Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1996-06-18
1998-05-12
Czaja, Donald E.
Paper making and fiber liberation
Processes and products
Non-fiber additive
1621812, 162189, 210605, 210610, 210903, D21H 1701, C02F 330
Patent
active
057500061
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for making paper and cardboard, wherein at least one compound with formula (I), as specified hereinafter, is added to the aqueous disperse system of the fibers as sizing agent, and wherein the process wastewater is subjected to a biological denitrification treatment so that it can be reused.
Paper sizing processes are known in which aluminum salts, such as sulfate and particularly basic aluminum polychloride (PAC), are used as sizing agents. However, total or otherwise significant recycling of the process wastewater is practically impossible when using these inorganic sizing agents. The reason for this is that the anion of the salt used as sizing agent accumulates in the recycled water, and this can produce corrosion and/or deposits on the equipment if products containing chloride ions or sulfate ions, respectively, are used.
The Applicant has now surprisingly discovered--and this is the subject of the present invention--that if at least one compound with formula (I), as specified hereinafter, is used in paper sizing, one obtains the same advantages provided by the use of aluminum polychloride and it is also possible to eliminate all drainage and thus close the water cycle of the paper mill, minimizing water consumption simply subjecting the process wastewater to be recycled to a biological denitrification treatment.
The present invention therefore relates to a process for making paper and cardboard, wherein the aqueous dispersion of fibers and filler material, to which an addition of a cellulose-reactive rosin size has been given, receives the addition, in any stage of the process prior to the forming of the paper or cardboard sheet, of an aqueous solution of at least one compound represented by the formula (I) as sizing agent: partially reused, is subjected to a biological denitrification treatment by using a denitrifying anoxic sludge which is able to denitrify in the absence of molecular oxygen,
with the proviso that the wastewater to be treated, before being denitrified, contains:
(a) a carbon-containing organic substrate (C.O.D.) in an amount, with respect to the nitrogen expressed as nitric nitrogen, to meet at least the weight ratio C.O.D.:N=5:1; and
(b) an amount of phosphorus to meet at least the weight ratio P:N=1:5.
Preferably, according to the invention, Me is Al in formula (I).
If nitrate or basic aluminum nitrate is used as sizing agent in the sizing of paper with conventional resin-based size, one obtains first of all a good sizing effect but also excellent retention of the fibers and conventional additives that form the mixture.
In particular, when aluminum salts are used as well, the sizes used in paper sizing are cellulose-reactive rosin sizes which can generally be of three types, i.e. saponified resinates, reinforced resinates and emulsified resinates. This list, however, is non-limitative.
In the particular case of the use of basic aluminum nitrate, it is furthermore possible to use fillers that react with the acid environment, such as calcium carbonate, since good sizing is achieved even when the pH is near to neutrality. This usually entails both a better stability of the paper in the course of time as well as a reduced forming of CO.sub.2 foam originating from acid attack of the carbonates.
In the preferable case of the use of basic aluminum nitrate, the process according to the present invention is therefore characterized in that the aqueous disperse system of fibers and filler material, with the addition of a cellulose-reactive rosin size, receives the addition, in any stage of the process prior to the forming of the sheet of paper or cardboard, of an aqueous solution the concentration of which is equal to a content of 10 to 20% Al.sub.2 O.sub.3, of basic aluminum nitrate which has the formula (II) :
In this particular embodiment, the amount of basic aluminum nitrate added to the fiber-containing disperse system depends on the amount of size used, in a percentage ranging from 0.4% to 3% of the product in terms of the total dry substances
REFERENCES:
patent: 4039438 (1977-08-01), Anderson
patent: 4715958 (1987-12-01), Fuchs
patent: 5124039 (1992-06-01), Brautigam
G. Rheinheimer et al., "Stickstoffkreislauf Im Wasser", 1988, R. Oldenbourg Verlag. pp. 118-361.
Database WPI, Week 7842, Derwent Publications Ltd., London, GB; An 78-75094A & JP, A, 53 103 654 (Yamada K.K) 9, Sep. 1978.
Donelli Giordano
Dore Fausto
Rosellini Massimiliano
Taliento Raffaella
Coleman Henry D.
Czaja Donald E.
Industrie Chimiche Caffaro, S.p.A.
Leavitt Steven B.
Sudol R. Neil
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