Process for Making a Flexible Polyurethane Foam Having a Hardness Gradient

Abstract

A molded flexible polyurethane foam having a hardness gradient going from soft to hard from the top to the bottom of the foam. The hardness gradient in the foam is a result of a foam elasticity gradient which arises from a polymer elasticity gradient and/or density gradient. A method for producing a flexible foam having a hardness gradient and a reactive mixture suitable for making said flexible foam is disclosed. Furthermore, the use of the flexible foams having a hardness gradient in matrasses, cushions for seating (more in particular for use in automotive seating), furniture, automotive under-carpets and dash insulators is disclosed.

Claims

1. A molded flexible polyurethane comprising foam with a hardness gradient, wherein said foam comprises at least: a top layer which has a thickness (height) which corresponds to around 25% of the total thickness (height) of the foam, a bottom layer which has a thickness (height) which corresponds to around 25% of the total thickness (height) of the foam, a foam elasticity E.sub.f in the bottom layer of said foam which is at least 3 times higher than in the top layer of said foam and wherein said foam elasticity corresponds to formula [2]: $\begin{array}{cc}{E}_f={\omega }_n^2\frac{mh}{A}& \left[2\right]\end{array}$ With ω.sub.n=the natural frequency m=a fixed mass h=the thickness of the foam sample A=the cross-section area of the foam sample and wherein said foam is made using a reactive foam formulation, said reactive formulation formed by mixing at an isocyanate index in the range 70-130: An isocyanate-reactive composition (a) comprising a polyether polyol (a1) having an oxypropylene (PO) content of 51-100% by weight, an oxyethylene (EO) content of 0-49% by weight, an average nominal hydroxyl functionality of 2-4 and an average molecular weight of 2000-7000, and optionally a polyether polyol (a2) having an oxyethylene content of 50-95% by weight, calculated on the weight of this polyol wherein the weight ratio of polyol (a2) in the isocyanate-reactive composition (a) is in the range of 0 to 20% by weight, calculated on the total weight of the isocyanate-reactive composition (a), and a polyisocyanate composition (b) having an NCO value in the range 21 up to 27%.

2. The molded flexible foam according to claim 1, having a polymer elasticity E.sub.p in the bottom layer of said foam which is at least 2 times higher than in the top layer of said foam and wherein said polymer elasticity corresponds to formula [1]: $\begin{array}{cc}{E}_p=\frac{E_f}{R^2}& \left[1\right]\end{array}$ With Relative density (R) defined as $R=\frac{{\rho }_f}{{\rho }_p}$ Polyurethane polymer density (ρ.sub.p)=1200 kg/m.sup.3 Polyurethane foam density (ρ.sub.f) being measured according to ISO 845

3. The molded flexible foam according to any of claim 1, having a foam density ρ.sub.f in the bottom layer of said foam which is 10% up to 40% higher than in the top layer of said foam.

4. The molded flexible foam according to claim 1, having a polymer elasticity E.sub.p in the bottom layer of said foam which is at least 2 times higher than in the top layer of said foam and wherein said polymer elasticity corresponds to formula [1] and a hardness gradient has a foam density r.sub.f in the bottom layer of said foam which is 10% up to 40% higher than in the top layer of said foam.

5. The molded flexible foam according to claim 1, having a polymer elasticity E.sub.p in the top layer which is lower than the polymer elasticity E.sub.p in the core (middle section) of the foam.

6. The molded flexible foam according to claim 1, having a foam density ρ.sub.f in the bottom half of the foam which is higher than the foam density ρ.sub.f in the top half of the foam.

7. The molded flexible foam according to claim 1, having a polymer elasticity E.sub.p in the top layer which is lower than the polymer elasticity E.sub.p in the middle section of the foam and a foam density ρ.sub.f in the bottom half of the foam which is higher than the foam density ρ.sub.f in the top half of the foam.

8. The reactive foam formulation for making the molded flexible foam according to claim 1, wherein the polyisocyanate composition (b) comprises 0-12% by weight methylene diphenyl 2,4′-diisocyanate (2,4 MDI) calculated on the total weight of all polyisocyanate compounds in the polyisocyanate composition.

9. The reactive foam formulation for making the molded flexible foam according to claim 1, said formulation further comprising a filled polyether polyol (a3) wherein the weight ratio of polyol (a3) in the isocyanate-reactive composition (a) is in the range of 0 to 30% by weight calculated on the total weight of the isocyanate-reactive composition (a).

10. The reactive foam formulation for making the molded flexible foam according to claim 1, wherein the polyisocyanate composition (b) is first pre-reacted with a polyol and the amount reacted polyol in the polyisocyanate composition (b) is in the range 0-40% by weight calculated on the total weight of the polyisocyanate composition (b).

11. The reactive foam formulation for making the molded flexible foam according to claim 1, further comprising blowing agents, catalysts, chain extenders, fire retardants, fillers, and surfactants.

12. The reactive foam formulation for making the molded flexible foam according to claim 1, wherein the reactive foam formulation further comprises blowing agents, said blowing agent comprising at least water and the amount of water used is 0.5 up to 10% by weight calculated on the total weight of all ingredients being present in the isocyanate-reactive composition (a) used to form the reactive foam formulation according to the invention.

13. A process for making the molded flexible foam according to claim 1, said process comprising at least the steps of: i. mixing the polyisocyanate composition (b) with the isocyanate-reactive composition (a) at an isocyanate index in the range 70-130 to obtain the reactive foam formulation according to any of claim 1, and then ii. casting the reactive foam formulation obtained in step i. into a mold to obtain flexible foam having a hardness gradient, and then iii. demoulding the obtained flexible foam having a hardness gradient characterized in that step iii. is performed such that there is a temperature difference (ΔT) of at least 25-30° C. between the temperature of the reactive foam formulation (T.sub.chemicals) and the temperature of the mold (T.sub.mold).

14. The process according to claim 13, wherein the temperature difference ΔT between the initial reactive foam formulation used (T.sub.chemicals) and the temperature of the mold (T.sub.mold) is at least 35-55° C.

15. The process according to claim 13, wherein the minimum temperature of the initial the reactive foam formulation used (T.sub.chemicals) is 10-15° C.

16. (canceled)

Description

FIGURES

[0169] FIG. 1a illustrates the tool set up used to measure the natural frequency c of a foam sample and FIG. 1b illustrates that the natural frequency c of the system is the frequency at which the transmissibility, ratio of the accelerations measured by sensors, is at its maximum.

[0170] FIG. 2a illustrates the processing conditions used to make comparative example 1 not according to the invention wherein the reactive foam formulation has a temperature of 30° C. and the mold has a temperature of 45° C. such that the temperature difference (ΔT) between the reactive foam formulation (T.sub.chemicals) and the temperature of the mold (T.sub.mold) is around 15° C.

[0171] FIG. 2b illustrates the processing conditions according to the invention used to make a flexible foam having a hardness gradient (corresponding to example 1) wherein the reactive foam formulation has a temperature of 20° C. and the mold has a temperature of 65° C. such that the temperature difference (ΔT) between the reactive foam formulation (T.sub.chemicals) and the temperature of the mold (T.sub.mold) is around 45° C.

[0172] FIG. 3a illustrates the foam elasticity E.sub.f obtained in the different layers in a foam according to the invention (example 1) and a foam not according to the invention (comparative example 1).

[0173] FIG. 3b illustrates the polymer elasticity E.sub.p obtained in the different layers in a foam according to the invention (example 1) and a foam not according to the invention (comparative example 1).

[0174] FIG. 4a illustrates the foam elasticity E.sub.f obtained in the different layers in a foam according to the invention (example 2) and a foam not according to the invention (comparative example 2).

[0175] FIG. 4b illustrates the polymer elasticity E.sub.p obtained in the different layers in a foam according to the invention (example 2) and a foam not according to the invention (comparative example 2).

[0176] FIG. 5a illustrates the foam density (ρ.sub.f) obtained in the different layers in foams according to the invention for example 1 and comparative example 1. FIG. 5b illustrates the foam density (ρ.sub.f) obtained in the different layers in foams according to the invention for example 2 and comparative example 2.

[0177] FIG. 6 illustrates a foam sample divided into different layers used to analyze the foam properties and to determine the gradient in density, polymer elasticity and foam elasticity in a foam. The top layer of a foam as defined in the invention corresponds to layer 1 and the bottom layer of a foam as defined in the invention corresponds to layer 4.

[0178] FIG. 7 illustrates a foam material comprising polymer material and air.

EXAMPLES

[0179] Chemicals Used: [0180] Suprasec® 2525, a polyisocyanate prepolymer composition comprising about 10 wt % 2,4 MDI calculated on the total weight of all isocyanate compounds in Suprasec® 2525 (the remaining isocyanate compounds being polymeric MDI and 4,4 MDI) and having an NCO value of about 25.5%. [0181] Suprasec® 4801, a polyisocyanate composition comprising about 7 wt % 2,4 MDI calculated on the total weight of all isocyanate compounds in Suprasec® 4801 (the remaining isocyanate compounds being polymeric MDI and 4,4 MDI) and having an NCO value of about 23%. [0182] Suprasec® 7007, a polyisocyanate composition comprising about 15 wt % 2,4 MDI calculated on the total weight of all isocyanate compounds in Suprasec® 7007 (the remaining isocyanate compounds being polymeric MDI and 4,4 MDI) and having an NCO value of about 29.5%. [0183] Daltocel® F428, a polyoxyethylene polyoxypropylene polyol with hydroxyl functionality of 3, a molecular weight of about 6000 and an ethylene oxide content of 15 wt % (at the end of all (all tipped)). [0184] Daltocel® F526, a polyoxyethylene polyoxypropylene polyol with hydroxyl functionality of 3, a molecular weight of about 6000 and an ethylene oxide content of 93 wt %. [0185] Alcupol® P-2321, styrene and acrylonitrile graft reactive polyether polymer with 35% solid content, hydroxyl number of 23 mg KOH/g and molecular weight of 2680 g/mol. [0186] Jeffcat® DPA, polyurethane catalyst [0187] Jeffcat® DMEA, polyurethane catalyst [0188] Jeffcat® LED204 36%, polyurethane catalyst [0189] DELA, crosslinker [0190] Tegostab® B8734LF, surfactant [0191] Tegostab® B8745, surfactant [0192] Tegostab® KE 810L, surfactant [0193] Tegostab® B8738, surfactant [0194] Water.

Example 1 and 2 According to the Invention and Comparative Example 1 and 2

[0195] Flexible polyurethane foam examples 1 and 2 according to the invention having a hardness gradient were prepared by mixing a polyisocyanate composition (b) and an isocyanate-reactive composition (a) to form a reactive foam formulation according to the invention. This reactive foam formulation which has a temperature around room temperature was filled into a mold where the temperature difference (AT) between the temperature of the reactive foam formulation (T.sub.chemicals) and the temperature of the mold (T.sub.mold) is around 45° C.

[0196] When example 1 was repeated using the same reactive foam formulation as in example 1 but with a temperature difference (AT) between the temperature of the reactive foam formulation (T.sub.chemicals) and the temperature of the mold (T.sub.mold) not according to the invention the obtained foam (comparative example 1) did not have a hardness gradient as defined in the invention. The reactive foam formulation in comparative example 1 has a temperature of 30° C. and the mold was at a temperature of 45° C. such that the temperature difference (AT) between the temperature of the reactive foam formulation (T.sub.chemicals) and the temperature of the mold (T.sub.mold) is around 15° C. which is not sufficient to achieve the flexible foam having a hardness gradient according to the invention.

[0197] Comparative example 2 comprises too much 2,4′-MDI content in its polyisocyanate composition used to make the reactive foam formulation and did not yield into a hardness gradient foam according to the invention. In comparative example 2 the polyisocyanate composition comprises 15 wt % 2,4′-MDI calculated on the total weight of all isocyanate compounds in the polyisocyanate composition.

[0198] The composition of reactive foam formulations used to make example 1, example 2, comparative example 1 and comparative example 2 are illustrated in Table 1.

TABLE-US-00001 TABLE 1 Comparative Comparative Example 1 Example 2 Example 1 example 2 Chemicals wt % wt % wt % wt % Polyisocyanate composition (b) Suprasec ® 2525 100 100 Suprasec ® 4801 100 Suprasec ® 7007 100 Isocyanate-reactive composition (a) Daltocel ® F428 81.6 95.5 81.6 95.5 Daltocel ® F526 3.1 3.1 Alcupol ® P-2321 10 10 Jeffcat ®DPA 0.62 0.62 Jeffcat ® DMEA 0.2 0.2 Jeffcat ® LED204 0.15 0.15 36% Jeffcat ® ZF-10 0.1 0.1 DELA 0.26 0.26 Tegostab ® B8738 0.2 0.2 Tegostab ® B8745 0.4 0.4 water 3.1 3.1 3.1 3.1 Isocyanate Index 80 90 80 90

[0199] The properties obtained for example 1 and 2 according to the invention and for comparative example 1 and 2 are indicated in Tables 2, 3 and 4.

[0200] In Table 2 the foam elasticity ratio (foam elasticity/average foam elasticity) of different layers of foam is compared. In example 1 and 2 there is a clear increasing foam elasticity going for the top layer to the bottom layer. In comparative example 1 and 2 the top and bottom layers have higher foam elasticity than the core layers.

[0201] In Table 3 the foam density ratio (foam density/average foam density) of different layers of foam is compared. In example 1 and 2 the bottom layer has a higher foam density than the other layers. In comparative example 1 and 2 the top and bottom layers of the foam have a higher foam density than the core of the foams.

[0202] In Table 4 the polymer elasticity ratio (polymer elasticity/average polymer elasticity) of different layers of foam is compared. The polymer elasticity of each layer is derived from the foam elasticity according to the formula in the definition of polymer elasticity. In example 1 the top two layers have a much lower polymer elasticity than the other two layers. In example two the polymer elasticity of the top layer is much lower than the other layers. In comparative example 1 and 2 there is limited variation in polymer elasticity of each layer. From these results in example 1 and the variation in the foam elasticity comes mainly from the variation in polymer elasticity in the foam with a second effect being the variation in density, whereas in comparative example 1 and 2 the variation of foam elasticity in the top and bottom layer comes from the density variation.

[0203] FIGS. 3a and 3b illustrate the foam elasticity and polymer elasticity in the different layers in foams obtained from example 1 and comparative example.

[0204] FIG. 4a illustrates the foam elasticity E.sub.f obtained in the different layers in a foam according to the invention (example 2) and a foam not according to the invention (comparative example 2). FIG. 4b illustrates the polymer elasticity E.sub.p obtained in the different layers in a foam according to the invention (example 2) and a foam not according to the invention (comparative example 2).

[0205] FIG. 5a illustrates the foam density (ρ.sub.f) obtained in the different layers in foams according to the invention for example 1 and comparative example 1.

[0206] FIG. 5b illustrates the foam density (ρ.sub.f) obtained in the different layers in foams according to the invention for example 2 and comparative example 2.

[0207] To analyze the foam properties the foam sample was divided in different layers as illustrated in FIG. 6.

TABLE-US-00002 TABLE 2 Comparative Comparative Example 1 Example 1 Example 2 Example 2 Foam Foam Foam Foam Elasticity Elasticity Elasticity Elasticity Layer Ratio Ratio Ratio Ratio 1 (top layer) 0.2 1.3 0.4 1.2 2 0.6 0.7 0.9 0.6 3 1.4 0.7 1.2 0.7 4 (bottom layer) 1.7 1.3 1.4 1.3

TABLE-US-00003 TABLE 3 Comparative Comparative Example 1 Example 1 Example 2 Example 2 Density Density Density Density Layer Ratio Ratio Ratio Ratio 1 (top layer) 1.0 1.1 0.9 1.1 2 1.0 0.8 0.9 0.8 3 1.0 0.8 1.0 0.8 4 (bottom layer) 1.1 1.0 1.2 1.0

TABLE-US-00004 TABLE 4 Comparative Comparative Example 1 Example 1 Example 2 Example 2 Polymer Polymer Polymer Polymer Elasticity Elasticity Elasticity Elasticity Layer Ratio Ratio Ratio Ratio 1 (top layer) 0.3 1.0 0.5 1.0 2 0.7 0.9 1.2 0.9 3 1.6 0.9 1.3 0.9 4 (bottom layer) 1.4 1.1 1.0 1.1