JPH08244179A - Transparent rubber modified styrene resin sheet - Google Patents

Abstract

PURPOSE: To provide a sheet which performs practical strength such as more excellent impact resistance than that of a graft copolymerization type transparent HIPS sheet. CONSTITUTION: A sheet made of a material in which b-SBR having 0.02 or less of the difference of refractive indexes from a graft copolymerization type transparent HIPS is blended with the HIPS is used as an intermediate layer and sheets or film layers made of graft polymerization type transparent HIPS are laminated on both side surfaces of the intermediate layer. Thus, the intermediate layer shares the mechanical strength of the sheet, and the surface layers share the functions of the gloss and the smoothness of the sheet. In this manner, the transparency and the surface smoothness are maintained, and simultaneously the practical strength physical properties such as impact resistance can be simply improved.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a transparent packaging material for food and drink,
The present invention relates to a transparent rubber-modified styrene-based resin sheet that can be widely used in containers and the like, and molded products thereof.

[0002]

2. Description of the Related Art Transparent rubber-modified styrene resin (hereinafter referred to as H
IPS) is a blend type transparent HI of styrene / butadiene / block copolymer rubber (hereinafter referred to as b-SBR) and a styrene resin, or a blend type transparent HI of a styrene / butadiene / block copolymer resin and a styrene resin.
It is roughly classified into a graft-copolymerization type transparent HIPS obtained by graft-copolymerizing PS, a styrene-based monomer, and a (meth) acrylic acid alkyl ester in the presence of a rubbery polymer.

Of these, blend type transparent HIPS is a mixed material of 2 to 4 kinds of various styrene polymers.
Even if the mixing ratio is slightly changed, the transparency of the obtained sheet itself does not change much. In addition, the sheet obtained by using the blended transparent HIPS and the heat-molded product thereof have good surface smoothness and excellent transparency. Also blend type transparent HI
In the case of PS, the content ratio of the rubber component is as wide as about 5 to 20%, and the demand for physical strength can be met by a combination of various kinds of materials, so that the range of use is wide. However, the blended transparent HIPS has a drawback that the physical properties such as tensile strength and tensile elastic modulus in the sheet extrusion direction (MD direction) and the direction perpendicular to the sheet direction (TD direction) are poor.

On the other hand, the graft copolymer type transparent HIPS developed in recent years has improved the drawbacks of the blend type transparent HIPS, and when it is used as a sheet product, it has a balanced physical property as compared with other materials. Demand for food packaging containers and various trays is expected (Chemical Economy 1994.
March issue P. 68-74). There is also known a laminate having excellent oil resistance in which a first layer mainly composed of such a graft copolymerization type HIPS and a second layer mainly composed of a resin other than the graft copolymerization type HIPS are laminated (Japanese Patent Application Laid-Open No. Hei 10 (1999) -242242). 6-182
948). Such a graft copolymer type transparent HI
Although PS has just been developed in recent years and there are few grades on the market and the material is not easily available, the details are unknown, but the content of the rubber component is usually about 5 to 10 wt%.
Probably because of this, the sheet or thermoformed product obtained by processing the graft copolymer type transparent HIPS may lack practical strength. As a countermeasure in this case, it is conceivable to increase the thickness of the sheet or increase the addition rate of the raw material rubber component at the time of polymerization, but the former is limited in its effectiveness in improving impact resistance and the latter is There is a drawback in that the number of grades increases as well as process restrictions.

Also, this graft copolymer type transparent HIPS
Realizes transparency by matching the refractive indices of the rubber component of the dispersed phase and the styrene-based polymer of the continuous phase. Therefore, even if a small amount of other resin is mixed in the graft copolymer type transparent HIPS, Cloudy often occurs. For example, as the simplest means for improving impact resistance, a graft copolymer type transparent HI
A method of adding a rubber component as a second component to PS is conceivable, but the resulting sheet becomes milky white, or due to an increase in the compounding ratio of the rubber component, the surface smoothness of the processed sheet suddenly deteriorates and becomes a frosted glass. However, there is a drawback that the apparent transparency is lowered.

In order to improve the surface smoothness, a means for strongly press-bonding the sheet with a cooling roll at the time of manufacturing the sheet to improve the smoothness of the sheet surface is also generally used. This method has drawbacks such as a limit in terms of rigidity of the chill roll and the resulting sheet having a matt finish at the heating stage during thermoforming.

[0007]

Therefore, in the present invention, there is provided a graft copolymer type transparent HIPS sheet which retains the original excellent transparency and surface smoothness, and exhibits more excellent practical strength such as impact resistance. An object of the present invention is to provide a transparent rubber-modified styrene resin sheet which can be easily and widely selected and a molded product thereof.

[0008]

Means for Solving the Problems The present inventors have completed the present invention as a result of various studies on a method for improving impact resistance and a method for improving surface smoothness of a graft copolymer type transparent HIPS. That is, the present invention provides a styrene / butadiene / block copolymer type rubbery polymer (b-SBR) having a difference in refractive index of 0.02 or less with a graft copolymer type transparent rubber-modified styrene resin. A sheet made of a blended material is used as an intermediate layer, and a sheet or a film layer made of a graft copolymer type transparent rubber-modified styrene resin not blended with b-SBR is laminated on both surfaces thereof. It is a transparent rubber-modified styrene resin sheet.

Hereinafter, the present invention will be described in detail. The graft copolymer type transparent rubber-modified styrene-based resin in the present invention means one or two of a styrene-based monomer and a (meth) acrylic acid alkyl ester in the presence type of a rubbery polymer such as polybutadiene or styrene-butadiene. It is obtained by graft copolymerization as an essential component. This graft copolymer resin has a structure which usually comprises a rubber component forming a dispersion layer, a styrene copolymer forming a continuous layer, and a graft copolymer at the interface thereof, and forms a dispersion layer. It is important in terms of transparency and surface smoothness that the average particle size of the rubber component is usually 1 μm or less, preferably 0.1 to 0.6 μm.

Here, as the styrene-based monomer, styrene, α-methylstyrene, ο-methylstyrene, р-
Methyl styrene, ethyl styrene, isoburu styrene, etc. are mentioned, but styrene is preferable among them. In the present invention, acrylonitrile copolymerizable with other styrenic monomers, vinyl cyanides such as methacrylonitrile, unsaturated carboxylic acids such as (meth) acrylic acid, maleimides, etc. are converted into styrenic monomers within a range not impairing transparency. It can be blended. Examples of (meth) acrylic acid alkyl ester to be added as an essential component include methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate,
Examples thereof include acrylic acid-n-butyl, acrylic acid-iso-butyl, and 2-ethylhexyl acrylate.

These can be copolymerized with the styrenic monomer alone or in combination of two or more kinds. In particular, a combination of a ternary system of a styrene monomer, methyl methacrylate and -n-butyl acrylate is preferable. As the rubber-like polymer, polybutadiene rubber, styrene-butadiene copolymer rubber, etc. can be used. Graft copolymerization type transparent rubber-modified styrenic resin is a rubber-like polymer, a styrene-based monomer, and one or two kinds of (meth) acrylic acid alkyl ester, which are appropriately heat-polymerized or the presence of an organic peroxide catalyst. Under the bulk polymerization method,
It can be obtained by graft copolymerization by a solution polymerization method or the like.

In the present invention, in order to exert the superior impact resistance of such a graft copolymer type transparent rubber-modified styrene resin, a styrene / butadiene / block copolymer type having a difference in refractive index of 0.02 or less. Rubbery polymer (b-
SBR) is blended. When the difference in refractive index is 0.02 or more, the intermediate layer becomes milky white and the transparency is significantly reduced. The rubbery polymer (b-SBR) blended in this case preferably has a styrene content of 30 to 50 wt%. The blending amount of b-SBR is not particularly limited because the two have a refractive index close to each other and do not deteriorate transparency. However, if the blending amount is too large, the surface smoothness of the sheet as the intermediate layer will be hindered.
-The compounding ratio of SBR is 30 Wt% or less, preferably 1 to 15 Wt
It is within the range of%.

As a method for producing a single-layer sheet made of a material for the intermediate layer containing b-SBR, a usual T-die method can be used. The thickness of the sheet of the intermediate layer is not particularly limited, but it is sufficient if it can be used for vacuum forming, pressure forming and the like as a laminate with the front and back double-sided layers, from the viewpoint of 0.2 to 1.0 mm. Is preferred. It should be noted that since only a single-layer sheet made of an intermediate layer material containing b-SBR having a difference in refractive index of 0.02 or less as used in the present invention is frosted glass-like and has poor apparent transparency, it is used as it is. Can not. Therefore, in the present invention, such a drawback is solved by laminating the surface layer of the film or sheet of the graft copolymerization type transparent HIPS which does not contain the above-mentioned b-SBR on both surfaces of such a single layer sheet. .

In this case, as a method for producing a film or sheet, there are a T-die method, an inflation method and the like, and the thickness of these sheet films is 0.01 to 0.2 mm.
It is preferably within the range. That is, in the present invention, the intermediate layer shares the mechanical strength of the sheet, and the surface layer shares the functions of gloss and smoothness of the sheet. The method for obtaining the sheet laminate is not particularly limited, for example, a method of thermocompression bonding an intermediate layer sheet and a sheet or film to be a surface layer with an ordinary heating roll without an adhesive, on the intermediate layer sheet surface. Examples thereof include a method of extruding and laminating the surface layer and a method of coextruding the intermediate layer sheet and the surface layer. Particularly preferred is the coextrusion method or the extrusion laminating method. In the present invention, the thickness of the surface layer may be smaller than that of the intermediate layer, but the thickness and / or the thickness ratio of each of the intermediate layer and the surface layer is not particularly limited.

[0015]

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In addition, each physical property measurement was calculated | required by the following method.・ Refractive index JIS K7105 ・ Total light transmittance JIS K7105 ・ Haze value JIS K7105 ・ Falling weight impact strength 50 according to JIS K7211
%% breaking energy is measured Diameter of tip of weight = 38 mm-Rubber content rate Measured by adding bromine to double bond. Measured by WIJS method.

Example 1 95 parts of graft copolymer type transparent HIPS (rubber content 7.3 Wt%) having a refractive index of 1.543 and 5 parts of b-SBR having a styrene content of 40 Wt% and a refractive index of 1.550 are blended. A sheet having a thickness of 0.5 mm obtained from the above material as an intermediate layer,
A three-layer sheet having a 0.05 mm thick sheet obtained from the graft copolymerization type transparent HIPS = 100% as a surface layer was produced by a coextrusion method. Table 1 shows the measurement results of physical properties of the obtained laminated sheet. Further, this laminated sheet was excellent in impact resistance without being matt during the heating step during thermoforming, and had good surface smoothness and transparency.

Example 2 The same graft copolymer type transparent HIPS 90 as in Example 1
Parts, styrene-butadiene with a styrene content of 40 Wt%
Table 1 shows the measurement results of the same physical properties of the same laminated sheet as in Example 1 except that the blend material was changed to 10 parts of the block copolymer. Also, this laminated sheet has excellent impact resistance without glossing during the heating step during thermoforming,
Both surface smoothness and transparency were good.

Comparative Example 1 The same graft copolymer type transparent HIPS 95 as in Example 1
Parts, styrene-butadiene with a styrene content of 40 Wt%
Using a material consisting of 5 parts of block copolymer, wall thickness =
A 0.6 mm single layer sheet was produced. The obtained sheet was superior in impact resistance to the sheet of Example 1, but had poor surface smoothness, was frosted glass-like, and had apparently low transparency. Table 1 shows the measurement results of each physical property value.

Comparative Example 2 A single-layer sheet having a wall thickness of 0.6 mm was produced using only the graft copolymer type transparent HIPS used in Example 1. The obtained sheet had good surface smoothness and good transparency, but the impact resistance was extremely low. Table 1 shows the measurement results of each physical property value.

Comparative Example 3 Graft copolymerization type transparent HIPS 9 having a refractive index of 1.543
A single layer sheet having a wall thickness of 0.6 mm was produced by using a material composed of 5 parts and 5 parts of a styrene-butadiene block copolymer having a styrene content of 75 wt% and a refractive index of 1.573. The resulting sheet had an impact resistance equivalent to that of the sheet of Example 1, but the transparency was obviously low. Table 1 shows the measurement results of each physical property value.

Comparative Example 4 Graft copolymerization type transparent HIPS 9 having a refractive index of 1.543
A material consisting of 5 parts and 5 parts of GPPS having a refractive index of 1.590 was used to produce a single-layer sheet having a wall thickness of 0.6 mm.
The obtained sheet was milky white. Table 1 shows the measurement results of each physical property value. The excellent effects of the present invention are clear from the evaluation results of the transparency, impact resistance, etc. collectively shown in Table 1 of the sheets produced in Examples 1 and 2 and Comparative Examples 1 to 4 above.

[0022]

[Table 1]

[0023]

According to the present invention, the intermediate layer shares the mechanical strength of the sheet, and the surface layer shares the functions of gloss and smoothness of the sheet. As a result, the graft copolymer type transparent HIP
While maintaining the original transparency and surface smoothness of the S sheet, it is possible to easily improve practical strength properties such as impact resistance. Therefore, it is possible to obtain a sheet which is much more transparent and has a higher commercial value than a conventional sheet processed by adding a rubber component or the like. Further, in the laminated transparent material sheet, the intermediate layer and the material forming the surface layer have a sufficient affinity, and no interlayer peeling occurs in the state of being processed into a sheet. Further, the styrene / butadiene / block copolymer may cause a problem in food packaging containers due to the odor caused by the trace amount of the polymerization solvent and the like, but the present invention provides a graft copolymer type transparent HIPS having almost no odor problem. Since the layer is used, there is an advantage that diffusion of odorous components in the intermediate layer can be suppressed. INDUSTRIAL APPLICABILITY The HIPS sheet of the present invention can be widely used in the field of food and drink packaging such as trays and containers, which is required to have transparency and impact resistance, the industrial field of building materials and the like, the field of electronic components and the like.

Claims (3)

[Claims] 1. A material in which a graft copolymer type transparent rubber-modified styrene resin is blended with a styrene / butadiene / block copolymer type rubbery polymer having a refractive index difference of 0.02 or less. A transparent rubber-modified styrene comprising a sheet as an intermediate layer, and a sheet or a film layer made of a graft copolymer type transparent rubber-modified styrene resin not blended with a rubbery polymer is laminated on both surfaces thereof. Series resin sheet. 2. The graft copolymerization type transparent rubber-modified styrene resin is obtained by graft-copolymerizing a styrene monomer and one or two kinds of (meth) acrylic acid alkyl ester in the presence of a rubbery polymer. The transparent rubber-modified styrene resin sheet according to claim 1. 3. The transparent rubber-modified styrene-based resin sheet according to claim 1, wherein the rubber-like polymer having a difference in refractive index of 0.02 or less has a styrene content of 30 to 50 Wt%.