US2285028A - Rosin size emulsion - Google Patents

Description

Patented June 2, 1942 UNITED STATES PATENT OFFICE ROSIN SIZE EMULSION Edmund A. Georgi and Arthur L. Osterhof, Wilmington, Del., assignors to Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Application September 16,1940, Serial No. 357,007

.precipitated on the stock fibres by means of alum or other suitable precipitant. Such saponified rosin size emulsions are in general prepared by reacting gum or wood rosin with an alkali, such as sodium hydroxide or sodium carbonate,

whereby at least a part of the abietic and other salt during storage or upon dilution. Other objects will be apparent from the following detailed description of the invention.

1 have found that the above objects may be attained in rosin size emulsions prepared from wood rosin which has been subjected to heattreatment at temperatures below its decomposition temperature. be sufiicient to reduce substantially the tendency for the rosin to deposit 3:1 salt upon subsequent saponiflcation, but should not be suflicient to destroy the crystallizability of the rosin, since heat-treatment to such an extent causes the rosin acids present in the rosin are converted into 4 their water-soluble alkali-metal salts, and thereafter forming a dilute emulsion of the reaction product in water. Emulsification is readily effected since the alkali-metal resinates act as emulsifying agents for the unsaponified portion of the rosin. I

Although rosin size emulsions prepared in this manner are widely used in the paper-sizing art, they possess several serious disadvantages, among which is a tendency to induce frothing or foaming of the sized stock during the subsequent paper-forming operations. Foam not only interferes with the proper operation of the papermaking machine by accumulating on the screens and in the head boxes and by carrying considerable quantities of fibre, filling material and size into the waste, but also results in the formation of inferior paper having characteristic surface imperfections known as froth spots.

The prior art rosin size emulsions, particularly those containing a large proportion of free rosin as a result of being prepared from only partially saponified wood rosin, have the further disad-' vantage of tending to deposit a crystalline product upon standing. This crystalline product is known in the art as 3:1 salt" and is a double salt consisting of three molecules of abietic acid and one molecule of an alkali-metal abietate. During the paper-making process it collects as a sludge in the dilution and storage tanks and constitutes a source of great inconvenience to the paper-maker.

It is accordingly an object of this invention to provide rosin size emulsions which do not induce frothing or foaming during paper-making operations. Another object is to provide rosin size emulsions which do not deposit a sludge of 3:1

formation of considerable amounts of rosin oils. The presence of such oils is undesirable in the size since they are not readily emulsified and are lacking in sizing value, contain corrosive constituents, and may become the cause ofsurface imperfections on the paper web. The size emulsions prepared according to the invention,- how-. ever, contain only very smallamounts of the undesirable rosin oils and at the same time are substantially free from 3:1 salt formation and foaming during papermaking operations. They are further advantageous in that they have unusual stability without the use of protective colloids, even when containing as high as 40 per cent of free rosin. a

As hereinbefore mentioned, the new and im-- proved size emulsions provided by the present invention are prepared from wood rosin which has been heat-treated to an extent sufficient to effect a substantial reduction in the tendency of its saponlflcation product to form 3:1 salt but insufllcient to destroy its crystallizability. Such heat-treatment may be carried out batch-wise simply by heating wood rosin, which has preferably but not necessarily been color-refined, for

example, by selective solvent extraction, at a temperature below its decomposition temperature, e. g. between about 250 C. and about 350 C.

and preferably under non-oxidizing conditions,

' until the desired change in the rosin has taken place.

More'pneferably, however, the heat-treatment is carried out continuously as described in detail in the co-pending application of Henry A. Johnstone, Serial No. 356,958, filed September 16, 1940. I

. Such method consists essentially in'passing the Such heat-treatment should the required length of time. The reaction vessel is vented to provide exit for any gaseous or highly volatile products which may be formed, but it will be noted that the heating is carried out in such manner that substantially no distillation of the rosin takes place.

The time required to effect the desired changes in the rosin varies with the temperature at which the heat-treatment is carried out as well as with the particular type and grade of rosin employed. Ordinarily, however, it will be found that from minutes treatment at 350 C. to about 5 hours treatment at 250 C. will be satisfactory. The extent of the heat-treatment may also be measured by determining the specific rotation of the rosin. Rosin which has been heat-treated until its specific rotation in the solid state has been raised from a negative value to a value above about +5 is substantially free from 3:1 salt formation, whereas rosin which has been heat-treated until its specific rotation has been raised to above +20 will have lost its crystallizability and will contain an undesirable proportion of rosin oils. Accordingly, the rosins which are suitable for use according to the invention are those whose specific rotation as determined in the solid state has been increased to a value between about +5 and +20, preferably between about and about by heating at temperatures between about 250 C. and 350 C. k

The heat-treatedrosin is then saponifled by adding it in the solid or molten state to a hot aqueous solution of an alkali, such as sodium carbonate, potassium hydroxide, ammonia, sodium hydroxide, etc., and heating the mixture until the reaction is complete. The concentration of the aqueous alkali solution is usually so adjusted that upon completion of the reaction suflicient water is present to form a paste size of deperature of about 80 C. and thereafter further diluting to the desired concentration and quickly chilling by admixture with cold water. If de sired, stabilizing agents, such as proteins, watersoluble gums, etc., may be incorporated into the size emulsion, although the use of such agents is not required.

The following example illustrates one way in which the principle of the invention has been applied but is not to be construed aslimiting the same:

Two hundred and seventy pounds of K wood rosin was placed in a stainless steel kettle and heated at a temperature of about 300 C. for 30 l5 -minutes, after which it was cooled as quickly as possible by spraying water on the sides of the kettle. After cooling it was found that the specific rotation of the rosin in the solid'state had been raised to a .value of about +10.4 by the heat-treatment but that the rosin was readily crystallizable. One hundred pounds of this material was then saponifled by mixing with 59 sired consistency and solids content. The proportion of alkali employed varies with the par-' ticular alkali as well as with the type of size desired. In preparing neutral sizes, for example, suflicient alkali is employed to react with all of the saponifiables in the rosin, whereas in preparing high free rosin sizes wherein the rosin is only partially saponified a smaller quantity of alkali is used, the exact proportion depending upon the proportion of free rosin desired in the size. The saponification may. also be carried out inthe cold, employing a variety of alkalies and special procedures adapted to modify certain characteristics of the size. For example, it may be carried out as described in U. S. Patent No. 2,134,911, whereby the size is spray-dried to form a dry finely-divided powder. Other varipounds of hot 22 per cent by weight aqueous sodium carbonate and heating at a temperature of about 85 C. for about 40 minutes. The rosin size so prepared was a thick paste containing about '79 per cent by weight solids, 19 per cent by weight of which was free rosin as determined by titration. This material was then emulsified to form an aqueous emulsion containing 3 per cent by weight solids by the gradual dilution method, 1. e. by diluting it with approximately 5.8 parts by weight of water at a temperature of about 80. C. and thereafter mixing the diluted size with about 3.5 parts by weight thereof of hot water with violent agitation. The emulsion so prepared was stable and did not precipitate 3:1 salt upon storage over long periods of time at elevated temperatures.

The tendency of the emulsion to form 3:1 salt was estimated quantitively bydissolving a 50 gram sample of the heat-treated rosin from which it had been prepared in 50 grams of warm ations will readily occur to those skilled in the art.

The dilution of the saponifled heat-treated 6o rosin to form the size emulsion may be carried out in a number of ways, the simplest of which consists merely in adding the thick size to hot water with violent a-gitation.- The emulsion may also be formed by the so-called gradual dilution method which consists in thinning the size to about a 15- percent solids content with hot water and then adding the diluted size to acetone, and thereafter adding sufficient dilute aqueous sodium hydroxide to neutralize onefourth of the acids present in the rosin. The acetone solution was allowed to cool to room temperature and was seeded with a crystal of 3:1 salt. After standing for 24 hours the solution was filtered and the residue weighed, whereby there was obtained a 0.10 per cent yield of 3: 1 salt. Wood rosin which had not been heattreated yielded 29.4 per cent by weight of 3:1 salt when tested by this method.

A similar emulsion was prepared by diluting the paste size to 16. per cent concentration with distilled water at a temperature of-"?v C. and thereafter further diluting to 3 per cent concentratibn at C. The emulsion was then cooled and tested directly for 3:1 salt formation by storing in an oven maintained at 75 C.

After 24 hours storage, the emulsion had acquired only a very faint turbidity, whereas similar size emulsions prepared from rosin which has not been heat-treated thicken andbecome completely opaque when tested in thismanner.

The follow table presents data obtained by subjecting several typical rosin size emulsions prepared in a manner similar to that described above to a standard foam test under conditions simulating those encountered during paper-sizing. Comparative data are also included on similar rosin size emulsions prepared from rosin which had not been heat-treated as well as on a typical commercial size. The foaming test was carried out. by diluting l milliliters of the3 per cent aqueous size emulsion with 500 milliliters of water and thereafter adding per cent aqueous aluminum sulfate until the diluted emulsion had a pH of about 4.5. The mixture was then placed in a foam-testing apparatus which consists of a cylindrical glass vessel having a co-axially mounted hollow metal tube running to the bottom thereof. Within the tube is mounted a shaft carrying a propeller at its lower end. When the mixture is placed in the cylinder and the propeller rotated athigh speed, air is sucked in through the hollow tube and is violently agitated with the mixture, thereby causing foaming. The height to which the foam rises in the vessel is read by means of graduations on the side of the vessel, each one-tenth inch of foam being considered as one foam unit.

Table Size composition Expqeriment Foam o. unit Free Rosin Solids rosin l Percent Percent 1 Heat-treated.-. 70. 2 l8. 2 2- o 69.2 26.1 3- do 59.8 16l7 4. Not heat-treated. 70. 0 19. 0 5 d0 71. 2 21 8 6 Commercial size 69. 8 20. 0

C. and about 350 C. for I from about 5 minutes to about 5 hours, said heattreatment being suflicient toreduce substantially the tendency of the rosin to form 3:1 salt upon subsequent saponification but insufiicient to destroy its crystallizability.

2. A dilute aqueous emulsion of a rosin size prepared by at least partially s'aponifying wood rosin whose specific rotation in the solid state has been raised to a value between about '+5 and about +20 as the result of having been heated at a temperature between about 250 C. and about 350 0. forfrom about 5 minutes to about 5 hours, said heat treatment being suflicient to reduce substantially the tendency of the rosin to form 32-1 salt upon subsequent saponification but insufiicient to destroy its crystallizability. 3. A' dilute aqueous emulsion of a rosin size prepared by at least partially saponifying wood rosin whose specific rotation in the solid state has been raised to a value between about +10 and about +15 as the result of having been heated at a temperature between about 280 C. and about 325 C. for from about 5 minutes to about 5 hours, said heat treatment being suflicient to reduce substantially the tendency of the rosin to form 3:1 salt upon subsequent saponification but insuflicient to destroy its crystallizability.

4. A dilute aqueous emulsion of a rosin size prepared by at least partially saponifying wood rosin which has been heat-treated at a temperature between about 250 C. and about 350 C. for from about 5 minutes to about 5 hours to an extent suflicient to reduce substantially its tendency to form 3:1 salt upon subsequent saponification but insuflicient to destroy its crystallizability,

said saponification being efiected by means of an aqueous alkali selected from the group consisting of sodium hydroxide and sodium carbonate.

EDMUND A. GEQRGI. ARTHUR L. OS'I'ERHOF.