JPS59196223A - Method for forming thermoplastic resin film - Google Patents

Abstract

PURPOSE:To form a sheet that is free from bubble traces and is excellent in flatness, by bringing an extruded thermoplastic resin film in firm contact with a cooling roll under pressure by a static electricity application method. CONSTITUTION:A thermoplastic resin is made in the melted state, and is extruded from a mouthpiece 2 having a slit into a film 10. Then it is cooled on a cooling roll 6 to be solidified. During the period from the extrusion to the cooling and solidification, the film is exposed to a pressurized atmosphere in the pressurized chamber 4 that is at or over a gauge pressure of 0.2kg w/cm<2>. The cooling roll 6 is electrically insulated from the earth, the pressurized chamber 4 and the mouthpiece 2, and a high voltage is applied onto the surface of the cooling roll 6 with which the film is brought in firm contact to be cooled. Then the cooled and solidified film is led by nip rolling rubber rolls 9 from the pressurized chamber 4 and is taken out as a film 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for forming a thermoplastic resin film.

[Prior art]

A method for forming a polymer film involves extruding a molten thermoplastic resin through a nozzle with slits, applying a voltage between the nozzle and a cooling roll, and electrostatically solidifying the molten film on the surface of the cooling roll. , is already well known. However, method 1, for example, Japanese Patent Publication No. 50-8743
In the method described in No. 9, the forming speed of the film was at most 40 m/min.

When this speed was exceeded, air bubbles were trapped between the cooling roll and the molten film, making it impossible to obtain a film with good flatness.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a method for forming a film with excellent flatness without any traces of air bubbles due to air bubble entrapment at high speed.

[Structure of the invention]

In order to achieve the above object, the present invention has a secondary structure, that is, after extruding a thermoplastic resin in a molten state into a sheet film through a die having slits.

In a film forming method in which the molten film is brought into close contact with a cooling roll by an electrostatic application method in which a voltage is applied between the die and the cooling roll, and the film is cooled and solidified, the atmosphere on both sides of the molten film is set at a gauge pressure of 0.2 kgW/ The present invention is characterized by a method for forming a thermoplastic resin film that maintains a pressurized MK of at least cIn''.

The present invention involves extruding a thermoplastic resin in a molten state into a film through a die having slits, cooling the molten film by an electrostatic application method in which a voltage is applied between the die and a cooling roll, and applying the film to the roll. It can be applied to a well-known film forming method in which bodies are brought into close contact and solidified by cooling.

In addition, in the case of a device in which one cap is grounded and the cooling roll is electrically insulated from the ground, one terminal of the power supply for voltage application is grounded, and the other terminal is cooled. Voltage can be applied by connecting to the roll, and conversely, if the base is electrically insulated from the ground and the cooling roll is grounded, one terminal of the power supply is grounded, Stain pressure can be applied by connecting the other terminal to the cap. However, the ground wire of the molding equipment and the terminal on the ground side of the power supply may be directly connected.
Mata. The molding device and the power source may be connected together by insulating them from the earth without grounding the ground side.

Among these voltage application methods, one terminal of the power supply is insulated from the ground and connected to a running cooling roll.
It is preferable that the other terminal and the cap are grounded. The voltage applied between the cooling roll and the cap may be either alternating current or direct current, but direct current is preferable, and the terminal connected to the cooling roll may be either pressure or negative, but negative is preferable.

In the present invention, the atmosphere on both sides of the melt-extruded film (or sheet) between the nine nozzles and the cooling roll, that is, the molten film, is set to a gauge pressure of 0.2 kgw/cm" or more,
Preferably 0.2 to I Dkgw/cn', more preferably 05 to 5 kgw/cm! -l- It is necessary to pressurize the turnip. At small pressures in this range.

It is difficult to obtain the effects of the present invention. Although there is no particular limit to the pressure, a pressure greater than 10 kgw/cm' may cause trouble in extruding the film-like material from the die.

Trouble is likely to occur when taking the film out of the cooling process.

Note that the pressurized state is a static pressure state, preferably a film forming state in which the wind speed of the atmosphere between the die and the cooling roll is 0.5 m.
/second or less, preferably 0.1 m 7 seconds or less (wind speed is measured with an Anemo Master #AM-B 11/Ii-211 type anemometer manufactured by Nippon Kagaku Kogyo. be able to). In addition, the pressurized state is 1. For example, in dynamic pressure where a gas flow is blown from only one side of the film,
;-〒The electric current applied to the static electricity with the temporary lid fluctuates and tends to trap air bubbles, so it is not very suitable.

Gases used to maintain the pressurized state include air, nitrogen, charcoal gas, argon, helium, Freon gas, SF6.
Alternatively, a mixture of these gases may be used;
Air, nitrogen, Flemen gas.

SF6 is small. More preferably, from the viewpoint of economy, the entire surface of the film-like material in the trench that contacts the cooling roll is surrounded as a pressurizing chamber, and this trench and a part of the cooling roll are all included. Although this is preferable, especially for the cooling roll, it is preferable to include the entire circumferential surface, preferably the entire circumferential surface, because the apparatus is simpler. Although the members forming this pressurizing chamber are not particularly limited, it is desirable that they be electrically insulated from the cooling roll.

In order to electrically insulate the cooling hole from the ground, it is already known to use a highly electrically insulating liquid such as paraffin oil or trichlorethylene.

In addition to using Freon alone or a mixture thereof as a cooling liquid, the bearings of the cooling roll, the joint between the cooling roll drive shaft and the drive source, the joints of the cooling liquid supply and discharge ports, etc. are each covered with insulating material 9. For example, a method of insulating with an electrically insulating material such as fluororesin 1 Teflon'' (manufactured by DuPont, trade name) or a similar electrical insulating material may be used.

In addition to the method described above, a metal conductive film is placed on the surface of a commonly used metal cooling roll through an insulating sheet of fluorocarbon resin (Teflon). It is also possible to connect the terminals of 9, and in this method, water, which is commonly used, can be used as the cooling liquid.However, the former method is preferable in terms of cooling efficiency as the speed increases.

Next, the method for manufacturing the film of the present invention will be explained based on the drawings.

FIG. 1 is a schematic sectional view of an apparatus showing one embodiment of the film forming method of the present invention.

In the figure, 1 is a supply pipe through which molten thermoplastic resin is supplied, 2 is a mouthpiece, a filter is a pressurized atmosphere, 4 is a pressurizing chamber, 5 is a pressure gauge, 6 is a cooling roll, and 7 is a pressurized gas supply 8 is a separating roller, 9 is a nip rotating rubber roll, and 10 is a melt-extruded film.

11 is a cooled and solidified film, and 12 is a power supply device. As shown in the figure, after the film 10 is extruded from the nozzle 2, it is exposed to a pressurized atmosphere B until it is cooled and solidified on the cooling roll 6, and is not close to the nozzle 2 and is not in contact with the film 10. The surface of the cooling roll B is also exposed to the pressurized atmosphere B. The cooling liquid of the cooling roll B is connected by a conduit to a heat exchange device including an electrically insulating high pump.

This conduit is partially made of an insulating material in order to electrically insulate the cooling roll 6 from the earth and the above-mentioned apparatus.

Furthermore, the cooling roll 6 is electrically insulated from the pressurizing chamber 4 and the base 2 as well. One terminal of the power supply device 12 is connected to the cooling roll drive shaft to apply a high voltage to the surface of the cooling roll B. The other terminal is grounded, and the cap 2 is also grounded. Preferably, the power supply device 12 is connected to a DC high voltage. The applied voltage is 5 to 100 kV, preferably 15 to 80 kV,
It is preferably 25 to 70 kV. When the applied voltage is applied within this range, there is no problem of causing minute abnormal discharges to the cap, and surface defects due to discharges are less likely to occur. Further, troubles such as insulation between the cooling roll and other members can be prevented, which is preferable.

Thermoplastic resins to which the present invention can be applied include polyethylene,
There are polypropylene, copolymers thereof, polystyrene, polyvinyl chloride, polynispur, polyamide resins, fluororesins, polysulfone resins, polyphenylene resins, etc.9 The present invention is particularly applicable to polyesters, such as polyethylene terephthalate resins and Suitable for copolymer resins.

The thickness of the film is not particularly limited, but is 10μ711~
5 sam is quite large. Inert inorganic particles in the film.

It may also contain ultraviolet absorbers, dyes, facial washers, fluorescent whitening agents, antistatic agents, and the like.

The temperature of the pressurized atmosphere is not particularly limited, but
~650°0. Preferable lj: The range of '$o to 150°C is desirable.

In addition, the surface temperature of the cooling roll is not particularly limited, but -
A range of 20 to 150°C is preferred.

〔Effect of the invention〕

According to the method of the present invention, a molten film extruded from two nozzles passes through a pressurized atmosphere in which nine surfaces are in an equilibrium state before contacting the cooling roll.

Preferably, the surface of the cooling roll in the same pressurized atmosphere is brought into close contact with the surface of the cooling roll by electrostatic application. There is no embedding at all, so high-speed film forming can be achieved.

Next, one embodiment of the present invention will be explained based on an example.

Examples 1 to 5 A polyethylene terephthalate resin having an intrinsic viscosity of 065 was melted at 290°C using an extruder, and using the apparatus shown in Figure 1,
From the nozzle kept warm at 285°C, slit width 1.0 plate,
It was extruded to a length of 400 mm. Next, coolant “Freon-1”
13" (manufactured by Mitsui Fluorochemical Co., Ltd.) with a diameter of 800 square meters and a roll surface temperature of 35'c, the film was brought into close contact with the film by electrostatic application, and the solidified film was taken off via a nip rotating rubber roll. The thickness of the film is constant with respect to the drawing speed, so all samples are
The extrusion amount was adjusted so that it became 0 μm.

Compressed air at room temperature was used as the pressurizing gas, and the atmospheric temperature in the pressurizing chamber at this time was 8'a to 90°C near where the molten film came into contact with the cooling roll. .

The maximum take-up speed was determined, and the presence or absence of micro-discharge was observed immediately before the molten film contacted the cooling roll.

As shown in Table 1, high speed was achieved with no traces of bubbles on the film surface and no micro discharges. In Example 3, very slight discharge was observed.

Comparative Examples 1 to 4 Example 1 except that the atmospheric pressure was pressurized to 0 kgw/♂ (i.e., atmospheric pressure) or 0.1 kgw/- in terms of gauge pressure.
Films were manufactured in the same manner as in ~5. Table 1 Comparative Example 1
As shown in Figures 4 to 4, only 9 lower take-off speeds were obtained. When the pressure was insufficient as in Comparative Example 4, even if the speed could be increased slightly, minute discharges occurred significantly, and defects due to the discharge appeared on the film surface.

Examples 6 to 8 Films were produced in the same manner as in the above-mentioned Examples and Comparative Examples except that nitrogen was used as an atmospheric gas instead of air. As shown in Examples 6 to 8 of Table 1, films could be produced at high speed without any microdischarge.

The criteria for determining microdischarge in Table 1 are shown below.

O: No minute discharge.

Δ...A small amount of micro discharge occurs discontinuously.

×: Extremely small discharges occur continuously.

Table 1

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of an apparatus showing an example of the film forming method of the present invention. 1: Molten resin supply pipe 2: Mouth 3: Pressurized atmosphere 4: Pressure chamber 5: Pressure gauge 6 = Cooling roll 7: Pressurized gas supply port 8: Separation roll 9: Nip rotating rubber roll 10: Melt film 11: Cooled and solidified film 12: Power supply device patent applicant Toshi Co., Ltd.

Claims (1)

[Claims] After extruding a molten thermoplastic resin into a film through a slit-shaped die, the molten film is brought into close contact with a cooling roll by an electrostatic application method that applies a voltage between the die and the cooling roll, and is cooled and solidified. A method for forming a thermoplastic resin film, the method comprising maintaining the atmosphere on both sides of the molten film at a pressure of 0.2 kg w/Cm' or more in terms of gauge pressure.