WO2007110200A1

WO2007110200A1 - Solvent-free, flow-resistant adhesives and sealants

Info

Publication number: WO2007110200A1
Application number: PCT/EP2007/002583
Authority: WO
Inventors: Hans-Detlef Deike
Original assignee: Bostik SA
Current assignee: Bostik SA
Priority date: 2006-03-24
Filing date: 2007-03-23
Publication date: 2007-10-04
Anticipated expiration: 2008-09-24
Also published as: DE102006014092A1; DE102006014092B4

Abstract

The invention discloses composition, application and production of aqueous bitumen emulsions modified with aqueous acrylate and/or acrylate-copolymer dispersions with total water contents below 20% by mass and their use preferably for repairing defects on flat roofs and also for sealing at edge regions and corner regions, roof apertures and outlets on flat roofs.

Description

Solvent-free, flow-resistant adhesives and sealants

The present invention provides solvent-free, flow-resistant adhesives and sealants composed of aqueous bitumen emulsions and aqueous acrylate dispersions and/or acrylate copolymer dispersions and also of a casein stabilizer and further auxiliaries. The adhesives and sealants of the invention are intended preferably for sealing and bonding jobs on flat-roof coatings.

In order to ensure that flat roofs protect against moisture they are widely covered with bitumen or polymer-bitumen sheeting. To affix these roofing sheets, and also to repair damaged areas, which form readily at transitions and at the edges, there are a range of means available.

In the case of the process known as welding, the bitumen sheets are fused using a gas torch at temperatures around 200⁰C. This process, however, is poorly suited to repairs and smaller laying jobs, owing to the high levels of technical complexity and of toxic emissions. A similarly critical view is taken of working with liquid bitumen melt with temperatures of around 250⁰C.

Cold-bonding bitumen adhesives are either aqueous bitumen emulsions or solutions of bitumen in organic solvents, mostly petroleum hydrocarbons. If bonds are carried out with such bitumen solutions, there are high levels of solvent emission, which on environmental grounds is generally considered critical and, furthermore, necessitates fire protection measures. Products of this kind are therefore rarely employed.

The position with aqueous bitumen emulsions is more favourable; these products can be used in interior and exterior spaces. A disadvantage found, however, when bonding roofing sheets or when undertaking repair jobs is the high water content of such formulations, of 40% to 70% by mass. As the water dries from the adhesive layers, though, there is a risk that the water fractions will be unable to escape, or to escape sufficiently, and that bubbles will consequently be formed. Another, very disadvantageous feature found with these cold-bonding adhesives have been the long drying times.

Further disadvantages of bituminous adhesives result from the intrinsic properties of the bitumen itself. This is because, for many applications, bitumen possesses inadequate elasticity and a tendency to react to weathering by embrittlement and cracking. Accordingly there has been no lack of attempts to modify bitumen emulsions with thermoplastics. Attempts, however, to provide sufficient stabilization to mixtures of aqueous bitumen emulsions and aqueous polymer dispersions for applications in construction have not to date brought any convincing solutions. Another reason for these failures lies in the inadequate stability of such mixtures. Before such products can be marketed and employed, indeed, it must be possible to guarantee a shelf life of 2 to 3 years.

To overcome these difficulties a variety of proposals have been elaborated. A series of patent applicants describe two-component formulations, composed of an aqueous bitumen/polymer mixture and a hardener component, often cements (cf. DE 4330399). The fundamental disadvantage of such two-component systems over their one-component counterparts lies in the additional mixing work and the risk of the user either failing to observe the mixing ratio or failing to mix homogeneously, or both.

If only aqueous dispersion adhesives, acrylate-based ones for example, are used, then the high levels of water necessitate long drying times. In the case of adhesive bonds there is a risk, moreover, of the water being unable to escape completely and of the formation of bubbles beneath the coverings. A further disadvantage of such formulations is that they are susceptible to condensation and, under the influence of moisture, undergo detachment from the substrate and/or from the adhered bitumen sheets. In addition, the known acrylate adhesives have a tendency to shrink severely as they dry out, something which can likewise lead easily to the parting of the bond.

The applicants of EP 1102816 propose an improvement involving preparing mixtures of bitumen emulsions and copolymers of ethylene oxide and propylene oxide in the presence of polyethoxylated compounds, alkylphenols for example. The copolymers described, with molar masses of around 1000 g/mol, however, are unable to provide sufficient improvement in the bitumen properties.

DE 3938063 discloses a method of dispersing chlorinated and nonchlorinated polymers in bitumen emulsions. However, this requires up to 22% by mass of organic solvents, preferably solvent naphtha.

DE 3043297 discloses the modification of bitumen emulsions with polycyclic polycarboxylic acids which can be obtained by nitric acid oxidation of coal. To date there has been no technical verification of the process. DE 3043297 describes bitumen emulsions which comprise aqueous polymer dispersions and comprise, as stabilizers, nonionic and/or partly ionic polysaccharides.

It was an object of the present invention to provide solvent-free and flow-resistant adhesives and sealants, comprising aqueous bitumen emulsions, which by virtue of their thermoplastic acrylate and/or acrylate copolymer fraction are permanently elastic and can be prepared in a storage-stable form. In terms of their technical complexity, these adhesives and sealants ought to be able to be used even by DIYers for the repair of damage on flat roofs or roofs with a shallow pitch.

This object is achieved by means of the features disclosed in Claims 1 to 6.

Bitumen is obtained as a residue in petroleum distillation. It comprises dark-coloured compositions of low volatility with no exact melting point. Viewed chemically, bitumen is composed predominantly of higher hydrocarbons, and can be described as a dispersion of relatively high molecular mass asphaltenes in oily maltenes.

Bitumen emulsions are colloidal mixtures of certain types of bitumen with water. To prevent the finely divided bitumen droplets coalescing necessitates addition of emulsifier. Suitability for the preparation of the adhesives and sealants of the invention is possessed advantageously by anionic bitumen emulsions having water contents of 30% to 60% by mass. These bitumen emulsions are available inexpensively on the market. Further properties and the modes of production of the bitumen emulsions are prior art and therefore need not be treated further here (cf. K.-D. Ledwoch: Kittel - Lehrbuch der Lacke und Beschichtungen, Vol. 3, S. Hirzel Verlag, Stuttgart, 2001).

The other component of the adhesives and sealants of the invention that is critical, besides bitumen, is constituted by the aqueous acrylate dispersions. These dispersions comprehend not only straight acrylates but also acrylic ester copolymers, especially acrylic ester-acrylonitrile copolymers. Particularly suitable for the adhesives and sealants claimed are copolymers of acrylic acid alkyl esters and small fractions of acrylonitrile. Suitable alkyl groups, which originate formally from the esterifying alcohol, include the methyl, ethyl, n-propyl, isopropyl, n-butyl and isobutyl groups. All of these acrylates are used in the form of their aqueous dispersions. The amount of pure resin in these aqueous dispersions can fluctuate between 30% to 70% by mass.

According to a further feature of the present invention, acrylates and/or acrylate copolymers should be selected such that the glass transition temperatures of the pure, solid polymers are below 5°C. This is beneficial for the drying of the adhesives and sealants at typical outdoor temperatures.

Acrylates and acrylate copolymers have been sold freely on the market for many years. Their preparation and their properties are prior art. Any further description is therefore unnecessary here. Mention may be made, however, of a few important properties of the aqueous polymer dispersions employed: the pH ought to fluctuate around the neutral point, i.e. pH values of between 4 and 9 are the aim.

Outstanding suitability for stabilizing the adhesives and sealants of the invention is possessed, as has surprisingly been found, by aqueous casein solution. This solution, moreover, can be easily prepared from powder-form casein, water and aqueous ammonia.

Casein is a protein which can easily be obtained from milk. It is insoluble in water but readily soluble in bases. Casein is available generally, and its production and properties are prior art (cf. K.-D. Ledwoch: Kittel - Lehrbuch der Lacke und Beschichtungen, Vol. 1 , S. Hirzel Verlag, Stuttgart, 1998).

According to a further feature of the present invention the adhesives and sealants claimed contain 0.1% to 3.0% by mass of bentonite thickener. Bentonites are naturally occurring clay minerals with a layer structure. They effect thickening in the water phase via gel formation, which is caused by the spatial orientation of the leaflet-shaped mineral particles.

In order to obtain adhesives and sealants which can easily be smoothed, 0.1% to 3.0% by mass of fumed silica is added advantageously to the formulations. These silicas are obtained by hydrolysing chlorosilanes in an oxyhydrogen flame. On account of their fine division, their designation as highly disperse silica is also common. Besides a thixotropic effect, these silicas are beneficial for the smoothing characteristics of the adhesives and sealants claimed.

As a further important constituent the adhesives and sealants comprise chalk powder and/or finely ground slate, with mass fractions of 25% to 60%. The particle size ought to be situated within the range from 2 to 50 μm. Finely ground slate has the advantage over chalk that it strongly repels moisture.

According to an additional feature of the invention, the adhesive/sealant formulations comprise swellable acrylate thickeners and associative polyurethane thickeners. The amounts are in each case 0.1% to 2.0% by mass.

The acrylate thickeners employed are alkali-swellable compounds which as a result have a strong thickening action, an example being the product Latekoll D from BASF, Ludwigshafen, with solids contents of around 25% by mass.

The polyurethane thickeners, suitable examples being the Borchi gel types from Borchers, Langenfeld, attach themselves to the surfaces of bitumen and/or acrylates by way of hydrophobic groups in the molecule, and form micelle-like complexes of high molecular mass. As a result it is possible to exert a beneficial effect on the levelling characteristics and on the viscosity of the adhesives and sealants claimed. The solids contents of the PU thickeners range around 50% by mass.

The solvent-free, flow-resistant adhesives and sealants claimed may in certain cases further comprise additional auxiliaries. Mention here might be made of plasticizers, colour pigments, fillers, other pigments, preservatives, defoamers and adhesion promoters.

For plasticization it is possible to have recourse to established compounds. Mention might here be made primarily of the known phthalic esters, in mass fractions of 0.5% to 15%. A plasticizer which has been found to be particularly suitable is isobutyl phthalate.

Suitable defoamers for the production operation include silicone defoamers, with preference being given to compounds from the class of the dialkylsiloxanes. These compounds are commercially customary.

Suitable preservatives are available from the trade. Active substances from the class of the isothiazolin-3-ones have been found to be appropriate. They are readily dispersible in aqueous formulations. Pure active substance levels of around 0.05% by mass have proved to be sufficient.

Also possible is the addition of colour pigments, such as titanium dioxide, carbon black or organic colour pigments, and of fillers, such as dolomite, heavy spar or kaolin, for example.

The production of the adhesives and sealants of the invention takes place in two stages, first a casein stock solution is prepared from water, casein powder and concentrated aqueous ammonia. In this context a casein content of approximately 15% by mass has been found to be appropriate. In a second stage the aqueous acrylate and/or acrylate copolymer dispersions are charged to a mixer, the bentonite thickeners are mixed in, then plasticizer and the casein stock solution are added, and the components are carefully homogenized. Then defoamer, preservative and silica are mixed in. The next to be added are the acrylate thickeners and the bitumen emulsion, which are added slowly and with stirring. Then the chalk powder and/or the finely ground slate are/is incorporated with shearing. Finally, at a high stirring speed, polyurethane thickener is added until the desired consistency is attained.

The resultant, solvent-free, flow-resistant, bitumen-based adhesives and sealants are suitable for applications in the industrial sector, in the craft sector and for DIYers. Examples of applications are the sealing of cracks and joints in bitumen coatings, the sealing of roof openings and domed roof lights, and also renovation works in edge regions and corner regions of bitumen-coated areas.

The adhesives and sealants of the invention are solvent-free and flow-resistant, viscoelastic compositions based on bitumen. They contain no solvents and can therefore be classified as environmentally friendly.

The adhesives and sealants can be applied by trowel or knife in one step in layer thicknesses of up to 5 mm. The material is water-resistant; the contraction is low, owing to the small amounts of water; and the applied material can be overcoated with solvent-based and aqueous dispersion-based coating materials.

The invention will be illustrated with reference to two examples.

Example 1 :

The adhesive and sealant is produced in two stages. Stage 1 :

8.1 kg of water are charged to a mixer and 1.5 kg of milk casein powder are metered in with slow stirring. Thereafter 0.4 g of aqueous ammonia (25% by mass) is added with stirring, and stirring is continued until a largely clear solution has formed. Stage 2:

23 kg of aqueous ethyl acrylate-acrylonitrile-copolymer dispersion with an acrylonitrile fraction of 5% by mass and a solids content of 60% by mass are charged to a planetary mixer and mixed homogeneously with 0.3 kg of bentonite thickener. Then 6 kg of diisobutyl phthalate and 3 kg of casein solution are added. Next, 0.3 kg of silicone defoamer, 0.2 kg of aqueous preservative and 0.7 kg of highly disperse silica are incorporated homogeneously with shearing. Subsequently, 0.2 kg of acrylate thickener (25% by mass solids content), 14 kg of anionic bitumen emulsion (40% by mass solids content), 26 kg of chalk powder and 26 kg of finely ground slate and, lastly, 0.5 kg of polyurethane thickener (50% by mass solids content) are added and the mixture is homogenized. The finished formulation is dispensed into cartridges.

For the purpose of testing, a number of variables were determined: the results are found in Table 1.

Example 2:

Production takes place in two stages.

Stage 1 : The casein solution is prepared as described in Example 1.

Stage 2:

25 kg of aqueous straight-acrylate dispersion with a solids content of 55% by mass were charged to an intensive mixer, 0.3 kg of bentonite thickener was incorporated homogeneously, and then, with slow stirring, 6 kg of diisononyl phthalate, 3 kg of the casein solution (15% by mass), 0.3 kg of defoamer, 0.1 kg of preservative and

0.3 kg of fumed silica and 0.2 kg of acrylate thickener were added.

Only then are 14 kg of bitumen emulsion (40% by mass solids content) added and 53 kg of calcium carbonate (average particle size 25 μm) incorporated with shearing. Lastly the viscosity of the batch is adjusted using a polymer thickener of Borchigel L type.

The adhesive/sealant mixture obtained is dispensed into metal buckets and given an airtight seal.

Characteristic data are compiled in Table 1. Table 1 :

Characteristic data of the adhesives/sealants from Examples 1 and 2

Claims

Claims:

1. Solvent-free, flow-resistant adhesives and sealants having a water content below 20% by mass and based on bitumen emulsions, characterized in that they comprise aqueous polyacrylic ester dispersions and/or polyacrylic ester copolymers in aqueous dispersion, the glass transition temperatures of the water-free polymers and/or copolymers being below 5°C.

2. Solvent-free, flow-resistant adhesives and sealants according to Claim 1 , characterized in that they comprise an aqueous casein solution as a stabilizer for the mixture of bitumen emulsion and acrylate dispersion and/or acrylate copolymer dispersion.

3. Solvent-free, flow-resistant adhesives and sealants according to Claim 1 and

2, characterized in that they comprise an aqueous straight-acrylate dispersion, composed of polyacrylic esters and polymethacrylic esters, and/or polyacrylic ester- polyacrylonitrile copolymers in aqueous dispersion.

4. Solvent-free, flow-resistant adhesives and sealants according to Claims 1 to

3, characterized in that they comprise

3% to 25% by mass of an aqueous bitumen emulsion having a solids content of 20% to 60% by mass,

5% to 30% by mass of an aqueous polyacrylic ester dispersion and/or polyacrylic ester copolymer dispersion having in each case a solids content of 30% to 70% by mass,

0.1% to 3.0% by mass of bentonite thickener, 0.1 % to 3.0% by mass of fumed silica,

0.5% to 15% by mass of phthalic acid alkyl esters having alkyl radicals with 1 to 12 carbon atoms,

0.1% to 2.0% by mass of polyurethane thickener having a solids content of 10% to

60% by mass, 25% to 60% by mass of chalk powder and/or finely ground slate and/or finely ground rock,

0.1% to 10% by mass of acrylate thickener having a solids content of 10% to 50% by mass, and, if desired, additives customary in the art, such as pigments, fillers, preservatives, defoamers and adhesion promoters.

5. Solvent-free, flow-resistant adhesives and sealants according to any one of the preceding claims, characterized in that they are used for the elastic bonding and sealing of bituminous roof-coating materials.

6. Process for producing solvent-free, flow-resistant adhesives and sealants according to at least one of Claims 1 to 4, characterized in that in a first step an aqueous casein solution is prepared from aqueous ammonia and casein and in a second step first bentonite thickener is incorporated into an aqueous acrylate dispersion and/or an acrylate copolymer dispersion and then plasticizer and the casein solution are added, and defoamer, preservative, acrylate thickener and then the bitumen emulsion are mixed into this mixture, lastly the chalk powder and/or finely ground slate and/or finely ground rock is incorporated with shearing, and thereafter the viscosity is adjusted with the polyurethane thickener.