Two-component polyurethane sealants, a process for preparing them and their use for bonding a windscreen

Abstract: Two-component polyurethane sealants, comprising (A) a pasty polyurethane component containing a polyurethane prepolymer having free isocyanate groups, and a curing agent, and (B) a pasty solvent-containing component, where component (A) contains at least one latent, solvent-activatable curing agent which can be activated by means of solvents, and component (B) contains a polar, aprotic solvent and water reversibly bonded to a carrier substance which liberates water in a delayed manner after components (A) and (B) have been mixed. They are prepared by mixing components (A) and (B) using a static mixer, having only from 15 to 75 % of the number of mixing elements necessary for achieving homogeneous mixing of components (A) and (B) in the ratio by volume of 1:1. Application to a method for bonding a windscreen.

Description: The invention relates to two-component polyurethane sealants, in particular for the direct glazing of motor vehicle windscreens, comprising (A) a pasty polyurethane component containing a polyurethane prepolymer having free isocyanate groups, and a curing agent, and (B) a pasty component. Sealants of this type have been disclosed in GB-A-1 104 831 and EP-A-371 370, the curing agent being liberated by water and component (B) containing water as essential constituent. The invention also relates to a process for preparing such sealants and a particular component (B) for use in such sealants. A fundamental problem of sealants of this type is that, on the one hand, the processing time must be sufficiently long to ensure flawless processing of the sealant before it cures, but, on the other hand, the curing must, for obvious reasons, take place as rapidly as possible when processing is complete. Finally, the polyurethane component (A) must also have an adequate shelf life. Although the known two-component polyurethane sealants have sufficient strength, for example, one hour after mixing, the processing time is, however, too short, which means problems can arise even during mixing of components (A) and (B) due to premature gelling of the sealants. It has now been found that a particularly favourable behaviour with respect to processing time and curing rate is obtained in two-component polyurethane sealants of the type mentioned above if the curing agent of component (A) is solvent-activable and component (B) contains solvents and water reversibly bonded to a carrier substance, which liberates water in a delayed manner after components (A) and (B) have been mixed. The invention accordingly provides two-component polyurethane sealants, in particular for the direct glazing of motor vehicle windscreens, comprising (A) a pasty polyurethane component containing a polyurethane prepolymer having free isocyanate groups, and a curing agent, and (B) a pasty solvent-containing component, characterized in that component (A) contains a latent curing agent which can be activated by means of solvents, and component (B) contains a polar, aprotic solvent and water, reversibly bonded to a carrier substance which liberates water in a delayed manner after components (A) and (B) have been mixed. As shown by the examples below, the sealants according to the invention have, on the one hand an entirely adequate processing time or gelling time of from about 5 to 10 minutes, while, on the other hand, a shear strength of approximately 0.1 N/mm 2 is achieved after one hour and virtually the final shear strength of about 4 N/mm 2 is achieved after 24 hours. In component (B), the carrier substance ensures that a delayed release of water takes place, which results in an extension of the processing time, but neverless with a rapid achievement of the final strength. Suitable carrier substances for binding water in component (B) are all substances which are capable of reversibly binding water and liberating water in a delayed manner after components (A) and (B) have been mixed. Examples of preferred carrier substances are ground cellulose, starch and cork. The carrier substance is preferably finely particulate, so that, for example, at least 50 % of the particles have a size of less than 40µm. Examples of suitable commercial products are cellulose powder or native potato starch. Ground cellulose and starch are capable of reversibly binding water up to a maximum ratio by weight of 1:1. In a preferred embodiment, the carrier substance is dispersed in an inert viscous liquid in order to achieve the desired pasty consistency. Suitable viscous liquids here are in principle all those which do not react, in particular, with the isocyanate groups of the polyurethane prepolymer of component (A) and also have no other disadvantageous effect on the cured sealant. The inert viscous liquids are preferably plasticisers for the cured sealant, preference being given to alkylsulphonic acid esters methylstyrene adducts and phtalic acid esters. Examples of suitable commercial products are alkylsulphonic acid esters of phenol or cresol, ACTREL® 400 (product of the addition reaction of methylstyrene and binuclear, partially hydrogenated aromatics) from ESSO and benzyl butyl phtalate. Component (B) contains a polar, aprotic solvent, such as, for example, n-butyrolactone, γ-butyrolactone, chlorobenzene, acetonitrile, dimethylformamide, dioxane, methyl ethyl ketone, N-methylpyrrolidone, tetrahydrofuran or N-vinylpyrrolidone. In addition to said solvent, component (B) also contains water, in an amount of at most 10 % by weight, preferably less than 5 %, based on the total weight of component (B). Furthermore, component (B) preferably contains a thixotropic agent, carbon black being particularly preferred. Component (B) may also contain further conventional additives and processing aids, such as catalysts, dyes, pigments, fillers or wetting agents. In a preferred embodiment, component (B) contains a wetting agent. Wetting agents contribute to compatibility and thus improve the smoothness of the sealant. Preferred examples of suitable wetting agents are sorbitan monolaurate and polyoxyethylene (10) oleyl alcohol. Suitable polyurethane prepolymers are known to persons skilled in the art. These prepolymers contain terminal free isocyanate groups, which are capable of reacting both with the curing agent present in component (A) and with water introduced through component (B), with enlargement of the molecule and curing. This involves the following reactions occurring simultaneously. The solvent from component (B) activates the curing agent, the latter reacting with the polyurethane prepolymer ; however, water present in component (B) can also react directly with the isocyanate groups. The curing agent of component (A) is preferably a complexed amine. A preferred complexed amine is the NaCl complex compound of 4,4'-diaminophenylmethane. Suitable curing agents of component (A) are also amine complexes with sodium bromide, sodium iodide, sodium nitrite, lithium chloride, lithium bromide, lithium iodide, lithium nitrite or sodium cyanide, amine complex compounds of the alkali metal or alkaline earth metal salt type and microencapsulated, solvent-activatable polyamines or polyols. Solvent-activatable curing agents of this type are disclosed in EP-A-0 351 728. In a further preferred embodiment, component (A) contains a thixotropic agent, with carbon black being particularly preferred. Although the isocyanate groups of the polyurethane prepolymer are also capable of reacting with water of atmospheric moisture, the main reaction, due to the early shear strength which is desired, is the crosslinking reaction with water liberated from the carrier substance of component (B) or with the solvent-activated curing agent in component (A). The ratios can be selected so that there is either a stoichiometric excess or a substoichiometric amount of free NCO groups relative to the reactive groups present in the curing agent. The former case is preferred since the processing time can then be better adjusted via the water/carrier substance ratio and the amount of water in component (B). If the solvent-activatable curing agent is used in a substoichiometric amount, the curing rate in the sealants according to the invention can be controlled, within certain limits which are of practical importance, by the ratio of carrier substance to water. Both components (A) and (B) are in pasty form, i.e. are not free-flowing. In addition to the pasty consistency of components (A) and (B), the non-Newtonian properties (thixotropic behaviour) also play a part in the mixing behaviour of the components. Control may in each case be effected through the choice of the type and amount of the inert viscous liquid and of the thixotropic agent. As far as the amount of component (B) relative to component (A) is concerned, the molar amounts of curing agent on the one hand and the free isocyanate groups in component (A) on the other hand must again be taken into account, preference being given, as stated above, to a stoichiometric excess of NCO. In the sealants according to the invention, component (A) contains from about 20 to 80 parts by weight, preferably from 35 to 55 parts by weight, in particular from 40 to 45 parts by weight, based on 100 parts by weight of component (A), of the polyurethane prepolymer, and from 20 to 120 eq-%, preferably from 40 to 80 eq-%, in each case based on the number of equivalents of isocyanate in the polyurethane prepolymer, of the curing agent. If component (A) contains a thixotropic agent, the latter is present in such amounts that the material is firm and not free-flowing. In the case of carbon black, amounts of about 7 parts by weight per 100 parts by weight of component (A) are generally necessary for this purpose. Component (B) contains the carrier substance in an amount sufficient for complete binding of water. The ratio between the carrier substance and water is generally from about 1:0.25 to 1:1, preferably from 1:0.5 to 1:0.8. The carrier substance (with water bonded thereto) is preferably dispersed in an inert viscous liquid. If component (B) contains a thixotropic agent, for example carbon black, the latter is preferably present in such amounts that a pasty consistency is produced. To this end, amounts of about 7 to 25 % by weight, based on component (B), are generally sufficient. Preferably components (A) and (B) are employed in a ratio by volume of at least 2 : 1, and more preferably from about 5 : 1 to 100 : 1. The invention furthermore relates to a process for preparing a sealant as hereinabove described, especially those where components (A) and (B) are employed in a ratio by volume of at least 2:1, comprising mixing components (A) and (B) using a static mixer, which process is characterized in that the said static mixer has only from about 15 to 75 % of the number of mixing elements necessary for achieving homogeneous mixing of components (A) and (B) in the ratio by volume of 1:1. In a preferred embodiment, mixing is carried out using a static mixer which has only from 40 to 50 % of the number of mixing elements necessary to mix components (A) and (B) homogeneously in the ratio by volume of 1:1. In a further embodiment, a component (B) which contains water in free form and not bonded to a carrier substance is used in the mixing process. In order to ensure an appropriate processing time it is necessary in this case to use a component (A) with low reactivity. In a specific embodiment, a component (B) which contains no water is employed in the mixing process. Neverless, the curing agent is, here too, used in substoichiometric amounts, since the curing reaction otherwise proceeds too rapidly. Complete curing is effected by atmospheric moisture in this case. The static mixer used for mixing preferably has an internal diameter in the range from about 5 to 30 mm, in particular in the range from 10 to 20 mm. Statics mixers, also known as motionless mixers, have non-moving, i.e. static, guide or mixing elements built into the flow channel. In this respect, see Perry's Chemical Engineers Handbook, 6th Edition (1984), 19-22 to 19-23. Particularly preferred static mixer designs are the Kenics® mixer and the Package® mixer. Preference is given to a Kenics® mixer which has only from 4 to 18, in particular from 8 to 12, mixing elements instead of the at least 24 mixing elements necessary to homogeneously mix components (A) and (B) in the ratio by volume of 1:1. If a Package® mixer is used, it preferably has only from 4 to 21, in particular from 11 to 14, mixing elements instead of the at least 28 mixing elements necessary to homogeneously mix components (A) and (B) in the ratio by volume of 1:1. In the process of the invention, mixing of components (A) and (B) is not continued until homogeneity is achieved. The reduced number of mixing elements in the mixer allows the operating pressure to be reduced, so that satisfactory discharge rates are possible using conventional spray guns. Processing by means of shortened static mixer results in a less than homogeneous state. As a consequence, due to the limitation on the diffusion, the curing agent of component (A) is not displaced in a sudden manner by the solvent of component (B), which in turn means that curing, preferably amine curing, of the polyurethane prepolymer only sets in gradually, while, on the other hand, the diffusing water from component (B) is itself also capable of reacting with the isocyanate groups. Overall, this achieves a particularly balanced ratio between processing time and early shear strength. The sealants according to the present invention are especially advantageous and designed for bonding windscreens of cars and automotives, and more particularly those cars with directly glazed windows. Therefore according to the present invention we provide a method for bonding a windscreen by applying a two-component polyurethane sealant comprising (A) a pasty polyurethane component containing a polyurethane prepolymer having free isocyanate groups, and a latent curing agent which can be activated by means of solvents and (B) a pasty component containing a polar, aprotic solvent and water, reversibly bonded to a carrier substance which liberates water in a delayed manner after components (A) and (B) have been mixed. In further detail, components (A) and (B) of the polyurethane sealant used in the said method will be as described hereinabove. The examples below illustrate the invention. Unless otherwise stated, parts are by weight. I - Preparation of component (A1) 21.35 parts of octyl decyl phtalate (WITAMOL® 118 from HÜLS AG), 7.143 parts of diphenylmethane 4,4'-diisocyanate (DESMODUR® 44MS from BAYER AG), 21.69 parts of polypropylene oxide triol (DESMOPHEN® 1919U from BAYER AG), 11.21 parts of polypropylene oxide diol (DESMOPHEN® 1900U from BAYER AG), 0.10 part of p-toluenesulphonamide and 21.00 parts of carbon black (ELFTEX® 465 from CABOT) are dispersed over the course of 30 minutes. 0.1 part of Bi catalyst (COSCAT 83 from ERBSLÖH) and 7.565 parts of octyl decyl phtalate (WITAMOL® 118) were then added, and the mixture was stirred for one hour. 0.2 part of Bi catalyst (COSCAT 83), 0.032 part of tosyl isocyanate (BAYER AG), 7.305 parts of octyl decyl phtalate (WITAMOL® 118) and 5.53 parts of the NaCl complex of 4,4'-diaminophenylmethane (CAYTUR® 21 from UNIROYAL) were then stirred in at room temperature. The pasty mixture obtained is transferred into cartridges (in the absence of air). II - Préparation of a component (A2) As far Al, but only 0.56 times the amount of amine was employed. III - Preparation of a component (B1) 22.5 parts of carbon black (ELFTEX® 465), 3.6 parts of water, 4.5 parts of cellulose (XX-01® from MIKRO-TECHNIK) and 74.4 parts of butyrolactone are dispersed for 30 minutes. The pasty mixture obtained is transferred into cartridges. IV - Preparation of a component (B2) 23.75 parts of carbon black (ELFTEX ® 465), 1.1 parts of water, 1.375 parts of cellulose (XX-01®) 38.702 parts of butyrolactone, 38.762 parts of phenol alkylsulphonic acid ester (MESAMOLL® from BAYER AG) were dispersed for 30 minutes. The pasty mixture obtained is transferred into cartridges. V - Preparation of a component (B3) 96.4 parts of butyrolactone are mixed with 3.6 parts of water and transferred into cartridges. Application of the adhesive using a Kenics ® mixer A cartridge containing component (A) and a cartridge containing component (B) (cartridge length 150 mm, diameter 46 mm (component (A)) or 17.2 mm ( component (B) ), A : B volume ratio = 100:14) were connected, via an adaptor, to a Kenics® mixer (diameter 13 mm) having 12 elements. The cartridges attached to the mixer were placed in a twin-cartridge hand gun (model "HILTI P2000"), and the adhesive was forced out onto primed steel test specimens (primer : Primer Clear®, BOSTIK ; bonded area : 25 x 10 mm with a film thickness of 2 mm). Pot time B1 B2 B3 A1 2 min 5 min inadequate mixing A2 5 min 10 min inadequate mixing Shear strength (as a function of the curing time) : Combination Curing time at room temperature 1 h 24 h 7 days A1/B1 0.34 N/mm 2 1.9 N/mm 2 2.9 N/mm 2 A1/B2 0.6 " 5.0 " 5.4 " A2/B1 0.09 " 4.0 " 4.5 " A2/B2 0.07 " 3.8 " 4.5 " Application of the adhesive using a Package ® mixer The appplication was carried out in the same manner as described above, but, instead of the Kenics® mixer, a Package® mixer (TAH Industries No. 020-064, diameter 18.75 mm) having 14 mixing zones was connected to the two cartridges. Pot time B1 B2 B3 A1 2 min 5 min inadequate mixing A2 5 min 10 min inadequate mixing Shear strength (as a function of the curing time) : Combination Curing time at room temperature 1 h 24 h 3 days A1/B1 0.3 N/mm 2 1.5 N/mm 2 2.8 N/mm 2 A1/B2 0.1 " 3.5 " 4.0 " A2/B1 0.09 " 3.4 " 3.9 " A2/B2 0.06 " 3.2 " 3.8 " Tables I and III show that mixing of the pure solvent mixture B3 with the pasty component A does not take place since the viscosity and consistency of the two components is different. It can be seen from Tables II and IV that the shear strength of the combinations A1/B1 and A1/B2 is sufficiently high after only 1 hour.

Claims: Two-component polyurethane sealants, comprising (A) a pasty polyurethane component containing a polyurethane prepolymer having free isocyanate groups, and a curing agent, and (B) a pasty solvent-containing component, where component (A) contains at least one latent, solvent-activable curing agent, and component (B) contains a polar, aprotic solvent and water reversibly bonded to a carrier substance which liberates water in a delayed manner after components (A) and (B) have been mixed. Sealant according to Claim 1, characterized in that the polar, aprotic solvent is selected from n-butyrolactone, γ-butyrolactone, chlorobenzene, acetonitrile, dimethylformamide, dioxane, methyl ethyl ketone, N-methylpyrrolidone, tetrahydrofuran and N-vinylpyrrolidone. Sealant according to Claim 1 or 2, characterized in that the carrier substance is selected from ground cellulose, starch and cork. Sealant according to one of claims 1 to 3, characterized in that the carrier substance is dispersed in an inert viscous liquid. Sealant according to one of claim 4, characterized in that the viscous liquid is a plasticiser for the cured sealant. Sealant according to Claim 5, characterized in that the plasticiser is selected from alkylsulphonic acid esters, methylstyrene adducts and phtalic acid esters. Sealant according to one of claims 1 to 6, characterized in that component (B) further contains a thixotropic agent. Sealant according to one of claims 1 to 7, characterized in that component (B) further contains additives and processing aids. Sealant according to Claim 8, characterized in that component (B) contains a wetting agent. Sealant according to one of claims 1 to 9, characterized in that component (A) contains a complexed amine as curing agent. Sealant according to claim 10, characterized in that the complexed amine is an amine complex compound of the alkali metal or alkaline earth metal salt type. Sealant according to claim 11, characterized in that the complexed amine is the NaCl complex compound of 4,4'-diaminophenylmethane. Sealant according to claim 11, characterized in that the complexed amine is an amine complex with sodium bromide, sodium iodide, sodium nitrite, lithium chloride, lithium bromide, lithium iodide, lithium nitrite or sodium cyanide. Sealant according to one of claims 1 to 9, characterized in that component (A) contains, as curing agent, microencapsulated, solvent-activable polyamines or polyols. Sealant according to one claims 1 to 14, characterized in that component (A) contains a thixotropic agent. Sealant according to claim 15 or claim 7, characterized in that the thixotropic agent is carbon black, pyrogenic silica or a urea compound. Sealant according to any of claims 1 to 16, characterized in that components (A) and (B) are employed in a ratio by volume of at least 2:1. Sealant according to claim 17, characterized in that components (A) and (B) are employed in a ratio by volume in the range from 5:1 to 100:1. Process for preparing a sealant according to claim 17, comprising mixing components (A) and (B) using a static mixer, characterized in that the said static mixer has only from 15 to 75 % of the number of mixing elements necessary for achieving homogeneous mixing of components (A) and (B) in the ratio by volume of 1:1. Process according to Claim 19, characterized in that the said static mixer has only from 40 to 50 % of the number of mixing elements necessary to homogeneously mix components (A) and (B) in the ratio by volume of 1:1. Process according to one of Claim 19 and 20, characterized in that the said static mixer has an internal diameter of from 5 to 30 mm. Process according to one of Claims 19 and 21, characterized in that a Kenics™ mixer which has only from 4 to 18 mixing elements or a Package™ mixer which has from 4 to 21 mixing elements is used. A method for bonding a windscreen by applying a two-component polyurethane sealant according to any of claims 1 to 16.

Inventors: MULLER BODO, PIESTERT GERHARD, MULLER, BODO, PIESTERT, GERHARD
Applicants: JOINT FRANCAIS, LE JOINT FRANCAIS SNC
Application year: 1991
Main classification: C09K3
IPC codes: C09K3, C09J175, C08G18, C08L75