JPS6241850B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a two-layer molded body integrally molded using a thermosetting resin for the inner body and a thermoplastic resin for the outer body. More specifically, it is possible to use a container for an electrical appliance that has a built-in blade holder spring or an electric opening/closing mechanism, or to use a container for an electrical appliance that covers an inner body with a molded blade at the same time and an elastic outer body. The present invention relates to a method for manufacturing a two-layer molded body used for containers and the like that requires dimensional stability based on rigidity and resistance to breakage based on elasticity.

The containers and bodies of the electrical appliances mentioned above are generally made of thermosetting resin because they hold or cover the conductive metal that is the live part, so heat resistance and rigidity are required. However, the thermosetting resin has no elasticity and could break or crack if dropped or stepped on. Therefore, as shown in FIGS. 1a and 1b, it has been proposed to use a two-layer molded body consisting of an inner body (A) made of a thermosetting resin and an outer body (B) made of a thermoplastic resin. C indicates the blade holder spring, and D indicates the plug blade.

Conventionally, in the production of two-layer molded bodies, due to the difference in molding temperature of both resins, the usual method is to mold an inner body made of a thermosetting resin, cool it, and then mold an outer body on the inner body. Molding is inefficient because the molding of the inner body and the molding of the outer body are not continuous, and if the molded body is bowl-shaped, it is not possible to mold it integrally with the outer body after the inner body has cooled and make them stick together. Due to the dimensional shrinkage of the outer body after molding, the adhesion between the inner body and the outer body may deteriorate, and the dimensional shrinkage of the outer body may cause distortion in the inner body, causing warpage in the entire molded body. .

This invention was made in view of the above-mentioned drawbacks, and after forming an inner body with a thermosetting resin, an outer body is formed with a thermoplastic resin having a melting point higher than the molding temperature of the thermosetting resin. By forming the outer body, it is possible to form the outer body without cooling the inner body, thereby shortening production time, and by cooling the inner and outer bodies almost simultaneously, it is possible to reduce the shrinkage of the outer body. It is an object of the present invention to provide a method for manufacturing a two-layer molded body that prevents the accompanying peeling from the inner body.

Embodiments of the present invention will be described in detail below.

FIG. 2 shows an example in which the two-layer molded product A of the present invention is used for the cover and base of a table tap. 1 is a base, 2 is a cover, and a blade receiving spring 4 is housed in a cavity 3 formed by the base 1 and the cover 2. The base 1 and cover 2 have an inner body 5 made of a thermosetting resin such as urea resin, melamine resin, or phenol resin, and a mold temperature of the thermosetting resin constituting this inner body 5 (for example, in the case of urea resin, 140℃～160
Thermoplastic resins such as polyamide resins, polyethylene terephthalate resins, polycarbonate resins (melting point of thermoplastic resins: Polyamide resin・
Approx. 215-288℃, polyethylene terephthalate resin: approx. 220℃, polycarbonate resin: approx. 230℃)
This is a two-layer molded body A in which an outer body 6 made of the following is integrally molded and tightly bonded. An undercut is provided in the inner body 5 as an engagement means 5d for solidifying the engagement between the inner body 5 and the molding die. This engaging means 5d may be of a type that makes the drawing taper of the ribs 2e, 2e, etc. zero. In order to strengthen the connection between the inner body 5 and the outer body 6, a hole 5a is provided in the inner body 5, and an enlarged portion 6a larger than the diameter of the hole 5a is formed integrally with the outer body 6 when the outer body 6 is molded. A coupling portion 7, a coupling portion 8 formed by providing a protrusion 5b on the inner body and protruding the protrusion 5b within the outer body 6, etc. may be provided. Furthermore, in order to improve the adhesion between the inner body 5 and the inner body 6, the joint surface 8 is
The surface of the inner body 5 may be textured. Furthermore, 4a
is a terminal board electrically connected to the blade holder spring 4;
b is a terminal screw. 2a and 2c are plug blade insertion ports,
2b indicates an outlet for the cord 4c. 2d is a screw that connects the base 1 and the cover 2. As shown in the figure, in this embodiment, one side of the inner body 5 is not entirely covered with the outer body 6, and the vicinity of the plug blade insertion opening 2a, the cord outlet 2b, and the end portion 5c of the inner body are not covered.

FIG. 3 shows an embodiment in which the present invention is applied to a body of a plug. The plug blades 9, 9 to which the core wires 10a, 10a of the cord 10 are connected are buried in an inner body 5 made of a thermosetting resin, and the thermosetting resin has a melting point higher than the mold temperature of the thermosetting resin on the outside of the inner body 5. A two-layer molded body A integrally molded with an outer body 6 made of a thermoplastic resin having
That is. Incidentally, reference numeral 5d denotes an engaging portion formed by a conical protrusion of the mold in order to firmly engage the inner body 5 with the mold.

FIG. 4 shows a two-layer molded body A made from a cylindrical object.

Next, a method for manufacturing this two-layer molded body A will be explained. Fig. 5 shows a turret type molding machine for producing a two-layer molded product A. By rotating a rotary plate 12 with fixed molds 11 attached to each of the four sides, injection of thermosetting resin is performed. The first movable mold 13 can be removed and thermoplastic resin can be injected at different positions. The fixed mold 11 has a sixth
As shown in Figures a and b, a protrusion 15 having a substantially rectangular cross section is provided at the center of the abutment surface 14, and a groove 16 is provided around the abutment surface 14 at the protruding base of the protrusion 15. A material reservoir 17, which is shallower and wider than the groove 16, is recessed in the external contact surface 14 of the groove 16 over substantially the entire circumference. Furthermore, a minute groove 15a is provided on the side surface of the protrusion 15 to linearize the engagement with the inner body 5. As shown in FIG. 7, a recess 19 having a larger diameter than the protrusion 15 is provided approximately at the center of the contact surface 18 of the first movable mold 13. A first cavity 20 having a substantially U-shaped cross section can be formed between the portion 15 and the recess 19. The second movable mold 21 has substantially the same shape as the first movable mold 13, and the recess 22 is similar to the recess 19.
The diameter is slightly larger than that of the recess 22 and the first
Between the inner body 5 formed in the cavity 20 and the second
A cavity 24 can be formed. Therefore, when continuously double-molding thermosetting resin and thermoplastic resin, the fixed mold 11 with the rotary disk 12 attached and the first movable mold 13 are clamped at the position A in FIG. A first cavity 20 is formed by the protrusion 15 and the recess 19, and a thermosetting resin is injected into the first cavity 20 to form the inner body 5 having a substantially U-shaped cross section. A flange-shaped burr prevention part 24 is provided around the outer lower part of the inner body 5 using a thermosetting resin. Next, the rotary disk 12 is rotated approximately 90 degrees to remove the first movable mold 13 at the position B in FIG. 1, and the laciner is projected so that the inner body 5 covers the protrusion 15 as shown in FIG. 8. , remove burrs. Next, after rotating the rotary disk 12 to the position C in FIG.
1 to form a second cavity 24 with the inner body 5, the recess 22, and the burr prevention part 23, and as shown in FIG. The outer body 6 is integrally formed so as to cover the outer body 6, and the end portion of the outer body 6 is brought into contact with the burr winding prevention part 23. Next, move the rotary disk 12 to D in Figure 5.
Rotate it to the position, remove the second movable mold 21, heat the fixed mold 11 side to harden the inner body 5, and then take out the two-layer molded body A consisting of the inner body 5 and the outer body 6. . Generally, the curing temperature of thermosetting resin is high;
For example, urea resin hardens at about 140℃ to 160℃ when the injection pressure is 250 to 300Kg/ ^cm2 , so the fixed mold 1
The temperature of No. 1 is 150°C ± 10°C, and on the other hand, many thermoplastic resins have a low melting point; for example, there is no difference between the melting point of vinyl chloride resin, styrene resin, etc. and the temperature of a thermosetting resin mold. If you try to integrally mold the inner body 5 with the outer body 6 immediately after molding the inner body 5, the mold temperature of the inner body 5 will be high, so it will not harden, and the inner body 5 will not be able to be molded in two layers with the outer body 6 until the inner body 5 is cooled. However, by constructing the outer body 6 from a thermoplastic material having a melting point higher than the thermosetting resin molding temperature as in the present invention, the inner body 5 can be molded immediately after the inner body 5 is molded. It is possible to form the outer body 6 by molding and tightly bond them together, which is efficient, and eliminates the need for operations such as once removing the inner body 5 from the mold and cooling it.

Since the inner body 5 is provided with a locking means 2e that firmly engages with the molding die, the inner body 5 is fixed to the fixed die 11.
The second movable mold 21 for molding the outer body is moved to the second movable mold 21 for molding the outer body while the second movable mold 21 is placed between the inner body 5 and the second movable mold 21.
Even when the cavity 24 is formed and molded, the inner body 5 can be molded without moving due to injection pressure. In addition, a second movable mold 21 for molding the outer body
The temperature is approximately 90°C for polyamide resin.

Also, any molding material undergoes dimensional shrinkage when cooled after molding. Therefore, when the outer body 6 is formed integrally with the inner body 5 by molding and closely joined after the inner body 5 is cooled, the inner body 5 shrinks in size after almost all of it shrinks, and then the outer body 6 shrinks in size, so that the inner body 5 and the outer body 5 shrink in size. The adhesion of the body 6 may deteriorate and the outer body 6 may peel off from the inner body 5.
In order to prevent this, if a means for firmly connecting the inner body 5 and the outer body 6, such as a connecting portion 7, is provided, there is a risk that warping may occur due to the force bending the inner body 5 in the direction of the outer body 6.

However, with the configuration of the present application, the outer body 6 can be integrally formed by molding immediately after the inner body 5 is molded, and the outer body 6 can be tightly joined. Furthermore, the inner body 5 and the outer body 6 simultaneously shrink in size, so that the above-mentioned problem can be avoided. There is no risk of distortion, the adhesion between the inner body 5 and the outer body 6 is increased, and warpage does not occur.

Furthermore, if a melamine resin is used as the thermosetting resin and a polyamide resin is used as the thermoplastic resin, the shrinkage rates of both materials are similar, so that the effect is even more effective. The molding shrinkage rate of melamine resin is 0.6-1.5%, and that of polyamide resin is 0.9%-1.5%. By adding inorganic fillers such as calcium carbonate, alumina, diatomaceous earth, etc. to this polyamide resin, the molding shrinkage rate can be reduced, and by adjusting the amount added, the molding shrinkage rate of melamine resin can be reduced. Since it is possible to make them almost the same, the adhesion between the inner body 5 and the outer body 6 becomes even better.

And if the product is being used in the atmosphere, the inner body 5
Even when the outer body 6 absorbs heat and dimensional changes occur, the dimensional change rates of the melamine resin and the polyamide resin are close to each other as shown in FIG. 10, and are the most appropriate combination.

Figure 10 shows test pieces of urea resin, melamine resin, and polyamide resin left in an atmosphere with a temperature of 40°C and humidity of 90%, and weight changes and dimensional changes are measured at 24-hour intervals for up to 168 hours and graphed. This is the value.

As described above, the present invention involves injection molding thermosetting resin into the first cavity formed by the fixed mold and the first movable mold to form the inner body, and then removing the first movable mold and then removing the first movable mold. After attaching the second movable mold to the fixed mold and forming a second cavity with the second movable mold and the inner body, the temperature of the thermosetting resin constituting the inner body is lowered to the second cavity. The inner and outer bodies are integrally molded by injection molding the outer body by injecting a thermoplastic resin that has a high melting point and a shrinkage rate similar to that of the thermosetting resin. After forming the inner body with thermosetting resin, the outer body is formed with thermoplastic resin having a melting point higher than the mold temperature of the thermosetting resin, so the outer body can be formed without cooling the inner body immediately after forming the inner body. As a result, it has the advantage that the time required to produce a two-layer molded body is shortened.
That is, there is no need to temporarily remove the inner body from the mold and cool it. In addition, if the outer body is formed after cooling the inner body, the outer body will peel off from the inner body as the outer body contracts, but the inner body and the outer body are made of materials with similar shrinkage rates. Moreover, since the outer body can be formed without cooling the inner body, there is an advantage that the outer body does not separate from the inner body.

[Brief explanation of the drawing]

FIGS. 1A and 1B are sectional views showing a conventional example of the two-layer molded article of the present invention and its manufacturing method. Figures 2 to 4
The figure shows a two-layer molded body formed by the manufacturing method of the present invention, and FIG. 2 is a diagram showing an example, FIG. 2 a is a side view, and FIG. 2 b is a plan view with the cover partially cut away. , FIG. 2c is a side view partially showing the cover and base in cross section, and FIG. 2d is a partially enlarged view showing the combined state of the cover and the base. FIG. 3 shows a sectional view of another example, and FIG. 4 shows a perspective view of still another example. 5 to 10 are diagrams showing the manufacturing method, in which FIG. 5 is a schematic explanatory diagram of a molding machine for manufacturing the two-layer molded body A, FIG. 6a is a perspective view of the same fixed mold,
Fig. 6b is a sectional view taken along the line X-X in Fig. 6a, Fig. 7 is a perspective view of the first movable mold as above, Fig. 8 is a perspective view of the inner body 5 as above, and Fig. 9 is a perspective view of the same as above. A side cross-sectional view when the outer body 6 is molded is shown. FIG. 10 is a graph showing dimensional changes of urea resin, melamine resin, and polyamide resin due to water absorption. 5...Inner body, 6...Outer body, 5d...Engagement part, 1
1... fixed mold, 13... first moving mold, 20...
...First cavity, 21...Second moving mold, 2
4... Indicates the second cavity.

Claims (1)

[Claims] 1 After forming the inner body by injection molding a thermosetting resin into the first cavity formed by the fixed mold and the first movable mold, the first movable mold is removed, and then the second movable mold is replaced by the fixed mold. After being attached to the mold and forming a second cavity with the second movable mold and the inner body, a thermosetting resin having a melting point higher than the mold temperature of the thermosetting resin constituting the inner body, and A method for manufacturing a two-layer molded body, comprising integrally molding an inner body and an outer body by injection molding an outer body by injecting a thermoplastic resin having a shrinkage rate comparable to that of the thermosetting resin.