Лако-красочные материалы — производство

(Courtesy of Shell Chemicals)

In this example, butyl glycol is the solvent. Hydroxyl functionality comes from hydroxy ethyl methacrylate. If required, the resin can be neutralised and dispersed or supplied as is for the coating formulators to add the amines of their choice.

Procedure

1. Charge reactor with VeoVa 10, 60% of the styrene and 40% of the solvent.

2. Heat to 80°C and commence the addition of monomer mixture comprising all the acrylic monomers, the remainder of the styrene and solvent, plus 70% of the peroxide charge.

3. The monomer addition should be carried out over a five hour period of time, the temperature being maintained at 140°C.

4. When the addition of monomers is complete, hold at temperature for 15 minutes.

5. Add 10% of the peroxide charge and hold at temperature.

6. After 30 minutes add another 10% of the peroxide charge.

1. After 30 minutes add the remainder of the peroxide and hold for a further 30 minutes.

Resin Characteristics

Solid content 70 ± 1%

Acid value 90 mg KOH/g

Hydroxyl value 75 mg KOH/g

In this example a solution is prepared using standard techniques. The polymer is then

solubilised by neutralising the acrylic acid with DMAE Although the paint is claimed to

be aqueous there is a proportion of solvent (butyl glycol) present. This technique of preparing aqueous vinyl polymers is quite common.

The use of di-methylaminoethanol to neutralise the acid groups of the polymer is preferred to ammonia in stoving finishes. Ammonium salts of carboxylic acids can give amides on heating and they also react with formaldehyde, reducing the efficiency of the crosslinking resin. On standing, the pH of ammonia solutions tends to drop with a consequent rise in viscosity, whereas DMAE solutions have good viscosity stability on ageing.

The polymer composition raises several interesting points. Hydroxy ethyl methacrylate could be replaced effectively wt./wt. by hydroxy ethyl acrylate. The hydroxyethyl acrylate reacts more readily with melamine resins than carboxylic acids. The acrylic acid is added to give water solubility when neutralised. Note that in the absence of the hydroxy monomer, more acrylic acid would be required to solubilise the polymer. The VeoVa has a softening effect on the copolymer and also contributes water resistance to the film.

For this to be made into a paint for spraying ammonium p-tuolenesulphate and Tegoflow would be added. The sulphonic acid salt is added as a latent catalyst which reverts to the acid on heating. The Tegoflow is a flow control additive which prevents pin holing.

This paint has anti-corrosion properties similar to those of conventional paints containing chromate or other pigments which inhibit rusting.

For spraying, use a larger nozzle than usual, e. g. 3.5 mm, because of the relatively high viscosity. The sprayed film is stoved at 160°C for 30 minutes.