JPS6011344A - Method of improving moldability of thermoplastic resin foamed sheet - Google Patents

Abstract

PURPOSE:To retain the secondary foamability of a sheet, by packing a thermoplastic resin foamed sheet that has been allowed to stand under the atmospheric pressure in a film having the permeability of the foaming agent therein up to 0.2g/m<2>.24hr.atm. per 0.01mm. at 20 deg.C. CONSTITUTION:After a thermoplastic resin such as polystyrene, polyethylenes, etc. is melted and kneaded together with a foaming agent such as trichlorofluoromethane, etc. under heating and pressure, the mixture is extruded at normal temperatures under normal pressures into a thermoplastic resin foamed sheet. Then enough air is allowed to penetrate into the cells in the sheet and after the sheet is allowed to stand in the atmosphere to be aged, the sheet is packed in a film having the permeability of the foaming agent therein up to 0.2g/m<2>.24hr.atm. per 0.01mm. at 20 deg.C. According to this method, a large quantity of a foamed sheet can be produced previously to improve the production efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving the moldability of a thermoplastic resin foam sheet.

A foamed sheet obtained by extruding and foaming a thermoplastic resin containing a blowing agent in a molten state under a low-pressure atmosphere is heated and softened again to form a predetermined shape. However, in order to increase the foaming ratio of the conventional container to a higher foaming ratio, the foaming ratio of the two foam sheets must be increased, and for this reason, the foam sheet is Hypertension foam sheets have the disadvantage of being inconvenient to transport and store.

On the other hand, when the foamed sheet is left in the atmosphere, the foaming agent in the cells of the foamed sheet is replaced by air.

At this time, the rate at which air permeates into the bubbles is faster than the rate at which the blowing agent inside the bubbles escapes, as shown in Figure 1 (Figure 1 shows polystyrene containing butane as a blowing agent). This shows the change in the internal pressure of the bubbles over time when the foam sheet is left under atmospheric pressure.) Since the internal pressure of the bubbles in the foam sheet changes, the foam sheet is left under atmospheric pressure for a predetermined period of time to increase the internal pressure of the bubbles. Container molding is performed in a state where secondary foaming ability is imparted, and the foaming ratio of the container can be increased by secondary foaming of the sheet. However, since the state in which the internal pressure of the cells in the foamed sheet is increased cannot be maintained for a long period of time, there is a natural limit to the period from the manufacture of the foamed sheet to the molding of the container, that is, the life of the foamed sheet.

The present invention was developed in view of the above-mentioned drawbacks of the prior art, and maintains the secondary foaming ability of the foam sheet regardless of the length of time from the production of the foam sheet to the container molding, and always eliminates the variation in expansion ratio. The purpose of the present invention is to provide a method for improving the moldability of a thermoplastic resin foam sheet that can be molded into a molded object such as a container or the like.

That is, a thermoplastic resin foam sheet obtained by extruding and foaming a thermoplastic resin containing the foaming agent of the present invention in a molten state under a low-pressure atmosphere is left to mature under atmospheric pressure for a predetermined period of time, and is then injected into the cells of the foam sheet. After infiltrating air, the permeability of the foaming agent contained in the cells of the foam sheet is 20°C.
0.01 Toto') + 0.2 +li' /
The gist of the present invention is a method for improving the moldability of a thermoplastic resin foam sheet, which is characterized by packaging the foam sheet with a film having a strength of less than m.m ·24 hrs-atm.

Thermoplastic resin foam sheet expansion used in the present invention.

Conventionally known thermoplastic resins such as polystyrene, polyethylene, and polypropylene are used as base resins, and blowing agents such as Pronokun, butane, dichlorodifluoromethane, and trichlorofluoromethane are added to these resins to a concentration of 100 to 18%.
It is produced by melting and kneading under heating and pressure at 0'C, 50 to 150 hours/crA (G), and then extruding and foaming at room temperature and pressure.

The foamed sheet is left to mature under atmospheric pressure for a predetermined period of time, and this period is usually preferably 4 to 10 days. If the period of aging of the foam sheet under atmospheric pressure is less than the above period, the amount of air permeation into the cells of the foam sheet will not be sufficient, and the expansion ratio of the container may be increased by secondary foaming during container molding. However, if the above-mentioned period is exceeded, the foaming agent in the cells will escape, and therefore containers obtained by molding such sheets have problems such as the secondary expansion ratio not being improved, which is not preferable. Therefore, in the present invention, leaving the foam sheet to mature under atmospheric pressure for a predetermined period of time means (1) allowing air to sufficiently penetrate into the cells of the foam sheet, and leaving the sheet for a period in which the foaming agent in the cells does not escape, and allowing the cell internal pressure to rise to 1. It is to ripen it so that it becomes atm or higher. A foamed sheet that has been aged under atmospheric pressure to increase the internal pressure of the cells has a thickness of 0 at 20°C and a permeability of the blowing agent contained in the foamed sheet.
, 01 w toF) 0.2 ,! i' / m ・24
Packed in a film of less than hrs/atm. Examples of the film for wrapping the wife include synthetic resin films such as polyethylene naterephthalate, polyamide, and polyvinyl alcohol, and the thickness of these films is usually 50 μm to 200 μm. In addition, in the case of a laminated film, the film as a whole has o, o at 20°C.
i v+m current blowing agent permeability is 0.27i/m
The film is constructed to be less than 24 hrs-atm.

In the present invention, the permeability of the foaming agent contained in the foamed sheet is 0.2 g per 0.01 mm at 20°C.
/ m' ・24hrs ・For films less than atm.

By packaging a foam sheet with a high internal pressure, the foaming agent inside the cells can be prevented from escaping, as shown in Figure 2M2. This shows the change in bubble internal pressure over time when the cell was left under atmospheric pressure and then wrapped in a polyamide film with a thickness of 60 μm.) The state in which the bubble internal pressure was increased can be maintained for a long period of time.

For the packaging of the foam sheet, 9 foam sheets are wound up into a roll, and the permeability of the foaming agent is 0.211/rrj ・24hrs ・at
It may be wrapped in a film with a thickness of less than 100 ft.

Alternatively, the t=it packaging film may be formed into a packaging shape in advance, and the foamed sheet wound into a roll may be stored in the bag and sealed.

As explained above, in the present invention, a thermoplastic resin foam sheet is aged under atmospheric pressure for a predetermined period of time to allow air to penetrate into the cells of the foam sheet, and then the foam sheet is heated to a thickness of 0.01 mm at 20°C. The blowing agent permeability of Totoshi is 0.2 p/
・24hrs ・By packaging the food with a film of less than ATM, air is infiltrated into the bubbles to increase the bubble internal pressure, and the foaming agent in the bubbles of the foam sheet is prevented from escaping, increasing the bubble internal pressure. It is possible to maintain an elevated state above l atm.

Therefore, even if the sheet is kept in a tube for a long period of time after manufacturing the second foam sheet, a container with a predetermined expansion ratio can be obtained without causing a decrease in the secondary expansion ratio during container molding. Since it is not necessary to manufacture foam sheets in accordance with molding demands and it is possible to mass-produce two foam sheets in advance, the manufacturing efficiency of foam sheets can be improved.

In addition, a film with a foaming agent permeability of less than 0.011 mm in thickness and less than 24 hrs.atm was used as the film for wrapping the foam sheet.

The foaming agent can be prevented from escaping within the cells of the foamed sheet without increasing the thickness of the film, and there is no need to increase the tension of the film for packaging the foamed sheet, thereby increasing costs. For example, since the internal pressure of the cells in the foam sheet can be maintained at a high level until the time of container molding, the foaming ratio of the container can be increased due to secondary foaming during molding.

There is no need to increase the foaming ratio of the foam sheet in order to obtain a highly foamed container, and it is possible to prevent the foam sheet from becoming hypertonic and reduce the cost required for transporting and storing the foam sheet.

The present invention will be explained in more detail below by giving Examples and Comparative Examples.

Examples 1 to 4 Polystyrene foam sheets (thickness: 2.3 mm, foaming ratio: 13:9, foaming agent: butane) were aged for 5 days at room temperature and normal pressure, and then sealed and packaged in a film-like bag as shown in Table 1. After that, the foamed sheet was stored at room temperature and under normal pressure, and a portion of the foamed sheet was taken out every time the period shown in the table had elapsed, and a container was formed. The foaming ratio of the obtained container is shown in the same table.

COMPARATIVE EXAMPLE The same foam sheet as in the example was stored bare at room temperature and under normal pressure, and containers were molded using the foam sheet after the same period of time as in the example. The foaming ratio of the obtained container is
Also shown in the table.

[Brief explanation of drawings]

Figure 1 is a graph showing how the internal pressure of the bubbles changes over time when a polystyrene foam sheet is left bare under atmospheric pressure. Figure 2 is a graph showing the change in the internal pressure of the bubbles over time when a polystyrene foam sheet is exposed to atmospheric pressure for 5 days. FIG. 2 is a graph showing the change over time in the internal pressure of the bubbles immediately after the foam sheet was produced when the foam sheet was left to ripen and then wrapped in a polyamide film. FIG. Patent applicant Nippon Styrene Peno 4-Co., Ltd. Japan Zannosic Co., Ltd. Agent Patent attorney Isamu Hosoi, ~゛71

Claims (1)

[Claims] A thermoplastic resin foam sheet obtained by extruding and foaming a thermoplastic resin containing a blowing agent in a molten state under a low-pressure atmosphere is left to mature under atmospheric pressure for a predetermined period of time to allow air to penetrate into the cells of the foam sheet. After that, the permeability of the foaming agent contained in the cells of the foamed sheet becomes 0.0 at 20°C.
A method for improving the moldability of a thermoplastic resin foam sheet, which comprises wrapping the foam sheet in a film having a pressure of less than 0.21/Z/24 hrs-atm.