JPH08197612A - Manufacture of thermoplastic resin film - Google Patents

Abstract

PURPOSE: To manufacture a thermoplastic resin film having small surface roughness by a method wherein a thermoplastic resin is melted with heat and sent to a flat die, expanded in the cross direction, cooled to a specified temperature, and an extruded melting sheet is stuck to a cooling drum having water liquid film so as to cool and solidify. CONSTITUTION: A thermoplastic resin such as a polyolefin resin and a polyamide resin is melted by heating to a melting completion temperature or higher and sent to a flat die. The resin is expanded in the cross direction at a manifold in the die. Thereafter, the thermoplastic resin is cooled to the melting completion temperature or lower and a down temperature crystallization start temperature or higher at a land of the die and extruded so as to form a melting sheet. The melting sheet is stuck to a cooling drum having water liquid film, cooled, and solidified so as to obtain a desired film. At this time, electrostatic charge is preferably applied to the melting sheet, and the thickness of the water liquid film is set to 0.01-1μm. A surface roughness Ra of a thermoplastic resin film obtained in this way is made to be 1μm or below.

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 uneven thickness of the film 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 uneven thickness of a film. Especially, uneven thickness of 10 Hz or less, that is, a thickness irregularity of 10 Hz or less that appears periodically when Fourier analysis of the waveform of the uneven thickness is performed. Since it is largely due to the film vibration of the molten resin between the die and the drum, a high-viscosity polymer has been used or the cause of vibration such as wind has been removed, but the effect was insufficient. Therefore, the melted thermoplastic resin is melted below the melting end temperature Tme,
Proposals have been made (so-called supercooling extrusion method) to reduce the thickness unevenness due to film vibration of the molten resin by increasing the rigidity of the molten resin by cooling to a temperature lowering crystallization temperature Tcb or higher (for example, Japanese Patent Application No. 6-70789).

[0003]

However, although the above-described supercooling extrusion method has a great effect of reducing the thickness unevenness of 10 Hz or less, it has a drawback that the surface of the obtained film is rough. . Therefore, the present invention is 10
It is an object of the present invention to provide an extrusion molding method for a thermoplastic resin film having a reduced thickness unevenness of Hz or less and having a small film surface roughness.

[0004]

According to the method for producing a thermoplastic resin film of the present invention which meets this object, a thermoplastic resin is heated and melted to a melting end temperature Tme or higher and fed into a flat die, and a manifold portion in the die is melted. In the land portion of the die, the thermoplastic resin was cooled to a temperature below the melting end temperature Tme and to a temperature falling crystallization start temperature Tcb or more, and the extruded molten sheet had a water film. It is characterized in that it is closely adhered to a cooling drum to be solidified by cooling.

The present invention will be described in detail below. 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,
A polyester resin such as 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. In addition, various known additives such as antioxidants, antistatic agents, crystal nucleating agents, and inorganic particles may be added to these resins.

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 "Plastic extrusion molding and its application" by Keiji Sawada (Seibundo Shinkosha), it has a cylindrical shape 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 of applying static electricity to the sheet-shaped molten resin to bring it into close contact with the surface of the drum for rapid cooling and solidification, for example, the method described in JP-B-37-6142 is preferably used.

In the conventional method for producing a film by extrusion molding of a thermoplastic resin, the resin which is 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, 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 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 at a temperature lower than Tme and higher than 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.

In the present invention, the relationship between the resin temperature Tin (° C.) at the die land inlet 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 molten sheet thus extruded is closely 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, but in the case of the present invention, a method of blowing moisture-containing air onto a cooling drum surface kept below its dew point to cause dew condensation is uniform. Is preferable, in terms of reproducibility and thin film coating. In the case of the present invention, the thickness of the liquid film is 0.01
˜1 μm, preferably 0.02 to 0.5 μm. If it is less than 0.01 μm, the surface of the film becomes rough due to air entrapment. On the other hand, if it exceeds 1 μm, the adhesion between the molten sheet and the drum is significantly reduced, and only a film with large thickness unevenness can be obtained. is there. Also,
Since water drops often remain on the surface of the cooling body after the sheet is peeled from the cooling drum, it is necessary to completely remove the water drops. As a removing method, a combined method of an air blowing method and a suction method is particularly preferable.

The molten sheet extruded by the above-mentioned supercooling extrusion method is brought into close contact with a cooling drum having a liquid film of water to be rapidly cooled and solidified, so that the film surface roughness having a small thickness unevenness of 10 Hz or less can be obtained. It is a small film. It is most preferable that there be no thickness unevenness of 10 Hz or less, preferably 5 Hz or less, and more preferably 1 Hz or less, but even if thickness unevenness in the region is recognized, it is 10% or less of the total thickness unevenness at a frequency within the practical range. Is preferred.

The surface roughness Ra (center line average roughness) of the film of the present invention is 1 μm or less, preferably 0.3 μm.
Hereafter, it is more preferably 0.1 μm or less.
If the Ra exceeds 1 μm, dropouts are likely to occur in the case of a magnetic tape film, and resolution and printability problems are likely to occur in the case of a thermal transfer ribbon. Furthermore, in the case of a capacitor insulating film, This is because defects such as variations in the dielectric breakdown voltage and reductions in the value become apparent.

The use of the film of the present invention is not particularly limited, but it is particularly suitable for use in thin film thickness such as magnetic tape use, heat-sensitive transfer ribbon use, and electric insulating capacitor use.

[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) Thickness unevenness of film 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, 10 m length, preferably 20 m length is continuously measured. Maximum thickness Tmax (μm) and minimum Tmin (μ
R = Tmax-Tmin was calculated from m), and thickness unevenness (%) = R / Tave × 100 was calculated 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". In addition, the thickness irregularity of 10 Hz or less, that is, the period of the abnormal thickness that appears regularly when the waveform of the thickness irregularity is Fourier analyzed is 10 Hz.
The following thickness unevenness is less than 5% of the total thickness unevenness "○", 5% or more less than 15% is "△", 15%
The above was designated as "x". In order to obtain the thickness unevenness of 10 Hz or less, a wave number of 3 (1 / m) or less in the Fourier analysis may be adopted.

(3) Surface Roughness Ra According to JIS-B-601-1976, a portion having a measurement length d is extracted from the roughness curve in the direction of the center line, and the center line of this extracted portion is the X axis, The direction of 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 "⊚" when the Ra is less than 0.1 μm, 0.1 μm
"○" when the thickness is 0.3 μm or more and 0.3 μm or more
Those having a size of less than μm were evaluated as “Δ”, and those having a size of not less than μm were evaluated as “x”.

(4) Resin Temperature The resin temperature in the die was measured by forming a hole into which a rod-shaped thermocouple was inserted at the desired measurement point, inserting the thermocouple, and providing a seal to prevent leakage of the resin. 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) Water film thickness Measured using an IR-300 infrared trace moisture meter manufactured by CHINO CORPORATION. The calibration curve was obtained by absorbing the water on the drum with a paper absorbent and plotting the weight thereof on the scale of the moisture meter.

[0025]

EXAMPLES In order to make the effects of the present invention easier to understand,
Examples and comparative examples will be described below. Example 1 As a thermoplastic resin, polyethylene terephthalate having an intrinsic viscosity of 0.65 (0.34% by weight of colloidal silica having a true spherical shape of 0.25 μm in diameter as a slipping agent was added) was used.
When thermal characteristics were measured using DSC, Tmb: 24
0 ° C, Tm: 255 ° C, Tme: 268 ° C, Tcb: 2
It was 03 degreeC, Tc: 188 degreeC, Tce: 174 degreeC.
The polyethylene terephthalate pellets are heated to 180 ° C.
Vacuum dry for 3 hours and feed to an extruder with a diameter of 90 mm.
It was melted at 90 ° C. and supplied to a T die. T-die has a width of 1
The one having a size of 250 mm, a lip gap of 1 mm and a land length of 150 mm was used. The land portion of the T-die has a structure in which a plurality of holes having a diameter of 7 mm are opened in the width direction and water is allowed to flow therethrough to cool the land. The temperature of the die hopper is 290
C. and cooling water of 25.degree. C. was passed through the land portion at 5 kg / min to cool the land portion. The resin was melt-extruded in this state, and a water film having a thickness of 0.07 μm was formed by a condensation method on the molten film extruded from the die while applying an electrostatic charge. The film was closely cooled and solidified to obtain a cast film. The die manifold inlet temperature was 290 ° C and the land inlet resin temperature was 28 ° C.
The resin temperature at the outlet of the land portion was 9 ° C. and 245 ° C.
Further, the cast film was stretched 4 times by a longitudinal roll stretching machine kept at 95 ° C., then stretched 4 times by a width direction stretching machine kept at 100 ° C., and further in the width direction at 205 ° C. A 3% relaxing 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 Instead of a cooling drum having a surface temperature of 15 ° C. on which a water film having a thickness of 0.07 μm was formed by the condensation method used in Example 1, the surface temperature was kept at 25 ° C. in a dry atmosphere. A biaxially stretched film having a thickness of 8 μm was obtained in exactly the same manner as in Example 1 except that the dripping drum was used.

Comparative Example 2 Without using the supercooled extrusion method used in Example 1, that is,
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 portion was set to the same temperature as the die manifold portion, 290 ° C., without flowing cooling water to the die land portion. It was

Comparative Example 3 A biaxially stretched film having a thickness of 8 μm was prepared in the same manner as in Example 1 except that the normal extrusion method used in Comparative Example 2 and the normal electrostatic cast used in Comparative Example 1 were used. Got

As shown in Table 1, by combining the supercooling extrusion method and the method of casting on a drum having a water film, it can be seen that 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 of Example 1 was changed from 245 ° C to 26 ° C.
Except for changing the temperature to 0 ° C., the thickness is 8
A biaxially stretched film of μm was obtained.

Example 3, Comparative Example 4 The thickness of the water film on the drum in Example 1 was changed to 0.0 μm from 0.6 μm and 1.2 μm in the same manner as in Example 1 except that the thickness was changed. An 8 μm biaxially stretched film was obtained. Table 2 shows each characteristic of the obtained film.

[0033]

[Table 2]

[0034]

According to the method of the present invention, a thermoplastic resin is heated and melted at a melting end temperature Tme or higher and fed into a flat die, and is expanded in the width direction at a manifold portion in the flat die, and then the land of the die is expanded. In the part, the thermoplastic resin is melted at a temperature lower than Tme, and a temperature falling crystallization start temperature Tc.
The following effects are produced by bringing the molten sheet extruded by cooling to b or higher (supercooling extrusion method) into close contact with a cooling drum having a water film of water to solidify by cooling. (1) It is possible to eliminate or reduce the thickness unevenness, particularly the thickness unevenness of 10 Hz or less, that is, the thickness unevenness caused by the film vibration between the molten sheet and the drum. (2) Moreover, the surface roughness Ra of the obtained film is small, and the film becomes smooth. (3) A die streak due to a thermal decomposition product is unlikely to occur, and the productivity is excellent. (4) The film has a low oligomer content. (5) The film thickness is 25 μm, especially for magnetic tape applications, heat-sensitive transfer ribbon applications, and electrical insulation capacitors.
Suitable for thin applications below.

Claims (4)

[Claims] 1. A thermoplastic resin is melted by heating to a melting end temperature Tme or higher and fed into a flat die, expanded in the width direction at a manifold portion in the die, and then melted at the land portion of the die. Less than the end temperature Tme,
A method for producing a thermoplastic resin film, characterized in that a molten sheet extruded after being cooled to a temperature falling crystallization start temperature Tcb or higher is adhered to a cooling drum having a liquid film of water to be cooled and solidified. 2. The method for producing a thermoplastic resin film according to claim 1, wherein an electrostatic charge is applied to the molten sheet. 3. The liquid film of water has a thickness of 0.01 to 1 μm.
The method for producing a thermoplastic resin film according to claim 1 or 2. 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.