JP5261997B2 - Biaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high quality optical laminated polyester film which has excellent heat resistance, excellent light transmittance, mechanical strength, and thickness accuracy, which are inherent in a biaxially stretched film, and exhibits less distortion in heat process, and has inconspicuous interference spots and little flaw when a cured material layer made of ultraviolet curable or electron beam curable acrylic resin is provided on an adhesion modifying layer. <P>SOLUTION: A simultaneously biaxially stretched polyester film is provided with an adhesion modifying layer made of composition comprising the adhesion modifying layer and particles on one side. The biaxially oriented polyester film is characterized in that a plane orientation degree (&Delta;P) is 0.080-0.160, and a thickness unevenness of film is less than 8%. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a biaxially oriented polyester film. Specifically, the present invention is used as a base material for a hard coat film used as a member for liquid crystal displays (hereinafter abbreviated as LCD), PDP applications, etc. It is related with the biaxially-oriented polyester film which is excellent in initial adhesiveness with an optical functional layer, wet heat-resistant adhesiveness, and light resistance.

  Conventionally, polyester films, especially biaxially oriented films of polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical properties, heat resistance, and chemical resistance, and are used for magnetic tapes, photographic films, packaging films, and electronic components. It is widely used as a material for films, metal laminate films, films to be attached to glass surfaces such as glass displays, protective films for various members, release films and the like.

  In recent years, a hard coat layer made of an electron beam, an ultraviolet ray, or a thermosetting resin is laminated on a base made of a transparent plastic film on the front surface of a display such as a touch panel, a computer, a television, or a liquid crystal display device, or a decoration material. Many hard coat films are used. Moreover, as a transparent plastic film of a base material, a transparent biaxially oriented polyester film is generally used, and in order to improve the adhesion between the base material polyester film and the hard coat layer, the intermediate layer is in close contact. In many cases, a property modification layer is provided.

  The hard coat film is required to have temperature, humidity, light durability, transparency, chemical resistance, scratch resistance, antifouling property, and the like. Moreover, since a hard coat film is used for a display, a decoration material, etc., visibility and designability are requested | required. Therefore, in order to suppress glare and iris-like color caused by reflected light when viewed from an arbitrary angle, the antireflection of a multilayer structure in which a high refractive index layer and a low refractive index layer are laminated on top of the hard coat layer. It is common practice to provide a layer.

  However, in recent years, applications such as displays and decorative materials have been required to have a larger screen (larger area) and higher quality, and accordingly, the required level for suppressing iris-like colors (interference fringes) especially under fluorescent lamps. Is getting higher. In addition, fluorescent lamps have become a three-wavelength type for daylight color reproducibility, and interference fringes are more likely to occur. Such interference spots tend to be particularly noticeable when the display is turned off, and this has been a factor that impairs display quality in plasma display panel filters, CRT anti-fracturing films, and the like. Further, even when used as a clear coat on the back surface of the LCD diffusion plate, reduction of interference spots is required. Further, there is an increasing demand for cost reduction by simplifying the antireflection layer. Therefore, it is demanded to suppress interference fringes as much as possible even with a hard coat film alone.

  The interference fringes of the hard coat film have a large difference between the refractive index of the base polyester film (for example, 1.65 for polyethylene terephthalate resin) and the refractive index of the hard coat layer (for example, 1.49 for acrylic resin). It is thought to occur. Therefore, in order to suppress interference fringes, it is desirable to reduce the difference in refractive index.

  As a method of reducing the refractive index difference between the base film and the hard coat layer and preventing the occurrence of interference fringes, there is a method of increasing the refractive index of the hard coat layer by adding metal oxide fine particles to the hard coat layer. It is disclosed (see, for example, Patent Document 1).

JP-A-7-151902

  However, the addition of metal oxide fine particles to the hard coat layer lowers the original functions of the hard coat layer, such as transparency, chemical resistance, scratch resistance, and antifouling properties. Further, when an antireflection layer is further provided on the hard coat layer, it is necessary to optimize the antireflection layer in accordance with the change in the refractive index of the hard coat layer due to the addition of metal oxide fine particles.

  In addition, as another method for suppressing interference fringes in the hard coat layer, an invention in which the width or area ratio of the interference fringes is specified by focusing on the thickness unevenness of a film or the like is disclosed (for example, Patent Documents 2 and 3). reference). Furthermore, paying attention to the back surface reflectance of the film itself, a method of laminating a hard coat having a specific hardness while suppressing the back surface reflectance is also disclosed (for example, see Patent Document 4).

JP 2001-71439 A JP 2002-241527 A JP 2002-210906 A

  However, in the methods described in Patent Documents 2 and 3, it is necessary to strictly control the thickness of each layer, which is problematic in terms of productivity. Moreover, in the method described in Patent Document 4, it is necessary to provide a coat layer having a specific refractive index and a specific thickness on the opposite surface of the hard coat layer of the hard coat film in order to reduce the back surface reflectance.

  On the other hand, the base film generally contains inert inorganic particles and the like in order to improve the slipperiness (slidability). However, when these particles are included in the polyester film, the unevenness of the film surface not only provides easy lubrication but also makes the interference spots less noticeable, but on the other hand, the most important characteristic of the polyester film substrate for optics Tends to hinder transparency. That is, it has been extremely difficult to reduce interference spots while having high transparency.

  Also, as in Patent Document 5, an organic compound having a condensed polycyclic aromatic and a metal element is blended in the adhesion modified layer, the refractive index of the adhesion modified layer is adjusted, and interference fringes are reduced. A method is disclosed. In the configuration described in Patent Document 5, there is a concern about the performance degradation of the adhesion modified layer, and it is necessary to adjust the film thickness of the adhesion modified layer itself with high accuracy in order to reduce interference fringes. Yes, it is not enough in terms of stable production.

JP 2006-175627 A

  As described above, the reason why the interference fringes occur when the hard coat layer is provided on the polyester film provided with the adhesion modifying layer is that of the refractive index of the base polyester film and the hard coat layer. This is because the difference is large. Therefore, it can be considered that interference fringes can be reduced if the refractive index of the polyester film can be simply lowered. When light passes through the medium, it is affected by the molecular structure of the medium. In the case of a polyester film, the refractive index of light is considered to change depending on the molecular orientation state of the long-chain polymer in the film. Therefore, when the molecular orientation state in the polyester film, that is, the degree of plane orientation (ΔP) is low, the refractive index of light is considered to be small.

  The polyester film is generally subjected to stretching about 3 to 5 times in the longitudinal direction and width direction and heat treatment at about 180 to 240 ° C. from the viewpoint of physical properties, chemical resistance and heat resistance. From the viewpoint of physical strength and chemical resistance, it is desirable to have a certain degree of plane orientation (ΔP). However, as the draw ratio in the longitudinal direction and the width direction increases, the degree of plane orientation (ΔP) increases and the refractive index in each direction increases. Further, since the stretching stress increases as the stretching temperature decreases, the degree of plane orientation (ΔP) increases and the refractive index increases. As described in Patent Document 6, when stretching the unstretched film in the longitudinal direction in order to lower the refractive index, the stretching ratio is reduced, and as described in Patent Document 6, stretching in a flat section where stress does not increase Therefore, the strain is not fixed with respect to the stress, the draw ratio varies depending on the location, and the thickness unevenness deteriorates. When transverse stretching is performed using such a uniaxially stretched film having poor thickness unevenness, only the resulting uneven thickness of the biaxially stretched film can be obtained.

Japanese Patent Laid-Open No. 06-210719

  Further, Patent Document 7 describes a polyester film having a low draw ratio, but the degree of plane orientation (ΔP) of the polyester film depends on the drawing temperature, the drawing speed, the drawing ratio, and the heat setting temperature conditions. Therefore, the refractive index of the film does not decrease simply by setting the draw ratio low.

JP 2007-31496 A

  In view of the above problems, the object of the present invention is made of polyester with high crystallinity and has a degree of plane orientation within a specific range, so that the biaxially stretched film inherently has excellent heat resistance and excellent light transmittance. When the hard coat layer made of UV curable or electron beam curable acrylic resin is provided on the adhesion modified layer, which has mechanical strength and thickness accuracy, is less twisted during thermal processing Another object of the present invention is to provide a high-quality laminated polyester film for optics in which interference spots are not noticeable.

  The optical polyester film that can solve the above-described problems is as follows. That is, the first invention in the present invention is a polyester film in which an adhesion modifying layer comprising a composition containing an adhesion modifying resin and particles is provided on at least one surface, and the degree of plane orientation (ΔP) is 0. The biaxially oriented polyester film is characterized in that the film thickness is 0.080 to 0.160 and the thickness unevenness of the film is less than 8%.

A preferred embodiment is shown below.
(A) The heat shrinkage in the film longitudinal direction and width direction at 150 ° C. is 3.0% or less.
(B) The film has a thickness of 50 to 350 μm.
(C) The maximum strain of the orientation main axis measured with a microwave transmission type molecular orientation meter is within 30 degrees.
(D) The polyester film is made of polyethylene terephthalate.
(E) It was obtained by simultaneous biaxial stretching.
(F) A hard coat layer made of an ultraviolet curable or electron beam curable acrylic resin is provided on the surface of the adhesion modified layer of the polyester film of the present invention.

  The laminated polyester film for optics of the present invention has a constitution in which an adhesion modifying layer comprising a composition containing an adhesion modifying resin and particles is provided on at least one side, so there is no need to add particles to the base film. In addition, when laminating a hard coat layer made of an ultraviolet resin or an electron beam curable acrylic resin with excellent transparency, by controlling the degree of plane orientation (ΔP) within a specific range by simultaneous biaxial stretching, There is an advantage that interference spots can be made inconspicuous. In addition, since the thermal dimensional stability is high and the distortion in the physical properties in the width direction is small, a polyester film having good processing characteristics can be provided.

<Characteristics of biaxially oriented polyester film>
(Thickness unevenness)
The biaxially oriented polyester film of the present invention preferably has a thickness variation measured by the following method of 8% or less. 7.0% or less is more preferable, and 6.5% or less is more preferable. In particular, the thickness unevenness when the biaxially oriented polyester film is composed of polyethylene terephthalate is preferably 6.0% or less, and more preferably 5.0% or less. Although it is desirable that the thickness unevenness is small, it is technically difficult to make the thickness unevenness 0.1% or less, and since there is no significant difference in practical quality, the lower limit of the thickness unevenness is 0. It may be 1%.

[Evaluation of thick spots]
A tape-like sample (length 3 m) continuous in the longitudinal stretching direction is collected, and 100-point thickness is measured at a pitch of 1 cm using an electronic micrometer manufactured by Seiko EM Co., Ltd. and Millitron 1240. From the measured values, the maximum value (dmax), the minimum value (dmin), and the average value (d) of the thickness were obtained, and the thickness unevenness (%) was calculated by the following formula. In addition, the measurement was performed 3 times and the average value was calculated | required.
Thickness unevenness (%) = ((dmax−dmin) / d) × 100

  When the thickness unevenness of the film exceeds 8%, when the film is wound on a roll, wrinkles and bumps are likely to occur, and the flatness of the film is impaired. As a result, the luminance of the light exit surface in the backlight unit becomes non-uniform, which is not preferable because the original purpose of the optical film cannot be achieved.

(Plane orientation (ΔP))
It is important that the biaxially oriented film of the present invention has a degree of plane orientation (ΔP) of 0.080 to 0.160. The plane orientation degree (ΔP) is more preferably 0.100 to 0.150, and further preferably 0.110 to 0.140. When the degree of plane orientation (ΔP) exceeds 0.160, when a hard coat agent is applied on the adhesion modifying layer, interference fringes are conspicuous, which is not preferable. On the other hand, when the degree of plane orientation (ΔP) is less than 0.080, the characteristics as a biaxially stretched film are lost, and the mechanical strength is remarkably lowered. Also, the film thickness uniformity deteriorates.

(Maximum strain of orientation main axis)
By lowering the draw ratio and reducing the degree of plane orientation, it is possible to reduce the distortion of the orientation main axis with respect to the width direction of the film. That is, at the normal stretching ratio (3 to 5 times) by successive stretching, the orientation main axis is distorted with respect to the width direction due to the so-called bowing phenomenon at the end in the width direction of the film, so there is a difference in the physical properties of the film in the axial direction. Occurs. However, in the biaxially oriented polyester film of the present invention, since the draw ratio is lowered and the degree of plane orientation is lowered, the distortion of the orientation main axis is small even at the end, thereby reducing the physical property difference in the width direction. The maximum strain of the orientation main axis of the film of the present invention is preferably 30 ° or less. In particular, when the biaxially oriented polyester film is composed of polyethylene terephthalate, the maximum strain of the orientation main axis is preferably 25 ° or less, and more preferably 20 ° or less. When the distortion of the orientation main axis exceeds 30 °, the distortion of twist or deflection and flatness generated during thermal processing increases.

The maximum strain of the alignment main axis in the present invention is determined as follows. A rectangular film having a width of 500 mm in the longitudinal direction and a full width in the width direction is cut out from the roll film. A 100 mm square film is cut out of the film from the longitudinal direction and the center of the film at right angles with respect to either the longitudinal direction or the width direction axis. Here, the both end portions and the central portion are the center portion at the positions of 10% and 90% when the end edge is 0% and the other end edge is 100% with respect to the distance in the film width direction. Corresponds to the 50% position. The orientation angle (θ) of the molecular chain principal axis (orientation principal axis) relative to the film width direction was measured using a MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments. Among them, the largest orientation angle (θ) was used, and the value obtained from the following formula was used as the maximum strain (ξ) of the distribution main axis of the film.
When | θ | ≦ 45 ° ξ = | θ |
When | θ |> 45 ° ξ = | 90 °-| θ ||

(Heat shrinkage)
The thermal contraction rate of the biaxially oriented polyester film of the present invention is preferably 3.0% or less, and 2.0% or less in a heat treatment at 150 ° C. for 30 minutes in both the longitudinal direction and the width direction. More preferably, it is 1.0% or less. When the heat shrinkage rate at 150 ° C. is 3.0% or less, even when the heat processing is performed by a hard coat layer forming process or the like, it can be suitably processed with little twist and deformation.

(Thickness)
The thickness of the biaxially oriented polyester film of the present invention is preferably 50 to 350 μm. The upper limit of the thickness of the film is more preferably 300 μm, and further preferably 250 μm. The intensity | strength preferable as an optical use can be ensured as thickness is 50 micrometers or more. Moreover, it is desirable from the point of cost that thickness is 350 micrometers or less.

  Moreover, when using the biaxially-oriented polyester film of this invention as an optical use film by which high transparency is calculated | required, the minimum of a total light transmittance is 85%, More preferably, it is 88% or more. Moreover, the upper limit with preferable haze is 2.0%, and a more preferable upper limit is 1.5%.

  Furthermore, the biaxially oriented polyester film of the present invention preferably has a tensile strength of 60 MPa or more in both the vertical and horizontal directions from the viewpoint of mechanical strength. In particular, when high mechanical strength is required, the polyester film is preferably composed of polyethylene terephthalate. In this case, the tensile strength is preferably 150 MPa or more in both the vertical and horizontal directions.

(Polyester raw material)
In the present invention, the polyester used for the polyester film may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by condensation polymerization of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid, 2.6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, 1.4-butanediol, and 1.4-cyclohexanedimethanol. . Examples of such polyester include polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, and the like. Among these, polyethylene terephthalate can be suitably used from the viewpoint of physical strength, heat resistance, and chemical resistance.

  On the other hand, examples of the dicarboxylic acid component of the copolyester include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2.6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxylcarboxylic acid, and the like. Examples of the component include one or more of ethylene glycol, diethylene glycol, propion glycol, 1.4-butanediol, 1.4-cyclohexanedimethanol, neopentyl glycol and the like. In any case, the polyester referred to in the present invention refers to a polyester that is polyethylene terephthalate or the like in which 60% by mole or more, preferably 80% or more is an ethylene terephthalate unit.

  In the polyester layer in the present invention, particles can be blended in order to impart slipperiness. The kind of particle | grains mix | blended will not be specifically limited if slipperiness can be provided. Specific examples include particles such as silica, calcium carbonate, magnesium carbonate, kaolin, aluminum oxide, and titanium oxide. Further, heat resistant organic particles can be used as the particles. Examples of the heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like.

The shape of the particles to be used is not particularly limited, and any of a flat shape, a spherical shape, a lump shape, a rod shape, and an aggregate may be used. If necessary, two or more types may be used in combination.

  About the average particle diameter of the particle | grains to be used, it is 0.01-4 micrometers normally, Preferably it is the range of 0.02-3 micrometers. When the average particle size is less than 0.01 μm, the particles tend to aggregate and the dispersibility becomes insufficient. On the other hand, if it exceeds 4 μm, the surface roughness of the film may become too rough.

  Furthermore, the content of the particles in the polyester layer is usually 0.003 to 1% by weight, preferably 0.005 to 0.5% by weight. When the particle content is less than 0.003% by weight, the slipperiness is insufficient and scratches caused by contact with a roll or the like in the process are generated. On the other hand, when it is added exceeding 1% by weight, the transparency of the film becomes insufficient.

  In the case of a polyester film having a three-layer structure obtained by the co-extrusion method, it is desirable to add a polyester film layer containing particles to both outermost layers from the viewpoint of transparency. The total thickness of both outermost layers is usually in the range of 2 to 20 μm, preferably 4 to 18 μm. When the total thickness of both outermost layers is less than 2 μm, the added particles may fall off. On the other hand, if it exceeds 20 μm, the transparency of the film becomes insufficient.

  Moreover, the biaxially-oriented polyester film which does not contain a particle | grain substantially from a highly transparent viewpoint may be sufficient. In this case, scratches caused by contact with the roll in the process are likely to enter the film surface, so it is necessary to pay careful attention to the prevention of dirt on the roll used in the process, the surface roughness, the material, and the film cooling method. It becomes. The term “substantially free of particles” means, for example, in the case of inorganic particles, when inorganic elements are quantified by fluorescent X-ray analysis, they are 50 ppm or less, preferably 10 ppm or less, most preferably the detection limit or less. Means content. This means that even if particles are not actively added to the polyester, contaminants derived from foreign substances, raw material resin, or dirt attached to the line or device in the film manufacturing process will be peeled off and mixed into the film. This is because there are cases.

  In addition to the above-mentioned particles, conventionally known UV absorbers, antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments, etc. may be added to the polyester film in the present invention as necessary. Can do.

  In the case of a polyester film having a three-layer structure obtained by a co-pressing method, a polyester resin pellet as a polyester raw material for the outermost layer (A layer) and the intermediate layer (B layer), and a polyester resin pellet containing particles as required are predetermined. Mix in proportions. Using this as a raw material for each layer, drying and crystallization, respectively, using two extruders, a three-layer manifold or a merge block, the film layers constituting each layer are laminated, and two types 3 from the die The sheet of layers is extruded, extruded into a sheet form from a slit-shaped die, and cooled and solidified on a casting roll to form an unstretched film. When high transparency is required, a polyester raw material that substantially does not contain particles is used for both the A layer and the B layer.

  During melt extrusion, high-precision filtration is preferably performed at any place where the molten resin is kept 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 excellent in removing aggregates and high-melting-point organic substances mainly composed of Si, Ti, Sb, Ge, and Cu. Therefore, it is preferable. Further, the filter particle size (initial filtration efficiency 95%) of the filter medium is preferably 20 μm or less, particularly preferably 15 μm or less. When the filter particle size of the filter medium (initial filtration efficiency 95%) exceeds 20 μm, foreign matters having a size of 20 μm or more cannot be sufficiently removed. By performing high-precision filtration of molten resin using a filter medium having a filter particle size (initial filtration efficiency of 95%) of 20 μm or less, productivity may be reduced, but a film with few protrusions due to coarse particles is obtained. This is an important process. Here, the initial filtration efficiency refers to a numerical value measured by ANSI / B93.36-1973.

(Adhesion modified layer)
The polyester film of the present invention preferably has an adhesion modified layer on at least one surface, and may further have an adhesion modified layer on both sides. A preferable coating amount after drying is in the range of 0.005 to 0.20 g / m ² . By providing the coating layer on the film surface, generation of reflected light on the film surface can be suppressed, and the total light transmittance can be further increased. Moreover, when performing a hard coat process, it is necessary to provide easy adhesion for adhesion modification.

  When the coating solution for forming an adhesion modified layer is applied to an unstretched sheet, it can be selected from any known method, for example, reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll Examples thereof include a brush method, a spray coating method, an air knife coating method, a wire bar coating method, a pipe doctor method, an impregnation coating method, a curtain coating method, and the like, and these methods are applied alone or in combination.

  The adhesion modifying resin constituting the adhesion modifying layer is a copolymer polyester resin, polyurethane resin, and acrylic from the viewpoint of ensuring better adhesion to other members in optical polyester film applications. It is preferable that the main component is one or more selected from the group consisting of resin. These resins are also recommended from the viewpoint of suppressing the generation of reflected light on the film surface. The “main component” means that at least one of the resins listed above is 50% by mass or more in 100% by mass of the resin constituting the layer.

  Regarding the adjustment of the coating solution used for forming the adhesion improving layer, an example of a coating solution comprising a copolymerized polyester resin and a polyurethane resin will be described below.

(Copolymerized polyester resin)
The copolymerized polyester resin used in the adhesion modified layer of the present invention has a branched glycol component as a constituent component. The branched glycol component referred to here 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 branched glycol component is contained in the total glycol component in a proportion of preferably 10 mol% or more, more preferably 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, 1,4 cyclohexanedimethanol or the like may be used.

  As the dicarboxylic acid component contained as a constituent component in the copolymer polyester resin, terephthalic acid and isophthalic acid are most preferable. If the amount is small, other dicarboxylic acids; diphenylcarboxylic acid and 2,6-naltalenedicarboxylic acid aromatic dicarboxylic acid may be added and copolymerized.

  In addition to the dicarboxylic acid component, 5-sulfoisophthalic acid is preferably used in the range of 1 to 10 mol% in order to impart water dispersibility. For example, sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfo Mention may be made of naphthaleneisophthalic acid-2,7-dicarboxylic acid and 5- (4-sulfophenoxy) isophthalic acid and salts thereof.

(Polyurethane resin)
The polyurethane resin used in the adhesion modified 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), a heat-reactive water-soluble type Examples include urethane. Examples of the isocyanate group blocking agent include bisulfites and sulfonic acid group-containing phenols, alcohols, lactam oximes and active methylene compounds. The blocked isocyanate group makes the urethane prepolymer hydrophilic or water-soluble. When heat energy is applied to the resin during drying or heat setting during film production, the blocking agent is released from the isocyanate group, so the resin fixes a water-dispersible copolyester resin mixed in a self-crosslinked stitch. And reacts with the terminal groups of the resin. The resin under preparation of the coating solution is hydrophilic and has poor water resistance, but when the thermal reaction is completed by coating, drying and heat setting, the hydrophilic group of the urethane resin, that is, the blocking agent is released, so the water resistance is good. A coating film is obtained. Among the above blocking agents, bisulfites are most preferred as those that are suitable for heat treatment and heat treatment and are widely used industrially.

  The chemical composition of the urethane prepolymer used in the above resin is (1) an organic polyisocyanate having two or more active hydrogen atoms in the molecule, or a molecular weight having at least two active hydrogen atoms in the 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 has a terminal isocyanate group.

  The compound (1) generally known is a compound containing two or more hydroxyl groups, carboxyl groups, amino groups or mercapto groups in the terminal or molecule, and particularly preferred compounds include polyether polyols. And polyether ester polyols.

  Examples of polyether polyols are compounds obtained by polymerizing alkylene oxides such as ethylene oxide and propylene oxide, styrene oxide and epichlorohydrin, or the like, or random polymerization, block polymerization, or addition polymerization to a polyhydric alcohol. There are compounds. Examples of the polyester polyol and the polyether ester polyol mainly include linear or branched compounds. Polyvalent saturated or unsaturated carboxylic acids such as succinic acid, adipic acid, phthalic acid and maleic anhydride, or the carboxylic acid anhydride, ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 1 Condensation with polyvalent saturated and unsaturated alcohols such as 1,6-hexanediol and trimethylolpropane, polyalkylene ether glycols such as relatively low molecular weight polyethylene glycols and polypropylene glycols, or mixtures of these alcohols Can be obtained.

Further, polyesters obtained from lactones and hydroxy acids can be used as the polyester polyol, and polyether esters obtained by adding ethylene oxide or propylene oxide to a polyester produced in advance can also be used. Examples of the organic polyisocyanate (2) include isomers of toluylene diisocyanate, aromatic diisocyanates such as 4,4-diphenylmethane diisocyanate, aromatic aliphatic diisocyanates such as xylylene diisocyanate, isophorone diisocyanate and 4,4. -Alicyclic diisocyanates such as dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and aliphatic diisocyanates such as 2,2,4-trimethylhexamethylene diisocyanate, or a single or a plurality of these compounds with trimethylolpropane and the like in advance. Examples include added polyisocyanates.

  Examples of the chain extender having at least two active hydrogens in (3) above include glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, and 1,6-hexanediol, glycerin, trimethylolpropane, and Examples include polyhydric alcohols such as pentaerythritol, diamines such as ethylenediamine, hexamethylenediamine, and piperazine, amino alcohols such as monoethanolamine and diethanolamine, thiodiglycols such as thiodiethylene glycol, and water. In order to synthesize the urethane polymer of the above (3), it is usually 5 minutes to several times at a temperature of 150 ° C. or less, preferably 70 to 120 ° C., by a single-stage or multi-stage isocyanate polyaddition method using the chain extender. Let react for 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. Further, the content of free isocyanate groups may be 10% by weight or less, but in view of the stability of the urethane polymer aqueous solution after being blocked, it is preferably 7% by weight or less.

  The urethane prepolymer obtained is preferably blocked using bisulfite. Mix with aqueous bisulfite solution and allow reaction to proceed with good agitation for about 5 minutes to 1 hour. The reaction temperature is preferably 60 ° C. or lower. Thereafter, it is diluted with water to an appropriate concentration to obtain a heat-reactive water-soluble urethane composition. When the composition is used, it is prepared to have an appropriate concentration and viscosity. However, when heated to about 80 to 200 ° C., the bisulfite of the blocking agent is dissociated and the active isocyanate group is regenerated, so that the prepolymer A polyurethane polymer is produced by a polyaddition reaction that occurs within or between the molecules of the polymer, and has the property of causing addition to other functional groups.

  As an example of the resin (B) containing a block-type isocyanate group described above, a trade name Elastron manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. is typically exemplified. Elastolone is a compound in which an isocyanate group is blocked with sodium bisulfite, and is water-soluble due to the presence of a carbamoylsulfonate group having strong hydrophilicity at the molecular end.

  When the coating liquid is prepared by mixing the copolymerized polyester resin (A) containing a branched glycol component and the resin (B) containing a block type isocyanate group used in the present invention, the resin (A) and the resin The weight ratio of (B) is preferably (A) :( B) = 90: 10 to 10:90, more preferably (A) :( B) = 80: 20 to 20:80. If the ratio of the said resin (A) with respect to solid content weight is less than 10%, the applicability | paintability to a polyester film will be unsuitable, and the adhesiveness between a surface layer and this film will become inadequate. On the other hand, when the content is less than 10%, practical adhesiveness cannot be obtained in a hard coating agent made of an ultraviolet curable or electron beam curable acrylic resin.

  In order to promote the thermal crosslinking reaction, a catalyst may be added to the aqueous coating solution used in the present invention, such as various inorganic substances, salts, organic substances, alkaline substances, acidic substances and metal-containing organic compounds. These chemicals are used. Moreover, in order to adjust pH of aqueous solution, you may add an alkaline substance or an acidic substance.

  When applying the aqueous coating solution to the surface of the base film, a known anionic surfactant and nonionic surfactant are required to increase the wettability of the film and coat the coating solution uniformly. An amount can be added and used. As the solvent used in the coating solution, alcohols such as ethanol, isopropyl alcohol and benzyl alcohol may be mixed in addition to water until the ratio of the total coating solution is less than 50% by weight. Furthermore, if it is less than 10 weight%, you may mix in the range which can melt | dissolve organic solvents other than alcohol. However, the total of alcohols and other organic solvents in the coating solution is less than 50% by weight.

  If 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 appearance of the coating film is improved as compared with the case of using only water. If it exceeds 50% by weight, the evaporation rate of the solvent is fast, the coating solution concentration changes during coating, the viscosity rises and the coating property decreases, and there is a risk of causing poor appearance of the coating film, Furthermore, there is a risk of fire.

  In order to increase the transparency of the film, if the particles are not contained in the intermediate layer (B layer) or only a small amount is contained in the outermost layer (A layer) to the extent that the transparency is not hindered, the film easily slips. May be insufficient and handling may be deteriorated. Therefore, you may add the particle | grains aiming at slipperiness | lubricity provision to said adhesive improvement layer. For these particles, it is important to use particles having an extremely small average particle diameter equal to or smaller than the wavelength of visible light in order to ensure transparency.

  Examples of the particles 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; crosslinked polymer particles; calcium oxalate And organic particles. Silica is particularly preferable when the coating layer is formed mainly of the copolymer polyester resin. Since silica has a refractive index relatively close to that of polyester, it is most preferable in that it can secure a biaxially stretched film for optics that is more excellent in transparency.

  The average particle size (SEM observation particle size) of the particles to be included in the adhesion modified layer is 0.005 to 1.0 μm, which ensures transparency, handling properties, and scratch resistance of the optical polyester film. It is preferable from the point. The upper limit of the average particle size of the particles is more preferably 0.5 μm, particularly preferably 0.2 μm, from the viewpoint of transparency. Further, the lower limit of the average particle diameter of the particles is more preferably 0.03 μm from the viewpoints of handling properties and scratch resistance.

In addition, the measurement of the average particle diameter of said particle | grain is performed with the following method.
Take a picture of the particles with a scanning electron microscope (SEM), at a magnification such that the size of one smallest particle is 2-5 mm, the maximum diameter of 300-500 particles (between the two most distant points) The average value is taken as the average particle diameter. Moreover, when calculating | requiring the average particle diameter of the particle | grains contained in an adhesive property modification layer, it apply | coated with the magnification | multiplying_factor which makes the size of one smallest particle | grain 2-5mm using a transmission electron microscope (TEM). The cross section of the film is photographed, and the maximum diameter of the particles existing in the cross section of the adhesion modified layer is determined. The average particle diameter of the particles composed of aggregates is obtained by taking 300 to 500 cross-sections of the adhesion modified layer of the coated film using an optical microscope at a magnification of 200 times and measuring the maximum diameter.

  The content of the particles of the adhesion modified layer is 0.1 to 60% by mass with respect to the total amount of the constituent components of the adhesion modified layer. From the viewpoint of ensuring scratch resistance. The upper limit of the content of particles is more preferably 50% by mass, particularly preferably 40% by mass, from the viewpoints of transparency and adhesion. Further, the lower limit of the content of the particles is more preferably 1% by mass from the viewpoints of handling properties and scratch resistance.

  Two or more kinds of the particles may be used in combination, and the same kind of particles having different particle sizes may be blended, but in any case, the average particle size of the whole particles and the total content are within the above range. Is preferably satisfied.

  Since the biaxially oriented polyester film of the present invention has a low degree of plane orientation and a low refractive index, the occurrence of interference spots can be suppressed even if a hard coat layer having a low refractive index is provided on the surface of the adhesion modified layer. As the hard coat agent used in the present invention, an ultraviolet curable or electron beam curable acrylic resin is suitably used from the viewpoint of suppression of interference spots and production efficiency. A commercially available resin can be suitably used. Examples of such are Seika Beam EXF01 (Dainippon Seika) and Z7501 (JSR).

(Production method of biaxially oriented polyester film)
The method for obtaining the biaxially oriented polyester film in the present invention is preferably a simultaneous biaxial stretching method. That is, in order to lower the refractive index of the base film to such an extent that interference spots are suppressed when a hard coat layer having a refractive index of about 1.49 is provided, the plane orientation indicating the orientation of the polymer constituting the film The degree (ΔP) is preferably small. The degree of plane orientation (ΔP) can be reduced by lowering the draw ratio. However, in the biaxial stretching method, when stretching is performed at a lower stretching ratio, the stretching in the flat section where the stress does not increase with respect to the strain in Patent Document 7 is performed, so the first-axis stretching is performed against the strain. Since the stretching is performed in a flat section where the stress does not increase, the strain is not fixed with respect to the stress, the stretching ratio varies depending on the location, and the thickness unevenness deteriorates.

  Simultaneous biaxial stretching is suitable as a method for solving this problem and obtaining a product with good thickness unevenness while having a low degree of plane orientation. The reason for this is that the conventional sequential stretching is performed in a flat section where the stress does not increase with respect to the strain, so the strain does not become constant with respect to the stress and the thickness unevenness deteriorates. Because the film is oriented in the transverse direction at the same time in the transverse direction, the film is also oriented in the direction perpendicular to the stretching direction. In stretching, stretching is performed in a section where stress increases with respect to strain. For this reason, with respect to thickness unevenness, even in a region where the degree of plane orientation is low, which is a region deteriorated by sequential biaxial stretching, a product can be obtained without deterioration of the thickness unevenness by simultaneous biaxial stretching.

  However, in order to reduce the refractive index of the base film to such an extent that interference spots are suppressed, as in Patent Document 8, simply reducing the stretch ratio causes thickness spots to a degree that is not problematic for practical optical use. It was not possible to suppress it.

  In the production of a biaxially oriented polyester film by simultaneous biaxial stretching, the present inventor has an important relationship between the stretching ratio, the stretching speed, and the stretching temperature in order to obtain a polyester film having a small plane orientation and a small thickness unevenness. As a result, the present invention was achieved by highly controlling the stretching ratio, stretching speed and stretching temperature. That is, the lower the stretching speed and the higher the stretching temperature, the lower the orientation of the long-chain polymer and the lower the degree of plane orientation (ΔP). Therefore, in order to reduce the degree of plane orientation (ΔP), it is possible to produce a biaxially oriented polyester film with less thickness unevenness by not only reducing the draw ratio but also highly controlling the drawing speed and drawing temperature. became. Hereinafter, although each will be described in detail, the biaxially oriented polyester film having the characteristics of the present invention is included in the scope of the present invention even if it is obtained by a method other than the following method.

(1) Stretch ratio It is important that the above-described biaxial stretching is performed at a stretch ratio of 2.5 times or more in the longitudinal, lateral and both directions. In addition, the draw ratio defined by this invention is the actual draw ratio by which the film was actually extended | stretched. This stretch ratio can be grasped by writing a mass change rate per unit area before and after each stretching step and a lattice-shaped magnification marker on an unstretched film. If the draw ratio in either the machine direction or the transverse direction is less than 2.5 times, the degree of plane orientation (ΔP) becomes too low, and the original excellent heat resistance and mechanical strength of the biaxially stretched film cannot be obtained. . In addition, the film thickness uniformity is significantly deteriorated. The lower limit of the preferred stretching ratio in the present invention is 2.6 times, and the more preferred lower limit is 2.7 times. The preferable upper limit of the draw ratio is 4.0 times, the more preferable upper limit is 3.5 times, and the particularly preferable upper limit is 3.3 times. When the draw ratio exceeds 4.0 times, the degree of surface orientation increases, and interference spots tend to occur when a hard coat is provided.

(2) Stretching speed In the biaxial stretching in the present invention, it is particularly important to perform stretching in both the longitudinal and transverse directions at a stretching speed of less than 80% / second, more preferably at a stretching speed of 70% / second or less. It is. The stretching speed in the present invention represents the deformation rate of the film per unit time based on the dimensions of the unstretched film, and the stretching speed in the machine direction and the transverse direction (unit:% / second) is Each is defined by the following formula.

  Longitudinal drawing speed (% / sec) = Acceleration during film running (m / sec / sec) ÷ Unstretched film speed (m / sec) × 100

  Stretching speed in the transverse direction (% / second) = width change rate per second (m / second) ÷ width of unstretched film (m) × 100

  Then, all stretching in the machine direction and transverse direction from the start of stretching to the end of stretching is completed at a stretching speed of less than 80% / second. By making the stretching speed less than 80% / second, it is possible to stably produce a product having a surface light distribution of 0.080 to 0.160 while using crystalline polyester as a matrix polymer. It becomes. As a result, the biaxially stretched polyester has high total light transmittance and reduced interference fringes generated when a cured product layer made of an ultraviolet curable or electron beam curable acrylic resin is provided on the surface of the adhesion modified layer. The film can be manufactured with excellent thickness accuracy.

  On the other hand, the lower limit of the stretching speed is not limited, but if the stretching speed is slowed more than necessary, it is not preferable because the production of the film on an industrial scale decreases the productivity of the film or requires excessive capital investment. . Therefore, in the present invention, the maximum stretching speed from the start of stretching to the end of stretching is preferably 3% / second or more, and more preferably 5% / second or more.

(3) Stretching temperature When polyethylene terephthalate or a copolymer thereof is used as a film material, the preferred stretching temperature is 96 ° C to 120 ° C. When the stretching temperature (maximum temperature) exceeds 120 ° C., it becomes difficult to control the degree of plane orientation of the film to 0.080 or more, and physical characteristics peculiar to the biaxially oriented polyethylene film cannot be obtained. Furthermore, the uniformity such as the thickness accuracy of the film also decreases. On the other hand, when the stretching temperature (maximum temperature) is less than 96 ° C., it is difficult to uniformly control the plane orientation degree of the film to 0.160 or less. A more preferable stretching temperature is 98 ° C to 118 ° C, and a more preferable stretching temperature is 100 ° C to 115 ° C.

  The heat treatment temperature of the film is preferably in the range of 200 ° C. to 235 ° C., and the heat treatment time is preferably in the range of 10 seconds to 100 seconds. Furthermore, treatment at 210 to 225 ° C. is preferable. When heat treatment is performed at a temperature higher than 235 ° C., the distortion of the orientation main axis increases, and the twist and deflection generated during the heat processing and the distortion of planarity increase. When the heat treatment temperature is 200 ° C. or lower, the heat treatment is insufficient, and as a result, the thermal stability is deteriorated. Moreover, you may perform the relaxation process of the vertical direction and / or a horizontal direction simultaneously with heat processing or after heat processing.

  The heat treatment temperature of the film is preferably in the range of 200 ° C. to 235 ° C., and the heat treatment time is preferably in the range of 10 seconds to 100 seconds. Furthermore, treatment at 210 to 225 ° C. is preferable. When heat treatment is performed at a temperature higher than 235 ° C., the distortion of the orientation main axis increases, and the twist and deflection generated during the heat processing and the distortion of planarity increase. When the heat treatment temperature is 200 ° C. or lower, the heat treatment is insufficient, and as a result, the thermal stability is deteriorated. Moreover, you may perform the relaxation process of the vertical direction and / or a horizontal direction simultaneously with heat processing or after heat processing.

  As a biaxial stretching machine that can control the stretching speed in the machine direction and the transverse direction as described above, it guides to the tenter while holding both ends of the film with clips, and controls the width between clips and the transport speed of clips. Thus, a tenter type simultaneous biaxial stretching machine equipped with a mechanism capable of continuous stretching in both the longitudinal and lateral directions is suitable. As long as the equipment has this function, the clip transport mechanism is optional and is not particularly limited, but a conventionally known apparatus such as a pantograph system, a linear motor system, or a screw system can be adopted.

  Next, the effect of this invention is demonstrated using an Example and a comparative example. First, the evaluation method of the characteristic values used in the present invention is shown below.

(1) Measurement of total light transmittance and haze (cloudiness value) In accordance with JIS K 7105 “Testing methods for optical properties of plastics”, a total light transmittance was measured using a haze meter (Nippon Denshoku model TNDH2000). The haze was measured.

(2) Film Refractive Index In accordance with JIS K 7142 “Plastic Refractive Index Measuring Method”, a polarizing plate is attached to an eyepiece using an Abbe refractometer 4T manufactured by Atago Co., Ltd. Each was adjusted, and the refractive index (Nz) in the film thickness direction, the refractive index (Ny) in the width direction, and the refractive index (Nx) in the longitudinal direction were measured. Jodomethane was used as an intermediate solution. The refractive index in each direction was measured on both sides of the film with n = 3 for each sample, and the average value was taken as the refractive index in each direction. Here, the width direction means a direction perpendicular to the roll unwinding direction, and the longitudinal direction means a direction parallel to the roll unwinding direction. The degree of plane orientation (ΔP) was determined by the following formula.
ΔP = (Nx + Ny) / 2−Nz

(3) Thermal contraction rate In the direction to be measured, the film is cut into a width of 10 mm and a length of 250 mm, marked at intervals of 200 mm, and the distance (A) between the marks is measured under a constant tension of 5 gf. Next, the film is placed in an oven in an atmosphere of 150 ° C., subjected to heat treatment at 150 ± 3 ° C. for 30 minutes under no load, and then the mark interval (B) is measured under a constant tension of 5 gf. The thermal shrinkage rate was calculated from the following formula.
Thermal contraction rate (%) = (A−B) / A × 100

(4) Tensile strength Measured according to JIS C 2318-1997 5.3.3 “Tensile strength and elongation”.

(5) Evaluation of thickness spots A tape-like sample (3 m in length) continuous in the longitudinal direction was collected, and a thickness of 300 points was measured at a 1 cm pitch using a Seiko EM electronic micrometer, Millitron 1240. To do. From the measured values, the maximum value (dmax), the minimum value (dmin), and the average value (d) of the thickness were obtained, and the thickness unevenness (%) was calculated by the following formula. In addition, the measurement was performed 3 times and the average value was calculated | required.
Thickness unevenness (%) = ((dmax−dmin) / d) × 100

(6) Distortion of orientation main axis
A rectangular film having a width of 500 mm in the longitudinal direction and a full width in the width direction is cut out from the roll film. With respect to the film, a 100 mm square film is cut out of the film specimen from both ends and the center with respect to the width direction at a right angle with respect to either the longitudinal direction or the width direction axis. The both end portions and the central portion are 10% and 90% at both ends when the edge is 0% and the other edge is 100% with respect to the distance in the film width direction. It corresponds to the position of 50%. The orientation angle (θ) of the molecular chain principal axis (orientation principal axis) relative to the film width direction was measured using a MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments. Among them, the largest orientation angle (θ) was used, and the value obtained from the following formula was used as the maximum strain (ξ) of the distribution main axis of the film.
When | θ | ≦ 45 ° ξ = | θ |
When | θ |> 45 ° ξ = | 90 °-| θ ||

(7) Interference fringe evaluation method The obtained film was cut into an area of 10 cm × 15 cm, and a hard coat agent (Seika Beam EXF01, manufactured by Dainichi Seika Co., Ltd.) was applied to the surface of the adhesion modified layer of the film obtained in Examples and Comparative Examples. (B)) was applied with a # 8 wire bar to a dry thickness of 3 μm, dried at 70 ° C. for 1 minute to remove the solvent, then 200 mJ / cm ² with a high-pressure mercury lamp, irradiation distance 15 cm, traveling speed 5 m / min. The hard coat agent was cured under the above conditions to form a hard coat layer having a thickness of 3 μm.

Next, a black glossy tape is attached to the surface opposite to the hard coat surface of the film to make it easy to see, and from the hard coat surface side of the film, a three-wavelength light (National Parrook, three-wavelength daylight white (F.L 15EX-N 15W )), And the reflected light was observed visually from above. The results of visual observation are ranked according to the following criteria.
○: Almost no interference spots can be confirmed ○
△: Interference fringes confirmed to be thin enough to cause no problem △
×: Interference fringes clearly observed ×

(8) Evaluation of film twist amount during heat processing A rectangular film having a width of 500 mm in the longitudinal direction and a full width in the width direction is cut out from the roll film. The film was cut into a sheet of 150 mm in the longitudinal direction and 150 mm in the width direction at three positions, both ends and the center with respect to the width direction, and heat-treated at 120 ° C. for 30 minutes in an unloaded state. . The both end portions and the central portion are 10% and 90% at both ends when the edge is 0% and the other edge is 100% with respect to the distance in the film width direction. It corresponds to the position of 50%. The film twisted by heating is placed on a horizontal glass plate with the convex part down, and the vertical distance between the glass plate and the lower end of the four corners of the rising film is measured using a ruler in units of a minimum scale of 0.5 mm. Measurement was made, and the maximum value among the measured values at these four locations was taken as the sample film twist amount. Three samples were prepared at each position, the same measurement was performed on these samples, and the average value of the twist amount of the sample film was defined as the film twist amount. In addition, the case where twist amount was 1 mm or less was set to (circle), 1.1-2.0 mm to (triangle | delta), and 2.1 mm or more was set to x.

Example 1
(1) Production method of polyester (M1) The temperature of the esterification reaction can was raised, and when it reached 200 ° C, a slurry consisting of 86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol was charged. While stirring, 0.017 parts by mass of antimony trioxide and 0.16 parts by mass of triethylamine were added as catalysts. Next, the pressure was increased and the pressure esterification reaction was performed under the conditions of a gauge pressure of 3.5 kgf / cm ² and 240 ° C. Thereafter, the inside of the esterification reaction vessel was returned to normal pressure, and 0.071 part by mass of magnesium acetate tetrahydrate and then 0.014 part by mass of trimethyl phosphate were added. Furthermore, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 part by mass of trimethyl phosphate and then 0.0036 part by mass of sodium acetate were added. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can, gradually heated from 260 ° C. to 280 ° C. under reduced pressure, and subjected to a polycondensation reaction at 285 ° C.

  After completion of the polycondensation reaction, filtration is performed with a nylon filter having a filtration particle size of 5 μm (initial filtration efficiency of 95%), extruded from a nozzle in a strand shape, and preliminarily filtered (pore diameter: 1 μm or less) using cooling water. Then, it was cooled and solidified, and cut into pellets. The obtained polyester (M1) has a heat of crystal fusion of 35 mJ / mg, a melting point of 256 ° C., an intrinsic viscosity of 0.616 dl / g, an Sb content of 144 ppm, an Mg content of 58 ppm, a P content of 40 ppm, and a color L The value was 56.2, the color b value was 1.6, and inert particles and internally precipitated particles were not substantially contained.

(2) Manufacturing method of polyester (M2) In the manufacturing method of polyester (M1), it is the same except having added 0.3 mass part of the silica particle to which 2.5 micrometers of average particle diameter (Coulter counter method) was disperse | distributed to ethylene glycol. Polyester (M2) was obtained by the method.

(3) Production method of copolymerized polyester (M3) In a first esterification reaction can containing a reaction product in advance, 100 mol% of high-purity terephthalic acid (TPA) as a dicarboxylic acid component and ethylene glycol (glycol component) EG) 70 mol%, neopentyl glycol (NPG) 30 mol%, and a slurry in which the molar ratio of all glycol components to dicarboxylic acid components is 2.0, so that the production polymer is 1 ton / h. Continuously fed. Furthermore, the antimony trioxide was continuously supplied to the first esterification reaction can as an ethylene glycol solution of 12 g / L so that the Sb content was 0.025 mol% with respect to the produced polymer. While stirring at 0.05 MPa, the reaction was carried out at about 250 ° C. for an average residence time of about 3 hours.

  This reaction product was transferred to a second esterification reaction can, and the reaction was carried out for about 1 hour as an average residence time at about 260 ° C. with stirring at a can internal pressure of 0.05 MPa. Next, this reaction product was transferred to a third esterification reaction can, and the reaction was carried out to a predetermined reactivity at about 260 ° C. with stirring at a can internal pressure of 0.05 MPa.

  The oligomer obtained at this time had an acid value of the end group of 380 eq / ton. To this oligomer, magnesium acetate tetrahydrate in an ethylene glycol solution of 50 g / L was used, and trimethyl phosphate was 65 g / L so that the Mg content (M) was 0.17 mol% with respect to the produced polymer. As an ethylene glycol solution, sodium acetate as a 10 g / L ethylene glycol solution so that the P content (P) is 0.079 mol% (M / P = 2.2; molar ratio) with respect to the produced polymer. Separately, cobalt acetate tetrahydrate as a 50 g / L ethylene glycol solution so that the Na content is 0.018 mol% with respect to the produced polymer, and 0.0035 mol% with respect to the produced polymer. Were continuously fed to the third esterification reaction can through the feed port.

  This esterification reaction product is continuously supplied to the first polycondensation reaction vessel, and is stirred at about 265 ° C. and 35 hPa for about 1 hour, and then stirred in the second polycondensation reaction vessel at about 270 ° C. and 5 hPa. The polycondensation was carried out for about 1 hour at about 280 ° C. and 0.5 to 1.5 hPa with stirring in the final polycondensation reaction vessel for about 1 hour. After the polycondensation, it was passed through a tubular polymer filter with a leaf made of stainless steel long fibers having a filtration particle size of 60 μm (initial filtration efficiency 95%). Next, the molten resin was extracted in a strand form from the die, cooled with water in a water tank, and then cut into a chip shape to obtain a copolymerized polyester (M3) having an intrinsic viscosity (IV) of 0.74 dl / g.

(4) Preparation of coating solution (M4) 95 parts by mass of dimethyl terephthalate, 95 parts by mass of dimethyl isophthalate, 35 parts by mass of ethylene glycol, 145 parts by mass of neopentyl glycol, 0.1 part by mass of zinc acetate and 0.1% of antimony trioxide A mass part was charged in a reaction vessel, and a transesterification reaction was performed at 180 ° C. over 3 hours. Next, 6.0 parts by mass of 5-sodium sulfoisophthalic acid was added, and esterification was performed at 240 ° C. over 1 hour, and then at 250 ° C. under reduced pressure (10 to 0.2 mmHg) over 2 hours. A polycondensation reaction was performed to obtain a copolymerized polyester resin having a number average molecular weight of 19,500 and a softening point of 60 ° C.

  7.5 parts by mass of a 30% by mass aqueous dispersion of the obtained copolyester resin and a 20% by mass aqueous solution of a self-crosslinking polyurethane resin containing an isocyanate group blocked with sodium bisulfite (manufactured by Daiichi Kogyo Seiyaku) , Elastron H-3) 11.3 parts by mass, Elastron catalyst (Daiichi Kogyo Seiyaku, Cat 64) 0.3 parts by mass, water 39.8 parts by mass and isopropyl alcohol 37.4 parts by mass, respectively. Mixed.

  Furthermore, colloidal silica (manufactured by Nissan Chemical Industries, Snowtex OL; average particle) as 10 parts by mass of a 10% by weight aqueous solution of a fluorine-based nonionic surfactant (manufactured by Dainippon Ink and Chemicals, MegaFuck F142D) and particles A 2.3 mass parts of a 20 mass% aqueous dispersion having a diameter of 40 nm), and 3.5 mass% aqueous dispersion of dry process silica (Nippon Aerosil, Aerosil OX50; average particle diameter 200 nm, average primary particle diameter 40 nm) as particles B 0.5 parts by mass of the liquid was added. Next, the pH of the coating solution is adjusted to 6.2 with a 5% by weight aqueous sodium bicarbonate solution, and the solution is precisely filtered with a felt type polypropylene filter having a filtration particle size of 10 μm (initial filtration efficiency: 95%). It was adjusted.

(4) Production of biaxially oriented polyester film As raw materials for both outermost layers (B), 90 parts by mass of polyester (M1) and 10 parts by mass of polyester (M2) were each dried at 135 ° C. under reduced pressure for 6 hours (1 Torr). Then, they were mixed and supplied to the extruder 2. Further, 100 parts by mass of polyester (M1) as a raw material for the support layer (A) was dried under reduced pressure (1 Torr) at 135 ° C. for 6 hours, and then supplied to the extruder 1. The raw material supplied to the extruder 2 and the extruder 1 has a resin temperature of 280 ° C. until the melting part, kneading part, polymer tube, gear pump, and filter of the extruder, and 275 ° C. in the subsequent polymer tube. It laminated | stacked using the seed 3 layer confluence | merging block, and melt-extruded in the sheet form from the nozzle | cap | die. In addition, the thickness ratio of the (A) layer and the (B) layer was controlled using the gear pump of each layer so that it might become B: A: B = 7: 84: 7. In addition, a filter material of a sintered stainless steel having a filtration particle size of 10 μm (initial filtration efficiency: 95%) was used for each of the filters. The temperature of the die was controlled so that the temperature of the extruded resin was 275 ° C.

  Then, the extruded resin was cast on a cooling drum having a surface temperature of 30 ° C. and adhered to the surface of the cooling drum using an electrostatic application method to be cooled and solidified, thereby producing an unstretched film having a thickness of about 1.15 mm. .

Subsequently, the adhesive property modification layer was apply | coated to the single side | surface of the obtained unstretched film. As the coating solution, a solution obtained by subjecting the coating solution (M4) to microfiltration with a felt type polypropylene filter medium having a filtration particle size of 5 μm (initial filtration efficiency of 95%) was used. Moreover, the reverse roll method was employ | adopted for the coating method, and it apply | coated so that the coating amount after drying might be 0.01 g / m < ² >. Thereafter, in a drying furnace divided into two zones, the coated surface was dried at a first zone temperature of 100 ° C., a wind speed of 20 m / second, for 10 seconds, at a second zone temperature of 70 ° C., a wind speed of 20 m / second, for 10 seconds.

  Next, both ends of the unstretched film having the coating layer were held by clips and guided to a simultaneous biaxial stretching machine, and a biaxially stretched film was prepared under the following conditions.

  After preheating for 24 seconds with hot air of 112 ° C., simultaneous biaxial stretching was performed at 105 ° C. at a stretching ratio of 2.7 times in the machine direction and 3.0 times in the transverse direction. At this time, the stretching ratio in the longitudinal and lateral directions was controlled so that the maximum stretching speed in the longitudinal direction was 8.9% / second and the maximum stretching speed in the lateral direction was 10.4% / second. Next, heat treatment was performed at 220 ° C. for 12 seconds with a constant tenter width and a constant clip interval. Further, in the process of cooling to 60 ° C. over 15 seconds, 3% relaxation treatment was performed in the vertical and horizontal directions.

  Next, the clip that had gripped both ends of the film was released, and both ends of the film were trimmed and wound into a roll to produce a biaxially stretched film having a thickness of about 125 μm. In addition, when the actual draw ratio was measured with a grid-like magnification marker written on the unstretched film, the MD direction draw ratio was an average of 2.8 times, and the TD draw ratio was an average of 3.1 times. Table 1 shows the characteristics of the biaxially stretched film obtained in Example 1.

Example 2
The speed and discharge amount of the cooling drum when the resin extruded in Example 1 was cast on the cooling drum were finely adjusted to obtain an unstretched film having a coating layer. After gripping both ends of the obtained film with a clip and guiding it to a simultaneous biaxial stretching machine, after preheating for 27 seconds with hot air of 112 ° C., at 105 ° C., 3.0 times in the vertical direction and in the horizontal direction 3. Simultaneous biaxial stretching at a stretching ratio of 2 times. At this time, the longitudinal and lateral stretching ratios were controlled so that the maximum stretching speed in the longitudinal direction was 10.2% / second and the maximum stretching speed in the lateral direction was 11.2% / second. Otherwise, a biaxially stretched film having a thickness of about 110 μm was produced in the same manner as in Example 1. In addition, when the actual draw ratio was measured with a lattice-like magnification marker written on the unstretched film, the MD direction draw ratio was an average of 3.0 times, and the TD draw ratio was an average of 3.3 times. The characteristics of the biaxially stretched film obtained in Example 2 are shown in Table 1.

Example 3
The speed and discharge amount of the cooling drum when the resin extruded in Example 1 was cast on the cooling drum were finely adjusted to obtain an unstretched film having a coating layer. After gripping both ends of the obtained film with clips and guiding it to a simultaneous biaxial stretching machine, after preheating for 4.3 seconds with hot air at 105 ° C., 3.0 times in the vertical direction at 100 ° C. Simultaneous biaxial stretching was performed at a stretching ratio of 3.2 times in the direction. At this time, the stretching ratio in the longitudinal and transverse directions was controlled so that the maximum stretching speed in the longitudinal direction was 63.0% / second and the maximum stretching speed in the lateral direction was 70.0% / second. Next, heat treatment was performed at 230 ° C. for 4 seconds with a constant tenter width and a constant clip interval. Otherwise, a biaxially stretched film having a thickness of about 51 μm was produced in the same manner as in Example 1. In addition, when the actual draw ratio was measured with a lattice-like magnification marker written on the unstretched film, the MD direction draw ratio was an average of 3.0 times, and the TD draw ratio was an average of 3.3 times. The properties of the biaxially stretched film obtained in Example 3 are shown in Table 1.

Example 4
The speed and discharge amount of the cooling drum when the resin extruded in Example 1 was cast on the cooling drum were finely adjusted to obtain an unstretched film having a coating layer. After gripping both ends of the obtained film with clips and guiding it to a simultaneous biaxial stretching machine, after preheating for 37 seconds with hot air of 112 ° C., at 270 ° C., 2.7 times in the vertical direction and in the horizontal direction Simultaneous biaxial stretching was performed at a stretching ratio of 3.0. At this time, the stretching ratio in the longitudinal and transverse directions was controlled so that the maximum stretching speed in the longitudinal direction was 5.9% / second and the maximum stretching speed in the transverse direction was 6.9% / second. Thereafter, a biaxially stretched film having a thickness of about 190 μm was produced in the same manner as in Example 1. In addition, when the actual draw ratio was measured with a grid-like magnification marker written on the unstretched film, the MD direction draw ratio was an average of 2.7 times, and the TD draw ratio was an average of 3.1 times. The properties of the biaxially stretched film obtained in Example 4 are shown in Table 1.

Example 5
In Example 1, a biaxially stretched film was produced by the same method except that 100 parts by mass of polyester (M1) was used as a raw material for both outermost layers (B). The properties of the biaxially stretched film obtained in Example 5 are shown in Table 1.

Reference example 1
In Example 1, a biaxially stretched film was produced in the same manner except that a mixed raw material of 50 parts by mass of polyester (M1) and 50 parts by mass of polyester (M3) was used as the raw material for the support layer (A). Table 1 shows the characteristics of the biaxially stretched film obtained in Reference Example 1 .

Comparative Example 1
The speed and discharge amount of the cooling drum when the resin extruded in Example 4 was cast on the cooling drum were finely adjusted to obtain an unstretched film having a coating layer. After gripping both ends of the obtained film with a clip and guiding it to a simultaneous biaxial stretching machine, after preheating for 12 seconds with hot air at 95 ° C., at 95 ° C., 3.4 times in the vertical direction and in the horizontal direction. Simultaneous biaxial stretching was performed at a stretching ratio of 3.4 times. At this time, the stretching ratio in the longitudinal and transverse directions was controlled so that the maximum stretching speed in the longitudinal direction was 34.4% / second and the maximum stretching speed in the transverse direction was 34.4% / second. Next, heat treatment was performed at 240 ° C. for 12 seconds with a constant tenter width and a constant clip interval. Further, in the process of cooling to 60 ° C. over 15 seconds, 3% relaxation treatment was performed in the vertical and horizontal directions.
Thereafter, a biaxially stretched film having a thickness of about 190 μm was produced in the same manner as in Example 1. In addition, when the actual draw ratio was measured with a lattice-like magnification marker written on the unstretched film, the MD direction draw ratio was an average of 3.4 times, and the TD draw ratio was an average of 3.5 times. Table 1 shows the characteristics of the biaxially stretched film obtained in Comparative Example 1.

Comparative Example 2
In Comparative Example 1, a biaxially stretched film was produced in the same manner except that the biaxial stretching was performed at a stretching ratio of 2.8 times in both the longitudinal and lateral directions. At this time, the stretching ratio in the longitudinal and transverse directions was controlled so that the maximum stretching speed in the longitudinal direction was 27.1% / second and the maximum stretching speed in the transverse direction was 27.1% / second. Table 1 shows the characteristics of the biaxially stretched film obtained in Comparative Example 2.

Comparative Example 3
The speed and discharge amount of the cooling drum when the resin extruded in Example 1 was cast on the cooling drum were finely adjusted to obtain an unstretched film having a coating layer. The film was gripped at both ends with clips and guided to a simultaneous biaxial stretching machine, preheated with hot air at 122 ° C. for 25 seconds, then at 122 ° C., 2.1 in the vertical direction, and 2. in the horizontal direction. Simultaneous biaxial stretching was performed at a stretching ratio of 3 times. At this time, the stretching ratios in the longitudinal and transverse directions were controlled so that the maximum stretching speed in the longitudinal direction was 6.1% / second and the maximum stretching speed in the transverse direction was 7.1% / second. Next, heat treatment was performed at 220 ° C. for 12 seconds with a constant tenter width and a constant clip interval. Thereafter, a biaxially stretched film having a thickness of about 125 μm was produced in the same manner as in Example 1. In addition, when the actual draw ratio was measured with a grid-like magnification marker written on the unstretched film, the MD direction draw ratio was an average of 2.0 times, and the TD draw ratio was an average of 2.4 times. Table 1 shows the characteristics of the biaxially stretched film obtained in Comparative Example 3.

Comparative Example 4
The speed and discharge amount of the cooling drum when the resin extruded in Example 1 was cast on the cooling drum were finely adjusted to obtain an unstretched film having a coating layer. Next, after preheating the film with a roll group heated to 75 ° C., the film was heated to 96 ° C. using a non-contact infrared heater, and longitudinally stretched 3.4 times between rolls having different peripheral speeds. At this time, the distance between the contact points of the film was 200 mm, and the peripheral speed of the low-speed roll was 12 m / min. If the film speed between rolls is represented by an intermediate value between the low-speed roll peripheral speed and the high-speed roll peripheral speed, the film speed between rolls is 26.4 m / min, and the passing time between rolls is about 0.45 seconds. . Therefore, it is 3.4 times, that is, 240% stretching is performed in 0.45 seconds, and the stretching speed is about 530% / second.

  Next, both ends of the above-mentioned longitudinally stretched film were gripped with clips, and transversely stretched. The transverse stretching temperature was 135 ° C., the transverse stretching ratio was 4.0 times, and the transverse stretching speed was constant at 25% / second. Next, a heat treatment was performed at 240 ° C. for 12 seconds, and 2.5% relaxation treatment was performed in the width direction in the process of cooling to 60 ° C. Next, the clip that had gripped both ends of the film was released, and both ends of the film were trimmed and wound into a roll to produce a biaxially stretched film. Table 1 shows the characteristics of the biaxially stretched film obtained in Comparative Example 1.

Comparative Example 5
In the same manner as in Comparative Example 4, except that the longitudinal stretching ratio was 2.7 times, the transverse stretching ratio was 3.0 times, the longitudinal stretching speed was 401% / second, and the heat treatment temperature was 220 ° C. A biaxially stretched film was produced. Table 1 shows the characteristics of the biaxially stretched film obtained in Comparative Example 5.

  The biaxially oriented film of the present invention is made of polyester with high crystallinity and has a specific range of plane orientation. Therefore, the biaxially stretched film inherently has excellent heat resistance, excellent light transmittance, mechanical properties. Interference spots are observed when a cured product layer made of an acrylic resin of UV curable type or electron beam curable type is provided on the adhesion modified layer. It is an object to provide a high-quality laminated polyester film for optics that is not conspicuous and has few scratches.

Claims (5)

It is a polyethylene terephthalate film provided with an adhesion modifying layer comprising a composition containing an adhesion modifying resin and particles on at least one surface, and the degree of plane orientation (ΔP) is 0.080 to 0.160, An optical biaxially oriented polyethylene terephthalate film having a thickness variation of less than 8%,
The polyethylene terephthalate adhesion modifying layer surface ultraviolet-curable or electron beam curable acrylic polyethylene optical biaxially oriented used as the base material of the hard coat film formed by providing a hard coat layer comprising a resin terephthalate film of the film . 2. The biaxially oriented polyethylene terephthalate film for optical use according to claim 1, wherein the thermal shrinkage in the film longitudinal direction and the width direction at 150 ° C. is 3.0% or less. The biaxially oriented polyethylene terephthalate film for optical use according to claim 1 or 2, wherein the film has a thickness of 50 to 350 µm. The biaxially oriented polyethylene terephthalate film for optical use according to any one of claims 1 to 3, wherein the maximum strain of the orientation main axis measured with a microwave transmission type molecular orientation meter is within 30 degrees. A hard coat in which a hard coat layer made of an ultraviolet curable or electron beam curable acrylic resin is provided on the surface of the adhesion modified layer of the optically biaxially oriented polyethylene terephthalate film according to claim 1. the film.