WO2017188756A1 - Polarizing plate and liquid crystal display device comprising same - Google Patents

Abstract

The present invention provides a polarizing plate and a liquid crystal display device comprising the same, the polarizing plate comprising: a polyvinyl alcohol-based polarizer; and a protective coating layer formed on at least one surface of the polarizer, wherein the protective coating layer is formed from a composition for forming a protective coating layer, containing: a cellulose-based resin comprising 20-60 wt% of one or more substituents selected from the group consisting of a C₁-C₈ alkyl group, an acetyl group, a hydroxyethyl group, a phenyl group, a benzoyl group, a propanoyl group and a butanoyl group; and a cross-linking agent. According to the present invention, the polarizing plate can provide a polarizer protection effect by means of excellent durability and adhesive strength and enables a lightweight thin film to be implemented without using an adhesive layer.

Description

Polarizing plate and liquid crystal display including the same

The present invention relates to a polarizing plate and a liquid crystal display including the same, and more particularly, to a polarizer protecting effect that can provide a polarizer protection effect with excellent durability and adhesion, and to reduce the thickness of a thin film and a liquid crystal display including the same.

Liquid crystal display devices (LCDs) are used in various applications such as notebooks, mobile phones, liquid crystal TVs, etc., and generally include liquid crystal cells and polarizing plates containing liquid crystals, as adhesive layers or adhesive layers for bonding them. It is composed.

In addition, a polarizer used in a liquid crystal display device generally includes a polarizer (also referred to as a 'polarizing film') in which an iodine compound or a dichroic dye is adsorbed onto a polyvinyl alcohol (PVA) resin film arranged in a predetermined direction. It includes, on both sides of the polarizer has a multilayer structure in which the first and second polarizer protective film, which is represented by a triacetyl cellulose (TAC), respectively, are laminated through an adhesive.

JP 2013-033237 A describes that a film made of a specific methacryl-based resin is excellent in heat resistance, moisture resistance, scratch resistance, mechanical strength, adhesiveness with a polarizer, and optical isotropy, and is useful as a protective film for polarizers. It is described.

However, the protective film described in the above document is bonded to the polarizer using an adhesive, and thus, when the adhesive is required for lamination of the protective film, it is difficult to reduce the weight of the polarizing plate due to the presence of the adhesive layer, and the adhesive strength of the adhesive layer is If not enough, the protective film may cause a problem of peeling from the polarizer.

The present invention is to solve the above problems, one object of the present invention is to provide a polarizer protective effect with excellent durability and adhesion, and to provide a polarizing plate that can be reduced in weight thin film.

Another object of the present invention is to provide a liquid crystal display device having the polarizing plate on at least one side of a liquid crystal cell.

On the other hand, the present invention is a polyvinyl alcohol polarizer; And a protective coating layer formed on at least one surface of the polarizer, wherein the protective coating layer is selected from the group consisting of C ₁ -C ₈ alkyl group, acetyl group, hydroxyethyl group, phenyl group, benzoyl group, propanoyl group and butanoyl group It provides a polarizing plate formed from a composition for forming a protective coating layer comprising a cellulose-based resin and a crosslinking agent containing 20 to 60% by weight of at least one substituent.

In one embodiment of the present invention, the cellulose-based resin may include a glucose unit of Formula 1 below.

[Formula 1]

Where

R ₁ , R ₂ and R ₃ are each independently hydrogen, an alkyl group of C ₁ -C ₈ , an acetyl group, a hydroxyethyl group, a phenyl group, a benzoyl group, a propanoyl group or a butanoyl group,

At least one of R ₁ , R ₂ and R ₃ is hydrogen.

In one embodiment of the present invention, the crosslinking agent may include a compound capable of acetalizing, urethanating, etherifying, or esterifying hydroxyl groups of the cellulose-based resin.

On the other hand, the present invention provides a liquid crystal display device having the polarizing plate on at least one side of the liquid crystal cell.

The polarizing plate according to the present invention may include a protective coating layer capable of providing a polarizer protection function with excellent durability and adhesion, and thus may be manufactured thinly without using an adhesive layer and may have excellent durability.

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

Polarizing plate according to an embodiment of the present invention is a polyvinyl alcohol polarizer; And a protective coating layer formed on at least one surface of the polarizer, wherein the protective coating layer is selected from the group consisting of C ₁ -C ₈ alkyl group, acetyl group, hydroxyethyl group, phenyl group, benzoyl group, propanoyl group and butanoyl group It is formed from a protective coating layer-forming composition comprising a cellulose-based resin and a crosslinking agent containing 20 to 60% by weight or more of the substituents.

<Polarizer>

In one embodiment of the present invention, the polarizer is a dichroic dye adsorbed on a polyvinyl alcohol-based film.

The polyvinyl alcohol-based resin constituting the polarizer can be obtained by saponifying a polyvinyl acetate-based resin. As polyvinyl acetate type resin, the copolymer etc. of vinyl acetate and the other monomer copolymerizable with this besides the polyvinyl acetate which is a homopolymer of vinyl acetate are mentioned. As another monomer copolymerizable with vinyl acetate, an unsaturated carboxylic acid type, an unsaturated sulfonic acid type, an olefin type, a vinyl ether type, an acrylamide type monomer which has an ammonium group, etc. are mentioned. The polyvinyl alcohol resin may be modified, for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used.

The saponification degree of the polyvinyl alcohol-based resin is usually 85 to 100 mol%, preferably 98 mol% or more. In addition, the degree of polymerization of the polyvinyl alcohol-based resin is usually 1,000 to 10,000, preferably 1,500 to 5,000.

What formed such a polyvinyl alcohol-type resin into a film is used as a raw film of a polarizer. The film formation method of polyvinyl alcohol-type resin is not specifically limited, A well-known method can be used. The film thickness of the polyvinyl alcohol-based master film is not particularly limited, and may be, for example, 10 to 150 μm.

A polarizer is normally manufactured through the process of uniaxially stretching the above-mentioned polyvinyl alcohol-type film, the process of dyeing and adsorbing with a dichroic dye, the process of treating with boric acid aqueous solution, and the process of washing with water and drying.

The process of uniaxially stretching the polyvinyl alcohol-based film may be performed before dyeing, may be simultaneously performed with dyeing, or may be performed after dyeing. When the uniaxial stretching is performed after dyeing, it may be performed before boric acid treatment, or may be performed during boric acid treatment. Of course, it is also possible to perform uniaxial stretching in these plural steps. For uniaxial stretching, rolls or heat rolls with different circumferential speeds can be used. In addition, uniaxial stretching may be dry stretching extending | stretching in air | atmosphere, or wet extending | stretching extending | stretching in the state swollen with a solvent may be sufficient as it. The draw ratio is usually 3 to 8 times.

As a process of dyeing a stretched polyvinyl alcohol-type film with a dichroic dye, the method of immersing a polyvinyl alcohol-type film in the aqueous solution containing a dichroic dye can be used, for example. As a dichroic dye, iodine or a dichroic dye is used. In addition, the polyvinyl alcohol-based film is preferably swelled by dipping in water before dyeing.

When using iodine as a dichroic dye, the method of immersing and dyeing a polyvinyl alcohol-type film in the aqueous dyeing solution containing iodine and potassium iodide can be used normally. Usually, the content of iodine in the aqueous solution for dyeing is 0.01 to 1 part by weight based on 100 parts by weight of water (distilled water), and the content of potassium iodide is 0.5 to 20 parts by weight based on 100 parts by weight of water. The temperature of the aqueous solution for dyeing is usually 20 to 40 ° C., and the immersion time (dyeing time) is usually 20 to 1,800 seconds.

On the other hand, when using a dichroic organic dye as a dichroic dye, the method of immersing and dyeing a polyvinyl alcohol-type film in the aqueous dyeing solution containing a water-soluble dichroic organic dye can be used normally. The content of the dichroic organic dye in the aqueous solution for dyeing is usually 1 × 10 ^-4 to 10 parts by weight, preferably 1 × 10 ^-3 to 1 part by weight based on 100 parts by weight of water. This dyeing aqueous solution may further contain inorganic salts such as sodium sulfate as a dyeing aid. The temperature of the aqueous solution for dyeing is usually 20 to 80 ° C., and the immersion time (dyeing time) is usually 10 to 1,800 seconds.

Boric acid treatment of the dyed polyvinyl alcohol-based film can be carried out by immersing in a boric acid-containing aqueous solution. Usually, the content of boric acid in the aqueous solution containing boric acid is 2 to 15 parts by weight, preferably 5 to 12 parts by weight with respect to 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide, and its content is usually 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight with respect to 100 parts by weight of water. The temperature of the boric acid-containing aqueous solution is usually 40 ° C or higher, preferably 40 to 85 ° C, more preferably 50 to 80 ° C, and the immersion time is usually 60 to 1,200 seconds, preferably 150 to 600 seconds, more preferably 200 to 400 seconds.

After the boric acid treatment, the polyvinyl alcohol-based film is usually washed with water and dried. Water washing treatment can be performed by immersing the boric acid-treated polyvinyl alcohol-based film in water. The temperature of the water of a water washing process is 5-40 degreeC normally, and immersion time is 1-120 second normally. A polarizer can be obtained by drying after washing with water. Drying process can be normally performed using a hot air dryer or a far-infrared heater. The drying treatment temperature is usually 30 to 100 ° C, preferably 50 to 80 ° C, and the drying time is usually 60 to 600 seconds, preferably 120 to 600 seconds.

<Protective coating layer>

In one embodiment of the present invention, the protective coating layer formed on at least one side of the polarizer is one selected from the group consisting of C ₁ -C ₈ alkyl group, acetyl group, hydroxyethyl group, phenyl group, benzoyl group, propanoyl group and butanoyl group It can be formed from a protective coating layer-forming composition comprising a cellulose-based resin and a crosslinking agent containing 20 to 60% by weight or more of the substituents.

The cellulose-based resin may include a glucose unit of Formula 1 below.

[Formula 1]

Where

R ₁ , R ₂ and R ₃ are each independently hydrogen, an alkyl group of C ₁ -C ₈ , an acetyl group, a hydroxyethyl group, a phenyl group, a benzoyl group, a propanoyl group or a butanoyl group,

At least one of R ₁ , R ₂ and R ₃ is hydrogen.

The cellulose-based resin may include 20 to 60% by weight of one or more substituents selected from the group consisting of C ₁ -C ₈ alkyl, acetyl, hydroxyethyl, phenyl, benzoyl, propanoyl and butanoyl groups. When the substituent content is less than 20% by weight, it may be difficult to secure water resistance due to high hydrophilicity, and when the content of the substituent exceeds 60% by weight, it may be difficult to express adhesion. In particular, the content of the substituent to ensure excellent water resistance and adhesion at the same time may be 30 to 55% by weight.

The cellulose-based resin may have a number average molecular weight (Mn) of 10,000 to 100,000. If the number average molecular weight (Mn) is less than 10,000, the mechanical properties of the coating layer may not be secured, and if the number average molecular weight (Mn) exceeds 100,000, the coating liquid may have a high viscosity and may be difficult to coat.

The content of the cellulose-based resin is not particularly limited, and may be, for example, 70 to 99% by weight of the total weight of the solid content of the composition for forming the protective coating layer. If the content is less than 70% by weight, the viscosity is difficult to apply, the adhesion is lowered, it may be difficult to form a coating layer exhibiting a sufficient protective effect. If the content is more than 99% by weight, the content of the crosslinking agent may be insufficient, which may lower mechanical properties.

In one embodiment of the present invention, the crosslinking agent is not particularly limited as long as it is a compound capable of appropriately crosslinking the cellulose-based resin, and the hydroxyl group of the cellulose-based resin may be acetalized, urethaneized, etherified, or esterified. Compound and the like can be used.

Examples of the acetalizable crosslinking agent include glyoxalic acid, 4-oxo-2-butanoic acid and 2-methyl-3-oxopropanoic acid (2-methyl -3-oxopropanoic acid), 4-formyl-cyclohexanecarboxylic acid, 4-formyl-2-methyl-3-furancarboxylic acid (4-formyl-2-methyl- 3-furancarboxylic acid), 5-formyl-3-isoxazolecarboxylic acid, glutaraldehyde, and the like.

As said isocyanate type isocyanate crosslinking agent, For example, diisocyanate compounds, such as tolylene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, 2, 4- or 4, 4- diphenylmethane diisocyanate; The adduct which reacted 3 mol of diisocyanate compounds with 1 mol of polyhydric alcohol compounds, such as trimethylol propane, the isocyanurate body which self-condensed 3 mol of diisocyanate compounds, etc. can be used.

Examples of the etherifying crosslinking agent include divinylsulfone, 1,3-divinylsulfonyl-2-hydroxypropane, epoxy group, oxetane group or Aziridine group containing compound can be used.

As said crosslinkable agent which can be esterified, malonic acid, succinic acid, glutaric acid, adipic acid, oxalic acid, tartaric acid, citric acid, 1,2,3,4-butanetetracarboxylic acid, or derivatives thereof, etc. are mentioned, for example. .

The crosslinking agents exemplified above may be used alone or in admixture of two or more, and may be particularly an isocyanate-based crosslinking agent.

The crosslinking agent may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the cellulose-based resin. When the content of the crosslinking agent is less than 0.1 part by weight, the cohesion force may be reduced due to insufficient crosslinking degree, and the durability may be deteriorated. have.

The protective coating layer-forming composition may further include a solvent such that the cellulose-based resin can be applied on the polarizer, and then removed by drying to form a coating layer.

Examples of the solvent include methanol, ethanol, butanol, acetone, isopropyl alcohol, ethylene glycol, diethylene glycol, methyl ethyl ketone, toluene, N-methyl-2-pyrrolidone, and the like. It is preferable to mix and use 2 or more types of solvent from a stability and the ease of drying.

If necessary, the protective coating layer-forming composition may further include additives such as plasticizers, silane coupling agents, antistatic agents, leveling agents, and basic substances known in the art within the scope of not impairing the desired effect in the present invention. Can be.

The protective coating layer may have a thickness of, for example, 10 to 60 μm, preferably 10 to 50 μm. If the thickness is less than 10 μm, the polarizer protection effect may not be sufficient. If the thickness is more than 60 μm, bubbles may occur during drying of the coating solution, thereby causing a problem of appearance defects of the polarizing plate.

Polarizing plate according to an embodiment of the present invention can be prepared by applying and drying the protective coating layer-forming composition on at least one surface of the polyvinyl alcohol-based polarizer.

The coating method of the composition for forming the protective coating layer is not particularly limited, and for example, slit coating method, knife coating method, spin coating method, casting method, micro gravure coating method, gravure coating method, bar coating method, roll coating method, Wire bar coating method, dip coating method, spray coating method, screen printing method, gravure printing method, flexographic printing method, offset printing method, ink jet printing method, dispenser printing method, nozzle coating method, capillary coating method and the like can be used. .

Drying of the applied composition can be carried out by methods known in the art, such as hot air, far infrared rays and the like. The drying temperature may be for example 60 to 100 ° C. and the drying time may be for example 1 to 10 minutes. If the drying temperature and time is within the above range, the coating quality is excellent.

The polarizing plate of the present invention can be applied to any conventional liquid crystal display device, and specifically, a liquid crystal display device including a liquid crystal panel in which the polarizing plate is bonded to at least one surface of a liquid crystal cell can be configured.

Accordingly, one embodiment of the present invention relates to a liquid crystal display device having the polarizing plate on at least one side of a liquid crystal cell.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples. These examples and experimental examples are only for illustrating the present invention, it is apparent to those skilled in the art that the scope of the present invention is not limited thereto.

Preparation Example 1 Preparation of Polarizer

The polyvinyl alcohol resin film having a thickness of 75 µm and an average polymerization degree of about 2,400 and a degree of hydrolysis of 99.9 mol% or more were stretched by about 1.5 times while immersing in 30 ° C pure water for 2 minutes. Then, the solution was stretched by about 2.0 times while immersing for 3 minutes in a dye bath containing an aqueous solution having a weight ratio of 0.01 / 1.0 / 100 of iodine / potassium iodide / water and having a temperature of 30 ° C. Then, the film was stretched about 2.0 times while immersing for 1 minute at 53 ° C. in an aqueous solution in which potassium iodide / boric acid / water was mixed at a weight ratio of 10/5/100. Then, the resultant was washed with 15 ° C. pure water for 1.5 seconds and dried at 50 ° C. for 5 minutes to prepare a polarizer having iodine adsorbed on polyvinyl alcohol.

Examples and Comparative Examples:

To 100 parts by weight of cellulose resin (Cellulose acetate, Mn: 30,000, acetyl 39.8wt%, Eastman), 3 parts by weight of a crosslinking agent (Coronate-L, TMP adduct of TDI, Nippon Urethane Co., Ltd.) was added and a leveling agent -378) A coating layer having a thickness of 40 μm was formed on both surfaces of the polarizer with a coating solution made by adding 0.3 parts by weight. Thereafter, the polarizing plate of Example 1 was prepared by standing at 23 ° C. and 60% for 3 days.

The remaining examples and comparative examples were prepared in the same manner as in Example 1 to the composition of Table 1 below.

		Example								Comparative example
		One	2	3	4	5	6	7	8	One	2
Suzy	A-1	100	100	100	100	100	100			100
	A-2							100
	A-3								100
	A-4										100
Crosslinking agent	B-1	3.0				1.0	7.0	3.0	3.0		3.0
	B-2		3.0			3.0
	B-3			3.0			3.0
	B-4				3.0
Leveling agent	C	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3

A-1: Cellulose acetate, Mn: 30,000, Acetyl 39.8wt%

A-2: Cellulose acetate, Mn: 50,000, Acetyl 39.7wt%

A-3: Cellulose acetate butyrate, Mn: 70,000, Acetyl 13.5wt%, Butanoyl 38wt%

A-4: Cellulose, Mn: 50,000, Acetyl 0wt%

B-1: Coronate-L, TDI's TMP Adduct, Japan Urethane Co., Ltd.

B-2: Glutaraldehyde

B-3: CL-427, Menadiona

B-4: malonic acid

C: leveling agent (BYK-378, BWK Chemisa)

Experimental Example  1: Forced peel test

A sheath (half cut) was put in one side of the protective coating layer of the polarizer of an Example and a comparative example. Subsequently, the polarizing plate was deformed until the half cut portion was convex. Thereafter, the state of the coating layer at the bent portion was visually observed and the results are shown in Table 2 below. Evaluation criteria are as follows.

<Evaluation Criteria>

○: no peeling

△: less than 0.5mm

×: 0.5 mm or more

Experimental Example  2: durability test

The polarizing plates of Examples and Comparative Examples were cut to 50 mm × 50 mm with Thomson's blades, and the state after being left to stand for 500 hours at 80 ° C. and 60 ° C. and 90% RH atmosphere was observed. Evaluation criteria are as follows.

<Evaluation Criteria>

(Circle): No film edge part peeling, the transmittance | permeability and the difference with before the start of the durability test of haze are less than 3%

X: There exists a film edge part peeling, the transmittance | permeability and the difference with before the start of the durability test of haze are 3% or more

Experimental Example  3: Thermal shock  exam( Polarizer  crack)

The polarizing plates of the Example and the comparative example were cut out to 50 mm x 50 mm with Thompson blade, and it was set as the test piece. The thermal shock test was repeated 100 cycles for 1 hour at 80 ° C and 1 hour at -40 ° C. After the thermal shock was observed in the stretching direction of the polarizer, the presence of polarizer cracks were observed from the end of the polarizing plate, and when the polarizer cracks were observed, the length of the cracks was measured and listed in Table 2 below. In the case where a plurality of cracks were observed, evaluation was made using the average value. Evaluation criteria are as follows.

<Evaluation Criteria>

○: no polarizer crack

△: less than 0.5mm

×: 0.5 mm or more

	Example								Comparative example
	One	2	3	4	5	6	7	8	One	2
Forced peeling	△	○	△	△	△	○	△	△	×	△
Heat resistant (80 ℃)	○	○	○	○	○	○	○	○	○	○
Moisture-resistant heat (60 degrees Celsius, 90%)	○	○	○	○	○	○	○	○	○	×
Thermal Shock (-40 ~ 80 ℃)	○	○	○	○	△	○	○	△	×	×

As can be seen in Table 2, 20 to 60% by weight of one or more substituents selected from the group consisting of C ₁ -C ₈ alkyl, acetyl, hydroxyethyl, phenyl, benzoyl, propanoyl and butanoyl groups The polarizing plate of the embodiment formed with a protective coating layer formed from a composition containing a cellulose-based resin and a crosslinking agent was found to be excellent in adhesion between the polarizer and the protective coating layer and excellent in durability. On the other hand, in the comparative example, the adhesion or durability was poor.

Having described the specific part of the present invention in detail, it is apparent to those skilled in the art that this specific technology is only a preferred embodiment, which is not intended to limit the scope of the present invention. Do. Those skilled in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Therefore, the substantial scope of the present invention will be defined by the appended claims and equivalents thereof.

Claims (9)

1. Polyvinyl alcohol polarizers; And a protective coating layer formed on at least one surface of the polarizer, wherein the protective coating layer is selected from the group consisting of C ₁ -C ₈ alkyl group, acetyl group, hydroxyethyl group, phenyl group, benzoyl group, propanoyl group and butanoyl group A polarizing plate formed from a composition for forming a protective coating layer comprising a cellulose-based resin and a crosslinking agent containing 20 to 60% by weight of one or more selected substituents.
2. The polarizing plate of claim 1, wherein the cellulose-based resin comprises a glucose unit represented by Formula 1 below:

   [Formula 1]

   

   Where

   R ₁ , R ₂ and R ₃ are each independently hydrogen, an alkyl group of C ₁ -C ₈ , an acetyl group, a hydroxyethyl group, a phenyl group, a benzoyl group, a propanoyl group or a butanoyl group,

   At least one of R ₁ , R ₂ and R ₃ is hydrogen.
3. The polarizing plate of claim 1, wherein the cellulose-based resin has a number average molecular weight (Mn) of 10,000 to 100,000.
4. The method of claim 1, wherein the crosslinking agent is glyoxalic acid (oxoethanoic acid), 4-oxo-2-butanoic acid, 2-methyl-3-oxopropanoic acid (2-methyl-3 -oxopropanoic acid), 4-formyl-cyclohexanecarboxylic acid, 4-formyl-2-methyl-3-furancarboxylic acid (4-formyl-2-methyl-3- furancarboxylic acid), 5-formyl-3-isoxazolecarboxylic acid, and polar tar selected from the group consisting of glutaraldehyde.
5. The method of claim 1, wherein the crosslinking agent is selected from the group consisting of a diisocyanate compound, an adduct obtained by reacting 3 moles of the diisocyanate compound with 1 mole of the polyhydric alcohol compound, and an isocyanurate body self-condensing 3 moles of the diisocyanate compound. Polarizer.
6. The method of claim 1, wherein the crosslinking agent is divinylsulfone, 1,3-divinylsulfonyl-2-hydroxypropane, and an epoxy group, an oxetane group, or A polarizing plate selected from the group consisting of aziridine group-containing compounds.
7. The polarizing plate of claim 1, wherein the crosslinking agent is selected from the group consisting of malonic acid, succinic acid, glutaric acid, adipic acid, oxalic acid, tartaric acid, citric acid, and 1,2,3,4-butanetetracarboxylic acid.
8. The polarizing plate of claim 1, wherein the crosslinking agent is included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the cellulose-based resin.
9. A liquid crystal display device comprising a polarizing plate according to any one of claims 1 to 8 on at least one side of a liquid crystal cell.