JPH0452766B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a method for producing synthetic resin molded products with no weld lines by injection molding, and is suitable for use in covers, housings, nameplates, etc. of electronic and electrical equipment, home appliances, machines, etc. It is possible to provide high quality products without weld lines.

[Conventional technology and its problems]

The manufacturing method of synthetic resin molded products by injection molding has the advantages of high productivity, the ability to easily mold products with complex shapes, and the ability to obtain products with excellent appearance. It is used in a wide range of areas.

However, if there are holes in the desired synthetic resin molded product, if the wall thickness is significantly uneven, or if a mold with two or more gates is used, merging points of molten resin may occur. However, in practice, weld lines are undesirable because they cause a decrease in strength and commercial value.

Generally, the methods for eliminating weld lines are: (1) A method in which the resin in the weld area is released by installing a flow tab. (2) A method in which the molding temperature is set high and the resin is filled at high speed.

(3) Method of vacuuming the weld area.

There are methods such as, but methods (1) and (2) cannot completely eliminate weld lines, and method (3) is not commonly used because the mold production cost is high and additional equipment is required. Not the point.

[Means for solving problems]

The occurrence of weld lines in conventional normal molding is thought to be due to the fact that the injected molten resin flowing tip comes into direct contact with the mold, which causes confluence and bonding in a cooled state, resulting in incomplete welding. The present invention has been completed as a method to solve this problem.

That is, in the present invention, a thermoplastic plastic film or sheet that is welded to the resin used for injection molding is previously attached to the surface of the injection mold where the weld line occurs so as to cover the surface of the mold. This invention relates to a weld line elimination method characterized by injecting molten resin into a mold and welding the film or sheet with the injected resin to form an integrally molded product. The plastic film or sheet acts as a heat insulating layer, and the leading edge of the molten resin reaches the confluence point without being cooled and is completely integrated, eliminating weld lines.

The point at which a weld line occurs can be approximately predicted based on the gate position, opening position, wall thickness distribution, etc., and can be predicted with high accuracy using flow analysis.

In order to provide thermal insulation properties with a thermoplastic plastic film or sheet, a thickness of 100 μm or more is sufficient, and when such a thin film or sheet is attached, the flow resistance is reduced due to the reduced thickness of the area where the molten resin flows. The increase is almost negligible.

Therefore, there is no need to increase the overall thickness of the molded product in order to attach a film or sheet as a heat insulating layer, and there is no need to change the product design.

Additionally, thin thermoplastic films or sheets can be easily cut into shapes that fit into molds.
It also has excellent productivity because it can be punched out.

The method of the present invention is applicable to injection molding of all thermoplastic resins, such as polycarbonate, polyarylate, polysulfone, polystyrene, polymethyl methacrylate (PMMA), acrylonitrile-styrene copolymer (AS resin), and polycarbonate resin. - Transparent to opaque materials such as polybutylene terephthalate resin compositions, modified polyphenylene ether resins (modified PPE), rubber-modified vinyl aromatic compound copolymers (ABS, MBS, MAS, MMAS resins, etc.), acetyl cellulose, etc. Plastics are exemplified, and transparent plastics are particularly suitable for improving not only weld strength but also appearance quality.

Examples of the thermoplastic plastic used for the thermoplastic plastic film or sheet include those similar to the plastics used in the injection molding described above, and if the resins are of the same quality, they can be completely melted and integrated. Furthermore, even in the case of different materials, ABS can be used for polycarbonate films or sheets as long as they have good weldability to each other.
Furthermore, an adhesive layer to be welded to the molding material may be provided on the film or sheet in advance.

The thickness of the film or sheet is usually 100 to 1000 μm, especially 200 to 500 μm, and the opposite side to the welding side should have a hard coat or
Products can also be made functional by applying treatments such as antistatic coating, matte coating, and anti-glare treatments.

In addition, it is recommended that the melt viscosity of the plastic used for the film or sheet be higher than that of the thermoplastic plastic used for injection molding, that is, that it has a higher molecular weight. This is more preferable in terms of preventing deformation.

A thermoplastic plastic film or sheet is attached and fixed to the mold surface where a weld line occurs in an injection mold, usually the mold surface on the cavity side, so as to cover the mold surface.

The plastic film or sheet can be easily fixed to the mold cavity by electrostatic or vacuum suction, pinning, or other conventionally known methods.

Next, in order to facilitate understanding of the present invention, the present invention will be explained using drawings.

Fig. 1 is a perspective view of a perforated disc-shaped model molded product for explaining the method of the present invention, and Fig. 2 is a weld portion (film attached to the mold surface) in cross section A-A' in Fig. 1. FIG. 3 is a partial sectional view illustrating the case of normal molding (A--A in FIG. 1).
FIG. 3 is a partial cross-sectional view illustrating a weld portion in cross section A'. In FIG. 2, resin layers 7 and 7' formed by injection molding of molten resin flowing through a sprue 4, a runner 5, and a gate 6 are welded together at a weld line generation area 2, and are attached to a mold in advance. The thermoplastic film or sheets 8, 8' are laminated together, and since the films or sheets 8, 8' are attached, the weld line is almost impossible to visually confirm. .

On the other hand, in the case of FIG. 3, the molten resin in the weld line generation area 2 where the molten resin layers 7 and 7' join comes into contact with the molds 9 and 9' and is cooled, resulting in no welding. The product becomes complete and has weld lines.

Although the above description has been made with reference to the drawings, the shape of the synthetic resin molded product of the present invention, the usage form of the film or sheet, etc. are not limited to those shown in the drawings, and various forms can be taken.
For example, it is one of the preferred embodiments of the present invention to attach the film or sheet on one side, partially attach it, use a combination of different types, or integrally mold the frame, the attachment part, the attachment tool, etc. depending on the shape or design of the molded product.

〔Example〕

Examples will be explained below.

Example 1 The nameplate of a touch channel for a color television has many holes in the molded product, and when molded with a side gate, weld lines occur around the holes.

The molding material used is flame-retardant grade polycarbonate.

A polycarbonate film with a thickness of 200 μm is punched out using a Thomson blade in the shape of the molded product of this nameplate, and this film is attached to both sides of the mold cavity.
A molded product was obtained by injection molding using Iupilon N-3).

In this molded product, the polycarbonate film and the injection resin were completely integrated, and no weld lines were observed at all. Additionally, the flow mark at the gate had also disappeared.

〔Effect of the invention〕

As described above, the present invention can easily eliminate weld lines in injection molding by preventing cooling and solidification of molten resin due to contact with molds, and can be used for covers, housings, etc. of electronic and electrical equipment, home appliances, machines, etc. It is possible to provide high quality products with no weld lines, such as nameplates.

Furthermore, the method of the present invention (1) eliminates weld lines and improves commercial value.

(2) There is virtually no decrease in the strength of the weld part.

(3) By attaching a film or sheet,
Furthermore, the occurrence of flow marks at the gate portion is eliminated, and the fluidity of the molten resin within the mold is also improved.

It shows the characteristics such as.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a model molded product for explaining the method of the present invention, FIG. 2 is a partial sectional view for explaining the weld part in the A-A' section of FIG. 1, and FIG. A- in Figure 1 for molding
FIG. 3 is a partial cross-sectional view illustrating a weld portion in cross section A'. The numbers in the figure are respectively: 1... Molded product, 2... Weld part, 3... Hole part, 4...
Sprue, 5...runner, 6...gate, 7,7'
...resin layer, 8,8'...film or sheet,
9, 9′...indicates a mold.

Claims (1)

[Claims] 1. A thermoplastic plastic film or sheet that is welded to the resin used for injection molding is attached to the surface of the injection mold where the weld line occurs so as to cover the surface of the mold, and then the inside of the mold is A method for eliminating weld lines, which comprises injecting a molten resin into the film or sheet and welding the film or sheet with the injected resin to form an integrally molded product.