POLYAMIDES HAVING IMPROVED WATER SOLUBILITY USEFUL AS FLEXOGRAPHIC/GRAVURE INK BINDERS

Abstract: Polyamide resins useful as binders in flexographic/­ gravure inks are provided which are essentially free of polymeric fat acids. These polyamide resins exhibit im­ proved water solubility yet still retain the other many desirable properties of polyamide reisns based on polymeric fat acids.

Description: This invention relates to polyamide resins having improved water solubility which are useful as flexographic/gravure ink binders. More particularly, this invention relates to polyamide resins which are essentially free of dimeric and higher polymeric fat acids. U.S. Patent No. 3,776,865 discloses polyamide resins obtained by reacting an acid component comprised of a polymeric fat acid and another dicarboxylic acid with an amine component comprising isophorone diamine or mixtures thereof with an alkylene diamine. The patent discloses that these resins are useful as binders applied by aqueous systems, particularly in flexographic/gravure inks where water reducibility is desired. Polyamide resins prepared from dimeric and/or higher polymeric fatty acids for use in flexographic/gravure inks are dissolved in volatile organic solvents, such as the lower alkanols. Environmental concern over the amounts of volatile organic solvents in the atmosphere has led to a desire to use aqueous solutions that have less volatile organic solvents contained therein. In order to accommodate the reduced levels of volatile organic solvents, the polyamide resins used as binders in flexographic/gravure inks should have increased water solubility and yet retain the other desirable properties of polyamide resins, based on polymeric fat acids. The present invention provides polyamide resin wherein polymeric fat acids are absent or constitute not more than 5 equivalent precent of the polyamide formed from a mixture comprising: (i) X equivalent percent of a medium-chain dicarboxylic acid having from 13 to 25 aliphatic carbon atoms; (ii) Y equivalent percent of a short-chain acid selected from: (a) a short-chain acyclic aliphatic dicarboxylic acid having from 2 to 8 aliphatic carbon atoms; (b) a short-chain aliphatic monocarboxylic acid having from 3 to 5 aliphatic carbon atoms, and (c) mixtures thereof; and (iii) Z equivalent percent of a diamine having from 2 to 12 aliphatic carbon atoms or mixtures thereof; wherein the ratio of Z to the sum of X and Y is less than 1. The preferred polyamides are those wherein the ratio of Z to the sum of X and Y is less than 0.9, more preferably ranges from 0.50 to 0.85, and most preferably from 0.65 to 0.85. The invention also provides binder compositions for flexographic/gravure ink compositions containing such resins. It has been found that the polyamide resins of this invention are more soluble in flexographic/gravure ink compositions containing more water and less volatile organic solvent than flexographic/gravure ink compositions containing polyamide resins based on polymeric fat acids. In spite of this increased water solubility, however, the polyamide resins yield ink coatings with acceptable water-resistance and other desirable properties. The polyamide resins of the present invention are prepared by polymerizing a mixture which contains at least two different carboxylic acids with at least one diamine. These resins are acid terminated resins in that an equivalent excess of the dicarboxylic acids are used in relation to the diamine. A monobasic acid can be used as a chain stopper. The ratio of equivalents of the diamines to the equivalents of the acids is therefore less than 1, preferably less than 0.9, more preferably ranges from 0.50 to 0.85, and most preferably 0.65 to 0.85. The carboxylic acids useful in the present invention can be divided into two groups on the basis of chain length. The acids of one group have medium-chain length and the acids of the other group have short-chain length. The medium-chain aliphatic dicarboxylic acids, i.e. those having from 13 to 25 aliphatic carbon atoms, are present in all of the polyamide resins of this invention. The other group of acids, i.e. the short-chain carboxylic acids used to prepare the polyamide resins of this invention, can be further subdivided into two groups on the basis of functionality. In general, it is preferred that the short-chain acyclic aliphatic dicarboxylic acids be used to the exclusion of the short-chain aliphatic monocarboxylic acids, especially when the diamine chosen is isophorone diamine, and that the short-chain aliphatic monocarboxylic acids be used to the exclusion of the short-chain acyclic aliphatic dicarboxylic acids, especially when the diamine chosen is ethylene diamine. The medium-chain aliphatic dicarboxylic acids (hereinafter referred to as the medium-chain diacids) necessary in this invention have from 13 to 25 aliphatic carbon atoms, preferably from 16 to 21. This class of dicarboxylic acids includes not only the homologous series beginning with dodecanedioic acid and extending to the 24 carbon diacid, but also includes dicarboxylic acids that have branched alkyl chains and alicyclic structures in the molecule as well. A preferred class of medium-chain diacids are those having a carbocyclic ring and three substituents wherein one substituent is a carboxyl group, a second substituent is an alkyl group having more than three aliphatic carbon atoms, and a third substituent is an alkyl group that is terminally substituted with a carboxyl group. Examples of the medium-chain diacid of this preferred class may be obtained as the Diels Alder reaction products of acrylic acid with a fatty acid having two conjugated ethylenic unsaturations. A preferred example of the medium-chain diacids is 2-n-hexyl-5-(7-carboxyl-n-heptyl)-cyclohex-3-ene-carboxylic acid which is available from Westvaco, Charleston Heights, South Carolina. The short-chain acyclic aliphatic dicarboxylic acids (hereinafter referred to as short-chain diacids useful in this invention) have from 2 to 8 aliphatic carbon atoms in an unbranched hydrocarbon chain. The short-chain diacids can be characterized as a homologous series of dicarboxylic acids which begins with ethanedioic acid, ends with decanedioic acid, and includes each member in-between. The preferred short-chain diacids are azaleic acid and adipic acid. The amounts of short-chain diacid and medium-chain diacid used in the polyamides of this invention are preferably chosen such that the ratio of equivalents of the short-chain diacid to equivalents of the medium-chain diacid range from 4:1 to 0.66:1, more preferably from 3:1 to 0.8:1, and most preferably from 1:1 to 2:1. The short-chain aliphatic monocarboxylic acids (hereinafter referred to as short-chain monoacid) useful in this invention have from 3 to 5 aliphatic carbon atoms. The short chain acids are exemplified by propionic acid, n-butanoic acid, isobutanoic acid, and the like. The preferred short-chain acid is propionic acid. The amounts of the medium-chain diacid and short-chain monoacid used in the polyamides of this invention are preferably chosen such that the ratio of equivalents of the medium-chain diacid to the equivalents of the short-chain monoacid ratio of 1:1 to 5:1, more preferably from 2:1 to 4:1, and most preferably 3:1. The polyamides of this invention are prepared from mixtures that are substantially free of polymeric fat acids. These polymeric fat acids are described in U.S. Patent No. 3,776,865. These polymeric fat acids are derived by polymerizing unsaturated fatty acids. The diamine component is iso-phorone diamine or a mixture with an alkylene diamine and the acid component is 12.5 to 75 equivalent percent polymeric fat acid and 25 to 87.5 equivalent percent of a C₆ - C₂₀ diacid or mixture thereof. It has been found that the amount of polymeric fat acid used in the polyamides of this invention should be minimized to obtain improved water solubility in the polyamide resin. The mixtures from which the resins of this invention are prepared are substantially free of polymeric fat acids, i.e. they may contain an amount of a polymeric fat acid equal to as much as 5 equivalent percent of the polyamide reaction mixture but less than 5 equivalent percent and most preferably zero equivalent percent. The diamine used to form the polyamide resins of this invention is comprised of at least one aliphatic diamine having from 2 to 12 aliphatic carbon atoms. The preferred diamines can be divided into two preferred groups. One group consists of cyclic aliphatic diamines having from 8-12 aliphatic carbon atoms, e.g. isophorone diamine. The other preferred group is comprised of short-chain alkylene diamines which can be represented by the formula: H₂N-R-NH₂ wherein R is an alkylene radical having from 2 to 8 carbon atoms. R may be branched or straight chained, the straight chain radicals being preferred. Specific examples of short-chain alkylene diamines are ethylene diamine, diamino-propane, diamino-butane, and hexamethylene diamine. The resins are prepared from mixtures containing a dicarboxylic acid component and a diamine component by known methods for the polymerization of diacids and diamines to form polyamides. In general, a mixture of the diacid component and the diamine component is heated to a temperature between 100°C and 250°C in a vessel equipped for the removal of the by-product water formed in the polyamidification reaction; e.g. a vessel fitted with a distillation column and condenser so as to remove water from the reaction zone. Typically the reaction mixture will be heated at lower temperatures initially to avoid any volatilization and loss of any short chain monoacid which may be employed, after which the temperature is raised to the higher reaction temperature. Thus, it is common to heat at 140°C. for 1 hour followed by raising the temperature to 250°C and reacting for 1.5-3 hours. Similarly, a portion of the charge of the medium-chain diacid can be reserved from the initial charge of reactants. The initial reactant mixture can be initially reacted to ensure that substantially all of the short-chain monoacid is incorporated into the resin. The reserved portion of medium-chain diacid is then charged and the resulting mixture is allowed to react to obtain an acid terminated product. For example, from 25% to 50% of the medium-chain diacid to be charged is reserved from the initial charge which is heated at 140°C for one hour. The reserved portion of medium-chain diacid is then added to the reaction mixture and the temperature is raised to 250°C for 1 1/2 to 3 hours to obtain a product having acid termination. The degree of polymerization of the mixture should be controlled, along with the choice of ratio of diamine to diacids, to obtain a polyamide having a high acid value. The acid value of the polyamide should be greater than 10, more preferably greater than 20 and most preferably between 30 and 100. The polyamide resins of this invention form the binder compositions of this invention when dissolved in an aqueous solvent containing an organic amine. The resin is added to the solvent in an amount of 30% to 40% resin solids based on the weight of the solvent. Examples of suitable organic amines include primary, secondary and tertiary amines which can act as a base to salt the acid terminated polyamides. Particularly preferred organic amines are the dialkylaminoalkanols, such as 2-(N,N-dimethylamino)ethanol and 2-(N,N-diethylamino)ethanol. The organic amine is present in the aqueous solution in an amount sufficient to solubilize the chosen polyamide resin. In general, the organic amine will be present in the aqueous solution in an amount sufficient to theoretically neutralize the acid groups of the polyamide, i.e. the amount of organic amine is stoichiometrically equivalent to or greater than the acid value of the polyamide. For example, a 7.4% solution of dimethylaminoethanol is stoichiometrically equivalent to a polyamide resin having an acid value of 70 used at the level of 40% resin solids. A large excess of organic amine should be avoided because retention of the organic amine in the cured binder may adversely affect the water retention of the binder. These binders are particularly useful in flexographic/gravure ink compositions. The flexographic/gravure ink compositions of this invention are preferably made by dispersing a flexographic/gravure ink pigment in the binder compositions of this invention. It is an advantage of the present invention that less volatile organic solvent is needed to solubilize the resins in the binder compositions used to make flexographic/gravure ink compositions of this invention than is needed to solubilize the dimer acid resins of U.S. Patent 3,776,865. Generally, the flexographic/gravure ink compositions of this invention can contain less than 25% by volume volatile organic solvent. The preferred resins can be used to prepare binders which contain even less volatile organic solvent, e.g. 5% to 20%, but which still yield flexographic/gravure ink coatings having good water resistance. EXAMPLES The following Examples show the preparation and properties of polyamide resins representative of the polyamide resins of this invention and the preparation and properties of comparative polyamide resins. The polyamide resins of this invention are denoted by an arabic numeral and the comparative polyamide resins are denoted by a letter. Definitions : In the following Examples, the following terms, abbreviations and symbols have the following meanings: MCD: 2-N-hexyl-5-(7-carboxyl-N-heptyl)-cyclohex-3-ene carboxylic acid. ADA: adipic acid AZA: azelaic acid PRA: propionic acid IPD: isophorone diamine EDA: ethylene diamine RESIN PREPARATION The resins described in the Examples below were prepared by charging the acid and amine reactants shown in the Tables to a reactor along with about 1% of an 85% solution of phosphoric acid as a catalyst. In Example 5, a portion of the MCD was indicated was reserved from the initial charge and added after most of the PRA had reacted. The reaction mixture was heated to 250°C and held for 2 hours at that temperature. The resulting resins had the softening point as determined by the Ball and Ring method and the acid value, reported in milligram KOH per gram of sample, in Table I below. The resins of Comparative Examples A, B and C were prepared using a polymeric fat acid available from Henkel Corporation as VERSADYME® 204 which has the following analysis: Saponification Value (S.V.) 198.5 Acid Value (A.V.) 189.2 Thermosel Viscosity (25°.) 54.4(poises) d Pa.s Color (Gardner - no solvent) 7+ Fe 3.7 ppm P 25 ppm S 44 ppm Iodine Value 99.9 % Monomer (M) 10.9 % Intermediate (I) 5.3 % Dimer (D) 71 .1 % Trimer (T) 12.6 The solubility of the resins described in Table I in the following two solvents was determined. Solvent #1 was a mixture of 92.6% deionized water and 7.4% dimethylaminoethanol. Solvent #2 was a mixture of 77.1% deionized water, 21.8% diethylaminoethanol, and 1.1% dimethylaminoethanol The solubility of the resins in the indicated solvents are indicated in the table by the use of the following symbols: + soluble/fluid - very high in viscosity - insoluble fluid -G insoluble/gel BG borderline gel +G soluble/gel The remaining symbols in the table indicate the Gardner-Holdt viscosity of the solution obtained by mixing the resin and the indicated solvent. The results shown in Table II show that the representative resins of this invention have better solubility, particularly in a solvent having a very low concentration of organics, than the comparative polyamides prepared from polymeric fat acids. Samples of the polyamide resins shown in Table I were mixed with n-propanol and titanium dioxide to prepare white inks containing 33.3% by weight titanium dioxide, 20% by weight resin, and 46.7% by weight n-propanol. These inks were rolled out at 1 1/2 ml wet on glass to yield inks having the gloss shown in Table III. Samples of the inks were also rolled out on polyethylene and allowed to dry. The polyethylene samples were then immersed in water at 25°C for 24 hours. The samples were then subjected to 50 manual rubs with cotton wadding. The samples were rated on a scale of 1-10 with 10 representing a finding that the test had no effect on the ink coating. The gloss of the resulting inks and the results of the wet rub tests are shown in Table III below. INK GLOSS AND WATER RESISTANCE EXAMPLE GLOSS WET RUB 60° 20°C 1 85 16 10 2 78 39 10 3 76 45 10 4 64 17 10 5 67 20 10 A 89 76 10 B 82 51 10 C 86 61 10 The results shown in Table III indicate that the resins of this invention yield inks having good gloss and excellent resistance to water.

Claims: A polyamide resin wherein polymeric fat acids are absent or constitute not more than 5 equivalent percent of the polyamide formed from a mixture comprising: (i) X equivalent percent of a medium-chain dicarboxylic acid having from 13 to 25 aliphatic carbon atoms; (ii) Y equivalent percent of a short-chain acid selected from: (a) a short-chain acyclic aliphatic dicarboxylic acid having from 2 to 8 aliphatic carbon atoms; (b) a short-chain aliphatic monocarboxylic acid having from 3 to 5 aliphatic carbon atoms, and (c) mixtures thereof; and (iii) Z equivalent percent of a diamine having from 2 to 12 aliphatic carbon atoms or mixtures thereof; wherein the ratio of Z to the sum of X and Y is less than 1. The polyamide resin of claim 1 wherein the ratio of Z to the sum of X and Y is from 0.50:1 to 0.85:1. A polyamide resin in accordance with claim 1 wherein the medium-chain dicarboxylic acid has a carbocyclic ring substituted by a carboxyl group, an alkyl group having 3 or more aliphatic carbon atoms, and an alkyl group having 3 or more aliphatic carbon atoms and a carboxyl group as a terminal substituent. A polyamide resin in accordance with claim 3 wherein the medium-chain dicarboxylic acid is 2-n-hexyl-5-(7-carboxyl-n-heptyl)-cyclohex-3-enecarboxylic acid. A polyamide resin in accordance with claim 1 wherein an acyclic dicarboxylic acid having 4, 7, or 8 aliphatic carbon atoms is chosen as the short-chain acid. A polyamide resin in accordance with claim 1 wherein propionic acid is chosen as the short-chain acid. A polyamide resin in accordance with claim 1 wherein the diamine is isophorone diamine. A polyamide resin in accordance with claim 1 wherein the diamine is ethylene diamine. A polyamide resin in accordance with claim 1 wherein the short-chain acid is a mixture of acyclic aliphatic dicarboxylic acids and aliphatic monocarboxylic acids. A polyamide resin in accordance with claim 1 wherein the diamine is a mixture of diamines. A polyamide resin in accordance with claim 1 wherein the short-chain acid is a monocarboxylic acid and the diamine is an alkylene diamine having from 2 to 8 carbon atoms. A polyamide resin in accordance with claim 11 wherein the monocarboxylic acid is propionic acid and the alkylene diamine is ethylene diamine. A polyamide resin in accordance with claim 1 wherein the short-chain acid is an acyclic aliphatic dicarboxylic acid and the diamine is a cyclic diamine having from 8 to 12 aliphatic carbon atoms. A polyamide resin in accordance with claim 13 wherein the short-chain acid is adipic or azaleic acid and the diamine is isophorone diamine. A binder composition which comprises a polyamide resin of claim 1 and an aqueous solvent containing an organic amine. A binder composition in accordance with claim 15 wherein the aqueous solvent contains an organic amine in an amount greater than about 5% of the aqueous solvent. A flexographic/gravure ink composition comprised of the binder composition of claim 15 and a flexographic/gravure ink pigment. A flexographic/gravure ink composition in accordance with claim 17 wherein the aqueous solvent contains an organic amine in an amount greater than about 5% by weight of the aqueous solvent.

Inventors: MENKE, JOHN M., WHYZMUZIS, PAUL D.
Applicants: HENKEL CORPORATION (A DELAWARE CORP.)
Application year: 1986
Main classification: C08G69
IPC codes: C08G69, C09D11