FIELD

The present invention relates to a liquid crystal cured layer and production method therefor, an optical film, a polarizing plate, and a display device.

BACKGROUND

As an optical film such as a phase difference film, there is known an optical film produced with a liquid crystal composition. This optical film usually includes a liquid crystal cured layer formed of a cured product of a liquid crystal composition. This optical film can exhibit various optical properties by adjusting the orientation of the liquid crystal compound contained in the liquid crystal cured layer. Patent Literatures 1 to 3 have proposed a technology for orienting the liquid crystal compound in the thickness direction of the liquid crystal cured layer in such a liquid crystal cured layer.

Although most of liquid crystal compounds in prior art have a forward wavelength dispersion property, a liquid crystal compound having a reverse wavelength dispersion property has recently been proposed (Patent Literature 4).

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent No. 4174192 BPatent Literature 2: Japanese Patent Application Laid-Open No. 2006-106662 APatent Literature 3: Japanese Patent No. 5209223 BPatent Literature 4: Japanese Patent Application Laid-Open No. 2010-084032 A

SUMMARY

Technical Problem

A liquid crystal compound having a reverse wavelength dispersion property sometimes exhibits properties different from those of a liquid crystal compound having a forward wavelength dispersion property. Therefore, with a liquid crystal compound having a reverse wavelength dispersion property, it is difficult to obtain an intended orientation state by mere application of the prior art technology for orienting the liquid crystal compound. Especially, it is particularly difficult to increase a tilt angle formed by a main chain mesogen of the liquid crystal compound with respect to a layer plane for achieving orientation in the thickness direction.

The present invention has been devised in view of the aforementioned problem, and has as its object to provide a liquid crystal cured layer formed of a cured product of a liquid crystal composition containing a polymerizable liquid crystal compound having a reverse wavelength dispersion property, in which a tilt angle formed by the main chain mesogen of the polymerizable liquid crystal compound with respect to the layer plane of the liquid crystal cured layer can be increased, and a method for producing such a liquid crystal cured layer; an optical film including the liquid crystal cured layer; a polarizing plate including the liquid crystal cured layer; and a display device including the liquid crystal cured layer.

Solution to Problem

The present inventor has attempted to form a liquid crystal cured layer on an orientation film with a liquid crystal composition that includes a combination of a polymerizable liquid crystal compound having a reverse wavelength dispersion property and a certain copolymer functioning as an orientation aid. As a result, the present inventor has found that, in the liquid crystal cured layer, the main chain mesogen of the polymerizable liquid crystal compound was oriented in the thickness direction of the liquid crystal cured layer. Based on such findings, the present inventor has completed the present invention.

That is, the present invention includes the following.

<1> A liquid crystal cured layer formed of a cured product of a liquid crystal composition, wherein

the liquid crystal composition contains a polymerizable liquid crystal compound having a reverse wavelength dispersion property, and a copolymer containing a monomer unit A including a monovalent group containing an aromatic ring and a monomer unit B containing a monovalent aliphatic hydrocarbon group optionally having a substituent,

a main chain mesogen of the polymerizable liquid crystal compound in the liquid crystal cured layer is oriented at a tilt angle of 85° to 90° with respect to a layer plane of the liquid crystal cured layer.

<2> The liquid crystal cured layer according to <1>, wherein the polymerizable liquid crystal compound is represented by the following formula (I):


(in the formula (I),

Ar is a group represented by any of the following formulae (II-1) to (II-7), wherein the group represented by any of the following formulae (II-1) to (II-7) may optionally have a substituent other than D1to D6,


(in the formulae (II-1) to (II-7),

the symbol “*” represents a position for bonding with Z1or Z2,

each of E1and E2independently represents a group selected from the group consisting of —CR11R12—, —S—, —NR11—, —CO—, and —O—, and each of R11and R12independently represents a hydrogen atom or an alkyl group of 1 to 4 carbon atoms,

each of D1to D3independently represents an aromatic hydrocarbon ring group optionally having a substituent or an aromatic heterocyclic ring group optionally having a substituent,

each of D4to D5independently represents a non-cyclic group optionally having a substituent, and D4and D5may together form a ring,

D6represents a group selected from the group consisting of —C(Rf)═N—N(Rg)Rh, —C(Rf)═N—N═C(Rg)Rh, and —C(Rf)═N—N═Ri, Rfrepresents a group selected from the group consisting of a hydrogen atom; and an alkyl group of 1 to 6 carbon atoms, Rgrepresents a group selected from the group consisting of a hydrogen atom; and an organic group of 1 to 30 carbon atoms optionally having a substituent, Rhrepresents an organic group having one or more aromatic rings selected from the group consisting of an aromatic hydrocarbon ring of 6 to 30 carbon atoms and an aromatic heterocyclic ring of 2 to 30 carbon atoms, and R1represents an organic group having one or more aromatic rings selected from the group consisting of an aromatic hydrocarbon ring of 6 to 30 carbon atoms and an aromatic heterocyclic ring of 2 to 30 carbon atoms),

each of Z1and Z2independently represents one selected from the group consisting of a single bond, —O—, —O—CH2—, —CH2—O—, —O—CH2—CH2—, —CH2—CH2—O—, —C(═O)—O—, —O—C(═O)—, —C(═O)—S—, —S—C(═O)—, —NR21—C(═O)—, —C(═O)—NR21—, —CF2—O—, —O—CF2—, —CH2—CH2—, —CF2—CF2—, —O—CH2—CH2—O—, —CH═CH—C(═O)—O—, —O—C(═O)—CH═CH—, —CH2—C(═O)—O—, —O—C(═O)—CH2—, —CH2—O—C(═O)—, —C(═O)—O—CH2—, —CH2—CH2—C(═O)—O—, —O—C(═O)—CH2—CH2—, —CH2—CH2—O—C(═O)—, —C(═O)—O—CH2—CH2—, —CH═CH—, —N═CH—, —CH═N—, —N═C(CH3)—, —C(CH3)═N—, —N═N—, and —C≡C—, and each of R21's independently represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms,

each of A1, A2, B1, and B2independently represents a group selected from the group consisting of a cyclic aliphatic group optionally having a substituent, and an aromatic group optionally having a substituent,

each of Y1to Y4independently represents one selected from the group consisting of a single bond, —O—, —C(═O)—, —C(═O)—O—, —O—C(═O)—, —NR22—C(═O)—, —C(═O)—NR22—, —O—C(═O)—O—, —NR22—C(═O)—O—, —O—C(═O)—NR22—, and —NR22—C(═O)—NR23—, and each of R22and R23independently represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms,

each of G1and G2independently represents an organic group selected from the group consisting of an aliphatic hydrocarbon group of 1 to 20 carbon atoms; and a group having a structure obtained by substituting one or more of methylene groups contained in an aliphatic hydrocarbon group of 3 to 20 carbon atoms with —O— or —C(═O)—, wherein a hydrogen atom contained in the organic group of G1and G2may be substituted with an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms, or a halogen atom, with a proviso that methylene groups at both ends of G1and G2are not substituted with —O— or —C(═O)—,

each of P1and P2independently represents a polymerizable functional group, and

each of p and q independently represents 0 or 1).

<3> The liquid crystal cured layer according to <1> or <2>, wherein

the monomer unit A is represented by the following formula (A), and

the monomer unit B is represented by the following formula (B):


(in the formula (A),

Ra1represents a hydrogen atom or a methyl group,

each of Xa1and Xa2independently represents a divalent linking group,

Ra2represents at least one selected from the group consisting of an alkyl group of 1 to 6 carbon atoms, an alkoxy group of 1 to 6 carbon atoms, a halogen atom, a cyano group, and an isocyanate group,

n1 represents an integer of 1 to 14,

n2 represents an integer of 1 or 2, and

n3 represents an integer of 1 or 2.),


(in the formula (B),

Rb1represents a hydrogen atom or a methyl group,

Xb1represents a single bond or a divalent linking group, and

Rb2represents a monovalent aliphatic hydrocarbon group optionally having a substituent.).

<4> The liquid crystal cured layer according to any one of <1> to <3>, wherein a molar ratio of the monomer unit A relative to the monomer unit B is 90:10 to 60:40.

<5> An optical film comprising the liquid crystal cured layer according to any one of <1> to <4>.

<6> The optical film according to <5>, further comprising an orientation film.

<7> The optical film according to <5> or <6>, further comprising a substrate.

<8> The optical film according to any one of <5> to <7>, further comprising a λ/4 plate.

<9> A polarizing plate comprising the optical film according to any one of <5> to <8>, and a linear polarizer.

<10> A display device comprising the polarizing plate according to <9>.

<11> A method for producing the liquid crystal cured layer according to any one of <1> to <4>, comprising:

a step of forming an orientation film;

a step of forming a layer of a liquid crystal composition on the orientation film; and

a step of curing the layer of the liquid crystal composition to obtain the liquid crystal cured layer.

Advantageous Effects of Invention

The present invention can provide a liquid crystal cured layer formed of a cured product of a liquid crystal composition containing a polymerizable liquid crystal compound having a reverse wavelength dispersion property, in which a tilt angle formed by the main chain mesogen of the polymerizable liquid crystal compound with respect to the layer plane of the liquid crystal cured layer can be increased, and a method for producing the liquid crystal cured layer; an optical film including the liquid crystal cured layer; a polarizing plate including the liquid crystal cured layer; and a display device including the liquid crystal cured layer.

