Compositions: coating or plastic – Coating or plastic compositions – Corrosion inhibiting coating composition
Reexamination Certificate
2000-08-25
2002-09-10
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Corrosion inhibiting coating composition
C106S014220, C106S014240, C106S014340, C106S014350, C106S014360, C106S014370, C106S014420, C106S206100, C106S216100
Reexamination Certificate
active
06447590
ABSTRACT:
The invention relates to the field of compositions for the treatment of metal surfaces, intended to provide both a prelubricating effect and a temporary corrosion protection effect.
The prelubricating effect is characterized by an improvement in the tribological properties of the surface treated in this way and then oiled in a conventional manner; this effect is beneficial for facilitating the forming operations, for example drawing operations.
The corrosion protection effect is temporary in the sense that a simple cleaning of the treated surface allows the treatment layer to be removed; this ability to be cleaned is important, for example when preparing to paint the surface.
These metal surface treatments are generally carried out in two steps:
application of a liquid homogeneous layer of the treatment composition on the surface;
drying of the layer applied, suitable for removing almost all of the liquid water from this layer, at a low enough temperature to avoid any deterioration of the treatment components.
The so-called “dry” film that is obtained may then also contain large amounts of water included in the composition of the film (as water of hydration, for example).
Compositions are sought which can be applied homogeneously as thin films and are effective with a low surface density; the desired surface density, measured in the dry state, is then generally less than 2.5 g/m
2
.
Conventionally, these surface treatment compositions comprise, as essential components in solution or in emulsion, at least one sufficiently film-forming binder, at least one lubricant and at least one surfactant for promoting film spread over the surface to be treated.
In the case of an emulsion, the emulsifiers used generally have a surfactant effect promoting film spread.
These treatment compositions generally furthermore comprise corrosion inhibitors which may also have a surfactant effect.
The invention relates more particularly to the field of compositions for treating a metal surface, which comprise a binder based on pregelatinized starch and are intended to form a homogeneous dry film on this surface.
Pregelatinization of the starch is a specific operation, carried out by the producer, which destroys the crystalline structure of the starch granule and reduces the hydrogen bonds responsible for this structure. This operation is carried out, at approximately 100° C., by rolling or extension. Pregelatinized starch is then obtained which is in the form of a powder. It is this operation, known per se, which allows the (partially gelatinized) starch to be soluble in cold water and allows low-viscosity solutions to be obtained. This pregelatinization operation will make it possible to control (particularly with regard to viscosity) the phenomena of gelatinization or gelling in the presence of water.
Starch is essentially a homopolymer of D-glucose (highly hydroxylated glucosyl monomer) composed mainly of a mixture of two types of polymer:
amylose, an essentially linear molecule, capable of complexing hydrophobic molecules such as fatty acids, able to react with emulsifiers and known for its film-forming properties—T(melting)≈120° C.;
amylopectin, an essentially branched molecule having a very high molecular mass (10
7
to 10
8
)—T(melting)≈45° C.
The amylose content of the starch depends on its plant origin, as indicated in Table I: certain genetically modified varieties may give starches richer in amylose.
TABLE I
Average amylose contents of various starches
Plant origin of the
Amylose content
starch
(%)
Normal maize
28%
waxy maize
<1%
Maize “rich in amylose”
65-70%
Corn
25-28%
Potato
19-22%
Waxy potato
<1%
Smooth pea
33-35%
The binding effect of the pregelatinized starch results from chemical mechanisms described below.
The water absorption by the starch grains is manifested by a reversible swelling of the amorphous part and the formation, firstly, of interchain hydrogen bonds; secondly, the water acts as a plasticizer which allows alignment of the crystallites by extension of the inter-crystalline amorphous phases and a large part of the absorbed water is then bound to the structure: at least 30% water is necessary for the plasticization to occur; the plasticization lowers the glass transition temperature (of the amorphous part).
A pregelatinized starch gel can then be described as a discontinuous phase composed of swollen starch granules enriched with amylopectin dispersed in a continuous phase of dissolved amylose.
Among the various products coming from the pregelatinization of starches, there are, among others:
fluid starches;
crosslinked starches;
dextrins, which are linear or branched oligosaccharides generally containing from 5 to 10 glucosyl units;
starch esters, such as starch acetates or phosphates;
starch ethers, such as O-alkyl starch ethers.
To achieve these various products coming from the gelatinization of starches, various modification means are used, such as “enzymatic” modifications, “depolymerization” modifications and chemical “crosslinking”, “substitution”, “dextrinization” or “saccharification” modifications.
Document FR 2,508,051 (ROQUETTES) describes (see especially claim
13
) a surface treatment composition, especially for temporary corrosion protection, comprising, with respect to the dry matter:
from 30 to 95% of an extruded waxy starch;
from 1 to 25% of a plasticizer;
from 0.5 to 5% of a surfactant or wetting agent.
According to that document (page 5, lines 17-32), the plasticizer added to the starch-based composition makes it possible to prevent crazing and flaking of the film resulting from the treatment; this plasticizer is chosen from the group comprising not only sorbitol, a polyethylene glycol or glycerol, but also glucose syrups, lactates, gluconates, emulsifiable waxes, urea, thiourea and nitrates.
According to that document (page 6, lines 2 et seq), for effective temporary protection in wet environments, the treatment composition must also contain a resin or an insolubilising or crosslinking agent, generally 2 to 30%, such as resorcinol-formaldehyde or cyanamid-formaldehyde; consequently, the film resulting from the treatment is at least partially crosslinked, thereby impairing its ability to be cleaned.
According to that document (page 7, lines 27-28), the surface treatment composition may also contain anti-rust agents, that is to say a corrosion inhibitor.
That document describes the application of this composition to steel surfaces (example 1), but, in order to obtain effective corrosion protection, the surface density to be applied must be very high, namely 100 g/m
2
on page 16 and 200 g/m
2
on page 19.
The object of the invention is to provide a surface treatment composition which is effective at much lower surface densities, both for temporary corrosion protection and for prelubrication; the object of the invention is to provide an easily cleanable surface treatment composition.
For this purpose, the subject of the invention is an easily cleanable aqueous composition for treating a metal, especially steel, surface, characterized in that it comprises, as an emulsion, at least 2% by weight of pregelatinized starch and at least 1% of vegetable wax or oil, or at least 1% of synthetic oil or wax of equivalent chemical nature.
Using specifically an emulsified plant-based oil or wax in the treatment composition based on pregelatinized starch it is thus possible, according to the invention, to obtain both effective corrosion protection in a wet atmosphere and a prelubricating effect, even if this composition is applied as a thin film and without a crosslinking agent, so as to be easily cleanable.
The invention may also have one or more of the following characteristics:
the said starch is crosslinked;
the said starch is a potato or maize starch;
the amylose content of the said starch is less than or equal to 25%;
the pH of the composition is between 6.5 and 8;
the weight content of pregelatinized starch is less than or equal to 7% and the weight content of oil or wax in the said composition is less than or equal to 5%;
the said vegetable wax or o
Kefferstein Ronald
Scherer Lothaire
Green Anthony J.
Sughrue & Mion, PLLC
Usinor
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