JPS58168536A - Thin injection-molded product with thick parts and molding die thereof - Google Patents

Abstract

PURPOSE:To prevent the formation of weld line in thin parts and consequently obtain a product with high strength by a method wherein gates of molten resin are located at the positions symmetric with respect to thick parts in both sides of the respective thick part in the injection-molding of a belt-like product with thick and thin parts of respective specified thickness. CONSTITUTION:In order to injection-mold a belt-like resin product having the thin parts 3 and thick parts 4 and 5, the thickness of which are more than 120% of that of the thin parts such as an endless belt with nibs for feeding frames of a camera film, the gates 8 of molten resin are radially located at the intermediate point between one thick part (or nib) 4 and the adjoining thick part 4 in order to injection-mold. Owing to the arrangement of the gates as mentioned above, weld lines are formed in the thick parts, resulting in enabling to reduce the lowering of the strength of the product.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin-walled thermoplastic resin injection molded product with a thick-walled part with improved physical strength and a method for manufacturing the same, and particularly relates to a thin-walled belt-shaped conductive member, such as a film frame feeder for a camera. etc.1
/C Concerning endless belts with claws, etc. used, and molds for forming the same.

When injection molding a belt-shaped product with thick and thin parts, the injection port (dart) for thermoplastic resin was conventionally placed in one place, and it was placed in the thick part (Figure 4). 0) When inlets were installed in two or more locations, they were generally attached to thick parts (Figures 3 and 6). Generally, the part where thermoplastic resin molds and resin flows converge is called a weld bind, but this confluence part has poor strength and is prone to cracking. In the conventional method, this merging part is located in a thin part, which causes a problem in that the strength of a belt-shaped product is greatly reduced.

Even if a thick-walled part called a reinforcing lip is attached to reinforce the strength of the belt, it is difficult to avoid the convergence of the thin-walled part, and the strength cannot be effectively improved. Furthermore, due to the ease with which the rib portion flows, sink marks (shrinkage after molding) may occur, causing problems in terms of dimensional accuracy.

These problems are particularly important in the case of an endless belt with claws for feeding film frames in a camera, which is one embodiment of the present invention. Conventionally, frame-by-frame advancement of film has been carried out by inserting the tooth width of a sprocket into the perforations of the film and rotating this sprocket. As a new method that improves this, a method has been devised in which frame-by-frame feeding is carried out using an endless belt type caterpillar with a sliding claw that engages the grooves of the film (pending application by the same applicant). Showa 56
-3766'6>. When this belt is manufactured by injection molding of thermoplastic resin, if the joining part is located in a thin part, the strength will be extremely reduced and it will not be practical. Become. A new injection molding method is needed to meet the demands of this product.

The object of the present invention is to provide a new injection molding method that solves the conventional problems, and a belt-shaped molded product with excellent strength obtained by the method.

That is, the present invention provides an injection molded product such as a belt-shaped endless belt made of a thick part and a thin part obtained by injection molding a thermoplastic resin. The thickness of the thick part is determined to be 20% or more thicker than the thickness of the thin part. -1 The mold for molding the molded article of the present invention has similar characteristics.

The present invention will be explained in detail below.

The belt-shaped molded product of the present invention consists of a thin wall portion and a thick wall portion.

It does not apply to flat belt-shaped molded products with a certain thickness. Thickness ratio of thin part and thick part 1d1: 1.2 to 1
: 30.0, preferably 1 : 1.5 to 1 :
15.0, particularly in the range of 13 to 1:10.

Unless the thickness of the thick portion is 20% or more thicker than the thickness of the thin portion, the effect of the invention will be unclear. Note that the shape of the thick portion is not necessarily limited to a continuous shape such as a rib, but may be a 7-screw shape or an intermittent protrusion. The effect of the present invention may be manifested in molded products with different wall thicknesses other than belt-like molded products, but in general, for products with complex shapes, the convergence part is set to a previously anticipated wall thickness part. It is difficult to do so, and the necessity of reinforcing thin parts is not always present in the case of belt-shaped molded products. In the case of a belt-shaped molded product, the thin part occupies a large portion of the entire molded product, and the strength of this part often dominates the overall strength. In many applications, tensile stress is concentrated in this thin part, so improving this strength is of great significance.

The molding method of the present invention consists in arranging the resin injection port, which was conventionally installed in the thick part, at a specific position in the thin part. The injection ports are arranged symmetrically at two or more locations when viewed from the thick part, and are preferably opened in the long sleeve of the obi in the straight direction. By changing the position of the injection port, the resin flows from the thin section to the thick section and merges at the thick section. In this way, the merging portion with poor strength can be located in the thick portion. In addition,
In conventional methods, confluences usually occur in thin-walled areas, and even a small amount of external force can cause them to break immediately. By the method of the present invention, the strength of the entire belt could be increased by more than 10 times. 1. It has been found that shrinkage after molding is small and dimensional stability is improved. This is because when a confluence is formed in a thick part, the resin is mixed and the flow is turbulent, making it difficult for faults (weld lines) to form, and even if a fault does form, it will be strengthened to a considerable extent due to the thickness. it is conceivable that. In contrast, in the conventional method, the resin flows through thin parts and merges in a laminar flow state, which is likely to cause faults and create parts where the tensile strength is extremely low. This effect can also be confirmed by measuring the strength of a flat plate with ribs 1. When reinforcing ribs are attached to a flat injection molded product, when ribs are attached on a line connecting two injection ports (Figure 6), and when two injection ports are attached. When attaching a rib perpendicular to the midpoint of the line connecting (Figure 7)
When compared, the tensile strength of the molded product is 5 to 15 times better in the latter.

In addition, the present invention is effective for tearing thin parts.
Applicable to general resins such as polypropylene and polyethylene, which usually have a reading value of 0.2 to 5.0, especially 0.2 to 5.0.
It is effective for those of 4 to 2.5 theories.

However, the thickness of this thin portion is not necessarily limited, and can be varied to some extent depending on the material, shape, etc.

An embodiment in which the injection molded product of the present invention is applied to an endless belt for feeding film frames will be described below as an example.

Figure 1 shows a state in which an endless belt-type caterpillar with claws (hereinafter simply referred to as the caterpillar) 3 is removed from the driving pulley 1 (Figure 1a) and the driven pulley 2 (Figure 1b) (Figure 1). It is a perspective view of C). FIG. 2 is a schematic plan view of a combination of the driving pulley 1, driven pulley 2, and caterpillar 3. The caterpillar 3 is shaped like an endless belt, and is spaced at equal intervals from the film perforation rows. A caterpillar driving pulley engaging pawl 5 is provided for engaging the film formation engaging pawl 4, the drive pulley 1, and the driven pulley 2. The caterpillar drive pulley is provided with recesses 6 and 7 for engagement with the engaging pawl 5.As shown in FIG. , the caterpillar drive pulley engaging pawl of the caterpillar 3 engages, and by applying power to the drive pulley, the caterpillar 3 is driven, and the film safety oration retaining pawl of the caterpillar 3 engages with the groove formation row of the film. As long as the caterpillar can be reliably driven, a timing belt or the like can be used as shown in Fig. 13.When injection molding this endless belt, it is necessary to 20% or more than the belt part, preferably 50%
%~301) 0%, particularly preferably 50%~1500
% thicker, and two or more thermoplastic resin injection ports are placed on the belt portion at symmetrical positions on both sides of the claw. The shape of the claw can be various, such as a cylinder, a cone, or a prism, but in any case, the shape is 0.
．． 2 to 5.0 - preferably 0.24 to 2.5 mm on the top and bottom or either side of the belt with a thickness of 0.4 to 2.5 mm
3. The protruding parts of Omm are attached at regular intervals.

-1; To describe the injection molding of an endless belt having 11 claws, the method of the present invention starts from 11 thermoplastic resin inlets arranged radially at the midpoints between all the claws. The injected resin flows from the thin belt part to the thick claws and is molded. In addition, in the conventional method, all injection ports were attached to the claw part, creating a reverse flow. Figure 3 shows the difference in the position of the injection port.
It is shown in FIG. The injection molding method of the present invention shown in FIG. 5 and the conventional method shown in FIGS.
, +41. It can be seen that the product (4) of the present invention has improved durability of the belt and claws compared to the conventional product (3).

The resin used here is polypropylene (MS-630 manufactured by Tokuyama Soda KK) made by polymerizing polyethylene into a block shape.
Silicone oil (dimethylpolysiloxane Shin-Etsu Silicone M (manufactured by KF) was added to this as a substance to improve the flow of the resin.
-96) 1 weight, 2 carbon black as coloring agent
Weight is added.

The preferred amount of carbon black is 1 to 10%.
The most preferable range is 2 to 3%. At a ratio of 1 or less, whitening may occur, and at a ratio of 10 or more, the strength decreases significantly. By using thermoplastic resin alone or by adding various fillers, extenders, additives, or by mixing two or more resins, the bending strength of the molded product can be 0.5 to 12 Kg/mA, preferably 1.0 to 6 K? /mA tensile strength 1.5Kg/-
All those having a tensile modulus of elasticity of preferably 2.1 Kg/mA or more, 0.25 to 5 K9/mA X 10'', preferably 0.6 to 2.5 K9/mA X 10' can be used. Particularly desirable in terms of properties are various polypropylene/or polypropylene copolymers, various polyethylenes or polyethylene copolymers, either alone or reinforced with various additives.If necessary, various pigments, dyes, metal powders and antistatic agents are used. A lubricant, a lubricant, and an antioxidant may be blended.Carbon black is particularly desirable, and the blending amount is 1-10 wt%, preferably J, 5-6 wt%, and more preferably 2-3 wt%.Silicon is a resin. It is preferable to use 0.2 to 10wt, preferably 0.5 to 10wt, as it improves the flow and mold release properties.
I'm in charge of wt.

Carbon black is most commonly used as a coloring agent for blackening. Titanium oxide is also used for whitening. The test results for "6", 1 cup using titanium oxide instead of carbon black are shown in Table 1 (5).
). After 20,000 uses, some whitening was observed in the area where the tabs came into contact with the perforations, but it was found that a belt with practical strength could be obtained. In addition to polypropylene, thermoplastic resins used for endless belts include high-density polyethylene, polystyrene, ABS nylon ester resins, low-density polyethylene, medium-density polyethylene, and low-pressure low-density polyethylene (L, L).
It is a resin etc. that has a thicker tensile elastic modulus by adding a light filler etc. to DPE) or the like.

Alternatively, copolymer resins thereof, and mixed resins of two or more of these can be considered. In any case, the bending strength is 0.5
~121 T/-1 Tensile modulus of elasticity is 025~51 (7/
Any thermoplastic resin having mA X of 10' can be used.

Furthermore, depending on the purpose and application, it is possible to increase the strength of even low-strength products compared to conventional injection molded products.
Generally useful. (2) in Table 1 shows that the bending strength is 0.
5 + < 9/ less than m4, tensile modulus of elasticity is 0, 151 (
An example is shown in which low density polyethylene with f/mA x 102 is used. Compared to the corresponding (3), it is considerably inferior and cannot be used for now. The additives to be added to the thermoplastic resin' include carbon black, various pigments other than titanium oxide, dyes, metal powders such as aluminum powder,
Antistatic agents, lubricants, silicone oils, surfactants, antioxidants, etc. can be added as necessary. Further, a reinforcing material such as glass fiber can also be used.

If the thin claw endless belt of the present invention were to be made of metal without using thermoplastic resin, holes would be made in the belt and claws would be caulked into the holes from above and below. but,
Not only is this expensive to manufacture, but it also cannot withstand Tenkawa in terms of strength. The results are shown in Table 1 (1). The comparison conditions are as follows.

Thin part thickness 0.05 threshold x width 2.4 throat, claw part Pituna 4.
75 ji total thickness 275 x diameter 16.5 φ, ring length 4.7
5 shouts x 11 claws - 52,25mm metal is 5US304
It is.

(Hereafter referred to as Eihaku) (Comprehensive one-time durability test) Load the film into the camera,
After actually feeding and rewinding the tape several times (one round trip is counted as one time), it was checked to see if the tabs had worn out or turned white.

The test conditions were: temperature -10°C, winding speed approximately 1 turn/1 sec, film pull-out resistance], 5Ks+ or less (commercially available film was used).

Next, the injection mold of the present invention will be described.

As shown in FIGS. 8 to 12, the molding die has injection ports located symmetrically on both sides of the thin-walled portion with respect to the thick-walled portion. The direction of the inlet with respect to the plane of the thinned part may be perpendicular or parallel to the plane of the thinned part, or in the paternal direction, perpendicular to, parallel to, or oblique to the thinned part axis, but it is important to maintain a symmetrical relationship with respect to the thickened part. Condition.

The injection ports may be located on the left and right sides of the plane of the thin portion, or on the front and back sides.

Figure 8 shows the endless belt for frame-by-frame feeding of the film used in 2.3 and 4.5 of Table 1, and the thermoplastic resin injection ports are located at 11 symmetrical positions on both sides of the thin-walled part with respect to the 11 thick-walled parts.
It is provided in the direction perpendicular to the plane of the thin part.
Since the molding time was short and the resin confluence was located in the thick part (claw), a product with high strength, low mold shrinkage, and good dimensional stability was obtained.

FIG. 9 is an enlarged schematic cross-sectional view of the portion B-C in FIG. 8.11.12.

FIG. 10 is a plan view of FIG. 9 viewed from the thermoplastic resin injection port.

Figure 11 is a modification of Figure 8, with 15 thick-walled parts and a total of 5 thermoplastic I or 1 fat inlets for every third thick-walled part in a direction perpendicular to the plane of the thin-walled part. The confluence of dovetail resin is located only in the thick part (claw) A marked with diagonal lines.

It is provided in a direction perpendicular to the plane of the thin part.11
The merging part of 1 fat is located only in the thick part (claw) A where the body part is located. In this case, the shapes in which the resin completely flows are cylindrical or conical (including those at the zenith), trapezoids, cross sections, circular (or semicircular) cross sections, and wall shapes perpendicular to the long axis of the belt ( (continuous, intermittent, partial), etc. can be selected as appropriate, and thin portions that protrude on one or both sides are permitted.

4 Drawing 1 (t + yearly explanation Figure 1 is a perspective view with the caterpillar removed from the drive pulley and slave pulley. Figure 2 is a perspective view of the caterpillar being engaged with the drive pulley and driven pulley. A schematic plan view of the combined state, FIGS. 3 and 4 are both schematic cross-sectional views showing an example of a conventional injection molding method, and FIG. 5 is a schematic cross-sectional view showing an example of the injection molding method of the present invention.

FIGS. 6 and 7 are perspective views showing an example of a method of injection molding a ribbed flat plate. FIG. 8 shows an example of the present invention in which a tab for advancing film frames is inserted. Figure 11 shows a molded product with a runner with a larger number of tabs than in Figure 8.The thermoplastic resin injection ports are one for every three tabs, for a total of 5 holes.The confluence of 411 resins is placed only in tab A. It is located.

In FIG. 12, the number of tabs is reduced by one from that in FIG. 8, and the thermoplastic resin inlet is placed by 2 tkl, so that the confluence of the resin is located only at tab A. Fig. 13 shows an example of a timing belt in which the caterpillar drive pulley retaining claw 5 of Fig. 2 is modified.

1. Caterpillar drive pulley, 2.. Driven pulley, 3.. Endless belt with claws (thin part), 4.5
...Claw (thick part), 8...Thermoplastic resin injection port, 8
Next: Thermoplastic resin inlet of runner, 9: Thin plate portion with ribs, 10: Rib (thick portion), 11: Runner.

Applicant: Fuji Photo Film Co., Ltd. Agent Patent Attorney Asami Kafuji Figure 3 Figure 4 Figure 5 Figure 6 78 Figure 8 Figure 11 Figure 13

Claims (1)

[Scope of Claims] 1) In an injection molded product, such as a belt-like belt consisting of a thick part and a thin part obtained by injection molding a thermoplastic resin, especially a belt with claws, a thermoplastic resin injection port is An injection molded product, characterized in that the thick part is injection molded at symmetrical positions on both sides of the thin part, and the thickness of the thick part is 20 inches or more thicker than the thickness of the thin part. 2) In a mold for molding a thermoplastic resin injection molded product, such as a belt-like part consisting of a thick part and a thin part, especially a tab belt, etc., the thermoplastic resin inlet is placed symmetrically on both sides of the thin part with respect to the thick part. 1. A mold for forming an injection molded product, characterized in that the thickness of the thick part is 20% or more thicker than the thickness of the thin part.