KR20150091302A - Method for manufacturing stretched film - Google Patents

Abstract

A stretched film, particularly a stretched film for optical use, which is excellent in transparency, has few scratches, and is suitable for various processing applications.
The method for producing a stretched film according to the present invention is characterized in that the stretching roll on the upstream side (hereinafter referred to as a first stretching roll) and the stretching roll on the downstream side (hereinafter referred to as a second stretching roll (Hereinafter, referred to as a longitudinal stretching step), wherein the nip rolls adjacent to the first stretching roll have two or more and two or more nip rolls close to the first stretching roll, And two or more nip rolls approaching the stretching roll.

Description

METHOD FOR MANUFACTURING STRETCHED FILM [0002]

The present invention relates to a stretched film, particularly a method for producing a stretched film for optical use.

BACKGROUND ART Biaxially oriented thermoplastic resin films such as polyester are widely used as various optical films for use in a state in which light is transmitted and reflected because of excellent transparency, dimensional stability, and chemical resistance. In particular, in applications such as a base film for a prism sheet used for a liquid crystal display (LCD), a base film for a hard coat, a base film for an antireflection (AR) film, a base film for light diffusion, and a transparent conductive film used for a touch panel A relatively thick film is used because excellent strength and dimensional stability are required.

Such optical films are required to have excellent transparency, excellent adhesiveness such as prismatic lens processing, hard coat processing, and a coat layer for processing at the time of AR processing, and the film is required to have very few optical defects.

Patent Document 1 discloses a method for improving handling properties (releasability, windability, blocking resistance, etc.) and scratch resistance of a film.

Further, in order to obtain a film having more excellent transparency, the content of the particles in the base film is reduced or made into a non-particle. In this case, however, transparency is increased while scratch resistance is lowered and scratches on the surface It becomes easier to do. As a technology for suppressing the occurrence of such scratches, Patent Document 2 discloses a polyester-based optical film having a surface of 20 mm or more and a maximum depth of 0.5 m or more and having a scratch of 10 / m < 2 & . However, it is difficult to suppress the occurrence of a minute scratch and does not satisfy the level required for recent optical films.

Japanese Patent Application Laid-Open No. 62-214518 Japanese Patent Laid-Open No. 9-183201

In the method disclosed in Patent Document 1, transparency of the film is lowered by the voids formed around the particles at the time of film stretching, so that the method is not suitable for a production method of an optical film which requires a high degree of optical transparency and homogeneity.

Further, in the method disclosed in Patent Document 2, it is difficult to suppress the occurrence of a minute scratch, and the level required for a recent optical film is not satisfied.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for producing a stretched film which is suitable for optical applications, which is excellent in transparency and has few scratches and is suitable for various processing applications.

As a result of studying the above problems, it was found that two stretching rolls were disposed at a distance and a nip roll close to the two stretching rolls was set as follows when roll longitudinal stretching was performed on a film made of a thermoplastic resin, And the present invention has been accomplished. That is, the present invention is as follows.

1) a step of subjecting the film to a longitudinal stretching treatment using a stretching roll on the upstream side (hereinafter referred to as a first stretching roll) and a stretching roll on the downstream side (hereinafter referred to as a second stretching roll) In the production method of the present invention,

Wherein the nip rolls adjacent to the first stretching roll have two or more nip rolls.

2) There are two nip rolls approaching the first stretching roll. Of the two nip rolls close to the first stretching roll, the upstream nip roll is referred to as a ninth nip roll, the downstream nip roll is referred to as a first nip roll, And a portion to be fitted to the first stretching roll and the ninth nip roll is referred to as a first gripping portion, and a portion where the first nip gripping portion, the first stretching roll and the first nip roll are sandwiched is referred to as a first gripping portion,

The position of the first grip portion is an upstream end portion in the contact region of the film and the first stretching roll and the position of the first grip portion is the downstream end in the contact region of the film and the first stretching roll (1). ≪ / RTI >

3) A process for producing a stretched film according to 1) or 2), wherein the number of nip rolls in the vicinity of the second stretching roll is two or more.

4) Two nip rolls approaching the second stretching roll, two of the two nip rolls approaching the second stretching roll are referred to as the second nip roll, the downstream nip roll is referred to as the third nip roll, And a portion to be fitted to the second stretching roll and the second nip roll is referred to as a third gripping portion, the portion sandwiching the second gripping portion, the second stretching roll and the third nip roll,

The position of the second gripping portion is an upstream end portion in the contact region of the film and the second stretching roll and the position of the third gripping portion is the downstream end in the contact region of the film and the second stretching roll The method of producing a stretched film according to any one of 1) to 3).

5) The ninth nip roll has a cleaning mechanism (hereinafter referred to as a first cleaning mechanism)

The method for manufacturing a drawn film according to any one of claims 1 to 4, wherein the first cleaning mechanism is capable of cleaning the first transport roll located on the upstream side of the first stretch roll.

6) The third nip roll has a cleaning mechanism (hereinafter referred to as a second cleaning mechanism)

The method according to any one of 1) to 5), wherein the second cleaning mechanism is capable of cleaning the second transport roll located on the downstream side of the second stretching roll.

(Effects of the Invention)

The production method of the stretched film of the present invention can suppress the occurrence of scars, and can provide a film reduced in defects caused by the scratches, particularly optical defects.

1 is a schematic view of a manufacturing method of the present invention.

Hereinafter, the present invention will be described.

The film in the present invention is not particularly limited, but means a thermoplastic resin film.

The thermoplastic resin film is not particularly limited, but typical examples thereof include polyethylene terephthalate, polyethylene-2,6-naphthalate, nylon-6, polyphenylene sulfide, and the like.

In order to produce such a film, a pellet containing substantially no particle-containing pellets or particles is prepared by using the above-mentioned material such as polyethylene terephthalate. In the film for optical use, pellets containing no particles are preferred in order to ensure transparency. These are suitably dried, fed to a known melt extruder, and filtered by a polymer filter.

Extruded into a sheet form from a slit-shaped slit die, cooled and solidified on a casting roll to produce an unoriented (unoriented) film. The stretched film can be obtained by successively biaxially stretching the unoriented polyester film in the longitudinal direction and the transverse direction of the film.

The present invention relates to a process for performing a longitudinal stretching process on a film by using a stretching roll on the upstream side (hereinafter referred to as a first stretching roll) and a stretching roll on the downstream side (hereinafter referred to as a second stretching roll) Hereinafter referred to as a stretching process). That is, in the present invention, it is important to use two stretching rolls to perform the longitudinal stretching process.

More specifically, heating is carried out while conveying using a stretching roll, and heating is performed to a predetermined temperature. In order to suppress the occurrence of scratches, the surface roughness Ra of the stretching roll is preferably 0.1 탆 or less. In the production method of the present invention, the heating temperature immediately before the first stretching roll is preferably 68 to 83 캜, more preferably 70 to 80 캜, and still more preferably 72 to 75 캜. If the heating temperature immediately before the first stretching roll is lower than 68 캜, the film tends to be broken. If the heating temperature is higher than 83 캜, the film may adhere to the roll, and surface defects may easily occur.

Hereinafter, the longitudinal drawing step in the method for producing a drawn film of the present invention will be described with reference to Fig. 1 is only one embodiment, and the present invention is not limited to this.

In the present embodiment, the first stretching roll 5 and the second stretching roll 6 are disposed at a distance in order to stretch the film 7.

In the present invention, it is important that there are two or more nip rolls near the first stretching roll. In the present invention, the number of nip rolls adjacent to the first stretching roll is not particularly limited as long as it is two or more, but is preferably 2 to 3, particularly preferably 2. That is, according to Fig. 1, there are two nip rolls approaching the first stretching roll. Of the two nip rolls adjacent to the first stretching roll, the upstream nip roll is referred to as a ninth roll, The first nip roll is characterized in that the nineteenth nip roll (1) and the first nip roll (2) are disposed in the vicinity of the first stretching roll to grip the film in the first stretching roll. If only the first nip roll, that is, only one nip roll close to the first stretching roll, is present, the stretching tension can not be sufficiently blocked so that the film is slipped in the first transport roll 12 located on the upstream side of the first stretching roll There is a problem that scratches are likely to occur.

In the present invention, when a portion sandwiched between the first stretching roll and the ninth nip roll is referred to as a first gripping portion, and a portion sandwiched between the first gripping roll, the first stretching roll, and the first nip roll is referred to as a first gripping portion, Is an end on the upstream side in the contact region between the film and the first stretching roll and the position of the first gripping portion is an end on the downstream side in the contact region between the film and the first stretching roll. That is, according to Fig. 1, it is preferable that the position of the zeroth grip portion held by the ninth nip roll on the first stretching roll is an end on the upstream side in the contact region 8 between the film and the first stretching roll. More preferably, the position of the first grip portion held by the first nip roll on the first stretching roll is preferably the downstream end in the contact region of the film and the first stretching roll. By doing so, the film does not slip on the first stretching roll, and the occurrence of scratches can be suppressed.

In the present invention, it is preferable that there are two or more nip rolls close to the second stretching roll. In the present invention, the number of nip rolls adjacent to the second stretching roll is preferably two or more, more preferably two to three, and particularly preferably two. That is, according to Fig. 1, there are two nip rolls close to the second stretching roll, the nip rolls on the upstream side among the two nip rolls close to the second stretching roll are referred to as the second nip roll, In the case of the third nip roll, it is preferable that the second nip roll 3 and the third nip roll 4 are disposed in the vicinity of the second stretching roll in order to grasp the film in the second stretching roll. If only the second nip roll, that is, only one nip roll close to the second stretching roll, is present, the stretching tension can not be sufficiently blocked, and the film is slipped in the second transport roll 13 located on the downstream side of the second stretching roll There is a case where a wound may occur.

In the present invention, when a portion sandwiched between the second stretching roll and the second nip roll is referred to as a third gripping portion, the portion sandwiched between the second gripping portion, the second stretching roll, and the third nip roll, It is preferable that the position is the end on the upstream side in the contact region of the film and the second stretching roll and the position of the third gripping portion is the end on the downstream side in the contact region of the film and the second stretching roll. That is, according to Fig. 1, it is preferable that the position of the third grip portion held by the third nip roll on the second stretching roll is an end on the downstream side in the contact region 9 between the film and the second stretching roll. More preferably, the position of the second grip portion held by the second nip roll on the second stretching roll is preferably the upstream end in the contact region of the film and the second stretching roll. By doing so, the film does not slip on the second stretching roll, and the occurrence of scratches can be suppressed.

In the present invention, it is preferable to have a cleaning mechanism for the transport roll at any one of the longitudinal stretching processes. In the present invention, the ninth nip roll has a cleaning mechanism (hereinafter referred to as a first cleaning mechanism), and the first cleaning mechanism is preferably capable of cleaning the first transport roll located on the upstream side of the first draw roll Do. That is, according to Fig. 1, it is preferable that the ninth nip roll has a first cleaning mechanism (10) and is capable of cleaning the first transport roll located on the upstream side of the first stretch roll. This is because if the film is produced for a long time, the stretching roll may become dirty and cause scratches. Therefore, by having a mechanism capable of cleaning without cutting the film, the generation of the residue can be minimized.

The cleaning mechanism referred to herein means that a cleaning cloth or the like can be pressed against and contacted with the roll at a constant load to move in the width direction. By using this cleaning mechanism, it is possible to safely clean the film without cutting it.

In the present invention, it is preferable that the third nip roll has a cleaning mechanism (hereinafter referred to as a second cleaning mechanism), and the second cleaning mechanism is capable of cleaning the second transport roll located on the downstream side of the second stretching roll. That is, according to Fig. 1, it is preferable that the third nip roll has a second cleaning mechanism and the second conveying roll located on the downstream side of the second stretching roll can be cleaned. This is because if the film is produced for a long time, the stretching roll may become dirty and cause scratches. Therefore, by having a mechanism capable of cleaning without cutting the film, the generation of the residue can be minimized.

In the present invention, it is preferable to have a mechanism for raising the temperature of the film between the first stretching roll and the second stretching roll in a non-contact manner. Examples of such a mechanism include an infrared heater and the like.

The film temperature at the time of drawing in the longitudinal drawing process is, for example, 70 to 130 占 폚, preferably 75 to 120 占 폚, and more preferably 80 to 110 占 폚. When the film temperature at stretching in the longitudinal stretching process is lower than 70 ° C, the film tends to be broken. When the film temperature at stretching is higher than 130 ° C, the polymer is hardly aligned, and is likely to be broken when stretched in the width direction. Here, the film temperature at the time of stretching in the longitudinal stretching process means the film temperature in the region between the first stretching roll and the second stretching roll.

The drawing magnification of the longitudinal drawing process is, for example, 2.5 to 5.0 times, preferably 2.7 to 3.5 times. When the longitudinal stretching magnification is less than 2.5 times, it is difficult to obtain the strength. On the other hand, when the stretching magnification of the longitudinal stretching process is larger than 5.0 times, the orientation of the polymer is strong, and it tends to be broken when stretched in the width direction.

After the longitudinal stretching process, it is possible to apply the adhesive layer to both sides or one side of the stretched film and to pass the film through the transverse stretching process. The coating method is not particularly limited, and for example, a reverse coating method, a gravure coating method, a rod coating method, a bar coating method, a wire bar coating method, a die coating method, a spray coating method and the like can be used.

The uniaxially stretched film (stretched film of the present invention) obtained by the above-described method is stretched, for example, at 80 to 160 캜, preferably 85 to 130 캜, more preferably 90 For example, 2.5 to 6.0 times, preferably 3.0 to 5.5 times, more preferably 3.5 to 5.0 times in the transverse direction at 120 deg. If the temperature and magnification are out of the range, there may be a problem such as elongation deviation or film breakage. In particular, if the stretching temperature in the transverse stretching process is lower than 80 캜, the film tends to be broken, which may be difficult to manufacture. On the other hand, if the stretching temperature in the transverse stretching step is higher than 160 캜, sufficient strength may not be obtained for releasing use.

After stretching, it is also possible to perform heat fixation at 200 to 240 캜, preferably 205 to 235 캜, more preferably 210 to 230 캜, and then relax within 25% as required. Particularly, when the temperature of the open-and-close time is lower than 200 ° C, the crystallinity does not progress, so that the structure of the polyester may not be stabilized.

The manufacturing method of the present invention may have a transverse stretching process after the longitudinal stretching process, but it is preferable that the edge portion having a thick thickness after the transverse stretching process is cut and removed along with the embossing process portion in the cutting process.

The stretched film obtained by the present invention can be used for various optical films because it is excellent in transparency and few scratches and is suitable for various processing applications as described above. In particular, it can be used for a prism sheet base film, a hard coat base film, (AR) film, a base film for light diffusion, a transparent conductive film, and the like.

(Example)

Hereinafter, the present invention will be described in detail in Examples. The evaluation method of the effect is as follows.

(One). Visual inspection

A sheet-like sample (product width x 1 to 2 m) was taken from the surface of the film roll having a predetermined winding length, and the number of wounds having a maximum diameter of 500 탆 or more in the dark room was observed with naked eyes, The number of wounds of the sugar was converted into the following categories.

Class A: 50 pieces / ㎡ or less

Class B: Greater than 50 / ㎡ and less than 75 / ㎡

C grade: greater than 75 pieces / ㎡ and less than 100 pieces / ㎡

Class D: more than 100 pieces / ㎡ and less than 120 pieces / ㎡

E rating: greater than 120 pieces / ㎡ (failed)

Among the above criteria, the film having the grade D or higher is a level that can be practically used without any problem, but a grade C or higher is preferable.

(Production example)

The pellets of polyethylene terephthalate were dried at 160 DEG C for 8 hours, and then fed to an extruder, melt-extruded at 275 DEG C and filtered. Thereafter, the film was wound on a cooling roll through a slit die maintained at 285 DEG C by a casting drum having a surface temperature of 25 DEG C by electrostatic casting to cool and solidify to obtain an unstretched film.

In order to stretch in the longitudinal direction, the temperature of the unstretched film was raised to 74 DEG C on a roll having a surface roughness Ra of 0.1 mu m. The film temperature at stretching in the longitudinal drawing process was maintained at 74 캜. In the longitudinal stretching process, stretching is performed by applying a speed ratio of 3.0 times between the first stretching roll and the second stretching roll. A first nip roll is provided in the vicinity of the first stretching roll (only one nip roll in the vicinity of the first stretching roll), and the position of the first gripping portion where the first nip roll grips the film is the position And a second nip roll (there is only one nip roll in the vicinity of the second stretching roll) in the vicinity of the second stretching roll, and the second nip roll Position is located at the upstream end of the region where the film is in contact with the second stretching roll. In the longitudinal stretching step, the film is stretched while heating the film with an infrared heater between the first stretching roll and the second stretching roll. This method is called the basic longitudinal drawing method.

(Example 1)

In addition to the basic longitudinal stretching method described above, the nineteenth nip roll has a nineteenth nip roll in the vicinity of the first stretching roll, and the position of the zipper gripping portion of the nineteenth nip roll grasps the upstream And the other side was stretched in the longitudinal direction in the same manner as in Production Example.

Thereafter, the stretched film was introduced into a tenter, stretched 3.6 times in the width direction at a temperature of 100 占 폚, and then heat-treated at a constant width of 225 占 폚. Thereafter, a 6% relaxation treatment was further performed in the width direction to obtain a biaxially oriented polyester film having a thickness of 188 탆.

Table 1 shows the number of scratches of the obtained stretched film. Table 1 also shows the wound level after one day of production.

(Example 2)

A biaxial oriented film was obtained in the same manner as in Example 1 except that the position of the zeroth grip portion in the longitudinal stretching step of Example 1 was changed to the upstream side end portion in the contact region of the first stretching roll and the film.

Table 1 shows the number of scratches of the obtained film. Table 1 also shows the wound level after one day of production.

(Example 3)

The third nip roll has a third nip roll in the vicinity of the second stretching roll in the longitudinal stretching process of the second embodiment and the third gripping portion where the third nip roll grasps the film is positioned at the contact area between the second stretching roll and the film The biaxially stretched film was obtained in the same manner as in Example 2 except that it was located on the upstream side from the end on the downstream side by 30 °.

Table 1 shows the number of scratches of the obtained film. Table 1 also shows the wound level after one day of production.

(Example 4)

A biaxially stretched film was obtained in the same manner as in Example 3 except that the position of the third grip portion in the longitudinal stretching step of Example 3 was changed to the position of the downstream side end portion in the contact region between the second stretching roll and the film .

Table 1 shows the number of scratches of the obtained film. Table 1 also shows the wound level after one day of production.

(Example 5)

A biaxially oriented film was obtained in the same manner as in Example 4 except that the first cleaning mechanism was provided on the nineteenth nip roll in the longitudinal drawing step of Example 4.

Table 1 shows the number of scratches of the obtained film. The first conveying roll was cleaned using the first cleaning mechanism after 1 day from the production and 1 day after the production, and the number of the scratches of the film obtained thereafter is shown in Table 1.

(Example 6)

A biaxially oriented film was obtained in the same manner as in Example 5 except that the second cleaning mechanism was provided in the third nip roll in the longitudinal drawing step of Example 5. [

Table 1 shows the number of scratches of the obtained film. Also, the first and second transport rolls were cleaned using the first and second cleaning mechanisms one day after the production and one day after the production, and the number level of the scratches of the film obtained thereafter is shown in Table 1 Respectively.

(Comparative Example 1)

Table 1 shows the wound number level of the biaxially oriented film obtained by the basic longitudinal drawing method and the wound number level after one day of production.

In Comparative Example 1, there is one nip roll close to the first stretching roll, but the portion sandwiched by the nip roll and the first stretching roll is the downstream end in the contact region between the film and the first stretching roll In the table, the portion sandwiched by the nip roll and the first stretching roll is handled as the first grip portion.

In Examples 1 and 2 and Comparative Example 1, there is only one nip roll close to the second stretching roll, but the portion sandwiched by the nip roll and the second stretching roll is in contact with the film and the second stretching roll In the table, the portion sandwiched by the nip roll and the second stretching roll is handled as the second grip portion and described.

(Industrial availability)

Since the stretched film obtained by the production method of the present invention has an advantage of being excellent in transparency and being suitable for various processing applications with few scratches, it is preferable to use various optical films, particularly base films for prism sheets, base films for hard coating, (AR) film, a base film for light diffusion, a transparent conductive film, and the like.

1: ninth nip roll 2: first nip roll
3: second nip roll 4: third nip roll
5: first stretching roll 6: second stretching roll
7: Film 8: First contact area
9: second contact area 10: first cleaning device
11: second cleaning mechanism 12: first conveying roll
13: second conveying roll

Claims (6)

A step of subjecting the film to a longitudinal stretching treatment using a stretching roll on the upstream side (hereinafter referred to as a first stretching roll) and a stretching roll on the downstream side (hereinafter referred to as a second stretching roll) In the method,
Wherein the nip rolls adjacent to the first stretching roll have two or more nip rolls. The method according to claim 1,
Two nip rolls approaching the first stretching roll, two of the two nip rolls adjacent to the first stretching roll are referred to as a nip roll on the upstream side and a nip roll on the downstream side is referred to as a first nip roll , A portion where the first stretching roll and the ninth nip roll are sandwiched by the first grip portion, the first stretching roll, and the first nip roll is referred to as a first grip portion,
The position of the first grip portion is the upstream end portion in the contact region of the film and the first stretching roll and the position of the first grip portion is the downstream end in the contact region of the film and the first stretching roll Wherein the stretched film is formed by stretching the stretched film. 3. The method according to claim 1 or 2,
And the nip rolls adjacent to the second stretching roll are two or more rolls. 4. The method according to any one of claims 1 to 3,
Two nip rolls approaching the second stretching roll, two of the two nip rolls approaching the second stretching roll, the nip roll on the upstream side is referred to as a second nip roll, and the nip roll on the downstream side is referred to as a third nip roll , And a portion to be fitted to the second stretching roll and the second nip roll is referred to as a third gripping portion, the portion which is sandwiched between the second gripping portion, the second stretching roll and the third nip roll,
The position of the second gripping portion is an upstream end portion in the contact region of the film and the second stretching roll and the position of the third gripping portion is the downstream end in the contact region of the film and the second stretching roll Wherein the stretched film is formed by stretching the stretched film. 5. The method according to any one of claims 1 to 4,
The ninth nip roll has a cleaning mechanism (hereinafter referred to as a first cleaning mechanism)
Wherein the first cleaning mechanism is capable of cleaning the first transport roll located on the upstream side of the first stretch roll. 6. The method according to any one of claims 1 to 5,
The third nip roll has a cleaning mechanism (hereinafter referred to as a second cleaning mechanism)
And the second cleaning mechanism is capable of cleaning the second transport roll located on the downstream side of the second stretch roll.

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