JPS59106935A - Preparation of polyester resin film - Google Patents

Abstract

PURPOSE:To make it possible to form a film by high speed electrostatic peening without applying a special device to an electrode, by setting film forming conditions such as the take-up angle of the film, viscosity or a draft ratio so as to reduce the curling at the end parts of the molten film. CONSTITUTION:A formula (1) is given by using the density (g/cm<3>) of a molten film, the air gap S(cm) imparted by the length ranging from the extrusion die lip A to the contact point B on a rotary cooling surface, neck-in delta(cm) shown by 1/2 of the difference between a die lip width L1 and the film width L2 at the contact point B, the draft ratio lambda(-) imparted by the value obtained by dividing the speed of the rotary cooling surface by the average emitting speed at the outlet of the extrusion die, the viscosity mu(gsec/cm) corresponding to the temp. and shearing speed of resin and the angle alpha deg. formed by the tangential line in a film flowing direction and a vertical direction and, when a film is formed under such a condition that the value rho shown by the formula (1) is 25.0(cm<2>/sec) or more, film curling is hardly generated and, if an electrostatic pining method is applied under said condition, a film forming speed of 40m/min or more can be easily achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyester resin film with excellent thickness uniformity and low crystallinity with high efficiency.

In the process of extruding polyester resin from a die and receiving it on the surface of a 9-rotating cooling body to form a film, a wire or knife-shaped electrode to which a high voltage is applied is provided on the opposite side of the film from the side that contacts the rotating cooling body surface. A method of forming a film while rapidly cooling the film by depositing an electrostatic charge on the surface and bringing the film into close contact with the rotary cooling surface using electrostatic attraction acting between the surface and the grounded rotating cooling surface (this method uses the electrostatic pinning method). ) is an effective method for improving thickness uniformity, transparency, etc., and is widely used. However, this method becomes more difficult as the speed of the rotating cooling surface increases, and as the film speed increases, air bubbles tend to become trapped between the melt film and the rotating cooling surface. When the electrostatic pinning method is used, the molten film is strongly pressed against the rotating cooling body surface by electrostatic attraction and is rapidly cooled. Therefore, if air bubbles are trapped between the molten film and the surface of the rotary cooling body, cooling will be inhibited and not only will a homogeneous film not be formed, but also unevenness will occur on one surface. Therefore, the entrainment of air bubbles is a fatal defect in this film forming process, and it puts a limit on the film forming speed.

Conventional improvement proposals made to increase the film forming speed using the electrostatic pinning method are related to electrodes9.
A method of strengthening the binding force to generate a large amount of ions using an auxiliary electrode as shown in Japanese Patent No. 180. Related to ambient air 9 For example, as shown in JP-A No. 53-143659, the temperature near the electrode is raised to facilitate ionization of the air, and a large amount of static charge is applied to the film surface to strengthen the binding force. Method. As shown in Japanese Patent Publication No. 50-28108, the vicinity of the electrode is covered with a gas that has a large discharge current before dielectric breakdown, and by passing a large amount of current, a large amount of static charge is applied to the film surface to strengthen the binding force. how to. Regarding raw materials, 1. For example, as shown in Japanese Patent Publication No. 53-40231, etc., high-speed processing is possible by improving the electrical conductivity of molten polyester resin. Others use a suction type air knife as shown in Japanese Patent Publication No. 55-22257. There are some methods that use infrared rays as shown in Japanese Patent Publication No. 55-10365, but
There is no improvement regarding the film forming technology itself.

The present inventors believe that when applying the electrostatic pinning method to polyester resin films, there is a limit to the conventional film forming method with the above-mentioned improvement proposals. 9 various devices that should be improved to be suitable for use.

We performed extrusion film formation using an electrostatic pinning method using resin, and investigated the cause of air bubble entrainment. As a result, we learned that controlling the curl at the edges of the molten film is extremely important in order to increase the film forming speed without entraining bubbles. (a) When the molten film is divided into a central part and a monument part, the bending of the edges is smaller than that of the central part, and as a result, the edges appear to be curled up.

(b) A curl in which the edge of the molten film is clearly located above the straight line connecting the first point of contact with the extrusion die lip and the rotating cooling surface.

5- etc. exist. It is difficult to completely explain the curls in (a) and (b) theoretically.

These curls are thought to be subtly influenced by transverse melt tension 9 surface tension directed toward the center of the melt film, memory phenomenon, etc., and increase as the film forming rate increases. As a result, the edge of the film becomes neck in and thicker toward the center. Also, the water reaches the rotating cooling surface later than the central part. Therefore, when the electrodes are installed in a straight line,
It becomes impossible to optimize the binding force throughout the film. This is because the electrostatic charge that creates the binding force on the film is determined by the distance between the film and the electrode. For example, if the electrodes are placed to provide the best binding force relative to the center of the film, the ends of the film will be extremely close together. As a result, a spark discharge occurs at the electrode and the film end portion, which inhibits the deposition of charges, hinders the binding operation, and entrains air bubbles.

In order to avoid this, it is necessary to place the electrodes at a sufficient distance from the curled ends of the film.

6- Such a spacing is greater than that required to produce the best restraint force in the central portion, resulting in the entrainment of air bubbles between the film and the rotating cooling surface.

In order to solve this difficulty, as shown in Japanese Patent Laid-Open No. 56-53037, a blade electrode is used to curve the blade electrode at a position corresponding to the edge of the film so as to cross the entire width of the film. A method of substantially conforming to the cross-section of the film, by curving the blade electrode at a position corresponding to the film edge toward the center of the film so that the grade electrode does not extend beyond the film edge. Several methods have been proposed.

However, in these methods, first, it is difficult to determine the degree of curvature to be applied to the electrode, and manufacturing is difficult.

Second, it is almost impossible to apply the electrode once completed to films of different film widths.

Very difficult to use. Third, there are difficulties in positioning and attaching the electrodes to the film.

The inventors of the present invention have made extensive studies on improvements to the prior art, and have found that there is a close relationship between the curl of the film edge, the film take-up angle, viscosity, draft ratio, etc. Through mechanical considerations and repeated detailed experiments on the above factors, we improved the film forming conditions and developed a method that enables high-speed electrostatic pinning film forming without special devising of electrodes. I found it.

That is, the density of the molten film ρ(F//ct/l),
The air gap 5 (Crn) is given by the length measured along the molten film at the point where the molten film first contacts the rotating cooling surface from the extrusion die lip, and the molten film extruded from the extrusion die is placed on the rotating cooling surface. Neck-in δ (tM), expressed as the amount of transverse reduction at each edge before initial contact (1/2 of the difference between the die lip width and the film width at the point of contact); At average discharge speed.

The draft ratio λ (
−), the temperature of the resin passing through the extrusion die lip.

Viscosity μ (11 sec/cJ) corresponding to shear rate e
Angle α (degrees) between the tangent to the flow direction and the vertical direction at the midpoint between the flow direction and the transverse direction of the molten film between the extrusion die and the position where it first contacts the rotating cooling surface
If the film is formed under conditions such that the value P shown by is 25.0 (all/sec) or more, curling will not occur.
They discovered that if the electrostatic pinning method was applied under these conditions, it was possible to increase the film forming rate relatively easily.

The meaning of P will be explained next.

In general, a fluid with a tensile viscosity η is strained at a strain rate dv/dx (V
is the moving speed, and X is the length measured along the streamline of the fluid to the point of consideration), then the tension acting per unit area of the fluid is given by the following equation.

Since the polyester resin for film molding can be regarded as a Neilton fluid under normal molding conditions, the tensile viscosity 9-η has approximately the following relationship with the general melt viscosity (shear viscosity) μ.

η = 3μ Since the tension per unit width is balanced at any point in the flow direction at the center where there is no influence from the edge of the film, and the flow rate per unit width is constant, v 3μT-=constant x Tv = Q (constant) (T is the film thickness at the connecting point, Q is the flow rate per unit width) Therefore, if the film thickness at the die lip discharge point is Toe, the air gap length is S, and the draft ratio is λ, the following relationship is obtained. .

OT=□□ -λS 10- The above relationships were determined for the center portion of the film, but applying these relationships to the edge portions of the film should not result in any serious errors. The part that is strongly affected by the free edge of the film.

In other words, if we consider the end 1] to be B (this concept is shown in FIG. 2), the tension at that part can be approximated by the following equation.

At this time, the weight W of this part is approximately (T' is the average thickness of the edge, δ is the neck-in amount on one side of the film, and ρ is the film density). Therefore, the force W that tries to bend the edge of the film ( α is the angle between the tangent to the film's flow direction and the vertical direction, and it is approximated that the center and edges are the same.) If the amount of deflection is D, the following approximate mechanical balance should be established at the edges of the film. (The above relationship is shown in Figure 3. F is the tension at the end).

Since Q/T' corresponds to speed, the deflection amount index p is given by the following equation.

As described in detail above, it is clear that the parameter P is a characteristic value related to at least the amount of deflection at the edge of the film, even if it cannot represent the actual amount of deflection.

In other words, the meaning of P is that if P is large, the deflection at the end will be large and the curl will be small, assuming the same take-up speed, and if the same deflection, that is, the same curl, is considered, P will be thicker. This value indicates that the higher the take-up speed V is, the more the take-up speed V can be increased.

The present inventors have taken up P as an important parameter for determining film forming conditions suitable for the electrostatic pinning method.

Detailed experiments were conducted using nine different raw materials, extrusion dies of various shapes, extrusion temperatures, extrusion conditions, withdrawal conditions, etc. As a result, air gap: 20% to 150%.

Draft ratio: 5-20. Melt viscosity: 1500pois
It was found that under film forming conditions in the range of e to 5000 poise and take-up angle of 30 to 90, P was quite good as shown in the m1 diagram, indicating the state of bubble entrainment.

In Figure 1, under each film forming condition, cases where air bubble entrainment occurred are indicated by X marks, 9 cases where bubble entrainment did not occur are indicated by ○ marks (-).This figure shows small curls and no air bubble entrainment. The range shows that the faster the take-up speed is, the larger the P value must be, and the larger P is, the more the take-up speed can be increased.P≧25.0 (
ad/see), it is possible to easily achieve a take-up speed of 40 m7'm or more, which was difficult to achieve using conventional wire electrodes.

The term "polyester" as used herein refers to a polyester having film-forming ability obtained from a dibasic acid and a dihydric alcohol, or a copolymer thereof. Of course, the third component may be a polyester copolymerized with a dibasic acid such as isophthalic acid, adipic acid, or triethyl-13-lengelicol, or a dihydric alcohol.

Further, the stabilizer 2 may contain additives such as a coloring agent.

The low-crystalline unstretched film with excellent thickness uniformity produced in this way is particularly useful when making biaxially stretched polyester films that have strict requirements for thickness accuracy, such as stretchability, toughness, and optical properties. This makes it the perfect material.

In order to obtain the best effect of the method of the present invention on the entire line under general conditions, one more consideration becomes important. That is, it is the discharge angle of the extrusion die. Conventionally, an extrusion die was installed near the top of the rotary cooling body, and the extrusion film was formed with the discharge direction vertical or at an angle close to vertical. This method is advantageous in achieving mechanical accuracy, thickness accuracy, etc.
For this reason, this has been a common method in the past. Conventional techniques for tilting the direction of the extrusion die include 2, for example, Japanese Patent Publication No. 5
No. 1-31267, but this method simply tilts the extrusion die to prevent vibration of the molten film, and unlike the present invention, it prevents dirt on the lip of the extrusion die, that is, "eye mucus". The present invention does not describe a method for reducing the molten film, nor does it describe the angle between the extrusion direction and the flow direction of the molten film at the tip of the extrusion die lip. If the method of the present invention is specifically carried out to find conditions in which curling is less likely to occur, as the drawing speed becomes higher, the drawing angle becomes considerably larger. In such a case, if the extrusion die is installed with its lip direction vertical or close to vertical, the direction of discharge of the die and the flow direction of the molten film at the tip of the die lip will inevitably have a large angle (this relationship is schematically shown below). (shown in Figure 4).

If the film forming operation is continued under such conditions, molten resin and its carbide, called "eye mucus", will adhere to the die lip.
9 Thickness unevenness 9 surface irregularities occur in the film, making it impossible to continue the film forming operation. Frequent cleaning of the die lip significantly reduces efficiency. As a result of various studies on this problem, we found that the angle between the discharge direction at the die lip and the flow direction of the molten film at the tip of the die lip has a strong relation to the adhesion of "eye mucus", and that reducing this angle will reduce the adhesion of "eye mucus". (The arrangement at this time is schematically shown in FIG. 5). This seems to be related to the surface tension, viscosity, density, and sharpness of the die lip of the molten resin, but when using polyester resin and a die lip with normal sharpness,
It has been found that if the angle formed is smaller than 60, the adhesion of "eye mucus" is significantly reduced. This is shown in Figure 6 (showing the shape when the angle between the discharge direction and the flow direction of the molten film at the die lip tip is small) and Figure 7 (the shape when the angle between the discharge direction and the flow direction of the molten film at the die lip tip is large). If the angle between the discharge direction of the die lip and the flow direction of the molten film at the tip of the die lip is 60 or less, the molten resin will not go around the edge of the die lip and adhere, but if it exceeds 60, the molten resin will not adhere to the die lip. This is thought to be due to the fact that it moves around the edge, adheres or stagnates, and carbonizes. Furthermore, under the film forming and taking-off conditions under which the effects of the present invention are manifested, the flow direction of the molten film at the tip of the die lip can be considered to be approximately the same as α.

As shown above, the present invention improves the film forming method itself, which has not been achieved in the past, in a film forming method using electrostatic pinning, and thereby achieves a high speed of film forming very easily. This book is of great industrial value.

Examples and comparative examples are shown below.

Example 1 Polyethylene terephthalate having a relative viscosity of 1.41 measured at 20° C. was extruded into a film at 280° C. using a 1:1 mixed solution of phenol and carbon tetrachloride. At this time, the melt viscosity of the resin passing through the die lip was 3450 poise.

Other film forming conditions were air gap: 50%, neck-in 38%, and take-up speed: 42 m/am.

Draft ratio: 6.7. The film was formed with a film thickness of 120 μm and a take-off angle of 52 μm. At this time, the electrostatic pinning conditions were as follows: 150μ diameter SUS steel wire was used as the electrode, voltage near, Okv
, current: 0.035 mA/crn, distance between electrode and film: 5.0%. At this time, P value 25.7 (c
J/see) 17-. At this time, no curling occurred and no air bubbles were observed.

Example 2 The same polyester resin as in Example 1 was extruded into a film at 290°C. At this time, the melt viscosity of the resin passing through the die lip is 2
It was 930 poise. Other film forming conditions are air gap: 50%, neck-in: 45%, take-up speed: 45ff! //da, draft ratio: 8.4°, film thickness = 120μ, and take-up angle: 50.

Further, the electrostatic pinning conditions were as follows: using the same electrode as in Example 1, voltage: 6.5 kv, current: 0.03 mk/cm, and distance between electrode and film: 5.0 square meters. The P value at this time is 28 (ctd/see). No curling occurred at this time.

No air bubbles were observed.

Example 3 The relative viscosity measured in the same manner as in Example 1 was 1.3.
Polyethylene terephthalate No. 8 was extruded into a film at 290°C. At this time, the melt viscosity of the resin passing through the die lip is 2
It was 040 poise. Other film forming conditions include air gap: 45%, neck-in 18-=42%, take-up speed: 50 m/frame, draft ratio: 9.1
゜Film thickness: 90μ, take-up angle: 55.

At this time, the electrostatic pinning conditions used the same electrodes as in Example 1,
Voltage near, 2kv, current: 0. (140mA/cm
, the distance between the electrode and the film was 5.0%. At this time P
The value is 31.1. At this time, no curling occurred and no air bubbles were observed.

Example 4 The same polyester resin as in Example 3 was extruded into a film under the same conditions as in Example 3. Air gap: 45% as film forming conditions
, Neck in: 42~. Pick-up speed: 60 m/”,
Draft ratio: 10.9. Film thickness = 75μ,
Take-off angle: 55. The electrostatic pinning conditions at this time were to use the same electrodes as in Example 1, voltage near, 0kv, and current:
0.046 mA/crn, distance between electrode and film: 40%. At this time, the P value is 28.4 (ti/
sec).

At this time, no curling occurred and no bubble entrainment was observed. Comparative Example 1 As a material corresponding to Example 1, the same resin as Example 1,
A film was formed by extrusion at the same temperature. Film forming conditions are take-up speed 42m/”
, Draft ratio: 6.7. Film thickness: 120μ,
When the take-off angle was 30 and the air gap was 50%, the neck-in was 42%. The P value at this time is 17.5
(ca/see). At this time, curls occur,
The edges of the film were about 3% closer to the electrodes than the center of the film. Films were formed under various pinning conditions, but a film free from air bubble entrainment could not be obtained.

Comparative Example 2 As a product corresponding to Example 2, the same resin as Example 2 was extruded into a film at the same temperature. The film forming conditions were a take-up speed of 45 m/m,
Draft ratio: 8.4. Film thickness 120μ,
When the take-off angle was 40 and the air gap was 50%, the neck-in was 46%. The P value at this time is 24.0
(crl/sec). At this time, curling occurred, and the edges of the film were about 2% closer to the electrodes than the center of the film. Films were formed under various pinning conditions, but a film free from air bubble entrainment could not be obtained.

Comparative Example 3 As a product corresponding to Example 3, the same resin as in Example 3 was extruded to form a film at the same temperature. Film forming conditions are take-up speed: 50m/
m, draft ratio: 9.1. Film thickness: 90
μ, the take-off angle was 35, and when the air gap was 45%, the neck-in was 44%. At this time, the P value is 22.0
(ctl/see). At this time, curling occurred, and the edges of the film were about 2% closer to the electrodes than the center of the film. We searched for pinning conditions that would not entrain air bubbles, but we were unable to find any.

Example 5 The angle between the discharge direction of the extrusion die and the flow direction of the molten resin at the tip of the die lip was set to 40, and the same resin as in Example 1 was
Draft ratio 6.7 at 90°C. Extrusion film formation was carried out at a take-up speed of 4 Q m/m to obtain a 120μ film.

At this time, the film forming time per lip cleaning was approximately 180 hours.

Example 6 Extrusion film formation was carried out under the same conditions as in Example 5, except that the angle between the discharge direction of the extrusion die and the flow direction of the 21-molten resin at the tip of the die lip was set to 55 degrees. At this time, the film forming time per lip cleaning was about 160 hours.

Comparative Example 4 Corresponding to Examples 5 and 6, the angle between the extrusion die discharge direction and the flow direction of the molten resin at the tip of the die lip was set to 6
Extrusion film formation was carried out under the same conditions as in Example 5, except that the number was changed to 5. At this time, the film forming time per lip cleaning was about 40 hours.

Example 7 - The same resin as in Example 3 was extruded into a film under the same conditions as in Example 5. As a result, the film forming time per lip cleaning was about 180 hours.

Example 8 The same resin as in Example 7 was extruded into a film under the same conditions as in Example 6. As a result, the film forming time per lip cleaning is 160
It was about an hour.

Comparative Example 5 As a product corresponding to Example 7.8, extrusion film formation was carried out under the same conditions as Example 7 except that the angle between the extrusion die 22-discharge direction and the flow direction of the molten resin at the tip of the die lip was set to 65. As a result, the film forming time per lip cleaning was about 32 hours.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a diagram showing whether or not electrostatic pinning is possible with respect to P value and take-up speed. FIG. 2 is a front view during film formation. FIG. 3 is a side view thereof. Figure 4 shows the case where the take-off angle is increased in a normal T-die arrangement, and Figure 5 shows the case where the take-off angle is increased to reduce the angle between the extrusion direction and the take-off direction of the molten resin at the tip of the extrusion die lip. FIG. 3 is a diagram showing a tilted die. 6 is an enlarged view of the extrusion die lip shown in FIG. 5, and FIG. 7 is an enlarged view of the extrusion die lip shown in FIG. 4. The number 1 character shown in the figure is as follows. ]...Die, 2...Rotary cooling body, 3...Film, 4...Film end, 5.6...Die lip. 7
...It's molten resin. Patent Applicant Unitika Co., Ltd. 23- Figure 1 Collection: rLl ('%;-) Age 4 Figure 1 Year Off Prisoner

Claims (1)

[Claims] 1. Molten polyester resin is extruded from an extrusion die onto a rotating cooling surface in the form of a film, and an electrode is placed near the contact point between the film and the rotating cooling surface to deposit electrostatic charges on the film surface. In the step of forming a film by adhering to the rotary cooling surface and rapidly cooling it by electrostatic attraction acting between the grounded rotary cooling surface and the grounded rotary cooling surface, the density ρ (#/ff1) of the molten film is increased from the extrusion die lip to the rotary cooling surface. The air gap S (crn) is given by the length measured along the molten film up to the point where it first contacts the molten film above, Neck-in δ (m) expressed as the transverse amount of reduction at the edge (1/2 of the difference between the die lip width and the film width at the contact point), 9 revolutions at the average transverse discharge speed at the exit of the extrusion die The draft deadness (-) given by the cooling surface velocity divided by the melt viscosity μ (g se
e/i) - the angle α (in degrees) between the vertical direction and the tangent to the flow direction at the midpoint between the flow direction and transverse direction of the molten film between the extrusion die and the first point of contact with the rotating cooling surface; A method for producing a polyester resin film, characterized in that a parameter P expressed by the formula is set to 25.0 (a/I/see) or more. 2. The method for producing a polyester resin film according to claim 1, wherein the angle between the discharge direction of the extrusion die lip and the vertical direction is 1α-01≦60, where θ (degrees) is the angle formed by the extrusion die lip discharge direction and the vertical direction.