Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/50—Multilayers
  • B05D7/56—Three layers or more
  • B05D7/58—No clear coat specified
  • B05D7/582—No clear coat specified all layers being cured or baked together
  • B05D7/5823—No clear coat specified all layers being cured or baked together all layers being applied simultaneously
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D1/00—Processes for applying liquids or other fluent materials
  • B05D1/28—Processes for applying liquids or other fluent materials performed by transfer from the surfaces of elements carrying the liquid or other fluent material, e.g. brushes, pads, rollers
• • 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
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
  • D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
  • D21H23/22—Addition to the formed paper
  • D21H23/52—Addition to the formed paper by contacting paper with a device carrying the material
• • 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
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
  • D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
  • D21H23/22—Addition to the formed paper
  • D21H23/70—Multistep processes; Apparatus for adding one or several substances in portions or in various ways to the paper, not covered by another single group of this main group
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C1/00—Apparatus in which liquid or other fluent material is applied to the surface of the work by contact with a member carrying the liquid or other fluent material, e.g. a porous member loaded with a liquid to be applied as a coating
  • B05C1/04—Apparatus in which liquid or other fluent material is applied to the surface of the work by contact with a member carrying the liquid or other fluent material, e.g. a porous member loaded with a liquid to be applied as a coating for applying liquid or other fluent material to work of indefinite length
  • B05C1/08—Apparatus in which liquid or other fluent material is applied to the surface of the work by contact with a member carrying the liquid or other fluent material, e.g. a porous member loaded with a liquid to be applied as a coating for applying liquid or other fluent material to work of indefinite length using a roller or other rotating member which contacts the work along a generating line
  • B05C1/0826—Apparatus in which liquid or other fluent material is applied to the surface of the work by contact with a member carrying the liquid or other fluent material, e.g. a porous member loaded with a liquid to be applied as a coating for applying liquid or other fluent material to work of indefinite length using a roller or other rotating member which contacts the work along a generating line the work being a web or sheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C5/00—Apparatus in which liquid or other fluent material is projected, poured or allowed to flow on to the surface of the work
  • B05C5/007—Slide-hopper coaters, i.e. apparatus in which the liquid or other fluent material flows freely on an inclined surface before contacting the work
  • B05C5/008—Slide-hopper curtain coaters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C9/00—Apparatus or plant for applying liquid or other fluent material to surfaces by means not covered by any preceding group, or in which the means of applying the liquid or other fluent material is not important
  • B05C9/04—Apparatus or plant for applying liquid or other fluent material to surfaces by means not covered by any preceding group, or in which the means of applying the liquid or other fluent material is not important for applying liquid or other fluent material to opposite sides of the work
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05C9/00—Apparatus or plant for applying liquid or other fluent material to surfaces by means not covered by any preceding group, or in which the means of applying the liquid or other fluent material is not important
  • B05C9/06—Apparatus or plant for applying liquid or other fluent material to surfaces by means not covered by any preceding group, or in which the means of applying the liquid or other fluent material is not important for applying two different liquids or other fluent materials, or the same liquid or other fluent material twice, to the same side of the work
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2252/00—Sheets
  • B05D2252/10—Applying the material on both sides
• • 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
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
  • D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
  • D21H23/22—Addition to the formed paper
  • D21H23/52—Addition to the formed paper by contacting paper with a device carrying the material
  • D21H23/56—Rolls
  • D21H23/58—Details thereof, e.g. surface characteristics, peripheral speed
  • D21H23/60—Details thereof, e.g. surface characteristics, peripheral speed the material on the applicator roll being subjected to a particular treatment before applying to the paper

Definitions

• the present invention concerns a method according to the preamble of claim 1 for producing coated paper or cardboard.
• a base paper or cardboard web is provided with a coating layer, which at least partially contains pigments and binder.
• Coated papers are big volume paper products on the markets nowadays. These kinds of papers normally serve as high quality printing bases. Printing papers are expected to simultaneously exhibit properties of high brightness, gloss and smoothness.
• a coating colour comprises mineral pigments, water and a binding polymer.
• the mineral pigment can be kaolin clay, gypsum, ground or precipitated calcium carbonate, titanium dioxide etc.
• the best opacity forming pigments are titanium dioxide (TiO 2 ) and Precipitated Calcium Carbonate (PCC). The best pigments are also the most expensive ones.
• each layer contains particles having different medium size and possibly different mineral particle qualities. Small mineral particle size will retain more "pixels" at printing. This is the reason why particles having particle sizes in the range of 0.5 to 1.0 ⁇ m are usually employed in the topmost layer, forming the surface of the coated paper.
• the coating colour is applied on the surface of a base paper or cardboard web with a number of different coating methods.
• blade coating, rod coating, spray coating and transfer coating can be mentioned.
• blade and rod coating are the ones most frequently used.
• Transfer of the coating film from a precoated roll onto the paper web in a roll nip is also a widely used method.
• the film is in wet condition when transfer takes place.
• a rather new coating method is spray coating, where tiny coating colour droplets are sprayed to the webs surface.
• Dry coating is also known, and in a method of this kind, dry particles of mineral pigments are sprayed to the web with electrical forces and fixed with glue, which is already present on the surface.
• US Patent No. 6,645,335 discloses a paper web coating using a method, where "barrier and printing properties" are improved by casting a mixture of mineral pigments and water on a smooth surface formed by a polished steel or other metal belt or roll or a smooth polymer belt, drying the mineral layer on the belt and then transferring the dried mineral layer with a glue or adhesive to the paper web.
• the known method gives rise to a smooth surface of the topmost coating layer because the surface of the coating layer abutting against the metal belt will be smoothened when the surface particles - usually finely divided pigments - become densely packed against the metal band.
• a polymer adhesive is used for picking up the coating layer from the smooth surface.
• the present invention is based on the idea of forming multilayer coating layers from at least two overlapping coating layers, which are first transferred from a non-contacting coater onto the smooth surface, where they are combined into a multilayer coating layer.
• the smooth surface is preferably heated up to aid in the drying of the coating layer against the surface.
• the precast coating layer is transferred onto a paper or cardboard surface in a coating nip.
• a coating nip By building up the coating nip from at least one pair of smooth-surfaced cylinders, both having polished surfaces, it is possible to use the cylinders of the coating nip both for smoothening and polishing the surface of the precast coating layer and for transferring the layer onto the paper or cardboard surface.
• the present invention is mainly characterized by what is stated in the characterizing part of claim 1.
• a method partially similar to the know process described in US Patent No. 6,645,335 is used for achieving a precast coating layer.
• multiple layers of mineral coatings are applied to a polished hot belt or cylinder.
• finely divided particles need only be used in the coating layer abutting the polished cylinder or belt, whereas the second or second and further layers can be made up by more inexpensive pigments.
• the second layer can comprise normal amounts of polymeric binders, such as latexes.
• a problem related to curtain coating is that the curtain "lives" due to the unevenness of the paper or board web and because of air, which accompanies the web.
• a smooth roller or steel belt is much more stable than a conventional web and with a roller or belt as an intermediate coating surface, it becomes much -easier to prevent the generation of air flows during the transfer of the coating film from the application nozzles to the substrate and to make the curtain more stable during the curtain application stage.
• the ready-made coating layer can then easily be transferred from the roller or belt onto the web without interference.
• Another problem associated with curtain coating is the difficulties in achieving proper coating of the area close to the edge of the web. Often, that edge is either over- or undercoated in the sense that the coating layer either leaves an uncoated area along the edge of the web, or the coating curtain extends past the edge. With the use of an intermediate roller or belt of the above-discussed kind it is possible to lever out the edge of the coating layer with a blade (such as a conventional coating blade) to obtain perfect match of the coating with the web when the coating layer is transferred onto the web.
• a blade such as a conventional coating blade
• Figure 1 shows in a schematic fashion the sideview of a first embodiment of the invention, involving the use of two opposing metal belts which run horizontally over two cylinders which form a coating nip
• Figure 2 shows in a schematic fashion the sideview of a simplified second embodiment of the invention, in which the coating layers are cast directly onto the surfaces of two cylinders forming a coating nip.
• the method of coating paper or cardboard webs comprises the steps of
• the coating colour is preferably applied onto the heated smooth surface by curtain coating, which ensures high-speed operation.
• the mineral layer(s) i.e. layers of mineral pigments
• the mineral layer(s) need not be completely dried.
• the remaining water is present in sufficiently small amounts in the last cast layer, the swelling of the body stock paper or board is insignificant and keeps the surface smooth.
• the moisture content of the last cast layer i.e. the layer abutting with the web, is in the range of 5 - 40 weight-%, preferably about 10 to 30 weight-%.
• the coating colour used according to the present invention for forming a precast coating layer contains from 10 to 100 parts by weight of at least one pigment or mixture of pigments, from 0.1 to 30 parts by weight of at least one binder and from 1 to 10 parts by weight of other additives known per se.
• the first layer there can be a single finely divided mineral pigment, or a mixture of several finely divided pigments as follows:
• Coating pigment I 10 - 90 parts by weight for example, fine carbonate
• Water is added to this kind of a coating colour so that the dry solids content is typically from 50 to 75%.
• the typical composition of the coating colour used for forming the second layer is as follows:
• Water is added to the precoating mix so that the solids content is generally from 40 to 70%.
• the present invention is applicable to any pigment.
• Precipitated calcium carbonate, ground calcium carbonate, calcium sulphate, calcium oxalate, aluminium silicate, kaolin (hydrous aluminium silicate), aluminium hydroxide, magnesium silicate, talc (hydrous magnesium silicate), titanium dioxide and barium sulphate, and mixtures thereof can be mentioned as examples of the pigments.
• Synthetic pigments can also be used.
• the main pigments are kaolin, calcium carbonate, precipitated calcium carbonate and gypsum, which in general constitute over 50 % of the dry solids in the coating mix.
• Calcined kaolin, titanium dioxide, satin white, aluminium hydroxide, sodium silicoaluminate and plastics pigments are additional pigments, and their amounts are in general less than 25 % of the dry solids in the mix.
• special pigments special-quality kaolins and calcium carbonates, as well as barium sulphate and zinc oxide, should be mentioned.
• the present invention is applied especially preferably to calcium carbonate, calcium sulphate, aluminium silicate and aluminium hydroxide, magnesium silicate, titanium dioxide and/or barium sulphate, as well as mixtures thereof, in which case, especially preferably, the principal pigment in the pre-coat mixes is calcium carbonate or gypsum and in surface-coat mixes and single-coat mixes the principal pigment consists of mixtures of calcium carbonate or gypsum and kaolin.
• the first layer, forming the surface of the coated paper or cardboard can be very thin, containing high quality and small mineral particles, such as TiO 2 or PCC or mixtures thereof, in order to give the best possible printing and print ink holding properties.
• the other layers can comprise coarse materials, such as ground calcium carbonate or china clay.
• the particles of the first layer can have an average particle size, which is 1/3 to 1/50, preferably 1/5 to 1/20, in particular about 1/6 to 1/15, of the average particle size of the second layer(s).
• the particles of the first layer can have an average particle size in the range of 0.2.to 1.0 ⁇ m, and the thickness of the first layer is preferably about 0.5 to 5 ⁇ m, preferably about 1 to 3 ⁇ m.
• the thickness of the second layer is typically about 4 to 15 ⁇ m.
• binders generally employed in paper production as binders in the coating colours.
• binders it is also possible to use mixtures of binders.
• typical binders include synthetic latexes made up of polymers or copolymers of ethylenically unsaturated compounds, e.g. copolymers of the butadiene- styrene type, which possibly also have a comonomer containing a carboxyl group, such as acrylic acid, itaconic acid or maleic acid, and polyvinyl acetate having comonomers that contain carboxyl groups.
• the water-soluble polymers starch, CMC, hydroxyethyl cellulose and polyvinyl alcohol as binders.
• additives and auxiliary agents such as dispersants (e. g. sodium salt of polyacrylic acid), agents affecting the viscosity and water retention of the mix (e. g. CMC, hydroxyethyl cellulose, polyacrylates, alginates, benzoate), so-called lubricants, hardeners used for improving water-resistance, optical auxiliary agents, anti-foaming agents, pH control agents, and preservatives in the coating composition.
• dispersants e. g. sodium salt of polyacrylic acid
• agents affecting the viscosity and water retention of the mix e. g. CMC, hydroxyethyl cellulose, polyacrylates, alginates, benzoate
• so-called lubricants so-called lubricants
• hardeners used for improving water-resistance e. hydroxyethyl cellulose, polyacrylates, alginates, benzoate
• hardeners used for improving water-resistance
• optical auxiliary agents
• lubricants include sulpfonate oils, esters, amines, calcium or ammonium stearates; of agents improving water resistance, glyoxal; of optical auxiliary agents, diaminostilbene disulfonic acid derivatives; of anti-foaming agents, phosphate esters, silicones, alcohols, ethers, vegetable oils; of pH control agents, sodium hydroxide, ammonia; and finally of preservatives, formaldehyde, phenol, quaternary ammonium salts.
• the present invention can be characterized as a semi-dry transfer coating method, which differs from film transfer coating in that the coating layer is, as a whole, substantially dry.
• the conditions at which this happens are, according to a preferred embodiment, such that the first layer is totally or essentially dry, the second and any third and further layers are partially dry so that the layer closest to the paper or cardboard web is still suitable tacky for gluing the layers to the web by transfer from the polished belt.
• no separate polymeric binder layer is needed for transferring the precast coating layer onto the paper or cardboard web.
• the transfer can be carried out in a pressure nip or pressure belt.
• the coating can be made at high speed and the coatings do not need any kind of drying after the transfer.
• the first layer comprising finely divided particles
• the first layer is advantageously provided with a small amount of hydrophilic polymer for preventing surface dusting of the ready product.
• This hydrophilic polymer can be carboxyl-methyl cellulose, gelatin, dextrin, starch or a similar polymer, which is used in small amounts of about 1 to 3 % calculated by the weight of the layers.
• the invention is very advantageous that in the first layer, if expensive titanium dioxide is used, it is mixed before with fine PCC particles which partially agglomerate on the surface of the titanium dioxide particles. This will improve the optical properties, when the TiO 2 particles do not come into direct contact with each other.
• the glue is selected from the group of "hot melt” glues, and it can be applied to the uppermost surface layer immediately before transfer. This prevents paper surface swelling at transfer.
• non-contact application of the layers onto the smooth, polished metal surface can be carried out by curtain coating.
• curtain coating it is preferred to have a minimum volumetric flow rate/width of more than 1.0 cm 2 /s, in particular at least 1.5 cm 2 /s, to obtain a stable curtain from the applicator to the transfer surface.
• the dynamic surface tension of the coating colour should be about 20 to 60 mN/m, in particular about 35 - 55 mN/m, typically less than about 40 mN/m.
• the coating curtain is applied onto the transfer surface vertically from above.
• the clearance between the nozzle of the curtain coater and the transfer surface is about 1 - 1000 mm, preferably about 1 - 500 mm, in particular about 10 - 500 mm.
• the height depends on the amount of coating colour and the coating speed.
• the thickness of the film is usually about 0.1 - 10 mm, in particular about 1 - 5 mm, during free falling the film is thinned to below 100 micrones.
• Figure 1 there is shown a sideview of an embodiment of the invention, where coating colours are precast on polished metal belts.
• a paper web 1 which is adapted to move vertically from an upper roll 2 to a lower roll 3, is coated in a coating nip 4 formed between two cylinders 5 and 6.
• the cylinders both support a polished metal belt 7 and 8, which run in opposite directions, such that belt 7 runs clockwise in the drawing and belt 8 counter-clockwise.
• the cylinders 5 and 6 can have a surface layer of, e.g. rubber or other thermoelastic material for increasing friction between the cylinder surface and the metal belt.
• the coating colours are spread onto the casting surfaces 7, 8 by non-contact application.
• Such application can be achieved with a curtain coating unit 9, 10.
• These coaters allow for the formation of two or more overlapping layers which form an integral film 11, 12, which is free-falling from the applicator nozzle to the surface of the metal belt.
• Figure 2 shows a simplified working example of the previous embodiment, where the coating colours are precast directly on the cylinders 25, 26 forming the coating nip 24.
• the paper web 21 is adapted for vertical movement from an upper roll 22 to a lower roll 23, and it is double-sided coated in the coating nip 24.
• the cylinders 25 and 26 both have polished metal surfaces.
• the metal or polymeric surfaces of the belts 7, 8 and cylinders 25, 26, respectively are smooth. Generally, a roughness of about 0.1 to 1 um is acceptable for the present invention.
• the smooth surfaces are preferably heated, in particular the first layers are dried against heated surfaces having temperatures higher than the boiling point of water, typically at least 110 °C, preferably about 120 to 300 0 C, in particular at about 180 to 250 °C, in order to evaporate the water and/or solvent of the coating colour.
• temperatures higher than the boiling point of water typically at least 110 °C, preferably about 120 to 300 0 C, in particular at about 180 to 250 °C, in order to evaporate the water and/or solvent of the coating colour.
• the smaller the pigments, the higher temperatures should be used for drying.
• the polished metal belt or drum is then preferably cooled down at point just before the coating layer is transferred to the paper or cardboard surface in order to promote separation from the metal surface.
• the width of the combined layer can be adjusted to match the actual width of the paper or cardboard web by, e.g. cutting any overlapping parts of the curtain with a blade before the precast layer is transferred to the web.
• the precast layer is cast to a width that is at least somewhat greater, preferably about 1 to 20 %, in particular about 1.5 to 10 % greater, than the width of the web, which is to be coated.
• the present invention can be employed for coating any desired paper or board or polymer industrial web or sheet-formed product.
• paper or “paper web” is herein used to designate both “paper” and “paperboard” and “paper web” and “paperboard web”, respectively.
• paper and paperboard refer to sheet-formed products containing cellulosic or lignocellulosic fibres.
• Paperboard is synonymous with “cardboard” or simply “board”.
• the grammage of the paper or board can vary within broad ranges from about 30 to about 500 g/m 2 .

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

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Cited By (4)

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Citations (2)

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• 2004
  • 2004-12-31 FI FI20041706A patent/FI121086B/sv not_active IP Right Cessation
• 2005
  • 2005-12-30 WO PCT/FI2005/000562 patent/WO2006070064A1/en active Application Filing
  • 2005-12-30 EP EP05823380A patent/EP1834041A4/en not_active Withdrawn

Patent Citations (2)

Non-Patent Citations (1)

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