JP2008302581A - Method for producing stretched optical film - Google Patents

Abstract

The present invention provides a method for producing a stretched optical film that is easy to produce and that can produce a biaxially stretched optical film that is homogeneous not only in thickness but also in Re value and orientation angle at low cost.
An unstretched film is continuously supplied to a stretching machine having a plurality of grippers, both ends of the unstretched film are gripped by the grippers, and the unstretched film is moved by moving the grippers. A method for producing a stretched optical film, comprising a step of simultaneously biaxially stretching the film in the longitudinal and lateral directions, wherein the simultaneous biaxial stretching step has a pitch of 10 when the gripper grips the unstretched film. When the one of the two grippers facing each other reaches the end of stretching, a line connecting the centers of the pair of grippers and a direction perpendicular to the film transport direction in the film plane A method for producing a stretched optical film, characterized in that the angle formed between and is controlled to be within 0.5 °.
[Selection] Figure 3

Description

  The present invention relates to a method for producing a stretched optical film, and more particularly to a method for producing a stretched optical film by simultaneous biaxial stretching.

  2. Description of the Related Art Conventionally, in order to produce a miscellaneous goods film made of materials such as polyethylene terephthalate and nylon, a method of biaxially stretching a film of the material to make a stretched film has been widely used. As the biaxial stretching method, sequential biaxial stretching and simultaneous biaxial stretching are known. Simultaneous biaxial stretching is adopted as a method with higher productivity than sequential biaxial stretching.

  As a simultaneous biaxial stretching machine, a linear motor system, a pantograph system, a motor chain drive system, and the like are known. Among these, the pantograph type stretching machine has an advantage that the structure is simple and the entire production line including the stretching machine can be quickly started up.

  A pantograph type simultaneous biaxial stretching machine is, for example, an endless link device in which a plurality of link plates are connected in a zigzag manner, as disclosed in Patent Document 1 (Japanese Patent Publication No. 4-62530). A gripper provided and a guide rail for guiding the link device are provided. In the stretching machine, the unstretched resin film continuously supplied from a die or the like is gripped at both ends by a gripper. The link device that grips the unstretched resin film with the gripper, the zigzag contracted by the guide rail extends, and the resin film extends in the lateral direction (perpendicular to the direction in which the resin film travels on the surface of the resin film). Direction). That is, the gripper proceeds obliquely with respect to the traveling direction of the resin film, whereby the resin film before stretching is simultaneously stretched in both the longitudinal direction (direction in which the resin film travels) and the transverse direction perpendicular thereto, Simultaneous biaxial stretching of the resin film is achieved.

  Even in other types of simultaneous biaxial stretching machines, it is common in that the unstretched film that is continuously fed can be stretched simultaneously in both the horizontal and longitudinal directions by moving multiple grippers. To do.

  When manufacturing the stretched film used as the above-mentioned general goods, the film is stretched at a high stretch ratio of 7 times or more in the longitudinal and lateral directions, for example. In the production of biaxially stretched films used for optical applications, which have been increasing in demand in recent years, it is expected that high-performance stretched optical films can be efficiently produced by applying such simultaneous biaxial stretching. .

  In addition, when a stretched optical film is produced by conventional sequential biaxial stretching, the resin is once cooled between stretching in one direction and stretching in the other direction, resulting in thermal relaxation, and the resulting biaxially stretched film However, the simultaneous biaxial stretching is expected to avoid the disadvantage that the resin is once cooled.

However, when producing stretched optical films by simultaneous biaxial stretching, there are the following problems.
When producing a stretched optical film, it is required that uniform stretching with high accuracy is performed at a low stretch ratio of about 2 times or less in each of the longitudinal and lateral directions. In simultaneous biaxial stretching, stretching is performed at such a low stretch ratio. And the unevenness | strength of a draw ratio tends to become large in the vicinity of a holding element and a distant place. Therefore, in order to use a film obtained by simultaneous biaxial stretching as a stretched optical film, the thickness of the film and the uniformity of retardation (Re) in the in-plane direction are insufficient. Furthermore, in the case of simultaneous longitudinal and transverse stretching in simultaneous biaxial stretching, it is difficult to accurately control the stretching direction in the width direction and the flow direction, so it is also difficult to control the orientation angle of the obtained stretched film. .

Japanese Examined Patent Publication No. 4-62530

  An object of the present invention is to provide a method for producing a stretched optical film, which is easy to manufacture and can produce a biaxially stretched optical film that is homogeneous not only in thickness but also in Re value and orientation angle at low cost. There is.

According to the present invention, the following is provided:
[1] A step of continuously supplying an unstretched film to a stretching machine having a plurality of grippers, a step of gripping both ends of the unstretched film with grippers, and the unstretched by moving the grippers A method for producing a stretched optical film comprising a step of simultaneously biaxially stretching a film in the longitudinal and lateral directions, wherein a pitch when the gripper grips an unstretched film in the simultaneous biaxial stretching step is 10 When one of the two grippers facing each other reaches the end of stretching, a line connecting the centers of the grips of each pair and a direction perpendicular to the film conveyance direction in the film plane are A method for producing a stretched optical film, wherein an angle formed is within 0.5 °.
[2] The method for producing the stretched optical film, wherein the distance between the grips is made equal by adjusting the positions of the opposing grippers at the stretching end portion.
[3] The method for producing a stretched optical film according to claim 1, wherein the position of the opposing grippers at the stretching end portion is adjusted by changing the speed at the stretching end portion of each of the opposing grippers.
[4] The method for producing a stretched optical film according to claim 1, wherein the position of the opposing grippers at the stretch end portion is adjusted by changing the longitudinal stretch ratio.
[5] The stretched optical film having an area of a surface in contact with the film of the gripper of 75 to 1000 mm ² and a shape of the surface in contact with the film being a circle, an ellipse, or an approximate ellipse. Manufacturing method.
[6] The step of continuously supplying the unstretched film includes a step of melt-extruding a thermoplastic resin to form the unstretched film, and the formed unstretched film is subsequently conveyed inline to the stretcher. A process for producing the stretched optical film, comprising a step.

  In the method for producing a stretched optical film of the present invention, a biaxially stretched optical film that is homogeneous not only in thickness but also in Re value and orientation angle can be produced at low cost.

  In the manufacturing method of the extending | stretching optical film of this invention, the process of supplying an unstretched film continuously to the extending | stretching machine provided with a some holding element, the process of carrying out simultaneous biaxial stretching in the vertical and horizontal direction is included. In this step, both ends of the unstretched film are gripped by the gripper, and simultaneous biaxial stretching is achieved by moving the gripper. In addition, the both ends of an unstretched film mean the both ends of the width direction.

  In the production method of the present invention, simultaneous biaxial stretching means longitudinal stretching (that is, extension of the film length along the film transport direction) and lateral stretching (that is, perpendicular to the film transport direction). Stretching the width of the film along the direction) refers to a mode of stretching performed at least in part at the same time. Preferably, stretching in the machine direction and the transverse direction is started simultaneously and ended simultaneously.

  In the production method of the present invention, the “stretch end portion” refers to a position in the film production line where both longitudinal and transverse stretching ends, preferably where longitudinal and lateral stretching ends simultaneously.

  The stretching machine that performs simultaneous biaxial stretching is not particularly limited as long as it is a stretching machine having a plurality of grippers, and linear motor systems, pantograph systems, motor chain drive systems, and the like can be used. A pantograph type stretching machine is preferable because of its advantage that the structure is simple and the entire production line including the stretching machine can be quickly started up.

  The pantograph type stretching machine includes a link device in which a plurality of link plates are connected in a zigzag manner, and each of the link plates has the plurality of grippers for gripping a stretched material. Here, the “link device” refers to a pair of devices that guide a gripper that grips both ends of a film in a stretching machine so as to stretch the film. In addition, here, the “link plate” means a generally plate-like member that constitutes the link device, specifically, members indicated by reference numerals 102a to 102d in FIG. It can be set as the member of the shape shown by code | symbol 302a-302d in FIG. A link plate is usually called a link “plate” because it consists of a combination of roughly plate-shaped members. However, the link plate is not limited to a plate-like shape as long as it has a similar function. Any shape can be used. In addition, the “end portion” of the link plate here is not usually the end portion of all the link plates constituting the zigzag, but the link plate 102a in FIG. 4 or the link plates 302a and 302c in FIG. Moreover, it can be set as the edge part of the link plate which has an edge part in the position nearest to a film among all the link plates which comprise a link apparatus.

In the simultaneous biaxial stretching step, the pitch when each of the plurality of grippers grips the unstretched film is 10 to 60 mm, preferably 25 to 45 mm. Here, the pitch of the grippers refers to the distance between the centers of the gripping portions of adjacent grippers. Further, in the present invention, the grip area of Hajiko is preferably 75～1000Mm ^2, more preferably 155~495mm ^2. Here, the gripping area of the gripper means an area in contact with one surface of the film when the gripper grips the film. By keeping the gripper pitch and gripping area within the above specified range, the distance between the grippers can be maintained while securing a sufficient gripping force at a short pitch. Homogeneous stretching can be performed. If the gripping area of the gripper is less than the above specific range, the film may be broken when the film is stretched, which is not preferable. If the link pitch and the grip area of the gripper exceed the specific range, the stretched optical film may not be uniform in thickness and orientation, which is not preferable.

  The shape of the surface on which the gripper comes into contact with the film is not particularly limited, but can be a circular shape, an elliptical shape, or an approximate elliptical shape, and a circular shape is preferable. The approximate ellipse refers to a shape with rounded corners of a polygon, such as a shape with rounded corners of a rectangle. In the case where the contact surface is circular, specifically, for example, a circular shape having a diameter of about 10 to 30 mm, preferably 14 to 25 mm can be used.

  In the production method of the present invention, the draw ratio can be appropriately adjusted according to desired conditions, but preferably 1.1 to 2 times, more preferably 1.2 to 1 in the longitudinal direction and the transverse direction, respectively. .5 times. The longitudinal and lateral stretching ratios do not have to be the same, and can be appropriately different depending on desired characteristics. By setting it as the draw ratio of this range, the stretched film suitable for an optical film can be obtained, and the thickness and orientation of a stretched optical film can be made uniform.

  When the pantograph type stretching machine is used in the simultaneous biaxial stretching process, stretching is achieved by extension of the link device, but in addition, lateral stretching guides the progress and extension of the link device. It is also achieved by means for performing (a guide rail or the like; hereinafter, this means is simply referred to as a guide rail). That is, by providing the guide rail track so that the link device track shifts in the lateral direction as the link device extends, the width of the lateral extension due to the extension of the link device can be adjusted. Further, by further providing means for supporting the guide rail in a state in which the track of the guide rail can be adjusted in the lateral direction, the stretching width in the lateral direction can be adjusted and stretching at a desired stretching ratio can be achieved. . Examples of the support means include configurations of a drive shaft, which will be described in detail later, and a holding unit attached to the drive shaft as necessary. The drive shaft is preferably a plurality of drive shafts that can independently adjust the positions of the left and right guide rails in the lateral direction. By making the guide rail track adjustable in this way, the orientation of the stretched optical film can be controlled more precisely.

  The unstretched film stretched in the simultaneous biaxial stretching step of the production method of the present invention is usually a flat plate-shaped thermoplastic resin film, which is continuously supplied in the length direction. Although the width | variety of a film is not specifically limited, 450-2000 mm, Preferably it can be 1000-1500 mm. The thickness of the film is not particularly limited, but can be 40 to 400 μm, preferably 60 to 300 μm.

  In the production method of the present invention, in the step of simultaneous biaxial stretching, when one of the opposing grippers reaches the stretching end portion, a line connecting the centers of the pair of grippers and the in-plane of the film The angle formed by the direction perpendicular to the film conveying direction is within 0.5 °. Here, the opposing grippers refer to each of a pair of grippers that are positioned symmetrically about the film transport direction and grip both ends of the film.

  The configuration requirements will be described with reference to FIG. FIG. 6 is a top view schematically showing an example of a stretching machine used in the simultaneous biaxial stretching process in the present invention. In FIG. 6, for the sake of explanation, the pair of link devices 601 </ b> R and 601 </ b> L is schematically illustrated only by indicating the position of the gripper 608 with a circle. In FIG. 6, a pair of link devices 601R and 601L is driven by sprockets 106a and 106b, and is rotated in the direction indicated by arrow A1 symmetrically about the transport direction A5 of the film 105. The gripper 608 grips both ends of the film 105 until the film 105 reaches the stretching start portion 655 indicated by a dotted line 655, and then the longitudinal direction ( The film 105 is simultaneously stretched in a direction parallel to the transport direction A5) and in a lateral direction perpendicular thereto, and reaches a stretching end portion indicated by a dotted line 652 (this line is a straight line parallel to the film lateral direction). Here, of the gripping elements 608R and 608L facing each other, 608R has reached the stretching end portion. At this time, the angle formed by the line 651 connecting the centers of the gripping elements 608R and 608L and the dotted line 652 is 0.5. If it is controlled so that it is within the range of °, the above-mentioned configuration requirements are satisfied.

  As described above, as a method for adjusting the positions of the two grippers at the extending end portion so as to satisfy the predetermined requirement, (i) a method for equalizing the distance between the grippers, And (iii) a method of changing the longitudinal draw ratio, and combinations thereof.

  In the adjustment method (i), `` equal spacing between grips '' means that the distance between each gripper facing when the simultaneous biaxial stretching machine is driven and the gripper adjacent to each other is as follows: It means that the opposites are equal. For example, as shown in FIG. 8, in each of the opposing link devices 601R and 601L, the distance R1 between the gripper 608R1 and the gripper 608R2 adjacent thereto, the distance R2 between the gripper 608R2 and the gripper 608R3 adjacent thereto, The distance R3 between the gripper 608R3 and the gripper 608R4 adjacent thereto is the distance L1 between the gripper 608L1 and the gripper 608L2 adjacent thereto, and the distance between the gripper 608L2 and the gripper 608L3 adjacent thereto, respectively. When the distance L3... Between L2 and the gripper 608L3 and the gripper 608L4 adjacent to the gripper 608L3 is equal to the distance between the grippers, the “interval is equal”. In this way, the state in which the distance between the gripping elements is “equal” specifically refers to, for example, the difference between the lengths of the opposing block pairs in the opposing link devices, with 10 adjacent gripping elements as one block. The state may be within a range of 0.05% of the average block length. The length of the block can be measured, for example, by measuring the elongation of the link device as 1.1 times the pitch when gripping an unstretched film. The average block length is an average value of the block lengths.

  In the adjustment method (ii), the speed of the outlet sprocket (sprocket 106a in the examples shown in FIGS. 6 and 7) is controlled independently on the left and right sides while monitoring the timing when the gripper reaches the end of stretching, and the gripping is performed This can be executed by adjusting the deviation of the timing at which the child reaches the stretching end portion to a minimum.

  The control method (iii) can be executed, for example, by appropriately adjusting the position of the guide rail that guides the link device.

In the production method of the present invention, after the film has reached the stretch end portion (dotted line 652 in FIG. 6), the stretched state is usually held by the gripper downstream in order to stabilize the stretched state. The gripper releases the film. Here, even after the gripper reaches the end of stretching and until the gripper releases the film, a line connecting the opposing grippers and a direction perpendicular to the film transport direction in the film plane are formed. It is preferred that the angle be controlled to be within 0.5 °, more preferably within 0.3 °. This preferred embodiment will be described with reference to FIG. 7. An angle formed by a line 651 connecting each of the opposing grippers 608 after reaching the stretching end portion 653 and a direction 653 perpendicular to the transport direction A5 of the film 105. θ (θ ₁ and θ ₂ ) is controlled to be within 0.5 ° until the opposing gripper reaches the grip end portion 656. For convenience, if the angle of the direction indicated by θ ₁ in FIG. 7 is positive and the angle of the direction indicated by θ ₂ is negative, both the positive direction and the negative direction are controlled to be within 0.5 °. The When the gripper reaches the gripping end portion 656, the gripping of the gripper is released. The gripper releases the film and is guided upstream of the apparatus by the sprocket 106a. By controlling in this way, the thickness, Re value, and orientation angle of the stretched optical film can be made more uniform.

  In the production method of the present invention, the film to be stretched is not particularly limited, but in particular, it is difficult to perform biaxial stretching with high optical accuracy even in conventional sequential biaxial stretching, and a thermoplastic resin with high thermal relaxation properties. Can also be satisfactorily biaxially stretched. Preferred examples of the thermoplastic resin include alicyclic structure-containing polymers. The thermoplastic resin may contain an optional component such as an ultraviolet absorber. In the method for producing a stretched optical film of the present invention, it is preferable to perform the biaxial stretching at a temperature of Tg-5 (° C.) to Tg + 30 (° C.), where Tg is the glass transition temperature of the thermoplastic resin.

  In the method for producing a stretched optical film of the present invention, it is preferable to control the temperature unevenness in the region where the film is stretched within ± 0.5 ° C. By performing such temperature control, the orientation of the stretched optical film can be made uniform, which is particularly preferable when a thermoplastic resin film is used as the film. As a preferable configuration of the simultaneous biaxial stretching machine that achieves the temperature control, it is possible to include an oven that surrounds a region where stretching is performed. Furthermore, the oven has a staggered heater, a fan connected to each heater, a duct that distributes the hot air from the fan to the top and bottom of the oven, and a nozzle that blows the hot air from the duct to the film in the oven over a wide range. By providing, temperature control can be achieved more satisfactorily. Furthermore, a sensor for detecting the temperature in the vicinity of the film in the oven, and a controller for controlling the operation of the heater and the fan manually or automatically based on data detected by the sensor can be further provided. Further, a valve for manually or automatically controlling the distribution of the hot air from the fan to the upper and lower ducts based on instructions from the sensor and the control device can be further provided as necessary.

  Furthermore, the heating means of the oven can include a filter such as a HEPA filter for removing foreign matters such as dust in the air blown out from the nozzle to the film in the oven. Thereby, a higher quality optical film can be manufactured.

  In the method for producing a stretched optical film of the present invention, it is preferable to control the moving speed of the film in the oven in the longitudinal direction with high accuracy. Specifically, the drive device that rotates the sprocket that drives the link device is preferably a drive device having a rotational accuracy of 1 / 30,000. By performing such control, a film having a more uniform orientation can be produced.

  In the production method of the present invention, the mode of supplying the unstretched film to the stretching machine is not particularly limited, and the film can be fed out from a previously prepared roll of unstretched film or supplied by heat. It is also possible to melt-extrude the plastic resin to form an unstretched film, which is then continuously conveyed and supplied inline to a stretching machine. In particular, the latter case is preferable because there are advantages that the manufacturing process can be made more efficient and the manufacturing equipment can be downsized.

  Next, the production of a film by the method for producing a stretched optical film of the present invention, and a preferred stretching machine for performing the production and an example of the operation thereof will be specifically described with reference to the drawings.

  FIG. 1 is a schematic top view of a main part relating to film stretching in an example of a simultaneous biaxial stretching machine for carrying out the method for producing a stretched optical film of the present invention. In FIG. 1, a thermoplastic resin film 105 to be stretched is supplied from a feeding device (not shown) in a state of a raw material processed into a plate shape having a width indicated by an arrow B1, and is along the direction of an arrow A5. Then, it is introduced into the portion where stretching is performed. The resin film 105 is guided by a guide rail 104 and guided by a link device (not shown in FIG. 1, which will be described later) driven by sprockets 106a and 106b. The film is stretched in the transverse direction at the same time as indicated by A5) and sent out as a stretched optical film having a width indicated by an arrow B2. Since the guide rail 104 is supported by the holding unit 130, and the position of the holding unit 130 can be adjusted by the drive shaft 120, the width of the guide rail 104 can be adjusted by operating the drive shaft 120 from the outside of the oven 191. It is possible to adjust the position of the direction.

  The portion where the stretching is performed is preferably surrounded by a housing such as an oven 191 and kept at a constant temperature suitable for stretching. The air in the oven 191 can be heated by the heater 255 and the fan 254 to a temperature suitable for stretching the thermoplastic resin film. As shown in the drawing, more uniform heating is achieved by staggering the heaters 255 and the fans 254 along the vertical direction.

  FIG. 2 schematically shows a more specific example of the heating means. FIG. 2 is a partial cross-sectional view of the apparatus of FIG. 1 along a vertical plane parallel to the film width direction. The air heated by the heater 255 is sent from the fan 254 to the duct 252a for the upper nozzle and the duct 252b for the lower nozzle, and is ejected from the openings 251a and 251b of the upper nozzle 250a and the lower nozzle 250b, respectively. Keep on. The ejected air is returned to the heater 255 through the suction duct 256. By arranging such heating means in a zigzag manner as shown in FIG. 1, it is possible to achieve uniform heating, preferably temperature variation within ± 0.5 ° C. within the oven.

  FIG. 3 is a plan view schematically showing a drawing mechanism by a link device in an example of a simultaneous biaxial drawing machine for carrying out the manufacturing method of the present invention, and FIG. 4 is a link device 101 shown in FIG. It is a longitudinal cross-sectional view explaining one unit 107.

  3 and 4, the link device 101 is mainly composed of a plurality of link plates 102a to 102d connected in a zigzag shape. The link device 101 is normally an endless link device in which a plurality of link plates are connected in a ring shape, but in FIG. In addition, a pair of link devices 101 are usually provided at both ends in the longitudinal direction (the advancing direction of the thermoplastic resin film to be stretched, indicated by arrow A5), but one end side is omitted in FIG. Yes. The link device 101 rotates in the direction indicated by the arrow A1 when the bearing rollers 103a and 103b pass through the grooves formed by the guide rails 104a to 104c and are driven by the sprockets 106a and 106b.

  A grip 108 is provided at the end of the link plate 102 a, and the grip 108 includes a top 111 and a grip 110. In the example shown in FIG. 4, the gripper 108 is urged by a spring 109 and the gripping part 110 is closed. However, before the gripper top part 111 enters the area indicated by the dotted line D1 in FIG. The resin 105 can be gripped in the region D1 by configuring the stretching machine to be pushed and returned after entering the region D1 (not shown). Further, as the width of the guide rail 104 is increased or decreased, the link device 101 is completely contracted in the region D1, and the link pitch at the time of contraction, that is, the pitch when gripping the unstretched film is the length indicated by P1 in FIG. Become. According to the manufacturing method of the present invention, the pitch P1 is controlled to an interval of 10 to 60 mm.

  After the link device 101 reaches the stretching start portion 655, the link device 101 progresses toward the end in the advancing direction A5 of the film in the oven while stretching, and when it reaches the stretching end portion 652, the link device 101 is stretched. The length is indicated by P2. By the progress of the end spread, the thermoplastic resin film is stretched in the transverse direction at a stretch ratio of (B2 / B1) times and stretched in the longitudinal direction at a stretch ratio of (P2 / P1) times. Both the value of (B2 / B1) and the value of (P2 / P1) are preferably adjusted to 1.1 to 2 times as described above, and this magnification can be fixed or variable. By configuring the gripper top 111 to be pushed again in the direction of arrow A3 before the link plate 102 exits the region D2, the gripper 108 releases the stretched optical film 105, and then the link plate 102 is returned toward the region D1. It is.

  Here, in the extending | stretching completion part 652, the manufacturing method of this invention can be implemented by controlling an opposing gripper as demonstrated above with reference to FIG.6 and FIG.7.

  FIG. 5 is a plan view showing a more specific structure of a part of the link device and an example of contraction and extension thereof. In the example shown in FIG. 5, one unit of the link device includes (a) both a bearing roller 303 a on the outer side (the side opposite to the film 305 in the oven) and a bearing roller 303 b on the inner side (the side closer to the film 305 in the oven). A link plate 302a having a fulcrum on top and extending further inward and having a gripper 308 at the inner end thereof; (b) having a common fulcrum on the link plate 302a and the bearing roller 303b; and another bearing roller 303a A link plate 302b extending to another upper fulcrum, (c) a link plate 302c having a fulcrum at a portion between the fulcrums of the link plate 302b, extending inwardly therefrom, and having a gripper 308 at the inner end; and (D) There is a fulcrum between the inner end and the outer end of the link plate 302c, and it extends outward from there. Adjacent link plates having a fulcrum on a unit of the link plates 302a 302d, mainly composed.

  In the link device shown in FIG. 5, the link pitch can be changed from the contracted state to the extended state by reducing the groove interval W1 of the guide roller to W2. In the apparatus shown in FIG. 5, the link pitch P1 during contraction and the link pitch P2 during extension are half the distances 2xP1 and 2xP2 between the bearing rollers, respectively. The desired short shrinkage link pitch in the manufacturing method of the invention can be obtained.

  In the simultaneous biaxial stretching machine used in the production method of the present invention, it is preferable that the link pitch at the time of contraction of the gripper and the gripping area of the gripper have the above specific values. As a result, for example, in the case shown in FIG. 5, the link pitch (P1, P2) is short, the distance between the grippers (P3, P4) is kept at a certain distance, and a sufficient gripping force is obtained. A biaxially stretched optical film that is homogeneous not only in thickness but also in orientation can be produced.

  The holding parts 103a and 103b that support the guide rail 104 and the drive shaft 120 that supports the holding part so that the position of the holding part 104 can be adjusted are shown schematically in FIG. 3, and the interval is not particularly limited. Is preferably 200 to 5000 mm.

  Although the foregoing disclosure has described the invention with reference to the preferred embodiments for purposes of illustration, the invention is intended to be limited only by the scope of the claims and their full scope of equivalents. Various modifications and changes can be further made in the above embodiment.

  Hereinafter, the present invention will be described in more detail based on examples. In addition, this invention is not limited to the following Example.

Example 1
(1-1: stretching machine)
As a stretching machine for carrying out biaxial stretching, a pantograph-type stretching machine schematically shown in FIGS. 1 to 7 was prepared. The stretching machine includes a pair of loop-shaped link devices each having an oven length of about 20 m and a gripper having a circular contact surface with a diameter of 20 mm. The device comprises 1000 grippers.

(1-2: Link device adjustment)
Prior to driving the drawing machine, the length of the link device was adjusted. First, the block to which the link device unit for 10 grippers was connected was removed from the link device. This was placed on a measurement rail whose link pitch was adjusted to a width that is 1.1 times the link contraction. One side of the block was fixed with a jig, and a load of 20 kg was applied using only a spring on the opposite side. In this state, the length between adjacent grippers was measured with a caliper. The measurement was performed three times for each block, the average was taken as the measurement value, and the total was added to obtain the length of the block for 10 grippers.

  The link device was adjusted so that the difference between the lengths of the respective pairs of blocks corresponding to the opposing positions when driving the link device was within 0.05% of the average block length. The adjustment was performed by appropriately replacing the link device unit in the block with that in another block.

(1-3: Adjustment of stretching machine)
Further, by adjusting the guide rail in the stretching machine, the pitch P1 when the link contracts (that is, when gripping the unstretched film) is 40 mm, and the pitch P2 when the link is stretched is 48 mm. The distance between the grips at both ends when not stretched was 1160 mm, and the distance between the grips at both ends when stretching was completed was 1740 mm. The starting point and the ending point of the longitudinal stretching and the lateral stretching were the same.

(1-4: Production and measurement of stretched film)
A pellet of a norbornene resin (trade name “ZEONOR1420”, glass transition point = 136 ° C., manufactured by Nippon Zeon Co., Ltd.) was dried at 100 ° C. for 5 hours. The pellets are supplied to an extruder, melted in the extruder, and extruded from a T die onto a casting drum having a surface temperature of 120 ° C. at a draft ratio (ratio of die opening to film thickness) of 5: 1 and cooled. An unstretched film having a thickness of 150 μm and a width of 1200 mm was continuously produced. This was directly supplied in-line to a simultaneous biaxial stretching machine. In a stretching machine, biaxial stretching is performed at a line speed of 30 m / min, a stretching temperature of 145 ° C., a longitudinal magnification of 1.2 times, and a transverse magnification of 1.5 times, and further from the central portion 1500 mm in the transverse direction of the stretched film. The outer ends were cut off as clip portions to obtain a stretched film having a width of 1500 mm and an average Re value of 60 nm.

  During stretching, the gripper displacement at the end of stretching was measured by the following measuring method. Moreover, the orientation angle and Re value of the obtained stretched film were measured by the following measuring methods. The results are shown in Table 1.

<Measurement method of gripper displacement>
The passing timing of each gripping means was sampled using the Keyence GR 3000 by the gripper detection proximity sensor installed at the end of stretching, and the distance of the shift was calculated from the time difference between the corresponding left and right grippers. The angle between the maximum value of all the measured values when the loop of the link device makes a round, and the line connecting the centers of both grips and the direction perpendicular to the film transport direction in the film plane, which is obtained from the measured value Table 1 shows θ (the angle in the direction of θ ₁ shown in FIG. 7 is positive and the angle in the direction of θ ₂ is negative).

<Measurement method of orientation angle>
Using an Olympus polarizing microscope BX51, the slow axis direction was measured at 180 points of 30 points in the width direction × 6 points in the flow direction at intervals of 50 mm in the width direction of the film and 1000 mm in the flow direction. The angle of the slow axis was determined by setting the parallel direction to 0 °, and the average value was calculated. Moreover, the maximum value-minimum value among all measured values was regarded as variation. The results are shown in Table 1.

<Re value measurement method>
Using Oji Scientific Co., Ltd. KOBRA-21ADH, measurements were made at 180 points of 30 points in the width direction × 6 points in the flow direction at intervals of 50 mm in the width direction of the film and 1000 mm in the flow direction. Moreover, the maximum value-minimum value among all measured values was regarded as variation. The results are shown in Table 1.

(Example 2)
Without adjusting the link device of (1-2), instead, in the simultaneous biaxial stretching process, the speed of the gripper at the stretching end part is adjusted by changing the rotational speed of the outlet sprocket, and the stretching end part A stretched film was produced in the same manner as in Example 1 except that the deviation between the positions of the two grippers opposed to each other was controlled to be within 10 mm, and the shift of the gripper was measured, and the orientation angle and Re value were measured. did. The results are shown in Table 1.

(Example 3)
(1-2) The link device is not adjusted, but instead, the pitch P2 at the time of link extension is adjusted by adjusting the position of the guide rail, and the positions of the opposing grippers at the end of the extension are adjusted. A stretched film was produced in the same manner as in Example 1 except that the deviation was controlled to be within 10 mm, the deviation of the gripper was measured, and the orientation angle and Re value were measured. The results are shown in Table 1.

(Comparative Example 1)
The length of the block is measured as in Example 1, and manufacturing is performed with a link device having a maximum difference in the length of the pair of blocks of 0.2% of the average block length. Re value was measured.

  From the results shown in Table 1, it can be seen that the stretched optical film produced by the production method of the present invention is homogeneous in both Re value and orientation angle.

FIG. 1 is a schematic top view of a main part related to stretching of a film in an example of a simultaneous biaxial stretching machine used for carrying out the production method of the present invention. FIG. 2 is a longitudinal sectional view showing a specific example of means for heating the film in the example of FIG. FIG. 3 is a top view schematically showing a stretching mechanism by a link device in an example of a simultaneous biaxial stretching machine used in the production method of the present invention. FIG. 4 is a longitudinal sectional view for explaining one unit 107 of the link device 101 shown in FIG. FIG. 5 is a top view schematically showing a more specific example of the link device in an example of the simultaneous biaxial stretching machine used for carrying out the manufacturing method of the present invention. FIG. 6 is a top view showing an aspect of gripper control in the manufacturing method of the present invention. FIG. 7 is a top view showing an aspect of gripper control in the manufacturing method of the present invention. FIG. 8 is an upper view showing an aspect of a gripper having an equal interval in the manufacturing method of the present invention.

Explanation of symbols

101, 601L, 601R Link device 102a-102d, 302a-302d Link plate 103a, 103b, 303a, 303b Bearing roller 104a-104c Guide rail 105, 305 Film 106a, 106b Sprocket 107 One unit 108, 308, 608 of the link device Child 109 Spring 110 Gripping part 111 Gripping element top part 120 Drive shaft 130a-130b Holding part 191 Oven 250a Upper nozzle 250b Lower nozzle 251a Upper nozzle opening 251b Lower nozzle opening 252a Duct for upper nozzle 252b Duct for lower nozzle 253 HEPA filter 254 Fan 255 Heater 256 Suction duct

Claims (6)

The step of continuously supplying an unstretched film to a stretching machine having a plurality of grippers, the step of gripping both ends of the unstretched film with grippers, and the longitudinal direction of the unstretched film by moving the grippers And a method of producing a stretched optical film comprising a step of simultaneously biaxially stretching in the transverse direction,
In the simultaneous biaxial stretching step,
A line connecting the centers of the two grippers of each pair when the pitch when gripping the unstretched film of the grippers is 10 to 60 mm and one of the opposing grippers reaches the end of stretching; A method for producing a stretched optical film, wherein an angle formed by a direction perpendicular to the film conveyance direction in the film plane is within 0.5 °.   2. The method for producing a stretched optical film according to claim 1, wherein the positions of the opposing grippers at the stretching end portion are adjusted by equalizing the distance between the grippers.   The method for producing a stretched optical film according to claim 1, wherein the position of the opposing grippers at the stretching end portion is adjusted by changing the speed at the stretching termination portion of each of the opposing grippers. .   2. The method for producing a stretched optical film according to claim 1, wherein the position of the opposing grippers at the stretch end portion is adjusted by changing the longitudinal stretch ratio. The stretched optical element according to claim 1, wherein an area of a surface of the gripper that contacts the film is 75 to 1000 mm ² , and a shape of the surface that contacts the film is a circular shape, an elliptical shape, or an approximate elliptical shape. A method for producing a film.   The step of continuously supplying the unstretched film includes a step of melt-extruding a thermoplastic resin to form the unstretched film, and a step of continuously conveying the formed unstretched film inline to the stretcher. The manufacturing method of the stretched optical film of any one of Claims 1-5 characterized by the above-mentioned.

Images