JP2628891B2 - Molded article of biaxially stretched styrene resin sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a molded article formed by forming a biaxially stretched sheet of a syndiotactic polystyrene resin, and for example, heat-cooking an oil-containing fat food as a container for a microwave oven. The present invention relates to a novel molded article that can be used as a container having high temperature oil resistance that does not cause deformation even when it is formed.

(Prior art) A molded article of a biaxially stretched sheet of polystyrene is used in a large amount for a lightweight container or the like because of its excellent transparency and rigidity. However, since these containers have poor heat resistance, they have not been used at all in applications that come into direct contact with boiling water or in applications for heating and cooking with a microwave oven that has rapidly spread in recent years.

(Problems to be Solved by the Invention) The present invention has solved the above-mentioned problems, that is, to provide a molded article which has heat resistance and can be used for an application in direct contact with boiling water and an application for cooking by heating in a microwave oven. Things.

(Means for Solving the Problems) That is, the present invention relates to a molded product obtained by molding a syndiotactic polystyrene resin, wherein the syndiotactic polystyrene resin is represented by the following formula: Wherein R represents a hydrogen atom, a halogen atom, or carbon,
Oxygen, nitrogen, phosphorus or a substituent containing a silicon atom,
n shows the integer of 1-3. ) The molded article has a total light transmittance of 90% or more, and
The density at 25 ° C. of the molded body is 1.00 to 1.15, and
Provided is a molded article formed by molding a syndiotactic polystyrene resin sheet, wherein the molded article has a dimensional change of less than 5% when heated in a dry heat oven at 120 ° C. for 5 minutes. Is what you do.

 Hereinafter, the present invention will be described in detail.

First, the above constituent requirements, that is, the formula Wherein R represents a hydrogen atom, a halogen atom, or carbon,
Oxygen, nitrogen, phosphorus or a substituent containing a silicon atom,
n shows the integer of 1-3. ) Syndiotactic polystyrene resin having high stereoregularity has a steric structure in which phenyl or substituted phenyl groups as side chains are mainly alternately located in the opposite direction to the main chain formed from carbon-carbon bonds. The tacticity is determined by nuclear magnetic resonance (NMR). Tacticity measured by this NMR method can be represented by a ratio of a plurality of continuous structural units, for example, a diad for two, a triad for three, and a pentad for five. However, the structure of the syndiotactic polystyrene resin referred to in the present invention is usually 85% or more in diameter,
Alternatively, it means a pentad having a syndiotactic structure of 50% or more.

Next, gel permeation chromatography (1,2,
The weight average molecular weight measured by 4-trichlorobenzene at 130 ° C.) is preferably selected from the range of 1 × 10 ^{4 to} 5 × 10 ⁶ .

Examples of the syndiotactic polystyrene resin include polystyrene, various alkyl-substituted polystyrenes such as polyalkylstyrene, polyhalogenated styrene, polyhalogen-substituted alkylstyrene, polyalkoxystyrene, polycarboxyalkylstyrene, and polyalkylether styrene. Is mentioned. Specific examples of the nuclear-substituted polystyrene include polymethylstyrene, polydimethylstyrene, polybutylstyrene, polychlorostyrene, polybromostyrene, polyfluorostyrene, polymethoxystyrene, polyethoxystyrene, polycarboxystyrene, polyvinylbenzylpropyl ether,
And polytrimethylsilylstyrene.

Next, the total light transmittance of the second component is 90% or more transparency, the density at 25 ° C. is 1.00 to 1.15,
A molding method for obtaining a molded body having a dimensional change of less than 5% when heated in a dry heat oven at 120 ° C. for 5 minutes will be described. First, the syndiotactic polystyrene resin is formed into a substantially amorphous sheet. As a molding method, a sheet molded using a press or a T-die at a temperature not lower than the melting point of the syndiotactic polystyrene resin is cooled using a cooling press or a cooling roll, preferably at a cooling rate of 150 ° C./min or more. By quenching at a speed, a substantially amorphous sheet can be obtained. At this time, if the cooling rate is low, crystallization proceeds and causes opacity and embrittlement of the sheet.

Next, the substantially amorphous sheet thus obtained is stretched in a temperature range from its glass transition temperature to its cold crystallization temperature.

The glass transition temperature and the cold crystallization temperature vary depending on the type of syndiotactic polystyrene resin and the microtacticity. For example, in the case of polystyrene having a syndiotacticity of 99% or more, the glass transition temperature is 93%. ° C, the cold crystallization temperature was 144 ° C, and the melting point was 268 ° C. If the stretching temperature is outside the above temperature range, a stretched sheet having desired physical properties cannot be obtained, and the object of the present invention cannot be achieved.

As the stretching method, for example, a method such as simultaneous or sequential biaxial stretching can be used using a rolling device or an extension stretching device.

Further, it is necessary to heat-treat the stretched sheet under tension at a temperature equal to or higher than the cold crystallization temperature and lower than the melting point. About 10 minutes to 2 hours is enough for this heat treatment. Without such heat treatment, a heat-treated sheet having sufficiently satisfactory physical properties cannot be obtained.

As a method for obtaining a molded body from the heat-treated sheet thus obtained, a hot plate contact heating type air pressure molding method can be employed. This is heated while holding the heat-treated sheet in contact with the heated hot plate, and after reaching a predetermined temperature,
This is a molding method in which a heat-treated sheet is spread in a mold with compressed air. As the molding conditions, the temperature of the hot plate can be selected from a temperature range of 30 to 45 ° C. from the softening temperature (Vicat softening point) of the resin, and the heating time can be selected from 4 to 8 seconds.

This molded article is characterized in that the dimensional change of the molded article when heated in a dry heat oven at 120 ° C. for 5 minutes is less than 5%.

When this molded article is used as a food packaging container, when evaluated under steam sterilization conditions, it is necessary that there is no dimensional change, whitening, change in appearance, and the molded article of the present invention is particularly useful in this field. is there.

 Hereinafter, the present invention will be described specifically with reference to Examples.

(Examples) 1. Measurement method of total light transmittance It was measured according to ASTM-D1003.

2. Measurement method of density (JISK7112-C method) The measurement was carried out at 25 ° C by a floatation method using a mixed solvent of water, ethanol and zinc dichloride.

Example 1 (1) Production of syndiotactic polystyrene In a stainless steel autoclave having an inner volume of 1500 ml replaced with an inert gas, 600 ml of toluene and 120 ml of methylaluminoxane (manufactured by Toyo Stophor) and 0.6 of tetraethoxy titanium were added.
Then, 600 ml of styrene was added, and polymerization reaction was performed at 50 ° C. for 2 hours. After completion of the reaction, the reaction was stopped with hydrochloric acid and methanol, and the produced polymer was separated by filtration and dried. The obtained porstyrene was 92 g.

The content of the insoluble portion of methyl polystyrene in this polystyrene is 96%, and the stereoregularity of the insoluble portion is determined by 13C NMR.
As a result of spectrum analysis, it was found to have a syndiotactic structure of 99% or more. The gel permeation chromatography of this syndiotactic polystyrene (1,
The weight-average molecular weight measured in 2,4 trichlorobenzene at 130 ° C.) was 48.7 × 10 ⁴ , and the melting points measured using a differential scanning calorimeter were 256 ° C. and 266 ° C.

(2) Manufacture of syndiotactic stick polystyrene biaxially stretched sheet
After being melted and formed by the press described above, the mixture was rapidly cooled to room temperature using a cooling press to obtain a transparent amorphous sheet having a density of 1.05 g / cm ³ .

A calorimetric analysis of this substantially amorphous sheet using a differential scanning calorimeter revealed a glass transition temperature of 93 ° C, a cold crystallization temperature of 144 ° C, and a melting point of 268 ° C.

The sheet was simultaneously biaxially stretched at 110 ° C. with a stretching ratio of 3.0 × 3.0 using a sheet stretcher, and after further stretching, heat-treated at 160 ° C. for 30 minutes while being set on the sheet stretcher.

The obtained sheet has a density of 1.10 g / cm ^{3 and a} total light transmittance of 92.5.
% Transparency.

(3) Opening 170 × 110mm, bottom 150mm × 90mm, depth 40m
Manufacture of m square tray Molding machine; Hot plate heating contact type air pressure molding machine manufactured by Fujita Tekko Co., Ltd. Molding condition: Hot plate surface temperature 180 ° C Heating time 6 seconds, forming time 3 seconds Forming pressure 3.0 kg / cm ³ Using a biaxially stretched sheet, molding was performed under the molding conditions of, to obtain a square tray.

This molded product has a total light transmittance of 91% and a density of 1.11 g / cm ^3.
It was.

The dimensional change of the depth of the molded body when the molded body was heated in a drying oven at 120 ° C. for 5 minutes was 0.56%.

(Effects of the Invention) According to the present invention, there is provided a molded article having heat resistance, which can be used for direct contact with boiling water and for heating and cooking using a microwave oven.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C08L 25:00

Claims (1)

(57) [Claims] 1. A molded article formed by molding a syndiotactic polystyrene resin sheet, wherein the syndiotactic polystyrene resin has a formula Wherein R represents a hydrogen atom, a halogen atom, or carbon,
Oxygen, nitrogen, phosphorus or a substituent containing a silicon atom,
n shows the integer of 1-3. ) The molded article has a total light transmittance of 90% or more, and
The density at 25 ° C. of the molded body is 1.00 to 1.15, and
A molded article obtained by molding a syndiotactic polystyrene resin sheet, wherein a dimensional change of the molded article when heated in a dry heat oven at 120 ° C. for 5 minutes is less than 5%.