JPH07100877A - Method and device for manufacture of injection molded plastic product without generating sink mark on its visible face - Google Patents

Abstract

PURPOSE:To control the generation of sink marks on the surface of a product by installing a pressurizing means for pushing out a product into a visible face side on the mold side in contact with an invisible face of the product and setting the bonding force of invisible face side of the product smaller than that of the visible face side by the pressurizing means. CONSTITUTION:A core 2 on the invisible side of a product and a cavity 3 on the visible side of the product are set to be opened and closed, and a recessed section 4 corresponding to the external shape of an injection molded product (a) is formed on the core 2, and molten plastic is poured from an injection molding machine into the recessed section 4 to form the plastic molded product (a) through a sprue 5 on the given site of the cavity 3. A fluid such as compressed air is injected from outside into between an invisible face (d) of the molded product and the core 2 through a ventilation tube 7 and a sintered metal material 6. As a result, the control of the positions for the generation of sink marks can be performed so that the bonding force of resin of the invisible face (d) of the molded product and the surface of the core 2 gets smaller to eliminate the generation of sink marks on a visible face (e) of the plastic molded product and to generate sink marks on the invisible face (d) of the molded product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses a thermoplastic resin as a material, and lowers the adhesion between the material resin and the product invisible surface side mold surface, or forces the material resin and the product invisible surface side mold surface. TECHNICAL FIELD The present invention relates to a method for manufacturing an injection-molded plastic product which does not generate a sink mark on a product visible surface by controlling a sinking position by using an injection molding die having a device for separating physically, and an apparatus (die) thereof.

[0002]

2. Description of the Related Art When a plastic product having bosses, ribs or uneven thickness portions is injection-molded, a sink mark is generated on the surface of a portion where the thickness of the product is greatly different. The cause of this sink is that when the molten thermoplastic resin cools in the mold and solidifies, it shrinks, but in the part where the wall thickness is thicker than the surroundings, cooling is slower and the surroundings solidify and solidify with shrinkage. Because it does. In particular, the cavity side, which is usually the product visible part of plastic products, is flat against the core side that has complex structures such as bosses and ribs, and because it is easy to cool, it is released earlier than the core side and post-contraction occurs. However, sink marks are likely to occur.

The sink marks are concave dents on the surface of the product, which impair the appearance of the product and reduce the value thereof, and also hinder the uniform coating to impair the aesthetics, resulting in high repair costs.

As a measure to prevent sink marks, a method of providing a thin portion on the periphery of the thick portion of the product to make cooling uniform,
Known methods include a method of after-filling with shrinkage, a method of heating or cooling a mold within a range where temperature control water is possible, and the like.

[0005]

However, in the above-mentioned conventional method, it is difficult to deal with the complicated product shape because it requires a machining process that requires a fixed space around the boss hole on the non-visible surface side of the product. However, even in the case of post-filling, the period during which filling is possible is limited, and there is a problem that a sufficient filling effect cannot be expected depending on the product shape.

[0006] Also, the heating or cooling method is not always able to obtain a sufficient effect because the temperature range is limited to about temperature control water.

The present invention was devised in view of the above circumstances, and provides a method and apparatus for manufacturing a plastic product capable of controlling the occurrence of sink marks on the product surface, which can be applied even when the product shape is complicated. The purpose is to

[0008]

The method of manufacturing an injection-molded plastic product which does not cause sink marks on the visible surface and the structure of the apparatus according to the present invention are as follows.

1. In injection molding of plastic products that generate sink marks, a pressure means for pushing the product to the visible surface side is attached to the mold side that comes in contact with the product invisible surface, and the adhesion force on the product invisible surface side by this pressure means Is set to be smaller than the visible surface side, and a method for manufacturing an injection-molded plastic product that does not cause sink marks on the visible surface.

In the injection molding of a plastic product which causes a sink mark, a pressurizing means is attached only to the surface of the die which is invisible to the product and is in contact with a portion which easily induces a sink mark. Injection molding that does not generate

2. In a mold for injection molding of a plastic product that generates a sink mark, a minute vent hole as a pressurizing means is formed on the surface of the mold that comes into contact with the product invisible surface, and this minute vent hole is connected to a pressurizing device. The adhesion of the surface of the mold that contacts the invisible surface of the product is made smaller than the adhesion of the surface of the mold on the visible side, and this pressure is used to visualize the adhesion between the invisible surface and the mold. A device for manufacturing injection-molded plastic products that does not generate sink marks on the visible surface, which is configured to be controlled smaller than the surface side.

As the means for forming the minute air holes, there are air-permeable metals such as sintered metal, ceramics, or minute holes and grooves formed by machining.

Further, the minute vent holes may be formed only in a portion where sink marks are easily generated.

3. In the injection molding device (mold) for plastic products that generate sink marks, the invisible surface side mold is
An injection-molded plastic product that does not cause sink marks on the visible surface, characterized in that the visible surface side mold is positioned below and the weight of the product is set to the visible surface side to set the adhesion force on the invisible surface side to be small. Molding equipment.

4. In the injection molding device (mold) for plastic products that generate sink marks, after the resin is poured into the mold, the product invisible surface side mold is retracted to force the resin invisible surface side surface. A molding device for injection-molded plastic products that does not cause sink marks on the visible surface, characterized by being configured to be peeled off.

As a method of forcibly peeling off the mold surface of the product invisible surface side from the resin, a wedge, a toggle, etc. are provided so that both molds do not open when the product invisible surface and visible surface molds are closed. It is possible to employ a method in which the resin is fixed by using it and a part of the invisible surface side mold is retracted to the side opposite to the product resin by an electric drive mechanism or a cylinder drive mechanism using a fluid.

The resin to which the present invention can be applied is not only a general-purpose resin such as a polyolefin resin, a polystyrene resin, an ABS resin or an industrial resin such as a polycarbonate resin or a polyamide resin, but also a mixture of various resins or a reinforcing agent. May be mixed, and there is no particular limitation.

[0018]

[Function] As described above, by lowering (decreasing) the adhesion between the resin and the invisible surface side mold surface or forcibly separating the product, the product is relatively released on the visible surface side mold surface. It becomes difficult to do this, and during this time it is cooled through the mold. On the other hand, the non-visible surface side is first released and thermally insulated, so that the surface does not solidify and the shrinkage greatly affects the shrinkage. As a result, the sink marks are concentrated on the root portions of the bosses and ribs on the non-visible surface side and do not occur on the visible surface side.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic sectional view of an injection molding die.

The injection molding die 1 shown in FIG. 1 is roughly divided into a core 2 on the product invisible surface side and a cavity 3 on the product visible surface side, both of which are connected to an injection molding machine (not shown). The core 2 and the cavity 3 can be opened and closed. The core 2 has a recess 4 corresponding to the outer shape of the injection-molded product a.
A molten plastic is poured into the concave portion 4 from an injection molding machine (not shown) through a sprue 5 provided at a predetermined position of the cavity 3 to form a plastic molded product a.
Are to be molded. The bosses and ribs of the core 2 are formed of a sintered metal material 6 having air permeability as a mold releasing means, and through a ventilation pipe 7 connected thereto, between the molded product invisible surface d and between the core 2 and the outside. Is breathable. Also, through the ventilation pipe 7 and the sintered metal material 6,
It is possible to inject a fluid such as compressed air from the outside between the molded product invisible surface d and the core 2.

This plastic molded product a has a boss b and a rib c. The non-visible surface d of the plastic molded product where the boss b and the rib c exist is the core 2, and the visible surface e of the plastic molded product is the cavity. Touching 3.

Next, the above embodiment will be described more specifically.

The apparatus of FIG. 1 and polystyrene (HH501,
(Showa Denko), with the cross-sectional structure as shown in FIG. 1, the product invisible surface e has an outer diameter of φ15 mm, an inner diameter of φ6 mm, and a height of 10
A plate-like product having a product size of 150 × 200 mm and a wall thickness of 2.5 mm having a boss of mm and a rib having a thickness of 7 mm and a height of 18 mm was molded.

As a method for lowering the adhesion between the resin and the surface of the core ² , compressed air was injected from the outside through the ventilation pipe 7 and the sintered metal 6 at a pressure of several kg / cm ² .

As shown in FIG. 2, no sink marks were generated on the visible surface e of the obtained plastic molded product, and sink marks were generated on the invisible surface of the molded product. "Comparative Example" A comparative example was molded under the same conditions as those of the above-mentioned example except that the ventilation pipe 7 in Fig. 1 was closed. As shown in FIG. 3, this product had sink marks on the visible surface e of the plastic molded product and no sink marks on the invisible surface d of the molded product, contrary to the examples.

A second embodiment of the present invention will be described with reference to FIGS. 4 and 5. FIG. 4 is a schematic outline view of the vertical injection molding apparatus.

Core 2 on the product invisible surface side of the injection molding die
The cavity 3 on the visible surface side of the product and the cavity 3 on the visible surface side of the product are respectively fixed to the movable mold mounting board 8 and the stationary mold mounting board 9 of the injection molding apparatus, and the movable mold mounting board 8 to which the core 2 is mounted is mounted.
However, it can be opened and closed by moving up and down by the ram 10. Molten plastic as a product material is passed through the nozzle 11 of the injection molding machine to the core 2 and the cavity 3.
The product is formed by being poured into a mold composed of the above. The structure of the mold is the same as that of the first embodiment, but a conventional mold without the ventilation pipe 7 and the sintered metal material 6 is also possible.

According to the present embodiment, the positional relationship of the molds is such that the core 2 on the product invisible surface side is on the top and the cavity 3 on the product visible surface side is on the bottom, and the product weight is applied to the cavity 3 side.

FIG. 5 is a schematic outline view of a conventional vertical injection molding apparatus shown for comparison with the second embodiment of the present invention. The operation is the same as that of FIG. 4 except for the difference in the positional relationship, but the core 2 on the product invisible surface side is on the bottom and the cavity 3 on the product visible surface side is on the top. The product dead weight is configured to be applied to the core 2 side.

Next, a third embodiment of the present invention will be described with reference to FIGS. 6 and 7. 6 and 7 are schematic cross-sectional views of the injection molding die, and the order of FIGS. 6 and 7 is in accordance with the operation process.

The injection molding die 1 is roughly divided into a core 2 on the product invisible surface side and a cavity 3 on the product visible surface side, and a part of the core 2 is composed of a movable insert piece 12. . The movable insert piece 12 can be moved forward and backward toward the cavity 3 by sliding the slide insert piece 13 in contact with the movable insert piece 12 at the same taper angle with the cylinder body 15 via the cylinder shaft 14. It is possible.

FIG. 6 shows a sprue 5 from an injection molding machine (not shown).
FIG. 9 is a diagram in the process of pouring the molten plastic into the concave portion 4 corresponding to the outer shape of the injection-molded product a via the slide insertion piece 13 is inserted in the mold center direction by the cylinder 15, whereby the movable insertion piece 12 is inserted. Advances toward the cavity 3 to form a recess 4 corresponding to the outer shape of the injection-molded product a.

After the molten plastic has been poured into the recess 4, as shown in FIG. 7, the slide insert piece 13 is pulled out toward the outside of the mold by the cylinder 15, whereby the movable insert piece 12 is moved toward the cavity 3 direction. Then, the non-visible surface d of the plastic molded product and the movable insert piece 12 are separated from each other by breaking the contact.

[0034]

EFFECTS OF THE INVENTION According to the molding method and the apparatus therefor, a sink mark is selectively generated on one surface of a plastic product,
The sink position can be controlled so that sink marks are not generated on the other surface (visible surface). For this reason, the appearance and accuracy of the plastic molded product are great, and the effect of reducing product defects is extremely large.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an injection molding die according to a first embodiment of the present invention.

FIG. 2 is an explanatory view showing a state of sink marks generated on the product surface of a plastic molded product molded by the injection molding die according to the first embodiment of the present invention.

FIG. 3 is an explanatory view showing a state of sink marks generated on the product surface of a plastic molded product molded by a conventional injection molding die.

FIG. 4 is an external view showing an example of a vertical injection molding apparatus according to a second embodiment of the present invention.

FIG. 5 is an external view showing an example of a conventional vertical injection molding apparatus according to a second embodiment of the present invention.

FIG. 6 is a cross-sectional view showing the operation of the injection molding die according to the third embodiment of the present invention.

FIG. 7 is a sectional view showing the operation of the injection molding die according to the third embodiment of the present invention.

[Explanation of symbols]

 1 Mold 2 Core 3 Cavity 4 Recess 5 Sprue 6 Sintered Metal Material 7 Vent Pipe 8 Mold Mounting Movable Plate 9 Mold Mounting Fixing Plate 10 Ram 11 Injection Nozzle 12 Movable Insert 13 Slide Insert 14 Cylinder Shaft 15 Cylinder Main body a Plastic molded product b Boss c Rib d Plastic molded product invisible surface e Plastic molded product visible surface f Marked area

Claims (11)

[Claims] 1. In injection molding of a plastic product producing a sink mark, a pressure means for pushing the product to the visible surface side is attached to a mold side in contact with the product invisible surface, and the product invisible state is obtained by this pressure means. A method of manufacturing an injection-molded plastic product that does not cause sink marks on the visible surface, by setting the adhesion on the surface side to be smaller than that on the visible surface. 2. The injection molding of a plastic product producing a sink mark, wherein the pressurizing means is attached to the surface of the mold which is in contact with a site which is likely to induce a sink mark on the product invisible surface side. Of injection-molded plastic products that does not cause sink marks on the visible surface of. 3. In a mold for injection molding of a plastic product which causes a sink mark, a minute vent hole is formed as a pressurizing means on the surface of the mold which comes into contact with the product invisible surface, and the minute vent hole is pressed. It is configured so that the adhesive force on the surface of the mold that is in communication with the device and in contact with the invisible surface of the product is controlled to be smaller than the adhesive force on the surface of the mold on the visible surface side. Injection molding that does not cause sink marks on the visible surface. Equipment for manufacturing plastic products. 4. An apparatus for producing an injection-molded plastic product which does not cause sink marks on a visible surface according to claim 3, wherein the minute vent holes are formed of a metal having air permeability. 5. An apparatus for producing an injection-molded plastic product which does not cause sink marks on the visible surface according to claim 3 or 4, wherein the minute vent holes are formed of sintered metal. 6. An apparatus for producing an injection-molded plastic product which does not cause sink marks on a visible surface according to claim 3, wherein the minute vent holes are formed of ceramics. 7. An apparatus for producing an injection-molded plastic product which does not cause sink marks on a visible surface according to claim 3, wherein the minute vent holes are formed by machining. 8. An apparatus for producing an injection-molded plastic product which does not generate sink marks on the visible surface according to claim 3, 4 or 5 or 6 or 7, wherein minute vent holes are formed in a portion where sink marks are likely to occur. 9. In an injection molding device (mold) for a plastic product that generates a sink mark, after the resin is poured into the mold, the product invisible surface side mold is retracted so that the mold surface is removed from the resin. A molding device for injection-molded plastic products that does not cause sink marks on the visible surface, characterized by being configured to forcibly peel off. 10. An injection molding apparatus (mold) for a plastic product that generates a sink, wherein the product invisible surface is configured to retract the mold only at a portion that easily induces a sink. Injection molding plastic product manufacturing equipment that does not cause sink marks. 11. In an injection molding device (mold) for a plastic product that generates a sink, a non-visible surface side mold is placed above,
An injection-molded plastic product that does not cause sink marks on the visible surface, characterized in that the visible surface side mold is positioned below and the weight of the product is set to the visible surface side to set the adhesion force on the invisible surface side to be small. Molding equipment.