Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G7/00—Selection of materials for use in image-receiving members, i.e. for reversal by physical contact; Manufacture thereof
  • G03G7/006—Substrates for image-receiving members; Image-receiving members comprising only one layer
  • G03G7/0066—Inorganic components thereof
• • 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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/66—Salts, e.g. alums
• • 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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/21—Macromolecular organic compounds of natural origin; Derivatives thereof
  • D21H17/24—Polysaccharides
  • D21H17/28—Starch
  • D21H17/29—Starch cationic
• • 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
  • D21H21/14—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 function or properties in or on the paper
  • D21H21/16—Sizing or water-repelling agents

Definitions

• This invention relates to the use of a treatment composition for enhancing the suitability of paper for printing by so-called "colour digital presses" of the kind which use a liquid toner or ink.
• Colour digital presses were first commercialised on a significant scale around the early 1990's. They are particularly suited to short printing runs for which traditional colour offset printing can be uneconomic and slow because of the high cost and time penalties involved in producing printing plates and setting up the press at the start of the run. By contrast, a colour digital press has no printing plates or comparable set-up costs. It therefore permits a rapid response to print orders ("fast turnaround"), and the cost per impression is not significantly influenced by the total number of impressions being made. These factors make a digital press ideal for short-run colour printing, say for up to about 3000 impressions.
• variable and non-variable information can be merged between every consecutively printed copy, so that individual impressions within a print run can be personalised or customised so as to be specific to a particular recipient or reader.
• Colour digital press technology is based on non-impact printing or imaging technology of the same general kind as is used in plain paper photocopiers and laser printers, i.e. on the use of an electrostatically-charged roll and charged toner particles for image formation.
• An electrostatically-charged photosensitive roll (the "photoreceptor") is exposed to light in an imagewise configuration such that the surface electrostatic charge on the exposed areas of the photoreceptor is dissipated. Toner is then brought into contact with the photoreceptor, and adheres strongly to it in the unexposed (and thus still electrostatically-charged) areas of its surface, from which it can be transferred to the paper either directly or indirectly via an offset roll.
• a single pass through the printing unit provides a monochrome image, but a colour print of a quality comparable to that obtainable by traditional colour offset printing can be achieved either by multiple passes through a printing unit using differently-coloured toners or by a single pass through an array of printing units each of which applies a differently-coloured toner.
• Typically four passes or printing units are used, three of which apply coloured toners and the other of which applies a black toner.
• the coloured toners are such that when used individually and in suitable combinations, they can provide a complete spectral range for the finished print, in much the same way as is achieved in conventional colour printing by the use of a black and three differently-coloured inks.
• toners are of a fine particulate nature, with each particle comprising pigment particles bound together in a thermally-fusible polymeric binder matrix. Once the toner has been applied to the paper, heat is used to melt the polymeric binder component of the toner and so "fuse” the toner particles together and to the paper.
• liquid toners comprise toner particles dispersed in a fairly high-boiling organic liquid vehicle, together with dispersed binder particles.
• the toner is heated to an elevated temperature (typically 70 - 90°C) sufficient to convert the binder particles to a liquid state. Removal of the vehicle results in an increase in toner viscosity, which facilitates transfer of the toner to the offset roll (if used) and to the paper, with the paper surface absorbing the residual liquid vehicle.
• the binder reverts to a solid state after the toner has been applied to the paper and so fixes the image (there is no subsequent "fusing" of the toner after its transfer to the paper, such as occurs in dry toner processes).
• the paper used with colour digital presses must be carefully chosen if good print quality and runnability through the digital press is to be achieved.
• the paper requirements are similar to those for plain paper copying and laser printing, primarily a smooth surface, good stiffness, a relatively low moisture content, good dimensional stability under conditions of variable humidity, compatibility with toner so as to permit good toner adhesion and ability to withstand the heat of the toner fusing stage without excessive curling, wavy edge production or blistering.
• Such papers are readily available at acceptable cost, and so paper availability has not been a significant constraint on market penetration of dry toner colour digital press technology.
• the invention resides in the use, for the purpose of enhancing the printability of paper by means of a liquid toner colour digital press, of a treatment composition comprising an aluminate salt or a salt of a weak acid and a strong base in an amount such as to impart an alkaline surface pH value to the paper.
• the invention provides a method of printing paper by means of a liquid toner colour digital press, characterised in that the paper being printed has been surface treated with an aluminate salt or a salt of a weak acid and a strong base in an amount such as to give an alkaline surface pH value.
• the treatment composition comprising the aluminate salt or the salt of a weak acid and a strong base preferably contains starch or another surface agent, so that the treatment composition also functions as a surface sizing composition. This reduces the cost of the treatment (since no additional paper processing is required beyond the normal size press treatment). It also facilitates uniform application of the active treating ingredient (the salt) across the whole surface of the paper, since the sizing agent functions as an extender.
• the surface size is typically a starch, but could in principle be a latex, polyvinyl alcohol, gelatin, a cellulose derivative such as carboxymethylcellulose, or other known surface sizing material. Combinations of these materials can be used.
• Size press application is a particularly convenient and therefore preferred method of applying the treatment composition, coating, spraying or other application techniques can be used.
• Size-presses as referred to in this application include not only traditional size presses but also so-called “metered” size presses of the kind commercialised under the name "Speedsizer” by Voith, “Sym-Sizer” by Valmet, “Twin-HSM” by BTG and “Filmpress” by Jagenberg.
• the aluminate salt is preferably sodium aluminate, and the salt of a weak acid and a strong base is preferably sodium hydrogen carbonate (sodium bicarbonate). Less preferred alternatives include disodium tetraborate, trisodium phosphate and sodium acetate.
• Sodium salts have been referred to because they are the most readily available, but it will be understood that the corresponding potassium salts could equally well be used, as could calcium salts, provided that they are adequately soluble.
• Sodium aluminate has so far been found to give the best results, possibly because the presence of polyvalent aluminium enhances affinity to toner materials.
• the amount of aluminate salt or salt of a weak acid and a strong base to be used varies in accordance with the type of paper being treated, for example its absorbence and inherent hold-out characteristics and the level and type of internal sizing used. Guidance as to suitable treatment levels is obtainable from the Examples given below. Generally the amount of aluminate or salt of a weak acid and a strong base will be such as to produce an alkaline surface pH value, for example 8 - 8.5 or higher.
• a small amount of pigment e.g. colloidal precipitated calcium carbonate
• the treatment composition if the effect is not such as to change the fundamental character of the final treated paper, i.e. to convert it from what would be perceived as an "uncoated" grade to a conventional coated product.
• a 10% solution was prepared of an oxidised maize starch of the kind conventionally used for surface sizing of paper. This solution was divided into five batches. One of these was used as a control and the others were each made up into treatment compositions according to the invention by the addition of respective salts as listed below: Salt Mix Designation Disodiumtetraborate, Na 2 B 4 O 7 .10H 2 O A Sodium acetate trihydrate, NaC 2 H 3 O 2 .3H 2 O B Trisodium orthophosphate, Na 3 PO 4 .12H 2 O C Sodium aluminate, Na 2 Al 2 O 4 D ----- Control
• the addition level of the salts was 1% on a dry basis in each case, calculated as weight of dry salt present (as the hydrate form where indicated) in relation to the weight of dry starch present. Starch therefore made up 99% of the treatment composition.
• Each treatment composition was airknife-coated on to a smooth wove-finish 100 g m -2 business letterhead base paper stock by means of an intermediate-scale pilot coater.
• This base paper had been internally-sized with alkyl ketene dimer (i.e. it was neutral/alkaline sized) and had also been conventionally surface-sized.
• Two different coatweights of treating composition were applied, namely ca. 3 g m -2 and ca. 2 g m -2 (dry, in both cases).
• the resulting reels were then sheeted to SRA3 size and test printed on a liquid toner colour digital press (an INDIGO E-PRINT 1000 press supplied by Indigo N.V. of the Netherlands).
• the extent to which the various samples accepted the ink in a satisfactory manner was assessed visually, and the level of toner adhesion was assessed by "tape pull" and "rub toner adhesion” tests.
• a batch of 2201 of an 8% solution of cationic potato starch was prepared. 3kg sodium hydrogen carbonate were dissolved in this solution with stirring to produce a treating composition of which starch comprised ca. 85%.
• the resulting composition was fed to the size press of a paper machine producing a 90 g m -2 rosin/alum internally sized wove printing paper. The resulting paper was sheeted, printed and tested in the same way as in Example 1.
• Example 1 This compares the results obtained with a sodium aluminate treatment composition applied by means of an intermediate scale coater in two different ways, namely by airknife coating and by means of a size press coating head.
• the treatment composition was prepared as described with reference to Mix D of Example 1 and the dry coatweight applied was ca. 2 g m -2 in each case (per side in the case of the size press treated paper).
• the paper to which the compositions were applied had not been surface sized but was otherwise as in Example 2. After treatment, the paper was sheeted, printed and tested as described in Example 1.

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Paper (AREA)
• Glass Compositions (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Developing Agents For Electrophotography (AREA)

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Applications Claiming Priority (2)

Publications (3)

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Family Applications (1)

Country Status (7)

Cited By (5)

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Citations (2)

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• 1997
  • 1997-05-20 GB GBGB9710282.6A patent/GB9710282D0/en not_active Ceased
• 1998
  • 1998-05-19 DK DK98303925T patent/DK0879917T3/da active
  • 1998-05-19 ES ES98303925T patent/ES2227775T3/es not_active Expired - Lifetime
  • 1998-05-19 DE DE69825938T patent/DE69825938T2/de not_active Expired - Lifetime
  • 1998-05-19 AT AT98303925T patent/ATE275219T1/de active
  • 1998-05-19 EP EP98303925A patent/EP0879917B1/fr not_active Expired - Lifetime
  • 1998-05-19 PT PT98303925T patent/PT879917E/pt unknown

Patent Citations (2)

Non-Patent Citations (1)

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