Paper Coatings
KADY® Mills have been in use in paper coating plants world wide for forty years. The strength of the KADY® Mill lies in three basic areas:
- Extremely high speed dispersion.
- The ability to mechanically control batch temperature.
- The capability of removing air from a liquid/solid mass.
COLOR MAKE DOWN
The KADY® mill will disperse dry or slurried clay and combinations of clay and titanium dioxide and/or calcium carbonate at percentages of solids as required by the coater. The KADY® Mill will accept dry clay loaded at a rate of up to 500 lbs. per minute. Preslurried clay or pigments may be pumped into the mill at any rate desired.
(Use our illustration to see how the KADY® Mill fits into the "make down" process.)
Though the fineness of the dispersion will be related to the ultimate particle size of the pigment, the development of the highest gloss and opacity possible will be assured in a very short period in KADY®. Through the high speed dispersion/impingement approach of the KADY® Mill, pigment agglomerates are eliminated quickly, providing batch uniformity and ideal application characteristics.
A further advantage of this fine dispersion lies in the formulator's ability to reduce the usual amount of adhesive normally required. The adhesive is distributed more evenly thereby increasing the surface area which in turn lessens the quantity required.
Of all the KADY® Mill's strengths, the greatest lies in its ability to perform the make down in one piece of equipment. As we shall later discuss, the KADY® Mill will even cook the starches required, concurrent with the normal batch cycle required to do the finish color.
Many installations require nothing more than a single stop/start station, where as others involve the KADY® Mill as part of a totally automated system wherein all the raw materials are metered to the KADY®, mixed in a timed cycle and the finished color is discharged to storage or freed tanks.
The preparation of finished coating color utilizing precooked starches has been in as brief a span as 20 to 30 minutes, utilizing the following approach:
The total liquid to be used for the pigment dispersion and adhesive is charged into the mill with the appropriate dispersing aids the mill is then started and the dry pigment is charged. For a clay/casein or protein formulation, alkali is added followed immediately by the dry casein. The machine is run without jacket cooling until a batch temperature of approximately 110 degrees is reached. At this point it is desirable to turn on the jacket cooling to control the batch temperature. About 5 minutes before shutting the machine off, the latex is added. The batch is then completed and discharged into the holding tanks ready for the coating operation.
As previously mentioned, the KADY® Mill will cook starch, not just separately, but in the presence of the pigment during the make down itself. Appropriate temperatures can be developed by the KADY® Mill unit alone, however, hot water may be circulated through the jacket to hasten the cooking process. To further reduce the cooking time, the KADY® Mill may be provided with steam jackets and/or steam spurges to introduce live steam directly to the batch from existing steam sources. As a result, temperature increases the subsequent cooling may be effected in very rapid succession depending upon the formulator's requirements. Currently many operations are producing complete 2000 gallon batches in an hour or less.
Continuous make down can be accomplished by using multiple KADY® Mills. A number of such installations are currently in use and are generally engineered on as-need-be bass for the individual end user. Specific installations are engineered by Kinetic Dispersion Corp., to suit individual requirements.
DEAERATION
(Use our illustration to see how the KADY® Mill fits into the "deaeration" process.)
The KADY® Mill has the ability to remove all of the air from the recirculated color returned from the coater. In many existing operations where older mixing methods are utilized, the KADY® Mill will also improve the fineness of the dispersion on a pass-through basis from that equipment and will help maintain a uniformity of viscosity, as well as adhesive value.
Specifically, when the excess color is returned from the coating head to the feed/storage tank, a considerable amount of air is whipped into the color. As much as 30% by volume may be trapped in this returned color. The presence of air in the color can cause imperfections such as streaks in the coating on the sheet. To overcome this problem, the KADY® Mill, in line, is run continuously with a fixed volume in the vessel. The retention time generally runs one and one half to two minutes on the average. No screening is required between the KADY® Mill and the coater and for all practical purposes, the KADY® Mill completely deaerates the coating. After a brief retention time, the color is then piped back to the feed/storage tank ready for the coater in its renewed state. Color processed in this manner greatly improves the application continuity, which in turn assures the product quality and consistency which your customers require.