GB2264502A - A method of adhering cured rubber to uncured or cured urethane and the resulting product - Google Patents

Abstract

A method of adhering a polyurethane to a structural material, eg a cured rubber, comprises contacting the material with a polyurethane prepolymer with unreacted hydroxyl and an excess of blocked polyisocyanate followed by curing at less than 250 DEG F (about 120 DEG C) curing at a temperature of 300 DEG - 450 DEG F (about 115 - 230 DEG C) for several hours, usually 4 to 24 hours to cause the blocked isocyanate to unblock and the free isocyanate group to react with the excess polyol. The shaping may occur in a mould, eg a tyre mold having a centrally located hub 6 of metal or structural plastic so as to produce a tyre or tyred wheel. <IMAGE>

Description

A METHOD OF ADHERING CURED RUBBER TO UNCURED OR CURED URETHANE AND THE RESULTING PRODUCT Technical Field This invention relates to a method of adhering a cured polyurethane to a reactive polyurethane mixture to chemically adhere the two polyurethane together to permit novel shaped products such as tires having a tread of a different composition from the body or carcass of the tire. Also, this method permits shaped articles to be formed having different flexibility and/or hardness to mention some of the unique features of the molded shaped articles of this invention.

Technical Background Art The chemistry of polyurethane is extremely old with some of the features being over fifty years old.

Since polyurethane mixtures are used widely, it has been a problem to get these reactive polyurethane mixtures to react or adhere to cured rubbers, including cured polyurethanes. Usually the gums such as polyamide resins are used to achieve this adhesion but this approach causes problems in use, say use of a tire.

Although thermosetting and thermoplastic polyurethanes are known and used widely, they are not known to provide a solution to the adhesion problem.

Likewise, the so-called blocked polyisocyanates and blocked polyurethanes are known, they are not known to solve this adhesion problem either.

Summary of Invention We have discovered that by making a thermoplastic polyurethane using an excess of a polyol, it can be mixed with a so-called blocked polyisocyanate and be shaped into a manufactured article that then can be cured at a relatively high elevated temperature to render the thermoplastic urethane thermoset to give essentially a fully cured shaped article resistant to separation of its parts and particularly resistant to softening.

The Drawings Figure 1 is a vertical cross-section through a mold having a solid polyurethane tire molded on the hub of a tire wheel.

Figure 2 is a view showing another embodiment having at least two types or kinds of rubber joined in the recapped tire.

The Method of Making the Shaped Article and the Best Modes Reference to the drawings will further illustrate the best modes of this invention and its embodiments.

Fig. 1 shows the mold 5 with a hub 6 positioned centrally therein and a shaped polyurethane7 adhered to the hub with the injection means 8 and vent ports 9 for filling the mold. The tire-wheel combinations of Fig. 1 shows a solid tire such as is used on industrial lift trucks or carts used in warehouses and loading docks that generally have a tread that is flat and free of grooves or tread pattern. In Fig. 2 the tire is shown with two types of rubber identified by numerals 11 and 12. Numeral 13 shows where rubber11 is adhered to the metal or plastic hub.

Thermoplastic urethanes normally are reacted with about 1:1 ratio of a organic polyisocyanate to polyol.

Preferably a diisocyanate is chosen from aliphatic, cycloaliphatic or aromatic diisocyanate such as butane diisocya e, cyclohexane diisocyanLe or toluene diisocyanate and the family of methylene bis (phenylisocyanates), the so-called MDI's, to a polyol to give the thermoplastic urethane. The thermoplastic urethanes useful in this invention are reacted with an excess of polyol to give a thermoplastic urethane with an excess of polyol, usually about 2 to about 15 mole percent and preferably about 5 to about 10 percent.

Thus, all the NCO groups has reacted with a hydroxyl group to leave some of the hydroxyls in the polyol unreacted. Normally thermoplastic urethanes are characterized by being readily extruded as measured by olensis test and has a well known flow rate as characterized by this test.

The blocked polyisocyanates useful in this invention are blocked with reactive hydrogen organic materials which are materials monofunctional and usually hydroxyls such as the phenols or reactive hydrogen such as caprolactam, to mention only a few of the well known monofunctional hydroxyls useful in this invention. Usually a 1:1 ratio of organic polyisocyanate to polyol on a molar NCO to hydroxy basis is used, although the ratio may vary slightly from the 1:1 ratio, say about a 0.98 to 1.02 ratio.

The organic polyisocyanate are preferably diisocyanates such as toluene diisocyanate or the other well known diisocyanates.

The polyols may be of low molecular weight but the polymeric ones of 500 to 10,000 molecular weight are desired and usually those of 500 to 800 to 5,000 to 6,000 molecular weight are very suitable and more desirable. Especially desired polyols are the poly(oxytetramethylene) glycols or mixtures of poly(oxytetramethylene-oxytrimethylene) glycols. The other polyether glycols may be used. The polyester glycols such as the adipate esters of propylene glycols, ethylene glycol, butylene glycols and their mixtures are highly desirable where higher physicals are desired.

The thermoplastic urethanes having unreacted polyol are mixed with sufficient blocked polyisocyanate to react with the free or unreacted polyol, usually a slight excess to about 15% blocked polyisocyanate is used. Then this mixture is poured, cast or injected into a shaper to give the shaped article such as the tire of the drawings. Where two kinds of rubber are to be joined in Fig. 2, rubber 14 may be, for example, a rubber such as a diene rubber or a polyurethane that has been used until the tire is ready to be recapped. Then part 15, the tread part, is removed as in a normal recapping operation, and then a new treadl2 is molded by injecting the mixture of the thermoplastic polyurethane and blocked isocyanate into the mold via injection ports 8 to fill it and the air in the mold is removed by vents 9.

Then, the molded tread portion on the recapped tire is heated in the mold to 350 to 4500F for an hour or so, usually overnight to cause the blocked isocyanate to become unblocked and the unblocked isocyanate will react with the excess polyol to fully cure the mixture. Alternately, the molded tire is taken from the mold and cured in a hot room at about 300 to about 4500F to unblock the blocked isocyanate and allow the unblocked isocyanate to react with the excess or freed polyol.

In another example, a toluidine diisocyanate is reacted with an excess of poly(oxytetramethylene) glycol of about 1000 molecular weight to give about 5 to 10% excess polyol. This polyurethane is blended with a slight excess of a blocked isocyanate composed essentially of the reaction product of a 1 to 1 molar mixture of phenol and toluene diisocyanate. The mold of Fig. 1 was mounted in a spinning relationship on an axle and the mold spinning was partially filled with this mixture and causeto react to set the mixture usually at 100 to 2000F. Then the unfilled portion of the mold is filled with a mixture of a slight excess of the above blocked isocyanate and a thermoplastic polyurethane composed of a toluene diisocyanate reacted with an excess of a polybutane diol-1,4 of 800 to 2000 molecular weight and allowed to react until set The tire is stripped from the mold and cured in a hot air oven for 4-6 hours at 325 to 4500F to give a thermoset polyurethane.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

Claims (10)

CLAIMS:

1. A method of converting a thermoplastic urethane prepolymer having unreacted polyol, i.e., hydroxyl groups to a thermoset urethane comprising making a prepolymer by reacting essentially all of the NCO groups of an organic polyisocyanate with excess polyol to give an extrudable product, (2) blocking an organic polyisocyanate by reacting the organic polyisocyanate with an organic monofunctional reactive hydrogen to form a urethane group, (3) forming a mixture by mixing said prepolymer urethane with free hydroxyl with sufficient blocked organic polyisocyanate to react with the free hydroxyls of the prepolymer and shaping said mixture by curing at a temperature less than about 2500F and then post curing at about 3500F to 4500F to react the polyol of the thermoplastic urethane with the blocked isocyanate to form a post cured polyurethane.

2. The method of claim 1 wherein the shaping occurs in a mold.

3. The method of claim 2 wherein the mold is a tire mold that has a hub centrally positioned therein to allow the urethane to be adhered to the surface of the hub.

4. The method of claim 3 wherein the hub is metal.

5. The method of claim 3 where the hub is a structural plastic.

6. A method of adhering a polyurethane to a structural material comprising contacting said structural material with a mixture of (a) a polyurethane prepolymer having an excess of 1 to 10% polyol to give an excess of hydroxyl to NCO groups, and (b) an excess of a blocked polyisocyanate where the blocking agent is present as an excess of an organic monofunctional reactive hydrogen reagent.

7. The method of claim 6 wherein the structural material is selected from the class consisting of a fabric, a metal and a castable plastic.

8. The method of claim 6 wherein the monofunctional agent is selected from the class consisting of phenol and caprolactam.

9. A method according to Claim 1 substantially as hereinbefore described with reference to the accompanying Drawings.

10. A method in accordance with any one of Claims 1 to 9 for making a tire or tired wheel.