JPS6365491B2 - - Google Patents

Description

Detailed description of the invention: Expansion ratio produced by incorporating low boiling point organic substances such as propane, butane, freon, etc. into polystyrene, a copolymer resin mainly composed of styrene and copolymerizable with styrene, such as butadiene, methyl acrylate, etc. 8 to 18 times larger thermoplastic foam resin sheet, or polystyrene (PS), high impact polystyrene (HIPS) on one or both sides of this sheet,
Molded product containers based on foamed composite sheets made by laminating unexpanded thermoplastic films made of unoriented polypropylene (CPP), polyethylene (PE), etc., generally have sharp dimensions and shapes as their quality characteristics. In addition to this, it is required to maintain a stable stacking height and to have sufficient resilience strength when subjected to bending and deflection deformation.

For ordinary molded containers, the rising angle of the side walls is always determined by the shape design, but in this case, stacking, especially whether or not the side walls are in contact with each other, is important. First, the stacking height is simply determined by the influence of the side wall thickness. That is, if the side wall thickness is made thick, the stacking height must be maintained high, and conversely, if the side wall thickness is made thin, the stacking height can be maintained low.

Note that the stacking height of molded product containers made from foamed sheets is generally much larger than those made from non-foamed sheets; This is unavoidable due to the characteristics of molded products.

However, from the perspective of transportation and inventory, it is more economical to keep the stacking height as low as possible because it increases the number of items loaded and keeps the inventory space smaller for the same number of items. On the other hand, when considering the deflection deformation strength required for molded product containers, it is easy to see that the same type of base material, basis weight, foaming degree, etc. When it comes to things, it is better to simply make the shape as thick as possible because you can maintain a high overall rigidity, which is advantageous on the contrary, and in the end,
Both exhibit superiority and inferiority in contradictory directions. Under such circumstances, the present invention is designed to reduce the deflection deformation strength that acts around the mouth of a molded product container not only due to the influence of the overall thick-walled shape, but also due to the wall thickness around the mouth and the area around the rise of the bottom. There is a particularly strong correlation with the wall thickness of the material, and this tendency is particularly noticeable for containers with relatively low stretching ratios, such as meat trays or lunch boxes, and which have a rectangular shape. I discovered this and arrived at this invention. That is, as a means of increasing the thickness, the structure has a void larger than the thickness of the formed stretched sheet, and the surrounding area can be air-tight with a clamp, so that it is -500 mmHg from both surfaces of the base material.
(gauge pressure) or higher vacuum pressure, such as -600mmHg (gauge pressure) or -650mmHg (gauge pressure), and for male molds, the temperature is controlled at 50 to 60℃ to enable in-mold foaming. When the heated sheet is introduced into the mating mold and molded, the area to be reinforced is the area excluding the side wall part that affects the stacking height, that is, the area around the mouth, the bottom, and the area around the rising part of the bottom. In order to make this part even more highly foamed and thick-walled in part or all, we created a shape with the maximum free foaming structure achieved by maintaining the inside of the mold under a vacuum atmosphere. The molding method has been improved in order to obtain a molded container having the highest strength within the stacking height limit even with the base materials.

This invention uses a thermoplastic foam resin sheet or a composite foam resin sheet in which a non-foamed thermoplastic resin layer is laminated on a thermoplastic foam resin sheet to be heat-plasticized and vacuum-formed in a male-female mold. In the method of molding a container, the wall thickness of the side wall of the molded product is regulated on the mold surface so that it is less than or equal to the maximum free foaming degree wall thickness achieved by in-mold foaming, and some or all of the other parts are -500mmHg from both sides of the male and female molds so that the maximum free foaming degree of in-mold foaming is greater than the wall thickness.
The content is a double-sided vacuum forming method by applying the above vacuum pressure.

Fig. 1 shows a schematic cross-sectional view of an example of the mold according to the present invention in a state where the molded product shape is finally achieved, and Fig. 1 shows a schematic cross-sectional view of an example of the mold according to the present invention in a state in which the shape of the molded product is finally achieved. Although this is a mold for forming a thermoplastic foaming resin sheet with in-mold foaming, a schematic cross-sectional view is shown in which the wall thickness of the molded product is regulated on both surfaces of the mold. In addition, in order to clearly show the difference in the specific content between the two, enlarged views of the bubble shape and cross-sectional shape associated with the in-mold foaming of the heated stretched foam sheet around the mouth are shown below. I will explain about it.

Generally, in the molding operation itself, a heated sheet that has been plasticized, softened, and foamed is led to a molding station, and at the same time stretch molding is first carried out in molds 2 and 3, 2' and 3', and the foamed sheet is formed around the mold mouth. With the air tightness created by mold clamping, vacuum pressure is applied from the vacuum pump through the pores 4 and 4' that communicate with both surfaces of the mold via piping 5 and 5', so that the mold is still in a plasticized state. Stretched sheet 1, 1' kept
foaming occurs within the mold under the balance between the gas pressure within the closed cells and the tension caused by the viscoelastic force of the thermoplastic resin forming the bubbles, and finally the mold surfaces 2, 3, 2',
The molded shape is achieved by removing the resin temperature from 3' and cooling and solidifying, and there is no particular difference between the two in terms of the molding operation itself.

However, as shown in the figure, the molding method for the thermoplastic foam resin sheet in this case is called a mated mold, in which both male and female molds are fitted together. , the gap shape is designed to be the same as the target cross-sectional shape of the molded product, and in that case, the wall thickness of each part of the molded product is less than the maximum foaming degree achieved by in-mold foaming. Whereas the inner and outer shapes of the molded product and its wall thickness are completely controlled by the mold surface, in the method of the present invention, as shown in FIG. The shape of the mouth area, bottom area, and surrounding area, excluding the wall thickness, is restricted only from one side of the mold. In other words, whether the shape of the molded product is to follow the male mold or the female mold is determined by the market demand in each case, but the vacuum applied to both sides of the stretched sheet is Any shape can be selected by using a pressure regulating valve to create a pressure difference, but in any case, the shape is restricted only from one side, and this part is achieved by in-mold foaming. Since the molded product is constructed with the maximum free-foaming thickness, the major feature is that it aims to strengthen the deflection deformation strength that occurs at the mouth.

Example 1 Average when an extruded sheet with a thickness of 2 mm and a foaming ratio of 11.3 times made of polystyrene as a base material using Freon as a blowing agent was heated for 10 seconds in a far-infrared heating furnace set at an internal temperature of 180°C after curing. Foaming thickness is 4.2
It was warm in mm. This has vertical and horizontal external dimensions of 160 x 160 mm, drawing depth of 22 mm, rising angle of 35.5°, and side wall mold gap.
Meat tray mold with a free foam structure of 3.37 mm and a height range of 5.5 mm from the top and bottom of the mouth, male surface vacuum - 650 mmHg (gauge pressure), female mold surface vacuum -
The meat tray, which is molded using 600mmHg (gauge pressure), has a wall thickness around the mouth of 4.7mm and a wall thickness at the side wall.
3.37 mm, the inner surface shape of the bottom rising wall thickness of 4.6 mm matches the surface shape of the male mold, the stacking height per 100 sheets is 580 mm, and a concentrated deformation strain of 5 mm is applied to the center around the mouth. It had a repulsion strength of 390 g when

In contrast, molding was performed using a conventional mold with a mold gap of 3.37 mm and a vacuum level of -600 mmHg, where both the inner and outer walls of the molded product were regulated by the mold surface shape. The wall thickness of each part is 3.37mm,
Stacking height per 100 sheets is 580mm, 5mm around the mouth.
The repulsion strength when subjected to intensive deformation strain is 340g
It had the following characteristics.

Example 2 Average when an extruded sheet with a thickness of 2 mm and a foaming ratio of 14 times, made of polystyrene as a base material using Freon as a blowing agent, was heated for 6.5 seconds in a far-infrared heating furnace set at an internal temperature of 200°C after curing. Foaming thickness is 3.7mm
It was hot. This has vertical and horizontal external dimensions of 250 x 100 mm, drawing depth of 15 mm, rising angle of 35.5°, and side wall mold gap of 3.37 mm.
mm, the meat tray mold has a free foaming structure at a height of 5.8 mm from the top and bottom of the mouth, and the vacuum level on the male mold side is -650 mmHg (gauge pressure), and the vacuum level on the female mold side is -600.
The meat tray molded using mmHg (gauge pressure) has a wall thickness around the mouth of 4.5 mm, a side wall thickness of 3.37 mm,
The inner shape of the bottom rising wall thickness of 4.8 mm matches the surface shape of the male mold, the stacking height per 100 sheets is 580 mm, and when a concentrated deformation strain of 5 mm is applied to the center around the mouth. It had a repulsion strength of 375 g.

In contrast, with a conventional mold where the mold gap between each part is 3.37 mm and the thickness of the molded product on both the inner and outer surfaces is regulated by the mold surface shape, -600 mmHg (gauge pressure)
The thickness of each part is 3.37mm, the stacking height per 100 sheets is 580mm, and the repulsion strength is 325g when a concentrated deformation strain of 5mm is applied around the mouth. It had the following characteristics.

[Brief explanation of drawings]

Figure 1 is an explanatory sectional view showing the state of the molding die of the present invention at the end of molding, Figure 2 is an enlarged sectional view of the area around the mouth of the molded container, and Figure 1 is a conventional conventional An explanatory cross-sectional view showing the state of the molding die at the end of molding, and FIG. 2 is an enlarged cross-sectional view of the vicinity of the mouth of the molding container. 1, 1' are molded thermoplastic foam resin sheets; 2,
3, 2', 3' are molds, 4, 4' are vacuum holes,
5, 6 and 5', 6' are piping from the vacuum pump.

Claims (1)

[Scope of Claims] 1. After heating and plasticizing a thermoplastic foaming resin sheet or a composite foaming resin sheet in which a non-foaming thermoplastic resin layer is laminated on a thermoplastic foaming resin sheet, In the method of molding a container in A double-sided vacuum forming method for containers characterized by applying a vacuum pressure of -500 mmHg or more from both sides of male and female molds to achieve the maximum free foaming thickness of in-mold foaming without restricting the thickness on the mold surface. . 2. The double-sided vacuum forming method according to claim 1, wherein the portion other than the side wall of the container is the bottom of the container, a rising portion around the bottom, and/or the periphery of the mouth.