U.S. patent application number 12/864986 was filed with the patent office on 2011-06-02 for method for production of paper.
This patent application is currently assigned to Akzo Nobel N.V.. Invention is credited to Hubert Igel, Jonas Liesen, Marie Turunen.
Application Number | 20110126995 12/864986 |
Document ID | / |
Family ID | 39363350 |
Filed Date | 2011-06-02 |
United States Patent
Application |
20110126995 |
Kind Code |
A1 |
Turunen; Marie ; et
al. |
June 2, 2011 |
METHOD FOR PRODUCTION OF PAPER
Abstract
The present invention relates to a method for the production of
paper from a suspension containing cellulosic fibers comprising
adding to the suspension and/or to a formed paper prepared from the
cellulosic suspension i) a nitrogen-containing organic compound
separately and/or in conjunction with, ii) an aqueous dispersion of
an acid anhydride and iii) at least one shading dye, draining the
suspension on a wire to form a paper.
Inventors: |
Turunen; Marie; (Spekerod,
SE) ; Liesen; Jonas; (Jorlanda, SE) ; Igel;
Hubert; (Gauriac, FR) |
Assignee: |
Akzo Nobel N.V.
Arnhem
NL
|
Family ID: |
39363350 |
Appl. No.: |
12/864986 |
Filed: |
January 26, 2009 |
PCT Filed: |
January 26, 2009 |
PCT NO: |
PCT/EP2009/050813 |
371 Date: |
October 4, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61062598 |
Jan 28, 2008 |
|
|
|
Current U.S.
Class: |
162/162 ;
162/158; 162/181.6 |
Current CPC
Class: |
D21H 17/14 20130101;
D21H 17/07 20130101; D21H 21/30 20130101 |
Class at
Publication: |
162/162 ;
162/158; 162/181.6 |
International
Class: |
D21H 21/28 20060101
D21H021/28; D21H 23/04 20060101 D21H023/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 2008 |
EP |
08150723.8 |
Claims
1. A method for production of paper from an aqueous suspension
containing cellulosic fibers comprising adding to the suspension
and/or to a paper web prepared from the suspension i) a
nitrogen-containing organic compound, ii) an aqueous dispersion of
an acid anhydride; and iii) at least one shading dye, draining the
suspension on a wire to form a paper.
2. The method according to claim 1, wherein the shading dye absorbs
electromagnetic radiation in the visible spectrum without
significantly emitting electromagnetic radiation or without
emitting electromagnetic radiation.
3. The method according to claim 2, wherein electromagnetic
radiation is absorbed in the spectrum from about 380 nm up to about
750 nm.
4. The method according to claim 2 or 3, wherein electromagnetic
radiation is absorbed in the spectrum from about 380 nm up to about
495 nm and/or from about 590 nm up to about 750 nm.
5. The method according to any of the preceding claims, wherein the
dye is selected from the group consisting of dioxazines and organic
compounds comprising at least a phthalocyanine moiety.
6. The method according to any of the preceding claims, wherein the
nitrogen-containing organic compound has a molar mass of up to
about 500 g/mol.
7. The method according to any of the preceding claims, wherein the
nitrogen-containing organic compound is an amine or a quaternary
ammonium compound thereof.
8. The method according to any of the preceding claims, wherein the
nitrogen-containing organic compound is an amine or quaternary
ammonium compound thereof having a molar mass up to about 180
g/mol.
9. The method according to any of the preceding claims, wherein the
nitrogen-containing organic compound is comprised in the aqueous
dispersion comprising an acid anhydride.
10. The method according to claim 9, wherein the aqueous dispersion
comprising an acid anhydride further comprises an anionic
polyelectrolyte.
11. The method according to claim 10, wherein the anionic
polyelectrolyte comprises colloidal silica-based particles.
12. The method according to claim 11, wherein the colloidal
particles have a particle size from about 1 to about 100 nm.
13. The method according to any of the preceding claims, wherein
the cellulosic fibers have a kappa number of less than about 8.
14. The method according to any of the preceding claims, wherein
the cellulosic fibers have a brightness of more than about 83.
15. The method according to any of the preceding claims, wherein
the conductivity of the cellulosic suspension is at least about 2.0
mS/cm.
16. The method according to any of the preceding claims, wherein
the suspension further comprises at least one optical brightening
agent.
17. Paper obtainable according to the method as defined by any of
the preceding claims.
18. Paper comprising acid anhydride and/or derivatives thereof, a
nitrogen-containing organic compound and at least one shading dye,
wherein the paper has no visual agglomerations of pigments.
19. The paper according to claim 18, wherein the pigments are
bluish.
20. Use of a nitrogen-containing organic compound being an amine or
quaternary ammonium compound thereof having a molar mass less than
about 180 g/mol in a method for producing paper from a suspension
as an additive for improving the distribution of dyes in the paper,
wherein the suspension comprises at least one shading dye.
21. The use according to claim 20, wherein the nitrogen-containing
organic compound is comprised in an aqueous dispersion comprising
an acid anhydride.
Description
[0001] The present invention refers to papermaking and more
specifically to a method for the production of paper wherein a
nitrogen-containing organic compound, an aqueous dispersion of an
acid anhydride and at least one shading dye are added to a
cellulosic suspension.
BACKGROUND
[0002] In the papermaking art, an aqueous suspension containing
cellulosic fibers, and optional fillers and additives, referred to
as stock, is fed into a headbox which ejects the stock onto a
forming wire. Water is drained from the stock through the forming
wire so that a web of paper is formed on the wire, and the web is
further dewatered and dried in the drying section of the paper
machine. The obtained water, usually referred to as white water and
containing fine particles such as fine fibers, fillers and
additives, is usually recycled in the papermaking process. When
producing paper where the aesthetic impression, including
properties such as whiteness, brightness and/or the printability is
important, hereinafter referred to as higher grade paper or high
grade paper, the amount and number of fillers and additives are
often increased compared to papers of lower quality. While the
performance chemicals are added to the suspension or to the paper
web to improve the runnability of the papermaking machine and/or
increase the quality, they may influence the performance of each
other.
[0003] Commonly, papers of higher grade, such as white fine paper,
need some degree of resistance to wetting and penetration of
aqueous liquids. Therefore, sizing agents, such as
cellulose-reactive sizing agents, are typically added to the
cellulosic suspension and/or the paper web. Cellulose-reactive
sizing agents including ketene dimer based sizing agents and acid
anhydrides are frequently used in neutral to slightly alkaline
stocks. Acid anhydrides are often used in papermaking processes
requiring fast curing of the sizing agent. Fast curing, i.e. high
rate of obtaining hydrophobic properties of the paper, is often
required for coated paper grades. Furthermore, paper sized with
acid anhydrides achieves better runnability in printing processes
e.g. with respect to reduced tendency of agglomeration of reactive
sizing agent related derivatives in the printing machinery compared
to e.g. paper sized with ketene dimer agents. Yet, when acid
anhydrides are used in a papermaking process where performance
chemicals having an impact on the aesthetic properties of the
formed paper, such as color and whiteness, are present in the
suspension, uneven distribution of dyes in the finished paper may
occur which is perceived as color spots.
[0004] US 2003/0188393 A1 refers to a process for controlling the
brightness of paper while using shading dyes.
[0005] WO 2007/073321 relates to an aqueous dispersion of
cellulose-reactive sizing agent, a method for preparing the
dispersion, and a process for producing paper comprising adding the
dispersion to the suspension.
[0006] However, an irregular distribution of pigments (dyes),
perceived by the human eye as colored spots, may be observed in
white paper, such as white fine paper, when shading dyes are
present in the cellulosic suspension and acid anhydrides are used
as a sizing agent. The presence of colored spots in the paper may
occur during initial production. However, colored spots tend to
increase over time. Shading dyes are typically added to a
cellulosic suspension in order to increase the whiteness.
Accordingly, it is an objective with the present invention to
reduce or eliminate the presence of colored spots in paper. A
further object is to reduce or eliminate the presence of colored
spots in paper obtained from a process for production of paper
comprising adding an acid anhydride to a cellulosic suspension
comprising at least one shading dye. A still further object is to
reduce or eliminate irregular distribution of shading dye in paper
obtained from a process for production of paper comprising adding
an acid anhydride to a cellulosic suspension comprising at least
one shading dye. Further objects will appear hereinafter.
THE INVENTION
[0007] The present invention relates to a method for the production
of paper, paper which may be obtained by the method, and the use of
a nitrogen-containing organic compound as further defined
herein.
[0008] More specifically, the present invention relates to a method
for production of paper web from an aqueous suspension containing
cellulosic fibers comprising adding to the suspension and/or to a
paper web prepared from the suspension i) a nitrogen-containing
organic compound, ii) an aqueous dispersion of an acid anhydride;
and iii) at least one shading dye, draining the suspension on a
wire to form a paper. The invention further pertains to the use of
a nitrogen-containing organic compound being an amine or quaternary
ammonium compound thereof having a molar mass less than about 180
g/mol in a method for producing paper from a suspension as an
additive for improving the distribution of dyes in the paper,
wherein the suspension comprises at least one shading dye.
According to one embodiment of the invention the
nitrogen-containing organic compound is comprised in the aqueous
dispersion comprising an acid anhydride.
[0009] Also, the present invention pertains to paper obtainable
from the method as disclosed herein, and paper comprising acid
anhydride and/or derivatives thereof, a nitrogen-containing organic
compound and at least one shading dye, wherein the paper has no
visual agglomerations of pigments.
[0010] Shading dyes, are believed to be more evenly distributed in
the paper when a nitrogen-containing organic compound is added to a
cellulosic suspension comprising at least one shading dye and sized
by the addition of an aqueous dispersion of an acid anhydride.
[0011] It has been observed that acid anhydride sizing of
cellulosic suspensions comprising shading dyes used for the
manufacturing of paper has resulted in paper containing
agglomeration of pigment rendering visual spots of color, often of
bluish color. Surprisingly, the addition of a nitrogen-containing
organic compound counteracts the agglomeration of dyes in the
formed paper. What is more, agglomeration of white pigments is also
reduced by the addition of a nitrogen-containing organic
compound.
[0012] As used herein, by paper is meant paper intended for
printing, such as office paper and paper for graphic production,
commonly simply referred to as printing paper. Usually, the paper
is white, nevertheless, the term "paper" may include any kind of
colored papers. The present invention is, however, advantageous for
the production of white paper, including white printing paper.
According to one embodiment, the paper, suitably white paper, has a
grammage up to about 350 g/m.sup.2. According to one embodiment,
the term "paper" does not embrace board and paper board. Yet, paper
according to the present invention can be applied as the top layer
of board and paper board.
[0013] As whiteness is an issue of the paper manufactured according
to the present invention, cellulosic fibers, often referred to as
pulp, should preferably have a .kappa. (kappa number) of less than
about 8 (ISO 302), less than about 4, less than about 3, or less
than about 2. The cellulosic fibers may be obtained by any pulping
processes as long as the fibers can be used for the production of
paper. Pulping processes include mechanical, thermal,
semi-mechanical, semi-chemical, and chemical pulping processes.
Commonly chemical processes are sulfite and sulphate processes, the
latter also referred to as the kraft pulping process. Cellulosic
fibers obtained by chemically pulping processes, suitably fibers
from the kraft process, are preferred. The cellulosic fibers are
usually also bleached in order to reduce the content of lignin and
to achieve a high brightness of the fibers. In order to obtain
cellulosic fibers with a high brightness and low content of lignin,
raw fiber material is commonly subjected to a chemical (kraft)
pulping process and subsequently bleached. The bleaching sequence
usually comprises several bleaching operations interrupted by
washing stages and alkaline extraction. Bleaching chemicals include
e.g. chlorine dioxide, peroxides such as hydrogen peroxide, oxygen,
ozone, and peracetic acid. Preferred cellulosic fibers are
chemically delignified fibers subsequently bleached using an
elemental chlorine free (ECF) bleaching sequence or a total
chlorine free (TCF) bleaching sequence.
[0014] According to one embodiment, the cellulosic fibers used in
the present invention have a brightness of above about 83 (ISO
3688), above about 88, or above about 90. Cellulosic fibers may
have a .kappa. (kappa number) of less than about 4 and a brightness
above about 88.
[0015] Fiber raw material used in the above pulping processes may
include but are not limited to wood such as hardwood, softwood,
agricultural residues e.g. straw, annual plants (hemp, jute, kenaf,
bamboo, etc), recycled or secondary fibers, and any type of deinked
fibers.
[0016] In order to further improve the quality of the paper with
respect to e.g. whiteness, brightness, several non-fiber
constituents can be added to the cellulosic suspension and/or to
the dewatered paper web. The cellulosic suspension and finished
paper can contain mineral fillers such as kaolin, china clay,
titanium dioxide, gypsum, talc, calcium carbonate e.g. chalk,
ground marble and precipitated carbonate. According to one
embodiment, the cellulosic suspension contains more than about 5%
by weight of mineral fillers based on dry cellulosic suspension and
optional fillers, such as more than about 10% by weight.
[0017] According to the present invention at least one shading dye
is present in the cellulosic suspension. Shading dyes, are
compounds which further improve the whiteness of the paper.
Whiteness is the sensation of those colors perceived by the human
eye as being white. In physical terms a substrate is perceived as
white if all visible light (to the human eye) impinging on the
substrate is reflected without any loss of intensity. By visible
light is meant the part of the electromagnetic spectrum which can
be detected by the human eye. Very few substrates and chemical
compounds reflect the entire spectrum of light without absorbing
certain wavelengths of the visible electromagnetic radiation.
Clouds and new fallen snow reflect most of the light, also some
pigments, notably titanium dioxide, have such a property. However,
usually some light is absorbed by the object, commonly light in the
blue range of the spectrum, rendering a yellowish appearance. In
order to improve the whiteness of paper, e.g. decrease of
yellowness, shading dyes may be added in the production process.
Fluorescent whitening agents (FWA), including optical brightening
agents (OBA) can also be added to the cellulosic suspension,
improving inter alia the brightness of the paper. OBA and FWA are
fluorescent molecules improving the brightness of paper through an
additive color mixing process since they emit most of the absorbed
light. Shading dyes, on the other hand, are compounds typically
increasing the whiteness by subtracting color mixing.
[0018] As used herein, shading dyes are the group of compounds
enhancing the perceived whiteness of paper, however, without
including brightening agent, i.e. compounds emitting radiation
(fluorescent compounds).
[0019] Shading dyes may be selected from naturally and synthetic
inorganic compounds and synthetic organic compounds. One preferred
group of compounds are synthetic organic compounds. Suitably, the
structure of the synthetic organic compounds comprises a system of
conjugated double bonds. Said conjugate double bonds can oscillate
more or less freely. Typically, the synthetic organic compounds
comprise one or more of same or different chromophoric groups
(electron acceptors groups) such as ethylene-, keto-, thioketo-,
azo-, and carbon-nitrogen-groups.
[0020] Compounds improving the whiteness of paper may be selected
from the group consisting of azo dyes, anthraquinone dyes, indigoid
dyes, polymethine dyes, aryl-carbonium dyes, phtalocyanine dyes and
nitro dyes.
[0021] Azo-group containing compounds usually contain the moiety
A-N.dbd.N-D, where A and D often are aromatic moieties. The
A-N.dbd.N-D moiety may be part of a ring system, e.g. hydrazones,
or the azo-group containing compound may form metal complexes. The
azo-containing compound may have up to four azo-groups.
[0022] Synthetic organic compounds comprising keto groups include
compounds having a anthraquinone moiety, such as 9,10-quinone.
9,10-quinone may be substituted by electron donator groups in the
free positions 1 to 4 and 5 to 8, specifically in the positions 1,
4, 5, and 8.
[0023] Indigoid compounds include the structure element
--CO--CX.dbd.CY--CO--, where X, Y is selected from O, S, Se, or NH.
Indigo (1) and substituted indigo compounds are examples of
indigoid compounds.
##STR00001##
[0024] Polymethine compounds comprise the general structure (2).
Polymethine compounds may be cationic, neutral or anionic,
depending on the character of groups A and B.
[0025] [A=CR--(X.dbd.Y).sub.x--B].sup.Z (2), wherein X and Y
independently can be C or N, x is an integer, and z being +n, 0 or
-n (n being an integer). Cyanines (Cl basic red 12) and
hemicyanines (Cl basic violet 7) are examples of cationic
polymethines where both X and Y are carbon atoms. Diazahemicyanines
(Cl basic blue 41), azacarbocyanines (Cl basic yellow 11) and
diazacarbocyanines (Cl basic yellow 28) are examples of
polymethines where X and Y are nitrogen or a combination of
nitrogen and carbon. Neutral polymethine compounds may be
exemplified by meroxyanine and anionic polymethines by oxonol.
[0026] Aryl-carbonium compounds include a group of compounds
comprising the general structure (3),
##STR00002##
wherein m and n is 0 or 1, X is C or N, Y is O, S or NR, A and B
are independently O, S or NR, and R is an alkyl- or aryl-group.
[0027] Other compounds improving the whiteness of paper may include
phthalocyanine compounds and nitro containing compounds. The latter
typically comprises two or more aromatic rings, usually benzene or
naphthalene, containing at least one nitro-group and an electron
donor group such as NH.sub.2 or OH.
[0028] Shading dyes are dyes which absorb light (electromagnetic
radiation) in the visible spectrum without significantly emitting
electromagnetic radiation or without emitting electromagnetic
radiation in addition to the reflected radiation. Accordingly,
shading dyes do not increase the intensity of the reflected
radiation in the visible spectrum of the substrate, i.e. they do
not emit radiation (light) or they do not significantly emit
radiation. Shading dyes can, thus, be referred to as subtractive
dyes. Shading dyes (subtracting dyes) absorb the complementary
wavelength region to the wavelength region leading to yellowness.
Shading dyes may be defined as non-fluorescent compounds (dyes)
absorbing radiation in the visible spectrum in such a way that the
perceived whiteness of the paper is increased. Shading dyes
typically absorb light in the bluish portion of the visible
spectrum (from about 380 nm to about 495 nm), and/or in the
orange-reddish portion of the visible spectrum (from about 590 nm
to about 750 nm). Shading dyes may be referred to as organic
molecules comprising conjugated systems, i.e. conjugated organic
molecules, absorbing electromagnetic radiation in the visible
spectrum, i.e. from about 380 nm up to about 750 nm, preferably in
the range of from about 380 nm to about 500 nm and/or in the range
of from about 580 nm to about 750 nm). As used here a conjugated
system denotes a delocalisation of electrons across adjacent
parallel aligned p orbitals of atoms.
[0029] A preferred class of dyes is dyes under the name
Viscofil.RTM.. Another preferred group of shading dyes are
phthalocyanine compounds (organic compounds comprising a
phthalocyanine moiety) including but not limited to metal
phthalocyanine compounds optionally comprising solubilising groups
such as sulphonic acid functions, e.g. salts of
phthalocyanine-sulfonic acids such as sodium or ammonium salts of
copper phthalocyanine. Organic amine salts of sulfonic acids may
also be comprised in the phthalocyanine type compounds.
Phthalocyanine type compounds are able to co-ordinate hydrogen
and/or metal cations in the centre. Common coordinated metal
cations are copper and cobalt. Other phthalocyanine dyes include
derivatives of metal phthalocyanine and organic amines. Yet further
preferred classes of dyes are triphenodioxazines commonly referred
to as dioxazines. Preferred dioxazines include dihalide
triphenodioxazine such as 9,10-dichlorotriphenodioxazine and
triphenodioxazines comprising a acetylamino or bezoylamino group,
ethoxy group, halide atom or an HNCOCH.sub.3 group. Preferred
shading dyes are also selected from the group consisting of
dioxazines and organic compounds comprising a phthalocyanine
moiety.
[0030] Examples of shading dyes are Viscofil.RTM. dyes from
Clariant.RTM. and Levanyl.RTM. dyes from Laxness.RTM., including
but not limited to Viscofil.RTM.: Orange GG, Orange S-RL, Red R 30,
Red BL, Red F5RK, Bordo BB, Violet BLN, Blue B2G, Blue BLF,
Levanyl.RTM. Violet 23. Further shading dyes are Cartasol.RTM. F,
Cartasol.RTM. K, Cartasol.RTM. M, Carta.RTM. dyes, Carta.RTM.
powder dyes, Cartazine.RTM., Diresul.RTM. P, Cartaren.RTM.,
Flexonyl.RTM., Cartacrom.RTM., Hostatint.RTM..
[0031] According to one embodiment of the present invention, the
cellulosic suspension may also contain at least one fluorescent
compound e.g. OBAs, such as fluorescent organic compounds absorbing
ultraviolet light (e.g. from daylight at 300-430 nm) and emitting
most of the absorbed energy as blue fluorescent light in the range
of from about 400 up to about 500 nm. Examples of OBAs are those
OBAs sold under the name Leucophor.RTM..
[0032] The shading dyes and OBAs may be added to the cellulosic
suspension and/or applied to the surface of a cellulosic sheet or
web of paper. They may be added at any point to the cellulosic
suspension starting from the mixing chest up to and including the
head box and/or to the formed web of paper after the head box. The
sequence of addition of the shading dye(s) and/or the OBAs,
dispersion of acid anhydride, and nitrogen-containing organic
compound, where appropriate, the sequence of the addition of the
shading dyes and/or the OBAs and the acid anhydride dispersion
comprising a nitrogen-containing organic compound may vary and may
be in any order.
[0033] The total amount of added shading dye(s) is usually up to
about 400 g/t based on dry cellulosic suspension and optional
fillers, suitably less than about 300 g/t. The shading dye(s) may
be added to the mixing chest. OBAs, if present in the formed paper,
are typically added to the suspension in an amount of up to about
30 kg/t based on dry cellulosic suspension, suitably up to about 20
kg/t. Commonly, OBAs are added to the cellulose suspension up to
and including the level box. If both shading dyes and OBAs are
used, the shading dyes may be added prior to the addition of the
OBAs. Shading dyes may e.g. be added to the mixing chest and OBAs
to the level box.
[0034] The nitrogen-containing organic compound may be selected
from amines such as primary, secondary and tertiary amines; and
quaternary ammonium compounds thereof. Suitable nitrogen-containing
organic compounds further include monoamines, diamines and
polyamines and quaternary ammonium compounds thereof. Suitable
quaternary ammonium compounds include protonated, alkylated,
arylated and alkarylated amines of the above-mentioned types, which
can be formed by reaction of the amines with, for example, acids,
e.g. hydrochloric acid, and methyl chloride, dimethyl sulphate and
benzyl chloride. According to one embodiment, the
nitrogen-containing organic compound is an amine or quaternary
ammonium thereof optionally having one or more hydroxyl groups.
Preferably, one or more hydroxyl groups are present in a terminal
position of one or more substituents of the nitrogen-containing
compound, i.e. a hydroxyl group terminated amine or quaternary
ammonium compound thereof.
[0035] Examples of suitable nitrogen-containing organic compounds
include the following amines and their quaternary ammoniums:
diethylene triamine, methylene tetramine, hexamethylene diamine,
diethyl amine, dipropyl amine, di-isopropyl amine, cyclohexylamine,
pyrrolidine, guanidine, triethanol amine, monoethanol amine,
diethanol amine, 2-methoxyethyl amine, aminoethylethanol amine,
alanine and lysine. Further examples of suitable
nitrogen-containing organic compounds include choline hydroxide,
tetramethyl ammoniumhydroxide, tetraethyl ammoniumhydroxide.
Preferred nitrogen-containing organic compounds include triethanol
amine and quaternary ammonium compounds thereof.
[0036] The molar mass of the nitrogen containing organic compound
can vary within wide limits. As used herein, nitrogen-containing
organic compounds refer to non-polymeric compounds, i.e. compounds
not comprising repetitive structural units. Typically, the molar
mass of the nitrogen-containing organic compound is up to about 500
g/mol, e.g. up to about 400 g/mol, or up to about 180 g/mol.
[0037] In one embodiment of the invention, the molar mass of the
amine or quaternary ammonium compound thereof is less than about
180 g/mol, e.g. up to about 170 g/mol or up to about 160 g/mol. The
molar mass is usually at least about 30 g/mol. As stated herein,
the molar mass of a quaternary ammonium of an amine means the molar
mass of the cationic part of the quaternary ammonium compound,
meaning that the anionic part of the quaternary ammonium compound
is not included in the molar mass given above. For
nitrogen-containing organic compounds which are selected from
amines and quaternary ammoniums thereof having one or more hydroxyl
groups, the molar masses may be higher, e.g. less than about 500
g/mol and usually less than about 300 g/mol, although the
above-mentioned molar masses are also suitable for such
compounds.
[0038] The nitrogen-containing organic compound may be added
separately/singly to the cellulosic suspension or in conjunction
with other additives such as the acid anhydride sizing agent, e.g.
comprised in the aqueous dispersion of the acid anhydride. If added
singly, the nitrogen-containing organic compound can be added to
the aqueous cellulosic suspension and/or to the formed paper web,
typically at any point starting from the machine chest up to and
including the head box and/or to the paper web after the head box.
The amount of nitrogen-containing organic compound as a single
addition can be from about 0.0004 up to about 0.1% by weight based
on dry cellulosic suspension and optional fillers, e.g. from about
0.0008 up to about 0.01% by weight.
[0039] According to one embodiment, the nitrogen-containing organic
compound is added in conjunction with the sizing agent.
[0040] According to one embodiment, the nitrogen-containing organic
compound is comprised in an aqueous dispersion comprising the acid
anhydride.
[0041] According to yet a further embodiment of the invention the
aqueous dispersion comprising an acid anhydride and a
nitrogen-containing organic compound additionally comprises an
anionic polyelectrolyte.
[0042] The anionic polyelectrolyte according to the invention can
be selected from organic and inorganic compounds and it can be
derived from natural or synthetic sources. The anionic
polyelectrolyte has two or more anionic groups which can be of the
same or different types. Examples of suitable anionic groups, i.e.
groups that are anionic or rendered anionic in an aqueous phase,
include silanol, aluminosilicate, phosphate, phosphonate, sulphate,
sulphonate, sulphonic and carboxylic acid groups as well as salts
thereof, usually ammonium or alkali metal (generally sodium) salts.
The anionic polyelectrolytes may be water-soluble, e.g. linear and
branched anionic polyelectrolytes, or water-dispersable, e.g.
cross-linked and/or particulate anionic polyelectrolytes. According
to one embodiment, the water-dispersable and particulate anionic
polyelectrolytes are colloidal, i.e. in the colloidal range of
particle size. The colloidal particles suitably have a particle
size from 1 to 100, e.g. from 2 to 70 or from 2 to 40 nm. The
water-dispersable and particulate anionic polyelectrolytes may
contain aggregated and/or non-aggregated particles.
[0043] Examples of suitable organic anionic polyelectrolytes
include anionic polysaccharides like starches, guar gums,
celluloses, chitins, chitosans, glycans, galactans, glucans,
xanthan gums, mannans, and dextrins. Further examples of suitable
organic anionic polyelectrolytes include synthetic anionic polymers
such as condensation polymers, e.g. polyurethanes and
naphthalene-based and melamine-based polymers, e.g. condensated
formaldehyde naphthalene sulfonates and polymers based on
melamine-sulfonic acid, and vinyl addition polymers prepared from
ethylenically unsaturated monomers including anionic or potentially
anionic monomers, e.g. acrylic acid, methacylic acid, maleic acid,
itaconic acid, crotonic acid, vinylsulfonic acid, sulfonated
styrene and phosphates of hydroxyalkyl acrylates and methacrylates,
optionally copolymerized with non-ionic ethylenically unsaturated
monomers, e.g. acrylamide, alkyl acrylates, styrene and
acrylonitrile as well as derivatives of such monomers, vinyl
esters, and the like.
[0044] Examples of further suitable organic anionic
polyelectrolytes include water-soluble branched polymers and
water-dispersible crosslinked polymers obtained by polymerization
of a monomer mixture comprising one or more ethylenically
unsaturated anionic or potentially anionic monomers and,
optionally, one or more other ethylenically unsaturated monomers,
in the presence of one or more polyfunctional crosslinking agents.
The presence of a polyfunctional crosslinking agent in the monomer
mixture renders possible preparation of branched polymers, slightly
crosslinked polymers and highly crosslinked polymers that are
water-dispersible. Examples of suitable polyfunctional crosslinking
agents include compounds having at least two ethylenically
unsaturated bonds, e.g. N,N-methylene-bis-(meth)acrylamide,
polyethyleneglycol di(meth)acrylate, N-vinyl (meth)acrylamide,
divinyl-benzene, triallylammonium salts and
N-methylallyl(meth)acrylamide; compounds having an ethylenically
unsaturated bond and a reactive group, e.g. glycidyl
(meth)acrylate, acrolein and methylol(meth)acrylamide; and
compounds having at least two reactive groups, e.g. dialdehydes
like glyoxal, diepoxy compounds and epichlorohydrin.
[0045] The organic anionic polyelectrolyte usually has a degree of
anionic substitution (DSA) from 0.01 to 1.4, e.g. from 0.1 to 1.2
or from 0.2 to 1.0. The anionic polyelectrolyte may contain one or
more cationic groups as long as it has an overall anionic charge.
The molar mass of the anionic polyelectrolyte can vary within wide
ranges; usually the molar mass is above 200 such as above 500,
whereas the upper limit is usually 10 million such as 2 million
g/mol.
[0046] Examples of suitable inorganic anionic polyelectrolytes
include anionic siliceous materials, e.g. anionic silica-based
materials prepared from silicic acid and clays of the smectite
type. Usually, these anionic polyelectrolytes have negative
silanol, aluminosilicate or hydroxyl groups. Examples of suitable
inorganic anionic polyelectrolytes include polysilicic acid,
polysilicates, polyaluminiumsilicates, colloidal silica-based
particles, e.g. particles of silica, aluminated
(aluminium-modified) silica and aluminiumsilicate, polysilicate
microgels, polyaluminiumsilicate microgels, silica gels and
precipitated silica, smectite clays, e.g. montmorillonite,
bentonite, hectorite, beidelite, nontronite and saponite. Preferred
anionic polyelectrolytes include silica-based materials, e.g.
colloidal silica-based particles.
[0047] The acid anhydride can be any acid anhydride-based sizing
agent known in the art. Suitably, the sizing agent is a hydrophobic
acid anhydride. Suitable hydrophobic acid anhydrides can be
characterized by the general formula (I) below, wherein R.sup.1 and
R.sup.2 are independently selected from saturated or unsaturated
hydrocarbon groups which suitably contain from 8 to 30 carbon
atoms, or R.sup.1 and R.sup.2 together with the --C--O--C-- moiety
can form a 5 to 6 membered ring, optionally being further
substituted with hydrocarbon groups containing up to 30 carbon
atoms.
R.sup.1--(C.dbd.O)--O--(C.dbd.O)--R.sup.2
[0048] Examples of suitable acid anhydrides include alkyl and
alkenyl succinic anhydrides, e.g. iso-octadecenyl succinic
anhydride, iso-octadecyl succinic anhydride, n-hexadecenyl succinic
anhydride, dodecenyl succinic anhydride, decenyl succinic
anhydride, octenyl succinic anhydride, tri-isobutenyl succinic
anhydride, 1-octyl-2-decenyl-succinic anhydride and
1-hexyl-2-octenyl-succinic anhydride. Examples of suitable acid
anhydrides further include the compounds disclosed in U.S. Pat.
Nos. 3,102,064; 3,821,069; 3,968,005; 4,040,900; 4,522,686; and Re.
29,960, which are hereby incorporated herein by reference.
[0049] The cellulose-reactive sizing agent may contain one or more
acid anhydrides, e.g. one or more alkyl and/or alkenyl succinic
anhydrides. Usually, the acid anhydride of this invention is liquid
at room temperature.
[0050] The dispersion suitably contains a dispersant, or dispersant
system, comprising an anionic polyelectrolyte and a
nitrogen-containing organic compound. When used in combination,
these compounds are effective as a dispersant for the acid
anhydride sizing agent although the anionic polyelectrolyte and
nitrogen-containing organic compound may not be effective as a
dispersant when used singly. Preferably, the dispersion is anionic,
i.e. the dispersant, or dispersant system, has an overall anionic
charge.
[0051] With respect to the embodiment where the nitrogen-containing
organic compound is comprised in the dispersion of the acid
anhydride, the acid anhydride may be present in an amount of from
about 0.1 to about 50, e.g. from 0.1 to about 30, or from about 1
to about 20% by weight, based on the weight of the aqueous
dispersion. The optional anionic polyelectrolyte is usually present
in an amount of up to about 100% by weight, usually from 0.1 to 15%
by weight, suitably from 0.5 to 10, e.g. from 1 to 7% by weight,
based on the weight of the acid anhydride. The nitrogen containing
organic compound can be present in an amount of up to 20% by
weight, usually from 0.1 to 15, such as from 0.5 to 10, or from 1
to 7% by weight, based on the weight of the acid anhydride. In
addition to the acid anhydride, anionic polyelectrolyte and
nitrogen containing organic compound, optional additional compounds
may be present in the dispersion. Examples of such compounds
include mono-, di- and poly-anionic and non-ionic surfactants and
dispersing agents, stabilizers, extenders and preservative agents
such as, for example, hydrolyzed acid anhydrides, e.g. hydrolyzed
alkyl and alkenyl acid anhydrides as mentioned above, preferably
hydrolyzed alkenyl succinic anhydrides, e.g. hydrolyzed acid
anhydrides in the form of carboxylic acid and/or carboxylic acid
ester derivatives, anionic surfactants like phosphate esters, such
as ethoxylated phosphate esters, alkyl sulphates, sulphonates and
phosphates, alkylaryl sulphates, sulphonates and phosphates, e.g.
sodium lauryl sulphonate and ethoxylated, phosphated
isotridecylalcohol. If present, the content of such additional
compounds in the dispersion can be from 0.1 to 15, e.g. from 1 to
10, or from 2 to 7% by weight, based on the weight of the acid
anhydride. Water is also present in the dispersion and may
constitute the remainder of the dispersion up to 100% by
weight.
[0052] The aqueous dispersion comprising the nitrogen-containing
organic compound, the acid anhydride and optionally an anionic
polyelectrolyte can be produced by forming a mixture containing the
acid anhydride, anionic polyelectrolyte and nitrogen-containing
organic compound as defined above and dispersing the mixture in the
presence of water. The components of the dispersion may be admixed
in any order but preferably the anionic polyelectrolyte and the
nitrogen-containing organic compound are mixed and diluted with
water to appropriate concentration, and then the acid anhydride is
dispersed therein. According to an embodiment the dispersion
containing the anionic polyelectrolyte, nitrogen-containing organic
compound and acid anhydride is mixed with starch prior to the
addition to the cellulosic suspension and/or to the paper web. The
starch which is premixed with the acid anhydride dispersion may
form part of the retention system. The mixture may be dispersed by
using suitable dispersing equipment providing sufficient degree of
dispersing, e.g. a static mixer providing relatively low shear
forces. The obtained dispersion contains droplets of acid anhydride
usually having a droplet size of from 0.1 to 10 .mu.m in
diameter.
[0053] The aqueous dispersion of acid anhydride comprising the
nitrogen-containing organic compound may be added to the cellulosic
suspension, i.e. anywhere between and including the machine chest
and head box, or alternatively to the cellulosic web or sheet, e.g.
at the size press. According to one embodiment, the aqueous acid
anhydride dispersion is added to the cellulosic suspension prior to
the head box.
[0054] The amount of acid anhydride sizing agent added to the
cellulosic suspension or applied to the cellulosic sheet or web can
be from about 0.01 up to about 1% by weight based on dry cellulosic
suspension and optional fillers, such as from about 0.05 up to
about 0.5% by weight.
[0055] The method and the use of the nitrogen-containing compound,
and the aqueous sizing dispersions are also useful in the
manufacture of paper from an aqueous cellulosic suspension having a
high conductivity. The conductivity of the suspension that is
dewatered on the wire can be within the range of from 0.3 mS/cm to
10 mS/cm. According to this invention, good results can be achieved
when the conductivity is at least 2.0, e.g. at least 3.5 or at
least 5.0, such as at least 7.5 ms/cm. Conductivity can be measured
by standard equipment such as, for example, a WTW LF 330 instrument
supplied by Christian Berner. The values referred to above are
suitably determined by measuring the conductivity of the cellulosic
suspension that is fed into or present in the headbox of the paper
machine or, alternatively, by measuring the conductivity of white
water obtained by dewatering the suspension. High conductivity
levels mean high contents of salts (electrolytes) which can be
derived from the materials used to form the stock, from various
additives introduced into the stock, from the fresh water supplied
to the process, etc. Further, the content of salts is usually
higher in processes where white water is extensively recirculated,
which may lead to considerable accumulation of salts in the water
circulating in the process.
[0056] The invention also relates to a paper obtainable from the
method as defined herein and to a paper comprising acid anhydride
and/or derivatives thereof, a nitrogen-containing organic compound
and at least one shading dye; and optionally at least one optical
brightening agent, wherein the paper has no visual agglomerations
of pigments.
[0057] The paper may be used in any conventional application.
However, the paper can typically be used as printing paper or
copying paper or any other use involving good printability
properties of the paper.
[0058] The invention is further illustrated by the following
examples, which, however, are not intended to limit the same. Parts
and % relate to parts by weight and % by weight, respectively,
unless otherwise stated.
EXAMPLE 1
[0059] Aqueous dispersions of alkenyl succinic anhydride (ASA) were
prepared by dispersing 10 g ASA based on an olefin fraction
comprising iso-hexadecenyl and iso octadecenyl succinic anhydride
in 190 g water containing 200 mg/l calcium chloride. All dispersion
were prepared by using an Osterizer laboratory mixer. The aqueous
phase was first added to the mixer. After addition of the ASA and
optional amine containing silica sol (dispersion no. 2), the
compositions were dispersed at high speed for 2 minutes.
[0060] ASA dispersion no. 1 was prepared by dispersing 10 g ASA
(EKA SA 420) in the presence of 190 g water containing 200 mg/l
calcium chloride at a temperature of 0.degree. C. (ASA content of
5% by weight).
[0061] ASA dispersion no. 2 was prepared by dispersing 10 g ASA
(EKA SA 820 SF) in 190 g water containing 200 mg/l calcium chloride
at a temperature of 12.degree. C. in the presence of 5 g of a
silica sol having a content of SiO.sub.2 of 8.0% by weight and
containing 50 (42.5% as active) % by weight of triethanol amine
(TEA) based on SiO.sub.2 (ASA content of 5% by weight, triethanol
amine content of 0.1% by weight, as active 0.085% by weight).
[0062] ASA dispersion no. 3 was prepared by dispersing 10 g of 100%
hydrolysed ASA in 190 g water containing 200 mg/l calcium chloride
at a temperature of 12.degree. C. (ASA content of 5% by
weight).
[0063] To all of the above prepared ASA dispersions were added 3.3
g of blue shading dye (undiluted Viscofil.RTM. blue BLF,
Clariant.RTM.) and 28.6 g of violet shading dye (undiluted
Levanyl.RTM. Violet BN-LF, Lanxess.RTM.). If the ASA dispersions
(5%) correspond to an addition of 30 kg ASA/t dry fiber then the
addition of shading dyes correspond to an addition of 100 g/t
(blue) and 860 g/t (red/violet), respectively. After mixing the
shading dye containing dispersions were allowed to rest for 20
minutes.
EXAMPLE 2
[0064] Paper sheets were prepared according to a process in which
the shading dye containing ASA dispersions of example 1 were added
to an aqueous cellulosic suspension comprising 80% of softwood
fibers and 20% of hardwood fibers (based on total fibers) having a
fiber concentration of 5 g/l, 7% of ground calcium carbonate (GCC),
a conductivity of 2 mS/cm (by the addition of calcium chloride), a
pH of 7.9, and 1.75 kg/t optical brightener agent (OBA)
(Leuchophore, UKO). The dispersions were added in an amount of 30
kg/t calculated as ASA based on dry cellulosic suspension. A
retention system was used comprising 5 kg/t of cationic starch
having a D.S. of 0.047 (Perlbond 970) and 7 kg/t polyaluminium
chloride (PAC). After addition of the ASA dispersion to the aqueous
cellulosic suspension the so formed cellulosic suspension was mixed
during 10 sec. prior to the formation of a sheet using a KCL sheet
former. The sheets were subsequently pressed during 8 minutes at
3.5 bar and thereafter dried. In this example, all amounts are
based on dry cellulosic suspension if not otherwise indicated.
Evaluation of the paper sheets with respect to color spots. Each
paper was divided into four equal parts, each measuring 8.times.8
cm, which were labelled 1 through 4. Seven individuals (people)
were given the task to count the number of blue and white spots in
each paper section and record the total. The average number of
spots recorded for each sheet is displayed in table 1 below.
TABLE-US-00001 TABLE 1 Blue spots White spots Sheet sizing system
Average Average ASA dispersion no. 1 13 1 ASA dispersion no. 2 0 0
ASA dispersion no. 3 >25 >25
EXAMPLE 3
[0065] In this example, all amounts are based on dry cellulosic
suspension if not otherwise indicated. In a full scale trial
printing and writing paper with a basis weight of 100-280
gram/m.sup.2 was manufactured using a papermaking process
comprising a Fourdrinier Bruderhaus with a multi-cylinder drying
process. The furnish suspension contained 50% virgin fibers, 15-20%
dry broke, 17% dry broke, and 3-12% GCC or precipitated calcium
carbonate (PCC) filler. The pH range of the furnish composition was
between 6.8 and 7.4. To the wet end of the process the following
components were added:
TABLE-US-00002 TABLE 2 Wet-end chemicals and dosages: Chemicals
Quality Dosage Point of addition ASA Eka SA 420 (a) 0.6-0.8 kg/t
before screen Eka SA 820SF (b) Starch Cationic 4.2-5.1 kg/t machine
chest Filler GCC 3-12% after level box PAC 18% 50 l/hr after level
box Shading Blue Viscofil .RTM. 50 g/t mixing chest dyes blue BLF
Violet, 430 g/t Levanyl .RTM. Violet BN-LF OBA Blancophore .RTM. 15
kg/t level box
a) According to Prior Art
[0066] The acid anhydride sizing dispersion (Eka ASA 420) was fed
into a starch stream prior to addition to the suspension. A
nitrogen-containing organic compound was not present in the
dispersion nor in the cellulosic suspension
b) According to Invention
[0067] The acid anhydride sizing agent EKA SA 820SF was emulsified
into a stream of silica sol having a content of SiO.sub.2 of 8.0%
by weight and containing 50% (42.5% as active) by weight of
triethanol amine (TEA) based on SiO.sub.2 with a weight ratio of
2:1 prior to feeding the obtained dispersion into a cationic starch
stream prior to addition to the suspension.
[0068] While using the EKA ASA 420 sizing dispersion, blue spots
visually appeared in the paper after less than 5 days.
[0069] When using a sizing dispersion comprising Eka SA 820 SF and
silica sol having a content of SiO.sub.2 of 8.0% by weight and
containing 50% (42.5% as active) by weight of triethanol amine
(TEA) based on SiO.sub.2 the paper had no visual blue spots after
125 day of continuous running.
* * * * *