JPH0380606B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a synthetic resin molded product that prevents sink marks that occur during molding such as injection molding, compression molding, and phase shift molding.

Generally, when injection molding thermoplastic resins (hereinafter simply referred to as synthetic resins) to mold thick and unevenly-walled synthetic resin products, differences in the cooling rate of the synthetic resin on the surface and inside may cause partial shrinkage differences. This causes sink marks (concave depressions) on the product. In particular, large sink marks appeared in areas where the wall thickness suddenly changed or where the insert was buried inside and the wall pressure of the synthetic resin substantially changed, resulting in a deterioration of the appearance. For example, when injection molding a vehicle steering wheel,
As shown in FIGS. 1 and 2, a ring portion 1 and a spoke portion 2 of the steering wheel after molding are shown.
Sink marks 3 are likely to occur at the connection points. For this reason, in the past, sink marks were prevented by increasing the cooling time of the molded product after injection molding, by taking out the molded product and cooling it rapidly, or by creating a hollow in the product. Therefore, the number of manufacturing steps increases, and the process becomes longer and more complicated.

This invention was made to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a method for manufacturing synthetic resin molded products that can prevent the occurrence of sink marks in molded products using a simple method and a small number of man-hours. shall be. For this purpose, the present invention provides a method for manufacturing a synthetic resin molded product in which the molded product has a thick wall part and a non-pressure wall part, after injecting the synthetic resin into the cavity.
At the point where the thick wall part is to be formed in the cavity,
It is configured to push the synthetic resin that has entered the push-in member or the push-in recess to prevent sink marks at specific locations.

Embodiments of the present invention will be described below based on the drawings. FIG. 3 shows a cross-sectional view of an injection mold for a steering wheel, and the movable mold 4 of this mold includes:
A pushing device 5 used to prevent sink marks is installed in thick-walled parts and uneven-walled parts where sink marks are likely to occur.
That is, a hole-shaped push-in recess 7 is formed in communication with the cavity 6 at the connection point between the ring part and the spoke part in the movable mold 4, and a piston-shaped push-in member 8 is inserted into this push-in recess 7 so as to be vertically slidable. has been done. The pushing member 8 has its lower base fixed to the tip of the piston rod 10 of the hydraulic cylinder 9 with a fixture 11 to prevent rotation. 12
is the upper limit stopper of the piston rod 10 attached to the lower part of the push-in recess 7;
At the upper limit of 0, the tip end surface of the pushing member 8 is formed to form a part of the inner wall of the cavity 6. Note that 13 is a fixed mold, and 14 is a core metal of the steering wheel.

Using the above injection mold, the steering wheel is injection molded as follows.

First, the piston rod 10 of the hydraulic cylinder 9 is pulled back, and a thermoplastic resin is injected into the cavity 6 with the push-in recess 7 formed at the front of the push-in member 8. Then, the push-in recess 7 is also filled with the synthetic resin. And after injection, 10~
After 15 seconds have elapsed, the hydraulic cylinder 9 is operated to push out the synthetic resin in the push-in recess 7 into the cavity 6.
When the cavity 6 is colder than the synthetic resin inside.
It is pushed into areas where sink marks are likely to occur. At this time, the synthetic resin that has cooled to a certain extent and hardened is pushed into the area where sink marks are likely to occur, so the filling density becomes locally high inside that area, and the cooling rate is also accelerated, which prevents sink marks from occurring on the surface. Occurrence is prevented. After natural cooling, the molded product is taken out from the mold.

In addition, in the above example, a method was adopted in which the resin overflowed into the area where sink marks are likely to occur was pushed back into the cavity. However, if leaving a recess on the back side of the product is not a problem, use the pushing member when injecting the resin. Raise the pressing member to a position where no recess is formed, and after 10 to 15 seconds have elapsed after injection, push the pressing member into the cavity and cool it in this state to prevent sink marks from occurring on the surface. You can also do it.

Further, the size, shape, and number of the push-in member and the push-in recess are appropriately determined depending on the range and depth where sink marks occur.

As described above, according to the method for manufacturing a synthetic resin molded article according to the present invention, in the method for manufacturing a synthetic resin molded article in which the molded article has a thick part and a non-thick part,
After injecting synthetic resin into the cavity of the mold, the push-in member or the thermoplastic resin in the push-in recess is pushed into the cavity to prevent sink marks at specific locations, so it can be done using simple equipment and methods. , synthetic resin molded products without sink marks can be manufactured with fewer man-hours.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a sink portion of a steering wheel, FIG. 2 is a sectional view taken along line AA in FIG. 1, and FIG. 3 is a sectional view of a mold used in an embodiment of the present invention. 4... Movable type, 5... Pushing device, 6... Cavity, 7... Pushing recess, 8... Pushing member,
9...Hydraulic cylinder.

Claims (1)

[Scope of Claims] 1. In a method for manufacturing a synthetic resin molded product in which the molded product has a thick wall portion and a non-thick wall portion, a push-in recess is provided in communication with a portion of a mold cavity where the thick wall portion is to be molded. A push-in member that can be slid from the outside is inserted into the push-in recess, a thermoplastic resin is injected into the cavity and the push-in recess with the push-in member pulled back, and after a certain period of time, the push member is pushed out. A method for manufacturing a synthetic resin molded product, characterized in that thermoplastic resin in a push-in recess is pushed into a cavity to prevent sink marks in the molded product. 2. In a method for manufacturing a synthetic resin molded product in which the molded product has thick-walled parts and non-thick-walled parts, a pushing member is pushably disposed in the part of the cavity of the mold where the thick-walled part is to be molded, and Production of a synthetic resin molded product, characterized in that a thermoplastic resin is injected into a cavity of a mold, and after a certain period of time, the pushing member is pushed into a thick-walled part forming part in the cavity to prevent sink marks in the molded product. Method.