JPH0465220A - Method and device for press molding of synthetic resin sheet - Google Patents

Abstract

PURPOSE:To obtain uniformly high quality articles irrespective of the material of sheets even in a case where a number of stacked material sheets are pressed together into the article by a single pressing action by setting metal dies and the material sheets at predetermined temperatures using water as a heating medium. CONSTITUTION:A synthetic resin sheet 3 is immersed in a water tank 7 containing the water having a predetermined temperature so as to be preheated. After completion of the preheating, the synthetic resin sheets 3 are pressed together to be shaped between metal dies 1 and 2 provided under the water in the tank in the as-immersed condition. The sheets formed into a predetermined shape is taken out from the metal die, the water is removed therefrom and shaped sheets are cooled and dried. The metal dies and a preheating tank 4 are both provided under the water and the material sheets 3 are subjected to a so-called water tank formation wherein the sheets 3 are preheated and shaped in the water tank containing the water having a predetermined temperature, whereby the stacked material sheets are impregnated with the water having a predetermined temperature to be heated uniformly. Also, since the water is large in specific heat, there is little variation in the temperature of this device taking place by changes in ambient temperature and a stable temperature can be set.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a press molding method and apparatus for thermosetting and thermoplastic synthetic resin sheets, and in particular, when molding a large number of stacked synthetic resin sheets with one compression, the molding process remains constant regardless of the material of the sheet. The present invention relates to a press molding method and an apparatus for the press molding that can produce high quality molded products.

[Conventional technology]

BACKGROUND ART Conventionally, as a simple apparatus for press-molding a synthetic resin sheet (hereinafter referred to as a material sheet), an apparatus as shown in FIG. 2 has been widely used. This device consists of a brass mold (a lower mold 1 and an upper mold 2), a nichrome wire heater 8 for heating the mold, a temperature sensor 9 for adjusting the mold temperature, and a control section 10. Ru. The mold temperature (molding temperature) is controlled on and off by a control unit according to the input value from the temperature sensor, and the precision of this control is nominally ±1°C. For example, in the case of polyvinyl chloride resin (PVC), a material sheet (thickness: 0.16 cm) is placed on the upper surface of the lower mold 1 at a molding temperature of 80°C.
The upper die 2 is pressed from above and press-molded for about 6 seconds, and then the molded products are released and cooled to form multiple final products (food containers, food containers, etc.) in the same shape.
Miscellaneous goods, stationery, etc.) can be obtained at the same time.

[Problem to be solved by the invention]

However, according to the above press molding apparatus (method),
It was found that some material sheets could not be compressed in multiple sheets in one compression (resulting in defective molding). In other words, some material sheets have a narrow temperature range in which they can be thermally deformed (hereinafter referred to as the heat deformation temperature range), and if the temperature falls outside that temperature range, the material sheet will melt ( (high temperature side), and the material sheet does not reach the deformation temperature, resulting in poor molding or breakage (sheet folding) (low temperature side). For example, in the case of two-wheel stretched polystyrene sheets with a narrow heat deformation temperature range, if three sheets of 0.15mm thickness are stacked and press-formed using conventional equipment (mold temperature set at 80°C), the center It is known that the sheet may be defective in forming. Incidentally, in the case of a PVC sheet having a relatively wide heat deformation temperature range, this problem did not occur even in the conventional apparatus. Here, the origin of the problem of the present invention lies in the safety problem related to disposable containers for foods and the like. In other words, PVC sheets, which had no problems when processed using conventional equipment, have restrictions that restrict their use in some food products (under the Food Sanitation Law), so two-wheel stretched polystyrene sheets, etc., are used as materials that meet legal regulations. However, the latter method poses processing problems as described above. Examples of products that comply with this legal regulation include "Stylo Sheet" (registered trademark) manufactured by Asahi Kasei Corporation, and the material is compliant with the Food Sanitation Law, synthetic resin equipment containers and packaging standards (polyethylene, polypropylene).
(Ministry of Health and Welfare Notification No. 20 of 1982).

[Means to solve the problem]

The present invention has been made in view of the above-mentioned problems, and even when a large number of material sheets are stacked and press-formed in one compression, uniform and high-quality molding can be achieved regardless of the material (thermal deformability) of the material sheets. In order to obtain a product, there is a preheating step in which a synthetic resin sheet is immersed in a water tank at a predetermined temperature and preheated for a predetermined time, and after the preheating is completed, the synthetic resin sheet is immersed in a water tank at a predetermined temperature and the water surface of the water tank is heated. A press-molding method for a synthetic resin sheet, which comprises a press-molding process in which pressure is applied by a mold placed below, and a cooling-drying process in which a molded product of a predetermined shape is taken out from the mold after press-molding, water is removed, and the product is cooled. a water tank containing water at a predetermined temperature; a preheating tank made of a synthetic resin sheet located within the water tank and located below the water surface of the water contained in the water tank; and a preheating tank made of a synthetic resin sheet located within the water tank and located below the water surface. The present invention also provides an apparatus for press-molding a synthetic resin sheet, comprising a mold for press-molding the synthetic resin sheet.゛

[For use]

In the apparatus and method of the present invention, the entire mold and preheating tank are placed below the water surface, and each step of preheating and forming the material sheet is performed in a water tank containing water at a predetermined temperature (so-called water tank molding).
Water at a predetermined temperature permeates every nook and cranny of each stacked material sheet, resulting in a uniform heating state. At the same time, water has a large specific heat, so the temperature fluctuation within the equipment system due to external temperature changes is extremely small, and if the amount used is large compared to the volume of equipment such as molding equipment, the temperature will be extremely stable. A configuration state can be brought about. In addition, under atmospheric pressure, the boiling point of water is around 100°C, and even if heated using a heat source (such as an electric heater), the boiling point will not be exceeded, so the molding temperature (set temperature) is 100°C. No special temperature control is required for material sheets below (or around) °C. Furthermore, according to the press forming method of the present invention, each step of preheating and forming the material sheet is performed in water at a predetermined temperature (mainly around 100°C), so the material sheet can be sterilized simultaneously with the progress of these steps. It can be performed. rExample The method for press-molding a synthetic resin sheet according to the present invention and the apparatus therefor will be described in detail below. FIG. 1 shows an apparatus according to an embodiment of the present invention, which includes brass molds (lower mold 1, upper mold 2), a preheating tank 4 that temporarily stores a material sheet 3 for preheating, a water tank 7 containing water 6 for submerging the mold and preheating tank 4; an immersion type electric heater 5 for heating the water 6 in the water tank;
It consists of Incidentally, the upper surface of the lower mold 1 is adjusted to be at a position "d" below the water surface. This is to ensure that the plurality of stacked material sheets 3 are all immersed in water. For example, the value of d is approximately 20 mm when the thickness of the material sheet is 0.15 mm and 10 sheets are stacked. At the same time, it is desirable that the height of the sheet placement part (bottom of the tank) of the preheating tank 4 is made to match the height of the upper surface of the lower mold 1. This is because by matching the heights in this way, the same temperature conditions are given to the material sheet both during preheating and during molding. On the other hand, the type of heating element, power consumption (generated heat amount), etc. of the electric heater 5 need only be sufficient to boil the water 6 in the water tank 7. A method for press-forming the material sheet 3 using the apparatus having the above configuration will be described below. The material sheet 3 is a thermoplastic and thermosetting synthetic resin sheet with a heat deformation temperature (18,6
kg/ctlT (when pressurized) is approximately 110°C or less. For example, vinyl chloride resin (PVC), polystyrene, polyethylene, etc. The material sheet 3 is first placed in a preheating tank 4 and preheated for about 23 seconds (
preheating process). There are 23 to 32 material sheets 3 (thickness 0.
15 mm) is preferable. After preheating, the material sheet 3 is placed at a predetermined position on the upper surface of the lower mold 1, and is pressed against the upper mold 2 from above so as to match the recess of the lower mold 1 for about 23 seconds (press molding). process). The molding pressure applied by the upper die 2 can be appropriately selected depending on conditions such as the material of the material sheet and the number of sheets. Further, the upper die 2 can be pressurized either manually or automatically. After the press molding process is completed, the molded material sheet 3 (molded product) is released from the lower die 1, and the molded product is left at a predetermined position (not shown) outside the water tank 7 for water removal and cooling. . Thereafter, a final product (molded article) is obtained through a drying process such as natural drying or vacuum drying (cooling drying process).

【example】

The water in the water tank 7 in which the molds (lower mold 1, upper mold 2) and preheating tank 4 are arranged is brought to a boil by heating with an electric heater 5 (the amount of heat generated is about 1:1 or more for water 51). After holding for 30 minutes (to keep the temperature of the upper and lower molds in a steady state and prepare for the subsequent continuous press molding), a biaxially oriented polystyrene sheet (registered trademark "Styro Sheet") manufactured by Asahi Kasei Corporation (trademark) (
Thickness 0.15mm, length and width 150 x 150 am) 3
The two stacked sheets were placed in a preheating tank 4 for 23 seconds to preheat them, then the sheets were placed on the top of the lower mold 1 (for food containers, concave) and pressed for 23 seconds with the upper mold 2 (convex). After that, the molded product was taken out, cooled, and air-dried. All 32 of the molded products obtained had a uniform and beautiful shape (without damaging the material), and maintained the same transparency as the material itself.

【Effect of the invention】

As explained in detail above, according to the method and apparatus for press-molding a synthetic resin sheet of the present invention, the temperature of the mold and material sheet is set using water as a heating medium, so a large number of material sheets are stacked. Even in the case of press molding with one compression, a uniform and high quality molded product can be obtained regardless of the material (thermal deformability) of the material sheet.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the press molding apparatus of the present invention, and FIG. 2 is an explanatory diagram showing a conventional press molding apparatus. Code explanation Lower mold Upper mold material sheet Preheating tank Electric heater Water tank Nichrome wire Temperature sensor Control part

Claims (2)

[Claims] (1) A preheating step in which the synthetic resin sheet is immersed in a water tank at a predetermined temperature and preheated for a predetermined time, and after the preheating is completed, the synthetic resin sheet is placed under the water surface of the water tank while being immersed in the water tank at the predetermined temperature. A press-molding method for a synthetic resin sheet, which comprises a press-molding process in which pressure is applied using a mold that has been press-molded, and a cooling-drying process in which the molded product in a predetermined shape is removed from the mold after press-molding, water is removed, and the product is cooled. (2) a water tank containing water at a predetermined temperature; a preheating tank made of a synthetic resin sheet disposed within the water tank and located below the water surface of the water contained in the water tank; An apparatus for press-molding a synthetic resin sheet, comprising a mold located below and press-molding the synthetic resin sheet.