Polyurethane-polyisocyanurate foam

Abstract

Polyurethane-polyisocyanurate foams are prepared using a polyether polyol made from an alkylene oxide mixture that contains a specified proportion of ethylene oxide. The selection of proper polyol equivalent weight and ethylene oxide content leads to the production of foams having a useful combination of properties.

Claims

1. A polyurethane-polyisocyanurate foam that is a reaction product of a reaction mixture comprising one or more isocyanate-reactive materials, a polyisocyanate component, a physical blowing agent, a foam-stabilizing surfactant, at least one trimerization catalyst and at least one catalyst for the reaction of an isocyanate group towards water, wherein: a) greater than 70% by weight of the one or more isocyanate-reactive materials is at least one polyether polyol having a hydroxyl equivalent functionality of 3 and a hydroxyl equivalent weight of at least 100 but less than 400, wherein the at least one polyether polyol is selected from the group consisting of a copolymer of ethylene oxide and propylene oxide, a mixture of a homopolymer of propylene oxide and a homopolymer of ethylene oxide, or a mixture of a copolymer of ethylene oxide and propylene oxide with a homopolymer of ethylene oxide and/or a homopolymer of propylene oxide and the at least one polyether polyol has an average oxyethylene content of greater than 40% but less than 80% by weight and correspondingly an average oxypropylene content at least 20% but less than 60% by weight based on the combined weight of oxyalkylene groups present in the at least one polyether polyol, provided that when the at least one polyether polyol has an average hydroxyl equivalent weight greater than 200, the one or more isocyanate-reactive materials further include at least one crosslinker having a hydroxyl functionality of at least 3 and a hydroxyl equivalent weight of less than 100 such that the equivalent weight of the at least one polyether polyol and the at least one crosslinker combined is less than 200; b) less than 25% by weight of the one or more isocyanate-reactive materials is a polyester polyol; c) water constitutes no more than 0.5% of the weight of the one or more isocyanate-reactive materials; d) the polyisocyanate component includes one or more aromatic polyisocyanates, the one or more aromatic polyisocyanates having an average isocyanate functionality of at least 2.7 and an average isocyanate equivalent weight of up to 150; e) the isocyanate index is 200 to 400; and f) the reaction mixture contains 3 to 9 parts by weight, per 100 parts by weight of the one or more isocyanate-reactive materials, of the at least one trimerization catalyst.

2. The polyurethane-polyisocyanurate foam of claim 1 which has a foam density of 20 to 30 kg/m.sup.3.

3. The polyurethane-polyisocyanurate foam of claim 2 which exhibits a k-factor, as measured according to ASTM C-518, that at 4° C. average plate temperature is equal to or lower than at 24° C. average plate temperature.

4. The polyurethane-polyisocyanurate foam of claim 3 wherein at least 90% by weight of the one or more isocyanate-reactive materials is the at least one polyether polyol.

5. The polyurethane-polyisocyanurate foam of claim 4 wherein at least 95% by weight of the one or more isocyanate-reactive materials is the at least one polyether polyol.

6. The polyurethane-polyisocyanurate foam of claim 3 wherein no more than 5% by weight of the one or more isocyanate-reactive materials is a polyester polyol.

7. The polyurethane-polyisocyanurate foam of claim 3 wherein the one or more isocyanate-reactive materials are devoid of a polyester polyol.

8. The polyurethane-polyisocyanurate foam of claim 3 wherein the at least one trimerization catalyst includes at least one alkali metal carboxylate salt.

9. The polyurethane-polyisocyanurate foam of claim 8 wherein the reaction mixture contains 4 to 8 parts by weight, per 100 parts by weight of the isocyanate-reactive materials, of the at least one alkali metal carboxylate salt.

10. The polyurethane-polyisocyanurate foam of claim 8 wherein the reaction mixture includes at least one flame retardant.

11. A boardstock comprising the polyurethane-polyisocyanurate foam of claim 1 and a facer material applied to at least one surface of the polyurethane-polyisocyanurate foam.

Description

EXAMPLES 1-2 AND COMPARATIVE SAMPLES A-B

(1) Comparative Sample A below is a reference polyester polyol-based foam. Polyurethane-polyisocyanurate foams Examples 1 and 2 and Comparative Sample B are made from the formulations set forth in Table 1 below. The amount of catalyst in each case is selected to attempt to bring the gel time into the range of 7 to 10 seconds.

(2) Polyol A is a polyether made by polymerizing a mixture of 66% by weight ethylene oxide and 34% by weight propylene oxide onto glycerin to produce a polyether polyol having a nominal hydroxyl functionality of 3 and a hydroxyl equivalent weight of 150.

(3) Polyol B is a polyether made by polymerizing a mixture of 66% by weight ethylene oxide and 34% by weight propylene oxide onto glycerin to produce a polyether polyol having a nominal hydroxyl functionality of 3 and a hydroxyl equivalent weight of 334.

(4) Polyol C is a polyether made by homopolymerizing ethylene oxide onto glycerin to produce a polyether polyol having a nominal hydroxyl functionality of 3 and a hydroxyl equivalent weight of 133.

(5) Polyol D is a polyether made by homopolymerizing propylene oxide onto glycerin to produce a polyether polyol having a nominal hydroxyl functionality of 3 and a hydroxyl equivalent weight of 150.

(6) Polyol E is a polyether made by polymerizing a mixture of 66% by weight ethylene oxide and 34% by weight propylene oxide onto glycerin to produce a polyether polyol having a nominal hydroxyl functionality of 3 and a hydroxyl equivalent weight of 200.

(7) The Polyester Polyol is an aromatic polyester polyol having a nominal hydroxyl functionality of 2 and a hydroxyl equivalent weight of about 240. It is sold as Stepanpol® PS-2352 by Stepan Company.

(8) TCPP is tris(1-chloro-2-propyl)phosphate.

(9) Trimerization Catalyst A is a solution of 70% potassium octoate in 30% diethylene glycol.

(10) Trimerization Catalyst B is a solution of 70% potassium acetate in 30% ethylene glycol.

(11) The Urethane Catalyst is a commercially available pentamethyl diethylene triamine.

(12) The surfactant is a non-ionic polyether surfactant sold commercially available as Vorasurf™ 504 from The Dow Chemical Company.

(13) The Isocyanate is a polymeric MDI having an isocyanate equivalent weight of 136.5 and an isocyanate functionality of 3.0.

(14) TABLE-US-00001 TABLE 1 Parts by Weight Ingredient Comp. B* Ex. 1 Ex. 2 Polyol A 50 75 100 Polyester Polyol 50 25 0 TCPP 10 10 10 Trimerization Catalyst A 1.93 1.82 1.82 Trimerization Catalyst B 6.74 6.36 6.36 Urethane Catalyst 0.34 0.32 0.32 Surfactant 5 5 5 Water 0.25 0.25 0.25 n-Pentane 31.1 32.9 34.9 Total Weight Isocyanate-Reactive 102.85 102.7 102.7 Materials.sup.1 Wt. -% Polyester Polyol.sup.2 48.6 24.3 0 Wt. -% Trimerization Catalyst.sup.3 5.9 5.6 5.6 Isocyanate Index 250 250 250 *Comparative. .sup.1Includes weight of polyol(s), water and isocyanate-reactive solvent in the trimerization catalyst products. .sup.2Based on total weight of isocyanate-reactive materials. .sup.3Weight of active catalysts divided by total weight of isocyanate-reactive materials, including the weight of the solvents in the catalysts.

(15) The foam in each case is made by blending all ingredients except the polyisocyanate to form a polyol component. The temperature of the polyol component and the polyisocyanate composition each are separately adjusted to within the range of 20-25° C. The components are then mixed through an impingement mixing machine and dispensed into a 28×28×15 cm lidded wooden box and cured without applying additional heat. Gel and tack-free time are determined by pressing a wooden tongue depressor onto the surface of the reaction mixture. Gel time is the time at which polymer strings from when the tongue depressor is removed from the surface. Tack-free time is the time at which the reaction mixture no longer leaves a residue on the tongue depressor. The foam is allowed to cure and conditioned for 24 hours at room temperature and ambient humidity before foam property testing. Core foam densities are obtained according to ASTM D-1622. Compressive strength is measured according to ASTM D-1621. K-factor is determined in accordance with ASTM C-518. Results are as indicated in Table 2 below.

(16) TABLE-US-00002 TABLE 2 Property Comp. A* Comp. B* Ex. 1 Ex. 2 Wt. % EO 66 66 66 in polyether polyol(s).sup.1 Equivalent Weight, 150 150 150 polyether polyol Wt. % Polyester Polyol.sup.2 >25% 48.6 24.3 0 Wt. % Trimerization Catalyst.sup.3 5.9 5.6 5.6 Gel time, s 8 7 8 Tack-free time, s 13 10 12 Density, kg/m.sup.3 27.1 24.8 28.0 28.7 k-factor, 24°C., mW/m-° K. 23.7 24.6 23.6 24.0  k-factor, 4° C., mW-m-° K. 26.6 27.2 24.5 23.1 % Change.sup.4 +12% +10.5% +3.7% −3.8% Compressive Strength, kPa 135 128 135 145 Comparative. N.D.-not done. .sup.1Weight of oxyethylene as percentage of the weight of all alkylene oxides polymerized in making the polyether polyol (s). .sup.2Based on total weight of all isocyanate-reactive materials, including the solvents contained in the catalysts. .sup.3The weight of the active trimerization catalysts divided by the total weight of the isocyanate-reactive materials, including the solvents in the catalyst products. .sup.4Calculated as (24° C. k-factor-4° C. k-factor) ÷ 24° C. k-factor.

(17) Comparative Sample A illustrates the problem with conventional polyurethane-polyisocyanurate foams made using a large proportion of a polyester polyol. Foam density and compressive strengths are acceptable, as is the k-factor at 24° C., but the 4° C. k-factor is 12% greater than the k-factor at 24° C.

(18) In Comparative Sample B, the polyether polyol has the proper equivalent weight, functionality and ethylene oxide content, but at this high level of polyester polyol a large loss of k-factor is seen at the 4° C. average plate temperatures. The absolute values also are high at both the 24° C. and 4° C. average plate temperatures.

(19) Example 1 and Example 2 further demonstrate the benefit of reducing the amount of polyester polyol. When the amount of polyester polyol is reduced to slightly less than 25% (Ex. 1), the k-factor at 4° C. is only slightly increased compared to the 24° C. k-factor. Eliminating the polyester polyol (Ex. 2) causes the 4° C. k-factor to actually become lower than the 24° C. k-factor. The 24° C. k-factors for each of Examples 1 and 2 are comparable to those of Comp. Sample A and better than Comp. Sample B.

(20) Note also that the compressive strengths of Examples 1 and 2 are at least equal to that of Comp. Sample A.

EXAMPLES 3-4 AND COMPARATIVE SAMPLES C-E

(21) Polyurethane-polyisocyanurate foams are made from the formulations set forth in Table 3 below, and tested in the same manner as in previous examples. Results of the testing are as indicated in Table 4. The results from testing Example 2 above are repeated in Table 4.

(22) TABLE-US-00003 TABLE 3 Parts by Weight Comp. Comp. Comp. Ingredient C* D* Ex. 3 Ex. 2 Ex. 4 E* Polyol A 0 60 75.8 100    60   0  Polyol C 0 0 0  0  40   100    Polyol D 100 40 24.2 0  0  0  Polyol E 0 0 0  0  0  0  TCPP 10 10 10   10   10   10   Trimerization 4.55 3.21   2.30   1.82   1.93   1.93 Catalyst A Trimerization 15.91 11.23   8.05   6.36   6.74   6.74 Catalyst B Urethane 0.80 0.56   0.40   0.32   0.34   0.34 Catalyst Surfactant 5 5 5  5  5  5  Water 0.25 0.25   0.25   0.25   0.25   0.25 n-Pentane 39.6 37.3  35.75 34.9 36.2 28.1 Total Weight 106.39 104.58 103.36 102.7  102.85 102.85 Isocyanate- Reactive Materials.sup.1 Wt. -% 13.5 9.7  7.0  5.6  5.9  5.9 Trimerization Catalyst.sup.3 Isocyanate 250 250 250    250    250    250    Index *Comparative. .sup.1Includes weight of polyol(s), water and isocyanate-reactive solvent in the trimerization catalyst products. .sup.2Weight of active catalysts divided by total weight of isocyanate-reactive materials, including the weight of the solvents in the catalysts.

(23) TABLE-US-00004 TABLE 4 Comp. Comp. Comp. Property C* D* Ex. 3 Ex. 2 Ex. 4 E* Wt. % EO in polyether polyol.sup.1    0       40       50       66        78.4    100   Average Equivalent   150        150        150        150        143      133   Weight, polyether polyol Wt. % Trimerization Catalyst.sup.2    13.5        9.7        7.0        5.6        5.9      5.9 Gel time, s    9        7        8        8        7     15  Tack-free time, s   12       10       12       12       10     17  Density, kg/m.sup.3    24.4       28.4       28.2       28.7       27.7    40  k-factor, 24° C., mW/m-° K.    24.0       24.9       24.7       24.0       26.9     23.5  k-factor, 4° C., mW-m-° K.    24.5       25.6       25.1       23.1       27.2    N.D. % Change.sup.3   +1.9%   +3.0%   −1.9%   −3.8%   +1.1% N.D. Compressive Strength, kPa   172        132        139        145        153      190   *Comparative. N.D.-not done. .sup.1Weight of oxyethylene as percentage of the weight of all alkylene oxides polymerized in making the polyether polyol(s). .sup.2The weight of the active trimerization catalyst divided by the total weight of the isocyanate-reactive materials, including the solvents in the catalyst products. .sup.3Calculated as (24° C. k-factor − 4° C. k-factor) ÷ 24° C. k-factor.

(24) This set of experiments illustrates the effect of the average oxyethylene content in the polyether polyols that have a functionality of at least 3 and a hydroxyl equivalent weight of 100 to less than 400. At 0% oxyethylene content, very large amounts of trimerization catalyst are needed to produce foam at reasonable gel and tack free times. Increasing the oxyethylene content to just below 40% still requires almost 10% trimerization catalyst. When the oxyethylene content is 50 to 78.4%, much lower levels of trimerization catalyst are needed to produce good foam. In each case, the 4° C. k-factor is very close to or even below that at 24° C. When the oxyethylene content is 100%, foam density becomes very high.

EXAMPLE 5 AND COMPARATIVE SAMPLE F

(25) Polyurethane-polyisocyanurate foams are made from the formulations set forth in Table 5 below and tested in the same manner as in previous examples. Results of the testing are as indicated in Table 6. The results from testing Example 2 above are repeated in Table 6.

(26) TABLE-US-00005 TABLE 5 Parts by Weight Ingredient Ex. 5 Comp. F* Polyol B 87.5 0 Polyol E 0 100 Glycerin (Crosslinker) 12.5 0 TCPP 10 10 Trimerization Catalyst A 2.25 1.20 Trimerization Catalyst B 7.86 4.21 Urethane Catalyst 0.39 0.21 Surfactant 5 5 Water 0.25 0.25 n-Pentane 35.7 28.1 Total Weight Isocyanate-Reactive 103.28 101.87 Materials.sup.1 Wt. -% Trimerization Catalyst.sup.2 6.85 3.7 Isocyanate Index 250 250 *Comparative. .sup.1Includes weight of polyol(s), water and isocyanate-reactive solvent in the trimerization catalyst products. .sup.2Weight of active catalysts divided by total weight of isocyanate-reactive materials, including the weight of the solvents in the catalysts.

(27) TABLE-US-00006 TABLE 6 Property Ex. 5 Ex. 2 Comp. F* Wt. % EO in polyether polyol.sup.1 66 66 66 Equivalent Weight, polyether polyol + 150 150 200 crosslinker combined Wt. % Trimerization Catalyst.sup.2 6.85 5.6 3.7 Gel time, s 7 8 10 Tack-free time, s 9 12 15 Density, kg/m.sup.3 25.3 28.7 26.6 k-factor, 24° C., mW/m-° K. 26.8 24.0 23.7  k-factor, 4°C, mW-m-° K. 26.4 23.1 N.D. % Change.sup.3 −1.1% −3.8% N.D. Compressive Strength, kPa 125 145 108 Comparative. N.D.-not done. .sup.1Weight of ethylene oxide as percentage of the weight of all alkylene oxides polymerized in making the polyether polyol. .sup.2The weight of the active trimerization catalyst divided by the total weight of the isocyanate-reactive materials, including the solvents in the catalyst products. .sup.3Calculated as (24° C. k-factor-4° C. k-factor) ÷ 24° C. k-factor.

(28) Example 5 demonstrates that the beneficial effects of the invention are obtained using a polyether polyol of somewhat higher equivalent weight (334) if a crosslinker is provided such that the equivalent weight of the polyether and crosslinker combined is under 200. Some loss of compressive strength is seen in this case due to the presence of the higher equivalent weight material. Comp. Sample F shows the effect of having too high of a polyether polyol equivalent weight (without the additional presence of a crosslinker). The foam compressive strength decreases dramatically.