Note: Descriptions are shown in the official language in which they were submitted.
,. 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.
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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
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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
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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.
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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
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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.
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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
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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
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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
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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
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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.
TABLE 1
Test Examples Compar
ison
1 2 3 4 5
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.
