JP2000135723A - Resin barrel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a small barrel through an easy molding process requiring no extra working strain by making the surface roughness of the inner face of the barrel heavier than the surface roughness of the outer face. SOLUTION: The surface roughness of the inner face of a lead holding member 12 of a mechanical pencil as a barrel is made heavier than the surface roughness of the outer face. Consequently the roughness of the surface of a lead coincides with the surface roughness of the inner face of the lead holding member, so that their mutual roughness works to fit projecting parts into recessed parts and thereby a lead is prevented more effectively from rotating with the lead holding member 12. In addition, during molding the lead holding member 12, a fine indented pattern which configuratively matches the fine projecting and recessed parts formed on the inner face of the lead holding member 12, is formed on the surface of a core pin 19 for which a through hole is formed in the lead holding member 12. Further the inner face of a cavity 18 where the outer face of the lead holding member 12 is formed is smoothed. Therefore, the molded product (the lead holding member 12) is easily released from the core pin 19 on account of the fine indented pattern of the core pin 19 and the action of the member 12 to stick to the cavity 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder formed by injection molding.

[0002]

2. Description of the Related Art The applicant of the present application has previously made an invention in which a lead holding member of a mechanical pencil is formed of a resin cylinder and the cylindrical body is provided in a core protection tube disposed at the tip of the mechanical pencil. And applied for it (Japanese Patent Application Laid-Open No. 9-183294).
No.).

According to the invention, the lead holding member is arranged at the tip of the mechanical pencil, so that the lead can be used as efficiently as possible without waste. However, there is still room for development. .

[0004]

There is a problem in productivity of the cylindrical body serving as the core holding member. Although this cylinder is formed by injection molding, the cylinder adheres to the core pin, and it is extremely difficult to remove an extremely small cylinder from the core pin. Incidentally, the size of the cylindrical body is about 5 mm in length, about 1 mm in diameter, and about 0.5 mm in inner diameter. Here, generally, several tens to several hundreds of cylinders are formed at a time. This is a so-called “multi-cavity” molding method. For this reason, the interval between the core pins is narrow. Therefore, if the cylinder body is firmly attached to the core pin located in the middle, the difficulty in removing the cylinder body has been significantly improved. Therefore, it has been considered to attach an extruding plate 103 for ejecting the core holding member (molded product) 102 to the core pin 101. However, not only does the die apparatus become large, but when the extrusion is performed, the molded product is small. If you compress or slightly
It may cause buckling (see FIG. 8), which is not practical.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is directed to a cylinder formed by injection molding, wherein the inner surface of the cylinder has a reduced surface roughness. The gist is that it is rougher than the surface roughness.

[0006]

The minute irregularities on the inner surface of the molded product slide on the fine irregularities on the surface of the core pin, come off the core pin, and then the molded product left in the cavity shrinks.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first example will be described with reference to FIGS. Shaft barrel 1
A wick tank 2 for storing a plurality of wicks is arranged to be able to move back and forth. An eraser 3 and a knock cap 4 are detachably attached to the rear end of the core tank 2. On the other hand, in front of the lead tank 2, a chuck body 6 for holding and releasing the lead is fixed via a relay member 5. A chuck ring 7 for opening and closing the chuck body 6 is surrounded by a front portion of the chuck body 6. Code 8
Is a tip member screwed to the tip of the barrel 1, and a center detent member 9 for preventing return of the core is press-fitted and fixed inside the tip member 8, but is not always necessary. Not something. Reference numeral 10 denotes a repellent member such as a coil spring, which urges the chuck body 6 rearward together with the core tank 2.

At the front end of the tip member 8, a core protection tube 11 made of a metal pipe is press-fitted and fixed.
For example, it may be integrally formed by injection molding or the like, and may be formed integrally with the tip member by insert molding or the like, though it is a separate member. A cylindrical core holding member 12 formed by injection molding is arranged inside the core protection tube 11. Further, fixing rings 13 and 14 for preventing the core holding member 12 from falling off from the core protection tube 11 are press-fitted into the core protection tube 11 before and after the core holding member 12. Of course, the inner diameter of the fixing rings 13 and 14 is larger than the diameter of the core used. As a method for preventing the core holding member 12 from falling off, the inner surface step 8 a
The fixing ring 14 may be press-fitted in the front (see FIG. 3), or a step may be formed on the front inner surface of the core protection tube 11 to prevent the core protection tube 11 from falling off. You can try it.

Here, the core holding member 12 will be described in detail. The outer diameter of the lead holding member 12 is formed to be substantially the same as or slightly larger than the inner diameter of the lead protection tube 11. On the other hand, the inner diameter of the lead holding member 12 is formed to be slightly smaller than the outer diameter of the lead to be used. Therefore, when the lead is inserted into the lead holding member 12, the lead holding member 12 is compressed by its own elasticity, and pinches the lead by its reaction force, escapes outward, and presses against the inner surface of the lead protection tube 11. By these actions, the rotation of the lead with respect to the lead holding member 12 and the lead holding member 1
The rotation of the core protection tube 11 with respect to the second core protection tube 11 is prevented, so that the rotation of the core (residual core) separated from the chuck body 6 is prevented, so that writing can be performed on the residual core without any discomfort.

The inner and outer surfaces of both ends of the lead holding member 12 are chamfered. The inner chamfer 15 is provided to facilitate guiding the lead to the lead holding member 12, while the outer chamfer 16 is provided for the lead holding member 1.
2 is provided to make it easier to assemble the core protection tube 11. Further, the surface roughness of the inner surface of the core holding member 12 is formed to be larger than the surface roughness of the outer surface. This is also in consideration of productivity at the time of molding, which will be described later. By forming the inner surface of the core holding member 12 that is in contact with the core roughly, the roughness of the surface of the core matches the surface roughness of the inner surface of the core holding member. Without
An effect that the effect of preventing rotation of the lead with respect to the lead holding member is further enhanced is also generated.

Examples of the material of the core holding member include silicone rubber and acrylonitrile-butadiene rubber. A mixture of the above materials containing a crystalline resin, for example, polypropylene or polyethylene, or only a crystalline resin is used. A preferred example is one molded with. It is a substance having a high shrinkage rate of a molded article after injection molding described later, and thus having a good releasability from the cavity.

Next, a method of forming the core holding member 12 will be described. Reference numeral 17 denotes a cavity plate in which a cavity 18 in which a core holding member (molded product) is molded is formed, into which a core pin 19 that forms a through hole in the core holding member protrudes. The core pin 1
Fine irregularities for forming minute irregularities on the inner surface of the core holding member to be molded are formed on the surface of 9. Specifically, the surface of the core pin 19 is blasted with particles of about 100 to 400. On the other hand, the inner surface of the cavity 18 in which the outer surface of the core holding member is formed is not subjected to a process such as blasting to make the surface rough, and therefore,
The outer surface of the molded core holding member has a substantially smooth surface.

Next, the operation will be described. First, FIG.
Injection molding is performed by flowing resin into the cavity from the state shown in FIG. Next, the cavity 18 and the core pin 19 are separated from each other. At this time, the molded product (core holding member 12) is formed by the fine unevenness of the core pin 19 and by the sticking action of the molded product to the cavity. And remains in the cavity 18 (see FIG. 5). Here, the molded product in the cavity shrinks as it cools down with time, so that it is easy to separate (peel) from the cavity at this point. Finally, air or the like is blown to the cavity, and the core holding member (molded product) is discharged from the cavity. The outer surface of the lead holding member obtained by the injection molding has a smooth surface (small but minute irregularities are formed: see FIG. 6).
However, as shown in FIG. 7, the inner surface has a high density of minute irregularities. That is, the inner surface of the core holding member
It is rougher than the outer surface.

[0014]

According to the present invention, the surface roughness of the inner surface of the cylindrical body formed by injection molding is made larger than the surface roughness of the outer surface. Can be molded and produced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a first example.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is an enlarged view of a main part showing another example of a method of fixing the lead holding member.

FIG. 4 is a sectional view of a main part at the start of injection molding.

FIG. 5 is a sectional view of a main part when injection molding is completed.

FIG. 6 is an enlarged external view of the outer surface of the lead holding member.

FIG. 7 is an enlarged external view of the inner surface of the lead holding member.

FIG. 8 is a sectional view of a main part showing a conventional injection molding method.

[Explanation of symbols]

 Reference Signs List 1 shaft cylinder 2 core tank 3 eraser 4 knock cap 5 relay member 6 chuck body 7 chuck ring 8 tip member 9 core detent member 10 resilient member 11 core protection tube 12 core holding member 13 fixing ring 14 fixing ring 15 inner chamfer 16 External chamfer 17 Cavity plate 18 Cavity 19 Core pin

Claims (3)

[Claims] 1. A resin cylinder formed by injection molding, wherein a surface roughness of an inner surface of the cylinder is made larger than a surface roughness of an outer surface. 2. The resin cylinder according to claim 1, wherein
A resin cylinder characterized in that the resin cylinder contains at least a crystalline resin. 3. The resin cylinder according to claim 1, wherein
A resin cylinder wherein the resin cylinder is used as a lead holding member of a mechanical pencil.