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Substitution of Cobalt Driers and Methyl Ethyl Ketoxime

5 Description of evaluated systems

5.1 Products

Oxidative drying systems are available in a variety of products covering a broad range of application areas. The products included in this project for testing the alternative driers and anti-skinning agents have been chosen in such a manner that they cover the most relevant and broadest possible area of air-drying systems on basis of the coating systems made available from the participating manufacturers. The selection has been made on basis of the information the manufacturers have provided on their own systems.

Eight manufacturers have supplied products for the project within the area of do-it-yourself coating (also called decorative coating), industrial coating and printing inks. Two products from each coating and printing ink manufacturer had been included in the testing of the alternatives. The products included for testing have been made anonymous and it was agreed with the manufacturers which specific information that should be published and communicated. No additional information on the products can be given without the consensus of the manufacturers.

The products were typically received in pairs. One sample was the original product containing cobalt driers and methyl ethyl ketoxime (or hydroquinone in the case of printing inks), which from now on is referred to as reference products. The other sample was a product sample without any driers and anti-skinning agents.

5.1.1 Do-it-yourself products

Eight products within the area of do-it-yourself coatings (DIY coatings) were included to test the efficiency of the alternatives. All products are alkyd coatings mainly of the long oil alkyd type. The alkyds are either based on tall oil, linseed oil or soybean oil. A few products contain thixotropic alkyds (polyamide modified alkyds). Six of the products are wood stains and two are enamels. Two of the stains are waterborne products and two are high solids coatings.

All the solvent-borne products contain methyl ethyl ketoxime as anti-skinning agent. In most of the products, a Co/Ca/Zr drier system is used containing cobalt drier as primary drier and zirconium and calcium driers as secondary driers.

A few systems contain zinc driers instead of zirconium and one product used barium as an additional secondary drier. A general description of the do-it-yourself products is given in table 5.1.

Table 5.1
General descriptions of do-it-yourself products included in the project.

* Methyl ethyl ketoxime

5.1.2 Industrial products

Within the area of industrial coatings five products were included. Two of the products are alkyd primers, one waterborne and one solvent-borne. One product is an alkyd topcoat. Two of the products are urethane modified alkyd products, one wood primer and one wood lacquer.

The industrial products are more diverse in the use of driers than the do-it-yourself products, even though they basically use the same four metal driers. All the products except one contain cobalt driers. A general description of the industrial products is given in table 5.2. Product IND-P9 is included for substitution of methyl ethyl ketoxime. All the solvent-borne products contain methyl ethyl ketoxime.

Table 5.2
General descriptions of the industrial products included in the project.

* Methyl ethyl ketoxime

5.1.3 Printing inks

Four printing inks (two cyan and two magenta) for sheet-fed offset were used for test of the efficiency of alternative driers and anti-skinning agents in printing inks. The inks are either based on blends of long oil alkyd, soybean oil and linseed oil or on blends of alkyd, linseed oil and wood oil (tung oil). All the original printing inks contain drier systems based on Co and conventional Mn driers. The antioxidant used is hydroquinone. Reference inks containing the original driers and antioxidants were used for comparative test.

Table 5.3
General descriptions of the printing inks included in the project.

5.2 Alternative Cobalt free drier systems

5.2.1 Alternatives to Co-driers

During the search for alternatives available on the market at present only manganese and vanadium came up as alternatives to Co driers. Various driers of both metal types have been investigated and evaluated. Of these 8 were manganese driers and 3 were vanadium driers. As the intention of the project was to investigate if alternatives to cobalt driers exist and not to promote one commercial drier product in preference to another the driers have been coded. The commercial name of the driers will though be made available on request from the participating paint and ink manufacturers and other interested parties. The investigated alternative driers are described in table 5.4.

Table 5.4
The investigated alternatives to cobalt driers. It is indicated if a drying accelerator is build into the drier product and if the drier product is made for waterborne systems only. Furthermore is it indicated in how many systems the driers have been tested in.
*Used as a second primary drier, not as an alternative to cobalt driers.

Mn traditional is a traditional manganese carboxylate drier, which needs to be combined with a drying accelerator (2,2-bipyridyl) to increase its catalytic activity to become a potential alternative to cobalt driers. In the case of the printing ink, Mn traditional was not used as an alternative to Co driers, but as a second primary drier.

The drier coded Mn1 is developed primarily for use in waterborne systems, but was suggested as a Co alternative in both solvent-borne and waterborne systems even though the drier manufacturer has a similar drier product intended for solvent-borne systems, namely Mn7. That is mainly due to Mn1 having a better environmental profile than the solvent-borne alternative and due to the fact that Mn1 actually performs well in solvent-borne systems.

Mn2, Mn3 and Mn4 are manganese based driers intended for use in solvent-borne oxidative drying coatings, but they can also be used in waterborne systems. Mn1, Mn2, Mn3, Mn4 and Mn7 contain all a drying accelerator (complexing agent). Mn1, Mn2, Mn3 and Mn4 have more or less all been tested in all the air-drying systems included in the project. Table 5.4 also gives an indication of how many products the specific alternatives have been tested in for each of the three product groups.

Mn4 was included late in the project compared to the other manganese driers. Mn7 has only been included in the environmental and health screening, not in the technical evaluation. Mn5(w) and Mn6(w) are manganese based driers developed specifically for waterborne systems, both containing drying accelerators. These driers have only been tested in the waterborne systems. All the tested Mn dries are commercially available either as commodity driers or at least as trial products.

V1 and V2 are commercially available vanadium based driers for solvent-borne coatings. V2 is primarily intended for use in high solids paints, which have a relatively low solvent content. After the technical evaluations had ended it was realised, according to the manufacturer descriptions that V2 can be combined with a drying accelerator to achieve optimal catalytic effect. This was not done in this project.

In the case of V1 it has not been indicated by the manufacturer that a drying accelerator should be used in combination with it. No information has been given if the drier product, V1, contains a drying accelerator. V3(w) is a laboratory product made specifically for waterborne systems and has only been tested in these. As it is a laboratory product the composition is confidential, for which reason it is unknown if a drying accelerator is built into the drier product.

Vanadium driers have only been tested in the do-it-yourself products and in two printing inks. In the case of printing ink only one vanadium based drier system was tested and as no significant drying was induced no further testing was performed with vanadium driers. The vanadium driers were not tested in the industrial products as the drier manufacturers beforehand had indicated that manganese driers are expected to perform best in these products.

The alternative primary driers need in most cases, just like cobalt driers, to be combined with other driers to enhance through-drying as well as other film properties. These driers are described in brief in the following section. A listing of these driers can be seen in table 6.1. All the presented driers, the cobalt drier, the alternatives and the secondary driers have all, if possible, been screened with regard to environmental and health effects before they were included in the technical evaluation performed.

5.2.2 Other driers

Cobalt driers were included for comparison in the environmental and health screening. A Co drier has been used for making cobalt based drier systems for the printing ink samples used in the test of the alternative anti-skinning agents.

Zirkonium (Zr), barium (Ba), bismuth (Bi), strontium (Sr) and aluminium (Al) are all metals used for through-driers. Zr driers have been present in most of the tested alternative drier systems. Bi, Sr and Ba driers have been tested in a few products, where they have been combined with a few of the alternative driers. Only the Ba drier turned out to be useful in the drier combinations investigated in this project. The Al drier has not been tested in any of the alternative drier systems.

Calcium (Ca) driers are used in almost every tested alternative system, at least the solvent-borne ones. Zinc (Zn) and potassium (K) driers have been included in the testing as well. The potassium drier has only been tested in alternative drier systems in one product and without any successful outcome. Zn has been tested in several alternative drier systems combined with different Mn driers.

5.3 Alternative anti-skinning agents

Six alternative anti-skinning agents have been received. Five are commercial or trial products and one is a laboratory product. One of the alternatives was intended for printing inks only. The other alternatives have been tested both in paints and printing inks.

Two of the alternatives are amino/amido based compounds and two are phenolic based compounds. The last alternative is acetone oxime, which so far is not labelled as strictly as methyl ethyl ketoxime. Vitamin E has furthermore been tested as an alternative anti-skinning agent in some of the products, mainly the printing inks.

Methyl ethyl ketoxime and a hydroquinone product have also been included, both in the skinning test and in the drying time test, as reference compounds. The alternatives are presented in table 6.2 in next chapter. As it was the case with the driers the anti-skinning agents are not presented with their commercial product names. The alternative anti-skinning agents were also screened before including them in the technical evaluation.

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Version 1.0 December 2003, © Danish Environmental Protection Agency