Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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
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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
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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
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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.
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~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
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¦ ~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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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.
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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.
EXAMPLE 3
A coating was prepared by adding, to the 106 ml of the
above-mentioned commercially available Primalo paint, 5 g of
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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
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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,
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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:
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