JPH0410846B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for manufacturing a thick-walled molded product, and more specifically, a method for manufacturing a molded product such as a container or a plate having a wall thickness of 10 mm or more. The present invention relates to a compression molding method that can produce good thick molded products without forming cavities.

[Prior art]

Conventionally, extrusion molding methods or compression molding methods are generally used to manufacture thick molded products. However, the extrusion molding method can successfully mold sheets with a thickness of 2 to 3 mm, but for example, if the wall thickness is
When molding a very thick plate, about 10mm thick, the molten sheet that comes out of the die sags under its own weight, making stable molding impossible, and the resulting molded product only has uneven thickness and large deformations. .
On the other hand, although it is possible to produce thick-walled molded products using compression molding, the volume of the mold becomes large due to the large amount of pellets and powder used as raw materials, and the air that exists between the pellets and powder particles increases. There is a problem in that defoaming is not successful and only molded products with cavities can be obtained. Therefore, as a method for obtaining such thick-walled molded products, for example,
As described in Publication No. 25480, a technology has been proposed in which a molten resin is extruded into a sheet form from an extruder, and the sheets are continuously laminated while still in a molten state so as to be folded to produce a block-like object. . However, this technique requires complicated and large equipment, and it is difficult to obtain molded products with complex shapes. In addition, Japanese Patent Publication No. 58-40018 discloses that two or more thermoplastic resin sheets of the same or different types are uniformly preheated as a whole at a temperature 30°C lower than the maximum heat deformation temperature and lower than the minimum melting point, and then A technique is disclosed in which preheated sheets are laminated and compressively deformed under a pressure of 400 kg/cm ² or less to produce a thick-walled molded product. This technology not only makes it possible to miniaturize the mold, but also allows the production of molded products that are relatively free of cavities, but even with soft resins such as ethylene-vinyl acetate copolymers, high compression rates of 100 kg/cm ² or more are often required. If you don't apply force to the sheet, it won't integrate properly. Moreover, if this method is applied to a normal compression molding method using pellets or powder, there is still a problem in that only thick-walled molded products with cavities can be obtained.

[Purpose of the invention]

The inventors of the present invention have conducted repeated studies on a compression molding method that can produce thick-walled molded products with low compressive force and no cavities, regardless of the shape of the thermoplastic resin material. discovered that the objective could be achieved by pre-treating the thermoplastic resin material in a process suitable for defoaming gases such as air present in the material, and then performing normal compression molding.

[Structure and outline of the invention]

In other words, the present invention involves the process of repeatedly subjecting a thermoplastic resin material filled in a mold to depressurization and pressurization within a certain temperature range to degas the gas in the material; In a method for forming a thick-walled molded product that includes heating a resin material above its melting temperature and compression molding, the above-mentioned certain temperature range is above the softening temperature of the resin having the highest softening temperature among the thermoplastic resins. This is a method for molding a thick-walled product, characterized in that the melting temperature is lower than the melting temperature of the resin having the lowest melting temperature among the thermoplastic resins.

Thermoplastic resin material The thermoplastic resin material used in the method of the present invention is
Thermoplastic resin sheets, films, pellets,
It can be in any shape such as flakes or powder,
Thermoplastic resins include low-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, or ethylene, propylene, 1-butene, 4-methyl-1-pentene, etc. Polyolefins such as random or block copolymers of α-olefins, ethylene/acrylic acid copolymers, ethylene/vinyl acetate copolymers, ethylene/vinyl acetate copolymers, etc.
Vinyl alcohol copolymer, ethylene/vinyl compound copolymer such as ethylene/vinyl chloride copolymer, polystyrene, acrylonitrile/styrene copolymer, ABS, methyl methacrylate/styrene copolymer, α-methylstyrene/styrene copolymer Styrene resins such as polymers, polyvinyl chloride, polyvinylidene chloride, vinyl chloride/vinylidene chloride copolymers, polyvinyl compounds such as polymethyl acrylate, polymethyl methacrylate, nylon 6,
Nylon 6-10, nylon 11, nylon 12
polyamide, polyethylene terephthalate, etc.
Any resin such as thermoplastic polyester such as polybutylene terephthalate, polycarbonate, polyphenylene oxide, or a mixture thereof may be used.

Molding In the compression molding method of the present invention, thick-walled molded products are manufactured using materials of various shapes made of the various thermoplastic resins mentioned above. Gas such as air existing between the resin materials is defoamed by repeatedly subjecting the resin material to decompression treatment and pressurization treatment within a certain temperature range. Here, within a certain temperature range means that the temperature is higher than or equal to the softening temperature of the resin having the highest softening temperature (hereinafter referred to as the highest softening temperature) among the thermoplastic resin materials constituting the material, and Although it is lower than the melting temperature of the resin with the lowest melting temperature (hereinafter referred to as the "minimum melting temperature"), in order to defoam at low pressure and in a short time, it is especially necessary to
A temperature range of 10)°C to (minimum melting temperature -30)°C is preferred. If the temperature range is below the maximum softening point, defoaming does not occur completely, and the thick-walled molded product obtained by the compression molding process described below will have cavities. If the temperature is higher than the minimum melting temperature, a portion becomes molten, and degassing in this portion becomes insufficient, resulting in a molded product containing voids. In addition, when the thermoplastic resin for producing a thick molded article is not a mixture of a plurality of resins, the maximum softening temperature and the minimum melting temperature are the softening temperature and melting temperature of the resin, respectively. Pressure conditions for pressurization and depressurization vary depending on the size and thickness of the molded product, but generally the upper limit is 100Kg/cm ² or less, often 50Kg/cm ² or less, and the lower limit is 0Kg/cm ² or more. . In particular, when reducing the pressure, a state of 0 kg/cm ² (atmospheric pressure) with no applied pressure is preferable. There are no particular restrictions on the cycle of pressurization and depressurization; for example, as in the example described later, pressurization is performed for 3 seconds and depressurization is performed for 2 seconds for 15 to 2 seconds.
An example is repeating 20 times, but the cycle is not limited to this in any way.

There are no particular restrictions on the method for bringing the thermoplastic resin material into the above-mentioned temperature range; for example, heating the material inside the mold by heating the mold after filling it into a compression mold, or heating the material inside the mold before filling it into the mold. An example is a method in which the temperature is preheated using a heating device.

The material from which the gas present in the material has been defoamed by the above defoaming process is then processed at the melting temperature (hereinafter referred to as the highest melting temperature) of the resin having the highest melting temperature among the thermoplastic resins constituting the material. ) and compression molded. At this time, it is preferable to heat to about 10°C or higher above the maximum melting temperature if possible. Moreover, the pressure for compression molding is higher than the pressure applied in the defoaming process.

In this way, the compression molding method of the present invention removes gas existing between the materials by applying pressure fluctuations while all the thermoplastic resin is softened but not melted. After foaming, all the resin is melted and pressure is applied to completely melt and add it together to obtain a thick-walled molded product without voids.

A preferred example of the present invention is a technique for manufacturing a thick plate or block-like object using a plurality of sheets or films of thermoplastic resin. That is, it is heated to the highest softening temperature and lower than the lowest melting temperature of the thermoplastic resins constituting the sheet or film made of the same or different thermoplastic resins. The heating method may be performed by heating a plurality of sheets in parallel or in series in advance in a heater, or by heating the mold while stacking the sheets in a mold. The sheets or films that have been heated to within the target temperature range are placed in a stacked state into a heated mold, and then placed in the mold while the temperature is maintained by continuing to heat the mold. Therefore, pressurization and depressurization are repeated multiple times. Next, under pressure, the mold temperature is raised to a temperature higher than the maximum melting temperature, and compression molding is performed. After that, the mold is cooled, the mold is opened, and the molded product is taken out. The boundaries between each sheet or film of the molded product thus obtained are completely integrated by fusion, especially if the sheets or films of the same type of resin are If only one is used, the boundary will not be recognized at all and the result will be completely integrated. In particular, when using this sheet, thick-walled products can be manufactured in a short time by using a sheet with a thickness of 2 to 6 mm. The number of sheets is not limited and can range from several sheets to several tens of sheets, and the dimensions of each sheet may also be different, and the shape may be any shape such as a round sheet, a square sheet, a polygonal sheet, etc. Furthermore, if necessary, a wire mesh, metal rod, porous ceramic membrane, etc. may be interposed between each sheet.

〔Effect of the invention〕

Hereinafter, the characteristics of the compression molding method of the present invention will be described again. Thick-walled molded products without cavities can be produced.

It can be applied to any shape of thermoplastic resin material.

Can be molded with low compression force.

The strength of the molded product is high.

etc. can be mentioned.

〔Example〕

Preferred examples of the present invention are shown below as Examples, but the present invention can take any form as long as the purpose is not impaired and is not limited to these Examples.

Note that the Vikatsu softening point was measured according to JIS K7206.

Moreover, the melting point was measured according to ASTM D3417-75.

Example 1 Poly4-methyl-1-pentene (TPX
Pellets of MX004 (Mitsui Petrochemical Industries, Ltd., melting point: 240°C, Vikatsu softening point: 160°C) were filled into a mold set in a press at 220°C, and preheated at a resin pressure of 100 kg/cm ² for 30 minutes. Then 0Kg/cm ² and 100
After repeating depressurization and pressurization of Kg/cm ² 20 times, the press temperature was reset to 270°C, and compression molding was carried out at a resin pressure of 100 Kg/cm ² . After 15 minutes, the mold was transferred to a water-cooled press and cooled for 15 minutes at a resin pressure of 100 Kg/cm ² .

After cooling, a disc-shaped molded product with a thickness of 20 mm and a diameter of 180 mm was taken out. When the molded product was cut, the pellets were completely adhered and integrated, and no nests were formed.

Comparative Example 1 The same poly-4-methyl-1-pentene pellets as in Example 1 were filled into a mold set in a press at 270°C and preheated for 30 minutes at a resin pressure of 100 kg/cm ² . Next, after repeating 20 times of depressurization and pressurization of 0 Kg/cm ² and 100 Kg/cm ² , compression molding was performed at a resin pressure of 100 Kg/cm ² . After 15 minutes, the mold was transferred to a water-cooled press and cooled for 15 minutes at a resin pressure of 100 Kg/cm ² .

After cooling, a disk-shaped molded product with a thickness of 20 mm and a diameter of 180 mm was taken out. A nest had developed inside the molded product.

Example 2 Two 7.8 mm thick sheets of the same poly-4-methyl-1-pentene as in Example 1 were prepared, filled into a mold set in a press at 220°C, and heated to 30 kg/cm ²
The resin pressure was preheated for 30 minutes. Then 0Kg/cm ²
After repeating 20 times of depressurization and pressurization at 30 kg/cm ² , the press temperature was reset to 240° C., and compression molding was carried out at a resin pressure of 30 kg/cm ² . After 15 minutes, the mold was transferred to a water-cooled press and cooled for 30 minutes at a resin pressure of 30 kg/cm ² .

After cooling, a disk-shaped molded product with a thickness of 14 mm and a diameter of 330 mm was taken out. When the molded product was cut,
Even though there were only two sheets made, they stuck together perfectly and became one, and no nests were formed.

Comparative Example 2 Two 7.8 mm thick sheets of the same poly-4-methyl-1-pentene as in Example 1 were prepared, filled into a mold set in a press at 220°C, and heated at 30 kg/cm ^2. Preheated at resin pressure for 30 minutes. Next, the temperature of the press was reset to 240°C, and compression molding was carried out at a resin pressure of 30 kg/cm ² . After 15 minutes, the mold was transferred to a water-cooled press and cooled for 30 minutes at a resin pressure of 30 Kg/cm ² .

After cooling, a disk-shaped molded product with a thickness of 14 mm and a diameter of 330 mm was taken out. A nest had developed inside the molded product.

Example 3 A total of three sheets, two 7.8 mm thick sheets and one 5 mm thick sheet, of the same poly-4-methyl-1-pentene as in Example 1 were prepared and set in a press at 220°C. The resin was filled into a mold and preheated for 1 hour at a resin pressure of 20 kg/cm ² . Then 0Kg/cm ² and 20Kg/cm ²
After repeating the pressure reduction and pressure application 20 times, the press temperature was reset to 250°C and compression molding was carried out at a resin pressure of 20 kg/cm ² . After 1 hour, water was flowed through the press while maintaining the resin pressure at 20 kg/cm ² to cool the press for about 1 hour. After cooling, a disc-shaped molded product with a thickness of 17 mm and a diameter of 700 mm was taken out. When the molded product was cut,
Even though it was made of three sheets, they were completely adhered and integrated, and there were no nests.

Claims (1)

[Claims] 1. A step of repeatedly subjecting a thermoplastic resin material filled in a mold to depressurization treatment and pressurization treatment within a certain temperature range to degas the gas in the material; In a method for molding a thick-walled molded product that includes a step of heating a thermoplastic resin material above its melting temperature and compression molding, the above-mentioned certain temperature range is the softening of a resin having the highest softening temperature among the thermoplastic resins. 1. A method for molding a thick-walled product, characterized in that the temperature is higher than the melting temperature of the resin having the lowest melting temperature among the thermoplastic resins. 2 Thermoplastic resin material is made of multiple sheets and/or
Alternatively, the molding method according to claim 1, wherein films are stacked one on top of another. 3. The molding method according to claim 1, wherein the thermoplastic resin material is in the form of pellets. 4. The molding method according to claim 1, wherein the thermoplastic resin material is in powder form.