JP3095542B2 - Method for producing polysilane alignment film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polysilane alignment film applicable to a liquid crystal alignment film and the like.

[0002]

2. Description of the Related Art Polysilane is a polymer compound having a main chain consisting of Si--Si bonds, and its characteristics of this main chain are being applied to various materials, particularly in the form of thin films. For example, a polysilane thin film has a molecular orientation, ie, S
It is confirmed that the liquid crystal molecules are strongly aligned along the i-Si main chain along the direction of the i-Si main chain along the i-Si main chain. Based on this characteristic, if a polysilane thin film is used as an alignment film in a liquid crystal display element, that is, a film (liquid crystal alignment film) for aligning liquid crystal molecules in a certain direction on a surface in contact with the liquid crystal, the performance of the element can be expected to be improved.

Conventionally, polysilane thin films have been formed by various general film forming processes such as spin coating, casting, and LB (Langmuir-Blodgett). However, in the polysilane thin film formed by these processes, the orientation of the polysilane molecules is not constant. For this reason, the characteristics of the Si-Si main chain do not function sufficiently, and the performance expected as various materials is not achieved. For example, in the case where the polysilane thin film is used as a liquid crystal alignment film as described above, the liquid crystal molecules are uniformly and regularly distributed over the entire film surface due to the Si-Si main chain not being oriented in a certain direction. Orientation cannot be achieved.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems.
An object of the present invention is to provide a method for manufacturing a polysilane alignment film, which can obtain a polysilane alignment film in which a Si main chain is uniformly and uniformly aligned in a certain direction over the entire surface.

[0005]

According to the present invention, there is provided a method for producing a polysilane alignment film, comprising the steps of: (a) forming a polysilane thin film on a substrate;

(B) By making the polysilane thin film absorb an energy ray having a vibration component in a specific direction, of the polysilane molecules in the polysilane thin film, the direction of the vibration component of the energy ray is substantially orthogonal. Selectively leaving the component oriented in the direction.

According to the method of the present invention, in step (a), a polysilane thin film is formed according to a general process. Next, in the step (b), of the polysilane molecules in the polysilane thin film, a component oriented in the same direction or a direction close to the vibration component of the irradiated energy ray absorbs the energy ray and differs therefrom. It changes into a molecule with a structure and the molecular weight is reduced. On the other hand, the component oriented in a direction substantially perpendicular to the direction of the vibration component of the energy ray selectively remains without changing the molecular structure. That is, in the polysilane molecules present in the thin film after the step (b), only a component oriented in a certain direction remains.
Thus, a thin film in which the polysilane molecules are orientated in a certain direction, ie, an alignment film, is obtained. Hereinafter, the present invention will be described in detail.

[0008] The polysilane that can be used in the method of the present invention is not particularly limited as long as it is a polymer compound having a Si-Si main chain. As a specific example, the following general formula (1)
And a polysilane having a repeating unit represented by the following formula:

[0009]

Embedded image Where R ¹ , R ² , X indicate the following, respectively. R ¹ : A substituted or unsubstituted alkyl group having 1 to 24 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 24 carbon atoms. R ² : Divalent organic group having 1 to 24 carbon atoms.

X: a hydroxyl group, an amino group, a carboxylic acid group, or a hydrophilic group having at least one selected from the group consisting of an amide bond, an ester bond, a carbamate bond, and a carbonate bond.

The polysilane having the repeating unit (1) has a hydrophilic group X on one side chain and a hydrophobic group R ¹ on the other side chain with respect to the Si—Si main chain. , Ie, amphiphilic.

In the step (a) of the method of the present invention, various kinds of film forming processes can be adopted. Specific examples thereof include a roll coater method, a spin cast method, and an LB method.

Among these methods, in the roll coater method and the spin casting method, first, polysilane is dissolved in an organic solvent, and the obtained polymer solution is applied on a predetermined substrate. Subsequently, the substrate after application is dried using a hot plate or a drier to form a polysilane thin film having a predetermined thickness.

On the other hand, the formation of a thin film by the LB method is performed using an amphiphilic polysilane having the repeating unit (1) as described above. First, a polysilane having the repeating unit (1) is dissolved in an organic solvent, and the obtained polymer solution is dropped on a liquid surface such as water. At this time, in the polysilane having the repeating unit (1), the hydrophilic group X comes into contact with the liquid surface and the hydrophobic group R
¹ Is oriented so as to move away from the liquid surface, so that a very stable monomolecular film is formed. Next, the monomolecular film is compressed to a predetermined surface pressure, and while the surface area is controlled and the surface pressure is kept constant, a substrate previously subjected to a hydrophobic treatment or the like is perpendicular to the film surface. Immerse in the direction, then pull up. In this operation, the monolayer is transferred onto the substrate during immersion and / or withdrawal of the substrate. Subsequently, this operation of immersing the substrate is repeated a plurality of times to obtain a polysilane thin film (cumulative film) on the substrate. The above operation by the LB method can be performed using a general LB film manufacturing apparatus.

[0015] In the polysilane thin film formed by the LB method as described above, most of the Si-Si main chains are arranged parallel to the substrate surface, and the Si-Si of many polysilane molecules is formed.
The Si main chain is oriented in the direction in which the substrate is pulled from the liquid surface, and the arrangement state of the molecules is already controlled over the entire film. Therefore, if the LB method is adopted as the step (a), an alignment film in which the polysilane molecules are aligned in a higher order can be finally obtained.

In the step (b) of the method of the present invention, for example, ultraviolet rays are used as energy rays to be absorbed by the polysilane thin film. In this step, ultraviolet rays are passed through a polarizer such as a deflecting prism, so that energy or a line having a vibration component in one specific direction, that is, polarized UV, is applied to the polysilane thin film obtained in the step (a).
Here, the irradiation amount of the energy ray is preferably about 0.1
mJ / cm ² -10 J / cm ² Degree.

At this time, of the polysilane molecules in the polysilane thin film, the components oriented in the same direction or in the direction close to the irradiated UV vibration component are Si-
The Si main chain absorbs UV and changes into molecules having a siloxane structure (Si-O structure), and the molecular weight is reduced. On the other hand, for the component oriented in a direction substantially perpendicular to the direction of the UV vibration component, the Si-Si main chain remains without change.

In the step (b), by appropriately setting the direction of the vibration component of the energy ray absorbed in the polysilane thin film, it is possible to intentionally leave only the polysilane molecules oriented in a specific direction in the thin film. it can. As a result, it becomes possible to freely produce a polysilane alignment film having any molecular arrangement state.

When a polysilane thin film is formed by the LB method in the step (a), in the thin film, most of the Si—Si main chain is already oriented in the direction of pulling the substrate from the liquid surface before irradiation with energy rays. ing. Therefore, in this case, in the step (b), the direction of the vibration component of the energy ray to be absorbed by the thin film is set to a direction substantially perpendicular to the pulling direction of the substrate, and a small number of Si atoms oriented in a direction greatly different from the pulling direction. It is preferable to change the -Si main chain to another structure. Thus, an alignment film in which the polysilane molecules are oriented in the pulling direction of the substrate in a high order can be obtained.

The method of the present invention and the polysilane alignment film formed by the method can be applied to an alignment film in a liquid crystal display element, that is, a liquid crystal alignment film. Hereinafter, a liquid crystal display device using a polysilane alignment film obtained by the method of the present invention as a liquid crystal alignment film will be described with reference to FIGS.

FIG. 1 is a diagram showing a sectional structure of the liquid crystal display device. In the figure, reference numerals 11 ₁ and 11 ₂ denote substrates formed of a material such as glass.
ITO (Indium Tin Oxide), a transparent electrode 12 ₁ (display electrode) made of material and 12 ₂ (scanning electrodes) are formed. The transparent electrode 12 ₁ and 12 ₂ of the surface, respectively,
Liquid crystal alignment films 13 ₁ and 13 ₂ are formed. Furthermore,
Liquid crystal 14 is sealed between the liquid crystal alignment films 13 ₁ and 13 ₂ .

In the device having such a structure, a polysilane alignment film formed by the method of the present invention is used as the liquid crystal alignment films 13 ₁ and 13 ₂ . That is, the liquid crystal alignment films 13 ₁ and 13 ₂ correspond to the transparent electrodes 12 ₁ and 12 _{2, respectively.}
It is a polysilane alignment film formed by applying the method of the present invention above. The orientation of the molecules of the enclosed liquid crystal 14 is controlled by the orientation of the polysilane molecules in the orientation film.

In this case, the liquid crystal alignment films 13 ₁ and 13
_{Since the} polysilane alignment film used as ₂ has a semiconducting property, for example, all polysilane molecules are changed to a siloxane structure on the driving unit such as a display electrode, or an insulating polymer such as polyimide is used in advance to prevent short circuit. It is preferable to form a film to increase the insulating property. 2, the alignment state of the polysilane molecules constituting the liquid crystal alignment film 13 _1, and the alignment state of the liquid crystal molecules is controlled by this is shown schematically in Figure 1.

In FIG. ₁ , the liquid crystal alignment film 131 has S
While the polysilane molecules 21 having the i-Si main chain are oriented in a certain direction, the siloxane molecules 22 having the Si—O structure are not oriented other than the orientation direction of the polysilane molecules 21.
Are randomly arranged. This liquid crystal alignment film 13 ₁
According to the method of the present invention, a polysilane thin film in which Si-Si main chains are randomly arranged is formed by absorbing polarized UV having a vibration component in a certain direction. That is, when the above-mentioned polarized UV is irradiated to the above-mentioned polysilane thin film, the direction 2 of the vibration component of the polarized UV is obtained.
The Si-Si main chain oriented in a direction substantially perpendicular to 4 remains, while the Si-Si main chain oriented in the same direction as or near the direction 24 of the vibration component of the polarized UV light is:
It absorbs UV and changes into a siloxane structure to reduce the molecular weight, and as a result, the orientation state of the polysilane molecules 21 is formed as described above.

[0025] Here, among the molecules constituting the liquid crystal alignment film 13 _1, polysilane molecule 21 having a Si-Si backbone
Has a large polarizability along the direction of the main chain, and thus has an alignment control ability for the liquid crystal molecules 23. On the other hand, other molecules such as the siloxane molecules 22 hardly contribute to the alignment of the liquid crystal molecules 23. Thus, the liquid crystal molecules 23 are ordered well aligned in the vicinity of the surface of the liquid crystal alignment film 13 ₁ along the alignment direction of the polysilane molecule 21. For example, when butyl (m-hydroxyphenyl) polysilane is used, the P-type liquid crystal molecules are aligned with good order along the Si-Si main chain.

In a liquid crystal display device using such a polysilane alignment film as a liquid crystal alignment film, liquid crystal molecules of any type and molecular weight may be used. However, when N-type liquid crystal molecules are used, the alignment state of the liquid crystal molecules slightly changes.
In addition, the liquid crystal display device can be applied to a general liquid crystal display system, that is, any of a simple matrix system and an active matrix system. However, when applied to the latter type, a driving element such as a thin film transistor (TFT) or an MIM element is mounted in contact with the display electrode.

Conventionally, as a liquid crystal alignment film, an insulating polymer film such as polyimide is formed on a substrate, and the surface of the film is subjected to a rubbing treatment, that is, the film surface is rubbed with a roller covered with a fibrous substance (rubbing). ) Treatment to give alignment controllability to liquid crystal molecules. However, in this method, static electricity is generated during the rubbing treatment, which causes contamination and destruction of the device. Further, since the rubbing treatment is insufficient in accuracy, the obtained liquid crystal alignment film is not uniformly provided with the ability to control the alignment of liquid crystal molecules over the entire film.

On the other hand, when the polysilane alignment film formed by applying the method of the present invention as described above is used as a liquid crystal alignment film, the method employs only a chemical process such as polysilane thin film formation and polarized UV irradiation. Due to this, no static electricity is generated, and contamination and destruction of the element are prevented. In addition, the obtained liquid crystal alignment film composed of a polysilane alignment film has an alignment control ability evenly provided over the entire surface of the film, and furthermore, has a small absorption of light in a visible light region, and thus has a light transmittance. Are better. As a result, in a liquid crystal display device using such a polysilane alignment film as a liquid crystal alignment film, various performances such as a VT characteristic and a moving image display state are further improved.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to embodiments. These examples are described for the purpose of facilitating understanding of the present invention, and do not particularly limit the present invention. Example 1 [Formation of polysilane alignment film]

Dissolve butyl (m-hydroxyphenyl) polysilane (average molecular weight: 200,000) in cyclohexanone, and use the obtained solution having a concentration of 0.224% by weight.
According to the LB method, a polysilane thin film (LB) is formed on a transparent substrate.
Film) was formed. The conditions of the LB method are set as follows, and the cumulative numbers 2, 4, 6, 10, 20, 30, 40, 50
8 types of LB films were formed.・ PH: 7.0 ・ Film formation speed (substrate immersion-pulling speed): 5 mm / cm ・ Surface pressure: 20 dyn / cm ・ Water temperature: 15.2-15.3 ° C. ・ Room temperature: 21-23 ° C. ・ Substrate Method of transferring monolayer on top: vertical immersion method

Subsequently, using a parallel exposure machine (PLA-105: manufactured by Nikon Corporation), the surface of the LB film is irradiated with ultraviolet rays, that is, polarized UV rays, through a polarizing prism capable of transmitting ultraviolet rays. Was. UV irradiation at 44 mJ / cm per minute
^Two The irradiation time was set to 6 minutes.

Next, the degree of orientational order S was determined from the values of the dichroic ratios of the polarized UV spectrum of the LB film after irradiation with the ultraviolet light and the LB film not irradiated with the ultraviolet light for comparison. still,
The degree of orientational order S is a physical quantity that quantitatively represents the arrangement and orientation state of the molecules constituting the film, and is calculated according to the following equation. S = (R-1) / (R + 2) R = polarization UV spectrum dichroic ratio

FIG. 3 shows the relationship between the number of LB films and the degree of orientational order. However, the degree of orientational order when the cumulative number was 0 was approximated by the value of the degree of orientational order in a thin film (cast film) formed by the casting method using the same polysilane molecule as described later.

From the results shown in the figure, it is understood that the polysilane molecules are oriented in a higher order as the number of layers of the LB film, that is, the cumulative number is larger. Further, it can be seen that the degree of orientational order is significantly improved by irradiating polarized UV, and that an excellent polysilane orientation film is formed. [Evaluation with liquid crystal display element]

Of the substrates on which the polysilane alignment film is formed, two substrates having the same number of LB films are combined, and
The production of a liquid crystal cell and the enclosing of a liquid crystal were performed in accordance with the conventional methods. Thus, a liquid crystal display device having the polysilane alignment film as a liquid crystal alignment film was manufactured.

With respect to each of these devices, the alignment state of the enclosed liquid crystal molecules was evaluated. This evaluation was performed by comparing the image display characteristics with an element having a liquid crystal alignment film formed by a conventional rubbing method. That is, the comparison was made with the display characteristic of the device having the liquid crystal alignment film formed by the rubbing method as 1. FIG. 4 shows the relationship between the alignment state (display characteristics) of liquid crystal molecules in a liquid crystal display element having such a polysilane alignment film as a liquid crystal alignment film.

From the results shown in the figure, it can be seen that as the number of layers of the LB film is larger, the orientation state of the liquid crystal molecules is improved due to the higher order orientation of the polysilane molecules in the polysilane orientation film. . Example 2 [Formation of polysilane alignment film]

A butyl (m-hydroxyphenyl) polysilane (average molecular weight: 200,000) was dissolved in cyclohexanone, and the resulting solution having a concentration of 2.5% by weight was used to spin-cast a polysilane thin film on a transparent substrate. Cast film) was formed. The conditions of the spin casting method were set as follows. -Spinner rotation speed: 500rpm, 5sec, 2500rpm.
25sec ・ Room temperature: 22 ℃

Subsequently, using a parallel exposure machine (PLA-105: manufactured by Nikon Corporation), the surface of the cast film was
UV irradiation through a polarizing prism capable of transmitting UV light,
That is, irradiation of polarized UV was performed. In this example, the irradiation amount was 44 mJ / cm ² per minute. And the irradiation time is 3 minutes, 6
Minutes, 9 minutes, 12 minutes, and 15 minutes to obtain five types of cast films having different ultraviolet irradiation amounts.

Next, for the cast film irradiated with ultraviolet rays for 6 minutes and the cast film not irradiated with ultraviolet rays (irradiation time 0) for comparison, the orientation order S was determined in the same manner as in Example 1. In the irradiated cast film, S =
S was about 0 in the unirradiated cast film.
In FIG. 3, the value of the degree of orientational order in the cast film irradiated with the ultraviolet rays is plotted as the value when the number of layers of the LB film is 0.

From the above results, it can be seen that by irradiating the polysilane thin film formed by the casting method with polarized UV, the degree of orientational order is remarkably increased, and an excellent polysilane oriented film is formed. [Evaluation with liquid crystal display element]

Of the substrates on which the polysilane alignment film was formed, two substrates each having the same ultraviolet irradiation time were combined, and a liquid crystal cell was fabricated and a liquid crystal was sealed in accordance with a conventional method. Thus, a liquid crystal display device having the polysilane alignment film as a liquid crystal alignment film was manufactured. For comparison, a liquid crystal display device was manufactured using one set of substrates on which a cast film not irradiated with ultraviolet light was formed. For each of these devices, the orientation state (display characteristics) of the sealed liquid crystal molecules was evaluated in the same manner as in Example 1.

FIG. 5 shows the relationship between the irradiation time of ultraviolet light to the cast film and the alignment state of liquid crystal molecules (display characteristics) in a liquid crystal display element having such a polysilane alignment film as a liquid crystal alignment film.

From the results shown in the figure, it can be understood that the longer the irradiation time of the ultraviolet rays is, the more the polysilane molecules are oriented in the polysilane alignment film in a higher order, and thus the alignment state of the liquid crystal molecules is improved.

FIG. 4 plots the values of the display characteristics of a liquid crystal display element having a cast film as a liquid crystal alignment film having a UV irradiation time of 6 minutes as values when the number of LB films is zero.

[0046]

As described in detail above, according to the present invention,
It is possible to obtain a polysilane alignment film in which the Si—Si main chain of the polysilane molecule is uniformly and uniformly oriented in the entire surface. This polysilane alignment film can be suitably used for various materials such as a liquid crystal alignment film by utilizing the characteristics of the Si-Si main chain, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a structure of a liquid crystal display device using a polysilane alignment film formed by a method of the present invention.

FIG. 2 is a schematic diagram showing the alignment state of polysilane molecules constituting the film and the alignment state of liquid crystal molecules controlled by using the polysilane alignment film formed by the method of the present invention as a liquid crystal alignment film. FIG.

FIG. 3 is a characteristic diagram showing a relationship between the number of polysilane alignment films (LB films) and the degree of orientational order of the polysilane alignment films.

FIG. 4 is a characteristic diagram showing a relationship between the number of layers of a polysilane alignment film (LB film) and an alignment state of liquid crystal molecules in a liquid crystal display element.

FIG. 5 is a characteristic diagram showing a relationship between an irradiation time of ultraviolet light to a polysilane alignment film (cast film) and an alignment state of liquid crystal molecules in a liquid crystal display element.

[Explanation of symbols]

11 ₁ , 11 ₂ ... substrate, 12 ₁ , 12 ₂ ... transparent electrode, 1
3 ₁ , 13 ₂ : liquid crystal alignment film, 14: liquid crystal, 21: polysilane molecule, 22: siloxane molecule, 23: liquid crystal molecule, 2
4: Direction of vibration component of polarized UV

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor: Shinji Murai 1 Toshiba-cho, Komukai-shi, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Research Institute, Inc. (72) Shuji Hayase 1 Toshiba-cho, Komukai-shi, Kawasaki-shi, Kanagawa Address Toshiba Research Institute, Inc. (56) References JP-A-3-252606 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/1337 530

Claims (1)

(57) [Claims] (A) forming a polysilane thin film on a substrate; and (b) causing the polysilane thin film to absorb an energy ray having a vibration component in a specific direction, thereby forming a polysilane in the polysilane thin film. Selectively resting, among the molecules, a component oriented in a direction substantially perpendicular to the direction of the vibration component of the energy ray.