Method and system for preparing ASA emulsion

Details Method and system for preparing ASA emulsion Method and system for preparing ASA emulsion

1998-08-19

2001-03-27

Lovering, Richard D. (Department: 1712)

Colloid systems and wetting agents; subcombinations thereof; pro

Continuous liquid or supercritical phase: colloid systems;...

Aqueous continuous liquid phase and discontinuous phase...

C162S168100, C366S136000, C366S176100, C366S340000, C516S076000, C516S924000

Reexamination Certificate

active

06207719

ABSTRACT:

This invention relates to means for and methods of apply an ASA sizing or coating to paper and more particularly a system having means for preventing a build up of ASA on inside surfaces of apparatus that is used to produce the sizing.
Reference is made to my U.S. Pat. 5,653,915 for more information on ASA coating systems. As good as it is, this system, like most paper coating systems, suffers from a build-up of ASA on inside surfaces of pipes, nozzles, valves, and other parts of the system. This build-up generally required a periodic back flushing and clean out every 2-4 months. With the invention, this periodic period can be increased many fold.
This build-up occurs because, when it is added to pulp stock during a paper making process, a hydrocarbon based ASA polymer material forms a protective barrier, resists moisture intrusion into the paper, and provides a conditioned surface for the application of inks to paper. Those same characteristics tend to form a similar barrier on the inside surfaces of the system pipes, valves, nozzles, etc.
Accordingly, a desired feature of the invention is to reduce the area of the inside surface, and in particular, to eliminate minute spaces where the build-up quickly forms and decreases the quality of the emulsion produced by the system. One such minute space is the atomizing nozzle which reduces the ASA to a spray of fine particles which may be thought of as tiny droplets of oil suspended in a liquid, such as water, for example. Heretofore, these particles have been formed by atomization, but the atomizer nozzles have tended to be clogged by the ASA. Another concern is the large amount of surface not presented by the plurality of inter-connecting piping in contact with the ASA emulsion during the processing.
The quality of the ASA coating is largely dependent on the particle size of the colloidal droplets. Particle counters, particle size analyzers, and microscopes are available to estimate the particle size. While these tools are effective, they are also tedious and more importantly, intermittent, so that there is no continuous monitoring of particle size during the production thereof. Heretofore, samples had to be drawn from an emulsification unit and analyzed in a laboratory in order to determine particle size. With such an intermittent testing, any changes in the quality of the emulsion on-line would not be detected in time to prevent at least some poor sizing performance on the paper machines. My U.S. Pat. 5,730,937 describes a monitor and sensor which is able to continuously monitor a flowing stream for particle size and concentration, and to send control signals in response thereto.
ASA emulsions are stabilized either by cationic starches (a natural polymer) or by proprietary synthetic polymers. From the viewpoint of someone practicing this invention, the customer usually prescribes not only the surfactant to use along with an identification of the polymer to be processed, but also supplies a blend with the surfactant already in the ASA. Regardless of whether a cationic starch or a synthetic polymer is used, an additional surfactant has been required in the emulsification step. The surfactant provides a boundary layer resistance to shear for the ASA particles. This surfactant is normally a non-ionic alkyl phenol ethoxylate. The composition of most surfactants is a trade secret which is closely held by the manufacturer, causing an increased uncertainty which makes the design of a general purpose system more difficult. Since the user of my system must accept and process the prescribed blends, it must be versatile enough to work with virtually all blends.
Putting these thoughts together, a system has to impart enough energy to a blend of ASA emulsifier and surfactant to break it into very fine particles. My above identified patent supplies the energy by a combination of a nozzle, subject to clogging, and a high speed pump. To eliminate the nozzle, another form of device must be provided to impart the energy. If, in the process of imparting such energy, a substantial cost savings can be realized, the system is even better. Since the nozzle and high speed pump were among the more costly parts of my earlier system, improvements of the described type are highly desired.
In keeping with an aspect of the invention, the system uses any of various mechanically means to break-up the blend of ASA and surfactant into fine particles. These means involve devices such as turbines, blender and the like. The invention solves the problem of reducing the internal surface area of the system by drilling holes in a block of metal so that the bores of the holes perform the functions of pipes. The longest of those bores is only a few inches. I have reduced the costs of the system by a factor of 40-50% as compared to the cost of prior art systems. Also, I have formed ways of making systems having a capacity in a range from very small to very large with only a small amount of system modification.
The term particle “size” refers to the average mean diameter/volume of the particles. Of course, the actual size of the particles will be distributed in a manner described by the well known Gaussian or bell shaped curve Therefore, some particles will be larger and some smaller than the average cited in this specification.
The success of the sizing is directly related to the quality of the emulsion (ASA particle size). A high level of size retention is mandatory in any ASA sizing system. If the ASA colloidal particle size is not small enough, there is a less stable emulsion and a lower retention of the size. A high retention means less re-circulation of ASA in a white water system and fewer problems associated with hydrolyzed ASA which forms a gum like particle called a “stickie”. One of the reasons why smaller particle size is so important is that it does less damage to paper making machines which tend to gum-up, if the particle size is too large.
The conflict for the system designer is to make the particles as small as possible without breaking the molecules of the starch and causing the ASA to react with water. In general, the smaller the particles, the better, a useful average mean diameter range being about 0.1 micron-3.0 micron; with a range of about 0.5 micron-1.5 micron preferred.
Because the internal phase is made up of the ASA, the emulsion is classified as an oil in water (“O/W”) emulsion. The two most common natural polymer emulsifiers (external phase) are corn and potato starch which are chemically modified to enhance their cationic charge characteristics. Another approach utilizes synthetic polymers in lieu of starch. The starch or polymer surrounds and protects the ASA thus encapsulating the ASA to keep it from hydrolyzing. In effect, the starch is the protective barrier for the particles of oil (ASA) to be spread on the paper. The “oil” is an internal coating which makes the paper water resistant and receptive to ink.
One consideration which goes into the design of my system involves a calculation of how much energy is required to produce the ASA particles having a desired particle size. In an exemplary mill application, the ASA and starch (or other suitable emulsifier) are metered through an emulsification unit designed to impart energy to the mixture to create a suitable and stable emulsion. The emulsion is then metered onto the paper. There the ASA emulsion combines with the furnish.
I have found that I can produce superior results with a mixing head costing under $1,000 and using standard commercial items, such as those shown in
FIGS. 5-10
. For example, a turbine that is useful with the invention may be almost any of those manufactured by MTH PUMPS of 401 West Main Street, Piano, Ill. 60545, although one of their turbines may be preferred over other of their turbines for any given installation. To this mixing head, there must also be added the cost of controls, sensors, and the like. However, the cost for controlling these standard commercial products is generally less than the controls which must be designed for special equipment. I have found t

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