HK1021382A - Microcellular elastomeric polyurethane foams - Google Patents

Description

Microcellular elastomeric polyurethane foams

The present invention relates to the preparation of microcellular elastomeric polyurethane foams.

Conventional polyurethane elastomers are prepared from formulations having a hard block content of about 30 to 40% by weight (hard block content is defined herein as the sum of the amounts of polyisocyanate, chain extender and, optionally, crosslinking agent, as a percentage by weight relative to the total polymer).

Formulations with a higher hard block content are difficult to process and the resulting products have a very high hardness.

Elastomeric polyurethane foams have been prepared with formulations comprising high amounts of 4, 4' -MDI and polyether polyols having a high EO content, examples being found in EP-A547764, EP-A547765 and EP-A549120.

Processes for preparing elastomeric polyurethanes from polyether polyols having a low Ethylene Oxide (EO) -content are also known, examples being found in U.S. Pat. No. 3, 5122548 and EP-A13487.

Surprisingly, it has now been found that it is possible to produce microcellular polyurethane elastomeric foams which have a very high hard block content without an excessively high hardness and which are nevertheless readily processable in a wide density range.

Thus, according to the present invention there is provided a process for preparing microcellular elastomeric polyurethane foam which comprises reacting a reaction mixture comprising: a polyisocyanate component, a polyol composition, a chain extender, water and optionally a cross-linker, wherein the polyisocyanate component comprises at least 85% by weight of 4, 4' -diphenylmethane diisocyanate or a variant thereof; the polyol composition comprises at least one polyoxyalkylene polyol containing oxyethylene residues, the polyol composition having an average nominal hydroxyl functionality of 2 to 6, an average hydroxyl equivalent weight of at least 1300 and an average oxyethylene content of between 50 and 85% by weight; and a chain extender having an average hydroxyl equivalent weight of from 15 to 250; the hard block content is greater than 45% by weight.

The polyisocyanate component content used in the process of the present invention may consist essentially of pure 4,4 ' -diphenylmethane diisocyanate or a mixture of diisocyanates with one or more other organic polyisocyanates, especially other diphenylmethane diisocyanate isomers, e.g. the 2,4 ' -isomer optionally in combination with the 2,2 ' -isomer. The polyisocyanate component may also be an MDI variant derived from a polyisocyanate composition containing at least 85% by weight of 4, 4' -diphenylmethane diisocyanate. MDI variants are well known in the art and, for use in accordance with the present invention, include in particular liquid products obtained by introducing uretonimine (uretonimine) and/or carbodiimide groups into the polyisocyanate composition and/or reacting with one or more polyols.

Preferred as the polyisocyanate component is a polyisocyanate composition containing at least 90% by weight of 4, 4' -diphenylmethane diisocyanate. Most preferred are polyisocyanate compositions having at least 95% by weight of 4, 4' -diphenylmethane diisocyanate.

The term "average nominal hydroxyl functionality" as used herein means: the average functionality (number of hydroxyl groups per molecule) of the polyol composition is on the assumption that the average functionality of the polyoxyalkylene polyol present therein is the same as the average functionality (number of active hydrogen atoms per molecule) of the initiator used in its preparation, although in practice it will generally be less because some terminal unsaturation is used. The average nominal hydroxyl functionality of the polyol composition is preferably from 2 to 4, with the most preferred polyoxyalkylene polyol being a diol or triol.

The composition may comprise a single polyoxyalkylene polyol, which is preferably a poly (oxyethylene-oxypropylene) polyol having the desired average nominal hydroxyl functionality, hydroxyl equivalent weight and oxyethylene content. Such polyols are known in the art and can be obtained in a conventional manner by reacting ethylene oxide and propylene oxide simultaneously and/or sequentially with an initiator having 2 to 6 active hydrogen atoms, such as water, a polyol, a hydroxylamine or a polyamine, and the like. Examples of polyol initiators are: ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1, 3-propanediol, neopentyl glycol, 1-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, glycerol, trimethylolpropane, erythritol, xylitol, glucose, fructose, mannitol, or sorbitol.

Alternatively, the polyol composition may comprise a mixture of two or more polyols such that the overall composition has the desired average nominal hydroxyl functionality, average hydroxyl equivalent weight, and oxyethylene content. The other polyols may be selected from: a polyether, polyester, polythioether, polycarbonate, polyacetal, polyolefin, or polysiloxane.

The polyether polyol can be, for example, a polyoxypropylene polyol, a polyoxyethylene polyol, or a poly (oxyethylene-oxypropylene) polyol containing less than 50% or greater than 85% by weight oxyethylene residues.

Useful polyester polyols include: hydroxyl-terminated reaction products of diols such as ethylene glycol, propylene glycol, diethylene glycol, 1-butanediol, neopentyl glycol, 1, 6-hexanediol or cyclohexanedimethanol or mixtures of these diols, and reaction products of dicarboxylic acids or ester-forming derivatives thereof, for example succinic acid, glutaric acid and adipic acid or its dimethyl ester, sebacic acid, phthalic anhydride, tetrachlorophthalic anhydride or dimethyl terephthalate or mixtures thereof.

Polyesteramides may be obtained by including amino alcohols such as ethanolamine in polyesterification mixtures.

Useful polythioether polyols include products obtained by concentrating thiodiglycol, alone or with other glycols, oxiranes, dicarboxylic acids, formaldehyde, amino alcohols or aminocarboxylic acids.

Useful polycarbonate polyols include products obtained by reacting diols such as 1, 3-propanediol, 1-butanediol, 1, 6-hexanediol, diethylene glycol or tetraethylene glycol with diaryl carbonates, for example diphenyl carbonate, or with phosgene.

Useful polyacetal polyols include those prepared by reacting a diol such as diethylene glycol, triethylene glycol or hexanediol with formaldehyde. Suitable polyacetals may also be prepared by polymerizing cyclic acetals.

Suitable polyalkene polyols include hydroxy-terminated butadiene homo-or copolymers, while suitable polysiloxane polyols include polydimethylsiloxane diols.

Other polyols which may be used include dispersions or solutions of addition or condensation polymers of polyols of the types described above. These modified polyols, commonly referred to as "polymer" polyols, have been described in detail in the prior art and include products obtained by the in situ polymerization of one or more vinyl monomers, such as styrene or acrylonitrile, in polymeric polyols, such as polyether polyols, or by the in situ reaction of polyisocyanates with amino-and/or hydroxy-functional compounds, such as triethanolamine, in polymeric polyols.

Preferably, the polyol composition has an average hydroxyl equivalent weight of at least 1500. The average oxyethylene content of the polyol composition is preferably from 60 to 85% by weight.

Suitable low molecular weight chain extenders include: aliphatic diols such as ethylene glycol, 1, 3-propanediol, 2-methyl-1, 3-propanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 2-propanediol, 1, 3-butanediol, 2, 3-butanediol, 1, 3-pentanediol, 1, 2-hexanediol, 3-methylpentane-1, 5-diol, 2-dimethyl-1, 3-propanediol, diethylene glycol, dipropylene glycol and tripropylene glycol, and aminoalcohols such as ethanolamine, N-methyldiethanolamine, N-ethyl-diethanolamine and the like. Ethylene glycol is preferred.

Suitable amounts of water are less than 2% by weight, and preferably less than 1% by weight, based on the total weight of the isocyanate-reactive compounds.

In another aspect, the present invention relates to a microcellular elastomeric polyurethane foam having a density of less than 1000 kilograms per cubic meter and a Shore A hardness of at least 75. Preferred densities are less than 800 kg/m and a schuler a hardness of at least 80. Most preferred are microcellular elastomeric polyurethane foams having a density of less than 600 kg/m and a schuler a hardness of at least 85.

In another aspect, the present invention provides a reaction system comprising:

a polyisocyanate containing at least 85% by weight of 4, 4' -diphenylmethane diisocyanate or a variant thereof;

(ii) a polyol composition comprising at least one oxyethylene-residue-containing polyoxyalkylene polyol, the polyol composition having an average nominal hydroxyl functionality of from 2 to 6, an average hydroxyl equivalent weight of at least 1300 and an average oxyethylene content of from 50 to 85% by weight;

(iii) a chain extender having an average hydroxyl equivalent weight of from 15 to 250;

(iv) water, and optionally

(v) one or more additives in a conventional elastomer formulation.

The reaction system is used to make microcellular elastomeric polyurethane foams.

The term "reaction system" is defined as a system in which the polyisocyanate is placed in a separate container from the isocyanate-reactive components.

The isocyanate index of the present reaction system, calculated to include the polyol composition, water and any other isocyanate-reactive species, such as chain extenders or crosslinkers, may be as low as 85 or as high as 120. Preferably, the isocyanate index is between 90 and 110.

The hardblock-content is preferably at least 50% by weight of the total composition.

Low molecular weight isocyanate-reactive compounds having an average functionality of 3 or more, such as glycerol, pentaerythritol or triethanolamine, may be added as crosslinking agents.

The foam-forming reaction mixture may contain one or more additives conventionally used in such reaction mixtures. These additives include catalysts, such as tertiary amines and tin compounds, surfactants and foam stabilizers, such as siloxane-oxyalkylene copolymers, flame retardants, organic and inorganic fillers, pigments, and internal mold release agents.

The process may be carried out according to the "one shot", "semi-prepolymer" or "prepolymer" method.

A wide range of elastic products can be made by the process of the present invention.

The elastomers produced by the process of the present invention can be used in a wide variety of applications, such as shoe soles and steering wheels.

The invention is illustrated by the following examples in which all parts, percentages and ratios are by weight.

The following terms are included to distinguish reaction components, and are not otherwise distinguished in the examples.

Noun (name)

Polyisocyanate I: pure 4, 4' -MDI (Supersec MPR; commercially available from ICI PLC; Supersec is a trademark of ICI PLC).

Polyisocyanate II: uretonimine modified MDI (Superasec 2020; available from ICIPLC; Superasec is a trademark of ICI PLC).

Polyol A Arcol 2580, a polyether triol having random oxyethylene and oxypropylene residues, having an oxyethylene content of 76% and an OH-value of 42 mg KOH/g, commercially available from ARCO; ARCOL is a trademark of ARCO.

Polyol B: EO/PO triol having an EO tip (tip) of 10% and an OH value of 36 mg KOH/g.

Polyol C: EO/PO diol with 75% random EO-base and MW = 4000.

Catalyst: dabco EG (33% EG solution of Dabco available from Air products; Dabco is a trademark for Air products).

EG: ethylene glycol.

DEG: diethylene glycol.

Examples 1-3 and comparative examples 1-4

The elastic was molded in a 15X 10X 1 cm mold by conventional methods from the following formulation.

First watch

	Example 1	Example 2	Example 3	Comparative example 1	Comparative example 2	Comparative example 3	Comparative example 4
Polyol A	100	100	-	100	-	-	-
								Polyol B	-	-	-	-	100	100	100
Polyol C	-	-	100	-	-	-	-
								EG	16.3	14	20	7.23	7.46	16.56	14.2
DEG	-	14	-	-	-	-	14.2
								Catalyst and process for preparing same	0.5	0.5	0.7	1	1	0.5	0.5
Water (W)	0.3	1	0.7	0.3	0.3	0.3	1
Polyisocyanate I	Index 100	Index 100	-	Index 100	Index 100	Index 100	Index 100
								Polyisocyanates II	-	-	Index 100	-	-	-	-
Hard Block content (% by weight)	50	50	57	35	35	50	50
Properties of
								Density kg/m	702	536	420	650	651	Fragile material	Fragile material
Hardness of Shure A	89	90	85	42	72
						ASKER (ASKER) C hardness	93	90	89	66	82	Non-foam body	Non-foam body
Ball rebound	36	26	N.M.(*)	64	57

N.M.(^*): not measured

These examples show that the use of polyols with high oxyethylene content in high hardness block formulations gives elastomers with valuable properties which are still processable to high hardness, which is not possible or very difficult with polyol formulations containing low oxyethylene content.

Claims (13)

1. A process for preparing a microcellular elastomeric polyurethane foam having a reaction mixture comprising: a polyisocyanate component, a polyol composition, a chain extender, water and optionally a cross-linker, wherein the polyisocyanate component comprises at least 85% by weight of 4, 4' -diphenylmethane diisocyanate or a variant thereof; the polyol composition comprises at least one polyoxyalkylene polyol containing oxyethylene residues, the polyol composition having an average nominal hydroxyl functionality of 2 to 6, an average hydroxyl equivalent weight of at least 1300 and an average oxyethylene content of 50 to 85% by weight; and a chain extender having an average hydroxyl equivalent weight of from 15 to 250; the hard block content is greater than 45% by weight.

2. A process according to claim 1 wherein the polyisocyanate component contains at least 90% by weight of 4, 4' -diphenylmethane diisocyanate or a variant thereof.

3. A process according to claim 2 wherein the polyisocyanate component comprises at least 95% by weight of 4, 4' -diphenylmethane diisocyanate or a variant thereof.

4. The method according to any of the preceding claims, wherein the polyoxyalkylene polyol containing oxyethylene residues is a poly (oxyethylene oxypropylene) polyol.

5. A process according to any one of the preceding claims wherein the polyol composition has an average nominal hydroxyl functionality of from 2 to 4.

6. A process according to any one of the preceding claims wherein the polyol composition has an average hydroxyl equivalent weight of at least 1500.

7. A process according to any one of the preceding claims wherein the average oxyethylene content of the polyol composition is from 60 to 85% by weight.

8. The method according to any of the preceding claims, wherein the hard block-content is at least 50 wt. -%.

9. The process according to any of the preceding claims, which is carried out at an isocyanate index of from 90 to 110.

10. A microcellular polyurethane elastomeric foam having a density of less than 1000 kilograms per cubic meter and a Shore a hardness of at least 75.

11. A microcellular polyurethane elastomeric foam according to claim 10 having a density of less than 800 kg/m and a schuler a hardness of at least 80.

12. A microcellular polyurethane elastomeric foam according to claim 11 having a density of less than 600 kg/m and a schuler a hardness of at least 85.

13. A reaction system, comprising:

a polyisocyanate containing at least 85% by weight of 4, 4' -diphenylmethane diisocyanate or a variant thereof;

(ii) a polyol composition comprising at least one polyoxyalkylene polyol containing oxyethylene residues, the polyol composition having an average nominal hydroxyl functionality of 2 to 6, an average hydroxyl equivalent weight of at least 1300 and an average oxyethylene content of 50 to 85% by weight;

(iii) a chain extender having an average hydroxyl equivalent weight of from 15 to 250;

(iv) water, and optionally

(v) a crosslinking agent and one or more additives used in conventional elastomer formulations.