JP2785385B2 - Method for manufacturing resin molded product without silver streak - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a resin molded product free from silver streaks (silver streaks) when a resin molded product is produced by injection molding of a synthetic resin. .

[Prior art] When injection molding of synthetic resin is performed, along the direction of flow of the resin on the surface of the molded product, a white silver streak pattern called silver streak is generated, which may reduce the commercial value. is there. This silver streak is formed by linear fine grooves, and gas contained in the injected resin or gas instantaneously generated between the resin and the mold surface is applied to the mold surface together with the flow of the resin. When moving along, it is said that the resin is generated by the heat taken by the mold surface and solidifying. It is presumed that such gas is generated due to moisture contained in the resin, moisture attached or generated on the mold surface, volatile components in the resin, and the like.

Conventional methods for preventing the generation of silver streaks include raising the temperature of the mold surface, cleaning the mold surface, etc., but despite the difficulty in operation and control, complete It was not a preventive measure.

On the other hand, as a method to prevent the occurrence of weld lines,
A method has been proposed in which a sheet or film of a thermoplastic resin is mounted in advance at a location where a weld line of an injection mold occurs, and the resin is injected to integrally mold the resin (for example, JP-A-60-260313). It does not help prevent streaks. In addition, as a method of manufacturing a resin molded product with excellent weather resistance, a resin-like sheet made of a thermoplastic resin having a coating or a process with excellent weather resistance is attached to a mold surface of an injection molding die to inject the resin. In addition, there has been proposed a method of integrally molding (for example, JP-A-60-250925-6 and JP-A-60-2535).
Nos. 18 to 9), none of them suggest silver streaks.

[Problems to be solved by the invention]

An object of the present invention is to provide a method for manufacturing a resin molded product free of silver streaks by completely preventing silver streaks by a simple operation using a conventional injection mold.

[Means for solving the problem]

In the present invention, after placing a gas-permeable sheet material having a higher heat insulating property than the hard material on the mold surface of an injection mold made of a rigid material having rigidity, a liquid resin is injected into the cavity. The resin is filled so that the resin comes into contact with the sheet material and does not come into direct contact with the mold surface, and is pressurized while the resin is in a flowable state. This is a method for producing a resin molded product free of silver streaks, which is characterized by being adhered to a material.

The sheet-shaped material used in the present invention has a higher heat insulating property than the material of the injection molding die, and is made of a material having high gas permeability at the time of pressurization, and generally has a melting point higher than the melting point of the injection resin. Sheets, films, and other sheet-like materials made of synthetic resin can be used. The thickness of the sheet material is not particularly limited, but is preferably about 0.1 to 1 mm from the viewpoint of workability and handleability, and particularly preferably from 0.2 to 0.7 mm from the viewpoint of gas permeability and heat insulation. Polycarbonate resin, ABS resin, PPO
Resin, polyamide resin, polypropylene resin and the like can be used.

(Operation)

In the method for producing a resin molded product free of silver streaks of the present invention, a gas-permeable sheet material is placed on the mold surface of an injection mold, and then a liquid resin is injected into a cavity, and the resin is formed into a sheet. Filled so as to be in contact with the material and not directly on the mold surface, pressurize while the resin is in a flowable state, allow the gas on the resin side to pass through and discharge the resin through the sheet-like material, and put the resin into the sheet-like material. A resin molded product free of silver streaks is manufactured by being in close contact with each other.

At this time, the heated and melted high-temperature resin is injected into the cavity through the gate, but since the injected resin does not come into direct contact with the mold surface of the molding die, there is no sharp drop in temperature, and the molded product Since the resin forming the surface of the substrate is in close contact with the mold surface via a highly heat-insulating sheet-like material, the temperature drop is gradual.

Therefore, even if moisture adheres to the mold surface, the moisture is interposed between the sheet-like material and the mold surface and does not come into direct contact with the molten resin. In addition, even if it is gently heated and becomes steam, it is discharged from the suction path or the mating surface of the mold, or even if a part remains between the sheet-like material and the mold surface, it affects the surface of the molded product. Never.

Most of the gas (including water vapor) generated from the resin is discharged from the mating surface of the mold due to the flow of the resin. And even if gas remains between the sheet-like material and the molten resin, the cavity is filled with the resin, and when in a pressure-holding state where it can flow, a pressure equivalent to several tens to several hundreds of kg per 1 cm ² is applied. Therefore, the gas permeates through the sheet material to both sides of the mold and is discharged. Along with this, the dent of the part where the gas was present, the resin flows so as to fill that part with the gas discharge,
Adheres closely to the sheet material surface.

Generally, the higher the temperature and the pressure of the sheet material, the higher the gas permeability, so that the gas is almost completely permeated and discharged when the pressure is maintained, and does not remain between the sheet material and the resin. During this time, the mold surface side of the sheet-shaped material contacts the mold surface and loses heat, so that the sheet material is kept in a solid state without melting.

Therefore, silver streaks do not occur on the inner and outer surfaces of the sheet material, and a molded product having a uniform surface can be obtained. In addition, since the sheet-shaped material has heat insulating properties, a molded article having no resin solidified locally in the portion close to the mold surface, the resin flowing over the entire cavity, and a defect in the surface and the like can be obtained. Since the entire sheet-like material can be formed to be thinner than a resin mold, the molded product can be easily cooled.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of an injection mold in an embodiment, FIGS. 2 and 3 are partially enlarged views of FIG. 1 showing a state during injection molding, and FIG. 4 is a sectional view of a resin molded product.

In FIG. 1, reference numeral 1 denotes an injection mold, in which liquid resin is injected from a runner 5 through a gate 6 into a cavity 4 formed between a metal cavity mold 2 and a core mold 3. Suction paths 9 and 10 are opened in the mold surfaces 7 and 8 facing the cavity 4 of the cavity mold 2 and the core mold 3 through fine holes 9a and 10a, and a gas-permeable sheet material is formed in the mold surfaces 7 and 8. 11 and 12 can be installed.

The sheet-like materials 11 and 12 are made of a gas-permeable thermoplastic resin sheet having a higher heat insulating property than the material of the molding die 1 and having the same or a higher melting point as the resin to be injected. A resin having no compatibility is used. It is preferable to use the sheet-like materials 11 and 12 which are formed by bending into shapes corresponding to the mold surfaces 7 and 8. However, when the plastic materials can be deformed along the mold surfaces, or when the mold surfaces 7 and 8 are deformed. In the case of a flat surface, it is not necessary to bend in advance.

The method of manufacturing resin molded products without silver streaks
First, as shown in FIG.
Then, gas-permeable sheet materials 11 and 12 are placed on the mold surfaces 7 and 10 and attached to the mold surfaces 7 and 8 by suction from the suction passages 9 and 10 and the pores 9a and 10a connected thereto. After the mold is closed, a liquid resin 13 is injected from the runner 5 through the gate 6 into the cavity 4 as shown in FIG.
The cavity 4 is filled so as to contact the molds 11 and 12 and not directly to the mold surfaces 7 and 8. And as shown in FIG.
Pressure is applied while the resin 13 is in a flowable state, and gas 14 on the resin 13 side is transmitted through the sheet materials 11 and 12 to the mold surfaces 7 and 8, and the suction passage 9 is formed through the fine holes 9 a and 10 a. The resin 13 is discharged from 10 and the resin 13 is brought into close contact with the sheet materials 11 and 12 to produce a resin molded part 15 having no silver streaks.

At this time, the heated and melted high-temperature resin 13 is injected into the cavity 4 through the gate 6.
Since there is no direct contact with the mold surfaces 7 and 8 of the mold 1, there is no sharp drop in temperature, and the resin 13 forming the surface of the molded article 15 passes through the highly heat-insulating sheet-like materials 11 and 12. The temperature drop is gradual because it is in close contact with the mold surfaces 7 and 8. Therefore, even if moisture adheres to the mold surface, the moisture intervenes between the sheet-like materials 11 and 12 and the mold surfaces 7 and 8 and does not come into direct contact with the molten resin 13, so that the water vapor rapidly Will not be. Also, even if it is gently heated and becomes steam, it is discharged from the suction passages 9 and 10 through the pores 9a and 10a or from the mating surface 16 of the mold, or a part thereof is formed into the sheet-like materials 11 and 12 and the mold surface. Molded product even if it remains between 7 and 8
Does not affect 15 surfaces.

Most of the gas generated from the resin 13 is discharged from the mating surface 16 of the mold due to the flow of the resin 13. And even if the gas 14 remains between the sheet-like materials 11, 12 and the resin 13,
When the cavity 13 is filled with the resin 13 and a pressure is maintained in a flowable holding pressure state, a pressure corresponding to several tens to several hundreds kg per 1 cm ² is applied. 8
From the suction passages 9 and 10 through the pores 9a and 10a.
Or it is discharged from the mating surface 16 of the mold. With this, gas
The resin 13 flows so as to fill the dents in the portion where the 14 was present as the gas is discharged, and adheres to the surfaces of the sheet materials 11 and 12.

Generally, the higher the temperature and pressure of the sheet-like materials 11, 12, the higher the gas permeability, so that the gas 14 is almost completely permeated and discharged at the time of pressure-holding, and between the sheet-like materials 11, 12 and the resin 13. Will not remain. During this time sheet-like material 1
Since the mold surfaces 7 and 8 of 1 and 12 come into contact with the mold surfaces 7 and 8 to remove heat, they maintain a solid state without melting.

Therefore, silver streaks do not occur on the inner and outer surfaces of the sheet-like materials 11 and 12, and a molded product 15 having a uniform surface can be obtained. Also, sheet materials 11, 12
Has heat insulating properties, so that the resin 13 near the mold surfaces 7 and 8
Is not solidified locally, and the entire cavity 4 is made of resin.
Thus, a molded product 15 having no defect on the surface or the like can be obtained. Since the sheet-like materials 11 and 12 can be formed to be entirely thinner than the resin mold 1, the molded product 15 can be easily cooled.

As shown in FIG. 4, the resin molded product 15 thus obtained is taken out of the molding die 1, the sheet materials 11 and 12 are peeled off, and the gate 17 is cut in the X direction to obtain a product. In this case, the sheet-like material 1
A release material such as mineral oil can be applied to the surfaces of 1 and 12.

Since the surface of the molded article 15 is influenced only by the inner surfaces of the sheet-like materials 11 and 12, even if mirror-like smoothness is required, the sheet-like materials 11 and 12 having smooth surfaces may be used. It is not necessary to mirror-finish the mold surfaces 7 and 8 of the mold 1. Conversely, it is preferable to have a small gas-passing gap between the sheet materials 11 and 12 and the mold surfaces 7 and 8 from the viewpoint of easily discharging the gas. For this reason, as shown in FIGS. 2 and 3, the mold surfaces 7 and 8 can be rough or semi-finished rough surfaces.

In the above embodiment, the sheet-like materials 11 and 12 are made of a resin having no compatibility with the resin 13 because the sheet-like materials 11 and 12 are peeled off from the molded product 15. However, a material made of a resin having compatibility with the resin 13 is used. And may be integrally formed with the resin 13. In this case, an adhesive may be interposed between the two.

Further, in the above embodiment, the sheet materials 11 and 12 are mounted on both sides of the cavity 4, but may be mounted only on the outer surface of the molded product 15. If the molded article 15 is transparent, it is preferable to mount it on both sides.

Further, in the above-described embodiment, an example is shown in which the resin 13 that has been heated and melted is injected, but reaction injection molding (RIM) using a reactive resin as the resin 13 may be used.

〔The invention's effect〕

As described above, according to the present invention, on the mold surface of the injection mold,
After placing a highly heat-insulating gas-permeable sheet material,
Injecting and filling the cavity with liquid resin, pressurizing while the resin is in a flowable state, discharging gas on the resin side through the sheet material, and bringing the resin into close contact with the sheet material, Using a conventional injection mold, it is possible to completely prevent the generation of silver streaks by a simple operation and to manufacture a resin molded product free of silver streaks.

[Brief description of the drawings]

FIG. 1 is a sectional view of an injection mold in an embodiment, FIGS. 2 and 3 are partially enlarged views of FIG. 1 showing a state during injection molding, and FIG. 4 is a sectional view of a resin molded product. In the drawings, the same reference numerals denote the same or corresponding parts, 1 denotes an injection mold, 4 denotes a cavity, 7, 8 denotes a mold surface, 9 and 10 denote suction paths, 9a and 10a denote pores, and 11 and 12 denote sheets. Shaped material, 13 is a resin, 14 is a gas, and 15 is a resin molded product.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B29C 45/00-45/84 B29C 33/00-33/76

Claims (1)

(57) [Claims] 1. A gas-permeable sheet material having higher heat insulation than the hard material is placed on a mold surface of an injection mold made of a hard material having rigidity, and then a liquid resin is injected into the cavity. The resin is filled so that the resin contacts the sheet material and does not directly contact the mold surface, pressurizes while the resin is in a flowable state, discharges gas on the resin side through the sheet material, and discharges the resin into the sheet. A method for producing a resin molded article free of silver streaks, wherein the resin molded article is brought into close contact with a sheet-like material.