Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
1998-11-23
2001-04-17
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S178000, C106S205010, C106S205600, C106S205700, C106S206100, C106S215100
Reexamination Certificate
active
06217709
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to blends of cationic starch and cationic galactomannan gum such as guar, locust bean, fenugreek gum, etc. useful as strength and drainage aids in papermaking.
2. Description of the Prior Art
Cationic starch and cationic guar gum are used effectively as strength and drainage aids by the paper industry. Typically, only one of these products is added to the wet end of the paper machine. Cationic starch is more commonly used. However, there has been reports of separate addition of these products at different points to a paper machine. Cationic starch is commonly added earlier in the process to provide strength. Cationic guar gum is added closer to the paper machine to provide drainage and fiber retention.
Up to 40 pounds of cationic starch can generally be added to obtain desired strength benefits. Cationic guar gum addition levels are usually in the 1- to 8-lb. range. Both products are supplied to paper mills in powder form. Cationic starch is typically slurried in water at 10-15% solids, subjected to high temperatures, and diluted before addition to the paper machine. High levels of starch can create problems in the process such as increased biological oxygen demand (BOD) and starch build-up, lowering starch etfectiveness. Cationic guar gum must be dispersed using an eductor, and dissolved in water at low solids, typically less than 1%. High amounts of fresh water needed for making guar gum solutions are becoming more difficult to get, as paper mills are closing their water systems. Dust associated with guar-based powder are also safety hazards, which can lead to falls and respiratory problems. Cost and handling problems associated with cationic guar gum have limited its use in paper dry strength applications.
Larsson, U.S. Pat. No. 4,755,259 discloses the separate addition to the papermaking machine of cationic starch, cationic guar and colloidal silica. Larsson does not disclose the addition of a combined cationic starch cationic guar blend in the papermaking machine.
Rushmere, U.S. Pat. No. 4,927,498 discloses the separate addition to the paper machine of cationic polymer, such as either cationic starch or cationic guar gum or cationic polyacrylamide, and anionic polysilicate microgels. The cationic polymers are used interchangeably and not added together as a blend.
“Application of New Gums for Enhancing Strength and Productivity”, K. E. Burnfield, TAPPI Press, Apr. 26, 1995, discloses the use of cationic guar gum added to a papermaking system which contains cationic starch in order to improve drainage of the starch containing system. The cationic guar gum and the cationic starch were added separately to the papermaking system and not as a blend.
Before the discovery of the present invention it was considered by those familiar with starch and guar gum chemistry to be difficult or nearly impossible to blend dry cationic starch and dry cationic guar gum for the purpose of adding them to the papermaking machine using conventional techniques, i.e., starch cookers.
SUMMARY OF THE INVENTION
According to the present invention there is provided a composition comprising cationic starch, cationic galactomannan gum and acid.
Further provided according to the present invention is a composition for improving the dry strength and/or drainage of paper products comprising an aqueous paper pulp slurry and a composition comprising cationic starch, cationic galactomannan gum and acid.
Still further provided according to the present invention is a process for improving the dry strength and/or drainage of paper products providing an aqueous paper pulp slurry, adding the composition comprising cationic starch, cationic galactoinannan gum and acid to the paper pulp slurry and recovering the paper product in a dry sheet form.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a blend of cationic starch, cationic galactomannan gum, (such as borated cationic guar gum), and acid. The product as a powder can be handled and put into solution using conventional starch preparation systems presently in place at paper mills. The present invention eliminates cationic guar gum solution make-up, which can be hazardous and water demanding. The invention delivers a solution of blended cationic guar gum and cationic starch to the paper machine. Surprisingly, the addition of the blended product results in paper strength improvement over addition of cationic guar gum or cationic starch alone, or cationic starch and cationic guar gum added to the machine at separate addition points. The two products have been rarely added to the same machine, and even when they were added to the same machine, they were added at different points in the process of pulp stock preparation.
Cationic guar is the most preferred cationic galactomannan gum for use in the present invention. The present invention refers to guar or cationic guar specifically in certain instances, however, the person of ordinary skill in the art will recognize that these teachings apply to galactomannan gums or cationic galactomannan gums in general.
It is known in the art that cationic guar gum and cationic starch improve drainage and strength of paper when added individually as solutions during the papermaking process. It might be expected that adding both cationic starch and cationic guar gum during the papermaking process would increase strength and drainage over either cationic starch or cationic guar gum added alone. It has surprisingly been discovered by the present invention that preblending cationic guar gum and cationic starch before addition to the paper machine increased paper strength as much as 20% above that seen with adding cationic starch and cationic guar gum separately without preblending. Another important feature of the present invention is that drainage improvements seen with separate addition of cationic starch and cationic guar gum were maintained with addition of the blend. Furthermore, it was discovered that a dry product containing the required ratios of cationic guar gum and cationic starch could be formulated such that the blend could be processed identically to starch prior to addition to the paper machine. Before the present invention viscosities encountered during the make-down of a cationic starch/cationic guar gum blend would be too high to process, resulting in costly equipment alterations and unacceptable water requirements.
The cationic galactomannan gum can be selected from the group consisting of cationic guar, locust bean and fenugreek gums, preferably the cationic galactomannan Gum is cationic guar and cationic locust bean, and most preferably it is cationic guar gum.
The cationic guar gum can be a hydroxypropyl trimethylammonium chloride guar derivative prepared by the reaction of guar gum with N-(3-chloro-2-hydroxypropyl) trimethylammonium chloride, such as Quat 188 available from Dow Chemical, Midland, Mich. The cationic guar gum can be purified cationic guar gum such as Galactasol® SP 813D or blends of cationic/anionic guar products such as AQU D-3376D or AQU D-3373D, available from Hercules Incorporated. Ratio of the hydroxypropyl trimethyl ammonium chloride moiety to guar gum saccharide unit can be 0.03 to 0.2, but preferably 0.07 to 0.15. The reaction is conducted in the presence of water and sodium hydroxide. Boron, in the form of sodium borate, boric acid, borax, or other water soluble boron containing compound, is added either before or after the reaction, but before drying of the guar product.
The cationic starch used in the present invention is quaternary amine modified starch. The starch can be a waxy maize, potato, corn, wheat or tapioca starch such as Cato® 232 from National Starch and Chemical Corporation, STA•LOK® 400 from A. E. Staley Manufacturing Corporation, Chargemaster® R430 from Grain Processing Corporation. Preferably, the cationic starch is cationic corn, potato or waxy maize starch and most preferably it is cationic corn starch. The ratio of cationic starch of cationic guar gum in the formulati
Chin Peter
Hercules Incorporated
Sloan Martin F.
Szanto Ivan G.
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