KR101894814B1 - Stress resistant anti hazing resin film - Google Patents

Abstract

The present invention relates to a resin composition comprising acrylic resin and core-shell rubber particles represented by the following formula (1) and formed by a solvent casting method, and even when a considerable stress is concentrated by impact, smoothness of the film surface is maintained, There is an excellent whitening effect in the internal stress which can maintain a high transparency.
[Chemical Formula 1]
MMA-BA
Here, MMA represents methyl methacrylate unit and BA represents butyl acrylate unit.

Description

{STRESS RESISTANT ANTI HAZING RESIN FILM} BACKGROUND OF THE INVENTION Field of the Invention [0001]

The present invention relates to an in-stress white papermaking film which maintains high transparency even when a core shell rubber (CSR) particle is introduced at the time of forming an acrylic resin film by a solvent casting method and the film is folded or pulled will be.

2. Description of the Related Art In recent years, a liquid crystal display device which 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 cellular 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 extremely high, so that the required temperature and humidity conditions are strict as compared with a normal television or a personal computer monitor. A polarizing plate is used in a liquid crystal display device to enable the display. In a liquid crystal display device requiring such a strict temperature and 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-based resin in which a dichroic dye is adsorbed and oriented. Conventionally, triacetylcellulose (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-based 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 films have been manufactured by melt casting method. However, Solvent Casting method has many advantages in terms of environment-friendliness such as thinning, mass production and recycling of resin. 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 make a film. Optimized particles are added to increase impact strength and slip property for film transfer. The above 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 curing agent composition, which causes a crosslinking reaction by radicals generated in the initiator by light irradiation It is possible to omit the aging step at the time of curing and to simplify the manufacturing process, and furthermore, it is possible to reduce the amount of the photopolymerizable acrylic polymer and the polymerization initiator, Discloses 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. The film A and the film B are bonded together through an ultraviolet curable adhesive.

However, when the acrylic film made by the conventional melt extrusion is folded or pulled, the film may cause a poor opacity. This is caused by the addition of CSR particles to improve the impact resistance of acrylic. As a result, stress concentration occurs in the equatorial direction of CSR particles having low modulus of elasticity, and microcracks occur in this portion, And haze is lowered. As the stress concentrates on the acrylic film, it is required to improve the transparency.

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

DISCLOSURE Technical Problem The present invention has been devised to solve the above-mentioned problems, and it is an object of the present invention to provide a heat-resistant white film produced by a solvent casting method which maintains transparency even when stress is concentrated on a film by folding or pulling .

The present invention relates to an acrylic resin composition comprising 80 to 98 parts by weight of methyl methacrylate units and 2 to 20 parts by weight of butyl acrylate units based on 100 parts by weight of the acrylic resin represented by the following formula (1) Characterized in that a haze is maintained at 0.5% or less even after 24 hours have elapsed from a main dope liquid made of core shell rubber (CSR) particles by a solvent casting method and folded at an angle of 90 ° It is the whitening film in the stress.

[Chemical Formula 1]

MMA-BA

Here, MMA represents a unit of methyl methacrylate (Methyl methacrylate), and BA represents a unit of butyl acrylate (Butyl Acrylate).

The core shell rubber of the present invention is composed of one or more core selected from the group consisting of Styren Butadiene (PBD) and Acrylic Ester, and is composed of methyl methacrylate Shell structure in which a shell is formed by graft copolymerization with one or more species selected from the group consisting of MMA, Styren, and Acrylic Ester, the diameter of which is 100 to 300 nm, It is preferably 3 to 10 parts by weight based on 100 parts by weight of the dope solution.

It is preferable that the solvent of the solvent casting of the present invention is mixed with a halogenated hydrocarbon and an alcohol.

Further, the stress-resistant white light-emitting film of the present invention preferably has a film thickness of 30 to 120 탆 and a Tg of 110 캜 or more.

The intrinsic stress-resistant film of the present invention is easy to form a highly transparent acrylic film and has good thickness uniformity and transparency, thus making it possible to produce a natural thin film. The impact resistance is improved compared with the existing technology, and the stress concentration such as folding or pulling Various types of surface decorations can be applied because excellent transparency can be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing the structure of core shell rubber (CSR) particles of the present invention. FIG.

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 a film and transfer the film when the acrylic film of the thin film is manufactured by the solvent casting method. As a result, the molecular weight of the acrylic resin is in the range of 300,000 to 2,500,000 g / It has been found that when a main doping liquid containing a specific component is formed, a protective film which is easy to form and transport can be obtained, and thus the present invention has been completed.

The acrylic film of the present invention is formed from a main dope liquid containing acrylic resin and core shell rubber (CSR) particles represented by the following general formula (1), and after 24 hours in a state of being folded at an angle of 90 ° And the haze is maintained at 0.5% or less.

[Chemical Formula 1]

MMA-BA

Here, MMA represents methyl methacrylate unit and BA represents butyl acrylate unit.

First, the acrylic resin of the present invention will be described. The acrylic resin of the present invention is an acrylic resin comprising a methyl methacrylate unit and a butyl acrylate unit and each of the monomer units is contained in the form of a repeating unit.

It is preferable that 80 to 98 parts by weight of methyl methacrylate, 2 to 20 parts by weight of butylacrylate (butyl acrylate) are added to 100 parts by weight of acrylic resin in consideration of optical characteristics, transparency, compatibility, workability, .

When the content of methyl methacrylate units is in the above range, excellent retardation and optical characteristics can be obtained. When the methyl methacrylate unit content is less than 80 parts by weight, the optical performance of the protective film deteriorates. When the methyl methacrylate unit content exceeds 99 parts by weight, the thickness uniformity of the protective film is lowered.

The content of the butyl acrylate unit is preferably 2 to 20 parts by weight based on 100 parts by weight of the acrylic resin. When the content of the butyl acrylate unit is within the above range, preferable optical properties can be obtained.

In the present invention, by adding core-shell rubber particles (CSR) which are insoluble in a solvent and do not deform in the acrylic resin, the impact strength of the film is increased, thereby facilitating film formation and film transfer. The core shell rubber particle (CSR) particles preferably have a diameter of 100 nm or more and 300 nm or less. When the diameter of the core-shell rubber particle (CSR) particle is less than 100 nm, the effect of the object of the present invention is not sufficiently exhibited, and when it exceeds 300 nm, the quality of the protective film becomes poor. The core-shell rubber particle (CSR) particle is preferably 3 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the main dope solution. When the core-shell rubber particle is less than 3 parts by weight, sufficient impact resistance can not be obtained. When the core-shell rubber particle is more than 10 parts by weight, transparency is deteriorated.

The molecular weight of the acrylic resin of the present invention is preferably 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 g / mol, the molding process is not easy. The glass transition temperature (Tg) of the acrylic resin of the present invention is preferably 110 ° C or more. 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 30 to 120 탆. When the thickness of the protective film is less than 30 탆, sufficient retardation characteristics can not be exhibited. When the thickness of the protective film exceeds 120 탆, it is not suitable for use in a thin polarizing plate.

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

Manufacture of acrylic resin

In order to produce the recurring film of the present invention, first, a copolymer resin solution of a methyl methacrylate monomer and a butyl acrylate 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 main dope liquid 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 main dope liquid obtained by dissolving an acrylic resin in a casting solvent is cast on a support, and the solvent is evaporated to form a film. The main dope solution is prepared by mixing the acrylic resin and the auxiliary additive in the casting solvent.

When a film is produced by a solvent casting method, an organic solvent is preferred as the solvent for preparing the main dope solution. 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.

In the production of the acrylic film, auxiliary additives may further be used. To the main dope liquid, various auxiliary additives depending on the use in each production step, for example, an auxiliary additive such as an ultraviolet ray inhibitor, a fine particle, an infrared absorbent, and a releasing agent may be added. 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 main dope liquid preparation may be performed.

In the present invention, core-shell rubber particles (CSR) are used as an additive, and the diameter of the particles is 100 to 300 nm, and the content thereof is preferably 3 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the main doping solution. When the core-shell rubber particle is less than 3 parts by weight, sufficient impact resistance can not be obtained. When the core-shell rubber particle is more than 10 parts by weight, transparency is deteriorated. The structure of the nanoparticles can be illustrated as shown in Fig.

The main dope liquid obtained as described above can be produced by an ordinary temperature, high temperature or low temperature dissolution method.

Film forming process

In the solvent casting method of the present invention, the main dope liquid is poured on a metal support from a nozzle of a pressure 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 main dope liquid obtained as described above 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 stretching 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 present invention produced according to the above method is characterized in that the haze is maintained at 0.5% or less even after 24 hours has elapsed in a state of being folded at an angle of 90 °.

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 >

Acrylic acid represented by the following formula (2) was used.

(2)

≪ Step 2 > Preparation of main dope liquid containing CSR particles

100 parts by weight of the initiator solution and 5 parts by weight of the nanoparticle additive solution were added, and sufficiently mixed with an inline mixer. The composition of the main dope solution was 64.17 parts by weight of methylene chloride, 7.13 parts by weight of methanol, 27.98 parts by weight of acrylic resin, 0.72 parts by weight of Tinvuin 928 (manufactured by BASF) and 5 parts by weight of CSR. The size of the CSR particles was 200 nm.

≪ Step 3 >

delete

Then, the main dope liquid was uniformly plied to a stainless steel band support having a width of 2000 mm by 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 °. After the stretching, the stretching was maintained for a few seconds, the tension in the width direction was relaxed, the stretching was performed in the width direction, the stretching was continued for 35 minutes in the drying section set at 90 DEG, An acrylic film having a thickness of 40 m and a knurling width of 10 mm and a height of 8 m was produced.

Comparative Example 1

≪ Step 1 >

A copolymer of 96 parts by weight of methyl methacrylate unit and 4 parts by weight of methyl acrylate was used with respect to 100 parts by weight of the acrylic resin.

<Step 2> Acrylic elastomer

As the acrylic elastomer particles, the inner layer is made of butyl acrylate as a main component and styrene and a small amount of aralkyl methacrylate are polymerized to form a flexible soft elastic body; the outer layer is a hard polymer obtained by polymerizing methyl methacrylate with a small amount of ethyl acrylate Layer elastic elastomer particles having a number average particle diameter of 75 nm.

&Lt; Step 3 >

The pellets of the acrylic resin and the acrylic elastomer particles were mixed in a super mixer at a ratio of 7: 3 and melt-kneaded by a twin-screw extruder to prepare an acrylic resin composition pellet. The pellets of the acrylic resin composition were poured into a 65 nm phi 1-axis extruder, extruded through a T-die having a set temperature of 275 DEG C, and the two faces of the film were sandwiched between two polishing rolls (metal rolls) And cooled to obtain an acrylic melt extruded film having a thickness of 125 탆.

Comparative Example  2

A film was prepared in the same manner as in Comparative Example 1 except that the film had a thickness of 45 μm.

After a significant amount of stress concentration Hayes  evaluation

The thus prepared films of Example 1 and Comparative Examples 1 and 2 were measured for haze before concentration of stress using a hazemeter, and the film was folded at an angle of 90 ° to maintain the stress concentration for 24 hours, And the results are shown in Table 1. &lt; tb &gt; &lt; TABLE &gt;

division thickness Before fold After folding evaluation Example 1 40μm 0.22% 0.25% Not white Comparative Example 1 125μm 2.52% 25.92% Whitening Comparative Example 2 40μm 1.95% 20.33% Whitening

As shown in Table 1, it can be seen that the whitening film produced by the present invention maintains excellent transparency even though it is thin compared to the acrylic film produced by conventional melt extrusion in whitening by stress concentration.

Claims (4)

An acrylic resin composition comprising 80 to 98 parts by weight of methyl methacrylate units and 2 to 20 parts by weight of butyl acrylate based on 100 parts by weight of an acrylic resin represented by the following formula (1) An inner whitening film is formed by a solvent casting method from a main dope liquid made of core shell rubber (CSR) particles,
The core shell rubber is made of one or more selected from the group consisting of styrene butadiene (PBD) and acrylic ester, and is made of methyl methacrylate (MMA) Shell structure in which a shell is formed by graft polymerization from one or more species selected from the group consisting of styrene, styrene, and acrylic ester. The diameter of the core-shell structure is 100 to 300 nm, Is 3 to 10 parts by weight based on 100 parts by weight,
Stretching the stretching yarn so that the stretching magnification in the width direction is 1.5 times and relaxing the stretching force in the width direction while maintaining the stretching magnification in the width direction and loosening in the width direction, Lt; / RTI &gt;
Wherein the haze is maintained at 0.5% or less even after 24 hours have elapsed in the state of being folded at an angle of 90 DEG.

[Chemical Formula 1]
MMA-BA
Here, MMA represents a unit of methyl methacrylate (Methyl methacrylate), and BA represents a unit of butyl acrylate (Butyl Acrylate). delete The method according to claim 1,
Wherein the solvent of the solvent casting is mixed with a halogenated hydrocarbon and an alcohol. The method according to claim 1,
Wherein the whitened film has a thickness of 30 to 120 占 퐉 and a Tg of 110 占 폚 or more.

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