GB2118955A

GB2118955A - Polyurethanes

Info

Publication number: GB2118955A
Application number: GB08309880A
Authority: GB
Inventors: Albrecht Blau; Edward William Duck
Original assignee: Henkel Teroson GmbH
Current assignee: Henkel Teroson GmbH
Priority date: 1982-04-23
Filing date: 1983-04-12
Publication date: 1983-11-09
Also published as: GB8309880D0

Abstract

A polyurethane prepolymer useful as a sealant that will cure upon exposure to moisture is obtained by reacting a polyol with polyisocyanate comprising paraphenylenediisocyanate.

Description

SPECIFICATION Polyurethanes It is well known to formulate sealant compositions based on prepolymers formed by reaction of a polyol and a polyisocyanate. A polyisocyanate that is often used for this purpose at present is diphenylmethane-4,4-diisocyanate (MDI). As described in, for example US Patent Specification No. 3707521 such prepolymers can be formulated in moisture curable compositions, with the result that final curing occurs when the composition is exposed to the atmosphere. A disadvantage of such prepolymers is that their rate of curing can be slower than is desired and the resultant cured product may have stability to heat and ultraviolet that is lower than is desired.

Ways of accelerating the rate of cure and improving the stability of the final product are known but involves the incorporation into the compositions of extra components, and this can be undesirable.

The present invention relates to a novel prepolymer that is capable of being more easily cured and that is capable of giving products of improved heat and ultraviolet light stability.

A composition according to the invention comprises a polyurethane prepolymer obtained by .reacting a polyol with polyisocyanate comprising paraphenylenediisocyanate (PPDI). The composition may consist only of the prepolymer, or it may contain other components.

The polyisocyanate may consist solely of PPDI or it may consist a mixture of PPDI with other polyisocyanate, generally with other diisocyanate.

It may be a mixture of PPDI and MDI. The mixture may contain from 10 to 90%, on a molar basis, PPDI and generally contains at least 20% and often at least 50% PPDI. The choice of proportions will be made having regard to the properties desired. The use of mixtures of PPDI and MDI, and in particular mixtures containing a minor amount of PPDI, can be desirable since a sealant formed from such a mixture can have very fast initial setting properties, upon initial exposure to the atmosphere.

The polyurethane prepolymer of the invention must have free isocyanate groups and so can be regarded as a "isocyanate tipped" polyurethane prepolymer wherein, at each or most of the hydroxy groups of the polyol, a urethane linkage has been formed between that hydroxy group and one isocyanate group of the polyisocyanate, the other isocyanate group or groups remaining free for subsequent reaction with, for instance, water.

The polyurethane is preferably formed by reaction of substantially equivalent amounts of polyol and polyisocyanate for this reaction. For instance 0.8 to 1.2 equivalents, preferably 0.95 to 1.05, equivalents of polyol are reacted with the polyisocyanate. When the polyisocyanate is diisocyanate the molar ratio polyol:diisocyanate is therefore preferably 1:1.6 to 1:2.4 when the polyol is a diol and 1:2.4 to 1:3.6 when the polyol is a triol.

Greater amounts of polyol may be used. In this event, depending upon the reaction conditions, the prepolymer may include unreacted hydroxyl groups or may include urethane linkages formed by the reaction of both isocyanate groups of a mqlecule of PPDI with hydroxy groups of the polyol, resulting in chain lengthening of the polyurethane.

Preferably however there is substantially no chain lengthening and the molecular weight of the prepolymer is substantially the same as the molecular weight of the polyol, except for the increase brought about by the "tipping" with PPDI or other polyisocyanate.

The polyol preferably has an average molecular weight of from 500 to 20,000, most preferably from 1,000 to 10,000. When the polyol is a diol the average molecular weight is preferably from 1 ,200 to 8,000. When it is a triol the average molecular weight is preferably from 2,000 to 10,000.

Preferably part at least of the polyol has a functionality greater than 2, with preferred products being formed using triol alone or a mixture of triol and diol, the mixture generally containing at least 10% and usually at least 20%, typically around 50%, of triol (on a molar basis).

The polyol may be a polyether polyol or a polyester polyol and the polyols known for use as polyurethane prepolymers in sealant compositions can be used in the invention. The preferred polyethers are polyalkylene ether polyols. Polyalkylene glycols such as polyethylene glycol or polypropylene glycol can be prepared by the condensation of polyethylene oxide or polypropylene oxide (or a mixture) with a lower alkylene diol such as ethylene glycol or propylene glycol. Polyalkylene ether triols can be prepared by condensing ethylene oxide or propylene oxide (or a mixture) with an alkylene triol such as glycerin, or trimethylol propane.

The prepolymer can be formed by reacting the polyol with PPDI, and optionally other polyisocyanate, in the desired proportions. Generally it is preferred to react the isocyanate initially with a small excess, up to 20% molar, of the polyol and then to add further isocyanate to bring the final proportion to the desired substantially equivalent amounts. If it is desired that the prepolymer should have a molecular weight substantially greater than the polyol then this can be achieved by reacting the polyol with the polyisocyanate in substantially equivalent amounts and then reacting the product with further polyol, provided that the additional amount or the reaction conditions are such that the final prepolymer still contains free isocyanate groups.

The reaction may be carried out in the presence of a solvent, at ambient temperatures or, preferably, at elevated temperatures such as 40 to 80cm. A suitable solvent is xylene but any other conventional solvent customarily used in the formation of polyurethane prepolymers may be used instead of xylene.

The free isocyanate groups of the prepolymer may be temporarily blocked, for example by reaction with dimethylmalonate or other conventional and easily removable blocking groups. This blocking may be effected after formation of the polyurethane or one group only of PPDI may be blocked prior to the reaction of PPDI with the polyol.

A sealant composition according to the invention comprises the described prepolymer together with conventional sealant additives such as one or more additives selected from fillers, plasticisers, solvents, accelerators and pigments and is curable upon exposure to the atmosphere, generally upon exposure to atmospheric moisture.

Curing may be brought about as a result of the effect of moisture on a component in the composition other than the prepolymer. For example a component in the composition may decompose in contact with moisture to form a rectant that causes polymerisation of the prepolymer. Alternatively the moisture may cause the removal of blocking groups so as to permit polymerisation of the prepolymer. Preferably however, the prepolymer reacts spontaneously with atmospheric moisture to result in curing of the polymer as a result of the formation of urethane linkages between isocyanate groups.

The composition may include a blend of prepolymers provided at least one is formed from PPDI, as described above. Generally each prepolymer is formed, at least in part, from PPDI.

Often one prepoiymer in a blend is based on diol and the other on triol, the amount of trio prepolymer generally being at least 10% or 20%, and often at least 50%, by weight of the weight of the blend.

The other additives may be selected in known manner such that the composition has the desired physical properties. For instance it may be adequately tacky to adhere to the surfaces to be sealed but to avoid contaminating the hands of workmen and it can be formulated to be highly thixotropic and viscous, such that it can be extruded from a cartridge to a ribbon or other shape that does not sag or flow.

Suitable fillers include chalk, clay, carbon black and powdered polyvinyl chloride.

The composition may include materials to absorb any liberated carbon dioxide, for example calcium oxide, and materials to improve adhesion, for example silanes such as epoxy silanes. If chemicals to promote curing are required, for example amines or other catalysts for accelerating the curing reaction, then these also are included in the composition.

Typically a suitable sealant composition comprises, by weight, 25 to 50% prepolymer, 10 to 30% plasticiser and 20 to 60% filler.

The composition can have excellent storage stability provided it is packed in a sealed container, such as a cartridge or drum, from which atmospheric moisture is excluded, It may be extruded from the container under pressure into the chosen location where it is to serve as a sealant. For instance it may be used as an expansion joint sealant or construction sealant or as an adhesive sealant for dirct glazing of , for instance, automobile windscreens or windows in commercial vehicles and buses.

As an example, prepolymers are formed based on triol and diol. The prepolymer based on triol is made by reaction in 10 parts xylene of 8 parts by weight PPDI with 81 parts by weight of a triol that has an average molecular weight of 4,900 and that is formed mainly of propylene oxide blocks and ethylene oxide end groups. When the reaction is completed one part by weight PPDI is added.

The prepolymer based on diol is formed in a similar manner except that, instead of using 8 parts PPDI and 81 parts triol, there is used 12.5 parts PPDI and 76.5 parts diol, and the diol has an average molecular weight of 2,000 and is formed mainly of propylene oxide blocks and ethylene oxide end groups.

A sealant composition is formed by blending under anhydrous conditions 20 parts by weight of each of the prepolymers with 26.5 parts by weight powdered polyvinyl chloride, 3 parts by weight dispersed silica, 20 parts by weight plasticiser, 3 parts by weight xylene and 7.5 parts by weight other additives including calcium oxide and silane adhesion improvers.

The resultant composition can be extruded under pressure for use as a sealant for automobile windscreens, whereupon it cures rapidly to give a seal that has very high heat and ultraviolet stability.

Claims

1. A composition comprising a polyurethane prepolymer obtained by reaction of polyol with polyisocyanate comprising paraphenylenediisocyanate.

2. A composition according to claim 1, in which the polyisocyanate comprises a mixture of paraphenylenediisocyanate with other polyiso cya nate.

3. A composition according to claim 1, in which the polyisocyanate comprises a mixture of paraphenylenediisocyanate with diphenylmethane-4,4-diisocyanate.

4. A composition according to any preceding claim, in which the polyol comprises a diol having an average molecular weight of 1200 to 8000.

5. A composition according to any preceding claim, in which the polyol comprises a triol having an average molecular weight of 2000 to 10,000.

6. A composition according to any of claims 1 to 3 or 5, in which the polyol consists only of triol.

7. A composition according to any of claims 1 to 5, in which the polyol comprises a mixture of diol with triol.

8. A composition according to claim 1 comprising a polyurethane prepolymer obtained by reaction of a polyol comprising a diol with polyisocyanate and a polyurethane prepolymer obtained by reaction of a polyol comprising a triol with a polyisocyanate and in which the polyiso cyanate for at least one of the polyurethane prepolymers comprises paraphenylenediisocyanate.

9. A composition according to any preceding claim that is a sealant composition and that comprises also one or more sealant additives selected from fillers, plasticisers, solvents, accelerators and pigments and that cures upon exposure to the atmosphere.

10. A composition according to claim 9 that cures upon exposure to moisture.

11. A composition according to claim 9 or claim 10 that is sufficiently thixotropic and viscous that it can be extruded from a cartridge as a substantially non-flowing and non-sagging shape and that has a thickness sufficient that it can adhere to surfaces to be sealed but not to the hand.

12. A composition according to claim 1 substantially as herein described.

New claims or amendments to claims filed on

13 June 1 983 New or amended claims: 1 3. A method in which a composition according to claim 11 is extruded under pressure from a container to a location where it is to serve as a sealant and is exposed to moisture at that location whereupon it cures as a seal.

14. A method according to claim 13 in which the composition is extruded from a container for use as a sealant for auto windscreens.