JPH06315955A - Method and apparatus for injection molding without causing visible sink mark on product - Google Patents

Abstract

PURPOSE:To control the sink-developing site to the invisible surface side of a product so as to make a molded article look more attractive by a method wherein injection molding is carried out with molds, in which the adhesion between the surface of the product visible surface side mold contacting with resin and the resin is to be higher than the adhesion between the surface of the product invisible surface side mold contacting with the resin. CONSTITUTION:On an injection-mold 1 consisting of a product invisible surface side core 2 and a product visible surface side cavity 3, the recessed part 4 corresponding to the external shape of an injection-molded article (a) is formed on the core 2 and the cavity 3. The plastic molded article (a) is formed by flowing molten plastic through a sprue 5 in the recessed part 4. In this case, on the cavity 3 (or a recessed part 4) on the side facing to the visible part (e) of the molded article, rough surface 6 is produced so as to enhance the adhesion between the recessed part and the resin. Thus, the releasing of a product is made easier at the invisible surface side than at the visible surface side. During the releasing, the visible surface side product surface is cooled through the molds, while, on the invisible surface side, the releasing brings heat insulated condition, resulting in developing sing through the retardation of the solidification of the invisible surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a thermoplastic resin as a material, and controls the location of sink marks by using an injection molding die surface-treated to enhance the chemical or physical adhesion with the material resin. TECHNICAL FIELD The present invention relates to a method for manufacturing an injection-molded plastic product and a device (mold) for the same that do not cause sink marks on the visible surface.

[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 with shrinkage. Because it does. In particular, the cavity side, which is the product visible part of plastic products, is flat against the core side that has complicated structures such as bosses and ribs, and mold release is faster than the core side that is the product invisible part because it is easy to cool. After that, it causes post-contraction and 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 cope with the complicated product shape because the core side boss hole needs to be machined around, and the period during which filling is possible is limited even in the case of post-filling. However, there is a problem in 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 does not require complicated processing of a molding die and can control the position of occurrence of a sink mark on the visible surface regardless of the product shape. An object of the present invention is to provide a method of manufacturing a molded plastic product and an apparatus thereof.

[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. During injection molding of plastic products that generate sink marks, a mold that sets the adhesive force with the resin on the mold surface on the visible surface side of the product to be higher than the adhesive force on the mold surface on the invisible surface side A method for producing an injection-molded plastic product, characterized by controlling the occurrence of sink marks on the invisible side by performing injection molding using the same.

2. Product This is an apparatus for manufacturing injection-molded plastic products that does not cause sink marks on the visible surface, by setting the adhesive force on the surface of the visible surface side mold to be higher than the adhesive force on the surface of the invisible surface side mold.

As a method for increasing the adhesion between the resin surface on the visible surface side of the product and the resin, physical methods such as sandblasting and sandpaper are used to mechanically make the surface of the die uneven, and chemicals such as etching are used. It is possible to employ a method of making unevenness on the surface of the mold by a general corrosive action, a method of expecting an anchor effect or the like. As the chemical method, a method such as plating in which the same kind of resin as that used in the molded product or finely dispersed resin fine powder, modification of the mold surface, coating, coating, film sticking and the like can be adopted.

The treatment for improving the adhesion does not necessarily have to be applied to the entire surface of the mold on the visible surface side of the product, and can be applied only to the portion where sink marks are likely to occur in terms of suppressing sink marks.

Sandblast and sandpaper are
Etching is a well-known means used for finish processing of a mold or the like after fabrication processing, but none of them is used for the purpose of controlling sink marks.

Resins to which the present invention can be applied include not only general-purpose resins such as polyolefin resins, polystyrene resins and ABS resins and industrial resins such as polycarbonate resins and polyamide resins, but also resins containing various resins and reinforcing agents. It may be a mixture, and there is no particular limitation.

[0015]

[Function] In the resin and the mold, by increasing the adhesion force of the surface of the product visible surface side mold that causes sink marks, the product is more visible on the invisible surface side than on the invisible surface side. It becomes difficult to release the mold.During this, the visible surface side product surface is cooled through the mold, while the non-visible surface side is released and insulated, so the surface does not solidify and is greatly affected by shrinkage. The sink mark develops. 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.

[0016]

Embodiments 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. A recess 4 corresponding to the outer shape of the injection molded product a is formed in the core 2 and the cavity 3, and a molten plastic is injected from a non-illustrated injection molding machine through a sprue 5 provided at a predetermined position of the cavity 3. Is poured into the concave portion 4 to mold the plastic molded product a. The 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 are present is the core 2, and the plastic molded product visible portion e is shown in FIG.
As described above, it is in contact with the uneven surface 6 of the cavity 3 having unevenness in order to enhance the adhesion with the resin.

Next, the above embodiment will be described more specifically.

The apparatus of FIG. 1 and polystyrene (HH501,
(Showa Denko) and has a boss with an outer diameter of φ15 mm, an inner diameter of φ6 mm, a height of 10 mm, and a rib with a thickness of 6 mm and a height of 20 mm on the back surface of the product with a cross-sectional structure as shown in FIG.
A plate-like product having a product size of 150 × 200 mm and a wall thickness of 2.5 mm was molded.

As a treatment for increasing the adhesiveness between the resin and the surface of the cavity 3, the surface of the cavity 3 in contact with the visible portion of the product was mechanically roughened to about 1 to 2 μm.

As shown in FIG. 3, no sink mark was generated in the visible part e of the obtained plastic molded product, and a sink mark f was generated on the back surface of the molded product.

"Comparative Example" As shown in FIG. 1, molding was carried out under the same conditions as in the above-mentioned Example except that the uneven surface 6 portion of the cavity 3 was not treated. As shown in FIG. 4, the product had a sink mark f on the visible part e of the plastic molded product and no sink mark on the non-visible surface d of the molded product, contrary to the embodiment.

In addition to the treatment for enhancing the physical adhesion between the resin and the mold as described above, as a method for enhancing the chemical adhesion, a polystyrene or acrylic rubber thin film is applied to the cavity surface under the same conditions. The same result as that of the example was obtained even when it was molded. Therefore, the means for increasing the adhesion in the present invention is not particularly limited.

[0024]

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 cross-sectional view showing an example of an injection molding die according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a cavity side surface.

FIG. 3 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 embodiment of the present invention.

FIG. 4 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.

[Explanation of symbols]

 1 Mold 2 Core 3 Cavity 4 Recess 5 Sprue 6 Uneven Surface a Plastic Molded Product b Boss c Rib d Plastic Molded Product Invisible Surface e Plastic Molded Product Visible Surface f Marked Place

Claims (6)

[Claims] 1. Adhesion between a resin and the resin on the surface of the visible surface side of the product that comes into contact with the resin is set to be higher than the adhesion of the surface of the invisible surface side mold during injection molding of a plastic product that causes a sink mark. By performing injection molding using a mold,
A method for manufacturing injection-molded plastic products that controls the occurrence of sink marks on the non-visible side of the product and does not cause sink marks on the visible side of the product. 2. The injection molding is carried out using a mold in which the adhesive force of only the portion that easily induces sink marks is set higher than the adhesive force of the invisible surface side mold surface on the product visible surface side mold surface. Item 1. A method for producing an injection-molded plastic product which does not cause sink marks on the visible surface. 3. An apparatus for producing an injection-molded plastic product, which does not cause sink marks on the visible surface, in which the adhesive force on the surface of the product visible surface side mold is set higher than the adhesive force on the surface of the invisible surface side mold. 4. An apparatus for producing an injection-molded plastic product which does not cause a sink mark on a visible surface according to claim 3, wherein the adhesive force only on a portion that easily induces a sink mark is set to be higher than the adhesive force on the surface of the die on the invisible surface side. . 5. The sink mark does not occur on the visible surface according to claim 3 or 4, wherein fine undulations are formed on the surface of the mold on the visible surface side of the product by a method such as blasting or etching as means for increasing the adhesion. Equipment for manufacturing injection-molded plastic products. 6. The surface of the product visible surface side mold is treated by resin dispersion plating, various surface modifications, coating, coating, film sticking and the like as means for enhancing the adhesion.
Alternatively, the apparatus for manufacturing an injection-molded plastic product according to 4, which does not cause sink marks on the visible surface.