width direction was parallel to the transmission axis direction of the polarizing plate.

First, each of the long protective films was cut into a square of 100mm in the longitudinal direction × 100mm in the width direction. After the protective film was cut, the dimension in the width direction (L0) was measured by using a two-dimensional measuring instrument "NEXIV VMR-12072" (manufactured by Nikon Corporation). Similarly, the dimension in the longitudinal direction was also measured.

Then, the protective film was left to stand at 85 ℃ for 1 hour (humidity: 5%). After this step, the width-direction dimension (L85) and the length-direction dimension of the protective film were measured in the same manner as described above.

The dimensional change rate (%) was obtained from the following equation, and the dimensional change rate in the width direction (85 ℃) and the dimensional change rate in the length direction of the protective film were calculated.

Dimensional change rate (85 ℃) [ (L0-L85)/L0] × 100

Further, after calculating the dimensional change rate in an environment of 85 ℃, the same sample was left to stand at a temperature of 23 ℃ and a humidity of 55% for 15 minutes, and then left to stand at a relative humidity of 95% at 30 ℃ for 0.5 hour. After this step, the width-direction dimension (L30) and the length-direction dimension of the protective film were measured in the same manner as described above. The dimensional change rate (%) was obtained from the following equation, and the dimensional change rate in the width direction and the dimensional change rate in the length direction of the protective film were calculated. "L030" means a film size after measurement of a dimensional change rate (85 ℃ C.) in a direction (longitudinal direction or width direction) parallel to the transmission axis direction of the polarizing plate and leaving the film at 23 ℃ and 55% humidity for 15 minutes.

Dimensional change rate (30 ℃) [ (L030-L30)/L0] × 100

The absolute value of the difference between the obtained dimensional change rate (85 ℃ C.) and dimensional change rate (30 ℃ C.) was calculated. These results are shown in Table 1. In the table, "F_TD"is an abbreviation that represents the absolute value of the difference between the dimensional change rate (85 ℃ C.) and the dimensional change rate (30 ℃ C.). Note that F of the polarizing plate_pzThe measurement was also carried out by the same method as described above.

Further, Δ F was calculated_TD(Absolute value F of difference in dimensional change rate of polarizing plate_PZAbsolute value F of the difference between the dimensional change rate of the protective film and the dimensional change rate of the protective film_PFThe difference of (d). Further, Δ F was calculated_TDRelative to F_PZRatio of (Δ F)_TD/F_PZ). The results are shown in Table 1.

[ Table 1]

The polarizing plate is F_PZ

[ Cold-Heat shock Environment test and dew condensation Cold-Heat shock Environment test ]

The polarizing plate with an adhesive layer prepared as described above was cut into pieces of 100mm × 60mm, and the release film was peeled from the first adhesive layer side thereof, and was bonded to a glass plate via the exposed adhesive layer. The obtained evaluation samples were subjected to a cold-hot impact environment test and a dew condensation cold-hot impact environment test, which will be described later.

[ Cold and Heat shock Environment test ]

The cold-hot impact environment test was performed in the following manner: in a state where a polarizing plate was bonded to a glass plate, the plate was subjected to 1 cycle of a high temperature condition (85 ℃ C.) for 30 minutes and a low temperature condition (40 ℃ C.) for 30 minutes using a thermal shock test apparatus (product name "TSA-71L-A-3" sold by ESPEC Corp.). The temperature change time is set to 1 minute, and the condition that condensation does not occur in the optical member is set without introducing outside air when the temperature change time during temperature change is 0 minute. This cycle was repeated for 400 cycles and the test was performed.

[ dew condensation cold and thermal shock environmental test ]

The dew condensation cold-hot impact environment test was performed under conditions in which condensation was intentionally generated in the optical member by introducing outside air into the apparatus for 5 minutes at the time of temperature fluctuation in the cold-hot impact environment test. This cycle was repeated for 400 cycles and the test was performed.

In this test, the temperature of the outside air was 23 ℃ and the relative humidity was 55%.

[ determination ]

After the cold-heat shock environment test (number of cycles: 400) and the dew condensation cold-heat shock environment test (number of cycles: 400), the presence or absence of cracking was visually confirmed. The case where the light leakage did not occur under the cross prism after the test, and the case where the light leakage occurred under the cross prism after the test was not changed from before the test was marked as "o", and the case where the light leakage occurred under the cross prism after the test was marked as "x".

Further, the maximum length of a crack generated in the sample was measured under a cross prism for the sample subjected to the dew cold thermal shock environment test. The results obtained in the cold-hot impact environment test and the dew condensation cold-hot impact environment test are shown in table 2.

[ Table 2]

From these results, it is understood that the polarizing plate of the present invention has excellent effects in both the cold and hot impact environment test and the dew condensation cold and hot impact environment test. That is, according to the present invention, a polarizing plate which does not cause light leakage in a polarizer under high temperature and high humidity conditions and has excellent durability can be provided. In addition, the polarizing plate of the present invention can exhibit good polarization characteristics without light leakage, cracks, and the like even under such an environment that high temperatures and low temperatures are repeated.

In the polarizing plate of the present invention, the maximum length of the crack generated by the dew condensation cold and heat impact environment test was significantly shorter than that of the polarizing plate of the comparative example. Therefore, the polarizing plate of the present invention can suppress the crack growth of the polarizer even under a humid condition where dew condensation occurs, and can maintain good polarization characteristics.

[ Cold-thermal shock environmental test after puncture ]

A pressing flaw was formed on the surface of the polarizing plate, and the polarizing plate was subjected to a cold and heat impact environmental test to confirm the presence or absence of a crack in the polarizing plate. Specifically, the evaluation was performed through the following procedure.

The polarizing plate manufactured in the above manner was cut into 100mm × 60 mm. The release film on the first adhesive layer was peeled off, and a polarizing plate was bonded to alkali-free glass (EAGLE XG (registered trademark)) via the first adhesive layer. A load of 3N was applied to the surface of the polarizing plate by a scratch type durometer (model 318, manufactured by ERICHSEN, germany, ball diameter of 0.75mm) at a position 1.0mm from the end of the polarizing plate attached to the glass, thereby giving a pressing flaw. The depth of the compression scar is 1 μm or less, and the size is 0.2mm in diameter.

Further, a sample was prepared by applying a load of 5N by a scratch type durometer at a position 1.0mm from the end of the other polarizing plate bonded to the glass, and further applying a load of 10N to the surface of the other polarizing plate.

The flaw caused by the operation of applying a load to the surface of the polarizing plate is a flaw generated when the following is assumed: in general, the protective film laminated on the polarizing plate is peeled off with a sharp tool such as tweezers, the backlight is attached to the polarizing plate, or the polarizing plate is attached with a foreign substance being caught.

A cold and heat impact environmental test (250 cycles) was performed at 85 ℃ and-40 ℃ (1 cycle for 30 minutes each) for a polarizing plate having a pressing flaw formed on the surface by applying a load of 3N, 5N, or 10N. The determination is as follows. The results are shown in Table 3.

[ determination ]

When any load was applied, the case where no light leakage of the polarizing plate occurred under the cross prism after the cold-heat shock environment test was marked as "o". When any load was applied, a case where cracks were observed in the polarizing plate after the cold/heat shock environment test, and light leakage was observed under crossed prisms or visually was indicated as "X"

[ Table 3]

Industrial applicability of the invention

The present invention can provide a polarizing plate which is less likely to cause light leakage under high-temperature conditions and high-humidity conditions and has excellent durability. In addition, the polarizing plate of the present invention can exhibit good polarization characteristics without light leakage, cracks, and the like even under such an environment that high temperatures and low temperatures are repeated. Further, according to the present invention, the polarizing plate can be made thin, and even when a flaw is generated on the surface of the protective film, the crack of the polarizing plate can be suppressed.

The present application claims priority based on Japanese patent application 2015-223443, filed 11/13/2015, and Japanese patent application 2016-079655, filed 4/12/2016, the entire contents of which are incorporated herein by reference.

Description of the reference numerals

11 polarizing plate

12 protective film (first protective film)

13 adhesive layer (first adhesive layer)

22 second protective film

23 second adhesive layer

40 glass substrate

100 polarizing plate

Claims

1. A polarizing plate having a polarizer, a protective film and an adhesive layer,

the polarizing plate, the protective film and the adhesive layer are laminated in this order,

the polarizing plate and the protective film are laminated only via an adhesive layer,

a second protective film is laminated on the side of the polarizing plate opposite to the protective film via a second adhesive layer,

and the second protective film is laminated on the polarizing plate only via the second adhesive layer,

the dimensional change rate of the protective film after 1 hour at 85 ℃ with a relative humidity of 5% was recorded as the dimensional change rate of the protective film (85 ℃),

the absolute value of the difference between the dimensional change rate (85 ℃) of the protective film and the dimensional change rate (30 ℃) of the protective film is 0.02 to 0.50,

the thickness of the protective film is 5-30 μm,

the protective film is a transparent resin film containing at least 1 selected from cellulose ester-based resins, polyester-based resins, polycarbonate-based resins, and (meth) acrylic resins.

2. The polarizing plate according to claim 1, wherein the polarizer has a thickness of 10 μm or less.

3. The polarizing plate of claim 1 or 2, wherein the second protective film is a brightness enhancement film.

4. The polarizing plate according to claim 1 or 2, wherein a dimensional change rate of the polarizer after 1 hour under a condition of a relative humidity of 5% at 85 ℃ in a transmission axis direction of the polarizer is referred to as a dimensional change rate of the polarizer (85 ℃),

the dimensional change rate of the polarizing plate after 0.5 hours at 30 ℃ and 95% relative humidity in the transmission axis direction of the polarizing plate was taken as the dimensional change rate of the polarizing plate (30 ℃),

the absolute value of the difference between the dimensional change rate (85 ℃ C.) of the polarizing plate and the dimensional change rate (30 ℃ C.) of the polarizing plate was designated as F_PZ，

Subjecting said F to_PZSubtracting said F_PFThe difference obtained is denoted Δ F_TDAnd is and

ΔF_TDrelative to F_PZRatio of (1), i.e. Δ F_TD/F_PZIs in the range of 0.5 to 0.95.

5. A liquid crystal display device, wherein the polarizing plate according to any one of claims 1 to 4 is laminated on a liquid crystal cell via the adhesive layer.

6. An organic electroluminescent display device, wherein the polarizing plate according to any one of claims 1 to 4 is laminated on an organic electroluminescent display through the adhesive layer.