Spray-resistant aqueous foam, its production and use

Details Spray-resistant aqueous foam, its production and use Spray-resistant aqueous foam, its production and use

1995-06-27

2001-10-16

Foelak, Morton (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S072000, C521S078000

Reexamination Certificate

active

06303665

ABSTRACT:

In the coating of various substrates with foamed aqueous compositions in which it is desired that the foam structure is maintained in the coating and where the compositions are aqueous compositions containing a hardenable polymer, the foam may be produced in various ways, e.g. by a chemical reaction of the components with development of gasous reaction products or by addition of suitable blowing agents or further by mechanical foaming of the composition with an added inert gas, in particular with air.
Since by mechanical foaming there are, in general, obtainable finer foam structures than with gases generated in situ, it is desired to employ mechanically formed foams—at least in those cases, in which the fineness of the foam structure plays a role. In mechanically formed foams an undesired appearance is, however, the instability of the generated foam, which means that for instance during provisional storage the foam is, at least in part, altered by collapsing or subsiding and/or may loose its foam structure during application, in particular when using spraying apparatuses, so that it is practically impossible to apply the foam as such on a substrate with conventional spray-apparatuses (especially with spray-guns). In their production these unstable foams are mostly expanded to such a degree at the point of discharge from the foaming machine, that also by this a collapsing of the foam is favoured.
It has now been found that employing the components stated below there may be obtained very fine and stable aqueous foams, which are of such a stability, be it during intermediate provisional storage, be it during processing, that they can be applied in the form of foam even with conventional spray-apparatuses (in particular spray-guns) and also after drying the foam structure is substantially maintained.
The invention relates to the below defined aqueous foams, their production and use.
A first object of the invention, thus, is an aqueous, spray-resistant foam (S) produced by mechanical foaming of a corresponding aqueous composition (W), wherein the aqueous phase contains
(A) a curable polymer system, which consists of
(U) an ionomeric polyurethane or a mixture of ionomeric polyurethanes and optionally
(P) one or more further polymers curable at least together with (U),
and (B) at least one foam-stabilizer,
and the liter-weight of (S) at 20° C. and normal pressure is in the range of 400 to 700 g.
As polyurethanes (U) come, in general, into consideration conventional ionomeric polyurethanes, in particular those dispersible in water, principally as are obtainable by the reaction of dimethylolalkane-carboxylic acids and diols, in particular macrodiols, with diisocyanates and optionally diaminocompounds.
As diisocyanates come, in general, into consideration conventional diisocyanates, preferably those in which at least a part thereof is aliphatic, in particular aliphatic (open-chain or/and at least in part cycloaliphatic) or/and aromatic diisocyanates.
The diisocyanates contain in the hydrocarbon radical, to which the two isocyanate groups are bound, advantageously 6 to 15 carbon atoms.
As aliphatic open-chain diisocyanates come into consideration, e.g. hexamethylenediisocyanate or trimethylhexylene-1,6-diisocyanate (in particular 2,2,4-trimethylhexylene-1,6-diisocyanate and 2,4,4-dimethylhexylene-1,6-diisocyanate). As cyclic diisocyanates come principally into consideration mono- and dicyclic diisocyanates, e.g. 2,4- or 2,6-tolylenediisocyanate, m-phenylenediisocyanate, xylylenediisocyanate, 4,4′-diphenylmethane-diisocyanate, 3,3′-dimethyl-4,4′-diphenylmethanediisocyanate, dicyclohexyl-methane-4,4′-, -4,2′- or -2,2′-diisocyanate wherein each cyclohexyl radical may optionally further bear a methyl group, 1,3-cyclohexylenediisocyanate, methylsubstituted 1,3-cyclohexylenediisocyanate and isophoronediisocyanate.
Among the mentioned diisocyanates the aliphatic ones (open-chain or/and cyclic) are preferred.
According to a preferred feature of the invention there are employed open-chain and cycloaliphatic diisocyanates, the molar ratio of the cycloaliphatic to the non-cyclic diisocyanates being advantageously in the range of 0.8:1 to 3.5:1, in particular 1:1 to 3.2:1.
As diols come, in general, into consideration known diols as are employed for polyurethanes dispersible in water, principally macrodiols, in particular polyetherdiols, polyesterdiols or polyesteretherdiols, among which polyalkyleneglycols are preferred, in particular polypropyleneglycols, polybutyleneglycols and mixed polypropylene- and -butyleneglycols. The polybutyleneglycols are principally those comprising oxygen-linked butylene-1,2-, -1,3-, 2,3- or -1,4-groups. Polypropyleneglycols and polybutylene-glycols, or corresponding mixed polyetherdiols, are principally addition products of the corresponding cyclic oxides (in particular oxiranes or tetrahydrofuran) to water or starting diols, which in particular contain 2 to 6 carbon atoms, e.g. ethyleneglycol, propyleneglycol, butyleneglycol, neopentylglycol or hexamethylenediol. Polypropeleneglycols are preferred.
The average molecular weight {overscore (M)}
W
of the macrodiols is preferably in the range of 300 to 5000. By suitable choice of the diols the properties of the polyurethanes may be influenced. A preferred group of diols are lower-molecular macrodiols, in particular polyetherdiols with an average molecular weight {overscore (M)}
W
in the range of 500 to 1800, in particular 800 to 1500. A further preferred group of diols are higher molecular macrodiols, in particular polyetherdiols, with an average molecular weight {overscore (M)}
W
in the range of 1000 to 5000, preferably 1200 to 4000, in particular 1500 to 3500. The difference between the two molecular weights is advantageously in the range of 200 to 3000, preferably 400 to 2200.
When using those categories of macrodiols the weight ratio of the lower molecular ones to the higher molecular ones is advantageously in the range of 1:0.4 to 1:4, preferably in the range of 1:0.7 to 1:3.
As dimethylolalkanecarboxylic acids that can be employed for the production of the ionomeric polyurethanes come, in general, into consideration known carboxylic acids as are employed as carboxy-group-containing diols in the production of ionomeric carboxy-group-containing polyurethanes, in particular &agr;,&agr;-dimethylolalkane-carboxylic acids. Principally they correspond to the formula
in which R signifies hydrogen or C
1-8
-alkyl.
Preferably R signifies hydrogen or C
1-4
-alkyl, in particular hydrogen or methyl.
The molar ratio of the total non-ionogenic diols, in particular macrodiols, to the carboxy-group-containing diol is advantageously in the range of 1:0.2 to 1:2, preferably in the range of 1:0.3 to 1:1.2.
Per mole of total employed diol compounds (macrodiols and carboxy-group-containing diols) there are employed advantageously 0.9 to 3 moles of isocyanate compounds. If the diols and isocyanates are reacted to isocyanate terminated oligourethanes, which are then chain-extended with diamino compounds, the molar ratio of the total diol compounds to the isocyanate compounds is advantageously in the range of from 1:1.05 to 1:2.5, preferably 1:1.2 to 1:2.2. The polyaddition of the isocyanate-compounds and diol-compounds may take place in a manner known per se, e.g. in the presence or absence of solvents (as solvents come, in particular, into consideration aprotic solvents, e.g. dialkylketones, such as methylethylketone, cyclohexanone or aliphatic carboxylic acid esters such as acetic acid ethylester or ethoxyethylester, which may optionally be blended with aromatic solvents such as toluene or xylene—preferably there are however employed no aromatic solvents), at elevated temperature (e.g. in the temperature range of 40° C. to reflux temperature) and, if desired, in the presence of suitable catalysts, such as tinn-II-octoate or dibutyltinndilaurate. Preferably the process is carried out in the absence of any solvents and catalysts. The temperature is kept advantageously in the range of 70 to 90° C.,

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