Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1996-02-07
2000-08-01
Dawson, Robert
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
428418, 523208, 523212, C08K 336, C08L 6304
Patent
active
060968079
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to powder coatings containing epoxy resins, phenolic crosslinking agents, catalysts, fillers and, if desired, auxiliaries and additives. The invention further relates to processes for the exterior coating of metal pipes using these powder coatings, and to the use of the powder coatings for the one-layer exterior coating of metal pipes.
Nowadays, metal pipes are usually protected against corrosion by being coated with reactive powder coatings. It is known to use for this purpose powder coatings based on epoxy resins and suitable crosslinking agents. The powder coatings which are suitable for this one-layer coating process for metal pipes must meet stringent requirements with regard to protection against corrosion, hot water exposure and cathodic delamination. Powder coatings suitable for exterior coating of pipes are known, for example, from EP-B-104 719 and U.S. Pat. No. 4,122,060. The powder coatings known from EP-B-104 719 are epoxy resins which are crosslinked using, for example, phenolic curing agents. The powder coatings described also contain catalysts, and calcium oxide as filler.
U.S. Pat. No. 4,122,060 describes powder coatings based on epoxy resins, curing agents, fillers and catalysts, the filler employed preferably being amorphous silicic acids. Furthermore, it is known to employ felspars and barytes or alternatively precipitated barium sulfate as fillers in epoxy powder coatings for pipe coating.
The previously known powder coatings based on epoxy resins, suitable crosslinking agents, catalysts and fillers such as, for example, amorphous silicic acids, felspars, barytes and precipitated barium sulfates, have the disadvantage that they exhibit poor properties with respect to resistance to hot water and to cathodic delamination (DIN 30671).
The object of the present invention was therefore to eliminate the disadvantages of the prior art by providing powder coatings which are based on epoxy resins, on suitable crosslinking agents such as, for example, phenolic curing agents, on fillers and on catalysts and which are suitable for the exterior coating of metal pipes. The pipes coated with these powder coatings should have good protection against corrosion, improved resistance to hot water and improved resistance with regard to cathodic delamination. Furthermore, the coatings obtained should be of high flexibility.
The object of the invention is achieved by powder coatings comprising epoxy resins, phenolic crosslinking agents, catalysts, fillers and, if desired, auxiliaries and additives. The powder coatings are characterized in that the fillers used are crystalline silicic acid modifications which are functionalized with glycidyl groups.
Suitable epoxy resins are all solid epoxy resins having epoxide equivalent weights of between about 400 and 3000. These are predominantly epoxy resins based on bisphenol A and bisphenol F. Particular preference is given to employing epoxidized novolak resins. Also suitable are mixtures of bisphenol A or bisphenol F resins and novolak resins. The epoxy resins based on bisphenol A and bisphenol F possess, in general, a functionality<2, the epoxidized novolak resins a functionality>2. The resins used with particular preference in the powder coatings according to the invention are epoxidized novolaks having an average functionality in the range from 2.4 to 2.8 and with an epoxide equivalent weight in the range from 600 to 850. In the epoxidized novolak resins the phenolic hydroxyl groups are etherified with alkyl, aryl or similar groups. By reacting the phenolic hydroxyl groups with epichlorohydrin, epoxide groups are incorporated into the molecule. Starting from novolaks, the so-called epoxy novolak is formed in this process. The epoxidized novolaks are structurally related to bisphenol A resins. Epoxidized novolak resins can be prepared by epoxidation of novolaks consisting, for example, of from 3 to 4 phenol rings which are joined to one another via methylene bridges. The novolak resins used can also be alkyl-substituted phenols w
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Registry number 14808-60-7 the chemical names which are common, NA.
Blomer Werner
Rademacher Josef
Reiter Udo
Aylward D.
BASF Coatings AG
Dawson Robert
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