JPH07323464A - Method of extrusion-forming thermoplastic resin film - Google Patents

Abstract

PURPOSE:To restrain the unevenness of a film in its thickness by heat-melting thermoplastic resin at a melt-completion temperature or higher to be forwarded Into a die, and cooling it at the low temperature crystallization Initiating temperature or higher in the land part of the die to be extruded thereafter. CONSTITUTION:In the case where a sheet cast film is obtained by melt-extruding thermoplastic resin In use of a flat die, thermoplastic resin is heat-melted at a fusion completion temperature Tme or higher to be melted and then forwarded into the die. After it is subsequently expanded in its width direction in the die, so that thermoplastic resin is subjected to a process to be extruded after being cooled at Tmc or lower and high temperature crystallization initiating temperature Tcb or higher. The cast film is preferred to be substantially an unstretched film with a birefringence rate lower than 0.01, and the relation of the temperature Tout of thermoplastic resin at the outlet of the die land part is preferably set to be Tin>Tout+20 deg.C. By making resin Into a low temperature and high rigidity in this manner, the film vibration and unevenness of the thickness can be restrained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a thermoplastic resin film. More specifically, the present invention relates to a method for producing a thermoplastic resin film capable of reducing unevenness in film thickness during extrusion molding.

[0002]

2. Description of the Related Art Thickness uniformity is an important basic quality in producing a thermoplastic resin film. Taking polyester as an example of the thermoplastic resin, the polyester film is used in various industrial applications such as base films for magnetic recording media, electrical insulation applications such as capacitors, and OA applications such as printer ribbons because of its excellent properties. However, these applications require a high degree of dimensional accuracy for the film thickness. Therefore, it is extremely important to suppress the uneven thickness of the film.

Causes of uneven thickness include fluctuations in the discharge amount when melt-extruding and extruding into a sheet on a cooling drum, film vibration of resin between the die and the drum, and uneven rotation of the drum. In the case of using a biaxially stretched film, in addition to these factors, there are temperature unevenness and rotation unevenness of the roll during longitudinal stretching, and temperature unevenness and wind speed unevenness inside the tenter during lateral stretching. Therefore, various methods have been conventionally proposed for improving the thickness unevenness. For example, a method for suppressing uneven rotation of a casting drum that cools and solidifies the molten resin (Japanese Patent Laid-Open No. 55-93420) or a resin that is easily subjected to electrostatic force when the molten resin is brought into close contact with the casting drum by electrostatic force However, the effect is not sufficient.

As a method of extruding a thermoplastic resin at a temperature below its melting point, for example, Japanese Patent Publication No. 19625/1978,
Japanese Patent Publication No. 1-55087 can be mentioned. However, these methods use a circular die and are not applied to a flat die like the present invention. In the case of a circular die, since it is discharged in a cylindrical shape,
There is no edge, and it is difficult to disturb the flow even if cooled below the melting point,
When a flat die is used, there is a problem that the end is more likely to be solidified first and the flow is easily disturbed. Also, these publications cool the resin to below the melting point before the land of the die,
It uses a configuration that supplies cooled resin to the land. More specifically, the resin is solidified by cooling it below the melting point inside the die, and then the resin is supplied to the land and extruded while shearing. Therefore, a very high extrusion pressure is required, extrusion is difficult with an ordinary extruder, a special extruder for high pressure is required, and the extrusion stability is poor. Further, a large load is applied to the die body and the die, which causes deformation and deterioration of durability. Further, it is extremely difficult to widen the resin solidified in this way, and even if the resin can be widened, the thickness unevenness is poor due to the unevenness of the flow, and the effect of reducing the thickness unevenness that the present invention aims at can be expected. Not a thing.

[0005]

As described above, there is a strong demand for improving the unevenness of the thickness of the film, and various improving methods have been proposed for that purpose, but the effect is still insufficient. The present invention provides a method for producing a film having excellent thickness unevenness by a small modification of an existing die to meet such requirements.

[0006]

That is, the present invention is a method for obtaining a sheet-shaped cast film by melt-extruding a thermoplastic resin using a flat die, wherein the thermoplastic resin is heated and melted at a melting end temperature Tme or higher. After being fed into the die and expanded in the width direction in the die, the thermoplastic resin is less than Tme at the land portion of the die, and the temperature-falling crystallization start temperature T
The method is an extrusion molding method for a thermoplastic resin, which comprises cooling to cb or more and extruding.

As a result of diligent research, we have found that the cause of the uneven thickness of the cast film is mostly film vibration between the die and the cooling drum when the resin is extruded into a sheet. An object of the present invention is to provide a method for obtaining a film in which the resin is made to have a high rigidity by a low temperature to suppress the film vibration and the thickness unevenness is remarkably improved.

The present invention will be described in detail below.

Examples of the thermoplastic resin in the present invention include polyolefin resins such as polyethylene, polypropylene and polymethylpentene, polyamide resins such as nylon 6 and nylon 66, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate and poly. A polyester resin such as -1,4-cyclohexanedimethylene terephthalate, a polyacetal resin, a polyphenylene sulfide resin, or the like can be used. Further, these resins may be homo resins, or may be copolymerized or blended within a range not impairing crystallinity. Also, in these resins,
Various known additives, for example, antioxidants, antistatic agents,
A crystal nucleating agent and inorganic particles may be added.

The melting end temperature Tme and the falling temperature crystallization start temperature Tcb in the present invention can be determined by DSC. DSC is a differential scanning calorimetry method that is usually used in thermal analysis, and is a method of measuring endothermic and exothermic states accompanied by state changes such as melting, crystallization, phase transition, and thermal decomposition of a substance.
A known method can be used to measure the melting temperature of the thermoplastic resin at the time of temperature increase and the crystallization temperature at the time of temperature decrease by DSC, but the point to note here is the temperature increase and cooling rate during the measurement. is there. For example, when measuring the melting temperature, the melting temperature shifts to the high temperature side if the rate of temperature rise is too high. On the contrary, if the heating rate is too low, the melting temperature will shift to the low temperature side.
In selecting the actual extrusion conditions, a suitable temperature raising / lowering rate is usually 10 to 30 ° C./min.

In the present invention, the thermoplastic resin is DSC.
It is necessary to heat above the end temperature Tme of the endothermic peak at the time of melting to obtain a molten state. This step is usually done in an extruder. Start temperature T of the endothermic peak when the resin temperature melts
If it is less than mb, the resin has almost no fluidity and cannot be extruded by an ordinary extruder. Further, if the resin temperature is higher than Tmb but lower than Tme, some unmelted resin remains, so that clogging of the filter and foreign matter defects of the film after molding may occur, which is not preferable.
Therefore, the heating and melting of the resin is not less than Tme, preferably (Tme + 10) in order to obtain a completely molten state without unmelted resin.
(° C) or higher.

The flat die in the present invention is not particularly limited, but for example, as described in “Extrusion molding of plastics and its application” by Keiji Sawada (Seibundo Shinkosha), a cylindrical shape is formed inside. Any of a manifold die having a groove (manifold), a fish tail die having a shape like a fish tail, and a coat hanger die having an intermediate shape may be used. The flat die is usually a portion called a die hopper that spreads the molten resin in the width direction and a final portion that is formed into a target shape after the resin is spread in the width direction, and is a parallel portion having a constant slit gap. It is composed of a part called the land part. The resin is extruded onto the cooling drum immediately after passing through the land portion. At this time, a method in which static electricity is applied to the sheet-shaped molten resin to bring it into close contact with the drum for rapid cooling and solidification is preferably used.

In the conventional method of producing a film by extrusion molding of a thermoplastic resin, the resin heated and melted at a temperature higher than the melting point in the extruder is sent to a die through a pipe connecting a filter, a gear pump and the like. The resin sent to the die is molded into a desired shape by the die and then extruded. The resin temperature during this extrusion is usually equal to or higher than the melting end temperature Tme. In contrast, in the present invention, the resin has a melting end temperature T
The temperature is lowered to less than me and higher than the temperature falling crystallization start temperature Tcb. This cooling needs to occur at the land of the die. If the cooling is done before the resin enters the die, the viscosity will rise and the fluidity will deteriorate, resulting in abnormal extrusion and abnormal flow, and load on the extruder, filter and gear pump. It is not preferable because it causes deformation or shortens the life. In addition, it is not preferable to cool the resin before the land portion (die hopper portion) even in the die because it is a process in which the resin is molded into a desired shape and causes temperature unevenness and abnormal flow. Especially in the flat die, since the resin flow path length varies in the width direction, the heat history is not uniform due to the difference in cooling time, and temperature unevenness occurs in the width direction, resulting in poor moldability and sufficient thickness unevenness. Not only the improvement effect cannot be obtained, but also the thickness unevenness may worsen, which is not preferable. On the other hand, if the cooling is performed at the land portion of the die, the cooling is performed after the resin is expanded in the width direction and formed into a shape to be extruded, and uniform cooling is possible. The land portion is a portion having the smallest gap in the die, and is suitable for high heat exchange efficiency. Further, since the resin is extruded immediately after cooling, it is possible to minimize an increase in filtration pressure and an abnormal extrusion due to an increase in viscosity.

In the present invention, it is necessary to cool the resin at the land portion at a temperature lower than Tme and higher than Tcb. Even if the molten resin is cooled below Tme, it will not solidify in a short time.
A so-called supercooled liquid phase state can be maintained. Moreover, the resin in this state has a high viscosity, is stable against film vibration and disturbance between the die and the cooling drum after being extruded from the land portion, and a film having a small thickness unevenness can be obtained. In order to increase the viscosity of the resin, a method of increasing the molecular weight and a method of adding a thickener can be considered. However, these methods are not preferable because they result in different resins. On the other hand, if the die of the present invention is used,
It is excellent in that the resin and equipment used in the current film manufacturing can be used as is, and that a film with less uneven thickness can be obtained. Further, it is necessary to cool the resin to the temperature lowering crystallization start temperature Tcb of the resin or higher. When the temperature is lower than Tcb, the resin starts to crystallize, and the surface of the extruded film is roughened, the extrusion is abnormal, the flow is uneven, and the resin solidifies over time, which is not preferable anymore.
In the present invention, the resin is cooled to below the melting point at the land portion of the die, but in that case, the important thing is
It means that the resin is never solidified. It is important to use the supercooled state of the polymer to extrude it in the liquid state, although it is below the melting point.

The means for cooling the land portion of the die is not particularly limited, but for example, there is a method in which holes are provided in the land portion for cooling and a coolant is passed through the holes. As the refrigerant, air or various liquid refrigerants can be used,
A desired temperature can be set by controlling the temperature and flow rate of the refrigerant.

Further, in the present invention, the relationship between the temperature Tin of the thermoplastic resin at the inlet of the land portion of the die and the temperature Tout of the thermoplastic resin at the outlet of the land portion of the die is Tin> Tout + 20 ° C. Is preferred. That is, the resin is cooled at the land portion, but at that time, it is preferable that the resin is extruded in a cooling transient state. Due to the transient state, the vicinity of the thick edge is left in a relatively high temperature state, and solidification from the edge portion can be suppressed. When Tin ≦ Tout + 20 ° C., the resin is sufficiently cooled in the land part and becomes a steady state body, the edge part also becomes the same temperature as the central part, and the solidification phenomenon from the edge part easily occurs. .

The formed film having excellent thickness uniformity obtained by the present invention may be directly used as a cast film in a product, or may be stretched and heat-treated to be oriented and crystallized to improve its properties. . In this case, it is desirable that the birefringence of the cast film is suppressed to less than 0.01 and the film is substantially unoriented so that the stretchability is not deteriorated. As a method for imparting orientation, stretching is carried out in the machine direction between rolls having different peripheral speeds, then transverse stretching in a tenter, sequential biaxial stretching method in which heat treatment is performed, and biaxial simultaneous stretching in the longitudinal and transverse directions in the tenter, and heat treatment. A known method such as the simultaneous biaxial stretching method for performing the above can be used. By using the present invention, it is possible to obtain a film having excellent thickness uniformity even after stretching.

[0018]

[Method of evaluating physical properties]

(1) Thermal characteristics Using a differential scanning calorimeter DSC3100 manufactured by Mac Science Co., Ltd., 5 mg of a sample was melt-held at 300 ° C. for 5 minutes and rapidly cooled and solidified with liquid nitrogen.
The temperature was raised at ° C / min. The start temperature of the melting endothermic peak observed at this time was Tmb, the peak temperature was Tm, and the peak end temperature was Tme. Further, 5 mg of the sample was melt-held at 300 ° C. for 5 minutes and then cooled at a temperature lowering rate of 20 ° C./minute. At this time, the starting temperature of the temperature falling crystallization exothermic peak is Tcb,
The peak temperature was Tc and the peak end temperature was Tce.

(2) Unevenness of film thickness Using a film thickness tester KG601A manufactured by Anritsu and an electronic micrometer K306C, 3 in the longitudinal direction.
The thickness of a film sampled to have a width of 0 mm and a length of 10 m is continuously measured. Maximum thickness Tmax at 10m length
R = Tmax-Tmin was calculated from (μm) and the minimum value Tmin (μm), and thickness unevenness (%) = (R / Tave) × 100 was calculated from R and the average thickness Tave (μm) of 10 m length.

(3) Birefringence By a polarizing microscope equipped with Berek compensator,
The retardation Rd of the film was determined. Rd was divided by the thickness of the film to give birefringence.

(4) Resin Temperature The resin temperature in the die was measured by forming a hole into which a rod-shaped thermocouple was inserted at a position to be measured, inserting the thermocouple, and providing a seal for preventing resin leakage. As for the temperature of the outlet of the land portion of the die, the temperature of the discharged resin was directly measured by a contact thermometer.

[0022]

EXAMPLES The present invention will be described based on examples.

Example 1 Polyethylene terephthalate having an intrinsic viscosity of 0.65 was used as the thermoplastic resin. When thermal characteristics were measured using DSC, Tmb: 240 ° C., Tm: 255 ° C., Tme:
268 ° C, Tcb: 203 ° C, Tc: 188 ° C, Tce: 1
It was 74 ° C. The polyethylene terephthalate pellets were vacuum dried at 180 ° C. for 3 hours, and the extruder (caliber 3
0 mm), a molten state was obtained at 290 ° C., and the mixture was supplied to a molding die. The die has a lip gap of 1 mm and a width of 150 m.
A manifold die with m and a land length of 100 mm was used. The land of the die has a structure in which a plurality of holes having a diameter of 7 mm are opened in the width direction and air is passed through the holes to cool the land. The temperature of the die hopper is 290 ° C, and the cooling air of 25 ° C is supplied to the land at a flow rate of 35000 cm ³ /
It was cooled by separating. In this state, the resin was extruded, and the film extruded from the die was rapidly cooled and solidified on a cooling roll whose surface temperature was kept at 25 ° C. while applying static electricity, and was wound up. The resin temperature at the die inlet is 290 ° C, the resin temperature at the land portion inlet is 289 ° C, and the resin temperature at the land portion outlet is 25 ° C.
It was 5 ° C. The thickness unevenness of the obtained film in the longitudinal direction was 1.5%, and a film having good thickness unevenness was obtained.

Example 2 In Example 1, the air flow rate of the land portion was 79000c.
A film was obtained at m ³ / min. Resin temperatures at the die inlet, land portion inlet, and land outlet are 290 ° C and 2 respectively.
It was 88 degreeC and 236 degreeC. The thickness unevenness of the obtained film was 0.8%, and a film having a better thickness unevenness was obtained.

Comparative Example 1 A film was obtained under the same conditions as in Example 1, except that air was not passed through the land. The resin temperature at the die inlet, the land portion inlet, and the outlet was 290 ° C. in all cases. The thickness unevenness of the obtained film was 8.0%.

COMPARATIVE EXAMPLE 2 In Example 1, the air flow rate in the land portion was 143000.
cm ³ / min, and the other conditions were the same. The temperature at the die entrance, land entrance, and exit is 290 ° C,
It was 285 degreeC and 198 degreeC. The resin began to solidify over time and it was impossible to obtain a film.

Comparative Example 3 In Example 1, the temperature of the die inlet, the land portion inlet, and the outlet was 290 ° C. and 253, respectively, by cooling the entire die.
C. and 238.degree. However, the flow of the resin extruded with time deteriorated, and finally the extruded resin could not be extruded because the resin did not bite into the extruder due to the increased extrusion pressure.

[0028]

As is clear from the above description, according to the thermoplastic resin molding method of the present invention, it is possible to obtain a thermoplastic resin film in which unevenness in thickness is remarkably improved.
Moreover, since the resin is cooled at the land of the die in the long melt line from the extruder to the die outlet, only a small modification of the existing die is required, and more load than is necessary for the extruder, filter, etc. is required. There is also the advantage that it does not need to be applied, and the effect that clasp stripes and oligomers are less likely to occur.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Tsunashima 1-1-1, Sonoyama, Otsu City, Shiga Prefecture Toray Co., Ltd. Shiga Plant

Claims (5)

[Claims] 1. A method for obtaining a sheet-shaped cast film by melt-extruding a thermoplastic resin using a flat die, wherein the thermoplastic resin is heated and melted to a melting end temperature Tme or higher and fed into the die, and the width direction in the die. The thermoplastic resin extrusion molding method, wherein the thermoplastic resin is extruded after being cooled to a temperature lower than Tme and not lower than the temperature falling crystallization start temperature Tcb in the land portion of the die. 2. The extrusion molding method for a thermoplastic resin according to claim 1, wherein the cooling is performed by air. 3. The extrusion molding method for a thermoplastic resin according to claim 1, wherein the cooling is performed with a liquid. 4. The extrusion molding method for a thermoplastic resin according to claim 1, wherein the cast film is a substantially unoriented film having a birefringence of less than 0.01. 5. The relationship between the temperature Tin of the thermoplastic resin at the inlet of the land portion of the die and the temperature Tout of the thermoplastic resin at the outlet of the land portion of the die is Tin> Tout + 20 ° C.
The extrusion molding method for a thermoplastic resin according to any one of claims 1 to 4, wherein