JPH01247124A - Double-injection molding method - Google Patents

Abstract

PURPOSE:To improve the appearance of a product by eliminating the generation of irregular flashes, by molding a hard molded body wherein a protruding weir, which protrudes in a mold opening direction and can be brought into contact with the wall surface of a mold under pressure, is formed to the vicinal region of a boundary line to which a soft part is connected and subsequently forming the soft part by injection molding. CONSTITUTION:A reciprocally movable mold 53, wherein a fine groove 53A and fine grooves 53B, 53B are respectively formed to the region A and regions B, B in the vicinity of a boundary line where the first and second soft plastic bodies 30, 40 are formed, is used and hard plastic is injected in the cavity formed between said mold 53 and a rotary mold 51 to mold a hard molded body having protruding weirs 11A, 21B, 21B protruding in a mold opening direction. Subsequently, when the injection molding of soft plastic 31 is performed in correspondence to an opening 11 so that a stepped part 34 notched outwardly is formed to the outer peripheral edge of the first plastic body 31, the burr formed in the vicinity of the boundary line is adjusted by the protruding weir 11A and becomes constant to be bonded. The second soft plastic body 40 is formed to a mount seal surface 21 by injection molding and, at this time, flash is controlled by both protruding weirs 21B, 21B to form definite shape.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a double molding method for synthetic resin parts.

(Prior art) Conventionally, it has been proposed to manufacture synthetic resin parts by double molding, which consists of a first step of injection molding a hard part and a second step of injection molding and joining a soft part to the hard molded body. has been done.

For example, in order to reduce weight, timing gear covers for internal combustion engines are made with the main part of the cover made of highly rigid hard plastic, and areas susceptible to mechanical vibrations are lined with or formed with soft plastic to achieve high sound insulation performance. It has been proposed to provide a synthetic resin cover member. However, as shown in FIG. 2, (a) mobile type A in the first step
After the completion of (b) injection and (c) mold opening, product shrinkage occurs when the hard molded body hardens, and in the second process (d) of mold matching between movable mold C and fixed mold B. Because the surface of the cured molded product does not adhere accurately to the mold surface, and a slight gap is created, during injection molding of the soft part (e), the soft material wraps around, especially on the outer surface side, at the joint with the hard part, which may cause a break. There is a problem that occurs. Furthermore, this type of spacing has a problem in that the gaps are not constant and therefore irregular, which significantly impairs the appearance of the product.

(Problem of the Invention) An object of the present invention is to provide a double molding method for synthetic resin products that solves the above-mentioned problems and has excellent product appearance.

(Means for Solving the Problems) Although it is difficult to predict product shrinkage after the first process and design a mold for the second process so that no flash occurs, the present invention This was done based on the fact that it is easy to improve the mold and form a weir in the injection molded product to adjust the shape of the particles generated in the second process to a certain shape. In manufacturing synthetic resin parts by double molding, which consists of a first step of injection molding and a second step of injection molding and joining a soft part to the hard molded body, as shown in FIG. In the first step, a movable mold A in which fine grooves are formed in the area near the boundary line where the soft part is joined.
Using (a) injection molding of the hard part, b) molding a hard molded body in which a convex weir that protrudes in the mold opening direction near the boundary line and can be pressed against the mold wall surface in the second step is formed. C), Next, in the second step, the movable mold C is pressed against the convex weir (d), and then the soft part is injection molded (e). The method is a molding method.

In the above case, micro grooves were formed in the mold in the first step to form a convex weir, but as shown in FIGS. 3(a) to (c), (a) the mold ASB in the first step is made slightly larger on the boundary line side where the soft part is joined, considering the shrinkage rate, and injection molded by matching the molds.(b) When the mold is opened and cooled, the thick part is in the center and corner. A convex portion remains at the corner due to the difference in shrinkage and amount from the convex part, and has the same function as the convex weir, so in the (c) second step, the movable mold C is pressed against the convex part. When the soft part is injection molded after the mold matching as described above, the soft part is stopped by the convex part and is joined to the hard part without any flaws. Therefore, double molding may be performed by such a method. It should be noted that although the latter method is effective in forming thick parts, it may not be possible to form the desired convex parts in thin parts.

(Function) According to the present invention, since the convex weir protruding in the mold opening direction is formed near the boundary line of the hard part to which the soft part is joined, the second
In the process, by aligning the mold so that it comes into pressure contact with the convex weir [Fig. 1(d)], the cracks in the soft part are limited by this weir [Fig. 1(e)] L has a beautiful appearance. It will be adjusted.

Hereinafter, the present invention will be explained in detail based on specific examples shown in the accompanying drawings.

(Example) Fig. 4 is a plan view showing the inside of a cover member for a timing belt cover according to the present invention, Fig. 5 is a left side view, Fig. 6 is a right side view, and Fig. 7 is a lower end view. , the cover member 1 includes a substantially flat cover wall surface 10 parallel to the cover mounting surface, a rim wall surface 20 rising perpendicularly from the periphery of the wall surface, and a mounting seal i? located at the tip thereof. j21, and has a roughly U-shaped cross section.

The cover member 1 is made by injection molding of a hard plastic, for example, a raw material whose main component is polypropylene containing an appropriate amount of inorganic material. It is molded by double molding, which consists of a first step and a second step of injection molding a raw material whose main component is a soft plastic, for example, an olefin elastomer, from the same direction.

In addition, specific examples of the above-mentioned hard plastic raw materials include polypropylene alone, a mixture of 100 parts by weight of polypropylene and 20 parts by weight of talc, and 1 part by weight of polypropylene.
00 parts by weight, 15 parts by weight of glass fiber, 10 parts by weight of talc
A mixture of parts by weight can be used.

A two-layer injection molding apparatus shown in FIG. 8 is preferably used for such double molding. In other words, in the center! There is a rotating device 50 that rotates in units of 80 degrees, and two rotating molds 51 and 52 are fixed at symmetrical positions. Reciprocating molds 53 and 54 are arranged opposite to each other with a rotating device 50 in between, and both reciprocating molds 53 and 54 are moved relative to the rotary molds 51 and 52 from the setup state (a) to close the mold (rotation). ), hard plastic is injected from the left injection machine 55, while soft plastic is injected from the right injection machine 56 (c). Next, the mold is opened (D), and the right-side secondary molded product is extracted, while the left-side secondary molded product is moved to the right by operating the rotating device 50, and the mold is closed again.

Therefore, in the first step on the left side, the cover member l
The cover wall surface 10 is made of hard plastic, and the central portion thereof has a circular opening II from above, an overall rectangular opening 12 divided by a plurality of ribs 14 extending in the width direction, and a rectangular opening 12 divided by the ribs 14. A semicircular opening 13 is formed as a whole, and a bolt socket 22 is attached to the rim wall surface 20 which stands up at right angles from the periphery of the cover wall surface IO and overhangs the rim wall surface 20 reinforced by the ribs 14 and appropriate surrounding areas thereof. is made of hard plastic. Next, the second step on the right side is applied to the molded body made of hard plastic, and the openings II and 1 are
2, the first soft plus deck body 30 to block +3
At the same time, a second soft plastic body 40 is injection molded on at least the contact surface of the mounting seal surface 21 at the tip of the rim wall surface 20. In the present invention, in the first step, as shown in FIG. As shown, a region A near the boundary line where the first soft plastic body 30 is joined as a soft part and the second soft plastic body 40
Fine grooves 53A and 5 are formed in area B near the boundary line where
3B and 53B are used to inject hard plastic into the cavity formed between the rotary mold 51 and the opening 11 as shown in FIG. 1θ.
Stepped part 1 cut inward from the inner peripheral edge of (12, 13)
Convex weir 1 protruding in the mold opening direction near the boundary line of 5
1A (12ASl 3A) and a hard molded body in which convex weirs 21B and 21B are formed near the boundary line of the mounting seal surface 21 is molded. Next, the first soft plastic body 30 consists of 31, 32, and 33 corresponding to the openings 11, 12, and 13, respectively, and is formed between it and the rotary mold 51 using a reciprocating mold 54 in a second step. When the soft plastic is injection molded so that an outwardly cut stepped portion 34 is formed on each outer peripheral edge of the first soft plastic body with respect to the opening in the cavity, a convex shape is formed. The edges formed near the boundary lines at the weirs 11A (12A, 13A) are adjusted, become constant, and are joined. On the other hand, the second soft plus deck body 40 has a convex weir 21B formed near the boundary line with respect to the mounting seal surface 21.
121B is formed by injection molding of soft plastic, and is limited by both convex weirs 2IB, 21B, so that the paris has a fixed shape.

Specific examples of olefin elastomers for soft plastics include PR (propylene rubber) and EPT.
A mixture of appropriate amounts of (ethylene propylene terpolymer), polypropylene, and a low molecular weight additive can be used.

(Effects of the Invention) As is clear from the above description, according to the present invention, the first step of injection molding a hard part and the second step of injection molding and joining a soft part to the hard molded body In manufacturing synthetic resin parts by double molding, in the first step, the hard part is injection molded using a mold with fine grooves formed in the area near the boundary line where the soft part is joined. In the second step, a hard molded body is formed with a convex weir that can be pressed against the mold wall surface in a second step that protrudes in the mold opening direction in the vicinity, and then, in the second step, the mold is pressed against the convex weir. After the molds were matched, the soft part was injection molded, so a convex weir protruding in the mold opening direction was formed near the boundary line of the hard part to which the soft part was joined, and the metal was molded in the second step. By fitting the molds so as to press against the convex weir, the breakage of the soft portion is limited by the weir, and a double-molded synthetic resin part with a beautiful appearance can be manufactured.

Therefore, by focusing on the sound insulation performance of soft plastics, it is possible to provide a manufacturing method suitable for manufacturing cover parts, etc., in which a rigid hard plastic cover part is lined with a soft plastic by using a double molding method. .

[Brief explanation of the drawing]

FIG. 1 is a principle diagram showing the steps of the double molding method according to the present invention, FIG. 2 is a principle diagram showing the steps of the conventional double molding method,
FIG. 3 is a principle diagram showing the other side of the double molding method according to the present invention, FIG. 4 is a plan view showing the inside of the cover member for a timing belt cover according to the present invention, and FIG. 5 is a left side view. figure,
FIG. 6 is a right side view, FIG. 7 is a lower end view, and FIG. 8 is a principle diagram of a molding device to which the double molding method according to the present invention can be applied.
FIG. 9 is a cross-sectional view showing the first step mold configuration when the method of the present invention is applied to the specific example shown in FIG. 4, and FIG. 10 is a cross-sectional view of the primary molded product formed from the mold shown in FIG. 11 are cross-sectional views showing the state during molding using the second process mold. 1...Cover part, 10...Cover wall surface, 20...
・Rim wall surface, 21... Mounting seal surface, 30... 1st
Soft plastic, 40...Second soft plastic 5
1.52... Rotating mold, 53.54... Reciprocating mold, lOA, 21B... Convex weir, 53A, 53B...
fine groove

Claims (1)

[Claims] 1. In manufacturing synthetic resin parts by double molding, which consists of a first step of injection molding a hard part and a second step of injection molding and joining a soft part to the hard molded body. In the first step, the hard part is injection molded using a mold in which fine grooves are formed in the area near the boundary line where the soft part is joined, and in the second step, the hard part is protruded in the mold opening direction in the vicinity of the boundary line. Then, in the second step, the mold is matched so as to press against the convex weir, and then the soft part is injected. A double molding method characterized by molding.