JPH053373B2 - - Google Patents

Abstract

PURPOSE:To prevent the occurrence of cold marks and burrs by cooling locally the adjacency of the sliding part of a female mold and/or the adjacency of the sliding part of a male mold, while feeding molten thermoplastic resin into between both female and male molds which are not yet perfectly closed. CONSTITUTION:When an upper male mold 3 and a lower female mold 4 are closed, the clearance between their sliding parts 5, 6 is caused to be 0.08mm. The hot water heated at 85 deg.C is caused to pass through the paths 7, 7' for heating medium, and 20 deg.C water is made to pass through the paths 8, 8' for cooling water. The molten polypropylene resin heated at 260 deg.C is supplied on the bottom force and the top force fitted to an upper platen is lowered, thereby compression molding said resin. Consequently, the molded product excellent in appearance without occurrence of burrs, having no cold marks on the whole surface of the product including its bottom, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to compression molding (including injection compression molding) of thermoplastic resins. Thermoplastic resin (hereinafter referred to as resin) is plasticized and melted using an extruder, etc.
The molded product obtained by supplying this between molds that are not yet completely closed and cooling under pressure is as follows when compared with the injection molded product obtained by supplying molten resin between fully closed molds. There are advantages. In injection molding, molten resin is press-fitted into a closed mold space through a gate, which causes the resin to become oriented and leave residual strain in the molded product. Since strong residual strain remains, this becomes a physical weakness. On the other hand, in compression molding (including injection compression molding), the molten resin supplied between the molds, which have not yet been completely closed, is made to flow uniformly over the mold surface under the pressure of mold clamping. Therefore, a molded product with almost no residual strain and less deformation can be obtained. When molding with this method, a hermaphroditic mold is usually used in which a portion of the side surface slides closed. However, there is a problem in that a portion of the thermoplastic resin leaks from the sliding portion and burrs are likely to occur. The occurrence of burrs can be substantially prevented by keeping the clearance of the sliding portion below a certain value determined by the viscosity characteristics of the thermoplastic resin used, molding conditions, etc. In the case of materials with high melt viscosity, the clearance required to prevent the occurrence of burrs is relatively large, so it is important to control mold manufacturing accuracy, the parallelism of the platen of the molding machine mold clamping device that attaches the male and female molds, and the temperature difference between the male and female molds. Even if it is somewhat bad, the occurrence of burrs can be prevented relatively easily.
However, in the case of materials with low melt viscosity, such as high-flow grade polypropylene, the clearance that does not cause burrs is small, and as a result, the accuracy of mold manufacturing, the parallelism of the platen of the mold clamping device of the molding machine that attaches the male and female molds, Strict precision and control are required for temperature differences between male and female molds.

The inventors of the present invention have discovered that the temperature of the sliding parts of the male and female dies has a very large effect on the clearance that does not cause burrs, leading to the present invention. That is, a male mold and a female mold whose side surfaces partially slide to close are used, and the vicinity of the sliding part of the male mold and/or the vicinity of the sliding part of the female mold is locally cooled. That is, the present invention supplies a thermoplastic resin in a molten state between male and female molds that are not yet completely closed, and slides a part of the inner surface of the female mold and the outer surface of the male mold. Close both molds, apply pressure,
This is a thermoplastic resin molding method characterized by locally cooling the vicinity of the sliding part of the female mold and/or the vicinity of the sliding part of the male mold when cooling to obtain a molded product.

According to the method of the present invention, molding can be performed while preventing the occurrence of burrs using male and female molds having sliding parts with relatively large clearance.

From the perspective of preventing burrs, cooling the entire mold can achieve the objective, but if the mold temperature is low, the fluidity of the material will deteriorate, and the supplied molten resin will start to cool down the mold even before it is pressurized. Compared to other areas, areas that come into contact with the surface may have problems such as significantly lower gloss or the appearance of small wrinkles. This trouble is hereinafter referred to as a cold mark. In order to prevent these problems and also prevent the occurrence of burrs, it is extremely effective to locally cool the area near the sliding part of the male die and/or the area of the sliding part of the female die, as described above. be.

The implementation of the present invention will be explained using the drawings. FIG. 1 is a schematic cross-sectional view of a compression molding mold section attached to a platen.

FIG. 2 is a perspective view of a molded article obtained by the method of the present invention. In FIG. 1, reference numeral 1 denotes an upper platen of a press machine which is lowered and raised by hydraulic pressure. 2 is a lower platen of the press; 3 and 4 are an upper mold (male) and a lower mold (female) respectively attached to the platen, and sliding parts 5, 6 is provided. 7,
Reference numeral 7' denotes a passage for a heating medium, and the temperature of the heating medium flowing through this passage is set at a temperature that does not generate cold marks or impede the fluidity of the thermoplastic resin, as described above. Reference numerals 8 and 8' denote cooling water passages provided near the upper mold sliding part 5 and the lower mold sliding part 6, respectively. 9 is the supplied molten resin. Using such an apparatus, molten resin 9 is supplied onto the lower mold, and then the upper mold 4 attached to the upper platen is lowered to perform compression molding.

Example 1 In the above device, the clearance between the sliding parts 5 and 6 when the upper and lower male and female molds 3 and 4 are closed is
0.08mm, and 85℃ in the heating heat medium passages 7 and 7'.
20°C water is passed through cooling water passages 8 and 8', and polypropylene resin (Sumitomo Noblen) heated to 260°C is placed on the lower mold.
AY564) was supplied, and the upper mold attached to the upper platen was lowered to perform compression molding. As a result, a molded product with a good appearance and no cold marks and no burrs was obtained over the entire surface of the molded product including the bottom (part A in FIG. 2).

Comparative Example 1 Molding was performed in the same manner as in Example 1 except that 85°C hot water was passed through passages 8 and 8', and burrs were observed at the end of the molded product (section B in Figure 2). There has occurred.

Embodiment 2 FIG. 3 is a schematic cross-sectional view of the injection compression molding mold section attached to the platen when the platen is moved to the molten resin supply position. In Fig. 3, 11 is a fixed platen, 12 is a movable platen, 13, 1
4 is a core mold (male) attached to each platen;
Cavity type (female), each with sliding part 1
5 and 16 are provided. When the core mold and cavity mold were closed, the clearance between the sliding parts 15 and 16 was 0.18 mm. Cartridge heaters 17 and 17' are arranged near the surface of the mold.
Reference numerals 18 and 18' designate cooling water passages provided near the core-type sliding part 15 and the cavity-type sliding part 16, respectively, and 19 designates molten resin supplied through the gate part 20. Although not shown, the gate portion 20 has a built-in valve that opens only when molten resin is supplied and is closed at other times. Water at 20°C is passed through the cooling water passages 18, 18' and 21, 2.
After setting the mold surface temperature at 1' to approximately 60°C and moving the platen 12 to the state shown in Fig. 3,
ABS resin heated and melted at 240℃ (Clarastick)
SHF) was supplied, and after the supply, the platen 12 was further moved to apply pressure, the cartridge heater was turned off, and the product was taken out after cooling. As a result, a molded product with a good appearance and no curl marks was obtained over the entire surface of the molded product including the bottom part (section A in FIG. 2) and no burrs were generated. In addition, after removing the product,
Turn on the power to the court storage heater to prepare for the next cycle.

Although the above embodiments have been described, the present invention is not limited thereto, and the types of materials, supply methods, heating methods, heating timing, time, etc. may be freely changed within the scope of not impairing the purpose of the present invention. You can choose.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a press molding die attached to a platen, and FIG. 2 is a perspective view of a molded product obtained by the method of the present invention. FIG. 3 is a schematic cross-sectional view of the injection compression molding mold section attached to the platen. 1, 2: Platen of press machine, 3, 4: Compression molding mold, 5, 6: Sliding parts of male mold and female mold, 7,
7': heating medium passage, 8, 8': cooling water passage,
9: Molten resin, 11, 12: Injection compression molding platen, 13, 14: Core mold (male), cavity mold (female), 15, 16: Core mold, cavity mold sliding part, 17, 17': Cartridge heater, 18,
18': cooling water passage, 19: molten resin, 20: gate section, 21, 22': mold surface section.

Claims (1)

[Claims] 1. Thermoplastic resin in a molten state is supplied between male and female molds that are not yet completely closed, and the inner surface of the female mold and a part of the outer surface of the male mold are slid to close both molds. , when pressurizing and cooling to obtain a molded product,
A method for molding a thermoplastic resin, comprising locally cooling the vicinity of the sliding part of the female mold and/or the vicinity of the sliding part of the male mold.