KR102111335B1 - Acryl Film - Google Patents

Abstract

The present invention relates to an acrylic film made of an acrylic resin composed of a methyl methacrylate unit and a butyl methacrylate unit, wherein the amount of the residual solvent is controlled by controlling the content of the butyl methacrylate unit, and methyl meth It provides an acrylic film comprising 85 to 94 parts by weight of acrylate (Methyl Methacrylate) units, 6 to 15 parts by weight of butyl methacrylate units, and manufactured through a solvent casting method. .

Description

Acrylic film

The present invention relates to an acrylic film produced by controlling the amount of residual solvent by adjusting the content of butyl methacrylate unit in the acrylic resin.

2. Description of the Related Art In recent years, liquid crystal display devices having low power consumption, low voltage operation, and light weight and thinness have 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 bonded 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 triacetylcellulose is stacked has high moisture permeability of triacetylcellulose, so that the polarizing performance may deteriorate or the protective film and the polarizing film peel off when used for a long time in a high-humidity heat environment. 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.

Existing acrylic-based protective films have been manufactured by a melt casting method, but have many advantages in terms of eco-friendliness, such as thinning of the film, mass production, and recycling of resins when manufacturing by the solvent casting method. Solvent casting method is to produce a film through the process of drying the solvent in a belt after extruding the main solution in which the acrylic resin is dissolved in a solvent with a T-die, and then adding optimized particles to impact the film. The above process is possible only when the strength is increased and sufficient slip property is secured for transferring the film. In addition, the particles added at this time should not be dissolved or deformed in the solvent. In particular, since the amount of the solvent remaining in the film acts as an important factor in terms of slip properties, it is important to control the amount of the residual solvent.

Korean Registered Patent No. 12,500,7 discloses an adhesive polarizing plate in which light leakage of an image display device does not easily occur even due to a change in the use environment.The acrylic polymer constituting the adhesive layer has a predetermined amount of (meth) ) Containing an acrylate monomer unit, its content is determined according to the value of the photoelastic coefficient X of the transparent protective film, and when the phase difference value of the transparent protective film changes due to environmental changes such as heating, the pressure-sensitive adhesive layer is a transparent protective film It has been proposed to adjust to generate a phase difference change of the opposite sign.

Korean Registered Patent No. 1114354 is a protective film for an optical member having an adhesive layer containing a cured product of a photopolymerizable acrylic polymer, an antistatic agent, and a polymerization agent composition, and undergoes a crosslinking reaction by radicals generated in an initiator by light irradiation. A composition containing a photopolymerizable acrylic polymer and a polymerization initiator in which a photoactive group that can be introduced is introduced in a predetermined ratio, an appropriate amount of an antistatic agent is added, and the aging process during curing can be omitted, thereby simplifying the manufacturing process. , A protective film excellent in antistatic properties when peeling or using.

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

Japanese Unexamined Patent Publication No. 2014-240905 has a film thickness and an elastic modulus within a specific range, and a protective film containing acrylic resin as a main component in order to produce a polarizing plate excellent in adhesiveness, reworkability, flatness and visibility with a polarizer. , Polarizers, glucose skeletons are stacked in the order of retardation film B, which mainly comprises a cellulose derivative having an ether bond and a substituent, and both films A and B are bonded through an ultraviolet curable adhesive.

Therefore, there is still a need to improve the technology on the aspect of securing slip properties for film transfer when the acrylic protective film is manufactured by a solvent casting method.

Korean Registered Patent No. 1265007 Korean Registered Patent No. 1114354 Korean Patent Publication No. 2015-0061591 Japanese Patent Publication No. 2014-240905

The present invention has been devised to solve the above problems, and when the acrylic film is produced by solvent casting, the amount of residual solvent can be easily controlled by adjusting the content of butyl methacrylate in the acrylic resin within a specific range. In the process of performing peeling during the film forming process of the film, it is intended to provide an acrylic film having a quality that is prevented from being deteriorated due to residual solvent amount.

Acrylic film according to embodiments of the present invention is represented by the following formula (1), methyl methacrylate (Methyl Methacrylate) unit 85 to 94 parts by weight, butyl methacrylate (Butyl Methacrylate) unit 6 to 15 parts by weight of acrylic It is characterized in that it comprises a resin, and is produced through a solvent casting method.

MMA-BMA

(In Formula 1, a and b are 1 or more, MMA represents a methyl methacrylate unit, and BMA represents a butyl methacrylate unit.)

The residual solvent amount of the film may be 900 ppm or less.

The solvent of the solvent casting is an organic solvent containing Cl, and the residual Cl content of the film may be 900 ppm or less.

The film may have a thickness of 10 to 60 μm, and the weight average molecular weight of the acrylic resin is preferably 300,000 to 2,500,000 g / mol.

Since the acrylic film of the present invention is manufactured in a controlled state of the amount of the residual solvent, the amount of the residual solvent in the process of peeling during the film forming process can be prevented from deteriorating the film quality that may occur due to too little or too much, and thus has excellent quality. An acrylic film can be provided.

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 acrylic film according to embodiments of the present invention is represented by the following Chemical Formula 1, and comprises an acrylic resin consisting of 85 to 94 parts by weight of methyl methacrylate units and 6 to 15 parts by weight of butyl methacrylate units, and a solvent casting method. It is characterized by being manufactured through.

[Formula 1]

MMA-BMA

(In Formula 1, a and b are 1 or more, MMA represents a methyl methacrylate unit, and BMA represents a butyl methacrylate unit.)

First, the acrylic resin of the present invention will be described. The acrylic resin of the present invention is a copolymer resin composed of methyl methacrylate units and butyl methacrylate units, and each of the monomer units is included in the form of a repeating unit.

Considering optical properties, transparency, compatibility, processability and productivity, the methyl methacrylate unit is 85 to 94 parts by weight, preferably 85 to 91 parts by weight, more preferably 85 to 100 parts by weight of the acrylic resin It is preferable that 88 parts by weight and the butyl methacrylate unit consist of 6 to 15 parts by weight, preferably 9 to 15 parts by weight, and more preferably 12 to 15 parts by weight. This is because when the content of the methyl methacrylate unit is in the above range, the residual solvent amount is maintained in a desirable range, and excellent retardation characteristics and optical characteristics can be obtained. When the methyl methacrylate unit content is less than 85 parts by weight, the optical performance of the acrylic film is deteriorated, and when it exceeds 94 parts by weight, the thickness uniformity of the acrylic film may be deteriorated.

In addition, the content of the butyl methacrylate unit can also obtain excellent retardation properties and optical properties within the above range. If the content of the butyl methacrylate unit is less than 6 parts by weight, the optical performance of the protective film deteriorates, and if it exceeds 15 parts by weight, the processability of the film may be deteriorated. In addition, when the content of the butyl methacrylate unit is within the above range, the amount of the residual solvent in the film can be optimized, thereby preventing degradation of the quality of the film due to the residual solvent.

Deterioration of the quality of the film by the residual solvent may occur when the main dope solution in which the acrylic resin is dissolved in the solvent in the solvent casting process is coated on a metal support to form a semi-dried film and then peeled from the support. Therefore, after the production is completed, the properties as optical and protective films are insufficient. That is, the residual solvent amount can have a significant effect on the quality of the acrylic film, so its control is essential. For example, if the amount of the residual solvent is too small, peeling the film from the support becomes difficult to peel, and damage to the film may occur. When the amount of the residual solvent is too large, the film becomes too soft and lacks self-support. The film may be stretched due to the peeling tension, which may be a problem. In addition, when the amount of the residual solvent is large in the stretching and / or drying process during the film forming process, shrinkage may occur excessively in the film, which may adversely affect the properties of the film. In addition, if the amount of the organic solvent remaining in the film is large, it may be a problem in terms of the harmfulness of the product. However, the solvent mainly used in the solvent casting method is a highly volatile organic solvent, and it is not easy to control the amount of the residual solvent. In the present invention, the content of the butyl methacrylate unit contained in the acrylic resin is limited to a certain range. The amount of residual solvent can be easily controlled.

Acrylic resins composed of only methyl methacrylate and / or methyl acrylate units have less inter-molecular free volume compared to triacetylcellulose materials, and the diffusion of solvent remaining therein is relatively slow when made into a film. As a result, a difference in the drying speed of the solvent occurs on the surface and inside of the film during the film forming process, and surface solidification occurs, whereby a larger amount of the solvent may remain inside the film. In the present invention, by including the butyl methacrylate unit as a component constituting the acrylic resin in a specific range of content, the gap between the molecular chains of the acrylic resin occurs as the steric hindrance widens and remains inside the resin The diffusion of solvents can be accelerated. As a result, the solidification of the film is delayed as the solvent present therein diffuses toward the surface of the film. Accordingly, drying of the residual solvent can be more efficiently performed through the film forming process, and thus the amount of the residual solvent can be more easily performed. Can be controlled.

The residual solvent amount of the acrylic film according to the embodiments of the present invention may be 900 ppm or less. Since the acrylic film of the present invention is peeled in a range most suitable for carrying out the peeling in order to transfer the film in a semi-dry state from the support during the film forming process, it is possible to prevent deterioration in the quality of the film that may occur due to excessive or little residual solvent. . In addition, because of this, the acrylic film finally produced contains a low amount of residual solvent of 900 ppm or less, so it may not cause a problem of harmfulness when using the film as a film suitable for the regulation of harmful substances in the protective film.

The acrylic film according to the embodiments of the present invention is prepared through a solvent casting method, and the solvent used in the solvent casting is an organic solvent containing Cl, and the content of Cl remaining in the film is 900 ppm or less, preferably May be 600 ppm or less. The content of Cl can be measured, for example, by 'a combustion method of a single material made of PMMA', and the calculated content of residual Cl may be 900 ppm or less.

The acrylic resin used in the present invention preferably has a molecular weight of 300,000 to 2,500,000 g / mol. At this time, if the molecular weight is less than 300,000 g / mol, the production efficiency of the film decreases, and if it exceeds 2,500,000 g / mol, molding processing is not easy.

The glass transition temperature (Tg) of the acrylic resin according to the embodiments of the present invention is preferably 105 ° C or higher, preferably 108 ° C or higher. When the glass transition temperature is less than 105 ° C, the handling property of the film is poor, which is undesirable.

It is preferable that the acrylic film of the present invention has a film thickness of 10 to 60 µm. When the thickness of the protective film is less than 10 µm, sufficient retardation characteristics as an optical film are not exhibited, and when the thickness of the protective film exceeds 60 µm, it is not suitable for use in thin polarizing plates.

In the acrylic film according to the embodiments of the present invention, the in-plane retardation (Ro) and the thickness direction retardation (Rth) defined by the following Equation 1 are preferably 10 nm or less under the conditions of 23 ° C. and 55% RH.

[Equation 1]

Ro = (nx-ny) * d

Rth = {(nx + ny) / 2-nz} * d

In Equation 1, d is the thickness (nm) of the film, nx is the maximum refractive index in the horizontal direction in the plane of the film, ny is the maximum refractive index in the vertical direction in the film plane, and nz is the maximum refractive index in the thickness direction of the film. When the in-plane and thickness direction retardation exceeds 10 nm, the performance as an isotropic optical film deteriorates.

The acrylic film according to embodiments of the present invention may exhibit a low haze value of 0.40% or less, preferably 0.35% or less, through the above-described features. Therefore, the acrylic film may have excellent optical properties for use in a polarizing plate protective film or the like.

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

Preparation of acrylic resin

To prepare the acrylic film of the present invention, first, a copolymer resin (acrylic resin) of methyl methacrylate monomer and butyl methacrylate monomer is prepared. When preparing the acrylic resin, methyl methacrylate is 85 to 94 parts by weight, and butyl methacrylate is 6 to 15 parts by weight based on the monomer constituting the acrylic resin.

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.

Notes containing acrylic resin additives Dope  Produce

In the present invention, a film is produced 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 solvent (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 with a solvent.

When producing a film by a solvent casting method, the solvent for preparing the main dope solution is preferably an organic solvent. It is preferable to use halogenated hydrocarbons as the organic solvent, and halogenated hydrocarbons include chlorinated hydrocarbons, methylene chloride, and chloroform, 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, and 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, -trifluoroethanol, 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.

In the production of the acrylic film, auxiliary additives may be further used as necessary. In the main dope solution, various auxiliary additives according to the use in each manufacturing process, for example, UV inhibitors, core-shell rubber (CSR) particles or fine particles such as silica particles, infrared absorbers, and auxiliary additives such as release agents Can be added. The CSR particles include styrene butadiene rubber, polybutadiene (PBD), acrylic ester (Acrylic Ester), one or two or more cores, and methyl methacrylate (MMA) ), Styrene (Styrene), acrylic esters (Acrylic Ester) is preferably one or two or more selected from the group consisting of a graft copolymer having a core-shell structure, but is not limited thereto. 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 auxiliary additives is determined according to the type of each additive. A process of adding an additive at the end of the main dope preparation may be carried out.

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

Production process

In the solvent casting method of the present invention, the main dope liquid is flexible on the metal support from the nozzle of the 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 this stretching step, it is possible to improve the film uniformity and retardation value of the protective 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 main dope while transporting the main dope liquid 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 main dope solution, but if it is too high, the main dope solution may be foamed or flattened. Therefore, the surface temperature of the metal support may vary depending on the solvent used, but 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 transferred to a tender and undergoes a stretching step in the tender. 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 process 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 grippers 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 stretching in one direction and contracting the other by relaxing the tension. The preferred 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 to heat the micro web instead of the wind. Too rapid drying tends to impair the flatness of the finished film.

Since the acrylic film of the present invention manufactured according to the above method is manufactured by controlling the amount of the residual solvent, it can exhibit excellent quality in slip properties during the film forming process, no appearance stain after production, and excellent durability and dimensional stability.

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 resin

The content of butyl methacrylate units An acrylic resin having 6 parts by weight and having a molecular weight of 650,000 g / mol shown in the following Chemical Formula 1 and having a Tg of 115 ° C was used.

[Formula 1]

(In Formula 4, a and b are each 1 or more)

<Step 2> Preparation of main dope liquid

The main dope was prepared by sufficiently mixing 25 parts by weight of the acrylic resin and 75 parts by weight of a mixed solvent in which methylene chloride and methanol were mixed in a 9: 1 (weight ratio) manner with an in-line mixer.

<Step 3> Production process

Thereafter, the main dope 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 by a tender, and stretched so that the draw ratio in the TD direction was 1.5 times in a 130 ° temperature environment. After stretching, the width is maintained for a few seconds, the tension in the width direction is relaxed, the width direction is relaxed, and then dried by conveying for 35 minutes in a drying section set at 90 °, width is 1900 mm, and further ends An acrylic film having a width of 10 mm and a thickness of 8 μm and a thickness of 40 μm was prepared.

Example  2

When preparing the acrylic resin, it was carried out in the same manner as in Example 1, except that the content of the butyl methacrylate unit was adjusted to 9 parts by weight.

Example  3

When preparing the acrylic resin, it was carried out in the same manner as in Example 1, except that the content of the butyl methacrylate 아크릴 unit was adjusted to 12 parts by weight.

Example  4

When preparing the acrylic resin, it was carried out in the same manner as in Example 1, except that the content of the butyl methacrylate 아크릴 unit was adjusted to 15 parts by weight.

Comparative example  One

When the acrylic resin was prepared, it was carried out in the same manner as in Example 1, except that the content of the methyl methacrylate unit was adjusted to 100 parts by weight without adding a butyl methacrylate monomer.

Comparative example  2

The content of butyl methacrylate unit It was carried out in the same manner as in Example 1, except that it was adjusted to 5 parts by weight.

Property measurement

Each of the acrylic films prepared in Examples 1 to 4 and Comparative Examples 1 and 2 was prepared into samples cut into pieces of a certain size according to each measuring method, and the physical properties were measured by the following methods, and the results are shown in the following table. It is shown in 1.

1. Evaluation of residual solvent

The amount of the solvent component released while slowly heating each acrylic film sample was measured by Gas Chromatography.

2. Residual Cl content evaluation

It was measured based on the combustion method and XRF method of a single material of PMMA material.

3. Haze measurement

Haze was measured according to JIS K7136.

4. Measurement of glass transition temperature

It was measured using a DSC (Differential Scanning Calroimeter).

division BMA unit content
(Parts by weight) Residual solvent amount
(ppm) Residual Cl content
(ppm) Hayes
(%) Resin glass transition temperature
(℃) Comparative Example 1 0 15000 10500 0.36 118 Comparative Example 2 5 1500 1100 0.33 116 Example 1 6 900 710 0.32 115 Example 2 9 630 420 0.31 113 Example 3 12 500 370 0.31 112 Example 4 15 100 85 0.30 108

Referring to Table 1, it can be seen that the acrylic film of Examples 1 to 4 had a significantly lower residual solvent amount and residual Cl content than Comparative Example 1. The haze value was also low as 0.33% or less, and the glass transition temperature was found to be suitable for manufacturing into a film. Therefore, it can be seen that the acrylic film according to the embodiments of the present invention is a protective film showing excellent optical properties by being manufactured by controlling the amount of residual solvent.

Claims (4)

An acrylic resin represented by the following Chemical Formula 1, consisting of 85 to 94 parts by weight of methyl methacrylate units, and 6 to 15 parts by weight of butyl methacrylate units; Including,
Manufactured through solvent casting method,
The residual solvent amount of the film is 900ppm or less,
The solvent of the solvent casting is an organic solvent containing Cl,
Acrylic film, characterized in that the residual Cl content of the film is 900ppm or less.
[Formula 1]

MMA-BMA
(In Formula 1, a and b are 1 or more, MMA represents a methyl methacrylate unit, and BMA represents a butyl methacrylate unit.)
delete delete According to claim 1,
The acrylic resin has a weight-average molecular weight of 300,000 to 2,500,000 g / mol, and the film has an thickness of 10 to 60 μm.