Solid, self-bondable isocyanate-containing organic polymers and methods for using same

Abstract

Solid, non-melting polyurethanes having a glass transition temperature of at least 40° C. and free isocyanate groups are self-bonding materials that are useful in a variety of adhesive and molding operations. Under conditions of heat and moisture, these polyurethanes will self-bond. The polyurethanes can be used as adhesive coatings, which are solid and non-tacky and thus can be transported and stored easily under ambient conditions. These polyurethane adhesives are especially useful in applications in which, due to the location and/or orientation of the substrates, liquid or melting materials cannot be applied easily or will run off the substrates.

Claims

1. A method for forming a bonded mass of adhered solid pieces, comprising: a) forming a reactive mixture of at least one polyol and at least one polyisocyanate compound in which the isocyanate index is at least 1.40 and curing the reactive mixture to form multiple pieces that have on at least a contacting surface thereof a solid, non-melting organic polymer having a main glass transition temperature as measured by dynamic mechanical thermal analysis of at least 40° C., a density of at least 500 kg/m.sup.3 and at least 3.5% by weight free isocyanate groups; b) forming a mass of the pieces such that a contacting surface of each of said solid pieces is in contact with a contacting surface of one or more adjacent solid pieces at one or more bondlines; and c) heating the mass at a bonding temperature of at least 40° C. in the presence of water to bond the solid pieces at the bondline or bondlines to form the bonded mass.

2. The method of claim 1 wherein in step a) the reactive mixture is applied to the surface of multiple substrate pieces, and partially cured thereon to form multiple substrate pieces coated with the solid, non-melting organic polymer.

3. The method of claim 1, wherein the solid, non-melting organic polymer contains at least 4% by weight free isocyanate groups.

4. The method of claim 3, wherein the solid, non-melting organic polymer has a main glass transition temperature of 50 to 80° C. or 90 to 125° C.

5. The method of claim 1 wherein the bonding temperature is no more than 40° C. above or below the main glass transition temperature of the organic polymer.

6. The method of claim 5 wherein the bonding temperature is no more than 20° C. above the main glass transition temperature of the organic polymer.

7. A method for forming a bonded mass of adhered solid pieces, comprising: a) forming a mass of two or more separate solid pieces, such that a contacting surface of each of said solid pieces is in contact with a contacting surface of one or more adjacent solid pieces at one or more bondlines, wherein said contacting surfaces each are of a solid, non-melting organic polymer having a main glass transition temperature as measured by dynamic mechanical thermal analysis of at least 40° C., a density of at least 500 kg/m.sup.3 and at least 3.5% by weight isocyanate groups; and b) heating the mass at a bonding temperature of at least 40° C. in the presence of water to bond the solid pieces at the bondline or bondlines to form the bonded mass.

8. The method of claim 7 wherein the separate solid pieces are made by forming a coating of a solid, non-melting organic polymer having a main glass transition temperature as measured by dynamic mechanical thermal analysis of at least 40° C., a density of at least 500 kg/m.sup.3 and at least 3.5% by weight free isocyanate groups onto multiple substrate pieces.

9. The method of claim 7, wherein the organic polymer is a polymer of at least one organic polyisocyanate having an average functionality from 1.9 to 4 and an average isocyanate equivalent weight from 80 to 200.

10. The method of claim 7, wherein the organic polymer is a reaction product of (1) a polyol or mixture of polyols, the polyol or mixture having an average hydroxyl equivalent weight from 130 to 400 and an average hydroxyl functionality of at least 2.5 to 6, with (2) an organic polyisocyanate or mixture thereof having an isocyanate functionality of 2 to 3.5 and an isocyanate equivalent weight from 85 to 150, at an isocyanate index of at least 1.4.

11. The method of claim 7, wherein the solid, non-melting organic polymer has a main glass transition temperature of 50 to 80° C. or 90 to 125° C.

12. The method of claim 7 wherein the bonding temperature is no more than 40° C. above or below the main glass transition temperature of the organic polymer.

13. The method of claim 12 wherein the bonding temperature is no more than 20° C. above the main glass transition temperature of the organic polymer.

14. The method of claim 7 wherein the isocyanate index is at least 2.75 and the reactive mixture contains an isocyanate trimerization catalyst.

Description

EXAMPLES 1-7

(1) Polyurethane blocks are made and evaluated for their ability to bond together under conditions of heat, moisture and applied pressure.

(2) Polyurethane examples 1-7 are made from the components listed in Table 1, using the following general procedure. The polyol(s) are weighed into a mixing cup of a high speed laborator mixer and combined with the catalyst(s) for several seconds at room temperature. The polyisocyanate is then added and mixed in for about 15 seconds, again at room temperature. The resulting mixture is then emptied into a circular 3/16 inch (4.8 mm) deep steel mold that has been treated with an external mold release spray, and allowed to cure at room temperature until the exothermic reaction ceases and the resulting polyurethane polymer has cooled back down to room temperature. The polymer is demolded and then post-cured under conditions as set forth in Table 1. The polymers in all cases are hard, non-tacky solids at room temperature.

(3) Dynamic mechanical thermal analysis (DMTA) is performed on the samples, at an oscillation frequency of 1 hertz and a heating scan rate at 3° C./second. The temperature corresponding to the peak of the tan delta curve is taken as the glass transition temperature (T.sub.g) of the specimen tested.

(4) The ability of the polymer to bond to itself at 50° C. in the presence of moisture is evaluated as follows. Two 25.4 mm×25.4 mm×4.8 mm samples are cut, completely wet with water, and stacked atop each other. The contacting surfaces are the top surfaces of the polymer as molded, i.e., the surface that was not in contact with the mold surface that was coated with the external mold release spray. The stack is wrapped in a wet paper towel and placed onto the bottom plate of a hot press (1 ft by 1 ft (30.5 cm×30.5 cm)) surface for both top and bottom plate) that is preheated to 50° C. The press is closed with minimal applied pressure for 5 minutes, to allow the samples to heat to 50° C. The press is then brought to an applied force of 7 tons (6350 kg) for 10 minutes. The pressure is then released, and the samples are visually inspected as to whether they have fused to each other.

(5) The glass transition temperature and results of the bonding evaluation are reported in Table 1.

(6) TABLE-US-00001 TABLE 1 Ingredient Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 236-equivalent weight 30.0 30.0 30.2 0 0 30.1 0 poly(PO) triol 360 equivalent weight 0 0 0 21.0 24.1 0 0 poly(PO) triol 156 equivalent 0 0 0 9.0 6.0 0 15.9 weight, 4.5 functionality poly(PO) polyol Dibutyltin dilaurate 0.07 0.07 0.07 0.07 0.07 0.07 0.05 144.5 equivalent 26.9 26.9 0 0 0 27.5 0 weight, 2.1 average functionality “liquid MDI” 136.5 equivalent 0 0 0 24.6 22.2 0 47.8 weight, 3.0 average functionality polymeric MDI 131.5 equivalent 0 0 26.1 0 0 0 0 weight, 2.3 average functionality polymeric MDI Isocyanate index 1.47 1.47 1.55 1.55 1.55 1.49 3.43 Polyisocyanate mass 47.3% 47.3% 46.4% 45.0% 42.5% 47.7% 74.9% fraction Calculated NCO 4.4 4.4 5.3 4.9 4.6 4.6 17.2 content, weight % Postcuring conditions 80/25 80/25 80/20 80/15 80/15 80/30 50/30 (° C., min.) T.sub.g, ° C. 54 51 56 54 44 51 59 Bonding results Bonds Bonds Bonds Bonds Bonds Bonds Bonds

(7) The organotin polyurethane catalyst used in these examples is a strong urethane catalyst but at most a weak isocyanate trimerization catalyst. Therefore, due to the large stoichiometric excess of the polyisocyanate and the lack of effective trimerization catalyst, the polyurethane of each of examples 1-7 have a significant quantity of free isocyanate groups, despite having a glass transition temperature well above room temperature. The polymer in each case is a hard, non-tacky solid. The quantity of free isocyanate groups (“calculated NCO content”) is calculated from the amounts of starting materials. The results in Table 1 show that a polymer having a glass transition temperature close to that of the bonding temperature can bond to itself under conditions of moisture and applied pressure.

(8) When duplicate samples of Examples 4 and 5 are heated and pressed under the same conditions, but without added moisture, they do not bond. This indicates that the bonding is not due to melting or surface softening effects, but instead suggests that the bonding is due to reactions involving free isocyanate groups and the water molecules.

EXAMPLES 8-11

(9) Examples 8-11 are prepared and tested in the same general manner as described with respect to Examples 1-7. The formulations and testing results are as indicated in Table 2.

(10) TABLE-US-00002 TABLE 2 Ingredient Ex. 8 Ex. 9 Ex. 10 Ex. 11 156 equivalent weight polyether 15.5 13.1 20.0 18.7 (100% propylene oxide (“PO”) polyol (sucrose/glycerin initiated, starter functionality = 4.5) Dibutyltin dilaurate 0.05 0.05 0.04 0.04 2-hydroxy-N,N,N-trimethylpro- 0.10 0.10 0.08 0.08 pane-1-ammonium 2-ethylhex- anoate in ethylene glycol = DABCO* TMR from Air Products 136.5 equivalent weight, 3.0 46.4 52.5 50.1 51.2 average functionality polymeric MDI Isocyanate index 3.43 4.57 2.86 3.12 Polyisocyanate mass fraction 74% 79% 71% 73% Calculated NCO content in molar 7.7 10.8 7.7 7.9 excess of polyol OH groups, % weight Postcuring conditions (° C./min.) 50/30 50/30 50/30 50/30 T.sub.g, ° C. 80 59 77 80 Bonding results Bonds Bonds Bonds Bonds

(11) Polymer samples 8-11 are all made with a large excess of polyisocyanate but, due in part to the presence of the trimerization catalyst, all have glass transition temperatures significantly above room temperature. The polymers are not fully cured, and therefore have significant quantities of free isocyanate groups, as indicated by the glass transition temperatures, which would be expected to be close to or above 130° C. if fully cured. Therefore, these samples are believed to contain oligomers and/or unreacted polyisocyanates which plasticize the polymers and thus reduce the glass transition temperature to the indicated ranges. As seen from the data in Table 2, good bonding is achieved even when the polymer has a glass transition temperature 30° C. higher than the bonding temperature, when the isocyanate index is high.

(12) When Example 10 is repeated at an isocyanate index of 2.30, the resulting polymer has a glass transition temperature of 91° C. This indicates that the polymer has achieved a greater stage of cure and corresponding contains fewer residual isocyanate groups. That polymer does not bond at 50° C., but is expected to bond at a temperature closer to its glass transition temperature.

(13) When Example 11 is repeated at an isocyanate index of 2.58, the resulting polymer has a glass transition temperature of 74° C., slightly below that of Example 11, and does not bond on the 50° C. bonding test. This is believed to be due to the lower number of free isocyanate groups that remain in the polymer after the curing step. It is believed that the glass transition temperature of the polymer generally needs to be close to or less than the bonding temperature for good bonding to occur. However, greater latitude in the glass transition temperature can be tolerated with good results if more free isocyanate groups are present in the polymer. Thus, Example 11 is believed to bond well at 50° C., whereas the same polymer system at the 2.58 isocyanate index bonds poorly at that same temperature, because Example 11 is made at a higher isocyanate index and contains more residual isocyanate groups. The 2.58 isocyanate index polymer is expected to bond well at temperatures closer to its glass transition temperature.