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
2001-05-11
2002-09-24
Michl, Paul R. (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...
Reexamination Certificate
active
06455625
ABSTRACT:
The invention relates to a composition for the application of enamel and to a process for enameling metal components.
The document U.S. Pat. No. 5,325,580—Bayer—discloses a process for the production of shaped components made of enameled sheet metal, in which:
before shaping, at least one enamel application composition layer comprising a vitrifiable enamel frit dispersed in a polymer binder is applied to a steel sheet and then this at least one layer is dried and/or cured,
the metal sheet is subsequently shaped into the shape of the component,
optionally, at least one other layer of vitrifiable enamel frit is subsequently applied to the component,
the component is subsequently fired at a temperature of between 560° C. and 850° C. under conditions suited to the nature of the steel and of the enamel frit which are used, in order to obtain vitrification of the enamel.
The optional curing before shaping is a crosslinking curing of the polymer binder, whereas the firing after shaping is a vitrification firing of the enamel at a temperature greater than the glass transition temperature T
g
of the vitrifiable enamel frit.
Thus, the temperature of the first curing (crosslinking) is far below the temperature of the second firing (vitrification).
During the first curing, the polymer binder is “consolidated” by crosslinking, whereas, during the second firing, it is “removed” by thermal decomposition and/or pyrolysis.
The metal sheet obtained is coated with a wholly inorganic layer of “vitreous enamel” comprising a continuous vitreous phase in which inorganic opacifying and/or coloring fillers are dispersed; throughout the continuation of the document, the terms “vitrifiable enamel” or “vitreous enamel” are denoted more concisely by “enamel”; this adopted term is thus completely different from vitreous or nonvitreous polymer coatings with a high content of fillers formed of inorganic components, sometimes denoted as “enamel”, in particular because they do not comprise a continuous vitreous phase.
Such a process is highly advantageous as application to flat sheet metal of an enameling layer before shaping makes it possible to avoid all the complications relating to an operation for the application of the same layer to a preshaped component.
Furthermore, steel sheets precoated with enameling composition but not yet shaped can, in this intermediate state, be transported and stored while awaiting the shaping and the vitrification firing of the enamel.
The enamel application composition essentially comprises a polymer binder in solution in a solvent and an enamel frit in suspension in the solution; in addition, this composition generally comprises a suspension (or antisettling) aid, wetting agents and air release agents.
According to Example 1 of the document U.S. Pat. No. 5,325,580, use is made, as binder, of thermoplastic blends of polyhydroxypolyacrylate and polyhydroxy-polyester polymers (proportions 9:1 to 6:4); these blends are devoid of nitrogen or of halogens; these blends do not crosslink during the drying operation (<50° C.) carried out after application of the enameling composition.
In these blends, the percentage by weight of “hydroxyl” groups is between 0.5 and 10% by weight.
The viscosity of the 50% solutions of these polymers is generally between 3 000 and 10 000 mPa.s at 23° C.
The choice is made, as polyhydroxypolyesters, of known polyesterpolyols which are, for example, based on (1) aliphatic, aromatic or cycloaliphatic dicarboxylic acids (and corresponding anhydrides) and (2) aliphatic polyhydric alcohols.
Use is made, for example, of dicarboxylic acids having an average molecular mass of between 146 and 150, such as adipic acid, phthalic acid, tetrahydro-phthalic acid, hexahydrophthalic acid or their mixtures.
Use is made, for example, of polyhydric alcohols having a molecular weight of between 62 and 150, such as ethylene glycol, propylene glycol, butane-1,4-diol, hexane-1,6-diol, glycerol, trimethylolpropane or their mixtures.
These polyesterpolyols are prepared conventionally from these dicarboxylic acids and these polyhydric alcohols and, in the polyhydroxypolyester, the proportion of “hydroxyl” groups is adjusted according to the excess of polyhydric alcohol.
According to Example 1 of the abovementioned document, it is thus possible to use a thermoplastic binder comprising 80% of hydroxypolyacrylate (obtained by radical polymerization in the presence of di-t-butyl peroxide) and 20% of hydroxypolyester (obtained by polymerization by condensation of a mixture of phthalic anhydride, adipic acid and 1,2-propylene glycol with trimethylolpropane).
According to Example 4 of the document U.S. Pat. No. 5,325,580, use is made, as binder, of a thermosetting blend of acid-functionalized polyhydroxy-polyacrylate polymers and of epoxy-functionalized polyhydroxypolyacrylate polymers (in this instance: glycidyl methacrylate); this blend then crosslinks during the curing operation (>50° C., in this instance 350° C.), carried out after application of the enameling composition, by reaction of the acid functional groups with the epoxy functional groups of the polymers.
Use is made, as frit, of, for example, a vitreous base suited to the enameling of sheet metal and exhibiting the following composition:
For the base enameling, intended for the first layer in contact with the metal:
Frit
Weight %
SiO
2
40-51
Al
2
O
3
1-5
B
2
O
3
11-18
K
2
O
0-5
CaO
2-13
Na
2
O
7-15
Li
2
O
0-6
BaO
0-15
ZrO
2
0-6
CoO
0.5-1.5
MnO
0-2
CuO
0-3
NiO
1-4
P
2
O
5
0-3
F
2
0-3
For the “white” enameling, intended for the surface layer, applied before or after shaping:
Frit
Weight %
SiO
2
35-45
Al
2
O
3
0-4
B
2
O
3
14-20
K
2
O
2-9
Na
2
O
7-11
Li
2
O
0-2
TiO
2
13-22
ZnO
0-2
MgO
0-2
CaO
—
P
2
O
5
0-4
F
2
0-5
Use is made, as solvent, of, for example, a mixture of xylene and methoxypropyl acetate, or an aromatic mixture with a high boiling point, such as the product referenced Solvesso 150 from Exxon, or cyclohexanone, or glycol ether esters.
Use may be made, as agent for holding in suspension, of, for example, magnesium silicate hydrate.
To prepare the enamel application composition, the following procedure, for example, is carried out:
a component of the polymer binder is heated,
the agent for holding in suspension is added thereto, slowly and with stirring,
the frit is subsequently added, followed by the solvent with the wetting agents, the air release agents and other additives,
the mixture is ground until a satisfactory dispersion of the enamel frit is obtained,
after cooling, the other component of the polymer binder, for example the epoxy-functionalized polyacrylate, is subsequently added.
Introduction of the binder in two stages is particularly important in the case of thermosetting binders, as it is a question of preventing or of limiting the crosslinking of the mixture at this stage in the preparation.
The proportions of the main constituents of the enamel application composition obtained are given in the following table:
U.S. Pat. No. 5 325 580:
Example 1
Example 4
Solvent
16.1%
23.9%
Binder
17.1%
14.0%
Frit
63.3%
56.2%
Additives:
3.5%
5.9%
By expressing the viscosity of the enamel application composition thus obtained according to Standard DIN 53 211 (by using a DIN-4 flow cup with an opening of 4 mm), times of between 40 and 200 seconds are obtained, according to the application method used and the desired coat thickness (for example 110 &mgr;m after drying).
The enamel application compositions obtained are subsequently applied with a roll coater on untreated steel sheets which have simply been degreased.
To obtain significant enamel thicknesses, it is possible to apply a composition in several successive coats (2 wet coats with a thickness of 110 &mgr;m for example).
In the case of a polyacrylate-polyester thermoplastic binder (Example 1 already mentioned), drying is subsequently carried out of the coat applied at ambient temperature for approximately 1 minute.
In the case of a polyacrylate thermosetting binder based on a blend of acid-functionalized polymers and of
Cholet Vincent
Genevay Jean-Pierre
Hellouin Rémy
Michl Paul R.
Sollac
Sughrue MIon, PLLC
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