Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
1998-09-14
2001-10-16
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S158000, C162S162000, C162S181800
Reexamination Certificate
active
06302999
ABSTRACT:
The present invention relates to a simplified method for increasing the whiteness of paper by the application of optical brighteners, also known as fluorescent whitening agents.
Optical brightener formulations together with swellable layered silicates have been described in German laid-open Patent Application 19538029, as additives for detergents with improved properties.
Surprisingly, it has now been found that such formulations can advantageously be utilized for the optical brightening of paper either in the pulp mass, the size press, the metering press or in coating.
The subject of the present invention is hence a method for the optical brightening of paper, which comprises the use of a formulation essentially consisting of a swellable layered silicate and an optical brightener.
The swellable layered silicates are e.g. natural or synthetic clay minerals or sodium silicates. A suitable natural clay mineral is e.g montmorillonite, beidelite, saponite, or hectorite; preferred synthetic species are the zeolites (type A, X or &bgr;, etc.) and acid- or alkaline-modified bentonites.
The inventively used formulations may be in the form of a dry mixture or, alternatively, in the form of an aqueous dispersion.
Thereby the known advantages of the swellable layered silicates, which are e.g. natural or synthetic clay minerals or synthetic sodium silicates, such as high opacity, high whiteness, ion-exchange properties and improved retention properties can simply be combined with the properties of the optical brighteners without loosing the desired fluorescence effect of the latter.
Preferably the aqueous formulation contains 0.1 to 15% by weight, preferably 1 to 10% by weight of optical brightener, based on the weight of the swellable layered silicate.
Where the formulation is in the form of an aqueous dispersion, this contains about 2 to 60% by weight of the swellable layered silicate. The preferred range of the bentonites is about 2 to 25%, and mostly preferred 2 to 20%, by weight; for the synthetic zeolites the suitable range is about 2 to 50% by weight.
Dispersing agents, such as polycondensates of naphthalene sulfonic acid and formaldehyde or lignin sulfonates can be used as auxiliaries.
Where the formulation is in the form of a dry mixture, this may contains 0.1 to 90% by weight preferably 1 to 50% by weight of the optical brightener, based on the weight of the swellable layered silicate.
The optical brightener used in the method of the present invention is preferably a derivative of 4,4′-bis-(triazinylamino)-stilbene-2,2′-disulphonic acid, a derivative of 4,4′-distyryl-biphenyl, or a derivative of dibenzofuranylbiphenyl.
Preferably the 4,4′-bis-(triazinylamino)-stilbene-2,2′-disulphonic acid optical brightener is of the formula:
in which R
1
and R
2
, independently, are phenylamino, mono- or disulphonated phenylamino, morpholino, —N(CH
2
CH
2
OH)
2
, —N(CH
3
)(CH
2
CH
2
OH), —NH
2
, —N(C
1
-C
4
alkyl)
2
, —OCH
3
, —Cl, NHCH
2
CH
2
SO
3
H, CH
2
CH
2
OH or ethanolaminopropionic acid amide; and M is H, Na, Li, K, Ca, Mg, ammonium, or ammonium that is mono-, di-, tri- or tetrasubstituted by C
1
-C
4
alkyl, C
1
-C
4
hydroxyalkyl or a mixture thereof.
Preferably the 4,4′distyryl-biphenyl optical brightener is of the formula:
in which R
3
and R
4
, independently, are H, SO
3
M, SO
2
N(C
1
-C
4
alkyl)
2
, O(C
1
-C
4
alkyl), CN, Cl, COO(C
1
-C
4
alkyl), CON(C
1
-C
4
alkyl)
2
or (CH
2
)
3
N
+
(CH
3
)
2
An
−
, in which M is H, Na, Li, K, Ca, ammonium, or ammonium that is mono-, di-, tri- or tetrasubstituted by C
1
-C
4
alkyl, C
1
-C
4
hydroxyalkyl or a mixture thereof and An is an anion, e.g. of a mineral acid (hydrochloric or sulfuric acid) or lower (C
1-4
)-carboxylic acid.
Preferably the dibenzofuranylbiphenyl optical brightener is of the formula
which is unsubstituted or mono- or polysubstituted by radicals R═hydrogen, C
1
-C
4
-alkyl,
C
1
-C
4
-alkoxy, halogen, preferably chlorine, phenoxy and benzyloxy,
R
1
is hydrogen, C
1
-C
4
-alkyl, halogen, preferably chlorine, phenyl, or SO
3
M,
M is hydrogen and/or one equivalent of a non-chromophoric cation and
n is zero, 1 or 2.
Preferred compounds of formula (3) are those of the formula
wherein M, R and R
1
have the indicated meanings, R and R
1
being preferably methyl.
Most preferably the optical brightener is of the formula:
R
x
CH
2
CH
2
OH (6a)
R
x
CH
3
(6b)
or mixtures of at least two of the compounds (5) to (10).
Using the method of the present invention, it has been found that it is possible to increase the whiteness of a lignin-containing pulp by a process which comprises adding to an aqueous slurry comprising a lignin-containing pulp, during pulp manufacture, prior to the drying step or paper making step if the pulp is not isolated, an effective amount of an optical brightener. While the optical brightener can be added to the aqueous slurry comprising the lignin-containing pulp at any processing step, to minimize losses, it is advantageously added in the latter stages of pulp manufacture, prior to the final dewatering and drying steps. Preferably it is added after completion of the last bleaching step.
By “a lignin-containing pulp” is meant any pulp that still contains about 5% or more of lignin by weight on a dry basis. By definition, lignin is that portion of the pulp which is insoluble in 72 weight percent sulfuric acid. Suitable test procedures for lignin content are given in TAPPI T 223 and ASTM D 1106.
The process of this invention is useful to produce significant whitening of pulps containing from about 5% lignin on a dry weight basis up to 100% of the lignin present in an equivalent amount of wood chips. Thus the process can be employed, e.g. on relatively low-lignin-containing pulps such as certain bleached kraft pulps up to and including higher lignin content pulps such as thermomechanical pulps, bleached chemi-thermomechanical pulps (CTMP), and even deinked bleached thermomechanical pulps. Preferably the pulps contain at least 10% of lignin by weight on a dry weight basis; most preferably they contain at least 15%. The range of brightness that can be obtained varies from about 50 to 90+ depending on starting pulp brightness and the type of pulp employed.
It is known to employ chelating agents in processes to bleach pulps from mechanical pulping processes. See V. N. Gupta, Pulp Paper Mag. Can., 71 (18), T391-399 (1970). The addition of a chelating agent to an aqueous pulp slurry controls the natural yellowing tendency of glucuronic acids, extractives and lignin present in the pulp by removing or minimizing iron and other heavy metals such as copper, zinc and manganese metals that catalyze color-forming side reactions. The iron and other heavy metals are converted into the form of their highly soluble chelates and largely removed in the dewatering steps. This decreases the incorporation of the heavy metal ions into the pulp. Additionally the chelating agent sequesters the salts of iron and other heavy metals which remain and which, in their own right would otherwise relax the excited state of optical brighteners and render them ineffective.
Depending on the processing parameters used in the pulp mill, this metal control step may be done as matter of course in pulping processes where reductive bleaching (e.g., bisulfite, hydrosulfite, or formamidine sulfite bleaching) or oxidative bleaching (e.g., peroxy- or peroxide bleaching) is employed. The addition of a chelating agent to an aqueous pulp slurry, if necessary, should be carried out prior to the addition of the optical brightener.
The background level of residual iron and other heavy metals and their ions in wood chips is generally about 10-25 ppm, although it is rather dependent on geography and species considerations. The amount of iron and other heavy metals and their ions in the water used in pulping mills varies widely. Significant additional amounts of iron and other heavy metals and their ions are introduced during mechanical pulping of wood chips as well as in recycling newsprint. Thus the amo
Engelhardt Thomas
Rohringer Peter
Chin Peter
Ciba Specialty Chemicals Corp.
Mansfield Kevin T.
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