JPH0363499B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a highly horizontally oriented film using a clip-type tenter stretching machine. More specifically, in the transverse stretching of a longitudinally creasing film of thermoplastic resin using a clip-type tenter stretching machine, by creasing the space between each clip more than the gap between the clips, the film is substantially The long film is preheated before stretching and heated during stretching to loosen its wrinkled structure, and due to the tension during stretching, both ends of the film enter between the clips and inside the predetermined position, causing the film to become The present invention relates to a method of manufacturing a film with high horizontal axis orientation by preventing a difference in stretching ratio between the gripped portion and the ungridded portion.

[Prior art] Highly oriented transversely oriented films have high uniaxial orientation in the lateral (width) direction, so they can be used as base films for lateral high strength, high elasticity films and polarizing films, and also because of their easy lateral tearability. It is used in applications that require a high degree of molecular orientation, such as raw material films for split yarns.

A method for manufacturing such a film with high horizontal axis orientation is generally a method using a tenter stretching machine, and it is known that a method in which an unstretched film that has been wrinkled in the longitudinal (longitudinal) direction is stretched to a high ratio is particularly effective. ing.
(For example, Japanese Unexamined Patent Publication No. 55-77530) Usually, in a tenter stretching method for continuously producing a horizontally stretched film, both ends of the film to be stretched are gripped by two pairs of endless belts disposed so as to widen at the ends. A belt-type tenter stretching method in which the film is moved forward by rotating the belt and simultaneously stretched and expanded in the width direction continuously; The film is rolled up and processed into a bead shape, two pairs of slits are arranged so as to widen at the ends so that the bead-shaped portions do not come out, and the film, which has bead-shaped portions at both ends, is passed between the two pairs of slits, and the film is continuously processed. A slit-type tenter stretching method in which the width is expanded in the lateral direction while sliding the film, while continuously inserting both ends of the stretched film into pins arranged in an endless chain that expands the width in the direction of travel. The pin-type tenter stretching method continuously stretches and expands the film, and the stretched film is continuously gripped by clips connected to an endless chain that widens both ends of the film in the direction of travel. An example of this is a clip-type tenter stretching method that stretches and expands the material.

When applying these tenter-type stretching methods to a method of stretching a partially stretched film that has been wrinkled in the longitudinal (longitudinal) direction to a high magnification, in the belt-type tenter stretching method, the wrinkled film is stretched between two pairs of belts. The film is heated and deformed while being continuously gripped by the belt, and a wrinkled structure remains on the outside of the belt, so even if stretching tension is applied, the edge of the film will not slip out inside the belt gripping area, and the film will be continuously held in a stable state. It is possible to produce a laterally high oriented film by stretching. However, the disadvantage of this method is that the gripping strength of the belt is limited, so it is not suitable for high-magnification stretching.
In the slit-type tenter stretching method, the bead-shaped portion may be deformed by the tension of the stretching machine and may slip out of the slit, making it unsuitable for stretching at high tension and high magnification. In the case of the pin-type tenter stretching method, the film is torn at the portion pierced by the pins due to the tension during stretching, so it is not suitable for a method of stretching with high tension and high efficiency. When performing lateral stretching under high tension, it is said that the clip-type tenter stretching method is most suitable because the gripping portion has excellent tensile strength.
However, in the clip-type tenter stretching method, there is usually a gap of about 3 to 10 mm between the clips, depending on the spread angle of the endless chain.
There is. This part is not gripped and fixed at all, so
Preheating before stretching and heating during stretching may unwrinkle the film, and the tension during stretching may cause the film to enter inside from a predetermined position, resulting in a difference in the stretching ratio between the clip-held portion and the unclipped portion. Become.

The extent to which the ungridded portion of the film enters the inside is hardly a problem when a normal flat film (non-wrinkled film) is stretched, as long as a normal clip-type tenter stretching machine is used.
However, when stretching using a creasing-treated stretching machine,
Since the film is present in a wrinkled state in this unclipped portion, the actual length of the film is longer than the distance between the clips. For example, if the wrinkle curvature is 50%, a film with an actual length of 20 mm exists between 10 mm clips. The difference between the length between the clips and the actual length of the wrinkled film further increases as the wrinkle curvature increases. Between clips
The wrinkled film, which is substantially longer than the distance between the clips, will have its wrinkled structure loosened by preheating before stretching and heating during stretching, and will further penetrate inward from between the clips due to the tension during stretching. .
Therefore, variations in the degree of orientation occur due to the difference in stretching ratio between the gripped portion and the ungridded portion, which becomes a very serious problem when manufacturing a laterally highly oriented film having uniform quality.

[Problem to be solved by the invention]

An object of the present invention is to provide a method for stretching a thermoplastic resin film that has been subjected to a creasing treatment in the longitudinal direction using a general clip-type tenter stretching machine. As a result of the treatment, the film, which exists in a substantially long state, will have its wrinkled structure unraveled by preheating before stretching and heating during stretching, and will further penetrate into the inside from between the clips due to the tension during stretching. It is an object of the present invention to provide a method for stably producing a film with a high horizontal axis orientation having a uniform stretching ratio and with a good yield.

[Means to solve the problem]

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have found that after carrying out a thermocompression process on both ends of a thermoplastic resin film that has been subjected to a longitudinally creasing process, the film can be gripped with the clips of a clip-type tenter. We have found that stretching is an effective method for preventing the ungridded portion of the film from entering inside from between the clips, and have finally arrived at the present invention.

That is, the present invention provides a method for producing a highly oriented film by stretching a thermoplastic resin film that has been wrinkled in the longitudinal (longitudinal) direction in the transverse (width) direction using a clip-type tenter stretching machine. This is a method for producing a film with a high horizontal axis orientation, characterized in that the curved portion is made thicker than the center portion of the film by heat-pressing treatment.

According to the present invention, it is possible to prevent the unclamped portions between the clips from unraveling, and further,
Even when stretching tension is applied, it is possible to prevent the unclipped portion from entering inside the predetermined position. Therefore, uniform stretching becomes possible, and it becomes possible to stably produce a highly horizontally oriented film having a uniform stretching ratio.

The thermoplastic resin film in the present invention is a film that is formed into a film shape by hot melt molding or solution cast molding, and is stretchable.

Examples include films made of homopolymers or copolymers such as polyolefin, polyester, polyamide, polyacrylate, polyether, polycarbonate, and polystyrene.

The thickness of these is usually 0.01 to 5 mm, preferably
It is 0.05 to 2 mm.

In the present invention, prior to stretching, the thermoplastic resin film is wrinkled in the longitudinal direction to reduce the tensile strength in the longitudinal direction that accompanies transverse stretching.

As the creasing treatment method, a known method may be adopted, such as a method in which two pairs of gears are meshed, the film is passed between them, and the film is crumpled in a wave-like cross-sectional shape in the longitudinal direction.

The degree of wrinkling varies depending on the desired product, but in order to achieve as high orientation as possible, the apparent length (plane It is desirable to wrinkle it so that it becomes the projected length.

In the present invention, both ends of the unstretched film are reinforced so that the portions of the crumpled unstretched film that are not gripped by the clips at both ends do not enter inside a predetermined position due to tenter stretching.

Examples of reinforcing methods include (a) laminating the same or different types of resin in film form on both ends of an unstretched film, or applying it in melt or solution form and drying, and (b) bending thin metal wires. (c) A method in which the thickness of the unstretched film itself is made thicker in the unstretched portions at both ends than in the central stretched portion. In the present invention, method (c) is adopted because of its ease of processing.

A specific method for increasing the thickness of both parts in (c) is to increase the thickness in advance when forming the thermoplastic resin film, or by creasing a film with a uniform thickness in the width direction in the vertical direction. After the treatment, only the ends of the film are heated to a temperature range from the softening point of the film to +100°C above the softening point, and then pressurized to deform and thicken the film. For example, in the case of crystalline resins, the temperature range is T _g (glass transition point) to _{T n} (melting point) + 10°C, preferably T _g (glass transition point) to T _cc
The deformation process is performed by heating to a temperature range of (crystallization start temperature) and applying pressure. Among the methods (c), the method of heat deformation treatment (heat compression bonding treatment) is the most preferred. If the temperature is below the softening point, the effect of the heat deformation treatment will be insufficient, and the ungrasped portions will move inward from a predetermined position due to the heating and stretching stress during stretching, which is not preferable. Also, the softening point + about 100
If the temperature is higher than .degree. C., the fluidity of the resin during thermocompression bonding may be too high and the thickness may become thinner than the target thickness, which is not preferable.

The thickness ratio of both ends of the film to the center of the film by heat-pressing treatment is 2 times or more, preferably 5 times or more, and the larger the ratio, the better, but the upper limit is about 10 times in terms of processing workability. It is.

The reason why both ends of the wrinkled film are made thicker than the center part of the film by heat-pressing is as follows. When a crumpled film whose ends are not crimped is supplied to a clip-type tenter, the actual length of the crumpled film placed between the clips is substantially longer than the length between the clips (for example, If the wrinkle curvature is 50%, there will be 20 mm of film between 10 mm of clips), the wrinkled state will be solved by preheating before stretching in a tenter stretching machine and heating during stretching, and the tension between each clip will be removed by the tension during stretching. The end of the film in the ungridded portion enters inside, and as a result, the stretching ratio of the film changes due to the difference in the position of the film gripping part and the ungripped part, causing variations in the stretching ratio. Therefore, in order to prevent the ends of the crumpled film from entering inside from a predetermined position between the clips, both ends of the crumpled film are stretched in the thickness direction of the film to the extent that the wrinkles do not come undone during heating before stretching. It is necessary to carry out a heat-pressing process, and it is more preferable to carry out a heat-pressing process until it becomes a flat plate.

The specific heat and pressure bonding method is to attach a 1mm to 30mm wide strip at both ends of the crumpled film, or at a position slightly closer to the center of the film than both ends, but not deeper into the center of the film than the clip gripping part. Pressing is performed at a constant pressing force for a certain period of time using a roll heated to a temperature range from the softening point to about 100°C above the softening point or a press machine that can be driven continuously. The pressure at this time varies depending on the heating temperature and heat sealability of the resin, but it is usually 1 to 50 kg/cm ²
pressure range. For example, in the case of crystalline resin, the range is preferably 5 to 50 Kg/cm ² if the temperature range is T _g to T _cc , and 1 to 10 Kg/cm if the temperature range is T _cc to T _n +10°C. A range of ² is preferred. If the pressure is lower than these pressure ranges, the effect of the heat deformation treatment will be insufficient, and the heat and stretching stress during stretching will cause the sheet to penetrate inside the predetermined position of the ungridded portion, which is not preferable. Further, although a pressure higher than these pressure ranges may be used, it is not preferable because the apparatus for the pressurizing section becomes large-scale.

The pressurization time depends on the applied pressure and the operating speed of the stretching machine, and is preferably 0.01 seconds to 10 seconds for each temperature range.
It is about 0.05 seconds to 5 seconds. If the time is shorter than 0.01 seconds, the crimping effect will be insufficient. From the point of view of work efficiency, it is preferable to take less than 10 seconds.

The unstretched film whose ends have been subjected to the creasing treatment and the heat-pressing treatment in the above method is fed to a clip-type tenter stretching machine and is laterally stretched.

The clip-type tenter stretching machine used in the present invention usually has clips that grip both ends of the film, and a stretching section that continuously stretches the film in the transverse direction while spreading at a constant angle with respect to the direction of travel. This is a horizontal stretching device. Therefore, a large number of clips are connected to the endless chain by a distance of about 3 to 10 mm. The distance between the clips varies depending on the stretching ratio and the spreading angle determined by the length of the stretching machine, but it is desirable to use a tenter stretching machine with the narrowest possible clip distance.

The transverse stretching conditions are appropriately selected depending on the resin film composition, quality design of the final product, longitudinal creasing treatment conditions, etc. Normally, the magnification is 2 times or more, preferably 4 times or more, at a temperature of T _g or higher, for example, in the case of crystalline resins, in the temperature range of T _g (glass transition point) -10°C to T _cc (crystallization initiation temperature). A film with high horizontal axis orientation is produced by stretching at a high magnification. Furthermore, if necessary, it is also possible to perform an annealing treatment using a heat treatment section within the stretching machine or another heat treatment machine to remove distortion or improve dimensional stability of the film.

The clip gripping position of a crumpled film whose both ends have been heat-pressed is the unheated and crimped part located closer to the center of the film than the heated and crimped part, and the position between the heated and crimped part and the unheated and crimped part to the center of the film. It does not matter if it is mounted on both sides or only in the heat-pressing processing section. In other words, if there is a heat-pressed part outside the clip-biting position, including the clip-biting position, the ungridded part of the film between the clips will enter inside, causing the film's stretching ratio to be uneven. There will be no more turning it into something.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Polyethylene terephthalate resin (IVO.61)
A film is formed using a T-die extruder, and the edges are slit so that the thickness in the horizontal (width) direction is almost uniform.
A substantially amorphous film of 300 mm and 150 μm in thickness was wound up. On this flat film, a line with a length of 1000 mm is drawn in the width direction over the entire width of the film.
After marking at 20mm intervals, the film was passed through a gear roll made up of two meshed gears with a pitch of 8.5mm and a depth of 7.5mm, and the length of the marks was approximately 550mm when measured using a flat scale. It was created. Next, both extreme ends of the wrinkled film are
A 10mm wide part is heated to 180℃ and the surface is coated with hard chrome plating with a pressure of 0.5 kg/cm.
The film was pressed for seconds and subjected to heat deformation treatment (heat compression treatment) so that the maximum thickness was 1 mm, thereby obtaining a crumpled film with increased end thickness. Preheat this to 80℃,
The film is heated to 80°C in the stretching part and 190°C in the heat treatment part, and then supplied to a clip-type tenter stretching machine (the shape of the film gripping part of the clip is 100mm long x 15mm wide, the distance between the clips is 4mm), and the film is heated to 10mm inside from the crimping part. The wrinkled film portion was held with a clip, stretched in the transverse direction at a stretching ratio of 5.0 times, and then heat-set to continuously produce a film with a thickness of about 50 μm and highly oriented in the transverse axis. At this time, almost no intrusion of the unstretched ends into the gap between the clips was observed. The actual stretching magnification read from the markings made at 20 mm intervals across the entire width of the film showed no difference between the gripped and ungripped parts, and was uniformly about 5.2 times. The results of measuring the crystal (molecular chain axis) orientation using X-ray diffraction photographs of the center portion of the film in the clip-held and unclipped portions show that both are highly uniaxially oriented, consisting of spot-shaped diffraction points. A photograph was obtained. Further, the birefringence of the film determined from the refractive index measured using an Atsube refractometer was approximately 0.20 for both the central portion of the film in the clip-held portion and the unclipped portion. Furthermore, the film variation in the longitudinal direction was as good as ±2 μm.

Example 2 A film was crimped horizontally under the same conditions as in Example 1, except that the crimping positions in Example 1 were 10 mm inside from both ends of the film, the crimping width was 15 mm, and only the crimping portion was gripped. Continuously produced highly axially oriented films. In this case as well, the same results as in Example 1 were obtained.

Example 3 Except for Example 1, where the crimping processing position was 10 mm inward from both ends of the film, the crimping processing width was 10 mm, and the gripping position was added to the crimping processing section and 5 mm inside adjacent to the processing section. A highly horizontally oriented film was continuously produced under the same conditions as in Example 1.
In this case as well, the same results as in Example 1 were obtained.

Comparative Example 1 A highly oriented film was produced by transverse stretching in the same manner as in Example 1, except that the deformation treatment (pressure bonding treatment) using a hot plate at both ends of the unstretched film was not performed. At this time, it was observed that both unstretched ends entered between all the clips. The actual stretching magnification read from the markings made at 20 mm intervals across the entire width of the film was approximately 5.2 times in the gripped portion of the film, and approximately 4.5 times in the ungripped portion, showing a clear difference. The results of measuring the crystal (molecular chain axis) orientation by X-ray diffraction photographs of the center portion of the film in the clip-held portion and the unclipped portion of the obtained film also show that both have a uniaxial orientation consisting of spot-like diffraction points. A photograph was obtained, but it was found that the diffraction points in the X-ray diffraction photograph of the central part of the film in the unclipped portion were in a broad state, indicating that the degree of orientation was poor. In addition, the birefringence of the central film, determined from the refractive index measurements using an Atsube refractometer, is approximately
0.20, and the ungrasped portion was 0.15, which clearly showed that the degree of orientation of the ungrasped portion was poor. Furthermore, the film variation in the longitudinal direction was as much as ±6 μm, which was worse than in the example.

〔Effect of the invention〕

According to the present invention, the wrinkled film existing between the clips of a clip-type tenter stretching machine is unwrinkled by preheating before stretching in the stretching machine and heating during stretching, and further stretching tension is applied. This can prevent the unclipped portion of the film from entering inside the predetermined position. Therefore, there is no variation in the stretching ratio, and it becomes possible to stably produce a film with a high horizontal axis orientation, which is useful for applications that particularly require optical uniformity, such as polarizing films and retardation compensators.

Claims (1)

[Claims] 1. In a method for producing a highly oriented film by stretching a thermoplastic resin film that has been wrinkle-treated in the longitudinal (longitudinal) direction in the transverse (width) direction using a clip-type tenter stretching machine, the wrinkle-treated portions at both ends of the film are 1. A method for producing a film with a high transverse axis orientation, the method comprising making the film thicker than the center portion thereof by heat-pressing treatment.