JPS6356048B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the screw of an injection molding machine for improving the mixing and dispersion of a thermoplastic resin and inorganic fibers such as glass fibers.

Regarding the screws of conventional resin molding machines, the screws of the conventional resin molding machines are described in the publications of JP-A-56-92039 ``Screws for Thermoplastic Resin Molding'' and JP-A-58-31728 ``Plasticizing and Kneading Apparatus for Plastic Extrusion Machines.'' It is disclosed that the resin including the unmolten resin is completely mixed and kneaded by the interlocking action of the mixing groove provided in the mixing section and the inner surface of the cylinder.

That is, to explain this with reference to FIGS. 1 and 2, 1' is a screw type screw, 2' is a flight, 3' is a mixing part, 3'a is its outer diameter, and 3'
b is the outer diameter 3'a to improve resin flow.
The outer diameter of the part (indicated by diagonal lines) that has been partially removed,
4'a, 4'b, . . . are mixing grooves, 5' is the inner surface of the cylinder, and S' is the gap between the inner surface of the cylinder 5' and the mixing groove 3'b. In this way, in the conventional mud screw type screw, the resin charged from the hopper side passes through each process and flows through the mixing grooves 4'b, 4'c, ... and the gap S' as shown by the solid line. , heated, melted, and mixed to completely disperse the resin.

However, when glass fibers are mixed with resin, kneading and dispersion are extremely difficult for the following reasons. In other words, when directly kneading glass fibers and resin, several hundred glass fibers with a thickness of 10 to 30 μm are bundled, cut into pieces of several mm, and put together with the resin through a hopper, heated, compressed, etc. The resin and glass fibers are mixed and sent by flight to the mixing section, then kneaded along the route of groove 4'b → gap S' → groove 4'c, and injection molded into a mold. However, the problem was that the dispersibility was poor and bundles of glass fibers remained in various parts of the molded product.

As a result, the strength of the molded product is uneven, the tensile strength is low, and the appearance is very poor. To explain this with reference to Fig. 3, A is a mixture of 80% resin and 20% glass fiber, kneaded and molded using the conventional screw type screw, 6' is a molded product, 7'a, 7''b...' is a state in which the glass fibers are not sufficiently dispersed and form a bunch,
Part of it is a test piece 8′ (size 50 x 50 mm)
The situation in which the image is cut out and a portion 9' of the image is further enlarged is shown in FIG. 10'a and 10'b are clusters of glass fiber bundles, which are shown in Photo 1. As shown in samples 10'a and 10'b, it is clearly seen that the dispersion was insufficient and the appearance was not good.

As described above, since it is extremely difficult to mix and knead the resin and glass fiber with the conventional screw type screw, current production of FRP is difficult.
In all cases, appropriate amounts of resin and glass fiber are mixed to produce pellets, and the pellets are fed into a hopper to produce FRP, which is a cause of high costs.

The present invention improves the above drawbacks. That is, when manufacturing FRP by kneading resin and glass fiber, the pellet manufacturing process is omitted,
To provide a screw for a resin injection molding machine that directly kneads resin and glass fiber to uniformly disperse the glass fiber, has excellent strength, and has a good appearance.

To this end, the inventors have repeatedly conducted various tests regarding the arrangement and shape of the grooves for mixing in the mixing section where resin and glass fiber are kneaded, and as a result, we have found that the length of the mixing section is approximately the same as the length of the mixing section. A groove (hereinafter referred to as a 1-stage mixing groove) is provided, and both ends of the 1-stage mixing groove are dead ends, and then a groove corresponding to approximately 1/2 of the length of the mixing section is installed parallel to the 1-stage mixing groove. Grooves (hereinafter referred to as two-stage mixing grooves) are arranged in series, and the first-stage mixing groove and the second-stage mixing groove are arranged alternately, and one end of each of the two-stage mixing groove is connected to the hopper side and the second-stage mixing groove. 1 which communicates with the nozzle side and is adjacent to the opposite rotation direction side of the screw shaft of the 2-stage mixing groove located on the hopper side among the 1-stage mixing groove and the 2-stage mixing groove.
A part of the outer shape of the mixing part is cut out to make it easy for the resin and cut glass fibers to pass between the mixing groove of the first stage and the nozzle adjacent to the mixing groove of the first stage in the counter-rotational direction of the screw rotation shaft. A part of the outer shape of the mixing part was removed between the two mixing grooves on the side to create a passage for the resin and glass fibers, and the inner surface of the cylinder of the injection molding machine where the screw operates and the outer diameter of the mixing part were removed. This is the structure of the mixing section that forms a gap S with the wall surface.

In a mixing section with such a structure, molten resin material and cut glass fibers as a filler enter from the hopper side of the two-stage mixing groove, move forward while rotating and mixing in the groove, After passing through the gap _S1 , it flows into the first stage of mixing groove,
It moves forward while rotating and mixing inside this one-stage mixing groove, then flows into one of the two-stage mixing grooves through gap S ₂ , repeats further rotation and mixing, and is sent to the nozzle side. . In this case, the glass fibers are transferred from the second mixing groove to the first mixing groove, and from the first mixing groove to the second mixing groove, and each time they pass through the gaps S ₁ , S ₂ ..., the glass fibers become stronger. The glass fibers are subjected to shearing force, and the shearing force acts to loosen the bundle, and the resin and glass fibers in each of the mixing grooves pass through the gap two or more times due to the rotation of the screw. The glass fibers are no longer bunched together and can be dispersed very effectively.

As a result, with this device, (1) it is possible to directly manufacture FRP from resin and glass fibers without going through the pellet manufacturing process, (2) the glass fibers are no longer bundled and can be uniformly dispersed, and ( 3) The tensile strength of FRP is also improved by 10 to 20%, and (4) significant cost reductions can be achieved by shortening the process.

There are other effects.

Examples will be specifically described below with reference to FIGS. 4 to 6.

1 is a screw, 2 is a flight, 3 is a mixing section, 3a is its outer diameter, and 3b is an outer diameter obtained by removing a part of the outer diameter of 3a (indicated by diagonal lines). Reference numeral 4 denotes a one-stage mixing groove, which is slightly shorter than the length of the mixing section, and both ends 4a and 4b of the groove have a dead-end shape, and two-stage mixing grooves 5 and 6 are provided in parallel to the first-stage mixing groove. , the end of the groove consists of a communicating part 5a with the hopper side and a dead end part 5b,
The other groove 6 of the two-stage mixing groove also consists of a dead end portion 6b and a communicating portion 6a to the nozzle side.

The screw 1 rotates clockwise in FIG. There is a partially removed gap for the material to pass between the mixing groove and the two-stage mixing groove on the nozzle side adjacent to the opposite rotation direction of the screw. 7 is a cylinder, 7a is the inner surface of the cylinder, the gap S between 7a and 3b is approximately 0.5 mm, and the gap between 7a and 3a is within 0.1 mm.

In the above configuration, the resin fed from the hopper side and the cut glass fibers are distributed between two mixing grooves, a gap S 1, a first mixing groove, and a gap _S1 .
S ₂ , two-stage mixing groove, flowing out to the nozzle side, A
→B→C→D→E→F→G, the glass fiber bundle is sheared by skimmers S ₁ and S ₂ ,
Mixing and kneading are repeated by rotating the materials within each groove, and the glass fibers are uniformly dispersed.

FIG. 6 is an external view of a product 9 injection-molded according to the present invention, in which the glass fibers are not bunched together, and the actual product is shown in Photo 2, which is enlarged approximately 30 times by taking a test piece 10. This photo clearly shows that the glass fibers are neatly and evenly distributed one by one.
In this way, the strength when uniformly dispersed, that is,
The tensile strength when 20% glass fiber is mixed into polypropylene resin is 460 kg/cm ² , which is 10 to 15% higher than conventional products.

[Brief explanation of the drawing]

Figure 1 is an external view of a conventional screw, Figure 2 is an enlarged view of it, A is a side view of the mixing section, B is a sectional view of A, and Figure 3 is a molded product according to the conventional example. A is a perspective view, B is a partially enlarged view, C is a further enlarged explanatory view, and FIG. 4 shows an embodiment of the present invention, A is a side view, and B is a sectional view of A. , Fig. 5 shows a cross-section of the mixing part, A is a cross-sectional view of the first-stage mixing groove, B is a cross-sectional view of the second-stage mixing groove, and Fig. 6 is a perspective view of the molded product based on this example. It is a diagram. 1...screw, 3...mixing department, 4...
...1st stage mixing groove, 5, 6...2nd stage mixing groove, S, S ₁ , S ₂ ... gap.

Claims (1)

[Claims] 1 Of the cylinder and screw that constitute the injection section of an injection molding machine, the screw is provided with a mixing section having a plurality of mixing grooves, and among the mixing grooves, one stage of mixing approximately corresponds to the length of the mixing section. A groove and two mixing grooves arranged in series parallel to the first mixing groove, and between the first mixing groove adjacent to the two mixing grooves on the hopper side in the direction opposite to the screw rotation direction. An injection method characterized in that a gap is provided in which the injection molding material flows, and a gap in which the injection molding material flows is provided between the first mixing groove and the adjacent nozzle-side mixing groove on the opposite side of the screw rotation direction. Molding machine screw.