WO2003082588A1

WO2003082588A1 - Output or printing base

Info

Publication number: WO2003082588A1
Application number: PCT/FI2003/000197
Authority: WO
Inventors: Ulf Enkvist; Leif Fagerholm; Tiina Gäddnäs; Anu Kopperoinen; Heikki Korpela; Rune SKÅTAR
Original assignee: Walki Wisa Oy
Priority date: 2002-04-02
Filing date: 2003-03-17
Publication date: 2003-10-09
Also published as: AU2003216938A1; FI20020629A; FI20020629A0

Abstract

The invention relates to the manufacture of an output or printing base, preferably intended for ink-jet printing and comprising a base layer and a printing layer which is of a pigmented polymer. The printing layer is a film which has been oriented mono- or biaxially in such a way that the bonds between said pigments and the polymer material of the film have been, at least to a significant degree on at least some edge of the pigment particle, released and form slits in the order of a micrometer or a nanometer on the surface which absorbs, primarily or secondarily, ink and/or its solvent during printing.

Description

Output or printing base

The invention relates to the manufacture of an output or printing base, "listing paper", to be used for printing, particularly for printing by ink-jet printers and in particular for the printing of images recorded in digital format.

With the increased use of personal computers and digital cameras, the need for high-quality printouts has greatly increased and is still increasing. In such printing bases, the substrate is either paper or a plastic film, an ink receiving layer being applied thereon. At best, this layer is such can it will quickly absorb the ink in the solvent layer in the vertical direction (Z) but will not spread the ink at all in the directions X, Y. Furthermore, the layer could be such that it chemically binds the colouring agents of the ink permanently in the receiving layer and does not change their colouring nature nor the colour tone.

Known printing papers or printing bases are made by applying an aqueous solution or dispersion on them, wherein the binding agent and the ink receiving pigment are left on the surface after the water has evaporated.

US patent 6,210,808 discloses a method for producing a good ink-jet printing base by using, as the ink-receiving layer, a polymer mixture with a water-soluble polymer and a water-insoluble polymer present as a micell, and which are both cross-linked by UV irradiation.

US patent 6,228,475 discloses an ink-jet printing base with two layers on top of each other, a) a solvent-absorbing porous polyolefin material and b) a colloid silica which is bound to the adhesive polymer by means of silanes.

US patent 6,290,814 presents a printing base consisting of pigmented paper, on top of which gelatin is applied together with hydroxyethyl starch in an aqueous solution. US patent 6,248,432 teaches an ink-jet printing base, in which the ink receiving layer consists of an adhesive and a water-insoluble organic pigment (Oji Paper) which contains amino groups and has at least one epoxy group per molecule. By the described arrangement, the typical inks remain well on the printing base and have excellent resistance to light.

EP-A-650850 presents a printing paper in which the paper is coated with polyolefin, and an absorption layer containing a synthetic hydro- philic polymer is applied on it in an aqueous solution.

In all these inventions and technical solutions, different approaches have been made to achieve the same purpose, that is, to provide a layer, a printing layer, which receives ink well and in which the ink solvent (water) is absorbed fast and leaves the colouring agents on the surface so that they will not be carried in the X, Y directions.

To achieve the above-mentioned aim, the surface layer should be either porous and hydrophilic or only hydrophilic, or contain hydrophilic particles or such particles which fix the molecules of the colouring agent by a chemical bond (cf. US 6,248,432).

In the described patents, the ink receiving layer is always applied by a typical method in which said material is introduced onto the surface of paper or coated paper and the solvent (water) is evaporated by heating.

In many of the described ink-jet receiving bases, the adhesive contains pigments and the adhesive has been in an aqueous solution at the time of applying the coating; consequently, the solvent (normally water) of the ink jet must first be diffused through a kind of an adhesive film before it reaches the pigment particle which absorbs the solvent of the ink by its capillary pores.

In the present invention, a method has been developed, whereby said output or printing bases can be formed in a quite new way and whereby it is possible to achieve technical possibilities with a larger range of variation.

According to the invention, a base web which can be either plastic or paper, paperboard, or paper or paperboard coated with plastic, preferably a base web whose material is not curved, is coated with a polymer film which contains at least one pigment grade and which has been oriented in such a way, preferably biaxially, that at least partly or to a great extent, a microscopic fracture or slit has been formed between the pigment and the adhesive, as a result of the orientation. The polymer film is attached to the surface of the base web which forms the actual support structure and where it forms the printing layer to receive and absorb ink during printing. The grammage of the base web can be selected according to the rigidity required of the printing base. The base web should be flexible so that it can be used to form a sufficiently flexible printing base which can be easily treated by various output and printing methods, particularly in ink-jet printing, and which can be, for example, in the form of single sheets.

The polymer layer present in the base web or forming the base web in itself may contain pigments 0.5 to 10 wt-% of the weight of the polymer layer to increase brightness and to improve opacity.

After the separately formed and oriented, pigment-containing polymer film has been attached to the surface of the base web, said fracture or slit in the film will quickly absorb the solvent of the ink, and the pigment adjacent to said slit will be in contact with the solvent of the ink at once.

Thanks to the above-described procedure, the adhesive may be either hydrophilic or even slightly hydrophobic up to a certain limit.

A advantageous situation is achieved, if the pigment to be used is an agglomerated pigment, wherein slits are also formed within the pigment, as a result of stretching in the orientation process.

According to the invention, a polymer film is formed by a blow or film extruder from a polymer raw material in the conventional way. Before the film formation, the polymer matrix of the raw material has been blended with as much fine-grained pigment as possible, such as precipitated chalk, gypsum, talc, ground calcite, silica, aluminium hydroxide, calcinated paper clay, or conventional fine-grained paper clay. It is also possible to use a mixture of said pigments. Similarly, it is possible to use a pigment whose particles consist of two different substances, particularly a pigment coated with another pigment, such as titanium dioxide coated with PCC, paper clay coated with PCC, paper clay coated with silica, or talc coated with silica, or calcium carbonate coated with silica .

Furthermore, advantageous pigments include known molecular sieve pigments, such as K-aluminate silicates, Na-aluminate silicates, aluminium oxide hydroxy dihydrate, and amoφhous silicic acid, and mix- tures of these.

Moreover, in the invention it is advantageous but not necessary that the particle size of the pigments is as fine as possible, preferably smaller than 5 μm and more advantageously smaller than 1 μm, and the pigments have a surface area and a pore volume ranging from 100 to 700 m²/g and from 0.5 to 2 m|/g, respectively.

Furthermore, it is advantageous in the invention that the matrix polymer used as an adhesive in the printing layer is at least partly hydrophilic as such. This is achieved by using, as the adhesive, typical water-soluble polymers which can be extruded in thermoplastic form. Film formation from these polymers may be accomplished by known melt processing methods of polymers.

Furthermore, it is advantageous to use plasticizers in said polymers, which plasticizers are water-soluble, for example carboxy methyl cellulose or corresponding other cellulose derivatives, polyvinyl pyr- rolidine, dextrane, ethoxylated starch, gelatine, xanthan rubber or other natural polymers which bind a large quantity of water, or their methoxy or ethoxy derivatives. When the pigments are mixed with said polymers in the pre-mixing part of the extruder, desirable effects, in addition to those mentioned above, can also be achieved if the pigments are slightly moist, which moisture content should be < 0.3 %, because the vapour will be discharged from the interface between the pigment and the polymer.

The blending of the pigments with the matrix polymer can also be made before the actual extrusion during melt mixing, to secure homogeneity.

Said advantageous polymers, which are used as matrix polymers, include for example K- and Na-acrylate polymers and their copolymers, neturalized poly acrylic acid, polyvinyl alcohols at various stages of saponification and with various polymer weights, polyethoxy oxaline / polyethoxy oxazoline, and polyethylene oxide.

The pigments may but do not need to be pre-treated with substances which evaporate at least partly from the surface of the pigments during the extrusion and leave a weak bond between the polymer matrix and the pigment, which bond slit is easily penetrated by the solvent of the printing ink, normally water, during printing.

The polymer film, which is formed of the matrix polymer and the pigment and contains the above-described pigments preferably 10 to 60 % of the total weight of the film, is oriented in the conventional manner from 50 to 500 %, typically 300 %.

After the orientation, the polymer film is attached to the surface of the base web, which forms the bottom part in the finished output or printing base, either by glueing or by extrusion lamination by means of a polymer used as a binding layer. As the adhesive, it is possible to use, for example, caseine glue, PV glue or polyurethane glue, which are only mentioned as some advantageous adhesives. The quantity of application of the adhesives typically ranges from 1 to 5 g/m².

In extrusion lamination, the binding layer used can be polyolefins, known polyolefin based copolymers and terpolymers, and very advantageously known ionomers, such as known acrylic acid ionomers, which are partly cross-linked or neutralized by cations, such as for example Na, K, Ca, Mg, Zn. This layer may simultaneously be used as a barrier between the base web and the printing layer.

After the film, oriented and pigmented according to the invention, has been attached to its base, which may be paper or paperboard, possibly surface-sized, paper or paperboard coated with a polymer, such as polyolefin, or a single polymer film (PE, PP, PA, PET, PEN, or a combination of these), said oriented film can preferably be still "surface-lacquered" to optimize the desired gloss degree or other printing finish. The surface lacquer is preferably applied as an aqueous solution or dispersion whose dissolved/dispersed constituents form the outermost surface layer after the removal of the water.

The quantity of said "surface lacquer layer" can be 0.5 to 5 g/m², and it may preferably contain water-soluble polymers, such as polyvinyl alcohol, polyvinyl pyrroline, carboxy methyl cellulose, polyethylene oxide, acrylates, styrene/acrylate copolymers, gelatin, and/or their pigmented forms, in which the pigments may be fine-grained silicas or aluminium silicates or organic pigments. The layer may contain known optical brighteners and preferably also cross-linkers, such as glyoxal, zircon- ates and/or boric compounds. At the same time, boric compounds also act as advantageous anti-mould agents; typically, these include boric acid and Na-tetraborate.

Preferably, the lacquer layer may also contain cationic additives to fix the pigment in the layer, polyacrylamide, polydiallyl dimethyl ammonium chloride, or quaternary ammonium compounds, but the substances are not limited to these directly. When the aim is to achieve a high gloss degree with the lacquer layer, it is advantageous to use col- loid silica having a particle size of < 300 nm, and when a matt finish is aimed at, it is advantageous to use particles in the order of about 1 μm and larger. Particularly advantageous agents to form a matt finish are organic polymethyl metacrylate pigments.

By methods known as such, the lacquer layer is applied or transferred to the final surface of the product in an aqueous solution and dried. However, according to the invention, this layer is not compulsory but an additional embodiment. The invention can thus vary within the scope of the inventive idea presented in the claims. The finished product comprises at least a supporting base web (based on paper or plastic) which forms the base layer, and a previously formed, mono- or biaxially ori- ented film attached on top of it and forming the printing layer. On top of this layer, there may be mainly a thin surface layer, "surface lacquer", intended to control the properties of the outermost surface. The backside of the base layer may be provided with additional layers, if necessary.

Claims

Claims:

1. An output or printing base, preferably a product intended for ink-jet printing, comprising a base layer and a printing layer which is of pig- mented polymer, characterized in that the printing layer is a film which has been oriented mono- or biaxially in such a way that the bonds between said pigments and the polymer material of the film have been, at least to a significant degree on at least some edge of the pigment particle, released and form slits in the order of a micrometer or a nanometer on the surface which absorbs, primarily or secondarily, ink and/or its solvent during printing.

2. Base according to claim 1 , characterized in that the pigments are primarily agglomerated pigments and that during stretching of said film, the pigment agglomerates have been partly disintegrated also within the agglomerates.

3. The product according to claim 1 or 2, characterized in that the polymer layer is of polyvinyl alcohol, Na- or K-acrylate polymer, their copolymer or neutralized polyacrylic acid, polyethoxy oxaline, polyethoxy oxazoline or polyethylene oxide, or a mixture of these.

4. The base according to any of the preceding claims 1 to 3, characterized in that the pigment in the oriented polymer film is calcium car- bonate, kaoline, calcinated kaoline, silica, amoφhous silicic acid, Na- or K-aluminium silicate, aluminium oxide hydroxy hydrate, or a mixture of these, or aggregate pigments or pigments made of these materials and coated with one another before the mixing with the polymer.

5. The base according to any of the preceding claims 1 to 4, characterized in that the ink-absorbing printing layer has been coated with a thin water-soluble surface lacquer layer whose square mass is preferably 0.5 to 5 g/m².

6. The base according to any of the preceding claims 1 to 5, characterized in that the pigment content is 10 to 60 wt-% of the total weight of the printing layer.

7. The base according to any of the preceding claims 1 to 6, characterized in that its bottom layer, onto which the film is attached, consists of paper, paperboard, surface-sized paper or paperboard, poly- mer-coated paper or paperboard, or a polymer film.

8. The base according to any of the claims 1 to 7, characterized in that the printing layer is attached to the base layer by adhesive lamination.

9. The base according to any of the claims 1 to 7, characterized in that the printing layer is attached to the base layer by extrusion lamination.

10. The base according to claim 9, characterized in that the printing layer is attached to the base layer by extrusion lamination by means of polyolefin, a polyolefin-based copolymer, a polyolefin-based terpoly- mer, or an ionomer.

11. The base according to claim 8, characterized in that the adhesive lamination glue is caseine glue, PVA glue or polyurethane glue, and its content is preferably 1 to 5 g/m².

12. The base according to any of the preceding claims 5 to 13, char- acterized in that the surface lacquer layer contains, as a gloss improving substance, colloid silica whose particle size is < 300 nm.