KR102492892B1 - High heat resistant acrylic copolymer and light diffuser composite sheet comprising thereof - Google Patents

Abstract

The present invention relates to an acrylic copolymer having excellent heat resistance and optical properties and a composite sheet for a light diffuser including the same. In more detail, a high heat resistance acrylic copolymer is polymerized using a specific dispersion stabilizer and a monomer having a cyclic structure, and a composite sheet for a light diffusion plate is prepared using the same, thereby providing a composite sheet for a light diffusion plate having high heat resistance and high brightness. can do.
The composite sheet for a light diffuser according to the present invention is prepared by including an acrylic copolymer having excellent heat resistance and low yellowness, and has excellent heat resistance and optical properties. Therefore, it can withstand the ever-increasing intensity and temperature of light sources, making it suitable for use in signboards, lighting fixtures, protective covers for car turn indicators, and direct backlight units for large displays that generate a lot of heat.

Description

High heat resistance acrylic copolymer and composite sheet for light diffuser containing the same

The present invention relates to an acrylic copolymer having excellent heat resistance and optical properties and a composite sheet for a light diffuser including the same.

A light diffusion plate is a device that uniformly diffuses light generated from LED lamps and various lamps, and is used in signboards, lighting fixtures, protective covers for automobile direction indicators, and direct-type backlight units (BLUs) for displays. In general, a light diffuser plate requires excellent light transmittance and light diffusivity basically because it is necessary to implement a uniform brightness while a rear light or an internal material is not visible from the outside.

As the resin for the light diffusion plate, methacrylic resin (PMMA), polycarbonate resin (PC), and polystyrene resin (PS) are mainly used. PMMA has excellent transparency and weather resistance, but has poor heat resistance and impact resistance, and PC has excellent heat resistance, weather resistance, hygroscopicity and impact strength, but has low transmittance and poor optical properties such as luminance and processability. PS has good processability, but has a disadvantage of poor weather resistance and heat resistance, and also has a problem in that brightness and transparency are reduced when heat resistance is increased.

Recently, ultra-large products such as large-inch displays are being released, and accordingly, the intensity of light emitted from a light source and the number of lamps are gradually increasing. Therefore, the heat emitted from the light source becomes stronger and the temperature affecting the light diffuser plate gradually increases, changing the shape of the light diffuser plate, resulting in stains on the image screen, inability to maintain high brightness for a long time, or yellowing or warping. At the same time as problems arise, there is a limit to the increase in luminance. Therefore, development of a resin for a light diffusion plate having more excellent heat resistance, weather resistance, and optical properties than resins used in conventional diffusion plates is underway.

Korean Patent KR 10-2010-0020430 A prepared an acrylic copolymer with improved heat resistance and impact resistance using PS and PC. Although the heat deflection temperature is slightly improved compared to the case of using pure PS, there is still a problem in newly applying it as a light diffusion plate because of its insufficient physical properties such as yellow index and heat resistance.

In US Patent US 4558098 A, a resin with improved heat resistance was prepared using methyl methacrylate, maleic anhydride, styrene or alpha methyl styrene. Although this can improve the heat distortion temperature, there are problems in that transparency is lowered due to heat discoloration or luminance is low.

In the prior art, various attempts have been made to solve the above problems, such as mixing and using resins or applying special monomers. However, problems of improving optical properties such as heat resistance, transparency, weather resistance, workability, and luminance still exist.

Therefore, it is necessary to develop a resin for a light diffuser plate that has high heat resistance and satisfies optical properties such as excellent transparency and high luminance and processability so as to withstand the increasing intensity and temperature of a light source.

KR 10-2010-0020430 A (2010.02.22) US 4558098 A (1985.12.10)

In order to solve the problems of the prior art as described above, an object of the present invention is to polymerize an acrylic copolymer having excellent heat resistance, and to provide a composite sheet for a light diffusion plate having high heat resistance and high brightness including the same.

In order to achieve the above object, the present inventors have continuously studied for the manufacture of a composite sheet for a light diffuser plate having excellent heat resistance and excellent optical properties such as luminance. As a result, (A) an alkyl methacrylic monomer and (B) cyclohexylmaleimide, When a composite sheet for a light diffuser is prepared using an acrylic copolymer polymerized by including at least two comonomers selected from phenylmaleimide, alpha methyl styrene and methyl acrylate, and (C) a specific dispersion stabilizer, brightness and heat resistance properties are surprisingly This highly enhancing effect was discovered and the present invention was completed.

Specifically, the composite sheet for a light diffuser according to the present invention has a glass transition temperature of 120 ° C. or more and at the same time satisfies the following Equation 1 in terms of luminance, thereby finding an effect capable of simultaneously satisfying excellent optical properties and heat resistance, thereby concluding the present invention. completed.

[Equation 1]

In Equation 1, L1 is the luminance of the composite sheet for a PS light diffusion plate having a thickness of 2.5 mm, and L2 is the luminance of the composite sheet for a light diffusion plate of the present invention.

In Equation 1, L1 and L2 denote luminance measured with the same amount of light using a sheet having the same thickness. That is, the composite sheet for a light diffuser according to the present invention can exhibit 5% or more superior luminance than the composite sheet for a PS light diffuser.

As seen in the prior art, in order to improve the heat resistance of composite resins for light diffuser plates, acrylic copolymers polymerized by including monomers having a cyclic structure may be used. However, such a method may cause problems such as a decrease in polymerization stability and a decrease in transparency due to an increase in yellowness. However, in the present invention, through a continuous research process, polymerizing an acrylic copolymer having excellent heat resistance and low yellowness even though it contains a monomer having a cyclic structure, and providing a composite sheet for a light diffuser plate having high brightness and high heat resistance using the same Could.

One aspect of the present invention for achieving the above object is a composite sheet for a light diffusion plate comprising an acrylic copolymer and a light diffusing agent, wherein the acrylic copolymer is (A) an alkyl methacrylic monomer and (B) cyclohexyl maley A dispersion stabilizer prepared by including at least two comonomers selected from mead, phenylmaleimide, alphamethylstyrene, and methylacrylate, and (C) Formula 1, Formula 2, and alkyl (meth)acrylate-based monomers. It is a copolymer, and the composite sheet for a light diffuser plate has a glass transition temperature of 120° C. or more, and luminance satisfies the following Equation 1.

[Formula 1]

In Formula 1, R ₁ is hydrogen or C1 to C3 alkyl, n is an integer selected from 1 to 3, and M is any one selected from lithium, sodium, potassium, and ammonium salts.

[Formula 2]

In Formula 2, R ₂ is hydrogen or C1 to C3 alkyl, and M is any one selected from lithium, sodium, potassium, and ammonium salts.

[Equation 1]

In Equation 1, L1 is the luminance of the composite sheet for a PS light diffusion plate having a thickness of 2.5 mm, and L2 is the luminance of the composite sheet for a light diffusion plate of the present invention.

In one aspect of the present invention, the acrylic copolymer may have a light transmittance of 90% or more and a yellowness of 1.0 or less as measured according to ASTM D1003.

In one aspect of the present invention, the acrylic copolymer may include 1 to 20 parts by weight of a comonomer based on 100 parts by weight of the acrylic monomer.

In one aspect of the present invention, the acrylic copolymer may include 0.001 to 10 parts by weight of a dispersion stabilizer based on 100 parts by weight of the acrylic monomer.

In one aspect of the present invention, the composite sheet for the light diffusion plate may have a temperature of 320° C. or higher at which 2% weight loss occurs.

In one aspect of the present invention, the composite sheet for the light diffusion plate may have a haze of 80% or more and a light diffusivity (Td) of 45% or more, measured according to ASTM D1003.

According to one aspect of the present invention, the light diffusion coefficient of the composite sheet for the light diffusion plate may satisfy Equation 3 below.

[Equation 3]

In Equation 3, D1 is the light diffusion coefficient of the composite sheet for the PS light diffusion plate having a thickness of 2.5 mm, and D2 is the light diffusion coefficient of the composite sheet for the light diffusion plate of the present invention.

In one aspect of the present invention, a difference between a maximum value and a minimum value of each of the color coordinate values Wx and Wy of the composite sheet for a light diffuser may be 2/100 or less.

In one aspect of the present invention, the composite sheet for the light diffusion plate may include 0.01 to 10 parts by weight of the light diffusion agent based on 100 parts by weight of the acrylic copolymer.

In one aspect of the present invention, the composite sheet for the light diffusion plate may further include any one or two or more additives selected from the group consisting of antioxidants, UV absorbers, UV stabilizers, lubricants, and mixtures thereof.

Another aspect of the present invention provides a molded article manufactured including the composite sheet for a light diffusion plate according to the above aspect. The molded article can be used in fields requiring excellent optical properties and heat resistance, for example, signboards having light sources with high heat generation such as LEDs, lighting fixtures, protective covers for automobile turn indicators, and direct backlight units for the latest large-scale displays. etc. may be included.

Another aspect of the present invention is a master batch chip comprising an acrylic copolymer and a light diffusing agent, wherein the acrylic copolymer is (A) an alkyl methacrylic monomer and (B) cyclohexylmaleimide, phenyl A copolymer prepared by including at least two comonomers selected from maleimide, alpha methyl styrene and methyl acrylate, and (C) a dispersion stabilizer prepared by including the following formulas (1) and (2) and alkyl (meth)acrylate-based monomers In master batch chip (Master Batch Chip) is provided.

[Formula 1]

In Formula 1, R ₁ is hydrogen or C1 to C3 alkyl, n is an integer selected from 1 to 3, and M is any one selected from lithium, sodium, potassium, and ammonium salts.

[Formula 2]

In Formula 2, R ₂ is hydrogen or C1 to C3 alkyl, and M is any one selected from lithium, sodium, potassium, and ammonium salts.

In another aspect of the present invention, the master batch chip may further include any one or two or more additives selected from the group consisting of antioxidants, UV absorbers, UV stabilizers, lubricants, and mixtures thereof.

The composite sheet for a light diffuser according to the present invention is prepared by including an acrylic copolymer having excellent heat resistance and low yellowness, and has excellent heat resistance and excellent optical properties such as brightness. Therefore, it can withstand the ever-increasing intensity and temperature of light sources, making it suitable for use in signboards, lighting fixtures, protective covers for car turn indicators, and direct backlight units for large displays that generate a lot of heat.

Hereinafter, the present invention will be described in more detail through specific examples or examples including the accompanying drawings. However, the following specific examples or examples are only one reference for explaining the present invention in detail, but the present invention is not limited thereto, and may be implemented in various forms.

Also, unless defined otherwise, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms used in the description in the present invention are merely to effectively describe specific embodiments and are not intended to limit the present invention.

Also, the singular forms used in the specification and appended claims may be intended to include the plural forms as well, unless the context dictates otherwise.

In addition, when a certain component is said to "include", this means that it may further include other components without excluding other components unless otherwise stated.

In the present specification, "comonomer" means a mixture of two or more monomers that are raw materials for copolymers.

In the present specification, "(meth)acryl" is meant to include both acryl and methacryl.

Hereinafter, a preferred embodiment and a method for measuring physical properties of the highly heat-resistant acrylic copolymer of the present invention and a composite sheet for a light diffuser plate containing the same will be described in detail.

The present invention may be better understood by the following examples, which are for illustrative purposes of the present invention and are not intended to limit the scope of protection defined by the appended claims.

One aspect of the present invention is a composite sheet for a light diffusing plate comprising an acrylic copolymer and a light diffusing agent, wherein the acrylic copolymer is (A) an alkyl methacrylic monomer and (B) cyclohexylmaleimide, phenylmaleimide, alpha A copolymer prepared by including a comonomer selected from two or more of methyl styrene and methyl acrylate and (C) a dispersion stabilizer prepared by including the following formulas 1 and 2 and an alkyl (meth)acrylate-based monomer, wherein the light diffusion The composite sheet for a light diffuser plate of the composite sheet for a light diffuser plate has a glass transition temperature of 120° C. or more, and luminance satisfies Equation 1 below.

[Formula 1]

In Formula 1, R1 is hydrogen or C1 to C3 alkyl, n is an integer selected from 1 to 3, and M is any one selected from lithium, sodium, potassium, and ammonium salts.

[Formula 2]

In Formula 2, R2 is hydrogen or C1 to C3 alkyl, and M is any one selected from lithium, sodium, potassium, and ammonium salts.

[Equation 1]

In Equation 1, L1 is the luminance of the composite sheet for a PS light diffusion plate having a thickness of 2.5 mm, and L2 is the luminance of the composite sheet for a light diffusion plate of the present invention.

More specifically, the compound represented by Formula 1 is 3-sulfopropyl acrylate potassium salt, 3-sulfopropyl methacrylate potassium salt, 2-sulfoethyl methacrylate sodium salt and 2-sulfoethyl acrylate sodium salt A species or two or more species may be selected, but is not limited thereto. As a more specific example, it may be 2-sulfoethyl methacrylate potassium salt.

Alkyl (meth)acrylate-based monomers used in the preparation of the dispersion stabilizer are not limited as long as they are well-known compounds in the art. More specifically, the alkyl (meth)acrylate-based monomers are methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, benzyl It may be any one or a mixture of two or more selected from methacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, butoxymethyl methacrylate, hydroxyethyl methacrylate, etc., but is not limited thereto. . More preferably, it may be methyl methacrylate.

The content range of the dispersion stabilizer mixture may consist of 10 to 85 wt% of the monomer of Formula 1, 5 to 45 wt% of the monomer of Formula 2, and 10 to 45 wt% of the alkyl (meth)acrylate monomer, and the dispersion The stabilizer may be a copolymer obtained by homogeneously polymerizing a monomer mixture within the above range in an aqueous solution.

The weight average molecular weight of the dispersion stabilizer may be 20,000 to 300,000 g/mol. Specifically, it may be 50,000 to 200,000 g/mol, and more specifically, it may be 60,000 to 80,000 g/mol, but is not particularly limited thereto.

The content of the dispersion stabilizer is not limited, but may include 0.001 to 10 parts by weight of the dispersion stabilizer based on 100 parts by weight of the alkyl methacrylic monomer. More preferably, 0.01 to 5 parts by weight may be included, and polymerization stability may be improved in the above range, but is not limited thereto.

In addition, a dispersion aid may be further included as needed, and any dispersion aid known in the art may be used without limitation. As specific examples, magnesium sulfate, sodium sulfate, and ammonium sulfate may be used.

The alkyl methacrylate-based monomer may use any one or a mixture thereof selected from alkyl methacrylates or derivatives thereof, among which methyl methacrylate, ethyl methacrylate, hydroxy ethyl methacrylate, isobornyl It may be any one or a mixture of two or more selected from methacrylate, cyclohexyl methacrylate, and the like. Preferably it may be methyl methacrylate.

The comonomer is selected from two or more selected from cyclohexyl maleimide, phenyl maleimide, alpha methyl styrene, and methyl acrylate, and may include 1 to 20 parts by weight of the comonomer based on 100 parts by weight of the acrylic monomer. Specifically, it may be 1 to 15 parts by weight, more specifically 3 to 12 parts by weight, but is not particularly limited as long as the glass transition temperature and the temperature at which the 2% weight loss occurs are not lowered.

According to one aspect of the present invention, the comonomer may be one using cyclohexylmaleimide and methyl acrylate. The cyclohexylmaleimide and methyl acrylate may be in a weight ratio of 1 to 5:1. Preferably it may be 2 to 4: 1 weight ratio.

According to one aspect of the present invention, the comonomer may be a mixture of phenyl maleimide, alpha methyl styrene, and methyl acrylate. The phenyl maleimide, alpha methyl styrene and methyl acrylate may have a weight ratio of 1 to 10:1 to 5:1. Preferably, it may be 5 to 10: 1 to 3: 1 weight ratio.

In one aspect of the present invention, the acrylic copolymer may have a light transmittance of 90% or more and a yellowness of 1.0 or less as measured according to ASTM D1003. Specifically, the light transmittance may be 90 to 99%, and the yellowness may be 0.1 to 1.0. More specifically, the light transmittance may be 90 to 95%, and the yellowness may be 0.5 to 0.9. When a composite sheet for a light diffusion plate is prepared by mixing with a light diffusion agent within the above range, it is possible to provide a light diffusion plate having excellent heat resistance, low yellowing and high luminance while achieving sufficient light transmittance.

The polymerization method of the acrylic copolymer may be prepared by bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization using a conventional free radical polymerization method, but suspension polymerization is preferable in minimizing contamination by foreign substances.

As the polymerization initiator used in the polymerization of the acrylic copolymer, commercially available peroxide initiators and azo-based initiators by free radical polymerization may be used, but are not limited thereto. Specifically, for example, 2,2`- Azobisisobutyronitrile, benzoyl peroxide, etc. can be used. The amount of the polymerization initiator is not limited, but it is preferable to add 0.0001 to 0.5 parts by weight based on 100 parts by weight of the total monomer composition.

The acrylic copolymer may further include a chain transfer agent to control the molecular weight of the polymer. The chain transfer agent is not limited as long as it is a compound clearly known in the art, and is preferably a (C1-C12) alkyl mercaptan having one thiol functional group or a polythiol mercaptan having two or more thiol functional groups. may be used, and for example, n-octyl mercaptan may be used, but is not limited thereto.

According to one aspect of the present invention, the composite sheet for a light diffusion plate may have a glass transition temperature of 120° C. or higher, and may satisfy Equation 1 below in luminance. More specifically, the glass transition temperature may be 122 to 130 ° C, and the luminance may satisfy Equation 2 below. In the case of the composite sheet for light diffuser in the above range, it has excellent heat resistance and can withstand the increasing intensity and temperature of a light source, and at the same time has high brightness, so it has a high heat generation signboard, lighting fixtures, protective covers for automobile direction indicators, and the latest It is very suitable for application to a direct type backlight unit for a large display.

[Equation 1]

[Equation 2]

In Equations 1 and 2, L1 is the luminance of the composite sheet for a PS light diffusion plate having a thickness of 2.5 mm, and L2 is the luminance of the composite sheet for a light diffusion plate of the present invention.

In Equations 1 and 2, L1 and L2 denote luminance measured with the same amount of light using a sheet having the same thickness. That is, the object to be compared in Equations 1 to 2 may be a composite sheet for a light diffusion plate made of a polystyrene resin alone and a composite sheet for a light diffusion plate made of the acrylic copolymer of the present invention. This can be compared when the manufacturing conditions, such as the thickness, light transmittance, and light diffusion agent content of the composite sheet for light diffusion plates, and the test conditions, such as the type, intensity, number, and amount of light used in the test, are the same. Equations 1 and 2 can be satisfied.

Specifically, in the case of a composite sheet for a general PS light diffuser, when the light transmittance is 70%, the haze is 60.9%, the light diffusivity is 42.9%, the luminance is 3116 cd, and the color coordinates (Wx, Wy) are (0.2873, 0.2918 ) and a light diffusion coefficient of 22.6. That is, in the case of the composite sheet for a light diffusion plate of the present invention that satisfies Equations 1 and 2 above, an effect of improving luminance by 5% or more, more preferably 10% or more compared to the composite sheet for a PS light diffusion plate can be exhibited.

In one aspect of the present invention, the composite sheet for the light diffusion plate may have a temperature of 320° C. or higher at which 2% weight loss occurs. Specifically, it may be 320 to 350 °C, and more specifically, it may be 325 to 340 °C. It is applicable to a composite sheet for a light diffusion plate within the above range, and is also suitable for application to a composite sheet for a light diffusion plate such as a recent direct-type display in which a high amount of light is used, but is not limited thereto.

In one aspect of the present invention, the composite sheet for the light diffusion plate may have a haze of 85% or more and a light diffusivity (Td) of 45% or more measured according to ASTM D1003. Specifically, it may have a haze of 85 to 88% and a light diffusivity (Td) of 50 to 70%. Although not limited thereto, when a composite sheet for a light diffusion plate satisfying the above range is prepared using the acrylic copolymer of the present invention, even when applied to a direct type display, a lattice mura phenomenon, that is, light It is possible to provide a high-quality composite sheet for a light diffuser plate in which a phenomenon in which light is projected in a circular shape to a site where there is a small amount occurs.

According to one aspect of the present invention, the light diffusion coefficient of the composite sheet for the light diffusion plate may satisfy Equation 3 below.

[Equation 3]

In Equation 3, D1 is the light diffusion coefficient of the composite sheet for the PS light diffusion plate having a thickness of 2.5 mm, and D2 is the light diffusion coefficient of the composite sheet for the light diffusion plate of the present invention.

In the case of a general PS light diffusion plate composite sheet, the light diffusion coefficient is 22.6 based on the light transmittance of 70%. The light diffusion coefficient of the composite sheet for a light diffusion plate according to the present invention is 1.5 times higher than that of the composite sheet for a PS light diffusion plate, so that high heat resistance and excellent optical properties can be exhibited at the same time.

In one aspect of the present invention, a difference between a maximum value and a minimum value of each of the color coordinate values Wx and Wy of the composite sheet for a light diffuser may be 2/100 or less. Specifically, when the color coordinates of 63 outgoing light passing through the composite sheet for light diffuser plate of the present invention are measured using an LED light source and a luminance meter, the value obtained by subtracting the minimum value from the maximum value of the color coordinate Wx value is 2/100 or less, and the color coordinate A value obtained by subtracting the minimum value from the maximum value of the Wy value may be 2/100 or less. The smaller the difference between the maximum and minimum values of the color coordinate values, the better, and the lower limit is not particularly limited. In the above range, the color and brightness of the light source emitted through the composite sheet for a light diffuser of the present invention can be uniformly implemented, and at the same time, a high-brightness composite sheet for a light diffuser can be provided.

According to one embodiment of the present invention, the composite sheet for the light diffusion plate includes the acrylic copolymer and the light diffusion agent. The light diffusing agent includes calcium carbonate particles, barium sulfate particles, titanium oxide particles, aluminum hydroxide particles, silica particles, mica particles, magnesium oxide particles, zinc oxide particles, acrylic crosslinked particles, silicone crosslinked particles, styrenic crosslinked particles, and these It may be selected from the group consisting of mixtures, preferably any one or a mixture of two or more selected from silica particles, styrenic crosslinking particles, acrylic crosslinking particles, titanium oxide particles, etc. Any diffusion agent may be used without limitation.

The average particle diameter of the light diffuser may be 1 to 50 μm, more specifically 1 to 10 μm, but is not particularly limited as long as the optical properties of the composite sheet for light diffuser are not deteriorated.

In addition, the light diffusing agent may have a refractive index difference of 0.01 to 0.2 with the acrylic copolymer. More preferably, it may be 0.01 to 0.15, but it is not particularly limited as long as the optical properties of the composite sheet for light diffusion plates are not deteriorated.

According to one aspect of the present invention, the light diffusing agent may include 0.01 to 10 parts by weight based on 100 parts by weight of the acrylic copolymer. It is preferably 0.1 to 5 parts by weight, but it is not particularly limited as long as the optical properties such as the luminance and light diffusion coefficient are not deteriorated.

The composite sheet for light diffusion according to an embodiment of the present invention may further include additives commonly used in the art according to purposes and uses. For example, an antioxidant, a UV absorber, a UV stabilizer, a lubricant, and the like may be further included. In this case, the additives may be included in an appropriate amount within a range that does not impair the physical properties of the composite sheet for light diffusion.

The UV absorber may be a benzotriazine-based or benzotriazole-based UV absorber, but besides, dibutylhydroxytoluene, nonylphenylphosphite, and dibutylmethylphenol (2-6 -di-tert-butyl-4-methylphenol) or HALS-based UV stabilizers, but the types and contents of these are not particularly limited as long as they do not harm the physical properties of the composite sheet for light diffusion. It is not.

The benzotriazole-based UV absorber, for example, 2-(2'-hydromethylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-bis(α,α-dimethylbenzylphenyl)) Benzotriazole, 2-(2`-hydroxy-3`,5`-dibutylphenyl)benzotriazole, 2-(2`-hydroxy-3`-tert-butyl-5`-methylphenyl)-5 -Chlorobenzotriazole, 2-(2`-hydroxy-3`,5`-di-tert-butylphenyl)-5-chlorobenzotriazole, etc., and the benzotriazine-based UV absorber Examples thereof include bisethylhexyloxyphenol methoxyphenyltriazine and the like, and it is preferable to use BASF's Tinuvin®.

The lubricant serves to improve fluidity and suppress frictional heat during extrusion molding, and may be selected from the group consisting of hydrocarbon-based, carboxylic acid-based, alcohol-based, amide-based, ester-based compounds, and mixtures thereof. The types and contents of these are not particularly limited as long as the physical properties of the composite sheet for light diffusion plates are not impaired, and Henkel's Loxiol G70 can be used preferably.

Another aspect of the present invention provides a molded article manufactured including the composite sheet for a light diffusion plate according to the above aspect. The molded product may be used in industrial fields requiring excellent optical properties and heat resistance, and the industrial fields may include signboards, lighting fixtures, protective covers for automobile turn indicators, and direct-type backlight units for displays.

Another aspect of the present invention is a master batch chip comprising an acrylic copolymer and a light diffusing agent, wherein the acrylic copolymer is (A) an alkyl methacrylic monomer and (B) cyclohexylmaleimide, phenyl A copolymer prepared by including at least two comonomers selected from maleimide, alpha methyl styrene and methyl acrylate, and (C) a dispersion stabilizer prepared by including the following formulas (1) and (2) and alkyl (meth)acrylate-based monomers In master batch chip (Master Batch Chip) is provided.

[Formula 1]

In Formula 1, R ₁ is hydrogen or C1 to C3 alkyl, n is an integer selected from 1 to 3, and M is any one selected from lithium, sodium, potassium, and ammonium salts.

[Formula 2]

In Formula 2, R ₂ is hydrogen or C1 to C3 alkyl, and M is any one selected from lithium, sodium, potassium, and ammonium salts.

In another aspect of the present invention, the master batch chip may further include any one or two or more additives selected from the group consisting of antioxidants, UV absorbers, UV stabilizers, lubricants, and mixtures thereof. Examples of specific compounds of the additives are the same as those described above.

Examples of specific compounds of the light diffusing agent are the same as those described above. The light diffusing agent may include 0.1 to 45 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight of the acrylic copolymer. When a composite sheet for a light diffuser plate is manufactured using the highly concentrated master batch chips in the above range, the uniformity of the distribution and content of the light diffuser and additives can be improved, so that the quality of the final processed product can be improved.

The master batch chip may be included in an amount of 0.5 to 25 parts by weight based on 100 parts by weight of the acrylic copolymer introduced when manufacturing the composite sheet for a light diffusion plate according to the above aspect. Specifically, in the case of using a conventional extruder, 5 to 25 parts by weight may be added, in the case of a single screw extruder with a separate kneading section, 1 to 25 parts by weight, and in the case of a twin screw extruder, it is preferable to add 0.5 to 25 parts by weight. do. The additive content of the finally manufactured composite sheet for light diffusion plates may be determined by adjusting the input amount of the master batch chips.

The present invention will be described in more detail based on the following Examples and Comparative Examples. However, the following Examples and Comparative Examples are only one example for explaining the present invention in more detail, and the present invention is not limited by the following Examples and Comparative Examples.

<Method of measuring physical properties>

1) Temperature at which 2% weight loss occurs (2% Td)

The temperature at which 2% weight loss occurs was measured in the range of 25 to 250 °C at a rate of 10 °C/min for the light diffuser plate specimens prepared in Examples and Comparative Examples using a thermal gravimetric analysis (ThermalGravimetric Analysis).

2) Glass transition temperature (Tg)

The beads prepared in Examples and Comparative Examples were measured in the range of 25 to 250 ℃ at a rate of 5 ℃ / min using a DSC (Differential scanning calorimeter, TA DSC 2010) machine.

3) Light Transmission (LT) and Yellow Index (YI)

After extruding the beads prepared in Examples and Comparative Examples, the light transmittance and yellowness were measured according to ASTM D1003 after injection molding to a thickness of 3.0 mm, respectively. In addition, the light transmittance of the light diffusion plate specimens prepared in Examples and Comparative Examples was measured according to ASTM D1003.

4) Haze and light diffusivity

The light diffuser plate specimens prepared in Examples and Comparative Examples were measured according to ISO 14782 using a haze transmittance meter (HR-100, Murakami Color Research Laboratory).

5) Diffusion factor

The scattering light distribution was measured in all directions (-90 to +90 degrees) using a goniophotometer (Goniophotometer, GP-5, Murakami Color Research Laboratory) for the light diffuser plate specimens prepared in Examples and Comparative Examples, and as follows The light diffusion coefficient was calculated.

D: light diffusion coefficient

I(n): measured value of scattered light in n degrees (luminous intensity)

6) Luminance and color coordinates

Using a luminance measuring device (HS-1000, AT system) using a reflective film on the bottom surface and an edge-type LED light source for the light diffuser plate specimens prepared in Examples and Comparative Examples, the average value of the luminance of the emitted light and the average value of the color coordinates were measured. measured.

<Manufacture of dispersion stabilizer>

[Production Example 1]

In a three-necked flask with a condenser, 24.2 g of methyl methacrylate and 15.9 g of potassium hydroxide (KOH, purity 85%) were put together with 2,000 g of water and reacted at room temperature in a nitrogen atmosphere for 1 hour. 180 g of 2-sulfoethyl methacrylate potassium salt and 700 g of water were further added thereto, 45 g of methyl methacrylate, 2,2'-azobis (2-amidinopropane) dihydrochloride (2,2'-Azobis 0.3 g of (2-amidinopropane) dihydrochloride) was added and polymerization was started at 50°C. When the reaction temperature reached 60 ° C., 4.5 g of methyl methacrylate monomer was added in 6 separate portions at intervals of 6 minutes from 15 minutes onwards. After reacting at the same temperature for a total of 6 hours, it was cooled to obtain a 5 wt % polymer aqueous solution.

[Example 1]

3000 g of distilled water, 3 g of the dispersion stabilizer of Preparation Example 1, and 10 g of sodium sulfate as a dispersion aid were added to a 5 liter reactor and dissolved. 6 g of n-octylmer captan as a chain transfer agent and 1.5 g of benzoyl peroxide as an initiator were added to 1,500 g of a monomer mixture in which 1440 g of methyl methacrylate (MMA), 45 g of cyclohexyl maleimide (CHMI), and 15 g of alpha methyl styrene (AMS) were mixed. After dissolution, it was introduced into a reactor and dispersed in an aqueous phase while stirring at 500 rpm to prepare a suspension. The mixture was polymerized at 80 °C for 1 hour and 20 minutes, heated to 110 °C, further polymerized for 30 minutes, and then cooled to 30 °C. The beads obtained by the polymerization reaction were repeatedly washed with distilled water and dehydrated, and then dried to prepare an acrylic copolymer. The prepared acrylic copolymer has a glass transition temperature of 122° C., a light transmittance of 92.2%, and a yellowness of 0.78.

Based on 100 parts by weight of the acrylic copolymer, 0.7 parts by weight of crosslinked polystyrene particles (Sekisui, SBX-4) having an average particle diameter of 4 μm and a refractive index of 1.59 as a diffusion agent and 0.01 parts by weight of TiO ₂ , a HALS-based UV stabilizer as a UV stabilizer ( Ciba specialty chemicals, Tinuvin 770) 0.1 part by weight, 0.05 part by weight of a benzotriazole-based UV absorber (BASF, Tinuvin®) as a UV absorber, and 0.05 part by weight of pentaerythritol adipate stearate (Henkel, Loxiol G70) as a lubricant Tumbler After mixing using an extruder to obtain pellets, and after sufficiently drying the pellets, a light diffuser plate specimen having a light transmittance of 70% in the form of a sheet having a width, length, and thickness of 70 mm x 75 mm x 2.5 mm was prepared using an extruder. Physical properties were measured and are shown in Table 1 below.

[Example 2]

3000 g of distilled water, 3 g of the dispersion stabilizer of Preparation Example 1, and 10 g of sodium sulfate as a dispersion aid were added to a 5 liter reactor and dissolved. 3 g of n-octylmercaptan as a chain transfer agent in 1,500 g of a monomer mixture in which 1350 g of methyl methacrylate (MMA), 105 g of phenylmaleimide (PMI), 30 g of alpha methyl styrene (AMS), and 15 g of methyl acrylate (MA) were mixed, After dissolving 1.5 g of benzoyl peroxide as an initiator, it was introduced into a reactor and dispersed in an aqueous phase while stirring at 500 rpm to prepare a suspension. The mixture was polymerized at 80 °C for 1 hour and 20 minutes, heated to 110 °C, further polymerized for 30 minutes, and then cooled to 30 °C. The beads obtained by the polymerization reaction were repeatedly washed and dehydrated with distilled water, and then dried to prepare an acrylic copolymer. The glass transition temperature of the prepared acrylic copolymer is 127 ° C, light transmittance is 91.0%, and yellowness is 0.8.

The acrylic copolymer was processed in the same manner as in Example 1 to prepare a light diffuser plate specimen having a light transmittance of 70% in the form of a sheet having width, length, and thickness of 70 mm x 75 mm x 2.5 mm. Physical properties were measured and are shown in Table 1 below.

[Comparative Example 1]

It was prepared in the same manner as in Example 1 except that 200 ppm of polyvinyl alcohol (NIPPON GOHSEI, KH-17) as a dispersing agent and 1.58% by weight of boric acid compared to PVA were used as a dispersing aid. The prepared acrylic copolymer has a glass transition temperature of 119°C, light transmittance of 85.0% and yellowness of 3.4.

The acrylic copolymer was processed in the same manner as in Example 1 to prepare a light diffuser plate specimen having a light transmittance of 70% in the form of a sheet having width, length, and thickness of 70 mm x 75 mm x 2.5 mm. Physical properties were measured and are shown in Table 1 below.

[Comparative Example 2]

Except for using a polystyrene product (Hyundai EP Co., Ltd., Solarene® G116) having a glass transition temperature of 100°C instead of the acrylic copolymer, a sheet having a width, length, and thickness of 70 mm x 75 mm x 2.5 mm was processed in the same manner as in Example 1. A light diffuser plate specimen having a light transmittance of 70% was prepared. Physical properties were measured and are shown in Table 1 below.

[Comparative Example 3]

Except for using a polymethyl methacrylate product (LG MMA, IH830L) having a glass transition temperature of 110 ° C instead of the acrylic copolymer, it was processed in the same manner as in Example 1 to obtain a width, length and thickness of 70 mm x 75 mm x 2.5 mm. A light diffuser plate specimen having a light transmittance of 70% in the form of a sheet was prepared. Physical properties were measured and are shown in Table 1 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tg (℃) 122 127 119 100 110 2% Td (℃) 331 326 322 137 311 Haze (%) 85.8 85.9 66.4 60.9 85.8 Light diffusivity (%) 61.6 62.0 50.2 42.9 61.2 Luminance (cd) 3432 3471 2866 3116 3369 color coordinates Wx 0.2969 0.2997 0.2890 0.2873 0.2964 Wy 0.3012 0.3058 0.2993 0.2918 0.3003

MMA: methyl methacrylate

CHMI: cyclohexyl maleimide

PMI: phenyl maleimide

MA: methylacrylate

AMS: Alpha Methyl Styrene (α-Methyl Styrene)

PVA: polyvinylalcohol

As shown in Table 1, Examples 1 and 2 had a light transmittance of 90% or more and a yellowness of 1 or less, whereas Comparative Example 1 did not satisfy this. Therefore, it was confirmed that even if a monomer having a cyclic structure vulnerable to color change was used, an acrylic copolymer having excellent light transmittance and low yellowness could be obtained by using the dispersion stabilizer of Preparation Example 1 and properly adjusting the content.

Comparing Example 1 and Comparative Example 1 in Table 1, when the composite sheet for a light diffuser plate is manufactured using the high heat-resistant acrylic copolymer of the present invention, haze, light diffusion The surprising effect of the present invention was confirmed by confirming that optical properties such as degree, luminance and color coordinates were similar or better, and heat resistance was superior.

In Table 1, it was confirmed that the luminance of Examples 1 and 2 increased by 10% or more compared to the luminance of Comparative Example 2 using a general polystyrene product, and in the case of the light diffusion coefficient, Example 1 was 35.4 and Example 2 was 34.6. Comparative Example 2 was measured as 22.6, and it was confirmed that Examples 1 and 2 had a light diffusion coefficient 1.5 times or more superior to Comparative Example 2 using general polystyrene products. In addition, when the composite sheet for a light diffuser according to the present invention uses the composite sheet for a light diffuser according to the present invention, when the difference between the maximum and minimum values of each color coordinate value Wx and Wy is 2/100 or less, color and luminance can be evenly expressed. confirmed that there is.

Therefore, it was confirmed that Examples 1 and 2 satisfy both excellent heat resistance and optical characteristics, which can withstand the increasingly higher intensity and temperature of the light source, thereby suppressing phenomena such as warping or yellowing. In addition, it is very suitable for application to signboards with high heat generation, lighting fixtures, protective covers for car turn indicators, and direct backlight units for large displays.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and it will be said that not only the claims to be described later, but also all modifications equivalent or equivalent to these claims belong to the scope of the present invention. .

Claims (13)

A composite sheet for a light diffusion plate comprising an acrylic copolymer and a light diffusion agent,
The acrylic copolymer is (A) an alkyl methacrylic monomer, (B) any one of cyclohexyl maleimide or phenyl maleimide, any one or more comonomers selected from alpha methyl styrene and methyl acrylate, and (C) the following It is a copolymer prepared by including a dispersion stabilizer prepared by including Formula 1, Formula 2 and alkyl (meth)acrylate-based monomers,
The composite sheet for a light diffusion plate has a glass transition temperature of 120 ° C. or more, and has a luminance satisfying the following formula 1.
[Formula 1]

In Formula 1, R ₁ is hydrogen or C1 to C3 alkyl, n is an integer selected from 1 to 3, and M is any one selected from lithium, sodium, potassium and ammonium salts.
[Formula 2]

In Formula 2, R ₂ is hydrogen or C1 to C3 alkyl, and M is any one selected from lithium, sodium, potassium, and ammonium salts.
[Equation 1]

In Equation 1, L1 is the luminance of the composite sheet for a PS light diffusion plate having a thickness of 2.5 mm, and L2 is the luminance of the composite sheet for a light diffusion plate of the present invention. According to claim 1,
The acrylic copolymer has a light transmittance of 90% or more and a yellowness of 1.0 or less as measured according to ASTM D1003. According to claim 1,
The acrylic copolymer comprises 1 to 20 parts by weight of a comonomer based on 100 parts by weight of the acrylic monomer. According to claim 1,
The acrylic copolymer comprises 0.001 to 10 parts by weight of a dispersion stabilizer based on 100 parts by weight of the acrylic monomer. According to claim 1,
The composite sheet for a light diffusion plate has a temperature of 320 ° C. or higher at which a 2% weight loss occurs. According to claim 1,
The composite sheet for a light diffusion plate has a haze of 85% or more and a light diffusivity (Td) of 45% or more measured according to ASTM D1003. According to claim 1,
The composite sheet for a light diffusion plate has a light diffusion coefficient satisfying Equation 3 below.
[Equation 3]

In Equation 3, D1 is the light diffusion coefficient of the composite sheet for the PS light diffusion plate having a thickness of 2.5 mm, and D2 is the light diffusion coefficient of the composite sheet for the light diffusion plate of the present invention. According to claim 1,
A composite sheet for a light diffuser, wherein a difference between the maximum and minimum values of the color coordinate values Wx and Wy of the composite sheet for a light diffuser is 2/100 or less. According to claim 1,
The composite sheet for a light diffusion plate includes 0.01 to 10 parts by weight of a light diffusion agent based on 100 parts by weight of the acrylic copolymer. According to claim 1,
The composite sheet for a light diffusion plate further comprises any one or two or more additives selected from the group consisting of antioxidants, UV absorbers, UV stabilizers, lubricants, and mixtures thereof. A molded product manufactured by including the composite sheet for light diffusion plate according to any one of claims 1 to 10. As a master batch chip containing an acrylic copolymer and a light diffusing agent,
The acrylic copolymer is (A) an alkyl methacrylic monomer, (B) any one of cyclohexyl maleimide or phenyl maleimide, any one or more comonomers selected from alpha methyl styrene and methyl acrylate, and (C) the following A master batch chip that is a copolymer prepared by including Chemical Formulas 1 and 2 and alkyl (meth)acrylate-based monomers.
[Formula 1]

In Formula 1, R ₁ is hydrogen or C1 to C3 alkyl, n is an integer selected from 1 to 3, and M is any one selected from lithium, sodium, potassium and ammonium salts.
[Formula 2]

In Formula 2, R ₂ is hydrogen or C1 to C3 alkyl, and M is any one selected from lithium, sodium, potassium, and ammonium salts. According to claim 12,
The master batch chip further comprises any one or two or more additives selected from the group consisting of antioxidants, UV absorbers, UV stabilizers, lubricants, and mixtures thereof.