JPWO2019239625A1 - Optical film and its manufacturing method - Google Patents

Abstract

The optical film manufacturing method includes a casting step (S2) of casting a dope containing no fine particles on a metal support to form a web, a peeling step (S3) of peeling the web from the metal support, and peeling. The surface of the web is provided with a concavo-convex forming step (S4) of forming a concavo-convex shape by a processing roll and a winding step (S10) of winding the web having the concavo-convex shape as an optical film. The wound optical film has one or more irregularities within a range of 250,000 μm2 on the surface, and the surface roughness Sa around the irregularities is 1.5 nm or less within the above range.

Description

The present invention relates to an optical film and a method for producing the same.

In recent years, the replacement of glass with optical films has been progressing in parts for applications such as smartphones that require weight reduction and thinning. If this alternative is realized, there are merits such as cost reduction as well as weight reduction and thin film reduction. However, in order for the optical film to replace glass, it is necessary to bring the haze value of the optical film closer to that of glass.

Here, an optical film having a low haze is disclosed in, for example, Patent Document 1. In Patent Document 1, by incorporating fine particles into an optical film together with a surface conditioner, the fine particles are unevenly distributed on one side of the optical film to impart slipperiness, thereby reducing the content of the fine particles and reducing the haze. I am 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, sandwiched between a pair of rolls consisting of a mat roll and a rubber roll, and pressed to transfer the mat pattern of the mat roll to a film. I am trying to get a low gloss matte film. 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 on one surface of the web By ejecting droplets by an inkjet head method, landing and adhering them to form a fine convex structure, the amount of matting agent in the optical film is reduced and the slipperiness is improved.

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

By the way, even if the conventional optical film has a low haze, it is not as good as glass. This is because not a little organic or inorganic fine particles are added to the optical film to improve the handleability during manufacturing, 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 respect, all of the above-mentioned optical films of Patent Documents 1 to 3 contain fine particles, and it is difficult to realize 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 imparted with slipperiness, so that there is a concern that the handleability is lowered and the yield is lowered. That is, if the optical film has poor slipperiness, the film is transported while being attached to a roll (for example, a mirror surface roll) during manufacturing, so that small transport scratches may be formed on the film surface. Further, when the optical film having poor slipperiness is strongly attached to the rolls, strong wrinkles are generated between the plurality of rolls, and in the worst case, the optical film may be broken.

Therefore, in order to realize a low haze close to that of glass, an optical film having good transportability is required, which is less likely to cause transport scratches during manufacturing and can reduce the occurrence of wrinkles even if the structure does not contain fine particles. , It has not yet been realized to produce such an optical film by the same mass-produceable manufacturing method as before.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to realize a low haze close to that of glass, so that even if the structure does not contain fine particles, transport scratches are less likely to occur during manufacturing. , The occurrence of wrinkles can also be reduced, and as a result, an optical film that can be manufactured by a manufacturing method that can be mass-produced and that can achieve both low haze and good transportability during manufacturing, and a manufacturing method thereof. To provide.

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

The 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. The optics that has been wound up by having a concavo-convex forming step of forming a concavo-convex shape on the surface of the peeled web by a processing roll and a winding step of winding the web having the concavo-convex shape as an optical film. The film has ^{one or more irregularities within a range of 250,000 μm 2 on} the surface, and the surface roughness Sa around the irregularities within the range is 1.5 nm or less.

The optical film according to another aspect of the present invention is an optical film containing no fine particles. The optical film has ^{one or more irregularities within a range of 250,000 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 manufacturing and wrinkles can be reduced, which enables optical production using a mass-produceable manufacturing method (for example, solution casting film forming method). In addition to being able to produce a film, it is possible to achieve both low haze close to that of glass and good transportability during production.

It is explanatory drawing which shows the schematic structure of the optical film manufacturing apparatus which concerns on embodiment of this invention. It is a flowchart which shows the flow of the manufacturing process of the said optical film. It is explanatory drawing which shows typically the calculation method of the maximum height Ry. It is sectional drawing which shows typically the cross-sectional shape of the said optical film. It is explanatory drawing which shows typically the calculation method of the surface roughness Sa. It is explanatory drawing which shows typically the calculation method of the surface roughness Ra. It is explanatory drawing which shows typically the calculation method of the maximum height roughness Rz. It is explanatory drawing which shows typically the relationship between the measurement range of the surface roughness Sa in the optical film of an Example, and the calculation range of the number of irregularities. It is explanatory drawing which shows typically the cross-sectional shape along the width direction of each film which wrinkled or wrinkled.

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

[Manufacturing method of optical film]
First, an outline of the method for manufacturing the optical film of the present embodiment will be described. FIG. 1 is an explanatory diagram showing a schematic configuration of the optical film manufacturing apparatus 1 of the present embodiment. Further, FIG. 2 is a flowchart showing the flow of the manufacturing process of the 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. 2, a stirring preparation step (S1), a casting step (S2), and a peeling step. (S3), unevenness forming step (S4), first drying step (S5), stretching step (S6), second drying step (S7), cutting step (S8), embossing step (S9), winding step (S9) S10) is included. Hereinafter, each step will be described.

<Stirring preparation process>
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 a dope that spreads on the support 3. The support 3 is a metal support made of, for example, stainless steel (SUS). The support 3 is composed of, for example, an endless belt, but may be composed of a drum. In the present embodiment, the dope does not contain fine particles (matting agent) for improving transportability.

As the resin, any one of a cellulose ester resin, a cycloolefin resin (COP), a polyimide resin, and a 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 the property of dissolving the resin (solubility), and includes 1,3-dioxolane, THF (tetrahydrofuran), methyl ethyl ketone, acetone, methyl acetate, methylene chloride (dichloromethane, methylene chloride), and the like. Tetrahydrofuran and the like correspond to this. On the other hand, the poor solvent means a solvent that does not have the property of dissolving the resin by itself, and methanol, ethanol, or the like corresponds to this.

<Hypersalivation process>
In the casting step, the dope prepared in the stirring preparation step is sent to the casting die 2 by a conduit through a pressurized metering gear pump or the like, and the dope is poured from the casting die 2 to the casting position on the support 3. Postpone. Then, the cast dope is dried on the support 3 to form the web 5 as a cast film. The inclination of the casting die 2, that is, the ejection direction of the dope from the casting die 2 to the support 3, is 0 ° to 90 ° at an angle with respect to the normal of the surface of the support 3 (the surface on which the doping is spread). It 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) located between them. One or both of the rolls 3a and 3b is provided with a driving device (not shown) for applying tension to the support 3, whereby the support 3 is used in a tensioned state.

In the casting step, the web 5 formed by the dope cast on the support 3 is heated on the support 3, and the solvent is evaporated from the support 3 until the web 5 can be peeled by the peeling roll 4. Let me. To evaporate the solvent, there are a method of blowing wind from the web side, a method of transferring heat from the back surface of the support 3 with a liquid, a method of transferring heat from the front and back surfaces by radiant heat, etc., and they are used individually or in combination as appropriate. Just do it.

<Peeling process>
In the above casting step, the web 5 is dried and solidified or cooled and solidified on the support 3 until the web 5 has a peelable film strength, and then in the peeling step, the web 5 is kept self-supporting. It is peeled from the support 3 by the peeling roll 4.

The amount of residual solvent of the web 5 on the support 3 at the time of peeling is preferably in the range of 25 to 80% by mass depending on the strength of the drying conditions, the length of the support 3, and the like. When peeling at a time when the amount of residual solvent is larger, 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. The amount of solvent is determined. The amount of residual solvent is defined by the following formula.

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

<Concavo-convex formation process>
In the unevenness forming step, an uneven shape is formed on the surface of the peeled web 5 by a processing roll 20. The processing roll 20 is surface-treated so that the maximum height Ry is 2 μm or more. When the web 5 comes into contact with the rotating processing roll 20, the convex portion on the surface of the processing roll 20 bites into the surface of the web 5. As a result, on the surface of the web 5, the portion in contact with the convex portion of the processing roll 20 is dented, and at the same time, the periphery thereof is raised, and an uneven shape is formed on the surface of the web 5. The maximum height Ry of the processing roll 20 may 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 determining the distance (Ry) between the peak line and the valley bottom line of the extracted portion in the vertical direction of the roughness curve. It is measured in the direction of magnification and this value is expressed in micrometers (μm). JIS is an abbreviation for "Japanese Industrial Standards", which indicates Japanese Industrial Standards.

<First drying process>
The web 5 having irregularities formed on its surface by the processing roll 20 is dried by the drying device 6. In the drying device 6, the web 5 is conveyed by a plurality of conveying rolls, and the web 5 is dried between them. The drying method in the drying device 6 is not particularly limited, and generally, the web 5 is dried using hot air, infrared rays, a heating roll, microwaves, or the like. From the viewpoint of simplicity, a method of drying the web 5 with hot air is preferable. The first drying step may 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 one of a film transport direction (MD direction; Machine Direction), a width direction (TD direction; Transverse Direction) perpendicular to the transport direction in the film plane, and both of these directions. In the stretching step, a tenter method 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.

The stretching step of S6 may be performed as needed and can be omitted. For example, when the optical film is wound and then stretched, the stretching step before winding can be omitted.

<Second drying process>
If necessary, the web 5 stretched by the tenter 7 is dried by the drying device 8. In the drying device 8, the web 5 is conveyed by a plurality of conveying rolls, and the web 5 is dried between them. The drying method in the drying device 8 is not particularly limited, and generally, the web 5 is dried using hot air, infrared rays, a heating roll, microwaves, or the like. From the viewpoint of simplicity, a method of drying the web 5 with hot air is preferable.

After being dried by the drying device 8, the web 5 is conveyed as an optical film F toward the winding device 11.

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

After the cutting step, both ends of the optical film F in the width direction are embossed (knurled) by the embossing portion 10. The embossing process is performed by pressing a heated embossing roller against both ends of the optical film F. Fine irregularities are formed on the surface of the embossing roller, and by pressing the embossing roller against both ends of the optical film F, the irregularities are formed on both ends. By such embossing, winding misalignment and blocking (sticking between films) in the next winding process can be suppressed as much as possible.

<Winding process>
Finally, the optical film F for which the embossing process has been completed is wound by the winding device 11 to obtain the original winding (film roll) of the optical film F. That is, in the winding step, a film roll is manufactured by winding the optical film F around the winding core while conveying it. As the winding method of the optical film F, a commonly used winder may be used, and there are methods for controlling the tension such as a constant torque method, a constant tension method, a taper tension method, and a program tension control method with a constant internal stress. You can use them properly. The winding length of the optical film F is preferably 1000 to 7200 m. Further, the width at that time is preferably 1000 to 3200 mm, and the film thickness is preferably 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 above manufacturing method. As described above, in the unevenness forming step, the surface of the optical film F produced by forming the uneven shape on the surface of the web 5 by the processing roll 20 is ^{within the range of 250,000 μm 2} (500 μm × 500 μm). unevenness F _PV corresponding to the unevenness of the web 5 is present 1 or more. That is, the optical film F of the particulate-free has one or more irregularities F _PV within the 250000Myuemu ² surface. As a result, on the surface of the optical film F, the concavo-convex region Fa on which the concavo- _{convex F PV} is formed and the non-concavo-convex region Fb excluding the concavo-convex _{F PV coexist.} The number of upper and lower limits of irregularities F _PV within the range of the area, so that the irregular region Fa and the non-shaped regions Fb mixed, the magnitude of the irregularities F _PV (depth, diameter) in accordance with the It may be set as appropriate. Here, the pair of the concave portion and the convex portion on the surface of the optical film F is referred to as "concavo-convex". Therefore, for example, one unevenness means a set of one concave portion and one convex portion.

The surface of the optical film F, the surface roughness Sa of the peripheral (non-shaped regions Fb) of irregularities F _PV is at 1.5nm or less, most close to the plane (flat). In this embodiment, the preferred range of the surface roughness Sa of the surrounding asperities F _PV is less 0.9 nm.

FIG. 5 is an explanatory diagram schematically showing a calculation method of the surface roughness Sa. Surface roughness Sa is a parameter of ISO 25178 surface texture (surface roughness measurement). ISO is an abbreviation for "International Organization for Standardization", which indicates the International Organization for Standardization. The surface roughness Sa is a parameter obtained by extending the surface roughness Ra (arithmetic mean height of the line) to the surface, and represents the average of the absolute values of the unevenness (height of each point _{) with respect to the average surface SAVE of the surface.}

FIG. 6 is an explanatory diagram schematically showing the above-mentioned calculation method of the surface roughness Ra for reference. The surface roughness Ra, also called an arithmetic mean roughness, is a value defined by JIS B0601-1994 or JIS B0601-2001. For the surface roughness Ra, only the reference length L is extracted from the roughness curve in the direction of the average line m, the X axis is taken in the direction of the average line m of the extracted portion, and the Y axis is taken in the direction of the longitudinal magnification. When the roughness curve is expressed by y = f (x), the value obtained by the formula in the figure is expressed in micrometer (μm).

Further, the surface of the optical film F, the major axis of the unevenness F _PV, a 5 to 15 [mu] m, the maximum height roughness Rz is 100 to 1000 nm. Major axis and a maximum height roughness Rz of the unevenness F _PV, for example, by selecting the maximum of different working roll 20 height Ry leave plurality prepared, appropriate work roll 20 from a plurality of work rolls 20 using It 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 μm units and is generally used in fields such as metal polishing. The parameters of the film surface state, are often used maximum height roughness Rz expressed in nm, here, it represents the unevenness F _PV by using the maximum height roughness Rz.

In the present embodiment, in the production of the optical film F described above, the processing roll 20 forms an uneven shape on the surface of the web 5. As a result, even if the web 5 does not contain fine particles, the web 5 is imparted with slipperiness. Therefore, even when the web 5 is subsequently conveyed by each roll in the drying device 6 and the tenter 7, it is possible to reduce the sticking of the web 5 to each roll. As a result, small transport scratches are less likely to occur on the surface of the web 5. Further, if the slipperiness of the web 5 is poor, the web 5 is easily pulled between a plurality of rolls during transportation, and the web 5 is likely to have wrinkles or wrinkles. However, the web 5 is imparted with slipperiness and sticks to the web 5. Therefore, the web 5 can be satisfactorily transported while reducing the occurrence of such wrinkles and wrinkles. The detailed definitions of wrinkles and wrinkles will be described later.

Further, the surface of the optical film F, the surface roughness Sa of the surrounding asperities F _PV (non-shaped regions Fb) is 1.5nm or less. Since the non-concavo-convex region Fb is substantially flat and the surface haze is small, it is possible to realize a low haze close to that of glass as a whole film.

That is, even if the optical film F does not contain fine particles, it is difficult to cause transport scratches during manufacturing, and it is possible to reduce the occurrence of creases and wrinkles, whereby a manufacturing method capable of mass production (for example, solution casting) The optical film F can be produced by the film method), and both low haze close to that of glass and good transportability during production can be achieved at the same time.

Further, even when the optical film F once wound up is re-rolled out and conveyed in order to bond the optical film F to another film or to apply some functional layer (for example, a hard coat layer) on the optical film F, the optical film F may be unwound and conveyed. can optical film F is reduced by the presence of irregularities F _PV from sticking to conveyor roll, it is possible to achieve a good transport of the optical film F.

Further, when the surface roughness Sa of the non-concavo-convex region Fb is 0.9 nm or less, the surface haze of the non-concavo-convex region Fb becomes smaller, so that the optical film F having a low haze can be surely realized. Also, if uneven F _PV exists 20 or less 2 or more in the range of 250000Myuemu ² of surface of the optical film F, because the concave-convex region Fa and the non-shaped regions Fb present good balance, and the effect of haze reduction, The effect of ensuring good transportability during manufacturing can be obtained in a well-balanced manner.

_{Further, by forming the concavo-convex F PV} on the optical film F by the method described above, the concavo-convex F PV is left in order to ensure good transportability until the optical film F is wound, and the concavo-convex F _PV is left. When the optical film F is used, the uneven _FPV can be eliminated or alleviated by feeding out the optical film F and performing heat treatment. This makes it possible to use the optical film F containing no fine particles as a film having good optical characteristics. Incidentally, the above relaxation, the size or height of the irregularity F _PV which means that smaller by heat treatment.

Here, the principle of eliminating or alleviating the uneven F _PV by heat treatment, are inferred 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. The web 5 formed on the support 3 in which the solvent does not permeate in this way dries and hardens only in the vicinity of the surface after peeling from the support 3, but since a large amount of solvent remains inside the web 5. soft. In this state, when the web 5 is conveyed on the processing roll 20, unevenness is formed on the web 5 by the processing roll 20, but the dent is in a state where the soft portion inside is 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) in the optical film F is restored to its original shape (state) by molecular motion. trying to restore, this depending on whether the irregularities F _PV is lost, is relaxed.

Further, in the unevenness forming step, the uneven shape is formed on the surface of the web 5 by the processing roll 20 which has been surface-treated so that the maximum height Ry is 2 μm or more, so that the final optical film F is 250,000 μm on the surface. there uneven F _PV or more one within ² range, the surface roughness Sa of the surrounding asperities F _PV can be reliably realize an optical film F is 1.5nm or less.

Further, when unevenness is formed on the surface of the web 5 by using a processing roll 20 having a maximum height Ry of less than 2 μm, the major axis and the maximum height roughness Rz of the unevenness become small, and the web 5 is transported. There is a concern that the effect of reducing sticking will be reduced and the effect of improving transportability will be reduced. When the maximum height Ry of the processing roll 20 is 2 μm or more, the effect of improving the transportability of the web 5 can be surely 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 roll 20 is 4 μm or more.

As described above, when a concavo-convex shape is formed on the surface of the web 5 using a processing roll 20 having a maximum height Ry of 2 μm or more, a concavo-convex F having a major axis of 5 to 15 μm and a maximum height roughness Rz of 100 to 1000 nm. It is known from the examples described later that an optical film F in which _{PV is formed on the surface can be obtained.} Thus, the surface of the optical film F, a major diameter 5~15μm of irregularities F _PV, if the maximum height roughness Rz of 100 to 1000 nm, the transport during manufacture of the optical film F (during conveyance of the web 5) It can be said that the effect of improving sexuality can be surely obtained.

By the way, in the unevenness forming step, if the residual solvent amount of 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 contact with the processing roll 20. It becomes difficult to form. Therefore, in the optical film F, the smaller the diameter and the maximum height roughness Rz of the unevenness F _PV, the effect of transportability improver is not easily obtained. On the contrary, when the residual solvent amount exceeds 35% by mass, the web 5 becomes soft and unevenness is likely to be formed on the web 5 by contact with the processing roll 20. Therefore, in the optical film F, the long diameter and a maximum height roughness Rz of the unevenness F _PV increases, the effect of eliminating or alleviating the uneven F _PV by subsequent heat treatment becomes difficult to obtain.

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

Further, the dope flowing on the support 3 contains a resin and a solvent, and the resin may be a cycloolefin-based resin (COP). In this case, when the optical film F is produced by the solution casting film forming method using COP, the effect of the present embodiment described above can be obtained.

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

<Example 1>
(Preparation of doping)
Cycloolefin resin (G7810, manufactured by JSR Corporation)
120 parts by mass Dichloromethane 357 parts by mass Ethanol 19 parts by mass or more was put into a closed container, and it was completely dissolved while heating and stirring. 24 was used for filtration 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 spread on the stainless band support (support 3). The solvent was evaporated on the support until the residual solvent amount reached 40% by mass, and the web was peeled off from the stainless band support. Then, in a state where the residual solvent amount was 12% by mass, a processing roll having a maximum height of Ry = 4 μm was used to impart an uneven shape to the web. Then, the obtained web was dried for 15 minutes while being conveyed in a drying device at 130 ° C. by a large number of rollers, slit to a width of 1.0 m, wound around a winding core, and an optical film made of a cycloolefin resin. 101 was obtained. The thickness of the optical film 101 was 15 μm, and the winding length was 5000 m.

(Measurement of surface roughness Sa)
Using a white interference microscope Zygo, the surface roughness Sa on both sides of the optical film 101 after winding was measured. More specifically, five locations were randomly selected on the surface of the optical film 101, and the surface roughness was measured by the white interference microscope Zygo in a field of view (range of about 85 μm × 85 μm) in which irregularities were not included in each selected location. Sa was measured at each (5 points), and the average value was taken as the final surface roughness Sa. As a result, the surface roughness Sa on both sides 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 the number of irregularities)
Using an optical microscope (lens 20 times, using a differential interference filter), the number of irregularities of the optical film 101 visible in the field of view was measured, and this was converted into the number in the region of ^{500 μm × 500 μm = 250,000 μm 2.} At this time, five locations are randomly selected on the surface of the optical film 101, the number of irregularities is measured at each selected location, converted into the number in the above region, and then the average value of the five locations is calculated, and the final value is calculated. The number of unevenness was set. As a result, the number of irregularities of 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 major axis of unevenness, maximum height roughness Rz)
Five uneven parts were randomly selected on the surface of the optical film 101, and the major axis and the maximum height roughness Rz of the uneven parts were measured by a white interference microscope Zygo at each of the selected parts. Then, the average value of the five points was taken as the major axis of the final unevenness and the maximum height roughness Rz. 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 the support, a support (manufactured by PET) with intentionally uneven dents on the surface is used, the same dope as in Example 1 is cast on the support, the web is peeled off, and then the web is peeled off. The web was transported without adding unevenness by the processing roll. The optical film 201 was produced in the same manner as in Example 1 except for the above. The unevenness of the surface of the support was 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 surface roughness Sa, the number of irregularities, the major axis of the irregularities, and the maximum height roughness Rz were measured by the same method as in Example 1. As a result, the surface roughness Sa on both sides was 1.8 nm, the number of irregularities was ^{3 per 250,000 μm 2} , the major axis of the irregularities was 10 μm, and the maximum height roughness Rz was 240 nm.

<Comparative example 2>
The optical film 202 was produced by the method described in Patent Document 2. Specifically, using the melt casting film forming method, pelletized resin used in Example 1 is melt-extruded from a T-die into a film, sandwiched between a mat roll and a rubber roll, and pressed to form a mat roll. The 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 on both sides of the optical film 202 was measured in the same manner as in Example 1. As a result, the surface roughness Sa on the contact side with the mat roll in the film 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 in an uneven state, the number of irregularities and the like cannot be measured.

<Comparative example 3>
Inorganic fine particles (Aerosil R812) were added in an amount of 1.0 part by mass to the dope used in Example 1, the dope was cast on the support, the web was peeled off, and then unevenness was added by a processing roll. Transported the web without doing. The 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 were measured on the optical film 203 by the same method as in Example 1. As a result, the surface roughness Sa on both sides was 2.3 nm. In addition, no unevenness was found in the region of ^{250,000 μm 2.}

<Comparative example 4>
The optical film 204 was produced by the method described in Patent Document 3. Specifically, the same dope as in Example 1 is cast on the support to form a web, and when the residual solvent amount of the web is 200% by mass, fine particles having an average grain diameter of 25 to 200 nm are formed. The contained fine particle dispersion was ejected as droplets from the inkjet head and landed and adhered to one surface of the web to form a fine convex structure. Then, after the web was peeled off, the web was conveyed without imparting unevenness by a processing roll. 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 by the same method as in Example 1. As a result, the surface roughness Sa of the unevenness-imparted surface was 8.3 nm, the number of irregularities was ^{50 per 250,000 μm 2} , the major axis of the irregularities was 10 μm, and the maximum height roughness Rz was 120 nm. ..

<Evaluation>
(Transportability)
<Tsure, wrinkles>
Visually observe the surface of the optical film being transported when the once wound optical film is unwound and transported in a subsequent process to confirm the presence or absence of wrinkles and wrinkles, and based on the following criteria. The quality of the film was evaluated. Here, the transfer speed of the optical film was set to 20 m / min, the transfer tension was set to 100 N, and the portion where the film was conveyed while being held by the mirror surface roll at an angle of 90 ° was observed.

The above-mentioned wrinkle refers to a film deformation that does not leave a mark (returns to the original state) even if it occurs, and in English, for example, "wrinkle" corresponds to this. Further, the above-mentioned wrinkle refers to a film deformation (folded wrinkle) that leaves a mark when it occurs, and in English, for example, "crease" corresponds to this. FIG. 9 schematically shows a cross-sectional shape of each film having wrinkles or wrinkles along the width direction. As shown in the figure, the film deformation having a wavy cross section returns to the original non-deformed cross-sectional shape when the film is held by the roll (when the film comes into contact with the outer peripheral surface of the roll). The deformation is a twist. On the other hand, the deformation such that the film folds is wrinkled because it remains even after being held by the roll (because it does not return to the original cross-sectional shape without deformation).
"Evaluation criteria"
⊚: No wrinkles or wrinkles were confirmed.
◯: One spot was confirmed, but no wrinkles were confirmed, and there was no problem.
Δ: Multiple spots were confirmed, but no wrinkles were confirmed, and there was no problem.
X: It was confirmed that wrinkles were generated.

<Transport scratches>
The wound optical film was unwound, and the presence or absence of scratches (scratch resistance) was visually inspected by the following method. That is, the unwound optical film is irradiated with light from the outside of the film by lighting a sodium lamp (KNL-35D, manufactured by Lytest Co., Ltd.) and a commercially available three-wavelength fluorescent lamp in a dark room, and irradiating the film surface. A directional defect with a length of 2 mm or more was recognized as a scratch. The scratches were identified at the portion excluding the range of 5 cm from the edge of the film (the surface portion inside the film from the above range). Then, the scratches (transportation scratches) were evaluated based on the following criteria.
"Evaluation criteria"
⊚: No scratches were confirmed.
◯: Almost no scratches were confirmed.
Δ: Scratches were slightly confirmed, but there is 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 Kogyo Co., Ltd.). Then, the haze was evaluated based on the following evaluation criteria.
"Evaluation criteria"
⊚: 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: The haze value is 0.30% or more.

(Disappearance of unevenness due to heat treatment)
The produced optical film was heat-treated by heating it at a fixed end state for 5 minutes or more at a temperature of Tg + 5 ° C. or higher, with Tg as the glass transition temperature of the resin. Then, the number of irregularities on the surface of the optical film after the heat treatment was measured by the same method as above using an optical microscope, and converted into the number of regions at ^{250,000 μm 2.} Further, the maximum height roughness Rz of the unevenness of the optical film was measured by the same method as described above using a white interference microscope Zygo. Then, based on the following evaluation criteria, the effect of eliminating (relaxing) unevenness by heat treatment was evaluated.
"Evaluation criteria"
⊚: No unevenness was found in the range of ^{250,000 μm 2.}
◯: In ^{the range of 250,000 μm 2} , the number of irregularities was 3 or less, 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.

From Table 1, in Comparative Example 1, the haze value of the film is high. It is considered that this is because the smoothness of the surface of the web becomes extremely low in the method of transferring the surface unevenness of the support to the web. Further, in Comparative Example 2, it is considered that the haze value of the film is high because the matte roll forms irregularities on the entire surface of the film without gaps. Further, in Comparative Example 2, the effect of eliminating the unevenness by the heat treatment is not obtained. It is considered that 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. Further, in Comparative Example 3, it is considered that the haze value is high because the film contains fine particles. In Comparative Example 4, the surface irregularities are formed on the film by the inkjet method, but it is considered that the haze value is high because the number of irregularities is large. Further, since the surface unevenness formed by the inkjet method is not due to the deformation of the film, the film deformation is not restored by the heat treatment, and there is no effect of eliminating the unevenness by the heat treatment.

On the other hand, in Example 1, good results were obtained in all of the transportability (scratches, wrinkles, transport scratches), haze, and the effect of eliminating unevenness by heat treatment. In Example 1, since one or more irregularities are present on the film surface ^{within the range of 250,000 μm 2} , even if the web does not contain fine particles, the unevenness imparts slipperiness to the web, and as a result. It is considered that the web is less likely to be scratched and less likely to be scratched or wrinkled, resulting in better transportability. Further, since the surface roughness Sa around the unevenness is 0.9 nm and the surface is almost flat, it is considered that the surface haze is small and low haze close to that of glass can be realized. Further, with the above-mentioned number (density) of irregularities, the irregularities can be eliminated or alleviated by heat treatment. Therefore, at the time of use, the wound film is unwound again to perform heat treatment to eliminate or alleviate the irregularities on the surface and perform optics. It can be said that it is possible to obtain a film having good characteristics. Further, since the surface of the film has irregularities until the film is unwound and heat-treated, it is possible to ensure good transportability.

It should be noted that 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 where the above effect can be obtained between 0.9 nm of Example 1 and 1.8 nm of Comparative Example 1 (for example, 1.5 nm). Therefore, in order to obtain the above effect, the surface roughness Sa may 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 irregularities were formed on the surface of the web with the processing roll having the maximum height Ry shown in Table 2. Then, the surface roughness Sa, the number of irregularities, the major axis of the irregularities, and the maximum height roughness Rz were measured for the produced optical films 102 to 107 in the same manner as in Example 1.

Table 2 shows the evaluation results of the produced optical films 102 to 107 of Examples 2 to 7 together with the results of the optical films 101 of Example 1.

From Table 2, the effect of improving the transportability of Example 2 is smaller than that of other Examples 3 and the like. In Example 2, since the maximum height Ry of the processing roll is as small as 1 μm, it is possible to scoop (scratch) the surface of the web with the unevenness of the processing roll to form unevenness of an appropriate size on the surface of the web. This is probably because the effect of reducing the sticking of the web to the roll during transportation is reduced. On the other hand, in Examples 1, 3 to 7, the effect of improving the transportability is high. In Examples 1, 3 to 5, since the maximum height Ry of the processing roll is 2 μm or more, the surface of the web is scooped out by the unevenness of the processing roll to form unevenness of an appropriate size on the surface of the web. It is considered that this is because the effect of reducing the sticking of the web to the roll during transportation is increased.

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

Even if the maximum height Ry of the processing roll is 1 μm of Example 2 (even when irregularities having a major axis of 4 μm and a maximum height roughness Rz of 85 nm are formed on the surface of the film), the transportability The results are not practically problematic. From this, it can be said that the maximum height Ry of the processing roll may be 1 μm or more, and that the surface of the film may have 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>
Except for forming irregularities on the surface of the web with the processing roll having the maximum height Ry shown in Table 3 and changing the amount of residual solvent at the time of applying the irregularities by the processing roll as shown in Table 3, the same as in Example 1. In the same manner, the optical films 108 to 114 of Examples 8 to 14 were produced, respectively. Then, the surface roughness Sa, the number of irregularities, the major axis of the irregularities, and the maximum height roughness Rz were measured for the produced optical films 108 to 114 in the same manner as in Example 1.

Table 3 shows the evaluation results of the produced optical films 108 to 114 of Examples 8 to 14 together with the results of the optical films 101 of Example 1.

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, since the amount of residual solvent in the web when the unevenness is applied by the processing roll is as small as 4% by mass, the web is hard and the unevenness is less likely to be formed on the web due to contact with the processing roll. It is considered that the effect of reducing the sticking of the web to the roll during transportation is reduced. Further, in Examples 11 and 14, the effect of eliminating the unevenness by the heat treatment is small. In Examples 11 and 14, since the amount of residual solvent in the web at the time of applying the unevenness is as large as 37% by mass, the web is soft, and unevenness having a large major axis and maximum height roughness Rz is formed on the web by contact with the processing roll. It will be easier. Therefore, even if the heat treatment is performed after that, it is considered that the unevenness is hard to disappear, and even if it is alleviated, the amount thereof becomes very small.

On the other hand, in Examples 8, 9 and 13, the effect of improving the transportability and the effect of eliminating the unevenness by the heat treatment are obtained in a well-balanced manner. In Examples 8, 9 and 13, since the residual solvent amount of the web at the time of applying the unevenness is 6 to 33% by mass, the sticking of the web to the roll during transportation is reduced and the unevenness is eliminated by heat treatment. It is considered that the unevenness of an appropriate size is formed on the web.

When the amount of residual solvent on the web at the time of imparting unevenness was 4% by mass of Examples 10 and 12, the effect of improving transportability was small, and the amount of residual solvent was 6% by mass of Example 8. Occasionally, since the above effect is large, it is considered that there is a critical point for increasing the above effect between 4% by mass of Examples 10 and 12 and 6% by mass of Example 8 (for example, 5% by mass). .. 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 applying the unevenness was 37% by mass of Examples 11 and 14, the effect of eliminating the unevenness by the heat treatment was small, and the residual solvent amount was 33% by mass of Examples 9 and 13. At some point, since the disappearance effect is large, a 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 disappearance effect, the residual solvent amount is preferably 35% by mass or less, and more preferably 33% by mass or less.

Even if the amount of the residual solvent is 4% by mass of Examples 10 and 12, the result that there is no practical problem in transportability is obtained, and the amount of the residual solvent is 37% by mass of Examples 11 and 14. Even so, practically no problem has been obtained with respect to the above-mentioned disappearance effect. From this, it can be said that the residual solvent amount may be 4% by mass or more and 37% by mass or less.

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

[Other]
The optical film of the present embodiment described above and the method for producing the same can be expressed as follows.

1. 1. A casting step of casting a fine particle-free dope onto a metal support to form a web,
A peeling step of peeling the web from the metal support,
An unevenness forming step of forming an uneven shape on the surface of the peeled web by a processing roll,
It has a winding step of winding the web having the uneven shape as an optical film.
The wound optical film has one or more irregularities within a range ^{of 250,000 μm 2 on the surface.}
A method for producing an optical film, wherein the surface roughness Sa around the unevenness within the above range is 1.5 nm or less.

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

3. 3. The optics according to 1 or 2, wherein in the uneven forming step, the uneven shape is formed on the surface of the web by the processing roll subjected to the surface processing having a maximum height Ry of 2 μm or more. Film manufacturing method.

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

5. The optical film according to any one of 1 to 4, wherein the amount of residual solvent in the web when the uneven shape is formed by the processing roll in the uneven forming step is 5 to 35% by mass. Manufacturing method.

6. The method for producing an optical film according to any one of 1 to 5, wherein the optical film has ^{2 or more and 20 or less of the irregularities within a range of 250,000 μm 2 on the surface.}

7. The dope contains a resin and a solvent.
The method for producing an optical film according to any one of 1 to 6, wherein the resin is a cycloolefin-based resin.

8. An optical film that does not contain fine particles
The optical film has one or more irregularities within a range ^{of 250,000 μm 2 on the surface.}
An optical film having a surface roughness Sa around the unevenness within the above range of 1.5 nm or less.

9. The optical film according to 8, 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.
8. The optical film according to 8 or 9, wherein the maximum height roughness Rz is 100 to 1000 nm.

11. The optical film according to any one of 8 to 10, wherein the optical film has 2 or more and 20 or less of the irregularities within a range ^{of 250,000 μm 2 on the surface.}

12. The optical film according to any one of 8 to 11 above, which comprises a cycloolefin-based resin.

Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to this, and can be extended or modified within a range that does not deviate from the gist of the invention.

The present invention can be used when an optical film containing no fine particles is produced by a solution casting film forming method.

3 Support (metal support)
5 Web 20 Processing roll F _PV Concavo-convex Fb Non-concave area F Optical film

Claims (12)

A casting step of casting a fine particle-free dope onto a metal support to form a web,
A peeling step of peeling the web from the metal support,
An unevenness forming step of forming an uneven shape on the surface of the peeled web by a processing roll,
It has a winding step of winding the web having the uneven shape as an optical film.
The wound optical film has one or more irregularities within a range ^{of 250,000 μm 2 on the surface.}
A method for producing an optical film, wherein the surface roughness Sa around the unevenness within the above range is 1.5 nm or less. The method for producing an optical film according to claim 1, wherein the surface roughness Sa is 0.9 nm or less. The production of the optical film according to claim 1 or 2, wherein in the uneven forming step, the uneven shape is formed on the surface of the web by the processing roll subjected to the surface processing having a maximum height Ry of 2 μm or more. Method. On the surface of the optical film
The major axis of the unevenness is 5 to 15 μm.
The method for producing an optical film according to any one of claims 1 to 3, wherein the maximum height roughness Rz is 100 to 1000 nm. The method for producing an optical film according to any one of claims 1 to 4, wherein in the uneven forming step, the amount of residual solvent in the web when the uneven shape 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 irregularities within a range of 250,000 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-based resin. An optical film that does not contain fine particles
The optical film has one or more irregularities within a range ^{of 250,000 μm 2 on the surface.}
An optical film having a surface roughness Sa around the unevenness within the above range of 1.5 nm or less. The optical film according to claim 8, wherein the surface roughness Sa is 0.9 nm or less. On the surface of the optical film
The major axis of the unevenness is 5 to 15 μm.
The optical film according to claim 8 or 9, wherein the maximum height roughness Rz is 100 to 1000 nm. The optical film according to any one of claims 8 to 10, wherein the optical film has 2 or more and 20 or less of the irregularities within a range ^{of 250,000 μm 2 on the surface.} The optical film according to any one of claims 8 to 11, which comprises a cycloolefin-based resin.

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