JP7115540B2 - Optical film and its manufacturing method - Google Patents

Description

The present invention relates to an optical film and its manufacturing method.

In recent years, there has been a growing shift from glass to optical films in the parts of smartphones and other applications that require lighter weight and thinner films. If this substitution is realized, there are merits such as not only weight reduction and thinning but also cost reduction. However, in order for an optical film to replace glass, it is necessary to make the haze value of the optical film close to that of glass.

Here, a low-haze optical film is disclosed in Patent Document 1, for example. In Patent Document 1, fine particles are contained in an optical film together with a surface modifier, so that the fine particles are unevenly distributed on one side of the optical film to impart lubricity. We are trying to realize an optical film.

Further, in Patent Document 2, a polycarbonate resin containing fine particles is melt-extruded from a die into a film, and the film is sandwiched and pressed between a pair of rolls consisting of a mat roll and a rubber roll to transfer the mat pattern of the mat roll to the film. Trying to get a matte film with low gloss. Further, in Patent Document 3, in the production of an optical film by a solution casting film forming method, when the amount of residual solvent in the web is within a predetermined range, a fine particle dispersion liquid containing fine particles is formed on one surface of the web. Liquid droplets are ejected by an inkjet head system, landed, and adhered to form a fine convex structure, thereby reducing the amount of matting agent in the optical film and improving slipperiness.

JP 2017-122855 A (see claim 1, paragraphs [0009], [0010], [0018], etc.) Japanese Patent No. 3676896 (Claim 1, paragraphs [0004] to [0006], [0024], see FIG. 1, etc.) Japanese Patent No. 5182092 (Claim 1, paragraphs [0005] and [0024], see FIG. 1, etc.)

By the way, conventional optical films, even those with low haze, are not as good as glass. This is because not a little organic or inorganic fine particles are added to the optical film in order to improve handling properties during production, and the film surface is not flat. Therefore, in order to realize a low haze close to that of glass in an optical film, it is desired to realize an optical film containing no fine particles. In this regard, the optical films of Patent Documents 1 to 3 described above all contain fine particles, and it is difficult to achieve a low haze close to that of glass.

On the other hand, when the optical film does not contain fine particles, the optical film is not provided with slipperiness, so there is a concern that the handleability is lowered and the yield is lowered. In other words, if the slipperiness of the optical film is poor, the film may be transported while sticking to a roll (for example, a mirror-finished roll) during production, resulting in small scratches on the surface of the film during transport. In addition, since the optical film with poor slipperiness sticks strongly to the rolls, strong wrinkles are generated between the rolls, and in the worst case, the optical film may break.

Therefore, in order to achieve a low haze close to that of glass, there is a demand for an optical film with good transportability that is less likely to be scratched during transportation and less wrinkled during production, even if it does not contain fine particles. However, it has not yet been realized to manufacture such an optical film by a mass-producible manufacturing method similar to the conventional one.

The present invention has been made to solve the above problems, and its purpose is to realize a low haze close to that of glass, so that even if it has a structure that does not contain fine particles, it is less likely to be scratched during transportation during production. An optical film that can reduce the occurrence of wrinkles, thereby being able to be manufactured by a manufacturing method that allows mass production, and that can achieve both low haze and good transportability during manufacturing, and a method for manufacturing the same. to provide.

The above object of the present invention is achieved by the following manufacturing method or configuration.

A method for producing an optical film according to one aspect of the present invention includes a casting step of casting a dope containing no fine particles on a metal support to form a web, and a peeling step of peeling the web from the metal support. a step of forming unevenness on the surface of the peeled web with a processing roll; and a winding step of winding the web having the unevenness as an optical film. The film has one or more irregularities within an area of 250000 μm ² on the surface, and within said area, the surface roughness Sa around said irregularities is 1.5 nm or less.

An optical film according to another aspect of the present invention is a fine particle-free optical film. The optical film has one or more irregularities within a range of 250000 μm ² on the surface, and the surface roughness Sa around the irregularities within the range is 1.5 nm or less.

Even if the optical film does not contain fine particles, it is less likely to be scratched during transportation and less wrinkled. A film can be produced, and at the same time, it is possible to achieve both a low haze close to that of glass and good transportability during production.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows the structure of the outline of the manufacturing apparatus of the optical film which concerns on embodiment of this invention. It is a flow chart which shows a flow of a manufacturing process of the above-mentioned optical film. It is explanatory drawing which shows typically the calculation method of the maximum height Ry. It is a sectional view showing a section shape of the above-mentioned optical film typically. It is explanatory drawing which shows typically the calculation method of surface roughness Sa. It is explanatory drawing which shows typically the calculation method of surface roughness Ra. It is explanatory drawing which shows typically the calculation method of the maximum height roughness Rz. FIG. 4 is an explanatory diagram schematically showing the relationship between the measurement range of the surface roughness Sa and the calculation range of the number of irregularities in the optical film of the example. FIG. 4 is an explanatory view schematically showing a cross-sectional shape along the width direction of each film with wrinkles or wrinkles.

An embodiment of the present invention will be described below with reference to the drawings. In this specification, when a numerical range is expressed as A to B, the lower limit A and upper limit B are included in the numerical range. In addition, the present invention is not limited to the following contents.

[Method for producing optical film]
First, the outline of the method for manufacturing the optical film of the present embodiment will be described. FIG. 1 is an explanatory view showing a schematic configuration of an optical film manufacturing apparatus 1 according to this embodiment. Moreover, FIG. 2 is a flowchart which shows the flow of the manufacturing process of an optical film. The method for producing an optical film of the present embodiment is a method for producing an optical film by a solution casting film forming method, and as shown in FIG. (S3), unevenness forming step (S4), first drying step (S5), stretching step (S6), second drying step (S7), cutting step (S8), embossing step (S9), winding step ( S10). Each step will be described below.

<Stirring preparation step>
In the stirring preparation step, at least the resin and the solvent are stirred in the stirring tank 51 of the stirring device 50 to prepare the dope to be cast on the support 3 . The support 3 is a metal support made of stainless steel (SUS), for example. The support 3 is composed of, for example, an endless belt, but may be composed of a drum. In this embodiment, the dope does not contain fine particles (matting agent) for improving transportability.

As the resin, any one of cellulose ester resin, cycloolefin resin (COP), polyimide resin, and polyarylate resin can be used. As the solvent, a mixed solvent of a good solvent and a poor solvent can be used. The good solvent refers to an organic solvent having a property (solubility) to dissolve the resin, and includes 1,3-dioxolane, THF (tetrahydrofuran), methyl ethyl ketone, acetone, methyl acetate, methylene chloride (dichloromethane, methylene chloride), Toluene and the like correspond to this. On the other hand, the poor solvent refers to a solvent that does not have the property of dissolving the resin by itself, and examples thereof include methanol and ethanol.

<Casting process>
In the casting step, the dope prepared in the stirring preparation step is sent through a pressure-type metering gear pump or the like to the casting die 2 through a conduit, and the dope is flowed from the casting die 2 to the casting position on the support 3. defer. The cast dope is then dried on the support 3 to form a web 5 as a casting film. The inclination of the casting die 2, that is, the direction in which the dope is discharged from the casting die 2 to the support 3, is an angle of 0° to 90° with respect to the normal to the surface of the support 3 (the surface on which the dope is cast). may be appropriately set so as to be within the range of .

The support 3 is held by a pair of rolls 3a and 3b and a plurality of rolls (not shown) positioned therebetween. One or both of the rolls 3a and 3b are provided with a drive device (not shown) for applying tension to the support 3, whereby the support 3 is used under tension.

In the casting step, the web 5 formed from the dope cast on the support 3 is heated on the support 3 to evaporate the solvent until the web 5 can be peeled off from the support 3 by the peel roll 4. Let To evaporate the solvent, there are a method of blowing air from the web side, a method of transferring heat from the back side of the support 3 with a liquid, and a method of transferring heat from the front and back sides by radiant heat. Just do it.

<Peeling process>
In the above-described casting step, after drying and solidifying or cooling and solidifying the web 5 on the support 3 until it has a film strength that allows peeling, in the peeling step, the web 5 is kept self-supporting, It is peeled off from the support 3 by the peel roll 4 .

The amount of solvent remaining in the web 5 on the support 3 at the time of peeling is desirably in the range of 25 to 80 mass % depending on the strength of the drying conditions, the length of the support 3, and the like. When peeling when the amount of residual solvent is large, if the web 5 is too soft, the flatness at the time of peeling is impaired, and wrinkles and vertical streaks are likely to occur due to the peeling tension. A solvent amount is determined. The amount of residual solvent is defined by the following formula.

Residual solvent amount (mass%) = (mass of web before heat treatment - mass of web after heat treatment) / (mass of web after heat treatment) x 100
Here, the heat treatment for measuring the residual solvent amount means heat treatment at 115° C. for 1 hour.

<Unevenness formation process>
In the unevenness forming step, unevenness is formed on the surface of the peeled web 5 by the processing rolls 20 . The processing roll 20 is surface-processed so that the maximum height Ry is 2 μm or more. When the web 5 contacts the rotating processing roll 20 , the projections on the surface of the processing roll 20 bite into the surface of the web 5 . As a result, on the surface of the web 5 , the portions that come into contact with the convex portions of the processing roll 20 are dented, and at the same time, the periphery of the dents rises, forming an uneven shape on the surface of the web 5 . The maximum height Ry of the processing rolls 20 should be at least 1 μm.

FIG. 3 is an explanatory diagram schematically showing a method of calculating the maximum height Ry. The maximum height Ry is a value defined in JIS B 0601-1994. That is, the maximum height Ry is obtained by extracting only the reference length L from the roughness curve in the direction of the average line m, and measuring the interval (Ry) between the peak line and the valley bottom line of this extracted portion as the vertical height of the roughness curve. Measured in the direction of magnification, this value is expressed in micrometers (μm). JIS is an abbreviation of "Japanese Industrial Standards" indicating Japanese Industrial Standards.

<First drying step>
The web 5 , on which unevenness is formed on the surface by the processing rolls 20 , is dried by the drying device 6 . In the drying device 6, the web 5 is transported by a plurality of transport rolls, during which the web 5 is dried. The drying method in the drying device 6 is not particularly limited, and the web 5 is generally dried using hot air, infrared rays, heating rolls, microwaves, or the like. A method of drying the web 5 with hot air is preferable from the point of view of simplicity. In addition, the 1st drying process should just be performed as needed.

<Stretching process>
In the stretching step, the web 5 dried by the drying device 6 is stretched by the tenter 7 . The stretching direction at this time is either the film transport direction (MD direction; Machine Direction), the width direction (TD direction; Transverse Direction) perpendicular to the transport direction in the film plane, or both of these directions. In the stretching step, a tenter system in which both side edges of the web 5 are fixed with clips or the like and stretched is preferable in order to improve the flatness and dimensional stability of the film. In the tenter 7, drying may be performed in addition to stretching.

Note that the stretching step of S6 may be performed as necessary and can be omitted. For example, when the optical film is stretched after being wound, the stretching step before winding can be omitted.

<Second drying step>
The web 5 stretched by the tenter 7 as necessary is dried by the drying device 8 . In the drying device 8, the web 5 is transported by a plurality of transport rolls, during which the web 5 is dried. The drying method in the drying device 8 is not particularly limited, and the web 5 is generally dried using hot air, infrared rays, heating rolls, microwaves, or the like. A method of drying the web 5 with hot air is preferable from the point of view of simplicity.

The web 5 is dried by the drying device 8 and then transported as the optical film F toward the winding device 11 .

<Cutting process, embossing process>
A cutting section 9 and an embossing section 10 are arranged in this order between the drying device 8 and the winding device 11 . In the cutting section 9, a cutting step is performed in which both ends in the width direction of the optical film F are cut by a slitter while being transported. In the optical film F, the portion remaining after the cutting of both ends constitutes the product portion which will be the film product. On the other hand, the portion cut from the optical film F is collected by a shooter and reused as part of raw materials for film formation.

After the cutting step, both ends of the optical film F in the width direction are embossed (knurled) by the embossing section 10 . Embossing is performed by pressing both ends of the optical film F with a heated embossing roller. Fine unevenness is formed on the surface of the embossing roller, and by pressing the embossing roller against both ends of the optical film F, unevenness is formed on the both ends. Such embossing can minimize winding misalignment and blocking (sticking of films together) in the next winding process.

<Winding process>
Finally, the embossed optical film F is wound up by the winding device 11 to obtain the original roll of the optical film F (film roll). That is, in the winding process, the film roll is manufactured by winding the optical film F around the core while transporting it. The method of winding the optical film F may be by using a generally used winder, and there are methods of controlling tension such as a constant torque method, a constant tension method, a taper tension method, and a program tension control method with constant internal stress. You should use them properly. The winding length of the optical film F is preferably 1000 to 7200 m. Further, the width at that time is desirably 1000 to 3200 mm, and the film thickness is desirably 10 to 60 μm.

FIG. 4 is a cross-sectional view schematically showing the cross-sectional shape of the optical film F manufactured by the manufacturing method described above. As described above, in the unevenness forming step, by forming unevenness on the surface of the web 5 by the processing roll 20, the surface of the manufactured optical film F has an area of 250000 μm ² (500 μm×500 μm). There are one or more irregularities F _PV corresponding to the irregularities of the web 5 . That is, the fine particle-free optical film F has one or more irregularities F _PV within a range of 250000 μm ² on the surface. As a result, on the surface of the optical film F, the uneven area Fa having the unevenness F _PV and the non- uneven area Fb excluding the uneven F _PV are mixed. The upper and lower limits of the number of irregularities F _PV within the range of the above area are determined according to the size (depth, major axis) of the irregularities F _PV so that the irregular region Fa and the non-irregular region Fb are mixed. It may be set as appropriate. Here, a set (pair) of concave portions and convex portions on the surface of the optical film F is referred to as "unevenness". Therefore, for example, one unevenness refers to a set of one concave portion and one convex portion.

On the surface of the optical film F, the surface roughness Sa around the irregularities F _PV (non-irregular regions Fb) is 1.5 nm or less, which is almost flat. In this embodiment, the preferable range of the surface roughness Sa around the unevenness F _PV is 0.9 nm or less.

FIG. 5 is an explanatory diagram schematically showing a method of calculating the surface roughness Sa. The surface roughness Sa is a parameter of ISO 25178 surface texture (surface roughness measurement). ISO is an abbreviation for "International Organization for Standardization". The surface roughness Sa is a parameter obtained by expanding the surface roughness Ra (arithmetic average height of lines) to a plane, and represents the average of the absolute values of the unevenness (height of each point) with respect to the average plane S _AVE of the surface.

FIG. 6 is an explanatory diagram schematically showing the calculation method of the surface roughness Ra as a reference. The surface roughness Ra is also called calculated average roughness, and is a value defined in JIS B0601-1994 or JIS B 0601-2001. The surface roughness Ra is obtained by extracting only the reference length L in the direction of the average line m from the roughness curve, taking the X axis in the direction of the average line m of this extracted part, and the Y axis in the direction of the longitudinal magnification, When the roughness curve is represented by y=f(x), the value obtained by the formula in the figure is expressed in micrometers (μm).

On the surface of the optical film F, the irregularities F _PV have a major axis of 5 to 15 μm and a maximum height roughness Rz of 100 to 1000 nm. For the major diameter and maximum height roughness Rz of the unevenness F _PV , for example, a plurality of processing rolls 20 having different maximum heights Ry are prepared, and an appropriate processing roll 20 is selected from among the plurality of processing rolls 20 and used. can be adjusted by doing

FIG. 7 is an explanatory diagram schematically showing a method of calculating the maximum height roughness Rz. The definition of the maximum height roughness Rz is the same as the maximum height Ry, but the maximum height Ry is expressed in units of μm and is commonly used in fields such as metal polishing. Since the maximum height roughness Rz expressed in units of nm is often used as a parameter of the film surface condition, the maximum height roughness Rz is used to express the unevenness F _PV here.

In the present embodiment, in the production of the optical film F described above, the surface of the web 5 is formed with unevenness by the processing rolls 20 . This imparts lubricity to the web 5 even if the web 5 does not contain fine particles. Therefore, even when the web 5 is subsequently transported through the drying device 6 and the tenter 7 by each roll, sticking of the web 5 to each roll can be reduced. As a result, the surface of the web 5 is less likely to be scratched during transportation. In addition, if the slipperiness of the web 5 is poor, the web 5 is pulled between a plurality of rolls during transportation, and the web 5 tends to be wrinkled or wrinkled. is reduced, the web 5 can be conveyed satisfactorily while reducing the occurrence of such wrinkles and wrinkles. A detailed definition of wrinkles and wrinkles will be given later.

In addition, on the surface of the optical film F, the surface roughness Sa around the unevenness _FPV (non- unevenness area Fb) is 1.5 nm or less. Since the non-roughened region Fb is substantially flat and the surface haze is small, the entire film can achieve a low haze close to that of glass.

In other words, even if the optical film F does not contain fine particles, it is less likely to be scratched during transportation, and the occurrence of wrinkles and wrinkles can be reduced. The optical film F can be produced by the film method), and at the same time, it is possible to achieve both a low haze close to that of glass and good transportability during production.

In addition, even when the optical film F once wound up is reeled out and transported again in order to bond the optical film F to another film or to apply some kind of functional layer (for example, a hard coat layer) on the optical film F. The presence of the unevenness F _PV can reduce the sticking of the optical film F to the transport roll, and the optical film F can be transported well.

Further, when the surface roughness Sa of the non-irregularity region Fb is 0.9 nm or less, the surface haze of the non-irregularity region Fb becomes smaller, so that the optical film F with a low haze can be reliably realized. Further, when there are 2 or more and 20 or less unevennesses FPV within the range of ₂₅₀₀₀₀ μm ² on the surface of the optical film F, the unevenness areas Fa and the non- unevenness areas Fb are present in a well-balanced manner. It is possible to obtain a well-balanced effect of ensuring good transportability during manufacturing.

Further, by forming the unevenness F _PV on the optical film F by the method described above, the unevenness F _PV is left to ensure good transportability until the optical film F is wound up. is used, the unevenness F _PV can be eliminated or alleviated by unrolling the optical film F and performing heat treatment. This makes it possible to use the fine particle-free optical film F as a film with good optical properties. The above relaxation means that the size or height of the unevenness F _PV is reduced by heat treatment.

Here, the principle of eliminating or relaxing the unevenness F _PV by heat treatment is speculated as follows. That is, the support 3 is made of metal, and the solvent in the dope cast on the support 3 does not permeate the support 3 . In the web 5 formed on the support 3 impermeable to the solvent in this way, only the vicinity of the surface dries and becomes hard after peeling from the support 3. soft. When the web 5 is conveyed on the processing roll 20 in this state, unevenness is formed on the web 5 by the processing roll 20, but the dents are in a state in which soft portions inside are crushed. When the unevenness formed as described above is heat-treated at a high temperature equal to or higher than the glass transition temperature (Tg) of the resin, the above-mentioned portion (crushed portion) of the optical film F returns to its original shape (state) due to molecular motion. , whereby the unevenness F _PV disappears or is relaxed.

Further, in the step of forming unevenness, the surface of the web 5 is formed with unevenness by the processing roll 20 that has been subjected to surface processing such that the maximum height Ry is 2 μm or more. It is possible to reliably realize an optical film F in which one or more unevennesses F _PV exist within the range of ² and the surface roughness Sa around the unevennesses F _PV is 1.5 nm or less.

In addition, when unevenness is formed on the surface of the web 5 using the processing roll 20 having a maximum height Ry of less than 2 μm, the major diameter of the unevenness and the maximum height roughness Rz are reduced, and the web 5 is conveyed. There is concern that the effect of reducing sticking will be reduced, and the effect of improving transportability will be reduced. By setting the maximum height Ry of the processing rolls 20 to 2 μm or more, the effect of improving the transportability of the web 5 can be reliably obtained. From the viewpoint of more reliably obtaining the effect of improving the transportability of the web 5, it is desirable that the maximum height Ry of the processing rolls 20 is 4 μm or more.

As described above, when the uneven shape is formed on the surface of the web 5 using the processing roll 20 having a maximum height Ry of 2 μm or more, the unevenness F has a major axis of 5 to 15 μm and a maximum height roughness Rz of 100 to 1000 nm. It is known from Examples described later that an optical film F having _PV formed on the surface can be obtained. Therefore, on the surface of the optical film F, if the major axis of the unevenness F _PV is 5 to 15 μm and the maximum height roughness Rz is 100 to 1000 nm, the transportation during the production of the optical film F (during transportation of the web 5) It can be said that the effect of improving the property can be surely obtained.

By the way, in the unevenness forming step, if the amount of residual solvent in the web 5 when forming the unevenness by the processing roll 20 is less than 5% by mass, the web 5 becomes hard and the web 5 becomes uneven due to the contact with the processing roll 20. harder to form. For this reason, in the optical film F, the major axis and the maximum height roughness _Rz of the unevenness FPV become small, and it becomes difficult to obtain the effect of improving the transportability. Conversely, if the amount of residual solvent exceeds 35% by mass, the web 5 becomes soft and unevenness is likely to be formed on the web 5 due to contact with the processing rolls 20 . For this reason, in the optical film F, the major axis and the maximum height roughness Rz of the unevenness F _PV become large, and the subsequent heat treatment makes it difficult to obtain the effect of eliminating or relaxing the unevenness F _PV .

Therefore, from the above, it is desirable that the amount of residual solvent in the web 5 when forming the unevenness by the processing rolls 20 in the unevenness forming step is 5 to 35% by mass. A more desirable range for the amount of residual solvent is 6 to 33% by mass.

Also, the dope cast on the support 3 contains a resin and a solvent, and the resin may be a cycloolefin resin (COP). In this case, the effects of the present embodiment described above can be obtained when the optical film F is manufactured by the solution casting method using COP.

〔Example〕
EXAMPLES Hereinafter, examples of the present invention will be described with reference to comparative examples. In addition, the present invention is not limited to the following examples.

<Example 1>
(Preparation of dope)
Cycloolefin resin (G7810, manufactured by JSR Corporation)
120 parts by mass Dichloromethane 357 parts by mass Ethanol 19 parts by mass The above ingredients are placed in a sealed container, heated and stirred to dissolve completely, and then mixed with Azumi Filter Paper No. 1 (manufactured by Azumi Filter Paper Co., Ltd.). 24 to prepare a dope.

Next, using a belt casting film forming apparatus (manufacturing apparatus 1 in FIG. 1), a fine particle-free dope was uniformly cast onto a stainless steel band support (support 3). The solvent was evaporated on the support until the residual solvent amount reached 40% by mass, and the web was separated from the stainless steel band support. After that, in a state where the amount of residual solvent was 12% by mass, the web was provided with an uneven shape using a processing roll having a maximum height Ry of 4 μm. After that, the obtained web was dried for 15 minutes while being conveyed by a number of rollers in a drying apparatus at 130° C., slit to a width of 1.0 m, wound on a core, and an optical film made of a cycloolefin resin. 101 was obtained. The optical film 101 had a thickness of 15 μm and a winding length of 5000 m.

(Measurement of surface roughness Sa)
Using a white interference microscope Zygo, the surface roughness Sa of both surfaces of the wound optical film 101 was measured. More specifically, five locations are randomly selected on the surface of the optical film 101, and the surface roughness is measured with a white interference microscope Zygo in a field of view (approximately 85 μm×85 μm) in which unevenness is not included at each selected location. Sa was measured for each (five points), and the average value was taken as the final surface roughness Sa. As a result, the surface roughness Sa of both surfaces was 0.9 nm. The magnification of the eyepiece of the microscope was 2 times, and the magnification of the objective lens was 50 times.

(Measurement of number of irregularities)
Using an optical microscope (20x lens, using a differential interference filter), the number of irregularities on the optical film 101 visible within the field of view was measured and converted into the number in an area of 500 μm×500 μm=250000 μm ² . At this time, 5 points are randomly selected on the surface of the optical film 101, the number of unevenness is measured at each selected point, and after converting to the number in the above area, the average value of the 5 points is calculated, and the final number of irregularities. As a result, the number of irregularities on the optical film 101 was 4 per 250,000 μm ² . Incidentally, FIG. 8 schematically shows the relationship between the measurement range of the surface roughness Sa of the optical film 101 and the calculation range of the number of irregularities.

(Measurement of long diameter of unevenness and maximum height roughness Rz)
Five irregularities were randomly selected on the surface of the optical film 101, and the major axis and maximum height roughness Rz of the irregularities were measured at each of the selected points with a white interference microscope Zygo. Then, the average value of the five locations was used as the final major axis and maximum height roughness Rz of the unevenness. As a result, the major axis of the unevenness was 10 μm, and the maximum height roughness Rz was 200 nm. The magnification of the eyepiece of the microscope was 2 times, and the magnification of the objective lens was 50 times.

<Comparative Example 1>
As a support, a support (made of PET) intentionally provided with uneven dents on the surface was used. The web was transported without being roughened by the processing rolls. An optical film 201 was produced in the same manner as in Example 1 except for the above. The irregularities on the surface of the support were transferred to the web, and the amount of residual solvent in the web at this time was 200% by mass.

For this optical film 201, the same method as in Example 1 was used to measure the surface roughness Sa, the number of irregularities, the major axis of the irregularities, and the maximum height roughness Rz. As a result, the surface roughness Sa of both surfaces was 1.8 nm, the number of irregularities was 3 per 250000 μm ² , the major axis of the irregularities was 10 μm, and the maximum height roughness Rz was 240 nm.

<Comparative Example 2>
An optical film 202 was produced by the method described in Patent Document 2. Specifically, using a melt-casting film forming method, the resin used in Example 1 was pelletized, melt-extruded into a film form from a T-die, sandwiched between a mat roll and a rubber roll, and pressurized to form a mat roll. An optical film 202 was produced by transferring the matte pattern to the film surface. At this time, the maximum height Ry of the surface of the mat roll was 75 μm.

The surface roughness Sa of both surfaces of the optical film 202 was measured in the same manner as in Example 1. As a result, the surface roughness Sa on the side of the film in contact with the mat roll was 5.0 nm, and the surface roughness Sa on the opposite side was 1.5 nm. Since the entire surface of the optical film 202 is uneven, it was impossible to measure the number of unevenness.

<Comparative Example 3>
In the dope used in Example 1, 1.0 parts by mass of inorganic fine particles (Aerosil R812) was added, the dope was cast on a support, the web was peeled off, and unevenness was imparted with a processing roll. The web was conveyed without An optical film 203 was produced in the same manner as in Example 1 except for the above.

The surface roughness Sa and the number of irregularities of the optical film 203 were measured in the same manner as in Example 1. As a result, the surface roughness Sa of both surfaces was 2.3 nm. Also, no irregularities were found within the area of 250000 μm ² .

<Comparative Example 4>
An optical film 204 was produced by the method described in Patent Document 3. Specifically, the same dope as in Example 1 was cast on a support to form a web. The contained fine particle dispersion liquid was discharged as droplets from an inkjet head, and landed and adhered on one surface of the web to form a fine convex structure. After peeling the web, the web was transported without applying unevenness by the processing rolls. An optical film 204 was produced in the same manner as in Example 1 except for the above.

For this optical film 204, the surface roughness Sa, the number of irregularities, the major axis of the irregularities, and the maximum height roughness Rz were measured in the same manner as in Example 1. As a result, the surface roughness Sa of the uneven surface was 8.3 nm, the number of unevenness was 50 per 250000 μm ² , the major diameter of the unevenness was 10 μm, and the maximum height roughness Rz was 120 nm. .

<Evaluation>
(transportability)
<tresses, wrinkles>
When the optical film that has been wound up is unwound and conveyed in a post-process, the surface of the optical film during conveyance is visually observed to check for the occurrence of creases and wrinkles (folding wrinkles). to evaluate film quality. Here, the transport speed of the optical film was set to 20 m/min, the transport tension was set to 100 N, and the locations where the film was transported while being held by mirror rolls at an angle of 90° were observed.

The wrinkle mentioned above refers to film deformation that does not leave a trace (returns to its original state) even if it occurs, and corresponds to "wrinkle" in English, for example. The wrinkles mentioned above refer to film deformation (folding wrinkles) that leave traces when they occur, and for example, "crease" corresponds to this in English. FIG. 9 schematically shows the cross-sectional shape along the width direction of each film in which crimps or wrinkles are generated. As shown in the figure, when the film is held by the roll (when the film comes into contact with the outer peripheral surface of the roll), it returns to its original cross-sectional shape without deformation. Deformation is tsure. On the other hand, deformation such as folding of the film remains after being held by the rolls (because it does not return to the original cross-sectional shape without deformation), so it is a wrinkle.
"Evaluation criteria"
⊚: No creases or wrinkles were observed.
◯: One spot of wrinkles was observed, but no wrinkles were observed, and there was no problem.
Δ: A plurality of wrinkles were observed, but no wrinkles were observed, and there was no problem.
x: It was confirmed that wrinkles were generated.

<Conveyor Scratches>
The wound optical film was unwound, and the presence or absence of scratches (scratch resistance) was visually examined by the following method. That is, from the outside of the wound optical film, a sodium lamp (KNL-35D, manufactured by Lightest Co., Ltd.) and a commercially available three-wavelength fluorescent lamp are turned on in a dark room to irradiate the film with light. A directional defect with a length of 2 mm or more was recognized as a flaw. Note that the evaluation of scratches was performed on a portion of the film excluding a range of 5 cm from the end of the film (the surface portion of the film inside the above range). Scratches (conveyance scratches) were evaluated based on the following criteria.
"Evaluation criteria"
⊚: No scratches were observed at all.
◯: Almost no scratches were observed.
Δ: Slight scratches were observed, but no problem in practical use.
x: Scratches are clearly generated, and there is a problem in practical use.

(Haze)
The haze of the optical film was measured using a haze meter (NDH2000, manufactured by Nippon Denshoku Industries Co., Ltd.). Then, haze was evaluated based on the following evaluation criteria.
"Evaluation criteria"
A: The haze value is less than 0.10%.
○: The haze value is 0.10% or more and less than 0.20%.
Δ: The haze value is 0.20% or more and less than 0.30%.
x: Haze value is 0.30% or more.

(Disappearance of irregularities due to heat treatment)
The produced optical film was subjected to heat treatment by heating at a temperature of Tg+5° C. or higher in a fixed end state for 5 minutes or longer, where Tg is the glass transition temperature of the resin. Then, the number of irregularities on the surface of the optical film after heat treatment was measured using an optical microscope in the same manner as above, and converted to the number of regions at 250000 μm ² . Further, the maximum height roughness Rz of the unevenness of the optical film was measured using a white interference microscope Zygo in the same manner as above. Then, based on the following evaluation criteria, the effect of eliminating (relieving) unevenness due to heat treatment was evaluated.
"Evaluation criteria"
A: No unevenness was found in the range of 250,000 μm ² .
◯: The number of irregularities was 3 or less in the range of 250000 μm ² , and the maximum height roughness Rz was 50 nm or less.
Δ: In the range of 250,000 μm ² , the number of irregularities was 5 or less, and the maximum height roughness Rz was 150 nm or less.
x: In the range of 250,000 μm ² , the number of irregularities was 6 or more, and the maximum height roughness Rz was larger than 150 nm.

Table 1 shows the evaluation results of the optical film 101 of Example 1 and the optical films 201 to 204 of Comparative Examples 1 to 4 that were produced.

From Table 1, in Comparative Example 1, the haze value of the film is high. This is probably because the smoothness of the surface of the web is extremely low in the method of transferring the unevenness of the surface of the support to the web. Further, in Comparative Example 2, the haze value of the film is considered to be high because unevenness is formed on the entire surface of the film without gaps by the mat roll. Furthermore, in Comparative Example 2, the effect of eliminating irregularities by heat treatment is not obtained. This is probably because the melt-casting film forming method does not use a solvent, so that the formed irregularities are hard and cannot be flattened by deforming the irregularities by heat treatment. In Comparative Example 3, the haze value is considered to be high because the film contains fine particles. In Comparative Example 4, the surface irregularities were formed on the film by the inkjet method, and it is considered that the haze value is high because the number of irregularities is large. Further, since the unevenness of the surface formed by the inkjet method is not caused by the deformation of the film, the deformation of the film is not restored by the heat treatment, and the unevenness is completely eliminated by the heat treatment.

On the other hand, in Example 1, good results were obtained with respect to all of transportability (wrinkles, wrinkles, transport scratches), haze, and effect of eliminating unevenness due to heat treatment. In Example 1, since one or more unevennesses existed within the range of 250000 μm ² on the film surface, even if the web did not contain fine particles, the unevenness imparted slipperiness to the web. It is believed that the web is less likely to be scratched during transportation, and less prone to crimps and wrinkles, resulting in improved transportability. In addition, the surface roughness Sa around the irregularities was 0.9 nm, and since the surface was substantially flat, the surface haze was reduced, and it is considered that a low haze close to that of glass could be achieved. In addition, with the number (density) of the unevenness described above, the unevenness can be eliminated or alleviated by heat treatment. It can be said that it becomes possible to obtain a film with good properties. In addition, since the unevenness remains on the film surface until the film is unwound and heat-treated, it is possible to ensure good transportability.

In addition, when the surface roughness Sa around the unevenness is 0.9 nm in Example 1, there is an effect of reducing haze, and when the surface roughness Sa is 1.8 nm in Comparative Example 1, the above Since there is no effect, it is considered that there is a critical point between 0.9 nm in Example 1 and 1.8 nm in Comparative Example 1 (for example, 1.5 nm) at which the above effect is obtained. Therefore, in order to obtain the above effects, the surface roughness Sa should be 1.5 nm or less, and more preferably 0.9 nm or less.

<Examples 2 to 7>
Optical films 102 to 107 of Examples 2 to 7 were produced in the same manner as in Example 1, except that unevenness was formed on the surface of the web using a processing roll having the maximum height Ry shown in Table 2. Then, the optical films 102 to 107 produced were measured in the same manner as in Example 1 for the surface roughness Sa, the number of irregularities, the major axis of the irregularities, and the maximum height roughness Rz.

Table 2 shows the evaluation results of the optical films 102 to 107 of Examples 2 to 7 produced together with the results of the optical film 101 of Example 1. In addition, Example 2 is a mere reference example of the present invention, and does not belong to the scope of the present invention.

As can be seen from Table 2, in Example 2, the effect of improving the transportability is smaller than in Example 3 and the like. In Example 2, since the maximum height Ry of the processing rolls is as small as 1 μm, the surface of the web can be gouged (scratched) by the unevenness of the processing rolls to form unevenness of an appropriate size on the surface of the web. This is thought to be because the effect of reducing the sticking of the web to the roll during transport is reduced. On the other hand, Examples 1 and 3 to 7 are highly effective in improving transportability. In Examples 1, 3 to 5, since the maximum height Ry of the processing rolls is 2 μm or more, the unevenness of the processing rolls gouged the surface of the web to form unevenness of an appropriate size on the surface of the web. It is believed that this increases the effect of reducing sticking of the web to the rolls during transport.

When the maximum height Ry of the processing rolls is 2 μm or more, the surface of the film has irregularities with a major diameter of 5 to 15 μm and a maximum height roughness Rz of 100 to 1000 nm. Therefore, it can be said that the effect of improving transportability can be enhanced by forming such unevenness on the surface of the film.

In addition, even if the maximum height Ry of the processing roll is 1 μm as in Example 2 (even if irregularities having a major diameter of 4 μm and a maximum height roughness Rz of 85 nm are formed on the surface of the film), the transportability The result that there is no problem in practical use is obtained. From this, it is sufficient that the maximum height Ry of the processing roll is 1 μm or more, and that the surface of the film should be formed with irregularities having a major axis of 4 μm or more and a maximum height roughness Rz of 85 nm or more.

<Examples 8 to 14>
In addition to forming unevenness on the surface of the web with the processing roll having the maximum height Ry described in Table 3, the amount of residual solvent at the time of imparting unevenness by the processing roll was changed as shown in Table 3. Optical films 108 to 114 of Examples 8 to 14 were produced in the same manner. Then, the optical films 108 to 114 produced were measured in the same manner as in Example 1 for the surface roughness Sa, the number of irregularities, the length of the irregularities, and the maximum height roughness Rz.

Table 3 shows the evaluation results of the optical films 108 to 114 of Examples 8 to 14 produced together with the results of the optical film 101 of Example 1. It should be noted that Example 12 is merely a reference example of the present invention and does not belong to the scope of the present invention.

From Table 3, in Examples 10 and 12, the effect of improving the transportability is small. The reason for this is that in Examples 10 and 12, the amount of residual solvent in the web when the unevenness was imparted by the processing roll was as small as 4% by mass, so the web was hard and unevenness was hardly formed on the web due to contact with the processing roll. It is conceivable that the effect of reducing sticking of the web to the rolls during transportation is reduced. Further, in Examples 11 and 14, the effect of eliminating unevenness due to heat treatment is small. In Examples 11 and 14, since the amount of residual solvent in the web was as large as 37% by mass when the unevenness was applied, the web was soft, and unevenness having a large major diameter and a large maximum height roughness Rz was formed on the web by contact with the processing roll. easier. For this reason, even if the subsequent heat treatment is performed, the unevenness is unlikely to disappear, and even if the unevenness is alleviated, the amount of the unevenness will be very small.

On the other hand, in Examples 8, 9, and 13, the effect of improving the transportability and the effect of eliminating unevenness due to the heat treatment are obtained in a well-balanced manner. In Examples 8, 9, and 13, the amount of residual solvent in the web at the time of imparting unevenness was 6 to 33% by mass, so that the sticking of the web to the rolls during transportation was reduced, and the unevenness was eliminated by heat treatment. This is considered to be due to the formation of irregularities of suitable sizes on the web.

In addition, when the residual solvent amount of the web at the time of imparting unevenness is 4% by mass as in Examples 10 and 12, the effect of improving the transportability is small, and the residual solvent amount is 6% by mass as in Example 8. Sometimes, the above effect is large, so it is considered that there is a critical point between 4% by weight of Examples 10 and 12 and 6% by weight of Example 8 (for example, 5% by weight) to increase the above effect. . Therefore, from the viewpoint of increasing the effect, the residual solvent amount is preferably 5% by mass or more, and more preferably 6% by mass or more.

Further, when the residual solvent amount of the web at the time of imparting unevenness is 37% by mass as in Examples 11 and 14, the effect of eliminating unevenness by heat treatment is small, and the residual solvent amount is 33% by mass as in Examples 9 and 13. At some point, since the disappearance effect is large, the critical point for increasing the disappearance effect is between 37% by mass of Examples 11 and 14 and 33% by mass of Examples 9 and 13 (for example, 35% by mass). It is thought that there is Therefore, from the viewpoint of increasing the elimination effect, the residual solvent amount is preferably 35% by mass or less, and more preferably 33% by mass or less.

In addition, even when the residual solvent amount is 4% by mass in Examples 10 and 12, practically no problem in transportability is obtained, and the residual solvent amount is 37% by mass in Examples 11 and 14. However, practically no problems have been obtained with respect to the disappearance effect. From this, it can be said that the residual solvent amount may be 4% by mass or more and may be 37% by mass or less.

Therefore, the appropriate range of the residual solvent amount is a combination of the above lower limits (4% by mass, 5% by mass, 6% by mass) and the above upper limits (37% by mass, 35% by mass, 33% by mass). can be set with For example, the residual solvent amount may be 4 to 37% by mass (4% by mass or more and 37% by mass or less), but is preferably 5 to 35% by mass (5% by mass or more and 35% by mass or less). and more preferably 6 to 33 mass % (6 mass % or more and 33 mass % or less).

〔others〕
The optical film of this embodiment described above and the method for manufacturing the same can be expressed as follows.

1. a casting step of casting the particulate-free dope onto a metal support to form a web;
a peeling step of peeling the web from a metal support;
An unevenness forming step of forming an uneven shape on the surface of the peeled web with a processing roll;
a winding step of winding the web having the uneven shape as an optical film;
The wound optical film has one or more unevennesses within a range of 250000 μm ² on the surface,
A method for producing an optical film, wherein the surface roughness Sa around the unevenness is 1.5 nm or less within the above range.

2. 2. The method for producing an optical film as described in 1 above, wherein the surface roughness Sa is 0.9 nm or less.

3. 3. The optical system according to 1 or 2 above, wherein in the unevenness forming step, the unevenness is formed on the surface of the web by the processing roll that has undergone surface processing such that the maximum height Ry is 2 μm or more. Film production method.

4. On the surface of the optical film,
The major axis of the unevenness is 5 to 15 μm,
4. The method for producing an optical film as described in any one of 1 to 3 above, wherein the maximum height roughness Rz is 100 to 1000 nm.

5. 5. The optical film as described in any one of 1 to 4 above, wherein in the unevenness forming step, the amount of residual solvent in the web when the unevenness is formed by the processing roll is 5 to 35% by mass. manufacturing method.

6. 6. The method for producing an optical film as described in any one of 1 to 5 above, wherein the optical film has 2 or more and 20 or less of the unevenness within a range of 250000 μm ² on the surface.

7. The dope contains a resin and a solvent,
7. The method for producing an optical film as described in any one of 1 to 6 above, wherein the resin is a cycloolefin resin.

8. An optical film containing no fine particles,
The optical film has one or more unevenness within a range of 250000 μm ² on the surface,
The optical film, wherein the surface roughness Sa around the irregularities is 1.5 nm or less within the above range.

9. 9. The optical film as described in 8 above, wherein the surface roughness Sa is 0.9 nm or less.

10. On the surface of the optical film,
The major axis of the unevenness is 5 to 15 μm,
10. The optical film as described in 8 or 9 above, wherein the maximum height roughness Rz is 100 to 1000 nm.

11. 11. The optical film as described in any one of 8 to 10 above, wherein the optical film has 2 or more and 20 or less of the irregularities within a range of 250000 μm ² on the surface.

12. 12. The optical film as described in any one of 8 to 11 above, which contains a cycloolefin resin.

Although the embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and can be implemented by being expanded or modified without departing from the gist of the invention.

INDUSTRIAL APPLICABILITY The present invention can be used when producing an optical film containing no fine particles by a solution casting method.

3 support (metal support)
5 Web 20 Processing roll F _PV unevenness Fb Non- uneven area F Optical film

Claims (11)

a casting step of casting the particulate-free dope onto a metal support to form a web;
a peeling step of peeling the web from a metal support;
An unevenness forming step of forming an uneven shape on the surface of the peeled web with a processing roll;
a winding step of winding the web having the uneven shape as an optical film;
The wound optical film has one or more unevennesses within a range of 250000 μm ² on the surface,
Within the range, the surface roughness Sa around the unevenness is 1.5 nm or less ,
In the unevenness forming step, the unevenness is formed on the surface of the web by the processing roll that has been surface-treated so that the maximum height Ry is 2 μm or more . a casting step of casting the particulate-free dope onto a metal support to form a web;
a peeling step of peeling the web from a metal support;
An unevenness forming step of forming an uneven shape on the surface of the peeled web with a processing roll;
a winding step of winding the web having the uneven shape as an optical film;
The wound optical film has a surface area of 250000 μm ² has one or more unevenness within the range of
Within the range, the surface roughness Sa around the unevenness is 1.5 nm or less,
On the surface of the optical film,
The major axis of the unevenness is 5 to 15 μm,
A method for producing an optical film, wherein the maximum height roughness Rz is 100 to 1000 nm. 3. The method for producing an optical film according to claim 2, wherein in the unevenness forming step, the unevenness is formed on the surface of the web by the processing roll that has been surface-treated so that the maximum height Ry is 2 μm or more. The method for producing an optical film according to any one of claims 1 to 3, wherein the surface roughness Sa is 0.9 nm or less. The method for producing an optical film according to any one of claims 1 to 4, wherein in the unevenness forming step, the amount of residual solvent in the web when the unevenness is formed by the processing roll is 5 to 35% by mass. . The method for producing an optical film according to any one of claims 1 to 5, wherein the optical film has 2 or more and 20 or less of the unevenness within a range of 250000 µm ² on the surface. The dope contains a resin and a solvent,
The method for producing an optical film according to any one of claims 1 to 6, wherein the resin is a cycloolefin resin. An optical film containing no fine particles,
The optical film has one or more unevenness within a range of 250000 μm ² on the surface,
Within the range, the surface roughness Sa around the unevenness is 1.5 nm or less ,
On the surface of the optical film,
The major axis of the unevenness is 5 to 15 μm,
An optical film having a maximum height roughness Rz of 100 to 1000 nm . The optical film according to claim 8, wherein the surface roughness Sa is 0.9 nm or less. The optical film has a surface of 250000 μm ² 10. The optical film according to claim 8 or 9, having 2 or more and 20 or less of the unevenness within the range of . The optical film according to any one of claims 8 to 10, comprising a cycloolefin resin.

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