阅读说明：本技术 偏振板和圆偏振板 (Polarizing plate and circularly polarizing plate ) 是由 幡中伸行 于 2016-03-08 设计创作，主要内容包括：本发明涉及一种偏振板,其为具备基材和偏振片的偏振板,偏振片具备二色性色素发生取向且厚度为5μm以下的偏振层,偏振片的波长380～760nm处的吸收轴方向的吸光度(A1)为0.3以上且1.5以下、透射轴方向的吸光度(A2)为0.001以上且0.15以下。(The present invention relates to a polarizing plate comprising a substrate and a polarizing plate, wherein the polarizing plate comprises a polarizing layer having a thickness of 5 [ mu ] m or less and having a dichroic dye oriented therein, and wherein the polarizing plate has an absorbance (A1) in the absorption axis direction of 0.3 to 1.5 at a wavelength of 380 to 760nm and an absorbance (A2) in the transmission axis direction of 0.001 to 0.15.)

1. A circularly polarizing plate comprising a polarizing plate and an 1/4 wavelength plate,

the polarizing plate comprises a base material and a polarizing plate,

the polarizing plate comprises a polarizing layer having a thickness of 5 μm or less and having a dichroic dye aligned therein,

an absorbance A1 in the absorption axis direction of the polarizing plate at a wavelength of 380nm to 760nm is 0.3 to 1.5, an absorbance A2 in the transmission axis direction is 0.001 to 0.15,

the dichroic dye includes:

the azo compound includes a dichroic dye 1 having a maximum absorption at a wavelength of 380nm to 550nm and a dichroic dye 2 having a maximum absorption at a wavelength of 550nm to 700 nm.

2. The circularly polarizing plate of claim 1, wherein the dichroic pigment is an organic dye.

3. The circularly polarizing plate of claim 1 or 2, wherein the polarizing layer comprises a polymer of a polymerizable liquid crystal compound.

4. The circularly polarizing plate according to claim 3, wherein the polymerizable liquid crystal compound is a compound showing a smectic liquid crystal phase.

5. The circularly polarizing plate according to claim 4, wherein the polymerizable liquid crystal compound is a compound exhibiting a higher order smectic liquid crystal phase.

6. The circularly polarizing plate according to claim 1 or 2, wherein the polarizer shows a bragg peak in an X-ray diffraction measurement.

7. The circularly polarizing plate according to claim 1 or 2, which has a reverse wavelength dispersibility of the 1/4 wavelength plate, in which a birefringence with respect to light having a wavelength of 450nm, a birefringence with respect to light having a wavelength of 550nm, and a birefringence with respect to light having a wavelength of 650nm satisfy the relationships represented by the following formulae (II) and (III):

Δn(450)/Δn(550)≤1.00 (II)

1.00≤Δn(650)/Δn(550) (III)

in the formula, Δ n (λ) represents a birefringence with respect to light having a wavelength λ nm.

Technical Field

The present invention relates to a polarizing plate and a circularly polarizing plate.

Background

In an organic EL image display device, a circularly polarizing plate is used to prevent external light from reflecting in a bright place. As such a circularly polarizing plate, for example, a circularly polarizing plate including a polarizing plate (iodine-PVA polarizing plate) obtained by dyeing PVA (polyvinyl alcohol) with iodine is known (see patent document 1).

In particular, when a circularly polarizing plate is used for the organic EL image display device, a polarizing plate having low absorbance is desired so as not to absorb light emitted from the organic EL element. In the case of an iodine-PVA polarizing plate, the absorbance can be reduced by reducing the dyeing concentration of iodine.

Disclosure of Invention

Problems to be solved by the invention

However, the iodine-PVA polarizing plate having such a low concentration has the following problems depending on the use environment: problems such as iodine sublimation/deterioration, color change, and the like; the PVA is relaxed to be stretched, thereby causing a problem such as warpage. Further, the iodine-PVA polarizing plate is difficult to be made thin, and is limited in application to a display device requiring further thinning.

Accordingly, an object of the present invention is to provide a polarizing plate and a circularly polarizing plate having high light absorption selectivity and excellent heat resistance even in the case of a film.

Means for solving the problems

The invention comprises the following technical scheme.

[1] A polarizing plate comprising a substrate and a polarizing plate, wherein the polarizing plate comprises a polarizing layer having a thickness of 5 [ mu ] m or less and having a dichroic dye oriented therein, and wherein the polarizing plate has an absorbance (A1) in the absorption axis direction of 0.3 to 1.5 at 380 to 760nm and an absorbance (A2) in the transmission axis direction of 0.001 to 0.15.

[2] The polarizing plate according to [1], wherein the dichroic dye is an organic dye.

[3] The polarizing plate according to [1] or [2], wherein the polarizing layer comprises a polymer of a polymerizable liquid crystal compound.

[4] The polarizing plate according to [3], wherein the polymerizable liquid crystal compound is a compound showing a smectic liquid crystal phase.

[5] The polarizing plate according to [4], wherein the polymerizable liquid crystal compound is a compound exhibiting a higher order smectic liquid crystal phase.

[6] The polarizing plate according to any one of [1] to [4], which shows a Bragg peak in X-ray diffraction measurement.

[7] A circularly polarizing plate comprising the polarizing plate according to any one of [1] to [6] and an 1/4 wavelength plate.

[8] The circularly polarizing plate according to [7], which has reverse wavelength dispersibility such that a birefringence of the 1/4 wavelength plate with respect to light having a wavelength of 450nm, a birefringence of the plate with respect to light having a wavelength of 550nm, and a birefringence of the plate with respect to light having a wavelength of 650nm satisfy the relationships represented by the following formulae (II) and (III).

Δn(450)/Δn(550)≤1.00(II)

1.00≤Δn(650)/Δn(550)(III)

(wherein. DELTA.n (. lamda.) represents a birefringence index with respect to light having a wavelength of. lamda.)

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention can provide a polarizing plate and a circularly polarizing plate having high light absorption selectivity even in the case of a film and excellent heat resistance.

Drawings

Fig. 1 is a sectional view schematically showing one embodiment of a polarizing plate.

Fig. 2 is a sectional view schematically showing one embodiment of a circularly polarizing plate.

Fig. 3 is a sectional view schematically showing one embodiment of a circularly polarizing plate.

Fig. 4 is a sectional view schematically showing one embodiment of a circularly polarizing plate.

Detailed Description

The polarizing plate of the present embodiment is characterized by comprising a substrate and a polarizing plate, wherein the polarizing plate comprises a polarizing layer having a thickness of 5 [ mu ] m or less and having a dichroic dye oriented therein, wherein the polarizing plate has an absorbance (A1) in the absorption axis direction of 0.3 to 1.5 at a wavelength of 380 to 760nm and an absorbance (A2) in the transmission axis direction of 0.001 to 0.15.

1. Polarizing plate

The polarizing plate of the present embodiment includes a polarizing layer having a thickness of 5 μm or less in which dichroic dyes are aligned. The polarizing layer can be formed using a composition containing a dichroic dye (hereinafter, sometimes referred to as a "composition for forming a polarizing plate").

1-1. dichroic dye

As the dichroic dye, a dichroic dye having absorption in a wavelength range of 380 to 800nm can be used, and an organic dye is preferably used. Examples of the dichroic dye include azo compounds.

As the azo compound, a dichroic dye (1) having a maximum absorption in a wavelength range of 380 to 550nm can be used. Examples of the dichroic dye (1) include a compound represented by the following formula (1) (hereinafter, may be referred to as "compound (1)"). The geometrical isomerism of the azobenzene moiety of the compound (1) is preferably trans.

[ solution 1]

Y in formula (1) is a group represented by formula (Y1) or formula (Y2), preferably formula (Y1).

[ solution 2]

In the formulae (Y1) and (Y2), the straight lines at both ends represent connecting bonds, the connecting bond on the left side is bonded to the phenylene group having the azo group, and the connecting bond on the right side is bonded to the phenylene group having the R group²Is bonded to the phenylene group of (a). L is an oxygen atom or-NR-, R is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. Among them, L is preferably an oxygen atom or-NH-, and more preferably an oxygen atom.

R¹Is represented by the following formula (R)¹-1), formula (R)¹-2) or formula (R)¹A group represented by the formula (R) is preferably¹-2) or formula (R)¹-3) a group represented by. Wherein denotes a bond.

[ solution 3]

Formula (R)¹Each ma in the group represented by-2) is independently preferably an integer of 0 to 10, more preferably an integer of 0 to 5. The two mas may or may not be the same as each other, preferably the same.

R²Is of the formula (R)²-1), formula (R)²-2), formula (R)²-3) formula (R)²-4) formula (R)²-5) or formula (R)²A group represented by-6), preferably a group represented by the formula (R)²-2), formula (R)²-5) or formula (R)²A group represented by the formula (R) is more preferably²-6) is a group.

[ solution 4]

R²Is of the formula (R)²-1), formula (R)²-2), formula (R)²-3) formula (R)²-5) or formula (R)²-6), the group preferably contains mb in an integer of 0 to 10, more preferably 0 to 5.

Examples of the compound (1) include compounds represented by the following formulae (1-1) to (1-8).

[ solution 5]

Among them, the compound (1) is preferably a compound represented by the formula (1-1), the formula (1-2), the formula (1-3), the formula (1-5), the formula (1-7) or the formula (1-8), and more preferably a compound represented by the formula (1-1), the formula (1-2), the formula (1-3) or the formula (1-7).

Here, a method for producing the compound (1) will be described. The compound (1) can be produced from a compound represented by the formula (1X) [ compound (1X) ] and a compound represented by the formula (1Y) [ compound (1Y) ] by utilizing the reactions shown in the following diagrams, for example.

[ solution 6]

In the above drawing, R¹、R²And Y and the above-mentioned R¹、R²And Y has the same meaning as Re¹And Re²Are groups which react with each other to form a group represented by Y. As Re¹And Re²Examples of the combination of (b) include a combination of a carboxyl group and a hydroxyl group, a combination of a carboxyl group and an amino group (the amino group may be substituted by R), a combination of a carbonyl halide group and a hydroxyl group, a combination of a carbonyl halide group and an amino group (the amino group may be substituted by R), a combination of a carbonyloxyalkyl group and a hydroxyl group, and a combination of a carbonyloxyalkyl group and an amino group (the amino group may be substituted by R). Examples of R include alkyl groups having 1 to 4 carbon atoms. Furthermore, R is used herein to¹Compound (1X) and compound having R²The compound (1Y) of (2) is illustrated, but by making R¹Compounds protected by suitable protecting groups, R²The compound (1) can also be produced by reacting compounds protected with an appropriate protecting group with each other and then performing an appropriate deprotection reaction.

The reaction conditions for reacting the compound (1X) and the compound (1Y) may be appropriately selected from optimum known conditions depending on the kinds of the compound (1X) and the compound (1Y) to be used.

For example, as Re¹Is carboxyl, Re²The reaction conditions in the case where the hydroxyl group and Y are — C (═ O) -O-, include, for example, conditions in which condensation is carried out in a solvent in the presence of an esterification condensing agent. Examples of the solvent include chloroform and the like which can dissolve the compound (1X) and the compound (1Y) at the same time. Examples of the esterification condensing agent include diisopropylcarbodiimide (IPC). Here, it is preferable to further use a base such as Dimethylaminopyridine (DMAP) in combination. The reaction temperature depends on the species of the compound (1X) and the compound (1Y)The temperature is selected, and may be, for example, in the range of-15 to 70 ℃ and preferably in the range of 0 to 40 ℃. The reaction time may be, for example, in the range of 15 minutes to 48 hours.

The reaction time may be determined by appropriately collecting the reaction mixture during the reaction, and confirming the degree of disappearance of the compound (1X) and the compound (1Y) and the degree of formation of the compound (1) by a known analytical means such as liquid chromatography or gas chromatography.

Compound (1) can be obtained from the reaction mixture after the reaction by a known method such as recrystallization, reprecipitation, extraction, and various chromatographies, or by a combination of these operations.

As the azo compound, a dichroic dye (2) having a maximum absorption in a wavelength range of 550 to 700nm can be used.

The dichroic dye (2) may include a dichroic dye (2-1) having a maximum absorption at a wavelength of 550 to 600nm and/or a dichroic dye (2-2) having a maximum absorption at a wavelength of 600 to 700 nm. The dichroic dye (2-1) preferably has a maximum absorption at a wavelength of 570 to 600nm, and the dichroic dye (2-2) preferably has a maximum absorption at a wavelength of 600 to 680 nm.

Examples of the dichroic dye (2) include a compound represented by the following formula (2) (hereinafter, may be referred to as "compound (2)"). The geometrical isomerism of the azobenzene moiety of the compound (2) is preferably trans. In the formula (2), n is 1 or 2.

[ solution 7]

Ar¹And Ar³Each independently is a group represented by formula (AR-1), formula (AR-2), formula (AR-3) or formula (AR-4). Denotes a bond.

[ solution 8]

Ar²Is represented by the formula (AR2-1),A group represented by the formula (AR2-2) or the formula (AR 2-3).

[ solution 9]

A₁And A₂Each independently represents a group represented by any one of the formulae (A-1) to (A-9). In the formulae (A-2), (A-3), (A-5) and (A-6), mc is an integer of 0 to 10, and when two mc's are present in the same group, the two mc's may be the same as or different from each other.

[ solution 10]

Ar is converted into a compound (2) having a maximum absorption at a wavelength of 550 to 600nm¹、Ar²And Ar³The compounds (2) which can be used as the dichroic dye (2-1) can be identified by combination. Similarly, Ar is added to the mixture in such a manner that the compound (2) absorbs in the wavelength range of 600 to 700nm¹、Ar²And Ar³The compounds (2) which can be used as the dichroic dye (2-2) can be identified by combination.

Specifically, the compound (2) is exemplified by compounds represented by the formulae (2-11) to (2-39).

[ solution 11]

[ solution 12]

[ solution 13]

[ solution 14]

[ solution 15]

In specific examples of the compound (2), as the dichroic dye (2-1), compounds represented by formula (2-12), formula (2-13), formula (2-18), formula (2-20), formula (2-21), formula (2-22), formula (2-23), formula (2-24), formula (2-26), formula (2-27), formula (2-28), formula (2-29) and formula (2-30) satisfy the conditions, and as the dichroic dye (2-2), compounds represented by formula (2-31), formula (2-32), formula (2-33), formula (2-34), formula (2-35) and formula (2-36) satisfy the conditions. The compounds represented by the formulae (2-11), (2-15) and (2-16) are not dyes that exhibit absorption at wavelengths of 550 to 700nm, but may be used in combination with other dichroic dyes.

In specific examples of the compound (2), as the dichroic dye (2), compounds represented by the formulae (2-15), (2-16), (2-18), (2-20), (2-21), (2-22), (2-23), (2-27), (2-29), (2-31), (2-32), (2-33), (2-34) and (2-35) are preferable, respectively.

The dichroic dye (2) is produced by a known method described in, for example, Japanese patent application laid-open Nos. 58-38756 and 63-301850.

The dichroic dye may be used alone in 1 kind, or may be used in combination in 2 or more kinds. When the composition for forming a polarizing plate contains 2 or more kinds of dichroic dyes, the content of each dichroic dye is preferably 3 parts by mass or less, more preferably 0.1 parts by mass or more and 2.5 parts by mass or less, and further preferably 1 part by mass or more and 1.5 parts by mass or less, as represented by a content per 100 parts by mass of a polymerizable liquid crystal compound described later. When the content of the dichroic dye is within the above range, the dichroic dye in the composition for forming a polarizing plate exhibits sufficient solubility in a solvent, and therefore, when the composition for forming a polarizing plate is used to manufacture a polarizing plate, a polarizing plate free from defects is easily obtained. Thus, a polarizing plate having high light absorption selectivity even in the form of a film and excellent heat resistance can be easily produced. The total amount of the dichroic dye contained in the composition for forming a polarizing plate is preferably 9 parts by mass or less, more preferably 0.1 parts by mass or more and 7.5 parts by mass or less, and further preferably 1 part by mass or more and 4.5 parts by mass or less, as represented by a content relative to 100 parts by mass of a polymerizable liquid crystal compound described later.

1-2 polymerizable liquid crystal compound

The polarizing plate of the present embodiment preferably includes a polarizing layer made of a polymer containing a polymerizable liquid crystal compound. That is, the composition for forming a polarizing plate may contain both a dichroic dye and a polymerizable liquid crystal compound.

The polymerizable liquid crystal compound is a liquid crystal compound capable of polymerizing in an aligned state, and has a polymerizable group in a molecule. The composition for forming a polarizing plate containing a polymerizable liquid crystal compound is polymerized in a state where the polymerizable liquid crystal compound is aligned, thereby forming a cured film. The polymerizable group is particularly preferably a radical polymerizable group. The radical polymerizable group refers to a group participating in a radical polymerization reaction.

The polymerizable liquid crystal compound may exhibit a nematic liquid crystal phase (hereinafter, sometimes referred to as a "nematic liquid crystal phase"), a smectic liquid crystal phase (hereinafter, sometimes referred to as a "smectic liquid crystal phase"), both of the nematic liquid crystal phase and the smectic liquid crystal phase, and is preferably a polymerizable smectic liquid crystal compound exhibiting at least a smectic liquid crystal phase. The composition for forming a polarizing plate containing the polymerizable smectic liquid crystal compound can obtain a polarizing plate having good neutral color tone and more excellent polarizing performance by the interaction between the composition and the dichroic dye.

The smectic liquid crystal phase exhibited by the polymerizable smectic liquid crystal compound is more preferably a higher order smectic liquid crystal phase. The higher order smectic liquid crystal phase referred to herein means: among these, the smectic B phase, smectic D phase, smectic E phase, smectic F phase, smectic G phase, smectic H phase, smectic I phase, smectic J phase, smectic K phase and smectic L phase are more preferable.

If the polymerizable liquid crystal compound exhibits a smectic liquid crystal phase of these higher order smectic liquid crystal phases, a polarizing plate having a higher degree of alignment order can be produced. In addition, the polarizing plate made of the high-order smectic liquid crystal phase having a high degree of alignment order as described above can obtain bragg peaks derived from a high-order structure such as a hexagonal phase or a crystal phase in X-ray diffraction measurement. The bragg peak is a peak derived from a plane periodic structure of molecular orientation, and according to the composition for forming a polarizing plate of the present embodiment, a periodic interval ofThe polarizing plate of (1).

Whether or not the polymerizable liquid crystal compound exhibits a nematic liquid crystal phase or a smectic liquid crystal phase can be confirmed, for example, by the following procedure. After preparing an appropriate substrate and applying the composition for forming a polarizing plate to the substrate to form a coating film, the solvent contained in the coating film is removed by heat treatment or reduced pressure treatment under the condition that the polymerizable liquid crystal compound is not polymerized. Next, the liquid crystal phase exhibited by heating the coating film formed on the substrate to an isotropic temperature and slowly cooling it was examined by structural observation, X-ray diffraction measurement, or differential scanning calorimetry using a polarizing microscope. In particular, a polymerizable liquid crystal compound which exhibits a nematic liquid crystal phase by cooling and exhibits a smectic liquid crystal phase by further cooling in the inspection is preferable. The absence of phase separation between the polymerizable liquid crystal compound and the dichroic dye in the nematic liquid crystal phase and the smectic liquid crystal phase can be confirmed by, for example, surface observation with various microscopes or measurement of the degree of scattering with a haze meter.

Examples of the polymerizable liquid crystal compound include compounds represented by the formula (4) (hereinafter, may be referred to as "compound (4)").

U¹-V¹-W¹-X¹-Y¹-X²-Y²-X³-W²-V²-U²(4)

In the formula (4), X¹、X²And X³Independently of each other, represents a1, 4-phenylene group which may have a substituent, or a cyclohexane-1, 4-diyl group which may have a substituent. X¹、X²And X³At least 1 of them is preferably cyclohexane-1, 4-diyl which may have a substituent(s), X¹Or X³Particularly preferred is cyclohexane-1, 4-diyl which may have a substituent. -CH constituting cyclohexane-1, 4-diyl which may have a substituent₂-may be replaced by-O-, -S-or-NR-. R is C1-C6 alkyl or phenyl.

The cyclohexane-1, 4-diyl group which may have a substituent is preferably a trans-cyclohexane-1, 4-diyl group which may have a substituent, and more preferably a trans-cyclohexane-1, 4-diyl group which does not have a substituent. In formula (4), X¹、X²And X³At least 2 of them may be a1, 4-phenylene group which may have a substituent, and preferably a1, 4-phenylene group which does not have a substituent.

Examples of the substituent optionally having a1, 4-phenylene group which may have a substituent or a cyclohexane-1, 4-diyl group which may have a substituent include an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group and a butyl group, a cyano group and a halogen atom.

In the formula (4), Y¹And Y²Independently of one another represent-CH₂CH₂-、-CH₂O-, -COO-, -OCOO-, single bond, -N ═ N-, -CR^a＝CR^b-, -C.ident.C-or-CR^a＝N-。R^aAnd R^bIndependently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Y is¹Is preferably-CH₂CH₂-, -COO-or a single bond, Y²Is preferably-CH₂CH₂-, -COO-or-CH₂O-。

In the formula (4), U¹Is a hydrogen atom or a polymerizable group, and is preferably a polymerizable group. U shape²Is a polymerizable group. U shape¹And U²All of them are preferably polymerizable groups, and more preferably photopolymerizable groups. The photopolymerizable group means: an active radical generated from a photopolymerization initiator described later, and a group capable of participating in a polymerization reaction by an acid or the like. Polymerizable liquid crystal having photopolymerizable groupThe compound is advantageous from the viewpoint of being capable of polymerization at a lower temperature.

U¹And U²The polymerizable groups (b) may be different from each other, but are preferably the same type of groups. Examples of the polymerizable group include a vinyl group, a vinyloxy group, a 1-chloroethenyl group, an isopropenyl group, a 4-vinylphenyl group, an acryloyloxy group, a methacryloyloxy group, an epoxyethyl group and an oxetanyl group. Among them, as the polymerizable group, an acryloyloxy group, a methacryloyloxy group, a vinyloxy group, an epoxyethyl group, and an oxetanyl group are preferable, and an acryloyloxy group is more preferable.

In the formula (4), V¹And V²Independently represent optionally substituted alkanediyl having 1 to 20 carbon atoms, -CH constituting the alkanediyl₂-may be replaced by-O-, -S-or-NH-. Examples of the alkanediyl group having 1 to 20 carbon atoms include a methylene group, an ethylene group, a propane-1, 3-diyl group, a butane-1, 4-diyl group, a pentane-1, 5-diyl group, a hexane-1, 6-diyl group, a heptane-1, 7-diyl group, an octane-1, 8-diyl group, a decane-1, 10-diyl group, a tetradecane-1, 14-diyl group and an eicosane-1, 20-diyl group. V¹And V²Preferably C2-C12 alkanediyl, more preferably C6-C12 alkanediyl. Examples of the substituent optionally contained in the alkanediyl group having 1 to 20 carbon atoms include a cyano group and a halogen atom. The alkanediyl group is preferably unsubstituted, and more preferably unsubstituted and linear.

In the formula (4), W¹And W²Independently of one another, represents a single bond, -O-, -S-, -COO-or-OCOO-, preferably a single bond or-O-.

Examples of the compound (4) include compounds represented by the formulae (4-1) to (4-43). When a specific example of the compound (4) has a cyclohexane-1, 4-diyl group, the cyclohexane-1, 4-diyl group is preferably a trans-isomer.

[ solution 16]

[ solution 17]

[ solution 18]

[ solution 19]

The polymerizable liquid crystal compound may be used alone or in combination of 2 or more for the composition for forming a polarizing plate. When 2 or more polymerizable liquid crystal compounds are mixed, at least 1 is preferably the compound (4). The mixing ratio (mass ratio) of the polymerizable liquid crystal compound to the compound (4) other than the compound (4) is usually 1:99 to 50:50, preferably 5:95 to 50:50, and more preferably 10:90 to 50: 50.

Among the compounds (4), preferred are compounds represented by the formula (4-5), the formula (4-6), the formula (4-7), the formula (4-8), the formula (4-9), the formula (4-10), the formula (4-11), the formula (4-12), the formula (4-13), the formula (4-14), the formula (4-15), the formula (4-22), the formula (4-24), the formula (4-25), the formula (4-26), the formula (4-27), the formula (4-28) and the formula (4-29), respectively. These compounds can be easily polymerized under a temperature condition lower than the transition temperature of the crystal phase, that is, under a condition of sufficiently maintaining the liquid crystal state of the higher order smectic phase, by the interaction with other polymerizable liquid crystal compounds. Specifically, these compounds can be polymerized under the condition of sufficiently maintaining the liquid crystal state of the higher order smectic phase under the temperature condition of 70 ℃ or lower, preferably 60 ℃ or lower.

The content ratio of the polymerizable liquid crystal compound in the composition for forming a polarizing plate is preferably 50 to 99.9% by mass, and more preferably 80 to 99.9% by mass, based on the solid content of the composition for forming a polarizing plate. When the content ratio of the polymerizable liquid crystal compound is within the above range, the orientation of the polymerizable liquid crystal compound tends to be high. The solid components are as follows: the total amount of components obtained by removing volatile components such as a solvent from the composition for forming a polarizing plate.

The polymerizable liquid crystal compound is produced by a known method described in, for example, Lub et al, Recl.Trav.Chim.Pays-Bas,115,321- "328 (1996), Japanese patent No. 4719156, and the like.

1-3. solvent

The composition for forming a polarizing plate preferably contains a solvent. The solvent is preferably a solvent capable of completely dissolving the dichroic dye and the polymerizable liquid crystal compound. In addition, a solvent inert to the polymerization reaction of the polymerizable liquid crystal compound contained in the composition for forming a polarizing plate is preferable.

Examples of the solvent include alcohol solvents such as methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, and propylene glycol monomethyl ether; ester solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, γ -butyrolactone, propylene glycol methyl ether acetate, and ethyl lactate; ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane and heptane; aromatic hydrocarbon solvents such as toluene and xylene; nitrile solvents such as acetonitrile; ether solvents such as tetrahydrofuran and dimethoxyethane; and chlorine-containing solvents such as chloroform and chlorobenzene. These solvents may be used alone, or 2 or more of them may be used in combination.

The content of the solvent is preferably 50 to 98% by mass based on the total amount of the composition for forming a polarizing plate. In other words, the solid content in the composition for forming a polarizing plate is preferably 2 to 50 mass%. When the solid content is 2% by mass or more, a thin polarizing plate, which is one of the objects of the present invention, can be easily obtained. Further, if the solid content is 50 mass% or less, the viscosity of the composition for forming a polarizing plate is low, and therefore the thickness of the polarizing plate becomes substantially uniform, and unevenness is less likely to occur in the polarizing plate. The solid content may be determined in consideration of the thickness of the polarizing plate.

1-4. additives

The composition for forming a polarizing plate of the present embodiment may optionally contain an additive. As the additives, for example, polymerization initiators, photosensitizers, polymerization inhibitors, and leveling agents can be cited.

1-4-1 polymerization initiator

The composition for forming a polarizing plate preferably contains a polymerization initiator. The polymerization initiator is a compound that can initiate a polymerization reaction of the polymerizable liquid crystal compound. The polymerization initiator is preferably a photopolymerization initiator from the viewpoint of being able to initiate a polymerization reaction under low temperature conditions. Specifically, a compound that generates an active radical or acid by the action of light may be used as the photopolymerization initiator. Among the photopolymerization initiators, a polymerization initiator that generates active radicals by the action of light is more preferable.

As the polymerization initiator, for example, benzoin compounds, benzophenone compounds, alkylbenzene ketone compounds, acylphosphine oxide compounds, triazine compounds, iodonium salts, and sulfonium salts are cited.

Examples of the benzoin compound include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether.

Examples of the benzophenone compound include benzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, 4-benzoyl-4 ' -methyldiphenyl sulfide, 3 ', 4,4 ' -tetrakis (t-butylperoxycarbonyl) benzophenone and 2,4, 6-trimethylbenzophenone.

Examples of the alkylphenone compound include diethoxyacetophenone, 2-methyl-2-morpholino-1- (4-methylthiophenyl) -1-propanone, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -1-butanone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1, 2-diphenyl-2, 2-dimethoxy-1-ethanone, 2-hydroxy-2-methyl-1- [ 4- (2-hydroxyethoxy) phenyl ] -1-propanone, 1-hydroxycyclohexylphenylketone and 2-hydroxy-2-methyl-1- [ 4- (1-methylvinyl) phenyl ] -propanone Oligomers of 1-propanone.

As the acylphosphine oxide compound, for example, 2,4, 6-trimethylbenzoyldiphenylphosphine oxide and bis (2,4, 6-trimethylbenzoyl) phenylphosphine oxide can be cited.

Examples of the triazine compound include 2, 4-bis (trichloromethyl) -6- (4-methoxyphenyl) -1,3, 5-triazine, 2, 4-bis (trichloromethyl) -6- (4-methoxynaphthyl) -1,3, 5-triazine, 2, 4-bis (trichloromethyl) -6- (4-methoxystyryl) -1,3, 5-triazine, 2, 4-bis (trichloromethyl) -6- [ 2- (5-methylfuran-2-yl) vinyl ] -1,3, 5-triazine, 2, 4-bis (trichloromethyl) -6- [ 2- (furan-2-yl) vinyl ] -1,3, 5-triazine, 2, 4-bis (trichloromethyl) -6- [ 2- (4-diethylamino-2-methylphenyl) vinyl ] -1,3, 5-triazine and 2, 4-bis (trichloromethyl) -6- [ 2- (3, 4-dimethoxyphenyl) vinyl ] -1,3, 5-triazine.

The polymerization initiator may be any of those commercially available. Examples of commercially available polymerization initiators include "Irgacure (イルガキュア) 907", "Irgacure 184", "Irgacure 651", "Irgacure 819", "Irgacure 250" and "Irgacure 369" (BASF JAPAN); "SEIKUOL BZ", "SEIKUOL Z", "SEIKUOL BEE" (Seiko chemical Co., Ltd.); "kayacure (カヤキュアー) BP 100" (Nippon Kagaku Co., Ltd.); "UVI-6992" (manufactured by The DOW Chemical Company); "Adeka Optomer SP-152", "Adeka Optomer SP-170" (ADEKA Corporation); "TAZ-A", "TAZ-PP" (DKSH JAPAN company); and "TAZ-104" (Sanhe chemical Co., Ltd.).

When the composition for forming a polarizing plate contains a polymerization initiator, the content thereof may be appropriately adjusted depending on the kind and amount of the polymerizable liquid crystal compound contained in the composition for forming a polarizing plate, and the content of the polymerization initiator is usually 0.1 to 30 parts by mass, preferably 0.5 to 10 parts by mass, and more preferably 0.5 to 8 parts by mass, relative to 100 parts by mass of the total of the polymerizable liquid crystal compounds. When the content of the polymerizable initiator is within this range, the polymerizable liquid crystal compound can be polymerized without disturbing the alignment thereof, which is preferable.

1-4-2. photosensitizers

When the composition for forming a polarizing plate contains a photopolymerization initiator, the composition may further contain a photosensitizer. Examples of the photosensitizer include xanthone compounds such as xanthone and thioxanthone (e.g., 2, 4-diethylthioxanthone and 2-isopropylthioxanthone); anthracene compounds such as anthracene and alkoxy-containing anthracene (e.g., dibutoxyanthracene); phenothiazine and rubrene.

When the composition for forming a polarizing plate contains a photopolymerization initiator and a photosensitizer, the polymerization reaction of the polymerizable liquid crystal compound contained in the composition for forming a polarizing plate is further promoted. The content of the photosensitizer is appropriately adjusted depending on the kind and amount of the photopolymerization initiator and the polymerizable liquid crystal compound used in combination, and is usually 0.1 to 30 parts by mass, preferably 0.5 to 10 parts by mass, and more preferably 0.5 to 8 parts by mass, relative to 100 parts by mass of the content of the polymerizable liquid crystal compound.

1-4-3 polymerization inhibitor

The composition for forming a polarizing plate may contain a polymerization inhibitor in order to stably progress the polymerization reaction of the polymerizable liquid crystal compound. The polymerization inhibitor can control the degree of progress of the polymerization reaction of the polymerizable liquid crystal compound.

Examples of the polymerization inhibitor include radical scavengers such as hydroquinone, alkoxy-containing catechol (e.g., butylcatechol), biphenyltriol, and 2,2,6, 6-tetramethyl-1-piperidinyloxy radical; thiophenols; beta-naphthylamines and beta-naphthols.

When the composition for forming a polarizing plate contains a polymerization inhibitor, the content thereof may be appropriately adjusted depending on the kind and amount of the polymerizable liquid crystal compound used, the content of the photosensitizer, and the like, and is usually 0.1 to 30 parts by mass, preferably 0.5 to 10 parts by mass, and more preferably 0.5 to 8 parts by mass, relative to 100 parts by mass of the content of the polymerizable liquid crystal compound. When the content of the polymerization inhibitor is within the above range, polymerization can be preferably carried out without disturbing the alignment of the polymerizable liquid crystal compound contained in the composition for forming a polarizing plate.

1-4-4 leveling agent

The composition for forming a polarizing plate preferably contains a leveling agent. The leveling agent has a function of adjusting the fluidity of the composition for forming a polarizing plate and flattening a coating film obtained by coating the composition for forming a polarizing plate, and examples thereof include a surfactant. Examples of the leveling agent include a leveling agent containing a polyacrylate compound as a main component and a leveling agent containing a compound containing a fluorine atom as a main component.

Examples of leveling agents containing a polyacrylate compound as a main component include "BYK-350", "BYK-352", "BYK-353", "BYK-354", "BYK-355", "BYK-358N", "BYK-361N", "BYK-380", "BYK-381", and "BYK-392" [ BYK Chemie Co., Ltd ].

Examples of leveling agents containing a fluorine atom-containing compound as a main component include Megafac "R-08", "R-30", "R-90", "F-410", "F-411", "F-443", "F-445", "F-470", "F-471", "F-477", "F-479", "F-482", and "F-483" [ DIC Corporation ]; surflon "S-381", "S-382", "S-383", "S-393", "SC-101", "SC-105", "KH-40" and "SA-100" [ AGC SEIMI CHEMICAL CO., LTD. ]; "E1830", "E5844" [ DAIKIN INDUSTRIES, LTD., ]; eftop "EF 301", "EF 303", "EF 351" and "EF 352" [ Mitsubishi Materials Electronic Chemicals Co., Ltd. ].

When the composition for forming a polarizing plate contains the leveling agent, the content thereof is usually 0.3 parts by mass or more and 5 parts by mass or less, and preferably 0.5 parts by mass or more and 3 parts by mass or less, relative to 100 parts by mass of the content of the polymerizable liquid crystal compound. When the content of the leveling agent is within the above range, the polymerizable liquid crystal compound tends to be horizontally aligned, and the obtained polarizing plate tends to be smoother. If the content of the leveling agent relative to the polymerizable liquid crystal compound exceeds the above range, unevenness tends to occur in the obtained polarizing plate. The composition for forming a polarizing plate may contain 2 or more kinds of leveling agents.

The polarizing plate of the present embodiment has an absorbance (a1) in the absorption axis direction at a wavelength of 380 to 760nm of 0.3 or more and 1.5 or less, preferably 0.3 or more and 1.0 or less, more preferably 0.33 or more and 0.9 or less, and still more preferably 0.36 or more and 0.85 or less. The absorbance (a2) in the transmission axis direction is 0.001 or more and 0.15 or less, preferably 0.001 or more and 0.10 or less, more preferably 0.002 or more and 0.05 or less, and still more preferably 0.005 or more and 0.040 or less.

The absorbance can be appropriately adjusted by controlling the thickness of the polarizing plate by adjusting the type of the dichroic dye contained in the polarizing plate, the amount of the dichroic dye, and the solid content concentration or coating amount of the composition for forming a polarizing plate.

2. Method for forming polarizing plate

A method for forming a polarizing plate using the composition for forming a polarizing plate will be described. In the above method, the polarizing plate is formed by applying the composition for forming a polarizing plate to a substrate, preferably a transparent substrate.

2-1. base material

The transparent substrate means: a substrate having transparency to the extent that it can transmit light, especially visible light. The transparency means: the transmittance of light with a wavelength of 380-780 nm is more than 80%. Specifically, examples of the transparent substrate include a glass substrate and a plastic substrate, and a plastic substrate is preferable. Examples of the plastic constituting the plastic substrate include polyolefins such as polyethylene, polypropylene, and norbornene polymers; a cycloolefin resin; polyvinyl alcohol; polyethylene terephthalate; polymethacrylates; a polyacrylate; cellulose esters such as triacetyl cellulose, diacetyl cellulose, and cellulose acetate propionate; polyethylene naphthalate; a polycarbonate; polysulfones; polyether sulfone; a polyether ketone; polyphenylene sulfide and polyphenylene oxide. Among them, cellulose ester, cycloolefin resin, polyethylene terephthalate, and polymethacrylate are particularly preferable from the viewpoint of being easily available in the market or having excellent transparency. In order to prevent damage such as damage and facilitate handling when the polarizing plate is produced using a transparent substrate or when the transparent substrate is transported or stored, a support substrate or the like may be attached to the transparent substrate in advance. As described later, when a circularly polarizing plate is produced from a polarizing plate, a retardation property may be imparted to the plastic substrate. In this case, the plastic substrate may be subjected to a stretching treatment or the like to impart retardation.

When retardation is imparted to a plastic substrate, a plastic substrate containing a cellulose ester or a cycloolefin resin is preferred from the viewpoint of easy control of the retardation value.

Cellulose esters are obtained by esterifying at least a part of the hydroxyl groups contained in cellulose with acetic acid. Cellulose ester films comprising such cellulose esters are readily available from the market. Examples of commercially available triacetyl cellulose FILMs include "FUJITAC FILM" (FUJITAC FILM corporation); "KC 8UX 2M", "KC 8 UY", and "KC 4 UY" (Konica Minolta Opto Products Co., Ltd.). Such a commercially available triacetyl cellulose film can be used as a transparent substrate as it is, or as a transparent substrate after imparting a retardation as required. The surface of the prepared transparent substrate may be subjected to a surface treatment such as an antiglare treatment, a hard coat treatment, an antistatic treatment, or an antireflection treatment, and then used as a transparent substrate.

In order to impart retardation to the plastic substrate, as described above, a method of stretching the plastic substrate may be used. The plastic substrate containing a thermoplastic resin can be subjected to stretching treatment, but from the viewpoint of easy control of retardation, a plastic substrate containing a cyclic olefin resin is more preferable. The cycloolefin resin is a resin composed of a polymer or copolymer of a cycloolefin such as norbornene or polycyclic norbornene monomers. The cycloolefin resin may partially contain an open ring portion, and the cycloolefin resin containing the open ring portion may be hydrogenated. The cyclic olefin resin may be, for example, a copolymer of a cyclic olefin and a chain olefin or a vinylated aromatic compound (e.g., styrene), from the viewpoint of not significantly impairing transparency and not significantly increasing hygroscopicity. In addition, the cycloolefin resin may have a polar group introduced into the molecule.

When the cyclic olefin resin is a copolymer of a cyclic olefin and a chain olefin or an aromatic compound having a vinyl group, examples of the chain olefin include ethylene and propylene, and examples of the vinylated aromatic compound include styrene, α -methylstyrene and alkyl-substituted styrene. In such a copolymer, the content ratio of the structural unit derived from the cyclic olefin is 50 mol% or less, for example, about 15 to 50 mol% with respect to the total structural units of the cyclic olefin resin. When the cyclic olefin resin is a terpolymer obtained from a cyclic olefin, a chain olefin and a vinylated aromatic compound, for example, the content of the structural unit derived from the chain olefin is about 5 to 80 mol% with respect to the total structural units of the cyclic olefin resin, and the content of the structural unit derived from the vinylated aromatic compound is about 5 to 80 mol%. The cycloolefin resin of such a terpolymer has an advantage that the amount of the expensive cycloolefin used can be reduced as much as possible when the cycloolefin resin is produced.

The cycloolefin-based resin can be easily obtained from the market. Examples of commercially available cycloolefin resins include "Topas" [ Ticona (germany) ]; "ARTON" [ JSR Corp ]; "ゼオノア (ZEONOR)" and "ゼオネックス (ZEONEX)" [ Japanese ZEON Corporation ]; "APEL" [ manufactured by Mitsui chemical Co., Ltd ]. Such a cycloolefin resin can be formed into a film (cycloolefin resin film) by film-forming using a known film-forming means such as a solvent casting method or a melt extrusion method. Further, a cycloolefin resin film that has been commercially available as a film can also be used. Examples of such commercially available cycloolefin resin films include "Esushina" and "SCA 40" [ water chemical industry co. ]; "ZEONOR FILM" [ Optes Corp. ]; and "ARTON FILM" [ JSR corporation ].

Next, a method of imparting retardation to a plastic substrate will be described. The plastic substrate can be provided with retardation by a known stretching method. For example, a roll (wound body) is prepared by winding a plastic substrate into a roll, the plastic substrate is continuously pulled out from the wound body, and the pulled out plastic substrate is conveyed to a heating furnace. The temperature setting of the heating furnace is set to a range from the vicinity of the glass transition temperature of the plastic substrate (. degree. C.) to [ glass transition temperature +100] (. degree. C.), preferably to a range from the vicinity of the glass transition temperature (. degree. C.) to [ glass transition temperature +50] (. degree. C.). When the plastic substrate is stretched in the direction of advance or in the direction orthogonal to the direction of advance in a heating furnace, the conveyance direction and the tension are adjusted, and uniaxial or biaxial thermal stretching treatment is performed while being tilted to an arbitrary angle. The stretching magnification is usually about 1.1 to 6 times, and preferably about 1.1 to 3.5 times. The method of stretching in the oblique direction is not particularly limited as long as the orientation axis can be continuously tilted to a desired angle, and a known stretching method can be employed. Examples of such a stretching method include the methods described in Japanese patent application laid-open Nos. 50-83482 and 2-113920.

From the viewpoint that the weight is such a degree that it can be handled practically and from the viewpoint that sufficient transparency can be secured, the thickness of the transparent base material is preferably small, but if it is too small, the strength tends to be lowered and the processability tends to be poor. The glass substrate has a suitable thickness of, for example, about 100 to 3000 μm, preferably about 100 to 1000 μm. The plastic substrate has a suitable thickness of, for example, about 5 to 300 μm, preferably about 20 to 200 μm. The thickness of the transparent substrate is preferably about 20 to 100 μm when the polarizing plate of the present embodiment is used as a circularly polarizing plate to be described later, particularly when the polarizing plate is used as a circularly polarizing plate for mobile devices. When a retardation is imparted to a film by stretching, the thickness after stretching is determined by the thickness before stretching and the stretching ratio.

Fig. 1 is a cross-sectional view schematically showing one embodiment of a polarizing plate 10 of the present invention. The polarizing plate 10 includes a substrate 1 and a polarizer (polarizing layer) 3 provided on the substrate 1. The dichroic dye in the polarizing plate 3 is aligned 3 a. An alignment layer 2 described later can be formed on the substrate 1.

2-2. alignment layer

The substrate used for manufacturing the polarizing plate is preferably formed with an alignment layer. At this time, the composition for forming a polarizing plate is coated on the alignment layer. Therefore, the alignment layer preferably has solvent resistance to such an extent that it is not dissolved by coating the composition for forming a polarizing plate. Further, it is preferable that heat resistance is imparted to heat treatment for removing the solvent and performing liquid crystal alignment. The alignment layer may be formed of an alignment polymer.

Examples of the orientation polymer include polyamide, gelatin, polyimide, polyamic acid, polyvinyl alcohol, alkyl-modified polyvinyl alcohol, polyacrylamide, polyoxazoles, polyethyleneimine, polystyrene, polyvinylpyrrolidone, polyacrylic acid, and polyacrylate. Among these, polyvinyl alcohol is preferable. These alignment polymers may be used alone, or 2 or more kinds may be used in combination.

The alignment polymer is applied to the substrate in the form of an alignment polymer composition (solution containing the alignment polymer) dissolved in a solvent, whereby an alignment layer can be formed on the substrate. Examples of the solvent include water; alcohol solvents such as methanol, ethanol, ethylene glycol, isopropanol, propylene glycol, methyl cellosolve, butyl cellosolve, and propylene glycol monomethyl ether; ester solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, γ -butyrolactone, propylene glycol methyl ether acetate, and ethyl lactate; ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, methyl amyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane and heptane; aromatic hydrocarbon solvents such as toluene and xylene, and nitrile solvents such as acetonitrile; ether solvents such as tetrahydrofuran and dimethoxyethane; and chlorine-substituted hydrocarbon solvents such as chloroform and chlorobenzene. These solvents may be used alone or in combination of two or more.

As the alignment polymer composition, a commercially available alignment film material can be used as it is. Examples of commercially available alignment film materials include suniver (registered trademark, manufactured by nippon chemical industry co., ltd.) and OPTOMER (registered trademark, manufactured by JSR).

Examples of a method for forming an alignment layer on a substrate include a method in which an alignment polymer composition or a commercially available alignment film material is applied to a substrate and annealed. The thickness of the alignment layer obtained in this way is usually in the range of 10nm to 10000nm, preferably in the range of 10nm to 1000 nm.

In order to impart an orientation constraint force to the orientation layer, it is preferable to perform brushing (brushing method) as necessary. By applying an alignment restriction force, the polymerizable liquid crystal compound can be aligned in a desired direction.

Examples of the method for imparting orientation constraint by the brush-polishing method include the following methods: for example, a method is known in which a rotating brush-grinding roller is prepared, a laminate having an alignment layer forming coating film formed on a substrate is placed on a base, and the laminate is conveyed toward the rotating brush-grinding roller, so that the alignment layer forming coating film is brought into contact with the rotating brush-grinding roller.

The alignment layer may be a photo-alignment layer. The photo-alignment layer means: an alignment layer having an alignment restraining force is provided by applying a composition containing a solvent and a polymer or monomer having a photoreactive group (hereinafter, sometimes referred to as "composition for forming a photo-alignment layer") to a substrate and irradiating the substrate with polarized light (preferably polarized UV). The photoreactive group refers to a group having liquid crystal alignment ability by light irradiation. Specifically, a photoreaction, which is a source of liquid crystal alignment ability, such as a molecular alignment induction or isomerization reaction, a dimerization reaction, a photocrosslinking reaction, or a photolysis reaction, occurs by irradiation with light. The photoreactive group that undergoes a dimerization reaction or a photocrosslinking reaction is preferable from the viewpoint of excellent orientation and maintenance of a smectic liquid crystal state when forming a polarizing plate. The photoreactive group is preferably a group having an unsaturated bond, particularly a double bond, and more preferably a group having at least one selected from the group consisting of a carbon-carbon double bond (C ═ C bond), a carbon-nitrogen double bond (C ═ N bond), a nitrogen-nitrogen double bond (N ═ N bond), and a carbon-oxygen double bond (C ═ O bond).

Examples of the photoreactive group having a C ═ C bond include a vinyl group, a polyene group, a stilbene group (スチルベン group), a stilbenazolyl group (スチルバゾール group), an azastilbene group (スチルバゾリウム group), a chalcone group, and a cinnamoyl group. Examples of the photoreactive group having a C ═ N bond include groups having structures such as aromatic schiff bases and aromatic hydrazones. Examples of the photoreactive group having an N ═ N bond include groups having a basic structure of azoxybenzene, such as an azophenyl group, an azonaphthyl group, an aromatic heterocyclic azo group, a bisazo group, and a formazan group. Examples of the photoreactive group having a C ═ O bond include a benzophenone group, a coumarin group, an anthraquinone group, and a maleimide group. These groups may have a substituent such as an alkyl group, an alkoxy group, an aryl group, an allyloxy group, a cyano group, an alkoxycarbonyl group, a hydroxyl group, a sulfonic acid group, or a haloalkyl group. Among them, preferred are photoreactive groups that can undergo photodimerization, and cinnamoyl groups and chalcone groups are preferred because a small amount of polarized light irradiation is required for photo-alignment, and a photo-alignment layer having excellent thermal stability and temporal stability is easily obtained. Further, as the polymer having a photoreactive group, a polymer having a cinnamoyl group in which a terminal portion of a polymer side chain forms a cinnamic acid structure is more preferable.

The solvent used in the composition for forming a photo-alignment layer is preferably a solvent in which a polymer having a photoreactive group and a monomer are dissolved, and examples thereof include the solvents used in the above-described alignment polymer composition.

The concentration of the polymer or monomer having a photoreactive group with respect to the composition for forming a photo-alignment layer can be appropriately adjusted depending on the kind of the polymer or monomer having a photoreactive group and the thickness of the photo-alignment layer to be produced, and is preferably at least 0.2 mass%, more preferably 0.3 to 10 mass%, in terms of the solid content concentration. The composition for forming a photo-alignment layer may contain a polymer material such as polyvinyl alcohol or polyimide, or a photosensitizer, within a range not significantly impairing the characteristics of the photo-alignment layer.

As a method for applying the alignment polymer composition or the composition for forming a photo-alignment layer to the base material, a coating method such as a spin coating method, an extrusion method, a gravure coating method, a die coating method, a bar coating method, or a spray method; a printing method such as a flexographic printing method. When the polarizing plate is produced by a roll-to-roll continuous production method, a printing method such as a gravure coating method, a die coating method, or a flexographic method is generally used as a coating method.

Note that when brushing or polarized light irradiation is performed, if masking is performed, a plurality of regions (patterns) having different alignment directions can be formed.

2-3. method for manufacturing polarizing plate

The composition for forming a polarizing plate is applied to a substrate or an alignment layer formed on the substrate to obtain a coating film. Examples of the method of applying the composition for forming a polarizing plate include the same methods as those exemplified as the method of applying the alignment polymer composition or the composition for forming a photo-alignment layer to the substrate.

Next, the solvent is dried and removed under the condition that the polymerizable liquid crystal compound contained in the coating film is not polymerized, thereby forming a dry coating film. Examples of the drying method include natural drying, air drying, heat drying, and reduced-pressure drying.

In a preferred embodiment, the liquid crystal state of the polymerizable liquid crystal compound contained in the dry film is first converted to a nematic liquid crystal, and then the nematic liquid crystal phase is converted to a smectic liquid crystal phase. In order to form a smectic liquid crystal phase via a nematic liquid crystal phase in this way, for example, the following method can be employed: a method of heating the polymerizable liquid crystal compound contained in the dried film to a temperature not lower than a temperature at which the polymerizable liquid crystal compound exhibits a nematic liquid crystal phase, and then cooling the film to a temperature at which the polymerizable liquid crystal compound exhibits a smectic liquid crystal phase.

When the polymerizable liquid crystal compound in the dried film is brought into a smectic liquid crystal phase or the polymerizable liquid crystal compound is brought into a smectic liquid crystal phase via a nematic liquid crystal phase, the condition (heating condition) for controlling the liquid crystal state can be determined by measuring the phase transition temperature of the polymerizable liquid crystal compound. The conditions for measuring the phase transition temperature are described in the examples of the present specification.

Next, a polymerization step of the polymerizable liquid crystal compound will be described. Here, a method of incorporating a photopolymerization initiator into a composition for forming a polarizing plate, bringing the liquid crystal state of a polymerizable liquid crystal compound in a dried film into a smectic liquid crystal phase, and then photopolymerizing the polymerizable liquid crystal compound under a condition of maintaining the liquid crystal state of the smectic liquid crystal phase will be described in detail.

In photopolymerization, the light irradiated to the dry film may be appropriately performed by light selected from the group consisting of visible light, ultraviolet light, and laser light, or active electron beams, depending on the kind of a photopolymerization initiator contained in the dry film, or the kind of a polymerizable liquid crystal compound (particularly, the kind of a polymerizable group contained in the polymerizable liquid crystal compound) and the amount thereof. Among these, ultraviolet light is preferable from the viewpoint of controlling the progress of the polymerization reaction easily and from the viewpoint of using a device widely used in the art as a photopolymerization device. Therefore, it is preferable to select the types of the polymerizable liquid crystal compound and the photopolymerization initiator contained in the composition for forming a polarizing plate in advance so that photopolymerization can be performed by ultraviolet light. In addition, when polymerization is carried out, the polymerization temperature can also be controlled by cooling and drying the coating film by ultraviolet irradiation and an appropriate cooling mechanism at the same time. By using such a cooling mechanism, if the polymerization of the polymerizable liquid crystal compound can be carried out at a lower temperature, there are the following advantages: even when a material having low heat resistance is used as the base material, the polarizing plate can be appropriately formed. In addition, when photopolymerization is performed, a patterned polarizing plate can be obtained by masking and development.

By carrying out the photopolymerization as described above, the polymerizable liquid crystal compound is polymerized under the condition of maintaining a nematic liquid crystal phase or a smectic liquid crystal phase, preferably maintaining a high-order smectic liquid crystal phase as exemplified above, to form a polarizing plate. A polarizing plate obtained by polymerizing a polymerizable liquid crystal compound under the condition of maintaining a smectic liquid crystal phase has an advantage of higher polarizing performance than a conventional bulk-guest polarizing plate, that is, a polarizing plate obtained by polymerizing a polymerizable liquid crystal compound or the like under the condition of maintaining a liquid crystal state of a nematic liquid crystal phase. Further, the polarizing plate has an advantage of being superior in strength to a polarizing plate coated with only a lyotropic dichroic dye.

The thickness of the polarizing plate is preferably in the range of 0.5 μm to 5 μm, more preferably 1 μm to 5 μm. Therefore, the thickness of the coating film for forming a polarizing plate can be determined in consideration of the thickness of the polarizing plate obtained. The thickness of the polarizing plate can be determined by measurement with an interferometric film thickness meter, a laser microscope, or a stylus film thickness meter.

As described above, the polarizing plate to be formed is particularly preferably a polarizing plate capable of obtaining a bragg peak in X-ray diffraction measurement. Examples of the polarizing plate capable of obtaining a bragg peak include a polarizing plate showing a diffraction peak derived from a hexagonal phase or a liquid crystal phase.

The polarizing plate of the present embodiment is excellent in neutral tone property. The polarizing plate having excellent neutral color tone properties means that the color coordinate values a and b in the color system L a b (Lab) satisfy the relationship between the following formulas (1F) and (2F).

-3. ltoreq. color a. ltoreq.3 (1F)

-3. ltoreq. chromaticity b. ltoreq.3 (2F)

The color coordinates a and b are also referred to as "chromaticity a" and "chromaticity b", respectively. The closer to 0 (zero) the a and b are simultaneously, the more the polarizing plate showing a neutral color tone is judged. A display device provided with such a polarizing plate can realize good white display without coloring.

In the case where the color tone of the polarizing plate is calculated by superimposing two polarizing plates so that the absorption axes are orthogonal to each other in the same manner as described above, the orthogonal a and the orthogonal b more preferably satisfy the relationships of the following expressions (1F ') and (2F'), respectively. These orthogonality a and orthogonality b are indicators indicating whether or not the color tone of black display is neutral in a display device provided with a polarizing plate. The closer the orthogonality a and the orthogonality b are to 0 (zero) at the same time, the better a good black display without coloring can be realized.

-3. ltoreq. orthogonal a. ltoreq.3 (1F')

-3. ltoreq. orthogonal b. ltoreq.3 (2F')

In commercially manufacturing a polarizing plate, a method capable of continuously forming a polarizing plate is required. This continuous manufacturing process is based on a roll-to-roll format, sometimes referred to as the "present manufacturing process". In the present production method, the description will be given mainly on the case where the substrate is a transparent substrate. When the substrate is a transparent substrate, the final product is a polarizing plate having a transparent substrate and a polarizer.

The manufacturing method comprises the following steps: for example, a step of preparing a first roll in which a transparent base material is wound around a first core; continuously feeding out the transparent substrate from the first roll; a step of continuously forming an alignment layer on a transparent substrate; a step of continuously applying a composition for forming a polarizing plate on the alignment layer; a step of continuously forming a dry film on the alignment layer by drying the applied composition for forming a polarizing plate under a condition that the polymerizable liquid crystal compound is not polymerized; a step of continuously obtaining a film by forming the polymerizable liquid crystal compound contained in the dried film into a nematic liquid crystal phase, preferably a smectic liquid crystal phase, and then polymerizing the polymerizable liquid crystal compound while maintaining the smectic liquid crystal phase, thereby forming a polarizing plate; and a step of winding the continuously obtained polarizing plate around a second winding core to obtain a second roll.

The polarizing plate obtained by the present manufacturing method is a polarizing film having a long shape and a film shape. When the polarizing plate is used for a liquid crystal display device or the like described later, the polarizing plate is cut to a desired size according to the size of the liquid crystal display device or the like.

The polarizing plate may be a laminate of a transparent substrate, a light-alignment layer and a polarizer, but the polarizer may be obtained as a single layer by peeling off the light-alignment layer and the transparent substrate. In addition, the polarizing plate may be formed in a manner in which a layer or a film other than the transparent substrate, the light-alignment layer, and the polarizer is laminated. As described above, the polarizing plate may further include a retardation film, an antireflection layer, or a brightness enhancement film as the layers and films.

For example, the polarizing plate of the present embodiment is a circularly polarizing plate formed by including an 1/4 wavelength plate. Fig. 2 is a cross-sectional view schematically showing one embodiment of the circularly polarizing plate 100 of the present invention. The circularly polarizing plate 100 may include: the retardation film 4 is composed of a substrate 1 on which an alignment layer 2 is formed, a polarizing plate 3 provided on the alignment layer 2, and a 1/4 wavelength plate on the surface of the substrate 1 opposite to the surface on which the alignment layer 2 is formed. Further, the retardation film 4 may be formed on the polarizing plate 3 side. In this case, as shown in fig. 3, the circularly polarizing plate 110 may be configured such that the substrate 1, the alignment layer 2, the polarizer 3, and the retardation film 4 are arranged in this order.

In the production of the circularly polarizing plate, the substrate 1 or the polarizer 3 and the retardation film 4 may be bonded to each other via an adhesive layer formed of an adhesive using an appropriate adhesive.

By using the substrate 1 (retardation film 4) to which a retardation property is imparted in advance as the transparent substrate, the transparent substrate itself can also function as a retardation layer. The circularly polarizing plate or elliptically polarizing plate of the retardation film/light-alignment layer/polarizer system can also be produced by forming the transparent substrate itself as a retardation film. For example, when an 1/4 wavelength plate uniaxially stretched is used as the retardation film, a circularly polarizing plate can be produced by roll-to-roll setting such that the irradiation direction of polarized UV is set to approximately 45 ° with respect to the transport direction of the transparent substrate. The 1/4 wavelength plate used in the production of the circularly polarizing plate in this way preferably has a characteristic that the in-plane retardation value with respect to visible light becomes smaller as the wavelength becomes shorter. Fig. 4 is a cross-sectional view schematically showing an embodiment of the circularly polarizing plate 120 when the base material itself functions as a retardation film. The circularly polarizing plate 120 may be configured by the retardation film 4 having the alignment layer 2 formed thereon and the polarizer 3 provided on the alignment layer 2.

A circular polarizing plate having a wide band can also be produced by using 1/2 wavelength plates as the retardation film, producing a linear polarizing plate roll set by shifting the angle between the slow axis and the absorption axis of the polarizer, and further forming 1/4 wavelength plates on the opposite side of the surface on which the polarizer is formed.

It is preferable that the 1/4 wavelength plate used as the retardation film has reverse wavelength dispersibility in which the birefringence of the plate with respect to light having a wavelength of 450nm, the birefringence of the plate with respect to light having a wavelength of 550nm, and the birefringence of the plate with respect to light having a wavelength of 650nm satisfy the relationships expressed by the following formulas (II) and (III). In the formula, Δ n (λ) represents a birefringence with respect to light having a wavelength λ nm.

Δn(450)/Δn(550)≤1.00 (II)

1.00≤Δn(650)/Δn(550) (III)

A retardation film exhibiting such reverse wavelength dispersion characteristics can be produced by the method described in japanese patent No. 5463666.

4. Use of polarizing plates

The polarizing plate may be used for various display devices. The display device is a device having a display element, and includes a light-emitting element or a light-emitting device as a light-emitting source. Examples of the display device include a liquid crystal display device, an organic Electroluminescence (EL) display device, an inorganic Electroluminescence (EL) display device, an electron emission display device (e.g., a field emission display device (FED), a surface field emission display device (SED)), electronic paper (a display device using electronic ink or an electrophoretic element, a plasma display device, a projection-type display device (e.g., a Grating Light Valve (GLV) display device, a display device having a Digital Micromirror Device (DMD)), and a piezoelectric ceramic display) A display device or an inorganic EL display device.

As the electronic paper, there are listed: electronic paper that displays by molecules such as optical anisotropy and dye molecule orientation; electronic paper that displays by particles such as electrophoresis, particle movement, particle rotation, and phase change; electronic paper that displays by moving one end of the film; electronic paper that displays through color development/phase transition of molecules; electronic paper that displays by light absorption of molecules; and electronic paper or the like which displays by self-luminescence due to bonding of electrons and holes. More specifically, examples thereof include microcapsule electrophoresis, horizontal migration electrophoresis, vertical migration electrophoresis, spherical twist spheres, magnetic twist spheres, cylindrical twist sphere system, electrostatic toner, electronic powder fluid, magnetophoresis, magnetic thermosensitive system, electrowetting, light scattering (transparent/white turbidity change), cholesteric liquid crystal/photoconductive layer, cholesteric liquid crystal, bistable nematic liquid crystal, ferroelectric liquid crystal, dichroic dye/liquid crystal dispersion type, movable film, color development and decoloration by leuco dye, photochromic, electrochromic, electrodeposition, flexible organic EL, and the like. Electronic paper is used not only for text and images of a personal nature but also for advertisement displays (signboard boards) and the like. According to the polarizing plate of the present embodiment, the thickness of the electronic paper can be reduced.

As a stereoscopic display device, for example, a method of alternately arranging different retardation films like the micro-pore method has been proposed (japanese patent application laid-open No. 2002-185983), but if the polarizing plate of the present embodiment is used, a pattern can be easily formed by printing, ink-jet, photolithography, and the like, and therefore, the manufacturing process of the display device can be shortened and the retardation film is not necessary.