JPWO2016076058A1 - Optical film manufacturing method and optical film - Google Patents

Abstract

In the present invention, a solution casting film is formed by using a dope in which the casting film thickness when casting a dope onto a support is not stretched and becomes 400% or more of the film thickness after all the solvent is dried. The present invention relates to a method for producing an optical film containing cellulose ester and having a thickness of 30 μm or less.

Description

  The present invention relates to a method for producing an optical film that can be used for various functional films such as a protective film for a polarizing plate used for a liquid crystal display (LCD), a retardation film, a viewing angle widening film, and an antireflection film used for a plasma display. And an optical film obtained by the production method.

  Various optical films such as a transparent protective film for protecting the polarizing element of the polarizing plate are disposed in the image display region of the liquid crystal display device. As such an optical film, for example, a film having excellent transparency such as a cellulose ester film is used.

  Moreover, such an optical film is often manufactured as a long optical film by, for example, a solution casting film forming method. Specifically, the solution casting film forming method is a method in which a resin solution (dope) in which a transparent resin as a raw material resin is dissolved in a solvent is cast on a traveling support and dried to a peelable extent. This is a method for producing a long optical film by peeling off the obtained film from the support, and drying and stretching while carrying the peeled film with a carrying roller (for example, patent Literature 1 etc.).

  In recent years, there is an increasing demand for thinning a protective film used for a polarizing plate for a small and medium liquid crystal display device such as a smart phone or a tablet. However, when a thin film protective film is manufactured by solution casting as described above, a problem that a linear stripe in the width direction is periodically generated in the longitudinal direction when the hard coat (HC) is applied (so-called periodicity). It has been found that streak) occurs.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a method for producing a high-quality thin film optical film by a solution casting method, and an excellent optical film obtained by the production method. .

JP 2013-67074 A

  As a result of intensive studies, the present inventors have found that the above problems can be solved by a method for producing an optical film having the following configuration, and have further completed the present invention based on such findings.

  That is, one aspect of the present invention is to use a dope in which the cast film thickness when casting the dope to the support is 400% or more of the film thickness when all the solvent is dried without stretching. The present invention relates to a method for producing an optical film containing a cellulose ester and having a film thickness of 30 μm or less, characterized in that solution casting is performed.

FIG. 1 is a schematic view showing a basic configuration of an optical film manufacturing apparatus 1 by a solution casting method using an endless belt support 11.

  The present inventor has conducted research and the periodic streaks as described above occur when the film is a thin film of 30 μm or less, and the thinner the film, the shorter the interval (pitch) at which the streaks occur. I found.

  The reason for this was thought to be that the fine particle components were regularly aligned in the widthwise linear film thickness irregularities periodically generated in the longitudinal direction of the thin film, and high density unevenness was formed.

  Furthermore, the inventor of the present invention has a linear film thickness unevenness even in a conventional film having a normal thickness, but it is applied because the unevenness is relatively large due to the thin film and the pitch is short. It was thought that the irregularity of the liquid component became intense and the problem of periodic streaks occurred. Thus, the present invention has been achieved by finding that periodic streaks do not occur even when a hard coat is applied by casting the dope in a more diluted state and suppressing the height of short pitch unevenness due to drying. It came to do.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  The manufacturing method of the optical film which concerns on this embodiment is a method of manufacturing an optical film with a film thickness of 30 micrometers or less containing a cellulose ester by solution casting film forming.

  The solution casting film is generally formed by casting a resin solution (dope) in which a transparent resin containing cellulose ester is dissolved on a continuously running support. It is the manufacturing method of an optical film provided with the casting process which forms, the peeling process which peels the said casting film from the said support body, and the drying process which dries the peeled casting film.

  For example, it is performed by an optical film manufacturing apparatus using a solution casting film forming method as shown in FIG. In addition, as an optical film manufacturing apparatus, it is not limited to what is shown in FIG. 1, The thing of another structure may be sufficient.

  FIG. 1 is a schematic view showing a basic configuration of an optical film manufacturing apparatus 1 by a solution casting method using an endless belt support 11. The optical film manufacturing apparatus 1 includes an endless belt support 11, a casting die 20, a peeling roller 13, a drying device 14, a winding device 15, and the like. The casting die 20 casts a resin solution (dope) 16 in which a transparent resin is dissolved on the surface of the endless belt support 11. The endless belt support 11 is supported to be drivable by a pair of driving rollers and driven rollers, forms a casting film made of the resin solution 16 cast from the casting die 20, and is dried while being conveyed. The peeling roller 13 peels the dried cast film from the endless belt support 11. The peeled cast film is further dried by the drying device 14, and the dried cast film is wound around the winding device 15 as an optical film.

  The running speed of the support, the casting width of the casting film, and the like can be set as appropriate.

  In addition, the manufacturing apparatus of an optical film is not limited to the thing of said structure, For example, you may provide the extending | stretching apparatus etc. separately. Examples of the stretching device include a stretching device that stretches the film peeled from the endless belt support 11 in a direction (Transverse Direction: TD direction) orthogonal to the film transport direction.

  In this embodiment, as a dope used for the solution casting film forming method as described above, the casting film thickness when casting the dope to the support is unstretched and the film thickness when the solvent is completely dried is as follows. A dope that is 400% or more is used. The cast film thickness here is a calculated value of the average film thickness at the time of casting calculated by dividing the dope casting volume per time by the product of the casting width and the support running speed. In addition, the film thickness when the solvent is completely dried without being stretched means that the dope is dried on the support, and the film having self-supporting property is peeled off and stretched in the transport direction. It is the average value of the film thickness measured from 5 to 100 locations per meter in the width direction with respect to the film dried until the residual solvent amount is 0.5% by mass or less of the whole film without stretching. . The film thickness other than the cast film thickness and the film thickness when the solvent is completely dried without stretching may be stretched arbitrarily, and the solvent is completely dried with the cast film thickness and unstretched. When the relationship of the film thickness ratio is specified, it is the average value of the film thickness measured at 5 to 100 locations per 1 m in the width direction with respect to the film created under the conditions that satisfy it. .

  According to such a configuration, it is possible to manufacture a high-quality thin film optical film in which the generation of periodic stripes is suppressed.

  Hereinafter, the composition of the resin solution (dope) used in the present embodiment will be described.

  The dope used in the present embodiment is obtained by dissolving a transparent resin in a solvent.

  The transparent resin is not particularly limited as long as it is a resin having transparency when formed into a substrate by a solution casting film forming method or the like and contains a cellulose ester resin. It is preferable that production by a film forming method or the like is easy, adhesiveness with other functional layers such as a hard coat layer is excellent, optical isotropic property, and the like. Here, the transparency means that the visible light transmittance is 60% or more, preferably 80% or more, and more preferably 90% or more.

  Specific examples of the cellulose ester resin include cellulose acetate resin, cellulose propionate resin, cellulose butyrate resin, cellulose acetate butyrate resin, cellulose acetate propionate resin, cellulose triacetate resin, and cellulose diacetate. Examples thereof include resins. Of these, cellulose acetate resin is preferably used. These may be used alone or in combination of two or more.

  The number average molecular weight of the cellulose ester-based resin is preferably 30,000 to 200,000 in view of high mechanical strength when molded into an optical film and an appropriate dope viscosity in the solution casting film forming method. Moreover, it is preferable that weight average molecular weight (Mw) / number average molecular weight (Mn) exists in the range of 1-5, and it is more preferable that it exists in the range of 1.4-3.0.

  The average molecular weight and molecular weight distribution of a resin such as a cellulose ester resin can be measured using gel permeation chromatography or high performance liquid chromatography. Therefore, the number average molecular weight (Mn) and the weight average molecular weight (Mw) can be calculated using these, and the ratio can be calculated.

  The cellulose ester resin preferably has an acyl group having 2 to 4 carbon atoms as a substituent. As the substitution degree, for example, when the substitution degree of the acetyl group is X and the substitution degree of the propionyl group or butyryl group is Y, the total value of X and Y is 2.2 or more and 2.95 or less, X is preferably more than 0 and 2.95 or less.

  In addition, the portion not substituted with an acyl group usually exists as a hydroxyl group. These cellulose ester resins can be synthesized by a known method. The measuring method of the substitution degree of an acyl group can be measured according to the provisions of ASTM-D817-96.

  The cellulose that is the raw material of the cellulose ester resin is not particularly limited, and examples thereof include cotton linters, wood pulp (derived from coniferous trees and hardwoods), kenaf and the like. The cellulose ester resins obtained from them can be mixed and used at an arbitrary ratio, but it is preferable to use 50% by mass or more of cotton linter. When the acylating agent is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), these cellulose ester resins use an organic acid such as acetic acid or an organic solvent such as methylene chloride, It can be obtained by reacting with a cellulose raw material using such a protic catalyst.

  As the solvent used in the present embodiment, a solvent containing a good solvent for the transparent resin can be used. The good solvent varies depending on the transparent resin used. For example, in the case of a cellulose ester resin, the good solvent and the poor solvent change depending on the acyl group substitution degree of the cellulose ester. For example, when acetone is used as the solvent, the cellulose ester acetate ester (acetyl group substitution degree 2.4), cellulose Acetate propionate is a good solvent, and cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent. Therefore, since the good solvent and the poor solvent differ depending on the transparent resin used, the case of a cellulose ester resin will be described as an example.

  Examples of good solvents for cellulose ester resins include organic halogen compounds such as methylene chloride, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dioxolane derivatives, cyclohexanone, Ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3- Hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, etc. Can be mentioned. Among these, organic halogen compounds such as methylene chloride, dioxolane derivatives, methyl acetate, ethyl acetate, acetone and the like are preferable. These good solvents may be used alone or in combination of two or more.

  The dope may contain a poor solvent as long as the transparent resin does not precipitate. Examples of poor solvents for cellulose ester resins include alcohols having 1 to 8 carbon atoms such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol, methyl ethyl ketone, and methyl isobutyl. Examples include ketones, propyl acetate, monochlorobenzene, benzene, cyclohexane, tetrahydrofuran, methyl cellosolve, and ethylene glycol monomethyl ether. These poor solvents may be used alone or in combination of two or more.

  Further, the dope used in the present embodiment may contain other components (additives) other than the resin and the solvent as long as the effects of the present invention are not impaired. Examples of the additive include fine particles, a plasticizer, an ultraviolet absorber, a flame retardant, a lubricant, and a matting agent.

  Next, a preparation method using a cellulose ester resin will be described as an example of a method for preparing a dope.

  The method for dissolving the cellulose ester resin when preparing the dope is not particularly limited, and a general method can be used. Utilizing the fact that heating and pressurization can be combined as appropriate to allow heating above the boiling point of the solvent at normal pressure, it is possible to dissolve the cellulose ester resin in the solvent above the boiling point at normal pressure. It is preferable from the viewpoint of preventing the generation of objects. In addition, a method in which a cellulose ester resin is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

  Next, the obtained cellulose ester resin solution is filtered using a suitable filter medium such as filter paper. There is no restriction | limiting in particular in the material of a filter medium, A normal filter medium can be used.

  In this embodiment, when preparing the dope, the cast film thickness when casting the dope to the support is 400% or more of the film thickness when all the solvent is dried without stretching. Prepare to. Specifically, the solvent ratio is adjusted so that the film thickness of the cast film falls within the above range.

  In the present embodiment, the cast film thickness is a value calculated by dividing the dope cast volume per time by the product of the cast width and the support running speed.

  By preparing the dope in this way, it is considered that unevenness with a short pitch, which is a cause of periodic streaks, can be suppressed, and consequently generation of periodic streaks can be suppressed.

  On the other hand, if the casting dope is excessively diluted in order to suppress the film thickness unevenness of the short pitch that causes periodic streaks, there is a possibility that minute spot-like unevenness may be seen on the film. According to the inventor's research, such dot-like unevenness is caused by a minute gel-like material that seems to be formed by aggregation of foreign substances originally contained in the raw material (vinegar cotton) and cellulose esters such as cellulose acylate. It is thought that it occurs at. In other words, since the dope generally contains foreign matter that causes gel, the gel and the cause foreign matter are removed in the filtration process, but the dope is diluted in order to suppress the short pitch irregularities that cause periodic streaks. It is thought that this is because the trapping efficiency of the foreign matter deteriorates and remains, and the diluted dope is concentrated in the process of drying after casting and becomes a gel.

  Therefore, in order to suppress both periodic streaks and minute spot-like unevenness, it is preferable to cool the dope when filtering the dope diluted more than usual. Thereby, it is considered that precipitation and gel aggregation of foreign matters are promoted and trapped, generation of gel-like material after casting is prevented, and minute spot-like unevenness in the thin film can be suppressed.

  More specifically, it is preferable to cool the dope at a temperature of 12 ° C to 23 ° C during filtration. Thus, by cooling the dope at the time of filtration to 23 ° C. or less, it is possible to more reliably suppress the occurrence of spot-like unevenness in the diluted dope. Moreover, when filtration is performed at a temperature of less than 12 ° C., a visible gel-like material may be generated, which may make it difficult to continue filtration.

  The dope cooling means is not particularly limited, and a method of cooling the dope before filtration through a jacket pipe provided with a heat exchanger into which a refrigerant such as cooling water is introduced can be appropriately used.

  Furthermore, if the dope is cast with cooling after filtration, the leveling effect due to dilution is weakened, and the effect of suppressing the height of the linear film thickness unevenness may be reduced. Therefore, it is considered that both the periodic streak and the spot-like unevenness can be further suppressed by filtering and heating the dope again before casting.

  Although there is no particular limitation on the heating temperature at this time, from the viewpoint of preventing the leveling effect after dope casting and the surface quality of the film from being impaired by foaming of the solvent in the high temperature dope on the casting support, It is preferable to heat in the range of 30 to 38 ° C.

  The means for heating the dope before casting after filtration is not particularly limited, and a method of passing the dope through a jacket pipe into which hot water is introduced can be appropriately used.

  In the present embodiment, the amount of inorganic impurities in the dope after filtration is preferably 190 ppm or less. The inorganic impurities referred to in the present embodiment include, for example, calcium, magnesium, phosphorus, boron, and the like, which are included in the raw material cellulose ester and the like, and do not include an inorganic substance added at the time of dope preparation as an additive. If this amount of inorganic impurities exceeds 190 ppm, there is a risk of spot-like unevenness.

  The measurement of the amount of inorganic impurities can be performed in a film state in which the dope is dried, and can be calculated from the solid content concentration of the dope.

  When each of the additives is contained, for example, the additive may be dissolved in an organic solvent such as alcohol, methylene chloride, dioxolane and then added to the dope, or may be added directly to the dope composition. . In addition, for inorganic powders that do not dissolve in organic solvents, the additive and cellulose ester resin are added to the dope using a dissolver or sand mill with the additive dispersed in the cellulose ester resin. It is preferable.

  The method for dispersing the additive (particularly, fine particles) in the cellulose ester resin solution is not particularly limited. For example, the dispersion solvent and the fine particles can be stirred and mixed, and then dispersed using a disperser. This is a fine particle dispersion. The fine particle dispersion is added to the cellulose ester resin solution and stirred.

  According to the manufacturing method according to the present embodiment as described above, a high-quality thin-film optical film in which generation of periodic streaks is suppressed can be obtained.

  That is, the optical film obtained by the manufacturing method according to this embodiment is an optical film having a film thickness of 30 μm or less, including a cellulose ester, having a height of 100 nm or more and a peak interval with respect to the longitudinal direction of 5 mm or less. It has no widthwise linear stripe (periodic stripe).

  Here, the film thickness is an average film thickness of the produced film, and the film thickness is measured at 5 to 100 locations per 1 m in the width direction of the optical film with a contact film thickness meter manufactured by Mitutoyo Corporation. The average value of the measured values is shown as the film thickness. In addition, the optical film here refers to a film having a thickness of 1 μm or more.

  Further, the “height” of the periodic streaks here means the height relative to the film thickness minimum value in the vicinity of the width direction linear streaks, and is an optical interference type surface roughness meter (Canon). It can be measured by using New View 5030).

  Moreover, the peak interval with respect to the longitudinal direction means 0.05 mm or more of intervals in which the widthwise linear stripes having a height of 100 nm or more are generated.

  The optical film of this embodiment is used suitably for uses, such as a transparent protective film arrange | positioned on the polarizing element surface of a polarizing plate, for example.

  By using a polarizing plate provided with the optical film of the present embodiment, a high-quality liquid crystal display device or the like can be realized. In particular, since the optical film of the present embodiment is a thin film, it is preferably used for applications such as smart phones and tablets.

  As described above, the present specification discloses various modes of technology, of which the main technologies are summarized below.

  That is, one aspect of the present invention is to use a dope in which the cast film thickness when casting the dope to the support is 400% or more of the film thickness when all the solvent is dried without stretching. The present invention relates to a method for producing an optical film containing a cellulose ester and having a film thickness of 30 μm or less, characterized in that solution casting is performed.

  According to such a configuration, in a thin film optical film containing a cellulose ester and having a film thickness of 30 μm or less, it is possible to suppress so-called periodic streaks and improve cast film thickness unevenness (horizontal step unevenness).

  Moreover, in the manufacturing method of the said optical film, it is preferable to cool dope at the time of filtration before casting. Thereby, generation | occurrence | production of a minute spot-like nonuniformity can further be suppressed.

  Furthermore, it is preferable to heat the dope cooled as described above before casting. Thereby, it is considered that periodic streaks and dot-like unevenness can be more reliably suppressed.

  Moreover, in the manufacturing method of the said optical film, it is preferable that the temperature at the time of cooling dope at the time of filtration is 12 degreeC or more and 23 degrees C or less. Thereby, the above effect can be obtained more reliably.

  Moreover, in the manufacturing method of the said optical film, it is preferable that a cellulose ester is a cellulose acetate. Thereby, the above effect can be obtained more reliably.

  Furthermore, in the manufacturing method of the said optical film, it is preferable that the amount of inorganic impurities in dope after filtration is 190 ppm or less. Thereby, the above effect can be obtained more reliably.

  Moreover, the optical film which concerns on the other situation of this invention is obtained by the manufacturing method of the said optical film, and the width direction line whose height is 100 nm or more and the peak space | interval with respect to a longitudinal direction is 5 mm or less. It is characterized by having no stripes. In addition, the peak space | interval here refers to the thing of 0.05 mm or more. According to such a configuration, it is possible to provide a high-quality thin film optical film in which generation of periodic stripes, horizontal step unevenness, and minute spot-like unevenness is suppressed.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples.

[Example 1]
An optical film was produced by the following method.

(Preparation of dope)
The following materials were put into a sealed container, heated at 80 ° C., completely dissolved with stirring, filtered, and a dope was prepared. The temperature before filtration and after filtration (before casting) was set to 32 ° C. The following material ratio is an example of a prescription in which the film thickness ratio is 400% when the film thickness when cast is completely dried and unstretched, and the ratio of the film thickness when cast is completely dried when unstretched is changed. In this case, for example, the ratio of methylene chloride and ethanol to cellulose triacetate is adjusted.

Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Plasticizer (ethylphthalylethyl glycolate) 2 parts by weight Ultraviolet absorber (Tinuvin 326, manufactured by BASF Japan Ltd.) 1 part by weight Inorganic fine particles ( Aerosil 200V, manufactured by Nippon Aerosil Co., Ltd.)
0.2 parts by weight Methylene chloride 460.0 parts by weight Ethanol 29.4 parts by weight

  Moreover, when the amount of inorganic impurities in the dope after filtration was converted to the concentration in the dope from the measurement result of the amount of inorganic impurities in the film after drying by the ICP emission analysis (ICP-AES) method, it was 240 ppm. In addition, the amount of inorganic impurities is a value excluding the amount of inorganic substances due to inorganic fine particles in the dope formulation.

(Manufacture of cellulose acetate film)
First, a ceramic insulating film (thickness: 50 μm) was provided on the back surface of an endless belt support made of SUS316 by ceramic spraying. Then, the dope obtained as described above was cast at a dope temperature of 32 ° C. and at a temperature of 23 ° C. on the endless belt support by a casting die comprising a coat hanger die, with a casting width of 2 m and a casting volume of 900 L / Casting was performed at a casting time (running speed of the support) of 3000 m / hour (50 m / min) to form a casting film.

  The cast film thickness was 120 μm when calculated by dividing the dope cast volume per hour by the product of the cast width and the support running speed.

  In addition, the unstretched dry film thickness is the contact made by Mitutoyo Corporation after drying the cast dope after being peeled off from the support and drying until the residual solvent amount in the film is less than 0.5% by mass. It was 30 μm when 5 to 100 points were measured per 1 m in the width direction using a thickness gauge.

  Therefore, the cast film thickness / unstretched dry film thickness was 400%.

[Example 2]
A cellulose acetate film was produced in the same manner as in Example 1 except that the temperatures before filtration and before filtration (before casting) were each changed to 26 ° C. The amount of inorganic impurities in the dope after filtration was 200 ppm. The cast film thickness was 120 μm, and the unstretched dry film thickness was 30 μm. Therefore, the cast film thickness / unstretched dry film thickness was 400%.

[Example 3]
A cellulose acetate film was produced in the same manner as in Example 1 except that the temperatures before filtration and before filtration (before casting) were changed to 12 ° C., respectively. The amount of inorganic impurities in the dope after filtration was 140 ppm. The cast film thickness was 120 μm, and the unstretched dry film thickness was 30 μm. Therefore, the cast film thickness / unstretched dry film thickness was 400%.

[Example 4]
A cellulose acetate film was produced in the same manner as in Example 1 except that the temperatures before filtration and after filtration (before casting) were changed to 23 ° C. and 32 ° C., respectively. The amount of inorganic impurities in the dope after filtration was 190 ppm. The cast film thickness was 120 μm, and the unstretched dry film thickness was 30 μm. Therefore, the cast film thickness / unstretched dry film thickness was 400%.

[Example 5]
Cellulose acetate film in the same manner as in Example 1, except that the temperatures before filtration and after filtration (before casting) were changed to 23 ° C. and 32 ° C., respectively, and the casting dope volume per hour was changed to 600 L / hour. Manufactured. The amount of inorganic impurities in the dope after filtration was 190 ppm. The cast film thickness was 80 μm, and the unstretched dry film thickness was 20 μm. Therefore, the cast film thickness / unstretched dry film thickness was 400%.

[Example 6]
Cellulose acetate film in the same manner as in Example 1, except that the temperatures before filtration and after filtration (before casting) were changed to 23 ° C. and 32 ° C., respectively, and the casting dope volume per hour was changed to 450 L / hour. Manufactured. The amount of inorganic impurities in the dope after filtration was 190 ppm. The cast film thickness was 60 μm, and the unstretched dry film thickness was 15 μm. Therefore, the cast film thickness / unstretched dry film thickness was 400%.

[Example 7]
Cellulose acetate film in the same manner as in Example 1, except that the temperatures before filtration and after filtration (before casting) were changed to 23 ° C. and 32 ° C., respectively, and the casting dope volume per hour was changed to 300 L / hour. Manufactured. The amount of inorganic impurities in the dope after filtration was 190 ppm. Moreover, since the cast film thickness was 40 μm and the unstretched dry film thickness was 10 μm, the cast film thickness / unstretched dry film thickness was 400%.

[Comparative Example 1]
A cellulose acetate film was produced in the same manner as in Example 1 except that the composition of the dope was changed as follows.

Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Plasticizer (ethylphthalylethyl glycolate) 2 parts by weight Ultraviolet absorber (Tinuvin 326, manufactured by BASF Japan Ltd.) 1 part by weight Inorganic fine particles ( Aerosil 200V, manufactured by Nippon Aerosil Co., Ltd.)
0.2 parts by weight Methylene chloride 429.3 parts by weight Ethanol 27.4 parts by weight

  The amount of inorganic impurities in the dope after filtration was 190 ppm. Moreover, since the cast film thickness was 114 micrometers and the unstretched dry film thickness was 30 micrometers, the cast film thickness / unstretched dry film thickness was 380%.

[Reference example]
A cellulose acetate film was produced in the same manner as in Example 1 except that the composition of the dope was changed as follows and the casting dope volume per hour was changed to 1050 L / hour.

Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Plasticizer (ethylphthalylethyl glycolate) 2 parts by weight Ultraviolet absorber (Tinuvin 326, manufactured by BASF Japan Ltd.) 1 part by weight Inorganic fine particles ( Aerosil 200V, manufactured by Nippon Aerosil Co., Ltd.)
0.2 parts by weight Methylene chloride 414.0 parts by weight Ethanol 26.5 parts by weight

  The amount of inorganic impurities in the dope after filtration was 150 ppm. Moreover, since the cast film thickness was 129.5 micrometers and the unstretched dry film thickness was 35 micrometers, the cast film thickness / unstretched dry film thickness was 370%.

(Evaluation)
The following evaluation tests were performed on the optical films (Examples 1 to 7, Comparative Example 1 and Reference Example) obtained as described above.

(Thickness unevenness height of linear stripes in the width direction)
About each said optical film, the film thickness unevenness | corrugation height was measured by measuring with an optical interference type surface roughness meter.

(Periodic streak)
Each optical film is coated with a hard coat, and light in a fluorescent lamp is applied to check the widthwise linear stripes (periodic stripes) that appear periodically in the longitudinal direction, and on one side of the PVA polarizer. Make a polarizing plate with each optical film and the other side of the same optical film with a hard coat applied, and apply the light from the fluorescent lamp to the polarizing plate. confirmed. The periodic streak was evaluated according to the following rank.
◎ No periodic streaks were visible on the film and polarizing plate.
○ On the film, the periodic streaks looked thin, but not after polarizing.
Δ: Periodic streaks were clearly seen in the film, but after the polarizing plate formation, it was seen only thinly, and it was at a level not causing a problem in practical use.
X The periodic streaks were clearly visible even in the film and the polarizing plate using the film.

(Spotted unevenness)
Each optical film is irradiated with light from a fluorescent lamp to visually check minute spot-like unevenness that appears on the film, and each optical film is provided on one side of the PVA polarizer, and the same optical material is provided on the other side. A polarizing plate was prepared by attaching the film after the hard coat application, and the light from the fluorescent lamp was also applied to the polarizing plate to confirm minute spot-like unevenness. Evaluation of minute spot-like unevenness was performed according to the following rank.
◎ No minute spot-like unevenness was seen on the film and the polarizing plate.
○ Although the minute spot-like unevenness appeared weak on the film, it did not appear on the polarizing plate.
Δ: A small spot-like unevenness was seen on the film, but only a thin spot was seen on the polarizing plate, which was a level that would not cause a problem in practice.
X Fine spot-like unevenness was clearly visible even on the film and the polarizing plate using the film.
The results are summarized in Table 1.

[Discussion]
As can be seen from Table 1, Examples 1 to 3 using a dope in which the cast film thickness when the dope was cast on the support was not stretched and became 400% or more of the film thickness after all the solvent was dried. In the optical film of No. 7, since the film thickness unevenness height exceeding 100 nm was not observed, generation of periodic streaks was also suppressed.

  In Example 1, periodic streaks were not confirmed, but since the amount of inorganic impurities in the dope after filtration was large, minute spot-like unevenness was confirmed.

  In Example 2, since the temperature at the time of filtration was cooled to 25 ° C., minute dot-like unevenness was hardly confirmed, but since it was cast without heating, the periodic streak was generated so thinly that it could not be recognized after polarizing plate formation. did.

  In Example 3, when the temperature during filtration was lowered to 12 ° C., minute spot-like unevenness could not be confirmed, but the periodic streak slightly increased.

  In Example 4, after cooling at the time of filtration, the dope temperature was heated to 32 ° C. before casting, so neither periodic streak nor minute dot-like unevenness was confirmed. Similarly, in Examples 5 to 7, the periodic streak became stronger as the average film thickness was reduced after drying, but even in a thin film of 10 μm, it was a periodic streak that could not be recognized after polarizing plate formation. .

  On the other hand, in Comparative Example 1, since the ratio of the cast film thickness to the unstretched dry film thickness was less than 400% with a thin film of 30 μm, a strong periodic streak was generated by the coating solution.

  In the reference example having a film thickness of 35 μm, even if the ratio of the cast film thickness to the unstretched dry film thickness is less than 400%, there is a certain amount of thickness. It was not recognized by the plate.

  As mentioned above, according to the manufacturing method of the optical film which concerns on this embodiment, it was shown that the high quality thin film optical film by which generation | occurrence | production of the periodic stripe was suppressed was obtained.

  This application is based on Japanese Patent Application No. 2014-229956 filed on November 12, 2014, the contents of which are included in the present application.

  In order to express the present invention, the present invention has been described appropriately and sufficiently through the embodiments with reference to the drawings and the like. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that it can be done. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

The present invention has wide industrial applicability in the technical field of optical films used in display devices and the like and methods for producing the same.

Claims (7)

  In solution casting film formation, the film thickness when the dope is cast on the support is not stretched and the film thickness is 400% or more when the solvent is completely dried. A method for producing an optical film containing a cellulose ester and having a thickness of 30 μm or less.   The manufacturing method of the optical film of Claim 1 which cools dope at the time of filtration before casting.   The manufacturing method of the optical film of Claim 2 heated before casting dope after filtration.   The manufacturing method of the optical film of Claim 2 or 3 whose temperature when cooling dope at the time of filtration is 12 degreeC or more and 23 degrees C or less.   The manufacturing method of the optical film in any one of Claims 1-4 whose cellulose ester is a cellulose acetate.   The manufacturing method of the optical film in any one of Claims 1-5 whose amount of inorganic impurities in dope after filtration is 190 ppm or less. An optical film obtained by the production method according to claim 1,
An optical film characterized by having no widthwise linear stripes having a height of 100 nm or more and a peak interval with respect to the longitudinal direction of 5 mm or less.

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