Recording method and recording apparatus

Abstract: A recording medium comprises a recording layer formed on a substrate. The recording layer comprises a solid solution of a guest compound in a matrix polymer. The guest compound, such as a para-­ di-substituted benzene derivative, has a substantial second order micro-nonlinear optical constant β but shows substantially no nonlinear optical effect in its crystalline form. The matrix polymer is preferably a polyoxyalkylene. A part of the recording layer is caused to have a nonlinear optical effect when it is supplied with a combination of an external field such as an electric or magnetic field and heating followed by cooling for solidification, and is caused to lose its nonlinear optical effect when it is subjected to heating followed by cooling for solidifi­ cation in the absence of such an external field.

Description: The present invention relates to a method for recording a record on a medium which utilises a nonlinear optical effect. The aforesaid medium can be rewritten and enables high density records to be made. The invention also provides a method for reading a record made on the medium, and a method for erasing a record previously made on the medium. In a further aspect the invention provides a recording and reading apparatus using the medium, and a method for contact printing a photosensitive material using a medium on which a record has previously been made by the above mentioned method. Previously known rewritable high-density recording systems have used the phenomenon of phase transition, the photo-magnetic phenomenon, or the alignment or orientation of a polymer liquid crystal or a smectic liquid crystal under an electric field. Systems using the phenomenon of phase transition suffer from problems with respect to the storage stability of the record. Systems using a photomagnetic effect require a complicated and expensive recording apparatus in order to detect small variations in the rotation of the plane of polarisation of light. Furthermore, the recording medium is based on rare and expensive materials so that, from the standpoint of mass production, it suffers from difficulties regarding the cost and stability for supply of the materials required. Systems based on the alignment of a polymer liquid crystal or smectic liquid crystal under an electric field are read out by the scattering or birefringence effects. The recording medium is therefore required to have a defined minimum thickness, and involves the problems of insufficient sensitivity and density. A system for controlling a nonlinear optical effect by means of an external field is known, although it has not been used as a memory. The system involves incorporating a guest compound having a large nonlinear optical constant into host molecules and applying an electric or magnetic field to orient the mixture and control the crystalline structure. For example, a paper by Meredity, G.R., et al; Macromolecules, 15 , 1385 (1982) discloses the use of a polymer liquid crystal as a host and polar molecules as a guest, and the orientation of the polymer liquid crystal under an applied electric field to bring about alignment of the polar molecules. As a result, second harmonic generation (abbreviated as "SHD") was observed when the electric field was applied. A paper by Singer, K.D., Sohn, J.E. and Lalama, S.J.; Appl.Phys.Lett., 49 , page 248 (1986) discloses the alignment of polar molecules in an amorphous polymer. Polymethyl methacrylate resin containing a dissolved azo colorant was formed into a film, heated to a temperature above the glass transition point and subjected to a voltage to bring about alignment of the azo colorant molecules, after which the resultant structure was fixed by allowing the materials to cool. The resulting film exhibited a nonlinear optical constant of 6 x 10⁻⁹ esu. Patent Specifications US-A-4428873 and JP-A(Kokai) 57-45519 disclose the production of a polymeric nonlinear optical material by mixing a polymer with an organic compound having a nonlinear optical response. JP-A(Kokai) 62-84139 discloses a material having nonlinear optical properties which comprises an acrylamide resin as the host polymer and a guest material which is a compound having a nonlinear optical response. JP-A-62-246962 discloses the growth of crystals of a compound having an asymmetric centre in a polyoxyalkylene matrix. Such a nonlinear optical material is considered to be usable for data recording or display if recorded portions and non-recorded portions can be formed in the material and detected when present in the material based on the presence or absence of a nonlinear optical effect. However, as regards second order nonlinear optical effects, the result of incorporating a guest molecule which per se has a large polarisation β into a conventional polymer which is a centrosymmetric crystal is to produce a material which shows no or only a slight SHG activity. For this reason, it has generally been necessary to form the polymer blend into a film and to orient the film, for example by the application of an electric or magnetic field or by stretching. As described in the above mentioned paper by K.D. Singer et al, a good molecular orientation or a large nonlinear susceptibility has not been obtained because the electric field energy is smaller than the thermal energy. Furthermore, no polymeric optical modulation material obtained by adding an organic compound having a nonlinear optical response exhibits a nonlinear susceptibility exceeding that of the nonlinear optical-responsive organic compound alone, so that it has not been possible to provide a data recording or display medium in which a recording portion and a non-recorded portion can be discriminated by detecting differences in their nonlinear optical effects. U.S. Patent 4,659,177 discloses, inter alia, transparent nonlinear optical polymeric substrates having incorporated therein a distribution of dipolar quinodimethane guest molecules. When the transparent solid medium is noncentrosymmetric, it is stated to exhibit second order and third order nonlinear optical responses. If the distribution of guest molecules is random, it is explained that the optical substrate exhibits third order nonlinear optical properties, whereas if the guest molecules are at least partially uniaxial in molecular orientation then the optical medium is stated to exhibit second order nonlinear optical properties. However, this specification does not disclose the use of a nonlinear optical medium as a recording medium. JP-A-6192454 discloses a method of high density recording using an organic amorphous compound as the recording medium. The amorphous compound is polar and its direction can readily be changed by an applied electric field at a recording temperature giving optical anisotropy resulting from orientation of the dipole. However, there is no disclosure of the use of a guest compound in solid solution in a polymer. In one aspect the invention provides a method for recording a record on a medium as set out in claim 1 of the accompanying claims. In a second aspect the invention relates to a method for reading a record on a medium which has been recorded with the record by the method of any of claims 1 to 7 of the accompanying claims, the method being as defined in claim 8. In a third aspect the invention provides a recording and reading apparatus as defined in claim 10 of the accompanying claims. In a fourth aspect the invention provides a process for preparing a printing original form as defined in claim 16 of the accompanying claims. In a fifth aspect the invention provides a method for erasing a recording written by the method of any of claims 1 to 7 of the accompanying claims, the method being as defined in claim 20. Embodiments of the above mentioned method employ a recording medium which is suitable for mass production, and which is rewritable and permits high density high sensitivity recording. The recording medium can be recorded and erased repetitively. Embodiments of the above recording method based on a nonlinear optical material enable a printing original plate to be prepared. How the invention is to be put into effect will now be described by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A, 2A and 3A are schematic views each illustrating a recording system according to the present invention used for writing; Figures 1B, 2B and 3B are schematic views each illustrating a recording system according to the rpesent invention used for readout; Figure 4 is a graph showing the dependence of a nonlinear optical effect of a nonlinear optical material on applied voltage; and Figure 5 is a schematic view illustrating a system for preparing a printing original plate according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The recording medium used in the present invention has a recording layer on a substrate, and the recording layer comprises a solid solution in a matrix polymer of a guest compound which has a substantial second order micro-nonlinear optical constant of generally 5x10⁻³⁰ e.s.u. or more, preferably 10x10⁻³ e.s.u. or more, but shows substantially no nonlinear optical effect in its crystal form. The formation of a solic solution may be confirmed by the absence of a heat-absorption peak or shoulder attributable to the crystal of the guest compound when a sample is subjected to heating at a temperature at a rate of 5 - 10 °C/min by means of a DSC (differential scanning calorimeter). A most preferred example of the matrix polymer may be polyoxyalkylene. The polyoxyalkylene used in the present invention comprises oxyalkylene units represents by the formula: (R-O n ) wherein R denotes an alkylene group containing 1 - 6 carbon atoms (i.e., C₁ - C₆ alkylene group), and n is 2 or more, preferably 10 - 200,000, representing the total number of the oxyalkylene units in the polyoxyalkylene. The number of the alkylene units in the polyoxyalkylene can vary widely as described above as far as the polyoxyalkylene is provided with a film-formability and contains at least two successive oxyalkylene units. If the alkylene group R contains more than 6 carbon atoms, the polyoxyalkylene is caused to have a poor mutual solubility with an organic guest compound, thus failing to provide a film with excellent properties. It is especially preferred that the alkylene group R contains 2 - 4 carbon atoms. The polyoxyalkylene constituting the matrix of the nonlinear optical material according to the present invention may be a homopolymer consisting of the units represented by the formula (1) alone but can also be a copolymer or a derivative conaining the unit of the formula (1) as a partial structure including two or more, preferably 10 or more, successive polyoxyalkylene units in a proportion of 10 mol % or more, preferably 30 mol % or more in the polyoxyalkylene. Such a copolymer may assume various forms as follows. 1. A copolymer containing the unit of the formula (1) in its side chain represented by the following structure: wherein m is 10 or more, and n1 is 2 or more. The unit (R-O) n1 can be connected to at least a part of the main chain represented by (A) m and can also form a crosslinking structure. 2. A block polymer containing various forms of the unit (1) in its main chain as represented by the formula: 3. A copolymer assuming a cyclic structure as a comibnation of 1. and/or 2 as described above. In the above, the units A, B and C may for example be one selected from the following: recurring units derived from olefin derivatives, such as: and (CH₂-CH₂) recurring units derived from diolefin derivatives, such as recurring units derived from diolefin derivatives, such as recurrig units derived from ester derivativs, such as recurring units derived from azomethine derivatives such as recurring units derived from imide derivatives amide derivatives, such as Specific examples of the polyoxyalkylene containing the unit (1) as a partial structure include those represented by the following formulas: wherein R is a C₁ - C₆ alkylene group, R₁ and R₂ are each a C₁ - C₂₀ alkyl group, and n1 is 2 to 100,000; wherein R is a C₁ - C₆ alkylene group, R₃ and R₄ are each H or a C₁ - C₂₀ alkyl group, and nl and n2 are each 2 to 10,000; wherein R₁, R₂ and R₃ are each a C₁ - C₆ alkylene group, and n1, n2 and n3 are each 2 to 100,000; wherein R is a C₁ - C₆ alkylene group, X is -H, -CH₃ or a halogen radical, n1 is 10 to 20,000, and m is 10 to 100,000; wherein R is a C₁ - C₆ alkylene group, R₁ is a C₁ - C₁₈ alkylene, cyclohexylene, phenylene, biphenylene or tolylene group, n1 is 10 to 100,000 and m is 10 to 10,000; wherein R is a C₁ - C₆ alkylene group, R is a C₁ - C₁₈ alkylene, cyclohexylene, phenylene, biphenylene, terphenylene or tolylene group, n1 is 10 to 100,00, and m is 10 to 10,000. The polyoxyalkylene matrix of the present invention may be composed of the above-described polyoxyalkylene alone but can be a mixture with another material, such as polymers inclusive of poly(methyl methacrylate), poly(vinyl acetate), polystyrene, poly(vinylidene fluoride), poly(vinylidene cyanide-vinyl acetate), poly(vinylidene fluoride-tetraluoroethylene), poly(vinylidene cyanide-vinyl propionate), poly(vinylidene cyanide-vinyl benzoate), poly(vinyl alcohol), polyimide, etc., polymer liquid crystals, liquid crystals, and powder of inorganic compound. In such a case, it is preferred that the polyoxyalkylene constitutes more than 10 wt. %, particularly more than 30 wt. %, of the resultant mixture constituting the matrix. The guest compound or dopant used in the recording layer generally has at least one of an electron donative group and an electron attractive group. The guest compound may preferably be in the form of aromatic compounds, such as mono-substituted benzene derivative, di-substituted benzene derivative, tri-substituted benzene derivative, tetra-substituted benzene derivative, mono-substituted biphenyl derivative, di-substituted biphenyl derivative, tri-substituted biphenyl derivative, tetra-substituted biphenyl derivative, mono-substituted naphthalene derivative, di-substituted naphthalene derivative, tri-substituted naphthalene derivative, tetra-substituted naphthalene derivative, mono-substituted pyridine derivative, di-substituted pyridine derivative, tri-substituted pyridine derivative, tetra-substituted pyridine derivative, mono-substituted pyrazine derivative, di-substituted pyrazine derivative, tri-substituted pyrazine derivative, tetra-substituted pyrazine derivative, mono-substituted pyrimidine derivative, di-substituted pyrimidine derivative, tri-substituted pyrimidine derivative, tetra-substituted pyrimidine derivative, mono-substituted azulene derivative, di-substituted azulene derivative, tri-substituted azulene derivative, tetra-substituted azulene derivative, mono-substituted pyrrole derivative, di-substituted pyrrole derivative, tri-substituted pyrrole derivative, tetra-substituted pyrrole derivative, mono-substituted thiophene derivative, di-substituted thiophene derivative, tri-substituted thiophene derivative, tetra-substituted thiophene derivative, mono-substituted furan derivative, di-substituted furan derivative, tri-substituted furan derivative, tetra-substituted furan derivative, mono-substituted pyrylium salt derivative, di-substituted pyrylium salt derivative, tri-substituted pyrylium salt derivative, tetra-subsituted pyrylium salt derivative, mono-substituted quinoline derivative, di-substituted quinoline derivative, tri-substituted quinoneline derivative, tetra-substituted quinoline derivative, mono-substituted pyridazine derivative, di-substituted pyridazine derivative, tri-substituted pyridazine derivative, tetra-substituted pyridazine derivative, mono-substituted triazine derivative, di-substituted triazine derivative, tri-substituted triazine derivative, mono-substituted tetrazine derivative, di-substituted tetrazine derivative, mono-substituted anthracene derivative, di-substituted anthracene derivative, tri-substituted anthracene derivative, or tetra-substituted anthracene derivative. Examples of the electron donative group attached to the guest compound as described above may include: amino group, alkyl group (methyl, ethyl, isopropyl, n-propyl, n-butyl, t-butyl, sec-butyl, n-octyl, t-octyl, n-hexyl, cyclohexyl, etc.), alkoxy group (methoxy, ethoxy, propoxy, butoxy, etc.), alkylamino group (N-methylamino, N-ethylamino, N-propylamino, N-butylamino, etc.), hydroxyalkylamino group (N-hydroxymethylamino, N-(2-hydroxyethyl)amino, N-(2-hydroxypropyl)amino, N-(3-hydroxypropyl)amino, N-(4-hydroxybutyl)amino, etc.), dialkylamino group (N,N-dimethylamino, N,N-diethylamino, N,N-dipropylamino, N,N-dibutylamino, N-methyl-N-ethylamino, N-methyl-N-propylamino, etc.), hydroxyalkyl-alkylamino group (N-hydroxymethyl-N-methylamino, N-hydroxymethyl-N-ethylamino, N-hydroxymethyl-N-ethylamino, N-(2-hydroxyethyl)-N-methylamino, N-(2-hydroxyethyl)-N-ethylamino, N-(3-hydroxypropyl)-N-methylamino, N-(2-hydroxypropyl)-N-ethylamino, N-(4-hydroxybutyl)-N-butylamino, etc.), dihydroxyalkylamino group (N,N-dihydroxymethylamino, N,N-di-(2-hydroxyethyl)amino, N,N-di-(2-hydroxypropyl)amino, N,N-di-(3-hydroxypropyl)amino, N-hydroxymethyl-N-(2-hydroxyethyl)amino, etc.), mercapto group and hydroxy group. On the other hand, examples of the electron attractive group may include: nitro group, cyano group, haloge atom (fluorine, chlorine, bromine), trifluoromethyl group, carboxyl group, carboxy ester group, carbonyl group and sulfonyl group. Specific examples of the guest compound which may be used in the present invention may include the following: (1) 3-nitro-4-hydroxy-3-sodiumcarboxy-azobenzene, (2) 4-chloro-2-phenylquinazoline, (3) aminoadipic acid, (4) aminoanthracene, (5) aminobiphenyl, (6) 2-amino-5-bromobenzoic acid, (7) 1-amino-5-bromobenzoic acid, (8) 1-amino-4-bromonaphthalene, (9) 2-amino-5-bromopyridine, (10) amino-chlorobenzenesulfonic acid, (11) 2-amino-4-chlorobenzoic acid, (12) 2-amino-5-chlorobenzoic acid, (13) 3-amino-4-chlorobenzoic acid, (14) 4-amino-2-chlorobenzoic acid, (15) 5-amino-2-chlorobenzoic acid, (16) 2-amino-5-chlorobenzonitrile, (17) 2-amino-5-chlorobenzophenone, (18) amino-chlorobenzotrifluoride, (19) 3-amino-6-chloromethyl-2-pyrazinecarbonitrile-4-oxide, (20) 2-amino-4-chloro-6-methylpyridine, (21) 1-amino-4-chloronaphthalene, (22) 2-amino-3-chloro-1,4-naphthoquinone, (23) 2-amino-4-chloro-5-nitrophenol, (24) 2-amino-4-chloro-5-nitrotoluene, (25) 2-amino-4-chloro-4-phenol, (26) 2-amino-5-chloropurine, (27) 2-amino-5-chloropyridine, (28) 3-amino-2-chloropyridine, (29) 5-amino-2-chloropyridine, (30) aminochrysene, (31) 2-amino-p-cresol, (32) 3-amino-p-cresol, (33) 4-amino-p-cresol, (34) 4-amino-m-cresol, (35) 6-amino-m-cresol, (36) 3-aminocrotononitrile, (37) 6-amino-3-cyano-2,4-dimethylpyridine, (38) 5-amino-6-cyano-2-pyrazinyl acetate, (39) 4-[N-(2-methyl-3-cyano-5-pyrazinylmethyl)amino]-benzoic acid, (40) 3,5-dinitroaniline, (41) 4-(2,4-dinitroanilino)phenol, (42) 2,4-dinitroanisol, (43) 2,4-dinitrobenzaldehyde, (44) 2,6-dinitrobenzaldehyde, (45) 3,5-dinitrobenzamide, (46) 1,2-dinitrobenzene, (47) 1,3-dinitrobenzene, (48) 3,4-dinitrobenzoic acid, (49) 3,5-dinitrobenzoic acid, (50) 3,5-dinitrobenzonitrile, (51) 2,6-dinitro-p-cresol, (52) 4,6-dinitro-o-cresol, (53) 2,4-dinitrodiphenylamine, (54) dinitrodurene, (55) 2,4-dinitro-N-ethylaniline, (56) 2,7-dinitrofluorenone, (57) 2,4-dinitrofluorobenzene, (58) 1,3-dinitronaphthalene, (59) 1,5-dinitronaphthalene, (60) 1,8-dinitronaphthalene, (61) 2,4-dinitrophenol, (62) 2,5-dinitrophenol, (63) 2,4-dinitrophenylhydrazine, (64) 3,5-dinitrosalicylic acid, (65) 2,3-dinitrotoluene, (66) 2,4-dinitrotoluene, (67) 2,6-dinitrotoluene, (68) 3,4-dinitrotoluene, (69) 9-nitroanthracene, (70) 4-nitroanthranilic acid, (71) 2-amino-5-trifluoromethyl-1,3,4-thiazole, (72) 7-amino-4-(trifluoromethyl)-coumarine, (73) 9-cyanoanthracene, (74) 3-cyano-4,6-dimethyl-2-hydroxypyridine, (75) 5-cyanoindole, (76) 2-cyano-6-methoxybenzothiazole, (77) 9-cyanophenanthrene, (78) cyanuric chloride, (79) 1,2-diaminoanthraquinone, (80) 3,4-diaminobenzoic acid, (81) 3,5-diaminobenzoic acid, (82) 3,4-diaminobenzophenone, (83) 2,4-diamino-6-(hydroxymethyl)pteridine, (84) 2,6-diamino-4-nitrotoluene, (85) 2,3-dicyanohydroquinone, (86) 2,6-dinitroaniline, (87) 2-amino-5-iodobenzoic acid, (88) aminomethoxybenzoic acid, (89) 2-amino-4-methoxybenzothiazole, (90) 2-amino-6-methoxybenzothiazole, (91) 5-amino-2-metoxyphenol, (92) 5-amino-2-methoxypyridine, (93) 2-amino-3-methylbenzoic acid, (94) 2-amino-5-methylbenzoic acid, (95) 2-amino-6-methylbenzoic acid, (96) 3-amino-4-methylbenzoic acid, (97) 4-amino-3-methylbenzoic acid, (98) 2-amino-4-methylbenzophenone, (99) 7-amino-4-methylcoumarin, (100) 3-amino-5-methylisoxazole, (101) 7-amino-4-methyl-1,8-naphthylidene-2-ol. A preferred class of the guest compounds are those of a para-di-substituted benzene structure, particularly those represented by the formula (2) below: wherein D denotes an electron donative group and E denotes an electron attractive group, respectively as described above. Examples thereof may include the following: (111) 4-aminoacetophenone, (112) 4-aminobenzoic acid, (113) 4-amino-α,α,α-trifluorotoluene, (114) 4-amino-benzonitrile, (115) 4-aminocinnamic acid, (116) 4-aminophenol, (117) 4-bromotoluene, (118) 4-bromoaniline, (119) 4-bromoanisole, (120) 4-bromobenzaldehyde, (121) 4-bromobenzonitrile, (122) 4-chlorotoluene, (123) 4-chloroaniline, (124) 4-chloroanisole, (125) 4-chlorobenzaldehyde, (126) 4-chlorobenzonitrile, (127) 4-chanobenzaldehyde, (128) α-cyano-4-hydroxycinnamic acid, (129) 4-cyanophenol, (130) 4-cyanopyridine-N-oxide, (131) 4-fluorotoluene, (132) 4-fluoroaniline, (133) 4-fluoroanisole, (134) 4-fluorobenzaldehyde, (135) 4-fluorobenzonitrile, (136) 4-nitroaniline, (137) 4-nitrobenzamide, (138) 4-nitrobenzoic acid, (139) 4-nitrobenzyl alcohol, (140) 4-nitrocinnamaldehyde, (141) 4-nitrocinnamic acid, (142) 4-nitrophenol, (143) 4-nitrophenetole, (144) 4-nitrophenyl acetate, (145) 4-nitrophenylhydrazine, (146) 4-nitrophenyl isocyanate (147) 4-nitrotoluene (148) 4-nitro-α,α,α-trifluorotoluene. The para-di-substituted benzene derivative represented by the formula (2) has a large intramolecular dipole moment because it has an electron donative group and an electron attractive group at its para positions. On the other hand, the second order micro-nonlinear optical constant or polarization β of a molecule is represented by the following formula: β=- e 3 2h 2 (ri (gn) ) 2 Δri (n) ω 2 (ng) (ω 2 (ng) -ω 2 )(ω 2 (ng) -4ω 2 ) wherein ω (ng) denotes an energy difference between the ground and excited state; h, the Planch's constant, ri (gn) , a dipole matrix element between the ground and excited states; e, a unit electron charge; and Δri (n) =ri (nn) -ri (gg) (Ward, J.F.; Review of Modern Physics, Vol. 37, page 1 (1965)). As is understood from the above equation, a benzene derivative having polar substituents at its para-positions and having a large dipole moment provides a large second-order nonlinear constant β. However, a compound having a large dipole moment, such as a para-di-substituted benzene derivative, is liable to have an inversion symmetrical center and does not cause SHG in most cases. According to our study, however, it has been found possible to form a region showing a very excellent nonlinear optical effect by using a recording material comprising a solid solution of a compound having a large second order micro-nonlinear optical constant β represented by a para-di-substituted benzene in a matrix polymer represented by polyoxyalkylene, and by heating the material to a temperature sufficient to allow molecular movement of the guest compound, particularly a temperature above the melting temperature of the recording material, and simultaneously applying thereto an external field such as an electric field or magnetic field, followed by cooling for solidification of the recording material. The recording material constituting the recording layer in the form of a solid solution, when cooled from its molten state to solidifying, forms a region showing nonlinear optical effect because of a uniform alignment of molecules in the solidified portion, if the solidification proceeds under the application of an external field. On the other hand, if the solidification proceeds in the absence of an electric field, the material forms a region showing substantially no nonlinear optical effect because of disorder in molecular alignment. In the recording system of the present invention, at least a part of the recording medium, more specifically the recording layer, where data is to be recorded, is heated and cooled to solidify while at least a part of the recording layer is placed under the action of an external field, so that a part of the recording layer where data is (to be) recorded (hereinafter referred to as "recording part" or "record part" depending on whether it is before or after the recording) is cooled to solidify under the action of the external field, whereby the molecules and therefor the dipole moments thereof in the recorded part (or portion) are uniformly aligned to generate a nonlinear optical effect, thus effecting data writing. The heating means may be heat-mode laser, a thermal head as used in the field of thermal recording, etc. On the other hand, the external field may be an electric field or magnetic field. As described above, the part of the recording layer solidified under the external field (referred to as "record part" for convenience) shows a nonlinear optical effect, while the part of the recording layer solidified under no external field (referred to as "non-record part" for convenience) shows substantially no nonlinear optical effect. Accordingly, the recorded data may be read out by illuminating these parts with light (preferably, laser light) with a specific length (e.g., 700 - 1300 nm) to detect SHG as a nonlinear optical effect from the record part. Further, whole area easure of the record may be effected by heating the whole recording layer to or above the melting temperature, followed by cooling for solidification, in the absence of an external field or alternatively under application of a high-frequency alternating external field. Local or partial erasure of the record may be effected by heating only the record part to be erased to or above the melting temperature, followed by cooling for solidification, in the absence of an external field. By appropriately combining the above writing and erasure steps, repetitive writing and erasure becomes possible. The nonlinear optical effect of the recording material constituting the recording layer in the form of a solid solution used in the present invention can be controlled by an external field. Further, it is possible to record an analog or digital data at each recording pit by controlling an external field, so that a high-density recording becomes possible. The recording medium of the present invention can also be used for a display using a nonlinear optical effect. In this instance, gradational display is possible to provide a highly fine full color display. In the recording layer of the recording medium of the present invention, the guest compound may be contained in a proportion of generally 1 - 70 wt. %, preferably 10 - 50 wt. %, and the matrix polymer represented by polyoxyalkylene may be contained in a proportion of generally 30 - 99 wt. %, preferably 50 - 90 wt.%. The recording layer may preferably be disposed in a thickness of 0.1 - 20 µm on a substrate such as a sheet of glass or plastic such as polycarbonate. Hereinbelow, some embodiments of the recording system of the present invention using such a recording medium will be explained with reference to the drawings. Binary signals of 1 and 0 will be considered as signals to be recorded. Figures 1A and 1B are schematic views illustrating a writing mode and a readout mode, respectively, of a recording system according to the present invention. Referring to Figure 1A, a recording medium comprising a recording layer 2 on a disk-shaped transparent substrate 1 is disposed as shown. A part of the recording layer 2 where a signal of "1" is to be recorded, is irradiated by a writing laser 3 while supplied with an external electric field between electrodes 7A and 7B disposed to face the recording layer in parallel with each other, whereby the part of the recording layer is melted and solidified to cause alignment of the molecules to effect recording. On the other hand, a part of the recording layer 2 where a signal of "0" is to be recorded, is irradiated by the writing laser 3 in the absence of an electric field from the electrodes 7A and 7B, or no laser irradiation is effected if the part is already in a signal "0" state. The external electric field can be replaced by a magnetic field and the heating can be effected by a thermal head instead of the laser heating. Then, referring to Figure 1B, when the recording layer 2 is irradiated by a readout laser 4, a second harmonic of the incident light is generated from the "1" signal recorded part as a nonlinear optical effect and is detected by a spectral detector 5 to read out the "1" signal. At the non-record parts or "0" signal-recorded part, the molecules in the recording layer are not aligned so that substantially no second harmonic of the incident light is generated, whereby the "0" signal is read out. The direction of the external field may be horizontal as shown in Figure 1A or vertical as shown in Figure 2A wherein an electric field is given between a transparent electrode 7A and a back electrode 7B. Figure 3A shows a writing system where a thermal head is used as a heating means for writing. The readout mode shown in Figures 2B and 3B are similar to that explained with reference to Figure 1B. In the above embodiments, the recording medium in the shape of a disk is used and a recording position is determined by moving the recording medium preferentially. It is possible to form a recording medium in the form of a card and move the recording means such as laser beam preferentially. Further, in the above embodiments, the writing and readout have been explained so that they are conducted in separate positions but they can be effected at the same position. Further, by using a reflecting substrate, it is possible to use reflected light for readout. The SHG intensity is proportional to the square of the power density of an incident fundamental wave as shown in the following formula. As a result, by using the SHG intensity as a focusing signal, sharp focusing can be effected by a very single detecting system required of detecting only a light quantity. P 2ω =2( µ 0 ε 0 ) 3/2 ( ω 3 d 2 ℓ 2 n 3 ) sin 2 (Δkℓ/2) (Δkℓ/2) 2 (P ω ) 2 A wherein Δk = k 2ω - 2k ω (difference in light transmission speed), P ω /A = power density, d: nonlinear optical constant, ℓ: length of optical path, ε₀: di-electric constant of vacuum, µ₀: magnetic susceptibility of vacuum, ω: frequency of light, and P 2ω : power of optical second harmonic. The recording medium subjected to the recording method of the present invention and thus having a record, preferably an imagewise record (hereinafter referred to as "record sheet") may suitably be used for preparation of a printing original form in the following manner. Thus, the record sheet comprising a recording layer having a nonlinear optical image therein is caused to contact a photosensitive material which may comprise a sheet substrate and a layer of a photosensitive composition formed thereon. The photosensitive sheet in contact with the second sheet is irradiated with laser light and the thus exposed photosensitive sheet, more particularly the layer of the photosensitive composition, is developed to provide a printing original form. In a preferred embodiment, the recording layer comprises a nonlinear optical material in the form of a solid solution of a para-di-substituted benzene derivative represented by the above formula (2) in a polyoxyethylene matrix. When the nonlinear optical material is heaeted to temperature of the melting point or thereabove and is supplied with a DC electric field in this state, the para-di-substituted benzene derivative is oriented or aligned in the mixture to show a nonlinear optical effect and retains its state when it is cooled below the melting point as it is. Further, if the nonlinear optical material is heated above the melting temperature without application of a DC electric field, it is caused to show substantially no electric field any longer. By using such a property, a process for preparing a printing original form is provided. More specifically, the nonlinear optical material is applied on a support such as an aramide film, and is heated above the melting point and cooled under the application of a DC electric field, whereby a nonlinear optical film showing a nonlinear optical effect is prepared. Then, the nonlinear optical film is selectively or locally heated by means of a thermal head, etc., corresponding to given image data, whereby only the heated portion depending on the given image data loses the nonlinear optical effect. The thus formed nonlinear optical film having a portion showing a nonlinear optical effect and a portion not showing a nonlinear optical effect is caused to contact a photosensitive film, such as a dry film or a film coated with a photosensitive composition, and they were inclusively exposed to laser light having an emitted wavelength of 800 - 1000 nm. As a result, a photosensitive film having a sensitivity in the range of 400 - 500 nm equal to the wavelength of the second harmonic of the emitted laser light is photoreacted at a part contacting the portion of the nonlinear optical film showing a nonlinear optical effect, whereby image transfer is effected. Then, the exposed photosensitive film is developed by peeling off an overcoat film in the case of a dry film or by dipping in a developer liquid in the case of a photosensitive resin for relief printing, whereby a printing original form is prepared. Figure 5 is a schematic view for illustrating an embodiment of the preparation of a printing original form as described above. Referring to Figure 5, a nonlinear optical film 8a disposed on a support 8b is sent in the right direction and first heated by a heating roller under the application of an electric field given by a corona charger 10, whereby a para-di-substituted benzene derivative in the nonlinear optical film 8a is aligned so that the nonlinear optical film 8a is provided with a nonlinear optical effect. Then, the nonlinear optical film 8a is selectively heated imagewise by a heating means 11 such as a thermal head controlled by controlling means 12 for imagewise heating and setting a heating temperature, whereby the nonlinear optical film 8a is caused to lose its nonlinear optical effect selectively. Then, the nonlinear optical film 8a provided with a pattern of nonlinear optical effect is caused to contact a photosensitive film 20a comprising a photosensitive layer 20a and a support or overcoat layer 20b under the action of a pressing roller 13, and the superposed structure is uniformly exposed to laser light emitted from laser 17 and controlled by exposure means 12, whereby the photosensitive layer is photoreacted imagewise through the imagewise nonlinear optical effect of the nonlinear optical film 8. Then, the overcoat layer 16 (20b) is peeled off by the action of peeling rollers 14 to leave a printing original form 15. The nonlinear optical film is reversibly provided with and caused to lose a nonlinear optical effect, so that the nonlinear optical film can be used by rewinding it after the exposure of the photosensitive film. Thus, a remarkable economization of production cost can be expected. Hereinbelow, the present invention will be explained in more detail based on Examples. Example 1 1.03 g (23 mmol) of polyoxyethylene having a molecular weight of 2x10⁴ and 0.44 g (3 mmol) of paranitroaniline were added to 10 ml of benzene, and the mixture was heated for 5 hours for dissolution. The solution was applied onto a glass substrate to form a 10 µm-thick recording layer. The thus-prepared recording medium was irradiated with InP-semiconductor laser light (λ (wavelength) = 1.3 µm) under the application of a DC electric field of 1000 V/cm in a horizontal direction, thereby to effect writing. Then, the written part of the recording layer was illuminated with Nd-YAG laser light (λ = 1.064 µm), whereby the generation of an optical second harmonic (λ = 0.532 µm) was observed by a photomultiplier. On the other hand, no SHG (second harmonic generation) was observed from the non-written parts by similar illumination. Example 2 1.0 g of polyethylene glycol distearate (RCOO(CH₂CH₂) n COOR, R = C₁₇H₃₅, average molecular weight (Mw): about 1500, "Emanon 3299" available from Kao K.K.), 0.3 g of polyethylene oxide (Mw = 5x10⁶) and 0.2 g of p-nitroaniline were added to 30 ml of benzene, and an infrared absorber (IR-750, available from Nippon Kayaku K.K.) was added thereto, followed by 1 hour of heating for dissolution. The solution was applied by spin coating on a glass substrate coated with a transparent electrode of NESA film to form a 20 µm-thick uniform recording layer. Onto the recording layer, a glass substrate coated with a NESA transparent electrode was applied to form an intimate contact, and the recording layer was heated to 80°C and gradually cooled to room temperature under application of a DC electric field of 100 V. Then, the recording layer was irradiated with semiconductor laser light (λ = 780 nm, 30 mW) through a collimator lens and a condenser lens, thereby to effect recording. As a result of illumination with Nd-YAG laser light (λ = 1.064 µm), no SHG was observed from the thus recorded portion while the generation of an SHG (λ = 0.532 µm) was observed at the non-recorded portion through a photomultiplier. Then, the recording medium was heated to 80°C and cooled to room temperature under the application of a DC voltage of 100 V. Then, the recording layer was illuminated with Nd-YAG laser light (λ = 1.064 µm), whereby optical SHG was observed from the whole area thereof so that the above recorded portion was erased. Example 3 1.0 g of polyoxyethylene (Mw = 10⁶), 0.2 g of a polyethylene glycol derivative (Mw = about 400; "DA-350F" available from Nihon Yushi K.K.) represented by the formula: and 0.2 g of p-nitroaniline were dissolved in 20 ml of benzene and 10 mg of IR 750 (available from Nihon Kayaku K.K.) was aded thereto, followed by 1 hour of heating for dissolution. The solution was applied by spin coating on a glass substrate coated with a transparent electrode of NESA film to form a 10 µm-thick uniform recording layer. Onto the recording layer, a glass substrate coated with a NESA transparent electrode was applied to intimately contact the recording layer. A part of the recording layer was irradiated with semiconductor laser light (λ = 780 nm) initially at a power of 30 mW for heating and then at a gradually decreasing power for cooling to room temperature under the application of a DC voltage of 50 V, whereby recording was effected. The thus recorded part of the recording layer was illuminated with Nd-YAG laser light (λ = 1.064 µm) whereby an SHG (λ = 532 nm) was observed by a photomultiplier. Then, another part of the recording layer was selected and irradiated with semiconductor laser light initially at a power of 30 mW for heating and then at a gradually decreasing power for cooling to room temperature under the application of a DC voltage of 10 V. The thus-recorded part of the recording layer was again illuminated with Nd-YAG laser light (λ = 1.064 µm), whereby an optica second harmonic was detected at an intensity which was about 20 % of that obtained in the above-mentioned case of application of 100 V. Example 4 2.12 g of polyoxyethylene (Mw = 5x10⁶) and 1.57 g of para-nitroaniline were added to 100 ml of acetonitrile, followed by 5 hours of heating for dissolution. The solution was applied onto a 6 µm-thick aramide film placed on a hot plate heated at 60 - 80°C by means of an applicator and dried to form a coated film having a 50 µm thick recording layer. An aluminum foil was intimately applied on both sides of the coated film. The resultant laminate was heated on a hot plate to 80°C and then gradually cooled to room temperature while continually applying a DC electric field of 1000V. Then, the aluminum foil was peeled off, and the resultant laminate was heated imagewise to 120°C by means of a thermal head from the aramide film side to form a record sheet. Separately, polyvinylcinnamylidene acetate and 7 wt. % thereof of erythrosine were dissolved in ethyl acetate to form a photosensitive solution, which was then applied by an applicator on a 100 µm-thick aluminum sheet to prepare a photosensitive sheet having a 10 µm-thick photosensitive layer. The photosensitive sheet was caused to intimately contact the record sheet prepared above and illuminated through the record sheet with Nd-YAG laser light (λ = 1.064 µm). Then, the photosensitive sheet was dipped in aqueous ethyl acetate solution, whereby a good original form for letterpress printing. Example 5 A printing form was prepared by using a system as shown in Figure 5. The coated film 8 prepared in Example 4 was moved along a heat roller 9 at 100°C and a corona charge was provided on the side of the recording layer 8a by means of a corona charger 10 supplied with a voltage of 1.7 kV. Then, a thermal head 11 was controlled by given image signals to heat the recording layer 8a imagewise through the aramide support film 8b. Then, the coated film thus treated (record sheet) was superposed with Curomalin Film (available from E.I. Du Pont) 20 so that its recording layer 8a contacted the overcoat layer 20b of the Curomalin Film. Then, the superposed structure was illuminated with respect to the whole area from the second sheet side 8 by semiconductor laser light (λ = 833 nm) according to a luster scanning mode. Then, the Curomalin Film 20 was separated from the record sheet and the overcoat layer 20b was peeled therefrom, whereby a good original form for letterpress printing 15 was prepared. As described above, according to the present invention, a recording medium composed of an organic material is used, so that the production cost thereof is lower than the conventional system, such as photo-magnetic recording system. Particularly, the above-described solid solution of a para-di-substituted benzene derivative in polyoxyalkylene has a good solubility in a solvent, so that it is readily formed as by spin coating into a thin film having a sufficient mechanical strength. Thus, the recording medium is suited for mass production. Further, as compared from a conventional system wherein a quantitative change such as reflected light intensity or rotation angle of polarized plane is utilized for readout, a qualitative change, i.e., the presence or absence of second harmonic generation, is detected for readout of record, so that an improved sensitivity can be attained. Further, as compared with a conventional optical disk using an organic material, the system of the present invention is advantageous in that it allows re-utilization through erasure. As described above, according to the recording method and recording medium of the present invention, the presence or absence of a non-linear effect can be effectively utilized for data recording and display. Further, by utilizing the above recording method, it is possible to prepare a clear printing original form in a convenient and inexpensive manner.

Claims: A method for recording a record on a medium, said method comprising: providing a recording medium including a substrate (1) and a recording layer (2) formed thereon which comprises a solid solution of a guest compound in a polymer, said guest compound having a substantial second order micro-nonlinear optical constant β but showing substantially no nonlinear optical effect in its crystal form, the layer having the property that the result of its being heated and cooled under the application of an external field is that the layer shows a nonlinear optical effect and that the result of its being heated and cooled in the absence of an electric field is that the layer shows substantially no nonlinear optical effect; writing a record in the recording layer (2), the record comprising a combination of a part showing a nonlinear optical effect and a part showing substantially no nonlinear optical effect, said parts being formed by any of the procedures (a) to (c) below: (a) heating and cooling at least a part of the recording layer (2) and applying an external field to at least a part of the recording layer (2) so that at least a part of the recording layer (2) is cooled to solidify under the application of the external field to form a portion showing a nonlinear optical effect and a part of the recording layer (2) cooled to solidify in the absence of the external field is caused to form a portion showing substantially no nonlinear optical effect; (b) heating and solidifying at least a part of the recording layer (2) under the application of an external field thereby to provide said at least a part of the recording layer (2) with a nonlinear optical effect, and then heating and solidifying a prescribed part in said at least a part of the recording layer (2) in the absence of an external field to cause said prescribed part to lose the nonlinear optical effect; (c) applying an external field to substantially the whole part of the recording layer (2) while selectively heating and then solidifying a prescribed part of the recording layer (2) to provide said prescribed part with a nonlinear optical effect; the medium after recording having the property that when its recording layer (2) is illuminated an optical second harmonic is generated from the part showing the nonlinear optical effect but substantially no optical second harmonic is generated from the other part. A method according to claim 1, wherein writing is by the procedure (a) or (b) of claim 1 and said part of the recording layer solidified in the absence of an external field has a function of scattering laser light. A method according to claim 1, wherein writing is by the procedure (c) of claim 1 and said part of the recording layer (2) not heated and solidified has a function of scattering laser light. A method according to any preceding claim, wherein said guest compound is a para-di-substituted benzene derivative. A method according to any preceding claim, wherein said polymer comprises a polyoxyalkylene unit. A method according to any preceding claim wherein said external field is an electric field. A method according to any preceding claim, wherein said external field is a magnetic field. A method for reading a record on a medium which has been recorded with the record by the method of any of claims 1 to 7, said method comprising illuminating the recording layer (2) of the medium and detecting an optical second harmonic generated from the part of the medium which shows the nonlinear optical effect. The method of claim 8, wherein the medium is illuminated with laser light. A recording and reading apparatus, comprising: a recording medium including a substrate (1) and a recording layer (2) formed thereon which comprises a solid solution of a guest compound in a polymer, said guest compound having a substantial second order micro-nonlinear optical constant β but showing substantially no nonlinear optical effect in its crystal form, the layer having the property that the result of its being heated and cooled under the application of an external field is that the layer shows a nonlinear optical effect and that the result of its being heated and cooled in the absence of an electric field is that the layer shows substantially no nonlinear optical effect; external field application means (7A,7B); heating means (3), at least one of said external field applications means (7A,7B) and said heating means (3) being arranged so as to exert its function to a selected part of the recording layer (2) and form a record in the recording layer (2), comprising a part showing a nonlinear optical effect and a part showing substantially no nonlinear optical effect; laser illumination means (4) for illuminating said recording layer (2); and means (5) for detecting an optical second harmonic generated from the recording layer (2) in response to said laser illumination. An apparatus according to claim 10, wherein said heating means (3) is a heat-generating head (6). An apparatus according to claim 10, wherein said heating means (3) is a laser. An apparatus according to claim 10, 11 or 12, wherein said external field application means (7A, 7B) is electric field application means. An apparatus according to claim 10, 11 or 12, wherein said external field application means (7A, 7B) is magnetic field application means. An apparatus according to any of claims 10 to 14, wherein said laser illumination means (4) comprises a semiconductor laser illumination means. A process for preparing a printing original form comprising conducting a recording method according to any of claims 1 to 7, and then contacting the recording medium with a photosensitive material (20a) and exposing the photosensitive material (20a) in contact with the recording medium to laser light, and developing the exposed photosensitive material (20a), said photosensitive material (20a) having a sensitivity in the range of the second harmonic of said laser light (Fig. 5). A process according to claim 16, wherein said polymer comprises a polyoxyalkylene having oxyalkylene units represented by the formula: (R-0) n wherein R denotes an alkylene group having 1 - 6 carbon atoms, and n is the total number of the oxyalkylene units ranging from 100 to 200,000. A process according to claim 16 or claim 17, wherein said guest compound is a para-di-substituted benzene derivative represented by the formula: wherein D and E are an electron donative group and an electron attractive group, respectively. A process according to claim 18, wherein D denotes an electron donative group selected from amino, alkyl, alkoxy, alkylamino, hydroxyalkylamino, dialkylamino, hydroxyalkyl-alkylamino, dihydroxyalkylamino and mercapto; and E denotes an electron attractive group selected from nitro, cyano, halogen, trifluoromethyl and carbonyl. A method for erasing a record written by the method of any one of claims 1 to 7, the method comprising the steps of heating and then cooling to solidify a region of said recording medium in the absence of an external field or under the application of a high-frequency alternating external field.

Inventors: MITSUTAKE HIDEAKI, MIYAGAWA MASASHI, YAEGASHI HISAO, YOSHINAGA KAZUO, MITSUTAKE, HIDEAKI, MIYAGAWA, MASASHI, YAEGASHI, HISAO, YOSHINAGA, KAZUO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: G11B7
IPC codes: G11B7, G02F1