U.S. patent application number 10/498085 was filed with the patent office on 2005-03-24 for production of paper board and cardboard.
Invention is credited to Blum, Thierry, Bohlmann, Klaus, Hemel, Ralf, Linhart, Friedrich.
Application Number | 20050061461 10/498085 |
Document ID | / |
Family ID | 7709591 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050061461 |
Kind Code |
A1 |
Linhart, Friedrich ; et
al. |
March 24, 2005 |
Production of paper board and cardboard
Abstract
Paper, board and cardboard are produced by draining a paper
stock in the presence of at least one cationic polymer on a wire by
a process in which a mixture of at least one substantially linear,
cationic polyelectrolyte and an optical brightener is added to the
paper stock before sheet formation, said mixture containing at
least two parts by weight of the polyelectrolyte per part by weight
of the optical brightener.
Inventors: |
Linhart, Friedrich;
(Heidelberg, DE) ; Blum, Thierry; (Neustadt,
DE) ; Hemel, Ralf; (Worms, DE) ; Bohlmann,
Klaus; (Ludwigshafen, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
7709591 |
Appl. No.: |
10/498085 |
Filed: |
June 10, 2004 |
PCT Filed: |
December 6, 2002 |
PCT NO: |
PCT/EP02/13843 |
Current U.S.
Class: |
162/158 ;
162/162; 162/168.2; 162/168.3 |
Current CPC
Class: |
D21H 17/47 20130101;
D21H 17/72 20130101; D21H 21/30 20130101; D21H 23/04 20130101 |
Class at
Publication: |
162/158 ;
162/162; 162/168.2; 162/168.3 |
International
Class: |
D21H 023/04; D21H
017/55 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 2001 |
DE |
101620527 |
Claims
1. A process for the production of paper and cardboard comprising
draining a paper stock in the presence of at least one cationic
polymer on a wire, and wherein a mixture comprising at least one
substantially linear, cationic polyelectrolyte selected from
polymers containing vinylamine units, copolymers of acrylamide and
cationic monomers or polymers of diallyldimethylammonium chloride,
one or more optical brighteners, one or more solvents, and
optionally, a retention and drainage aid, is added to the paper
stock before sheet formation, and wherein at least two parts by
weight of the polyelectrolyte is used per part by weight of the
optical brightener.
2. The process as claimed in claim 1, wherein the at least one
cationic polyelectrolyte is a hydrolyzed homopolymer of
N-vinylformamide having a degree of hydrolysis from 1 to 99 mol
%.
3. The process as claimed in claim 1, wherein the at least one
cationic polyelectrolyte is selected from copolymers of acrylamide
and cationic monomers, and wherein the cationic monomers are
monomers containing an amino group or an ammonium group.
4. The process as claimed in claim 1, wherein at least 5 parts by
weight of at least one cationic polymer is used per part by weight
of optical brighteners.
5. The process as claimed in claim 1, wherein the mixture
comprises: (i) from 0.05 to 5% by weight of the one or more optical
brighteners, (ii) from 1 to 30% by weight of the at least one
substantially cationic polymer, (iii) from 98.95 to 65% by weight
of the one or more solvents and optionally the retention and
drainage aid.
6. A process for producing paper, board or cardboard, each having
high degree of whiteness, comprising adding to paper stock a
mixture comprising: (i) from 0.05 to 5% by weight of at least one
optical brightener, (ii) from 1 to 30% by weight of at least one
substantially cationic polymer selected from polymers containing
vinylamine units, copolymers of acrylamide and cationic monomers or
polymers of diallyldimethylammonium chloride, and (iii) from 98.95
to 65% by weight of at least one solvent and optionally a retention
and drainage aid.
7. A paper, board or cardboard obtained by a process as claimed in
claim 1.
8. The process as claimed in claim 2, wherein at least 5 parts by
weight of at least one cationic polymer is used per part by weight
of optical brighteners.
9. The process as claimed in claim 3, wherein at least 5 parts by
weight of at least one cationic polymer is used per part by weight
of optical brighteners.
10. The process as claimed in claim 2, wherein the mixture
comprises: (i) from 0.05 to 5% by weight of the one or more optical
brighteners, (ii) from 1 to 30% by weight of the at least one
substantially cationic polymer, (iii) from 98.95 to 65% by weight
of the one or more solvents and optionally the retention and
drainage aid.
11. The process as claimed in claim 3, wherein the mixture
comprises: (i) from 0.05 to 5% by weight of the one or more optical
brighteners, (ii) from 1 to 30% by weight of the at least one
substantially cationic polymer, (iii) from 98.95 to 65% by weight
of the one or more solvents and optionally the retention and
drainage aid.
12. The process as claimed in claim 4, wherein the mixture
comprises: (i) from 0.05 to 5% by weight of the one or more optical
brighteners, (ii) from 1 to 30% by weight of the at least one
substantially cationic polymer, (iii) from 98.95 to 65% by weight
of the one or more solvents and optionally the retention and
drainage aid.
13. A paper, board or cardboard obtained by a process as claimed in
claim 2.
14. A paper, board or cardboard obtained by a process as claimed in
claim 3.
15. A paper, board or cardboard obtained by a process as claimed in
claim 4.
16. A paper, board or cardboard obtained by a process as claimed in
claim 5.
17. A composition comprising: (i) from 0.05 to 5% by weight of at
least one optical brightener, (ii) from 1 to 30% by weight of at
least one substantially cationic polymer selected from polymers
containing vinylamine units, copolymers of acrylamide and cationic
monomers or polymers of diallyldimethylammonium chloride, and (iii)
from 98.95 to 65% by weight of at least one solvent and optionally
a retention and drainage aid.
Description
[0001] The present invention relates to a process for the
production of paper and cardboard by draining a paper stock in the
presence of at least one cationic polymer on a wire.
[0002] It is generally known that paper substantially comprises
fibers, consisting of wood and/or of cellulose, and, if required,
of mineral fillers, in particular calcium carbonate and/or aluminum
silicate, and that the essential process in papermaking consists in
separating these fibers and fillers from a dilute aqueous
suspension of these substances with the aid of at least one wire.
It is also known that certain chemicals are added to the suspension
of fibers and fillers in water, both for improving the separation
process and for achieving or improving certain properties of the
paper. A very up-to-date overview of the paper chemicals which can
be generally used and their use is to be found in--Paper Chemistry,
J. C. Roberts ed., Blackie Academic & Professional, London,
Second edition 1996 (ISBN 0 7514 0236 2)--and in--Applications of
Wet-End Paper Chemistry, C.O. Au and I. Thorn eds., Blackie
Academic & Professional, London, 1995 (ISBN 0 7514 0034 3). As
is evident from the literature cited, many of the paper chemicals
used are cationic water-soluble polymers or, in other words,
cationic polyelectrolytes or are polycations preferably having a
medium or high molecular weight. These products are added to the
very dilute paper fiber suspension before the paper sheet is formed
therefrom on the wire. Depending on their composition, they ensure,
for example, that more fine material remains behind on the wire or
that the water is separated off more rapidly on the wire or that
certain substances are fixed on the paper fibers and hence do not
enter the white water, it being possible for both cleanliness of
the white water and the effect of the fixed substances, e.g. dyes
or sizes, on the properties of the final paper product to be
important in the case of the latter property. However, polycations
can also increase the strength of the paper or impart improved
residual strength to the paper in the wet state. If the object of a
cationic polyelectrolyte is to retain more fine material on the
wire and to accelerate the removal of the water on the wire, it is
referred to as a retention aid. If the cationic polyelectrolyte is
to bind undesired or desired substances, for example anionic
oligomers and polymers, resins, tacky impurities, dyes, sizes,
strength agents, etc., to the fibers, the term fixing agent is
used. If the cationic polyelectrolyte improves a paper property
relevant to strength, it is a strength agent.
[0003] One of the most important objects in the production of
papers and cardboards which are to be written on or printed on,
also referred to below as graphic arts papers, is a high level of
whiteness of the surface of the paper or of the cardboard. A high
level of whiteness not only imparts the impression of cleanliness
and safety but also increases the legibility of the script as a
result of the greater contrast to the ink, especially in poor
illumination. A particular advantage of the high level of whiteness
is evident if the paper or cardboard is to be printed on, written
on or painted in color. The whiter the surface, the better and more
natural is the color contrast, particularly when writing on,
printing on or painting with light or translucent colors or pastel
shades. As a result of the recently increasing use of wastepaper in
the production of graphic arts papers, the papermaker's product is
substantially grayer than with the use of fresh fibers.
[0004] For these reasons, the papermakers are making considerable
efforts to increase the whiteness of their product, particularly if
it is paper for graphic arts purposes. As early as during the
preparation of the raw materials, whether chemical pulp, mechanical
pulp, deinked wastepaper stock or pigment, a major effort is made
to obtain these raw materials in as white a form as possible.
During the actual papermaking, an attempt is made to avoid all
assistants and conditions which might impair the whiteness of the
paper.
[0005] A known method for increasing the whiteness and brightness
of paper is the use of optical brighteners, which, according to the
prior art to date, is added to the paper pulp during various
operations of papermaking and of paper conversion or is applied to
the paper.
[0006] These are dye-like fluorescent compounds which absorb
shortwave, ultraviolet light invisible to the human eye and emit it
again as longer-wave blue light, with the result that the human eye
perceives a higher level of whiteness and the degree of whiteness
is thus increased.
[0007] The optical brighteners used in the paper industry are
generally 1,3,5-triazinyl derivatives of
4,4'-diaminostilbene-2,2'-disulfonic acid, which derivatives may
carry additional sulfo groups, for example 2, 4 or 6 altogether. An
overview of such brighteners is to be found, for example, in:
Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 2000
Electronic Release, OPTICAL BRIGHTENERS--Chemistry of Technical
Products. However, more recent brightener types are also suitable,
for example derivatives of 4,4'-distyrylbiphenyl, as also described
in the abovementioned Ullmann's Encyclopedia of Industrial
Chemistry.
[0008] The optical brighteners can be used in various phases of
papermaking and paper conversion. The optical brighteners can be
added, for example, to the paper pulp but also in a size press
together with surface sizes or strength agents, e.g. starch, or
together with further assistants. Most frequently, optical
brighteners are used in paper coating slips with which paper and
cardboard are coated. The use in the pulp is particularly
advantageous when the uniformity of the brightening and good
fastness to bleeding are important (cf. for example W. Bieber, A.
Brockes, B. Hunke, J. Krusemann, D. Loewe, F. Muller, P.
Mummenhoff, in Blankophor.RTM.--Optische Aufheller fur die
Papierindustrie, Bayer, Geschftsbereich Farben, Leverkusen, SP 600,
8.89, page 51). Even when optical brighteners are used in the paper
coating slips, adding optical brighteners to the paper pulp is
advisable (see above, W. Bieber, et al.; K. P. Kreutzer,
Grundprozesse der Papiererzeugung 2: Grenzflchenvorgnge beim
Einsatz chemischer Hilfsmittel, H.-G. Volkel and R. Grenz (eds.),
PTS Munich, 2000, PTS manuscript: PTS-GPE--SE 2031-2, Chapter 8,
page 21).
[0009] However, the use of optical brighteners leads to optimum
success only when they are present in the paper not only in an
optimum distribution but also in optimum chemical structure and
conformation, since, for example in the case of stilbenes, only the
trans form is optically active and this exhibits maximum
fluorescence only when it is distributed in monomolecular form and
is fixed in a plane (see above, K. P. Kreutzer). When added to the
paper pulp, this generally results through adsorption onto the
cellulose. The brighteners used are chemically modified so that
they have a high affinity to cellulose and therefore require no
additional fixing agents or brightener enhancers, i.e. carriers. On
the contrary, when the optical brighteners are used in the paper
pulp, it is necessary to pay greater attention to ensuring that no
further chemicals in the pulp reduce the effects of the brighteners
(cf. literature above). The presence of cationic polymers is
considered to be particularly harmful to the action of optical
brighteners. In the paper industry, they are generally considered
as fluorescence extinguishers, cf. W. Bieber et al,
Blankophor.RTM.--Optische Aufheller fur die Papierindustrie, Bayer
AG, SP600, 8.89, page 59.
[0010] EP-A-0 192 600 discloses stable solutions of optical
brighteners. They contain from 10 to 500 parts by weight of a
polyethylene glycol having an average molar mass of from 1 000 to 3
000 and at least 20% by weight, based on the total mixture, of
water per 100 parts by weight of a brightener. The mixtures are
used as optical brighteners in paper coating slips.
[0011] EP-A-0 071 050 discloses linear, basic polymers which
contain 90-10 mol % of vinylamine units and 10-90 mol % of
N-vinylformamide units in polymerized form. They are prepared by
free radical polymerization of N-vinylformamide and subsequent
partial hydrolysis of the polymer thus obtained. The partially
hydrolyzed poly-N-vinylformamides are used, for example, as
retention aids, drainage aids and flocculants in papermaking.
[0012] The prior German Application 101 38 631.1 discloses a
process for the production of coated paper having a high level of
whiteness, a base paper or a precoated paper being treated with at
least one substance which enhances the efficiency of optical
brighteners and then being coated with a paper coating slip which
contains an optical brightener. Examples of compounds which enhance
the efficiency of optical brighteners are homo- and copolymers of
N-vinylcarboxamides or the polymers obtainable therefrom by
hydrolysis and containing vinylamine units.
[0013] The prior German Application 101 42 887.1 discloses a
process for the production of coated papers having a high level of
whiteness, for example mixtures of
[0014] (i) from 0.05 to 5% by weight of at least one optical
brightener,
[0015] (ii) from 1 to 30% by weight of at least one polymer which
contains N-vinylcarboxamide units and
[0016] (iii) from 98.95 to 65% by weight of a solvent being applied
to the surface of the paper.
[0017] It is an object of the present invention to provide an
improved process for the production of paper, board and cardboard,
products having a higher degree of whiteness compared with the
known processes being obtained.
[0018] We have found that this object is achieved, according to the
invention, by a process for the production of paper, board and
cardboard by draining a paper stock in the presence of at least one
cationic polymer on a wire, if a mixture of at least one
substantially linear, cationic polyelectrolyte and an optical
brightener is added to the paper stock before sheet formation, at
least two parts by weight of the polyelectrolyte being used per
part by weight of the optical brightener.
[0019] Cationic polyelectrolytes are to be understood as meaning
polymers which carry positive charges and which are distributed
over the polymer chain. Cationic polyelectrolytes are furthermore
to be understood as meaning those substances which may be nonionic
in the dry state but, owing to their basic character, are
protonated in water or other solvents and hence carry positive
charges.
[0020] The mixtures which are added to the paper stock before sheet
formation usually contain
[0021] (i) from 0.05 to 5, preferably from 0.1-3, particularly
preferably 0.2-2,% by weight of an optical brightener,
[0022] (ii) from 1 to 30, preferably 2-20, particularly preferably
5-15,% by weight of at least one substantially cationic polymer
and
[0023] (iii) from 98.5 to 65, preferably 97.9-77, particularly
preferably 94.8-83,% by weight of at least one solvent,
[0024] the sum always being 100% by weight. If other assistants
typical for paper (see below) are also present, the content of
solvent iii) is reduced correspondingly.
[0025] The results obtained by the novel process were not to be
expected because, according to the general knowledge, it was to be
assumed that cationic polyelectrolytes would lead to extinguishing
of the fluorescence of the conventional optical brighteners (cf.
for example K. P. Kreutzer, loc. cit., Chapter 8, page 22; cf. W.
Bieber et al., loc. cit., pages 58, 65 and 71; F. Colling, The use
and mis-use of dyestuffs and fluorescent whitening agents, in
Applications of Wet-End Paper Chemistry, C.O. Au and I. Thorn ed.,
Blackie Academic & Professional, London, 1995, ISBN 0 7514 034
3, pages 130, 132-135). In addition, it is known from the prior art
that optical brighteners and cationic electrolytes are mutually
precipitated (cf. W. Bieber et al., loc. cit., page 59). Besides,
these views are widespread in the paper industry.
[0026] It is furthermore surprising that highly effective optical
brighteners which, owing to poor substantivity, cannot be used in
the paper pulp, for example stilbene derivatives having 6 sulfo
groups, are also suitable for the novel process (S. G. Murray, Dyes
and fluorescent whitening agents for paper, in Paper Chemistry, ed.
J. C. Roberts, 2.sup.nd edition, Blackie Academic &
Professional, Glasgow (1996), page 187). When they are used, no
fluorescence is detectable in the white water.
[0027] The cationic polyelectrolytes (ii) which can be used in the
novel process are known. For example, polymers which are known by
the following chemical trivial names can be used: polyvinylamine,
polyallylamine, poly(diallyldimethylammonium chloride), cationic
polyvinylformamide, cationic polyvinylpyrrolidone, cationic
polyvinylacetamide, cationic polyvinylmethylformamide, cationic
polyvinylmethylacetamide, poly(dimethylaminopropylmethacrylamide),
poly(dimethylaminoethyl acrylate), poly(diethylaminoethyl
acrylate), poly(acryloylethyltrimethyla- mmonium chloride),
poly(acrylamidopropyltrimethylammonium chloride),
poly(methacrylamidopropyltrimethylammonium chloride), cationic
polyacrylamide, poly(vinylpyridine), hexadimethrine bromide,
poly(dimethylamine-co-epichlorohydrin),
poly(dimethylamine-co-epichlorohy- drin-co-ethylendiamine),
poly(amidoamine-epichlorohydrin) and their salts if they are basic
polymers. Polymers containing vinylamine units, such as cationic
polyvinylformamides and polyvinylamine, and furthermore cationic
polyacrylamide and poly(diallyldimethylammonium chloride) are
preferred. Polymers which contain vinylamine units and are in the
form of the free bases or salts are particularly preferred.
[0028] The preparation of the cationic polyelectrolytes has long
been very well known.
[0029] The cationic polyelectrolytes (ii) which can be used in the
novel process have different molecular weights which are
characterized below with the aid of the Fikentscher K values. The
molecular weights of the cationic polyelectrolytes which can be
used according to the invention are not limited. As a rule, they
correspond to K values of from 20 to 200, preferably from 30 to
150, particularly preferably from 40 to 100 (the stated K values
are determined according to H. Fikentscher in 5% strength aqueous
sodium chloride solution at pH 7, 25.degree. C. and a polymer
concentration of 0.1% by weight).
[0030] The very particularly preferred polymers containing
vinylamine units, such as cationic polyvinylformamides, contain
vinylamine and vinylformamide units according to the formula (I)
1
[0031] where the ratio n:m is from 99:1 to 1:99 and p may be from
30 to 30 000. Some or all of the vinylamine units of the polymers
may be present as salts with mineral acids, such as hydrochloric
acid, sulfuric acid or phosphoric acid, or as salts with organic
acids (e.g. formic acid, acetic acid, propionic acid,
toluenesulfonic acid, benzenesulfonic acid or methanesulfonic
acid). The polymers containing vinylamine units are prepared by
polymerizing, for example, N-vinylformamide of the formula (II)
2
[0032] to give a polyvinylformamide of the formula (III) and partly
cleaving this with removal (or hydrolysis) of the formyl group to
give the copolymer (I). On complete hydrolysis of the formyl groups
of polyvinylformamides, polyvinylamines are obtained. The free
bases of the polymers containing vinylamine units are formed if the
hydrolysis is carried out using bases, such as sodium hydroxide
solution or potassium hydroxide solution, whereas the vinylamine
units of the polymers are present in salt form on hydrolysis with
acids. 3
[0033] A preferred degree of hydrolysis of the carboxamido groups
is from 5 to 90, particularly preferably from 10 to 50, mol %,
based on the N-vinylcarboxamide units contained in the
N-vinylcarboxamide polymers. The cleavage of the N-vinylcarboxamide
units contained in the polymer is preferably effected in the
presence of bases, for example sodium hydroxide, potassium
hydroxide, alkaline earth metal hydroxides, ammonia or amines.
[0034] Cationic polymers of N-vinylformamide are obtained in a
particularly suitable manner by hydrolytically cleaving
homopolymers of N-vinylformamide with defined amounts of acid or
base to give the desired degree of hydrolysis, as described in
EP-B-0 071 050 mentioned as prior art. The amino groups formed
thereby on the polymer chain are protonated to a greater or lesser
extent depending on the pH of the solution and thus impart a more
or less cationic character to the polymer.
[0035] If elimination of the formyl group is desired after the
polymerization, this can be carried out, for example, in water.
Elimination of the formyl group during the hydrolysis is effected
in general at from 20 to 200.degree. C., preferably from 40 to
180.degree. C., in the presence of acids or bases. The hydrolysis
in the presence of acids or bases is particularly preferably
carried out at from 70 to 90.degree. C.
[0036] From about 0.05 to 1.5 equivalents of an acid, such as
hydrochloric acid, hydrobromic acid, phosphoric acid or sulfuric
acid, per formyl group equivalent in the poly-N-vinylformamide are
required, for example, with the acidic hydrolysis. The pH in the
acidic hydrolysis is, for example, from 2 to 0, preferably from 1
to 0.
[0037] In addition the hydrolysis of the formyl groups of the
poly-N-alkyl-N-vinylformamide can also be carried out in an
alkaline medium, for example at a pH of from 11 to 14. This pH is
preferably established by adding alkali metal bases, e.g. sodium
hydroxide solution or potassium hydroxide solution. However, it is
also possible to use ammonia, amines and/or alkaline earth metal
bases. From 0.05 to 1.5, preferably from 0.4 to 1.0, equivalents of
a base are used for the alkaline hydrolysis.
[0038] The cleavage can also be carried out at high temperatures,
for example above 100.degree. C., preferably from 120 to
180.degree. C., particularly preferably from 140 to 160.degree. C.,
in the presence of a solvent, e.g. water, in the absence of acids
or bases. This is preferably carried out under conditions above the
critical point of the solvent, for example using supercritical
water.
[0039] In the hydrolysis (i.e. the formyl group is eliminated from
the poly-N-vinylformamide in water in the presence of acids or
bases), carboxylic acid, for example formic acid, or a salt thereof
is obtained as the byproduct. The solutions thus obtainable can be
used without further working-up in the novel process, but the
hydrolysis or solvolysis products can also be separated off. For
separating off low molecular weight fractions, for example neutral
salts, the solutions obtained are treated, for example, with ion
exchangers or subjected to an ultrafiltration.
[0040] The cationic polyacrylamides which can be used for the novel
process are known, cf. D. Horn, F. Linhart, in Paper Chemistry, ed.
J. C. Roberts, 2.sup.nd edition, Blackie Academic &
Professional, Glasgow (1996), pages 66-67, and literature cited
there.
[0041] They frequently consist of polymers of the formula (IV),
4
[0042] where A is oxygen or an NH group, R1 may be hydrogen or
lower alkyl of 1-3 carbon atoms, R2 and R3 may be lower alkyl of
1-5 carbon atoms or benzyl and R5 may be hydrogen or methyl, the
ratio n:m may be from 99:1 to 0:100, q may be 1 or 2, p may be from
50 to 50 000 and X.sup.- may be any desired anion, e.g. chloride,
bromide, 1/2 sulfate, hydrogen sulfate, methylsulfate,
ethylsulfate, nitrate, formate, acetate or toluenesulfonate. In
addition, acrylic acid or methacrylic acid can be incorporated as
polymerized units into the polymer chain up to an amount such that
the total charge of the polymer remains positive.
[0043] The poly(diallyldimethylammonium chloride) which can be used
in the novel process can be characterized, for example, with the
aid of the formula (V) 5
[0044] where n may be from 30 to 30 000. Such polymers have been
known for many years, cf. D. Horn, F. Linhart, in Paper Chemistry,
ed. J. C. Roberts, 2.sup.nd edition, Blackie Academic &
Professional, Glasgow (1996), page 70; G. Butler, in Polymeric
Amines and Ammonium Salts, ed. E. J. Goethals, Pergamon Press,
Oxford 125, (1980).
[0045] Other diallyldialkylammonium chlorides are also suitable,
for example those of the polymer formula (VI), 6
[0046] where R.sup.1 and R.sup.2, independently of one another, may
be alkyl of 2 to 4 carbon atoms, it also being possible for R.sup.1
or R.sup.2 to be hydrogen, and where n may be from 30 to 30
000.
[0047] Preferably used cationic polyelectrolytes are hydrolyzed
homopolymers of N-vinylformamide having a degree of hydrolysis of
from 1 to 99 mol %, copolymers of acrylamide and cationic monomers
(e.g. amino- or ammonium-containing monomers), polymers of
diallyldimethylammonium chloride and the
polyamidoamine/epichlorohydrin resins which can be used as wet
strength agents.
[0048] Cationic polyelectrolytes which are obtainable by
copolymerization of starting monomers of the abovementioned
polyelectrolytes can of course also be used for the novel process.
For example, copolymers of vinylformamide (formula (II)) and
diallyldimethylammonium chloride or of vinylformamide and basic
acrylates, as described in EP-B-0 464 043, and also copolymers of
acrylamide and diallyldimethylammonium chloride or other
diallyldialkylammonium chlorides can also be used. The solubility
of the cationic polyelectrolytes in the solvent (iii) used is as a
rule from at least 1% by weight to complete solubility, for example
at 20.degree. C.
[0049] The mixing ratios in the mixtures of the optical brighteners
and the cationic polyelectrolytes may be from 1:2 to 1:100, but a
substantial excess of cationic polyelectrolytes is advantageous.
Particularly advantageous is the use of optical brighteners and
cationic polyelectrolytes in the weight ratio of from 1:2 to 1:50,
very particularly preferably from 1:5 to 1:20.
[0050] All optical brighteners (i) can be used for the novel
process. For example, brighteners as described in Ullmann's
Encyclopedia of Industrial Chemistry, Sixth Edition, 2000
Electronic Release, OPTICAL BRIGHTENERS--Chemistry of Technical
Products, Section 2.1 to Section 2.9, can be used.
[0051] Suitable optical brighteners (i) belong, for example, to the
group consisting of the distyrylbenzenes, for example
cyano-substituted 1,4-distyrylbenzenes having cyano groups in the
positions 2' and 3" [CAS Reg. No. 79026-03-2] or in positions 2'
and 2" [13001-38-2], 3' and 3" [36755-00-7], 3' and 4" [79026-02-1]
and 4' and 4" [13001-40-6], or amphoteric compounds, e.g.
[84196-71-4], which carry a
--O--(CH.sub.2).sub.2--N.sup.+(C.sub.2H.sub.5).sub.2--CH.sub.2COO.sup.-
[0052] group in each case in the 2' and 2" positions, to the group
consisting of the distyrylbiphenyls, for example
4,4'-di(2-sulfostyryl)bi- phenyl disodium salt [27344-41-8],
4,4'-di(3-sulfostyryl)biphenyl disodium salt [51119-63-2],
4,4'-di(4-chloro-3-sulfostyryl)biphenyl disodium salt [42380-62-1],
4,4'-di(6-chloro-3-sulfostyryl)biphenyl disodium salt [60477-28-3],
4,4'-di(2-methoxystyryl)biphenyl [40470-68-6] or a
4,4'-di(styryl)biphenyl which carries a
--O--(CH.sub.2).sub.2--N.sup.+(CH.sub.3)(C.sub.2H.sub.5).sub.2.CH.sub.3OSO-
.sub.3.sup.-
[0053] group in position 2 on the styryl radical [72796-88-4], to
the group consisting of the divinylstilbenes, for example
4,4'-di(ethoxycarbonylvinyl)stilbene [60683-03-6] or
4,4'-di(cyanovinyl)stilbene [60682-87-3], to the group consisting
of the triazinylaminostilbenes, e.g. 1,3,5-triazinyl derivatives of
4,4'-diaminostilbene-2,2'-disulfonic acid, such as anilino
derivatives which carry the following radicals in each case in
position 3 on the triazine rings: methoxy (CAS Reg. No.
[3426-43-5]), aminomethyl [35632-99-6], ethylamino [24565-13-7],
hydroxyethylamino [12224-16-7], N-hydroxyethyl-N-methylamino
[13863-31-5], bis(hydroxyethyl)amino [4193-55-9], morpholino
[16090-02-1], phenylamino [133-66-4],
N-2-aminocarbonylethyl-N-2-hydroxyethylamino [68444-86-0] or such
as anilinosulfonic acid derivatives which carry the following
radicals in each case in position 3 on the triazine rings:
N-hydroxyethylamino and additionally on the anilino group in
position 5 of the triazine ring, sulfo in position 3 (CAS Reg. No.
[61968-74-9]), N-bis(hydroxyethyl)amino and, additionally on the
anilino group, sulfo in position 3 (CAS Reg. No. [12224-02-1]),
N-bis(2-hydroxypropyl)amino and, additionally on the anilino group,
sulfo in position 4 (CAS Reg. No. [99549-42-5]),
N-bis(hydroxyethyl)amino and, additionally on the anilino group,
sulfo in position 4 (CAS Reg. No. [16470-24-9]),
N-hydroxyethyl-N-methyl-amino- and, additionally on the anilino
group, sulfo in position 4 (CAS Reg. No. [74228-28-7]),
diethylamino and, additionally on the anilino group, sulfo in
positions 2 and 5 (CAS Reg. No. [83512-97-4]),
N-bis(hydroxyethyl)amin- o and, additionally on the anilino group,
sulfo in positions 2 and 5 (CAS Reg. No. [76482-78-5]), or
morpholino and, additionally on the anilino group, sulfo in
positions 2 and 5 (CAS Reg. No. [55585-28-9]), or to the group
consisting of the stilbenyl-2H-triazoles, e.g.
stilbenyl-2H-naphtho[1,2-d]triazoles, such as the sodium salt of
4-(2H-naphtho[1,2-d]triazol-2-yl)stilbene-2-sulfonic acid
[6416-68-8] or those which carry sulfo in position 6 on the
naphthol ring and at position 2 of the stilbene skeleton
[2583-80-4], or cyano in position 2 and chlorine in position 4' on
the stilbene skeleton [5516-20-1] or, for example,
bis(1,2,3-triazol-2-yl)stilbenes, such as
4,4'-bis(4-phenyl-1,2,3-triazol-2-yl)stilbene-2,2'-disulfonic acid
dipotassium salt [52237-03-3] or
4,4'-bis(4-(4'-sulfophenyl)-1,2,3-triazo-
l-2-yl)stilbene-2,2'-disulfonic acid tetrasodium salt [61968-72-7],
or to the group consisting of the benzoxazoles, e.g.
stilbenylbenzoxazoles, for example
5,7-dimethyl-2-(4'-phenylstilben-4-yl)benzoxazole [40704-04-9],
5-methyl-2-(4'-(4"-methoxycarbonyl)-phenylstilben-4-yl)-benzoxazole
[18039-18-4] or those which carry other heterocycles in the 4"
position, e.g. [64893-28-3], or bis(benzoxazoles), e.g. ethylene-,
thiophene-, naphthylene-, phenylethylene- or stilbene-bridged
bisbenzoxazoles, such as those having the CAS numbers [1041-00-5],
[2866-43-5], [7128-64-5], [5089-22-5], [1552-46-1], [1533-45-5] or
[5242-49-9].
[0054] It is furthermore possible to use furans, benzo[b]furans and
benzimidazoles, e.g. bis(benzo[b]furan-2-yl)biphenyls, for example
sulfonated 4,4'-bis(benzo[b]furan-2-yl)biphenyls, or cationic
benzimidazoles, for example 2,5-di(1-methylbenzimidazol-2-yl)furan
[4751-43-3], [72829-17-5], [74878-56-1], [74878-48-1] or
[66371-25-3], or 1,3-diphenyl-2-pyrazolines, e.g.
1-(4-amidosulfonylphenyl)-3-(4-chlorophe- nyl)-2-pyrazoline
[2744-49-2], [60650-43-3], [3656-22-2], [27441-70-9], [32020-25-0],
[61931-42-8] or [81209-71-4], and tertiary and quaternary amine
salts of 1,3-diphenyl-2-pyrazoline derivatives, e.g. [106359-93-7],
[85154-08-1], [42952-22-7], [63310-12-3][12270-54-1] or
[36086-26-7], and coumarins, e.g. 7-diethylamino-4-methylcoumarin
[91-44-1] and [6025-18-9], [19683-09-1], [3333-62-8], [63660-99-1],
[26867-94-7][52725-14-1] and naphthalimides, e.g.
4-acetylamino-N-(n-buty- l)naphthalimide [3353-99-9],
4-methoxy-N-methylnaphthalimide [3271-05-4], [3271-05-4],
[22330-48-9], [25826-31-7], [26848-65-7] or [60317-11-5], and
1,3,5-triazin-2-yl derivatives, for example
(4,6-dimethoxy-1,3,5-tria- zin-2-yl)pyrene [3271-22-5] or
4,4'-di(4,6-diphenyl-1,3,5-triazin-2-yl)sti- lbene [6888-33-1].
[0055] 4,4'-Distyrylbiphenyl derivatives or stilbene derivatives
which are substituted by up to 6, particularly preferably by 2, 4
or 6, sulfo groups can preferably be used, preferably the
Blankophor.RTM. brands from Bayer AG, particularly preferably
Blankophor.RTM. P and Blankophor.RTM. PSG, preferably furthermore
the Tinopal.RTM. brands from Ciba Specialty Chemicals, particularly
preferably Tinopal.RTM. MC liquid, Tinopal.RTM. ABP-Z liquid,
Tinopals SPP-Z liquid and Tinopal.RTM. SK-B liquid and preferably
furthermore the Leukophor.RTM. brands from Clariant AG,
particularly preferably Leukophor.RTM. APN, UO, NS or SHR.
[0056] The optical brighteners and cationic polymers which contain
polymerized vinylformamide units can be added separately from one
another to the paper stock, the cationic polyelectrolyte being
metered first, followed by the optical brightener, or the sequence
of addition being reversed. Suitable solvents (iii) for the
mixtures are, for example, water, methanol, ethanol, isopropanol,
n-propanol, n-butanol, dimethylformamide and N-methylpyrrolidone,
water being preferred. The concentration should be chosen so that
the respective metering processes and subsequent dilution processes
can be carried out optimally owing to, for example, the viscosity
of the mixture. Optimum viscosities for various metering processes
and dilution processes are known to a person skilled in the art.
Customary concentrations of the mixtures are from 2 to 20% by
weight.
[0057] The molecular weight of the cationic polyelectrolyte to be
used according to the invention should be adapted to the respective
desired profile of the polyelectrolytes. If the cationic
polyelectrolyte is to act, for example, as a retention aid in
papermaking, cationic polymers having a very high molecular weight
are preferably used. If the cationic polymers are to be effective
as fixing agents or as strength agents, cationic polymers having
medium to low molecular weights are used. The addition of retention
aids and drainage aids to the paper stock before drainage on the
wire is part of the general prior art. The cationic polymers
generally used have very high molecular weights of from 2 to 20
million Dalton (cf. F. Linhart, Retention, PTS-Seminar--Grundlagen
der Chemie fur Papieringenieure, Part 2, J. Weigl and R. Grenz
(eds.), Munich: PTS Munich, 1991, CP--SE 111, Chapter 7, page 9).
However, cationic polymers having molecular weights of from 500 000
to 2 million Dalton are also successfully used as retention aids.
The amounts of these polymers used are from 50 g/t to 5 kg/t,
preferably from 100 g/t to 2 kg/t, based on dry paper stock.
[0058] The cationic fixing agents added in many cases to the paper
stock have substantially lower molecular weights which differ very
greatly depending on the chemical nature and the function of the
polymer and are from 10 000 to 500 000 Dalton. The amounts of
fixing agents used are from 100 g/t to 2 kg/t, based on dry paper
stock. The molecular weights of polymeric cationic strength agents
vary in the very wide range of from a few hundred Dalton, as is
possible, for example, in the case of reactive wet-strength agents
through 100 000 to 500 000 Dalton in the case of synthetic
dry-strength agents (J. Marton, Dry-Strength Additives, in Paper
Chemistry, J. C. Roberts ed., Blackie Academic & Professional,
London, Second edition 1996, ISBN 0 7514 0236 2) to extremely high
molecular weights in the case of cationic polysaccharides, such as
starches or vegetable gums. In the case of the strength agents the
amounts used may range from 0.5 to 100 kg/t.
[0059] The present invention also relates to the use of mixtures
of
[0060] (i) from 0.05 to 5% by weight of at least one optical
brightener,
[0061] (ii) from 1 to 30% by weight of at least one substantially
cationic polymer and
[0062] (iii) from 98.95 to 65% by weight of at least one
solvent
[0063] as an additive to the paper stock in the production of
paper, board and cardboard having a high degree of whiteness. The
mixtures may be dispersions or, preferably, solutions.
[0064] The mixtures of the two components (i) and (ii) are metered
into the paper stock by the methods customary in the paper
industry. This means that the mixtures are diluted with water
continuously or batchwise to concentrations of from 0.01 to 1% by
weight before addition to the paper stock, in order to achieve more
rapid and more uniform mixing with the paper stock. However, this
does not mean that the mixtures cannot be added undiluted or in
less dilute form to the paper stock. The feed point of the mixtures
depends on the requirements and on the desired profile of the
cationic polyelectrolyte in the mixture. If the mixture is intended
not only to increase the whiteness of the paper but also
simultaneously to increase the retention and the drainage rate,
addition in the low-density stock shortly before the head box,
before or after the pressure screen, is appropriate. When the
mixture is used as a whiteness-increasing fixing agent, the mixture
can be added throughout the stock preparation region, for example
also in the high-density stock, in the mixing chest, in the machine
chest or to the individual stock components before they are mixed.
If the cationic polyelectrolyte in the mixture is to act as a
strength agent, it is advisable to add the mixture at a point which
is customary for the addition of strength agents, for example in
the mixing chest or machine chest, but also before the beater or in
the low-density stock region. For all applications, the optimum
metering point must be determined in each individual case by
practical experiments.
[0065] The novel process is preferably used in the production of
highly white papers and cardboards whose starting materials should
already have sufficient basic whiteness. Highly white fibers and
fillers are therefore mainly used for this purpose. The fibers
which may be used primarily include chemical pulps, for example
bleached sulfate pulp based on conifers, birches or eucalyptus, and
beech sulfite pulp, based on spruces and on beeches and other
deciduous trees, but also chemical pulps which are obtained from
wood by other processes. Bleached mechanical pulps, e.g.
groundwood, pressure groundwood (PGW), refiner mechanical pulp
(RMP), thermomechanical pulp (TMP) or chemothermomechanical pulp
(CTMP, APTMP and further variants), based on conifers and aspen or
other suitable deciduous trees, are furthermore suitable. Also
suitable for this purpose are fibers from annuals, e.g. cotton,
cotton linters, bleached straw pulp from straw of various cereal
species, bleached bagasse pulp, hemp, flax, kenaf, etc. A very
important fiber of the novel process is a bleached fiber freed from
printing inks and based on waste graphic arts papers, i.e. deinked
pulp (DIP). The fillers suitable for the novel process are
generally aluminum silicates, such as kaolin or modifications
obtained by further treatment thereof, magnesium silicates, e.g.
talc, calcium carbonate in the form of ground marble or limestone
or in the form of natural or ground chalk or in the form of
precipitated calcium carbonate, calcium sulfate in the form of
gypsum, or titanium dioxide.
[0066] The papers, boards or cardboards produced by the novel
process can be printed on in conventional processes, for example
offset, letterpress or gravure printing processes, flexographic
printing processes or digital printing processes, e.g. laser
printing or inkjet printing processes, but can also be otherwise
processed or converted, e.g. coated.
[0067] The novel process helps the person skilled in the art to
perform the difficult task of producing papers, boards and
cardboards in an improved process or with higher quality and
simultaneously increased whiteness with relatively simple means and
high flexibility.
[0068] In the examples which follow, parts are by weight. The K
values of the polymers were determined according to H. Fikentscher,
Cellulose-Chemie, 13 (1932), 58-63 and 71-74, in 5% strength by
weight aqueous solution at pH 7, 25.degree. C. and a polymer
concentration of 0.1% by weight.
EXAMPLE
[0069] A paper having a basis weight of 80 g/m.sup.2 was produced
according to the prior art on an experimental paper machine from an
aqueous paper stock comprising 70 parts of birch sulfate pulp, 30
parts of pine sulfate pulp, 20 parts of chalk filler
(Hydrocarb.RTM. 60 from Pluss-Staufer AG), 0.05 part of stock
deaerator (Afranil.RTM. SLO from BASF Aktiengesellschaft), 1.0 part
of engine size (Basoplast.RTM. 2018 LC from BASF
Aktiengesellschaft) and 0.5 part of soluble cationic starch
(Solvitose.RTM. BPN from Avebe).
[0070] 1 part of an aqueous solution containing 10% by weight of a
medium molecular weight polyvinylformamide having a K value of
about 90 and a degree of hydrolysis of 30% and 0.5% (solid) of an
optical brightener having 4 sulfo groups (Tinopal.RTM. ABP-Z
liquid) was added as a retention aid, after the pressure screen.
The retention was determined by comparison of the solids
concentrations of the finally diluted paper pulp before the head
box and of the white water (cf. F. Linhart, Retention,
PTS-Seminar--Grundlagen der Chemie fur Papieringenieure, Part 2, J.
Weigl and R. Grenz (eds.), Munich: PTS Munich, 1991, CP--SE 111,
Chapter 7, page 1). The whiteness and the calorimetric values
according to the CIELAB system (DIN 6174) were determined for the
paper obtained as the end product. Furthermore, the paper obtained
as the end product was checked visually for fluorescence by
illumination with an ultraviolet lamp. The complete fixing of the
brightener in the paper was investigated by impregnating a strip of
highly absorptive white wood-free paper with white water and
checking visually for fluorescence under illumination with
ultraviolet light.
[0071] In the comparative experiment, 0.02 part of high molecular
weight cationic polyacrylamide (Polymin.RTM. PR 8140 from BASF
Aktiengesellschaft) was used according to the prior art as a
retention aid before the pressure screen, and 0.3 part of bentonite
activated with alkali (VO 004 from Erbsloh) was used after the
pressure screen.
[0072] The results of the investigations are recorded in the table
below.
1 TABLE Comparative Invention example Retention (%) 95.1 80.5 CIE
whiteness according to 94.3 81.4 DIN 6174 a* (Red shift) 1.18 0.38
b* (Blue shift) -0.53 2.39 Fluorescence of the paper strong none
Fluorescence of the white water none none
[0073] As is evident from the table, the novel process gives very
good retention and simultaneously greatly increases the whiteness
of the paper, the desired shift in hue to blue and red occurring.
Particularly surprising is the extent of the increase in whiteness
when it is considered that only 0.005 part of optical brightener,
based on about 122 parts of solid paper stock, was used as a
proportion of the mixture.
* * * * *