JPH0422128B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical scope to which the invention pertains] The present invention relates to the tip angle of a screw head in a plasticizing device of an injection molding machine and the gap formed between the screw head and the tapered inner wall surface of the heating cylinder tip facing the screw head when the screw advances. . [Conventional technology and its disadvantages] In recent years, plastic molded products are increasingly molded in one type and in many colors, and are often used in various home appliances, medical and hygiene products, etc. However, the time required for changing colors and resins, and the amount of time required for purging The cost of agents and resins continues to increase, and the operating rate of molding machines is also decreasing. In order to do this efficiently, we prepare multiple injection units each consisting of a screw and a cylinder.
A method of alternately using and replacing them has been considered, but this is not preferable from a cost standpoint. The difficult place to change the color is the tip of the screw head, where old resin and old color tend to remain near the gate of the molded product. This is because it is known that if the gap formed between the screw head, the tapered inner wall surface at the tip of the heating cylinder, and the nozzle is large, old resin will accumulate on each wall surface, and this accumulation will occur in the product. Not only does it gradually make the product inferior, but it also causes retention burns in ABS/PVC resins, etc. Here, a gap formed by the tapered inner wall surface of the conventional screw head and the tip of the heating cylinder,
To explain the shape of the vicinity of the nozzle hole, as shown in Fig. 3, the tip angle of the screw head 1 is 30 degrees, the tapered inner wall surface A of the head 2 at the tip of the heating cylinder is 24 degrees, and there is a gap in front of the screw head 1. When forming the part 3 and providing the nozzle hole 4 in front of this cavity 3, the old resin etc.
It stays in the "b" part, and this becomes mixed with old resin etc. around the gate, causing the color change and resin change to be delayed forever, and in the end, the nozzle and cylinder have to be replaced. . This is because the resin path formed between the screw head surface and the tapered inner wall surface of a heating cylinder, etc., is large, and the washing effect is not produced during resin flow.
This is because old resin and the like accumulate on the surface of the screw head of the molten resin and on the tapered inner wall surface of the heating cylinder. In order to eliminate this drawback, there is a method as shown in FIG. 4 in which the tip angle of the screw head 5 is set at 20 degrees to narrow the gap formed between it and the tapered inner wall of the heating cylinder. In this case, the gap became narrower, but the surface area of the screw head and tapered inner wall surface became larger, and the amount of resin adhering thereto increased. Also, although the amount of retained resin has been reduced slightly, the cross-sectional area of the flow path at the tip of the screw head has become smaller, and depending on the molding conditions and the type of resin, yellowing may occur due to resin burning, so it may be necessary to disassemble and clean it. [Object of the Invention] The object of the present invention is to provide a plasticizing device for an injection molding machine that eliminates the above-mentioned drawbacks, eliminates stagnation, and facilitates resin and color changes. [Summary of the Invention] In order to achieve the above-mentioned object, the angle of the screw tip is set to 50 to 80%, and when the screw advances, the gap formed between the screw head and the tapered inner wall surface of the heating cylinder tip facing the screw head is 3
The plasticizing device of the injection molding machine was designed to achieve a plasticization of less than mm. In addition, the resin path at the tip of the heating cylinder is formed in parallel from the tip of the screw head at the entrance, and reaches the nozzle hole, which is the exit of the resin path, and is gradually tapered from the parallel hole. This is a plasticizing device for an injection molding machine. [Embodiment] Next, an embodiment of the present invention will be described with reference to FIG. 1. Reference numeral 11 denotes a heating cylinder, and a screw 13 having a screw head 12 attached to its tip is fitted into the inner diameter surface. A heating cylinder head 14 is attached to the tip of the heating cylinder 11, and the inner diameter surface has a conical tapered surface B having an angle approximately equal to the tip angle of the screw head 12, and the gap formed between the screw head 12 and the tapered surface B is δ is 3 mm or less at the screw advance limit. Said screw head 1
The tip angle of the screw head 12 is 50 to 80 degrees, and the resin path 15 in front of the tip of the screw head 12 forms a parallel hole from the entrance side of the screw head 12 to the back (front) to reduce the inner surface area of the resin. However, the parallel hole is gradually tapered to reach the nozzle hole, which is the outlet of the passageway, so that a washing effect is sufficiently exerted on the inner wall surface of the hole, and the resin is prevented from stagnation. [Operation and Effect] With the configuration as explained above, test injections of color changing performance were performed using various combinations of the tip angle of the screw head, the tapered surface of the inner wall of the heating cylinder, and the gap formed by the screw head.The results are shown below. show. [Test 1] Resin: PP color change from red to natural Screw diameter: 50φ (1S150 manufactured by Toshiba Machine)

[Table] As understood from the above results, the tip angle is 50~
It can be seen that 80° is good and the gap δ between the screw head and the inner wall surface is 3 mm or less. In addition, when the tip angle of the screw head is 30 to 40 degrees or less, even if the gap δ is 3 mm or less, both the surface area of the screw head and the tapered inner wall surface become large, so the amount of resin retained and attached increases, and the screw discharge pressure when the screw rotates. While the resin reaches the tip of the screw head, the gap δ becomes smaller and the pressure decreases, reducing the resin washing effect. On the other hand, if the tip angle of the screw head exceeds 90°,
The distance I from the nozzle tip to the screw head increases, the amount of resin remaining in the resin path in front of the screw head increases, and the color changing performance deteriorates. [Test 2] Also, the test results regarding color change time are shown below.Resin: Replacing ABS black with PP natural Screw diameter: 125φ.Gap δ=3mm (IS1250CN
(manufactured by Toshiba Machine)

[Test 3]

Color change test Resin: PP (Tonen PPJ209, colored blue, white) Screw diameter: 125φ. Gap δ = 3mm Comparison method is blue molded product (box 190 x 300
After extrusion purging after extrusion purging of 50 x 50,

【table】

[Table] As can be understood from Tests 2 and 3, the resin change time and amount of resin change is 1/2 to 1/3 compared to the conventional method, and the color change is also 1/3 to 1/3 compared to the conventional method. 4 hours,
It can be seen that the amount of resin also decreased significantly. As explained above, it will be understood that the present invention greatly improves resin and color change, eliminates retention, and greatly improves the productivity of the molding machine.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment according to the present invention. Second
The figures are diagrams illustrating various examples of combinations of the screw head and the tapered inner wall surface according to the embodiment of the present invention. Third
FIG. 1 is a diagram showing a conventional method. FIG. 4 is a diagram of another conventional method. 12...Screw head, B...Tapered inner diameter surface, 15...Resin path, δ...Gap.

Claims (1)

[Scope of Claims] 1. The angle of the screw tip is 50 to 80 degrees, and when the screw advances, the gap formed between the screw head and the tapered inner wall surface of the heating cylinder tip facing the screw head is 3 mm or less. A plasticizing device for an injection molding machine featuring: 2. The resin passage at the tip of the heating cylinder forms a parallel hole from the tip of the screw head at the entrance, reaches the nozzle hole which is the exit of the resin passage, and is gradually tapered from the parallel hole to become thinner. A plasticizing device for an injection molding machine according to claim 1.