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
  • 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
  • D21H23/46—Pouring or allowing the fluid to flow in a continuous stream on to the surface, the entire stream being carried away by the paper
  • D21H23/48—Curtain coaters
• • 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
  • D21H19/10—Coatings without pigments
  • D21H19/14—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12
  • D21H19/20—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
• • 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
  • D21H19/56—Macromolecular organic compounds or oligomers thereof obtained by reactions only involving carbon-to-carbon unsaturated bonds
• • 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

Definitions

• the invention relates to a process for coating substrates with one or more layers containing polyvinyl acetals by curtain coating.
• the coating of substrates such as paper or cardboard is being carried out industrially for the production of photographic papers, ink-jet printing papers or food packaging. These coatings are said to provide the substrate with improved receptivity to inks or pigments, or to inhibit the absorption of fats or oils by a barrier effect.
• the binder used for such layers is preferably polyvinyl alcohol or its derivatives. Binder systems of this type are for example in EP 0 905 313 . US 4,418,119 . US 5,587,204 or US 6,193,831 disclosed.
• Coatings for papers must be applied in the paper industry for large areas of constant thickness at high paper web speeds.
• contact methods in which the substrate has mechanical contact with a tool and contactless methods in which this is avoided are used.
• Contact methods are e.g. Processes with size presses, film presses, doctor blade processes, blade processes or contour coating processes. These processes have considerable disadvantages, especially at high paper web speeds and high layer thicknesses. Thus, under the contact of the applicator tool, the paper web may tear, the film coating may have defects, or the coated surface may be irregular due to so-called "misting".
• Contactless methods are, for example, the slot die coating process, spray coating or curtain coating.
• the curtain coating process is particularly at high paper web speeds used and delivers uniform coating thicknesses in high quality.
• Curtain coating processes are, for example, in US 2003/0188839 A1 .
• the quality of the curtain coating process depends to a great extent on the consistency of the curtain of the liquid. In this case, only slight variations in the thickness of the curtain or the density of the liquid may occur, otherwise this would result in errors in the coating. Furthermore, the curtain must not tear off, which places high demands on the constancy of the viscosity of the liquids used for coating.
• curtain coating processes are used only for the coating colors and surface applications of polyvinyl alcohols or latices established in the paper industry, optionally combined with further binders such as starch and / or with fillers or pigments.
• binders such as starch and / or with fillers or pigments.
• the binder systems mentioned have certain disadvantages in the barrier action against fats and oils, which are due to their chemical composition. Furthermore, they are unable to disperse selected pigments in the desired manner without having to add a barrier-resistant dispersant.
• the object of the present invention was therefore to provide binder systems for the curtain coating process which have an improved barrier action against fats and oils and / or a sufficient dispersing action for pigments.
• the present invention therefore provides a process for coating a substrate with one or more layers comprising polyvinyl acetals by applying aqueous solutions or dispersions which contain one or more polyvinyl acetals as binders by means of curtain coating.
• the process according to the invention is used in particular for producing coatings having at least one (partial) layer with an oil-tight or grease-tight barrier effect.
• the process according to the invention makes it possible to produce coatings with outstanding barrier action against oils or greases.
• the applied layers or the solutions or dispersions used for this purpose comprise one or more polyvinyl acetals as binders and barrier formers and optionally pigments such as chalk, kaolin, talc, calcium carbonate, titanium dioxide, silica or aluminum oxide. It is possible to use additional binders, e.g. Latexes based on styrene butadiene, styrene-acrylate, pure acrylate, vinyl acetate, vinyl acetate copolymers or polyurethane, starch or cellulose derivatives. Furthermore, the applied layers or the solutions or dispersions used for this purpose may contain the additives customarily used in papermaking, such as optical brighteners, defoamers, if appropriate also crosslinkers, rheological additives or plasticizers.
• additives customarily used in papermaking such as optical brighteners, defoamers, if appropriate also crosslinkers, rheological additives or plasticizers.
• solutions or dispersions used preferably contain 10-100% by weight of polyvinyl acetal.
• solutions or dispersions containing pigments have a proportion of polyvinyl acetals of 10-50% by weight, preferably 10-25% by weight. Without pigments, the proportion of polyvinyl acetals can be between 100 and 50% by weight, in particular 100-75% by weight. All data relate to the dry mass of the solutions or dispersions. The remaining shares are possibly formed from the above-mentioned tools.
• the method according to the invention makes it possible to produce a coating which has a barrier effect for oils or fats.
• the barrier effect can be determined according to TAPPI T 559 kit test and / or TAPPI T 454.
• at least one layer has an oil or grease-tight barrier according to the TAPPI T 559 kit test greater than 5, particularly preferably from 6 to 12 and in particular from 7 to 12.
• at least one layer has an oil or grease-tight barrier of TAPPI T 454 greater than 950, in particular greater than 1050, preferably greater than 1100. Values greater than 1800 are usually no longer determined in the TAPPI T 454 test, whereby barrier effects of 3000 can be achieved in the process according to the invention.
• the barrier effect of TAPPI T 454 and / or TAPPI T 559 kit test refers to a single layer (i.e., a single application) and can be achieved by multiple application e.g. be significantly improved by two or three layers, wherein the barrier effects of several layers does not behave additively. Due to the filler, the barrier effect of layers with pigments is naturally lower than that of layers on almost pure polyvinyl acetal.
• the coating can be applied in several, in particular 2, 3 or 4 partial layers.
• the layers may have the same or a different composition. If the coating is composed of several partial layers, then at least one layer of the coating must have the required oil or grease-tight barrier effect.
• the oil- or grease-proof layer can be applied directly to the substrate and provided in the same operation with a further coating, which contains printable pigments, for example.
• a conventional surface sizing agent for example based on styrene-maleic anhydride, modified starch, styrene-acrylate or pure acrylate latex, followed by a coating based on polyvinyl acetal in the manner already described.
• Preferred substrates for the process according to the invention are papers, in particular those having a weight per unit area of 10 to 100 g / m 2 or board paper, in particular those having a basis weight of more than 100 g / m 2 .
• the substrates have a surface of paper or cardboard.
• the polyvinyl acetals used in the process according to the invention are preferably readily soluble in water in order to produce layers having a high solids content.
• Their water solubility, which is a function of the acetal content, should be at least high enough to obtain a homogeneous dispersion.
• the viscosities of the pure polyvinyl acetals in water range from 5-2000 mPa.s.
• the polyvinyl acetals used according to the invention preferably have a degree of acetalization of from 0.1 to 30 mol%.
• the proportion of vinyl acetate units is preferably 0.1 to 15 mol%.
• polyvinyl acetals which can be used in the process according to the invention are formally constructed as a terpolymer from the monomer units vinyl alcohol, vinyl acetate and vinyl acetal, but in addition olefin units, such as, for example, Include ethylene, propylene or butylene.
• polyvinyl butyral is used as the preferred polyvinyl acetal.
• polyvinyl acetals used can have silanol or carboxylate groups.
• one or more layers of polyvinyl acetals can be applied to the substrate.
• the layers may be in the nature of the polyvinyl acetal, in the thickness or in the added additives such as pigments or the like. differ. That's how it works
• Substrate for example, with several order layers (layers), each containing different polyvinyl acetals coated.
• various polyvinyl acetals have different degrees of acetalization, degrees of hydrolysis, or degrees of polymerization and / or are chemically different by substitutions or comonomers.
• solutions or dispersions used according to the invention preferably have a viscosity of 3 to 150 mPa.s at a solids content of 5 to 20% by weight. If solutions or dispersions with fillers or pigments are used according to the invention, the viscosity can be between 80 and 2000 mPa.s at a total solids content of 10 to 65% by weight.
• the aqueous solutions of the polyvinyl acetals After application of the aqueous solutions of the polyvinyl acetals, they must be dried, for example, by means of infrared dryers, hot-air dryers, etc. In the normal dryer operation of finished paper and cardboard with a final moisture of 1-10% drying is not critical.
• Solutions or dispersions having the compositions described in Table 1 (with pigments) and 3 (without pigments) were prepared using the polyvinyl alcohols described in the following examples (comparative examples 1-4 not according to the invention) or polyvinyl acetals (inventive examples 5-16).
• Example 1 Carboxyl-containing PVA Mowiol 15-99 (Kuraray Europe GmbH)
• Example 4 Cationized PVA R-Polymer Type 1130 (Kuraray Europe GmbH)

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• Paper (AREA)
• Paints Or Removers (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)

Priority Applications (1)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

Country Status (1)

Cited By (1)

Citations (9)

• 2006
  • 2006-10-17 EP EP06122420A patent/EP1914345A1/fr not_active Withdrawn

Patent Citations (9)

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