KR101197018B1 - Retardation film, polarizing plate and image display having the same - Google Patents

Abstract

The present invention is an acrylic copolymer that is polymerized including 70 to 90% by weight of methacryl monomer, 2 to 10% by weight of styrene monomer, 4 to 10% by weight of isobornyl monomer and 4 to 10% by weight of maleimide monomer. The present invention relates to a retardation film, a polarizing plate, and an image display device including the same, wherein the in-plane retardation value measured at a wavelength of 550 nm is -50 to +50 nm, and the thickness retardation value is -50 to +50 nm.
The retardation film, the polarizing plate, and the image display device including the same according to the present invention form a retardation film by using an acrylic resin including an isobonyl monomer and a maleimide monomer, thereby reducing the heat resistance and transparency of the film and forming processability. This remarkably improved, there is an advantage that the adhesion between the retardation film and the polarizer in the polarizing plate production.

Description

Retardation film, polarizing plate and image display device including the same {RETARDATION FILM, POLARIZING PLATE AND IMAGE DISPLAY HAVING THE SAME}

The present invention relates to a retardation film, a polarizing plate, and an image display device including the same, and more particularly, a molding processability is remarkably improved without a decrease in heat resistance and transparency of a film, and an acrylic resin having improved adhesion to a polarizer when manufacturing a polarizing plate. It relates to a retardation film, a polarizing plate and an image display device including the same.

In general, an image display apparatus is a device that outputs information as an image using a screen, and displays data such as characters, symbols, figures, images, etc. on a screen. A typical image display apparatus is a thinner and lighter image display apparatus than a CRT. Flat panel displays (FPDs) are used. Representative examples include LCD (liquid crystal display), TFT-LCD (thin film transistor liquid crystal display), PDP (plasma display), flexible display, organic light emitting diode (OLED), among them LCD (liquid crystal display) and TFT- An LCD (thin film transistor liquid crystal display) is an apparatus in which an image is expressed by adjusting the amount of light passing through the liquid crystal layer according to the arrangement characteristics of the liquid crystals showing optical anisotropy.

Various kinds of optical films such as prism sheets, diffusion films, brightness enhancement films, polarizing films, polarizer protective films, and retardation films are used to realize high quality display of such LCDs or TFT-LCDs.

Conventional polarizing film is formed by attaching a polarizer protective film that acts as a protector on both sides of the PVA (Poly Vinyl Alcohol: polarizer) film oriented by dyeing iodine compounds or dichroic materials arranged in a certain direction. The polarizer has a very large draw ratio of 4 to 5 times in the manufacturing process, and has a low heat resistance, which is very vulnerable to external stress, so application of a protective film is inevitable. The polarizer protective film is used to increase the durability and mechanical properties of the weak polarizer, in order to maintain optical properties such as polarization characteristics of the polarizer, transparency and isotropy are required, and heat resistance and adhesion to the adhesive / adhesive is important It acts as an argument.

As the polarizer protective film, a triacetyl cellulose (TAC) film is mainly used, and a polyester film, a polyacrylate film, a polycarbonate film, a norbornene film, and the like may be applied.

However, the triacetyl cellulose (TAC) film has a small phase difference value in the plane but has a relatively large phase difference value in the thickness direction, so that the phase difference value is expressed by the action of external stress, and the polyacrylate film has excellent transparency. Due to the weakness of external impact and brittleness and low heat resistance, there is a problem in that the polarization performance of the polarizing plate is degraded under high temperature and humidity conditions.

In addition, a liquid crystal cell of a liquid crystal display has a unique liquid crystal arrangement and optical anisotropy, and a retardation film has been proposed that compensates for such optical anisotropy and imparts a phase difference function to improve viewing angle characteristics. Regarding the retardation film as described above, a retardation film using various acrylic copolymers has been developed, and Korean Patent Laid-Open Publication No. 2010-0094425 (Patent Document 1) includes an acrylate monomer containing an alkyl acrylate monomer, an aliphatic and an aromatic ring, and an imide system. An optical film was prepared using an acrylic copolymer including a monomer and a styrene monomer.

In addition, Korean Patent Laid-Open Publication No. 2006-7020305 (Patent Document 2) and Japanese Patent Application Laid-Open No. 2010-164893 (Patent Document 3) control optical anisotropy by introducing a maleimide copolymer, and in Korea Patent Registration 1042477 (Patent Document 4), The invention is an increase in transparency and heat resistance by adding a styrene-maleic anhydride copolymer to a methacrylate polymer.

The conventional general polarizer protective film and the resin composition for retardation film as described above is significantly low heat resistance, there is a problem such as difficulty in processing and formability due to frequent breakage during film production.

Republic of Korea Patent Publication 2010-0094425 Republic of Korea Patent Publication 2006-7020305 Japanese Patent Laid-Open No. 2010-164893 Republic of Korea Patent Registration 1042477

The present invention is to solve the conventional problems, having a good transparency, heat resistance, film processability and optical isotropy enough to be used as a protective film or a retardation film of the polarizer, retardation to improve the adhesion with the polarizer when manufacturing a polarizing plate It is an object to provide a film.

Moreover, it aims at providing the polarizing plate containing the said retardation film.

Another object of the present invention is to provide an image display device including the polarizing plate.

According to the present invention for achieving the above object,

The retardation film of the present invention is an acrylic polymer, including 4 to 10% by weight of isobornyl monomer, 70 to 90% by weight of methacryl monomer, 2 to 10% by weight of styrene monomer and 4 to 10% by weight of maleimide monomer. It is made of a copolymer.

The isobonyl-based monomers give flexibility in manufacturing the film to improve processability and formability, and may improve warpage of the polarizer when laminating with the polarizer to prevent warpage of the polarizing plate.

The content of the isobornyl monomer is preferably 4 to 10% by weight in the total composition, more preferably 5 to 8% by weight. When the content of the isobornyl monomer is less than 4% by weight, too little isobornyl monomer is included so that a problem of minimizing the flexibility and adhesion of the film later occurs, and in the case of more than 10% by weight, The excessive amount of the carbonyl monomer is included, the polymerization stability is lowered during the copolymer production, the problem is that the heat resistance is reduced due to the drop in the glass transition temperature (Tg).

The isobornyl monomer is preferably at least one selected from isobornyl acrylate and isobornyl methacrylate, more preferably isobornyl acrylate.

The methacryl-based monomer plays a role in improving optical properties, weather resistance and mechanical properties such as transparency during film production. The content of the methacryl-based monomer is preferably 70 to 90% by weight of the total composition, more preferably 80 to 85% by weight. When the content of the methacrylic monomer is less than 70% by weight, there is a problem that the expected effect on the transparency, mechanical strength and weather resistance of the film occurs, the content of the methacrylic monomer is greater than 90% by weight In this case, there is a problem in that the film is easily broken during manufacture, and the mechanical properties and heat resistance are significantly reduced.

The methacrylate monomer refers to methacrylate or derivatives thereof, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate. At least one selected from the group consisting of benzyl methacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, butoxymethyl methacrylate, hydroxyethyl methacrylate, and oligomers thereof. It is most effective that it is preferably methyl methacrylate.

Since the styrene monomer has a poor copolymerizability between the methacryl monomer and the maleimide monomer, the styrene monomer serves to reduce the unreacted monomer by improving the copolymerizability. In addition, the styrene-based monomers are oriented in the stretching direction when the main chain is oriented in the stretching direction, the benzene ring having a relatively high electron density is oriented perpendicular to the stretching direction. Accordingly, by increasing the electron density in the direction perpendicular to the stretching direction, the optical axis is developed in the direction perpendicular to the stretching direction, and the phase difference value in the thickness direction becomes positive, thereby providing a phase expression property. do.

The content of the styrene monomer is preferably 2 to 10% by weight of the total composition, more preferably 3 to 5% by weight. When the content of the styrene-based monomer is less than 2% by weight, too small a styrene-based monomer is contained, there is a problem to minimize the effect of improving the copolymerizability of the methacryl-based monomer and maleimide-based monomer, the styrene-based When the content of the monomer is more than 10% by weight, too much of the styrene-based monomer is contained, the polymerization stability is lowered, there is a problem that the heat resistance of the copolymer is lowered.

The styrene monomer is preferably at least one selected from styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, t-butylstyrene or chlorostyrene, more preferably α-methyl Styrene is most effective.

The maleimide monomer serves to improve the heat resistance when preparing the copolymer and the film, the content of the maleimide monomer is preferably 4 to 10% by weight of the total composition, more preferably 5 to 7% by weight It is effective to be. When the content of the maleimide monomer is less than 4% by weight, there is a problem in that a too small amount of the maleimide monomer is included to obtain an expected effect of improving the heat resistance of the copolymer, and the content of the maleimide monomer exceeds 10% by weight. In this case, the polymerization stability is greatly lowered, productivity is lowered, the glass transition temperature (Tg) is excessively high, the film is difficult to process, the brittleness of the film is increased during the stretching process, the film is easily broken Occurs.

The maleimide monomer may be cyclohexyl maleimide, N-phenylmaleimide, N-orthomethylphenylmaleimide, N-orthochlorophenylmaleimide, N-orthomethoxyphenylmaleimide or maleimide having an alkyl group of C1 to C4. At least one of them is preferably selected, and most preferably cyclohexylmaleimide is effective.

The acrylic copolymer resin polymerized by including the monomers according to the present invention is a bulk polymerization, suspension polymerization or emulsion polymerization using an existing free radical polymerization method. In order to minimize the contamination by foreign matter, it is more preferable to be prepared by bulk polymerization or suspension polymerization.

The polymerization initiator used in the polymerization method is not particularly limited as a conventional initiator used in free radical polymerization, but it is effective to use a peroxide compound or an azo compound, and the amount of the initiator is reacted. It can adjust suitably according to factors, such as a monomer or reaction conditions which participate in, and is not specifically limited.

In addition, a chain transfer agent introduced to optimally control the molecular weight of the resin is not particularly limited, but is preferably a mercaptan series, more preferably n-butyl mercaptan and t-butyl mercaptan. at least one selected from n-decyl mercaptan, n-dodecyl mercaptan, hydroxyethyl mercaptan or n-octyl mercaptan, most preferably n-octyl mercaptan, most preferably It is effective for improving thermal stability. The content of the chain transfer agent is preferably 0.1 to 0.5 parts by weight based on 100 parts by weight of the monomer mixture in a range that does not impair physical properties. When the content of the chain transfer agent is less than 0.1 part by weight, the inhibition of disproportionation stop by chain transfer is insufficient. When the content of the chain transfer agent is more than 0.5 part by weight, the molecular weight of the resulting resin is excessively lowered. Occurs.

In addition to the above-described monomers, one or more components may participate in the copolymerization reaction, and the content of the components may be copolymerized within a range that does not impair the properties of the copolymer of the present invention.

In the zero retardation film according to the present invention, the in-plane retardation value represented by Equation 1 below is preferably -50 to +50 nm, and the thickness retardation value represented by Equation 2 below is -50 to +50 nm.

[Equation 1]

R _e = (N _x -N _y ) xd

&Quot; (2) "

R _th = (N _z -N _y ) xd

In Equations 1 and 2, N _x measured at a wavelength of 550 nm, respectively, is a planar refractive index in the film stretching direction, N _y is a planar refractive index in a direction perpendicular to the film stretching direction, and N _z is a film thickness direction Refractive index, and d is the thickness of the film.

Method for producing a retardation film according to the invention the film forming step of producing a film by melting and extruding the acrylic copolymer; And stretching the film in the longitudinal and / or transverse directions.

The film forming step may be carried out by a variety of known methods, solution casting or extrusion is preferred. In the extrusion method, the copolymer is vacuum dried to remove moisture and then melted at a high temperature using a single or twin screw extruder to obtain raw material pellets. The obtained raw pellet is vacuum dried and melted using a single screw extruder to coat a coat hanger type T. It is a method of manufacturing a film through a chrome plating casting roll, a drying roll, etc. by passing through a die.

The stretching step is a preheating step; Drawing step; And it can be divided into a heat treatment step, in the preheating step to preheat to a temperature range of about 90 to 120 ℃, the stretching step in the stretching temperature range of 100 to 140 ℃ and the heat treatment step heat treatment in the temperature range of 80 to 120 ℃ It is desirable to.

 It is preferable to extend | stretch a draw ratio 1.0-3.0 times. The draw ratio is set by the expression of the film thickness and the appropriate retardation value, but more preferably 1.1 to 1.5 times.

The retardation film prepared according to the manufacturing method of the present invention further includes an adhesive step of adhering the stretched film to the polarizer.

The polarizer is made of polyvinyl alcohol containing iodine or anisotropic dye and is in the form of a film. It is preferable to apply a UV curable adhesive to the retardation film according to the present invention on both sides of the polarizer. If necessary, surface treatments such as corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment, ultraviolet irradiation treatment or coating treatment can be performed.

 When the retardation film of the present invention is applied to only one side of the polarizer, heat resistance and durability are lowered due to the dimensional change of the polarizing plate, resulting in distortion, which causes problems such as light leakage. The ultraviolet curable adhesive is not particularly limited as long as it is a polyfunctional crosslinking agent capable of curing an acrylic polymer, but isocyanate crosslinking agent, epoxy crosslinking agent or metal chelate crosslinking agent is preferable, and further includes polyfunctional acrylate, silane coupling agent, photoinitiator and the like. It is composed.

Application of the adhesive may be a method of applying, injecting or coating the polarizer by using a known conventional means such as a bar coater or a comma coater after mixing each component to prepare an adhesive composition, to the applied adhesive composition It may be cured by irradiation with heat or light, which may be performed sequentially or simultaneously with the application process of the adhesive.

The retardation film of the present invention as described above can be used alone as a retardation film for controlling the phase difference of the liquid crystal, it can be used as a polarizer protective film that can be attached to both sides of the polarizer to protect the polarizer to be used as a polarizing plate.

The retardation film of the present invention and a polarizing plate using the same can be used in an image display device such as an LCD (liquid crystal display), a TFT-LCD (thin film transistor liquid crystal display), a plasma display (PDP) or a touch panel.

According to the retardation film, the polarizing plate of the present invention and the image display device including the same, by forming a retardation film using an acrylic resin containing an isobonyl monomer and a maleimide monomer, molding without reducing the heat resistance and transparency of the film, The workability is remarkably improved, and adhesiveness between the retardation film and the polarizer is improved in manufacturing the polarizing plate.

EMBODIMENT OF THE INVENTION Hereinafter, preferable embodiment and the physical property measuring method about the retardation film, polarizing plate, and image display apparatus using the same according to this invention are demonstrated in detail. The invention can be better understood by the following examples, which are intended for purposes of illustration of the invention and are not intended to limit the scope of protection defined by the appended claims.

The physical property measurement method of the retardation film by the Example and the comparative example of this invention was demonstrated in detail.

Property measurement

1) Glass Transition Temperature (Tg) Measurement

The glass transition temperature (Tg) of the film was measured at a temperature rising rate of 10 ° C./min using Differential Scanning Calorimetry (DSC).

2) Phase difference measurement

The retardation of the film was measured at intervals of 10 degrees from -50 degrees to +50 degrees in the extending direction and its vertical direction using AxoScan ™ of Axometrics. The in-plane retardation and the thickness direction retardation are defined by Re (in-plane retardation) and Rth (thickness retardation) in Equations 1 and 2, respectively.

3) transmittance

The transmittance was measured by using N & K Analyzer by cutting the width and length of the film into 40 mm each.

4) adhesion

TA. XT. Using a Plus (Stable Micro System) Texture Analyzer, the retardation film surface was fixed to a width of 2 cm, and the peeling force of 90 degrees was measured at a measuring distance of 5 cm.

5) Film fracture at stretching

The number of films to break when ten films were stretched was measured.

Example 1

Preparation of Copolymer

2000 g of distilled water was added to a 5 liter reactor, 8.4 g of a 5% polyvinyl alcohol solution (product of Kuraray's POVAL PVA217) as a dispersant, and 0.1 g of boric acid as a dispersing aid were dissolved. 1000 g of the monomers (methyl methacrylate, cyclohexyl maleimide, α-methylstyrene, isobornyl acrylate) described in Table 1 below, 2.0 g of n-octyl mercaptan as a chain transfer agent, and 2,2'-azobisiso as an initiator 2.0 g of butylonitrile (AIBN) was added thereto, and the monomer mixture was dispersed in an aqueous phase while stirring at 500 rpm.

The mixture was polymerized at 85 ° C. for 1 hour 30 minutes, heated to 110 ° C., further polymerized for 30 minutes, and then cooled to 30 ° C. The copolymer obtained by the polymerization reaction was washed with distilled water and dehydrated repeatedly, followed by drying.

Manufacture of film

The copolymer obtained by the polymerization reaction was melted through an extruder to obtain raw material pellets. The raw material pellets were vacuum dried and melted with an extruder at 250 ° C. and passed through a coat hanger type T-die, followed by a chrome plating casting roll and a drying roll. The film of 100 micrometers in thickness was produced through etc. The prepared film was stretched in the transverse and longitudinal directions at 110 ° C. and then heat treated at 90 ° C. for 30 minutes to produce an acrylic film having a thickness of 50 μm.

Preparation of Polarizer

100 parts by weight of normal butyl acrylate, 80 parts by weight of polyfunctional acrylate (trifunctional urethane acrylate, Aronix M-315, Dongwoo conventional), polyfunctional crosslinking agent (TDI isocyanate, Coronate L, Japan Nippon Poly) Urethane Co.) 2 parts by weight, hydroxycyclohexylphenyl ketone (Irg 184, Swiss Ciba Specialty Chemical Co., Ltd.) as a photoinitiator was prepared by mixing with a solvent so that the concentration of the solid content is 30% by weight, the polarizer polyvinyl alcohol resin The film was stretched and dyed with iodine and prepared by treating with boric acid solution.

The adhesive composition was applied between the corona-treated retardation film of the present invention and the polarizer, and irradiated with ultraviolet light (roughness: 250 mW / cm 2, light amount: 300 mJ / cm 2) using a high pressure mercury lamp to prepare a polarizing plate. The physical properties of the polarizing plate manufactured by the physical property measuring method described above were measured, and the results are shown in Table 2 below.

[Example 2]

Example 2 was carried out in the same manner as in Example 1 except for changing the composition ratio of the monomers supplied to the reactor, as shown in Table 1 below.

Comparative Example 1

Comparative Example 1 was carried out in the same manner as in Example 1 except for changing the content of isobornyl acrylate in the monomers supplied to the reactor, as shown in Table 1 below.

 Comparative Example 2

Comparative Example 2 was carried out in the same manner as in Example 1, except that the content of cyclohexylmaleimide and isobornyl acrylate in the monomers supplied to the reactor was changed as shown in Table 1 below.

[Comparative Example 3]

Comparative Example 3 was carried out in the same manner as in Example 1, except for changing the content of cyclohexylmaleimide and isobornyl acrylate in the monomers supplied to the reactor as shown in Table 1 below.

[Comparative Example 4]

Comparative Example 4 was carried out in the same manner as in Example 1, except for changing the content of cyclohexyl maleimide and isobornyl acrylate in the monomers supplied to the reactor as shown in Table 1.

TABLE 1 Composition of Copolymer (Unit: wt%)

[Table 2] Property Measurement Results

As shown in Table 2, when the retardation film was prepared according to the present invention, the adhesive force was excellent while maintaining the optimum glass transition temperature (Tg), and showed satisfactory phase expression with the retardation film. In addition, it was confirmed that the film breaking property, which is the most important characteristic when the film is stretched, is significantly improved.

In addition, Comparative Example 1 did not use the isobornyl acrylate, the adhesive strength could not be expected, Comparative Example 2 did not use cyclohexyl maleimide and isobornyl acrylate, the Tg was reduced and the heat resistance was significantly lowered Also, it was found that the adhesive force was also low, and thus the number of breaks of the film was increased, thereby making it difficult to manufacture the phase difference film.

In Comparative Example 3, when excessive amount of cyclohexylmaleimide was added and no isobornyl acrylate was added, the Tg was markedly increased, and the adhesiveness and the number of film breakages increased markedly, and thus the desired processability and adhesiveness could not be obtained. In Example 4, cyclohexylmaleimide was not added, and isobonyl acrylate was added in an excessive amount, so that Tg was significantly lowered, thereby improving adhesiveness. However, the mechanical properties as a retardation film were not sufficient. And it was found.

Therefore, when cyclohexylmaleimide and isobornyl acrylate were included in the composition of the retardation film of the present invention in the optimum content, it was confirmed that the heat resistance, adhesiveness and film breakability are significantly improved.

Although the preferred embodiment of the present invention has been described above, it is clear that the present invention can use various changes and equivalents, and can be applied in the same manner by appropriately modifying the above embodiment. Accordingly, the above description is not intended to limit the scope of the invention as defined by the following claims.

Claims (9)

Methacryl-based monomer 70 to 90% by weight,
2 to 10% by weight of styrene monomer,
4 to 10% by weight of isobornyl monomer and
It is made of an acrylic copolymer that is polymerized to include 4 to 10% by weight of the maleimide monomer,
At 550 nm wavelength, the in-plane retardation value represented by the following formula (1) is -50 to +50 nm, the thickness direction retardation value represented by the following formula (2) at the 550 nm wavelength is -50 to +50 nm.
[Equation 1]
R _e = (N _x -N _y ) xd
&Quot; (2) "
R _th = (N _z -N _y ) xd
In Equation 1 and Equation 2,
N _x is a planar refractive index in the film stretching direction,
N _y is a planar refractive index in the vertical direction of the film stretching direction,
N _z Is the refractive index in the film thickness direction,
d is the thickness of the film. The method of claim 1,
The styrene-based monomer is retardation film, characterized in that any one or two or more selected from styrene, α-methylstyrene, p-bromostyrene, p-methylstyrene or p-chlorostyrene. The method of claim 1,
The maleimide monomer has a cyclohexyl maleimide, N-phenylmaleimide, N-orthomethylphenylmaleimide, N-orthochlorophenylmaleimide, N-orthomethoxyphenylmaleimide or C ₁ to C ₄ alkyl group Retardation film, characterized in that any one or a mixture of two or more selected from maleimide. The method of claim 1,
The isobornyl monomer is retardation film, characterized in that any one or a mixture of two or more selected from isobornyl acrylate or isobornyl methacrylate. The method of claim 1,
The acryl-based copolymer is a retardation film characterized in that it further comprises a polymerization initiator and a chain transfer agent. 6. The method of claim 5,
The polymerization initiator is a peroxide compound or azo compound,
The chain transfer agent is a retardation film, characterized in that the mercaptan-based compound. The method according to claim 6,
The chain transfer agent is n-octyl mercaptan,
The content of n-octyl mercaptan is retardation film, characterized in that 0.1 to 0.5 parts by weight based on 100 parts by weight of the monomer mixture. The polarizing plate containing the retardation film of any one of Claims 1-7. An image display device comprising the polarizing plate of claim 8.