Rosin emulsion including starch derivative for paper sizing

Details Rosin emulsion including starch derivative for paper sizing Rosin emulsion including starch derivative for paper sizing

1999-11-08

2001-09-18

Brunsman, David (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Carbohydrate or derivative containing

C106S208500, C106S145200

Reexamination Certificate

active

06290765

ABSTRACT:

This application is a 371 of PCT/GB97/03197 filed on Dec. 1, 1997.
The present invention relates to a “one-shot” rosin emulsion incorporating a cationic starch derivative for use in paper sizing and also relates to a method of paper sizing using the one-shot composition.
It is well established practice to effect paper sizing by use of a rosin emulsion and a soluble aluminium salt such as aluminium sulphate (e.g. in the form of papermakers alum [Al
2
(SO
4
)
3
. 16-18H
2
O], aluminium chloride, poly-aluminium chloride or aluminium chlorohydrate. (Although the term “emulsion” is conventionally used to describe the rosin product it should more properly be called a dispersion since although made as an emulsion, the particles are effectively solid at ambient temperature). The rosin emulsion and aluminium salt are generally used as separate additions to the paper making process. It is however also known to formulate so-called “one-shot” compositions which are formed by pre-mixing a rosin emulsion and an aluminium salt. The use of a “one-shot” composition avoids the need for separate additions of rosin emulsion and aluminium salt to the paper making process.
“One-shot” composition may be produced by vigorous stirring of an anionic Bewoid rosin emulsion (e.g. stabilised with casein) and an aluminium salt such that agitation is continued beyond formation of an initial precipitate to convert the latter into a cationic emulsion. Production of such emulsions using this technique is disclosed in GB-A-2 050 453.
Cationic emulsions made by this type of technique are not in very common use although there are a few which are still on the market. A limitation of such cationic emulsions is that often they are not as stable as the anionic rosin emulsions from which they are derived, and obtaining reproducibility is not always easy. It has therefore been the practice to include a cationic stabiliser as one component of the emulsion formed from the anionic Bewoid emulsion and the aluminium salt. Examples of such cationic stabilisers include quaternised and other cationised starches.
There is however a problem with existing “one-shot” compositions incorporating a conventional cationic starch as a stabiliser in that only relatively low amounts of the starch may be used without the “one-shot” composition becoming excessively viscous for economic use in a paper making process. This is a problem because conventionally used cationic starches are of relatively low “cationicity” and therefore the amount of the starch which may be tolerated in the “one-shot” composition may be insufficient to bring about the charge reversal of the initial anionic emulsion to give a cationic emulsion.
It is therefore an object of the present invention to obviate or mitigate the abovementioned disadvantages.
According to the present invention there is provided a “one-shot” composition for use in paper sizing comprising an admixture of a rosin emulsion, a soluble aluminium salt and a cationic starch derivative which has a charged state of 0.5 to 5.0 m equivalents per gramme and which has been produced by a process in which the starch structure was split prior to the cationising step.
The composition of the invention thus incorporates a cationic polymer derived from a degraded starch and having a charge density (i.e. the average number of milliequivalents of cationised atoms per gramme of polymer) of 0.5 to 50. This is somewhat higher than conventional cationic starches which are generally considered to have a charge density in the range 0.1 to 0.3 m equivalents per gramme. Furthermore, the fact that the cationic polymer is produced from a degraded starch means that it (i.e. the cationic polymer) is of lower molecular weight than conventional cationic starches with a consequential reduction in viscosity. The low viscosity and higher charge of the cationic polymer permits the charge of an anionic rosin emulsion to be reversed at low concentrations of the cationic polymer to produce a useable cationic emulsion and to produce a range of cationicities that may be tailored to meet specific demands of a mill.
Preferably the cationic polymer has a charge density of 0.5 to 4.5 and more preferably 1 to 3.5 m equivalents per gramme.
Cationic polymers produced from degraded starch for use in the invention may be produced with a range of molar masses and degree of cationisation. Furthermore, it is possible for solutions of such polymers to be produced containing up to 55% by weight of the polymer without being excessively viscous. Therefore it is possible in accordance with the invention to produce a range of “one-shot” cationic compositions which have sufficient cationicity for a particular application without being too viscous.
It is preferred that the cationic polymer employed in the invention is a quaternised derivative of a degraded starch. Preferably such a derivative has a degree of substitution of at least 0.15, more preferably 0.15 to 1.30 and even more preferably 0.20 to 1.10 quaternary groups per glucose unit. Ideally this degree of substitution is 0.20 to 0.80 and most preferably 0.50 to 0.80.
The cationic polymers used in the present invention may be produced by treating starch with an agent which will partially “fragment” the polysaccharide chain (e.g. by use of an oxidising agent such as hydrogen peroxide) and subsequently cationising the “fragmented” product in a reaction in which the solids content is a minimum of 50% (more preferably at least 55%) by weight. The cationizing agent may be used in an amount of 20 to 160%, most preferably 80 to 120%, by weight of the amount of degraded starch thereby allowing the degree of cationization to be readily controlled.
The preferred quaternising chemical is 2,3-epoxypropyl trimethyl ammonium chloride although other cationizing agents may be used.
Preferred cationic polymers for use in the invention have a nitrogen content in the range of approximately 1-5% (for the cationizing chemical being 2,3-epoxypropyl trimethyl ammonium chloride). It is particularly preferred that cationic, oxidised starch derivatives for use in the invention have a nitrogen content of 3-5%, more preferably 3-4%, and ideally about 3.5% (for the cationizing chemical being 2,3-epoxypropyl trimethyl ammonium chloride).


REFERENCES:
patent: 4333795 (1982-06-01), Street
CAPLUS 1993:430260, Vihervaara et al, “Raifix-new cationic polymers for controlling . . .”.

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