JP3070821B2 - Method for producing thermoplastic resin film - Google Patents

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 film thickness unevenness caused by extrusion molding is small, and
The present invention relates to a method for producing a thermoplastic resin film having a small surface roughness.

[0002]

2. Description of the Related Art There are various causes of film thickness unevenness. In particular, the thickness unevenness of 10 Hz or less, that is, the thickness unevenness of which periodically appears when the waveform of the thickness unevenness is subjected to Fourier analysis, is 10 Hz or less. Since this is largely caused by the film vibration of the molten resin between the die and the drum, a high-viscosity polymer has been used, or the causes of vibration such as wind have been removed, but the effect has been insufficient. Therefore, the melted thermoplastic resin is melted at a temperature lower than the melting end temperature Tme,
There have been proposals (so-called supercooling extrusion method) in which the thickness unevenness caused by film vibration of the molten resin is reduced by increasing the rigidity of the molten resin by cooling the resin to a temperature lower than the cooling crystallization temperature Tcb (for example, supercooling extrusion method) Japanese Patent Application No. 6-70789).

[0003]

However, the above-mentioned supercooled extrusion method has a large effect of reducing the thickness unevenness of 10 Hz or less, but has a drawback that the surface of the obtained film is roughened. . Therefore, the present invention
It is an object of the present invention to provide a method for extruding a thermoplastic resin film having a small thickness unevenness at a frequency of 1 Hz or less and having a small film surface roughness.

[0004]

According to the present invention, there is provided a method of manufacturing a thermoplastic resin film according to the present invention, wherein a thermoplastic resin is heated and melted to a melting end temperature Tme or more, fed into a flat die, and a manifold section in the die. After being expanded in the width direction at the die, the molten sheet extruded by cooling the thermoplastic resin at a land portion of the die to a temperature lower than the melting end temperature Tme and higher than the temperature-lowering crystallization start temperature Tcb had a liquid film of water. It is characterized by being cooled and solidified in close contact with a cooling drum.

Hereinafter, the present invention will be described in detail. As the thermoplastic resin in the present invention, polyethylene, polypropylene, polyolefin resin such as polymethylpentene,
Polyamide resins such as nylon 6 and nylon 66, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, poly-1,
Polyester resins such as 4-cyclohexane dimethylene terephthalate, polyacetal resins, polyphenylene sulfide resins, and the like can be used. These resins may be homo resins, or may be copolymers or blends as long as crystallinity is not impaired. In addition, various known additives such as antioxidants, antistatic agents, nucleating agents, and inorganic particles may be added to these resins.

In the present invention, the melting end temperature (Tme),
The crystallization onset temperature (Tcb) can be determined by DSC. DSC is a differential scanning calorimetry method commonly used in thermal analysis, which involves melting, crystallization,
This is a method of measuring endothermic and exothermic accompanying a state change such as phase transition and thermal decomposition. When measuring the melting temperature of the thermoplastic resin at the time of temperature rise and the crystallization temperature at the time of temperature fall by DSC, a known method can be used, but the points to be noted here are the temperature rise and the cooling rate at the time of measurement. is there. For example, when measuring the melting temperature, if the heating rate is too high, the melting temperature will shift to the higher temperature side. Conversely, if the heating rate is too low, the melting temperature will shift to a lower temperature. 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 was employed.

In the present invention, the thermoplastic resin is DSC
Must be heated to a temperature equal to or higher than the end temperature (Tme) of the endothermic peak at the time of melting. This step is usually performed 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 little fluidity and cannot be extruded with a usual extruder. Further, if the resin temperature is higher than Tmb but lower than Tme, unmelted resin partially remains, which is not preferable because clogging of the filter and defects of foreign matters in the film after molding are caused as it is. Therefore, the resin must be heated and melted at a temperature equal to or higher than Tme, and preferably equal to or higher than (Tme + 10 ° C.) in order to obtain a completely molten state without unmelting.

[0008] The flat die in the present invention is not particularly limited. For example, as described in Keiji Sawada, "Plastic Extrusion Molding and Its Application" (Seibundo Shinkosha Co., Ltd.), a cylindrical inside is used. Any of a manifold die (also referred to as a T-die) having a groove (manifold), a fish tail die shaped like a fish tail, and a coat hanger die shaped in between. The flat die is a land called a die hopper that spreads the molten resin in the width direction, and a land that is a final portion that is formed into a desired shape after the resin is spread in the width direction and is a parallel portion having a fixed slit gap. It is composed of parts called parts. Immediately after passing through the land, the resin is released to the atmosphere and is extruded onto the cooling drum. At this time, a method in which static electricity is applied to the sheet-like molten resin to make it adhere to the drum and quench and solidify, for example, a method described in JP-B-37-6142 is preferably used.

In a conventional method for producing a film by extrusion molding of a thermoplastic resin, in an extruder, a resin heated and melted to a melting point or higher is sent to a die through a heated pipe connecting filters, gear pumps and the like. . The resin sent to the die is extruded after being formed into a desired shape by the die. 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 is cooled to a temperature lower than the melting end temperature (Tme) and equal to or higher than the temperature dropping crystallization start temperature (Tcb). This cooling must take place at the land of the die. If cooling occurs before the resin enters the die, the viscosity will increase,
Deterioration of fluidity occurs, and in some cases, it solidifies, so abnormal extrusion or flow may occur, or extrusion may not be possible.Loading the extruder, filter, gear pump, deforming or deforming It is not preferable because the life is shortened. In addition, even when cooling in a die, cooling before the land (die hopper) is a process in which the resin is molded into a desired shape, which causes temperature unevenness, abnormal flow, and uneven thickness. It is not preferable because it causes deterioration. In particular, since the flow path length of the flat die differs 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, but also the effect of improving the thickness unevenness is not sufficiently obtained, and the thickness unevenness may be deteriorated.

On the other hand, when 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 the narrowest portion in the die and has high heat exchange efficiency and is suitable. Further, since the resin is extruded immediately after cooling, an increase in filtration pressure due to an increase in viscosity, an abnormality in extrusion and an abnormality in flow due to solidification can be minimized.

In the present invention, the cooling of the resin at the land must be performed at a temperature lower than Tme and higher than Tcb. In the case of a polymer resin, a so-called supercooled liquid phase state that does not solidify in a short time even when the resin in a molten state is cooled to less than Tme can be maintained. In addition, 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 or a method of adding a thickener may 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 excellent in that a resin and an apparatus used in the production of the existing film can be used as they are, and a film having less unevenness in thickness can be obtained.

It is necessary to limit the cooling to a temperature equal to or higher than the temperature at which the resin begins to cool down and crystallize (Tcb). When the temperature is lower than Tcb, the resin starts to crystallize, causing the extruded film to have a rough surface, abnormal extrusion, uneven flow,
It is not preferable because it solidifies over time and can no longer be extruded with a normal extruder. In the present invention, the resin is cooled to the melting point or lower at the land portion of the die. In this case, it is important that the resin is never solidified. In other words, it is important to use a supercooled state of the polymer to extrude the polymer in a liquid state, although it is at or below the melting point.

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

In the present invention, the relationship between the resin temperature Tin (° C.) at the entrance of the land of the die and the resin temperature Tout (° C.) at the exit of the land of the die is T
It is preferable that in> Tout + 20 ° C. That is, the resin is cooled in the land portion, and at that time, it is preferable that the resin be extruded in a cooling transient state. Due to the transitional state, the vicinity of the thick edge is left at a relatively high temperature, and the solidification from the edge 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, and the temperature of the edge portion is also the same as that of the central portion, so that the solidification phenomenon from the edge portion easily occurs.

The extruded molten sheet is tightly cooled and solidified on a drum having a liquid film of water. Such a casting method is well known in British Patent No. 1,140,175 and Japanese Patent Publication No. 63-4492. As a method of interposing a liquid film of water, there are various methods. In the case of the present invention, in particular, a method in which air containing moisture is blown onto the surface of a cooling drum kept at a temperature lower than its dew point to form dew condensation is used. This is preferred from the viewpoint of reproducibility and thin film coating. In the case of the present invention, the thickness of the liquid film is 0.01
To 1 μm, preferably 0.02 to 0.5 μm. If the thickness is less than 0.01 μm, the roughness of the film surface due to air entrapment increases, while if it exceeds 1 μm, the adhesion between the molten sheet and the drum is greatly reduced, and only a film having a large thickness unevenness can be obtained. is there. Also,
Since water droplets often remain on the surface of the cooling body after the sheet is peeled off from the cooling drum, it is necessary to completely remove the water droplets. As a removing method, a combined method of the air blowing method and the suction method is particularly preferable.

The molten sheet extruded by the supercooling extrusion method in this manner is brought into close contact with a cooling drum having a liquid film of water and solidified by rapid cooling. The film becomes smaller. Most preferably, there is no thickness unevenness of 10 Hz or less, preferably 5 Hz or less, and more preferably 1 Hz or less, but even if the thickness unevenness of the region is recognized, 10% or less of the total thickness unevenness at a frequency within a practical range. It is preferred that

The surface roughness Ra (center line average roughness) of the film of the present invention is 1 μm or less, preferably 0.3 μm.
The thickness is more preferably 0.1 μm or less.
When the Ra exceeds 1 μm, in the case of a film for magnetic tape, dropout tends to occur, and in the case of a thermal transfer ribbon, a problem tends to occur in resolution and printability.In the case of a film for capacitor insulation, This is because the disadvantage that the breakdown voltage varies or the value becomes small becomes apparent.

Although the use of the film of the present invention is not particularly limited, it is particularly suitable for use in thin films such as magnetic tapes, heat-sensitive transfer ribbons, and capacitors for electrical insulation.

[Evaluation Methods of Physical Properties] (1) Thermal Characteristics Using a differential scanning calorimeter DSC3100 manufactured by Mac Science, 5 mg of a sample was melted and held at 300 ° C. for 5 minutes, quenched and solidified with liquid nitrogen, and then cooled to room temperature. Heating rate 20
The temperature was raised at a rate of ° 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 sample was
After melting and holding for 1 minute, the temperature was lowered at a temperature lowering rate of 20 ° C./minute.
The starting temperature of the cooling crystallization exothermic peak observed at this time is represented by T
cb, the peak temperature was Tc, and the peak end temperature was Tce.

(2) Film thickness unevenness Anritsu Corporation film thick nest tester KG60
Using 1A and the electronic micrometer K306, the thickness of a film sampled in a lengthwise direction of 30 mm width, 10 m length, preferably 20 m length is continuously measured. The maximum value Tmax (μm) and the minimum value Tmin (μm) at the measurement length
m), R = Tmax−Tmin was calculated, and from R and the average thickness Tave (μm) having a length of 10 m, thickness unevenness (%) = R / Tave × 100. At this time, the thickness unevenness was less than 3%, "○", and 3% or more and less than 10%, "△", 10%.
The above was rated as "x". Further, when the thickness unevenness of 10 Hz or less, that is, the waveform of the thickness unevenness is subjected to Fourier analysis, the period of the abnormal thickness that appears periodically is 10 Hz.
If the following thickness unevenness is less than 5% of the total thickness unevenness, “○” indicates that the thickness unevenness is 5% or more and less than 15%, and “△” indicates 15%.
The above was rated as "x". In order to obtain the thickness unevenness of 10 Hz or less, a wave number of 3 (1 / m) or less when the Fourier analysis is performed may be employed.

(3) Surface roughness Ra According to JIS-B-601-1976, a portion of the measured length d is extracted from the roughness curve in the direction of the center line, and the center line of the extracted portion is defined as the X axis. The direction of the vertical magnification is the Y axis,
When the roughness curve is represented by Y = f (X), Ra given by the following equation is represented in μm unit. Ra = 1 / d∫ ₀ ^d | f (x) | dx “Ra” where Ra is less than 0.1 μm is “◎”, 0.1 μm
○ means less than 0.3 μm and 0.3 μm or more
Those with a size of less than μm were marked with “Δ” and those with a size of 1 μm or more were marked with “×”

(4) Resin Temperature The resin temperature in the die was measured by opening a hole for inserting a rod-shaped thermocouple at a position to be measured, inserting the thermocouple, and applying a seal to prevent resin leakage. The temperature of the exit of the land portion of the die was obtained by directly measuring the temperature of the discharged resin with a contact thermometer.

(5) Film thickness of water Measured using an IR-300 infrared trace moisture meter manufactured by Chino Corporation. The calibration curve was determined by absorbing the water on the drum with a blotting paper and plotting the weight against the scale of the moisture meter.

[0025]

EXAMPLES In order to make the effects of the present invention easier to understand,
Hereinafter, examples and comparative examples will be described. Example 1 As a thermoplastic resin, polyethylene terephthalate having an intrinsic viscosity of 0.65 (adding 0.34% by weight of a perfect spherical colloidal silica having a diameter of 0.25 μm as a slipping agent) was used.
When thermal characteristics were measured using DSC, Tmb: 24
0 ° C., Tm: 255 ° C., Tme: 268 ° C., Tcb: 2
03 ° C, Tc: 188 ° C, Tce: 174 ° C.
This polyethylene terephthalate pellet is heated at 180 ° C.
And dried in a vacuum for 3 hours and fed to a 90 mm diameter extruder.
It was melted at 90 ° C. and fed to a T-die. T die has width 1
Those having a length of 250 mm, a lip gap of 1 mm, and a land length of 150 mm were used. A plurality of holes having a diameter of 7 mm are formed in the land portion of the present T-die in the width direction, and the structure can be cooled by flowing water therethrough. The temperature of the die hopper is 290
° C, and the land was cooled by passing 25 ° C cooling water at 5 kg / min. In this state, the resin was melt-extruded, and a 0.07 μm-thick water film was formed by a condensation method on a cooling drum having a surface temperature of 15 ° C. while applying an electrostatic charge to the molten film extruded from the die. The film was tightly cooled and solidified to obtain a cast film. The temperature at the inlet of the die manifold was 290 ° C., and the resin temperature at the inlet of the land was 28 ° C.
The resin temperature at the outlet of the land was 9 ° C, and the resin temperature at the outlet of the land was 245 ° C.
Further, the cast film is stretched 4 times by a longitudinal roll stretching machine kept at 95 ° C, subsequently stretched 4 times by a width stretching machine kept at 100 ° C, and further stretched in the width direction at 205 ° C. A 3% relax heat treatment was performed. The thickness of the obtained film was 8 μm, and the film characteristics are shown in Table 1.

Comparative Example 1 A water film having a thickness of 0.07 μm was formed by the dew condensation method used in Example 1, and the surface temperature was maintained at 25 ° C. in a dry atmosphere instead of the cooling drum having a surface temperature of 15 ° C. A biaxially stretched film having a thickness of 8 μm was obtained in exactly the same manner as in Example 1 except that the drum was used.

Comparative Example 2 Without using the supercooled extrusion method used in Example 1,
A biaxially stretched film having a thickness of 8 μm was obtained in exactly the same manner as in Example 1 except that the temperature of the die land was set to 290 ° C., the same as that of the die manifold, without flowing cooling water through the die land. Was.

Comparative Example 3 An 8-μm thick biaxially stretched film was produced in the same manner as in Example 1 except that the normal extrusion method used in Comparative Example 2 and the normal electrostatic application cast used in Comparative Example 1 were used. I got

As shown in Table 1, by combining the supercooling extrusion method and the method of casting on a drum having a water film, a film having a small thickness unevenness and a small surface roughness can be obtained. .

[0030]

[Table 1]

Example 2 The temperature at the outlet of the die land portion in Example 1 was raised from 245 ° C. to 26 ° C.
Except that the temperature is changed to 0 ° C., the thickness is 8
A biaxially stretched film of μm was obtained.

Example 3, Comparative Example 4 Except that the thickness of the water film on the drum of Example 1 was changed from 0.07 μm to 0.6 μm and 1.2 μm, the thickness was completely the same as in Example 1. An 8 μm biaxially stretched film was obtained. Table 2 shows each property of the obtained film.

[0033]

[Table 2]

[0034]

According to the method of the present invention, the thermoplastic resin is heated and melted to a temperature equal to or higher than the melting end temperature Tme, fed into a flat die, expanded in the width direction at a manifold portion in the flat die, and then landed on the die. Part, the thermoplastic resin is melted below the melting end temperature Tme,
The following effects are produced by bringing the molten sheet extruded by cooling to a temperature of b or more (supercooling extrusion method) into close contact with a cooling drum having a liquid film of water and solidifying it by cooling. (1) The thickness unevenness, particularly the thickness unevenness of 10 Hz or less, that is, the thickness unevenness of the molten sheet caused by the film vibration between the drum and the die can be eliminated or reduced. (2) In addition, the surface roughness Ra of the obtained film is small and a smooth film is obtained. (3) A base line due to a thermal decomposition product or the like is hardly generated, and the productivity is excellent. (4) A film having a low oligomer content is obtained. (5) Film thickness of 25 μm, especially for magnetic tapes, thermal transfer ribbons, capacitors for electrical insulation, etc.
It is suitable for thin applications such as the following.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-235615 (JP, A) JP-A-3-213324 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 47/00-47/96

Claims (4)

(57) [Claims] 1. A thermoplastic resin is heated and melted to a melting end temperature Tme or higher, fed into a flat die, expanded in a width direction at a manifold portion in the die, and then melted at a land portion of the die. Less than the end temperature Tme,
A method for producing a thermoplastic resin film, wherein a molten sheet extruded by cooling to a temperature equal to or lower than a crystallization start temperature Tcb is tightly cooled and solidified on a cooling drum having a liquid film of water. 2. The method for producing a thermoplastic resin film according to claim 1, wherein an electrostatic charge is applied to said molten sheet. 3. The thickness of the liquid film of water is 0.01 to 1 μm.
The method for producing a thermoplastic resin film according to claim 1 or 2, wherein 4. The method for producing a thermoplastic resin film according to claim 1, wherein the surface roughness Ra of the thermoplastic resin film is 1 μm or less.