JPH1130835A - Image recording medium, image forming method on recording medium and erasing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image recording medium formed by using a photochromic material which allows repetitive recording and erasing, has high resolution, is capable of making gradation expressing and has excellent self-holdability. SOLUTION: This recording medium is a sheet-like member constituted by successively forming a high-polymer liquid crystal layer 12a and a high-polymer liquid crystal layer 12b on a base 11. The respective high-polymer liquid crystal layers 12 are constituted to include a photochromic compd. The photochromic compd. is subjected to simultaneously to heating by heating means (heating elements 22 to 24) to the temp. above the glass transition temp. of the high- polymer liquid crystals and exposure of light of a first wavelength region, by which the respective high-polymer liquid crystal layers 12 are subjected to isomerization (a trans body to a cis body) or are selectively changed from the cis body to the trans body at need. Optical changes are thus induced with respect to the heating regions of the respective high-polymer liquid crystal layers 12 and image forming is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image recording medium capable of recording and erasing an image by exposure and heating.

[0002]

2. Description of the Related Art In recent years, rewritable marking technology has been actively researched as a hard copy technology instead of paper for reasons such as protection of the global environment such as protection of forest resources and improvement of office environment such as space saving. In particular, research on rewritable marking technology utilizing chemical change triggered by heating is actively pursued, such as leuco dye / amphoteric color reducing agent system, leuco dye / developer / polar organic compound system, leuco dye / long chain alkyl. Recording media using a color-reducing agent system or the like as a material have been proposed. Image formation on a recording medium using these leuco dyes is a chemical change type utilizing a color change caused by opening and closing of the lactone ring, and it is currently impossible to achieve both high black-and-white contrast and image maintainability. Have difficulty.

[0003] On the other hand, the use of a physical change type image formation in which the maintenance of an image is relatively easy to obtain is a polymer / polymer.
A recording medium using a long-chain alkyl low molecular weight system, a polymer blend system, a polymer liquid crystal system, or the like as a material has been proposed. The polymer / long-chain alkyl low-molecular-weight system controls light scattering by changing the internal voids according to the heating temperature. The polymer blend system controls the light scattering by changing the microphase separation state according to the cooling rate. It is a method to do. Further, the polymer liquid crystal system is a method of controlling light scattering by changing crystallinity mainly by a cooling rate. However, these methods of controlling the light scattering properties easily maintain the image, but have a low contrast and the application range of the product is limited.

Therefore, in addition to these techniques, a rewritable information recording technique using a photoisomerization reaction of an azobenzene derivative or the like has been proposed. Azobenzene derivatives are
Generally, the colorless trans-form is stable, but is irradiated to light of a specific wavelength in the ultraviolet region to isomerize into a cis-form having an absorption peak in blue. Such a phenomenon generally called photochromism has been known for a long time,
High energy efficiency during writing and erasing, high-density / high-resolution recording by not being affected by heat conduction, and elimination of thermal degradation of the base material by not passing through high-temperature conditions are utilized. Expected.

However, in the optical recording using the conventional photochromic material, the reading wavelength coincides with the erasing wavelength, so that the recording deteriorates within several to several tens of times of reproduction. There is a known problem that a record is erased when left under office lighting for one day or less. To solve such a problem,
In the invention disclosed in JP-A-109245, a cholesteric liquid crystal is provided with a photochromic function, and deterioration of recording is prevented by reading out a change in the selective reflection characteristic of the cholesteric liquid crystal in a wavelength region different from the erasing wavelength region of photochromism. .

Further, in the invention disclosed in Japanese Patent Application Laid-Open No. 64-88935, the recording information is stabilized by using a recording layer in which a liquid crystal having a photochromic function is encapsulated in microcapsules. JP-A-3-
In the invention described in 276127, a photoresponsive film in which a liquid crystal and an azobenzene derivative are dispersed in a polymer medium is disclosed.

That is, in the case where a sheet-shaped recording medium is formed by using photochromism due to a chemical change triggered by light as described above, a stable self-holding property for realizing the sheet-shaped form and under office lighting. There is a need for recording stability that allows long-term record keeping even if left unattended, visually necessary and sufficient display resolution, and a recording / erasing device that can use a general power supply in offices.

[0008]

However, although the above-described recording medium is stabilized so that recording can be held for a long time, it is presumed that the recording medium is used in a light-shielded housing. However, there is a problem in that it is extremely unstable under indoor lighting including blue wavelength light as erasing light.

When a semiconductor laser is used as an exposure light source to obtain a recording resolution, the quantum efficiency of photochemical reaction is low in addition to the low energy efficiency of light emission. However, there is a problem that the recording efficiency becomes extremely low for use as a hard copy due to low energy efficiency, or the apparatus and power consumption increase.

In addition, the above-mentioned recording medium can handle only binary information recording, and cannot realize functions such as gradation expression and color reproduction required for hard copy. Was. Furthermore, stable self-holding properties for realizing a sheet-like form were not sufficient.

The present invention has been made in view of the above circumstances, eliminates the drawbacks of a recording medium using a photochromic material, enables efficient recording with a small device, and enables high-resolution gradation expression and color reproduction. It is an object of the present invention to provide an image recording medium using a photochromic material which can be repeatedly recorded and erased and has excellent self-holding properties.
It is another object of the present invention to provide a method for forming and erasing an image on an image recording medium using a photochromic material.

[0012]

In order to achieve the above object, an image recording medium according to the present invention is a sheet-like member formed by forming a polymer liquid crystal film and forming a thin film liquid crystal liquid layer on a support. And is characterized by including the following configuration. The polymer liquid crystal layer includes a photochromic compound. The photochromic compound is configured to be isomerized by heating the polymer liquid crystal to a temperature equal to or higher than the glass transition point of the polymer liquid crystal by a heating unit and exposing to light in a first wavelength range. Then, an image is formed by causing an optical change in the polymer liquid crystal layer due to the isomerization of the photochromic compound. The light in the first wavelength range changes the molecule of the photochromic compound from a shape closer to a straight line to a shape far away from the straight line by performing exposure.

The photochromic compound preferably contains a chiral agent. This is to achieve excellent contrast in image formation. The polymer liquid crystal layer preferably has a configuration including a plurality of polymer liquid crystals having different glass transition points. This makes it possible to perform multicolor display.

The support used in the image recording medium of the present invention is a sheet-like object that can be used in the form of a hard copy.

[0015] The photochromic compound contained in the polymer liquid crystal layer refers to isomerization, ring opening,
It indicates at least one reaction among reversible chemical changes such as ring closure and association, and changes the physical properties such as the phase change temperature and the helical pitch of the polymer liquid crystal by this chemical change.

The polymer liquid crystal constituting the polymer liquid crystal layer is as follows.
A main-chain type polymer liquid crystal or a side-chain type polymer liquid crystal in which a mesogen group expresses a function of a liquid crystal is preferably used, but is not limited thereto. The polymer liquid crystal may have functions such as a photochromic compound and a chiral agent by itself, or may not have such a function. A situation arises that requires the addition of Further, it is desirable that the molecular weight of the polymer liquid crystal is as large as possible in order to secure stable self-holding property.

The chiral agent used in the present invention is an optically active substance capable of inducing a cholesteric phase when added to a substance exhibiting nematic liquid crystal properties as a single substance or as a mixture. An optically active substance, whether it is liquid crystal itself or not liquid crystal,
When added to the nematic phase, a cholesteric phase having a twisted structure can be produced.

The glass transition point of the polymer liquid crystal used in the present invention means that the behavior of the polymer liquid crystal typified by the main-chain polymer liquid crystal and the side-chain polymer liquid crystal is from solid to liquid. A temperature that changes to something or vice versa. At a temperature higher than the glass transition temperature, the liquid crystal polymer behaves like a liquid. Therefore, the orientation of the molecules of the liquid crystal is quickly changed by applying a relatively weak electric field. On the other hand, at a temperature lower than the glass transition point, the polymer liquid crystal behaves like a solid, and its molecular orientation hardly changes even when a relatively strong electric field is applied.

As a method of preparing a plurality of polymer liquid crystals having different glass transition points, there are a method of adjusting the rigidity of the main chain of the polymer liquid crystal, a method of utilizing a difference in the degree of polymerization, and a method of preparing a non-liquid crystalline monomer. Copolymerization, copolymerization of a plurality of types of polymer liquid crystal precursors, addition of a non-polymerizable liquid crystal component, addition of a non-polymerizable non-liquid crystal component, and the like can be used.

Further, the image forming method of the present invention is characterized in that the following procedure is performed on a recording medium having a polymer liquid crystal layer containing a photochromic compound formed on a support. A first wavelength band light that heats the polymer liquid crystal in the polymer liquid crystal layer to a temperature equal to or higher than the glass transition point and changes the molecules of the photochromic compound from a shape closer to a straight line to a shape far away from a straight line. Exposure is performed. Thus, the photochromic compound is isomerized, and the isomerization causes an optical change in the polymer liquid crystal layer to form an image on a recording medium.

In the image erasing method of the present invention, in a recording medium having a polymer liquid crystal layer containing a photochromic compound formed on a support, the photochromic compound is isomerized to cause an optical change in the polymer liquid crystal layer. It is characterized by performing the following procedure on an image formed by raising the image. Exposure is performed with light in a second wavelength range that changes the molecules of the photochromic compound from a shape far from a straight line to a shape close to a straight line. Simultaneously with this exposure, the polymer liquid crystal is heated to a temperature higher than the glass transition point. The image is erased by these exposure and heating.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. In the image recording medium according to the present invention, as shown in FIG. 1, a thin film polymer liquid crystal layer 2 is formed by depositing a polymer liquid crystal on a support 1 composed of a transparent member, and further protecting the film. It is composed of a sheet-like member provided with the layer 3. The polymer liquid crystal layer 2 is composed of a photochromic compound containing a chiral agent. This photochromic compound is heated to a temperature equal to or higher than the glass transition point of the polymer liquid crystal by a heating resistor (heating means such as a thermal head) (not shown) which is in close contact with the polymer liquid crystal layer 2;
Simultaneous exposure with light of a desired wavelength from the lower surface of the support plate 1 causes isomerization of a portion (the heated region) of the polymer liquid crystal layer 2, which causes a change in molecular orientation, and This is to form an image by causing an optical change in the heated area.

The photochromic compound contained in the polymer liquid crystal layer 2 exhibits at least one reaction of reversible chemical changes such as isomerization, ring opening, ring closing, and association by absorbing light. It is to change physical properties such as phase change temperature and helical pitch of polymer liquid crystal by chemical change. More specifically, examples include compounds having a skeleton such as azobenzene, stilbene, indigo, thioindigo, spiropyran, spirooxazine, fulgide, anthracene, and cinnamic acid. Among these, the geometry of the molecular skeleton changes significantly before and after the chemical change,
Compounds containing a skeleton such as azobenzene, stilbene, and thioindigo, which can relatively greatly change the phase change temperature, helical pitch, refractive index anisotropy, and the like of the polymer liquid crystal, are particularly preferable. These photochromic compounds are
Either a substance that exhibits the properties of a liquid crystal by itself or a substance that exhibits liquid crystallinity when mixed with a substance that exhibits liquid crystallinity may be used. It is preferable that the substance exhibit properties.

The polymer liquid crystal is preferably, but not limited to, a main-chain polymer liquid crystal or a side-chain polymer liquid crystal in which a mesogen group exhibits the function of a liquid crystal. More specifically, the main-chain polymer liquid crystal is a relatively rigid and highly anisotropic linear atomic group consisting of a mesogen group itself or a mesogenic group and a flexible atomic group alternately formed in a linear form. Is a polymer bound to Side-chain polymer liquid crystal is a liquid crystal in which a side chain consisting of a highly rigid mesogen group is bonded directly to the main chain consisting of flexible atomic groups or through a flexible atomic group. is there. The same mesogen group as the atomic group forming the central skeleton of the low-molecular liquid crystal is used.

Suitable atomic groups for the mesogen group include benzylideneaniline, azobenzene, azoxybenzene,
Examples include, but are not limited to, stilbene, phenylbenzoate, benzoylaniline, biphenyl, benzylideneacetophenone, benzylideneazine and the like. Of these, azobenzene, stilbene, and the like, which can be a photochromic compound, are particularly preferred. As the highly flexible atomic group, an alkyl chain, an oxyethylene chain, a siloxane copolymer chain and the like are suitable, but not limited thereto.

The support 1 is a sheet-like object that can be used in the form of a hard copy. Specifically, polyethylene, polyether sulfone, polystyrene, wood-based /
A film made of a non-wood-based cellulose resin or the like, wood paper, non-wood paper, synthetic paper, or the like can be used. These materials may form a support as a single substance or may be laminated to form a support. When recording with a thermal head, wood paper, non-wood paper, synthetic paper, etc., whose surface is not smooth, have an undercoat layer between the polymer liquid crystal layer 2 and the support 1 for smoothing the support surface. This is desirable to increase the efficiency of heat transfer required for recording.

The protective layer 3 is for protecting the surface of the display section of the polymer liquid crystal layer 2 and is preferably made of a silicone resin or a fluorine-containing resin because good properties can be obtained. In order to improve the critical surface energy, it is preferable to mix a silicone-based low molecular substance or a powder of a fluorinated resin. The content of these powders is preferably 20% by weight or less, more preferably
It is in the range of 1% to 10% by weight. The thickness of the protective layer is preferably in the range of 0.1 μm to 20 μm, particularly preferably in the range of 0.3 μm to 2 μm.

The chiral agent used in the present invention is specifically a substance containing at least one asymmetric carbon. Securing compatibility with the polymer liquid crystal and using a photochromic compound are requirements for obtaining a highly uniform image.
That is, when the photochromic compound is a chiral agent, excellent contrast can be achieved. Specifically, it is particularly desirable to introduce asymmetric carbon into a molecule having an atomic group such as azobenzene or stilbene to form a photochromic compound.

More specifically, A- (CH ₂ ) nC * HC
_{H 3 Et, A- (CH 2} ) nC * HCH 3 Et, A-O
(CH ₂ ) nC * HCH ₃ Et, A-OCOC * HCH ₃
OR, A-OC * HCH ₃ R, A-OCH ₂ C * HCH
₃ CH ₂ OCOR, A-CH ₂ C * HCH ₃ OCOR,
A-COOC * HCH ₃ R, A-OCOC * HCH ₃ E
t, A-OCH ₂ C * HCH ₃ OR, A-OCH ₂ C *
HCH ₃ OCOR, A-OCH ₂ C * HFR and the like (A is an atomic group such as azobenzene and stilbene).

For example, when an azobenzene derivative is used as the photochromic material, a shape close to a straight line is a trans form, and a shape far away from the straight form is a cis form. At this time, the wavelength of the first light used in the present invention is about 360 nm, which can be generated by a commercially available black lamp or the like. Second
Has a wavelength of about 420 nm and can be generated by a commercially available germicidal lamp or the like.

Therefore, since a light source having high energy efficiency such as a fluorescent lamp can be used instead of a light source having low energy efficiency such as a light source for exposure, image formation having high energy efficiency for recording and a high recording speed is possible. Becomes possible.

The glass transition point of the polymer liquid crystal used in the present invention is desirably between 80 and 150 ° C. in order to utilize a thermal head used for thermal recording and thermal transfer recording.

Next, a more specific process of recording and erasing an image on an image recording medium will be described with reference to FIG. An image recording medium 10 is formed by sequentially laminating a first polymer liquid crystal layer 12a and a second polymer liquid crystal layer 12b on a transparent support 11. Each polymer liquid crystal layer 12
Contains a side chain type polymer liquid crystal and a chiral agent containing an azobenzene atomic group as a photochromic structure. The first polymer liquid crystal layer 12a has a glass transition point Tg1 of about 13
At 0 ° C., the selective reflection wavelength λ1 is 600 nm, and the second polymer liquid crystal layer 12b has a glass transition point Tg2 of about 90 ° C. and a selective reflection wavelength λ2 of 480 nm (FIG. 2A).

The heating means 20 for heating the image recording medium 10 has a heating head in which a first heating element 22, a second heating element 23 and a third heating element 24 are formed on a substrate 21. ing. Each heating element of the heating means 20 can be arranged in close contact with the surface of the second polymer liquid crystal layer 12b of the image recording medium 10. In this heating means 20, the first heating element 22 and the second heating element 23
C., and each heating element is brought into close contact with the image recording medium 10 and, at the same time, light 31 having a wavelength of 360 nm is
(FIG. 2B).

First heating element 22 and second heating element 23
In the first heating area 41 and the second heating area 42 to which the liquid crystal molecules are adhered, the first polymer liquid crystal layer 12a and the second polymer liquid crystal layer 12b reach a temperature equal to or higher than the glass transition point, and the molecules are easily aligned. Become. At the same time, the light having a wavelength of 360 nm changes the azobenzene atomic group from a trans form in the initial state to a cis form. As a result, the function of the chiral agent containing azobenzene is weakened, and the first heating region 41 and the second heating region 42 lose selective reflection (FIG. 2C).

On the other hand, in the third heating region 43 where the heating by the third heating element 24 is not performed, the temperature of each polymer liquid crystal layer 12 is lower than the glass transition point, so that the steric hindrance of the molecules causes The trans-isomerization reaction of the azobenzene group hardly occurs, and therefore, the molecular orientation of the liquid crystal polymer does not change. Therefore, in the third heating region 43 of the polymer liquid crystal layer 12, both the first polymer liquid crystal layer 12a and the second polymer liquid crystal layer 12b maintain selective reflection (FIG. 2C).

Next, in the heating head, the second heating element 2
3 is heated to 100 ° C., and the heating element 23 is brought into close contact with the image recording medium. At the same time, light 32 having a wavelength of 460 nm is irradiated from the side of the image recording medium 10 opposite to the heating means (FIG.
(D)). In the second heating region 42, the temperature of the first polymer liquid crystal layer 12a is equal to or higher than the glass transition point, and the molecules are easily aligned. At the same time, the azobenzene atomic group changes from a cis form to a trans form by the light 32 having a wavelength of 460 nm. As a result, the function of the chiral agent containing azobenzene is strengthened, and the second heating region 42 is connected to the first polymer liquid crystal layer 12.
Selective reflection is obtained again only for the portion a (FIG. 2 (e)).

On the other hand, in the first heating region 41 and the third heating region 43, since the polymer liquid crystal layer 12 passes only at a temperature lower than the glass transition point, the wavelength 460
Even when the light 32 of nm is irradiated, the state does not change (FIG. 2E).

Next, the third heating element 2 in the heating head
4 is heated to 100 ° C., and the heating element 24 is moved to the image recording medium 10.
At the same time, light 33 having a wavelength of 360 nm is irradiated from the side of the image recording medium 10 opposite to the heating means (FIG. 2).
(F)). In the third heating region 43, the temperature of the second polymer liquid crystal layer 12b is equal to or higher than the glass transition point, and the molecules are easily aligned. At the same time, the light 33 having a wavelength of 360 nm changes the azobenzene atomic group from a trans form to a cis form. As a result, the function of the chiral agent containing azobenzene is weakened, and the third heating region 43 becomes the second polymer liquid crystal layer 12.
Only the portion b loses selective reflection (FIG. 2 (g)).

On the other hand, in the first heating area 41 and the second heating area 42, since the polymer liquid crystal layers only pass through the temperature below the glass transition point, the wavelength is 360 nm.
No change occurs even when the light 33 is irradiated (FIG. 2 (g)).

Therefore, by subjecting each part of the image recording medium 10 to the above-described heating and exposing processes, the first heating area 41 is finally selectively reflected by the polymer liquid crystal layers 12a and 12b. None (colorless),
The second heating region 42 is in a state where only the first polymer liquid crystal layer 12a is selectively reflected (color of the selectively reflected light of the first polymer liquid crystal layer 12a), and the third heating region 43 is a second polymer liquid crystal. Liquid crystal layer 1
2b is selectively reflected (second polymer liquid crystal layer 12a
Of the selectively reflected light). The selective reflection wavelength λ1 in the first polymer liquid crystal layer 12a is 600 nm.
(The color of the selective reflection light is red), and the selective reflection wavelength λ2 in the second polymer liquid crystal layer 12b is set to 480 nm (the color of the selective reflection light is blue). A color and a colorless state (three states) can be expressed, and a state in which the polymer liquid crystal layers 12a and 12b are both selectively reflected (a color in which the colors of the selectively reflected light of the polymer liquid crystal layers 12a and 12b overlap) ) (Background color), the image recording medium can display four colors, and can record multicolor images.

[0042]

Next, embodiments of the image recording medium according to the present invention will be described. (Embodiment 1) A first embodiment of an image recording medium will be described with reference to FIG. As a mesogenic monomer,
20 parts by weight of 4-methacrylohexyloxy 4′-cyanobiphenyl, 2 parts by weight of 4-methacrylohexyloxy 4′-cyanoazobenzene as a photochromic material,
Radical polymerization was carried out using 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator and 100 parts by weight of tetrahydrofuran as a solvent. The resulting polymer solution was purified by repeating precipitation three times using ethyl alcohol as a precipitation solvent, to obtain 14 parts by weight of a polymer liquid crystal. The average molecular weight of the polymer liquid crystal was 30,000. The glass transition temperature of the polymer liquid crystal was 90 ° C, and the Ch-I transition temperature was 150 ° C. On a support 51 made of a transparent PET film having a thickness of 75 μm, a solution prepared by dissolving 10 parts by weight of a polymer liquid crystal in 15 parts of methyl ethyl ketone was applied by a bar coater to form a polymer liquid crystal layer 52, and the image recording medium 10 was formed. (FIG. 3A). The thickness of the polymer liquid crystal layer 24 is about 8 μm
Met. This polymer liquid crystal layer 52 showed white by scattering.

The image recording medium 10 thus created
Is fixed on a glass plate 61 placed on a black lamp 60 manufactured by Toshiba Lighting & Technology Co., Ltd. having an emission wavelength peak at 360 nm, and 1 is fixed by a hot stamp 62 (heating means).
After heating at 40 ° C. for 3 seconds and cooling (FIG. 3
(B)), the portion of the polymer liquid crystal layer 52 heated by the hot stamp 62 loses scattering and becomes transparent (FIG. 3).
(C)). The transparent part 52a did not change even when left under office lighting at room temperature for three months.

(Embodiment 2) A second embodiment of the image recording medium will be described with reference to FIG. 20 parts by weight of 4-methacrylohexyloxy 4'-cyanobiphenyl as a mesogen monomer, 2 parts by weight of 4-methacrylohexyloxy 4'-cyanoazobenzene as a photochromic material, S (-)-2-methylbutyl methacrylate as a chiral agent Radical polymerization was carried out using 7 parts by weight, 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator, and 100 parts by weight of tetrahydrofuran as a solvent. The obtained polymer solution was purified by repeating precipitation three times using ethyl alcohol as a precipitation solvent to obtain 25 parts by weight of a polymer liquid crystal. The average molecular weight of the polymer liquid crystal was 28,000.
The glass transition temperature of the polymer liquid crystal was 87 ° C, and the Ch-I transition temperature was 140 ° C. On a support 51 made of a transparent PET film having a thickness of 75 μm, a solution prepared by dissolving 10 parts by weight of a polymer liquid crystal in 15 parts of methyl ethyl ketone was applied by a bar coater to form an image recording medium 10 as a polymer liquid crystal layer 52 ( FIG. 3 (a). The thickness of the polymer liquid crystal layer 52 was about 8 μm. This polymer liquid crystal layer 52 showed blue selectively reflected light.

The image recording medium 10 thus created
Is fixed on a glass plate 61 installed on a black lamp 60 manufactured by Toshiba Lighting & Technology Corporation, and heated at 140 ° C. for 3 seconds by a hot stamp 62 (heating means) (FIG. 3).
(B)) After cooling, the portion of the polymer liquid crystal layer 52 heated by the hot stamp 62 lost its selective reflection and became transparent (FIG. 3C). The transparent part 52a did not change even when left under office lighting at room temperature for three months.

(Embodiment 3) A third embodiment of the image recording medium will be described with reference to FIG. 20 parts by weight of 4-methacrylohexyloxy 4'-cyanobiphenyl as a mesogenic monomer and 4-methacrylohexyloxy 4'- as a photochromic material serving as a chiral agent
Radical polymerization was carried out using 2 parts by weight of S (-)-2 methylbutylazobenzene, 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator, and 100 parts by weight of tetrahydrofuran as a solvent. The resulting polymer solution was purified by repeating precipitation three times using ethyl alcohol as a precipitation solvent to obtain 20 parts by weight of a polymer liquid crystal. The average molecular weight of the polymer liquid crystal was 30,000. The glass transition temperature of the polymer liquid crystal was 110 ° C, and the Ch-I transition temperature was 180 ° C. On a support 51 made of a transparent PET film having a thickness of 75 μm, a solution prepared by dissolving 10 parts by weight of a polymer liquid crystal in 15 parts of methyl ethyl ketone was applied by a bar coater to form an image recording medium 10 as a polymer liquid crystal layer 52 ( FIG. 3 (a). The thickness of the polymer liquid crystal layer 52 was about 8 μm. This polymer liquid crystal layer 52 showed red selectively reflected light.

The image recording medium 10 thus created
Is fixed on a glass plate 61 placed on a black lamp 60 manufactured by Toshiba Lighting & Technology Corporation, and heated at 140 ° C. for 3 seconds by a hot stamp 62 (heating means) (FIG. 3).
(B)) After cooling, the portion of the polymer liquid crystal layer 52 heated by the hot stamp 62 lost its selective reflection and became transparent (FIG. 3C). The transparency of the transparent portion (transparent portion 52a) at this time was compared with that of Example 2 described above, and it was visually confirmed that better transparency was obtained. The transparent part 52a is kept at room temperature for three months.
It did not change when left under office lighting.

(Embodiment 4) After an image is formed on the image recording medium 10 described in Embodiment 3, the image recording medium 10 is placed in an oven and irradiated with light from a fluorescent lamp which emits light in the visible portion.
After leaving at 0 ° C. for 30 minutes, the temperature was returned to room temperature.
2a disappeared, and the whole showed selective reflection in red.

(Embodiment 5) A fifth embodiment of the image recording medium will be described with reference to FIG. 20 parts by weight of 4-methacrylohexyloxy 4'-cyanobiphenyl as a mesogenic monomer and 4-methacrylohexyloxy 4'- as a photochromic material serving as a chiral agent
Radical polymerization was carried out using 2 parts by weight of S (-)-2 methylbutylazobenzene, 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator, and 100 parts by weight of tetrahydrofuran as a solvent. The obtained polymer solution was repeatedly precipitated and purified three times using ethyl alcohol as a precipitation solvent to obtain 20 parts by weight of a first polymer liquid crystal. The first polymer liquid crystal has an average molecular weight of 35,000 and a glass transition temperature of 11
At 0 ° C., the Ch-I transition temperature was 180 ° C., and the selectively reflected light was red.

As the other mesogenic monomer, 10 parts by weight of 4-methacrylohexyloxy 4'-cyanobiphenyl and 10 parts by weight of 4-acrylohexyloxy 4'-cyanobiphenyl were used as photochromic materials to be used as chiral agents. -Methacrylohexyloxy 4 '
-S (-)-2 methylbutylazobenzene 4 parts by weight,
Radical polymerization was carried out using 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator and 100 parts by weight of tetrahydrofuran as a solvent. The obtained polymer solution was repeatedly precipitated and purified three times using ethyl alcohol as a precipitation solvent to obtain 20 parts by weight of a second polymer liquid crystal. The second polymer liquid crystal had an average molecular weight of 27000, a glass transition temperature of 80 ° C, a Ch-I transition temperature of 190 ° C, and blue selectively reflected light.

On a support 71 made of a transparent PET film having a thickness of 75 μm, a solution prepared by dissolving 10 parts by weight of a first polymer liquid crystal in 15 parts of methyl ethyl ketone was applied by a bar coater to form a first polymer liquid crystal layer 72. And The thickness of the first polymer liquid crystal layer 72 was about 8 μm. After a separation layer 73 made of polyvinyl alcohol having a thickness of 2 μm is formed on the first polymer liquid crystal layer 72, the second polymer liquid crystal 1 is formed.
A solution prepared by dissolving 0 parts by weight in 15 parts of methyl ethyl ketone was applied by a bar coater to form a second polymer liquid crystal layer 74. The thickness of the second polymer liquid crystal layer 74 was about 8 μm. First polymer liquid crystal layer 72 and second polymer liquid crystal layer 74
The overall appearance of the image recording medium 10 having a color was purple (FIG. 4A).

The image recording medium 10 thus created
Is fixed on a glass plate 61 placed on a black lamp 60 manufactured by Toshiba Lighting & Technology, and heated at 140 ° C. for 3 seconds by a hot stamp 62 (heating means) (FIG. 4).
(B) After cooling, the portions of the first polymer liquid crystal layer 72 and the second polymer liquid crystal layer 74 heated by the hot stamp 62 lose their selective reflection and become transparent (the transparent portion 72).
a, transparent portion 74a) (FIG. 4 (c)). The image recording medium 10 is placed in an oven, and the fluorescent lamp 6 having light emission in a visible portion.
3 for 30 minutes while irradiating the light of FIG.
After (d)), when the temperature was returned to room temperature, the transparent portion 74a of the second polymer liquid crystal layer 74 disappeared, and only the transparent portion 72a of the first polymer liquid crystal layer 72 remained (FIG. 4 (e)). )). Further, the image recording medium 10 is fixed on a glass plate 61 placed on a black lamp 60 manufactured by Toshiba Lighting & Technology Corp., and a hot stamp 62 (heating means) is provided so as to partially overlap the transparent portion 72 a of the first polymer liquid crystal layer 72. After heating at 105 ° C. for 3 seconds (FIG. 4F) and cooling, the portion of the second polymer liquid crystal layer 7 heated by the hot stamp 62 was heated.
4 loses selective reflection and becomes transparent (transparent portion 74b) (FIG. 4).
(G)).

The thus configured image recording medium 10
Is a blue display portion corresponding to a region where only the first polymer liquid crystal layer 72 is transparent, and a red display portion corresponding to a region where only the second polymer liquid crystal layer 74 is transparent with respect to the purple background. It was confirmed that display and recording of a total of four colors, that is, a colorless portion corresponding to a region where both the first polymer liquid crystal layer 72 and the second polymer liquid crystal layer 74 were transparent, were possible. Each transparent part did not change even when left under office lighting for 3 months at room temperature.

When recording was performed on the same image recording medium as above using a thermal head instead of a hot stamp as a heating means, recording was possible at 300 dpi, and halftone reproduction was also possible by pulse width modulation of the heat generating portion. It was confirmed that it was possible.

[0055]

According to the image recording medium of the present invention, a polymer liquid crystal layer containing a photochromic compound is formed in a thin film on a support, and the polymer liquid crystal is heated to a temperature higher than the glass transition point of the polymer liquid crystal by a heating means. And the exposure of light in the first wavelength range at the same time to isomerize the photochromic compound, and this isomerization causes an optical change in the polymer liquid crystal layer to form an image. This makes it possible to perform stable recording in which recording can be maintained for a long period of time even when left under office lighting.

According to the image forming method and the erasing method for the recording medium of the present invention, the polymer liquid crystal is heated to a temperature equal to or higher than the glass transition point, and at the same time, the photochromic compound is exposed by light in the first wavelength range. To form an image by isomerizing, and simultaneously exposing the light in the second wavelength range to the polymer liquid crystal and heating it to a temperature equal to or higher than the glass transition point, whereby the image can be erased. In addition, it is possible to repeatedly perform recording and erasing on a recording medium, and to form an image capable of expressing gradation with high resolution using a photochromic material having excellent self-holding property.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a sectional structure of an image recording medium of the present invention.

FIGS. 2A to 2G are process explanatory diagrams showing a process of recording and erasing an image on an image recording medium.

FIGS. 3A to 3C are a structural cross-sectional view of the image recording medium of the first to fourth embodiments, a heat-exposure recording process, and a recorded cross-sectional view, respectively. Is shown.

FIGS. 4A to 4G are a structural cross-sectional view and a process explanatory view showing a process of recording and erasing on an image recording medium according to a fifth embodiment of the image recording medium.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Support, 2 ... Polymer liquid crystal layer, 3 ... Protective layer, 1
0: image recording medium, 11: support, 12a: first polymer liquid crystal layer, 12b: second polymer liquid crystal layer, 22 ...
A first heating element (heating means), 23 a second heating element,
24: third heating element, 31: light having a wavelength of 360 nm,
32: light of 460 nm wavelength, 33: light of 360 nm wavelength, 41: first heating area, 42: second heating area, 43: third heating area, 51: support, 52
... Polymer liquid crystal layer, 52a ... Transparent part, 60 ... Black lamp, 61 ... Glass plate, 62 ... Hot stamp (heating means), 63 ... Fluorescent lamp, 71 ... Support,
72: first polymer liquid crystal layer, 72a: transparent portion, 7
3 separation layer 74 second polymer liquid crystal layer 74a
74b: transparent part

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 7/00 G11B 7/00 Q 7/24 516 7/24 516 9/00 9/00

Claims (5)

[Claims] 1. A sheet-like member comprising a polymer liquid crystal film formed on a support to form a thin film polymer liquid crystal layer, wherein the polymer liquid crystal layer contains a photochromic compound. The photochromic compound is isomerized by heating the polymer liquid crystal to a temperature equal to or higher than the glass transition point of the polymer liquid crystal by a heating means and exposure to light in a first wavelength range. An image recording medium for forming an image by causing various changes. 2. The image recording medium according to claim 1, wherein said photochromic compound contains a chiral agent. 3. The image recording medium according to claim 1, wherein said polymer liquid crystal layer comprises a plurality of polymer liquid crystals having different glass transition points. 4. A method for heating a polymer liquid crystal in a polymer liquid crystal layer to a temperature equal to or higher than a glass transition point with respect to a recording medium having a polymer liquid crystal layer containing the photochromic compound formed on a support, The photochromic compound is isomerized by performing exposure with light in a first wavelength range that changes a molecule of the molecule from a shape closer to a straight line to a shape far away from the straight line. Forming an image on the recording medium by causing an optical change in the recording medium. 5. An image formed on a recording medium having a polymer liquid crystal layer containing a photochromic compound formed on a support by isomerizing the photochromic compound to cause an optical change in the polymer liquid crystal layer. By exposing the photochromic compound to light in a second wavelength range that changes the shape away from the straight line to a shape close to the straight line, and simultaneously heating the polymer liquid crystal to a temperature equal to or higher than the glass transition point. An image erasing method comprising erasing the image.