JP6834573B2 - Manufacturing method of optical film - Google Patents

Description

The present invention relates to a method for producing an optical film.

The melt extrusion method is one of the methods for producing a film having optical properties by forming a resin into a film. In the melt extrusion method, for example, a molten film obtained by extruding a molten resin from a die is cooled on a cooling roll to obtain a raw film. Then, by stretching the obtained raw film, a long stretched film can be obtained. (Hereinafter, "raw film" and "stretched film" are collectively referred to as "optical film".)

Conventionally, a method for efficiently producing an optical film having excellent various performances by using a melt extrusion method has been studied. For example, there is known a method (electrostatic adhesion method) in which a molten film and a cooling roll are brought into close contact with each other to increase the cooling efficiency by supplying an electric charge to the molten film to charge the film surface. However, with the conventional electrostatic adhesion method, there are cases where the adhesion between the molten film and the cooling roll cannot be ensured.

In response to such a problem, for example, in Patent Document 1, when a molten thermoplastic resin is extruded from a base into a sheet on a rotary cooling drum and rapidly cooled and solidified on the rotary cooling drum to form a sheet, the resin is rotated. A method of blowing charged air onto a sheet-like object being molded on a cooling drum has been proposed. According to Patent Document 1, by blowing charged air onto the sheet-like material being molded, the adhesion of the sheet-like material on the rotary cooling drum is significantly improved, and the transparency of the sheet-like material is improved. Can be enhanced.

Japanese Unexamined Patent Publication No. 8-142162

However, in the above-mentioned conventional method, there is room for further improvement in the adhesion between the molten film and the cooling roll. For example, in the production of an optical film, a higher speed of the production line is required. However, if the line speed is increased by using the above-mentioned conventional method, the adhesion between the molten film and the cooling roll is lowered, which is obtained. Problems such as deterioration of the thickness accuracy of the optical film and meandering during transportation have occurred.

Therefore, the present invention provides a method for producing an optical film capable of sufficiently adhering a molten film and a cooling roll to suppress meandering during transportation of the optical film and to improve the thickness accuracy of the optical film. With the goal.

The present inventor has diligently studied to solve the above problems. Then, the present inventor is in order to improve the manufacturing method of the optical film in which the molten film is cooled on the cooling roll by the electrostatic adhesion method to obtain the raw film, when the electric charge is supplied and the film is cooled on the cooling roll. We focused on the cross-sectional shape of the molten film (thickness profile of the cross section in the width direction). Then, the present inventor has found that the cross-sectional shape of the molten film on the cooling roll is substantially equal to the cross-sectional shape of the raw film obtained after cooling (hereinafter, these two cross-sectional shapes are collectively referred to as "cross-sectional shape". Based on the knowledge that it may be said), it was found that the adhesion between the molten film and the cooling roll can be improved by adopting a predetermined cross-sectional shape, and the present invention has been completed.

That is, the present invention aims to advantageously solve the above problems, and the method for producing an optical film of the present invention melt-extrudes a resin composition containing a resin from a die to obtain a molten film. The raw film includes a step of bringing the molten film into close contact with a cooling roll and cooling it by supplying a charge to both ends in the width direction of the molten film to obtain a raw film, and the raw film has a central portion in the width direction. The average thickness of the film is less than 40 μm, and both ends in the width direction have a wall thickness region of 50 μm or more. If the above-mentioned predetermined cross-sectional shape is adopted, the molten film and the cooling roll can be sufficiently electrostatically adhered to each other. Then, in the process after the molten film is cooled, the meandering of the obtained raw film and the stretched film can be suppressed, and the thickness accuracy can be improved.
In the present invention, the "center portion in the width direction" of the film means a region where the distance from the center line in the longitudinal direction of the film is within 35% of the width of the film, and the "both ends in the width direction" of the film. , Refers to the area outside the width direction of the "central part in the width direction".
Further, in the present invention, the "average thickness of the central portion in the width direction" can be measured by using the method described in the examples of the present specification.
Then, in the present invention, the presence or absence of the "thickness region having a thickness of 50 μm or more" can be specified by using the method described in the examples of the present specification.

Here, in the method for producing an optical film of the present invention, the relative permittivity of the resin composition can be set to 2.5 or less. A molten film made of a resin composition having a low relative permittivity is generally difficult to electrostatically adhere to a cooling roll. However, if the method for producing an optical film of the present invention adopting the above-mentioned predetermined cross-sectional shape is used, the molten film and the cooling roll can be formed even when a resin composition having a relative permittivity of 2.5 or less is used. It can be sufficiently adhered.
In the present invention, the "relative permittivity" can be measured by using the method described in the examples of the present specification.

Then, in the method for producing an optical film of the present invention, both ends in the width direction of the raw film are thinner in the width direction of the raw film than in the thick region and thinner in the width direction than the thick region. It is preferable to have a flat region thicker than the portion. By adopting the cross-sectional shape having the flat region described above, the adhesion between the molten film and the cooling roll can be further improved.
In the present invention, the "flat region" refers to a region having a width of 10 mm or more in which the thickness change rate (degree of change in thickness with respect to the width direction distance) in the width direction of the raw film is 1 μm / 0.96 mm or less. , The presence or absence of a "flat region" can be identified using the methods described in the examples herein.

Further, in the method for producing an optical film of the present invention, it is preferable that the resin is an alicyclic polyolefin resin. By using the alicyclic polyolefin resin, the quality such as mechanical properties, heat resistance, and transparency of the obtained optical film can be improved in a well-balanced manner.

In the method for producing an optical film of the present invention, it is preferable that after the step of obtaining the raw film, the portion derived from the thick region is further removed so that the thick region is not wound as a product.

According to the method for producing an optical film of the present invention, the molten film and the cooling roll can be sufficiently brought into close contact with each other to suppress meandering during transportation of the optical film and improve the thickness accuracy of the optical film.

An example of a cross-sectional view in the width direction of the raw film in the method for producing an optical film of the present invention is schematically shown. Another example of the widthwise cross-sectional view of the raw film in the method for producing an optical film of the present invention is schematically shown. It is a figure which shows typically an example of the manufacturing method of the optical film of this invention.

Hereinafter, embodiments of the present invention will be described in detail.
In the method for producing an optical film of the present invention, a resin composition containing a resin is melt-extruded from a die to obtain a molten film (extrusion step), and the molten film is formed by supplying charges to both ends in the width direction of the molten film. It includes a step of obtaining a raw film by bringing it into close contact with a cooling roll (electrostatic close contact step), and optionally includes other steps. Then, in the method for producing an optical film of the present invention, a predetermined shape is adopted as the cross-sectional shape of the raw film. That is, the raw film is characterized in that the average thickness of the central portion in the width direction is less than 40 μm, and the both ends in the width direction have a wall thickness region of 50 μm or more.

According to the study by the present inventors, if a relatively thin molten film having an average thickness of less than 40 μm in the center of the raw film after cooling is used, the electric charge supplied to the surface of the molten film is somehow. It is presumed that this is because it does not sufficiently contribute to the generation of the Coulomb attraction, but it was found that the effect of improving the adhesion between the molten film and the cooling roll by the electrostatic adhesion method cannot be sufficiently obtained. However, in the method for producing an optical film of the present invention, the raw film has thick regions having a thickness of 50 μm or more at both ends in the width direction. The molten film, which is the pre-cooling stage of the raw film, also has a relatively large thickness at both ends in the width direction on the cooling roll (that is, a region corresponding to the thick region of the raw film). Will have. In the method for producing an optical film of the present invention, since electric charges are supplied to both ends in the width direction having a region having a relatively large thickness, it is presumed that the supplied electric charges can sufficiently contribute to the generation of the cooling force. However, the molten film and the cooling roll can be in good contact with each other. Then, by sufficiently adhering the molten film and the cooling roll in this way, the cooling unevenness on the cooling roll is suppressed, the thickness accuracy of the obtained optical film is improved, and the meandering during the transportation of the optical film is suppressed. It becomes possible to do.

(Cross-sectional shape of raw film)
Here, as described above, the cross-sectional shape of the molten film on the cooling roll substantially matches the cross-sectional shape of the raw film obtained after cooling. Therefore, in the present invention, by controlling the predetermined cross-sectional shape of the raw film that can be grasped precisely, the cross-sectional shape of the molten film on the cooling roll is also substantially controlled to obtain a desired effect. Can be done. Hereinafter, the cross-sectional shape of the raw film used in the present invention will be described.

<Center in the width direction>
First, the average thickness of the central portion of the raw film in the width direction needs to be less than 40 μm, and can be 30 μm or less. Further, the lower limit of the average thickness of the central portion in the width direction of the raw film is not particularly limited, but is usually 5 μm or more.

<Both ends in the width direction>
[Thick area]
It is necessary that a wall thickness region having a thickness of 50 μm or more exists in both ends in the width direction of the raw film.
FIG. 1 schematically shows an example of a cross-sectional view in the width direction of the raw film. In FIG. 1, the raw film 1 is composed of a central portion 2 in the width direction and both end portions 3 in the width direction, and has a wall thickness region 4a in both end portions 3 in the width direction.

The thickness of the wall thickness region needs to be 50 μm or more. If there is no thick region having a thickness of 50 μm or more in both ends in the width direction, the adhesion between the molten film and the cooling roll cannot be ensured. Further, the meandering during the transportation of the optical film cannot be suppressed, and the thickness accuracy of the optical film is also lowered. The upper limit of the thickness of the wall thickness region is not particularly limited, but is usually 300 μm or less.

Here, it is preferable that the wall-thick region extends in the longitudinal direction of the raw film. The width of the wall thickness region (in the width direction of the raw film) is preferably 10 mm or more, more preferably 20 mm or more, preferably 100 mm or less, and more preferably 90 mm or less. If the width of the wall thickness region is 10 mm or more, the adhesion between the molten film and the cooling roll can be further improved, and if it is 100 mm or less, the product yield is not excessively impaired.

[Flat area]
It is preferable that a flat region thinner than the wall thickness region and thicker than the center portion in the width direction exists inside both ends in the width direction of the raw fabric film in the width direction of the raw fabric film. If the above-mentioned flat regions are present at both ends in the width direction of the raw film, the regions corresponding to the flat regions of the raw film are also present at both ends in the width direction of the molten film. Therefore, it is presumed that the relatively thick regions existing at both ends in the width direction of the molten film are supported by the regions corresponding to the flat regions described above, which makes it easier to stand upright. The adhesion of the film can be further improved.

FIG. 2 schematically shows an example of a cross-sectional view in the width direction of the raw film. In FIG. 2, the raw film 1 is composed of a central portion 2 in the width direction and both end portions 3 in the width direction, and has a wall thickness region 4a and a flat region 4b in both end portions 3 in the width direction.

Here, the flat region preferably extends in the longitudinal direction of the raw film. The width of the flat region (in the width direction of the original film) is 10 mm or more, preferably 11 mm or more, preferably 20 mm or less, and more preferably 16 mm or less. If the width of the flat region is 10 mm or more, the adhesion between the molten film and the cooling roll can be further improved, and if it is 20 mm or less, the product yield is not excessively impaired.

The average thickness of the central portion in the width direction and the cross-sectional shape of the raw film such as the shapes of both end portions (thickness region and flat end region) in the width direction are, for example, the clearance and shape of the die lip (resin discharge portion) used for melt extrusion. , And can be adjusted by changing the extrusion rate of the raw film.
The width of the raw film is not particularly limited, but is preferably 1000 mm or more, more preferably 1200 mm or more, preferably 3000 mm or less, and more preferably 2500 mm or less.

Next, the extrusion step and the electrostatic adhesion step until the above-mentioned raw film is obtained from the resin composition will be described in detail.

(Extrusion process)
In the extrusion step, a resin composition containing a resin is melt-extruded from a die to prepare a molten film.

<Resin composition>
The resin composition is a composition containing a resin as a main component. Here, as the resin, a thermoplastic resin is usually used. Specific thermoplastic resins include, for example, polyester resin (polyethylene terephthalate, polybutylene terephthalate, etc.), polyolefin resin (polyethylene, polypropylene, ethylene-propylene copolymer, alicyclic polyolefin resin, etc.), polycarbonate resin (aromatic). Polycarbonate and the like), cellulose ester resins, acrylic resins (polymethyl acrylate, polymethyl methacrylate, polybutyl acrylate, polycyclohexyl acrylate, etc.), and other resins (polystyrene, polyvinyl chloride, etc.) can be mentioned. One of these may be used alone, or two or more of them may be combined at an arbitrary ratio. Among these, polyolefin resins are preferable, and alicyclic polyolefin resins are more preferable, from the viewpoint of being able to improve the quality such as mechanical properties, heat resistance, and transparency required for optical films in a well-balanced manner.

Further, the resin composition may contain additives such as a pinning agent (high dielectric constant agent). However, additives such as pinning agents may cause deterioration of optical properties such as transparency in the obtained optical film. Therefore, the blending amount of the additive such as the pinning agent is preferably 3 parts by mass or less, more preferably 1 part by mass or less, and 0.5 parts by mass or less per 100 parts by mass of the resin. Further, it is particularly preferably 0.1 part by mass or less, and most preferably 0 part by mass.
By using the method for producing an optical film of the present invention, sufficient adhesion between the molten film and the cooling roll can be ensured without increasing the relative permittivity of the resin composition with a pinning agent. The relative permittivity of the resin composition can be, for example, 2.5 or less, or 2.3 or less. The lower limit of the relative permittivity of the resin composition is not particularly limited, but is usually 1.5 or more. Examples of the resin that can form a resin composition having such a low relative permittivity include the above-mentioned polyolefin resin.

<Melting extrusion conditions>
The melt extrusion conditions for producing a molten film by melt-extruding the above-mentioned resin composition from a die are not particularly limited, and can be appropriately determined depending on the type of resin used and the like.
The width of the molten film on the cooling roll is not particularly limited, but is preferably 1000 mm or more, more preferably 1200 mm or more, preferably 3000 mm or less, and more preferably 2500 mm or less. preferable.

(Electrostatic adhesion process)
In the electrostatic adhesion step, electric charges are supplied to both ends of the molten film in the width direction to bring the molten film into close contact with the cooling roll and cool it. At this time, since there are regions having a relatively large thickness at both ends in the width direction of the molten film as described above, electric charges are supplied to both ends in the width direction having the regions, so that the molten film and the cooling roll are separated from each other. Good adhesion between them can be ensured. Then, by cooling the molten film on a cooling roll, a raw film which is an optical film can be obtained.

Here, the method of supplying charges to both ends in the width direction is not particularly limited, and a known charge supply means used in the electrostatic adhesion method can be adopted. For example, a method of applying a voltage to the electrodes close to both ends in the width direction to discharge the electrodes and a method of blowing charged air to both ends in the width direction can be mentioned, but the former method is preferable.
For example, in the example of FIG. 3, electric charges are supplied to both ends in the width direction of the molten film 1 extruded from the die lip 6 of the die 5 by electric discharge from the edge pinning 7 as an electrode, and the molten film 1 adheres to the cooling roll 8. To do. In FIG. 3, two edge pinnings 7 (four in total) are provided on both ends of the molten film, but the number of edge pinnings is not particularly limited and can be changed as appropriate.

(Other processes)
The method for producing an optical film of the present invention can include steps other than the extrusion step and the electrostatic adhesion step described above. For example, the method for producing an optical film of the present invention is a step of further stretching a raw film obtained by cooling a molten film with a cooling roll in an electrostatic contact step to obtain a stretched film (stretching step). ) May be included.
Further, the method for producing an optical film of the present invention preferably includes a step (trimming step) of removing a portion derived from a thick region of at least one of the raw film and the stretched film. In the trimming step, in addition to the portion derived from the thick region, the portion derived from the flat region may be removed.
Both the stretching step and the trimming step can be carried out by a known method. Further, the obtained optical film may be wound up if necessary (winding step).

In the method for producing an optical film of the present invention, the line speed is preferably 30 m / min or more, more preferably 40 m / min or more, from the viewpoint of improving production efficiency. The method for producing an optical film of the present invention can sufficiently secure the adhesion between the molten film and the cooling roll even when the line speed is as high as 30 m / min or more, and the optical film meanders. It is possible to improve the thickness accuracy while suppressing it. The upper limit of the line speed is not particularly limited, but is usually 80 m / min or less.
Here, in the present invention, the "line speed" means the transport speed of the raw film.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.
In Examples and Comparative Examples, the relative permittivity of the resin composition, the thickness of the raw film, the adhesion between the molten film and the cooling roll, the meandering amount of the raw film, and the total light transmittance and haze of the optical film are as follows. Measured and evaluated by the method of. The results are all shown in Table 1.

<Relative permittivity of resin composition>
Sampling was performed at a diameter of 40 mm from an arbitrary location on the raw film, and the relative permittivity was measured at a frequency of 1 MHz and a voltage of 1 V using a “Prescription LCR meter HP4284A” (manufactured by Hewlett-Packard). This measurement was performed a total of 5 times, and the arithmetic mean value thereof was taken as the relative permittivity of the resin composition used for preparing the raw film.
<Thickness of original film>
The thickness of the entire width of the raw film was measured every 0.48 mm in the TD direction of the raw film using a "contact web thickness meter RC-101" (manufactured by Meisan Co., Ltd.). Based on the obtained film thickness profile, the presence or absence of thick regions at both ends is specified from the maximum thickness in both ends in the width direction, and the flatness of both ends is determined from the rate of change in thickness in both ends in the width direction. The presence or absence of each area was identified. Furthermore, based on the obtained film thickness profile, the width of the wall thickness region and the width of the flat region at both ends are determined, respectively, and the average thickness (arithmetic mean value) and thickness standard deviation of the central portion in the width direction are determined. Was calculated.
<Adhesion between molten film and cooling roll>
Regarding the raw film obtained after the contact between the molten film and the cooling roll, any part that has passed under the edge pinning is cut out from both ends in a size of 20 mm in the width direction x 50 mm in the longitudinal direction, and an air mark (air pool) is formed. The number of was visually counted. The larger the number of the air marks, the stronger the molten film is pressed toward the cooling roll side by edge pinning, that is, the better the adhesion between the molten film and the cooling roll.
<Amount of meandering of raw film>
When the raw film was transported in the horizontal direction, the displacements at both ends of the raw film during transportation were measured using "LS-9120M" (manufactured by KEYENCE CORPORATION) at a sampling rate of 1 second for 10 minutes. The value obtained by subtracting the minimum value from the maximum value among the measured values was defined as the meandering amount (mm).
<Total light transmittance and haze of optical film>
After the trimming step, the wound optical film (raw film) was sampled at an arbitrary location at a 30 mm square and measured using a "turbidity meter NDH-300A" (manufactured by Nippon Denshoku Kogyo Co., Ltd.). This measurement was performed a total of 5 times, and their arithmetic mean values were taken as the total light transmittance and haze of the optical film.

(Example 1)
Pellets of an alicyclic polyolefin resin (product name "ZEONOR (registered trademark) 1420": manufactured by Nippon Zeon Corporation) were dried at 100 ° C. for 5 hours. The dried pellets were fed to an extruder, melted in the extruder, passed through a polymer pipe and a polymer filter, and extruded from a T-die (extrusion step). The molten film is discharged onto a cooling roll, and as shown in FIG. 3, electric charges are supplied to both ends of the molten film in the width direction by edge pinning, and cooling is performed while restraining 20 mm at both ends by the electrostatic adhesion method. This was performed to obtain a raw film (electrostatic adhesion step). The clearance of the lip of the T-die was adjusted in advance, and a raw film having a thick region and a flat region at both end portions in the width direction was obtained. The extrusion rate at this time was 75 kg / hour (extrusion weight per hour), and the line speed was 50 m / min.
Both ends of the obtained raw film (width 1790 mm) were trimmed by 150 mm (trimming step), and wound at a winding speed of 50 m / min, a winding tension of 100 N / m, and a touch pressure of 150 N / m. The take-up tension is set to gradually reduce the take-up tension at the end of winding to 85% of the take-up tension at the start of winding (15% down taper), and the touch pressure is the touch pressure at the end of winding. Was set to be gradually reduced (10% down taper) so as to be 90% of the touch pressure at the start of winding.

(Examples 2 to 4)
Each step was carried out in the same manner as in Example 1 except that the cross-sectional shape of the raw film was changed as shown in Table 1 by adjusting the lip clearance of the T-die and the film thickness was changed by adjusting the extrusion rate. did.

(Comparative Examples 1-2)
Each step was carried out in the same manner as in Example 1 except that the cross-sectional shape of the raw film was changed as shown in Table 1 by adjusting the lip clearance of the T-die and the film thickness was changed by adjusting the extrusion rate. did.

From Table 1, the molten film is brought into close contact with the cooling roll by the electrostatic adhesion method, and the original fabric has an average thickness of less than 40 μm at the center in the width direction and a wall thickness region of 50 μm or more at both ends in the width direction. It can be seen that in Examples 1 to 4 in which the film was obtained, the adhesion between the molten film and the cooling roll was excellent, meandering during transportation of the raw film was suppressed, and the obtained raw film was excellent in thickness accuracy.
On the other hand, the molten film is brought into close contact with the cooling roll by the electrostatic adhesion method, and the average thickness of the central portion in the width direction is less than 40 μm, and the original fabric having no wall thickness region of 50 μm or more in both ends in the width direction. In Comparative Examples 1 and 2 in which the films were obtained, the adhesion between the molten film and the cooling roll could not be ensured, a large meandering was confirmed when the raw film was conveyed, and it was found that the obtained raw film was inferior in thickness accuracy.

According to the method for producing an optical film of the present invention, the molten film and the cooling roll can be sufficiently brought into close contact with each other to suppress meandering during transportation of the optical film and improve the thickness accuracy of the optical film.

1 Raw film 2 Central part in the width direction 3 Both ends in the width direction 4a Thick area 4b Flat area 5 Die 6 Die lip 7 Edge pinning 8 Cooling roll

Claims (4)

A process of melt-extruding a resin composition containing a resin from a die to obtain a molten film,
A step of bringing the molten film into close contact with a cooling roll and cooling it by supplying electric charges to both ends in the width direction of the molten film to obtain a raw film.
Hints, the raw film is less than 40μm average thickness of the widthwise central portion, thickness have a wall thickness region above 50μm and the both widthwise end portions,
Production of an optical film having both ends in the width direction of the raw film having a flat region thinner than the thick region and thicker than the central portion in the width direction inside the raw film width direction with respect to the thick region. Method. The method for producing an optical film according to claim 1, wherein the resin composition has a relative permittivity of 2.5 or less. The method for producing an optical film according to claim 1 or 2 , wherein the resin is an alicyclic polyolefin resin. After the step of obtaining the raw film,
The method for producing an optical film according to any one of claims 1 to 3, further comprising a step of removing a portion derived from the thick region.

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