JP2904866B2 - Needle guide manufacturing method - Google Patents

Description

The present invention relates to a method of manufacturing a needle guide for holding a needle of a print head for a dot printer, and more particularly, to a guide hole interval suitable for high-density printing. The present invention relates to a method for manufacturing a needle guide for a print head having a very narrow width.

[Conventional technology]

The print head of a dot printer has a drive unit with a solenoid mechanism and a plurality of needles arranged on the circumference of the drive unit. It is known that the needle guide is converged in a trumpet shape up to the needle guide and reciprocates with each curvature.

The guide hole of the needle guide that guides this needle has an appropriate inner diameter with respect to the outer diameter of the needle, and requires mechanical strength that can withstand severe needle sliding for a long time and lubricity due to surface smoothness Further, the guide hole interval also affects the printing quality, so that it is necessary to provide the guide holes with high precision.

Therefore, this needle guide is made of ceramic having excellent mechanical strength and durability.
As shown in No. 64, it is known that it can be provided by a powder injection molding method.

Conventionally, when a needle guide is manufactured by powder injection molding, a method according to the following example is generally used.

First, a ceramic powder such as alumina or zirconia is kneaded with an organic binder such as wax or thermoplastic resin to obtain an injection molding material.

Secondly, this injection molding material is injection-molded into an injection mold by an injection molding machine to obtain a needle guide molded body.

Here, the molding die has a structure in which the molding pin forming the guide hole is connected to the mold at both ends in the axial direction so that a molded product having the guide hole penetrated is obtained. Injection is performed from a side gate in a direction perpendicular to the axial direction to obtain a molded body 40 having both ends of the guide hole 43 penetrated as shown in FIG. 4 (a).

Third, after the temperature is gradually increased to about 500 ° C. in the air or nitrogen atmosphere to perform a degreasing treatment for decomposing and removing most of the organic binder to obtain a degreased body, the degreased body is sintered in the air. Obtain a needle guide sintered body.

Fourthly, unnecessary parts such as the gate material 47 and the material pool 49 of the sintered body are removed by grinding or the like, the inner surface finish of the guide hole 43 and the finish of the tapered portion are wire-wrapped, and the edge is brush-wrapped. Then, a needle guide 41 shown in FIG. 4 (b) is obtained.

As described above, in the conventional manufacturing method, the molding pin forming the guide hole is a molding die whose both ends in the axial direction are connected to the mold, and the molding material is formed in a direction perpendicular to the axial direction of the molding pin. It is characterized in that a molded product is obtained by injecting from a certain side gate and having both ends of the guide hole penetrated.

[Problems to be solved by the invention]

In recent years, in order to improve the printing quality of a dot printer, a printing head having a remarkably increased number of dots has been strongly demanded, and a needle guide used in such a printing head needs to make the interval between guide holes as narrow as possible.
In the case of a print head in which one character is composed of dots, the thickness of the thin portion between the guide holes is extremely narrow, about 50 μm.

However, there is a problem that such a needle guide in which the guide hole interval is extremely narrow cannot be provided by the above-described conventional manufacturing method.

This is because the flow of the molding material flow 56 press-fitted from the side gate 58 is applied to the thin portion between the molding pins 53 as shown in the schematic diagram of the molding material flow in the conventional manufacturing method of FIG. In this case, the flow is hindered because the interval is too small, and the flow of molding material flowing on both sides of the molding pin row 56
However, this is because the thin line portion just between the guide holes collides from both sides to form a weld line WL.

The occurrence of the weld line is related to the ratio of the guide hole interval to the guide hole diameter, and when the ratio is less than one third, the occurrence becomes remarkable.

Due to the weld line, unevenness in density and defective filling of the molded body around the guide hole may occur, resulting in problems such as hole diameter accuracy of the guide hole of the sintered body after firing, unevenness of the surface of the hole, or strength of the hole. And it is difficult to provide.

To solve the problem of the weld line, we tried to increase the temperature of the mold or the temperature of the heating cylinder of the injection material. However, the molding material adhered to the mold and the mold release was poor. There are problems that the molding material deteriorates and deforms during the degreasing process, and that the sprue and the runner cannot be recycled.

In general, the roundness of the guide hole is determined by various defects in the thin portion between the guide holes, that is, partial filling due to the occurrence of a weld line, uneven density, chipping of the hole, unevenness of the hole surface, insufficient hole strength. Has a close relationship with the irregularity of the hole intervals, and the roundness improves as the number of the defects decreases.

Accordingly, an object of the present invention is to provide a method for producing a needle guide having a guide hole interval of not more than one-third of the guide hole by using ceramic injection molding, wherein the guide hole has excellent roundness. And

[Means for solving the problem]

The present invention obtains a molded body having an introduction guide portion by flowing a molding material from a gate of an introduction guide portion provided on the distal end side of a guide hole molding pin in injection molding, degreases, after firing,
The object of the present invention is to solve the above-mentioned problem and to provide a method of manufacturing a needle guide having excellent roundness of a guide hole by removing the introduction guide portion.

Here, as shown in FIGS. 2 (a) and 2 (b), the introduction guide portion is a guide hole of the original needle guide 21.
The exposed surface of the needle 23 is provided so as to seal all the guide holes 23 on the surface located on the distal end side of the needle.

The height H is determined by the molding pin interval D and the flow ratio R of the molding material.
By setting the temperature optimally, it is possible to suppress the occurrence of a weld line and to provide a guide hole with excellent roundness.

Here, the flow ratio R of the molding material means a ratio of a flow amount which is a passing amount of the molding material which varies with the molding pin interval D for the same unit passage area. The flow ratio is expressed as R = 1.0 on the basis of the flow amount at the point (1), and the flow ratio R is expressed as a small value when the molding pin interval D becomes narrow and the flow amount decreases.

The width and depth of the introduction guide section are set to be at least as large as the height of the introduction guide section (W1, W2) and expanded outward from the molding pins.

[Action]

The weld line which has conventionally occurred is, firstly, because the flowing molding material has high viscosity, it is difficult to flow between narrow guide holes, that is, between the guide hole forming pins, and secondly, the flow distance from the gate is long. Since the molding material is gradually cooled and becomes more viscous and the molding materials of different flows are hardly compatible with each other, the molding material tends to be generated particularly at the collision surface of the two flowing flows between the molding pins having a low temperature.

This tendency becomes more remarkable as the flow ratio R becomes smaller.

In the present invention, the injection guide of the molding material is provided in the injection molding die of the needle guide, and the gate of the molding material is provided in this introduction guide, so that the conventional molding pin can be oriented in a direction perpendicular to the axial direction. The flow of the molding material was changed to a flow in a parallel direction.

The change in the direction of the flow of the molding material with respect to the narrow thin portion of the molding pin, that is, the flow parallel to the molding pin, changes the form of collision of the flowing flow of the molding material, and significantly suppresses the occurrence of weld lines. .

In addition, the flow distance is shortest and not cooled in a narrow thin portion near the tip of the forming pin corresponding to the thin portion of the tip of the guide hole located on the tip end side of the needle which is most important as the needle guide. Since the molding material reaches and fills, it is more effective in suppressing weld lines.

Furthermore, by changing the height of the introduction guide portion in accordance with the flow ratio R of the molding material that changes with the guide hole interval, the flow direction of the molding material is intentionally controlled to some extent to suppress the occurrence of weld lines. I have.

However, at a flow ratio R as small as 0.05 or less, suppression of the weld line becomes extremely difficult.

Hereinafter, details of the present invention will be described with reference to the drawings and embodiments.

[Example 1] First, the production method according to the present invention employs an average particle size of 0.5 µm
100 parts by weight of zirconia powder, an atactic polypropylene, an ethylene-vinyl acetate copolymer and paraffin wax were added at 15:30 parts by weight of an organic binder consisting of a ratio of 40:30:30, and 100 parts by pressure kneader. Kneaded at 1 ° C. for 1 hour, cooled and pulverized to obtain a molding material.

Secondly, after filling the molding material into a heating cylinder of an injection molding machine and keeping the temperature of the heating cylinder at 150 ° C. to make the molding material in a molten state, the shrinkage due to sintering is expected in advance and the guide hole is A molding material is filled from the gate of the introduction guide using an injection molding die provided with an introduction guide on the tip end side of a molding pin, and the molded body with the introduction guide 15 shown in FIG.
Get ten.

Third, the molded body is placed in a degreasing furnace at 20 ° C. under a nitrogen atmosphere.
The temperature is raised to 500 ° C. at a rate of / hour to remove 97% of the organic binder to obtain a degreased body,
It is fired at 00 ° C. for 1 hour to obtain a sintered body.

Fourthly, the introduction guide portion 15 of the sintered body is removed by grinding to expose the through guide hole 13, thereby obtaining the completed needle guide 11 shown in FIG. 1 (b).

When the dimensions of each part of the needle guide manufactured by the manufacturing method according to the above-described process were measured and the cross section of the thin part between the guide holes was observed, in any part, 9
Dimensional accuracy of 9.8% or more is obtained, no weld line or underfill is found in the thin part between the guide holes, and the roundness of the guide hole expressed by the ratio of the maximum diameter to the minimum diameter is 99.8% or more. It was excellent.

[Example 2] In the same manufacturing method as in Example 1, the molding pin interval D of the mold for providing the molded body shown in FIGS. Thus, a needle guide was manufactured by changing the height of the introduction guide portion within a range of 1 to 3 times the interval between the molding pins.

The roundness of the guide hole of the obtained needle guide is measured, and the roundness of the guide hole exceeds 99.8% at the flow ratio R corresponding to each molding pin interval. As a result, it was found that the optimum height differs depending on the flow ratio R as shown in FIG.

This means that the height of the introduction guide must be changed in accordance with the flow ratio of the molding material, that is, the same injection condition in accordance with the same spacing of the bulk molding pins, but the height of the introduction guide is set unnecessarily large. Then, grinding and removal after sintering require a great deal of time and cost, and the flow parallel to the molding pin of the molding material, which is a feature of the present invention, is disturbed, and the roundness tends to deteriorate. is there.

Generally, when the flow ratio R of the molding material is 0.05 or less, molding is difficult, and when it is 0.4 or more, the influence of the molding pin interval is small.

The flow ratio of the molding material varies depending on the molding material composition, the mold temperature, the material temperature, the injection pressure, and the like even at the same molding pin interval.

Further, the shape of the molding pin may be a straight shape or a tapered shape. However, in the method of the present invention, a tapered shape having a particularly narrow thin portion is more effective.

In the above embodiment, zirconia was used as the ceramic powder. However, good results were obtained with a composite material of a high-hardness ceramic material such as alumina, silicon nitride, boron nitride, and silicon carbide or a lubricant.

〔The invention's effect〕

According to the method for manufacturing a needle guide according to the present invention, the molding material is uniformly and sufficiently filled in the gap between the adjacent molding pins in a state of good fluidity, so that the occurrence of weld lines can be significantly suppressed and the roundness is excellent. A needle guide having a guide hole with almost no defects can be mass-produced, and a printer head having a high print density has been commercialized.

In addition, the dimensional accuracy is extremely good, with the variation of the outer dimensions within 0.2%, the surface roughness of the guide hole is small, the secondary processing of the inner surface finish of the guide hole is unnecessary, and a molding pin with a tapered part is used. When used, the secondary processing of the edge of the guide hole was unnecessary.

As described above, the manufacturing method according to the present invention is excellent in productivity and economical efficiency such as not requiring functional elements such as manufacturing, dimensional accuracy and mechanical strength, and requiring no secondary processing.

[Brief description of the drawings]

FIG. 1 is a view showing an example of steps of a point of a manufacturing method according to the present invention, showing a molded body (a) having an introduction guide portion and a completed needle guide (b). FIG. 2 shows a top view (a) and a sectional view (b) of a molded article of a needle guide obtained by the production method of the present invention. FIG. 3 shows that the guide hole has a roundness of 99.8% at various flow ratios R.
FIG. 6 is a diagram showing a ratio of the height of the introduction guide portion to the molding pin, which exceeds the height of the guide pin. FIG. 4 is a view showing an example of main steps of a conventional method for manufacturing a needle guide, in which a molded body (a) having a through guide hole;
The completed needle guide (b) is shown. FIG. 5 is a schematic view of a flowing flow of a molding material in a conventional manufacturing method. 11… Needle guide, 13… Guide hole, 15… Introduction guide, 10… Molded body.

Continued on the front page (72) Inventor Masami Hoshi 6-11-12 Honcho, Tanashi-shi, Tokyo Citizen Watch Co., Ltd. Inside Tanashi Works (72) Inventor Shigeru Saito 840 Takeno Shimotomi, Tonozawa-shi, Tokorozawa-shi, Saitama Citizen Watch Examiner in Technical Research Institute, Inc. Toshihiko Ozaki (56) References JP-A-63-56460 (JP, A) JP-A-61-78657 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB Name) B41J 2/265

Claims (1)

(57) [Claims] 1. A method for producing a needle guide, wherein the thickness of a thin portion between guide holes in a row of through guide holes is not more than one third of the guide hole diameter by ceramic powder injection molding, In the injection molding, using a mold having an introduction guide portion provided so as to seal all outlets of one of the through guide holes, a molding material is injected through the introduction guide portion to obtain a molded body. Removing the introduction guide portion after firing.