JPS6394818A - Manufacture of biaxially stretched film - Google Patents

Abstract

PURPOSE:To simultaneously manufacture a plurality of very thin films by a method wherein a plurality of unstretched films made of thermoplastic resin, the glass transition temperature of which is below the specified value, are piled up one another under the condition that liquid the boiling point of which lies within a specified range, is held between the films, and, after that, stretched in longitudinal and lateral directions at a specified temperature and heat-treated and finally separated from one another. CONSTITUTION:A plurality of unstretched films are simultaneously obtained by extruding thermoplatic resin, the glass transition temperature (Tg) of which is 130 deg.C, or lower, through a die with a plurality of slits. The resultant films are piled up one another under the condition that liquid, the boiling point (Bp) of which is 100 deg.C or above and 150 deg.C or below, is held between the films. Further, the films are longitudinally stretched and, after that, laterally stretched at a temperature, which is above Tg of the thermoplastic resin and below Bp of the liquid +30 deg.C, Furthermore, the resultant films are heat-treated and cooled and, after the edge parts of the films are cut off, they are separated from one another. Thus, a plurality of stretched films made of the same polymer are simultaneously manufactured under the state that the breakages caused during stretching and separation operation are decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing a biaxially stretched film, and more specifically, a method for producing a biaxially stretched film, in which a plurality of unstretched thermoplastic resin films are superimposed and biaxially stretched, and then each stretched film is This invention relates to an improved method for simultaneously producing a plurality of separated biaxially oriented films.

BACKGROUND OF THE INVENTION In recent years, electrical equipment such as capacitors, thermal printers, audio, video, etc. have become increasingly smaller and more compact. And the film used for this is required to be even thinner.

Problems in producing such thin films are that the production volume cannot be increased because the films are thin, and that productivity is reduced due to breakage during film formation.

As a solution to this problem, a method has been proposed in which an extremely thin film is obtained by stretching different types of polymers in a laminated state and peeling off each layer from the obtained laminated stretched film (for example, Japanese Patent Application Laid-Open No. 60-255410). .

JP-A-60-178031, JP-A-51-39777
No., JP-A-58-5226, JP-A-57-17612
No. 5, JP-A-57-176126, JP-A-56-16
No. 4823, JP-A-52-37982, JP-A-56-
No. 113427, etc.). However, this method has the problem that when each layer is peeled off from a laminated stretched film, the release film is easily torn and defects such as pinholes are likely to occur.

Furthermore, since different types of polymers are handled, there is a large investment in equipment such as an extruder, and there is also the problem that the polymers cannot be recovered and reused because it is difficult to prevent mutual contamination of the polymers.

OBJECTS OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a method for simultaneously producing a plurality of ultrathin stretched films made of the same type of polymer.

Structure and Effects of the Invention According to the present invention, an object of the present invention is to improve the glass transition temperature (T
(1) A plurality of unstretched films made of a thermoplastic resin having a temperature of 130°C or less are placed between the films with a boiling point (Bp) of 100°C or less.
Layering while maintaining liquids at a temperature above ℃ and below 150℃,
In this superimposed state, T of the resin (1 or more and B of the liquid)
Stretched in the longitudinal and transverse directions at a temperature of p+30°C or less,
This is achieved by a method for producing a biaxially stretched film, which is characterized by further heat-treating and then separating the stretched films into individual parts.

The thermoplastic resin in the present invention has a glass transition temperature (To
) is 130°C or less, such as polyethylene terephthalate, polyethylene-2,6-naphthalate, polyvinyl chloride, polystyrene, polypropylene,
Examples include polyethylene, polycarbonate, polybutylene terephthalate, polyvinyl alcohol, and aromatic polyamide. These thermoplastic resins contain various additives such as matting agents such as titanium dioxide, phosphoric acid,
Stabilizers such as phosphorous acid and esters thereof, or hindered phenols, and lubricants such as particulate silica, china clay, calcium carbonate, etc. may be included.

Resins with a Tg higher than 130°C are not only difficult to melt process and mold, but also require a high boiling point of the liquid held between the films, making it difficult to completely evaporate the liquid during the stretching and heat treatment process. This is not desirable because it will not be possible.

Although the thermoplastic resin unstretched film in the present invention is not limited by its production method, the thermoplastic resin is extruded through a die having a plurality of slits, and the thermoplastic resin is extruded at the normal pressure boiling point (Bp
) is preferably quenched with a liquid at a temperature of 100°C or more and 150°C or less. According to this method, a plurality of unstretched films can be obtained at the same time, the liquid can be used as a liquid to intervene between the unstretched films, and the unstretched films can be stacked in a simple process. It will be done.

Such unstretched films are overlapped while a liquid having a boiling point (Bp) of 100° C. or more and 150° C. or less is maintained between the films. The number of stacked films may be two or three or more, but in the case of three or more films, it is necessary to hold the liquid between each film (between adjacent films). The liquid can be retained, for example, by allowing the liquid to exist only in the center of the film, and by bringing the films into close contact with each other on both side edges of the film. More specifically, methods for retaining liquid between melt-extruded thermoplastic resins include a method in which a plurality of extruded sheet-like melts are immersed in a liquid before they come into contact with each other, and a method in which a plurality of extruded sheet-like melts are immersed in a liquid, Examples include a method in which a liquid is injected between resins, or a method in which the inner surface of one of the adjacent resins is brought into contact with a roll impregnated with a liquid.

The liquid used in the present invention has a boiling point (Bp) of 100°C or higher.
There is no particular restriction as long as the temperature is 50°C or less. However,
It will be apparent from the intended use that this liquid does not substantially affect the film during cooling or stretching of the thermoplastic resin.

Such liquids include, for example, water; alcohols represented by amyl alcohol, isoamyl alcohol, isobutyl alcohol, 2-ethoxyethanol, crotyl alcohol, hexanol, etc.; allyl acetone, isobutyl methyl ketone, tylpropyl ketone, diisopropyl ketone, Ketones represented by diethyl ketone, dipropyl ketone, butyl methyl ketone, methyl propyl ketone, etc. Examples include acetal, cyclohebutane, butyl ether, and the like. Of these, water is most preferred.

If the boiling point is less than 100°C, the vapor pressure between the film layers will become too high as the temperature rises during stretching, leading to breakage, and when it comes into contact with the thermoplastic resin to be melted, it will evaporate immediately and cause the unstretched film to evaporate. This is not preferable because it will not be possible to hold the liquid uniformly.

On the other hand, if the boiling point is higher than 150° C., it is not preferable because the liquid cannot be completely evaporated in the heat treatment step after stretching.

In the present invention, stretching is carried out at a temperature not less than T ( ) of the thermoplastic resin and not more than Bp + 30°C of the liquid. A preferred temperature is T (1 or more and (Bp + 10) °C or less. When the stretching temperature is less than 79 If the film temperature is higher than (Bp +30) °C, the vapor pressure of the liquid between the overlapping films becomes too high;
Particularly when producing ultra-thin stretched films with a thickness of 4μ or less, breakage occurs frequently during stretching, and in some cases, the liquid becomes vapor and easily escapes from the edges, causing the films to stick together, causing breakage when each layer is peeled off. Therefore, it is not desirable.

If the stretching temperature in the longitudinal and transverse directions is 19 or above for the thermoplastic resin and below the boiling point of the liquid + 30°C, the space between the overlapping film layers during longitudinal and transverse stretching is filled with steam having an appropriate vapor pressure. Film comrades do not come into contact,
Not only is there no breakage during peeling due to close contact, but it is also possible to stretch the laminated state.

Stretching methods include the so-called sequential stretching method, in which unstretched films laminated with steam are stretched in the longitudinal direction and then in the transverse direction, or the simultaneous stretching method, in which the longitudinal and transverse directions are simultaneously stretched.
Examples include axial stretching methods, but the present invention is not limited to any of these stretching methods. The stretching ratio is preferably 4 times or more, more preferably 6 times or more, particularly 8 times or more in terms of area ratio. Further, it is preferable that the stretching ratio in each direction is at least 2 times.

The stretched film is usually heat-treated under conditions that completely evaporate the liquid held between the films.

From this point of view, the heat treatment temperature is preferably 200 to 250°C. During this heat treatment, steam between the films escapes through the gap between the clip grips. If the steam is retained until the cooling step following the heat treatment step, it will condense and stain the roll during peeling, causing wrinkles. For this reason, it is desirable to make a nip between the heat treatment step and the cooling step or to blow compressed air from both sides of the film to bring adjacent films into close contact with each other. Even if the heat-treated film is brought into close contact with the film in this manner, it will not fuse and can be easily peeled off.

Also, since the adjacent films at the clip gripping part are usually partially fused, peeling requires heat treatment.

This is done after cooling and cutting out the edges.

According to the present invention, it is possible to simultaneously produce a plurality of stretched films made of the same polymer with less breakage during stretching and less breakage during peeling due to close contact. Since a plurality of stretched films are manufactured at the same time, production efficiency is not only increased, but also ultra-thin films with a thickness of 4 μm or less can be easily manufactured due to less breakage.

Example The present invention will be further explained below with reference to Examples.

Example 1 Intrinsic viscosity (orthochlorophenol, 35'C) containing 0.5% by weight of kaolin with an average particle size of 0.9 μm
Pellets of 0.60 polyethylene terephthalate were dried at 170° C. for 3 hours.

This polyethylene terephthalate (Tg: 68°C),
The polymer was melt-extruded at 280°C into water controlled at 60°C through a die with two slits whose center lines were 10 mm apart, and after the polymer temperature reached approximately 90°C, it was extruded between two rolls. By pressing, an apparent single sheet consisting of two sheets each having a thickness of 20 μm was obtained. This sheet was heated 3.6 times in the longitudinal direction at 90°C and 3.6 times in the transverse direction at 100°C.
The film was sequentially biaxially stretched 9 times, further heat-treated at 220°C, and then wound up. Thereafter, each film was peeled off to obtain a stretched film with a thickness of 1.5 μm.

In this case, the rupture during stretching and peeling occurred during 8 hours of film formation.
It was good with no problems.

Comparative Example 1 An attempt was made to simultaneously obtain two stretched films with a thickness of 1.5μ by carrying out the same procedure as in Example 1 except that the longitudinal stretching temperature was 105°C and the transverse stretching temperature was 135°C. The space of the paper swelled abnormally, and many breaks occurred, making it impossible to wind it up.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the longitudinal stretching temperature was set to 65° C., which is lower than the Tg of polyethylene terephthalate, but the film broke during longitudinal stretching and a stable film could not be obtained.

Example 2 Polyethylene-2 instead of polyethylene terephthalate
, 6-naphthalate (Tg: 118°C), and 4.0 times in the longitudinal direction at 120°C and 3 times in the transverse direction at 130°C.
．． The same procedure as in Example 1 was carried out except for stretching 8 times, and the thickness was 1.
．． Two stretched films of 2μ were formed simultaneously.

In this case, the film broke once every 8 hours during stretching and once during peeling, but the process was relatively stable and satisfactory.

Comparative Example 3 An attempt was made to simultaneously obtain two stretched films with a thickness of 1.2μ by carrying out the same procedure as in Example 2 except that the longitudinal stretching temperature was 135°C, but the space between the films swelled abnormally during longitudinal stretching. ,
Many breaks occurred at the nip portion after stretching, and transverse stretching was not possible.

Comparative Example 4 Trichlorethylene (boiling point = 87
As a result, the same phenomenon as in Comparative Example 3 occurred, and it did not reach the point of transverse stretching.

Comparative Example 5 Two unstretched sheets of polyethylene-2,6-naphthalate with a thickness of 18 μm were made, and these were stacked on top of each other. Cumene (boiling point: 153°C) was made to exist between them, and 120
After stretching 4.0 times at 130° C. and 3.8 times in the transverse direction at 130° C., heat treatment was performed at 220° C., and once cooled, the film was peeled off. In this case, there was no breakage during stretching and peeling, but there were some areas where cumene remained in liquid form between the films, causing wrinkles and making it impossible to obtain a film in perfect form.

centre

Claims (1)

[Claims] 1. A plurality of unstretched films made of a thermoplastic resin having a glass transition temperature (Tg) of 130°C or less, in which a liquid having a boiling point (Bp) of 100°C or more and 150°C or less is held between the films. In this superimposed state, the films are stretched in the longitudinal and transverse directions at a temperature not lower than the Tg of the resin and not higher than the Bp of the liquid + 30°C, further heat-treated, and then the stretched films are separated into individual films. A method for producing a biaxially stretched film characterized by: 2. The manufacturing method according to claim 1, wherein the liquid interposed between the films is water. 3. A plurality of unstretched films melt-extrude thermoplastic resin from a die having a plurality of slits, and the boiling point (Bp) is 1.
The manufacturing method according to claim 1, which is an unstretched film cooled with a liquid at a temperature of 00°C or more and 150°C or less.