JPH0755535B2 - Biaxially stretched heat resistant styrene yarn resin sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biaxially stretched heat-resistant styrene-based resin sheet, and more specifically, is transparent and heat-resistant,
The present invention relates to a biaxially stretched heat resistant styrene resin sheet having excellent strength and moldability.

"Prior Art" Biaxially stretched polystyrene-based resin sheets are excellent in transparency and rigidity and have good moldability, so they are molded by a thermoforming method, etc., and are mainly lightweight for food packaging. Used in large quantities as containers.

However, although these containers can be suitably used for general food storage applications, they are used for direct contact with boiling water such as reheating of retort foods and for microwave oven heating applications that have rapidly spread in recent years. However, it cannot be used because its heat resistance is insufficient.

Under these circumstances, the appearance of a sheet that can be used for manufacturing a heat-resistant container that does not impair the excellent transparency, rigidity, and moldability of the polystyrene resin sheet and that can be used even under the high temperature conditions as exemplified above. Has been strongly desired.

Examples of the polystyrene-based resin sheet having transparency and rigidity and improved heat resistance include, for example, JP-A-55-7153.
Biaxially stretched sheet consisting of a mixture of polystyrene and a styrene / maleic anhydride copolymer as disclosed in JP-A No. 0-25031, and styrene and acrylic acid, methacrylic acid or anhydrous as disclosed in JP-A-62-25031. Biaxially oriented sheets and the like made of a copolymer with maleic acid have been proposed.

However, these sheets have a heat resistance limit of 110-1.
Since the temperature is around 20 ° C, the heat resistance is insufficient for reheating retort foods that require heat resistance up to about 140 ° C and manufacturing molded products for microwave oven heating. In addition, in order to produce the above-mentioned sheet, a specific copolymer, which is difficult to produce a copolymer having a uniform composition, is required, and the biaxially stretched film has suitable physical processing conditions and a uniform biaxially stretched condition. Due to reasons such as difficulty in obtaining a sheet and unsatisfactory practical strength of a molded product obtained by molding these sheets, a heat-resistant sheet satisfying the market demand has not been completed.

[Problems to be Solved by the Invention] The present invention is a novel biaxially stretched heat-resistant styrene resin sheet that solves the above-mentioned problems of conventional sheets, that is, transparent, sufficient strength and good moldability. It is an object of the present invention to provide a sheet having excellent heat resistance, which has less deformation even under high temperature conditions required for reheating retort foods, heating microwave ovens, and the like.

“Means for Solving the Problems” The inventors of the present invention have made extensive studies in order to solve the above problems. As a result, a biaxial shaft made of a mixed composition of general-purpose polystyrene and polyphenylene ether blended in a specific ratio The inventors have completed the present invention by finding that a stretched sheet having a specific orientation relaxation stress can achieve the object of the present invention.

Therefore, the gist of the present invention is a biaxially oriented sheet comprising a mixed composition of 95 to 50% by weight of general-purpose polystyrene and 5 to 50% by weight of polyphenylene ether, which complies with ASTM D-1504. Measured orientation relaxation stress is 3
The biaxially stretched heat-resistant styrene-based resin sheet is characterized by having a range of up to 15 kg / cm ² .

The present invention will be described in detail below.

In the present invention, the general-purpose polystyrene is not limited to a styrene homopolymer, and may be o-methylstyrene, m-methylstyrene, p-methylstyrene, dimethylstyrene, α-methylstyrene, p-chlorostyrene, It includes homopolymers of styrene derivatives such as 2,4-dichlorostyrene and copolymers of styrene and the above styrene derivatives.

These general-purpose polystyrene have a weight average molecular weight of
The range of 1.0 × 10 ^{5 to} 4.0 × 10 ⁵ is preferable. If a weight average molecular weight of less than 1.0 × 10 ⁵ is used, the strength of the biaxially stretched sheet becomes insufficient, which is not preferable, and if a weight average molecular weight of more than 4.0 × 10 ⁵ is used, the strength of the biaxially stretched sheet increases, It is difficult to form a sheet, which is not preferable. The copolymer has a high content of styrene residues, and it is preferable that the content of the derivative residues is suppressed to be low because of its excellent transparency. Usually, the content of styrene residues is 95 mol% or more. The ones are good.

In the present invention, the polyphenylene ether has the following general formula In the formula, R ₁ and R ₂ represent the same or different alkyl groups, aryl groups, halogens, monovalent residues such as hydrogen, and n is an integer representing the degree of polymerization.

And a specific example thereof is poly (2,6-dimethyl-1,4-phenylene) ether, poly (2,6-dimethyl-1,4-phenylene) ether, poly (2- Methyl-6-ethyl-1,4-phenylene) ether, poly (2-methyl-6-propyl-1,4-phenylene) ether, poly (2,6-dipropyl-1,4-phenylene) ether, poly ( 2-ethyl-6-propyl-1,4
-Phenylene) ether and the like, and particularly preferred is poly (2,6-dimethyl-1,4-phenylene) ether, which has extremely good compatibility with the general-purpose polystyrene.

The molecular weight of the polyphenylene ether is not particularly limited, but from the viewpoint of strength and moldability of a sheet using the polyphenylene ether, it is preferable that the weight average molecular weight is in the range of 1 × 10 ⁴ to 10 × 10 ⁴ , and particularly, 2 × 10 ^{4 to} 7 × 10 ⁴ is preferable
It is in the range of.

The biaxially stretched sheet according to the present invention is a general-purpose polystyrene 95
-50% by weight, preferably 90-50% by weight and polyphenylene ether 5-50% by weight, preferably 10-50% by weight. When the proportion of polyphenylene ether is less than 5% by weight, the heat resistance of the biaxially stretched sheet is insufficiently improved. When the proportion of polyphenylene ether exceeds 50% by weight, the heat resistance of the biaxially stretched sheet is improved, but the strength of the sheet is not further improved, and sheet formation and biaxial stretching operations are difficult and impractical.

Furthermore, the mixed composition for producing the biaxially oriented sheet according to the present invention preferably has a total amount of volatile components of less than 0.4% by weight. Volatile components are styrene monomers,
Dimers, trimers, and those brought mainly from general-purpose polystyrene such as toluene, xylene, and ethylbenzene, and can be measured by gas chromatography. The total amount of volatile components in the mixed composition is 0.4
When it is at least wt%, this volatile component floats on the surface of the biaxially stretched sheet and is unevenly distributed in the form of an oil film, reducing the commercial value of the sheet.

As described above, the composition of the biaxially stretched sheet according to the present invention comprises 95 to 50% by weight of general-purpose polystyrene and 5 to 50% by weight of polyphenylene ether. Various stabilizers, fillers, colorants, lubricants, antistatic agents, and other additives may be blended within a range that does not impair the properties.

The biaxially stretched sheet according to the present invention has an orientation relaxation stress measured according to ASTM D-1504 in the range of 3 to 15 kg / cm ² , preferably 4 to 10 kg / cm ² . The above orientation relaxation stress is
A sheet of less than 3 kg / cm ² has insufficient strength, and a sheet of more than 15 kg / cm ² has poor moldability when molding a container or the like by thermoforming, has poor moldability, or has uneven thickness of the sheet.
It cannot be said to be a practical biaxially stretched sheet because whitening easily occurs.

The biaxially stretched sheet according to the present invention has the above orientation relaxation stress of 3 or less.
In the range of ~15kg / cm ^2, and preferably the puncture impact value was measured according to JIS P8134 is 7 kg-cm or more, further preferably 10 kg-cm or more. The biaxially stretched sheet according to the present invention preferably has a thickness within the range of 0.1 to 1.0 mm. If the thickness is less than 0.1 mm, the impact resistance is insufficient and the thickness is too thin, which is not suitable for molding various containers, which is not preferable. If the thickness is larger than 1.0 mm, it is not preferable because a rib structure for reinforcing the wall surface of the container cannot be formed with high precision when the desired container is formed by the thermoforming method.

The biaxially stretched sheet according to the present invention is a mixed composition composed of general-purpose polystyrene and polyphenylene ether having the above composition ratio as a raw material, and extruded in a sheet shape while melt-kneading the mixed composition, a commonly known tenter. It can be produced by stretching in a biaxial direction by employing a stretching method or a tubular stretching method. In this case, the biaxial stretching is preferably 1.5 to 5.0 times in the biaxial direction, preferably 2.0 to 3.0 times, and further, in the biaxial direction, stretching is performed at substantially equal stretching ratios. Is preferred. The temperature condition for biaxial stretching may be appropriately selected and determined according to the composition of the raw material for sheet production so that the orientation relaxation stress of the obtained biaxially stretched sheet falls within the above range.

"Effect of the invention" The biaxially stretched heat-resistant styrene resin sheet according to the present invention,
It has the following characteristics and its industrial utility value is extremely high.

(1) The biaxially stretched sheet according to the present invention has transparency, strength, and moldability equal to or higher than those of conventional general-purpose polystyrene resin sheets, and has excellent heat resistance.

(2) The biaxially stretched sheet according to the present invention has a content of polyphenylene ether in the mixed composition as a raw material, which is changed to about 105 by variously changing the content within the range specified in the present invention.
It can be provided with heat resistance from ℃ to about 150 ℃, and can be used for manufacturing various molded products suitable for reheating retort foods and for microwave heating.

"Examples" Hereinafter, the present invention will be described based on Examples, but the present invention is not limited to the following examples unless the gist thereof is exceeded.

In the following examples and comparative examples, various physical properties of the obtained biaxially stretched sheet were measured and evaluated by the following methods.

(1) Measurement of orientation relaxation stress Measuring device conforming to ASTM D-1504 (DN manufactured by Nichiri KK)
Stress tester).

(2) Puncture impact value A puncture impact test was conducted and measured according to JIS P8134.

(3) Heat shrinkage initiation temperature First, a cut sheet sample having a length of 60 mm and a width of 30 mm was put into an Instron type tensile tester (IM-50 manufactured by Shimadzu Corporation).
Both ends were held by a 0 type autograph) clamp and the whole clamp was immersed in a silicone oil bath. Next, the oil bath bath is heated at a rate of 2 ° C./minute to raise the temperature, and the temperature at which the test piece starts to shrink abruptly is read from the change in shrinkage stress appearing in the tensile tester. And This heat shrinkage initiation temperature can be regarded as the heat resistant temperature of the sheet as it is.

(4) Thermoformability The molding machine, the mold, the molding conditions, and the moldability used for the thermoformability evaluation are as follows.

I. Molding machine: Kansai Automatic Molding Machine Co., Ltd. Contact heating type pneumatic molding machine PK-400 type b. Mold: Aluminum mold, cover with square rib
Outer diameter 130 × 170mm, depth 15mm (maximum) c. Molding conditions: Heating temperature; Temperature higher than the heat shrinkage start temperature of each sheet by 15 to 30 ° C. Heating time; 4 seconds Molding pressure; 3 kg / cm ² Molding time; 4 seconds d. Moldability evaluation criteria Good; Molded according to molding mold Poor; Partly whitened or broken, or mold that could not be reproduced because it did not extend (5) Total amount of volatile components For sheet preparation The mixed composition used was dissolved in chloroform, and the solution was used as a paper material and measured by gas chromatography (detector; FID).

[Measurement target and measurement conditions] Styrene (monomer), xylene, ethylbenzene, etc .: PEG-20M 25% (column packing) 115 ° C (column temperature) Styrene dimer, trimer: Silicon OV-17.3% (column) Filler) 190 ° C. (column temperature in case of dimer) 260 ° C. (column temperature in case of trimer) Example 1 95 parts by weight of polystyrene having a weight average molecular weight of 2.8 × 10 ⁵ and a weight average molecular weight of 5 × 5 parts by weight of 10 ⁴ of polyphenylene ether was dry blended with a tumbler,
While melting and kneading with a 40 mmφ vented extruder (L / D = 25) (cylinder temperature 210 ° C.), extruded into a sheet form from a T-die (die temperature 230 ° C.), then cooled by a cooling roll to thicken An unstretched sheet of about 0.9 mm was prepared. Next, this unstretched sheet was stretched 2.5 times in the biaxial direction under a temperature condition of 125 ° C. using a test stretching machine to obtain a biaxially stretched sheet having a good transparency of 0.15 mm in thickness. .

Various physical properties and moldability of the obtained biaxially stretched sheet were measured and evaluated based on the above methods.

The results are shown in Table 1 together with the conditions for producing the biaxially stretched sheet.

Examples 2 to 5 In the example described in Example 1, the composition of the mixture used as the raw material of the biaxially stretched sheet and the sheeting conditions were changed as shown in Table 1, respectively, in the same manner as in the same example, Four types of biaxially stretched sheets having good transparency with a thickness of 0.15 mm were obtained. However, in Example 4, as the general-purpose polystyrene, another lot having a weight average molecular weight of 2.8 × 10 ⁵ was used.

With respect to the obtained biaxially stretched sheet, various physical properties and moldability were measured and evaluated in the same manner as in the example. The results are shown in Table 1.

Comparative Example 1 In the example described in Example 1, the composition of the mixture used as the raw material of the biaxially oriented sheet was changed to 30% by weight of general-purpose polystyrene and 70% by weight of polyphenylene ether, and the sheeting conditions shown in Table 1 were used. Then, as in the same example,
Attempts were made to produce a biaxially stretched sheet, but the sheet broke during the process of biaxially stretching an unstretched sheet, and a stretched sheet could not be obtained.

Comparative Examples 2 to 4 In the same manner as in Example 1, except that the composition of the mixture used as the raw material of the biaxially stretched sheet and the conditions for forming the sheet in the example described in Example 1 were changed as shown in Table 1. Three types of transparent biaxially stretched sheets having a thickness of 0.15 mm were obtained.

With respect to the obtained biaxially stretched sheet, various physical properties and moldability were measured and evaluated in the same manner as in the example. The results are shown in Table 1.

Comparative Example 5 In the example described in Example 1, instead of the general-purpose polystyrene / polyphenylene ether mixture used as a raw material for the biaxially stretched sheet, a styrene / maleic anhydride copolymer having a styrene residue content of 92% by weight was used. A transparent biaxially stretched sheet having a thickness of 0.15 mm was obtained in the same manner as in the same example, except that the polymer was used under the sheeting conditions shown in Table 1.

In the process of biaxially stretching the unstretched sheet, breakage of the sheet often occurred, but for the obtained biaxially stretched sheet, various physical properties and moldability were measured and evaluated in the same manner as in the same example. .

The results are shown in Table 1.

The following are clear from Table 1 above.

(1) The biaxially stretched sheet according to the present invention has heat resistance in the range of 105 to 142 ° C, is transparent, has excellent strength, and has good moldability (Examples 1 to 5).

(2) The total amount of volatile components in the sheet material composition is about 0.
When it exceeds 3% by weight (Example 4), an oil film is generated on the surface of the obtained biaxially stretched sheet, which may impair the appearance of the sheet.

(3) When the proportion of polyphenylene ether in the sheet raw material composition exceeds 50% by weight (Comparative Example 1), it is difficult to produce a biaxially stretched sheet.

(4) The sheet having the orientation relaxation stress smaller than the range specified in the present invention (Comparative Example 2) has insufficient strength,
In addition, those exceeding the range regulated by the present invention (Comparative Example 3)
Has poor moldability due to whitening during molding.

(5) The sheet made of a styrene / maleic anhydride copolymer (Comparative Example 5) is inferior in heat resistance to the biaxially stretched sheet of the present invention and is difficult to operate in biaxial stretching.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B29L 22:00 C08L 25:00

Claims (2)

[Claims] 1. A biaxially stretched sheet comprising a mixed composition of 95 to 50% by weight of general-purpose polystyrene and 5 to 50% by weight of polyphenylene ether, and having an orientation relaxation stress of 3 measured according to ASTM D-1504. A biaxially stretched heat-resistant styrene-based resin sheet characterized by being in the range of up to 15 kg / cm ² . 2. The biaxially stretched heat-resistant styrene-based resin sheet according to claim 1, which has a puncture impact value of 7 kg-cm or more measured according to JIS P8134.