JPS61220820A - Manufacture of polymer sheet - Google Patents

Abstract

PURPOSE:To permit the speedup of casting speed by a method wherein guiding means are provided at the outside of both side ends of die slit while a contacting area between the guiding means and the edges of molten body is regulated so that the edges, the vicinities of the edges and the central section in the widthwise direction of the sheet-like molten body arrive at a cooling surface in parallel to the die slit substantially under keeping a linear configuration substantially. CONSTITUTION:The edge of the molten body, extruded out of the die slit, flows down on the surface of the guiding means 10 vertically substantially and flows to the side end 22 of a guiding surface along the bottom side 21 of the guiding surface into the take-off direction of the molten body, then, is released from the side end and arrives at the cooling surface through free space. In order to prevent the curl at the edge of sheet-like molten body and make the landing line of the sheet-like molten body to be a straight line, a releasing point 30 from the guiding means should be in the same plane as the stream line 13 of the central part of the body in case they are observed from a side direction. In case the landing point of the edge is moved to the upstream side of the landing point of the central part in the cooling surface, a high-speed casting effect, due to electrostatic adhesion, will not be changed.

Description

[Detailed description of the invention] Technical field The present invention relates to a method for manufacturing polymer sheets.

More specifically, a discharge electrode applies an electrostatic charge to a polymer melt extruded from a die into a sheet, and the sheet-like melt is brought into close contact with a cooling surface and cooled and solidified to form a polymer sheet. This is an improved technique of the so-called electrostatic adhesion method, in which the edges of a sheet-like molten material are guided by a guiding means, so that the edges in the width direction of the molten material reach the cooling surface at the same level or faster than the center of the sheet. The sheet-like molten material is guided to reach the cooling surface in a nearly straight line, and in particular, the edge portion is controlled so that there is no delay in reaching the cooling surface, thereby improving the adhesion of the discharge electrode. This invention relates to a method for effectively producing a polymer sheet.

The prior art electrostatic adhesion method reduces the uniformity of the thickness of the polymer sheet when the melt casting speed is low.

This is a method for manufacturing sheets with excellent surface smoothness.

However, the biggest problem with this method is that as the casting speed increases, the adhesion of the molten sheet to the cooling surface decreases, allowing air to flow in between the molten sheet and the cooling surface. This causes bubble-like defects on the surface of the sheet.

When we investigated the cause of this bubble-like defect, we found that the edge of the molten material curls in the free space between the contact pin and the cooling surface, and reaches the position where it reaches the cooling surface (hereinafter referred to as the landing line). The reason is that a straight discharge electrode cannot maintain suitable adhesion conditions over the entire width of the sheet because the discharge electrode is curved at the edge portion.

To explain this state with reference to the drawings, in FIG. Both ends of the molten material neck toward the center, increasing in thickness and curling toward the opposite side of the cooling surface. As a result, the sheet-like melt has a streamline 1 in its center.
3, the streamline 141'i at the end is located at a higher point away from the cooling surface, and while the central part of the reaching position to the cooling surface is 15, it is located near the edge (hereinafter referred to as the edge). )
Fi later reaches position 16 on the lower (lower [)] side.

That is, as is clear from the side view of FIG. 6, the arrival point Fi of the molten material to the cooling surface is 15 at the center and 16 at the edge, and the edge is delayed in the downstream direction. Also, the streamline at this time is die M14 at the edge part. It looks like a dotted line 13 in the center.

However, in order to cast the molten polymer in a good manner without causing bubble-like defects or uneven thickness on the sheet using the electrostatic adhesion method, it is necessary to (15 to 16) The variable range in which the relative position can be adjusted is generally limited to a narrow range.

Therefore, when casting a sheet-like molten material with a curved landing line as described above using a straight electrode, if the favorable conditions of the electrode are adjusted to the center of the molten material, defects will occur at the edges, and it will be difficult to adjust the landing line to the edges. This tends to cause defects in the center.

The curl of the m1 sheet-like melt increases as the casting speed increases, and the curvature of the landing line increases. Furthermore, as the casting speed increases, the amount of electrostatic charge per unit area of the melt sheet decreases, so the electrostatic adhesion force itself becomes weaker and the variable width of the electrode becomes even narrower.

The combination of these phenomena makes it difficult to increase the casting speed in the electrostatic adhesion method.

In particular, as a solution to problems related to curling of molten material,
In the prior art, for example, as disclosed in Japanese Unexamined Patent Publication No. 56-53037, a blade-shaped discharge electrode is curved at the edge of the molten material, and the shape of the blade is adjusted to the N of the molten material.
In accordance with the shape of the ground line, the relative position with respect to the landing line is designed to be constant over the entire width of the sheet-like molten material.

However, the size of the curl of the melt is
Because it changes depending on the thickness ζ, casting speed, etc.
It is almost impossible to always optimize the blade shape as casting conditions change.

The technique disclosed in Japanese Patent Application Laid-Open No. 59-150727 proposes to correct the curl by spraying a fluid onto the curling edge. However, if the fluid is sprayed on even a portion of the molten material with low elasticity, the molten material becomes a sheet-like material. This tends to cause vibrations, resulting in uneven thickness of the film sheet, and furthermore, the disturbance of the fluid around the electrodes tends to cause disturbances in the discharge state of the electrodes.
As a result, thickness λ spots or surface defects may occur on the film sheet. The technology disclosed in Japanese Patent Publication No. 106935/1983 optimizes the polymer extrusion conditions and the relative position between the goo and the cooling surface to reduce curling. However, it is difficult to completely eliminate curl, and the application of this technology may become a constraint when trying to optimize sheet thickness unevenness.

OBJECTS OF THE INVENTION The present invention solves the problems of the prior art and makes it possible to increase the casting speed, and also to reduce the width due to neck-in of the sheet-like melt and change in sheet width due to changes in manufacturing conditions. The purpose is to provide technology that can also control.

The constitution of the invention, that is, the present invention provides guide means at each of both ends of the die slit, and brings the end of the molten material into contact with the guide means, and then guides the melt to the cooling surface and brings it into close contact with the guide means. By devising the shape of this guide means, curling of the sheet-like molten material is prevented, and the shape of the edge landing line is controlled to be straight and parallel to the die slit, and in addition, the narrow width of the sheet is controlled. This is a method for producing a polymer sheet that also suppresses chemical reactions.

That is, the present invention melts a polymer, extrudes the melt into a die-slit sheet shape, applies an electrostatic charge to the wrinkled melt on a discharge electrode, brings it into close contact with the cooling surface, and cools and solidifies the sheet of polymer. A method for forming a sheet-shaped nuclear melt by providing guide means on the outer sides of both ends of a die slit so that the ends of the melt are guided to the cooling surface while contacting the guide means, and the width of the sheet-like nuclear melt is The contact area between the guide means and the m portion of the molten material is adjusted so that the end portion of the crest, its vicinity, and the central portion in the direction reach the cooling surface approximately parallel to the die slit at approximately T1II. This is a method for producing a polymer sheet characterized by the following.

The present invention will be explained.

The present invention is polyethylene, polybupyrene.

Polyhexamethylene adipamide, polytetramethylene adipamide, polyethylene terephthalate, polytetramethylene terephthalate.

It can be applied to the production of a sheet of 2.5% square or less and larger than 7+m5' null from a thermoplastic polymer such as polyethylene-2,6-su7thalene dicarpoxylate. The present invention is also a technique that can be used to produce polymer sheets by applying an electrostatic adhesion method, which is well known from, for example, US Pat. No. 3,427,686.

In the present invention, guide means are provided at both ends of the die slit of the die at a position where both ends of the extruded melt (extruded from the die slit in the form of a sheet) touch, and the melt is guided to the guide means. The feature is that it is guided to the cooling surface while making contact with it. The material of this guide means is stainless steel and aluminum.

It is made of metals such as brass, ceramics such as alumina, and heat-resistant resins such as polyimide resin, and has a size that allows it to be inserted into the free space between the die and the cooling surface. Attach near the end. This guide means is equipped with a heating and cooling device, and has a temperature control function to keep the molten material at a predetermined temperature so that it does not slip on the contact surface with the guide means and cool and solidify even if the molten material comes into contact with it. Preferably.

The object of the present invention is to effectively prevent curling of the melt. In order to explain the curl prevention effect of the guide means of the present invention, when observing the trajectory of the polymer flowing on the surface of the guide means 20, as shown in FIG. It first flows down the surface of the guide means 200 in a substantially vertical direction, then flows along the bottom 21KB of the guide surface in the direction in which the molten material is taken up to the side edge 22 of the guide surface, leaves the side edge, passes through free space, and is cooled. reaching the surface. The flow shape of the polymer on the guide surface is controlled by the melt viscosity of the melt, the temperature of the guide means, the pulling tension of the sheet-like melt, etc., and when the flow changes from the vertical direction to the flow dipping at the bottom, a small Although it may draw a curve, setting the departure point 30 from the guide means to be the bottom side edge of the guide means depends on the temperature of the guide means, the melt viscosity of the polymer (i.e., the temperature of the melt), This can be easily achieved by selecting the shape etc. of the guide means.

Therefore, curling of the edges of the sheet-like melt is prevented,
In order to make the landing line of the sheet-like melt a straight line, the departure point 30 from the guide means should be in the same plane as the central flow @ 13 when observed from the side. Conveniently, the landing points of the ends are located on the upper side of the cooling surface (to the right of the cooling drum 12 in the drawing) than the central landing points.
Even if it is moved, the adhesion effect (electrostatic adhesion effect) will not be reduced. In other words, even if the shape of the landing line of the molten material is over-adjusted so that it curves upstream at the edge, the high-speed casting effect in the electrostatic adhesion method is almost as good as when the landing line is straight. be. From this phenomenon, if the point at which the molten material leaves the guide means is in the same plane as the streamline in the center or is biased towards the cooling surface, a high-speed casting effect due to electrostatic adhesion can be achieved.

As shown in FIG. 4, the shape of the guide means of the present invention is such that the center of the die slit is the origin 40, the vertical direction 41 is the y direction,
With the vertical direction 42 as the X direction, the lower and left directions are the positive direction, respectively, and the streamline F(3:) at the center of the molten body, and the coordinates of the side end 22 at the bottom of the guide means (X, G (X), it must be in the relationship G(x)'J(x).However, it is assumed that G(x) must be in the free space between the goo and the cooling surface.

The streamlined shape of the molten material in contact with the guide means allows the molten material to flow to the side end of the bottom of the guide means, and this side end becomes the separation point without any hindrance, and the melt is melted at the contact surface of the guide means and its vicinity. This is particularly true if the shape does not interfere with the flow of the body.

Effects of the Invention The present invention has the effect that high-speed casting of a polymer sheet is possible by providing a guide means.

Another great effect of the present invention is that reduction in sheet width due to neck-in can be suppressed.

Generally, as the casting speed increases, the neck-in increases and the width of the sheet-like melt decreases. Therefore, an increase in the medium sanding speed to improve productivity may instead lead to a decrease in sheet width, which may have an adverse effect on productivity.

In the present invention, the edge portion of the sheet-like molten material flows along the guide means from the die slit halfway to the landing point, and during this period, changes in the sheet width are regulated. Although neck-in is unavoidable between the departure point of the guide means and the landing point, the effect of neck-in can be minimized by designing the size of the guide means to reduce this unrestrained interval. can.

The polymer sheet formed according to the present invention undergoes the following steps: -
Axial stretching, sequential biaxial stretching, and simultaneous biaxial stretching can be performed. At this time, since the surface of the sheet is smooth and has a uniform thickness, stretching and heat treatment can be carried out smoothly and high production can be achieved.

The present invention will be explained below with reference to Examples.

Example 1 The free space interval between the guide and the cooling surface is 20 m+e,
Polyethylene terephthalate with a thickness of 170grn was melted and extruded through the tie slit, and several lines of electrostatic charge were applied to the straight discharge electrode over the entire width of the sheet-shaped melt to electrostatically adhere to the cooling drum. When the taking speed of the polymer sheet was gradually increased, small bubble-like defects occurred at the edges of the polymer sheet at a speed of 45 m/min, and as the speed increased, the frequency of defects increased, and the defects at both ends and It expanded to about 40 fin widths nearby.

In order to measure the streamlines of the sheet-shaped melt shown in Fig. 6, a cassette meter was placed at a position 1.5 m above the extension Jl of the die slit, and in the coordinate system with the center of the die slit as the origin, the sheet When we measured the streamlines of a shaped melt, we found that
The height of the center at x = 25 mm is F(25)
= 12 degrees, and the daytime at the end is F(25) = 10
It was mm.

Therefore, the guide means shown in Fig. 4 has the coordinates of the position of the side end of the bottom side (25, IF), and the guide means is a rectangular parallelepiped made of stainless steel and equipped with a heater and a temperature measuring device, attached to both sides of the slit. Then, the respective ends of the melt are brought into contact with each other by maintaining the temperature at 280° C. As a result, each end of the melt separates from the vicinity of the side end of the guide means and reaches the cooling surface. In the free space between this guide and the cooling surface, no curling of the edges was observed, and the edges of the molten material and the streamlines in the center coincided. When the sheet take-up speed was gradually increased, no defects occurred under these conditions until it reached 52 m/min. Furthermore, when molded without using a guide tool, the sheet width was 340 mm, whereas when a guide tool was used, the sheet width was as wide as 372 mm.

Example 2 The guide tool in Example 1 was changed as follows. That is, the coordinates of the position of the side edge of the base are x=25arm, G(25
) = 15 A polymer sheet was molded under the same conditions as in Example 1 using a brass rectangular parallelepiped. As a result, the drawback of the sheet was that, as in Example 1, the take-up speed was 52
No occurrence was observed until the speed reached m/min. The width of the polymer sheet at this time was 383 +w, which further suppressed neck-in.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are perspective views (partial views) showing how the melt extruded from the die slit reaches the cooling surface in an embodiment of the present invention. FIGS. 3 and 4 are side views showing the situation in which the melt reaches the cooling surface according to the embodiment of the present invention. FIG. 5 is a perspective view of the melt from the die slit to the cooling surface in the prior art. Moreover, FIG. 6 is a side view showing the behavior of a molten body in the prior art. In the drawing, 10 is a melt (sheet-like unsolidified material), 11 is a die slit, 12 is a cooling surface, 13 is a streamline at the center of the melt, 14 is a streamline at the end of the Fi melt, and 15 is a melt 16e is the position at which the center of the body reaches the cooling surface, 16e is the position at which the end of the molten body reaches the cooling surface, 20 is the guide means, 21 is the bottom of the guide means, and 22 is the side end of the guide means. 30 points of departure of the molten material from the guiding means, 31#'i discharge electrode, 32 a support for the discharge 1m pole, 40 the position when the origin is the die slit discharge position, 41 the vertical direction (y-axis direction), 42 indicates the horizontal direction (X-axis direction).

Claims (1)

[Claims] A method of melting a polymer, extruding the melt in the form of a sheet through a die slit, applying an electrostatic charge to the melt using a discharge electrode, bringing it into close contact with a cooling surface, solidifying it by cooling, and forming a sheet of the polymer. Guide means are provided outside both ends of the slit so that the ends of the molten material are guided to the cooling surface while contacting the guide means, and the edges and the vicinity thereof in the width direction of the sheet-like molten material are and a central portion of the polymer sheet, characterized in that the contact area between the guide means and the end of the melt is adjusted so that the guide means and the end of the melt reach the cooling surface approximately parallel to the die slit and approximately in a straight line. Manufacturing method.