JP2000318013A - Die for extrusion molding for thermoplastic resin and molding method for polyester sheet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the productivity of a thermoplastic resin sheet excellent in its thickness uniformity and reduced in its surface defect to a large extent by increasing the rotational speed of a cooling drum at a time of the extrusion molding of a thermoplastic resin and suppressing the generation of deteriorated resin increased in generation frequency as an increase in the rotational speed of the cooling drum. SOLUTION: In an extrusion die used in forming an extrusion molded flat stretched film of a thermoplastic resin, difference in level is provided to the leading ends of a pair of die lips so that the leading end of the die lip on a sheet taking-over side among a pair of die lips is straight and the leading end of the die lip on a sheet anti-taking-over side among both die lips is longer than that of the die lip on the sheet taking-over side by 0.1-10.0 mm and the leading end of the die lip on the sheet anti-taking-over side of a center part is shorter than that of the die lip on the sheet taking-over side by 0.1-3.0 mm and the change range of the difference in level is within 200 mm from the edges of both sides of the die lips.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a die for thermoplastic resin extrusion molding and a method for molding a polyester sheet using the die. More specifically, when extruding a thermoplastic polyester, a molding die which is excellent in thickness uniformity and enables high-speed molding of a thermoplastic resin sheet having few surface defects, and a method of molding a polyester sheet using the same. About.

[0002]

2. Description of the Related Art As a molding method of a thermoplastic resin sheet,
An electrode is provided between the die and the rotary cooling drum so as to traverse the molten resin extruded from the slit of the die into a sheet, and a high voltage is applied to the electrode to apply static electricity to the molten resin. Is widely known to solidify the solid on a rotary cooling drum (for example, Japanese Patent Publication No. 37-6142).
No.). This method is usually called an electrostatic application casting method, and the electrode is adjusted to a position where a good thermoplastic resin sheet can be formed.

[0003] However, the above method has its limitations,
For example, when the rotation speed of the rotary cooling drum is increased to increase the molding amount of the thermoplastic resin sheet, a phenomenon occurs in which the accompanying airflow is caught between the thermoplastic resin sheet and the rotary cooling drum. Therefore, if the electrode position is brought closer to the anti-rotation direction of the rotary cooling drum, the surface defect at the center of the sheet is eliminated, but the adhesion to the rotary cooling drum near both ends of the sheet becomes unstable, and the sheet vibrates due to sheet thickness unevenness. Worsens. This is because, as the rotational speed of the rotary cooling drum increases, the curl amount on the rotary cooling drum increases near the both ends of the sheet. This is caused by the increase in size, which hinders uniform molding of the thermoplastic resin sheet. Also, when the adhesion between the molten resin and the rotary cooling drum is weakened, the cooling of the molten resin becomes insufficient, and depending on the type of the thermoplastic resin, the resin is crystallized and the transparency of the sheet is impaired, or the stretchability is deteriorated. In many cases, such a problem occurs.

[0004] A uniform sheet without these inconveniences can be obtained by the electrostatic application casting method, although it depends on the type of the thermoplastic resin, but usually the sheet extrusion speed (the peripheral speed of the rotary cooling drum) is 50. ６０60 m / min was the upper limit.

On the other hand, when a thermoplastic resin is extruded and formed into a sheet and stretched into a film by a flat method,
Streak-like defects called die streaks occur on the surface of the molded product.
The die streaks cause convex or dent streaks on the surface of the extruded sheet when the extruded molten resin comes into contact with foreign matters or polymer degradation products attached to the tip of the die lip. In particular, when the thermoplastic resin is polyester, the generation of degraded products due to thermal decomposition is remarkable. When extruded for a long time, the degraded products (hereinafter referred to as eyes) adhere to the die lip and grow. It causes die muscle.

[0006] Polyester films are used for magnetic tapes, photographic applications, plate making applications, and the like, but films with die streaks do not become products, resulting in a large loss in production. Also, the number of eyes that occur once increases over time,
The size also tends to increase. For this reason, when the die streaks exceed the control limit, it is necessary to interrupt the production and remove the stuck to the die lip with a metal spatula such as copper, but the frequency increases as the rotation speed of the rotary cooling drum is increased . Therefore, the die streaks not only lower the product quality but also significantly lower the productivity.

As a method for suppressing the occurrence of die streaks, for example, Japanese Patent Application Laid-Open No. Hei 3-231826 discloses a method in which a die lip of a pair of die lips is made longer than a tip of a lip opposite to a sheet withdrawal side. There is disclosed a method of inclining the flow path by providing a step, but in this method, as the rotation speed of the rotary cooling drum is increased, the polymer exiting the die slit is drawn along the lower surface of the sheet take-up side lip. In addition, since the difference between the landing point on the cooling drum near the center of the sheet and the vicinity of both ends of the sheet is large, uniform forming of the thermoplastic resin sheet is hindered, and the rotation speed of the rotary cooling drum cannot be increased.

Japanese Unexamined Patent Application Publication No. 9-207195 proposes a method of providing a step on a die lip of a pair of die lips such that the leading end of the lip is opposite to the leading end of the sheet. However, even with this method, as the rotational speed of the rotary cooling drum is increased, the difference between the center of the molten sheet that has exited the die slit and the landing point on the cooling drum near the both ends of the sheet increases. I can't raise it.

[0009]

As apparent from the above, an object of the present invention is to increase the rotation speed of a rotary cooling drum when extruding a thermoplastic resin.
In addition, the present invention provides a method capable of significantly improving the productivity of a thermoplastic resin sheet having excellent thickness uniformity and having few surface defects by suppressing the occurrence of eyes and eyes whose frequency of occurrence increases as the rotation speed of the rotary cooling drum is increased. It is in.

[0010]

An object of the present invention is to provide a die used for forming a film of a thermoplastic resin according to the present invention, which is formed by extrusion-forming a flat drawing method. The lip ends at both ends of the lip on the sheet retrieving side are 0.1 to 10.0 mm longer than the lip tip on the sheet retrieving side, and the lip tip at the center of the die lip on the sheet retrieving side is the sheet retrieving lip. A step is provided at the tip of the die lip opposite to the sheet take-up side so as to be 0.1 to 3.0 mm shorter than the leading end, and the range in which the step changes is 200 mm from both ends of the die lip.
mm, which is achieved by an extrusion die.

In a method of forming a polyester film by melt-extrusion molding of a thermoplastic polyester and then biaxially stretching the flat polyester film, a tip of a pair of die lips on a sheet taking-off side has a straight shape, and a sheet is pulled back. The lip tips at both ends of the take-up lip are longer than the sheet take-up side lip tip by 0.1 to 10.0 mm, and the lip tip at the center of the die lip opposite to the sheet take-up side is larger than the sheet take-up side lip tip. 0.1 or more
A step is provided at the tip of the die opposite to the sheet take-off side so as to be shorter than 0 mm, and the range in which the step changes is within 200 mm from both ends of the die lip. This is achieved by a molding method.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The die streak referred to in the present invention, when observed in a cross section in the sheet extrusion forming direction, shows a shape as shown in FIG.
For example, a defect that becomes a convex streak 2 or a concave streak 3 on the surface of the polyester sheet 1 in the same direction as the extrusion direction,
A sheet having a thickness of 100 μm often has a height or depth of about 0.2 to 2 μm. Large ones can be observed with the naked eye, while small ones can be observed when sandwiched between two deflection plates.

In photographic and plate making applications, a polyester film is coated with a halogenated emulsion to produce a product.
The defects such as the die streaks 2 and 3 shown in FIG. 1 cause uneven coating of the emulsion. Therefore, even die streaks which cannot be observed with the naked eye are unacceptable. Therefore, production must be interrupted as soon as die streaks occur, and the streaks attached to the die lip must be removed with a metal spatula such as copper. The effect of suppressing die streaks can be evaluated by the number of continuous production days until the die streaks generated by the streaks attached to the die lip exceed the control limit and must be removed.

The thermoplastic resin in the present invention includes polyesters, polyolefins such as polyethylene and polypropylene, polyamides such as nylon 6 and nylon 66,
Polyimides, polystyrenes, polycarbonates,
It refers to resins used for melt extrusion molding such as polyvinyls, and is particularly suitable for thermoplastic polyester in which die streaks are enhanced by biaxial stretching.

The thermoplastic polyester in the present invention includes terephthalic acid, isophthalic acid, naphthalene-2,6
-Polyester obtained by polycondensing an aromatic dicarboxylic acid such as dicarboxylic acid or an ester thereof with a glycol such as ethylene glycol, diethylene glycol, tetramethylene glycol or neopentyl glycol. Polyester can be obtained by directly polycondensing an aromatic dicarboxylic acid and glycol, or by subjecting a polyalkylation of an aromatic dicarboxylic acid dialkyl ester and glycol to a transesterification reaction, or by polycondensing an aromatic dicarboxylic acid diester. And the like. Representative examples of such a polymer include polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, and the like, and copolymers thereof. Further, the third component may be copolymerized.

The thermoplastic resin may contain a stabilizer, a lubricant, a pinning agent, a viscosity modifier, an antioxidant, a pigment, a coloring dye, a fluorescent brightener, an ultraviolet absorber, an antistatic agent and the like. .

The present invention can be applied to extrusion molding of a thermoplastic resin, and can be particularly preferably applied to an extrusion-molded flat stretching film forming method. Extrusion molding Flat stretching film forming method is to extrude molten resin from a die with parallel slits, form it into a sheet, and then sequentially or simultaneously stretch it in a vertical or horizontal biaxial direction with a roll, stenter, etc. to form a film And a conventionally known method can be applied.

For example, the polyester is melt-extruded and solidified on a rotary cooling drum to form an unstretched sheet.
A method of sequentially stretching or simultaneously stretching two to six times in the longitudinal direction by a roll peripheral speed difference and two to six times in the horizontal direction by a stenter method or the like and performing heat fixing at about 160 to 250 ° C. can be mentioned.

However, the present invention is effective in the case where the biaxial stretching of the flat method emphasizes the die streaks generated at the die lip and becomes conspicuous. Is not applicable.

FIG. 2 is a cross-sectional view of the die end (most edge) of the present invention, and FIG. 3 is a cross-sectional view of the die center part (center part).
FIG. 4 shows the shape of the tip of the lip on the sheet take-up side, and FIG. 5 shows the shape of the tip of the lip on the opposite side of the sheet.

In the pair of die lips, the sheet take-up side lip tips 5 and 9 have a straight shape, and the sheet opposite take-up side lip tips 8 and 9 at both ends of the die are separated from the sheet take-up side lip tips 6 and 7. 0.1 or more and 10.0m
m, preferably 1.0 to 5.0 mm. On the other hand, the lip tip 11 of the tie center portion 10 opposite to the sheet take-up side lip tip 5 is 0.1% more than the lip tip 5 of the sheet take-up side.
Not less than 3.0 mm, preferably not less than 0.2 and 1.0 mm
Steps 12 and 13 are provided at the tip of the die lip so as to be shorter, and the range 14 and 15 where the step changes are within 200 mm, preferably 100 mm, from the outermost edges 6 and 7 on both sides of the die lip.

Here, the opposite side of the sheet is referred to as a side opposite to the direction in which the molten resin 16 is extruded, formed into a sheet 17, and taken out as shown in FIG.

At the two extreme ends of the die lip, if the lip tips 8 and 9 on the opposite side of the sheet are longer than the lip tip 5 by less than 0.1 mm, the landing point of the rotary cooling drum 18 at the sheet edge is It is difficult to adjust the electrode 19 because it is greatly deviated from the center, and the rotation speed of the rotary cooling drum cannot be increased. Conversely, if it exceeds 10 mm, the polymer separation point at the lip tips 8 and 9 on the sheet reverse side will fluctuate,
The edge portion of the sheet becomes unstable, which is not preferable.

When the length of the lip tip 11 of the die lip center portion 10 on the side opposite to the sheet take-up side lip is less than 0.1 mm than the lip tip 5 of the sheet take-up side, the effect of suppressing the occurrence of blemishes is small, and when it exceeds 3.0 mm. The effect of suppressing the occurrence of pits is saturated, and the molten resin easily adheres to the lower surface of the lip on the sheet take-up side, deteriorates to become pits, and it is difficult to remove the pits attached to the lip, which is not preferable.

The range 14, 1 in which the step of the die lip changes
If 5 exceeds 200 mm from the outermost edges 6 and 7 on both sides of the die lip, it is not preferable because the film in the range where the step changes can not be commercialized and the width yield decreases. Also,
The change of the die lip length may be continuous from both ends of the edge toward the center as shown in FIG. 5, or may be changed within a certain range, but a step-like change is not preferable.

In the present invention, the tip of the lip is finished at a right angle, but the tip is preferably sharp, and the radius is preferably about 10 to 50 μm due to the restriction of machining accuracy.

According to the study of the present inventor, when the polyester resin is melt-extruded, the molten resin under the lip swells due to a phenomenon called a ballast effect, and the extruded molten resin approaches the lower surface of the lip on the sheet take-off side. It has been found that the eyes and the edges are easily attached to the tip of the take-off side lip, and die streaks are easily generated. As a countermeasure against this, the extruded molten resin swells to the sheet reverse side by providing a step in the die lip so that the tip of the sheet reverse side on the center of the pair of die lips is shorter than the sheet reverse side lip. Therefore, it moves away from the lower surface of the lip on the sheet take-up side. As a result, it is considered that the deteriorated material is less likely to adhere to the lower surface of the lip on the sheet take-up side, adhesion and growth on the eyes is suppressed, and generation of die lines is suppressed.

The resin flow path surface of the die and the lower surface from the tip of the lip can be plated with chromium, nickel, titanium, zinc, platinum or the like, or can be coated with a ceramic coating such as tungsten carbide, chrome carbide or alumina. When the tip of the die lip is scratched, a streak is generated from the scratch. Therefore, plating or ceramic coating can improve the scratch resistance. In particular, hard chrome plating and tungsten carbide coating are preferred.

When extruding using the die of the present invention, as shown in FIG. 6, if the die 4 is tilted from 6 degrees to 40 degrees toward the sheet retraction side, the die line suppression effect and the sheet forming speed are increased. Can be. As described above, it is effective to keep the lip away from the sheet taking-up side lip and the sheet. Therefore, the effect of the present invention can be further enhanced by inclining the die toward the sheet taking-up side. However, if it is less than 6 degrees, it is almost the same as the vertical direction, and if it inclines beyond 40 degrees, the molten resin adheres to the lip on the opposite side at the start of extrusion, which is not preferable. When the die is tilted, it is difficult to clean the lip. However, when the die according to the present invention is used, the occurrence of blemishes is suppressed, so that it is almost unnecessary to perform the lip cleaning. Also, by inclining the die as shown in FIG. 6, the landing points of the center and both ends of the molten resin sheet extruded from the die lip on the rotary cooling drum are reduced, and the rotation speed of the rotary cooling drum can be increased.

[0030]

The present invention will be described in more detail with reference to the following examples.

Example 1 Intrinsic viscosity: 0.63 dl / g
Polyethylene terephthalate pellets (measured in o-chlorophenol at 35 ° C.) were dried at 160 ° C. for 4 hours, then supplied to an extruder and melt-extruded. The length of the die slit in the cross direction of the sheet was 1 m, and the die was mounted vertically. The tip of the die lip on the sheet pickup side lip is straight, the edge of the sheet opposite the lip on both sides of the die lip is 3.0mm longer than the tip of the sheet pickup side lip, A step is provided on the die lip so that it is shorter by 1.0 mm than the tip of the lip on the sheet take-up side, and the range of the step change is 50 mm from the top edge on both sides of the die lip, and the step is continuously changed from the top edge part It was used. The temperature of the die was 280 ° C, and the set temperature of the cooling drum was 25 ° C. Assuming that the thickness of the sheet extruded from the die was 100 μm and the rotational speed of the rotary cooling drum capable of forming a uniform sheet was determined, the upper limit rotational speed was 70 m.
/ Min, and the sheet was continuously formed at this speed. Then, the formed sheet was 3.7 times with a vertical stretching machine and 4.times. With a horizontal stretching machine.
After stretching 0-fold, both sides were slit by heat fixing to obtain a biaxially stretched polyester film.

The effect of suppressing the occurrence of die streaks was evaluated by the continuous molding time until the die streaks exceeded the control limit. As the control limit value, an increase / decrease value of the film thickness due to the die streak was used. Specifically, the thickness of the die streak portion was set to ± 0.40% of the film thickness. As a result, it was possible to operate smoothly at high speed without interruption of production for six consecutive days.

[Example 2] Polyester was prepared in the same manner as in Example 1 except that a step was provided on the die lip so that the tip of the lip on the sheet opposite to the sheet take-up side at the die center portion was 0.3 mm shorter than the tip of the lip on the sheet take-up side. The sheet was continuously formed. As a result, the upper limit rotation speed of the rotary cooling drum capable of forming a uniform sheet was 70 m / min, and the die streaks at the same level as in Example 1 occurred on the fourth day.

Example 3 A polyester sheet was continuously formed in the same manner as in Example 2 except that the die of Example 1 was tilted by 20 degrees from the vertical direction to the opposite take-off side. As a result, the upper limit rotation speed of the rotary cooling drum capable of forming a uniform sheet is 80.
At m / min, the same level of die streaks as in Example 1 occurred on day 8.

Example 4 A polyester sheet was continuously formed in the same manner as in Example 2 except that hard chrome plating was performed from the molten resin flow path surface to the lower surface of the sheet take-up side lip and the sheet non-take-up side lip of the die of Example 1. Molded. As a result, the upper limit rotation speed of the rotary cooling drum capable of forming a uniform sheet was 70 m / min, and die streaks at the same level as in Example 1 were generated on the eighth day.

Example 5 A polyester sheet was prepared in the same manner as in Example 1 except that the die was coated with tungsten carbide from the surface of the molten resin flow path to the lower surface of the lip on the sheet take-up side and the sheet opposite take-up side lip. Continuous molding. As a result, the upper limit rotation speed of the rotary cooling drum capable of forming a uniform sheet was 70 m / min, and the die streaks at the same level as in Example 1 occurred on the ninth day.

[Comparative Example 1] Polyester was prepared in the same manner as in Example 1 except that a step was formed on the die lip so that the tip of the lip on the sheet opposite to the sheet take-up side at the die center was 4.0 mm shorter than the tip of the lip on the sheet take-up side. Extrusion was started by melting the resin, but when the molten resin came out of the die lip, the molten resin flowed along the lower surface of the sheet take-up side lip, and a normal sheet could not be obtained.

Comparative Example 2 Polyester was prepared in the same manner as in Example 1 except that a step was provided on the die lip so that the tip of the lip on the sheet opposite to the sheet take-up side at the die center portion was longer by 1.0 mm than the tip of the lip on the sheet take-up side. The sheet was continuously formed. As a result, the upper limit rotation speed of the rotary cooling drum capable of forming a uniform sheet was 60 m / min, and the die streaks at the same level as in Example 1 occurred on the first day. As compared with Example 1, the rotation speed of the rotary cooling drum became slower, the continuous film forming time until the die streaks exceeded the control limit was shortened, and the productivity was reduced.

Comparative Example 3 Polyester was prepared in the same manner as in Example 1 except that the tip of the lip on the sheet opposite side of the die center and the tip of the lip on the sheet pickup side were made the same length so that there was no step in the die lip. The sheet was continuously formed. As a result, the upper limit rotation speed of the rotary cooling drum capable of forming a uniform sheet was 70 m / min, but the die streaks at the same level as in Example 1 occurred on the second day. As compared with Example 1, the continuous film forming time until the die streaks exceeded the control limit was shortened, and the productivity was reduced.

[Comparative Example 4] The tip of the lip on the opposite side of the die lip was made 1.0 mm shorter than the tip of the lip on the opposite side of the sheet and the lip tip on the opposite side of the die lip. A polyester sheet was continuously formed in the same manner as in Example 1 except that the step was not formed between the outermost edge and the center of the die lip. As a result, the upper limit rotation speed of the rotary cooling drum capable of forming a uniform sheet is 40 m / min, and the rotation speed of the rotary cooling drum is 40 m / min.
At m / min, die streaks at the same level as in Example 1 occurred on the eighth day. As compared with Example 1, the upper limit rotation speed of the rotary cooling drum was significantly reduced, and the productivity was reduced.

[0041]

According to the present invention, the tip of the pair of die lips has a straight lip on the sheet take-up side, and the outermost edge of the sheet on both sides of the die lip is more than the tip of the lip on the sheet take-up side. A step is provided at the tip of the die lip so that the tip of the lip at the center opposite to the sheet taking-up side is shorter than the tip of the lip at the sheet taking-up side by 0.1 to 3.0 mm. Range from the edge on both sides of the die lip to 200
In the extrusion die that is within mm, and in the method of forming a polyester sheet using the same, it is possible to increase the rotation speed of the rotary cooling drum in addition to suppressing the occurrence of die streaks and extending the continuous operation time. As a result, productivity can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view in the lateral direction of a sheet (explanation of a die streak shape).

FIG. 2 is a cross-sectional view of the die edge of the present invention.

FIG. 3 is a sectional view of a die center according to the present invention.

FIG. 4 shows the shape of the tip of the lip on the sheet take-off side according to the present invention.

FIG. 5 shows the shape of the tip of the lip of the sheet withdrawal side according to the present invention.

FIG. 6 is a layout view when the die is inclined according to the present invention.

Claims (5)

[Claims] 1. A die used for forming a thermoplastic resin by extrusion molding and flat stretching, wherein a tip of a lip on a sheet take-off side of a pair of die lips has a straight shape, and an end of both ends of a lip on a sheet opposite to a take-off side. The lip tip is longer than the sheet take-up side lip tip by 0.1 to 10.0 mm.
In addition, the tip of the lip at the center of the die lip on the opposite side of the sheet is 0.1 to 3.0 m longer than the tip of the lip on the sheet withdrawal side.
A die for extrusion molding, wherein a step is provided at the tip of the die lip on the opposite side of the sheet so as to be shorter than m, and the range in which the step changes is within 200 mm from both extreme ends of the die lip. 2. The extrusion die according to claim 1, wherein the resin flow path surface inside the die and the lower surface of the lip are hard chrome plated. 3. The extrusion die according to claim 1, wherein the inner resin flow path surface and the lower surface of the lip are coated with tungsten carbide. 4. A method for melt-extruding a thermoplastic polyester and thereafter forming a polyester film by biaxial stretching in a flat method, wherein the extrusion die according to any one of claims 1 to 3 is used. Of forming polyester sheet. 5. The method for forming a polyester sheet according to claim 4, wherein the die is inclined in a range of 6 degrees or more and 40 degrees or less in a direction opposite to the sheet withdrawing side.