Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
1999-09-14
2001-02-27
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S175000, C162S164600, C162S181700, C162S168200
Reexamination Certificate
active
06193844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to finely divided particles of water insoluble compounds that exhibit high negative zeta potentials at pH 7-8, small particle size, plus high adsorption of cationic material and compositions including such particles for use as drainage/retention aids in papermaking.
More particularly the present invention concerns sub-micron particles of metallic silicates such as crystalline alumino silicates (zeolites) and amorphous alumino silicates.
2. Brief Description of the Prior Art
The use of a variety of microparticle-based retention aids and drainage aids in systems that employ combinations of colloidal particles along with polymers such as cationic starches and/or synthetic cationic polymers is well established.
The pioneering system was EKA-Nobel's CompoSil™, based on colloidal silica and cationic potato starch. This was soon followed by Nalco's “Positek” TM System based on colloidal silica, cationic potato starch and an anionic polymer. Other systems employ variants of these ingredients, including Du Pont's work on silica-based microgels and Allied Colloid's “Hydracol”™, system based on bentonite. These technologies provide materials which are combined in a novel way to enhance the paper-making process.
While the concept of retention aids is well understood from an electro-chemical point of view, finding effective, low cost microparticles that emulate the performance of silica or bentonite has proven difficult.
Conceptually, the role of microparticles in these systems is to provide a large number of very small point sources of anionic charge around which cationic polymers, fine paper fibers and fillers form into flocs which aid in their retention. These fast forming, shear sensitive flocs also represent areas of high solids consistency and, therefore, act as dewatering mechanisms when they are “captured” by larger fibers. Because of their small size, they enhance paper formation. The high retention of polymers that they provide translates into strength advantages in the finished paper.
The desirable properties of ideal microparticles are: high numbers of low cost, non-toxic, small particles with stable (>20 millivolt) surface charges with a minimum impact on other paper making properties such as color, printability, porosity etc.
Presently, EKA-Nobel, Nalco and DuPont produce their own colloidal silicas in the United States and have provided retention aids systems for the paper industry based upon these silicas. Allied Colloids has a similar system that uses bentonite clay particles as a macroparticle in a competitive system.
SUMMARY OF THE INVENTION
The alkaline paper making industry prepares its furnishes at pH 7-8. The zeta potentials of silica, alumina and bentonite clays are well known. At pH 7-8 colloidal silica and bentonite clays have zeta potentials of minus sixty (−60) millivolts and minus forty (−40) millivolts respectively.
Systems employing either colloidal silica or bentonite clay are the primary commercial microparticles being used in retention/drainage aid systems on paper machines.
Surprisingly, many other compounds exhibit similar zeta potentials in the same pH range. However, these materials have not been used, apparently due to their comparatively large particle size and low surface area available for cationic adsorption.
The present invention provides aqueous suspensions of colloidal particles for use as microparticulate floc formers in two to three component systems used as retention aids and drainage aids on papermaking machines.
One object of this invention is to provide processes for the production of such aqueous suspensions of colloidal particles. In one such process, these alternative materials are processed through an agitated media mill in order to significantly reduce the particle size and thereby increase the surface area available for the adsorption of the various cationic materials found in paper furnishes. In another such process, a known process for preparing an aqueous sol comprising agglomerated particles of amorphous sodium aluminosilicate is modified to significantly reduce the particle size of the sol particles, once again thereby increasing the surface area available for adsorption of cationic materials.
Another object of the present invention is to provide stable dispersions of these materials in water or organic liquids, and to provide a method for producing such dispersions.
Stable dispersions of such particles are convenient, in that they allow the particles to be transported, while simultaneously inhibiting the particles from coalescing into larger agglomerates.
These and other objects and advantages have been achieved by the present invention wherein colloidal-sized particles of insoluble compounds with high anionic charges and high surface area can be provided by means of a high energy mill, such as a media mill, even though commercial suppliers of such milling equipment do not suggest that such particles sizes can be achieved. Alternatively, sols comprising colloidal-sized particles of amorphous insoluble compounds with high anionic charges and high surface area can be employed. Sols suitable for use in the present invention can be prepared by the process disclosed in U.S. Pat. No. 2,974,108, incorporated herein by reference, and modified as herein below described.
The present invention provides a drainage/retention aid system for papermaking, the system comprising finely divided particles (that is, “microparticles”) of a water insoluble solid having an anionic charge of at least 20 millivolts, and preferably from about 40 to 60 millivolts. The particle size of the microparticles is preferably no greater than 0.1 micron, with a particle size no greater than about 0.04 micron being more preferred. The water insoluble solid is preferably a solid chemical compound is selected from the group consisting of amorphous aluminosilicates, such as amorphous sodium alumino silicate, and mixtures of crystalline alumino silicates and amorphous alumino silicates, such as mixtures of amorphous sodium aluminosilicate and zeolite A. For example, the water-insoluble solid can be amorphous aluminosilicate having the formula MAIO
2
XAl
2
O
3
.YSiO
2
, where X ranges from 0 to 25, Y ranges form 1 to 200, and M is a monovalent cation selected from the group consisting of elements of group 1A of the periodic table, ammonium, and substituted ammonium ions, and the Si:Al mole ration is from 1:1 to 50:1. Alternatively, the water insoluble solid can be mixture of amorphous aluminosilicate having the formula MAIO
2
XAl
2
O
3
.YSiO
2
and zeolite A.
The drainage/retention aid system can also include a fluid vehicle such as water and a dispersion agent, such as a dispersion agent selected from the group consisting of wetting agents, anionic surfactants, and potassium pyrophosphate.
In addition to the microparticles, the drainage/retention aid system can also comprise a cationic starch and a cationic polyelectrolyte flocculant.
The microparticles of the present invention can be provided as a substantially aggregate-free sodium aluminosilicate sol. The substantially aggregate-free sol is preferably prepared by a two-step process. The first step of the process is the formation of a sodium aluminosilicate sol according to the process disclosed in U.S. Pat. No. 2,974,108. The sol resulting from this process has been found to be highly aggregated and thus not suitable for use in the process for making paper of the present invention. Consequently, a second step is employed whereby the sol is deaggregated to provided suitable microparticles.
Preferably, in the first step an agglomerated reaction product is formed by adding simultaneously, but as separate solutions, an aqueous solution containing about from 1 to 3 percent by weight calculated as SiO
2
, of active silica and an aqueous solution of an alkali metal aluminate to a vigorously agitated body of water at a temperature from 80 to 100 degrees C. Preferably, there is dissolved therein an amount o
Linsen Paul G.
McLaughlin John R.
Chin Peter
Fortuna Jos'e A.
Paul & Paul
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