KR20200088028A - Acryl film and manufacturing method of the same - Google Patents

Abstract

An acrylic film can comprise: an acrylic resin comprising 70-98 parts by weight of a methyl methacrylate unit and 2-30 parts by weight of a butyl methacrylate unit; 5-40 parts by weight of core-shell rubber on the basis of 100 parts by weight of the acrylic resin; and 1000- 4000 ppm of poly methyl methacrylate particles.

Description

ACRYLIC FILM AND MANUFACTURING METHOD OF THE SAME

The present invention relates to an acrylic film and its manufacturing method.

2. Description of the Related Art In recent years, a liquid crystal display device having a low power consumption, operating at a low voltage, and being lightweight and thin has been widely used in information display devices such as mobile phones, portable information terminal computer monitors, and televisions. Reliability in such a harsh environment is required for such information display devices. For example, a liquid crystal display device for a car navigation system may have a very high temperature and humidity in a car in which it is placed, and the required temperature and humidity conditions are stricter than that of a conventional television or personal computer monitor. In addition, a polarizing plate is used in the liquid crystal display device to enable the display. In the liquid crystal display device in which such strict temperature and/or humidity conditions are required, it is required that the polarizing plate constituting it has 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. And conventionally, triacetyl cellulose (TAC) is widely used for this protective film, and the protective film is adhered to the polarizing film through an adhesive made of an aqueous solution of a polyvinyl alcohol-based resin. However, the polarizing plate on which the protective film made of triacetyl cellulose is laminated has high moisture permeability of triacetyl cellulose, and therefore, when used for a long time in a high-humidity heat environment, the polarization performance may deteriorate or the protective film and the polarizing film may peel off. have. In order to solve this problem, it has been attempted to use a (meth)acrylic resin film having a low moisture permeability as compared to a triacetyl cellulose film as a protective film for a polarizing plate.

The existing acrylic protective film has been manufactured by a melt casting method, but has many advantages in terms of eco-friendliness such as thinning, mass production, and recycling of resins when manufacturing by the solvent casting method. Solvent casting method is to dissolve the acrylic film in a solvent and extrude it with T-Die, then dry the solvent in the belt to make the film. It is necessary to increase the impact strength by adding optimized particles and secure slip properties for film transfer. The process is possible. In addition, the particles added at this time should not dissolve or deform in the solvent.

On the other hand, in general, the acrylic film causes surface defects such as pressing and black band due to its unique ductility and weak surface hardness, and thus, it is difficult to wind up, thereby causing a problem that the yield of the polarizing plate containing the film is lowered.

In order to solve the above problems, a method of adding silica-based particles to an acrylic film has been used in the past, but when controlled by the size and content of the silica-based particles, haze is expressed inside the film, and the surface roughness expression is weak. Is done.

In addition, there is a method to solve the above-mentioned problems through a method such as coating the surface of the film with silica, but such a method causes a problem that the coating layer is detached due to moisture when surface roughness is exhibited, thereby deteriorating stability over time. do.

An object of the present invention is to provide an acrylic film capable of expressing surface roughness without expressing haze inside the film and a method for manufacturing the same.

The acrylic film according to an embodiment of the present invention is an acrylic resin consisting of 70 to 98 parts by weight of methyl methacrylate units and 2 to 30 parts by weight of butyl methacrylate units; 5 to 40 parts by weight of core shell rubber with respect to 100 parts by weight of the acrylic resin; And 1000 to 4000 ppm of polymethyl methacrylate particles.

In this case, the polymethyl methacrylate particles are monodisperse polymethyl methacrylate particles having a particle diameter of 0.5 to 10 μm, and the dispersed particle diameter (D ₅₀ ) of the polymethyl methacrylate particles may be 5 μm or less.

Alternatively, the polymethyl methacrylate particles are polydisperse polymethyl methacrylate particles having a particle diameter of 0.5 to 30 μm, and the dispersed particle diameter (D ₅₀ ) of the polymethyl methacrylate particles may be 10 to 20 μm. .

In addition, the haze of the acrylic film is 2.0% or less, the surface roughness Ra may be 10 ~ 15nm, Rz may be 400 ~ 500nm.

According to an embodiment of the present invention, the acrylic film is capable of expressing surface roughness without expressing haze inside the film. In addition, it is possible to induce an air layer between films through expression of the film surface roughness, thereby preventing damage to the film surface.

In addition, surface defects do not occur due to the surface roughness of the film, and thus, the film can be wound up to 3,900 m or more, and the yield of the film and the polarizing plate including the same can be improved, and stability over time can be secured.

The present invention can be variously modified and may have various forms, and specific embodiments will be described in detail in the text. However, this is not intended to limit the present invention to a specific disclosure form, and it should be understood that all modifications, equivalents, and substitutes included in the spirit and scope of the present invention are included.

In this application, the terms "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, actions, components, parts or combinations thereof are not excluded in advance. In addition, when a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case of being "just above" the other part but also another part in the middle. Conversely, when a portion of a layer, film, region, plate, etc. is said to be “under” another portion, this includes not only the case “underneath” another portion, but also another portion in the middle. In addition, in the present application, being referred to as being "on" may include the case of being disposed on the lower part as well as the upper part.

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

The acrylic film according to an embodiment may include 5 to 40 parts by weight of the core shell rubber with respect to 100 parts by weight of the acrylic resin, and may include 1000 to 4000 ppm of polymethyl methacrylate particles.

First, the acrylic resin is based on methyl methacrylate (Methyl Methacrylate), other phenyl maleimide (Phenyl Male Imide), cyclohexyl maleimide (Cyclohexyl Male Imide), methyl acrylate (Methyl Acrylate), butyl acrylic It is preferably made of one or two or more copolymerized monomers selected from the group consisting of Butyl Acrylate, Alpha Methyl Styrene, Poly Carbonate, and Methacrylic Acid. It is not limited.

At this time, the acrylic resin is more preferably made of a methyl methacrylate unit and a butyl methacrylate unit, and may be a copolymer resin in which each of the monomer units is included in the form of a repeating unit.

On the other hand, considering the optical properties, transparency, compatibility, processability and productivity, with respect to 100 parts by weight of acrylic resin, methyl methacrylate (Methyl Methacrylate) unit 70 to 98 parts by weight, butyl methacrylate (Butyl Methacrylate) unit 2 It is preferably made of 30 parts by weight. When the content of the methyl methacrylate unit is in the above range, excellent retardation characteristics and optical properties can be obtained, and when the methyl methacrylate unit content is less than 70 parts by weight, the optical performance of the protective film deteriorates, and exceeds 98 parts by weight If it does, the thickness uniformity of the protective film may be lowered.

In addition, with respect to 100 parts by weight of the acrylic resin, the content of the butyl methacrylate unit is preferably made of 2 to 30 parts by weight. When the content of the butyl methacrylate unit is in the above range, desirable optical properties can be obtained.

The acrylic resin preferably has a molecular weight of 500,000 to 1,000,000 g/mol. At this time, when the molecular weight is less than 500,000 g/mol, the production efficiency of the film decreases, and when it exceeds 1,000,000 g/mol, a problem that molding processing is not easy occurs. In addition, the glass transition temperature (Tg) of the acrylic resin is preferably 110 ~ 150 ℃. When the glass transition temperature is out of the above range, the handleability is poor and it is not preferable.

The core-shell rubber particles (CSR) do not dissolve in a solvent and do not deform, and by adding them to an acrylic resin, the impact strength of the film is improved to facilitate film formation and film transfer. The core-shell rubber (Core Shell Rubber) is made of one or two or more cores selected from the group consisting of Styrene Butadiene Rubber, Polybutadiene (PBD), and Acrylic Ester. , It is preferable that the shell is made of one or two or more graft copolymers selected from the group consisting of methyl methacryl (MMA), styrene, and acrylic ester.

At this time, the diameter of the core-shell rubber particles (CSR) is preferably 100 to 300nm. When the diameter of the core-shell rubber particles (CSR) is less than 100 nm, the effect of the desired invention does not sufficiently appear, and when it exceeds 300 nm, the quality of the protective film may be deteriorated.

In addition, the core-shell rubber particles (CSR) preferably contains 5 to 40 parts by weight based on 100 parts by weight of the acrylic resin, and can provide a protective film excellent in both hardness and flexibility in the above range.

In general, acrylic films have surface defects such as pressing and black band due to their unique ductility and weak surface hardness, and thus, there is a problem that the yield of the polarizing plate containing the film is lowered due to difficulty in winding up. On the other hand, in the prior art, by adding the silica-based particles to the acrylic film to solve the above problem, when controlled by the size and content of the silica-based particles haze is expressed inside the film, the surface surface roughness expression is a weak problem occurs. . On the other hand, there is a method to solve the above-mentioned problems through a method such as coating the surface of the film with silica, but this method causes a problem that the coating layer is detached due to moisture when surface roughness is expressed, thereby deteriorating stability over time. do.

On the other hand, the acrylic film of the present invention includes a polymethacrylate particle as a slip agent, thereby expressing surface roughness, thereby inducing an air layer between films to prevent damage to the film surface. In addition, surface defects do not occur due to the surface roughness of the film, and accordingly, the film can be wound up to 3,900 m or more, and the yield of the film and the polarizing plate containing the film can be improved, and stability over time can be secured.

At this time, the polymethyl methacrylate particles are preferably a cross-linked structure for high durability against heat and solvents. Moreover, it is preferable that it is monodisperse polymethylmethacrylate particle whose particle diameter is 0.5-10 micrometer or polydisperse polymethylmethacrylate particle whose particle diameter is 0.5-30 micrometer. In addition, the said mono-dispersed poly (methyl methacrylate) dispersed particle diameter (D ₅₀₎ of particles 5㎛ below, the polydispersity poly (methyl methacrylate) is dispersed particle diameter (D ₅₀₎ preferably in the 10 ~ 20㎛ of particles. Non-limiting examples of the monodisperse polymethyl methacrylate particles include MX150 and HX180, and non-limiting examples of polydisperse polymethyl methacrylate particles include LDX120 and MD100.

In addition, the content of the polymethyl methacrylate particles is preferably 1000 to 4000ppm, more preferably 2500 to 3500ppm. When the content is less than 1000ppm, the surface roughness expression of the film does not sufficiently appear, and when the content exceeds 4000ppm, the overall haze of the film exceeds 2.0%, resulting in a problem that transparency decreases.

Meanwhile, the acrylic film may further include additives such as UV absorbers in addition to the above-described components. It is preferable in terms of securing heat resistance to the film to use one or two or more selected from the group consisting of triazole, benzotriazole, and oxanilide as the UV absorber.

The acrylic film as described above may have a haze of 2.0% or less, a surface roughness Ra of 10 to 15 nm, and a Rz of 400 to 500 nm.

A method of manufacturing an acrylic film according to the present invention comprises forming a film by solvent casting a resin composition comprising acrylic resin, core shell rubber, and polymethylmethacrylate particles; And stretching the film at a stretching temperature of 100 to 200° C. and a stretching ratio of 120 to 200% at a rate of 30 to 90%/min, when the residual solvent before stretching is 5 to 20% by weight. .

Hereinafter, a method of manufacturing an acrylic film according to an embodiment of the present invention will be described in detail.

First, in order to prepare the acrylic film of the present invention, a copolymer resin solution of methyl methacrylate monomer and butyl methacrylate monomer is prepared. There is no particular limitation on the method for producing a copolymer of these monomers, and it may be prepared according to a method for preparing a copolymer resin well known in the art, such as suspension polymerization, emulsion polymerization, bulk polymerization or solution polymerization.

Thereafter, a film can be prepared from the resin solution by a solvent casting method (solution film forming method). The solvent casting method is a method of casting a main dope obtained by dissolving an acrylic resin in a casting solvent on a support, and evaporating the solvent to form a film. The main dope solution is prepared by mixing the above-mentioned acrylic resin and co-additive in a casting solvent.

When a film is prepared by a solvent casting method, an organic solvent is preferably used as a solvent for preparing the main dope solution. It is preferable to use halogenated hydrocarbons as the organic solvent, and chlorinated hydrocarbons, methylene chloride and chloroform are used as the halogenated hydrocarbons, and methylene chloride is most preferred.

Further, if necessary, an organic solvent other than halogenated hydrocarbons may be mixed and used. Organic solvents other than halogenated hydrocarbons include esters, ketones, ethers, alcohols and hydrocarbons. As the ester, methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acylate, ethyl acylate, pentyl acylate, etc. can be used. Acetone, methyl ethyl ketone, diethyl ketone, di as ketone Isobutyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone, etc. can be used, and diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxane can be used as ether. Solan, tetrahydrofuran, anisole, phenitol, etc. can be used, and alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1-pentanol, 2 -Pentanol, 2-methyl-2-butanol, cyclohexanol, 2-fluoroethanol, 2,2,2,-triflooroethanol, 2,2,3,3-tetrafluoro-1-propanol, etc. Use

More preferably, methylene chloride may be used as the main solvent, and alcohol may be used as the sub-solvent. Specifically, the mixing ratio of methylene chloride and alcohol is preferably a mixed solvent mixed in a weight ratio within the range of 80:20 to 95:5. More preferred is a solvent mixed with a methylene chloride and methanol 90:10 weight ratio.

In the production of the acrylic film, auxiliary additives may be further used. In the main dope solution, various auxiliary additives according to the use in each manufacturing process, for example, ultraviolet additives, particulates, infrared absorbers, and auxiliary additives such as release agents may be added. Specific types of these additives can be used without limitation as long as they are commonly used in the field, and the content is preferably used in a range that does not degrade the physical properties of the film. The timing of adding the additive depends on the type of additive. A process of adding an additive at the end of the main dope preparation may be performed.

In the present invention, core-shell rubber particles (CSR) and polymethyl methacrylate particles may be used as additives, and the core-shell rubber particles and polymethacrylate particles are the same as described above.

The main dope obtained as described above may be prepared according to a normal temperature, high temperature or low temperature melting method.

At this time, the solvent casting method is mentioned as an example of the film formation method, but it is also possible to use a melt extrusion method or the like in addition to the solvent casting method. Specifically, mixing the acrylic resin pellets, various auxiliary additives, and melt-kneading with a twin-screw extruder to prepare an acrylic resin composition pellet; And by inserting the acrylic resin composition pellets into a single screw extruder and extruded through a T-type die, an acrylic melt compressed film can be produced by sandwiching both sides of the film on a metal roll and cooling it.

In the solvent casting method of the present invention, the main dope liquid is flexible on a metal support from a nozzle of a press die and left for a predetermined time to form a semi-dried film. Thereafter, the film in the semi-dried state is peeled from the metal support, transferred to a drying system, and dried to remove the solvent. Then, a uniaxial stretching step or a biaxial stretching step is performed on the dried film. By performing such a stretching process, it is possible to improve the film uniformity and retardation value of the acrylic film.

Specifically, the main dope 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 stock solution while transferring the casting stock solution on the sheet extruded from the die to form a film with an acrylic film. The support or the surface thereof is made of metal, and the surface is preferably mirror-finished, and a metal belt such as a stainless steel belt is preferably used as the support. The surface temperature of the metal support is advantageous because the higher the temperature, the faster the evaporation of the solvent present in the casting stock solution, but if it is too high, the casting stock solution foams or the flatness suffers, and depending on the solvent used, Although it may vary, 0 to 75°C is preferable, and 5 to 45°C is more preferable. As the support, a metal support in the form of a flat conveyor belt may be used.

The acrylic sheet thus formed is subjected to a stretching step in a tender, and in the preheating process, the glass transition temperature (Tg) of the acrylic flake is 110°C or higher. The acrylic film of the present invention may be completed through a drying step in a dryer after removing the left and right ends of the film whose surface is damaged by a clip or pin of the tender, after the stretching step in the tender under the above conditions.

When using a tender stretching apparatus, it is preferable to use the apparatus which can control the gripping length of a film from left and right by means of the left and right holding means of a tender. The stretching operation may be performed in multiple stages, or biaxial stretching in the flexible direction and the width direction is also preferable. In addition, when biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be carried out stepwise. In this case, stepwise, it is also possible to sequentially perform stretching in different stretching directions, dividing stretching in the same direction into multiple stages, and adding stretching in different directions to any one of them. In addition, simultaneous biaxial stretching also includes a case in which stretching is performed in one direction and the other side is tensioned and contracted. The preferable stretching ratio of simultaneous biaxial stretching can be taken in a range of 1.01 to 2.0 times in both the width direction and the length direction.

As the drying means, it is common to blow hot air on both sides of the web, but there is also a means for heating by applying a micro web instead of the wind. Too rapid drying tends to impair the flatness of the finished film.

On the other hand, the above-described stretching process, at a stretching temperature of 100°C to 200°C, when the residual solvent before stretching is 5% to 20% by weight, the stretching rate is 120% to 200% at a stretching rate of 30%/min to 90%/min. It is preferable to stretch to.

When the stretching temperature is less than 100°C, the stretchability of the film decreases, and when it exceeds 200°C, the defective rate of the film increases. In addition, even when the residual solvent before stretching has a weight ratio of less than 5%, stretchability is deteriorated, and when the weight ratio exceeds 20%, a defect rate of the film increases. In addition, if the elongation rate is less than 30%/min, the problem of inferior economy occurs. If the elongation rate exceeds 90%/min, the property of the film decreases. When the elongation is less than 120%, the modulus of the film decreases, and when it exceeds 200%, haze increases and tear strength decreases.

The width of the acrylic film finally obtained is 1,000 to 2,500 m, and is wound on a winding roller. As described above, the acrylic film of the present invention contains polymethacrylate particles as a slip agent, so that surface defects do not occur due to the surface roughness of the film, and thus the film can be wound up to 3,900 m or more, and the film And it is possible to improve the yield of the polarizing plate comprising the same, it is also possible to secure stability over time.

Hereinafter, the present invention will be described in detail through examples. However, the following examples are only to illustrate the present invention, the present invention is not limited by the following examples.

[Example 1]

The content of the butyl methacrylate unit was 5 parts by weight, and an acrylic polymer resin having a molecular weight of 650,000 g/mol and a Tg of 115°C shown in Chemical Formula 1 was used.

Methylene chloride 65.18 parts by weight, methanol 14.31 parts by weight, acrylic resin 16.48 parts by weight, CSR (Kaneka's acrylic type M-210 grade) 3.69 parts by weight, UV absorber Tinvuin 928 (manufactured by BASF) 0.34 parts by weight and slip zein A main dope solution containing 2,500 ppm of polymethyl methacrylate (MX150 from Soken, an average particle size of 1.5 µm) was prepared.

Thereafter, the dope solution was uniformly flexible to a stainless band support having a width of 2000 mm using a belt casting device. The solvent was evaporated on the stainless band support and peeled from the stainless band support. Subsequently, both ends of the web were gripped with a tender, and stretched to a draw ratio of 130% in the TD direction at a rate of 60%/min in a 130°C temperature environment when the residual solvent before stretching was 20.0 wt%. After stretching, the width is maintained for a few seconds, the tension in the width direction is relaxed, the width direction is relaxed, and the drying is performed by conveying for 35 minutes in a drying section set at 90° C. to perform a width of 2000 mm, and also an end An acrylic film having a thickness of 10 mm and a thickness of 8 μm and a thickness of 40 μm was prepared.

[Formula 1]

a and b are 1 or more as an integer.

[Examples 2 to 3 and Comparative Examples 1 to 6]

Except for adjusting the type and content of the slip agent as shown in Table 1, an acrylic film was prepared through the same process as in Example 1 (MD100 of Sunjin Chemical, average particle size 25㎛).

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Slip agent Kinds MX150 MX150 MD100 MX150 MX150 MX150 MD100 R972 R812 content
(ppm) 2500 3500 2500 0 500 6000 6000 5000 5000 film
Haze all(%) 1.1 1.6 1.7 0.2 0.4 2.5 3.5 0.4 0.4 inside(%) 0 0 0 0 0 0 0 0.05 0.05 film
surface
Roughness Ra(nm) 13.5 15 15 5 6 19 20 8 7 Rz(nm) 420 440 500 200 380 500 520 150 130 Rmax(nm) 500 550 600 250 440 620 680 240 210 Winding
Exterior pressed Not occurring Not occurring Not occurring Occur Some occurrence Not occurring Not occurring Occur Occur Black belt Not occurring Not occurring Not occurring Occur Some occurrence Not occurring Not occurring Occur Occur Stability over time OK OK OK NG NG OK - - -

Referring to Table 1, it can be seen that the acrylic film prepared according to the example shows that the overall haze of the film is lower than 2.0%, and surface defects (pressing, black band) do not occur due to the surface roughness of the film. Accordingly, it can be seen that it is possible to secure stability over time. It is believed that the surface roughness Ra is expressed in 10-15 nm and Rz is 400-500 nm, thereby inducing an air layer between films, thereby preventing damage to the film surface.

On the other hand, when the polymethyl methacrylate content is less than 1000ppm (Comparative Examples 1 and 2), it can be seen that it is difficult to secure stability over time due to defects such as pressing and black bands on the film surface. In addition, when the polymethyl methacrylate content exceeds 4000ppm (Comparative Examples 3 and 4), it can be seen that the total haze of the film exceeds 2.0%, resulting in a decrease in transparency. On the other hand, when the silica particles (R972, R182) are included as a slip agent (Comparative Examples 5 and 6), it can be seen that haze is expressed inside the film and defects such as pressing and black bands are generated on the film surface. It is expected that it will be difficult to take over 3,900m.

Although described above with reference to preferred embodiments of the present invention, those skilled in the art or those of ordinary skill in the art will depart from the spirit and scope of the invention described in the claims below. It will be understood that various modifications and changes may be made to the present invention without departing from the scope.

Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims (4)

Acrylic resin consisting of 70 to 98 parts by weight of methyl methacrylate units and 2 to 30 parts by weight of butyl methacrylate units;
5 to 40 parts by weight of core shell rubber with respect to 100 parts by weight of the acrylic resin; And
An acrylic film comprising 1000 to 4000 ppm of polymethyl methacrylate particles. According to claim 1,
The polymethyl methacrylate particles are monodisperse polymethyl methacrylate particles having a particle diameter of 0.5 to 10 μm,
An acrylic film having a dispersion particle diameter (D ₅₀ ) of the polymethyl methacrylate particles of 5 μm or less. According to claim 1,
The polymethyl methacrylate particles are polydisperse polymethyl methacrylates having a particle diameter of 0.5 to 30 μm,
An acrylic film having a dispersion particle diameter (D ₅₀ ) of the polymethyl methacrylate particles of 10 to 20 μm. According to claim 1,
The acrylic film has an haze of 2.0% or less, the surface roughness Ra is 10 ~ 15nm, Rz is an acrylic film of 400 ~ 500nm.