GB2232990A - Process for preparing low density polyurethane foam - Google Patents

Abstract

A process for producing high resilience polyurethane foam having both low density (i.e. less than 35 kgm<.3>) and an improved skin aspect comprises preparing a formulation from (a) one or more polyols, (b) at least 3.0 parts by weight water per one hundred parts of polyol, (c) one or more isocyanates having a functionality greater than or equal to 2, (d) a foam stabiliser and (e) one or more catalysts for the formation of urethane linkages from (a) and (c), at least one of the catalyst being an amine which has been blocked with an organic acid.

Description

PROCESS FOR PREPARING LOW DENSITY POLtUzETHANE FOAM The present invention relates to a process for preparing low density polyurethane foam employing a catalytically effective amount of a catalyst system including a tertiary amine blocked with an organic acid. In particular, the process is one in which high resilience polyurethane foam of low density is prepared.

High resilience (HR) polyurethane foam is now well established as a desirable material for the furniture and automotive industry since, relative to conventional hot cure foams, such materials have improved physical properties making them, for example, more comfortable and supportive. They are produced at lower temperatures ie less than lOO0C.

For reasons of economy, it is becoming desirable to manufacture HR foam mouldings having a lower density. However, unlike hot cure foams, this has proved difficult to do.

In general, there are two approaches to reducing the density of polyurethane. Both approaches rely on increasing the amount of blowing agent. The first approach, which involves adding relatively large amounts of chlorofluorocarbons (CFC) to the formulation is not attractive, particularly at a time when the use of such materials is being banned for environmental reasons.

The second approach, which involves increasing the amount of water in the formulation, thus generating extra carbon dioxide, is not suitable for manufacturing foams having densities lower than 35 kg/m3. This is because the use of large amounts of water and hence isocyanate cause a large amount of heat to be generated. This heat causes a significant increase in reaction rates. Thus, the blowing and gelling of the foam formulation all take place fast and usually gas evolution occurs so rapidly that it is difficult to maintain foam stability. For mouldings, this effect manifests itself as shear collapse, poor skin aspect or instability around the vents of the mould.

One approach to solving this problem is to use highly reactive polyether polyols and special silicone surfactants. Such highly reactive polyether polyols are characterised by high primary hydroxyl group contents (80-85X) relative to the polyether polyols usually used in the moulding (65-75Z). Appropriate silicone surfactants are for example those sold by Union Carbide Corporation under the trade names Y-10459, Y-10515 and Y-10366. However, whilst this approach can solve the problem of foam stability, the material still has a poor skin aspect. This manifests itself as a skin having a harsh rather than a smooth feel to it.

The problem to be solved therefore is to produce high resilience polyurethane foam having both low density (i.e. less than 35 kgm3) and an improved skin aspect.

According to the present invention there is provided a process for preparing high resilience polyurethane foam having a density of less than 35 kg.m3 which comprises preparing a formulation from (a) one or more polyols, (b) at least 3.0 parts by weight water per one hundred parts of polyol, (c) one or more isocyanates having a functionality greater than or equal to 2, (d) a foam stabiliser and (e) one or more catalysts for the formation of urethane linkages from (a) and (c), at least one of the catalyst being an amine which has blocked with an organic acid.

The invention solves the problem of poor skin aspect encountered in the prior art foams by employing a catalyst which at least in part consists of an amine blocked with a carboxylic acid.

In addition this approach reduces the rate of blowing and hence gives a better balance between blowing and gelling.

Any of the polyols currently used in making flexible cold cure polyurethane foam are suitable for this application. Illustrative of these polyols are polyoxyalkylene polyols which are alkylene oxide adducts of polyhydroxyalkanes. Alkylene oxides are for instance, ethylene, propylene, butylene oxide.

Polyhydroxyalkanesare for instance, glycerine, l,l,l-trimethylolpropane, penta erythritol sorbitol and the like.

The range of polyol used in this invention is however limited to those which are capped with ethylene oxide which give a high amount of primary OH groups and have high functionality. Suitably, the polyols must have at least 70X of primary OH groups as measured by ASTM D-4273, preferably between 75 - 90Z. The polyol functionality is defined as the number of OH group per molecule of polyol. For instance, while the nominal functionality of a polyol derived from glycerine is 3.0, the final value is generally lower.

Preferably, this value must be at least 2.6 or higher.

In addition to these polyols, polymer-polyols or grafted polyols can be used as such or blended with the above polyols. Such grafted polyols are obtained by polymerising one or more ethylenically unsaturated monomers dissolved in the polyol to form a stable dispersion of polymer particles in the polyol. Preferably, these monomers are styrene and acrylonitrile, although a variety of monomers may be utilised. Other suitable grafted polyols are obtained by polymerising hydrazine or alkanolamine with isocyanate.

Suitable isocyanates that contain at least two isocyanate groups and which are useful in producing polyurethane foams are well known in the art. Examples of preferred isocyanates are toluene diisocyanate (TDI - preferably a mixture of the 2.4 and 2.6 isomers) and crude MDI which is the product obtained by phosgenation of aniline. the crude MDI, which consists of the isomers of bis (isocyanato phenyl) methane and polymeric analogues thereof, can be used itself. Alternatively the isomers of bis (isocyanato phenyl) methane can be separated from crude MDI and used by themselves as can the polymeric analogues.

The amount of blowing agent, i.e. water, will depend upon the final foam density which is desired. For a density of less than 35 kgm~3 at least 3.5 parts by weight of water is required per hundred parts by weight of polyol. The invention is especially suitable for preparing foams of density less than 35 Kg.m'3 particularly in situations where no additional CFC blowing agent is used.

The use of silicone surfactants as foam stabilisers is well known in the art. In this application, preferable silicone surfactants belong to the 'non-hydrolysable" polysiloxane polyoxyalkylene block copolymers, where the polysiloxane moiety is linked to the polyoxyalkylene through carbon-silicon bonds, rather than via oxygen-silicon bonds.

Any known catalysts useful in producing flexible polyurethane foam may be employed. Typically, two classes of catalysts are important: (a) tertiary (and secondary) amine and (b) organotin catalysts. Examples of amine catalysts (a) are bis(2,2'-dimethylaminoethyl)ether, triethylamine, trimethylamine, N-ethylmorpholine, N-methylmorpholine, N,N-dimethylbenzylamine, N,N-dimethylethanolamine, N,N,N,N'-tetramethyl-1,3-butanediamine, pentamethyldipropylenetriamine, diethanolamine, triethanolamine, triethylenediamine, DBU, N,N dimethyl aminopropylamine and the like. Among organotin compounds are dialkyltin salts of carboxylic acids, e.g. dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dilauryltin diacetate, dioctyltin diacetate, dibutyltindilaurylmercaptide, and the like.

It is a feature of the present invention that at least part of the total catalyst is provided in the form of an amine whose reactivity has been blocked with an organic acid. The organic acid employed is suitably a monocarboxylic acid or a dicarboxylic acid, most suitably an aliphatics monocarboxylic or dicarboxylic acid having from 1 to 8 carbon atoms. Preferred monocarboxylic examples include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid and 2-ethylhexanoic acid. Preferred dicarboxylic examples include oxalic acid, malonic acid, succinic acid, fumaric acid and maleic acid.

The blocking reaction which forms the blocked amine is suitably a quaternisation reaction which yields a quaternary ammonium salt of the amine and the carboxylic acid. Such a quaternisation reaction involves reacting an appropriate amine with the organic acid, optionally in a solvent at or slightly above room temperature.

Preferred amines are those described above, the most preferred being bis-(2,2'-dimethylaminoethyl) ether and triethylenediamiize. The amount of blocked amine used in the formulations defined above is suitably in the range 0.01 to 2 parts by weight per hundred parts by weight of polyol, preferably in the range 0.05 to 0.5. Preferably at least 502 of the amine in the catalyst is blocked. In the case where some of the catalyst is left unblocked then it is preferable to use an excess of amine during the quarterisation reaction.

The formulation defined above is suitably prepared by mixing or blending methods well known to those skilled in the art.

Industrially, this will generally be achieved by employing automated or computer controlled mixing heads which mix the various components together before dosing an appropriate mould with the mixture. After the mould has been dosed, the mould is generally closed and the contents allowed to react, foam and subsequently cure. When cure is complete the final foam may be demoulded in the usual way. The foams produced are particularly suitable for furniture and automotive seating applications.

The invention is now illustrated by the following Examples.

Examples The following abbreviations are used: Polvol A: A polyether polyol made by reacting propylene oxide with glycerol in the presence of potassium hydroxide, capping with ethylene oxide and refining to remove the catalyst. The polyol contains about 16.5 weight percent ethylene oxide as a cap and has a hydroxyl number of about 35 and 75Z primary hydroxyl groups (Polyol 1735 - ex BPCI).

Polyol B: A polyether polyol made by reacting propylene oxide with glycerol in the presence of potassium hydroxide, capping with ethylene oxide and refining to remove the catalyst. The polyol contains about 19 weight percent ethylene oxide as a cap and has a hydroxyl number of about 35 and 85Z primary hydroxyl groups (ex BPCI).

Polmer-o1yol A: A grafted polymer-polyol having 16.5X of polystyrene and 18.5X of polyacrylonitrile in polyether polyol A as decribed above. The final hydroxyl number is approximately 25.

Polymer-polyol B: A grafted polymer-polyol having 19.6X of polystyrene and 8.4X of polyacrylonitrile in polyether polyol B as described above. The final hydroxyl number is approximately 25.

Catalyst A. B. C. D: quaternary ammonium salts as described in Example 1.

Catalyst E: dibutyltin dilaurylmercaptide.

Catalyst F: bis-(2-dimethylaminoethyl)ether (70Z in dipropylene glycol).

Catalyst G: triethylenediamine (33Z in dipropylene glycol).

Silicone A: A silicone surfactant sold for use in high resilience moulding foam by Union Carbide Corporation as "Silicone Surfactant Y-10.366".

TDI: A mixture of 80 weight percent 2,4-tolylene diisocyanate and 20 weight percent of 2,6-tolylene diisocyanate.

Example 1 The following example gives the preparation of catalyst as described in this invention. The other ammonium salts in the following Examples were prepared in a similar way (Table 1).

To a solution (70X) of bis-2(2-dimethyl aminoethyl)ether in dipropylene glycol (188g, 0.82 moles) in a vessel equipped with stirrer, dropping funnel and condenser, was added formic acid (34g, 0.74 mole). As the reaction is exothermic, the rate of addition is adjusted so that the temperature is kept below 40-C. After the addition of formic acid, the mixture is continuously stirred for another 15 minutes.

Table 1

Component Weight No. (vt 2) Ratio Amine:Acid Catalyst A 1 70.0 5.53 3 30.0 Catalyst B 2 33.0 8.79 3 67.0 Catalyst C 1 13.2 12.33 2 14.6 3 72.2 Catalyst D 1 23.6 7.41 2 20.1 3 56.3 ComPonents 1. Bis-(2-dimethyl aminoethyl)ether 2. Triethylenediamine 3. Dipropylene glycol ExamPle 2 In this example and the following, the moulding conditions are given hereafter. This comparative examples gives formulations using 4.0 php of water. Density obtained is approximately 33 kg/m3.

Processing Conditions Mixer (rpm : 2300 Premixing time(s) : 30 Mould type : Square 9 litres Mould temperature (C) : 60 Release agent : LK-260 (from Goldschmidt) Demould time (mins) : 6 Dosage : 50g Formulation 1 2 Polyol A 70 70 Polymer-polyol A 30 30 DEOA (885) 1.0 1.0 Water 4.0 4.0 Catalyst D - 0.5 Catalyst E 0.05 Catalyst F 0.15 0.15 Catalyst G 0.2 Silicone A 1.5 1.5 TDI 46.2 46.2 Reactivity Data Cream time(s) 7 7 Gel time(s) 62 50 Rise time(s) 75 70 Foam density (kg/m3) 33.0 33.0 Foam surface aspect Harsh and Smooth Paper-like skin Skin Example 3 This comparative example gives formulations using 5.0 php of water. Density obtained is approximately 29 kg/m3.

Formulation 1 2 Polyol A 60 60 Polymer-polyol A 40 40 Water 5.0 5.0 DEOA (88Z) 1.0 1.0 Catalyst C - 0.5 Catalyst E 0.025 Catalyst F 0.15 0.15 Catalyst G 0.2 Silicone A 1.5 1.5 TDI 55.6 55.6 Re act ivity Data Cream time(s) 7 7 Gel time(s) 67 64 Rise time(s) 79 83 Foam density (kg/m) 29.0 29.0 Foam surface aspect Total skin peeling No skin peeling - uniform smooth skin Example 4 This comparative examples gives formulations using 5.5 php of water. Density obtained is approximately 27 kg/m3.

Formulation 1 2 Polyol A 60 60 Polymer-polyol A 40 40 Water 5.5 5.5 Glycerol 1.0 1.0 DEOA (88%) 1.0 1.0 Catalyst A - 0.2 Catalyst B - 0.3 Catalyst E 0.03 Catalyst F 0.1 0.1 Catalyst G 0.2 Silicone A 1.5 1.5 TDI 61.5 61.5 Reactivity Data Cream times) 12 11 Gel time(s) 80 64 Rise time(s) 95 83 Foam density (kg/m3) 27.0 27.0 Foam sirface aspect Harsh, partial No skin peeling skin peeling Uniform smooth skin Example 5 This comparative example gives formulations using 6.0 php of water. Density obtained is approximately 25 kg/m3.

Formulation 1 2 Polyol 3 50 50 Polymer-polyol B 50 50 Water 6.0 6.0 Glycerol 1.5 1.5 DEOA (885) 1.2 1.2 Catalyst A - 0.2 Catalyst B - 0.3 Catalyst E 0.03 Catalyst F 0.1 0.1 Catalyst G 0.2 Silicone A 1.5 1.5 TDI 69.7 69.7 Reactivity Data Cream time(s) 11 11 Gel time(s) 81 74 Rise time(s) 93 75 Foam density (kg/m3) 25.0 25.0 Foam surface aspect Harsh and No skin major skin peeling peeling

Claims (1)

1. CLAIMS 1. A process for preparing high resilience polyurethane foam having a density of less than 35 kgm-3 which comprises preparing a formulation from (a) one or more polyols, (b) at least 3.0 parts by weight water per one hundred parts of polyol, (c) one or more isocyanates having a functionality greater than or equal to 2, (d) a foam stabiliser and (e) one or more catalysts for the formation of urethane linkages from (a) and (c), at least one of the catalyst being an amine which has blocked with an organic acid.