IN-SITU FORMATION OF LOW DENSITY THERMOPLASTIC POLYURETHANE FLEXIBLE FOAMS

Abstract

A reactive mixture and method for making a thermoplastic polyurethane (TPU) flexible foam having a predominantly open-cell structure (open-cell content of ≥50% by volume calculated on the total volume of the foam and measured according to ASTM D6226-10) and an apparent density below 200 kg/m.sup.3.

Claims

1. An in-situ method for making a thermoplastic polyurethane (TPU) flexible foam having an open-cell content of ≥50% by volume calculated on the total volume of the foam and measured according to ASTM D6226-10 and density below 200 kg/m.sup.3, said method comprising combining at an isocyanate index between 90 and 110 in situ at least following ingredients to form a reactive mixture: a) a polyisocyanate composition comprising at least 75% by weight difunctional isocyanate compounds calculated on the total weight of all isocyanate compounds in the polyisocyanate composition, and b) an isocyanate reactive composition comprising at least 75 wt % difunctional isocyanate reactive compounds calculated on the total weight of all isocyanate reactive compounds in the isocyanate reactive composition and wherein said difunctional isocyanate reactive compounds are selected from at least one linear high molecular weight difunctional polyol having a molecular weight in the range 500-20000 g/mol and at least one low molecular weight difunctional chain extender having a molecular weight <500 g/mol, and c) at least one polyurethane forming catalysts, and d) a blowing agent composition wherein at least 90 wt % of the blowing agents are selected from physical blowing agents and/or non-reactive chemical blowing agents having no isocyanate reactive groups, and e) at least one compound acting as a surfactant, and f) optionally further additives such as flame retardants, fillers, pigments and/or stabilizers and wherein the reactive mixture contains less than 0.1 wt % water calculated on the total weight of the reactive mixture and wherein said in-situ method is selected from a moulding process, a free-rise spray process or a free-rise slabstock process.

2. The method according to claim 1, wherein the isocyanate index is between 90 and 110.

3. The method according to claim 1, wherein the low density TPU flexible foam according to the invention has an open-cell content of ≥60% by volume calculated on the total volume of the foam and measured according to ASTM D6226-10).

4. The method according to claim 1, wherein the physical blowing agents are selected from CO.sub.2, N.sub.2, or mixtures thereof.

5. The method according to claim 1, wherein the blowing agent composition comprises >95 wt % physical blowing agents selected from CO.sub.2, and/or N.sub.2, or mixtures thereof.

6. The method according to claim 1, wherein the blowing agent composition comprises >95 wt % of physical blowing agents and/or non-reactive chemical blowing agents having no isocyanate reactive groups based on the total weight ofthe blowing agent composition and wherein the amount of blowing agents is from 5 to 60 per hundred weight parts isocyanate reactive compounds.

7. The method according to claim 1, wherein the reactive mixture comprises less than 0.075 wt % of water calculated on the total weight of the reactive mixture calculated on the total weight of the blowing agent composition.

8. The method according to claim 1, wherein the physical blowing agents are selected from isobutene, methylformate, dimethyl ether, methylene chloride, acetone, t-butanol, argon, krypton, xenon, chloro fluoro carbons (CFCs), hydro fluoro carbons (HFCs), hydro chloro fluoro carbons (HCFCs), hydro fluoro olefins (HFO's), Hydro Chloro Fluoro Olefins (HCFO's), and hydrocarbons such as pentane, isopentane and cyclopentane, or mixtures thereof.

9. The method according to claim 1, wherein the polyisocyanate composition contains at least 85% by weight of difunctional isocyanate compounds calculated on the total weight of all isocyanate compounds in the polyisocyanate composition.

10. The method according to claim 1, wherein the polyisocyanate composition contains at least 95 wt % 4,4′-diphenylmethane diisocyanates calculated on the total weight of the polyisocyanate composition.

11. The method according to claim 1, wherein the polyisocyanate component in the polyisocyanate composition is an isocyanate-terminated prepolymer which is prepared by reaction of an excessive amount of the polyisocyanate having at least 85% of 4,4′-diphenylmethane diisocyanate with a difunctional polyol and wherein the NCO value of the isocyanate-terminated prepolymer is above 5 wt %.

12. The method according to claim 1, wherein the high molecular weight difunctional polyols are selected from polyester diols, polyether polyols and/or polyester polyether polyols having a molecular weight in the range 500 g/mol up to 10000 g/mol.

13. The method according to claim 1, wherein the isocyanate reactive composition comprises at least 85 wt % difunctional polyols calculated on the total weight of the isocyanate reactive composition.

14. The method according to claim 1, wherein the difunctional chain extenders have a molecular weight<500 g/mol and are selected from 1,6 hexanediol, 1,4-butanediol and/or ethylene glycol in an amount of 2-10 wt % calculated on the total weight of the isocyanate reactive composition.

15. The method according to claim 1, said method comprising at least the steps of: i. pre-mixing the ingredients b) up to e) and optionally f), and then ii. mixing the polyisocyanate composition with the composition obtained in step i) in situ to form a reactive mixture, and iii. allowing the reactive mixture obtained in step ii) to foam to obtain a thermoplastic elastomer polyurethane foam.

16. (canceled)

17. A thermoplastic polyurethane (TPU) flexible foam made according to claim 1, wherein the amount of blowing agent used is such that the foam has an apparent density in the range 100-200 kg/m.sup.3 measured according to ISO 845 and having a hardblock content in the range 15 up to 65%, and an open-cell content of at least 50% by volume measured according to ASTM D6226-10, and a trousers tear strength>1000 N/m measured according to DIN 53356

18. A thermoplastic polyurethane (TPU) flexible foam made according to claim 1, wherein the amount of blowing agent used is such that the foam has an apparent density in the range 10-100 kg/m.sup.3 measured according to ISO 845 and having a hardblock content in the range 15 up to 65%, and a trousers tear strength>100 N/m measured according to DIN 53356, and an open-cell content of at least 50% by volume measured according to ASTM D6226-10

19. (canceled)

20. A process for melting and/or recycling the thermoplastic polyurethane (TPU) flexible foam made according to claim 1, by applying a heat and/or compression process to the TPU at temperatures above the melting temperature of the thermoplastic material.

Description

FIGURES

[0169] FIG. 1 illustrates the temperature dependent rheological properties (G′ and G″) corresponding to the polymer of a foam according to the invention made using a reactive mixture with no added water in the reactive mixture (example 8).

[0170] FIG. 2 illustrates the temperature dependent rheological properties (G′ and G″) corresponding to the polymer of a foam not according to the invention made using a reactive mixture with 0.5 wt % water calculated on the total weight of the reactive mixture (example 9).

[0171] FIG. 3 illustrates the temperature dependent rheological properties (G′ and G″) corresponding to the polymer of a foam not according to the invention made using a reactive mixture with 1 wt % water calculated on the total weight of the reactive mixture (example 10).

EXAMPLES

[0172] Chemicals Used:

[0173] Polyols [0174] Caradol® ED56: Polypropylene glycol from with a hydroxyl value of 56.0 mg KOH/g. [0175] Terathane® 650: polytetramethylene glycol with a hydroxyl value of 172.6 mgKOH/g. The polyol was dehydrated by vacuum distillation. [0176] Terathane® 1000: Polytetramethylene glycol with a hydroxyl value of 112.2 mg KOH/g. The polyol was dehydrated by vacuum distillation. [0177] Terathane® 2000: Polytetramethylene glycol with a hydroxyl value of 56.1 mg KOH/g. The polyol was dehydrated by vacuum distillation. [0178] Daltorez® P708: hydroxyl terminated reaction product of 1,4-butanediol and adipic acid with a hydroxyl value of 50 mg KOH. The polyol was dehydrated by vacuum distillation.

[0179] Chain Extenders [0180] 1,4-butanediol: glycol chain extender. Dehydrated by vacuum distillation. [0181] 1,2-ethyleneglycol: glycol chain extender. Dehydrated by vacuum distillation. [0182] Caprinoguanamine (2,4-diamino-6-nonyl-1,3,5-triazine). Obtained from Evonik.

[0183] Blowing Agent [0184] Opteon® 1100: hydrofluoroolefin blowing agent with a boiling point of 33° C. [0185] Distilled water

[0186] Isocyanate [0187] Suprasec® 1306: a mixture of 98% by weight of 4,4′-diphenylmethane diisocyanate and 2% by weight of 2,4′-diphenylmethane diisocyanate. [0188] Prepolymer: A prepolymer was prepared using 46.5 wt % Terathane® 2000 and 53.5 wt % Suprasec® 1306.

[0189] Catalyst [0190] Tin(II)octoate: Tin(II) 2-ethylhexanoate, dissolved in dioctyladipate, applicable in examples 1-7. [0191] Tin(II)octoate: Tin(II) 2-ethylhexanoate [0192] Coscat® 83: Bismuth trineodecanoate [0193] Dabco® S: 1,4-diazabicyclo[2.2.2]octane

[0194] Surfactants [0195] Tegostab® B8494: Silicone surfactant [0196] Tegostab® B8466: Silicone surfactant [0197] Tegostab® B8716: Silicone surfactant

[0198] Test Methods [0199] The compression stress at a strain of 40% (CLD 40) was measured according to the norm ISO 3386-1 on a foam slab with a surface of 10 by 10 cm and a thickness of 5cm cut from the centre of the foam bun. [0200] Trouser tear strength was measured according to DIN 53356 on a foam slab cut from the centre of the foam bun. [0201] The resilience of the foams was determined according to ISO 8307 on a foam slab with a thickness of 5 cm cut from the centre of the foam bun in case of foams with an apparent density lower than 100 kg/m.sup.3. Resilience of foams with an apparent density higher than 200 kg/m3 was measured on foam slabs with a thickness of at least 15 mm. [0202] The apparent density was determined by dividing the mass of a foam slab by its volume. The volume of the foam slab was determined by measuring the foam slab ribs with a calliper or ruler. [0203] Rheology was measured using A TA ARES-G2 rotational rheometer together with electrically heated plate temperature system including an environmental cover and heated purge gas to perform rheology tests. According to ASTM D4440-08 (2008), small-amplitude oscillatory shear mode is used and samples are subjected to a homogeneous sinusoidal strain. The strain amplitude is forced to be constant at 1% during all temperature sweep and is sufficiently small such that the response is in the materials' linear regime. The frequency is fixed to 1 Hz over the entire experiment. Parallel plate geometry configuration of diameter equal to 25 mm is used. A solid preform disk of thickness about 1.65 mm of thermoplastic or thermoset polyurethanes polymer is placed between the two plates. Solid preform disks were prepared compressing a foam block in between two preheated metal plates.

Example 1

According to the Invention

[0204] 522.46 g of Caradol ED56, 94.05 g of 1,4-butanediol, 1.91 g of Tegostab B8466, 2.86 g of Tegostab® B8716 and 74.71 g of Opteon® 1100 were weighed in a plastic cup of one litre and mixed gently. To this blend 341.93 g of Suprasec® 1306 and 3.0 g of catalyst solution (10 wt %) were added. The polyurethane formulation has a hard-block content of 45.5% and an isocyanate index of a 103.6%. The reactive mixture was mixed vigorously for 20 seconds and poured into a wooden mould where it rose freely. The foam bun was subsequently post-cured for 65 hours in an oven set at 120° C.

[0205] Foam slabs cut from the center of the foam bun had an apparent density of 84 kg/m.sup.3, a CLD hardness at 40% compression measured according to ISO 3386/1 of 11.7 kPa and a resilience of 25%.

Example 2

According to the Invention

[0206] 350.0 g of Terathane 650, 42.66 g of 1,2-ethyleneglycol, 1.40 g of Tegostab B8466, 2.10 g of Tegostab B8716 and 56.38 g of Opteon® 1100 were weighed in a plastic cup of 5 litre and mixed gently. To this blend 319.53 g of Suprasec® 1306 and 0.25 g of catalyst solution (20 wt %) were added. The polyurethane formulation has a hard-block content of 50.9% and an isocyanate index of a 104.0%. The reactive mixture was mixed vigorously for 10 seconds and poured into a wooden mould where it rose freely. The foam bun was subsequently post-cured for 18 hours in an oven set at 120° C.

[0207] Foam slabs cut from the center of the foam bun had an apparent density of 72 kg/m.sup.3, a CLD hardness at 40% compression measured according to ISO 3386/1 of 10.9 kPa and a resilience of 25%.

Example 3

According to the Invention

[0208] 23.77 g caprinoguanamine and 594.22 g of Terathane 2000 were heated in a glass jar to 110° C., followed by cooling down to room temperature. 280.85 g of this blend was weighed in a 1 litre plastic cup, followed by 0.41 g of Tegostab° 8494, 54.70 g of 1,4-butanediol and 75.40 g of Opteon° 1100. This blend was mixed gently before addition of 204.26 g of Suprasec® 1306 and 0.08 g of pure Tin(II) octoate. The polyurethane formulation has a hard-block content of 50.0% and an isocyanate index of a 102.0%. The reactive mixture was mixed vigorously for about 5 seconds and poured into a wooden mould where it rose freely. The foam bun was subsequently post-cured for 18 hours in an oven set at 120° C.

[0209] Foam slabs cut from the center of the foam bun had an apparent density of 38 kg/m.sup.3, a CLD hardness at 40% compression measured according to ISO 3386/1 of 11.81 kPa and a resilience of 25%.

Example 4

According to the Invention

[0210] For synthesis of the prepolymer 983.29 g of Terathane 2000 was slowly added to 748.47 g of Suprasec® 1306 at a temperature between 70 and 80° C. over the course of 2 hours. After overnight storage at 50° C. the titrated NCO-value was 12.02 wt %. For the polyol blend 9.54 g caprinoguanamine and 163.20 g Terathane® 1000 were weighed in a 250 ml glass bottle and heated in an oven set at 110° C. until a homogeneous aspect is obtained. The polyurethane foam was prepared by weighing in a plastic cup 54.26 g of the polyol blend, 0.765 g of Tegostab® B8494 solution and 12.7 g of Opteon® 1100. These chemicals were mixed gently before addition of 46.9 g of the prepolymer and 0.25 g of catalyst solution. The reactive mixture was then mixed vigorously for about 7 seconds and allowed to rise freely in the cup. The foam bun was subsequently post-cured for 16 hours in an oven set at 90° C.

[0211] The polyurethane formulation has a hard-block content of 23.6 wt % and an isocyanate index of a 105.0%.

[0212] A foam slab cut from the center of the foam bun had an apparent density of 78 kg/m.sup.3, a CLD hardness at 40% compression measured according to ISO 3386/1 of 7.96 kPa and a resilience of 72%.

Example 5

According to the Invention

[0213] In a 425 ml cardboard cup 55.0 g Daltorez® P708, 10.15 g 1,4-butanediol, 0.21 g Tegostab® B8466, 0.31 g Tegostab® B8716 and 7.82 g of Opteon® 1100 were weighed and mixed gently. Afterwards 36.10 g of the Suprasec® 1306 is added, followed by 0.15 g of catalyst solution. The reactive mixture was mixed vigorously for about 20 seconds and poured in a 1 L plastic cup where the foam rose freely. The foam bun was subsequently post-cured for 18 hours in an oven set at 120° C. The polyurethane formulation has a hard-block content of 46 wt % and an isocyanate index of a 103.6%.

[0214] A foam slab cut from the centre of the foam bun had an apparent density of 81 kg/m.sup.3, a CLD hardness at 40% compression measured according to ISO 3386/1 of 15.51 kPa and a resilience of 45%.

Example 6

According to the Invention

[0215] In a 425 ml cardboard cup 55.00 g Daltorez® P708, 10.15 g 1,4-butanediol, 0.21 g Tegostab® B8466, 0.31 g Tegostab® B8716 and 7.82 g of Opteon® 1100 were weighed and mixed gently. Afterwards 36.10 g of Suprasec® 1306 is added, followed by 0.15 g of catalyst solution. The reactive mixture was mixed vigorously for about 20 seconds and poured in a 1 L plastic cup where the foam rose freely. The foam bun was subsequently post-cured for 18 hours in an oven set at 120° C. The polyurethane formulation has a hard-block content of 46 wt % and an isocyanate index of a 103.5%.

[0216] A Foam slab cut from the centre of the foam bun had an apparent density of 80.6 kg/m.sup.3, a CLD hardness at 40% compression measured according to ISO 3386/1 of 15.5 kPa and a resilience of 45%.

Example 7

According to the Invention

[0217] In a 1000 ml plastic cup 275.62 g Terathane® 2000, 49.99 g 1,4-butanediol, 1.00 g Tegostab® B8466, 1.51 g Tegostab® B8716 and 38.20 g Opteon® 1100 were weighed and mixed gently. Afterwards 178.84 g Suprasec® 1306 is added, followed by 0.75 g of catalyst solution. The reactive mixture was mixed vigorously for about 20 seconds and poured in a 5 L plastic bucket where the foam rose freely. The foam bun was subsequently post-cured for 18 hours in an oven set at 120° C. The polyurethane formulation has a hard-block content of 45 wt % and an isocyanate index of a 102%.

[0218] A Foam slab cut from the centre of the foam bun had an apparent density of 72 kg/m.sup.3, a CLD hardness at 40% compression measured according to ISO 3386/1 of 23.85 kPa, a resilience of 33% and a trouser tear strength of 1887 N/m measured according to DIN 53356.

Example 8

According to the Invention

[0219] A polyol blend was prepared by mixing 509.86 g Terathane 2000, 88.94 g 1,4-butanediol and 0.7501 g Tegostab® B8466. A catalyst solution was prepared by combining 0.5027 g Dabco® S, 4.9850 g Terathane® 2000, 0.4953 g Tin(II)octoate, 1.0021 g Coscat® 83 and 13.4928 g dioctyladipate. For preparation of the foam 47.95 g polyol blend, 2.054 g catalyst solution and 11.0 g Opteon® 1100 were mixed in a 400 ml cardboard cup. Afterwards 52.38 g prepolymer was added to the cup, followed by vigorous mixing for about 12 seconds. The reactive mixture contains no added water. The reactive mixture was poured in a 1 L plastic cup, where the foam rose freely. The polyurethane formulation of the foam has a hard-block content of 34.9 wt % and an isocyanate index of a 100.0%.

Example 9

Not According to the Invention

[0220] A polyol blend was prepared by mixing 521.76 g Terathane 2000, 70.04 g 1,4-butanediol, 0.8184 g Tegostab® B8466 and 6.752 g distilled water. A catalyst solution was prepared by combining 0.5027 g Dabco® S, 4.9850 g Terathane® 2000, 0.4953 g Tin(II)octoate, 1.0021 g Coscat® 83 and 13.4928 g dioctyladipate. For preparation of the foam 44.41 g of the polyol blend, 1.997 g catalyst solution and 5.55 g Opteon 1100 were mixed in a 400 ml cardboard cup. Afterwards 55.35 g prepolymer was added to the cup, followed by vigorous mixing for about 12 seconds. The reactive mixture contains 0.5 wt % water calculated on the total weight of the reactive mixture. The reactive mixture was poured in a 1 L plastic cup, where the foam rose freely. The polyurethane formulation of the foam has a hard-block content of 35.2 wt % and an isocyanate index of a 100.3%.

Example 10

Not According to the Invention

[0221] A polyol blend was prepared by mixing 535.96 g Terathane® 2000, 48.04 g 1,4-butanediol, 0.87 g Tegostab® B8466 and 14.44 g distilled water. A catalyst solution was prepared by combining 0.5027 g Dabco® S, 4.9850 g Terathane® 2000, 0.4953 g Tin(II)octoate, 1.0021 g Coscat® 83 and 13.4928 g dioctyladipate. For preparation of the foam 41.48 g of the polyol blend, 2.033 g catalyst solution and 5.54 g Opteon® 1100 were mixed in a 400 ml cardboard cup. Afterwards 58.60 g prepolymer was added to the cup, followed by vigorous mixing for about 12 seconds. The reactive mixture contains 1 wt % water calculated on the total weight of the reactive mixture. The reactive mixture was poured in a 1 L plastic cup, where the foam rose freely. The polyurethane formulation of the foam has a hard-block content of 35.5 wt % and an isocyanate index of a 100.2%.

[0222] FIGS. 1-3 show the temperature dependent rheological properties, G′ and G″ curves, from 60° C. to 230° C. for the example 8, example 9 and example 10, respectively. FIG. 2 and FIG. 3, corresponding to foams made using a reactive mixture with 0.5 wt % water (example 9) and 1 wt % water (example 10) calculated on the total weight of the reactive mixture, clearly show the typical behaviour of a chemically cross-linked polymer, i.e. thermoset material, with a stable plateau of G′ and G″ up to 120° C. followed by a gradual decrease of moduli' values at high temperatures. The two materials do not show any melting and the samples are still in their solid state. Indeed, G′ is always three or more-times higher than G″ for example 9 and seven or more-times higher than G″ for example 10. Conversely, FIG. 1 corresponding to a foam made using a reactive mixture with no added water (example 8) shows the typical temperature dependent behaviour of uncross-linked partially crystalline polymer, i.e. thermoplastic material, with a rubber-elastic plateau between 60° C. and 120° C. followed by a very sharp decrease of both G′ and G″ and an increase of ration of G″ to G′. Moreover, around 210-220° C. the polymer is so much viscous that G″ becomes higher than G′, i.e. melting region.