CN110103452B

CN110103452B - Film stretching apparatus and method for producing retardation film

Info

Publication number: CN110103452B
Application number: CN201910093366.0A
Authority: CN
Inventors: 清水享; 千田裕树; 山本真士
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2018-02-01
Filing date: 2019-01-30
Publication date: 2022-09-27
Anticipated expiration: 2039-01-30
Also published as: CN110103452A; JP2019133063A; JP7020942B2

Abstract

The invention provides a film stretching device and a method for manufacturing a retardation film, wherein a clamp for holding the film is smoothly opened after the oblique stretching is finished. A clamp type film stretching device comprises variable-pitch left and right clamps which pass through a stretching zone while holding left and right ends of a film to be stretched, and in which the clamp pitch in the longitudinal direction of at least one clamp changes as the clamp passes, wherein the clamps comprise upper and lower holding members which hold and hold the ends of the film, and at least the corners on the inner side of the upper holding member in the film width direction are chamfered portions having a chamfer size of more than 0mm and 20mm or less.

Description

Film stretching apparatus and method for producing retardation film

Technical Field

The present invention relates to a film stretching apparatus and a method for producing a retardation film.

Background

In image display devices such as Liquid Crystal Displays (LCDs) and organic electroluminescent displays (OLEDs), circularly polarizing plates are used for the purpose of improving display characteristics and antireflection. Typically, a circularly polarizing plate is formed by laminating a polarizer and a retardation film (typically, a λ/4 plate) so that the absorption axis of the polarizer and the slow axis of the retardation film form an angle of 45 °. Conventionally, a retardation film is typically produced by uniaxial stretching or biaxial stretching in the longitudinal direction and/or the transverse direction, and therefore, the retardation axis thereof is in many cases expressed in the transverse direction (width direction) or the longitudinal direction (longitudinal direction) of a film roll. As a result, in order to produce a circular polarizing plate, the following operations are required: the retardation film was cut at an angle of 45 ° with respect to the width direction or the longitudinal direction and laminated one by one.

In order to solve such a problem, the following technique is proposed: the retardation film is stretched in an oblique direction by holding the left and right end portions (end portions in the width direction) of the elongated film with the left and right clamps of a variable pitch type having a variable clamp pitch in the longitudinal direction, and changing the clamp pitch of at least one of the left and right clamps to thereby cause the retardation axis of the retardation film to appear in an oblique direction (for example, patent document 1). However, with such an oblique stretching technique, the stretched film may be caught by a clamp and the clamp may not be smoothly opened.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4845619

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above problems, and an object of the present invention is to smoothly open a clamp that holds a film after oblique stretching is completed.

Means for solving the problems

In accordance with 1 aspect of the present invention, there is provided a clip type film stretching apparatus having variable-pitch left and right clips which pass through a stretching region while gripping left and right end portions of a film to be stretched, and in which a clip pitch in a longitudinal direction of at least one of the clips changes as the passing passes. In the film stretching apparatus, the jig includes an upper holding member and a lower holding member, the upper holding member and the lower holding member hold an end portion of the film therebetween, and at least a corner portion on an inner side in a film width direction of the upper holding member is a chamfered portion having a chamfered dimension of more than 0mm and 20mm or less.

In 1 embodiment, the corner portions on the inner side in the film width direction of both the upper holding member and the lower holding member are chamfered to have a chamfer dimension of more than 0mm and 20mm or less.

In 1 embodiment, in any one of the left and right grippers, the chamfered portion is formed only at a corner portion on the downstream side in the direction of travel and on the inside in the direction of film width of both the upper gripping member and the lower gripping member, and in the other gripper, the chamfered portion is formed only at a corner portion on the upstream side in the direction of travel and on the inside in the direction of film width of both the upper gripping member and the lower gripping member.

In 1 embodiment, the position of the film at a distance of 20mm or more from the left and right end edges is held by the jig.

In 1 embodiment, a length of a film gripping surface defined by overlapping of a bottom surface of the upper gripping member and an upper surface of the lower gripping member in a direction orthogonal to a traveling direction of the jig is 15mm or more.

In 1 embodiment, a length of a film gripping surface defined by an overlap between a bottom surface of the upper gripping member and an upper surface of the lower gripping member in a traveling direction of the jig is 30mm or more.

By adopting another technical scheme of the invention, the invention provides a manufacturing method of the phase difference film, which comprises the following steps: gripping left and right ends of a film to be stretched by left and right variable-pitch clamps having a variable clamp pitch in the longitudinal direction; preheating the film; a step of obliquely stretching the film by changing the distance between the left and right clamps; and opening the jig holding the film. In the method for producing a retardation film, the jig has an upper holding member and a lower holding member, the upper holding member and the lower holding member hold an end portion of the film by sandwiching the film, and at least a corner portion on an inner side in a film width direction of the upper holding member is a chamfered portion having a chamfered dimension of more than 0mm and 20mm or less.

In 1 embodiment, the method for producing the retardation film is performed using the clip film stretching apparatus.

In 1 embodiment, the method for producing a retardation film is performed using the above-described jig-type film stretching device, and the film is obliquely stretched by changing the pitch of at least one of the left and right clamps such that the clamp in which only the inner corner portion in the film width direction and the downstream corner portion in the traveling direction of both the upper holding member and the lower holding member are chamfered advances first, and the clamp in which only the inner corner portion in the film width direction and the upstream corner portion in the traveling direction of both the upper holding member and the lower holding member are chamfered advances later.

In 1 embodiment, the above-mentioned oblique stretching comprises transverse stretching.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the film stretching apparatus and the method for producing a retardation film of the present invention, since the film is stretched in an oblique direction by using the jig having the chamfered portion, the film can be prevented from being caught by the jig, and therefore the jig can be smoothly opened.

Drawings

Fig. 1 is a schematic plan view illustrating the overall configuration of a stretching apparatus according to 1 embodiment of the present invention.

Fig. 2 is a schematic plan view of a main part for explaining a link mechanism for changing a clip pitch in the stretching apparatus of fig. 1, and shows a state where the clip pitch is minimum.

Fig. 3 is a schematic plan view of a main part for explaining a link mechanism for changing a clip pitch in the stretching apparatus of fig. 1, and shows a state where the clip pitch is maximum.

Fig. 4 is a side view of the main part for explaining the structure and the opened state of the clamp.

Fig. 5 is a side view schematically showing a main part for explaining the structure and the closed state of the clip.

Fig. 6 is a schematic diagram showing a top view of an upper holding member or a lower holding member that can be used in the present invention.

Fig. 7 is a schematic diagram illustrating the amount and length of film gripping by the film gripping surface, the gripping position, and the distance between the grippers.

Fig. 8 is a schematic view illustrating a method for producing a retardation film according to 1 embodiment of the present invention.

Fig. 9 is a schematic diagram illustrating an example of oblique stretching.

Fig. 10 is a graph showing the relationship between each step of the oblique stretching shown in fig. 9 and the clamp pitch.

Fig. 11 is a schematic diagram illustrating a relationship between an example of oblique stretching and the formula (1).

Fig. 12 is a schematic diagram illustrating the jig moving speed and the equation (1) on the left and right sides in an example of oblique stretching.

Fig. 13 is a schematic diagram illustrating the jig moving speed and the equation (1) on the left and right sides in another example of the oblique stretching.

Fig. 14 is a schematic plan view of a main part of a stretched film with an enlarged end portion for explaining a method of measuring a neck-in amount.

Fig. 15 is a schematic view of a gripping state in which an end portion of a film is gripped by a gripper as viewed in a horizontal direction.

Description of the reference numerals

10L, endless loop; 10R, endless loop; 20. a clamp; 22. a lower holding member; 22b, a chamfer portion; 26. an upper holding member; 26a, a pressing portion; 26b, a chamfer part; 28. a film holding surface; 30. a clamp carrying member; 70. a reference track; 90. a pitch setting track; 100. a stretching device; 200. a film.

Detailed Description

A. Film stretching device

In accordance with 1 aspect of the present invention, there is provided a clip type film stretching apparatus having variable-pitch left and right clips which pass through a stretching zone while gripping left and right end portions (end portions in a width direction) of a film to be stretched, and in which a clip pitch in a longitudinal direction of at least one of the clips changes as the passing passes. Hereinafter, 1 embodiment of the film stretching apparatus of the present invention will be described, but the present invention is not limited to these embodiments.

1 embodiment of a film stretching apparatus according to the present invention will be described with reference to fig. 1 to 5. Fig. 1 is a schematic plan view illustrating the overall configuration of an example of the film stretching apparatus of the present invention. Fig. 2 and 3 are schematic plan views of main portions for explaining a link mechanism for changing a clip pitch in the stretching apparatus of fig. 1, respectively, fig. 2 showing a state where the clip pitch is minimum, and fig. 3 showing a state where the clip pitch is maximum. Fig. 4 and 5 are schematic side views of main portions for explaining the structure and the open/close state of the jig.

As shown in fig. 1, the stretching device 100 has an endless loop 10L and an endless loop 10R in bilateral symmetry on both left and right sides in a plan view, and the endless loop 10L and the endless loop 10R have a plurality of jigs 20 for film gripping. In the present specification, the left-side endless loop is referred to as a left-side endless loop 10L, and the right-side endless loop is referred to as a right-side endless loop 10R, as viewed from the inlet side of the film. The jigs 20 of the left and right

endless loops

10L and 10R are guided by the reference rails 70 to circulate in a loop. The left endless loop 10L circularly moves in the counterclockwise direction, and the right endless loop 10R circularly moves in the clockwise direction. In the stretching apparatus, a holding zone a, a preheating zone B, a stretching zone C, and a releasing zone D are provided in this order from the sheet inlet side toward the sheet outlet side. The respective regions are regions where the film to be stretched is substantially gripped, preheated, stretched, and released from the jig, and do not mean mechanically and structurally independent regions. In addition, it should be noted that the ratio of the lengths of the respective regions is different from the ratio of the actual lengths. Further, an area for performing an arbitrary appropriate process may be provided between the stretch zone C and the release zone D as needed, which is not shown. Examples of such treatment include longitudinal shrinkage treatment and transverse stretching treatment.

In the holding zone a and the preheating zone B, the left and right

endless loops

10L and 10R are configured to be substantially parallel to each other with a separation distance corresponding to the initial width of the film to be stretched. In the stretching zone C, the distance separating the left and right

endless loops

10L and 10R gradually increases from the preheating zone B toward the discharge zone D to a width corresponding to the stretched width of the film. In the release zone D, the left and right

endless loops

10L, 10R are configured to be substantially parallel to each other with a separation distance corresponding to the stretched width of the film.

The jig (left jig) 20 of the left endless loop 10L and the jig (right jig) 20 of the right endless loop 10R are capable of independent circulating movement. For example, the driving

sprockets

11 and 12 of the left endless loop 10L are driven by the

electric motors

13 and 14 to rotate counterclockwise, and the driving

sprockets

11 and 12 of the right endless loop 10R are driven by the

electric motors

13 and 14 to rotate clockwise. As a result, a traveling force is applied to the jig carrier member 30 engaged with the driving rollers (not shown) of the driving

sprockets

11 and 12. Thereby, the left endless loop 10L circularly moves in the counterclockwise direction, and the right endless loop 10R circularly moves in the clockwise direction. By driving the left electric motor and the right electric motor independently, the left endless loop 10L and the right endless loop 10R can be independently circulated.

The jig (left jig) 20 of the left endless loop 10L and the jig (right jig) 20 of the right endless loop 10R are variable pitch type jigs, respectively. That is, the left and

right jigs

20, 20 can change the jig pitch in the longitudinal direction independently of the movement. The variable pitch type configuration can be realized by adopting a known drive system such as a zoom system, a linear motor system, and a motor/chain system. Hereinafter, a link mechanism (pantograph mechanism) will be described as an example.

As shown in fig. 2 and 3, a jig carrier member 30 having a rectangular shape elongated in the transverse direction in plan view is provided for carrying the jigs 20 one by one. The jig carrier member 30 is formed into a strong frame structure having a closed cross section by an upper beam, a lower beam, a front wall (a wall on the jig side) and a rear wall (a wall on the side opposite to the jig side), and is not shown. The jig carrier member 30 is provided so as to roll on the

travel paths

81 and 82 by the travel wheels 38 at both ends thereof. In fig. 2 and 3, the traveling wheels on the front wall side (traveling wheels that roll on the traveling road surface 81) are not shown. The

travel surface

81, 82 is parallel to the reference rail 70 over the entire area. On the rear side (the side opposite to the side where the jig is located) of the upper beam and the lower beam of the jig carrying member 30, long holes 31 are formed along the longitudinal direction of the jig carrying member, and sliders 32 are engaged with the long holes 31 so as to be slidable in the longitudinal direction of the long holes 31. One 1 st shaft member 33 is provided vertically so as to penetrate the upper beam and the lower beam in the vicinity of the end portion of the jig 20 side of the jig carrier member 30. On the other hand, one second shaft member 34 is provided to the slider 32 of the jig carrier member 30 so as to vertically penetrate the slider 32. One end of a main link member 35 is pivotally connected to the 1 st shaft member 33 of each of the jig carrier members 30. The other end of the main link member 35 is pivotally coupled to the 2 nd shaft member 34 of the adjacent jig carrier member 30. The 1 st shaft member 33 of each of the jig carrier members 30 is pivotally connected to one end of a sub link member 36 in addition to a main link member 35. The other end of the sub link member 36 is pivotally coupled to the intermediate portion of the main link member 35 via a pivot shaft 37. With the link mechanism composed of the main link member 35 and the sub link member 36, as shown in fig. 2, the distance between the jig carrier members 30 adjacent in the longitudinal direction decreases (as a result, the distance between the carried jigs decreases) as the slider 32 moves to the rear side (the opposite side to the jig side) of the jig carrier member 30, and as shown in fig. 3, the distance increases as the slider 32 moves to the front side (the jig side) of the jig carrier member 30. The slide 32 is positioned by the pitch setting track 90. As shown in fig. 2 and 3, the larger the pitch, the smaller the separation distance between the reference rail 70 and the pitch setting rail 90. Further, the link mechanism is a well-known mechanism in the art, and therefore, a more detailed description is omitted.

The jig 20 grips the film 200 so that the film 200 can be engaged with and disengaged from the jig. In the embodiment illustrated in fig. 4 and 5, the jig 20 has: a jig main body 21 having a longitudinal sectional shape substantially shaped like japanese コ; a lower holding member 22 having a substantially rectangular flat plate shape and attached to the jig main body 21; an elevating lever 24 rotatably attached to the jig main body 21 via an attachment shaft member 23; and an upper holding member 26 attached to a lower end of the lifter lever 24 via an attachment shaft member 25 so as to be swingable, the upper holding member 26 having a pressing portion 26a having a substantially rectangular flat plate shape.

The lower holding member 22 is fixed to the jig main body 21 by any fixing method such as screwing, bonding, welding, or the like.

The upper gripping member 26 moves up and down in accordance with the rotation of the lifting lever 24. Specifically, the upper holding member 26 is obliquely lifted toward the outside in the width direction of the film as the lift lever 24 rises in the vertical direction. At this time, the clamp is opened and the film is not gripped (fig. 4). On the other hand, when the lift lever 24 is rotated obliquely about the mounting shaft member 23, the upper holding member 26 is also lowered obliquely inward in the film width direction, and the end of the film 200 is gripped by the pressing portion 26a and the lower holding member 22 (fig. 5). Further, although fig. 4 and 5 show a jig for gripping a film in a so-called slide-in manner, the upper gripping member may be lowered in a vertical direction to grip the film, unlike the example shown in the figure. The upper gripping member 26 does not have to be a separate member from the lift lever, and may be integrally formed at the lower end of the lift lever.

In the present invention, at least the corner portion on the inner side in the film width direction of the upper gripping member 26 (specifically, the pressing portion 26a) is formed as the chamfered portion 26 b. As illustrated in fig. 4 and 5, the corners of the upper gripping member 26 (specifically, the pressing portion 26a) and the lower gripping member 22 on the inner side in the film width direction are preferably chamfered

portions

26b and 22 b. By forming the

chamfered portions

26b, 22b, the film can be prevented from being caught on the clip when the clip is opened. The reason for this effect is not necessarily determined, but can be estimated as follows, for example. That is, in the oblique stretching, stress is generally easily concentrated on the corners of the jig (specifically, the upper holding member and the lower holding member), and the film is inserted into and deformed at the corners on the inner side in the film width direction, which causes a problem that the film is shaken when the jig is opened and the film is caught by the jig. In contrast, by chamfering the corner portions, even if the film is deformed, it is possible to suppress the problem that the jig is fitted into the film. As a result, it is possible to prevent the film from shaking when the clip is opened and to prevent the film from being caught by the clip.

Fig. 6 (a) to 6 (f) are schematic diagrams each showing a plan view shape of an upper holding member or a lower holding member that can be used in the present invention (the upper side in the drawing is the inner side in the film width direction). As shown in fig. 6 (a) to 6 (f), the upper holding member or the lower holding member has a substantially rectangular shape having at least 1 corner portion on the inner side in the film width direction in a plan view, which is a chamfered

portion

26b or 22 b. Specifically, in the embodiments illustrated in fig. 6 (a), 6 (d), and 6 (f), the chamfered portion is formed only at one corner portion on the inner side in the width direction, whereas in the embodiments illustrated in fig. 6 (b) and 6 (e), the chamfered portions are formed at both corner portions on the inner side in the width direction. In addition, the chamfered portion may be formed not only at the corner portion on the inner side in the width direction but also at one or both corner portions on the outer side in the width direction. For example, in the embodiment shown in fig. 6 (c), 4 corners are each set as a chamfered portion.

The

chamfered portions

26b and 22b may be formed linearly or in a curved shape. In the present specification, even when chamfering is performed in a plurality of straight lines in a plurality of stages, the chamfered

portions

26b and 22b are chamfered linearly. For example, the chamfered

portions

26b and 22b are curved so-called R chamfered portions in the embodiment shown in fig. 6 (a) to 6 (C), straight so-called C chamfered portions in the embodiments shown in fig. 6 (d) and 6 (e), and chamfered straight in three stages in the embodiment shown in fig. 6 (f). The present invention is not limited to the above-described examples. For example, a combination of a linear chamfer and a curved chamfer may be provided. Further, two or more chamfered portions having different chamfer sizes may be provided to 1 holding member.

In 1 embodiment, in any one of the left and right clamps, the chamfered portion is formed only at the corner portion on the inner side in the film width direction and on the downstream side in the traveling direction of both the upper gripping member (specifically, the pressing portion) and the lower gripping member, and in the other clamp, the chamfered portion is formed only at the corner portion on the inner side in the film width direction and on the upstream side in the traveling direction of both the upper gripping member (specifically, the pressing portion) and the lower gripping member. By providing the chamfered portions in a left-right asymmetrical manner as described above, it is possible to preferably prevent the film from wobbling when the jig is opened and the film from being caught on the jig, and to preferably exhibit the effect of preventing the film from being deformed by the jig (specifically, the upper holding member and the lower holding member), thereby suppressing the film from being broken due to the necking-down and stretching. The effect of preventing the film from being deformed by the jig will be described later.

The

chamfered portions

26b and 22b are formed so that chamfer dimensions (lengths of sides cut from the corner tips) x and y are both greater than 0mm and 20mm or less. The chamfer dimension x and the chamfer dimension y may be equal to each other or different from each other. Preferably, are arranged equal to each other. When the chamfer size is increased, the effect of preventing the film deformation by the jig is impaired, and the neck-in tends to increase, and the film tends to be easily broken during stretching. Therefore, the chamfer size is preferably small within a range in which the effects of the present invention can be obtained. For example, the chamfer dimensions x and y may be each preferably 1mm or more and 15mm or less, more preferably 3mm or more and 10mm or less, and still more preferably about 5 mm.

Typically, the chamfered portion is formed by chamfering (cutting) a target corner portion, but the method of forming the chamfered portion is not limited as long as the corner portion is a chamfered portion, and for example, the chamfered portion may be formed using a die or a mold.

When the film is gripped, the pressing portion 26a of the upper gripping member and the lower gripping member 22 may have outer circumferential shapes that completely overlap in a plan view, or may have a non-overlapping portion in a plan view. In the case where there is a non-overlapping portion, from the viewpoint of preferably obtaining the effect of the present invention, it is preferable that the pressing portion 26a and the lower gripping member 22 are overlapped so that the peripheries of the edge on the inner side in the film width direction and the chamfered portions (corner portions in the case where there are chamfered portions) at both ends thereof are in the same position in a plan view.

When gripping the film, the gripper (specifically, the upper gripping member and the lower gripping member) preferably grips the film at a position spaced apart from the left and right end edges by a distance of 20mm or more, and more preferably at a position spaced apart from the left and right end edges by a distance of 25mm or more. To describe in more detail with reference to fig. 7, the film is gripped such that a distance D from the edge of the film 200 to the innermost portion (hereinafter, also referred to as a "nip position") in the film width direction of the film gripping surface 28 is preferably 20mm or more. By holding such a position with a jig, breakage of the thin film can be suppressed. Further, the neck-in can be suppressed, and as a result, the uniformly stretched region is enlarged, so that the effect of increasing the effective area can be obtained. The upper limit of the distance from the edge of the film to the nip position may be, for example, 60 mm. In the present specification, the film gripping surface refers to a surface of the film sandwiched between the upper gripping member 26 (specifically, the pressing portion 26a) and the lower gripping member 22, and is defined by the overlap between the bottom surface of the upper gripping member 26 and the upper surface of the lower gripping member 22 when the film is gripped. The clamping position can be controlled by adjusting the separation distance of the reference rails, for example.

As shown in fig. 7, when the length of the film gripping surface 28 in the running direction of the jig (extending direction of the reference rail) is defined as a gripping length (L) and the length of the film gripping surface 28 in the direction orthogonal to the running direction of the jig is defined as a gripping amount (W), the gripping amount (W) is preferably 15mm or more, more preferably 20mm or more, and still more preferably 25mm or more. The holding amount (W) can be, for example, 60mm or less. On the other hand, the holding length (L) is, for example, 20mm or more, preferably 30mm or more, more preferably 35mm or more, and further preferably 40mm or more. The grip length (L) can be, for example, 80mm or less. By setting the gripping amount or the gripping length within such a range, the film gripping surface becomes a large surface, and therefore, stress concentration to the peripheral edge of the jig can be alleviated, and breakage of the film can be suppressed. Further, the clip (specifically, the upper holding member and the lower holding member) functions as a wall for preventing deformation of the film, and can suppress the neck-in.

The grip ratio represented by the following formula is preferably 50% or more. The holding ratio is more preferably 70% or more, still more preferably 80% or more, and still more preferably 90% or more. When the holding ratio is within such a range, the film can be prevented from breaking or shrinking. Further, the film can be prevented from being deformed or broken by being caught by the clip when the clip is opened.

The holding ratio (%) — holding amount/distance from the film edge to the holding position × 100

B. Method for producing retardation film

By adopting another technical scheme of the invention, the invention provides a manufacturing method of the phase difference film, which comprises the following steps: a step (gripping step) of gripping the left and right ends of a film to be stretched by a variable-pitch-type left and right gripper having a variable gripper pitch in the longitudinal direction; a step of preheating the thin film (preheating step); a step of obliquely stretching the film by changing the distance between the left and right clamps (oblique stretching step); and a step (opening step) of opening the jig holding the film. In the method for producing a retardation film, a jig having an upper holding member and a lower holding member is used, the upper holding member and the lower holding member hold an end portion of a film by sandwiching the film, and at least a corner portion on the inner side in the film width direction of the upper holding member is a chamfered portion having a chamfered dimension of more than 0mm and 20mm or less. Preferably, the chamfered portion is provided at an inner corner in the film width direction of both the upper holding member and the lower holding member. The chamfer size may be preferably 1mm or more and 15mm or less, more preferably 3mm or more and 10mm or less, and still more preferably about 5 mm. According to the method for producing a retardation film, since the film can be prevented from being caught by the jig when the jig is opened, a retardation film having a retardation axis in an oblique direction (for example, in a direction of 45 ° with respect to the longitudinal direction) can be efficiently produced.

The method for producing the retardation film is preferably carried out by using the stretching apparatus described in the above item A. Hereinafter, each step will be described in detail using an embodiment in which the stretching apparatus described in item a is used as a specific example. In the present specification, the "jig pitch in the longitudinal direction" (which may be simply referred to as a "jig pitch") refers to a distance between centers of the jigs adjacent in the longitudinal direction in the traveling direction (more specifically, a distance between centers of the film gripping surfaces in the traveling direction), and is a distance indicated by P in fig. 7.

[ B-1. holding Process ]

The film to be stretched is first gripped at both ends thereof by the grippers 20 of the left and right

endless loops

10L and 10R at a constant gripper pitch equal to each other or at different gripper pitches from each other in the gripping zone a (an entrance of the stretching apparatus 100 into which the film is taken). The jig pitch of the left and right jigs in the gripping step can be appropriately set according to a desired phase difference, shaft angle, and the like. The clamp pitch can be, for example, 50mm to 180 mm. In this specification, the end portion of the film means a uniform region which is spaced from the end edge of the film by the entire width of the film.

The position to be sandwiched in the holding step is preferably a position at which the longitudinal film is spaced apart from the left and right end edges (end edges in the width direction) by a distance of 20mm or more, and more preferably a position at which the longitudinal film is spaced apart from the left and right end edges (end edges in the width direction) by a distance of 25mm or more. The distance from the edge of the film to the nip position may be, for example, 60mm or less. By holding such a position with a jig, breakage of the thin film can be suppressed. Further, since the contraction can be suppressed, and as a result, the uniformly stretched region is enlarged, an effect of increasing the effective area can be obtained.

The film holding surface is preferably a large surface. By making the film holding surface a large surface, stress concentration on the jig can be relaxed, and breakage of the film can be suppressed. Further, the jig functions as a wall for preventing deformation of the film, and can suppress the neck-in. Specifically, as described in the above item a, the gripping amount (W) of the jig can be preferably 15mm or more, more preferably 20mm or more, further preferably 25mm or more, and for example, 60mm or less. The gripping length (L) may be, for example, 20mm or more, preferably 30mm or more, more preferably 35mm or more, further preferably 40mm or more, and, for example, 80mm or less.

The film is conveyed to the preheating zone B by the movement of the left and right

endless loops

10L, 10R (substantially the movement of each of the jig carrying members guided by the reference rails 70) without being stretched in the lateral direction and the longitudinal direction while being held by the jig.

[ B-2. preheating step ]

In the preheating zone B, the left and right

endless loops

10L and 10R are configured to be substantially parallel to each other with a separation distance corresponding to the initial width of the film to be stretched as described above, and therefore the film can be heated without being stretched substantially in the transverse direction and the longitudinal direction. However, in order to avoid the occurrence of defects such as deflection of the film due to preheating, contact with the nozzle in the oven, and the like, the distance between the left and right clamps (distance in the width direction) may be slightly increased.

In the preheating, the film was heated to a temperature T1 (. degree. C.). The temperature T1 is preferably not lower than the glass transition temperature (Tg) of the film, more preferably not lower than Tg +2 ℃, and still more preferably not lower than Tg +5 ℃. On the other hand, the heating temperature T1 is preferably Tg +40 ℃ or lower, more preferably Tg +30 ℃ or lower. The temperature T1 is, for example, 70 ℃ to 190 ℃ and preferably 80 ℃ to 180 ℃ although the temperature varies depending on the film used.

The temperature rise time at the temperature T1 and the holding time at the temperature T1 can be appropriately set depending on the constituent material of the film and the production conditions (for example, the film transport speed). These temperature rise time and holding time can be controlled by adjusting the moving speed of the jig 20, the length of the preheating zone, the temperature of the preheating zone, and the like.

[ oblique drawing step ]

In the stretching zone C, the film is obliquely stretched by changing the nip pitch in the longitudinal direction of at least one of the left and right nips 20. More specifically, by changing the clip pitch in the longitudinal direction of at least one of the left and right clips 20 during the passage in the stretching zone C, the film can be obliquely stretched by advancing the one clip first and advancing the other clip later. Typically, the rate of change in the clip pitch of the left and right clips at the end of the stretching zone C, that is, at the end of the oblique stretching (clip pitch at the end of the oblique stretching/clip pitch before the oblique stretching) is substantially equal to each other.

In the 1 embodiment, as shown in fig. 8, the jig (in the illustrated example, the left jig) in which the chamfered portion is formed only at the corner portion on the inner side in the film width direction and on the downstream side in the traveling direction of both the upper holding member and the lower holding member is advanced first, and the jig (in the illustrated example, the right jig) in which the chamfered portion is formed only at the corner portion on the inner side in the film width direction and on the upstream side in the traveling direction of both the upper holding member and the lower holding member is advanced later. By forming the chamfered portions at these corner portions having a higher stress concentration than the other corner portions, not only the effect of the present invention can be obtained favorably, but also the other corner portions can be maintained, and as a result, the effect of preventing deformation of the film can be maintained, and breakage of the film due to necking-in and stretching can be suppressed favorably.

The oblique stretching may or may not include the transverse stretching. For example, as in the illustrated example, the stretching may be performed while the distance between the left and right clamps (the distance in the width direction) is increased, or the stretching may be performed while the distance between the left and right clamps is maintained, unlike the illustrated example. Preferably, the oblique stretching comprises transverse stretching.

In the case where the oblique stretching includes transverse stretching, the stretching ratio in the Transverse Direction (TD) (width W of the film after the oblique stretching) _final Relative to the initial width W of the film _initial Ratio of (W) _final /W _initial ) Preferably 1.05 to 6.00, and more preferably 1.10 to 5.00.

In 1 embodiment, the oblique stretching can be performed by: the jig pitch of each of the left and right jigs is increased or decreased to a predetermined pitch in a state where a position where the jig pitch of one of the left and right jigs starts to increase or decrease and a position where the jig pitch of the other of the left and right jigs starts to increase or decrease are different in the longitudinal direction. For the oblique stretching of this embodiment, for example, patent document 1, japanese patent application laid-open No. 2014-238524 and the like can be referred to.

In another embodiment, the diagonal stretching can be performed by: in a state where the jig pitch of one of the left and right jigs is fixed, the jig pitch of the other jig is increased or decreased to a predetermined pitch and then returned to the original jig pitch. For the oblique stretching of this embodiment, for example, reference can be made to the descriptions of japanese patent application laid-open nos. 2013-54338 and 2014-194482.

In yet another embodiment, the diagonal stretching can be performed by: (i) increasing the jig pitch of one of the left and right jigs and decreasing the jig pitch of the other jig, and (ii) changing the jig pitches of the respective jigs so that the decreased jig pitch and the increased jig pitch become a predetermined equal pitch. For the oblique stretching of this embodiment, for example, reference can be made to the description of japanese patent application laid-open No. 2014-194484 and the like. The oblique stretching of this embodiment may include the steps of: stretching the film in an oblique direction by increasing the distance between the left and right clamps, while increasing the clamp pitch of one clamp and decreasing the clamp pitch of the other clamp (1 st oblique stretching step); and obliquely stretching the film by maintaining or decreasing the clamp pitch of the left and right clamps so that the clamp pitches of the left and right clamps are equal while increasing the distance between the left and right clamps, and increasing the clamp pitch of the other clamp (2 nd obliquely stretching step).

In the first oblique stretching step 1, the film is obliquely stretched while one side edge portion thereof is elongated in the longitudinal direction and the other side edge portion thereof is contracted in the longitudinal direction, whereby the retardation axis can be formed in a desired direction (for example, a direction at 45 ° to the longitudinal direction) with high uniaxiality and in-plane orientation. In the 2 nd oblique stretching step, the oblique stretching is performed while reducing the difference between the left and right jig pitches, whereby the stretching can be sufficiently performed in the oblique direction while relaxing the excessive stress. Further, since the film opening step can be performed in a state where the moving speeds of the left and right clamps are equal, a deviation in the film feeding speed and the like is less likely to occur when the left and right clamps are opened, and the film can be wound up after that.

An example of the oblique stretching in this embodiment will be described below specifically with reference to fig. 9 and 10. First, in the preheating zone B, the clamp pitches on the left and right sides are all set to P ₁ . Typically, P ₁ Is the clamp pitch when holding the film. Next, while the film enters the 1 st diagonal stretching zone C1, the nip pitch of one side (right side in the illustrated example) of the nips starts to increase, and the nip pitch of the other side (left side in the illustrated example) of the nips starts to decrease. In the 1 st diagonal stretching region C1, the clamp pitch of the right clamp is increased to P ₂ Reducing the clamp pitch of the left clamp to P ₃ . Thus, at the terminal end of the 1 st diagonal stretching zone C1 (the starting portion of the 2 nd diagonal stretching zone C2), the left clamps are at the clamp pitch P ₃ Moving, right side clamps by a clamp pitch P ₂ And (4) moving. Further, the ratio of the jig pitches can approximately correspond to the ratio of the moving speeds of the jigs. Therefore, the ratio of the clamp pitch of the left clamp to the clamp pitch of the right clamp can substantially correspond to the ratio of the stretch ratio in the machine direction (MD direction) of the right side edge portion of the film to the stretch ratio in the machine direction (MD direction) of the left side edge portion of the film.

In fig. 9 and 10, both the position where the right-side jig starts to increase in the jig pitch and the position where the left-side jig starts to decrease in the jig pitch are set as the start portions of the 1 st diagonal stretching region C1, but unlike the illustrated example, the jig pitch of the left-side jig may start to decrease after the jig pitch of the right-side jig starts to increase, or the jig pitch of the right-side jig may start to increase after the jig pitch of the left-side jig starts to decrease (not illustrated). In 1 preferred embodiment, the clip pitch of the clip on one side starts to increase and then the clip pitch of the clip on the other side starts to decrease. In this embodiment, since the film is already stretched in the width direction to a certain extent (preferably about 1.2 to 2.0 times), even if the clamp pitch on the other side is greatly reduced, wrinkles are less likely to occur. Therefore, the oblique stretching at a sharper angle can be performed, and a retardation film having high uniaxiality and in-plane orientation can be obtained.

Similarly, in fig. 9 and 10, the jig pitch of the right-side jig is continuously increased and the jig pitch of the left-side jig is continuously decreased until the end of the 1 st diagonal stretching zone C1 (the start of the 2 nd diagonal stretching zone C2), but unlike the illustrated example, the increase or decrease of the jig pitch is terminated before the end of the 1 st diagonal stretching zone C1, and the jig pitch may be maintained until the end of the 1 st diagonal stretching zone C1.

The increased rate of change (P) of the clip pitch ₂ /P ₁ ) Preferably 1.05 to 1.75, more preferably 1.10 to 1.70, and still more preferably 1.15 to 1.65. In addition, reduced rate of change of fixture pitch (P) ₃ /P ₁ ) For example, the content is 0.50 or more and less than 1, preferably 0.50 to 0.95, more preferably 0.55 to 0.93, and still more preferably 0.55 to 0.90. If the rate of change of the clip pitch is within such a range, the slow phase axis can be expressed with high uniaxiality and in-plane orientation in a direction of substantially 45 degrees with respect to the longitudinal direction of the film.

As described above, the jig pitch can be adjusted by adjusting the separation distance between the pitch setting rail and the reference rail of the stretching device and positioning the slider.

Stretching ratio (W) in the width direction of the film in the first oblique stretching step ₂ /W ₁ ) Preferably 1.05 to 3.0 times, more preferably 1.1 to 2.5 times, and still more preferably 1.15 to 2.0 times. If the draw ratio is less than 1.05 times, a corrugated (japanese: トタン -shaped) wrinkle may occur in the side edge portion on the contraction side. When the stretching ratio exceeds 3.0 times, the obtained retardation film has high biaxiality, and when the film is applied to a circularly polarizing plate or the like, the field of view may be increasedThe angular characteristics are degraded.

In 1 embodiment, the 1 st oblique stretching is performed such that the product of the rate of change in the inter-jig distance of the jig on one side and the rate of change in the inter-jig distance of the jig on the other side is preferably 0.7 to 1.5, more preferably 0.8 to 1.45, and still more preferably 0.85 to 1.40. When the product of the change rates is within such a range, a retardation film having high uniaxiality and in-plane orientation can be obtained.

Then, the grip interval of the left grip starts to increase while the film enters the 2 nd diagonal stretching region C2. In the 2 nd diagonal stretching region C2, the grip pitch of the left grip is increased to P ₂ . On the other hand, the clamp pitch of the right clamp is maintained at P in the 2 nd diagonal stretching region C2 ₂ . Thus, at the terminal end portion of the 2 nd diagonal stretching zone C2 (the start portion of the release zone D), both the left and right clamps are at the clamp pitch P ₂ And (4) moving.

The increased rate of change (P) of the jig pitch ₂ /P ₃ ) There is no limitation as long as the effects of the present invention are not impaired. The rate of change (P) ₂ /P ₃ ) For example, 1.1 to 4.0, preferably 1.2 to 3.0.

In 1 embodiment, the 1 st and 2 nd oblique stretching are performed so that the oblique stretching magnification S obtained by the following formula (1) is, for example, 1.5 or more, preferably 2.0 or more, more preferably 2.0 to 4.0, and still more preferably 2.5 to 3.5. When the oblique stretching magnification is less than 1.5, the biaxial orientation is high and the in-plane orientation is low in some cases.

Mathematical formula 1

(in the formula, W ₁ The width of the film before the 1 st oblique stretching is shown,

W ₃ the width of the film after the 2 nd oblique stretching is shown,

v 3' represents the jig moving speed when the jig pitch of the jig is changed to a predetermined jig pitch in the oblique drawing step 2 for the jig on the side where the jig pitch is increased in the oblique drawing step 1,

t3 represents the time from the start of the 2 nd diagonal stretching step to the end of the preheating zone when the jig on the side where the distance between the jigs is decreased in the 1 st diagonal stretching step enters the preheating zone,

t 3' represents the time from the start of the 2 nd diagonal stretching step to the end of the preheating zone when the jig on the side where the distance between the jigs is increased in the 1 st diagonal stretching step enters the preheating zone. )

With respect to v 3', the predetermined jig pitch is a jig pitch (corresponding to P in the description using fig. 9 and 10) in the case where the jig pitch after completion of the increase in the 1 st oblique stretching step is maintained in the 2 nd oblique stretching step ₂ Corresponding) or the reduced jig interval in the 2 nd oblique stretching process. In addition, in the case where the jig pitch of the jig on the side where the jig pitch is increased in the 1 st oblique stretching step is changed to the predetermined jig pitch in the 1 st oblique stretching step (the predetermined distance P from the predetermined distance P in the explanation using fig. 9 and 10) ₂ Corresponding to the above, when the moving speed of the jig is v2 ', when v2 ' is v3 ', the t3 is represented by the following formula (2), the t ' 3 is represented by the following formula (3), when v2 ' > v3 ', the t3 is represented by the following formula (4), and the t ' 3 is represented by the following formula (5).

The following describes formulae (2) to (5). In the description of each symbol in the formula, fig. 11 to 13 can be referred to. In addition, the asterisk marks (, v) in equations (1) to (5) are multipliers. The unit of the film width is m, the unit of the speed is m/sec, the unit of the distance is m, and the unit of the time is sec.

Mathematical formula 2

t3＝(1/a1)*In(a1*L3+b1)-(1/a1)*In(a1*L2+b1)+(1/a)*In(a*L2+b)

- (1/a) ln (a L1+ b) + L1/v1 formula (2)

(in the formula, a1 is (v2-v3)/(L2-L3),

b1＝v3-a1＊L3，

a＝(v1-v2)/(L1-L2)，

b＝v2-a＊L2，

v1 is the moving speed of the jig when the jig on the side where the distance between the jigs is decreased in the 1 st oblique stretching step passes through the preheating zone,

v2 is the jig on the side where the jig pitch is decreased in the 1 st oblique stretching step, and the jig pitch of the jig is decreased to a predetermined jig pitch (P in the explanation using fig. 9 and 10) ₃ Corresponding) of the jig is calculated,

v3 represents that the distance between the jigs is decreased in the oblique drawing step 1, and the distance between the jigs is increased to a predetermined distance between the jigs in the oblique drawing step 2 (corresponding to P in the explanation using fig. 9 and 10) ₂ Corresponding) to the moving speed of the jig,

l1 is the distance from the inlet of the preheating zone to the position where the distance between the holders of the side where the distance between the holders was decreased in the 1 st diagonal drawing step started to decrease (in 1 embodiment, the distance from the inlet of the preheating zone to the outlet of the preheating zone),

l2 is the distance from the inlet of the preheating zone to the position where the distance between the holders of the side where the distance between the holders was decreased in the 1 st diagonal stretching step started to increase (in 1 embodiment, the distance from the inlet of the preheating zone to the outlet of the 1 st diagonal stretching zone),

l3 is the distance from the inlet of the preheating zone to the position where the distance between the jaws of the jaw on the side where the distance between the jaws is decreased in the 1 st inclined stretching step ends to increase (in 1 embodiment, the distance from the inlet of the preheating zone to the outlet of the 2 nd inclined stretching zone). )

Mathematical formula 3

t3 '((L1'/v 1 ') + (1/a'). In (a '. times.l 2' + b ') - (1/a'). times.in (a '. times.l 1' + b ') + (L3' -L2 ')/v 3') (3)

(in the formula, a ' ═ v1 ' -v2 ')/(L1 ' -L2 '),

b’＝v3’-a’＊L2’，

v 1' is the moving speed of the jigs when the jigs on the side where the distance between the jigs is increased in the 1 st oblique stretching step pass through the preheating zone,

v 2' is a jig on the side where the jig pitch is increased in the 1 st oblique stretching step, and the jig pitch of the jig is increased to a predetermined jig pitch in the 1 st oblique stretching step (corresponding to P in the description using fig. 9 and 10) ₂ Corresponding) of the jig is calculated,

v 3' is the moving speed of the jigs at the time when the jigs pass through the 2 nd diagonal stretching region, for the jigs on the side where the distance between the jigs is increased in the 1 st diagonal stretching step,

l1' is the distance from the inlet of the preheating zone to the position where the distance between the holders on the side where the distance between the holders is increased in the 1 st obliquely stretching step starts to increase (in 1 embodiment, the distance from the inlet of the preheating zone to the outlet of the preheating zone),

l2' is the distance from the inlet of the preheating zone to the position where the distance between the jaws of the jaws on the side where the distance between the jaws is increased in the 1 st inclined stretching step ends to increase (in 1 embodiment, the distance from the inlet of the preheating zone to the outlet of the 1 st inclined stretching zone),

l3' is the distance from the inlet of the preheating zone to the outlet of the 2 nd inclined stretching zone. )

Mathematical formula 4

t3＝(1/a1)*In(a1*L3+b1)-(1/a1)*In(a2*L2+b1)+(1/a)*In(a*L2+b)

- (1/a) In (a L1+ b) + L1/v1 formula (4)

(wherein a1, b1, a, b, v1, v2, v3, L1, L2 and L3 are as defined for the formula (2))

Mathematical formula 5

t3′＝(L1′/v1′)+(1/a′)*In(a′*L2′+b′)-(1/a′)*In(a′*L1′+b′)+(1/a″)*In(a″*L3′+b″)

- (1/a ') In (a'. L2 '+ b') (5)

(in the formula, a ' ═ v1 ' -v2 ')/(L1 ' -L2 '),

b’＝v2’-a’＊L2’，

a”＝(v2’-v3’)/(L2’-L3’)，

b”＝v3’-a”＊L3’，

v 2' is a jig for the side where the jig pitch is increased in the 1 st oblique stretching step, and the jig pitch of the jig is increased to a predetermined jig pitch in the 1 st oblique stretching step (corresponding to P in the explanation using fig. 9 and 10) ₂ Corresponding) of the jig is calculated,

v 3' is the jig moving speed at which the jig pitch of the jig is decreased to the predetermined jig pitch in the oblique drawing step 2 with respect to the jig on the side where the jig pitch is increased in the oblique drawing step 1,

l3' is the distance from the inlet of the preheating zone to the position where the distance between the jigs on the side where the distance between the jigs is increased in the 1 st diagonal stretching step is completely decreased to the predetermined distance between the jigs in the 2 nd diagonal stretching step (in 1 embodiment, the distance from the inlet of the preheating zone to the outlet of the 2 nd diagonal stretching zone). )

Representatively, the oblique stretching can be performed at a temperature T2. The temperature T2 is preferably from Tg-20 to Tg +30 ℃, more preferably from Tg-10 to Tg +20 ℃, and particularly preferably around Tg, with respect to the glass transition temperature (Tg) of the resin film. The temperature varies depending on the resin film to be used, but the temperature T2 is, for example, 70 to 180 ℃ and preferably 80 to 170 ℃. The difference between the temperature T1 and the temperature T2 (T1-T2) is preferably. + -. 2 ℃ or more, more preferably. + -. 5 ℃ or more. In 1 embodiment, T1 > T2, and thus, the film after being heated to a temperature T1 in the preheat zone can be cooled to a temperature T2.

The longitudinal shrinkage treatment and the transverse stretching treatment are performed after the oblique stretching. For these treatments after the oblique stretching, reference can be made to paragraphs 0029 to 0032 of jp 2014-194483.

[ opening step ]

Finally, the jig holding the film is opened to obtain the retardation film. Typically, the clamps are opened after the film is cooled below Tg. The film is heat-treated to fix the stretched state as necessary, and after cooling, the jig is opened.

Typically, the heat treatment can be performed at a temperature T3. The temperature T3 may vary depending on the film to be stretched, and there are cases where T2. gtoreq.T 3 and T2 < T3. In general, when the thin film is an amorphous material, the crystallization treatment is performed by setting T2 ≧ T3, and when the thin film is a crystalline material, the crystallization treatment is performed by setting T2 < T3. When T2 is not less than T3, the difference between the temperatures T2 and T3 (T2-T3) is preferably 0 ℃ to 50 ℃. The heat treatment time is typically 10 seconds to 10 minutes.

After the clamps are opened, the clamp holding portions at both ends of the film are cut off, and the film can be wound into a roll shape.

C. Film to be stretched and retardation film obtained by stretching

The film preferably used in the production method of the present invention is any suitable longitudinal film that can be used as a retardation film. The width of the film to be stretched is, for example, 300mm or more, preferably 500mm or more, and more preferably 500mm to 2000 mm.

Examples of the material constituting the film include polycarbonate resins, polyvinyl acetal resins, cycloolefin resins, acrylic resins, cellulose ester resins, cellulose resins, polyester carbonate resins, olefin resins, polyurethane resins, and the like. Preferred are polycarbonate resins, polyvinyl acetal resins, cellulose ester resins, polyester resins, and polyester carbonate resins. This is because, with these resins, a retardation film showing so-called wavelength dependence of reverse dispersion (long wavelength dependence of japanese) can be obtained. These resins may be used alone or in combination according to desired characteristics.

As the polycarbonate-based resin, any appropriate polycarbonate-based resin can be used. For example, a polycarbonate resin containing a structural unit derived from a dihydroxy compound is preferable. Specific examples of the dihydroxy compound include 9, 9-bis (4-hydroxyphenyl) fluorene, 9-bis (4-hydroxy-3-methylphenyl) fluorene, 9-bis (4-hydroxy-3-ethylphenyl) fluorene, 9-bis (4-hydroxy-3-n-propylphenyl) fluorene, 9-bis (4-hydroxy-3-isopropylphenyl) fluorene, 9-bis (4-hydroxy-3-n-butylphenyl) fluorene, 9-bis (4-hydroxy-3-sec-butylphenyl) fluorene, 9-bis (4-hydroxy-3-tert-butylphenyl) fluorene, 9-bis (4-hydroxy-3-cyclohexylphenyl) fluorene, 9, 9-bis (4-hydroxy-3-phenylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) phenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-methylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-isopropylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-isobutylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-tert-butylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-cyclohexylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-phenylphenyl) fluorene, 9, 9-bis (4- (2-hydroxyethoxy) -3, 5-dimethylphenyl) fluorene, 9-bis (4- (2-hydroxyethoxy) -3-tert-butyl-6-methylphenyl) fluorene, 9-bis (4- (3-hydroxy-2, 2-dimethylpropoxy) phenyl) fluorene. The polycarbonate resin may contain a structural unit derived from a dihydroxy compound such as isosorbide (isosorbide), isomannide (isomannide), isoidide (isoidide), spiroglycol, dioxane glycol, diethylene glycol, triethylene glycol, polyethylene glycol, or a bisphenol, in addition to the structural unit derived from a dihydroxy compound.

The details of the polycarbonate resin as described above are described in, for example, Japanese patent laid-open Nos. 2012 and 67300 and 3325560. The description of this patent document is incorporated by reference into this specification.

The glass transition temperature of the polycarbonate resin is preferably 110 ℃ or higher and 250 ℃ or lower, and more preferably 120 ℃ or higher and 230 ℃ or lower. When the glass transition temperature is too low, heat resistance tends to be poor, and there is a possibility that dimensional change may be caused after film formation. When the glass transition temperature is too high, the molding stability during film molding may be deteriorated, and the transparency of the film may be impaired. The glass transition temperature was determined in accordance with JIS K7121 (1987).

As the polyvinyl acetal resin, any suitable polyvinyl acetal resin can be used. Typically, the polyvinyl acetal resin can be obtained by subjecting at least two aldehyde compounds and/or ketone compounds to a condensation reaction with a polyvinyl alcohol resin. Specific examples of polyvinyl acetal resins and detailed production methods thereof are described in, for example, Japanese patent laid-open No. 2007-161994. This description is incorporated by reference into this specification.

The retardation film obtained by stretching the film to be stretched preferably has a refractive index characteristic in a relationship of nx > ny. The retardation film preferably functions as a λ/4 plate. The in-plane retardation Re (550) of the retardation film is preferably 100nm to 180nm, more preferably 135nm to 155 nm. In the present specification, nx is a refractive index in a direction in which an in-plane refractive index is maximized (i.e., a slow axis direction), ny is a refractive index in a direction orthogonal to the slow axis in the plane (i.e., a phase advance direction), and nz is a refractive index in a thickness direction. Further, Re (. lamda.) is an in-plane retardation of the film measured at 23 ℃ with light having a wavelength of (. lamda.nm). Thus, Re (550) is the in-plane retardation of the film measured at 23 ℃ with light having a wavelength of 550 nm. Re (λ) is obtained by the formula "Re (λ) ═ nx-ny) × d" where d (nm) is the thickness of the film.

The in-plane retardation Re (550) of the retardation film can be within a desired range by appropriately setting the oblique stretching conditions. For example, methods for producing a retardation film having an in-plane retardation Re (550) of 100nm to 180nm by oblique stretching are disclosed in detail in Japanese patent laid-open Nos. 2013-54338, 2014-194482, 2014-238524, 2014-194484, and the like. Therefore, those skilled in the art can set appropriate oblique stretching conditions in light of this disclosure.

The retardation film can be used as an optical laminate by laminating another optical film. For example, the retardation film obtained by the production method of the present invention can be bonded to a polarizing plate and can be preferably used as a circular polarizing plate. The angle formed by the absorption axis of the polarizing plate and the retardation axis of the retardation film is preferably 30 ° to 60 °, more preferably 38 ° to 52 °, still more preferably 43 ° to 47 °, and particularly preferably about 45 °.

The retardation film obtained by the production method of the present invention is longitudinal and has a retardation axis in an oblique direction (direction at, for example, 45 ° to the longitudinal direction). In many cases, the longitudinal polarizing plate has an absorption axis in the longitudinal direction or the width direction. Therefore, when the retardation film obtained by the production method of the present invention is used, a so-called roll-to-roll process can be used, and a circular polarizing plate can be produced with extremely high production efficiency. The roll-to-roll method is a method of continuously laminating films while aligning the longitudinal directions of the films with each other while conveying the films each having a longitudinal shape by a roller.

Examples

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Further, the measurement and evaluation methods in the examples are as follows.

(1) Thickness of

The thickness was measured using a direct-reading thickness meter (manufactured by PEACOCK, Inc., product name "DG-205 type pds-2").

(2) Glass transition temperature (Tg)

The glass transition temperature (Tg) was measured based on JIS K7121.

(3) Amount of neck-in

As shown in fig. 14, the distance (mm) from the clamping position to the valley portion of the neck-in was measured at 5 positions on each of the left and right end edges, and the average value of the distances (mm) was used as the neck-in amount.

< example 1 >

(preparation of a polyester carbonate resin film)

The polymerization was carried out using a batch polymerization apparatus composed of two vertical reactors each including a stirring blade and a reflux cooler controlled at 100 ℃. 29.60 parts by mass (0.046mol) of bis (9- (2-phenoxycarbonylethyl) fluoren-9-yl) methane, 29.21 parts by mass (0.200mol) of ISB, 42.28 parts by mass (0.139mol) of SPG, 63.77 parts by mass (0.298mol) of DPC and 1.19X 10 as a catalyst were charged ^－2 Mass portion (6.78X 10) ^－5 mol) of calcium acetate monohydrate. After the pressure inside the reactor was reduced and nitrogen was replaced, the reactor was heated by a heating medium, and stirring was started when the internal temperature reached 100 ℃. After 40 minutes from the start of the temperature increase, the internal temperature was brought to 220 ℃, the pressure reduction was started while controlling to maintain the temperature, and the pressure in the reactor was brought to 13.3kPa within 90 minutes after the temperature reached 220 ℃. Phenol vapor as a by-product of the polymerization reaction was introduced into a reflux condenser at 100 ℃, a monomer component contained in a slight amount in the phenol vapor was returned to the reactor, and the phenol vapor that was not condensed was introduced into a condenser at 45 ℃ and recovered. Nitrogen was introduced into the 1 st reactor, and after the pressure was once returned to atmospheric pressure, the reaction solution after oligomerization in the 1 st reactor was transferred to the 2 nd reactor. Subsequently, the temperature increase and pressure reduction in the 2 nd reactor were started, and the internal temperature and pressure were set to 240 ℃ and 0.2kPa, respectively, in 50 minutes. Thereafter, the polymerization was carried out until a predetermined stirring power was obtained. When the predetermined power was reached, nitrogen was introduced into the reactor to recover the pressure, the produced polyester carbonate was extruded into water, and the strands were cut to obtain pellets. The Tg of the polyester carbonate resin obtained was 140 ℃.

The obtained polyester carbonate resin was vacuum-dried at 80 ℃ for 5 hours, and then a long resin film was produced using a film-producing apparatus comprising a uniaxial extruder (manufactured by Toshiba machine Co., Ltd., cylinder set temperature: 250 ℃), a T-die (width: 200mm, set temperature: 250 ℃), a chill roll (set temperature: 120 ℃ C. -130 ℃ C.), and a winder.

(stretching)

The long polyester carbonate resin film obtained as described above was obliquely stretched using a clip type film stretching apparatus shown in fig. 1 to 5. Both the upper holding member (specifically, the pressing portion thereof) and the lower holding member of the jig attached to the stretching apparatus are rectangular flat plates each having R-chamfered portions with a chamfer dimension of 5mm formed at both corners on the inner side in the film width direction, and have the same plan view shape (plan view shape shown in fig. 6 (b)).

Specific stretching methods are as follows. First, a polyester carbonate resin film (width: 765mm) was held by a jig at the inlet (holding region) of a stretching device so that the distance (D) from the left and right edge sides of the film to the nip position became 30 mm. At this time, as shown in fig. 15 (a), the film is gripped such that the bottom surface of the upper gripping member and the upper surface of the lower gripping member completely overlap each other. The distance between the left and right clamps is 150 mm. The film gripping surface had a gripping length of 45mm and a gripping amount of 30 mm.

Next, a polyester carbonate resin film (thickness 150 μm, width (W)) was formed in the preheating zone B ₁ )765mm) was preheated to 145 ℃. In the preheating zone B, the holder pitch (P) of the holders on the left and right sides ₁ ) Is 150 mm. Next, while the film entered the 1 st diagonal stretching zone C1, the grip interval of the right-hand grip started to increase and the grip interval of the left-hand grip started to decrease. Rate of change of clip pitch (P) of right-hand clips at terminal end portion of 1 st oblique stretching zone C1 ₂ /P ₁ ) Is 1.42, rate of change of jig pitch (P) of the left jig ₃ /P ₁ ) Is 0.72. Width of obliquely stretched film No. 1 (W) ₂ ) Is 1092mm (TD stretch ratio (W) ₂ /W ₁ ) 1.45 times).

Next, the grip interval of the left grip is started to increase while the film enters the 2 nd diagonal stretching region C2, and in order to make the grip interval from P ₃ Increase to P ₂ To be provided withRate of change of grip pitch (P) of left grip in 2 nd diagonal stretching region C2 ₂ /P ₃ ) The value was set to 1.97. On the other hand, the grip interval of the right grip is maintained at P in the 2 nd diagonal stretching region C2 ₂ . Further, the stretching ratio (W) in the width direction in the 1 st oblique stretching step and the 2 nd oblique stretching step ₃ /W ₁ ) The ratio was set to 1.9 times.

However, the film was broken during the 2 nd oblique stretching step. The film was observed from the outlet of the stretching machine, and the MD magnification and TD magnification of the broken portion were determined according to the position where the breakage occurred. The oblique stretching ratio at the time of fracture was calculated from the MD ratio and TD ratio of the site at which fracture occurred and using the above formula (1), and as a result, the oblique stretching ratio was 2.43 times. Further, both the 1 st oblique stretching and the 2 nd oblique stretching were conducted at 142 ℃.

Next, the neck-in at the time of fracture was determined as follows.

The jig pitch P of the right jig in the 1 st diagonal stretching zone C1 was adjusted so that the diagonal stretching magnification at the end of the diagonal stretching step was reduced by 0.01 times (i.e., 2.42 times) from the diagonal stretching magnification at the time of fracture ₂ And the clamp pitch P of the left clamp in the 2 nd diagonal stretching region C2 ₂ Otherwise, the oblique stretching (i.e., P) was performed in the same manner as described above ₁ 、P ₃ And the stretching ratio in the width direction at the time of the 1 st oblique stretching or the 2 nd oblique stretching) is not changed). Next, in the release zone, the film was held at 125 ℃ for 60 seconds and heat-set. After the film after the heat fixation was cooled to 100 ℃, the left and right clamps were opened. As a result, an obliquely stretched film was obtained without causing breakage. The obtained obliquely stretched film was regarded as a film to be broken, and the neck-in amount thereof was measured as a neck-in amount to be broken.

< example 2 >

The film was obliquely stretched until the film was broken in the same manner as in example 1 except that the chamfer size of the upper holding member and the lower holding member was set to 10mm, the oblique stretching ratio at the time of breaking was calculated, a film to be broken was produced from the oblique stretching ratio at the time of breaking, and the neck-in at the time of breaking was determined.

< example 3 >

The film to be broken was produced from the diagonal stretching magnification at the time of breaking and the amount of reduction at the time of breaking was determined by calculating the diagonal stretching magnification at the time of breaking, in the same manner as in example 1, except that R chamfered portions were provided only at the corners on the inner side in the film width direction and on the downstream side in the advancing direction of both the upper gripping member and the lower gripping member of the right-hand gripper, and R chamfered portions were provided only at the corners on the inner side in the film width direction and on the upstream side in the advancing direction of both the upper gripping member and the lower gripping member of the left-hand gripper.

< example 4 >

The film was obliquely stretched until the film was broken in the same manner as in example 1 except that the chamfer size of the upper holding member and the lower holding member was set to 15mm, the oblique stretching ratio at the time of breaking was calculated, a film to be broken was produced from the oblique stretching ratio at the time of breaking, and the neck-in at the time of breaking was determined.

< example 5 >

The film was obliquely stretched until the film was broken in the same manner as in example 1 except that the chamfer size of the upper holding member and the lower holding member was set to 20mm, the oblique stretching ratio at the time of breaking was calculated, a film to be broken was produced from the oblique stretching ratio at the time of breaking, and the neck-in at the time of breaking was determined.

< comparative example 1 >

Other than not providing the R-chamfered portions on the upper and lower gripping members (as a result, the film gripping surface was a rectangle having a gripping length of 45mm and a gripping amount of 30 mm), oblique stretching was performed until the film was broken in the same manner as in example 1, and the oblique stretching ratio at the time of breaking was calculated.

< comparative example 2 >

The film was held by a jig so that the distance (D) from the film edge to the nip position became 15mm as shown in fig. 15 (b), except that the film was held by using an upper holding member and a lower holding member which do not have an R-chamfered portion and which have different sizes (as a result, the film holding surface was rectangular with a holding length of 21.5mm and a holding amount of 2 mm), and the film was obliquely stretched until the film was broken in the same manner as in example 1, and the oblique stretching ratio at the time of breaking was calculated, and a film to be broken was produced from the oblique stretching ratio at the time of breaking, and the neck-in amount at the time of breaking was calculated.

< evaluation of open State of Clamp >

In the production of the retardation films (films to be broken) of the examples and comparative examples, the case where 100 or more of the jigs were not caught by the film and could be continuously opened was evaluated as "good", and the case where the film was caught by the jig more than once was evaluated as "bad". The results are shown in table 1 together with the stretch ratio and the neck-in at the time of film break.

TABLE 1

< evaluation >

As shown in table 1, in the example in which the chamfered portions were formed at the inner corners in the film width direction of the left and right clamps, the clamps could be opened without the stretched film being caught on the clamps. Further, it is found that the smaller the chamfer size is, the better the reduction of the neck-in and the realization of the higher draw ratio can be achieved at the same time. Further, by forming the chamfered portion only at the corner portion on the inner side in the film width direction and on the downstream side in the running direction of the previously running jig and forming the chamfered portion only at the corner portion on the inner side in the film width direction and on the upstream side in the running direction of the subsequently running jig, it is possible to achieve both reduction in the neck-in amount and achievement of a high stretch ratio at a higher level.

Industrial applicability

The method for producing a retardation film of the present invention can be preferably used for producing a retardation film, and as a result, can contribute to the production of an image display device such as a liquid crystal display device (LCD) or an organic electroluminescence display device (OLED).

Claims

1. A clip type film stretching apparatus having variable-pitch type left and right clips which hold left and right end portions of a film to be stretched and which pass through a stretching zone while changing a clip pitch in a longitudinal direction of at least one of the clips with the passing, wherein,

the clamp has an upper holding member and a lower holding member which clamp and hold an end portion of the film,

at least the corner portion on the inner side of the upper holding member in the film width direction is a chamfered portion having a chamfer dimension of more than 0mm and not more than 20mm,

in the jig on either side of the left and right sides, the chamfered portion is formed only at a corner portion on the inner side in the film width direction and on the downstream side in the traveling direction of both the upper holding member and the lower holding member,

in the other jig, the chamfered portion is formed only at a corner portion on the inner side in the film width direction and on the upstream side in the traveling direction of both the upper holding member and the lower holding member.

2. The clip-type film stretching apparatus according to claim 1,

the corner portions on the inner side in the film width direction of both the upper holding member and the lower holding member are chamfered to have a chamfer dimension of more than 0mm and 20mm or less.

3. The clip type film stretching apparatus according to claim 1 or 2,

the film is held by the jig at a position spaced apart from the left and right end edges by a distance of 20mm or more.

4. The clip type film stretching apparatus according to claim 1 or 2,

a length of a film gripping surface defined by an overlap between a bottom surface of the upper gripping member and an upper surface of the lower gripping member in a direction orthogonal to a traveling direction of the jig is 15mm or more.

5. The clip type film stretching device according to claim 1 or 2,

the length of the film gripping surface defined by the overlap between the bottom surface of the upper gripping member and the upper surface of the lower gripping member in the advancing direction of the jig is 30mm or more.

6. A method for manufacturing a retardation film, comprising the steps of: gripping left and right ends of a film to be stretched by left and right variable-pitch clamps having a variable clamp pitch in the longitudinal direction; preheating the film; a step of obliquely stretching the film by changing the distance between the left and right clamps; and a step of opening a jig holding the film, wherein,

the method for producing a retardation film is carried out by using the clip film stretching apparatus according to claim 1,

the film is obliquely stretched by changing the distance between the left and right clamps such that only the clamp having the inner corner in the film width direction and the downstream corner in the direction of travel of both the upper and lower gripping members is advanced, and only the clamp having the inner corner in the film width direction and the upstream corner in the direction of travel of both the upper and lower gripping members is advanced.

7. The method of producing a retardation film as claimed in claim 6,

a method for producing a retardation film, which comprises using the clip type film stretching apparatus according to any one of claims 2 to 5.

8. The method for producing a retardation film according to claim 6 or 7, wherein,

the oblique stretching comprises transverse stretching.