KR100762884B1 - Styrenic Resin and Light Diffusing Sheet Produced Thereby - Google Patents

Abstract

The present invention relates to a styrene resin having a branched structure prepared by continuous polymerization of a mixture composed of 100 parts by weight of a styrene monomer and 0.001 to 0.1 parts by weight of a polyfunctional initiator, and having a weight average molecular weight of 200,000 to 500,000. The styrene polymer prepared by the present invention has excellent fluidity and shows a slope of 0.5 or less when the absolute molecular weight and the molecular rotation radius are calculated in a graph.

Styrene polymer, continuous polymerization, multifunctional initiator, branch structure, light diffusion plate

Description

Styrene Resin and Light Diffusing Sheet Produced Thereby

Field of invention

The present invention relates to a styrene resin. More specifically, the present invention relates to a branched styrene resin prepared by introducing an appropriate amount of a multifunctional initiator into a styrene monomer mixture and having a high molecular weight and excellent fluidity.

Background of the Invention

In general, styrene resins, in particular styrene polymers (polystyrenes), are known to have excellent steric stability and sufficient stiffness and high transmittance. In addition, it is used as a variety of molded products because of the low cost. For example, it is applied to food containers, electrical appliances, etc. However, the styrene polymer has a problem of inferior strength compared to other transparent resins (styrene-acrylonitrile copolymer, styrene-methyl methacrylate copolymer, etc.).

In order to improve strength, there is a method of increasing the molecular weight of the polymer. However, since the fluidity deteriorates when molecular weight is high, it is the most to add the plasticizer for increasing fluidity. Adding a plasticizer improves fluidity but lowers heat resistance.

In general, the flow characteristics of the resin are closely related to the chemical structure of the resin, and it is known that, for an olefin resin such as polyolefin, the flow characteristics are improved as compared with the case where the resin structure is a branched structure.

Therefore, several methods have been proposed to exploit the advantages of this branching structure.

US Pat. No. 6,573,349 describes a method for preparing a high molecular weight styrene resin by introducing furfuryl acrylate, and US Pat. No. 4,918,159 uses a multifunctional mercaptan to prepare a styrene resin. The method is presented. However, when suspension polymerization is carried out using a polyfunctional mercaptan, the reactivity is low, and the dispersion system becomes unstable as the polymerization reaction proceeds.

US Patent No. 5,059,667 proposes a method for preparing a resin suitable for injection molding using a polyfunctional monomer, divinylbenzene. However, divinylbenzene may be useful for suspension polymerization, but in the case of continuous polymerization, it generates gels and is not suitable for continuous production ("Modern Styrenic Polymer", John scheirs and Duane Priddy, 2003, 559-560).

Recently, resin plates having light diffusing properties have been widely used in lighting covers, light diffusion plates of LCD panels, lighting signs, and the like. In general, in the case of the LCD panel light diffusion plate methacryl-based resin is used a lot, there is a problem having hygroscopicity in the nature of the molecular structure. This hygroscopic property acts as a major cause of deterioration of the bending property of the diffusion plate. Moreover, methacryl-type resin is inferior in workability compared with styrene resin.

Therefore, in consideration of cost competitiveness and warpage characteristics, a light diffusion plate may be manufactured using a styrene polymer. However, it is true that conventional styrene polymers lack mechanical properties such as strength. In addition, it is essential that the styrene polymer prepared through continuous polymerization have a high molecular weight in order to be applied to the light diffusion plate.

Accordingly, in order to solve the above problems, the present inventors have developed a styrene resin having sufficient mechanical properties and suitable fluidity by preparing a branched styrene polymer using a multifunctional initiator.

An object of the present invention is to provide a styrene resin having a high molecular weight and excellent fluidity.

Another object of the present invention is to provide a styrene resin suitable for the production of a light diffusion plate.

The above and other objects of the present invention can be achieved by the present invention described below.

Summary of the Invention

The present invention relates to a styrene resin having a branched structure prepared by continuous polymerization of a mixture composed of 100 parts by weight of a styrene monomer and 0.001 to 0.1 parts by weight of a polyfunctional initiator, and having a weight average molecular weight of 200,000 to 500,000. The styrene polymer prepared by the present invention has excellent fluidity and shows a slope of 0.5 or less when the absolute molecular weight and the molecular rotation radius are calculated in a graph.

Hereinafter, specific contents of the present invention will be described in detail below.

Detailed Description of the Invention

In the present invention, the multifunctional initiator used to form the branched structure is preferably used in an amount of 0.001 parts by weight or more and 0.1 parts by weight or less with respect to 100 parts by weight of the styrene monomer, and more preferably 0.01 to 0.05 parts by weight. If it is less than 0.001, it is difficult to obtain a desired branching structure. If it is more than 0.1 part by weight, the gel content of the polymer increases, making it difficult to control the reaction.

 In the present invention, the styrene monomer is not particularly limited, but styrene, o-, m-, p-methyl styrene, α-methyl styrene, o-, m-, p-ethyl styrene, or the like may be used.

Multifunctional initiators that can be used in the present invention are useful for bi-functional and 4-functional peroxides. In particular, in order to obtain a high molecular weight polymer, a cyclic perketals type initiator is suitable. More specifically, as the 2-functional peroxide, 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-hexylperoxy) cyclohexane and 1,1-bis (t-butylperoxy) -2-methylcyclohexane are suitable and 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, n-butyl 4,4-bis (t-butylperoxy) valerate and the like can also be applied. As the 4-functional peroxide, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane is suitable. Four-functional initiators may be somewhat advantageous for preparing high molecular weights. In the present invention, the multifunctional initiator may be used alone or in combination of two or more of the above compounds.

In the present invention, in addition to the polymerization initiator described above, lubricants, ultraviolet absorbers, heat stabilizers, dyes, pigments and the like may be added as necessary. The additive may be added during the polymerization process and the method is not particularly limited.

In this invention, superposition | polymerization temperature can apply a known temperature condition. In general, in the case of continuous polymerization containing styrene as a main component, it is appropriate to carry out the polymerization while stirring to maintain a constant temperature in the range of 100 to 150 ° C, and the same also in the present invention.

The reactor used in the present invention is not particularly limited, but is preferably equipped with a double helical type stirrer to allow sufficient mixing throughout the reactor.

The styrene polymer of the present invention preferably has a weight average molecular weight (M _w ) in the range of 200,000 to 500,000. If it exceeds 500,000, the gel content increases and the solution viscosity increases, making process control difficult. If it is less than 200,000, the mechanical properties required for the light diffuser plate is less than the limit of the application.

The invention will be further elucidated by the following examples which are set forth for the purpose of illustrating the invention and are not intended to limit the protection scope of the invention.

Example

Example  One

100 parts by weight of the styrene monomer and 0.03 parts by weight of 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane were mixed well to make it completely homogeneous, and then continuously transferred to the reactor. The residence time in the entire reactor was maintained for about 3 hours, the polymerization temperature was maintained at 120 ℃, 65% conversion. The reaction mixture containing the unreacted material was transferred to a devolatilization process to recover unreacted monomers. The unreacted styrene monomer of the final polymer was 2,300 ppm and the weight average molecular weight (Mw) was 380,000.

Example  2

The same procedure as in Example 1 was carried out except that 0.03 parts by weight of 1,1-bis (t-butylperoxy) cyclohexane was added as the polyfunctional initiator. The unreacted styrene monomer of the final polymer was 2,100 ppm and the weight average molecular weight was 336,000.

Comparative Example  One

Except that 0.03 parts by weight of benzoyl peroxide as an initiator was carried out in the same manner as in Example 1. The unreacted styrene monomer of the polymer was 2,800 ppm and the weight average molecular weight was 183,000.

Comparative Example  2

The same process as in Example 1 was carried out except that thermal polymerization was performed without adding an initiator. The unreacted styrene monomer of the polymer was 3,200 ppm and the weight average molecular weight was 237,000.

Comparative Example  3

The same procedure as in Example 1 was carried out except that 0.20 part by weight of 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane was added. In this case, a viscosity increase rapidly occurred, and a resin could not be manufactured.
Comparative Example 4
The same procedure as in Example 1 was carried out except that 0.05 part by weight of 1,1-bis (t-butylperoxy) cyclohexane was added as the polyfunctional initiator. The unreacted styrene monomer of the polymer was 1,900 ppm and the weight average molecular weight was 341,000.

Property evaluation method

(1) Molecular weight: Measured using GPC (Gel Permeation Chromatography).

(2) Unreacted monomer: measured by gas chromatography.

(3) Gradient: GPC-Multi Angle Laser Light Scattering was analyzed and the result was measured.

(4) Oligomer: Measured by analysis by gas chromatography.

(5) VST (Vicat softening temperature): It measured based on ASTMD-1525 and 5 kg conditions.

(6) Flexural strength: measured according to ASTM D-790, 2.8 min / min, 23 ℃ conditions.

Comparative Example 3: fail due to viscosity increase.

Referring to Table 1, it can be observed that in Examples 1 and 2, due to the addition of the multifunctional initiator of the present invention, the weight average molecular weight (M _w ) of the styrene polymer is high, and the concentration of the unreacted styrene monomer is relatively low. In addition, when the absolute molecular weight and the molecular rotation radius are calculated in a graph, the slope is less than 0.5.

On the other hand, in Comparative Example 1 in which benzoyl peroxide was added as an initiator and in Comparative Example 2 without an initiator, the weight average molecular weight (M _w ) of the styrene polymer was relatively low, and the concentration of the unreacted styrene monomer was increased. Can be observed. In Comparative Example 3, the resin could not be prepared due to the rapid viscosity increase due to the excessive addition of the 4-functional initiator.

Manufacture of Light Diffusion Plate

First resin composition

100 parts by weight of the styrene polymer prepared in each example was prepared using acrylic cross-linked particles (Ganz, GM-0806S) and polymethylsilsesquioxane-based organosilica particles (GE-TOSHIBA, TOSPEARL) having an average particle diameter of 6 μm. 5 parts by weight was added by mixing in a weight ratio of.

Second resin composition

5 parts by weight of 8 μm acrylic crosslinked particles (GE-TOSHIBA, TOSPEARL) were added to 100 parts by weight of the styrene polymer prepared in each example.

Light diffusion plate  Produce

In order to laminate | stack the application layer which consists of a 2nd resin composition on both surfaces of the base material layer which consists of a 1st resin composition, the said 1st resin composition was prepared into one extruder, and the 2nd resin composition was put into two extruders, respectively. And melted and kneaded to form a laminate having a three-layer structure.

The light transmittance and the light scattering properties of the manufactured laminates were measured with a haze meter (Σ80, manufactured by Japan Electronics Corporation) and the results are shown in Table 2 below.

표 2의 광학적 특성과 표 1의 기계적 물성을 고려할 때, 스티렌 중합체의 중량평균분자량(M_w)이 200,000 이상 400,000 미만의 범위를 갖는 실시예 1 내지 2의 경우가 광확산판에 요구되는 기계적 물성과 광학적 물성을 동시에 충족시키는 것을 관찰할 수 있다.

Considering the optical properties in Table 2 and the mechanical properties in Table 1, the examples 1 to 2 in which the weight average molecular weight (M _w ) of the styrene polymer ranges from 200,000 to less than 400,000 are required for the light diffusion plate. It can be observed that at the same time meets the optical properties.

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The present invention has an effect of providing a styrene resin having excellent mechanical properties by introducing a suitable amount of a multifunctional initiator in the styrene polymer manufacturing process to have a high molecular weight and a branched structure.

Simple modifications and variations of the present invention can be readily used by those skilled in the art, and all such variations or modifications can be considered to be included within the scope of the present invention.

Claims (3)

A styrene resin for light-diffusion plates prepared by continuous polymerization of a mixture of 100 parts by weight of a styrene monomer and 0.001 to 0.03 parts by weight of a multifunctional initiator, having a weight average molecular weight of 200,000 or more and less than 400,000. The method of claim 1, wherein the multifunctional initiator is 1,1-bis (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1 , 1-bis (t-hexylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -2-methylcyclohexane, 1,1-bis (t-hexylperoxy) -3,3, 5-trimethylcyclohexane, n-butyl 4,4-bis (t-butylperoxy) valerate, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane and mixtures thereof Styrene-based resin selected from the group consisting of. A light diffusing plate manufactured by using the styrene resin according to any one of claims 1 and 2.