KR101838496B1 - Low humidity polarizer - Google Patents

Abstract

A polarizer with low moisture permeability is formed by a solvent casting method from a resin composition comprising an acrylic resin and a silica particle represented by chemical formula 1. The polarizer has a water vapor permeability of 150g/m^2·day or less after being left for 500 hours in the high temperature and high humidity environment at 60°C with 90%RH. Chemical formula 1 is MMA-MAA, wherein MMA denotes a unit of methyl methacrylate and MAA denotes a unit of methacrylic acid.

Description

Low humidity polarizer < RTI ID = 0.0 >

The present invention relates to a polarizing plate having high resistance to the external environment by using an acrylic film having low moisture permeability as a protective film.

2. Description of the Related Art In recent years, a liquid crystal display device that consumes a small amount of power and operates at a low voltage and is lightweight and thin has been widely used in information display devices such as a mobile phone, a monitor for a portable information terminal computer, and a television. Such an information display device is required to have reliability under a severe environment depending on its use. For example, in a car navigation system liquid crystal display device, the temperature and humidity inside the vehicle in which it is placed may become very high, and the temperature and humidity conditions required are more stringent than those of ordinary monitors for a television or a personal computer. In a liquid crystal display device, a polarizing plate is used to enable the display. In a liquid crystal display device requiring such a strict temperature and / or humidity condition, a polarizing plate constituting it is required to have high durability.

The polarizing plate usually has a structure in which a transparent protective film is laminated on both sides or one side of a polarizing film made of a polyvinyl alcohol resin in which a dichroic dye is adsorbed and oriented. Conventionally, triacetyl cellulose (TAC) is widely used for this protective film, and this protective film is bonded to the polarizing film through an adhesive composed of an aqueous solution of a polyvinyl alcohol resin. However, the polarizing plate in which the protective film made of triacetylcellulose is laminated has a high moisture permeability of triacetyl cellulose, so that when the polarizing plate is used for a long time under a high humid environment, the polarization performance deteriorates or the protective film and the polarizing film peel off have. In order to solve these problems, attempts have been made to use a (meth) acrylic resin film having a lower moisture permeability as a protective film of a polarizing plate than a triacetylcellulose film.

Conventional acrylic protective films have been manufactured by melt casting method. However, solvent casting method has many merits in terms of environment-friendliness such as thinning, mass production, and recycling of resin when manufactured. The solvent casting method is to melt the acrylic film in a solvent and extrude it into a T-die. Then, the solvent is dried in the belt to form a film. It is necessary to increase the impact strength by adding the optimized particles and secure the slip property for transporting the film. Process is possible. Also, the added particles should not be dissolved or deformed in the solvent.

Korean Patent No. 1265007 discloses a pressure-sensitive type polarizing plate in which light leakage of an image display device does not occur even by a change in use environment. In the pressure-sensitive adhesive type polarizing plate in which the acrylic polymer constituting the pressure-sensitive adhesive layer has an aromatic ring structure ) Acrylate monomer unit and its content is determined according to the value of the photoelastic coefficient X of the transparent protective film, and when the retardation value of the transparent protective film changes due to environmental changes such as heating, the pressure- It is proposed to adjust so as to cause a phase difference change of the opposite sign.

Korean Patent No. 1114354 discloses a protective film for an optical member having a pressure-sensitive adhesive layer containing a photopolymerizable acrylic polymer, an antistatic agent and a cured product of a polymerization initiator composition, wherein a crosslinking reaction is caused by a radical generated in the initiator An appropriate amount of an antistatic agent is added to a composition containing a photopolymerizable acrylic polymer into which a photoactivating group capable of causing photoinitiator is introduced and a polymerization initiator in a predetermined ratio so that the aging process at the time of curing can be omitted and the manufacturing process can be simplified , And a protective film excellent in antistatic property during peeling or use.

Korean Patent Laid-Open Publication No. 2015-0061591 discloses a composition comprising a first functional layer (low moisture-permeable layer) formed using a compound having a cyclic aliphatic hydrocarbon group and an ethylenically unsaturated double bond group, and a composition containing urethane acrylate thereon There is proposed a technique for obtaining a polarizing plate protective film having excellent interlayer adhesion and wind non-uniformity resistance by using a specific amount of a fluoroaliphatic group-containing copolymer having a second functional layer formed thereon and having a specific structure in the first functional layer .

Japanese Patent Application Laid-Open No. 2014-240905 discloses a polarizing plate having a film thickness and a modulus of elasticity within a specific range and having an acrylic resin as a main component in order to produce a polarizing plate excellent in adhesion with a polarizer, , A polarizer, and a retardation film B composed mainly of a cellulose derivative having at least an ether bond and a substituent in a glucose skeleton, and the film A and the film B are bonded together through an ultraviolet curable adhesive.

Therefore, there is a need to improve the technique of securing the slip property for film transfer while still facilitating the film forming process when the acrylic protective film is still produced by the solvent casting method.

Korea Patent No. 1265007 Korea Patent No. 1114354 Korean Patent Publication No. 2015-0061591 Japanese Laid-Open Patent Application No. 2014-240905

SUMMARY OF THE INVENTION The present invention has been devised to solve the problems as described above, and it is an object of the present invention to provide a polarizer which is free from defective appearance unevenness by applying an acrylic protective film resistant to moisture.

The present invention relates to a polarizing plate comprising 70 to 99 parts by weight of a methyl methacrylate unit and 1 to 30 parts by weight of a methacrylic acid unit based on 100 parts by weight of an acrylic resin represented by the following formula (1) An acrylic film formed by a solvent casting method from a composition comprising one or two kinds of nanoparticles selected from the group consisting of acrylic resin and core shell rubber particles or silica particles is applied on at least one side of the polarizer And has a moisture permeability of 150 g / m < 2 > day or less even after being left in a reliable environment at 60 DEG C and 90% RH for a long time.

[Chemical Formula 1]

MMA-MAA

Here, MMA represents a unit of methyl methacrylate, and MAA represents a unit of methacrylic acid.

In the present invention, the diameter of the nanoparticles is 100 nm to 300 nm, the content of the silica particles is 0.01 to 0.1 parts by weight based on 100 parts by weight of the initiator, the content of the CSR particles is 3 to 10 parts by weight .

In the present invention, it is preferable that the resin composition includes an acrylic film having a molecular weight of 300,000 g / mol to 2,500,000 g / mol.

In the present invention, it is preferable to use a mixture of a halogenated hydrocarbon and an alcohol as a solvent for solvent casting.

The present invention is excellent in film forming property and reliability and can be applied to a polarizing plate to produce a high quality polarizing plate having no appearance unevenness and low moisture permeability even after being left in a high temperature and high humidity environment for a long time.

Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited to these.

The inventors of the present invention have conducted research to develop an acrylic film which is easy to form film and transfer film when a thin film acrylic film is manufactured by a solvent casting method. As a result, it has been found that the average molecular weight of the resin composition is in the range of 300,000 to 2,500,000 g / mol , It has been found that a protective film which is easy to form and transport can be obtained when a film is formed by a resin composition containing a specific component, and thus the present invention has been completed.

The polarizing plate of the present invention comprises a protective film A formed from a resin composition comprising an acrylic resin and nanoparticles represented by the following formula (1) and a protective film B having a film thickness of 20 to 100 탆 containing a cellulose ester sandwiched by a polarizer (PVA) And has a moisture permeability of not more than 150 g / m < 2 > day after leaving for 500 hours in a reliable environment at 60 DEG C and 90% RH using a high temperature and high humidity chamber without any appearance unevenness.

[Chemical Formula 1]

MMA-MAA

Here, MMA represents a unit of methyl methacrylate, and MAA represents a unit of methacrylic acid.

First, the acrylic resin of the present invention will be described. The acrylic resin of the present invention is a copolymer resin comprising a methyl methacrylate unit and a methacrylic acid unit, wherein each of the monomer units is contained in the form of a repeating unit.

(Meth) acrylic acid unit (meth) acrylate unit is preferably used in an amount of 70 to 99 parts by weight, methacrylic acid unit: 1 to 30 parts by weight based on 100 parts by weight of the acrylic resin in consideration of optical characteristics, transparency, compatibility, By weight. When the content of methyl methacrylate units is in the above range, excellent retardation and optical characteristics can be obtained. When the methylmethacrylate unit content is less than 70 parts by weight, the optical performance of the protective film deteriorates. When the methylmethacrylate unit content exceeds 99 parts by weight, the thickness uniformity of the protective film is lowered. The content of the methacrylic acid unit is preferably 1 to 30 parts by weight based on 100 parts by weight of the acrylic resin. When the content of the methacrylic acid unit is within the above range, preferable optical properties can be obtained.

In the present invention, by adding silica particles which are insoluble in a solvent and are not deformed in the acrylic resin, impact strength of the film is improved, and film formation and film transfer are facilitated. The diameter of the silica particles of the present invention is preferably 100 to 300 nm. When the diameter of the nanoparticles is less than 100 nm, the effect of the intended invention is not sufficiently exhibited, and when the diameter exceeds 300 nm, the quality of the protective film becomes poor. When the content of the silica particles of the present invention is in the above range, it is possible to provide a protective film excellent in both hardness and flexibility.

The resin composition of the present invention preferably has a molecular weight of 300,000 to 2,500,000 g / mol. If the molecular weight is less than 300,000 g / mol, the production efficiency of the film is lowered. If the molecular weight exceeds 2,500,000, the molding process is not easy. The glass transition temperature (Tg) of the resin composition of the present invention is preferably 120 ° C or higher. Even if the glass transition temperature is lower than the above-mentioned range, handling becomes poor, which is not preferable.

The acrylic film of the present invention preferably has a film thickness of 10 to 60 탆. When the thickness of the protective film is less than 10 mu m, sufficient retardation characteristics are not exhibited. When the thickness of the protective film exceeds 60 mu m, it is not suitable for use in a thin polarizer.

The acrylic film of the present invention preferably has an in-plane retardation Ro and a thickness direction retardation Rth of 10 nm or less under conditions of 23 ° C and 55% RH. When the in-plane and thickness retardation exceeds 10 nm, the performance as an isotropic optical film is deteriorated.

Hereinafter, a preferred manufacturing method of the present invention will be described in detail.

Preparation of acrylic polymer resin

To prepare the protective film of the present invention, first, a copolymer resin solution of a methyl methacrylate monomer and a methacrylic acid monomer is prepared. There is no particular limitation on the method for producing the copolymer of these monomers, and the copolymer can be produced according to a method for producing a copolymer resin well known in the art such as suspension polymerization, emulsion polymerization, bulk polymerization or solution polymerization.

Preparation of Dilute Solutions Containing Acrylic Resin and Nanoparticles

In the present invention, a film is produced by a solvent casting method (solution film forming method). In the solvent casting method, a solution (dope) obtained by dissolving an acrylic copolymer in a casting solvent is cast on a support, and the solvent is evaporated to form a film. The preparation of the dope is carried out by mixing the acrylic copolymer resin solution and the auxiliary additive in the casting solvent.

When a film is produced by a solvent casting method, an organic solvent is preferable as a solvent for preparing an acrylic resin composition (dope). As the organic solvent, it is preferable to use halogenated hydrocarbons, and halogenated hydrocarbons include chlorinated hydrocarbons, methylene chloride and chloroform, among which methylene chloride is most preferably used.

If necessary, organic solvents other than halogenated hydrocarbons may be mixed and used. Organic solvents other than halogenated hydrocarbons include esters, ketones, ethers, alcohols and hydrocarbons. Examples of the ester include methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acylate, ethyl acylate and pentyl acylate. Examples of the ketone include acetone, methyl ethyl ketone, diethyl ketone, di Isobutyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone and the like can be used. As the ether, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, Ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1-pentanol, 2-butanol and the like can be used. 2-butanol, cyclohexanol, 2-fluoroethanol, 2,2,2, -trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol and the like Lt; / RTI >

More preferably, methylene chloride may be used as the main solvent, and alcohol may be used as the minor solvent. Concretely, a mixed solvent in which the mixing ratio of methylene chloride and alcohol is in the range of 80:20 to 95: 5 is preferable. A solvent mixed with methylene chloride and methanol at a weight ratio of 90: 10 is more preferable.

In the production of the acrylic protective film, auxiliary additives may further be used. To the acrylic copolymer solution (dope), auxiliary additives such as ultraviolet ray inhibitor, fine particles, infrared absorbing agent and exfoliating agent may be added in various manufacturing processes depending on the application. The specific kind of such additives can be used without limitation as long as they are commonly used in the field, and the content thereof is preferably used within a range that does not deteriorate the physical properties of the film. The timing of adding the additives depends on the type of additive. A step of adding an additive to the end of the doping treatment may be performed.

In the present invention, silica nanoparticles are used as an additive, and the diameter of the nanoparticles is 100 to 300 nm, and the content thereof is preferably 0.01 to 0.1 weight ratio with respect to 100 weight ratio of the initiator.

The acrylic resin composition thus obtained can be prepared by ordinary temperature, high temperature or low temperature dissolution.

Film forming process

In the solvent casting method of the present invention, an acrylic resin composition solution is poured on a metal support from a nozzle of a pressurizing die and allowed to stand for a predetermined time to form a semi-dry film. Thereafter, the semi-dried film is peeled from the metal support, transferred to a drying system, and dried to remove the solvent. Then, a uniaxial stretching process or a biaxial stretching process is performed on the dried film. By this stretching process, it is possible to improve the film uniformity and the retardation value of the protective film.

Specifically, the acrylic resin composition solution thus obtained is cast on a support through a casting die to form an acrylic sheet. Here, the support serves to evaporate the solvent present in the casting solution while casting the casting solution on the sheet extruded from the die, thereby forming an acrylic film. The support or the surface thereof is preferably made of a metal and has a mirror finished surface, and a steel belt such as a stainless steel belt is preferably used as the support. The surface temperature of the metal support is advantageous because it can accelerate the evaporation of the solvent present in the casting stock solution as the temperature is higher. However, if the temperature is too high, the casting stock solution tends to foam or deteriorate in planarity, But it is preferably 0 to 75 占 폚, more preferably 5 to 45 占 폚. As the support, a metal support in the form of a planar conveyor belt may be used.

The acrylic sheet thus formed is subjected to a drawing step in a tenter, and a glass transition temperature (Tg) of an acryl flake is 120 ° C or more in a preheating step. The acrylic film of the present invention may be completed in the dryer under the above conditions after having been subjected to the stretching step in the tenter and then the left and right ends of the film whose surface has been damaged by the clip or pin of the tenter are removed.

In the case of using the tenter stretching device, it is preferable to use a device capable of controlling the holding length of the film from the left and right by the left and right gripping means of the tenter. The stretching operation may be carried out by dividing into a plurality of steps or biaxially stretching in the machine direction and the width direction. When biaxial stretching is carried out, simultaneous biaxial stretching may be carried out or may be performed stepwise. In this case, the stepwise means that the stretching in different stretching directions can be performed sequentially, the stretching in the same direction can be divided into multiple steps, and the stretching in the other direction can be added to any one of them. The simultaneous biaxial stretching may include stretching in one direction and relaxation of the other stretch by shrinking. The preferred stretching magnification of the simultaneous biaxial stretching can be in the range of 1.01 to 2.0 times in both the width direction and the longitudinal direction.

The drying means generally blows hot air on both sides of the web, but there is also a means of heating the micro web in place of the wind. Too rapid drying tends to impair the planarity of the finished film.

The polarizing plate produced using the acrylic film of the present invention produced according to the above method is characterized by a polarizing plate having a moisture permeability of 150 g / m < 2 > day or less even after being left in a reliable environment at 60 DEG C and 90% RH for a long time.

Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited by the following examples.

Example  One

≪ Step 1 >

The content of the methacrylic acid unit was 5%, and acrylic represented by the following formula (2) was used.

(2)

<Step 2> Preparation of Diluted Acrylic Polymer Solution Containing Silica Particles

20.0 parts by weight of the acrylic polymer solution, 1.5 parts by weight of silica particles, and 78.5 parts by weight of a mixed solvent of 9: 1 (by weight) of methylene chloride and methanol were mixed to prepare a diluted acrylic polymer solution containing nanoparticles.

&Lt; Step 3 > Production of protective film A

100 parts by mass of the initiator solution and 5 parts by mass of the silica particle additive solution were added, and sufficiently mixed with an inline mixer. At this time, the composition of the dope was 64.17 parts by weight of methylene chloride, 7.13 parts by weight of methanol, 27.94 parts by weight of acrylic polymer, 0.72 parts by weight of Tinvuin 928 (manufactured by BASF) and 0.04 parts by weight of Silica.

The dope liquid was uniformly plied to a stainless steel band support having a width of 2000 mm using a belt softener. The solvent was evaporated on the stainless steel band support and peeled off from the stainless band support. Then, both ends of the web were held with a tenter and stretched so that the stretching magnification in the TD direction was 1.5 times in a temperature environment of 130 ° C. After the stretching, the stretching was maintained for a few seconds, the tensile force in the width direction was relaxed, the stretching was performed in the width direction, the stretching was continued for 35 minutes in a drying section set at 90 ° C, An acrylic film having a knurling width of 10 mm and a height of 8 占 퐉 and having a film thickness of 40 占 퐉 was prepared at the end.

&Lt; Step 4 > Production of protective film B

A cellulose ester butyrate (CAB) resin having an average acyl group substitution degree (DS) of 2.75 was prepared under the same conditions as in Example 1, and the stretching was carried out at 130% in the temperature of 180 ° C.

<Step 5> Polarizing plate production

PVA was laminated using the protective films A and B to prepare a polarizing plate.

Example  2,3

A dope was prepared under the same conditions as in Example 1 except that a butyl acrylate resin having an MAA content of 10% (Example 2) and 30% (Example 3) of an acrylic resin was used.

Comparative Example  One

A dope was made under the same conditions as in Example 1, except that a resin having an MAA content of 50% of an acrylic resin was used.

Comparative Example  2

The dope was prepared under the same conditions as in Example 1, except that the acrylic resin represented by the following Chemical Formula 3 was used.

(3)

Comparative Example  3

A triacetyl cellulose resin having an average degree of acetyl substitution (DS) of 2.86 was used in the preparation of the dope under the same conditions as in Example 1, and the stretching was conducted at 130% in the condition of 170 ° C.

1. Polarizer Reliability Evaluation

With respect to the polarizing plates obtained by laminating PVA using the protective films A and B of Examples 1 to 3 and Comparative Examples 1 to 3 thus obtained, the presence or absence of apparent staining was observed using a backlight, and a high temperature and high humidity chamber The sample was allowed to stand in a reliability environment of 60 ° C and 90% RH for 500 hours, and the moisture permeability was evaluated using the following specifications and equipment. The results are shown in Table 1.

Applicable standards: KS A1013, KS M6886

Model: KP-M6680

sample Protective film A Protective film B Polarizer characteristic Remarks After the reliability, the moisture permeability (g / ㎡ · day) Appearance stain One COOH Acrylic
(MAA content 5%) CAB 110 none Example 1 2 COOH Acrylic
(MAA content 10%) CAB 115 none Example 2 3 COOH Acrylic
(MAA content 30%) CAB 120 none Example 3 4 COOH Acrylic
(MAA content 50%) CAB 121 none Comparative Example 1 5 Plain acrylic CAB 115 has exist Comparative Example 2 6 TAC CAB 753 none Comparative Example 3

As shown in Table 1, it can be seen that the polarizing plate manufactured using the acrylic protective film manufactured by Solvent Casting according to the present invention can produce a high quality polarizing plate which is resistant to moisture and has no appearance unevenness.

Claims (4)

Polarizer and
An acrylic resin composition comprising 90 to 99 parts by weight of a methyl methacrylate unit and 1 to 10 parts by weight of a methacrylic acid unit based on 100 parts by weight of an acrylic resin represented by the following formula (1) Wherein at least one surface of the polarizer is coated with an acrylic film formed by a solvent casting method from a composition comprising one or two kinds of nanoparticles selected from the group consisting of core shell rubber particles and silica particles The polarizer plate has a moisture permeability of 150 g / m &lt; 2 &gt; day or less even after being left in a reliable environment at 60 DEG C and 90% RH for 500 hours.
[Chemical Formula 1]
MMA-MAA
Here, MMA represents a unit of methyl methacrylate, and MAA represents a unit of methacrylic acid. The method according to claim 1,
Wherein the nanoparticles have a diameter of 100 nm to 300 nm and the content of the silica particles is 0.01 to 0.1 parts by weight based on 100 parts by weight of the initiator and the content of the core shell rubber particles is 3 to 10 parts by weight Wherein an acrylic film is provided on at least one side of the polarizer. The method according to claim 1,
Wherein the acrylic resin has a molecular weight of 300,000 g / mol to 2,500,000 g / mol, wherein the acrylic film is provided on at least one side of the polarizer. The method according to claim 1,
Wherein the solvent of the solvent casting is mixed with a halogenated hydrocarbon and an alcohol, and the acrylic film is provided on at least one side of the polarizer.