Alkyl ketene dimer dispersion

Abstract: Stabilized dispersions of alkyl ketene dimer paper sizing agents that comprise up to about 30% by weight of ketene dimer, a water soluble cationic starch, and a lignin sulfonate, and also contain about 0.15 to about 1.5% of aluminum sulfate and from about 0.1 to about 5% of a car­ boxylic acid having from 1 to 10 carbon atoms, a pKa of up to about 5 and a solubility of at least about 0.1 parts in 100 parts of water (the percentages being based upon the weight of the dimer), are disclosed.

Description: The present invention relates to stabilized dispersions of alkyl ketene dimer paper sizing agents. Aqueous dispersions of alkyl ketene dimer (AKD) are well known sizing formulations in the manufacture of paper. Ketene dimers, which bond directly to the hydroxyl groups on the cellulose fibers, are cost-efficient sizing agents for paper at a neutral or slightly alkaline pH. They are normally sold as convenient aqueous diapersions that are usually prepared with cationic starch and sodium lignin sulfonate, which are inexpensive and have FDA approval. The term dispersion is used to mean a two phase system with solid particles in a continuous liquid medium, while the term emulsion is used to mean a two phase system with liquid droplets in a continuous liquid medium. Alkyl ketene dimers have melting points of about 45°C. Therefore, mixtures of alkyl ketene dimer in water are emulsions above 50°C and dispersions below 40°C. To be useful, alkyl ketene dimer dispersions must remain fluid enough to be pumped and diluted up until the time they are added to the paper machine. Often, this is a matter of weeks, with average temperatures as high as 32°C. It has been difficult to meet these conditions, because of the inherent colloidal instability of such dispersions. An unstable ketene dimer dispersion will increase in viscosity until it cannot be pumped or even until it gels. This problem gets worse with higher levels of the dimer solids, and limits the total solids to less than 15% for most applications. For instance, BE-A-817,130 of Tenneco teaches that the known ketene dimer cationic starch emulsifier combinations having solids content above 12% result in products that increase in viscosity so much that even after one week of storage at ordinary temperatures they turn into pastes. The process of stabilizing such dispersions with solids contents of less than 15% of alkyl ketene dimer, using cationic starch and sodium lignin sulfonate, is well known, e.g. from Example 5 of FR-A-2 474 042. Furthermore, DE-A-2,306,542 of BASF discloses that while amine modified cationic starches permit preparation of only dilute dispersions of AKD, alkyl ketene dimer dispersions containing up to 30 weight percent can be made by adjusting the pH to 3-4.5 and by using a polyvinyl alcohol protective colloid. The pH is adjusted with organic carboxylic acids such as acetic acid, propionic acid, or lactic acid, and particularly with polymeric carboxylic acids, such as polyacrylic acids. Acetic acid is used in an amount of about 2% based on the dimer when only a 10% solids dispersion is obtained. Preferentially the DE-A discloses adding small amounts of benzene, toluene, cyclohexene, or octane to the molten alkyl ketene dimer before emulsification in order to obtain the high solids dispersion at the lover consistency. The use of surfactants and fungicides is also disclosed. DE-A-2,514,128 (BASF) also teaches that amine modified starches can be used to make aqueous diapersions of ketene dimers, but only with low solids levels of about 3-8 weight percent in order to avoid dispersions having excessively high viscosity. The DE-A discloses dispersions with up to 30 percent by weight of ketene dimer, using a polyvinyl lactam, such as polyvinylpyrrolidone and polyvinyl caprolactam, and anionic, cationic or nonionic emulsifiers. The use of water insoluble inert solvents, and adjustment of the pH of the emulsions to 2-4.5 with water-soluble organic acids, such as formic, acetic, propionic, or malonic acid, in a proportion of one carboxy group of the acid for each unit of vinyl lactam monomer in the polyvinyl lactam. Also, the above-mentioned BE-A-817,130 of Tenneco discloses stable, high solids ketene dimer diapersions prepared without the use of cationic starch by using polyvinyl alcohol and sodium ligno-sulphonate as the emulsifiers, and containing 25% AKD. The dispersions contain polyvinyl alcohol, sodium lignosulphonate dicyandiamide/formaldehyde condensate and hydrochloric acid. US-A-4,240,935 of Hercules Incorporated discloses ketene dimer dispersions with solids contents higher than 15%, using AKD, water soluble cationic resin (e.g. an epichlorohydrin derivative), and sodium lignin sulfonate and/or sodium naphthalene sulfonate-formaldehyde resin as anionic surfactants. According to the invention, an aqueous dispersion comprising up to about 30% by weight of ketene dimer, a water soluble cationic starch carrying sufficient cationic amino groups to render the starch positively charged in solution, and a sulfonate, is characterized in that it also contains from about 0.15 to about 1.5%, based upon the weight of dimer, of aluminum sulfate, and from about 0.1 to about 5%, based upon the weight of the dimer, of a carboxylic acid having from 1 to 10 carbon atoms, a pKa of up to about 5 and a solubility of at least about 0.1 parts in 100 parts of water, the amount of cationic starch is from about 10 to about 30%, based upon the weight of the dimer, the sulfonate comprises from about 1 to about 5%, based upon the weight of dimer, of a salt of lignin sulfonic acid or of a condensation product of formaldehyde and a salt of naphthalene sulfonic acid, and the aqueous dispersion is subject to a viscosity increase of less than 100 mm² S⁻¹ (centistokes) upon quiescent aging at 32°C (90°F) for a period of 672h (4 weeks). These dispersions remain fluid for more than 672 hours (four weeks) at 32°C. This result is surprising because carboxylic acids are not known to be dispersion stabilizers. The same benefit is not seen when sulfuric, hydrochloric or other mineral acids are used without the organic acid. The carboxylic acids used in the present invention can contain substituted hetero-atoms, such as nitrogen the halogens, and sulfur, and include, for instance, acetic, adipic, citric, formic, fumaric, lactic, itaconic, benzoic, phthalic, 2-hydroxybenzoic, 3-hydroxybenzoic, 4-hydroxybenzoic, propionic, butyric, pentanoic, hexanoic, heptanoic. 2-ethylhesanoic, nitroacetic, 2-nitropropanoic, chloroacetic, bromoacetic, mercaptoacetic, and 1-mercaptopropionic acids. The preferred carboxylic acids include acetic, lactic, adipic, citric, fumaric, itaconic, and salicylic acids. Mono-protic carboxylic acids, without an adjacent hydroxy group, and 0.1 parts solubility in 100 parts water, are the more preferred acids. and acetic acid is the most preferred of the mono-protic acids, because it gives the lowest initial viscosity and particle size, combined with the least amount of hydrolysis of the dimer. Also, it has FDA approval for use in the United States. The other mono-protic carboxylic acids produce dispersions that do not last as long as those containing acetic acid. Although di- and tri-protic acids do not work as well, and hydroxy groups can react with the ketene dimer, lactic and salicylic acids both give excellent shelf life equal to or better than given by acetic acid, but with a reduced concentration of the ketene dimer. Salicylic acid is only marginally soluble in water. The carboxylic acid is generally present in an amount of from about 0.1 to about 5% by weight dimer, preferably from about 0.15 to about 0.5% by weight and most preferably from about 0.2 to about 0.3% by weight. The ketene dimers have the following well-known general formula: in which R₁ and R₂ are, respectively, hydrocarbon groups having 8-30 carbon atoms. They conventionally include octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl, docosyl, tetracosyl, phenyl, benzyl, beta-naphthyl and cyclohexyl ketene dimers, as well as made from naturally occurring mixtures of fatty acids. The preferred dimers are those in which the R₁ and R₂ radicals in the above formula are saturated or mono-unsaturated hydrocarbon groups having 12-20 carbon atoms. Most preferred dimers are those in which the R₁ and R₂ radicals are both a saturated hydrocarbon group having 14-16 carbon atoms, such as hexadecyl and octadecyl ketene dimers and their mixtures. Stable dispersions can be made within the range of from about 12 to about 30 weight percent ketene dimer. The preferred concentration of ketene dimer in these dispersions is from about 15 to about 25 weight percent, most preferably about twenty weight percent. The preferred and most preferred concentration is a compromise between longer shelf life for lower solids dispersions and more efficiency for higher solids dispersions. The cationic starch stabilizer used in the present invention is any water soluble starch carrying sufficient cationic amino groups to render the starch positively charged in solution. The preferred starches are cationic waxy maize starches of low to moderate viscosity (Brookfield viscosity of from about 50 to about 200 mm² S⁻¹ (cst), with either tertiary or quaternary amino groups as the source of the charge. The best starches to use are tertiary amino modified waxy maize having a Brookfield viscosity of from about 50 to about 80 mm²S⁻¹ (cst), such as ®Amaizo 2187 (sold by American Maize-Products Co.) or a quaternary amino modified waxy maize of the same viscosity, such as ®Stalok 140 (sold by A. E. Staley Manufacturing Co.). In this specification, moderate viscosity means a Brookfield viscosity of from about 101 to about 200mm²S⁻¹ (centistokes , cst) measured with a #2 spindle at 100 rpm and 38°C (100°F) using a 10% by weight solution of starch in water at a natural pH of 4.5-6.0, after cooking at 95°C for 30 minutes. Low viscosity means a Brookfield viscosity of from about 50 to about 100mm² S⁻¹ (cst). The starch can be present in an amount of from about 10 to about 30% by weight dimer. Preferably the starch is present in an amount of from about 15 to about 25% by weight and most preferably from about 18 to about 22% by weight. The sulfonate stabilizers of the present invention are various salts of lignin sulfonic acid and the condensation product of formaldehyde and various salts of naphthalene sulfonic acid and mixtures thereof. The type of salt formed from the acids is important for colloid stability and cost efficiency. Alkali metal, alkaline earth metal and ammonium salts of lignin sulfonic and naphthalene sulfonic acid are suitable. Ammonium, calcium, magnesium, potassium, and sodium salts are preferred, because they are more readily available, and they are less expensive. The sodium salt is most preferred, because it increases ionic strength the least, thus enhancing the colloid stability of the ketene dimer dispersion. Also the sodium salt does not react with the ketene dimer and therefore it does not lessen sizing efficiency. Calcium and other divalent ions raise the ionic strength of the continuous phase much more than sodium ions. This extra ionic strength does not favor dispersion stability. Ammonia can react with ketene dimer to form a compound that does not size. This lessens the sizing efficiency of ketene dimer dispersions stabilized with the ammonium salt. The preferred amount of the sulfonate stabilizer is about 1.8 to about 4%, and the most preferred range is from about 2 to about 2.2% by weight. The presence of aluminum sulfate is necessary to obtain the best stability. Its level should preferably be from about 0.15 to about 0.6% by weight of ketene dimer, and most preferably from about 0.3 to about 0.5% by weight. As the solids are increased go should the amount of aluminum sulfate. The best formulation depends upon the total solids desired. The ratio of the ingredients in the four-part formula must be varied as the amount of dimer is increased. At 12% solids a ratio of 6 parts starch to 1 part sodium lignin sulfonate, and 4 parts dimer to one part starch may be used with up to 0.5 parts off acetic acid with satisfactory results. As the solids increase to 30 parts dimer, the ratio of dimer to starch becomes 5:1, the ratio of starch to sodium lignin sulfonate becomes 10:1, and the amount of organic acid decreases to 0.1 parts by weight dimer. The following examples are given for the purpose of illustrating the present invention. All parts and percentages are by weight unless otherwise indicated. Evaluation off the stability of the ketene dimer dispersions was based on the change in viscosity after aging, either on a shelf at room temperature (shelf life), or in a 32°C oven. The aging period was not less than 672h (four weeks). The viscosity was measured with a Brookfield viscometer, number two spindle, at 60 rpm. Dispersions with viscosities above 100mm² S⁻¹ (cst) are normally not useful in practice. Example 1 (1) Charges For a 1500 gram batch: 300 g Alkyl Ketene Dimer 67.5 g Cationic Starch (®Amaizo 2187) 6 g Sodium Lignin Sulfonate (®Lignasol XD) 15 g Acetic Acid (at 5% by weight) 19.8 g Aluminum sulfate (Reagent at 5% by weight in water) 1.5 g ®Biocide N521 1090.2 g Water (Distilled) (2) Procedure To 1090.2 grams off distilled water were added 67.5 grams of cationic starch (commercially available as ®Amaizo 2187, which has 13% bound water) and 6 grams off sodium lignin sulfonate (commercially available as ®Lignasol XD sold by Reed Lignin Inc.). The pH was adjusted to 5.5 with 0.1 M HCl. The mixture was weighed after heating and the water lost during heating was added back along with 15 grams of 5% by weight acetic acid. After cooling to 80°C, 300 grams of a mixture of hexadecyl and octadecyl ketene dimer flake (sold as Aquapel® 364 by Hercules Incorporated) were blended in and melted. The temperature was adjusted to 65°C (as necessary). The mixture was circulated through a Gaulin model 15M single stage laboratory homogenizer without pressure and then with 20,862 KPa (3000 psig) applied (all at 65°C) for one pass. The total solids of the mixture was determined by placing 1.5 gram: in a 150°C oven for 15 minutes. From this the percent ketene dimer actually present was calculated. To the hot homogenizate was added 0.33% (by weight ketene dimer) of a 5% by weight solution of reagent grade aluminum sulfate. The homogenizate was cooled to 25°C, and 1.5 grams of tetrahydro-3,5- dimethyl-2H-1,3,5-thiadiazine-2-thione (®Biocide N521 sold by Vinings Chemical Co. of Atlanta, GA) was added. The pH was adjusted to 3.6 with 0.1 M HCl (as necessary) after waiting two hours for equilibration. (3) Stability result Viscosity as made was 20 mm²S⁻¹ (cst). Viscosity after 840 hours (5 weeks) at 32°C was 35 mm²S⁻¹ (cst). This small increase in viscosity satisfies our test for stability indicating that the present invention results in alkyl ketene dimer dispersed well enough to be practical. Example 2 This example compares the stability off dispersions of alkyl ketene dimer made with and without acetic acid. The procedure is the same for all dispersions at any level of ketene dimer, with the exception of the acetic acid. The amount for each ingredient is given in terms of ketene dimer. The dimer amount will vary between 6 and 20% of the total dispersion and is represented by "X" in the recipe. The amount of water required for each level of ketene dimer can be calculated using the equation at the end of parts (1) and (3). (1) Charges For Ketene Dimer Dispersions at 20% with Acetic Acid For a 500 gram Batch (with all additives by weight dimer) X % Alkyl Ketene Dimer (Where X is the % dimer listed in Table 1.) 22.5% Cationic Starch (®Amaizo 2187) 2.0% Sodium Lignin Sulfonate (®Lignasol XD) 6.6% Aluminum Sulfate (Reagent at 5% by weight in water) 0.5% ®Biocide N521 Grams 0.01M Acetic acid solution = 500 - 500[X + .225X + .020X + 0.066X + 0.005X] (2) Procedure for Ketene Dimer Dispersions at 20% by weight with Acetic Acid. (100 g Ketene Dimer) To 368.4 grams of 0.01 M acetic acid in water were added 22.5 grams of starch (®Amaizo 2187) and 2 grams of sodium lignin sulfonate (®Lignasol XD). The pH was adjusted to 5.5 with 0.1 M HCl. The mixture was weighed after heating and the acetic acid solution that was evaporated off was added back. After cooling to 80°C, 100 grams of a mixture of hexadecyl and octadecyl ketene dimer flake (Aquapel® 364) were blended in and melted. The temperature was adjusted to 65°C (as necessary). The mixture was sheared in a Microfluidics model T110 Microfluidizer (at 65°C) at 20,862 KPa (3000 psig) for one minute. The total solids of the mixture was determined by placing 1.5 grams in a 150°C oven for 15 minutes. From this the percent ketene dimer actually present was calculated. To the hot homogenisate was added 0.33% (by weight ketene dimer) of a 5% by weight solution of reagent grade aluminum sulfate. The homogenizate was cooled to 25°C, and 0.5 grams of ®B iocide N521 was added. The pH was adjusted to 3.6 with 0.1 M HCl (as necessary) after waiting two hours for equilibration. To get the ratio of ingredients for lower solids dispersions, the percent ketene dimer replaces the "X" in the charges section above. For example, a 6% dispersion would have 0.06 times 500 g or 30 g of ketene dimer, 6.75 g of starch, 1.17 g of Sodium lignin sulfonate, 1.98 g of 5% alum solution, 0.15 g biocide, and 460.5 g of 0.01M acetic acid solution. (3) Charges for Ketene Dimer Dispersions at 20% without Acetic Acid Acid For a 500 gram Batch (with all additives by weight dimer) X % Alkyl Ketone Dimer (Where X is the % dimer listed in Table 1.) 22.5% Cationic Starch (®Amaizo 2187) 3.9% Sodium Lignin Sulfonate (®Lignasol XD) 6.6% Aluminum Sulfate (Reagent at 5% by weight in water) 0.5% ®Biocide N521 Grams Water = 500 - 500(X + .225X + .039X + 0.066X + 0.005X) (distilled) (4) Procedure for Ketene Dimer Dispersions at 20% by weight without Acetic Acid The dispersions made without acetic acid followed the procedure of this example but with the above charge. Again, the additives were given in percent of hetene dimer and the amount of water was found by the equation at the end of the charge section. Viscosities of Ketene Dimer Dispersions in mm²S⁻¹ (Centistokes) Dispersion As Made 672h (4 Weeks): 25°C 1344h (8 Weeks): 25°C 6% dimer with acetic acid 4.0 7.5 7.5 6% dimer without acetic acid 3.5 7.5 5.0 12% dimer with acetic acid 5.0 10.0 15.0 12% dimer without acetic acid 6.0 10.0 17.5 15% dimer with acetic acid 7.0 12.5 15.0 15% dimer without acetic acid 9.0 20.0 80.0 20% dimer with acetic acid 21.0 37.5 155.0 20% dimer without acetic acid 35.0 117.0 gel Alkyl ketene dimer dispersions made with acetic acid, according to the present invention, pass the four week stability test. Dispersions of ketene dimer made without cetic acid fail the test at 20% dimer solids. Since 672h (four weeks) stability is required to be commercially useful, carboxylic acid is an essential ingredient. Example 3 (1) Charges For a 1500 gram batch: 300 g Alkyl Ketene Dimer 1.5 g ®Biocide N521 about 1090 g Water (Distilled) all other additives given in Table 2 in percent by weight based on ketene dimer. (2) Procedure The procedure is identical to Example 1 with the proper adjustments made for the variation in the levels off the starch, sodium lignin sulfonate, acetic acid, and aluminum sulfate. Starch SLS Acetic Acid Alum AKD % by wt of Dispersion Viscosity mm²S⁻¹ (cst) As made 1440h (2 months) at 32°C 23.0 1.8 .25 .40 20 20 63 20.5 2.0 .28 .35 20 20 65 20.5 2.0 .25 .35 20 20 80 20.5 2.2 .25 .35 20 15 80 23.0 2.2 .28 .30 20 20 110 25.5 1.8 .25 .35 20 20 205 20.5 2 .23 .4 20 20 215 A change of 10% in any of the essential ingredients will not cause the dispersion of ketene diner to fail. Therefore, there is sufficient flexibility in the composition of the dispersions of the present invention to allow successful commercial application. Example 4 (1) Charges For a 1500 gram batch: 450 g Alkyl Ketene Dimer 102.6 g Cationic Starch (®Amaizo 2187) 9 g Sodium Lignin Sulfonate (®Lignasol XD) 22.5 g Acetic Acid (at 5% by weight) 39.6 g Aluminum Sulfate (Reagent at 5% by weight in water) 2.3 g ®Biocide N521 874 g Water (Distilled) (2) Procedure This procedure was the same as in Example 1. (3) Stability result Viscosity as made was 110mm²S⁻¹ (cst). The dispersion was fluid for 504h (three weeks) and gelled after four weeks at 32°C.

Claims: An aqueous dispersion comprising up to about 30% by weight of ketene dimer, a water soluble cationic starch carrying sufficient cationic amino groups to render the starch positively charged in solution, and a sulfonate, characterized in that it also contains from about 0.15 to about 1.5%, based upon the weight of dimer, of aluminum sulfate, and from about 0.1 to about 5%, based upon the weight of the dimer, of a carboxylic acid having from 1 to 10 carbon atoms, a pKa of up to about 5 and a solubility of at least about 0.1 parts in 100 parts of water, the mount of cationic starch is from about 10 to about 30%, based upon the weight of the dimer, the sulfonate comprises from about 1 to about 5%, based upon the weight of dimer, of a salt of lignin sulfonic acid or of a condensation product of formaldehyde and a salt of naphthalene sulfonic acid, and the aqueous diapersion is subject to a viscosity increase of less than 100 mm²S⁻¹ (centistokes)upon quiescent aging at 32°C (90°F) for a period of 672h (4 weeks). An aqueous dispersion as claimed in claim 1, further characterized in that the amount of the acid is from about 0.15 to about 0.5% based upon the weight of the dimer. An aqueous dispersion as claimed in claim 2, further characterized in that the amount off the acid is from about 0.2 to about 0.3% by weight. An aqueous dispersion as claimed in claim 1, 2 or 3, further characterized in that the carboxylic acid is acetic acid. An aqueous dispersion as claimed in any of the preceeding claims, further characterized in that of the aluminum sulfate is from about about 0.15 to about 0.6% based upon the weight of the dimer. An aqueous dispersion as claimed in any of the preceding claims, further characterized in that the amount of the aluminum sulfate is from about 0.3 to about 0.5% by weight. An aqueous dispersion as claimed in any of the preceding claims, further characterized in that the amount of the sulfonate stabilizer is about 1.8 to about 4.0% based upon the weight of the dimer. An aqueous dispersion as claimed in any of the preceding claims, further characterized in that the amount of the sulfonate stabilizer is about 2 to about 2.2% based upon the weight of the dimer. An aqueous dispersion as claimed in any of the preceding claims, further characterized in that the sulfonate is sodium lignin sulfonate. An aqueous dispersion as claimed in any of the preceding claims, further characterized in that the cationic starch is tertiary or quaternary amine modified waxy maize starch having a Brookfield viscosity of from about 50 to about 200 mm² S⁻¹ (centistokes).

Inventors: EDWARDS DEREK WAYNE, TOWNSEND DAVID FRANCIS
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1989
Main classification: D21H17
IPC codes: C08L3, D21H17