U.S. patent application number 10/475771 was filed with the patent office on 2004-09-02 for fibrous web and process for the preparation thereof.
Invention is credited to Leskela, Markku, Meuronen, Jari, Silenius, Petri.
Application Number | 20040168782 10/475771 |
Document ID | / |
Family ID | 8561047 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040168782 |
Kind Code |
A1 |
Silenius, Petri ; et
al. |
September 2, 2004 |
Fibrous web and process for the preparation thereof
Abstract
The invention relates to a fiber web and a method for preparing
it. The fiber web comprises a filler-containing base web, which is
possibly coated with a pigment-containing coating layer. According
to the invention, 5-100% of the filler in the base web is made up
of cellulose fibrils or lignocellulose fibrils with
light-scattering material particles deposited thereon. These coated
cellulose fibrils or lignocellulose fibrils constitute at maximum
approx. 70% of the weight of the base web. The base web according
to the invention contains more than 20% less retention agents than
does a web which has the same formation but in which more than 95%
of the filler is made up of filler particles known per se.
Inventors: |
Silenius, Petri; (Lohja as,
FI) ; Meuronen, Jari; (Espoo, FI) ; Leskela,
Markku; (Muijala, FI) |
Correspondence
Address: |
Kubovcik & Kubovcik
The Farragut Building
Suite 710
900 17th Street NW
Washington
DC
20006
US
|
Family ID: |
8561047 |
Appl. No.: |
10/475771 |
Filed: |
April 22, 2004 |
PCT Filed: |
April 24, 2002 |
PCT NO: |
PCT/FI02/00344 |
Current U.S.
Class: |
162/181.1 ;
162/158; 162/181.2; 162/181.8 |
Current CPC
Class: |
D21H 11/16 20130101;
D21H 17/28 20130101; D21H 17/67 20130101; D21H 17/69 20130101 |
Class at
Publication: |
162/181.1 ;
162/181.2; 162/181.8; 162/158 |
International
Class: |
D21H 017/69; D21H
011/16 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2001 |
FI |
20010847 |
Claims
1. A fiber web comprising a filler-containing base web possibly
coated with a pigment-containing coating layer, characterized in
that 5-100% of the filler in the base web is made up of cellulose
fibrils or lignocellulose fibrils with light-scattering material
particles deposited thereon, and the coated cellulose fibrils or
lignocellulose fibrils constitute at maximum approx. 70% of the
weight of the base web, the base web containing more than 20% less
of retention agents than a web that has the same formation but
wherein more than 95% of the filler is made up of filler particles
known per se.
2. The fiber web according to claim 1, characterized in that the
filler comprises cellulose fibrils or lignocellulose fibrils
prepared from vegetable fibers by beating and screening and having
an average thickness smaller than 10 .mu.m, preferably at maximum 5
.mu.m.
3. The fiber web according to claim 2, characterized in that the
light-scattering material particles are deposited on fibrils which
correspond to a fraction passing a 50 mesh screen and/or the
average thickness of which is 0.01-5 .mu.m and average length
10-1500 .mu.m.
4. The fiber web according to any of claims 1-3, characterized in
that the light-scattering material particles are inorganic or
organic salts which can be formed from their source materials by
precipitation in an aqueous medium.
5. The fiber web according to claim 4, characterized in that the
light-scattering material particles are calcium carbonate, calcium
oxalate, calcium sulfate, barium sulfate or a mixture thereof.
6. The fiber web according to any of claims 1-5, characterized in
that the material particles are deposited on fibrils in order to
produce a string-of-pearls-like filler.
7. The fiber web according to claim 6, characterized in that the
amount of the calcium compound in proportion to the fiber amount is
0.0001-90% by weight.
8. The fiber web according to any of the preceding claims,
characterized in that it is coated with calcium carbonate, gypsum,
aluminum silicate, kaolin, aluminum hydroxide, magnesium silicate,
talc, titanium dioxide, barium sulfate, zinc oxide, synthetic
pigment, or a mixture thereof.
9. The fiber web according to any of the preceding claims,
characterized in that the filler comprising cellulose fibrils or
lignocellulose fibrils with light-scattering material particles
deposited thereon constitutes 10-100% by weight of the filler in
the base web.
10. The fiber web according to any of the preceding claims,
characterized in that the filler comprising cellulose fibrils or
lignocellulose fibrils with light-scattering material particles
deposited thereon constitutes 10-50% by weight of the fiber
material in the base web.
11. The fiber web according to any of the preceding claims,
characterized in that the light-scattering material particles in
the filler of the web are present in a substantially unflocculated
form in the fiber web.
12. The fiber web according to any of the preceding claims,
characterized in that at a formation level of 10 it contains
retention agents in an amount of 0-0.40% by weight of the mass of
the fiber.
13. The fiber web according to claim 12, characterized in that it
is substantially free of ionic retention agents.
14. The fiber web according to any of the preceding claims,
characterized in that it comprises coated fine paper or printing or
writing paper.
15. The fiber web according to any of the preceding claims,
characterized in that 5-90% of the filler in the base web is made
up of cellulose fibers or lignocellulose fibers with
light-scattering material particles deposited thereon.
16. The fiber web according to claim 15, characterized in that the
balance is made up of conventional pulverous fillers such as
calcium carbonate (natural or precipitated), kaolin, talc,
hydrogenated aluminum oxides (aluminum trihydroxides), calcium
sulfate, barium sulfate, calcium oxalate or titanium dioxide.
17. A method for preparing a fiber web, according to which method
there is prepared from a fiber material a slush from which a fiber
web is formed in a paper or board machine, characterized in that to
the slush of fiber material there is added as a filler a product
comprising cellulose fibrils or lignocellulose fibrils with
light-scattering material particles deposited thereon, this product
constituting 5-100% of the filler and its amount being at maximum
70% of the mass of the fiber material, and retention agents are
dosed into the slush in an amount of 0-0.40% by weight of the mass
of the fiber material.
18. The method according to claim 17, characterized in that a
filler is used which comprises cellulose fibrils or lignocellulose
fibrils prepared from vegetable fibers by beating and screening and
having an average thickness smaller than 10 .mu.m, preferably at
maximum 5 .mu.m.
19. The method according to claim 18, characterized in that a
filler is used wherein the light-scattering material particles are
deposited on fibrils which correspond to a fraction passing a 50
mesh screen and/or the average thickness of which is 0.1-5 .mu.m
and average length 10-1500 .mu.m.
20. The method according to any of claims 17-19, characterized in
that a filler is used wherein at minimum 90% of precipitated
light-scattering pigment particles are attached to fibrils.
21. The method according to any of claims 17-20, characterized in
that the base web is coated in the paper machine with a
pigment-containing coating mix.
Description
[0001] The present invention relates to the fiber web according to
the preamble of claim 1.
[0002] A fiber web such as this in general comprises a
filler-containing base web possibly coated with a
pigment-containing coating layer.
[0003] The invention also relates to the method according to the
preamble of claim 17 for the preparation of a fiber web.
[0004] The slush in papermaking is made up of cellulose fibers or
lignocellulose fibers, fines and fillers. Many of these components,
in particular fillers, are so small in size that they will not
adhere mechanically to the wire and they have to be bound to larger
fibers or to each other by flocculation. For flocculation there are
used retention chemicals which are added to the slush before the
forming of the web. Retention chemicals to be mentioned include
polymeric products such as polyethylene imine, low molar mass
polyacrylamide and polyamine, as well as cationic starch, guar or
polyacrylamine combined with colloidal silica, alumina or
montmorillonite. The amount of retention chemicals is in general at
least 0.5% of the dry matter of the fiber, typically approx. 0.6-1%
of the dry matter of the fiber.
[0005] In papermaking, the evenness of the web, i.e. formation, and
the remaining of slush components on the wire, i.e. retention, are
normally always compromises of some degree; when one of them is
improved, the other one deteriorates. This is logical, since
retention normally requires the flocculation of small particles
into clusters, whereupon the evenness (i.e. formation) of paper
deteriorates. For this reason it is often necessary to run the
paper with a lower than desired retention in order to produce even
paper, which increases the amount of solids in the circulation
waters and generates various problems. Furthermore, the retention
systems at present available commercially are very sensitive to
chemical changes in circulation water.
[0006] It is an object of the present invention to eliminate the
disadvantages associated with the state of the art and to provide a
totally novel solution for producing a fiber web that has
simultaneously both good retention and good formation.
[0007] The invention is based on the observation that the amount of
conventional retention agents can be reduced significantly by
replacing at least a portion of the conventional mineral fillers,
i.e. pulverous mineral pigments, with a composite pigment
containing light-scattering material particles deposited on the
surface of the fines. A filler product of this type is known from
FI patent publication 100729. The product comprises strings of
pearls made up of calcium carbonate particles deposited on the
fines and of fine fibrils. According to the patent publication, it
is characteristic of this filler of a novel type that calcium
carbonate is deposited on fine fibrils prepared from cellulose
fibers and/or mechanical pulp fibers by beating. The size
distribution of the fines fraction mainly corresponds to wire
screen fraction P100.
[0008] On the basis of the said patent publication, by means of the
filler it is possible to increase the concentration of calcium
carbonate in paper, whereby the grammage of the paper can be
reduced without changing the "other important" properties of the
paper. The filler retention is good. The results of the publication
are based on results measured from laboratory sheets by standards
SCAN-C 26:76 and respectively SCAN-M 5:76. In the laboratory
sheets, cationic starch was used in an amount of 0.65% and silica
in an amount of 0.15% of the mass of the fiber.
[0009] In connection with the present invention it has been
observed unexpectedly that with the composite fillers described
above there is obtained at a high level of formation so high a
fiber slush retention in the paper or board machine that
conventional retention agents are not required at all, or their
amount is considerably lower than in conventional base webs.
[0010] According to the invention, 10-100% of the filler in the
base web is made up of cellulose fibrils or lignocellulose fibrils
on which there are deposited light-scattering material particles,
and these coated cellulose or lignocellulose fibrils constitute at
maximum approx. 70% of the weight of the base web.
[0011] More precisely, the fiber web according to the invention is
characterized in what is stated in the characterizing part of claim
1.
[0012] The method according to the invention for the preparation of
a fiber web is for its part characterized in what is stated in the
characterizing part of claim 17.
[0013] The invention provides considerable advantages. Thus, by
means of the invention, paper of uniform quality as well as a high
level of formation and high retention can be produced; additionally
the circulation waters are substantially cleaner and the retention
agent requirement is reduced. The invention does not require any
flocculation of the filler, contrary to the commercially available
retention systems; this has a fundamental effect on formation and
the optical effect of the filler.
[0014] Better formation leads to smoother and glossier paper. If
the paper is coated, the cover provided by the coating is better,
which makes smaller amounts of coating possible. Problems
associated with the unevenness of gloss and print quality are
reduced.
[0015] The base web does not contain any conventional retention
agents, or their amount is over 20% smaller, preferably up to 50%
smaller, than that of a web that has the same level of formation
and contains conventional particulate fillers. The option according
to the invention therefore decreases the chemicals costs in the
preparation of a fiber web and facilitates the recycling of waters
in a paper or board machine. According to the invention it is
possible to decrease the amounts of both conventionally used
nanoparticles and polymers (cf. above), or either one of them. The
said reduction of 20% can thus be calculated separately from one of
the components or from both components in total. In Example 3
below, the amount of the polymer component has been reduced by
slightly less than 30% by weight while the quantity of
nanoparticles has remained unchanged.
[0016] The invention will be described below in greater detail with
the help of a detailed specification and a few embodiment
examples.
[0017] FIG. 1 shows, of the results of Example 2, the web formation
as a function of the total retention, and
[0018] FIG. 2 shows the formation as a function of the wire water
consistency.
[0019] In the examples below, the filler used contains a fines
fraction comprising fibrils obtained from a chemical pulp. By
"chemical pulp" is meant in this context a pulp that has been
treated with digestion chemicals for the delignification of
cellulose fibers. According to one preferred embodiment, the
fibrils used in the invention are fibrils obtained by beating from
pulps prepared by the sulfate process and by other alkaline
processes. In addition to chemical pulps, the invention is also
suited for fillers produced from fibrils obtained from
chemimechanical and mechanical pulps.
[0020] Typically the average thickness of cellulose or
lignocellulose fibrils is smaller than 1 .mu.m. The fibrils are
characterized by one or both of the following criteria:
[0021] a. they correspond to a fraction which passes a 50 mesh
screen;
[0022] b. their average thickness is 0.01-10 .mu.m (most suitably
at maximum 5 .mu.m) and their average length is 10-1500 .mu.n.
[0023] The source material for the fibrils, i.e. the fines based on
cellulose or other fibers, is fibrillated by beating in a pulp
refiner. The desired fraction may, when necessary, be separated
using a screen, but the fines need not always be screened. Suitable
fibril fractions include wire screen fractions P50-P400. Preferably
refiners with grooved blades are used.
[0024] The light-scattering material particles in the filler are
inorganic or organic salts which can be formed from their source
materials by precipitation in an aqueous medium. Such compounds
include calcium carbonate, calcium oxalate, calcium sulfate, barium
sulfate, and mixtures thereof. The material particles are
precipitated on the fibrils in order to produce an aggregate
resembling a string-of-pearls. The amount of the inorganic salt
compound is approx. 0.0001-95% by weight, preferably approx.
0.1-90% by weight, most suitably approx. 60-80% by weight,
calculated from the amount of filler, and approx. 0.1-60% by
weight, preferably approx. 0.5-50% by weight of the paper.
[0025] The invention is discussed below by using the product
according to FI patent publication 100729 as an example, but it is
clear that it is possible to use in the invention any other of the
above-mentioned products which contain various light-scattering
pigments.
[0026] The filler is prepared by depositing the mineral pigment on
the surface of fine fibrils prepared from cellulose fibers and/or
mechanical pulp fibers. For example, the precipitation of calcium
carbonate can be carried out by feeding into an aqueous slush of
fibrils an aqueous calcium hydroxide mixture, which possibly
contains solid calcium hydroxide, and a compound that contains
carbonate ions and is at least partly dissolved in water. It is
also possible to introduce carbon dioxide gas into the aqueous
phase, which gas in the presence of calcium hydroxide produces
calcium carbonate. There form string-of-pearls-like calcium
carbonate crystal aggregates which are held together by fibrils,
i.e. fine strands, and in which the calcium carbonate particles are
deposited onto the fine fibrils and attached to them. The fine
fibrils together with calcium carbonate form string-of-pearls-like
strands, which primarily resemble strings of pearls in a pile. In
water (slush) the ratio of the effective volume of the aggregates
to the pulp is very high compared with the corresponding ratio of
conventional calcium carbonate used as filler. By "effective
volume" is meant the volume required by the pigment.
[0027] The diameter of the calcium carbonate particles in the
aggregates is approx. 0.1-5.1 .mu.m, typically approx. 0.2-3 .mu.m.
Usually fibrils corresponding in the main (at least more than 55%)
to wire screen fractions P50-P400 are used.
[0028] The paper pulp is slushed in a manner known per se to a
suitable consistency (typically a solids content of approx. 0.1-1%)
and is spread onto the wire. There is added to the fiber slush,
most suitably in the headbox of the paper or board machine, the
above-mentioned filler, usually in an amount of approx. 1-100% by
weight of the weight of the fibers in the fiber pulp, in other
words the amount of filler may be up to equal to the amount of the
actual fiber pulp. Usually the disclosed filler constitutes at
least 5% by weight, most suitably 10-100% by weight, of the filler
in the base web, and respectively 10-50% by weight of the fiber
material in the base web. It is in principle also possible to
prepare a base web in which the fiber material in its entirety is
made up of filler fibrils, and thus in general the present filler
may constitute 1-100% by weight of the fiber material in the base
web. Preferably coated cellulose fibrils or lignocellulose fibrils
constitute at maximum approx. 70%, e.g. approx. 10-65%, of the
weight of the base web, in which case the rest of the web comprises
conventional mechanical and/or chemical pulp used in papermaking
and/or conventional fillers and/or other additives.
[0029] A portion (at maximum 95%, usually 90-10% by weight, of the
total amount of filler) of the filler used in the slush may consist
of conventional fillers, such as calcium carbonate (natural or
precipitated), kaolin, talc, hydrogenated aluminum oxides (aluminum
trihydroxides), calcium sulfate, barium sulfate, calcium oxalate,
or titanium dioxide. Preferably, however, at least 80%, especially
preferably at least 90%, of the precipitated light-scattering
pigment particles are attached to fibrils.
[0030] By "conventional filler" is meant here a particulate filler
which is pulverous and comprises loose particles, whereas in the
present invention the filler used is mainly a product in which the
particles are not loose but attached to fibrils. According to one
viewpoint of the invention, the formation and retention of paper
are improved by using a portion of the filler in a form bound to
fibrils. Thus, according to this embodiment, the filler used is at
least partly for example calcium carbonate, calcium oxalate,
calcium sulfate or barium sulfate, of which a portion is in a
pulverous form and a portion in a form attached to fibrils. In this
embodiment, in order to improve formation, a portion (at least
approx. 5% by weight, preferably at least 10% by weight, most
suitably at least 20% by weight) of the pulverous filler is
replaced with a product attached to fibrils.
[0031] In the paper or board machine the fiber pulp is formed into
a paper or board web. The fiber web is dried and most suitably
coated, and optionally after-treated by for example
calendering.
[0032] The web can be coated with, for example, calcium carbonate,
gypsum, aluminum silicate, kaolin, aluminum hydroxide, magnesium
silicate, talc, titanium dioxide, barium sulfate, zinc oxide,
synthetic pigment, or mixtures thereof.
[0033] The light-scattering material particles of the filler in the
web are present in the fiber web in a substantially unflocculated
form. This means that the formation of the web is quite good. Thus,
at formation level 10 the web contains conventional retention
agents, such as cationic starch and/or silica, in total at maximum
0.40% by weight of the mass of the fiber. According to an
especially preferred embodiment the web is substantially or
entirely free of ionic retention agents. "Conventional retention
agents" in particular include those used together with conventional
fillers.
[0034] With the help of the invention it is possible to produce
coated and optionally also calendered cellulose-containing material
webs having excellent printing properties, high smoothness, as well
as high opacity and whiteness. By "cellulose-containing material"
is meant here generally paper or board or a corresponding
cellulose-containing material derived from a
lignocellulose-containing raw material, in particular wood or
annual or perennial plants. The said material may be
wood-containing or woodfree, and it may be prepared from
mechanical, semimechanical (chemimechanical) or chemical pulp. The
chemical pulp and the mechanical pulp may be bleached or
unbleached. The material may also contain recycled fibers, in
particular recycled paper or recycled board. The grammage of the
material web varies typically within the range 35-500 g/m.sup.2, in
particular it is approx. 50-450 g/m.sup.2.
[0035] In general the grammage of base paper is 20-250 g/m.sup.2,
preferably 30-80 g/m.sup.2. By coating a base paper of this type,
having a grammage of approx. 50-70 g/m.sup.2, with 10-20 g of
coating/m.sup.2/side and by calendering the paper, there is
obtained a product having a grammage of 70-110 g/m.sup.2, whiteness
of at least 90% and opacity of at least 90%. An especially
preferred product is a coated offset paper in which high gloss and
high opacity and bulk are combined. The invention is also suited
for the production of coated fine papers, possibly also containing
mechanical pulp, as well as writing and printing papers.
[0036] The following non-restrictive examples illustrate the
invention. The measuring results indicated in the examples for the
properties of the paper were determined by the following standard
methods:
[0037] Surface roughness: SCAN-P76:95
[0038] Porosity: SCAN-P60
[0039] Air resistance: SCAN-M8, P19
EXAMPLE 1
[0040] Preparation of filler
[0041] Beating of Chemical Pulp
[0042] Birch sulfate pulp was beaten in Valmet's JC-01 refiner in
order to produce a pulp suitable for the preparation of filler. The
consistency during the beating was approx. 4%, its total energy
consumption 343 kWh/t and its specific edge load 0.5 J/m.
[0043] The properties of the product are shown in Table 1.
1TABLE 1 Fiber properties before and after beating Before After
beating beating Fiber length (length), mm 0.86 0.58 Fiber length
(weight), mm 1.00 0.77 SR.degree. 16 86
[0044] Carbonation of Fiber Pulp
[0045] Carbonation was carried out in tap water in accordance with
what is disclosed in FI patent 100729. An aqueous slurry having a
dry matter content of 2.22% was obtained. The concentration of
CaCO.sub.3 in the final product was 69.7% and its specific surface
area was 10.6 m.sup.2/g. The PCC particle size was of an order of
magnitude corresponding to that in Example 1 of the FI patent.
EXAMPLE 2
[0046] The product described in Example 1 was used as filler in
coated fine papers. The following table depicts the results of a
fine paper test run carried out in Stockholm with STFI's pilot
machine (FEX):
2TABLE 2 Results of fine paper runs Filler Wire water
concentration, consistency, Total % g/l retention, % Formation, %
PCC 18.8 2.03 72.9 10.6 PCC 21.0 2.68 66.9 11.1 SuperFill 17.8 0.48
91.1 10.4 SuperFill 22.4 0.67 88.3 9.5
[0047] The PCC used in the tests was Albacar LO product supplied by
Specialty Minerals.
[0048] The advantage of the invention is well visible when the
properties are examined simultaneously in the same coordinate
system in the manner shown in accompanying FIGS. 1 and 2.
[0049] The method is provided special value by the fact that the
above-mentioned combinations of properties are achieved
simultaneously with better optical properties and strengths.
EXAMPLE 3
[0050] Mill Trial
[0051] Preparation of Filler-Containing Base Paper
[0052] For purposes of coating, base paper having a grammage of 56
g/m.sup.2 was prepared in mill conditions. The slush consisted of a
mixture of birch pulp (74%) and pine pulp (24%). After beating, the
SR number of the pine pulp was 32-34.degree. and that of the birch
pulp was 22-25.degree.. The SR number of the pulp in the head box
was 35-40.degree..
[0053] The wire section of the paper machine was Valmet's hybride
wire (Sym-former), and the wet press end comprised Valmet's
Sym-Press II having a triple press and a conventional drying
section.
[0054] Three different fillers were used in the base paper, namely
Finntalc F 15 SL (talc of Mondo Minerals), Albacar HO (PCC of
Specialty Minerals), and the composite filler described in Example
1, of which the name "SuperFill" is also used hereinafter. Talc was
used as filler in amounts of 10% and 15%, and PCC and SuperFill in
amounts of 10%, 15% and 20%.
[0055] The retention chemicals used were nanoparticles and cationic
starch (Compozil Plus: EKA NP 780 nanoparticle and EKA PL 1510
C-Pam, supplier: EKA Chemicals). For talc and PCC the doses were as
follows: nanoparticle 280 g/t, polymer 70 g/t, and those for
SuperFill were: nanoparticle 280 g/t, polymer 50 g/t. The amounts
of cationic starch and resin size used were 8 kg/t and 5.2 kg/t.
Alum was dosed for talc in an amount of 13 kg/t and for PCC and
SuperFill in an amount of 19 kg/t.
[0056] Results
[0057] The different fillers showed no notable differences in
circulation water conductivity, COD, pH, cation requirement, or
dissolved calcium concentrations. Filler retention was best with
SuperFill (40-50%) even though the dose of retention polymers was
considerably smaller than with other fillers. The filler retention
with talc and PCC was only 30-40%. The good retention of SuperFill
significantly reduces the consistency and turbidity of circulation
water as compared with the other fillers. No differences were
observable in beta formation among the different filler and filler
concentrations.
* * * * *