One-pass method for preparing paper size emulsions

Details One-pass method for preparing paper size emulsions One-pass method for preparing paper size emulsions

1998-12-15

2001-10-02

Brunsman, David (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Heterocyclic

C106S150300, C106S174100, C106S205100, C106S209100, C162S164100, C162S174000, C162S175000, C162S177000, C162S178000, C366S176100, C366S182200, C366S262000, C524S112000

Reexamination Certificate

active

06296696

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a one-pass method through a non-tolerance dependent dispersion system for preparing paper size emulsions. More particularly, the paper size emulsions comprise an aqueous emulsion of a substituted cyclic dicarboxylic anhydride, a colloidal stabilizer, and a surfactant wherein the emulsion after one-pass through a dispersion system has an average particle size of less than 2 microns.
BACKGROUND OF THE INVENTION
Paper and paperboard are often sized with various hydrophobic compounds including, for example, wax emulsions, ketene dimers, isocyanate derivatives, fatty acid complexes, fluorocarbons, certain styrene-maleic anhydride copolymers, and substituted cyclic dicarboxylic acid anhydrides such as alkenyl succinic anhydride (ASA). These compounds are referred to as sizes or sizing compounds and may be introduced during the actual paper making operation wherein the process is known as internal sizing. Sizing compounds may also be applied to the surface of the finished web or sheet in which case the process is known as external or surface sizing.
In the case of ASA size, in order to have effective sizing agents with ability for uniform size dispersion throughout the fiber slurry it must be emulsified into a fine particle size emulsion. Typically such emulsions are prepared with the aid of ionically modified starches, carboxymethyl cellulose, natural gums, gelatin, synthetic polymers, or polyvinyl alcohol, all of which act as colloidal stabilizers. In commercial practice, ASA is emulsified with these materials with or without surfactant. The desired particle size for a good quality emulsion is a majority of the particles having a particle size of less than 2 microns. Emulsions having an average particle size of greater than 2 microns negatively affects the retention mechanism and creates deposits of undesired hydrolysates throughout the papermaking process. This adds to the product quality problems and necessitates disassembly and cleaning of the papermaking equipment.
Most presently used emulsification systems are designed on high homogenizing shear and/or pressure, and high tolerance between the stationary and rotating blades, with a flow recirculation loop. In these systems, emulsion prior to attaining its workable property must pass through the turbine emulsification apparatus multiple times, generally in excess of nineteen passes. This high shear, heat generating process has a negative impact on the quality of the final product. It also adds to the cost and complexity of the equipment since extra controls and additional equipment/space is required for the process.
Therefore, it would be advantageous to prepare a paper size emulsion having an average particle size of less than 2 microns through one-pass, non-tolerance dependent dispersion system.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for preparing paper size emulsions.
It is another object of the invention to provide a method for preparing paper size emulsions having an average particle size of less than 2 microns.
It is also an object of the invention to minimize the number of passes through a dispersion system which are required to reduce the average particle size of a paper size emulsion to less than 2 microns.
It is a further object of the invention to provide a dispersion system which effectively emulsifies immiscible materials and is economical.
With regard to the foregoing and other objects, the present invention provides a one-pass method through a non-tolerance dependent dispersion system for preparing a paper size emulsion wherein the emulsion after one-pass through a dispersion system has an average particle size of less than 2 microns, said method comprising:
(I) preparing raw materials which comprise at least one substituted cyclic dicarboxylic anhydride, at least one colloidal stabilizer, and water;
(II) adding the raw materials prepared in Step (I) to a dispersion system comprising:
a housing having a bottom chamber and an upper chamber wherein said housing has a means for cooling in contact therewith;
a motor mounted to said housing for turning a shaft extending into said housing;
a baffle plate mounted to said housing to separate said upper chamber from said lower chamber, said baffle plate having an aperture for receiving said shaft therethrough and forming an annular passage therebetween;
at least two kinetic baffles mounted within said lower chamber to form pressure zones;
an inlet cap mounted to said housing and having a primary inlet and a secondary inlet for delivering said plurality of materials into said lower chamber; and,
at least two blades mounted to said shaft, at least one of said blades disposed in said lower chamber and at least one of said blades disposed in said upper chamber; and
(III) emulsifying the raw materials in the dispersion system at a temperature of from about 40° F. to about 160° F. to form a paper size emulsion.
According to a preferred embodiment of the invention, the emulsion after one-pass through the dispersion system has an average particle size of about 1 micron.
One-pass through the dispersion system of the invention is sufficient to form an emulsion having an average particle size of less than 2 microns, preferably about 1 micron. More preferably, at least 95%, most preferably at least 98%, of the emulsion particles after one-pass through the dispersion system have a particle size of less than 2 microns.
Paper size emulsions prepared using the one-pass, non-tolerance dependent method of the invention which are added in the papermaking process provide paper with liquid resistance. Moreover, the one-pass, non-tolerance dependent method for preparing the paper size emulsion eliminates the need for repeated passes through the dispersion system in order to achieve an emulsion having the required small particle size which is a cost advantage to paper manufacturers. In addition, the dispersion system of the invention is more cost effective to manufacture due to the nontolerant equipment specifications and the lack of recirculation. Furthermore, the novel dispersion system of the invention operates at lower temperatures and pressures than prior art emulsification equipment which allows for longer equipment life. Such lower operating temperatures also provide a paper size emulsion product with improved stability which adds to the efficiency of the sizing.


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