JPH07304071A - Molded product with inconspicuous weld line and production thereof - Google Patents

Abstract

PURPOSE:To produce a molded product characterized by that a weld line is inconspicuous and excellent in production efficiency without requiring a complicated post treatment process by forming a thin-walled part on the rear surface of the molded product in the vicinity of a gate so that the resin injected from the gate flows out uniformly. CONSTITUTION:A resin is injected from gates 1, 2 at two or more points to mold a molded product. A continuous thin-walled part T is formed on the rear surface of the molded product in the vicinity of the gates so that the resin injected from the gates 1, 2 flows out uniformly. Herein, the position and thickness of the thin-walled part T formed on the rear surface of the molded product are appropriately set by the shape, size and the thickness of the molded product but it is pref. to form the thin-walled part having a width (d) of 2-1.5mm. Since a weld line becomes conspicuous when the interval between the gates becomes wide, the interval is set to 50mm or less especially pref.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a molded product having no noticeable weld line and a molded product obtained by the molding method.

[0002]

2. Description of the Related Art Generally, when a resin is injected from two or more gates to form a molded product, a weld line is formed at a portion where the resin injected from each gate is joined, that is, a weld portion. Occurs, but
Such a weld line significantly impairs the commercial value of the molded product, and conventionally, a resin material in which the weld line is inconspicuous has been developed. However, these resin materials are special ones, are likely to be expensive, and often depend on the shape of the molded product, so that selection of the resin material is extremely complicated. Film gates and disk gates are gates that do not generate weld lines. This is because the resin is linearly injected into the molded product rather than dots, so there is virtually no portion where the resin is joined, so no weld line occurs.However, these film gates and disk gates Since it is in linear contact with the molded product, a post-treatment process after molding is required, and if the molded product is complicated and dense, this post-treatment process will significantly reduce the productivity. .

[0003]

As a result of intensive studies on the above problems, the present inventors have found that the flow of resin causing weld lines and the shapes of film gates and disk gates in which weld lines do not occur. The present invention has been completed by focusing attention on the idea of incorporating this as the shape of the molded product near the gate.

That is, according to the present invention, when a resin is injected from two or more gates to form a molded product, the resin injected from each gate uniformly flows out to the back surface of the molded product near the gate. It is intended to provide a method for molding a molded product with inconspicuous weld lines, which is characterized by molding so as to form a continuous thin portion.

The present invention will be described in detail below. In the molding method of the present invention, the resin is injected from two or more gates. As such a gate, a generally known gate can be adopted, and particularly, a side gate and a tab gate. , Pin gates, submarine gates and the like are preferable because the effects of the present invention can be effectively exhibited.

Further, according to the present invention, the back surface of the molded product near the gate is molded so as to form a continuous thin portion through which the resin injected from each gate flows out uniformly. By this, a molded product with inconspicuous weld lines can be obtained. This is to change the flow of points from each gate into a linear flow by allowing the resin injected from each gate to pass through the thin portion. The principle that does not occur is applied.

The position and thickness of the thin portion formed on the back surface of the molded product can be appropriately set depending on the shape and size of the molded product and the thickness of the molded product, but preferably from the gate to the molded product. 1-10 mm in the direction,
Preferably, on the back surface of the molded product with a distance a of 1 to 5 mm,
The thickness b is 0.5 to 2.0 mm, preferably 0.7 to 1.
5 mm, width d of 2 mm or more, preferably 2 to 15 mm
It is preferable that the thin portion has

Further, since the weld line tends to be conspicuous when the gate spacing is too wide, the gate spacing is preferably 70 mm or less, and particularly 5
It is preferably within 0 mm.

In the present invention, it is indispensable to provide a thin portion on the back surface of the molded product near the gate. If necessary, ribs may be installed as long as the effect is not impaired.

The resin used in the present invention includes ABS resin, AES resin, ACS resin, AS resin,
Styrene resin such as PS resin, polyolefin such as polyethylene and polypropylene, polycarbonate, polybutylene terephthalate, polyethylene terephthalate,
Examples thereof include thermoplastic resins such as polyamide, polyphenylene oxide, and polysulfone, and polymer alloys thereof.

Further, in the present invention, if necessary, in addition to these resins, inorganic fibers such as glass fiber, alumina fiber, carbon fiber, silicon carbide fiber, ceramic fiber, asbestos fiber, metal fiber, heat resistant organic fiber, etc. Fibrous fillers, talc, kaolin, sericite, mica, clay, wollastonite, bentonite, asbestos, silicates such as alumina silicate, metal oxides such as alumina, silicon oxide, magnesium oxide, zirconium oxide, titanium oxide And a granular filler such as calcium carbonate, magnesium carbonate, barium sulfate, glass beads, boron nitride and silicon carbide can be blended. Also,
Other known lubricants, release agents, ultraviolet absorbers, antioxidants, antistatic agents, coloring agents, flame retardants, flame retardant aids, foaming agents,
A crosslinking agent, a heat stabilizer and the like can be optionally used.

[Examples] The present invention will be described in detail below with reference to Examples. Example 1 ABS resin (Clarastic MC manufactured by Sumitomo Dow Co., Ltd.)
-4) was injection-molded using a 4-ounce injection molding machine at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C., and the two gates (gate interval 40 mm) were used to form 3 pieces in the direction of the molded product.
A molded product having a shape shown in FIG. 1 having a length of 100 mm × width of 60 mm × thickness of 3 mm provided with a thin portion having a distance a of 1 mm, a thickness b of 1 mm and an interval d of 5 mm was obtained. In the obtained molded product, a slight weld line was observed in the approximate center between the gate 1 and the gate 2 for about 3 mm (distance a) from the end of the molded product on the gate side. The molded product had almost no weld line.

Comparative Example 1 A molded product having a length of 100 mm, a width of 60 mm and a thickness of 3 mm was obtained in the same manner as in Example 1 except that the thin portion was not provided.
The obtained molded product was a molded product in which a weld line was formed in approximately the center between the gate 1 and the gate 2 over about 15 mm from the end of the molded product on the gate side, and the weld line was very noticeable.

Example 2 ABS resin (Clarastic MC manufactured by Sumitomo Dow Co., Ltd.)
-4) was injection-molded using a 4 ounce injection molding machine at a cylinder temperature of 230 ° C. and a mold temperature of 50 ° C., and 3 from each of the four gates (gate interval 35 mm) toward the molded product.
An inner diameter of 45 mm and an outer diameter of 200 provided with thin-walled portions having a distance a of mm, a thickness b of 1.2 mm, and a distance d of 7 mm.
A donut-shaped molded product having a thickness of 2.5 mm and a thickness of 2.5 mm shown in FIG. 2 was obtained. In the obtained molded product, although there were some weld lines approximately 3 mm (distance a) from the end of the molded product on the gate side, the weld line was formed in the center of each molded product as a whole. The molded product was almost inconspicuous.

Comparative Example 2 A donut-shaped molded product having an inner diameter of 45 mm, an outer diameter of 200 mm and a thickness of 2.5 mm was obtained in the same manner as in Example 2 except that the thin portion was not provided. The obtained molded product is approximately 15 m from the gate-side molded product end, approximately in the center between each gate.
A weld line was generated over the length of m, and the molded product had a very noticeable weld line.

[0016]

As described above, by adopting the method of the present invention, a molded product with markedly less noticeable weld lines can be obtained, and a complicated post-treatment step after molding is not required. Molded articles with excellent production efficiency (for example, various electric / electronic parts, automobile parts, compact discs, etc.) can be obtained.

[Brief description of drawings]

FIG. 1 is a molded article according to Example 1 of the present invention,
(A) is a plan view and (B) is a sectional view.

FIG. 2 is a molded article according to Example 2 of the present invention,
(A) is a plan view and (B) is a partial sectional view taken along line I-II.

[Explanation of symbols]

 1 to 4 ... Gate part T ... Thin part

Claims (2)

[Claims] 1. When the resin is injected from two or more gates to form a molded product, a continuous thin wall in which the resin injected from each gate uniformly flows out to the back surface of the molded product near the gate. A method for molding a molded product in which a weld line is inconspicuous, which is characterized by molding so as to form a portion. 2. A molded product in which the weld line is inconspicuous, which is obtained by the molding method according to claim 1.