Patent Application
20070260031
As used herein in the specification and claims, including as used in the examples and unless otherwise expressly specified, all numbers may be read as if prefaced by the word “about”, even if the term does not expressly appear. Also, any numerical range recited herein is intended to include all sub-ranges subsumed therein.
As NCO-terminated prepolymers with isocyanate contents of 1 to 20 wt. %, preferably 2 to 16 wt. %, are to be understood reaction products of aliphatic polyisocyanates with hydroxyl polyesters and/or hydroxyl polyethers which cure as such or formulated with plasticisers, fillers, rheology aids by the reaction with atmospheric moisture and/or substrate moisture to high-molecular polyurethane polyureas.
Of the possible aliphatic polyisocyanates are to be understood in particular hexamethylene diisocyanate, isophorone diisocyanate and 4,4′-diisocyanato-dicyclohexylmethane in the form of its steric isomer mixtures. Included therewith are of course also the use or incorporation of the afore-mentioned diisocyanates in the form of their derivatives, such as for example biurets, allophanes, uretdiones and trimers and mixed forms of these derivatisations.
The hydroxyl polyesters include reaction products of aliphatic dicarboxylic acids, such as for example adipic, azelaic, sebacic and/or dodecanoic diacid and/or aromatic dicarboxylic acid, such as ortho, iso or terephthalic acid with glycols of the type ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,4-butanediol, neopentyl glycol or 1,6-hexanediol and/or triols such as for example glycerol or trimethylol propane. The reaction is a normal melt condensation as described in Ullmanns Enzyklopadie der technischen Chemie, “Polyester”, 4th edition, Verlag Chemie, Weinheim, 1980. The result, depending on the composition, are liquid grades, amorphous grades with glass transition temperatures of >20° C. or crystalline polyester polyols with melt ranges of 40-90° C. The molecular weight range of 200 to 30000. The molecular range of 400 to 5000 is particularly preferred.
Appropriate hydroxyl group-terminated poly-ε-caprolactone and/or hydroxyl group-terminated polyesters of carbon dioxide such as for example hexanediol-1,6-polycarbonate or mixtures of carbon dioxide and ε-hydroxycarboxylic acid can also be used.
To be named here are also in particular the products which are derived from reaction products of glycerol and hydroxyl fatty acids, in particular castor oil and its derivatives, such as for example singly dehydrated castor oil.
Of the polyether polyols are to be named in particular those normally by base-catalysed addition of propylene oxide and/or ethylene oxide to starting molecules, such as for example water, 1,2-propanediol, 2,2-bis(4-hydroxyphenyl)propane, glycerol, trimethylolpropane, ammonia, methylamine or ethylene diamine with molecular weights of 200 to 6000, in particular 200 to 5000. In particular, the polypropylene ether polyols are also those which can be obtained by double metal catalysts and enable the synthesis of very high-molecular well-defined polyether polyols with molecular weights of up to 25000. The polyether polyols with therein dispersed organic fillers, such as for example addition products of tolyulene diisocyanate with hydrazine hydrate or copolymers of styrene and acrylonitrile, are of course also possible.
The polytetramethylene ether glycols, obtainable by polymerisation of tetrahydrofuran, with molecular weights of 400 to 4000 but also polybutadienes containing hydroxyl groups can also be used.
Mixtures of the mentioned polyols in mixture with low-molecular polyols such as for example ethylene glycol, butanediol, diethylene glycol or 1,4-butanediol can of course also be used.
The afore-mentioned polyols can of course be reacted with all polyisocyanates, aromatic and also aliphatic, before the actual prepolymerisation to urethane modified hydroxyl compounds.
The production of the isocyanate-terminated prepolymers takes place in accordance with known methods by causing the polyols to react with a stoichiometric excess of aliphatic polyisocyanates at temperatures of 30 to 150° C., preferably 60 to 140° C. This can take place discontinuously in vessels or continuously in vessel cascades or via mixers.
It is particularly preferred that the hydroxyl compounds are reacted with a high excess of diisocyanates and that the monomer diisocyanate still present is extracted from the prepolymer according to known techniques, such as for example via a thin layer evaporator at elevated temperature and reduced pressure. In this way, prepolymers with a low monomer content which depending on the residual monomer content are no longer subject to labelling, are obtained.
Modified aliphatic polyisocyanates can be added to all these products before, during or preferably after the reaction to fine control the properties. Such products are commercially available, such as for example under the names Desmodur® N 100 (HDI biuret modification) or Desmodur® N 3300 (HDI trimerisation) of Bayer AG or Vestanat® (IPDI trimer).
According to the end viscosity to be expected which depending on the formulation can vary between low viscosity to high viscosity, various aggregates are possible.
The catalyst bis(dimethylaminoethyl)ether is added to the prepolymers before, during or preferably after the end of prepolymer formation.
The quantity of this catalyst added depends on the desired processing time. As a rule, quantities of 0.02 to 3.0 wt. %, preferably 0.1 to 2.0 wt. %, particularly preferably 0.5 to 1.5 wt. %, based on the prepolymer, are sufficient.
In addition, solvents, fillers, colorants and rheology aids as known in practice can be added to the prepolymers.
Chalk, barytes, and also fibrous fillers such as polyamide fibres or polyacrylonitrile fibres may be mentioned as fillers. Among the rheology aids, in addition to the common industrial additives such as aerosils, bentonites or hydrated castor oil, can also be named lower-molecular amines which in combination with polyisocyanates very quickly form a pseudoplasticity. With all these additives it must be ensured that moisture is excluded absolutely because this would cause a premature reaction in the container.
Application of the adhesives and sealants takes place for example by knife application, spraying, brush application or even in more compact form in the form of a bead.
A good method for assessing the different curing phases of such systems is possible for example using commercial equipment such as for example Drying Recorder BK 10 (The Mickle Laboratory Engineering Co. Ltd) which is widely used in the coatings, adhesives and sealants industry. A needle if necessary loaded with a weight is passed at constant speed through a thin film of the prepolymer to be assessed on a support (e.g. glass plate). Three phases which according to the definition are designated by the terms “processing time” and “through-hardening time” are observed.
At first the needle runs through the liquid film and the track of the needle disappears more or less completely, which is to be correlated with the processing time. The end of the processing time, also termed skinning time, open time or contact tack time, is indicated by the first appearance of a permanent track of the needle.
There then follows a fairly long section (corresponding to time passed) in which the needle leaves a track. When the film is sufficiently through-hardened, the needle is no longer able to penetrate the polymer film, the needle runs track-free over the polymer film which is to be designated in measurement terms through-hardening time. The beginning of this state is connected in measurement terms of course in addition to the general composition of the adhesive to the weight with which the needle is loaded and cannot therefore be synonymous with the time in which the polymer reaches its end properties. The time however correlates very well with terms such as for example reaching the “manual strength”, “folding strength”, etc.
The practitioner wants the time between the end of the processing time and achieving the through-hardening time to be as short as possible.
Shortening this time with as far as possible any processing time and as far as possible unimpaired storability of NCO-terminated prepolymers is the subject matter of the invention.
The subject matter of the invention is also the use of thus catalysed prepolymers as adhesives and/or sealants in which curing of the aliphatic isocyanate groups takes place with moisture. Possible applications inter alia are the bonding of wood specimens, such as for example dovetail joints, wooden boards or beams. Likewise, bonding wood shavings, woodchips or wood flour into sheets or shaped bodies is possible. In these applications, prepolymers with isocyanate contents of approx. 10 to 20% are particularly suitable. Lower isocyanate contents are more suitable for low-module polymers, such as for example for the use of non-discolouring light joint sealants or for the range of reactive polyurethane hotmelts in which such a prepolymer is applied at temperatures of over 80° C. and on cooling builds strength on the basis of physical processes and the end reaction takes place with moisture (cf EP-A 0 354 527).
The following examples should explain the invention.
1000 g (4.587 mol) polypropylene glycol with a hydroxyl value of 515 mg KOH/g and 3850 g (22.94 mol) hexamethylene diisocyanate are reacted at approx. 80 to 90° C.
The prepolymer shows at the end of the reaction time of 6 hours a constant NCO value of 31.5%. The prepolymer is then largely freed of excess monomers at 160° C. and 0.1 mm Hg using a short path evaporator.
A medium-viscosity prepolymer with an isocyanate content of 12.5% and a viscosity of 4500 mPas at 23° C. is obtained. The residual monomer content is 0.35%.
1000 g (1.0 mol) polyester polyol based on diethylene glycol and adipic acid with a hydroxyl value of 112 mg KOH/g and an acid number of 10.9 mg KOH/g and 888 g (4.0 mol) isophorone diisocyanate are reacted at approx. 100° C.
The prepolymer shows at the end of the reaction time of 9 hours a constant NCO value of 13.2%. The prepolymer is then largely freed of excess monomers at 180° C. and 0.1 mm Hg using a short path evaporator.
A high-viscosity prepolymer with an isocyanate content of 5.8% and a viscosity of 6000 mPas at 50° C. is obtained. The residual monomer content is 0.25%.
Using a doctor blade (250 μm), a film is applied to a glass plate previously cleaned with ethyl acetate and immediately placed in the drying recorder. The needle is loaded with 10 g and moves over a period of 360 minutes over a 35 cm section.
The drying recorder is situated in a climatic chamber at 23° C. and 50% relative humidity.
100 g of the prepolymer from Example 1 are mixed with various commercially available catalysts such that a processing time (visible appearance of a permanent track of the needle in the film) of approx. 25 to 60 minutes is produced with the drying recorder.
The through-hardening time is given at the time the permanent track of the needle disappears from the film.
As can be seen from the table, only with the amine catalysts (Example 3B, 3 C and 3H, or 3 I) at doses of 1 wt. % and less are greatly shortened processing times achieved with certainty.
Long-term storage tests were carried out at 60° C. in aluminium bottles with catalysts Example 3B, 3 C and 3H.
The NCO values, viscosity at 50° C. processing time were determined.
Test 4 B was terminated prematurely due to lack of storage stability (gelation after 1 week).
Test 4 C was terminated prematurely due to lack of stability of the catalyst (increasing deactivation).
The advantages of the catalyst according to the invention bis(dimethylaminoethyl)ether are clear (Example 4D). A slight impairment of the storage stability compared with the uncatalysed prepolymer is observed, but the drop in the NCO value or rise in viscosity over a storage period of 112 days (4 weeks) at 60° C. is to be tolerated in view of the enormous acceleration in the water reaction.
561 g prepolymer from Example 1 was mixed with 339 g Desmodur® N 3300 from Bayer AG (trimer of hexamethylene diisocyanate with 21.8% NCO content and 0.1% free HDI monomer) and 100 g chalk (Omya Kreide). The result is an adhesive mixture with approx. 14.5% NCO content. The adhesive is tested with and without 0.45% wt. % bis(dimethylaminoethyl)ether as adhesive for beechwood test pieces (split-free).
The prepolymer was coated on one side and the test pieces (50×20×5 mm) for 10×20 mm overlapping kept in the press at 5 bar at 23° C. and 50% relative humidity. The adhesive strength is then measured using the tensile shear test (10 test pieces each).
The following results are obtained
The catalysed adhesives according to the invention give good composite strengths after a short period.
Parallel to this, 1 mm thick films on cardboard were exposed to intensive sunlight for 7 weeks.
For the uncatalysed film, a yellowness index (measured with the colour difference “Micro Color” measuring device of Dr. Lange, reference number LMG 051/052) of 5.5 and for the catalysed variant a yellowness index of 6.8 is observed.
Result: no drastic increase in colour as is occasionally observed with tert. aliphatic amine catalysts.
100 g of the prepolymer from Example 2 are mixed with various commercially available catalysts such that a processing time (visible appearance of a permanent track of the needle in the film) of approx. 25 to 60 minutes is produced with the drying recorder.
The through-hardening time is given at the time the permanent track of the needle disappears from the film.
As can be deduced from the table, only with the amine catalysts (Examples 6D and 6 G, or 6H) at doses of 1 wt. % and less are greatly shortened processing times achieved with safety.
Storage stability tests at 60° C. are done in aluminium cartridges with the mixtures (zero sample Example 2; mixture Example 6D and Example 6H).
The NCO values, viscosity at 50° C. processing time were determined.
Test 7 B was terminated prematurely due to lack of storage stability (gelation after 1 week).
Test 7 C was terminated prematurely due to lack of stability of the catalyst (increasing deactivation).
The advantages of the catalyst according to the invention bis(diethylaminoethyl)ether are clear (Example 7D). A virtually identical storage stability compared to the zero sample is observed. The processing time can be drastically reduced.
4000 g of a hexanediol adipate (Baycoll® AD 5027 from Bayer AG) with a hydroxyl value of 28 mg KOH/g (1.0 mol) are dewatered at 120° C. for 60 minutes under vacuum. 399.6 g (1.8 mol) 3,5,5-trimethyl-3 isocyanatomethylene-cyclohexylisocyanate (Desmodur® I from Bayer AG) are added at 120° C.
After 60 minutes it is filled in cartridges and then post-cured at 100° C.
The storage stability is tested after 4, 24, 48 and 72 hours at 100° C.
4000 g of a hexanediol adipate (Baycoll® AD 5027) with a hydroxyl value of 28 mg KOH/g (1.0 mol) are dewatered at 120° C. for 60 minutes under vacuum. 399.6 g (1.8 mol) 3,5,5-trimethyl-3 isocyanatomethylene-cyclohexylisocyanate (Desmodur® I from Bayer AG) are added at 120° C.
1.8 g (0.5 wt. %) bis(dimethylaminoethyl)ether are added after 60 minutes and homogenised.
After 30 minutes it is filled in cartridges and then post-cured at 100° C.
The storage stability is tested after 4, 24, 48 and 72 hours at 100° C.
The cure characteristic is determined by means of the “folding test”. For this, a 0.1 mm thick prepolymer film is knife-applied to a glass plate, the solidified prepolymer subjected to a folding test after certain times (at 23° C. and 50 relative atmospheric humidity) by folding the polymer film 180°. Only a largely reacted polymer will survive the test. Unreacted polymers break because no sufficiently high molecular weight is constructed.
Again for the range of reactive polyurethane hotmelts, the catalyst according to the invention bis(dimethylaminoethyl)ether shows only insignificantly impaired storability compared with the uncatalysed system, with a significantly more rapid curing.
The adhesive heated to 130° C. is applied with a doctor blade to beechwood test pieces and bonded immediately with a PVC film
The strength is determined in the peel test.
The adhesive heated to 130° C. is applied to beechwood test pieces on one side and bonded immediately with another beechwood test piece and torn in the tensile shear test.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102006020605.3 | May 2006 | DE | national |
