WO2009127598A1

WO2009127598A1 - Coating formulation for an offset paper and paper coated therewith

Info

Publication number: WO2009127598A1
Application number: PCT/EP2009/054312
Authority: WO
Inventors: Anne-Sophie Gombart; Wim Ballet
Original assignee: Sappi Netherlands Services B.V.
Priority date: 2008-04-15
Filing date: 2009-04-09
Publication date: 2009-10-22
Also published as: EP2279299A1

Abstract

A coated paper for offset printing comprising at least on one side a top coating layer, is described, said top coating layer comprising a pigment part, the 100 parts in dry weight thereof consisting of a) in the range of 50 -100 parts in dry weight of a fine particulate pigment with a particle size distribution such that at least 50% of the particles have a size of below or equal to 1 μm and/or that at least 80% of the particles have a size of below or equal to 2 μm, b) in the range of 0 - 50 parts in dry weight of a fine particulate pigment with a particle size distribution such that at least 50% of the particles have a size of below or equal to 3 μm and/or that at least 40% of the particles have a size of below or equal to 2 μm, as well as c) in the range of 0 - 50 parts in dry weight of a further fine particulate pigment, the parts a), b) and c) supplementing to 100 parts in dry weight a binder part with in the range of 2 - 20 parts in dry weight of binder, an additive part with in the range of 0 - 8 parts in dry weight of additive(s), wherein the binder part comprises a synthetic auto-oxidative resinous binder or at least partly (modified) natural resinous binder with auto-oxidative drying functionality as well as optionally at least one further non-resinous binder.

Description

SPECIFICATION

TITLE

Coating formulation for an offset paper and paper coated therewith TECHNICAL FIELD The present invention relates to the field of matt, silk/medium gloss or glossy/high gloss coated papers for offset printing comprising at least on one side a top coating layer to be printed.

BACKGROUND OF THE INVENTION

In the field of sheet- fed offset printing it is desirable to be able to further reprint and process freshly printed sheet as quickly as possible, while at the same time still allowing the printing inks to settle in and on the surface of the paper in a way such that the desired print gloss and the desired resolution can be achieved. Relevant in this context are on the one hand the physical ink drying process, which is connected with the actual absorption of the ink vehicles into an image receptive coating, e.g. by means of a gradual system of fine to coarse pores or a special system of very fine pores. On the other hand there is the so-called chemical drying of the ink, which is connected with solidification of the ink in the surface and on the surface of the ink receptive layer, which normally takes place due to an oxidative cross-linking (oxygen involved) of cross-linkable constituents of the inks. This chemical drying process can on the one hand also be assisted by IR-irradiation, it may however also be sped up by adding specific chemicals to the inks which catalytically support the cross-linking process. The more efficient the physical drying during the first moments after the application of the ink, the quicker and more efficient the latter chemical drying takes place.

Nowadays typically times until reprinting and converting are in the range of several hours (typical values until reprinting for standard print layout: about 1-2 h; typical values until converting for standard print layout: 12 - 14h; matt papers are more critical than glossy papers in these respects), which is a severe disadvantage of the present ink and/or paper technology, since it slows down the complete printing processes and necessitates intermediate storage. Today shorter times are possible if for example electron beam curing or UV irradiation is used after the printing step, but for both applications special inks and special equipment is required involving high costs and additional difficulties in the printing process and afterwards.

An improvement in this respect is described in WO-A-2007/006794 as well as WO-A- 2007/006796. In a preferred embodiment of these two disclosures, the highly advantageous quick ink setting properties and chemical drying properties for offset printing are achieved by using a specific amorphous silica pigment, namely silica gel with a high (nano) fine internal porosity.

EP 0850880 proposes a method for the preparation of an aqueous slurry of calcium carbonate particles suitable as a base pigment in the preparation of a paper coating composition having high water retentivity and high solid concentration with good fiowability, which contains precipitated and ground calcium carbonate particles in combination in a specified weight proportion and characterized by several parameters. In the examples a standard binder, specifically SBR latex is used. There is no information in the document that this could be some kind of a specific resin type binder. US 2006/005 4291 is rather similar in that the only place where mention is made about a specific type of binder, conventional SBR latex is discussed. Also in EP 1245730 in the examples only conventional SBR latex binder is used.

EP 1577438 relates to specific latex formulations to be used as a binder for coating formulations. Considering the claims which one can however not find any indication that the final latex which is used as a constituent of the coating formulation has the possibility of hardening, cross-linking, or the like.

EP 795588 relates to coating formulations using conventional binders. Conventional binders such as latex are proposed. GB 2139606 is focusing on particle size distributions of the pigment part and the binding agents used in this document are again conventional binders and not resins.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide an improved coating and/or coated paper for offset printing comprising at least on one side a top coating layer, which can be matt, medium gloss or high gloss.

This object is achieved by providing a coated paper for offset printing with, in case of a matt grade, a TAPPI 75° (Tappi 480, 75°, DIN EN ISO 8254-T1+2-03 (75°)) gloss value of below 35%, in case of a medium gloss grade, a TAPPI 75° gloss value of in the range 35 - 70 % and in case of a glossy grade, a TAPPI 75° gloss value of at least 70%, said coated paper comprising at least on one side a top coating layer, said top coating layer comprising a pigment part, the 100 parts in dry weight thereof consisting of a) in the range of 50-100 parts in dry weight of a fine particulate pigment with a particle size distribution such that at least 50% of the particles have a size of below or equal to 1 μm and/or that at least 80% of the particles have a size of below or equal to 2 μm, b) in the range of 0 - 50 parts in dry weight of a fine particulate pigment with a particle size distribution such that at least 50% of the particles have a size of below or equal to 3 μm and/or that at least 40% of the particles have a size of below or equal to 2 μm, as well as c) in the range of 0-50 parts in dry weight of one or several further fine particulate pigment, the parts a), b) and c) supplementing to 100 parts in dry weight a binder part with in the range of 2 - 20 parts in dry weight of binder, an additive part with in the range of 0 - 8 parts in dry weight of additive(s), wherein the binder part comprises a synthetic or at least partly (modified) natural resinous binder, each with built-in auto-oxidative drying functionality, as well as optionally at least one further non-resinous binder. Preferably the synthetic or at least partly (modified) natural resinous binder with built-in auto-oxidative drying functionality is normally free from significant amounts of catalyzing agent or hardener.

The pigments of the parts a), b) and c) are, as can be seen from the particle size distributions, typically different pigments. Generally a resin is to be understood as a viscous liquid capable of hardening and/or film formation. However, the most abundant types of resins on the market, epoxy resins and saturated and unsaturated resins (constituting more than 75% of total resin usage) do require additional reactive co- reactants and/or substantially enhanced stoving or curing temperatures to be capable of hardening and film formation, normally resulting in total unsuitability as binder in the paper production process. This shall be further explained in the following discussion of the specific chemistry of such epoxy resins and saturated and unsaturated polyester resins.

Epoxy resins: Most common thermosetting epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A. Their curing (i.e. cross-linking polymerisation reaction) is only possible by intensively mixing them with a catalyzing agent or hardener (e.g. amine type components), possibly at required elevated temperature. Such catalyzing agents or hardeners among other problems normally have the potential to interact with other constituents of coating formulations leading to a negative influence thereof and are therefore highly undesirable.

Spontaneous air-induced oxidative drying (auto-oxidation) via cross-linking polymerisation is not possible for such epoxy resins.

Saturated polyesters: Saturated polyesters (SP) are produced by the polyesterification of bifunctional or higher-functional alcohols with polyfunctional (predominantly bifunctional) saturated aliphatic or cycloaliphatic or aromatic carboxylic acids or the corresponding anhydrides. Together with chemical composition and functionality, average molecular weight (distribution) and degree of cross-linking, the glass temperature, which in mechanical terms is reflected in the hardness, is of particular importance for coating applications. Linear homopolyesters produced from only one dicarboxylic acid and one diol are more or less crystalline. Copolyesters for coating applications consisting of very irregularly structured molecules are practically amorphous.

Coating behaviour: some relatively soft, long-chain, linear to slightly branched polyesters are physically drying only. However, the vast majority of polyesters have to be chemically cross-linked, specifically (forced) as a two-component system with polyisocyanate at a temperature of 20-80°C. Other methods for cross-linking: via reaction (stoving) with amino resins (e.g. melamine resin); via reaction (stoving) with blocked polyisocyanate; via reaction (stoving) with epoxy resin. Water-thinnable polyesters are generally low-molecular, hydroxyl-functional, branched polycarboxylates. They are normally available commercially either dissolved in water- miscible solvents without neutralisation (e.g. to 80% in butyl glycol) or pre-neutralised and dissolved or emulsified in a mixture of water and water-miscible solvent (co- solvent), e.g. to 50% in isobutanol/butyl glycol. These water-thinnable polyesters can be modified with diisocyanates and other components to give aqueous polyurethane dispersions. Film forming is usually achieved by stoving with water-thinnable melamine resins or blocked polyisocyanates, but also with free polyisocyanate.

Spontaneous air-induced oxidative drying (auto-oxidation) via cross-linking polymerisation is not possible for such saturated polyesters.

Unsaturated polyesters:

If diols are esterified with a mixture of maleic anhydride and other dicarboxylic acids (e.g. maleic acid, fumaric acid) or dicarboxylic anhydrides, un unsaturated polyester (UP) is obtained. The double bonds contained in the polyester molecule are now capable of radical copolymerisation with monomeric (meth)acrylates, allyl compounds and other unsaturated monomers (especially styrene). During copolymerisation with styrene (initiated by organic peroxides or hydroperoxides or with a photoinitiator), the relatively short polyester chains are cross-linked by short bridges consisting on average of two styrene units, resulting in a densely cross-linked thermoset. The styrene here also serves as a 'reactive thinner' (= solvent and being incorporated in polymer network). These UP-systems are commercially also available as self-emulsifying 100% sytems suitable for water-thinnable systems. The conventional curing of UP resins can proceed either as a hot cure or -following addition of accelerators, e.g. cobalt octoate or tertiary aromatic amines- at room temperature (cold cure), which is normally being applied for UP -based coatings. Also radiation curing via photo-initiators is practised.

Spontaneous air-induced oxidative drying (auto-oxidation) via cross-linking polymerisation is however not possible for such unsaturated polyesters.

In accordance with the invention, not any kind of resinous binder is used but specifically a combination of: • Resins with built-in auto-oxidative drying functionality in order to provide inner pore surface with optimum compatibility (best matched surface energy) towards the mineral oil solvent part of the printing ink, with cohesive binding force and with interlinking-crosslinking advantages. • A porous top coating with sufficiently fine pore system (by applying at least partly dedicated very fine carbonates like Hydrocarb 95 or Setacarb HG) to afford fast physical ink setting.

Accordingly in the coating of the invention therefore the resinous binder is a resin with built-in auto-oxidative drying functionality, further abbreviated as an auto-oxidative resinous binder or auto-oxidative resin. This means that it is auto-oxidative at around room temperature as such, and without absolutely necessitating the significant presence of for example a curing or hardening agent and/or curing irradiation or the like. At around room temperature means, as current in physics, around 20°C, wherein typically this means that the above-mentioned property (auto-oxidative) is given to a substantial amount at temperatures above or equal to 15⁰C. This lower temperature limit originates from an estimation of the temperature dependent auto-oxidative cross-linking reactivity, based upon e.g. its specific activation energy, and extrapolated down to lowest practical value. Preferentially the auto-oxidative resinous binder is selected from the group of alkyd resins, modified alkyd resins (such as urethanated alkyd resins), polyurethane resins and modified polyurethane resins and mixtures and combinations thereof. Most preferably these resins are drying oil/unsaturated fatty acid modified resins, more preferably natural drying oil/unsaturated fatty acid modified resins, as these types of resins show particularly beneficial printing (particularly quick ink setting) properties essentially without drawbacks in other properties of the printing paper. Generally it is preferred if the unsaturation or poly-unsaturation is of the conjugated type for increased reactivity.

Without being bound to any theoretical explanation, the following mechanism for the unexpected influence of the auto-oxidative resinous binder on the printing properties seems relevant: The primary property, essentially giving rise to experienced rapid convertibility (even up to powder-less application) and enhanced chemical drying is about very fast ink setting behaviour. After deposition of a printed ink layer upon the porous pigmented top coating layer of the coated paper, immediately a selective (almost chromatographic) absorptive process of the mineral oil solvent part of the printing ink will start. The velocity, selectivity and completeness of this absorption process is determined by the so-called capillarity of the porous top coat layer and in turn the capillarity is determined by items like pore size/ pore size distribution (-^velocity of absorptive process), pore volume (-> storage capability), surface energy properties of internal pore system (-> compatibility with mineral oil solvent phase). After completion of the absorption step the residual high- viscous ink part (ink pigment/resin/vegetable oil) is 'set' as semi-solid on/in the outer coat surface. Due to the selective removal of the mineral oil solvent the individual polymer chains of the unsaturated vegetable oil/resin vehicle are in closest vicinity to have them 'automatically' and relative rapidly cross-linked by oxygen molecules present in surrounding air (so-called auto-oxidative cross-linking step, this chemical ink drying step optionally catalytically supported by drying agents/siccatives present in most commercial printing inks). In this way the semi-solid character of the 'set' ink layer is improved even further, better enabling to withstand mechanical forces as being encountered during the further converting steps.

So the unexpectedly improved properties when using auto-oxidative resins of the type as mentioned in this invention to either completely or partially replace the conventional binder in a paper coating seem to result from a number of factors. Indeed if such auto- oxidative resin is used as a binder in a paper coating, its binding property will at least partially be established by the auto-oxidative cross-linking properties of the resin, as during the coating and subsequent drying process of the paper as such at usually elevated temperatures will lead to cross-linking of this binder for the generation of the cohesive forces within the coating. Nevertheless a residual or maybe even substantial fraction of the auto-oxidative resin will remain uncross-linked. This is non-cross-linked part of this auto-oxidative resin binder which is available at the moment of printing, together with the chemical similarity/compatibility of the mineral oils/resins usually used in ink formulations and the auto-oxidative resin binders according to this invention as also present at inner pore surface contributes to the quick ink setting (indeed one can say that preferably generally the unsaturated oil/fatty acid constituent of the auto- oxidative resin used as the binder should be chemically similar and/or analogous to the corresponding systems used in offset printing ink formulations). It even seems that there is an interlinking cross-linking between unsaturated resin constituents of the ink and the residual uncross-linked binder part of the coating. This process can be enhanced or supplemented by siccatives present in the ink formulations. This seems to be an explanation for the very high IGT surface strength encountered with papers of the inventive type (IGT - m/s - is a measurement of the surface strength of the paper. A tacky ink is applied to a sample of the paper at an increasing speed. As the speed increases the peeling force applied to the paper also increases and the speed at which the fibres begin to be pulled from the sheet is recorded as the IGT. A high IGT (>300) indicates a strong surface strength suitable for demanding offset applications).

In case of a silicagel based top coating the typical outmost fine pore sizes in the silicagel particles itself, combined with its rather large pore volume and suitable (but sometimes not optimal) surface energy properties of the inner pore surface, especially seem to define its very fast ink setting properties.

In line with the above theory the paper according to the invention shows an ink set-off of less than 0.3 at 30 sees, preferably of in the range of between 0.15 to 0.25 or of approx. 0.2 at 30 seconds. Such a paper can e.g. be used in a sheet fed offset printing process, wherein in that process reprinting and converting takes place within less than one hour, preferably within less than 0.5 hours, preferably it is reprinted within less than 30 minutes, even more preferably within less than 15 minutes and converted within less than one hour, preferably within less than 0.5 hours. In the present invention the experienced very fast ink setting seems to be especially determined by a very advantageous combination of a regularly fine porous system (applying very fine carbonates like Hydrocarb 95 or Setacarb HG) with a significantly enhanced compatibility between the inner pore walls and the mineral oil solvent of the printing ink. This is because all active auto-oxidative resins of the invention appear to be essentially equipped with oxidative drying functionality, by means of pendant groups consisting of unsaturated fatty acids or unsaturated 'drying oils'. These pendant (thus in fact externally located around the basic resin molecule 'back-bone') oil or oil-type chains do cause, when applying the auto-oxidative resins concerned as alternative binders, that the inner pore surface is being equipped with a molecular 'oily' -like layer, this layer having optimum compatibility (or best matched surface energy resemblance) with the mineral oil solvent part of the ink to be absorbed. This in turn apparently can result in ink setting behaviour, at least comparable with that of a silicagel based top coating concept.

In line with this, it seems preferential for the invention to apply a combination of: • Resins with built-in auto-oxidative drying functionality in order to provide inner pore surface with optimum compatibility (best matched surface energy) towards the mineral oil solvent part of the printing ink, with cohesive binding force and with interlinking-crosslinking advantages.

• A porous top coating with sufficiently fine pore system (by applying at least partly dedicated very fine carbonates like Hydrocarb 95 or Setacarb HG) to afford fast ink setting.

To achieve this, the resinous binder is, according to a preferred embodiment, an at least partially unsaturated oil/fatty acid modified alkyd resin. This alkyd resin preferably is of the medium-oil type with 40-60% at least partially unsaturated oils/fatty acid content. Even more preferably it is of the long-oil type with more than 60% at least partially unsaturated oil/fatty acid, preferably with more than 70% at least partially unsaturated oil/fatty acid content.

The unsaturated oil/fatty acid modified alkyd resin can be of the medium or long oil type grafted with at least partially unsaturated oils/fatty acids with 12 to 26 carbon atoms, preferably as mono-unsaturated fatty acids, bi-unsaturated fatty acids, tri- unsaturated fatty acids or quadric-unsaturated fatty acids or other (poly) unsaturated fatty acids (preferably of the conjugated type) for example obtained from animal or vegetable oils. Generally it is preferred if the unsaturation or poly-unsaturation is of the conjugated type for increased reactivity. Preferably therefore it is a vegetable or plant derived unsaturated fatty acid modified alkyd resin, preferably based on linseed oil, peanut fatty acid, soy oil, soy bean fatty acid, linoleic oil and combinations and derivatives thereof.

All these types of auto-oxidative resinous binders can either fully or only partly replace the binder content of a coating formulation. According to preferred embodiment, these auto-oxidative resinous binders are combined with (a minor or major, preferably minor proportion) styrene butadiene and/or a styrene acrylate latex binder types (also carboxylated types) as for example available under the trade names Acronal, Basonal and the like. The combination with these types of binders which are non-resinous provides an almost ideal combination of the advantageous influence of the auto- oxidative resinous (in particular alkyd resin based) binders with the advantageous properties of the latex binder types, leading to a synergistic effect.

Generally one can say that the non-resinous binder can be selected from the group of: polymeric latex, in particular styrene-butadiene, styrene-acrylate, styrene-butadiene- acrylonitrile, styrene-acrylic, in particular styrene-n-butyl acrylic copolymers, styrene- butadiene-acrylic latex, acrylate vinylacetate copolymers, starch, polyacrylate salt, polyvinyl alcohol, soy, casein, carboxymethyl cellulose, hydroxymethyl cellulose, and copolymers as well as mixtures thereof, preferably provided as an anionic colloidal dispersion in the production of coatings wherein latexes based on styrene-butadiene, if need be styrene-acrylate are particularly preferred.

According to a further preferred embodiment, the total binder part is constituted by 5-15 parts in dry weight, preferably by 8-12 parts in dry weight of the total coating formulation, and preferably the ratio between the auto-oxidative resinous binder (either one type or also a mixture of several different types of auto-oxidative resinous binders) and the further non resinous binder (also here one single non-resinous binder but also a combination of several different non-resinous binders is possible) is in the range of 1 :2 to 3:1, typically around 2:1. Alternatively formulated, the binder part preferentially comprises 2-8 parts in dry weight of auto-oxidative resinous binder and 2-9 parts of non-resinous binder, preferably a styrene-butadiene latex binder. A further preferred embodiment is characterised in that the additive part is in the range of 0.5 - 4 parts in dry weight, and for example comprises constituents selected from the group of co-binder such as polyvinylalcohol, rheology modifier, defoamers, colorants, brighteners, dispersants, thickeners, water retention agents, preservatives, crosslinkers, lubricants and pH control agents or mixtures thereof. As mentioned above, the intrinsic porosity of the pigment parts or the resulting porosity of the coating of these pigments is also influential on the total coating properties. According to a further preferred embodiment therefore, the fine particulate pigment in the pigment parts a), b) and/or c) are selected from the group of calcium carbonate, preferably a ground calcium carbonate or precipitated calcium carbonate, kaoline, talcum, plastic pigment, titania, silica, preferably silica gel, most preferably amorphous silica gel, clay, gypsum, barium sulphate, alumina tri-hydroxide, satin white or mixtures thereof, wherein preferably it is a ground or precipitated calcium carbonate. Also possible systems like a fine particulate ground calcium carbonate with surface and internal structure modification as a result of treatment with one or more medium to strong H₃O⁺ ion providers and eventually with additional treatment of gaseous carbon dioxide.

According to a further preferred embodiment, a) is in the range of 60-90 preferably 70- 80 parts in dry weight and is selected of a fine particulate calcium carbonate pigment with a particle size distribution such that at least 50% of the particles have a size of below or equal to 0.8 μm or below or equal to 0.6 μm, and/or that at least 90% of the particles have a size of below or equal to 2 μm, wherein b) in the range of 10 - 40, preferably 20-30 parts in diy weight and is selected of a fine particulate calcium carbonate pigment with a particle size distribution such that at least 50% of the particles have a size of below or equal to 2 μm, and wherein c) is in the range of 0-10 parts in dry weight of one (or several) further fine particulate pigment.

Normally, the paper has, in case of a matt grade, a TAPPI 75° gloss value of below 35%, in case of a medium gloss grade, a TAPPI 75° gloss value of in the range 35 - 70 % and in case of a high gloss grade, a TAPPI 75° gloss value of at least 70% . Typically the top coating layer is applied with a grammage in the range of 5 - 30 gsm, preferably in the range of 10-20 gsm. It can be applied on a raw paper, on a sized paper but also on pre-coated paper which is already provided with one or several middle coating layers onto which the top coating layer is deposited. According to a further preferred embodiment, therefore beneath said top coating layer there is a middle coating layer, wherein this middle coating layer comprises a pigment part, the 100 parts in dry weight thereof comprising 10-100 parts in dry weight of a calcium carbonate pigment with a particle size distribution such that at least 60% of the particles, preferably at least 85 or 90% of the particles are smaller than 2 micrometer or a mixture thereof.

Preferably, the paper is calendered for medium or high gloss or essentially uncalendered for matt papers.

To summarise, the binder part preferentially comprises 2-8 pails, preferably 5-7 parts in dry weight of at least one unsaturated oil/fatty acid modified alkyd resin of the medium or long oil type and 2-9 parts, preferably 3-4 parts of non-resinous styrene butadiene latex binder. The pigment part preferably essentially consists of a) constituted by in the range of 70-80 parts in dry weight and selected of a fine particulate calcium carbonate pigment with a median particle size in the range of 0.4-0.5 μm, and b) constituted by in the range of 20-30 parts and selected of a fine particulate calcium carbonate pigment with a median particle size in the range of 1.5 μm.

Furthermore the present invention relates to the use of a paper as defined above in an offset printing process, preferably with reduced use or without the use of offset powder and/or without irradiative drying after printing and/or with reduced use or without use of overprint varnish. In addition to that the present invention relates to the process of making a paper as defined above in a coating process using a blade coater, roll coater, spray coater or curtain coater.

Further embodiments of the present invention are outlined in the dependent claims. SHORT DESCRIPTION OF THE FIGURES In the accompanying drawings preferred embodiments of the invention are shown in which: Figure 1 is a schematic cut through a coated printing sheet; and Figure 2 is a schematic representation of an alkyd resin structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same, figure 1 shows a schematic view of a coated printing sheet. The coated printing sheet 4 is coated on both sides with layers, wherein these layers constitute the image receptive coating. In this particular case, a top coating 3 is provided which forms the outermost coating of the coated printing sheet. Beneath this top layer 3 there is provided as second layer 2. In some cases, beneath this second or middle coat layer there is an additional third layer, which may either be a proper coating but which may also be a sizing layer.

Typically a coated printing sheet of this kind has a base weight in the range of 80 - 400 g/m², preferably in the range of 100-250 g/m². The top layer e.g. has a total dried coat weight of in the range of 3 to 25 g/m², preferably in the range of 4 to 15 g/m², and most preferably of about 6 to 12 g/m². The second layer may have a total dried coat weight in the same range or less. An image receptive coating may be provided on one side only, or, as displayed in figure 1, on both sides.

The main target of this invention is to provide a matte, medium or high gloss coated printing sheet for quick physical ink setting and enhanced chemical ink drying performance, preferably ink-scuff-free and suited for powder-less printing and ideal fast converting (e.g. no or minimal/acceptable blocking or markings at folding and cutting) applications for sheet-fed offset or roll-offset papers in combination with standard inks, with appealing attractive printed image. As concerns analytical tests and methods, of which results are mentioned in this experimental section, like short time ink setting, multi-colour ink setting, chemical ink drying, ink scuff/dry ink rub, converting tests like cutting and folding etc. reference is specifically made to the documents WO-A-2007/006794 as well as WO-A-2007/006796 in which the same methods also used here are detailed. As concerns the disclosure of these analytical and test methods these documents WO-A-2007/006794 as well as WO- A-2007/006796 are thus included into this specification.

As mentioned above, one of the key elements of the present invention is to use, next to a conventional binder, a auto-oxidative resinous binder. Different types of chemistries exist and therefore first the general chemistry of this type of auto-oxidative resinous binders shall be discussed.

Alkyd resins:

The term alkyd is derived from the combination of alcohol and acid. Alkyd resins can be defined in brief as polyesters modified (grafted) with fatty acids or fatty oils inclusive of higher synthetic carboxylic acids. The molecules consist of a saturated and/or unsaturated polyester backbone, which may be scarcely to moderately branched, from which fatty acid groups project as side chains. Excess (free) hydroxyl and residual carboxyl groups are also present. The average molecular weight is normally between 2000-5000g/mol. The structure of an alkyd resin typically consists of oil (Fatty oils - for 'oil alkyds' - or a mixture of fatty oils - for 'mixed oil alkyds' - or free fatty acids - for 'fatty acid alkyds'), additional glycerol and ortho-phthalic acid and is simplified represented in Figure 2.

The polyester backbone component is responsible for physical (surface) film formation and other properties (e.g. gloss retention, freedom from yellowing), the unsaturated oil or fatty acid component for the suppleness of the films formed (internal plasticization) and above all for the capability of air-induced (auto-) oxidative cross-linking (thus a self-curing one-component system at room temperature). Thus the strengths of alkyd resins are: • Self-curing at room temperature or above ambient as a one-component system

* Very broad compatibility and solubility spectrum

• Virtually unlimited variability of properties by appropriate choice of raw materials and synthesis conditions • Good pigment wetting

• Attractive flow properties, leading to good spreadability of coats

• Relatively low costs (major components derived from low cost renewable resources) Chemistry generally classifies (unmodified) alkyd resins on the basis of their oil content or their fatty acid content calculated as triglyceride content, and of the type of oil or fatty acid ('linseed oil alkyd', 'soya bean oil alkyd', 'peanut fatty acid alkyd' etc.). Classification according to the oil content (triglyceride content) of the resin is based on the following nomenclature: • Less than 40% oil: 'short oil alkyd' resin

• 40 to 60% oil: 'medium oil alkyd' resin

• Over 60 to 70% oil: 'long oil alkyd' resin

• Over 70 to 85% oil: 'very long oil alkyd' resin

With regard to the oil type or the type of fatty acid incorporated, the first step is to distinguish between two categories: drying or non-drying. It is important to remember that a medium or long oil alkyd resin of a semi-drying oil such as soya bean is completely drying, since the oxidative film of the oil component is accompanied by the physical film formation of the polyester component.

Long oil alkyds always dry by oxidation. The high oil content promotes good flow, high flexibility and easy manual processing. If conjugate oil(s) or acid(s) are additionally used in the resin synthesis, rather faster drying resins are produced. Most long oil alkyds are based on soya bean oil and oils of a related composition. Linseed oil alkyds are particularly suitable for printing inks, but are more prone to yellowing because of their high content of linoleic acid. Medium oil alkyd resins may cure by oxidation (but mostly slower than long oil alkyds) or may equally be externally or non-cross-linking. Their universal compatibility is frequently utilised in combinations with a variety of other film formers, e.g. with hard resins to increase hardness and gloss. Melamine resins, which react with the free hydroxyl groups in the alkyd resins, are often used as curing agent resins in stoving coatings.

Short oil alkyds: much of what has been said for medium oil alkyds also applies here, except that their fatty acid content is normally too low to allow them to cross-link independently by oxidation. Curing is generally achieved as a stoving cure with melamine resin. Alternatively cross-linking can be performed in a two-component system with e.g. polyisocyanates at room temperature or up to 80°C.

At least part of the alkyd resin comprises oxidatively drying groups, i.e., unsaturated, aliphatic compounds, at least a portion of which is polyunsaturated. Thus the alkyd resin may be prepared from unsaturated and saturated fatty acids, polycarboxylic acids, and di- or polyvalent hydroxyl compounds. The number of unsaturated fatty acids eligible for use in the preparation of the alkyd resins to be employed is exceedingly large. Preference is given to the use of mono- and polyunsaturated fatty acids, preferably those containing 12 to 26 carbon atoms. Specific examples are mono-unsaturated fatty acids (e.g. lauroleic acid, oleic acid) and bi-unsaturated fatty acids (e.g. linoleic acid) and tri- unsaturated fatty acids (e.g. linolenic acid) and quadric-unsaturated fatty acids (e.g. arachidonic acid) and other (poly-)unsarurated fatty acids obtained from animal or vegetable oils.

The number of saturated fatty acids is also exceedingly large. Preference is given to the use of saturated fatty acids containing 12 to 26 carbon atoms, e.g. lauric acid, palmitic acid, stearic acid, arachidic acid. Other monocarboxylic acids suitable for use include tetrahydrobenzoic acid and hydrogenated or non-hydrogenated abietic acid or its isomer. If so desired, the monocarboxylic acids in question may be used wholly or in part as triglyceride, e.g., as vegetable oil, in the preparation of the alkyd resin. If so desired, mixtures of two or more of such monocarboxylic acids or triglycerides may be employed, optionally in the presence of one or more saturated, (cyclo)aliphatic or aromatic monocarboxylic acids, e.g. pivalic acid, 2-ethylhexanoic acid, lauric acid, palmitic acid, stearic acid, 4-tert.butyl-benzoic acid, cyclopentane carboxylic acid, naphthenic acid, cyclohexane carboxylic acid, 2,4-dimethyl benzoic acid, 2-methyl benzoic acid and benzoic acid. Examples of the polycarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid. If so desired, the carboxylic acids in question may be used as anhydrides or in the form of an ester, e.g. an ester of an alcohol having 1-4 carbon atoms. Examples of suitable divalent hydroxy! compounds are ethylene glycol, 1,3 -propane diol. Examples of suitable trivalent hydroxyl compounds are glycerol and trimethylol propane. Suitable polyvalent hydroxyl compounds are pentaerythritol, sorbitol and etherification products of the compounds in question, such as ditrimethylol propane. Preferably, use is made of compounds having 3-12 carbon atoms, e.g. trimethylol propane and pentaerythritol. The alkyd resins can be obtained by direct esterification of the constituent compounds, with the option of a portion of these components having been converted already into ester diols or polyester diols. Alternatively, the unsaturated fatty acids can be added in the form of a drying oil, such as sunflower oil, linseed oil, tuna fish oil, dehydrated castor oil, (dehydrated) coconut oil. Transesterification with the other added acids and diols will then give the final alkyd resin. The number average molecular weight of such alkyd resins ranges from about 1000 - 5000.

Alkyd resins are intrinsically rendered water-reducible by the grafting process with olefinically unsaturated carboxylic acids (e.g. methacrylic acid) or by co-condensation with polycarboxylic acids (e.g. tetrahydrophtalic acid), imparting hydrophilicity after being neutralised with alkaline compounds to provide a sufficient number of anionic groups in the resin molecules. Neutralisation with ammonia and/or amine and any addition of water take place during manufacture of the coating. Alkyd resins can also be emulsified in water with relatively large quantities (e.g. 2-30 wt.%) of emulsifier (e.g. non-ionic surfactants). Also phase-inversion emulsification can be applied for this purpose. The rather slow drying behaviour of aqueous alkyd resin emulsions can be improved via hybrids of water borne alkyds and water borne relatively high-molecular weight acrylic polymers. Siccatives or driers (e.g. cobalt or magnesium metal salts of octanoic acid, eventually assisted by drying accelerating ligands like 2,2'-bipyridyl) can also be used to promote rather slow oxidative curing behaviour of the alkyd resin. Modified alkyd resins: The wide variety of (unmodified) alkyd resins can be expanded by the simultaneous chemical incorporation in the polymer backbone of 'non-alkyd resin' components, such as styrene, acrylate, diisocyanate, epoxy resin, silicone etc.. The following listing of most important types with typically improved properties can be made: • Urethanated alkyd resins (urethane alkyds) -> surface drying, abrasion resistance

• Natural resin-modified alkyd resins (with e.g. colophony) -^ surface drying, bond strength

• Styrenated alkyd resins -> surface drying • Acrylated alkyd resins -> surface drying

« Epoxy (resin) modified alkyd resins -> bond strength

• Silicone modified alkyd resins -^ heat resistance

• Polyamide modified alkyd resins -^ stability of the wet film

The capability of air-induced (auto-) oxidative cross-linking is thus fully maintained and often even enhanced by these modifications.

(Modified) polyurethane resins:

If an isocyanate - a compound with the linear atomic grouping R-NCO - is reacted with an alcohol, a urethane, i.e. an ester of carbamic acid, is obtained. Unlike free carbamic acids, urethanes are both thermally and chemically very stable. Now if a diisocyanate is reacted with a bifunctional alcohol (diol), a 'linear polyurethane' (PU) is obtained. If higher functional isocyanates and/or polyols are also used, a branched or even cross- linked polymer is formed.

Auto-oxidisably cross-linkable polyurethane polymers containing unsaturated fatty acid residues are preferably obtained from the reaction of at least one organic polyisocyanate with at least one isocyanate-reactive organic compound bearing unsaturated fatty acid residue(s), optionally (but preferably) with isocyanate-reactive organic compound bearing water-dispersing groups. Optionally, the reactants may also include a low molecular weight isocyanate-reactive compound, usually an organic polyol and/or a high molecular isocyanate-reactive compound, also usually an organic polyol - such compounds, if used, bearing neither unsaturated fatty acid residues nor water-dispersing groups. Isocyanate-reactive groups include -OH, -NH and -NH₂. The polyurethane polymer may be prepared in a conventional manner by reacting the organic polyisocyanates with the isocyanate-reactive compounds by well-known synthesis. Preferably an isocyanate-terminated polyurethane pre-polymer is first formed, which is chain extended with an active hydrogen containing compound. If the polymer is made in such manner, the unsaturated fatty acid residue(s) bearing compound is introduced into the the polyurethane backbone during the pre-polymer formation and/or during the chain extension step. Alternatively a polyurethane may be made by capping an isocyanate-terminated polyurethane with monofunctional isocyanate-reactive compounds or by using an excess of compounds having isocyanate-reactive groups during polymer preparation. Optionally (but preferably) monomer(s) bearing non-ionic or ionic water-dispersing or emulsifier groups (or groups that can be converted thereto) are included in the pre- polymer formation to provide the facility of self-dispersibility in water of the polyurethane pre-polymer and the final auto-oxidisably cross-linkable polyurethane polymer. Preferred concerned isocyanate-reactive compounds bearing unsaturated fatty acid residue(s) may be obtained from a reaction, using techniques known in the art, of a suitable fatty acid with a hydroxyl donor (preferably an alcohol or polyol) or amine donor to provide a fatty acid residue-bearing compound with at least one (or better at least two) hydroxyl or amine isocyanate-reactive groups.

Preferred unsaturated fatty acids (notably for all the above types of resins, not only of the PU-type) include fatty acids derived from castor oil, soybean oil, sunflower oil, tallow oil, linseed oil and fatty acids such as linoleic acid, palmitoleic acid, linolenic acid, oleic acid, oleosteric acid, licanic acid, arachidonic acid, ricinoleic acid and/or mixtures thereof. Suitable polyisocyanates include aliphatic, cycloaliphatic, araliphatic and/or aromatic polyisocyanates (e.g. ethylene diisocyanate, 2-4-toluene diisocyanate). Mixtures of these polyisocyanates can be used and also further (e.g. urea) modified polyisocyanates. Other isocyanate-reactive organic compounds bearing neither unsaturated fatty acid residues nor water-dispersing groups which may be used in the preparation of polyurethanes or polyurethane pre-polymers preferably contain at least one (better at least two) isocyanate-reactive groups, and more preferably organic polyols. The organic polyols particularly include diols and triols and mixtures thereof but higher functionality polyols may be used. The polyols may be members of any of the chemical classes of polyols used in the polyurethane formulations. In particular the polyols may be polyesters, polyesteramides, polyethers, polythioethers, polycarbonates, polyacetals, polyolefms or polysiloxanes. Low molecular weight organic compounds containing at least one (better at least two) isocyanate-reactive groups (e.g. ethyleneglycol, 1-propanol).

The water-dispersing group content of the polyurethane should be sufficient to provide the polyurethane with the required degree of water-dispersibility. Water-dispersing groups are optionally incorporated into the polyurethane by including an isocyanate- reactive and/or isocyanate compound bearing non-ionic and/or ionic water-dispersing groups (or groups which may be subsequently converted to such water-dispersing groups) as reactants in the preparation of the polymer or pre-polymer. Typically, ionic water-dispersing groups are ionic salt groups, for example carboxylate, sulphonate and phosphonate salt groups. Examples of such compounds include carboxy group containing diols and triols, e.g. 2,2-dimethylolpropionic acid. The conversion of any acid groups present in the pre-polymer to anionic salt groups may be effected by neutralizing these acidic groups before, after or simultaneously with formation of an aqueous dispersion of the pre-polymer. Non-ionic water-dispersing groups are preferably pendant polyoxyalkylene groups, particularly polyoxyethylene groups. The polyurethane polymer or pre-polymer may have a combination of ionic and non-ionic water-dispersing groups.

An aqueous polyurethane dispersion can be prepared by dispersing the isocyanate- terminated polyurethane pre-polymer in an aqueous medium (using surfactants and/or by utilising the self-dispersibility of the pre-polymer) and chain extending the pre- polymer with active hydrogen-containing chain extender (e.g. polyols, amino-alcohols, primary or secondary diamine or polyamine, hydrazine) in the aqueous phase. Also water may serve as an indirect chain extender. The pre-polymer may also be chain extended to form the polyurethane polymer while dissolved in organic solvent (usually acetone) followed by the addition of water to the polymer solution (under agitation) until water becomes the continuous phase and the subsequent removal of the solvent by distillation to form the aqueous polyurethane dispersion.

Residual resin systems:

Acrylic resins (polyacrylates, acrylate resins, polyacrylate resins), phenolic resins, melamine resins, benzoguanamine resins, urea resins, epoxy resins are possible as well, normally they are however not meant to be provided with functionalities for air-induced (auto-) oxidative cross-linking. Also possible are natural resins (like colophony) or modified natural resins.

Experimental section:

Description of resin types in the experimental program: hi the experimental program 18 different 'unsaturated' resin types of 4 different suppliers (DSM = DSM Coating Resins or DSM NeoResins), Nuplex, Corn. Van Loocke and Hexion) have been applied.

Via available Technical Specification Sheets (TSP) all 15 resin types can be classified according the classes mentioned above:

• 7 alkyd resins « 2 urethanated alkyd resins

• 6 polyurethane resins

All 15 resin samples were provided with auto-oxidative drying functionality, though only a limited number have been modified towards relatively fastest drying 'long-oil' types. Details can be found in Table 1 :

Table 1, the terms Rx given in the column Description is used in the following, and the types are defined as follows: alkyd resin : I, urethanated alkyd resin : II, (modified) polyurethane resin: III.

Experiments part 1 Idea to evaluate applicability potential of alkyd resin type ink binder Rl 8-1 which is compatible with the conventional paper coating process. A basic reference top coat was used as given in table 2 below and indicated as refl. In the actual experiment the conventional latex binder used in refl was fully replaced by the binder Rl 8-1 as given in table 1 to be checked for applicability. Runnability on the coater was good, and the most striking property is the very fast ink setting in case of Rl 8-1, relative to Eurolatex 7031. Surface strength (IGT oil pick / MCMP) in case of Rl 8-1 is good relative to Eurolatex 7031 and Tappi 75° paper gloss after calendering is comparable.

The coating formulations as well as the resulting coating properties are summarised in Table 2.

Table 2

Eurolatex 7031: is a SB latex of supplier EOC. It can be replaced with other latexes (SB or SA type).

HC 95: Ground calcium carbonate pigment "HYDROCARB HC 95 GU", as available e.g. from OMYA, CH, has a median particle diameter in the range of approximately 0.4-0.5 micrometer, and the particle size distribution is such that approximately 95% of the particles are smaller than 2 micrometer and approximately 78 % of the particles are smaller than 1 micrometer.

Mowiol 4 - 98: is a PVA type additive, supplier Kuraray, acts as additive/co-binder, indicated as 'fully' hydrolysed from polyvinylacetate, hydrolysis degree 98,4 +/- 0,4 mol%, viscosity of a 4% ds aqueous solution at 2O⁰C = 4,5 +/- 0,5, average Mw=27000 (g/mol). Experiments part 2

The idea is to compare performance of auto-oxidative resin binders with conventional latex binder in the presence of silica gel in the pigment as part of the coating formulation. The basic reference top coat is given as ref2 in table 3 below. Apart from the binder Rl 8-1 as given in table 1 a poly-functional aromatic epoxy resin available under the name EPI-rez 5003 (available from Hexion Speciality Chemicals, NL) was used. The examples with EPI-rez 5003 shall serve as a proof that not any kind of resin binder shows promising effects in accordance with the present invention. Indeed for the desired affect the resin is binder must be auto-oxidative at around room temperature which is not the case for this epoxy resin. A coated base paper was used for end weight 250 gsm. The top coat was applied at 16 gsm/side. Set-off: Rl 8-1 very fast, even faster than (silica-gel type) ref2. Chemical ink drying (dot dry): Rl 8-1 slightly better than ref2.

The coating formulations as well as the resulting coating properties are summarised in Table 3.

Table 3

Miragloss 90: Fine particle kaolin pigment, as available from BASF, DE, with a Sedigraph particle size of 92% < 1 micrometer.

HC 90: Ground calcium carbonate pigment "HYDROCARB HC 90 GU", as available e.g. from OMYA, CH, has a median particle diameter in the range of 0.7 - 0.8 micrometer, and the particle size distribution is such that approximately 90% of the particles are smaller than 2 micrometer and approximately 66 % of the particles are smaller than 1 micrometer Syloid : Amorphous silica gel as available under trade names like Syloid 72 or Syloid 244 or Syloid C803 from Grace Davidson, DE, with a total pore volume in a range of approximately 1.1-2.0 ml/g, an median particle size in micrometer in the range of approximately 3.1- 6 micrometer, a surface area (BET) in the range of 300-390 m2/g and an anionic surface charge. Basonal: Latex binder according multi-monomer concept based on the monomers acrylonitrile, butadiene, butyl acrylate and styrene, as available from BASF, DE.

Acronal: is available from BASF, DE. It is provided as a 50% aqueous latex dispersion of a copolymer based upon butylacrylate, styrene and acrylonitrile. As a white latex dispersion it has a pH value of in the range of 7.5 to 8.5 and apparent viscosity (DIN EN ISO 2 555) of 250 to 500 mPas.

Experiments part 3

All top coating formulations have the same pigment composition of 97 parts in dry weight of HC 95 and 3 parts in dry weight of HC60. They furthermore have a non- resinous binder content of 9 parts in dry weight of a combination of two latex binders as for example available under the name of Litex P2090 (aqueous, anionic styrene- acrylic copolymer dispersion, available from Polymer Latex, DE, 6 parts in dry weight) or L0607 (carboxylated styrene butadiene latex as available from EOC, 3 parts in dry weight). Furthermore one part in dry weight of Mowiol 4-98 and additives of approximately 0 .5 parts in dry weight are present. This is the coating formulation for the reference paper (designated as ref3). In case of the experiments E3-2 and E3-4 these coating formulations are simply supplemented by additional auto-oxidative resinous binder Rl 5 from table 1 as indicated in table 4. So the test top coats are the reference top coat + additional 4 or 6 parts R15-III. Rod laboratory coater was used, coating applied on one side, coat layer weight: 12-15 gsm. The results are summarised in table 4.

Table 4 Findings:

Set-off: At 4 parts resin: R15-III clearly faster than ref. At 6 parts resin: R15-III somewhat faster than ref. It should be noted that due to the fact that Rl 5 is just added to the total binder content and does not replace the other binder, there is rather too much binder in the coating system which at least partially clogs up the porous system leading to somewhat distorted and less pronounced results.

MCI: At 4 parts resin: R15-III about as fast as ref. At 6 parts resin: R15-III about as fast as ref. ; WIR (120 min): Both at 4 and 6 parts resin: R15-III somewhat worse than ref.; Chemical ink drying (dot dry): At 4 parts resin: R15-III as fast as ref. (>8 h). At 6 parts resin: R15-III slightly worse than ref. (>8 h)

Experiments part 4

Using the same reference coating as in experimental part 3, here indicated as ref 4, each test top coating was given as the reference coating plus additional 8 parts in dry weight of several further auto-oxidative resinous binder types. The rest of the conditions was identical to the ones as described under part 3.

Again, as in part 3, it should be noted that due to the fact that the auto-oxidative resinous binder is just added to the total binder content and does not replace the other binder, there is rather too much binder in the coating system which at least partially clogs up the porous system leading to slightly distorted and less pronounced results.

The results as well as the formulations are summarised in table 5 given below.

κ

Table 5

Findings:

Set-off: R8-I and R3-I much faster than ref. R9-I and R4-I about as fast as ref. R7-II, R6-I, R5-I, R17-II, R16-III, R13-III, R12-IV, RI l-III, RlO-III, slower than ref, which is at least partly due to the fact that the resinous binder is just added to the total binder content and does not replace the other binder, so the rather the too high binder content at least partially clogs up the porous system leading to slightly distorted results.

MCI: About same trend as set-off; WIR (120 min): R9-I, R8-I and R3-I better than ref. All other resins rather worse than ref.

Experiments part 5

Using the same reference coating as in experimental part 3, here indicated as ref 5, each test top coating was given as the reference coating wherein the 6 parts of regular latex binder are replaced by 6 parts of several further auto-oxidative resinous binder types. So in contrast to experimental parts 3 and 4 here the auto-oxidative resinous binder is not just added to the total binder content but replaces the other latex binder. The rest of the conditions was identical to the ones as described under part 3.

The results as well as the formulations are summarised in table 6.

Table 6

Findings:

Set-off: R8-I, R3-I and Rl 8-1 much faster than ref. Rl l-III about as fast as ref.

MCI: About same trend as set-off WIR (120 min): R8-I and Rl l-III about as good as ref. R3-I and Rl 8-1 somewhat worse than ref.

MCMP (Huber 48001): Rl l-III best result (5x free) but less good than ref (8x free); R3- I and R8-I and Rl 8-1 much worse (0 or Ix free)

The same experiments (the 6 parts of regular latex binder are replaced by 6 parts of several further auto-oxidative resinous binder types) were carried out for further auto- oxidative resins of table 1 leading to the following results:

Set-off: R9-I, R8-I, R4-I and R3-I much faster than ref. R6-I, rather faster than ref. R7-

II, R17-II, R16-III, R13-III, R12-III, RlO-III slightly faster than ref. RI l-III slightly slower than ref. MCI: R9-I, R8-I, R4-I and R3-I much faster than ref. R6-I, R7-II, R17-II, R16-III, R12-

III, RlO-III about as fast as ref. R13-III, Rl l-III slower than ref.

WIR (120 min): All tested resins somewhat worse than ref., specifically. RI l-III, Rl- III, R16-III.

Experiments part 6 m this experiment a specifically pre-coated paper (Middle coating layer formulation designated with M in table 7) was pilot coated with two different top coating layers (top coating layer formulation designated with D in table 7), one reference coating (refβ, D) and one coating comprising a resinous binder (E6, D). Compared to the reference coating in E6 the latex binder is partially replaced by the auto-oxidative resinous binder R 18 of table 1. The top coat is applied at two sides, about 12 gsm/side. Printing tests were carried out at a commercial printer.

The coating formulations are summarised in table 7 and the resulting printing properties are summarised in table 8 given below.

Table 7

Table 8

Findings:

Set-off: Rl 8-1 very fast and even faster than (silicagel) refό.

Printability (evenness solids, evenness screens, mottle cyan, mottle cyan/magenta): Rl 8-1 average printability vs. ref. below average

Blocking test (4-colours, no powder, no IR-drying): Rl 8-1 (top) very light markings all fields and Rl 8-1 (bottom) very light markings 300% and 400% areas vs. ref. (top) light markings all fields and ref. (bottom) markings all fields

WIR (300% area black, cyan, magenta): Rl 8-1 better than ref. Ink rub resistance (100% black): Rl 8-1 somewhat worse than ref. Wet picking: Rl 8-1 no sign of picking, just as for ref.

Converting: Minor differences between Rl 8-1 and ref. Folding markings acceptable in Rl 8-1 and ref. Rl 8-1 and ref. can be converted after 30 minutes

SC HG: Ground calcium carbonate pigment "SETACARB HG GU", as available e.g. from OMYA, CH, has a mean particle diameter in the range of 0.4 - 0.6 micrometer, and the particle size distribution is such that approximately 98% of the particles are smaller than 2 micrometer and approximately 90% of the particles are smaller than 1 micrometer .

Mistrobond : Surface treated microcrystalline talcum as available under the trade name Mistrobond C or almost equivalent Mistrobond RlOC from Talc de Luzenac, FR, with a median particle size of approximately 2.9 micrometer and a particle size distribution such that approximately 95% of the particles are smaller than 11 micrometer, with a surface area (BET) of approximately 11 m2/g. It comprises more than 98% talcum (rest e.g. 0.5% chlorite and 1% dolomite) and has a hardness of 1 Mohs. The surface treatment comprises an organo-functional silane component (so-called coupling agent) comprising a primary amino-alkyl functional group.

C*Film: thermally modified starch available from Cerestar. Experiments part 7

In this experiment the specific purpose was to show whether one can further can improve the paper to make it printable without picking, applying the auto-oxidative resinous binder Rl 8-1 next to regular latex binder. Therefore the latex amount was increased in these coating recipes from 3 to 6 parts, keeping in mind that the off-set speed should still be at least as fast as the referent. This target has been reached, all resinous coatings are still faster in set-off as well as in multi colour ink setting speed. The pick resistance tests are showing better numbers of pick resistance for these coatings, and at the initial print tests there was no problem with picking of the coating on the blanket (after 500 prints) as was observed in the previous test series.

The print tests of the auto-oxidative resinous coated papers were positive in all aspects: evenness, mottle, blocking test and cutting test were mostly better than the referent.

Ink rub values were better as for the referent. Especially D52 with 15 parts of Mistrobond scored very good with an ink rub value of only 1 ,2.

Gloss levels of the resinous coating were higher than the referent. TAPPI75 gloss of the referent was up to 20% while the resinous coatings had gloss values ranging from 35 to 45%. This gloss level will benefit also the ink rub resistance.

A coated base paper was used for end weight 250 gsm. The top coat was applied at 16 gsm/side.

Table 9 gives the coating formulations of the top coating of part 7, all of them using Rl 8 as given in table 1. All the coatings further comprise additives in an amount of approximately 0.5 parts per dry weight. The solids content of the coating formulations is around 70%. D51 is the referent coating in this case.

Table 9

Hydragloss 90: Fine particulate kaolin pigment, as available from OMYA, CH, with a Sedigraph particle size of approximately 97% < 1 micrometer.

HC V40 ME: Speciality co-structured calcium carbonate/Talcum pigment slurry Hydrocarb VP-ME V40 T 60%, as available from OMYA, CH, and as broadly described in WO 99/52984, it has a mean particle diameter in the range of 0.7-0.8 micrometer, and the particle size distribution is such that approximately 84% of the particles are smaller than 2 micrometer and approximately 62% of the particles are smaller than 1 micrometer.

The following properties were measured using the final papers:

AU trials can be printed without anti-set-off powder and IR drying. Trial D54 shows no markings at all. Convertibility is on a good level. Trial D52 shows the least markings in the wet ink rub test. Also D53 performs better than the referent, D54 is slightly worse.

In the ink rub tests all trial points perform better than the referent, especially D52 has a very good ink rub resistance. All 4 trials are on a good level. D52 has the best wet ink rub resistance level and is relatively constant over time. D53 is on a slightly lower level than D52 but still better than the referent. D54 appears to show lesser wet ink rub resistance as function of time.

The cutter tests were for all trial points as good as the referent. No differences were observed.

Trial D54 has the best printability and is on above average level. The other trials are also performing better than the referent. Two sidedness was present in all samples (is common for Vestra papers) but was also better for the trial points than for the referent.

Referent trial D51 has the fastest chemical ink drying and is chemically dry after 24 hours. The other trials have very little to none chemical ink drying. After 24 hours none of these trials are fully chemically dry.

Chemical ink drying (White gas test) results are given in table 10 below as well as set off values for the papers investigated.

The auto-oxidative resin containing coatings show a set-off level that is faster than the silica containing referent.

Table 10 Summary of the results of part 7:

Set-off speed of auto-oxidative resinous coatings with increased latex content still faster than referent; picking resistance increased (no problems with picking while printing test form); gloss levels of the auto-oxidative resinous coating were higher. Summary:

There is a clear positive finding that alkyd resins and polyurethane resins with built-in auto-oxidative drying functionality, when applied as alternative binder in paper top coating, very significantly enhance the ink setting behaviour (physical drying), up to the level of silica- gel based coated paper or even better.

According commercial printing trial this leads to a very attractive convertibility behaviour (about 30 minutes) and generally good printability profile.

Typical composition of resin containing coating:

75 parts of fine ground calcium carbonate, e.g. d₅₀ value is about 0,4-0,5 μm (e.g. HC95)

25 parts of less fine ground calcium carbonate, e.g. d₅₀ value is about 1,5 μm (e.g. HC60)

3-9 parts of latex, preferably an SB-type

4-8 parts of resinous binder with built-in auto-oxidative drying functionality Additives: 1 parts of co-binder as additive, preferably highly hydrolyzed poly vinylalcohol (4-98 grade); 0,4 parts of optical brightener; 0,1 parts of a synthetic thickener.

The total amount of binder (latex + auto-oxidative resin) is normally at least 8 and maximum 12 parts, typically 9 parts of binder are used of which 6 parts are auto- oxidative resin and 3 parts are latex. The ratio latex : auto-oxidative resin can vary between 2:1 and 1 :3 but is typically 1 :2.

In fact a limited number of resin types are particularly suited for the present invention as alternative binders in paper coatings with pronounced side-effects like ink setting and convertibility:

• Alkyd resins, preferentially long-oil alkyd resins

• Modified alkyd resins, e.g. urethanated alkyd resins • Normally a prerequisite of all suited resins is that they have been equipped with built-in auto-oxidative drying functionality, by means of pendant groups consisting of unsaturated fatty acids or unsaturated 'drying oils'.

One gist of this invention is to just partly up to totally replace the regular SA-type or SB-type latex binder in the top coating by suitable and relatively low-cost members of the wide field of resins with built-in auto-oxidative drying functionality, by means of pendant groups consisting of unsaturated fatty acids or unsaturated 'drying oils'. Most preferred resins so far are the so-called long-oil type alkyd resins. This is based both upon their experienced attractive equivalent technical performance (e.g. fast ink setting, rapid convertibility) and their estimated about comparable bulk cost-price versus the present bulk cost-price of regular SA-type binders or SB-type binders, without the need for specific expensive pigments.

Another preferred group of resins to be applied according the invention is the group of so-called polyurethane resins with built-in auto-oxidative drying functionality.

Claims

1. Coated paper for offset printing comprising at least on one side a top coating layer, said top coating layer comprising a pigment part, the 100 parts in dry weight thereof consisting of a) in the range of 50-100 parts in dry weight of a fine particulate pigment with a particle size distribution such that at least 50% of the particles have a size of below or equal to 1 μm and/or that at least 80% of the particles have a size of below or equal to 2 μm, b) in the range of 0 - 50 parts in dry weight of a fine particulate pigment with a particle size distribution such that at least 50% of the particles have a size of below or equal to 3 μm and/or that at least 40% of the particles have a size of below or equal to 2 μm, as well as c) in the range of 0-50 parts in dry weight of at least one further fine particulate pigment, the parts a), b) and c) supplementing to 100 parts in dry weight a binder part with in the range of 2 - 20 parts in dry weight of binder, an additive part with in the range of 0 - 8 parts in dry weight of additive(s), characterized in that the binder part comprises a synthetic or at least partly (modified) natural resinous binder as well as optionally at least one further non-resinous binder, wherein the resinous binder is an auto-oxidative resinous binder, which is auto- oxidative at around room temperature without curing agent and/or curing irradiation and is selected from the group of alkyd resins, modified alkyd resins, modified polyurethane resins and mixtures and combinations thereof.

2. Coated paper according to claim 1, the resins are unsaturated oil/fatty acid modified resins, preferably natural unsaturated oil/fatty acid modified resins.

3. Coated paper according to claim 1 or 2, wherein the resinous binder is an at least partially unsaturated oil/fatty acid modified alkyd resin.

4. Coated paper according to any of the preceding claims, wherein the resinous binder is of the medium-oil type with 40-60% at least partially unsaturated oils/fatty acid content.

5. Coated paper according to any of the preceding claims 1-3, wherein the resinous binder is of the long-oil type with more than 60% at least partially unsaturated oil/fatty acid, preferably with more than 70% at least partially unsaturated oil/fatty acid content.

6. Coated paper according to one of claims 3-5, wherein the unsaturated oil/fatty acid modified alkyd resin is of the medium or long oil type grafted with at least partially unsaturated oils/fatty acids with 12 to 26 carbon atoms, preferably as mono-unsaturated fatty acids, bi-unsaturated fatty acids, tri-unsaturated fatty acids or quadric-unsaturated fatty acids or other unsaturated fatty acids obtained from animal or vegetable oils, wherein it is preferably a vegetable or plant derived fatty acid modified alkyd resin, preferably based on linseed oil, peanut fatty acid, soy oil, soy bean fatty acid, linoleic oil and combinations and derivatives thereof.

7. Coated paper according to any of the preceding claims, wherein the non-resinous binder is selected from the group of: polymeric latex, in particular styrene- butadiene, styrene-butadiene-acrylonitrile, styrene-acrylic, in particular styrene- n-butyl acrylic copolymers, styrene-butadiene-acrylic latex, acrylate vinylacetate copolymers, starch, polyacrylate salt, polyvinyl alcohol, soy, casein, carboxymethyl cellulose, hydroxymethyl cellulose and copolymers as well as mixtures thereof, preferably provided as an anionic colloidal dispersion in the production wherein latexes based on acrylic ester copolymer which are based on butylacrylate, styrene and if need be acrylonitrile are particularly preferred.

8. Coated paper according to any of the preceding claims, wherein the total binder part is constituted by 5-15 parts in dry weight, preferably by 8-12 parts in dry weight, wherein the ratio between the resinous binder(s) and the further non resinous binder(s) is in the range of 1:2 and 3:1, and/or wherein the binder part comprises 2-8 parts in dry weight of resinous binder and 2-9 parts of non- resinous binder, preferably a SB latex binder.

9. Coated paper according to any of the preceding claims, wherein the additive part is in the range of 0.5-4 parts in dry weight, and comprises constituents selected from the group of co-binder such as polyvinyl alcohol, rheology modifier, defoamers, colorants, brighteners, dispersants, thickeners, water retention agents, preservatives, crosslinkers, lubricants and pH control agents or mixtures thereof.

10. Coated paper according to any of the preceding claims, wherein the fine particulate pigment in the pigment parts a), b) and/or c) are selected from the group of calcium carbonate, preferably a ground calcium carbonate or precipitated calcium carbonate, kaoline, talcum, plastic pigment, titania, silica, preferably silica gel, most preferably amorphous silica gel, clay, gypsum, barium sulphate, alumina tri-hydroxide, satin white or mixtures thereof, wherein preferably it is a ground and/or precipitated calcium carbonate.

11. Coated paper according to any of the preceding claims, wherein a) is in the range of 60-90 preferably 70-80 parts in dry weight and is selected of a fine particulate calcium carbonate pigment with a particle size distribution such that at least 50% of the particles have a size of below or equal to 0.8 μm and/or that at least 90% of the particles have a size of below or equal to 2 μm, wherein b) in the range of 10 - 40, preferably 20-30 parts in dry weight and is selected of a fine particulate calcium carbonate pigment with a particle size distribution such that at least 50% of the particles have a size of below or equal to 2 μm, and wherein c) is in the range of 0-10 parts in dry weight of one or several further fine particulate pigment.

12. Coated paper according to any of the preceding claims, wherein the paper has, in case of a matt grade, a TAPPI 75° gloss value of below 35%, in case of a medium gloss grade, a TAPPI 75° gloss value of in the range 35 - 70 % and in case of a high gloss grade, a TAPPI 75° gloss value of at least 70% .

13. Coated paper according to any of the preceding claims, wherein beneath said top coating layer there is a middle coating layer, wherein this middle coating layer comprises a pigment part, the 100 parts in dry weight thereof comprising 10-100 parts in dry weight of a calcium carbonate pigment with a particle size distribution such that at least 60% of the particles, preferably at least 85 or 90% of the particles are smaller than 2 micrometer or a mixture thereof.

14. Coated paper according to any of the preceding claims, wherein the paper is calendered for medium or high gloss or uncalendered for matt papers.

15. Coated paper according to any of the preceding claims, wherein the binder part comprises 2-8 parts, preferably 5-7 parts in dry weight of at least one unsaturated oil/fatty acid modified alkyd resin of the medium or long oil type and 2-9 parts, preferably 3-4 parts of non-resinous styrene butadiene latex binder.

16. Coated paper according to any of the preceding claims, wherein the pigment part essentially consists of a) constituted by in the range of 70-80 parts in dry weight and selected of a fine particulate calcium carbonate pigment with a median particle size in the range of 0.4-0.5μm, and b) constituted by in the range of 20- 30 parts and selected of a fine particulate calcium carbonate pigment with a median particle size in the range of 1.5 μm.

17. Coated paper according to any of the preceding claims, wherein the resinous binder is a linseed oil modified alkyd resin, preferably of the long-oil type with more than 60% at least partially unsaturated oil/fatty acid, preferably with more than 70% at least partially unsaturated oil/fatty acid content.

18. Use of a paper according to any of the preceding claims in an offset printing process, preferably with reduced use or without the use of offset powder and/or without irradiative drying after printing and/or with reduced use or without use of overprint varnish.