JP4664643B2 - Molding method for plastic products - Google Patents

Description

  The present invention relates to a plastic product molding method, and more particularly to a plastic product molding method using an injection molding machine having a slide core.

  When the most common injection molding method is used as a molding method for plastic products, a portion called a weld is almost inevitably generated at a joining portion of resin flows. In particular, a portion of the molded product that is away from the injection gate becomes a confluence of the resin flow at a low temperature, and the weld portion clearly appears on the surface of the molded product as a line called a weld line. Since such a weld line is unavoidable in the injection molding, an idea is made to make the injection gate position inconspicuous by devising the injection gate position so that the weld line is generated in an inconspicuous position or by overheating the weld line position.

  With such a technique, the weld line can be made as inconspicuous as possible. However, even if such a process is performed, the joining of the resin flows in the vicinity of the weld line cannot be avoided. In this regard, particularly in a resin molded product having a metallic color, the resin flow direction is easily clearly recognized in appearance. For example, when light is applied to a molded product, irregular reflection of light occurs in such a weld portion, so that the weld portion of the molded product may appear to be a striped pattern, or may appear to be iridescent.

Such welds are generated by the flow of the resin flow. Therefore, the planar or curved shape, that is, the flat shape is less noticeable and less conspicuous. Therefore, in the molding of a plastic product having a projecting part called a member boss part having a hole in particular, immediately after the planar shape is once molded, the pin that forms the hole or the boss part is moved to move the pin. There is a method of forming a hole or a boss portion (for example, Patent Document 1 as a manufacturing method of a molded product having a boss portion). According to this method, it is possible to suppress the occurrence of welds that occur in the vicinity of the hole or the boss.
JP-A-7-32433

  However, even if it is a flat shape without holes or bosses, if the molded product has a corner on its outer edge, such as a box shape or a polygonal plate shape, the resin flow may merge or be disturbed at the corner portion. As a result, it appears as a weld on the surface of the molded product. For this reason, when it was made into a product, there was a problem in design.

  As a method for solving the above problem, if a large number of two-dimensional plate-shaped molded products are manufactured, a method of forming a large single plate and punching it into an appropriate size later can be considered. However, such a forming method is not suitable for forming a three-dimensional shape such as a box shape. In addition, since the number of processes is increased, it is not a practical method from the viewpoint of cost unless the same-shaped product is manufactured in large quantities.

Furthermore, as a method for producing a rectangular box-shaped molded product without a weld line, there is a molding method using an injection compression molding machine that compresses the inside of a cavity after resin melt injection (for example, Patent Document 2). However, since the initial introduction cost of the injection compression molding machine is high and the running cost is higher than that of a normal injection molding machine, application to an inexpensive molded product has not been realistic.
Japanese Utility Model Publication No. 46-9267

  In the present invention, in view of the above-mentioned present situation, as a molding method in the case where a plastic product is a molded product having a corner at an outer edge portion, an economical molding method is provided even in a small amount of production in which no weld occurs in the corner portion. Is an issue.

  As a result of intensive studies, the present inventors have determined that when molding the molded product using an injection molding machine having a slide core as a method of molding a molded product having a corner at the outer edge in the plastic product molding method, An injection molding step in which the outer edge portion is extended to provide a cut-out portion, and the cut-out portion is deleted by the movement of the slide core after the injection molding step and before or simultaneously with the removal of the molded product. The above-described problems have been solved by using a molding method having at least a process as a main means.

  In other words, the weld that originally occurs around the corner is generated in the cut-out portion provided extending from the outer edge of the molded product, and this is deleted so that no weld remains in the molded product. It is.

  According to the molding method of the present invention, it is possible to obtain a molded product having no weld with an economical method without going through a complicated process after injection molding for a molded product having a corner at the outer edge.

  The present invention will be described below with reference to the drawings, but the embodiments of the present invention are not limited to the embodiments shown in the drawings.

  The resin that can be used in the molding method of the present invention is not particularly limited as long as it is a resin that can be molded by injection molding. Among these, a thermoplastic resin can be preferably used. The molding conditions such as the melting temperature and the injection speed vary depending on properties such as the melting temperature and viscosity (number of molecules) of the resin, but known molding conditions can be used.

  In particular, the molding method of the present invention is useful when a resin contains metal flakes such as aluminum flakes or metal powder in order to produce a metallic plastic product. In this case, since the metal flakes and powders are oriented along the resin flow, the weld is more conspicuous. Further, in the case of a glossy metallic color, the influence on the appearance due to irregular reflection of light is large. For this reason, when manufacturing a metallic plastic product, it is necessary to remove not only the weld line that can be clearly recognized from the appearance, but also the influence of the weld in the vicinity thereof.

  The shape of the molded product 1 obtained by the molding method of the present invention may be a planar shape or a three-dimensional shape, but is a shape having a corner 2 at the outer edge thereof. This is because the present invention is a method for obtaining a plastic product having no influence of weld around the corner, even if the molded product 1 has corners. The corner of the outer edge referred to in the present invention refers to a portion of the outer edge that is bent at an angle (acute angle, vertical, obtuse angle) less than two right angles (180 degrees). Examples of such a shape having the corner 2 include a columnar shape having a polygonal bottom surface such as a rectangle as shown in FIG. 1 and a polygonal plate shape. In addition to the polygonal shape, for example, a shape like a star shape has a corner 2 at the outer edge. Further, considering that the movement of the slide core is usually a linear movement, the shape of the molded product having the corners of the present invention is such that at least one of both bottom surfaces or each side surface is a protrusion or depression such as a boss portion, Furthermore, a shape that does not hinder the linear movement of the slide core, such as torsion, is preferable.

(Injection molding process)
In the injection molding step of the molding method of the present invention, when the resin melt is injected from the injection gate 4 and the molded product 1 having the corner 2 at the outer edge is formed, the outer edge of the outer edge is further extended and molded. Then, the cutout portion 3 to be deleted from the molded product 1 is molded at the same time. FIG. 1 is a diagram schematically showing a state in which a molded product 1 provided with a cutout portion 3 is molded in the molding method of the present invention. The cutout portion provided by extending the outer edge portion does not necessarily need to be extended in the direction in which the outer edge is extended as it is. Rather, it is preferable to extend in the direction perpendicular to the direction of the outer edge as shown in FIG. This is because if the cutout portion is provided in such a direction, the cutout portion 3 can be easily cut by a slide core, which will be described later, and the cut portion trace of the molded product 1 after the cutout portion 3 is deleted can be easily processed.

  As shown in FIG. 1 by hatching as the weld generation portion in FIG. 1, the cutout portion 3 generates the weld that should have occurred around the corner 2 of the outer edge of the molded product 1 from the periphery of the corner 2. Part. Therefore, the cutout portion 3 is provided to extend further outward from the corner 2 portion. In other words, the position of the cut-out portion is provided further from the position of the corner 2 of the outer edge portion when viewed from the injection gate 4.

  The size and shape of the cut-out portion 3 can be appropriately determined as long as welds are generated in the cut-out portion 3 and are large enough not to affect the periphery of the corner 2 of the molded product outer edge. The size of the cutout can be determined experimentally or theoretically from the calculation of fluid dynamics.

(Cut part deletion process)
The injection molding machine used for the molding method of the present invention needs to have a slide core on which the core part moves. This is because the cutout portion 3 is deleted by moving the slide core. An injection molding machine having a slide core is a known machine. The removal of the cut-out portion 3 by the movement of the slide core is performed after molding of the molded product 1 and before mold opening or simultaneously with mold opening. By appropriately adjusting conditions such as the temperature of the molded product 1 and the moving speed of the slide core when the slide core starts to move after the type of resin, the cut portion trace of the molded product 1 can be made inconspicuous, or Processing becomes easy. FIG. 2 is a view schematically showing a state in which the slide core moves from the state of FIG. 1 and the cutout portion 3 is being deleted from the molded product 1. In the mode of FIG. 2, when the slide core moves downward, the molded product 1 also moves downward, and only the cutout portion 3 is left in the original position, so that it is deleted from the molded product 1.

  In the molded product 1 having the corner 2 at the outer edge obtained through such a process, the influence of the weld does not appear. Therefore, a plastic product that is preferable in design can be obtained. In addition, in the case of a molded product having a corner at the outer edge portion and having a boss portion and a hole together, in addition to the molding method of the present invention, the weld removal around the boss portion and the hole described in the above-mentioned conventional technology column Methods can also be used.

  The molding method of the present invention can be widely used as a method of molding a plastic product having no weld on the surface thereof.

In the shaping | molding method of this invention, it is the schematic diagram which showed a mode that the molded article which provided the cut-off part was shape | molded. In the shaping | molding method of this invention, it is the schematic diagram which showed the mode in the middle of deleting the cut part from a molded article by the movement of a slide core.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molded product 2 Corner of molded product outer edge part 3 Cut-out part 4 Weld generating part 5 Injection gate

Claims (2)

A plastic product molding method for molding a molded product having a corner at an outer edge by an injection molding machine having a slide core,
When the resin melt is injected from the center upper injection gate to form a molded product having a corner at the outer edge, the outer edge of the outer edge is positioned perpendicular to the direction of the outer edge. To extend further, to shape the cutout,
An injection molding process for generating a weld from the periphery of the corner in the cut portion ; and
After the injection molding process, before the molded product is taken out or at the same time as the molded product is taken out, the molded product is also moved by the movement of the slide core, and only the cut portion is left in the original position. A method of molding a plastic product, comprising at least a step of deleting a part. The method for molding a plastic product according to claim 1, wherein the resin melt contains metal flakes or metal powder.

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