JP3760360B2 - Mold for vacuum forming - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel mold structure for vacuum molding using a plastic sheet or vacuum / pressure molding, and is particularly suitable for vacuum molding of a PET sheet.
[0002]
[Prior art]
Conventionally, molds made by plastic sheet vacuum or vacuum / pneumatic molding methods (hereinafter simply referred to as “vacuum molding method”) are often used in large quantities by repeatedly using the same mold. Because it was produced, because the heat of the sheet preheated in the heater zone and sent while this process is repeated, the mold temperature on both the upper and lower sides rises, causing unnecessary thermal distortion and deformation in the product, The conventional technique is to use this type of mold for cooling.
[0003]
On the other hand, with the advent of C-PET or the like in recent years, it is necessary to maintain the mold temperature at the time of molding at a high temperature as opposed to the vacuum molding of the conventional plastic sheet as described above, and the mold is heated to a predetermined temperature. The method that came to be adopted. As the molding method, it is necessary to ensure good physical properties and dimensional stability of the PET sheet at a high temperature, and the amorphous / unstretched PET sheet is stretched and oriented to cause partial crystallization. It is known to let That is, one mold (in many cases a female mold) is heated to a preferable temperature of 170 ° C. to 190 ° C., and the above PET sheet preheated and softened through a heater zone is replaced with another mold (male mold). ) And is biaxially oriented while being closely adhered to a high-temperature female mold and crystallized, and this is shrunk back to the male mold side heated to a glass transition temperature (90 to 100 ° C.) or less of the PET sheet. Vacuum forming technology was widely adopted.
[0004]
However, the molds used in the vacuum molding method as described above, for example, when a female mold is heated to the above-mentioned predetermined temperature, depending on the size of the molded product, a normal mold has a considerable number (4 to 4). Since it is composed of 20 unit molds, means for installing electric heat and other heat sources in each of the female molds has been taken.
[0005]
[Problems to be solved by the invention]
In the heating mold for molding a PET sheet according to the above-described prior art, an electric heater or hot oil can be circulated for each unit mold (for example, a female mold) arranged in a large number. Not only is the production cost of the mold high, but there are many temperature spots and heat loss between the molds, and there is a common problem that failures and troubles such as disconnection or oil leakage frequently occur.
[0006]
[Means for Solving the Problems]
The invention rather base to solve many problems described above, inside provided an electric heater or a heating oil can be circulated between the heat plate is connected to the heater zone of the sheet, aligning a predetermined number of female to the heat plate lower surface In this manner, a means is provided in which a male mold that can be fitted is installed while retaining a small fitting gap with the female mold in correspondence with the female mold.
[0007]
Further, a means for separating the heat source circulation path inside the hot plate into two or more systems of the outer peripheral portion and the inner portion and keeping the temperature of the outer peripheral portion higher than that of the inner portion was also used.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the embodiment of the present invention shown in the drawings will be described in more detail on the basis of the hot plate type that circulates the hot oil illustrated in the drawings. In FIG. 1, (H) is a heater zone for preheating and softening a PET sheet 1 and 2 are male and female vacuum molding dies provided in connection with the heater zone (H), and 3 is one mold 1 (a female mold in the present embodiment) via a table 4 described later on the lower surface. ) Can be detachably fixed, and the hot plate 3 forms a hot oil circulation path 3a along the vicinity of the lower surface so that the oil temperature is evenly transmitted throughout the lower surface. It is a thing. The table 4 includes a vacuum suction hole 4a that communicates with a suction hole 1a penetrating the female mold 1, for example.
[0009]
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 fitted while maintaining a fixed fitting gap with the female mold inner surface. The fixed fitting gap between the female mold 1 is excluding the thickness (usually 0.45 mm) of the PET sheet that is interposed between the male and female molds and is sucked and adhered to the female mold side. Ideally, a gap of 0.2 to 0.3 mm exists. This is necessary to stretch the PET sheet by the two male surfaces and to shrink back the crystallized PET sheet formed in close contact with the high temperature female surface to the low temperature (around 70 ° C) male side. It is a gap. In order to maintain the temperature of the male mold 2 at about 70 ° C., which is lower than the glass transition temperature of the PET sheet, it is necessary to use a hot plate as seen in the female mold 1 that requires the high temperature heating plate described above. Instead, a generally used temperature adjusting device or the like may be used.
[0010]
Therefore, as another embodiment of the hot plate 3, as shown in FIG. 2, the circulation path 3a perforated in the hot plate 3 is divided into two systems of internal heating 3b and outer peripheral heating 3c, or By dividing the above into independent circulation paths, for example, by circulating hot oil of 200 ° C. through the internal circulation path 3b, the inner surface temperature of the female mold 1 fixed to the lower surface is the crystallization temperature (175 of the PET sheet). ℃), the circulation path 3c in the outer peripheral portion that is easily affected by the outside air temperature is allowed to circulate hot oil 10 to 20% higher than the internal oil temperature in anticipation of the heat radiation. Is. Of course, the circulation path 3a in the hot plate 4 may use another heat source such as an electric heater instead of supplying the hot oil.
[0011]
Next, the usage procedure of the vacuum molding die having the above-described structure according to the present invention will be described with reference to FIG. 1. In the figure, (S) is a PET sheet, (H) is a heater zone, and a PET sheet having a predetermined spread. (S) is preheated and softened in the heater zone (H), and quickly supplied between the molding dies 1 and 2 by a clipper or the like (not shown) that operates by gripping the corners of the sheet, The PET sheet (S) is stretched by the male mold 2 fitted into the female mold 1, and at the same time, the sheet (S) is vacuum-sucked by the female mold 1 heated to a predetermined temperature (around 175 ° C.) (in this case) The air may be sprayed from the side of the male mold 2 to assist the adhesion of the sheet to the female mold), the crystallization is promoted, and the sheet (S) is further cooled (around 70 ° C.). Shrink back to the male mold 2 side and then open both molds The molded product is obtained by releasing from the mold, and this process is the same as the case of using this kind of vacuum molding mold in the past, but according to the mold structure of the present invention, both male and female molds are used. There is a feature that a product with particularly high molding accuracy in the corner portion can be obtained by the fitting of 1 and 2 and vacuum suction.
[0012]
【The invention's effect】
As described above in detail, the vacuum molding means and process using the molding die of the present invention are not much different from those of conventional molds for PET sheet molding, but the present invention uses a hot plate. Since a large number of unit molds (female molds) that do not have a heat source are detachable, a desired unit mold is placed on the lower surface of the hot plate, particularly in vacuum molding of products that require high-temperature heating. By attaching, a PET molded product having a different shape can be obtained at any time.
[0013]
In addition, it is possible not only to save the trouble of incorporating a heat source into individual molds as in the prior art, but the mold itself is remarkably inexpensive, and a hot plate having a wide heat surface is broken due to disconnection of the heat source, oil leakage, etc. Is greatly eliminated, and a particularly excellent effect is obtained in that a PET product with a high yield can be obtained.
[0014]
Furthermore, the molding die having the above-described configuration according to the present invention is not limited to the vacuum molding of a PET sheet that requires high-temperature molding as described in the text, and the circulation path of the hot plate is replaced with hot oil. By circulating the cooling water, it can be used as it is for molding a normal plastic sheet, and the molding accuracy can be further improved as compared with a conventional mold structure.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a central portion of an entire vacuum mold according to the present invention.
FIG. 2 is a bottom view showing an example of a heat plate.
[Explanation of symbols]
1 Mold (Female)
2 Mold (male)
3 Hot plate 4 Table 1a, 4a Vacuum suction hole

Claims (2)

A heating plate is connected to the heater zone, and a predetermined female mold is aligned and fixed detachably on the lower surface of the heating plate, while a male mold provided corresponding to the female mold has a slight fitting gap. A mold for vacuum molding characterized by being held and freely fitted into a female mold. The vacuum molding die according to claim 1, wherein a heated portion inside the hot plate is separated 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 inside.

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