JPH08197607A - Manufacture of thermoplastic resin film - Google Patents

Abstract

PURPOSE: To prevent generation of surface defect of a film, particularly striping defect by specifying a product of a draft ratio for film extrusion and a film thickness when a sheet-like cast film is to be obtained by melting and extruding a thermoplastic resin by using a flat die. CONSTITUTION: In a method wherein a sheet-like cast film is manufactured by melting and extruding a thermoplastic resin by using a flat die, when a film thickness d is 100μm or less, a product Rd of a draft ratio R for film extrusion and the film thickness d is set to 1000 or above. When the film thickness d exceeds 100μm, the draft ratio R of the extrusion is set to 10 or aboves. In manufacturing, the thermoplastic resin is melted by heating to a melting completion temperature or higher and sent to the die. After the thermoplastic resin is expanded in the die in the cross direction, it is cooled, at a land of the die, to the melting completion temperature or lower and a down temperature crystallization start temperature or higher, and then extrusion molding is performed. Thus, a film having a little ferrule stripe is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. 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 manufacturing method in which unevenness in the thickness of the film is reduced during extrusion molding, and the surface defects of the obtained film, particularly, the surface defects in the form of lines are not generated.

[0002]

2. Description of the Related Art Various methods have been adopted to reduce unevenness in film thickness. Particularly, the thickness irregularity having a relatively long cycle of 10 Hz or less is mainly caused by the film vibration of the molten sheet between the die and the cooling drum, but the present inventors have already pressed at a temperature not higher than the melting temperature of the thermoplastic resin. A so-called supercooling extrusion method has been proposed in which the rigidity of the molten sheet is increased to prevent film vibration (for example, Japanese Patent Application No. 6-70789).

[0003]

However, although the thickness unevenness of the film formed by the above-mentioned supercooling extrusion method becomes small, the surface of the obtained film is frequently subject to surface defects called so-called die streaks. It has a serious drawback that only low quality films can be obtained. That is, it was difficult to obtain a film having a small thickness unevenness and no surface defects.

Therefore, an object of the present invention is to obtain a thermoplastic resin film having a small thickness unevenness and free from surface defects, particularly streaky surface defects.

[0005]

According to the present invention, there is provided a method for producing a thermoplastic resin film, which comprises a flat die for melt-extruding a thermoplastic resin to obtain a sheet-shaped cast film. d (μm)
Is 100 μm or less, the product Rd of the draft ratio R for extrusion of the film and the film thickness d (μm) is 1000 or more, and the film thickness d (μm) is 100 μm.
When it exceeds, the draft ratio R of the extrusion is set to 10 or more.

In the present invention, as the thermoplastic resin,
Polyester resins typified by polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polycyclohexane dimethylene terephthalate, polyamide resins such as nylon 6, nylon 66, polymetaxylylene adipamide, polyolefins such as polypropylene, polyethylene and polymethylpentene. Examples of the resin include resins, polyphenylene sulfide, polycarbonate, polyacetal and the like. Of course, these resins may be copolymerized with other monomers, and known additives such as a slip agent, an antioxidant, an antistatic agent, and a terminal blocking agent may be added.

In the film of the present invention, its thickness d
When (μm) is 100 μm or less, the product Rd of the draft ratio R for extrusion of the film and the film thickness d (μm) is 1
It is necessary to be 000 or more, preferably 1500 or more, and more preferably 2000 or more. This is because when the product Rd is as small as less than 1000, die streaks frequently occur and only a film having many surface defects can be obtained.

For example, in the case of a film having a thickness of 100 μm, the product Rd is set in the above range and the draft ratio is set to 10 or more, preferably 15 to 20 or more, so that the die streak is further reduced and there is no surface defect. The film is easier to obtain.

Further, in order to reduce the thickness unevenness, in particular, a supercooling extrusion method, that is, a thermoplastic resin is heated and melted at a melting end temperature Tme or higher and fed into a die, and the die is expanded in the width direction in the die. When the thermoplastic resin is extruded after being cooled to a temperature lower than Tme and higher than or equal to the temperature falling crystallization start temperature Tcb in the land portion, the above effect is more remarkable.

Further, the cast film thickness d (μm)
However, when it exceeds 100 μm, the draft ratio R of the extrusion is
It must be 10 or more, preferably 15 or more. This is the same reason as when the film thickness is 100 μm or less.

The melting end temperature (Tme) in the present invention,
The temperature falling crystallization onset temperature (Tcb) can be determined by DSC. DSC is a differential scanning calorimetry method usually used in thermal analysis, and includes melting, crystallization, and
It is a method of measuring endothermic and exothermic heat associated with state changes such as phase transition and thermal decomposition. 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, 20 ° C./min is adopted.

In the present invention, the thermoplastic resin is DSC.
It is necessary to heat it to a temperature above the end temperature (Tme) of the endothermic peak at the time of melting to bring it into a molten state. This step is usually done in an extruder. If the resin temperature is equal to or lower than the start temperature (Tmb) of the endothermic peak at the time of melting, 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, unmelted resin remains in part, so that clogging of the filter and foreign matter defects of the film after molding occur as it is, which is not preferable. Therefore, it is necessary to heat and melt the resin at a temperature of Tme or higher, preferably (Tme + 10 ° C.) or higher in order to obtain a completely molten state without unmelting.

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) (also referred to as a T-die), 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 that has a certain slit gap. It is composed of parts called parts. Immediately after passing through the land portion, the resin is released to the atmosphere and extruded onto the cooling drum. At this time, a method is preferably used in which static electricity is applied to the sheet-shaped molten resin so that the molten resin is brought into close contact with the drum to be rapidly cooled and solidified.

In the conventional method for 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 heated 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). On the other hand, in the present invention, the resin is cooled to a temperature below the melting end temperature (Tme) and above 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 increase,
Since the fluidity deteriorates and it solidifies in some cases, it may cause abnormal extrusion or abnormal flow, or it may become impossible to extrude, applying a load to the extruder, filter, or gear pump to cause deformation or deformation. It is not preferable because it causes a decrease in life. Even in the case of cooling in the die, cooling before the land portion (die hopper portion) is a process in which the resin is molded into a desired shape, which causes temperature unevenness and abnormal flow and causes uneven thickness. It is not preferable because it causes deterioration. Especially in the flat die, since the flow path length of the resin is different in the width direction, the heat history is not uniform due to the difference in cooling time, and temperature unevenness in the width direction may occur.
It is not preferable because not only the moldability is deteriorated, a sufficient effect of improving the uneven thickness is not obtained, but also the uneven thickness is deteriorated.

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 molded 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 due to an increase in viscosity, an abnormal extrusion, and an abnormal flow due to solidification.

In the present invention, it is necessary to cool the resin at the land portion below Tme and above Tcb. In the case of the polymer resin, it is possible to maintain a so-called supercooled liquid phase state in which the resin in a molten state is not solidified in a short time even if it is cooled below Tme. 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, the use of the die of the present invention is advantageous in that the resin and apparatus used in the production of the existing film can be used as they are, and a film with less uneven thickness can be obtained.

Further, it is necessary to cool the resin to a temperature lower than the crystallization start temperature (Tcb) of the resin. When the temperature becomes lower than Tcb, the resin begins to crystallize, resulting in surface roughness of the extruded film, abnormal extrusion, uneven flow,
It is not preferable because it solidifies over time and can no longer be extruded by a usual extruder. In the present invention, the resin is cooled down to the melting point or less at the land portion of the die. What is important in this case is that the resin is never solidified. In other words, 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, various liquid refrigerants such as air or water can be used, and the desired temperature can be set by controlling the temperature and flow rate of the refrigerant.

Further, in the present invention, the relationship between the resin temperature Tin (° C.) at the inlet of the die land portion and the resin temperature Tout (° C.) at the die land outlet is T
It is preferable that in> Tout + 20 ° C. 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 transitional state, the vicinity of the thick edge is left in a relatively high temperature state, and solidification from the edge portion can be suppressed. Tin ≦ Tout + 2
When the temperature is 0 ° C., the resin is sufficiently cooled in the land portion and is in a steady state, the edge portion also has the same temperature as the central portion, and the solidification phenomenon from the edge portion easily occurs.

The angle formed by the flow direction of the molten polymer exiting the die with respect to the flow direction of the molten polymer at the land of the flat die is 30 degrees or less, preferably 15 degrees.
It should be no more than 8 degrees, more preferably no more than 8 degrees.
If this angle exceeds 30 degrees, it is easy for streak lines to appear,
This is because it becomes a surface defect of the film.

The film of the present invention is excellent in thickness uniformity and has no surface defects and can be used for various purposes. Further, the film of the present invention is stretched and heat-treated to improve various properties. And can be used for many more applications. As the stretching, any known uniaxial stretching method as a film or biaxial stretching method can be applied.

The film thus obtained is effective as a base film for magnetic recording, a film for heat-sensitive recording, a film for electrical insulation, a film for stamping and the like.

[Evaluation Method of Physical Properties] (1) Thermal Properties Using a differential scanning calorimeter DSC3100 manufactured by Mac Science Co., 5 mg of a sample was melt-held at 300 ° C. for 5 minutes, rapidly cooled and solidified with liquid nitrogen, and then from room temperature. Temperature rising rate 20
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. In addition, 5 mg of the sample at 5 ° C
After melting and holding for 1 minute, the temperature was decreased at a temperature decreasing rate of 20 ° C./minute.
At this time, the starting temperature of the temperature falling crystallization exothermic peak observed is
cb, the peak temperature was Tc, and the peak end temperature was Tce.

(2) Film thickness unevenness Anritsu Corporation film thickest tester KG60
Using 1A and an electronic micrometer K306, the thickness of a film sampled in the longitudinal direction of 30 mm width and 10 m length is continuously measured. Maximum thickness Tm at 10m length
From the ax (μm) and the minimum value Tmin (μm), R = Tmax−Tmin was obtained, and the thickness unevenness (%) = R / Tave × 100 was obtained from R and the average thickness Tave (μm) of 10 m length. At this time, the thickness unevenness is less than 3% is "○", 3% or more and less than 10% is "△", 10%
The above was designated as "x".

(3) Judging by observing the surface of the spinner film under polarized light and the height of irregularities on the surface of the film. The judgment was based on the criteria shown in Table 1.

[0027]

[Table 1]

(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 desired position, inserting the thermocouple, and sealing the resin to prevent leakage. The temperature at the outlet of the land of the die was obtained by directly measuring the temperature of the discharged resin with a contact thermometer.

(5) Draft ratio R The molten thermoplastic resin has a linear velocity Vd (m / min) flowing through the land portion of the die, and a take-up velocity Vc (of the thermoplastic resin film cooled and solidified by casting. m
/ Min). That is, R = Vc / Vd. If it is difficult to obtain Vd, this value R is
For simplification, it may be calculated by R = film thickness obtained (μm) / lip gap of the die (μm).

[0030]

【Example】

Examples 1 to 5 and Comparative Examples 1 to 2 As a thermoplastic resin, polyethylene terephthalate (intrinsic viscosity 0.65, Tme 270 ° C., Tcb 200 ° C., 0.13 weight of a true spherical spherical colloidal silica having a diameter of 0.25 μm as an additive). % Content) was vacuum dried and then fed to a conventional extruder and melted at 285 ° C. to change the lip gap from 1.1 mm to 3.3 mm.
The mold was introduced into a die (land length 150 mm, a large number of holes having a diameter of 7 mm were formed in the width direction in the land portion to provide a water-permeable structure). Cooling water of 20 ° C. is flown through the land portion, the resin sheet heated to 285 ° C. by the die manifold is cooled to 238 ° C. by the land portion, and the molten sheet is extruded in the flow direction of the land portion of the die. (Θ = 0 degree). An electrostatic charge was applied to the extruded film to bring it into close contact with a drum kept at 25 ° C. to be cooled and solidified to change the draft ratio.
A cast film of 300 μm was obtained. The properties of the various films thus obtained are shown in Table 2.

[0031]

[Table 2]

As shown in Table 2, the film thickness d (μ
When m) is 100 μm or less, the product Rd of the draft ratio R of extrusion of the film (sheet) and the film thickness d (μm) is 1000 or more, preferably 1500 or more, more preferably 2000 or more. Is necessary in order to prevent uneven thickness of the film and to prevent streak on the die. When the film thickness d (μm) exceeds 100 μm, the draft ratio R of the extrusion must be 10 or more. Is.

Examples 6, 7 and Comparative Example 3 The angle θ formed by the flow direction of the molten polymer discharged from the die with respect to the flow direction of the molten polymer at the land portion of the flat die of Example 3 was 0 ° to 45 °. The same procedure as in Example 3 was performed except that the temperature was changed.

As a result, as shown in Table 3, the θ value is 30.
It is understood that the degree is preferably 15 degrees or less, preferably 15 degrees or less, and more preferably 8 degrees or less.

[0035]

[Table 3]

[0036]

According to the method of the present invention, after melting the thermoplastic resin, it is cooled to below the melting end temperature Tme and above the temperature falling crystallization start temperature Tcb and extruded, a so-called supercooling extrusion method and a specific draft. Ratio, that is, film thickness d
When (μm) is 100 μm or less, the product Rd of the draft ratio R of the film extrusion and the film thickness d (μm) is 1
000 or more, film thickness d (μm) is 100 μm
If the draft ratio R of the extrusion is more than 10, when the extrusion ratio is 10 or more, a film having a small thickness unevenness, particularly a thickness unevenness of 10 Hz or less, and having no surface defect can be obtained.

Claims (3)

[Claims] 1. A method of obtaining a sheet-shaped cast film by melt-extruding a thermoplastic resin using a flat die, wherein when the film thickness d (μm) is 100 μm or less, the draft ratio R of the film extrusion and the draft ratio R A thermoplastic resin film, wherein the product Rd with the film thickness d (μm) is 1000 or more, and when the film thickness d (μm) exceeds 100 μm, the draft ratio R of the extrusion is 10 or more. Manufacturing method. 2. A thermoplastic resin is heated and melted at a melting end temperature Tme or higher and fed into a die, expanded in the width direction in the die, and then the thermoplastic resin is less than the melting end temperature Tme in the land portion of the die. , Falling temperature crystallization start temperature Tcb
The method for producing a thermoplastic resin film according to claim 1, which comprises cooling and extruding as described above. 3. The angle θ formed by the flow direction of the molten polymer exiting the die with respect to the flow direction of the molten polymer at the land portion of the flat die is 30 degrees or less. 1. A method for producing a thermoplastic resin film according to 1 or 2.