JPS634491B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in extrusion molding dies.

Extrusion molding of plastic sheets, films, etc. is usually carried out using T-dies, coat hanger dies, etc., but in order to achieve high productivity of the product (extrudate), increasing the extrusion molding speed,
With the conventional extrusion molding die described above, defects such as shark skin or melt fracture occur in the product, so there is a limit extrusion molding speed, which hinders increasing the extrusion molding speed. For this reason, there is a tendency to make products wider in order to increase product productivity, but when the width of the product is made wider, a problem arises in that the quality of the product becomes more uneven in the width direction. The cause is abnormal flow of raw materials in the die due to increased extrusion speed, or local viscoelastic effects due to non-uniformity of shear rate, residence time, temperature, etc. in the width direction of the die. It is known that this is due to the difference.

Conventionally, therefore, the above-mentioned non-uniformity has been corrected by using a choke bar provided in the flow path within the die, a lip opening at the die outlet, or the like. This method has the effect of making the thickness of the product uniform, but
Not only is it impossible to make the quality of the product uniform in terms of optical selectivity, haze, Young's modulus, yield strength, etc., and it is not possible to obtain a good product, but the molding equipment has become larger and the quality of the extruded product has increased. If you are aiming for productivity,
This cannot necessarily be said to be an efficient method.

The present invention eliminates the defects and problems associated with the conventional extrusion molding die, enables high extrusion speed, and provides high productivity and good extrusion molded products with uniform quality. This was proposed with the aim of providing an extrusion molding die capable of extrusion molding. The resin inflow angle α along the molten plastic streamline in the die width direction
This relates to an extrusion molding die characterized in that it is set constant.

Hereinafter, the present invention will be specifically explained with reference to embodiments shown in FIGS. 1 and 2. In those figures, 1
2 is the die body, 2 is the die lip, 3 is the manifold, 4 is the resin inflow part from the manifold 3 to the die lip 2, and 5 is the inflow of plastic that has been uniformly melted and kneaded by a plasticizing device (not shown) such as an extruder. , 6 is the resin inflow angle α from the manifold 3 to the resin inflow part 4, 7 is the width a of the manifold 3, and 8 is the resin inflow width b from the manifold 3 to the resin inflow part 4.
are shown respectively.

In the extrusion molding die having the above configuration, the plastic is uniformly melted and kneaded by a plasticizing device such as an extruder (not shown), enters the inflow section 5, passes through the manifold 3 to the die lip 2, and exits the die in the form of a continuous sheet. In this case, when the molten plastic flows from the manifold 3 into the die lip 2 through the resin inlet 4, it is elastically shaped by shearing in the resin inlet 4. As mentioned above, shark skin, melt fractures, etc. occur, which limits the production rate. Therefore, the inventor of the present invention conducted extensive research on how to prevent the occurrence of the above-mentioned shark skin and melt fracture, and increase the production speed, and as a result, the relationship between the resin inflow angle α and the critical production speed Scr was determined. It was found that the relationship shown in Figure 3 exists. In other words, when the resin inflow angle α becomes smaller, the limit production rate suddenly decreases.
It has been found that Scr increases and the increasing effect is significant when the inflow angle α is 60° or less, preferably 30° or less. However, when the inflow angle α is set small, the critical production rate Scr becomes highly dependent on the inflow angle α, and when extrusion molding is performed under the limit conditions, the resin inflow angle α along the plastic flow line in the die width direction increases.
It was also confirmed in the above study that unless the .

In the conventional extrusion molding die shown in FIG.
4a, when the flow line of the plastic solution inside the die body 01 moves away from the resin inflow part 05, the distance to the die lip 02 becomes longer, and when the inflow angle α is kept constant, the width of the manifold 03 becomes larger than the die lip 02. It becomes too large at the end, and the design condition of manifold 03, which requires an appropriate width dimension, cannot be satisfied, and it cannot be used as a practical die.In addition, if the inflow angle α is made small, the die structure will melt. The resin becomes longer in the flow line direction, and the die exit opening phenomenon occurs due to the resin pressure inside the die. Therefore, it has been found that in order to prevent the opening phenomenon at the die exit, conventional extrusion molding dies have a problem in that the rigidity of the die must be extremely increased.

Therefore, the present inventor has determined that the inflow angle α of the molten resin is
As a result of further intensive research in order to provide an extrusion molding die with a small and uniform inflow part and a short length of the inflow part, as shown in Fig. 4, the width a of the manifold 3 and the width b of the inflow part 4 were The ratio b/a is approximately 0.5
It has been found that in the above case, the critical production rate Scr remains constant.

The present invention has been proposed based on the findings from such test research, and the ratio b/a of the width a of the manifold 3 to the width b of the resin inflow portion 4 is
By discontinuously connecting the manifold 3 and the resin inflow part 4 in a range of 0.5 or more, and gradually changing the value of the ratio b/a to a larger value along the die end direction,
It was possible to provide an extrusion molding die in which the resin inflow angle α was kept constant without increasing the length l of the die body 1.

The extrusion molding die of the present invention is constructed as described above, and the molten plastic that enters from the resin inflow section 5 reaches the die lip 2 from the manifold 3 through the inflow section 4, and is formed into a sheet shape outside the die. The product is cooled and solidified, but in this case, in the extrusion molding die of the present invention, the width a of the manifold 3 is
Since the ratio b/a between the width b and the width b of the inflow section 4 is set to approximately 0.5 or more, the limit production speed Scr is the fourth
As shown in the figure, the flow rate is maintained constant, preventing the occurrence of shear skin, melt fracture, etc. in the inflow section 4, and improving the production speed.

Since the extrusion molding die of the present invention has the above-described configuration and function, the present invention eliminates the defects and problems of the conventional extrusion molding die and achieves high productivity. Furthermore, the present invention has the practical effect of realizing an extrusion molding die that can produce excellent extrusion molded products with uniform quality.

It goes without saying that even if a conventional die yoke bar or die lip adjustment mechanism is added to the die of the present invention, these additional members will have the same functions and effects as conventional ones.

[Brief explanation of the drawing]

1 and 2 are schematic explanatory diagrams of one embodiment of the present invention, where FIG. 1 is a front sectional view, and FIG. 2 is an A of FIG.
- A cross-sectional view, Figure 3 is a graph showing the relationship between the inflow angle and the limit production speed, and Figure 4 is the relationship between the limit production speed when the inflow angle is 30°, the width a of the manifold and the width b of the inlet part. FIG. 5 is a sectional view corresponding to FIG. 2 of a conventional extrusion molding die. 1: die body, 2: die lip, 3: manifold, 4: inlet, 5: resin inlet, a: width of manifold, b: width of inlet, α: inflow angle.

Claims (1)

[Claims] 1 Ratio b/
The value of a is formed in a range of approximately 0.5 or more and gradually increases toward the ends in the width direction of the die body, and the resin inflow angle α along the molten plastic streamline in the die width direction is kept constant. An extrusion molding die characterized by being set to.