JPH02179609A - Display device - Google Patents

Abstract

PURPOSE:To execute stable driving even if the temp. of the use environment changes by detecting the temp. of a display layer consisting of a high-polymer liquid crystal compsn. which exhibits a ferroelectric property and changing the driving signal for driving the liquid crystal according to the detected temp. CONSTITUTION:In general, the rate of the polarization inversion of the high- polymer liquid crystal by the impression of an electric field thereto is low as the viscosity of the system increases with a decrease in temp. Such change in the reaction rate can be kept within a specified range by changing the driving voltage or driving frequency, etc., according to the temp. of the display layer. A temp. detecting part 6 is provided on the surface of one substrate 1 of the display device having the display layer 5 consisting of the high-polymer liquid crystal compsn. which exhibits the ferroelectric property between a pair of the substrates 1 and 1a and the temp. change detection signal 9 detected therein is introduced to a driving signal generating part 7. The driving signal 10 from the driving signal generating part 7 is passed through a segment side driving part 11 and a common side driving part 12, by which the voltage or driving frequency, etc., of striped electrodes 2, 2a are changed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical modulation device, and particularly to a display device using a polymer liquid crystal having ferroelectric properties.

[Prior Art] Conventionally, a liquid crystal display device displays images or information by configuring a scanning electrode group and a signal electrode group in a 7-trix shape, and filling a liquid crystal compound between the electrodes to form a large number of pixels. is well known. The driving method for this display element is time-division driving, in which an address signal is selectively and periodically applied to a group of scanning electrodes, and a predetermined information signal is selectively applied in parallel to a group of signal electrodes in synchronization with the address signal. It has been adopted.

Most of these were put to practical use, for example, in “Applied Physics Letters” (“Applied Physics Letters”).
d Physics Letters” Volume 18, No. 4 (published February 15, 1971), pp. 127-128
“Voltage Dependant Optical Activity ° of Twisted Nematic Liquid Crystal” co-authored by M. Chadt (M, 5chadt) and Doublenie Helfrich (W, He1frich), published on the page. (“Vo I ta
geDependent 0ptical Activ
ity of a TwistedNe+1atic
Twisted nematic shown in “1quid Crystal”
It was a model LCD.

In recent years, as an improved version of conventional liquid crystal elements, the use of bistable liquid crystal elements has been proposed by both C1ark and Lagerwal (Japanese Unexamined Patent Publication No. 107216/1983, U.S. Pat. Patent No. 4367924 specification, etc.). Liquid crystals with bistability are generally chiral smectic C phase (Sm”
(:) or H phase (Sm”H) is used. In these states, in response to an applied electric field, either a first optically stable state or a second optically stable state is used. It has the property of maintaining the same state when no electric field is applied, that is, it has stability, and it responds quickly to changes in the electric field, so it is expected to be widely used in fields such as high-speed and memory-type display devices. has been done.

Furthermore, due to its excellent viewing angle characteristics, it has a large capacity and
It is considered suitable as a material for large-area displays. However, when actually forming a liquid crystal cell, it is difficult to monodomain over a wide area, and there are technical problems in producing a large screen display element.

To solve this problem, it has been reported that a ferroelectric smectic liquid crystal monodomain is created by an epitaxial method using interfacial energy. (U.S. Pat. No. 4,561,726) However, the monodomains obtained in this way are not inherently stable and are easily converted into multidomains by pressure or thermal stimulation, making it difficult to increase the area.

On the other hand, polymer liquid crystal devices have been proposed as devices that are easy to fabricate and suitable for large-area displays. As a device driven by an electric field, US Pat. No. 42:194:15 and the like are known.

Furthermore, British Patent No. 2146787 is known for addressing using heat, typically laser light, and JP-A-52-14114 is known for addressing using a thermal head or the like.

Although devices using these polymer liquid crystal devices are suitable for large-area, high-definition displays, they have a drawback in that they have slow response speeds, making them unsuitable for applications that require moving images or high-speed rewriting.

Various studies have been made to eliminate the above drawbacks. One of them is N. Brate et al., "Polymer Bulletin 412, p. 299, (1984) [
N, A, PIate etal, Polymer B
ulletin, 12° 299 (1984)], a ferroelectric polymer liquid crystal has been reported. This ferroelectric polymer liquid crystal is easy to form into devices such as film formation, making it suitable for large-area displays, and its response speed is greatly improved compared to conventional polymer liquid crystals, so it is expected to be put into practical use. .

[Problem to be Solved by the Invention] However, in the conventional example described above, when the temperature of the display layer changes due to a change in the environmental temperature, the electrical characteristics such as the responsiveness of the ferroelectric polymer liquid crystal to the drive signal change. The disadvantage was that the characteristics changed and stable driving was not possible, especially at low temperatures.

The present invention has been made in order to improve the drawbacks of the prior art, and provides a display device that can perform stable driving even when the temperature of the usage environment changes and the temperature of the display layer changes. The purpose is to provide the following.

[Means for Solving the Problems] That is, the present invention provides a means for detecting the temperature of the display layer in a display device having a display layer made of a polymeric liquid crystal composition exhibiting ferroelectricity, and a method according to the detected temperature. 1. A display device characterized by having a means for changing a drive signal.

The present invention will be explained in detail below.

The display device of the present invention has a means for detecting the temperature of the display layer and a means for changing the drive signal according to the detected temperature, thereby controlling the temperature characteristics of the electrical properties of the ferroelectric polymer liquid crystal. It has been improved and can be used in environments where the operating temperature changes significantly, whether indoors or outdoors.

FIG. 1 is an explanatory diagram showing an example of a display device of the present invention.

In FIG. 1, the polymer liquid crystal element A used in the present invention has a striped electrode 2.2a and an alignment film 3 on the surface.
, 3a formed thereon, a pair of substrates 1 and 1a made of glass plates or plastic plates, etc., are held at a predetermined distance by spacers 4, and a display layer 4 made of a polymeric liquid crystal composition exhibiting a ferroelectric phase is placed between the substrates. It has a structure in which a polarizing plate 8 is provided on the outside of each substrate. If the polymeric liquid crystal can be formed into a film by itself, the spacer 4 is not necessarily necessary, and the peripheral portion may simply be bonded using a suitable adhesive.

On one substrate 1, an electrode group consisting of a plurality of striped electrodes 2 (for example, a segment-side electrode group in a matrix electrode structure) or a predetermined pattern such as a strip pattern is formed. Further, on the other substrate 1a, an electrode group (for example, a common-side electrode group in a matrix electrode structure) consisting of a plurality of transparent electrodes 2a intersecting with the transparent electrode 2 described above is formed. A temperature detection section 6 is provided on the surface of one of the substrates l, and a temperature change detection signal 9 is generated by detecting a change in the substrate surface temperature by the temperature detection section 6.
is introduced into the drive signal generator 7, and the drive signal generator 7 generates a drive signal IO1 corresponding to the change in the substrate surface temperature, for example, V(T) in FIG. 2 and 1/F(T) in FIG. Then, the voltage or driving frequency of the striped electrode 2.2a is changed through the segment side drive section 11 and the common side drive section 12, respectively, and varies depending on the temperature. This compensates for differences in stable driving conditions.

Factors that change the temperature of the display layer of a liquid crystal display device include changes in the temperature of the environment in which the device is used (indoors and outdoors);
Also, the temperature of the substrate increases due to the backlight source due to long-term use.

In the present invention, there is a means for detecting the temperature of the display layer, but as a method for detecting (monitoring) the temperature change of the display layer due to the change in the use environment as described above, for example, the temperature detection means may be used to detect the temperature of the display layer. One method is to indirectly know the temperature of the display layer by knowing the surface temperature.

Furthermore, the present invention is characterized by having means for changing the drive signal according to the temperature detected by the temperature detection means, and among the drive signals, the parameter to be changed according to the temperature is, for example, a voltage. , drive frequency (width of l pulse), etc.

As a method of modulating the above driving parameters, for example,
As shown in FIG. 2 in the embodiment, a step-like method according to temperature changes may be used, but the method is not necessarily limited to this method.

In the present invention, the ferroelectric polymer liquid crystal composition that forms the display layer may be a ferroelectric polymer liquid crystal alone or a mixture of a ferroelectric polymer liquid crystal and a low molecular liquid crystal. You may also use

The ferroelectric polymer liquid crystal preferably has a chiral smectic phase, more preferably a Sac
“phase, SmH” phase, Sml” phase, SmJ” phase,
In addition, as the ferroelectric polymer liquid crystal, those having main chain type, side chain type, and main chain-side chain type structures are used. Examples of ferroelectric polymer liquid crystals include polyester, polyether, polyazomethine, polythioester, polythioether, and polysiloxane.

Polyamide type, polyimide type, etc. can be used.

As the side chain type ferroelectric polymer liquid crystal, polymethacrylic, polyacrylic, polychloroacrylic, polyether, etc. can be used. The above-mentioned main chain type, side chain type, main chain-side Ta type casting dielectric polymer liquid crystal may be used alone, or polymer liquid crystal compounds of the same type or different types thereof may be used. ! The above may be mixed or copolymerized.

Next, specific examples of ferroelectric polymer liquid crystals that can be used in the present invention are shown below, but the invention is not limited thereto.

m≧5. n=4-18 m≧5 +CH2−CH+ +CH2-C11)=- the law of nature 1-2. ni = 1~2° j=0 or l.

n=4~18゜m≧5 R=1~2. k=1~2. n=4~1
8゜j=0 or 1. m≧5 1%-CH□-CH)-- Lightning 1-2. ni=1~2゜j=0 or l.

n=4~18゜m≧5 1+-CI□-CH$ y=0.1~10mm = 4~12゜n≧3 In addition, optical activity that can develop ferroelectricity by blending If polymer liquid crystal is also used, 1=1~2. ni=
1-2. n=4~18゜j=o or l, m≧5.

A specific example is shown below.

(Shoes 2 = 2~15° x+y=l) CI! .

R3= -cH, cH-+ C1 (2→-R4=-+
CH2→- (x+y=1, Meal 2=2~15) (x+y=1
．． recommendation=2~15) (X+y=l, 112=2~15) (■i=1~5) (s,=1~3.j!=1~20) (kai,=0~5) (x+y =1) (l5=0~5) (m, =o~5) (x+y=1) (■, =0~5) In the present invention, the display layer includes the ferroelectric polymer liquid crystal and the low molecular weight Is it possible to use a polymer liquid crystal composition containing a liquid crystal?As the low molecular liquid crystal, a ferroelectric liquid crystal is preferably used as it has good compatibility with a ferroelectric polymer liquid crystal. It does not need to be a ferroelectric liquid crystal as long as it does not impair the characteristics of the molecular liquid crystal. The content of low molecular liquid crystal in the mixture of ferroelectric polymer liquid crystal and low molecular liquid crystal is 1 to 99
% by weight, preferably from 5 to 50% by weight.

[Function] Generally, the speed of polarization reversal of a ferroelectric polymer liquid crystal due to the application of an electric field slows down as the viscosity of the system increases as the temperature decreases. In the display device of the present invention, this change in response speed can be suppressed within a certain range by changing the drive signal of the drive voltage, drive frequency, or both in accordance with the temperature detected by the temperature detection means of the display layer. Can be done.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 A polymer liquid crystal composition system in which 5% by weight of ferroelectric liquid crystal C3-1014 manufactured by Chisso Corporation was added to a polymer liquid crystal represented by the following structural formula (21). The temperature range showing "Sac" was 10°C to 75°C. This polymeric liquid crystal composition was rubbed with polyimide as an alignment film on a striped electrode whose gap was controlled by 1.5H bead-like spacers. Sandwiched between two treated glass substrates, 90
A uniaxially oriented cell was obtained by pressure bonding at °C and then slowly cooling to room temperature.

Next, as shown in Figure 1, a thermocouple was set on the surface of the substrate, and the indoor temperature was changed from 2o''C to 50℃.At this time, depending on the substrate surface temperature detected by the thermocouple, When the driving voltage was changed stepwise as shown in FIG. 2, stable driving was obtained, and the display contrast was not affected by temperature.

Example 2 Using the same liquid crystal display device as used in Example 1, the substrate temperature was changed from 20°C to 50°C.

Here, when the frequency of the drive signal was varied as a function of temperature as shown in FIG. 3, a good display with no unevenness was obtained as in Example 1.

[Effects of the Invention] As explained above, according to the present invention, it is possible to achieve the effect that stable driving can be performed even when the temperature of the usage environment changes and the temperature of the display layer of the display device changes. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of the display device of the present invention, FIG. 2 is a graph showing a state where the drive voltage is changed stepwise as a drive signal according to the temperature of the substrate surface, and FIG. 3 is a graph showing the surface of the substrate. 3 is a graph showing a state in which the frequency of the drive signal is changed in steps according to the temperature of the drive signal. 1, la--Substrate 2.2a--Striped electrode

Claims (1)

[Claims] A display device having a display layer made of a polymeric liquid crystal composition exhibiting ferroelectricity, characterized by having means for detecting the temperature of the display layer and means for changing a drive signal according to the detected temperature. display device.