JPS63330A - Preparation of foamed polystyrene sheet - Google Patents

Abstract

PURPOSE:To make it possible to shorten the curing period after preparing a foamed sheet and to obtain a foamed polystyrene sheet having fine cells, by using a specified quantity of a foaming agent comprising both a low b.p. org. compd. and carbon dioxide in a specified ratio against polystyrene resin. CONSTITUTION:In preparing a foamed polystyrene sheet, 0.01-0.20mol of a foaming agent in which the molar ratio of a low b.p. org. compd. to carbon dioxide is 95:5-20:80 is used per 100g of the resin. As the low b.p. org. compd., hydrocarbon compd. such as propane, butane, pentane, hexane etc., and halogenated hydrocarbon compd. such as Freon-11, Freon-12, chloroform, methyl chloride etc., can be used. Carbon dioxide can be used either in a liquid or gaseous state, but it is preferable to use it by mixing in a gaseous state with a low b.p. org. compd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improved method of manufacturing expanded polystyrene sheets.

[Prior Art] Generally, expanded polystyrene sheets are thermoformed and widely used in various food containers such as trays, lunch boxes, bowls, and cups. Each of these containers is required to have the necessary strength, and for this reason, it is important to control the thickness of the container, that is, the thickness of the foamed polystyrene sheet that is the raw material.

Conventionally, foamed polystyrene sheets maintain the strength of containers by utilizing secondary foaming during processing, but if a predetermined period of time does not pass after sheet extrusion, the secondary thickness of the container will deteriorate even if molded under certain conditions. It has the problem that it cannot hold S and requires several days of curing.

In addition, increasing the amount of low-boiling organic compounds mixed to increase the thickness of the sheet will reduce the strength of the container, especially if the above-mentioned container is used at high temperatures, such as pouring boiling water or heating the contents in a microwave. When heated, the strength decreases significantly.

[Means for Solving the Problems] The inventors of the present invention manufactured a sheet under the above-mentioned conditions, and were able to maintain the strength of the container even after thermoforming with a short curing process, and maintain the strength even when the contents were at high temperatures. We have conducted extensive research into a method for manufacturing foamed polystyrene sheets by thermoforming containers with minimal degradation.
The present inventors have discovered that it is effective to use a mixture of a low-boiling point organic compound and carbon dioxide gas as a blowing agent, and have completed the present invention.

That is, the present invention provides a method for manufacturing expanded polystyrene sheets, in which 0.01 to 0.20 m of a blowing agent having a molar ratio of a low boiling point organic compound and carbon dioxide to 100 g of resin is 95:5 to 20:80. .

The present invention summarizes a method for producing a foamed polystyrene sheet characterized by using l.

In the present invention, low-boiling organic compounds are those commonly used as blowing agents for polystyrene, such as hydrocarbon compounds such as propane, butane, pentane, hexane, petroleum ether, freon-11, freon-12, Representative examples include halogenated hydrocarbon compounds such as Freon-113, Freon-114, chloroform, methyl chloride, and methylene chloride, with fluorine-based and hydrocarbon-based compounds being particularly preferred.

Furthermore, although the carbon dioxide of the present invention can be used in either liquid or gaseous form, carbon dioxide in gaseous form is preferably used by mixing it with the above-mentioned low-boiling point organic compound.

The mixing ratio of low boiling point organic compound and carbon dioxide is 9 mol%
5:5 to 20:80, preferably so: 20 to
It is 40:60.

If the carbon dioxide content is less than 5 mol %, the strength will be greatly reduced when hot contents are poured into a container, such as a cup, and the curing period after sheet extrusion cannot be shortened, so the effect of carbon dioxide injection will be poor. On the other hand, if carbon dioxide exceeds 80 mol%, it will separate from the resin and roughen the sheet surface when released from the mold attached to the tip of the extruder.

The injection amount of the blowing agent, which is a mixture of a low-boiling organic compound and carbon dioxide, is selected depending on the thickness and density of the desired expanded polystyrene sheet and the composition ratio of the blowing agent.
The amount is 0.01 to 0.20 mol, preferably 0.02 to 0.15 mol, per 0.00 g. In addition, when the mixing ratio of carbon dioxide is large, it is preferable to use a large amount. If the injection amount of the blowing agent is less than O1O1mo1, the injection amount of the blowing agent mixed with a low boiling point organic compound and carbon dioxide is selected depending on the desired thickness and density of the foamed polystyrene sheet and the composition ratio of the blowing agent. However, resin 1
0.00g/0. O1 to 0.20 mol, preferably 0.02 to 0.15 mol. In addition, when the mixing ratio of carbon dioxide is large, it is preferable to use a large amount. When the amount of foaming agent injected is 0.01 moJ, the expanded polystyrene sheet extruded once is likely to crack. On the other hand, if the injection amount exceeds 0.20 mol, the melt viscosity decreases and the surface of the extruded polystyrene foam sheet becomes rough.

The polystyrene used in the present invention is not particularly limited, and in addition to general-purpose polystyrene and impact-resistant polystyrene, copolymerized polystyrene with α-methylstyrene, maleic anhydride, methacrylic acid, etc. can also be used.

In the present invention, talc is also used as a cell conditioner.

There is no problem in adding a small amount of inorganic substances such as silica gel and calcium carbonate.

The method of the present invention can be achieved by injecting carbon dioxide together with a low-boiling point organic compound into a conventional extruder for expanded polystyrene sheets. A good sheet can be obtained by maintaining the pressure released from the mold.

[Effects of the Invention] According to the present invention, the use and waste of low-boiling point organic compounds is significantly reduced when extruding foam sheets of the same thickness and density;
The curing period can be shortened and the inventory burden can be reduced.

Another feature of the present invention is that since carbon dioxide is used, the cells can be made finer, without the use of inorganic substances or chemical blowing agents that were conventionally added for the purpose of making cells finer. Or at least a foamed polystyrene sheet with fine cells can be obtained.

Therefore, non-uniformity of the foamed sheet, dirt on the mold at the tip of the extruder, and associated defects, which are presumed to be caused by such inorganic substances or chemical foaming agents, are greatly reduced.

Furthermore, when using a flammable low-boiling organic compound as a blowing agent, the flammable low-boiling organic compound volatilizes at the tip of the extruder, which is dangerous, but with the present invention in which carbon dioxide is mixed, this risk is much greater. It has been greatly eased.

[Example] The present invention will be explained below with reference to Examples.

Examples 1 to 4 0.1 part by weight of talc was added to 100 parts of polystyrene, and the mixture was melt-kneaded using an extruder with an inner diameter of 50 mmφ.
A blowing agent was press-injected in the proportions shown in Table -■. The foamed sheets were discharged into the atmosphere from a mold attached to the tip of the extruder to obtain foamed sheets with a thickness of 1.5 mm, and the densities of each were listed in Table I. Example 1.2 is for a shrink-molded cup, Example 3.4
is a foamed polystyrene sheet for vacuum forming trays.

In addition, the expanded polystyrene sheet obtained as described above was manufactured in 1
After 1 day and 30 days, the sample was left in a dryer at 150° C. for 1 minute, and the change in thickness was measured and expressed as the secondary expansion ratio. A comparison was made 1 day and 30 days after sheet production, and there was almost no difference.

Furthermore, a cup with a diameter of 70 mm and a depth of 85 mm was manufactured using the foamed sheet of Example 10 that had been manufactured for 10 days.
When the cup was filled with water at a predetermined temperature (85°C and 25°C) and the load required to compress the center of the cup by 10 mm was measured. A 97% loading of 150 gG) was required.

Comparative Example 1 Using the same equipment as in Example 1, 0.5 parts by weight of talc was added to 100 parts by weight of polystyrene to obtain a foamed sheet having the same thickness and density as Freon-12 alone. When the talc was used as in Example 1, the cells were coarse and a foamed sheet with an excellent appearance could not be produced.

A cup was made in the same manner as in Example, and the load was measured. When water was added at 25°C, it was the same as in Example 1, but at 85°C, the weight decreased to 73%, indicating that it was weak. .

Furthermore, there was a considerable difference in the secondary foaming ratio between 1 day and 30 days after production.

Comparative Example 2 A foamed sheet having the same thickness and density as in Example 3 was obtained by extrusion in the same manner as in Example 3 except that the foaming agent was changed to Freon-12 alone.

The secondary foaming ratio of this foam sheet is listed in Table-■,
There was a large difference between 1 day and 30 days after sheet production, and after 1 day, the secondary foaming was insufficient for use as an original fabric for trays. (The secondary foaming ratio is normally required to be 1.8 to 2.2 times.) Comparative Example 3 Using the same equipment as in Example 1, the foaming agents shown in Table 1 were injected. Because the amount of carbon dioxide used was excessive, the resin released into the atmosphere from the mold attached to the tip of the extruder had uneven thickness, making it impossible to obtain a uniform extruded sheet.

Claims (1)

[Claims] In the method of manufacturing expanded polystyrene sheet, resin 1
00g, a blowing agent in which the molar ratio of low boiling point organic compound and carbon dioxide is 95:5 to 20:80.
A method for producing a foamed polystyrene sheet, characterized in that 20 mol is used.