Flexible polyurethane foam having prolonged recovery time

Abstract

Recovery times and/or airflow of flexible polyurethane foam is increased by including certain tackifiers in the foam formulation. The tackifiers are characterized in being incompatible with polyol or polyol mixture used to make the foam, having a viscosity of at least 5,000 centipoise at 25 #C and having a glass transition temperature of at most 20 #C. The tackifier is pre-blended with certain monols to form a lower-viscosity blend that is combined with one or more other polyols and a polyisocyanate to form a reaction mixture for producing a polyurethane foam.

Claims

1. A method of making a flexible polyurethane foam, comprising reacting, at an isocyanate index of 60 to 110, a reaction mixture comprising A) a polyether polyol having a hydroxyl equivalent weight of no greater than 225 or mixture of two or more such polyether polyols, wherein the polyol or mixture of polyols (i) has a number average hydroxyl functionality of 2 to 4; (ii) includes at least one polyether polyol that has a hydroxyl number of less than 170 and (iii) has an oxyethylene content of at least 10% by weight and/or includes at least one polyether polyol that contains at least 40% by weight oxyethylene units; B) 1 to 5 parts by weight water per 100 parts by weight of component A), with C) at least one organic polyisocyanate, in the presence of D) at least one catalyst for the reaction of an isocyanate group with water and/or an alcohol; E) at least one foam stabilizing surfactant, F) 1 to 45 parts by weight of a tackifier per 100 parts by weight of component A) wherein (i) the tackifier has a viscosity of at least 5,000 centipoise at 25° C., and (ii) the tackifier has a glass transition temperature of at most 20° C., and G) 0.05 to 10 parts by weight per 100 parts by weight of component A) of at least one monoalcohol, the monoalcohol being characterized in having at least 4 carbon atoms, a molecular weight of up to 300 g/mol and a viscosity of up to 500 cps at 25° C. as measured using a cone-and-plate viscometer, provided further that the weight proportion of components F) and G) is at least 20:80 but not greater than 95:5; wherein components F) and G) are pre-blended prior to being combined with either of components A) and C) to form a pre-blend having a viscosity of no greater than 20,000 cps at 25° C. as measured using a cone-and-plate viscometer.

2. The method of claim 1, wherein the tackifier includes one or more of a rosin, a hydrogenated and/or esterified rosin, a polyterpene, a C5 aliphatic resin, a C9 aromatic resin, a C5/C9 copolymer resin, a hydrogenated C5 or C9 resin, a polymer or copolymer of butane, an epoxy resin, a styrene/conjugated diene copolymer, an ethylene-acrylic acid copolymer, an ethylene-higher alpha-olefin copolymer having a density of less than 0.900 g/cc a silicone oil, a cellulosic, cationic polyacrylamide, para-t-octyl phenol formaldehyde resin, a polyester having a number average molecular weight of 400 to 2000, a urethane acrylate oligomer, and a room temperature liquid ethylene-propylene-diene resin.

3. The method of claim 2, wherein the tackifier includes at least one rosin.

4. The method of claim 2, wherein the tackifier includes at least one polyterpene.

5. The method of claim 2 wherein the amount of tackifier is 5 to 25 parts by weight per 100 parts by weight of component A).

6. The method of claim 2 wherein the amount of tackifier is 7.5 to 20 parts by weight per 100 parts by weight of component A).

7. The method of claim 2 wherein the monoalcohol has at least 5 carbon atoms and a molecular weight of up to 250.

8. The method of claim 2 wherein the monoalcohol has a Hansen Dispersion Parameter of 13.9 to 17.4 (J/cc).sup.1/2, a Hansen Polar Parameter of 1.7 to 9.2 (J/cc).sup.1/2, a Hansen Hydrogen Bonding Parameter of 3.8-13.9 (J/cc).sup.1/2.

9. The method of claim 2 wherein component G) is one or more of 1-pentanol, 2-pentanol, 3-pentanol, 1-hexanol, 2-hexanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol, 1-octanol, 2-ethyl-1-hexanol, propylene glycol mono-n-butyl ethyl, dipropylene glycol mono-n-butyl ether, tripropylene glycol mono-n-butyl ether, 2,6-dimethyl-4-heptanol, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol n-butyl ether, ethylene glycol mono-n-hexyl ether, diethylene glycol mono-n-hexyl ether, triethylene glycol mono-n-hexyl ether, diethylene glycol monophenyl ether, triethylene glycol monophenyl ether, propylene glycol monophenyl ether, dipropylene glycol monophenyl ether and tripropylene glycol monophenyl ether.

10. The method of claim 9 wherein component G) is selected from one or more of propylene glycol mono-n-butyl ethyl, dipropylene glycol mono-n-butyl ether, tripropylene glycol mono-n-butyl ether, 2,6-dimethyl-4-heptanol, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol n-butyl ether, ethylene glycol mono-n-hexyl ether, diethylene glycol mono-n-hexyl ether and triethylene glycol mono-n-hexyl ether.

11. The method of claim 2 wherein the flexible polyurethane foam has a recovery time of at least one second.

12. The method of claim 2 wherein the flexible polyurethane foam has a recovery time of at least two seconds.

13. The method of claim 2 wherein the flexible polyurethane foam exhibits an airflow of at least 1.4 L/s and has a density of 24 to 64 kg/m.sup.3.

14. The method of claim 2 wherein the flexible polyurethane foam has a resiliency of at most 30%.

15. A polyurethane foam made in accordance with the method of claim 1.

16. The flexible polyurethane foam of claim 15 wherein the tackifier occupies 2.5 to 40% of the surface area of internal surfaces of the polyurethane foam.

17. The flexible polyurethane foam of claim 16 wherein the tackifier is present on internal surfaces of the polyurethane foam in the form of discontinuous regions having longest dimensions of 10 nm to 200 μm.

Description

EXAMPLES 1-4 AND COMPARATIVE SAMPLES A-C

(1) The tackifier used in these experiments is a polyterpene resin sold as Sylvares® TR A25L by Kraton Corporation. This product has a softening temperature of 22-28° C. and a glass transition temperature of −20° C., as reported by its manufacturer. Being a solid, its viscosity at 25° C. is too high to measure. Its viscosity at 50° C. is 4450 cps, as reported by its manufacture. This polyterpene resin is incompatible with the mixture of Polyols A-C described in these examples. It is inert to the polyol mixture, water and polyisocyanate under the conditions of the foaming reaction.

(2) Pre-blends of the tackifier and each of several diluents (5 monols and one polyester polyol) are made by combining the ingredients in a Flecktac high-speed mixer operated at 2500 rpm for 1 minute. In each case, the ratio of tackifier and diluent is varied to produce a pre-blend having a viscosity below 10,000 cps at 25° C. Additional pre-blends are made using ethylene glycol mono-n-hexyl ether at varying concentrations. The amounts of tackifier and diluent and Hansen parameters for the monol diluents as indicated in Table 1.

(3) TABLE-US-00001 TABLE 1 Pre- Hansen Solubility parameters.sup.1 Wt.-% Wt.-% Blend Diluent δ.sub.d δ.sub.p δ.sub.h Tackifier Monol A Ethylene glycol mono-n-hexyl ether 16.0 6.9 10.9 91 9 B Ethylene glycol mono-n-hexyl ether 16.0 6.9 10.9 78.4 21.6 C Ethylene glycol mono-n-hexyl ether 16.0 6.9 10.9 20 80 D Dipropylene glycol monophenyl ether 16.9 4.9 10.2 68 32 E Ethylene glycol monophenyl ether 17.8 5.7 14.3 60 40 F 175 equivalent weight diethylene — — — 20 80 glycol/phthalic anhydride polyester diol.sup.1 .sup.1δ.sub.d is Hansen dispersion parameter; δ.sub.p is Hansen polar parameter; δ.sub.h is Hansen hydrogen bonding parameter, all values in (J/cc).sup.1/2. .sup.1This product has a molecular weight of about 350 and a viscosity of about 1750 cps at 25° C.

(4) Flexible polyurethane foams are made using each of Pre-Blends A-F. The foam formulations are as indicated in Table 2. (The amounts of tackifier and monol per 100 parts Polyols A-C are indicated separately at the bottom of Table 2.) All components except catalyst and polyisocyanate are mixed at room temperature for 15 seconds at 2400 rpm using a high-speed pin mixer. The catalyst is then added and mixed for 15 seconds at 2400 rpm, followed by the polyisocyanate addition and mixing for 3 seconds at 3000 rpm. The resulting reaction mixture is poured into a 38 cm×38 cm×24 cm box where it reacts, rises and cures to produce a flexible polyurethane foam. The foams are allowed to cure overnight.

(5) TABLE-US-00002 TABLE 2 Parts by Weight Ingredient A* 1 2 B* 3 4 C* Polyol A 20 20 20 20 20 20 20 Polyol B 60 60 60 60 60 60 60 Polyol C 20 20 20 20 20 20 20 Water 2 2 2 2 2 2 2 Pre-Blend None A, 16.48 B, 19.13 C, 75 D, 22.06 E, 25 F, 75 (type, amount) Surfactant 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Catalyst 0.25 0.25 0.25 0.25 0.25 0.25 0.25 PMDI (index) 82 82 82 82 82 82 82 Pphp tackifier 0 15 15 15 15 15 15 Pphp monol 0 1.48 4.13 60 7.06 10 60 *Not an example of the invention.

(6) To measure foam properties, the foam skins are first removed, and the samples are conditioned for 24 hours. Foam density, IFD, compression set, tensile, tear resistance, airflow, and resilience are tested following ASTM standard D3574. Recovery time is measured as described hereinbefore. Results are as indicated in Table 3.

(7) TABLE-US-00003 TABLE 3 Value A* 1 2 B* 3 4 C* Property Density, pcf 3.25 (52.1) 8.67 (139) 3.85 (61.7) Foam 5.64 (90.3) 6.1 (97.7) 4.4 (70.5) (kg/m.sup.3) Collapsed Recovery time, s 2.0 2.5 6.1 5.9 40 >180 Resiliency, % 3.0 2.0 2.0 1.0 1.4 7.4 Air flow, ft.sup.3/min 3.3 (1.56) 8.7 (4.11) 5.9 (2.78) 5.6 (2.64) 6.1 (2.88) 4.9 (L/s) IFD, lbf (N) 25% 12.1 (53.8) 6.7 (29.8) 5.8 (25.8) 6.1 (27.1) 1.5 (6.7) 31.1 (138) 65% 24.3 (108) 15.4 (68.5) 12.3 (54.7) 13.4 (59.6) 4.8 (21.4) 77.4 (344) return 25% 11.2 (49.8) 6.1 (27.1) 5.3 (23.6) 5.5 (24.5) 0.9 (4.0) 19.2 (85.4) Tear Strength, 1.1 (192) 1.0 (175) 0.9 (158) 0.9 (158) 0.5 (87) 6.8 (1190) pli (N/m) Tensile Str., 8.3 (57.2) 3.8 (26.2) 4.2 (29.0) 4.2 (29.0) 1.6 (11.0) 26.3 (18.1) psi (kPa) Elongation, % 119 111 142 131 182 138 90% 11.1 1.3 1.8 15.5 88.4 0.6 Compression Set, % *Not an example of the invention.

(8) Comparative Sample A represents a baseline with no tackifier. Recovery time is 2 seconds. This is increased to 2.5 seconds, 6.1 seconds, 5.9 seconds and 40 seconds, respectively, in Examples 1-4.

(9) Example 4 shows the effect of using a monol that does not have the preferred Hanson solubility parameters. This monol performs less well as a diluent (as shown below), so a large amount of the monol is needed to carry in the same amount of tackifier as in the other examples and samples. The resulting foam is a recovery time of 40 seconds, which is greater than preferred. Additionally, the compression set becomes higher.

(10) Comparative Sample B shows the effect of having too much of the monol. The foam collapses and properties cannot be meaningfully measured.

(11) Comparative Sample C shows the effect of using a low molecular weight polyester diol as a diluent for the tackifier, rather than a monol. The recovery time is >180 seconds and the foam is generally stiff and hard.

(12) Viscosity Reduction Effect of Additional Pre-Blends

(13) Additional pre-blends are made in a manner similar to Pre-blends A-F. In each case the proportion of tackifier is 91.16:9.84. The tackifier is the polyterpene resin used in Pre-Blends A-F. The viscosity of each of the pre-blends is determined using an AR2000 cone-and-plate rheometer from TA Instruments. The cone plate diameter is 25 mm, the shear rate is 10 rad/s and the frequency sweeping is in the range of 0.01 to 100 rad/s. Results are as indicated in Table 4.

(14) TABLE-US-00004 TABLE 4 Hansen Solubility Parameters.sup.1 Pre-Blend Monol δ.sub.d δ.sub.p δ.sub.h Viscosity, cps Propylene glycol mono-n-butyl ether 15.2 4.2 10.5 3300 Dipropylene glycol mono-n-butyl ether 14.8 2.5 8.7 6500 Tripropylene glycol mono-n-butyl ether 14.8 1.7 7.9 9300 2-ethyl hexanol 15.9 3.3 11.8 11,250 2,6-Dimethyl-4-heptanol (nonyl alcohol) 14.9 3.1 10.8 8450 Ethylene glycol mono-n-butyl ether 16.0 7.6 12.3 4000 Ethylene glycol mono-n-hexyl ether 16.0 6.9 10.9 4100 Diethylene glycol mono-n-hexyl ether 16.0 6.0 10.0 7700 Dipropylene glycol monophenyl ether 16.9 4.9 10.2 >20,000 Propylene glycol monophenyl ether 17.4 5.3 11.5 17,500 2-Ethyl-1-butanol 15.8 4.3 13.5 6600 Ethylene glycol monophenyl ether 17.8 5.7 14.3 125,000 None (neat tackifier) >300,000 .sup.1δ.sub.d is Hansen dispersion parameter; δ.sub.p is Hansen polar parameter; δ.sub.h is Hansen hydrogen bonding parameter, all values in (J/cc).sup.1/2.

(15) The results shown in Table 4 demonstrate the surprising effectiveness of monols having the preferred Hansen Solubility Parameters as described herein. At less than 10% concentration, these reduce the viscosity of the tackifier by twenty-fold or more. When the Hansen parameters of the monol are outside the designated range, as with ethylene glycol monophenyl ether, the monol is much less effective as a viscosity reducer. Much more of the monol is needed to achieve the desired low viscosity in that case; it becomes difficult to incorporate an effective amount of tackifier into the foam formulation without using very large quantities of the monol, as shown in Tables 2 and 3 above.

(16) The monols containing aromatic groups are generally less effective diluents than are those that are entirely aliphatic in nature, and are less preferred.