Classifications

• • 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
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/14—Secondary fibres
• • 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
  • D21H19/72—Coated paper characterised by the paper substrate
• • 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
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
  • D21H19/46—Non-macromolecular organic compounds
• • 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
  • D21H19/80—Paper comprising more than one coating
  • D21H19/82—Paper comprising more than one coating superposed
• • 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
  • D21H19/80—Paper comprising more than one coating
  • D21H19/82—Paper comprising more than one coating superposed
  • D21H19/828—Paper comprising more than one coating superposed two superposed coatings, the first applied being non-pigmented and the second applied being pigmented

Definitions

• CELLULOSIC SHEET MATERIAL The invention relates to cellulosic sheet material, for example paper or paperboard, prepared from a base material which has dispersed within it particles of hydrophobic contaminating materials.
• a sheet-forming composition generally comprises a dilute suspension of cellulosic fibres and, usually, a proportion of inorganic filler particles which are added to improve the brightness and opacity of the sheet material which is formed from the composition.
• the incidence of hydrophobic contaminants is often especially high when the mixture used as the source of cellulosic fibres contains a high proportion of recycled waste paper.
• eucalyptus is an example of such a tree.
• a typical coating composition generally com ⁇ prises an aqueous suspension of a pigment, which is usually, but not always, white in colour, and an adhesive.
• a dispersing agent for the pigment is generally also required, and other additives to modify the rheological or optical properties of the composition may be included.
• the most commonly used pigments in paper coating compositions include natural and calcined kaolinitic clays, calcium carbonate, calcium sulphate, barium sulphate, titanium dioxide and talc.
• Paperboard is generally made from relatively low quality pulp and tends to be darker in colour and rougher in texture than good quality printing paper. However, for packaging purposes, it is often required to apply a printed image to at least one surface of the paperboard. Paperboard may be made by forming a relatively thick and heavy layer of cellulosic fibres on the wire mesh belt of a sheet forming machine, but usually it is preferred to manufacture paperboard by laminating together several layers of thinner sheet material. The inner layers tend to be of relatively low quality cellulosic material, and sheets of better quality material may be used to form the outer layers. However, it is usually necessary to coat even the sheet material used for the outer layers if a printed image of acceptable quality is to be applied.
• the sheet material used for the outer layers of paperboard may contain stickies which repel aqueous coating composition, with the result that the coating does not adhere to these locations, and unsightly spots remain in the coated surface.
• stickies which repel aqueous coating composition
• the problem of coating a cellulosic sheet material containing "stickies" has been tackled by either (i) applying a white liner material comprising paper usually of good quality onto the appropriate surface of the sheet material and coating the liner material; such a process for coating sheet material is expensive; or (ii) applying a conventional coating and accepting that the quality of the final product is limited by appearance of defects caused by the stickies.
• a method of coating a sheet of cellulosic material with a coating composition comprising an aqueous suspension of pigment material and an adhesive, wherein the sheet of cellulosic material contains one or more defect spots visible to the naked eye comprising one or more hydrophobic contaminants, characterised in that a wetting agent having hydrophobic and hydrophilic moieties is applied to at least one surface of the sheet to enable the spot or spots to be contacted by a water containing composition and the said surface is coated by the coating composition to form a coating which is uniform and substantially free of uncoated spots.
• the wetting agent if preferably applied to the said surface in a water containing composition.
• Such composition may be the said coating composition or, alternatively, a material applied as an intermediate layer on which the said coating material is subsequently deposited, eg. after drying.
• Such an intermediate layer (apart from the surfactant) may for example be one of the intermediate coatings applied in the prior art, eg. a so called "wash pre-coat", eg. comprising a binder, eg. latex or starch, in water optionally together with a coarse pigment material generally in a water based composition containing less than 50% by weight solids.
• the said wetting agent may for example comprise a known wetting agent, eg. a surfactant or surface active agent.
• the said wetting agent may for example be applied to the sheet of cellulosic material in an amount ranging from 0.2% to 2% by weight based upon the dry weight of pigment or pigments present in the added coating composition.
• defect spots there may, for example, be at least two of the said defect spots present in each 0.01m 2 unit of surface area of the sheet of cellulosic material treated.
• a sheet of paperboard of dimensions 10cm by 20cm may have four or five spots on its surface.
• the said defect spot or spots may comprise one or more spots which are dark in colour compared to the defect-free areas of the treated surface of the sheet of cellulosic material.
• the said defect spot or spots may for example be spots which have an average diameter of at least 100 micrometres (lOO ⁇ m).
• the hydrophobic material contained within the defect spots may for example comprise fats or fatty acids or mixtures thereof.
• the sheet of cellulosic material treated by the method of the present invention may comprise a paper product, eg. a sheet of paper or a paper board, eg. manufactured in a known way, eg. as described hereinbefore.
• the present invention is especially suitable for coating sheets of cellulosic materials wherein the presence of stickies is known to be common, eg. in paper products produced from pulps derived from large amounts eg. 50% to 100% of waste paper or in products produced from pulps derived from certain tree types, eg. trees from tropical and sub-tropical regions which may product large amounts of organic solvent extractives.
• the surfactant may be of the anionic, cationic, non-ionic or amphoteric type.
• Surfactants of the non-ionic type are preferred because, in general, they have a smaller tendency to generate foam in the coating composition than the other types.
• a surfactant of the non-ionic type having a hydrophile/lipophile balance (HLB) value of at least 8, especially in the range of from 8 to 14 is especially advantageous because it provides suitable spot wetting without excessive detergent or solvent activity.
• HLB hydrophile/lipophile balance
• the coating composition employed in the method according to the present invention may comprise a known paper coating composition which (apart from the wetting agent), may be made in one of the ways well known to those skilled in the art.
• the pigment material employed in the coating composition may comprise a kaolin clay in its natural or hydrous state or a kaolin clay which has been calcined to drive off chemically combined water.
• the pigment may comprise calcium carbonate, calcium sulphate, barium sulphate, talc, satin white or titanium dioxide.
• a mixture of two or more pigment materials is frequently desirable.
• the pigment or pigments are conveniently first mixed with water containing a dispersing agent to form a relatively concentrated suspension to which other components of the coating composition are added.
• Suitable dispersing agents are well known per se and include water soluble salts of polysilicic acids, water soluble condensed phosphate salts and water soluble salts of poly (acrylic acid), of poly (methacrylic acid) and of polymers of related ethylenically unsaturated acids and blends and copolymers of these species.
• the quantity of the dispersing agent used may be in the range of from 0.05% to 1% by weight, based on the dry weight of the pigment material(s).
• the adhesive employed in the coating composition may comprise an adhesive of the carbohydrate type, such as a starch or one of the various derivatives of starch and cellulose, of the protein type, such as casein, or of the latex type, such as latices of styrene butadiene rubber or of various acrylic polymers.
• an adhesive of the carbohydrate type such as a starch or one of the various derivatives of starch and cellulose
• the protein type such as casein
• the latex type such as latices of styrene butadiene rubber or of various acrylic polymers.
• the amount of adhesive used is in the range of from about 4% to about 20% by weight, based on the dry weight of pigment material in the composition.
• Other known optional additives may be included in the composition.
• the surfactant is added to the composition after all the other ingredients have been added, but it is also possible to add the surfactant at an earlier stage in the preparation of the composition.
• the coated sheet of cellulosic material may be dried in a known way, eg. by infra-red heating and/or evaporative drying in warm air.
• the thickness of the coating composition applied will depend upon the make-up of the coating composition, the base material being coated, and the nature of the defect spots (eg. darkness of the spots).
• the coating composition may be added to the sheet of cellulosic material to be coated in a manner well known in the art. More than one coating layer may be applied. One or more of these may be one of the intermediate pre-coatings referred to above. Alternatively, or in addition, multiple coatings of the final coating composition may be made. For example a first coating layer may be applied and allowed to dry and then a second coating layer may be applied and then allowed to dry. Overall, the amount of the coating composition applied may be such that the weight per unit area after drying of the coating composition is at least 5gm ⁇ 2 (grammes per metre squared) desirably at least lOgm" 2 .
• a coated sheet of cellulosic material which has been produced by the method according to the first aspect.
• the present invention allows the problem of coating sheets of cellulosic material containing defect spots comprising hydrophobic material or "stickies" as described hereinbefore to be solved without using an expensive additional paper liner material as described hereinbefore.
• Example 1 Coating compositions were prepared according to the following general formulation:
• the hydrous clay was an English kaolin clay having a particle size distribution such that 80% by weight of the particles had an equivalent spherical diameter smaller than 2 ⁇ m.
• This clay was introduced into the composition in the form of an aqueous suspension containing 68% by weight of the dry clay and 0.3% by weight, based on the weight of dry clay, of a sodium polyacrylate dispersing agent and 0.08% by weight, based on the weight of dry kaolin, of sodium hydroxide.
• the calcined clay was prepared by calcining a fine kaolin from Georgia, U.S.A. and had a particle size distribution such that 90% by weight of the particles had an equivalent spherical diameter smaller than 2 ⁇ m. This clay was introduced into the composition in the form of an aqueous suspension containing 49% by weight of the dry calcined kaolin and 0.1% by weight, based on the weight of dry calcined kaolin, of a sodium polyacrylate dis ⁇ persing agent.
• the two clay suspensions were blended in a laboratory mixer in the proportions of 90 parts by weight of dry hydrous clay to 10 parts by weight of dry calcined clay.
• the latex adhesive which contained 50% by weight of a carboxylated styrene-butadiene copolymer, was then mixed into the blended clay suspension.
• the sodium carboxymethyl cellulose was then added to the stirred mixture in the form of a 10% by weight solution in water. Sufficient of a 10% by weight solution of sodium hydroxide was then added to raise the pH to 8.5.
• the surfactant was mixed in with stirring.
• the following surfactants were used: Anionic:- Al - Sodium dodecylbenzenesulphonate A2 - Sodium dioctylsulphosuccinate
• compositions were diluted with sufficient water to give a low shear viscosity as measured using a Brookfield Viscometer [at lOOrpm using Spindle No.3 of 350mPa.s.
• Brookfield Viscometer at lOOrpm using Spindle No.3 of 350mPa.s.
• the solids content of the composition was 51% by weight.
• Surfactant Ami caused thickening of the composition and, in this case, the solids content was reduced to 41% by weight to give the required low shear viscosity level.
• compositions were coated onto sheets of paperboard each measuring 10 x 20cm using a No.10 wire wound coating bar. Each composition was coated on to 10 of the small sheets.
• the paperboard was light brown in colour and each sheet had up to 4 or 5 visible spots which were caused by the presence of stickies. After drying, the average weight of coating on the test sheets was found to be lOg.rrf 2 .
• the accompanying Figure shows photographic images of the surfaces of 1 the uncoated brown paperboard, 2 the paperboard which had been coated with a composition containing no surfactant, and 3 the paperboard which had been coated with the composition containing surfactant N3. It will be noted that, although dark spots are visible in the uncoated paperboard 1, and in coated paperboard 2, coated paperboard 3 shows no visible spots.
• Coating compositions were prepared as described above containing surfactants A2 and N3. In this case the complete compositions were diluted before coating with sufficient water to reduce the low shear viscosity, as measured with a Brookfield Viscometer at lOOrpm using Spindle No.5, to 1600mPa.s. The compositions were coated on to the same light brown paperboard as was described in Example 1 using a laboratory paper coating machine of the type described in British Patent Specification No. 1032536 at a speed of 400m.min" 1 , a blade angle of 45° and at a blade deflection which was adjusted to give a coat weight of 14g.m" 2 .
• the two previous Examples concern coating compositions containing kaolin clay as the sole coating pigment.
• This further Example shows the effect of using a coating composition in which a proportion of the clay is substituted with calcium carbonate.
• the composition was prepared according to the following general formulation:
• Latex adhesive (polymer solids) 12 Sodium carboxymethyl cellulose 1.5
• the hydrous clay was an English kaolin clay having a particle size distribution such that 80% by weight of the particles had an equivalent spherical diameter -IP- smaller than 2 ⁇ m.
• This clay was introduced into the composition in the form of an aqueous suspension containing 68% by weight of the dry clay and 0.3% by weight, based on the weight of the dry clay, of a sodium polyacrylate dispersing agent and 0.8% by weight, based on the weight of dry clay, of sodium hydroxide.
• the calcium carbonate had a particle size distribution size such that 90% by weight of the particles had a equivalent spherical diameter smaller than 2 ⁇ m.
• This carbonate was introduced into the composition in the form of an aqueous suspension containing 75% by weight of the dry calcium carbonate and 0.6% by weight, based on the weight of dry calcium carbonate, of a sodium polyacrylate dispersing agent.
• the two pigment suspensions were blended in a laboratory mixer in the proportions of 50 parts by weight of the dry hydrous clay to 50 parts by weight of calcium carbonate.
• the latex adhesive which contained 50% by weight of a carboxylated styrene - butadiene copolymer, was then mixed into the blended suspension.
• the sodium carboxymethyl cellulose was then added to the stirred mixture in the form of a 10% by weight solution in water. Sufficient of a 10% by weight solution of sodium hydroxide was then added to raise the pH to 8.5. Finally the surfactant was mixed in with stirring.
• Example 1 the composition was diluted with sufficient water to give a low shear viscosity as measured using a Brookfield Viscometer [at lOOrpm using Spindle No. 3] of 350mPa.s.
• the solids content of the composition containing surfactant was 10% by weight.
• composition was coated onto sheets of light brown paperboard using exactly the same method as described in Example 1.
• a composition prepared in the same way but containing no surfactant was coated onto the base paperboard in the same manner.

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• 1995
  • 1995-06-03 KR KR1019970700906A patent/KR970704942A/ko not_active Application Discontinuation
  • 1995-06-06 GB GBGB9511419.5A patent/GB9511419D0/en active Pending
• 1996
  • 1996-06-03 JP JP9500214A patent/JPH11502904A/ja active Pending
  • 1996-06-03 WO PCT/GB1996/001312 patent/WO1996039559A1/en not_active Application Discontinuation
  • 1996-06-03 GB GB9611527A patent/GB2301785A/en not_active Withdrawn
  • 1996-06-03 EP EP96919957A patent/EP0774023A1/de not_active Withdrawn
  • 1996-06-03 AU AU58418/96A patent/AU695916B2/en not_active Ceased

Non-Patent Citations (1)

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