Anticorrosion binders comprising phosphate or phosphonate...

Details Anticorrosion binders comprising phosphate or phosphonate... Anticorrosion binders comprising phosphate or phosphonate...

1999-05-28

2001-04-17

Wu, David W. (Department: 1713)

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...

C524S461000, C524S710000, C526S193000, C526S201000

Reexamination Certificate

active

06218456

ABSTRACT:

The invention relates to an aqueous polymer dispersion obtainable by emulsion polymerization of a monomer mixture A) comprising from 50 to 100% by weight of C
1
-C
18
alkyl (meth)acrylates, vinyl esters, vinylaromatic compounds, or mixtures thereof, in the presence of a protective colloid B) composed of
b
1
) from 2 to 40% by weight of ethylenically unsaturated copolymerizable compounds (monomers) having at least one phosphate or phosphonate group
b
2
) from 0 to 98% by weight of C
1
-C
18
alkyl (meth)acrylates, vinyl esters or vinylaromatic compounds
b
3
) from 0 to 50% by weight of further monomers, the amounts by weight being based on the protective colloid.
The invention additionally relates to anticorrosion coating compositions comprising the aqueous polymer dispersion.
Phosphate-functional binders for anticorrosion coating compositions are known, for example, from EP-A-305850 and EP-A-221498. The binders of EP-A-305850 are solution polymers prepared by polymerization in an organic solvent and subsequently dispersed in water. The molecular weights of such solution polymers are generally low, and for this reason alone their polymers are less suitable for coating compositions having good performance properties. The binders of EP-A-221498 are copolymers whose comonomers include specific, surface-active phosphates with polyether groups.
Emulsion polymers prepared in the presence of a protective colloid are known, for example, from EP 727441.
There is a desire for anticorrosion binders which offer good corrosion protection with a low content of phosphate or phosphonate groups.
It should be possible if appropriate to do without additional anticorrosion pigments. The polymers should be very easy to prepare, and readily available monomers should be used in particular. The aqueous polymer dispersions obtained should be stable and largely free of coagulum, while the resulting coatings should exhibit good performance properties, examples being high hardness and elasticity.
The binders known to date for anticorrosion coatings do not go a sufficient way toward meeting these requirements.
It is an object of the present invention, therefore, to provide binders for anticorrosion coatings which go as far as possible toward meeting the various requirements set out above.
We have found that this object is achieved by the polymer dispersion defined at the outset and by anticorrosion coating compositions which comprise the polymer dispersion.
The aqueous polymer dispersion is preferably prepared by emulsion polymerization of the monomer mixture A) in the presence of a protective colloid B).
The term monomer as used below represents free-radically copolymerizable compounds having at least one ethylenically unsaturated group.
The protective colloid contains preferably from 5 to 35% by weight and, with particular preference, from 10 to 20% by weight of the monomers b
1
).
The protective colloid consists in particular, for example, of from 5 to 35, preferably from 10 to 20% by weight of monomers b
1
) from 60 to 95, preferably from 70 to 90% by weight of monomers b
2
) from 0 to 30, preferably from 0 to 20% by weight of monomers b
3
).
These amounts by weight are based in each case on the protective colloid B).
Monomers b
1
) are those having a phosphate or phosphonate group and at least one, preferably copolymerizable, ethylenically unsaturated group. The molecular weight of suitable monomers b
1
) is preferably below 1000 g/mol, with particular preference below 500 g/mol and, with very particular preference, below 280 g/mol. Phosphate groups are groups of the formula
Phosphonate groups are groups of the formula
K in the above formulae is a cation, n and m are each 1 or 2, and the product n·m=2. K can be an alkali metal or ammonium, for example.
Suitable monomers b
1
) with phosphonic acid groups are, for example, vinyphosphonic acid, 2-methacrylamido-2-methylpropanephosphonic acid, propene-2-phosphonic acid or &agr;-phosphonostyrene.
Examples of monomers containing phosphoric acid groups are monoesters of phosphoric acid with compounds obtainable from diols and acrylic or methacrylic acid by monoesterification, such as 2-hydroxyethyl methacrylate, hydroxypropyl (meth)acrylate, 4-hydroxybutyl acrylate and 2-hydroxybutyl acrylate.
Prior to or during the transfer of the protective colloid to the aqueous phase the acids are neutralized—that is, the acid groups are converted to salt groups, as set out in detail later on below.
Examples of monomers b
2
) (principal monomers) are (meth)acrylic acid alkyl esters having a C
1
-C
9
, especially C
1
-C
8
, alkyl radical, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, n-butyl methacrylate, lauryl (meth)acrylate or stearyl (meth)acrylate.
Mixtures of the (meth)acrylic acid alkyl esters are also suitable, in particular.
Examples of vinyl esters of C
1
-C
20
carboxylic acids are vinyl laurate, stearate, propionate and acetate.
Suitable vinylaromatic compounds are vinyltoluene, &agr;- and p-methylstyrene, &agr;-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and, preferably, styrene.
The monomers b
2
) are also preferably employed in a mixture.
Vinylaromatic compounds such as styrene are frequently employed, for example, as a mixture with C
1
-C
18
-alkyl (meth)acrylates, especially with C
1
-C
8
-alkyl (meth)acrylates.
Examples of further ethylenically unsaturated monomers b
3
) are hydroxyl-containing monomers such as hydroxyalkyl (meth)acrylates, examples being hydroxypropyl or hydroxyethyl (meth)acrylate, amides or substituted amides of ethylenically unsaturated mono- or dicarboxylic acids, examples being acrylamide, methacrylamide, N-methylolacrylamide and N-methylolmethacrylamide, and also the N-methylolacrylamides and N-methylolmethacrylamides that are etherified with C
1
-C
6
-monohydric alcohols. While it is possible to include crosslinking monomers, having, for example, two vinyl groups, it is preferred for the protective colloid B not to contain any crosslinking monomers or at most only small proportions of these monomers—for example, less than 0.2% by weight, based on the protective colloid B. Further monomers b
3
) include those having carboxylic acid, sulfonic acid, acid anhydride or amide groups, which contribute to the emulsifying action of the protective colloid B); however, it is not necessary to use such monomers, since monomers b
1
) have a sufficient emulsifying action.
Mention may also be made of nitriles, vinyl halides, and nonaromatic hydrocarbons.
The weight-average molecular weight (M
w
) of the protective colloid B) is preferably more than 10,000, with particular preference from 20,000 to 200,000 and, with very particular preference, from 40,000 to 120,000 (determined by gel permeation chromatography using polystyrene as standard and tetrahydrofuran as eluent).
The protective colloid B) can be prepared, for example, by bulk polymerization, i.e., without solvent, or, preferably, by solution polymerization.
The protective colloids B) prepared by bulk or solution polymerization are preferred because the polymers are relatively uniform in composition and include, incorporated in them, a hydrophobic (oil-soluble) initiator.
Examples of suitable solvents are those having a boiling point of less than 100° C. at 1 bar or those which together with water form an azeotrope which can easily be removed by distillation, if desired, from the aqueous polymer dispersion. Advantageously, it is also possible for the solvents used to include what are known as film-forming auxiliaries, such as butyl glycol, butyl diglycol or butoxypropanol. In this way, it is unnecessary to add these auxiliaries later.
Examples of suitable solvents that may be mentioned are butanol, isobutanol, propanol, ethanol, methanol and methyl ethyl ketone.
The polymerization of the ethylenically unsaturated monomers can be carried out, for example, in a conventional manner by anionic or, preferably, free-radical polymerization, preferably in the presence of initiators. Examples of free-radical initiators that ma

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