JP3560092B2 - Thermoplastic resin foam sheet molding method - Google Patents

Description

[0001]
[Industrial applications]
The container molded from the thermoplastic resin foam sheet is used with the contents contained therein, and its strength is very important. An inexpensive and high-strength container is strongly desired in industry.
In particular, the strength of the container needs to be balanced as a whole, but it is important to give strength to the mouth or the side wall due to the characteristics of use or structure of the container. In order to secure the strength of a container made of a thermoplastic resin foam sheet, it is generally attempted to increase the basis weight or increase the thickness to secure the strength, but increasing the basis weight is economically disadvantageous, and If the thickness is increased, the stacking height is increased and the capacity is increased, which is disadvantageous in storage or transportation of containers. Furthermore, in recent years, a tray called a low stack tray has been put on the market to reduce the stacking height of containers for the purpose of lowering distribution costs, press and thin the side walls, foam the bottom with vacuum on both sides, and secure the bottom thickness strength. ing. However, since the thickness of the side wall portion is small, the strength is apt to decrease, and it is generally necessary to increase the sheet basis weight, which is economically disadvantageous. Therefore, a container having a low weight and a sufficient strength is required.
[0002]
[Problems to be solved by the invention]
Thermoplastic resin foam sheet is heated in a heating furnace to soften and foam, then transferred to the forming section, stretched using a male and female fitting mold, pressed with a mold, and molded into a container of a predetermined shape Generally it is.
A vacuum is often used at the time of molding to secure the pattern at the bottom, the appearance of characters, or the thickness of the mouth or the bottom. The vacuum system is composed of one male and one female system. The timing of the vacuum can be adjusted by increasing the vacuum of the female mold to reduce the number of sheets brought into the molded product, reducing the weight of the container and reducing the wall thickness. Strength drops. Conversely, if the sheet is pulled in with a male mold, the meat is concentrated on the bottom, the basis weight at the mouth or side wall is reduced, the basis weight within the container is poor, and sufficient container strength cannot be obtained. For this reason, a method of using a sheet with a higher basis weight or finely controlling the vacuum timing to make the basis weight of the container bottom and side uniform has been tried. I can't concentrate more on the club.
[0003]
Then, the present inventors have solved the above-mentioned problems, and have invented a method of forming a low-cost thermoplastic resin foam sheet to obtain higher container strength and economically advantageous inexpensive containers.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a method of heating and plasticizing a thermoplastic resin foam sheet, forming a container with a fitting mold by vacuum suction of at least a side wall portion of an outer surface of the container. A method for forming a thermoplastic resin foam sheet, characterized in that the vacuum suction of the side wall is separated from the vacuum suction of the bottom, and the mouth or the side wall is suctioned earlier than the bottom , and the basis weight distribution is on the side. This is a method of obtaining a high-strength container from a concentrated thermoplastic resin foam sheet .
[0006]
Further, it is preferable that the thermoplastic resin foam sheet is foamed polystyrene.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
1 to 4 show a concrete example of a method of forming a container when a foamed polystyrene sheet is used as a thermoplastic resin foam sheet.
[0008]
The male-female fitting mold A is composed of a male mold 1 and a female mold 2. First, as shown in FIG. 1, the expanded polystyrene sheet 3 is fed between the opened male mold 1 and female mold 2. Here, the sent expanded polystyrene sheet 3 is plasticized and softened in a heating furnace, and is partially drawn in by the male mold 1 as shown in FIG. Suction is performed at a degree of vacuum of 650 mmHg from vacuum holes 4 provided at intervals of 15 mm around the sheet, and the sheet 3 is brought into close contact as shown in FIG. 3, and then male and female molds are fitted. Both sides are sucked through the vacuum holes 5 and 6, and as shown in FIG. 4, the bottom is secured in thickness and molded into a predetermined container shape.
[0009]
Specifically, container shape vertical 150 mm, horizontal 250 mm, a depth 25 mm, was compared with the general method of molding by the basis weight and strength of each part of the molded article obtained in this example and comparative examples. In the comparative example, a vacuum hole was not provided in the side wall, and the bottom and the mouth were fitted in a mold, and then a double-sided vacuum was applied.
[0011]
According to the method of the present example, a molded product having a sufficient strength was obtained, while being a raw material having a low basis weight .

[0012]
【The invention's effect】
As is clear from the above description, the following operations and effects are achieved.
According to the method for molding a thermoplastic resin foam sheet according to the present invention, the thermoplastic resin foam sheet is heated in a heating furnace, softened and foamed, then transferred to the molding section, and the sheet is stretched using a male and female fitting die, Pressing and molding with vacuum together with a mold to mold into a container of a predetermined shape, the series of vacuum at the time of fitting the female mold is vacuum suction at the container mouth or side wall and vacuum suction at the bottom. Separate and precede the timing of vacuum suction at the bottom.Simultaneously or slightly delay pulling in the sheet with a male mold, perform vacuum suction on the side, adhere the sheet to the side, and distribute the basis weight on the side. To form a high-container container. That is, by bringing the sheet into close contact with the die mouth or the side wall portion, it is prevented from shifting to the bottom portion of the sheet, and a portion having a high basis weight distribution is formed at the mouth or the side wall portion. Ensure the strength of the part.
[0013]
In other words, this molding method is characterized in that even if the thickness of the side portion such as a low stack tray is reduced to reduce the stacking height, the strength is maintained by securing the basis weight of the side wall portion. The degree of the portion having a high basis weight distribution of the side wall portion can be appropriately adjusted by the position of the side wall portion vacuum hole, the degree of vacuum applied, and the like. The bottom part is also attributed to the container strength to some extent, but the bottom thickness does not affect the stacking height compared to the side part, so it is easy to secure the thickness by double-sided vacuum etc.Thickness strength can be obtained, and even if the basis weight distribution decreases, the strength decreases Does not significantly affect. Therefore, it is effective to secure the bottom thickness by vacuuming on both sides to a thickness that does not affect the stacking height, and it is particularly useful to use them together in the present invention.
For forming the sheet, compressed air from the male mold may be used to bring the sheet into the female mold.
[0014]
In the present invention, the foamed thermoplastic resin sheet is preferably made of a copolymer mainly composed of polystyrene and styrene, such as butadiene, maleic anhydride, and methacrylic acid, which can be copolymerized with styrene. Further, a non-foamed thermoplastic resin film made of polystyrene, high-impact polystyrene, polyethylene, polypropylene or the like may be laminated on one or both sides of the thermoplastic resin foam sheet.
[Brief description of the drawings]
FIG. 1 is a process chart showing a method for forming a thermoplastic resin foam sheet according to one embodiment of the present invention. FIG. 2 is a process chart showing a method for forming a thermoplastic resin foam sheet. FIG. 3 is a thermoplastic resin foam sheet. FIG. 4 is a process diagram showing a method for forming a thermoplastic resin foam sheet. [Description of symbols]
A male and female mating mold 1 male mold 2 female mold 3 expanded polystyrene sheet 4 side wall vacuum hole 5 bottom vacuum hole 6 base vacuum hole

Claims (3)

In a method in which a thermoplastic resin foam sheet is heated and plasticized, and at least the side wall of the outer surface of the container is vacuum suctioned to form a container with a fitting die , the vacuum suction at the mouth or side wall of the outer surface of the container is separated from the vacuum suction at the bottom. And forming a foamed thermoplastic resin sheet by suctioning a mouth or a side wall portion ahead of a bottom portion . The method for molding a thermoplastic resin foam sheet according to claim 1, wherein the basis weight distribution is concentrated on the side portions to obtain a high-strength container from the thermoplastic resin foam sheet. The molding method according to claim 1 or 2, wherein the thermoplastic resin foam sheet is foamed polystyrene.

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