TW202328230A - Optical film, multilayer film and method for producing same, and polarizing plate - Google Patents

Abstract

The present invention provides an optical film which contains a copolymer that comprises a polycyclic aromatic vinyl compound unit and a (meth)acrylic compound unit, wherein the proportion of the (meth)acrylic compound unit in the copolymer is 5% by weight to 40% by weight.

Description

Optical film, multilayer film, manufacturing method thereof, and polarizing plate

The present invention relates to an optical film, a multilayer film, a manufacturing method thereof, and a polarizing plate.

Polymers produced using polycyclic aromatic vinyl compounds such as ethylene naphthalene are sometimes used as materials for optical films. The above-mentioned polymer must generally be a polymer containing polycyclic aromatic vinyl compound units, so as to exert excellent optical properties. For example, Patent Documents 1 and 2 describe techniques in which a polymer produced using ethylene naphthalene is used as a material for an optical film.

"Patent Documents" "Patent Document 1" Japanese Patent Laid-Open No. 2006-111650 "Patent Document 2" International Patent Publication No. 2020/066174

Polymers containing polycyclic aromatic vinyl compound units are sometimes used as materials for optical films having in-plane retardation. In general, an optical film is required to be excellent in retardation development from the viewpoint of thickness reduction.

In addition, an optical film made of a polycyclic aromatic vinyl compound unit-containing polymer may be bonded to other members and used. However, this optical film is prone to delamination in the past. Delamination means delamination accompanied by destruction (coagulation failure) inside the film body. Accordingly, if the optical film bonded to a certain component is delaminated, the optical film is usually destroyed, so a part of the optical film may remain on the component. If such an optical film remains, it may cause the reworkability of an optical film to be inferior.

Specifically, after temporarily bonding an optical film to a certain member, it may be required to peel off the optical film and bond the optical film to the member again. The property that the parts can be easily peeled off and reattached is called "reworkability". For example, excellent reworkability is required when the optical film is peeled off from the display panel and reattached again after bonding the optical film to a display panel (such as a liquid crystal panel) of an image display device. However, if delamination occurs when the optical film is peeled off from the component, a part of the damaged optical film may remain on the surface of the component. If a part of the optical film remains on the surface of the part, even if the optical film is reattached again, it is difficult to obtain a product of the same quality as the first lamination.

In view of the aforementioned circumstances, the development of a technique capable of effectively suppressing delamination in an optical film comprising a polymer containing a polycyclic aromatic vinyl compound unit has been demanded.

The present invention was first made in view of the aforementioned problems, and its object is to provide an optical film comprising a polymer containing a polycyclic aromatic vinyl compound unit and having excellent retardation development and peeling resistance; a multilayer film comprising the optical film; and A manufacturing method thereof; and a polarizing plate provided with the multilayer film.

The inventors of the present invention have devoted themselves to research in order to solve the aforementioned problems. As a result, the present inventors have found that an optical film comprising a copolymer comprising a polycyclic aromatic vinyl compound unit and a (meth)acrylic compound unit in a specific range ratio has both retardation development and delamination resistance. Excellent, and further complete the present invention.

That is, the present invention includes the following.

(1) An optical film comprising a copolymer comprising polycyclic aromatic vinyl compound units and (meth)acrylic compound units, The ratio of the said (meth)acrylic compound unit in the said copolymer is 5 weight% or more and 40 weight% or less.

(2) The optical film as described in (1) whose weight average molecular weight Mw of the said copolymer is 50,000-500,000.

(3) The optical film according to (1) or (2), wherein the copolymer contains a repeating unit having a structure obtained by polymerizing ethylene naphthalene.

(4) The optical film as described in any one of (1)-(3) whose glass transition temperature of the said copolymer is 110 degreeC or more.

(5) The optical film described in any one of (1) to (4), wherein the optical film has a ratio Re/d of in-plane retardation Re to thickness d at a measurement wavelength of 550 nm of 10.0×10 ⁻³ above.

(6) A multilayer film comprising a base film and the optical film as described in any one of (1) to (5).

(7) The multilayer film as described in (6), wherein the base film comprises an alicyclic structure-containing polymer.

(8) A method for producing a multilayer film, which is a method for producing a multilayer film comprising a base film and an optical film, Including coating a coating solution comprising a copolymer on the aforementioned base film, wherein the aforementioned copolymer contains polycyclic aromatic vinyl compound units and (meth)acrylic compound units, and the aforementioned (meth)acrylic compound in the aforementioned copolymer The amount of the unit is 5% by weight or more and 40% by weight or less.

(9) A polarizing plate comprising the multilayer film and a polarizing film as described in (6) or (7).

According to the present invention, it is possible to provide an optical film comprising a polymer containing a polycyclic aromatic vinyl compound unit and having excellent retardation development property and delamination resistance; a multilayer film comprising the optical film and a method for producing the same; and a multilayer film comprising the same polarizer.

Embodiments and examples are disclosed below to describe the present invention in detail. However, the present invention is not limited to the implementation forms and examples disclosed below, and can be implemented with arbitrary changes within the scope not departing from the scope of the patent application and its equivalent scope.

In the following description, the in-plane retardation Re represents a value represented by Re=(nx−ny)×d unless otherwise noted. Retardation Rth in the thickness direction represents a value represented by Rth=[(nx+ny)/2-nz]×d unless otherwise noted. nx represents the refractive index in the direction perpendicular to the thickness direction (in-plane direction) and gives the maximum refractive index (slow axis direction), and ny represents the refraction in the direction perpendicular to the nx direction in the aforementioned in-plane direction rate, nz represents the refractive index in the thickness direction, and d represents the thickness. Measurement wavelength, unless otherwise noted, is 550 nm. Retardations such as in-plane retardation and retardation in the thickness direction were measured using a retardation meter ("AxoScan" manufactured by Axometrics).

In the following description, the slow axis means the slow axis in the in-plane direction unless otherwise noted.

In the following description, the angle formed by the optical axes (absorption axis, transmission axis, slow axis, etc.) of each layer in a part with multiple layers means that the aforementioned layers are viewed from the thickness direction unless otherwise noted. body angle.

In the following description, the directions of the so-called elements are "parallel", "perpendicular" and "orthogonal". Unless otherwise noted, it can also include, for example, within the range of ±5° within the range that does not impair the effect of the present invention. error.

In the following description, the so-called "long strip" film refers to a film having a length of 5 times or more relative to the width, preferably 10 times or more in length, and specifically refers to a film with a length that can be rolled up. A film of such length as to be stored or transported in roll form. The upper limit of the length of the elongated film is not particularly limited, and may be, for example, 100,000 times or less relative to the width.

In the following description, "polarizing plate", "circular polarizing plate", "λ/2 plate", and "λ/4 plate" include not only rigid parts but also films made of resin, unless otherwise noted. Generally flexible parts.

In the following description, "a polymer having a positive intrinsic birefringence value" and "a resin having a positive intrinsic birefringence value" respectively mean "the direction in which the refractive index in the extending direction becomes higher than that perpendicular to the extending direction." A polymer with a larger refractive index" and "a resin whose refractive index in the direction of stretching becomes larger than that in a direction perpendicular to the direction of stretching". In addition, "a polymer having a negative intrinsic birefringence value" and "a resin having a negative intrinsic birefringence value" respectively mean that "the refractive index in the extending direction becomes higher than that in the direction perpendicular to the extending direction." A polymer that is still smaller" and "a resin whose refractive index in the direction of stretching becomes smaller than that in the direction perpendicular to the direction of stretching". Intrinsic birefringence values are calculated from the permittivity distribution.

In the following description, the so-called bonding agent, unless otherwise noted, is not limited to bonding agents in the narrow sense, but also includes adhesives whose shear storage modulus of elasticity at 23°C is less than 1 MPa. The so-called bonding agent in a narrow sense means a bonding agent having a shear storage elastic modulus of 1 MPa to 500 MPa at 23° C. after energy ray irradiation or heat treatment.

<1. Outline of Optical Film>

An optical film related to an embodiment of the present invention includes a copolymer containing polycyclic aromatic vinyl compound units and (meth)acrylic compound units. The polycyclic aromatic vinyl compound unit means a repeating unit having a structure obtained by polymerizing a polycyclic aromatic vinyl compound. In addition, the (meth)acrylic compound unit means a repeating unit having a structure formed by polymerizing a (meth)acrylic compound. However, the formation method of the polycyclic aromatic vinyl compound unit and the (meth)acrylic compound unit is not limited. Accordingly, the polycyclic aromatic vinyl compound unit may be formed by methods other than polymerization of the polycyclic aromatic vinyl compound. In addition, the (meth)acrylic compound unit may be formed by methods other than polymerizing a (meth)acrylic compound.

In the aforementioned copolymer comprising a polycyclic aromatic vinyl compound unit and a (meth)acrylic compound unit, the amount of the (meth)acrylic compound unit is within a specific range. Hereinafter, the said copolymer containing the (meth)acrylic compound unit of the quantity of a specific range in this way may be called a "specific copolymer." The optical film related to this embodiment is generally formed by a resin containing a specific copolymer. In the following description, the aforementioned resin containing a specific copolymer may be referred to as "specific resin". Accordingly, the optical film related to this embodiment usually contains a specific resin, preferably only a specific resin. This particular resin is usually a thermoplastic resin.

The optical film related to this embodiment can be excellent in retardation development property and delamination resistance.

<2. Specific copolymer>

The specific copolymer contains polycyclic aromatic vinyl compound units and (meth)acrylic compound units. Usually, an optical film is formed through a specific resin containing the specific copolymer, so the optical film contains the specific copolymer.

The polycyclic aromatic vinyl compound unit means a repeating unit having a structure obtained by polymerizing a polycyclic aromatic vinyl compound as described above. The polycyclic aromatic vinyl compound means a compound "containing a polycyclic aromatic group containing a plurality of aromatic rings and a vinyl group that is bonded to at least one aromatic ring of the polycyclic aromatic group". Aromatic rings usually follow Huckel's rule that the number of electrons contained in the π electron system on the ring is 4n+2 (n represents an integer greater than 0, preferably representing a natural number.). Polymerization of this polycyclic aromatic vinyl compound is usually carried out in the form of addition polymerization utilizing vinyl groups. Accordingly, the polycyclic aromatic vinyl compound unit has a main chain formed by polymerization of vinyl groups and side chains including polycyclic aromatic groups bonded to the main chain.

Generally, when the molecules of a specific copolymer are oriented by the stretching treatment, the main chain must be arranged parallel to the stretching direction, and on the other hand, the side chains must be arranged in a direction crossing the stretching direction (for example, a direction perpendicular to the stretching direction). Accordingly, the structure of the polycyclic aromatic groups included in the side chains reflects the refractive index of the optical film in a direction crossing the alignment direction. Therefore, the structure of the polycyclic aromatic group is preferably selected in response to the refractive index of the optical film to be displayed in the direction crossing the orientation direction, and even in response to the in-plane retardation of the optical film, the retardation in the thickness direction, etc. It is better to choose the characteristics.

The polycyclic aromatic group may, for example, be a condensed aromatic group or a ring-assembled aromatic group. The term "condensed aromatic group" means a group containing an aromatic condensed ring. In addition, the term "ring-assembled aromatic group" means a group including a plurality of aromatic rings linked through intermediary bonds. The aromatic ring can also be an aromatic heterocyclic ring, but an aromatic hydrocarbon ring is preferred. In addition, the polycyclic aromatic group may contain 1 or 2 or more substituents other than the vinyl group. Examples of substituents include alkyl groups such as methyl groups and ethyl groups; alkoxy groups such as methoxy groups and ethoxy groups; and the like. Among them, the polycyclic aromatic group preferably does not have the aforementioned substituents.

Examples of the polycyclic aromatic vinyl compound containing a condensed aromatic group include vinyl naphthalene such as 1-vinylnaphthalene and 2-vinylnaphthalene, and vinyl anthracene such as 1-vinyl anthracene, 2-vinyl anthracene and 9-vinyl anthracene. Furthermore, examples of the polycyclic aromatic vinyl compound containing a ring-assembled aromatic group include vinyl biphenyl, vinyl terphenyl, and the like. Among them, polycyclic aromatic vinyl compounds containing condensed aromatic groups are preferred, and vinyl naphthalene is particularly preferred. Accordingly, the specific copolymer preferably contains a repeating unit having a structure obtained by polymerizing ethylene naphthalene (hereinafter sometimes referred to as "ethylene naphthalene unit").

A polycyclic aromatic vinyl compound may be used individually by 1 type, and may use it in combination of 2 or more types. Accordingly, the specific copolymer may contain only one type of polycyclic aromatic vinyl compound unit, or may contain two or more types.

The proportion of polycyclic aromatic vinyl compound units in the specific copolymer is preferably at least 60% by weight, more preferably at least 65% by weight, and most preferably at least 70% by weight, based on 100% by weight of the specific copolymer , and preferably below 95% by weight, preferably below 90% by weight, and especially preferably below 85% by weight. When the ratio of the polycyclic aromatic vinyl compound unit is within the aforementioned range, the optical film can be made particularly excellent in retardation development property and delamination resistance. Especially when the ratio of a polycyclic aromatic vinyl compound unit is more than the said lower limit, the retardation development property of an optical film can be improved effectively.

The ratio of the polycyclic aromatic vinyl compound units in a specific copolymer can be adjusted, for example, by the insertion ratio of the polycyclic aromatic vinyl compound. Here, the inclusion ratio of the polycyclic aromatic vinyl compound means the ratio of the amount of the polycyclic aromatic vinyl compound to the entire monomers of the specific copolymer. Usually, the ratio of the polycyclic aromatic vinyl compound unit in a specific copolymer is made to correspond to the insertion ratio of the polycyclic aromatic vinyl compound.

The (meth)acrylic compound unit means a repeating unit having a structure formed by polymerizing a (meth)acrylic compound as described above. The (meth)acrylic compound means a compound containing a (meth)acryl group. In addition, the (meth)acryl group includes acryl group, methacryl group, and combinations thereof. The carbon-carbon unsaturated bond contained in the (meth)acryl group of (meth)acrylic compound and the carbon-carbon unsaturated bond contained in the vinyl group of polycyclic aromatic vinyl compound or other (meth)acrylic acid The carbon-carbon unsaturated bonds contained in the compound react to polymerize.

Examples of the (meth)acrylic compound include acrylic acid, acrylic acid derivatives, methacrylic acid, methacrylic acid derivatives, and the like. Examples of acrylic acid derivatives include acrylate, acrylamide, and the like. Moreover, as a methacrylic acid derivative, a methacrylate, a methacrylamide, etc. are mentioned, for example. Examples of acrylates include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, secondary butyl acrylate, tertiary butyl acrylate, n-hexyl acrylate ester, cyclohexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, n-decyl acrylate, n-dodecyl acrylate, etc. In addition, as methacrylate, for example: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate Esters, secondary butyl methacrylate, tertiary butyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, n-decyl methacrylate, methyl n-dodecyl acrylate, etc. Furthermore, (meth)acrylates, such as the said acrylate and methacrylate, may have a substituent, such as a hydroxyl group and a halogen atom. Examples of (meth)acrylates having substituents include: 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, glycidyl methacrylate, and the like.

From the viewpoint of improving the adhesiveness between the optical film and other members, as the (meth)acrylic compound, acrylic acid and methacrylic acid are preferred, and acrylic acid is particularly preferred. Furthermore, from the viewpoint of suppressing moisture absorption of the optical film and improving water resistance and water vapor barrier properties, as the (meth)acrylic compound, acrylate and methacrylate are preferred, and acrylate is particularly preferred.

The (meth)acrylic compound may be used alone or in combination of two or more. Accordingly, the specific copolymer may contain only one type of (meth)acrylic compound unit, or may contain two or more types.

The ratio of the (meth)acrylic compound unit in the specific copolymer is usually at least 5% by weight, preferably at least 10% by weight, particularly preferably at least 15% by weight, based on 100% by weight of the specific copolymer, and Usually it is 40% by weight or less, preferably 35% by weight or less, especially preferably 30% by weight or less. When the ratio of the (meth)acrylic compound unit is within the aforementioned range, the optical film can be made particularly excellent in retardation development property and delamination resistance. Especially when the ratio of the (meth)acrylic compound unit is more than the said lower limit, the delamination tolerance of an optical film can be improved effectively.

The ratio of the (meth)acrylic compound unit in a specific copolymer can be adjusted, for example, by the insertion ratio of the (meth)acrylic compound. Here, the inclusion ratio of the (meth)acrylic compound means the ratio of the amount of the (meth)acrylic compound to the entire monomers of the specific copolymer. Usually, the ratio of the (meth)acrylic compound unit in a specific copolymer should correspond to the incorporation ratio of a (meth)acrylic compound.

The specific copolymer may also contain any combination of structural units up to polycyclic aromatic vinyl compound units and (meth)acrylic compound units. An arbitrary structural unit generally has a structure different from that of a polycyclic aromatic vinyl compound unit and a (meth)acrylic compound unit. For example, any structural unit may have a structure formed by polymerizing any compound other than polycyclic aromatic vinyl compounds and (meth)acrylic compounds containing carbon-carbon unsaturated bonds.

The specific copolymer preferably has a weight average molecular weight Mw within a specific range. Specifically, the range of the weight average molecular weight Mw of the specific copolymer is preferably not less than 50,000, more preferably not less than 100,000, and preferably not more than 500,000, more preferably not more than 300,000. When the weight average molecular weight Mw of a specific copolymer exists in the said range, the retardation development property and delamination resistance of an optical film can be made especially excellent.

The weight average molecular weight Mw of the polymer can be measured in terms of polyisoprene or polystyrene by gel permeation chromatography (GPC) using cyclohexane as a solvent. Toluene can also be used as a solvent for GPC in case the polymer is not soluble in cyclohexane.

The particular copolymer preferably has a glass transition temperature Tg within a particular range. Specifically, the range of the glass transition temperature Tg of the specific copolymer is preferably above 110°C, preferably above 115°C, especially above 120°C, preferably below 180°C, and preferably below 170°C. Preferably, it is especially preferably below 160°C. When the glass transition temperature Tg of a specific copolymer exists in the said range, the retardation development property and delamination resistance of an optical film can be made especially excellent. The aforementioned range of the glass transition temperature Tg of the specific copolymer may also be the same as the range of the glass transition temperature of the specific resin containing the specific copolymer.

The glass transition temperature Tg was measured using a differential scanning calorimeter ("DSC7000X" manufactured by Hitachi High-Tech Science Corporation) at a heating rate of 10°C/min. The measurement of this glass transition temperature Tg was performed based on JIS K 6911.

Certain copolymers generally have negative intrinsic birefringence values. Therefore, a particular resin comprising this particular copolymer must also have a negative intrinsic birefringence value.

The production method of the specific copolymer is not particularly limited. The specific copolymer can be produced, for example, by a method including copolymerizing a polycyclic aromatic vinyl compound and a (meth)acrylic compound, and optionally an optional compound. In this copolymerization, a polymerization initiator may also be used if necessary. As a polymerization initiator, for example: lauryl peroxide, diisopropyl peroxydicarbonate, bis(2-ethylhexyl peroxydicarbonate), tertiary butyl peroxypivalate, peroxypivalate Organic peroxides such as oxy-3,3,5-trimethylhexanoyl; azo compounds such as α,α'-azobisisobutyronitrile; ammonium persulfate; and potassium persulfate, etc. A polymerization initiator may be used individually by 1 type, and may use it combining 2 or more types by arbitrary ratios.

The proportion of the specific copolymer contained in the specific resin forming the optical film is preferably at least 80% by weight, more preferably at least 90% by weight, more preferably at least 95% by weight, based on 100% by weight of the specific resin. A specific resin may also contain only a specific copolymer. Accordingly, the optical film may contain only the specific copolymer.

<3. Any ingredient>

The specific resin for forming the optical film may further include arbitrary components combined with the specific copolymer. Examples of optional components include stabilizers such as antioxidants, heat stabilizers, light stabilizers, weather-resistant stabilizers, ultraviolet absorbers, and near-infrared absorbers; plasticizers; and the like. Optional components may be used alone or in combination of two or more.

<4. Characteristics and dimensions of optical film>

The optical film can have high retardation development. The retardation development property of an optical film can be represented by the ratio Re/d of the in-plane retardation Re of an optical film, and thickness d. The measurement wavelength of the in-plane retardation Re is 550 nm unless otherwise noted. Specifically, the ratio Re/d of the optical film is preferably 10.0×10 ⁻³ or higher, more preferably 11.0×10 ⁻³ or higher, more preferably 12.0×10 ⁻³ or higher, and 13.0×10 ⁻³ or higher Excellent. The upper limit of the ratio Re/d of the optical film is not particularly limited, and may be, for example, 20.0×10 ⁻³ or less, 18.0×10 ⁻³ or less, 16.0×10 ⁻³ or less, and the like.

Optical films can have high delamination resistance. The delamination resistance of the optical film can be expressed by the size required to peel the part after the optical film is bonded to the part. Hereinafter, this force may be referred to as "peel strength". Specifically, the range of the peel strength is preferably 1.0 N/15 mm or more, more preferably 2.0 N/15 mm or more, and most preferably 5.0 N/15 mm or more. The upper limit of the peel strength of the optical film is not particularly limited, and may be, for example, 20.0 N/15 mm or less, 15.0 N/15 mm or less, and the like. The peel strength of the optical film can be measured by the method described in <Measurement method of peeling resistance> of the embodiment described later.

The optical film preferably has an in-plane retardation according to its use.

For example, optical films can also have small in-plane retardation. To give a specific example, the in-plane retardation Re of the optical film at a measurement wavelength of 550 nm may be, for example, 10 nm or less, 7 nm or less, 5 nm or less, or 0 nm. The optical film also has excellent advantages other than retardation development, so for example, in the case of using advantages other than retardation development, the optical film can also be an optical film having a small in-plane retardation Re as described above. Isotropic membrane. In addition, the optical film may be an optically anisotropic film having a small in-plane retardation Re as described above but a large thickness direction retardation Rth.

The in-plane retardation Re of the optical film may be, for example, within a range where the optical film can function as a λ/4 plate. In the case where the optical film can function as a λ/4 plate, the in-plane retardation Re of the optical film at a measurement wavelength of 550 nm is preferably 80 nm or more, preferably 100 nm, and most preferably 110 nm or more , and preferably below 170 nm, preferably below 150 nm, especially preferably below 140 nm.

The in-plane retardation Re of the optical film may be, for example, within a range where the optical film can function as a λ/2 plate. In the case where the optical film can function as a λ/2 plate, the in-plane retardation Re of the optical film at a measurement wavelength of 550 nm is preferably 220 nm or more, preferably 240 nm, and most preferably 250 nm or more , and preferably below 310 nm, preferably below 290 nm, especially preferably below 280 nm.

The optical film may also have a slow axis. The direction of the slow axis of the optical film is not particularly limited. For example, the slow axis of the elongated optical film may be parallel to or perpendicular to the width direction of the optical film. In addition, the slow axis of the elongated optical film may form an angle close to 45° with respect to the width direction of the optical film. To give a specific example, the angle formed by the slow axis of the elongated optical film relative to the width direction of the optical film is preferably 40° or more, preferably 42° or more, so that It is more preferably 43° or more, especially preferably 44° or more, preferably 50° or less, more preferably 48° or less, and more preferably 47° or less, so that It is more preferably below 46°.

The total light transmittance of the optical film is preferably above 80%, preferably above 85%, and most preferably above 90%. The total light transmittance can be measured with an ultraviolet-visible light spectrometer at a wavelength of 400 nm to 700 nm.

The haze of the optical film is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, and ideally 0%. Haze can be measured using a haze meter in compliance with JIS K7361-1997.

The optical film can be a film body cut into sheets, or a strip-shaped film body.

The thickness of the optical film is not particularly limited, but it is preferably thin from the viewpoint of obtaining a thin optical film by making use of excellent retardation development properties. The specific thickness range of the optical film is preferably above 0.5 μm, more preferably above 1 μm, especially above 5 μm, preferably below 100 μm, preferably below 80 μm, and preferably below 70 μm The following are preferred.

The use of the above-mentioned optical film is not limited. Optical films can be used in a wide range of applications in the optical field alone or in combination with other components. As an example of the use of an optical film, a retardation film, a viewing angle compensation film, a polarizing plate protective film, etc. are mentioned. Among them, the optical film is preferably used as a multilayer film in combination with a base film from the viewpoint of making effective use of the excellent delamination resistance.

<5. Manufacturing method of optical film>

The manufacturing method of the optical film is not particularly limited. Optical films can be manufactured by methods including, for example, transmission injection molding, extrusion molding, press molding, inflation molding, blow molding, calender molding, die casting, compression molding Resin forming method such as method to form specific resin. In addition, the optical film can also be produced by a method including, for example, applying a coating liquid containing a specific resin and a solvent on an appropriate surface and drying the applied coating liquid to remove the solvent.

The manufacturing method of an optical film may also include extending an optical film. By stretching, the optical film can be made to exhibit a desired retardation, or the thickness of the optical film can be adjusted. The extending direction is not limited, and examples thereof include a longitudinal direction, a width direction, and an oblique direction. Here, the oblique direction means a direction perpendicular to the thickness direction and neither parallel nor perpendicular to the width direction. In addition, the extending direction may be one direction, or two or more directions. Accordingly, examples of stretching methods include a method of uniaxially stretching an optical film in the longitudinal direction (longitudinal uniaxial stretching method), and a method of uniaxially stretching an optical film in the width direction (transverse uniaxial stretching method). Equal uniaxial stretching method; simultaneous biaxial stretching method in which the optical film is stretched in the longitudinal direction while stretching in the width direction, stretching the optical film in one of the longitudinal direction and the width direction and then stretching in the other The biaxial stretching method such as the successive biaxial stretching method; the method of stretching the optical film in an oblique direction (oblique stretching method); etc.

The elongation ratio is preferably at least 1.1 times, more preferably at least 1.2 times, more preferably at most 5.0 times, more preferably at most 3.0 times, and most preferably at most 2.0 times.

The stretching temperature is preferably above "Tg-5°C", preferably above "Tg+5°C", preferably below "Tg+50°C", and preferably below "Tg+30°C". Here, "Tg" represents the glass transition temperature of a specific copolymer.

<6. Multilayer film>

A multilayer film related to an embodiment of the present invention includes a base film and the above-mentioned optical film.

As the base film, a resin film is used. Accordingly, the base film usually contains resin, preferably only resin. The resin forming the resin film is preferably a thermoplastic resin, preferably a thermoplastic resin having a positive intrinsic birefringence value.

The resin forming the base film generally contains a polymer. Since the resin forming the substrate film preferably has positive intrinsic birefringence, the polymer contained in the resin preferably also has positive intrinsic birefringence. Examples of polymers having positive intrinsic birefringence include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyphenylene sulfide and other polyolefins; Arylene sulfide; polyvinyl alcohol; polycarbonate; polyarylate; cellulose ester; These polymers may be used alone or in combination of two or more. Among them, alicyclic structure-containing polymers, cellulose esters, and polycarbonates are preferred, and alicyclic structure-containing polymers are particularly preferred.

The alicyclic structure-containing polymer is a polymer containing an alicyclic structure in a repeating unit, and is usually an amorphous polymer. As the alicyclic structure-containing polymer, either a polymer containing an alicyclic structure in the main chain or a polymer containing an alicyclic structure in a side chain can be used. Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, but a cycloalkane structure is preferable from the viewpoint of thermal stability. The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, especially 6 or more, and preferably 30 or less, more preferably 20 or less , preferably less than 15.

In the polymer containing an alicyclic structure, the proportion of repeating units containing an alicyclic structure is preferably at least 50% by weight, more preferably at least 70% by weight, and most preferably at least 90% by weight. When the ratio of the repeating unit containing an alicyclic structure is within the aforementioned range, a multilayer film excellent in heat resistance can be obtained.

Examples of polymers containing an alicyclic structure include: (1) nor-alkene-based polymers, (2) monocyclic cyclic olefin polymers, (3) cyclic conjugated diene polymers, (4) ethylene Alicyclic hydrocarbon polymers and their hydrogenated products, etc. Among these, cyclic olefin polymers and northene-based polymers are preferred, and northene-based polymers are particularly preferred. Examples of norrene-based polymers include ring-opening polymers of monomers containing norrene structures, ring-opening copolymers of monomers containing norrene structures and other monomers capable of ring-opening copolymerization, and These hydrides; addition polymers of monomers containing a northylene structure, addition copolymers of monomers containing a northylene structure and other copolymerizable monomers, etc. Among these, hydrogenated products of ring-opening polymers of monomers containing a northylene structure are particularly preferable from the viewpoint of transparency. The aforesaid alicyclic structure-containing polymer can be selected from polymers disclosed in Japanese Patent Publication No. 2002-321302, for example.

The weight-average molecular weight Mw of the polymer contained in the resin forming the base film is preferably at least 10,000, more preferably at least 15,000, particularly preferably at least 20,000, and preferably at most 100,000, more preferably at most 80,000. Good, preferably below 50,000. When the weight average molecular weight Mw is within the aforementioned range, the mechanical strength and moldability of the base film can be highly balanced.

The molecular weight distribution (weight average molecular weight (Mw)/number average molecular weight (Mn)) of the polymer contained in the resin forming the base film is preferably 1.2 or more, preferably 1.5 or more, particularly preferably 1.8 or more, and It is better to be below 3.5, more preferably below 3.0, and most preferably below 2.7. When the molecular weight distribution is more than the lower limit of the aforementioned range, the productivity of the polymer can be improved and the production cost can be suppressed. In addition, when the molecular weight distribution is below the upper limit, the amount of low-molecular components decreases, so that relaxation during high-temperature exposure can be suppressed, and the stability of the base film can be improved.

The proportion of the polymer in the resin forming the base film is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, and most preferably 90% by weight to 100% by weight. When the ratio of the polymer is in the aforementioned range, the base film can have high heat resistance and transparency.

The resin forming the base film may further include any components combined with the polymer. As an arbitrary component, the thing similar to the arbitrary component contained in an optical film is mentioned, for example. Optional components may be used alone or in combination of two or more.

The glass transition temperature Tg of the resin forming the substrate film is preferably 110°C or higher, more preferably 115°C or higher, particularly preferably 120°C or higher, and preferably 180°C or lower, preferably 170°C or lower More preferably, it is especially preferred to obtain a temperature below 160°C. The glass transition temperature of resins can be measured in the same way as the glass transition temperature of polymers.

The base film preferably has an in-plane retardation corresponding to the application of the multilayer film.

For example, the substrate film may also have small in-plane retardation. To give a specific example, the in-plane retardation Re of the base film at a measurement wavelength of 550 nm may be, for example, 10 nm or less, 7 nm or less, 5 nm or less, or 0 nm. A base film having such a small in-plane retardation is an optically isotropic film in the in-plane direction.

And, for example, the in-plane retardation Re of the substrate film at a measurement wavelength of 550 nm is preferably 80 nm or more, preferably 100 nm or more, especially preferably 110 nm or more, and is in the range of The thickness is preferably not more than 170 nm, more preferably not more than 150 nm, and most preferably not more than 140 nm. A base film having an in-plane retardation in this range can function as a λ/4 plate.

Furthermore, for example, the in-plane retardation Re of the substrate film at a measurement wavelength of 550 nm is preferably 220 nm or more, more preferably 240 nm, especially 250 nm or more, and The thickness is preferably less than 310 nm, more preferably less than 290 nm, and most preferably less than 280 nm. A base film having an in-plane retardation in this range can function as a λ/2 plate.

The in-plane retardation of the base film and the in-plane retardation of the optical film may be the same or different. When the in-plane retardation of the base film is different from the in-plane retardation of the optical film, these differences may also be within a specific range. For example, the difference between the in-plane retardation of the substrate film and the in-plane retardation of the optical film is preferably at least 100 nm, more preferably at least 110 nm, and preferably at most 180 nm, preferably at least 160 nm The following are preferred. In this case, the in-plane retardation of the base film may be larger than the in-plane retardation of the optical film, and the in-plane retardation of the base film may be smaller than the in-plane retardation of the optical film.

The base film may also have a slow axis. The direction of the slow axis of the base film is not particularly limited. For example, the slow axis of the substrate film may also be slightly perpendicular to the slow axis of the optical film. The so-called "slightly perpendicular" between the slow axis of the substrate film and the slow axis of the optical film means that the angle between the slow axis of the substrate film and the slow axis of the optical film is within a range close to 90°. To give a specific example, the angle between the slow axis of the substrate film and the slow axis of the optical film is preferably 85° or more, more preferably 87° or more, and more preferably 88° or more. Preferably, it is more preferably 89° or more, and it is better to be 95° or less, it is better to be 93° or less, it is more preferably 92° or less, and it is 91° or less. Excellent.

The thickness of the base film is not particularly limited. The specific thickness range of the substrate film is preferably above 0.5 μm, preferably above 1 μm, especially preferably above 5 μm, preferably below 100 μm, preferably below 70 μm, and preferably below 50 μm. It is preferably not more than μm.

The multilayer film may also have any layers other than the base film and the optical film as required. As an example of an arbitrary layer body, the arbitrary layer body which has optical isotropy is mentioned. The in-plane retardation of this optically isotropic arbitrary layer at a measurement wavelength of 550 nm is usually 10 nm or less. Examples of optional layers having optical isotropy include a protective film layer for protecting a base film and an optical film, and a bonding layer for joining layers such as a base film and an optical film. Furthermore, as another example of the arbitrary layer body, an arbitrary layer body having optical anisotropy can be mentioned. The optical characteristics of this optional layer having optical anisotropy are preferably set so that the multilayer film has a desired retardation as a whole. To give a specific example, it can also be set in such a way that any layer body having optical anisotropy and one or both of the base film and the optical film can function as a λ/4 plate or a λ/2 plate. Optical properties of any layer.

The multilayer film preferably has an in-plane retardation according to its application.

For example, the range of the in-plane retardation Re of a multilayer film with a measurement wavelength of 550 nm is preferably 100 nm or more, preferably 115 nm or more, especially 125 nm or more, and 180 nm or less. Best, preferably below 160 nm, especially preferably below 150 nm. A multilayer film having an in-plane retardation Re in such a range can function as a λ/4 plate. A multilayer film having in-plane retardation in such a range can be obtained, for example, by appropriately adjusting the in-plane retardation and slow axis direction of the base film and the in-plane retardation and slow axis direction of the optical film.

The in-plane retardation Re(450), Re(550) and Re(650) of multi-layer films with wavelengths of 450 nm, 550 nm and 650 nm is better to satisfy the relationship of Re(450)<Re(550). It is preferable to satisfy the relationship of Re(450)<Re(550)<Re(650). A multilayer film having in-plane retardation Re(450), Re(550) and Re(650) satisfying this relationship can exhibit inverse wavelength dispersion. Specifically, the multilayer film generally has a larger in-plane retardation at longer measurement wavelengths. Accordingly, the multilayer film can function as a broadband wavelength plate capable of uniformly converting the polarization state of light passing through the multilayer film over a wide wavelength range. Multilayer films with in-plane retardation Re(450), Re(550) and Re(650) satisfying this relationship, for example, can be adjusted by moderately adjusting the in-plane retardation and slow axis direction of the substrate film and the optical film The in-plane retardation and the direction of the slow axis are obtained.

The total light transmittance of the multilayer film is preferably above 80%, preferably above 85%, and especially preferably above 90%.

The haze of the multilayer film is preferably less than 5%, more preferably less than 3%, especially preferably less than 1%, and ideally 0%.

The multilayer film can be a film cut into sheets, or a strip-shaped film.

The thickness of the multilayer film is not particularly limited. The specific thickness of the multilayer film is preferably above 5 μm, more preferably above 10 μm, especially above 15 μm, preferably below 150 μm, preferably below 120 μm, and below 80 μm Excellent.

<7. Manufacturing method of multilayer film>

The production method of the multilayer film is not particularly limited. A multilayer film can also be produced, for example, by a method including a step of preparing a base film, a step of preparing an optical film, and a step of bonding the base film and the optical film together. Furthermore, the multilayer film can also be produced, for example, by a method including a process of co-extruding a resin forming a base film and a specific resin forming an optical film. From the viewpoint of producing a multilayer film with high productivity, the multilayer film is preferably produced by a production method including coating a coating liquid containing a specific copolymer on a base film. This favorable manufacturing method will be described below.

The method for producing a multilayer film related to a good example includes coating a coating liquid containing a specific copolymer on a base film. The substrate film can be produced, for example, by a melt forming method or a solution casting method. Among them, the melt molding method is preferable. Among the melt molding methods, extrusion molding, inflation molding, or pressure molding are preferred, and extrusion molding is particularly preferred. The substrate film thus manufactured is an optically isotropic film whose in-plane retardation is generally 10 nm or less at a measurement wavelength of 550 nm. The coating liquid can also be applied to an optically isotropic substrate film. In addition, the base film may be stretched before the application of the coating liquid so that the base film may exhibit an in-plane retardation, if necessary.

After the substrate film is prepared, a coating solution containing a specific copolymer is coated on the substrate film. The coating solution is a liquid composition containing a specific copolymer, and may contain a specific copolymer and a solvent. In addition, the coating solution may contain arbitrary components combined with specific copolymers and solvents. As the solvent, those capable of dissolving or dispersing the specific copolymer are preferable, and those capable of dissolving the specific copolymer are particularly preferable. Moreover, a solvent may be used individually by 1 type, and may use it in combination of 2 or more types. The concentration of the specific copolymer in the coating solution is preferably adjusted so that the viscosity of the coating solution falls within a range suitable for coating, and may be, for example, 1% by weight to 50% by weight.

The coating method of the coating liquid is not limited. Examples of coating methods include curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, inclined plate coating, print coating, rotogravure coating, Die coating method, gap coating and dipping method, etc.

By applying the coating liquid, a layer of the coating liquid is formed on the base film. According to this, by drying the coating liquid as needed to remove the solvent, an optical film including a specific copolymer can be formed on a substrate film to obtain a multilayer film. The drying method is not limited, and drying methods such as heating drying and reduced-pressure drying may be used.

The manufacturing method of the multilayer film may also include extending the multilayer film as required. In the following description, the multilayer film before stretching may be referred to as "multilayer film before stretching", and the multilayer film after stretching may be referred to as "stretched multilayer film". The extension may be performed only once, or may be performed more than two times.

The stretching ratio of the multilayer film before stretching can be set according to the optical characteristics of the stretched multilayer film. The specific range of the stretching ratio of the multilayer film before stretching is preferably 1.05 times or more, preferably 1.1 times or more, more preferably 1.2 times or more, especially 1.3 times or more, and preferably 3.0 times or less. It is preferably not more than 2.5 times, more preferably not more than 2.0 times. When stretching is performed two or more times, it is preferable that the stretching magnifications of each stretching are within the aforementioned ranges. In addition, when stretching is performed two or more times, the stretching magnifications of the respective stretches may be the same or different.

The stretching temperature of the multilayer film before stretching should be set according to the optical properties of the stretched multilayer film. The specific stretching temperature range of the multilayer film before stretching is preferably above Tg (low) - 5°C, preferably above Tg (low) - 3°C, especially preferably above Tg (low) - 1°C, and It is preferably below Tg (high) + 20°C, more preferably below Tg (high) + 15°C, and most preferably below Tg (high) + 12°C. Here, Tg (low) represents the lower of the glass transition temperature of the resin forming the base film and the glass transition temperature of the specific resin forming the optical film, and Tg (high) represents the glass of the resin forming the base film. The higher of the transition temperature and the glass transition temperature of the specific resin forming the optical film. When stretching is performed two or more times, the stretching temperature of each stretch may be the same or different.

The stretching direction of the multilayer film before stretching can be set according to the optical properties of the stretched multilayer film. In addition, stretching may be uniaxial stretching in only one direction, or biaxial stretching in two directions. In addition, when stretching is performed two or more times, the stretching direction of each stretch may be the same or different. For example, after performing uniaxial stretching along a certain first stretching direction, uniaxial stretching can also be carried out along a second stretching direction slightly perpendicular to the first stretching direction. Specifically, the range of the angle between the first extending direction and the second extending direction is preferably 85° or more, more preferably 87° or more, more preferably 88° or more, so that It is more preferably 89° or more, more preferably 95° or less, more preferably 93° or less, more preferably 92° or less, and most preferably 91° or less.

According to the production method including stretching the multilayer film before stretching, one or both of the base film and the optical film can exhibit birefringence through stretching. Accordingly, a multilayer stretched film having desired optical properties can be obtained.

The manufacturing method of the multilayer film may further include any combination of steps as the above-mentioned steps. For example, in the case of obtaining a long multilayer film, the method for producing the multilayer film may also include a trimming step of cutting the obtained multilayer film into a desired shape. Through the trimming process, a multilayer film cut into sheets with a desired shape can be obtained. In addition, the method for producing a multilayer film may include, for example, a step of providing a protective layer on the multilayer film.

<8. Polarizing plate>

A polarizing plate related to an embodiment of the present invention includes the multilayer film and polarizing film related to the above-mentioned embodiment.

As the polarizing film, a film that functions as a linear polarizer is used. As an example of a polarizing film, a film obtained by uniaxially stretching in a boric acid bath after adsorbing iodine or a dichroic dye to a polyvinyl alcohol film, and a film obtained by adsorbing iodine or a dichroic dye on a polyvinyl alcohol film A polyvinyl alcohol film is stretched and further modified to obtain a part of the polyvinyl alcohol unit in the molecular chain into a polyethylene unit. Among them, a polarizing film is preferably a film containing polyvinyl alcohol.

If natural light is incident on the polarizing film, usually only one polarized light will pass through. The degree of polarization of the polarizing film is not particularly limited, but is preferably above 98%, preferably above 99%. Moreover, the thickness of the polarizing film is preferably 5 μm to 80 μm.

The polarizing plate preferably functions as a circular polarizing plate. In this case, the multilayer film preferably has an in-plane retardation capable of functioning as a λ/4 plate. In addition, the angle formed by the polarization transmission axis of the polarizing film and the slow axis of one or both of the base film and the optical film is preferably in a specific range close to 45°. Specifically, the above-mentioned angle is preferably above 40°, more preferably above 42°, more preferably above 43°, especially above 44°, preferably below 50°, and preferably below 48°. Preferably, it is more preferably below 47°, and most preferably below 46°. When a polarizing plate that can function as a circular polarizing plate is provided on the display surface of an image display device, reflection of external light can be suppressed.

The polarizing plate may also include a polarizing film, a substrate film, and an optical film in this order. In addition, the polarizing plate may include a polarizing film, an optical film, and a base film in this order. The specific order can be set according to the in-plane retardation of the substrate film and the optical film.

The above-mentioned polarizing plate may further include any layer. Examples of optional layers include: a protective film layer for polarizers; a bonding layer for laminating polarizing films and multilayer films; a hard coat layer such as an impact-resistant polymethacrylate resin layer; Base layer; antireflection layer; antifouling layer; antistatic layer; etc. Such arbitrary layers may be provided in only one layer, or may be provided in two or more layers.

[9. Video display device]

The above-mentioned optical film can be installed in an image display device. For example, it is also possible to prepare a polarizing plate provided with an optical film, and install this polarizing plate on an image display device. As a good example, an organic EL image display device (organic electroluminescence display device) provided with a polarizing plate that can function as a circular polarizing plate is mentioned. This organic EL image display device includes a circular polarizing plate and an organic electroluminescent element (hereinafter sometimes referred to as an "organic EL element" appropriately). The organic EL image display device generally comprises a polarizing film, a multilayer film and an organic EL element in sequence.

An organic EL element generally includes a transparent electrode layer, a light-emitting layer, and an electrode layer in this order, and the light-emitting layer can generate light by applying a voltage from the transparent electrode layer and the electrode layer. Examples of materials constituting the organic light-emitting layer include poly(parastyrene)-based, polyoxene-based, and polyvinylcarbazole-based materials. Furthermore, the light-emitting layer may have a stack of a plurality of layers with different luminescent colors, or a mixed layer doped with a dye different from the layer of a certain dye. Furthermore, the organic EL device may include functional layers such as a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, an equipotential surface forming layer, and a charge generation layer.

The aforementioned organic EL image display device can suppress the reflection of external light on the display surface. Specifically, the incident light from the outside of the device becomes circularly polarized light when only a part of the linearly polarized light passes through the polarizing film, and then passes through the multi-layered film. Circularly polarized light is reflected by the components that reflect light in the image display device (reflective electrodes in organic EL elements, etc.), and passes through the multilayer film again, thereby becoming a vibration direction that is perpendicular to the vibration direction of the incident linearly polarized light The linearly polarized light does not pass through the polarizing film. Here, the vibration direction of the linearly polarized light means the vibration direction of the electric field of the linearly polarized light. Thereby, the function of reflection suppression is achieved.

"Example"

Examples are disclosed below to specifically illustrate the present invention. However, the present invention is not limited to the embodiments disclosed below, and can be implemented with arbitrary changes within the scope not departing from the scope of the patent application and its equivalent scope.

In the following descriptions, "%" and "parts" indicating amounts are based on weight unless otherwise noted. In addition, the operations described below were carried out under the conditions of normal temperature (23° C.), normal pressure (1 atmosphere) and the atmosphere, unless otherwise noted.

<Measuring method of molecular weight of polymer>

The weight average molecular weight of the polymers produced in Examples and Comparative Examples described below was measured in terms of polystyrene conversion using a high-speed GPC device "HLC-8420GPC" manufactured by Tosoh Corporation.

<Measuring method of glass transition temperature of polymer>

The glass transition temperature Tg of the polymer produced in the Examples and Comparative Examples described below was measured at a heating rate of 10° C./min using a differential scanning calorimeter (“DSC7000X” manufactured by Hitachi High-Tech Science Corporation).

<Measurement method of delay appearance>

1 g of the polymer produced in Examples and Comparative Examples described below was pressed using a press under conditions of 250° C., 5 MPa, and 1 minute to produce a sheet with a thickness of 100 μm.

The obtained sheet was cut to form a rectangular pre-stretch film with a size of 50 mm×100 mm. Free-width uniaxial stretching was applied to this unstretched film. The extension was carried out using a tensile test device equipped with a constant temperature bath manufactured by Instron Corporation. The stretching conditions were set at the stretching temperature Tg+10°C, the stretching ratio was 1.5 times, and the stretching speed was 33% per minute. As a result, a retardation film as an optical film was obtained.

The obtained retardation film was measured for in-plane retardation Re at a wavelength of 550 nm using a retardation meter ("AxoScan" manufactured by Axometrics). Re/d was obtained by dividing the obtained in-plane retardation Re by the film thickness d.

<Measuring method of film thickness>

The thickness d of the film was measured with a film thickness measuring device (Mitutoyo's "caliper gauge").

<Measuring method of delamination resistance>

A substrate film (glass transition temperature 160° C., thickness 100 μm, unstretched film manufactured by Zeon Japan Co., Ltd.) formed of a resin containing a northylene-based polymer was prepared. Corona treatment was applied to one side of the substrate film.

Corona treatment was applied to one side of the retardation film obtained in the aforementioned <Measurement Method of Retardation Appearance>. An adhesive is attached to the corona-treated surface of the retardation film and the corona-treated surface of the base film, and the adhesive-attached surfaces are bonded together to cure the adhesive. As the adhesive, an ultraviolet curing adhesive is used. A sample film having a layered structure of retardation film/adhesive layer/substrate film was obtained by the aforementioned lamination.

Cut the sample film to a width of 15 mm to obtain a sample sheet. An intermediary adhesive (double-sided bonding tape "CS9621" manufactured by Nitto Denko Co., Ltd.) on the retardation film side of the sample sheet was bonded to the surface of the slide glass.

A 90-degree peel test was performed by sandwiching the base film between the front end of the load cell and stretching it along the normal direction of the surface of the slide glass. At this time, the force measured when the substrate film is peeled off is the force required to peel the retardation film from the substrate film, so the magnitude of this force is measured as the peel strength.

Generally, the greater the aforementioned peel strength, the better the peel resistance. Furthermore, since the larger the peel strength is, the more the damage of the retardation film can be suppressed when the film is reattached, it means that the reworkability is more excellent. Then, when the peel strength was 5.0 N or more, the delamination resistance was judged as "excellent". And when the peeling strength was 2.0 N or more and less than 5.0 N, the delamination resistance was judged as "good". In addition, when the peeling strength was 1.0 N or more and less than 2.0 N, the peeling resistance was judged as "acceptable". In addition, when the peel strength was less than 1.0 N, the delamination resistance was judged as "poor".

In addition, in each of the Examples and Comparative Examples, observation of the surface of the phase difference film after peeling revealed that cohesion failure occurred in the surface layer portion of the phase difference film, and the surface became rough. Accordingly, in any of the Examples and Comparative Examples, it was confirmed that the delamination of the retardation film occurred, not the delamination at the interface between the base film and the adhesive or the interface between the adhesive and the retardation film.

<Example 1>

Take 1.5 g of methyl acrylate, 28.5 g of ethylene naphthalene, and 6.0 g of tetrahydrofuran into a pressure vessel for nitrogen replacement. Thereafter, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was performed at 60° C. for 24 hours. This reactant was poured into a large amount of 2-propanol, and the polymer was precipitated and separated. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 110,000. Also, the glass transition temperature of the polymer measured by differential scanning calorimetry was 138°C.

A retardation film was manufactured from the obtained polymer by the method described above in <Measurement of Retardation Appearance>, and the retardation was measured, and the result was that Re/d was 14.89×10 ⁻³ . In addition, the delamination resistance was evaluated by the method described in the above-mentioned <Measurement method of delamination resistance>, and the result was "possible".

<Example 2>

Take 3.0 g of methyl acrylate, 27.0 g of ethylene naphthalene, and 6.0 g of tetrahydrofuran into a pressure vessel for nitrogen replacement. Thereafter, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was performed at 60° C. for 24 hours. This reactant was poured into a large amount of 2-propanol, and the polymer was precipitated and separated. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 109,000. Also, the glass transition temperature of the polymer measured by differential scanning calorimetry was 135°C.

A retardation film was manufactured from the obtained polymer by the method described in the above-mentioned "Measurement method of retardation manifestation", and the retardation was measured, and the result was that Re/d was 14.74×10 ⁻³ . In addition, the delamination resistance was evaluated by the method described in the above-mentioned <Measurement method of delamination resistance>, and the result was "possible".

<Example 3>

Take 6.0 g of methyl acrylate, 24.0 g of ethylene naphthalene, and 6.0 g of tetrahydrofuran into a pressure vessel for nitrogen replacement. Thereafter, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was performed at 60° C. for 24 hours. This reactant was poured into a large amount of 2-propanol, and the polymer was precipitated and separated. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 119,000. Also, the glass transition temperature of the polymer measured by differential scanning calorimetry was 124°C.

A retardation film was manufactured from the obtained polymer by the method described above in <Measurement Method of Retardation Appearance>, and the retardation was measured, and the result was that Re/d was 14.66×10 ⁻³ . In addition, the delamination resistance was evaluated by the method described in the above-mentioned <Measurement method of delamination resistance>, and the result was "good".

<Example 4>

Take 9.0 g of methyl acrylate, 21.0 g of ethylene naphthalene, and 6.0 g of tetrahydrofuran into a pressure vessel for nitrogen replacement. Thereafter, 10 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was performed at 60° C. for 24 hours. This reactant was poured into a large amount of 2-propanol, and the polymer was precipitated and separated. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 250,000. Also, the glass transition temperature of the polymer measured by differential scanning calorimetry was 117°C.

A retardation film was manufactured from the obtained polymer by the method described in the above-mentioned "Measurement method of retardation manifestation", and the retardation was measured, and the result was that Re/d was 13.75×10 ⁻³ . In addition, the delamination resistance was evaluated by the method described in the above-mentioned <Measurement method of delamination resistance>, and the result was "good".

<Example 5>

Take 9.0 g of methyl acrylate, 21.0 g of ethylene naphthalene, and 6.0 g of tetrahydrofuran into a pressure vessel for nitrogen replacement. Thereafter, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was performed at 60° C. for 24 hours. This reactant was poured into a large amount of 2-propanol, and the polymer was precipitated and separated. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 97,000. Also, the glass transition temperature of the polymer measured by differential scanning calorimetry was 117°C.

A retardation film was manufactured from the obtained polymer by the method described above in <Measurement Method of Retardation Appearance>, and the retardation was measured, and the result was that Re/d was 13.55×10 ⁻³ . In addition, the delamination resistance was evaluated by the method described in the above-mentioned <Measurement method of delamination resistance>, and the result was "good".

<Example 6>

Take 9.0 g of acrylic acid, 21.0 g of ethylene naphthalene, and 6.0 g of tetrahydrofuran into a pressure vessel for nitrogen replacement. Thereafter, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was performed at 60° C. for 24 hours. This reactant was poured into a large amount of 2-propanol, and the polymer was precipitated and separated. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 126,000. Also, the glass transition temperature of the polymer measured by differential scanning calorimetry was 179°C.

A retardation film was manufactured from the obtained polymer by the method described above in <Measurement Method of Retardation Appearance>, and the retardation was measured, and the result was that Re/d was 13.63×10 ⁻³ . In addition, the delamination resistance was evaluated by the method described in the above-mentioned <Measurement method of delamination resistance>, and the result was "excellent".

[Example 7]

(First step: preparation of substrate film)

A granular resin containing a northylene-based polymer (hereinafter referred to as a northylene-based resin; manufactured by Nippon Zeon Co., Ltd.; a glass transition temperature of 126° C.) was prepared as a resin having a positive intrinsic birefringence value, and was heated at 100° C. Let dry for 5 hours. The dried northylene-based resin is supplied to the extruder, passed through a polymer tube and a polymer filter, and extruded from a T-shaped mold on a casting drum to form a thin sheet. The northylene-based resin extruded into a sheet was cooled to obtain a long unstretched film with a thickness of 60 μm as a base film. Thickness and optical properties are measured for unstretched films. The obtained unstretched film is wound into a roll for recycling.

The polymer prepared in Example 1 was mixed and dissolved with 1,3-dioxanol to obtain a resin solution as a coating liquid. The resin concentration of this resin solution was 15% by weight.

(coating process)

The unstretched film serving as the base film is pulled out from a roll, and the aforementioned resin solution is coated on the pulled out unstretched film.

(drying process)

Thereafter, the coated resin solution was rapidly dried at 120° C., and a layer (thickness: 30 μm) of the polymer prepared in Example 1 was formed on an unstretched film as a base film as an optical film. Thereby, a multilayer film having a layer body of the unstretched film as the base film and the polymer prepared in Example 1 as the optical film was obtained.

(Third process: stretching of multilayer film)

The obtained multilayer film was cut to obtain a rectangular multilayer film before stretching with a size of 50 mm×100 mm. Free-width uniaxial stretching was applied to this multilayer film before stretching. The extension was carried out using a tensile test device equipped with a constant temperature bath manufactured by Instron Corporation. The stretching conditions were set at the stretching temperature Tg+10°C, the stretching ratio was 1.5 times, and the stretching speed was 33% per minute. As a result, a stretched multilayer film including a stretched base film and a stretched retardation film as an optical film was obtained.

The retardation film was peeled off from the multilayer stretched film. This retardation film is a single-layer film of the polymer prepared in Example 1. The in-plane retardation at a wavelength of 550 nm was measured for this retardation film using a retardation meter ("AxoScan" manufactured by Axometrics). Re/d was obtained by dividing the obtained in-plane retardation Re by the film thickness d. Re/d is 14.85×10 ⁻³ .

And, except using the aforementioned retardation film produced in Example 7 instead of the retardation film obtained in the aforementioned <Measurement Method of Retardation Development Property>, it was evaluated by the same method as <Measurement Method of Delamination Resistance> Delamination resistance, the result is "OK".

[Example 8]

(First step: preparation of substrate film)

As a resin having a positive intrinsic birefringence value, a granular norrylene-based resin containing a norrylene-based polymer (manufactured by Nippon Zeon Co., Ltd.; glass transition temperature: 126° C.) was prepared, and dried at 100° C. for 5 hours. The dried northylene-based resin is supplied to the extruder, passed through a polymer tube and a polymer filter, and extruded from a T-shaped mold on a casting drum to form a thin sheet. The northylene-based resin extruded into a sheet was cooled to obtain a long unstretched film with a thickness of 60 μm as a base film. Thickness and optical properties are measured for unstretched films. The obtained unstretched film is wound into a roll for recovery.

The polymer prepared in Example 2 was mixed and dissolved with 1,3-dioxanol to obtain a resin solution as a coating liquid. The resin concentration of this resin solution was 15% by weight.

(coating process)

The unstretched film serving as the base film is pulled out from a roll, and the aforementioned resin solution is coated on the pulled out unstretched film.

(drying process)

Thereafter, the applied resin solution was rapidly dried at 120° C., and a layer (thickness: 30 μm) of the polymer prepared in Example 2 was formed on an unstretched film as a base film as an optical film. Thereby, a multilayer film having a layer body of the unstretched film as the base film and the polymer prepared in Example 2 as the optical film was obtained.

(Third process: stretching of multilayer film)

The obtained multilayer film was cut to obtain a rectangular multilayer film before stretching with a size of 50 mm×100 mm. Free-width uniaxial stretching was applied to this multilayer film before stretching. The extension was carried out using a tensile test device equipped with a constant temperature bath manufactured by Instron Corporation. The stretching conditions were set at the stretching temperature Tg+10°C, the stretching ratio was 1.5 times, and the stretching speed was 33% per minute. As a result, a stretched multilayer film including a stretched base film and a stretched retardation film as an optical film was obtained.

The retardation film was peeled off from the multilayer stretched film. This retardation film is a single-layer film of the polymer prepared in Example 2. The in-plane retardation at a wavelength of 550 nm was measured for this retardation film using a retardation meter ("AxoScan" manufactured by Axometrics). Re/d was obtained by dividing the obtained in-plane retardation Re by the film thickness d. Re/d is 14.85×10 ⁻³ .

And, except using the aforementioned retardation film produced in Example 8 instead of the retardation film obtained in the aforementioned <Measurement Method of Retardation Development Property>, it was evaluated by the same method as <Measurement Method of Delamination Resistance> Delamination resistance, the result is "OK".

<Comparative example 1>

After putting 500 mL of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst in a pressure-resistant reactor that has been dried and replaced with nitrogen, add 35 g of 2-vinylnaphthalene and allow it to react at 25°C for 1 Hour. As a result, a reactant containing poly(2-vinylnaphthalene), which is a homopolymer of 2-vinylnaphthalene, was obtained. This reactant was poured into a large amount of 2-propanol, and poly(2-vinylnaphthalene) was precipitated and separated. The obtained poly(2-vinylnaphthalene) was dried at 200° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the poly(2-vinylnaphthalene) measured by GPC was 250,000. Furthermore, the glass transition temperature of poly(2-vinylnaphthalene) measured by differential scanning calorimetry was 142°C.

A retardation film was manufactured from the obtained poly(2-vinylnaphthalene) by the method described in the above-mentioned "Measurement method of retardation manifestation", and the retardation was measured, and the result was that Re/d was 15.04×10 ⁻³ . In addition, when the delamination resistance was evaluated by the method described in the above-mentioned <Measurement method of delamination resistance>, the result was "poor".

<Comparative example 2>

After putting 500 mL of toluene as a solvent and 0.60 mmol of n-butyllithium as a polymerization catalyst in a pressure-resistant reactor that was dried and replaced with nitrogen, 35 g of 2-vinylnaphthalene was added and reacted at 25°C for 1 Hour. As a result, a reactant containing poly(2-vinylnaphthalene), which is a homopolymer of 2-vinylnaphthalene, was obtained. This reactant was poured into a large amount of 2-propanol, and poly(2-vinylnaphthalene) was precipitated and separated. The obtained poly(2-vinylnaphthalene) was dried at 200° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the poly(2-vinylnaphthalene) measured by GPC was 100,000. Furthermore, the glass transition temperature of poly(2-vinylnaphthalene) measured by differential scanning calorimetry was 142°C.

A retardation film was manufactured from the obtained poly(2-vinylnaphthalene) by the method described in the above-mentioned "Measurement method of retardation manifestation", and the retardation was measured, and the result was that Re/d was 15.04×10 ⁻³ . In addition, when the delamination resistance was evaluated by the method described in the above-mentioned <Measurement method of delamination resistance>, the result was "poor".

<Comparative example 3>

Take 0.6 g of methyl acrylate, 29.4 g of ethylene naphthalene, and 6.0 g of tetrahydrofuran into a pressure vessel for nitrogen replacement. Thereafter, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was performed at 60° C. for 24 hours. This reactant was poured into a large amount of 2-propanol, and the polymer was precipitated and separated. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 112,000. Also, the glass transition temperature of the polymer measured by differential scanning calorimetry was 140°C.

A retardation film was manufactured from the obtained polymer by the method described above in <Measurement Method of Retardation Appearance>, and the retardation was measured, and the result was that Re/d was 15.11×10 ⁻³ . In addition, when the delamination resistance was evaluated by the method described in the above-mentioned <Measurement method of delamination resistance>, the result was "poor".

<Comparative example 4>

Take 15 g of methyl acrylate, 15 g of ethylene naphthalene, and 6.0 g of tetrahydrofuran into a pressure vessel for nitrogen replacement. Thereafter, 20 mg of AIBN (azobisisobutyronitrile) was added, and a polymerization reaction was performed at 60° C. for 24 hours. This reactant was poured into a large amount of 2-propanol, and the polymer was precipitated and separated. The obtained polymer was dried at 180° C. for 24 hours using a vacuum dryer. The weight average molecular weight of the polymer measured by GPC was 115,000. Also, the glass transition temperature of the polymer measured by differential scanning calorimetry was 100°C.

A retardation film was manufactured from the obtained polymer by the method described in the above-mentioned "Measurement method of retardation manifestation", and the retardation was measured, and the result was that Re/d was 9.02×10 ⁻³ . In addition, the delamination resistance was evaluated by the method described in the above-mentioned <Measurement method of delamination resistance>, and the result was "good".

[Comparative Example 5]

(First step: preparation of substrate film)

As a resin having a positive intrinsic birefringence value, a granular norrylene-based resin containing a norrylene-based polymer (manufactured by Nippon Zeon Co., Ltd.; glass transition temperature: 126° C.) was prepared, and dried at 100° C. for 5 hours. The dried northylene-based resin is supplied to the extruder, passed through a polymer tube and a polymer filter, and extruded from a T-shaped mold on a casting drum to form a thin sheet. The northylene-based resin extruded into a sheet was cooled to obtain a long unstretched film with a thickness of 60 μm as a base film. Thickness and optical properties are measured for unstretched films. The obtained unstretched film is wound into a roll for recovery.

The poly(2-vinylnaphthalene) prepared in Comparative Example 2 was mixed and dissolved with 1,3-dioxalanthene to obtain a resin solution. The resin concentration of this resin solution was 15% by weight.

(coating process)

The unstretched film serving as the base film is pulled out from a roll, and the aforementioned resin solution is coated on the pulled out unstretched film.

(drying process)

After that, the coated resin solution was rapidly dried at 120°C, and a layer (thickness: 30 μm) of poly(2-vinylnaphthalene) prepared in Comparative Example 2 was formed on the unstretched film as the base film as an optical film. . Thereby, a multilayer film including a layer body of an unstretched film as a base film and poly(2-vinylnaphthalene) synthesized in Comparative Example 2 as an optical film was obtained.

(Third process: stretching of multilayer film)

The obtained multilayer film was cut to obtain a rectangular multilayer film before stretching with a size of 50 mm×100 mm. Free-width uniaxial stretching was applied to this multilayer film before stretching. The extension was carried out using a tensile test device equipped with a constant temperature bath manufactured by Instron Corporation. The stretching conditions were set at the stretching temperature Tg+10°C, the stretching ratio was 1.5 times, and the stretching speed was 33% per minute. As a result, a stretched multilayer film including a stretched base film and a stretched retardation film as an optical film was obtained.

The retardation film was peeled off from the multilayer stretched film. This retardation film is a single-layer film of poly(2-vinylnaphthalene) prepared in Comparative Example 2. The in-plane retardation at a wavelength of 550 nm was measured for this retardation film using a retardation meter ("AxoScan" manufactured by Axometrics). Re/d was obtained by dividing the obtained in-plane retardation Re by the film thickness d. Re/d is 15.05×10 ⁻³ .

And, except using the aforementioned retardation film manufactured in Comparative Example 2 instead of the retardation film obtained in the aforementioned <Measurement Method of Retardation Appearance>, evaluation was performed by the same method as <Measurement Method of Delamination Resistance> Delamination resistance, the result is "poor".

<result>

The results of the above-mentioned examples and comparative examples are disclosed in the table below. In the table below, the value in the column of Re expressibility shows the magnitude of the value of Re/d in each example or comparative example when the value of Re/d in Comparative Example 1 is set to 100%. And, in the table below, the abbreviations have the following meanings. AA: Acrylic. MA: methyl acrylate. VN: ethylene naphthalene. Mw: weight average molecular weight. Tg: glass transition temperature. Re/d: the ratio of the in-plane retardation Re to the thickness d at the measurement wavelength of 550 nm.

[Table 1] [Table 1. Results of Examples and Comparative Examples] monomer polymer Evaluation results MA [wt%] AA [wt%] VN [wt%] mw Tg [℃] Re/d [×10 ^-3 ] Revisibility[%] Delamination resistance Example 1 5 0 95 110000 138 14.89 99 Can 2 10 0 90 109000 135 14.74 98 Can 3 20 0 80 119000 124 14.66 96 good 4 30 0 70 250000 117 13.75 92 good 5 30 0 70 97000 117 13.55 90 good 6 0 30 70 126000 179 13.63 91 excellent 7 Same as Example 1 (co-extension) 14.85 99 Can 8 Same as Example 2 (co-extension) 14.70 98 Can comparative example 1 0 0 100 250000 142 15.04 100 bad 2 0 0 100 100000 142 15.04 100 bad 3 2 0 98 112000 140 15.11 100 bad 4 50 0 50 115000 100 9.02 60 good 5 Same as Comparative Example 2 (co-extension) 15.05 100 bad

<discuss>

From the results of Comparative Examples 1 and 2, it was confirmed that the delamination resistance of the optical film formed of a homopolymer of a polycyclic aromatic vinyl compound such as polyethylene naphthalene is poor.

Furthermore, from the results of Comparative Example 3, it was confirmed that the copolymer containing 2% by weight of the (meth)acrylic compound unit did not see improvement in delamination resistance.

Furthermore, from the results of Comparative Example 4, it was confirmed that the retardation development property of the copolymer containing 50 weight% of (meth)acrylic compound units was inferior.

In contrast, in Examples 1 to 6, since an appropriate amount of (meth)acrylic compound units and polycyclic aromatic vinyl compound units were combined, both of retardation development property and delamination resistance were excellent. In particular, Example 6 was excellent in delamination resistance. The particularly excellent delamination resistance of Example 6 is conceivably obtained because the (meth)acrylic compound unit is derived from acrylic acid and has a carboxyl group.

Furthermore, in Examples 7 and 8 and Comparative Example 5, a multilayer film before stretching including a base film and an optical film was produced, and this multilayer film before stretching was stretched. By stretching the multilayer film before stretching, the base film and the optical film are co-extended, so that a stretched retardation film as an optical film can be obtained. From the results of Examples 7 and 8 and Comparative Example 5, it is clear that even when the substrate film and the optical film are co-extended to produce a retardation film, it is possible to obtain a retardation film having the same characteristics as that obtained by stretching the optical film alone. Retardation and delamination resistance retardation film as an optical film.

In the aforementioned examples and comparative examples, the proportions of polycyclic aromatic vinyl compound units and (meth)acrylic acid compound units contained in the produced polymers were measured by ¹ H-NMR. From the aforementioned measurement, it was confirmed that the insertion ratio of the polycyclic aromatic vinyl compound as a monomer coincided with the ratio of the polycyclic aromatic vinyl compound unit contained in the polymer. Furthermore, it was confirmed from the aforementioned measurement that the ratio of the incorporated (meth)acrylic compound as a monomer coincides with the ratio of the (meth)acrylic compound unit contained in the polymer.

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Claims (9)

An optical film comprising a copolymer containing a polycyclic aromatic vinyl compound unit and a (meth)acrylic compound unit, wherein the proportion of the (meth)acrylic compound unit in the copolymer is 5% by weight or more and 40% by weight %the following. The optical film according to claim 1, wherein the weight average molecular weight Mw of the copolymer is 50,000 to 500,000. The optical film according to claim 1, wherein the copolymer contains a repeating unit having a structure formed by polymerizing ethylene naphthalene. The optical film according to claim 1, wherein the glass transition temperature of the copolymer is above 110°C. The optical film according to Claim 1, wherein the ratio Re/d of the in-plane retardation Re to the thickness d of the optical film at a measurement wavelength of 550 nm is 10.0×10 ⁻³ or more. A multilayer film comprising a substrate film and the optical film as claimed in claim 1. The multilayer film according to claim 6, wherein the base film comprises a polymer containing an alicyclic structure. A method for producing a multilayer film, which is a method for producing a multilayer film comprising a substrate film and an optical film, comprising coating the substrate film with a coating solution comprising a copolymer, wherein the copolymer contains a polycyclic aromatic vinyl compound unit and a (meth)acrylic compound unit, the amount of the said (meth)acrylic compound unit in the said copolymer is 5 weight% or more and 40 weight% or less. A polarizing plate comprising the multilayer film and polarizing film as described in claim 6 or 7.