KR101194065B1 - Polarizing plate and manufacturing method thereof - Google Patents

Abstract

As a polarizing plate in which a water-based adhesive bond layer and an easily bonding layer are interposed in order on at least one surface of a polarizer, and the protective film of polyester resin is provided,

The water-based adhesive layer comprises at least one resin, a crosslinking agent and water selected from a polyvinyl alcohol-based resin and a urethane resin, wherein the crosslinking agent is formed by including 0.5 to 1.8% by weight of the resin content A polarizing plate is disclosed. Polarizing plate according to the present invention is excellent in adhesive strength, adhesive appearance and harsh conditions durability.

Polarizing plate, easily adhesive layer, crosslinking agent, drying

Description

Polarizer and its manufacturing method {POLARIZING PLATE AND MANUFACTURING METHOD THEREOF}

The present invention relates to a polarizing plate and a manufacturing method thereof.

Liquid crystal displays (LCDs) are one of the most widely used flat panel displays. It comprises a liquid crystal display panel including two display panels on which an electric field generating electrode is formed and a liquid crystal layer interposed therebetween, by applying a voltage to the electric field generating electrode to generate an electric field in the liquid crystal layer. The image is displayed by determining the orientation of the molecules and controlling the polarization of the incident light. In addition, a polarizing plate is provided on the outside of the liquid crystal display panel. The polarizer may control polarization by selectively transmitting light in a specific direction among light incident from the backlight and light passing through the liquid crystal layer.

The polarizer includes a polarizer capable of polarizing light in a specific direction and a protective film for supporting and protecting the polarizer. The protective film must be highly transmissive and have sufficient mechanical strength to support and protect the polarizer. Although a triacetyl cellulose (TAC) film has been used as the protective layer, such a triacetyl cellulose film has a high price, which is a factor in increasing the price of the liquid crystal display device having the same. Accordingly, research on a protective film that can replace a triacetyl cellulose film has recently been conducted in various ways.

An object of the present invention is to provide a polarizing plate and a method of manufacturing the polarizer and the protective film is attached to each other via an adhesive layer and an easily adhesive layer having a good adhesive strength, excellent adhesion appearance and durability.

Technical problems to be achieved by the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above object,

According to one aspect of the invention,

As a polarizing plate in which a water-based adhesive bond layer and an easily bonding layer are interposed in order on the at least one surface of a polarizer, and the protective film of polyester resin is provided,

The water-based adhesive layer comprises at least one resin, a crosslinking agent and water selected from a polyvinyl alcohol-based resin and a urethane resin, characterized in that it comprises the crosslinking agent in the range of 0.5 to 1.8% by weight of the resin content, A polarizing plate can be presented.

In addition, according to another aspect of the present invention,

A polarizer or a protective film of a polyester resin with an easily adhesive layer, comprising at least one resin, a crosslinking agent and water selected from a polyvinyl alcohol resin and a urethane resin, wherein the crosslinking agent is 0.5 to 1.8 of a resin content. Applying a water-based adhesive comprising a weight percent range to face each other,

And curing the water-based adhesive by a drying process, and forming an adhesive layer.

A water-based adhesive layer and an easily adhesive layer are interposed in order on the at least one surface of a polarizer, and can provide the manufacturing method of the polarizing plate in which the protective film of polyester resin is provided.

In addition, according to another aspect of the present invention, it is possible to present an image display device including the polarizing plate.

By optimizing the drying conditions, the adhesive layer composition ratio, the concentration of the curing agent in the adhesive, and the like after the adhesive lamination of the polyethylene terephthalate protective film and the polarizer, the mechanical properties and the high moisture permeability of the polyethylene terephthalate are maximized to have high resistance to external harsh conditions. A highly durable polarizing plate can be produced.

Hereinafter, the present invention will be described in more detail.

The polarizing plate of this invention has a structure in which the water-based adhesive bond layer, an easily bonding layer, and the protective film of polyester-type resin are laminated | stacked on at least one surface of the polyvinyl alcohol-type polarizer in order. That is, a polarizer and a protective film are bonded through the water-based adhesive agent and the easily bonding layer.

In the manufacturing process of a polarizing plate, although the adhesiveness between the polarizing element which is a polyvinyl alcohol-type film, and a protective film is important, in order to improve such adhesiveness, formation of the said easily bonding layer is needed.

That is, in order to replace the triacetyl cellulose-based film used as a conventional protective film, when applying a polyester-based film such as polyethylene terephthalate, the hydrophobic surface of the polyethylene terephthalate film is converted to hydrophilic in an aqueous adhesive environment I need to make it work.

In order to convert the hydrophobic surface of the film to hydrophilic, there is also a method of modifying the surface by using sodium hydroxide, but this has a problem of damaging the film. Accordingly, the inventors of the present invention have sought to improve the adhesive strength by effectively modifying the surface without the problem of damaging the film, and forming an adhesive layer between the adhesive layer and the protective film, and the material of the adhesive layer. By differently blending and by varying the crosslinking agent concentration of the adhesive and drying under specific temperature conditions, the desired purpose could be achieved.

Thereby, this invention is a polarizing plate in which the water-based adhesive bond layer and the easily bonding layer are interposed in order on the at least one surface of a polarizer, and the protective film of polyester resin is provided,

The water-based adhesive layer comprises at least one resin, a crosslinking agent and water selected from polyvinyl alcohol-based resin and urethane resin, characterized in that it comprises the crosslinking agent in the range of 0.5 to 1.8% by weight of the resin content, Present a polarizing plate.

Since the polarizer is polyvinyl alcohol-based resin, the aqueous adhesive layer is particularly preferably polyvinyl alcohol-based resin.

As polyvinyl alcohol-type resin which comprises a polarizer, what saponified polyvinyl acetate type resin can be used. As polyvinyl acetate type resin, besides polyvinyl acetate which is a homopolymer of vinyl acetate, the copolymer etc. with the other monomer copolymerizable with vinyl acetate are illustrated. As another monomer copolymerizable with vinyl acetate, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, acrylamide which has an ammonium group, etc. are mentioned, for example. The saponification degree of the polyvinyl alcohol-based resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may also be modified. For example, polyvinyl formal, polyvinyl acetal, or the like modified with aldehydes may also be used. Moreover, the polymerization degree of polyvinyl alcohol-type resin is about 1,000 to 10,000 normally, Preferably it is about 1,500 to 5,000.

When a polyvinyl alcohol-based resin is used as the main component of the adhesive, such polyvinyl alcohol-based resins include carboxyl group-modified polyvinyl alcohol, acetacetyl group-modified polyvinyl alcohol, in addition to partially saponified polyvinyl alcohol or fully saponified polyvinyl alcohol. Modified polyvinyl alcohol-type resins, such as a methylol group modified polyvinyl alcohol and an amino group modified polyvinyl alcohol, may be sufficient. When polyvinyl alcohol-type resin is used as an adhesive agent, the said adhesive agent is manufactured as an aqueous solution of polyvinyl alcohol-type resin in many cases. The concentration of the polyvinyl alcohol-based resin in the adhesive is usually about 0.1 to 20 parts by weight, and preferably 1 to 5 parts by weight with respect to 100 parts by weight of water.

In order to improve adhesiveness, it is preferable to add the crosslinking agent represented by curable components, such as glyoxal and a water-soluble epoxy resin, to the adhesive agent containing polyvinyl alcohol-type resin as a main component. As a water-soluble epoxy resin, it is obtained by making epichlorohydrin react with the polyamide polyamine obtained by reaction of the polyalkylene polyamine like diethylene triamine and triethylene tetraamine, and the dicarboxylic acid like adipic acid, for example. Polyamide polyamine epoxy resin to be mentioned.

The amount of these crosslinking agents added is preferably in the range of 0.5 to 1.8 wt%, preferably 0.7 to 1.5 wt% of the polyvinyl alcohol-based resin content. If the added amount is less than 0.5% by weight, the water resistance is lowered, and if it exceeds 1.8% by weight, there is a problem that the gelation proceeds quickly.

As the protective film of the polarizer, polyester-based films such as polyethylene terephthalate, polyethylene butyrate and polyethylene naphthalate may be used. In particular, polyethylene terephthalate films having a very low moisture permeability can be used. The polarizing plate using the said polyethylene terephthalate film as a protective film is excellent in mechanical strength, etc., and can aim at thickness reduction. In the present invention, the polyethylene terephthalate constituting the polyethylene terephthalate-based film means a resin in which 80 mol% or more of the repeating unit is composed of ethylene terephthalate, and may include a structural unit derived from another copolymerization component. . As another copolymerization component, isophthalic acid, p- (beta) -oxyethoxy benzoic acid, 4,4'- dicarboxy diphenyl, 4,4'- dicarboxy benzophenone, bis (4-carboxyphenyl) ethane, adipic acid, Dicarboxylic acid components such as sebacic acid, 5-sodium sulfoisophthalic acid and 1,4-dicarboxycyclohexane; And diol components such as propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol and polytetramethylene glycol. Such dicarboxylic acid component and diol component can be used in combination of 2 or more type as needed. Moreover, oxycarboxylic acid, such as p-oxybenzoic acid, can also be used together with the said carboxylic acid component and diol component. As other copolymerization components, dicarboxylic acid components and / or diol components containing small amounts of amide bonds, urethane bonds, ether bonds, carbonate bonds and the like may be used.

The polyethylene terephthalate film may have a thickness of 20 to 100 μm, and an adhesive layer is preferably provided on the surface thereof. The easy-adhesive layer can be provided on both surfaces or one surface of polyethylene terephthalate.

When the surface of the film is modified using the adhesive layer, the adhesiveness between the surface functional group of the film and the adhesive and crosslinking agent currently in use should be good. Such adhesiveness may be controlled by the composition of the adhesive layer disclosed in the present invention.

Although the component which comprises the said easily bonding layer is not specifically limited, For example, polyester type resin, urethane type resin, acrylic resin, etc. which have a polar group in frame | skeleton, and are comparatively low molecular weight and low glass transition temperature are independent or mixed. Can be used.

In particular, when the protective film is made of polyethylene terephthalate resin, and the main component of the water-based adhesive agent is a polyvinyl alcohol resin, it is preferable that the easily adhesive layer is also composed of these components. Specifically, the polyvinyl alcohol and polyethylene terephthalate resin may be included in the weight ratio 1: 1.3 to 1.9, preferably 1: 1.5 to 1.7. When the polyethylene terephthalate resin is included in less than 1.3 to 1 weight of the polyvinyl alcohol, the adhesion between the primer layer and the polyethylene terephthalate film may be lowered, and when included in excess of 1.9, the adhesion between the primer layer and the adhesive layer may be reduced.

As a method of bonding a polyethylene terephthalate film to the surface of a polarizer using an adhesive agent, a conventionally well-known method can be used, For example, the casting method, the Meyer bar coating method, the gravure coating method, the comma coating method And a method of applying an adhesive to the adhesive surface of the polarizer and / or the film to be bonded thereto by the doctor blade method, the die coating method, the dip coating method, the spray method, or the like, and overlapping the two. The casting method is a method of flowing and spreading an adhesive downward on the surface while moving a film, which is a coated object, in a substantially vertical direction, a substantially horizontal direction, or an inclined direction therebetween. After apply | coating an adhesive agent by the above-mentioned method, both are bonded by sandwiching a polarizer and the film bonded to it with a nip roll etc., and bonding. Moreover, after dripping an adhesive agent between a polarizer and the film bonded to this, the method of pressing this laminated body with a roll etc. and pressing it uniformly can also be used. In this case, it is possible to use a metal, rubber | gum, etc. as a material of a roll. Moreover, after dripping an adhesive agent between a polarizer and a film bonded to this, the method of passing this laminated body between a roll and a roll, and pressurizing and spreading is also employ | adopted preferably. In this case, these rolls may be the same material, or may be another material.

The laminated body bonded through the said water-based adhesive agent is normally subjected to a drying process, and drying and hardening of an adhesive bond layer are performed. Drying process can be performed, for example by attaching hot air. Drying temperature is about 40-100 degreeC, Preferably it is selected from the range of 70-90 degreeC. When the drying temperature is less than 40 ° C, the bonding itself between the polyethylene terephthalate and the polyvinyl alcohol resin is weakened to cause separation at the interface between the film and the adhesive layer, and when the temperature exceeds 100 ° C, warpage of the polarizing plate occurs severely. There is a problem that the color changes. Drying time is 20 second-about 10 minutes, for example, and the thickness of the adhesive bond layer after drying can be made into 0.001-5 micrometers normally.

1 is a schematic cross-sectional view of a general liquid crystal display device.

The liquid crystal display device includes a liquid crystal display panel 10, a backlight portion 13 positioned on the back side of the liquid crystal display panel 10, and a pair of polarizing plates attached to both surfaces of the liquid crystal display panel 10, respectively. (11, 12). The backlight unit 13 supplies light to the liquid crystal display panel 10 and may include a fluorescent lamp or a light emitting diode (LED).

The polarizers 11 and 12 include a front polarizer 11 attached to the front side of the liquid crystal display panel 10 and a rear polarizer 12 attached to the rear side of the liquid crystal display panel 10. do. The front polarizer 11 and the rear polarizer 12 may have different structures. The polarizer of the present invention can be used for the front polarizer and the rear polarizer, and is preferably used for the front polarizer.

2 is a schematic diagram illustrating a front polarizer according to an embodiment of the present invention. The front polarizer 11 includes a polarizer 21, a protective layer 23 positioned on the polarizer 21, and an optical compensation film 27 positioned on the lower side of the polarizer 21. In addition, the adhesive layer 22a for bonding the polarizer 21 and the protective layer 23 and the adhesive layer 22b for bonding the polarizer 21 and the optical compensation film 27 may be included. In addition, a release layer 30, which is removed when the upper polarizing plate 11 is attached to the liquid crystal display panel 10 under the optical compensation film 27, is disposed between the optical compensation film 27 and the release film 30. 28).

The protective layer 23 may include a polyethylene terephthalate protective film 24 of the present invention and a coating layer 26 exhibiting anti-glare having a haze value of about 20 to 35%. An adhesive auxiliary layer 25a may be interposed between the coating layer 26 and the polyethylene terephthalate protective film 24, and an easily adhesive layer 25b may be interposed between the polyethylene protective film layer 24 and the adhesive layer 22a. .

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are merely for the purpose of explanation and should not be construed to limit the scope of the invention.

Manufacturing example  One

80 mol of water was mixed with 1 mol of polyvinyl alcohol, the solution was completely dissolved by stirring at 90 ° C. for 1 hour, and then vacuum dried at 40 ° C. for 40 hours to prepare a film. The prepared film was stretched twice at 50 ° C., adsorbed with iodine, and stretched 2.5 times in an aqueous boric acid solution at 40 ° C. to prepare a polarizer.

Example  One:

Polyethylene alcohol (PVA) and polyethylene terephthalate film (50 μm in thickness, Mitsubishi) equipped with an easily-adhesive layer formed from a composition in which polyvinyl alcohol (PVA) and polyethylene terephthalate (PET) were mixed in a weight ratio of 1: 1.5 on one side of the polarizer obtained in Preparation Example 1. Plastic) was bonded to a polyvinyl alcohol adhesive by drying for 6 minutes with 70 degreeC hot air. The adhesive had a polyvinyl alcohol content of 3 parts by weight based on 100 parts by weight of water, and prepared using glyoxal crosslinking agent to contain 0.7% of the polyvinyl alcohol content. Subsequently, the triacetyl cellulose film was laminated | stacked and the polarizing plate of this invention was produced. The curing agent concentration, the composition ratio of the adhesive layer and the drying temperature conditions are shown in Table 1.

Example  2:

A polarizing plate was manufactured in the same manner as in Example 1 except that the crosslinking agent concentration was changed to 1.5 wt% in Example 1.

Example  3:

A polarizing plate was manufactured in the same manner as in Example 1 except that the composition of the easily adhesive layer was changed to polyvinyl alcohol and polyethylene terephthalate 1: 1.7 (weight ratio).

Example  4:

A polarizing plate was manufactured in the same manner as in Example 3 except that the crosslinking agent concentration was changed to 1.5 wt% in Example 1.

Comparative example  One:

A polarizing plate was prepared in the same manner as in Example 1 except that the concentration of the crosslinking agent in Example 1 and the composition of the easily adhesive layer were changed to polyvinyl alcohol and polyethylene terephthalate 1: 1 (weight ratio).

Comparative example  2:

A polarizing plate was prepared in the same manner as in Example 1 except that the concentration of the crosslinking agent in Example 1 and the composition of the easily adhesive layer were changed to polyvinyl alcohol and polyethylene terephthalate 1: 2 (weight ratio).

Comparative example  3:

A polarizing plate was prepared in the same manner as in Example 1 except that the concentration of the crosslinking agent in Example 1 was 0.5 wt% and the composition of the easily adhesive layer was changed to polyvinyl alcohol and polyethylene terephthalate 1: 1.6 (weight ratio).

Comparative example  4:

A polarizing plate was manufactured in the same manner as in Example 1, except that the crosslinking agent concentration was 2% by weight and the composition of the easily adhesive layer was changed to polyvinyl alcohol and polyethylene terephthalate 1: 1.6 (weight ratio).

[Table 1]

Test Example  1: Evaluation of Polarizing Plate

1. Appearance evaluation visually evaluated the adhesive appearance state over time. Specifically, the degree of bubble inflow in the polarizing plate, or the degree of lifting and adhesion failure of the film generated during drying after adhesion was evaluated.

2. Durability of the polarizing plate was stored for 48 hours under the heat-resistant condition of 85 ℃ or 60 ℃, 95% RH heat and humidity in a constant temperature and humidity chamber, the shrinkage of the polarizer was observed under a microscope to compare the shrinkage length. From the four sides of the polarizing plate, the average of the lengths in which the polarizer contracted from the first state was measured.

3. After leaving the humidity condition of item 2, the separation test was carried out using a knife, and the adhesion strength was evaluated by observing whether the interface was separated or whether the film was destroyed due to cohesive failure.

First, when two pieces of polarizing plate are overlapped and reflected on the light, when the polarization breakdown occurs, peeling occurs in the form of cohesive fracture, and when the polarization breakdown does not occur, interfacial separation occurs. As a second evaluation, it was inserted into the cross section of the polarizing plate through the knife in the horizontal direction of the plate to determine in which plane peeling occurred. Look at the delamination form between the easy-adhesive primer layer and the adhesive layer to observe whether interfacial separation or cohesive failure occurs. In the case of cohesive failure, the adhesive force is strong enough to break the film or the adhesive layer, which is an excellent case. The difference in power divided the stages of excellence and a little excellence. When interfacial peeling occurred, the peel strength between the polarizing element and the polyethylene terephthalate was evaluated by setting the standards such as surface peeling and flake peeling. That is, the case where the whole surface peeled was the case where adhesiveness was the weakest, and peeling occurred in the small part evaluated moderate.

As shown in Table 1, in the manufacturing process of the polarizing plate, by controlling the composition ratio of the easily adhesive layer and the concentration of the curing agent in a preferred range, excellent appearance properties, durability and adhesive strength are expressed.

At the core of the bonding process is a drying process, which requires a system that can maximize the intermolecular forces between polymers by evaporating moisture without affecting the mechanical properties of the film as much as possible. The composition of the adhesive layer and the concentration of the adhesive curing agent effectively maintain the adhesion between functional groups that are the source of the intermolecular bonding force, and maintain the strength when the bonding position is reached.

Therefore, as in the present invention, by forming the composition ratio of the adhesive layer and the concentration of the crosslinking agent in a preferred range to make the bonding conditions of the polarizer and the protective film as effective as possible, it is possible to produce a highly durable polarizing plate that can withstand external moisture and the like.

While the embodiments of the present invention have been described with reference to the accompanying tables, the present invention is not limited to the above embodiments, but may be embodied in various forms, and a person of ordinary skill in the art to which the present invention pertains. It will be appreciated that the present invention may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

1 is a schematic view showing a general liquid crystal display device;

2 is a schematic diagram illustrating a front polarizer according to an embodiment of the present invention.

21: polarizer

22a, 22b: adhesive layer

23: protective layer

24: polyethylene terephthalate film

25b: adhesive layer

25a: adhesive auxiliary layer

26: coating layer

27: optical compensation film

28: adhesive layer

30: release film

Claims (11)

As a polarizing plate in which a water-based adhesive bond layer and an easily bonding layer are interposed in order on at least one surface of a polarizer, and the protective film of polyester resin is provided, The water-based adhesive layer comprises at least one resin, a crosslinking agent and water selected from polyvinyl alcohol resin and urethane resin, characterized in that it comprises the crosslinking agent in the range of 0.5 to 1.8% by weight of the resin content, The said easily bonding layer is a polarizing plate which consists of a polyvinyl alcohol resin and polyester-type resin in the weight ratio 1: 1.3-1.9. The polarizing plate of Claim 1 whose resin which comprises a polarizer and an aqueous adhesive layer is a polyvinyl alcohol resin. delete The polarizing plate of claim 1, wherein the water-based adhesive layer is formed by drying at 70 to 90 ° C. The polarizing plate according to claim 1, wherein the polyester resin is polyethylene terephthalate. A polarizer or a protective film of a polyester resin with an easily adhesive layer, comprising at least one resin, a crosslinking agent and water selected from a polyvinyl alcohol resin and a urethane resin, wherein the crosslinking agent is 0.5 to 1.8 of a resin content. Applying a water-based adhesive comprising a weight percent range to face each other, Curing the water-based adhesive by a drying process, and forming an adhesive layer, The easily adhesive layer comprises a polyvinyl alcohol resin and a polyester resin in a weight ratio of 1: 1.3 to 1.9 The manufacturing method of the polarizing plate in which the water-based adhesive bond layer and the easily bonding layer are interposed in order at least one surface of a polarizer, and the protective film of polyester resin is provided. delete The method of claim 6, wherein the polyester resin is polyethylene terephthalate. The manufacturing method of the polarizing plate of Claim 6 whose resin which comprises a polarizer and an aqueous adhesive layer is polyvinyl alcohol resin.  The method of claim 6, wherein the drying process is performed at 70 to 90 ° C. 8. An image display device comprising the polarizing plate of claim 1.

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