CA1177004A

CA1177004A - Protective coating compositions and techniques

Info

Publication number: CA1177004A
Application number: CA000392848A
Authority: CA
Inventors: Fernand P. Janssen Bennynck; Marcel R. Piens
Original assignee: ASSOCIATION SANS BUT LUCRATIF CORI (COATINGS RESEARCH INSTITUTE)
Current assignee: ASSOCIATION SANS BUT LUCRATIF CORI (COATINGS RESEARCH INSTITUTE)
Priority date: 1980-12-22
Filing date: 1981-12-21
Publication date: 1984-10-30
Also published as: JPS57128758A; DK566281A; PT74176B; BR8108459A; ES508707A0; PT74176A; GR76956B; EP0055240B1; ES8305028A1; NO814374L; ATE10506T1; EP0055240A1; DE3167421D1

Abstract

ABSTRACT OF THE DISCLOSURE
Oxidation of a base material is prevented by promoting a process of catalytic deoxygenation in a protective coating. The coating includes at lease one couple formed by an enzyme and a substrate, or its precursor, which is oxidized by the enzyme.
The materials which produce the enzymatic catalysis, and thus the deoxygenation, may be incorporated in paints or the like and may be applied to the base to be protected either jointly as a single layer or separately in successively applied layers.

Description

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Tl;~C'I'IV:E COl~'r~NG COMPOS~ CONS I~ND '~CElN:tQUES

~ack~round of the 1:nvention:
(1) Fie]~d oE the Invention The present invention relates to the protection of base materials, particularly metals, from oxidation and especially to the deoxygenation of protective coatings such as paints, fillers and varnishes. More specifically, this invention is directed to protective coatings which undergo catalytic deoxygenation and particularly enzymatic catalysis. Accordingly, the general objects of the present invention are to provide novel and improved methods and materials of such character.

(2) Description of the Prior Art The action of oxygen which is in~ under or migrates through surface-protecting coatings, i.e., paints, fillers and varnishes for example, results in problems which are well known in the art. These problems are enhanced by the present trend toward incre~sing use of latex type, i.e., aqueous dispersions or solutions, coating materials. As an example o the type of problem encountered, storage of liquid paints in metallic containers, because of the presence of oxygen, results in the corrison and ultimately leakage of such containers.
Another prevalent problem is apparent in the painting of metallic base materials such as sand-blasted steel plates. A
phenomenon known in the art as "flash rusting", which is manifested by the rapid rust-colored spotting of the metallic surface, appears during the application of an aqueous rust proofing primer coating~ These spots are visible through a light-colored coating andf although the phenomenon does not substantially reduce the eficacy of the protection obtained '7~

with the coat:ing, -the unsightty app~arance has preven-ted the employmen-t of primers of liyht hue. The phenoménon of "flash rusting" is discussed in U.S.Patent 4,045,393 which describes a prior art attempt to overcome the problem.
The provision of an anti-corrosive coating on a me-tal base, particularly the application of a rust-preventative paint, dictates the forma-tion of a protective film which will prevent corrosion of the metal as a consequence of the oxidizing action of the medium which is or might be in contact with the metal base. Presently available coating materials, in their applied film form, are not always totally impervious to air or water and their effectiveness as a barrier to the migration of air or moisture to the surface of the base metal is known to degrade with time. Accordingly, in order to improve the protection of a metal surface underlying a prior art anti-corrosive coating, it has been suggested that the physical barrier afforded by the coating be enhanced by the establishment of a supplemental chemical barrier. The function oE this chemical barrier would be to consume oxygen which penetrates into the coating. Most o~
the reducing agents that could be used for such a deoxygenating role have one or more defficiencies. Thusl the reducing agents may cause lixiviation, i.e. the extraction of some of the soluble compounds in the coating materials through contact with water. Other detrimental effects of prior reducing agents are that they cause chemical disassociation and an increase in the conductivity of the water that goes into the paint film when exposed to moisture and these, in turn, result in an increase in corrosion currents. Also, prior art reducing agents _ 3 often interact with other constituents of the paint or other coating ma~erial to produce a substantial deterioration thereof. Further r many presently available anti-corrosive pigments are toxic and thus the use thereof is preferrably avoided.
As noted above, the use of water-based systems, i.e. r paints in aqueous dispersions or solutions, is increasing at the expense of solvent-based systems. The water-based coating systems aggravate those above-discussed problems and further present the specific problems of flash rusting of the base and increased water sensibility of the coating.
The problem discussed above has been addressed, without notable success r by the application of a passivation agent which contains a self-oxidizable binder to an iron or steel base prior to the painting. A technique of this type is disclosed and published German Patent application 1,664,737. The technique of the referenced German application involves a catalytic passivation system which decomposes peroxides. This catalytic passivation system employs, as catalysts, siccative agents or undisclosed materials whichare reported to have a catalytic efEect.
Summary of the Invention In accordance with the present invention there is provided a process for the enhancement of an oxidation preventing coating comprising:
providing an enzyme-substrate couple in the coating ,~

,.. ,, l~t7~7~3 whereby catalytic deoxygenation will occur therein, -the enzyme being selected from the yroup of oxygenases and oxid ases and the substrate being an organic material which is oxidized by the enzyme, both the enzyme and substrate material being added to the coating.
A~o in accordance with the invention there is provided a paint or varnish coating composition including therein:
an enzyme; and an organic substrate material which is oxidized by the enzyme whereby oxygen in said composition will be consumed by catalytic deoxygenation~
Further in accordance with the:invention there is provided a process for prev nting oxidation of a metal base comprising:
coating the base with a formulation which includes an enzyme-substrate couple, the enzyme being selected from the group of oxygenases and oxidases, whereby consumption of oxygen will occur in the coating through catalytic deoxygenation.
Thus the present invention overcomes the above-briefly discussed and other deficiences and disadvantages of the prior art by providing for the deoxygenation of coating compositions and particularly to the incorporation, into a coating composition, of at least one couple comprising at least one enzyme, the enzyme being selected from the group of oxyganases or oxidases, and a specific substrate or the - 4a precursor of the substra~e. The present invention also encompasses paint or varnish coating compositions, which may be employed either as single or plural layers, which present on the surface of the base to be protected a coating including material which will undergo an enzymatic reaction to fix oxygen.
While not limited thereto in its utility, the present invention is particularly well suited~for use in aqueous phase systems. The present invention encompasses the incorporation of the aforesaid materials for enzymatic catalysis for the purpose of preventing corrosion of metallic containers, to avoid "flash rusting" during the application of a~ueous paints and to enhance the performance of various other liquid compositions which may be employed to form films which act as rust preventative surface coatings.
In ~ccordance with the present invention the deoxygenation of a paint or varnish coating composition is achieved through anzymatic catalysis. The enzymatic reaction comprises the oxidiz-ing of a specific organic substra~e with molecular oxygen.
Exemplary enzymes useful in the practice of the present inven-tion are glucose oxidase, lipoxygenase, glycollate oxidase, galactose oxidase, alcohol oxidase, diamine oxidase and aldehyde oxidase.
These enzymes, in the course of inducing the oxidation of their specific substrates, will cause the impoverishment in oxygen of the meduim in which the reaction takes place.
A particularly unique aspect of the present invention resides -in the fact that the enzymatic activity continues to '7~

occur in mediums such as pa:int in liql~id form, a film of the same paint duriny its drying process and a dried paint film~ It would have been expected by those skilled in the art, taking into account the almost complete absences of mobility of the enzymes and/or the chemical or physical characteristlcs of the paints, particularly the vicosity of the drying or dried film, that no substantial enzymatic reaction would occur.

Brief Description of the Drawing The present invention may be better understood by reference to the drawing wherein:
FIGURE 1 is a graphical representation of the rate of deoxygenation of three samples, two of which were prepared in accordance with the present invention; and FIGURE 2 is a graphical representation of the results of tests which show the maintainence of the enzymatic activity in compositions prepared in accordance with the present invention after application to a matallic base material.
, .
~ion of the Pref~ed E~b~di~en~
It is to be observed that the use of substances that may 20 generally be referred to as oxidase in food products is discussed in the literature. Thus, for example, French Patent lt460,551 mentions a process for the preparation of purified glucose oxidase to withdraw glucose or oxygen from various compositions of essentially alimentary substances. Thus, the technique of the referenced French patent may be employed in the extraction of glucose from albumen or the extractian of oxygen ~ ~7'~V~

¦ ~rom ~oodstuffs or drinks. Slmilarly, U.S. Patent 3,005/714 discusses the preparation of pure galactose oxidase for use in extraction of galatose from foodstuffs. Both of the referenced l French and U.S. Patents require the production of a very pure, ¦ and consequently a specific, product which is added to a particular medium which contains the substrate of the enzyme.
These publications do not teach or suggest the introduction of the enzyme-substrate couple into a medium.
¦ The practice of the present invention may follow several ¦ different procedures. Thus, by way of example, the ¦ enzyme-substrate couple may be introduced into the coating composition, i.e~, the paint, in various forms. Several non-limiting examples are as follows:
l a. The addition of a determined quantity of the enzyme 15 ¦ and substrate to the liquid paint;
b. The addition of a solution containing the enzyme and its substrate to the liquid paint;
c~ The addition of the enzyme, or a solution containing l the enzyme, to a paint ancl the adc3ition of the substrate, or 0 ¦ a solution containing the substrate, to another sample of the same or a different paint.
In this pro~edure the enzymatic catalysis, and resultant ¦ consumption of oxygen, will occur only when both paint ¦ coatings have been applied to the same base and such 5 ¦ application can be in either order;
¦ d. The addition of one or more enzymes which are able to provide, from a precursor, the substrate required by the ¦ first enzyme. For example, glucose oxidasey or a solution containing glucose oxi~ase, may be added to a paint in which there is, or will be, incorporated another enzyme-substrate couple which provides the substrate which reacts with the glucose oxidase (starch -~G~ -amylase, starch or dextrine amyloglucosidase, cellulose + cellulase, starch and dextrine ~c~
-amylase + amyloglucosid~se).
In each of the above-mentioned techniques, the enzyme can be immobilized if desired in a macromolecular network such as, for example, polyacrylamide gel, carboxymethyl-cellulose, or the enzyme can be microencapsulated.
The exact formulation of the coating materials with which the present invention may be employed will, of course, be adjusted to the selected coating procedure in a manner well known to those skilled in the art.
The present invention will be better understoo~ by consideration of the following non-limiting e~amples.
EXAMPLE l - The activity of an enzymatic system in accordance with the invention was studied in formulations of commercial rust protective paints with enzymes MAXAZYME-GOL 1500 (Trade Mark:
Gist-Brocades).
Coating materials were prepared in air by adding a solution containing 5 g glucose and 0.3 ml glucose oxidase of technical grade (activity of 0.1 ml enzyme = 150 Sarrett Units) to 100 g of a paint comprising an emulsion of styrene-acrylate copolymer (Ercusol AS 250 (Trade Mark) resin obtainin from Bayer) in waterO This paint is sold under the Trade Mark Primalo by Societe Libert.

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~17'7~(~4 FilTns comprising this co~ting material were corrlp~red with films comprised of the same material but withou't the glucose,.
For the co~parison, the films were applied to a tin plate and air dried over a period of several days. ~hereafter, the samples were introduced, on the tin base, into an Erlenmeyer flask filled with distilled water. The flask was capped and the consumption of oxygen measur,ed. The film surface area in contact with the water was the same for each sample.
Referring to FIGURE 1, the curve labelled (1) was plotted for a film of paint applied in one layer and containing only the glucose. The slight decrease in the oxygen content of the water may be attributed to drift of the measuring probe since subsequent test verified that the tin base plate did not consume any of the oxygen.
Curve (2) was plotted for a flim containiny both the enzyme and glucose. The ability of the paint to consume the oxygen disolved in the solution is readily apparen-t from curve (2).
Curve (3) was obtained with a film applied in air to the tin l base plate in two layers. The first layer contained only the glucose. The second layer contained only the enzyme~ Be~ore oxygen may be consumed in the second layer, the water must first penetrate into the paint and allow the diffusion oE the glucose toward the outside of the system. The oxygen consumption i5 f accordingly, delayed or prevented during drying o the films upon initial application. Accordingly, the concentration of glucose in the dry multi-layer film is at a high level relative to its initial value andf as clearly shown by the curve, the rate of oxygen consumption of this system is 9reatly improved.

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Restated, ~he separation of the enzyme and its substrate into two layers oE paint results in the reduction of the activity of the couple during drying of the protective coating and ~hus maintains the effectiveness of the dried multi~layer film as a chemical barrier to oxygen. By way of contrast, in the example represented by curve (~) r the intense enzymatic activity in the liquid paint results in the oxidation of a substantial quantity of glucose during the drying of the paint.
When applying a paint of the type represented by curve (2) in an aqueous dispersion of white color on sand blasted steel, a complete absence of "flash rusting" was observed. However, without the presence of the enzyme-substrate couple, rust stains are clearly apparent through the paint. The incorporation of the enzyme-substrate couple is a particularly desirable manner to avoid the corrosion of the container in which it is stored by liquid paints.
EXAMP~E 2 The activity of an enzyme in an aqueous dispersion of a styrene~aceylate resin was also studied. The resin Ercusol AS
250 was selected due to th~ fact that its aqueous dispersion, widely used in the formulation of anti-corrosion paints, allows an easy dissolution of the glucose and enzyme and because the concentration of dissolved 2 may be readily measured. ~ive (5 g) grams of glucose and 0.1 ml of the enzyme of example 1 were added to 100 ml of the Ercusol AS 250 dispersion. The 2 content of the air saturated solution was initially 8 ppm and, dropped to less than 1 ppm within one hour. The solutivn was stirred gently to allow correct measurement with an 2 probe.

_~_ The solution was then placed in storage for 8 weeks in a closed flask. Thereater, 0~ was bubbled through the solution until an oxygen content of 18 ppm was measured. Two hours s~bsequent to the measurement of the 18 ppm 2 content, the quantity of dissolved 2 had decreased to 3 ppm.
A second 2 bubbling was carried out in the same solution for several hours until an 2 content of 40 ppm was measured, this level being commensurate with the saturation of this solution with 2~ During the second 2 bubbling, the enzymatic activity resulted in the oxidation of a large quantity of the glucose contained in the solution as shown by the following observations:
(1~ After plugging the flask containing the solution, the reduction in 2 content was measured over a period of time. The consumption of oxygen was found slower than during the first bubbling since 42 hours were necessary for the oxygen content to fall from the 40 ppm level to 13.S ppm.
(2) Upon adding a new quantity of substrate, 5 g, without any adclitional enzyme, the 2 consumption was accelerated and fell from 13.5 ppm to 0.3 ppm within 24 hours.
The above observations clearly show that the enzymatic activity will be retained in a dispersion containing the enzyme and its 2 substrate even after storage in a closed container at room temperature.

A coating was prepared by adding, to the 106 ml of the above-mentioned commercially available Primalo paint, 5 g of ~7~7~

glucose and/or 0 45 g glucose oxidase. These paints were applied, in two layers, to a tin plate in the amblent atmosphere. After drying in air, the plate was placed in a closed enclosure with 100% L elative humidity. The coating layers were not, however, in contact with liquid water. Various tests were made and the variation in 2 content with time was measured. Referring to FIGU~E 2, the value of 100~ 2 corresponds to the usual 2 content in air.
Curve (l) depicts the 2 consumption for a tin plate which did not have a protective coating.
Curve (2) was plotted for a plate having applied thereto two successive layers of paint with each layer containing the indicated amount of glucose but no en~yme.
Curve ~3) is for a plate to which were applied successively a first layer of paint containing the indicated quantity of enzyme and a second layer o~ paint containing the indicated quantity of glucose.
Curve ~4) is for a plate with the same two layers as reported above with a plate o~ curve (3) but with the layers being reversed, i.e., the layer first applied to the plate contained the glucose and the outer layer contained the enzyme.
Curve (5) is for a plate which had applied thereto two ¦ successive layers of paint of identical composition, i.e., each ¦ layer contained both the indicated quantity of glucose and ¦ enzyme.
¦ The curves of Example 3 clearly show that the activity of ¦ the glucose oxidase is maintained in a commercial paint, ¦ particularly a water-based paint, during storage and also after J~1'7'70~ ~

the application of the paint to a base. Thus, it will be obvious to those skilled in the art that the enzyme-substrate couple of the present invention is a new and valuable corrosion inhibitor which, because of its characteristics of non-dissociability and specificity, are particularly useful in the paint industry.
In the embodiment of the present invention wherein glucose and glucose oxidase are employed, glu¢onic acid is formed. The metal-sequestering power of gluconic acid is well known and thus the by-products of the deoxygenizing reaction of the present invention will further increase the corrosion inhibiting characteristics of compositions in accordance with the invention.
The corrosion inhibiting systems of the present invention can be substituted totally or partially for the toxic pigments previously employed. Further~ the present invention may be utilized to improve the corrosion preventative characteristics of existing protective ~oatings and to reduce or eliminate the toxicity of such coatings.
Examples of industrial uses of the present invention are the prevention of corrosion of metallic containers~ the prevention of skin formation on oxidative drying paints, the suppression of flash rusting and, by consumption of the molecular oxygen migrating through a coating film, corrosion inhibition and thus an improvement in anti-corrosion paints.
It is particularly to be noted that while the above discussion of preferred embodiments has made reference to paints, the present invention is applicable to other coatings such as fillers and varnishes. It is also to be observed that, ' _~,_ l~'Y~7~

while the mixture of the enzyme and substrate with the coating composition during the preparation thereoE has been discussed, the enzyme-substrate couple can be provided in a form of separate liquid preparations which will be mixed at the time of application of the coating a base. Similarly, one or both of the en~yme and substrate may be added to a primer coating and the other or both constituents included in a second or intermediate coating or coatings.
A particularly significant aspect of the present invention is that the enzymes employed do not need to be of pure grade.
Thus, the technical grade enzyme mentioned above, which is of moderate expensive, is more than adequate for the practice of the present invention and it is possible to employ a less purified, and thus less expensive, material~ Also, it is to be noted that the presence o~ catalase, instead of being an inconvenience, is advantageous because it destroys the hydrogen peroxide produced by the action of the glucose oxidase.
¦ While preferred embodiments have been described1 various modifications and suhstitutions may be made thereto without departing from the spirit and scope of the invention. Thus, by way of example only~ the present invention encompasses the addition of anti-microbian agents or other additives to a coating composition produced in accordance with the present invention to suppress the growth of mold or bacteria~
Accordingly, it will be understood that the present invention has been described by way of illustration and not limitation.
What is claimed is:

-1~-

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the enhancement of an oxidation preventing coating comprising:
providing an enzyme-substrate couple in the coating whereby catalytic deoxygenation will occur therein, the enzyme being selected from the group of oxygenases and oxidases and the substrate being an organic material which is oxidized by the enzyme, both the enzyme and substrate material being added to the coating.

2. The process of claim 1 wherein the enzyme and sub-strate material are separately added.

3. The process of claim 1 wherein the coating is applied in at least two layers, the enzyme being included in one layer and the substrate material being included in the other layer.

4. The process of any one of claims 1, 2 and 3 wherein the substrate material comprises a precursor for the substrate required by the enzyme.

5. The process of any one of claims 1, 2 and 3 and comprising the additional step of incorporating the enzyme in a micromolecular network or in microcapsules.

6. The process of any one of claims 1, 2 and 3 wherein the substrate material comprises a precursor for the substrate required by the enzyme, and comprising the additional step of incorporating the enzyme in a micromolecular network or in microcapsules.

7. The process of any one of claims 1, 2 and 3 comprising the additional step of selecting the enzyme from the group consisting of glucose oxidase, lipozygenase, glycollate oxidase, galactose oxidase, alcohol oxidase, diamine oxidase and aldehyde oxidase.

8. The paint or varnish coating composition including therein:
an enzyme; and an organic substrate material which is oxidized by the enzyme whereby oxygen in said composition will be consumed by catalytic deoxygenation.

9. The paint or varnish coating composition of claim 8, wherein the coating composition is a paint and wherein the enzyme and substrate are separately mixed with quantities of the paint, the separately mixed quantities being success ively applied to a base to form a multi-layer coating containing an enzyme-substrate couple.

10. The paint or varnish coating composition of claim 8 or 9 wherein the enzyme is selected from the group comprising glucose oxidase, lipozygenase, glycollate oxidase, galactose oxidase, alcohol oxidase, diamine oxidase and aldehyde oxidase.

11. The paint or varnish coating composition of claim 8 or 9 wherein the substrate material comprises a precursor for a substrate required by the enzyme.

12. The paint or varnish coating composition of claim 8 wherein the enzyme is glucose oxidase and the substrate is glucose.

13. The paint or varnish coating composition of any one of claims 8, 9, and 12 wherein the coating material is a paint based on an aqueous emulsion.

14. A process for preventing oxidation of a metal base comprising:
coating the base with a formulation which includes an enzyme-substrate couple, the enzyme being selected from the group of oxygenases and oxidases, whereby consumption of oxygen will occur in the coating through catalytic deoxygenation.

15. The process of claim 14 wherein the coating is performed in two steps whereby an enzyme-substrate couple is not established until the base is coated.

16. The process of claim 14 further comprising:
mixing the substrate with a paint; and adding the enzyme to the paint to form the coating composition.

17. The process of claim 14 further comprising:
mixing the substrate with the enzyme; and adding the mixture containing the enzyme and sub-strate to a paint.

18. The process of claim 14 further comprising:
adding substrate material to a paint to form a first coating composition;
adding the enzyme which reacts with the substrate to the paint to form a second coating composition; and applying the first and second coating compositions separately to the base.