JP2001221915A - Optical film, polarizer protective film consisting of that film, and polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film having small phase difference, small angle dependence of the phase difference, improved tensile fracture strength without decreasing the low moisture permeability and heat resistance of a noncrystalline thermoplastic resin. SOLUTION: The optical film used consists of a stretched noncrystalline cyclic olefin copolymer and has <=20 nm phase difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical film made of an amorphous thermoplastic resin and having a small retardation. More specifically, the present invention relates to an optical film using an amorphous cyclic olefin-based resin having excellent transparency and surface properties, a small retardation, and an improved tensile strength at break.

[0002]

2. Description of the Related Art As plastics used for optical applications, polycarbonates, acrylic resins, amorphous cyclic olefin resins, etc., having excellent transparency are used. Among these, the amorphous cyclic olefin resin is particularly superior to other resins in terms of characteristics such as low retardation, low photoelastic coefficient, and low moisture permeability. It is of interest as an alternative to the triacetylcellulose-based films that have been used. However, for example, when the film thickness is used as an optical film used for a liquid crystal display, the mechanical strength is low, and there is a problem in handling in a manufacturing process.

[0003] Stretching a film is used as one of the techniques for improving mechanical strength. JP-A-2-19
No. 6832 has an application for a cyclic olefin copolymer sheet or film characterized by being biaxially stretched. The examples in the application describe that the stretching ratio is 4 to 10 times, the mechanical strength is improved, and transparency and low retardation are characteristic. However, no mention is made of the angle dependence of the phase difference. Patent 2615
No. 957 filed an application that the stretching ratio in the longitudinal (MD) direction was set to 2 times or less, and the film was stretched 3 to 8 times in the transverse (TD) direction, whereby a film having excellent tearability in the transverse direction could be obtained. However, in this patent, it is easily presumed that the high draw ratio in the transverse direction causes a decrease in strength in the transverse direction in applications where tearing is not required, which is a practical problem. No further reference is made to the phase difference.

Japanese Patent Application Laid-Open No. Hei 9-234786 discloses an application relating to a biaxially oriented film having a thickness of 25 μm and comprising an amorphous cyclic olefin copolymer having a tensile elongation at break within a certain range. Although the thinner the film, the better in terms of flexibility and cost, the problem arises when the mechanical strength under actual use conditions does not reach the required level.

Japanese Patent Application Laid-Open No. 2-256003 discloses a film obtained by uniaxially or biaxially stretching an extruded film of a thermoplastic polymer, and has a retardation of 1200 nm or less and a retardation of 1200 nm or less. There is an application for an optical film characterized in that the deflection width is 10% or less. In the examples of the application, although it is stated that a biaxially stretched film 1.7 to 2 times the cast film of polystyrene or styrene / acrylonitrile copolymer is almost non-oriented in the plane, No mention is made of typical retardation or its angular dependence.

If a resin that easily causes orientation birefringence is used, strength can be improved by stretching, but a large retardation occurs in the obtained stretched film, and it is a problem to use it as a polarizer protective film. There is. Plastic, vol. 38, no. As described in 7, P15, for example, polycarbonate is a resin having a high birefringence and orientation birefringence easily occurs.

It is considered that an amorphous cyclic olefin resin having a relatively small orientation birefringence is relatively unlikely to cause a phase difference due to stretching. However, even when an amorphous cyclic olefin resin is used, the stretching ratio can be increased. It has been known from the study of the present inventors that a phase difference will occur if this occurs.

In addition, the present inventors have studied clearly that, although the triacetylcellulose-based film has a retardation (Re (0)) of 9 nm, the problem that the angle dependence of the retardation is large even in an unstretched state. became. For example, Re
(45) / Re (0) was 3.2. A liquid crystal display incorporating a polarizing plate using such a film having a large phase difference angle dependency as a polarizer protective film has a problem that the viewing angle becomes narrow. Further, there is also a problem that moisture permeability is high due to the primary structure.

[0009]

DISCLOSURE OF THE INVENTION The present invention has a small phase difference and a small angle dependence of the phase difference without impairing the low moisture permeability and heat resistance of the amorphous thermoplastic resin. An object of the present invention is to provide an optical film having improved tensile breaking strength.

[0010]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and as a result, an optical film comprising a stretched amorphous cyclic olefin-based copolymer and having a retardation of 20 nm or less. The inventors have found that such a problem can be solved by using the present invention, and have completed the present invention.

That is, the present invention provides a novel optical film having the following constitution, thereby achieving the above object. 1) An optical film having a thickness of 30 μm or more, comprising a stretched amorphous cyclic olefin copolymer and having a retardation value of 20 nm or less. 2) The film is made of a stretched amorphous cyclic olefin-based copolymer, and has a retardation value (Re (0)) measured from the front of the film of 45 ° in a direction perpendicular to the film optical axis.
° The ratio (R (45)) of the value (Re (45)) measured from the tilted direction
= Re (45) / Re (0)) is 3 or less, the optical film as described in 1) above, wherein (3) The optical film as described in (1) or (2) above, wherein the optical film is made of a stretched amorphous cyclic olefin copolymer and has a tensile strength at break of 1.25 times or more that of the unstretched state. 4) A polarizer protective film comprising the optical film described in 1) to 3) above, and a polarizing plate comprising the polarizer protective film.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Amorphous cyclic olefin copolymer used in the present invention (hereinafter sometimes abbreviated as COC)
Is an amorphous polymer having a cyclic olefin structure, preferably 50 to 250 ° C, more preferably 80 to 250 ° C.
It has a glass transition temperature of 200C, particularly preferably 80-160C. If the glass transition temperature is less than 50 ° C., the rigidity is low, and deformation tends to occur in a high temperature environment. If the glass transition temperature exceeds 250 ° C., processing becomes difficult, which is not preferable. The COC used in the present invention is preferably 1 to 9 based on the total amount of COC.
9 parts by weight of a cyclic olefin, preferably of the formula
I, III, IV, V, VI, or VII

[0013]

Embedded image

(Wherein R ^{1 to} R ⁸ represent a hydrogen atom or C ₁
A hydrocarbon group having -C _20, may be the same or different among the constituting units. When the number of carbon atoms is 2 or more, a ring may be formed. . In addition, n in Formula VII is 2
It is an integer of 10. ), And 99 to 1 part by weight of at least one acyclic olefin, preferably of the formula VIII

[0015]

Embedded image

(Wherein R ^{9 to} R ¹² are a hydrogen atom or C ₁ to
A hydrocarbon group of C _20, may be the same or different among the constituting units. ), And a vinyl structural unit containing a double bond in an amount of 0 to 20 parts by weight as charged during polymerization (100 parts by weight in total). More preferably, the formulas I to VI are based on the total amount of COC.
40 to 90 parts by weight of a cyclic olefin represented by I, a formula VIII
(A total of 100 parts by weight).

Preferred COCs are cyclic olefins having a norbornene basic structure, particularly preferably norbornene or tetracyclododecene or a cyclic olefin having a structure derived therefrom, and a non-cyclic olefin having a terminal double bond such as α-olefin. It consists of an olefin, particularly preferably ethylene or propylene. Of these, copolymers of norbornene / ethylene, norbornene / propylene, tetracyclododecene / ethylene, and tetracyclododecene / propylene are particularly preferred.

As the COC used in the present invention, commercially available products such as "APEL" manufactured by Mitsui Chemicals and "ZEONOR" manufactured by Zeon Corporation can be used.

In the present invention, a graft-modified amorphous cyclic olefin resin can also be used. The graft-modified amorphous olefin resin can be obtained, for example, by subjecting the amorphous cyclic olefin resin and a vinyl monomer to a graft reaction in the presence of a radical initiator.

These resins may be used alone or as a mixture.

In the present invention, as long as the object of the present invention is not impaired in the amorphous cyclic olefin resin, a resin component other than the amorphous cyclic olefin resin, a rubbery polymer, an antioxidant, and an ultraviolet absorber , A leveling agent, an adhesion-imparting agent, and the like. Further, the amounts of these components can be appropriately used according to the purpose of the compounding.

The optical film obtained by the present invention can be produced by a melt molding method or a solution casting method. When manufacturing by a melt molding method, a method using a T-die or the like can be applied. When manufacturing by a solution casting method, a bar coater, a comma coater, a T-die, a T-die with a bar, a doctor knife,
It can be cast on a support using a Meir bar, a roll coat, a die coat, or the like.

In the present invention, the film obtained in this manner is stretched by a stretching machine at a longitudinal stretching ratio and a transverse stretching ratio of 1.05.
By stretching in a range of up to 3.0 times, a film having a small angle dependence of the retardation is obtained. When the stretching ratio is smaller than 1.05, the effect of stretching is insufficient, and the tensile strength at break is hardly in a desired range. When the stretching ratio is larger than 3.0, the angle dependence of the phase difference becomes large, and the viewing angle characteristics are likely to be deteriorated (Re (45) / Re (0) becomes large). The stretching temperature condition is not particularly limited as long as the stretching effect is produced, but it is desirable to carry out the stretching within a temperature range from 30 ° C. lower than the glass transition temperature of the film to 50 ° C. higher than the glass transition temperature. When stretching is performed in these temperature ranges,
The effect of stretching is sufficiently obtained, and the tensile strength at break tends to be in a desired range.

As the stretching means, general stretching techniques such as roll stretching and tenter stretching can be used. The stretching may be performed by any of uniaxial, sequential biaxial, and simultaneous biaxial methods.

In the present invention, the thickness of the stretched film can be selected according to the application. Generally, 10
A range of 500 μm, preferably 20 to 300 μm, more preferably 30 to 100 μm is used. Further, the film thickness of the raw film before stretching may be set to a film thickness considering the influence of stretching.

The optical film obtained by the production method of the present invention can be used for various applications, but has excellent transparency,
It can be used for liquid crystal display devices such as a polarizer protective film and a transparent conductive film by utilizing the surface properties and low retardation. When used as a polarizer protective film,
Affixed to a polarizing film obtained by impregnating iodine and organic dye into stretched polyvinyl alcohol,
It can be a polarizing plate. Since the polarizing plate using the film obtained in the present invention has excellent phase difference angle dependency (viewing angle characteristics), it can be applied to a liquid crystal display and the like which are large in size. In particular, it is particularly useful when used in a liquid crystal television or the like.

[0027]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples. Each physical property value of the film was measured as follows. Film thickness: Five test pieces were cut out of the film in a size of 10 mm × 150 mm in each of the longitudinal (MD) and width (TD) directions. At a temperature of 23 ° C. ± 2 ° C. and a humidity of 50% ± 5%, five points of each test piece were measured using a Mitutoyo Digimatic Indicator, and the average value was taken as the film thickness. Residual solvent amount (W): 100 mm x 100 from film
A test piece was cut out at a size of mm and weighed (W ₁ ).
The film was put into a dryer at 180 ° C. for 1 hour and weighed again (W ₂ ). From these, according to the following formula,
I asked. W = ((W ₁ −W ₂ ) / W ₁ ) × 100 Glass transition temperature: Approximately 10 mg of a test piece was cut out of a film, and 200 g was measured using a DSC-50 manufactured by Shimadzu Corporation.
The temperature was measured at a heating rate of 20 ° C / min up to ° C. The glass transition temperature was determined from the changing point of the DSC profile. Haze: A test piece was cut out from the film at a size of 50 mm × 50 mm, and measured at a temperature of 23 ° C. ± 2 ° C. and a humidity of 50% ± 5% using a turbidimeter 300A manufactured by Nippon Denshoku Industries. Phase difference: Measured at a temperature of 23 ° C. ± 2 ° C. and a humidity of 50% ± 5% at a wavelength of 515 nm and an incident angle of 0 ° using KOBRA-21AD manufactured by Oji Scientific Instruments, and Re (0)
And The viewing angle characteristics of the phase difference were measured in the same manner as described above by inclining by 45 ° in the direction perpendicular to the optical axis (incident angle: 45 °), and this was measured as Re (45). (R
e (0)), R = Re (45) / Re (0) was calculated. Tensile breaking strength: A test piece was cut out from the film at a size of 200 mm × 15 mm with the longitudinal (MD) direction as a major axis, and measured using an autograph (AG-200A) manufactured by Shimadzu Corporation based on JIS K7127. The distance between the chucks was 100 mm, and the pulling speed was 30 mm / min. Production Example 1 A toluene solution of Apel 6013 manufactured by Mitsui Chemicals (resin concentration =
22% by weight) to obtain a dope. Using a bar coater, the dope was cast on polyethylene terephthalate (Tetron HS manufactured by Teijin, thickness 125 μm),
After being left at room temperature for 60 minutes, it was further dried at 80 ° C. for 12 hours to obtain a 90 μm raw material (residual volatile content = 0.9 wt.
%, Tg = 123 ° C.). Examples 1 to 3 The film produced in Production Example 1 was stretched under the conditions shown in Table 1. Table 1 shows the optical properties and tensile strength at break of the obtained stretched film. Example 4 A raw (unstretched) film of a film produced in the same manner as in Production Example 1 except that the film thickness was changed to 125 μm, was stretched 4 times uniaxially in the machine direction, and the same as in Example 1 except for the stretching ratio. did. Comparative Example 1 Table 1 shows the optical properties, tensile strength at break, and the like of the raw (unstretched) film produced in Production Example 1.

[0028]

[Table 1]

Production Example 2 A dope was prepared by adjusting a xylene solution (resin concentration = 35% by weight) of Zeonor 1420R manufactured by Zeon Corporation. The dope was cast on polyethylene terephthalate (Tetron HS manufactured by Teijin, thickness 125 μm) using a bar coater, allowed to stand at room temperature for 60 minutes, and further dried at 80 ° C. for 12 hours to obtain a raw material of 89 μm. (Residual volatile content = 1.
0 wt%, Tg = 127 ° C). Examples 5 and 6 The film produced in Production Example 2 was stretched under the conditions shown in Table 2. Table 2 shows the optical properties and tensile strength at break of the obtained stretched film. Comparative Example 2 Table 2 shows the optical properties, tensile strength at break, and the like of the raw (unstretched) film produced in Production Example 1. Comparative Example 3 The raw (unstretched) film produced in Production Example 2 was stretched 4 times uniaxially in the machine direction except that the film thickness was changed to 125 μm, and the same as in Example 5 except for the stretching ratio.

[0030]

[Table 2]

[0031]

According to the present invention, the retardation is small, the angle dependence of the retardation is small, and the tensile strength at break is maintained without impairing the low moisture permeability and heat resistance of the amorphous thermoplastic resin. Can be provided with improved optical film. Since the polarizing plate using the film obtained in the present invention has excellent phase difference angle dependency (viewing angle characteristics), it can be applied to a liquid crystal display and the like which are large in size.

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Claims (5)

[Claims] 1. An optical film having a thickness of 30 μm or more, comprising a stretched amorphous cyclic olefin copolymer and having a retardation value of 20 nm or less. 2. A film made of a stretched amorphous cyclic olefin copolymer and having a retardation value (Re (0)) measured from the front of the film and a direction inclined by 45 ° in a direction perpendicular to the optical axis of the film. 2. The optical film according to claim 1, wherein a ratio (R = Re (45) / Re (0)) of a value (Re (45)) measured from (3) is 3 or less. 3. The optical film according to claim 1, wherein the optical film is made of a stretched amorphous cyclic olefin copolymer, and has a tensile strength at break of 1.25 times or more that of the unstretched state. . 4. A polarizer protective film comprising the optical film according to claim 1. 5. A polarizing plate comprising a polarizer protective film comprising the optical film according to claim 1.