Recording material with an extrusion coated PVA layer

Details Recording material with an extrusion coated PVA layer Recording material with an extrusion coated PVA layer

2001-04-05

2002-06-11

Schwartz, Pamela R. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S195100, C428S522000, C156S129000, C427S362000, C427S407100, C427S411000

Reexamination Certificate

active

06403202

ABSTRACT:

BACKGROUND, SUMMARY AND DESCRIPTION OF THE INVENTION
The invention relates to a recording material for the ink-jet printing process.
The ink-jet recording method is used to produce color graphics, full-color copies and also for text printings, so it covers a very wide field of applications. The recording material must fulfill various requirements are made of this recording material, such as high gloss, good drying, high color density, good wet rub-off properties, low mottle, and high water fastness.
The ink-jet recording method is used to produce color graphics, full-color copies and also for text printings, so it covers a very wide field of applications. The recording material must fulfill various requirements that are made of this recording material, such as high gloss, good drying, high color density, good wet rub-off properties, low mottle, and high waterfastness.
High-performance ink-jet printers for producing photographic-quality printings use inks with a high water content as solvent. In addition, the ink application volume by these printers is greater than that with traditional ink-jet printers. Films were initially used as ink-receiving materials, because they are characterized by a high dimensional stability when wetted with water, but they have poor drying properties. One possibility of producing glossy, photographic-quality ink-jet printings is the use of resin-coated papers that are provided with an ink-receiving layer. DE 19 618 607 A describes the use of polyolefin-coated papers to achieve high gloss values. However, the long drying time of these papers is a disadvantage, because with this material the ink fluid cannot be diverted into the paper support. The resin coating acts as a barrier layer with respect to the ink fluid.
The object of the invention is to provide a recording material for the ink-jet printing method, which provides images with a high color density, good wet rub-off fastness, good water fastness, low mottle and beyond that rapid drying after printing with aqueous ink and high gloss.
This object is achieved by a recording material which comprises a raw base paper, a layer containing polyvinyl alcohol (PVA) extruded on the raw base paper, and an ink-receiving layer applied from an aqueous dispersion or solution.
The recording materials according to the invention show a very good adhesion of the PVA layer on the raw base paper, brilliant gloss after calendering or treatment in a chill roll and excellent drying properties after printing with aqueous inks. The drying properties are particularly improved in view of ink-jet recording materials which have a polyolefin layer formed on the paper support. A pretreatment of the raw base paper in order to improve adhesion of the PVA layer on the raw base paper by corona treatment or flame treatment or applying a separate adhesive layer between the paper and the PVA layer is not necessary.
Polyvinyl alcohols which may be used according to the invention are all polyvinyl alcohols which are extrudable or which are made extrudable by the addition of appropriate additives such as plasticizers. Polyvinyl alcohols which may be used according to the invention are in particular polyvinyl alcohol homopolymers, polyvinyl alcohol copolymers and/or mixtures thereof. Suitable PVA copolymers are in particular those which contain ethylene and/or vinyl acetate as polymerizable monomers.
According to a preferred embodiment of the invention, the polyvinyl alcohol is hydrolyzed to an extent of 75 to 99 mol %, and it may have a degree of polymerisation of 200 to 2500. The melt flow index (MFI) of the polyvinyl alcohol resins to be used according to the invention may be 10 to 50 g/10 minutes, preferably 20 to 30 g/10 minutes. The extruded layer containing polyvinyl alcohol may contain 5 to 95 wt % of the extrudable polyvinyl alcohol.
Additives which improve the extrusion properties of the polyvinyl alcohol are, for example, plasticizers. A plasticizer may be incorporated into the polymer matrix during the preparation of the polyvinyl alcohol or may simply be added to the extruder and mixed therein with the polyvinyl alcohol. Suitable plasticizers are all PVA compatible plasticizers such as hydrophylic plasticizers. Suitable plasticizers are in particular polyhydric alcohols, such as glycerol, polyethylene glycol, ethylene glycol, diethylene glycol and mannitol. The plasticizer or a plasticizer mixture containing several plasticizers may amount to 1 to 30 wt %, preferably 5 to 20 wt %, based on the weight of the extrusion coated layer.
Polymers or copolymers which may be included in the layer which is extruded on the raw base paper may contain, for example, polyurethanes, polyolefins, ethylene copolymers, polyalkylene oxides, such as polyethylene oxyethanol, polycarbonates, polyesters, polyamides and polyesteramides.
The PVA layer extruded on the raw base paper may contain those additives which are usually contained in the polyolefin coating of photobase papers. These are in particular white pigments, color pigments, colorants, fillers, optical brighteners and phosphoric acid which is used to improve thermal stability of PVA. A conventional white pigment is titanium dioxide. Further fillers and pigments are calcium carbonate, ultramarine, cobalt blue, carbon black, alumina and silica. In particular, silica is useful for shortening the time required for drying of the ink.
The coating weight of the extruded layer may be 10 to 60 g/m
2
, preferably 20 to 40 g/m
2
. The extrusion on the raw base paper is performed according to methods which are known to the skilled worker in the paper manufacturing industry. The extruder is, for example, a screw extruder. According to a preferred embodiment of the invention, the temperature in the extruder or the temperature in different sections of the extruder is adjusted to 140 to 230° C., in particular 160 to 180° C. In particular, in a two-inch extruder it is preferred to compound the resins and further optional additives with screw speeds of more than 50 rpm, in particular more than 75 rpm, and to extrude the resulting mixtures. If an extruder other than a two-inch extruder is used, it is preferred to adjust the screw speed in such a way that the viscosity of the material to be extruded corresponds to the viscosity of a material which is compounded and extruded in a two inch screw extruder at screw speeds of more than 50 rpm and a temperature of 140 to 230° C.
In order to achieve high gloss it is preferred to use a high gloss chill roll. Very good gloss results are also obtained with the chill rolls of DE 198 12 445.
As support material any kind of raw base paper may be used. Preferably surface sized papers, calendered or non-calendered papers or highly sized raw base papers may be used. The raw base paper may be sized with acidic or neutral sizing agents. Especially suitable are papers with a surface roughness of less than 300 Sheffield units determined according to Tappi T538 roughness. The raw base paper shall have a high dimensional stability and should be able to absorb the water which is contained in the ink without formation of curl. Papers with a high dimensional stability which are manufactured from pulp mixtures, comprising softwood sulphate fiber pulp and eucalyptus pulp are particularly suited. The disclosure of DE 196 02 793 B1, which discloses a raw base paper for a ink-jet recording material, is incorporated herein by reference.
According to a preferred embodiment the raw base paper is not too strongly sized in order to allow a paper surface with an open pore structure. Particularly preferred papers are those having a roughness of less than 200 Sheffield units. The basis weight of the raw base paper may be 60 to 250 g/m
2
.
The raw base paper may contain further additives which are conventional in the paper manufacturing industry such as colorants, optical brighteners, pigments, and defoaming agents. It is also possible to use waste pulp and processed recycled paper.
Onto the extruded PVA layer any known ink receiving layer may be applied from an aqueous phase, for example, by

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