JP2767791B2 - Reversible recording material and recording method thereof - Google Patents

Description

The present invention relates to a reversible recording material, in particular, a polymer film, paper, a metal surface, a polymer liquid crystal thin film formed on other solid surfaces, The present invention relates to a recording material that can be rewritten by light or heat. [Summary of the Invention] The present invention provides an isotropic phase transition temperature (clearing
A new reversible recording material that is rewritable by light or heat and can achieve gradation recording by forming a photothermal recording layer mainly composed of a nematic polymer liquid crystal whose point is higher than the glass transition temperature. It is intended to provide. [Related Art] In recent years, the amount of documents in office work has been steadily increasing, and a recording medium that can be replaced with paper is desired from the viewpoint of saving space and resources. Such recording media include thinness,
Flexibility, rewritability, and easy recording with a laser printer or a thermal printer are required. From this demand, various recording materials have been proposed,
For example, Japanese Patent Application Laid-Open No. Sho 60-193691 discloses a thermal recording paper utilizing a fluoran-based color developing reaction of writing by a thermal head and erasing by water or water vapor. However, this method has a problem that the recording method is limited to the thermal head, so that the resolution is limited and the long-term storage property is poor. Alternatively, Japanese Patent Application Laid-Open No. 60-180887 discloses a reversible recording example based on a difference in light scattering between a uniform layer and a non-uniform layer caused by phase separation of a blended polymer. Considering the narrow separation area and the high annealing temperature at the time of erasing (gradual cooling from 200 ° C. to 5 ° C./min), there are restrictions on use conditions. Furthermore, JP-A-58-125247 discloses a rewritable recording medium using a polymer liquid crystal. However, an electric field must be applied during either the recording or the erasing process. A sandwich structure sandwiched between the electrodes must be adopted, which complicates the structure. Shibaev and colleagues also recorded a state in which the temperature of the liquid crystal was raised and radiated with laser light while maintaining it at a temperature slightly lower than the clearing point, and the resulting heating disturbed the orientation of the liquid crystal and caused light scattering. And then rearrange the liquid crystal in one direction by applying an electric field bias and then erasing (Polymer Communications No. 24).
364 pages (1983). However, it cannot be said that practicality is high in that heat retention and electric field application are required. In addition, in the lectures of the 4th Annual Meeting of the Japan Society of Applied Physics, Spring Meeting 1986, 4p-B-13 and 4p-B-14, and Japan Display (Abstract Page 290 of Japan Display '86), a cholesteric polymer liquid crystal base was used. A method of performing writing by disturbing the crystal orientation using a laser beam or a thermal head was announced. However, a circularly polarizing plate is required for reading, which is not practical as a substitute for paper. [Problems to be Solved by the Invention] As described above, in the related art, the configuration of the recording material is complicated, peripheral devices such as a polarizing plate are necessary for reading, and the use temperature is high. There was a problem. Further, in any of the above methods, gradation recording has not been achieved. Therefore, in the present invention, excellent handleability, resolution, long-term stability, without the need for peripheral devices for electric field application and reading,
It is another object of the present invention to provide a useful reversible recording material capable of coping with gradation recording and copying. [Means for Solving the Problems] The present inventors have conducted intensive studies over a long period of time to achieve the above-mentioned object, and as a result, it has been found that certain polymer liquid crystals are reversibly transparent and opaque by light or heat. It was found that it was useful as a recording material of this type. The reversible recording material of the present invention has been completed based on such knowledge, and a photothermal recording layer mainly composed of a polymer nematic liquid crystal having an isotropic phase transition temperature higher than a glass transition temperature is formed on a substrate. By applying light or heat to the photothermal recording layer in which the polydomain structure of the polymer nematic liquid crystal has been frozen and which has been formed, it is transformed into an isotropic phase state by quenching, and is rapidly cooled below the glass transition temperature. The phase state is frozen and information is recorded. Further, the recording method of the present invention comprises a photothermal recording layer mainly composed of a polymer nematic liquid crystal having an isotropic phase transition temperature higher than a glass transition temperature formed on a substrate, and the polymer nematic liquid crystal of the photothermal recording layer is formed. Irradiation of pulse width modulated laser light on a reversible recording material with a frozen polydomain structure results in the formation of a stepwise isotropic phase, which is frozen below the glass transition temperature, and gradation recording is performed. It is characterized by doing. First, it is considered that a side chain type high liquid crystal is most suitable as a material of the photothermal recording layer in the present invention. The reason is that the mobility of the side chain mesogen is decoupled from the motion of the main chain by the flexible alkyl chain, so that the electric field response and the speed of phase transition can be expected to be increased. The following are examples of side-chain polymer liquid crystals that can be used in the present invention, but are not limited thereto. These polymer liquid crystals are characterized by having a clearing point in a temperature range higher than the glass transition point.
Here, the clearing point is defined as the point at which the optical anisotropy significantly increases due to the formation of a liquid crystal phase as the temperature rises in observation using a cross polarizer, and after this, the transmitted light intensity reaches a peak. , The temperature at which the intensity of transmitted light sharply becomes zero due to the transition to the isotropic phase. The molecular weight of the high-molecular liquid crystal is desirably in the range of 10,000 to 200,000, and in a region smaller than this, the film formability is poor, and in a region larger than this, there is a practical problem that solubility in a solvent during film formation is low. There is. For example, the following table summarizes an example of examining the molecular weight, thermal properties, and optical properties of the cyanobiphenyl-based polymer liquid crystal. These differences in molecular weight are attributed to differences in the initial monomer concentration during polymerization. , But all show the same translocation mechanism. Among them, a sample having a molecular weight of 29.4 × 10 ⁴ is practically inappropriate for the above-mentioned reason. Next, regarding the configuration of the recording material, basically, a material in which a photothermal recording layer is formed on an appropriate substrate such as glass, a polymer material, paper, or metal is used. On the other hand, depending on the application, a metal deposited film or a colored film serving as a reflection film may be provided between the substrate and the photothermal recording layer, or a polymer film may be laminated for the purpose of protecting the surface of the photothermal recording layer. Is also good.
For example, in the case of application to an optical recording medium or the like, a substrate (1) and a photothermal recording layer (3) as shown in FIG.
A reflective film and an aluminum vapor-deposited film (2) as a heat diffusion layer are required between the light-heat recording layer and the light-heat recording layer by contact with the head when the recording medium is intended to be used for printing with a thermal head. In order to prevent the occurrence of scratches, a protective film is required. Further, a dye for light-heat exchange having an appropriate absorption wavelength region is dispersed in the light-heat recording layer as needed. This allows
Efficient writing becomes possible. As a recording method for the photothermal recording material thus configured, pit generation by laser, gradation recording by laser scanning, contact exposure by a negative mask and flash light, direct recording by a thermal printer, and the like are considered. . Here, the procedure of recording and erasing will be described using the generation of pits by a laser as an example. First, the polymer liquid crystal is dissolved in an appropriate solvent, applied on a glass substrate on which aluminum has been previously deposited, and dried. In this state, the photothermal recording layer is in an amorphous state and is optically transparent. When this material is annealed at a certain temperature between the glass transition point and the clearing point, fine liquid crystal domains are generated, and light having a wavelength of 600 nm or less is scattered, and the light appears slightly cloudy. When a laser beam hits the material whose reflectivity has been reduced in this way, the dye dispersed in the irradiated part converts light energy into heat energy, and the temperature of that part rises above the clearing point . Then, the liquid crystal domains are melted into an isotropic phase, and further cooled rapidly to become an amorphous phase, so that the liquid crystal domain becomes transparent and the scattering effect is reduced, while the reflectance of the underlying aluminum film is increased. At this time, the contrast between the cloudy background and the transparent recording portion can be adjusted by adjusting the amount of the dye added to the polymer liquid crystal. This recorded information can be completely erased by annealing from a temperature of about 120 ° C. corresponding to a clearing point. At this time, the original transparent liquid crystal glass state is restored within a few seconds, and the liquid crystal glass can be used repeatedly. [Operation] The recording principle in the present invention is based on the following phase transition behavior of the liquid crystal. That is, in FIG. 2, the liquid crystal always has a lower energy state unless supercooling or overheating occurs. First, when the temperature of the liquid crystal glass phase (A) is increased, the liquid crystal phase (B) is formed at a point beyond the glass transition point (T _g ), and the clearing point (T _ct ) is further increased.
And the phase shifts to an unstable low liquid crystal phase (C). However, since the unstable liquid crystal layer (C) is in a high energy state, an isotropic phase (D) is actually achieved. When it cools down again,
Usually, the unstable phase (E) changes to a more stable liquid crystal phase (B) without taking a route from the isotropic phase (D) to the isotropic amorphous phase (F) via the unstable phase (E). Further, the isotropic amorphous phase (F) shifts to a more stable liquid crystal glass phase (A). However, this polymer liquid crystal for freezing the molecular motion at a temperature lower than the glass transition temperature T _g, isotropic amorphous phase (F) also appears. The liquid crystal glass phase (A) scatters light due to the presence of the liquid crystal domains and thus appears cloudy, while the isotropic amorphous phase (F) is transparent. Therefore, the recording process utilizing this phenomenon is as shown in FIG. In this figure, after performing a heating process from a liquid crystal glass phase (A) to a liquid crystal phase (B) to an isotropic phase (D), the isotropic phase (D) passes through an unstable phase (E). If the temperature-lowering process to the isotropic amorphous phase (F) is rapidly performed, the change from the unstable phase (E) to the liquid crystal phase (B) is suppressed, and the photothermal recording layer is isotropically maintained while maintaining the isotropy. Can be frozen in the crystalline amorphous phase (F). On the other hand, in the erasing process, as shown in FIG. 3 (B), during the heating process from the isotropic amorphous phase (F) through the unstable phase (E) to the isotropic phase (D), By lengthening (annealing) the holding time in the phase (E), the photothermal recording layer is shifted to the energetically stable liquid crystal phase (B), and further cooled and frozen in the liquid crystal state. The reversible recording material of the present invention is composed of a nematic side-chain type polymer liquid crystal having a clearing point in a temperature range higher than the glass transition point. The information can be recorded with the change in reflectance when the structure changes, and this can be maintained at room temperature. In other words, clearing
When the recording layer is annealed from a temperature lower than the point to form a liquid crystal phase (white turbidity), it receives light or heat to form an amorphous phase in that portion and becomes transparent. When this recording layer is heated again to the clearing point or higher and then annealed, it returns to the original liquid crystal state, enabling repeated recording. EXAMPLES Hereinafter, the present invention will be described with reference to specific examples, but it goes without saying that the present invention is not limited to these examples. Example 1 First, a cyanobiphenyl-based liquid crystal monomer was synthesized.
The method for synthesizing this liquid crystal monomer is as follows. That is, 5-bromovaleric acid was refluxed in benzene in the presence of thionyl chloride, and the reaction mixture was heated at 65 ° C and 0.05 ° C.
Distillation under reduced pressure at mmHg gave 5-bromovaleric acid chloride in 88% yield (Formula 1). The acid chloride was reduced in anhydrous ether at room temperature using lithium aluminum hydride as a catalyst, and the reaction mixture was distilled under reduced pressure at 125 ° C. and 20 mmHg to give 5-bromo-1-pentanol in a yield of 74%. (Equation 2). On the other hand, an aqueous solution of potassium hydroxide was added to 4-hydroxy-4'-cyanobiphenyl to form a potassium salt, and water was removed by an evaporator and a vacuum dryer (formula 3). This potassium salt was dissolved in methanol previously dehydrated with a molecular sieve,
By slowly dropping -bromo-1-pentanol and refluxing for 12 hours, 4-n- (1-hydroxypentyloxy) -4'-cyanobiphenyl was synthesized in a yield of 54% (Formula 4). . In the thin layer chromatogram of the reaction product,
Since three spots were observed in addition to the target substance and the starting material, separation and purification were performed by silica gel column chromatography using hexane: ether (1: 1) as a developing solvent. Further, 4-n- (1-hydroxypentyloxy) -4'-cyanobiphenyl is mixed with acrylic acid chloride and reacted in benzene in the presence of triethylamine at room temperature to give an acrylate liquid crystal monomer in a yield of 80%. (Equation 5). The yield thus far was 30% based on the starting material. The above reaction is represented by the following equation. Next, a side chain type polymer liquid crystal was synthesized by radical polymerization of the liquid crystal monomer. Upon synthesis, the above monomer was dissolved in dimethylformamide, and the
AIBN (azobisisobutylnitrile) as a polymerization initiator was added at a ratio of 5% by weight, and reacted at 60 ° C. for 48 hours in an ampoule degassed by a rotary pump. The polymerization product was reprecipitated twice in methanol and separated from unreacted monomers (80-90% yield). At this time, the degree of polymerization can be changed by appropriately selecting the initial monomer concentration. In this example, a polymer liquid crystal having a molecular weight of 3.2 × 10 ⁴ was obtained with the monomer concentration being 10% by weight. Using the acrylate polymer liquid crystal obtained in this way, recording with an argon laser, helium, neon,
A photothermal recording material for laser reproduction was prepared.
That is, 200 mg of the above-mentioned polymer liquid crystal is dissolved in 1 ml of cyclohexane, and it absorbs at 514.4 nm corresponding to the wavelength of an argon laser, and is transparent at 633 nm corresponding to the wavelength of a helium-neon laser. −
β-naphthol) was added to the polymer liquid crystal in an amount of 0 to 20%. This mixed solution was applied to a thickness of 0.3 to 1.5 μm using a spinner on a glass substrate on which aluminum was vacuum-deposited to a thickness of 0.2 μm in advance, and dried under reduced pressure at 60 ° C. for 2 hours. FIG. 4 shows reflection spectra of a liquid crystal glass state (I) and an amorphous glass state (II) in a polymer liquid crystal thin film recording material containing 5% of Sudan I. As can be seen, the absorption at 514.5 nm is large, but hardly at 633 nm, and there is a difference of about 40% in the reflectance at both points. Therefore, recording and reproduction with high sensitivity can be performed by selectively using the two types of lasers for recording and reproduction. Using this material, an argon laser (beam diameter 1.5
μm, output 15 ~ 60mW, pulse rate 50 pulse / sec, pulse width 150nsec, 500nsec, 1μsec, 10μsec), when the pulse width is 150μsec ~ 1μsec, the irradiated part becomes amorphous without forming relief, A pit having a diameter of 2 μm was formed (a relief was formed at 10 μsec). Furthermore, when this material was annealed from 120 ° C., it could be returned to the original glass state in a few seconds, and repeated recording was possible. In a material in which 10 parts by weight of Sudan I was added to 100 parts by weight of a polymer liquid crystal, a startup sensitivity of 0.09 J / cm ² and a threshold energy density of 0.63 J / cm ² at which a reflectance change of 20% was achieved were achieved. Example 2 In order to enable recording / reproduction with a semiconductor laser (780 nm), an infrared absorbing dye (manufactured by Mitsui Toatsu;
Example 1 was prepared using a polymer liquid crystal thin film to which trade name PA-1006) was added.
It was created in the same way as. However, the molecular weight of the polymer liquid crystal used in this example was 7.1 × 10 ⁴ . In addition, recording is performed when the dye concentration is 5% or more. However, relief is likely to occur as it is, and the surface is roughened by repeated recording.
To prevent this, a 9 μm thick PET film was laminated on the material surface. As a result, the interference based on the polymer liquid crystal thin film disappears, and the film thickness control for securing the change in reflectance becomes easy. When this material is recorded / reproduced with a semiconductor laser, the pit diameter is 2 μm, the rise sensitivity is 1 J / cm ² , and the threshold energy density is 10 J / cm ² , which causes a 20% reflectance change.
No reduction in sensitivity and no relief formation due to lamination were observed. If light having a wavelength not included in the absorption region of the infrared absorbing dye (for example, 633 nm of helium-neon laser) is used as the reproduction light, a large difference in reflectance can be obtained. Example 3 The possibility of image formation by contact exposure and laser scanning was examined. The structure of the photothermal recording material used in this experiment is the same as that shown in FIG. 1, and a 1.2 μm thick photothermal recording layer is provided on a glass substrate (11) via a 0.2 μm thick aluminum vapor deposition layer (12). After forming (13),
Although not shown in the figure, lamination was performed according to the method described in Example 2. Sudan I or Sudan blue was used as an additive dye. However, the molecular weight of the polymer liquid crystal used is 3.
2 × 10 ⁴ , 3.2 × 10 ⁴ , 7.1 × 10 ⁴ ,
There were three types of 16.5 × 10 ⁴ . i) Adhesion exposure As shown in FIG. 5 (A), a negative type mask (14) is adhered to the surface of a photothermal recording material composed of a polymer liquid crystal, and a flash light of TORAEN-UP TU-250 made by Riso Kagaku Kogyo is used. Exposure was performed using As a result, as shown in FIG. 5 (B), it was found that the irradiated portion (13a) was recorded as an amorphous glass phase and had a resolving power enough to sufficiently draw a 10 μm-wide line. ii) Laser scan The experimental system used in this example is shown in FIG. In this figure, the light emitted from an argon laser oscillator (6) undergoes a pulse width modulation at a modulator (7) with a pulse rate of 100 kHz, and thereafter galvano mirrors (8a) and (8b) arranged at right angles to each other. Are scanned in the main scanning direction and the sub-scanning direction, and are irradiated on the photothermographic material (10) via the lens (9). Laser irradiation conditions were as follows: when Sudan I was used, the laser output was 100 mW, the scan frequency was 5 Hz, and the scan time was 4 minutes and 40 seconds. At this time, a continuous gradation was obtained by the liquid crystal glass phase gradually changing to an amorphous glass phase. As described above, the materials used in i) and ii) of Example 3 are as follows:
Repeated recording was possible by annealing. Further, when recording was made in a negative type, it was possible to project on a screen by reflection type projection. Example 4 An attempt was made to create a material on paper that was easy to handle by using three types of polymer liquid crystals having a molecular weight of 3.2 × 10 ⁴ , 7.1 × 10 ⁴ , and 16.5 × 10 ⁴ . That is, a solution prepared by dissolving 1 part by weight of a polymer liquid crystal in 5 parts by weight of cyclohexane and adding a Sudan blue or an infrared absorbing dye at a ratio of 2 to 5% based on the weight of the polymer liquid crystal is previously prepared with a thickness of 0.2 μm. A4 size PET film (100μm thick) with aluminum deposited on it, coated with a coater, dried under reduced pressure at 60 ° C for 2 hours,
A 5 μm thick polymer liquid crystal thin film was formed. When this material was exposed to flash light according to the method described in i) of Example 3, the contrast ratio was optimum when both dyes were added at a ratio of 2%, and the contrast ratio was 4.
1 and 10 for infrared absorbing dyes. In addition, any of the materials could be repeatedly recorded by annealing. Example 5 When a material described in Example 4 and a similar material containing no dye were recorded by a usual thermal printer, the heated portion was recorded in an amorphous glass phase. The generation of scratches on the material due to the contact of the head was solved by providing a protective film on the surface of the material. The recorded results can be viewed directly with the naked eye, and copies can be made. In addition, even when the recording was performed by the thermal head in this manner, repeated recording was possible by annealing. Example 6 In the same materials as those described in Examples 4 and 5, even when a colored film or paper was interposed as a base instead of the aluminum reflective film, the thickness of the polymer liquid crystal was reduced to 10 to 10. By setting the thickness to 100 μm, image formation by flash light and recording by a thermal printer could be performed, and the underlying portion of the recorded portion was seen through. Repeated recording was possible by annealing. [Effect of the Invention] Conventionally, there are several types of information recording utilizing the phase transition of liquid crystal.For example, in the case of applying smecticity, an electric field must be applied to either recording or erasing, and In the case of applying the cholesteric property, it takes time to form a planar structure, and there is inconvenience in handling such that a circularly polarizing plate is required for reading. On the other hand, in the reversible recording material of the present inventors, a liquid crystal phase in which molecules are randomly oriented is used as a base, and during recording, amorphous vitrification occurs instantaneously (1 μsec or less) instead of growing the liquid crystal over time. Therefore, the response is fast and the erasing time by annealing is short. In addition, since the light scattering of the liquid crystal domain is applied, there is no need to apply an electric field to orient the molecules in a specific direction, which simplifies the composition of the material. You can see the recording result with. Further, by performing pulse width modulation during laser scanning, it is possible to form an amorphous glass phase in a stepwise manner and achieve gradation recording. Further, for example, an acrylate-based polymer liquid crystal has a glass transition temperature of about 40 ° C., which is higher than room temperature, and therefore has a high stability in a normal storage environment because its molecular motion is frozen. The reversible recording material of the present invention can be used not only as a thermosensitive recording paper or an optical recording medium, but also on a screen or copied.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a configuration example of a reversible recording material to which the present invention is applied, FIG. 2 is a characteristic diagram showing a relationship between free energy of liquid crystal and temperature, and FIG. A) is a conceptual diagram showing a recording process using a reversible recording material, FIG. 3 (B) is a conceptual diagram showing an erasing process, and FIG. 4 is a characteristic showing a reflection spectrum change accompanying a phase change of the reversible recording material. FIG. 5 (A) is a sectional view showing a state before recording of a reversible recording material in contact exposure,
FIG. 5 (B) is a cross-sectional view showing a state after recording of the same material, and FIG. 6 is a configuration diagram showing an example of an image forming apparatus by laser scanning. 1 ... substrate 2 ... aluminum deposition film 3 ... photothermal recording layer

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Junetsu Seto 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (56) References JP-A-58-125247 (JP, A) JP-A-58-125247 JP-A-61-160847 (JP, A) JP-A-62-157341 (JP, A) JP-A-1-308487 (JP, A) JP-A-62-66990 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) B41M 5 / 28,5 / 34,5 / 36

Claims (1)

(57) [Claims] A photothermal recording layer mainly composed of a polymer nematic liquid crystal having an isotropic phase transition temperature higher than the glass transition temperature is formed on a substrate, and the photothermal recording layer in which the polydomain structure of the polymer nematic liquid crystal is frozen is formed. A reversible recording material characterized in that the material is transformed into an isotropic phase state by applying light or heat, and the quenching freezes the isotropic phase state below the glass transition temperature to record information. 2. 2. The reversible recording material according to claim 1, wherein the molecular weight of the polymer nematic liquid crystal is 10,000 to 200,000. 3. 2. The reversible recording material according to claim 1, wherein a photothermal recording layer is formed on the base via a reflective layer, and a surface protective film is formed so as to cover the photothermal recording layer. 4. A photothermal recording layer mainly composed of a polymer nematic liquid crystal having an isotropic phase transition temperature higher than a glass transition temperature is formed on a substrate, and the polydomain structure of the polymer nematic liquid crystal of the photothermal recording layer is frozen and reversible. A recording method characterized by forming a stepwise isotropic phase by irradiating a pulse width modulated laser beam to a target recording material, freezing the phase at a temperature lower than the glass transition temperature, and performing gradation recording.