Description:
This invention relates to synthetic polyamides comprising dimeric fatty acids and to methods for making the same. In particular, this invention relates to synthetic polyamides notable either for their good solubility in alcohols, particularly in ethanol, or for good solubility in solvent mixtures coupled with a high-softening point, and to methods of making such polyamides.
The polyamides of the invention are used to advantage as printing ink binders.
Polyamides comprising polymerized unsaturated fatty acids and ethylene diamine, and having a molecular weight range of from 3,000 to 5,000, are known in the art. However, only butanolic solutions of such products are stable at room temperature.
It has also been proposed in the prior art to increase the solubility of polyamides by the incorporation therein of branch-chain alkylol amines or branched dicarboxylic acids, or of branch-chain diamines having an amino group on a tertiary carbon atom.
Although certain progress has been made in the prior art toward increasing the solubility of polyamides, the disadvantages of prior art polyamides include a strong tendency toward blocking in sheets printed with inks comprising the polyamides as binders, an insufficient resistance of solutions of the polyamides to gelation, and a lack or low degree of reversibility of gel formation in such solutions. A further disadvantage in those prior art polyamides having improved solubility is that their softening point is too low to permit them to be used as printing ink binders.
The present invention concerns new polyamides and their preparation by the thermal polycondensation of monocarboxylic acid, diamine, and dimerized fatty acid which may optionally contain smaller quantities of trimeric fatty acid and monomeric fatty acid. The monocarboxylic acid is a straight-chain unsubstituted (i.e. hydrocarbon) aliphatic carboxylic acid having one to five carbon atoms, suitably a lower alkanoic monoacid such as acetic acid. As the diamine are used mixtures of ethylene diamine with either: (1) a branched or straight-chain unsubstituted (i.e. hydrocarbon) aliphatic codiamine having six to twelve carbon atoms, particularly a C 6 -C 12 alkylene diamine; or (2) certain aromatic and cycloaliphatic codiamines or (3) certain ether codiamines.
In particular, aromatic amines of the formulas ##SPC1## and cycloaliphatic diamines of the formula ##SPC2## wherein x is zero or a small integer and wherein R 1 -R 6 are hydrogen or lower alkyl. Those cyclic amines in which at most two of the substituents R 1 -R 6 are lower alkyl are of particular interest because of their current commercial availability.
As ether codiamines, materials having the formula
can be used, wherein n is an integer from 3 to 5 inclusive, x is an integer from 0 to 3 inclusive, and R is an alkylene radical having from one to 12 carbon atoms, which radical may optionally have one or two alkyl substituents having from 1to 4 carbon atoms thereon.
According to the invention, suitable aromatic and cycloaliphatic codiamines include p-phenylene diamine, m-toluylene diamine; 4,4° -diamino diphenylmethane; 3,3''-dimethyl-4,4' -diamino diphenylmethane;4,4'-diamino diphenylpropane; 4,4'diamino dicyclohexylmethane; 3,3' -dimethyl-4,4' -diamino dicyclohexyl-methane; xylylene diamine; bis-(β-aminoethyl) benzene; bis-(β-aminoethyl)-dimethylbenzene; bis-(aminomethyl)-cyclohexane; 3-aminomethyl-3,5,5-trimethyl-cyclohexylamine; 1-methyl-4(1-amino-1-methyl-ethyl)-cyclohexylamine; and 9,9-bis-( 3-aminopropyl)-fluorene.
Suitable ether codiamines include 1,7-diamino-4-oxa-heptane; 1,11-diamino-6-oxa-undecane; 1,7-diamino-3,5-dioxa-heptane; 1,10-diamino-4,7-dioxa-decane; 1,10-diamino-4,7-dioxa- 5-methyl-decane; 1,11-diamino-4,8-dioxa-undecane; 1,11-diamino- 4,8-dioxa-5-methyl-undecane; 1,12-diamino-4,9-dioxa-dodecane; 1,13-diamino-4,10-dioxa-tridecane; 1,14-diamino-4,11-dioxa-tetradecane; 1,11-diamino-4,8-dioxa-5,6-dimethyl-7-propionyl- undecane; 1,14-diamino-4,7,10-trioxa-tetradecane; 1,13-diamino- 4,7,10-trioxa-5,8-dimethyl-tridecane; 1,16diamino-4,7,10,13-tetra-oxa hexadecane; 1,11-diamino-4,8-dioxa-6,6-dimethyl-undecane; and 1,20-diamino-4,17-dioxa-eicosane.
Preferred embodiments of the invention include those in which the equivalence ratio between ethylene diamine and the codiamine is between 0.8:0.2 and 0.5:0.5, especially at 0.7:0.3, and in which the equivalence ratio between the dimeric fatty acid and the monocarboxylic acid lies between 0.8:0.2 and 0.7:0.3, particularly at 0.75:0.25.
In the process of the invention, the greater the proportion of the aromatic, cycloaliphatic, long chain, or ether codiamine present, the better are the solubility properties of the resultant polyamide. The greater the proportion of ethylene diamine present, the higher is the softening point of the resultant polyamide.
The polyamides of the present invention do not have the disadvantages earlier described for known polyamides. They are soluble, even at room temperature, up to 60 percent in lower alcohols, particularly ethanol. The solutions are resistant to gelation, and any gelation occurring at low temperatures is reversible at room temperature. Sheets printed with compositions comprising the polyamides of the invention show little tendency to block, in contrast with those printed with known ethanol-soluble printing ink resins. Also, ink resins according to the invention show outstanding adherence and good shine on conventional carriers, especially on pretreated polyethylene. The scratch resistance of printed sheets is excellent, particularly for those polyamides comprising an ether codiamine. Resistance to cracking and scaling is also at high levels. The mechanical properties of the resin films, such as hardness and elasticity, as well as the properties desirable in the coating arts, all meet the demands imposed on them.
Production of the polyamide resins of the invention involves reaction of the diamines, dimeric fatty acid, and monocarboxylic acid at condensation temperatures between about 180° C. and about 250° C., especially at about 230° C. Any remaining water of condensation is conveniently removed by applying a vacuum for one to two hours. In place of the free dimeric fatty acids, their amide-forming derivatives can also be used, such as their esters, in particular those which easily undergo aminolysis, such as the methyl and ethyl esters.
For preparation of the polyamides of the invention, those dimeric fatty acids are used which can be obtained by the free radical, ionic, or thermal polymerization of fatty acids. The fatty acid can be a saturated or a mono- or poly-ethylenically or acetylenically unsaturated natural or synthetic aliphatic monobasic acid, suitably having 8 to 24 carbon atoms. These fatty acids can be polymerized by different means, but all give functionally similar products which can generally be characterized as polymeric fatty acids. The polymer products usually contain a predominant amount of dimeric fatty acids, and smaller amounts of trimeric or higher polymeric, as well as monomeric, fatty acids. The term "dimeric fatty acid" as used in the specification and claims is to be understood to refer also to such mixtures containing small quantities of non-dimeric materials.
Polymerization of saturated fatty acids can be carried out at elevated temperatures with peroxide catalysts such as di-t-butyl-peroxide, for example. The straight chain and branch-chain acids such as caprylic, pelargonic, capric, lauric, myristic, palmitic, isopalmitic, stearic, arachidic, behinic, and lignoceric acids are suitable saturated fatty acids. However, this process is of little interest because of the small yield.
The polymerization of ethylenically unsaturated fatty acids is much more common. This can be done with or without catalysts, but uncatalyzed polymerization requires higher temperatures. Suitable catalysts are acid or alkaline clays, di-t-butyl-peroxide, boron trifluoride and other Lewis acids, anthroquinone, sulfur trioxide, and the like. The monomeric fatty acids commonly polymerized include the branched-chain and straight-chain, poly- and/or mono-ethylenically unsaturated acids such as 3-octene acid, 11-dodecene acid, linderic acid, lauroleic, oleic, elaidic, vaccenic, gadoleic, cetoleic, erucic, linoleic, linolenic, elaostearic, arachidic, clupanodonic, nisinic, and chaulmoogra oil acid.
The acetylenically unsaturated fatty acids, which can be polymerized in the absence of catalysts because of their higher reactivity, seldom occur in nature and are expensive to synthesize. For this reason they are economically less interesting. A number of acetylenically unsaturated fatty acids, either straight chain or branch chain, mono-unsaturated or polyunsaturated, can be used for the preparation of polymeric fatty acids. For example, 6-octadecyn, 9-octadecyn, 13-dokosyn, and 17-octadecen-9,11-diyn acids can be mentioned.
Because of their low cost and relatively easy polymerizability, oleic acid and linoleic acid are preferred as starting materials for the preparation of polymeric fatty acids.
The usual approximate composition of the commercial dimeric fatty acid product prepared from an unsaturated C 18 -fatty acid is: 5-15 percent by weight of C 18 -monocarboxylic acid, 60-80 percent by weight of C 36 -dicarboxylic acid, and 10-35 percent by weight of C 54 -tricarboxylic acid and higher carboxylic acid products.
The mixtures obtained by polymerization can be fractionated by the usual distillation or solvent extraction methods. They can be hydrogenated before or after distillation in order to decrease the degree of unsaturation using high pressure hydrogen in the presence of a hydrogenation catalyst.
The preferred content of dimeric fatty acids in the fatty acid used in the present invention is between 55 and 100 percent by weight. The content of mixtures of monomeric, dimeric, and trimeric fatty acids can be determined either by gas chromatography or according to the microdistillation method of Paschke, J. Am. Oil Chem. Soc. XXXI, No. 1, 5 (1954).
A better understanding of the present invention and of its many advantages will be had by referring to the following specific examples, given by way of illustration.
Example 1
400 grams of a commercially available dimerized fatty acid (0.75 equivalent) prepared from an unsaturated C 18 -fatty acid and having a content of about 75 percent dimeric fatty acid, 15 percent trimeric fatty acid, and 10 percent monomeric fatty acid, 28.1 grams of glacial acetic acid (0,25 equivalent), 39.45 grams of ethylene diamine (0,70 equivalent), and 32.7 grams of hexamethylene diamine (0,3 equivalent) were mixed together and heated to 125° C. over a period of about 15 minutes under a nitrogen atmosphere with stirring. This temperature was maintained for half an hour, then the mixture was raised to 225° C. over a period of two hours and held at this temperature for three additional hours. Finally, a vacuum of 15 mm. Hg. was applied for one more hour at a temperature of 225° C.
The resulting product had an amine number of 2.64, an acid number of 2.02, and a ring-and-ball softening point of 113° C.
The polyamide obtained was soluble in ethanol throughout the entire concentration range up to 60 percent.
Examples 2-10 tabulated in tables I and II below were prepared in analogous fashion using other monocarboxylic acids and aliphatic codiamines. The polyamide products are all soluble in ethanol, and their alcoholic solutions can be prepared either cold or at the boiling point. ##SPC3## ##SPC4##
Example 11
200 grams of dimeric fatty acid (0.75 equivalent), 14.05 grams of acetic acid (0.25 equivalent), 19.7 grams of ethylene diamine (0.7 equivalent), and 17.15 grams of m-toluylene diamine (0.3 equivalent) were mixed and heated to 125° C. over a period of 15 minutes. This temperature was maintained for 30 minutes.
Thereafter, the temperature was raised over a period of 2 hours to 225° C. and held at this temperature for a further 3 hours. Finally, a vacuum of about 15 mm. Hg. was applied for a further hour.
The polymer product had an amine number of 2,23, an acid number of 3.69, and a softening point (ring and ball) of 112° C.
Additional polyamides were prepared according to the invention in an analogous fashion. Tables III and IV summarize the results of further examples 12-24. ##SPC5## ##SPC6##
Solutions of the polyamides according to the invention can be prepared in concentrations of at least 30 percent either at boiling temperatures or at room temperature.
For purposes of comparison, examples 1 and 20 of U.S. Pat. No. 2,450,940 were repeated. The product prepared according to example 1 of the patent is insoluble in ethanol. A 30 percent solution in isopropanol gels at room temperature. A 30 percent solution in butanol showed a strong increase in viscosity after several weeks standing. The polyamide prepared according to example 20 of the patent also did not given stable 30 percent solutions in the alcohols mentioned.
Example 25
Four-hundred grams of dimerized fatty acid (0.75 equivalent), 28.1 g. of acetic acid (0.25 equivalent), 45.08 g. of ethylene diamine (0.8 equivalent), and 25.12 g. of 1,7-diamino-4-oxaheptane (0.2 equivalent) were mixed with one another and heated to 125° C. with stirring in an inert gas atmosphere. The temperature was held at 125° C. for one-half hour, then raised to 225° C. over a period of two hours, and left at the latter temperature for five hours. During the last two hours, a vacuum of about 15--20 mm./Hg. was applied.
The resulting polyamide resin had an amine number of 2.59, an acid number of 2.64, and a ring and ball softening point of 120.5° C. The product could easily be dissolved in ethanol by shaking, either at room temperature or at the boiling point.
Additional polyamides were prepared according to the invention in an analogous fashion. Tables V and VI summarize the results of further examples 26-35. ##SPC7## ##SPC8##