Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
1997-07-25
2001-09-25
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S341000, C528S403000, C528S480000, C528S486000, C528S493000, C528S503000, C525S430000, C525S435000, C525S436000, C524S420000, C524S538000, C524S031000, C523S414000, C523S416000, C523S417000, C523S418000, C523S420000
Reexamination Certificate
active
06294645
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to resin systems useful for imparting dry-strength to paper. The invention also relates to a process for incorporating these resin systems into paper and paper produced containing the resin systems.
BACKGROUND OF THE INVENTION
It is well known to add certain resins to paper, usually during the paper-making process, to improve dry-strength of the resultant paper. It is also well known to add certain resins to paper to improve wet-strength of the resultant paper. It is also well known that certain additives increase both a paper's wet-strength and and dry-strength. However, it is not always desirable that paper with increased dry-strength also exhibit an increased wet-strength since increasing a paper's wet-strength makes paper more difficult to repulp. If it is difficult for a paper product to be repulped, the papermaker will find it difficult to reprocess the material thereby increasing the amount of unusable waste associated with the papermaking process.
Many polymers that improve a paper's dry-strength are anionic under normal papermaking conditions, e.g., sodium carboxymethylcellulose, carboxymethyl guar, and copolymers of acrylamide and acrylic acid or sodium acrylate. A cationic compound may be used to retain these anionic substances on the pulp fibers which are themselves anionic by nature. These cationic compounds may be wet-strength agents such as polyaminoamide-epichlorohydrin resins, highly cationic polymers such as poly(diallyldimethylammonium chloride), polymers of dimethylamine and epichlorohydrin, modified starches, aluminum compounds, etc.
In U.S. Pat. No. 5,338,406 to Smith, a dry-strength system for a “water-soluble, linear, high molecular weight, low charge density cationic polymer having a reduced specific viscosity greater than two deciliters per gram (>2 dl/g) and a charge density of 0.2 to 4 milliequivalents per gram” with “at least one water-soluble, anionic polymer having a charge density less than 5 meq/g” is disclosed. The polyelectrolyte complex of Smith is useful as an additive for providing dry-strength to all types of paper, particularly for those papers which are produced using unbleached pulp.
In U.S. Pat. No. 5,338,407 to Dasgupta, a process for enhancement of paper dry-strength without reducing its softness is disclosed. The process comprises adding a mixture of an anionic carboxymethyl guar, carboxymethyl bean gum or carboxymethyl hydroxyethyl guar with various cationic additives to a bleached pulp furnish. The cationic additive may be a polyamidoamine-epichlorohydrin resin. If the cationic additive is a wet-strength resin, the paper's dry-strength is enhanced without reducing its softness. Additionally, the wet-strength of the paper is increased.
In Canadian Patent No. 1,110,019, “a process for manufacturing paper having improved dry-strength which comprises mixing an essentially alum-free pulp slurry with a water-soluble cationic polymer and subsequently adding a water-soluble anionic polymer to the essentially alum-free pulp slurry” is disclosed.
In addition to the above, polyamidoamine-epichlorohydrin resins have been used extensively as wet-strength agents for paper. Typically, these resins are prepared in a two-step process. In a first step, a polyamidoamine prepolymer is prepared from a diacid (e.g. adipic acid) and a polyamine (e.g. diethylenetriamine). In a second step, the polyamidoamine prepolymer is reacted with epichlorohydrin in an amount equal to or greater than the amount of secondary amine groups in the prepolymer. A small amount of epichlorohydrin reacts to effect branching of the prepolymer, accompanied by an increase in molecular weight. However, a majority of the epichlorohydrin reacts with the prepolymer to give reactive functional groups, specifically, either aminochlorohydrin or azetidinium. It is well known to those skilled in the art of papermaking that the above-described polyamidoamine-epichlorohydrin resins may be used in combination with anionic acrylamides or anionic cellulose derivatives. However, papers containing these combinations exhibit increased wet-strength as well as increased dry-strength, thereby making papers containing these combinations difficult to repulp.
SUMMARY OF THE INVENTION
The invention relates to a dry-strength system for paper comprising: a cationic component and an anionic component. The cationic component comprises a reaction product of an intralinker and a polyamidoamine. The intralinker to amine is in a ratio of about 0.75:1 or less on a molar basis. Preferably, the intralinker to amine is in a ratio of between about 0.02:1 to about 0.75:1, more preferably the intralinker to amine is in a ratio of between about 0.10:1 to about 0.40:1, more preferably about 0.20:1 to about 0.30:1.
The cationic component comprises a reaction product of an intralinker and a polyamidoamine wherein the polyamidoamine prior to reacting with the intralinker has a reduced specific viscosity of less than about 0.125 dl/g. Reduced specific viscosity (“RSV”) is used as a measure of the polyamidoamine prepolymer's molecular weight. Higher RSV values are indicative of higher molecular weights. Preferably, the polyamidoamine prior to reacting with the intralinker has a reduced specific viscosity of 0.05 to about 0.125 dl/g. More preferably, the polyamidoamine prior to reacting with the intralinker having a reduced specific viscosity of 0.065 to about 0.1 dl/g, more preferably, a reduced specific viscosity of 0.07 to about 0.09 dl/g.
The intralinker may be selected from the group consisting of epihalohydrins and diepoxides.
In one embodiment, the cationic component may comprise a cationic polyamidoamine epihalohydrin polymer. When the cationic component comprises a cationic polyamidoamine epihalohydrin polymer, the intralinker comprises epihalohydrin. The epihalohydrin may be selected from the group consisting of epichlorohydrin, epibromohydrin, epiiodohydrin, epifluorohydrin and alkyl-substituted epihalohydrins. Preferably, the epihalohydrin comprises epichlorohydrin.
In another embodiment, the intralinker may be a diepoxide. The intralinker may be selected from the group consisting of 1-bromo-3,4-epoxybutane, chloroepoxyhexane, and iodoepoxyisobutane, ethylene glycol diglycidyl ether (i.e., EGDGE) and 1,4-butanediol diglycidyl ether (i.e., BDDGE), 1,2,7,8-diepoxyoctane, 3-(bis(glycidoxymethyl)-methoxy)-1,2-propanediol, 1,4-cyclohexanedimethanol diglycidyl ether, 4-vinyl-1-cyclohexene diepoxide, 1,2,5,6-diepoxycyclooctane, and bisphenol A diglycidyl ether.
The anionic component comprises an anionic component consisting of copolymers of acrylamide and at least one member selected from the group consisting of acrylic acid, itaconic acid, methacrylic acid and 2-acrylamido-2-methyl-1-propanesulfonic acid and salts thereof. Alternatively, the anionic component comprises an anionic component selected from the group consisting of carboxylmethylcellulose, carboxymethyl guar, alginic acid, pectin, poly(2-acrylamido-2-methyl-1-propanesulfonic acid), and salts thereof. Preferably, the salts of the anionic component are the sodium salts thereof.
Alternatively, the anionic component may be an amphoteric polymer having a net negative charge. The amphoteric polymer comprising a polymer of acrylamide, at least one anionic monomer selected from the group consisting of acrylic acid, itaconic acid, methacrylic acid and 2-acrylamido-2-methyl-1-propanesulfonic acid and salts thereof and at least one cationic monomer selected from the group consisting of methacryloyloxyethyltrimethylammonium chloride (MTMAC), methacryloyloxyethyltrimethylammonium sulfate (MTMMS), acryloyloxyethyltrimethylammonium chloride (ATMAC), methacryloyloxyethylbenzyldimethylammonium chloride (MBMAC), dimethylaminoethylmethacrylate (DMAEMA) and salts thereof, 3-(methacrylamido)propyltrimethylammonium chloride (MAPTAC), diallyldimethylammonium chloride (DADMAC), and diallyldiethylammonium chloride (DADEAC).
The ratios of anionic and cationic resins in the dry-strength system may range from a
Allen Anthony J.
Echt Elliott
Maslanka William W.
Peters Jeffrey C.
Hampton-Hightower P.
Hercules Incorporated
O'Brien Robert P. O'Flynn
Samuels Gary A.
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