Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1995-02-13
1997-03-04
Jordan, Charles T.
Paper making and fiber liberation
Processes and products
Non-fiber additive
1621818, 2523132, 2523155, 2523156, D21H 2302, D21H 1713, D21H 1763
Patent
active
056075529
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to aqueous suspensions of colloidal particles which particles are both silica based anionic particles and hydrated particles of clays of smectite type which expand in water. The invention also relates to a process for the production of the suspensions and to the use of these as flocculating agents in combination with amphoteric or cationic polymers, particularly in the production of paper and pulp, but also for water purification.
During recent years systems based on anionic colloidal particles and cationic or amphoteric synthetic or natural polymers have gained an increased use, particularly at the production of paper for increasing retention and dewatering. The anionic colloidal particles have hereby been silica based or have consisted of clay materials such as bentonite. Such systems are for example disclosed in the European patents 41056, 218674 and 0235893. Generally a fairly high amount of bentonite is required while the considerably more expensive silica sols give good results at substantially lower dosages. From the European patent 0310959 it is also known to use both silica sol and bentonite together with cationic starch. The silica sol and the bentonite can hereby be added simultaneously or after each other and it is also indicated that it is possible to mix the bentonite with the silica sol just prior to addition to the stock.
Silica based particles are delivered in the form of aqueous sols of varying dry contents, mainly dependent on the size of the sol particles. Sol particles are essentially spherical. Clay materials, such as for example bentonite, shall be hydrated at use to give the desired effect, and in this form they cannot be supplied as stable aqueous preparations of sufficiently high dry content to be stored and transported. Bentonite is thus handled in powder form and immediately before use the powder is wetted to give the required swelling and high shear forces are necessary to set surfaces free. In contrast to silica particles clay particles have a flake-like structure. Handling of powder materials is not desirable since all handling of powder materials gives rise to dust problems and dosage problems and since every user needs equipment for wetting.
According to the present invention it has surprisingly been found that it is possible to prepare stable aqueous suspensions which contain both colloidal anionic silica based particles and colloidal hydrated particles of expandable clays of smectite type. The term suspension as such means a system in which small solid particles are essentially uniformly dispersed in a liquid medium. In the present suspensions the different types of colloidal particles, the spherical silica particles and the flake-like clay particles, are thus essentially uniformly dispersed in water. The suspensions according to the invention can have comparatively high dry contents, up to about 40 per cent, and the pre-prepared suspensions can be delivered to the customer who then avoids the above mentioned problems with handling of powder materials. The suspensions have very good effect both in combination with natural and synthetic polymers and are very cost-efficient. Considerably higher effect can be obtained with the suspensions than what could have been expected by the amount of the particles of the respective type in the suspensions. Particularly good effect is obtained when the suspensions are used in combination with synthetic polymers such as cationic polyacrylamide. With suspensions according to the invention silica based particles having a comparatively low specific surface area, i.e. comparatively high particle size (about 50 to 400 m.sup.2 /g, corresponding to about 50 to about 7 nm) can be used with good results. Silica sols with these larger particle sizes have themselves not given sufficiently good results to be commercially used within the field of retention-dewatering.
The present invention thus relates to suspensions as further defined in the claims.
Silica based particles, i.e. particles based on SiO.sub.2, which can be
REFERENCES:
patent: 4388150 (1983-06-01), Sunden et al.
patent: 4872993 (1989-10-01), Harrison
patent: 5030286 (1991-07-01), Crawford et al.
Andersson Kjell
Johansson Hans
Lindgren Erik
Tokarz Marek
Eka Nobel AB
Hardee John R.
Jordan Charles T.
Mancini Ralph J.
Morris Louis A.
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