Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/30—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using chemical colour formers
  • B41M5/323—Organic colour formers, e.g. leuco dyes

Definitions

• thermographic materials and methods have been previously described in a number of domestic and foreign patents. These materials frequently have the advantage of simplicity over certain photographic processes in that they produce a direct positive image of the original upon exposure to radiant energy (e.g., infrared radiation).
• radiant energy e.g., infrared radiation
• certain of these known thermographic materials possess properties which make them of limited utility in the production of facsimile copies on a commercial scale. For example, certain of these thermographic materials are only slightly sensitive to heat, and therefore require prolonged exposures. Other materials contain metallic ions which may stain the material upon which the heat-sensitive layer is coated.
• Yet other thermographic materials have the disadvantage of being excessively sensitive to visible light, and hence these materials must be handled in the dark until they are first exposed. Still other heat-sensitive copying materials exhibit thermotrophy and therefore lose their developed color when the heat-sensitive material is cooled to ambient temperature.
• thermographic copying material disclosed in Crevling et al. US. Pat. 2,899,334.
• the thermographic materials disclosed in that patent comprise a p-quinone compound and dihydroxybenzene compound which are maintained in physically distinct but chemically interactive relationship, so that upon exposure to heat they react with one another and undergo a rapid color change.
• These thermographic materials are particularly preferred over other thermographic materials disclosed in the prior art because they do not require prolonged exposure, they are not sensitive to visible light, and upon cooling the heat induced color change is intensified.
• thermographic materials disclosed in Crevling et al. US. Pat. 2,899,334 have the further advantage that the images formed on exposure to heat can be erased and the heat-sensitive element regenerated.
• Commonly assigned Fierke et al. US. patent application Ser. No. 506,325, filed Nov. 4, 1965 now US. Pat. 3,414,423 discloses a process for erasing and regenerating the thermographic materials of the Crevling et al. patent in 3,515,568 Patented June 2, 1970 ice which exposed materials are treated with certain solvents to convert the colored quinhydrone complex to the pquinone compound and dihydroxybenzene compound. This regeneration process is extremely useful in that it permits the same element to be used a number of times.
• the solvent treatment step sufiers from the ditficulties associated with any wet processing procedure, and it would be desirable if a dry process for erasing and regenerating thermographic materials could be obtained.
• thermographic material it is an object of this invention to provide a process for regenerating exposed thermographic material.
• thermographic material is erased and regenerated without using a solvent.
• thermographic materials which can be erased and regenerated.
• thermographic materials which can be erased and regenerated by a dry process.
• the colored quinhydrone complex which is formed by the reaction of a p-quinone compound and a dihydroxybenzene compound can be erased by heating the quinhydrone complex to a temperature between C. and C.
• a temperature within this range it has been found that the dark quinhydrone complex dissociates and is converted back to the pale colored mixture of the p-quinone compound and the dihydroxybenzene compound.
• the particular temperature within this range at which the dissociation occurs will vary with the particular pair of p-quinone and dihydroxybenzene compounds which are employed. However, dissociation will generally occur at a narrow temperature range within the broader range of 60 C. to 100 C.
• the dark colored quinhydrone complex is heated to a temperature below this selected narrow temperature range, it will not dissociate and will not change color; if the complex is heated to a temperature above the selected range, it will initially dissociate to the pale mixture, but upon cooling will revert to the dark colored quinhydrone complex.
• an element containing the p-quinone compound and the dihydroxybenzene compound can be exposed to heat in an imagewise manner to cause formation of the quinhydrone complex in image areas, thereby giving a dark image on a light background. After this image has served its purpose, the entire sheet can be raised to a temperature at which the quinhydrone complex reconverts to the p-quinone compound and the dihydroxybenzene compound. The sheet can then be reused, and this cycle can be repeated several times.
• an element in which the quinhydrone complex has been uniformly formed can be exposed to heat in an imagewise manner to heat the element to a temperature at which the quinhydrone complex is converted to the p-quinone and the dihydroxybenzene compound.
• a light image on a dark background After the image has served its purpose, it can be erased by heating the sheet to a temperature above that at which the quinhydrone complex is converted to the p-quinone compound and the dihydroxybenzene compound. Upon cooling, the sheet again has the uniform dark color of the quinhydrone complex. This procedure can be repeated several times.
• dihydroxybenzene compounds useful in practicing our invention comprise the hydroquinones, pyrocatechols, pyrogallols, etc. These dihydroxybenzenes can contain one or more of the conventional substituents of the type common in organic chemistry. We have found that these substituents do not generally interfere with the colorforming reaction upon which the instant therrnographic process depends.
• a particularly useful group of dihydroxybenzene compounds comprise those represented by the following general formula:
• R and R each represents a hydrogen atom, an *alkyl group (e.g., methyl, ethyl, n-propyl, isopropyl, nbutyl, isobutyl, tert-butyl, n-amyl, isoamyl, tert-amyl, nhexyl, isohexyl, 2-ethylbutyl, n-octyl, isooctyl, tert-octyl, n-nonyl, n-decyl, n-lauryl, n-hexadecyl, sec-hexadecyl, noctadecyl, etc.), an alkenyl group (e.g., allyl, crotyl, etc.), a halogen atom (e.g., chlorine, bromine, etc.), a hydroxyl group, an acyl group (e.
• R and R each represents a hydrogen atom, an alkyl group (e.g., methyl, ethyl, n-propyl, isopropyl, nbutyl, isobutyl, tert-butyl, n-amyl, isoamyl, tert-amyl, n-hexyl, isohexyl, Z-ethylbutyl, n-octyl, isooctyl, tertoctyl, n-nonyl, n-decyl, n-lauryl, n-hexadecyl, sec-hexadecyl, n-octadecyl, etc.), an alkenyl group (e.g., allyl, crotyl, etc.), a halogen atom (e.g., chlorine, bromine, etc.) a hydroxy
• nondermatitic p-quinone and dihydroxybenzene compounds are especially preferred because these compounds do not induce a dermatitic reaction in individuals handling them, as do certain other of the p-quinone and dihydroxyben- Zene compounds described above.
• These nondermatitic p-quinone and dihydroxybenzene compounds include those wherein at least one of R and R and at least one of R and R represents a carboxyalkyl group (e.g., carboxybutyl, carboxypropyl, carboxypentyl, etc.), a carboxyaryl group (e.g., carboxyphenyl, carboxynaphthyl, etc.), an acyloxyalkyl group (e.g., succinoxypropyl, malonoxyethyl, etc.), or an acyloxyaryl group (e.g., succinoxy-phenyl, malonoxyphenyl, etc.).
• a carboxyalkyl group e.g., carboxybut
• Typical of the p-quinone and dihydroxybenzene compounds which are useful in the practice of the present invention are those which are tabulated in columns 3 and 4 of Crevling et al. US. Pat. No. 2,899,334.
• the binders which are employed in coating the quinone and dihydroxybenzene compounds in an element affect both the color-forming reaction between the quinone and dihydroxybenzene compounds to form the quinhydrone complex and the dissociation reaction in which the quinhydrone complex reverts to the quinone and dihydroxybenzene compounds.
• the dissociation reaction does not take place in all binders.
• Those binders in which the dissocciation reaction can occur are primarily the polymeric resins. However, certain polymeric resins hinder the color-forming reaction if sufiicient quinone compound is not present.
• these resins contain a large number of free hydroxyl groups which compete with the dihydroxybenzene compound for the quinone compound, thus tying up the quinone compound and inhibiting the formation of the colored quinhydrone complex. If these binders are used, it is necessary to provide in the element a sufficient excess of quinone compound to react both with the free hydroxyl groups of the binder and with the dihydroxybenzene compound. Therefore, it is preferred that the polymeric binders employed contain less than one mole of free hydroxyl groups per mole of quinone compound present in the element.
• Typical polymeric resins which are useful in the practice of the present invention as binders include: polyvinyls (e.g., polystyrene, polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, etc.), polyesters (e.g., polyethylene terephthalate, polyethylene terephthalate-isoterephthalate, cellulose acetate'butyrate etc.), polycarbonates (e.g., poly[4,4 (2-norbornylidene) diphenyl carbonate], the polycarbonate formed by the reaction of bisphenol A with diphenyl carbonate, etc.), and the like.
• polyvinyls e.g., polystyrene, polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, etc.
• polyesters e.g., polyethylene terephthalate, polyethylene terephthalate-isoterephthalate, cellulose acetate'butyrate etc
• a dark colored element containing the quinhydrone complex can be formed by coating a mixture of a p-quinone compound and a dihydroxybenzene compound in a binder, such as is described above, using certain solvents.
• the colored element thus formed can be used directly to prepare negative light colored images on a dark background without having to uniformly heat the element to form the quinhydrone complex.
• the element is prepared and then heated in image areas to a temperature at which the dissociation reaction occurs, thus giving a light image on a dark background.
• the solvents which exhibit this ability to cause the quinone and dihydroxybenzene compounds to complex as the quinhydrone upon coating are the coordinate solvents such as halogenated hydrocarbons (e.g., carbon tetrachloride, methylene chloride, 1,1-dichloroethane, chloroform, etc.), toluene, cyclohexane, and the like.
• coordinate solvents such as halogenated hydrocarbons (e.g., carbon tetrachloride, methylene chloride, 1,1-dichloroethane, chloroform, etc.), toluene, cyclohexane, and the like.
• Elements useful in the practice of the present invention can be prepared in any well-known manner.
• a dispersion of the p-quinone and dihydroxybenzene in a suitable binder can be coated on a support by any of the well-known coating procedures, such as dip coating, hopper coating, doctor-blade coating, etc.
• the pquinone and dihydroxybenzene compounds can be dispersed in separate binders and the two dispersions then combined prior to coating, or the p-quinone and a dihydroxybenzene compounds can be dispersed together in a single binder and then coated on a support.
• Suitable supports for the elements of this invention include paper, polyethylene coated paper, metal foils, polymeric film base such as cellulose acetate, cellulose acetate-butyrate, cellulose acetate-propionate, polyethylene terephthalate, etc., and the like.
• an element containing the quinhydrone complex is exposed to heat in an imagewise manner to raise the temperature of the element in image areas to a temperature between 60 C. and 100 C. at which the dissociation reaction occurs.
• This can be accomplished in a variet of manners.
• the element can be contacted with an image which is maintained at the temperature at which the dissociation reaction takes place.
• the element can be contacted with an original containing infrared-absorbing image areas and the element in contact with the original can be exposed to infrared radiation for a period of time sufficient to heat the areas of the element in contact with the image areas to the temperature at which the dissociation reacion occurs. In both of these instances a negative copy of the original is obtained.
• the element contains light-colored image areas on a dark background.
• a uniformly dark element containing the quinhydrone complex This element can be obtained either by heating an element containing the quinone compound and the dihydroxybenzene compound to a temperature at which the quinhydrone complex is formed, or the quinhydrone complex can be formed in the element by the method described above in which the quinone compound and the dihydroxybenzene compound are coated from a solvent.
• ment can be obtained by the coating process described in the Crevling et al. patent, or a dark-colored element containing the quinhydrone complex can be heated uniformly to a temperature at which the dissociation reaction occurs. The element can then be exposed to heat in the manner described above to form the quinhydrone complex in image areas. Thus a dark positive image on a light background will be obtained.
• the image formed in the elements of our invention can be erased and the element rendered suitable for reuse by a relatively simple procedure.
• the element can be heated either to the temperature at which the dissociation reaction occurs or to a temperature above this temperature.
• the quinhydrone complex will dissociate to the quinone and dihydroxybenzene compounds thus giving a uniformly light colored element.
• the quinhydrone complex will initially dissociate to the p-quinone and dihydroxybenzene compounds, but upon cooling the quinhydrone complex will reform uniformly in the element.
• a coating solution is prepared by mixing 3 g. of 2,5- di-n-octylquinone, 2 g. of 2,5 -di-n-octylhydroquinone and 10 g. of polystyrene (Koppers 8X, sold by Koppers Co., Pittsburgh, Pa.) in 100 m1. of methyl chloroform.
• This solution is coated at a thickness of .005 inch on a polyethylene terephthalate film base which is subbed with a terpolymer of methylacrylate, vinylidene chloride, and itaconic acid. After drying at approximately 70 C. a blue coated element is obtained.
• a strip of the coated film is then contacted with a heated surface which varies in temperature along its length from approximately 50 C. to approximately 100 C. at a rate of approximately 7 C. per inch of length. While in contact with the heated surface, the areas of the strip which are below approximately 74 C. remain blue while the area above 74 C. clear to a pale yellow color. Upon removal of the coated film from the variable temperature surface and cooling, the pale yellow section of the film reverts to the blue color except for a narrow band which had been exposed to a surface temperature of between 74 C. and 76 C. This narrow band remains pale yellow in color.
• EXAMPLE 2 A coated element is prepared as described in Example 1. The element is then heated uniformly to a temperature of 75 C. in an oven. There is thus obtained a pale yellow element. This element is then placed in contact with an original containing black infrared absorbing image areas on a white background and is exposed by passing the element in contact with the original through an exposure unit containing a 1350 watt infrared lamp at a distance of 1 cm. from the element. There is thus obtained a positive copy of the original document having dark blue image areas on 'a light background. This copy is erased by again heating the element to 75 C. to obtain a uniformly pale yellow element. This exposure anderasure procedure is repeated several times. After each exposure a positive blue copy on a pale yellow background is obtained.
• EXAMPLE 3 A coated element is prepared as described in Example 1. The dark blue element is placed in contact with an original containing black infrared image areas on a white background and is exposed by passing the element in contact with the original through the exposure unit described in Example 2 to heat the image areas to a temperature of approximately 75 C. There is thus obtained a negative copy having pale yellow image areas on a dark blue background. The image is erased by heating the element to 100 C. and cooling to 40 C. to produce a uniform blue coating. This exposure and erasure procedure is repeated several times, and after each exposure a negative light-colored image on a blue background is obtained.
• EXAMPLE 4 A coated element is prepared by the procedure described in Example 1, using 3 g. of 2-(w-carboxy-npentyl)-5-methyl hydroquinone and S g. of Z-(w-carboxyn-pentyD-S-n-octyl quinone as the heat-sensitive components, and 5 g. of polystyrene (Koppers 8X, sold by Koppers Co., Pittsburgh, Pa.) as the binder.
• the element thus obtained is treated and exposed as described in Example 2. A positive copy of the original is obtained. This element is erased and exposed several times. After each exposure a good positive copy is obtained.
• EXAMPLE 5 A coated element is prepared as described in Example 1, using the heat-sensitive components of Example 4 and 5 g. of a polyester of terephthalic acid and a mixture of ethylene glycol (1 part by weight) and 2,2-bis(4-hydroxyethoxyphenyl)propane (9 parts by weight) (Vitel PIE-101 sold by Goodyear Tire and Rubber Co., Akron, Ohio) as the binder.
• This element is exposed as described in Example 3, and a negative copy of the original is obtained. The element is erased and exposed several times. After each exposure a good negative copy is obtained.
• R is a member selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a halogen atom, a hydroxyl group, an acyl group, an acyloxyl group, a carbonyl group, an aryl group, a carboxyalkyl group, a carboxyalkryl group, an acyloxyalkyl group, and an acyloxyaryl group;
• R is a member selected from the group consisting of a hydrogen atom and groups which together with R represent the atoms necessary to complete an aromatic ring; and R when R represents a hydrogen atom, is a member selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a hydroxyl group, a halogen atom, an acyl group, an acyloxy group, an aryl group, a carboxyalkyl group, a carboxyaryl group, an acyloxyalkyl group and an wherein
• polymeric resin binder is a polystyrene
• polymeric resin binder is a polyethylene terephthalate.
• a process for erasing from a thermographic element a. quinhydrone complex carried in a polymeric resin binder which is substantially free from hydroxyl groups, said quinhydrone complex being formed from 2-(w-carboxy-npentyD-S-methyl hydroquinone and 2-(w-carboxy-npentyl) -5-n-octyl quinone, there initially being present at least 1.1 mole of the quinone compound for each mole of the hydroquinone compound, the process comprising heating the element to a temperature of between 72 C. and 77- C. to convert the quinhydrone complex to the quinone compound and the dihydroxybenzene compound.
• thermographic element uniformly coated with a quinhydrone complex which comprises coating a support with a mixture in a coordinate solvent of 1.1 mole of a quinone compound per mole of a clihydroxybenzene compound, and evaporating the solvent from the element, said dihydroxybenzene compound having the formula:
• R is a member selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a halogen atom, a hydroxyl group, an acyl group, an acyloxy group, a carbonyl group, an aryl group, a carboxyalkyl group, a carboxyaryl group, an acyloxyalkyl group, and an acyloxyaryl group;
• R is a member selected from the group consisting of a hydrogen atom and groups which together with R represent the atoms necessary to complete an aromatic ring; and
• R when R represents a hydrogen atom is a member selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a hydroxyl group, a halogen atom, an acyl group, an acyloxy group, an aryl group, a carboxyalkyl group, a carboxyaryl group, an acyloxyalkyl group and an acyl
• R3 R4 w wherein R is a member selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a halogen atom, a hydroxyl group, an acyl group, an acyloxyl group, a carbonyl group, an aryl group, a carboxyalkyl group, a carboxyaryl group, an acyloxyalkyl group, and an acyloxyaryl group; R is a member selected from the group consisting of a hydrogen atom and groups which together with R represent the atoms necessary to complete an aromatic ring; and R when R represents a hydrogen atom, is a member selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a hydroxyl group, a halogen atom, an acyl group, an acyloxyl group, an aryl group, a carboxyalkyl group, a carboxyaryl group, an acyloxyalky
• a process as defined in claim 10 wherein the solvent is selected from the group consisting of carbon tetrachloride, methylene chloride, 1,1-dichloroethane, chloroform, toluene and cyclohexane.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Heat Sensitive Colour Forming Recording (AREA)
• Thermal Transfer Or Thermal Recording In General (AREA)

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Citations (3)

• 1967
  • 1967-07-03 US US650634A patent/US3515568A/en not_active Expired - Lifetime
• 1968
  • 1968-07-02 BE BE717491D patent/BE717491A/xx unknown

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