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(11) | EP 1 982 017 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
PROCESS FOR PRODUCING OPTICALLY BRIGHTENED PAPER VERFAHREN ZUR HERSTELLUNG VON OPTISCH AUFGEHELLTEM PAPIER PROCÉDÉ DE PRODUCTION DE PAPIER OPTIQUEMENT ÉCLAIRCI |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[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 350-380nm and converting it into visible blue light with a maximum wavelength of 440nm.
[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 und Verhalten im Papier" by F. Müller, D. Loewe and B. Hunke in Wochenblatt für 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 0.6mm.
[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)
where in formula (1)
R1 to R8 independently of one another are hydrogen, C1-C20-alkyl or groups of the formula -COOR9, where R9 is hydrogen, C1-C20-alkyl or phenyl, or R1 to R8 are a group of the formula -SO2R10, where R10 is hydrogen, C1-C10-alkyl or C1-C10-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 R1 to R8 independently of one another are hydrogen or C1-C4-alkyl, and A is stilbene, naphthalene, phenylene, thiophenylene or biphenylene.
[0015] Most preferred optical brighteners are compounds of formula (1) where R1 to R8 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® PSM, commercially available from Clariant) and 1000 parts water for 5 minutes to form a 0.5% dispersion of optically brightened fibres.
[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°. 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 R457 Brightness on a calibrated Minolta 3270D spectrophotometer.
[0026] Accelerated ageing experiments are conducted by exposing the papers in a Xenotest apparatus. R457 Brightness 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 1
| % Brightened fibres in paper | R457 Brightness before exposure | R457 Brightness after 70h | R457 Brightness after 140h | R457 Brightness after 280h |
| 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] 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
[0028] A paper sheet is made as in the Example, containing 25% (x = 250) optically brightened polyester fibres.
Comparative Example 2: Unbrightened pulp
[0029] A paper sheet is made as in the Example, but without the addition of optically brightened polyester fibres.
Comparative Example 3: Unbrightened polyester fibres
[0030] 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)
[0031] 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)
[0033] 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.
[0034] Accelerated ageing experiments are conducted as in the Example. The results are shown below in tabular (Table 2) and graphical (Fig 2) forms.
TABLE 2
| Comparative Example | R457 Brightness before exposure | R457 Brightness after 70h | R457 Brightness after 140h | R457 Brightness after 280h |
| 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 |
[0035] The Comparative Examples demonstrate the advantage of the invention in providing a bright paper with excellent lightfastness.
[0036] 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).
1. Process for optical brightening of paper wherein a filler composition comprising optically
brightened plastic fibres is added to the pulp suspension.
2. Process according to claim 1 wherein the fibres are made from polyester, polyethylene,
polypropylene or polyamide.
3. Process according to claim 2 wherein the fibres are made from polyester.
4. Process according to claim 3 wherein the fibres have a fineness between 1 and 10 dtex
and are cut to a length of between 0.1 and 1 mm.
5. Process according to claim 4 wherein the fibres have a fineness between 1 and 2 dtex
and are cut to a length of between 0.2 and 0.6 mm.
6. Process according to any of the preceding claims wherein the fibres are optically
brightened with compounds of formulae (1) to (4)
and where in formula (1)
and where in formula (1)
R1 to R8 independently of one another are hydrogen, C1-C20-alkyl or groups of the formula -COOR9,
R9 is hydrogen, C1-C20-alkyl or phenyl, or
R1 to R8 are a group of the formula -SO2R10, where
R10 is hydrogen, C1-C10-alkyl or C1-C10-hydroxyalkyl, and
A is stilbene, naphthalene, phenylene, thiophenylene or biphenylene,
or mixtures of said compounds.7. Process according to claim 6 wherein the fibres are optically brightened with a compound
of formula (1) wherein
R1 to R8 independently of one another are hydrogen or C1-C4-alkyl, and
A is stilbene, naphthalene, phenylene, thiophenylene or biphenylene.
8. Process according to claim 7 wherein
R1 to R8 independently of one another are hydrogen or methyl, and
A is stilbene.
9. Process according to any of claims 2 to 8 wherein the optically brightened plastic
fibres contain between 10 and 500 ppm optical brightener.
10. Process according to claim 9 wherein the optically brightened plastic fibres contain
between 20 and 250 ppm optical brightener.
11. Process according to any of the preceding claims 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. Process according to claim 11 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. Process according to claims 11 or 12 wherein the optically brightened filler composition
is added to the pulp suspension in the form of an aqueous dispersion.
14. Optically brightened paper produced by a process according to any of the preceding
claims.
1. Verfahren zum optischen Aufhellen von Papier, bei dem man der Stoffsuspension eine
optisch aufgehellte Kunststoffasern enthaltende Füllstoffzusammensetzung zusetzt.
2. Verfahren nach Anspruch 1, bei dem es sich bei den Kunststoffasern um Polyester, Polyethylen,
Polypropylen oder Polyamid handelt.
3. Verfahren nach Anspruch 2, bei dem es sich bei den Kunststoffasern um Polyester handelt.
4. Verfahren nach Anspruch 3, bei dem die Kunststoffasern einen Titer zwischen 1 und
10 dtex und eine Schnittlänge zwischen 0,1 und 1 mm aufweisen.
5. Verfahren nach Anspruch 4, bei dem die Kunststoffasern einen Titer zwischen 1 und
2 dtex und eine Schnittlänge zwischen 0,2 und 0,6 mm aufweisen.
6. Verfahren nach einem der vorhergehenden Ansprüche, bei dem die Kunststoffasern mit
Verbindungen der Formeln (1) bis (4)
wobei in Formel (1)
wobei in Formel (1)
R1 bis R8 unabhängig voneinander für Wasserstoff, C1-C20-Alkyl oder Gruppen der Formel -COOR9,
R9 für Wasserstoff, C1-C20-Alkyl oder Phenyl stehen oder
R1 bis R8 für eine Gruppe der Formel -SO2R10 stehen, wobei R10 Wasserstoff, C1-C10-Alkyl oder C1-C10-Hydroxyalkyl bedeutet, und
A für Stilben, Naphthalin, Phenylen, Thiophenylen oder Biphenylen steht, oder Mischungen der genannten Verbindungen optisch aufgehellt sind.
7. Verfahren nach Anspruch 6, bei dem die Kunststoffasern mit einer Verbindung der Formel
(1) optisch aufgehellt sind, bei der
R1 bis R8 unabhängig voneinander für Wasserstoff oder C1-C4-Alkyl und
A für Stilben, Naphthalin, Phenylen, Thiophenylen oder Biphenylen stehen.
R1 bis R8 unabhängig voneinander für Wasserstoff oder C1-C4-Alkyl und
A für Stilben, Naphthalin, Phenylen, Thiophenylen oder Biphenylen stehen.
8. Verfahren nach Anspruch 7, bei dem
R1 bis R8 unabhängig voneinander für Wasserstoff oder Methyl und
A für Stilben stehen.
R1 bis R8 unabhängig voneinander für Wasserstoff oder Methyl und
A für Stilben stehen.
9. Verfahren nach einem der Ansprüche 2 bis 8, bei dem die optisch aufgehellten Kunststoffasern
zwischen 10 und 500 ppm an optischem Aufheller enthalten.
10. Verfahren nach Anspruch 9, bei dem die optisch aufgehellten Kunststoffasern zwischen
20 und 250 ppm an optischem Aufheller enthalten.
11. Verfahren nach einem der vorhergehenden Ansprüche, bei dem man der Stoffsuspension
bezogen auf das Gewicht des Trockenstoffs 2 bis 60 Gew.-% der optisch aufgehellten
Füllstoffzusammensetzung zusetzt.
12. Verfahren nach Anspruch 11, bei dem man der Stoffsuspension bezogen auf das Gewicht
des Trockenstoffs 10 bis 40 Gew.-% der optisch aufgehellten Füllstoffzusammensetzung
zusetzt.
13. Verfahren nach Anspruch 11 oder 12, bei dem man die optisch aufgehellte Füllstoffzusammensetzung
der Stoffsuspension in Form einer wässrigen Dispersion zusetzt.
14. Optisch aufgehelltes Papier, hergestellt nach einem Verfahren gemäss einem der vorhergehenden
Ansprüche.
1. Procédé pour l'azurage optique de papier, dans lequel une composition de charge comprenant
des fibres plastiques optiquement azurées est ajoutée à la suspension de pâte à papier.
2. Procédé selon la revendication 1, dans lequel les fibres sont composées de polyester,
de polyéthylène, de polypropylène ou de polyamide.
3. Procédé selon la revendication 2, dans lequel les fibres sont composées de polyester.
4. Procédé selon la revendication 3, dans lequel les fibres présentent une finesse comprise
entre 1 et 10 dtex et sont découpées à une longueur comprise entre 0,1 et 1 mm.
5. Procédé selon la revendication 4, dans lequel les fibres présentent une finesse comprise
entre 1 et 2 dtex et sont découpées à une longueur comprise entre 0,2 et 0,6 mm.
6. Procédé selon l'une quelconque des revendications précédentes, dans lequel les fibres
sont optiquement azurées avec des composés de formules (1) à (4).
et où dans la formule (1)
R1 à R8 sont, indépendamment les uns des autres, un atome d'hydrogène, un groupe alkyle en C1-C20 ou des groupes de formule -COOR9,
R9 est un atome d'hydrogène, un groupe alkyle en C1-C20 ou un groupe phényle, ou
R1 à R8 sont un groupe de formule -SO2R10, dans laquelle
R10 est un atome d'hydrogène, un groupe alkyle en C1-C10 ou un groupe hydroxyalkyle en C1-C10, et
A est un groupe stilbène, un groupe naphtalène, un groupe phénylène, un groupe thiophénylène ou un groupe biphénylène, ou des mélanges desdits composés.
et où dans la formule (1)
R1 à R8 sont, indépendamment les uns des autres, un atome d'hydrogène, un groupe alkyle en C1-C20 ou des groupes de formule -COOR9,
R9 est un atome d'hydrogène, un groupe alkyle en C1-C20 ou un groupe phényle, ou
R1 à R8 sont un groupe de formule -SO2R10, dans laquelle
R10 est un atome d'hydrogène, un groupe alkyle en C1-C10 ou un groupe hydroxyalkyle en C1-C10, et
A est un groupe stilbène, un groupe naphtalène, un groupe phénylène, un groupe thiophénylène ou un groupe biphénylène, ou des mélanges desdits composés.
7. Procédé selon la revendication 6, dans lequel les fibres sont optiquement azurées
avec un composé de formule (1), dans laquelle
R1 à R8 sont, indépendamment les uns des autres, un atome d'hydrogène ou un groupe alkyle en C1-C4, et
A est un groupe stilbène, un groupe naphtalène, un groupe phénylène, un groupe thiophénylène ou un groupe biphénylène.
R1 à R8 sont, indépendamment les uns des autres, un atome d'hydrogène ou un groupe alkyle en C1-C4, et
A est un groupe stilbène, un groupe naphtalène, un groupe phénylène, un groupe thiophénylène ou un groupe biphénylène.
8. Procédé selon la revendication 7, dans lequel
R1 à R8 sont, indépendamment les uns des autres, un atome d'hydrogène ou un groupe méthyle, et
A est un groupe stilbène.
R1 à R8 sont, indépendamment les uns des autres, un atome d'hydrogène ou un groupe méthyle, et
A est un groupe stilbène.
9. Procédé selon l'une quelconque des revendications 2 à 8, dans lequel les fibres plastiques
optiquement azurées contiennent entre 10 et 500 ppm d'azurant optique.
10. Procédé selon la revendication 9, dans lequel les fibres plastiques optiquement azurées
contiennent entre 20 et 250 ppm d'azurant optique.
11. Procédé selon l'une quelconque des revendications précédentes, dans lequel de 2 à
60 % en poids, par rapport au poids de la pâte à papier sèche, de la composition de
charge optiquement azurée sont ajoutés à la suspension de pâte à papier.
12. Procédé selon la revendication 11, dans lequel de 10 à 40 % en poids, par rapport
au poids de la pâte à papier sèche, de la composition de charge optiquement azurée
sont ajoutés à la suspension de pâte à papier.
13. Procédé selon les revendications 11 ou 12, dans lequel la composition de charge optiquement
azurée est ajoutée à la suspension de pâte à papier sous la forme d'une dispersion
aqueuse.
14. Papier optiquement azuré produit par un procédé selon l'une quelconque des revendications
précédentes.
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.
Patent documents cited in the description
Non-patent literature cited in the description
- F. MüllerD. LoeweB. HunkeOptische Aufheller - neuere Erkenntnisse zu Eigenschaften und Verhalten im PapierWochenblatt für Papierfabrikation, 1991, vol. 6, 191-203 [0003]