Scale inhibitors

Details Scale inhibitors Scale inhibitors

2000-07-10

2002-05-28

Kopec, Mark (Department: 1751)

Liquid purification or separation

Processes

Preventing, decreasing, or delaying precipitation,...

C210S699000, C210S700000, C252S180000, C510S253000, C510S247000, C510S223000, C510S230000, C510S361000, C510S434000, C510S476000, C510S533000, C134S022190

Reexamination Certificate

active

06395185

ABSTRACT:

The present invention relates to the inhibition of (poly)phosphate salt scale in aqueous systems.
It is well known that in hard water areas high concentrations of magnesium and calcium ions can lead to the formation of insoluble calcium and magnesium carbonate deposits (scaling) on washed articles. This is visible, as a white deposit, particularly on glassware when such articles, are washed in automatic dishwashing machines, and also on machine parts especially heater elements. Similar precipitation problems also occur in laundry washing, these cause the fabric to become stiff and rough to the touch and give coloured fabrics a faded appearance. Tap water with relatively high water hardness and the use of insufficient water softening chemicals increase the problem dramatically. Other factors involved in causing scaling are temperature (more scaling occurs at higher temperatures) and pH (higher pH also increases scaling). Since the mid 1960's, sodium tripolyphosphate (STPP) has been used in large quantities in most detergent formulations as a “builder”; that is an agent which is able to sequester positive cations such as magnesium and calcium in the washing solution and prevent them from depositing as salts (carbonate, silicate etc.) on the items being washed.
However, it is now known that the presence of phosphate, for example in the form of STPP, in lakes and rivers serves as a nutrient for algae growth and this results in a deterioration of water quality. These environmental concerns have lead to the removal of STPP in detergent formulations and their replacement with other sequestering compounds. Unfortunately, the changes that occur in the washing process without inclusion of phosphate are more complex than those expected from the simple decrease in sequestration capacity of the detergent matrix. The multi-purpose capabilities of the STPP in the areas of emulsification of oily particles, stabilisation of solid soil suspension, peptisation of soil agglomerates, neutralisation of acid soils, etc. are all key to obtaining an excellent wash end result.
To try to maintain as many of the desirable properties of STPP as possible, whilst at the same time limiting its environmental impact, reduced STPP levels are used. However, this in itself brings new scaling problems. When high levels of STPP are used in the wash bath of dishwashing and laundry washing machines, the predominant species formed in the aqueous system is a water soluble 1:1 metal ion:STPP complex (eg. CaP
3
O
10
−3
). As STPP levels decrease, water insoluble calcium and magnesium salts of tripolyphosphate (eg. Ca
5
(P
3
O
10
)
2
) and pyrophosphate (eg. Ca
2
P
4
O
7
) are formed which consequently precipitate from the aqueous system.
Prior art documents are known, for example U.S. Pat. No. 3,806,367, U.S. Pat. No. 3,928,196, and U.S. Pat. No. 3,898,037, which address the problem of controlling scale in STPP free systems. However, there is no teaching of any effective way to control the (poly)phosphate scales which are formed using low-STPP levels (ie. through the use of “Ultra” or “Compact” detergent formulations) where the concentration of the STPP in the wash bath is, for example, below 1500 ppm. The precise amount of scale observed will depend upon the concentration of divalent cation in the wash bath. For comparison, typical high-STPP wash bath concentrations in current commercial use, have greater than 2000 ppm of STPP.
The term “(poly)phosphate scale” used herein refers to phosphate, tripolyphosphate and pyrophosphate scales collectively. Also, the term “copolymer” is used to mean polymers containing at least one strong acid and at least one weak acid, as well as polymers containing one or more additional types of monomers.
The problem addressed by the present invention, therefore, is to provide a method of controlling (poly)phosphate salt scale in aqueous systems and to also provide detergent formulations which have good anti-filming performance characteristics when used in machine dishwashing detergents and good anti-encrustation and anti-deposition performance characteristics when used in laundry washing detergents.
Accordingly, the present invention provides a method of controlling (poly)phosphate scale comprising treating the aqueous system with at least one copolymer comprising the following monomers in polymerized form:
(I) 50-98% by weight of one or more weak acid;
(II) 2-50% by weight of one or more strong acid;
(III) 0-30% by weight of one or more monoethylenically unsaturated C
4
-C
8
dicarboxylic acid; and
(IV) 0-30% by weight of one or more monoethylenically unsaturated monomers polymerizable with (I), (II), and (III);
wherein the total of monomers (1), (II), (III) and (IV) equals 100% by weight of copolymer.
The invention further provides a method of controlling (poly)phosphate scale in aqueous systems comprising treating the aqueous system with at least one copolymer comprising polymerized units of the following polymers:
(I) 50-98% by weight of one or more monoethylenically unsaturated C
3
to C
6
monocarboxylic acid;
(II) 2-50% by weight of one or more unsaturated sulphonic acid;
(III) 0-30% by weight of one or more monoethylenically unsaturated C
4
to C
8
dicarboxylic acid;
(IV) 0-30% by weight of one or more monoethylenically unsaturated monomer polymerizable with (I), (II) and (III); wherein the total of monomers (I), (II), (III) and (IV) equals 100% by weight of the copolymer.
Preferably, the copolymer comprises polymerized units of the following monomers:
(I) 50-90% by weight of one or monoethylenically unsaturated C
3
-C
6
monocarboxylic acid;
(II) 10-50% by weight of unsaturated sulphonic acid;
(III) 0-30% by weight of one or more monoethylenically unsaturated C
4
-C
8
dicarboxylic acid; and
(IV) 0-30% by weight of one or more monoethylenically unsaturated monomer polymerizable with (I), (II) and (III), wherein the total of monomers (I), (II) (III) and (IV) equals 100% by weight of the copolymer.
Advantageously, the copolymer of the present invention comprises polymerized units of the following monomers:
(I) 60-90% by weight of one or monoethylenically unsaturated C
3
-C
6
monocarboxylic acid
(II) 10-40% by weight of unsaturated sulphonic acid.
(III) 0-30% by weight of one or more monoethylenically unsaturated C
4
-C
8
dicarboxylic acid; and
(IV) 0-30% by weight of one or more monoethylenically unsaturated monomer polymerizable with (I), (II) and (III), wherein the total of monomers (I), (II) (III) and (IV) equals 100% by weight of the copolymer.
A copolymer with particularly good (poly)phosphate scale inhibition properties comprises polymerized units of the following monomers:
(I) 77% by weight of one or monoethylenically unsaturated C
3
-C
6
monocarboxylic acid
(II) 23% by weight of unsaturated sulphonic acid.
The monoethylenically unsaturated C
3
-C
6
monocarboxylic acid is preferably (meth)acrylic acid.
The unsaturated sulphonic acid monomer is preferably one of the following: 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propanesulphonic acid, 3-methacrylamido-2-hydroxy-propanesulphonic acid, allylsulphonic acid, methallylsulphonic acid, allyloxybenzenesulphonic acid, methallyloxybenzenesulphonic acid, 2-hydroxy-3-(2-propenyloxy)propanesulphonic acid, 2-methyl-2-propene-1-sulphonic acid, styrene sulphonic acid, vinylsulphonic acid, 3-sulphopropyl acrylate, 3-sulphopropyl methacrylate, sulphomethylacrylamide, sulphomethylinethacrylamide, and water soluble salts thereof.
The monoethylenically unsaturated C
4
-C
8
dicarboxylic acid is preferably maleic acid, and the monoethylenically unsaturated monomer polymerizable with (I), (II) and (III) is preferably selected from one or more of C
1
-C
4
alkyl esters of (meth)acrylic acid; C
1
-C
4
hydroxalkyl esters of (meth)acrylic acid; acrylamide; alkyl substituted acrylamide, N,N-dialkyl substituted acrylamides; sulphonated alkyl acrylamides; vinylsulphonates; vinyl sulphonic acid. (meth)allylsulphonic acid; vinylphosphonic acid; vinyl actetate; allyl alcohols; sulphonated allyl alcohols, a

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