U.S. patent application number 12/223267 was filed with the patent office on 2010-09-16 for process for producing optically brightened paper.
Invention is credited to Achim Kohler.
Application Number | 20100230061 12/223267 |
Document ID | / |
Family ID | 36636660 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100230061 |
Kind Code |
A1 |
Kohler; Achim |
September 16, 2010 |
Process for Producing Optically Brightened Paper
Abstract
The instant invention relates to a process for the production of
optically brightened paper by treating the pulp suspension with an
optically brightened filler composition comprising optically
brightened plastic fibres, preferably polyester fibres, which leads
to a surprising high lightfastness of the resulting paper.
Inventors: |
Kohler; Achim; (Heilbronn,
DE) |
Correspondence
Address: |
CLARIANT CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
4000 MONROE ROAD
CHARLOTTE
NC
28205
US
|
Family ID: |
36636660 |
Appl. No.: |
12/223267 |
Filed: |
December 22, 2006 |
PCT Filed: |
December 22, 2006 |
PCT NO: |
PCT/EP2006/070148 |
371 Date: |
July 25, 2008 |
Current U.S.
Class: |
162/157.3 ;
162/157.2; 162/157.5 |
Current CPC
Class: |
D21H 13/26 20130101;
D21H 13/24 20130101; D21H 13/14 20130101; D21H 21/30 20130101 |
Class at
Publication: |
162/157.3 ;
162/157.2; 162/157.5 |
International
Class: |
D21H 13/24 20060101
D21H013/24; D21H 13/10 20060101 D21H013/10; D21H 13/14 20060101
D21H013/14; D21H 13/26 20060101 D21H013/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2006 |
EP |
06001577.3 |
Claims
1. A process for optical brightening of paper comprising the step
of adding an optically brightened filler composition comprising at
least one optically brightened plastic fiber to a pulp
suspension.
2. A process according to claim 1, wherein the at least one
optically brightened plastic fiber comprises a polymer selected
from the group consisting of: polyester, polyethylene,
polypropylene and polyamide.
3. A process according to claim 1 wherein the at least one
optically brightened plastic fiber comprises polyester.
4. A process according to claim 1, wherein the at least one
optically brightened plastic fiber has a fineness between 1 and 10
dtex and is cut to a length of between 0.1 and 1 mm.
5. A process according to claim 1, wherein the at least one
optically brightened plastic fiber has a fineness between 1 and 2
dtex and is cut to a length of between 0.2 and 0.6 mm.
6. A process according to claim 1, wherein the at least one
optically brightened plastic fiber is optically brightened with at
least one compound of formulae (1) to (4) ##STR00004## where in
formula (1) R.sub.1 to R.sub.8 independently of one another are
hydrogen, C.sub.1-C.sub.20-alkyl or groups of the formula
--COOR.sub.9, R.sub.9 is hydrogen, C.sub.1-C.sub.20-alkyl or
phenyl, or R.sub.1 to R.sub.8 are a group of the formula
--SO.sub.2R.sub.10, where R.sub.10 is hydrogen,
C.sub.1-C.sub.10-alkyl or C.sub.1-C.sub.10-hydroxyalkyl, and A is
stilbene, naphthalene, phenylene, thiophenylene or biphenylene, or
a mixture thereof.
7. A process according to claim 6, wherein the at least one
optically brightened fiber is optically brightened with at least
one compound of formula (1) wherein R.sub.1 to R.sub.8
independently of one another are hydrogen or C.sub.1-C.sub.4-alkyl,
and A is stilbene, naphthalene, phenylene, thiophenylene or
biphenylene.
8. A process according to claim 7, wherein R.sub.1 to R.sub.8
independently of one another are hydrogen or methyl, and A is
stilbene.
9. A process according to claim 1, wherein the at least one
optically brightened plastic fiber contains between 10 and 500 ppm
optical brightener.
10. A process according to claim 1, wherein the at least one
optically brightened plastic fiber contains between 20 and 250 ppm
optical brightener.
11. A process according to claim 1, wherein 2 to 60% by weight,
based on the weight of the dry pulp, of the optically brightened
filler composition is added to the pulp suspension.
12. A process according to claim 1, wherein 10 to 40% by weight,
based on the weight of the dry pulp, of the optically brightened
filler composition is added to the pulp suspension.
13. A process according to claim 1, wherein the optically
brightened filler composition is added to the pulp suspension in
the form of an aqueous dispersion.
14. An optically brightened paper produced by a process according
to claim 1.
Description
[0001] The present invention relates to a process for the
production of optically brightened paper by treating the pulp
suspension with an optically brightened filler composition.
[0002] A high degree of brightness is a desirable property of paper
and cardboard articles. The most important raw material of the
papermaking industry is pulp, which naturally absorbs blue light
and therefore is yellowish in color and imparts a dull appearance
to the paper. Optical brighteners are used in the papermaking
industry to compensate for the absorption of blue light by
absorbing UV-light with a maximum wavelength of 350-380 nm and
converting it into visible blue light with a maximum wavelength of
440 nm.
[0003] Optical brighteners of the triazinylaminostilbene type have
been used almost exclusively to brighten paper either by
application to pulp or to the paper surface. It is well-known
however that the lightfastness of brighteners of this type is no
better than poor to moderate, or 1 to approximately 3 on the "Blue
Wool Scale". (See "Optische Aufheller--neuere Erkenntnisse zu
Eigenschaften and Verhalten im Papier" by F. Muller, D. Loewe and
B. Hunke in Wochenblatt fur Papierfabrikation 1991, 6, pages
191-203.) There is therefore a demand to protect optically
brightened papers from yellowing in light.
[0004] In order to provide optically brightened papers of high
lightfastness, it is generally recognized that brighteners other
than those of the triazinylaminostilbene type must be used; in
particular, brighteners typically used for the optical brightening
of textiles, such as those of the benzoxazole, naphthalimide,
triazolylcoumarin or triazinylpyrene types. Such brighteners are
however typically much more expensive, and can only be applied with
difficulty to either pulp or to the paper surface.
[0005] EP-A-801 700 overcomes some of these problems by describing
the use of optically brightened polyacrylonitrile powder to prepare
white coating slips for paper. Preferred optical brighteners are
those typically used to provide a high lightfastness on textiles,
for example of the triazolylcoumarin or benzoxazole type. Papers
prepared using such coating slips show excellent whitening effects
with high lightfastness. There is no suggestion however that this
approach could be used to prepare optically brightened papers by a
more economic pulp application.
[0006] The economic use of textile brighteners to prepare optically
brightened papers is therefore a difficult problem to which a
satisfactory solution has not yet been found.
[0007] Surprisingly, it has now been found that by treating a pulp
suspension with a filler composition comprising finely divided
optically brightened plastic fibres, an optically brightened paper
of high lightfastness is obtained in an economic manner.
[0008] Therefore an object of the instant invention is a process
for optical brightening of paper wherein a filler composition
comprising optically brightened plastic fibres is added to the pulp
suspension.
[0009] Said fibres preferably can be made from polyester,
polyethylene, polypropylene or polyamide. Most preferably the
fibres are made from polyester.
[0010] The fibres have a fineness between 1 and 10 dtex and are cut
to a length of between 0.1 and 1 mm, preferably they have a
fineness between 1 and 2 dtex and a length between 0.2 and 0.6
mm.
[0011] The preparation of polyester fibres is well-known and is
described, for example, in "Handbook of Fiber Chemistry" by
Menachem Lewin published in 1998 by Marcel Dekker, page 18.
[0012] The production of optically brightened polyester is equally
well-known and is described, for example, in GB 835,898 and EP-A-1
379 585.
[0013] For the purpose of the present invention, the fibres are
preferably optically brightened with compounds of formulae (1) to
(4)
##STR00001##
where in formula (1) R.sub.1 to R.sub.8 independently of one
another are hydrogen, C.sub.1-C.sub.20-alkyl or groups of the
formula --COOR.sub.9, where R.sub.9 is hydrogen,
C.sub.1-C.sub.20-alkyl or phenyl, or R.sub.1 to R.sub.8 are a group
of the formula --SO.sub.2R.sub.10, where R.sub.10 is hydrogen,
C.sub.1-C.sub.10-alkyl or C.sub.1-C.sub.10-hydroxyalkyl, and A is
stilbene, naphthalene, phenylene, thiophenylene or biphenylene, or
mixtures of said compounds.
[0014] More preferred optical brighteners are compounds of formula
(1) where R.sub.1 to R.sub.8 independently of one another are
hydrogen or C.sub.1-C.sub.4-alkyl, and A is stilbene, naphthalene,
phenylene, thiophenylene or biphenylene.
[0015] Most preferred optical brighteners are compounds of formula
(1) where R.sub.1 to R.sub.8 independently of one another are
hydrogen or methyl, and A is stilbene.
[0016] The optically brightened plastic fibre contains between 10
and 500 ppm optical brightener, preferably between 20 and 250
ppm.
[0017] The pulp may be any conventional pulp used to produce paper,
for example stone groundwood pulp, thermomechanical pulp,
chemithermomechanical pulp, semichemical pulp, sulphite pulp or
kraft pulp, or a mixture of these.
[0018] In general the pulp suspension is treated with 2 to 60%,
preferably 10 to 40% by weight, based on weight of dry pulp, of the
instant filler composition.
[0019] The filler composition may be added to the pulp suspension
either in dry form or, preferably, in the form of an aqueous
dispersion. It may be useful to add a dispersing agent,
particularly suitable dispersing agents being of the type described
in EP-A-964 015. Finally, the paper is formed on a wire screen of a
conventional paper machine, pressed and dried.
[0020] The present invention also provides an optically brightened
paper produced according to the instant process and which comprises
2 to 60%, preferably 10 to 40% by weight, based on weight of dry
pulp, of the filler composition of the instant invention.
[0021] The optically brightened paper may also contain other
additives commonly employed in the papermaking industry. Examples
of such additives include sizing agents (for example, rosin,
starch, alkyl ketene dimer, alkenyl succinic anhydride), wet
strength resins (for example, poly-aminoamide-epichlorohydrin
resins), retention- and drainage aids (for example, poly-aluminium
chloride, polydiallyldimethylammonium chloride), and shading
dyes.
[0022] The following example further serves to illustrate the
invention. All parts and all percentages are by weight, unless
indicated to the contrary.
EXAMPLE
[0023] 5 parts polyester fibres of fineness 1.7 dtex made by known
methods, containing 0.014% of a mixture of optical brighteners of
structures 5a-c in an approximate ratio of 30:50:20, and cut to 0.5
mm, are stirred with 0.025 parts dispersing agent (Cartaspers.RTM.
PSM, commercially available from Clariant) and 1000 parts water for
5 minutes to form a 0.5% dispersion of optically brightened
fibres.
##STR00002##
[0024] x parts of the 0.5% dispersion of optically brightened
fibres are then added to (1000-x) parts of a stirred 0.5% aqueous
suspension of a 50:50 mixture of bleached birch and spruce wood
pulps beaten to a Schopper-Riegler freeness of 35.degree.. A paper
sheet is then made by drawing the dispersed suspension through a
wire mesh. After being pressed and dried, the optically brightened
paper contains between 5% (x=50) and 30% (x=300) optically
brightened polyester fibres, equivalent to an optical brightener
content of between 7 ppm and 42 ppm.
[0025] Each paper sheet is measured for R457Brightness on a
calibrated Minolta 3270D spectrophotometer.
[0026] Accelerated ageing experiments are conducted by exposing the
papers in a Xenotest apparatus. R457Brightness measurements are
made at intervals of 70, 140 and 280 hours. The results are shown
below in tabular (Table 1) and graphical (FIG. 1) forms.
TABLE-US-00001 TABLE 1 R457 R457 R457 R457 % Brightened Brightness
Brightness Brightness Brightness fibres in paper before exposure
after 70 h after 140 h after 280 h 0 82.6 83.6 84.3 85.9 5 84.0
85.0 85.3 86.3 10 86.1 86.6 86.6 88.0 15 88.0 88.6 88.6 89.3 20
89.0 89.5 89.3 90.1 25 91.0 91.6 91.3 91.7 30 91.4 92.0 91.8
92.3
[0027] FIG. 1: Effect of exposure to light over 280 hours on R457
Brightness of papers containing 5-30% optically brightened
polyester fibres.
[0028] It is clear from the results that the present invention
provides an optically brightened paper of high lightfastness, with
the additional advantage that a surprisingly low concentration
(7-42 ppm) of optical brightener is required to achieve a high
degree of brightness.
COMPARATIVE EXAMPLES
Comparative Example 1
Brightened Polyester Fibres
[0029] A paper sheet is made as in the Example, containing 25%
(x=250) optically brightened polyester fibres.
Comparative Example 2
Unbrightened Pulp
[0030] A paper sheet is made as in the Example, but without the
addition of optically brightened polyester fibres.
Comparative Example 3
Unbrightened Polyester Fibres
[0031] A paper sheet is made as in the Example, but containing 25%
(x=250) unbrightened polyester fibres in place of the optically
brightened polyester fibres.
Comparative Example 4
Unbrightened Polyester Fibres and Optical Brightener (5a-c)
[0032] A paper sheet is made as in the Example, but containing 25%
(x=250) unbrightened polyester fibres and--added separately to the
1000 parts of 0.5% aqueous suspension of fibres--0.000175 parts of
a mixture of optical brighteners of structures (5a-c) in an
approximate ratio of 30:50:20, all in place of the optically
brightened polyester fibres.
Comparative Example 5
Unbrightened Polyester Fibres and Optical Brightener (6)
##STR00003##
[0034] A paper sheet is made as in the Example, but containing 25%
(x=250) unbrightened polyester fibres and--added separately to the
1000 parts of 0.5% aqueous suspension of fibres--0.004 parts of an
optical brightener of structure (6), all in place of the optically
brightened polyester fibres.
[0035] Accelerated ageing experiments are conducted as in the
Example. The results are shown below in tabular (Table 2) and
graphical (FIG. 2) forms.
TABLE-US-00002 TABLE 2 R457 R457 R457 R457 Comparative Brightness
Brightness Brightness Brightness Example before exposure after 70 h
after 140 h after 280 h 1 92.1 93.0 92.9 92.7 2 83.8 85.6 86.5 87.5
3 85.3 87.0 87.7 88.5 4 85.5 87.1 87.8 88.4 5 97.5 90.5 88.7
87.5
[0036] FIG. 2: Effect of exposure to light over 280 hours on R457
Brightness of papers.
[0037] The Comparative Examples demonstrate the advantage of the
invention in providing a bright paper with excellent
lightfastness.
[0038] It is clear that the addition of optically brightened
polyester fibres (Comparative Example 1) gives a much brighter
paper than does the addition of unbrightened polyester fibres
(Comparative Example 3). It is equally clear that the optical
brightener must be incorporated into the polyester fibre, rather
than added separately (Comparative Example 4). Whereas the separate
addition of an optical brightener (6) of the triazinylaminostilbene
type gives a particularly bright paper, the lightfastness of said
paper is poor (Comparative Example 5).
* * * * *