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
  • B41M5/0035—Uncoated paper
• • 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
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/50—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by form
  • D21H21/52—Additives of definite length or shape

Definitions

• the present invention relates generally to the manufacture of inkjet recording paper. More particularly, the invention relates to a process for reducing or preventing cockle or wrinkling of inkjet recording paper during the printing process.
• Papers for inkjet printing can be divided into two types, (a) uncoated for low quality printing, and (b) coated for high quality (usually multi-colored) printing.
• Uncoated papers generally contain high surface area pigments, either as fillers or added at the size press to help control dot spread. The objective is to make the sheet absorptive enough to permit rapid ink penetration, but to minimize feathering and retain good circularity of dots after printing.
• Coated inkjet papers used for high quality multi-color printing are also required to have rapid ink absorption while still being able to dissipate the ink vehicle.
• print quality is superior to that of an uncoated sheet where the ink and ink vehicle has deeply penetrated the substrate.
• both types of inkjet recording papers must include some amount of sizing so as to keep the cellulose fibers from absorbing too much of the ink vehicle, otherwise the sheet becomes cockled or wrinkled during printing.
• inkjet inks are aqueous based formulations which may contain from 85-95% water (by weight). Where low levels of sizing are used in the paper substrate, the cellulose fibers tend to absorb excess water which destroys the dimensional stability of the sheet and produces cockle. Where high levels of sizing are employed, the cellulose fibers absorb little or no water, so that print performance is impaired and drying times are unduly long.
• cockle refers to the swelling of paper fibers and the deformation of paper while wet with ink, which may occur immediately after printing.
• U.S. Patent No. 5,207,824 discloses the use of between 15-50% by weight of an anti-cockle agent in the ink to reduce cockle.
• U.S. Patent No. 5,419,644 discloses a printer control mechanism for regulating the pen-to-sheet spacing during printing to reduce cockle.
• U.S. Patent No. 5,431,724 the addition of a water-soluble solvent or salt to the inkjet ink is disclosed as reducing paper cockle during printing.
• the present invention relies on a modification to the paper basestock used to make the inkjet sheets. Whether the inkjet sheet is coated or uncoated, it must have a high ink-absorbing capacity such that the ink vehicle is rapidly absorbed into the substrate while the images received on the recording sheet appear to be dry. This must be accomplished while still providing a high resistance to the tendency of curling and cockling. Generally, since the tendency of curling and cockling is increased with an increase in the ink absorption of the recording sheet, the requirement for enhancing the ink-absorption of the recording sheet is contradictory to the requirement of preventing the tendency of curling and cockling. Yet, in accordance with the present invention, this seemingly contradictory result is accomplished in a highly effective and cost efficient manner.
• U.S. Patent No. 5,213,873 describes the use of a neutral paper sheet for inkjet recording having a highly absorbent top coating containing fine silica particles for achieving superior print performance
• U.S. Patent No. 5,985,424 discloses a moderately sized sheet (Hercules size of from about 300-900 seconds), onto which there is applied both a base coating and an ink receptive top coating for achieving superior print performance.
• Another object of the present invention is to reduce the cockle of the inkjet recording sheet during printing by a cost effective modification to the paper basestock used to make the inkjet recording sheet.
• the preferred high surface area pigments of the present invention have a specific surface area in the range of 80-650 m 2 /g, as compared with the specific surface area of 5-15 m 2 /g for conventional filler pigments.
• the pigments of the present invention most preferably have a bulk density of from about 0.14 to 0.26 g/cm 3 as compared with the bulk density of conventional inkjet pigments which range from about 0.4 to 1.0 g/cm 3 , and an internal pore volume as measured by an oil absorption test of from about 1.35 to 2.80 cm 3 /g as compared with the pore volumes of conventional inkjet pigments which range from about 0.10 to 0.50 cm 3 /g by the oil absorption test.
• the preferred substitution rate of such high specific surface area pigments for conventional pigments in the present invention is less than about 5% by weight, and on the order of about 1-5% by weight.
• a pigment having a specific surface area of from about 80-650 m 2 /g) was sized to a level greater than 1000 seconds as measured by the Hercules sizing test, the paper so made absorbed more water in a given length of time (as measured by Cobb sizing degree), than paper containing only the conventional pigments which was sized to the same degree.
• the low bulk density of the high specific surface area pigments due primarily to the large pore volume of such pigments, results in a paper basestock with reduced density and a reduced tendency to produce cockle upon printing with typical inkjet inks, while still providing enhanced print quality at a minimum ink drying time.
• the subject matter of the present invention comprises a method for reducing the cockle of a paper inkjet recording sheet during inkjet printing wherein even if the paper fibers are given a high degree of sizing to prevent moisture penetration, the recording sheet is still provided with a high degree of water absorption capability by replacing a minor but effective portion of the conventional low specific surface area pigments normally used in the manufacture of inkjet paper with high specific area pigments having a large internal pore volume.
• the paper basestock made according to the present invention may be advantageously used as an uncoated sheet for low quality printing or it may be coated with one or more ink receptive coatings for use in making high quality, color prints.
• the density of the paper made is reduced as compared with the density of paper made with conventional inkjet paper pigments.
• the advantage of reduced density vis-a-vis improved ink absorption is fully disclosed in U.S. Patent No. 5,589,259 wherein it is noted that when the apparent density of the base paper in an inkjet recording sheet is reduced, the internal voids of the base paper is enlarged resulting in better ink absorption.
• such paper could also be advantageously used in coverstock, paperboard and other paper products benefitting from reduced density.
• handsheets of approximately 75 g/m 2 were made with a blend of hardwood Kraft and softwood Kraft pulp with 0 to 4% added high surface area pigments from the families of silica, calcium silicate, and sodium aluminosilicate. It was found that the presence of the high surface area pigments, particularly those with large internal void volumes, resulted in lower paper density, preferably at levels of 2-3% filler.
• Two inch square samples from this initial experiment were taped to a sheet of office paper and printed blue on an HP 870 Cse printer and evaluated for cockle, with improvements seen in several samples. Formulations and results for several of the products are summarized below in Table 1.
• Handsheets were calendered at 97.7 kg/linear 2.54 cm (200 pounds/linear inch) between 2 steel nips and compared for physical and optical properties.
• a 2.54 cm by 17.78 cm (1 inch by 7 inch) black strip was printed (using an Epson 740 inkjet printer) onto calendered paper and observed for cockle. Paper was also coated with a proprietary inkjet basecoat and topcoat, then printed with test patterns on a Epson 740 inkjet printer.
• Basestock made with Hubersorb or FK-310 had 5% lower density after calendering than did the control paper.
• the basestock made with FK-310 filler exhibited reduced cockle after printing of the black strip. Formulations and results are summarized below in Table 2.
• Examples of conventional pigment filler materials useful in inkjet recording sheets include inorganic pigments such as talc, clay, kaolin, diatomaceous earth, calcium carbonate, precipitated calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc carbonate, aluminum silicate, calcium silicate, aluminum hydroxide, aluminum oxide, synthetic amorphous silica, colloidal silica, and/or organic pigments such as urea resin pigments, plastic pigments, etc., if desired, all having a fairly low specific surface area on the order of from about 5-15 m 2 /g.
• inorganic pigments such as talc, clay, kaolin, diatomaceous earth, calcium carbonate, precipitated calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc carbonate, aluminum silicate, calcium silicate, aluminum hydroxide, aluminum oxide, synthetic amorphous silica, colloidal silica, and/or organic pigments such as
• examples of high specific area pigments useful in the present invention include Huber Hubersorb 250 calcium silicate (specific surface area 120 m 2 /g); Degussa FK-310 silica (specific surface area 650 m 2 /g); and, Speciality Minerals Jetcoat 30 precipitated calcium carbonate (specific surface area 80 m 2 /g).
• These and other silica based pigments which have a low bulk on the order of from about 0.14 to 0.26 g/cm 3 and a large internal pore volume as measured by an oil absorption test of from about 1.35 to 2.80 cm 3 /g, e.g., the Dibutyl Phthlate (DBP) absorption test, are preferred for use in the present invention.
• DBP Dibutyl Phthlate

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• 2000
  • 2000-09-29 NO NO20004890A patent/NO20004890L/no not_active Application Discontinuation
  • 2000-10-05 EP EP00402745A patent/EP1149949A3/fr not_active Withdrawn
  • 2000-10-24 JP JP2000324256A patent/JP2001310554A/ja active Pending

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