At least 24 months from the date of manufacture in the original sealed container at ambient temperature. Store away from excessive heat and humidity in tightly closed containers. Films can be force dried or baked to accelerate cure. The information contained herein is offered without charge for use by technically qualified personnel at Allentown, PA their discretion and risk.

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Coatings based on epoxy resins are important industrial products. The largest volume of these products is used for the protection and decoration of large metal or concrete structures such as bridges, ships, industrial tanks, etc. Epoxy coatings of this type have proven themselves to offer an excellent combination of corrosion resistance, water resistance, abrasion resistance, solvent resistance and other desirable coatings properties, and do so in a cost effective manner.

Most epoxy resin coatings designed for ambient application employ polyfunctional amines as the curing agent, either alone or in some cases in combination with other curing agents. Several classes of amine curing agents are used commercially, including aliphatic amines, amidoamines, amine adducts, Mannich bases, and polyamides.

They are described more fully in W. Ellis ed. Among these curing agents, polyamides are a particularly important class of curing agent for the formulation of coatings. Polyamides comprise the reaction products of dimerized fatty acid dimer acid and polyethyleneamines, and usually but optionally, a monomeric fatty acid.

Dimer acid is prepared by the oligomerization of certain monomeric fatty acids, usually tall oil fatty acid TOFA , though sometimes other vegetable acids are substituted. Polyamides are employed because they allow for the formulation of coatings with an excellent combination of water and corrosion resistance, most likely due to the hydrophobicity imparted by the fatty nature of the starting materials. They also can offer excellent flexibility, reasonable cure speeds drying times , and less of a tendency to exude to the surface to cause surface appearance problems known in the industry as exudate, blush and bloom than some of the other hardener classes.

In addition, due to the relatively low cost of fatty acids and dimer acid, polyamides are among the most cost effective of curing agents available. Nevertheless, there are several properties of polyamide curing agents that would benefit from improvement. As a result of environmental regulations, and also as the need to reduce solvent levels in coatings has been perceived by coatings manufacturers and their customers, there has been a need to reduce the viscosity of the binders employed in coatings, and epoxy based coatings are no exception.

Polyamide curing agents have for some time been supplied in several grades of differing viscosity. Thus, one manufacturer Air Products and Chemicals, Inc. However, as the viscosity of the curing agent is reduced in these products, it is generally found the amine hydrogen equivalent weight AHEW also decreases.

For the polyamides described above, the AHEWs are , , and respectively. Epoxy resins are also available in many viscosities. Such epoxy resins are generally difunctional or slightly less than difunctional, and characterized by their epoxy equivalent weight EEW. At an equivalent weight of about or so epoxy resins partially crystallize at a fairly rapid rate to a semi-solid, and above an equivalent weight of about they are solids, and thus their viscosities cannot be measured at room temperature.

In the formulation of coatings, it is frequently advantageous to employ higher molecular weight epoxy resins, such as those with an equivalent weight of to known in the industry as '1 type' resins.

High molecular weight resins dramatically decrease the dry-to-touch time of the coating. Furthermore, higher molecular weight epoxy resins yield more flexible and impact resistant coatings than do lower molecular weight epoxy resins. Unfortunately, the high viscosity of the higher molecular weight epoxy resins requires the use of high levels of solvent in order to achieve a suitable application viscosity.

An approach to reducing the amount of solvent required in a coating formulation is to employ hardeners with reduced viscosity. However, as shown above, polyamide curing agents with lower viscosities also have lower equivalent weights. Normally, epoxy resins are combined with hardeners at stoichiometries of about epoxy groups per amine hydrogen. At this ratio, most properties of the film, such as tensile strength, crosslink density, solvent resistance, etc.

The Ancamide curing agent cuts the viscosity to some intermediate level. In practice, the final viscosities of these formulations are not dramatically different, and thus there is only a modest decrease in the amount of solvent required in the coating.

Clearly, there is a need for low viscosity polyamide curing agents with higher equivalent weights than polyamides of the current art. In many cases, restrictions on the use of solvents require that low molecular weight epoxy resins be used in place of the preferred, higher molecular weight epoxy resins irrespective of the viscosity curing agent employed. As mentioned above, this increases the dry-to-touch time of the coating. Thus, there is a need for curing agents that reduce dry-to-touch times of epoxy coatings, particularly those based on liquid epoxy resins.

As mentioned above, there is a tendency for curing agents to rise to the surface of a coating during the cure. This can leave a greasy film on the surface of the coating which detracts from the appearance and which can also lead to intercoat adhesion failure if the epoxy is a primer or mid-coat.

While polyamides are better than certain classes of curing agents, particularly amidoamines and unmodified polyethylene-amines, in this regard, they are still far from perfect. In addition, the high viscosity polyamides of the current art tend to exhibit less exudate and blush than the lower viscosity polyamides. It is found that by waiting a period of time, generally 0.

This is known as an induction time. As solvent levels and epoxy molecular weight have been reduced in epoxy coating formulations, however, it has been found that pot lives have also been reduced. The pot life is the time available after mixing the amine and epoxy components of the formulation during which the viscosity remains low enough to allow application. The decrease in pot life is the result of simple chemical kinetics: reduction of solvent content and equivalent weight both result in an increase in the concentration of functional groups, and hence an increase in the rate of reactions that lead to increased viscosity.

Thus, there is a need for curing agents with decreased exudate and blush, so that induction times can be reduced or eliminated. For good protection of metallic substrates, it is necessary that the coating maintain good adhesion to the substrate, particularly under wet conditions such as the Cleveland condensing humidity test. While epoxy coatings generally have good adhesion, there is still a need for improved adhesion, particularly over poor substrates such as cold-rolled steel CRS.

Finally, there is a need for curing agents that can lead to epoxy coating compositions with greater corrosion resistance, leading to coatings with longer life in service. US 2,, and US 2,, both describe the preparation of polyamide resins useful for curing epoxy resins by the condensation of dimerized or polymerized fatty acids with polyethyleneamines such as ethylenediamine EDA and DETA.

US 5,, describes the preparation of polyamides from polymerized fatty acid and a mixture of amines comprising a polyalkylene polyamine and an N-aminoalkylpiperazine, preferably N-aminoethylpiperazine AEP. The polyamides are utilized as adhesion promoters for PVC plastisols. Because high amine content in such an adhesion promoter destroys the acid catalysts employed in top coats applied to such plastisols, this invention is directed toward the preparation of polyamides with an amine value less than about Thus, these products are very high in viscosity, and of little value in modern coatings applications, where environmental regulations require that only limited amounts of solvent can be utilized in the final coating formulation.

CS discloses an extremely broad range of polyamide resins prepared by condensing carboxylic acids av. By incorporating a specific range of amounts of piperazine ring containing polyamines having an N-H functionality of 2 or 3 per mole selected from the group consisting of piperazine and N-aminoalkylpiperazine into polyamide compositions comprising fatty acid, dimer acid, and a polyethyleneamine having the structure.

The fatty acids of the current invention are those composed primarily of C12 to C22 monocarboxylic acids containing from 0 to about 4 units of unsaturation. Usually, such fatty acids will be mixtures derived from triglycerides of natural products. Pure fatty acids or mixtures of pure fatty acids, such as stearic, palmitic, oleic, linoleic, linolenic, etc.

Also of utility is isostearic acid, also known as monomer acid. Monomer acid is the mostly C18 fatty mono-acid stream derived from the preparation of dimer acid. The preferred fatty acids are tall oil fatty acid and soya fatty acid. The most preferred fatty acid is tall oil fatty acid. They are described more fully in T. Breuer, 'Dimer Acids', in J.

Kroschwitz ed. They are prepared by polymerizing fatty acids under pressure, and then removing most of the unreacted fatty mono-acids by distillation. The final dimeric acid product usually consists of some fatty mono-acid, mostly dimeric acids, and trimeric and higher acids.

The dimeric acid product can be prepared with various, controlled levels of fatty mono-acids. The ratio of dimeric acids to trimeric and higher acids is variable, depending on processing conditions and the unsaturated acid feedstock. The dimer acid may also be further processed by, for example, hydrogenation, which reduces the degree of unsaturation and the color of the product. Esters of dimer acids, particularly the C 1 to C 4 alkyl esters, can also be employed in the current invention.

The ratio of equivalents of fatty mono-acid in the reaction mixture to dimer acid can be varied from about 0. The equivalents of acid can be obtained by titration with alcoholic hydroxide, as is well known in the art.

Although a fatty mono-acid is a required component of the reaction mixture which can be added separately, the requisite fatty mono-acid component may be present in the dimer acid component because the dimer acid component, as a result of its manufacture, will most likely contain some starting fatty mono-acid. In addition, the dimer acid may be processed to supply the requisite equivalent amount of fatty mono-acid, or optionally, supplemental fatty mono-acid may be added. The polyethyleneamines of the current invention are those of the structure:.

Mixtures of polyethyleneamines can be employed as well. The piperazine ring containing polyamines having an N-H functionality of 2 or 3 per mole are selected from the group consisting of piperazine and N-aminoalkylpiperazine, where the alkyl chain is a C2 to C6 alkyl chain.

Preferred piperazine ring containing polyamines are piperazine and AEP. It has been discovered that condensation of AEP with carboxylic acids occurs preferentially on the primary amine, leaving only one active hydrogen for reaction with epoxy resin.

If piperazine reacts on only one end with a carboxylic acid, it likewise leaves only one active hydrogen for reaction with epoxy resin. In this way, the equivalent weight of the final polyamide is increased, leading to the desirable result of reduced viscosity when formulated with high viscosity epoxy resin.

The ratio of moles of piperazine ring containing polyamine to polyethyleneamine is also crucial to the practice of this invention. As is obvious from the above, this ratio has a significant effect on the AHEW of the final product. It has also been determined that adhesion to cold rolled steel CRS substrates after exposure to condensing humidity is improved by including piperazine ring containing polyamines in the polyamide composition.

The ratio of moles of piperazine ring containing polyamine to polyethyleneamine can range from about 0. The ratio of total moles of polyamine including the piperazine ring containing polyamines to equivalents of acid is a crucial parameter in determining the properties of the resulting polyamides. This parameter will have a large influence on the molecular weight and hence the viscosity of the polyamide produced. Indeed, if the excess of amine to acid is not large enough, then the entire composition can gel.

Furthermore, this ratio also influences the AHEW of the final product, and has an effect upon the amount of unreacted polyamine present after completion of the condensation reaction.

Suitable ratios of moles of polyamine to equivalents of acid range from about 0. If desired, the composition can be optionally modified by the incorporation of additional polyethylene amine or other polyamines.

The composition can be modified by adding these polyamines to the polyamide after completion of the condensation reaction. Polyamides of the current invention can be manufactured by any number of processes known to those skilled in the art. Heat is then supplied to raise the temperature as water is condensed from the reaction mixture.

Heating is normally continued until the specified amount of water is removed that will yield a product with the desired imidazoline and amide content. Optionally, vacuum can be applied particularly in the late stages of the process to aid in the removal of water from the mixture.

To reduce foaming, which can be a problem particularly under vacuum conditions, small amounts of defoamers may be added to the polyamide composition.


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