JP2023001907A - Film - Google Patents

Abstract

To provide a film that achieves both thickness reduction and visibility (rainbow unevenness prevention) and is excellent in productivity.SOLUTION: A film contains a polyester resin as a main component. A dicarboxylic acid unit constituting the polyester resin includes a naphthalene dicarboxylic acid in an amount of more than 50 mol% and 100 mol% or less. The film has a phase difference of 3000 nm or more and 30000 nm or less. The film has both a tear strength in a longitudinal direction and a tear strength in a width direction of 2 N/mm or more.SELECTED DRAWING: None

Description

The film of the present invention relates to a film suitable for polarizer protection applications.

A polarizing plate generally includes a transparent film on one or both sides of a polarizer for the purpose of protecting the polarizer. As a polarizer, for example, a polyvinyl alcohol (PVA)-based film on which iodine is adsorbed and whose molecules are oriented by stretching or the like is widely used. Cellulose-based films such as triacetylcellulose (TAC) films are widely used as the transparent protective film to be attached to the surface of the polarizer because of their excellent adhesiveness to PVA-based polarizers. Under such circumstances, replacement of the conventional TAC film with a biaxially stretched polyester film for the polarizer protective film has been actively studied for the purpose of cost reduction and thinning of the polarizing plate.

However, the biaxially stretched polyester film has a higher retardation than the TAC film due to the orientation of the polymer during stretching. There is a problem that the display quality is degraded. To solve this problem, it has been shown that the rainbow unevenness can be solved by making the polarizing axis of the polarizer and the main alignment axis of the polyester film, which is a protective film of the polarizer, substantially parallel and setting the retardation to 3000 to 30000 nm (Patent Document 1). Further, it has been shown that iridescent unevenness is further reduced by introducing a naphthalene dicarboxylic acid unit into the structural units of a polyester resin (Patent Document 2).

Japanese Patent Application Laid-Open No. 2020-73951 JP 2016-38534 A

However, polyester films containing naphthalenedicarboxylic acid units have weaker tear propagation resistance than polyethylene terephthalate (PET) films. There was a problem that it became easy to tear along and it was difficult to form a film stably. The object of the present invention was made against the background of the above-mentioned problems of the prior art, and while using naphthalene dicarboxylic acid units as main structural units, it is possible to achieve both thin film formation and visibility (rainbow unevenness), which were difficult in the past. Another object of the present invention is to provide a film excellent in productivity.

The film of the present invention has the following constitutions in order to solve the above problems. That is, the main component is a polyester resin, and more than 50 mol% and 100 mol% or less of the dicarboxylic acid units constituting the polyester resin are naphthalene dicarboxylic acid units, and the retardation is 3000 nm or more and 30000 nm or less, and in the longitudinal direction. and a tear strength in the width direction of 2 N/mm or more.

Further, the film of the present invention can be configured as follows in order to solve the above problems, and an image display device equipped with the film of the present invention can also be provided.
(1) a polyester resin as a main component, more than 50 mol% and 100 mol% or less of dicarboxylic acid units constituting the polyester resin are naphthalene dicarboxylic acid units, a retardation is 3000 nm or more and 30000 nm or less, and longitudinal A film having both directional and transverse tear strengths of 2 N/mm or more.
(2) A layer mainly composed of a polyester resin (polyester resin A) in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid units are naphthalene dicarboxylic acid units, and a resin different from the main component of the A layer. The film according to (1), wherein the B layer as a component has a structure in which at least 5 to 100 layers are alternately laminated.
(3) A layer mainly composed of a polyester resin (polyester resin A) in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid units are naphthalene dicarboxylic acid units, and a resin B different from the polyester resin A as the main component. A B layer and a C layer having a different composition from the A layer and the B layer have a structure in which the A layer, the C layer, the B layer, and the C layer are repeatedly laminated in this order, and in the C layer , the content of the polyester resin A is less than the layer B, the content of the resin B is less than the layer B, and the total number of the layers A, B, and C is 5 or more and 100 The film of (1), which is no more than a layer.
(4) The film according to (3), wherein the layer C contains the polyester resin A and the resin B.
(5) The film according to (3), wherein the layer C comprises a copolymer containing the polyester resin A structural unit and the resin B structural unit as a main component.
(6) The film according to (3), wherein the layer C has an alloy structure in which one of the polyester resin A and the resin B is a domain and the other is a matrix.
(7) The film according to any one of (1) to (6), wherein the ratio of the refractive index in the longitudinal direction/the refractive index in the width direction is 1.03 or more.
(8) The film according to any one of (1) to (7), which has an average reflectance of 20% or less in a wavelength band of 300 to 2500 nm.
(9) The film according to any one of (2) to (8), wherein the layer B has a DSC heat of crystal fusion of 5 J/g or more.
(10) The main component of the layer B is a polyester resin (polyester resin B), and the glycol units constituting the polyester resin B are cyclohexanedimethanol units, 2,2-bis(4′-β-hydroxyalkoxyphenyl ) The film according to any one of (2) to (8), comprising at least one propane unit.
(11) Any one of (1) to (10), wherein an easy-adhesion layer and a hard coat layer are laminated in this order on at least one surface, and the easy-adhesion layer has a layer thickness of 70 nm or more and 120 nm or less. Film as described.
(12) The film according to any one of (1) to (11), which is used for protecting a polarizer.
(13) An image display device comprising the film according to any one of (1) to (12).

ADVANTAGE OF THE INVENTION By this invention, the film which can ensure the favorable visibility by which generation|occurrence|production of iridescent unevenness was suppressed even if it changes an observation angle though it is a thin film can be provided. Moreover, since the film of the present invention also has high mechanical strength, it is possible to reduce troubles associated with breakage during the film-forming process and the process of using the film as a product.

The film of the present invention will be described below. The film of the present invention contains a polyester resin as a main component, more than 50 mol% and 100 mol% or less of the dicarboxylic acid units constituting the polyester resin are naphthalene dicarboxylic acid units, and the retardation is 3000 nm or more and 30000 nm or less, Moreover, the tear strength in both the longitudinal direction and the width direction is 2 N/mm or more.

It is important that the film of the present invention has a retardation of 3000 nm or more and 30000 nm or less from the viewpoint of achieving both reduction of iridescent unevenness and improvement of handleability. Here, the retardation means an in-plane retardation (the product of the thickness and the refractive index difference between the main alignment axis and the azimuth axis tilted by 90° from the main alignment axis). If the retardation is less than 3000 nm, when used as a polarizer protective film, strong rainbow unevenness is exhibited when observed from an oblique direction, and good visibility cannot be ensured. From the above point of view, the preferable lower limit of the retardation is 4000 nm, more preferably 4500 nm, still more preferably 6000 nm. On the other hand, if the retardation exceeds 30,000 nm, not only is there no substantial effect of improving visibility, but the film thickness is considerably increased, resulting in poor handling as an industrial material. The phase difference of the present invention can be measured using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments Co., Ltd.), and detailed measurement conditions are shown in Examples.

As a method for adjusting the retardation to 3000 nm or more and 30000 nm or less, or the above preferred range, a method of appropriately adjusting the draw ratio, the draw temperature, and the thickness of the film can be used. Since the retardation is the product of the film thickness and the refractive index anisotropy, the thicker the film, the higher the retardation. In the case of biaxial stretching, the higher the stretching ratio of either the longitudinal stretching or the lateral stretching, and the lower the stretching temperature, the higher the refractive index of one of them, which tends to result in a high retardation. Ultimately, uniaxial stretching is the stretching method that increases the retardation.

In addition, by stretching the film at a high magnification in the uniaxial direction, the refractive index anisotropy increases and the retardation increases, while at the same time tearing in the direction of stretching becomes easier. This tendency is particularly noticeable in films containing a naphthalenedicarboxylic acid component. In other words, there is a trade-off relationship between improvement in retardation and tear resistance, so it is also important to balance the two. In the case of a film with a laminated structure, if an amorphous component is used in a specific layer, the thickness of the layer that exhibits refractive index anisotropy changes according to the lamination ratio, so even if the film thickness is the same, the amorphous component A higher retardation value is not obtained as compared with the case without the layer. In the case of a laminated film, by increasing the thickness ratio of the resin layer exhibiting refractive index anisotropy in the entire film, it is possible to obtain a mode exhibiting a high retardation. However, when both resins constituting the laminated film exhibit refractive index anisotropy, the lamination ratio may be appropriately adjusted according to the degree of anisotropy to satisfy the above retardation range.

The film of the present invention, from the viewpoint of achieving both a thin film and a retardation, contains a polyester resin as a main component, and more than 50 mol% and 100 mol% or less of the dicarboxylic acid units constituting the polyester resin are naphthalenedicarboxylic acid units. This is very important. When the polyester resin, which is the main component, contains more than 50 mol % of the naphthalenedicarboxylic acid unit, the retardation can be increased while suppressing the film thickness. Therefore, it can be suitably used as a polarizer protective film with little iridescent unevenness when observed from an oblique direction. From the above viewpoint, the naphthalenedicarboxylic acid unit in the polyester resin, which is the main component, is more preferably 70 mol % or more and 100 mol % or less of the dicarboxylic acid units constituting the polyester resin.

Here, the polyester resin is a resin obtained by polymerization from a monomer having an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol as main constituents. It refers to a component contained in more than 50% by mass and up to 100% by mass when expressed as % by mass.

Further, in a film having a lamination structure described later, it is necessary that the naphthalene dicarboxylic acid unit is more than 50 mol % and not more than 100 mol % of the dicarboxylic acid units contained in the entire film. For example, in a two-layered film in which layers A and B are alternately laminated, a polyester resin in which all the dicarboxylic acid units are naphthalene dicarboxylic acid units is used as the resin constituting the A layer, and a dicarboxylic acid resin is used as the resin constituting the B layer. Assuming that a polyester resin containing no acid units is used, if the lamination ratio is 1 (A layer: B layer = 1:1), the ratio of naphthalenedicarboxylic acid units to the dicarboxylic acid units in the entire film is 50 mol %. As another example, if the film has the same structure and a lamination ratio of 2 (A layer: B layer = 2: 1), the polyester resin constituting the A layer tightens 2/3 of the entire film, so the dicarbonate of the entire film The ratio of the naphthalenedicarboxylic acid units to the acid units is 67 mol %. Moreover, when the resin constituting the B layer is a resin such as an olefin resin that does not contain dicarboxylic acid units, it can be treated as containing 0 mol % of dicarboxylic acid units.

Furthermore, if the above resin is used and the laminated film is composed of five layers of (AB) ₂ A and the lamination ratio is 1, the ratio of the A layer to the entire film is 3/5 = 60%. The ratio of naphthalenedicarboxylic acid units to the total dicarboxylic acid units is 60 mol %. Thus, the naphthalene dicarboxylic acid units in the dicarboxylic acid units in the film are calculated from the mol % of the naphthalene dicarboxylic acid units of each resin, the number of layers, the repeating unit, and the layering ratio. This interpretation can be interpreted in the same way for a film having the structure (ACBC)x (where x is a natural number representing the number of repeating units), which will be described later.

Examples of components (subcomponents) that are not main components include inorganic components other than thermoplastic resins and low-molecular-weight organic components. Specific examples include light absorbers (ultraviolet absorbers, dyes, pigments, heat-absorbing agents), antioxidants, light stabilizers, quenching agents, heat stabilizers, weather stabilizers, organic lubricants, fillers, antistatic agents, nucleating agents, flame retardants, and the like. Since the laminated film of the present invention is suitably used as a polarizer protective film, it preferably contains an ultraviolet absorber in order to prevent PVA used in the polarizing plate from deteriorating due to ultraviolet rays.

Dicarboxylic acids include aromatic dicarboxylic acids and aliphatic dicarboxylic acids. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid (among these, 1,4-naphthalenedicarboxylic acid, 1,5- -naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid.), 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, and the like. can. Examples of aliphatic dicarboxylic acids include adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid and their ester derivatives.

These dicarboxylic acid components may be used alone or in combination of two or more as long as the resulting polyester resin has more than 50 mol% and 100 mol% or less of the dicarboxylic acid units being naphthalene dicarboxylic acid units. Furthermore, hydroxy acids such as hydroxybenzoic acid may be partially copolymerized. Among them, 2,6-naphthalenedicarboxylic acid is preferable because it has a high intrinsic birefringence and the retardation can be easily controlled by stretching. Therefore, compared with other polyesters, even if the film thickness is thin, a large retardation can be obtained relatively easily, so it is the most suitable material constituent component.

Examples of diol components include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. , 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4- hydroxyethoxyphenyl)propane, isosorbate, spiroglycol, and the like. Among them, neopentyl glycol and ethylene glycol are preferably used. These diol components may be used alone, or two or more of them may be used in combination.

In the latter case, neopentyl glycol units are preferably contained because neopentyl glycol hardly lowers the refractive index in the thickness direction during stretching and makes it difficult to see iridescent unevenness when formed into a film. On the other hand, if the neopentyl glycol unit is excessive, the mechanical strength of the film is significantly reduced, so the neopentyl glycol unit may be in the range of 5 mol% or more and 30 mol% or less of the diol units constituting the polyester resin. preferable.

Of the ethylene glycol components, the polyethylene glycol component, which is a polymer, can be combined with naphthalene dicarboxylic acid to improve brittleness and improve the stretchability and moldability of the film, and the tear strength in the present invention is somewhat improved. Since it is enhanced, it is preferable as a copolymer component to be combined. On the other hand, excessive inclusion of polyethylene glycol units in a copolymer may lead to a significant decrease in mechanical strength when formed into a film, similar to neopentyl glycol units. Therefore, when the polyester resin contains a polyethylene glycol unit, it is preferable that the polyethylene glycol unit is in the range of 2 mol % or more and 30 mol % or less in 100 mol % of all structural units.

Moreover, the film of the present invention has a tear strength of 2 N/mm or more in both the longitudinal direction and the width direction. The tear strength depends on the type of other polyester resin to be laminated, compatibility, crystallinity, film thickness, draw ratio (ratio), heat treatment temperature, and in the case of laminated films described later, the relationship between the number of layers and film thickness. do. Among them, the tear strength is particularly strongly dependent on the draw ratio, and in order to obtain a high retardation film having a retardation of 3000 nm or more and 30000 nm or less, according to the stretching method described later, either the longitudinal direction or the width direction It is necessary to make the draw ratio relatively large. On the other hand, at such a high draw ratio, the tear strength of the film in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid units constituting the polyester resin is naphthalene dicarboxylic acid units is low, and the film is easily broken during stretching. This makes stable stretching difficult. Furthermore, in order to prevent breakage during post-processing steps such as bonding, it is more preferable that the tear strength in both the longitudinal direction and the width direction is 4 N/mm or more.

Tear strength can be measured by the following method. In addition, the tear strength in the longitudinal direction is described in the following measurement method, but the tear strength in the width direction can be similarly measured by changing the measurement direction. As a measuring device, for example, a light load tear tester (No. 193) manufactured by Toyo Seiki Seisakusho is used. A specific measurement method using the apparatus is as follows. First, the film was sampled into a rectangle of 63.5 mm in the longitudinal direction and 50.8 mm in the width direction, and a 12.7 mm long cut was made in the sample in parallel with the longitudinal direction from the central end of 50.8 mm in the width direction. , each of the scored 25.4 mm wide sample strips is clamped in a tension clamp. Subsequently, tear the remaining 50.8 mm in the longitudinal direction along the cut to determine the tear force (N) in the longitudinal direction. The tearing force is divided by the thickness of the film to obtain the longitudinal tearing strength (N/mm). The above measurements are performed on 10 samples, and the average value of 8 data, excluding the highest and lowest values, is used as the final tear strength. Here, in a film having a laminated structure, which will be described later, delamination may be observed during measurement instead of tearing parallel to the cutting direction. At this time, the data is not adopted, and the same analysis is repeated so that the n number is 10, and a total of 10 points of data are obtained.

As a method of setting the retardation to 3000 nm or more and 30000 nm or less and setting the tear strength in both the longitudinal direction and the width direction to 2 N / mm or more or the above preferred range, the draw ratio ratio in the longitudinal direction and the width direction (stretch ratio in the longitudinal direction / The stretch ratio in the width direction) is 3.50 or more or 0.286 or less, and at least 5 to 100 layers are laminated according to a certain repeating unit, and at least 2 or more layers containing different resins as main components are laminated. It is preferable to have Further, even in the case of a single film, it is possible to achieve both retardation and tear strength by using a resin containing a copolymer component exhibiting flexibility such as polyethylene glycol and by satisfying the above draw ratio. can be done. More preferably, the stretch ratio in the longitudinal direction and the width direction is 4.00 or more or 0.250 or less, and the above two or more layers are laminated in at least 10 to 50 layers according to a certain repeating unit. To have. A preferred combination of the two or more types of layers will be described later.

First, the case of a laminated film in which two types of layers are alternately laminated will be described. From the viewpoint of achieving both film formability and tear resistance, the film of the present invention contains a polyester resin (polyester resin A) in which more than 50 mol% and 100 mol% or less of dicarboxylic acid units are naphthalenedicarboxylic acid units as a main component. It is preferable to have a structure in which at least 5 layers or more and 100 layers or less of layers A and layers B whose main component is a resin different from the main component of the A layer are alternately laminated.

Alternating lamination means that the A layer and the B layer are composed of repeating units of (AB)x or (BA)x (where x is a natural number representing the number of repeating units). The outermost surface of the laminated film may be made of the same resin on both sides, or may be made of different resins. That is, the laminate structure of the film may be any of the patterns (AB)xA, (AB)x, (BA)xB, and (BA)x.

On the other hand, as in the manufacturing method described later, when stretching in the longitudinal direction using the peripheral speed difference of the rolls or stretching in the width direction by gripping with clips, the layers located on both outermost surfaces are the same layer. preferably. This is because stretching is often performed under fixed temperature conditions in general film formation, and if the two outermost layers are different, the temperature conditions suitable for one layer may be unsuitable for the other layer. As a result, the film may break during film formation due to adhesion to rolls and clips. Therefore, among the structures described above, it is preferable to have a laminated structure of (AB)xA or (BA)xB (where the same resin layer is arranged on both surfaces) (where a natural number represents the number of repeating units). Among them, when the A layer is mainly composed of a polyester resin (polyester resin A) in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid units are naphthalene dicarboxylic acid units, the A layer has sufficient oriented crystallinity and In order to exhibit thermal crystallinity, a (AB)xA lamination structure having the A layer as the outermost layer is more preferable in terms of enhancing the film forming stability.

A monolayer film formed of a polyester resin (corresponding to the main component of the layer A) having naphthalenedicarboxylic acid units strongly stretched in a specific direction tends to tear in a direction parallel to the stretching direction due to the properties of the resin. On the other hand, by alternately laminating the A layer and the B layer, the B layer acts as a support layer, making it difficult for the tearability of the A layer to propagate throughout the film, thereby improving the tear strength of the entire film. Specifically, before the tearing due to the cleavage of the resin occurs, the peeling of the A layer and the B layer and the step of elongating the B layer intervene, so that the tearing of the A layer containing a large amount of naphthalenedicarboxylic acid component, and eventually the film Overall tearing is less likely to occur. In order to enhance this effect, it is effective to increase the adhesion (compatibility) between the A layer and the B layer, or to control the number of layers within a specific range.

Furthermore, from the viewpoint of further increasing the tear strength of the laminated film, the film of the present invention contains a polyester resin (polyester resin A) in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid units are naphthalene dicarboxylic acid units as a main component. A layer, a B layer mainly composed of a resin B different from the polyester resin A, and a C layer having a different composition from both the A layer and the B layer are the A layer, the C layer, the B layer, and the C layer in that order. Having a repeatedly laminated structure, in the C layer, the content of the polyester resin A is less than the B layer, and the content of the resin B is less than the B layer, and the total number of the A layer, the B layer, and the C layer is preferably 5 to 100 layers. In addition, the C layer may be configured such that one or both of the polyester resin A and the resin B are not included.

By adopting such a laminated structure, there is a C layer that can be a buffer layer that enhances adhesion between the A layer and the B layer of the alternately laminated structure, and the alternately laminated film has insufficient adhesion depending on the combination. Adhesion can be improved even with the resin combination of the A layer and the B layer. As a result, the force required for the peeling process before the film is torn increases, and the tear resistance of the laminated film itself can be improved. Hereinafter, the structure in which the A layer, the C layer, the B layer, and the C layer are repeatedly laminated in this order is referred to as (ACBC)x structure (x is a natural number representing the number of repeating units) for convenience. In particular, the average layer thickness of the A layer, which strongly affects the retardation, is preferably 3.0 μm or more from the viewpoint of reducing optical interference due to reflection at the layer interface, and the average layer thickness of the B layer and the C layer is 1.0 μm or less. is preferred. From the above viewpoint, the average thickness of the layer A is more preferably 3.5 μm or more, and the average thickness of the layers B and C is more preferably 0.7 μm or less.

Improved tear strength in films having the (ACBC)x configuration can be achieved by controlling the resin design and processing process. Preferred conditions for increasing the tear strength of the film of this configuration are described below, but it is not essential to employ all of these conditions at the same time, and they can be employed singly or in combination as appropriate.

Preferred resin designs from the viewpoint of improving tear strength are described below. For example, the layer C contains the polyester resin A and the resin B, the main component is a copolymer containing the constituent units of the polyester resin A and the constituent units of the resin B, or the polyester resin A and the resin B By having an alloy structure with domains on one side and matrix on the other, the tear strength of the film with the (ACBC)x configuration can be improved.

In the thermoplastic resin constituting the C layer, the amount of common components to be mixed, copolymerized, or kneaded with an alloy (ratio of structural units common to the resins constituting the A layer and B layer) is When the total amount of structural units is 100 mol %, the content of structural units having a common chemical structure is 60 mol % or more and 95 mol % or less, so that the tear strength can be easily improved.

In the case of polyethylene naphthalate, for example, the constituent units are 50 mol % of naphthalenedicarboxylic acid units, which are dicarboxylic acid units, and 50 mol % of ethylene glycol units, which are diol units, for a total of 100 mol %. If the layer A consists only of polyethylene naphthalate and the layer C consists only of polyethylene terephthalate containing 10 mol% of naphthalene dicarboxylic acid units, the ethylene glycol units are common to both, and 20% of the dicarboxylic acid units (total 10 mol %) are common, the common component of the A layer and the C layer is 60 mol %. Moreover, the amount of the common component of the B layer and the C layer can also be calculated by the same way of thinking.

When the amount of the common component in the C layer with the A layer and the B layer exceeds 60 mol %, the mutual molecules easily form an intermolecular interaction, and the compatibility is enhanced. This method is the simplest method, but since components with different basic skeletons coexist in the thermoplastic resin that mainly constitutes the layer, depending on the dispersed and mixed state, the layer will mainly consist A component having a different basic skeleton exists in a thermoplastic resin as a large domain that causes light diffusion, which may increase the degree of cloudiness (haze) and impair the transparency of the film. Such a domain problem can be solved by increasing the degree of dispersion of thermoplastic resins. It is possible to increase the degree of kneading by increasing the number ratio or by changing the arrangement of the segments related to kneading of the screws so that the screws are deeply meshed with each other. Alternatively, it is also preferable to include an additive (dispersant) having a common skeleton that enhances the interaction of the thermoplastic resin.

On the other hand, as another method for increasing the tear strength in terms of resin design, the adjacent thermoplastic resin layer on one side contains a terminal functional group component that reacts with the unreacted functional group component contained in the thermoplastic resin layer on the other side. Formulations that allow the Specifically, the unreacted terminal group contained in the thermoplastic resin forming the thermoplastic resin layer on one side, or the terminal group contained in the additive previously added in the layer on one side, and the reactive additive In this method, a component having the same basic skeletal structure as that of the adjacent thermoplastic resin layer is added by reacting to enhance the interaction. Such a reaction is, for example, when one layer contains a terminal carboxyl group, an additive containing a terminal group highly reactive with a carboxyl group such as a phenol group, an epoxy group, or an amino group is used as a reactive additive. Moreover, when the layer on one side contains an alkoxysilyl group terminal, it can be realized by adding an additive containing an inorganic filler or a metal component as a reactive additive. In the case of this method, as in the case of copolymerizing, alloying, or blending thermoplastic resins, in addition to the problem of haze increase due to the state of dispersion, unreacted additives are heated before the lamination process. In some cases, the reaction progresses further when it is applied, and the rheological properties change, causing a problem of lamination disturbance in the lamination process.

Therefore, as another aspect, there is a prescription in which the adjacent thermoplastic resin layer on one side contains an unreacted functional group that reacts with the unreacted functional group component contained in the thermoplastic resin layer on the other side. In this method, the thermoplastic resins supplied from individual extruders in the lamination process react at the interface only when they come into contact with each other during the lamination process in the lamination device. This is preferable because it does not change the rheological behavior of before the lamination step, and the occurrence of lamination disorder can be reduced to improve adhesion. As a combination of functional groups that realizes such a reaction, the combination of functional groups described above can be used.

Further, as a lamination process capable of increasing the tear strength of the film of the present invention, in the case of the stretching process described later as an example, the temperature in the heat treatment process in the tenter is set to the melting point of the thermoplastic resin forming the outermost layer of the film. It is preferably lower than the melting point of the thermoplastic resin forming the thermoplastic resin layer with the lowest melting point. More preferably, among the thermoplastic resins constituting the plurality of thermoplastic resin layers forming the (ACBC)x structure, the thermoplastic resin having the highest melting point next to the thermoplastic resin of the thermoplastic resin layer corresponding to the outermost layer is the melting point of the thermoplastic resin or more. It is to heat-treat at When a thermoplastic resin that exhibits crystallinity is used as the main component of the thermoplastic resin layer different from the thermoplastic resin layer arranged on the outermost layer in the film by heat treatment in the above temperature range, crystals of the present resin are used. is melted into an amorphous molecule, and its molecular motion is activated by heat. As a result, the adjoining thermoplastic resin macromolecules at the interface diffuse into each other and the molecules become entangled with each other, increasing the compatibility between the two. In the case where the layer other than the thermoplastic resin layer corresponding to the outermost layer of the film is an amorphous thermoplastic resin that does not exhibit a melting point, at a temperature below the melting point of the thermoplastic resin forming the outermost thermoplastic resin layer, It is preferable that the heat treatment is performed at a high temperature as close to the melting point as possible. The heat treatment temperature of the laminated film can be grasped from the crystallite melting temperature (Tmeta) when the thermal properties of the film are measured with a differential scanning calorimeter (DSC) in the measurement method described later.

In the film of the present invention, crystalline indicates a melting enthalpy of 10 J/g or more, semicrystalline indicates a melting enthalpy of 0.1 J/g or more and less than 10 J/g, and amorphous indicates any of the above. It is defined as the case where neither All of the crystallinity, semi-crystallinity, and amorphousness referred to herein can be determined using a differential scanning calorimetry (DSC) instrument. The thermoplastic resin constituting the crystalline and semi-crystalline thermoplastic resin layers is characterized by exhibiting three points: a glass transition temperature, an endothermic peak of crystallization enthalpy, and an exothermic peak of melting enthalpy. Depending on the type of crystalline thermoplastic resin, the glass transition temperature may not fall within the measurement range described later, so here the degree of crystallinity is determined from the magnitude of the melting enthalpy.

Preferred laminate structures and film properties that should be common to the film having the (AB)x structure and the film having the (ACBC)x structure are described below.

In the above laminated film, in order to satisfy the range of retardation that can reduce rainbow unevenness, among the resins contained in the entire film, a naphthalenedicarboxylic acid component (naphthalenedicarboxylic acid unit) that exhibits high birefringence due to stretch orientation is The total content is preferably 50 mol % or more and 100 mol % or less. In order to achieve such an aspect, only the A layer in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid units are naphthalenedicarboxylic acid units contains naphthalenedicarboxylic acid, and the A layer has a lamination ratio showing a laminated film. Even in a film design that occupies the majority, at least two of the plurality of resins constituting the film contain naphthalenedicarboxylic acid units, and the ratio of these resins in the film is the majority. good too. Among them, as described above, considering that the adhesion at each interface of the laminated film has an effect on increasing the tear strength, it has a structural unit of (ACBC) x and contains 50 mol% of the dicarboxylic acid unit. In addition to the layer A in which more than 100 mol % or less of the naphthalenedicarboxylic acid unit is included, at least the resin that is the main component of the layer C that is the intermediate layer is preferably formed from a polyester resin containing the naphthalenedicarboxylic acid unit.

From the viewpoint of achieving both film formability and tear resistance, the number of layers of the film of the present invention is preferably 5 to 100 layers, more preferably 10 to 64 layers, and still more preferably 10 layers or more. 50 layers or less, most preferably 16 to 32 layers. When the number of layers is 5 or more, the effect of suppressing the propagation of breakage due to the presence of multiple interfaces is sufficient, and breakage during the film forming process is reduced. In particular, a film with high uniaxial molecular orientation such as a uniaxially oriented film is likely to break during the film-forming process, and it is important to impart tear resistance. Conversely, when the number of laminated layers is 100 or less, the layer thickness per layer does not become excessively thin, and loss of tear resistance effect can be reduced. From the viewpoint of preventing optical interference due to reflection at layer interfaces, the average layer thickness obtained by dividing the total thickness excluding thick layers such as the outermost layer and the intermediate layer by the number of layers is preferably 0.9 μm or more, more preferably 1 μm. .2 μm or more.

As a lamination method for obtaining the laminated structure of the film of the present invention, a multi-manifold die method or a feed block method in which lamination is performed in front of the spinneret may be used. It is better to use a special coextrusion method in which the number of layers is sequentially increased by expanding, cutting, or superimposing the molten resin layer like a method. Therefore, it is preferable.

In addition, although the advantages of the above-mentioned laminated structure of 5 or more layers cannot be obtained, from the viewpoint of film formation stability, more than 50 mol% and 100 mol% or less of the dicarboxylic acid unit is a polyester resin (polyester When layer A is mainly composed of resin A) and layer B is mainly composed of a resin different from that of layer A, a two-layer structure of A/B or a three-layer structure of A/B/A is obtained. is also preferred. At this time, from the viewpoint of film-forming properties, using a resin with high crystallinity on the surface layer side reduces adhesion to rolls and clips in the film-forming method described later, and also allows uniform film formation due to the stretch orientation of the resin. It is preferable in that stretchability can be obtained. The crystallinity (degree of crystallinity) is higher when the heat of crystal fusion ΔHm that can be measured with a thermal differential scanning meter is larger, and a resin with high crystallinity can be suitably used as the resin arranged in the outermost layer.

In the film of the present invention, the ratio of the refractive index in the longitudinal direction/the refractive index in the width direction is preferably 1.03 or more, more preferably 1 0.05 or more, more preferably 1.09 or more. When the ratio of the refractive index in the longitudinal direction/the refractive index in the width direction is 1.03 or more, the uniaxial anisotropy is increased, and the occurrence of iridescent unevenness due to observation angles is less likely to occur. On the other hand, as described above, the higher the uniaxial anisotropy, the easier it is to tear the film in the orientation direction, and the film-forming properties are significantly reduced. 1.20 is preferred. The refractive index in each direction can be measured with an Abbe refractometer at 25° C. using a sodium D line (wavelength of 589 nm) as a light source and methylene iodide as a mounting liquid.

In addition, in the case of refractive index measurement using an Abbe refractometer, in the case of a structure in which multiple resins are laminated, a refractive index value obtained by mixing the refractive indices of both resin layers can be obtained. Orientation may not be evaluated. This is because in the case of a laminated film, the highly crystalline resin layer determines the orientation state of the film. This is because the layer A, whose main component is a polyester resin (polyester resin A) that is an acid unit, determines the orientation state of the laminated film. Therefore, in the case of a laminated film, the refractive index of the A layer mainly composed of a polyester resin (polyester resin A) in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid units are naphthalene dicarboxylic acid units is is obtained by measuring the prism coupler described in the section. Here, when the A layer mainly composed of a polyester resin (polyester resin A) in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid units are naphthalene dicarboxylic acid units is not located on the film surface, the maximum By placing the A layer on the surface, the refractive index of the A layer can be measured by the prism coupler method.

As a method for setting the ratio of the refractive index in the longitudinal direction/the refractive index in the width direction to 1.03 or more or the above preferable range, it is possible to use a method of increasing the refractive index in the longitudinal direction compared to the refractive index in the width direction. can. Specific examples of such methods include a method in which the stretching ratio in the longitudinal direction is higher than that in the width direction, and a method in which the film is uniaxially stretched only in the longitudinal direction.

From the viewpoint of reducing the intensity of iridescent unevenness and interference fringes, the film of the present invention preferably has an average reflectance of 20% or less in the wavelength band of 300 to 2500 nm. When the average reflectance is 20% or less, rainbow unevenness due to interference reflection is reduced. The average reflectance can be calculated from the value obtained by measuring the reflectance measured with a sub-white plate of aluminum oxide as a reference (details such as conditions are shown in Examples). Examples of methods for reducing the average reflectance in the wavelength band of 300 to 2500 nm to 20% or less include a method of reducing the number of layers to 40 or less, or a method of lowering the surface reflectance by providing an easy-adhesive hard coat layer. be done. As the number of layers increases, the reflectance increases due to the difference in refractive index at the interface. Therefore, the number of layers is preferably 40 or less. The average reflectance is more preferably 15% or less. Even in the case of a film having a relatively large number of laminations, which is preferable for tear strength, if the tear strength can be reduced to 15% or less, the appearance of iridescent unevenness and interference fringes can be improved.

In the film of the present invention, the heat of crystal fusion of the layer B in DSC is preferably 5 J/g or more from the viewpoint of setting the retardation in a preferable range. When the heat of crystal fusion of the DSC of the B layer is 5 J / g or more, the phase difference can be easily made 3000 nm or more, and the birefringence due to the orientation is obtained, so that the A with the highest refractive index difference Refractive index difference with the layer is suppressed and expression of interference color is reduced.

The heat of crystal fusion in DSC can be measured and analyzed according to JIS K-7121-1987 and JIS K-7122-1987. Specifically, the heat of crystal fusion (ΔHm) is obtained by subtracting the baseline of the endothermic peak obtained from the DSC curve when the sample is heated from 25° C. to 350° C. at 20° C./min.

As a method for increasing the DSC heat of crystal fusion of the B layer to 5 J/g or more, for example, a method using a crystalline polyester resin as the main component of the B layer can be mentioned. When the above-mentioned dicarboxylic acid and diol are combined, a crystalline polyester having a heat of crystal fusion of 5 J/g or more can be obtained if each unit is of the same type, but when two or more types are used together, the crystallinity decreases. Crystal melting heat is reduced. Therefore, the amount of heat of crystal fusion can be adjusted by increasing or decreasing the amount of the copolymerization component of the polyester resin constituting the B layer.

In the film of the present invention, the main component of the B layer is a polyester resin (polyester resin B), and the glycol units constituting the polyester resin B are cyclohexanedimethanol units, 2,2-bis(4'-β-hydroxyalkoxy It preferably contains at least one phenyl)propane unit. The above structural units occupying all the structural units of the polyester resin B are preferably 1 mol% or more in total, more preferably 5 mol% or more in total, still more preferably 10 mol% or more in total, and particularly preferably 20 mol% or more in total. is. The upper limit of the above structural units in polyester resin B is preferably 80 mol%, more preferably 70 mol%, still more preferably 50 mol%, and particularly preferably 30 mol%. When the ratio of the above structural unit is 1 mol % or more, the effect of improving the tear resistance and the effect of improving the elongation at break are at a sufficient level. When the ratio of the above-mentioned structural units is 80 mol% or less, the heat shrinkage rate does not become excessively high, and the post-processability, particularly the dimensional stability and stiffness when used as a base film for magnetic recording are maintained. is suitable for use.

Preferred examples of 2,2-bis(4′-β-hydroxyalkoxyphenyl)propane include 2,2-bis(4′-β-hydroxymethoxyphenyl)propane, 2,2-bis(4′-β- hydroxyethoxyphenyl)propane, 2,2-bis(4′-β-hydroxypropoxyphenyl)propane, 2,2-bis(4′-β-hydroxybutanoxyphenyl)propane and the like, particularly 2 ,2-bis(4'-β-hydroxyethoxyphenyl)propane is preferred in the present case. A polyester obtained by copolymerizing 2,2-bis(4'-β-hydroxyalkoxyphenyl)propane can be melt-polymerized by reacting an ethylene oxide adduct of bisphenol A as a diol component with a dicarboxylic acid component. is easier and cheaper to manufacture.

The thickness of the film of the present invention is preferably in the range of 10 µm to 50 µm. When the thickness is 50 μm or less, it is easy to apply to a thin film polarizing plate, and it is possible to provide a member suitable for thinning displays and curved/folded shapes in recent years. It becomes easy to make it 3000 nm or more. From the above viewpoint, the thickness of the film is more preferably 15 μm to 38 μm. The thickness of the film can be adjusted by adjusting the lip gap of the die, the extrusion rate, the rotation speed of the cast drum, and the like. More specifically, the thickness of the film can be increased by increasing the lip gap of the die, increasing the extrusion rate, and slowing down the rotation of the cast drum.

Since the film of the present invention has little iridescent unevenness, it is preferably used for protecting a polarizer. Specifically, it is suitably used as a polarizer protective film on the light incident surface side of the polarizing plate or as a polarizer protective film on the light exit surface side of the polarizing plate. When the film is used for only one of the two polarizer protective films constituting the polarizing plate, any polarizer protective film (for example, TAC film, etc.) can be used for the other. When this film is employed as a polarizer protective film on the liquid crystal cell side of the polarizing plate arranged on the light incident surface side and as a polarizer protective film on the liquid crystal cell side of the polarizing plate arranged on the light exit surface side, the polarization of the liquid crystal cell Since there is a possibility of changing the characteristics, the polarizer protective film at these positions should not be used as a polarizer protective film other than the film (for example, TAC film, acrylic film, birefringence such as typified by norbornene film). film) is preferably used.

The film of the present invention can be combined with various image display devices. In other words, the image display device of the present invention is equipped with the film of the present invention. Image display devices include liquid crystal image display devices, organic EL display devices, quantum dot displays, digital signage for outdoor use, goggles that enable AR/VR/MR display that realizes augmented reality and virtual reality. apparatus. In addition, various display systems such as a head-up display system that allows display information to be superimposed and displayed in the field of view through a transparent glass element, an aerial display system that enables aerial imaging, etc. An image display device such as an organic EL display is combined, and films exhibiting various functions are arranged inside various displays.

The film of the present invention can be used, for example, as a film shown below in each image display device. In particular, it can be preferably applied to an optical film arranged on the viewing side than the display portion of an image display device, and in the case of a liquid crystal image display device, including a polarizer protective film constituting the above-described polarizing plate, and a retardation film. , a surface treatment film attached to the front surface of a display to add functions, a transparent conductive substrate film used for ITO and the like, an ultraviolet protection film for a touch sensor member, and the like. In the case of an organic EL display device, a λ/4 retardation film that constitutes a circularly polarizing plate arranged on the visible side (upper side) of the light-emitting layer, a surface treatment film that is attached to the front surface of the display to impart functions, and an external Examples include various optical films incorporated for the purpose of protecting contents from light. In the case of quantum dot displays, there are mainly two types: a quantum dot liquid crystal display that includes a liquid crystal panel equipped with a color filter for dimming, and a quantum dot organic EL display that combines a blue organic EL layer and a color filter. . In these devices, the backlight portion of the liquid crystal image display device and the light emitting layer portion of the organic EL display device are replaced with a quantum dot structure. Therefore, also in these displays, the laminated film of the present invention can be used in the same arrangement and application as the various films used in the liquid crystal image display layer and the organic EL display described above.

When used as an optical film for an image display device, bending is often required due to the recent trend of display development. In the case of a film exhibiting uniaxial orientation such as that of the present invention, when bending is attempted around the direction of strong orientation, bending stress is concentrated in the bent portion due to bending with a small diameter, resulting in delamination and cleavage. Sometimes. Therefore, when the film of the present invention is applied to a bendable display, it is preferable to consider the cutting direction so that the film is bent around the weak orientation direction.

When combined with an image display device, the outermost surface of the laminated film of the present invention is provided with an adhesive layer for imparting adhesiveness, or for adding functions such as scratch resistance, dimensional stability, adhesiveness and adhesion. may be provided with a hard coat layer composed mainly of a curable resin.

In particular, the latter hard coat layer can prevent the surface of the laminated film from being scratched due to friction between the roll and the film when the film of the present invention is transported by roll-to-roll for mounting on a product. Furthermore, even if the resin oligomer component in the film and various additives that can be added to the film may bleed out due to high-temperature heat treatment or long-term continuous use, by providing the hard coat layer on the outermost surface, A hard coat layer with a high cross-linking density can exhibit a precipitation suppressing effect. In addition, by laminating a curable resin layer, it is possible to suppress the dimensional change of the film due to heat treatment, and it is possible to suppress the change in film thickness and optical properties such as phase difference due to heat shrinkage.

The hard coat layer is also preferably laminated and combined with the film of the present invention from the viewpoint of reducing surface reflection and reducing iridescent unevenness. Specifically, it is preferable that an easy-adhesion layer and a hard coat layer are laminated in this order on at least one surface, and the easy-adhesion layer has a layer thickness of 70 nm or more and 120 nm or less. Surface reflection is caused by a large refractive index difference between the in-plane refractive index of the resin arranged on the outermost surface of the film and the refractive index of the atmosphere (n=1). In particular, in the film of the present invention, since the layer A, which is the outermost layer, contains a naphthalenedicarboxylic acid component, it exhibits a considerably high refractive index among a number of thermoplastic resins exhibiting birefringence, so the influence of surface reflection increases. Therefore, in order to suppress surface reflection, it is preferable to provide a hard coat layer made of a resin having a low refractive index on the outermost surface of the film so that the difference between the refractive index and that of the atmosphere is small. A configuration in which an easy-adhesion layer is interposed is preferable so that the coat does not separate from the film.

The refractive index of the easy-adhesion layer is preferably a numerical value between the refractive index of the layer A containing the naphthalene dicarboxylic acid component disposed on the outermost surface of the film and the refractive index of the resin constituting the hard coat layer. More preferably, the refractive index is intermediate between the two resins (where α is the refractive index of polyester A and β is the refractive index of the resin constituting the hard coat layer, 0.98 × (α + β) / 2 or more and 1.02 × ( α+β)/2 or less).

In addition, the thickness of the easy-adhesion layer is controlled in the thickness range of 70 nm or more and 120 nm or less for the purpose of further suppressing surface reflection due to the optical relationship formed at the interface between the hard coat layer, the easy-adhesion layer, and the A layer on the outermost surface of the film. preferably. By controlling this easy-adhesion thickness, when the light reflected at the interface between the hard coat layer and the easy-adhesion layer and the light reflected at the interface between the easy-adhesion layer and the outermost layer of the film interfere with each other, phases can be canceled, and the influence of surface reflection can be minimized. More preferably, it is controlled within the range of 80 nm or more and 110 nm or less.

The resin used for the hard coat layer provided in the film of the present invention is preferably highly transparent and durable. Resins can be used alone or in mixtures. In terms of curability, flexibility, and productivity, the resin forming the hard coat layer is preferably made of active energy ray-curable resin such as acrylic resin represented by polyacrylate resin and polyurethane acrylate resin. On the other hand, when mainly imparting scratch resistance, it is also possible to use a thermosetting urethane acrylic resin. In addition, a compound having an alicyclic epoxy group, a polyol polyacrylate, an oxetane compound, and an alkyl acrylate are used as resins for forming a hard coat layer that is used to add adhesion and adhesion to other constituent members. A photo-curing resin composed of a combination of four types of polymers as monomer units can be used. Since this photocurable resin exhibits a good effect in adhesion with PVA generally used as a polarizer, it can be suitably used in optical films for displays.

Further, in order to further lower the refractive index, low refractive index particles such as hollow particles having voids inside the particles can be added to the hard coat layer.

Hereinafter, the method for producing the film of the present invention will be specifically described by taking a uniaxially oriented multilayer laminated film as an example. However, the method for obtaining the film of the present invention is not limited to the following.

First, pre-dried polyethylene naphthalate and copolymerized polyethylene naphthalate are supplied to separate extruders and melted at temperatures above their respective melting points. At this time, at least one of the copolymerized polyethylene naphthalates supplied to each extruder may contain particles such as aggregated silica. After that, the amount of resin extruded is made uniform by a gear pump or the like, and after removing foreign matter, denatured resin, etc. through a filter, the resin is extruded from each extruder while adjusting the amount of extruder. Thereafter, a molten resin laminate having a desired configuration is formed using a feed block, static mixer, and multi-manifold die, and is extruded into a sheet from a die. While static electricity is applied using a wire-shaped, tape-shaped, needle-shaped or knife-shaped electrode, this is brought into close contact with a casting drum and rapidly cooled and solidified to obtain a cast film.

Thereafter, the film is stretched in the machine direction (longitudinal direction) to a desired magnification by the difference in peripheral speed of the heated roll group to obtain a uniaxially oriented film. The uniaxially oriented film obtained here is subjected to surface treatment such as corona treatment, flame treatment, plasma treatment, etc., as necessary, and then it is easy to apply functions such as slipperiness, easy adhesion, and antistatic properties. The adhesive layer can be applied by in-line coating. The obtained uniaxially oriented film is guided to a tenter, and while holding both ends, heat treatment is performed in the tenter as necessary, and the uniaxially oriented film can be obtained by slowly cooling to room temperature and winding. The stretching temperature, heat treatment temperature, and the like can be appropriately adjusted according to the resin composition, the use of the resulting film, and the like.

As a stretching method different from the above, it is also possible to use a method in which the cast film cooled by the casting drum is stretched only in the width direction without undergoing the longitudinal stretching step. Stretching in the width direction refers to stretching for imparting orientation in the width direction to the sheet, and is usually carried out using a tenter while gripping both ends of the sheet in the width direction with clips. In addition, immediately before the film is stretched by the tenter, an easily adhesive layer having functions such as slipperiness, adhesiveness, and antistatic properties can be applied by in-line coating, if necessary. The stretching temperature is preferably between the glass transition temperature and the glass transition temperature+120° C. of the resin having the highest glass transition temperature among the resins constituting the laminated film. The film uniaxially stretched in the width direction in this manner is heat-treated in a tenter at a temperature not lower than the drawing temperature and not higher than the melting point, uniformly slowly cooled, and then cooled to room temperature and wound up. In addition, if necessary, when the heat treatment is followed by slow cooling in order to impart thermal dimensional stability, relaxation treatment or the like may be performed in combination in the longitudinal direction and/or the width direction.

Alternatively, a biaxially stretched film may be strongly stretched in a specific direction instead of being uniaxially stretched. In this case, the stretching may be biaxially stretched successively or may be biaxially stretched simultaneously. Further, re-stretching may be performed in the longitudinal direction and/or the width direction. In sequential or simultaneous biaxial stretching, the ratio of the draw ratio in the direction of strong drawing to the draw ratio in the direction of weak drawing is preferably 3.5 or more and 6.0 or less. If the ratio of the draw ratio is lower than 3.5, the film is oriented in the weakly drawn direction, and the difference in refractive index cannot be obtained, and the iridescent unevenness may not be sufficiently reduced. If the ratio of the draw ratio is higher than 6.0, the polymer will be in an extended chain state, and may break during film formation without being oriented when drawn in the other direction.

In the case of simultaneous biaxial stretching, the cast sheet is guided to a simultaneous biaxial tenter, conveyed while gripping both ends in the width direction of the sheet with clips, and stretched simultaneously and/or stepwise in the longitudinal direction and the width direction. . As the simultaneous biaxial stretching machine, there are pantograph system, screw system, drive motor system, and linear motor system. A linear motor system is preferred. The stretching temperature is preferably between the glass transition temperature and the glass transition temperature+120° C. of the resin having the highest glass transition temperature among the resins constituting the laminated film.

The film thus simultaneously biaxially stretched is provided with an easy-adhesion layer with functions such as slipperiness, easy-adhesion, and antistatic properties by in-line coating as necessary, and then imparts flatness and dimensional stability. For this purpose, it is preferable to subsequently perform a heat treatment at a temperature higher than the stretching temperature and lower than the melting point in the tenter. In order to suppress the distribution of the main orientation axis in the width direction during this heat treatment, it is preferable to instantly relax the film in the longitudinal direction immediately before and/or after entering the heat treatment zone. After the heat treatment in this manner, the film is cooled uniformly to room temperature and wound up. In addition, if necessary, relaxation treatment may be performed in the longitudinal direction and/or the width direction during slow cooling after the heat treatment. In addition, immediate longitudinal relaxation treatment may be performed immediately before and/or after entering the heat treatment zone.

The laminated film obtained as described above is trimmed to a required width through a winding device, and wound in a roll state so as not to have wrinkles. Note that both ends of the sheet may be embossed in order to improve the winding shape during winding.

EXAMPLES The present invention will be described in more detail below using examples, but the present invention is not limited to these. Further, evaluation of physical property values in each example was performed by the following methods.

(Evaluation method for each characteristic)
(1) Heat of crystal fusion Using a differential scanning calorimeter (manufactured by Seiko Instruments Inc.: SII robot DSC (model EXSTAR DSC6220, data analysis "Standard Analysis"), JIS K-7121-1987, JIS K-7122- Measurement and analysis were carried out in accordance with 1987. The integrated value obtained by subtracting the baseline of the endothermic peak obtained from the DSC curve when heating a 5 mg sample from 25 ° C. to 300 ° C. at 20 ° C./min was Heat of crystal fusion (ΔHm) Samples were taken by tearing the laminated film with the tear propagation resistance of (2) by the method described later, peeling each layer, and examining the peeled surface with a microscope microscope. It was carried out by observing within double magnification and cutting the B layer portion.

(2) Tear strength Measurement was performed using a light load tear tester (No. 193) manufactured by Toyo Seiki Seisakusho in the following procedure. First, the film was sampled into a rectangle of 63.5 mm in the longitudinal direction and 50.8 mm in the width direction, and a 12.7 mm long cut was made in the sample in parallel with the longitudinal direction from the central end of 50.8 mm in the width direction. , the scored 25.4 mm wide sample pieces were each held in a tension clamp. Then, the remaining 50.8 mm in the longitudinal direction was torn with a pendulum along the cut to determine the tearing force (N) in the longitudinal direction. This force was divided by the thickness of the film to obtain the longitudinal tear strength (N/mm). This measurement was performed on 10 samples, and the average value of 8 data, excluding the highest and lowest values, was used as the final tear strength. Here, in a film having a laminated structure, if delamination instead of tearing parallel to the cut direction is observed during measurement, the data is not adopted, and the same analysis can be performed so that the number of n is 10. was carried out and used as a measurement value. Also, the tear propagation resistance (N/mm) in the width direction was similarly measured by rotating the sampling and the tearing direction by 90°.

(3) Retardation/orientation angle Using "KOBRA-21ADH" manufactured by Oji Scientific Instruments Co., Ltd., the film is cut into a rectangular shape of 4 cm in the width direction × 3 cm in the length direction from the center position in the width direction of the film, and the width direction is the main measurement. The film was placed in the apparatus so that the angle defined by the apparatus was 0°, and the in-plane retardation at a wavelength of 590 nm and the orientation axis direction (orientation angle) of the film were measured.

(4) Film Formation Stability Judgment was made according to the following criteria from the frequency of occurrence of film breakage due to tearing in the longitudinal direction during continuous film formation for 12 hours. A tear in the longitudinal direction refers to a phenomenon in which the film breaks substantially parallel to the running direction (longitudinal direction) of the film. The time from the occurrence of tearing to the restart of operation was not counted.
(double-circle): There was no tear.
◯: Breaking occurred once △: Breaking occurred 2 to 3 times.
x: Four or more tears occurred.

(5) Iridescent unevenness The orientation axis of the film obtained in each example was bonded via an adhesive so that the absorption axis of the polarizer was parallel. After that, when the white LED backlight was irradiated from the lower surface, the transmitted light was visually observed from all directions at an angle of 50°, and the presence or absence of iridescent unevenness was observed and evaluated according to the following criteria.
A: Rainbow unevenness was not observed.
◯: Rainbow unevenness was slightly observed, but the intensity was extremely weak and could not be recognized unless one was conscious of it.
Δ: Iridescent unevenness was slightly observed, and although the intensity was weak, its presence could be confirmed at a glance.
x: Rainbow unevenness was remarkably strongly observed.

(6) Appearance A sample of A4 size was cut out from the central portion in the width direction of the film. Next, a fluorescent lamp having an emission spectrum of F10 (three-wavelength neutral white) defined by CIE (International Commission on Illumination) and a black cardboard on which the sample was placed were prepared. The prepared fluorescent lamp, the sample on the black cardboard, and the viewing direction were placed so that the relation between them was specular reflection. After that, the occurrence of interference colors and interference fringes and the transparency of the film were visually observed and evaluated according to the following criteria.
A: No interference color or interference fringes were observed, and the transparency was good.
◯: Interference color and interference fringes could not be confirmed, but looked slightly low and whitish.
Δ: Green or red interference fringes were blurred and could be slightly confirmed, or looked white.
x: The interference color was clearly visible.

(7) Refractive index/refractive index ratio In the case of a single-layer film, sodium D line (wavelength: 589 nm) is used as a light source, methylene iodide is used as a mounting liquid, and the longitudinal direction of the film is measured using an Abbe refractometer at 25°C. Refractive indices in the direction and width direction (nMD and nTD, respectively) were determined. From the obtained refractive index, the ratio of the refractive index in the longitudinal direction/the refractive index in the width direction was calculated. Specifically, it was measured according to JIS K7142 (2014) A method using Abbe refractometer 4T (manufactured by Atago Co., Ltd.). A test piece with a refractive index of 1.74 was used.

In the case of a film having a laminated structure, the A layer mainly composed of a polyester resin (polyester resin A) in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid units are naphthalene dicarboxylic acid units is the outermost surface of the film. Then, after peeling off the layer or scraping it with a grinder, the refractive index of layer A was measured using a prism coupler (SPA-4000) manufactured by Sairon Technology. The film sample after the treatment is physically adhered to a prism by air pressure, irradiated with a 632.8 nm laser, and measured in TE mode to measure the in-plane refractive index of the outermost thermoplastic resin layer in TM mode. By measuring, the normal refractive index of the same layer was measured. Specifically, in TE mode, the orientation axis direction obtained by the KOBRA measurement in (3) is set parallel to the depth direction of the device, so that the refractive index Nx in the X-axis direction is perpendicular to the depth direction of the device. The refractive index Ny in the direction perpendicular to the orientation axis was measured by installing the device in each direction. From the obtained refractive indices, the ratio of the refractive index in the longitudinal direction/the refractive index in the width direction was calculated.

(8) Average Reflectance A 5 cm×5 cm sample was measured using an integrating sphere attached to a spectrophotometer (U-4100 Spectrophotometer) manufactured by Hitachi, Ltd., using an aluminum oxide auxiliary white plate attached to the apparatus as a reference. In the reflectance measurement, the sample was placed behind the integrating sphere with its longitudinal direction oriented vertically. The measurement conditions were a sampling interval of 1 nm, a slit of 2 nm (visible)/automatic control (infrared), a gain of 2, a scanning speed of 600 nm/min, and reflection in a wavelength band of 300 to 2500 nm at an azimuth angle of 0 degrees. got the rate. The average reflectance of the obtained reflectance at a wavelength of 380 to 2500 nm was calculated.

<Thermoplastic resin>
The thermoplastic resins used in the examples of the present invention are described below. Among the thermoplastic resins shown below, resins 1, 3 to 7 are crystalline thermoplastic resins, resin 2 is amorphous thermoplastic resin, and resin 8 is semi-crystalline thermoplastic resin.
Resin 1: Polyethylene 2,6 naphthalate (PEN) having an intrinsic viscosity of 0.65 dl/g, a glass transition temperature of 119°C and a melting point of 264°C.
Resin 2: Polyethylene terephthalate (CHDM copolymer PET) copolymerized with 32 mol% of cyclohexanedimethanol, exhibiting an intrinsic viscosity of 0.72 dl/g and a glass transition temperature of 80°C.
Resin 3: Polyethylene terephthalate (BPA) copolymerized with 8 mol% of 2,2-bis(4′-β-hydroxyethoxyphenyl)propane, exhibiting an intrinsic viscosity of 0.66 dl/g, a glass transition temperature of 78° C., and a melting point of 233° C. -EO copolymer PET)
Resin 4: Polyethylene 2,6 naphthalate (NPG copolymer PEN) copolymerized with 10 mol% of neopentyl glycol, exhibiting an intrinsic viscosity of 0.65 dl/g, a glass transition temperature of 109°C, and a melting point of 246°C.
Resin 5: Polyethylene 2,6 naphthalate copolymerized with 5 mol% of isophthalic acid (isophthalic acid copolymerized PEN) having an intrinsic viscosity of 0.65 dl/g, a glass transition temperature of 105°C and a melting point of 256°C.
Resin 6: Polyethylene terephthalate (PET) having an intrinsic viscosity of 0.65 dl/g, a glass transition temperature of 78°C and a melting point of 255°C.
Resin 7: Polyethylene 2,6 naphthalate (PEG-copolymerized PEN) copolymerized with 10 mol% of polyethylene glycol 400, exhibiting an intrinsic viscosity of 0.67 dl/g, a glass transition temperature of 90°C and a melting point of 252°C.
Resin 8: Polyethylene 2,6-naphthalate (NPG/ CHDM copolymer resin).
Resin 9: A BPA-EO copolymer obtained by copolymerizing 8 mol% of 2,2-bis(4'-β-hydroxyethoxyphenyl)propane, exhibiting an intrinsic viscosity of 0.70 dl/g, a glass transition temperature of 89°C and a melting point of 238°C. Polymerized PET and polyethylene 2,6 naphthalate NPG copolymerized PEN copolymerized with 10 mol % of neopentyl glycol are strongly kneaded using a twin-screw extruder at a Q/Ns of 0.1 or less to form an alloy.

(Example 1)
As polyester resin A, pellets of resin 1 were vacuum-dried at 180°C for 3 hours and fed to extruder 1 heated to 290°C. As polyester resin B, pellets of Resin 2 were dried in a hot air dryer at 80°C for 12 hours, and then supplied to twin-screw vent extruder 2 heated to 280°C. The polyester resins A and B melted and extruded from each extruder are once laminated into a three-layer ABA structure (lamination thickness ratio A/B = 10/1), and this is mixed in a square mixer section. A total of 5 layers of layers A and B were laminated alternately in the thickness direction so as to form layers, and a multilayer sheet was extruded from a T-die. The melt-extruded multilayer sheet was adhered and solidified by electrostatic force on a cooling drum having a surface temperature of 25° C. to obtain a non-oriented amorphous cast film. After that, it is preheated by rolls heated to 120°C, stretched 4.0 times in the longitudinal direction, led to a tenter, preheated with hot air at 130°C, stretched 1.1 times in the transverse direction, and further inside the tenter. A fixed-length heat treatment was performed with hot air at 170° C., and after slow cooling to room temperature, it was wound around a core at 50 m/min. Table 1 shows the evaluation results of the obtained film.

(Example 2)
A film was formed under the same conditions as in Example 1, except that the number of layers was changed to 11 by changing the number of elements in the mixer, and the film thickness was changed to 25 μm. Table 1 shows the evaluation results of the obtained film. The film thickness was adjusted to a predetermined thickness by adjusting the film forming speed (cast take-up speed). The same applies to other examples and comparative examples below.

(Example 3)
A film was formed under the same conditions as in Example 2, except that the number of layers was changed to 41 by changing the number of elements in the mixer. Table 1 shows the evaluation results of the obtained film.

(Example 4)
A film was formed under the same conditions as in Example 2, except that Resin 3 was used as the polyester resin B. Table 1 shows the evaluation results of the obtained film.

(Example 5)
A film was formed under the same conditions as in Example 4, except that the lamination thickness ratio A/B was 1/1 and the film thickness was 30 μm. Table 1 shows the evaluation results of the obtained film.

(Example 6)
A film was formed under the same conditions as in Example 2, except that Resin 4 was used as the polyester resin A. Table 1 shows the evaluation results of the obtained film.

(Example 7)
A film was formed under the same conditions as in Example 6, except that the number of laminated layers was changed to 31 by changing the number of elements in the mixer, and the film thickness was changed to 80 μm. Table 1 shows the evaluation results of the obtained film.

(Example 8)
A film was formed under the same conditions as in Example 7, except that the film thickness was 35 μm. Table 1 shows the evaluation results of the obtained film.

(Example 9)
A film was formed under the same conditions as in Example 6, except that resin 5 was used as the polyester resin A, the lamination ratio was changed to A/B=6/1, and the thickness was 35 μm. Table 1 shows the evaluation results of the obtained film.

(Example 10)
A film was formed under the same conditions as in Example 2 except that resin 7 was used as the polyester resin A and a single film was formed without using a mixer. Table 1 shows the results obtained.

(Example 11)
A film was formed under the same conditions as in Example 3, except that the draw ratio was as shown in Table 1 and the cast take-up speed was adjusted to a film thickness of 35 μm. Table 1 shows the results obtained.

(Example 12)
Pellets of resin 4 as polyester resin A were vacuum-dried at 180°C for 3 hours and fed to extruder 1 heated to 280°C. As polyester resin B, resin 3 was fed to twin-screw vent extruder 2 heated to 280°C. Furthermore, as polyester resin C, resin 2 was supplied to twin-screw vent extruder 3 heated to 280°C. Each resin melted and extruded from each extruder 1 to 3 is led to a multi-manifold type feed block with a total of 17 layers in which both outermost layers are A layers and are laminated in ACBC repeating units, and the lamination thickness ratio A A multilayer sheet was extruded from a T-die by lamination under the condition of /C/B=10/1/1. The melt-extruded sheet was adhered and solidified by electrostatic force on a cooling drum having a surface temperature of 25° C. to obtain a non-oriented amorphous cast film. After that, the film was preheated by a group of rolls heated to 120° C. and stretched 4.0 times in the longitudinal direction to obtain a uniaxially stretched film. This was guided to a tenter, preheated with hot air at 130°C, stretched 1.1 times in the horizontal direction, subjected to constant-length heat treatment with hot air at 170°C in the tenter, slowly cooled to room temperature, and cored at 50 m / min. wound up in Table 1 shows the evaluation results of the obtained film.

(Example 13)
A film was obtained in the same manner as in Example 12, except that the combination of resins shown in Table 1 was used. Table 2 shows the evaluation results of the obtained film.

(Examples 14, 15, 16)
Except that the combination of resins shown in Table 1 was used, and the outermost layer was layer A, and a total of 29 layers of slit-type feedblocks laminated in ACBC repeating units were used to form a film in which 29 layers were laminated in the thickness direction. obtained a film in the same manner as in Example 13. Table 2 shows the evaluation results of the obtained film.

(Example 17)
A film was obtained in the same manner as in Example 13, except that the constant-length heat treatment in the tenter was performed with hot air at 230°C. Table 2 shows the evaluation results of the obtained film.

(Example 18)
In Example 3, both surfaces of the uniaxially stretched film obtained by stretching in the longitudinal direction were subjected to corona discharge treatment in air to set the wetting tension on both surfaces to 55 mN/m. After that, on both sides of the uniaxially stretched film, a coating composition containing 3% by mass of colloidal silica with a particle size of 100 nm and mainly composed of a polyester resin was applied with a #4 meta bar so that the thickness after drying was 90 nm. (The refractive index of the coating layer after drying the coating composition is 1.60.). After that, it is introduced into a tenter, preheated with hot air at 130°C, stretched 1.1 times in the horizontal direction, further subjected to constant-length heat treatment with hot air at 170°C in the tenter, slowly cooled to room temperature, and stretched at 50 m/min. wound on the core. A hard coat layer was uniformly laminated on one outermost surface of the obtained film by die coating so that the thickness after curing was 3 μm. Specifically, the coating was performed using a continuous coating device having a die coater, which will be described later. The continuous coating apparatus consists of a coating process, drying processes 1 to 3, and a curing process. In the coating process, the film is continuously conveyed from the roll and continuously coated with a constant coating thickness through the die coating device. As a coating material, a urethane-acrylic coating material having a refractive index of 1.49 using methyl ethyl ketone as a solvent was used. A total of three chambers are provided for the drying process (drying processes 1 to 3 in order), and have a nozzle capable of blowing hot air parallel to the conveying direction of the laminated unit and a far-infrared heater. In each drying process, the temperature and hot air speed (fan speed) can be set independently, and these are the same for the hard coat lamination side and the back side of the lamination unit. The temperatures in drying steps 1 to 3 were set to 60° C., 80° C., and 80° C., respectively, and the fan output was adjusted so that the differential pressure in drying step 1 with respect to the coating step was 3 MPa. The curing step is performed following the drying steps 1 to 3, and has a UV irradiation device, on a drum roll temperature-controlled to 40° C., under a nitrogen atmosphere (oxygen concentration 0.1% by volume or less), It was carried out under the conditions of an integrated light quantity of 200 mJ/cm ² and an irradiation light intensity of 160 W/cm. Table 2 shows the evaluation results of the hard coat laminated film obtained by winding in this manner.

(Comparative example 1)
As polyester resin A, pellets of resin 6 were vacuum-dried at 180° C. for 3 hours, supplied to an extruder heated to 280° C., and extruded with a T-die to form a single film sheet. The melt-extruded sheet was adhered and solidified by electrostatic force on a cooling drum having a surface temperature of 25° C. to obtain a non-oriented amorphous cast film. After that, the film is preheated by a group of rolls heated to 90°C, stretched 4.0 times in the longitudinal direction, led to a tenter, preheated with hot air at 100°C, stretched 1.1 times in the transverse direction, and further inside the tenter. A fixed-length heat treatment was performed with hot air at 170° C., and after slow cooling to room temperature, it was wound around a core at 50 m/min. The thickness of the obtained film was 25 μm. Table 2 shows the evaluation results of the obtained film.

(Comparative example 2)
A film was formed under the same conditions as in Example 2 except that resin 1 was used as the polyester resin A and a single film was formed without using a mixer. Table 2 shows the evaluation results of the obtained film.

(Comparative Example 3)
A film was formed under the same conditions as in Comparative Example 2, except that the draw ratio in the longitudinal direction was 3.3 times and the draw ratio in the transverse direction was 3.5 times. Table 2 shows the results obtained.

(Comparative Example 4)
A film was formed under the same conditions as in Example 2, except that the number of layers was changed to 161 by changing the number of elements in the mixer. Table 2 shows the evaluation results of the obtained film.

(Comparative Example 5)
A film was formed under the same conditions as in Example 2, except that Resin 6 was used as the polyester resin A. Table 2 shows the evaluation results of the obtained film.

(Comparative Example 6)
A film was formed under the same conditions as in Example 5, except that Resin 2 was used as the polyester resin B. Table 2 shows the evaluation results of the obtained film.

When the film of the present invention is used as a polarizer protective film, the occurrence of iridescent unevenness is suppressed at any viewing angle, and good visibility can be obtained. In addition, the space required for thinning the device and securing the battery capacity can contribute to the thinning of the film, so the industrial applicability is extremely high.

Claims (13)

The main component is polyester resin,
More than 50 mol% and 100 mol% or less of the dicarboxylic acid units constituting the polyester resin are naphthalene dicarboxylic acid units,
The phase difference is 3000 nm or more and 30000 nm or less,
A film having a tear strength of 2 N/mm or more in both the longitudinal direction and the width direction. A layer mainly composed of a polyester resin (polyester resin A) in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid units are naphthalene dicarboxylic acid units, and a resin different from the main component of the A layer. 2. The film according to claim 1, wherein the layer B has a structure in which at least 5 layers or more and 100 layers or less are alternately laminated. A layer mainly composed of a polyester resin (polyester resin A) in which more than 50 mol% and 100 mol% or less of the dicarboxylic acid unit is a naphthalene dicarboxylic acid unit, and B mainly composed of a resin B different from the polyester resin A A layer and a C layer having a different composition from both the A layer and the B layer have a structure in which the A layer, the C layer, the B layer, and the C layer are repeatedly laminated in this order, and the C layer includes the polyester The content of the resin A is less than that of the layer B, the content of the resin B is less than that of the layer B, and the total number of the layers A, B, and C is 5 or more and 100 or less. 3. The film of claim 1, wherein a 4. The film of claim 3, wherein said C layer comprises said polyester resin A and said resin B. 4. The film according to claim 3, wherein the layer C comprises a copolymer containing a structural unit of the polyester resin A and a structural unit of the resin B as a main component. 4. The film according to claim 3, wherein the layer C has an alloy structure in which one of the polyester resin A and the resin B is a domain and the other is a matrix. 4. The film according to any one of claims 1 to 3, wherein the ratio of the refractive index in the longitudinal direction/the refractive index in the width direction is 1.03 or more. The film according to any one of claims 1 to 3, which has an average reflectance of 20% or less in a wavelength band of 300 to 2500 nm. 4. The film according to claim 2, wherein the layer B has a DSC heat of crystal fusion of 5 J/g or more. The main component of the B layer is a polyester resin (polyester resin B), and the glycol units constituting the polyester resin B are cyclohexanedimethanol units and 2,2-bis(4′-β-hydroxyalkoxyphenyl)propane units. 4. The film of claim 2 or 3, comprising at least one of The film according to any one of claims 1 to 3, wherein an easy-adhesion layer and a hard coat layer are laminated in this order on at least one surface, and the easy-adhesion layer has a layer thickness of 70 nm or more and 120 nm or less. The film according to any one of claims 1 to 3, which is used for protecting a polarizer. An image display device comprising the film according to any one of claims 1 to 3.