JP3364236B2 - Biaxially stretched heat-resistant styrene resin sheet - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretched heat-resistant styrenic resin sheet, and more particularly, to the use of polyphenylene ether to improve heat resistance. The present invention relates to a biaxially stretched heat-resistant styrene resin sheet whose surface appearance is improved by reducing hard spots due to unmelted polyphenylene ether. [0002] Biaxially stretched styrene resin sheets are excellent in transparency and rigidity and have good moldability.
It is used in large quantities mainly as lightweight containers for food packaging by die forming by a thermoforming method or the like. However,
Containers made of biaxially stretched styrene-based resin sheets have insufficient heat resistance, so they are used for direct contact with boiling water, such as for retort foods, and for microwave ovens, which have spread rapidly in recent years. Can not do. Under these circumstances, there has been a strong demand for the appearance of a sheet that can be used in the production of a heat-resistant container that can be used under high-temperature conditions without impairing the excellent transparency, rigidity, and moldability of the styrene-based resin sheet. ing. As a method for improving the heat resistance of a styrene resin sheet, a method of forming a composition with polyphenylene ether is known. Such a method utilizes the property that polyphenylene ether and polystyrene can be mixed in a wide composition range and temperature range to form a completely compatible system. However, since polyphenylene ether has a high softening point and low fluidity, it is actually difficult to completely dissolve polyphenylene ether in polystyrene. The unmelted polyphenylene ether in the raw material composition is not particularly conspicuous and is not a serious problem in the case of an injection molded product, but is an important problem in the case of a biaxially stretched sheet. That is, in the case of a biaxially stretched sheet, unstretched polyphenylene ether floats on the surface by stretching, and appears as a hard spot due to a difference in refractive index from polystyrene, and the surface appearance is significantly deteriorated. [0004] By increasing the kneading temperature and lengthening the residence time in the kneader, it is possible to reduce the amount of unmelted polyphenylene ether which is insufficiently compatible in the raw material composition. The color tone deteriorates significantly due to
Further, the processing cost increases. On the other hand, a method of polymerizing a styrene monomer in the presence of polyphenylene ether has also been proposed (for example, Japanese Patent Application Laid-Open No. 55-137130).
No., JP-A-58-117213). However, the above method is for improving the processability and chemical resistance of an injection-molded product, and does not mention a biaxially stretched sheet. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a biaxially stretched heat-resistant styrene resin sheet having an improved surface appearance. That is, the gist of the present invention is to provide a polymer obtained by polymerizing 30 to 95 parts by weight of a styrene monomer in the presence of 5 to 70 parts by weight of polyphenylene ether. the resin composition sheet containing the a) 25 to 100 parts by weight of styrene polymer (B) 0 to 75 parts by weight
And then biaxially 1.5-5.
A biaxially stretched heat-resistant styrene-based resin sheet characterized in that it is stretched 0 times to have a thickness of 0.1 to 1.0 mm . Hereinafter, the present invention will be described in detail. In the present invention, polyphenylene ether refers to a polymer having a repeating unit represented by the following chemical formula [Formula 1]. In the chemical formula [Formula 1], R ₁ and R ₂ are an alkyl group,
Represents an aryl group, a halogen atom, a hydrogen atom or the like, and n represents an integer. R ₁ and R ₂ may be the same or different from each other. [0007] Specific examples of the above polyphenylene ether include poly (2,6-dimethyl-1,4-phenylene) ether and 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. A particularly preferred polyphenylene ether is poly (2,6-dimethyl-1,4-phenylene) ether, which has very good compatibility with general-purpose polystyrene. The molecular weight of the above-mentioned polyphenylene ether is not particularly limited. However, from the viewpoint of moldability and strength when formed into a sheet, the weight-average molecular weight is 1 × 1.
0 ⁴ to 10 × 10 ⁴ , preferably 2 × 10 ^{4 to} 7
× 10 ⁴ range. In the present invention, the styrene monomer is
In addition to styrene alone, o-methylstyrene, m-methylstyrene, p-methylstyrene, dimethylstyrene, α-
Refers to styrene derivatives such as methylstyrene, p-chlorostyrene, and 2,4-dimethylstyrene, and mixtures thereof. In the present invention, the polymer (A), which is one component of the raw resin composition, comprises polyphenylene ether 5 to 7
It is obtained by polymerizing 30 to 95 parts by weight of a styrene monomer in the presence of 0 parts by weight. Then, as a particularly preferred embodiment, prior to polymerization, polyphenylene ether is sufficiently dissolved in the styrene monomer. If the amount of the polyphenylene ether is less than 5 parts by weight, a sufficiently heat-resistant styrene-based resin composition cannot be obtained. It will be difficult. Further, as the polymer (A), the styrene resin portion contained therein has a weight average molecular weight of 1 × 10 ⁵
Those having a range of from 10 to 10 ⁵ are preferable. When the weight average molecular weight of the styrene resin portion is smaller than the above range, the strength of the biaxially stretched sheet becomes insufficient, and when it is larger than the above range, it becomes difficult to form a sheet. Furthermore, as the polymer (A), a polymer having a high content of styrene residues in the styrene resin portion contained therein and having a low content of styrene derivative residues is preferable because of excellent transparency. Therefore, the content of the styrene residue in the styrene resin portion of the polymer (A) is preferably set to 95 mol% or more. The dissolution of the polyphenylene ether into the styrene monomer is carried out by using an appropriate dissolution tank and
C., preferably 70-90.degree. C., by stirring for 1-2 hours. When the dissolution temperature is lower than 60 ° C., the polyphenylene ether is not sufficiently dissolved to form a slurry, and when it exceeds 100 ° C., thermal polymerization of styrene is promoted. The type of polymerization may be any of suspension polymerization, solution polymerization and bulk polymerization, but suspension polymerization is advantageous. Suspension polymerization is performed by a radical polymerization initiator in an aqueous medium. As the radical polymerization initiator,
For example, t-butyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, 1,1-bis (t-
Butylperoxy) cyclohexane, 1,1-bis (t
Organic peroxides such as -butylperoxy) -3,3,5-trimethylcyclohexane and 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propanone, azobisisobutyronitrile, azobis-2 , 4-
Examples thereof include azo compounds such as dimethylvaleronitrile, azobiscyclohexanecarbonitrile, methyl azobisisobutyrate, azobiscyanovaleric acid, 1-t-butylazo-1-cyanocyclohexane, and 1,1'-azobiscyclohexane-1-carbonitrile. The polymerization initiator is
The styrene-based monomer can be used in an appropriate amount for polymerization, but is preferably 0.1 to 10% by weight based on 100 parts by weight of the styrene-based monomer. [0015] The amount of water in the aqueous medium may be any amount as long as the suspension of the reaction system can be improved.
70 parts by weight or more, preferably 10 parts by weight, based on 100 parts by weight of the total of the styrene monomer and the polyphenylene ether.
The range is from 0 to 300 parts by weight. It is preferable to add a dispersion stabilizer to the aqueous medium. As a dispersion stabilizer, polyvinyl alcohol,
Examples include gelatin, agar, starch, glycerin, polyacrylic acid or its sodium salt, polyethylene glycol, ethylene glycol, polyacrylamide, and styrene-maleic anhydride copolymer. The amount of the dispersion stabilizer is not particularly limited, but is generally 0.1 to water.
001 to 3% by weight, preferably 0.01 to 1.5% by weight
It is. Further, if a surfactant is added to the aqueous medium, the effect of stabilizing the suspension state of the reaction system and smoothing the bead surface of the produced polymer can be obtained. As the surfactant, any surfactant of cationic, anionic or nonionic type may be used, and specifically, hydroxymethylcellulose, carboxymethylcellulose, methylcellulose, rosin soap, sodium glycolate, sodium dodecylbenzenesulfonate, sodium stearate , Polyoxyethylene lauryl ether, polyoxyethylene distearate, lauryl trimethyl ammonium chloride and the like. The surfactant is not necessarily required when a dispersion stabilizer is used, but when used, is preferably used in the range of 0.0005 to 0.5% by weight based on water. If a water-insoluble inorganic compound is added to the aqueous medium as a so-called anti-adhesive agent, the beads of the produced polymer can be stabilized. As such inorganic compounds, specifically, calcium, magnesium,
Carbonates such as lead or barium, silicates, sulfates or phosphates, alumina, bentonite, talc, clay,
Oxides such as titanium oxide and lead oxide, silicates, and the like can be given. The amount of the inorganic compound is not particularly limited, but is preferably in the range of 0.01 to 5% by weight based on water. Still further, a water-soluble inorganic salt, for example, sodium sulfate, can also be used for facilitating the polymerization. Each of the above-mentioned additives can be used alone or as a mixture of two or more, and a plasticizer, a lubricant, a coloring material, a stabilizer, and the like, as long as they do not adversely affect the polymerization of the styrene compound, It can be added in advance during polymerization. In the present invention, the polymer (B) as another component of the raw material resin composition is a styrene polymer. The styrene-based polymer can be obtained from the above-mentioned styrene-based monomer according to a known polymerization method. The weight average molecular weight of the styrene-based polymer as the polymer (B) is, for the same reason as in the case of the styrene resin portion in the polymer (A),
It is preferred to be in the range of 1 × 10 ⁵ to 10 × 10 ⁵ . The biaxially stretched heat-resistant styrenic resin sheet of the present invention is prepared from a resin composition containing 25 to 100 parts by weight of the polymer (A) and 0 to 75 parts by weight of the styrene-based polymer (B). can get. The above resin composition preferably has a volatile component of less than 0.4% by weight. The volatile components include styrene-based monomers, dimers, trimers, and toluene, xylene, and ethylbenzene mainly brought from general-purpose polystyrene. These volatile components
It can be measured by gas chromatography. When the content of the volatile component of the resin composition exceeds the above range, the volatile component may emerge on the surface of the sheet and be ubiquitous in the form of an oil film, which may reduce the commercial value of the biaxially stretched sheet. . The above resin composition contains various stabilizers, fillers, coloring agents, lubricants, antistatic agents, etc. within a range that does not impair the transparency, strength, moldability, etc. of the biaxially stretched sheet. Additives can be blended. The biaxially oriented heat-resistant styrenic resin sheet of the present invention, be prepared by employing a tenter stretching scheme of stretching extruded biaxially in a flat sheet shape while melting the resin composition Can be. In this case, the biaxial stretching needs to be performed at a stretching ratio of 1.5 to 5.0 times, preferably 2.0 to 3.0 times in the biaxial direction. It is preferable that the stretching ratio in each direction is substantially equal. Stretching temperature conditions may be appropriately selected and determined according to the composition of the resin composition so that the orientation relaxation stress of the obtained biaxially stretched sheet is in the following range. The biaxially stretched heat-resistant styrene resin sheet of the present invention preferably has an orientation relaxation stress measured in accordance with ASTM D1504 in the range of ³ to 15 kg / cm ² . Particularly preferred orientation relaxation stress is in the range of 4 to 10 kg / cm ² . A sheet having an orientation relaxation stress less than the above range has insufficient strength, and a sheet exceeding the above range has poor moldability at the time of molding a container or the like by thermoforming, and has poor mold followability. Uneven thickness and whitening easily occur. Further, the biaxially stretched heat-resistant styrenic resin sheet of the present invention preferably has a puncture impact value of 7 kg · cm or more as measured according to JIS P8134. A particularly preferred puncture impact value is 10 kg · cm or more. The thickness of the biaxially stretched heat-resistant styrene resin sheet is in the range of 0.1 to 1.0 mm . A sheet having a thickness smaller than the above range has insufficient impact resistance and is unsuitable for molding various containers. A sheet having a thickness larger than the above range has a disadvantage that a rib structure or the like for reinforcing a container wall surface cannot be formed with high accuracy when formed into a desired container by a thermoforming method. The biaxially stretched heat-resistant styrenic resin sheet of the present invention is excellent in transparency and rigidity, has good moldability, and has sufficient heat resistance. It is suitably used for lightweight food packaging containers that can be heated by a microwave oven. EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but it should not be construed that the present invention is limited to the following Examples as long as the gist of the present invention is not exceeded. In the following examples, the results of the appearance and physical property measurement of the processed sheet product are shown in Table 1 below. Example 1 [Polymerization Step] A polyphenylene ether (weight average molecular weight 5 × 1) was placed in a 50 L dissolution tank equipped with an irrigated stirring blade.
0 ⁴⁾ 5.0 kg, was heated to 80 ° C. Put styrene 15.0 kg. Stirring was continued for 60 minutes to sufficiently dissolve the polyphenylene ether in styrene. Thereafter, 20 kg of hot deionized water, sodium dodecylbenzenesulfonate 1.
0 g, 2% aqueous solution of polyacrylate suspension 450
g and 100 g of sodium sulfate, and the temperature was raised to 120 ° C. After reaching 120 ° C., dicumyl peroxide 30
g was added and the temperature was raised to 150 ° C. over 5 hours, and further maintained for 1 hour to complete the reaction. [Kneading Step] After the beads obtained by the above polymerization method were dried, they were melt-kneaded in a single screw (40 mmφ) extruder at 260 ° C. for one pass to obtain pellets. [Sheet processing step] The above pellets were further melted and kneaded in an extruder equipped with a 40 mmφ vent,
After being extruded into a sheet shape from a T-die at a temperature of 0 ° C., it was cooled by a cooling roll to produce an unstretched sheet having a thickness of about 0.9 mm.
Next, using a test stretching machine, the above unstretched sheet was
The film was stretched 2.5 times in each of the biaxial directions at a temperature of 25 ° C. to obtain a biaxially stretched sheet having a good transparency and a thickness of 0.15 mm. Example 2 [Polymerization step] The same procedure as in Example 1 was carried out except that 10.0 kg of polyphenylene ether and 10.0 kg of styrene were used, and the amount of dicumyl peroxide was changed to 20 g. (Kneading step) After drying the beads obtained by the above polymerization method,
50 parts of the peed and 50 parts of polystyrene pellets (weight average molecular weight: 2.8 × 10 ⁵ ) are dry-blended by a tumbler and melt-kneaded in a single screw (40 mmφ) extruder at 260 ° C. for one pass to obtain pellets. Was. [Sheet processing step] This was performed in the same manner as in Example 1. Comparative Example 1 [Kneading Step] 25 parts by weight of polyphenylene ether (weight average molecular weight 5 × 10 ⁴ ) and 75 parts by weight of polystyrene pellets (weight average molecular weight 2.8 × 10 ⁵ ) were dry-blended in a tumbler, 2 by shaft (40mmφ) extruder
Pellets were obtained by melt-kneading one pass at a setting of 60 ° C. [Sheet processing step] This was performed in the same manner as in Example 1. Comparative Example 2 Polyphenylene ether (weight average molecular weight 5 × 10 ⁴ )
25 parts, polystyrene (weight average molecular weight 2.8 × 1
0 ⁵ ) 75 parts were dry-blended using a tumbler, and melt-kneaded in a two-pass extruder (30 mm) at 300 ° C. for 2 passes to obtain pellets. [Sheet processing step] The same processing as in Example 1 was carried out, but the stretching could not be carried out satisfactorily. Table 1 Example Comparative Example 1 1 2 1 2 Hard spots (number) ^{* 1} 0.2 mm ² or more 600 800 ∞ 1200 0.1 mm ² or less 1500 1400 ∞ 4700 Sheet appearance (visual) ^{* 2} ○ ○ × △ Sheet thickness (mm) 0.15 0.15 − 0.15 Orientation relaxation stress ^{* 3} 7.0 7.5 − 7.3 Puncture impact strength ^{* 4} 36 38 −32 Thermal shrinkage onset temperature ^{* 5} 123 122 − 123 Thermoformability ^{* 6} ○ ○ − ○ Volatility Total amount of components ^{* 7} 0.35 0.32 0.26 0.21 The meanings of the notes in Table 1 are as follows. (* 1): Particles (unmelted solids) appearing on the sheet surface were quantified by the following method. That is, an arbitrary portion (10 cm × 10 cm) of a sheet is cut out, and a loupe of 0.2 mm ² or more and 0.1 mm are used.
Divide into ² or less and count them, multiply them by 100, and
Number of hard spots per square meter. However, Δ indicates that the number of hard spots is so large that counting is impossible. (* 2): Determined in the following three stages. ：: Uniformly compatible, surface bumps (unmelted solid)
And occurrence of sheet formation failure is not recognized. Δ: Almost uniformly compatible, but occurrence of bumps is observed on the surface. ×: Not compatible, and uneven molding due to uneven skin roughness and sheet thickness, etc., are observed. (* 3): Measured using a measuring device (DN-type stress tester manufactured by NIRI KOGYO CO., LTD.) Based on ASTM D-1504, and expressed as an average value in vertical and horizontal directions (Kg / cm ² ). (* 4): Based on JIS P8134 (Kg · cm) (* 5): Indicates the temperature (° C.) measured by the following method. First, both ends of a sheet sample cut to a length of 60 mm and a width of 30 mm are held by clamps of an Instron type tensile tester (IM-500 type autograph manufactured by Shimadzu Corporation), and the clamps are immersed in a silicon oil bath. . Next, the oil bath is heated and heated at a rate of 2 ° C./min, and the temperature at which the test piece starts to rapidly shrink is read by the change in shrinkage stress appearing in a tensile tester. The above temperature was defined as the heat shrink start temperature. This heat shrinkage starting temperature can be regarded almost as it is as the heat resistant temperature of the sheet. (* 6): The following molding machine and mold were used and evaluated according to the following criteria under molding conditions. 1. 1. Molding machine: Kansai Automobile Molding Machine Co., Ltd., contact heating type pneumatic molding machine PK-400 type 2. Molding type: aluminum mold die cover with square rib, cover outer diameter 130 × 170mm, depth 15mm (maximum) Molding conditions: The heating temperature was 15 to 30 ° C. higher than the heat shrinkage starting temperature of each sheet, the heating time was 4 seconds, the molding pressure was 3 kg / cm ² , and the molding time was 4 seconds. 4. Criteria for evaluation of moldability: に: Molded in the same manner as the mold ×: Whitened or torn in part, or not fully expanded and the mold could not be reproduced [0037] (* 7): Sheet Was dissolved in chloroform, and this solution was used as a sample for measurement by gas chromatography (detector; FID). The measurement conditions are as follows. 1. Styrene (monomer), xylene, ethylbenzene,
The measurement of toluene and the like was performed at a column temperature of 115 ° C. using “PEG-20M 25%” (column packing material). 2. For measurement of styrene dimer and trimer, refer to “Silicon OV
-17, 3% "(column packing material), column temperature 190 ° C (for dimer), 260 ° C (for trimer)
Performed in The biaxially stretched heat-resistant styrenic resin sheet of the present invention has the following characteristics, and its industrial utility value is extremely large. (1) The sheet of the present invention has transparency, strength and moldability equal to or higher than those of a conventional general-purpose polystyrene resin sheet, and also has excellent heat resistance. (2) The sheet of the present invention can be prepared by changing the content of the polyphenylene ether in the mixed composition as a raw material within the range specified in the present invention in a range from about 105 ° C. to about 150 ° C.
It can be provided with heat resistance up to ° C, and can be used for the production of various molded products suitable for reheating foods for retort foods and for heating microwave ovens. (3) Since the sheet of the present invention does not require severe conditions for processing of the raw material composition, coloring due to thermal deterioration can be suppressed, and processing cost can be reduced to about 1/5.

Continuation of front page (56) References JP-A-58-111817 (JP, A) JP-A-57-144728 (JP, A) JP-A-57-105445 (JP, A) JP-A-57-105414 (JP) JP-A-56-34716 (JP, A) JP-A-55-137130 (JP, A) JP-A-53-66991 (JP, A) JP-A-52-108455 (JP, A) JP-A-50-51197 (JP, A) JP-A-50-51150 (JP, A) JP-A-48-81985 (JP, A) JP-A-5-24155 (JP, A) JP-A-2-55122 (JP, A A) JP-A-2-218724 (JP, A) JP-A-1-146918 (JP, A) JP-A-4-168153 (JP, A) JP-B-49-5226 (JP, B1) JP-B-48 -12197 (JP, B1) JP-B 47-23184 (JP, B1) JP-B 47-1782 (JP, B1) JP-B 47-1210 (JP, B1) (58) Fields surveyed (Int. . ^7, DB name) G08F 283/08 C08J 5/18 C08L 1/00 - 101/16 B29C 53/00 - 55/30 CA (STN) REGISTR (STN)

Claims (1)

(57) [Claim 1] 25 to 100 parts by weight of a polymer (A) obtained by polymerizing 30 to 95 parts by weight of a styrene monomer in the presence of 5 to 70 parts by weight of polyphenylene ether Part and a styrene-based polymer (B) in an amount of from 0 to 75 parts by weight , extruded into a sheet form, and then extruded in a biaxial direction with 1.
A biaxially stretched heat-resistant styrene-based resin sheet, which is stretched 5 to 5.0 times to have a thickness of 0.1 to 1.0 mm .