JP5959371B2 - Shaft cylinder forming method - Google Patents

Description

  The present invention relates to a method for forming a shaft cylinder by two-color molding.

  As a typical example of this type of molding method, it is known to mold a shaft cylinder for a writing instrument by two-color molding. In this case, the two-color molding includes primary molding for molding a shaft cylinder body made of a hard resin and secondary molding for molding a grip made of a soft resin on the shaft cylinder body.

  In secondary molding, a gate is typically provided on the outer peripheral surface of the grip, and a gate mark is left on the outer peripheral surface of the grip after molding. This gate mark may cause discomfort when gripping the grip or may deteriorate the appearance design.

  In order to alleviate this problem, Patent Documents 1 and 2 disclose that a gate is provided not at the outer peripheral surface of the grip but at the end of the grip in the secondary molding.

JP 2002-67567 A JP 2003-54180 A

  In the inventions described in Patent Documents 1 and 2, the gate mark is left on the end portion of the grip instead of on the outer peripheral surface of the grip. However, in this case as well, the opportunity for the user to see the gate trace cannot be completely eliminated. In addition, since the gate is provided at the end of the grip having a small area, restrictions are imposed on the die design such as the gate diameter or runner handling, which leads to an increase in molding defects.

  Therefore, there is a demand for a method of forming a shaft cylinder that can completely hide the gate marks on the outer surface of the shaft cylinder from the eyes of the user without restricting the mold design.

According to the present invention, a shaft cylinder is formed by two-color molding, and a first part of a shaft cylinder having a through hole on the outer surface of the core pin is molded by primary molding in which a molding material is supplied from the outside of the core pin. A first step, a second step of molding the second part of the shaft cylinder on the outer surface of the first part by secondary molding for supplying molding material from the inside of the core pin through the through hole, and the core pin together with a runner inside the core pin A method is provided that includes a third step of removing from the first part and a fourth step of dividing the core pin and removing the runner from the core pin .

  In a preferred aspect, the core pin is provided with a runner cavity extending in the axial direction of the core pin and a gate hole extending from the runner cavity so as to penetrate the outer surface of the core pin at a position corresponding to the through hole. In the process, the molding material of the second part is poured onto the outer surface of the first part through the runner cavity, the gate hole, and the through hole in order.

  In this case, it is preferable that the gate hole extends in the radial direction of the core pin so as to penetrate the outer surface of the core pin from the runner cavity.

  The present invention may include heating the runner cavity and the gate cavity of the core pin in the second step.

  According to the present invention, the runner and the gate in the secondary molding can be relatively freely arranged in the core pin, so that the gate mark is formed on the inner surface of the shaft tube without excessively restricting the mold design. Can be completely hidden from the user's eyes. For this reason, it is possible to prevent uncomfortable feeling due to contact with the gate mark when the shaft cylinder is gripped and deterioration in design property due to the gate mark without increasing molding defects due to excessive mold design.

FIG. 1 shows a writing instrument provided with a barrel formed according to the present invention. FIG. 2 shows a shaft cylinder formed according to the present invention. FIG. 3 schematically shows the inside of the first mold in the primary molding in a longitudinal sectional view. FIG. 4 schematically shows the inside of the second mold in the secondary molding in a longitudinal sectional view. FIG. 5 shows a perspective view of one half of the core pin used in the present invention.

  Hereinafter, the present invention will be described with reference to the accompanying drawings. In the accompanying drawings, the same components are denoted by the same reference numerals.

  FIG. 1 shows a writing instrument 1 provided with a front barrel 2 formed according to the present invention. The writing instrument 1 is a knock-type ballpoint pen in this example. In the present specification, the tip, that is, the pen tip side of the writing instrument 1 is defined as the “front” side of the writing instrument 1, and the side opposite to the pen tip of the writing instrument 1 along the axis of the writing instrument 1 is “back” of the writing instrument 1. Define as side.

  The writing instrument 1 includes a front barrel 2, a rear barrel 3 connected to the front barrel 2, a refill (not shown) housed in the front barrel 2 and the rear barrel 3, and a rear barrel. 3 and a knock portion 4 arranged at the rear end portion. The front barrel 2 is gripped by a human finger during use. The refill is configured by mounting a ballpoint pen tip on the front end of an ink containing tube containing ink. The knock part 4 moves the front end part (ballpoint pen tip) of the refill through the front end part of the front barrel 2 by moving it forward and backward with a finger. The front barrel 2, the rear barrel 3, the refill and the knock portion 4 are made separately and then assembled together.

  FIG. 2 shows the front barrel 2 before assembly. The front barrel 2 includes a barrel main body 5 and a grip 6 formed on the outer surface of the barrel main body 5. The front shaft cylinder 2 has a cylindrical hollow shape so as to allow refills to pass therethrough. A spiral groove is formed in the rear portion of the shaft cylinder body 5, and the front shaft cylinder 2 is connected to the rear cylinder 3 by screwing.

  Typically, the shaft cylinder body 5 is made of a hard resin material such as polypropylene or polycarbonate, while the grip 6 is made of a soft resin material such as a thermoplastic elastomer (TPE). The front barrel 2 is molded by two-color molding which is a kind of injection molding. The two-color molding includes primary molding for molding the shaft barrel body 5 and secondary molding for molding the grip 6 on the outer surface of the shaft barrel body 5.

  Hereinafter, the two-color molding method according to the present invention and the configuration of the mold used for the two-color molding will be described in detail.

  FIG. 3 schematically shows the inside of the first mold 7 in the primary molding in a longitudinal sectional view. The first mold 7 used for primary molding includes a cylindrical core pin 8 extending in the front-rear direction and a first cavity 9 surrounding the core pin 8. The outer surface of the core pin 8 has a shape complementary to the inner surface of the shaft body 5. Further, the gap between the core pin 8 and the first cavity 9 is formed so as to correspond to the outer shape of the shaft cylinder body 5. Accordingly, the molding material injected from the nozzle (not shown) of the injection molding machine is injected from the sprue (not shown) into the gap through the runner flow path 10 in the first cavity 9 to thereby inject the shaft body 5. can do.

  The core pin 8 is provided with a runner cavity portion 11 extending in the axial direction from the rear end portion of the core pin 8 and a gate hole portion 12 extending radially from the runner cavity portion 11 so as to penetrate the outer surface of the core pin 8. The runner cavity 11 and the gate hole 12 are relatively freely arranged in the core pin 8. For example, the runner cavity 11 may extend from the front end of the core pin 8 in the axial direction. A plurality of gate holes 12 may be provided, and may extend obliquely from the runner cavity 11 so as to penetrate the outer surface of the core pin 8. Moreover, the gate diameter in the gate hole part 12 can be changed according to the characteristics of the injection molding machine and molding material used.

  The runner cavity 11 and the gate hole 12 are used in secondary molding described later. In the primary molding, the exit of the gate hole 12 from the core pin 8 is sealed by the protrusion 13 of the first cavity 9. This prevents the molding material from flowing into the gate hole 12 and prevents the molding material from flowing into the protrusion 13 of the first cavity 9, so that a through hole is formed in a part of the outer surface of the shaft cylinder body 5. Is done. The through hole has a shape complementary to the protrusion 13 of the first cavity 9. After the primary molding, the outside of the shaft cylinder body 5 and the runner cavity 11 are communicated with each other through a through hole and a gate hole 12.

  After the primary molding, the first cavity 9 is opened, and the core pin 8 including the molded shaft body 5 is rotated from the first mold 7 to the second mold 14 used for the secondary molding. Is moved by. FIG. 4 schematically shows the inside of the second mold 14 in the secondary molding in a longitudinal sectional view. The second mold 14 includes a core pin 8 used in the first step, and a second cavity 15 surrounding the core pin 8 and the shaft cylinder body 5. A gap between the shaft body 5 and the second cavity 15 is formed so as to correspond to the outer shape of the grip 6. Accordingly, the molding material injected from the nozzle (not shown) of the injection molding machine is sequentially passed from the sprue (not shown) to the runner cavity 11 and the gate hole 12 in the core pin 8 and the through hole of the shaft body 5. The grip 6 can be injection molded by pouring through the gap. In the secondary molding, the inner surface of the grip 6 is welded to the outer surface of the shaft cylinder body 5, so that the grip 6 is prevented from coming off from the shaft cylinder body 5 during use thereafter.

  After the secondary molding, the core pin 8 is removed from the shaft cylinder body 5 by being moved rearward with respect to the shaft cylinder body 5. At this time, the hardened molding material (runner) in the core pin 8 is separated from the grip 6 at the exit from the core pin 8 of the gate hole portion 12 by the tensile force due to the movement of the core pin 8 and together with the core pin 8, the shaft cylinder body 5. Extracted from. At this time, since a uniform force is applied to the runner in the gate hole portion 12 extending in the radial direction, the runner is separated from the grip 6 without remaining on the inner surface of the grip 6. For this reason, it is not necessary to perform gate processing on the inner surface of the grip 6.

  After the core pin 8 is removed, the second cavity 15 is opened and the molded front barrel 2 is removed.

  In order to process the runner remaining in the core pin 8 and reuse the core pin 8 for the next two-color molding, the following two methods are conceivable. In the first method, the core pin 8 can be divided, and the runner is removed from the core pin 8 by dividing the core pin 8 removed from the shaft body 5. Thereafter, the core pin 8 can be reassembled and reused for the next two-color molding. FIG. 5 shows a perspective view of the half half 8a of the core pin divided into two. The number of divisions of the core pin 8 may be three or more depending on the shape of the core pin 8.

  In the second method, the second mold 14 can heat the runner cavity 11 and the gate hole 12 of the core pin 8 with a heater or the like. For this reason, since it can be made to melt | dissolve again by heating the runner in the core pin 8 at the time of the next secondary shaping | molding, the core pin 8 can be reused. In this case, as a matter of course, the core pin 8 does not need to be divided.

  In the above, the method of forming the shaft cylinder of the knock type ballpoint pen has been described. However, the method of forming the shaft cylinder of the present invention is not limited to the above embodiment, and the shaft cylinder of another writing instrument such as a mechanical pen. Or it can apply similarly to shaft cylinders, such as cosmetics.

DESCRIPTION OF SYMBOLS 1 Writing instrument 2 Front shaft cylinder 3 Rear shaft cylinder 4 Knock part 5 Shaft cylinder main body 6 Grip 7 1st metal mold 8 Core pin 8a One half part of a core pin 9 1st cavity 10 Runner flow path 11 Runner cavity part 12 Gate hole part 13 First Projection part of one cavity 14 Second mold 15 Second cavity

Claims (4)

A method of forming a shaft cylinder by two-color molding,
A first step of forming a first part of the shaft cylinder having a through hole on an outer surface of the core pin by primary molding in which a molding material is supplied from the outside of the core pin;
A second step of molding the second part of the shaft cylinder on the outer surface of the first part by secondary molding for supplying a molding material from the inside of the core pin through the through hole;
A third step of removing the core pin from the first part together with a runner inside the core pin ;
A fourth step of dividing the core pin and removing the runner from the core pin . The core pin is provided with a runner cavity extending in the axial direction of the core pin and a gate hole extending so as to penetrate the outer surface of the core pin from the runner cavity at a position corresponding to the through hole.
2. The method according to claim 1, wherein in the second step, the molding material of the second part is poured onto the outer surface of the first part through the runner cavity, the gate hole, and the through hole in order. .   The method of claim 2, wherein the gate hole extends in a radial direction of the core pin so as to penetrate the outer surface of the core pin from the runner cavity. The method according to claim 2 or 3, comprising heating the runner cavity and the gate hole in the second step.

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