Patent Application
20100029861
The invention relates to polyoxyalkylene-polysiloxane block polymers, to a process for preparing them, and to their use as deformers in aqueous dispersions.
Defoamers intended for defoaming aqueous and nonaqeuous media and comprising, as the active ingredient critically influencing the defoaming, linearly structured polyoxyalkylene-polysiloxane block copolymers exhibit particular activity and stability. This includes not only the inhibition of foam, the defoaming, a very good long-term stability, but also outstanding compatibility in aqueous and nonaqueous media. All of these factors are of great importance for modern-day processes in the surface technology field.
The term “defoamer” in the present case encompasses not only products but also formulations which prevent foam, and also those which destroy foam and allow air to escape. In practice the transitions between these products are fluid, which is why the common collective term “defoamers” is used here.
In numerous industrial processes, particularly those operated in aqueous media, it is necessary to suppress or entirely prevent the unwanted formation of foam during the production or processing operations, since foam, or foam crowns, which accumulate during stirring and dispersing operations or in the containers during the dispensing procedure, may prolong production times or else reduce the effective volume of the plant, or even prevent its correct operation (overflows, lack of color transfer).
This foam suppression or prevention can be achieved by adding defoamers, which—even when used at very low concentrations, starting at about 0.001% by weight—are capable of preventing or destroying unwanted foam, and at the same time, following application of the systems, of not giving rise to any surface defects. In practice it is necessary to take account of this last factor to at least the same extent as effective defoaming.
Surface defects are, for the user, unwanted characteristics such as pinholes, craters, loss of gloss, orangepeel effect, wrinkling, and loss of adhesion in the coating system. For the user, however, a corresponding long-term stability on the part of the formulations is also very important, since, often, products such as paints are not used immediately but occasionally are used only after prolonged storage. In the case of storage under extreme climatic conditions (heat) the activity of a defoamer formulation may occasionally break down after just a short time.
Prior art defoamers are, for example, oils, such as silicone oils, natural oils, paraffin oils, and mineral oils, but also hydrophobic polyoxyalkylenes, long-chain alcohols, and mixtures of these products with one another, and their emulsions.
To boost the activity it is common to add what are called hydrophobic solids in amounts from 0.1% to 10% by weight, which provide for targeted promotion of dewetting processes at foam lamellae and hence very effectively support foam collapse. Suitable hydrophobic solids are corresponding silicas, metal stearates, polyolefins, and natural or synthetic waxes such as paraffin waxes, polyolefin waxes, and amide waxes.
By adding suitable emulsifiers it is also possible to convert defoamer formulations of this kind into aqueous emulsions.
It is likewise known to use polyoxyalkylene-polysiloxane block copolymers as defoamers. Thus it is specified in DE 10 12 602, for example, that one of the possible applications of water-soluble block copolymers of the general formula
R′[(R2SiO)y]a[(CnH2nO)x]bR″
in which
DE 24 43 853 describes preparations with a defoaming action which contain not only linear but also branched polyoxyalkylene-polysiloxane block copolymers. The linear component of this mix may be described as follows:
RO-A(BA)n-R
in which
U.S. Pat. No. 4,028,218 describes a method of preventing or destroying foam in aqueous solutions or dispersions, using a similar preparation to that described in DE 24 43 853. The preparation differs essentially in the additional presence of organic oil, which likewise has a defoaming action.
Suitable organic oils are the esters of alcohols and fatty acids, such as vegetable or animal oils, for example, or mineral oils, polybutadiene oils or polypropylene glycols.
Comparable to U.S. Pat. No. 4,028,218, in DE 31 23 103 a mineral-oxide-free mixture of:
These polyoxyalkylene-polysiloxane block copolymers, included in the mixture in an amount from 1% to 20% by weight, can have the structure A′-[B′-A′]z, where z can adopt a value from 1 to 3.
These preparations known from the prior art and comprising silicone oils or polyoxyalkylene-polysiloxane block copolymers are suitable, to a more or less pronounced extent, for preventing the formation of foam by aqueous solutions or aqueous dispersions, or for destroying foam which has already formed. It has been found, however, that aqueous dispersions to which preparations of this kind are added have performance disadvantages as a result of the addition of such defoamers. In particular it has been found that dispersions of binders, coating materials, and adhesives to which polysiloxanes or polyoxyalkylene-polysiloxane block copolymers have been added for the purpose of defoaming exhibit wetting defects when applied to surfaces. This disadvantage is countered by DE 38 07 247 through the use of polyoxyalkylene-polysiloxane block copolymers in which the polyoxyalkylene block of the average formula (CnH2nO—)y is constructed from oxyethylene, oxypropylene and/or oxybutylene units in such a way that n takes on a value of 2.8 to 4.0.
It has further been found, however, that dispersions of binders, coating materials, and adhesives to which the aforementioned polysiloxanes or polyoxyalkylene-polysiloxane block copolymers have been added for the purpose of defoaming often exhibit inadequate storage stability. However for inks and paints this parameter is essential, since products are stored for up to several months prior to preparation, and at temperature ranges of just above 0° C. to approximately 50° C.
It is an object of the present invention, therefore, to provide suitable polyoxyalkylene-polysiloxane block copolymers whose aqueous dispersions exhibit good defoaming properties but at the same time do not give rise to any wetting defects when applied to a surface and, furthermore, exhibit improved stability on storage.
This object that forms the basis for the invention can surprisingly be achieved using polyoxyalkylene-polysiloxane block polymers of the general formula (I)
C-B-(AB)a-C1 (I).
The invention accordingly provides polyoxyalkylene-polysiloxane block polymers of the general formula (I)
C-B-(AB)a-C1 (I)
in which
The invention further provides for the use of the polyoxyalkylene-polysiloxane block polymers of the general formula (I) for defoaming aqueous dispersions.
Further subject matter of the invention is characterized by the claims.
The polyoxyalkylene-polysiloxane block polymers of the invention are prepared by methods which are known per se, by reacting the alcohol components A and C, C1 with chloropolysiloxanes in the molar ratio range of
A:C, C1 from 3 to 40, preferably from 3 to 10,
(A+C, C1):chloropolysiloxanes from 1.3 to 1.05, preferably from 1.3 to 1.1,
at temperatures from 50° C. to 150° C., and subsequently carrying out neutralization with ammonia.
The polyether alcohols are preferably polyetherdiols, polyetherpolyols, or mixtures of polyetherdiols and polyetherpolyols (component A) and also a polyethermonool (component C, C1).
The chloropolysiloxanes, based on the polyoxyalkylene block siloxanes B, are linear or branched or are composed of mixtures of linear and branched chloropolysiloxanes.
The polyether alcohols A are prepared by addition reaction of alkylene oxides, in accordance with the invention preferably ethylene oxide, propylene oxide, with polyhydric starter alcohols of the general formula
R2-[O—H]e
in which
The polyether alcohols C and C1 can be prepared in principle in the same way as the polyether alcohols A, with the modification that the starter alcohols used are monofunctional compounds Z-OH in which Z can be an alkyl, alkylene, alkylaryl or aryl radical which optionally is branched and/or contains multiple bonds and which has 1 to 20 C atoms, preferably 1 to 10 C atoms.
The polysiloxane block corresponds to the average general formula
It can be straight-chain (f=0) or branched (f>0 to 20). Preferred in accordance with the invention are compounds with f=0. Within the polysiloxane block, R may have identical or different definitions. R may be an alkyl radical having 1 to 4 C atoms or a phenyl radical. Examples of radicals R are the methyl, ethyl, propyl, n-butyl, and isobutyl radical. At least 90% of the radicals R, however, ought to be methyl radicals, preference being given to those polysiloxane blocks in which all of the radicals R are methyl radicals.
In accordance with the prior art it is possible to add up to 20% by weight of finely divided organic or inorganic solids to the polyoxyalkylene-polysiloxane block copolymers for use in accordance with the invention, said amount being based on these copolymers. Examples of inorganic solids are optionally hydrophobized silica, aluminum oxide or similar typical finely divided solids known from the prior art. As finely divided organic substances it is possible to use the alkaline earth metal salts, known for this purpose, of long-chain fatty acids having 12 to 22 carbon atoms, or the amides of these fatty acids. Further suitable organic solids are derivatives of urea and can be obtained by reacting isocyanates with amines.
The defoamers of the invention display an outstanding defoaming capacity in conjunction with very good long-term stability of the defoaming effect and a very good compatibility in the coating formulation, and can be employed in a multiplicity of industrial operations, such as, for example, for the defoaming of cooling lubricants, polymer dispersions, coatings such as paints, varnishes, and printing inks, adhesives, in paper coating, etc.
They can be added in an amount from about 0.05% to 3%, directly or in dissolved form, but preferably as an aqueous emulsion, to the liquids with a tendency to form foam, or can be added by dripping or spraying of the defoamer in the working region of stirrer mechanisms and pumps. If they are added in a pure, unpredispersed form, appropriate incorporation must be ensured.
The polyetherdiols are prepared in a conventional way, with a starter alcohol being subjected to addition reaction with different alkylene oxides at temperatures from 80° C. to 180° C. in different proportions, in the presence of a catalyst, more particularly potassium methoxide. After the polyadditon reaction, the polyethers are neutralized with dilute phosphoric acid and the phosphate formed is precipitated as a salt, by removal of the water, and removed by filtration. Chemical characterization is carried out through determination of the OH number.
The following polyetherdiols and -triols were prepared (Table 1):
The polyethermonools are prepared in the same way as described for the polyetherdiols, but with the difference that exclusively monools are used as starter alcohols (Table 2).
The linear and branched chloropolysiloxanes are prepared in a conventional way, with a mixture of the cyclic compounds D4 and D5 being mixed in a defined proportion with dimethyldichlorosilane or methyl-trichlorosilane, respectively, where appropriate with addition of water to control chain length and degree of branching, and this reaction mixture being, additionally, equilibrated by addition of what is called an equilibration catalyst, such as sulfuric acid, methanesulfonic acid, trifluoromethanesulfonic acid or iron(III) chloride, for example. In this reaction an equilibrium is formed between the cyclic compounds and a chlorine-functional dimethyl-polysiloxane. This reaction mixture can be used immediately for the further reaction. Where iron(III) chloride is the catalyst used, however, it is advisable to remove the catalyst with activated carbon beforehand, in order to rule out unwanted discoloration resulting from the presence of the iron catalyst. Where linear chloropolysiloxanes are used, the method with iron(III) chloride is preferred. Chemical characterization is carried out through determination of the acid value. The dimensional unit is reported in acid equivalents per kg of chlorodimethylpolysiloxane (Table 3).
A 1-litre four-neck flask with stirrer, thermometer, distillation system, and gas inlet tube is charged with 250 g of polyetherdiol P1 together with 21.3 g of polyether K1. The mixture of polyoxyalkylene oxides is then heated to 110° C. with introduction of dry nitrogen. When the desired temperature has been reached, the unit is evacuated using a rotary oil vacuum pump, and a vacuum of approximately 10 mm is set by introduction of nitrogen. After 1 hour the water content of the mixture is <0.02% and the mixture has therefore been prepared for reaction with the chloropolysiloxane. The batch is cooled to 50° C.
Under inert conditions, under a nitrogen countercurrent, 248.5 g of chloropolysiloxane S1 are weighed out using a syringe into a dropping funnel which has been dried at 100° C. beforehand and has gas compensation, gas inlet tubes, and a top-mounted drying tube. The distillation apparatus is then swapped for this dropping funnel, and the chloropolysiloxane is added dropwise over the course of 30 minutes. Ammonia is introduced to accelerate the reaction, and ammonium chloride is precipitated. After 1 hour the batch is heated to 80° C. and the introduction of ammonia is continued until a sample on moist pH paper no longer shows any traces of acid. The dropping funnel is then swapped again for the distillation system, and the excess, dissolved ammonia is removed from the reaction mixture by application of a vacuum of approximately 133 Pa. After cooling to room temperature, the batch is filtered. This gives a liquid, clear, colorless end product having a Höppler viscosity at room temperature of approximately 2000 mPas.
The products listed in Table 4 can be obtained by operating in general accordance with the preparation instructions above.
For the purpose of testing, the polyethersiloxanes were admixed with disperse, hydrophobized silica (3% by weight) and were converted using nonionic emulsifiers (mixture of polyoxyethylene fatty alcohol ether and polyoxyethylene triglyceride, with a mixture HLB of 13) into a 20%, aqueous defoamer emulsion.
The tested emulsions (Example E1 to E4) were prepared with the polyethersiloxanes according to Table 5.
At 20° C., 100 g of the colored paper coating slip Unilabel T from SICPA S.A. Germany, 71522 Backnang, to which 0.2% defoamer has been added, are introduced into a 250 ml glass beaker (6 cm diameter) and stirred at 2500 rpm using a turbine stirrer (4 cm diameter) for 1 minute. The stirred coating slip is then immediately introduced into a tared volumetric flask, made up to the calibration mark, and the weight is ascertained by weighing. The weight is dependent on the proportion of air incorporated by stirring, and is therefore a measure of the effectiveness of the antifoam tested. The air content can be calculated using the following formula:
% by volume of air=100−(g*2)/D
g=weight of 50 ml of stirred coating slip
D=density of air-free coating slip
To test the compatibility, the dispersion with defoamer added is knife-coated onto a PE film. After the coating has dried it is then inspected (Table 6).
To test the defoaming action of the inventive products in comparison to prior art products, an open-pored foam roller test and a stirring test are carried out.
In the case of the foam roller test, the products to be tested are incorporated into a high-gloss emulsion paint based on a straight acrylate dispersion and, respectively, into woodblock flooring varnishes (1-component and 2-component respectively). After an ageing time of 24 hours at room temperature, the defoamer emulsions present in the paints and varnishes, respectively, are tested for their defoaming action.
For this test, 40 g of the paint (15 g in the case of the woodblock flooring varnish) are applied to a painted contrast chart (24 cm×21 cm, black/white) and distributed uniformly using the open-pored foam roller (or using a mohair roller in the case of the woodblock flooring varnish). After a drying time of 24 hours at room temperature for the paint or the varnishes, the surface of the coat is inspected for foam bubbles and defects (wetting defects). Thereafter the results are graded in accordance with a rating system (from 1, for no foam bubbles and no wetting defects, to 5, for numerous foam bubbles and numerous wetting defects (craters)).
In addition a stirring test is carried out with the varnish from formula 3. The purpose of this stirring test is also to test the products for their defoaming action. For this test, 50 g of the varnish are weighed out into a 180 ml PE beaker and are stirred at 3000 rpm using a dispersing disk, d=30 mm, for 3 minutes. Immediately after the end of the stirring test, 45 g of the stirred varnish are dipped into a measuring cylinder and the volume (plus foam height) is read off. The lower the volume or the foam height, the more effective the defoamer. Thereafter the varnish is tipped off onto a polyester film which in turn is affixed to an inclined wall (with a deviation of 25° from the vertical). During and after the drying of the varnish, the film is assessed for wetting defects. As in the case of the assessment described above, again, the wetting defects and also the foam present are assessed according to ratings of 1 to 5 (Tables 7 to 10).
Thoroughly disperse the following:
Take part 2 and add part 1 with stirring.
Combine all of the components with stirring.
Thoroughly disperse the following:
Take part 2 and add part 1 with stirring.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 056 305.0 | Nov 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP07/61641 | 10/30/2007 | WO | 00 | 5/28/2009 |
