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
  • B41M5/50—Recording sheets characterised by the coating used to improve ink, dye or pigment receptivity, e.g. for ink-jet or thermal dye transfer recording
  • B41M5/52—Macromolecular coatings
  • B41M5/5218—Macromolecular coatings characterised by inorganic additives, e.g. pigments, clays
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/38—Coatings with pigments characterised by the pigments
  • D21H19/40—Coatings with pigments characterised by the pigments siliceous, e.g. clays

Definitions

• This invention relates to coated paper suitable for printing by a gravure, particulary a rotogravure process of an offset lithography process, to a method of preparing the coated paper and to a method of printing using such a coated paper.
• Gravure printing is a form of intaglio printing, i.e. printing which uses a plate or cylinder into the surface of which the subject matter to be printed is etched or engraved.
• a liberal film of fluid printing ink is applied to the whole printing surface and the surface is then wiped, for example by a doctor blade, in order to remove all the ink from the unindented parts of the surface leaving ink only in the indentations or cells.
• Paper in a continuous web or in separate sheets is then pressed into contact with the inked surface in order to receive an impression of the subject matter.
• Gravure printing paper is typically coated with a pigment consisting predominantly of calcium carbonate or a layer lattice silicate such a kaolin clay. Neither calcium carbonate nor kaolin clays swell appreciably in water and aqueous coating compositions comprising such pigments may contain a relatively high proportion of the pigment without becoming unworkable due to high viscosity.
• a paper coated with such a pigment will typically have a coat weight of at least 5 gm ⁇ 2 and normally in the range of from 5 to 15gm ⁇ 2. It has previously been considered impractical to use a smectite-type clay as the primary pigment in paper-­coating owing to its tendency to swell in water and to viscosify the coating suspension, even at relatively low solids contents. Moreover, many smectite-type clays do not posses the desirable degree of whiteness necessary to be usable as paper coating pigments.
• An offset lithography machine In offset lithography printing an inked image is first printed on a rubber sleeve or "blanket" surrounding a metal cylinder and then transferred to paper.
• An offset lithography machine generally has three main rolls, a plate roll round which is fastened a metal printing plate, a blanket roll and an impression roll which biases the paper in contact with the blanket roll.
• the printing plate first comes into contact with a series of moistening rollers which cause the non-printing areas of the plate to retain water.
• the printing plate then passes beneath inking rollers which apply ink to the areas of the plate to be printed.
• the water-retaining, non-printing areas reject the greasy printing ink.
• US-4549930 describes an un-coated paper, suitable for rotogravure printing with water-immiscible inks containing an organic solvent, in which the cellulosic fibres of the paper are partially or totally enveloped by a clay hydrogel, the clay being hydratable, colloidal and film-forming.
• EP-0046416 discloses an ink jet recording sheet comprising a paper support which may be applied on at least one surface with a composition comprising polyvinylpyrrolidone, a vinylpyrrolidone-vinyl acetate copolymer or a mixture thereof, and a white filler. Although a number of so-called “white-fillers” are suggested, the only ones exemplified are talc and calcium carbonate.
• GB-2039789 discloses an electrostatic imaging sheet, one surface of which is electrically conductive and the other side of which either has a continuous dielectric layer comprising a mixture of a smectite clay and an electrically insulating polymer or has a layer of a smectite clay which forms a barrier between the electrically conductive layer and a dielectric layer of an insulating polymer. It is evident from the examples that the smectite clay forms only a very small proportion of the total pigment in the coating applied to the sheet.
• GB-933928 discloses a method of making copies from hectographic printing master sheets.
• the copy sheets which are moistened with a solvent before printing, are coated, inter alia , with a composition comprising a bentonite and a binder.
• a method of gravure printing comprising printing onto paper coated with a composition including a pigment which consists predominantly of a water-swellable smectite-type clay, the coat weight being no greater than 5 gm ⁇ 2.
• a gravure printing paper provided with a coating including a pigment consisting predominantly of a water-swellable smectite-type clay, the coat weight being no greater than 5 gm ⁇ 2.
• the smectite clay may be bentonite, montmorillonite, hectorite, saponite or fullers earth, but especially preferred is a natural bentonite which has, or has been treated to have, predominantly sodium ions in its exchangeable cation sites.
• the coat weight is no greater than 1 gm ⁇ 2 and is typically of the order of 0.5 gm ⁇ 2.
• the pigment consists predominantly of the smectite-type clay.
• the pigment comprises at least 70% by weight, more preferably 80% by weight and most preferably more than 90% by weight of the smectite-type clay.
• the pigment is wholly smectite-type clay.
• Any secondary pigment present may be of the conventional type, for instance kaolin clay or calcium carbonate.
• the coating may also include an adhesive which assists in binding the clay particles to each other and to the sheet member of the paper.
• the adhesive may be any conventional adhesive used in paper coating, for example, starch, latex, casein, gelatine or other synthetic resin latexes. Particularly advantageous results have been obtained when the adhesive is starch or latex.
• a method of preparing a printing paper which comprises the step of applying to the surface of a cellulosic sheet material an aqueous suspension comprising up to 20% by weight of a pigment which consists predominantly of a water-swellable smectite-type clay, the suspension being applied in an amount sufficient to provide a coating on the sheet material having a coast weight no greater than 5 gm ⁇ 2.
• the aqueous suspension will contain less than 10% by weight of the pigment.
• the aqueous suspension of the smectite clay may also contain an adhesive to assist in bonding the clay to the fibres of the cellulosic sheet; but this is not essential as it is found that adquate adhesion of the clay to the cellulosic fibres is achieved in the absence of an adhesive.
• an adhesive it is found that for a paper intended for rotogravure printing a starch or a latex adhesive is preferred and especially an acrylic copolymer latex.
• any conventional adhesive is operable.
• the quantity of adhesive used will be in the range from 1 to 300 parts by weight of dry polymer to 100 parts by weight of dry smectite clay.
• Hand-coated paper sheets were prepared by coating sheets of a Scandinavian supercalendered magazine paper of substance weight 60 gm ⁇ 2 by means of a wire-wound bar which was wound with a wire of diameter 15 microns and thus adapted to provide a coat weight in the range from 0.25 gm ⁇ 2 to 0.5 gm ⁇ 2.
• the hand-coated sheets were coated with one of the following two coating compositions:-
• a further measurement of print density was performed on the reverse side of the paper in the region of the solid black area in order to determine the degree of "strike through" of the printing ink.
• a Scandinavian base paper of substance weight 57 gm ⁇ 2 was coated by means of laboratory coating machine of the type described in British Patent Specification No. 1032536 with paper coating compositions which consisted of suspensions containing varying quantities of Wyoming sodium bentonite in water.
• two coating compositions were used which contained 9% by weight of the bentonite and 5% by weight and 10% by weight respectively of a paper coating adhesive which was a 50% by weight latex of an acrylic copolymer, each percentage by weight representing the percentage of dry copolymer based on the weight of dry bentonite.
• a rotogravure printing base paper of substance weight 60 gm ⁇ 2 was coated by means of the laboratory coating apparatus used in examples 2 and 3 running at a speed of 400 m.min ⁇ 1 with compositions containing various proportions by weight of a European bentonite having sodium and calcium exchangeable cations, together with, in most cases, either a starch paper coating adhesive or an acrylic copolymer latex adhesive.
• a supercalendered newsprint paper of substance weight 39 gm ⁇ 2 was coated by means of the laboratory paper coating apparatus used in Examples 2 and 3 running at a speed of 400 m min ⁇ 1 with a composition consisting of a suspension of 5% by weight of a European bentonite having sodium and calcium exchangeable cations.
• Samples of the coated paper were tested for offset lithography printing properties by means of an IGT Model AC2 printability tester.
• the paper samples were clipped to the moving sector of the instrument which was set to move at a constant velocity of 1 ms ⁇ 1.
• An aluminium alloy damping roll of face width 25 mm and a rubber covered printing roll of face width 20 mm were rotatably and removably mounted on spindles provided on the fixed part of the instrument with the damping roll contacting the surface of the paper sample 70 mm in advance of the line of contact of the printing roll with the paper surface in the sense of the direction of relative motion betwen the sector bearing the paper sample and the rolls.
• each paper sample was printed with a strip of solid colour 20 mm in width, the first 70 mm being printed on dry paper and the remaining 140 mm on prewetted paper.
• the damping roll was biased against the paper sample with a force of 25 kg and the printing roll was biased against the sample with a force of 50 kg. Both the damping roll and the printing roll had an overall diameter of 68 mm.
• the damping roll was loaded with a substantially identical weight of water, namely approximately 0.6 g of water per square metre of roll surface area by condensation of water vapour on the surface of the roll.
• the damping roll was placed in a refrigerator having an internal temperature of -8 ⁇ 1°C and a coiled temperature probe connected to a digital thermometer was placed in the central spindle hole of the roll.
• a desiccator in which a humidity of 55% RH was maintained by means of a saturated solution of sodium dichromate.
• the temperature of the atmosphere in the thermometer had fallen to +5°C the roll was transfered to a desiccator in which a humidity of 55% RH was maintained by means of a saturated solution of sodium dichromate.
• the temperature of the atmosphere in the laboratory was controlled at 20 ⁇ 1°C.
• the roll was left in the desiccator for a time of 1 minute 55 seconds and the printability test was performed after another 5 seconds using a printing roll which had been pre-inked with Ault & Wiberg 4-Colour Process Gloss Magenta offset lithography ink.
• the block of solid colour printed on the dry and prewetted areas, respectively, of the paper samples was tested for print gloss by means of a Hunterlab Glossmeter Model D16 and at an angle of 75° with the normal to the paper surface in accordance with TAPPI Standard NO.T480ts-65, the mean of five determinations for each area being recorded.
• the block of solid colour printed on the dry and prewetted areas, respectively was also tested for print density by means of a Macbeth RD514 Reflection Densitometer, in this case, the means of ten determinations for each area being recorded.

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• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Paper (AREA)

Applications Claiming Priority (2)

Publications (1)

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Cited By (4)

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Citations (8)

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• 1987
  • 1987-03-20 GB GB878706634A patent/GB8706634D0/en active Pending
• 1988
  • 1988-03-15 FI FI881227A patent/FI881227L/fi not_active Application Discontinuation
  • 1988-03-18 EP EP88302386A patent/EP0283300A1/fr not_active Withdrawn
  • 1988-03-18 NO NO881225A patent/NO881225L/no unknown
  • 1988-03-18 GB GB08806416A patent/GB2202464A/en active Pending
  • 1988-03-21 BR BR8801272A patent/BR8801272A/pt unknown
  • 1988-03-22 JP JP63067981A patent/JPS646194A/ja active Pending

Patent Citations (8)

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