JPH01154129A - Image forming medium - Google Patents

Abstract

PURPOSE:To intensify the scattering of light and to increase contrast so that an image having good visibility is obtd. with an image forming medium for which a high-polymer liquid crystal 1 is used by adding one kind of fluorescent agent into the high-polymer liquid crystal compsn. CONSTITUTION:The high-polymer liquid crystal into which the fluorescent 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 light projected to the high-polymer liquid crystal layer 2 is absorbed by the fluorescent brightening dye 3 in a scattering state 301 and the light having the wavelength longer than the wavelength of the absorbed light is emitted. The light which is not absorbed is scattered to form the scattered light. Namely, not only the scattered light but the individual fluorescent brightening dyes 3 emit light to improve the efficiency of scattering in the scattering state. On the other hand, the optical scattering film forms an amorphous state 302 and acts to transmit or scatter the light when said film is heated to the transparent point of the high-polymer liquid crystal or above. The scattering of the light is thereby intensified and the contrast is improved by the emitted light. The image having the good visibility is thus 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.

[Prior Art] Conventionally, video output from a television or VTR or output from interaction with a computer is displayed on a display monitor such as a CRT or TN (twisted nematic) liquid crystal display, and is also displayed on a word processor, facsimile, etc. High-definition images such as document 9 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 achieved thinner devices, they have had problems such as the labor involved in manufacturing them, such as sandwiching the liquid crystal between glass substrates, and the screen being dark. .

Furthermore, CRTs and TN liquid crystals have drawbacks such as the fact that they do not have a stable image memory even while outputting the above-mentioned still image, so 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 images,9 documents, and data have been increasing in recent years, and various elemental technologies and systems 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 for information storage. However, large-capacity memory is required in order to handle huge amounts of information and to store image information, and from this point of view, high-density memory is required, especially in optical memories, such as optical cards, optical disks, and optical tapes. , is attracting attention because of its large capacity.

ROM type and DRaW type optical memories are common, but due to the current demand for rewritable memories, image forming media using photochromic materials such as spiropyran and liquid crystals are being used. It is being said.

[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, mixed systems of high-molecular liquid crystal compounds and low-molecular liquid crystal compounds have been developed.

Alternatively, image forming media using so-called polymer liquid crystal compositions, such as polymer liquid crystal systems, 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 of the liquid crystal element, and it is easy to reduce the film thickness and control the film thickness. This method is effective in that it solves problems such as gap control between cell substrates, which has conventionally been done with low-molecular-weight liquid crystals.

However, image forming media using polymeric liquid crystals do not have strong light scattering, resulting in low contrast and poor image visibility. Another object of the present invention is to provide an image forming medium that can improve contrast by emitting light and form 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 different kinds of fluorescent agents.

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 1) so-called side-chain polymer liquid crystals in which low-molecular liquid crystals with main chains of methacrylic acid polymers, siloxane polymers, etc. Main chain polymer liquid crystals such as polyester-based or polyamide-based liquid crystals are used. In addition, discotic liquid crystals and the like may also be used.

Furthermore, by introducing asymmetric carbon into the polymer liquid crystal, 5rsC"
A polymer liquid crystal having a phase exhibiting ferroelectricity can also be preferably used.

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

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

Thereafter, when it was left in a 95°C atmosphere for 10 minutes, a white scattering film was formed. This film thickness was over 10 gm when the weight percent of the polymer liquid crystal was 20%.

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 was introduced onto a black background, a clear black display on a white background was obtained.

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

Next, the entire surface of the sheet on which the above pattern was recorded is
When heated to 90°C and then held at approximately 90°C 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 occurs in a film state below the glass transition point in which the polymeric liquid crystal maintains a stable memory state, in a liquid crystal film state in which it can substantially transition to an optically scattering state, and in a film state in which the polymer liquid crystal maintains a stable memory state; It can be controlled because it can take three isotropic film states.

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 an optical scattering state, not only can it be used as an output display medium like white paper, but it can also be used repeatedly, so there is no need to discard large quantities like paper. It has 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 temperature.

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.

[Example] Hereinafter, the present invention will be explained in detail with reference to an example, 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 fluorescent agent (fluorescent whitening dye) is coated on a substrate. The substrate 1 is made of PET (polyethylene terephthalate) having a thickness of 100 JLII.A solution in which the liquid crystal polymer shown in the structural formula (I) is dissolved in dichloroethane and the fluorescent agent 3 is mixed therein is applied to the substrate. At this time, the polymer liquid crystal concentration is preferably 10 to 20 wt% based on the total weight. In addition, the amount of fluorescent whitening dye added should be within the range that does not adversely affect the coating, and should be 0.01% relative to the amount of polymer liquid crystal.
Wt% to 25wt% is desirable.

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

In this way, the solution is applied to the substrate, and the liquid crystal temperature (80 to 80
By maintaining the temperature at 110° C. for a certain period of time, a polymer liquid crystal layer 2, which is a stable optical scattering film, is formed. Here, to describe the fluorescent whitening dye 3 in detail, the fluorescent whitening dye 3 includes stilbene type, diaminodiphenyl type, imidazole, imidasilone, triazole type, thiazole,
Oxazole type, coumarin, carbostyryl type, naphthalimide type, etc. can be used. Fluorescent whitening dye 3
is contained in an amount of 0.01 to 10 wt% based on the total weight.

In the scattering state 301, the light irradiated onto the polymer liquid crystal layer (arrow in the figure) is absorbed by the fluorescent whitening dye 3 and emits light with a longer wavelength than the absorbed light, and the unabsorbed light is scattered and becomes scattered light. becomes. That is, in the scattering state, not only the scattered light but also the individual fluorescent whitening dyes 3 emit light, improving the scattering efficiency.

On the other hand, the optical scattering film formed as described above forms an amorphous state (isotropic state) 302 by heating above the Tcj) (clearing point) of the polymer liquid crystal. This amorphous state is transparent to light. Also, 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 higher, the temperature is maintained at the liquid crystal temperature.
By cooling, a scattering state is formed again, and the scattering state is fixed at 7 g or less.

In the transparent state, light is transmitted or absorbed by the fluorescent whitening dye and emits light. This emission passes through the transparent state. Furthermore, the light that has traveled through the layer is scattered at the boundary with the scattering state, so the amount of light increases especially at the boundary.
The transparent/scattering boundary becomes clear.

Example 2 A fluorescent whitening pigment as an additive was added to a polymeric liquid crystal in the same manner as in Example 1 to form an optical scattering film. As fluorescent whitening pigments, the various dyes shown in the above examples can be used as acrylic,
It is dissolved in a resin such as vinyl chloride, alkyd, urea, melamine, penzoquanamine, etc., and made into a fine powder with a particle size of 1 pm or less. When the L pigment is used, as in Example 1, scattering is increased due to light emission, and contrast is not only improved, but also the pigment itself can provide a light scattering effect, resulting in an even higher contrast.

In Example 1, PET (polyethylene terephthalate) was 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 substrate is transparent to light. It may be a reflective substrate, or it may be colored black or the like. Although the thickness is 100 p and 100 m, the thickness is not limited to this.

A large number of polymeric liquid crystals that can be used in the present invention can be synthesized in addition to those shown in the structural formula (I).

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

(CH2-CH)n ■? H3 4CH2-C)n In addition to the above-mentioned digloroethane, INF, cyclohexane, etc., solvents for coating and forming these films include
Tetrahydrofuran (THF), acetone, ethanol, other polar or non-polar solvents, or mixed solvents of these are used, and these vary depending on their solubility with the polymer liquid crystal used and the material or surface of the substrate to which it is coated. Needless to say, the material may be selected depending on factors such as wettability with the surface layer provided on the surface layer and film formability.

Furthermore, as fluorescent agents, fluorescent whitening dyes and pigments were mentioned, but
It is not limited to these as long as it has the same effect as above. Also, multiple types of fluorescent agents may be used. Furthermore, a nucleating agent or the like can be added at the same time to adjust the scattering state. Further, the layer containing the fluorescent agent may be provided as a separate thin layer.

Types and particle sizes of the fluorescent whitening dye and pigment particles.

The weight ratio and the like are determined by conditions such as the brightness of the light source, the emission wavelength, the arrangement, and the distance between the light source and the image forming medium.

Further, it is preferable that the light source includes not only visible light but also ultraviolet light for irradiation.

This can increase the effect of the fluorescent agent.

Further, although the image forming medium is coated on a substrate, the substrate may be removed after the solvent evaporates to form a single layer structure. Further, a protective layer may be provided to protect the surface of the polymer 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 type of fluorescent agent to the polymer liquid crystal composition, light scattering is strengthened and the light scattering is enhanced. The contrast can be improved by emitting light, and it becomes possible to form an image with good visibility.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an image forming medium of the present invention. 1: Substrate, 2: Polymer liquid crystal layer, 3: Fluorescent agent.

Claims (1)

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