JPH06315954A - Forming mold of thermoplastic elastomer of the like - Google Patents

Abstract

PURPOSE:To favorably deaerate and contrive to reduce fraction defective by a method wherein an air vent hole is formed having a diametrically expanding part, the diameter of which increases gradually, and characteristic dimensions is produced so as to face to a cavity portion, in which air tends to leave at molding, in a mold. CONSTITUTION:In order to produce a fountain pen filler, the mold concerned is equipped with a top mold 1 having a core 3 and a bottom mold 2 having a recess, between the core 3 and which a cavity 4 as comparatively narrow gap is formed, and in which a stepped through hole 5 is produced along the axis center line of the core 3. Further, into the through hole 5, a pin member 10, on which an air vent hole 6 is produced, is fitted. The air vent hole 6 is provided so as to face to the cavity 4 and produced by continuously providing a small hole portion 7 having the length of 300mum or less and the hole diameter of 5-100mum and a diametrically expanding part 8, which diametrically expands conically at the other end. Thus, deaeration is favorably carried out and the air vent hole 6 is prevented from being clogged by molding material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to natural rubber, synthetic rubber,
Regarding a mold used when molding a thermoplastic resin or a thermoplastic elastomer, in particular, it has excellent air bleeding property,
The present invention relates to a mold capable of molding a product having an excellent appearance, in which no air pockets or unfilled parts remain.

[0002]

2. Description of the Related Art In molding rubber, thermoplastic resin or thermoplastic elastomer, a compression molding method in which a cavity of an open mold is filled with a material and then the mold is closed and pressurized,
Alternatively, an injection molding method in which a material is injected into a cavity of a closed mold and molded is known, and in any of the molding methods, air in the mold is discharged from the joint of the mold to the outside as the material is filled. It is generally discharged, but if the shape of the molded product is complicated or if the molded product has a bag shape, depending on only the discharge of air from the mold seam, Air deficiency is incomplete, and air remains in the mold, leaving unfilled parts of the material in the molded product due to the remaining air pockets, forming recesses and holes that impair the appearance and performance of the product. There is a problem that it ends up.

Various proposals have heretofore been made to prevent such air remaining in the mold. For example, a large air vent hole is formed in the mold, and a sintered metal or a bound needle-shaped metal is provided therein. In addition to the proposal to fill and block only the air, Japanese Patent Publication No. 57-20890 proposes to provide an air vent hole smaller than 0.01 inch in the mold, and Japanese Patent Publication No. 1-51451. 0.5 mm
Proposal of tightly fitting a pipe provided with a smaller air vent hole into the pipe fitting hole, and further, JP-A-4-1911.
No. 7 proposes that a pin is inserted into the gas vent hole and the gap between the pin and the hole wall is made a rough surface for venting air.
In addition, in consideration of air bleeding and prevention of material outflow after air bleeding, it is proposed to provide a valve head made of a heat-expandable material in the air bleeding hole and close the hole by expansion of the heat-expandable material heated immediately after bleeding air. (JP-A-63-3218
No. 19) has also been done.

[0004]

However, in the above-mentioned various techniques for venting air, which have been proposed in the past, there is a problem in repeated use of a mold, especially a filling material having high fluidity at the time of molding. There is a problem that it is not sufficiently taken into consideration when molding a product using (for example, liquid silicone rubber).

That is, for example, when a material having a high viscosity and a relatively low fluidity in the mold is used, only air is discharged when the mold having the air vent holes as described above is filled with the material. This material does not substantially enter the air holes, so there is no major problem with repeated use of the mold,
When a material with high fluidity is used, after the air is exhausted, the material enters the air vent hole and solidifies, and the air vent hole of this mold is blocked during the next molding, so proper air venting is not possible. Often appears.

For this reason, in a mold having a small air vent hole, there has been a problem that a cleaning operation for removing a material which is clogged in the air vent hole and solidified after performing one molding operation is troublesome.

As a measure for avoiding such an adverse effect, for example, it is conceivable to increase the diameter of the air vent hole. However, as is well known, when this is done, a hole mark remains on the molded product and a burr of the molded product is left. This results in a problem that the removal work is troublesome.

Due to the above problems, there is also a method of bleeding air from the mold by repeatedly performing bumping after injection or compression, but with this method, reliable air bleeding reliability is doubtful, and it takes time. Therefore, it is not popular because it results in a drastic decrease in production efficiency in molding such as injection molding where the original molding time is short.

In view of the current state of the art as described above, the inventor of the present invention eliminates burrs in a mold that requires an air vent hole because it has a complicated or bag-shaped cavity, and therefore has a large hole. It can be performed satisfactorily without leaving traces, and the burden of cleaning the mold is extremely high, especially when molding is repeated using a highly fluid material such as liquid silicone rubber. The present invention has been completed with the object of providing a mold that can efficiently perform a molding operation with few and high productivity.

[0010]

In order to achieve the above object, the present inventor has completed the present invention described in each claim of the above claims.

One of the features of the molding die used for molding the rubber, the thermoplastic synthetic resin or the thermoplastic elastomer (hereinafter collectively referred to as "thermoplastic elastomer, etc.") according to the present invention is that air is used during molding. A cavity portion in the mold where there is a risk of being left behind, and an air vent hole having one end facing the other end and communicating with the outside air is provided in the mold, and the air vent hole is an end facing the cavity on the one end side. The hole diameter is 5 within the range of 300 μm or less from the part position.
It has a small hole portion of ˜100 μm, and has a diameter-expanded portion whose diameter gradually increases from the end portion of the small hole portion forming range toward the other end side.

The air vent hole of this mold is provided with a pin member formed to have the above-mentioned specified hole shape, and a large-diameter through hole that communicates with the outside air from the cavity in the mold,
It is also possible to provide the pin member so as to be tightly fitted in the through hole.

According to the present invention having the above-mentioned structure, since the small hole portion having a narrow hole diameter of 5 to 100 μm is provided, a material having a high fluidity when the air escapes from the mold. Is prevented from coming out of the mold in a large amount, and the small-diameter portion is limited to a total length of 300 μm or less, and has a hole shape having a diameter-increasing portion whose diameter gradually increases from the end toward the outside air. Therefore, the material that remains in the small diameter part and solidifies can easily escape to the expanded diameter part in the next molding, simplifying the cleaning of the mold during repeated molding operations (clogging the air vent hole). Can be omitted).

Further, since the hole diameter of the air vent hole facing the cavity in the mold is limited to 100 μm or less, no noticeable marks are left on the molded product.

In order to obtain such an effect, if the hole diameter of the small diameter portion is set to 5 μm or less, even if the effect of the air vent hole can be obtained, it is not easy to form a hole having such a hole diameter. 100 μm, preferably 10-100
It is preferable to make a small hole portion having a hole diameter of about μm.

The flowable molding material flowing into the air vent hole is crosslinked or cooled to lose its fluidity and solidify to be clogged in the air vent hole. In the present invention, however, the length of the small hole portion is 300 μm. , Preferably 200μ
Since it is limited to m, the pressure of the molding material that flows into this hole at the time of the next molding or the pressure of the air that remains in the cavity pushes it out to the expanded diameter side, which hinders the air vent hole at the next molding. Given without. If the length of the small hole portion exceeds 300 μm, the extrusion due to the molding material or the like at the time of the next molding becomes poor and the air vent hole effect cannot be obtained, so the above range is set.

The enlarged diameter portion provided on the outside air side following the small diameter portion is provided so that the hole diameter increases from the small diameter portion on the sloped surface having a taper, but the degree of the diameter expansion is not particularly limited. Instead, the point is that the material has a wide diameter so that the material solidified and clogged in the small diameter portion can be smoothly pushed out to the outside. Although the size of the diameter is not particularly limited, it is not particularly necessary to make the diameter too large, and therefore it may be provided several tens to several hundreds times as large as the small diameter portion.

A plurality of air vent holes of the mold of the present invention can be provided at necessary places.

As a more preferable construction of the present invention, a large-diameter through hole communicating from the cavity inside to the outside air is provided in the mold, and the small-diameter portion and the enlarged-diameter portion are formed in series in the through-hole. The one in which the pin member is tightly fitted can be mentioned as a preferable structure that is easier to machine than the direct hole machining in the mold, and further, this pin member is divided into two in the surface including the shaft. A pin member formed by joining a pair of the above members is recommended as a particularly preferable structure. For example, a flat surface forming a diameter portion of a pair of semi-cylindrical members is subjected to groove processing corresponding to a small hole portion and a diameter-enlarged portion, and these are combined and joined so as to be closely fitted in a through hole of a mold. If so, the machining becomes extremely easy as compared with the case where the hole processing is performed.

The present invention is one in which molding (compression molding, injection molding) is performed using a material having high fluidity in a molten state, for example, a mold of natural rubber, synthetic rubber, thermoplastic synthetic resin, thermoplastic elastomer or the like. It can be used for molding and can be particularly effectively used for molding liquid silicone rubber exhibiting high fluidity. It can also be used for molding thermosetting resins.

[0021]

EXAMPLES The present invention will be further described below based on Examples shown in Examples. Example 1 FIG. 1 shows an example of a structural outline of a molding die of the present invention used for molding a dropper. In this figure, 1 is an upper mold having a core 3 and 2 is this core 3. Is a lower mold having a recess forming a cavity 4 as a relatively narrow gap between the lower mold 2 and the lower mold 2. A stepped through hole 5 is formed, and the pin member 10 shown in FIG. 3 is tightly fitted in the through hole 5.

An air vent hole 6 is formed in this pin member 10 in this example.

The air vent hole 6 is made up of a small hole portion 7 provided so as to face the cavity in the mold, and a diameter-expanding portion 8 which has a conical diameter on the other end side. The section 8 is communicated with the outside air via the straight tube section 9 (see FIG. 3).

The pin member 10 having such a configuration is used as the through hole 5
When the air vent hole is tightly fitted to the air vent hole, the air vent hole faces the cavity 4 in the molding die through the opening of the small diameter portion 7 of the air vent hole 6 and the outside air through the straight tubular portion of the large opening. By exchanging this pin member, the hole diameter and length of the air vent hole can be easily changed.

Reference numeral 11 denotes an injection port for injection molding material provided on the mating surfaces of the upper mold 1 and the lower mold 2.

Silicone rubber was molded under the following conditions using the molding die having the structure shown in FIGS.

Dimension of core of upper mold 1: Diameter 10 mm, axial length 50 mm Dimension of cavity 4: 12 mm Dimension of air vent hole: As shown in Table 1 Molding material: Liquid silicone rubber KE-195
5-60 (manufactured by Shin-Etsu Chemical Co., Ltd.) Molding temperature: 170 ° C. Injection pressure: 300 kg / cm ² or more, injection molding was repeated 30 times, and the results are shown in Table 1 below.

As a result, as shown in FIG. 2, an extruded body in which a bell-shaped solidified material is connected is seen in the expanded portion 8 of the air vent hole, and almost no traces of air traps or air vent holes are found in the product. It was The number of air traps and air vent holes is 1
The ones that were observed when observed with a 0 × magnifying glass but were hardly visible to the naked eye were marked with “◯”, and those visible to the naked eye were marked with “x”.

Example 2 Injection molding was performed in the same manner as in Example 1 except that the dimensions of the air vent holes were changed (see Table 1), and the results are shown in Table 1.

In this example, as the pin member 10, a pair of stepped semi-cylindrical members 101 and 102 are combined as shown in FIG. 4, and the air vent holes 6 to be described below are formed on the opposing planes.
Is used, and other configurations are the same as in the first embodiment. Injection molding was performed and the results are shown in Table 1. The dimensions of the air vent hole 6 are shown in Table 1.

The structure of the pin member in this example is as follows. That is, one of the stepped semi-cylindrical members 101 forms a flat surface in the extended length range of the small hole portion 7, and the other stepped semi-cylindrical member 102 has the extended length range of the small hole portion 7. In which a small hole portion as a scribing groove is formed, and the pair of stepped semi-cylindrical members 101,
The small hole portion 7 is formed by joining the 102 to each other in the plane. Further, the other ends of the small hole portions 7 of the pair of stepped semi-cylindrical members 101 and 102 are connected to a diameter-expanding portion 8 that has a conical diameter-expanding diameter. It is communicated with the outside through the air (see FIG. 3). The joining plane of the pair of stepped semi-cylindrical members 101 and 102 is a surface that has been appropriately polished so that the molding material does not enter the joining surface portion.

Example 3 Injection molding was performed in the same manner as in Example 1 except that the dimensions of the air vent holes were changed (see Table 1), and the results are shown in Table 1.

Comparative Examples 1 and 2 Injection molding was carried out in the same manner as in Example 1 except that an air vent hole having a hole diameter of 150 μm and a hole length of 50 μm and a pin member having an air vent hole of 100 μm and a hole length of 500 μm were used. Was repeated and the results are shown in Table 1.

[0034]

[Table 1]

As is clear from the above results, in the case of the example, air was satisfactorily discharged, and the obtained product showed almost no air traps or air vent hole traces. In the case of the comparative example, it was confirmed that the air could not be sufficiently released due to the air traps remaining, and that the product had the air vent hole traces.

[0036]

According to the present invention, air can be satisfactorily vented from the air reservoir inside the mold, which is a problem when molding a material having high fluidity, and the air vent hole traces are formed in the molded product. It is possible to obtain the effect that almost no residue remains, the product value is improved, and the defective product rate is also reduced.

Further, when continuously molding, the work of removing the solidified material clogged in the air vent hole can be substantially omitted, so that the cleaning work can be simplified and the productivity can be improved. .

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a molding die according to the present invention,

FIG. 2 is an enlarged view of a small hole portion of an air vent hole,

FIG. 3 is a vertical cross-sectional view of a pin member tightly fitted in a through hole of a mold for forming an air vent hole.

FIG. 4 is a plan view of the pin member viewed from the open end side of the small hole portion.

[Explanation of symbols]

1 ... Upper mold, 2 ... Lower mold, 3 ... Core, 4 ...
Cavity, 5 ... Through hole, 6 ... Opening, 7 ...
Small hole part, 8 ... expanded diameter part, 9 ... straight tube part, 10 ...
-Pin members, 101, 102 ... Stepped semi-cylindrical members.

Claims (3)

[Claims] 1. A mold for molding fluid rubber, thermoplastic synthetic resin or thermoplastic elastomer,
The mold is provided with an air vent hole, one end of which faces the cavity portion in the mold where air may be left behind during molding and the other end of which communicates with the outside air. 300 μm from the end position facing the
In the following range, there is a small hole portion having a cross hole diameter of 5 to 100 μm, and there is an enlarged diameter portion whose diameter gradually increases from the end of the small hole portion forming range toward the other end side. Mold for molding thermoplastic elastomers. 2. A large-diameter through hole communicating with the outside air from a cavity in the mold is provided, and the through hole has a hole diameter of 5 to 100 μm over a range of 300 μm or less from one end side.
And a pin member having an air vent hole including an enlarged diameter portion whose diameter gradually increases from the end portion of the small hole portion forming range toward the other end side. A mold for molding a thermoplastic elastomer or the like having an air vent hole according to claim 1. 3. The molding die according to claim 1, which is for molding a liquid silicone rubber.