JPS62170319A - Extruder die for thermoplastic melt - Google Patents

Abstract

PURPOSE:To reduce neck-in quantity to a substantial extent and uniform the thickness of both ends by protruding the discharging end of a die lip constituting a channel gap to the discharging direction of thermoplastic melt at both ends of an extruder die. CONSTITUTION:A thermoplastic melt 1 resulting from heat fusion is extruded out through a manifold 3 of an extruder die 2 and die lip 4, 5 and 5' and discharged downward in a form of membrane. Both ends 5 and 5' of die lip protrude out of the central part of die lip 4 in a shape of arc. The extreme end is terminated with a side plate 8. The flow gap of a die lip in the extruder die 2 is adjusted with gap adjustment bolts disposed to the direction of die width. The fusing substance flows from a die inlet 9 to the direction of an arrow mark 10, passes through a flow gap constituted with a die lip 4, 5 and 5' and forms a membrane shape 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an extrusion die for thermoplastic melts, which is used when extruding thermoplastic melts to form films, sheets, flat plates, and the like.

(Prior Art and Problems to be Solved) The biggest problem with extrusion molding of thermoplastic melts is the so-called neck-in problem. This is because the thermoplastic molten material discharged from the extrusion die contracts inward in the width direction, so that both ends become thicker than the center. The edges where neck-in occurs are not made into products because of their uneven thickness, and are slit and discarded, which reduces the product width, wastes raw materials, and increases raw material costs. This is extremely uneconomical as it increases. For this reason, various die structures have been devised and put into practical use in order to reduce the neck-in area and adjust the non-uniformity of the thickness. For example, the shape of the extrusion die may not be changed and the known shape may be maintained, but an insert having guide surfaces for guiding the molten material may be provided at both ends of the die.

There are those in which the flow of the molten substance is guided outward in the width direction (for example, JP-A-58-124618), and those in which the shape of the extrusion die is changed and the slit width of the die land following the manifold is made into a sin function curve ( For example, JP-A-54-95
No. 662).

These require special processing such as a backing device or a moving device, or are not easy to manufacture.

In recent years, there has been further improvement in thickness uniformity. There is also a demand for extrusion molding dies that reduce raw material loss. The purpose of the present invention is to solve these problems and provide a new extrusion die for thermoplastic melts that is simple and of 1η construction.

(Means for Solving Problems According to the Invention) The present invention was discovered as a result of intensive studies to prevent neck-in that occurs when forming films, sheets, flat plates, etc. using an extrusion die.

By providing protrusions at both ends of the extrusion die.

It was found that neck-in was prevented. The structure of the present invention based on this knowledge is as follows. That is,
In an extrusion die for a thermoplastic molten substance having a channel gap for extruding a thermoplastic molten substance, the discharge end of the die lip constituting the channel gap protrudes in the direction of discharging the thermoplastic molten substance at both ends of the extrusion die. This is a characteristic feature. As long as the shape of this protrusion is almost continuous and the length of the protrusion increases as it goes outward, the cross section may be arcuate, elliptical, linear, etc. It depends on the type of molten substance, its properties such as fluidity and workability, discharge amount, processing speed, etc.
It is desirable to select the shape to be adopted by experiment under the conditions to be used. In addition, the size of this protrusion (i.e., the maximum protrusion length (in the extrusion direction)) and the width of the protrusion will vary depending on the type and properties of the thermoplastic melt material used, processing conditions, etc., and will be determined through experiments under the conditions to be used. It is desirable to do so.

(Example) The present invention will be described below with reference to drawings showing examples. FIG. 1 is a sectional view showing one embodiment of the present invention, in which a hot melted thermoplastic molten substance 1 is extruded through a manifold 3 and die lips 4, 5° 5' of an extrusion die 2, and is formed into a film. This shows how the liquid is being discharged downward. Both ends 5.5' of the die lip protrude from the central die lip portion 4 in an arcuate manner, and the final ends terminate in the side plate 8. Here, the flow path gap t between the die lips in the extrusion die 2 is adjusted by generally known gap adjustment bolts (not shown) arranged in the die width direction.

The molten material flows from the die inlet 9 in the direction of arrow 10 and is extruded into a film 1 through the channel gap defined by the lips (4, 5, 5''').

FIG. 2 is a partially enlarged sectional view showing another embodiment of the present invention. In the figure, one end 6 of the die lip protrudes with a linear slope in the direction in which the thermoplastic molten material 1 is discharged. h is the maximum protruding length of the die lip, jl! indicates the width of the protrusion. Quite good results were also obtained by extending the slope to the center of the extrusion die 2 and providing slopes from the center of the extrusion die to both ends of the die, but (1) usually gives preferable results in the range of about 5 to 1001. The protruding length h of the die lip is preferably in the range of about 1 to 70 mm.

More preferably, the range is about 20 to 40 mm.

However, h is set within the air gap between the cooling roll and the center of the die. Generally air gap is 80~160m+
It is s.

In the embodiment shown in FIGS. 1 and 2, the length d of the die lip in the discharge direction is constant;
．． As shown by 7', the length d of the die lip in the discharge direction can be increased to d' at the two tips. In that case,
The extrusion flow path resistance at the tip can be further increased.

(Experiment example) Thermoplastic polyolefin resin (low density polyethylene) M
, 1. 7.2 using an extrusion die as shown in Fig. 4, with a die lip channel gap of 11ffl and a die discharge width of 400 mm.
・Discharge amount 72kg/h, processing speed 100m/win
, air gap 100m1. It was processed into a film at a temperature of 310°C. At this time, an extrusion die without a protruding die lip and an extrusion die with a protruding die lip were used under the same conditions as described above. The extrusion die with a protruding die lip had a die lip of 30a+m, h-30wm and a linear sloped cross section. Use both.

The amount of neck-in and the thickness of both ends of the film were measured. The measurement results are shown in Table 1.

Table 1 (Unit: 1111m) (Note) In the steady thickness (center) 0.030 neck-in amount, the number in parentheses indicates the neck-in amount on one side.

(Functions and Effects) As is clear from Table 1, when a die with a protruding die lip according to the present invention is used, the amount of neck-in can be reduced by half or less compared to when a conventional die without a protrusion is used. can be reduced. Also, according to the die according to the present invention, the maximum thickness at both ends is 0.033 mm or less, which can be kept within 10% of the average steady thickness of 0.030.

Generally, the larger the air gap, the greater the amount of neck-in; however, in the present invention, by protruding die lips at both ends of the extrusion die, the air gap at both ends of the die is reduced, thereby reducing the amount of neck-in. is realized.

It also contributes to increase the flow resistance of the thermoplastic melt at both ends by having the die lip protrude at both ends of the die. Furthermore, by using the flow path gap and the bolt bolt in combination, it becomes possible to easily adjust the thickness of the extruded material at both ends of the die to make it uniform.

As described above, the extrusion die according to the present invention can significantly reduce the neck-in amount of an extrusion molded product and easily make the thickness of the extrusion molded product uniform at both ends. Therefore, there is no waste of raw materials, and production efficiency can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention. FIG. 2 is a partially enlarged sectional view of another embodiment of the present invention. Figure 3 is a sectional view taken along line ■-■ in Figure 1. FIG. 4 shows cross-sectional views of other embodiments used in the experimental examples. 1... Thermoplastic molten substance 2... Extrusion die 3... Manifold 4.5.5', 6... Die lip t... In the channel gap... Width h of the protruding part... protrusion length

Claims (1)

[Claims] In an extrusion die for a thermoplastic molten substance having a channel gap for extruding a thermoplastic molten substance, the discharge ends of the die lip constituting the channel gap protrude in the direction of discharging the thermoplastic molten substance at both ends of the extrusion die. Features an extrusion die for thermoplastic melt materials.