WO2007093381A1

WO2007093381A1 - One-component, solvent free contact adhesive

Info

Publication number: WO2007093381A1
Application number: PCT/EP2007/001235
Authority: WO
Inventors: Hans-Detlef Deike
Original assignee: Bostik S.A.
Priority date: 2006-02-14
Filing date: 2007-02-13
Publication date: 2007-08-23
Also published as: DE102006006975A1

Abstract

The adhesive is composed of a mixture of silane- terminated polyoxypropylenes and silane-terminated alkyl acrylates of together 25% to 70% by mass, 20% to 70% by mass of chalk powder, 0.5% to 5% by mass of drying agents, 0.5% to 5% by mass of curing catalysts, 0.2% to 3% by mass of adhesion promoter and, if desired, further, customary additives. The contact adhesive is suitable for the primerless contact adhesive bonding of two or more materials after a waiting time of 10 to 30 minutes.

Description

One-component, solvent-free contact adhesive

The present invention relates to a one-component, solvent-free contact adhesive composed of a mixture of particular silane-terminated polymers, and of chalk powder, drying agents, adhesion promoters, curing catalysts and further additives, and also to production processes and application methods.

By adhesive bonding is meant the joining of two or more like or different materials by means of an adhesive. When using what are called contact adhesives, at least one of the components to be bonded, or, more frequently, both components, are coated with the contact adhesive and, after a waiting time which depends on the particular adhesxve, are assembled. The initial strength of such bonds is relatively high.

Contact adhesives have been used for many years to bond a wide variety of different components. Contact adhesives are suitable particularly for the flat bonding of textile coverings, flexible plastic coverings, films and foils etc. in the interior fitment of living spaces and business spaces.

For different users and different technical requirements, a large number of contact adhesives has been developed over the course of time. Fundamentally, distinctions are made between one-component and multi- component, mostly two-component, contact adhesives. Examples of two-component contact adhesives are systems based on polyurethanes, epoxides or silicones. Fundamental disadvantages of these two-component systems over one-component systems lie in the additional mixing effort and the risk of the user not accurately observing the mixing ratio and/or not carrying out homogeneous mixing. Processing errors are also likely as a result of the failure to observe pot lives and flash-off times.

The one-component contact adhesives can most easily be subdivided according to their setting mechanism: the physically setting contact adhesives include the solvent-containing systems and the water-containing systems. In connection with the problem of solvent emissions and the possible risks arising therefrom with regard to health and the environment, there has been a sharp retreat in the use of these adhesives.

Although aqueous contact adhesives do not have these disadvantages, they do require long waiting times before the components can be assembled. For many technical applications these drying-off times are too long. Moreover, in the course of the drying process, the aqueous contact adhesives contract by up to 30%, as a result of giving up their water, and wood and other organic substrates swell under water exposure.

One-component, water-free or solvent-free adhesives are made available by the relevant industry in the form of polyurethanes, cyanoacrylates or silicones. These products, however, mostly cannot be used as contact adhesives. Although polyurethanes can be employed as contact adhesives, toxicological problems - owing to the presence of isocyanates - have given rise to a desire for less toxic products.

One-component silicone adhesives cure under the influence of atmospheric humidity. The best-known systems are the acetate systems, which give off acetic acid on curing. A disadvantage with these systems is the inadequate adhesion to the typical substrates in the construction industry. Moreover, the weathering stability is often inadequate for outdoor applications. Against this background as long ago as about 25 years hybrid polymers were developed, composed of typical scaffold polymers, such as polypropylene oxide, polyacrylates or polymethacrylates and silanes, for example. The silane groups here carry predominantly methoxy groups, from which, as a result of atmospheric humidity, methanol is released during the curing process. The silanol groups formed then react further, with crosslinking.

These hybrid polymers or, more accurately, prepolymers, are marketed by the industry under the name MS polymers (modified silane polymers). G. Habenicht gives an overview of this technology in the book "Kleben", Springer Verlag, 3rd edition, Berlin, 1997. A further description here is therefore unnecessary.

To date, however, the pure MS polymers have been unable to establish themselves in contact adhesive applications, in spite of their fundamentally advantageous properties. The reasons for this failure lay in the difficulty of application, since with pure MS polymers it is impossible to build up sufficient film thicknesses. Greater film thicknesses, such as those required for certain bonds in the construction industry, for example, delivered unsatisfactory results, since the MS polymers cured too slowly or since there were instances of deformation developing rapidly on the applied adhesive prior to contact bonding. This assessment of the technical situation is also demonstrated by a series of patent applications which attempted to overcome the problems .

DE 41 19 484 and EP 0 345 800 recommend making additions to the MS-based contact adhesives in order to accelerate the curing ("drying-off") . For example, fluoro surfactants or polybutadiene oil are said to be suitable for this purpose. Such preparations, however, have been unable to establish themselves, owing to the considerable technical complexity and also the lack of stability of such mixtures.

EP 0 824 574 and DOS 10 2004 022 150 describe two- component adhesives in which one component comprises MS polymers and the second component comprises water and/or water-containing constituents. The two components must be mixed immediately prior to application and therefore have the known disadvantages, already mentioned above, of two-component systems. According to the applicants, however, the individual components are also not stable on storage over an industrially relevant time period of 1 to 2 years.

Other approaches attempt to overcome these problems through the addition of specific polymers.

EP 0 339 666 proposes adding acrylates and methacrylates to the silane-terminated polyoxyalkylenes in order to accelerate curing. The quality of the bonds obtainable with these adhesives suffers, however, as a result of the high acrylate fraction, and it is for this reason that the proposal has not to date been implemented industrially.

DOS 10 237 271 recommends, finally, the use of specific catalysts in order to activate the curing of the silane-terminated polymers.

Against this background it is an object of the present invention to provide a formulation for a one-component, solvent-free and water-free contact adhesive, based on MS polymers, which is suitable for a coat applied at up to 1.5 mm, reacts within 15 to 30 minutes to an extent that contact bonding can be performed, and has an initial strength sufficiently high for industrial adhesive bonds. This object is achieved by a one-component, solvent- free contact adhesive, characterized in that it is composed of a mixture of silane-terminated polymers of together 25% to 70% by mass, 20% to 70% by mass of chalk powder, 0.3% to 5% by mass of drying agents, 0.5% to 3% by mass of curing catalysts, 0.2% to 3% by mass of adhesion promoter and, if desired, pigments, plasticizers, fillers, light stabilizers and heat stabilizers .

The contact adhesive of the invention adheres very well to all typical components, such as wood, textile coverings, concrete, plastics and metals, for example, thereby obviating pretreatment with a primer. The contact adhesive claimed can also be employed on damp substrates; no blistering is observed.

The contact adhesive cures through a cycle of hydrolysis reactions and condensation reactions of the silane groups. The trigger for these reactions is the atmospheric humidity. 10 to 30 minutes after the adherends have been coated, or else after only one adherend has been coated, especially in the construction industry, a sufficiently tacky surface layer has formed, and the parts can be assembled under gentle pressure. The adhesive layer subsequently reacts under the action of water vapour in the ambient air, and, with elimination of methanol from the methoxy groups, an elastic and insoluble polymer network is formed in the bonded joint.

According to a preferred embodiment, the mixture of silane-terminated polymers is a mixture of silane- terminated polyoxyalkylenes and silane-terminated poly(alkyl (acrylates and/or methacrylates) ) having alkyl groups of 1 to 10 carbon atoms, in a mass ratio of 2:1 to 1:3. As a result of this combination of the two types of MS polymers it is possible to tailor the proportion of cohesion to adhesion in the adhesives of the invention.

According to a preferred embodiment, the silane- terminated polyoxyalkylenes employed comprise silane- terminated polyoxypropylenes, and preferably bis [3-

(methyldimethoxysilyl) propyl] polyoxypropylene. These silane-terminated polymers, more accurately prepolymers, which crosslink after hydrolytic elimination of methanol from the methoxysilane groups, make it possible to formulate weathering-stable contact adhesives .

In addition, the use of silane-terminated polyoxy- propylenes of different viscosities makes it possible to tailor the viscosity of the contact adhesive claimed. The viscosity of the silane-modified polyoxypropylene prepolymers is determined by the molar masses and/or molar-mass distribution of the MS polyoxy- propylenes. From a practical viewpoint the number- average molar mass of the silane-terminated polyoxypropylene prepolymers employed, i.e. prior to hydrolytic elimination of the methoxy groups, ought to vary between 1000 and 30 000 g/mol.

In accordance with a further particularly preferred embodiment of the invention, silane-terminated polyurethanes are used in addition. The preparation of silane-terminated polyurethanes is prior art and can take place, for example, by reaction of isocyanate- containing prepolymers with aminosilanes . In this way it is possible to combine the favourable properties of the polyurethanes with the properties of silicones, while avoiding the toxicological problems of isocyanates.

According to another preferred embodiment, the one- component, solvent-free contact adhesive comprises 30% to 60% by mass of chalk powder hydrophobized with stearate. The chalk materials used are hydrophobized with typical stearates, such as calcium stearate, or else with stearic acid. The stearate content ought not to exceed 3%.

The addition of chalk has the function, generally speaking, of tailoring the physical and mechanical properties of the contact adhesive claimed to the specific application, as far as possible. The bond strengths, especially, are favourably influenced through the addition of chalk. At the same time it is possible to adjust the viscosity to the desired level.

The particle size of the chalk powders employed can range within a broad spectrum, as a function of the target film thicknesses. For the purposes of the present invention, however, preference is given to using chalk powders with particle sizes of less than 20 μm and most preferably less than 10 μm.

Since on exposure to moisture the methoxy groups of the silane-terminated prepolymers undergo hydrolysis and crosslinking, it is necessary when producing the contact adhesive claimed to add a drying agent with the function of a water scavenger. This makes it possible to ensure that the contact adhesive can be stored. Particularly suitable for this function is vinyltrimethoxysilane. As a result of the electronic structure of that compound, the methoxy groups hydrolyse very much more rapidly than the methoxy groups of the MS polymers employed. Only when the drying agent has been largely consumed are the MS polymers crosslinked. The amounts of vinyltrimethoxysilane added are guided by the water content of the ingredients; commonly, however, they are around 1% by mass.

In order to improve the adhesive properties of the contact adhesive on surfaces to be assembled it is possible in addition to add adhesion promoters, especially silane-based adhesion promoters. Additions of 0.3% to 3% by mass of aminopropyltriethoxysilane or aminopropyltrimethoxysilane have proved to be sensible.

In order to accelerate the curing of the contact adhesive of the invention following application, silanol condensation catalysts (curing catalysts) are added at the production stage. Those which have proven to be suitable include carboxylates and chelates of tin, of titanium and of aluminium. Particularly suitable are mixtures of dibutyltin diacetylacetonate and tetraethyl silicate. The mass fractions of the two catalysts, calculated together, are 0.2% to 5% by mass, preferably 0.5% to 1.5% by mass. The mass ratio of dibutyltin diacetylacetonate to tetraethyl silicate can vary from 5:1 to 2:1.

In addition it is possible for the contact adhesive claimed to comprise customary auxiliaries, such as, in particular, colour pigments, plasticizers, light stabilizers and fillers.

Examples of suitable colour pigments are titanium dioxide, iron oxide, carbon black or organic colour pigments .

For plasticization it is possible to have recourse to established compounds. Mention might be made here primarily of the known phthalic esters, cyclohexanedicarboxylic esters or polypropylene oxide.

In addition it is possible to improve the light stability of the contact adhesive by means of light stabilizers. Especially suitable for this purpose are the compounds known as HALS compounds (sterically hindered light stabilizers), such as bis (2 , 2, 6, 6-tetra- methyl-4-piperidyl) sebacate or compounds from the group of the benzotriazoles, such as 2, 4-di-tert-butyl- 6- (5-chlorobenzotriazol-2-yl) phenol, for example.

Other possible additions which may be of benefit in specific cases are finely divided fillers, coated or uncoated. Examples that may be cited here include the following: dolomite, talc, mica and heavy spar.

The production of the contact adhesive of the invention takes place in batchwise-operated vacuum mixers. The liquid silane-terminated polymer components (MS polymers) are weighed out and charged to the mixer; then, if desired, plasticizer is added. These ingredients are carefully mixed and then the solid components, principally chalk powder, are incorporated with strong shearing under a simultaneously applied weak vacuum (approximately 50 mbar) .

After the cooling of the batch to approximately 50⁰C or below, the drying agent is incorporated. After that the curing catalysts can be added and mixed in. Since after admission of air it is possible for gas bubbles to have formed in the batch, degassing is carried out briefly again.

If silane-terminated polyurethanes are used, they ought, in accordance with Claim 12, to be incorporated only after the drying agent has been added, in order to avoid premature reactions with residual moisture.

The one-component, solvent-free and water-free contact adhesive accessible in this way finds application in the techoindustrial sector, in craft and among D-I-Yers. It is especially suitable for flat adhesive bonds in the construction industry, on account of its excellent adhesion capacity to concrete screeds, wood, plastics, ceramic, painted surfaces and metals. For the application of the contact adhesive of the invention, either both or one of the surfaces to be assembled are given a thin coat of the contact adhesive, ranging from 0.2 mm up to a maximum of 1.5 mm, using a short-hair brush, coating knife or toothed applicator. Applying the contact adhesive to one surface is advisable particularly in the case of extensive bonding of, for example, carpets, plastic coverings or foils and films. For that purpose it is usually the floor screed that is coated with the contact adhesive. After a waiting time of 10 to 30 minutes the curing reaction has taken place sufficiently, as evident from the fact that a finger test produces strings of contact adhesive from the adhesive coating; at that point the two materials to be bonded are pressed against one another. Long pressing times bring no advantages with regard to the strength of the bonds; the pressing pressure, on the other hand, has a beneficial effect, and can be exerted by pressing with a roller, for example.

The contact adhesive of the invention is a one- component formulation. It contains no organic solvents and also no water. The adhesive bonds are water- resistant and of long-term elasticity. The adhesion, even without primer, to all common substrates is excellent, at 1 to 5 MPa. The bonded joints can be painted if necessary using agueous emulsion paints or solvent-borne paints.

Examples :

Example 1 :

17 kg of polyoxypropylene, silane-terminated and with a viscosity of 10 to 15 Pa- s, are charged together with 25 kg of polymethyl acrylate, silane-terminated, and 4 kg of polyoxypropylene, silane-terminated and with a viscosity of about 0.5 Pa* s, and also 4 kg of diisodecyl phthalate, to an evacuable planetary mixer, and these ingredients are carefully homogenized under atmospheric pressure. Thereafter 50 kg of chalk powder (hydrophobized with 1% by mass of calcium stearate and with a particle size of 90% by mass < 10 μm) are sheared under vacuum at 50 mbar.

The mixture is allowed to cool to about 40⁰C and under atmospheric pressure 1 kg of vinyltrimethoxysilane is carefully mixed in. Thereafter 1 kg of aminopropyl- triethoxysilane, as adhesion promoter, is added and briefly stirred in. Finally, the curing catalysts, 1 kg of dibutyltin diacetylacetonate and 0.5 kg of tetraethyl silicate, are added and the mixture is stirred until smooth. Subsequently, with slow stirring, degassing is briefly repeated.

For testing purposes, the resulting contact adhesive is applied with a coating knife to an aluminium plate and/or a plywood panel in a film thickness of 1.0 mm. The characteristic values measured, after a storage time of 5 days at 20⁰C and 60% relative humidity, are compiled in Table 1.

Example 2 : 25 kg of polyoxypropylene, silane-terminated and with a viscosity of 12 Pa- s, 25 kg of polyethyl acrylate, silane-terminated, and 5 kg of polyoxypropylene, silane-terminated and with a viscosity of about 0.5 Pa-s, are charged to a vacuum mixer and 40 kg of hydrophobized chalk powder, < 10 μm particle diameter, are added. Then the mixture is sheared under a weak vacuum (75 mbar) at moderate rotational speed (35 rpm) until it is homogeneous. It is cooled to room temperature, 0.5 kg of vinyltrimethoxysilane is added, and the ingredients are mixed under atmospheric pressure for 15 minutes. Thereafter aminopropyl- triethoxysilane is stirred in. Finally, the catalyst mixture, consisting of 1 kg of dibutyltin diacetylacetonate and 0.5 kg of tetraethyl silicate, is added, the ingredients are stirred until homogeneous, and further degassing is carried out briefly, in order to remove bubbles of air and gas.

The resulting contact adhesive is applied to specimens of aluminium and to plywood panels in a thickness of 1.0 mm and, after it has dried off (5 days at 20⁰C and 60% relative humidity) , it is tested. Results of testing are compiled in Table 1.

Example 3

20 kg of polyoxypropylene, silane-terminated and with a viscosity of 13 Pa- s, 20 kg of polyethyl acrylate, silane-terminated, and 4 kg of diisodecyl phthalate are charged to a vacuum mixer and mixed homogeneously with 50 kg of chalk powder (hydrophobized, particle size 90% < 10 μm) under a pressure of 20 mbar. Thereafter 1.5 kg of vinyltrimethoxysilane, as drying agent, are added and the ingredients are mixed for 15 minutes under atmospheric pressure in the absence of atmospheric humidity. Subsequently, silane-terminated polyurethane resin is added and mixed in slowly. Only then are the adhesion promoter (1 kg of aminopropyltriethoxysilane) and the catalyst mixture ( 1 kg of dibutyltin acetylacetonate and 0.5 kg of tetraethyl silicate) mixed in, in succession, followed by stirring of the batch under vacuum (75 mbar) until smooth.

The resulting contact adhesive is tested as indicated in Example 1. The results are found in Table 1. Table 1:

Claims

1. One-component, solvent-free contact adhesive, characterized in that it is composed of a mixture of silane-terminated polymers of together 25% to 70% by mass, 20% to 70% by mass of chalk powder, 0.3% to 5% by mass of drying agents, 0.5% to 3% by mass of curing catalysts, 0.2% to 3% by mass of adhesion promoter and, if desired, pigments, plasticizers, fillers, light stabilizers and heat stabilizers .

2. One-component, solvent-free contact adhesive according to Claim 1, characterized in that it comprises as silane-terminated polymers a mixture of silane-terminated polyoxyalkylenes and silane- terminated poly(alkyl (acrylates and/or methacrylates) ) having an alkyl group of 1 to 10 carbon atoms, in a mass ratio, based on polyoxy- alkylenes to poly (alkyl (acrylates and/or methacrylates)), of 2:1 to 1:3.

3. One-component, solvent-free contact adhesive according to Claims 1 to 2, characterized in that it comprises as silane-terminated polyoxyalkylenes bis [3- (methyldimethoxysilyl) propyl] polyoxy- propylene .

4. One-component, solvent-free contact adhesive according to Claims 1 to 3, characterized in that it comprises 30% to 60% by mass of chalk powder hydrophobized with stearates.

5. One-component, solvent-free contact adhesive according to Claims 1 to 4, characterized in that it comprises as drying agent 0.3% to 5% by mass of vinyltrimethoxysilane .

6. One-component, solvent-free contact adhesive according to Claims 1 to 5, characterized in that it comprises as adhesion promoter 0.2% to 3% by mass of aminopropyltriethoxysilane .

7. One-component, solvent-free contact adhesive according to Claims 1 to 5, characterized in that it comprises as curing catalyst a mixture of tin catalysts, such as dibutyltin diacetylacetonate, and tetraethyl silicate in a mass ratio of 5:1 to 1:2.

8. Use of the contact adhesive composition according to any one of the preceding claims for the elastic adhesive bonding of two or more like and/or different materials.

9. Method of primerless joining of two or more like and/or different materials, characterized in that contact adhesives according to at least one of Claims 1 to 7 are applied to a component or to two of the components to be joined, in a film thickness of up to 1.5 mm, and after a waiting time of 10 to 30 minutes the components to be bonded are assembled.

10. Process for producing a one-component, solvent- free contact adhesive according to Claims 1 to 7, characterized in that in a vacuum mixer first the liquid, silane-terminated polyoxyalkylenes and silane-terminated alkyl acrylates are mixed with the liquid and solid additives and the mixture is degassed and then, in succession, drying agents, adhesion promoters and curing catalysts are incorporated individually, after which the mixture is again degassed.

11. Process for producing a one-component, solvent- free contact adhesive according to Claims 1 to 7, characterized in that in a vacuum mixer first the liquid, silane-terminated polyoxyalkylenes and silane-terminated alkyl acrylates are mixed with the liquid and solid additives and the mixture is degassed and then the drying agent is incorporated, after which the silane-terminated polyurethanes are mixed in and then, in succession, adhesion promoter and curing catalyst are incorporated and the mixture is degassed.