U.S. patent application number 10/475774 was filed with the patent office on 2004-09-09 for coated fibrous web and process for the production thereof.
Invention is credited to Leskela, Markku, Meuronen, Jari, Silenius, Petri.
Application Number | 20040173329 10/475774 |
Document ID | / |
Family ID | 8561046 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040173329 |
Kind Code |
A1 |
Silenius, Petri ; et
al. |
September 9, 2004 |
Coated fibrous web and process for the production thereof
Abstract
The present invention relates to a coated fibrous web and a
method for producing it. According to the present invention, a
coated fibrous web comprises a filler-containing base web that has
a pigment-containing coating layer on at least one surface. The
filler of the base web consists at least partially of cellulose or
lignocellulose fibrils, on the surface of which light scattering
material particles have been deposited. The filler comprises
cellulose or lignocellulose fibrils having an average thickness
less than 5 .mu.m produced from plant fibres by refining and
screening. Considerable advantages are achieved with the present
invention. With the help of the composite filler, the formation of
the fibrous web can be improved significantly without impairing the
retention, which makes is possible to achieve an extremely smooth
substrate for the coating. The smoothness of the surface can also
be improved. Furthermore, the fines-based carrier fraction of the
filler compresses the surface of the base paper so that the coating
does not penetrate too much into the fibre network. Due to these
reasons even a small amount of coating produces good coverage and
quality improving cost-efficiency.
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
Washington
DC
20006
US
|
Family ID: |
8561046 |
Appl. No.: |
10/475774 |
Filed: |
April 22, 2004 |
PCT Filed: |
April 24, 2002 |
PCT NO: |
PCT/FI02/00341 |
Current U.S.
Class: |
162/135 ;
162/181.1; 162/181.2; 427/212 |
Current CPC
Class: |
D21H 11/16 20130101;
D21H 17/69 20130101; D21H 15/12 20130101 |
Class at
Publication: |
162/135 ;
162/181.1; 162/181.2; 427/212 |
International
Class: |
D21H 017/69 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2001 |
FI |
20010846 |
Claims
1. A coated fibrous web comprising a filler-containing base web,
which has a pigment-containing coating layer at least on one of the
surfaces, characterised in that the filler of the base web consists
at least partially of cellulose or lignocellulose fibrils, on which
light scattering material particles have been precipitated.
2. A fibrous web according to claim 1, characterised in that the
filler comprises cellulose or lignocellulose fibrils that have an
average thickness of less than 5 .mu.m, produced by refining and
screening of plant fibres.
3. A fibrous web according to claim 2, characterised in that the
light scattering material particles are precipitated on fibrils,
which correspond to a fraction passing through a 50-mesh screen
and/or having an average thickness of 0.01 to 5 .mu.m and an
average length of 10 to 1500 .mu.m.
4. A fibrous web according to any of claims 1 to 3, characterised
in that the light scattering material particles are inorganic salts
that can be formed from their source materials by precipitating in
an aqueous medium.
5. A fibrous web according to claim 4, characterised in that the
light scattering material particles are calcium carbonate, calcium
oxalate, calcium sulphate, barium sulphate or mixtures thereof.
6. A fibrous web according to any of claims 1 to 5, characterised
in that the material particles are precipitated on the fibrils.
7. A fibrous web according to claim 6, characterised in that the
amount of the light scattering material particle in proportion to
the amount of fibrils is 0.0001 to 95% by weight, preferably about
0.1 to 90% by weight, most suitably about 60 to 80% by weight,
based on the amount of filler, and about 0.1 to 60% by weight,
preferably 0.5 to 50% by weight of paper.
8. A fibrous web according to any of the preceding claims,
characterised in that it is coated with calcium carbonate, gypsum,
aluminium silicate, kaolin, aluminium hydroxide, magnesium
silicate, talc, titanium oxide, barium sulphate, zinc oxide,
synthetic pigment or mixtures thereof.
9. A fibrous web according to any of the preceding claims,
characterised in that the filler, which comprises cellulose or
lignocellulose fibrils, over which the light scattering material
particles have been precipitated, forms from 10 to 100% by weight
of the filler of the base web.
10. A fibrous web according to any of the preceding claims,
characterised in that the filler, which comprises cellulose or
lignocellulose fibrils, on which the light scattering material
particles have been precipitated, forms from 10 to 100% by weight
of the fibre material of the base web.
11. A fibrous web according to any of the preceding claims,
characterised in that it comprises coated, wood-containing or
wood-free paper.
12. A method of producing a fibrous web, according to which method
a pigment-containing coating layer is applied at least on one
surface of a base web containing fibre material, characterised by
forming the base web from a slush of the fibre material, to which a
product comprising cellulose or lignocellulose fibrils, on which
light scattering material particles have been deposited, is added
as a filler.
13. A method according to claim 12, characterised by using a filler
that comprises cellulose or lignocellulose fibrils having an
average thickness of less than 5 .mu.m produced by refining and
screening plant fibres.
14. A method according to claim 12, characterised by using a
filler, the light scattering material particles of which have been
deposited on fibrils, which correspond to a fraction, which passes
through a 50-mesh screen and/or have an average thickness of 0.1 to
10 .mu.m and an average length of 10 to 1500 .mu.m.
15. A method according to any of claims 12 to 14, characterised by
using a filler in which at least 80% of the light scattering
pigment particles are attached to the fibrils.
16. A method according to claim 12, characterised by coating the
base web in a paper machine with a pigment containing coating
mixture.
Description
[0001] The present invention relates to a coated fibrous web
according to the preamble of claim 1.
[0002] This kind of a fibrous web generally comprises a base web
with a filler, having a pigment-containing coating layer on at
least one surface.
[0003] The present invention relates also to the method according
to the preamble of claim 12 for producing a coated fibrous web.
[0004] The printability of paper and board--properties of the
printing surface and the printing process--are improved by coating
the paper with different mineral coatings. The purpose of the
coating is to cover the fibres and the fibre flocks of the paper
and board and, by these measures, to decrease the roughness of the
surface and the size of the pores of the surface. The coatings
usually consist of pigments and binders, as well as of various
additives.
[0005] The coatability of paper, in other words the capability of
the base paper to be covered with a coating, has become even more
important with the increased demand for lightweight paper grades.
Although the coverage can be affected by the properties of the
coating mix and the coating manner, the qualities of the base paper
are also important. Good formation and smoothness as well as
suitable air resistance and porosity are properties of the base
paper that are the most important factors affecting the
coatability, especially when good quality is aspired with a small
amount of coating. The fibre web to be coated usually contains
filler. The filler improves the formation of the paper web by
filling the spaces between the fibres. Also the opacity of the web
can be improved with the help of the filler.
[0006] Finnish Patent Specification No. 100729 discloses a
papermaking filler comprising porous aggregates formed by
precipitated calcium carbonate particles on the surface of fines.
What characterises this new kind of filler is that, according to
the patent specification, the calcium carbonate is precipitated on
fine fibrils produced by refining cellulose fibres and/or
mechanical pulp fibres. The size distribution of the fines fraction
corresponds mainly to the wire screen fraction P100.
[0007] Based on said patent specification it is possible to
increase the content of calcium carbonate in paper, whereby the
grammage of the paper can be lowered without changing "other
important" properties of paper. The results of the publication are
based on the data measured on laboratory sheets by the standards of
SCAN-C 26:76 and SCAN-M 5:76, respectively. No mention about the
coatability of the paper is made in the publication.
[0008] According to the present invention it has now been found,
quite surprisingly, that by filling the paper or board web or a
corresponding fibre web with the above-described filler, not only
the other important properties of paper remain intact but also the
coatability of fibre web is considerably improved.
[0009] Furthermore, within the scope of the present invention it
has been found that also other fillers consisting at least partly
of cellulose or lignocellulose fibrils, over which light scattering
material particles has been precipitated, can be used as fillers.
These particles are typically inorganic salts precipitating in an
aqueous phase, such as calcium carbonate, calcium sulphate, barium
sulphate and calcium oxalate.
[0010] More specifically, the method according to the present
invention is mainly characterised by what is stated in the
characterising part of claim 1.
[0011] The method according to the present invention is
characterised by what is stated in the characterising part of the
claim 12.
[0012] The present invention provides considerable advantages.
Thus, a composite filler consisting of fibrils and mineral pigments
has been found to provide the base paper with properties that are,
as far as coatability is concerned, better than what can be
achieved with fillers that are at the present commercially
available. Since the composite filler used in the present invention
surprisingly can improve considerably the formation of the fibre
web without impairing retention, a very smooth coating substrate
can be obtained by means of the present invention. The smoothness
of the surface can also be improved. Furthermore, the fines-based
carrier fraction makes the surface of the base paper denser so that
the coating does not penetrate too much into the fibre network. Due
to these reasons, even a small amount of coating provides good
coverage and a high quality of the coating, improving the cost
efficiency.
[0013] In the following, the present invention will be examined
more closely with the help of a detailed description and some
working examples.
[0014] In the examples below, the filler used in the present
invention is based on fibrils obtained from chemical pulp. In this
context, chemical pulp refers to a pulp, which has been treated
with cooking chemicals for delignification of the cellulose fibres.
According to a preferred embodiment, fibrils have been obtained by
refining a pulp produced by the sulphate process or by another
alkaline pulping process. The present invention can also be applied
to modification of fibrils obtained from chemimechanical and
mechanical pulp, in addition to chemical pulps.
[0015] Typically, the average thickness of cellulose or
lignocellulose fibrils is smaller than 5 .mu.m, conventionally
smaller than 1 .mu.m. The fibrils are characterized by at least one
of the following criteria:
[0016] a. they correspond to a fraction which passes a 50-mesh (or
preferably a 100-mesh) screen; and
[0017] b. their average thickness is 0.01-10 .mu.m (preferably at
maximum 5 .mu.m and in particular at maximum 1 .mu.m) and their
average length is 10-1500 .mu.m.
[0018] The source material for the fibrils, i.e. the fines based on
cellulose or other fibers, is fibrillated by beating it in a pulp
refiner. The desired fraction may, when necessary, be separated by
using a screen, but fines need not always be screened. Suitable
fibril fractions include wire screen fractions P50-P400. Preferably
refiners with grooved blades are used.
[0019] The light-scattering material particles in the filler are
inorganic or organic salts that can be formed from their source
materials by precipitation in an aqueous medium. Such compounds
include calcium carbonate, calcium oxalate, calcium sulphate,
barium sulphate, and mixtures thereof. The material particles are
deposited on the fibrils. The amount of an inorganic salt compound
in proportion to the fibril amount 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.
0.1-80% by weight, preferably approx. 0.5-50% by weight, of the
paper.
[0020] In the following, the present invention is examined with
particular reference to a product according to FI Patent
Specification No. 100729, but it is clear that the present
invention can be adapted for other products mentioned hereinbefore
by changing appropriately the source materials of the light
scattering pigment.
[0021] The filler is produced by precipitating a mineral pigment on
the surface of fine fibrils prepared from cellulose fibres and/or
mechanical pulp fibres. For example, the precipitation of calcium
carbonate can be carried out by feeding into an aqueous slush of
fibrils an aqueous calcium hydroxide solution which possibly
contains a solid calcium hydroxide, and a compound which contains
carbonate ions and is at least partly dissolved in water (e.g.
sodium carbonate or ammonium carbonate). It is also possible to
introduce into the aqueous phase carbon dioxide gas that, in the
presence of calcium hydroxide, produces calcium carbonate. There
are formed 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, and the
calcium carbonate aggregates 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, in this case, the volume
required by the pigment.
[0022] The diameter of the calcium carbonate particles in the
aggregates is about 0.1 to 5 .mu.m, typically about 0.2 to 3 .mu.m.
In particular, the fibrils correspond to wire screen fractions P50
(or P100) to P400. In the filler at least 80%, preferably up to
90%, of the light scattering pigments are attached to the
fibrils.
[0023] The paper pulp is slushed by a process known per se
(typically to solids content of about 0.1 to 1%) and it is spread
on the wire. The above-mentioned filler is added to the fibre slush
most suitably in the headbox of a paper or board machine, usually
in an amount of about 1 to 100% by weight of fibres of pulp. In
other words, the amount of the filler can be up to equal to--or
greater than--the amount of the actual pulp. In principle, it is
also possible to produce a base web, the fibre material of which
consists totally of fibrils of the filler, which implies that the
present filler can form from 1 to 100% by weight of the fibre
material of the base web.
[0024] The pulp is webbed in a paper or board machine to form a
paper or board web. The fibre web is dried and coated and possibly
processed further, for example, by calendering.
[0025] Coating can be carried out as single-coating or
double-coating, whereupon the coating colour can be used as
single-coat mixes and as so called precoating and surface-coat
mixes. Also triple coatings are possible. In general, the coating
colour according to the present invention contains from 10 to 100
parts by weight of at least one pigment or mixture of pigments,
from 0.1 to 30 parts by weight of at least one binder and from 1 to
10 parts by weight of other additives known per se.
[0026] The typical composition of a precoating mixture is as
follows:
1 Coating pigment 100 parts by weight (for example, coarse calcium
carbonate) Binder 1-20% of the weight of the pigments Additives and
auxiliary agents 0.1-10% of the weight of the pigments Water the
rest
[0027] Water is added to the precoating mix so that the solids
content is generally from 40 to 70%.
[0028] According to the present invention, the composition of the
surface-coat mixture or single-coat mixture is as follows:
2 Coating pigment I 10-90 parts by weight (for example, fine
carbonate) Coating pigment II 10-90 parts by weight (for example
fine kaolin) Pigment total 100 parts by weight Binder 1-20 parts by
weight Additives and auxiliary agents 0.1-10 parts by weight Water
the rest
[0029] Water is added to this kind of a coating colour so that the
dry solids content is typically from 50 to 75%.
[0030] According to the present invention, in the coating colours
presented above it is possible to use pigments that have a steep
particle size distribution, so that the case at maximum 35% of the
pigment particles are smaller than 0.5 .mu.m, preferably at maximum
15% are smaller than 0.2 .mu.m.
[0031] The present invention is applicable to any pigment.
Precipitated calcium carbonate, ground calcium carbonate, calcium
sulphate, calcium oxalate, aluminium silicate, kaolin (hydrous
aluminium silicate), aluminium hydroxide, magnesium silicate, talc
(hydrous magnesium silicate), titanium dioxide and barium sulphate,
and mixtures thereof can be mentioned as examples of the pigments.
Synthetic pigments can also be used. Of the pigments mentioned
above, the main pigments are kaolin, calcium carbonate,
precipitated calcium carbonate and gypsum, which in general
constitute over 50% of the dry solids in the coating mix. Calcined
kaolin, titanium dioxide, satin white, aluminium hydroxide, sodium
silicoaluminate and plastics pigments are additional pigments, and
their amounts are in general less than 25% of the dry. solids in
the mix. Of the special pigments, special-quality kaolins and
calcium carbonates, as well as barium sulphate and zinc oxide,
should be mentioned.
[0032] The present invention is applied especially preferably to
calcium carbonate, calcium sulphate, aluminium silicate and
aluminium hydroxide, magnesium silicate, titanium dioxide and/or
barium sulphate, as well as mixtures thereof, in which case,
especially preferably, the principal pigment in the pre-coat mixes
is calcium carbonate or gypsum and in surface-coat mixes and
single-coat mixes the principal pigment consists of mixtures of
calcium carbonate or gypsum and kaolin.
[0033] It is possible to use any known binders generally employed
in paper production as binders in the coating colours. Besides the
individual binders, it is also possible to use mixtures of binders.
Examples of typical binders include synthetic latexes made up of
polymers or copolymers of ethylenically unsaturated compounds, e.g.
copolymers of the butadiene-styrene type, which possibly also have
a comonomer containing a carboxyl group, such as acrylic acid,
itaconic acid or maleic acid, and polyvinyl acetate having
comonomers that contain carboxyl groups. Together with the
materials cited above, it is also possible to use, for example, the
water-soluble polymers, starch, CMC, hydroxyethyl cellulose and
polyvinyl alcohol as binders.
[0034] Furthermore, it is possible to use conventional additives
and auxiliary agents, such as dispersants (e. g. sodium salt of
polyacrylic acid), agents affecting the viscosity and water
retention of the mix (e. g. CMC, hydroxyethyl cellulose,
polyacrylates, alginates, benzoate), so-called lubricants,
hardeners used for improving water-resistance, optical auxiliary
agents, anti-foaming agents, pH control agents, and preservatives
in the coating composition. Examples of lubricants include
sulpfonate oils, esters, amines, calcium or ammonium stearates; of
agents improving water resistance, glyoxal; of optical auxiliary
agents, diaminostilbene disulfonic acid derivatives; of
anti-foaming agents, phosphate esters, silicones, alcohols, ethers,
vegetable oils; of pH control agents, sodium hydroxide, ammonia;
and finally of preservatives, formaldehyde, phenol, quaternary
ammonium salts.
[0035] The coating mix can be applied to the material web in a
manner known per se. The method according to the present invention
for coating paper and/or board can be carried out with a
conventional coating apparatus, i.e. by blade coating, or by film
coating or JET application.
[0036] During coating, a coating layer having a grammage of 5-30
g/m.sup.2 is formed at least on one surface, preferably on both
surfaces. An uncoated side can be treated, for example, by web
sizing.
[0037] With the aid of the present invention, coated and optionally
calendared cellulose-containing material webs having excellent
printing properties, good smoothness and high opacity and
brightness, can be produced. By "cellulose-containing material" we
refer to the paper or board or a corresponding cellulosic material
derived from a lignocellulose-containing raw material, in
particular from wood or from annual or perennial plants. The said
material can be wood-containing or wood-free, and it can be
produced from mechanical, semi-mechanical (chemimechanical) or
chemical pulp. Chemical pulp or mechanical pulp may be bleached or
unbleached. The material may also contain recycled fibers, in
particular recycled paper or recycled board. The material may also
contain recycled fibers, in particular recycled paper or recycled
board. The grammage of the material web ranges typically from 35 to
500 g/m.sup.2, typically it is about 50 to 450 g/m.sup.2.
[0038] In general the grammage of the base paper is 20-250
g/m.sup.2, preferably 30-80 g/m.sup.2. By coating a base paper of
this type, the grammage of which is approx. 50-70 g/m.sup.2, with
10-20 g of coating/m.sup.2/side and by calendering the paper a
product that has a grammage of 70-110 g/m.sup.2, a brightness of at
least 90%, an opacity of at least 90% is obtained. An especially
preferred product is a coated offset paper in which high gloss and
high opacity and bulk are combined. The present invention is
suitable also for production of coated fine paper, possibly also
for those that contain mechanical pulp.
[0039] The following non-limiting examples illustrate the present
invention. The measurement results indicated for the paper
properties in the examples-have been determined by the following
standard methods:
[0040] Surface roughness: SCAN-P76:95
[0041] Porosity: SCAN-P60
[0042] Resistance of air permeability: SCAN-M8,P19
EXAMPLE 1
[0043] Production of Filler
[0044] Refining of Chemical Pulp
[0045] Birch sulphate pulp was refined with a Valmet JC-01 refiner
to produce pulp that is suitable for production of the filler. The
consistency of refining was about 4% and the total energy
consumption was 343 kWh/t and the specific edge load was 0.5
J/m.
[0046] Properties of the product are presented in Table 1.
3TABLE 1 Fibre properties before and after refining Before refining
After refining Fibre length (length), mm 0.86 0.58 Fibre length
(weight), mm 1.00 0.77 SR.degree. 16 86
[0047] Carbonating of Pulp
[0048] Carbonating was performed in tap water according to the FI
Patent Specification No. 100729. The water slurry was obtained, the
dry matter content of which was 2.22% and total amount 248 m.sup.3.
The final product had CaCO.sub.3 content of 69.7% and a specific
surface area 10.6 m.sup.2/kg.
EXAMPLE 2
[0049] Production of Base Paper
[0050] The product produced in Example 1 was used as a filler in
coated fine papers. The following table presents the results that
were obtained in the test where fine paper was produced on the
pilot machine (FEX) of STFI in Stockholm:
4TABLE 2 Properties of the surface of fine paper Resistance Filler
Porosity of air Roughness content, Formation, Ml/min permeability,
ml/min Filler % % (Bendtsen) s (Gurley) (Bendtsen) PCC 18.0 10.6
761 17.6 814 PCC 21.0 11.1 799 16.1 862 SuperFill 17.8 10.4 543
26.5 771 Superfill 22.4 9.5 439 32.3 611
[0051] It appears from the results of the table that a fines-based
filler described in this invention improves formation and
smoothness of the base paper in comparison to a commercial PCC
filler to the degree that the effect on the coatability of paper is
surprisingly good. The effect grows in direct relation to the
amount of the filler. Moreover, the impermeability or density of
the surface is greater with the filler in question (SuperFill), a
property, which can be taken advantage of, especially in the
context of the lightweight papers, as the coatability of the mix is
better.
EXAMPLE 3
[0052] Mill Trial
[0053] A1. Production of Filler-Containing Paper
[0054] A base paper that has a grammage of 56 g/m.sup.2, was
produced in factory conditions for coating. The slush consisted of
a mixture of birch pulp (74%) and pine pulp (24%). After refining,
the SR value of the pine was 32 to 34.degree. and that of birch was
22 to 25.degree.. The SR value of the pulp in the headbox was 35 to
40.degree..
[0055] The wire compartment of the paper machine had a hybride wire
of Valmet (Sym-former), and the wet pressing compartment consisted
of a Valmet Sym-Press II that has a triple compressor and a
conventional drying section.
[0056] Three different fillers were used in the base paper, namely
products Finntalc F 15 SL (talc of Mondo Minerals), Albacor HO (PCC
of Specialty Minerals) and a composite filler described in the
Example 1, refered to hereinafter as "SuperFill". Talc was used as
filler in amounts of 10% and 15% and SuperFill in amount of 10%,
15% and 20%.
[0057] Nanoparticles and cationic starch (Compozil Plus: EKA NP 780
nanoparticle and EKA PL 1510 C-PAM, supplier: EKA Chemicals) were
used as retention chemicals. The dosage amounts in the case of talc
and PCC were as follows: nanoparticle 280 g/t, polymer 70 g/t, and
with SuperFill: nanoparticle 280 g/t, polymer 50 g/t. The amounts
of cationic starch and resin adhesive used were 8 kg/t and 5.2 g/t.
The alum was administered for talc at 13 kg/t and with PCC and
SuperFill at 19 kg/t.
[0058] A2. Results
[0059] The coulter-oil porosity was measured from the base paper
samples. No significant differences were observed in the pore size
distribution with low filler contents. 75% of all pores were in the
range of 1.2 to 1.8 .mu.m (around the maximum point). When the
filler content was increased to 20%, significant differences were
observed. In the case of PCC, the median of the pore size increased
as the amount of filler was increased. The median decreased and the
distribution narrowed with the SuperFill filler, whereupon 75% of
the values were around 0.8 .mu.m. The same effect can be seen with
talc but in a smaller scale. When the filler content is 20% with
Superfill as the filler, the median of the pore size was only 60%
of the corresponding value of the PCC, and the width of the pore
size distribution (75% of values) was only 34% of values obtained
with the PCC.
[0060] Thus, it can be concluded from the data that the SuperFill
provides paper, the surface of which is more enclosed than the
surface of the paper filled with PCC, which facilitates the coating
and improves the quality of paper due to the better coverage. In
other words, better glossier and smoother surface is obtained as
the coating pigments cannot penetrate into the base paper as
easily.
[0061] B1 Online-Coating
[0062] The base paper described hereinbefore was coated one-side
and the other side was surface-sized. The ABC single-blade coater
of BTG was used for coating. The surface sizing was performed in
the same unit by film transferring on the backing-roll of the
coater. The machine velocity was 750 m/min and length of the reeler
of the web was 252 cm. Online-coating was carried out after the
fourth drying group and the coating was dried with drying cylinders
(the 5.sup.th drying group).
[0063] Online-coating was made on base papers that had fillers
containing 15% of talc or SuperFill, respectively. Only the wire
side was coated (13 g/m.sup.2), the surface side was surface-sized
(0.5 g/m.sup.2).
[0064] Runnability of the online-coater was good with the
SuperFill. The coating conditions were kept constant and they are
presented in the Table 3. The composition of the coating mix or
solids content did not change during the test.
5TABLE 3 Coating conditions Talc SuperFill Basis weight of base
paper, g/m.sup.2 53.8 53.0 Basis weight of roller, g/m.sup.2 70.1
68.5 Basis weight of coating, g/m.sup.2 13.1 12.6 Moisture of base
paper, % 1.5 1.7 Moisture of roller, % 5.9 5.4 Blade pressure, kPa
188.7 182.9 Thickness, .mu.m 86.0 94.0
[0065] Properties of coated and calendered papers were
determined.
[0066] The coated and calendered paper that contains SuperFill has
about 5% units better gloss and 0.1 pps units better smoothness
than a corresponding paper filled with talc. This is a very good
result, taking into account that the coater amounts of the
SuperFill papers were even slightly smaller. The light scattering
factor and brightness of the SuperFill papers were also
considerably better than the corresponding papers filled with
talc.
[0067] On the basis of these results, it can be concluded that with
composite pigments the penetration of the coating colour into the
base paper can be effectively decreased and a better coverage and
gloss of the coating obtained. This is probably due to the fact
that the pores of the paper are small, their size distribution is
narrow and the smoothness of the base paper is extremely good.
* * * * *