KR101304589B1 - Composition for optical film having excellent transparency, strength and heat resistance and optical film comprising the same - Google Patents

Abstract

The present invention is 5 to 30 parts by weight of cyclohexyl methacrylate units; 40 to 70 parts by weight of methyl methacrylate units; 10 to 30 parts by weight of styrene units; And it provides a copolymer comprising 3 to 15 parts by weight of maleic anhydride units, a resin composition for an optical film and an optical film comprising the same.

Description

Composition for optical films with excellent transparency, toughness, and heat resistance, and optical films including the same {COMPOSITION FOR OPTICAL FILM HAVING EXCELLENT TRANSPARENCY, STRENGTH AND HEAT RESISTANCE AND OPTICAL FILM COMPRISING THE SAME}

The present invention relates to a composition for an optical film and an optical film comprising the same, and more particularly, to an optical film composition and an optical film comprising the same excellent in transparency, toughness and heat resistance.

Recently, with the development of optical technology, various displays such as Plasma Display Panel (PDP), Liquid Crystal Display (LCD), Organic EL Display (Organic Emitting Light Display (OLED)), and so on, replace conventional CRTs. Display technology of the type is proposed and marketed.

In such display devices, various plastic optical films are used to improve optical performance and image quality. The most widely used materials for such optical films include a triacetyl cellulose film (TAC film) or a cycloolefin polymer film (CycloOlefin Polymer Film, COP). TAC film and COP film is mainly used as a polarizing plate protective film or retardation film, these films have problems such as deterioration in optical properties, peeling occurs with a polarizing film when used for a long time in a high temperature or high humidity atmosphere. In addition, these films have problems such as high cost and complicated manufacturing process.

Therefore, there is a need to develop a new composition for an optical film having excellent optical properties, heat resistance, and the like that can replace these films.

The present invention is to solve the above problems, and to provide a novel optical film resin composition excellent in heat resistance, toughness and transparency and an optical film using the same.

To this end, the present invention in one aspect, cyclohexyl methacrylate units; Methyl methacrylate units; Styrene units; And maleic anhydride units are provided.

In another aspect the invention provides cyclohexyl methacrylate units; Methyl methacrylate units; Styrene units; And copolymers containing maleic anhydride units; And optionally a high molecular weight acrylic copolymer resin and / or a heat stabilizer.

In another aspect, the present invention provides an optical film comprising the resin composition for an optical film as described above.

The optical film produced by using the copolymer and the resin composition of the present invention is excellent in optical properties such as light transmittance and haze properties, and excellent in toughness and heat resistance, so that it is not easily damaged even in a high temperature and high humidity environment.

The present inventors have conducted research to develop a novel optical film material with excellent optical properties, heat resistance and durability. As a result, a copolymer made of cyclohexyl methacrylate, methyl methacrylate, styrene and maleic anhydride is used. When manufacturing the optical film, it was found that the optical film that satisfies all of these characteristics is produced, the present invention was completed.

In one aspect, the invention relates to a copolymer comprising (1) cyclohexyl methacrylate units, (2) methyl methacrylate units, (3) styrene units, and (4) maleic anhydride units.

As used herein, "copolymer" means that two or more kinds of monomers are included as repeating units, and the form thereof is not particularly limited, and any type of copolymer, for example, an alternating copolymer, a block copolymer, It should be understood as a concept that includes both random copolymers and graft copolymers.

In the copolymer of the present invention, the cyclohexyl methacrylate unit is to improve the toughness of the copolymer by the characteristics of the molecular structure and also to improve the compatibility with the high molecular weight acrylic copolymer, the content It is preferable that it is about 5-30 weight part. If the content is less than 5 parts by weight, the compatibility with toughness and acrylic copolymer is lowered, and if it exceeds 30 parts by weight, there is a problem that the heat resistance is lowered.

In addition, the methyl methacrylate unit plays a role of providing transparency of the copolymer, the content is preferably about 40 to 70 parts by weight. When the content of the methacrylate unit is in the above range, performance such as transparency is most preferable.

The styrene unit is for imparting a phase difference, and the content thereof is preferably about 10 to 30 parts by weight. If the content is less than 10 parts by weight or more than 30 parts by weight, the retardation characteristics are not suitable as a retardation film for IPS mode.

The maleic anhydride unit is for improving heat resistance, and is preferably about 3 to 15 parts by weight. If the content is less than 3 parts by weight, the heat resistance is lowered. If the content is more than 15 parts by weight, it is difficult to control the polymerization rate, and a decrease in transparency also occurs.

The copolymer of the present invention including the above units has a glass transition temperature of 120 ° C. or more, more preferably about 120 ° C. to 200 ° C. In general, since the optical film used in the display device is easily deformed or damaged by heat generated from a backlight, it is required to have high heat resistance. The copolymer of the present invention has a high glass transition temperature of 120 ° C., so that it is not easily damaged even in a high temperature environment. Do not.

In addition, in consideration of film properties and manufacturing convenience, the copolymer preferably has a weight average molecular weight of about 80,000 to 130,000.

The copolymer of the present invention may be prepared by a general copolymer production method used in the art, for example, solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization and the like. For example, the copolymer of the present invention may be prepared by mixing a cyclohexyl methacrylate monomer, a methyl methacrylate monomer, a styrene monomer and a maleic anhydride monomer in a polymerization solvent, and then adding a polymerization initiator to cause a polymerization reaction. Can be. When the polymerization reaction is completed, the unreacted monomer and the solvent may be removed from the copolymer, and then extruded to prepare a pellet resin.

The copolymer of the present invention prepared by the above method may be used alone as a resin composition for an optical film, or may be used as a resin composition for an optical film by blending with a heat stabilizer and / or a high molecular weight acrylic copolymer resin. .

At this time, 70 to 99 parts by weight of the copolymer comprising the resin composition cyclohexyl methacrylate unit, methyl methacrylate unit, styrene unit, and maleic anhydride unit for the optical film; And 1 to 30 parts by weight of the high molecular weight acrylic copolymer resin and 0.1 to 1 part by weight of the heat stabilizer.

On the other hand, when used in combination with a heat stabilizer and / or a high molecular weight acrylic copolymer resin in the resin composition, the resin composition is compounded with a heat stabilizer and / or high molecular weight acrylic copolymer resin in the quaternary copolymer resin of the present invention. It can be prepared by blending according to methods well known in the art such as law.

In this case, as the heat stabilizer, Irgafos 168, Irganox 1076, Irganox 1010, Irganox 245, or the like can be used.

In addition, as the high molecular weight acrylic copolymer resin, for example, but not limited thereto, a polymethyl methacrylate copolymer may be used. Of these, copolymers of butyl acrylate and methyl methacrylate are particularly preferred. On the other hand, the high molecular weight acrylic copolymer resin preferably has a weight average molecular weight of about 100,000 to 3 million. This is because when the high molecular weight acrylic copolymer resin having a weight average molecular weight within the above range is used, the toughness is excellent at the time of stretching the film and no breakage occurs.

On the other hand, the resin composition for optical films of the present invention as described above preferably has a weight average molecular weight of about 80,000 to 130,000, and the glass transition temperature is preferably 120 ° C or more, preferably 120 ° C to 200 ° C. . If the weight average molecular weight of the resin composition is less than 80,000, breakage may occur at the time of stretching the film, and if it exceeds 130,000, problems may occur in the film formability. In addition, when the glass transition temperature is low, heat shrinkage may occur due to heat generated from a light source after mounting on the display device, and when the glass transition temperature is high, problems may occur in workability.

The resin composition for an optical film of the present invention as described above can be prepared as an optical film using a film production method well known in the art, such as solution casing method or extrusion method, the produced film is uniaxial or It is biaxially stretched. At this time, an improvement agent etc. can be added as needed.

The stretching may be performed in the longitudinal direction (MD) stretching, in the transverse direction (TD) stretching, or both. In the case where both longitudinal stretching and transverse stretching are performed, either stretching may be performed first, and then stretching may be performed in another direction, or both directions may be simultaneously stretched. In addition, the stretching may be carried out in one step, or may be carried out in multiple steps.

The stretching is preferably performed at a temperature of about (Tg-20) ° C. to (T + 30) ° C. when the glass transition temperature of the resin composition is Tg, and more preferably at a glass transition temperature. . The glass transition temperature refers to a region from the temperature at which the storage modulus of the resin composition begins to decrease, and thus the loss modulus becomes larger than the storage modulus, to a temperature at which the orientation of the polymer chain is relaxed and disappears. Can be measured by

The stretching speed is preferably in the range of 1 to 100 mm / min in the case of a universal teating machine (Zwick Z010) and in the range of 0.1 to 2 m / min in the case of a pilot stretching machine. It is preferable that elongation is about 5 to 300%.

It is preferable that the optical film of this invention manufactured by the above method has a light transmittance of 90% or more.

The optical film preferably has a plane direction retardation value of 80 to 200 nm and a thickness direction retardation value of about 80 to 300 nm at a thickness of 60 μm and a wavelength of 580 nm. More preferably, the plane direction retardation value is 100-150 nm, and it is preferable that the thickness direction retardation value is about 100-200 nm.

Moreover, it is preferable that ratio (Nz) of thickness direction retardation value / planar retardation value is about 1-1.5, in the optical film of the said this invention. More preferably, the ratio Nz of the thickness retardation value / plane retardation value is about 1.2 to 1.4.

Here, the planar retardation value (Rin) refers to a value defined by the following [Equation 1], and the thickness direction retardation value (Rth) refers to a value defined by the following [Equation 2].

[Formula 1]

R _in = (n _x -n _y ) x d

[Formula 2]

R _th = (n _z -n _y ) x d

In [Formula 1] and [Formula 2],

n _x is a refractive index of the direction of the largest refractive index in the plane direction of the film,

n _y is the refractive index of the vertical direction of the nx direction in the plane direction of the film,

n _z is the refractive index in the thickness direction,

d is the thickness of the film.

The optical film of the present invention having the above characteristics can be used as a compensation film for the IPS mode, in this case it can be carried out an appropriate post-process for adjusting the retardation value of the film, if necessary.

Hereinafter, the present invention will be described in detail with reference to specific examples.

Example

In the embodiment of the present invention, the physical property evaluation method is as follows.

1. Haze and light transmittance: It measured according to ASTM1003 method.

2. Toughness: The film having a thickness of 60 µm was measured in a state of bending by hand 10 times, and ○ was cut 1 to 3 times, and ◎ was not cut at all.

3. Weight average molecular weight (Mw): The prepared resin was dissolved in tetrahydrofuran and measured by gel osmosis chromatography (GPC).

4. Tg (glass transition temperature): Pyris 6 Differential Scanning Calorimeter (DSC) by Perkin Elmer.

5. Phase difference value (Rth / Rin): After stretching at the glass transition temperature of the film was measured using Elli-SE of Ellipso Tech.

1. Copolymer Preparation

The monomers of the content (part by weight) described in the following [Table 1] were mixed with toluene, which is a polymerization solvent, in a monomer: toluene = 80: 20, and 0.03 parts by weight of dicumyl peroxide as a polymerization initiator and t as a molecular weight regulator were added to the mixed solution. -0.5 parts by weight of dodecyl mercaptan was added to prepare a polymerization solution. The polymerization solution was continuously introduced into a 16 L reactor at a rate of 10 L per hour to carry out a continuous polymerization reaction. Then, after removing the unreacted monomer and the solvent in a 230 ℃ volatilization, and extruded to prepare a copolymer A to K from the resin of the pellet state. The weight average molecular weights of the prepared copolymers are as described in [Table 1].

[Table 1]

CHMA: cyclohexyl methacrylate

MMA: methyl methacrylate

SM: Styrene

MAH: Maleic Anhydride

2. film manufacturing

0.2 parts by weight of the thermal stabilizer Iganox was mixed with 100 parts by weight of the copolymers A to K prepared in 1, and blended using a co-extruder to prepare a resin in a pellet state. The resin thus prepared was formed into a film of 120 μm using a T-die extruder, and stretched in a stretching machine in an MD direction of 80%, in a TD direction of 20% or in an MD direction of 60% and in a TD direction of 40% to produce a 60 μm film. It was. Physical properties of the produced film were measured, and the results are shown in [Table 2] and [Table 3].

[Table 2]

[Table 3]

In addition, the thermal stabilizer Iganox and the acrylic copolymer were mixed with the copolymers B, C, and D prepared in 1 according to the contents described in [Table 4], and blended using a co-extruder to prepare a resin in a pellet state. The resin thus prepared was formed into a film of 120 μm using a T-die extruder, and stretched in a stretching machine in an MD direction of 80%, in a TD direction of 20% or in an MD direction of 60% and in a TD direction of 40% to produce a 60 μm film. It was. The physical properties of the prepared film were measured and the results are shown in [Table 4].

[Table 4]

As shown in [Table 2] to [Table 4], in the case of the copolymers A to G according to the present invention, it can be seen that the optical properties, toughness, light transmittance, and glass transition temperature are all excellent.

Claims (15)

5 to 30 parts by weight of cyclohexyl methacrylate units;
40 to 70 parts by weight of methyl methacrylate units;
10 to 30 parts by weight of styrene units; And
A copolymer comprising 3 to 15 parts by weight of maleic anhydride units.
The method of claim 1,
The copolymer has a glass transition temperature of 120 ° C to 200 ° C.
The method of claim 1,
The copolymer has a weight average molecular weight of 30,000 to 130,000.
5 to 30 parts by weight of cyclohexyl methacrylate units;
40 to 70 parts by weight of methyl methacrylate units;
10 to 30 parts by weight of styrene units; And
The resin composition for optical films containing the copolymer containing 3-15 weight part of maleic anhydride units.
delete 5. The method of claim 4,
A resin composition for an optical film, further comprising at least one of a high molecular weight acrylic copolymer resin and a heat stabilizer.
The method according to claim 6,
The high molecular weight acrylic copolymer resin is a polymethyl methacrylate copolymer resin composition for an optical film.
The method of claim 7, wherein
The high molecular weight acrylic copolymer resin is a resin composition for an optical film, which is a copolymer of butyl acrylate and methyl methacrylate.
The method according to claim 6,
The high molecular weight acrylic copolymer resin has a weight average molecular weight of 100,000 to 3 million resin composition for an optical film.
The method according to claim 6,
The resin composition comprises 70 to 99 parts by weight of a copolymer comprising a cyclohexyl methacrylate unit, a methyl methacrylate unit, a styrene unit, and a maleic anhydride unit; And
At least one of 1 to 30 parts by weight of the high molecular weight acrylic copolymer resin and 0.1 to 1 part by weight of the heat stabilizer.
The optical film containing the resin composition for optical films of any one of Claims 4 and 10-10.
12. The method of claim 11,
The optical film has an optical transmittance of 90% or more.
12. The method of claim 11,
The optical film has a plane direction retardation value of 80 to 200 nm and a thickness direction retardation value of 80 to 300 nm at a thickness of 60 μm and a wavelength of 589 nm.
12. The method of claim 11,
The optical film has an optical film having a thickness retardation / plane direction retardation value Nz of 1 to 1.5.
12. The method of claim 11,
The optical film is an optical film is a compensation film for IPS mode.