Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G11/00—Selection of substances for use as fixing agents
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G13/00—Electrographic processes using a charge pattern
  • G03G13/20—Fixing, e.g. by using heat

Definitions

• ABSTRACT 521 US. (:1. ..117/2ls1,71/1,75/l1 7.l51, 71/12/5251, Dry powderimagesm fixed on paperby eating the powder Int Cl 344d U094 g 844d l image igat ad paper withanaqueous dispersion of afilm formu 5s FieldofSearch ..117/l7.5,28,29,33,76P, mgsy e 117/155, 13 5Claims,No Drawings METHOD ()F FIXING IMAGES CONSISTING F DRY POWDERS 0N PAPER
• the invention relates to a method of fixing images of dry powders on paper.
• Dry colored powders are used in different printing methods, particularly silk screening and electrostatic printing.
• the adhesion of such a powder to paper is only small.
• the image obtained by a dry powder must always be fixed in a separate operation. Several methodsof fixation are known.
• the powder contains a thermoplastic component and/or the paper to be printed is provided with a coating of material which softens upon heating. Upon softening of the resin component, the powder and the paper are permanently connected together.
• Heat can be applied to the material provided with an image of dry powder, for example, by hot air, infrared radiators, heated plates or drums.
• the paper surface bearing an image is provided by means of spraying, rolling or dipping, with a film consisting of a solvent having a low boiling point, which dissolves a certain component of the powder and/or the paper surface, and hence establishes an adhesion between paper and powder, after evaporation.
• Solvents suitable for this purpose are, however, either inflammable (for example toluene) poisonous (for example, trichloroethylene) or only slowly dissolve the active component in the powder or the paper and evaporate slowly (for example, water).
• the image powder does not contain components which can be softened by heat or can be dissolved in manageable solvents and if the paper does not include coatings which possess these properties, then it is alternatively possible to coat the paper provided with a powder image with a solution of a transparent substance which forms a film in the solid state. It must also in this case be possible for the solvent to be evaporated by heating.
• a lacquer solution which is commercially indicated as a fixative. All solvents usable for this purpose have, however, the previously mentioned drawbacks.
• the said methods of fixation have great drawbacks which impede particularly their use in electrostatic high-speed printing machines which must cooperate with data-processing machines. Temperatures above 100 C. must be used for fixation by means of heating. The required heat is therefore 10-20 kw. per sq. m. of paper in which up to 5 g. of water per sq. m. of paper is simultaneously evaporated. When printing quantities of 0.5 to 1.0 sq. m. of paper per second, the working space is generally loaded to an inadmissibly great extent by exhausted heat and water vapors including decomposition products of the adhesive in the paper. Separate devices for removing the decomposition products require additional investments.
• An object of the present invention is to provide a simple method of fixing images consisting of dry powders on paper, by which the described drawbacks are obviated and in which, as a rule, no special devices for the removal of possible decomposition products are required.
• the method according to the invention is characterized in that the paper provided with a dry powder image is coated with a dispersion of a synthetic resin in water.
• an aqueous dispersion of a synthetic resin is preferably used which forms a film at a low temperature.
• a synthetic resin film of approximately 2-4 pm. thick on the paper is generally amply sufficient for fixation.
• the solidv substance content of dispersions suitable for this purpose is. generally more than 40 percent. Since the synthetic resin in the dispersion is present in the form of small particles of at least 0.2 gm. diameter the viscosity of even a very highly concentrated dispersion only differs little from that of pure water.
• the paper is not soaked by the dispersion as in the case of a solution, and therefore not only a fraction but the entire solid substance content of the coating provided is available for the formation of a film. Quantities of provided coatings of 4 to 8 g. of dispersion per sq. m. of paper are therefore amply sufiicient.
• the fixation process takes some tenths of a second, and the porous structure of the paper greatly contributes thereto.
• the water is sucked away from the dispersion in the paper under the influence of capillary forces, so thatthe dispersion breaks.
• the dispersed particles are, as it were, filtered off.
• the particles form a loose network on the paper in the pores of the surface and above the powder image provided, which network, however, flows together to a coherent transparent film when the lowest temperature at which a film is formed by the dispersed substance is below the operation temperature.
• the lowest temperature at which a film is formed is dependent on the kind of synthetic resin used, but by suitable choice this temperature is substantially arbitrarily adjustable between +3 C. and C.
• the added quantity of water is only approximately 24 g. per sq. m. of paper surface, that is to say, 5 to 10 percent of the quantity of paper.
• This quantity of water is approximately as large as the quantity which is normally present in the paper at the usual air hunridities.
• the additional load of the paper by water caused by the fixation can therefore be accepted without further drying steps. If nevertheless an immediately dry paper provided with an image would be desired, then there is the possibility to use predried paper which not until fixing reaches a moisture content which is balanced by the air humidity.
• the dispersions may efficiently be provided with the aid of a follower roller.
• Auxiliary rollers may apply the suitable quantity of dispersion to the roller by means of which the dispersion is provided. Spraying on the dispersions is only possible at a great mechanical stability of the dispersions, for otherwise the dispersion breaks in the spraying nozzle. Due to the low viscosity of dispersions which substantially corresponds to that of water the provision of the dispersion presents few difficulties. When providing the dispersion of occurrence of stripping forces must be avoided as much as possible in order that the powder image is not wiped out. An equalization of the film provided is, however, not necessary because freedom from pores is not required and because the thickness is very small anyway.
• the properties of the transparent coatings are adjustable with respect to color tone, gloss, writing possibility and smoothness
• auxiliary substances such as substances suppressing the formation of foam, wetting agents and thickening agents can be added to the dispersions.
• a method of fixing dry powder images on paper comprising coating the side of a paper on which a dry powder image is present with an aqueous dispersion of a filmforming synthetic resin, said coating step being carried out at a temperature sufficiently high to cause the synthetic resin to form a film on the paper.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Paper (AREA)
• Printing Methods (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=7380167

Family Applications (1)

Country Status (8)

Cited By (8)

Citations (5)

• 1969
  • 1969-03-08 NL NL6903627A patent/NL6903627A/xx unknown
  • 1969-03-10 CH CH353069A patent/CH489840A/de not_active IP Right Cessation
  • 1969-03-11 US US806271A patent/US3640749A/en not_active Expired - Lifetime
  • 1969-03-11 GB GB02765/69A patent/GB1221615A/en not_active Expired
  • 1969-03-11 SE SE03333/69A patent/SE352751B/xx unknown
  • 1969-03-12 BE BE729761D patent/BE729761A/xx unknown
  • 1969-03-14 FR FR6907317A patent/FR2014112A1/fr not_active Withdrawn
  • 1969-03-14 CA CA045,669A patent/CA939567A/en not_active Expired

Patent Citations (5)

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