EP0710733A1 - Metal corrosion inhibiting mixture - Google Patents

Abstract

Mixts. comprising (A) 1-99 pts. wt. poly-4-5 C amino acids and (B) 1-99 pts. wt. 1-99 pts. wt. at least one other corrosion inhibitor different to (A) are useful for protecting metals against corrosion.

Description

The invention relates to the use of mixtures of polyamino acids and conventional corrosion inhibitors for the corrosion inhibition of metals.

It is known that organic compounds can be used as metal passivators, for example for copper or brass, in functional media such as hydraulic liquids or in antifreeze solutions for surface protection against corrosion. Known compounds for this include, for example, benzimidazole, benzothiazole and benzotriazole derivatives.

The latter compounds are described for example in GB-PS 1 061 904. However, benzotriazole itself and many of its derivatives are of limited use because of their low solubility, especially in aqueous systems.

Metal passivators which have a high solubility are particularly advantageous for functional media of this type, so that they can be distributed quickly and well in the media in which they are used, thereby ensuring optimum protection for the metal objects.

From EP-A 604 813 it is known that polyaspartic acid is particularly effective as a corrosion inhibitor for brass. Surprisingly, it has now been found that poly-C₄-C₅-amino acids in combination with conventional corrosion inhibitors further improve their effect.

• A. 1 bis 99 Gew.-Teilen, vorzugsweise 20 bis 80 Gew.-Teilen, Poly-C₄-C₅-aminosäure und
• B. 1 bis 99 Gew.-Teilen, vorzugsweise 20 bis 80 Gew.-Teilen, mindestens eines von A verschiedenen Korrosionsinhibitors

zur Korrosionshemmung von Metallen.The invention therefore relates to the use of mixtures of

• A. 1 to 99 parts by weight, preferably 20 to 80 parts by weight, poly-C₄-C₅-amino acid and
• B. 1 to 99 parts by weight, preferably 20 to 80 parts by weight, of at least one corrosion inhibitor different from A.

for corrosion inhibition of metals.

Preferred polyamino acids A include especially polyaspartic acid and polyglutamic acid as well as the salts of these acids and their anhydrides, e.g. Polysuccinimide. Preferred salts are the sodium and potassium salts.

The production of polyaspartic acid and its derivatives has long been the subject of numerous publications. Thus, the production can be carried out by thermal polycondensation of aspartic acid (J. Org. Chem. 26 , 1084 (1961).

US Pat. No. 4,839,461 (= EP-A 256 366) describes the preparation of polyaspartic acid from maleic anhydride, water and ammonia. Then maleic anhydride is converted into the monoammonium salt in an aqueous medium with the addition of concentrated ammonia solution.

This maleic acid monoammonium salt can preferably be subjected to thermal, optionally continuous polymerization at 150 to 180 ° C. in a reactor with a residence time of 5 to 300 minutes, and the polysuccinimide obtained can be converted to polyaspartic acid or a salt thereof by hydrolysis.

• a)
  
  und
• b)
  

Im allgemeinen liegt der Anteil der β-Form bei mehr als 50 %, insbesondere mehr als 70 %, bezogen auf die Summe a + b.In a preferred embodiment, the polyaspartic acid contains essentially repeating units of the following structure;

• a)
  
  and
• b)
  

In general, the proportion of the β-form is more than 50%, in particular more than 70%, based on the sum a + b.

• c) Äpfelsäureeinheiten der Formeln
  
• d) Maleinsäureeinheiten der Formel
  
• e) Fumarsäureeinheiten der Formel
  

Die " weiteren" wiederkehrenden Einheiten können in Mengen bis zu 100 Gew.-%, bezogen auf die Summe a + b, in der Polyasperaginsäure enthalten sein.In addition to the repeating aspartic acid units a) and b), further repeating units can be included, for example

• c) Malic acid units of the formulas
  
• d) Maleic acid units of the formula
  
• e) Fumaric acid units of the formula
  

The "further" recurring units can be contained in the polyasperic acid in amounts of up to 100% by weight, based on the sum a + b.

Preferred polyamic acids A have, as a weight average, molecular weights determined by gel permeation chromatography (calibrated with polystyrene) from 500 to 10,000, preferably 1,000 to 5,000, in particular 2,000 to 4,000.

Preferred corrosion inhibitors B are polyphosphates, molybdates, chromates, zinc salts, sodium metasilicates, benzoates, phosphonates such as aminomethylene phosphonate (AMP), aromatic azoles such as optionally substituted benzimidazoles, benzothiazoles and benzotriazoles such as mercaptobenzothiazole, benzotriazole, 4- and 4-C₁-benzo-4-C₁ -Methylbenztriazol, 5-methylbenztriazole and the mixtures of these isomers, 4-butylbenztriazole, homo- and copolymers based on acrylic acid, methacrylic acid and / or maleic acid, lignin sulfonates, tannins, complexing agents, citric acid, tartaric acid and gluconic acid. Particularly preferred corrosion inhibitors B are benzotriazole, 4- and 5-methylbenztriazole.

The components of the mixtures to be used according to the invention can be added to the medium in which they are intended to act, individually or mixed, solid or dissolved or dispersed in a liquid, preferably water.

The amount of the mixture to be used can be 0.1 mg to 10 g, preferably 1 mg to 0.1 g, in each case per kg of the medium in which they are intended to act.

Depending on requirements, additional auxiliaries can be added to the mixtures according to the invention or their aqueous solutions, which increase their useful properties. This can, for example, improve wetting, suppress the growth of microorganisms (addition of microbicides) or prevent precipitation of substances which are dissolved in the aqueous substances.

Examples 1. Testing for corrosion inhibition in brass

Bare and degreased brass samples were used for the corrosion test. Artificial seawater according to ASTM D 665-IP 135, to which the substance to be examined was added, served as the test solution. During the test period of 7.5 hours, the metal samples were completely immersed in the 55 ° C test solution, into which approx. 100 ml air / min was introduced.

wobei

m

= Massenverlust der Metallprobe ohne Inhibitor (Blindprobe) und

m₁

= Massenverlust der Metallprobe mit Inhibitor

bedeuten.After the test, the samples were cleaned in 18 wt% hydrochloric acid for 15 seconds and washed with water and acetone. The dry metal samples were weighed before and after the test. The percentage protective effect S, based on a blank sample, was calculated from the loss of mass: $$\text{S =}\frac{{\text{mm}}_{\text{1}}}{\text{m}}\text{x 100}$$

in which

m

= Loss of mass of the metal sample without inhibitor (blank sample) and

m₁

= Loss of mass of the metal sample with inhibitor

mean.

The results of the percent protective effect are given in the table below. Table 1 Polyaspartic acid Na salt Tolyltriazole % Protective effect 10 mg / l - 46.2 - 1 mg / l 64.6 10 mg / l 1 mg / l 80.5

2nd Corrosion inhibition test for copper

Bare and degreased copper samples were tested according to the procedure described under 1). The results are shown in the table below. Table 2 Polyaspartic acid Na salt Tolyltriazole % Protective effect 25 mg / l - 0 - 2 mg / l 53 10 mg / l 2 mg / l 79.4

Claims (4)

Use of mixtures of A. 1 to 99 parts by weight of poly-C₄-C₅-amino acid and B. 1 to 99 parts by weight of at least one corrosion inhibitor different from A. for corrosion inhibition of metals. Use according to claim 1, wherein these mixtures
20 to 80 parts by weight of A and
Contain 20 to 80 parts by weight B. Use according to claim 1, wherein component A is selected from the series polyaspartic acid, polyglutamic acid, the salts of these acids, polysuccinimide. Use according to claim 1, wherein component B is selected from the series benzotriazole, 4-C₁-C₄-alkylbenztriazole and 5-C₁-C₄-alkylbenztriazole.