POLYAMIDESThis invention is concerned with improvements in and relating to polyamides and, more particularly, is concerned with polyamides suitable for use as resinous vehicles in printing inks, especially flexographic printing inks, and printing inks containing such polyamides.
Thermoplastic polyamides derived, inter alia, from so-called "dimer acids" have been used as components of printing inks for some years. In particular such polyamides may be used as components of flexographic inks and may be formulated to meet the requirements of such inks, namely good adhesion to a wide variety of substrates, rapid drying, the use of solvents which will not attack rubber stereos, low print odour and good resistance properties. The polyamides may be used alone in flexographic inks or in combination with other resinous materials, especially nitrocellulose. In particular, thermoplastic polyamides of the sort described above may be used in flexographic inks used in the packaging industry, for printing on polyethylene and other extruded film.In this application, the polyamide may be used to impart good adhesion and flexibility in combination with nitrocellulose which will impart good gloss and hardness to the final ink. Polyamide resins are also used in gravure inks for printing treated polyolefin, nylon and polyester films. Their main advantages are that they show excellent pigment wetting properties, high gloss, excellent water and deep freeze resistance. Most designs for the frozen foods polyethylene market use polyamide resins exclusively.
The suitability of the resins claimed in the patent for use in overprint varnishes (high gloss lacquers on various packaging designs) largely depends on the skill of the formulator. All these resins make extremely good starting point materials due to their high gloss, toughness and flexibility, combined with good grease and water resistance.
Whilst commercially available polyamides have generally acceptable properties, these could advantageously be improved by increased solubility in alcohol (ethyl alcohol or industrial methylated spirits) and resistance to gelation in alcohol.
The known polyamides mentioned above are prepared by the polycondensation of three essential components, namely a polybasic acid component comprising a polymeric fatty acid (a "dimer" acid), a polyamino component comprising one or more polyamines, generally one or more diamines, and a chain terminating component comprising a monobasic acidic or amino component, generally the former.
It has now been found, in accordance with the present invention, that such polyamides having improved alcohol solubility and gelation characteristics may be prepared by including, in the diamine component, one or more branched chain diamines.
According to one embodiment of the invention, therefore, there is provided a thermoplastic polyamide derived from the polycondensation of: (i) a polybasic acid component comprising a polymericfatty acid, and optionally, one or more otherpolybasic acids which may be aliphatic or aromaticin character; (ii) a polyamino component comprising one or morediamines, at least one of which is a branchedchain diamine; and (iii) a monomeric component comprising a monoamine or amonocarboxylic acid, preferably the latter.
The polybasic acid component preferably comprises only the polymeric fatty acid. The term polymeric fatty acid, as used herein, is intended to refer to the product of the polymerisation of ethylenically unsaturated monocarboxylic acids containing from 8 to 22 carbon atoms. These products may be obtained by the process described in US-A-3157681 and may be produced by a catalytic or non-catalytic polymerisation process.
Generally unsaturated aliphatic monocarboxylic acids containing from 16 to 18 carbon atoms are preferred as starting materials and the most preferred starting materials are unsaturated aliphatic monocarboxylic acids containing 18 carbon atoms such as linoleic and oleic acids. After polymerisation in the presence or absence of a catalyst, the resulting mixture contains predominantly dimeric fat acids, some trimeric and higher polymeric fat acids and some unpolymerised monomeric fat acids. Typically such polymer acids contain from 5 to 15% by weight of monocarboxylic acids, from 60 to 80% by weight of dicarboxylic acids and from 10 to 35% by weight of tri or higher carboxylic acids.
In view of the preponderance of the dimeric species, such polymeric fatty acids are frequently referred to as "dimer acid" and this terminology will be used in the following description.
These mixtures may be fractionated by high vacuum distillation or solvent extraction to obtain dimer acid cuts of higher concentration if desired. Suitable commercially available dimer acids for use in accordance with the invention are those sold under the Trade names "Craymer" (Cray Valley Limited) and "Empol" (Unichema).
The diamino component preferably consists of diprimary diamines and, especially, comprises a mixture of a straight chain lower diamine (such as ethylene diamine or propylene diamine) together with a long chain (e.g. C3-C12) branched chain diamine, as required in the present invention. In such a mixture the lower straight chain diamine suitably forms from 5 to 95 mole of total diamine, preferably 50 to 70W thereof, the branched chain diamine forming the balance.
The third component from which the polyamide is formed is, as noted above, preferably a monobasic carboxylic acid, especially an aliphatic monocarboxylic acid containing from 2 to 18 carbon atoms. This monomeric component acts, of course, as a chain stopper and the amount thereof relative to the dimer acid will effectively control the molecular weight of the final polyamide. Typically, the monomeric fatty acids suitably provides from 10 to 70 mole of the total carboxyl functionality of the mixture, preferably from 45 to 65 mole% thereof. In general it is preferred to use total acid and total amine components in substantially stoichiometric amounts.
The polyamides of the invention are produced in a conventional manner, that is by polycondensing the acid and amine components at elevated temperature, e.g. 80 to 2300C, whilst distilling off water evolved during the condensation reaction. Reaction is suitably carried out until the reaction mixture has a maximum amine value of 4 mgKOH/g and a maximum acid value of 4 mgKOH/g.
The resultant polyamides may be used in printing inks, especially flexographic inks to give products having good adhesion, scratch resistance, water resistance and deep freeze resistance whilst, at the same time, having improved solution properties as indicated by a lower gel temperature and a lower gel recovery temperature.
Accordingly, another embodiment of the invention provides an ink or varnish comprising a polyamide as defined above dissolved in an ethanolic solvent and also containing in the case of an ink, a colorant such as a pigment or dyestuff. Typically such an ink or vanish may also contain other resinous material especially nitrocellulose and, in this latter instance, the proportion of polyamide to nitrocellulose is suitably from 0.1 to 20:1.
In order that the invention may be well understood the following Examples are given by way of illustration only.
Examples 1-6Polyamides were prepared, following the process described above, from the components listed in Table 1 below.
TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Dimer acid 707.34 696.36 690.11 579.11 699.06 663.65Propionic acid 119.20Acetic acid 95.13 79.12Isobutyric acid 88.72 140.12 133.08Phosphoric acid 0.07 0.07 0.07 0.07 0.07 0.07Antifoam 0.04 0.04 0.04 0.04 0.04 0.04 2,2-dimethyl- 99.91 180.08 pentamethylene diamine 2,2,4- 119.55 327.22 trimethyl hexamethylene diamine 2-methylpenta- 88.11 methylene diamine 2-butyl-2- 134.11 ethylpentan1,5-diamineEthylene 71.44 12.44 70.60 67.08 diamine 1,3-propane 86.85 38.98 diamineTopanol CA 2.00 2.00 2.00 2.00 2.00 2.00 1000.00 1000.00 1000.00 1000.00 1000.00 1000.00 Typical formulations for inks containing the abovepolyamides are as follows: a.White Flexoaraphic ink
% Weight Titanium Dioxide 37.00 Nitrocellulose 4.50 Polyamide 14.00 Crayvallac 62 2.00 n-Propanol 14.40 Industrial Methylated Spirit 17.60 Ethyl acetate 10.50 100.00 b. Black flexographic ink
% Weight Pigment Black No.7 13.20 Alcohol soluble 10.30 Nitrocellulose Polyamide 16.90 Crayvallac 62 0.80 n-Propanol 18.50
Industrial Methylated Spirit 21.20 Ethyl acetate 13.20 Plastisiser 5.90 100.00 * Dispercel Carbon black F-A - Runneymede Dispersions Ltd.
c. White Gravure Ink
% Weight Titanium Dioxide 34.00 Nitrocellulose 6.00 Polyamide 12.80 Crayvallac 62 1.60 n-Propanol 13.00 Industrial Methylated Spirit 20.40 Ethyl acetate | 12.20 100.00 The polyamides of Examples 5 and 6 were incorporated into Cyan, Magenta and White ethanolic flexographic inks. By way of comparison a conventional polyamide was incorporated in the same inks. The gelation characteristics of the inks were evaluated to give the following Gel temperature/recovery values ( C).
Ink PolyamideConventional Example 5 Example 6Cyan -8/-6 -12/-b -1i/-9 White -8/-7 -11/-10 -11/-10Magenta -10/-8 -12/-11 -12/-11