EP2770105A1 - Substrate paper for decorative coating materials - Google Patents

Abstract

Base paper comprises raw paper unsized in the mass, comprising a surface application which comprises an alkaline earth metal salt. An independent claim is also included for producing a decorative coating material, comprising printing a paper unsized in the mass and provided with the surface application with a digital printing method, impregnating with a thermoplastic resin, and drying.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a base paper for decorative coating materials, which can be impregnated with a thermally curable impregnating resin and printed by ink jet method, the use of the base paper for the production of decorative coating materials and a method for producing coating materials using the base paper.

BACKGROUND OF THE INVENTION

Decorative papers are needed for the production of decorative laminates, which are used as building materials in furniture production and interior design. The decorative laminates are mainly high pressure laminates (HPL) and low pressure laminates (LPL). To produce a high-pressure laminate, the decorative paper is impregnated in the unprinted or printed state with a resin and with one or more layers of kraft paper sheets, which were soaked in phenolic resin (core papers), in a laminating press at a temperature of about 110 to 170 ° C and a Pressed pressure of about 5.5 to 11 MPa. Subsequently, the resulting laminate (HPL) is glued or glued with a carrier material such as HDF or chipboard. A low pressure laminate is prepared by directly pressing the unprinted or printed decorative paper impregnated with a resin at a temperature of about 160 to 200 ° C and a pressure of about 1.25 to 3.5 MPa to the backing plate.

The refinement of material surfaces may be of an optical nature (by appropriate coloring) and / or physical nature (by coating the plate surface with appropriate functionality and structure). Decorative papers can be processed with or without a printed pattern. For this purpose, the printed or unprinted decorative paper is usually soaked in one or more stages with synthetic resins, then dried, wherein the resin remains reactive, and then pressed in sheets or rolls with a carrier material irreversibly hot. When pressed, the resin hardens. As a result of this hardening, not only does the composite bond to the plate, but the paper is completely chemically physically closed. Suitable synthetic resins are the impregnating resins commonly used in this technical field, in particular melamine-formaldehyde resin, urea-formaldehyde resin, phenol-formaldehyde resin, polyacrylates, acrylic ester-styrene copolymers. The impregnating resin may be used in an amount of 40 to 250%, preferably 80 to 125%, of the basis weight of the decorative base paper.

The application of the printing pattern is usually done by gravure printing. Particularly in the production of commercially available printing patterns, this printing technique has the advantage of being able to print on large quantities of paper at high machine speed.

However, the gravure process is not profitable for smaller amounts of decor paper and is insufficient in terms of print quality for complicated patterns. From the printing techniques that meet the requirements for flexibility and quality Withstand the ink-jet printing process (ink-jet printing) is therefore becoming increasingly important.

To make decorative base papers printable by the ink-jet printing process, they are coated with one or more functional layers for receiving the ink and fixing the dyes. Such decorative base papers which can be printed by the ink-jet printing process are described, for example, in US Pat DE 199 16 546 A1 and the EP 1 044 822 A1 described.

The ink receiving layers usually contain pigments, water-soluble or water-dispersible polymers as binders, dye-fixing substances and other auxiliaries commonly used in such layers.

Decorative base papers differ in their properties, however, fundamentally different from normal commercial ink-jet papers. Decorative base papers should have an open surface, so that they can be impregnated quickly and evenly with an impregnating resin.

Although a decorative base paper provided with one of the above-described ink receiving layers has good ink jet printability, it has at least on one side of the paper a largely covered paper structure. The intermediate spaces between the fibers are largely closed and are thus available only to a limited extent for the absorption of impregnating resins.

The EP 1 749 626 A1 proposes, therefore, a method in which the base paper provided with an ink receiving layer is impregnated from the back side. The WO 2009/097986 A1 beats before, the ink composition, the main constituents of which are barium sulfate, titanium dioxide and silicates, apply as a pigment coating such that no closed planar layer is formed and thus the fiber interstices remain largely open. The disadvantage of this procedure is that it is not possible to achieve a sufficiently good printing result.

SUMMARY OF THE INVENTION

Consequently, it is an object of the invention to provide a base paper for decorative coating materials, which does not show the disadvantages described above and a sufficient Impregnatability despite one-sided good printability by a digital printing method, in particular ink-jet printing method has.

This object is achieved with a base paper for decorative coating materials with a raw paper unsealed in the mass, wherein the base paper has a surface coating containing an alkaline earth metal salt.

The invention further relates to the use of the base paper according to the invention for the production of laminates and laminates of all kinds.

The invention also provides a process for the preparation of a decorative coating material comprising the step of applying to a base unsized base paper containing an alkaline earth salt, printing the paper by means of a digital printing process, impregnating it with a thermoplastic resin and drying it. The impregnated and dried paper can be varnished.

It has surprisingly been found that the surface application according to the invention, even without a polymeric binder, provides good printability by means of digital printing processes, in particular the ink-jet printing process, and the problem of "dusting out" of pigments which is to be expected due to the absence of the binder does not occur. However, the paper surface is largely free and open for receiving the impregnating agent.

Another advantage of the omission of binders is a lower viscosity of the application liquid and thus a simplification of the application process and the cleaning of the application units.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Particularly suitable alkaline earth metal salts are alkaline earth halides and alkaline earth metal nitrates having a water solubility of at least 400 g / l (measured at 20 ° C). These can also be used in a mixture. Particularly preferred is the use of calcium chloride, magnesium nitrate or mixtures thereof.

The effect according to the invention is achieved in particular if the surface application additionally contains an inorganic pigment having a specific surface area, measured by BET, of 100 to 400 cm ² / g. Particularly preferred are inorganic pigments having a specific surface area of 200 to 330 cm ² / g. Such preferred inorganic pigments are, for example, aluminum oxide, aluminum hydroxide, boehmite and / or silica. Of the silicas, a cationized fumed silica is particularly preferred.

The mass ratio alkaline earth salt / pigment in the surface application may be 70:30 to 30:70, preferably 60:40 to 40:60.

The surface coating may also contain other auxiliaries such as dispersing aids, color fixing agents such as polyaluminum salts, polyammonium salts, pH regulators and other auxiliaries customary in the paper industry. Preferably, the surface application is free of a binder.

The surface application can be carried out with conventional application units used in the paper coating. In particular, "inline" can be applied in the paper machine with a size press. The application weight may preferably be 1 to 10 g / m ² , in particular 2 to 8 g / m ² , based on the mass of the dry substance.

The surface of the base paper according to the invention may have a pH of 4.5 to 8, preferably 6 to 7.

By treating the surface of the decorative base paper with the surface application according to the invention, a sufficient impregnating ability of the base paper is obtained and the paper is given very good printability by the ink-jet printing process. The base papers produced according to the invention have an air permeability according to Gurley of less than 25 s / hml, in particular 10 to 22 s / hml.

The base paper according to the invention can be rolled up or divided into sheets. The base paper can then be in high quality using a wide variety of inkjet processes be printed. In a subsequent step, the printed paper can then preferably be impregnated with an impregnating resin, in particular with a melamine resin, and dried. The base paper can then be pressed hot in a coating press onto a wood-based panel or into a laminate. Optionally, transparent, unprinted and resinated paper (overlay or underlay) can be used as a further layer as a protective and / or adhesive layer. Alternatively, however, it is also possible to use a different adhesive layer. The printed product can also be sealed with a varnish.

The decorative base papers which can be used according to the invention are those which have undergone neither sizing in the mass nor surface sizing. These consist essentially of celluloses, pigments and fillers and conventional additives. Common additives may be wet strength agents, retention aids and fixatives. Decorative base papers differ from conventional papers due to the much higher filler content or pigment content and the lack of standard paper sizing or surface sizing on paper. The decorative base papers which can be used according to the invention usually contain a wet strength agent.

Softwood pulps, hardwood pulps or mixtures of both pulp types can be used to produce the decorative base papers. Preference is given to the use of 100% hardwood pulp. But mixtures of softwood / hardwood pulps in the ratio 5:95 to 50:50, in particular 10:90 to 30:70 can be used. The base papers can be produced on a Fourdrinier paper machine or a Yankee paper machine. For this purpose, the pulp mixture be ground at a consistency of 2 to 5 wt .-% to a freeness of 10 to 45 ° SR. In a mixer, fillers and / or pigments, color pigments and / or dyes and wet strength agents such as polyamide / polyamine-epichlorohydrin resin, cationic polyacrylates, modified melamine-formaldehyde resin or cationized starches may be added to conventional amounts in the production of decorative papers and with the Pulp mixture are mixed well.

The fillers and / or pigments can be added in an amount of up to 55% by weight, in particular 10 to 45% by weight, based on the weight of the pulp. Suitable pigments and fillers are, for example, titanium dioxide, talc, zinc sulfide, kaolin, aluminum oxide, calcium carbonate, corundum, aluminum and magnesium silicates or mixtures thereof.

The thick stock produced in the mixing chest can be diluted to a consistency of about 1%. If necessary, other auxiliaries such as retention aids, defoamers, dyes and other auxiliaries mentioned above or mixtures thereof may be added. This thin material is fed to the wire section via the headbox of the paper machine. A non-woven fabric is formed and, after dewatering, the base paper is obtained, which is subsequently dried. The basis weights of the papers produced can be 30 to 200 g / m ² .

• glatt, d.h. mit Glätte nach Bekk über 80 s,
• alternativ ungeglättet mit einer Glätte nach Beck < 80 s,
• mit einem Yankeezylinder oder mit einem Kalander geglättet,
• sehr luftdurchlässig mit Gurley-Werten unter 20 s/hml oder dichter mit Gurley-Werten über 20 s/hml.

Depending on the intended application and the quality requirements for this application, the decorative base papers used according to the invention may have the following properties:

• smooth, ie with Bekk smoothness over 80 s,
• alternatively unsmoothed with a smoothness of Beck <80 s,
• smoothed with a Yankee cylinder or with a calender,
• very air permeable with Gurley values below 20 s / hml or denser with Gurley values above 20 s / hml.

The decorative base paper according to the invention can be dyed. For coloring inorganic color pigments such as metal oxides, metal hydroxides and metal oxide hydrates, metal sulfides, metal sulfates, metal chromates and Metallmolybdate or mixtures thereof, and organic color pigments and / or dyes such as carbonyl colorants (quinones, quinacridones), cyanine colorants, azo colorants, azomethines and methines, phthalocyanines or dioxazines used become. Particular preference is given to mixtures of inorganic color pigments and organic color pigments or substances. The mass of the color pigment or color pigment mixture or dye or dye mixture may be from 0.0001 to 5 wt .-%, based on the mass of the pulp, depending on the type of dye.

The coloring of the base paper according to the invention is constantly adjustable. This is more complicated and more expensive in the case of a decorative base paper coated with a separate ink receiving layer.

In a particular embodiment of the invention, the surface application liquid may contain coloring additives. These may be the same color pigments and / or dyes with which the raw paper is dyed.

According to one embodiment, the invention relates to a method for producing a decorative coating material or decorative paper. For this purpose, we base paper according to the invention with a digital printing process, such as the ink-jet printing process printed. The printed base paper can then be impregnated with a thermoplastic resin and dried. The drying can be carried out in such a way that the impregnating resin is completely cured or only partially cured. Partially cured means that the curing of the thermoplastic resin has occurred at 70% and more, 80% and more, or 90 and more.

The application of the decorative coating material or decorative paper on a permanent support in a known manner under the action of heat and pressure and optionally with the additional use of an adhesive known for this purpose.

The following examples serve to further illustrate the invention.

EXAMPLES Example 1 (B1)

To prepare the pulp suspensions, a pulp mixture of 80% by weight of eucalyptus pulp and 20% by weight of pine sulfate pulp was milled at a stock density of 5% to a freeness of 33 ° SR. This was followed by the addition of 1.8 wt .-% epichlorohydrin resin as a wet strength agent. This pulp suspension was adjusted to a pH of 6.5 to 7 with aluminum sulfate. Thereafter, the pulp suspension became a mixture of 40 wt .-% titanium dioxide and 5 wt .-% talc, 0.11 wt .-% of a retention aid and 0.03 wt .-% of an antifoam added and a decorative base paper with a basis weight of 90 g / m ² and manufactured an ash content of about 32 wt .-% The weights are based on the mass of the pulp. In the next step, the decorative base paper was treated with the application liquid described below in the size press and then dried. The coating weight was 2 g / m ² (dry).

Application liquid for surface application: water 80% by weight Calcium chloride (solid) 20% by weight

The pH of the coating liquid had been adjusted to pH 5 with NaOH.

Example 2 (B2)

A pulp suspension of 100% by weight eucalyptus pulp was milled at a stock consistency of 5% to a freeness of 33 ° SR. This was followed by the addition of 1.8 wt .-% epichlorohydrin resin as a wet strength agent. This pulp suspension was adjusted to a pH of 6.5 to 7 with aluminum sulfate. Thereafter, a mixture of 36 wt .-% titanium dioxide and 5 wt .-% talcum, 0.11 wt .-% of a retention aid and 0.03 wt .-% of a defoamer was added to the pulp suspension and from a decorative base paper with a basis weight of about Made 80 g / m ² and an ash content of about 30 wt .-%. The weights are based on the mass of the pulp. In the next step was the decorative base paper treated with the following Auftragflüssigkei in the size press and then dried. The coating weight was 6 g / m ² (dry).

Application liquid for surface application: water 80% by weight Calcium chloride (solid) 10% by weight Pyrogenic silica (solid) 10% by weight (Aerosil ^® 300, Evonik)

The pH of the coating liquid had previously been adjusted to 5 with NaOH.

Example 3 (B3)

A decorative base paper prepared according to Example 1 was impregnated with the following application liquid in the size press and then dried. The coating weight was 8 g / m ² (dry).

Application liquid for surface application: water 80% by weight Magnesium nitrate (solid) 10% by weight Cationized pyrogens Silica (solid) 10% by weight (Aerosil ^® 300, Evonik)

The pH of the coating liquid had previously been adjusted to pH 5 with NaOH.

COMPARATIVE EXAMPLES Comparative Example 1 (V1)

A decorative base paper produced according to Example 1 was used as base paper without further application of glue liquor.

Comparative Example 2 (V2)

A decorative base paper prepared according to Example 1 was treated with the following application liquid in the size press and then dried. The coating weight was 8 g / m ² (dry).

Application liquid the surface application: water 50% by weight Thickness C-Film 7311 (Cerestar) 30% by weight Calcium chloride (solid) 10% by weight Cationized Fumed Silica (Aerosil ^® 300, Evonik) 10% by weight

Comparative Example 3 (V3)

A decorative base paper prepared according to Example 1 was prepared according to the examples of EP 1 044 822 B1 coated with an ink receiving layer. The application weight was 5 g / m ² . This was the following composition of the ink receiving layer: Polyvinyl alcohol 20% solution (MOWIOL 26-88, Kuraray Europe GmbH) 33% by weight Polyamine 20% solution (Magnaflox 1597, BASF SE) 9% by weight Acrylate-styrene polymer 20% dispersion (Basoplast 265D, BASF SE) 10% by weight Amorphous silica 20% dispersion (Gasil 200DF, PQ Corporation) 48% by weight

APPLIED TESTING METHODS

The base papers prepared according to the Examples and Comparative Examples were printed in an ink jet printer (EPSON 4800 with pigmented inks).

The impregnation ability was tested on the unprinted base papers. The printed base papers were rated for image quality and ink penetration on the back of the paper.

The methods used to test the papers are described below.

Air resistance to Gurley

The purpose of the test is the characterization of the porosity of the paper structure and thus for the impregnation ability. It measures the time taken for a given amount of air to flow through a paper surface at a constant pressure. The measurement is carried out on the basis of ISO 5636-5 with the help of the densometer 121D from Lorenzen & Wettre. The readings are given in Gurley seconds / 100 ml. Values less than 25 s / hml show papers with very good air permeability. Values higher than 60 s / hml indicate a compacted structure and thus poor permeability.

color density

The image quality is evaluated by measuring the color density for the primary colors cyan, magenta, yellow and black. The color densities are measured with the densitometer SpectroEye from x-rite.

Penetration of the ink

Penetration of the ink is a punctiform or even partial penetration of the ink towards the back of the paper. Especially with decorative papers with high permeability there is a risk of penetrating the ink into the interior of the paper and thus the penetration to the back of the paper sheet.

• + kein Durchschlagen, gute Tintenfixierung
• o leichtes Durchschlagen, mittlere Tintenfixierung
• - Durchdringen der Tinte auf die Rückseite, schlechte Tintenfixierung

The visual evaluation of the breakdown behavior provides a measure of the fixation of the ink on the surface of the base paper.

• + no penetration, good ink fixation
• o easy penetration, medium ink fixation
• - Penetration of the ink on the back, poor ink fixation

The test results are summarized in the following table: color density Air resistance s / hml punch cyan magenta yellow black B1 0.40 0.55 0, 63 0, 99 18 O B2 0, 41 0.57 0, 64 1, 02 22 + B3 0.41 0.57 0.62 1.00 22 + V1 0.38 0.34 0.50 0.52 14 - V2 0.40 0.58 0.63 1.07 28 + V3 0.40 0.71 0.68 1.30 50 +

Claims (15)

Base paper for decorative coating materials with a raw paper unsealed in the mass, characterized in that the base paper has a surface coating containing an alkaline earth metal salt. Base paper according to claim 1, characterized in that the alkaline earth metal salt is a water-soluble calcium salt. Base paper according to claim 1, characterized in that the alkaline earth metal salt is calcium chloride or calcium nitrate. Base paper according to one of claims 1 to 3, characterized in that the surface coating contains an inorganic pigment having a specific surface area, measured by BET, of 100 to 400 cm ² / g. Base paper according to claim 4, characterized in that the specific surface area of the inorganic pigment, measured according to BET, is 200 to 330 cm ² / g. Base paper according to claim 4 or 5, characterized in that the inorganic pigment is an aluminum oxide, an aluminum hydroxide, a boehmite and / or a silica. Base paper according to claim 4 or 5, characterized in that the inorganic pigment is a cationized fumed silica. Base paper according to at least one of claims 4 to 7, characterized in that the ratio of alkaline earth salt / inorganic pigment, based on the mass, is 60:40 to 40:60. Base paper according to at least one of claims 1 to 8, characterized in that the surface application contains no polymeric binder. Base paper according to at least one of claims 1 to 9, characterized in that the surface application in an amount of 1 to 10 g / m ² , based on the mass of the dry substance, is applied. Base paper according to at least one of claims 1 to 10, characterized in that the surface of the base paper has a pH of 4.5 to 8. Use of the base paper according to at least one of claims 1 to 11 for the production of laminates and laminates of all kinds. A process for the preparation of a decorative coating material, characterized in that printing on a non-sized and provided with a surface application, which contains an alkaline earth salt, paper with a digital printing process, impregnated with a thermoplastic resin and dried. Process for the preparation of a decorative coating material according to claim 13, characterized in that it is impregnated with a thermoplastic resin Paper dries so that the thermoplastic resin is only about 80% cured. A method for producing a decorative coating material according to claim 13 or 14, characterized in that applying to the base paper surface a surface coating, which additionally contains an inorganic pigment having a specific surface area, measured by BET, of 100 to 400 cm ² / g.