Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
1998-08-31
2001-10-16
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C106S206100
Reexamination Certificate
active
06303000
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for manufacturing paper and more particularly to adding to a dilute paper pulp slurry prior to sheet formation a modified starch dispersion of a cationic starch which has been gelatinized and reacted with a blocked glyoxal resin.
Industrial starch may be utilized in a wide variety of applications including as coatings for paper or paper board and as a bonding wet end additive in papermaking. Starch compositions may desirably be prepared in the form of aqueous dispersions capable of being added to the pulp slurry.
For many commercial applications starch is gelatinized by the end user prior to being used. Gelatinization occurs after starch granules are dispersed as a slurry in water with the resultant aqueous slurry being heated to over 50° C. and usually over about 65° C. Under such conditions starch grains tend to absorb water, swell, and eventually rupture to allow starch fragments and molecules to disperse in water. This rupturing and dispersion is generally referred to as “gelatinization” and is an irreversible reaction resulting in a relatively thick starch dispersion.
The cross-linking of starches with multi functional reagents which are reactive with starch hydroxyl groups is well known. Glyoxals and polyaldehyde compounds and resins have been previously utilized as cross-inkers. The simple mixing of glyoxal with a starch dispersion will provide a gel. U.S. Pat. No. 4,455,416 describes a paper coating containing starch binder and a cyclic urea/glyoxal/polyol condensate as an insolubilizer for the binder. As an insolubilizer the glyoxal condensate is inactive until the coating is applied and cured upon drying whereupon the glyoxal crosslinks the starch to impart water resistance. U.S. Pat. No. 4,021,260 describes ethoxylated fatty alcohols as starch viscosity control agents. U.S. Pat. No. 3,324,057 discloses the use of dialdehyde starch in the preparation of paper coatings. U.S. Pat. No. 3,740,391 describes the production of aqueous dispersions of a starch first reacted with an acrylamide and, subsequently, with glyoxal. U.S. Pat. No. 4,013,629 discloses a glyoxal binder system. U.S. Pat. No. 4,425,452 discloses coating paper material via an enzymatically converted starch. British Patent No. 2017124 discloses polysaccharides cross-linked with glyoxal.
A stable fluid aqueous modified starch dispersion is prepared in U.S. Pat. No. 5,032,683, the disclosure of this patent being incorporated herein by reference. This starch dispersion is prepared by gelatinizing an aqueous slurry of a starch and reacting with a glyoxal compound. The present invention has found that a cationic starch dispersion modified with blocked glyoxal resin when added in the wet end of a papermaking process provides significant improvements in strength to the resultant paper.
BRIEF DESCRIPTION OF THE INVENTION
It is an object of this invention to provide a process of manufacturing paper having improved strength.
This and other objects are achieved by introducing into the paper pulp in the wet end of a papermaking process an aqueous starch dispersion of a gelatinized cationic starch and a blocked glyoxal resin.
DETAILED DESCRIPTION OF THE INVENTION
An aqueous cationic starch dispersion modified with a blocked glyoxal resin is prepared which is readily flowable and wherein gelation and viscosity increases over time are inhibited. The starch dispersion is prepared by gelatinizing an aqueous suspension or slurry of starch granules and adding, preferably reacting the starch with a blocked glyoxal resin at temperatures of at least 70° C., preferably 85 to 95° C. Preferably gelatinization and the reaction with the blocked glyoxal resin are carried out simultaneously, although the starch can be pre-gelatinized and then reacted with the glyoxal compound with heating.
It is theorized that by reacting gelatinized starch at the higher temperatures with the blocked glyoxal resin the amylose is derivitized with the glyoxal so that retrogradation of the amylose and the formation of amylose fatty acid complexes upon cooling is inhibited, resulting in aqueous dispersions having a flowable viscosity and in which gelation and viscosity increases over time are inhibited. Without intending to be bound by theory it is believed that the glyoxals react with amylose to make highly labile hemi-acetals which disrupt the crystallinity of amylose, thus significantly inhibiting retrogradation. Further, it is believed that glyoxal added after gelatinization and cool-down does not form hemi-acetals with the same efficiency as those added during heating because after gelatinization and cool-down crystallization occurs which limits the sites of reaction with glyoxal. Further, the use of a blocked glyoxal resins provides improved starch rheology reducing the tendency for gelling and is less prone to retrogradation and precipitation.
The starch dispersion prepared according to this invention will generally have a viscosity of less than 1000 cps, preferably less than 350 cps. Except where otherwise indicated, viscosity readings set forth herein are taken in aqueous solution at 35% solids content (by weight), are Brookfield viscosities (RV, #3 spindle at 100 rpm), and viscosity readings are taken at room temperature.
Suitable blocked glyoxal resins which may be used in accordance with the invention are described in U.S. Pat. No. 4,695,606 and include but are not limited to cyclic urea/glyoxal/polyol condensates, polyol/glyoxal condensates, urea or cyclic urea/glyoxal condensates and glycol/glyoxal condensates. The amount of glyoxal compound may be adjusted within broad limits, but is generally from about 3% to about 30%, preferably 9 to 20%, of the total dry weight of starch (and/or derivatives thereof) present.
In accordance with the invention, an aqueous slurry of cationic starch is prepared. Preferably the starch is an amylose containing starch. The starch may be obtained from any conventional source, including potato, corn, waxy corn, red milo, white milo, wheat and tapioca and may be pearl or lightly thinned and may have been oxidized, hydroxyalkylated,acid modified, enzyme converted or various combinations thereof. Also, suitable to this invention are thin-boiling starches that have been additionally chemically modified to reduce the setback or retrogradation tendencies of the starch. The prior art describes methods for making a wide variety of starch derivatives that display reduced setback. Higher molecular weight starches are preferred because of greater strength than low molecular weight starches. In certain preferred embodiments a blend of hydroxyethylated starch and an acid and/or enzyme-converted starch may be utilized with cationic starch. For example, cationic corn or potato starch may be utilized together with an acid modified or an oxidized hydroxyethylated starch such as a hydroxyethylated potato starch.
It is important for the starch to contain cationic functionality to enhance retention on the anionic paper fibers. Such functionality is commonly introduced via tertiary or quaternary amino groups appended to the starch.
Preferably, the blocked glyoxal resin is added to the aqueous starch slurry and the slurry is heated to about 90° C. for at least about 30 minutes to gelatinize the starch. The starch slurry and blocked glyoxal resin may be heated briefly to higher temperatures such as those obtained with a steam injection cooker. The heat beneficially drives the reaction of the blocked glyoxal resin and starch simultaneously with starch gelatinization. The resulting gelatinized starch composition is then preferably treated with a biocide if it will be stored, preferably after it has been allowed to cool to about 40° C. Biocide is preferably added at a concentration by weight, of about 10 ppm to about 500 ppm. Suitable biocides include Kathon® LX from Rohm & Haas which is a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4isothiazolin-3-one and Proxel® GXL from ICI which is 1,2 benzothiazolin-3-one. Gelatinization in the presence of t
Dragner Louis R.
Floyd William C.
Thompson Nolan
Chin Peter
Hudak Daniel J.
OMNOVA Solutions Inc.
Rywalski Robert F.
LandOfFree
Paper making process utilizing a reactive cationic starch... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Paper making process utilizing a reactive cationic starch..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Paper making process utilizing a reactive cationic starch... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2590584