AU2013101162A4 - Low viscosity dimethoxy amino silane polyurethane with triethoxy silyl groups for sealants and adhesives with easy processing,high tensile strength and low methanol emissions on curing - Google Patents

Abstract

Wolantech Patent Application(DS) dated September 2013 Low viscosity dimethoxy amino silane polyurethane with triethoxy silyl groups for sealants and adhesives with easy processing, high tensile strength and low methanol emissions on curing. A moisture curable easy processing polymer of low viscosity is disclosed that uses methyl dimethoxy and triethoxy silyl groups on a single chain of polyether where the reduction in hydrogen bonding across polymer chains is reduced by several means. The low moisture sensitivity of the silyl groups allows processing with wet calcium carbonates and the use of triethoxy groups allows faster cure where the vinyl silane content allows alkoxy exchange to occur. Methanol emission on cure is also reduced.

Description

Wolantech Patent Application(DS) dated September 2013 Low viscosity dimethoxy amino silane polyurethane with triethoxy silyl groups for sealants and adhesives with easy processing, high tensile strength and low methanol emissions on curing. Field of Invention A composition of silylated polyurethane combining the use of different alkoxy molecules for low viscosity, fast cure and easy processing with wet calcium carbonate fillers. References to Foreign patents US 5,990,257 Johnstone et al C08G, 528/28 US 2004/0116639 Al Lim et al C08G, 77/00,528/10 US 2010/0204384 Al Huang et al C08G, 524/500 Background Of invention The development of silane terminated polyether and polyurethane polymers to replace standard isocyanate capped polyurethane prepolymers in one component moisture curing compositions have in the last 15 years shown these polymers are of lower toxicity, easy to process and a good alternate polymer to replace Polyurethane (PU) prepolymers . The new higher molecular weight double metal cyanide complex catalyst (DMC) containing low monol polyether polyols manufactured by most manufacturers have also made a big improvement in physical properties of these silane cross linked polymers .There has now been substantial replacement of solvent and some free isocyanate monomer containing sealants and adhesives in many market segments using traditional TDI or MDI based PU adhesives .The advantages of good UV resistance of these 1 silane modified polyether polymers has been very significant and is due to absence of any aromatic molecular groups. These difunctional methoxy silane capped polyether polymers have easy processing properties where the reinforcing precipitated calcium carbonates and carbon black fillers can be processed undried with the polymer and then dried with a moisture scavenger such as vinyl trimethoxy silane .This is a great advantage over polyurethane polymers that are a isocyanate group (NCO) terminated prepolymer, where the powders need to be very dry before mixing with the prepolymers. There is however a minor issue with methanol emission on curing and high catalyst and amino silane content needed for fast curing adhesives. An alternate polymer design where an isocyanate terminated prepolymer is capped with a secondary amino propyl trimethoxy silane ( of various types) has shown the benefits of better crosslinking of the trimethoxy silane and the benefit of low monol DMC process with the use of high molecular weight polyether. This type of polymer design allows the use of high DIDP plasticizer content as used with standard PU prepolymers. They produces sealants and adhesives with good elastic recovery, low tin catalyst content, and are a good alternate to PU prepolymers. However the huge disadvantage is the high polymer viscosity in the range of 50000 Mpas to 100000 Mpas, with the need to use plasticizer contents of at least 20 percent in the polymer to make the polymer process able in a sealant factory. Drums of these polymers are impossible to empty satisfactorily. Moisture sensitivity of the trimethoxy silanes is an issue in manufacturing and these polymers need to be processed with completely dry calcium carbonates or alternately the calcium carbonates are dried with the plasticizer before mixing into the polymer. High plasticizer content in the formulation can result in soft sealants and a tacky surface on cure. The high viscosities of PU prepolymers and also the secondary amino silane capped polyurethane polymers are due to the hydrogen bonding developed between the urea groups where the double bonded oxygen atom and the hydrogen on the Nitrogen atoms in adjacent polymer chains form the known cross chain hydrogen bond and increase viscosity markedly. The viscosity can be reduced by adding a bulky group to the nitrogen of the secondary amino silane and the use of phenyl, cyclohexyl, aspartame ester and diethyl maleate or octyl maleate and other groups is documented and exists in a number patents. . As the polymer chains are three dimensional and the hydrogen bonding exists in 3 dimensions viscosity reducing methods can vary in efficiency. Other viscosity reduction methods have been to add propylene carbonate and long chain alcohols as a plasticizer to reduce viscosity of these silane terminated polyurethane prepolymers where secondary amino silanes are used. There is a need for improvement. To replace standard TDI and MDI based prepolymers that contain solvents like xylene or toluene in the prepolymer, along with some free NCO containing monomer that is very difficult to remove, we need to give formulators and their Factories a safer low toxicity and lower viscosity polymer and a method where they are able to manufacture sealants in a very similar process to what is currently used with current prepolymers and formulations. They need stable thinner polymers and moisture scavengers and cure inhibitors so they are able to formulate products that are able to be manufactured in equipment that is normally used for high volume PU sealant production. They also need to be able to replace current proven PU sealant formulations with less development and advantages in physical properties such as UV exposure resistance and better adhesion with no primers. The advantage of methyl dimethoxy silane terminated end capping of polyurethanes is known, they have low moisture sensitivity and an easier manufacturing process. However viscosity is still a major problem that needs to be tacked to make these polymers commercially viable. We have made some progress in this area. 2 SUMMARY OF THE INVENTION We have now developed further the family of alcoxysilane terminated polymers which have the benefit of the use of methyl dimethoxy gamma silane terminated polyurethanes by combining the secondary amino silane end capping process with an end cap of isocyanato propyl triethoxy silane. The resultant polymer has a low viscosity in the range of 10000 to 20000 Mpas and the use of the methyl dimethoxy and triethoxy silanes maintains the low moisture sensitivity needed to process the polymer with powders that contain some moisture and can be dried with moisture scavengers like vinyl trimethoxy silane. Curing speeds are also improved. Using our discovery of the polyether chain with two different alkoxy end groups with some hydrogen bonding reduction molecules added, allows us to give the formulator the ability to manufacture in a simpler process a sealant or adhesive with an open time from 15 minutes to 1.0 hours. The polymer is used in sealants and adhesives with good UV resistance, good adhesion to various surfaces and the advantage of lower methanol emission on curing as the triethoxy silane molecule has emission of the less toxic ethanol upon cure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The polymers are composed of a backbone of polyurethane, polyether, polyester, polyacrylate and can be any polymer or polyether of linear or cross linked composition with free reactive hydroxyl groups available for reaction. The choice of the backbone is chosen to give the required hardness, tensile and elongation properties when capping hydroxyl groups with a difunctional isocyanate and secondary amino silane in the first step, and an isocyanato triethoxy silane in the second step .The final process is to add several viscosity reducing molecules that also have secondary benefits in the composition. The DMC process low monol polyether polyols are the preferred option. These diol or triol polyols or a combination of diols and triols with two or more OH groups at each chain end are first changed to a NCO terminated prepolymer where 30 percent to 50 percent of the OH groups are reacted with a diisocyanate with IPDI being the preferred molecule. The slower NCO groups on the IPDI molecule attached to the end of a polyether are then capped with a secondary amino silane with cyclohexyl amino propyl methyl dimethoxy silane being the preferred molecule. The final step is to react the remaining 70 percent to 50 percent of the unreacted hydroxyl groups of the polyether with an isocyanato propyl triethoxy silane. It has also been surprisingly found that a small amount of vinyl trimethoxy silane and methanol at less than one percent each inhibit the normal urea hydrogen bond formation across adjacent chains as normally found in polymers that contain these groups. The small methanol and vinyl trimethoxy silane molecules hydrogen bond to the carbamate and nitrogen groups in normal hydrogen bonding, and block the hydrogen bonding between adjacent polymer chains resulting in a lower polymer viscosity . The methanol also has the function of retarding the moisture reaction of the methoxy silane groups to the silanol molecule which is the first stage of methoxy cross linking. The methanol is removed under vacuum in the sealant manufacturing process and has the secondary effect of helping reduce moisture levels as water is very soluble in methanol .The methanol also very efficiently caps any residual NCO groups to ensure the final polymer is NCO free. In the normal sealant manufacturing process where residual moisture is reduced under vacuum, there is a need for additives to help reduce moisture levels before catalyst is added. It is common in PU sealant formulation practice to use the very toxic paratoluenesulphonicisocyanate, known as PTSI, a fast moisture scavenger to reduce moisture content as the reaction is faster than the capped isocyanate polymers. The sealant formulator using methyl dimethoxy and triethoxy silane terminated polyether polymers has the safer vinyl trimethoxy silane as the moisture scavenge, and some is present in the polymer and has thus two functions .Using vinyl silane at 50 degree C in the drying process, enables one of the ethoxy molecules on the 3 triethoxy silane to be interchanged with one of the methoxy molecules on the vinyl silane. This interchange speeds up the curing rate of the trimethoxy silane, well known to be slow. For the methyl dimethoxy silane polyurethane cap combined with the triethoxy isocyanato cap on the same polyether chain, it is sufficient to use vinyl silane as the moisture scavenger combined with a process where a high shear step is included with high vacuum to eliminate residual moisture from calcium carbonate fillers. The dimethoxy silane and triethoxy silanes are slower to react with moisture compared with trimethoxy vinyl silanes. Temperatures of about 50 degree C with high vacuum are sufficient to dry the sealant or adhesive before catalyst addition to form a one part RTV composition. With these combinations of alkoxy terminated polyether chains and several small additions of commonly used chemicals, we are able to offer the sealant and adhesive formulators a new low viscosity polymer and a production method that has the advantage of lower methanol release on cure, the ability to control curing rates and adhesive strength and use currently know tin containing catalysts and secondary amino silanes as the catalyst system. Below we demonstrate some aspects of the invention without restricting it. EXAMPLES, that show the process and not limited to this specific example. Methyl dimethoxy silane and triethoxy capped Hybrid Polymer, A. In a standard 5 litre laboratory flask with good stirring, 4000 grams of low monol DMC catalyst based polyether blend of diol and triol were loaded with an OH value of 10.0. This mixture was dried at 80 degree C for 1 hour under vacuum to eliminate moisture. The dry polyether was then cooled and reacted under Nitrogen at 40 degree C, with 80.0 grams IPDI isocyanate to cap half the OH groups with a NCO group . The free NCO groups of the partially formed polyurethane chain were then reacted in a second step at 40 degree C with 83.0 grams of cyclohexyl amino methyl dimethoxy silane until the reaction showed very little residual NCO by FTIR . This results in half the polyether ends being capped with a dimethoxy silane molecule that can be reactive to moisture and crosslinking with other silanes. The mixture was then heated to 70 degree centigrade and an addition of 75.0 grams of isocyanato propyl triethoxy silane was made. This was reacted for 3 hours until the NCO of the polymer was very low and reached the target as measured by Shimazdu FTIR. All the original OH groups of the polyether are now reacted and contain a reactive silane group. This can be seen on the changed FTIR trace. The above polymer was cooled in the laboratory flask to 30 degree C and an addition of 40 grams of Vinyl trimethoxy silane and 40 grams dry laboratory grade methanol and mixing was continued for 10 minutes and then packed into 1 litre metal cans. The methanol addition ensures any residual NCO is reduced to zero. A reduction in viscosity developed over 24 hours. The resultant polymer was cooled and viscosity the next day was 16000 Mpas at 25 degree C. Open time before skinning of this hybrid polymer when mixed with 1% TIB KAT 226 diketonate tin catalyst and 1% KBM603 silane is approx 20 minutes at 25 C and 50% humidity in laboratory glass dish. Shore A hardness is approx 35 after 5 days cure. The cured polymer is very stable in a closed 1 litre metal container, with no change in viscosity for 6 months. SEALANT FORMULATION WITH HYBRID POLYMER A of the Innovative invention 4 In a standard 5 litre laboratory planetary mixer, with nitrogen, vacuum and small press we were able to produce some adhesive samples from Hybrid polymer A. We did not need separate powder drying facilities and were able to use the method where the fillers with some moisture content were loaded with the polymer, heated to 50 degree C under high shear and high vacuum to remove most of the powders moisture, and then chemically dried at 50 degree C for 1 hour with vinyl trimethoxy silane .After drying with vinyl silane the adhesive is checked for moisture content with Carl Fisher process. When satisfactory, the final additions of secondary amino silane, UV inhibitor, tin catalyst and some vinyl silane for open time control were added. The adhesive was packed into aluminium/HDPE lined hermetic cardboard cartridges and tested. The base formulation is in grams and was adjusted for the mixer used. Hybrid polymer A 1000 grams Ultra-Pflex PCC 1000 grams Carbon black 50 grams Vinyl silane 50 grams Amino KBM603 20 grams TIB KAT 226 catalyst 20 grams Tinuivin B75 10 grams Vinyl silane 50 grams The mechanical properties of the above black Industrial adhesive using Hybrid polymer A are listed below. Tack free time 15 minutes Viscosity Mpas 1,500,000 Slump resistance very good VOC 1.20 percent loss SG g/cm3 1.45 Tensile at break 3.40 n/mm2 Elongation % 245 at break HardnessShore A 60 This is a basic formula and can be adjusted in many ways to suit specific adhesive and sealant requirements. The addition of DIDP plasticizer in the formulation to replace some of the polymer results in a lower tensile strength with increased elongation. 5 While the major embodiments of the innovation are illustrated and described herein, it is not intended that these illustrate all possible uses of the innovation, rather the methods describe how the combined methyl dimethoxy amino silane and triethoxy silane hybrid polymers can be used to produce low viscosity less toxic and commercially viable compositions suitable as an alternate to PU prepolymers. The examples show sealant properties close to commercial PU sealants based on TDI and MDI isocyanate. The DMC polyether Polyol which are preferred are blended to achieve a target OH value and consistent tensile properties as the variation from Manufacturers of polyether OH value is significant. Resins or polymers with mixtures of diols and triols result in enhanced properties as is well known in Polyurethane technology. Precipitated calcium carbonate usage allows the development of thicker sealants at less cost. Processing of this polymer design is excellent and easy compared to polyurethane prepolymers. 6

Claims (9)

1. High viscosities of secondary amino silane capped polyurethane resins or polymers are due to the hydrogen bonding developed between adjacent polymer chains where the double bonded oxygen atoms and the hydrogen atoms on nitrogen atoms in the polyurethane or urea segments in the chain form hydrogen bonds.

2. The use of vinyl trimethoxy silane and methanol molecules at low levels bond to urethane groups on polymer chains and stop the development of hydrogen bonding across polymers chains and reduce viscosity markedly.

3. At low levels of less than 1 percent that the methanol atoms are added to the polymer chain, with a hydrogen bond to the chain the methanol molecule is a hydrogen bonded molecule rather than a typical solvent where the methanol atoms are free to move and hydrogen bond weakly to each other.

4. The use of two specific alkoxy silane molecules in the one polyether chain to reduce the viscosity of a polymer by simple stearic hindrance, while maintaining low moisture sensitivity and easy processing with PCC and Carbon black that will contain small content of moisture.

5. The use of IPDI isocyanate at low temperature to cap 30 to 50 percent of a polyether chain using the differential reactivity of the IPDI isocyanate to produce a simple quasi polymer where crosslinking is eliminated and 1 prepolymer viscosity is reduced to a minimum. The process is carried out in the polyether.

6. The capping of a partially reacted NCO terminated polyether with a secondary amino silane molecule ,then reacting and capping the remaining OH groups with isocyanato propyl triethoxy silane, to reduce viscosity in a polymer which is moisture cured and easily processed.

7. A method of manufacture of a hybrid polymer using a secondary amino methyl dimethoxy silane to cap a simple NCO capped prepolymer where the percentage capped can vary from 25% to 75 percent of the original OH groups available for reaction.

8. A method of adding a fast moisture scavenger such a vinyl trimethoxy silane to a polymer to enable the sealant manufacturer to eliminate moisture from fillers and plasticizers in a manufacturing process at the same time.

9. A sealant manufacturing process using the existing commercially available moisture scavengers and additives in current equipment used to produce sealants that are a safer alternate to the common commercial polyurethane sealants and adhesives. Solvent free and no free isocyanate monomers. 2