The invention relates to a recording materialfor inkjet printing, which has the character of paperand whose printed images applied to the recording layerhave extremely high water resistance and lightfastness.
Prior ArtDE 30 18 342 A describes a synthetic paper forinkjet printing which, after printing in the inkjetprinter, is rendered transparent by the action of heatin order to obtain multicolor inkjet recordings havinghigh recording density, good color reproduction andhigh water resistance. The print which initiallyappears pale acquires high contrast and waterresistance only as a result of subsequent melting.Papers of this type then have the disadvantage of lowopacity (high transparency). The inventors areattempting to overcome this disadvantage by means oftwo- or three-ply papers having an opaque layer whichcannot be rendered transparent and an outer layer orouter layers which can be rendered transparent andwhich comprises or comprise plastics fibers. However,fiber-containing recording layers always give aninadequate printed image with respect to defined spotdiameter and bleeding of the ink in the recordingsurface.
EP-A-01 64 196 discloses a recording layer forinkjet methods on a sheet-like base material which alsocontains papers of synthetic fibers, the layercontaining both a cationic polymer and a polyvalentmetal salt for fixing aqueous inks. In addition,water-penetratable or water-swellable binders, such as,for example, polyvinyl alcohol, and pigments, such as,for example, calcium carbonate, kaolin orurea/formaldehyde fillers, may be contained in such alayer. The water resistance of recordings applied byinkjet methods is relatively low owing to the choice ofthe components used (PVA; polyvalent metal salt; cation polymer) even if the water resistance test described(one minute immersion in water following by drying) ispresented as positive. The object of this applicationwas primarily to produce a rapidly drying, stackable(non-offsetting) paper having a brilliant appearance ofthe recordings.
DE 4446551 C1 describes a water-resistantrecording material comprising a synthetic paper and apigment layer which is bound to make it water-resistantand which serves for ink absorption. The fixing of theanionic ink dyes is achieved by means of cationicfixing agents so that a recording which is water-resistantoverall is achieved. The disadvantage ofthese layers is the porous structure of the coating,which is capable of further absorption of dyes orforeign substances/impurities, and the lowlightfastness and document resistance of the recordingsowing to the large internal surface area for theabsorption of the ink dyes.
EP 0575 644 B1 describes a microporous coatingby formation of an open-pore polymer matrix onexceeding the solubility limits of the chosen polymerin the solvent (mixture) or by sintering togetherindividual polymer particles. This coating is alsosaid to be printable by inkjet printing, it beingpossible for the coating to be rendered transparent bymeans of heat, pressure or solvents after printing, andthe absorbed ink dyes thereby being encapsulated. Anadvantage is the increased durability of the recordingswhich is present after the imparting of transparency,in particular a durable resolution. The production ofsuch layers is extremely difficult since precipitationreactions of polymers and sintering together ofpolymers are difficult to control.
US-A-5,242,739 describes a transfer materialfor fabrics which comprises a paper, for example alatex-impregnated paper, an optional release layer anda coating of thermoplastic polymer particles and afilm-forming binder. The material is first written on or painted by hand or printed by means of mechanicalprinters (dot matrix printers). The coating with theprinted image can then be transferred to textiles athigh temperature, for example by ironing, i.e. is notfirmly bonded to the substrate material. Suitabilityfor inkjet prints is not mentioned.
US-A-5,194,317 describes a recording materialfor inkjet printing, comprising a transparent plasticsfilm as a substrate material and a recording layerwhich is applied thereon and contains a binder andplastics beads. The publication contains noinformation on the fusibility of the recording layer.
For applications outdoors or in the securityarea under persistent influence of water, humidity andlight, inkjet papers known to date are unsuitablewithout further process steps, such as, for example,overlamination with film, since the water resistance ofthe base papers and of the printed recording layer isinsufficient. Precisely in applications such as, forexample, construction plans, maps, layout plans,labels, signs, markings, passes, tickets andsecurities, inkjet prints which are mechanically stableand have unlimited color stability even under theinfluence of water, humidity and light are required.
It is therefore the object of the presentinvention to provide a recording material for inkjetsprinting which is suitable for the applicationdescribed and resists any type of humidity or waterinfluence and the influence of light. Both mechanicalstrength of the substrate paper under the influence ofwater and water resistance and light stability of theinkjet image are required for this purpose.Furthermore, a brilliant, high-contrast, colored orblack inkjet print with high resolution and very crispedges is required.
Summary of the InventionAccording to the invention, this object isachieved by a recording material for the inkjet methodwith aqueous inks, comprising a substrate paper whichcontains synthetic fibers and has a content of from 10%by weight to 90% by weight of cellulose fibers and acontent of from 40% by weight to 1% by weight ofsynthetic fibers and a binder content of from 50% byweight to 5% by weight, based on the total weight ofthe substrate paper, and comprising a fiber-free porousrecording layer which is arranged on one or both mainsurfaces of the substrate paper and consists of from atleast 60% by weight to 95% by weight of finely dividedunfused thermoplastic particles having a mean particlesize of from 0.5 to 40 µm, a self-supporting filmaccording to ISO R527, produced from said unfusedthermoplastic particles by fusion, having an elongationat break of more than 5% and a tensile strength of morethan 5 MPa, and, as the remainder, of film-formingbinders and, if required, inorganic pigments andassistants and additives conventional in such layers;and wherein after action of heat on the recording layerand formation of a cohesive film of fused or sinteredplastics particles, and after storage for 1 week inwater at 30°C, the recording material still has 80% ofthe tear strength of the dry paper, measured accordingto DIN 53128, based on the initial value after the heattreatment.
The mean particle size of the plasticsparticles is preferably from 5 µm to 20 µm.
The achievement of the object includes aprocess for the production of a stable recording on arecording material as claimed in one or more of patentclaims 1-9 by producing one-color or multicolorrecordings by applying ink(s) by means of inkjetmethods and subsequently treating the printed recordinglayer with heat at temperatures of 80-200°C, preferably 100-180°C, in order to form a cohesive film from thefused or sintered plastics particles, and the opticaldensity, measured according to DIN 4512 of coloredrecordings of the primary colors applied by said inkjetmethod is after storage for 1 week in water at 30°Cstill at least 90%, based on the initial values afterthe heat treatment.
Preferably, the surface of the recording layeris subjected to high pressure in addition to the heat.
Detailed description of the inventionThe substrate paper preferably also containsfillers and/or pigments in addition to the cellulosefibers and the binder or binders, the binder contentbeing correspondingly reduced by their presence.Suitable pigments are kaolin, barium sulfate, calciumcarbonate, calcium sulfate and TiO2. The pigment/fillercontent may be from 2.0% by weight to 30% by weight.The wet strength of the substrate paper may be adjustedby the concomitant use of crosslinking agents for thebinder and/or wet strength agents, depending on therequirements. Preferred binders are polyvinyl acetate,polyvinyl acetate copolymers, styrene/butadienecopolymers, styrene/butadiene/acrylonitrile terpolymers,styrene/(meth)acrylate copolymers (meth)acrylicpolymers, ethylene/(meth)acrylic acid copolymers,polyvinyl alcohol, carboxymethylcellulose,hydroxyethylcellulose, starch, starch derivatives,casein or mixtures thereof. Such film-forming polymersare commercially available.
For example, melamine/formaldehyde resins orurea/formaldehyde resins may be used as crosslinkingagents. The substrate paper is produced onconventional paper machines by known methods and isprovided with the binder preferably in the size pressand/or by subsequent coating in a conventional coatingmachine. For example, polyamide fibers, polyesterfibers, viscose fibers, polyethylene fibers or mixtures thereof may be present as synthetic fibers in thesubstrate paper. The basis weight of the substratepaper may be from 50 g/m2 to 300 g/m2, preferably from80 g/m2 to 200 g/m2.
By subsequently applying the binder to theentire surface, it is also possible to ensure that thecoated or impregnated substrate paper does not absorbwater or absorbs water only very slowly. It isparticularly advantageous if such a coating is appliedbefore the application of the porous, fiber-freerecording layer capable of forming the film. Thiscoating or impregnation of the substrate paper preventsink dyes applied to the porous recording layer duringprinting from penetrating into the substrate paper andhence not being fixed in the recording layer during thesubsequent heat treatment and any pressure treatment.
Owing to the low absorptivity of the substratepaper for aqueous inks, direct printing by means of aninkjet printer gives a poorly drying non-water-resistantimage which has run. The substrate paperitself has excellent wet strength, which is manifestedby high tear strength in the completely wet state.
A porous recording layer which can rapidlyabsorb the ink applied in the inkjet method and giveshigh-resolution images/prints having crisp edges istherefore applied to one side or both sides of thissubstrate paper. This coating contains from 60% to 95%of finely divided hydrophobic thermoplastic particleshaving a mean particle size between 1 µm and 40 µm,preferably from 5 to 20 µm. Furthermore, this coatingcontains one or more film-forming binders and furtherconventional assistants, such as, for example, wettingagents, antifoams, inorganic pigments, fillers, dyes,UV absorbers, plasticizers and antioxidants. Theinitially porous recording layer is formed from anaqueous or solvent-containing coating composition byapplication to the substrate paper and drying attemperatures, in the recording layer, below thesoftening temperature of the thermoplastic particles. However, the plastics particles can be fused orsintered by the action of heat and, if required,pressure on the recording layer to give a cohesivefilm. The porous structure of the recording layer issubstantially destroyed and a film of the thermoplasticparticles (organic pigment particles) forms, in whichthe further components of the layer and the applied inkdyes are enclosed and thus fixed.
Surprisingly, it was found that, after printingand heat/pressure treatment, the combination of thespecial paper, which contains synthetic fibers, withrecording layers based on thermoplastic organicpigments leads to an abrasion-resistant and extremelywater-resistant recording material which retains itsstrength even, for example, after storage for 1 week inwater, and the applied image information is abrasion-resistantand shows virtually no loss of contrast underthe action of water. Furthermore, the recordings thusobtained have extremely high light stability, incontrast to the inkjet prints known to date and theprinted material not converted into a film.
The porous recording layer formed on thesynthetic base paper permits rapid ink absorption andfixing of the dyes contained in the printing ink.Furthermore, the recording layer must adhere well tothe base paper, both in the wet and in the dry state,before and in particular after said layer has beenconverted into a film. The recording layer itself musthave sufficiently high cohesion per se so that moderatemechanical stress due to flexing, pleating, folding orrubbing, for example during the printing process, doesnot lead to damage to the layer or to the printedimage. After film formation, the recording layer mustnot be damaged even under high stresses.
To ensure good absorptivity of aqueous inks, ahydrophobic thermoplastic pigment which has a meanparticle size of between 0.5 µm and 40 µm, preferablyfrom 5 to 20 µm, is preferably used in the recordinglayer. The individual polymer particles may be spherical or in the form of hollow spheres; the pigmentpreferably consists of irregularly shaped particles.The melting point of the polymer used for the particlesshould be between 80°C and 200°C, preferably between100°C and 160°C. If it is lower, coating of thepolymer particles from a suspension/emulsion is notpossible without premature melting and binding togetherof the particles during formation of the layer; if themelting point is higher, the treatment step to becarried out after printing is often not possiblewithout decomposition of the coating or of thesubstrate material. The particle size distribution ofthe pigments may be broad or narrow; sufficient inkabsorptivity of the coating owing to its porosity isimportant for the choice. In particular, porousthermoplastic pigments having a high cavity volume, ascan be obtained in the precipitation of polymers fromsolution, are advantageous for this purpose.
Water-insoluble homopolymers or copolymers ofthe following classes of compounds may be used aspolymers for the thermoplastic pigment: polyacrylates,polymethacrylates, polyesters, polyamides,polyurethanes, polyethylene, polypropylene,polystyrene, polyvinyl acetate, polyvinyl chloride,polyvinylidene chloride, cellulose derivatives, starchderivatives and polyepoxides. The presence of definedparticles having a predetermined size and shape isimportant for the choice of a suitable thermoplasticpigment, in order to obtain coatings which are asporous as possible for rapid ink absorption. It isadvantageous to use particles as can be obtained, forexample, during mechanical comminution, for examplemilling, of polymers or during precipitation ofpolymers from solution. The dried coating shouldtherefore have a porosity of at least 0.2 ml/g, whichis to be determined by the gravimetric absorption ofwater in the course of 1 minute on dried coatingmaterial. The mean particle size of the thermoplasticpigments should be between 0.5 and 40 µm, preferably between 5 µm and 20 µm, in order to ensure optimumdrying during printing, crisp edges and highresolution. Layers having smaller pigment particlesdry more poorly while layers having a mean particlesize of more than 40 µm are rough and do not giveimages having crisp edges.
Mechanical properties of the thermoplasticpigments essentially determine the properties of thelayer in the form of a film. A self-supporting filmproduced from the unfused thermoplastic pigmentparticles by fusiuon has an elongation at break of morethan 5%, in particular more than 20%, and a tensilestrength of more than 5 MPa (ISO R 527). Amechanically stable, flexible recording layer is thusobtained on the base paper after film formation.
In order to obtain a recording layer which isabrasion-resistant prior to film formation, it isnecessary to choose, for the thermoplastic pigment, abinder which, after drying of the generally aqueouscoating composition, fixes the pigment particles on thesubstrate paper without reducing the porosity of thelayer too greatly. Plastics dispersions, such as, forexample, vinyl acetate homopolymers or copolymers,acrylate (co)polymers, styrene/butadiene copolymers,ethylene or vinyl chloride copolymers and polyurethanedispersions have proven particularly suitable for thispurpose. In order to ensure flexibility of the layerand adhesion to the paper, dispersions having a minimumfilm formation temperature between -20°C and +50°C,preferably between -10°C and +20°C, are preferablyused.
Water-soluble binders, such as, for example,polyvinyl alcohol, polyvinylpyrrolidone, starch, starchderivatives, polyacrylamide, casein, water-soluble orammonia-soluble polyacrylates or polymethacrylates andcopolymers thereof, for example with styrene, cellulosederivatives, such as cellulose ether andcarboxymethylcellulose, may furthermore be used. Inorder to increase the strength further, it is possible to incorporate into the coating solution crosslinkingagents which react when the layer is dried. Suitablesubstances include urea/formaldehyde or melamine/formaldehyde resins, aziridines,polyfunctional isocyanates and boric acid (for PVA).
Furthermore, optical brighteners, wettingagents, further pigments in small amounts, for examplesilica, aluminum hydroxides or aluminas, kaolin orcalcium carbonate, and dyes for colored papers,adhesion promoters, antifoams, thickeners (for exampleacrylate dispersions, polyacrylic acid, etc.),dispersants, etc. may be present as assistants in thelayer. In order to influence the melting point, thesoftening temperature and the flow behavior of thethermoplastic pigment, a plasticizer may also be used.Suitable plasticizers are available for virtually allpolymers, for example phthalates and fatty esters.
The use of assistants for fixing the anionicink dyes is possible but not preferred. The cationicpolymers usually used for fixing the anionic dyes, suchas, for example, cationic acrylates, acrylamides,polydiallyldimethylamine chloride, polyallylamine,polydiallylamine, polyimine, etc., generally have anadverse effect on the lightfastness. The use of suchcompounds must therefore be checked for their effectswith regard to lightfastness of the ink dyes.
The ink absorption layer is applied to thesynthetic paper by applying the coating compositionwith the aid of conventional coating methods, forexample by roller application and metering with an airbrush or rotating doctor, preferably from aqueousdispersion, and is dried with hot air. The amount ofthe dried coating composition applied is between 10 and50 g/m2, preferably from 25 to 40 g/m2. This appliedamount is necessary for rapid adsorption of the inkliquid in the coating during printing and hence forpreventing running of the image lines. The weight ofrecording layer applied can be varied depending on theprinter and amount of ink to be subsequently used.
The ink absorption layer of the presentinvention adheres sufficiently to the synthetic basepaper and, prior to film formation, has good cohesion and flexibility so that it withstands mechanicalstresses. After film formation, the load capacityincreases so that it is extremely difficult to damagemechanically, both in the dry and in the wet state.This is necessary, for example, in all applications inwhich forgery-proof characteristics, document security,etc. must be ensured.
After printing by means of inkjet printing, thepaper is brought to a temperature above the meltingpoint/softening point of the thermoplastic pigmentused, the pore structure of the coating being destroyedand a thermoplastic film which contains the assistantsused and the applied ink dyes being formed. Thisaftertreatment of the print results in the ink dyesbecoming insensitive to the influence of water. Thisapplies both to the water-soluble, generally anionicdyes used in conventional aqueous inkjet inks and topigment colorants. Surprisingly, it was also foundthat the light stability of the heat-treated printsincreases to an extreme extent, in particular whensoluble dyes are used. The formation of a plasticsfilm from the layer containing the thermoplasticpigment can be accelerated and completed by theadditional influence of pressure.
Suitable methods for film formation areavailable, for example IR irradiation, hot pressing,ironing, heatable rollers or fixing means, are to befound in copiers or hot lamination apparatuses.
As a result of the film formation, the surfacebecomes water-repellent and therefore cannot absorbfurther ink. This helps to make the prints veryforgery-proof. Furthermore, it is as a ruleunnecessary to apply a protective laminating film overthe print. This has enormous advantages with regard tothe process and costs.
The coated paper also has high resistance tomechanical stress, i.e. initial tearing and completetearing of the paper is possible only with a great dealof force, both in the dry and in the wet state. In the completely wet state, the paper has in particular over80% of the tear strength of the dry paper, measuredaccording to DIN 53128.
The paper described in the present inventioncan be printed on commercial inkjet printers with ahigh-contrast, high-resolution image which has crispedges and is colored in the case of color printers.The paper rapidly absorbs the generally aqueous orpredominantly aqueous ink in the coating and is dry andsmudge-resistant shortly after printing. Suitableprinters are, for example, printers which operate withaqueous inks according to the bubble jet principle, thepiezoelectric principle or the continuous inkjetmethod, as offered in various versions, for example byCanon, Epson, Hewlett Packard, Iris, Lexmark, Encad,etc. Both small-size (DIN A3 and A4) and large-sizeprints, for example on rolls for posters, are possible.In addition to water and anionic dyes, the inks used inthe abovementioned printers contain, as a rule, furtherassistants, such as, for example, high boilers(glycols, NMP, etc.) and wetting agents.
After the heat treatment, the printed image isextremely resistant to flexing, pleating, folding andscratching, both in the wet and in the dry state, sothat the image information is completely retained evenunder extreme environmental conditions. Inks whichhave high light stability to UV light too arepreferably chosen for image production. Owing to thefixing of the dyes and the water resistance of thecoating itself, the material withstands even theprolonged action of water. Thus, the color intensity(contrast) of the printed image does not decrease ordecreases only slightly in the course of storage for 1week in water at 30°C. In any case, the colorstability under these conditions is so good that, afterthis treatment, the optical density of colored surfacesof the primary colors black, cyan, magenta, yellow,blue, red and green is still at least 90%, based on theinitial values.
As a result of the film formation, the lightstability of ink dyes increases. Particularly in thecase of water-soluble dyes, an increase in thelightfastness by a factor of 2 or more is found, whichincrease can be calculated from the quotient of theexposure times to UV light up to the time when aprinted colored surface has only 90% of the opticaldensity of the fresh print.
The papers described in this application aresuitable for intended uses in which very high stressesoccur, in particular in association with humidity orwater or the influence of light. Thus, for example,construction plans, maps, layout plans, posters,labels, banners, flags, signs, markings, passes,tickets and securities can be produced from the papersand, after printing and film formation, have very highmechanical strength under all conditions and anindestructible printed image substantially stable toenvironmental influences. Particularly in the case ofsecurities, security features may additionally beincorporated or applied, such as, for example,fluorescent prints or fibers, magnetic stripes,laminating films, RF circuits, etc.
Test methods:Tear strength of the wet paper and stability of theprinted imageA test image which contains in particularrelatively large color surfaces of all primary colors(cyan, magenta, yellow and black) and of the binarymixed colors (blue, green and red) is applied to theinkjet paper according to the invention by means of aninkjet printer. 10 minutes after production of thetest image, the recording layer is converted into afilm by means of a hot press. After cooling, therecording sheet is completely immersed in water at 30°Cfor 1 week. After this storage time, the mechanicalstrength of the paper is determined in the longitudinal direction and transverse direction in the wet stateaccording to DIN 53128 (tear strength). The tearstrength of the dry paper conditioned at 23°C and 50%relative humidity is also determined.
Furthermore, the paper stored in water for 1week is dried in a drying oven at 80°C for 5 minutes.Subsequently, as directly after conversion of the testprints into a film, the optical density of each coloredsurface is determined by means of an RD 920densitometer from MacBeth according to DIN 4512. Thepercentage residual value of the optical density,calculated from the measurements before and afterstorage of the respective colored area in water, is ameasure of the change in the printed surfaces or of thefixing of the dyes of the inkjet inks. The colorsblack, red, green and blue were measureddensitometrically without filters, and the colorsyellow, magenta and cyan with the appropriate filters.
The light stability is determined by means of aUV accelerated weathering apparatus (Suntest fromHaereus). For this purpose, the surfaces of the fourprimary colors black, cyan, magenta and yellowdescribed above are exposed and are measured regularlyusing the abovementioned densitometer with colorfilters. The plot of the measured values as a functionof time then permits the evaluation of the colorstability under UV light, for example by extension ofthe time until the measured values decrease to 90% ofthe initial measured values.
Example 1A commercial synthetic paper (Pretex KL 43.095from Papierfabrik Lahnstein GmbH, Lahnstein) of 95 g/m
2and comprising 18% of cellulose fibers, 33% ofsynthetic fibers, 18% of binders, 28% of pigments andassistants is coated with the following coatingmaterial in a coating weight (solid) of 40 g/m
2 by meansof a rotating doctor and is dried in a drying oven at 100°C for 5 minutes:
| Water | 40.0 g |
| Rhopaque HP91, styrene/acrylate hollow bodied dispersion (from Rohm & Haas) mean particle size 1.05 µm; 25% strength | 85.0 g |
| Polyvinyl alcohol (MOWIOL 4/88, from Hoechst) | 2.0 g |
| Ammonia (25% strength) | 1.5 g |
| Polyethylene glycol, molar mass 400 g/mol | 2.0 g |
| Wetting agent (SURFYNOL 440, Air Products Inc.) | 0.5 g |
The coating material has a solids content ofabout 19% by weight and a pH of 7.5. It contains 84%,based on the solid substance, of thermoplastic pigment.
The matt paper coated in this manner is printedwith a test print by means of a Novajet III inkjetprinter from Encad using commercial ink cartridges fromAmerican Inkjet Corp. and the coating is converted intoa film at 140°C by means of a hot press in the courseof 30 seconds. After this treatment, the now glossyprint shows a high-contrast, high-resolution imagehaving crisp edges. It has extremely high waterresistance: the image-bearing paper stored for 1 weekin water at 30°C has a tear strength (Elmendorf, DIN53128) of 3.8 N in the longitudinal direction and of4.0 N in the transverse direction, compared with 2.1 Nin the longitudinal direction and 2.7 N in thetransverse direction in the dry state.
As a result of the water treatment, the coloredsurfaces exhibit only very little or no color changescompared with the initial color values (Table 1).
The lightfastness of the printed parts isincreased by at least a factor of 2 (cf. Table 2)compared with the material not converted into a film.After film formation, scarcely any change in a print isdetectable even after UV irradiation for 200 hours.
Example 2A commercial synthetic paper (Pretex KL 30.120from Papierfabrik Lahnstein GmbH, Lahnstein) of 120 g/m
2, comprising 61% of cellulose fibers, 4% ofsynthetic fibers, 12% of synthetic binders andassistants and precoated on both sides with about 5 g/m
2of a plastics dispersion comprising styrene/butadienecopolymer is coated with the following coating materialin a coating weight (solid) of 35 g/m
2 by means of arotating doctor and is dried in a drying oven at 100°Cfor 5 minutes:
| Water | 156.0 g |
| Precipitated copolyamide having a melting point of 140°C (mixture of ORGASOL 3501 ExDNAT1 and ORGASOL 3502 DNAT1, ELF ATOCHEM S.A.), bimodal average particle size 10 µm and 20 µm | 68.0 g |
| Plastics dispersion (50% solids) of vinyl acetate copolymer (Vinnapas EP 400, Wacker Chemie GmbH, Munich) having a minimum film formation temperature of 0°C and a mean particle size 0.8 µm | 18.4 g |
| Thickener: polyacrylate (STEROCOLL D, BASF AG) | 4.0 g |
| Ammonia: (25% strength) | 3.5 g |
| Plasticizer: N-n-butylbenzenesulfonamide | 7.0 g |
| Wetting agent (SURFYNOL 440, Air Products Inc.) | 1.5 g |
The coating material has a solids content ofabout 33% by weight and a pH of 8.5. It contains 78%,based on the solid substance, of thermoplastic pigment.
The matt paper coated in this manner is printedwith a test print by means of a Novajet III inkjetprinter from Encad using commercial ink cartridges fromAmerican Inkjet Corp. and the coating is converted intoa film at 160°C by means of a hot press in the courseof one minute. After this treatment, the now glossyprint shows a high-contrast, high-resolution imagehaving crisp edges. It has extremely high waterresistance. The image-bearing paper stored for oneweek in water at 30°C has a tear strength (Elmendorf,DIN 53128) of 4.0 N in the longitudinal direction and4.2 N in the transverse direction, compared with 2.4 Nin the longitudinal direction and 2.8 N in the transverse direction in the dry state.
As a result of the water treatment, the colorsurfaces show only very little or no color changescompared with the initial color values (Table 1). TheUV stability of the colored surfaces is excellent. Theprinted image exhibits virtually no change even aftermore than 200 hours (Table 2).
Example 3A commercial synthetic paper (Pretex KL 43.095,Papierfabrik Lahnstein GmbH, Lahnstein) of 95 g/m
2 andcomprising 18% of cellulose fibers, 33% of syntheticfibers, 18% of binders, 28% of pigments and assistantsis coated with the following coating material in acoating weight (solid) of 40 g/m
2 by means of a rotatingdoctor and is dried in a drying oven at 100°C for 5minutes:
| Water | 155.0 g |
| Precipitated copolyamide having a melting point of 140°C (mixture of ORGASOL 3501 ExDNAT1 and ORGASOL 3502 DNAT1, ELF ATOCHEM S.A.), bimodal average particle size 10 µm and 20 µm | 77.9 g |
| Styrene/butadiene copolymer dispersion (50% solid) (LITEX PS 5520, Hüls AG) | 26.3 g |
| Thickener (ROHAGIT S hv, Rohm GmbH) | 0.4 g |
| Ammonia (25% strength) | 8.4 g |
| Plasticizer: N-n-butylbenzenesulfonamide | 5.8 g |
| Wetting agent (SURFYNOL 440, Air Products Inc.) | 0.34 g |
| Dispersant (CARBOSET 524 H, BF Goodrich) 40% strength dispersion | 5.7 g |
The coating composition has a solids content ofabout 36% by weight and a pH of 10. It contains 76%,based on the total solid in the composition, ofthermoplastic pigment.
The matt paper coated in this manner is printedwith a test image by means of a NOVAJET III inkjetprinter from Encad using commercial ink cartridges from American Inkjet Corp. and the coating is converted intoa film at 160°C by means of a hot press in the courseof one minute. After this heat treatment, a high-contrastimage having crisp edges is present. Therecording has very high water resistance. The materialprovided with an inkjet print and stored for one weekin water at 30°C has a tear strength (Elmendorf, DIN53128) of 3.9 N in the longitudinal direction and 4.0 Nin the transverse direction, compared with 2.4 N in thelongitudinal direction and 2.8 N in the transversedirection in the dry state.
As a result of the water treatment, the coloredsurfaces show only very little or no color changescompared with the initial color values (Table 1). TheUV stability of the colored surfaces is excellent. Theprinted image shows virtually no change even after over200 hours (Table 2).
Comparative ExampleThe paper from Example 1 is coated and printedas described there. However, the test for resistanceto water and UV light is carried out in the statewithout converting to a film (without heat treatment).The water resistance of the prints (Table 3) isinsufficient since the ink dyes are dissolved to agreat extent from the porous, printed layers.Furthermore, the coating of the synthetic paper in thewet state can be readily damaged mechanically so thatthe printed image is destroyed. The light stability ispoor; under UV irradiation, the colors fade veryrapidly (Table 2).
| Percentage residual value of the optical density after storage for 1 week in water at 30°C, in % |
| Example | Black | Cyan | Magenta | Yellow | Blue | Red | Green |
| 1 | 96 | 98 | 93 | 99 | 100 | 98 | 97 |
| 2 | 92 | 94 | 99 | 94 | 93 | 96 | 98 |
| 3 | 94 | 94 | 98 | 96 | 95 | 96 | 97 |
| Comparison | 20 | 36 | 41 | 67 | 45 | 56 | 41 |
| Light stability of the primary colors |
| Example 1 |
| Time in SUNTEST | Optical density (Macbeth densitometer RD 920) |
| Black | Cyan | Magenta | Yellow |
| 0 hours | 1.53 | 1.36 | 1.21 | 1.06 |
| 72 hours | 1.54 | 1.33 | 1.18 | 1.06 |
| 144 hours | 1.52 | 1.30 | 1.12 | 1.05 |
| 216 hours | 1.48 | 1.29 | 1.10 | 1.03 |
| Example 2 |
| Time in SUNTEST | Optical density (Macbeth densitometer RD 920) |
| Black | Cyan | Magenta | Yellow |
| 0 hours | 1.57 | 1.54 | 1.53 | 1.43 |
| 72 hours | 1.53 | 1.54 | 1.51 | 1.42 |
| 144 hours | 4.45 | 1.48 | 1.42 | 1.41 |
| 216 hours | 1.43 | 1.43 | 1.31 | 1.41 |
| Example 3 |
| Time in SUNTEST | Optical density (Macbeth densitometer RD 920) |
| Black | Cyan | Magenta | Yellow |
| 0 hours | 1.55 | 1.49 | 1.48 | 1.39 |
| 72 hours | 1.54 | 1.49 | 1.46 | 1.38 |
| 144 hours | 1.42 | 1.45 | 1.40 | 1.37 |
| 216 hours | 1.41 | 1.41 | 1.35 | 1.36 |
| Comparative Example |
| Time in SUNTEST | Optical density (Macbeth densitometer RD 920) |
| Black | Cyan | Magenta | Yellow |
| 0 hours | 1.53 | 1.36 | 1.21 | 1.06 |
| 72 hours | 1.28 | 1.26 | 0.65 | 0.87 |
| 144 hours | 1.15 | 1.21 | 0.37 | 0.74 |
| 216 hours | 1.04 | 1.19 | 0.27 | 0.6 |