JPH0116654B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for molding a container using a foam sheet. Conventionally, the method of forming cup-shaped or bowl-shaped containers from foamed sheets such as expanded polystyrene sheets involves stretching and deforming the heated foamed sheet along a mold corresponding to the shape of the container. Molding the container. In particular, when molding is performed using only a male die or a male die and a female die, the center tip of the male die first contacts the foam sheet during molding, and the male die is moved toward the foam sheet side. The foam sheet is stretched and deformed by pushing it in. However, in the above method, the part of the foam sheet where the center tip of the male mold is in contact is constantly stretched toward the periphery, and the wall thickness of that part, which becomes the bottom of the container, is thinner than other parts. I get used to it. As a result, the strength of the container decreases, and the bottom surface may become dented due to the pressing force applied to the bottom surface of the container by the knots used to remove the product during trimming after molding, and the bottom surface may become deformed due to hot water being poured into the container during use. There were some inconveniences. In particular, when the container is a deep container, the above problem becomes important, and improvements have been desired. Therefore, in this invention, we have developed a method for molding containers, especially deep containers, that does not reduce the wall thickness of the bottom of the container and improves the overall thickness distribution, and its structure is as follows: A method of molding a deep container by heating and softening a thermoplastic resin foam sheet and expanding and deforming it in a mold having at least a male die, the method comprising applying friction to at least a portion of the male die corresponding to the vicinity of the bottom of the container. A knurling process consisting of a fine unevenness that is made difficult to slip due to resistance is applied, and the container is formed at the knurled part of the male die while suppressing the expansion and contraction deformation of the foam sheet that comes into contact with the knurled part. There is. Next, embodiments of the present invention will be illustrated below with reference to the drawings. First, as the molding die used in this invention, any method using at least a male mold can be freely applied to known vacuum forming and other various sheet forming methods. In the illustrated embodiment, a pair of male and female molds are used to mold a beverage cup. The male mold 1 shown in Fig. 1 basically has the same structure as a normal molding die, and is formed into an elongated truncated cone shape corresponding to the inner surface shape of the cup container to be molded. There is. Although the shape and dimensions of the male mold 1 can be freely changed depending on the container to be molded, in this invention, the shape and dimensions of the male mold 1 are
As shown in Fig. 5, it is applied to containers with a steep slope angle A of 15° or less, and is applied to deep containers with a ratio H/D of depth H to opening diameter D of 0.7 or more. Since it is preferable, the aperture angle A' of the side surface of the male die 1 should also be within 15 degrees and the ratio H of the height H' (corresponding to the depth H of the container) to the base diameter D' (corresponding to the opening diameter D of the container). ′/D′ too
0.7 or more, and form the shape and size range according to the container. However, there are other effects such as shrinkage after molding, so
In some cases, the dimensions of the container 5 and the dimensions of the male mold 1 do not completely match. Then, the tip of male mold 1 (corresponding to the bottom of the container)
10, and a part of the side surface 11 near the tip surface 10 side is knurled 20. The shape of the knurling part 20 can be any shape as long as fine irregularities are formed on one surface, for example, JIS-B0951 (knurling).
Those stipulated in the above can be used. In the case of the figure, the knurled portion 20 is formed at a knurling angle of 30° as stipulated in the above-mentioned JIS standard. However, the knurling angle may be from 30 to 90 degrees, and either cross stitch or flat stitch can be used. In addition, in the case of a flat sheet, it is preferable to form the knurled grooves on the side surface 11 so that the direction is perpendicular to the generatrix direction in order to increase frictional resistance with the foam sheet described later. In addition, the module size varies depending on the shape and dimensions of the container to be molded, but the module size is 0.2~
A value of 0.5 is appropriate, and a value as small as possible can yield better results. Side surface 11 of the male die 1 of the knurled portion 20
The width h at the part is preferably 1/3 to 1/4 of the total height H' of the side surface 11;
can also be formed. Further, in the bottom surface 10 portion, in addition to forming the knurled portion 20 over the entire bottom surface 10, the knurled portion 20 is formed only near the outer periphery of the bottom surface 10, so that the bottom surface 1
Even if the knurled part 20 is not formed in the central part of the mold 0, the practical effect can be sufficiently exhibited (see Fig. 6). As shown in Fig. 2, the mold 3 has a concave shape larger than the outer shape of the male mold 1 by the thickness of the container, and a foam sheet is inserted between the female mold 3 and the male mold 1. Apply molding. Note that the provision of vacuum suction holes and pressurized air blowing holes in both molds 1 and 3, and the provision of a movement mechanism for the molds 1 and 3 are performed in the same manner as in conventional molding equipment, but illustrations are omitted. are doing. A method for molding a container using the molding molds 1 and 3 described above will be explained step by step. First, as the foam sheet 4 used for molding, a foam sheet made of polystyrene, crosslinked polystyrene, polypropylene, or other various thermoplastic resins can be used. It is also possible to use a layered resin film. The foamed sheet 4 is heated in advance to a predetermined temperature suitable for molding, and then held in the center of the male mold 1 and the female mold 3 (see FIG. 2). Although not shown, the ends of the foamed sheet 4 are fixed and held using a suitable clamp mechanism. Next, when the male mold 1 is moved to the female mold 3 side, the male mold 1
When the tip end surface 10 of the foam sheet 4 comes into contact with the foam sheet 4 and the male mold 1 is pushed into the female mold 3, the foam sheet 4 is stretched and deformed while being drawn toward the female mold 3 (see FIG. 3). At this time, since the tip surface 10 of the male mold 1 forms a knurled portion 20, the frictional resistance between it and the foamed sheet 4 is large, making it difficult for slippage to occur. Therefore, in the process of pushing in the male die 1, the central portion of the foam sheet 4 that contacts the tip end surface 10 of the male die 1 does not expand and its thickness does not decrease, and the peripheral portions of the foam sheet 4 mainly expand. It is stretched and drawn into the female mold 3. Furthermore, when the male mold 1 is pushed into the female mold 3,
The foam sheet 4 extends from the tip end surface 10 to the side surface 11 of the male die 1.
is subjected to elongation deformation while sequentially abutting from the distal end side to the base side. Since the frictional resistance increases at the point where the knurled portion 20 contacts the foamed sheet 4, the expansion and deformation does not occur much further and the wall thickness does not decrease. When the male die 1 is completely pushed into the female die 3 side, the foamed sheet 4 is formed into a predetermined container shape with inner and outer surfaces along the male die 1 and the female die 3 (see FIG. 4). Thereafter, the mold is opened and the molded foam sheet 4 is taken out and trimmed to produce a cup container 5 (see FIG. 5). On the inner surface of the cup container 30 manufactured as described above, an uneven shape of knurling may be formed at the part where the knurling part 20 of the male mold 1 was in contact, but normally, a fine knurling is formed. If it is an eye, it is hardly noticeable in appearance. In addition, the shape of the container to be molded in this invention may be, in addition to the illustrated cup shape, a bowl shape or bowl shape, and in addition to a cylindrical shape, a rectangular tube shape or other irregularly shaped tube shapes may be used.
However, the conditions regarding the aperture angle A of the side surface and the ratio H/D between the depth H and the opening diameter D are applied in the same manner as those for the illustrated shape. Note that this invention can be applied as is to a molding method that uses the male mold 1 alone, but in this case, it is necessary to form vacuum suction holes in the male mold 1 and adopt a so-called vacuum forming method. be. According to the present invention configured as described above, at least the portion near the bottom surface of the container 5, which is the part of the foamed sheet 4 that is most likely to undergo elongation deformation and decrease in wall thickness, has a fine uneven shape that is made difficult to slip due to frictional resistance. By molding using the male mold 1 in which the knurled portion 20 consisting of It is possible to prevent a decrease in the wall thickness around the bottom surface of the container 5 caused by excessive stretching of the container. If the bottom surface of the container 5 has a sufficient wall thickness, the strength of the bottom surface and the strength of the entire container will increase, and the stability when placing the container will also improve. Furthermore, even when hot water is poured into the container, there is no need to worry about it deforming due to heat, as the wall is thick enough. Furthermore, when trimming a molded container, even if the bottom surface of the container is pressed with a knotter, the bottom surface is strong enough to prevent dents or deformation. Next, the central part of the foam sheet 4 that is in contact with the knurling part 20 is not stretched so much, and the peripheral part is retracted into the molding, improving the so-called pull-in rate. ,
The wall thickness or weight of the entire container increases, improving container performance such as strength and heat insulation. By improving the pull rate mentioned above, the elongation of the original fabric will improve, so the mold temperature during molding can be set lower, improving cooling efficiency and reducing cooling time.
It also has a great effect on shortening the overall molding time, that is, speeding up the molding cycle. Therefore, it is an excellent molding method that can successfully mold deep containers, which have conventionally been difficult to manufacture and have had many problems with finished quality. Further, since the knurling portion is simply formed on the male mold 1, the processing cost and equipment cost of the device do not increase, and conventional molding equipment can be used as is, which is convenient. Example 1 Mold shape (male mold) Base diameter D'=76mmφ Tip diameter=46mmφ Height H'=84mmφ H'/D'≒1.1 Aperture angle A'=8゜35' Number of cavities in 1 shot 25 pieces Knurling position Tip surface and side knurling at h = 25 mm from the tip surface m0.2, cross stitch, 30゜2 Resilient foam sheet Expanded polystyrene sheet Width 640 mm, Basis weight 350 g/m ² Thickness 2.0 mm, Expansion ratio 6 times 3 Molding conditions Molding shot length 640mm Furnace temperature (atmosphere) 110℃ Heating time 8.0 seconds Molding time 6.5 seconds Vacuum suction time 4.0 seconds Molding mold set temperature 70℃ Molding timing Male mold precedence 4 Molding results Molded under the above conditions The following table shows the results of various tests conducted on the container of the Example, together with the container of the Comparative Example molded using a male mold without knurling.

【table】

[Table] In the table, the dents on the bottom of the trimming were measured by pressing the bottom of the container with a knob and trimming.
The draw rate is a percentage of the basis weight of the original fabric. The lip strength is the strength in the circumferential direction at the opening of the container, and the top and bottom strength is the strength when the container is pressed in the vertical direction. From the table above, it is clear that the performance of the containers manufactured according to the present invention is much better than the conventional ones.

[Brief explanation of drawings]

The figures illustrate embodiments of the present invention; FIG. 1 is a perspective view of a male mold, FIGS. 2 to 4 are sectional views showing the sequential molding process, and FIG. 5 is a sectional view of a manufactured container. FIG. 6 is a perspective view of a modified example. 1...Male type, 10...Tip surface, 11...Side surface,
20...Knurled portion, 3...Female mold, 4...Foam sheet, 5...Container.

Claims (1)

[Scope of Claims] 1. A method of molding a deep container by heating and softening a thermoplastic resin foam sheet and expanding and contracting it in a molding mold having at least a male mold, the method comprising: A knurling process consisting of a finely uneven shape that makes it difficult to slip due to frictional resistance is applied to the corresponding location in the vicinity, and the male knurling part is used to control the expansion and contraction deformation of the foam sheet that comes into contact with the knurled part, while the container is being knurled. A method for forming a container using a foamed sheet, the method comprising forming a container. 2. The method for molding a container according to claim 1, wherein the squeezing angle during molding is within 15°. 3. The method for molding a container according to claim 1, which molds a deep container having a ratio of container depth to opening diameter of 0.7 or more.