JP4811225B2 - Method for producing molded thermoplastic resin - Google Patents

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 surface of a pair of molds used for manufacturing the molded body is heated in advance by high-frequency induction heating, and then a molten thermoplastic resin between the molds A method for producing a molded body by cooling and cooling is proposed. (See Patent Document 1)

Further, in Patent Document 2, in a method of manufacturing 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 interposed between the molds. A method is disclosed in which a mold without weld is produced by partially heating a mold with the temperature adjusting insert when supplying the mold.
Japanese Patent Publication No. 58-40504 JP 7-290541 A

However, in the method described 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 inferior. Further, in the method disclosed in Patent Document 2, although the molding cycle is shortened and the production efficiency is improved, the portion of the surface of the obtained molded body in contact with the mold heating portion and the portion in contact with the mold non-heating portion Transfer unevenness may occur.
The present invention provides a method for efficiently producing a thermoplastic resin molded article having good appearance and no weld or transfer unevenness in a short molding cycle.

  That is, the present invention pre-heats a part of one or both of the mold cavity surfaces of a pair of male and female molds and starts supplying molten thermoplastic resin between the molds, A method of manufacturing a thermoplastic resin molded body in which mold clamping is performed while supplying a plastic resin or after completion of the supply, and cooling is performed, wherein the molten thermoplastic resin is supplied at a rate of 800 cc / sec or more. The manufacturing method of a plastic resin molding is provided.

  According to the method for producing a thermoplastic resin molded article of the present invention, a thermoplastic resin molded article having no appearance and unevenness in appearance and 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. 2, 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 installation location and number of the gates are appropriately determined depending on the shape and size of the molded body to be manufactured. .
As will be described later, when the means for heating the mold cavity surface is high-frequency induction heating, the material of the male and female dies 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. Examples of the driving device include a hydraulic driving device and an electric driving device.

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 from the outside between the male and female molds (FIG. 7), and the heating means is further connected to one mold cavity. A part of the mold cavity surface can be heated close to the 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 portion where a defect such as a flow mark is expected to occur. However, if the heating part is made too wide, the apparatus cost increases and the cooling time also becomes long. Therefore, it is preferable from the cost and cycle side to heat the narrowest possible range, and the short side dimension of the heating part is about 200 mm or less. It is preferable that For example, in the thermoplastic resin molded body shown in FIG. 1, when there are two gate portions (2) as shown in FIG. 2, the molten thermoplastic resin supplied from the mold gate corresponding to each gate portion is Welds are expected to occur in the vicinity of the joining middle part (A). Therefore, it is preferable to heat the mold cavity portion in contact with the portion (C) in FIG. 3 where the occurrence of weld (A) is expected. Further, in the case of the thermoplastic resin molded body shown in FIG. 4, the resin supplied from the mold gate corresponding to the gate portion (2) is separated at the opening portion (3) and separated at the downstream portion (B). Since the molten thermoplastic resin merges, the occurrence of welds is expected in the vicinity of the merged portion. For this reason, it is preferable to heat the mold cavity part in contact with (D) of 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 when the molten thermoplastic resin is supplied between the molds, the temperature of the heated portion is higher than the temperature before heating. Is preferably 20 ° C. or higher. As for the temperature of a heating part, it is more preferable that the maximum temperature is more than the deflection temperature under load of the thermoplastic resin used by this invention.
After heating a part of the mold cavity surface, retract the heating coil, close the mold and supply the molten thermoplastic resin, because the temperature of the heated part of the mold cavity surface decreases, It is necessary to perform heating in consideration of the temperature drop in advance. 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 mold cavity surface after heating a part of the mold cavity surface has a temperature difference between a portion heated by the heating coil and a portion not heated. If this temperature difference is too large, transfer unevenness may occur on the surface of the thermoplastic resin molding. Here, it is preferable that the largest temperature gradient among the temperature gradients of the heated portion and the non-heated portion is 8 ° C./cm or less at the start of supplying the molten thermoplastic resin between the molds. More preferably, it is not more than cm.
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 mold cavity surface, or using a radiation thermometer, etc. And a temperature gradient at the time of supplying the molten thermoplastic resin may be calculated.

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 is usually almost the same as the thickness of the molded body to be manufactured, but is smaller than the thickness of the molded body depending on the usage, 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 mold clamping speed when performing mold clamping is preferably 30 mm / sec or more.
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. The mold cavity surface in the vicinity of the merged portion of the molten thermoplastic resin is heated in advance by a heating coil, so that the cooling is delayed, and welds and uneven transfer can be made inconspicuous.

The speed at which the molten thermoplastic resin is supplied from the gate needs to be 800 cc / sec or more, and more preferably 1000 cc / sec or more. Conventionally, when only a part of the mold cavity surface is heated and molded, the temperature of the resin in contact with the heated part is higher than that of the other part, so it is considered that the part of the molded body was easily transferred. . By increasing the supply speed of the resin, the molten thermoplastic resin supplied between the molds can be filled between the mold cavities in a short time. Therefore, the entire surface of the mold cavity surface can be transferred before the temperature of the molten thermoplastic resin is lowered so much, and as a result, a thermoplastic resin molded body having no transfer unevenness and good appearance can be obtained.
In the case where molten thermoplastic resin is supplied from a plurality of gates, it is necessary to satisfy the above speed with respect to the total amount of molten thermoplastic resin supplied between the mold cavities at a certain point in time.

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 body, and the thermoplastic resin molded body having good appearance and no weld or transfer 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 can be used.
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, etc. of the target molded article, 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 pressed into the molten thermoplastic resin and supplied between the mold cavities.

  A skin material may be bonded and integrated on a part of the surface of the thermoplastic resin molded article obtained in the present invention. Examples of the skin material used in the present invention include woven fabrics and knitted fabrics such as moquettes and tricots, nonwoven fabrics such as needle punch carpets, metal foils, sheets and films of thermoplastic resins and thermoplastic elastomers, and the like. When the skin material is bonded and integrated to a part of the surface of the molded body, the skin material is previously placed at a predetermined position between the dies before heating the mold cavity surface, and the same as described above. What is necessary is just to shape | mold. However, if the skin material is bonded and integrated at a location corresponding to the heated portion of the mold cavity surface, the texture of the skin material may be impaired. For this reason, it is preferable not to heat the mold cavity surface corresponding to the site where the skin material is bonded and integrated.

Examples of the fibers constituting the nonwoven fabric include natural fibers such as cotton, wool, silk, and hemp, and synthetic fibers such as polyamide, polyester, and nylon. The nonwoven fabric may be composed of a single type of fiber or may be composed of two or more types of fibers. Moreover, you may be comprised with the mixture of a natural fiber and a synthetic fiber. Nonwoven fabrics are classified into needle punch, thermal bond, spunbond, meltblown, and spunlace types, and any nonwoven fabric produced by any method can be applied to the present invention.
Synthetic resin sheets and films include, for example, thermoplastic resins such as polypropylene and polyethylene, and polyolefin thermoplastic elastomer sheets and films. Good fusion with thermoplastic resins used as base resins. Are preferably used.

These skin materials may be multilayer skin materials having a foam layer or a backing layer.
Examples of the foam layer include polyolefin foams such as polypropylene and polyethylene, polyvinyl chloride foams, soft or semi-rigid polyurethane foams, and the like.
Moreover, as a backing layer, a nonwoven fabric, a synthetic resin sheet, a film, etc. are mentioned, for example.

  These multi-layer skin materials have good heat-fusibility with a thermoplastic resin from the viewpoint of adhesion to a base material portion made of a thermoplastic resin, or a molten thermoplastic resin is impregnated on the back surface of a skin material. Thus, those capable of bonding to the base resin are preferably used.

[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. Molding was performed using a die (two-point gate) shown in FIG. A range of 150 mm in width near the center of the female cavity (near the merged portion of the molten thermoplastic resin) was heated by a heating coil using a high-frequency induction heating device with a high-frequency oscillation frequency of 20 kHz and an output of 50 kW. The mold was closed to a predetermined cavity clearance, a molten thermoplastic resin was supplied into the mold cavity, and after cooling, the mold was opened to obtain a thermoplastic resin molded body. The obtained molded body had no weld or transfer unevenness and had a good appearance.
<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
<Molding conditions>
Resin temperature 230 ℃
Mold temperature 60 ℃
Mold cavity clearance 2.5mm when resin is supplied
Thermoplastic resin supply rate 1100cc / sec
Pressurized surface pressure 3MPa
Cooling time 30sec

[Comparative Example 1]
A thermoplastic resin molded article was molded in the same manner as in Example 1 except that the thermoplastic resin supply rate was 400 cc / sec. In the obtained molded product, no weld was found near the center, but transfer unevenness occurred.

An example of the thermoplastic resin molded body produced by the method of the present invention is shown in a plan view. An example of the thermoplastic resin molded body produced by the method of the present invention is shown in a plan view. An example of the thermoplastic resin molded body 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. A part of manufacturing process of this invention is shown with the schematic of the cross section of a metal mold | die. A part of manufacturing process of this invention is shown with the schematic of the cross section of a metal mold | die. A part of manufacturing process of this invention is shown with the schematic of the cross section of a metal mold | die. A part of manufacturing process of this invention is shown with the schematic of the cross section of a metal mold | die. A part of 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 (7)

A part of one or both mold cavities of a pair of male and female dies are heated in advance, and supply of the molten thermoplastic resin between the molds is started, and the molten thermoplastic resin is supplied. Or a method of manufacturing a thermoplastic resin molded body that is clamped after completion of supply and cooled and molded, wherein the molten thermoplastic resin is supplied at a rate of 800 cc / sec or more. A method for producing a plastic resin molding. 2. The method for producing a thermoplastic resin molded body according to claim 1, wherein a preheated portion of the mold cavity surface has an uneven shape, and the groove depth of the unevenness is 50 μm or more and 200 μm or less. A method for producing a thermoplastic resin molded article. The method for producing a thermoplastic resin molded article according to claim 1 or 2, wherein the means for heating the mold cavity surface is high-frequency induction heating. The portion of the mold cavity surface that is preheated includes a portion that is in contact with a joining portion of the molten thermoplastic resin when the molten thermoplastic resin is supplied between a pair of male and female molds. The manufacturing method of the thermoplastic resin molding in any one of 1-3. The method for producing a thermoplastic resin molded article according to claim 4, wherein the molten thermoplastic resin is supplied from a plurality of gates. The temperature of the highest temperature part of the mold cavity surface at the start of supplying the molten thermoplastic resin is equal to or higher than the deflection temperature under load of the thermoplastic resin. The manufacturing method of the thermoplastic resin molding of description. The largest temperature gradient among the temperature gradients of the heated portion and the non-heated portion of the mold cavity surface at the start of supply of the molten thermoplastic resin is 8 ° C / cm or less. A method for producing a thermoplastic resin molded article according to any one of the above.

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