JPH09203902A - Liquid crystal element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal element with which the formation of orientation control films at a low baking temp. is possible and a process for producing the same. SOLUTION: Many pieces of ruggedness are formed on the surfaces of insulating layers 5a, 5b, 6a, 6b, by which the baking temp. for forming the orientation control films 8a, 8b on substrates 2a, 2b by imidizing polyimide based materials applied on the surfaces of the insulating layers 5a, 5b, 6a, 6b is lowered. The ruggedness is formed by incorporating many particles 7 having the height size large than the layer thickness of the outer insulating layers 6a, 6b among the insulating layers 5a, 5b, 6a, 6b into insulating layer forming materials.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device using a chiral smectic liquid crystal and a method for manufacturing the same, and more particularly to a firing temperature of an alignment control film formed on a substrate surface.

[0002]

2. Description of the Related Art Display devices of the type that control transmitted light rays by combining the refractive index anisotropy of liquid crystal molecules and a polarizing element are Clark and Lagerw.
all) (JP-A-56-1072).
16 publication, U.S. Pat. No. 4,367,924, etc.).

This liquid crystal generally has a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) in a specific temperature range, and in this state, it has a first optical stability corresponding to an applied electric field. State or the second optically stable state, and has the property of maintaining that state when no electric field is applied, that is, bistability. It also has a quick response to changes in the electric field and high speed. In addition, it is expected to be widely used as a memory type display element.

By the way, as an alignment method for the chiral smectic liquid crystal, especially for the chiral smectic liquid crystal having a non-helical structure, for example, US Pat.
6 is well known, and the alignment state including the chevron structure of the smectic layer is shown in FIG.
This can be explained by two types of orientation models, Cl orientation 32 and C2 orientation 33 as shown in FIG.

This smectic liquid crystal generally has a layered structure. However, when the SmA phase transitions to the SmC phase or the SmC ^* phase, the layer spacing shrinks, so that the layer is bent as shown in FIG. 5 (chevron structure) 31. Will be taken. There are two types of bending directions, Cl orientation 32 and C2 orientation 33, as shown in the figure. As is well known, the liquid crystal molecules at the substrate interface form an angle with the substrate by rubbing. However, because of this angle, the C1 orientation 32 and the C2 orientation 33 are not equivalent in terms of elastic energy, and a transition occurs at a certain temperature.

Here, when such a transition occurs, as shown in the figure, the C1 orientation 32 toward the rubbing direction A is obtained.
From the C2 orientation 33 to the C2 orientation 33, a so-called lightning defect having a zigzag shape occurs at the boundary 34.
At the boundary 35 when moving to the 1-direction 32, a hairpin defect is formed in a wide and gentle curved shape.

By the way, the liquid crystal element using the chiral smectic liquid crystal is provided with a pair of substrates that are parallel to each other and are uniaxially aligned in the same direction for alignment. Now, the pretilt of the chiral smectic liquid crystal is used. When the angle is α, the tilt angle (1/2 of the cone angle) is Θ, and the tilt angle of the SmC ^* layer is δ (see FIG. 5), and the orientation state represented by the formula 1 is obtained, the C1 orientation state is obtained. Form a bistable state (uniform state).

[0008]

Α> Θ−δ On the other hand, if the apparent tilt angle when there is no electric field is θa, the state showing the relationship of the equation 2 is called a uniform state.

[0009]

## EQU00002 ## .THETA.>. Theta.a> .THETA. / 2 Here, .alpha. That generally satisfies the equation 1 is 10.degree.

Further, in the uniform state, it is considered that the director is not twisted between the upper and lower substrates in view of the optical conditions. FIG. 6A is a schematic view showing the arrangement of directors at respective positions between the substrates in each state of C1 orientation. In the figure, 41 to 44 show the state in which the director is projected on the bottom surface of the cone in each state and seen from the bottom surface direction, 41 and 42 are spray states, 43 and 4
Reference numeral 4 denotes an arrangement of directors considered to be in a uniform state.

As can be seen from the figure, the uniform 2
In the states 43 and 44, the positions of the liquid crystal molecules on either the upper or lower substrate interface are replaced with the positions in the spray state. FIG. 6B shows the C2 orientation, and there are two states 45 and 46 due to internal switching without interface switching. The uniform state of the C1 orientation produces larger θa than the conventionally used bistable state of the C2 orientation, and has a large luminance and a high contrast.

By the way, a polyimide film, a polyamide film or the like is generally used as an alignment control film of a liquid crystal element. An alignment control film solution in which a polyamic acid is dissolved in a solvent is used for forming the polyimide film, and a method of applying the solution to a glass substrate and then baking at 240 ° C. to 300 ° C. for dehydration ring closure is used. . The baking temperature is a temperature at which the imidization ratio of the applied film becomes 100%.

The imidization ratio will be described below.

When the IR spectrum of the polyimide film formed by coating the glass substrate with the polyamic acid used in the present invention and baking it, the spectrum shown in FIG. 7 was obtained. Absorption A ₁₃₇₀ observed at ₁₃₇₀ cm ^-1 is C-of imide
The absorption A ₁₅₀₀ observed at 1500 cm ⁻¹ can be attributed to the N stretching vibration, and can be attributed to the C═C stretching vibration of the benzene ring.

FIG. 8 is a graph of A ₁₃₇₀ / A _{1500 with} respect to the firing temperature when the firing time is constant. In the figure, imidization is completed at a temperature above which A ₁₃₇₀ / A ₁₅₀₀ is almost constant. Can be regarded as Incidentally, the A ₁₃₇₀ / A ₁₅₀₀ value in this case is 100% and the percentage imidization ratio of A ₁₃₇₀ / A ₁₅₀₀ value for each sintering temperature in the case, the minimum calcination temperature for this imidization ratio is 90% or more X.

[0016]

By the way, in the liquid crystal element manufactured by such a conventional manufacturing method,
When the orientation control film (polyimide film) is baked at a high temperature of 0 ° C. to 300 ° C., the pretilt α is relatively high, and the result that α for each element created is small is changed. In addition, the color filter and the flattening layer formed thereon are damaged.

Therefore, it is necessary to lower the firing temperature in order to prevent such damage of the color filter or the like, but when the firing temperature is lowered in this way, α becomes small and C2 orientation occurs. . And like this, C2
When the alignment occurs, there is a problem that a lightning defect and a hairpin defect occur, which makes it difficult to construct a chiral smectic liquid crystal display device having a practically sufficient performance.

The present invention has been made under the above circumstances, and an object of the present invention is to provide a liquid crystal element capable of forming an alignment control film at a low firing temperature and a method for manufacturing the same. .

[0019]

According to the present invention, a substrate having an alignment control film formed by imidizing a polyimide-based material applied to the surface of an insulating layer and the substrate placed oppositely are injected. A liquid crystal device including a chiral smectic liquid crystal is characterized in that a large number of irregularities are formed on the surface of the insulating layer so as to lower the firing temperature for imidizing the polyimide material.

The present invention is also characterized in that the large number of irregularities are formed by a large number of particles mixed in an insulating layer forming material and having a height dimension larger than the layer thickness of the insulating layer. Is.

Further, the present invention is characterized in that the particles are spherical particles.

The present invention is also characterized in that the particles are formed of a non-conductive substance.

Further, the present invention is characterized in that the irregularities are respectively formed on the surfaces of the insulating layers of the substrates arranged to face each other.

Further, according to the present invention, the polyimide-based material applied to the insulating layer formed on the surface of the substrate is imidized to form an orientation control film on the surface of the insulating layer, while the substrate on which the orientation control film is formed is formed. In a method of manufacturing a liquid crystal device, in which a chiral smectic liquid crystal is injected between the substrates while facing each other, the insulating material is formed so as to lower the firing temperature for imidizing the polyimide-based material. It is characterized in that a large number of irregularities are formed on the surface of the layer.

The present invention is also characterized in that the minimum temperature of the firing temperature is a temperature at which the imidization ratio of the polyimide material is 90% or more.

Further, the present invention is characterized in that the orientation control film is fired within a temperature range from a minimum firing temperature to a firing temperature higher than the minimum firing temperature by a predetermined temperature.

Further, the present invention is characterized in that the orientation control film is fired within a temperature range from the lowest firing temperature to a temperature higher by 30 ° C.

Further, the present invention is characterized in that, when the orientation control film is formed of a fluorine-containing polyamic acid, the minimum firing temperature is 210 ° C. and the predetermined temperature is 30 ° C. .

Further, the present invention is characterized in that the large number of irregularities are respectively formed on the surfaces of the insulating layers of the substrates arranged to face each other.

The present invention is also characterized in that the large number of irregularities are formed by a large number of particles mixed in an insulating layer forming material and having a height dimension larger than the layer thickness of the insulating layer. Is.

By forming a large number of irregularities on the surface of the insulating layer in this way, the baking temperature for forming the orientation control film on the substrate by imidizing the polyimide material coated on the surface of the insulating layer is lowered. be able to. By mixing a large number of particles having a height dimension larger than the layer thickness of the insulating layer into the insulating layer forming material, such a large number of irregularities can be formed on the surface of the insulating layer. Furthermore, by forming the particles with spherical particles of a non-conductive substance, it is possible to form a large number of irregularities having a uniform height and having non-conductivity.

On the other hand, in a method of manufacturing a liquid crystal element, in which a substrate on which an orientation control film is formed is arranged to face each other and a chiral smectic liquid crystal is injected between the substrates to manufacture a liquid crystal element, a surface of an insulating layer is formed. By forming a large number of irregularities, the firing temperature for imidizing a polyimide material can be lowered.

The minimum firing temperature is set to a temperature at which the imidization ratio of the polyimide material is 90% or more, and the polyimide material is fired at a predetermined firing temperature, preferably 30 ° C. higher than the lowest firing temperature. The orientation control film is baked by imidization within the temperature range.

[0034]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic view showing a cross section of a liquid crystal element according to the present invention. In the figure, 1 is a chiral smectic liquid crystal element (hereinafter referred to as a liquid crystal element), and 2a and 2b are two substrates arranged opposite to each other. 1 mm thick glass substrate, 3 spacers having a diameter of 1.5 μm provided between the glass substrates 2a and 2b, and 4 glass substrate 2
It is a chiral smectic liquid crystal injected between a and 2b.

By the way, the surfaces of the glass substrates 2a, 2b, in the present embodiment, both glass substrates 2a, 2b.
On the surface of b, 600 Å thick first insulating layer 5a,
5b is formed by heating. In addition, this first insulating layer 5
a and 5b are insulating layer solutions (for example, T
It is formed by printing and applying (i: Si = 1: 1 solution) by a spin color development method, and then heating at 240 ° C.

On the other hand, on the first insulating layers 5a and 5b,
The second insulating layers 6a and 6b having a layer thickness of 170Å are the first insulating layers 5
a and 5b are formed by heating in the same manner as described above, and thus at least two insulating layers 5 are formed on the surfaces of the substrates 2a and 2b.
By forming a, 5b, 6a and 6b, the insulating property between the glass substrates 2a and 2b is improved.

By the way, the second insulating layers 6a and 6b are spherical particles having a height dimension larger than the layer thickness, and are made of SiO ₂ which is a non-conductive material and have a diameter of several hundred liters. _A lot of ₂ particles 7 are mixed, and this Si
The O ₂ particles 7 form a large number of concave portions 9b and convex portions 9a on the surfaces of the second insulating layers 6a and 6b.

Here, by forming such a large number of irregularities with spherical and non-conductive SiO ₂ particles 7, the irregularities can be made uniform in height and the insulating layers 6a, The non-conductivity of 6b can be ensured. Although SiO ₂ particles are used as spherical and non-conductive particles in the present embodiment, the present invention is not limited to this, and TiO ₂ particles or the like may be used.

Further, these insulating layers 5a, 5b, 6
Alignment control films 8a and 8b having a thickness of 200 Å are provided on a and 6b. Here, the alignment control films 8a and 8b are
It is a product obtained by printing and coating a fluorinated polyamic acid containing NMP (N-methylpyrrolidone) and n-butyl cellosolve as a solvent, and then firing it.

When a large number of irregularities are formed on the surfaces of the second insulating layers 6a and 6b, the minimum firing temperature for firing the orientation control films 8a and 8b, in the present embodiment, the imide in the fluorinated polyamic acid-containing acid. The minimum firing temperature at which the conversion rate is 90% or more is 210 ° C., which is lower than the conventional firing temperature (240 ° C. to 300 ° C.) as described above.

By lowering the minimum firing temperature in this way, damage to the color filters and the like during firing of the orientation control films 8a and 8b can be prevented, and the range of selection of materials for the color filters and the like can be widened. Will be able to. On the other hand, as a method for manufacturing such a liquid crystal element, first, an insulating layer solution is printed and applied on the glass substrates 2a and 2b by a spin color development method, and then the insulating layer solution is applied to
The first insulating layers 5a and 5b having a thickness of 600 Å are formed by heating at ℃.

Next, an insulating layer solution containing SiO ₂ particles 7 having a diameter of about 100 Å is applied by printing onto the first insulating layers 5a and 5b by printing, and then heated at 240 ° C. to 170
The second insulating layers 6a and 6b having a layer thickness of Å are formed. When the second insulating layers 6a and 6b are formed in this manner, for example, the surface of the second insulating layer 6b of the lower glass substrate 2b may be formed on the surface of FIG.
As shown in FIG. 5, a large number of concave portions 9b and convex portions 9a having uniform height are formed.

Next, after the fluorine-containing polyamic acid-containing acid is applied by printing onto the second insulating layers 6a and 6b on which the large number of irregularities are formed, the orientation control film 8b is baked. Here, the firing temperature is set to a minimum firing temperature (X = 210 ° C.) and a temperature higher than the minimum firing temperature by a predetermined temperature, in the present embodiment, X + 30 ° C., that is, a firing range of 240 ° C. There is.

In this way, the orientation control film 8b is formed at 210 ° C. lower than the conventional baking temperature (240 ° C. to 300 ° C.).
By firing in the temperature range of 240 ° C., the orientation control film 8b can be fired more easily.

In the present embodiment, the firing temperature is set to 240 ° C. so that the orientation control film 8b can be reliably fired. However, this firing temperature (240 ° C.) is
It is the same as the formation temperature of the insulating layers 5a, 5b, 6a, 6b.
By making the formation temperatures of a, 5b, 6a, and 6b the same, temperature control in the manufacturing apparatus can be made simpler. Finally, after rubbing treatment, spacers 3 having a diameter of 1.5 μm are scattered on the surface of the substrate, and the substrates 2a and 2b are bonded to each other via a sealing agent made of epoxy resin to form a cell 1a. A chiral smectic liquid crystal 4 is injected into the cell 1a thus manufactured to manufacture a chiral smectic liquid crystal display device (hereinafter simply referred to as device A). By the way, the second insulating layer 6a having such unevenness is formed.
In the device A having 6b, the pretilt angles α of a plurality (five) of liquid crystal device samples prepared by rubbing the alignment control films 8a and 8b at 240 ° C. and under the same conditions.
As a result of measurement, the result is as shown in the table of FIG. In addition,
In the same table, the element B shows a liquid crystal element provided with an insulating layer containing no particles, in which the orientation control film is baked at 240 ° C.

Here, as is apparent from the figure, in the case of the element B, α is as small as 10 ° or less, and there is variation between samples, whereas in the element A, α is 18 ° to 20 °.
It was found to be as high as ° and there was little variation between samples. As described above, by providing unevenness on the surfaces of the second insulating layers 6a and 6b, it is possible to obtain α sufficient for the chiral smectic liquid crystal to have C1 uniform orientation even when firing is performed at (X + 30) ° C. or less. found.

This α was measured by the crystal lotion method (Jpa. J. Appl. Phys. Vo. 11).
9 (1980) No. Short Notes 203
It was determined by 1). That is, as a liquid crystal for measuring the pretilt angle, a ferroelectric liquid crystal (CS-1014 manufactured by Chisso Corporation) mixed with 20% by weight of a compound represented by the following structural formula was injected as a standard liquid crystal for measurement.

[0049]

Embedded image In addition, this mixed liquid crystal composition has a SmA
Phase.

The measurement procedure is as follows. While rotating the liquid crystal panel on the plane perpendicular to the upper and lower substrates and including the alignment treatment axis (rubbing axis), the helium / neon laser light having the deflection surface forming an angle of 45 ° with the rotation axis is rotated. Irradiate from the direction perpendicular to the axis,
On the opposite side, the transmitted light intensity was measured with a photodiode through a deflection plate having a transmission axis parallel to the incident deflection surface. Then, the pretilt angle α was obtained by a simulation of fitting the theoretical curve, Formulas 3 and 4, to the spectrum of the transmitted light intensity generated by the interference.

[0051]

(Equation 3) N _o: ordinary refractive index, N _e: extraordinary refractive index, phi: rotation angle of the liquid crystal panel, T (φ): transmitted light intensity, d: cell thickness,
λ: wavelength of incident light

[0052]

(Equation 4) When the alignment state of the liquid crystal of these two elements A and B was observed under a polarization microscope, C1 (uniform) orientation was obtained over the entire surface of element A as shown in the table shown in FIG. In B, the C1 (uniform) orientation and the C2 (spray) orientation were mixed. That is, it was found that the element A had less defects and a better contrast than the element B.

Further, FIG. 4 shows a case where nine kinds of liquid crystal elements having different firing temperatures of the orientation control films were prepared for the element A and the element B, and the pretilt angle α thereof was measured. The orientation control film is baked at 210 and 22 respectively.
0,230,240,250,260,270,28
The temperature is 0,300 ° C., the alignment film material is fluorine-containing polyamic acid, and the temperature X at which the imidization ratio is 90% is 21.
0 ° C.

As a result of the α measurement at this time, as shown in the same figure, the α of the element A showed a higher value than the α of the element B at each temperature. Especially, the orientation control film was baked at 210 to 240 ° C. When it did, the difference was remarkable. In other words, 270 ℃
At ˜300 ° C., the α of the element A was about 1.3 times that of the element B, while it was about twice the low temperature side. Also,
It was found that the value of α (= 19.3 °) of the element A baked at 240 ° C. was almost the same value as the value of α (= 20.1 °) of the element B baked at 280 ° C.

From this, it was found that the predetermined α value was obtained even when the firing temperature was 210 ° C. to 240 ° C., which is lower than the conventional firing temperature.

[0056]

As described above, according to the present invention, the firing temperature can be lowered by mixing particles in the insulating layer to form irregularities on the surface of the insulating layer. As a result, even when the alignment control film is baked at a lower temperature than before, it is possible to obtain a pretilt sufficient to form a chiral smectic liquid crystal display device with few defects and high contrast.

By allowing the orientation control film to be fired at a lower temperature than before, damage to the color filter and the flattening layer formed thereon is suppressed, and other color filters and the flattening film are flattened. It is possible to broaden the selection range of the layer material, and it is possible to provide an even better chiral smectic liquid crystal element.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross section of a liquid crystal element according to the present invention.

FIG. 2 is a diagram showing a part of a manufacturing process of the liquid crystal element.

FIG. 3 is a diagram showing a difference in pretilt value and alignment state between the liquid crystal element having unevenness formed on the insulating layer and the conventional liquid crystal element having no unevenness formed thereon.

FIG. 4 is a diagram showing a change in pretilt value due to a change in firing temperature of an orientation control film.

FIG. 5 is an explanatory view showing a layer structure of C1 alignment and C2 alignment of a conventional chiral smectic liquid crystal.

FIG. 6 is a schematic diagram showing the arrangement of directors at respective positions between substrates in each of the C1 orientation and C2 orientation of the chiral smectic liquid crystal.

FIG. 7 is a diagram showing an IR spectrum of a polyimide film.

FIG. 8 is a view showing a change in imidization ratio depending on a firing temperature.

[Explanation of symbols]

1 liquid crystal element 2a, 2b glass substrate 4 chiral smectic liquid crystal 5a, 5b first insulating layer 6a, 6b second insulating layer 7 SiO ₂ particles 8a, 8b orientation control film 9a, 9b unevenness X minimum firing temperature α pretilt angle

Claims (12)

[Claims] 1. A liquid crystal comprising a substrate having an orientation control film formed by imidizing a polyimide-based material applied to the surface of an insulating layer, and a chiral smectic liquid crystal injected between the substrates arranged to face each other. In the device, the liquid crystal device is characterized in that a large number of irregularities are formed on the surface of the insulating layer so as to lower the firing temperature for imidizing the polyimide material. 2. The plurality of irregularities are formed by a large number of particles mixed in an insulating layer forming material and having a height dimension larger than a layer thickness of the insulating layer. Liquid crystal element. 3. The liquid crystal device according to claim 2, wherein the particles are spherical particles. 4. The liquid crystal device according to claim 2, wherein the particles are formed of a non-conductive substance. 5. The liquid crystal device according to claim 1, wherein the unevenness is formed on each surface of the insulating layers of the substrates arranged to face each other. 6. A polyimide-based material applied to an insulating layer formed on the surface of a substrate is imidized to form an orientation control film on the surface of the insulating layer, while the substrates on which the orientation control film is formed face each other. In addition, a method of manufacturing a liquid crystal device by injecting a chiral smectic liquid crystal between the substrates to manufacture a liquid crystal device, the surface of the insulating layer to lower the firing temperature for imidizing the polyimide-based material. A method for manufacturing a liquid crystal element, characterized in that a large number of irregularities are formed on the surface. 7. The method for producing a liquid crystal element according to claim 6, wherein the minimum firing temperature is a temperature at which the imidization ratio of the polyimide material is 90% or more. 8. The firing method according to claim 6, wherein the orientation control film is fired within a temperature range from a minimum firing temperature to a firing temperature higher than the minimum firing temperature by a predetermined temperature. Liquid crystal device manufacturing method. 9. The method of manufacturing a liquid crystal element according to claim 8, wherein the orientation control film is fired within a temperature range from the lowest firing temperature to a temperature higher by 30 ° C. 10. The minimum firing temperature is 210 when the alignment control film is formed of a fluorine-containing polyamic acid.
9. The method for manufacturing a liquid crystal element according to claim 7, wherein the predetermined temperature is 30 ° C. 11. The method of manufacturing a liquid crystal device according to claim 6, wherein the plurality of irregularities are formed on the surfaces of the insulating layers of the substrates arranged to face each other. 12. The large number of irregularities is formed by a large number of particles mixed in an insulating layer forming material and having a height dimension larger than the layer thickness of the insulating layer. 11. The method for manufacturing a liquid crystal element according to item 11.