Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-07-17
2001-08-14
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S173000, C162S164300, C162S164600, C162S168200, C162S180000, C162S183000
Reexamination Certificate
active
06273997
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to rosin sizes for paper.
BACKGROUND OF THE INVENTION
Sizing agents are used by the paper industry to give paper and paperboard some degree of resistance to wetting and penetration by aqueous liquids. There are two basic categories of sizing agents: acid and alkaline. Acid sizing agents are intended for use in acid papermaking systems, traditionally less than pH 5. Analogously, alkaline sizing agents are intended for use in alkaline papermaking systems, typically at a pH greater than 6.5.
Most acid sizing agents are based on rosin. The development of sizing with a rosin-based size is dependent upon its reaction with papermaker's alum, Al
2
(SO
4
)
3
•14-18 H
2
O. Since aluminum species that exist predominantly at a low pH (<pH 5) are required for the appropriate interactions needed to effect sizing, rosin and alum have been used primarily in acid papermaking systems. It has been shown that, by proper selection of addition points in the papermaking system and by using cationic dispersed rosin sizes, rosin-based sizes can be used in papermaking systems up to about pH 7, thus extending the range of acid sizes. However, due to the limitations imposed by alum chemistry, the efficiency of rosin-based sizes decreases above about pH 5.5.
Sizing agents developed for papermaking systems above pH 6.5 are generally based on alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA). AKD sizes function by forming covalent bonds with cellulose to give proper orientation and anchoring of the hydrophobic alkyl chains. This covalent bond formation makes AKD sizing very efficient and resistant to strong penetrants. However, AKD sizes have some limitations: small changes in the amount of size added can lead to large differences in sizing (steep sizing response curve), and there is a slow rate of sizing development (cure).
The other major alkaline sizing agent is based on ASA. As with AKD, the development of sizing with ASA sizes is also dependent on the formation of covalent bonds with cellulose to give proper orientation and anchoring. ASA is more reactive than AKD, resulting in the greater development of sizing on-machine. However, the reaction rate with water is also greater, producing a hydrolyzate that is an inefficient sizing agent in alkaline systems and contributes to the formation of deposits on the papermaking machine. To minimize the formation of hydrolyzate, ASA is typically emulsified at the mill immediately before addition to the papermaking system.
Cationic resins have been used previously in the papermaking process, although not the cationic resins of this invention in combination with a rosin/hydrocarbon blend in the absence of alum or with amounts of alum ≦0.3%, based on the dry weight of paper pulp. For example, U.S. Pat. No. 3,193,449 discloses sizing paper with an aqueous emulsion of a partially saponified terpene resin, 1-5% alum, and optionally a partially saponified rosin. U.S. Pat. No. 4,323,425 discloses sizing in the absence of alum with an aqueous dispersion of fortified rosin, an optional hydrocarbon resin and a vinyl imidazoline polymer as a retention aid. Canadian Patent 746,057 discloses a sizing composition for paper comprising an aqueous dispersion of partially neutralized rosin, a terpene polymer, and 1-5% aluminum sulfate, based on the dry weight of the pulp.
There is still a need for a rosin sizing system for use at a neutral to alkaline pH that does not have the disadvantages of ASA and AKD sizes.
SUMMARY OF THE INVENTION
The method of this invention for sizing paper or paperboard comprises incorporating into the paper pulp at a pH of about 5.0 to about 8.5 a sizing composition consisting essentially of (a) rosin, (b) at least one hydrocarbon resin, (e) a cationic component consisting essentially of a cationic polyamine resin, wherein the weight ratio of the rosin/hydrocarbon resin blend to cationic polyamine is about 5:1 to about 1:2. preferably about 1:1, and the cationic polyamine is selected from the group consisting of polyalkyleneamine-epihalohydrin resins, polyalkyleneaminedicyandiamide-epihalohydrin resins, poly(diallylamine•HCl)-epihalohydrin resins, poly(methyldiallylamine•HCl)-epihalohydrin resins, epihalohydrin-modified polyethyleneimine resins, amine-modified poly(methyldiallylamine•HCl)-epihalohydrin resins and mixtures thereof, and (d) up to 0.3% alum, based on the dry weight of the pulp.
The rosin-based sizes of this invention are effective at a neutral to slightly alkaline pH. In papermaking, a pH of 6.5-7.5 is considered to be “neutral”. Rosin-based sizes do not have the shortcomings associated with AKD and ASA alkaline sizing agents. Rosin sizes do not depend on covalent bond formation, therefore they do not have on-machine size development problems. Rosin is tacky, not waxy, therefore it is not expected to contribute to slip. It is also possible to make high solids (up to 50%) dispersions that have a relatively long shelf life of six months to a year. The sizing response curve for rosin sizes is gradual, not steep, and the sizes are relatively inexpensive.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention it has been discovered that rosin-based sizes can be used at a pH of about 5.0 to about 8.5, preferably about 5.5 to about 8.0, and most preferably about 6.0 to about 7.5, when certain cationic epihalohydrin-modified polyamine resins are present. The cationic resins are used to anchor the rosin to the paper pulp. The cationic polyamine resins suitable for use in the present invention are selected from the group consisting of polyalkyleneamine-epihalohydrin resins, polyalkyleneamine-dicyandiamide-epihalohydrin resins, poly(diallylamine•HCl)epihalohydrin resins, poly(methyldiallylamine•HCl)epihalohydrin resins, epihalohydrin-modified polyethyleneimine resins, and amine-modified poly(methyldiallylamine•HCl)-epihalohydrin resins. The weight ratio of rosin to cationic polyamine resin is preferably about 5:1 to about 1:2, more preferably about 1:1.
Exemplary cationic polyamine resins useful in accordance with the present invention include bis-hexamethylentriamine-epichlorohydrin resin, poly(methyldiallylamine•HCl)-epichlorohydrin resin, diethylenetriamine-dicyandiamide-epichlorohydrin resin, epichlorohydrin-modified polyethyleneimine resin, hexamethylenediamine-epichlorohydrin resin, poly(diallylamine•HCl)-epichlorohydrin resin, diethylenetriamine/epichlorohydrin resin, triethylenetetraamine/epichlorohydrin resin, tetraethylenepentaamine/epichlorohydrin resin, imino-bis-propylamine/epichlorohydrin resin, and 1-6 hexamethylenediamine-co-1,2-dichloroethane/epichlorohydrin resin.
The rosin used in the process of this invention can be any of the commercially available types of rosin such as, for example, wood rosin, gum rosin, tall oil rosin, and mixtures thereof, in their crude or refined state. Fortified rosin, partially or substantially completely hydrogenated rosins and polymerized rosins, as well as rosins that have been treated to inhibit crystallization such as by heat treatment or reaction with formaldehyde can also be used. Fortified rosins are typically prepared by well known procedures involving reacting rosin with acid compounds, including &agr;,&bgr;-unsaturated monobasic and polybasic organic acids and acid anhydrides such as acrylic, maleic, fumaric, itaconic, and citraconic acids and their anhydrides. Preparation of fortified rosins is disclosed in U.S. Pat. Nos. 2,628,918 and 2,684,300, the disclosures of which are incorporated herein by reference. “Rosin size” also includes sizes prepared from rosin containing various amounts of fatty acids or fatty acid mixtures, e.g., a tall oil rosin fraction obtained from the fractional distillation of tall oil and containing up to several percent of a tall oil fatty acid mixture. The amounts of rosin useful in accordance with the method of the present invention typically vary from about 0.1 to about 1 weight %, based on the dry weight of the pulp used.
Preferably, a
Ehrhardt Susan M.
Evans D. Bruce
Chin Peter
Hercules Incorporated
Samuels Gary A.
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