Storage stable, humidity curing adhesives

A morpholine group comprising catalyst of the general formula, ##STR1## wherein n+m is >1 and R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8, R.sub.9, R.sub.10, R.sub.11, R.sub.12, R.sub.13 and R.sub.14 are independently from each other hydrogen or an alkyl group, particularly a methyl or an ethyl group, is described. Said catalyst is particularly suitable for the use in storage stable polyurethane (PU)-compositions usable as adhesives, sealings, coatings or pretreatments with a primer. Said PU compositions have a delayed skinning time and thus an extended assembly time but nevertheless a fast development of strength, and they are suitable for the application on metal, glass, ceramics, wood, cementitious substratums and plastic substratums.

CROSS REFERENCE TO RELATED APPLICATIONS 
This application claims the priority of Swiss Application No. 1464/96, 
filed Jun. 12, 1996, the disclosure of which is incorporated herein by 
reference in its entirety. 
FIELD OF THE INVENTION 
The present invention regards a catalyst, particularly a catalyst for usage 
in polyurethane systems and especially for the use in humidity reactive 
polyurethanes (PU), its production and its use. Particularly the invention 
concerns a catalyst which is suitable for being used in adhesive, sealing 
and coating compositions and pretreatments with a primer, which are 
storage stable if stored under exclusion of humidity. Said compositions 
are on the basis of humidity reactive polyurethanes (PU) which are fast 
curing in the presence of humidity. 
BACKGROUND OF THE INVENTION 
Adhesive, sealing and coating compositions and pretreatments with a primer 
on the basis of polyurethane prepolymers which are humidity curing are 
known and are broadly used for coating, connecting and sealing building 
and construction materials such as e.g. plastics, glass, ceramics, 
varnished sheet metals, metals, wood, concrete and other substratums. 
Such compositions do advantageously comprise little or no solvents and they 
contain isocyanate groups comprising prepolymers which are prepared in a 
known manner by reacting bifunctional or polyfunctional polyols with an 
excess of diisocyanate or polyisocyanate, whereby the monomers content in 
the whole formulation is as low as possible, i.e. smaller than 1%, 
preferably smaller than 0.5%. 
In the presence of e.g. humidity, the isocyanate groups of the monomers as 
well as the isocyanate groups at the ends of the polyurethane (PU) 
prepolymer chains react with water under formation of an instable carbamic 
acid group that spontaneously decomposes to amines and carbon dioxides. 
Said amino group then does fast react with a further isocyanate group 
under the formation of a urea group. Said cross-linkage reaction causes a 
molecule growth and leads to a hard or tough elastic composition suitable 
for adhesive sealing and coating purposes. 
By the admixture of catalysts, the reaction of water with isocyanate groups 
can be accelerated. Known catalysts are titanates, organometal compounds 
such as e.g. tin or lead compounds that can also be combined with other 
catalysts, particularly tertiary amines. Generally the catalysts are used 
in amounts of up to 2% referred to the whole formulation. 
If large amounts of catalyst are used to speed up the curing throughout the 
layer, on the one hand the stability of the PU system is affected, making 
an application after short storage time impossible due to an enhancement 
in the viscosity. On the other hand the temperature stability of the cured 
composition is reduced due to depolymerisation. Desired is a PU system 
that is still applicable after a storage time of more than 6 months. 
U.S. Pat. No. 4,780,520 describes the use of dimorpholinodiethylether 
(DMDEE) as catalyst for the formulation of a storage stable fast curing PU 
system, whereby DMDEE is used in an amount of 0.2 to 1.75% referred to the 
whole composition. 
GB patent application No. 2,231,879 shows that the use of 0.2 to 2% of 
tetramethyl substituted DMDEE also enables the formation of a storage 
stable PU-system, whereby the strength development at low temperature and 
low humidity, i.e. at 5.degree. C. and 50% relative humidity, is faster 
than with a DMDEE catalysed PU-system. 
In U.S. Pat. No. 4,705,840 2,2'-dimorpholinylalkylethers are disclosed 
which at 24.degree. C. and 55% relative humidity show the same early 
strength as DMDEE, i.e. 7.5 minutes after application of an orthopaedic 
bandage, at half the concentration of DMDEE, i.e. with 5% by mole. 
The use of the above mentioned catalysts for the formulation of fast curing 
PU systems with fast strength development has the disadvantage that the 
assembly time is reduced to below 8 to 10 minutes. The assembly time, also 
termed open time, is defined as the time between the application and the 
assembling for which a good adhesion is granted. The skinning time 
according to experience is shorter than or identical with the assembly 
time and is an efficient method for the approximate determination of the 
assembly time (see examples). 
SHORT DESCRIPTION OF THE INVENTION 
The goal of the present invention was to provide catalysts on the basis of 
morpholine, which catalysts are suitable for the production of fast 
curing, storage stable PU systems providing a fast strength development at 
low temperatures and low humidity (e.g. 5.degree. C. and 80% relative 
humidity or 23.degree. C. and 20% rel. humidity, respectively). Said 
catalysts provide furthermore, compared to state of the art products, an 
extended assembly time, i.e. more than 10 minutes, and a good temperature 
stability. 
This goal was achieved by the inventive catalysts of the following formula 
##STR2## 
wherein n+m is &gt;1 and wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, 
R.sub.6, R.sub.7, R.sub.8, R.sub.9, R.sub.10, R.sub.11, R.sub.12, 
R.sub.13, R.sub.14 independently from each other represent hydrogen or an 
alkyl group, particularly a methyl group or an ethyl group. 
The inventive catalysts primarily enhance the reactivity of the isocyanate 
groups and therefore are suitable for single-component (sc) systems as 
well as two-component (tc) systems which cure with water or curing agents 
on the basis of e.g. reactive OH groups or NH.sub.2 groups. The inventive 
catalysts can be used alone as well as in combination with each other or 
in combination with known catalysts, e.g. catalysts on the basis of 
organometallic tin and/or titanium catalysts (see above). 
The inventive catalysts are particularly suitable for humidity curing 
single-component systems. 
The effect of the above described morpholine derivatives in humidity curing 
systems possibly can be seen in that the hydrophilic part--similar to a 
crown ether--transports water into the matrix and thus in the proximity of 
the reactive isocyanate groups, and that the two tertiary amines 
catalytically assist in the reaction of said water with the isocyanate 
group. 
Therefore the inventive catalysts are very suitable for the use in 
single-component systems. The catalytic effect possibly involves a proton 
transfer to the amide nitrogen of the isocyanate group (literature 
thereto: Herlinger Heinz, Habilitationsschrift "Struktur und Reaktivitat 
der Isocyanate", Universitat Stuttgart, 1970, p. 24). After the reaction 
of the isocyanate with water on the one hand carbon dioxide is formed, on 
the other hand the catalyst, the morpholine derivative, is again 
liberated. As already mentioned above, this explanation of a possible kind 
of action is only a probable explanation. Said explanation is not intended 
to limit the invention in any way. 
In a particularly favourable embodiment, the hydrophilic behaviour of the 
morpholine derivative is enhanced. Said enhancement is achieved by the 
incorporation of a polyethylene oxide between two morpholine groups. The 
water absorbing character of the inventive catalysts and therewith the 
diffusion gradient of the PU system is thus, that the water from the 
environmental humidity enters the PU composition prior to it being caught 
by the isocyanate groups present at the surface. Thereby the skinning time 
is somewhat delayed and the assembly time is extended with simultaneously 
fast strength development. This combination of features is very 
advantageous for the user. Furthermore, the traces of water present on the 
surface of the substratum are transported away from the interface between 
adhesive and substratum due to the hygroscopic character of the PU 
composition. Thereby an immediate cross-linking is avoided leading to an 
improved wetting of the substratum and thereby to improved adhesive 
properties. 
The inventive PU compositions that are catalysed by the inventive 
catalysts, due to their excellent stability can be processed at enhanced 
temperatures, i.e. at temperatures up to 95.degree. C., and thus enable 
the production of storage stable humidity reactive hot melts. Of all one 
component curing systems such humidity reactive hot melts have the best 
strength development due to the enhancement in the viscosity upon cooling 
after application and due to the binder system that is fast curing upon 
contact with humidity. 
The inventive PU compositions are particularly suitable as adhesives, 
sealings, coating materials and pretreatments with a primer. They exhibit 
fast strength development and, in comparison with the state of the art, a 
delayed skinning time and therewith an extended assembly time. They are 
suitable for the application on metal, glass, ceramics, wood, cementitious 
and plastic substratums. 
DETAILED DESCRIPTION OF THE INVENTION 
The inventive catalyst is a morpholine group comprising compound of general 
formula 
##STR3## 
wherein n+m is &gt;1 and R.sub.1 to R.sub.14 are independently from each 
other either hydrogen or an alkyl group, particularly a methyl group or an 
ethyl group. In preferred catalysts the sum of n+m is between 2 and 10, 
particularly between 2 and 5. Specific catalysts that are relatively easy 
to produce are those, wherein 
R.sub.1 to R.sub.14 are hydrogen 
R.sub.1 to R.sub.4 and R.sub.9 to R.sub.14 are hydrogen and R.sub.5 or 
R.sub.6 and/or R.sub.7 or R.sub.8 are methyl groups, whereby those 
R.sub.5, R.sub.6, R.sub.7 and R.sub.8 which are not methyl groups are 
hydrogen, 
R.sub.1, R.sub.3, R.sub.11 and R.sub.13 are methyl groups and R.sub.2, 
R.sub.4 to R.sub.10, R.sub.12 and R.sub.14 are hydrogen. 
The inventive catalysts can e.g. be produced according to methods of the 
Canadian patent application 2,103,730 of Miles Inc., USA (1992). 
They are especially suitable for the use in isocyanate groups containing 
single-component polyurethane systems and two-component polyurethane (PU) 
systems. In particular, the inventive catalysts are very suitable for 
being used in single-component systems. 
The isocyanate groups comprising PU prepolymers which are present in the 
inventive systems as the main component, are the reaction products of 
isocyanate groups comprising substances with any compound that is reactive 
towards isocyanate groups (isocyanate reactive compound). Such compounds 
are e.g. compounds comprising aliphatic or aromatic polyol groups, 
polyamine groups or polymercapto groups, whereby the reaction can be 
performed in known manner at temperatures of about 80.degree. C. and 
optionally in the presence of a catalyst, e.g. dibutyl tin dilaurate, 
usually in stoichiometric amounts, i.e. for each group with an active 
hydrogen one at least two isocyanate groups comprising monomer. 
Usually polyols with a functionality of between 1.5 and 3 as well as with a 
molecular weight of between 400 and 10,000 are used, preferably such 
polyols with a molecular weight ranging from 1000 to 6000. Such polyols 
are e.g. polyalkylene polyols (e.g. polyethylene oxide, polypropylene 
oxide, polybutylene oxide, polytetrahydrofurane), polycarbonates, 
polycaprolactones, polyesters etc. 
The isocyanate groups comprising monomers can be aliphatic, cycloaliphatic 
or aromatic monomers such as e.g. 4,4'-diphenylmethane diisocyanate, 
2,4-toluene diisocyanate, hexamethylene diisocyanate, isophorone 
diisocyanate, perhydro-2,4'-diphenylmethane diisocyanate etc. 
The above described PU prepolymers preferably have a content of free 
isocyanate in the range of 1 to 3%, and usually the prepolymer is present 
in amounts referred to the whole composition of 20 to 60%, particularly of 
20 to 50%. 
The PU-systems of the present invention comprise at least one PU-prepolymer 
and an inventive curing catalyst. 
Said systems optionally can comprise usual additives and adjuvants such as 
e.g. emollients, fillers, latent curing agents, adhesion promoters, dyes, 
pigments, UV adsorbers, stabilisers, antioxidants, surface active 
additives, flame-retardants, fungistatically active substances etc. The 
kind and amount of said additives or adjuvants is dependent on the 
intended use of the inventive compositions. 
The amount of inventive isocyanate/water curing catalyst generally is in 
the range of 0.1 to 2% by weight, particularly 0.4 to 1% by weight, 
referred to the total weight of the composition. While with an amount of 
below 0.1% the desired curing effect is not achieved, an amount of more 
than 2% affects the storage stability of the PU-System. 
If necessary, the inventive catalysts can be combined with other, 
conventional catalysts, e.g. organometallic catalysts or catalysts on the 
basis of tertiary amines. 
During the production of the inventive single-component compositions care 
has to be taken that no humidity is introduced. All components used should 
largely be free of water and it is appropriate to admix to the PU system 
water binding or water reactive substances such as e.g. calcium oxide, 
molecular sieves, monofunctional isocyanate groups comprising compounds 
ortho formate etc. The ancillary processing is made in known manner with 
humidity exclusion, e.g. in cartridges, barrels etc. 
The inventive PU systems can, according to the requirement, be used for 
assembling, sealing or coating purposes and have numerous applications in 
the construction field as well as in industry, e.g. in the vehicle 
production, the marine etc., whereby application on very different 
materials such as e.g. glass, ceramics, plastics, PU elastomers, metals 
and varnished metals, is possible. Possibly a pretreatment with a primer 
is necessary to get the best possible adhesion. 
The invention is further described by means of examples regarding 
single-component adhesives. These examples however, are not intended to 
restrict the scope of the invention in any way.

EXAMPLES 
Examination of the Storage Stability of the Adhesive Compositions 
The viscosity of the adhesive composition was determined by extrusion of a 
cartridge at 23.degree. C. and with a pressure of 6 bars through a 3 mm 
nozzle resulting in a value in grams per minute. Said measurement was 
performed after storage at room temperature for 7 days (=&gt;original 
extrusion rate), 1 month and 3 months, respectively, as well as after heat 
ageing at 60.degree. C. for 7 days. Additionally the skinning time was 
determined for each sample in order to examine the influence of the 
storage conditions on the reactivity of the adhesive or the curing 
catalyst, respectively. 
Storage of the Specimen 
The specimen have been stored under two different climatic conditions, in 
order to determine the influence of said conditions on the open time and 
the strength development: 
climate I: 23.degree. C. and 50% relative humidity (standard climate), 
climate II: 5.degree. C. and 80% relative humidity 
Determination of the Skinning Time (ST) 
The skinning time is the time after application until the sample is track 
free. 
Determination of the Early Strength 
The development of the strength was determined using lap shear specimens 
consisting of two glass plates according to DIN 53504 (cross-head speed: 
200 mm/min, thickness of the adhesive layer: 5 mm) after storage of the 
specimens under the two above defined climatic conditions, whereby the 
measurement was made after 30 min., 60 min., 90 min. and 3 hours. The 
value of the lap shear strength (LSS) is indicated in N/cm.sup.2. 
Catalysts 
The following catalysts have been compared: 
1. DMDEE (2,2'-dimorpholino ethyl ether) of Nitroil, Germany 
2. TMDMDEE (tetra methyl-DMDEE) of Nitroil, Germany 
3. DMPEG 200 (dimorpholino polyethylene oxide glycol), (n+m about 3) 
While the two catalysts 1 and 2 belong to the state of the art, 3 
represents an inventive catalyst (for formula, production, see below). 
Formulation of the Adhesive Composition 
The kind of action of the catalysts was examined in a standard formulation 
based, besides of carbon black and chalk, on a prepolymer consisting of a 
trifunctional polyetherpolyol with a molecular weight of about 4500 and an 
aromatic isocyanate group comprising monomer, MDI (methylene-4,4'-diphenyl 
diisocyanate). The amount of catalysts was calculated thus that the 
morpholine content was 0.4% based on equivalents. This is for DMDEE about 
0.5% by weight, for TMDMDEE about 0.4% by weight and for the inventive 
catalyst DMPEG 200 about 0.8% by weight, all % by weight being referred to 
the whole adhesive formulation. 
Preparation of the Inventive Catalyst DMPEG 200 (According to the Canadian 
Patent Application CA 2103730/Miles Inc. USA/1992) 
A) Production of the Dimesylate of PEG 200 
##STR4## 
11.41 g polyethyleneglycol 200 (Fluka, pract.), 13.1 g triethylamine and 22 
ml methylene chloride (Fluka, puriss.) in a 250 ml three-necked flask, 
provided with reflux condenser, 25 ml dropping funnel and thermometer, are 
cleansed with nitrogen. Then the mesylchloride is slowly dropped from the 
dropping funnel into the flask under inert gas and with stirring by means 
of a magnetic stirrer. Since the reaction taking place is very exothermic, 
the flask is cooled in iced water and the dropping speed is regulated in a 
way that the temperature does not exceed 25.degree. C. During the 
reaction, a white/yellow precipitate is formed. When the dropping has 
finished, the funnel is washed with 20 ml methylene chloride that are 
dropped into the flask. The ice water container is omitted and the mixture 
is stirred for another 1.5 hours at ambient temperature and then carefully 
neutralised with a concentrated sodium hydroxide solution (5.1 g NaOH 
(Fluka No. 71691) in 20 ml water). Thereby the precipitate is dissolved 
leading to a yellow phase. After stirring for another hour, the phase is 
concentrated using a water jet pump. Thereby the temperature of the water 
bath is slowly raised to 70.degree. C. (the collecting flask 
advantageously is cooled with ice water in order to collect the methylene 
chloride for a further use). During the concentration, again a yellow 
precipitate is formed. This intermediate was not further purified. The 
thus obtained intermediate was directly further processed. 
B) Production of DMPEG 200 
##STR5## 
The milky residue of the intermediate is diluted with 20 ml methylene 
chloride and 15.87 g morpholine, 112 ml isopropanol and 20.1 g water free 
sodium carbonate (Fluka puriss No. 71350) (dried in an oven at 130.degree. 
C. over night) are added. The reaction mixture is then heated to reflux 
(bath temperature .about.85.degree. C.) and kept at said temperature for 
about 5 hours. The reaction product is filtered through a glass frit 
(porosity 4) and separated from a white residue, from which some further 
small amounts of the product can be separated by ether extraction. The 
slightly yellow coloured filtrate is then concentrated by means of a water 
jet pump and then the bath temperature is raised to 80.degree. C. and kept 
at this temperature for one hour. During said procedure a small amount of 
solid again precipitates. Said residue now is separated from volatile 
parts by means of a vacuum generated by a rotary pump during three hours. 
Then 100 ml diethyl ether (Fluka purum, F 31700) (PEROXIDE FREE!) are 
added, the mixture is stirred for 15 minutes and then filtered through a 
glass frit (porosity 4). The resulting filtrate is concentrated by 
distilling the ether under ambient pressure and then for one hour at 
80.degree. C. bath temperature under a vacuum generated by a water jet 
pump. The remaining solution is then completely dried under a vacuum 
generated by a rotary pump (pressure about 10.sup.-1.5 mbar) for 2 hours. 
About 14.7 g of thus cleaned product DMPEG 200 are obtained corresponding 
to a yield of about 73%. It comprises less than about 0.04% water 
(determined by Karl-Fischer titration). 
Results of the Comparison Tests 
The valuation was made in comparison to the DMDEE-catalysed PU adhesive, 
whereby the symbols used have the following meaning: 
same performance 
extended skinning time/faster strength development 
shorter skinning time/slower strength development 
A) ST and Strength Development in Climate I (23.degree. C./15% Relative 
Humidity (r.h.)) 
______________________________________ 
adhesive with: 
DMDEE TMDMDEE DMPEG 
______________________________________ 
ST (minutes) 
10 10 25 
LSS after 30' 
6.6 6.4 7.8 
LSS after 60' 
9.4 9.5 9.7 
LSS after 90' 
14.4 13.7 13.8 
LSS after 3 h 
21.5 20.8 32.1 
______________________________________ 
B) ST and Strength Development in Climate II (5.degree. C./80% r.h.) 
______________________________________ 
adhesive with: 
DMDEE TMDMDEE DMPEG 
______________________________________ 
ST (minutes) 
17 17 25 
LSS after 30' 
6.7 6.5 8.7 
LSS after 60' 
8.1 10.7 12.3 
LSS after 90' 
9.0 11.6 13.8 
LSS after 3 h 
14.0 17.6 24.0 
______________________________________ 
C. Determination of the Storage Stability 
The valuation was made by mentioning the percentual change with regard to 
the original value. The PU adhesive catalysed with DMDEE, according to 
experience obtained in practice, has satisfying storage stability. 
______________________________________ 
Extruded amount 
______________________________________ 
adhesive with: 
DMDEE TMDMDEE DMPEG 
______________________________________ 
1 month at rt 
&lt;20% &lt;20% &lt;20% 
3 months at rt 
&lt;40% &lt;40% &lt;40% 
______________________________________ 
Skinning Time 
______________________________________ 
adhesive with: 
DMDEE TMDMDEE DMPEG 
______________________________________ 
1 month at rt 
&lt;10% &lt;10% &lt;10% 
3 months at rt 
&lt;10% &lt;10% &lt;10% 
______________________________________ 
rt = room temperature