A PROCESS FOR MOLDING MICROCELLULAR ELASTOMERIC POLYURETHANE ARTICLES AND MICROCELLULAR ELASTOMERIC POLYURETHANES THEREFOR

Abstract: Described is a novel, particularly flexible, process for molding microcellular elastomer polyurethane articles. Described is furthermore the preparation of microcellular elastomer polyurethanes especially suitable for said molding process. The process according to the invention is particularly suitable for being automated by means of a processor.

Description: A PROCESS FOR MOLDING MICROCELLULAR ELASTOMERIC POLYURETHANE ARTICLES AND MICROCELLULAR ELASTOMERIC POLYURETHANES THEREFOR The instant invention relates to a novel process for mold¬ ing articles of microcellular elastomeric polyurethane (here- inbelow indicated, or the sake of brevity, simply as M.E.P.). More particularly, the instant invention relates to a parti¬ cularly flexible process for molding a microcellular elasto¬ meric polyurethane. It is an object of the instant invention to provide a mold ing process which allows to make a wide range - from the poin of view of the physico-mechanicl characteristics - of M.E.P. articles without the need for changing or substituting the starting materials. Another object of the instant invention is that of provid- ing a process for making M.E.P.s particularly suitable for said molding process,in which starting materials are employed having a well defined composition. A further object of the instant invention is that of pro¬ viding a process for molding M.E.P. articles wherein the reaction for producing the polyurethane is driven in a step preceding the molding of the article in order to form bases with a controlled and stable structure. A further object yet of the instant invention is that of providing a process for molding M.E.P. articles which allows to make M.Ξ.P.s having different physico-mechanical charac¬ teristics, only by means of cross-linking agents. Another important object of the instant invention is to provide a process for molding M.E.P. articles which can be automated by means of a processor. These objects and others yet will be more clearly illus¬ trated by the description hereinbelow. As it is known, M.E.P. is generally made by reacting εtoi- chiometric quantities of a polyol and of a prepolymer. Practically, said reagents are taken from tanks and con¬ veyed to the mixing heads by means of dosing pumps. The blend¬ ing takes place as a result of the rapid increase of the flow speed of the materials introduced into the head,where they flow into one only zone of relatively limited dimensions so that there is a very high probability that the molecules both of the reagents and of the catalyst may interact and that therefore the reaction product is sufficiently homogeneous notwithstanding the very high reaction speed. However, since for economic reasons very short withdrawal times are demanded in the industrial process, it was necessary to use consider¬ able quantities of catalysts which, by remaining within the finished article,caused the deterioration of the latter's physico-mechanical.characteristics. Furthermore, since the polyols used for making M.E.P. do not consist of single components but instead of mixtures of different components,some of which are hardly or not at all soluble, this gives rise to the drawback of having to subject the polyol mixtures to homongenization before use: not only, but these mixtures must be constantly stirred during their use . A further inconvenience of the state of the art processes lies in the fact that the quantity of reagents to be stocked for the molding process must not only be proportional to the quantity to be worked, but also to the type of article to be made. This implies the interruption of the production to allow for the change or the modification of one or both rea¬ gents (polyol, isocyanate) and/or the catalyst. These changes and/or modifications,besides lowering productivity, imply too the loss of starting materials and the use of solvents for washing the tanks and equipment. Last but not least, said changes and/or modifications almost always demand the re-ad¬ justment of the operating conditions of the plant with conse- quent problems ■ of adjusting the production to the market re¬ quirements. Evident are the shortcomings of the state of the art pro¬ cesses from what -has briefly been described hereinabove. Consequently, the object of the instant invention is that of providing a process for molding M.E.P. articles, that does not present the shortcomings of the processes known from the art. It has now been found that when using strictly defined compounds (hereinafter called quasi-polyurethanes or, in short Q-PUR), as the starting materials, instead of prepolymers and polyols, it is possible to make M.E.P. articles the specific gravity, surface hardness, elasticity, compressive strength and abrasion resistance of which can be modified by acting exclusively on the quantity of the starting materials. According to the process of the instant invention, the basic components are polymerized to the highest degree compat¬ ible with the molding plant. This allows to attain Q-PURs by means of strictly timed reactions and not by random blending in the mixing head. More precisely, the inventive process provides the use - instead of a prepolymer and of a polyol (which, as is known, is in actual fact a mixture of several polyols, sometimes of a not strictly defined composition) - of two bases or Q-PURs which not only do not contain foreign materials, be they dis¬ solved or not, such as solvents or fillers of various kind, but they have a strictly defined chemical composition. The first of these bases consists of a quasi-polyurethane (Q-PUR-1) with a molecular weight of between 600 and 2200, preferably between 650 and 1500 and even more,preferably between 700 and 1100, and a percentage of free isocyanate (-NC0) groups of between 14 and 3.8, preferably between 12.9 and 5.6 and even more preferably between 12 and 7.6. The second base consists of a quasi-polyurethane (Q-PUR-2) havin a molecular weight of between 3000 and 8000, preferably between 3500 abd 5000 and even more preferably between 3750 and 4500 and with a percentage of free hydroxyl (-0H) groups of between 1.13 and 0.48, preferably of between 0.97 and 0.68 and even more preferably between 0.9 and 0.75. In the blending step, the free -NC0 groups of Q-PUR-1 are saturated with aqueous glycol solutions and glycol/catalyst solutions so as to make polyurethane polymers of different specific weight. The chemical structure of the M.E.P. is modified, according to the process of the instant invention, by means of Q-PUR-2. More precisely, said chemical structure varies in proportion to the quantity of Q-PUR-2 employed. According to the instant invention, the isocyanates and the resins are reacted in a vessel according to per se known pro¬ cesses which allow to steer the reaction in such a manner as to attain a regular distribution of the molecular weights. In the course of the molding step ,the glycol develops its chain-lengthening and cross-linking activity. In turn, the Q-PUR-2 (which at each extremity of the molecule has a free hydroxyl group)reacts with the Q-PUR-1 ,via the latte 's free isocyanate groups,in order to form a longer straight chain. In this manner the inner plasticizing of the polymer structure is achieved. The skilled artisan will immediately appreciate the ad¬ vantage of using an inner rather than an external,i.e.an heter- ogeneous-phase plasticizing process as that which occurs when conventional (reactive or inert) plasticizers are used. Hence this is a further advantage offered by the process according to the instant invention. As already mentioned hereabove, the Q-PUR-ls, suitable for the process according to the instant invention, preferab¬ ly have a molecular weight of between 600 and 2200, preferab¬ ly between 650 and 1500 and even more preferably between 700 and 1100 and a percentage of free isocyanate groups ranging between 14 and 3.8, preferably between 12.9 and 5.6 and even more preferably between 12 and 7.6. This polyurethane resin of the instant invention is preferably made by reacting a diphenylmethane diisocyanate with a saturated polyester, such as e.g. glycol adipate, having a molecular weight of between 1500 and 2500. The Q-PUR-1 constitutes the basic component for the M.Ξ. formulation and,contrary to what happens with conventional polymers, by saturating the isocyanate groups with glycols the whole cross-linking process of the system is completed, the final characteristics of which are predetermined by the type of saturated polyester used, by the molecular weight of Q-PUR-1 as well as by the type of glycol used. The reaction is catalyzed with triethylene diamine and the specific weigh is determined by the water content. On the other hand, Q-PUR-2 consists of a polyurethane resi having a molecular weight ranging between 3000 and 8000, pre¬ ferably between 3500 and 5000 and even more preferably betwee 3750 and 4500, containing a percentage of free hydroxy groups ranging between 1.13 and 0.48, preferably between 0.97 and 0.68, and even more preferably between 0.9 and 0.75. Prefer¬ ably, this resin is made by reacting, according to per se known methods, diphenylmethane diisocyanate with a saturated polyester having a molecular weight of 1500 to 2500, in the molar ratio of 1:2. The Q-PUR-2 thus obtained constitutes the component cap¬ able of steering the M.E.P. characteristics. As already men¬ tioned previously, one of the main advantages of the inven¬ tive process is represented by its flexibility. In fact,as it can be taken from the Table herebelow, depending upon how t h e various components are combined, it is possib l e to o b tain molecular structures that differ even very much the ones from t h e others, so much so that end products can be o b taine d hav ¬ ing comp l etely different physico-mechanical characteristics the ones from the others. It should not be overlooked that in ¬ s id e each main group it is possible -to arrange for one of the p h ysico-mechanical characteristics to prevail over another one. T A B L E 1 Cross-points of reference - o 9 - Considering that the reaction partners useful for the instant invention are all strictly defined materials as far as their chemical composition is concerned, the inventive process particularly lends itself to automation using a processor. After having generally outlined the process according to the instant invention, it will now be better illustrated by way of some working examples which, for the sake of brevity, do not contemplate all the starting materials or the possible combinations of the reaction partners. This fact, however, s h all not constitute a limitation of the scope of protection of the instant invention inasmuch - as appears evident to the skilled artisan - the forms of embodiment of the process according to the instant invention can vary widely,be it with regard to the starting materials as to the reaction condi¬ tions, so as to adapt them to the specific circumstances. Once the skilled artisan has become acquainted with the fundamental principles on which the present process is based, he will have no difficulty whatsoever in adapting the para- meters of the process so as to attain the M.E.P. having the desired characteristics, without thereby departing from the gist of the invention. EXAMPLE 1 Preparation of a quasi-polyurethane using free -NCO groups (Q-PUR-1) . A 10,000 liter steel reaction vessel provided with stir- rer, thermoregulator and suitable device for providing an inert environment, is fed with 3751 kg MDI (diphenylmethane diisocyanate) at a temperature of 38 to 42°C under stirring and in a dry nitrogen environment,to which is added 3,748 kg saturated polyester resin (made by reacting adipic acid with onoethylene glycol of m.w. = 1500, containing a percentage of water lower than 0.1 and with an acid number lower than 1 (AN<1). This resin, at a temperature of 80°C, is fed to the MDI mass through a line (at the extremity of which is an anti-bubbling continuous flow device) dosed at a flow rate of 70-80 1/min by means of a metering pump. Since the reaction is exothermic, the temperature of the reaction mass tends to increase, which must therefore be cooled so as not to exceed 90°C. After the addition of the resin has been completed, the reaction mass is stirred for 2 hours,between 85 and 90°C, taking care that the atmosphere is saturated with nitrogen. The reaction has been completed once the following values have been obtained: free -NCO : 14% molecular weight: 600 EXAMPLES 2 to 7 By operating in like manner to what is described in Example 1 but using the reagents indicated quali/quantitative- ly in the Table hereinbelow,are prepared the Q-PUR-ls having the characteristics as shown. T- A B L E 2 MDI RESIN RESIN %-NCO MOL. WEIGHT kg k RESIN (*) fmol. weight) ( final) (final) 2) 3280 4219 monoeth.gly- col/diethyl- 1750 12 700 ene glycol 3) 2499 5000 diethylene glycol 1/4 2000 8,4 1000 butane diol 4) 1748 5751 1/4 butane diol 2500 5,25 1600 5) 1532 5967 1/4 butane diol monoeth. glycol 3000 4,66 1800 6) 1322 6177 diethylene glycol onoe th. glycol /tri- methylol propane 40C0 4,2 2000 7) 1104 6395 diethylene glycol trimethylol 5000 3 a 22C propane (*) Note: "RESIN" stands for a polyester resin made from adipic acid and the respectively indicated alcohol. EXAMPLE 8 Preparation of a quasi-polyurethane using free -OH groups (Q-PUR-2) A 10,000 liter steel reaction vessel provided with stirrer, thermoregulator and suitable device for providing an inert en¬ vironment, is fed with 8,000 saturated polyester resin (made by reacting, at a temperature of 120°C, adipic acid with mono- ethylene glycol having a m.w. = 1500, containing a percentage of water lower than 0.1 and an ANCl). Under stirring and in a dry nitrogen environment is then added, very cautiously, 613 kg MDI, at a temperature of 38 to 42°C, while the flow capacity of the metering pump must not exceed 8 1/min; the blades of the stirrer must not thrust the MDI against the walls of the reaction vessel. The environment must be carefully controlled and secured throughout the entire reaction. After the addition has been completed, the reaction mass is left to cool down to 60°C, still under stirring. The reaction has been completed once the following values are obtained: free -OH : 1.13% molecular weight : 3000. EXAMPLES 9 to 14 By operating in like manner to what is described in Exam¬ ple 8 but using the reagents indicated quali/quantitatively in the Table hereinbelow, are prepared the Q-PUR-2s having the characteristics as shown. T A B L E 3 MDI RESIN RESIN Ϊi-OH O .WEIGHT g_ 3ESIN <*) 571 8000 monoeth.gly- co /diethyl- ene glycol 1750 0,9 3750 10) 500 8000 diethylene Sl " '1 { h . 2000 0.8 4250 butane diol 11) 342 8000 j_/4 butane diol 2500 0.75 4500 12) 266 8000 1/4 butane diol 0 monoech. lycol 3000 0,68 5000 13 ) ιeι 8000 diethylene glycol- monoeth. glycol/ t ri¬ me chvlol propane ' V F 4000 0,56 6000 14) 95 8000 diethylene glycol crime hviol 6000 0,48 7000 propane _ ζ ( * ) NOTE: "RESIN" stands for a polyester resin made from adipic acid and the respectively indicated alcohol. In Examples 1 thru 14 a polyester has always been employeα. However, it is possible to use instead a polyether made - as is known to the skilled artisan - by polymerizing propylene oxide with monσglycols or polyglycols containing one or more reactive hydrogen atoms. Generally, it has been found that the use of polyethers yields Q-PUR-l and Q-PUR-2 having the same molecular weight, yet consi d era b ly less viscous than the corresponding quasi- polyurethane originating from a polyester and, hence, having improved workability. At any rate, the choice depends on the physico-mechanical characteristics of the quasi-polyurethane desired. Examples 15 to 17 Preparation of the "catalyst-foaming agent" solutions Herebelow is given the composition (the parts are expres¬ sed in percent) of three typical solutions having a catalytic foaming activity, useful for the process of the instant inven¬ tion for affecting the reaction velocity and/or physico- mechanical characteristics of the M.E.P. SOLUTION 1 SOLUTION 2 SOLUTION 3 ( chain ( foaming COMPONENT (catalyst) lengthener) agent ) Monoethylene glycol 70 100 70 Dabco 30 0 Water 0 30 % Total 100 100 100 The preparation of these solutions does not demand parti¬ cular procedures, however the temperature must be kept at about 60°C and precaution must be taken to operate in a mois¬ ture free environment. Dabco, as is known to the skilled artisan, is triethylene diamine. The molding of M.E.P. according to the inventive process is illustrated in the Examples that follow. Into a mixing head are fed all the reaction partners: Q-PUR-l (base 1) Q-PUR-2 (base 2) SOLUTION 1 (catalyst) SOLUTION 2 (chain lengthener) SOLUTION 3 (foaming agent) The tanks containing the bases 1 and 2 are thermoregu- lated at a temperature of 50-60°C and provided with a moisture trap. A gear pump, having a volume proportional to the quantity of product mass used per unit of time, maintains the base (1 or 2) in continuous and constant circulation between the tank and the mixing head. The tanks containing the additives are thermoregulated at a temperature of 20-30°C and provided with moisture traps. In this case too it will be a gear pump, yet having a volume twenty times lower than the previously cited one, that keeps the recycling in the head. The flow rate of all these pumps is governed by a manager program of the molding cycle. The program, stored in a proces¬ sor's memory, stabilizes, according to demand, the quantities of the various partners which take part in the ' reaction. Shortly before injection, the speed of the motors connected to the pumps is adjusted by the processor's inter¬ faced control cards to the r.p.m.s necessary for the speci¬ fic situation. At the command START-INJECTION open up only the valves corresponding to the materials that have to take part in the reaction producing that given type of polyure¬ thane. The valves remain open so as to interrupt recycling and to feed the reaction partners into the mixing zone for the time required to fill the mold. The products crossing the mixing zone come into close con¬ tact thanks to a mechanical impeller. The ejection from the head occurs through an orifice at the extremity of the head itself. Once the injection is finished, the dedicated software re- directs the output according to the program and the cycle con- continues , allowing for the production of a continuously dif¬ ferentiated series of M.E.P. Example 18 An M.E.P. of low specific gravity, having sufficient compres- sive strength to permit its use for producing shoe bottoms. DOSAGE OF THE COMPONENTS : flow rate (g/s) SOLUTION 1 - Catalyst 0.32 SOLUTION 3 - Foaming Agent 0.26 SOLUTION 2 - Chain Lengthener 2.75 BASE 1 BASE 2 TOTAL BASES TOTAL FLOW RATE This M.E.P. has the following chemical composition: MDI 35.50 Dabco 0.20 Water 0.16 TOTAL 100.00 EXAMPLE 19 An M.E.P. of low specific weight, with such characteristics of softness as to permit its use for producing innersoles for footwear. DOSAGE OF THE COMPONENTS; SOLUTION 1 - Catalyst SOLUTION 3 - Foaming Agent SOLUTION 2 - Chain Lengtherener Total Additives 0.61 BASE 1 13.65 BASE 14.74 TOTAL BASES 28.39 TOTAL FLOW RATE 29.00 This M.E.P. has the following chemical composition: MDI 20.93 EXAMPLE 20 An M.E.P., with specific gravity greater than 1, very re¬ silient, particularly suitable for producing an.tislip sur¬ faces exposed to climatically critical environments (tempera¬ tures between -20 and -50°C) DOSAGE OF THE COMPONENTS : flow rate (g/s) SOLUTION 1 - Catalyst 0.14 SOLUTION 3 - Foaming Agent 0.00 SOLUTION 2 - Chain Lengthener 0.72 Total additives 0.86 BASE 1 13.65 BASE 2 14.74 TOTAL BASES 28.39 TOTAL FLOW RATE 29.25 This M.E.P. has the following chemical composition: MDI 20.75 Polyester 1 28.90 Polyester 2 47.43 MEG (*) Dabco Water TOTAL EXAMPLE 21 An M.E.P., with specific gravity greater than 1, very stiff, particularly suitable for being worked with machine tools and cut into slabs, cylinders, and so forth. DOSAGE OF THE COMPONENTS SOLUTION 1 - Catalyst SOLUTION 3 - Foaming Agent SOLUTION 2 - Chain Lengthener Total additives 3.51 BASE 1 45.50 BASE 2 0.00 TOTAL BASES 45.50 TOTAL FLOW RATE 49^01 This P.E.M. has the following chemical composition: MDI 35.37 Polyester 1 57.47 Polyester 2 0.00 MEG (*) 6.99 Dabco 0.17 Water 0.00 TOTAL 100.00 EXAMPLE 22 An M.E.P., specifically produced for making the soles of sport shoes that require particular stress resistance pro¬ perties. DOSAGE CF THE COMPONENTS : flow rate ( /s) SOLUTION 1 - Catalyst 0.23 SOLUTION 3 - Foaming Agent 0.19 SOLUTION 2 - Chain Lengthener 1.64 Total additives 2.06 BASE 1 29.57 BASE 2 7.37 TOTAL BASES 36.94 TOTAL FLOW RATE 9^00 This M.E.P. has the following chemical composition : MDI 30.01 Polyester 1 46.95 Polyester 2 17.78 TOTAL 100.00 MEG (*) = monoethylene glycol. The M.E.P. 's that can be made with the process of the instant invention can be used in the widest range of fields such as e.g. shoe manufacturing in order to produce: poly¬ urethane bottoms for any kind of shoe, innersoles, leggings, footwear and sandals; in the marine sector for producing : the inner sheels cf ships, buoys, antislip' carpets, handles and handrails; in road works to produce: expansion joints, obstacles for reducing the speed of vehicles, remov¬ able buffers; in the car industry to produce: bumpers, steer¬ ing wheels, protective sumps, panellings; in the sector of technical articles to produce: joints, suckers, gears,shock absorbers, protection gloves; in the furniture sector to pro¬ duce: furniture, frames, paving tiles, decorations.

Claims: 11305 C L A I M S 1. A process for molding microcellular elastomeric polyurethane articles characterized by the fact that in a mixing head are reacted, according to per se known methods, a quasi-polyurethane having a molecular weight of from 600 to 2200 and a free isocyanate group percent content of from 14 to 3.8,with : a) an other quasi-polyurethane having a molecular weight of from 3000 to 8000 and a free hydroxyl group per¬ cent content of from 1.13 to 0.48, and water; or b) an other quasi-polyurethane having a molecular weight of from 3000 to 8000 and a free hydroxyl group per¬ cent content of from 1.13 to 0.48, a glycol and water; or c) an other quasi-polyurethane having a molecular weight of from 3000 to 8000 and a free hydroxyl group per¬ cent content of from 1.13 to 0.48, and a glycol; or d) an other quasi-polyurethane having a molecular weight of from 3000 to 8000 and a free hydroxyl group per¬ cent content of from 1.13 to 0.48, or e ) a glycol and water; or f) a glycol . 2. A molding process according to claim 1, characterized by the fact that said microcellular elastomeric polyurethane is made by reacting a quasi-polyurethane,having a molecular weight of from 700 to 1100 and a free isocyanate group per¬ cent content of from 12 to 7.6, with an other quasi-poly¬ urethane having a molecular weight of from 3750 to 4500 and a free hydroxyl group percent content of from 0.9 to 0.75, and water. 3. A molding process according to claim 1, characterized by the fact that said microcellular elastomeric polyurethane is made by reacting a quasi-polyurethane,having a molecular weight of from 700 to 1100 and a free isocyanate group per¬ cent content of from 12 to 7.6, with an other quasi-poly¬ urethane having a molecular weight of from 3750 to 4500 and a free hydroxyl group percent content of from 0.9 to 0.75, and a glycol and water. 4. A molding process according to claim 1, characterized by the fact that said microcellular elastomeric polyurethane is made by reacting a quasi-polyurethane, having a molecular weight of from 7.00 to 1100 and a free isocyanate group per¬ cent content of from 12 to 7.6, with an other quasi-poly- urethane having a molecular weight of from 3750 to 4500 and a free hydroxyl group percent content of from 0.9 to 0.75, with a glycol. 5. A molding process according to claim 1, characterize by the fact that said microcellular elastomeric polyurethan is made by reacting a quasi-polyurethane, having a molecula weight of from 700 to 1100 and a free isocyanate group per¬ cent content of from 12 to 7.6, with an other quasi-poly¬ urethane having a molecular weight of from 3750 to 4500 and a free hydroxyl group percent content of from 0.9 to 0.75. 6. A molding process according to claim 1, characterize by the fact that said microcellular elastomeric polyurethane is made by reacting a quasi-polyurethane, having a molecula weight of from 700 to 1100 and a free isocyanate group per¬ cent content of from 12 to 7.6, with a glycol and water. 7. A molding process according to claim 1, characterized by the fact that said microcellular elastomeric polyurethane is made by reacting a quasi-polyurethane, having a molecular weight of from 700 to 1100 and a free isocyanate group per¬ cent content of from 12 to 7.6, with a glycol. 8. A molding process according to any one of claims 1 to 7, characterized by the fact that the quasi-poly¬ urethane, having a moleculare weight of from 600 to 2200 and a free isocyanate group percent content of from 14 to 3.8, is made by reacting, according to per se known methods, a diphenylmethane diisocyanate with a saturated polyester having a molecular weight of from 1500 to 2500, in a molar ratio of 1 : 2. 9. A molding process according to any one of claims 1 to 7, characterized by the fact that the quasi-polyure¬ thane,having a molecular weight of from 600 to 2200 and a free isocyanate group percent content of from 14 to 3.8, is made by reacting, according to per se known methods, a di¬ phenylmethane diisocyanate with a polyether having a mole¬ cular weight of from 1500 to 2500, in a molar ratio of 1 : 2.

Inventors: SCARNATO ELIO, SPAGNOLI MAURIZIO, SCARNATO, ELIO, SPAGNOLI, MAURIZIO
Applicants: MILANESE CHIM ORGANICA IND, C.O.I.M. CHIMICA ORGANICA INDUSTRIALE MILANESE S.P
Application year: 1991
Main classification: C08G18
IPC codes: C08G18, C08G101, C08J9