JP2006112014A - Cap part for safety helmet that is made of reinforcing fiber-including thermoplastic resin and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cap part for a safety helmet that is made of reinforcing fibers (for example, glass fibers)-including thermoplastic resin and a method for producing the same. <P>SOLUTION: This is a cap part for a safety helmet that is made of a thermoplastic resin reinforced with fibers and is equipped with a thick convex part 15 on the part corresponding to the gate 25, when the cap part 13 is formed by injection, and the skin layer covering the fibers are arranged on the surface of this thick convex part 15. In this production method, the fiber-reinforced thermoplastic resin is injected from the gate 25 set to the hot runner mold 17 into the cavity 23 formed between the male mold 19 and the female mold 21 in the hot runner mold 17 and the gate 25 is closed with the valve pin 47 set on the hot runner mold 17. Then, a skin layer is formed on the contacting part between the top end face of the valve pin 47 and the fiber-reinforced thermoplastic resin and the skin layer is cooled down until the skin layer peels off from the valve pin 47, then the male mold 19 and the female mold 21 are released and the cap part 13 is taken out from the cavity 23. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a cap body of a safety cap such as an industrial safety cap and a method for manufacturing the same, and more particularly, to a safety cap molded by a fiber reinforced thermoplastic resin containing a reinforcing fiber such as a glass fiber. The present invention relates to a cap body and a manufacturing method thereof.

  Conventionally, a cap body of a safety cap having a configuration in which a reinforcing fiber such as glass fiber is included in a thermosetting resin is manufactured as follows. That is, a mold in which a surface is previously formed in a shape corresponding to the shape of the cap body is used, and air is sucked from minute suction holes provided on the surface of the mold, and reinforcing fibers are dispersed on the surface of the mold. Then, the reinforcing fibers are sucked and laminated on the surface of the mold, and the reinforcing fibers are preformed into a shape corresponding to the shape of the cap body.

  Thereafter, the preformed reinforcing fibers are set in a cavity in a compression molding die, and a thermosetting resin is supplied as a molding material in the cavity, and the molding material in the die is heated and pressed to perform compression molding. As a result, the cap body including the reinforcing fiber is manufactured.

  As described above, when a cap body including reinforcing fibers such as glass fibers is manufactured by a compression molding method, a large number of minute bubbles are included in the resin. Since the effective thickness required for insulation is reduced by the amount of the bubbles, there is a problem that the withstand voltage is inferior and the standards of the Ministry of Labor Notification No. 3 disconnection protection device etc. are rejected.

In view of this, there has been proposed a cap body for a safety cap that includes a reinforcing fiber such as glass fiber and has improved withstand voltage performance and a method for manufacturing the same. (For example, Patent Document 1)
JP 2003-105620 A

  The manufacturing method of the cap body of the said patent document 1 manufactures the thermoplastic resin containing glass fiber by injection molding. FIG. 4 shows a schematic diagram of the manufacturing method disclosed in Patent Document 1. In FIG. That is, when a thermoplastic resin containing glass fibers is injection-molded from a sprue gate (direct gate) 9 into a cavity 7 formed between the male mold 3 and the female mold 5 in the molding die 1, FIG. As shown, the cap body 13 provided with the sprue 11 is molded.

  When a molten thermoplastic resin containing glass fibers is poured into the cavity 7, the glass fibers tend to be aligned in the flow direction. Accordingly, the glass fibers tend to be aligned in a state substantially parallel to the longitudinal direction of the sprue 11 in the sprue 11 portion. As described above, in the configuration in which the sprue 11 is provided in a part of the cap body 13, the sprue 11 needs to be cut.

  As described above, when the cap body 13 is set in the water of a withstand voltage test container in order to perform a withstand voltage test in a state where the sprue 11 is simply cut, an end portion of the glass fiber is obtained by cutting the sprue 11. May be exposed on the surface, and water may enter the cap body 13 due to capillary action or the like of the glass fiber portion. Thus, if even a small amount of water enters the cap body 13, there is a problem that the insulation against high voltage during the withstand voltage test is lowered, the probability of passing the withstand voltage test is lowered, and the yield is deteriorated.

  Therefore, in the past, it is necessary to prevent the capillary phenomenon from occurring by cutting the sprue 11 as well as applying an adhesive, molten resin, paint, or the like to the cut surface. That is, there is a problem that after the cap body 13 is injection-molded, gate processing (processing such as cutting of a sprue and application of an adhesive or the like to the cut surface) is necessary. Further, even when an adhesive or the like is applied to the cut surface of the sprue 11 as described above, a crack may occur due to an impact or the adhesive may be peeled off in a long time. There's a problem.

  The present invention has been made in view of the conventional problems as described above, and is a cap body of a safety cap manufactured from a fiber-reinforced thermoplastic resin, and a portion corresponding to a gate when the cap body is injection-molded. A thick convex portion is provided, and a skin layer covering the fibers is provided on the surface of the thick convex portion.

  A method of manufacturing a cap body of a safety cap using a fiber reinforced thermoplastic resin, wherein a gate provided in the hot runner mold is provided in a cavity provided between a male mold and a female mold in the hot runner mold. After injecting the fiber reinforced thermoplastic resin from and closing the gate with a valve pin provided in the hot runner mold, a skin layer is formed on the contact portion between the tip surface of the valve pin and the fiber reinforced thermoplastic resin. Then, after the skin layer is cooled and solidified to such an extent that the valve pin and the skin layer are peeled, the male mold and the female mold are separated, and the cap body is taken out from the cavity.

  According to the present invention, the portion corresponding to the gate when the cap body of the safety cap is injection-molded is provided with a convex thick portion, and the skin layer that covers the fiber is provided on the surface of the thick portion. Therefore, the end portion of the fiber does not appear on the surface, the capillary phenomenon of the fiber portion can be prevented, and the withstand voltage can be improved.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Components having the same functions as those of the conventional technology described above are denoted by the same reference numerals, and redundant description is omitted.

  Referring to FIG. 1, a cap body 13 of a safety cap according to an embodiment of the present invention has the same shape as a conventional general cap body. The cap body 13 is formed by injection-molding a fiber reinforced thermoplastic resin including appropriate reinforcing fibers such as glass fiber in a thermoplastic resin, and the cap body 13 is injection-molded. A thick convex portion 15 is provided at a portion corresponding to the gate in the injection molding die.

  As already understood, since the cap body 13 is formed by injection molding with a fiber reinforced thermoplastic resin, the cap body 13 is reinforced so as to be substantially aligned in the resin flow direction during the injection molding. Fibers are included, and the thick convex portions 15 also include reinforcing fibers. However, a skin layer covering the reinforcing fiber is formed on the surface of the convex portion 15, and the reinforcing fiber is not exposed on the surface of the convex portion 15.

  As the fiber reinforced thermoplastic resin, as described in Patent Document 1, for example, an appropriate thermoplastic resin such as polyolefin, polyamide, polystyrene, acrylic resin, ABS resin, polyester, polycarbonate, and thermoplastic polyurethane can be used. As an example of the reinforcing fiber, an appropriate amount of glass fiber may be included.

  However, as a fiber reinforced thermoplastic resin, the glass fiber content rate with respect to the said thermoplastic resin is 10-70 mass%, Preferably 15-50 mass% is desirable. The fiber length used for molding is 50 mm at maximum, preferably 25 mm, more preferably 15 mm. Further, the mass average fiber length is 0.6 mm or more, preferably 2 mm or more. In addition, since the calculation method of the mass mean fiber length of glass fiber is described in the said patent document 1, since it is well-known, description is abbreviate | omitted.

  An injection mold 17 for injection-molding the cap body 13 is a hot runner mold and includes a male mold 19 and a female mold 21 as shown in FIG. A cavity 23 for injection-molding the cap body 13 is formed between the female mold 21 and the female mold 21. In order to inject the fiber reinforced thermoplastic resin into the cavity 23, a gate 25 is formed on one of the male mold 19 and the female mold 21 as appropriate.

  By the way, whether the gate 25 for injecting the resin into the cavity 23 is provided on the male die 19 side or the female die 21 side is merely a design matter. 25 is provided on the male mold 19 side.

  More specifically, a hot nozzle 27 is embedded in the male mold 19. The resin flow part 29 in the hot nozzle 27 is formed so that the molten resin does not stay inside. That is, the connecting portion between the resin flow portion 29 and the sprue portion 31 communicating with the gate 25 is formed in a tapered shape with the sprue portion 31 gradually becoming smaller in diameter. A heater 33 is provided around the hot nozzle 27 in order to control the molten resin in the resin flow section 29 to an appropriate temperature. Between the heater 33 and the male mold 19, a heat insulating portion 34 for suppressing heat transfer from the heater 33 to the male mold 19 is provided. As a structure of this heat insulation part 34, it can be set as the structure of space (heat insulation space) and the structure which heat-insulated the interior.

  A mold mounting plate 35 provided integrally with the male mold 19 is provided with a sprue bush 39 having a spherical recess 37 that can be engaged with and disengaged from a nozzle provided in an injection molding machine (not shown). The plate 35 is provided with a locate ring 41. The concave portion 37 provided in the sprue bush 39 and the resin flow portion 29 are communicated by a communication passage 42 provided in the sprue bush 39 and the hot nozzle 27.

  The die mounting plate 35 is formed with an annular fluid pressure cylinder 43 surrounding the sprue bush 39, and a piston 45 is fitted in the fluid pressure cylinder 43 so as to be capable of reciprocating. The piston 45 is integrally attached with a base end portion of a valve pin 47 that can be opened and closed with a tip portion of the sprue portion 31 of the hot nozzle 27. FIG. 2 shows a state in which the sprue portion 31 is closed by the tip end portion of the valve pin 47.

  In the configuration as described above, the working fluid is supplied into the fluid pressure cylinder 43 from the port P1 provided on the die mounting plate 35, and in FIG. 2, the piston 45 is moved upward to release the closing of the sprue portion 31 by the valve pin 47. As shown in FIG. 3, when the fiber reinforced thermoplastic resin is supplied from the nozzle in the injection molding machine to the concave portion 37 of the sprue bush 39 when the sprue portion 31 is in the open state, the thermoplastic resin is connected to the communication path. 42, the resin flow part 29, and the sprue part 31 are injected from the gate 25 into the cavity.

  As the thermoplastic resin, a polyolefin resin is preferable in view of characteristics such as economy and molding conditions and functionality when it becomes a helmet. More preferably, polypropylene is used.

  As described above, the temperature of the molten thermoplastic resin when the fiber-reinforced thermoplastic resin is injection-molded into the cavity 23 is 190 to 290 ° C, preferably 200 to 280 ° C, and the mold temperature is 10 to 110 ° C, preferably 20 ˜90 ° C. is desirable. The time for injecting the resin into the cavity 23 is 0.5 to 10 seconds, preferably 1 to 8 seconds.

  In addition, although the above-mentioned temperature condition and time condition, and the temperature condition time described later are described in the case of polypropylene, when changing to the above-described thermoplastic resin other than polypropylene, the condition is changed according to the characteristics. Of course, it is possible to cope with this.

  That is, when the resin temperature is 190 ° C. or lower, the fluidity of the resin decreases and the injection pressure needs to be increased, which is not desirable because the drive system tends to increase in size. Further, when the resin temperature is 290 ° C. or higher, the viscosity of the resin is lowered, and the distribution of the glass fiber relative to the resin tends to be non-uniform, and the glass fiber is exposed to the surface due to the difference in specific gravity between the resin and the glass fiber. There is a problem that it is difficult to get a glossy surface. When the mold temperature is 10 ° C. or lower, the temperature drop of the resin injected into the cavity 23 is large and the fluidity of the resin decreases, which is not desirable. Conversely, the mold temperature is 110 ° C. or higher. Then, it takes a long time for the resin in the cavity 23 to cool and solidify, which is not desirable in view of improvement in productivity. Further, when the injection time is 0.5 sec or less, the resin may not be sufficiently filled into the cavity 23. Conversely, when the injection time is 10 sec or more, the productivity of a molded product with good quality is lowered. So it is not desirable.

  As described above, when the fiber reinforced thermoplastic resin is injected into the cavity 23, the skin layer is formed at the contact portion between the inner surface of the cavity 23 and the resin because the inner surface of the cavity 23 is lower than the resin temperature. Is formed. Then, when the resin is pressurized and filled into the cavity 23, a skin layer is formed over the entire inner surface of the cavity 23, the skin layer gradually becomes thicker, and the core layer at the center of the resin is cooled and solidified. The entire injection molded product is cooled and solidified.

  By the way, the factors that can form the skin layer covering the glass fiber described in the present invention on the surface of the thick ridge 15 of the gate portion are related to the difference in specific gravity between the resin and the glass fiber, the surface tension, and the like. It seems that there is.

  That is, in the hot runner mold 17, when the fiber reinforced thermoplastic resin is filled from the gate 25 into the cavity 23, the glass fibers in the resin tend to be aligned in the resin flow direction. Therefore, in the portion of the gate 25, the length direction of the reinforcing fiber such as glass fiber is in a direction substantially orthogonal to the radial direction of the gate 25. Here, after filling the cavity 23 with resin, the working fluid is supplied into the fluid pressure cylinder 43 from the port P2 provided in the mold mounting plate 35, and in FIG. 3, the piston 45 is moved downward, As shown in FIG. 2, when the sprue portion 31 is closed by the tip portion (tip surface) of the valve pin 47, the molten resin in the sprue portion 31 is pressed and flowed by the rapid movement of the valve pin 47 and the resin is supplied to the cavity 23. Is suddenly stopped.

  In this case, if the flow of the resin is suddenly stopped due to the stop of the movement of the valve pin 47 in the gate 25 portion, the difference between the flow rate of the glass fiber and the flow rate of the resin is caused by the difference in specific gravity between the molten resin and the glass fiber. The glass fiber is slightly immersed in the resin. Further, only the resin in the gate 25 is in a state of being brought into contact with the tip surface of the valve pin 47 by surface tension. The heat at the tip of the valve pin 47 in contact with the resin is transferred to the male mold 19 side, which is lower in temperature than the resin melted by heat conduction, and the temperature at the tip of the valve pin 47 is lower than the resin temperature. Therefore, a resin layer free of glass fiber can be generated at the contact portion between the tip surface of the valve pin 47 and the resin in the gate 25, and the resin layer is quickly cooled by the pulp pin 47 having a low temperature, As a result, a thin skin layer containing almost no glass fiber is formed. When the skin layer is cooled and solidified to some extent, the viscosity of the resin is lowered, so that the peelability between the tip surface of the valve pin 47 and the resin in the gate 25 is improved, and the helmet is fixed to the valve pin 47 when detached from the mold. There is an effect that does not.

  As described above, after the resin in the gate 25 and the valve pin 47 are separated through the injection molding process, the engagement between the male mold 19 and the female mold 21 is released, and the injection molding from the cavity 23 is performed. By removing the product, the cap body 13 shown in FIG. 1 can be obtained.

  The cap body 13 obtained by injection molding as described above has a configuration in which a convex portion 15 thicker than the cap body 13 is provided in a portion corresponding to the gate 25, and the surface of the convex portion 15 is provided. Since a thin skin layer covering the fibers in the resin is formed, the reinforcing fibers such as glass fibers do not come out on the surface, and the capillary phenomenon of the fiber portion as described above can be prevented. That is, the withstand voltage can be maintained satisfactorily.

  As can be understood from the above description, the cap body can be injection-molded without forming a large protruding sprue, and the thick convex portion 15 corresponding to the gate 25 has a skin layer on the surface. Since the fiber is covered, the conventional problem can be solved.

It is a section explanatory view of a cap concerning an embodiment of the present invention. It is a section explanatory view of a hot runner metallic mold for manufacturing a cap concerning an embodiment of the present invention, and the state where a gate was closed is shown. It is a section explanatory view of a hot runner metallic mold for manufacturing a cap concerning an embodiment of the present invention, and has shown a state where a gate was opened. It is sectional explanatory drawing of the injection mold for manufacturing a cap body by the conventional manufacturing method, and sectional explanatory drawing of a cap body.

Explanation of symbols

13 Cap body 15 Convex part 17 Hot runner mold 19 Male mold 21 Female mold 23 Cavity 25 Gate 47 Valve pin

Claims (2)

  A cap body of a safety cap manufactured from a fiber-reinforced thermoplastic resin, and having a thick convex portion at a portion corresponding to the gate when the cap body is injection-molded, and the surface of the thick convex portion And a cap layer for the safety cap, characterized by further comprising a skin layer covering the fibers.   A method of manufacturing a cap body of a safety cap using a fiber reinforced thermoplastic resin, wherein the hot runner mold includes a cavity provided between a male mold and a female mold, and a gate provided in the hot runner mold. After injecting a fiber reinforced thermoplastic resin and closing the gate with a valve pin provided in the hot runner mold, a skin layer is formed on the contact portion between the tip surface of the valve pin and the fiber reinforced thermoplastic resin, A cap body of a safety cap characterized in that after the skin layer is cooled and solidified to such an extent that the valve pin and the skin layer are peeled, the male mold and the female mold are separated and the cap body is taken out from the cavity. Production method.

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