JPH11140254A - Heat resistant resin composition and heat resistant stretched sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a heat resistance, etc., without impairing the forming property, transparency, etc., of a polystyrene sheet. SOLUTION: This heat resistant stretched sheet is obtained by stretching a heat resistant resin composition containing (A) 5-95 wt.% aromatic vinyl-based polymer having 1.575-1.600 refractive index and 1.5×10<5> -4.0×10<5> weight-average molecular weight, (B) 5-95 wt.% polycarbonate having 1.5×10<4> -4.0×10<4> weight- average molecular weight, and further (C) 0.1-30 wt.% copolymer consisting of 75-95 wt.% aromatic vinyl-based monomer unit and 5-25 wt.% N-substituted melemimide-based monomer based on the components (A) and (B), having 4.0×10<4> -3.0×10<5> weight-average molecular weight, biaxially in an equivalent fold within 1.1-5.0-fold range. Since the sheet is excellent in forming property, transparency, heat resistance, etc., it is possible to utilize as a food packing container such as a retort food container, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant resin composition which is transparent, has little coloring, and can be used as a material for producing a sheet having heat resistance and mechanical strength suitable for food packaging. The present invention also relates to a heat-resistant stretched sheet suitable for food packaging using the heat-resistant resin composition.

[0002]

2. Description of the Related Art Polystyrene sheets are excellent in transparency and rigidity, and therefore, those formed by thermoforming are widely used mainly as lightweight containers for food packaging. . However, although the container made of polystyrene sheet is suitable as a general food packaging container, it has insufficient heat resistance, so it is used for heating in boiling water, such as retort food, or heated in a microwave oven. It cannot be used for applications that do. Therefore, there is a need for a technique for improving heat resistance without impairing the transparency, rigidity, and moldability of a polystyrene sheet so that it can be used in these fields.

JP-A-55-71530 proposes a biaxially stretched sheet comprising a mixture of polystyrene and a styrene / maleic acid copolymer.
No. 31 proposes a biaxially stretched sheet made of a copolymer of styrene and acrylic acid, methacrylic acid or maleic anhydride. However, since these sheets have narrow processing conditions suitable for biaxial stretching, it is difficult to obtain those having uniform physical properties, and the practical strength of molded articles obtained from these sheets is not satisfactory.

Japanese Patent Application Laid-Open No. Sho 60-125634 proposes a biaxially stretched sheet comprising a styrene / maleimide copolymer. However, this sheet is heavily colored, and the molded article has insufficient practical strength.

[0005] Also, JP-A-2-55122 discloses that
Biaxially stretched sheets comprising a mixture of polystyrene and polyphenylene ether have been proposed. However, the difference in glass transition temperature between polystyrene and polyphenylene ether is large, so that it is difficult to obtain a uniform mixture. Therefore, it is difficult to obtain a sheet having uniform physical properties, and coloring is severe.

Attempts have been made to blend polycarbonate with polystyrene in order to improve the heat resistance of polystyrene, but it is difficult to control the melt-mixing operation due to the low compatibility between polystyrene and polycarbonate.
Therefore, conventionally, a mixture of polycarbonate and a styrene-based resin obtained by copolymerizing styrene, acrylonitrile, methyl methacrylate, acrylic acid, methacrylic acid, or unsaturated dicarboxylic acid has been used. However, such styrene-based resins and polycarbonates have different refractive indices, and thus are not practically satisfactory in terms of transparency.

The present invention solves such problems of the prior art, and does not impair the transparency, rigidity and moldability of the polystyrene sheet, and has a practical 100 ° C. required as a food packaging container. An object of the present invention is to provide a heat-resistant resin composition capable of obtaining a sheet material having the above heat resistance and mechanical strength. Another object of the present invention is to provide a heat-resistant stretched sheet suitable for a food packaging container using the heat-resistant resin composition.

[0008]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that the refractive index can be approximated by a combination of an aromatic vinyl polymer having a specific molecular weight and the like and polycarbonate. It has been found that the compatibility of the two components can be improved by blending a copolymer of an aromatic vinyl monomer and an N-substituted maleimide monomer as the third component, and completed the present invention. is there.

That is, according to the present invention, (A) the refractive index is 1.575
~ 1.600 with a weight average molecular weight of 1.5 x 10 ⁵ ~
⁵ to 95% by weight of an aromatic vinyl polymer of 4.0 × 10 ⁵ and (B) a weight average molecular weight of 1.5 × 10 ⁴ to 4.
It contains 5 to 95% by weight of a polycarbonate of 0 × 10 ⁴ , and (C) has a weight average molecular weight of 4.0 × 1
0 ⁴ to 3.0 aromatic vinyl-based monomer units of 75 to 95 wt% is a × 10 ^5, a copolymer comprising 5 to 25 wt% N-substituted maleimide monomer unit, (A) and (B) An object of the present invention is to provide a heat-resistant resin composition characterized by containing 0.1 to 30% by weight based on components.

The present invention also provides a heat-resistant stretched sheet obtained by stretching the heat-resistant resin composition in a uniaxial or biaxial direction by a factor of 1.1 to 5.0. It is.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The aromatic vinyl polymer as the component (A) used in the present invention is styrene, o-methylstyrene,
Homopolymers of aromatic vinyl monomers such as m-methylstyrene, p-methylstyrene, ethylstyrene, dimethylstyrene, α-methylstyrene, p-chlorostyrene, 2,4-dichlorostyrene, and copolymers of two or more types It is a polymer. The aromatic vinyl polymer of the component (A) has an α-methylstyrene unit of 5 to 2 in order to improve heat resistance.
It is preferable to contain 5% by weight, that is, to use 5 to 25% by weight of α-methylstyrene as a production raw material.

The aromatic vinyl polymer as the component (A) has a refractive index of 1.575 to 1.600, preferably 1.58, in order to impart sufficient transparency to the heat-resistant stretched sheet.
0 to 1.575. The aromatic vinyl polymer as the component (A) has a sufficient melt tension and imparts sufficient impact resistance and elongation to the heat-resistant stretched sheet. × 10 ^{5 to} 4.0 × 10 ⁵
And preferably from 2.0 × 10 ^{5 to} 3.0 × 10 ⁵ .

The polycarbonate as the component (B) used in the present invention imparts sufficient heat resistance to the heat-resistant stretched sheet,
In order to reduce the viscosity difference with the component (A) and facilitate the melt mixing operation, the weight average molecular weight is 1.5 × 10 ^{4 to} 4.0.
× 10 ⁴ , preferably 2.0 × 10 ^{4 to} 3.0 × 1
0 of ^4. The refractive index of the component (B) is not particularly limited, but is preferably close to the refractive index of the component (A).

In order to impart sufficient heat resistance and moldability to the heat-resistant stretched sheet, the proportion of the component (A) is preferably from 5 to 95% by weight, more preferably from 5 to 95% by weight. It is 40 to 80% by weight, and the component (B) is 5 to 95% by weight, preferably 20 to 60% by weight.

The component (C) used in the present invention is a copolymer comprising an aromatic vinyl monomer unit and an N-substituted maleimide monomer unit.

As the aromatic vinyl monomer used in the production of the component (C), the same aromatic vinyl monomers as those of the component (A) can be mentioned, and among them, styrene is preferable. Also,
Examples of the N-substituted maleimide-based monomer include N-methylmaleimide, N-ethylmaleimide, N-butylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N- (2-chlorophenyl) maleimide,
(3-chlorophenyl) maleimide, N- (3-methylphenyl) maleimide, N- (3,5-dimethylphenyl) maleimide, N-benzylphenylmaleimide, N
Examples thereof include-(3-methoxyphenyl) maleimide, and among them, N-cyclohexylmaleimide is preferable.

The copolymer of the component (C) improves the dispersibility of the components (A) and (B) and obtains a homogeneous molded product. To improve the transparency and improve the aromatic vinyl monomer unit 75 to
It is composed of 95% by weight, preferably 80 to 85% by weight, and 5 to 25% by weight, preferably 15 to 20% by weight, of an N-substituted maleimide monomer unit.

The component (C) has a weight-average molecular weight of 4.0 × to increase melt tension, impart sufficient impact strength to molded products, and enhance elongation during molding.
10 ^{4 to} 3.0 × 10 ⁵ , preferably 4.5 × 10 5
^{4 to} 1.0 × 10 ⁵ .

The mixing ratio of the component (C) in the present invention is as follows:
In order to improve the dispersibility of the component (A) and the component (B) with respect to the total amount of the components (A) and (B) and obtain a homogeneous molded product, the components (A) and (C) Is 0.1 to 30% by weight, and preferably 2 to 20% by weight, in order to improve the compatibility by improving the transparency.

The heat-resistant resin composition of the present invention may further contain a plasticizer such as a mineral oil for further improving the moldability. The mixing ratio of the plasticizer is preferably 0.05 to 2% by weight, and more preferably 0.1 to 2% by weight.
2 to 1% by weight. Further, in order to prevent blocking, a styrene-grafted butadiene rubber having an average particle diameter of 2 to 10 μm is preferably 100 to 10 in terms of butadiene.
00 ppm can be blended, and 20 to 2000 ppm of polystyrene crosslinked beads can be blended.

[0021] Further, other components and types within a range not impairing the object of the present invention, such as heat stabilizers, ultraviolet absorbers, phosphorus-based, sulfur-based or hindered phenol-based antioxidants, silica beads, calcium phosphate , A filler such as barium sulfate, talc, zeolite and divinylbenzene cross-linked beads, a coloring agent, a lubricant such as a fatty acid ester, an antistatic agent, a styrene-butadiene block copolymer, and the like.

The heat-resistant resin composition of the present invention has a volatile component content of 0.4 in order to prevent the appearance of an oil film pattern on the sheet surface from impairing the appearance and reducing the commercial value.
%, Preferably less than 0.15% by weight. The volatile components include unreacted aromatic vinyl monomers, dimers, trimers, toluene, xylene, ethylbenzene and the like used as solvents.

The heat-resistant stretched sheet of the present invention is obtained by stretching the above-mentioned heat-resistant resin composition uniaxially or biaxially. This stretching method is not particularly limited, and after extruding the composition obtained by heating and melting the composition into a sheet, a general roll stretching, tenter stretching or tubular stretching method or the like can be applied. Preferably, the film is stretched biaxially. The temperature during stretching is 130 to 200
C is preferred.

The stretching ratio at the time of stretching is preferably from 1.1 to 5 in order to impart sufficient toughness to the sheet and to prevent unevenness in the thickness of the sheet when producing a container by vacuum forming or pressure forming. 1.0 times, and preferably from 1.3 to 1.3 times.
2.0 times. In the case of biaxial stretching, the stretching ratio in the longitudinal and transverse directions is preferably the same within the above range.

The heat-resistant stretched sheet of the present invention is prepared by appropriately combining an antistatic agent, an anti-fogging agent such as sucrose fatty acid ester, glycol fatty acid ester, polyglycol fatty acid ester, and a release agent such as silicone oil, on both sides or one side Can be applied.

[0026] The heat-resistant stretched sheet of the present invention has an ASTM
The orientation relaxation stress measured according to D-1504 is preferably from 1.0 to 10 kg / cm ² , more preferably from 1.3 to 5 kg / cm ² . The heat-resistant stretched sheet of the present invention has sufficient impact strength and refraction strength and excellent moldability by having such orientation relaxation stress.

[0027]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Example 1 The refractive index was 1.591 and the weight average molecular weight was 2.5 × 10
⁵ polystyrene (α-methylstyrene unit 0% by weight)
30% by weight, 70% by weight of a polycarbonate having a weight average molecular weight of 2.0 × 10 ⁴ , and further, a weight average molecular weight of 4.9 × 10 ⁴ composed of 81% by weight of styrene units and 19% by weight of N-cyclohexylmaleimide units. Copolymer 10
Wt% (amount based on the two components) was dry blended with a tumbler. After that, screw diameter 30mm
Was melt-kneaded with a twin screw extruder to obtain a pellet-like heat-resistant resin composition. Note that the content of the volatile component was 0.3% by weight.

Next, this heat-resistant resin composition was extruded from a T-die into a sheet while being melt-kneaded (cylinder temperature 240 ° C.) using an extruder (L / D = 28) having a screw diameter of 30 mm ( Die temperature 240 ° C). Thereafter, the sheet was cooled by a cooling roll to obtain an unstretched sheet having a thickness of about 0.6 mm. Next, the unstretched sheet is stretched 1.5 times in each of the biaxial directions at a temperature of 177 ° C. using a table stretching machine to obtain a colorless and transparent heat-resistant stretched sheet having a thickness of about 0.25 mm. Obtained.

With respect to the molded article of the heat-resistant resin composition in the form of a pellet and the heat-resistant stretched sheet, each measurement in the following Test Examples 1 and 2 was performed. Table 1 shows the results. Table 1
Are the percentages by weight.

Test Example 1 (Physical Properties of Heat-Resistant Resin Composition) (1) Compatibility Using a pellet-shaped heat-resistant resin composition, 9 cm long and 5 cm wide
Then, a plate having a three-stage structure having a thickness of 1 mm, 2 mm and 3 mm was injection-molded, and the breaking state when the boundary between the 1 mm and 2 mm steps was manually broken was evaluated according to the following criteria. ：: Cracking without peeling in the flow direction ×: Cracking while partially peeling in the flow direction.

(2) Impact Resistance Izod impact strength was measured according to ASTM D-256.

(3) Heat Resistance The deflection temperature under load and the Vicat softening temperature were measured in accordance with ASTM D-648 and ASTM D-1525.

(4) Transparency A plate having a thickness of 3 mm was injection-molded from the heat-resistant resin composition in the form of pellets, and the total light transmittance was measured.

Test Example 2 (Physical Properties of Heat-Resistant Stretched Sheet) (1) Appearance of Sheet The appearance of the heat-resistant stretched sheet was observed with the naked eye, and transparency and coloring compatibility when used as a food packaging container were examined. evaluated.

(2) Heat resistance Five heat-resistant stretched sheets were placed in an oven at 120 ° C. for 5 hours.
The vertical and horizontal dimensional change rates in the case of being left for a minute were measured, the total average value including the vertical and horizontal directions was obtained, and the heat resistance was evaluated according to the following criteria. A: Less than -2% O: -2% or more and less than -5% X: -5% or more.

(3) High temperature oil resistance Five heat-resistant stretched sheets were placed in a salad oil at 110 ° C.
The haze value when immersed for one minute was measured in accordance with ASTM D1003, an average value was obtained, and evaluated according to the following criteria. ◎: less than 5% ：: 5% or more and less than 10% ×: 10% or more.

(4) Contact-Heating Type Pneumatic Formability Using the heat-resistant stretched sheet obtained in Example 1, contact-heating type pneumatic forming was performed using PK-450 manufactured by Kansai Automatic Co., Ltd. under the following conditions. The rain drop, forming wrinkle and deep drawability were evaluated.

Raindrop Evaluation method: The upper limit temperature at which raindrops began to be generated was determined and evaluated according to the following criteria. The raindrop is a raindrop-like pattern generated on the surface of the molded product, and has a diameter of 3 to
It is about 20 mm. ◎: 135 ° C. or more ○: 120 ° C. or more and less than 135 ° C. ×: less than 120 ° C.

Molding jig Mold: cylindrical cup with opening diameter 90m and depth 50mm Evaluation method: arbitrarily select 20 pieces from multiple molded products,
The number of molding wrinkles observed in them was counted with the naked eye, the average number of occurrences (X) per molded article was obtained, and evaluated according to the following criteria. The molding wrinkle is an earthworm-like pattern generated on the surface of the molded product, and has a width of 0.5 to 1.5 mm and a length of about 1 to several cm. ◎: X ≦ 0.1 ：: 0.1 <X ≦ 0.3 Δ: 0.3 <X ≦ 0.7 ×: 0.7 <X.

Deep drawability Mold: A cylindrical cup with an opening diameter of 90 mm and a depth of 2.5
Die for deep drawability evaluation that can be changed from 2.5 to 90 mm at mm intervals Evaluation method: Ten pieces were arbitrarily selected from a plurality of molded products obtained by appropriately setting and changing the depth, and the mold reproducibility was determined by the naked eye without molding cracking and whitening of the molding (setting depth).
Were counted, and the maximum drawing depth where the number was 9 or more was obtained and evaluated according to the following criteria. ◎: 50 mm or more ○: 45 mm or more and less than 50 mm Δ: 37.5 mm or more and less than 45 mm ×: less than 37.5 mm.

Examples 2 to 5 A heat-resistant stretched sheet was obtained in the same manner as in Example 1 using the heat-resistant resin composition having the composition shown in Table 1 under the conditions shown in Table 1. Using this heat-resistant stretched sheet, each measurement in Test Examples 1 and 2 similar to Example 1 was performed. Table 1 shows the results.

Comparative Examples 1 to 6 Stretched sheets were obtained in the same manner as in Example 1 under the conditions shown in Table 2 using the resin compositions having the compositions shown in Table 2. The same measurement as in Example 1 was performed using this stretched sheet. Table 2 shows the results. In addition, the compounding quantity shown in Table 2 is a weight% display.

[0044]

[Table 1]

[0045]

[Table 2]

The molded articles of the resin compositions of Examples 1 to 5
Due to the action of the component (C), the compatibility of the components (A) and (B) is good, and the refractive indices of the components (A) and (B) are close to each other, so that impact resistance, heat resistance and transparency are improved. It was excellent. Further, the stretched sheets of Examples 1 to 5 were excellent in moldability, transparency and heat resistance.

The molded articles of the resin compositions of Comparative Examples 2, 3, and 6 were inferior in transparency due to the difference in the refractive indices of the constituent components. For this reason, the stretched sheet also had a remarkable degree of white turbidity, and was unsuitable as a molded article material such as a food packaging container. The resin composition of Comparative Example 1 was inferior in impact resistance due to the inferior compatibility of the components, but the same results as in Examples 1 to 5 were obtained for the stretched sheet. Although the resin composition of Comparative Example 1 can be applied as a material for manufacturing a normal food packaging container, it has been recognized that there is room for improvement in application to applications where a large external force is applied.

[0048]

The heat-resistant stretched sheet obtained from the heat-resistant resin composition of the present invention does not impair the transparency, rigidity and moldability of the polystyrene sheet, and is practically required as a food packaging container. Heat resistance and mechanical strength. Therefore, it can be applied to applications where heat resistance of 100 ° C. or higher is practically required, for example, where conventional polystyrene containers cannot be applied, such as retort food applications and microwave oven applications.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 69:00 B29L 7:00

Claims (6)

[Claims] (A) a refractive index of 1.575 to 1.600
And ⁵ to 95% by weight of an aromatic vinyl polymer having a weight average molecular weight of 1.5 × 10 ^{5 to} 4.0 × 10 ⁵ and (B) a weight average molecular weight of 1.5 × 10 ^{4 to} 4.0. It contains 5 to 95% by weight of a polycarbonate of × 10 ⁴ , and (C) a weight average molecular weight of 4.0 × 10 ^{4 to} 3.0 × 10 ^5.
75 to 95% by weight of an aromatic vinyl monomer unit
And 5 to 25% by weight of an N-substituted maleimide monomer unit
A heat-resistant resin composition comprising 0.1 to 30% by weight of a copolymer consisting of the components (A) and (B). 2. An aromatic vinyl polymer as the component (A),
The heat-resistant resin composition according to claim 1, wherein the composition contains 5 to 25% by weight of an α-methylstyrene unit. 3. The heat-resistant resin composition according to claim 1, wherein the N-substituted maleimide monomer unit of the component (C) is derived from N-cyclohexylmaleimide. 4. The heat-resistant resin composition according to claim 1, wherein the content of the volatile component is less than 0.4% by weight. 5. The heat-resistant resin composition according to claim 1, which is stretched in a uniaxial or biaxial direction by a factor of 1.1 to 5.0. Stretched sheet. 6. The heat-resistant resin composition according to any one of claims 1 to 4, which is stretched in the biaxial direction at a magnification of 1.1 to 5.0 times. Characterized heat-resistant stretched sheet.