JP3579447B2 - Method for producing polycarbonate resin sheet for optical use - Google Patents

Description

【００１８】
【発明の効果】
本発明によれば、特別繁雑な工程を必要とせず、極めて簡単な操作で全面のリターデーションが４０ｎｍ以下、更には２０ｎｍ以下の光学用途に適したポリカーボネート樹脂シートの提供が可能であり、その奏する工業的効果は格別なものである。
【図面の簡単な説明】
【図１】本発明を実施するに適したシートの成形法の一例を示す概略図
【図２】シートのたるみの状態を説明するための概略図
【符号の説明】
１ Ｔ型ダイ
２ 第１冷却ロール
３ 第２冷却ロール
４ 第３冷却ロール
５ 第１移送ロール
６ 引取りロール[0001]
[Industrial applications]
The present invention relates to a polycarbonate resin sheet for optical use. More specifically, the present invention relates to an optical polycarbonate resin sheet having excellent biplanarity in which the birefringence (absolute value of retardation, hereinafter simply referred to as retardation) of the entire surface is 40 nm or less and substantially free of warpage.
[0002]
[Prior art]
Polycarbonate resin is used for optical discs and optical cards that use laser light because of its excellent transparency and dimensional stability, and high heat resistance and impact resistance. Use for a phase difference correction plate or the like is also being studied. In order to use a polycarbonate resin sheet for such an application, it is necessary to lower the retardation of the entire surface of the sheet. However, the polycarbonate resin has a high melt viscosity, and it is extremely difficult to produce a sheet having a low overall retardation by a normal extrusion molding method.
[0003]
Conventionally, various methods for reducing the retardation of a polycarbonate resin sheet have been proposed. For example, Japanese Patent Application Laid-Open No. 62-140817 proposes a method in which a sheet is sandwiched between stainless steel plates and heat-treated under pressure to obtain a sheet having a retardation of 20 nm or less. However, in this method, distortion due to pressure remains in the sheet, and it is difficult to obtain a sheet having a retardation of 20 nm or less in the entire width direction. According to the method described in JP-A-63-47139, a sheet having a retardation of 0 to 8 nm is obtained. However, this method requires a complicated process of superimposing two sheets in parallel with each other so that the optical axis forms an angle of 90 °, so that it is difficult to industrially adopt the method. In the method described in Japanese Patent Publication No. 5-71026, a sheet having a retardation of 17 to 18 nm is obtained, but in this method, the retardation at both ends in the width direction is significantly increased. Further, according to the method described in JP-A-4-166319, a sheet having a retardation of 7 to 29 nm is obtained. However, the molecular weight of the polycarbonate resin sheet used in this method is as low as 14500 to 18900 in terms of viscosity average molecular weight, and is inferior in durability, so that it has not been put to practical use. Further, Japanese Patent Application Laid-Open No. Sho 60-214923 proposes a manufacturing method in which the speed ratio of a plurality of cooling rolls is set respectively to apply no tension to a sheet. However, in this method, it is difficult to obtain a sheet having low birefringence over the entire extrusion width, and none of these proposals is an industrially advantageous method.
[0004]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a method for industrially advantageously producing a polycarbonate resin sheet useful for optical applications, in which retardation in the width direction of an extruded sheet is uniformly low, and is substantially uniform and excellent in durability. It is to be.
[0005]
The present inventor has achieved the above object, and as a result of intensive studies on the sheeting conditions of the polycarbonate resin, in order to stably reduce the birefringence in the entire width direction, the speed of the take-off roll at the time of take-off is more than the speed of the cooling roll. It has been found that it is effective to make the sheet in the cooling process less likely to receive a stress at the time of take-off by delaying and causing the sheet between the final cooling roll and the first transfer roll to be slackened. The present invention has been completed as a result of further studies based on this finding.
[0006]
[Means for Solving the Problems]
The present invention extrudes a molten polycarbonate resin into a sheet from a T-die of an extruder, cools it with a plurality of cooling rolls, and then transfers it with a plurality of transfer rolls to produce a polycarbonate resin sheet. The surface temperature of the sheet to be peeled off from the cooling roll is maintained at a temperature equal to or higher than the second transition point, the surface temperature of the sheet in contact with the first transfer roll is adjusted to a temperature equal to or lower than the second transition point, and the final cooling roll and the first transfer roll The following formula [1] is obtained when the slack in the section of the above is defined as L ( cm ) as the linear distance from the sheet separation point of the final cooling roll to the contact point of the sheet of the first transfer roll, and h ( cm ) as the slack distance .
0.1L ≦ h ≦ L [1]
Birefringence and satisfying the is following manufacturing method of an optical polycarbonate resin sheet 40 nm.
[0007]
The polycarbonate resin referred to in the present invention is an aromatic polycarbonate resin obtained by reacting a dihydric phenol with a carbonate precursor by a solution method or a melting method, and may be a mixture of two or more polycarbonate resins. Its molecular weight is preferably about 19000 to 35,000 as represented by a viscosity average molecular weight. The dihydric phenol used here is mainly 2,2-bis (4-hydroxyphenyl) propane (commonly known as bisphenol A), but a part or all of the dihydric phenol may be replaced with another dihydric phenol. Other dihydric phenols include, for example, bis (4-hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, , 2-bis (4-hydroxy-3-methylphenyl) propane, bis (4-hydroxyphenyl) sulfide, bis (4-hydroxyphenyl) sulfone and the like. Examples of the carbonate precursor include carbonyl halide, carbonate ester, and haloformate, and specific examples include phosgene, diphenyl carbonate, and dihaloformate of a dihydric phenol. In producing a polycarbonate resin, a molecular weight regulator, a catalyst, a branching agent for improving processability, and the like can be used as necessary. Further, the polycarbonate resin, if necessary, additives such as release agents such as esters or partial esters of polyhydric alcohols and fatty acids, phosphites, phosphates, heat stabilizers such as phosphonates, benzotriazoles, An acetophenone-based or salicylate-based ultraviolet absorber, an antistatic agent, a coloring agent, a whitening agent, a flame retardant, or the like may be blended.
[0008]
In the method for forming a polycarbonate resin sheet, which is the object of the present invention, the molten polycarbonate resin is extruded into a sheet shape from a T-die of an extruder, cooled by a plurality of cooling rolls, and then transferred by a plurality of transfer rolls to draw. This is a melt extrusion method in which 2 to 4 cooling rolls are usually used, and 5 to 20 transfer rolls are usually used. FIG. 1 is a schematic view showing an example of a sheet forming method suitable for carrying out the present invention, in which 1 is a T-die, 2 is a first cooling roll, 3 is a second cooling roll, 4 is a third cooling roll. A cooling roll, 5 is a first transfer roll, and 6 is a take-up roll. This will be described below with reference to FIG.
[0009]
In the present invention, the temperature is maintained at a temperature equal to or higher than the secondary transition point until a point at which the sheet surface temperature finally separates from the cooling roll passing therethrough. That is, the surface temperature of the sheet at the time of peeling from the third cooling roll is maintained at the second transition point or higher. If the surface temperature of the sheet at the time of this peeling is lower than the secondary transition point, strain due to heat shrinkage stress is generated on the cooling roll, so that the birefringence increases, and the target retardation in the target width direction is uniformly low. Becomes difficult to obtain. If the surface temperature of the sheet at the time of peeling is too high, the sheet may be wound around the cooling roll. Therefore, the surface temperature of the sheet at the time of peeling should be in a range of 2 ° C. higher than the second transition point to 15 ° C. higher. Is particularly preferred. In order to maintain the surface temperature of the sheet at the time of peeling from the third cooling roll at or above the second transition point, for example, the temperature of the third cooling roll is controlled, or a heater or the like is provided from outside the sheet on the third cooling roll. An arbitrary method such as heating control is adopted.
[0010]
When the sheet peeled off from the third cooling roll comes into contact with the first transfer roll, that is, the first transfer roll, it is necessary to cool the sheet until its surface temperature becomes equal to or lower than the secondary transition point. Although the sheet surface temperature at the time of contact with the first transfer roll may be low, the birefringence increases at the second transition point or higher because the stress at the time of taking over remains in the state of being applied to the sheet. In particular, it is preferable to cool the surface temperature of the sheet when coming into contact with the first transfer roll to a temperature lower than the second transition point by 5 ° C. or more. In order to cool the surface temperature of the sheet to a temperature equal to or lower than the secondary transition point before the sheet peeled off from the third cooling roll comes into contact with the first transfer roll, an arbitrary method is adopted. It is preferable that the space between the first transfer rolls is appropriately adjusted for air cooling.
[0011]
In the present invention, when the sheet is cooled between the third cooling roll and the first transfer roll, the sheet is given a slack. Here, the retardation in the width direction can be reduced uniformly by allowing the sheet to be slack and cooling. If the sag is extremely small, it is difficult for the retardation in the width direction to be sufficiently low. If the sag is extremely large, the sheet may be deformed and conversely the birefringence may increase. FIG. 2 shows a state in which the sheet is slackened. In the figure, reference numeral 4 denotes a third cooling roll, and 5 denotes a first transfer roll. The linear distance from the sheet separation point of the third cooling roll to the contact point of the sheet of the first transfer roll is L (cm), and the slack distance is h. (Cm) and the following formula [1]
0.1L ≦ h ≦ L [1]
Is preferably sagged.
[0012]
Any method is used to cause the sheet to sag. For example, a method in which the surface speed of the take-off roll is made slower than the surface speed of the cooling roll to generate a predetermined slack, and then returned to a speed equivalent to the surface speed of the cooling roll, the nip roll is incorporated into the transfer roll, and the surface speed of the nip roll and A method for controlling the distance is preferable.
[0013]
If the thickness of the sheet is too thin, the sheet will meander during take-off, and if it is too thick, the sheet will be deformed and it will be difficult to obtain a flat product. Particularly preferred is 2 to 0.8 mm.
[0014]
【Example】
Examples will be further described below with reference to examples. The measurement of retardation and warpage of the sheet was performed by the following methods.
(1) Retardation: Using an automatic birefringence measuring device (ADR-200 B type) manufactured by Oak Manufacturing Co., Ltd., a He-Ne laser was used as a light source, and a retardation corresponding to a wavelength of 632.8 nm was applied from the end of the sheet. It measured at the position of 10, 20, 30, 40, 50, 60, 70, 80, 90 cm.
(2) Warp ratio: Deformation in a concave or convex shape in a direction parallel to a side in accordance with the test method of JIS K-6911 is referred to as warpage, and is expressed as a percentage (%) of the maximum warpage with respect to a length of 1000 mm. The larger is the larger the warpage is.
[0015]
[Examples 1-3 and Comparative Examples 1-4]
A sheet was manufactured by an extruder provided with the apparatus shown in FIG. The T-die 1 uses a mirror surface roll having a width of 1100 mm and the first, second and third cooling rolls each having a diameter of 300 mm, and is a straight line from the sheet separation point of the third cooling roll to the contact point of the sheet of the first transfer roll. The distance L was set to 60 cm.
A polycarbonate resin powder having a viscosity average molecular weight of 24,500 and a secondary transition point of 140 ° C. produced by a solution method from bisphenol A and phosgene is extruded from a T-die set at 282 ° C. at a discharge rate of 280 kg / hour, and is extruded at the first, second, and second positions. (3) A sheet having a width of 1000 mm and a thickness of 0.4 mm was obtained through a cooling roll and a transfer roll. The surface speeds of the first, second and third cooling rolls are set to 8.10 m / min, the temperatures of the first and second cooling rolls are set to 140 ° C. and 152 ° C., respectively, and the temperature of the third cooling roll is set forth in Table 1. , And the speed of the take-off roll was adjusted to maintain the amount of slack in the sheet between the third cooling roll and the first transfer roll at the amount shown in Table 1. Table 1 shows the surface temperature of the sheet when peeled from the third cooling roll, the surface temperature of the sheet when it comes into contact with the first transfer roll, and the characteristic values of the obtained sheet. As is evident from Table 1, all of the sheets of the examples have low retardation and are substantially homogeneous, whereas the sheets of the comparative examples have high retardation or large variations.
[0016]
[Example 4 and Comparative Example 5]
The surface speeds of the first, second and third cooling rolls are set to 2.7 m / min, the temperatures of the first and second cooling rolls are set to 120 ° C. and 130 ° C., respectively, and the temperature of the third cooling roll is set forth in Table 1. And the thickness of the sheet was adjusted in the same manner as in Example 1 except that the slack amount of the sheet between the third cooling roll and the first transfer roll was maintained at the amount shown in Table 1 by adjusting the speed of the take-off roll. Was 1.2 mm. Table 1 shows the surface temperature of the sheet when peeled from the third cooling roll, the surface temperature of the sheet when it comes into contact with the first transfer roll, and the characteristic values of the obtained sheet. As is evident from Table 1, the sheets of the examples have a low retardation and are substantially homogeneous, whereas the sheets of the comparative examples have a high retardation and large variations.
[0017]
[Table 1]

[0018]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the retardation of the whole surface is 40 nm or less, and the provision of the polycarbonate resin sheet suitable for the optical use of 20 nm or less can be provided by an extremely simple operation without the need for a complicated process. The industrial effects are exceptional.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a sheet forming method suitable for carrying out the present invention. FIG. 2 is a schematic diagram for explaining a state of a sheet sagging.
DESCRIPTION OF SYMBOLS 1 T-die 2 1st cooling roll 3 2nd cooling roll 4 3rd cooling roll 5 1st transfer roll 6 Take-up roll

Claims (1)

The molten polycarbonate resin is extruded into a sheet from a T-die of an extruder, cooled by a plurality of cooling rolls, and then transferred by a plurality of transfer rolls to produce a polycarbonate resin sheet. The surface temperature of the sheet to be heated is maintained at a temperature equal to or higher than the second transition point, the surface temperature of the sheet in contact with the first transfer roll is adjusted to a temperature equal to or lower than the second transition point, and sag in the section between the final cooling roll and the first transfer roll. However, when the linear distance from the sheet peeling point of the final cooling roll to the contact point of the sheet of the first transfer roll is L ( cm ), and the slack distance is h ( cm ), the following equation [1] is used.
0.1L ≦ h ≦ L [1]
A method for producing an optical polycarbonate resin sheet having a birefringence of 40 nm or less, characterized by satisfying the following.

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