阅读说明：本技术 用于偏光板的粘合膜、包括粘合膜的偏光板和包括粘合膜的光学显示器 (Adhesive film for polarizing plate, polarizing plate including the same, and optical display including the same ) 是由 俞美然 李承俊 郑宇镇 赵河润 金一镇 于 2021-03-05 设计创作，主要内容包括：本发明提供了用于偏光板的粘合膜、包括粘合膜的偏光板和包括粘合膜的光学显示器。用于偏光板的粘合膜由粘合剂组合物形成,该粘合剂组合物包含：(甲基)丙烯酸共聚物；粘合促进剂；异氰酸酯固化剂和碳二亚胺固化剂的混合物；以及UV吸收剂,其中该粘合膜的玻璃化转变温度为-47℃至-40℃,并且该粘合膜在380nm的波长下的透光率为3％或更小。(The present invention provides an adhesive film for a polarizing plate, a polarizing plate including the adhesive film, and an optical display including the adhesive film. An adhesive film for a polarizing plate is formed of an adhesive composition comprising: (meth) acrylic acid copolymers; an adhesion promoter; a mixture of an isocyanate curing agent and a carbodiimide curing agent; and a UV absorber, wherein the adhesive film has a glass transition temperature of-47 ℃ to-40 ℃, and a light transmittance of 3% or less at a wavelength of 380 nm.)

1. An adhesive film for a polarizing plate, formed of an adhesive composition comprising: (meth) acrylic acid copolymers; an adhesion promoter; a mixture of an isocyanate curing agent and a carbodiimide curing agent; and a UV absorber, wherein:

the adhesive film has a glass transition temperature of-47 ℃ to-40 ℃, and

the adhesive film has a light transmittance of 3% or less at a wavelength of 380 nm.

2. The adhesive film according to claim 1, wherein the adhesive film for a polarizing plate has a peel strength of 700 gf/inch or more at 25 ℃ relative to a glass plate and 25 ℃ C

The creep of the steel is 100 μm or less.

3. The adhesive film of claim 1 wherein the UV absorber is liquid at 25 ℃ and comprises a hydroxyphenyl triazine based UV absorber.

4. The adhesive film of claim 1 wherein the UV absorber has a wavelength of maximum absorption of from 300nm to 400 nm.

5. The adhesive film of claim 1 wherein the isocyanate curing agent comprises an aromatic isocyanate or an adduct of an aromatic isocyanate and a polyol compound.

6. The adhesive film of claim 1 wherein the adhesion promoter comprises an aromatic modified terpene resin having a glass transition temperature of 90 ℃ or greater.

7. The adhesive film of claim 6 wherein the aromatic modified terpene resin having a glass transition temperature of 90 ℃ or greater has a weight average molecular weight of 900 or greater.

8. The adhesive film according to claim 6, wherein the aromatic modified terpene resin having a glass transition temperature of 90 ℃ or more is present in an amount of 1 to 10 parts by weight with respect to 100 parts by weight of the (meth) acrylic copolymer.

9. The adhesive film of claim 1 wherein the (meth) acrylic copolymer comprises a copolymer of a monomer mixture comprising 60 to 99 wt% of an alkyl-containing (meth) acrylic monomer and 1 to 40 wt% of a hydroxyl-containing (meth) acrylic monomer.

10. The adhesive film of claim 1 wherein the adhesive composition comprises:

100 parts by weight of the (meth) acrylic copolymer,

0.1 to 3 parts by weight of the UV absorber,

0.5 to 20 parts by weight of the isocyanate curing agent,

0.01 to 0.5 parts by weight of the carbodiimide curing agent and

1 to 10 parts by weight of the adhesion promoter.

11. The adhesive film according to claim 1, wherein the adhesive film for a polarizing plate has a thickness of 15 μm or less.

12. A polarizing plate comprising:

a polarizer; and

the adhesive film for a polarizing plate according to any one of claims 1 to 11 formed on a surface of the polarizer.

13. An optical display comprising the polarizing plate according to claim 12.

Technical Field

The present invention relates to an adhesive film for a polarizing plate, a polarizing plate including the adhesive film, and an optical display including the adhesive film.

Background

Recently, as optical display devices become thinner, a method of reducing the thickness of an adhesive film for a polarizing plate has been studied.

However, as the thickness of the adhesive film for a polarizing plate is reduced, the adhesive film for a polarizing plate may be thin with high creep and reduced cohesive strength. Therefore, the thin adhesive film for a polarizing plate may have poor processability in cutting and/or processing. It is known that there is a trade-off between peel strength and cohesive strength in adhesive films. Therefore, when the cohesive strength of the adhesive film is increased, the peel strength is decreased, and when the cohesive strength is decreased, the peel strength is increased. Therefore, there is a need for an adhesive film for a polarizing plate, which is capable of securing cohesive strength and peel strength even when the adhesive film has a thin thickness.

Meanwhile, the organic light emitting device is likely to be damaged by UV light incident from the outside. Therefore, it is required to impart UV blocking properties to a polarizing plate or an adhesive film for a polarizing plate.

The background art of the present invention is disclosed in JP 2013-a 072951.

Disclosure of Invention

An aspect of the present invention provides an adhesive film for a polarizing plate, which has low light transmittance at a wavelength of 380 nm.

Another aspect of the present invention provides an adhesive film for a polarizing plate, which has a thickness of 15 μm or less, a peel strength with respect to an adherend of 700 gf/inch or more, and a creep at 25 ℃ of 100 μm or less.

Other aspects of the present invention provide an adhesive film for a polarizing plate, which has a thickness of 15 μm or less and does not bleed out a UV absorber.

One aspect of the present invention relates to an adhesive film for a polarizing plate.

1. An adhesive film for a polarizing plate is formed of an adhesive composition comprising: (meth) acrylic acid copolymers; an adhesion promoter; a mixture of an isocyanate curing agent and a carbodiimide curing agent; and a UV absorber, the adhesive film having a glass transition temperature of-47 ℃ to-40 ℃, and a light transmittance of 3% or less at a wavelength of 380 nm.

2. In embodiment 1, the adhesive film for a polarizing plate may have a peel strength of 700 gf/inch or more at 25 ℃ with respect to a glass plate, and a creep of 100 μm or less at 25 ℃.

3. In embodiments 1-2, the UV absorber may be liquid at 25 ℃, and may include a hydroxyphenyl triazine-based UV absorber.

4. In embodiments 1 to 3, the UV absorber may have a maximum absorption wavelength of 300nm to 400 nm.

5. In embodiments 1 to 4, the isocyanate curing agent may include an aromatic isocyanate or an adduct of an aromatic isocyanate and a polyol compound.

6. In embodiments 1-5, the adhesion promoter may include an aromatic modified terpene resin having a glass transition temperature of 90 ℃ or greater.

7. In embodiments 1 to 6, the aromatic modified terpene resin having a glass transition temperature of 90 ℃ or more may have a weight average molecular weight of 900 or more.

8. In embodiments 1 to 7, the aromatic-modified terpene resin having a glass transition temperature of 90 ℃ or more may be present in an amount of 1 part by weight to 10 parts by weight with respect to 100 parts by weight of the (meth) acrylic copolymer.

9. In embodiments 1 to 8, the (meth) acrylic copolymer may include a copolymer of a monomer mixture containing 60 to 99 wt% of the alkyl group-containing (meth) acrylic monomer and 1 to 40 wt% of the hydroxyl group-containing (meth) acrylic monomer.

10. In embodiments 1-9, the adhesive composition may comprise: 100 parts by weight of a (meth) acrylic copolymer, 0.1 to 3 parts by weight of a UV absorber, 0.5 to 20 parts by weight of an isocyanate curing agent, 0.01 to 0.5 parts by weight of a carbodiimide curing agent, and 1 to 10 parts by weight of an adhesion promoter.

11. In embodiments 1 to 10, the adhesive film for a polarizing plate may have a thickness of 15 μm or less.

Another aspect of the present invention provides a polarizing plate, including: a polarizer; and the aforementioned adhesive film for polarizing plates.

Other aspects of the present invention provide an optical display comprising the aforementioned polarizing plate or the aforementioned adhesive film.

According to an aspect of the present invention, there is provided an adhesive film for a polarizing plate, the adhesive film having low light transmittance at a wavelength of 380 nm.

According to another aspect of the present invention, there is provided an adhesive film for a polarizing plate, which has a thickness of 15 μm or less, a peel strength with respect to an adherend of 700 gf/inch or more, and a creep at 25 ℃ of 100 μm or less.

According to other aspects of the present invention, there is provided an adhesive film for a polarizing plate, which has a thickness of 15 μm or less and does not bleed out of a UV absorber.

Drawings

Fig. 1 is a schematic diagram showing the measurement of creep from a front view.

FIG. 2 is a schematic diagram showing the measurement of creep from a partial side view.

Detailed Description

Herein, some exemplary embodiments of the present invention will be described in further detail with reference to the accompanying drawings. However, it is to be understood that the present invention is not limited to the following embodiments and may be implemented in various ways. The following embodiments are provided to provide a thorough understanding of the present invention to those skilled in the art.

Herein, the "peel strength" of the adhesive film for a polarizing plate refers to 180 ° peel strength between the adhesive film and a glass plate as measured at 25 ℃ according to JIS 2107.

As used herein, the term "(meth) acrylic" refers to acrylic and/or methacrylic.

Herein, the "weight average molecular weight" is a value obtained by gel permeation chromatography with respect to a (meth) acrylic acid copolymer according to a polystyrene standard.

As used herein, "X to Y" means "X or greater to Y or less" or "X ≦ Y".

The adhesive film according to an embodiment of the present invention is an adhesive film for a polarizing plate, which is capable of bonding the polarizing plate and an organic light-emitting device panel. The adhesive film may have low light transmittance at a wavelength of 380nm, thereby preventing discoloration and/or damage of the organic light emitting device, no bleeding of a UV absorber, may obtain high peel strength of 700 gf/inch or more with respect to a panel of the organic light emitting device and creep deformation of 100 μm or less at 25 ℃, may be in a trade-off relationship with each other even when the adhesive film has a thin thickness of 15 μm or less, and may ensure excellent processability and durability.

Herein, an adhesive film for a polarizing plate according to an embodiment of the present invention (simply referred to as "adhesive film" herein) will be described.

The adhesive film may block UV light incident from the outside, thereby preventing discoloration and/or damage of the organic light emitting device. The adhesive film may have a light transmittance of 3% or less, for example, 0.001% to 3%, at a wavelength of 380 nm. Within this range, the adhesive film can prevent discoloration and/or damage of the organic light emitting device.

The glass transition temperature of the adhesive film may be from-47 ℃ to-40 ℃ (e.g., -47, -46, -45, -44, -43, -42, -41, or-40 ℃), and in one embodiment from-45 ℃ to-40 ℃. Within this range, even when the adhesive film has a thin thickness, the peel strength and the cohesive strength in a trade-off relationship with each other can be improved at the same time.

The thickness of the adhesive film may be 15 μm or less, for example, greater than 0 μm and 15 μm or less, and in one embodiment 10 μm to 15 μm. Within this range, a thinner polarizing plate can be obtained.

The adhesive film may have a peel strength of 700 gf/inch or more and a creep of 100 μm or less at 25 ℃. In the above creep range, the adhesive film laminated to the polarizing plate may be easily cut and processed, and thus excellent processability may be secured. Further, in the above peel strength range, the adhesive film may not be separated from the organic light emitting device panel even if the adhesive film has a thin thickness, and may have good durability without delamination or slight lifting even under high temperature/humidity conditions. In one embodiment, the adhesive film may have a creep of 50 μm to 100 μm, for example 50 μm to 80 μm, at 25 ℃. In one embodiment, the adhesive film may have a peel strength of 700 gf/inch to 1200 gf/inch (e.g., 700, 800, 900, 1000, 1100, or 1200 gf/inch).

The adhesive film may be formed from an adhesive composition comprising: (meth) acrylic acid copolymers; an adhesion promoter comprising an aromatic modified terpene resin having a glass transition temperature of 90 ℃ or greater; a mixture of an isocyanate curing agent and a carbodiimide curing agent; and a UV absorber.

Herein, the adhesive composition will be described in more detail.

[ UV absorber ]

The adhesive composition may comprise as UV absorber a UV absorber based on hydroxyphenyl triazine which is liquid at 25 ℃. The hydroxyphenyl triazine-based UV absorber that is liquid at 25 ℃ may impart light transmittance of 3% or less to the adhesive film at a wavelength of 380nm, and may help to obtain the adhesive film without bleeding of the UV absorber. If the UV absorber is not liquid at 25 ℃, or the UV absorber is liquid, but not a hydroxyphenyl triazine based UV absorber, the adhesive film obtained therefrom may have a light transmittance of more than 3% at a wavelength of 380nm and/or may suffer from bleed out.

In one embodiment, the hydroxyphenyl triazine based UV absorber that is liquid at 25 ℃ may have a maximum absorption wavelength of 300nm to 400nm (e.g., 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, or 400 nm).

Herein, the "maximum absorption wavelength" refers to a wavelength at which the maximum absorbance occurs when the absorbance is measured for a solution containing a UV absorber at a concentration of 10ppm in methyl ethyl ketone. For example, the UV absorber can be Tinuvin 477.

The UV absorber may be present in an amount of 0.1 to 3 parts by weight, and in one embodiment, 0.1 to 2 parts by weight, and 0.1 to 1.5 parts by weight, in terms of solid content, relative to 100 parts by weight of the (meth) acrylic copolymer. Within this range, the adhesive film may have a light transmittance of 3% or less at a wavelength of 380nm, and may not bleed out even at a thin thickness.

[ (meth) acrylic acid copolymer ]

The (meth) acrylic copolymer may have a weight average molecular weight of 1,200,000 or more. Within this range, the adhesive film may obtain increased peel strength, and may impart improved reliability under high temperature and high humidity conditions. For example, the (meth) acrylic copolymer can have a weight average molecular weight of 1,400,000 or more, more specifically 1,400,000 to 1,600,000.

The (meth) acrylic copolymer may have a glass transition temperature of-40 ℃ or less, for example, -43 ℃ to-40 ℃. Within this range, the adhesive film may impart improved reliability under high temperature and high humidity conditions.

The (meth) acrylic copolymer may form a matrix of the adhesive film and provide adhesive strength to the adhesive film. The (meth) acrylic copolymer may include a copolymer of a monomer mixture including a (meth) acrylic monomer including an alkyl group and a (meth) acrylic monomer including a crosslinkable functional group.

The alkyl group-containing (meth) acrylic monomer may be a C1 to C20 alkyl group-containing (meth) acrylate, and may include at least one of methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, and dodecyl (meth) acrylate, but is not limited thereto.

In one embodiment, the (meth) acrylic copolymer may be a copolymer including a mixture of a (meth) acrylic monomer having a crosslinkable functional group and at least one of n-butyl (meth) acrylate and 2-ethylhexyl (meth) acrylate.

The (meth) acrylic monomer containing a crosslinkable functional group may include at least one of a hydroxyl group-containing (meth) acrylic monomer and a carboxylic acid group-containing (meth) acrylic monomer. In one embodiment, the crosslinkable functional group-containing (meth) acrylic monomer includes a hydroxyl-containing (meth) acrylic monomer and excludes a carboxylic acid group-containing (meth) acrylic monomer. As a result, the acid value can be reduced, and corrosion of the metal adherend can be prevented.

The hydroxyl group-containing (meth) acrylic monomer may include a hydroxyl group-containing C₁To C₂₀Alkyl (meth) acrylic monomer, hydroxyl-containing C₃To C₂₀Cycloalkyl (meth) acrylic acid monomer and hydroxyl group-containing C₆To C₂₀At least one aromatic group (meth) acrylic acid monomer. For example, the hydroxyl group-containing (meth) acrylic monomer may include at least one of 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 1, 4-cyclohexanedimethanol mono (meth) acrylate, 1-chloro-2-hydroxypropyl (meth) acrylate, diethylene glycol mono (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 4-hydroxycyclopentyl (meth) acrylate, and 4-hydroxycyclohexyl (meth) acrylate.

In one embodiment, the monomer mixture may comprise 60 to 99 wt%, such as 90 to 99 wt%, of the alkyl group-containing (meth) acrylic monomer and 1 to 40 wt%, such as 1 to 10 wt%, of the hydroxyl group-containing (meth) acrylic monomer as the crosslinkable functional group-containing (meth) acrylic monomer. Within this range, the (meth) acrylic copolymer may have the above-described glass transition temperature and may exhibit adhesive properties.

The above ranges of the weight average molecular weight and the glass transition temperature of the (meth) acrylic copolymer can be achieved by controlling polymerization conditions such as temperature, polymerization time, amount of initiator, and the like during polymerization of the monomer mixture. In one embodiment, the polymerization may be carried out at 60 ℃ to 70 ℃ for 6 hours to 8 hours. As the initiator, any typical initiator may be used, including azo-based polymerization initiators and/or peroxide polymerization initiators, such as benzoyl peroxide or acetyl peroxide. The polymerization may be carried out by typical methods known in the art, such as suspension polymerization, emulsion polymerization, solution polymerization, and the like.

[ curing agent mixture ]

The curing agent cures the (meth) acrylic copolymer, and may help improve the adhesive strength of the adhesive film and ensure that the glass transition temperature of the adhesive film is-47 ℃ to-40 ℃.

The curing agent may comprise a mixture of an isocyanate curing agent and a carbodiimide curing agent. By using a mixture of an isocyanate curing agent and a carbodiimide curing agent, the adhesive film can ensure a creep of 100 μm or less at 25 ℃ and a peel strength of 700 gf/inch or more at 25 ℃, while preventing the UV absorber from oozing out when the adhesive film contains a liquid UV absorber at 25 ℃.

When only an isocyanate curing agent is used as a curing agent without using a carbodiimide curing agent, the adhesive film may have a creep of more than 100 μm at 25 ℃ because the cohesive strength of the adhesive film is reduced. When only a carbodiimide curing agent is used as the curing agent without using an isocyanate curing agent, there may be a problem in that the aging time of the adhesive increases.

If the curing agent contains a different type of curing agent in addition to the mixture of the isocyanate curing agent and the carbodiimide curing agent, the adhesive film cannot achieve the following properties: at 25 ℃, at a film thickness of 15 μm or less, the creep is 100 μm or less, and the peel strength is 700 gf/inch or more.

The isocyanate curing agent may be present in an amount of 0.5 to 20 parts by weight, in one embodiment 0.5 to 5 parts by weight, for example 0.5 to 2 parts by weight, relative to 100 parts by weight of the (meth) acrylic copolymer. Within this range, the adhesive film can attain a balance between the cohesive strength and the peel strength.

The carbodiimide curing agent may be present in an amount of 0.01 to 0.5 parts by weight, and in one embodiment, 0.02 to 0.2 parts by weight, relative to 100 parts by weight of the (meth) acrylic copolymer. Within this range, the adhesive film can attain a balance between the cohesive strength and the peel strength.

In the mixture of curing agents, the isocyanate curing agent may be present in an excess amount relative to the carbodiimide curing agent. In one embodiment, the isocyanate curing agent and the carbodiimide curing agent may be present in a weight ratio of from 2:1 to 150:1, such as from 2:1 to 100:1 (isocyanate curing agent: carbodiimide curing agent). Within this range, excellent performance can be obtained.

The isocyanate curing agent may include an aromatic isocyanate or an adduct of an aromatic isocyanate and a polyol compound. By using this, the adhesive film may have a creep of 100 μm or less at a thickness of 15 μm or less at 25 ℃. When an aliphatic isocyanate curing agent such as Hexamethylene Diisocyanate (HDI) or the like is included in the composition, the adhesive film cannot ensure a creep of 100 μm or less at 25 ℃.

The isocyanate curing agent may include at least one of Xylene Diisocyanate (XDI), such as m-xylene diisocyanate and the like, methylene bis (phenyl isocyanate) (MDI), such as 4,4' -methylene bis (phenyl isocyanate) and the like, naphthalene diisocyanate, Toluene Diisocyanate (TDI), or polyol modified adducts thereof. For example, the isocyanate curing agent may comprise a polyol-modified adduct of TDI isocyanate curing agent.

The carbodiimide curing agent may include a typical curing agent including at least two carbodiimide groups (— N ═ C ═ N —, where x is a connecting site) in a molecule. In one embodiment, the carbodiimide curing agent may include a curing agent obtained by a decarboxylation condensation reaction of a diisocyanate compound. The diisocyanate compound may include diphenylmethane diisocyanate, dimethoxydiphenylmethane diisocyanate, and the like.

The curing agent may be present in an amount of 0.5 to 5 parts by weight, and in one embodiment, 0.5 to 3 parts by weight, relative to 100 parts by weight of the (meth) acrylic copolymer. Within this range, the adhesive film may have improved processability and good adhesive strength.

[ adhesion promoter ]

The adhesive film comprises an adhesion promoter. The adhesion promoter may include an aromatic modified terpene resin having a glass transition temperature of 90 ℃ or greater. By using such an adhesion promoter, the adhesive film can have a peel strength of 700 gf/inch or more at 25 ℃ at a film thickness of 15 μm or less.

If the adhesion promoter has a glass transition temperature of 90 ℃ or more but contains a different type of adhesion promoter in addition to the aromatic-modified terpene resin, the adhesive film cannot achieve the effects of the present invention and may have increased haze due to poor compatibility with the (meth) acrylic copolymer. Also, if the adhesion promoter comprises an aromatic modified terpene resin, but the glass transition temperature is lower than 90 ℃, the adhesive film cannot achieve the effects of the present invention and may have increased haze due to poor compatibility with the (meth) acrylic copolymer.

In one embodiment, the aromatic modified terpene resin may have a glass transition temperature of from 90 ℃ to 120 ℃, in one embodiment from 90 ℃ to 110 ℃. Within this range, the adhesive film may have increased peel strength even at a thin thickness.

The aromatic modified terpene resin may have a weight average molecular weight of 900 or greater, in one embodiment, from 900 to 2,000, for example from 900 to 1500. Within this range, the adhesive film may have increased adhesive strength even at a thin thickness.

Adhesion promoters, such as aromatic modified terpene resins, may be present in amounts of 1 to 10 parts by weight (e.g., 1,2, 3, 4, 5, 6, 7, 8, 9, or 10 parts by weight), and in one embodiment, 1 to 5 parts by weight, relative to 100 parts by weight of the (meth) acrylic copolymer. Within this range, the adhesive film may have improved peel strength and reduced haze.

[ silane coupling agent ]

The adhesive composition may further comprise a silane coupling agent. The silane coupling agent can improve the adhesive strength of the adhesive film with respect to an adherend. The silane coupling agent may include typical silane coupling agents known to those skilled in the art. For example, the silane coupling agent may include an epoxy-containing silane coupling agent such as glycidoxypropyltrimethoxysilane, glycidoxypropylmethyldimethoxysilane, or the like, but is not limited thereto. The silane coupling agent may be present in an amount of 0.01 to 5 parts by weight, and in one embodiment, 0.05 to 1 part by weight, relative to 100 parts by weight of the (meth) acrylic copolymer. Within this range, the adhesive film may have improved adhesive strength.

[ additives ]

The adhesive composition may further comprise an additive. The additives may include, but are not limited to, one or more of reaction inhibitors, adhesion promoters, thixotropic agents, conductivity imparting agents, color adjusting agents, stabilizers, antistatic agents, antioxidants, and leveling agents.

Next, a polarizing plate according to an embodiment will be described.

The polarizing plate may include a polarizer; and an adhesive film for a polarizing plate formed on a surface of the polarizer, wherein the adhesive film is the adhesive film for a polarizing plate according to an embodiment of the present invention.

The polarizer may include a polarizer made of a polyvinyl alcohol resin film. In one embodiment, the polarizer may include a polyvinyl alcohol-based polarizer manufactured by dyeing a polyvinyl alcohol resin film with at least one of iodine and a dichroic dye, or may be a polyene-based polarizer manufactured by dehydrating the polyvinyl alcohol resin film.

In one embodiment, the polarizer may include a polarizer prepared by stretching a polyvinyl alcohol resin film having a thickness of 20 to 100 μm in a machine direction to a total stretching ratio of 2 to 10 times, preferably 4 to 8 times. In general, the shrinkage of the polarizer may depend on the total stretch ratio during the manufacturing process. The stretching may be performed by single-stage stretching or multi-stage stretching, but is not limited thereto.

In one embodiment, the polarizer may have a thickness of 5 μm to 30 μm, and in one embodiment, 5 μm to 20 μm. In this range, the polarizer can be used in the polarizing plate, and reduction in thickness of the polarizing plate can be achieved.

In one embodiment, the first protective layer and the second protective layer may be adhered to both surfaces of the polarizer by an adhesive for a polarizing plate. The adhesive used for the polarizing plate may be a typical adhesive known to those skilled in the art.

In one embodiment, the first protective layer may comprise a protective film or coating. The protective film may include a film formed of an optically transparent resin. In one embodiment, the resin may include: at least one of a cyclic polyolefin resin including an amorphous Cyclic Olefin Polymer (COP), a poly (meth) acrylate resin, a polycarbonate resin, a polyester resin including polyethylene terephthalate (PET), a cellulose ester resin including triacetyl cellulose (TAC), a polyethersulfone resin, a polysulfone resin, a polyamide resin, a polyimide resin, a non-cyclic polyolefin resin, a polyarylate resin, a polyvinyl alcohol resin, a polyvinyl chloride resin, and a polyvinylidene chloride resin. In one embodiment, the protective film may have a thickness of 5 μm to 200 μm, for example, 10 μm to 150 μm. When laminated with a polarizer, the first protective layer may be attached to the polarizer using conventional adhesives or bonding agents.

In one embodiment, the protective coating may be optically transparent and formed from an actinic radiation curable resin composition comprising an actinic radiation curable compound and an initiator. In one embodiment, the protective coating may have a thickness of 5 μm to 200 μm, for example 5 μm to 20 μm. Within this range, a protective coating may be used in the polarizing plate.

A second protective layer may be formed on the lower surface of the polarizer and the upper surface of the adhesive film for the polarizing plate to support the polarizer.

The second protective layer may be the same as or different from the first protective layer described above. In one embodiment, the second protective layer may have the thickness described above in the first protective layer.

Next, an optical display according to an embodiment will be described.

The optical display may include the polarizing plate according to an embodiment of the present invention. The optical display may include, but is not limited to, an organic light emitting display, a flexible organic light emitting display, and the like.

The present invention will be described in further detail with reference to some examples. It should be noted, however, that these examples are provided for illustrative purposes and should not be construed as limiting the invention in any way.

The details of the components used in examples and comparative examples are as follows.

(A) Copolymer (b): (meth) acrylic acid copolymer having a weight average molecular weight of 1,600,000 prepared by copolymerizing 90 wt% of n-butyl acrylate and 10 wt% of 2-hydroxyethyl acrylate.

(B1) Isocyanate curing agent: coronate L (adduct of aromatic diisocyanate and trimethylolpropane)

(B2) Carbodiimide curing agent: (V05S, Nisshinbo Chemical Inc.)

(B3) Aliphatic diisocyanate curing agent: CK164, NCI

(C1) Terpene resin: aromatic modified terpene resins (Dertoprene 1510, DRT, glass transition temperature: 100 ℃, weight average molecular weight: 1,000 to 1,500).

(C2) Terpene resin: an aromatic modified terpene resin (CK500L, NCI, glass transition temperature: 80 ℃, weight average molecular weight: 1,000).

(C3) Rosin resin: rosin resin (KE100, Arakwa, glass transition temperature: 90 ℃ C.) was used as an adhesion promoter.

(D1) UV absorber: tinuvin 477 (hydroxyphenyl triazine, BASF, liquid at 25 deg.C)

(D2) UV absorber: tinuvin 384 (hydroxyphenyl benzotriazole, liquid at 25 ℃ C.)

(D3) UV absorber: tinuvin 479 (hydroxyphenyl triazine, solid at 25 ℃ C.)

(E) Silane coupling agent: 3-glycidoxypropyltrimethoxysilane

Example 1

A composition for an adhesive film was prepared by mixing 100 parts by weight of (meth) acrylic copolymer (a), 0.5 parts by weight of isocyanate curing agent (B1), 0.15 parts by weight of carbodiimide curing agent (B2), 2 parts by weight of terpene resin (C1), 1 part by weight of UV absorber (D1) and 0.1 parts by weight of silane coupling agent (E) in terms of solid content, adding 20 parts by weight of methyl ethyl ketone, obtaining a mixture and stirring the mixture at 25 ℃ for 5 minutes. Then, the prepared composition was coated on a PET (polyethylene terephthalate) release film to a thickness of 20 μm, dried at 110 ℃ for 4 minutes, and left at 35 ℃ and 45% RH for 4 days, thereby preparing an adhesive sheet having an adhesive film of 12 μm thickness.

Examples 2 to 7

Each adhesive sheet was prepared in the same manner as in example 1 except that the contents of the components of the composition and the thickness of the adhesive film were changed as listed in table 1.

Comparative example 1 and comparative example 7

Each adhesive sheet was prepared in the same manner as in example 1 except that the contents of the components of the composition and/or the thickness of the adhesive film were changed as listed in table 2. In table 2, "-" indicates that this component is not included.

Physical properties of the adhesive films prepared in examples and comparative examples were evaluated by the following methods, and the results are shown in tables 1 and 2.

(1) Peel strength (unit: gf/inch): each adhesive film prepared in examples and comparative examples was cut into a size of 150mm × 25mm (length × width). A polarizing plate having a triacetyl cellulose film, a polarizer, and a triacetyl cellulose film stacked in this order was prepared. Then, an adhesive film was laminated on the triacetyl cellulose film of the polarizing plate, and the other side of the adhesive film was adhered to a glass plate (alkali-free glass), and then a 2kg roller was reciprocated once to prepare a sample. The peel strength was measured 20 minutes after the preparation of the test specimen. The peel strength was measured by peeling the polarizing plate from the glass plate at a peeling speed of 300mm/min and a peeling angle of 180 ° at 25 ℃ and 65% RH using a texture analyzer.

(2) Light transmittance (unit:%, @380 nm): for the adhesive films prepared in examples and comparative examples, light transmittance was measured using a UV spectrophotometer (V-650, JASCO co., ltd., Japan).

(3) Durability: each polarizing plate (100 mm. times.80 mm) was attached to a glass plate through the adhesive film prepared in examples and comparative examples and at 4 to 5kg/cm²To prepare a sample.

Some samples were left at 60 ℃ and 95% RH for 500 hours to evaluate their reliability against heat and humidity (first test).

Some of the test pieces were subjected to the following cycle 200 times to evaluate the thermal shock performance (second test):

1 cycle was performed in the following order: the sample was left at-40 ℃ for 20 minutes, heated from-40 ℃ to 80 ℃ within 10 minutes, left at 80 ℃ for 20 minutes, and cooled from 80 ℃ to-40 ℃ within 1 minute.

The durability was evaluated by visual inspection of the two test specimens of the first and second tests according to the following criteria:

in any of the samples of the first and second tests, no bubble on the adhesive film and no delamination between the adhesive film and the protective film were evaluated as "OK", and slight or significant bubbles or delamination occurred in any of the samples of the first and second tests and evaluated as "NG".

(4) Creep (unit: μm): referring to fig. 1 and 2, creep was measured with respect to an adhesive film for a polarizing plate. A polarizing plate was prepared by sequentially laminating a triacetyl cellulose film, a PVA polarizer, and a triacetyl cellulose film using a water-based adhesive. The adhesive films prepared in examples and comparative examples were laminated on one side of the triacetyl cellulose film of the polarizing plate, and then cut into a size of 50mm × 15mm (length × width) to obtain a sample 23 in which the polarizing plate 22 and the adhesive film 21 were laminated. Then, the sample 23 was laminated on the alkali-free glass plate 20 to form a laminated area of 15mm × 15mm (a × b). Creep was measured by using a texture analyzer ta.xt Plus (load cell 5kg, EKO Instruments). Creep was evaluated when the sample was left to stand at a constant temperature of 25 ℃ for 1,000 seconds under a load of 2250 g.

(5) Glass transition temperature (unit:. degree. C.) of adhesive film: the glass transition temperatures of the adhesive films prepared in examples and comparative examples were measured using a differential scanning calorimeter.

(6) Bleed out of UV absorber: the adhesive films prepared in examples and comparative examples were observed by naked eyes, and bleeding was evaluated according to the following criteria:

if the adhesive film did not become opaque, no bleed was considered and evaluated as "OK".

If the adhesive film became opaque, bleeding was considered to occur, and evaluated as "NG".

TABLE 1

TABLE 2

As shown in Table 1, the adhesive film for a polarizing plate according to the present invention showed low light transmittance even at a wavelength of 380nm, did not bleed out of a UV absorber, and ensured two properties of a peel strength of 700 gf/inch or more and a creep of 100 μm or less at 25 ℃ even at a thickness of 15 μm or less.

On the other hand, as shown in table 2, the adhesive films of comparative examples could not obtain all of the above properties.

It is to be understood that although a few exemplary embodiments have been described herein, various modifications, alterations, and equivalents may be made by those skilled in the art without departing from the spirit and scope of the invention.