JPH0832423B2 - Method for producing resin molded product having mixed color pattern - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a resin molded product and a resin molded product molded by the method, more specifically, a clear mixed pattern on the surface. And a bolt cap molded by the method.

(Prior Art) It is widely practiced to form various patterns full of color sense on a synthetic resin molded product to enhance added value as a product.

However, for example, a mixed color pattern such as a marble pattern or a marble pattern that makes the boundary part have an unclear depth is difficult to form at the same time as the molding of the synthetic resin, which is a technical problem.

In addition, a colorant is mixed into a synthetic resin as a masterbatch, the melting point and fluidity are changed with respect to the main resin, and a pattern is obtained by injection molding using a normal injection molding machine in a state of poor dispersion. A forming method is known, and this method has an advantage that it is simple, and is used as a pattern forming means in a large-sized molded product.

In addition, as a method for obtaining a resin molded product having a mixed color pattern, there is a method of performing injection molding using a plunger type injection molding machine, but this method has a problem that the molding time is long and the equipment is expensive. There is.

(Problems to be Solved by the Invention) However, when a molded product having a mixed color pattern is obtained by the masterbatch method, the uniformity of the mixed color pattern becomes a problem.

That is, in order to develop a mixed color pattern on the surface of a molded product, usually, the main material is of a similar color and the main material is light, and the flow pattern of a dark color of the masterbatch is developed therein. Uniformity of the color mixture here means that the proportion of the exposed masterbatch flow pattern of the molded product is virtually constant for each individual product. In general, various bath products,
In a large-sized molded article such as a beauty tool and a furniture part, since a wide surface is visually recognized, this uniformity does not cause a problem. However, with small molded products such as bolt caps, there are many patterns that should be exposed on the limited surface, and there are few patterns that are buried and buried in the main material, and individual patterns may appear. There is a problem that it is difficult to obtain a product having a visually uniform and clear color mixture pattern for each molded product.

Therefore, the present invention provides a molding method capable of expressing a uniform color-mixed pattern for each product by a masterbatch method even for small products, and a bottle cap as a resin molded product molded by the method. With the goal.

(Means for Solving the Problems) That is, according to the present invention, in a method for producing a resin molded article having a uniform color mixture pattern on a surface by injection molding a mixture of a resin and a masterbatch, a core and an injection mold are used. An injection gate is provided on the core using a cavity, and the mixture is injected through the gate while the temperature of the core is higher than the temperature of the cavity by 15 ° C. or more. A method of manufacturing is provided.

That is, the present invention succeeds in achieving the above-mentioned problems by performing injection molding using a so-called inside pin gate type mold.

(Explanation of Preferred Embodiment) Hereinafter, the present invention will be described in detail based on specific examples shown in the accompanying drawings.

In FIG. 1 showing an injection mold for suitably carrying out the manufacturing method of the present invention, this mold is composed of a cavity 1 and a core 2, and a resin is injected into a clearance 3 between them. A molded product having a desired shape can be obtained. The cavity 1 is provided with a cooling water flow path 4 on its outer surface, and the core 2 is provided with a heating and cooling water flow path 5 on its outer surface so that cooling and heating of these can be appropriately performed. Has become.

In the method of the present invention, the core 2 is provided with the pin gate 6 and the resin flow path 7, and the clearance 3 is provided from the nozzle 8 of the injection machine through the pin gate 6 and the resin flow path 7.
It is an important feature to inject the mixture of the main material and the masterbatch therein. According to the present invention, by adopting such a means, it is possible to form a clear color mixture pattern having excellent uniformity and a uniform color mixture on the surface of the molded product without variations among the molded products. This point will be described in comparison with a case where injection molding is performed using a so-called outside gate type mold.

FIG. 2 is a view showing the above-mentioned outside gate type mold, which is substantially the same as the mold shown in FIG. 1 except that the pin gate 10 and the resin flow channel 11 are formed in the cavity 1. Is the same as When a blend of the main resin and the masterbatch is injected using this mold, the masterbatch concentrates on the core 2 side, and many patterns appear on the inner surface side of the molded product. When viewed from the outside (that is, the appearance of the molded product), the pattern is unclear and the decorativeness is poor, and there are many variations among the molded products. By increasing the amount of the masterbatch used, the amount of the pattern on the surface of the molded product is increased to some extent. However, the unclearness is unavoidable and the pattern of each molded product varies widely. This is because the fluid main material resin flows quickly through the central portion of the clearance 3, but the masterbatch with poor fluidity is pressed toward the core 2 by the ejection force, and along the core 2 due to the flowing force of the main material. It is considered that as a result, many patterns appear on the inner surface side of the molded product, and variations in the pattern among the molded products also increase.

According to the present invention, however, as a result of the pin gate 6 and the resin flow path 7 being provided in the core 2, many masterbatches are gathered on the side of the cavity 1 and therefore many sharp patterns are formed on the outer surface side of the molded product. It is considered that an extremely clear mixed color pattern is uniformly formed without variations among molded products.

In the present invention, the temperature of the core 2 is 15 ° C. or higher than that of the cavity 1 during injection molding, preferably
The core 2 is heated so that the temperature becomes higher by 30 to 50 ° C. By performing such heating, the flow of the main material resin on the core 2 side is promoted, more master batches gather on the cavity 1 side, and a clear mixed color pattern is formed. In this case, if the heating of the core 2 is excessively performed beyond the above range, the cooling time will be extended and the molding cycle will be shortened.

In the present invention, as the main material resin and the masterbatch, those used for forming a mixed color pattern by the conventional masterbatch method can be used as they are. For example, as the main resin, any resin can be used as long as injection molding is possible,
Generally, olefin resins such as low-, medium-, high-density polyethylene, polypropylene, and ethylene-propylene copolymers, thermoplastic polyesters such as polyethylene terephthalate, poly (meth) acrylic acid, poly (meth) acrylate, etc. Acrylic resins and ethylene vinyl alcohol copolymer resins are preferably used.

As the masterbatch, a resin having a poor mixing and dispersibility with the above-mentioned main resin is generally used. For example, as the main resin, the melt flow rate (MFR, ASTM D 1236) is 15g
When a thermoplastic resin of / 10 min or more is used, it is preferable to use a thermoplastic resin having an MFR of 0.5 g / 10 min or less as a masterbatch. Further, the main resin and the masterbatch are generally 60:40 to 99: 1 by weight, particularly 90:10.
Or used at a ratio of 98: 2.

A colorant is blended with at least one of the main material resin and the masterbatch according to the target mixed color pattern.

(Example) Hereinafter, the present invention will be described in the following examples.

Reference example MFR15g / 10min polypropylene (containing 0.02% of yellow colorant) is used as the main resin, and it is used as a masterbatch.
MFR 0.5g / 10min polypropylene (containing 30% white colorant) was used.

A blend obtained by mixing the above main resin and the masterbatch in a weight ratio of 98: 2 was injection-molded by using an inside pin gate type mold shown in FIG. 1 to obtain 40 × 20 mm, height 27 m.
An oval shaped cap of m was obtained.

For comparison, injection molding was performed using the outside pin gate type mold shown in Fig. 2, and the diameter was 20 mm and the height was 30 mm.
I got a round cap.

The uniformity and appearance of the patterns of the obtained caps are as shown in Table 1.

The uniformity was evaluated by visually deciding 30 caps obtained by consecutive shots and by the number of caps that looked the same.

○… 28 or more △… 20 or more to 27 × × less than 20 Example MFR12g / 10min polypropylene (containing 0.05% white colorant) was used as the main resin, and it was used as a masterbatch.
MFR 0.5g / 10min polypropylene (containing 25% of pink colorant) was used.

A blend of the above-mentioned main material resin and masterbatch mixed in a weight ratio of 97: 3 was used to maintain the cavity at 10 ° C. using the in-sand pin gate type mold shown in FIG.
The core was heated with hot water and the core temperature was changed variously, and injection molding was performed to obtain a round cap with a diameter of 30 mm and a height of 30 mm.

Table 2 shows the relationship between core temperature, pattern uniformity, and molding cycle.

(Effects of the Invention) According to the present invention, a molding method and a molded product capable of uniformly forming a clear color mixture pattern on the surface of a small molded product such as a bottle cap without variation among the molded products. Will be provided.

[Brief description of drawings]

FIG. 1 is a view showing a mold preferably used in the method of the present invention, and FIG. 2 is a view showing a mold for comparison showing a conventional molding method. In the figure, 1: Cavity 2: Core 3: Clearance 4: Cavity cooling water channel 5: Core cooling water channel 6: Core pin gate 7: Core resin channel 8: Injection molding machine nozzle

Claims (1)

[Claims] 1. A method for producing a resin molded product having a uniform mixed color pattern on a surface by injection molding a mixture of a resin and a masterbatch, wherein an injection mold comprising a core and a cavity is used. A manufacturing method, characterized in that an injection gate is provided, and the mixture is injected through the gate while the core temperature is higher than the cavity temperature by 15 ° C. or more.