JPH0483619A - Injection mold structure of push button panel of thermoplastic elastomer - Google Patents

Abstract

PURPOSE:To eliminate defective molding by removing effectively air or gas, by a method wherein a protrusion is formed on a core piece of a corresponding part of the central part of the back of a key top and a cavity piece of an end part of a curved surface formed on the fringe of the top of the key top is made into a split mold. CONSTITUTION:A cavity 7 to obtain a push button panel molded product is formed of a cavity piece 5 and core piece 6. A curved surface 9 is formed on the fringe of the top 8c' of a key top within the cavity 7 of the cavity piece 5 and the cavity piece 5 on the final end part of the radiused surface 9 is made into cavity pieces 5a, 5b which are in a split mold structure. The title structure is constituted so that only air or generated gas of plastic which is compressed in an adiabatic state is liberated through a boundary surface. A gate 13 is formed on a core piece 6 position on a part corresponding to the central part of the back of the thick key top 8c. A protrusion 15 is formed on the core piece 6 of a part corresponding to the central part of the back of the key top 8c so that a recessed part 14 for liberation of sinks or gate flashes are formed in a gate 13 position to be formed in the core piece 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a mold structure used when injection molding a push button panel using a thermoplastic elastomer.

[Prior Art] It is generally known that thermoplastic elastomers have rubber-like elasticity at room temperature, are plasticized at high temperatures, and become the core of the thermoplastic.

Conventional push button panels made of various types of rubber such as silicone rubber have a plate-shaped base, a thin skirt that bulges out from the base, and a thick skirt that is supported at the top of the skirt and has a conductive contact on the back side. It is obtained by integrally molding the key top.

[Problems to be Solved by the Invention] However, since the rubber push button panel is molded by heat vulcanization, there are drawbacks in that the molding time is long and productivity is low.

Therefore, when injection molding is performed using a thermoplastic elastomer with properties similar to rubber, the mold cavity is rapidly filled with molten plastic, creating a gas vent around the top surface of the key top inside the mold cavity, resulting in insulation. The compressed air causes burns on the molded product, and the gas generated from the plastic causes problems similar to those caused by air, resulting in molding defects. In addition, when molding a gate with the gate located at the center of the back of a thick key top, sink marks and gate burrs may occur at the gate marks on the molded product, so conductive contacts should be formed on the back of the key top by means such as printing or gluing. In some cases, uneven sink marks and protruding gate burrs get in the way, which not only makes it difficult to form conductive contacts, but also causes the contacts to malfunction when turning on and off after the contacts are formed. . Furthermore, the thin skirt section causes clicks (buckling) when pressing the key top for on/off operation, but the load for pressing the key top can be adjusted by adjusting the thickness of the skirt section. Therefore, each time the load is adjusted according to the user's wishes, an expensive mold must be remade in order to form the skirt portion to a thickness corresponding to the load. Furthermore, since the skirt part has a thin wall structure, when the molten plastic fills the base part from the key top part of the cavity through the skirt part, the molten resin in the skirt part solidifies quickly and is located on the base side of the skirt part. There was a drawback that cracks were generated due to gas accumulation in the upper part of the thick base part.

The present invention has been made in view of the above-mentioned points, and its purpose is to prevent the periphery of the top surface of a key top in the cavity of a mold used when injection molding is performed using a thermoplastic elastomer with properties close to rubber. The gate of the molded product is used to prevent molded products from burning due to residual air and gas generated in the key top, and to effectively remove the air and gas to eliminate molding defects. In addition to eliminating the influence of sink marks and gate burrs that form on the base part, the key load can be adjusted appropriately according to the user's wishes with just one mold without having to make a new expensive mold. An object of the present invention is to provide an injection mold structure for a push button panel made of thermoplastic elastomer, which prevents cracks from occurring due to gas accumulation in the upper part of the push button panel.

[Means for Solving the Problems] The injection mold structure of the push button panel made of thermoplastic elastomer according to the present invention is such that a cavity piece is formed on the movable side template, a core piece is formed on the fixed side template, and the key top The gate formed on the core piece corresponding to the center part of the back surface has a protrusion formed on the core piece corresponding to the center part of the back surface of the key top, and is formed on the periphery of the top surface of the key top so that a recess for sink mark relief and gate burr escape can be obtained. The cavity piece at the end of the rounded surface is formed into a split mold.

In addition, a cavity piece is formed on the movable side template, and a core piece is formed on the fixed side template, and the gate formed on the core piece at the central part of the back surface of the key top is designed so that a recess for sink mark relief and gate burr relief can be obtained. A protrusion is formed on the core piece corresponding to the central part of the back surface of the key top, and the cavity piece at the end of the rounded surface formed on the periphery of the top surface of the key top is formed into a split shape, and the bottom periphery of the key top and the base part are formed with a protrusion. An injection mold for a push button panel made of thermoplastic elastomer, in which a gap is formed between the back surface of the cavity piece and the movable side template, and a spacer is provided in the gap so that the thickness of the skirt portion formed therebetween can be adjusted appropriately. It is a structure.

Furthermore, the skirt part formed between the lower periphery of the key top and the base part has a push button panel injection mold structure made of thermoplastic elastomer with a cavity piece protruding from the bottom part of the base part. It is something.

[Operation] Molten plastic is rapidly filled from the gate formed in the core piece at the center of the back surface of the key top toward the key top part of the mold cavity, and the molten plastic is filled into the top surface of the key top inside the mold cavity. Air or gas flows along the rounded surface of the peripheral edge and escapes from the split mold surface at the end of the rounded surface. In addition, after the molten plastic made from thermoplastic elastomer fills the key top part in the cavity, the molten plastic flows through the skirt part and from the bottom of the base part, so there is no chance of cracks occurring due to gas accumulation in this part. , a good molded product can be obtained.

[Example] Hereinafter, an example of the present invention will be specifically described based on the drawings.

As mentioned above, the thermoplastic elastomer used in the present invention has rubber elasticity at room temperature, is plasticized at high temperature, and has the properties of a thermoplastic. In this thermoplastic elastomer, the part exhibiting rubber elasticity is called the soft phase, and the restrained part is called the hard phase. For example, in polystyrene systems the soft phase is polybutadiene, polyisoprene or polyolefin and the hard phase is polystyrene. In polyolefin systems, the soft phase is EPDM or EPM and the hard phase is polypropylene. In polyurethane systems, the soft phase is polyether or polyester and the hard phase is a urethane structure. In polyester systems, the soft phase is polyether and the hard phase is polyester. In polyamide systems, the soft phase is polyester or polyether and the hard phase is polyamide. In fluororesin systems, the soft phase is fluororubber and the hard phase is fluororesin. In any case, any thermoplastic elastomer having the above properties and used for injection molding may be used.

Reference numeral 1 designates a movable template plate, which is attached to a mounting plate 2 via a spacer block 3. Reference numeral 4 denotes an ejector pin for ejecting the product, which is provided so as to penetrate through the movable mold plate 1. Reference numeral 5 denotes a cavity piece formed in a nested structure on the movable template 1. This cavity piece 5 and a core piece 6, which will be described later, form a cavity 7 for obtaining a push button panel molded product. The push button panel includes a plate-shaped base portion 8a and the base portion 8.
A thin skirt portion 8b that bulges out and rises from a, and a thick key top 8 that is supported by the upper part of the skirt portion 8b.
It is composed of c. Cavity 7 of cavity piece 5
A rounded surface 9 is formed on the periphery of the inner key top top surface 8c',
The cavity pieces 5 at the end portions of the rounded surface 9 are formed into cavity pieces 5a and 5b having a split structure. Only adiabatic compressed air and gas generated from plastic are allowed to escape from the interface between the split cavity pieces 5a and 5b.

Reference numeral 10 denotes a fixed side template, which is attached to a mounting plate 11 via a stripper plate 12.

13 is a core piece formed in a nested structure on the stationary template 10. A gate 13 is formed at the position of the core piece 6 at a portion corresponding to the center of the back surface of the thick key top 8c.

By forming the gate 13 at the center of the thick wall, molten plastic flows in a well-balanced manner from the thick key top 8c to the thin skirt portion 8b, thereby preventing sink marks and the like. The position of the gate 13 formed on the core piece 6 is such that a protrusion 15 is formed on the core piece 6 at a position corresponding to the center of the back surface of the key top 8c so that a recess 14 for sink mark relief and gate burr relief is obtained. The depth of the sink mark relief and gate burr relief recess 14 is such that the sink mark and gate burr 16 do not protrude from the back surface 80'' of the key top forming a conductive contact (not shown) (see FIG. 3(a)); As shown in FIG. 3(b), a recess 14 for sink mark relief and gate burr relief.
If the depth of the gate burr 16 is shallow, as shown in Figure 3(c),
protrudes from the back surface 80'' of the key top, and the conductive contact 19 formed on the back surface 80'' is no longer flat, resulting in a protruding shape, causing problems such as malfunctions when the contacts are turned on and off.

FIG. 2 shows a mold structure in which the thickness of the skirt portion can be adjusted as appropriate.

As shown in FIG. 5, the relationship between the stroke and the variation in the load that presses the key top 8c is a curve that is bent in the middle, and this bending point is the location where the so-called click movement of the base portion 8a is performed. The load can be changed to a desired load by appropriately changing the wall thickness of the base portion 8a.6 Normally, the load can be changed by changing the wall thickness of the base portion 8a from several microns to several tens of microns. Therefore, in order to appropriately adjust the thickness of the skirt portion 8b formed between the lower peripheral edge of the key top 8c and the base portion 8a, the distance between the back surface of the cavity piece 5 and the movable template 1 is from several microns to several tens of microns. A gap 17 with a thickness of about microns is provided, and one or more spacers 18 made of a heat-resistant material such as phosphor bronze are provided in the gap 17 in a laminated manner so that a load according to the user's wishes can be obtained. Adjust the thickness of the skirt portion 8b.

FIG. 4 is a sectional view showing the base of the skirt portion rising from the lower peripheral edge of the base portion.

As shown in FIG. 4, in order to form the skirt portion 8b, the cavity piece 5 is formed so that the base portion of the skirt portion 8b stands up from the lower peripheral edge of the base portion 8a. This eliminates the occurrence of cracks due to gas accumulation when molten plastic flows from the thick key top 80 portion in the cavity 7 to the thin skirt portion 8b.

[Effects of the Invention] As can be seen from the above description, the gate formed on the core piece at the central portion of the back surface of the key top is formed in a portion corresponding to the central portion of the back surface of the key top so that a recess for sink mark relief and gate burr relief can be obtained. A protrusion is formed on the core piece, and the cavity piece at the end of the rounded surface formed on the periphery of the top surface of the key top is formed into a split mold. Only the residual air and generated gas at the periphery of the top surface of the key top inside the cavity of the mold used for the mold escapes from the split mold part of the cavity piece, so that the periphery of the top surface of the key top is not burned and molding defects are avoided. It disappears. In addition, in the gate part, a protrusion is formed on the core piece at a portion corresponding to the central part of the back surface of the key top so that a recess for sink mark relief and gate burr escape can be obtained, so that sink marks and gate burrs can sink into the recess, so that the key top When forming conductive contacts on the back side, there is no effect of sink marks or gate burrs that form on the gate part of the molded product, and malfunctions are eliminated when the contacts turn on and off.

Furthermore, the present invention provides a gap between the back surface of the cavity piece and the movable side template so that the thickness of the skirt formed between the lower periphery of the key top and the base part can be adjusted appropriately, and a spacer is provided in the gap. Therefore, when adjusting the load according to the user's wishes, the thickness of the skirt can be easily changed by simply adjusting the thickness of the spacer without having to remake an expensive mold, and it can be manufactured at low cost. Become.

In addition, the skirt part formed between the lower periphery of the key top and the base part has a protruding cavity piece with its base raised from the lower periphery of the base part, so that molten plastic does not flow into the cavity as in the conventional case. When the base is filled from the key top through the skirt, the molten resin in the skirt solidifies quickly, causing cracks to form in the upper part of the thick base located at the base of the skirt due to gas accumulation. All defects are eliminated at once, and a good molded product without cracks can be obtained.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of a mold showing an embodiment of the present invention, Figure 2 is a structural diagram of a mold in which the thickness of the skirt portion can be adjusted as appropriate, and Figure 3 (a) is the main part of a push button panel. Cross-sectional view, Figure 3 (
b) is a sectional view of the main part showing an example of bad molding of a push button panel, 3rd
Figure (c) is a schematic diagram showing an example of poor molding in which the gate burr protrudes from the back surface of the key top, Figure 4 is a cross-sectional view of the base of the skirt part raised from the lower periphery of the base part, and Figure 5 is a key top burr. FIG. 3 is a diagram showing the relationship between stroke and load fluctuations that push the top. 1... Movable side template, 5... Cavity piece, 5a, 5b... Split cavity piece, 6...
... Core piece, 7 ... Cavity, 8a ... Base part, 8b ... Skirt part, C ... Key top, 9 ... ...Round surface, 0...Fixed side template, 13...
Gate, 4... Concavity for sink mark escape and gate burr escape, 5... Projection, 17... Gap, 8... Spacer. Figure 5 Stroke

Claims (3)

[Claims] (1) A cavity piece is formed on the movable side template, and a core piece is formed on the fixed side template, and the gate formed on the core piece at the central part of the back surface of the key top has a recess for sink mark relief and gate burr relief. Made of thermoplastic elastomer, characterized in that a protrusion is formed on the core piece corresponding to the central part of the back surface of the key top, and a cavity piece at the end of the rounded surface formed on the periphery of the top surface of the key top is formed into a split mold. Injection mold structure of push button panel. (2) A cavity piece is formed on the movable side template, and a core piece is formed on the stationary side template, and the gate formed on the core piece at the central part of the back surface of the key top has a concave part for sink mark relief and gate burr relief. A protrusion is formed on the core piece corresponding to the central part of the back surface of the key top, and a cavity piece at the end of the rounded surface formed on the periphery of the top surface of the key top is formed into a split mold, and the lower periphery of the key top and the base part are formed. A push button panel made of thermoplastic elastomer, characterized in that a gap is provided between the back surface of the cavity piece and the movable side template, and a spacer is provided in the gap so that the thickness of the skirt portion formed therebetween can be adjusted appropriately. injection mold structure. (3) The skirt portion formed between the lower periphery of the key top and the base portion has a cavity piece protrudingly formed such that the base portion thereof rises from the lower periphery of the base portion. Injection mold structure for push button panels made of thermoplastic elastomer.