JP2007223142A - Method for manufacturing thermoplastic resin molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for molding a molding having a good appearance. <P>SOLUTION: The method for manufacturing the thermoplastic resin molding includes a process (1) in which part or the whole of the surface of at least one mold cavity is heated by an external heating means, a process (2) in which at the latest, from a point of time when the heating is completed in the process (1) to a point of time when the supply of the molten thermoplastic resin between a pair of molds is started in a process (4), the surface of the mold cavity is kept warm by a heat insulating means to include the mold cavity part heated by the external heating means in the process (1), a process (3) in which a pair of the molds is clamped, the process (4) in which the molten thermoplastic resin is supplied between a pair of the molds through a resin supply opening formed in the mold, a process (5) in which both molds are cooled, and a process (6) in which the molds are opened, and the thermoplastic resin molding is taken out. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for producing a thermoplastic resin molded body.

Thermoplastic resin moldings are used in a wide range of fields such as interior and exterior parts of automobiles, home appliances, and housing-related products because of their economy, light weight, and good formability.
It is known that such a thermoplastic resin molded body can be manufactured by a molding method such as injection molding or compression molding. However, when manufacturing a molded product having a complicated shape with an opening by the above-described method, or when using a plurality of resin supply gates when molding the molded product, the resulting molded product has poor appearance such as welds. May occur

As a method for solving the above-mentioned defective appearance of the molded body, the cavity surfaces of a pair of molds used for manufacturing the molded body are previously heated by an external heating means (high frequency induction heating), and then melted between the molds. A method has been proposed in which a shaped resin is produced by supplying a glassy resin and cooling (see Patent Document 1).
Japanese Patent Publication No. 58-40504

However, in the method disclosed in Patent Document 1, after heating the mold cavity surface by high-frequency induction heating, the heating coil is retracted outside the mold and the mold cavity is closed to supply the molten resin. After that, it takes time to supply the molten resin, and there is a problem that the temperature drops during that time. For this reason, since it heats to the temperature which anticipated the temperature fall beforehand, heating time will become long.
Even when the present invention is a case where the mold cavity is heated by an external heating means, it is possible to suppress a temperature drop until the molten resin is supplied, so that the molding cycle is not made longer than necessary. The present invention provides a manufacturing method for forming a molded article having a good appearance.

That is, the present invention provides a method of supplying a molten thermoplastic resin between a pair of male and female molds through a resin supply port provided in the mold and cooling to produce a thermoplastic resin molded body. A part of or the entire surface of the mold cavity surface is heated in advance by an external heating means, and is heated by an external heating means at the latest from the completion of heating until the start of supplying molten thermoplastic resin between a pair of male and female dies. A method for producing a thermoplastic resin molded body, wherein the temperature is maintained by a heat retaining means so as to include a mold cavity portion.

According to the method for producing a thermoplastic resin molded article of the present invention, a thermoplastic resin molded article having a good appearance can be efficiently produced in a short molding cycle.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 shows an example of a thermoplastic resin molded article produced by the method of the present invention. Although there is no restriction | limiting in particular in the magnitude | size and shape of a thermoplastic resin molded object, the manufacturing method of this invention has a large molded object which requires a several resin supply port, and an opening part (3) as shown in FIG. It is suitable for the production of a thermoplastic resin molded body in which welds are likely to occur. The entire or part of the surface of the thermoplastic resin molded article obtained by the production method of the present invention may be provided with uneven patterns such as various texture patterns and pattern patterns. The groove depth of the unevenness is usually 10 μm or more and 500 μm or less, preferably 50 μm or more and 200 μm or less.
FIG. 6 shows a cross-sectional view of a mold for producing the thermoplastic resin molded body of FIG. 1, which consists of a male and female pair of a female mold (4) and a male mold (5). Resin supply ports (6) and (7) for supplying the molten thermoplastic resin are provided, and the molten thermoplastic resin is supplied into the cavity through the molten resin supply passage (8). The location and number of the resin supply ports are appropriately determined depending on the shape and size of the molded product, but the manufacturing method of the present invention is preferably applicable when a plurality of resin supply ports are used.
The female mold (4) is provided with a nozzle (9) connected to a hot air generator (not shown). The location and number of nozzles (9) are not particularly limited as long as the location and number are such that hot air can be efficiently blown onto the mold cavity surface.
The material of the male and female molds is preferably a magnetic material so that high-frequency induction heating can be performed efficiently.
In this pair of male and female molds, one of the molds is fixed to a stationary platen of a press device (not shown), and the other die is fixed to a movable platen. The mold is clamped by moving in the direction. This drive device may be hydraulic or electric.

The pair of male and female dies used in the present invention is provided with a heating means. For example, it comprises a heating means (10) and a conveying means (11) for conveying the heating means. The heating means (10) is inserted between male and female molds from the outside (FIG. 7), and the heating means (10) is further designed. The mold cavity surface can be heated close to the side mold cavity surface (FIG. 8). The external heating means is not particularly limited as long as it has means capable of heating, such as an electric heater or a heating coil by high-frequency induction heating. However, the heating coil capable of high-frequency induction heating can heat the surface of the mold cavity in a short time, and can be molded. Since the cycle can be shortened, it can be preferably applied. The heating coil to be used preferably has a copper tube having the same shape as the heating part of the mold cavity.

Hereinafter, a method for producing the thermoplastic resin molded body shown in FIG. 1 using the heating apparatus having the mold shown in FIG. 6 and a heating coil capable of high-frequency induction heating as the heating means will be described.
7 and 8 show that a heating coil is inserted between male and female molds from the outside, and the heating coil is heated close to the cavity surface of the female mold. The heating place may be the entire cavity surface or a part thereof, but partial heating is preferable in terms of cost and cycle. When a part of the cavity surface is partially heated, the thermoplastic resin molding obtained when a thermoplastic resin molded body is manufactured under the same conditions using the same mold except that heating is not performed by a heating coil. It is preferable to heat the body so as to include a mold cavity part in contact with a part where defects such as welds, silver streaks, and flow marks occur on the design surface side of the body. For example, in the case of the thermoplastic resin molded body shown in FIG. 1, since there are two resin supply portions (2) as shown in FIG. 2, an intermediate where the molten thermoplastic resins supplied from the respective resin supply portions merge together. Weld (A) is expected to occur near the area. For this reason, it is preferable to heat so as to include at least the mold cavity portion in contact with the portion C of FIG. 3 where the occurrence of weld (A) is expected. In the case of the thermoplastic resin molded body shown in FIG. 4, the resin supplied from the resin supply part (2) is separated at the opening (3), and the molten thermoplastic resin separated at the downstream part is joined. Therefore, the occurrence of weld (B) is expected near the junction. For this reason, it is preferable to heat so as to include at least the mold cavity portion in contact with the portion D in FIG. 5 where the occurrence of weld (B) is expected.

The heating time in the heating coil is a time for the temperature of the mold cavity surface to reach a predetermined temperature. The predetermined temperature may be appropriately set. After the heating coil is retracted from the mold, the male and female molds are closed and the molten thermoplastic resin is supplied between the molds. The temperature is preferably 20 ° C. or more higher than the previous temperature, and more preferably the load deflection temperature of the thermoplastic resin constituting the thermoplastic resin molded article obtained in the present invention. The deflection temperature under load is a temperature measured according to the method B of JIS K7191-2.
When the mold cavity surface is partially heated, a temperature difference occurs between the portion heated by the heating coil and the portion not heated. If this temperature difference is too large, defects such as uneven gloss may occur on the surface of the thermoplastic resin molded article, and therefore it is preferable to make the temperature difference as small as possible. In order to reduce the temperature gradient of the mold cavity surface, it is also effective to increase the temperature of the unheated portion of the mold cavity surface, and the mold temperature before heating by the external heating means is 50 ° C. or higher. It is preferable to keep it at 60 ° C. or higher.

Even if the mold cavity surface is heated in advance by the heating coil, the temperature of the mold cavity surface is lowered until the heating coil is retracted, the mold is closed, and the molten thermoplastic resin is supplied. Therefore, from the time when the mold cavity surface is completely heated by the heating coil until the supply of the molten thermoplastic resin is started, the temperature is maintained by the heat retaining means so as to include the mold cavity surface heated by the heating coil. The method of heat insulation is not particularly limited as long as it is a means capable of maintaining the temperature of the heated mold cavity surface or suppressing the temperature decrease, but heat insulation by blowing hot air onto the mold cavity surface is preferable from the viewpoint of cost. In FIG. 9, warm air is blown from a nozzle provided in the female mold to suppress a temperature drop on the female mold cavity surface. The temperature of the hot air to be blown is preferably equal to or higher than the temperature heated by the heating coil. The timing of starting the blowing of warm air may be before heating by the heating coil or from the time when heating is completed, but it is necessary to start blowing at least when heating is completed. Moreover, it is preferable that the timing of ending the blowing of warm air is until the start of supplying the molten thermoplastic resin. Thereby, since the initial heating temperature of the mold cavity surface in the heating coil can be set low, the heating time can be shortened and the cycle can be shortened.

Step (3) is a step of clamping a pair of molds, and step (4) is a step of supplying a molten thermoplastic resin between a pair of molds through a resin supply port provided in the mold. It is. The step (2) is continuously performed during the step (3) and until the time when the supply of the molten thermoplastic resin is started in the step (4).
FIG. 10 is a view corresponding to the step (4), and the resin supply port (6) and the resin supply port (7) through the molten resin supply passage (8) between the female mold (4) and the male mold (5). The state which started supply of the molten thermoplastic resin (12) from FIG. The cavity clearance of the male and female molds when starting the supply of molten thermoplastic resin may be almost the same as the thickness of the molded body, but the cavity clearance is smaller than the molded body thickness depending on the usage of the molded body, product shape, size, etc. Supply may be started, or supply may be started with a cavity clearance larger than the thickness of the molded body. When the supply of the molten thermoplastic resin is started with a cavity clearance larger than the thickness of the molded body, the mold is further clamped while supplying the resin or after the supply is completed. In the case of performing mold clamping after completion of the resin supply, it is preferable to start the mold clamping immediately after completion of the supply.
The molten thermoplastic resin supplied from the resin supply port (6) and the resin supply port (7) flows in the mold cavity and merges near the middle point (E) of each resin supply port as shown in FIG. To do. Since the mold cavity surface in the vicinity of the merged portion of the molten thermoplastic resin is heated in advance by a heating coil, cooling is delayed, and appearance defects such as welds and uneven gloss can be made inconspicuous.
Although the figure shows an example of clamping in the vertical direction, the clamping direction may be the vertical direction or the horizontal direction.

After cooling both molds in the step (5), the mold is opened in the step (6), and the thermoplastic resin molded body is taken out. FIG. 12 shows a place where the male and female molds are opened and the molded product is taken out, and the thermoplastic resin molded article having a good appearance and free from defects such as weld and gloss unevenness shown in FIG. 1 can be obtained.

As the thermoplastic resin used in the method of the present invention, resins usually used in compression molding, injection molding, extrusion molding and the like are applied as they are.
Examples of such resins include polypropylene, polyethylene, acrylonitrile-styrene-butadiene block copolymers, polyamides such as polystyrene and nylon, polyvinyl chloride, polycarbonate, acrylic resins, and styrene-butadiene block copolymers. Examples thereof include thermoplastic resins, thermoplastic elastomers such as EPM and EPDM, mixtures thereof, and polymer alloys using these.

In addition, these thermoplastic resins may contain fillers such as glass fibers, various inorganic or organic fillers that are usually used as necessary, and of course, various pigments, lubricants that are usually used, Various additives such as an antistatic agent and a stabilizer may be blended.

The thermoplastic resin may contain a foaming agent. As a foaming agent, the well-known chemical foaming agent currently used when manufacturing the foam of a thermoplastic resin can be used. Specifically, inorganic foaming agents such as sodium bicarbonate, ammonium bicarbonate and ammonium carbonate, nitroso compounds such as N, N'-dinitrosopentamethylenetetramine, azodicarbonamide, azo such as azobisisobutyronitrile Compounds, sulfonylsulfonyl hydrazides, toluenesulfonyl hydrazides, sulfonyl hydrazides such as diphenylsulfone-3,3′-disulfonyl hydrazide, and blowing agents such as p-toluenesulfonyl semicarbazide can be used. It is a preferable embodiment to add salicylic acid, urea and a foaming aid containing these as required.

The type of foaming agent is selected in consideration of the melting temperature of the thermoplastic resin to be used, the target foaming ratio, and the like. The amount added is adjusted in consideration of the strength, density and the like of the target molded product, but is generally 0.1 to 5 parts by weight with respect to 100 parts by weight of the resin.
In addition to the chemical foaming agent, liquid or gaseous carbon dioxide and / or nitrogen may be directly injected into the molten resin.

An example of a thermoplastic resin molded article produced by the method of the present invention is shown in a plan view. An example of a thermoplastic resin molded article produced by the method of the present invention is shown in a plan view. An example of a thermoplastic resin molded article produced by the method of the present invention is shown in a plan view. The other example of the thermoplastic resin molded object manufactured by the method of this invention is shown with the top view. The other example of the thermoplastic resin molded object manufactured by the method of this invention is shown with the top view. An example of the metal mold | die used for the method of this invention is shown with sectional drawing. The manufacturing process of this invention is shown with the schematic of the cross section of a metal mold | die. The manufacturing process of this invention is shown with the schematic of the cross section of a metal mold | die. The manufacturing process of this invention is shown with the schematic of the cross section of a metal mold | die. The manufacturing process of this invention is shown with the schematic of the cross section of a metal mold | die. The manufacturing process of this invention is shown with the schematic of the cross section of a metal mold | die. The manufacturing process of this invention is shown with the schematic of the cross section of a metal mold | die.

Explanation of symbols

1: Thermoplastic resin molding 2: Resin supply unit 3: Opening part 4: Female mold 5: Male mold 6: Resin supply port 7: Resin supply port 8: Molten resin supply passage 9: Nozzle 10: Heating means 11: Conveyance Device 12: Molten thermoplastic resin

Claims (7)

A method for producing a thermoplastic resin molded article by supplying a molten thermoplastic resin between a pair of male and female molds through a resin supply port provided in the mold and cooling them, comprising the following step (1): A method for producing a thermoplastic resin molded article comprising all of (6).
(1) Step of heating at least one of the mold cavity surfaces by the external heating means (2) From the time when heating is completed in step (1) at the latest, between the pair of molds in step (4) A step (3) of maintaining the mold cavity surface by the heat retaining means so as to include the mold cavity portion heated by the external heating means in the step (1) until the supply of the molten thermoplastic resin is started. (4) A step of supplying a molten thermoplastic resin between a pair of molds through a resin supply port provided in the mold (5) A step of cooling both molds (6) The process of opening the mold and taking out the thermoplastic resin molding 2. The method for producing a thermoplastic resin molded article according to claim 1, wherein the external heating means is a heating coil capable of high-frequency induction heating. The method for producing a thermoplastic resin molded article according to claim 1 or 2, wherein the heat retaining means is blowing warm air. The method for producing a thermoplastic resin molded article according to any one of claims 1 to 3, wherein the molten thermoplastic resin is supplied from a plurality of resin supply ports. The method for producing a thermoplastic resin molded body according to any one of claims 1 to 4, wherein a part of the mold cavity surface is heated by an external heating means. The temperature of the mold cavity surface at the time of starting to supply the molten thermoplastic resin between a pair of male and female molds is equal to or higher than the deflection temperature under load of the thermoplastic resin constituting the thermoplastic resin molded body. Item 6. A method for producing a thermoplastic resin molded article according to any one of Items 1 to 5. The method for producing a thermoplastic resin molded article according to any one of claims 1 to 6, wherein the mold is further clamped while supplying the molten thermoplastic resin between a pair of male and female molds or after completion of the supply. .

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