JPH10319408A - Homeotropic oriented liquid crystal layer and method for homeotropically orienting liquid crystal on plastic substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an homeotropic orientation technique which allows the used of the orthogonal liquid crystals, more particularly a mixture composed of nematic and smectic A liquid crystals on a plastic substrate for rapid homeotropic orientation and allows the application thereof to roll-to-roll coating on the plastic substrate. SOLUTION: This invention relates to the homeotropically oriented layer or thin film of the liquid crystals, more particularly the liquid crystals on the polymer substrate. The multilayered thin films including the homeotropic orientation anisotropic thin films is also possible. These layers and films may be prepd. by applying an oriented film on the substrate. The oriented film can be either of an org. surfactant fixed into the mixture of the polymer substances or an inorg. thin film of aluminum or Al2 O3 , etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a homeotropic alignment method suitable for an orthogonal liquid crystal on a plastic substrate, particularly for a nematic and smectic A liquid crystal mixture, and a liquid crystal film having a homeotropic alignment formed by such a method. It relates to a liquid crystal layer.

[0002]

2. Description of the Related Art Homeotropic alignment of liquid crystals occurs when the long axes of the molecules of the liquid crystal phase are, on average, substantially perpendicular to the substrate on which the thin film is formed. Very few materials will spontaneously orient in this direction, and therefore some kind of aligning agent is needed to produce this desired orientation. Orthogonal liquid crystal phases such as nematic liquid crystal phases and orthogonal smectic phases (eg, smectic A and smectic B) can be oriented in this direction. For an overview of liquid crystal alignment technology, see, for example, J.
Molecular Crystals Liquid Crystals, 7 by Cognard
8, Supplement 1 (1981), pages 1-77 and MCLC by JACastellano, 94 (1983), pages 33-41.

[0003] Conventional alignment agents for liquid crystals are designed to be effective on glass substrates; examples of such conventional organic alignment agents include lecithin, trichloro- and trimethoxypropylsilane, hexadecyltrimethyl. There are ammonium halide and alkyl carboxylate monochrome salts. In each case, a very small amount (typically less than 1%) of the active ingredient is dissolved in a suitable volatile solvent and then applied to the substrate by, for example, spin coating or other known methods. When the solvent is evaporated, a thin film of the organic alignment agent remains on the substrate. These materials are characterized by having polar end groups that are thought to be attracted to the polar glass surface, and long alkyl chains that are arranged perpendicular to the glass surface. In some cases, ie, for chlorosilane compounds that react with hydroxyl groups on a glass substrate, a chemical reaction is essential. Spontaneous homeotropic alignment of the liquid crystal occurs on such surfaces. Inorganic aligning agents can also be used. For example, SiO ₂ or MgF ₂ can be deposited on a glass substrate at a vertical angle to cause homeotropic alignment of the liquid crystal.

[0004]

However, the present invention relates to the alignment of orthogonal liquid crystal phases on a plastic substrate, in particular the nematic liquid crystal and the smectic A liquid crystal.
As the substrate, a flexible substrate, a plastic thin film, or a plastic substrate such as an anisotropic liquid crystal polymer thin film is used. A conventional alignment agent is effective for aligning the liquid crystal on such a plastic substrate. It turns out that it is not. Typically, or almost generally, it shows no or only a little orientation. It is assumed that the surface of the plastic substrate has poor affinity for the polar end groups of the alignment agent.

[0005] Inorganic aligning agents, typically used on glass surfaces, such as SiO ₂ , have better homeotropic alignment when sputter coated or deposited on plastic substrates than conventional organic aligning agents. Is known to bring However, substrates coated with TiO ₂ are not well oriented and are quite difficult to wet with conventional coating solvents.

One of the problems with this type of coating, which is common to SiO ₂ , TiO _{2, and the} like, is that these coatings tend to have exceptional surface roughness, which is Hinders peeling of the polymer thin film from the alignment film at This phenomenon is due to the well-known fact that the adhesion is significantly increased by using microscopically rough surfaces compared to smooth surfaces.
These coatings are usually high temperature stable substrates, such as polyethylene terephthalate (PET), which are birefringent due to the stretching step during their manufacture.
As deposited on top, the oriented polymer film must be separated from the substrate before the optical properties of the applied polymer itself are available. Accordingly, an object of the present invention is to solve the above-mentioned problems, and to use it for rapidly orientating orthogonal liquid crystals, particularly nematic and smectic A liquid crystal mixtures, on a plastic substrate, and also to use the plastic substrate. It is to provide a technique that can be applied to the above roll-to-roll coating.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that homeotropic alignment on a plastic substrate can be achieved by using certain organic and inorganic surfactants. The present inventors have found a technique that can be obtained and can be applied to roll-to-roll coating of a plastic substrate, and have completed the present invention. That is, in the present invention, in a liquid crystal film or a liquid crystal layer having homeotropic alignment, homeotropic alignment is obtained by an alignment film on a substrate, and the alignment film contains a surfactant fixed by a polymer liquid crystal matrix. The present invention relates to the above-mentioned liquid crystal film or liquid crystal layer, which is a film or an inorganic layer. A preferred embodiment lies in the orientation of the reactive liquid crystal mixture for the production of an anisotropic polymer thin film. The reactive liquid crystal is dissolved in a suitable solvent such as toluene, and then applied as a thin film on a flexible plastic substrate. When the solvent has evaporated and the reactive liquid crystal remains, the liquid crystal must be immediately aligned, for which high speed roll-to-roll coating of plastic substrates is possible. This is achieved by the method described below. The reactive liquid crystal is then polymerized using UV light acting on the photoinitiator mixed in the reactive liquid crystal. Alternatively, the reactive liquid crystal is polymerized by heat acting on a thermal initiator mixed in the reactive liquid crystal.

In this manner, a polymer thin film having alignment constituent molecules, that is, monomer molecules is produced. Photopolymerization of the oriented reactive liquid crystal produces a polymer thin film with molecules oriented in the same direction as the monomer reactive liquid crystal, thus freezing or stabilizing the orientation vector of this liquid crystal and preserving its anisotropic physical properties. It is well known that is achieved. Such thin films are identified and used by their optical properties. These are thin films having a uniaxial positive birefringence.

One such organic surfactant is represented by the surfactant FC431, a liquid dissolved in a solvent (3M, a registered trade name of a commercial product available from the United States). It is a family of perfluoroalkyl sulfonates. When added to a reactive liquid crystal (solid content 20%) in toluene at a concentration of 0.1-0.5%, preferably at a concentration of 0.2-0.4%, triacetyl cellulose (TAC) Is the Lonza company in Switzerland
Or polyethylene terephthalate (PET), which is a Melinex401 from the British ICI company
Facilitates homeotropic alignment on plastic surfaces (available under the registered trade name). To improve this orientation, corona discharge (CD) treatment of the substrate has been found to be effective. CD treatment can be attributed to increasing the surface polarity by the formation of hydroxyl and carboxyl groups. However, C
Even with D treatment, this orientation process is rather slow, taking several seconds after solvent evaporation, which has a detrimental effect on the speed at which all coating operations can proceed and is therefore unacceptable. The aligning agent must move from the reaction mass to a surface that is considered to have low suction on the aligning agent. Therefore, this alignment method is weak and slow.

[0010] Another feature of the present invention is that such surfactants are in a form suitable for roll-to-roll coating applications and induce more rapid orientation. Since this surfactant is a liquid, it is virtually impossible to apply it on the surface of a substrate when the substrate is in the form of a roll, unless two or more coating fields are available. Can not. However, surprisingly, when FC431 is embedded in a UV-curable polymer film, applied to a substrate, and then UV-cured, the resulting polymer film containing the surfactant retains its alignment ability. , And its orientation is faster,
A particularly desirable higher coating speed is obtained.

In accordance with the present invention, a mixture of 5% surfactant and 4% Irgacure 907 in an acrylate monomer mixture, such as a mixture of hexanediol diacrylate and ethylhexyl acrylate, is prepared, which is then PET (or TAC). It has been found that surfactants can be immobilized on a surface by coating on a thin film and then photocuring the mixture. This provides a faster orientation. The active polymerizable component can be a monomer or a mixture of monomers or a mixture of monomers and oligomers. These can be anisotropic compounds, but are preferably isotropic compounds. The preferred concentration range of surfactant in the monomer or monomer mixture or mixture of monomer and oligomer has been found to be 2-8% surfactant. Particularly preferred concentrations are 4-6%.

A suitable U which is useful in formulating an aligning agent
V-curable polymers can be prepared from known available mono-, di- and tri-acrylates, such as 2-methylhexyl acrylate and hexanediol diacrylate. It is often useful to incorporate mono- and di-acrylated oligomers, which can be based on all conventional materials such as urethanes or esters. A wide variety of such compounds are available from UCB, Belgium and other UV curable resin suppliers. These other reactive compounds can be used to improve other properties, such as good durability, flexibility, hardness and different surface energies to promote wetting.

In a preferred embodiment of the present invention, a polymerizable mesogen
The reactive mesogenic compound used in the mixture of
A compound represented by the following formula I: P- (Sp-X)_nIn the formula, P is a polymerizable group, and Sp is 1 to 20 carbon atoms.
X is -O-, -S-,-
CO-, -COO-, -OCO-, -OCO-O- or
Is a single bond, n is 0 or 1, MG is a mesogen
Or a mesogenic support group, preferably represented by the following formula:
Selected from groups represented by II:-(A¹ -Z¹) MA^Two-Z^Two-A^Three-II

Wherein A¹ , A^TwoAnd A^ThreeAre mutually independent
And is a 1,4-phenylene group, which is present in this group.
One or more CH groups are also replaced by N
Or 1,4-cyclohexylene
And one CH present in the group_TwoGroup or next
2 CHs not touching_TwoThe group is O and / or S
Or 1,4-six
Rohexenylene group or naphthalene-2,6-diyl group
Any of these groups is unsubstituted or
Represents one or more halogen, cyano,
Or a nitro group, or one or two in the molecule
Even if the above hydrogen atoms are replaced by F or Cl
Good alkyl, alkoxy having 1 to 7 carbon atoms
Or may be substituted by an acyl group;¹And
And Z^TwoIs each independently -COO-, -OCO-,
-CH_TwoCH_Two-, -OCH_Two-, -CH_TwoO-, -CH =
CH-, -C≡C-, -CH = CH-C00-, -OC
O-CH = CH- or a single bond, and m is 0,
1 or 2), and

R is an alkyl group having up to 25 carbon atoms, which is unsubstituted or has one or more halogen or CN as a substituent; independently one more CH ₂ groups not CH ₂ group or adjacent the existing Further another respectively in, as the oxygen atoms are not directly bonded to one another, -O -, - S- , -NH -, - N (CH 3) -, -
CO-, -COO-, -OCO-, -OCO-O-,-
May be replaced by S-CO-, -CO-S- or -C≡C-, or R is also halogen or cyano, or R is independently P- (Sp
-X) has one of the meanings given above for _n .

Particularly preferred polymerizable mixtures are at least 2
A mixture comprising at least one mesogenic compound, at least one of which is a compound of the formula I. In another preferred embodiment of the present invention, the reactive mesogenic compound is
In formula I, R is selected from compounds having one of the above meanings of P- (Sp-X) _n . Mesogenic compounds having two or three rings are preferred. Halogen is preferably F or Cl, most preferably F. Formula I
R is F, Cl, cyano, alkyl or alkoxy, or P- (Sp-X) _n
- have the meaning given above for, and the MG in formula II, Z ¹ and Z ² is -COO -, - OCO -, - C
_{H 2 CH 2 -, - CH} = CH-COO -, - OCO-CH
Compounds where ＝ CH— or a single bond are particularly preferred.

A narrow group of preferred mesogenic groups of the formula II is shown below. For simplicity, in these groups Phe represents a 1,4-phenylene group and PheL
Is 1,4-substituted by at least one L group
Represents a phenylene group, wherein L is F, Cl, CN or an optionally fluorinated alkyl, alkoxy or acyl group having 1 to 4 carbon atoms, preferably L is F or CH ₃ ), And Cyc is 1,
Represents a 4-cyclohexylene group.

[0018]

Embedded image

In these preferred groups, Z ¹ and Z
² has the meaning indicated for formula II above.
Preferred Z ¹ and Z ² are -COO-, -OCO-, -C
H ₂ CH ₂ — or —CH ＝ CH—COO—. L is preferably F, Cl, CN, or methyl, methoxy, ethyl, ethoxy, oxamethyl, oxaethyl or trifluoromethyl. When R is an alkyl group or an alkoxy group, that is, when the terminal CH ₂ group is —O
This group, when replaced by-, can be straight-chain or branched. This group is preferably
Linear, having 2, 3, 4, 5, 6 carbon atoms
, 7 or 8 and is therefore preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy or octoxy, and also methyl, nonyl , Decyl, undecyl,
Dodecyl, tridecyl, tetradecyl, pentadecyl,
Methoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy.

When oxaalkyl, ie one CH ₂ group is replaced by —O—, this group is preferably straight-chain 2-oxapropyl (= methoxymethyl), 2-(= ethoxymethyl ) Or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8
-Oxanonyl or 2-, 3-, 4-, 5-, 6
-, 7-, 8- or 9-oxadecyl. R can optionally be a chiral group. However, in most cases, compounds having a chiral group R are not suitable for mixtures having a nematic phase, which are preferred mixtures according to the invention. When R is a chiral group, this group is preferably selected from groups of the formula:

[0021]

Embedded imageWhere X¹ Has the meaning given above for X and Q¹Is carbon
Alkylene group or alkylene having 1 to 10 atoms
An oxy group or a single bond,^TwoIs 1 to 1 carbon atoms
An alkyl or alkoxy group having 0 groups,
Is unsubstituted, or one or
Having two or more halogens or CN,
One CH present in the group_Two Groups not adjacent or 2
More than CH_TwoThe groups are also each independently of the other
Assuming that the atoms do not bond directly to each other, -C≡C
-, -O-, -S-, -NH-, -N (CH3)-,-
CO-, -COO-, -OCO-, -OCO-O-,-
Replaced by S-CO- or -CO-S-
Or R may also be as described above for P-Sp-
Q^ThreeIs a halogen or cyano group
Or Q^TwoHas 1 to 4 carbon atoms different from
It is an alkyl group or an alkoxy group.

When a chiral group is used, examples of suitable chiral groups include 2-butyl (= 1-methylpropyl),
2-methylbutyl, 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl,
2-octyl, especially 2-methylbutyl, 2-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy,
2-ethylhexoxy, 1-methylhexoxy, 2-octyloxy, 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl, 2-methylhexyl
Nonyl, 2-decyl, 2-dodecyl, 6-methoxyoctoxy, 6-methyloctoxy, 6-methyloctanoyloxy, 5-methylheptyloxycarbonyl, 2-
Methylbutyryloxy, 3-methylvaleroyloxy,
4-methylhexanoyloxy, 2-chloropropionyloxy, 2-chloro-3-methylbutyryloxy, 2
-Chloro-4-methylvaleryloxy, 2-chloro-3
-Methylvaleryloxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl, 1-methoxypropyl-2-oxy, 1-ethoxypropyl-2-oxy, 1-propoxypropyl-2-oxy , 1-butoxypropyl-2-oxy, 2-fluorooctyloxy and 2-fluorodecyloxy.

In addition, mesogenic compounds of the formula I with achiral branched radicals R may in some cases be important as comonomers, for example these groups reduce the tendency to crystallize. Branched groups of this kind generally have 1
It has no more than one side chain. Preferred achiral branched groups are isopropyl, isobutyl (= methylpropyl),
Isopentyl (= 3-methylbutyl), isopropoxy, 2-methylpropoxy and 3-methylbutoxy. However, it is also possible to use reactive compounds having a chiral group selected from the group: cholesteryl groups,

[0023]

Embedded image Ethylene glycol derivative

Embedded image Wherein R ¹ is an alkyl group having 1 to 12 carbon atoms, terpenoid groups such as menthol

[0024]

Embedded image Or a group based on citronellol

Embedded image Preferably, R is an achiral group. In the orthogonal smectic phase, the effect of this chiral compound is generally rather small.

P is preferably CH ₂ ＣCW-COO
-, WCH = CH-O-,

Embedded image Or CH ₂ ＣＨCH-phenyl- (O) _k — (where W
Is H, CH ₃ or Cl, and k is 0 or 1.
Is). P is particularly preferably a vinyl, acrylate, methacrylate, propenyl ether or epoxy group, very particularly preferably an acrylate group.

As the spacer group Sp, any group known to those skilled in the art for this purpose can be used. This spacer group Sp is preferably linked to the polymerizable group P by an ester or ether group or a single bond. This spacer group Sp is preferably a carbon atom 1
20, particularly a straight-chain or branched alkylene group having 1 to 12 carbon atoms, this one CH ₂ group or not adjoining present in group two or more CH ₂ groups also, -O -, - S -, - NH -, - N (CH 3)
-, -CO-, -O-CO-, -S-CO-, -OC
OO-, -CO-S-, -CO-O-, -CH (halogen)-, -CH (CN)-, -CH = CH- or -C
It may be replaced by ≡C-. Representative spacer groups are for example _{- (CH 2) o -,} - (CH 2 CH
_{2 O) r-CH 2 CH} 2 -, - CH 2 CH 2 -S-CH 2 CH
₂ - or _{-CH 2 CH 2 -NH-CH 2} CH 2 - and is,
Where o is an integer from 2 to 12 and r is an integer from 1 to 3.

Examples of suitable spacer groups include ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylene-thioethylene, ethylene-N -Methyl-iminoethylene and 1-
There is methyl-alkylene. When R or Q ² is a group represented by the formula P-Sp-X- or P-Sp-, respectively, these spacer groups present on both sides of the mesogen center may be the same or different. Particularly preferred compounds are those of formula I wherein n is 1.
In another preferred embodiment, the compensating agent according to the present invention comprises
It is obtained by copolymerizing a mixture containing a compound in which n is 0 in formula I and a compound in which n is 1 in formula I.

Representative examples of polymerizable mesogenic compounds of the formula I are WO 93/22397; EP 0,2
61, 712; DE 195, 04, 224; DE 4, 4
08,171 or DE 4,405,316. However, the compounds described in these publications are given only by way of example and do not limit the scope of the invention. Furthermore, representative examples representing polymerizable mesogenic compounds are shown in the following compound list. However, they should be understood only by way of example and do not limit the scope of the invention:

[0029]

Embedded image

These Compound Nos. In 1 to 5, x
And y are each independently 1 to 12, A is 1,4-phenylene group or 1,4-cyclohexylene group, R ¹ is halogen or cyano, or 1 to 12 carbon atoms. And L ¹ and L ² are each independently H, halogen or CN, or an alkyl, alkoxy or acyl group having 1 to 7 carbon atoms . The reactive mesogenic compounds mentioned above and below are known per se and can be found in the publications cited above, for example Methoden der Organischen Chemie, by Houben-Weyl,
It can be produced by methods described in standard academic books on organic chemistry such as Thieme publisher, Stuttgart.

In a preferred embodiment of the invention, the compensation film is obtained from a mixture of polymerizable mesogenic substances consisting of: a ¹ ) at least one of the formulas I and II having one polymerizable functional group One of the mesogenic compounds 1
0-99 wt%, a ²⁾ 0 to 90 wt% of at least one mesogenic compound represented by Formula I and Formula II having two or more polymerizable functional groups, b) initiator 0.01 to 5% by weight, c) 0 to 20% by weight of a non-mesogenic compound having two or more polymerizable functional groups, d) 0 to 1000 ppm of a stabilizer, and e) organic surface activity 0-2% of the agent.

In a particularly preferred embodiment of the invention, the mixture of polymerizable mesogenic substances contains at least one mesogenic component a ¹ ) as described above in an amount of from 15 to 99% by weight, furthermore at least 5% At least one mesogenic compound a ² ), component b) and optionally c) and d). In a preferred embodiment, the mixture contains at least 0.1-1.5% of an organic surfactant, i.e. component e) above. The mixture according to this particularly preferred embodiment preferably contains one, two or three different mesogenic compounds of the formulas I and II having one polymerizable functional group. Most preferably, the mixture according to this particularly preferred embodiment has two or more, especially two to six, very particularly very different, formulas I and II having one polymerizable functional group. 2-3
Contains mesogenic compounds.

In a mixture according to this particularly preferred embodiment, 1
The proportion of each of the mesogenic compounds of the formulas I and II having one polymerizable functional group is preferably from 5 to 90% by weight, in particular from 10 to 80% by weight, very preferably from 15 to 90% by weight of the total mixture. 65% by weight. In mixtures according to the particularly preferred embodiments described above, the compounds of formulas I and II
Each various mesogenic compound represented in P present in the ^{molecule, Sp, X, A 1,} A 2, A 3, Z 1, Z 2
Preferably, at least one of R and R is different from each other between the mesogenic compounds. The mixtures according to this particularly preferred embodiment particularly preferably contain at least one compound of component a2) in a proportion of from 2 to 10% by weight, very particularly preferably of from 5 to 10%.

In another particularly preferred embodiment of the present invention, the polymerizable mesogenic material comprises: a ¹ ) at least one mesogenic compound of the formulas I and II having one polymerizable functional group 1
5 to 85 wt%, and a ²⁾ contains 5 to 80 wt% of two or at least one mesogenic compound represented by Formula I and Formula II having three or more polymerizable functional groups, further It also contains component b) above and optional components c) and d).
In one embodiment of the present invention, the organic surfactant is 0.0
It is used at a concentration of 1 to 1%, particularly preferably 0.1 to 1%.
It is used at a concentration of 0.5%, especially 0.1-0.3%.
However, in a preferred embodiment, the surfactant is used in a matrix of polymerizable acrylate monomers or a mixture of such monomers and / or oligomers. As is evident, in mixtures of anisotropically reactive monomers that are oriented to form an anisotropic layer or film, surfactants are generally unnecessary.

In both of the above embodiments, sulfonate surfactants are preferred. Fluorinated sulfonate surfactants are particularly preferred. The alignment film precursor preferably contains a non-mesogenic acrylate compound and a non-mesogenic oligomer together with a surfactant and a suitable initiator, preferably a UV initiator. In mixtures of monoacrylate and diacrylate compounds and / or oligomers, surfactants at a concentration of 2-10%, especially 4-6%, have been found to work very well. Particularly preferred mixtures contain at least one monoacrylate compound and one diacrylate compound and one oligomer together with a surfactant and an initiator. The concentration of the monoacrylate compound in this mixture is preferably from 10 to 80%, the concentration of the diacrylate monomer is from 10 to 50%, and the concentration of the oligomer is from 10 to 50%. The oligomer is preferably a multifunctional polyurethane or polyester. The photoinitiator is used at a concentration of 3-6%, a typical example of which is Irgacure 907.

This mixture is coated from toluene or methyl ethyl ketone. A 10-20% solution produces a thin film with a thickness less than 2 μm. However, the thickness of this film is not critical at all, and the preferred film thickness is 0.5-5 μm, most preferably 0.5-1.5 μm
It is. Without further elaboration, one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. Accordingly, the following examples are illustrative only, and are not meant to limit the remainder of the disclosure in any way. In the examples above and below, unless otherwise stated, all temperatures are uncorrected, given in degrees Celsius, and all parts and percentages are by weight. Unless otherwise stated, all physical data were obtained at a temperature of 20 ° C. To show the liquid crystal phase behavior of the compound,
Use the following abbreviations:

K = crystal; N = nematic; S = smectic; Ch: cholesteric; I = isotropic. The numbers between these symbols indicate the phase transition temperature in degrees Celsius. Wetting agents and adhesion promoters (eg, Cray Valley, USA,
And other components can be added (available from Akzo Ltd., Netherlands). Such components can also lead to homeotropic alignment. For example, examples of materials used as representative adhesion promoters that simultaneously induce homeotropic alignment include epoxy acrylate adhesion promoters, such as Crodomer UVE-150 from Croda, UK. This compound or these compounds are typically added to a mixture of reactive mesogenic compounds (reactive liquid crystal mixture) at a concentration of 0.01 to 1%. The preferred working concentrations of these components are from 0.
Between 0.5 and 0.2%, in particular about 0.1%.

In the case of a UV curing system, Irgacure (Ir
gacure) 907, 184, 651 and 369 and Daracur 1173, all of which are available from Ciba Geigy, Switzerland.
Photoinitiators such as must also be added to generate free radicals under the influence of UV light and promote acrylate polymerization. Alternatively, if the cure mechanism is to be induced by heat, a thermal photoinitiator such as benzoyl peroxide can also be used. However, this is generally ineffective and therefore not preferred. FC43
Other perfluoroalkyl sulfonate surfactants, such as 0 (also available from the 3M company, USA), also work in the same manner as FC431. This FC431 is mentioned only as a typical use example of perfluoroalkyl sulfonate.

Yet another suitable fluorosurfactant is also FC723 from 3M company. A wide range of similar useful surfactants are available at 3M company
Can be obtained from Furthermore, other perfluoro-based surfactants can advantageously be used. Furthermore, it is well known that an inorganic aligning agent is used for a glass substrate, and when applied on a substrate surface, the inorganic aligning agent is an effective aligning agent even on a plastic substrate as compared with a conventional organic aligning agent. is there. However, the inherent surface roughness of these inorganic coatings (ie, without the use of additional spacers) is attributed to the high surface energy of the thin film (this energy is typically tens of dynes,
(Eg, in the range of 60 dynes), there is a major problem of preventing the reactive liquid crystal from easily detaching from the surface after UV curing. In some cases, a release agent may be used in the coating solution to assist in the release of the polymer film.

However, in some cases, these release agents have a detrimental effect on orientation and, in some cases, produce fine liquid deposits in thin films. This effect is also called thin film blooming. In order to overcome these negative effects, it is preferable not to use a release agent. It has been found that these problems can be overcome by using a substrate coated with aluminum or sufficiently smooth Al ₂ O ₃ . The substrate can be any suitable plastic, such as TAC, polyethylene terephthalate, polyethylene naphthenate, polyamide and any other plastic. However, the substrate is usually PET because it is a tough and useful product that is also widely used in the packaging industry and is readily available. If an aluminum coated substrate is used, the same reactive liquid crystal mixture can be used as described above. However, in this case, the use of a surfactant is optional.

Aluminum-coated PET is commercially available in a variety of aluminum and PET thicknesses as a fairly high quality surface finish. Inevitably, this aluminum coating has a surface coating of aluminum oxide thereon. Since this aluminum coating film is obtained in a very smooth form necessary for obtaining a desired high reflectance, the liquid crystal is aligned on a glass substrate, for example, SiO 2
Like the coating used in ₂ , this oxide layer is also very smooth. This differs from aluminum oxide coatings obtained by vapor deposition or sputtering, which tend to result in a more porous and rougher surface. Smoother Al ₂ O ₃ coatings are also suitable, but they are generally not readily available. However, an Al ₂ O ₃ coating film on a PET film used for transparent food packaging is an exception.

Accordingly, an aluminum coating film having such a high reflectivity and a thin transparent Al ₂ O ₃ coating film are also suitable in the present invention. 0.5 OD or less to 1.0 O
Aluminum coating films having a low optical luminous intensity with an optical density up to D or less are less preferred. This is because they have a tendency to induce non-uniform orientation. Thick aluminum coatings with moderate and high optical densities are preferred because they form a uniform coating. An aluminum coating having a medium optical density has an optical luminous intensity of 1.0 to 2.0 OD. On the other hand, an aluminum coating film having a high optical density has the following characteristics.
It has an optical density greater than 0 OD. The reflectivity and conductive properties of this aluminum layer prevent it from being considered as an alignment film in a liquid crystal display using a glass substrate. However, such ideas have little relevance when used in the present invention.

A wide variety of coating techniques can be used to apply the reactive liquid crystal mixture solution onto the web, depending on the accuracy and coating weight of the final film. Non-limiting examples include three roll reverse coating, flexo, gravure, micro-gravure, slot die and metered slot die. The photopolymerization of the thin films according to the invention can advantageously be carried out using medium- or high-pressure mercury lamps. These medium- or high-pressure mercury lamps are advantageously passed through a dichroic filter or a filter using water to filter out light having a short wavelength and also reduce the heating effect. This additional undesired heating action can cause the reactive liquid crystal mixture to heat above its clearing point and consequently cause the liquid crystal phase to disappear. Other types of lamps such as metal halogen lamps and incandescent tubes can also be used, but in these cases typically an inert gas atmosphere is required to achieve sufficient surface hardening. About 80-100 watts / c
A mercury UV lamp with m irradiation is typically used. The emitted light is in the wavelength range of 300-400 nm.

The UV curing of the oriented polymer film must proceed at a modest temperature. In other words, particularly long curing times reduce the optical retardation of the final film. A curing time of 1 second to 5 minutes, especially 10 seconds to 2 minutes is preferred. The optimum temperature during curing is from above room temperature to about 20 degrees below the clearing point of the reactive liquid crystal mixture.
It is generally preferred that the mixture cure to the nematic phase as much as possible (ie, cure at the lowest possible temperature). This curing is preferably performed at least at about 65 ° below the clearing point, particularly preferably at least at 70 ° below the clearing point. Particularly preferred temperatures are between 20 ° C and 50 ° C, especially 2 ° C.
0 ° C to 40 ° C. Homeotropically oriented polymer films formed on aluminum coated PET, or otherwise on a polymer / surfactant surface, can be applied using a pressure sensitive adhesive applied on a non-birefringent substrate such as TAC. By peeling them off, they can be separated from the PET substrate.

The orientation and thickness of the thin film can be quantified by measuring the optical retardation of the thin film at an angle separated from normal incidence. In the case of homeotropic thin films, this retardation value is symmetric for normal incidence. Several methods are available for measuring optical retardation, for example, Berek
ek) compensator and polarizing microscope (both of which are
Olympus Microscopes). Qualitatively, this film appears black between crossed polarizers. The reactive liquid crystals can be in a form such that they exhibit a nematic or orthogonal smectic phase. However, the compounds mentioned above and listed above are most preferred. For example, in addition to the acrylate compounds described above, other reactive groups, such as methacrylate compounds, haloacrylate compounds and epoxide or vinyl ether compounds can also be used. This latter compound requires the use of a cationic photoinitiator.

In the case of a nematic liquid crystal, it is essential that the thin film be cured at a temperature below the clearing point of the nematic liquid crystal mixture and at a temperature at which the temperature of the thin film does not reach the temperature of the isotropic liquid phase. That is, it is certainly preferable to cure the thin film at a temperature of about 60 ° C. below the clearing point so that small local changes in temperature do not adversely affect the birefringence of the thin film. In the case of the smectic phase, it is preferred that the curing take place within the smectic phase range, but as long as the change in birefringence with temperature in the smectic phase is small, the application of a temperature within the smectic phase limit temperature is not critical. Absent. The alignment method of the present invention can be advantageously applied to homeotropic alignment of all kinds of orthogonal liquid crystals. The alignment method of the present invention can be preferably used for alignment of a conventional monomer-based non-polymerizable liquid crystal.
This alignment film can then be used, for example, as an optical compensation film in electro-optic display devices or as an active switching film in, for example, ECB or guest-host devices.

In the most preferred embodiment according to the present invention, the aligned liquid crystals are reactive, polymerizable compounds. These can be either nematic or orthogonal smectic. Polymerized thin films of these materials are obtained by curing the films in a suitable manner, that is, in a manner that prevents their anisotropic orientation. These thin films can be separated from the substrate, and can be laminated on another substrate if necessary. They are advantageously used alone or in combination with another anisotropic and / or isotropic thin film for compensating optically anisotropic devices such as liquid crystal displays. These multilayer films are also the subject of the present invention. In particular, the novel orientation method according to the invention described herein allows the layers in such multilayered thin films, typically the organic film itself, to have good orientation properties of the orientation layer of the invention on an organic substrate. Therefore, it can be used as a substrate.

[0048]

【Example】

Example 1 FC430 (1%) (3M, available from USA), Rexam Hardcoat (3
%) (Available from Rexam Custom Ltd., Wrexham, Wales and consisting of a mixture of acrylates, oligomers, adhesion promoters and photoinitiators), propan-2-ol (62%), toluene (16%), n-heptane (16
%) And Irgacure 907
(2%) (available from Ciba Geigy Ltd.) was mixed with Melinex 4
01 (this is available from ICI) and
A wet weight of ２０20 g / m ² was obtained. 10, 15 respectively
And three experiments with a wet weight of 18 g / m ² . These experiments are referred to as Examples 1a), 1b) and 1c), respectively.

Next to the thin film carrying the alignment film, RM
1 20% reactive liquid crystal mixture was dissolved in toluene was applied to give a wet film weight of about 15 g / m ^2. Evaporation of the solvent at 50 ° C. resulted in rapid homeotropic alignment in less than 1 second. The monomer film was polymerized by exposure to a medium pressure mercury UV lamp (under the conditions described above in this example) and by UV curing in air. Alternatively, UV curing was also performed under a nitrogen atmosphere with similar success. The thickness of the homeotropically oriented polymer film was about 3 microns. As used herein, the term wet weight refers to the weight of the solvent containing the reactive mesogenic compound. That is, it means the weight before being applied and the solvent being evaporated. The film was then passed through a 50 ° C. oven and then cured using a medium pressure mercury UV light source, which was located about 5 cm above the film and had an intensity of 100 watts / cm. This curing time is less than one second. A clear polymer thin film was obtained.

The reactive liquid crystal mixture RM1 consists of the following components:

Embedded image RM1 has a clearing point of T (NI) = 130 ° C.

Example 2 The reactive liquid crystal mixture RM1 from Example 1 was dissolved in toluene to give a solids content of 20%. This is a 100 micron thick PET coated with aluminum (this is RexamMetalli
Product Mel 400 available from sing, Thetford, UK
). The wet weight of this film is about 20g
/ M ² . The solvent was evaporated by heating the coated film to 50 ° C. for a short time (typically about 2 minutes). A clear thin film formed immediately. The monomer film was then photopolymerized by exposure to UV light from a medium pressure mercury UV lamp at a temperature of <50 ° C. (typically 3 seconds). The film was separated from the aluminum coated substrate using a pressure sensitive adhesive on a TAC substrate for testing and use. At this point, the retardation value of the thin film was measured to be 64 nm at a temperature of about 22 ° C. and a wavelength of 550 nm (green light) at an incident angle of 40 °.

Example 3 The reactive liquid mesogen mixture RM2 was dissolved in toluene as a 20% solids containing solution and then applied as in Example 2 on aluminum-coated PET (Mel 400). Evaporation of the solvent gave a clear thin film.
The film was then photopolymerized using a medium pressure mercury UV lamp as described in Example 2. The thin film was separated from the substrate and found to have good homeotropic alignment.
The reactive liquid crystal mixture RM2 consists of the following components:

Embedded image

The mixture RM2 shows a smectic A phase up to a temperature of 50 ° C. and a nematic phase up to 120 ° C. Example 4 As in example 1a), Melinex 401
Was coated with an aligning agent in a mixture of propan-2-ol and toluene. However, in this example, FC43
0 Instead of 1%, Crodomer UVE-1
50 (0.1%) (available from Croda, UK)
It was used. Other ingredients are Lexam Hard Coat (Re
xam Hardcoat) (3%), propan-2-ol (6
2.9%), toluene (16%), n-heptane (16%).
%) And Irgacure (2%)
Met. This thin film was processed as in Example 1. This also includes the reactive liquid crystal mixture RM1 (20% in toluene)
Was applied. Also in this case, homeotropic alignment was easily and quickly obtained for about 40 seconds. By UV curing in air using the conditions of Example 1,
A polymer thin film having a homeotropic alignment of about 3 μm was obtained.

Example 5 Example 1a) was repeated using FC723 (also 1%) (also available from 3M, USA) instead of FC430 (1%) in a solution of the aligning agent precursor. did. Other operating steps and the conditions of Example 1 were maintained as in Example 1. The wet weight of the thin film of this aligning agent was 17 g / m ² , while the wet weight of dissolved RM1 was 16 g / m ² . Polymer thin films with homeotropic alignment were also obtained. The thickness in this case is slightly thicker than 3 μm.

Example 6 Analogously to Example 3, the reactive liquid crystal mixture RM1 of Example 1 was dissolved in toluene (solids content 20%) and then applied on a substrate sheet to give a wet weight of 36 g / m ^2. Was. However, in this example, instead of aluminum-coated PET, aluminum oxide-coated PET (which is a Rexam Me
tallizing, manufactured by the United Kingdom). The thin film used was 100 micron thick PET, the thickness of which was trimmed for this experiment, but otherwise used for transparent food packaging, especially with respect to aluminum oxide coatings. It was identical to an aluminum oxide coated PET thin film typically having a thickness of 10-20 microns. The retardation value of the separated thin film having a dry weight of about 7.3 g / m ² is 2 at an incident angle of 40 °.
It was measured to be 120 nm at 2 ° C.

Example 7 As in Example 6, a 100 micron thick aluminum oxide coated PET was used as the substrate. In this example, as in Example 4, RM2 (20% in toluene) was used as the reactive mesogen mixture. Homeotropic polymer thin films were also obtained. The film was then separated from the substrate. Example 8 Example 2 is repeated, but in this example the wet weight of the thin film of the solution of RM1 was 35 g / m ² . The resulting polymerized thin film had a thickness of about 7 microns, and was confirmed to have a retardation value of 115 nm after transition at an incident angle of 40 ° and 550 nm at 20 ° C.

Example 9 The effect of wet weight and dry weight on the resulting optical retardation of a dry cured film was each systematically evaluated. As in Example 2, 20% of RM1 in toluene was coated on Mel400 from Rexam.
However, in this example, the wet weight was varied systematically over a wide range to obtain a dry weight in the range of ³ to 10 g / m ^{2 for} the thin film. The dry weight ranges from the weight of a circular sample consisting of a 113 mm diameter substrate having a dry thin film and the weight of a circular sample consisting of a 113 mm diameter substrate having no thin film after separation of the thin film, to an accuracy of +/- 0.01 g. It was measured. Within a few percent experimental error, the wet weight was found to be proportional to the dry weight by a factor of the solids content of the solution. This indicates sufficient evaporation of the solvent. The optical retardation value of the cured and separated thin film at room temperature of 22 ° C. was measured at 550 nm at an incident angle of 40 °. The results of this experiment are shown in FIG. 1 below as a function of dry weight. All of which are the average of at least three independent measurements on one coated film for both dry weight and retardation values.
Although there is some obvious variation in the experimental data, these results clearly show an increase in optical retardation values with increasing dry weight.

Example 10 Example 2 is repeated, but using several different curing temperatures ranging from 22 ° C to 55 ° C. It has been found that the higher the temperature during UV curing, the lower the resulting optical retardation value. This is attributable to a decrease in the order of the reactive liquid crystal mixture, which decreases with increasing temperature, even if the most favorable thermal equilibrium is not achieved during short curing times, which results in an effective birefringence. Is reduced.

[0059]

[Brief description of the drawings]

FIG. 1: R as a function of dry application weight as described in Example 9
22 ° C., 550 nm of cured and separated thin film of M1,
7 is a graph showing an optical retardation value at an incident angle of 40 °. All data points are the average of several independent measurements.

 ──────────────────────────────────────────────────続 き Continuation of front page (71) Applicant 591032596 Frankfurter Str. 250, D-64293 Darmstadt, Federal Republic of Germany (72) Inventor David Coates Germany Day-64293 Darmstadt Frankfurter Strasse 250 (72) Inventor Owen-Lille Paris Germany Day- 64293 Darmstadt Frankfurter Strasse 250 (72) Inventor Jeremy-Lewis Ward Germany Day-64293 Darmstadt Frankfurter Strasse 250 (72) Inventor David Joysee Germany Day-64293 Darmstadt Frank Furter Straße 250 (72) Inventor Kate Wilborn Germany Day-64293 Darmstadt Frankfurter Strutter Straße 250 (72) Inventor Column Dickson, Commonwealth of Germany Japan 6464 Darmstadt Frankfurter Strasse 250 (72) Inventor John Scott Germany 6464 Darmstadt Frankfurter Strasse 250

Claims (10)

[Claims] In a liquid crystal film or a liquid crystal layer having homeotropic alignment, homeotropic alignment is obtained by an alignment film on a substrate, and the alignment film contains a surfactant fixed by a polymer liquid crystal matrix. Or characterized in that it is an inorganic layer,
The liquid crystal film or liquid crystal layer. 2. The liquid crystal film or liquid crystal layer according to claim 1, wherein the substrate is a polymer material. 3. The liquid crystal film or liquid crystal layer according to claim 2, wherein the substrate is a plastic sheet or a film. 4. The liquid crystal film or the liquid crystal layer according to claim 1, wherein the substrate is subjected to a corona discharge treatment before applying the alignment film or its precursor to the substrate. . 5. The liquid crystal film or liquid crystal layer according to claim 1, wherein the alignment film is an organic substance containing a surfactant and a polymer matrix. 6. The liquid crystal film or liquid crystal layer according to claim 1, wherein the alignment film is an inorganic thin film. 7. The liquid crystal film or liquid crystal layer according to claim 6, wherein the alignment film is an aluminum coating or an Al ₂ O ₃ layer. 8. The liquid crystal film or liquid crystal layer according to claim 7, wherein the aluminum coating is a medium or high density coating. 9. A method for forming a homeotropically aligned liquid crystal film or a liquid crystal layer according to claim 1. 10. An electro-optical device comprising the liquid crystal film or the liquid crystal layer according to claim 1.