JP2006327050A - Forming method of optical film, optical film and phase difference film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method of an optical film suppressed in the generation of a crosslinked gel at the time of melt extrusion molding, reduced in appearance defect and capable of developing excellent display quality in the case incorporated in a liquid crystal display device or the like, the optical film and a phase difference film. <P>SOLUTION: The forming method of the optical film has a process for performing extrusion molding using a molding machine having a screw characterized in that the trough diameter of the screw of a resin charging part is 70-95% of the outer diameter of the screw and the pitch magnification in the flow direction of resin in a feed zone 2a is 20-100%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for producing an optical film, which suppresses the generation of a crosslinked gel during melt extrusion molding, has few appearance defects, and can exhibit excellent display quality when incorporated in a liquid crystal display device or the like. And a retardation film.

In recent years, along with the downsizing, thinning, and weight reduction of notebook personal computers, word processors, mobile phones, personal digital assistants, etc., liquid crystal display devices having the features of light weight and compactness are often used for these electronic devices. It is coming. In the liquid crystal display device, various films such as a polarizing film are used in order to maintain the display quality. In order to further reduce the weight of liquid crystal display devices for portable information terminals and mobile phones, liquid crystal display devices using plastic films instead of glass substrates have been put into practical use.

In addition to being optically transparent, a plastic film used in a device that handles polarized light such as a liquid crystal display device is required to have optical homogeneity. Furthermore, a film substrate for a plastic liquid crystal display device in which the glass substrate is replaced with a plastic film is required to hardly change a phase difference represented by a product of birefringence and thickness due to external stress or the like. In particular, when a plastic film is used as a polarizer protective film, such characteristics are strongly required for wide viewing angle and large screen. Also, when applied to various optical films for liquid crystal display devices, it is required that the change in retardation due to stress during processing or use be small.

As the plastic film used in the liquid crystal display device, an amorphous thermoplastic resin is usually used. For example, polycarbonate resin, polyarylate resin, polysulfone resin, polyethersulfone resin, thermoplastic saturation There are known films made of engineering plastics such as norbornene resins, vinyl chloride resins, acrylonitrile resins, styrene resins, polyolefin resins, cellulose resins such as triacetyl cellulose, and the like. Among these, the thermoplastic saturated norbornene-based resin has a relatively high glass transition temperature and a very small photoelastic constant, and therefore has excellent retardation stability against environmental changes. More preferably used as a polymer.

The retardation film is usually formed by optically producing these thermoplastic resins by casting (solution cast) film forming method, calender film forming method, melt extrusion film forming method, etc. It is manufactured by stretching in the direction and / or the transverse direction. As a method for forming an optical film, the melt extrusion method is the most efficient in consideration of high-speed productivity. However, in the melt extrusion method, the powder or granular resin charged in the extruder is contained in the extruder. There has been a problem that the appearance of the film formed is remarkably deteriorated due to the generated shear stress to form a crosslinked gel.

In recent years, cross-linked gels have been generated in extruders because of the recombination of polymer radicals generated by shear stress, and lubricants are added or low compression ratio screws are used. The method of suppressing generation | occurrence | production of bridge | crosslinking gel is performed.
However, the optical film obtained by such a method is not satisfactory as a film used in a liquid crystal display device or the like, and further film cleaning and appearance quality improvement are required.

Further, Patent Document 1 discloses a method for molding a cyclic olefin-based resin in which the shear rate at the metering portion of the screw is 10 sec ⁻¹ or more when performing melt-kneading extrusion. By making the shear rate at the metering part of a single screw higher than a predetermined value, the gel is broken and divided into fine gels to improve the appearance of the molded product, and the generation of crosslinked gel is fundamentally suppressed. It wasn't something to do.
JP 2003-311813 A

The present invention relates to a method for producing an optical film and an optical film capable of suppressing the generation of a crosslinked gel at the time of melt extrusion, having few appearance defects, and exhibiting excellent display quality when incorporated in a liquid crystal display device or the like. The purpose is to provide.

The present invention is a method of producing an optical film by a melt extrusion method, wherein the screw valley diameter of the resin charging portion is 70 to 95% of the screw outer diameter, and the pitch is increased in the flow direction of the resin in the feed zone. It is the manufacturing method of the optical film which has the process of extrusion-molding using the molding machine which has a screw whose rate is 20-100%.
The present invention is described in detail below.

As a result of intensive studies, the present inventors have conducted extrusion molding using a molding machine having a screw whose screw valley diameter in the resin charging portion and the pitch expansion rate in the flow direction of the resin in the feed zone are within a predetermined range. Thus, it was found that an optical film capable of suppressing the generation of a crosslinked gel and capable of expressing excellent display quality when incorporated in a liquid crystal display device or the like was obtained, and the present invention was completed. .

In the method for producing an optical film of the present invention, the screw trough diameter of the resin charging portion is 70 to 95% of the screw outer diameter, and the pitch expansion rate in the flow direction of the resin in the feed zone is 20 to 100%. It has the process of extrusion-molding using the molding machine which has a screw.

In the method for producing an optical film of the present invention, the screw trough diameter of the resin charging portion is 70 to 95% of the screw outer diameter, and the pitch expansion rate in the flow direction of the resin in the feed zone is 20 to 100%. A molding machine with a screw is used. By performing extrusion using such a screw, the shear stress generated in the extruder can be suppressed to the minimum, and the generation of crosslinked gel is reduced to the extent that there is no problem in the appearance quality of the optical film. be able to.

An example of the screw used in the method for producing an optical film of the present invention is shown in FIG. 1a is a schematic view of a screw used in the present invention, and FIG. 1b is a partially enlarged view of the screw shown in FIG. 1a. The screw used in the present invention is not limited to such a specific example.

As shown in FIG. 1a, the screw 1 is a single screw comprising a feed zone 2a, a compression zone 2b and a metering zone 2c, and is placed in a cylinder in the extruder. Can be used by fitting in a rotatable state. Here, the compression zone 2b has a screw valley diameter that increases toward the tip of the screw, and the feed valley 2a and the metering zone 2c have a uniform screw valley diameter. FIG. 1 illustrates a screw whose screw valley diameter gradually increases toward the tip of the screw in the compression zone 2b. However, in the present invention, the screw pitch increases toward the tip of the screw in the compression zone 2b. You may use the screw which becomes small gradually.
Thus, the compression zone 2b refers to a portion of the screw 1 where the screw trough diameter gradually increases toward the screw tip or the screw pitch gradually decreases toward the screw tip. The feed zone 2a refers to the part from the root of the screw to the compression zone 2b, and the metering zone 2c refers to the part from the compression zone 2b to the tip of the screw. The resin supplied from the feed zone 2a is transferred in the direction shown in the figure by the rotation of the screw, and is compressed and melt-kneaded.

FIG. 1 b is an enlargement of the feed zone 2 a of the screw 1. 3 indicates a resin charging part, d1 is a screw outer diameter, d2 is a screw valley diameter, P _1D is a pitch at a resin charging part, and P _5D is a pitch at an end of the feed zone opposite to the resin charging part. . As shown in FIG. 1b, the feed zone 2a has a structure in which the pitch is increased from the resin charging portion to the tip of the screw.

In the method for producing an optical film of the present invention, the screw 1 has a screw valley diameter d2 having a lower limit of 70% of the screw outer diameter d1 and an upper limit of 95% of the screw outer diameter d1.
By setting the screw valley diameter d2 within the above range, the amount of resin supplied in the resin charging section 3 can be made moderate, the heat transfer efficiency from the barrel of the extruder is improved, and shearing heat generation is suppressed. It becomes possible to do. As a result, the cross-linked gel generated by shearing can be reduced. If it is less than 70%, the barrel contact area per the amount of resin input becomes small, the heat transfer efficiency from the cylinder becomes poor, and the resin unmelted zone becomes long, so that a lot of gel is produced and the optical film obtained Affects appearance. If it exceeds 95%, the amount of resin supplied will decrease and productivity will decrease. A preferred lower limit is 80% of the screw outer diameter, and a preferred upper limit is 90%.

In the method for producing an optical film of the present invention, the lower limit of the pitch expansion rate in the resin flow direction in the feed zone 2a of the screw 1 is 20%, and the upper limit is 100%.
By setting the pitch enlargement ratio within the above range, the resin pressure in the semi-molten state is lowered, so that the shear stress can be suppressed and the cross-linked gel generated by the shear is reduced. Furthermore, since the contact area with the barrel increases, the amount of heat transfer also increases, and the resin can be melted while suppressing shearing heat generation. In addition, the screw used with the manufacturing method of the optical film of this invention increases a pitch gradually in the flow direction of resin in a feed zone, for example, in the screw 1, a pitch expansion rate can be represented by following formula (1). .
Pitch enlargement ratio (%) = (P _5D / P _1D −1) × 100 (1)

When the pitch enlargement ratio is less than 20%, a large shear stress is generated when the resin is melted, a large amount of crosslinked gel is generated, and the appearance of the obtained optical film is affected. If it exceeds 100%, not only will the resin filling rate be greatly reduced in the enlarged portion, it will not be possible to stably extrude, but also the phenomenon that the shear rate will increase due to the increase in the feed rate will occur. The object of the invention cannot be achieved. A preferred lower limit is 30% and a preferred upper limit is 50%.

The compression ratio of the screw is preferably less than 2.5. If it is 2.5 or more, a crosslinked gel may be generated due to the generated shear stress. The compression ratio refers to the ratio of the groove depth between the feed zone and the metering zone.

The screw shape other than the screw valley diameter at the resin charging portion and the pitch expansion rate at the feed zone is not particularly limited. However, when inconvenience such as a decrease in the filling rate occurs, the effect of the present invention is not impaired. You may adjust the depth of a groove, a flight width, etc. in the range.
Furthermore, the type of the screw is preferably a full flight screw.

The material of the screw is not particularly limited, but it is preferable that the surface is plated or ceramic coated from the viewpoint of preventing scorching and adhesion. Examples of the plating or coating include chrome plating, titanium carbide coating, and tungsten carbide coating.

Although it does not specifically limit as a molding machine which can use the said screw, For example, T-die extrusion molding machine (single layer and multilayer), injection molding machine, direct blow molding machine, injection blow molding machine, inflation molding machine , Calender molding machine, tenter method biaxial stretch molding machine, tubular method biaxial stretch molding machine, uniaxial stretch molding machine, calendar molding machine, profile extrusion molding machine, pipe molding machine, mandrel molding machine, extrusion spinning molding machine, etc. Can be used.

As a method of supplying the raw material resin when using the molding machine, apparatuses such as a vibration hopper, a hopper with a forced feeder, and a nitrogen substitution hopper can be used as long as they do not impair the purpose of the present invention. It is effective for suppression. The above-mentioned starvation feed is a method of melt extrusion by supplying a smaller amount of resin than the discharge amount when the hopper is filled with resin and performing melt extrusion, but a feeder is required as additional equipment It is.

The heating temperature at the time of extrusion molding using the molding machine is appropriately adjusted depending on the resin to be used, the performance desired to be imparted to the obtained optical film, etc., but the preferred lower limit is the glass transition temperature (Tg) of the raw material resin + 50 ° C. It is. By heating at Tg + 50 ° C. or higher, the viscosity of the resin is appropriately reduced, and even if the shear rate is increased, the shear stress is not so high, and the generation of a crosslinked gel can be prevented. If the temperature is Tg or more and less than Tg + 50 ° C., the viscosity of the resin becomes very high, and a large shear stress is generated in the extruder, so that a crosslinked gel is easily generated.
In the present specification, the glass transition temperature refers to a dynamic viscoelasticity measurement in which a raw material resin is formed into a film, 0.01% deformation is applied to the film at 10 Hz, and the temperature is raised to 25 to 250 ° C. This means the peak top temperature of the tensile loss elastic modulus E ″ obtained by the apparatus (RSA). The Tg of the resin generally indicates the displacement temperature measured by a differential scanning calorimeter (DSC). However, in the case of producing a film using the melt extrusion method, the displacement temperature in a dynamic environment in which stress is applied to the resin is important, not the displacement temperature in a static environment such as DSC. Therefore, Tg of the resin composition of the present invention means a temperature showing the peak top of E ″ measured by RSA under the above conditions in the film.

In the method for producing an optical film of the present invention, the set temperature of the cylinder at the time of extrusion molding is preferably increased to such an extent that yellowing and scorching do not occur. is there. By setting the set temperature of the cylinder in such a range, it is possible to suppress the formation of a crosslinked gel accompanying the generation of shear stress.

The optical film produced using the method for producing an optical film of the present invention has an appearance defect of 100 μm or more and 10 pieces / m ² or less. Such an optical film is also one aspect of the present invention.

When the appearance defect of 100 μm or more exceeds 10 pieces / m ² , the display quality is deteriorated when used in a liquid crystal display device or the like as an optical film. In order to satisfy the currently required display quality of the liquid crystal display device, the preferable upper limit is 3 / m ² , and the more preferable upper limit is 1 / m ² . In the present specification, the number of appearance defects is calculated by, for example, counting appearance defects having a major axis of 100 μm or more due to a cross-linked gel by a transmission method using a microscope, and converting the defect per unit area. It can be determined by a method or the like.

The optical film of the present invention is preferably composed of a copolymer of a norbornene monomer and an olefin monomer. The norbornene-based monomer represents an unsaturated compound having a norbornene ring structure represented by norbornene, tetracyclododecene or the like in the structure, and the olefin-based monomer is represented by a linear olefin or a cyclic olefin. An unsaturated hydrocarbon compound composed of carbon and hydrogen that does not have a norbornene ring.

Specific examples of commercially available copolymers of the norbornene-based monomer and the olefin-based monomer include “APEL” (manufactured by Mitsui Chemicals), “TOPAS” (manufactured by Ticona), and the like.

The norbornene-based monomer is not particularly limited as long as it has a norbornene ring. And known norbornene monomers described in Japanese Patent No. 3030953. Specifically, for example, norbornene, methanooctahydronaphthalene, dimethanooctahydronaphthalene, dimethanododecahydroanthracene, dimethanodecahydroanthracene, trimethanododecahydroanthracene, etc., and their substitutes; dicyclopentadiene, 2, Examples include 3-dihydrodicyclopentadiene, methanooctahydrobenzoindene, dimethanodecahydrobenzoindene, methanooctahydrofluorene, dimethanohydrooctafluorene and the like, and substituted products thereof. In addition, these norbornene-type monomers may be used independently and may use 2 or more types together.

The substituent in the above-mentioned substituent may be a known hydrocarbon group or polar group, and is not particularly limited. For example, an alkyl group, an alkylidene group, an aryl group, an alkoxycarbonyl group, a halogen group, a hydroxyl group Carboxylic acid group, hydroxyl group-free, ester group, amino group, pyridyl group, cyano group, silyl group, epoxy group, acrylic group, methacryl group and the like. These substituents may be used alone or in combination of two or more.

The norbornene-based monomer substituted with the above substituent is not particularly limited, and examples thereof include 5-methyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, and 5-ethylidene-2- Norbornene, 5-methoxycarbonyl-2-norbornene, 5,5-dimethyl-2-norbornene, 5-cyano-2-norbornene, 5-methyl-5-methoxycarbonyl-2-norbornene, 5-phenyl-2-norbornene, 5-phenyl-5-methyl-2-norbornene, 6-methyl-1,4: 5,8-dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 6-ethyl- 1,4: 5,8-dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 6-ethyl-1,4: 5,8 Ethylidene-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 6-chloro-1,4: 5,8-dimethano-1,4,4a, 5,6,7,8, 8a-octahydronaphthalene, 6-cyano-1,4: 5,8-dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 6-pyridyl-1,4: 5 8-Dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl-1,4: 5,8-dimethano-1,4,4a, 5,6,7 , 8,8a-octahydronaphthalene, 1,4-dimethano-1,4,4a, 4b, 5,8,8a, 9a-octahydrofluorene, 5,8-methano-1,2,3,4,4a , 5,8,8a-octahydro-2,3-cyclopentadienonaphthalene, , 9: 5,8-dimethano-3a, 4,4a, 5,8,8a, 9,9a-octahydro-1H-benzoindene, 4,11: 5,10: 6,9-trimethano-3a, 4 4a, 5, 5a, 6, 9, 9a, 10, 10a, 11, 11a-dodecahydro-1H-cyclopentanthracene and the like.

The olefin monomer is not particularly limited, and examples thereof include linear olefin monomers such as ethylene and α-olefin, and cyclic olefin monomers such as cyclopentene, cyclooctene, and 5,6-dihydrodicyclopentadiene. It is done.

The preferable lower limit of the number average molecular weight of the copolymer of the norbornene monomer and the olefin monomer is 5000, and the preferable upper limit is 150,000. If it is less than 5000, the mechanical strength of the resulting optical film may be reduced, and if it exceeds 150,000, the melt viscosity increases and the moldability may be reduced. A more preferable lower limit is 10,000, and a more preferable upper limit is 100,000. In addition, the said number average molecular weight means the standard polystyrene conversion value measured by the gel permeation chromatography method.

The optical film of the present invention is within the range that does not inhibit the effects of the present invention, in order to improve heat resistance, UV resistance, smoothness, moldability, etc. Agents, phenolic and other anti-thermal degradation agents, amine-based antistatic agents, aliphatic alcohol esters, polyhydric alcohol partial esters and higher fatty acids, and amides and other lubricants, benzophenone and benzotriazole You may contain additives, such as ultraviolet absorbers. In addition, the said additive may be used independently and may use 2 or more types together.

Examples of the antioxidant include 2,6-di-t-butyl-4-methylphenol, 2- (1-methylcyclohexyl) -4,6, dimethylphenol, and 2,2-methylene-bis- (4 -Ethyl-6-t-butylphenol), tris (di-nonylphenyl phosphite) and the like.

Examples of the ultraviolet absorber include pt-butylphenyl salicylate, 2,2′-dihydroxy-4-methoxy-benzophenone, 2- (2′-dihydroxy-4′-m-octoxyphenyl) benzotriazole, and the like. Is mentioned. Examples of the lubricant include paraffin phenos and hydrogenated oil, and examples of the antistatic agent include stearoazitopropyldimethyl-β-hydroxyethylammonium trate. In addition, when a powdery thing is added as the said lubricant, it is necessary to be careful because an apparatus and a process become complicated.

The minimum with the preferable thickness of the optical film of this invention is 10 micrometers, and a preferable upper limit is 500 micrometers. A more preferred lower limit is 30 μm, and a more preferred lower limit is 200 μm.

A retardation film can be produced by subjecting the optical film of the present invention to a stretching treatment. Such a retardation film is also one aspect of the present invention. In addition, it does not specifically limit as a specific method of extending | stretching process, A conventionally well-known method can be used.

According to the present invention, a method for producing an optical film that suppresses the generation of a crosslinked gel at the time of melt extrusion, has few appearance defects, and can exhibit excellent display quality when incorporated in a liquid crystal display device or the like, An optical film and a retardation film can be provided.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
As a copolymer of a norbornene monomer and an olefin monomer, a copolymer of tetracyclododecene and ethylene (APL6015T, manufactured by Mitsui Chemicals, Tg = 145 ° C.) is used, and this resin has a cylinder inner diameter of 30 mm. , the root diameter of the resin feeding section is 25 mm, a screw pitch of the resin feeding section _{(P 1D)} and the ratio _P 5D of the screw pitch _{(P 5D)} at the 5D section _/ P 1D = 1.33 at a full flight screw (L / It was supplied to an extruder having D = 28), melted and kneaded, and melt-extruded from a T-die to obtain an optical film having an average thickness of 100 μm.
The raw material was charged in a natural manner in which the hopper provided in the extruder was filled with the raw material and then charged by its own weight. Moreover, nitrogen was sent into the hopper from the resin charging port to discharge oxygen. Furthermore, the set temperature conditions were as follows.
C1 / C2 / C3 / C4 / AD1 / PF / AD2 / D = 200/230/250/250/250/250/250/250 ° C.
Here, C1 to 4 are set temperatures of each section obtained by equally dividing the cylinder of the extruder into four in the extruding direction, AD1 and 2 are each device connection unit adapter set temperature, D is a T die set temperature, and PF is The preset temperature of the sintered filter part which consists of a stainless fiber installed in the extrusion line is represented.

(Example 2)
An optical film was produced in the same manner as in Example 1 except that a copolymer of norbornene and ethylene (Topas 6013, manufactured by Ticona, Tg = 140 ° C.) was used as the copolymer of the norbornene monomer and the olefin monomer. did.

(Comparative Examples 1-3)
An optical film was produced in the same manner as in Example 1 except that the screw shown in Table 1 was used as the screw of the extruder.

(Evaluation)
(1) Evaluation of the number of appearance defects Ten samples each obtained by cutting the obtained optical film into 200 mm × 250 mm were prepared, and for such samples, the major axis caused by the crosslinked gel was measured by a transmission method using a microscope. Appearance defects of 100 μm or more were counted and converted per 1 m ^{2 of} unit area. In addition, based on the obtained result, it evaluated by the following references | standards.
A: The number of appearance defects was 10 / m ² or less.
X: The number of appearance defects exceeded 10 / m ² .

According to the present invention, a method for producing an optical film that suppresses the generation of a crosslinked gel at the time of melt extrusion, has few appearance defects, and can exhibit excellent display quality when incorporated in a liquid crystal display device or the like, An optical film and a retardation film can be provided.

It is a schematic diagram which shows an example of the screw used by this invention. It is the elements on larger scale of the screw used by this invention.

Claims (4)

A method for producing an optical film by a melt extrusion method,
Extrusion molding is performed using a molding machine having a screw with a screw trough diameter of 70 to 95% of the outer diameter of the resin and a pitch expansion rate in the flow direction of the resin in the feed zone of 20 to 100%. The manufacturing method of the optical film characterized by having the process to do. An optical film manufactured by the method for manufacturing an optical film according to claim 1,
An optical film having an appearance defect of 100 μm or more of 10 pieces / m ² or less. 3. The optical film according to claim 2, comprising a copolymer of a norbornene monomer and an olefin monomer. A retardation film comprising the optical film according to claim 2.

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