Cleaning and liquid contact with solids – Processes – Miscellaneous
Reexamination Certificate
1999-03-17
2001-10-09
Kopec, Mark (Department: 1751)
Cleaning and liquid contact with solids
Processes
Miscellaneous
C134S025200, C510S179000, C510S221000, C510S228000, C510S233000, C510S238000, C510S435000, C510S466000, C510S509000, C510S511000
Reexamination Certificate
active
06299701
ABSTRACT:
The present invention relates to a dishwasher detergent composition based on an alkali metal silicate, which is not corrosive towards glass, crystal, porcelain or patterns; it is also directed towards the use of the said non-corrosive dishwasher detergent composition, as well as to the dishwasher-washing process using it.
One of the major problems encountered in the use of dishwashers is the phenomenon of irreversible corrosion of the items being washed (glass, crystal, porcelain) which is observed after repeated washing.
In the case of glass, this irreversible corrosion is reflected first in a phenomenon of iridescence and then in a frosted white appearance of the glass; this is accompanied by a loss of mass.
The phenomenon of glass corrosion by aqueous solutions has been the subject of studies, in particular in the field of stability of inertization glasses for nuclear waste (“Corrosion of Glass, Ceramics and Ceramic Superconductor, Principles, Testing, Characterization and Application” edited by D. E. Clark and B. K. Zoitos, Noyes Publications, 1992). In applications of this type, the conditions under which the glass is attacked do not correspond to those encountered during washing in a dishwasher, whether as regards the pH of the solutions, the temperature or the dynamic nature of the corrosion in a dishwasher.
The use of silicates as detergent adjuvants in dishwasher detergent compositions is well known; certain authors mention the ability of these adjuvants to limit the corrosion of glass, porcelain and glazing on articles (E. J. Schuck, Proc. Mid-Year Meet, Chem. Spec. Manuf. assoc. (1972), Vol. 58, pp. 82-85; M. Hellsten, Tenside detergents, 9, Heft 4, pp. 178-182 (1972); U.S. Pat. No. 3,494,868; WO 96/17047).
Two types of formulations should be distinguished in this context (W. Buchmeir, Glatech. Ber. Glass Sci. Tecnol. (1996) No. 6, pp. 159-167),
very alkaline formulations based on metasilicate, developing a pH of about 12 to 13, giving little visible corrosion of plain glass, but leading to damage to patterned articles and glazings, and
moderately alkaline formulations, developing a pH of about 9 to 11.5, giving effective protection of patterned articles and glazings, but resulting in strong visible corrosion of clear glass.
The use of these two types of formulations leads to a loss of mass and to damage to the articles.
An in-depth study of the mechanisms of corrosion of glass and crockery has shown that this corrosion is due in particular to hydrolysis of the glass lattice accompanied by a phenomenon of leaching of the ions from the glass into the bath.
The Applicant has found a solution which simultaneously solves both problems, i.e. of loss of mass and of damage to articles.
The Applicant has put forward the hypothesis that the use of a washing bath comprising in its chemical composition a “silicate portion” similar to that of the silicic lattice of glass would eliminate the phenomenon of hydrolysis and thus limit, or even remove altogether, the corrosion of the glass at the hydrolysis stage by cleavage of Si—O—Si bonds in the glass lattice.
The Applicant has found that the phenomenon of glass corrosion by repeated washing in a dishwasher is greatly reduced, or even stopped, by the presence in the washing bath of a sufficient amount of protonated silicic monomer Si(OH)
4
; it has observed that this performance is also obtained on porcelain, patterns on glass or on porcelain, and crystal.
A first subject of the invention consists of the use, to eliminate or limit the corrosion of glass, crystal or porcelain articles and patterns on glass or porcelain by repeated washing in a dishwasher, of a detergent composition which generates a washing medium with a concentration of protonated silicic monomer Si(OH)
4
of at least 2.5×10
−3
mol/liter of washing medium, preferably of at least 3×10
−3
mol/liter of washing medium, most particularly from about 3×10
−3
to about 9×10
−3
mol/liter of washing medium.
A second subject of the invention consists of a process for the non-corrosive washing in a dishwasher of glass, crystal or porcelain articles which may be patterned, by using a detergent composition which generates a washing medium with a concentration of protonated silicic monomer Si(OH)
4
of at least 2.5×10
−3
mol/liter of washing medium, preferably of at least 3×10
−3
mol/liter of washing medium, most particularly from about 3×10
−3
to about 9×10
−3
mol/liter of washing medium.
The said washing medium preferably has a pH of greater than 9.8, most particularly from about 9.9 to about 11.1.
One means for obtaining this sufficient concentration of protonated silicic monomer Si(OH)
4
in the washing bath consists in using, via a detergent composition, a sufficient amount of at least one alkali metal silicate in order to obtain a high content of SiO
2
capable of generating the said monomer and in promoting the formation of the said monomer by adjusting the pH of the bath by means of the choice of the nature of the said silicate and of the other ingredients of the composition as a function of the silicate chosen.
Any amorphous or crystalline soluble alkali metal silicate with an SiO
2
/M
2
O ratio from about 1 to about 4.2 allows the desired aim to be achieved. Preferably, it is an amorphous soluble silicate.
One particularly favourable means consists in using, in the detergent composition, at least one soluble alkali metal silicate with an average SiO
2
/M
2
O molar ratio from about 2.5 to about 4.2, which is preferably amorphous, making it possible to obtain in the washing bath a high content of SiO
2
and promoting a low bath pH which is compatible with an adequate content of protonated silicic monomer Si(OH)
4
.
The term “soluble” silicate is intended to refer to any silicate in which at least 50% of the silica lattice is dissolved in the washing medium after 10 minutes under the washing conditions.
The term “average” SiO
2
/M
2
O molar ratio is intended to refer to the ratio of the total number of moles of SiO
2
to the total number of moles of M
2
O arising from the alkali metal silicate(s) present in the detergent composition.
A third subject of the invention consists of a dishwasher detergent composition based on at least one alkali metal silicate with an average SiO
2
/M
2
O molar ratio from about 1 to about 4.2, preferably from about 2.5 to about 4.2, M representing an alkali metal, this composition being non-corrosive towards glass, crystal, porcelain and patterns and generating, at the working concentration, a washing medium with a concentration of protonated silicic monomer Si(OH)
4
of at least 2.5×10
−3
mol/liter of washing medium, preferably of at least 3×10
−3
mol/liter of washing medium, most particularly from about 3×10
−3
to about 9×10
−3
mol/liter of washing medium.
In order to assist in the reading, the expression “alkali metal silicate” will be intended to refer hereinbelow both to an alkali metal silicate alone and to a mixture of several alkali metal silicates which can have different SiO
2
/M
2
O molar ratios; the expression “average SiO
2
/M
2
O molar ratio” thus corresponds either to a silicate alone, when only one silicate is present, or to a mixture of silicates, when several silicates with different molar ratios are present.
The concentration of protonated silicic monomer Si(OH)
4
in the washing medium depends on the total concentration of soluble SiO
2
in the washing medium and on the bath pH.
It is measured at 25° C. and expressed in mol/liter, according to equation (I) below:
[Si(OH)
4
]=[total SiO
2
in the washing medium]/{1+10
(pH−pK1)
+10
(2pH−pK1−pK2)
} (I)
in which equation:
“pH” represents the pH of the washing medium at 25° C.
“pK1” represents the first pKa acidity constant of the silicic acid corresponding to the equilibrium Si(OH)
4
<===> (SiO
4
H
3
)
−
; pK1 is equ
Aubay Eric
Froute Agnès
Guirauden Aude
Joubert Daniel
Burns Doane Swecker & Mathis L.L.P.
Kopec Mark
Mruk Brian P.
Rhone-Poulenc Chimie
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