MX2008009770A - Polyurethane cast elastomers formed from nco prepolymers based on 2,4'-mdi, a process for their preparation and their use - Google Patents

Abstract

The present invention relates to novel polyurethane (PUR) cast elastomers formed from NCO-functional prepolymers based on 2,4'-MDI and aminic chain extenders and/or crosslinkers, to a process for their preparation and to their use.

Description

ELASTOMEROS DE MOLDEO DE POLIURETA OR ELABORADOS DE PREPOLIMEROS DE NCO BASED ON DIISOCIANATO DE 2,4'- DIFENILME ANO, PROCESS FOR ITS PREPARATION AND ITS USE DESCRIPTION OF THE INVENTION The present invention relates to novel polyurethane molding elastomers made from NCO-functional prepolymers based on 2, 4 '-MDI and amine-based chain extenders and / or cross-linking agents, with a process for its preparation and its use. MDI (diphenylmethane diisocyanate) is a technically important group of polyisocyanates, has a very heterogeneous composition in terms of its structure and comprises grades of monomers characterized by having two aromatic structural elements linked via a single methylene bridge, and larger oligomers than they have more than two aromatic structural elements and have more than one methylene bridge, which are called polymeric MDI.

The monomeric MDI predominantly contains the 4,4 'and 2,4' isomers as a consequence of its synthesis. The 2,2 'isomer also occurs to a lesser degree, but does not have much technical value. The ratio of monomeric MDI to polymeric MDI, and the proportions of the 2,4 'and 4,4' isomers in the monomeric MDI, can vary within wide limits by varying the synthesis conditions of the precursor. The crude DI obtained in the synthesis of MDI is substantially separated by distillation, it being possible, depending on the technical expense, to separate quasi-isomerically pure fractions with proportions of 4,4 '-MDI, for example, of more than 97.5% by weight, or isomer mixtures with proportions of 4,4 '-MDI and 2,4' -MDI of approximately 50%, respectively.

In the past, due to the technical conditions, the pure 2,4 'isomer was commercially available, if at all, only in very limited amounts. Recently, however, more effort has been devoted to making this isomer more available also in high purity. A basic reason for this effort is the difference in reactivity of the 2- and 4'-NCO groups of 2, 4 '-MDI, in a manner similar to the differences in reactivity of the 2-4-NCO groups of diisocyanate of 2 , 4-toluylene (TDI, for its acronym in English). These differences in reactivity allow or facilitate the synthesis of monomer-poor NCO prepolymers. The NCO prepolymers are polyols with terminal NCO groups which are obtained by reacting a polyol with a polyisocyanate using a molar excess of NCO, based on the NCO reactive groups, at room temperature up to about 100 ° C. Depending on the initial molar proportions, the NCO prepolymers prepared in this way always contain free monomeric diisocyanate. In the case of 2,4-TDI, the driving force behind the preparation of NCO prepolymers from poor monomer content to virtually monomer-free is justified by its high vapor pressure and the resultant health hazards. NCO prepolymers based on aliphatic diisocyanates, for example, hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI), will be considered even more critical in this context. This aspect also has relevance for the MDI, although to a remarkably reduced degree because its vapor pressure is lower than that of the TDI. However, reducing the monomer content of the prepolymer results in polyurethanes that are softer than those prepared from monomer-containing prepolymers. The monomer-poor NCO prepolymers can be prepared in several different ways: a) Removal of the free monomeric diisocyanate by technically expensive film evaporation or short route evaporation. This is independent of whether the diisocyanates used have NCO groups of the same or different reactivity. Also, for example, entrainment agents can be used for this purpose. b) The use of diisocyanates with NCO groups of different reactivity or NCO groups of the same reactivity, and specially chosen stoichiometric proportions, for example, molar proportions of NCO to reactive groups of NCO less than 2: 1, and / or optionally under special catalysis. c) Combinations of both processes, for example, in such a way that the proportion of free monomeric diisocyanate is initially limited to a certain extent by process b) and then further minimized by process a). Such combinations may be useful when the viscosity of the prepolymers is to be minimized. The disadvantage of process b) is basically that reactions with stoichiometric ratios particularly less than 2: 1 result in a greater pre-extension, resulting, inherently, in a remarkable increase in the viscosity of the reaction product. WO 01/40340 A2 (Crompton Corp.) provides examples of the combinations wherein, in a first step, the diisocyanate is converted to an NCO prepolymer with the concomitant use of a catalyst that increases the selectivity, and the prepolymer is then released. of excess monomer by film evaporation. Particularly critical applications, for example in the food sector, are affected by the issue of industrial hygiene, which applies to a high degree to TDI and also to MDI. This is indicated by numerous patents having to do even with MDI prepolymers poor in monomers, for example O 03/006521 (Henkel KGaA), WO 03/033562 (Henkel KGaA), WO 03/055929 (Henkel KGaA), WO 03 / 051951 (Henkel KGaA), WO 93/09158 (Bayer AG) and EP 0 693 511 Al (Bayer AG). The object of the present invention was therefore to provide 2,4,4'-MDI-based polyurethanes having processing advantages compared to the state of the art, for example in the form of longer molding times and lower viscosities of the prepolymer , and at the same time they are equal to those of the state of the art in terms of their mechanical properties. Surprisingly, it has now been found that, in terms of mechanical properties (e.g., abrasion, ultimate strength, resistance to tear propagation, elongation at break), valuable PURs are obtained from NCO prepolymers based on 2, 4 '-MDI with a 2,4 isomer content of at least 85% by weight and a proportion of free monomeric MDI in the prepolymer of at least 1% by weight to 20% by weight, preferably at least 2% by weight % by weight to 18% by weight and particularly preferably from 3 to 15% by weight, based on the prepolymer. The low viscosity of the NCO prepolymers is an additional advantage.

It is further understood that the NCO prepolymers mean NCO prepolymers which have been prepared from pure 2,4'-MDI, contain at least 1% by weight and maximum 20% by weight of free monomeric diisocyanate, based on the prepolymer, and they have not been extracted or distilled. It is further understood that pure 2,4'-MDI means ID grades having a 2,4 'isomer content of at least 85% by weight, preferably at least 90% by weight, particularly preferably at least less 95% by weight and very particularly preferably at least 97.5% by weight. The present invention provides polyurethane elastomers which can be obtained (by the molding process) from a) NCO prepolymers based on diphenylmethane diisocyanate with a 2,4'-isomer content of at least 85% by weight, preferably of at least 90% by weight, particularly preferably of at least 95% by weight and very particularly preferably of at least 97.5% by weight, the proportion of 2,4'-free monomeric MDI being at least 1% by weight to 20% by weight, preferably 2 to 18% by weight and particularly preferably from 3 to 15% by weight, based on the NCO prepolymer, and polyols having OH numbers of 20 to 200 mg of KOH / g and functionalities from 1.95 to 2.40, preferably from 1.96 to 2.20. b) amine-based chain extenders and / or cross-linking agents, preferably amine-based chain extenders and / or cross-linking agents and c) optionally auxiliary substances and additives. The polyurethanes according to the invention are superior to those of the prior art in that they have particularly advantageous combinations of advantageous properties with respect to the viscosity of the prepolymer, molding time and mechanical and mechanical-dynamic properties. The invention also provides a molding process for the preparation of the polyurethane elastomers according to the invention, the process characterized in that A) diphenylmethane diisocyanate (MDI) with a 2,4'-isomer content of at least 85% in weight, preferably at least 90% by weight, particularly preferably at least 95% by weight and very particularly preferably at or below 97.5%, reacts with polyols having OH numbers from 20 to 200 mg KOH / g and functionalities from 1.95 to 2.40 to provide NCO prepolymers with a proportion of 2.4 M 'monomeric free from 1 wt% to 20 wt%, preferably from 2 to 18 wt% and particularly preferably from 3 to 15 % by weight based on the NCO prepolymer, and B) amine-based chain extenders and / or crosslinking agents and optionally auxiliary substances and additives are added to the prepolymer of A) in order to prepare the elastomer. The preparation of the elastomers by means of the molding process is a generally important use of prepolymers finished in NCO, the NCO prepolymers react with a chain extender directly after their preparation or are cooled to a lower temperature (storage temperature) and stored for the purpose of chain extension at a later stage. The synthetic route via prepolymers is favorable because part of the heat of reaction is already produced during the synthesis of the prepolymer, thus reducing the exothermicity of the actual prepolymer synthesis. This has a favorable effect on the speed of molecular weight accumulation and allows for longer molding times, representing a processing advantage. In a particularly preferred embodiment of the preparation of the PUR elastomers by the prepolymer process, the prepolymers are first degassed by the application of a reduced pressure at room temperature or at elevated temperature, and are then agitated with a chain extender, usually at High temperature. In the process according to the invention, the prepolymer is preferably heated to a temperature of 60 ° C to 110 ° C and degassed under vacuumwith agitation. The chain extender and / or crosslinking agent is then added in liquid form, optionally after having been heated to temperatures typically at least 5 ° C above its melting point. The reaction mixture is melted in pre-heated molds (preferably 90 ° C to 120 ° C) and cured at 90 ° C to 140 ° C for about 24 hours. The polyols that can be used are polyether-, polyester, polycarbonate- and polyether polyols having hydroxyl numbers of 20 to 200 mg KOH / g, preferably 27 to 150 and particularly 27 to 120. Polyether polyols are prepared starting from an initiator molecule and epoxides, preferably ethylene oxide and / or propylene oxide, either by means of alkaline catalysis or double metal cyanide catalysis, or optionally by means of alkaline catalysis and double metal cyanide catalysis in a graduated reaction, and have terminal hydroxyl groups. The initiators that may be used herein are compounds with hydroxyl and / or amino functional groups known to those skilled in the art and water. The functionality of the primers is at least 2 and at most 4. Of course, it is also possible to use mixtures of several primers. Mixtures of various polyterpolyols can also be used. The polyether polyols can be tetrahydrofuran oligomers with terminal hydroxyl groups. The polyester polyols are prepared in a manner known per se by polycondensation of aliphatic and / or aromatic acids having from 4 to 16 carbon atoms, optionally their anhydrides and optionally their low molecular weight esters, including cyclic esters, the reaction component being predominantly polyols having from 2 to 12 carbon atoms. The functionality of the structural components for polyester polyols is preferably 2, but can also be greater than 2 in individual cases, the components having functionalities greater than 2 are used only in small quantities in such a way that the functionality of average arithmetic number of the intervals of polyester polyols ranges from 2 to 2.5, preferably from 2 to 2.1.

The polyether polyols are prepared by the concomitant use of polyether polyols in the synthesis of polyester polyols. Polycarbonatopolols are obtained according to the state of the art by polycondensation of carbonic acid derivatives, for example dimethyl or diphenyl carbonate or phosgene, and polyols. Preferred chain extenders are amine-based chain extenders, for example, diethyloluenediamine (DETDA), 3, 3'-di c 1 or ro-4, 4 '-di aminodi f in i lme t an (MBOCA) , Isobutyl 3, 5-diamino-4-chlorobenzoate, 4-methyl-2,6-bis (meth i 11 io) -1,3-di-amino-benzene (Ethacure 300), di-p-aminoben zoat or trimethylene glycol (Polacure 740M) and 4,4'-diamino-2, 2'-dichloro-5,5'-diethyldiphenylmethane (MCDEA). MBOCA and 3, 5-d i ami no-4-c 1 or r obe n z or isobutyl are particularly preferred. Similarly, chain extenders based on aliphatic amines can be used (concomitantly). It is also possible to use auxiliary substances and additives, for example catalysts, stabilizers, UV stabilizers, hydrolysis stabilizers, emulsifiers, and colorants and colored pigments which are preferably capable of incorporation. Examples of catalysts are tria 1 qu i 1 ami s, di az ab icic 1 ooct an, tin dioctanoate, dibutyl dilaurate t year, -alternative pigment, octanoate of lead, zinc, calcium or magnesium and the corresponding naphthenates and p-ni t rofenat or. Examples of stabilizers are Broensted and Lewis acids, for example hydrochloric acid, benzoyl chloride, organomineral acids, for example, dibutyl phosphate, and also adipic acid, malic acid, succinic acid, tartaric acid or citric acid. Examples of UV stabilizers and hydrolysis stabilizers are 2, 6-dibu t i 1-4 -me t i 1 f ene 1 and sterically hindered carbodiimides. The dyes capable of incorporating are those which have active hydrogen atoms of Zere itinof f, that is, they can react with NCO groups. Other auxiliary substances and additives include emulsifiers, foam stabilizers, cell regulators and fillers. A survey can be found in G. Oertel, Manual de Po 1 i ur e t y s, 2a. edition, Cari Hanser Verlag, Munich, 1994, chapter 3.4. The polyurethane elastomers according to the invention can be used in a very wide variety of applications, for example as elastic moldings produced by the molding process, as well as in coatings and adhesive bonds produced by the spraying process, such as, for example, in coating systems for public parking, concrete repairs and corrosion protection. The invention will be illustrated in more detail with the help of the following Examples.

EXAMPLES Measurement methods used: Chemical substances used: Polyester polyol 1: poly (ethylene-co-butylene) adipate with an OH number of 56 mg / KOH / g from Bayer MaterialScience G; nominal functionality 2.0; 4,4-MDI: 4,4 'diphenylmethane diisocyanate, Desmodur (R) 44M from Bayer MaterialScience AG, 98.5% by weight of 4,4 'isomer. 2,4'-MDI: 2, 'diphenylmethane diisocyanate (laboratory product) from Bayer MaterialScience AG, 98.5% by weight of 2,4' isomer. 3, 5-diamino-4-chlorobenzoate isobutyl: Crosslinker RC 1604 from Rheinchemie, Rheinau. Example 1: Preparation of ester prepolymers based on MDI. Instructions for the preparation of prepolymers using prepolymer 2 as an example (Table 1): 25 parts by weight of 2,4 '-MDI heated at 70 ° C in a flask stirred under nitrogen and stirred rapidly with 100 parts by weight of polyester polyol 1 dehydrated heated to 70 ° C. The reaction was allowed to proceed for 2 hours and the physical properties were determined (see Table 1). Table 1: Formulations of ester prepolymers based on MDI (according to the invention and Comparative examples) C: Prepolymer 1 comparison: 100 parts by weight of polyester polyol 1 and 25 parts by weight of 4, 4 -MDI. Prepolymer 2: 100 parts by weight of polyester polyol 1 and 25 parts by weight of 2,4-MDI.

The comparison of the viscosity values for MDI prepolymers with an NCO content of 3.36% by weight shows the advantages of the prepolymer based on 2,4'-MDI (prepolymer 2, according to the invention) with respect to 4.4 'analogue (prepolymer 1C, not according to the invention). The mixing of these two prepolymers with additional MDI at NCO contents of 6.1% by weight of NCO (theoretical) obviously gave in all cases prepolymers with lower viscosities than the starting prepolymers (prepolymers 3C, 4C, 5 and 6C in the Table). 1) . It is also observed that the equally low viscosity of the prepolymers 3C and 5 (in each case 2900 mPas at 70 ° C) is not sufficient for the advantageous processing (for example molding time) to melt the elastomers. Only the prepolymer 5 could be advantageously processed further to an elastomer (see Tables 2 and 3). Examples 2: Preparation of molding elastomers according to the invention from the prepolymers 2 and 5 of Example 1. Instructions for the preparation of molding elastomers using the molding elastomer A as Example 1 or: 100 parts of the prepolymer 2 they were degassed at 90 ° C under vacuum, with slow agitation, until they were free of bubbles. This was then stirred with 9.05 parts of 3, 5-di ami no-c 1 or isobutyl isolate at 100 ° C, and the homogeneous reaction melt was molded in preheated molds at 110 ° C, with corresponding dimensions to the test standards. The melt was heated for 24 hours at 110 ° C and the mechanical properties listed in Table 2 were determined.

Table 2 Formulations, preparation and properties of the molding elastomers according to the invention Example 3: Preparation of molding elastomers not according to the invention from the prepolymers 1C, 3C, 4C and 6C of Example 1 The preparation was carried out as described according to Example 2.

Table 3: Formulations, preparation and properties of the molding elastomers not according to the invention.

The advantages of the systems according to the invention are clarified by comparing Tables 2 and 3. At comparable prepolymer temperatures (initial temperature) and comparable NCO contents, ie comparable formulations, the molding times of the prepolymers in accordance with invention (Table 2) are up to 3 times greater than those of systems not in accordance with the invention (Table 3), which represents a clear processing advantage. Particularly favorable combinations of the properties of "long molding time" and "low viscosity of the prepolymer" are achieved only by means of the systems according to the invention. The molding elastomers according to the invention also have advantages with respect to their mechanical properties: If, for example, the PUR prepared from the prepolymer 2 (molding elastomer A, Table 2) is compared to a PUR prepared from a prepolymer 1C (molding elastomer F, Table 3) - both polymers having the same NCO value of 3.36% NCO - the system according to the invention has better final strength, elongation at break, resistance to tear propagation and abrasion . If the PUR prepared from prepolymer 5 (Elastomer molding E, Table 2) is compared with a PUR prepared from the prepolymers 3C, 4C and 6C (molding elastomers G, H and I, Table 3) - all prepolymers having the same NCO value of 6.1% by weight of NCO- the system according to the invention has a final strength, elongation at break, resistance to the propagation of tearing, abrasion and permanent setting, comparatively good, within the limits of experimental error. The same applies in terms of dynamic mechanical properties (storage and loss modules and loss factor). The systems according to the invention have a unique combination of advantageous properties with respect to the viscosity of the prepolymer, molding time and dynamic mechanical and mechanical properties. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (2)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. Polyurethane elastomers, characterized in that they are obtained from: a) NCO prepolymers based on diphenylmethane diisocyanate with an isomer content of 2; , 4 'of at least 85% by weight, the proportion of free monomeric 2,4'-MDI being at least 1 to 20% by weight, based on the NCO prepolymer, and polyols having OH numbers from 20 to 200 mg KOH / g and a functionality from 1.95 to 2.40, b) amine-based chain extenders and / or crosslinking agents, preferably amine-based chain extenders and / or cross-linking agents and c) optionally excipients and additives 2. Polyurethane elastomers according to claim 1, characterized in that component b) is diethyltoluenediamine (DETDA), 3,3'-dichloro-, 4'-diaminodiphenylmethane (MBOCA), 3, 5-dimanino-4-chlorobenzoate. isobutyl, 4-methyl-2,6-bis (methylthio) -1,3-diaminobenzene
1. (Etacure 300), trimethylene glycol di-p-aminobenzoate (Placure 740M) and 4,4'-diamino-2, 2'-dichloro-5,5-diethyldiphenylmethane (MCDEA) or mixtures thereof. 3. A process for the preparation of the polyurethane elastomers according to claim 1 or 2, characterized in that A) diphenylmethane diisocyanate with a 2,4'-isomer content of at least 85% by weight reacts with polyols having OH numbers of 20 to 200 mg KOH / g and functionalities of 1.95 to 2.40 to provide NCO prepolymers with a free monomeric 2,4'-MDI ratio of 1% by weight to 20% by weight, based on the prepolymer of NCO, and B) chain extenders are added based on amine and / or crosslinking agents and optionally auxiliary substances and additives to the prepolymer of A) in order to prepare the elastomer. 4. The use of the polyurethane elastomers according to claim 1 or 2 for the production of moldings, as adhesives and as sealants. 5. Moldings, characterized in that they can be obtained from a polyurethane elastomer according to claim 1 or
2. 2.