JP2002086503A - Method for molding plastic molded product, and molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of efficiently obtaining an injection- molded product having high quality appearance, and the injection-molded product. SOLUTION: In a method for injection-molding a thermoplastic resin using a mold having a gate with the maximum diameter of 0.1-3 mm, the temperature of a mold, at a time when the thermoplastic resin is injected in the mold in a molten state, is set so as to become higher than the load deformation temperature of the injected thermoplastic resin by 0-100 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently obtaining a thermoplastic resin injection molded article having a high quality appearance which can be used without painting, and a molded article obtained by the method.

[0002]

2. Description of the Related Art In injection molding of a thermoplastic resin composition,
By using a mold having a pinpoint gate, gate cutting can be performed automatically, so that steps during molding can be reduced and automation can be performed. It is also known that the use of a pinpoint gate is advantageous for molding large molded products and thin molded products because a large number of gates can be easily provided. In addition, the tunnel gate has advantages that a large number of gates can be easily provided, gate cutting can be automatically performed, and that no trace of the gate remains on the decorative surface.

However, when a mold having a pinpoint gate or a tunnel gate is used, a problem arises in that appearance defects called gate marks appear on the surface of a molded product. The gate mark refers to uneven gloss in which the gloss of the surface of the molded article near the gate is sometimes lower and sometimes higher than the gloss of other parts. In general, gate marks are often generated on the back surface of the gate near the gate when the gate diameter is reduced. When a gate mark is generated, the appearance of the molded product is impaired, and a high-quality appearance cannot be obtained, which makes it difficult to use it without painting. Therefore, when a mold having a pinpoint gate or a tunnel gate is used, it is difficult to obtain a molded product having a high-quality appearance that can be used without painting.

When a molten thermoplastic resin is injected into a mold, the mold is injected under a condition set so that the temperature of the mold is 0 to 100 degrees higher than the load deformation temperature of the injected thermoplastic resin. An injection molding method of a thermoplastic resin to be molded is already disclosed in Japanese Patent Application Laid-Open No. H10-100216, which eliminates appearance defects such as weld lines and jetting, and appearance defects caused by inorganic fillers.

[0005]

SUMMARY OF THE INVENTION The present invention eliminates the occurrence of gate marks due to the use of a mold having a gate with a small gate diameter, such as a pinpoint gate or a tunnel gate, and provides injection molding having a high quality appearance. It is an object to provide a method for efficiently obtaining a product. Another object of the present invention is to provide a molded article having an excellent appearance that does not require secondary processing such as painting, plating, and sanding.

[0006]

SUMMARY OF THE INVENTION The present inventor has found that even when a mold having a pinpoint gate or a tunnel gate is used, when the molten thermoplastic resin is injected into the mold,
The temperature of the mold is injection-molded under conditions set to be 0 to 100 degrees higher than the load deformation temperature of the thermoplastic resin to be injected, whereby the occurrence of gate marks is solved,
The present inventors have found that an injection-molded article having a high-quality appearance can be efficiently obtained, and have reached the present invention.

That is, the present invention relates to a method for injection-molding a thermoplastic resin using a mold having a gate having a maximum diameter of 0.1 mm to 3 mm, wherein the thermoplastic resin is melted and injected into the mold. Wherein the temperature of the mold is set to be 0 to 100 degrees higher than the load deformation temperature of the thermoplastic resin to be injected.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The maximum diameter of a gate used in the present invention is 0.1 mm to 3 mm, preferably 0.2 mm to 2.5 mm, and more preferably 0.3 mm to 2 mm. If the gate diameter is larger than 3 mm, a large gate mark remains undesirably even when the method of the present invention is used. If the maximum diameter of the gate is smaller than 0.1 mm, the flow resistance at the gate becomes too large, which causes appearance defects such as silver streaks. Also, since a sufficient flow length cannot be obtained, a large-sized molded product cannot be formed, which is not preferable. The shape of the gate is not particularly limited and may be a circle, an ellipse, a polygon, or the like, but a circular shape is preferred. The number and position of the gates are not particularly limited, and are determined by the size and shape of the molded product, the fluidity of the resin used, and the like.

[0009] Representative examples of the above gates are a pinpoint gate and a tunnel gate. The pinpoint gate is a gate used in a three-plate mold, and means a gate that can be automatically cut by opening the mold. The tunnel gate means a gate at a position where the gate position enters the fixed mold side or the movable mold side from the parting line. A tunnel gate is usually used for the purpose of providing a gate on a surface opposite to a decorative surface.

The gate mark in the present invention means gloss unevenness generated on the surface of a molded article near the gate as described above. When a gate mark is generated, the appearance of the molded product is impaired, and a high-quality appearance cannot be obtained, which makes it difficult to use it without painting.

According to the present invention, when the molten thermoplastic resin is injected into the mold, the temperature of the mold is 0 to 100 ° C. higher than the load deformation temperature of the thermoplastic resin to be injected, preferably 20 ° C.
It needs to be set to be 80 ° higher, more preferably 20-70 ° higher. By setting the mold temperature higher than the load deformation temperature when injecting the molten resin, the molten resin can be filled in a sufficiently molten state without being rapidly cooled. By filling in the molten state in this way, the problem due to the small gate diameter,
For example, a molded product without a gate mark can be obtained.

Here, the load deformation temperature refers to a method based on ASTM D648 (test piece size: 127 mm × 12.7 mm × 6.4 mm, 18.6 k
g load). Usually, the load deformation temperature is used as an index indicating the heat resistance of the resin.

The method for setting the mold temperature to be higher than the load deformation temperature of the thermoplastic resin to be injected by 0 to 100 degrees is not particularly limited, but the method disclosed in JP-A-10-100216 is used. can do. In the mold temperature control system, for example, it is possible to set the mold temperature so as to be higher than the load deformation temperature of the thermoplastic resin by 0 to 100 ° C. by using hot water, heating oil or an electric heater alone or in combination. it can. More preferably, the mold temperature control system further includes a mechanism for cooling the mold such as cold water or cooling oil. When the temperature rises, cool water and cooling oil are stopped and hot water, heating oil or electric heater is used alone or in combination.When the temperature falls, hot water, heating oil or electric heater is turned off and cold water and cooling oil are used in the same mold It is most preferable to use a temperature control pipe or a separate mold temperature control pipe (see FIG. 1).

In the present invention, the mold temperature set to be 0 to 100 degrees higher than the load deformation temperature of the thermoplastic resin is:
It is held for at least a part of the period from the start to the end of the injection, and after the holding period, during the cooling, the mold temperature is 10 to 100 degrees lower than the load deformation temperature of the thermoplastic resin, preferably 20
It is further preferred that the temperature be controlled so as to be lower by 70 ° C, more preferably 30 ° C to 60 ° C. This is because the molding time can be shortened.

At this time, the molding cycle can be shortened as the temperature of the hot water or the heating oil used for raising the temperature is higher, the temperature of the cold water or the cooling oil used for lowering the temperature is lower, and the flow rate is larger. Become. As for the electric heater, the higher the power density, the better.

The greater the number of mold temperature control pipes provided within a range where there is no problem in mold strength, the higher the efficiency and the shorter the molding cycle.

The thermoplastic resin used in the present invention is not particularly limited. Examples of thermoplastic resins include polyphenylene ether resins, polystyrene resins, ABS resins, polyamide resins, polycarbonate resins, polyester resins, acrylic resins, polyetherimide resins, polyphenylene sulfide resins, and blends thereof. And a resin containing a substance as a main component.

The molded article molded by the above molding method is
Since there is no gate mark on the surface of the molded product and it has a good appearance, it can be used as it is without secondary processing such as painting.

Such molded articles include automobile parts such as wheel covers, headlamp lenses, headlamp reflectors, extension reflectors, door mirror housings, fenders, bumpers, pillar covers, roof rails, assist grips, door handles, finishers, tail lamps, Tailgate, door rail cover, center console, instrument panel,
Meter hoods, speaker grills, engine covers, fuel tank lids, and other home appliances such as televisions, video or audio equipment housings, mobile phones, cameras, VTR cameras and game consoles, washing machines, refrigerators, dishwashers and dryers Used for exterior parts and decorative parts of machines, fans, microwave ovens, dryers, vacuum cleaners, etc., and OA equipment such as printers, monitors, PCs, notebook PCs, copiers, faxes, keyboards, etc. Can be

Hereinafter, the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing a schematic configuration of a mold temperature control system suitable for implementing the present invention.

In this mold temperature control system, a hot water temperature controller 1 and a cooling water chiller 2 are provided and connected to a switching unit 3 respectively. The switching control unit 3 has an outlet 5 for supplying cold water and hot water to the mold 4 and a return port 6 for recovery. To achieve the desired mold temperature,
Control of inflow and outflow of hot water and cold water can be performed using the switching valves V _IN and V _R in the apparatus.

FIG. 2 is a sectional view of a mold. This mold is a three-plate mold having five pinpoint gates with a diameter of 1.5 mm, and a cavity is provided on the mating surface of the mold 7 and the mold 8.
The molded product 10 is formed by filling the resin in the cavity 10 and solidifying the resin. The molten resin flows from sprue 11 through runner 13 to pinpoint gate 12
To fill the cavity 7. The diameter of the gate 12 is 1.5 mm. The molded product molded by this mold is
It has a box shape with a bottom of 270mm x 200mm and side height of 8mm. The thickness is 1.5 mm.

[0023]

[Example] A method in accordance with ASTM D648 for the load deformation temperature of product name Cycoloy MC5400 (alloy material of polycarbonate resin and ABS resin, manufactured by GE Plastics Co., Ltd.)
(Test piece dimensions: 127 mm x 12.7 mm x 6.4 mm, 18.6 kg load).

Example 1 Using an apparatus having a mold temperature control system shown in FIG. 1 and a resin temperature 2 using a mold shown in FIG. 2 using Cycoloy MC5400 as a material.
Injection molding was performed at 50 ° C. The mold temperature at the time of injection was set to 110 ° C., and immediately after the injection, the mold temperature was cooled to 70 ° C. The cooling time was 20 seconds.

Comparative Example 1 Molding was performed under the same conditions as in Example 1 except that the mold temperature was kept constant at 70 ° C., and a comparison was made.

Digital variable-angle gloss meter (Suga Test Machine Co., Ltd.)
And a measurement angle of 60 °), and the difference in gloss between the gate portion and the portion other than the gate portion in the molded products of Examples and Comparative Examples was measured. Also, visually check the presence or absence of the gate mark,
The results are shown in Table 1.

[0027]

[Table 1] Example Comparative example Gloss difference Δ 0.2 Δ 2.2 Gate mark Not confirmed Clearly confirmed

Regarding the gate mark, the molded product of the comparative example has a gloss difference of Δ2.2 between the general portion and the gate portion, and the gate mark can be clearly and visually confirmed, whereas the molded product of the example has a gloss difference of Δ0.2. There was a level where the gate mark could not be confirmed visually.

[0029]

According to the method of the present invention, in injection molding of a thermoplastic resin, a product having excellent appearance quality can be automatically and stably molded. The molded article molded by the method of the present invention can omit secondary processing such as painting. Therefore, the present invention makes it possible to greatly simplify the steps.

[0030]

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration example of a mold temperature control system suitable for carrying out a molding method of the present invention.

FIG. 2 is a cross-sectional view of a mold used in an example.

[Explanation of symbols]

 1 Hot water temperature controller 2 Cold water chiller 3 Switching unit 4 Mold 5 Hot / cold water supply port to mold 6 Hot / cold water return port from mold 7 Fixed mold 8 Runner plate 9 Moving mold 10 Cavity 11 Sprue 12 Gate 12 Gate 12 Gate 13 Runner

Claims (4)

[Claims] 1. A method for injection molding a thermoplastic resin using a mold having a gate having a maximum diameter of 0.1 mm to 3 mm, wherein the thermoplastic resin is melted and injected into the mold. Wherein the temperature is set to be 0 to 100 degrees higher than the load deformation temperature of the thermoplastic resin to be injected. 2. The mold temperature is maintained for at least a part of a period from the start to the end of the injection, and after the holding period, during the cooling, the mold temperature is lower than the load deformation temperature of the thermoplastic resin by 10%.
2. The molding method according to claim 1, wherein the temperature is controlled so as to be lower by 100 degrees. 3. A molded product having no gate mark on the surface of the molded product, the molded product being molded according to the method of claim 1. 4. The molded article according to claim 3, wherein the molded article is used without painting.