CA2301300C - Decorative paper base - Google Patents

Abstract

A decorative paper base for manufacturing decorative papers or decorative films, formed out of a paper pulp containing pulp fibers and fillers, has a non-modified and cationically modified pulp as the pulp mixture, which yields an improved strength of the decorative paper base.

Description

,. CA 02301300 2000-03-17 DECORATIVE PAPER BASE
Hartmut Schulz Background, Summary and Description of the Invention The invention relates to a decorative paper base, and decorative films or decorative laminated plastics made with its use.
Decorative coating materials, so-called decorative paper-base or decorative films, are preferably used for applying surface coatings during furniture manufacture and interior finishing work. Decorative films encompass artificial resin-impregnated or artificial resin-impregnated and surface treated, printed or not printed paper web. Decorative films are glued or bonded to a platen.
Depending on the type of impregnating procedure, a distinction is made between decorative films with completely impregnated paper core and prepreg-based decorative films, in which the paper is only partially impregnated online in the paper machine. Laminated plastics (high-pressure laminates) are laminates made by press molding several impregnated papers laminated one on top of the other. The structure of these laminated plastics generally consists of a transparent overlay, which produces the highest surface resistance, an artificial resin-impregnated decorative paper and a phenolic resin smeared craft paper. Hardboard, chipboard and plywood are among the materials used as the substrate.

_ CA 02301300 2000-03-17 _ _ 2 _ , _ In the laminates manufactured according to the short-cycle procedure (low-pressure laminates), the decorative paper impregnated with artificial resin is directly press-molded with a substrate, e.g., a backing plate, at a low pressure.
The decorative paper used in the above coating materials is white or colored, and employed with and without additional imprinting.
Special requirements are placed on such decorative paper-bases as the starting materials for manufacturing the above coating materials, such as high opacity for better covering the substrate, uniform formation and grammature of the sheet to ensure uniform resin pick-up, high light resistance, high purity and uniformity of the color to ensure good reproducibility of the pattern to be imprinted, high water resistance to ensure a trouble-free impregnation process, corresponding absorbency to achieve the necessary degree of resin saturation, dry strength during re-rolling processes in the paper machine and imprinting in the printing machine.
Decorative paper bases generally consist of high-white sulfate pulp, primarily of hardwood pulp, up to 45 o pigments and fillers, as well as wet strength agents, retention agents and fixing agents. Decorative paper bases are distinguished from conventional paper by the much higher percentage of filler, and the lack of an internal or surface sizing common for paper using the known sizing agents like alkylketenedimers.
Opacity is among the most important properties of decorative paper base. It characterizes the covering capacity relative to the substrate. To ensure sufficient opacity, high amounts of filler are added to the fibrous material. To achieve good retention of the filler in the sheet, various retention agents are added to the paper pulp. On the other hand, the strength and impregnation _ CA 02301300 2000-03-17 _ _ 3 _ . _ characteristics of the paper deteriorate as the percentage of pigment and filler rises.
However, the strength of the decorative paper base, in particular the dry strength, is important for - continued processing, during transport through the printing machine, or in re-rolling processes in the paper - machine.
When using water-soluble resin systems to impregnate decorative papers, wet tensile strength is of great importance. Wet tensile strength is defined as the mechanical loadability in a wet state. It is normally influenced during the manufacture of paper by adding wet strength agents.
Since it is difficult to satisfy all the requirements placed on decorative paper bases at the same time, known decorative paper bases must still be improved. This applies in particular with respect to the properties of paper base opacity and strength.
Therefore, the object of the invention is to provide a decorative paper base with a high mechanical strength, high opacity and sufficient absorbency (impregnating capacity).
This object is achieved by using a decorative paper base comprised of a paper pulp consisting of pulp fibers and filler, along with conventional aids, wherein the pulp fibers consist of a mixture of non-modified and cationically modified pulp.
An improved dry strength was surprisingly found, even though no dry strength agent was added to the paper suspension. Adding the cationically modified pulp does not diminish other important properties of the decorative paper base, such as impregnating capacity or opacity.
Cationically modified pulps include those known from DAS PAPIER, Issue 12 (1980), pp. 575-579. Their use in _ CA 02301300 2000-03-17 _ _ 4 _ ..
decorative paper bases and the increased strength achieved as a result cannot be gleaned from prior art.
The pulp mixture preferably contains a percentage of cationically modified pulp fibers of at least 5 wt.o - relative to the weight of the pulp mixture. A percentage of 10 to 50 wt.%, in particular 10 to 20 wt.o, of the cationically modified pulp in the pulp mixture has proven to be especially advantageous.
In a special embodiment of the invention, the cationically modified pulp contained in the paper pulp exhibits an effective cationic charge of 20 to 300 mmol/kg pulp, determined according to internal method 4 of the Darmstadt Technical University. Pulp fibers with a charge density of 30 to 200 mmol/kg, in particular 30 to 100 mmol/kg, are preferred. The term "effective cationic charge" is understood as a charge density that was set off against the charge density of the non-cationized pulp. The charge density of the pulp depends on the quantity of cationic agent to be used. The quantity of cationizing agent can measure 0.005 to 200 g/1 kg pulp.
The pulp fibers can be cationically modified by reacting the fibers with epichlorohydrin and a tertiary amine, or by reacting with quaternary ammonium chlorides, such as chlorohydroxypropyltrimethyl ammonium chloride or glycidyltrimethyl ammonium chloride.
In addition, the pulp fibers can be cationized via the radical plugging of charged monomers, for example [2-(methacryloyloxy)ethyl]trimethyl-ammonium chloride (TMAEMA) with neutral comonomers such as acrylamide.
In a preferred embodiment of the invention, use is made of pulp fibers that are cationically modified via an addition reaction between quaternary ammonium compounds exhibiting glycidyl-functional groups and hydroxyl groups of the pulp.

_ - 5 - , .
The non-modified pulp and cationically modified pulp are preferably short-fiber pulps with an average fiber length of 0.5 to 0.7 mm, but long-fiber pulps or mixtures of both pulp types can also be used. Short fiber pulps - include aspen, beech or eucalyptus hardwood pulps, with eucalyptus being preferred. The pulp preferably has a ' freeness value of 30 to 45 °SR.
Suitable fillers include titanium dioxide, in particular rutile-type, zinc sulfide, calcium carbonate, kaolin, talcum or mixtures thereof. A rutile-type titanium dioxide surface-treated with A1203 is particularly preferred. The percentage of filler in the decorative paper base can measure up to 55 wt.%, especially 20 to 45 wt.%.
Wet strength agents include melamine/formaldehyde resins, polyamine derivatives or polyamide derivatives in amounts of 0.3 to 2 wt.% relative to the weight of the pulp.
Decorative paper base can contain additional substances such as organic and organic colored pigments, dyes, optical brighteners and dispersants, which are added while manufacturing the decorative paper base of the paper suspension.
The decorative paper bases according to the invention are manufactured in a known manner in a paper machine in a grammature range of 50 to 200 g/m2. To this end, the pulp mixture consisting of cationically modified pulp and non-modified pulp is refined to a freeness value of 30 to 45 °SR at a consistency of 2 to 4 wt.o. The filler and wet strength agent are added in a mixing tub, and mixed thoroughly with the pulp mixture. The thick matter obtained in this way is diluted to a consistency of about 1 % and, if necessary, combined with additional aids such as retention agents, defoamers, aluminum sulfate and, possibly, wet strength agents. This thin matter is routed to the wire section via the headbox of the paper machine. A fibrous web is formed; the decorative paper base is obtained after dewatering, and then dried.
In order to manufacture decorative papers, the decorative paper bases are impregnated or saturated with the artificial resin dispersions commonly used for this purpose.
Artificial resin dispersions commonly used for this purpose include those based on polyacryl or polyacrylmethyl esters, polyvinyl acetate, polyvinyl chloride or artificial resin solutions based on phenol/formaldehyde, urea/formaldehyde or melamine/formaldehyde precondensates or compatible mixtures thereof.
Impregnation can also take place in the size press of the paper machine. The decorative paper base can be impregnated in such a way that the paper is not completely impregnated all the way through. Such decorative papers are also referred to as preimpregnates. In this case, the percentage of the resin introduced into the decorative paper base via impregnation measures 25 to 30 wt.$ relative to the weight of the paper.
After drying, the saturated paper can also be lacquered and imprinted, and subsequently applied to a substrate, such as a wood plate. The lacquered and, if necessary, imprinted products are generally referred to as decorative films.
In one aspect, the present invention resides in a decorative paper base formed out of paper pulp containing pulp fibers and filler, wherein the paper pulp contains a pulp mixture comprising of a non-modified and a cationically modified pulp, wherein the cationically modified pulp exhibits an effective cationic charge of 20 to 300 mmol/kg, and wherein the share of cationically modified pulp in the pulp mixture measures at least 5 wt. o.

- 6a -In another aspect, the present invention resides in a decorative paper or decorative film, comprising a decorative paper base prepared by a pulp fiber and filler containing pulp mixture wherein the pulp mixture includes a non-modified and a cationically modified pulp, wherein the cationically modified pulp exhibits an effective cationic charge of 20 to 300 mmol/kg and that the share of can onically modified pulp in the pulp mixture measures at least 5 wt.$.
The invention will be described in more detail in the following examples. Information in percent by weight relate to the weight of the pulp, unless otherwise indicated.
Example 1 A pulp mixture consisting of 16.7 wt.o of a eucalyptus pulp modified via glycidyl trimethyl-ammonium _ 7 _ , .
chloride (Quab~ 151) with a charge density of 39.8 mmol/kg and 83.3 wt.% of a standard eucalyptus pulp with an average fiber length of 0.7 mm was refined at a consistency of 3 % to a freeness value of 33 °SR. 100 wt.% Ti02 (rutile, d=3.9 g/m3) and 2 wt.%
polyamide/polyamine-epichlorohydrine resin were then added to the pulp suspension, and a paper base with a G.S.M. of 97 g/m2 was fabricated from it.
Example 2 A pulp mixture consisting of 50 wt.% of a eucalyptus pulp modified via glycidyl trimethyl-ammonium chloride with a charge density of 34.8 mmol/kg and 50 wt.% of a standard eucalyptus pulp was refined at a consistency of 3 % to a freeness value of 33 °SR. The other substances specified in Example 1 were added to the pulp suspension, and a paper base with a G.S.M. of 95 g/m2 was fabricated from it.
Example 3 A pulp mixture consisting of 16.7 wt.% of a eucalyptus pulp modified via glycidyl trimethyl-ammonium chloride (Quab~ 151) with a charge density of 65.5 mmol/kg and 83.3 wt.% of a standard eucalyptus pulp was refined at a consistency of 3 % to a freeness value of 38 °SR.
The other substances specified in Example 1 were added to the pulp suspension, and a paper base with a G.S.M. of 95 g/m2 was fabricated from it.
Example 4 A pulp mixture consisting of 16 wt.% of a eucalyptus pulp modified via 3-chloro-2-hydroxypropyldimethyldodecyl -ammonium chloride (Quab~ 342) with a charge density of 56.5 mmol/kg and 84 wt.% of a standard eucalyptus pulp was refined at a consistency of 3 % to a freeness value - 8 - , of 39 °SR. The other substances specified in Example 1 were added to the pulp suspension, and a paper base with a G.S.M. of 95 g/m2 was fabricated from it.
- Example 5 A pulp mixture consisting of 16.7 wt.% of a eucalyptus pulp modified via 2-(methacryloyloxy)ethyltri-methyl-ammonium chloride and acrylamide with a charge density of 153.7 mmol/kg and 83.3 wt.% of a standard eucalyptus pulp was refined according to Example 1 and processed into a paper base with a G.S.M. of 96 g/m2 with the same substances (pigment and wet strength agent).
Comparison Example Substances were added to a pulp suspension consisting of 100 wt.% standard eucalyptus pulp with a consistency of 3 o and a pulp fiber freeness value of 36 °SR according to Example 1, and a paper base with a G.S.M. of 94 g/m2 was fabricated from it.
Test of Decorative Paper Basis Obtained According to the Examples and Comparison Example The following test procedures were used to evaluate the finished decorative paper bases:
Measurement of Cationic Charge in Pul The determination takes place according to internal method 4 at Darmstadt Technical University. The measuring method developed for determining cationic groups in pulps is a colorimetric procedure. The colorimetric method employs dye ions of the dye methyl orange to neutralize the charges in and on the fibers. The solution becomes depleted of dye ions in the process. This decrease in concentration is detected in a UV spectrometer. The _ g _ quantity of the methyl orange adsorbed by cationic groups is calculated from the difference between the quantity of methyl orange colorimetrically determined in the blind sample and that determined in the residual sample. The content of cationic groups is indicGted in mmol/kg of pulp.
Resin Absorption f°s The purpose of this test is to evaluate the ability of a decorative paper to absorb a melamine resin. To this end, 2 test strips (15 x 100 mm) were dipped in melamine resin MW 550, blotting paper is placed between the two strips over a flat surface, loaded with a contact weight for 15 s and then reweighed. Resin absorption is calculated in $ of amount weighed out.
Opacity Opacity is a measure for the light permeability of paper. It was measured on 8 x 8 cm paper test strips using the Elrepho~2000 colorimeter.
Dry Tensile Strength This test is used to determine the tensile strength and extensibility of paper bases. It is executed using 15 x 200 mm paper strips in a tensile tester made by Lorentzen & Wettre according to DIN 53112. The values are given in N. The higher the numerical value, the better the dry strength.
Wet Tensile Strencrth This test is performed to evaluate the wet tensile strength of the paper bases. To this end, 15 mm wide test strips were immersed in distilled water for 5 minutes.
The wet strips were then tested for wet tensile strength in a tensile testing machine. The measured values are *Trade Mark ' - 10 - ' given in N. The lower the numerical value, the poorer the wet strength.
Ash Content 1 g of paper in the form of a strip is conditioned for at least 30 min. at 23 °C/50 o relative humidity, and then introduced into the incinerator and reduced to ashes. The ash is transferred to a porcelain crucible and weighed. The ash in °s arises from the amount weighed out in g x 100. The ash content can be converted into g/m2.
Table 1 summarizes the test results.

Test Examples Compar ison Dry tensile strength, 30.0 32.0 29.6 25.1 29.6 24.4 N

Wet tensile strength [N] 6.1 6.0 4.8 4.8 6.1 6.1 Ash content [g/m'] 33.2 34.0 32.4 32.0 32.4 32.0 Opacity [%] 91.4 91.0 91.7 91.4 91.0 91.1 Resin absorption [~] 85.5 85.5 84.6 84.8 85.0 85.4 The results show that the dry strength of the decorative paper bases is improved through the use of cationically modified pulps, wherein the additional use of dry strength agents is unnecessary. The impregnating capacity and opacity of the decorative paper bases according to the invention are very good. Even an improved retention of the employed filler could be observed.
The decreased wet strength observed in several tests can be brought to the desired level by increasing the percentage of wet strength agent, or by adding anionic substances.

Claims (6)

1. A decorative paper base formed out of paper pulp containing pulp fibers and filler, wherein the paper pulp contains a pulp mixture comprising of a non-modified and a cationically modified pulp, wherein the cationically modified pulp exhibits an effective cationic charge of 20 to 300 mmol/kg, and wherein the share of cationically modified pulp in the pulp mixture measures at least 5 wt.%.

2. A decorative paper base according to claim 1, wherein the pulp fibers are modified with quaternary ammonium compounds with glycidyl function.

3. A decorative paper base according to claim 1 or claim 2, wherein the cationically modified pulp is a short-fiber pulp.

4. A decorative paper base according to any one of claims 1 to 3, wherein the paper pulp contains wet strength agents in an amount of 0.3 to 2 wt.% based on the weight of the pulp.

5. A decorative paper base according to any one of claims 1 to 4, wherein the filler is titanium dioxide, calcium carbonate, kaolin, talcum or a mixture thereof.

6. A decorative paper or decorative film, comprising a decorative paper base prepared by a pulp fiber and filler containing pulp mixture wherein the pulp mixture includes a non-modified and a cationically modified pulp, wherein the cationically modified pulp exhibits an effective cationic charge of 20 to 300 mmol/kg and that the share of cationically modified pulp in the pulp mixture measures at least 5 wt.%.