A thermal transfer material which has at least a light to heat converting layer and an image forming layer on a supporting body, and the image forming layer containing at least one compound which is selected from the compounds which are represented in the following general formula (1) and the following general formula (2). In the general formula (1), R1 represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom, or an alkoxy group having 1 to 5 carbon atoms; and R2 represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. n represents any integer of 1 to 4. In the general formula (2), R3 and R4 represent respectively independently a nitro group, a halogen atom, a methylsulfonyl group, or a cyano group.

1. Field of the Invention
The present invention relates to a thermal transfer material which thermal transfers by laser illumination and to an image forming material using the same. In particular, the present invention relates to a thermal transfer material which can be used for forming a color proof (DDCP: direct digital color proof) or a mask image in the field of printing by utilizing laser illumination based on a digital image signal, and to an image forming material using the thermal transfer material.
2. Description of the Related Art
An example of a conventional thermal transfer recording technique is as follows. An image receiving material and a thermal transfer material, in which a heat melting color material layer or a color material layer containing a heat sublimating dye is provided on a supporting body, are superposed. The thermal transfer material side is heated imagewise by a heating device, such as a thermal head, an energized head, or the like, which is controlled by an electric signal. Thus, the image is transferred and recorded onto the image receiving material.
Such a thermal transfer recording technique has the characteristics that noise is low, there is no need for maintenance, the cost is low, coloring is easy, digital recording is possible, and the like. This technique is utilized in many fields such as various types of printers, recorders, facsimiles, computer terminals, and the like.
The recent years, a so-called digital recordable recording method, with which resolution is higher, high speed recording is possible, and image processing is possible, has come to be demanded in the fields of medical care, printing, and the like. However, in the thermal transfer recording method using a heating device such as a thermal head, an energized head, or the like, the resolution is limited by a density at which the head heating elements are disposed. Moreover, due to the heat generating characteristics of the heating elements, it is difficult to control the heating temperature of the heating elements at high speed, and it is difficult to obtain an image having higher resolution even faster.
Therefore, in recent years, a laser recording technique which utilizes a light to heat converting operation by laser illumination has attracted attention and has been manufactured as a system which can obtain an image having higher resolution at high speed.
In an image forming system which utilizes this laser recording technique, in particular, a single mode laser is used in general from the standpoint of obtaining a beam which is extremely narrow and has a small focal point. Because such a single mode laser has good beam quality, an image having high resolution is obtained. Further, regarding the recording speed as well, an image can be formed at high speed as compared to recording by a conventional heating device such as a thermal head or the like.
However, in the laser recording, since the focus beam diameter of a laser light having comparatively large energy is converged to about 10 xcexcm and used, light-to-heat conversion is effected highly efficiently and extremely high heat energy is obtained as compared to a case using a heating device, such as a thermal head or the like, which is used for heat recording. As a result, the temperature of a region which is subjected to laser illumination reaches an extremely high temperature locally, and a coloring agent (pigment), which is included in the image forming layer, in the illuminated region may undergo thermal decomposition. When the coloring agent undergoes thermal decomposition, the hue of the coloring agent is lost, and the image density of an image which is transferred onto the image receiving layer decreases.
Further, in recent years, an attempt to increase the image recording speed has been made using a multimode semiconductor laser which has a higher output than the single mode laser. However, the multimode semiconductor laser has drawbacks in that it is difficult to converge a laser beam in the transverse direction and that the focus beam diameter cannot be converged to 20 xcexcm or less. Thus, when a highly minute image in which a sub-scanning pitch is approximately 10 xcexcm in the field of medical care, printing, or the like is recorded by using the multimode semiconductor laser, adjacent beams are overlapped with each other. As a result, the overlapped region is heated excessively, the thermal decomposition of a coloring agent as described above progresses even further, and the density of the transferred image is lowered even more.
Accordingly, also in cases in which recording is carried out using the above-described laser having high output and having overlapping of adjacent beams, there is still the demand for a material in which it is difficult for thermal decomposition to occur even at high temperatures.
In general, the coloring agent which is used in the image forming layer is a pigment or the like. However, there are often cases in which, when the pigment is subjected to thermal decomposition, substances which are harmful to the human body are discharged from the pigment. Consequently, in recent years, a technique which can prevent or reduce the generation of harmful substances has come to be demanded as there are demands for improving safety and the operation environment.
An object of the present invention is to solve the above-described conventional problems, and to provide a thermal transfer material and an image forming material, in which it is difficult for decomposition of a coloring agent to occur at the time of forming an image, which are very safe, and which can form a vivid image having good hue.
A first aspect of the present invention is a thermal transfer material which has at least a light to heat converting layer and an image forming layer on a supporting body, wherein the image forming layer contains at least one compound which is selected from compounds which are represented by following general formula (1) and following general formula (2):
wherein, R1 represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom, or an alkoxy group having 1 to 5 carbon atoms; R2 represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms; and n represents any integer of from 1 to 4;
wherein, R3 and R4 respectively and independently represent a nitro group, a halogen atom, a methylsulfonyl group, or a cyano group.
A second aspect of the present invention is an image forming material which is formed by a thermal transfer material and an image receiving material, wherein the thermal transfer material has at least a light to heat converting layer and an image forming layer on a supporting body, and the image forming layer contains at least one compound which is selected from compounds which are represented by following general formula (1) and following general formula (2), and the image receiving material having an image receiving layer on a supporting body:
wherein, R1 represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom, or an alkoxy group having 1 to 5 carbon atoms; R2 represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms; and n represents any integer of from 1 to 4;
wherein, R3 and R4 respectively and independently represent a nitro group, a halogen atom, a methylsulfonyl group, or a cyano group.
A third aspect of the present invention is a laser thermal transfer recording method, comprising the steps of: (a) manufacturing a thermal transfer material which includes formation of a light to heat converting layer on a supporting body and formation of an image forming layer which contains at least one compound which is selected form compounds represented by following general formula (1) and following general formula (2); (b) manufacturing an image receiving material which includes formation of an image receiving layer on a supporting body; (C) superposing the thermal transfer material and the image receiving material such that the image forming layer and the image receiving layer contact one another; (d) illuminating a laser imagewise; and (e) peeling the thermal transfer material and the image receiving material:
wherein, R1 represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom, or an alkoxy group having 1 to 5 carbon atoms; R2 represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms; and n represents any integer of from 1 to 4;
wherein, R3 and R4 respectively and independently represent one of a nitro group, a halogen atom, a methylsulfonyl group, or a cyano group.
A thermal transfer material of the present invention has the characteristic that, in the thermal transfer material which has at least a light to heat converting layer and an image forming layer, the image forming layer contains at least one compound (the compound may be hereinafter referred to as xe2x80x9ccompound of the present inventionxe2x80x9d) which is selected from the compounds represented by above general formula (1) and above general formula (2). An embodiment of the present invention includes, for example, a thermal transfer material in which the light to heat converting layer and the above image forming layer are superposed on a supporting body in that order. Moreover, an aspect of the present invention, which is applied to the thermal transfer material for forming a full color image, includes a thermal transfer material on which three image forming layers for cyan coloring, magenta coloring, and yellow coloring are superposed.
The above-described compound of the present invention functions as a magenta coloring agent in the image forming layer. Accordingly, in the above thermal transfer material for forming a full color image, it is preferable that the magenta coloring layer contains the compound. Further, in the image forming layer, it is preferable that the compound is used together with other magenta coloring agents. It is difficult for the above compound of the present invention to undergo thermal decomposition even if thermal energy is supplied thereto at the time of forming an image. Thus, generation of harmful substances such as benzidine or the like can be prevented, and lowering of the image density due to the decomposition of the coloring agent can be reduced. As a result, the thermal transfer material of the present invention is very safe and can form a vivid image having good hue.
In the above general formula (1), R1 represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom, or an alkoxy group having 1 to 5 carbon atoms. The above-described alkyl group may form a straight chain shape or a branched shape. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, or the like.
Examples of the halogen atom include a chlorine atom, a bromine atom, an iodine atom, or the like. Among them, a chlorine atom is preferable.
An alkyl portion of the above alkoxy group may be a straight chain-shaped alkyl group or a branch-shaped alkyl group. Examples of the above alkoxy group include a methoxy group, an ethoxy group, or the like. Among them, an ethoxy group is preferable.
R1 is preferably a hydrogen atom.
In the above general formula (1), R2 represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. The alkyl group may form a straight chain shape or a branched shape. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, or the like. Among them, R2 is preferably a hydrogen atom.
In the above general formula (1), n represents any integer of from 1 to 4. n is preferably 1 or 2.
Among the compounds represented by the above general formula (1), a compound in which R1 and R2 are hydrogen atoms is preferable from the standpoints of hue and thermal decomposition resistance.
In the above general formula (2), R3 and R4 respectively and independently represent a nitro group, a halogen atom, a methylsulfonyl group, or a cyano group.
Examples of the halogen atom include a chlorine atom, a bromine atom, an iodine atom, or the like. Among them, a chlorine atom is preferable.
Among the compounds represented by the above general formula (2), a compound in which R3 is a nitro group and R4 is a chlorine atom is preferable from the standpoints of hue and thermal decomposition resistance.
Concrete examples of the compound which is represented by the above general formula (1) (illustrative compounds (1)-1 to (1)-4) and concrete examples of the compound which is represented by the above general formula (2) (illustrative compounds (2)-1 and (2)-2) are shown below. However, the compounds which are used in the present invention are not limited to the following compounds.
The compound which is represented by the above general formula (1) and the compound which is represented by the above general formula (2) can be synthesized in accordance with general methods which are described, for example, in a pigment manual or the like.
The compound of the present invention may be used alone, or a combination of two or more compounds which are selected from the compounds represented by above general formula (1) and (2) may be used.
The above image forming layer may contain another coloring agent in addition to the compound of the present invention. In particular, as mentioned above, it is preferable that the image forming layer for magenta coloring contains the compound of the present invention together with another magenta coloring agent.
The magenta coloring agent which can be used together is preferably a magenta pigment. Examples of inorganic pigments include cadmium red, red iron oxide, vermilion, red lead, antimony vermilion, or the like. Moreover, examples of organic pigments include an azo pigment of azo lake system, an insoluble azo system (monoazo system, disazo system, condensed azo system), condensed azo pigment, an anthraquinone pigment which is a condensed polycyclic pigment, a thioindigo pigment, a perinon pigment, a perylene pigment, and a quinacridone pigment.
Examples of the azo pigment of azo lake system include brilliant carmine 6B (pigment Red 57:1), lake red (pigment Red 53:1), permanent red F5R (pigment Red 48), lithol red (pigment Red 49), Persian orange (pigment Orange 17), Croceine Orange (pigment Orange 18), helio orange TD (pigment Orange 19), pigment scarlet (pigment Red 60:1), brilliant scarlet G (pigment 64:1), hello red RMT (pigment Red 51), Bordeaux 10B (pigment Red 63), and helio Bordeaux BL (pigment Red 54).
Examples of the above insoluble azo system (monoazo system, disazo system, condensed azo system) include Para Red (pigment Red 1), lake red 4R (pigment Red 3), permanent orange (pigment Orange 5), permanent red FR2 (pigment Red 2), permanent red FRLL (pigment Red 9), permanent red FGR (pigment Red 112), brilliant carmine BS (pigment Red 114), permanent carmine FB (pigment Red 5), P.V. carmine HR (pigment Red 150), permanent carmine FBB (pigment Red 146), novapalm red F3RK-F5RK (pigment Red 170), novapalm red HFG (pigment Orange 38), novapalm red HF4B (pigment Red 187), novapalm orange HL.HL-70 (pigment Orange 36), P. V. carmine HF4C (pigment Red 185), hostapalm Brown HFR (pigment Brown 25), Vulcan orange (pigment Orange 16), pyrazolone orange (pigment Orange 13), and pyrazolone red (pigment Red 38).
Examples of yellow coloring agents include inorganic chrome yellow, cadmium yellow, yellow iron oxide, titan yellow, ochre, an acetoacetic anilide monoazo pigment of refractory metallic salt (azo lake), an acetoacetic anilide disazo pigment, a condensed azo pigment, a benzimidazole monoazo pigment, an isoindolinone pigment, and the like.
Examples of the above acetoacetic anilide monoazo pigment of refractory metallic salt (azo lake) include Hanza yellow G (C.I. No. pigment Yellow 1, and the same holds true hereinafter), Hanza yellow 10G (pigment Yellow 3), Hanza yellow RN (pigment Yellow 65), Hanza brilliant yellow 5GX (pigment Yellow 74), Hanza brilliant yellow 10GX (pigment Yellow 98), permanent yellow FGL (pigment Yellow 97), Simra lake fast yellow (pigment Yellow 133), lyonol yellow K-2R (pigment Yellow 169), and the like.
Examples of the above acetoacetic anilide disazo pigment include disazo yellow G (pigment Yellow 12), disazo yellow GR (pigment Yellow 13), disazo yellow 5G (pigment Yellow 14), disazo yellow 8G (pigment Yellow 17), disazo yellow R (pigment Yellow 55), permanent yellow HR (pigment Yellow 83), and the like.
Examples of the above condensed azo pigment include chromophthal yellow 3G (pigment Yellow 93), chromophthal yellow 6G (pigment Yellow 94), and chromophthal yellow GR (pigment Yellow 95).
Examples of the above benzimidazole monoazo pigment include hostapalm yellow H3G (pigment Yellow 154), hostapalm yellow H4G (pigment Yellow 151), hostapalm yellow H2G (pigment Yellow 120), hostapalm yellow H6G (pigment Yellow 175), and hostapalm yellow HLR (pigment Yellow 156).
Examples of the above isoindolinone pigment include illugadin yellow 3RLTN (pigment Yellow 110), illugadin yellow 2RLT, illugadin yellow 2GLT (pigment Yellow 109), fastgen super yellow GROH (pigment Yellow 137), fastgen super yellow GRO (pigment Yellow 110), and sandolin yellow 6GL (pigment Yellow 173).
In addition to the aforementioned, other examples of the yellow coloring agent are a thren pigment such as flavanthrone (pigment Yellow 24), anthramyrimidin (pigment Yellow 108), phthaloylamide type anthoraquinon (pigment Yellow 123), heliofast yellow E3R (pigment Yellow 99), or the like; a metallic complex pigment such as an azo nickel complex pigment (pigment Green 10), a nitroso nickel complex pigment (pigment Yellow 153), an azomethine copper complex pigment (pigment Yellow 117), or the like; a quinophthalone pigment such as a phthalimide quinophthalione pigment (pigment Yellow 138), or the like; and the like.
Examples of cyan coloring agents include an inorganic pigment (such as ultramarine, iron blue, cobalt blue, cerulean blue, or the like) and an organic pigment (such as phthalocyanine pigment or the like).
Examples of the above-described phthalocyanine pigment include fastgen blue BB (pigment Blue 15), Sumiton cyanine blue HB (pigment Blue 15), cyanine blue 5020 (pigment Blue 15:1), Sumika print cyanine blue GN-O (pigment Blue 15), fast sky blue A-612 (pigment Blue 17), cyanine green GB (pigment Green 7), cyanine green S537-2Y (pigment Green 36), Sumiton fast violet RL (pigment Violet 23), and the like.
Moreover, examples of the cyan coloring agent include indanthrone blue (PB-60P, PB-22, PB-21, PB-64) which is a thren pigment, methyl violet phosphorus molybdic acid lake (PV-3) which is a basic dye lake pigment, and the like.
When the compound of the present invention is used together with another pigment, it is preferable that, in the image forming layer, the contained amount of the compound of the present invention is 30% by mass or less based on the contained amount of the other pigment used, and it is more preferable that the contained amount thereof is from 5% by mass or more to 15% by mass or less. If the above-described contained amount exceeds 30% by mass, the amount of thermal decomposition of the pigment increases at the time of laser recording, and image defects such as reduction of image density, uneven transfer, or the like occur. Accordingly, there may be cases in which the desired hue is not obtained.
Further, in each image forming layer, the contained amount of the above coloring agent is preferably from 30% by mass to 70% by mass, and is more preferably from 30% by mass to 40% by mass. Moreover, when a magenta pigment is used as the magenta coloring agent and is used together with the compound of the present invention, in the image forming layer, the total contained amount of the magenta pigment and the compound of the present invention is preferably from 30% by mass to 70% by mass, and is more preferably from 30% by mass to 40% by mass.
The average particle size of the compound of the present invention and the coloring agent which, if desired, is used together therewith is preferably from 0.03 to 1 xcexcm, and is more preferably from 0.05 to 0.5 xcexcm. If the particle size is less than 0.03 xcexcm, dispersion cost may increase, the dispersed solution may be gelatinized, or the like. If the particle size exceeds 1 xcexcm, coarse particles within the coloring agent may prevent adhesion between a thermal transfer layer and the image receiving layer of an image receiving material.
It is preferable that the above image forming layer contains an amorphous polymer. When the image forming layer contains an amorphous polymer, it is preferable from the standpoint of improving the image quality and the standpoint of increasing the resolving power. In particular, an amorphous polymer having a softening point of from 40 to 150xc2x0 C. is more preferable due to the above-described points. Examples of the above amorphous polymer include a butyral resin, a polyamide resin, a polyethyleneimine resin, a sulfonamide resin, a polyester polyol resin, a petroleum resin, homopolymers or copolymers of styrene, derivatives of styrene and substitution products of styrene, such as styrene, vinyl toluene, xcex1-methylstyrene, 2-methylstyrene, chlorostyrene, vinyl benzoate, vinyl benzene sulfonic acid soda, aminostyrene, or the like; homopolymers or copolymers with other monomers of vinyl monomers, methacrylic esters and methacrylic acid such as methylmethacrylate, ethylmethacrylate, butylmethacrylate, hydroxyethylmethacrylate, or the like; acrylic esters and acrylic acid such as methylacrylate, ethylacrylate, butylacrylate, xcex1-ethylhexylacrylate, or the like; dienes such as butadiene, isoprene, or the like; acrylnitril; vinyl ethers; maleic acid and maleic acid esters; maleic anhydride; cinnamic acid; vinylchloride, vinylacetale and the like. a homopolymer of vinyl monomer such as chloroethene, vinyl acetate, or the like or copolymer of vinyl monomer with another monomer or the like.
The resins can be used in combination of two or more.
The amount of content of the above amorphous polymer is preferably from 30 to 70% by mass based on the total solid content mass of the image forming layer, and is more preferably from 40 to 60% by mass.
When a number of (e.g., three including yellow, magenta, and cyan, or four including yellow, magenta, cyan, and black) image forming layers (image forming layers on which images are formed) are repeatedly superposed on a supporting body and a multicolor image is formed, the image forming layers preferably include a plasticizer so as to enhance the adhesion between the images.
Examples of the plasticizer include phthalic acid esters such as dibutyl phthalate, di-n-octyl phthalate, di (2-ethylhexyl), dinonyl phthalate, dilauryl phthalate, butyllauryl phthalate, butylbenzyl phthalate, or the like; aliphatic dibasic acid esters such as di (2-ethylhexyl) adipate, di (2-ethylhexyl) sebacate, or the like; triester phosphates such as tricresyl phosphate, tri (2-ethylhexyl) phosphate, or the like; polyol esters such as polyethylene glycol ester or the like; epoxy compounds such as epoxy fatty acid ester, or the like.
Further, in addition to the aforementioned general plasticizers, acrylic acid esters such as polyethylene glycol dimethacrylate, 1,2,4-butane triol trimethacrylate, trimethyrol ethane triacrylate, pentaerytrite triacrylate, pentaerytrite tetraacrylate, pentaerytrite-polyacrylate, or the like can be suitably used depending on the type of binder to be used. The plasticizer may be used in combination of two or more.
Moreover, regarding the amount of the above plasticizer added, in the image forming layer in general, the content ratio (mass ratio) of the sum of the contained amount of pigment and the contained amount of amorphous organic high molecular copolymer to the contained amount of plasticizer is preferably from 100:0.5 to 1:1, and is more preferably from 100:2 to 3:1.
Still further, in addition to the above components, a surface active agent, a thickener, and the like can be added to the image forming layer as occasion demands.
The layer thickness (dry layer thickness) of the above image forming layer is preferably from 0.2 to 1.5 xcexcm, and is more preferably from 0.3 to 1.0 xcexcm. If the layer thickness exceeds 1.5 xcexcm, the resolution may decrease. If the layer thickness is less than 0.2 xcexcm, the stability of the pigment dispersed solution deteriorates and suitability for coating (application) may deteriorate.
The above respective components are dissolved into a solvent or the like and an application solution (application solution for an image forming layer) is prepared. The application solution is applied onto the supporting body in accordance with a known applying method, and then the supporting body is dried. Accordingly, the above image forming layer can be formed.
Examples of the solvent which can be used when the application solution for an image forming layer is prepared include alcohols such as ethyl alcohol, propyl alcohol, or the like; ketones such as acetone, methylethylketone, or the like; esters such as ethyl acetate or the like; aromatic hydrocarbons such as toluene, xylene, or the like; ethers such as tetrahydrofuran, dioxane, or the like; amides such as DMF, N-methylpyrrolidone, or the like; cellosolves such as methylcellosolve or the like; and the like. The solvent can be selected appropriately from the above-described solvents in accordance with the presence/absence of the light to heat converting layer or the like. The above solvents can be used alone or in combination of two or more.
In order to prevent damages, the image receiving material or a protective cover film such as a polyethylene terephthalate sheet, a polyethylene sheet, or the like can be usually superposed on the surface of the image forming layer.
The above-described light to heat converting layer contains a light to heat converting substance and a binder resin (hereinafter, the binder resin may be referred to as xe2x80x9clight to heat converting layer binder polymerxe2x80x9d). The light to heat converting layer contains other components as occasion demands.
The above light to heat converting substance is, in general, a laser light absorbable material, such as a dye or the like, which can absorb laser light. Examples of the dye (pigment or the like) include a black pigment such as carbon black, pigment of a macrocyclic compound, such as phthalocyanine, naphthalocyanine, or the like, which has absorption from a visible region to a near infrared region, an organic dye such as an organic dye which is used as a laser absorbing material for a high density laser recording such as an optical disk or the like (a cyanine dye such as an indolenine dye or the like, an anthraquinone dye, an azulene dye, a phthalocyanine dye), and an organic metal compound dye such as a dithiol nickel complex or the like.
From the standpoint of improving the recording sensitivity, it is preferable that the light to heat converting layer is as thin as possible. As a result, it is preferable to use a phthalocyanine dye or an infrared absorption dye, such as a cyanine dye or the like, which has a large absorption coefficient in a laser light wavelength region.
As the above laser light absorbable material, an inorganic material such as a metallic material or the like can be also used. The above-described metallic material is used in a granulated (e.g., blackened silver) state.
The optical density of the light to heat converting substance at a laser absorption wavelength is preferably from 0.1 to 2.0, and is more preferably from 0.3 to 1.2.
If the above optical density is less than 0.1, the sensitivity of the thermal transfer material may be reduced. If the optical density exceeds 2.0, the cost may increase.
The light to heat converting layer binder polymer is preferably a resin having a high glass transition point and a high heat conductivity. Further, it is preferable that the heat resistance (e.g., thermal deformation temperature or thermal decomposition temperature) of the light to heat converting layer binder polymer is higher than that of a material which is used for a layer which is provided on the light to heat converting layer. As the above light to heat converting layer binder polymer, general heat resistant resins can be used. Examples of the heat resistant resins are methyl polymethacrylate, polycarbonate, polystyrene, ethyl cellulose, nitrocellulose, polyvinyl alcohol, gelatin, polyvinyl pyrrolidone, polyparabanic acid, polyvinyl chloride, polyamide, polyimide, polyetherimide, polysulfone, polyethersulfone, aramid, or the like.
When a plurality of high power lasers such as multimode lasers or the like are disposed and recording is effected, it is preferable that the light to heat converting layer binder polymer uses a polymer having excellent heat resistance. It is more preferable to use a polymer having a glass transition point (Tg) of from 150 to 400xc2x0 C. and a thermal decomposition temperature (herein, the thermal decomposition temperature refers to a 5% mass reduction temperature Td (in a TGA method, programming rate of 10xc2x0 C./minute in the air)) of 450xc2x0 C. or more. It is most preferable to use a polymer having Tg of from 220 to 400xc2x0 C.
In particular, the polyimide resins which are expressed by the following general formulas (I) to (VII) are soluble in an organic solvent. Because the produceability of the thermal transfer sheet improves, these polyimide resins are preferably used. Further, the polyimide resins are preferable from the standpoints of improving the viscosity stability, the long-term preservability, and the moisture resistance of the application solution for a light to heat converting layer.
In the above general formulas (I) and (II), Ar1 denotes an aromatic group which is expressed by following structural formulas (1) to (3), and n denotes an integer of from 10 to 100.
In the above general formulas (III) and (IV), Ar1 denotes an aromatic group which is expressed by the following structural formulas (4) to (7), and n denotes an integer of from 10 to 100.
In the above general formulas (V) to (VII), n and m denote an integer of 10 to 100. In formula (VI), the ratio of n to m is from 6:4 to 9:1.
The standard for determining whether the resin is soluble into the organic solvent is set by dissolving 10 parts by mass or more of the resin into 100 parts by mass of N-methylpyrrolidone at 25xc2x0 C. When 10 parts by mass or more of the resin is dissolved, the resin is preferably used as the resin for a light to heat converting layer. When 100 parts by mass or more of the resin is dissolved into 100 parts by mass of N-methylpyrrolidone, the resin is more preferably used.
The application solution (application solution for a light to heat converting layer), into which the above light to heat converting substance and the light to heat converting layer binder polymer are dissolved, is prepared. The application solution is applied onto the above supporting body, and then the supporting body is dried. Accordingly, the light to heat converting layer can be provided.
Examples of an organic solvent for dissolving the above light to heat converting layer binder polymer include 1,4-dioxane, 1,3-dioxolan, dimethylacetate, N-methyl-2-pyrrolidone, dimethylsulfoxide, dimethylformamide, xcex3-butyrolactone, or the like.
A method of applying the application solution for a light to heat converting layer can be selected appropriately from known application methods.
The drying is usually carried out at 300xc2x0 C. or less. More preferably, the drying temperature is 200xc2x0 C. or less. When polyethylene terephthalate is used as the supporting body, the drying temperature is furthermore preferably within the range of from 80 to 150xc2x0 C.
The solid content mass ratio of the light to heat converting substance to the light to heat converting layer binder polymer (light to heat converting substance : binder) within the above light to heat converting layer is preferably from 1:20 to 2:1, and is more preferably from 1:10 to 2:1. If the amount of the binder is too small, the cohesive force of the light to heat converting layer is lowered. Thus, when the formed image is transferred onto the image receiving material, the light to heat converting layer is easily transferred together with the formed image and color mixture of the image may occur. If the amount of the above binder is too large, the layer thickness of the light to heat converting layer is increased in order to achieve a constant light absorption rate, such that the sensitivity may be reduced.
The layer thickness of the light to heat converting layer is preferably from 0.03 to 0.8 xcexcm, and is more preferably from 0.05 to 0.3 xcexcm.
Further, it is preferable that the light to heat converting layer has a maximum absorbance (optical density) within the range of from 0.1 to 1.3 (preferably, from 0.2 to 1.1) in the wavelength region of from 700 to 2000 nm.
A heat sensitive peeling layer which includes a heat sensitive material can be provided on the light to heat converting layer of the thermal transfer material. The heat sensitive peeling layer generates gas or discharges water applied thereto due to the action of heat which was generated at the light to heat converting layer. In this way, the heat sensitive peeling layer weakens the bonding strength between the light to heat converting layer and the image forming layer.
The above heat sensitive material can use a compound (polymer or low molecular compound) which itself decomposes or is altered by heat and generates gas, a compound (polymer or low molecular compound) which absorbs a considerable amount of liquefied gas such as water, or the like. Or, a combination of such compounds may be used.
Examples of the polymer which decomposes or is altered by heat and generates gas are an auto-oxidizable polymer such as nitro cellulose or the like; a halogen-containing polymer such as chlorinated polyolefin, chlorinated rubber, polyvinyl chloride, polyvinylidene chloride, or the like; an acrylic polymer, such as polyisobutyl methacrylate or the like, which absorbs a volatile compound such as water or the like; cellulose ester, such as ethyl cellulose or the like, which absorbs a volatile compound such as water or the like; and a natural high molecular compound, such as gelatin or the like, which absorbs a volatile compound such as water or the like. Examples of the low molecular compound which decomposes or is altered by heat and generates gas are compounds, such as a diazo compound, an azide compound, and the like, which generate gas by exothermic decomposition. The above-described decomposition, alteration, or the like of the heat sensitive material by heat preferably occurs at 280xc2x0 C. or less, and particularly preferably occurs at 230xc2x0 C. or less.
When the low molecular compound is used as the heat sensitive material, it is desirable that the compound is combined with a binder. As the binder, the above polymer which itself decomposes or is altered by heat and an ordinary polymer binder which does not have such characteristics can be used.
When the heat-sensitive low molecular compound and the binder are used in combination, the mass ratio of the former to the latter is preferably from 0.02:1 to 3:1, and is more preferably from 0.05:1 to 2:1.
It is preferable that substantially the entire surface of the light to heat converting layer is covered with the heat sensitive peeling layer. The layer thickness of the heat sensitive peeling layer is, in general, from 0.03 to 1 xcexcm, and above all, is preferably from 0.05 to 0.5 xcexcm.
In case of the thermal transfer material having a structure in which the light to heat converting layer, the heat sensitive peeling layer, and the image forming layer are superposed on the supporting body in that order, the heat sensitive peeling layer decomposes and is altered by the heat which is transmitted from the light to heat converting layer, and generates gas. Then, due to the decomposition or the generation of gas, a portion of the heat sensitive peeling layer disappears, or alternatively, cohesive failure occurs within the heat sensitive peeling layer. The bonding strength between the light to heat converting layer and the image forming layer is thereby lowered. As a result, depending on the behavior of the heat sensitive peeling layer, a portion thereof may adhere to the image forming layer and appear on the surface of an ultimately formed image. Thus, color mixing of the image may occur.
Therefore, it is desirable that the heat sensitive peeling layer is hardly colored (i.e., exhibits high permeability with respect to visible light) so that, even if transfer of the heat sensitive peeling layer occurs, color mixture does not appear visually on the formed image. More specifically, the light absorption rate of the heat sensitive peeling layer is, with respect to visible light, preferably 50% or less and is more preferably 10% or less.
Instead of providing an independent heat sensitive peeling layer, the light to heat converting layer may be a heat sensitive peeling layer as well as the light to heat converting layer by adding the heat sensitive material to the light to heat converting layer.
In order to improve the adhesion to the surface of the image receiving layer of the image receiving material, it is preferable that a cushion layer is provided between the supporting body and the light to heat converting layer of the thermal transfer material as an intermediate layer having cushioning ability.
The above-described cushion layer is a layer which is easily deformed when stress is applied to the image forming layer. The cushion layer has the effect of improving the adhesion between the image forming layer and the image receiving layer at the time of laser thermal transfer and an effect of improving the image quality. Moreover, even if foreign matter enters between the thermal transfer material and the image receiving material, due to the deformation action of the cushion layer, the space between the image receiving layer and the image forming layer is reduced. As a result, the cushion layer has the effect of reducing the size of image void defects. Further, when an image is once transferred and formed and then transferred onto a printing paper or the like which is separately prepared, the image receiving surface deforms in response to the convexoconcave surface of the paper. Accordingly, by improving the transferability of the image receiving layer, and further, by lowering the gloss of the object to be transferred, the cushion layer can also have the effect of improving the resemblance of the ultimately obtained image with the initial printed matter.
In order to impart cushioning ability, a material having a low modulus of elasticity, a material having rubber elasticity, or a thermoplastic resin which is easily softened by heating may be used.
The modulus of elasticity is preferably from 10 to 500 kgf/cm2 at room temperature, and is more preferably from 30 to 150 kgf/cm2 thereat.
Further, in order to immerse a foreign object such as a rubber or the like, penetration (25xc2x0 C., 100 g, 5 seconds) which is defined in JIS K2530 is preferably 10 or more.
Moreover, the glass transition temperature of the cushion layer is 80xc2x0 C. or less, and is preferably 25xc2x0 C. or less. In order to adjust the physical properties, e.g., Tg, a plasticizer can be added into the polymer binder suitably.
In addition to rubbers such as a urethane rubber, a butadiene rubber, a nitrile rubber, acrylic rubber, a natural rubber, or the like, the binder which forms the cushion layer may be, for example, polyethylene, polypropylene, polyester, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic copolymer, vinyl chloride-vinyl acetate copolymer, vinylidene chloride resin, vinyl chloride resin containing plasticizer, polyamide resin, phenol resin, or the like.
The layer thickness of the cushion layer differs in accordance with the conditions of the resin to be used or the like. Usually, the layer thickness is preferably from 3 to 100 xcexcm, and is more preferably from 10 to 50 xcexcm.
The supporting body which can be used for the thermal transfer material is not limited in particular, and various supporting body materials can be selected appropriately in response to the purpose.
Examples of the supporting body material include synthetic resin materials such as polyethylene terephthalate, polyethylene-2,6-naphthalate, polycarbonate, polyethylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, styrene-acrylonitrile copolymer, and the like. Among them, biaxially oriented polyethylene terephthalate is preferable from the point of dimensional stability With respect to mechanical strength or heat. When the thermal transfer material is used for preparing a color proof which utilizes laser recording, the supporting body is preferably a transparent synthetic resin material, through which a laser light permeates.
Further, an undercoat layer, which is subjected to a surface activating processing and/or is one layer or two layers or more, may be provided at the above supporting body for the purpose of improving adhesion to the light to heat converting layer which is provided thereon.
The above surface activating processing includes, for example, a glow discharge processing, a corona discharge processing, or the like.
The material for the above undercoat layer is preferably a material which provides both surfaces of the supporting body and the light to heat converting layer with a high adhesive property, has low thermal conductivity, and has excellent heat resistance. Examples of the material for the undercoat layer include styrene, styrene-butadiene copolymer, gelatin, or the like. The layer thickness of the undercoat layer is usually from 0.01 to 2 xcexcm.
Further, the surface of the supporting body, at which the light to heat converting layer is not provided, can be provided with various functional layers, such as an antireflection layer and the like, as occasion demands, or can be subjected to a surface processing.
An image forming material is formed by the thermal transfer material of the present invention and the image receiving material. The above-described image receiving material has an image receiving layer on a supporting body. The supporting body of the image receiving material may be the same as that of the above thermal transfer material or may be separate and independent therefrom. There is an aspect in which the image receiving material is formed by having other layers, such as an undercoat layer, a cushion layer, a peeling layer, an intermediate layer, and the like, between the supporting body and the image receiving layer. Further, the image receiving material may have a back layer on the surface which is opposite the side at which the image receiving layer is provided. In order to improve the conveying ability and the stacking ability, or when the image receiving material is taken up in a roll shape, or the like, it is preferable to have the back layer from the point of roughening the surface of the image receiving layer. Moreover, it is also preferable that an antistatic layer is provided separately from the layers, or that an antistatic agent is added to the above respective layers.
An aspect in which the above image receiving layer has at least a cushion layer and an image receiving layer on the supporting body and in which the above supporting body has a void is preferable.
The above-described image receiving layer is a layer which is formed by having an organic polymer binder as a principal component.
The above organic polymer binder (hereinafter, the organic polymer binder may be referred to as xe2x80x9cimage receiving layer binder polymerxe2x80x9d) is preferably a thermoplastic resin. Examples of the organic polymer binder include a homopolymer of acrylic monomer and a copolymer thereof such as acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, or the like; cellulose polymer such as methyl cellulose, ethyl cellulose, cellulose acetate, or the like; a homopolymer of vinyl monomer and a copolymer thereof such as polystyrene, polyvinyl pyrrolidone, polyvinyl butyral, polyvinyl alcohol, polyvinyl chloride, or the like; a condensed polymer such as polyester, polyamide, or the like; and a rubber polymer such as butadiene-styrene copolymer or the like.
From the standpoint of obtaining moderate adhesive strength with the image forming layer, the image receiving layer binder polymer is preferably a polymer whose glass transition temperature (Tg) is lower than 90xc2x0 C. To this end, a plasticizer can be added to the image receiving layer. Further, for the purpose of preventing blocking between the sheets, the Tg of the image receiving layer binder polymer is preferably 30xc2x0 C. or higher.
From the standpoint of improving the adhesion to the image forming layer of the thermal transfer material and improving the sensitivity or the image strength at the time of laser recording, it is especially preferable that the above image receiving layer binder polymer uses the same or a similar polymer as the binder polymer which is used for the image forming layer.
The layer thickness of the above image receiving layer is preferably from 0.3 to 7 xcexcm, and is more preferably from 0.7 to 4 xcexcm.
If the above layer thickness is less than 0.3 xcexcm, when retransfer is carried out onto a printing paper, the film is insufficient in strength and is easily torn. If the layer thickness is more than 7 xcexcm, the gloss of the image after retransfer onto the paper increases and resemblance of the ultimately obtained image with the initial printed matter may deteriorate.
The above plasticizer used can be the same as the aforementioned plasticizer which is usable for the image forming layer of the thermal transfer material.
The supporting body which is used for the image receiving material is generally a sheet-shaped base material such as a plastic sheet, a paper, a metallic sheet, a glass sheet, or the like.
Examples of the plastic sheet include sheets of polyethylene terephthalate, polyethylene naphthalate, polyethylene, polycarbonate, polyvinyl chloride, polyvinylidene chloride, polystyrene, or the like. Among them, in particular, a polyethylene terephthalate sheet is preferable.
Examples of the above paper include a printing paper, a coat paper, or the like.
Further, as the supporting body, a white material having a void inside is preferable from the standpoint of cushioning ability, visibility of an image, and the like. In particular, an expanded polyester supporting body is most preferable from the standpoint of mechanical characteristics.
Moreover, for the purpose of enhancing the adhesion to the image receiving layer, the surface of the supporting body may be subjected to a surface processing such as a corona discharging processing, a glow discharging processing, or the like.
The thickness of the above supporting body is usually from 10 to 400 xcexcm, and is particularly preferably from 25 to 200 xcexcm.
For the purpose of roughening the surface of the image receiving layer and improving the conveying ability within the recording device, additives such as particulates of silicon oxide, a surface active agent, an antistatic agent of tin oxide particulates, or the like may be added to the above back layer.
The additives can be added not only to the back layer but also to other layers including the image receiving layer as occasion demands.
Examples of the above particulates include inorganic particulates of silicon oxide, calcium carbonate, titanium dioxide, aluminum oxide, zinc oxide, barium sulfate, zinc sulfate, or the like; organic particulates which are formed by resins, such as a polyethylene resin, a silicon resin, a fluoroethylene resin, an acrylic resin, a methacrylic resin, a melamine resin, or the like; and the like. Among them, titanium dioxide, calcium carbonate, silicon oxide, a silicon resin, an acrylic resin, and a methacrylic resin are preferable. The average particle size of the above particulates is preferably from 0.5 to 10 xcexcm, and is more preferably from 0.8 to 5 xcexcm.
The content of the above particulates is preferably from 0.5 to 80% by mass based on the total solid content mass of the back layer or the image receiving layer, and is more preferably from 1 to 20% by mass.
Further, the above antistatic agent can be selected and used appropriately from various types of surface active agents and conductive agents so that the surface resistance of the layer is 1012 xcexa9 or less, and is more preferably 109xcexa9 under the environmental conditions of 23xc2x0 C. and 50% RH.
As described above, examples of the image receiving layer are (1) an aspect of having the image receiving layer on the supporting body, and (2) an aspect of having the image receiving layer on the one surface of the supporting body and having the back layer including particulates on the other surface thereof. However, the present invention is not limited to the same, and the following aspects are possible. Namely, the image receiving material may be:
(3) an aspect which is formed by providing a cushion layer between the supporting body and the image receiving layer; or (4) an aspect in which particulates which are the same as those used in the above back layer are further included in the image receiving layer of the above-described aspect (3).
In case of the above aspects (2) to (4), by taking up the image receiving material in a roll shape, the surface of the image receiving material can be roughened by the pressing force of the back layer including particulates.
Moreover, as in the above aspects (3) and (4), by providing the cushion layer as an intermediate layer of the image receiving layer, adhesion failure which occurs when the surface of the image receiving layer is rough can be prevented. Thus, these aspects are also applicable to the present invention.
For the purpose of improving the adhesion of the image forming layer of the thermal transfer material to the surface of the image receiving layer, it is preferable that a cushion layer is provided between the supporting body and the image receiving layer of the image receiving material as an intermediate layer having cushioning ability.
The structural components which can be used for the above cushion layer can be the same as those of the cushion layer which is formed at the above thermal transfer material, and the above cushion layer can have the same structure as the cushion layer formed at the thermal transfer material.
It is necessary that the image receiving layer and the cushion layer be adhered together until the stage of laser recording. However, in order to transfer the image onto the printing paper, it is preferable that the image receiving layer and the cushion layer are provided so as to be peelable. In order to facilitate peeling, a peeling layer having a thickness of approximately from 0.1 to 2 xcexcm is preferably provided between the cushion layer and the image receiving layer.
It is preferable that the peeling layer functions as a barrier to the application solvent when solvent is applied to the image receiving layer.
As the structure of the image receiving material, an example in which the supporting body/the cushion layer/the image receiving layer are superposed is shown. However, in some cases, there may be a structure in which the image receiving layer also has a cushioning ability, i.e., a structure of a supporting body/an image receiving layer having a cushioning ability, or a structure of a supporting body/an undercoat layer/ an image receiving layer having a cushioning ability. In this case as well, it is preferable that the image receiving layer having a cushioning ability is provided peelably so that retransfer of an image to the printing paper is possible. In this case, an image which is retransferred onto the printing paper is an image having excellent gloss.
The layer thickness of the cushion layer which also serves as an image receiving layer is preferably from 5 to 100 xcexcm, and is more preferably from 10 to 40 xcexcm.
When the image is temporarily formed on the image receiving layer and thereafter is retransferred onto a printing paper or the like, it is also preferable that at least one layer of the image receiving layer is formed from a photo-curing material.
The composition of the photo-curing material may be, for example, a combination which is formed by a) a photopolymerization monomer which is formed by at least one of a multifunctional vinyl compound or a multifunctional vinylidene compound which can form a photopolymer by addition polymerization, b) an organic polymer, and c) additives such as a photopolymerization initiator, and as occasion demands, a polymerization inhibitor or the like.
The above multifunctional vinyl monomer includes unsaturated esters of polyol, in particular, acrylic ester or methacrylic ester (e.g., ethylene glycol diacrylate, pentaerythritol tetraacrylate).
Examples of the organic polymer are the same as the above examples of the image receiving layer binder polymer.
Examples of the above photopolymerization initiator include ordinary photoradical polymerization initiators such as benzophenone, Michler""s ketone, or the like. The photopolymerization initiator can be used in an amount of from 0.1 to 20% by mass based on the total solid content mass in the layer.
When the above cushion layer is provided, for the purpose of preventing immersion of particulates when the back layer having a rough surface or the image receiving layer contains the particulates, an intermediate layer which is hardly deformed when stress is applied thereto can be provided. It is necessary that the layer uses a material which enables application to the cushion layer. The layer can be formed by containing a polymer having a comparatively high glass transition point, such as PMMA, polystyrene, cellulose triacetate, or the like.
Explanation will be given of a laser thermal transfer recording method in which image recording is carried out using the image forming material of the present invention.
The laser thermal transfer recording method is effected as follows. A superposed body, in which the image receiving material is superposed on the surface of the image forming layer of the thermal transfer material so that the image receiving layer abuts thereto, is prepared. Laser light is illuminated imagewise in time sequence onto the surface from the upper side of the thermal transfer material of the superposed body (the supporting body side of the thermal transfer material). Thereafter, the image receiving material and the thermal transfer material are peeled, such that the image receiving material, onto which the laser illuminated region of the above image forming layer was transferred, is obtained.
There are various methods of forming the above superposed body. For example, since it is unnecessary to control the temperature of a heat roller or the like and adhesion and superposition can be effected quickly and uniformly, a vacuum adhering method may be used.
In this case, the surface roughness may be decreased for the purpose of enhancing the adhesion as described above. However, it is impossible to reduce the pressure at high speed at the time of vacuumizing. Conversely, if the surface roughness is increased in order to carry out the vacuumizing at high speed, the degree of reduced pressure on the adhering surface between the image receiving layer of the image receiving material and the image forming layer of the thermal transfer material which contact each other improves. However, there are a number of micro voids on the contact surfaces, and accordingly, the thermal conductivity is inhibited and the transferability may be reduced.
In order to obtain appropriate adhesion for the image recording, it is preferable that the layer surface configuration on the adhering surface changes as the degree of reduced pressure on the adhering surface increases and that the image receiving layer and the image forming layer are in a completely and uniformly adhered state. Therefore, it is useful to provide the cushion layer at the thermal transfer material and/or the image receiving material from the point of improving transferability and forming an image having high image quality.
Moreover, in addition to the above vacuum adhering method, as another method of forming a superposed body, for example, a method in which the transferring side (image forming layer side) of the thermal transfer material and the image receiving side (image receiving layer side) of the image receiving material are superposed, pressurized, and conveyed through heat rollers is also preferable. In this case, the heating temperature is 160xc2x0 C. or less, or more preferably 130xc2x0 C. Further, a method in which the image receiving material is mechanically adhered onto a metal drum while pulling the image receiving material, and further, the thermal transfer material is mechanically adhered onto the image receiving material in the same manner while pulling the thermal transfer material is also preferable. Among the aforementioned, the vacuum adhering method is particularly preferable.
The adhesion between the thermal transfer material and the image receiving material may be carried out immediately before the laser light illuminating operation.
In the case of the vacuum adhering method, usually, the image receiving material side of the above superposed body is adhered by vacuumizing to the surface of a recording drum (rotating drum which has a vacuum forming mechanism inside and has a number of minute opening portions on the surface of the drum), the thermal transfer material which is larger than the image receiving material is superposed so as to cover the entire image receiving material, the pressure of the contact interfaces is reduced by vacuumizing, and the contact interfaces are adhered. The laser light illuminating operation is effected in this state by illuminating a laser light from the outer side of the superposed body, i.e., from above the thermal transfer material side. The illumination of the laser light is scaned so as to move reciprocally in the transverse direction of the drum, and the recording drum is rotated at a constant rotating speed during the illuminating operation.
The laser thermal transfer recording method can be utilized for manufacturing a black mask or forming a monochromatic image and can be also utilized advantageously for forming a polychromatic image. A method of forming a polychromatic image may be, for example, the aspects described below.
Namely, a first aspect of the method of forming a polychromatic image is effected as follows. The image receiving material is fixed onto the rotating drum of a recording device in accordance with a vacuum reduced pressure method. The thermal transfer material is superposed in the same way on the image receiving material in accordance with the vacuum reduced pressure method so that the image receiving layer and an image recording layer (hue 1) of the thermal transfer material contact. Next, a laser light which was modulated on the basis of a digital signal of the color separated image of a document image is illuminated from the supporting body side of the thermal transfer material while rotating the drum. Thereafter, the thermal transfer material is peeled from the image receiving material in a state in which the image receiving material is fixed. The thermal transfer materials having a hue 2, a hue 3, and a hue 4, as occasion demands, are superposed on the image receiving material, on which the image having a hue 1 was recorded, in accordance with the same method as described above. Then, the processes of laser recording and peeling are repeated sequentially. Accordingly, the image receiving material, on which a polychromatic image is formed by the above processes, can be obtained. In order to obtain a color proof image on a printing paper, the image receiving material, on which the polychromatic image was formed by the above processes, is superposed so that the image surface contacts the printing paper. Then, the image receiving material is heated through a laminater or the like, pressurized, and further, peeled. The image is transferred onto the printing paper with the image receiving layer, such that the color proof image can be obtained.
A second aspect of the method of forming a polychromatic image is carried out as follows. Each thermal transfer material has an image forming layer which contains a coloring agent having a different hue. The thermal transfer materials are superposed, such that superposed bodies are formed. Three types (three colors) or four types (four colors) of superposed bodies are independently prepared. Each superposed body is subjected to laser illumination on the basis of the digital signal of each color image which is obtained through a color separation filter and which corresponds to each superposed body. Thereafter, the thermal transfer material and the image receiving material are peeled. The color separated image of each color is independently formed a corresponding image receiving material. Then, each color separated image is successively superposed on an actual supporting body, such as a printing paper or the like, which is separately prepared or a supporting body which is similar to the actual supporting body. Accordingly, an image can be formed.
Examples of the laser light source which is used for the above image recording include a gas laser such as an argon ion laser, a helium neon laser, a helium cadmium laser, or the like; a solid state laser such as a YAG laser light or the like; a direct laser such as a semiconductor laser, a dye laser, an excimer laser, or the like; or a laser in which these lasers are converted into lasers whose wavelengths are halved through a secondary harmonic element. Among the aforementioned, a multimode semiconductor laser is preferable from the viewpoint of high output and high speed image formation, and a refractive index wave guiding type lateral multimode semiconductor laser is particularly preferable.
Further, in the laser thermal transfer recording method using the laser thermal transfer material of the present invention, it is preferable that the laser illumination is carried out under the condition in which the beam diameter on the light to heat converting layer is from 3 to 50 xcexcm, and more preferably from 7 to 30 xcexcm.
In accordance with the above laser thermal transfer recording method, even if the laser is used for the image recording, an image having high image density and high quality can be formed at high speed without having a harmful effect caused by thermal decomposition of the coloring agent.

Thermal transfer material and image forming material using the same


An elongated, vertical conduit has an upper end, communicating with the bottom opening in an upper container or ladle, and an open lower end disposed above the top surface of a bath of molten metal in a lower container or tundish. A descending stream of molten metal is directed from the conduit into the bath. A shroud encloses the conduit and the descending stream. The pressure within the shroud is lower than the outside pressure and is regulated. A mixture of transport gas and solid, particulate alloying ingredient prone to excessive fuming is injected into the descending stream within the shroud.

The present invention relates generally to methods and apparatuses for adding solid alloying ingredients to molten metal and more particularly to the addition of solid, particulate alloying ingredients to a stream of molten metal descending from an upper container to a lower container.
It is oftentimes desirable to add alloying ingredients, in solid, particulate form, to a molten metal stream descending from an upper container, such as a ladle, to a lower container, such as the tundish of a continuous casting apparatus. Certain alloying ingredients, such as lead, bismuth, tellurium and selenium, typically added to steel to improve the machinability thereof, have relatively low melting points compared to steel and are prone to excessive fuming when added to molten steel.
One procedure heretofore contemplated for adding these alloying ingredients to molten steel comprises injecting solid particles of these ingredients into a descending stream of molten metal contained within and completely filling the cross-section of an elongated conduit extending between and communicating with both the ladle and the tundish. The solid particles are mixed with a transport gas, and the mixture is introduced into the descending stream of molten metal through an injection port in the conduit. However, a number of problems can arise should this procedure be employed. For example, the molten metal can back up through the injection port, there can be a pulsing delivery of the solid particles rather than a uniform delivery thereof and there can be a plugging of the injection nozzle.

Apparatus for adding solid alloying ingredients to molten metal stream


The present invention provides novel compositions containing calcium and/or other minerals (as single mineral compositions or as multiple mineral compositions), methods for making these compositions, and methods for delivering the compositions. The compositions provide soluble bioavailable calcium and/or other minerals at a high concentration due to the high solubility attained through the processing method contained in this patent. Addition by these methods of other mineral(s) to calcium increases the stability and solubility of the calcium. The compositions of the present invention are powders that can be reconstituted in aqueous solutions. The compositions of the present invention also are very stable, allowing for a long shelf life of the compositions and of foods supplemented with the compositions.

The present invention relates to nutritional sources of solubilized calcium. More particularly, the present invention relates to sources of solubilized calcium having improved shelf life and stability.
Minerals are an essential part of the human diet. Sufficient quantities of most minerals can be obtained through the proper choice of foods and beverages; however, many people do not consume a well-balanced diet, and mineral supplements can be beneficial to many. Among other uses, calcium supplements are beneficial for the building and protection of bones and teeth, for the prevention and possibly the treatment of osteoporosis, and for use as cofactors to a number of essential enzymes such as those involved in the conversion of prothrombin to thrombin. Additionally, increased amounts of calcium may be required after heavy physical exercise, and the level of calcium in the blood stream has been shown to have an effect on neurological function. Magnesium is an essential cofactor to many of the body""s enzymatic reactions. Potassium is involved in basic cell metabolism and is used in high levels as a prescription for heart patients. Intake of potassium and magnesium has been found to reduce the risk of stroke. Zinc is also an essential mineral. Research is ongoing on the effects of specific minerals and mineral combinations on health.
Numerous attempts have been made to provide calcium nutritional supplements that are easily consumed by the public, are readily available, contain easily absorbable minerals, and have long storage times without degradation. To this end much of the work has focused on forms of calcium that can be added to drinks. For example, U.S. Pat. No. 5,500,232 to Keating claims a drink consisting essentially of citric acid, fumaric acid, calcium hydroxide and calcium glycerophosphate. But there is an xe2x80x9cacidxe2x80x9d flavor to all systems tested and this patent teaches to use this xe2x80x9ctartnessxe2x80x9d as part of the flavoring system. U.S. Pat. No. 5,474,793 claims a method for making calcium supplemented fruit juice. However, these systems of calcium supplementation do not meet the requirements for a stable food supplement that can provide high amounts of soluble, bioavailable calcium and/or other minerals in a nontart form convenient for the user.
None of the prior art addresses the issue of multiple mineral supplements in high levels that provide for a highly soluble, stable product with little or no taste or odor and which is essentially clear when reconstituted in water.

Highly soluble and stable mineral supplements containing calcium and magnesium and methods of making


A navigation system suitable for use by an automated vehicle includes a first sensor, a second sensor, a digital-map, and a controller. The digital-map includes a first data-group of navigation-features preferentially detected by the first sensor-technology, and a second data-group of navigation-features preferentially detected by the second sensor-technology. The controller determines, on the digital-map, first and second locations of the host-vehicle using the first and second sensors, respectively. The controller selects one of the first and second locations to navigate the host-vehicle based on a comparison of the first data-density and the second data-density. Alternatively, the controller determines a first feature-density and a second feature-density of navigation-features detected by the first and second sensors respectively, and selects one of the first location and the second location to navigate the host-vehicle based on a comparison of the first feature-density and the second feature-density.

It is known to navigate, control, or otherwise operate an automated vehicle (host-vehicle) using various sensors, e.g. camera, radar, lidar. It is also been suggested to use such sensors to determine a location of the host-vehicle on a digital map. However, each of the various sensor-technologies has advantages and disadvantages for detecting various types of navigation-features, so uncertainty can arise if locations on the digital-map determined by different sensors do not coincide with each other, and/or may not coincide with a location determined using a global-positioning-system (GPS).

Automated vehicle sensor selection based on map data density and navigation feature density


A method for improving photosynthesis of rice includes the step of knocking out IPS1 gene in rice. The IPS1 gene has a nucleotide sequence shown in SEQ ID NO: 1.

Rice is one of the most important crops in the world. Photosynthesis, which uses energy from sunlight to produce glucose from carbon dioxide and water, is a key factor in biomass synthesis during rice growth. Identification of genes with the function of high photosynthetic efficiency has an important application prospect.
CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 technology is a significant improvement of genome editing tools for gene functional analysis. A single guide RNA (sgRNA) is generated to direct Cas9 nuclease to a specific genomic location, and Cas9-induced double strand breaks are repaired. The repair is error prone and thus insertions/deletions may be introduced that can disrupt gene function by frame-shift mutation. Therefore, CRISPR/Cas9 can efficiently be used for knockout of target gene, and has been widely used in researches of gene function and application of molecular breeding.


A composite oxide for an exhaust gas purification catalyst is provided which can burn PM in diesel engine exhaust gas at low temperatures and has a good S desorption property. The composite oxide for an exhaust gas purification catalyst is composed of Ce, Bi, Pr, R, and oxygen in a molar ratio of Ce:Bi:Pr:R=(1−x−y−z):x:y:z. The ratios of Ce, Bi, Pr, and R satisfy 0<x+y+z≦0.5 and preferably 0<x≦0.1, 0<y≦0.25, and 0<z≦0.3. Particularly, when R is Zr, the composite oxide exhibits a good S desorption property at a temperature of about 600° C. and can recover its catalytic activity at low temperatures. Therefore, the exhaust gas purification catalyst is suitable as a PM combustion catalyst.

One problem with diesel engines is that the exhaust gas contains particulate matter (hereinafter may be referred to as "PM") that is composed mainly of nitrogen oxides (NOx) and carbon and causes environmental pollution. In one general method of removing PM that causes the problem, a diesel particulate filter (DPF) formed of a porous ceramic material is disposed in an exhaust gas passage to trap PM. Although the PM is accumulated in the DPF, the trapped PM is generally subjected to intermittent or continuous combustion treatment to remove the PM so that the DPF is regenerated to its original state before trapping of the PM.
General examples of the DPF regeneration treatment include a method in which PM is burned by forced heating from the outside using an electric heater, burner, and the like, and a method in which an oxidation catalyst is placed closer to the engine side than the DPF to convert NO contained in the exhaust gas to NO2 so that the oxidizing ability of NO2 is used to burn PM.
However, to use the electric heater or burner, an external power source must be provided. In addition, for example, a mechanism for actuating the electric heater etc. when the need for regeneration of the DPF arises must be provided separately. Accordingly, the exhaust gas purification system itself is complicated. When an oxidation catalyst is used, the combustion of PM may be insufficient in some cases because the temperature of the exhaust gas is not high enough for the catalyst to exhibit sufficient catalytic activity and because a sufficient amount of NO necessary for the combustion of PM can be obtained only under certain operating conditions.
A more preferred DPF regeneration treatment method that is being contemplated is to burn PM with its combustion start temperature reduced by the catalytic action of a catalyst supported on the DPF itself. The most preferred method is to burn the PM continuously at the temperature of the exhaust gas, and this is the ultimate goal.
At present, Pt, a catalyst metal, supported on high-specific surface area alumina or the like is used as an oxidation catalyst (PM combustion catalyst) for burning and removing PM trapped by a DPF. However, the catalytic action of Pt on the combustion of PM is low at the temperature level of is the exhaust gas from an engine. Therefore, may be difficult to burn PM continuously using the heat of the exhaust gas. Accordingly, means for forced heating from the outside must also be used. In addition, the price of Pt varies with the balance between supply and demand, and this can cause a problem of large fluctuations in cost.
A PM combustion catalyst may undergo a rapid temperature increase due to the heat generated by combustion of PM. Therefore, the PM combustion catalyst must have properties such that a reduction in catalytic performance (thermal degradation) after thermal history at high temperatures is as low as possible.
Patent Documents 1 to 3 disclose, as oxidation catalysts including a composite oxide of ceria as a base material and containing no noble metal element such as Pt, mixtures containing Ce, Bi, and an optional transition metal element.    Patent Document 1: Japanese Patent Application Laid-Open No. Hei 6-211525    Patent Document 2: Japanese Patent Application Laid-Open No. 2003-238159    Patent Document 3: Japanese Patent Application Laid-Open No. 2006-224032

Composite oxide for exhaust gas purification catalyst, method for manufacturing the same, coating material for exhaust gas purification catalyst, and filter for diesel exhaust gas purification


A fabrication method of the semiconductor device comprises forming an isolation layer and an active region, which is defined by the isolation layer, on a substrate, forming an insulating layer on the substrate, forming a plurality of pillar masks, which are spaced from one another by a first gap and a second gap that is smaller than the first gap, on the insulating layer, forming spacers on the plurality of pillar masks, forming mask bridges in regions where the plurality of pillar masks are spaced from one another by the second gap by partially removing the spacers and forming a contact hole, which exposes the active region, by etching the insulating layer using the plurality of pillar masks and the mask bridges.

The inventive concepts relate to semiconductor devices and fabrication methods thereof, and more particularly, to semiconductor devices having contact holes, fabrication methods of the semiconductor devices, and methods of forming the contact holes.
As the integration density of semiconductor devices continues to increase, the design rules for components of the semiconductor devices continue to be reduced. In particular, a gate length, which is a standard for the design rules for semiconductor devices that include a large number of transistors, continues to decrease, and the size of contact holes for electrically connecting conductive layers on different levels continues to decrease.

Methods of forming contact holes using pillar masks and mask bridges


A method is provided for monitoring the operation of intake valves of an internal combustion engine, where at least one or more cylinders of the engine have more than one intake valve, and adapted to operate in different modes where at least one of the intake valves for a particular cylinder can be selectively activated, or deactivated so as not to open during a firing sequence for the cylinder. The method includes a) monitoring the intake manifold air pressure; b) during a time window with respect to the intake phase for said respective cylinder, determining the condition of whether the manifold pressure drops by a threshold or to a particular threshold level; and c) determining the functionality of the intake valves dependent on the outcome of step b).

Skip fire methodology involves selective cylinder deactivation to increase engine operating efficiency by disabling engine valves to reduce pumping losses when fewer cylinders are required for a particular operating point.
In similar methodology, a method of operating multi intake valve engines (multi-cylinder skip fire internal combustion engine systems), that is to say where each cylinder has more than one intake valve, involves deactivating only one intake valve for each multi intake valve cylinders in order to produce a swirl motion for the incoming charge air. This "swirl" mode of operation can replace "swirl valve" actuators used in some commercially available engines today, if the engines were to have valve deactivation hardware instead.
It is an object of the invention to provide a method of diagnosing such operation.
Prior art U.S. Pat. No. 9,562,470B2 patent by Tula Technology Inc. presents some methods for detecting valve actuation faults in a multi-cylinder skip fire internal combustion engine specifically to the end goal of detecting faults during skip fire operation.

Method of monitoring an engine able to operate with selective valve deactivation


The invention relates to a block forming a dead form work element for the construction of a mechanically resistant concrete wall. The block essentially comprises two parts (1a, 1b) which can be assembled, each part consisting of a main surface (10a, 10b) which is integral with and acts as the starting point on one side for bracing elements in the form of a shaft (11a, 12a, 13a, 14a, 14b), whereby said parts when assembled rest against each other and interlock via the ends of the bracing elements. The invention can be used to improve the construction of swimming pools.

This invention relates to a block forming a dead form work element for a reinforced concrete wall, particularly for the construction of Civil Engineering works such as swimming pools or water tanks, which can be equipped with a liner (watertight inner pocket), since such works must comprise a mechanically-resistant reinforced concrete wall.
Many dead form work manufacturing processes and devices for the building of such works are already known.
Some processes use, for instance, dead form structures along the total height of the wall to be built, juxtaposed and assembled with one another by various means. Such form structures usually tend to be unpractical, their versatility of use is extremely limited, they are very costly, much too bulky for storage and transport purposes, and generally not suitable for the construction of a perfectly watertight continuous concrete wall.
In his prior patents FR 94 11182 and FR 95 01853, the applicant already described panels forming dead form structures for the building of such works. Said panels comprise essentially two surface sheets held together by means of bracing structures regularly distributed and attached between the two sheets, while leaving spaces between them to allow for the passage of the metal reinforcements and the on-site pouring of the concrete. Such panels constitute already quite a significant progress over the prior art, allowing in particular for a great versatility of use and necessitating less concrete. Yet, they do require, for the installation of the various elements of the swimming pool such as water inlet and outlet fittings and other equipment as well as for the installation of the liner, extensive work for the preparation and positioning of these devices on/or through the wall of the work.
In his prior patent FR 98 06382, the applicant also described a panel forming a dead form structure made of elementary blocks formed with two parts that can be assembled, each one having a main face on which bracing elements are integrally fastened on one side thereof, said two parts designed to bear on each other in the assembling position via the free extremities of said bracing elements. These two parts can fit inside each other when their respective position is inverted, so as to minimize bulk during storage or transport.
This invention relates to a block that somehow represents a synthesis of the two prior types of construction, while adding many other advantages, especially as to the ease and security of use, in particular regarding the installation, the sealing and the ease and precision of the setting of all the pool elements and operating pieces of equipments.
To this effect, an elementary block forming dead form structure, in particular for the building of Civil Engineering works, especially swimming pools or water tanks requiring a mechanically-resistant concrete wall, is, during use, in the shape of a rigid block, essentially a rectangular parallelepiped, with a hollow volume between its two opposite main faces to allow for the pouring of the concrete. Said elementary block consists essentially of two parts that can be assembled, each one comprising said main face with, integrally fastened on one side thereof, regularly distributed bracing elements. Said two parts come to bear on each other and to interlock in the assembling position via the free extremities of said bracing elements. According to a characteristic of this invention, said bracing elements are in the shape of a shaft with an essentially cylindrical section and with an occupancy volume of essentially at least 40% of the volume of the block and preferably about at least 45% of this volume.
Advantageously, said two parts of the elementary block are identical, their assembling and interlocking being carried out by complementary organs facing one another when said identical parts are brought together but rotated at 180xc2x0 relatively to one another, the adjacent elementary blocks interlocking by simply bearing onto one another by means of complementary locking means provided in particular on their edge.
According to an advantageous characteristic of this invention, the bracing elements in the shape of shafts with an essentially cylindrical section are designed with a polygonal section and occupy the major part of the block width. This configuration allows for a better resistance, for a same weight of matter, of the mechanical block consisting of these two interlocked parts and facilitates the connecting-interlocking of these two parts.
According to another characteristic of this invention, each elementary block comprises at its upper edge a recess in the shape of a groove for the hooking of the liner.
Advantageously, in a block forming element of a wall of the casting concrete along the height of the work wall, each said part of the block comprises several said bracing elements, lined up along the height, and a canal capable of housing a seal along the height and the edge of said part, this seal being compressed by the complementary edge in the next adjacent similar block.

Block forming dead form work element for a reinforced concrete wall


A method of determining reliability of electronic documents associated with an event occurring in connection with a computing device may comprise, with a processor, composing a number of search queries based on text included in an event message, searching for a number of electronic documents via a network, said searching performed based on the composed search queries, and ranking the electronic documents identified by said searching based upon an indication of reliability in addressing the event associated with the event message, in which, ranking the electronic documents comprises applying a content source ranking criteria.

As computing devices and systems, and their associated software and middleware component grow in complexity, the generation of events within the computing devices and systems proportionally increase. Events may be described as an occurrence of significance within a computing device or system, and may include completion or failure of an operation, or the change in state of a process within a computing device or system. Thus, events may reflect normal behavior as well as abnormal behavior (errors and outages) within computing devices and systems.
Events are used to alert a user of the current status of the computing devices or systems, and to help troubleshoot problems that may affect performance of the computing devices and systems. These events are often manifested by hardware and software in text form as messages provided to a user.
It is apparent that errors encountered while operating the computing devices or systems are also prevalent in view of the growth in computing technology. This situation is compounded by the fact that these computing devices and systems are continually inundated by viruses, malware, spyware, and other foreign files that slow or halt the computing device's ability to perform processes or otherwise function in an intended manner.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.

Determining reliability of electronic documents associated with events

Hewlett-Packard Development Company, L.P.


In an air-fuel ratio feedback control system including at least one air-fuel ratio sensor downstream of a catalyst converter provided in an exhaust gas passage, an actual air-fuel ratio is controlled in accordance with the output of the downstream-side air-fuel ratio sensor. When at least one of the air-fuel ratio feedback control conditions for the downstream-side air-fuel ratio sensor is not satisfied the controlled air-fuel ratio is made an air-fuel ratio by an open loop control, while all the air-fuel ratio feedback control conditions for the downstream-side air-fuel ration sensor are satisfied the controlled air-fuel ratio is made the stoichiometric ratio (.lambda.=1) in accordance with the output of the downstream-side air-fuel ratio sensor. For a period after all the air-fuel ratio feedback control conditions for the downstream-side air-fuel ratio sensor are satisfied, the control by the output of the downstream-side air-fuel ratio sensor is prohibited, but, the controlled air-fuel ratio is made the stoichiometric ratio (.lambda.=1) by an open loop control or by the output of an upstream-side air-fuel ratio sensor.

(1) Field of the Invention
The present invention relates to a method and apparatus for feedback control of an air-fuel ratio in an internal combustion engine having at least one air-fuel ratio sensor downstream of a catalyst converter disposed within an exhaust gas passage.
(2) Description of the Related Art
Generally, in a feedback control of the air-fuel ratio sensor (O.sub.2 sensor) system, a base fuel amount TAUP is calculated in accordance with the detected intake air amount and detected engine speed, and the base fuel amount TAUP is corrected by an air-fuel ratio correction coefficient FAF which is calculated in accordance with the output of an air-fuel ratio sensor (for example, an O.sub.2 sensor) for detecting the concentration of a specific component such as the oxygen component in the exhaust gas. Thus, an actual fuel amount is controlled in accordance with the corrected fuel amount. The above-mentioned process is repeated so that the air-fuel ratio of the engine is brought close to a stoichiometric air-fuel ratio.
According to this feedback control, the center of the controlled air-fuel ratio can be within a very small range of air-fuel ratios around the stoichiometric ratio required for three-way reducing and oxidizing catalysts (catalyst converter) which can remove three pollutants CO, HC, and NO.sub.X simultaneously from the exhaust gas.
In the above-mentioned O.sub.2 sensor system where the O.sub.2 sensor is disposed at a location near the concentration portion of an exhaust manifold, i.e., upstream of the catalyst converter, the accuracy of the controlled air-fuel ratio is affected by individual differences in the characteristics of the parts of the engine, such as the O.sub.2 sensor, the fuel injection valves, the exhaust gas recirculation (EGR) valve, the valve lifters, individual changes due to the aging of these parts, environmental changes, and the like. That is, if the characteristics of the O.sub.2 sensor fluctuate, or if the uniformity of the exhaust gas fluctuates, the accuracy of the air-fuel ratio feedback correction amount FAF is also fluctuated, thereby causing fluctuations in the controlled air-fuel ratio.
To compensate for the fluctuation of the controlled air-fuel ratio, double O.sub.2 sensor systems have been suggested (see: U.S. Pat. Nos. 3,939,654, 4,027,477, 4,130,095, 4,235,204). In a double O.sub.2 sensor system, another O.sub.2 sensor is provided downstream of the catalyst converter, and thus an air-fuel ratio control operation is carried out by the downstream-side O.sub.2 sensor is addition to an air-fuel ratio control operation carried out by the upstream-side O.sub.2 sensor. In the double O.sub.2 sensor system, although the downstream-side O.sub.2 sensor has lower response speed characteristics when compared with the upstream-side O.sub.2 sensor, the downstream-side O.sub.2 sensor has an advantage in that the output fluctuation characteristics are small when compared with those of the upstream-side O.sub.2 sensor, for the following reasons:
(1) On the downstream side of the catalyst converter, the temperature of the exhaust gas is low, so that the downstream-side O.sub.2 sensor is not affected by a high temperature exhaust gas.
(2) On the downstream side of the catalyst converter, although various kinds of pollutants are trapped in the catalyst converter, these pollutants have little affect on the downstream side O.sub.2 sensor.
(3) On the downstream side of the catalyst converter, the exhaust gas is mixed so that the concentration of oxygen in the exhaust gas is approximately in an equilibrium state.
Therefore, according to the double O.sub.2 sensor system, the fluctuation of the output of the upstream-side O.sub.2 sensor is compensated for by a feedback control using the output of the downstream-side O.sub.2 sensor. Actually, as illustrated in FIG. 1, in the worst case, the deterioration of the output characteristics of the O.sub.2 sensor in a single O.sub.2 sensor system directly effects a deterioration in the emission characteristics. On the other hand, in a double O.sub.2 sensor system, even when the output characteristics of the upstream-side O.sub.2 sensor are deteriorated, the emission characteristics are not deteriorated. That is, in a double O.sub.2 sensor system, even if only the output characteristics of the downstream-side O.sub.2 are stable, good emission characteristics are still obtained.
In the above-mentioned double O.sub.2 sensor system, for example, an air-fuel ratio feedback control parameter such as a rich skip amount RSR and/or a lean skip amount RSL is calculated in accordance with the output of the downstream-side O.sub.2 sensor, and an air-fuel ratio correction amount FAF is calculated in accordance with the output of the upstream-side O.sub.2 sensor and the air-fuel ratio feedback control parameter (see: U.S. Pat. No. 4,693,076). In this case, the air-fuel ratio feedback control parameter is stored in a backup random access memory (RAM). Therefore, when the downstream-side O.sub.2 sensor is brought to a non-activation state, such as a fuel cut-off state, to stop the calculation of the air-fuel ratio feedback control parameter by the down- stream-side O.sub.2 sensor, the air-fuel ratio correction amount FAF is calculated in accordance with the output of the upstream-side O.sub.2 sensor and the air-fuel ratio feedback control parameter which was calculated in an activation state of the downstream-side O.sub.2 sensor (i.e., an air-fuel ratio feedback control mode for the downstream-side O.sub.2 sensor) and was stored in the backup RAM. Note that, in a fuel cut-off state, an air-fuel ratio feedback control for the upstream-side O.sub.2 sensor is also prohibited.
In the above-mentioned double O.sub.2 sensor system, the air-fuel ratio feedback control conditions for the downstream side O.sub.2 sensor are as follows:
the coolant temperature is higher than a predetermined value;
the engine is not in an idling state;
the engine is not in a fuel cut-off state;
a secondary air suction system is not driven for forcibly causing the air-fuel ratio upstream of the catalyst converter;
the downstream-side O.sub.2 sensor is in an activation state.
Other conditions may be introduced. Therefore, even when all the air-fuel ratio feedback conditions for the downstream-side O.sub.2 sensor are satisfied, the downstream-side O.sub.2 sensor may be not completely in an activation state or the O.sub.2 storage effect of the three-way catalysts may remain. For example, when the engine is in a fuel cut-off state or in a lean driving state for forcibly causing the engine to be in a lean air-fuel ratio, regardless of the output of the O.sub.2 sensors, the three-way catalysts absorb O.sub.2 molecules, and therefore, immediately after the engine returns to a driving state of the stoichiometric air-fuel ratio, the three-way catalysts expel the stored O.sub.2 molecules therefrom. This is a so-called O.sub.2 storage effect. Particularly, at a descending driving mode, if racing occurs too frequently this invites fuel cut-off operations, and the O.sub.2 storage effect is remarkably exhibited. As a result, even when the air-fuel ratio upstream of the catalyst converter is actually rich, the air-fuel ratio downstream of the catalyst converter is lean for a long time, so that the output of the downstream-side O.sub.2 sensor indicates a lean state. Therefore, if an air-fuel ratio feedback control for the downstream-side O.sub.2 sensor is carried out immediately after the engine is switched to a driving state of the stoichiometric air-fuel ratio, the air-fuel ratio feedback control parameter may be so large or small that an air-fuel ratio feedback control by the upstream-side O.sub.2 sensor using the air-fuel ratio feedback control parameter produces an overrich air-fuel ratio, thus increasing the HC and CO emissions, and raising the fuel consumption. Particularly, in a system where the air-fuel ratio feedback control parameter is stored in the backup RAM in a fuel cut-off state or the like, as explained above, if frequent switching from a fuel cut-off state to a fuel cut-off recovery state and vice versa occurs, the controlled air-fuel ratio becomes further overrich, which means that an air-fuel ratio feedback control for the downstream-side O.sub.2 sensor is meaningless.
The above-mentioned overrich air-fuel ratio problem is true for a single O.sub.2 sensor system having only one O.sub.2 sensor downstream of the catalyst converter.

Air-fuel ratio feedback control system including at least downstream-side air-fuel ratio sensor