JP2001138463A - Easily adhesive film for optics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easily adhesive film for optics which shows superb transparency and easy adhesive properties and warps insignificantly even in an after-processing step such as prismatic lens fabrication. SOLUTION: This easily adhesive film for optics is a biaxially oriented polyester film formed of an easily adhesive layer consisting of a copolymer polyester resin and a polyurethane resin laminated on at least one of the faces of the film. In addition, the film is characterized in that the roughness(SRa) of the surface and the back of the film not including the easily adhesive layer is 10 nm or less and the absolute value of the difference in the roughness(SRa) between both surfaces is 5 nm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optically-adhesive film for optical use, and more particularly to an optically-adhesive film for optical use which is excellent in transparency and adhesiveness and has a small warp even after heat treatment.

[0002]

2. Description of the Related Art Biaxially oriented polyester films are widely used as various optical films because of their excellent transparency, dimensional stability and chemical resistance. In particular, applications such as a base film for a prism lens sheet, a base film for a touch panel, a base film for a backlight, a base film for an AR (anti-reflection) film, and a crush prevention film for a CRT used in a liquid crystal display device are:
100 μm because of excellent strength and dimensional stability
The above relatively thick films are preferably used. Films used for such optical films are required to have excellent transparency and excellent adhesion to prism lens processing, hard coat processing, and AR processing, as well as prism lens processing, hard coat processing, and AR processing. In the post-processing step, it is desired that the warpage of the film due to heat treatment during processing is as small as possible.

[0003]

However, it is generally known that a biaxially oriented polyester film generally has poor adhesion to other materials, for example, a prism lens or a hard coat mainly composed of an acrylic resin. . For this reason, various types of polyester films having an easily adhesive layer formed of a polyurethane resin or the like on the surface thereof have been proposed (for example, JP-A-6-340049). However, in the case of forming an easy-adhesion layer made of polyurethane resin, although the adhesive force with the outer layer such as the hard coat layer is improved, the adhesive force with the polyester film as the base material is not sufficient, and as a result, However, there was a problem that sufficient adhesiveness could not be obtained.

Also, heat treatment in post-processing steps such as prism lens processing, hard coat processing, and AR processing causes warpage due to shrinkage of the polyester film, deteriorating process passability, and further reducing productivity. There was a problem of inviting. In addition, there is a problem that a trouble occurs when the liquid crystal display device is incorporated. In view of the above problems, an object of the present invention is to provide an optical adhesive film having excellent transparency and easy adhesion, and having a small warpage even in a post-processing step such as prism lens processing. .

[0005]

That is, the above object of the present invention is achieved by the following means. 1. A biaxially oriented polyester film in which an easy-adhesion layer composed of a copolymerized polyester resin and a polyurethane resin is laminated on at least one side, and the front and back roughness (SRa) of the base film is 10 nm or less. An easy-to-use optical adhesive film, wherein the absolute value of the difference is 5 nm or less. 2. 3. An optical adhesive film having an adhesive property of 85% or more when a photocurable acrylic coating layer is provided on the adhesive layer according to 1 above. The adhesiveness mentioned above is
Based on the test method according to JIS-K5400, 8.5.1, it means the value obtained from the following formula. 2. Adhesiveness (%) = (1−peeled area / evaluated area) × 100 3. The optical adhesive film according to 1 or 2, wherein the haze value of the film is 1.0% or less.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the optically easy-to-adhesive film of the present invention will be described below. The biaxially oriented polyester film which is the base film of the present invention is made of polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate or a copolymer mainly composed of these resin components. Biaxially oriented films formed from polyethylene terephthalate are particularly preferred.

When a polyester copolymer is used as the resin forming the biaxially oriented polyester film, the dicarboxylic acid component includes aliphatic dicarboxylic acids such as adipic acid and sebacic acid, terephthalic acid, isophthalic acid, phthalic acid, and the like. Aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid and the like and polyfunctional carboxylic acids such as trimellilotic acid and pyromellilotic acid are used. As the glycol component, fatty acid glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, propylene glycol and neopentyl glycol;
aromatic glycols such as p-xylene glycol; 1,4
Alicyclic glycols such as cyclohexanedimethanol;
For example, polyethylene glycol having an average molecular weight of 150 to 20,000 is used. Preferred copolymer ratio is 20%
Is less than. If it is 20% or more, the film strength, transparency, and heat resistance may be poor. Further, the polyester-based resin may contain various additives. Examples of the additive include an antistatic agent, a UV absorber, and a stabilizer. Further, it is preferable that particles for the purpose of imparting lubricity are not added to the polyester base film of the present invention.

In addition, the intrinsic viscosity of the polyester resin pellet, which is a raw material of the biaxially oriented polyester film, is 0.1.
The range of 45 to 0.70 dl / g is preferred. If the intrinsic viscosity is less than 0.45 dl / g, the effect of improving tear resistance tends to deteriorate. On the other hand, the intrinsic viscosity is 0.70 dl /
If the amount exceeds g, the increase in filtration pressure becomes large and high-precision filtration tends to be difficult.

The easy-adhesion layer of the optically-adhesive film of the present invention is laminated on at least one surface of the biaxially oriented polyester film, and provided on at least one surface of the unstretched or uniaxially stretched polyester film. It is preferable to laminate by an in-line coating method of stretching and heat-setting at least in a uniaxial direction. By adding fine particles of an appropriate particle size to the easy-adhesion layer laminated by the in-line coating method and forming irregularities on the surface of the easy-adhesion layer, it is possible to impart good slipperiness, winding property, and scratch resistance. it can. For this reason, it is not necessary to contain fine particles in the biaxially oriented polyester, which is particularly effective for obtaining a highly transparent film having a haze value of 1.0% or less.

The term "easy adhesion" as used in the present invention means that the adhesiveness with the photocurable acrylic coat layer measured by the method described in "Adhesion with Photocurable Acrylic Coat Layer" below is 85. %, Preferably 9% or more.
It is at least 0%, particularly preferably at least 95%.

The adhesive layer of the optical adhesive film of the present invention is mainly composed of a copolymerized polyester resin and a polyurethane resin. When the copolymerized polyester resin alone is used, the adhesion to the polyester base film is sufficient, but the adhesion to the acrylic resin used for the prism lens or the hard coat is poor. In addition, the polyurethane resin alone has excellent adhesiveness with an acrylate resin but is inferior in adhesiveness with a polyester base film.

The main components of the copolymerized polyester resin used in the easily adhesive layer of the present invention are a dicarboxylic acid component and a branched glycol component. The branched glycol component is, for example, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol, 2-methyl-2-butyl-1,3. -Propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-2-isopropyl-1,3
-Propanediol, 2-methyl-2-n-hexyl-
1,3-propanediol, 2,2-diethyl-1,3
-Propanediol, 2-ethyl-2-n-butyl-
1,3-propanediol, 2-ethyl-2-n-hexyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2-n-butyl-2
-Propyl-1,3-propanediol, and 2,2-
Di-n-hexyl-1,3-propanediol and the like.

The above-mentioned branched glycol component is contained in all the glycol components preferably in a proportion of 10 mol% or more, more preferably in a proportion of 20 mol% or more. As the glycol component other than the above compounds, ethylene glycol is most preferable. If it is a small amount, diethylene glycol, propylene glycol, butanediol,
Hexanediol or 1,4-cyclohexanedimethanol may be used.

As the dicarboxylic acid component contained as a component in the copolymerized polyester resin, terephthalic acid and isophthalic acid or salts thereof are most preferred. If the amount is small, another dicarboxylic acid component, for example, an aromatic dicarboxylic acid such as diphenylcarboxylic acid or 2,6-naphthalenedicarboxylic acid may be added and copolymerized.

In addition to the dicarboxylic acid component, 5-sulfoisophthalic acid is used in an amount of 1 to 10 to impart water dispersibility.
It is preferably used in the range of mol%, for example, sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfonaphthaleneisophthalic acid-2,7-dicarboxylic acid and 5-
(4-Sulfophenoxy) isophthalic acid or salts thereof can be mentioned.

The polyurethane resin used in the easy-adhesion layer of the present invention is, for example, a resin containing a block-type isocyanate group, in which a terminal isocyanate group is blocked with a hydrophilic group (hereinafter referred to as a block), and is a heat-reactive type. And water-soluble urethane. Examples of the isocyanate group blocking agent include bisulfites and phenols containing sulfonic acid groups, alcohols, lactams, oximes, and active methylene compounds. The blocked isocyanate group can make the urethane prepolymer hydrophilic or water-soluble. Among the above blocking agents, bisulfites are most preferable as those which are appropriate for the temperature and time during the heat treatment and widely used industrially.

Further, when heat energy is given to the polyurethane resin in the drying step or the heat-setting treatment step in the production of the film, the blocking agent separates from the isocyanate group, so that the polyurethane resin is mixed with the self-crosslinked stitches. While immobilizing the water-dispersible copolymerized polyester resin, it reacts with the terminal groups of the resin.
The resin under coating liquid adjustment is poor in water resistance because it is hydrophilic, but when the thermal reaction is completed by applying, drying and heat fixing,
Since the hydrophilic group of the urethane resin, that is, the blocking agent comes off, a coating film having good water resistance can be obtained.

The urethane prepolymer used for the polyurethane resin includes (1) an organic polyisocyanate having two or more active hydrogen atoms in a molecule or a molecular weight having at least two active hydrogen atoms in a molecule. 200 to 20,000 compounds, (2) an organic polyisocyanate having two or more isocyanate groups in the molecule, or (3) a chain extender having at least two active hydrogen atoms in the molecule. The resulting compound having a terminal isocyanate group is exemplified.

The compound (1) is generally known to contain two or more hydroxyl groups, carboxyl groups, amino groups or mercapto groups at the terminal or in the molecule. Particularly preferred compounds are Examples include polyether polyols and polyether ester polyols.

Examples of the polyether polyol include (a) alkylene oxides such as ethylene oxide and propylene oxide, (b) a compound obtained by polymerizing styrene oxide, epichlorohydrin, and the like; (c) a random polymer or a block polymer thereof; d) Compounds obtained by addition polymerization to polyhydric alcohols are exemplified.

As the polyester polyol and the polyetherester polyol, linear or branched compounds are mainly mentioned. These include polyvalent saturated or unsaturated carboxylic acids such as succinic acid, adipic acid, phthalic acid, and maleic anhydride, or the carboxylic anhydrides, and ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl. Polyhydric saturated and unsaturated alcohols such as glycol, 1,6-hexanediol, trimethylolpropane, etc .; polyalkylene ether glycols such as relatively low molecular weight polyethylene glycol and polypropylene glycol; or alcohols thereof Can be obtained by condensation with a mixture of

Further, as the polyester polyol, polyesters obtained from lactone and hydroxy acid, and as the polyetherester polyol,
Polyetheresters obtained by adding ethylene oxide or propylene oxide to polyesters produced in advance can also be used.

As the organic polyisocyanate (2), isomers of toluylene diisocyanate, 4,4
-Diphenylmethane diisocyanate, aromatic diisocyanates such as xylylene diisocyanate, isophorone diisocyanate, alicyclic diisocyanates such as 4,4-dicyclohexylmethane diisocyanate,
Hexamethylene diisocyanate, and 2,2,4-
Examples thereof include aliphatic diisocyanates such as trimethylhexamethylene diisocyanate, and polyisocyanates in which these compounds are added alone or in combination with trimethylolpropane or the like in advance.

Examples of the chain extender having at least two active hydrogens of the above (3) include glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerin, and trimethylolpropane. And polyhydric alcohols such as pentaerythritol, diamines such as ethylenediamine, hexamethylenediamine, and piperazine; aminoalcohols such as monoethanolamine and diethanolamine; thiodiglycols such as thiodiethylene glycol; and water.

In order to synthesize the urethane polymer of the above (3), usually, at a temperature of 150 ° C. or less, preferably 70 to 120 ° C., by a one-stage or multi-stage isocyanate polyaddition method using the above chain extender. Let react for minutes to several hours. The ratio of isocyanate groups to active hydrogen atoms can be freely selected as long as it is 1 or more, but it is necessary that free isocyanate groups remain in the obtained urethane prepolymer.

The content of the free isocyanate group may be 10% by weight or less, but is preferably 7% by weight or less in consideration of the stability of the aqueous urethane polymer solution after blocking.

The obtained urethane prepolymer is preferably subjected to blocking using bisulfite.
The mixture is mixed with an aqueous bisulfite solution, and the reaction is allowed to proceed with good stirring for 5 minutes to 1 hour. The reaction temperature is preferably set to 60 ° C. or lower. Thereafter, the mixture is diluted with water to an appropriate concentration to obtain a heat-reactive water-soluble urethane composition. When using this composition, adjust to the appropriate concentration and viscosity,
Usually, when heated to 80 to 200 ° C., the bisulfite of the blocking agent is dissociated, and the active isocyanate group is regenerated, so that a polyurethane polymer is formed by a polyaddition reaction occurring within or between molecules of the prepolymer. , Or to other functional groups.

As an example of the resin (B) containing a block type isocyanate group described above, Elastron (trade name) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. is typical. Elastron is obtained by blocking an isocyanate group with sodium bisulfite, and is water-soluble due to the presence of a carbamoyl sulfonate group having strong hydrophilicity at the molecular terminal.

When preparing a coating solution by mixing the copolymerized polyester resin (A) containing a branched glycol component and the resin (B) containing a blocked isocyanate group used in the present invention, the resin (A) ) And the resin (B) preferably have a weight ratio of (A) :( B) = 90: 10 to 10:90, particularly preferably (A) :( B) = 80: 20.
20:80. When the ratio of the resin (A) is
When less than 10% by weight based on the total solid content of the coating layer,
The applicability to the base film is insufficient, and the adhesion between the application layer and the film is insufficient. The ratio of the resin (B) is 1 to the total solid weight of the coating layer.
When the amount is less than 0% by weight, practical adhesiveness cannot be obtained with the UV-curable hard coat layer.

A catalyst may be added to the aqueous coating solution used in the present invention in order to promote a thermal crosslinking reaction. Examples of the catalyst include inorganic substances, salts, organic substances, alkaline substances, acidic substances and metal-containing organic compounds. Various chemical substances are used. In order to adjust the pH of the aqueous solution, an alkaline substance or an acidic substance may be added.

When the aqueous coating solution is applied to the surface of the base film, a known anionic activator and a nonionic active agent are used in order to increase the wettability to the base film and uniformly coat the coating solution. A required amount of a surfactant can be added. The solvent used for the coating solution may be mixed with alcohols such as ethanol, isopropyl alcohol, and benzyl alcohol, in addition to water, until the proportion of the solvent in the total coating solution is less than 50% by weight. Further, when the content is less than 10% by weight, an organic solvent other than alcohols may be mixed in a range where it can be dissolved. However, the total of alcohols and other organic solvents in the coating liquid is preferably less than 50% by weight.

When the addition amount of the organic solvent is less than 50% by weight, the drying property is improved at the time of coating and drying, and the effect of improving the appearance of the coating film is obtained as compared with the case where only water is used. When the addition amount of the organic solvent is 50% by weight or more, the evaporation rate of the solvent is increased, and the concentration of the coating solution easily changes during coating. As a result, since the viscosity of the coating solution increases and the coating property decreases, there is a possibility that the appearance of the coating film may be deteriorated. Further, it is not preferable in terms of danger such as fire and health of workers. .

In the composition of the aqueous coating solution, an antistatic agent, an ultraviolet absorption inhibitor, a plasticizer, inorganic and / or organic inert particles, a pigment,
Various additives such as an organic lubricant and an antibacterial agent may be mixed. Further, since the coating liquid is aqueous, other water-soluble resins, water-dispersible resins, emulsions, and the like may be added to the coating liquid for improving the performance as long as the contribution effect is not lost.

The coating amount (solid weight per unit area of the film) of the easily adhesive layer is 0.05 to 0.50 g / m ^2.
Is preferred. When the coating amount is less than 0.05 g / m ² ,
Poor adhesion. If the coating amount exceeds 0.50 g / m ² , the haze value increases, which is not preferable.

The haze value of the easily adhesive optical film of the present invention is preferably 1.0% or less, more preferably 0.9% or less, and particularly preferably 0.6% or less. If the haze value is 1.0% or more, the film
When used as a lens film for D, a base film for backlight, or the like, the sharpness of the screen is likely to deteriorate, which is not preferable.

In order to make the haze value of the optically easily adhesive film of the present invention 1.0% or less, it is preferable that particles for imparting lubricity are not contained in the base film. When particles for imparting lubricity are not contained in the base film, in order to improve the scratch resistance of the adhesive layer and the winding property of the film, appropriate particles may be contained in the adhesive layer. preferable.

In the present invention, since inert particles for the purpose of imparting lubricity are not substantially contained in the base film, inert particles are added to the aqueous coating solution so that the surface of the film is appropriately coated. It is preferable to form a proper projection. Examples of inert particles added to the aqueous coating solution include inorganic particles such as calcium carbonate, calcium phosphate, silica, kaolin, talc, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, and molybdenum sulfide. And organic particles such as crosslinked polymer particles and calcium oxalate. Among these, silica has a relatively close refractive index to the polyester resin,
It is most preferable because a highly transparent film can be easily obtained.

The average particle size (observed by an electron microscope) of the inert particles added to the aqueous coating solution is 0.01 to 1.0 μm.
m is preferable, and more preferably 0.02 to 0.5 μm
m, particularly preferably 0.03 to 0.1 μm. When the average particle size of the inert particles exceeds 1.0 μm, the film surface tends to be rough, and the transparency of the film tends to decrease. On the other hand, if the average particle size of the inert particles is less than 0.01 μm, the slipperiness of the film becomes insufficient, which is not preferable.

The content of the inert particles in the coating layer after drying the coating solution is 0.01 to 60% by weight.
Is particularly preferable, and 0.1 to 40% by weight is particularly preferable. If the content of the inert particles in the coating layer exceeds 60% by weight, the adhesion to the film may be impaired. On the other hand, when the content of the inert particles is less than 0.01% by weight, the slipperiness of the film becomes insufficient, which is not preferable.

In the present invention, it is preferable that two types of particles (particle A and particle B) are contained in the easily adhesive layer. Particle A
Has an average particle size of preferably from 20 to 300 nm, more preferably from 30 to 100 nm. Particle A has an average particle size of 2
If it is less than 0 nm, the scratch resistance tends to deteriorate. On the other hand, when the average particle diameter of the particles A exceeds 300 nm, the haze value tends to increase.

Since the particle A alone has insufficient scratch resistance, in order to further improve the scratch resistance,
It is preferable that the particles B are contained in the easy adhesion layer in combination with the particles A. The average particle size of the particles B is 300 to 1000 nm
And more preferably 400 to 800 nm. If the average particle diameter of the particles B is less than 300 nm, the scratch resistance tends to be deteriorated. On the other hand, when the average particle diameter of the particles B exceeds 1000 nm, the haze value tends to increase. Further, the particles B are preferably aggregated particles in which primary particles are aggregated, and the ratio of the average particle size in the aggregated state to the average particle size of the primary particles is preferably 6 times or more from the viewpoint of scratch resistance. .

Further, the content ratio (A / B) of the particles A and the particles B in the easy-adhesion layer is set to 5 to 30, and the content of the particles B is set to 0.1 to 0.1 to the solid content of the easy-adhesion layer. The content of 1% by weight is suitable for obtaining an optically easy-to-adhesive film having a small haze value and excellent in slipperiness and scratch resistance. It is preferable to set the content of each particle so as to fall within the above range. In particular, for the solid content of the easily adhesive layer,
When the content of the particles B exceeds 1% by weight, transparency tends to deteriorate. The solid content of the easy-adhesion layer described above means the total of the solid contents of the resin A, the resin B, the particles A, and the particles B. As inert particles to be contained in the easy adhesion layer,
Using two types of silica particles having different particle diameters and forms, spherical monodisperse silica as particles A and aggregated silica as particles B are set to the contents and ratios in the above ranges, respectively, and the coating amount is set in the above range. This is particularly suitable for obtaining an optically easy-to-adhesive film having a small haze value and excellent in slipperiness and scratch resistance.

When applying the above coating solution, a filter medium is arranged so that the coating solution is subjected to microfiltration immediately before the application in order to remove coarse aggregates or contaminants due to precipitation of particles and resin in the coating solution. Is preferred.

It is preferable that the filter medium for finely filtering the coating liquid used in the present invention has a filter particle size of 25 μm or less (initial filtration efficiency: 95%). When a filter medium having a filtration particle size exceeding 25 μm is used, coarse aggregates and contaminants cannot be sufficiently removed, and many coarse aggregates that cannot be removed are subjected to a uniaxial stretching or biaxial stretching process after coating and drying. The film may spread due to the stretching stress in the film, and in some cases, may be recognized as an aggregate having a size of 100 μm or more. Therefore, in addition to an increase in the haze value of the film, the film may cause optical defects.

The type of the filter medium for finely filtering the coating solution is not particularly limited as long as it has the above-described foreign matter removing performance, and examples thereof include a filament type, a felt type, and a mesh type. The material of the filter medium for finely filtering the coating solution is not particularly limited as long as it has the above-described foreign matter removing performance and does not adversely affect the coating solution, and examples thereof include stainless steel, polyethylene, polypropylene, and nylon.

Next, the method for producing the easily adhesive polyester film for optics of the present invention will be described using polyethylene terephthalate (hereinafter abbreviated as PET) as an example.
Of course, it is not limited to this.

After sufficiently drying PET pellets substantially containing no inert particles, the pellets are fed to an extruder, melt-extruded into a sheet at about 280 ° C., and solidified by cooling to produce an unstretched PET sheet. Film. At this time, high-precision filtration is performed at an arbitrary place where the molten resin is maintained at about 280 ° C. in order to remove foreign substances contained in the resin. The filter medium used for high-precision filtration of the molten resin is not particularly limited, but the filter medium of the stainless sintered body is made of Si, Ti, Sb, G
It is excellent in the performance of removing aggregates containing e and Cu as main components and high-melting organic matter, and is suitable. The above “PET substantially free of inert particles” means that the content of inert particles in PET is less than the detection limit when analyzed by fluorescent X-ray. I do.

Further, the size of the filter particles of the filter medium (initial filtration efficiency 95%) is preferably 15 μm or less. If it is 15 μm or more, foreign substances of 20 μm or more cannot be sufficiently removed. The size of the filter particles of the filter medium (initial filtration efficiency 95%) is 15 μm
Productivity may be reduced by performing high-precision filtration of the molten resin using the following filter media, but it is indispensable to obtain an optical film with few optical defects.

Even in the case of fine foreign matter that passes through the filter medium in the step of extruding the molten resin, crystallization proceeds around the foreign matter in the process of cooling the sheet-like molten material, and this causes non-uniform stretching in the stretching step. A slight difference in thickness occurs. In the part where this minute thickness difference exists,
The light is refracted or scattered as if it has a lens, and when viewed with the naked eye, appears larger than an actual foreign object. This minute difference in thickness can be observed as a difference between the height of the projection and the depth of the depression. The height of the projection is 1 μm or more, and the depth of the depression adjacent to the projection is 0.5 μm or more. In this case, due to the lens effect, an object having a size of 20 μm may be visually recognized as a size of 50 μm or more, and may be further recognized as an optical defect having a size of 100 μm or more. In order to obtain a highly transparent film, it is desirable not to include particles for imparting lubricity in the base film, but as the particle content is lower and the transparency is higher,
Optical defects due to minute irregularities tend to be sharper.

In the case of a thick film, the cooling efficiency in the film thickness direction is insufficient compared with a thin film, and crystallization tends to proceed. Is required. As a method of cooling the unstretched sheet, a known method of extruding a molten resin into a sheet shape from a die on a rotary cooling drum (chill roll), and rapidly cooling the sheet-like melt into a sheet while closely contacting the sheet-like molten material on the chill roll. Can be applied. As a method of cooling the air surface (the surface opposite to the surface that comes into contact with the chill roll) of the sheet-like material, for example, a method of bringing the sheet surface into contact with a cooling liquid in a tank, a method of evaporating the sheet air surface with a spray nozzle And a method of cooling by blowing high-speed airflow. Above all, a method of cooling by blowing a high-speed airflow is effective.
In particular, when producing a thick optical film having a final thickness of 188 μm or more, it is preferable to use both of them. Further, as a method of bringing the sheet-like melt into close contact with the chill roll, for example, a method of using an air knife or a method of imposing an electrostatic charge on the sheet-like melt is preferable. Among these methods, the latter method of impressing the electrostatic charge is particularly preferable.

In the present invention, the definition of the front and back sides of the film is defined such that the surface (chill roll surface) where the sheet comes into contact with the chill roll at the time of production of the unstretched sheet is the “front”, and the surface (air surface) opposite to the surface contacting the chill roll is used. "Back".

The obtained unstretched sheet is longitudinally stretched 2.5 to 5.0 times in the longitudinal direction by a roll heated to 80 to 120 ° C. to obtain a uniaxially oriented PET film. The longitudinal stretching may be performed in one step, but may be performed in at least two or more steps from the viewpoint of productivity and reduction of uneven thickness. Furthermore, the end of the film is gripped with a clip and guided to a hot air zone heated to 80 to 180 ° C., and is laterally stretched 2.5 to 5.0 times in the width direction. Subsequently, the resultant is guided to a heat-setting treatment zone at 200 to 240 ° C. and subjected to a heat treatment for 1 to 60 seconds to complete the crystal orientation. During this heat-setting treatment step, a relaxation treatment of 1 to 12% may be performed in the width direction or the longitudinal direction as necessary. Furthermore, when the film is cooled to Tg or less after the heat setting, if the tension in the film flow direction is applied, the effect of the heat setting is reduced, so that it is preferable to provide a nip roll or a quenching zone for cutting the tension. At any stage during this step, an aqueous solution of the above-mentioned copolymerized polyester and polyurethane resin is applied to at least one surface of the polyester film.

The application of the aqueous coating solution can be carried out by any known method. For example, reverse roll coating, gravure coating, kiss coating, roll brushing, spray coating, air knife coating, wire barber coating, pipe doctor method,
Examples include an impregnation / coating method and a curtain coating method, and these methods can be performed alone or in combination.

The step of applying the aqueous coating solution may be a normal coating step, that is, an off-line step of applying to a base film which has been biaxially stretched and heat-set, but may be an in-line coating method of applying during the production step of the film. Is preferred.
More preferably, it is applied to the base film before the completion of the crystal orientation. When the above coating solution is applied to a polyester film substrate after unstretching or uniaxial stretching, and then dried and stretched, only a solvent such as water is removed in the drying step after coating, and the crosslinking reaction of the coating layer does not proceed. It is important to choose temperature and time. Drying temperature is 70-1
The drying is preferably performed at 40 ° C., and the drying time is adjusted according to the coating solution and the amount of coating. However, the temperature product of the temperature (° C.) and the time (second) is preferably 1000 to 3000.

The solid content concentration in the aqueous coating solution is 30% by weight.
Or less, particularly preferably 10% by weight
It is as follows. The film to which the aqueous coating solution has been applied and dried is guided to a tenter for stretching and heat setting, where it is heated to form a stable film by a thermal crosslinking reaction, and becomes a polyester-based laminated film. In order to obtain good adhesion to the ink, 100
It is preferable that the heat treatment is performed at a temperature of not less than 0 ° C. for at least 1 minute, and the application amount of the easy-adhesion layer after the heat treatment is 0.05 g / m ² or more.

The thickness of the obtained optically-easily-adhesive film of the present invention is preferably from 50 to 300 μm, particularly preferably from 100 to 250 μm. If the film thickness is less than 50 μm, the rigidity becomes insufficient, which is not preferable. On the other hand, if the thickness of the film exceeds 300 μm, the amount of foreign matter which becomes an optical defect existing in the film increases, which undesirably increases the haze value.

(Function) The present inventors have found that the conventional biaxially stretched polyethylene terephthalate film is warped in a post-processing step such as a prism lens processing step because of a difference in crystallinity between the front and back of the film. And
It has been found that the difference in crystallinity between the film front and back is reflected in the surface roughness of the film front and back. Therefore, as a result of intensive study, it was found that a difference in surface roughness between the front and back surfaces was used as a substitute characteristic, and by reducing this, a film with a small warpage could be obtained, which was suitable as a base material for optical members. .

In the optically-adhesive film of the present invention, the front and back surface roughness (SRa) of the substrate film must be 10 nm or less, preferably 7 nm or less. If the surface roughness (SRa) of the front and back surfaces of the base film exceeds 10 nm, transparency is undesirably hindered. Further, the absolute value of the difference in surface roughness (SRa) between the front and back of the base film is 5n.
m or less, and preferably 3 nm or less.

Generally, in the production of an unstretched sheet, one surface is cooled by a cooling roll and rapidly cooled. However, the thicker the product, the more the cooling efficiency in the film thickness direction is insufficient with cooling only on the chill roll surface, so the cooling on the air surface opposite to the chill roll surface is worse than that on the chill roll surface. This causes a difference in the crystallinity of both sides of the sheet. In particular, when a thick film having a final film thickness of 188 μm or more is manufactured, the tendency becomes remarkable. This difference in crystallinity appears as a difference in surface roughness between the front and back of the film. As the absolute value of the difference in surface roughness increases, the difference in deformation of the film also tends to increase. The present inventors have found that if the absolute value of the difference in surface roughness between the front and back surfaces of the polyester film is suppressed to 5 nm or less, the warpage can be reduced. For example, 300 mm × when heated at 150 ° C. for 3 hours. The amount of warpage at a size of 210 mm can be 3 mm or less. The method for reducing the absolute value of the difference in surface roughness between the front and back of the film to 5 nm or less is not particularly limited. For example, the cooling efficiency of the sheet in the process of producing an unstretched sheet during the production of a polyester film is increased. It is effective to increase the cooling efficiency of the air surface.

In order to increase the cooling efficiency of the air surface opposite to the chill roll, the cooling of the sheet air surface (the surface opposite to the contact surface with the chill roll) in the production process of the unstretched sheet must be reduced by 10%.
It is preferable to carry out at a temperature of at least ° C / sec. From the viewpoint of transparency, 20 ° C./sec or more is preferable. If the cooling rate of the air surface is less than 5 ° C./sec, the absolute value of the difference in surface roughness between the front and back of the film exceeds 5 nm, and when heated at 150 ° C. for 3 hours, the amount of warpage in a size of 300 mm × 210 mm. Tends to be 3 mm or more.

In order to make the absolute value of the difference in the surface roughness between the front and back surfaces of the film other than the casting step 5 nm or less,
For example, it is also possible to reduce the temperature difference between the front and back of the film before and during stretching in the longitudinal stretching step and the transverse stretching step. Conversely, it is also possible to correct the difference in surface roughness between the front and back surfaces in the longitudinal stretching step.

In the longitudinal stretching step and the transverse stretching step, if the temperature difference between the front and back surfaces of the film surface before and during stretching is 10 ° C. or more, the difference in the surface roughness between the front and back surfaces of the film tends to exceed 5 nm. Yes, when heated at 150 ° C. for 3 hours, the amount of warpage in a size of 300 mm × 210 mm tends to be 3 mm or more. Therefore, the temperature difference is preferably less than 10 ° C., and particularly preferably less than 5 ° C.

[0063]

Next, a method for producing an easily adhesive polyester film for optics of the present invention will be described with reference to polyethylene terephthalate (hereinafter abbreviated as PET) as an example, but is not limited thereto. “Parts” in Examples and Comparative Examples means “parts by weight” unless otherwise specified. The evaluation of the characteristics in the present specification was performed by the following methods.

(1) Three-dimensional center plane average surface roughness (SR
a) First, when manufacturing the films of Examples and Comparative Examples, after the start and end of the application of the easy-adhesion layer, the films are marked with magic and the films are wound up into a roll. The obtained roll-shaped film was cut into an A4 sheet shape, the portion where the easy-adhesion layer was not applied was sampled, and the SRa of the base polyester film was measured. The three-dimensional center plane average roughness (SRa) of the base film surface was measured using a stylus type three-dimensional surface roughness meter (ET-30HK) and a three-dimensional roughness analyzer (SPA-11) manufactured by Kosaka Laboratories. Used, stylus tip radius: 2 μm, stylus load: 0.2 mN, cut-off value:
0.08mm, measurement length: 1mm, feed speed: 100μ
m / sec, feed pitch: 2 μm.

(2) Measurement of haze value Haze meter (Model TC-H3D manufactured by Tokyo Denshoku Industries Co., Ltd.)
P).

(3) Warp value after heat treatment at 150 ° C. for 3 hours A film having a size of 300 mm × 210 mm was subjected to 150 ± 3.
After a heat treatment at 3 ° C. for 3 hours and standing on a flat table at room temperature for 30 minutes, the warpage value of the film from the table is measured with a caliper. The unit is mm.

(4) Adhesion to Photocurable Acrylic Coating Layer A hard coating agent (manufactured by Dainichi Seika Co., Ltd., Seika Beam EXF01) was applied to the surface of the easily adhesive layer of the films obtained in Examples and Comparative Examples.
(B)) using a # 8 wire bar, dried at 70 ° C. for 1 minute to remove the solvent, and then 200 m with a high pressure mercury lamp.
A 3 μm-thick hard coat layer was formed under the conditions of J / cm ² , irradiation distance of 15 cm and running speed of 5 m / min. The adhesiveness of the obtained film was determined by a test method according to JIS-K5400, 8.5.1. Specifically, 100 square-shaped cuts penetrating the easy-adhesion layer and reaching the base film were made using a cutter guide with a gap of 2 mm. Next, a cellophane adhesive tape (Nichiban 40
No. 5; 24 mm width) was adhered to the cut surface of the grid, rubbed with an eraser and completely adhered, and then peeled off vertically to visually determine the adhesiveness from the following formula. Adhesiveness (%) = (1−peeled area / evaluated area) × 100

(5) Film surface temperature in film forming process Non-contact infrared thermometer (IT2-80) manufactured by KEYENCE
It measured using. For places where it is difficult to measure the surface temperature of the front and back surfaces of the film, the heat transfer coefficient between the roll and air was determined in advance, and the temperature difference between the front and back surfaces calculated with the thermal conductivity of the PET film was estimated.

Example 1 (1) Preparation of Coating Solution A coating solution used in the present invention was prepared according to the following method.
95 parts of dimethyl terephthalate, 95 parts of dimethyl isophthalate, 35 parts of ethylene glycol, 145 parts of neopentyl glycol, 0.1 part of zinc acetate and 0.1 part of antimony trioxide are charged into a reaction vessel, and the ester is added at 180 ° C. for 3 hours. An exchange reaction was performed. Next, 6.0 parts of 5-sodium sulfoisophthalic acid was added, and
After performing the esterification reaction over time, the polycondensation reaction was performed at 250 ° C. under reduced pressure (13 to 0.3 hPa) for 2 hours to obtain a polyester resin having a molecular weight of 19,500 and a softening point of 60 ° C.

30% of the obtained polyester resin (A)
6.7 parts of an aqueous dispersion, 40 parts of a 20% aqueous solution of an isocyanate group-containing self-crosslinkable polyurethane resin (B) blocked with sodium bisulfite (Daiichi Kogyo Seiyaku Co., Ltd., trade name: Elastron H-3), 0.5 parts catalyst for Elastron (Daiichi Kogyo Seiyaku; product name Cat64) and 4 parts water
4.3 parts and 5 parts of isopropyl alcohol were mixed, 0.6 part of a 10% aqueous solution of an anionic surfactant was added, and spherical silica particles A (Nissan Chemical Industries, Ltd .: Snowtex OL, average particle size 40 nm) ) And 1.8 parts of a 4% aqueous dispersion of dry-processed silica particles B (manufactured by Nippon Aerosil Co., Ltd., Aerosil OX50, average particle diameter 500 nm, average primary particle diameter 40 nm) are added. A coating solution was obtained.

(2) Production of Easy Adhesive Film Example A polyethylene terephthalate resin pellet containing substantially no particles and having an intrinsic viscosity of 0.62 dl / g as a raw material polymer was dried under reduced pressure at 135 ° C. for 6 hours. (1.3 hPa), and then fed to an extruder,
It is melt-extruded into a sheet at 0 ° C. and quenched and solidified on a metal cooling drum (chill roll) maintained at a surface temperature of 20 ° C.
The sheet surface opposite to the chill roll was cooled by blowing high-speed airflow to obtain a cast film. At this time, the cooling rate of the air surface was 20.2 ° C./sec. Further, as a filter medium for removing foreign matters from the molten resin, a stainless filter medium having a filtration particle size (initial filtration efficiency of 95%) of 15 μm was used.

Next, the cast film was heated to 100 ° C. by a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction by a roll group having a peripheral speed difference to obtain a uniaxially oriented PET film. Was. The temperature difference between the front and back of the film immediately before longitudinal stretching was 0.2 ° C. Next, the coating liquid was filtered to a particle size (initial filtration efficiency 95%).
%) Precisely filtered through a 25 μm felt-type polypropylene filter medium, applied to one surface of a uniaxially oriented PET film by a reverse roll method, and subsequently applied, gripped at the end of the film with a clip, and heated to 80 ° C. in a preheating zone of a tenter.
After drying the coating layer for 20 seconds, the film was stretched 4.0 times at 130 ° C. in the width direction in the transverse stretching zone. Subsequently, a heat-setting treatment was performed at 240 ° C., and a lateral relaxation treatment of 3% was performed at 200 ° C. to obtain a biaxially oriented PET film having a thickness of 188 μm. The content ratio of the particles A and the particles B in the coating layer of the obtained film was 8, and the content of the particles B was 0.42% by weight in terms of the solid content ratio of the coating layer. The coating amount was 0.10 g / m ² as a solid content. Table 1 shows the results.

(Example 2) In the production of an easily adhesive film, except that the temperature difference between the front and back sides in the longitudinal stretching step was set at 8 ° C.
In the same manner as in Example 1, an easily adhesive film for optical was obtained.
Table 1 shows the results.

Example 3 In forming an easily adhesive film, except that the temperature difference between the front and back surfaces in the horizontal stretching step was set at 6 ° C.
In the same manner as in Example 1, an easily adhesive film for optical was obtained.
Table 1 shows the results.

Example 4 Example 1 was repeated except that the thickness of the film was 250 μm.
An easy-to-use optical adhesive film was obtained in the same manner as described above. Table 1 shows the results.

(Example 5) The same as Example 1 except that the air surface was cooled at 8.3 ° C / sec during the production of the unstretched sheet, and the temperature difference between the front and back sides in the longitudinal stretching step was 8 ° C. An easily adhesive film for optics was obtained by the method described above. Table 1 shows the results.

Comparative Example 1 An easily adhesive optical film was obtained in the same manner as in Example 1 except that the air surface was cooled at 8.3 ° C./sec during the production of the unstretched sheet. Table 1 shows the results
Shown in

(Comparative Example 2) An easily adhesive optical film was obtained in the same manner as in Example 1, except that the urethane resin (B) was not added in the preparation of the coating solution. At this time, the content ratio of the particles A and the particles B was 8, and the content of the particles B was 1.82% by weight based on the solid content of the easily adhesive layer. The amounts of water and isopropyl alcohol were adjusted while keeping the ratio between the two so that the solid content concentration in the coating solution was the same as in Example 1. Table 1 shows the results.

Comparative Example 3 An optical adhesive film was obtained in the same manner as in Example 1 except that the temperature difference between the front and back surfaces in the longitudinal stretching step was changed to 15 ° C. Table 1 shows the results.

Comparative Example 4 An optical adhesive film was obtained in the same manner as in Example 1 except that the temperature difference between the front and back surfaces in the horizontal stretching step was changed to 16 ° C. Table 1 shows the results.

Comparative Example 5 An easily adhesive optical film was obtained in the same manner as in Example 4, except that the air surface was cooled at 8.3 ° C./sec during the production of the unstretched sheet. Table 1 shows the results
Shown in

[0082]

[Table 1]

[0083]

The optically-adhesive film of the present invention has excellent adhesiveness and transparency and is excellent in flatness after post-processing, so that it can be used for various optical members. In particular, base film for prism lens sheet, base film for backlight, AR
(Anti-reflection) base film for film,
It is suitable for a crush prevention film for CRT and the like.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F100 AK25C AK41A AK41B AK41J AK51B AL01B AL05B BA02 BA03 BA07 BA10A BA10B BA10C BA15 BA16 CC00C EJ38A GB90 JB01 JB14C JK15A JL04 JL11B JN01 YY00B00

Claims (3)

[Claims] 1. A biaxially oriented polyester film in which an easy-adhesion layer comprising a copolymerized polyester resin and a polyurethane-based resin is laminated on at least one side, and the front and back roughness of the film not including the easy-adhesion layer ( SRa) is 10 nm or less, and the absolute value of the difference is 5 nm or less. 2. An easy-to-use optically-adhesive film having an adhesive property of 85% or more when a photocurable acrylic coating layer is provided on the easily-adhesive layer according to claim 1. The adhesiveness described above means a value obtained from the following formula based on a test method according to JIS-K5400, 8.5.1. Adhesiveness (%) = (1−peeled area / evaluated area) × 100 3. The easily adhesive film for optical use according to claim 1, wherein the haze value of the film is 1.0% or less.