JP2007245700A - Manufacturing method for embossed sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an embossed sheet excellent in flatness, free from the generation of horizontal streaks and low in phase difference, while securing surface and transfer properties. <P>SOLUTION: In the method for molding an embossed sheet having a thickness of 50 to 130 μm by pressing a thermoplastic resin M in a melting state extruded from a die 1 with a fixed rol 2 having its axial fulcrum fixed and its surface rugged for embossing and with a metal belt 3 disposed between two or more rolls 41, 42 with their axial fulcrums movable, the holding angle of the belt 3 relative to the fixed roll 2 is so set that the circular arc length of the contact part 31 of the belt 3 contacting to the surface of the fixed roll 2 under a surface pressure of 0.5 MPa or more is 10 to 20 mm. Particularly when the holding angle is so set as to have the circular arc length of 15 to 20 mm, an embossed sheet free from the generation of horizontal streaks and suitable for optical use can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an embossed sheet having a thickness of 50 to 130 μm mainly used as an optical sheet.

  As a general manufacturing method of an embossed sheet by a melt extrusion method, a two-roll method (see Patent Document 1 below) for forming a sheet by sandwiching a molten resin extruded from a die with a fixed roll and a pressure roll, A belt method is known in which a sheet is formed by sandwiching molten resin between a fixed roll and a metal belt (including a cylindrical forming drum made of a flexible thin-walled pipe) (see Patent Document 2 below).

  The two-roll system can be easily designed and the uneven shape on the surface of the fixed roll can be easily transferred by setting the pressure and temperature of the pressure-bonding roll. In the case of the two-roll method, since the pressure bonding time is instantaneous, it is difficult to cause distortion in the thickness direction of the sheet, and generally a sheet having a low phase difference can be formed. However, in the case of a thin sheet, its flatness is significantly deteriorated, causing flare such as a single thickness, which leaves a problem in the form of the product. In addition, in a two-roll type sheet, phase difference unevenness occurs in the width direction of the sheet, and when it is observed through a polarizing plate (particularly in an orthogonal state), it appears as a stripe having a width of several millimeters (hereinafter referred to as “horizontal stripe”). However, this is a fatal defect for optical applications.

  On the other hand, in the belt system, the flatness of the sheet is excellent and no horizontal stripes are observed, but on the other hand, the phase difference is high. In the case of the belt method, it is considered that the phase difference increases due to the stress in the thickness direction while the thickness unevenness is smoothed by increasing the pressure bonding time.

  If the flatness of the sheet is not good, various problems occur in the sheet forming process, the bonding process, and other processing processes. That is, when a sheet having poor flatness is used, a dimensional defect may occur when the sheet meanders on the line and is cut and punched at a specified length. In the case of an optical sheet, non-uniformity in optical performance is caused due to poor flatness. Even when there are horizontal streaks on the optical sheet, there is a problem that the optical sheet is visually perceived as shading unevenness through the liquid crystal display. On the other hand, when the phase difference of the sheet is high, the incident light is polarized, particularly when used for an optical sheet, and the amount of emitted light is reduced.

The factor that impairs the flatness of the sheet is that the sheet peels off from the surface of the fixed roll due to uneven temperature of the fixed roll and molten resin, resulting in distortion of the sheet. is there. In addition, the horizontal streak changes momentarily in the fluidity of the resin by swaying slightly in the flow direction until the molten resin exiting the die is pinched or microscopically producing bangs. This is considered to occur in the width direction of the sheet as a result of the occurrence of thickness unevenness in the flow direction.
In the belt method, since the contact time is appropriately long, the temperature can be lowered, but in the two-roll method, it is difficult.
In the two-roll system, as a means for improving the flatness of the sheet, it is considered that the sheet is sufficiently cooled and solidified on the fixed roll by lowering the resin temperature at the time of molding or the temperature of the fixed roll. When the surface property of the sheet is impaired and the surface of the fixing roll has a concavo-convex shape, the transfer property is deteriorated.
Further, in the two-roll method, as a means for eliminating the horizontal stripe as described above, there has been proposed one that uses elastic rubber for the pinching roll to lengthen the contact time and control the roll temperature and the like. However, when the temperature is lowered, it becomes difficult to manufacture the embossed sheet.
On the other hand, when the molten resin is rapidly cooled by means of a belt system, the residual stress inside the sheet becomes large and curling occurs after the sheet is formed, or the internal phase difference becomes large and cannot be used as an optical sheet.

Japanese Patent Laid-Open No. 9-528368 Japanese Patent Laid-Open No. 8-155959 Japanese Patent No. 3194904

  The present invention has been made in view of the above problems, and provides an embossed sheet having excellent flatness, no horizontal streak, and low phase difference while ensuring surface properties and transferability. The purpose is to do.

  The embossed sheet manufacturing method according to the present invention includes a molten thermoplastic resin extruded from a die, a fixed roll having a shaft fulcrum fixed and an embossed concavo-convex shape on the surface, and the shaft fulcrum is movable. In forming an embossed sheet having a thickness of 50 to 130 μm by clamping with a metal belt passed to two or more rolls, the holding angle of the belt with respect to the fixed roll is 0.5 MPa or more on the surface of the fixed roll. It is characterized by setting so that the arc length of the contact portion of the belt which contacts at a surface pressure of 10 to 20 mm.

  In the embossed sheet manufacturing method according to the present invention, particularly when the embossed sheet is used as an optical sheet, the holding angle of the belt with respect to the fixed roll is set so that the arc length of the contact portion is 15 to 20 mm. Is preferred.

  In the method for producing an embossed sheet according to the present invention, the arc length of the contact portion of the belt is measured, for example, with a “prescale ultra-low pressure sheet” manufactured by Fuji Photo Film Co., Ltd. capable of measuring pressure of 0.5 MPa or more. Can do.

  In the method for producing an embossed sheet according to the present invention, a plastic material having excellent transparency such as a polycarbonate resin, norbornene resin, acrylic resin or the like having good moldability is used as the thermoplastic resin used as the sheet material.

According to the present invention, it is possible to provide an embossed sheet having a thickness of 50 to 130 μm having excellent flatness and a low phase difference while ensuring the surface state of the sheet.
Further, when the holding angle of the belt with respect to the fixed roll is set so that the arc length of the contact portion is 15 to 20 mm, in addition to the above, there is no occurrence of horizontal stripes, and an embossed sheet suitable for optical applications is provided. can get.

Next, an embodiment of the present invention will be described with reference to FIG.
The embossed sheet manufacturing apparatus shown in FIG. 1 includes a T-die (1) for extruding a molten thermoplastic resin into a film, a fixed roll (2) having a fixed shaft fulcrum, and two movable shaft fulcrums. And a belt (3) passed to the rolls (41) and (42).

  The fixing roll (2) is made of metal, and the surface thereof has an uneven shape for embossing. A hollow portion is formed inside the fixed roll (2), and the temperature of the fixed roll (2) is adjusted by allowing a cooling medium to flow through the hollow portion as necessary.

  The belt (3) is a metal endless one, and a predetermined surface is provided on the surface of the fixed roll (2) via a molten thermoplastic resin (M) extruded from the die (1). Pressed with pressure. The surface of the belt (3) is usually a mirror surface, and the back surface of the thermoplastic resin (M) is glazed by this mirror surface portion. The holding angle of the belt (3) with respect to the fixed roll (2) can be appropriately adjusted by moving the shaft fulcrum of the rolls (41) and (42). The holding angle (overhang) of the belt (3) is such that the arc length of the contact portion (31) of the belt (3) contacting the surface of the fixed roll (2) with a surface pressure of 0.5 MPa or more is 10 to 20 mm (pre- (Measurement by scale). The temperature of the belt (3) is adjusted by, for example, setting one of the two rolls (41) and (42) to have the same cooling structure as that of the fixed roll (2).

  When manufacturing an embossed sheet using the manufacturing apparatus described above, while the fixed roll (2) and the belt (3) are rotated, while maintaining them at a required temperature by the cooling means, from the T die (1) The molten thermoplastic resin (M) is extruded into a film. Then, the extruded thermoplastic resin (M) is sandwiched between the fixed roll (2) and the belt (3) and shaped into a sheet, and the surface of the fixed roll (2) is uneven on the surface. The shape is transferred. The sheet thus formed is then sent to the first annealing roll (5) and the second annealing roll (6) to remove the stress, and after necessary processing is performed as necessary, it is wound up. Taken up by the machine.

Example 1
The sheet production apparatus shown in FIG. 1 is used to extrude a molten polycarbonate resin (“Panlite 1225LL” manufactured by Teijin Kasei Co., Ltd.) at 260 ° C. into a film from a T die (1) at a line speed of 15 m / min. By embossing between (2) and the belt (3), an embossed sheet having a thickness of 100 μm was formed. Here, the fixed roll (2) and annealing rolls (5) and (6) are 250φ, the belt (3) is 280φ, and the rolls (41) and (42) passing the belt (3) are 120φ. did. As the fixing roll (2), a surface having a concave shape with a square pyramid with a base of 50 μm and a height of 25 μm as viewed from the plane was used. The temperature was set such that the fixed roll (2) and the first annealing roll (5) were 130 ° C., the second annealing roll (6) was 90 ° C., and the belt (3) was 70 ° C. The holding angle of the belt (3) with respect to the fixed roll (2) is the horizontal distance (A) (side) when the axis of the two rolls (41) (42) passing the belt (3) is observed from the side. The observation distance was set to 5 mm. At this holding angle, the arc length (crimp distance) of the contact part (31) of the belt (3) that contacts the surface of the fixed roll (2) with a surface pressure of 0.5 MPa or more is measured with a prescale ultra-low pressure sheet. As a result, it was 10 mm.

(Example 2)
An embossed sheet having a thickness of 100 μm was formed in the same manner as in Example 1 except that the side observation distance (A) was set to 20 mm and the crimping distance was set to 18 mm.

(Comparative Example 1)
An embossed sheet having a thickness of 100 μm was formed in the same manner as in Example 1 except that the side observation distance (A) was set to 50 mm and the crimping distance was set to 40 mm.

(Comparative Example 2)
An embossed sheet having a thickness of 100 μm was formed in the same manner as in Example 1 except that the side observation distance (A) was set to 70 mm and the crimping distance was set to 60 mm.

(Comparative Example 3)
Using a two-roll type sheet manufacturing apparatus shown in FIG. 2, the line speed is 15 m / min, and a molten polycarbonate resin (“Panlite 1225LL” manufactured by Teijin Kasei Co., Ltd.) at 260 ° C. is formed into a film from the T die (1). An embossed sheet having a thickness of 100 μm was formed by extruding and pinching with a fixing roll (2) and a pressure-bonding roll (7). As the fixing roll (2), the pressure-bonding roll (7), and the annealing rolls (5) and (6), all having a size of 250φ were used. On the surface of the fixed roll (2), a concave shape having a square shape with a base of 50 μm and a square pyramid with a height of 25 μm as viewed from the plane was applied. The temperature was set such that the fixed roll (2) and the first annealing roll (5) were 130 ° C., the second annealing roll (6) was 90 ° C., and the pressure-bonding roll (3) was 70 ° C. The surface pressure of the pressure roll (7) was adjusted to be approximately 1 MPa.

  About the embossed sheet | seat shape | molded by Example 1, 2 and Comparative Examples 1-3, the transfer rate of the shape from a fixed roll to a sheet | seat, a phase difference, flatness, and a horizontal stripe were compared. The transfer rate is obtained by measuring the ratio of the sheet height to the actual ideal shaping of 25 μm. Regarding the phase difference, a birefringence phase difference with respect to a wavelength of 590 nm was measured with a “polarimeter SFII-C type” manufactured by Shinko Seiki Co., Ltd. using a halogen lamp as a light source. The flatness was determined visually. The horizontal streak is placed on a first polarizing plate placed on “Shawkasten (medical X-ray photography observation apparatus)”, and the second polarizing plate is placed on the optical axis with respect to the first polarizing plate. Were placed so as to be orthogonal, and the presence or absence of streaks was visually observed.

As is clear from the results in Table 1, in Examples 1 and 2, good results were obtained for all of the transfer rate, phase difference, and flatness as compared with Comparative Examples 1 to 3.
Further, when the horizontal streak is also taken into account, it can be seen that only Example 2 is in the optimum range specifically.

1 is a schematic view of an embossed sheet manufacturing apparatus according to an embodiment of the present invention. 5 is a schematic view of a two-roll embossed sheet manufacturing apparatus used in Comparative Example 3. FIG.

Explanation of symbols

(1): T die
(2): Fixed roll
(3): Belt
(41) (42): Roll
(M): Thermoplastic resin

Claims (2)

  The molten thermoplastic resin extruded from the die is passed to a fixed roll with a shaft fulcrum fixed and embossed on the surface, and to two or more rolls with a movable shaft fulcrum. In an embossed sheet manufacturing method for forming an embossed sheet having a thickness of 50 to 130 μm by clamping with a belt made of belt, the holding angle of the belt with respect to the fixed roll is brought into contact with the surface of the fixed roll at a surface pressure of 0.5 MPa or more. A method for producing an embossed sheet, wherein the arc length of the contact portion of the belt is set to 10 to 20 mm. The embossed sheet manufacturing method according to claim 1, wherein the holding angle of the belt with respect to the fixed roll is set so that the arc length of the contact portion is 15 to 20 mm.

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