Volatile Corrosion Inhibiting Article

This invention relates to corrosion inhibition. More particularly, this invention relates to novel plastic articles which provide volatile corrosion inhibition.

Volatile or vapor phase corrosion inhibitors have been used in a variety of applications where visible coatings such as oil or grease or other permanent coatings such as paints are unacceptable for various reasons. Sodium nitrite, amine nitrite salts, organic amines, carboxylic acids and organic amine carboxylic acid salts have all been disclosed singularly and in combination in volatile corrosion inhibiting compositions (e.g. as described in U.S. Pat. Nos. 2,629,649: 2,711,360: 2,986,447: 3,398,095: 3,433,577: 3,785,975: and 3,967,926). Sheet materials useful for packaging metal parts containing volatile corrosion inhibiting compositions have also been disclosed (e.g. as described in U.S. Pat. Nos. 2,717,843: 2,739,871: 2,829,080: and 3,080,211). Sodium nitrite is known as an effective volatile corrosion inhibitor when carbon dioxide and water are present in the air. However, in the absence of carbon dioxide, its effectiveness as a volatile corrosion inhibitor drops off abruptly, as described in Metaux 1972 47(558), 41-50.

We have unexpectedly discovered that a mixture of an inorganic nitrite, a trisubstituted phenol and fumed silica, when mixed with polyolefin polymer, yields a plastic article having highly effective volatile corrosion inhibiting properties regardless of carbon dioxide concentration in the environment. The novel article of the present invention comprises:

(a) polyolefin polymer;

(b) an inorganic nitrite salt:

(c) a 2,4,6-trisubstituted phenol containing 9 to 24 carbon atoms, and

(d) fumed silica.

The volatile corrosion inhibiting articles of the invention comprise (a) polyolefin polymer, (b) an inorganic nitrite salt, (c) a trisubstituted phenol and (d) fumed silica.

The organic polymers useful in the preparation of the volatile corrosion inhibiting articles of the present invention are those which can be thermally processed to make articles such as films or sheets, injection molded parts, or plastisols. Typical useful polymers include polyolefin polymers such as polyethylene, polypropylene, ethylene/vinyl acetate copolymers, vinyl acetate/vinyl chloride copolymers and polyvinyl chloride. Processing aids may optionally be included, such as plasticizers (e.g. dioctyl phthalate, tricresyl phosphate, etc). Other inert materials may also be included such as fillers, colorants and other conventional additives.

The inorganic nitrite salts useful include metal nitrites (preferably Group I and II metal nitrites) such as potassium nitrite, sodium nitrite and calcium nitrite. A particularly preferred nitrite salt is sodium nitrite.

The trisubstituted phenols which are useful are substituted in the 2,4 and 6 positions with alkyl, hydroxyalkyl, aryl, alkenyl or hydroxyalkenyl. A particularly preferred phenol is 2,6 di-t-butyl-4-methyl phenol.

The fumed silica which has proven useful is available commercially under the tradename "Cab-O-Sil" from the Cabot Corporation.

The invention is further illustrated by means of the following examples wherein the term parts refers to parts by weight unless otherwise indicated.

Examples 1 and 2 describe the preparation of volatile corrosion inhibiting articles by means of plastisol formation.

The plastisols were prepared by mixing all of the following ingredients together to form a uniform paste and then heating.

The plastisol formed by heating the mixture shown in Example 1 at 250.degree. F. for 30 minutes showed little degradation and demonstrated excellent volatile corrosion inhibiting properties using test method FTM-101B Method 4031.

A plastisol was formed as in Example 1 with the following composition similar to one described in U.S. Pat. No. 2,829,080:

The resulting plastisol exhibited considerable darkening and decomposition after being heated at 250.degree. F. for 30 minutes.

This example describes a volatile corrosion inhibiting article in the form of an extruded thermoplastic film. The following ingredients were mixed uniformly.

This mixture was extruded into film at a temperature of 300.degree. F. The resultant film showed no discoloration or gas formation and possessed excellent volatile corrosion inhibiting properties when tested against mild steel.