Rigid Polyurethane Foam and Multilayer Thermal Insulation Assemblies Containing the Foam

Abstract

Rigid polyurethane foams are made using a mixture of polyols that includes 4 to 33% by weight of triisopropanolamine. The mixture of polyols is reacted with an aromatic polyisocyanate in the presence of a blowing agent, a foam-stabilizing surfactant and a urethane catalyst to produce the foam. The foams are useful as thermal insulation layers in multilayer thermal insulation assemblies such as appliance cabinets and walls for industrial and commercial freezers and refrigerators.

Claims

1. A rigid polyurethane foam which is the reaction product of a polyurethane-forming reaction mixture characterized by an isocyanate index of 95 to 150, the polyurethane-forming reaction mixture comprising A) an aromatic polyisocyanate or mixture of aromatic polyisocyanates, the aromatic polyisocyanate or mixture of aromatic polyisocyanates having an isocyanate functionality of 2 to 4 and an isocyanate equivalent weight of 80 to 175; B) a mixture of polyols, the mixture of polyols having an average hydroxyl equivalent weight of 125 to 225 and an average hydroxyl functionality of 3.5 to 6 hydroxyl groups per molecule, wherein triisopropanolamine constitutes 4 to 33 weight percent of the mixture of polyols, at least one polyether polyol having 6 to 8, hydroxyl groups and a hydroxyl equivalent weight of 150 to 300 and which does not contain nitrogen atoms constitutes 30 to 90 weight percent of the mixture of polyols,_and the mixture of polyols contains no more than 12 weight percent of alkoxylated aromatic amine-initiated polyols; C) one or more blowing agents in an amount sufficient to produce a foam density of at most 42 kg/m.sup.3 and D) at least one urethane catalyst and E) at least one foam-stabilizing surfactant.

2. The rigid polyurethane foam of claim 1, wherein alkoxylated aromatic amine-initiated polyols constitute no more than 1 weight percent of the mixture of polyols.

3. The rigid polyurethane foam of claim 1 wherein the at least one polyether polyol having 6 to 8, hydroxyl groups and a hydroxyl equivalent weight of 150 to 300 and which does not contain nitrogen atoms constitutes 30 to 90 weight percent of the mixture of polyols is one or more sorbitol-initiated polyether polyols that constitute 40 to 70 weight percent of the mixture of polyols.

4. The rigid polyurethane foam of claim 3 wherein one or more polyether polyols having a hydroxyl equivalent weight of 300 to 750 and a hydroxyl functionality of 2 to 3 constitutes 5 to 35 weight percent of the mixture of polyols.

5. The rigid polyurethane foam of claim 3 wherein triethanolamine and aliphatic amine-initiated polyols different than triisopropanolamine together constitute no more than 5 weight percent of the mixture of polyols.

6. The rigid polyurethane foam of claim 3 wherein triisopropanolamine constitutes 6 to 20 weight percent of the mixture of polyols.

7. A method of making a rigid polyurethane foam of claim 1, comprising forming and curing a reaction mixture characterized by having an isocyanate index of 95 to 150 wherein the reaction mixture comprises A) an aromatic polyisocyanate or mixture of aromatic polyisocyanates, the aromatic polyisocyanate or mixture of aromatic polyisocyanates having an isocyanate functionality of 2 to 4 and an isocyanate equivalent weight of 80 to 175; B) a mixture of polyols, the mixture of polyols having an average hydroxyl equivalent weight of 125 to 225 and an average hydroxyl functionality of 3.5 to 6 hydroxyl groups per molecule, wherein triisopropanolamine constitutes 4 to 33 weight percent of the mixture of polyols, at least one polyether polyol having 6 to 8, hydroxyl groups and a hydroxyl equivalent weight of 150 to 300 and which does not contain nitrogen atoms constitutes 30 to 90 weight percent of the mixture of polyols,_and the mixture of polyols contains no more than 12 weight percent of alkoxylated aromatic amine-initiated polyols; C) one or more blowing agents in an amount sufficient to produce a foam density of at most 42 kg/m.sup.3 and D) at least one urethane catalyst and E) at least one foam-stabilizing surfactant.

8. A method of manufacturing a multilayer thermal insulation assembly, comprising 1) positioning an outer shell member and an inner shell member so as to define a cavity therebetween by holding the outer shell member and inner shell member in a mechanical apparatus that maintains them in a fixed position relative to each other; 2) introducing a polyurethane-forming reaction mixture characterized by an isocyanate index of 95 to 150 into the cavity; 3) curing the polyurethane-forming reaction mixture such that it expands and reacts to produce a polyurethane foam that fills the cavity and adheres to the outer shell member and to the inner shell member to produce the multilayer thermal insulation assembly, 4) and then demolding the multilayer thermal insulation assembly by removing it from the mechanical apparatus, wherein the reaction system comprises the polyurethane-forming reaction mixture comprising A) an aromatic polyisocyanate or mixture of aromatic polyisocyanates, the aromatic polyisocyanate or mixture of aromatic polyisocyanates having an isocyanate functionality of 2 to 4 and an isocyanate equivalent weight of 80 to 175; B) a mixture of polyols, the mixture of polyols having an average hydroxyl equivalent weight of 125 to 225 and an average hydroxyl functionality of 3.5 to 6 hydroxyl groups per molecule, wherein triisopropanolamine constitutes 4 to 33 weight percent of the mixture of polyols, at least one polyether polyol having 6 to 8, hydroxyl groups and a hydroxyl equivalent weight of 150 to 300 and which does not contain nitrogen atoms constitutes 30 to 90 weight percent of the mixture of polyols,_and the mixture of polyols contains no more than 12 weight percent of alkoxylated aromatic amine-initiated polyols; C) one or more blowing agents in an amount sufficient to produce a foam density of at most 42 kg/m.sup.3 and D) at least one urethane catalyst and E) at least one foam-stabilizing surfactant.

9. The method of claim 8 wherein step 4) is performed 2.5 to 20 minutes after step 2).

10. The method of claim 8 wherein step 4) is performed 3 to 6 minutes after step 2).

11. The method of claim 8, wherein alkoxylated aromatic amine-initiated polyols constitute no more than 1 weight percent of the mixture of polyols.

12. The method of claim 8 wherein the at least one polyether polyol having 6 to 8, hydroxyl groups and a hydroxyl equivalent weight of 150 to 300 and which does not contain nitrogen atoms constitutes 30 to 90 weight percent of the mixture of polyols is one or more sorbitol-initiated polyether polyols that constitute 40 to 70 weight percent of the mixture of polyols.

13. The method of claim 8 wherein one or more polyether polyols having a hydroxyl equivalent weight of 300 to 750 and a hydroxyl functionality of 2 to 3 constitutes 5 to 35 weight percent of the mixture of polyols.

14. The method of claim 8 wherein triethanolamine and aliphatic amine-initiated polyols different than triisopropanolamine together constitute no more than 5 weight percent of the mixture of polyols.

15. The method of claim 8 wherein triisopropanolamine constitutes 6 to 20 weight percent of the mixture of polyols.

Description

EXAMPLES 1-2 AND COMPARATIVE SAMPLE A

[0090] Rigid polyurethane foams are made using the ingredients as indicated in Table 1. All ingredients except the Polymeric MDI are premixed to form a formulated polyol. The viscosity of the formulated polyol is measured at 25° C. according to ASTM D4878-15. The formulated polyol and the Polymeric MDI are separately brought to 22-24° C. and processed using an Afros Canon A40 high pressure injection machine equipped with an L-shaped head at a mixing pressure of 150 bars and an output of 200 g/s. The resulting foam formulation is dispensed into a vertically-oriented, 20-liter (200 cm × 20 cm × 5 cm) “Brett” mold heated at 35C° and coated with release agent for evaluation of minimum fill density and post-demold expansion after various curing times. Foam is dispensed into a 30 cm × 20 cm × 20 cm box lined with a polyethylene film for measurement of free rise density.

[0091] Minimum fill density is determined by injecting various amounts of the foam formulation into the Brett mold to determine the minimum amount of foam formulation needed to produce a foam that fills the mold. The minimum fill density is the density of the resulting foam. Flow Index is calculated as the ratio of minimum fill density to free rise density.

[0092] Post-demold expansion is determined at various demold times by producing foams in a 70 cm × 40 cm ×10 cm “Jumbo Brett” mold. The foams are removed from the mold after a predetermined curing time and measuring its thickness. After a further 24 hours, the foam thickness is re-measured. The difference between the thickness after 24 hours and the initial thickness is an indication of the post-demold expansion of the foam.

[0093] Thermal conductivity is measured on 20 cm × 20 cm × 2.5 cm core specimens taken from the Brett molded foams according to EN 12667 using a Lasercomp Fox 200 heat flow meter. Average plate temperature is 10° C.

[0094] Cream, gel and tack free times are measured by combining the Polymeric MDI and formulated polyol in the high pressure machine and dispensing the resulting reaction mixture into a plastic bag Cream time is the time after pouring at which a visible reaction is observed. A spatula is pressed to the surface of the curing reaction mixture and removed to evaluate for gel time (the time after mixing at which strings of polymer stick to the spatula) and tack-free time (the time after mixing at which the polymer no longer sticks to the spatula).

[0095] Results of the various testing are as indicated in Table 2.

TABLE-US-00001 Ingredient Parts By Weight (Index) Comp. A.sup.∗ Ex. 1 Ex. 2 Polyol A 62.8 62.8 62.8 Polyol B 25.0 25.0 13.0 Polyol C 5.0 0 5.0 TIPA 0 5.0 12.0 Surfactant 2.5 2.5 2.5 Catalyst A 1.3 1.0 0.85 Catalyst B 0.2 0.2 0.2 Catalyst C 0.7 0.7 0.7 Water 2.5 2.5 2.5 Cyclopentane 14.5 14.5 14.5 Polymeric MDI 145 (1.14) 148 (1.14) 147 (1.14) .sup.∗Comparative.

TABLE-US-00002 Sample Comp. A.sup.∗ Ex. 1 Ex. 2 Formulated polyol viscosity, MPa.Math.s, 25° C. 677 668 674 Cream time, s 3 4 6 Gel Time, s 40 48 46 Tack Free Time, s 65 70 70 Free Rise Density, kg/m.sup.3 22.4 21.3 22.2 Minimum Fill Density kg/m.sup.3 30.2 27.9 29.4 Flow Index 1.35 1.31 1.32 Thermal Conductivity, mW/m-K 20.2 20.1 20.1 Post-Demold Expansion, 4 minute cure, % 9.6 6.5 7.7 Post-Demold Expansion, 5 minute cure, % 7.0 4.7 5.7 Post-Demold Expansion, 6 minute cure, % 6.2 4.1 2.9 .sup.∗Comparative.

[0096] Examples 1 and 2 demonstrate the effect of replacing all of another amine-initiated polyol (Polyol C) or a portion of a non-amine-initiated polyol (Polyol B) with TIPA. A small reduction in the amount of the urethane catalyst (Catalyst A) is made in each case to compensate for the expected catalytic activity of TIPA. As the data in Table 2 shows, cream, gel and tack-free times show little change when TIPA replaces a portion of the other polyols, even with the reduction in urethane catalyst. Thermal conductivity is improved slightly.

[0097] A large decrease in post-demold expansion is seen in the formulations that contain TIPA. The inventive foams exhibit less expansion after a 5-minute cure than the control does after curing for 6 minutes. Example 1 exhibits less post-demold expansion after a 4-minute cure than the control does after curing for 6 minutes. These results indicate that the demold time can be reduced from 6 minutes to 5 minutes or even less by incorporating TIPA into the foam formulation. This amounts to an increase in equipment utilization of about 15% or more, without loss of other desirable properties.

EXAMPLE 3 AND COMPARATIVE SAMPLES B-E

[0098] Polyurethane foams are made in the same general manner as in the previous example. Ingredients are as indicated in Table 3. The resulting foams are evaluated for cream, gel and tack free times, minimum foam density, and post-demold expansion after various cure times. Results are as indicated in Table 4.

TABLE-US-00003 Ingredient Parts By Weight (Index) Comp. B* Comp. C.sup.∗ Ex. 3 Comp. D* Comp. E* Polyol A 62.8 62.8 62.8 62.8 62.8 Polyol B 25.0 25.0 25.0 25.0 25.0 Polyol C 5.0 2.5 0 0 0 TIPA 0 2.5 5.0 0 0 Triethanolamine 0 0 0 5 0 Glycerin 0 0 0 0 5 Surfactant 2.5 2.5 2.5 2.5 2.5 Catalyst A 1.3 1.3 1.3 1.15 1.3 Catalyst B 0.2 0.2 0.2 0.2 0.2 Catalyst C 0.7 0.7 0.7 0.7 0.7 Water 2.5 2.5 2.5 2.5 2.5 Cyclopentane 14.5 14.5 14.5 14.5 14.5 Polymeric MDI 145 (1.14) 147 (1.14) 147 (1.14) 154 (1.13) 163 (1.14) .sup.∗Comparative.

TABLE-US-00004 Sample Comp. B* Comp. C.sup.∗ Ex. 3 Comp. D* Comp. E* Cream time, s 4 3 3 5 2 Gel Time, s 45 43 40 39 37 Tack Free Time, s 56 62 80 76 74 Minimum Fill Density, kg/m.sup.3 30.2 30.2 29.1 30.4 30.4 Post-Demold Expansion, 4 minute cure, % 6.9 6.4 5.1 6.5 7.2 Post-Demold Expansion, 5 minute cure, % 4.9 5.1 2.8 5.3 5.1 Post-Demold Expansion, 6 minute cure, % 3.3 4.2 2.6 4.5 4.5 .sup.∗Comparative.

[0099] Replacing 2.5 parts of Polyol C with TIPA provides no reduction in post demold expansion at the 4-minute and 5-minute cure times. By contrast, increasing the amount of TIPA to 5 parts as in Example 3 leads to very large reductions in post-demold expansion at all demold times under evaluation. As before, the post demold expansion of Ex. 3 after 5 minutes curing is less than that of the control (and the sample with only 2.5 parts TIPA) after 6 minutes curing. A 15% or greater increase in equipment utilization is possible.

[0100] Comparative Samples D and E show the effect of replacing Polyol C with triethanolamine and glycerin, respectively. Neither of these materials provides any benefit in post-demold expansion.

EXAMPLES 4 AND 5 AND COMPARATIVE SAMPLE F

[0101] Rigid polyurethane foams are made and evaluated as described in the earlier examples. The ingredients of the foam formulation are as indicated in Table 5. Results of testing are as indicated in Table 6.

TABLE-US-00005 Ingredient Parts By Weight (Index) Comp. F.sup.∗ Ex. 4 Ex. 5 Polyol A 45.0 50.0 50.0 Polyol B 20.0 14.0 18.0 Polyol D 22.8 19.8 15.8 Polyol E 4 0 0 TIPA 0 8 8 Surfactant 3.0 3.0 3.0 Catalyst A 0.45 0.45 0.44 Catalyst B 0.2 0.2 0.2 Catalyst D 1.04 1.04 1.04 Catalyst E 0.41 0.41 0.41 Catalyst F 0.8 0.8 0.8 Water 2.3 2.3 2.3 Cyclopentane 14.7 14.7 14.7 Polymeric MDI 147 (1.21) 156 (1.20) 156 (1.20) .sup.∗Comparative.

TABLE-US-00006 Sample Comp. F.sup.∗ Ex. 4 Ex. 5 Cream time, s 5 5 6 Gel Time, s 49 51 51 Tack Free Time, s 97 94 94 Free Rise Density, kg/m.sup.3 23.7 24.0 24.4 Minimum Fill Density kg/m.sup.3 33.5 33.9 33.9 Flow Index 1.45 1.47 1.44 Thermal Conductivity, mW/m-K 19.6 19.6 19.6 Post-Demold Expansion, 4 minute cure, % 2.8 1.9 2.1 Post-Demold Expansion, 6 minute cure, % 0.41 0.16 0.25 Post-Demold Expansion, 7 minute cure, % 0.19 0.00 0.00

[0102] Adding TIPA into this foam formulation has no significant effect on cream time, gel time, tack-free time, free rise density, minimum fill density, flow index or thermal conductivity. However, the foams made using TIPA exhibit substantially less post-demold expansion at the shorter cure times.

[0103] The low viscosity of TIPA allows the amount of the higher-viscosity sorbitol-initiated polyol to be increased. This allows the average functionality of the system to be increased, which further contributes to the shorter demold times and reduced post-demold expansion due to the greater crosslink density of the system.

EXAMPLES 6 AND 7 AND COMPARATIVE SAMPLE G

[0104] Rigid polyurethane foams are made and evaluated as described in the earlier examples. The ingredients of the foam formulation are as indicated in Table 7. Results of testing are as indicated in Table 8.

TABLE-US-00007 Ingredient Parts By Weight Comp. G* Ex. 6 Ex. 7 Polyol A 60 60 60 Polyol F 16 12 8 Polyol G 6.1 6.1 6.1 Polyol B 10 10 10 TIPA 0 4.0 8.0 Surfactant 2.8 2.8 2.8 Catalyst A 0.7 0.7 0.7 Catalyst F 1.2 1.2 1.2 Catalyst C 0.6 0.6 0.6 Catalyst B 0.1 0.1 0.1 Water 2.5 2.5 2.5 Cyclopentane 14.0 14.0 14 Polymeric MDI 150 154 155 .sup.∗Comparative

TABLE-US-00008 Sample Comp. G.sup.∗ Ex. 6 Ex. 7 Cream time, s 4 4 4 Gel Time, s 39 43 44 Tack Free Time, s 75 76 85 Free Rise Density, kg/m.sup.3 24.3 24.0 24.6 Minimum Fill Density kg/m.sup.3 32.2 31.9 32.2 Flow Index 1.32 1.33 1.31 Thermal Conductivity, mW/m-K 19.5 19.5 19.5 Post-Demold Expansion, 4 minute cure, % 6.9 5.2 6.2 Post-Demold Expansion, 5 minute cure, % 5.4 4.5 4.2 Post-Demold Expansion, 6 minute cure, % 4.5 3.7 3.9 .sup.∗Comparative

[0105] The data in Table shows the benefit of replacing a portion of an o-toluenediamine-initiated polyol with TIPA. Comparative Sample G is representative of very high quality thermal insulation foam characterized by excellent thermal conductivity and flow index, and which is already formulated for short demold times. TIPA is a drop-in replacement for the o-toluenediamine-initiated polyol on a weight-for-weight basis. Replacing the o-toluenediamine-initiated polyol with TIPA has no significant effect on cream, gel and tack-free times, free rise and minimum fill densities, flow index or thermal conductivity. Post-demold expansion is reduced at all cure times, although this effect is less pronounced in these formulations than in the previous examples, due to the already excellent performance of Comparative Sample G.