JPH1170578A - Mold for vacuum forming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dissolve problems of high mold production costs and disconnection and others by installing a prescribed number of female molds which are connected with a heater zone and arranged inside on the lower surface of an electric heater or a hot plate which can circulate a kind of heating oil attachably/detachably and freely engageable male molds which correspond to the female molds, keep narrow engagement clearances with female molds. SOLUTION: A hot plate 3 can fix a mold 1 (female mold) freely attachably/ detachably, installs a hot oil circulating route 3a, and transmits an oil temperature uniformly to the whole area of a lower surface. A molds 2 (male mold) corresponds to the female mold 1 and is constituted freely insertably at a given engagement clearance with the inner surface of the female mold. A PET sheet S is preheated in a heater zone H and softened, supplied between the molding female mold 1 and the male mold 2, stretched by the male mold 2 which is inserted into the female mold 1, simultaneously vacuum-sucked to the female mold 1 heated at a prescribed temperature, and crystallized. The sheet S is shrink-packed in a low temperature male mold 2, after mold opening, removed from the male mold 1 to obtain a molding. An attachable/detachable desired mold is attached to the female mold 1, and PET moldings of different shapes can be obtained at any time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel mold structure for vacuum molding or vacuum / pressure molding using a plastic sheet, and is particularly suitable for vacuum molding of a PET sheet.

[0002]

2. Description of the Related Art Conventionally, a vacuum or vacuum / pressure forming method for a plastic sheet (hereinafter simply referred to as "vacuum forming method"
In many cases, the same mold is used repeatedly to produce a large number of molded articles by repeatedly using the same mold. Therefore, during this process, a sheet heated and fed into the heater zone is fed into the heater zone. Since the heat raises the temperature of the upper and lower molds and causes unnecessary thermal distortion and deformation of the product, it has been a common practice to use cooling of this kind of mold.

On the other hand, with the advent of C-PET or the like in recent years, it has become necessary to maintain the mold temperature at the time of molding at a high temperature, contrary to the vacuum molding of generally existing plastic sheets as described above. The method of heating to the beginning came to be adopted. And, as the molding method, the above PE
In order to secure good physical properties and dimensional stability at high temperature of T sheet, stretch amorphous / unstretched PET sheet.
It is known to orient and further cause partial crystallization. That is, one mold (often a female mold) is heated to 170 ° C. to 190 ° C., which is a preferable temperature, and the above-mentioned PET sheet preheated and softened through a heater zone is heated to another mold (male mold). ), While stretching and biaxially aligning, crystallize by contacting with a high-temperature female mold, and shrink it back to the male mold side heated to a glass transition temperature (90 to 100 ° C.) or lower of the PET sheet. Vacuum molding technology was widely adopted.

However, when the female mold is heated to the above-mentioned predetermined temperature, for example, the mold used in the vacuum molding method described above depends on the size of the molded product. (4 to 20) unit dies, so that means for providing electric heating and other heat sources in each of the female dies has been taken.

[0005]

In the above-described heating mold for molding a PET sheet according to the prior art, an electric heater or hot oil is supplied to each of a number of unit molds (for example, female molds) aligned. Because it was made available for distribution, not only would the production cost of the molds be high, but also there would be many temperature irregularities and heat loss between the molds, and there would be many failures and troubles such as disconnection or oil leakage. Issues were found.

[0006]

According to the present invention, in order to solve the above-mentioned problems, as a result of intensive experiments and studies, it has become possible to circulate an electric heater or heating oil inside by connecting to a heater zone of a seat. A hot plate is provided, and a predetermined number of female dies are aligned and detachably provided on the lower surface of the hot plate, while a male die which can be freely fitted and held with a small fitting gap with the female die corresponding to the female die. It is a means of setting up.

Further, a means for separating the heat source circulation path inside the hot plate into two or more systems of the outer peripheral part and the inner part and keeping the temperature of the outer peripheral part higher than that of the inner part is also used.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of the present invention shown in the drawings will be described below in more detail based on a hot plate system in which hot oil is circulated as shown in the drawings.
Heater zones for preheating and softening the ET sheet, 1.2 are male and female vacuum molding dies provided in connection with the heater zone (H), and 3 is one mold 1 ( The hot plate 3 forms a hot oil circulation path 3a along the vicinity of the lower surface, and is uniformly formed over the entire lower surface. The oil temperature is transmitted. The table 4 has, for example, a vacuum suction hole 4a communicating with a suction hole 1a penetrating through each of the female dies 1.

Further, another mold 2 (in this case, a male mold) is provided corresponding to each of the female molds 1 and is configured to be freely fittable while maintaining a fixed fitting gap with the inner surface of the female mold. However, the fixed fitting gap between the female mold 1 and the female mold 1 means a thickness of the PET sheet (normally 0.45 mm) which is interposed between the male and female molds and is attracted to and adhered to the female mold. Except for 0.2-
Ideally, a gap of 0.3 mm exists. This is the stretching of the PET sheet by two male molds, and the PET sheet formed and crystallized in close contact with the high-temperature female mold is cooled at a low temperature (7.
This is the gap required to shrink back to the male side (around 0 ° C). Further, in order to maintain the temperature of the male mold 2 at about 70 ° C. below the glass transition temperature of the PET sheet, it is necessary to use a hot plate as in the female mold 1 which requires the above-described high-temperature heating plate. Instead, a commonly used temperature adjusting device or the like may be used.

As another embodiment of the hot plate 3, as shown in FIG. 2, a circulation path 3a formed in the hot plate 3 is provided.
Is divided into two or more systems of an internal heating 3b and an outer peripheral heating 3c, and each is made an independent circulation path. For example, hot oil of 200 ° C. is circulated through the internal circulation path 3b and fixed to the lower surface. Assuming that the inner surface temperature of the female mold 1 is the crystallization temperature (175 ° C.) of the PET sheet, the outer peripheral circulation path 3c, which is susceptible to the outside air temperature, takes into account the heat radiation, and The hot oil whose oil temperature is higher by 10 to 20% is circulated. The circulation path 3 in the hot plate 4
It goes without saying that a may use another heat source such as an electric heater in place of the supply of the hot oil.

Next, the procedure for using the vacuum forming mold according to the present invention will be described with reference to FIG. 1. In FIG. 1, (S) is a PET sheet, and (H) is a heater zone. The PET sheet (S) is preheated and softened in the heater zone (H), and is quickly moved by a clipper or the like (not shown) operated by gripping a corner of the sheet.
The PET sheet (S) is supplied between the molding dies 1 and 2, the PET sheet (S) is stretched by the male mold 2 fitted into the female mold 1, and the sheet (S) is heated at a predetermined temperature (around 175 ° C).
The heated female mold 1 is vacuum-sucked (in this case, compressed air may be injected from the male mold 2 side to help the sheet adhere to the female mold) to cause its crystallization. Further, the sheet (S) is shrunk back to the side of the male mold 2 at a low temperature (around 70 ° C.), and then both molds are opened to release from the male mold to obtain a molded product. With respect to this, it is the same as the case of this type of vacuum molding die before, but according to the die structure of the present invention, the fitting of the male and female molds 1 and 2 and the vacuum suction, particularly at the corners There is a feature that a product with high molding accuracy can be obtained.

[0012]

As described in detail above, in the means and process of vacuum molding by the molding die of the present invention, the conventional PET is used.
Although there is not much difference from the case of a mold for sheet molding, in the present invention, since a large number of unit molds (female dies) having no heat source in the hot plate are made detachable by using a hot plate, In particular, in the vacuum molding of a product requiring high-temperature heating, a PET molded product having a different shape can be obtained as needed by attaching a desired unit mold to the lower surface of the hot plate.

In addition, the mold itself is not only extremely inexpensive because the trouble of incorporating a heat source into each mold as in the prior art is eliminated, but also a hot plate having a wide hot surface is required for disconnection of the heat source and oil leakage. And other troubles are largely eliminated, and a particularly excellent effect of obtaining a PET product with a high yield can be obtained.

Further, the molding die having the above-mentioned structure according to the present invention is not limited to the vacuum molding of the PET sheet which requires high-temperature molding described in the present text. By circulating cooling water instead of
It can be applied directly to the molding of a normal plastic sheet as it is, and can further improve the molding accuracy as compared with the conventional mold structure.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a central portion of the entire vacuum molding die of the present invention.

FIG. 2 is a bottom view showing an example of a hot plate.

[Explanation of symbols]

 1 mold (female mold) 2 mold (male mold) 3 hot plate 4 table 1a ・ 4a vacuum suction hole

Claims (2)

[Claims] 1. A hot plate is provided connected to a heater zone, and a predetermined female mold is aligned and fixed removably on the lower surface of the hot plate, while a male mold provided corresponding to the female mold is slightly removed. A vacuum molding die characterized in that it can be fitted into a female mold while maintaining a suitable fitting gap. 2. The vacuum molding die according to claim 1, wherein a heating portion inside the hot plate is divided into a plurality of systems of an outer peripheral portion and an inner portion, and the temperature of the outer peripheral portion is kept higher than that of the inner portion. .