Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-05-21
2002-10-01
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S833000, C106S014110, C427S155000, C422S007000
Reexamination Certificate
active
06458887
ABSTRACT:
The invention relates to a process for preparing an aqueous emulsion based on polyacrylates, intended for treating metal, in particular steel, surfaces so as to form, on this surface, a prelubricating dry film for protecting against corrosion.
The protection is considered to be temporary if it is not designed to be permanent; in this case, the applied film should be easy to remove or “clean” when it is desired to make the metal surface “bare” again, for example for forming, painting or enameling.
It is desirable for the protective film to have lubricating properties, either by itself, or in synergy with oils which would be applied on the film; these oils may be whole oils or soluble oils, that is to say oil-in-water emulsions.
These lubricating properties, combined or otherwise with those of oils, are very useful for forming operations, in particular sheet metal drawing operations.
Aqueous compositions containing in suspension both oil and acrylic polymers are known.
Patent application WO 96-37SS4 by the company HENKEL describes a composition prepared from acrylic “terpolymer” latexes, which is intended to be applied on a metal, in particular steel, surface; these polymers are prepared from the following monomers, the values of the proportions of these monomers being given relative to the total mass of polymers in the composition:
A: methyl methacrylate or acrylonitrile, which provides good protection to the surface against corrosion (page 7, line 5) in particular if 30%<A<80%.
B: ethyl or butyl acrylate, which reinforces the flexibility of the film applied on the surface (page 7, line 11) if 10%<B<60%.
C: acrylic or methacrylic acid whose proportion should remain low—2%<C<10%—for preserving stable emulsions and obtaining a “suitable” deposit on the surface.
The polymerization of the monomers is carried out in aqueous emulsion; the average molecular masses obtained, M, are between 10
5
and 10
6
.
For a purely “temporary” (and nonpermanent) protection against corrosion, it is advisable to use compositions which do not risk becoming crosslinked under the application and drying conditions, so that the deposit—or protective film—obtained can be cleanable.
To improve the drawing operation for treated surfaces, that is to say to confer prelubricating properties on these compositions, it has been proposed to incorporate lubricating materials therein, as described by the documents cited below.
Patent EP 606 257 by the company PPG describes a composition intended to treat metal surfaces so as to form, on this surface, a temporary protective film against corrosion; the film obtained can be cleaned, is lubricating and is “weldable”.
The compositions described comprise:
(a) an acid functional acrylic polymer having as characteristics:
glass transition temperature: −30° C.<Tg<100° C.,
average molecular mass: 3 000<M<100 000.
(b) a lubricating material, in a proportion of 5 to 70%, preferably 5 to 20%, “in a quantity suitable for improving drawability” chosen from a hydrocarbon wax, carnauba wax or beeswax.
(c) an aqueous-alcoholic solvent where the alcohol does not contain more than 4 carbon atoms per molecule.
The flash point of these compositions should be greater than 37.7° C.
As an example of monomers leading to an acid functional polymer, acrylic acid, methacrylic acid and the esters of these acids are mentioned.
To incorporate the lubricating material into these compositions, it is proposed to prepare these compositions by polymerization in emulsion and in the presence of the lubricating material: “in the preferred method of preparation where the polymer is prepared with the lubricating material, it is thought that there is partial grafting of the polymer with the lubricating material.” (Col. 4, line 35).
Patent EP 421 250 by the company PPG describes a composition intended to treat sheet steel surfaces so as to form, on this surface, a temporary protective film against corrosion; the film obtained is cleanable, “drawable”, “weldable”; it is also “formable” in the sense that the bending of a sheet metal coated with this film does not cause cracks in the film.
The compositions described comprise:
an acid function polymer prepared in solution from:
at least one monomer comprising an acid function, in a proportion ≧5% (typically 10 to 30%), such as for example an acid chosen from acrylic, methacrylic, crotonic, itaconic or maleic acid;
at least one ethylenically unsaturated monomer such as for example a styrene, a vinyltoluene, an acrylic or methacrylic acid ester such as methyl methacrylate (MMA), butyl acrylate (BuA) or 2-ethylhexyl acrylate;
an oil, in a proportion ≧5% (typically 10 to 30%), whose melting point is close to 60° C., such as hydrocarbon wax, beeswax, carnauba wax, petroleum wax, or even a vegetable or hydrocarbon oil, or a fatty acid.
To improve the drawability of a sheet metal coated with this film and its cleanability, it is proposed to prepare these compositions by polymerization, in a solvent medium, of an organic mixture of monomers incorporating oil; the average molecular mass of the polymer obtained is between and 9×10
4
; these compositions are then emulsified so as to be easily applied as a thin film on sheet metals.
Because of the absence of “external” surfactants, the protective film obtained is less sensitive to water, which improves the resistance to corrosion.
This document gives examples of composition (samples: A, B, C) with the proportion (%) of acrylic components (BuA: butyl acrylate—Styr. : styrene—AA: acrylic acid—MDAEMA:dimethylaminoethyl methacrylate) and of oil (wax) and with the glass transition temperature of the polymer obtained; Table I summarizes Examples A, B and C.
TABLE I
EP 421 250-Examples of treatment composition
Sample
No.
Tg
Acrylic components (%)
Oil
A (≡E4)
+5° C.
BuA: 47
Styr.: 30
AA: 20
Wax: 15%
MDAEMA: 3
B (≡E2)
−11° C.
BuA: 60
Styr.: 20
AA: 20
Wax: 15%
C (≡E1)
−27° C.
BuA: 73
Styr.: 7
AA: 20
Wax: 15%
To apply the acrylic emulsion on the surface to be treated and to form a protective film, it is diluted in water until a proportion of solids of between 12% and 20% is obtained and it is applied on the sheet metal to be treated so as to obtain, after drying, a deposit of between 1 and 3 g/m
2
; the appropriate dilution of the solution and surface density depend on the roughness and the porosity of the substrate.
One disadvantage of the temporary protective compositions with improved lubricating properties described in documents EP 606 257 and 421 250 is that the protective film has a fatty character; this fatty character results from the proportion of oil in the composition and from the thickness of the deposit to be applied which are necessary in order to obtain both the desired effective protection and lubricating effect.
The object of the invention is to provide a process for preparing an emulsion of acrylic or methacrylic polymers for protecting against corrosion which, although containing little oil, preserves good lubricating properties while having a dry appearance after application in a film on sheet metal and drying.
The aim of the invention is also to improve the stability of the emulsions so as, in particular, to facilitate their application on sheet metal as a thin film having, in the dry state, a surface density of less than 6 g/m
2
.
The document JP 82 108114 A describes a process for preparing acrylic emulsions containing a wax (example of melting point: 60° C.) intended for the hydrophobization treatment of textile fibers; according to the process described, an emulsion of acrylic monomers and an emulsion of wax are prepared separately, then the emulsions are mixed, and the mixture of emulsions is polymerized; nothing indicates that the emulsion obtained has only one homogeneous organic phase; it is even possible that the emulsion obtained is composed of two phases, one polymeric, the other oily or waxy; it therefore stems therefrom that on applying this emulsion on a sheet metal, a film would be obtained having a fatty c
Calleja Agnès
Legros Philippe
Riess Gerard
Sully Yves
Sughrue & Mion, PLLC
Unisor
Yoon Tae H.
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