JPH01154130A - Image forming medium - Google Patents

Abstract

PURPOSE:To increase a response speed and contrast and to form an image having good visibility with an image forming device for which a high-polymer liquid crystal is used by adding one kind of nucleus forming agent into the high-polymer liquid crystal compsn. CONSTITUTION:The high-polymer liquid crystal into which the nucleus forming agent 3 is incorporated is coated on a substrate 1 to form the high-polymer liquid crystal layer 2 which is a stable optical scattering film. The crystal nuclei of the high-polymer liquid crystal are formed around the nucleus forming agent at this time and the domains of the crystals are formed to the crystal nuclei. Namely, the size of the crystal can be selected arbitrarily by selecting the grain size, amt. of addition and kind of the nucleus forming agent. The degree of scattering can, therefore, be selected as desired in the case of forming a scattering state 301. On the other hand, the optical scattering film forms an amorphous state 302 and attains a light transmission state when said film is heated to the transparent point of this high-polymer liquid crystal or above. The contrast and response speed are thereby improved and the image having the good visibility is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an image forming medium, and particularly to an image forming medium having a polymer liquid crystal layer containing a polymer liquid crystal compound.

[Conventional technology]

Traditionally, video output from televisions and VTRs, and output from interactions with computers, have been output to display monitors such as CRTs and TN (twisted nematic) liquid crystal displays, and documents from word processors and facsimiles9.
High-definition images such as graphics have been output and displayed on paper as hard copies.

Incidentally, although a CRT outputs a beautiful image when outputting a moving image, the visibility of an image that remains stationary for a long period of time is degraded due to flicker and scan results due to insufficient resolution.

Furthermore, although conventional liquid crystal displays such as the above-mentioned TN liquid crystal have been made thinner, they still have problems such as the labor involved in manufacturing them, such as sandwiching the liquid crystal between glass substrates, and the dark screen. Ta.

Furthermore, CRTs and TN liquid crystals have drawbacks such as the fact that they do not have a stable image memory even during the output of the above-mentioned still image, and therefore the beam and pixel voltage must be constantly accessed.

On the other hand, images output on paper can be obtained as high-definition and stable memory images, but if you use a large number of them, it takes space to organize them, and it is also a waste of resources to discard large quantities. There are problems such as not being able to do so.

On the other hand, various types of information such as photographs, TV images, VTR images9 documents, and data have been increasing more and more in recent years, and various elemental technologies and systemizations for transmitting, storing, and processing this information are being developed. Among these, memories such as IC memories, magnetic tapes, and magnetic disks are generally used to store information. However, large-capacity memory is required in order to handle a huge amount of information and to store image information. It is attracting attention for its high density and large capacity.

This optical memory is generally of the ROM type or DRaW type, but currently, due to the demand for rewritable memory, image forming media using photochromic materials such as spiropyran, liquid crystal, etc. are used.

[Problems to be Solved by the Invention] In image forming media using liquid crystals used in memories, displays, etc., low-molecular liquid crystals are often used to meet requirements such as high-speed response.

However, in recent years, due to the demand for large-screen displays and the simplification of mounting liquid crystal elements, so-called polymer liquid crystal compositions such as mixed systems of polymer liquid crystal compounds and low molecular liquid crystal compounds, or polymer liquid crystal systems have been developed. Image forming media using objects are being investigated.

By using such a polymeric liquid crystal composition, it is possible to form a film by solution coating, etc., and it is possible to realize a large-area liquid crystal element and also to make the film thin.

Because the film thickness can be easily controlled, the difficulties of conventional low-molecular liquid crystals, such as controlling the gap between cell substrates, can be overcome.
It is effective in the following points.

However, in image forming media using polymeric liquid crystals, contrast is low because light scattering is not strong.
Furthermore, since the response speed is slow, there is a drawback that the visibility of the image is not good.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming medium capable of solving the above-mentioned drawbacks of the conventional example, improving response speed and contrast, and forming an image with good visibility.

[Means for Solving the Problems] The image forming medium according to the present invention includes a liquid crystal layer made of a polymeric liquid crystal composition having at least one polymeric liquid crystal compound, and at least one polymeric liquid crystal compound in the polymeric liquid crystal composition. It is characterized by containing a type of nucleating agent.

As a polymeric liquid crystal that meets the above requirements, it is best to use a material that has thermotropic liquid crystal properties and exhibits a nematic phase, a smectic phase, a cholesteric phase, or the like. Examples of this include so-called side-chain polymer liquid crystals in which low-molecular liquid crystals with main chains such as methacrylic acid polymers and siloxane polymers are added in a pendant shape, and also used in the fields of high-strength, high-elasticity, heat-resistant fibers and resins. Main chain polymer liquid crystals such as polyester-based or polyamide-based liquid crystals are used.

Furthermore, a polymer liquid crystal having a phase exhibiting SmC. and exhibiting ferroelectricity by introducing asymmetric carbon into the polymer liquid crystal may also be preferably used.

[Function] The basic structure of the present invention will be explained in more detail below using a liquid crystal represented by the following structural formula (I) as one specific example of a polymer liquid crystal.

HH OHH0 %w = 9,000 to 10,000 The polymer liquid crystal was dissolved in dichloroethane, and this was applied with an applicator onto a polyester transparent substrate that had been washed with alcohol.

Thereafter, when it was left in an atmosphere of 95° C. for 10 minutes, a white scattering film was formed. This film thickness is wt% of polymer liquid crystal.
When is 2θ%, a value of just over 10 pm has been obtained.

When the thus obtained white sheet was scanned with a thermal head, the transparent portion was fixed according to the 9-character graphic pattern. When this sheet is placed on a black background, a clear display of black on a white background is obtained.

Furthermore, when the sheet was introduced onto a normal overhead projector, a clear negative projected image was obtained in which the characters and pattern portions were projected in white.

Next, the entire surface of the sheet on which the above pattern was recorded is
When heated to ℃ and then kept at about 90℃ for a few seconds,
The entire surface returned to its original white scattering state, and it remained stable even if returned to room temperature, and was recorded again.

The display has been made.

The above phenomenon is caused by the film state below the glass transition point in which the polymer liquid crystal maintains a stable memory state, the liquid crystal film state in which it can substantially transition to an optical scattering state, and the film state at which the polymer liquid crystal maintains a stable memory state; It can be controlled because it can take three states of isotropic film states, which are arrays.

When an image forming medium using polymeric liquid crystal is used for display, there is no flicker for images that remain stationary for a long time, and not only does it have high resolution and good visibility, but its memory property allows it to be used for long periods of time. It is possible to provide stable images. Furthermore, by using the optical scattering state, it is not only possible to use a blank background, that is, as an output display medium like paper, but also to use it as a green color, so it is not possible to dispose of it in large quantities like paper. It has no advantages.

On the other hand, image forming media using polymeric liquid crystals have a large memory capacity, are rewritable, and can maintain a stable memory state below the glass transition point. .

In addition to the above-mentioned characteristics, an image forming medium using the polymer liquid crystal is desired to have an increased contrast. For example, as a display medium, an increase in the difference between transparency and scattering (white state) is desirable for high visibility. It becomes an important point of gender.

Furthermore, in a memory, the presence or absence of a bit is detected by the difference in optical density, so it is desired to increase the difference in optical density. This not only simplifies reading of the presence or absence of a bit, but also provides the advantage of being able to perform error-free and stable reading.

Furthermore, from the viewpoint of high-speed display, high-speed recording/reproducing, and erasing, it is also desired to improve the response speed.

[Examples] Hereinafter, the present invention will be explained in detail by giving Examples, but the present invention is not limited thereto.

Example 1 FIG. 1 is a schematic cross-sectional view of an image forming medium in which a polymeric liquid crystal containing a nucleating agent is coated on a substrate. The substrate 1 is PET (polyethylene terephthalate) with a thickness of 100 IL. A solution prepared by dissolving the polymeric liquid crystal represented by the structural formula (I) in dichloroethane and mixing the nucleating agent 3 (titanium oxide fine particle powder) is applied to the substrate. At this time,
The polymer liquid crystal concentration is 20 wt% based on the total weight.

In addition, the amount of nucleating agent added should be within the range that does not adversely affect the coating, and should be 0.01 wt% to 25 wt% based on the amount of polymer liquid crystal.
wt% is desirable.

As the application means, a method using a spin cord, dipping, a wire bar, an applicator, or a printing means such as a screen can be used.

In this way, the solution is applied to the substrate, and the liquid crystal temperature (80 to 80
By keeping the temperature constant (100° C.), a polymer liquid crystal layer 2, which is a stable optical scattering film, is formed.

Here, the action of the nucleating agent will be explained in detail.

A nucleating agent (or nucleating agent) is a substance added to increase the number of crystal nuclei. As mentioned above, in the process of volatilizing the solvent in the prepared solution, or in the process of keeping the solvent at the liquid crystal temperature for a certain period of time after volatilization, crystal nuclei of polymer liquid crystal are formed around the nucleating agent, and the crystals are domains are formed. In other words, by selecting one kind of particle size and addition amount of the nucleating agent, the crystal size can be arbitrarily selected. Therefore, when forming a scattering state, the degree of scattering can be freely selected.

On the other hand, the optical scattering film formed as described above forms an amorphous card 8 (isotropic FC) by heating it above the Tcjl (clearing point) of the polymer liquid crystal.

This amorphous state becomes a light transmitting state. In FIG. 1, arrows represent light, a region 301 represents a scattering state, and a region 302 represents an amorphous state.

Further, after heating, the transparent state is maintained by rapidly cooling the liquid crystal to a temperature below the Tg (glass transition temperature) of the polymer liquid crystal.

After further heating to Tc1) or above, by holding and cooling at the liquid crystal temperature, a scattering state is formed again, and 7g
The scattering state is fixed in the following. In this case, the nucleating agent not only forms a strong scattering state but also promotes crystal growth, so it has advantages such as being able to form the scattering state more quickly than in the case without the nucleating agent.

Example 2 In the same imaging medium as in Example 1, phosphoric acid-2,2-methylenebis(2,6-sheeter) was used as a nucleating agent.
t-butylphenyl) sodium (trade name MARK N
A-11, Adeka Argus Chemical ■) and MARK NA
-10 (Adeka Argus Chemical ■) was used.

When this is used, the polymeric liquid crystal and the nucleating agent are dissolved simultaneously in the solution. Thereafter, in the process of volatilizing the solvent in the solution, or in the process of keeping the solvent at the liquid crystal temperature for a certain period of time after volatilization, the nucleating agent first precipitates. Thereafter, polymer liquid crystal crystal nuclei are formed around the nucleating agent, crystals grow on the crystal nuclei, and crystal domains are formed.

In order for the nucleating agent to precipitate before the polymeric liquid crystal, it is desirable that the temperature at which the nucleating agent dissolves is higher than the Tg of the polymeric liquid crystal, and more optimally higher than the Tc.

FIG. 2 is a schematic cross-sectional view similar to FIG. A quality state (region 304 in FIG. 2) or a scattering state (region 303 in FIG. 2) can be selectively formed. Also,
Since the nucleating agent of this example does not scatter like the titanium oxide particles in an amorphous state, the transparency is increased and the contrast is further increased.

In the above embodiments, PET and polyethylene terephthalate were used as the substrate, but resins such as polyimide or resin films, glass, metals such as aluminum, alloys, etc. may also be used, and the substrates are transparent to light. It may also be a reflective substrate or may be colored black or the like.

Further, although the thickness of the base body was set to 100Ji in the above description, it is not limited to this.

A large number of polymer liquid crystals that can be used in the present invention can be synthesized in addition to those shown in the above structural formula.

Several other examples are listed below, but the invention is not limited to these.

(CH2-CH) n ■ CH3 ■ (CH2-C) n ■ (SIll) In addition to the above-mentioned dichloroethane, DMF, cyclohexane, etc., solvents for coating and forming these films may be used.
Tetrahydrofuran (THF), acetone, ethanol, other polar or non-polar solvents, or mixed solvents thereof are used, and these solvents are determined by their solubility with the polymer liquid crystal used and the material or surface of the substrate to which they are coated. It goes without saying that the choice can be made depending on factors such as wettability with the provided surface layer and film formability, and the degree of flexibility of the polymeric liquid crystal and the nucleating agent is not limited to the above description.

Further, as the nucleating agent, titanium oxide and specific trade names such as MARK HA-11 and MARK NA-10 are mentioned, but in addition, fine particles of inorganic substances and organic substances can be used. Particularly preferably, salts such as phosphates are typically used. Further, a plurality of nucleating agents may be used.

Further, the imaging medium is coated on a substrate,
After the solvent evaporates, the substrate may be removed to form a single layer structure, or a protective layer may be provided to protect the surface of the polymeric liquid crystal layer from scratches and the like.

Note that as a means for heating the image forming medium, a heating resistor, infrared rays, etc. can be used, but in particular, in order to form an image pattern or a memory bit pattern, a thermal head capable of applying heat by an external signal is used. Alternatively, means such as adding an infrared absorbing dye or the like to the polymer liquid crystal layer and writing with a laser can be used.

[Effects of the Invention] As explained above, in an image forming medium using a polymer liquid crystal, by adding at least one kind of nucleating agent to the polymer liquid crystal composition, strong scattering can be obtained, and thermal signal application can be improved. When forming an image using this method, an image with high contrast can be obtained.

Further, in the crystal growth process of polymer liquid crystal, the nucleating agent promotes crystal growth, so that the thermal response speed can be increased.

As described above, the present invention can provide an image forming medium that can improve contrast and response speed and form an image with good visibility.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of the image forming medium of the present invention, and FIG. 2 is a schematic sectional view of the image forming medium in Example 2. 2: a polymer liquid crystal layer; 3: a nucleating agent.

Claims (1)

[Claims] (1) An image forming medium characterized by containing at least one type of nucleating agent in a polymeric liquid crystal composition having at least one type of polymeric liquid crystal compound.