U.S. patent application number 12/067818 was filed with the patent office on 2008-10-30 for reducing the water and water vapour absorbence and enhancing the dimensional stability of paper and paper products and use of coated paper products.
Invention is credited to Simon Champ, Roland Ettl.
Application Number | 20080264587 12/067818 |
Document ID | / |
Family ID | 37596227 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264587 |
Kind Code |
A1 |
Champ; Simon ; et
al. |
October 30, 2008 |
Reducing the Water and Water Vapour Absorbence and Enhancing the
Dimensional Stability of Paper and Paper Products and Use of Coated
Paper Products
Abstract
The invention relates to a method for reducing the absorption of
water and water vapor and for increasing the dimensional stability
of paper and paper products by treatment with an aqueous solution
and/or dispersion of at least one reactive material which reacts
with itself and/or cellulose fibers with crosslinking, cellulose
fibers or a paper product obtained therefrom by drainage on a wire
being compressed, the compressed paper product then being brought
into contact with an aqueous solution and/or dispersion of the
reactive material, the compression being eliminated with further
action of the aqueous solution and/or dispersion and the paper
product being dried and crosslinked, and to the use of the coated
paper products thus obtainable and/or of the coated cellulose
fibers which can be produced therefrom by defibrating as an
additive to thermoplastics and as an additive to heat-curable
plastics.
Inventors: |
Champ; Simon; (Ludwigshafen,
DE) ; Ettl; Roland; (Ketsch, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
37596227 |
Appl. No.: |
12/067818 |
Filed: |
October 12, 2006 |
PCT Filed: |
October 12, 2006 |
PCT NO: |
PCT/EP06/67304 |
371 Date: |
March 24, 2008 |
Current U.S.
Class: |
162/9 ;
162/164.1 |
Current CPC
Class: |
D21H 17/57 20130101;
D21H 23/28 20130101; D21H 17/37 20130101; D21H 17/49 20130101; D21H
21/16 20130101; D21H 17/48 20130101; D21H 17/52 20130101; D21H
17/51 20130101 |
Class at
Publication: |
162/9 ;
162/164.1 |
International
Class: |
D21C 9/00 20060101
D21C009/00; D21H 21/00 20060101 D21H021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 20, 2005 |
DE |
10 2005 050 658.5 |
Claims
1. A method for reducing the absorption of water and water vapor
and for increasing the dimensional stability of paper and paper
products comprising: treating cellulose fibers with an aqueous
solution and/or a dispersion of at least one reactive material
which reacts with itself and/or the cellulose fibers via
crosslinking, heating the treated cellulose fibers to a temperature
at which drying and crosslinking takes place, compressing the
cellulose fibers or a paper product obtained therefrom by drainage
on a wire, contacting the compressed paper product with an aqueous
solution and/or the dispersion of the reactive material,
eliminating the compression with further action of the aqueous
solution and/or the dispersion, and drying and crosslinking the
paper product.
2. The method according to claim 1, wherein the cellulose fibers
comprise at least 50% by weight of virgin fibers or a paper product
obtained therefrom by drainage on a wire, the cellulose fibers have
a water content of at least 0.7 g of water per g of dry cellulose
fibers, the cellulose fibers are compressed under a pressure of at
least 2.1 MPa, and the paper product is dried and is heated to a
temperature in the range of from 70 to 200.degree. C. for
crosslinking.
3. The method according to claim 1, wherein the aqueous solution
and/or the dispersion comprises, as reactive material, at least one
heat-curable binder from the group consisting of urea-formaldehyde
adducts, urea-glyoxal adducts, melamine-formaldehyde adducts,
phenol-formaldehyde adducts, one- and two-component systems based
on epoxy resins, polyurethanes or isocyanates, polyacrylates,
polymethacrylates, styrene-(meth)acrylate copolymer dispersions
and/or styrene-butadiene(meth)acrylic acid copolymer
dispersions.
4. The method according to claim 1, wherein the aqueous solution
and/or the dispersion comprises, as reactive material, (i) at least
one reactive substance which forms a polymer; (ii) optionally, at
least one C.sub.1-5-alcohol, at least one polyol or mixtures
thereof; and (iii) at least one catalyst.
5. The method according to claim 1, wherein the aqueous solution
and/or the dispersion comprises, as reactive material, (i) at least
one adduct selected from the group consisting of: at least one
urea-formaldehyde adduct, one urea-glyoxal adduct and at least one
melamine-formaldehyde adduct; (ii) optionally, at least one
C.sub.1-5-alcohol, at least one polyol or mixtures thereof; and
(iii) at least one catalyst.
6. The method according to claim 1, wherein the aqueous solution
comprises, as reactive material, (i)
1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one.
7. The method according to claim 1, wherein the aqueous solution
and/or the dispersion comprises, as reactive material, (i) at least
one compound selected from the group consisting of dimethylolurea,
bis(methoxymethyl)urea, tetramethylolacetylenediurea,
methylolmethyurea, 1,3-dimethyl-4,5-dihydroxyimidazonidin-2-one,
1,3-bis(hydroxymethyl)imidazolidin-2-one and mixtures thereof; (ii)
optionally, at least one C.sub.1-5-alcohol, at least one polyol or
mixtures thereof; and (iii) at least one catalyst.
8. The method according to claim 1, wherein the aqueous solution
and/or the dispersion of the reactive material comprises at least
one catalyst (iii) which is selected from the group consisting of
metal halides, metal sulfates, metal nitrates, metal
tetrafluoroborates and metal phosphates.
9. The method according to claim 4, wherein the catalyst used is
magnesium chloride.
10. The method according to claim 1, wherein the reactive material
used is a mixture of (a) a polymer which is obtained by free
radical polymerization and which comprises, incorporated in the
form of polymerized units, from 5 to 100% by weight of an
ethylenically unsaturated carboxylic anhydride or of an
ethylenically unsaturated dicarboxylic acid whose carboxyl groups
can form an anhydride group, and (b) at least one alkanolamine
which comprises at least two hydroxyl groups in the molecule and/or
at least one polyhydric alcohol.
11. The method according to claim 10, wherein aqueous mixtures of
polycarboxylic acids and polyhydric alcohols and/or polyfunctional
amines and/or alkanolamines are used as reactive material in
amounts such that the number of acid functions is equivalent to the
total number of alcoholic hydroxyl and amine functions.
12. (canceled)
13. A composition comprising: the paper products obtained by the
method according to claim 1 and/or coated cellulose fibers produced
by defibrating, and a thermoplastic.
14. A composition comprising: the paper products obtained by the
method according to claim 1 and/or coated cellulose fibers produced
by defibrating, and a heat-curable plastic.
Description
[0001] The invention relates to methods for reducing the absorption
of water and water vapor and for increasing the dimensional
stability of paper and paper products by treatment with an aqueous
solution and/or dispersion of at least one reactive material which
reacts with itself and/or with the cellulose fibers with
crosslinking, and heating of the treated materials to a temperature
at which drying and crosslinking takes place, and the use of coated
paper products and/or of the coated cellulose fibers which can be
produced therefrom by defibrating as an additive to thermoplastics
and as an additive to heat-curable plastics.
[0002] From the publication "Treatment of timber with water soluble
dimethylol resins to improve the dimensional stability and
durability", which appeared in Wood Science and Technology 1993,
pages 347-355, it is known that the shrinkage and swelling
properties of wood and the resistance to fungi and insects can be
improved by treating wood with an impregnating agent which consists
of an aqueous solution of dimethylol dihydroxyethyleneurea (DMDHEU
or 1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one) and a
catalyst. Catalysts used are metal salts, citric acid and amine
salts, individually or in combination. The DMDHEU is used in the
aqueous solution in concentrations of from 5% to 20%. The added
amount of catalyst is 20% based on the DMDHEU. The impregnation is
effected under reduced pressure. At elevated temperature, a
reaction of the DMDHEU with itself and with the wood takes place.
This reaction takes place for one hour in a drying oven at
temperatures of 80.degree. C. or 100.degree. C. The wood samples
thus treated exhibit an improvement in the shrinkage and swelling
properties of up to 75%, and do so at DMDHEU concentrations of 20%.
In this way, wood bodies having dimensions of 20 mm.times.20
mm.times.10 mm were investigated. The method described can be used
only in the case of small dimensions of the wood bodies, because
these tend to crack in the case of larger dimensions.
[0003] EP-B 0 891 244 discloses the impregnation of wood bodies
comprising solid wood with a biodegradable polymer, a natural resin
and/or a fatty acid ester--if appropriate with application of
reduced pressure and/or pressure. The impregnation takes place at
elevated temperatures. The pores in the wood are at least largely
filled, and a molding which comprises both wood and biodegradable
polymer forms. The polymer does not react with the wood. With this
treatment, the characteristic properties of wood, the
biodegradability and the mechanical properties are not lost. The
thermoplasticity can be increased. Depending on the proportion of
polymer introduced, there is an increase in the surface hardness by
the incorporation of the polymer into the wood matrix, so that
naturally soft woods are also suitable for high-quality floors.
[0004] SE-C 500 039 describes a method for hardening wood with
densification, in which untreated wood is impregnated with various
aminoplast monomers based on melamine and formaldehyde by means of
suitable vacuum pressure impregnation, then dried, and cured in a
press for densification at elevated temperature. Agents mentioned
are, inter alia, DMDHEU, dimethylolurea, dimethoxymethylurea,
dimethylolethyleneurea, dimethylolpropyleneurea and
dimethoxymethyluron. This method has the disadvantage that the
natural wood structure is lost as a result of the densification,
and the formaldehyde emission of the finished wood body is
relatively high, depending on the crosslinking agent used.
[0005] WO 04/033171 discloses a method for the production of a wood
body having high surface hardness and low formaldehyde emission, an
untreated wood body being impregnated with an aqueous solution of
[0006] A) an impregnating agent consisting of a
1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one modified
with a C.sub.1-5-alcohol, a polyol or mixtures thereof, and [0007]
B) a catalyst from the group consisting of the ammonium or metal
salts, organic or inorganic acids and mixtures thereof, dried, and
then cured at elevated temperature.
[0008] According to the method disclosed in WO 04/033170 the
durability, dimensional stability and surface hardness of a wood
body is improved by impregnating a wood body with a 1 to 50%
strength by weight aqueous solution of an impregnating agent
comprising a substance of group A and/or at least one substance of
group B and at least one substance of group C as a catalyst, and
causing the impregnating agent subsequently to react with itself
and with the wood under humid conditions for avoiding drying.
Suitable impregnating agents are, for example,
dimethyloldihydroxyethyleneurea (DMDHEU), urea-glyoxal adducts and
urea-formaldehyde adducts. Suitable catalysts are, for example,
magnesium chloride, zinc chloride, ammonium chloride or acids, such
as formic acid, maleic acid, hydrochloric acid or sulfuric
acid.
[0009] WO 2004/025019 discloses a method and an apparatus for
exchanging a liquid present in fibers with another liquid. The
procedure adopted here is to press out fiber cake to such an extent
that a considerable amount of the liquid which is present in the
fibers is transferred into the space between the fibers, to meter
the other liquid, which is to replace the first liquid, into the
compressed fiber cake during the compression step so that the first
liquid is removed from the space between the fibers, and then to
let down the pressure on the fiber cake under further action of the
other liquid which is to replace the first liquid, further
replacement liquid being absorbed. Liquid cleaners, chemical
treatment agents, liquid acids or bases, bleaches, delignification
agents, catalysts, complexing agents, fluorescence indicators,
metal ions, cationic or anionic polymers, colorants and inorganic
substances being mentioned as replacement liquid. With the aid of
the known method, it is possible, for example, at least partly to
remove lignin constituents from cellulose fibers and thus to
prepare a pulp having a better and more uniform quality.
[0010] Cellulose fibers and paper products produced therefrom, such
as paper, board and cardboard, readily absorb water and also water
vapor from the air. As a result, however, the dimensional stability
and the mechanical stability of the cellulose fibers and of the
paper products are reduced to an undesired extent. In order to
reduce the water absorption of paper products, a wet strength agent
can be added, to the paper stock, for example during production of
said products. Known wet strength agents are, for example,
urea-formaldehyde resins, which increase not only the wet strength
but also the dry strength of the paper (cf. EP-A 0 123 196 and U.S.
Pat. No. 3,275,605), melamineformaldehyde resins (DE-B 10 90 078)
and other commercially available products, for example
epichlorohydrin-crosslinked condensates of polyamidoamines, such as
the Luresin.RTM. brands (BASF Aktiengesellschaft).
[0011] It is the object of the invention to provide a method for
reducing the absorption of water and water vapor and for increasing
the dimensional stability of paper and paper products, such as
board and cardboard.
[0012] The object of the invention is achieved, according to the
invention, by a method for reducing the absorption of water and
water vapor and for increasing the dimensional stability of paper
and paper products by treatment with an aqueous solution and/or
dispersion of at least one reactive material which reacts with
itself and/or cellulose fibers with crosslinking, and heating of
the treated materials to a temperature at which drying and
crosslinking takes place, if cellulose fibers or a paper product
obtained therefrom by drainage on a wire are or is first
compressed, the compressed paper product is then brought into
contact with an aqueous solution and/or dispersion of the reactive
material, the compression is eliminated with further action of the
aqueous solution and/or dispersion and the paper product is dried
and crosslinked. The crosslinking of the reactive materials takes
place, for example, at temperatures above 30.degree. C., for
example in the temperature range of from 35 to 200.degree. C. The
method can be carried out continuously and also batchwise.
[0013] A preferred procedure is one in which cellulose fibers which
comprise at least 50% by weight of virgin fibers or a paper product
obtained therefrom by drainage on a wire, having a water content of
in each case at least 0.7 g of water by g of dry cellulose fibers,
are or is first compressed under a pressure of at least 2.1 MPa,
the compressed paper product is then brought into contact with an
aqueous solution and/or dispersion of the reactive material, the
compression is eliminated with further action of the aqueous
solution and/or dispersion, and the paper product is dried and is
heated to a temperature in the range of from 70 to 200.degree. C.
for crosslinking.
[0014] For example, the aqueous solution and/or dispersion
comprises, as reactive material, at least one heat-curable binder
from the group consisting of the urea-formaldehyde adducts,
urea-glyoxal adducts, melamine-formaldehyde adducts,
phenol-formaldehyde adducts, one- and two-component systems based
on epoxy resins, polyurethanes or isocyanates, polyacrylates,
polymethacrylates, styrene-(meth)acrylate copolymer dispersions
and/or styrene-butadiene-(meth)acrylic acid copolymer dispersions.
In some cases, the use of mixtures of at least two reactive
materials is of interest, for example mixtures of
melamine/urea-formaldehyde condensates. The reactive materials may
be present as aqueous solution or as aqueous dispersion. Here,
transitions between solution and dispersion are possible. If
dispersions are used for example, the mean particle diameter of the
polymer particles dispersed in water is less than 1 .mu.m,
preferably less than 500 nm and generally in the range of from 10
to 100 nm.
[0015] The aqueous solution and/or dispersion thus comprises, for
example, a group of a reactive, crosslinkable material which may
consist of [0016] (i) at least one reactive substance which forms a
polymer, [0017] (ii) if appropriate, at least one
C.sub.1-5-alcohol, at least one polyol or mixtures thereof and
[0018] (iii) at least one catalyst.
[0019] Examples of (i) a reactive substance which forms a polymer
are urea-glyoxal adducts and derivatives thereof, e.g.
1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one (referred to
below as "DMDHEU"). In the impregnation, it can be used either
alone or together with (ii) at least one C.sub.1-5-alcohol, a
polyol or mixtures thereof. If
1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one is used
together with an alcohol and/or polyol as the impregnating agent,
correspondingly modified
1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-ones (referred
to below as "mDMDHEU") form. Such compounds are disclosed, for
example, in U.S. Pat. No. 4,396,391 and WO 98/29393. These are
reaction products of
1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one with at
least one C.sub.1-5-alcohol, at least one polyol or mixtures
thereof.
[0020] The compounds of group (ii) include C.sub.1-5-alcohols, for
example methanol, ethanol, n-propanol, isopropanol, n-butanol,
isobutanol, tert-butanol and n-pentanol, preferably methanol, and
polyols, such as ethylene glycol, diethylene glycol, 1,2- and
1,3-propylene glycol, 1,2-, 1,3- and 1,4-butylene glycol, glycerol,
trimethylolpropane and polyalkylene glycols, such as polyethylene
glycol, polypropylene glycol, block copolymers of ethylene glycol
and propylene glycol. Polyethylene glycols of the formula
HO(CH.sub.2CH.sub.2O).sub.nH, where n is from 3 to 20, and
diethylene glycol are preferred.
[0021] In order to prepare modified
1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one (mDMDHEU),
DMDHEU and the monohydric alcohol and/or the polyol are mixed, the
monohydric alcohol and/or the polyol being used in an amount of
from 0.1 to 2.0 mol equivalents each, based on DMDHEU. The mixture
of DMDHEU, monohydric alcohol and/or polyol is reacted, for
example, at temperatures of from 20 to 70.degree. C. and a pH of
from 1 to 2.5, the pH being adjusted to 4 to 8 after the
reaction.
[0022] (i) a reactive substance which forms a polymer is to be
understood as meaning both urea-formaldehyde adducts and
urea-glyoxal adducts and in each case derivatives thereof. The
following compounds may be mentioned by way of example:
dimethyllolurea, bis(methoxymethyl)urea,
tetramethylolacetylenediurea, methylolmethylurea and
1,3-dimethyl-4,5-dihydroxyimidazolidin-2-one,
1,3-bis(hydroxymethyl)imidazolidin-2-one or mixtures thereof. These
compounds of group (i) can, if appropriate, also be used in the
presence of (ii) at least one C.sub.1-5-alcohol, at least one
polyol or mixtures thereof as the impregnating agent. Suitable
alcohols and polyols have already been mentioned above. Methanol,
diethylene glycol and mixtures thereof are preferred.
[0023] The aqueous solution of the impregnating agent comprises the
reactive compounds of group (i) and the compounds of group (ii),
for example, in a concentration of from 1 to 70% by weight,
preferably from 10 to 60% by weight and in particular from 20 to
60% by weight. The impregnating agent preferably comprises
1,3-bis(hydroxymethyl)-4,5-dihydroxyimidazolidin-2-one (DMDHEU) as
a compound of group (i).
[0024] In addition to (i) and, if appropriate, (ii), the
impregnating agent always comprises a catalyst (iii). Suitable
catalysts (iii) are, for example, metal salts from the group
consisting of metal halides, metal sulfates, metal nitrates, metal
tetrafluoroborates, metal phosphates or mixtures thereof.
individual examples of (iii) are magnesium chloride, magnesium
sulfate, zinc chloride, lithium chloride, lithium bromide, boron
trifluoride, aluminum chloride, aluminum sulfate, zinc nitrate and
sodium tetrafluoroborate. Said compounds can be used, either alone
or as a mixture, as a catalyst.
[0025] Further suitable catalysts (iii) are ammonium salts, such as
ammonium chloride, ammonium sulfate, ammonium oxalate, diammonium
phosphate or mixtures thereof. In addition, organic and/or
inorganic acids may be used as a catalyst. Examples of these are
maleic acid, formic acid, acetic acid, propionic acid, citric acid,
tartaric acid, oxalic acid, p-toluenesulfonic acid, hydrochloric
acid, sulfuric acid, boric acid or mixtures thereof.
[0026] Preferably used compounds of group (iii) are magnesium
chloride, zinc chloride, magnesium sulfate, aluminum sulfate or
mixtures of these compounds. Magnesium chloride is particularly
preferred.
[0027] The catalyst (iii) is present, for example, in a
concentration of from 0.1 to 10% by weight, preferably from 0.2 to
8% by weight, particularly preferably from 0.3 to 5% by weight,
based on the components (i)-(iii) of the reactive material.
[0028] Of the products which are described above and comprise
formaldehyde in the form of condensed units, in particular
low-formaldehyde condensates are used. In the present context,
low-formaldehyde is to be understood as meaning that the reactive
materials comprise no substantial amounts of free formaldehyde and
that no substantial amounts of formaldehyde are released even
during drying or curing of the cellulose fibers or paper products
treated therewith. In general, such reactive materials comprise
<100 ppm of formaldehyde.
[0029] Further reactive materials which react with themselves
and/or cellulose fibers with crosslinking are formaldehyde-free,
heat-curable binders. Such binders are described, for example, in
the following publications, which are hereby incorporated by
reference as disclosure content of the present invention, namely
U.S. Pat. No. 4,076,917, EP-A 0 445 578, EP-A 0 583 086, EP-A 0 651
088, WO 97/31036, page 4, line 12, to page 12, line 14, WO
97/31059, page 2, line 22, to page 12, line 5, WO-A-97/31060, page
3, line 8, to page 12, line 36, DE-A-199 49 591, page 3, line 5, to
page 7, line 38, WO 01/27163, page 5, line 34, page 22, line 2, and
the radiation-curable binders disclosed in DE-A 199 17 965.
[0030] In addition to the binders which are described in the
abovementioned publications, suitable heat-curable binders are all
curable binders which are described in the literature, for example,
for strengthening nonwovens and/or are used for this purpose in
practice, such as heat-curable resins based on phenol and
formaldehyde, the abovementioned melamine-formaldehyde and
urea-formaldehyde resins, urea-glyoxal resins and in particular
formaldehyde-free one- and two-component systems based on epoxy
resins or polyurethanes, polyacrylates, polymethacrylates,
polyvinyl acetates, styrene acrylate copolymer dispersions,
styrene-methacrylate copolymer dispersions,
styrene-butadiene-(meth)acrylic acid copolymer dispersions and
mixtures of said dispersions with a mixture of a polycarboxylic
acid and a polyhydric alcohol as crosslinking component.
[0031] Examples of preferred heat-curable binders are mixtures of
[0032] (a) a polymer which is obtainable by free radical
polymerization and which comprises, incorporated in the form
polymerized units, from 5 to 100% by weight of an ethylenically
unsaturated carboxylic anhydride or of an ethylenically unsaturated
dicarboxylic acid whose carboxyl groups can form an anhydride
group, and [0033] (b) at least one alkanolamine, which comprises at
least two hydroxyl groups in the molecule and/or at least one
polyhydric alcohol.
[0034] Specific examples of such mixtures are aqueous solutions
and/or dispersions of a copolymer of 80% by weight of acrylic acid
and 20% by weight of maleic acid, comprising from about 40 to 60%
by weight of solids and having a molar mass M.sub.w of from 15 000
to 900 000, in combination with triethanolamine or aqueous
solutions of a copolymer of 55% by weight of acrylic acid and 45%
by weight of maleic acid in combination with triethanolamine. These
binders can comprise, if appropriate, an esterification catalyst
and/or a compound comprising bound phosphorus, such as
hypophosphorous acid, as a reaction accelerator.
[0035] The copolymer (a) described above may be composed, for
example, of [0036] from 50 to 99.5% by weight of at least one
ethylenically unsaturated mono- or dicarboxylic acid, [0037] from
0.5 to 50% by weight of at least one ethylenically unsaturated
compound from the group consisting of the esters of ethylenically
unsaturated monocarboxylic acids and the monoesters and diesters of
ethylenically unsaturated dicarboxylic acids with an amine having
at least one hydroxyl group and [0038] up to 20% by weight of
another monomer.
[0039] Heat-curable, aqueous compositions which comprise at least
one copolymer (a) and at least one alkanolamine or
higher-functional .beta.-hydroxyalkylamine and/or at least one
polyhydric alcohol can, if appropriate, additionally comprise at
least one surfactant.
[0040] Further heat-curable binders are based on aqueous mixtures
of [0041] polycarboxylic acids, such as polyacrylic acid,
polymethacrylic acid, copolymers of acrylic acid and maleic acid,
copolymers of methacrylic acid and maleic acid, copolymers of
ethylene and maleic acid, styrene and maleic acid, or copolymers of
acrylic acid or methacrylic acid and esters of acrylic or
methacrylic acid with preferably monohydric alcohols comprising 1
to 24 carbon atoms, the polycarboxylic acids exhibit a K value of
from 50 to 100 (measured with the polycarboxylic acids in
unneutralized form according to H. Fikentscher in dimethylformamide
at 25.degree. C. and a polymer concentration of 0.1% by weight) and
[0042] polyhydric alcohols, such as trimethylolpropane, glycerol,
2-hydroxymethylbutane-1,4-diol and polyvinyl alcohol, and/or
polyfunctional amines and/or alkanolamines.
[0043] Polycarboxylic acids, polyhydric alcohols, alkanolamines and
polyfunctional amines are preferably used in amounts such that the
number of acid functions is equivalent to the total number of
alcoholic hydroxyl and amine functions, cf. EP-A 0 445 578. In
addition, crosslinkable materials which consist of an aqueous
solution of a polycarboxylic acid (homo- or copolymer), preferably
having a molar mass M.sub.w of 10 000 or less, and a polyol, such
as triethanolamine, and in which the ratio of the number of
equivalents of hydroxyl groups to the number of equivalents of
carboxyl groups is in the range of from 0.4:1 to 1.0:1 are
suitable, cf. EP-A 0 990 727.
[0044] In the method according to the invention, binders which are
sold under the trade name Acrodur.RTM. by BASF Aktiengesellschaft
are particularly advantageously used as reactive materials. An
example of this is an aqueous styrene-acrylate polymer dispersion
which is modified with a polycarboxylic acid and a polyhydric
alcohol as crosslinking component. It crosslinks at a temperature
of as low as 130.degree. C. However, in order to achieve high
production speeds, the crosslinking is preferably carried out at
temperatures of from 180 to 200.degree. C. A further
formaldehyde-free binder is commercially available, for example, as
a colorless to slightly yellowish, clear, aqueous solution of a
modified polycarboxylic acid with a polyhydric alcohol as
crosslinking component. It crosslinks, for example, at drying
temperatures of from about 160 to 180.degree. C.
[0045] Formaldehyde-free reactive materials which comprise at least
one polycarboxylic acid and at least one polyhydric alcohol and/or
alkanolamine or polyfunctional amine are particularly preferred.
Compositions which comprise these reactive agents can, if
appropriate, comprise even further formaldehyde-free polymers, e.g.
polyacrylates, which are sold under the trade name Acronal.RTM. by
BASF Aktiengesellschaft. The aqueous solutions and/or dispersions
of a reactive material which are used for the impregnation comprise
the reactive material, for example in an amount of from 1 to 70% by
weight, preferably from 10 to 60% by weight and generally from 30
to 50% by weight.
[0046] In the context of the invention, paper products are to be
understood as meaning, for example, paper itself and board and
cardboard. For the method according to the invention, it is
possible to start from cellulose fibers of all types, both from
natural and from recovered fibers, in particular from fibers from
waste paper, which, however, are used only as a mixture with virgin
fibers. Virgin fibers are to be understood as meaning cellulose
fibers which have not yet been processed to give a paper product or
which have not yet been dried. In fiber mixtures comprising virgin
fibers and fibers from waste paper, the amount of virgin fibers is,
for example, at least 50% by weight, preferably at least 70% by
weight. In the particularly preferred process variant, a pulp which
comprises 100% of virgin fibers is used as a starting material
Suitable fibers for the production of the pulps are all qualities
customary for this purpose, e.g. mechanical pulp, bleached and
unbleached chemical pulp and paper stocks from all annual plants.
Mechanical pulp includes, for example, groundwood, thermomechanical
pulp (TMP), chemothermomechanical pulp (CTMP), pressure groundwood,
semi-chemical pulp, high-yield pulp and refiner mechanical pulp
(RMP). For example, sulfate, sulfite and soda pulps are suitable as
chemical pulp. Unbleached chemical pulp, which is also referred to
as unbleached kraft pulp, is preferably used. Suitable annual
plants for the production of paper stocks are, for example, rice,
wheat, sugarcane and kenaf.
[0047] In contrast to dried cellulose fibers, virgin fibers have a
high porosity, cf. W. Gindl, F. Zargar-Yaghubi and R. Wimmer,
Bioresource Technology 87, 325-330 (2003). If a collection of moist
cellulose fibers is considered, the water is found both between the
individual cellulose fibers and in the interior of the cellulose
fibers. An aqueous slurry of cellulose fibers is pressed during
drainage on the wire of a paper machine to such an extent that the
sheets formed therefrom comprise from 0.7 to 1.0 g of water per g
of dry cellulose fibers, cf. G. V. Laivins and A. M. Scallan, TAPPI
Proceedings, Engineering Conference, Book 2, 741-747 (1993). After
pressing, for example with the aid of a size press, water is
present in the spaces between the fibers and in the interior of the
cellulose fibers. As long as the fibers have a sufficient porosity,
water can also be removed from the interior of the fibers by
pressing a fiber structure. In the method according to the
invention, the paper product drained on a wire is subjected to a
pressure such that water is forced out of the interior of the
cellulose fibers. This pressure is at least 2.1 MPa and may be, for
example up to 50 MPa. Preferably, it is in the range of from 2.5 to
10 MPa. As a result of the action of a pressure of at least 2.1 MPa
on the moist fiber product comprising a predominant proportion of
virgin fibers, the water content of the paper product is reduced to
values below 0.7 g of water per g of dry fibers. It is, for
example, from 0.3 to 0.5 g of water per g of dry cellulose fibers
and is generally in the range of from 0.3 to 0.4 g of water per g
of dry cellulose fibers.
[0048] The action of a pressure on the fiber structure and the
treatment of the fiber structure with an aqueous solution of a
reactive material can be effected continuously or batchwise. A
continuous procedure is disclosed in WO 2004/025019, page 5, line
3, to page 8, line 8, mentioned in connection with the prior art.
As explained in more detail there, a fiber cake on a wire or a belt
is passed through a nip formed by two compression rolls and is
compressed therein. As a result, a part of the water which is
present in the cellulose fibers is forced out of the interior of
the cellulose fibers into the spaces between the fibers of the
compressed fiber cake and partly out of the fiber cake. With the
aid of a compressible belt which revolves over a roll which,
together with the other roll, forms the nip for the compression of
the cellulose fiber cake, the compressed cellulose fiber structure
is brought into contact under pressure with an aqueous solution of
the reactive material. As a result, the water which originates from
the interior of the cellulose fibers and is present in the
intermediate spaces between the fibers is replaced by the aqueous
solution of the reactive material. After leaving the roll nip, the
compressed cellulose fiber structure is passed through an
interstice which is filled with an aqueous solution of a reactive
material. Relaxation of the compressed cellulose fibers begins.
Similarly to a compressed sponge, which is released, cellulose
fibers absorb aqueous solution of the reactive material. The
solution penetrates not only into the intermediate spaces of the
paper product but also into the interior of the cellulose fibers.
In this way, not only coating of the individual cellulose fibers of
the paper product with a reactive material but also at least
partial coating of the interior of the fibers is achieved. After
the treatment with an aqueous solution of a reactive material, the
paper product is dried and is heated to a temperature of, for
example, from 70 to 200.degree. C. for crosslinking the reactive
material.
[0049] In a batchwise embodiment of the method according to the
invention, for example, it is possible to adopt a procedure in
which first a paper machine wire having a mesh size of, for example
from 80 to 150 .mu.m and then a sheet which is produced from a
predominant portion of virgin fibers and has a basis weight of, for
example, from 50 to 500 g/m.sup.2, in general from 75 to 250
g/m.sup.2, and a water content of, for example, from 50 to 80% by
weight are placed in a press equipped with a perforated tray.
Thereafter, a papermaker's felt which is impregnated with an
aqueous solution of at least one reactive material and then a sheet
of plastic, e.g. polymethyl methacrylate, polystyrene or
polypropylene, are placed in succession on the paper sheet. A
pressure of at least 2.1 MPa is then exerted on the layers of said
materials which are present in the press with the aid of a piston
inserted into the press. Water which originates from the cellulose
fiber structure and the interior of the cellulose fibers, together
with excess aqueous solution of the reactive material is forced out
of the perforated tray. The duration of the action of the pressure
when the method according to the invention is carried out batchwise
is, for example, from 0.1 to 120 seconds, preferably from 0.5 to 20
seconds. In the continuous procedure, the duration of the pressure
is, for example, from 0.01 to 20 seconds, preferably from 0.02 to 1
second. After the end of the compression, the sheet absorbs further
aqueous solution of the reactive material on relaxation. It is then
removed from the press, and dried and heated to a temperature of,
for example, from 70 to 200.degree. C., preferably from 120 to
170.degree. C., for crosslinking the reactive material.
[0050] While a polymer application of <5 g/m.sup.2, in general
from 1 to 3 g/m.sup.2, is usually achieved in the case of
application of an aqueous polymer solution with the aid of a size
press, the polymer application in the method according to the
invention is, for example, >5 g/m.sup.2, e.g. from 5.5 to 8
g/m.sup.2. In comparison with known application methods, paper and
paper products which have a reduced absorption of water and water
vapor and a higher dimensional stability are therefore obtained by
the method according to the invention.
[0051] Suspensions of cellulose fibers can be produced from the
paper products obtained by the method according to the invention,
for example by disintegration of the paper or of the paper products
in water, from which suspensions in turn it is possible to obtain,
by removal of water, coated cellulose fibers which comprise the
coating material at least partly in the interior. These cellulose
fibers may be present, for example, in the form of a powder.
[0052] Both writing and printing papers and packaging papers,
corrugated board, wallpapers, cardboard, laminates of, for example,
a composite of board or paper and at least one film or sheet of a
thermoplastic, and construction elements can be produced by the
method according to the invention. Of particular interest are
mixtures of (i) the paper products obtainable by the method
according to the invention and/or the coated cellulose fibers which
can be produced by defibrating and (ii) thermoplastics or
heat-curable plastics. Moldings of any desired design can be
produced from such mixtures.
[0053] The invention therefore furthermore relates to the use of
the coated papers or paper products obtainable by the method
according to the invention and/or the coated cellulose fibers which
can be produced therefrom by defibrating as an additive to
thermoplastics and as an additive to heat-curable plastics.
[0054] Such mixtures comprise, for example, from 0.1 to 90% by
weight, preferably from 1 to 70% by weight and in general from 2 to
50% by weight of at least one component (i). The composite
materials are prepared, for example, by mixing at least one of the
coated materials with at least one thermoplastic or one
heat-curable material. The mixing can be effected, for example, in
an extruder, for example at least one product coated according to
the invention and a thermoplastic being heated to a temperature
which is in the respective softening range of the thermoplastic or
higher and the mixture being extruded.
[0055] Suitable thermoplastics are, for example, polyolefins, such
as polyethylenes, which are obtainable by the high-pressure or
low-pressure polymerization process, polypropylene, polybut-2-ene
or polybut-1-ene, polyisobutylene, polystyrene, polyamides, such as
polycaprolactam or condensates of hexamethylenediamine and adipic
acid, polyesters, such as polyethylene terephthalate, polymethyl
methacrylate, polycarbonate and polyvinyl chloride.
[0056] Examples of heat-curable plastics are all reactive materials
which have already been described above for the coating of paper
and paper products, e.g. urea-formaldehyde resins,
melamine-formaldehyde resins, one- and two-component systems based
on epoxy resins, polyurethane or isocyanates, crosslinkable
polyacrylates and crosslinkable polymethacrylates.
[0057] The mixtures of the components (i) and (ii) are suitable for
the production of moldings, in particular for the production of
construction elements, such as composites for the insulation of
walls, as a water vapor barrier, in the form of sheets for the
cladding of facades or in the interior for the production of doors
and claddings, as material for the production of pieces of
furniture which are used outdoors and inside, as housings for
electrical appliances, such as vacuum cleaners, kitchen machines,
televisions, radios, stereo units and computers, as material for
automotive parts, for example interior door trims, dashboards and
shelves for seats, as material for flower boxes, flowerpots,
watering cans, plant tubs, walls and supporting parts for summer
houses and for toys and as packaging material.
[0058] Unless otherwise evident from the context, the stated
percentages in the examples are percentages by weight.
EXAMPLES
Determination of the Water Absorption
[0059] Paper samples having the dimensions 4 cm.times.4 cm were
weighed, then stored for 30 minutes in distilled water at a
temperature of 20.degree. C., then removed, dried with an absorbent
cloth and weighed. The weight increase is calculated in %.
Determination of the Dimensional Stability
[0060] Paper samples having the dimensions 4 cm.times.4 cm were
stored for one week over silica gel at a temperature of 20.degree.
C. in a desiccator. They were then weighed. In addition, the paper
thickness (D.sub.1) was determined. The samples were then stored
over water for one week in a desiccator so that the paper was
saturated with water vapor. The samples were then weighed and the
thickness (D.sub.2) of the samples was determined. The dimensional
stability was determined as follows:
Dimensional stability = D 2 - D 1 D 1 100 [ % ] ##EQU00001##
[0061] In the formula, D.sub.1 is the thickness of the dry paper
and D.sub.2 is the thickness of the moist paper.
Determination of the Moisture Absorption
[0062] Paper samples having the dimensions 4 cm.times.4 cm were
stored for one week over silica gel at a temperature of 20.degree.
C. in a desiccator. Thereafter, they were weighed (W.sub.1) and
stored for one week over water in a desiccator so that the paper
was saturated with water vapor. The samples were then weighed
(W.sub.2). The moisture absorption was determined as follows:
Moisture absorption = W 2 - W 1 W 1 100 [ % ] ##EQU00002##
Determination of the Stiffness
[0063] The stiffness was determined by the beam method according to
DIN 53 121. For this purpose, samples having a size of
100.times.25.4 mm were cut out of the papers to be tested, clamped,
and measured under the following conditions: measuring length 1=100
mm, sample width b=25.4 mm, bending angle .alpha.=20.degree.. It
was ensured that a force F.sub.max of at least 15 mN was reached at
maximum deflection. Measurement was effected 5 times per
sample.
Example 1
[0064] A paper stock which consisted of a mixture of 70% of
bleached pine sulfate pulp and 30% of birch sulfate pulp and had a
freeness of 35.degree. SR (Schopper-Riegler) was drained in a Rapid
Ko then sheet former. The sheets had a basis weight of 80
g/m.sup.2. They were pressed in each case between filter papers to
a water content of 50% and impregnated by first placing a sheet in
a press whose base consisted of a paper machine wire having a mesh
size of 100 .mu.m, then placing in succession a papermaker's felt
which was impregnated with a 50% strength aqueous solution of
Kaurit.RTM. 210 (urea-formaldehyde resin) on the sheet and then
covering with a sheet of polymethyl methacrylate. A pressure of 2.1
MPa was then exerted on the content of the press for period of 5
seconds. Water which originated from the paper and aqueous solution
of the coating material from the papermaker's felt were forced from
the bottom of the press. Thereafter, the pressure was canceled and
the sheet impregnated in this manner was removed from the press.
The sheet was dried for 4 hours at a temperature of 130.degree. C.
Under these conditions, the resin which was in the fibers and had
been deposited thereon crosslinked. Stiffness, dimensional
stability and water absorption of the sheet thus obtained were then
tested. The results are shown in the table.
Examples 2-6
[0065] Example 1 was repeated with the only exception that in each
case an aqueous solution and/or dispersion of the heat-curable
binders shown in table 1 was used instead of the aqueous solution
of Kaurit.RTM. 210. The results thus obtained are shown in table
2.
Comparative Example 1
[0066] Example 1 was repeated with the only exception that the
papermaker's felt was now impregnated with distilled water instead
of the aqueous solution of Kaurit.RTM. 210. The results are shown
in table 2.
TABLE-US-00001 TABLE 1 Amount applied [g] Self-crosslinking
material Example no. 1 8.0 Heat-curable urea-formaldehyde resin
(Kaurit`.RTM. 210), 50% strength aqueous solution 2 7.5
Heat-curable melamine-formaldehyde resin (Kauramin 787), 60%
strength aqueous solution 3 8.0 Mixture of polycarboxylic acid and
polyfunctional amine (Acrodur .RTM. 910L), 35% strength aqueous
solution 4 8.2 Mixture of polycarboxylic acid and polyfunctional
amine (Acrodur .RTM. DS 3515), 35% strength aqueous dispersion 5
7.9 Heat-curable urea-formaldehyde resin (Fixapret .RTM. ECO), 70%
strength aqueous solution Comparative example no. 1 Impregnation
with water
TABLE-US-00002 TABLE 2 Decrease in dimensional Moisture stability
after Stiffness Water absorption moisture [mN] absorption [%] [%]
absorption [%] Example no. 1 1700 100 15 3 2 2200 50 9 5 3 2000 270
20 6 4 3521 250 20 7 5 3000 110 15 4 Comparative example no. 1 254
475 22 8
* * * * *