JP6110184B2 - Biaxially stretched film, polarizing plate, image display device, and method for producing biaxially stretched film - Google Patents

Description

  The present invention relates to a biaxially stretched film obtained by biaxially stretching an original film composed of a thermoplastic resin, and a polarizing plate and an image display device including the film. Moreover, this invention relates to the manufacturing method of the said biaxially stretched film.

  Amorphous vinyl polymers such as (meth) acrylic polymers represented by polymethyl methacrylate (PMMA) and aromatic vinyl polymers represented by polystyrene are highly polymerizable and relatively easy to produce. In addition to being excellent in optical transparency, it is widely used in optical applications. For optical applications, in addition to use as a bulk material such as a lens, use as a resin film (optical film) composed of a thermoplastic resin containing the polymer is also common. In recent years, optical films have been increasingly used in image display devices such as liquid crystal display devices (LCD) and organic electroluminescence display devices (OLED).

  Due to the design of the image display device, the optical film cannot be disposed close to a heating element such as a power supply unit, a light emitting unit, or a circuit board. For this reason, the optical film is required to have heat resistance. However, regarding the glass transition temperature (Tg), which is an index of heat resistance, the Tg of PMMA and polystyrene is less than 100 ° C., and an optical film that can sufficiently withstand use in an image display device cannot be obtained as it is. Therefore, by introducing a ring structure into the main chain of the polymer or copolymerizing with a monomer having a ring structure located in the main chain when the polymer is made, the heat resistance of the optical film can be improved. It has been planned. On the other hand, the ring structure of the main chain changes the mechanical properties of the polymer in a hard and brittle direction, so that the flexibility of the optical film containing such a polymer is reduced, and mechanical properties such as strength and The problem is that handling is reduced. One way to deal with this problem is to perform biaxial stretching. By biaxially stretching the resin film to obtain a biaxially stretched film, the flexibility of the film is increased and mechanical properties are improved (for example, Patent Document 1).

  In recent years, with the rapid spread of smartphones and tablet devices, where portability and design are important, optical films have improved heat resistance and mechanical properties, as well as ensuring the optical properties necessary for optical films. In addition, there is a strong demand to achieve a thin film at the same time.

JP 2010-72135 A

  An object of the present invention is to provide a biaxially stretched film in which optical properties, heat resistance, and mechanical properties as an optical film are ensured and a thin film is achieved.

The biaxially stretched film of the present invention is a biaxially stretched film composed of a thermoplastic resin, wherein the thermoplastic resin includes an amorphous vinyl polymer having a ring structure in the main chain, and the thermoplastic For the resin, the molecular weight Me ₀ between entanglements in the rubber-like flat region of the dynamic viscoelastic spectrum shown in the following formula (A) is 10,000 or more, and the entanglement number N shown in the following formula (B) is 10 or more. The temperature range of 500 or less is 25 ° C. or more, and the film has a thickness of 35 μm or less.
Me ₀ = 3cRT ₀ / E ′ ₀ (A)
N = (MwE ′) / (3cRT) (B)
[In the formulas (A) and (B), c is the density (g · m ⁻³ ) of the thermoplastic resin at 25 ° C., R is a gas constant (8.31 J · K ⁻¹ · mol ⁻¹ ), T is a temperature (K) of the thermoplastic resin, E ′ is a storage elastic modulus (Pa) of the thermoplastic resin at the temperature T, and T ₀ is an intermediate point of the rubber-like flat region in the thermoplastic resin. The temperature (K), E ′ ₀ is the storage elastic modulus (Pa) of the thermoplastic resin at the temperature T ₀ , and Mw is the weight average molecular weight of the thermoplastic resin]

  The polarizing plate of the present invention includes the biaxially stretched film of the present invention.

  The image display device of the present invention includes the biaxially stretched film of the present invention.

The method for producing a biaxially stretched film of the present invention is a method for forming a biaxially stretched film having a thickness of 35 μm or less by biaxially stretching an original film composed of a thermoplastic resin. Here, the thermoplastic resin contains an amorphous vinyl polymer having a ring structure in the main chain, and the thermoplastic resin is represented by the following formula (A), and is a rubber-like material having a dynamic viscoelastic spectrum. The temperature range in which the molecular weight Me ₀ between entanglement points in a flat region is 10,000 or more and the entanglement number N shown in the following formula (B) is 10 or more and 500 or less is 25 ° C. or more.
Me ₀ = 3cRT ₀ / E ′ ₀ (A)
N = (MwE ′) / (3cRT) (B)
[In the formulas (A) and (B), c is the density (g · m ⁻³ ) of the thermoplastic resin at 25 ° C., R is a gas constant (8.31 J · K ⁻¹ · mol ⁻¹ ), T is a temperature (K) of the thermoplastic resin, E ′ is a storage elastic modulus (Pa) of the thermoplastic resin at the temperature T, and T ₀ is an intermediate point of the rubber-like flat region in the thermoplastic resin. The temperature (K), E ′ ₀ is the storage elastic modulus (Pa) of the thermoplastic resin at the temperature T ₀ , and Mw is the weight average molecular weight of the thermoplastic resin]

  According to the present invention, it is possible to obtain a biaxially stretched film in which the optical properties, heat resistance and mechanical properties as an optical film are ensured and a thin film is achieved.

  In this specification, “thermoplastic resin (also simply referred to as resin)” is a broader concept than “polymer”. The thermoplastic resin can contain one kind or two or more kinds of polymers, and if necessary, contains materials other than the polymer, for example, additives such as ultraviolet absorbers, antioxidants, fillers, and plasticizers. You may go out. When the thermoplastic resin contains only one type of polymer, they are the same.

  The biaxially stretched film of this invention is comprised from the thermoplastic resin (D) containing the amorphous vinyl polymer (C) which has a ring structure in a principal chain. An amorphous vinyl polymer is excellent in optical transparency. Moreover, the Tg of the polymer is improved by introducing a ring structure into the polymer main chain. For this reason, the optical transparency and heat resistance as an optical film are ensured.

  In order to obtain a biaxially stretched film that is thinner than before while ensuring optical properties, heat resistance and mechanical properties as an optical film, the present inventor made a thin original film before biaxial stretching. The original film itself was thinned, or the original film was strongly stretched by increasing the stretch ratio, and the thickness of the stretched film was reduced. However, it is not possible to ensure sufficient strength of the obtained stretched film by simply reducing the thickness of the original film, and it is impossible to obtain the necessary retardation when the stretched film is a retardation film. On the other hand, when the stretching ratio is simply increased, the original film breaks during stretching, for example, a hole is formed in a part of the original film during stretching, and breakage occurs due to the gradual expansion of the hole, and biaxial stretching occurs. Formation of the film itself becomes difficult. However, an increase in the stretching ratio of the original film may increase the degree of orientation of the polymer contained in the film and improve the strength of the film after stretching. Moreover, also when setting it as a phase difference film, there exists a possibility that a required phase difference can be ensured by strong extending | stretching.

The biaxially stretched film of the present invention includes an amorphous vinyl polymer (C) having a ring structure in the main chain, Me ₀ represented by the formula (A) is 10,000 or more, and represented by the formula (B). It is a biaxially stretched film obtained by biaxially stretching an original film composed of a thermoplastic resin (D) having a temperature range T _{M in} which N is 10 or more and 500 or less and 25 ° C. or more. As a result, biaxial stretching can be performed at a high draw ratio, and even when the original film is thinned, strength can be ensured, and optical properties, heat resistance and mechanical properties as an optical film are ensured. In addition, the biaxially stretched film can be made thin. In addition, since the composition of a film does not change before and after biaxial stretching, the biaxially stretched film of this invention is comprised from the said thermoplastic resin (D).

[Thermoplastic resin (D)]
The thermoplastic resin (D) constituting the biaxially stretched film of the present invention contains an amorphous vinyl polymer (C) having a ring structure in the main chain. In the resin (D), the molecular weight Me ₀ between the entanglement points in the rubber-like flat region of the dynamic viscoelastic spectrum shown in the following formula (A) is 10,000 or more, and the entanglement number N shown in the following formula (B). Is a temperature range T _M where the temperature is 10 or more and 500 or less.
Me ₀ = 3cRT ₀ / E ′ ₀ (A)
N = (MwE ′) / (3cRT) (B)

In the formula (A), c is the density (g · m ⁻³ ) of the thermoplastic resin at 25 ° C., R is a gas constant (8.31 J · K ⁻¹ · mol ⁻¹ ), and T ₀ is the thermoplasticity. The temperature (K) and E ′ _{0 at} the midpoint of the rubber-like flat region in the resin are the storage elastic modulus (Pa) of the thermoplastic resin at the temperature T ₀ . In the formula (B), Mw is the weight average molecular weight of the thermoplastic resin, T is the temperature (K) of the thermoplastic resin, and E ′ is the storage elastic modulus (Pa) of the thermoplastic resin at the temperature T.

  A high molecular compound (polymer) is a compound in which each molecule has a long chain shape, and the movement of the molecule is restricted in a state of a resin composition corresponding to a so-called dense system, and the molecules are intertwined with each other. . As the temperature rises, the entanglement gradually disappears, and when it is completely eliminated, it enters a fluidized state (flow region). Take a state called. The rubber-like flat region has a smaller change in storage elastic modulus E ′ and loss elastic modulus E ″ in the dynamic viscoelastic spectrum of the polymer compound than in other regions. Ideally, E ′ and E ″ is an area expressed as a section that is substantially flat and does not change. In the rubbery region, the polymer molecules are “fixed” at the point where the main chains are entangled (entanglement points), but it is considered that the main chains can slide between adjacent entanglement points. In this region, the resin film can be stretched.

Formula (A), the temperature of the midpoint of the rubbery plateau region, more specifically, a typical (average) temperature in the rubbery plateau region, the starting temperature T _S and the end temperature of the region The molecular weight Me ₀ between the entanglement points at a temperature T ₀ (= (T _S + T _E ) / 2) intermediate between T _E is defined. As Me _{0 in the} formula (A) increases, the density of the entanglement points in the rubber-like flat region of the resin decreases, and it becomes difficult to stretch at a high magnification to realize a thin film. A low density of entanglement points means that the resin is close to a fluid state. For this reason, when part of the original film becomes hotter than other parts due to uneven heating during stretching, it becomes easy to stretch strongly because only that part is closer to the fluidized state, for example, holes are formed in part of the film. The breakage due to the expansion of the hole is likely to occur. In the strongly stretched portion, the temperature further increases due to friction between molecular chains, leading to further local stretching, which may be related to the occurrence of the above-described fracture. When the film thickness is large, the influence of such temperature non-uniformity is weakened, and even when the film is stretched at a high magnification, the film is hardly broken. However, when aiming at a thin film, the influence directly and surely inhibits high magnification stretching. A Me ₀ of 10,000 or more corresponds to the fact that the resin (D) is a resin that is difficult to stretch at a high magnification when aiming at thinning. In addition, the molecular weight Me between the entanglement points is known to those skilled in the art together with the formula Me = 3cRT / E ′ (may be expressed as Me = cRT / G ′). Me is generally not affected by the molecular weight of the polymer (resin).

Formula (B) defines an average (number of entanglements) N of the number of entanglement points in the molecular chain obtained by dividing the polymer (resin) weight average molecular weight Mw by the molecular weight Me between the entanglement points. An entanglement number N of 10 or more and 500 or less is suitable for high-magnification stretching of the original film. In the resin (D), the temperature range T _{M in} which the entanglement number N is 10 or more and 500 or less is 25 ° C. or more. This means that the temperature range of the rubber-like flat region is more than a certain level. More specifically, for example, when there is temperature unevenness in heating during stretching, even when the film is thin. It means that the resin constituting the film can be easily stretched without being in a fluid state. Thereby, even when aiming at thin film formation, it becomes possible to stretch the original film composed of the resin (D) having Me ₀ of 10,000 or more at high magnification. The temperature range T _M is preferably 27 ° C. or higher. The upper limit of the temperature range T _M is not particularly limited, is usually 100 ° C. or less, preferably 60 ° C. or less.

  The dynamic viscoelastic spectrum of the resin (D) and the storage elastic modulus E ′ on the spectrum are obtained by applying a known dynamic viscoelastic spectrum evaluation method to a film composed of the resin (D). Can do.

For the resin (D), the entanglement number N ₀ in the rubber-like flat region shown in the following formula (C) is preferably 9 or more. In this case, high-stretching of the original film composed of the resin (D) having Me ₀ of 10,000 or more can be more reliably performed. The entanglement number N ₀ is preferably 10 or more.
N ₀ = Mw / Me ₀ (C)

As long as Me _{0 of the} resin (D) is 10,000 or more, the amorphous vinyl polymer (C) having a ring structure in the main chain is not limited.

The polymer (C) is, for example, a (meth) acrylic polymer having a ring structure in the main chain. The Tg of the (meth) acrylic polymer typically does not reach 100 ° C., typically PMMA, but the Tg of the polymer is improved by the ring structure of the main chain (eg, 110 ° C. or higher) and includes the polymer. The heat resistance of the biaxially stretched film composed of the resin (D) is improved. In addition, the (meth) acrylic polymer has high optical transparency, high surface strength, and excellent properties such as molding processability. The polymer (C) is a (meth) acrylic polymer. In this case, a biaxially stretched film suitable for optical applications can be obtained. In addition, since the ring structure of the main chain sterically inhibits the entanglement between the molecular chains of the polymer, the (meth) acrylic polymer exhibiting a high Tg of 110 ° C. or higher, depending on the type and content of the ring structure. The Me ₀ is generally 10,000 or more.

  The (meth) acrylic polymer is a polymer having (meth) acrylic acid ester units in an amount of 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol% or more based on all structural units. The (meth) acrylic polymer may contain a ring structure that is a derivative of a (meth) acrylic acid ester unit. In this case, the total of the (meth) acrylic acid ester unit and the ring structure is 50 mol of all the structural units. If it is% or more, it becomes a (meth) acrylic polymer.

  The (meth) acrylic acid ester unit is, for example, an acrylic acid ester such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, cyclohexyl acrylate, benzyl acrylate; methacrylic acid Formed of a polymer of monomers such as methyl, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, and the like. Unit. Among them, since a biaxially stretched film having high transparency and heat resistance can be obtained, the polymer (C) which is a (meth) acrylic polymer having a ring structure in the main chain is a methyl methacrylate (MMA) unit. Are preferably included as structural units. The polymer (C) which is a (meth) acrylic polymer having a ring structure in the main chain may have two or more of these (meth) acrylic acid ester units.

  The ring structure is, for example, a ring structure having an ester group, an imide group or an acid anhydride group.

A more specific example of the ring structure is at least one selected from an N-substituted maleimide structure, a maleic anhydride structure, a glutarimide structure, a glutaric anhydride structure, and a lactone ring structure. Of these ring structures, the glutarimide structure having a nitrogen atom to which a substituent is bonded and the N-substituted maleimide structure have a greater effect of increasing Me ₀ of the polymer (C) than other ring structures. In other words, when the main chain has a glutarimide structure or an N-substituted maleimide structure, it is particularly difficult to reduce the thickness of the biaxially stretched film. According to the present invention, these ring structures are included in the main chain. Even in this case, it is possible to achieve a thin film while ensuring the optical properties, heat resistance and mechanical properties of the optical film.

  The (meth) acrylic polymer having a ring structure in the main chain is obtained by, for example, copolymerizing a (meth) acrylic acid ester and a monomer having a ring structure located in the main chain when the polymer is used. Alternatively, it can be formed by forming a (meth) acrylic polymer and then introducing a ring structure into the main chain of the polymer by advancing the cyclization reaction.

  The following formula (1) shows an N-substituted maleimide structure and a maleic anhydride structure.

In the formula (1), R ¹ and R ² are each independently a hydrogen atom or a methyl group, and X ¹ is an oxygen atom or a nitrogen atom. When X ¹ is an oxygen atom, R ³ does not exist, and when X ¹ is a nitrogen atom, R ³ is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, or a phenyl group. .

When X ¹ is a nitrogen atom, the ring structure represented by the formula (1) is an N-substituted maleimide structure. The (meth) acrylic polymer having an N-substituted maleimide structure in the main chain can be formed, for example, by copolymerizing an N-substituted maleimide and a (meth) acrylic ester.

When X ¹ is an oxygen atom, the ring structure represented by the formula (1) is a maleic anhydride structure. The (meth) acrylic polymer having a maleic anhydride structure in the main chain can be formed, for example, by copolymerizing maleic anhydride and (meth) acrylic acid ester.

  The following formula (2) shows a glutarimide structure and a glutaric anhydride structure.

R ⁴ and R ⁵ in the formula (2) are each independently a hydrogen atom or a methyl group, and X ² is an oxygen atom or a nitrogen atom. When X ² is an oxygen atom, R ⁶ does not exist, and when X ² is a nitrogen atom, R ⁶ is a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cyclopentyl group, a cyclohexyl group, or a phenyl group. .

When X ² is a nitrogen atom, the ring structure represented by the formula (2) is a glutarimide structure. The glutarimide structure can be formed, for example, by imidizing a (meth) acrylic acid ester polymer with an imidizing agent such as methylamine.

When X ² is an oxygen atom, the ring structure represented by the formula (2) is a glutaric anhydride structure. The glutaric anhydride structure can be formed, for example, by subjecting a copolymer of (meth) acrylic acid ester and (meth) acrylic acid to dealcoholization cyclocondensation within the molecule.

  Although the specific lactone ring structure which the polymer (C) may have in the main chain is not particularly limited, for example, it is a structure represented by the following formula (3).

In the formula (3), R ⁷ , R ⁸ and R ⁹ are each independently a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom.

  The organic residue is, for example, an alkyl group having 1 to 20 carbon atoms such as a methyl group, an ethyl group, or a propyl group; an unsaturated aliphatic carbonization having 1 to 20 carbon atoms such as an ethenyl group or a propenyl group A hydrogen group; an aromatic hydrocarbon group having 1 to 20 carbon atoms such as a phenyl group or a naphthyl group; one of hydrogen atoms in the alkyl group, the unsaturated aliphatic hydrocarbon group and the aromatic hydrocarbon group; One or more groups are substituted with at least one group selected from a hydroxyl group, a carboxyl group, an ether group and an ester group.

The lactone ring structure represented by formula (3) is obtained by, for example, copolymerizing a monomer group containing methyl methacrylate (MMA) and 2- (hydroxymethyl) methyl acrylate (MHMA), Adjacent MMA units and MHMA units in the coalescence can be formed by dealcoholization cyclocondensation. At this time, R ⁷ is H, and R ⁸ and R ⁹ are CH ₃ .

  The content of the ring structure in the polymer (C) which is a (meth) acrylic polymer having a ring structure in the main chain is, for example, 2 to 90% by weight, and preferably 5 to 85% by weight.

The polymer (C) which is a (meth) acrylic polymer having a ring structure in the main chain has one or two (meth) acrylate units and structural units other than the ring structure as long as Me ₀ is 10,000 or more. You may have more than one seed. The unit is a unit formed by polymerization of monomers such as styrene, vinyl toluene, α-methyl styrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, vinyl acetate, N-vinyl pyrrolidone. The polymer (C) is an α, β-unsaturated monomer unit having a heteroaromatic group, for example, at least selected from an N-vinylcarbazole unit, a vinylpyridine unit, a vinylimidazole unit, and a vinylthiophene unit. In this case, the degree of freedom in controlling the wavelength dispersibility in the biaxially stretched film is increased. For example, the wavelength dispersibility in which the birefringence (phase difference) decreases as the wavelength of light decreases. It can also be set as the biaxially stretched film which shows (reverse wavelength dispersion). An optical film exhibiting reverse wavelength dispersion contributes to improving display characteristics in an image display device, such as improving contrast.

Another example of the polymer (C) is a copolymer having an aromatic vinyl monomer unit and a unit (G) having a ring structure located in the main chain of the polymer (C) as constituent units ( H). In the copolymer (H), the aromatic vinyl monomer unit ensures optical transparency and molding processability, and the unit (G) improves the Tg and mechanical properties of the polymer (for example, , Tg can be 110 ° C. or higher). Also in this example, since the ring structure of the unit (G) sterically inhibits the entanglement between the molecular chains of the polymer, depending on the type and content of the unit (G), a high Tg of 110 ° C. or higher is required. The Me ₀ of the copolymer (H) shown is generally 10,000 or more.

The aromatic vinyl monomer unit is a unit represented by the following formula (4). R ¹⁰ in Formula (4) is an aromatic group, and R ^{11 to} R ¹³ are a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms.

  The aromatic vinyl monomer unit is a unit formed by polymerization of monomers such as styrene, α-methylstyrene, methoxystyrene, vinyltoluene and the like. Especially, since a biaxially stretched film with high optical transparency is obtained, a styrene unit is preferable.

  The aromatic vinyl monomer unit may be a vinyl monomer unit having a heteroaromatic group, for example, by polymerization of monomers such as N-vinyl carbazole, vinyl pyridine, vinyl imidazole, and vinyl thiophene. It may be a unit to be formed.

  The copolymer (H) may have two or more types of aromatic vinyl monomer units.

  The content rate of the aromatic vinyl monomer unit in a copolymer (H) is 3-97 mol%, for example, 5-95 mol% is preferable and 10-90% is more preferable.

  The unit (G) is, for example, at least one selected from an N-substituted maleimide unit, a glutarimide unit, a maleic anhydride unit, a glutaric anhydride unit, and a lactone ring structure unit. The copolymer (H) preferably has a styrene unit as an aromatic vinyl monomer unit and an N-substituted maleimide unit as a unit (G) having a ring structure. Such a copolymer (H) is, for example, a styrene / N-substituted maleimide copolymer.

  The N-substituted maleimide unit is as described above. More specifically, it is a unit formed by polymerization of monomers such as N-methylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-benzylmaleimide and the like. Of these, N-methylmaleimide, N-cyclohexylmaleimide, and N-phenylmaleimide are preferable.

  The copolymer (H) may have 2 or more types of units (G).

  The content rate of the unit (G) in a copolymer (H) is 3-97 mol%, for example, 5-95 mol% is preferable and 10-90% is more preferable.

  The copolymer (H) can be formed, for example, by copolymerizing an aromatic vinyl monomer and a monomer in which the unit (G) is formed by polymerization.

The copolymer (H) may have one or more structural units other than the aromatic vinyl monomer and the unit (G) as long as Me ₀ is 10,000 or more. The unit is, for example, the (meth) acrylic acid ester unit described above. When the copolymer (H) further has a (meth) acrylic acid ester unit as a constituent unit, it is expected to acquire characteristics derived from the acrylic unit such as an improvement in optical transparency or an improvement in surface hardness.

The content of the structural unit and the ring structure in the polymer (C) can be determined by a known method such as ¹ H nuclear magnetic resonance ( ¹ H-NMR), infrared spectroscopy (IR), or elemental analysis. The content of the lactone ring structure in the polymer (C) can be determined by the method described in JP-A-2001-151814.

  The Tg of the polymer (C) is, for example, 110 ° C. or higher. Depending on the type and content of the units and / or ring structures constituting the polymer (C), 120 ° C. or higher, 130 ° C. or higher, and further 140 It can be set to at least ° C.

  The weight average molecular weight (Mw) of the polymer (C) is, for example, 100,000 to 500,000, preferably 120,000 to 400,000, and more preferably 130,000 to 300,000.

  The polymer (C) can be formed by a known polymerization method.

Resin (D) which comprises the biaxially stretched film of this invention contains a polymer (C). The content of the polymer (C) in the resin (D) is not particularly limited as long as the resin (D) satisfies 10,000 or more for Me ₀ and 25 ° C. or more for T _M , but is usually 30% by weight or more, and 50 % By weight is preferable, and 70% by weight or more is more preferable.

Me ₀ of the resin (D) can be adjusted by the type and content of the polymer contained in the resin. This is because Me ₀ of the resin (D) changes depending on the balance of Me ₀ between the polymers contained in the resin. For example, Me ₀ of a resin obtained by mixing a polymer showing high Me _0H and a polymer showing low Me _0L is a value between Me _0H and Me _0L . In addition, in mixing of polymers, in order to ensure the optical transparency of a biaxially stretched film, it is necessary to consider the compatibility between these polymers.

Further, Me ₀ of the resin (D) can be adjusted by crosslinking between the polymers contained in the resin. However, when it is set as a general crosslinking density, it should be noted that the resin (D) can be a biaxially stretched film that is hard and brittle and has impaired mechanical properties. In addition, a resin (D) that is too rigid may make it difficult to form a film itself. For example, the Me ₀ of the resin (D) can be appropriately increased by using the resin (D) having a slightly increased crosslink density by using less crosslinking agent than usual. The crosslinking agent is, for example, a polyfunctional crosslinking agent such as divinylbenzene (DVB), diacrylate, or triacrylate. By using the crosslinking agent when forming the resin (D), the crosslinking density of the resin (D) is increased. It is possible to raise Me ₀ appropriately.

T _M of the resin (D) can be adjusted by the type and content of the polymer contained in the resin. T _M of the resin (D) is to change the balance of T _M of the polymer bodies contained in the resin. For example, the T _M of a resin obtained by mixing a polymer exhibiting a large T _MH and a polymer exhibiting a low T _ML is a value between T _MH and T _ML .

The molecular weight of the resin (D) (e.g., a resin (polymer contained in D) the molecular weight of (C)) can be adjusted T _M by. The larger the molecular weight of the resin (D), is because the greater the T _M of the resin. The molecular weight is, for example, a weight average molecular weight (Mw). In addition, T _M of the polymer (D), as well as Me _0, can be adjusted by crosslinking between the polymer contained in the resin.

  The Tg of the resin (D) is, for example, 110 ° C. or higher, and can be 120 ° C. or higher, 130 ° C. or higher, and further 140 ° C. or higher depending on the composition of the resin (D).

  As long as compatibility with the polymer (C) is ensured and the effect of the present invention is obtained, the resin (D) may contain a polymer other than the polymer (C). Examples of the polymer include olefin polymers such as polyethylene, polypropylene, ethylene-propylene polymer, and poly (4-methyl-1-pentene); halogen-containing polymers such as vinyl chloride and chlorinated vinyl resins; Acrylic polymers such as methyl methacrylate; polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate; polyamides such as nylon 6, nylon 66, nylon 610; polyacetals; polycarbonates; polyphenylene oxides; polyphenylene sulfides; Polysulfone; polyethersulfone; polyoxypentylene; polyamideimide; rubbery polymer. Resin (D) can contain 2 or more types of these polymers.

  As long as the effects of the present invention are obtained, the resin (D) can contain a material other than the polymer, for example, an additive. Additives include, for example, antioxidants, light stabilizers, weather stabilizers, heat stabilizers and other stabilizers; phase difference adjusting agents such as phase difference increasing agents, phase difference reducing agents, phase difference stabilizers; glass fibers, Reinforcing materials such as carbon fibers; UV absorbers; near infrared absorbers; flame retardants such as tris (dibromopropyl) phosphate, triallyl phosphate, antimony oxide; antistatic agents including anionic, cationic and nonionic surfactants Agents; colorants such as inorganic pigments, organic pigments, dyes; organic fillers, inorganic fillers, resin modifiers, plasticizers, lubricants. The content of the additive in the resin (D) is preferably less than 7% by weight, more preferably 2% by weight or less, and still more preferably 0.5% by weight or less.

  The formation method of resin (D) is not specifically limited. In the case of the resin (D) made of the polymer (C), the polymer (C) may be used as it is as the resin (D) (in this case, the polymer (C) = resin (D)), and the resin When (D) contains the other polymer and / or additive, it can be formed by mixing the polymer (C) and the other polymer and / or additive by a known mixing method. Mixing can be carried out, for example, by pre-blending with a mixer such as an omni mixer and then kneading the resulting mixture. In this case, the kneader is not particularly limited. For example, a known kneader such as an extruder such as a single screw extruder or a twin screw extruder or a pressure kneader can be used.

[Biaxially stretched film]
The biaxially stretched film of this invention is comprised from resin (D). As a result, the optical properties, heat resistance and mechanical properties of the optical film are ensured, and the film is thinned.

  Regarding optical properties, the biaxially stretched film of the present invention has high optical transparency. The total light transmittance of the film is, for example, 85% or more, preferably 90% or more, more preferably 91% or more. The total light transmittance is an index of optical transparency of the film. A film having a total light transmittance of less than 85% is not suitable for optical applications. The total light transmittance of the film can be determined in accordance with JIS K7361.

  The haze exhibited by the biaxially stretched film of the present invention is, for example, 5% or less with a thickness of 100 μm, and is 3% or less, and further 2% or less depending on the composition of the resin (D).

  The biaxially stretched film of the present invention is a zero-retarded film that exhibits a phase difference based on the composition of the resin (D) and stretching conditions, and that does not generate orientation birefringence and has a phase difference of almost zero. You can also. The film which shows retardation can be used as a retardation film, for example, or can be used as an antireflection film in combination with a polarizing plate. The zero retardation film can be used, for example, as a polarizer protective film. In this case, the protective film can be combined with a polarizer to form a polarizing plate. In the present specification, when the phase difference (the absolute value of the in-plane retardation Re and the thickness direction retardation Rth) is 5 nm or less, it is a zero retardation film in which no orientation birefringence occurs. To do. The absolute value of Re and Rth of the zero retardation film is preferably 3 nm or less, more preferably 1.5 nm or less, and further preferably 1 nm or less. In the biaxially stretched film of the present invention, the in-plane retardation Re for light having a wavelength of 550 nm may be 5 nm or less, and the absolute value of the retardation in the thickness direction for the light may be 5 nm or less.

  The in-plane retardation Re and the thickness direction retardation Rth are the refractive index in the slow axis direction in the film plane nx, the refractive index in the fast axis direction in the film plane ny, and the refractive index in the film thickness direction. When the rate is nz and the film thickness is d (nm), they are given by the equation (nx−ny) × d and the equation {(nx + ny) / 2−nz} × d, respectively. In the present specification, the refractive indexes nx, ny, and nz are refractive indexes with respect to light having a wavelength of 550 nm.

  Regarding mechanical properties, the biaxially stretched film of the present invention has high strength. The strength of the film can be represented by, for example, a film impact strength measured in accordance with ASTM D3420. The film impact strength of the biaxially stretched film of the present invention can be set to a sufficiently high value suitable for use as an optical film, for example, 0.2 J or more.

  Regarding heat resistance, the biaxially stretched film of the present invention has a high Tg. The Tg of the film is the same as the Tg of the resin (D) constituting the film, for example, 110 ° C. or higher, and depending on the composition of the resin (D), 120 ° C. or higher, 130 ° C. or higher, and 140 ° C. or higher. be able to. Such a biaxially stretched film exhibiting high heat resistance is suitable for use in an image display apparatus in which the power supply unit, the light emitting unit, and the circuit board are forced to be disposed close to each other.

  Regarding thinning, the biaxially stretched film of the present invention achieves a thickness of 35 μm or less while satisfying optical properties, heat resistance and mechanical properties. Depending on the composition of the resin (D) and the stretching conditions, a thickness of 30 μm or less, 25 μm or less, and further 20 μm or less is realized while satisfying the above-mentioned characteristics. The lower limit of the thickness is not particularly limited, but an optical film that is too thin may be, for example, 10 μm because handling properties may be reduced during the manufacture of the image display device.

  The biaxially stretched film of the present invention is, for example, 1.8 to 5.0 times stretched in at least one direction in biaxial stretching, and 2.2 to 5.0 times depending on the composition of the resin (D), Furthermore, it is a film that has been stretched 3.0 to 5.0 times. The biaxially stretched film of the present invention may be a film that has been stretched at these magnifications for stretching in both directions in biaxial stretching.

  Various functional coating layers may be formed on the surface of the biaxially stretched film of the present invention as necessary. Functional coating layers include, for example, antistatic layers, adhesive layers, adhesive layers, easy adhesion layers, antiglare (non-glare) layers, antifouling layers such as photocatalyst layers, antireflection layers, hard coat layers, and UV shielding layers. A layer, a heat ray shielding layer, an electromagnetic wave shielding layer, and a gas barrier layer. The functional coating layer can be formed at any time.

  The biaxially stretched film of the present invention can be used as various optical members in the same manner as conventional biaxially stretched films. The optical member is, for example, an optical protective film, specifically, a polarizing film used for a protective film for substrates of various optical disks (VD, CD, DVD, MD, LD, etc.), and a polarizing plate included in an image display device such as an LCD. It is a child protective film and a retardation film. You may use for a viewing angle compensation film, a light-diffusion film, a reflection film, an antireflection film, an anti-glare film, a brightness enhancement film, a conductive film for touch panels, etc.

  For example, a polarizing plate can be formed using the biaxially stretched film of the present invention.

  The biaxially stretched film of this invention can be formed with the manufacturing method of this invention shown below, for example.

[Production method]
In the manufacturing method of this invention, the biaxially stretched film of this invention whose thickness is 35 micrometers or less is formed by biaxially stretching the original film comprised from resin (D). What is necessary is just to implement similarly to manufacture of the conventional biaxially stretched film except using the original film comprised from resin (D).

  The formation method of the original film comprised from resin (D) is not specifically limited, For example, the casting method and the melt molding method (melt extrusion molding, press molding, etc.) are applicable.

  Known methods can also be applied to biaxial stretching of the original film. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. The stretching method, stretching temperature, and stretching ratio can be appropriately selected according to the properties of the target biaxially stretched film. The stretching temperature is, for example, Tg or more and Tg + 50 ° C. or less of the resin (D), and preferably Tg or more and Tg + 40 ° C. or less. In the present invention, the draw ratio can be made higher than in the prior art. For stretching in at least one direction in biaxial stretching, for example, 1.8 to 5.0 times, depending on the composition of the resin (D), 2 .2 to 5.0 times, and further 3.0 to 5.0 times. These stretching ratios can be set for stretching in both directions in biaxial stretching.

[Image display device]
The image display device of the present invention is not particularly limited as long as it includes the biaxially stretched film of the present invention. The image display device of the present invention is, for example, an LCD, and the image display unit of the LCD includes the biaxially stretched film of the present invention together with members such as a liquid crystal cell and a backlight.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples shown below.

  Initially, the evaluation method of the polymer, resin, and biaxially stretched film which were produced in the present Example is shown.

[Glass transition temperature (Tg)]
The Tg of the polymer and resin was determined in accordance with JIS K7121 regulations. Specifically, a differential scanning calorimeter (manufactured by Rigaku, DSC-8230) is used, and a sample of about 10 mg is heated from normal temperature to 200 ° C. (temperature increase rate: 20 ° C./min) in a nitrogen gas atmosphere. The DSC curve was evaluated by the starting point method. Α-alumina was used as a reference.

[Weight average molecular weight (Mw)]
The Mw of the polymer and resin was determined by gel conversion using gel permeation chromatography (GPC). The apparatus and measurement conditions used for the measurement of Mw are as follows.
System: Tosoh GPC system HLC-8220
Measurement side column configuration;
Guard column: Tosoh TSKguardcolumn SuperHZ-L
・ Separation column: Tosoh, TSKgel SuperHZM-M 2 in series connection Reference side column configuration;
Reference column: Tosoh TSKgel SuperH-RC
Developing solvent: Chloroform (Wako Pure Chemical Industries, special grade)
Flow rate of developing solvent: 0.6 mL / min Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit)
Column temperature: 40 ° C

[Film thickness]
The thickness of the film (original film and biaxially stretched film) was measured using a Digimatic Micrometer (manufactured by Mitutoyo).

[Film impact strength]
The film impact strength of the biaxially stretched film was determined using a film impact tester (manufactured by Tester Sangyo Co., Ltd.) under the conditions of 23 ° C. and 50% RH in accordance with the provisions of ASTM D3420.

[Molecular weight Me ₀ between entanglement points, entanglement number N ₀ , temperature range T _M where entanglement number N is 10 to 500]
An evaluation sample obtained by cutting the original film into a size of 5 mm × 30 mm was left to stand for 2 hours or more in an atmosphere of 25 ° C. and 60% RH, and then the humidity was adjusted. Then, a dynamic viscoelasticity measuring apparatus (TA instrument) RSA3), and the storage elastic modulus E ′, the loss elastic modulus E ″ and the ratio tan δ of the sample were determined. At this time, the distance between the grips of the sample was 20 mm, the measurement frequency was 1 Hz, and the temperature conditions were a start from 30 ° C. and a temperature increase rate of 5 ° C./min.

Next, the measured storage elastic modulus E ′ (Pa) is plotted on the vertical axis that is the logarithmic axis, and the temperature (K) is plotted on the horizontal axis that is the linear axis, and is located between the glass transition region and the flow region. The temperature T ₀ at the midpoint of the rubber-like flat region where E ′ does not change as compared to other regions, and in some cases shows a constant value, is intermediate between the start temperature T _S and the end temperature T _E of the rubber-like flat region. The temperature was determined from the temperature (= (T _S + T _E ) / 2). This T _0, from ₀ Metropolitan 'value E of' E in the T _0, the formula (A), was determined the entanglement molecular weight Me _0.

Separately from this, from the temperature T (K) in the rubber-like flat region, the storage elastic modulus E ′ (Pa) at the temperature T, and Mw separately evaluated, the number of entanglements N is obtained by the formula (B), and the number of entanglements obtained. N is plotted on the vertical axis which is the logarithmic axis, and the temperature (K) is plotted on the horizontal axis which is the linear axis. From the difference between the temperature at which the entanglement number N is 10 and the temperature at which the entanglement number N is 500, the entanglement number N is 10 to 500. A temperature range T _M was obtained.

[Phase difference]
The retardation of the biaxially stretched film is determined by using an retardation film / optical material inspection apparatus (Otsuka Electronics, RETS-100), in-plane retardation Re for light having a wavelength of 550 nm, and thickness direction for light having the same wavelength. It calculated | required as phase difference Rth. The phase difference was measured at one point near the center of the biaxially stretched film. However, regarding the retardation Rth in the thickness direction, the film thickness d, the average refractive index of the film measured with an Abbe refractometer, and the retardation value (Re ( 40 °)) and the three-dimensional refractive indexes nx, ny, and nz, and obtained from the formula Rth = {(nx + ny) / 2−nz} × d. nx is the refractive index in the slow axis direction of the film, ny is the refractive index in the fast axis direction, nz is the refractive index in the thickness direction of the film, and d is the thickness (nm) of the film. Regarding the direction of tilting the film, Re (S40 °) with the slow axis as the tilt axis and Re (F40 °) with the fast axis as the tilt axis are measured in advance, and Re (S40 °)> Re (F40 °). ) Is the slow axis, and when Re (S40 °) <Re (F40 °), the fast axis is the tilt axis.

(Production Example 1: Production of CHMI-MMA-St copolymer)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe and a dropping funnel, 45 parts by weight of methyl methacrylate (MMA), 40 parts by weight of styrene (St), antioxidant (made by ADEKA, ADK STAB 2112) 0.05 part by weight and 13 parts by weight of toluene as a polymerization solvent were charged. Next, while introducing nitrogen gas into the reaction vessel, the internal temperature was raised to 105 ° C., and when refluxing began, t-amyl peroxyisononanoate (Lukelox 570, manufactured by Arkema Yoshitomi) as a polymerization initiator 0. At the same time, dropwise addition of a mixture of 15 parts by weight of cyclohexylmaleimide (CHMI), 35 parts by weight of toluene and 0.308 parts by weight of t-amylperoxyisononanoate was started. While 80% by weight of this mixture was added dropwise over 4 hours and the remaining 20% by weight over 2 hours, solution polymerization was allowed to proceed at about 100 to 115 ° C. under reflux. In addition, 15.4 parts by weight of toluene was added at the time when 4 hours had elapsed from the start of dropping of the above mixture, and the polymerization solution was diluted. After completion of the dropwise addition, aging was further performed for 2 hours.

  Next, the obtained polymerization solution was introduced into a vent type screw twin screw extruder, devolatilized at a barrel temperature of 240 ° C., the polymer contained in the polymerization solution was pelletized, and cyclohexylmaleimide / methyl methacrylate / styrene co-polymerized. A transparent polymer (C-1) pellet as a polymer was obtained. The polymer (C-1) had a Tg of 122 ° C. and an Mw of 16,000.

Next, after pellets of the produced polymer (C-1) were dried in a dry air at 60 ° C. for 24 hours as a resin (D-1), a single screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm), and melt-extruded at 280 ° C., and the melt-extruded polymer was discharged onto a cooling roll having a temperature of 110 ° C. to give an unstretched film having a thickness of 122 μm (original film) ; (F-1) was obtained. Table 1 below shows T ₀ , Me ₀ , N ₀ and T _M of the original film (F-1). Hereafter, when the polymer (resin) was formed into a film, all were formed after drying in dry air at 60 ° C. for 24 hours.

(Production Example 2: Production of CHMI-St copolymer)
A reaction vessel equipped with a stirrer, temperature sensor, cooling pipe, nitrogen introduction pipe and dropping funnel was charged with 71 parts by weight of St and 0.05 parts by weight of antioxidant (ADEKA, ADK STAB 2112), and nitrogen gas was passed through it. The temperature was raised to 110 ° C. After raising the temperature, 0.045 parts by weight of t-amylperoxyisononanoate (Arkema Yoshitomi, Luperox 570) was added as a polymerization initiator, and at the same time, a mixture of 29 parts by weight of CHMI and 28 parts by weight of toluene as dropping system 1; As a dropping system 2, dropping of a mixture of 0.090 parts by weight of t-amylperoxyisononanoate and 7.5 parts by weight of toluene was started. 20 wt% of the dropping system 1 was dropped over 0.5 hours, and the remaining 80 wt% was further dropped over 3 hours. The total amount of the dropping system 2 was continuously dropped over 3.5 hours. Meanwhile, solution polymerization was allowed to proceed at about 115 to 125 ° C. under reflux. After completion of the dropwise addition, aging was further performed for 1.5 hours. When the composition ratio of the obtained polymerization solution was calculated using gas chromatography, the content of CHMI units in the polymer was 34% by weight, and the content of St units was 66% by weight.

  Next, the obtained polymerization solution is introduced into a vent type screw twin-screw extruder and devolatilized at a barrel temperature of 240 ° C., and the polymer contained in the polymerization solution is pelletized to obtain a cyclohexylmaleimide / styrene copolymer. A transparent polymer (E-1) pellet was obtained. The polymer (E-1) had a Tg of 146 ° C. and an Mw of 130,000.

Next, a film was formed in the same manner as in Production Example 1 using the produced polymer (E-1) pellets to prepare an unstretched film (original film); (F-2) having a thickness of 122 μm. Table 1 below shows T ₀ , Me ₀ , N ₀ and T _M of the original film (F-2).

(Production Example 3: Production of PMMA)
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, a nitrogen introduction pipe and a dropping funnel, MMA 30 parts by weight, antioxidant (manufactured by ADEKA, ADK STAB 2112) 0.05 part by weight and methyl ethyl ketone (MEK) 65 as a polymerization solvent The weight part was charged. Next, the inside temperature was raised to 80 ° C. while introducing nitrogen gas into the reaction vessel, and when refluxing started, t-amylperoxy-2-ethylhexanoate (manufactured by Arkema Yoshitomi, Luperox, Inc.) was used as a polymerization initiator. 575) 0.052 parts by weight and 5 parts by weight of MEK were added. After the addition, stirring was continued for 6 hours under reflux in a nitrogen stream.

  Next, the obtained polymerization solution is introduced into a vent type screw twin screw extruder and devolatilized at a barrel temperature of 240 ° C., and the polymer contained in the polymerization solution is pelletized to form polymethyl methacrylate (PMMA). A transparent polymer (E-2) pellet was obtained. Mw of the polymer (E-2) was 10.11,000.

(Production Example 4: Production of PMMA)
A transparent polymer (E-3) pellet of PMMA was obtained in the same manner as in Production Example 3, except that the amount charged into the reaction vessel was 45 parts by weight of MMA and 50 parts by weight of MEK. Mw of the polymer (E-3) was 153,000.

(Production Example 5: Production of (meth) acrylic polymer having glutarimide structure)
In Production Example 5, a (meth) acrylic polymer having a glutarimide structure was produced as follows with reference to Production Example 1 of International Publication No. 06/129573 and Examples of Japanese Patent Application Laid-Open No. 2011-246623. . First, PMMA (E-2) produced in Production Example 3 was introduced into a vent-type screw twin screw extruder having a barrel temperature of 260 ° C. having a side feeder, and 100 weight of polymer (E-2) from the side feeder. 5 parts by weight of monomethylamine was injected into the part, and an imidization reaction (glutarimide ring formation reaction) was allowed to proceed. While removing by-products and excess methylamine from the reaction from the vent port, the polymer formed in the extruder was extruded, pelletized, and a unit containing a glutarimide ring structure located in the main chain and unreacted MMA. A transparent polymer (E-4) pellet having a unit as a constituent unit was obtained. The polymer (E-4) had a Tg of 119 ° C., an Mw of 96,000, and an imidization ratio of 5%.

Next, a film was formed using the produced polymer (E-4) pellets in the same manner as in Production Example 1 to produce an unstretched film (original film); (F-3) having a thickness of 122 μm. Table 1 below shows T ₀ , Me ₀ , N ₀ and T _M of the original film (F-3).

(Production Example 6: Production of resin composition containing (meth) acrylic polymer and AS polymer of Production Example 5)
75 parts by weight of the polymer (E-4) produced in Production Example 5 and a styrene-acrylonitrile copolymer (manufactured by Asahi Kasei, Stylac AS783, content ratio of styrene units / acrylonitrile units is 73% by weight / 27% by weight) 25 parts by weight were kneaded using a twin screw extruder having a polymer filter disposed at the tip via a gear pump to obtain a resin (D-2). Resin (D-2) had a Tg of 115 ° C. and an Mw of 132,000. Incidentally, was mixed with the polymer (E-4) Styrene - where the Me ₀ acrylonitrile copolymer was separately measured, was 11000.

Next, the resin (D-2) was used to form a film in the same manner as in Production Example 1 to prepare an unstretched film (original film); (F-4) having a thickness of 122 μm. Table 1 below shows T ₀ , Me ₀ , N ₀ and T _M of the original film (F-4).

(Production Example 7: Production of (meth) acrylic polymer having glutarimide structure)
A glutarimide ring structure located in the main chain in the same manner as in Production Example 5 except that PMMA (E-3) produced in Production Example 4 was used instead of PMMA (E-2) produced in Production Example 3. A transparent polymer (C-2) pellet having a unit containing an unreacted MMA unit as a constituent unit was obtained. The polymer (C-2) had a Tg of 119 ° C., an Mw of 149,000, and an imidization ratio of 5%.

Next, using the polymer (C-2) pellets produced as a resin (D-3), a film was formed in the same manner as in Production Example 1, and an unstretched film (original film) having a thickness of 122 μm; (F -5) was produced. Table 1 below shows T ₀ , Me ₀ , N ₀ and T _M of the original film (F-5).

(Production Example 8: Preparation of (meth) acrylic polymer having glutarimide structure)
A commercially available (meth) acrylic polymer (E-5) having a unit containing a glutaramide ring structure located in the main chain (R ⁴ and R ⁵ in formula (2) are methyl groups) and an MMA unit as constituent units; A pellet made of Daicel-Evonik, plexiimide 8813, and a unit content containing a glutarimide ring (42% by weight) was prepared. The polymer (E-5) had a Tg of 132 ° C. and a weight average molecular weight of 143,000.

Next, the prepared polymer (E-5) pellets were used to form a film in the same manner as in Production Example 1 to prepare an unstretched film (original film); (F-6) having a thickness of 122 μm. Table 1 below shows T ₀ , Me ₀ , N ₀ and T _M of the original film (F-6).

(Production Example 9: Production of a resin composition containing the (meth) acrylic polymer and AS polymer of Production Example 8)
78 parts by weight of the polymer (E-5) prepared in Production Example 8 and 22 parts by weight of the styrene-acrylonitrile copolymer used in Production Example 6 were provided with a polymer filter disposed at the tip via a gear pump. The resin (D-4) was obtained by kneading using a shaft extruder. Resin (D-4) had Tg of 128 ° C. and Mw of 142,000.

Next, the resin (D-4) was used to form a film in the same manner as in Production Example 1 to prepare an unstretched film (original film); (F-7) having a thickness of 122 μm. Table 1 below shows T ₀ , Me ₀ , N ₀ and T _M of the original film (F-7).

(Production Example 10: Production of (meth) acrylic polymer having lactone ring structure in main chain)
In a reaction kettle equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introduction pipe, 229.6 parts by weight of MMA, 33 parts by weight of methyl 2- (hydroxymethyl) acrylate (MHMA), and 248.6 parts by weight of toluene as a polymerization solvent. Then, 0.138 parts by weight of an antioxidant (manufactured by ADEKA, Adeka Stub 2112) and 0.1925 parts by weight of n-dodecyl mercaptan were charged, and the temperature was raised to 105 ° C. through nitrogen.

  At the start of reflux accompanying the temperature rise, 0.2838 parts by weight of t-amylperoxyisonononanoate (manufactured by Arkema Yoshitomi, Luperox 570) was added as a polymerization initiator, and the above t-amylperoxyisonononanoate 0 was added. The solution polymerization was allowed to proceed under reflux at about 105 to 110 ° C. while adding 5646 parts by weight and 12.375 parts by weight of styrene dropwise over 2 hours, followed by further aging for 4 hours.

  Next, 0.206 parts by weight of stearyl phosphate (manufactured by Sakai Chemical Industry, Phoslex A-18) is added to the obtained polymerization solution as a catalyst for the cyclization condensation reaction (cyclization catalyst), and about 90 to 110 ° C. The cyclization condensation reaction for forming a lactone ring structure was allowed to proceed for 2 hours under reflux.

  Next, the obtained polymerization solution was passed through a multi-tube heat exchanger heated to 240 ° C. to complete the cyclization condensation reaction, and then the barrel temperature was 250 ° C. and the degree of vacuum was 13.3 to 400 hPa (10 to 300 mmHg). ), Rear vent number 1 and fore vent number 4 (referred to as the first, second, third and fourth vents from the upstream side), side feeders are provided between the third vent and the fourth vent In a vent type screw twin screw extruder (L / D = 52) having a leaf disk type polymer filter (filtration accuracy 5 μm) at the tip, the processing speed is 31.2 parts by weight (resin amount conversion). Introduced and devolatilized. At that time, ion-exchanged water was charged after the second vent at a charging rate of 0.47 parts by weight / hour.

  After completion of devolatilization, the polymer in the hot melt state remaining in the extruder is discharged while filtering through a polymer filter from the tip of the extruder, pelletized by a pelletizer, and having a lactone ring structure in the main chain, A transparent (meth) acrylic copolymer (C-3) pellet having a styrene unit as a constituent unit was obtained. The polymer (C-3) had Tg of 122 ° C. and Mw of 131,000.

Next, using the produced polymer (C-3) pellets as the resin (D-5), a film was formed in the same manner as in Production Example 1, and an unstretched film (original film) having a thickness of 122 μm; (F -8) was produced. Table 1 below shows T ₀ , Me ₀ , N _0, and T _M of the original film (F-8).

(Production Example 11: Production of (meth) acrylic polymer having lactone ring structure in main chain)
At the time of devolatilization in a twin screw extruder, a solution prepared by dissolving 0.66 parts by weight of an ultraviolet absorber (manufactured by ADEKA, ADK STAB LA-F70) in 1.23 parts by weight of toluene was added at 0.59 parts by weight / hour. A transparent (meth) acrylic copolymer (having a lactone ring structure in the main chain and having a styrene unit as a constituent unit, as in Production Example 10 except that it was further charged after the fourth vent at the charging speed ( Resin (D-6) pellets containing C-3) and an ultraviolet absorber were obtained. Resin (D-6) had Tg of 121 ° C. and Mw of 131,000.

Next, the resin (D-6) pellets were used to form a film in the same manner as in Production Example 1 to prepare an unstretched film (original film); (F-9) having a thickness of 122 μm. Table 1 below shows T ₀ , Me ₀ , N ₀ and T _M of the original film (F-9).

Example 1
After the original film (F-1) produced in Production Example 1 was cut into a size of 96 mm × 96 mm, the stretching temperature was changed to the polymer (C) using a sequential biaxial stretching machine (X-6S, manufactured by Toyo Seiki Seisakusho). -1) Tg + 15 ° C., stretching ratio was 2.2 × 2.2 times, stretching speed was 800 mm / min, and biaxial stretching was sequentially performed in the order of the machine direction (MD direction) and the transverse direction (TD direction). After stretching, the film was quickly taken out from the stretching machine and cooled to obtain a biaxially stretched film (FS-1). The produced biaxially stretched film (FS-1) had a thickness of 25 μm and film impact strengths of 0.22J and 0.2J or more, and was a biaxially stretched film having high strength at the same time as the film thickness was reduced. The properties of the film (FS-1) are shown in Table 2A below.

(Example 2)
Using the polymer (C-1) produced in Production Example 1 as a resin (D-1), a single-screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm) The polymer that was melt-extruded at 280 ° C. and melt-extruded was discharged onto a cooling roll having a temperature of 110 ° C. to obtain a 144 μm-thick unstretched film (original film); (F-1-2).

  Next, with respect to the produced original film (F-1-2), the stretching temperature was Tg + 20 ° C. of the polymer (C-1), and the stretching ratio was further set to 3.0 times × 3.0 times the high magnification. Produced a biaxially stretched film (FS-1-2) in the same manner as in Example 1. The thickness of the produced film (FS-1-2) was 16 μm, the film impact strength was 0.20 J and 0.2 J or more, and it was a biaxially stretched film having high strength at the same time while achieving further thinning. . The properties of the film (FS-1-2) are shown in Table 2A below.

(Example 3)
Example except that the original film (F-4) produced in Production Example 6 was used instead of the original film (F-1) produced in Production Example 1 and the stretching temperature was Tg + 15 ° C. of the resin (D-2). In the same manner as in Example 1, a biaxially stretched film (FS-4) was obtained. The produced biaxially stretched film (FS-4) had a thickness of 25 μm and film impact strengths of 0.24 J and 0.2 J or more, and was a biaxially stretched film having high strength at the same time as the film thickness was reduced. The properties of the film (FS-4) are shown in Table 2A below.

Example 4
The resin (D-2) produced in Production Example 6 was melt extruded at 280 ° C. using a single screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm), and melt extruded. The resin was discharged onto a cooling roll having a temperature of 110 ° C. to obtain a 144 μm-thick unstretched film (original film); (F-4-2).

  Next, with respect to the produced original film (F-4-2), the stretching temperature was Tg + 20 ° C. of the resin (D-2), and the stretching ratio was further set to 3.0 times × 3.0 times the high magnification. In the same manner as in Example 3, a biaxially stretched film (FS-4-2) was obtained. The thickness of the produced film (FS-4-2) was 16 μm, the film impact strength was 0.21J and 0.2J or more, and it was a biaxially stretched film having high strength at the same time while achieving further thinning. . The properties of the film (FS-4-2) are shown in Table 2A below.

(Example 5)
Implemented except that the original film (F-5) produced in Production Example 7 was used instead of the original film (F-1) produced in Production Example 1 and the stretching temperature was Tg + 15 ° C. of the polymer (C-2). In the same manner as in Example 1, a biaxially stretched film (FS-5) was obtained. The produced biaxially stretched film (FS-5) had a thickness of 25 μm and film impact strengths of 0.23 J and 0.2 J or more, and was a biaxially stretched film having high strength at the same time as the film thickness was reduced. The properties of the film (FS-5) are shown in Table 2A below.

(Example 6)
Using the polymer (C-2) produced in Production Example 7 as a resin (D-3), using a single screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm) The melt-extruded resin at 280 ° C. was discharged onto a cooling roll having a temperature of 110 ° C. to obtain a 144 μm-thick unstretched film (original film); (F-5-2).

  Next, with respect to the produced original film (F-5-2), the stretching temperature was Tg + 20 ° C. of the polymer (C-2), and the stretching ratio was further set to a high magnification of 3.0 × 3.0 times. Produced a biaxially stretched film (FS-5-2) in the same manner as in Example 5. The thickness of the produced film (FS-5-2) was 16 μm, and the film impact strength was 0.21J and 0.2J or more, and it was a biaxially stretched film having high strength while achieving further thinning. . The properties of the film (FS-5-2) are shown in Table 2A below.

(Example 7)
Example except that the original film (F-7) produced in Production Example 9 was used instead of the original film (F-1) produced in Production Example 1 and the stretching temperature was Tg + 15 ° C. of the resin (D-4). In the same manner as in Example 1, a biaxially stretched film (FS-7) was obtained. The produced biaxially stretched film (FS-7) had a thickness of 25 μm and film impact strengths of 0.24 J and 0.2 J or more, and was a biaxially stretched film having high strength at the same time as the film thickness was reduced. The properties of the film (FS-7) are shown in Table 2A below.

(Example 8)
The resin (D-4) produced in Production Example 9 was melt extruded at 280 ° C. using a single screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm), and melt extruded. The resin was discharged onto a cooling roll at a temperature of 110 ° C. to obtain a 144 μm-thick unstretched film (original film); (F-7-2).

  Next, with respect to the produced original film (F-7-2), the stretching temperature was Tg + 20 ° C. of the resin (D-4), and the stretching ratio was further increased to 3.0 times × 3.0 times the high magnification. In the same manner as in Example 7, a biaxially stretched film (FS-7-2) was obtained. The thickness of the produced film (FS-7-2) was 16 μm, and the film impact strength was 0.23 J and 0.2 J or more, and it was a biaxially stretched film having high strength at the same time while achieving further thinning. . The properties of the film (FS-7-2) are shown in Table 2A below.

( Reference Example 9)
Implemented except that the original film (F-8) produced in Production Example 10 was used instead of the original film (F-1) produced in Production Example 1 and the stretching temperature was Tg + 15 ° C. of the polymer (C-3). In the same manner as in Example 1, a biaxially stretched film (FS-8) was obtained. The produced biaxially stretched film (FS-8) had a thickness of 25 μm and film impact strengths of 0.26 J and 0.2 J or more, and was a biaxially stretched film having high strength at the same time as the film thickness was reduced. The properties of the film (FS-8) are shown in Table 2A below.

( Reference Example 10)
Using the polymer (C-3) produced in Production Example 10 as a resin (D-5), a single-screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm) The melt-extruded resin at 280 ° C. was discharged onto a cooling roll having a temperature of 110 ° C. to obtain a 144 μm-thick unstretched film (original film); (F-8-2).

Next, for the produced original film (F-8-2), the stretching temperature was Tg + 20 ° C. of the polymer (C-3), and the stretching ratio was further set to a high magnification of 3.0 × 3.0 times. Produced biaxially stretched film (FS-8-2) in the same manner as in Reference Example 9. The thickness of the produced film (FS-8-2) was 16 μm, and the film impact strength was 0.22J and 0.2J or more, and it was a biaxially stretched film having high strength while achieving further thinning. . The properties of the film (FS-8-2) are shown in Table 2A below.

( Reference Example 11)
Example except that the original film (F-9) produced in Production Example 11 was used instead of the original film (F-1) produced in Production Example 1, and the stretching temperature was Tg + 15 ° C. of the resin (D-6). In the same manner as in Example 1, a biaxially stretched film (FS-9) was obtained. The produced biaxially stretched film (FS-9) had a thickness of 25 μm and film impact strengths of 0.24 J and 0.2 J or more, and was a biaxially stretched film having high strength at the same time as the film thickness was reduced. The properties of the film (FS-9) are shown in Table 2A below.

( Reference Example 12)
The resin (D-6) produced in Production Example 11 was melt extruded at 280 ° C. using a single screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm), and melt extrusion. The resin obtained was discharged onto a cooling roll having a temperature of 110 ° C. to obtain a 144 μm-thick unstretched film (original film); (F-9-2).

Next, with respect to the produced original film (F-9-2), the stretching temperature was Tg + 20 ° C. of the resin (D-6), and the stretching ratio was further increased to 3.0 times × 3.0 times the high magnification. In the same manner as in Reference Example 11, a biaxially stretched film (FS-9-2) was obtained. The thickness of the produced film (FS-9-2) was 16 μm, and the film impact strength was 0.22J and 0.2J or more, and it was a biaxially stretched film having high strength while achieving further thinning. . The properties of the film (FS-9-2) are shown in Table 2A below.

(Comparative Example 1)
Implemented except that the original film (F-2) produced in Production Example 2 was used instead of the original film (F-1) produced in Production Example 1 and the stretching temperature was Tg + 15 ° C. of the polymer (E-1). In the same manner as in Example 1, an attempt was made to produce a biaxially stretched film. However, a biaxially stretched film could not be obtained due to the breaking of the original film.

(Comparative Example 2)
The polymer (E-1) produced in Production Example 2 was melt extruded at 280 ° C. using a single screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm), and melt extrusion. The resin obtained was discharged onto a cooling roll having a temperature of 110 ° C. to obtain a 144 μm-thick unstretched film (original film); (F-2-2).

  Next, with respect to the produced original film (F-2-2), the stretching temperature was Tg + 20 ° C. of the polymer (E-1), and the stretching ratio was further increased to 3.0 times × 3.0 times the high magnification. Tried to produce a biaxially stretched film in the same manner as in Comparative Example 1. However, a biaxially stretched film could not be obtained due to the breaking of the original film.

(Comparative Example 3)
Implemented except that the original film (F-3) produced in Production Example 5 was used instead of the original film (F-1) produced in Production Example 1 and the stretching temperature was Tg + 15 ° C. of the polymer (E-4). In the same manner as in Example 1, an attempt was made to produce a biaxially stretched film. However, a biaxially stretched film could not be obtained due to the breaking of the original film.

(Comparative Example 4)
The polymer (E-4) produced in Production Example 5 was melt extruded at 280 ° C. using a single screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm), and melt extrusion. The resin obtained was discharged onto a cooling roll having a temperature of 110 ° C. to obtain a 144 μm-thick unstretched film (original film); (F-3-2).

  Next, with respect to the produced original film (F-3-2), the stretching temperature was Tg + 20 ° C. of the polymer (E-4), and the stretching ratio was further increased to 3.0 times × 3.0 times the high magnification. Attempted to produce a biaxially stretched film in the same manner as in Comparative Example 3. However, a biaxially stretched film could not be obtained due to the breaking of the original film.

(Comparative Example 5)
A biaxially stretched film was produced in the same manner as in Comparative Example 3 except that the stretching temperature was raised to Tg + 20 ° C. of the polymer (E-4) based on the fact that the original film was broken in Comparative Example 3. It was. However, a biaxially stretched film could not be obtained due to the breaking of the original film.

(Comparative Example 6)
In Comparative Example 3, an attempt was made to produce a biaxially stretched film by reducing the stretch ratio while reducing the thickness of the original film based on the fact that the original film was broken.

  The polymer (E-4) produced in Production Example 5 was melt extruded at 280 ° C. using a single screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm), and melt extrusion. The resin obtained was discharged onto a cooling roll having a temperature of 110 ° C. to obtain a 56 μm-thick unstretched film (original film); (F-3-3).

  Next, with respect to the produced original film (F-3-3), a biaxially stretched film was produced in the same manner as in Comparative Example 3 except that the draw ratio was set to 1.5 times x 1.5 times of the low magnification. Tried. As a result, a biaxially stretched film (FS-3-3) having a thickness of 25 μm could be obtained, but the film impact strength of the produced film (FS-3-3) was as low as 0.06 J, which was suitable for optical applications. As a biaxially stretched film to be used, sufficient strength could not be secured, resulting in a brittle film. The properties of the film (FS-3-3) are shown in Table 2B below.

(Comparative Example 7)
Implemented except that the original film (F-6) produced in Production Example 8 was used instead of the original film (F-1) produced in Production Example 1 and the stretching temperature was Tg + 15 ° C. of the polymer (E-5). In the same manner as in Example 1, an attempt was made to produce a biaxially stretched film. However, a biaxially stretched film could not be obtained due to the breaking of the original film.

(Comparative Example 8)
The polymer (E-5) produced in Production Example 8 was melt extruded at 280 ° C. using a single screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm), and melt extrusion. The resin obtained was discharged onto a cooling roll having a temperature of 110 ° C. to obtain a 144 μm-thick unstretched film (original film); (F-6-2).

  Next, for the produced original film (F-6-2), the stretching temperature was Tg + 20 ° C. of the polymer (E-5), and the stretching ratio was further set to a high magnification of 3.0 times × 3.0 times. Attempted to produce a biaxially stretched film in the same manner as in Comparative Example 7. However, a biaxially stretched film could not be obtained due to the breaking of the original film.

(Comparative Example 9)
Based on the fact that the original film was broken in Comparative Example 7, an attempt was made to produce a biaxially stretched film by reducing the thickness of the original film and decreasing the draw ratio.

  The polymer (E-5) produced in Production Example 8 was melt extruded at 280 ° C. using a single screw extruder (φ = 20 mm, L / D = 25) and a coat hanger type T die (width 150 mm), and melt extrusion. The resin thus obtained was discharged onto a cooling roll at a temperature of 110 ° C. to obtain a 56 μm-thick unstretched film (original film); (F-6-3).

  Next, with respect to the produced original film (F-6-3), a biaxially stretched film was produced in the same manner as in Comparative Example 7 except that the draw ratio was set to 1.5 times x 1.5 times of the low magnification. Tried. As a result, a biaxially stretched film (FS-6-3) having a thickness of 25 μm could be obtained, but the film impact strength of the produced film (FS-6-3) was as low as 0.08 J, which was suitable for optical applications. As a biaxially stretched film to be used, sufficient strength could not be secured, resulting in a brittle film. The properties of the film (FS-6-3) are shown in Table 2B below.

As shown in Tables 2A and 2B, in Examples 1 to 8 and Reference Examples 9 to 12 in which Me ₀ ≧ 10000 and T _M ≧ 25 ° C. are satisfied for the polymer (resin), the optical properties (transparency) And retardation, which is suitable for a polarizer protective film in some cases, a retardation where Re and Rth are both near zero, heat resistance (Tg of 110 ° C. or more), and mechanical properties (film impact strength is 0.1). 2J or more) was secured, and a very thin biaxially stretched film of 16 to 25 μm could be realized.

  On the other hand, in Comparative Examples 1 to 5, 7, and 8, no biaxially stretched film was obtained due to breakage during stretching. In Comparative Examples 6 and 9, a thin biaxially stretched film could be formed by reducing the thickness of the original film and reducing the stretch ratio, but the film does not have sufficient strength as an optical film, The film was fragile and unbearable.

  The biaxially stretched film of this invention can be used for the same use as the conventional optical film. The application is, for example, a retardation film, a polarizer protective film, a polarizing plate, an antireflection film, a color compensation film, and a viewing angle compensation film used for image display devices such as LCDs and OLEDs.

Claims (15)

A biaxially stretched film composed of a thermoplastic resin,
The thermoplastic resin comprises an amorphous vinyl polymer having a cyclic structure in the main chain, having a weight average molecular weight of 100,000 or more ,
About the thermoplastic resin
It is shown in the following formula (A), rubber the entanglement in the plateau region molecular weight Me ₀ of dynamic viscoelasticity spectrum 1 23 00 or more and 10 or more entanglement number N represented by the following formula (B) 500 The following temperature range is 25 ° C. or higher,
Me ₀ = 3cRT ₀ / E ′ ₀ (A)
N = (MwE ′) / (3cRT) (B)
A biaxially stretched film having a thickness of 35 μm or less.
[In the formulas (A) and (B)
c is the density (g · m ⁻³ ) of the thermoplastic resin at 25 ° C.
R is a gas constant (8.31 J · K ⁻¹ · mol ⁻¹ )
T is the temperature (K) of the thermoplastic resin.
E ′ is the storage elastic modulus (Pa) of the thermoplastic resin at the temperature T
T ₀ is the temperature (K) at the midpoint of the rubber-like flat region in the thermoplastic resin.
E ′ ₀ is the storage elastic modulus (Pa) of the thermoplastic resin at the temperature T ₀ .
Mw is the weight average molecular weight of the thermoplastic resin] The biaxially stretched film according to claim 1, wherein the thermoplastic resin has an entanglement number N ₀ in the rubber-like flat region represented by the following formula (C) of 9 or more.
N ₀ = Mw / Me ₀ (C)   The biaxially stretched film according to claim 1 or 2, wherein the vinyl polymer is a (meth) acrylic polymer having a ring structure in the main chain.   The biaxially stretched film according to claim 3, wherein the ring structure is at least one selected from an N-substituted maleimide structure, a maleic anhydride structure, a glutarimide structure, a glutaric anhydride structure, and a lactone ring structure. The biaxially stretched film according to claim 3, wherein the ring structure is at least one selected from an N-substituted maleimide structure, a maleic anhydride structure, a glutarimide structure, and a glutaric anhydride structure. The biaxially stretched film according to any one of claims 3 to 5, wherein a content of the ring structure in the (meth) acrylic polymer is 5% by weight or more.   3. The copolymer according to claim 1, wherein the vinyl polymer is a copolymer having, as constituent units, an aromatic vinyl monomer unit and a unit having a ring structure located in the main chain of the polymer. Axial stretched film. The aromatic vinyl monomer unit is a styrene unit;
The biaxially stretched film according to claim 7 , wherein the unit having a ring structure is an N-substituted maleimide unit. The biaxially stretched film according to claim 7 or 8, wherein a content of the unit having the ring structure in the copolymer is 5 mol% or more. The biaxially stretched film according to any one of claims 1 to 9, which has a thickness of 30 µm or less. The biaxially stretched film according to any one of claims 1 to 10 , wherein an in-plane retardation Re for light having a wavelength of 550 nm is 5 nm or less, and an absolute value of a thickness direction retardation for the light is 5 nm or less. The biaxially stretched film according to any one of claims 1 to 11 , wherein a film impact strength measured in accordance with the provisions of ASTM D3420 is 0.2 J or more. Polarizing plate comprising a biaxially oriented film according to any one of claims 1 to 12. An image display device comprising a biaxially oriented film according to any one of claims 1 to 12. By biaxially stretching an original film composed of a thermoplastic resin, a biaxially stretched film having a thickness of 35 μm or less is formed,
The thermoplastic resin comprises an amorphous vinyl polymer having a cyclic structure in the main chain, having a weight average molecular weight of 100,000 or more ,
About the thermoplastic resin
It is shown in the following formula (A), rubber the entanglement in the plateau region molecular weight Me ₀ of dynamic viscoelasticity spectrum 1 23 00 or more and 10 or more entanglement number N represented by the following formula (B) 500 The manufacturing method of the biaxially stretched film whose temperature range used as the following is 25 degreeC or more.
Me ₀ = 3cRT ₀ / E ′ ₀ (A)
N = (MwE ′) / (3cRT) (B)
[In the formulas (A) and (B)
c is the density (g · m ⁻³ ) of the thermoplastic resin at 25 ° C.
R is a gas constant (8.31 J · K ⁻¹ · mol ⁻¹ )
T is the temperature (K) of the thermoplastic resin.
E ′ is the storage elastic modulus (Pa) of the thermoplastic resin at the temperature T
T ₀ is the temperature (K) at the midpoint of the rubber-like flat region in the thermoplastic resin.
E ′ ₀ is the storage elastic modulus (Pa) of the thermoplastic resin at the temperature T ₀ .
Mw is the weight average molecular weight of the thermoplastic resin]