Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-12-19
2002-04-30
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S164600, C162S183000, C423S335000, C516S081000
Reexamination Certificate
active
06379500
ABSTRACT:
The present invention generally relates to silica-based sols comprising an organic nitrogen-containing compound which sols are suitable for use as drainage and retention aids in papermaking. More particularly, the invention relates to silica-based sols, a process for the production of silica-based sols, and a process for the production of paper in which silica-based sols are used as additives.
BACKGROUND OF THE INVENTION
In the papermaking art, an aqueous suspension containing cellulosic fibres, 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 wet web of paper is formed on the wire, and the paper web is further dewatered and dried in the drying section of the paper machine. Drainage and retention aids are conventionally introduced into the stock in order to facilitate drainage and to increase adsorption of fine particles onto the cellulosic fibres so that they are retained with the fibres on the wire.
Silica-based particles are widely used as drainage and retention aids in combination with charged organic polymers like anionic and cationic acrylamide-based polymers and cationic and amphoteric starches. Such additive systems are disclosed in U.S. Pat. Nos. 4,388,150; 4,961,825; 4,980,025; 5,368,833; 5,603,805; 5,607,552; 5,858,174; and 6,103,064; and International Patent Applications WO 00/66491 and WO 00/66492. These systems are among the most efficient drainage and retention aids now in use.
Silica-based particles suitable for use as drainage and retention aids are normally supplied in the form of aqueous colloidal dispersions, so-called sols. Such commercially used silica-based sols usually have a silica content of about 7-15% by weight and contain particles with a specific surface area of at least 300 m
2
/g. Sols of silica-based particles with higher specific surface areas are usually more dilute to improve storage stability and avoid gel formation.
It would be advantageous to be able to provide silica-based sols with further improved drainage and retention performance and even better stability. It would also be advantageous to be able to provide a process for preparing silica-based sols exhibiting improved drainage, retention and stability properties. It would also be advantageous to be able to provide a papermaking process with improved drainage and retention.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided amine-modified silica-based sols which are suitable for use as drainage and retention aids in papermaking. The term “drainage and retention aids”, as used herein, refers to one or more components (aids, agents or additives) which, when added to a papermaking stock, give better drainage and/or retention than is obtained when not adding the said one or more components. The amine-modified silica-based sols of the invention especially result in improved drainage and/or retention in a paper making process when used in conjunction with charged organic polymers. Hereby the present invention makes it possible to increase the speed of the paper machine and to use a lower dosage of additives to give a corresponding drainage and/or retention effect, thereby leading to an improved papermaking process and economic benefits. The silica-based sols of the invention further exhibit very good stability over extended periods of time, notably very high surface area stability and high stability towards gelation, and hence they can be prepared and shipped at high specific surface areas and high silica concentrations. The sols have improved capability to maintain the high specific surface area on storage at high silica concentrations.
DETAILED DESCRIPTION OF THE INVENTION
The present invention thus relates to silica-based sols comprising an organic nitrogen-containing compound, the preparation of such sols and their use, as further defined in the appended claims. The invention also relates to a process for the production of paper from an aqueous suspension containing cellulosic fibres, and optional fillers, which comprises adding to the suspension a silica-based sol comprising an organic nitrogen-containing compound and at least one charged organic polymer, forming and draining the suspension on a wire, as further defined in the appended claims.
The silica-based sols according to the invention are aqueous sols that contain anionic silica-based particles, i.e. particles based on SiO
2
or silicic acid, including colloidal silica, different types of polysilicic acid, polysilicate microgels, colloidal borosilicates, aluminum-modified silica or aluminum silicates, polyaluminosilicate microgels, and mixtures thereof. The particles are preferably colloidal, i.e. in the colloidal range of particle size, and preferably amorphous or essentially amorphous. The silica-based particles suitably have an average particle size below about 50 nm, preferably below about 20 nm and more preferably in the range of from about 1 to about 10 nm. As conventional in silica chemistry, particle size refers to the average size of the primary particles, which may be aggregated or non-aggregated.
The silica-based sols according to the invention contain an organic nitrogen-containing compound, for example an amine which can be selected from primary amines, secondary amines, tertiary amines and quaternary amines, the latter also referred to as quaternary ammonium compounds. The amines can be aromatic, i.e. containing one or more aromatic groups, or aliphatic; the aliphatic amines usually being preferred. The nitrogen-containing compound is preferably water-soluble or water-dispersible. The amine can be uncharged or cationic. Examples of cationic amines include acid addition salts of primary, secondary and tertiary amines and, preferably, quaternary ammonium compounds, as well as their hydroxides. The organic nitrogen-containing compound usually has a molecular weight below 1,000, suitably below 500 and preferably below 300. Preferably, a low molecular weight organic nitrogen-containing compound is used, for example those compounds having up to 25 carbon atoms, suitably up to 20 carbon atoms, preferably from 2 to 12 carbon atoms and most preferably from 2 to 8 carbon atoms. In a preferred embodiment, the organic nitrogen-containing compound has one or more oxygen-containing substituents, for example with oxygen in the form of hydroxyl groups and/or alkyloxy groups. Examples of preferred substituents of this type include hydroxy alkyl groups, e.g. ethanol groups, and methoxy and ethoxy groups. The organic nitrogen-containing compounds may include one or more nitrogen atoms, preferably one or two. Preferred amines include those having a pKa value of at least 6, suitably at least 7 and preferably at least 7.5.
Examples of suitable primary amines, i.e. amines having one organic substituent, include alkylamines, e.g. propylamine, butylamine, cyclohexylamine, alkanolamines, e.g. ethanolamine, and alkoxyalkylamines, e.g. 2-methoxyethylamine. Examples of suitable secondary amines, i.e. amines having two organic substituents, include dialkylamines, e.g. diethylamine, dipropylamine and di-isopropylamine, dialkanolamines, e.g. diethanolamine, and pyrrolidine. Examples of suitable tertiary amines, i.e. amines having three organic substituents, include trialkylamines, e.g. triethylamine, trialkanolamines, e.g. triethanolamine, N,N-dialkylalkanolamines, e.g. N,N-dimethylethanolamine. Examples of suitable quaternary amines, or quaternary ammonium compounds, i.e. amines having four organic substituents, include tetraalkanolamines, e.g. tetraethanol ammonium hydroxide and tetraethanol ammonium chloride, quaternary amines or ammonium compounds with both alkanol and alkyl substituents such as N-alkyltrialkanolamines, e.g. methyltriethanolammonium hydroxide and methyltriethanolammonium chloride, N,N-dialkyldialkanolamines, e.g. dimethyldiethanolammonium hydroxide and dimethyldiethanolammonium chloride, N,N,N-trialkylalkanolamines, e.g. choline hydroxide and choline ch
Greenwood Peter
Johansson-Vestin Hans E.
Linsten Magnus Olof
Akzo Nobel NV
Chin Peter
Hug Eric
Mancini Ralph J.
Parker Lainie E.
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