KR101029620B1 - Method for preparing optical films having uniform retardation value - Google Patents

Abstract

The present invention provides a method for producing an optical film comprising the step of stretching the non-oriented film longitudinally while controlling the ratio of the width to the length of the stretching section.

Longitudinal uniaxial stretching, phase difference, optical film

Description

Manufacturing method of optical film with uniform phase difference {METHOD FOR PREPARING OPTICAL FILMS HAVING UNIFORM RETARDATION VALUE}

The present invention relates to a method for producing an optical film having a uniform retardation. More specifically, the present invention not only has a uniform phase difference in the width direction and the thickness direction, but also provides a plane direction phase difference value and a thickness direction phase difference value suitable for use as a compensation film of an LCD device in an in-plane switching (IPS) mode. It relates to a manufacturing method of an optical film having.

Recently, liquid crystal display devices are widely used as display devices for computers, word processors, small televisions, and the like. In particular, STN liquid crystal display systems have been put into practical use, and white STN display devices and color STN display devices have attracted attention.

However, the liquid crystal display device as described above is colored blue or yellow in relation to the birefringence of the liquid crystal cell and the visible light. In the liquid crystal display device of the white STN display device and the color STN display device, the coloring by the phase difference of the liquid crystal cell can be compensated by attaching a retardation film having a specific phase difference value to the substrate surface of the liquid crystal cell.

Stretched TAC (triacetyl cellulose), cycloolefin polymer (COP) (e.g., ZEONOR from ZEON Corp. and ARTON from JSR Corp.) and the like are used for such a retardation film. For example, Japanese Patent Laid-Open No. 2-191904 or Japanese Patent Laid-Open No. 2-42406 discloses an example in which a thermoplastic resin film is produced by longitudinal uniaxial stretching or transverse uniaxial stretching.

In the conventional longitudinal uniaxial stretching method, when the film is stretched, the deviation of the phase difference in the width direction and the thickness direction is large, and thus, the stretched film is manufactured using a method of locally adding heat to both ends of the film in order to control the film. It was.

On the other hand, among the liquid crystal displays of various modes recently introduced to improve the wide viewing angle, the in-plane switching liquid crystal display (IPS-LCD) is a liquid crystal molecules on the substrate surface in the non-driven state Since it has an almost horizontal and uniform arrangement, light can hardly change by the polarizing plate and pass through the liquid crystal layer as it is, resulting in an undriven state by the arrangement of the polarizing plates on the top and bottom surfaces of the substrate. It can indicate an almost complete dark state. In such a liquid crystal display device in a planar switching mode, an optical compensation film is used to improve viewing angle characteristics.

The inventors of the present invention can not only adjust the phase difference deviation in the width direction and the thickness direction by adjusting the ratio of length and width in the stretching section when the non-oriented film is longitudinally uniaxially stretched, and the range and thickness direction of the phase difference value in the plane direction. It was found that the range of the phase difference value can be adjusted. In addition, by adjusting the ratio of the width to the length in the stretching section at the time of longitudinal uniaxial stretching to the specific value or less, the plane direction retardation value and the thickness direction retardation value of the film in IPS (in-plane switching) mode It has been found that it can be adjusted within a range suitable for use as a compensation film of a liquid crystal display.

Accordingly, an object of the present invention is to provide a method for manufacturing an optical film having a uniform phase difference in the width direction and a thickness direction, and having a predetermined surface direction and thickness direction retardation values.

The present invention provides a method for producing an optical film comprising the step of stretching the non-oriented film longitudinally while controlling the ratio of the width to the length of the stretching section.

In addition, the present invention provides a method for producing an optical film comprising the step of stretching the non-oriented film longitudinally uniaxially while adjusting the ratio of the width to the length of the stretching section less than 3.

Hereinafter, the present invention will be described in detail.

The present invention is characterized in that the ratio of the width to the length of the stretching section of the film in the process of producing a stretched film by longitudinally uniaxially stretching the unstretched film. Here, the length means the direction in which the drawing is performed, that is, the longitudinal direction (L-MD), and the width means the vertical direction in the drawing direction, that is, the horizontal direction (L-TD). By adjusting the ratio of the width to the length of the stretching section in the stretching process, not only the phase difference in the width direction and the thickness direction can be adjusted, but also the phase difference values in the surface direction and the thickness direction can be adjusted. Accordingly, in the present invention, by adjusting the ratio of the width to the length of the stretch section of the film, a retardation value in the width direction and the thickness direction is uniform, and a film having various retardation values in the thickness direction with respect to the same surface retardation value can be produced. Can be.

In particular, when the film is stretched, the ratio of the width to the length of the stretch section of the film is less than 3, while heat-treating at a temperature of the glass transition temperature (Tg) -20 ° C. or more of the film, preferably the glass transition temperature (Tg) or more of the film. Preferably, when adjusted to 0.5 or more and less than 3, the flowability of the polymer chain is high, the molecular chain is oriented in the flow direction of the film, the shrinkage of the polymer chain in the width direction is free, so that the stretched film has a high thickness direction It has a phase difference value.

The ratio of the width to the length of the stretching section of the film is less than 3, preferably 0.5 or more and less than 3, more preferably 0.5 or more and 1.5 or less. When the ratio of the width to the length of the stretched section of the film is 3 or more, the length of the stretched section is shorter than the film width, thereby limiting the shrinkage in the width direction of the film, which causes the effect of simultaneous biaxial stretching in the film plane. Accordingly, a problem arises in that the orientation angle distribution of the polymer chain is generated, and the phase difference value in the thickness direction becomes smaller. In addition, if the ratio of the width to the length of the stretch section of the film is less than 0.5, the width of the film in the draw section is too short compared to the length, so the effective width of the film after stretching may be too small productivity.

In this invention, although it does not specifically limit as a unstretched film material which can be used for longitudinal uniaxial stretching, A cyclic olefin type copolymer unstretched film can be used.

Examples of the cyclic olefin copolymer include a ring-opening polymer of a monomer having a norbornene ring structure and a hydrogenated product thereof as a cyclic structure-containing polymer; Addition polymers of monomers having a norbornene ring structure and hydrogenated products thereof; It may be selected and used in addition copolymers of monomers having norbornene-based ring structures with vinyl compounds and hydrogenated products thereof. In this invention, it is especially preferable to use the copolymer of a norbornene-type monomer and an ethylene monomer as said cyclic olefin type copolymer. It is preferable that the ratio of a norbornene-type monomer and an ethylene monomer in the said copolymer is 65-83: 17-35 weight%.

The cyclic olefin copolymer which can be used in the present invention may include a repeating unit represented by the following formula (1).

As the cyclic olefin copolymer, a copolymer of a commercially available norbornene-based monomer and an ethylene monomer can be used.

When manufacturing an optical film using the cyclic olefin copolymer as described above, the heat resistance, low specific gravity, low birefringence, low light modulus, low wavelength dispersibility, etc. of the cyclic olefin copolymer, in particular norbornene-based resin, etc. At the same time, the phase contrast expression is high.

The method for producing the unstretched film of the cyclic olefin copolymer is not particularly limited, and for example, a melt extrusion method, a calender film forming method, a solution cast film forming method, or the like can be used. Among these, the melt extrusion method which is excellent in productivity is preferable. The melt extrusion method is a method in which a cyclic olefin copolymer is heated and melted in a cylinder, pressurized with a screw, and then discharged out from a die such as a T die.

In the present invention, in order to improve the heat resistance, ultraviolet resistance, smoothness, moldability, etc. of the optical film, the cyclic olefin copolymer at the time of film forming, phenol-based, anti-aging agents such as phosphorus, deterioration inhibitors such as phenol-based, amine-based Antistatic agents, such as esters of aliphatic alcohols, polyhydric alcohols, higher fatty acids, amides such as amides, ultraviolet absorbers such as benzophenones and benzotriazoles, and the like can be added within a range not impaired for the purpose of the present invention.

Method for producing an optical film according to the present invention is characterized in that the uniaxially stretched non-stretched film described above, the ratio of the width to the length of the stretching section of the film. The stretching step is described in detail as follows.

The longitudinal uniaxial stretching method according to the present invention can be carried out by performing a preheating step, a stretching step and a heat treatment step, respectively, which can be carried out continuously. The longitudinal uniaxial stretching method may be performed using a manufacturing apparatus provided in the order of a preheating zone, a stretching zone, and a heat treatment zone.

The preheating step refers to a step of preliminarily heating and softening so that the unstretched film can be well stretched in the subsequent stretching step.

In the preheating step, it is preferable to heat the unstretched film so that the film has a constant temperature in the range of Tg-30 ° C to Tg when the glass transition temperature of the film is Tg. It is preferable to make preheating time 1 to 10 minutes normally in order to suppress deformation more than necessary. In particular, in the present invention, when the preheating time is 5 minutes or more and 10 minutes or less, since the stretched film that has been subjected to the stretching step afterwards has a small variation in retardation value and is used as an optical compensation film of an IPS mode liquid crystal display device. It is possible to have a phase difference value within a suitable range. In particular, when the film is sufficiently preheated in the preheating step, the film is softened sufficiently so that the variation in retardation value at the time of stretching is small. However, preheating for a long time is a high degree of softening of the film is required to stretch high magnification, or it is difficult to express a sufficient birefringence.

In the stretching step proceeding after the preheating step, when the unstretched film is referred to as Tg, the glass transition temperature of the unstretched film is in the direction of the film in the temperature range of Tg-20 ° C to Tg + 20 ° C, that is, vertically 1 It is preferable to axially stretch. Here, the stretching temperature, the stretching speed, and the draw ratio may be determined by the type, thickness, in-plane retardation value of the optical film required, and the like. In such a longitudinal uniaxial stretching method, the stretching temperature is more preferably set to Tg to Tg + 20 ° C of the film. When the stretching temperature is lower than Tg-20 ° C of the unstretched film, the phase difference deviation of the stretched film obtained by concentrating stress when stretching is tended to be large, and when the stretching temperature is higher than Tg + 20 ° C of the unstretched film, It is difficult to express birefringence because the orientation is low.

Although the draw ratio in the stretching step is set by the expression of the thickness of the unstretched film and the appropriate retardation value, 1.1 to 3 times is usually preferable. When the draw ratio is lower than 1.1 times, it is difficult to obtain a film having a sufficient retardation due to the low birefringence, and when the draw ratio is higher than 3 times, the variation in the retardation value of the stretched film becomes large and the neck in increases. There is this.

In this invention, it is preferable that the extending | stretching speed at the time of extending | stretching a non-stretched film is extended | stretched at 10-500% / min.

The ratio of the width to the length of the stretching section of the film in the stretching step is preferably less than 3, preferably 0.5 or more and less than 3, more preferably 0.5 or more and 1.5 or less as described above. In general, the thickness direction retardation value can be adjusted by adjusting the size of the draw ratio, but it is difficult to control the thickness direction retardation value within the range of 0 to 30 nm, especially 0 to 15 nm. However, in the present invention, by adjusting the ratio of the width to the length of the stretching section of the film, the thickness retardation value of the stretched film can be adjusted in the range of 0 ~-30nm, preferably 0 ~-15nm, The phase difference can also be reduced.

As the ratio of the width to the length of the stretched region of the film is closer to 0.5 to 1.5, the shrinkage in the width direction at the time of stretching is free, and the thickness retardation value tends to be close to zero. Specifically, the thickness direction retardation value is a value represented by the difference between the refractive index Ny in the direction perpendicular to the stretching direction and the refractive index Nz in the thickness direction, so that the two refractive indexes are similar, the closer the thickness direction retardation value is to zero. When the shrinkage in the width direction is free, it is difficult to orient the polymer chain in the Ny direction, which results in a smaller Ny value and a smaller difference from the Nz value. In addition, since the shrinkage in the width direction is free and the entire surface of the film is stretched evenly during stretching, the phase difference variation and the thickness variation also decrease significantly.

In the heat treatment step performed after the preheating step and the stretching step, when the glass transition temperature of the film is Tg for the purpose of fixing the orientation of the longitudinal uniaxially stretched film, the temperature of the film is Tg-50 ° C to Tg- Heat-treat to cool to 20 ℃ range. Here, the heat treatment is a process of cooling to a temperature lower than the temperature in the stretching step, it is defined as heat treatment because the heat is applied even when cooling, and generally the last cooling zone during the film processing is called a heat treatment zone.

When the above-described manufacturing of the optical film according to the present invention is carried out using a manufacturing apparatus provided in the order of preheating zone, stretching zone and heat treatment zone, the film transferred into the preheating zone, the stretching zone and the heat treatment zone is continuously heated. Although stretched and heat treated to cool, some intermediate temperature region may inevitably occur at the boundaries of these zones. As a means for reducing this intermediate temperature range as much as possible, although not particularly limited, a narrow slit-shaped passage can be provided where the film moves between the zones. In addition, the other section can maintain the temperature of each zone by a method of shielding with a heat insulating partition wall, a shielding with an air curtain, or a combination thereof.

As described above, the optical film prepared according to the method of the present invention has a phase difference of 550 nm in a plane direction of 100 to 150 nm and a thickness direction of 0 to -30 nm, preferably of 0 to 15 nm, The deviation is small The optical film preferably has a widthwise retardation deviation of 30 nm or less, and more preferably 15 nm or less. Under these conditions, the optical film may not generate retardation stains. In addition, the thickness direction retardation deviation is preferably 10 nm or less, and more preferably 5 nm or less.

As used herein, the surface retardation and the thickness retardation are defined by R _in and R _th of Equations 1 and 2, respectively.

[Equation 1]

R _in = d × (Nx-Ny)

[Equation 2]

R _th = d × (Nz-Ny)

In Formulas 1 and 2, Nx is a planar refractive index in the stretching direction, Ny is a planar refractive index in the vertical direction in the stretching direction, Nz is a refractive index in the thickness direction, and d is the thickness of the film.

Since the optical film according to the present invention has a uniform retardation value, as long as such physical properties are required, the optical film is not limited thereto, and in particular, the optical film may be used as an optical compensation film for an IPS mode liquid crystal display device.

The present invention is explained in more detail using the following examples and comparative examples. The invention is not limited to the following examples.

Examples 1 to 5 and Comparative Example 1

Using a Ticona Topas 6013 (Tg 138 ° C) resin, a copolymer of norbornene-based monomers and ethylene monomers, melted with an extruder with screw L / D of 29, T-Die width of 1200 mm and Lip of 1 mm Extrusion produced a non-stretched film having a thickness of 100 μm. This unstretched film was extended | stretched on condition of 0.4 m / min of line speed at 50% of extending | stretching rate, and extending | stretching temperature 140 degreeC. The ratio of the width of the film to the length of the stretching section during stretching was adjusted to 0.5 to 3, the width of the film was 500 mm, and the optical film was prepared by stretching the length of the stretching section by uniaxial stretching. It was. The retardation value and the retardation deviation of the optical film manufactured as described above are shown in Table 1 below. R _in and R _th value is then cut by 20cm both ends of the manufactured optical film width was measured from above the central part, variation of R _in and R _th value is the maximum value of the retardation value of the width of the film (Max.) And the minimum value (Min.) Is shown.

In the length of the extension section
Width ratio of film against R _in [nm] R _th [nm] R _in deviation [nm] R _th deviation [nm] Example 1 0.5 130 -1.3 5 3 Example 2 1.0 129 -5.7 8 6 Example 3 1.5 127 -10.2 10 10 Example 4 2.0 123 -17.6 15 23 Example 5 2.5 119 -27.8 28 25 Comparative Example 1 3.0 114 -43.1 40 30

The present invention can easily reduce the phase difference by adjusting the ratio of the width to the length of the stretching section during the stretching of the film, it is possible to obtain a film having a plane direction and thickness direction retardation value of the desired value.

Claims (14)

Stretching the unstretched film made of a copolymer comprising a norbornene-based monomer and an ethylene monomer at a ratio of 65 to 83:17 to 35% by weight so that the ratio of the width of the film to the length of the stretching section is 0.5 to 1.5 so as to lengthwise uniaxial stretching Including the steps of: The method of manufacturing an optical film having an in-plane retardation value of 100 to 130 nm and a thickness direction retardation value of 0 to 15 nm at 550 nm. delete delete delete The method according to claim 1, wherein the cyclic olefin copolymer comprises a repeating unit represented by the following formula (1). <Formula 1>

The method according to claim 1, further comprising a preheating step, and a heat treatment step, The preheating step, the stretching step, and the heat treatment step is a manufacturing method of the optical film, characterized in that it is included in order. The method of claim 6, wherein the preheating is performed for 1 to 10 minutes in the range of Tg-30 ° C. to Tg when the glass transition temperature of the film is Tg. The method of claim 6, wherein in the stretching step, when the glass transition temperature of the film is Tg, at a stretching ratio of 1.1 to 3 times and a stretching speed of 10 to 500% / min at Tg-20 ° C to Tg + 20 ° C Method for producing an optical film. The method of claim 6, wherein the heat treatment is performed to maintain a temperature of Tg-50 ° C. to Tg-20 ° C. when the glass transition temperature of the film is Tg. delete delete delete The method of manufacturing an optical film according to claim 1, wherein the plane direction retardation deviation is 30 nm or less, and the thickness direction retardation deviation is 10 nm or less. The method of manufacturing an optical film for a compensation film according to claim 1, wherein the planar switching (IPS) mode liquid crystal display device.