Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-08-10
2002-09-17
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S181600, C162S181800, C162S183000
Reexamination Certificate
active
06451170
ABSTRACT:
FIELD OF THE INVENTION
The present disclosure is directed to improved starch compositions, and methods of making and using the improved starch compositions. In particular, the disclosure is directed to starch compositions for use in papermaking processes, and to methods of preparing, manipulating and using the starch compositions during manufacture of paper products.
BACKGROUND
Numerous paper products are manufactured from fibers. These products are often manufactured from an aqueous slurry containing modified cellulose fibers derived from various plant sources. The slurry is formed in the wet end of a papermaking machine, where paper fiber is formed into a dilute water slurry and combined with a variety of materials before being distributed onto a paper machine wire. The water is subsequently removed from the slurry in a controlled manner to form a web, which is pressed and dried to create a finished paper product.
Additives can be incorporated into the slurry to enhance the papermaking process and to improve the finished papers' aesthetic and functional properties. These additives can include starch compositions incorporated during the wet end of the papermaking process to improve drainage and retention, to add strength, and to improve formation properties of the paper. Starch compositions can increase ink penetration times, reduce lateral spread of printing inks, and improve imaging and contrast. Starch compositions can also increase the surface integrity of papers, thereby decreasing picking in uses such as printing and photocopying.
Other ingredients that can be incorporated into paper are microparticles, including specialty clays, silica, and other functional fine particles (also known as “fines”). These microparticles are often added during the wet end of the papermaking machine. Depending upon the type of paper being made, as well as the characteristics of the slurry, various different microparticles can be added. One of the challenges of using microparticles during papermaking is that the microparticles are not all retained on the web as the paper is formed. The microparticles that are not retained often end up being discharged, which can be expensive because the particles are not used. Therefore, it is desirable to enhance particle retention.
Drainage, or de-watering ability, is another important consideration in the manufacture of paper because it is related to how fast a paper machine can remove water from the web. Typically, improved dewatering corresponds to higher speeds on paper machines and to higher production rates of paper. Papermakers often seek to retain all fiber and particulates on the wire at the greatest speed economically possible, without sacrificing product quality. However, papermakers often experience drainage limitations while trying to maintain product quality, and therefore it is desirable to have high drainage values such that the paper can be made at high speeds and high quality.
Although papermakers and suppliers of paper ingredients realize that high retention and drainage are desirable, a considerable challenge in making consistent, high-quality paper has been that papermaking systems are not all alike and can show significant variation. This variation can be the result of changes in the ingredients in the paper furnish as well as variability in the papermaking equipment. These variations can make it difficult to produce quality paper at high speeds due to changes in particle retention and drainage.
Presently, most ingredients added to the papermaking slurry are optimized for use under specific conditions. This is true, for example, of starch compositions added to the wet end of the papermaking process. Unfortunately, conditions at most papermaking facilities vary over time as the ingredients and systems change. Therefore, a need exists for improvements that allow for satisfactory drainage and particle retention over a range of papermaking conditions.
SUMMARY OF THE DISCLOSURE
The present disclosure relates to starches, for example cationic crosslinked starches, and to the use of those starches in papermaking. More particularly, the present disclosure is directed to starch and its use in wet end processing of a paper machine. The practices of the disclosure are particularly adapted for customization of the starch properties for specific wet end systems, and allow for modification of the starch properties to correspond to variations in the wet end of the papermaking machine.
The starch can also be modified during production by adjusting the starch functionality in the papermaking process. By selectively changing the crosslinking level of the starch, the drainage and retention properties of the paper furnish containing the starch are altered, which permits the starch properties to be tailored to provide improved performance depending upon the characteristics of the paper furnish in which it will be used.
The starch properties can further be adjusted immediately prior to use in the wet end of the papermaking machine in order to tailor the starch to the specific conditions existing in the papermaking machine. In this manner, the starch can be tailored to improve drainage and retention. This customization occurs, for example, by modification of the temperature at which the starch composition is cooked prior to addition to the wet end, by changing the period of time for cooking the starch, by changing the pressure at which the starch is cooked, and/or by changing the solids content of the starch prior to cooking. By adjusting these parameters, either individually or in concert, the properties of the starch are altered and can be conformed to specific conditions of various papermaking processes. For example, by cooking at higher or lower temperatures the starch properties are altered, and these altered properties can be used to improve wet end performance.
One implementation of the disclosure is a process for improving a papermaking method. The process comprises providing a papermaking furnish containing cellulosic fibers in an aqueous slurry to which is added a starch composition. The starch composition is typically a crosslinked cationic starch. The starch is cooked prior to addition to the papermaking furnish at a cooking temperature typically below 330° F., and more typically from 180 to 250° F., and even more typically less than 220° F. or 230° F. Such cooking temperatures are typically average cooking temperatures, which corresponds to the average temperature measured from two or more temperatures over time.
Microparticles, including nanoparticles, are also incorporated into the papermaking furnish, and these microparticles typically have an average diameter of less than 1.0 micron, and more typically less than 0.1 microns. Suitable microparticles include, for example, various silica and clays.
The cationic crosslinked starch of the disclosure is typically mixed as a wet end additive into a paper furnish having a pH of from 5.0 to about 9.0 in the wet end. The general manufacturing process for paper, including the term “wet end”, is described generally in
Pulp
&
Paper Manufacture, Vol. III, Papermaking and Paperboard Making,
R. G. McDonald, editor, J. N. Franklin, tech. editor, McGraw Hill Book Co., 1970.
In specific implementations, the improved starch and methods are used to improve dewatering of papermaking furnishes. As the furnish is dewatered during the papermaking process, the dewatering rate is evaluated. If this dewatering rate is unsatisfactory, then the cooking temperature of the starch is modified in order to alter the dewatering properties. The modification of the cooking temperature should be sufficient to produce a modification in the dewatering or first pass retention of the papermaking furnish. Typically, the amount of modification in the temperature is greater than 1° F., and more typically at least 5° F. In specific implementations, the amount is from 5 to 10° F. In certain implementations the modification is at least about 10° F. The temperature is increased in certain implementations, and decreased in other i
Anderson Kevin Ray
Garlie David Edward
Cargill Incorporated
Chin Peter
Merchant & Gould P.C.
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