JP2006103239A - Optical film, its manufacturing method and t-die used for it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for obtaining a resin film having very high thickness precision required for an optical film by extrusion molding excellent in productivity. <P>SOLUTION: The optical film composed of a thermoplastic resin is manufactured by using an extrusion molding apparatus having a T-die fitted. An average of bright line widths of a lip edge 1d of the T-die is 50 μm or less, difference of the bright line widths is 2 μm/5 mm or less, and variance of straightness of a lip land 1c and a top face 1e is 0.5 μm/5 mm or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical film used for, for example, a retardation film in a liquid crystal display or the like, more specifically, an optical film obtained by extrusion molding and having little thickness unevenness, and further relates to a manufacturing method thereof and a T die used therefor.

  In recent years, in retardation films used for liquid crystal displays and the like, streaky color unevenness due to retardation unevenness has been a problem because quality deteriorates. In general, the retardation film is produced by stretching an unstretched raw fabric resin film to impart distortion. However, if the thickness unevenness occurs at the raw resin film stage, the retardation unevenness due to the thickness unevenness occurs in the retardation film obtained by stretching. That is, in order to reduce the unevenness of the retardation, it is necessary to reduce the unevenness of the thickness of the raw resin film, and it is important to form a resin film with excellent thickness accuracy in the manufacturing process of the raw fabric resin film. It has become to.

  From the above viewpoints, conventionally, in the production of a raw film resin film for an optical film, since the thickness accuracy can be increased, a production method by a solution casting method has been frequently used.

  However, film formation by the solution casting method has a problem that productivity is not sufficient and the solvent cost is high. Therefore, the adoption of a film forming method by melt extrusion has been studied.

  In melt extrusion, it is necessary to increase the accuracy of each facility in order to increase the thickness accuracy. In particular, the T die is the most important member for determining the thickness accuracy, and among them, the straightness of the lip land inside the tip of the T die is an indispensable element for increasing the thickness accuracy.

  The straightness of the lip land of the T-die is specified, and when the PVA film is manufactured using a roll film forming machine or a belt film forming machine, the straightness of the lip land surface is 200 μm or less in total width and two points separated by 200 mm. There has been proposed a method using a T-die having an accuracy of 50 μm or less (see Patent Document 1).

In addition, the present inventors previously proposed a method for manufacturing a film with high thickness accuracy by defining the difference in the bright line width of the lip edge of the T die (see Patent Document 2).
JP 2002-144401 A Japanese Patent Application No. 2004-100540

  However, as described in Patent Document 1, even if the straightness of the lip land surface is reduced, it is still very difficult to obtain a resin film having a high thickness accuracy as required for an optical film by extrusion molding. It was difficult.

  Moreover, even if the bright line width of the lip edge is defined as described in Patent Document 2, a film with sufficient thickness accuracy cannot be obtained.

The object of the present invention is to eliminate the above-mentioned disadvantages of the prior art and to obtain a resin film having a very high thickness accuracy required for an optical film by an extrusion method with excellent productivity. Another object of the present invention is to provide a T-die used in such a method and an optical film having a very high thickness accuracy obtained by this method.

  In the invention according to claim 1, when an optical film made of a thermoplastic resin is manufactured using an extrusion molding apparatus equipped with a T die, the average of the bright line width of the lip edge of the T die is 50 μm or less. A method for producing an optical film, wherein a difference in width is 2 μm / 5 mm or less and the straightness irregularities of the lip land and the top surface are both 0.5 μm / 5 mm or less.

The invention according to claim 2 is an optical film manufactured by the method according to claim 1, which is made of an amorphous thermoplastic resin, has an average thickness R of 200 μm or less, and uneven thickness R × 2. An optical film having a size of 5 × 10 ⁻³ μm / 5 mm or less.

  The invention according to claim 3 is the optical film according to claim 2 stretched at least in the longitudinal uniaxial direction.

  The invention according to claim 4 is the optical film according to claim 2 or 3, wherein the amorphous thermoplastic resin is a norbornene resin.

In the invention according to claim 5, the average bright line width of the lip edge is 50 μm or less, the bright line width difference is 2 μm / 5 mm or less, and the straightness unevenness between the lip land and the top surface is 0.5
It is a T die characterized by being not more than μm / 5 mm.

Throughout the claims and the entire specification, “bright line width difference a μm / 5 mm” means that the measured value of the bright line width at a certain measurement point is 5 mm away from the measured value in the T-die width direction as shown in FIG. It means that the absolute value of the difference from the measured value of the bright line width at another adjacent measurement point is a μm.

Throughout the claims and the entire specification, “straightness” refers to a value calculated by removing a fluctuation exceeding a period of 200 mm by Fourier analysis of a measured value of straightness. “Straightness difference b μm / 5 mm” means the straightness value obtained at a certain measurement point and 5 m in the T-die width direction from here.
It means that the absolute value of the difference from the straight value obtained at another adjacent measurement point separated by m is b μm.

Throughout the claims and the entire specification, “thickness variation c μm / 5 mm” means the absolute value of the difference between the thickness at a measurement point of the film and the thickness at a measurement point separated by 5 mm in the width direction of the film. Means c μm.

First, a T die used in the method for producing an optical film of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a channel surface of a T die. The T die 1 is provided via a molten resin supply path 1a, a manifold 1b provided at the tip thereof, a swelled lip land 1c provided at the tip thereof, and an inclined lip edge 1d provided at the tip thereof. And the top surface 1e.

The molten resin coming from the extruder enters the manifold 1b through the supply path 1a of the T die 1, passes through the lip land 1c, and is extruded into a film form from the lip edge 1d. The film does not touch the top surface 1e.

2 and 3 are perspective views schematically showing the inside of the T die, particularly the shapes of the lip land 1c and the lip edge 1d. The dimension A in the width direction of the lip edge 1d is the bright line width.

In general, the surface of the lip edge 1d is often inclined at 45 ° with respect to the surface of the lip land 1c, and the bright line width is measured after the microscope 3 is inclined at 45 ° with respect to the surface of the lip land 1c. It has been broken. However, there is a defect in the processing of the flow path surface and the top surface, and the inclination angle of the lip edge 1d may not be 45 ° partially. In such a case, when the emission line width is measured by tilting the microscope 3 at 45 ° with respect to the surface of the lip land 1c as described above, a value different from the actual emission line width may be obtained.

In the present invention, the average of the bright line width of the lip edge is 50 μm or less, and the bright line width difference is 2
It is less than μm / 5mm and the straightness unevenness of lip land and top surface is both 0.5μm
T-die that is / 5 mm or less is used.

A T die has a pair of lip land 1c, lip edge 1d, and top surface 1e, but in any case, the above conditions must be satisfied.

  By using the T die thus defined, an optical film having high thickness accuracy can be obtained. This is because defects in the processing of the flow path surface and the top surface as described above can be prevented, and the bright line width can be made substantially uniform. In addition, this can regulate the straightness of the lip land surface to make the flow rate of the resin discharged from the T die constant, and also define the top surface straightness to release the film from the T die. It can be made uniform.

  In the present invention, it is very important to make the bright line width uniform as described above, rather than reducing the average value of the bright line width. The total straightness of the lip land surface of the T die is preferably less than 10 μm, more preferably 5 μm or less. The surface roughness is preferably 0.1 μm or less in terms of the Ry value specified in JIS B0601. The obtained optical film preferably has no pits or pinholes. For that purpose, the size of the lip edge chip is preferably less than 15 μm from the edge tip toward the inflow direction.

  Next, the manufacturing method of the optical film of the present invention will be described in detail.

The thermoplastic resin used as a raw material in the production of the optical film according to the present invention is not particularly limited, but is preferably an amorphous thermoplastic resin. An amorphous thermoplastic resin is a polymer that maintains an amorphous state that hardly takes a crystal structure. The glass transition temperature Tg is not particularly limited because it varies depending on the resin, but is generally 100 ° C. or higher. Examples of the amorphous thermoplastic resin include polysulfone, polymethyl methacrylate, polystyrene, polycarbonate, polyvinyl chloride, and norbornene resin. As for an amorphous thermoplastic resin, only 1 type may be used and 2 or more types may be used together.

  Among these resins, norbornene resins are preferably used because of their low intrinsic birefringence and small photoelastic coefficient, and in particular, saturated norbornene resins with hydrogenated intramolecular double bonds are more stable. Desirable in terms of superiority. In addition, since norbornene-based resin is a resin that solidifies rapidly due to a decrease in temperature, the thickness variation at the contact point between the metal roll and the resin is more likely to occur than other amorphous thermoplastic resins. Therefore, when a norbornene resin is used, the effect of the manufacturing method of the present invention, that is, the effect of reducing thickness unevenness is remarkable.

  Examples of norbornene resins include hydrogenated products of ring-opening (co) polymers of norbornene monomers, addition (co) polymers of norbornene monomers and olefins, addition (co) polymers of norbornene monomers, And derivatives thereof. As for norbornene-type resin, only 1 type may be used and 2 or more types may be used together.

Examples of the norbornene-based monomer include bicyclo [2,2,1] hept-2-ene (norbornene) and 6-methylbicyclo [2,2,1] hept-2-ene which is a derivative of a norbornene-based monomer. 5,6-dimethylbicyclo [2,2,1] hept-2-ene, 1-methylbicyclo [2,2,1] hept-2-ene, 6-ethylbicyclo [2,2,1] hept-2 -Ene, 6-n-butylbicyclo [2,2,1] hept-2-ene, 6-isobutylbicyclo [2,2,1] hept-2-ene, 7-methylbicyclo [2,2,1] And hept-2-ene.

  The hydrogenated product of a ring-opening (co) polymer of a norbornene-based monomer is obtained by, for example, ring-opening polymerizing a norbornene-based monomer by a known method and then hydrogenating the remaining double bond. It may be a homopolymer of a system monomer, a copolymer of different norbornene-based monomers, or a copolymer of a norbornene-based monomer and another cyclic olefin-based monomer.

  The addition (co) polymer of a norbornene monomer and an olefin is, for example, a copolymer of a norbornene monomer and an α-olefin. The α-olefin is not particularly limited, but is preferably an α-olefin having 2 to 20 carbon atoms, more preferably 2 to 10 carbon atoms such as ethylene, propylene, 1-butene, 3-methyl-1-butene, 1- Examples include pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and the like. Among these, ethylene is preferably used because of excellent copolymerizability. Even when other α-olefins are copolymerized with a norbornene-based monomer, the presence of ethylene is preferable because copolymerization is enhanced.

  Any of the norbornene resins is known, and for example, those described in JP-A-1-240517 can be used. Commercially available norbornene resins include, for example, JSR brand name “Arton” series, Zeon Corporation brand name “Zeonoa” series, Mitsui Chemicals brand name “Apel” series, etc. Can be mentioned.

  Various additives may be added to the thermoplastic resin as the film raw material, if necessary, as long as the object of the present invention is not impaired. Examples of such additives include various additives that prevent deterioration of the thermoplastic resin and improve the heat resistance, ultraviolet resistance, smoothness, and the like of the molded optical film. For example, phenol-based or phosphorus-based antioxidants; lactone-based thermal deterioration-preventing agents; benzophenone-based, benzotriazole-based, acrylonitrile-based UV absorbers; aliphatic alcohol ester systems, polyhydric alcohol partial ester systems And a lubricant such as a partial ether type; and an antistatic agent such as an amine type. These additives may be used alone or in combination of two or more.

The optical film according to the present invention is obtained by the production method of the present invention, is made of an amorphous thermoplastic resin, has an average thickness R of 200 μm or less, and has an uneven thickness of R × 2.5 × 10 ^{−. It is 3} μm / 5 mm or less.

When the thickness unevenness of the film exceeds R × 2.5 × 10 ⁻³ μm / 5 mm, for example, when a film obtained by uniaxially stretching the film is used as a retardation film, retardation unevenness occurs depending on the thickness unevenness. There may be problems such as color unevenness.

  The optical film according to the present invention is preferably stretched at least in the longitudinal uniaxial direction.

FIG. 4 is a schematic view of a film production process used in the production method according to the present invention. As shown in the figure, the thermoplastic resin was extruded from the extruder 4 and attached to the tip of the extruder.
Supplied to the die 5. A thermoplastic resin film is formed by the T die 5, and the formed film 8 passes between the cooling roll 6 and the touch roll 7 for pressing the film against the roll 6, and is cooled by the cooling roll 6. Subsequently, the film 8 is sent to the take-up roll through the guide rolls 9 and 10, and is taken up by the roll.

  The semi-molten film 8 is discharged from the outlet of the T die 5, and the film 8 is brought into contact with the cooling roll 6. A shorter distance from the outlet of the T die 5 to the contact point at which the film 8 contacts the cooling roll 6, that is, an air gap, is preferable in that the thickness unevenness due to disturbance can be reduced. Therefore, the air gap is preferably 70 mm or less.

  Moreover, when the film 8 contacts the cooling roll 6, it is preferable that air does not enter between the cooling roll 6 and the film 8, and it is preferable that the cooling rate is uniform over the entire surface. Therefore, it is preferable to press the film 8 toward the cooling roll 6 by pressing means such as the touch roll 7 in the vicinity of the downstream side of the contact.

  The pressing means is not limited to the touch roll 7, and an air knife or electrostatic pinning may be used. A touch roll having a surface made of an elastic material is preferable because it is excellent in stability and the film 8 can be uniformly brought into pressure contact with the cooling roll 6.

The temperature of the cooling roll 6 varies depending on the type of resin constituting the film 8, but Tg-
It is preferably in the range of 10 ° C. to Tg-100 ° C. (Tg is the glass transition temperature of the resin).

  In order to ensure the smoothness and transparency of the optical film, the surface roughness of the cooling roll 6 is preferably 0.5 μm or less, more preferably 0.3 μm or less in terms of the Ry value defined in JIS B0601. . Although the cooling roll 6 can be comprised with various materials, Preferably it consists of metals, for example, what consists of metals, such as carbon steel and stainless steel, is preferable. When the metal cooling roll 6 is used, the temperature of the cooling roll 6 can be quickly maintained at a constant temperature, and the film 8 can be efficiently cooled.

  In general, since the roll temperature greatly affects the solidification point of the resin, it is preferable that the cooling roll 6 has a temperature adjustment mechanism connected to or built in the shaft core portion so that the temperature can be adjusted to various temperatures. As the temperature adjusting means, an electric heating type temperature adjusting means for heating the cooling roll 6 to set an appropriate temperature by incorporating a sheathed heater into the shaft core; temperature adjusting means by electromagnetic induction action by an induction heating coil; shaft Temperature adjusting means such as a heat medium circulation heating method in which a heat medium for temperature control is circulated through a flow path provided in the core portion to heat the cooling roll to a set temperature can be used. Particularly preferred is a heat medium circulation heating method, and the heat medium may be a gas or a liquid such as water or oil. A liquid such as water or oil is preferred because of its large heat capacity. Preferable examples of such a heat medium flow path include those having a two-row spiral structure or a four-row spiral structure inside.

  If the temperature of the T die 5 varies, the fluidity of the resin changes. Therefore, it is preferable that the temperature of the T die 5 is stable. The temperature of the molten resin contact portion of the T die 5 is preferably kept within a set temperature ± 0.5 ° C, more preferably within a set temperature ± 0.2 ° C.

  The width of the T die is not particularly limited, but is preferably 500 mm to 4000 mm for the convenience of the size of the T die grinding machine.

  The surface finish of the flow surface of the T die is preferably performed by hard chrome plating (HCr) because the surface becomes smooth.

  Conventionally, in order to make the bright line width small and so-called sharp edge, the T die lip surface finish has been performed by ceramic spraying such as tungsten carbide (WC).

  On the other hand, in the case of HCr plating, since the hardness is lower than that of ceramic spraying, it does not become a sharp edge and processing accuracy is also inferior, which is disadvantageous for film formation requiring high thickness accuracy such as an optical film. However, by defining the lip emission line width and straightness unevenness within a predetermined range as described above, a film having an accuracy equal to or higher than that of a ceramic spray mold can be obtained.

  According to the invention of claim 1, as the T die, the average of the bright line width of the lip edge is 50 μm or less, the bright line width difference is 2 μm / 5 mm or less, and the straightness unevenness of the lip land and the top surface is uneven. Since all use what is 0.5 micrometer / 5 mm or less, a film with very high thickness accuracy can be obtained. Therefore, an optical film having almost no thickness unevenness in the width direction can be stably produced by extrusion.

According to the invention of claim 2, an optical film made of an amorphous thermoplastic resin, having an average thickness R of 200 μm or less and an uneven thickness of R × 2.5 × 10 ⁻³ μm / 5 mm or less. Can be provided. Since the thickness unevenness in the width direction is very small as described above, this film can be suitably used as an optical film such as a retardation film.

  According to the invention which concerns on Claim 3, the optical film which concerns on Claim 2 extended | stretched at least to the longitudinal uniaxial direction can be provided. This film has little thickness unevenness not only in the width direction but also in the length direction, and is suitable as an optical film.

  According to the invention concerning Claim 4, the optical film which concerns on Claim 2 or 3 whose amorphous thermoplastic resin is norbornene-type resin can be provided. This film has a low intrinsic birefringence and a small photoelastic coefficient. Therefore, it is possible to provide an optical film that has not only small thickness unevenness but also excellent optical characteristics. Further, in the norbornene-based resin, thickness unevenness due to extrusion molding tends to occur, but according to the invention according to claim 4, an optical film made of norbornene-based resin with less thickness unevenness can be provided stably.

  According to the invention which concerns on Claim 5, T-die suitable for obtaining a film with high thickness precision can be provided.

  Next, the present invention will be specifically described based on examples. However, the present invention is not limited to the examples.

Example 1
(Manufacture of optical films)
A thermoplastic norbornene resin (manufactured by Nippon Zeon Co., Ltd., trade name “ZEONOR1420”, Tg = 135 ° C.) was preliminarily dried at a temperature of 110 ° C. for 3 hours.

In FIG. 4 showing the film manufacturing process, the thermoplastic resin is extruded from the extruder 4 and supplied to a T die 5 attached to the tip of the extruder. A thermoplastic resin is formed by the T die 5, and the film 8 exiting the T die 5 passes between the cooling roll 6 and the touch roll 7 for pressing the film against the roll 6 in contact with the cooling roll 6. 6 to cool. Next, the film 8 is sent to the take-up roll through the guide rolls 9 and 10, and is taken up by the roll. In this way, an optical film is manufactured by extrusion molding.

  In addition, the specification of each part of the manufacturing apparatus shown in FIG. 4 is as follows.

Extruder 4 ... single screw extruder, caliber = 100 mm, L / D = 32
T die 5: width 1800 mm, bending type automatic T die, surface finish of flow path surface = HCr plating.

  Cooling roll 6: A three-roll system, an outer diameter of 300 mm, an effective width of 1900 mm, and a built-in heat medium temperature adjusting mechanism. Heat medium = oil.

  Touch roll 7: A roll in which a metal core metal roll is subjected to rubber lining and the outermost layer is formed of a metal sleeve, outer diameter = 200 mm.

  Using the production apparatus described above, the extrusion speed from the extruder 4 is 120 kg / hour, the temperature of the T die 5 is 280 ° C., the temperature of the cooling roll 6 is 120 ° C., the temperature of the touch roll 7 is 110 ° C., and the film The effective width was 1400 mm, the air gap was 65 mm, and the film 8 was manufactured by extrusion molding.

  As the T die, one having the average of the bright line width, the maximum value of the bright line width difference, the straightness of the lip land surface, and the straightness of the top surface shown in Table 1 was used. The measurement of the bright line width and straightness of the T-die was performed by the following method.

(Measurement of bright line width)
The emission line width was measured using a microscope for emission line width measurement (manufactured by Keyence Corporation, Digital HF microscope VH8000). In FIG. 3 showing the method for measuring the bright line width, the microscope 3 is disposed in a direction inclined by 45 ° with respect to the lip land surface 1c, that is, in a direction facing the lip edge 1b. Next, the bright line width was measured at intervals of 5 mm with the microscope 3, and the absolute value of the difference in the bright line width at adjacent measurement points was calculated to obtain the bright line width difference.

(Measurement of straightness)
Straightness was measured using a non-contact displacement meter (manufactured by Keyence Corporation, LT9000). The obtained straightness measurement value was subjected to Fourier analysis, and the straightness was determined by removing fluctuations exceeding a period of 200 mm. The absolute value of the difference between the values at each adjacent measurement point in the values measured at intervals of 5 mm in the T-die width direction was defined as unevenness in straightness.

(Evaluation of optical film)
About the obtained optical film, the thickness was measured using the film thickness measuring device (The Seiko EM company make, contact-type thickness measuring device Millitron1240). The thickness was measured at intervals of 5 mm in the width direction of the film, and the average was obtained. Moreover, the absolute value of the difference in thickness at adjacent measurement points was determined. These results are shown in Table 1.

Comparative Examples 1 and 2
The same operation as in Example 1 was performed except that the T-die was replaced with one having the average bright line width, the maximum bright line width difference, the straightness of the lip land surface, and the straightness of the top surface shown in Table 1. An optical film was obtained and evaluated.

  As is apparent from Table 1, the average value of the bright line width difference of the lip edge of the T die is 50 μm or less, the bright line width difference is 2 μm / 5 mm or less, and the straightness of the lip land surface and the top surface is 0.5 μm / By setting the thickness to 5 mm or less, the thickness unevenness can be effectively reduced.

It is typical sectional drawing which shows the flow-path surface of T die. It is a perspective view which shows the internal shape of T-die roughly. It is a perspective view which shows roughly the method of measuring a bright line width. It is a flow sheet which shows the manufacturing process of a film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... T die 1a ... Resin inflow port 1b ... Manifold 1c ... Lip land 1d ... Lip edge 1e ... Top surface 3 ... Microscope 4 ... Extruder 5 ... T die 6 ... Cooling roll 7 ... Touch roll 8 ... Film 9, 10 ... Guide roll A ... Line width

Claims (5)

In manufacturing an optical film made of a thermoplastic resin using an extrusion molding apparatus equipped with a T-die, the average of the bright line width of the lip edge is 50 μm or less and the difference in bright line width is 2 μm / 5 mm or less. And a method for producing an optical film, wherein the lip land and the straightness unevenness of the top surface are both 0.5 μm / 5 mm or less. An optical film manufactured by the method according to claim 1, comprising an amorphous thermoplastic resin, having an average thickness R of 200 μm or less, and a thickness unevenness of R × 2.5 × 10 ⁻³ μm / An optical film having a thickness of 5 mm or less.   The optical film according to claim 2, which is stretched at least in the longitudinal uniaxial direction.   The optical film according to claim 2 or 3, wherein the amorphous thermoplastic resin is a norbornene resin. The average bright line width of the lip edge is 50 μm or less, the bright line width difference is 2 μm / 5 mm or less, and the straightness unevenness of the lip land and the top surface is both 0.5 μm / 5 mm or less. T-die.

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