JPS5978812A - Method of molding thermoplastic resin container and molds therefor - Google Patents

Abstract

PURPOSE:To mold a container having no flaw on the surface by a method wherein heated and softened sheet is held by clamps ad pushed by a small plug into the cavity of a female mold and then compressed air is injected into the plug and at the same time air in the cavity of the bottom force is sucked. CONSTITUTION:The thermoplastic sheet S heated to the temperature capable of thermal molding is put between split mold holds 3 and clamps 4, a bottom force 1 is moved toward the sheet, the split mold 2 is closed by pressing the split mold 2 against the hold 3 and the clamp 4 are moved to hold the sheet S by the holds 3 and the clamps 4. A protrusion 5 smaller than the cavity 6 of the bottom force 1 is inserted into the cavity 6 to push and strength the sheet S and then compressed air is injected into the cavity and the air between the sheet S and the bottom force 1 is sucked from the exhaust port 7 of the bottom force to mold a container by sticking the sheet S closely to the bottom force 1. After completion of molding, the split mold is opened in the form of a petal to take the container out of the female mold 1 and then to be trimmed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for molding a thermoplastic container by a plug-assisted thermoforming method and a mold used therefor.

More specifically, the present invention relates to a molding method suitable for manufacturing thermoplastic polyester containers suitable for plastic cans, and a mold used therein.

Vacuum forming involves heating and softening a thermoplastic plastic sheet, pressing it against the desired mold, eliminating air in the gap between the mold and the material, and molding the sheet closely to the mold using atmospheric pressure, or using compressed air at or above atmospheric pressure or vacuum. Thermoforming such as air pressure forming is widely used because the machinery and molds are relatively simple compared to injection molding and blow molding. The plug-assist molding method, which is one of the thermoforming methods, has the following advantages: (1) wall thickness can be adjusted, (11) there is no effect of molded parts that are in instant contact even in multi-cavity molding, and the 4iD outer surface can be precisely finished. Most concave molded products such as cups and refrigerator door liners are molded using this method.

On the other hand, as a soft drink container, instead of conventional glass bottles and metal cans, silk cans have been proposed, which have excellent impact resistance and are easier to dispose of than metal cans. Some thermoplastic polyester cans have been put into practical use because of their good barrier properties. However, plastic cans obtained by the conventional plug-assisted molding method have a diameter/depth ratio of 1/1 due to the relationship between the diameter of the can lid and the capacity.
It is a deep drawing of 5 to 1/2, and due to the forming method, (1) the mouth part is thick and it is difficult to seal it with the lid, (it) the degree of orientation in the vertical direction is large, Disadvantages include the fact that even a small impact can easily cause vertical cracking, and the diameter of the lid is larger than the can body, making it difficult to hang in a vending machine. As a molding method to make the mouth part thinner, the inner radius R of the tightening part of the plastic sheet is changed to the radius r of the container flange.
1.2 to 1.8 times
No. 7917) has been proposed, but although this method makes the mouth thinner, it does not improve vertical cracking resistance, the diameter of the lid cannot be made smaller than the can body, and the plug softens the can. When pushing the plastic sheet into the mold, the plastic sheet may rub against the corner of the mouth of the mold, potentially damaging the product surface. Therefore, the present inventors investigated a plug-assisted molding method for thermoplastic plastics that eliminates the above-mentioned drawbacks, and as a result, they arrived at the present invention.

That is, in the present invention, a thermoplastic sheet heated to the extent that it can be thermoformed is held by upper and lower clamps, and the sheet is molded into a female mold by a plug by passing through a split mold having an inner diameter smaller than the diameter of the female mold opening. After pushing it inward to form a recess, pressurized fluid is forced into the recess, or air between the female mold and the sheet is discharged by suction, and the sheet is brought into close contact with the female mold to form a container. Next, the method for molding a thermoplastic plastic container is characterized in that the split mold is opened in a petal-like manner to take out the container, and the mold is located at the outer edge of the female mold mouth when closed, which is suitable for molding the container. A split mold 2 that forms an inner diameter smaller than the diameter of the mold opening and opens and closes in a petal-like manner to a diameter equal to or larger than the diameter of the female mold opening when opened, an elastic body 10 that opens and closes the split mold, and a split mold that presses the split mold. The present invention provides a mold for plug assist thermoforming, which is characterized by comprising a presser foot 3 and a clamp 4 that faces the split die presser and grips a thermoplastic sheet.0 The thermoplastic plastic used in the present invention Specifically, the sheet includes, for example, polyethylene, polypropylene, borybutene, poly4-methyl-1-pentene, and ethylene.
Polyolefins such as vinyl acetate copolymers, polyvinyl chloride, fluororesins, polystyrene, polyvinyl acetals, polyvinyl compounds such as polymethyl methacrylate, nylon-6, nylon-6,6, nylon-6,10,
Nylon-6, 12, nylon-11 and nylon-1
Polyamides such as No. 2, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene isophthalate/terephthalate copolymers, polyacrylonitrile, polycarbonate, polyimide, and A
Extrusion molding and compression molding of thermoplastic plastics such as BSζ
It is in the form of a sheet or film obtained by injection molding or the like. Among the thermoplastic plastics, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene isophthalate/terephthalate copolymers are preferred because of their excellent rigidity, transparency, gas permeation resistance, and thermoformability.

The method of the present invention includes heating the thermoplastic sheet to the extent that it can be thermoformed, and forming the thermoplastic sheet through a split mold having an inner diameter smaller than the diameter of the female mold opening, preferably 0.8 to 0.95 times smaller. After gripping the sheet with a split mold presser and a clamp, and pushing the sheet into the female mold with a plug, preferably a plug having a diameter 0.6 to 0.8 times the diameter of the female mold opening. In this method, the air between the female mold and the sheet is discharged, the container is molded by bringing the sheet into close contact with the female mold, and then the split mold is opened like a petal to take out the container.

Since the method of the present invention performs thermoforming using a split mold having an inner diameter smaller than the diameter of the female mold opening, the diameter of the opening of the container is smaller than the diameter of the container body. That is, a container with a necking structure is obtained, and even when a metal lid is placed on the container and tightened, the lid portion does not protrude from the container body, and the container is hung in a vending machine.

Another object of the present invention is to form a female mold having an inner diameter smaller than the diameter of the female mold mouth when closed and located at the outer edge of the female mold mouth suitable for molding a thermoplastic plastic container having a necking structure. A split mold 2 that opens and closes like a petal with a diameter equal to or larger than the mouth diameter, an elastic body 10 that opens and closes the split mold, a split mold presser 3 that presses the split mold, and a thermoplastic plastic sheet facing the split mold press. An object of the present invention is to provide a mold for plug assist molding, which is equipped with a clamp 4 for gripping a plug assist mold.

The split mold 2 is located at the outer edge of the female mold mouth, and forms a donut-shaped object with an inner diameter smaller than the female mold mouth diameter when closing, that is, forming a container, and when opening, that is, taking out the molded container. It is a part that opens like a petal to a diameter equal to or larger than the diameter of the mold opening, so that it does not obstruct the removal of the container. The split mold 2 is divided into at least two parts, usually three or more parts, in order to open and close like petals. The cross-sectional shape of the split mold 2 is
As shown in FIG. 7, it is preferable that the inner surface forms a curved line that is continuous with the female inner surface shape and matches the shape of the intended container.

The split mold 2 is connected to the opening of the female mold by an elastic body 10 and a hinge member 11 so as to open like a petal except when forming a container. Specifically, the elastic body 10 includes coil springs and bamboo shoot springs such as compression springs, tension springs, and torsion springs;
Alternatively, a string or block made of rubber or urethane elastic material, or something that functions equivalently to these, such as an electromagnet, may be used.

The split mold presser 3 functions as a presser for closing the split mold 2, which is opened like a flower petal by means of an elastic body 10, during container molding, and also holds the thermoplastic sheet in opposition to a clamp 4, which will be described later. It is a part that The split mold presser 3 may have any shape as long as it does not protrude beyond the inner diameter of the split mold 2 when the split mold 2 is pressed, but it is preferably a plate with a circular hole or a ring shape. The diameter of the split mold presser 3 must also be larger than the diameter of the female mold in order to improve the ejection of the molded product.

The clamp 4 is a part that faces the split mold presser and grips the thermoplastic sheet, and the shape does not matter as long as it does not extend beyond the inner diameter of the split mold 2.
Preferably, in order to securely grip the sheet, a plate, ring, or cylindrical object having a circular hole of the same diameter facing the split die presser 6 is preferable.

An embodiment of the method and mold of the present invention will be described below with reference to the drawings.

FIGS. 1 to 6 show schematic diagrams of a method for forming a container. Approximately 1
After placing the polyethylene terephthalate sheet S heated to 50°C between the split die presser 3 and the clamp 4 (first
), the female mold 1 is moved in the sheet direction and the split mold 2 is pressed against the split mold presser 3 to close the split mold, and the split mold presser 6 is moved to connect the split mold presser 6 and the clamp 4.
The polyethylene terephthalate sheet S is gripped by (FIGS. 2 and 3). Next, after extending the plug 5 into the female mold (Fig. 4), 7 kg/apt was applied to the inside of the female mold.
At the same time, the compressed air of Step 2 is injected, and the air between the polyethylene terephthalate sheet S and the inside of the female mold 6 is discharged from the exhaust hole 7 at the bottom of the female mold at 600 mmI (g), and molded into a container 8. (Fig. 5). After the completion of molding, the female mold and male mold are raised or lowered, the split mold 2 is opened like petals, and the container 8 is taken out from the female mold 1 (Fig. 6). Trimming, etc. is performed on the product.

FIG. 7 and FIG. 8 show a mold used for thermoforming of the present invention. The female mold 1 is equipped with the above-mentioned split mold 2 at the outer edge of its mouth, and a space 6 corresponding to the intended can-shaped product is recessed inside the female mold 1.

A discharge outlet [J7] communicating with a pressure reducing device (not shown) is drilled at or around the bottom of the space B. split mold 2
An elastic body 10 and a hinge member 11 are attached to the upper peripheral edge of the female mold 1.
are connected by When the mold is opened, that is, when the split mold 2 cannot be pressed by the split mold presser 6, the split mold 2 is always held by the elastic body 10.
It is opened like a petal (Fig. 8). The mold is also equipped with a clamp 4 opposite the split die holder 3 for gripping a thermoplastic sheet (not shown).

The mold is further fixed to a base plate (not shown), and an opposing plug (not shown) is connected by toggle or hydraulic pressure.
It is now possible to move in the direction of

In addition, in FIG. 6, there is one space 6, but when trying to obtain a large number of molded products at once, two or more spaces 6 are provided in the mold and the space 6 is placed at the corresponding position. This can be done by providing a plug.

The female mold used in the present invention has a simple structure as a mold for manufacturing containers with a necking structure, so it prevents the equipment from becoming complicated and is less likely to break down, especially when trying to obtain containers by molding multiple pieces. It is extremely useful as it can improve the yield.

[Brief explanation of drawings]

1, 2, 3, 4, 5 and 6 are schematic sectional views of the container molding method of the present invention, and FIGS. 7 and 8 are schematic sectional views of the mold according to the present invention. FIG. 1...Female die 2...Split die 3...Split die presser foot 4...Clamp applicant Kazudai Yamaguchi, agent of Tamai Petrochemical Industry Co., Ltd. 1 Figure 2 Figure 3 Figure 4/ / Figure 5 Figure 6 Figure 7

Claims (4)

[Claims] (1) Hold a thermoplastic plastic sheet that has been heated enough to be thermoformed with upper and lower clamps, pass it through a split mold having an inner diameter smaller than the diameter of the female mold opening, and insert the sheet into the female mold using a plug. After pushing out the sheet to form a recess, pressurized fluid is injected into the recess and/or air between the female mold and the sheet is discharged by suction, and the sheet is brought into close contact with the female mold to form a container. . A method for molding a thermoplastic plastic container, comprising: then opening the split mold into petal shapes to take out the container. (2) The method according to claim (1), wherein the thermoplastic is a thermoplastic polyester. (3) The method according to claims (1) to (2), wherein the container is a can container. (4) A split mold 2 located at the outer edge of the female mold opening, which forms an inner diameter smaller than the female mold opening diameter when closed, and opens and closes like a petal to a diameter equal to or larger than the female mold opening diameter when opened; Plug-assisted thermoforming characterized by comprising an elastic body io1 for opening and closing the mold, a split mold presser 3 for pressing the mold 2, and a clamp 4 for gripping a thermoplastic sheet in opposition to the split mold presser 3. Mold.