JPH0523580B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method and apparatus for thermoforming thermoplastic resin sheets using an electroformed plate (body) having a large number of fine ventilation holes formed by electroforming as a heating body. . [Prior Art] Conventionally, various products have been molded from thermoplastic resin sheets using a hot plate heating type molding machine.
Among these various molded products, for example, containers are used for packaging foods, medicines, etc.
It is desired to improve transparency in order to increase the product value. Therefore, various measures have been taken to improve the transparency of the sheets used as materials, and these measures have achieved certain results. However, no matter how high the transparency of the sheets used as materials, if the transparency is lost or the surface properties are damaged during heating and molding, the optical properties such as transparency and gloss will be affected. It is difficult to obtain containers with excellent properties. In other words, if the surface of the heating plate is finished to a mirror finish to improve transparency, air will accumulate between the heating plate and the sheet, causing uneven heating and causing a raindrop phenomenon, impairing the surface quality and deteriorating the appearance of the container. Not only that, but it also causes wrinkles, which can cause sealing failure on the flange sealing surface. Conversely, if the surface of the heating plate is roughened, this will be transferred to the sheet, resulting in containers with poor transparency. In order to improve the above-mentioned drawbacks, a method of finishing the surface roughness of the heating plate to a smoothness of 3S or less (Japanese Patent Application Laid-Open No. 57-22012), and a paper buffing process to make the surface roughness 0.1 to 0.25 μ are proposed. How to do it (Unexamined Japanese Patent Publication No. 1983-
110413), or a method using sintered metal on the surface of the heating plate (Utility Model Publication Nos. 50-13899 and 50-13900),
In addition, a method of forming fine grooves on the surface of the heating plate (Tokuko Sho)
Nos. 47-13542 and 48-31457) have been proposed. [Problems to be solved] However, as a result of experiments, it has been found that containers can be molded without deteriorating the transparency of sheets and without causing defective phenomena such as lay drops, and have excellent surface properties such as transparency and gloss. It has been found that the above-mentioned methods are not necessarily sufficient to obtain this, and problems still remain. Additionally, a method has been proposed in which the surface of the heating plate is coated with polyolefin containing fluorine to a thickness of 1 to 200 μm (Japanese Patent Laid-Open No. 165211/1983), but this method Although it is effective in preventing staining, the surface must be rough due to the manufacturing process, making it impossible to obtain a container with good transparency and gloss. Furthermore, since the surface material was a heat insulating material, the thermal efficiency was poor and the molding cycle was reduced, and the durability was not sufficient. Further, each of the above-mentioned methods has the problem that the types of thermoplastic resins that can be molded are limited. Conventionally, there has been no material for heating plates that heat sheets by contacting them, which satisfies contradictory conditions such as having a smooth surface and breathability. could not be resolved. The present invention has been made in view of the above-mentioned prior art, and by essentially solving each of the problems, it is possible to produce containers with good transparency and gloss, as well as good appearance without the raindrop phenomenon. The object of the present invention is to provide a method and apparatus for molding thermoplastic resin sheets that can be efficiently molded without being limited by the above. [Means for solving the problem] In order to achieve the above object, a thermoplastic resin sheet is brought into contact with a heating body formed by electroforming and has a large number of fine ventilation holes, if necessary, by forced vacuum suction, and then heated. There is a method of molding a heated thermoplastic resin sheet into a product of a predetermined shape by vacuum forming and/or pressure forming. Further, the thermoforming apparatus for thermoplastic resin sheets of the present invention includes a contact heating body for sheets having a large number of fine ventilation holes formed by electroforming, and a forming section for forming the heated sheets into a predetermined shape. It has a configuration that includes the following. [Example] Hereinafter, an example of the present invention will be described with reference to the drawings. FIGS. 1 and 2 show an apparatus according to a first embodiment of the present invention, and show an example of a hot plate air pressure forming apparatus that heats and forms sheets in one step. In FIGS. 1 and 2, 11 is a heating and pressurized heating element, 15 is a mold plate, and these heating elements 1
1 and the mold plate 15 face each other in the vertical direction and are relatively movable up and down. The heating body 11 is provided with a heater 12 for heating, and has a ventilation hole 1 inside thereof that opens toward the surface side.
3 is formed. Reference numeral 14 denotes an air-permeable heating plate that heats the sheet 1 by contacting it, and is provided on the surface side of the heating body 11 so as to cover the ventilation holes 13. This heating plate 1
4 is formed of an electroformed plate having a large number of fine ventilation holes on the surface that is in direct contact with the sheet 1. Further, this electroformed plate (heating plate) 14 can be lined with a material 14a such as a metal powder or a sintered body of metal fibers having good air permeability and thermal conductivity (second figure). In the present invention, the surface roughness of the sheet contact surface of the electroformed plate 14 having a large number of fine ventilation holes, that is, the surface excluding the fine ventilation holes, is preferably 1S or less.
A mirror surface (glossy surface) of 0.8S or less, more preferably 0.5S or less. In this way, it becomes possible to mold a molded article with excellent transparency and gloss. In addition, the size of the micro ventilation holes is usually 5 to 300μ,
Preferably it is about 10 to 150μ, and the number of ventilation holes is
Usually 10-1000 pieces/cm ² , preferably 30-500 pieces/cm ²
That's about it. The method for producing an electroformed plate having such fine ventilation holes can be by a known method (for example,
JP-A-60-152692, JP-A No. 61-253392). All of these known methods are aimed at forming molds for molding, and they can be used to form molds with various complex shapes by electroforming (referred to as plating in a broad sense in the present invention). However, in the present invention, the shape is different in that it has a plate-like or cylindrical shape. Here, an example of the procedure for forming the electroformed plate 14 is schematically shown as follows. That is, a base material such as glass, a resin-coated polished metal plate, or an epoxy resin is prepared (Fig. 3a), and a metal with good conductivity and a material with poor conductivity are coated on the shiny surface (mirror surface) of this base material. Apply the mixture in a certain ratio. For example, the substrate is treated by spraying a mixture of pasty silver lacquer, butyl acetate, and vinyl chloride lacquer onto the substrate to form a layer of more than 10 microns, and drying the layer. By changing the blending amount of the vinyl chloride lacquer, the conductivity of the surface of the base material can be freely set, and as a result, the size and number of microporous holes can be freely controlled. Next, the metal materials are nickel, chrome,
It is electrolyzed in a plating liquid bath together with plating materials such as iron and copper to form a plating layer having a large number of fine ventilation holes (FIG. 3b). In this case, no surfactant is added to the plating solution to facilitate the formation of vent holes. Further, the diameter of the ventilation holes increases as the plating progresses, resulting in excellent air permeability and surface gloss. The thickness of the plating surface is usually 2
~20mm. Thereafter, this plating layer is easily peeled off from the base material via the spray layer, and becomes the electroformed plate 14. It is preferable to use nickel as the plating material. As a result, the electroformed plate 14 has a smooth and glossy surface and has many fine ventilation holes.
can be obtained. In addition, the electroformed plate 14 should be one with a near-mirror surface when thermoforming sheets that require optical performance such as transparency and gloss, and when transparency and gloss are not particularly required. Although it does not necessarily have to be a mirror surface, it is preferable to use one with low unevenness from the viewpoint of thermal conductivity. Furthermore, a container with an uneven pattern can be formed by heating sheets using an electroformed plate having an uneven pattern. On the other hand, the molding plate 15 is provided with a cavity portion 16 for molding containers, and a ventilation hole 17 is bored in the bottom of the cavity portion 16. This ventilation hole 17 is designed to supply compressed air when heating the sheet 1, and to perform vacuum suction or degassing during molding. Although a metal mold is generally used as the molding plate 15, it may also be a mold made of other materials, such as a resin mold. A part or all of the surface may be made of resin. Next, a molding method using the apparatus of the first embodiment described above will be explained. The sheet 1 is introduced between the heating body 11 and the mold plate 15, and then the heating body 11 and the mold plate 15 are moved up and down to clamp the sheet 1. Next, mold plate 1
Pressurized air is supplied from the ventilation hole 17 of the cavity part 16 of No. 5, and air is exhausted or taken in, preferably by forced vacuum suction, from the ventilation hole 13, and the sheet 1 is brought into contact with the surface of the heating plate (electroformed plate) 14 and heated. . When the sheet 1 is heated to a predetermined temperature by the heating plate 14, pressurized air is blown out from the ventilation hole 13, and the ventilation hole 1 in the cavity portion 16 of the mold plate 15 is blown out.
The sheet 1 is press-fitted into the cavity 16 to form a container. Thereafter, the heating body 11 and the mold plate 15 are separated, and the molded containers are taken out from the cavity part 16. FIG. 4 shows a second embodiment of the present invention, which is an example of a pressure forming apparatus having a preheating plate in front of the sheet forming section. In FIG. 4, 20 is a thermoforming device. This thermoforming device 20 is equipped with a sheet 1 that is intermittently transferred from a raw roll 2 by a guide roller 3.
The upper heating body 21a and the lower heating body 2 which press and heat the
1b, and a thermoforming section 2 that forms the sheet 1 heated by the heating section 21 into containers 1a.
5 are arranged in a straight line. Heating bodies 21a at the upper and lower parts of the heating section 21,
21b is a contact heating method that heats the sheet 1 by sandwiching it from above and below for the sole purpose of heating the sheet 1. Heat sources 22a and 22b such as heaters are embedded inside these heating bodies 21a and 21b. The sheet contact surfaces of these heating bodies 21a and 21b are formed by heating plates 23a and 2 which are formed by electroforming and are made of electroformed plates having a smooth surface and a large number of fine ventilation holes.
3b, and further provided with ventilation holes 24a and 24b for exhaust or intake. Next, a molding method using the molding apparatus of the second embodiment will be described. The sheet 1 is placed between the upper and lower heating bodies 21a and 2 of the heating section 21.
1b, sandwiched between heating bodies 21a and 21,
The heating plates 23a and 23b made of the electroformed plates mentioned above are brought into contact with each other, and air is exhausted or taken in through the ventilation holes 24a and 24b to heat from both sides. Next, the sheet 1 preheated in the heating section 21 is introduced into the thermoforming section 25, and is air-formed into a container. FIGS. 5a and 5b show third and fourth embodiments of the present invention, and show an example of a forming apparatus having a preheating roll in front of the forming section. FIG. 5a shows an example of an apparatus for drum forming.
In FIG. 5a, 1 is a thermoplastic resin sheet, 2 is a raw roll on which the sheet 1 as a molding material is wound, and the sheets 1 are sequentially sent to the molding process as required. A heating roll 31 is a direct heating means, and it comes into contact with one side I of the sheet 1 sent from the raw roll 2 and directly heats it. One side of sheet 1 I
On the surface of the heating roll 31 in contact with the heating body 31a, a roll-shaped electroformed body formed by electroforming and having a smooth surface and a large number of fine ventilation holes is provided as a heating body 31a, and air is evacuated or taken in from the inside. In the case of this roll-shaped electroformed body, lining and
Perform end face closure. The forming drum 33 is arranged parallel to and in line contact with the heating roll 31, and forms the pocket 1a on the sheet 1 heated to the forming temperature by the heating roll 31 and the heater 32. Reference numeral 34 denotes a filling supply device, which sequentially supplies a filling such as medicine or confectionery to the pockets 1a formed in the sheet 1. 4 is a film made of aluminum or the like, and the sheet 1 is heated by a heating roll 35 and a roll 36 provided with pocket holes 36a.
The filling material is laminated and welded to the opening side of the pocket 1a to which the filling is supplied, thereby sealing the opening of the pocket 1a. Next, a thermoforming method using the molding apparatus of the third embodiment will be described. One side I of the sheet 1 sent from the raw fabric roll 2 is directly brought into contact with a heating roll 31 having a roll-shaped electroformed body having a large number of fine ventilation holes on its surface, while exhausting or suctioning air from inside. Heat and raise to molding temperature. Next, in the forming drum 33, pockets 1 having a predetermined shape are formed into the sheet 1 heated to the forming temperature.
Form a. Thereafter, the filling is supplied from the filling supply device 34 into the pocket 1a, and the opening of the pocket 1a of the sheet 1 is sealed with a film 4 made of aluminum or the like. FIG. 5b shows a second example of a forming apparatus having a preheating roll, in which the heater 32 serving as indirect heating means is of a type having a predetermined width, and the pocket 1a is formed in an intermittent forming zone 37. This is done discontinuously.
In the case of this second device example, as in the case of the first device example, a roll-shaped electroformed body having a large number of fine ventilation holes formed by electroforming is provided on the surface of the heating roll 31, and the inside of the roll is further It is preferable to provide means for exhausting or inhaling air from the air. As mentioned above, according to a molding device using a heating body having a large number of fine ventilation holes formed by electroforming, sheets are not fused to the surface of the heating body regardless of the type of thermoplastic resin. Applicable to molding containers etc. from most thermoplastic resin sheets within the range. These sheets include single-phase sheets such as polyolefins such as polypropylene and polyethylene, GP-polystyrene, HI-polystyrene, polyester, polycarbonate, polyamide, and ethylene-vinyl alcohol copolymers, or modified adhesive resins made from these resins. There are multilayer sheets that are co-extruded using the same technology or laminated with sheets or films. Note that these sheets may contain large amounts of inorganic fillers, modifiers such as elastomers, and various additives. Further, the sheets may be unstretched sheets, uniaxially or biaxially stretched sheets. The present invention is suitable for molding containers with excellent optical properties and heat resistance from a sheet with excellent transparency and gloss, that is, a transparent crystalline resin sheet such as polypropylene, especially an unstretched sheet. . In addition, as a sheet, 100 μ ~ 3 mm, usually 120
Use one with a thickness of about 2 mm. Note that the heating roll made of electroforming having a large number of fine ventilation holes on its surface can be used not only in the above-mentioned molding apparatus of the present invention, but also in other heating apparatuses for thermoplastic resin sheets,
For example, it can be used as a roll for heat treatment, a roll for stretching and heating, and a roll for lamination. Further, a flat heating body having a large number of fine ventilation holes can also be used as a press heating plate for lamination, etc. Example of Γ forming A meat tray [external diameter: 150 mm x
85mm, depth: 30mm, three cavities] was molded. Conditions for Γ heating plate (electroformed plate) Surface roughness 0.2S Average number of holes 100/cm ² Average pore diameter 50μ Γ Heating conditions Pressure 1.5Kg/cm ² Vacuum 400mmHg Time 3sec Γ Molding conditions Pressure 4.5Kg/cm ² Vacuum 400mmHg Time 2sec Mold temperature 60℃

[Table] ΓAs a result, mold reproducibility is good, raindrop,
It was possible to obtain a meat tray with good transparency and gloss without any defective phenomena such as hot plate hole transfer, wrinkles, or whitening. As described above, according to the method and apparatus according to the embodiments of the present invention, it is possible to eliminate essential defective phenomena that thermoformed products have, such as raindrops, poor mold reproducibility, wrinkles, and whitening. In addition, it has good thermal efficiency and a fast molding cycle, which improves productivity.
For example, it can be easily molded from a thin sheet of 150μ. Furthermore, since the molding temperature range is widened, and the molding temperature can be expanded particularly to the high temperature side, it becomes possible to suppress stretching orientation and obtain a container with excellent heat resistance while maintaining the transparency of the crystalline resin. Thereby, containers for retort food and the like that require heat treatment after filling can be easily formed. Furthermore, since it is possible to directly heat a resin sheet that conventionally required indirect heating due to the above-mentioned problems, molding can be carried out with almost no restrictions on the type of resin sheet. As a result, it is extremely superior in terms of thermal efficiency, miniaturization of equipment, molding cycle, etc., and its contribution to industry is greater than that of conventional thermoforming methods and equipment. The molding method and molding apparatus of the present invention can be carried out in various compressed air and/or vacuum type thermoforming apparatuses that perform heating by bringing a heating plate into contact with sheets. Moreover, various products can be molded without being limited to containers. [Effects of the Invention] As described above, according to the present invention, a molded product with good mold reproducibility and a good appearance without raindrops, wrinkles, whitening, etc. can be obtained. In particular, it becomes possible to mold crystalline resin containers that require transparency and gloss, which were previously impossible.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of the apparatus according to the first embodiment of the present invention, FIG. 2 is a sectional view of the main part of FIG. 1, FIGS. FIG. 4 shows a longitudinal sectional view of a device according to a second embodiment of the invention, and FIGS. 5a and 5b are explanatory views of devices according to third and fourth embodiments of the invention. 1: Sheet, 11: Heating body, 14: Electroforming plate (heating plate), 15: Molding plate, 21: Heating part, 23a,
23b: heating plate, 25: thermoforming section, 31: heating roll, 31a: rolled heating plate.

Claims (1)

[Claims] 1 Thermoplastic resin sheets are brought into contact with a heating element having a large number of fine ventilation holes formed by electroforming and heated, and then the heated thermoplastic resin sheets are subjected to vacuum forming and/or Alternatively, a thermoforming method for thermoplastic resin sheets characterized by forming products into a predetermined shape by air pressure forming. 2. Heat treatment of thermoplastic resin sheets according to claim 1, characterized in that the thermoplastic resin sheets are heated by contacting them with a heating body whose surface excluding minute ventilation holes is a mirror surface of 1S or less. Molding method. 3. A method for thermoforming thermoplastic resin sheets according to claim 1 or 2, characterized in that the thermoplastic resin sheets are heated by bringing the thermoplastic resin sheets into contact with a heating body under vacuum suction. 4. Heat treatment of thermoplastic resin sheets characterized by comprising a contact heating body for sheets having a large number of fine ventilation holes formed by electroforming, and a molding section for molding the heated sheets into a predetermined shape. Molding equipment. 5 Claim 4, characterized in that the surface of the heating body excluding the micro ventilation holes is a mirror surface of 1S or less.
A thermoforming apparatus for thermoplastic resin sheets as described in 1.