Storage stable paper size composition containing ethoxylated castor oil

#This invention relates to a self-emulsifiable paper size composition characterized by improved shelf life and to a method for sizing paper and paperboard therewith. More particularly, the invention relates to a self-emulsifiable paper size composition comprising a mixture of a hydrophobic substituted cyclic dicarboxylic acid anhydride and an ethoxylated castor oil.

#Paper and paperboard are often sized with various hydrophobic materials including, for example, rosin, wax emulsions, mixtures of rosin waxes, ketene dimers, isocyanate derivatives, fatty acid complexes, fluorocarbons, certain styrene-maleic anhydride copolymers, as well as the substituted cyclic dicarboxylic acid anhydrides more particularly described hereinafter. These sizes may be introduced during the actual paper making operation wherein the process is known as internal or engine sizing, or they may be applied to the surface of the finished web or sheet in which case the process is known as external or surface sizing.

#In order to obtain good sizing with any of these sizing compounds, it is desirable that they be uniformly dispersed throughout the fiber slurry in a small particle size. It was general practice therefore, to add the sizes in the form of an aqueous emulsion prepared with the aid of emulsifying agents including, for example, cationic or ordinary starches, carboxymethyl cellulose, natural gums, gelatin, cationic polymers or polyvinyl alcohol, all of which act as protective colloids. The use of such emulsifying agents with or without added surfactants did, however, suffer from several inherent deficiencies in commercial practice. A primary deficiency concerned the necessity of utilizing relatively complex, expensive and heavy equipment capable of exerting high homogenizing shear and/or pressures, together with rigid procedures regarding emulsifying proportions and temperatures, etc., for producing a satisfactory stable emulsion of the particular size. Additionally, the use of many surfactants in conjunction with protective colloids was found to create operational problems in the paper making process such as severe foaming of the stock and/or loss in sizing.

#As noted above, the size mixtures described herein exhibit extended shelf life, and, when emulsified and used in the paper stock system, yield paper products having superior sizing properties, even after these extended storage periods. The following examples will further illustrate the embodiments of the present invention. In these examples, all parts given are by weight unless otherwise specified.

#This example illustrates the use of a size mixture representative of the size mixtures of this invention utilized in the form of an aqueous emulsion. This emulsion is compared, in terms of particle size and water resistance of the resulting sized paper, with a conventional emulsion made with a mixture of substituted cyclic dicarboxylic acid anhydride and a polyoxyalkylene alkyl-aryl ether.

#A size mixture was prepared by combining 7 parts of ethoxylated castor oil containing 40 moles ethylene oxide per mole castor oil and 93 parts of alkenyl substituted succinic acid anhydride wherein the alkenyl groups contained 15 to 20 carbon atoms (hereinafter referred to as ASA). The mixture was aged for varying lengths of time at 50.degree. C. When emulsification was desired, the emulsion was formed by agitating 2 parts of the mixture with 98 parts of a cooked aqueous dispersion of cationic corn starch (containing sufficient starch to provide 0.05% based on dry fiber weight) using a propeller-type agitator at moderate speed (500 rpm) for 10 seconds (Emulsion No. 1). A control was prepared in accordance with U.S. Pat. No. Re. 29,960 using 93 parts of the same ASA and 7 parts of polyoxyalkylene alkyl-aryl ether wherein the alkyl group contained 9 carbon atoms, the aryl radical was phenol, and the polyoxyalkylene moiety was formed with 9.5 moles of ethylene oxide.