JP2646281B2 - Substrate with liquid crystalline polymer thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a substrate with a liquid crystalline polymer thin film.
The present invention relates to a substrate with a highly oriented liquid crystal polymer thin film having a light control function and suitably used in the field of optoelectronics and the like.

(Problems to be Solved by the Related Art and the Invention) In order to use a liquid crystal material as a device, it is generally necessary to arrange liquid crystals in a certain arrangement (orientation). , Due to the influence of an external field such as shear force or interface. The liquid crystal is used in various optoelectronics fields by utilizing the change in optical properties accompanying this.

Liquid crystals are broadly classified into high-molecular liquid crystals (liquid-crystalline polymers) and low-molecular liquid crystals. Among them, liquid-crystalline polymers are more viscous in the liquid crystal state than low-molecular liquid crystals, so they are aligned in the liquid crystal state. Thereafter, by cooling to a temperature lower than the glass transition point, the alignment state of the liquid crystal can be fixed. Utilizing this, an alignment film for low molecular liquid crystal (Japanese Patent Application Laid-Open No. 61-42618), a nonlinear optical element (Japanese Patent Application Laid-Open No. 62-201419), an optical memory
62-66990) and optical filters (JP-A-60-19120).
No. 3) has been attempted in the field of optoelectronics. To achieve these, it is necessary to control the desired molecular orientation to a high degree. For example, a kind of optical filter, Super Twisted Nematic (ST
A color compensator for an N) type liquid crystal display element must be inserted between the liquid crystal cell and the polarizing plate of the STN type liquid crystal display element and function to return the elliptically polarized light by the liquid crystal cell to linearly polarized light. Such a function can be realized only by orienting the liquid crystalline polymer horizontally and in a certain direction with high order and uniformity.

In the case of a low-molecular liquid crystal, an alignment control method is almost established, but in the case of a liquid crystalline polymer, it is not sufficiently established. In a certain limited area, a technique is known in which any of nematic, smectic and cholesteric types is oriented with an order parameter higher than that of a low-molecular liquid crystal. However, these methods are methods that apply external force such as shear stress or electric or magnetic field, and it is impossible to control the orientation of a large area, or even if the horizontal orientation can be controlled, the in-plane uniaxial orientation cannot be controlled. Problem. When the method of injecting a liquid crystalline polymer into the gap between substrates that has been subjected to alignment treatment in the same way as a low-molecular liquid crystal is applied to the liquid crystalline polymer as it is, the viscosity of the liquid crystalline polymer is high. The liquid crystalline polymer is oriented along the flow, and the desired orientation cannot be obtained, or even if the area is large, it becomes difficult to inject.

The present invention has been made in view of the above-mentioned problems of the prior art, and has an object to be oriented in a uniform direction in a plane parallel to the substrate and parallel to the substrate without domain division. To provide a substrate with a liquid crystalline polymer thin film.

According to the present invention, a substrate, an alignment film formed on the substrate, and a thermotropic liquid crystalline polymer thin film formed on the alignment film are mainly composed according to the present invention. A substrate with a liquid crystalline polymer thin film, wherein the alignment film is a polyimide coated on the substrate with a breaking elongation of 15% or less and rubbed. You.

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a substrate with a liquid crystalline polymer thin film according to the present invention. Reference numeral 1 denotes a substrate, 2 denotes an alignment film, and 3 denotes a thermotropic liquid crystalline polymer thin film.

Glass, plastic, ceramics, or the like having a light transmitting property is preferably used for the substrate 1. As specific examples of the plastic, polyesters such as polyethylene terephthalate, polyarylate, polyethylene naphthalate, and polybutylene terephthalate, and films such as polyether sulfone, polyether ether ketone, polysulfone, and polyphenylene sulfide can be effectively used. Further, when the substrate with a liquid crystalline polymer thin film of the present invention is used for an optoelectronic device, it is required that the birefringence is further reduced. In such a case, a plastic such as polyarylate, polyether sulfone, polysulfone, or polyphenylene sulfide is used. , Glass and ceramics are particularly preferred.

The alignment film 2 is a rubbed polyimide film, which is obtained by thermally or chemically cyclizing a polyamic acid or a derivative thereof, which is a precursor of polyimide. Polyimide film thickness is 20
It is in the range of 0 to 10,000 °, preferably 300 to 300 °. If it is thinner than 200 mm, it is difficult to obtain a uniform orientation.
If the thickness is more than 0000 °, the yellow coloring characteristic of polyimide becomes remarkable, which is not preferable.

As will be described later, the alignment film used in the present invention needs to have high solvent resistance because it comes into direct contact with the liquid crystalline polymer solution during production. This solvent resistance can be achieved by using polyimide having a breaking elongation of 15% or less.

For reference, for example, a coating film of a soluble polyimide such as those represented by the following formulas (C-1), (C-2) and (C-3) which have already been imidized, or the following formula (C) −
Amide resins as represented by 4) and (C-5),
In an alignment film obtained by rubbing a coating film of a soluble nylon or the like, the alignment film 2 is dissolved after the application of the liquid crystalline polymer solution, or the alignment performance is greatly deteriorated even if the solution is not dissolved. However, these resins exhibit good orientation to low-molecular liquid crystals.

In addition, even after the application of the polyamic acid solution, even if a method is used in which an insoluble polyimide is used, if the material is such that the breaking elongation of the polyimide is greater than 15%, poor alignment occurs partially and uniform alignment cannot be obtained. There is. The elongation at break referred to in the present invention is the elongation of a thick film made of polyimide when the film is broken, and is measured according to ASTM-D638. The reason for the correlation between the bulk mechanical properties, elongation, and the solvent resistance of the alignment performance is not clear at present, but for materials with low elongation at break, the interaction between molecules is small, and the application of liquid crystalline polymers is difficult. Although it is not dissolved by the solvent, it is considered that the orientation regulating force is reduced by swelling of the surface or partial dissolution of the surface.

For this reason, in the present invention, the alignment film 2 needs to be formed of polyimide having a breaking elongation of 15% or less, which is obtained by ring-closing the polyamic acid film applied on the substrate 1 on the substrate. Rubbing treatment needs to be performed in order to uniaxially control the orientation of the hydrophilic polymer. The liquid crystalline polymer is oriented along such a rubbing direction.

In the present invention, the polyamic acid, which is a precursor of the polyimide that forms the alignment film, is obtained from an aromatic or aliphatic polycarboxylic acid or a derivative thereof, and an aromatic or aliphatic polyamine. Of these, it is preferable to use aromatic ones from the viewpoint of solvent resistance.

 The following are mentioned as a polycarboxylic acid.

In addition, examples of the polyamine include the following.

In order to reduce the elongation at break of the polyimide to 15% or less, a method of introducing an aromatic material, a material having a bulky substituent or a molecular structure having a low flexibility as a raw material polyamic acid or a derivative thereof is used. It is sufficient to take measures such as using a polymer having a high degree of polymerization.

The orientation of the liquid crystalline polymer is determined by sandwiching the obtained substrate sample with the liquid crystalline polymer thin film between orthogonal polarizing plates and rotating the sample to bring it to the extinction position and diagonal position. Can be quantified by taking The transmittance ratio and alignment uniformity of the substrates with liquid crystalline polymer thin films in which the alignment films were formed of polyimide having various breaking elongations were measured. The results are shown in Table 1. It is clear that good orientation can be obtained only when the elongation at break of the polyimide is 15% or less. Furthermore, the smaller the elongation, the better the orientation is obtained. Therefore, the elongation at break is 10
% Is more preferably used. The polyamic acid that is the precursor of the used polyimide is as follows.

PI-1: Toray SP510 PI-2: Toray SP710 PI-3: Nippon Synthetic Rubber JIB PI-4: Hitachi Chemical PIQ PI-5: Hitachi Chemical LG5200 PI-6: Toray The measurement was performed using a polyester-based liquid crystal polymer (P-1) as the liquid crystal polymer, applying a tetrachloroethane solution of the liquid crystal polymer, drying at 70 ° C. for 1 hour, Liquid crystalline polymer exhibits nematic phase at 130 ° C 3
This was performed after heat treatment for 0 minutes. The thickness is about 1 μm.

The liquid crystalline polymer film 3 has a thermotropic property. Specifically, the liquid crystal polymer film 3 is made of polyester, polyesteramide, polycarbonate, polyether, or the like and has a main chain type liquid crystal having the following structure having a liquid crystal residue in the main chain. Polymer: M ¹ -X ¹ A ¹ -X ² X ¹ , X ² : -COO-, -CONH-, -OCO-, -O-, etc. -Ph-Ph-COO-Ph, -Ph-N = CH-Ph- etc. (However, Ph is a phenylene group, Or * Represents a carbon atom, and n represents an integer of 0 to 18. ) Alternatively, a side chain type liquid crystal polymer having the following structure with a liquid crystal residue on the side chain using a vinyl polymer, polysiloxane, or the like: ^{M 2: -Ph-Ph-R} 3, -O-Ph-Ph-R 3, -Ph-COO-Ph-
^{R 3, -O-Ph-COO} -Ph-R 3, -Ph-COO-Ph-R 3, -O-P
^{h-OCO-Ph-R 3} , -Ph-Ph-COO-Ph-R 3, -O-Ph-Ph
^{-COO-Ph-R 3, -Ph} -COO-Ph-Ph-R 3, -O-Ph-COO
^{-Ph-Ph-R 3, -Ph} -Ph-OCO-Ph-R 3, -O-Ph-OCO-
^{Ph-Ph-R 3, -Ph} -OCO-Ph-Ph-R 3, -O-Ph-OCO-Ph
—Ph—R ^{3 and the} like (where R ³ is an alkyl group, an alkoxy group, a halogen atom, a nitro group or a cyano group, and n represents an integer of 0 to 18).

Next, a method for producing a substrate with a liquid crystalline polymer thin film of the present invention will be described with reference to FIG.

(A) First, a film 2 ″ containing a polyamic acid or a derivative thereof as a main component is formed on a substrate 1. As a method for forming a film, a solution of a polyamic acid is applied by a conventionally known spin coating method, dipping method, or the like. It is preferable to apply the solution on the substrate 1 by a gravure coating method, a roll coating method, or the like, and to evaporate the solvent by heating, and the solution concentration is in the range of 0.1 to 10% depending on the coating method and the liquid viscosity. Examples of the solvent include N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone, N-methylcaprolactam, dimethylsulfoxide, hexamethylphosphamide and the like.

(B) The polyamic acid is closed by heating to form a polyimide film 2 '. At this time, the required temperature is about 100-3
At 50 ° C, more preferably in the range of 130 ° C to 350 ° C. Ring closure can also be performed using a dehydration catalyst such as an acid anhydride or an organometallic compound.

(C) The surface of the formed polyimide film is rubbed in one direction with a rubbing material 4. As the rubbing material 4, a flocked cloth or cloth of cotton, polyester, nylon or the like, or a sponge of urethane, nylon or the like is suitably used.

In the present invention, unlike a normal liquid crystal display device, alignment control is performed on a single substrate, that is, only one side of the liquid crystalline polymer film is in contact with the alignment film, and the other is exposed to the outside air. For this reason, it is necessary that the liquid crystalline polymer sufficiently wets the alignment film. Therefore, generally speaking, it is desirable that the surface tension of the alignment film 2 is 35 dyn / cm or more, more preferably 40 dyn / cm or more.

(D) A solution 3 ′ in which a liquid crystalline polymer is dissolved in an organic solvent is applied on the polyimide alignment film 2. The solvent for the liquid crystalline polymer varies depending on the type of the liquid crystalline polymer used and the degree of polymerization, but generally, halogenated hydrocarbons such as chloroform, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, and orthodichlorobenzene; And phenol solvents such as phenol, o-chlorophenol and cresol; aprotic polar solvents such as dimethylformamide, dimethylacetamide and dimethylsulfoxide; ether solvents such as tetrahydrofuran and dioxane; and mixed solvents thereof.

The solvent concentration depends on the coating method, the viscosity of the polymer, the desired film thickness, and the like. Taking a compensator for a liquid crystal display device as an example,
Since the required film thickness is about 2 to 10 μm,
It is used in the range of 50% by weight, preferably in the range of 5 to 30% by weight. As a coating method, a spin coating method, a roll coating method, a gravure coating method, a dipping method, a screen printing method, or the like can be adopted.

(E) After applying the liquid crystalline polymer, the solvent is removed by drying,
After the liquid crystalline polymer is heat-treated at a temperature at which the liquid crystalline polymer exhibits liquid crystallinity for a predetermined time to orient the liquid crystalline polymer, it is cooled to a temperature below the glass transition point. The temperature at which the liquid crystalline polymer is oriented needs to be equal to or higher than the glass transition point of the liquid crystalline polymer, and lower than the transition temperature of the liquid crystalline polymer to an isotropic liquid. The lower the viscosity of the polymer is, the better the temperature is, in order to assist the alignment by the interface effect of the alignment film, but the higher the temperature, the higher the temperature. Generally, the range of 50 ° C to 300 ° C is preferable, and the range of 100 ° C to 250 ° C is particularly preferable.
Further, in relation to the phase of the liquid crystalline polymer, the liquid crystalline polymer is preferably in a nematic phase or a cholesteric phase at this processing temperature, and uniform alignment cannot be obtained in the smectic phase due to high viscosity. The heat treatment time varies depending on the composition and molecular weight of the polymer, but is generally preferably in the range of 10 seconds to 60 minutes, and particularly preferably in the range of 30 seconds to 30 minutes. If the treatment time is too short, the orientation will be insufficient, and if it is too long, the productivity will decrease, which is not preferable.

After the liquid crystal alignment is completed, the liquid crystalline polymer film is cooled to a temperature equal to or lower than the glass transition point, because this is intended to fix the alignment. The cooling rate is not particularly limited,
It is only necessary to move from a heating atmosphere to an atmosphere below the glass transition point. In addition, when the liquid crystalline polymer thin film is used with the orientation fixed and near room temperature, the glass transition temperature of the liquid crystalline polymer is preferably 30 ° C. or higher. If this is low, the fixed alignment structure may be undesirably destroyed. The thickness of the liquid crystalline polymer thin film 3 is preferably 100 μm or less, and particularly preferably 50 μm or less. When the thickness is more than 100 μm, it is difficult to obtain a uniform orientation.

As described above, the liquid crystalline polymer preferably has a cholesteric phase or a nematic phase in a phase series, and it is preferable that the heat treatment is performed in a temperature range of both phases. As a liquid crystalline polymer satisfying such conditions, a polyester having the following structural unit can be shown as a more preferable example.

Further, polyesters having the following structural units can also be exemplified.

X: a hydrogen atom, a halogen atom such as Cl or Br, a lower alkyl group, a lower alkoxy group k: 0 to 2R, the following structures can be exemplified.

CH _{2 n} (n is an integer from 2 to 20) Among these, the following are particularly preferred.

CH _{2 n} (n = 2,3,4,5,6,8,10,12) In the substrate with a liquid crystalline polymer thin film of the present invention, depending on the application, or introduce an optically active group into the liquid crystalline polymer,
A cholesteric phase can be exhibited by adding a liquid crystalline polymer having an optically active group, a low-molecular liquid crystal, a non-liquid crystalline substance, or the like. Such applications include circularly polarizing filters, notch filters, optical memories using selective reflection of cholesteric phase, and color compensators for STN-type liquid crystal display devices. In this case, the molecules of the liquid crystalline polymer in contact with the alignment film are arranged parallel to the rubbing direction, and have a twisted structure corresponding to the pitch of the liquid crystalline polymer in the thickness direction.

(Examples) Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A varnish of polyamic acid which is a precursor of PI-5 shown in Table 1 on a glass substrate was applied to a thickness of about 1000 ° by spin coating, and then baked at 270 ° C to form a polyimide film. Next, the polyimide film was rubbed in one direction with a Tetron flocking cloth to perform a rubbing treatment.

A tetrachloroethane solution (15% by weight) of a nematic liquid crystalline polyester-based liquid crystalline polymer represented by the following formula (A) is applied on the alignment film by spin coating. Then, drying was performed at 70 ° C. to form a liquid crystalline polymer film having a thickness of about 1 μm. Next, heat treatment was performed at 130 ° C. for 30 minutes, at which the polymer (A) exhibited a nematic phase. After quenching to room temperature, the obtained texture was observed to be monodomain homogeneous. The pinching the sample polarizer is perpendicular to, the transmittance T ₄₅ when the transmittance T ₀ diagonal position when the extinction position relative to white light was measured, a low orientation ratio T ₄₅ / T ₀ of the two As a result of evaluation of the degree, T ₄₅ / T ₀ = 90 in this sample, and excellent uniaxial orientation was confirmed.

Examples 2-3 A substrate with a liquid crystalline polymer thin film was produced in the same manner as in Example 1, except that PI-4 or PI-6 shown in Table 1 was used as polyimide. Even in these samples, uniform homogeneous orientation was obtained, and T ₄₅ / T ₀ was ₄₁ and 108, respectively, and extremely excellent uniaxial orientation was confirmed.

Example 4 A 15% by weight phenol / tetrachloroethane (60:40 weight ratio) solution of a polyester-based liquid crystal polymer represented by the following formula (B) was prepared as a liquid crystal polymer solution in the same manner as in Example 1. It was applied on the alignment-treated substrate and dried at 70 ° C. to form a liquid crystalline polymer film having a thickness of about 1 μm.

Then, the polymer (B) exhibits a nematic phase.
Heat treatment was performed at 30 ° C. for 30 minutes. After quenching to room temperature, the obtained texture was observed to be monodomain homogeneous. This sample is sandwiched between orthogonal polarizing plates, and the transmittance T ₀ at the extinction position and the transmittance T ₄₅ at the diagonal position for white light are measured, and the degree of orientation is determined by T ₄₅ / T ₀ of both. As a result of the evaluation, T ₄₅ / T ₀ = 100 in this sample, and excellent uniaxial orientation was confirmed.

Example 5 A 15% by weight phenol / tetrachloroethane (60%) mixture of the above polymer (B) and a polyester liquid crystalline polymer represented by the following formula (C) (weight ratio 95:15) was prepared as a liquid crystalline polymer solution. : 40 weight ratio) The solution was applied on an alignment-treated substrate produced in the same manner as in Example 1, and dried at 70 ° C to form a liquid crystalline polymer film having a thickness of about 1 µm.

Then, the mixture exhibits a nematic phase at 200 ° C.
For 30 minutes. After quenching to room temperature, the obtained alignment structure was observed, and a monodomain alignment was obtained. As a result of sandwiching this sample between polarizing plates and performing ellipsometry,
It was found that the retardation was 0.26 μm and the structure was twisted by 40 °, and it was found that the film had a uniform twisted nematic structure.

Example 6 Orientation prepared in the same manner as in Example 1 by using a 10% by weight N, N-dimethylformamide solution of an acrylic side-chain type liquid crystalline polymer represented by the following formula (D) as a liquid crystalline polymer solution: Coated on processing substrate and rubbed at 70 ° C to a film thickness of about 0.8μm
Was formed.

Next, the polymer (D) exhibits a nematic phase.
Heat treatment was performed at 30 ° C. for 30 minutes. After quenching to room temperature, the obtained alignment structure was observed, and a monodomain alignment was obtained. This sample was sandwiched between orthogonal polarizing plates, and the transmittance T ₀ at the extinction position and the transmittance T ₄₅ at the diagonal position for white light were measured, and the degree of orientation was determined by the ratio T ₄₅ / T ₀ of the two. As a result of the evaluation, T ₄₅ / T ₀ = 50 in this sample, and excellent uniaxial orientation was confirmed.

Example 7 Polyethersulfone film (manufactured by Sumitomo Bakelite)
A varnish of polyamic acid, which is a precursor of PI-6 shown in Table 1, was applied on FST-1330) to a thickness of about 1000 ° by spin coating, and then baked at 170 ° C to form a polyimide film. Next, the polyimide film was rubbed in one direction with a Tetron flocking cloth to perform a rubbing treatment.

A nematic liquid crystal polyester-based liquid crystal polymer (A) in tetrachloroethane solution (15% by weight) is spin-coated on the alignment film, and then dried at 70 ° C. to obtain a liquid crystal layer having a thickness of about 1 μm. A molecular film was formed. Then
Heat treatment was performed at 130 ° C. for 30 minutes at which the polymer (A) exhibited a nematic phase. After quenching to room temperature, the obtained texture was observed to be monodomain homogeneous. Sandwiched between a polarizing plate sample was orthogonal, the transmittance T ₄₅ when the transmittance T ₀ diagonal position when the extinction position relative to white light was measured, the ratio T ₄₅ / T ₀ of both, the orientation The degree was evaluated. As a result, T ₄₅ / T ₀ = 95 in this sample, and excellent uniaxial orientation was confirmed.

(Effect of the Invention) The substrate with a liquid crystalline polymer liquid crystal of the present invention has a breaking elongation of 15%.
Since a polyimide film having excellent solvent resistance is used below, even when a liquid crystalline polymer is formed by a solution coating method, there is no alignment deterioration, and a very uniform alignment of the liquid crystalline polymer can be obtained. Therefore, it is very useful in the field of optoelectronics. In addition, the substrate with a liquid crystalline polymer thin film of the present invention has an advantage that, unlike an ordinary liquid crystal display device, only one substrate is used, so that the device can be made extremely thin and light.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a substrate with a liquid crystalline polymer thin film according to the present invention, and FIG. 2 is an explanatory diagram of a method for manufacturing a substrate with a liquid crystalline polymer thin film according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Alignment film 3 ... Thermotropic liquid crystalline polymer thin film

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akihiko Kanemoto 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Shigeki Iida 2-228 Kosugicho, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture (72) Inventor Takehiro Toyooka 58-179 Honmoku Motomachi, Naka-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Hiroyuki Ito 2-8-17 Shinohara-Higashi, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture

Claims (1)

(57) [Claims] A substrate, an alignment film formed on the substrate, and a thermotropic liquid crystalline polymer thin film formed on the alignment film as main components, and the alignment film is formed on the substrate. The breaking elongation obtained by closing the applied polyamic acid film on the substrate is 15% or less,
A substrate with a liquid crystalline polymer thin film, which is subjected to a rubbing treatment.