JP2007223143A - Method for molding 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 of the surface of at least one mold cavity is heated to increase the temperature of the part by at least 20°C, and a temperature gradient is formed so that the maximum temperature gradient between the heated part and the non-heated part is 6°C/cm or below, a process (2) in which a pair of molds 4 and 5 are clamped, a process (3) in which the molten thermoplastic resin is supplied between the molds, a process (4) in which both molds are cooled, and a process (5) 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 of solving the appearance defect of the above-described molded body, the entire cavity surfaces of a pair of molds used for manufacturing the molded body are heated in advance by high-frequency induction heating, and then a molten resin is supplied between the molds. And the method of manufacturing a molded object by cooling is proposed (refer patent document 1).

  Further, in Patent Document 2, in a method for producing a molded body using a pair of molds, a mold having a temperature adjusting insert is used in the vicinity of a resin joining portion of the mold, and a resin is placed between the molds. At the time of supply, a method is disclosed in which a mold without weld is produced by partially heating a mold with the temperature adjusting insert.

Japanese Patent Publication No. 58-40504 JP 7-290541 A

However, in the method disclosed in Patent Document 1, since the entire mold cavity surface is heated, there is a problem that the cooling time becomes long and the production efficiency is poor. Moreover, in the method disclosed in Patent Document 2, although the molding cycle is shortened and the production efficiency is improved, gloss unevenness may occur on the surface of the obtained molded body.
The present invention provides a method for efficiently producing a thermoplastic resin molded article free from defects such as weld and gloss unevenness and having a good appearance in a short molding cycle.

That is, the present invention is a method for producing a thermoplastic resin molded body using a pair of male and female dies, and includes all of the following steps (1) to (5). A manufacturing method is provided.
(1) A part of at least one mold cavity surface is heated so that the temperature of the part is higher by 20 ° C. or more than before heating, and the maximum temperature gradient between the heating part and the non-heating part is 6 ° C./cm. (2) A step of clamping a pair of molds (3) A step of supplying a molten thermoplastic resin between the pair of molds (4) Both Step of cooling the mold (5) Step of opening the mold and taking out the thermoplastic resin molded body

  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. There is no particular limitation on the size and shape of the thermoplastic resin molded body produced by the method of the present invention, but the production method of the present invention is a large molded body that requires a plurality of gates or an opening as shown in FIG. It is suitable for the production of a thermoplastic resin molded body having a part (3) and being easily welded. 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). Gates (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 gates are appropriately determined depending on the shape and size of the molded product, but the manufacturing method of the present invention can be preferably applied when a plurality of gates are used.
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 (9) and a conveying device (10) for conveying the heating means. The heating means (9) is inserted between the male and female molds from the outside (FIG. 7), and the heating means is further designed on the design side. A part of the mold cavity surface can be heated close to the mold cavity surface (FIG. 8). The heating means (9) is not particularly limited as long as it has means capable of heating such as an electric heater or a blower for blowing warm air, but a heating coil capable of high-frequency induction heating is preferably applicable. High-frequency induction heating is preferable because the mold cavity surface can be heated in a short time, and the molding cycle can be shortened compared to other means. Moreover, it is preferable that a heating coil is made into the shape which matched the copper tube with the cavity shape of the heating site | part of a metal mold | die.
The heating means is not limited to the heating means from the outside of the mold, but may be a heating medium from the inside of the mold using a heating medium such as steam or an electric heater embedded in the mold.

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 a process in which 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. When the thermoplastic resin molding is manufactured under the same conditions using the same mold except that the heating coil is not used for heating, a weld or silver streak is formed on the design surface side of the obtained thermoplastic resin molding. In addition, it is necessary to include a mold cavity part in contact with a part where a defect such as a flow mark occurs. However, if the heating part is made too wide, the apparatus cost increases and the cooling time also becomes long. Therefore, it is preferable to heat the narrowest area as much as possible from the cost and cycle side, and the dimension on the short side of the heating part is 200 mm or less. It is preferable that it is 150 mm or less. For example, in the case of the thermoplastic resin molded body shown in FIG. 1, since there are two gate portions (2) as shown in FIG. 2, an intermediate portion where molten thermoplastic resins supplied from the respective gate portions merge ( A) Welding is expected in the vicinity. For this reason, it is preferable to heat the mold cavity part in contact with part C in FIG. 3 where the occurrence of weld (A) is expected. In the case of the thermoplastic resin molded body shown in FIG. 4, the molten thermoplastic resin separated from the downstream portion (B) is separated from the resin supplied from the gate portion (2) at the opening portion (3). Because of the merge, the occurrence of welds is expected near the junction. For this reason, it is preferable to heat the mold cavity portion in contact with 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 means that 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, so that the temperature of the heating unit is higher than the temperature before heating. Is a temperature higher by 20 ° C. or more. As for the temperature of a heating part, it is more preferable that the maximum temperature is more than the load deflection temperature of the thermoplastic resin which comprises the thermoplastic resin molded object obtained by this invention.
After the mold cavity surface is heated, the temperature of the mold cavity surface decreases before the heating coil is retracted, the mold is closed, and the molten thermoplastic resin is supplied. It is necessary to perform heating in anticipation of minutes. For this reason, it is preferable to shorten the time until the heating coil is retracted and the mold is closed after heating the mold cavity as much as possible, and the temperature drop during this period is reduced. Thereby, the heating time of the mold cavity surface can be shortened, and the cycle can be shortened. In addition, the deflection temperature under load in the present invention is a temperature measured according to the method B of JIS K7191-2.

The surface of the mold cavity surface at this time has a temperature difference between a portion heated by the heating coil and a portion not heated. If this temperature difference is too large, defects such as gloss unevenness occur on the surface of the thermoplastic resin molded article, so it is preferable to make the temperature difference as small as possible. Here, it is necessary that the largest temperature gradient among the temperature gradients of the heating part and the non-heating part is 6 ° C./cm or less at the time when the supply of the molten thermoplastic resin between the molds is started. When the temperature gradient exceeds 6 ° C./cm, uneven gloss occurs and the appearance is poor.
In order to reduce this temperature gradient, it is also effective to increase the temperature of the portion not heated in the mold cavity surface, and it is preferable to set the mold temperature before heating to 50 ° C. or higher, and 60 ° C. It is more preferable to keep it above.
The temperature gradient may be measured by attaching a temperature sensor to the mold, but using a thermocouple on the surface of the mold cavity or using a radiation thermometer, etc. You may measure and calculate the temperature gradient at the time of supplying molten thermoplastic resin.

FIG. 9 shows a state in which supply of the molten thermoplastic resin (11) is started from the gate (6) and the gate (7) through the molten resin supply passage (8) between the female mold (4) and the male mold (5). Show. The cavity clearance of the male and female dies when starting to supply the molten thermoplastic resin may be almost the same as the thickness of the molded body that is normally produced, but is smaller than the thickness of the molded body depending on the application, product shape, size, etc. of the molded body Supply may be started with a cavity clearance, 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 clamping is performed 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 gate (6) and the gate (7) flows in the mold cavity and merges in the vicinity of the middle point (E) of each gate as shown in FIG. 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.
In the figure, a part of the mold cavity surface is heated by the heating means, and then the mold is clamped and the molten thermoplastic resin is supplied, but the mold cavity surface is heated by the heating means from inside the mold. In this case, it is preferable to perform mold clamping before heating or while heating, and to complete the mold clamping before the heating is completed, so that the temperature drop of the mold cavity surface in the mold clamping process can be reduced.
Moreover, although the example which clamps in the vertical direction is shown in the figure, the clamping direction may be a vertical direction or a horizontal direction.

FIG. 11 shows a process of opening the male and female molds and taking out the molded product, 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 and various inorganic or organic fillers that are usually used as necessary. Of course, various pigments, lubricants, 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.
Further, in addition to the chemical foaming agent, liquid or gaseous carbon dioxide and / or nitrogen may be directly pressed into the molten thermoplastic resin.

[Example 1]
Using a Sumitomo Noblen AX568 (manufactured by Sumitomo Chemical Co., Ltd., MFR 65 g / 10 min, deflection temperature under load: 132 ° C.) as a thermoplastic resin, a molded body having dimensions of 400 × 600 mm and a thickness of 2.5 mm as shown in FIG. 1 is formed. did. A range having a width of 150 mm near the center of the female cavity was heated to 160 ° C. by a heating coil using a high frequency induction heating device having a high frequency transmission frequency of 20 kHz and an output of 50 kW. The mold was clamped and molten thermoplastic resin was supplied to the mold cavity. The temperature of the heating part on the mold cavity surface at the time of supplying the molten thermoplastic resin was 120 ° C., and the maximum temperature gradient between the heating part and the non-heating part was 6 ° C./cm. After cooling, the mold was opened to obtain a thermoplastic resin molded body. The obtained molded article had good appearance without defects such as weld and gloss unevenness.
<Heating conditions>
Heating time 20 seconds Heating temperature near the center of the mold cavity 160 ℃
Mold cavity surface temperature at the start of supplying molten thermoplastic resin 120 ° C
Maximum temperature gradient 6 ° C / cm
<Molding conditions>
Resin temperature 230 ℃
Mold temperature 60 ℃
Mold cavity clearance 2.5mm when resin is supplied
Pressurized surface pressure 3MPa
Cooling time 30sec

[Comparative Example 1]
A thermoplastic resin molded product is molded in the same manner as in Example 1 except that the clearance between the heating coil and the mold cavity surface at both ends of the heating part is 20 mm smaller than that in Example 1 and the temperature gradient is 8 ° C./cm. did. In the obtained molded product, no weld was observed in the vicinity of the center portion, but gloss unevenness occurred.

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.

Explanation of symbols

1: Thermoplastic resin molded body 2: Gate portion 3: Opening portion 4: Female die 5: Male die 6: Gate 7: Gate 8: Molten resin supply passage 9: Heating means 10: Conveying device 11: Molten thermoplastic resin

Claims (6)

A method for producing a thermoplastic resin molded article using a pair of male and female dies, comprising all of the following steps (1) to (5).
(1) A part of at least one mold cavity surface is heated so that the temperature of the part is higher by 20 ° C. or more than before heating, and the maximum temperature gradient between the heating part and the non-heating part is 6 ° C./cm. (2) A step of clamping a pair of molds (3) A step of supplying a molten thermoplastic resin between the pair of molds (4) Both Step of cooling the mold (5) Step of opening the mold and taking out the thermoplastic resin molded body 2. The method for producing a thermoplastic resin molded body according to claim 1, wherein the means for heating at least a part of the mold cavity surface is a heating coil capable of high-frequency induction heating. The thermoplastic resin molding according to claim 1 or 2, wherein the temperature of the mold cavity surface before heating a part of at least one mold cavity surface in the step (1) is 50 ° C or higher. Body manufacturing method. The part of the mold cavity surface heated in the step (1) includes a part that comes into contact with the joining portion of the molten thermoplastic resin when the molten thermoplastic resin is supplied between the pair of molds. The method for producing a thermoplastic resin molded article according to any one of claims 1 to 3. The maximum temperature of the mold cavity surface heated in the step (1) is equal to or higher than the deflection temperature under load of the thermoplastic resin constituting the thermoplastic resin molded body. A method for producing a thermoplastic resin molded article. The thermoplastic resin molded article according to any one of claims 1 to 5, wherein in the step (3), both molds are further clamped while supplying the molten thermoplastic resin or after completion of the supply. Manufacturing method.

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