KR102512601B1 - Method of producing optical anisotropic film - Google Patents

Abstract

(Problem) To provide an optically anisotropic film that hardly breaks the film during stretching, has uniform optical properties in the width direction, and has a wide effective width.
(Solution Means) The method for manufacturing an optically anisotropic film of the present invention comprises the steps of gripping both ends 11e in the width direction of a strip-shaped film to be stretched 10 with grippers 51; and a step of stretching the film in the transverse direction (TD) by increasing the distance between the gripping segments in the width direction while moving the gripper in the longitudinal direction (MD) of the film 10 . Gripping by the gripping tool 51 is performed in the state where the strip-shaped laying films 15 and 17 are superimposed on the width direction end portion 11e of the film 10 to be stretched. At least one layer of the laying film is made of the same material as at least one layer of the film to be stretched.

Description

Manufacturing method of optically anisotropic film {METHOD OF PRODUCING OPTICAL ANISOTROPIC FILM}

The present invention relates to a method for producing an optically anisotropic film such as a polarizer or retardation film.

BACKGROUND ART Optically anisotropic films such as polarizing plates and retardation plates are used in displays such as liquid crystal display devices. Optical anisotropy is imparted by stretching the polymer film in at least one direction. In the case of industrially stretching a polymer film, it is common to carry out the stretching treatment while moving the strip-like film in the longitudinal direction.

In the transverse stretching of the tenter method, both ends of the film are gripped by a gripper such as a clip, and the gripper is moved along a guide rail in the longitudinal direction (MD) while driving the gripper so that the interval in the width direction (TD) is widened. The film is stretched in the width direction. By employing a driving method such as a linear motor method, a pantograph method, or a motor chain method, the distance between clips in the width direction is widened while changing the distance between clips in the longitudinal direction, and simultaneous biaxial stretching or oblique direction stretching can be performed. (See, for example, Patent Document 1 and Patent Document 2). Hereinafter, as long as stretching in the width direction is performed, even when stretching or contraction in the longitudinal direction is performed, such as simultaneous biaxial stretching and oblique direction stretching, unless otherwise specified, it is considered to be included in "transverse stretching". do.

Transverse stretching is advantageous in that the direction of the optical axis of the film can be adjusted and an optically anisotropic film with a large width can be produced. On the other hand, in transverse stretching, breakage of the film may occur in the vicinity of a portion held by a pin or clip, and the tendency is remarkable as the stretching ratio in the width direction increases.

Patent Literature 1 discloses a method of bonding a tape 35 to both ends of a film 10 for the purpose of preventing breakage of the film during transverse stretching (see Fig. 3B). In Patent Literature 3, a reinforcing sheet having a higher tear strength than that to be stretched is superimposed on the edge of a strip-shaped film to be stretched, and the overlapping portion is held by a pin tenter, thereby causing separation or breakage of the film due to enlargement of pin holes. A method for suppressing is disclosed. Patent Literature 4 discloses that cracking at the ends of the film in the width direction during transverse stretching can be prevented by using a film formed of different resin materials for the central portion in the width direction of the film and the ends in the width direction of the film.

Japanese Unexamined Patent Publication No. 2013-54338 Japanese Unexamined Patent Publication No. 2014-54338 Japanese Unexamined Patent Publication No. 11-254521 Japanese Unexamined Patent Publication No. 2009-160900

Demands for thinning and large-area optical films are increasing, and it is now required to stretch a film having a smaller thickness at a high magnification to impart a predetermined optical anisotropy. In the case of producing an optically anisotropic film by transverse stretching, it is required that the end portion in the width direction be uniform in optical properties in addition to preventing breakage of the end portion or separation from the gripping tool. When the draw ratio in the width direction is increased, the deviation in the optical axis direction in the vicinity of the end portion in the width direction of the film increases, and it tends to be difficult to obtain a film with a large effective width.

As disclosed in Patent Literatures 1 and 2, the method of reinforcing the edge of the film with a reinforcing material such as tape can suppress breakage of the film in the vicinity of the gripping portion, but is not effective in uniformizing the optical properties in the width direction. Can not.

When a film disclosed in Patent Literature 3 is made of a material different from that of the central portion at the ends in the width direction, the central portion in the width direction of the film can be selectively stretched. A film is obtained. However, for a film in which the end portion in the width direction is made of a material different from that of the central portion, a special film forming method must be employed when forming the film, which increases cost. In addition, when the draw ratio increases, breakage tends to occur at the boundary between the center portion and the end portion, that is, in the vicinity of the joint portion of different types of resin materials. In addition, with an increase in the draw ratio, an imbalance in stress tends to occur in the vicinity of the bonding portion of the resin material, resulting in non-uniform optical properties in some cases.

In view of these considerations, the present invention provides an optical anisotropy in which the breakage of the film during stretching or separation from the holding tool hardly occurs even when the stretching ratio in the width direction is large, and the optical properties in the width direction are uniform and the effective width is wide. It aims to provide a film.

The manufacturing method of the optically anisotropic film of this invention comprises the step of gripping both ends of the strip-shaped film to be stretched in the width direction with a gripping tool; And a step of extending the distance between the gripping sections in the width direction and stretching the object film in the width direction while moving the holding tool in the longitudinal direction of the film to be stretched. Gripping with a gripping tool such as a clip is performed in a state where the strip-shaped laying film is superimposed on the edge of the film to be stretched in the width direction.

At least one layer of the laying film overlapping the film to be stretched is made of the same material as the at least one layer of the film to be stretched. When the film to be stretched is a single-layer film, the laid film is made of the same material as the film to be stretched. When the film to be stretched consists of a plurality of layers, the laid film includes a layer made of the same material as at least one layer of the plurality of layers constituting the film to be stretched.

As a method of overlapping a film to be stretched and a laid film made of the same material, a method of folding and overlapping the ends of the film to be stretched or a method of overlapping cut pieces of the film to be stretched can be cited. Preferably, the film to be stretched and the laying film are overlapped without an adhesive layer interposed therebetween.

According to the method of the present invention, even when the transverse stretch ratio is large, breakage of the film or separation from the holding tool is unlikely to occur, and the stability of the process is excellent. Further, according to the method of the present invention, an optically anisotropic film having uniform optical properties in the width direction and a wide effective width can be obtained.

1 is a plan view showing the outline of transverse stretching.
2A to 2D are schematic cross-sectional views each showing a holding state of a film end in the method of the present invention.
3A and 3B are schematic cross-sectional views each showing a holding state of a film end in the prior art.
Fig. 4 is a graph plotting the relationship between the neck-in rate and the range of the optical axis during transverse stretching in Example 1;
Fig. 5 is a graph plotting the relationship between the draw ratio and the effective width (the part where the optical axis is in the range of +/- 1°) during transverse stretching in Example 1;
6 is a conceptual diagram for explaining the outline of an oblique stretch method in Example 2;

In the method for producing an optically anisotropic film of the present invention, stretching (transverse stretching) is performed in the width direction (TD) while the strip-shaped film to be stretched is moved in the longitudinal direction (MD). The film to be stretched is stretched in TD by holding both ends of the TD of the film to be stretched with a gripper such as a clip and moving the gripper holding the film to the MD to increase the distance between the gripping segments in the TD.

[Target film for stretching]

The film to be stretched is a strip-shaped long film. The width of the film to be stretched is generally about 200 mm to 2500 mm. The length of the film to be stretched is generally about 20 m to 5000 m.

As the material of the film to be stretched, any suitable resin material can be used depending on the purpose. For example, cellulose-based resins such as acetyl cellulose, polyester-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, maleimide-based resins, polyolefin-based resins, (meth)acrylic-based resins, and cyclic polyolefin resins (norbornene-based resin), polyarylate-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, polysulfone-based resins, and mixtures or copolymers thereof.

The thickness of the film to be stretched (before stretching) is preferably from 25 μm to 300 μm, more preferably from 30 μm to 200 μm, still more preferably from 35 μm to 150 μm. If the thickness of the film is excessively small, breakage of the film in the vicinity of the gripping portion by the gripping tool or detachment of the film from the gripping tool tends to occur. On the other hand, if the thickness of the film is excessively large, the tension during stretching becomes excessive, which may cause the film to detach from the gripper or decrease the uniformity of optical properties.

The film to be stretched may be a single layer film composed of one layer or a laminated film in which a plurality of layers are tightly laminated. As a laminated film in which a plurality of layers are closely laminated, a multilayer film in which a plurality of layers are simultaneously formed by multilayer co-extrusion or overlapping coating, a laminate in which a thin film is formed on a support film by a sputtering method or a CVD method, and a resin on a support film A layered product in which a support film and a resin coating film are adhered and laminated by applying and drying the solution is exemplified.

[Gripping and Stretching of Film to be Stretched]

After gripping both ends of the film to be stretched in the TD with gripping tools, transverse stretching is performed by increasing the distance between the gripping segments in the TD while moving the gripping tool in the MD longitudinal direction.

1 is a plan view showing an outline of transverse stretching in a clip tenter method. In the form shown in Fig. 1, a chain is formed along a pair of guide rails (not shown), and a plurality of grippers 51 and 52 are formed in each chain. In Fig. 1, broken lines 41 and 42 indicate trajectories of chains. The gripper is typically a clip configured to sandwich the film from both sides. The shape of the clip is not particularly limited as long as it can hold the film, and examples thereof include a circular shape, an oval shape, and a square shape.

With both ends of the film to be stretched 10 held by the clips 51 and 52, the strip-shaped film to be stretched 10 is conveyed to the MD by moving the chain along the guide rail to the MD. When a pair of guide rails are formed so that the intervals along the MD are expanded, the distance between the clips 51 and 52 holding both ends of the film is also expanded along the MD, so that the film 10 to be stretched is moved to the TD. is elongated

In this aspect, since clips are formed on the chain at equal intervals, even when the chain is moved, the clip distance in MD is maintained, and the film is stretched only in TD. On the other hand, as a method of moving the gripper, a driving method such as a linear motor method, a pantograph method, a motor chain method, and the like is adopted, and simultaneous longitudinal and transverse biaxial stretching or oblique direction stretching may be performed by changing the clip interval of the MD. there is. In simultaneous biaxial stretching or oblique direction stretching, the film may be contracted in MD while stretching in TD by reducing the clip interval in MD.

<Clipping the film>

2A to 2D and FIGS. 3A and 3B each schematically show a state in which the TD end of the film 10 to be stretched is held by the clip 51, and is a cross section taken along line II-II in FIG. 1 are responding to In the present invention, as shown in FIGS. 2A to 2D, a film of the same material as the film to be stretched is overlapped on the TD end 11e of the film to be stretched 10 as a laid film, and the portion where the laid film is overlapped is It is gripped by the gripper.

As a method of overlapping the film to be stretched and the laid film of the same material, a method of folding and overlapping the film to be stretched at an end portion is exemplified. 2A, the film to be stretched 10 is folded back by bending it 180° at the bent portion 13 of the TD end, and the clip 51 is placed in a state where the folded portion 15 overlaps the film 10 to be stretched. ), the form of holding is shown.

The method of folding and overlapping the film to be stretched at the end is not particularly limited, and a film having the end folded and overlapped in advance may be used, or the end may be folded and overlapped while transporting the film before gripping by the gripper. The method of folding and overlapping the edge part of a film is not specifically limited, conveying a film. For example, the film may be folded back by bending the film along a flat plate or a U-shaped cross-section or a guide on the cross-section V. The edges of the film may be overlapped by double folding, or may be overlapped by triple or more folding. From the viewpoint of efficiency and accuracy, as shown in Fig. 2A, double folding and overlapping (folding once) is preferable.

The direction in which the edges of the film are folded back is not particularly limited. When the end of the film to be stretched is curled, it is preferable to fold the film along the curling direction from the viewpoint of facilitating introduction of the film to the guide and refolding of the film.

The width of the folded portion 15 of the film is not particularly limited as long as the clip 51 is within a range capable of sufficiently gripping the folded and overlapping portion. The width of the foldable part 15 is suitably adjusted in the range of about 20 mm to 100 mm, for example. The bent portion 13 is located outside the outer edge of the gripper, and the end of the folding portion 15 is located inside (center side) of the inner edge of the gripper so that the gripper can reliably grip the folded and overlapping portion. it is desirable

In the form shown in Fig. 2A, the folded portion 15 is connected at the bent portion 13 of the film folded at the end, but the plurality of overlapping films need not necessarily be continuous at the bent portion. For example, even if the film is cracked at the bent portion and the bent portion becomes discontinuous during folding or gripping by the gripping tool, there is no problem as long as the folded portion 15 can be gripped by the gripping tool.

As a method of overlapping the film to be stretched and the laid film of the same material, as shown in FIG. 2B, in addition to the method of folding and overlapping at the ends, a narrow band-shaped film 17 made of the same material as the film to be stretched 10 is , the method of overlapping on the TD edge part 11e of the film 10 to be stretched is mentioned. It is preferable to use a cut piece of the film to be stretched as the overlapping narrow band-shaped film because the material cost for preparing the laying film becomes unnecessary. As the cutting piece, a slit piece at the TD end can be used.

Cut pieces such as slit pieces can be prepared by previously slitting the TD end of the film to be stretched. In this case, as long as the film to be stretched and the material are the same, you may overlap the slit piece of the edge part of the film of a different production lot on the edge part of the film to be stretched. You may overlap the slit piece cut off at the edge part of the film to be stretched immediately before superposition|overlapping on the edge part of the film to be stretched after a slit. For example, if the slit of the TD end part is performed and the pass line of the slit piece is adjusted, the end slit and the slit piece can be overlapped in an in-line manner while the film to be stretched is driven.

In the case of overlapping the film to be stretched 10 and the cut piece 17, the end surfaces of both need not coincide, and the clip 51 sufficiently covers the overlapping portion of the film to be stretched 10 and the cut piece 17. You just need to be able to grip it. The width of the overlapping portion is appropriately adjusted within a range of about 20 mm to 100 mm, for example. The width of the cutting piece 17 is also appropriately adjusted in the range of about 20 mm to 100 mm. The outer end surface of the cutting piece 17 and the end surface of the film to be stretched are located outside the outer edge of the gripping tool, and the inner end surface of the cutting piece 17 is It is preferable to be located on the inner side (central side) of the inner edge.

When the folded film such as the folded portion 15 or the cut piece 17 is held by the clip 51 in a state of overlapping with the film 10 to be stretched, the thickness of the gripped portion is greater than that of the film to be stretched alone. Since it is large, the mechanical strength of the holding portion and its vicinity is increased, and breakage of the film is suppressed.

The material of the laying film and the film to be stretched is the same. Moreover, the material of the TD center part 11c and the edge part 11e of the film 10 to be stretched is also the same. Therefore, the material is the same throughout the clip-holding portion and non-clip-holding portion of the film to be stretched and the entire laid film, and the entire film exhibits the same mechanical properties and thermal behavior even in a heating environment during stretching. Therefore, even when the distance between the clips at both ends is widened and stretched by TD at high magnification, an optically anisotropic film that is resistant to local mechanical deformation such as stress concentration near the material boundary and has excellent optical uniformity in the width direction. is obtained

Laid films such as the folded portion 15 and the cut piece 17 may be directly superimposed on the film 10 to be stretched, or as shown in FIG. 2C and FIG. 2D, an adhesive layer 31 such as double-sided tape is formed. They may be interposed and bonded together. It is preferable that the stretched film and the laying film are overlapped without intervening other members such as an adhesive layer, from the viewpoint of making the material configuration of the end where the laying film is overlapped and the other portion the same, and reducing local mechanical strain. do.

<lateral stretch>

After the TD end of the film to be stretched on which the strip-shaped laying film is superimposed is gripped by the gripping tool, transverse stretching is performed by increasing the distance between the gripping segments in the TD while moving the gripping tool in the MD.

Transverse stretching is preferably performed in a heating environment. The stretching method may be air stretching or underwater stretching. In manufacture of retardation film, air stretching is generally performed within a heating furnace. In manufacture of a polarizer, processing, such as dyeing|staining of a dichroic substance, such as iodine, and bridge|crosslinking, may be performed by extending|stretching in heated water.

The stretching temperature and the stretching magnification (ratio W ₁ /W ₀ of the film width W ₁ after stretching to the film width W ₀ before stretching) may be set to any suitable value depending on the material of the film to be stretched, the optical properties required, and the like. can be set. The stretching temperature is typically set within a range of about ±50°C of the glass transition temperature Tg of the film to be stretched. The draw ratio is typically about 1.05 to 4 times.

In the film after transverse stretching, the width W ₁ of the portion held by the clip 51 is equal to the distance between the clips of TD, whereas the width W _ni of the non-hold portion not held by the clip is smaller than W ₁ , and the film The end of the curve becomes a curved shape (neck-in phenomenon). When neck-in occurs, since the direction of the stress becomes non-uniform, the orientation angle of the optical axis tends to become non-uniform at the TD end. As the range affected by the neck-in increases, the deviation of the orientation angle of the optical axis in the width direction increases, and the effective width of the optically anisotropic film (region where the orientation angle is within a predetermined range) decreases. In the present invention, stretching is performed in a state in which the film to be stretched and the laid film of the same material are overlapped, so that the effect of non-uniformity of the optical axis due to neck-in is limited to the vicinity of the TD end, and an optically anisotropic film with a wide effective width is obtained.

[Gripping and stretching of laminated film]

In the above, the description has been centered on the case where the film to be stretched is a single-layer film, but even when the film to be stretched is a laminated film composed of a plurality of layers, the optical properties in the width direction are obtained by overlapping the film to be stretched and a laid film made of the same material. This uniform optically anisotropic film is obtained.

When the film to be stretched consists of a plurality of layers, the laid film such as the folded portion 15 and the cut piece 17 may be a single-layer film or a film composed of a plurality of layers. When the laying film is a single layer film, the laying film may be made of the same material as at least one layer of the film to be stretched. When the laying film is a film composed of a plurality of layers, at least one layer of the laying film may be made of the same material as at least one layer of the film to be stretched.

From the viewpoint of equalizing the mechanical properties and thermal behavior of the entire film, the laid film is preferably a laminated film having the same laminated structure as the film to be stretched. On the other hand, when a specific layer in the film to be stretched dominates the mechanical properties and thermal behavior of the entire laminated film, the laid film should just have a layer made of the same material as the specific layer in the film to be stretched.

For example, when the film 10 to be stretched is a laminate in which a thin film is formed on a support film or a laminate in which a support film and a resin coating film are tightly laminated, the thickness of the support film is larger than that of the thin film or the resin coating film. , the characteristics of the support film dominate the thermal/mechanical behavior of the film to be stretched. Therefore, as long as the laying film has the same film as the support of the film to be stretched, it is not necessary for the thin film or resin coating film to be formed on the support.

In the case of forming a laminate in which the support film and the resin coating film are tightly laminated by applying and drying the resin solution on the support film, generally, since the resin solution is not applied near both ends of the support film, the vicinity of the end portion of the support film is resin. It becomes a coating film non-formation part. The resin coating film non-formation part is a support film alone, and the laminated body of the support body and the coating film has a different lamination structure. On the other hand, in the laminate of the support and the coating, since the thickness of the resin coating is smaller than that of the support film, the thermal and mechanical behavior of the laminate is equivalent to that of the support alone. Therefore, the non-coating film formation part and the coating film formation part exhibit the same thermal/mechanical behavior.

When the resin coating non-formation portion of the laminate in which the support film and the resin coating film are tightly laminated is used as the film to be stretched without being cut off, part or all of the folded portion at the end portion is the resin coating non-formation portion. Moreover, when overlapping the slit piece of a resin coating film non-formation part on the film to be stretched, a part or all of the slit piece is a resin film non-formation part. In this way, even if part or all of the in-plane surface of the laying film superimposed on the film to be stretched is not formed with a resin coating film on the support alone, the thermal/mechanical behavior of the laying film is similar to that of the film to be stretched having a resin coating film on the support body. Since they are equivalent, an optically anisotropic film having uniform optical properties in the width direction can be obtained, similarly to the case where a laminate of a support and a resin coating film is used as a laying film.

The method of stretching a laminate in which a support film and a resin coating film are tightly laminated is suitable for stretching a film having a small thickness (for example, less than 25 µm) and which is difficult to handle or transversely stretch as a single unit. When the support film is peeled off after stretching the laminate in which the support film and the resin coating film are tightly laminated, an optically anisotropic film having a small thickness can be easily obtained.

In addition, when a film heat-shrinkable in MD is used as the support film, when shrinking in MD at the same time as transverse stretching, uniform shrinkage is possible over the entire TD, and an optically anisotropic film excellent in uniformity of optical properties can be obtained. is obtained A support film capable of being heat-shrinkable in MD can be produced by performing a stretching treatment in advance in MD. As the material for the heat-shrinkable support film, polyolefins such as polyethylene and polypropylene, and polyesters are preferably used.

In a laminate in which a resin coating film is closely laminated on a support film, the end portion of the film tends to be easily curled so that the coating film formation surface is on the inside. Therefore, when the laminate is folded and overlapped at the end, the guide can be easily introduced into the film and folded, so that the coating film formation surface side is on the inside along the curling direction. It is preferable to carry out

[Use of Stretched Film as Optically Anisotropic Film]

The film after transverse stretching may be used as it is for practical use as an optically anisotropic film such as a retardation film or a polarizer. When the film to be stretched is a laminated film of a support and a coating film, the laminated film may be used as an optically anisotropic film as it is, or the supporter may be peeled off and the resin coating film after stretching may be used as an optically anisotropic film. The resin coating film may be transferred to another film to form an optically anisotropic film.

Example

Below, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[Example 1: Transverse stretching of laminated film]

In Example 1, a laminate in which a coating film was formed on a heat-shrinkable support film was transversely stretched, and the uniformity of the optical axis of the stretched film was evaluated according to the difference in gripping method of both ends of the film.

[Synthesis of Polyarylate Resin and Preparation of Dope]

In a reaction vessel equipped with a stirring device, 540 parts by weight of 2,2-bis(4-hydroxyphenyl)-4-methylpentane and 12 parts by weight of benzyltriethylammonium chloride were dissolved in a 1M sodium hydroxide solution. To this solution, a solution in which 304 parts by weight of terephthalic acid chloride and 102 parts by weight of isophthalic acid chloride were dissolved in chloroform was added at once while stirring, and stirred at room temperature for 90 minutes. Thereafter, the polymerization solution was subjected to static separation to separate the chloroform solution containing the polymer, followed by washing with acetic acid water and then washing with ion-exchanged water, and then poured into methanol to precipitate the polymer. The precipitated polymer was washed twice with distilled water and twice with methanol, and then dried under reduced pressure. The obtained polyarylate-type resin was dissolved in cyclopentanone to prepare dope having a solid content concentration of 20%.

[Laminate Film Production Example 1]

A non-stretched polyethylene-terephthalate/isophthalate (PETI) film is held at both ends of the TD by tenter clips of a simultaneous biaxial stretching machine, stretched in MD while maintaining the distance between clips of the TD, PETI having heat shrinkability A support film (thickness: 50 μm, width: 1490 mm) was obtained. While conveying this support to MD, after heating at 90°C for 15 seconds, the above dope was applied, dried at 100°C, and a polyarylate resin coating film having a thickness of 21 μm was formed on the support, and a laminate having a thickness of 71 μm was obtained. got the film

[Laminate Film Production Example 2]

A laminated film was obtained in the same manner as in Production Example 1, except that a biaxially stretched polypropylene (PP) film having a thickness of 50 µm was used as the support.

[Transverse stretching of laminated film]

Using a tenter clip type biaxial stretching machine, for each of Production Example 1 (PETI support) and Production Example 2 (PP support), both ends of the laminate were held with clips under the conditions of levels 1 to 5 below, At a temperature of 145°C, while stretching 1.3 times to 1.6 times in TD, the distance between clips in MD was reduced and shrunk by 0.75 times.

Level 1: Holding the laminated film by itself with clips at both ends as it is (see Fig. 3A)

Level 2: A heat-resistant tape (thickness of 79 µm including the adhesive layer, width of 40 mm) is pasted to both ends of the laminated film, and the tape bonded portion is held with a clip (see Fig. 3B)

Level 3: Overlapping the slit pieces (40 mm in width) of the laminated film on both ends of the laminated film, and holding the overlapping portion with clips (see Fig. 2B)

Level 4: Fold and overlap the both ends (40 mm in width) of the laminated film so that the coating film formation surface side is on the inside, and hold the overlapped portion with a clip (see Fig. 2A)

Level 5: Both ends of the laminated film are folded and overlapped so that the coating film formation surface side is inside, bonded and fixed with double-sided tape (thickness 108 μm, width 40 mm), and the overlapped portion is held with a clip (see FIG. 2C )

[evaluation]

(neck-in rate)

The neck-in rate was determined from the maximum width W ₁ of the layered product after stretching (the width of the part held by the clip) and the minimum width (the width of the part where the neck-in was the largest).

Neck-in rate (%) = 100 × (W ₁ - W _ni )/W ₁

(Range of optical axis)

The support is peeled off from the laminate after stretching, and the orientation angle of the optical axis is measured at 10 mm intervals in the TD in the range of 1400 mm in the center of the TD using a polarization/phase difference measurement system (manufactured by Axometrics, product name "AxoScan") , the difference between the maximum and minimum values was taken as the optical axis range. The effective width was the width of a region where the orientation angle of the optical axis was within a range of ±1° of the orientation angle of the optical axis at the center of the TD.

The neck-in ratio, effective width, and optical axis range after transverse stretching of the laminated films of Production Example 1 (PETI support) and Production Example 2 (PP support) are shown in Table 1 and Table 2, respectively. Fig. 4 shows a plot of the relationship between the neck-in rate and the optical axis range at each level. What plotted the relationship between the draw ratio and the effective width in each level is shown in FIG. Incidentally, in Tables 1 and 2 and Tables 3 and 4 described later, the case where a numerical value is not described indicates that the film broke during stretching.

In Table 1 and FIGS. 4(A) and 5(A) showing the results of transverse stretching of the laminated film using the PETI support, at level 1 where the end portion of the film was held as it was, breakage occurred even at a low draw ratio, and the optical axis It can be seen that the deviation is large and the effective width is small. In level 2 where a tape was bonded to the end of the film, breakage was less likely to occur than in level 1, and it was found that the deviation of the optical axis was small and the effective width increased even when contrasted at the same draw ratio. At level 5 where the film is folded back and fixed with double-sided tape, the stretchable magnification (stretch magnification within the range where no breakage occurs) is equivalent to that of level 2, but when compared at the same stretch magnification, the deviation of the optical axis becomes smaller than at level 2. Yes, the effective width has increased. From these results, it can be seen that an optically anisotropic film having a large effective width is obtained by overlapping the film of the same material on the edge portion of the TD, compared to the case where a tape is simply bonded.

In levels 3 and 4 in which films are superimposed without an adhesive layer such as tape interposed therebetween, the stretchable magnification is higher than in level 5. Further, when contrasted at the same draw ratio, it can be seen that at levels 3 and 4, the deviation of the optical axis is smaller than at level 5, and the effective width is increased. From these results, it can be seen that the stretchable magnification is increased and an optically anisotropic film with a large effective width is obtained by overlapping a film of the same material on the end portion of the TD without an adhesive layer interposed therebetween.

Table 2, Fig. 4(B) and Fig. 5(B) showing the results of transverse stretching of the multilayer film using the PP support also showed the same tendency as Table 1, Fig. 4(A) and Fig. 5(A), and It turns out that the optically anisotropic film with a large effective width was obtained because the film of material overlaps the edge part of TD. From these results, by carrying out transverse stretching while holding the folded portion of the film or the portion where the cut pieces overlap, film breakage is difficult to occur and stretching at a high draw ratio is possible, and the deviation of the optical axis is small, so that the effective width can be increased. It can be seen that a broad optically anisotropic film is obtained.

[Example 2]

In Example 2, as shown in Fig. 6, from the inlet side to the outlet side, the holding zone (A), the preheating zone (B), the stretching zone (C), the shrinking zone (D), and the release zone (E) Oblique stretching was performed using the stretching machine formed in this order. The drawing zone C is composed of an entry-side drawing zone C1 and an exit-side drawing zone C2. In these drawing zones, the clip pitches of the left and right clips 51, 52 are independently varied, respectively, and the inclination is Stretching was performed to prepare an obliquely stretched film having an optical axis in a direction of about 45° with respect to the MD. As in Example 1, the uniformity of the optical axis of the stretched film according to the difference in gripping methods of both ends of the film was evaluated.

[Example 2-1: Oblique Stretching of Polycarbonate Film]

As the bisphenol component, 9,9-[4-(2-hydroxyethoxy)phenyl]fluorene (BHEPF), isosorbide (ISB) and diethylene glycol (DEG) were used, BHEPF/ISB/DEG = 34.8/ A copolymerized polycarbonate film containing a molar ratio of 49.0/16.2 and having a thickness of 145 μm was used.

[Oblique Stretching]

Using a tenter clip type biaxial stretching machine, both ends of the polycarbonate film were held by clips under conditions of levels 1 to 5 as in Example 1, and oblique stretching was performed at a temperature of 143°C. The distance between the clips at both ends at the time of gripping was set to film width -50 mm (left and right clip width: 25 mm). At the same time that the film entered the entry-side drawing zone C1, transverse stretching was performed by increasing the distance between the left and right clips, while the pitch of the left clip 51 was reduced and the pitch of the right clip 52 was increased. In the exit-side drawing zone C2, transverse stretching is performed by increasing the distance between the left and right clips, while the pitch of the right clips 52 is kept constant, and the left clips are stretched until the pitch becomes the same as that of the right clips 52. (51) was increased.

Diagonal stretching was performed by changing the input film width (film width before stretching) and the stretching ratio, and the neck-in rate, the range of the optical axis, and the effective width were evaluated in the same manner as in Example 1. A draw ratio and evaluation result are shown in Table 3.

The MD shrinkage ratio and MD draw ratio in Table 3 are the rates of change in the pitches of the left clip and the right clip in the entry-side drawing zone C1, respectively. The TD stretch magnification is the ratio of the distance W ₀ between the clips at the time of holding to the distance W ₁ between the clips of the TD at the exit. The oblique stretch magnification is the ratio of the distance W ₀ between the left and right clips at the time of gripping and the distance W ₂ between the corresponding left and right clips at the exit. As in Example 1, the neck-in rate was calculated from the ratio of the maximum width to the minimum width in the width direction of the film after stretching. The optical axis range is the difference between the maximum value and the minimum value measured at 10 mm intervals by TD in the range of 1300 mm in the center of the TD, and the orientation angle of the optical axis is within the range of ± 3 ° of the optical axis orientation angle at the center of the TD. The width of is the effective width.

[Example 2-2: Oblique Stretching of Polyester Film]

Polyethylene naphthalate resin (Theonex manufactured by Teijin) was formed into a film by a melt extrusion method to obtain a film having a thickness of 200 μm. Using this film, oblique stretching was performed at a stretching temperature of 130°C in the same manner as in Example 2-1, and the neck-in rate, optical axis range, and effective width were evaluated for gripping methods of levels 1, 3, and 4. . In Example 2-2, the optical axis range was set to 1600 mm at the center of the TD, and the range of ±2° of the optical axis orientation angle was set as the effective width. Other than that, evaluation was performed on the same criteria as in Example 2-1. A draw ratio and evaluation result are shown in Table 4.

In Examples 2-1 and 2-2 subjected to oblique stretching, the same tendency as in Example 1 was observed. That is, compared to level 1 where the film end was held as it was and level 2 where the tape was bonded to the film end, at levels 3 to 5, stretching at a high draw ratio was possible, and it was found that the effective width could be expanded. .

In oblique stretching, compared to normal transverse stretching, since the difference in stretching behavior in the vicinity of the gripping portion by the clip and other portions is large, the effective width tends to be narrow and the deviation of the optical axis range increases. For example, at the level of 3 times the oblique stretch magnification of Example 2-2 (see Table 4), for a distance between exit clips of 2316 mm, the range of about 350 mm at both ends is removed, and 1600 mm in the center in the width direction is removed. The optical axis is measured in the range of In this way, even at the central part in the width direction, which is far away from the gripping position, there is a significant difference in the range of the optical axis between gripping level 1 and levels 2 and 3, and the difference in gripping method at both ends greatly affects the uniformity of the optical axis. it can be seen that there is

10: film to be stretched
15: laying film (folding part)
17: laying film (cut piece)
31: double-sided tape
35: tape
51, 52: gripper

Claims (8)

a step of gripping both ends of the band-shaped film to be stretched in the width direction with a gripper; And, while moving the gripper in the longitudinal direction of the film to be stretched, the distance between the grippers in the width direction is widened to stretch the film to be stretched in the width direction As a manufacturing method of an optically anisotropic film,
Gripping by the gripping tool is carried out in a state where a strip-shaped laying film is superimposed on the end of the stretching target film in the width direction,
At least one layer of the laying film superimposed on the film to be stretched is made of the same material as at least one layer of the film to be stretched,
The film to be stretched is a laminate in which a coating film is tightly laminated on a support film having heat shrinkability in the longitudinal direction,
In the step of stretching the film to be stretched in the width direction, the optically anisotropic film shrinks the film to be stretched in the longitudinal direction by increasing the distance between the grippers in the width direction and reducing the distance between the grippers in the longitudinal direction. manufacturing method. According to claim 1,
The manufacturing method of the optically anisotropic film in which the said laying film contains at least the said support film. According to claim 1,
The manufacturing method of the optically anisotropic film, wherein the laying film has the same laminated structure as the laminate. a step of gripping both ends of the band-shaped film to be stretched in the width direction with a gripper; And, while moving the gripper in the longitudinal direction of the film to be stretched, the distance between the grippers in the width direction is widened to stretch the film to be stretched in the width direction As a manufacturing method of an optically anisotropic film,
Gripping by the gripping tool is carried out in a state where a strip-shaped laying film is superimposed on the end of the stretching target film in the width direction,
At least one layer of the laying film superimposed on the film to be stretched is made of the same material as at least one layer of the film to be stretched,
In the step of stretching the film to be stretched in the width direction, the movement speed in the longitudinal direction of a gripper for gripping one end of the film to be stretched in the width direction and the other end in the width direction of the film to be stretched are gripped. A method for producing an optically anisotropic film, wherein the film to be stretched is obliquely stretched by different moving speeds in the longitudinal direction of the holding tool. According to claim 4,
The film to be stretched is a single layer film,
The method for producing an optically anisotropic film, wherein the laying film is made of the same material as the film to be stretched. According to any one of claims 1 to 5,
The method of manufacturing an optically anisotropic film, wherein the laying film is a folded portion obtained by folding and overlapping an end portion of the film to be stretched. According to any one of claims 1 to 5,
The method of manufacturing an optically anisotropic film, wherein the laid film is a cut piece of the film to be stretched. According to any one of claims 1 to 5,
A method for producing an optically anisotropic film in which the film to be stretched and the laid film are overlapped without an adhesive layer interposed therebetween.

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