JPS62267120A - Die for manufacturing multi-layer blown film - Google Patents

Abstract

PURPOSE:To make it possible to stably form a multi-layer blown film with little ununiform thickness by a structure wherein a plurality of flow passages are concentrically provided at a die flow passage part just before molten resin, which flows through an influx port, enters a die main body and throttling parts are provided along the circumferential direction of one flow passage. CONSTITUTION:A die flow passage parts 12 and 19 located at a position before one molten resin forks in a die main body 9, the other flow passage is arranged concentric to one passage along its outer periphery. Accordingly, the structure which gives no effect to the distribution of the temperature of the die even when the temperatures of the respective resins flowing in the die are different from each other can be realized. Consequently, the temperature distribution in the die easily tends to be uniformized circumferentially and the outflow of the die also becomes uniform, resulting in the formation of a film with little ununiform thickness possible. Further, because throttling parts 130 are provided in the other passage, the molten resin passed through the other passage with the throttling parts is uniformized in the flow rate and forked, resulting further in the reduction of the ununiformity in thickness of the film possible.

Description

[Detailed description of the invention]

1. Field of Industrial Application] The present invention relates to an apparatus for forming multilayer films, and in particular,
The present invention relates to a die for producing a multilayer blown film for forming a multilayer blown film made of a thermoplastic resin such as polyethylene or polypropylene.

[Conventional technology]

Referring to FIG. 3, a conventional die for producing a multilayer blown film and its forming (film forming) method will be described.
2 was provided and extruded from an extruder (not shown).
The molten resin advances in the -L direction through the flow path 3 in the die flow path section 10 provided in the length direction of the die body L, and then, after branching at an appropriate angle, is pushed out of the die from the lip cap 4. Ru. On the other hand, the other resin inlet 5 is provided in the lateral direction of the die body 1, and another molten resin extruded from an extruder (not shown) is passed through a channel 6 provided in the lateral direction of the die body 1.
, bends in the right angle direction at the upper part of the branched flow path 7 of the molten resin, and then branches into, for example, water flow,
It merges with the above-mentioned - molten resin and is extruded out of the die through the lip gap 4. Such coextrusion results in multilayer blown films. As shown in FIG. 3, in the conventional die for producing a multilayer blown film, after branching of the - molten resin, a branched channel 7 is provided around the channel 8 of the other molten resin. However, as shown in the same figure, before the branching, the - molten resin flow path 3 is located independently in the die flow path immediately in front of the die body l, and the other molten resin flow path 3 The flow path 6 also crosses the flow path 7 for the molten resin at only a portion thereof, and is located independently in the lateral direction of the die body l. In the case of coextrusion, since each resin has an appropriate extrusion temperature, the temperature at which the resin enters the die often differs. However, as mentioned above, in the conventional die, each resin flow path 3.6 before branching 7 of the - molten resin is independent, and it is difficult to control the temperature distribution in such a case. Temperature becomes uneven. Therefore, since the melt viscosity of thermoplastic resin is temperature dependent, the temperature distribution cannot be changed even if the flow rate in the circumferential direction of the die is different, and even if uneven thickness occurs in the film, it cannot be corrected. Ta. Incidentally, if the uneven thickness of the film becomes large, problems such as bending and wrinkling will occur during the printing process, bag making process, lamination process, etc., which will reduce the commercial value of the film itself by increasing the loss rate and reducing processing speed. Become. -4. In conventional dies for manufacturing blown film, in order to adjust the uneven thickness, the lip gap, which is the resin discharge port, is changed by rotating an adjustment bolt (not shown), which changes the pressure loss at the lip gap part. A mechanism is adopted to reduce uneven thickness by adjusting the resin discharge rate. However, the die gap gap for blown film production is annular, and partial thickness unevenness adjustment is in principle impossible, and there is a natural limit to thickness unevenness adjustment in the die circumferential direction. With conventional multilayer inflation dies, which have a structure in which the temperature distribution is uneven in the circumferential direction, it is difficult to obtain films with minimal thickness unevenness.

[
Problem 1 to be Solved by the Invention An object of the present invention is to eliminate the drawbacks of the prior art and to provide a technique that can stably form a homogeneous multilayer blown film with less uneven thickness. Other objects and novel features of the present invention will become apparent from the description herein and the accompanying drawings. Means for Solving Problems] The present invention provides a die for producing a multilayer blown film having a plurality of molten resin inlets, in which the molten resin flows through the die flow path section before entering the die main body. A die for producing a multilayer blown film is characterized in that a plurality of channels are arranged in a circular manner, and at least one channel is provided with a constriction portion extending in the circumferential direction. [Function 1] To explain the effects of the present invention together with typical examples thereof, in the present invention, in the die flow path section before the molten resin branches in the die body, another flow path is formed on the outer periphery of the flow path of -. Since the resins are arranged in concentric circles, even if the temperature of each resin flowing into the die is different, the structure does not affect the die temperature distribution, and the temperature distribution of the die is adjusted in the circumferential direction. The flow rate was also uniform, and a film with less uneven thickness could be stably formed. Furthermore, by providing a constriction part in the other flow path, the amount of molten resin passing through the other flow path having the constriction part is made uniform and branched, thereby further reducing uneven thickness of the film. [Embodiment 1] Next, the present invention will be explained based on an embodiment shown in the drawings. FIG. 1 is a sectional view of a die for producing a multilayer blown film according to the present invention, and FIG. 2 is a sectional view taken along the line A--A in FIG. An inflow path 11 is provided laterally on one side of the flow path portion IO at the bottom of the die body 9, through which the molten resin extruded from an extruder (not shown) flows. A cylindrical flow path 12 bent upward with respect to the inflow path 11
Proceeds through the flow path 13 having a constriction part 130, and then
The liquid is extruded out of the die from the lip cap 17 through a flow path 16 formed in a funnel shape by the lower branch part 14 and the upper spiral part 15. On the other hand, laterally on the other side of the flow path section 10 at the bottom of the die body 9,
An inflow path 18 is provided through which another molten resin extruded from an extruder (not shown) flows. Proceeds through a circular pipe (cylindrical)-shaped flow path 19 disposed inside the circular flow path 12 at the center, and then branches horizontally at the upper part of the − molten resin branch portion 14, and then branches into the spiral portion 20. , join together, and are extruded from the lip gap 17 to the outside of the die. That is, the die for producing a multilayer blown film illustrated here has two resin inlets 21 and 22,
The molten resin that has flowed in from the respective inflow ports 21 and 22 flows through a channel 19 that is vertically provided almost near the center of the die, and a channel that is parallel to the channel 19 and around the outer periphery of the channel 19. After passing through a known die through a double circular wave path 23 consisting of a flow path 12 provided therein, it is extruded out from a lip gap 17. At this time, a constriction section 130 is provided in the flow path 12. Aperture part 1
30, this example shows an example in which a recess is provided on the circumferential surface (inner circumferential surface) on the side closer to the flow path 19, but a recess is provided on the circumferential surface (outer circumferential surface) on the side far from the flow path 19. It may be constructed by providing four parts, and the convex and convex portions may be provided on the inner and outer circumferential surfaces.
It may also be set to 0. The constriction section 130 has an average flow velocity of the molten resin flowing through the constriction section, which is 1.5 to 30 times, preferably 3 to 30 times, the average flow velocity of the resin extruded from the lip gap section 17 of the die exit [1].
It is preferable to configure it so that it is 10 times as large. The average flow velocity is 1
．． If it is less than 5 times, the squeezing effect will be small and uneven thickness will occur, and if it exceeds 30 times, the pressure loss will become large, which is not preferable. The die according to the present invention is not limited to that shown in FIGS. 1 and 2, and when there are three or more resin inlets, the number of channels arranged in a concentric manner can be increased. It is also possible to increase the number, for example in the form of concentric quadruple circles. In addition, if the number of resin inflow ports is two, and the number of concentric channels is triple circular, and the number of multiple circular channels is increased, conversely,
It is also possible to merge the molten resins flowing in from a plurality of resin inlets and then guide them to the multiple concentric channels. The molten resin that has passed through the multiple concentric channels passes through a known branch section 14.24 and then through a known spiral section 15.20, but the structure after the multiple circular channels 23 may be determined by any method. It is also within the scope of the present invention to use a die. For example, in addition to the well-known spiral structure, it is possible to adopt a spiral structure or a spiral structure.Also, after passing through a concentric flow path, it can be separated into multiple parts and formed into multiple spiral parts. The scope of the present invention also includes the case where the molten resin is caused to flow into the spiral portion, and the case where the flow path has substantially multiple circular shapes is included in the scope of the present invention. Basically, the scope of the present invention includes the case where the die is made rotary if the centripetal flow path according to the present invention is applied. Further, regarding the structure of the circular flow path, a straight shape or a tapered structure may be considered, but if the gist thereof is substantially the same, it is included in the scope of the present invention. Next, an example of film production using a die for producing a multilayer blown film according to the present invention will be shown. Example 1 LLDPE (Linear Low Density Polyethylene) Shorex 608FS (
Manufactured by Showa Denko, density = 0.918, M F R =
500 manufactured by Yoshii Iron Works Co., Ltd.
LDPE (low density polyethylene) Shorex F113 (manufactured by Showa Denko Co., Ltd., density = 0.9) using the φ extruder (B)
20, MFR = 1.5 g/10 m1n) was extruded and passed through the double circular flow path shown in Fig. 1 using a 300 mm/mφ double double layer die.
As a result of forming a blown tube-like film with a width, the thickness deviation of the obtained film was 81L at the maximum and minimum difference. Note that the average flow velocity at the constriction section was set to 5 times the average flow velocity at the tongue gap section. Example 2゜Extrusion @A, B and the resin used were the same as in Example 1, and 30
After passing through the double circular channel shown in Figure 1 using a 0m/■φ double and triple layer die, the resin flowed in from extruder B was separated into inner and outer layers, and then flowed in from extruder A. As a result, a blown tube-like film of 50 #L x 800 m/paper width was formed using the resin as an intermediate layer. As a result, the thickness deviation of the obtained film was 61 L at the maximum and minimum difference. Note that the average flow velocity at the constriction section was 30 times the average flow velocity at the tongue gap section. Comparative Example Extruders A and B and the resin used were the same as in Example 1. Using the die shown in Figure 3, 507tX800+m/m
As a result of forming a blown tube-shaped film of different widths, the thickness deviation of the obtained film was as much as 20 warps at the maximum and minimum. 1. Effects of the invention l According to the present invention, a plurality of channels are arranged around the outer periphery of the negative channel, and the plurality of channels are arranged concentrically, so that the die temperature can be reduced. We were able to create a die structure that has little effect on distribution, and succeeded in stably forming a multilayer blown film with less uneven thickness. In addition, since a constriction part is provided in the above-mentioned flow path, the amount of molten resin passing through another flow path having the constriction part is made uniform and branched, thereby further reducing uneven thickness of the film. did it.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view taken along the line A--A in FIG. 1, and FIG. 3 is a sectional view showing a conventional example. 12...Flow path 19 Pot...Flow path 21...Inflow port 22...Inflow port 130--Φ constriction part

Claims (1)

[Claims] In a die for manufacturing a multilayer blown film having a plurality of molten resin inlets, a plurality of channels are arranged concentrically in the die flow path section before the molten resin flowing from the inlets enters the die body. A die for producing a multilayer blown film, characterized in that at least one flow path is provided with a constriction portion in the circumferential direction.