WO1997048757A1

WO1997048757A1 - Process for rigid polyurethane foams

Info

Publication number: WO1997048757A1
Application number: PCT/EP1997/002809
Authority: WO
Inventors: Walter Bazzo; Silvio Barettini; Colin Tweedale
Original assignee: Imperial Chemical Industries Plc
Priority date: 1996-06-20
Filing date: 1997-05-30
Publication date: 1997-12-24
Also published as: AU3169897A

Abstract

Process for the preparation of a rigid polyurethane or urethane-modified polyisocyanurate foam blown with a hydrochlorofluorocarbon, hydrofluorocarbon or hydrocarbon in the presence of tetramethylsilane as co-nucleating/co-blowing agent.

Description

DESCRIPTION

PROCESS FOR RIGID POLYURETHANE FOAMS

This invention relates to processes for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams, to foams prepared thereby, and to novel compositions useful m the process.

Rigid polyurethane and urethane-modified polyisocyanurate foams are in general prepared by reacting the appropriate polyisocyanate and lsocyanate- reactive compound (usually a polyol) in the presence of a blowing agent. One use of such foams is as a thermal insulation medium as for example in the construction of refrigerated storage devices. The thermal insulating properties of rigid foams are dependent upon a number of factors including, for closed cell rigid foams, the cell size and the thermal conductivity of the contents of the cells.

A class of materials which has been widely used as blowing agent in the production of polyurethane and urethane-modified polyisocyanurate foams are the fully halogenated chlorofluorocarbons, and in particular trichlorofluoromethane (CFC-11) . The exceptionally low thermal conductivity of these blowing agents, and in particular of CFC-11, has enabled the preparation of rigid foams having very effective insulation properties. Recent concern over the potential of chlorofluorocarbons to cause depletion 5 of ozone in the atmospnere has led to an urgent need to develop reaction systems m wnich chlorofluorocarbon blowing agents are replaced by alternative materials wnich are environmentally acceptable and which also produce foams naving the necessary properties for the many applications in wnich they are used. ϋ

Such alternative blowing agents proposed m the prior art include nydrochlorof±ucrocarbons, hydrofluorocarbons and especially hydrocarbons namely alkanes and cyc_^oalκanes such as n-pentane, isopentane, cyclopentane and mixtures thereot. Altnouq^ tnese materials are environmentally more s acceptable than chlorofluorocarbons they are inferior in thermal insulation

In order to improve the thermal insulation of rigid polyurethane and uretnane-modifled polyisocyanurate foams olown with such alternative blowing agents a variety of techniques have been proposed, most of them concentrated 0 on decreasing the foam cell sizes by adding insolub-e fluorinated compounds as descriDed in US 4972002, US 5034424, US 49818^"'9 But these insoluble fluorinated adαitives are expensive and detrimental to the environment.

Tnererore ±.t is an ooject cf tne present invention to provide rigic polyurethane or urethane-modified polyisocyanurate foams which have, even when blown with alternative environmentally acceptable blowing agents such as (cyclo) alkanes, satisfactory thermal insulation properties without detrimentally affecting the other physical properties.

It is another object of the present invention to provide rigid polyurethane or urethane-modified polyisocyanurate foams having cells of decreased size made without using insoluble fluorinated compounds.

These objects are met by using in the process of making rigid polyurethane or urethane-modified polyisocyanurate foams from polyisocyanates and isocyanate-reactive components in the presence of environmentally acceptable blowing agents such as hydrochlorofluorocarbons, hydrofluorocarbons and hydrocarbons alkylsilanes as co-blowing agents .

Foams prepared by the process of the present invention show better thermal insulation initially as well as aged than foams from the prior art prepared in the absence of alkylsilanes, largely due to a decrease in cell size, generally m the range 10 to 20 - . Cell sizes in the range 250 to 330 um are obtained whereas the reference foam has a cell size in the range 350 to 400 μm. Further physical properties are at least comparable or even improved (as is the case for compression strength) .

Examples of alkylsilanes to be used in the process of the present invention include tetramethylsilane, trimethylsilane and hexamethyldisilane. Especially tetramethylsilane is preferred.

Tetramethylsilane is known as a blowing agent for rigid polyurethane foam (see JP 52/6276C, JP 02/215845 and DE 4440026) . Its combination witn environmentally acceptable blowing agents has not been described heretooefore.

The alkylsilanes are used m the process of the present invention in an amount of from 0.1 to 10 pDw, preferably of from 0.1 to 5 pbw, more preferably of from 0.5 tc 3 pbw per 100 pow of isocyanate-reactive composition.

Suitable isocyanate-reactive compounds to be useα in the process of the present invention include any of those known in the art for tne preparation of rigid polyurethane or urethane-modified polyisocyanurate foams. Of particular importance for tne preparation of rigid foams are polyols and polyoi mixtures having average hydroxyl numbers of from 300 to 1000, especially from 300 to 700 mg KOH/g, and hydroxyl functionalities of from 2 to £ , especially from 3 to ≤. Suitable polyols have seen fully described in the prior art and include reaction products of alkylene oxides, for example ethylene oxide and/or propylene oxide, with initiators containing from 2 to 8 active hydrogen atoms per molecule. Suitable initiators include: polyols, for example glycerol, trimethylolpropane, tπethanolamine, pentaerythritol, sorbitol and sucrose; polyamines, for example ethylene diamine, tolylene diamine (TDA) , diaminodiphenylmethane (DADPM) and polymethylene polyphenylene polyamines; and aminoalcohols, for example ethanolamine and diethanolamine; and mixtures of such initiators. Other suitable polymeric polyols include polyesters obtained by the condensation of appropriate proportions of glycols and higher functionality polyols with dicarboxylic or polycarboxylic acids. Still further suitable polymeric polyols include hydroxyl terminated polythioethers, polyarmdes, polyesteramαdes, polycarbonates, polyacetals, polyolefins andpolysiloxanes.

Suitable organic polyisocyanates for use in the process of the present invention include any of those known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams, and in particular the aromatic polyisocyanates such as diphenylmethane dusocyanate in the form of its 2,4'-, 2,2'- and 4,4'-isomers and mixtures thereof, the mixtures 0 of diphenylmethane dusocyanates (MDI) and oligomers thereof known in the art as "crude" or polymeric MDI (polymethylene polyphenylene polyisocyanates) having an isocyanate functionality of greater than 2, toluene dusocyanate in the form of its 2,4- and 2,6-ιsomers and mixtures thereof, 1, 5-naphthalene dusocyanate and 1, 4-dιιsocyanatobenzene. Other 5 organic polyisocyanates which may be mentioned include the aliphatic dusocyanates such as isophorone dusocyanate, 1, 6-dιιsocyanatohexane and 4,4' -dnsocyanatodicyclohexylmethane.

The quantities of the polyisocyanate compositions and the polyfunctional ϋ isocyanate-reactive compositions to be reacted will depend upon the nature of the rigid polyurethane or urethane-modified polyisocyanurate foam to be produced and will be readily determined by those skilled in the art.

Tne process of the present invention is carried out in the presence of any " of tne environmentally acceDtable Dnysical blowing agents known in the art ror tne preparation of rigid polyurethane or urethane-modified po±yisocyanurate foams Such blowing agents include dialkyl ethers, alkyl αlκanoates, aliphatic and

hydrofluorocarbons,

fluorine-containing ethers and especially _^ nydrocaroors

Suitable hydrocarbon blowing agents include lower aliphatic or cyclic hydrocarbons such as isobutane, pentane, iso-pentane, cyclopentane, neopentane, nexane, ana cyclohexane and any mixtures thereof, especially mixtures of cyclopentane and isobutane and mixtures of cyclopentane and ISO- or n-pentane.

Suitable dialkyl ethers to be used as blowing agents include compounds having from 2 to 6 carbon atoms. As examples of suitable ethers there may be mentioned dimethyl ether, methyl ethyl ether, diethyl ether, methyl propyl ether, methyl isopropyl ether, ethyl propyl ether, ethyl isopropyl ether, dipropyl ether, propyl isopropyl ether, diisopropyl ether, methyl butyl ether, methyl isobutyl ether, methyl t-butyl ether, ethyl butyl ether, ethyl isobutyl ether, and ethyl t-butyl ether.

Suitable alkyl alkanoates which may be used as blowing agents include methyl formate, methyl acetate, ethyl formate and ethyl acetate.

Suitable hydrofluorocarbons which may be used as blowing agents include lower hydrofluoroalkanes, for example difluoromethane, 1, 2-dιfluoroethane, 1,1,1,4,4, 4-hexafluorobutane, 1,1,1,3, 3-pentafluorobutane, 1,1,1,3,3- pentafluoropropane, pentafluoroethane, 1, 1, 1, 2-tetrafluoroethane and 1,1,2, 2-tetrafluoroethane.

Suitable hydrochlorofluorocarbons which may be used as blowing agents include chlorodifluoromethane, 1, l-dιchloro-2, 2, 2-trιfluoroethane, 1, 1-dιchloro-l-fluoroethane, 1-chloro-l, 1-dιfluoroethane, 1-chloro- 2-fluoroethane, and 1, 1, 1, 2-tetrafluoro-2-chloroethane.

Suitable fluorine-containing ethers which may be used as blowing agents include bis- (trifluoromethyl ) ether, tπfluoromethyl difluoromethyl ether, metnyi fluoromethyl ether, methyl trifluoromethyl ether, bis- (difluoromethyl) ether, fluoromethyl difluoromethyl ether, metnyi difluoromethyl ether, bis- \ fluoromethylj ether, 2, 2, 2-trιfluoroethyl difluoromethyl ether, pentafluoroethyl trifluoromethyl ether, pentafluoroethyl difluoromethyl ether, 1, 1, 2, 2-tetrafluoroethyl difluoromethyl ether, 1, 2,2, 2-tetrafluoroethyl fluoromethyl ether, 1, 2, 2-trιfluoroethyl difluoromethyl ether, 1, 1-dιfluoroethyl metnyi ether, 1, 1, 1, 3, 3, 3-nexafluoroprop-2-yl fluoromethyl ether.

Preferred blowing agents for use in the process are those having coiling points oetween -70°C and +80°C at atmospheric pressure.

Examples of preferred blowing agents include isobutane, pentane, isopentane, cyclopentane, 1, 1-dιchloro-l-fluoroethane (HCFC 141b), 1,1,1,2- tetrafluoroethane (HFC 134a; and 1, 1, 1, 3, 3-pentafluoropropane (HFC 245fa) . Mixtures of cyclopentane and isooutane or cyclopentane and n- or isopentane are particularly preferred. In the case of hydrocarbon blowing a blend of tetramethylsilane and isopentane (35/65) as supplied by Huls under the name 'Huls additive 6562' can suitably be used.

Generally water or other carbon dioxide-evolving compounds are used together with the physical blowing agents. Where water is used as chemical co- blowmg agent typical amounts are in the range from 0.2 to 5 % , preferably from 0.5 to 3 ^ by weight based on the isocyanate-reactive compound.

The total quantity of blowing agent to be used in a reaction system for producing cellular polymeric materials will be readily determined by those skilled in the art, but will typically be from 2 to 25 % by weight based on the total reaction system.

In order to further reduce the cell sizes of the foam and accordingly to improve the thermal insulation properties an insoluble fluorinated compound may be used in the foam-forming process according to the present invention. Such insoluble fluorinated compounds include any of those disclosed in US 4981879, US 5034424, US 4792002, EP 508649 and WO 95/18176.

In addition to the polyisocyanate and polyfunctional isocyanate-reactive compositions and the blowing agents, the foam-forming reaction mixture will commonly contain one or more other auxiliaries or additives conventional to formulations for tne production of rigid polyurethane and urethane-modified polyisocyanurate foams. Such optional additives include crosslmking agents, for examples low molecular weight polyols such as triethanolamine, foam-staDilising agents or surfactants, for example siloxane-oxyalkylene copolymers, urethane catalysts, for example tin compounds such as stannous octoate or dibutyltm dilaurate or tertiary amines such as dimetnylcyclohexylamine or tπethylene diamine, fire retardants, for example halogenated alkyl phosphates sucn as tris chloropropyl phospnate, and fillers such as carbon black.

The alkylsilanes can be added to the polyisocyanate composition or to the isocyanate-reactive composition or to both.

Since tne alkylsilanes are generally not soluble _^n tne polyisocyanate and polyol compositions emuisifiers may be added. Suitable emulsifiers include silicones and Diock copolymers of ethylene oxide and/cr propylene oxide such as the TWEEN and SPAN range of products available rrom Imperial Chemical Industries.

The alkylsilanes are Dreferably added tc the isocyanate-reactive composition. In tnat case certain polyols might oe more suitable to emulsify tne

in the isocyanate-reactive composition. For example, particularly in the case of hydrocarbon blowing, such as C₅- (cyclo) alkane blowing (cyclopentane, n-pentane, isopentane), the use of aromatic amine initiated polyether polyols such as TDA and in particular DADPM initiated polyether polyols is beneficial; a further improvement in thermal insulation is observed. These aromatic aπune initiated polyether polyols are then used in an amount of at least 20 % by weight based on total isocyanate-reactive components.

In operating the process for making rigid foams according to the invention, the known one-shot, prepolymer or serrα-prepolymer techniques may be used together with conventional mixing methods and the rigid foam may be produced in the form of slabstock, mouldings, cavity fillings, sprayed foam, frothed foam or laminates with other materials such as hardboard, plasterboard, plastics, paper or metal.

It is convenient in many applications to provide the components for polyurethane production in pre-blended formulations based on each of the primary polyisocyanate and isocyanate-reactive components. In particular, many reaction systems employ a polyisocyanate-reactive composition which contains the major additives such as the blowing agent and the catalyst in addition to the polyisocyanate-reactive component or components.

Therefore the present invention also provides a polyisocyanate-reactive composition comprising an alkylsilane and a polyisocyanate composition comprising an alkylsilane.

The various aspects of this invention are illustrated, but not limited by the following examples.

The following formulation and reaction components are referred to in the examples:

Polyol 1 a polyether polyol of OH value 460 mg KOH/g. Polyol 2 a polyether polyol of OH value 310 mg KOH/g.

Polyol 3- a polyether polyol of OH value 495 mg KOH/g. Surfactant: a mixture of silicone surfactants

Catalyst: a mixture of amine catalysts.

Huls additive 6562: a tetrametnylsilane/isopentane blend (35/65) available from Huls. cyclopentane- tecnnical grade cyclopentane. SUPRASEC DNR: polymeric MDI available from Imperial Chemical Industries.

SUPRASEC is a trademark of Imperial Chemical Industries. EXAMPLE 1 :

Rigid polyurethane foams were prepared from the ingredients listed below in Table 1. Reaction profile was followed in respect of cream time and string time.

On the obtained foams the following properties were measured: full rise density, compression strength of a sample of density 33 kg/m³ (according to standard ISO 844), thermal conductivity of a sample of density 32 kg/m³ (lambda) (according to standard ASTM C 518) and cell size (according to the method described in "The Elimination of Radiative Heat Transfer in Fine Celled Polyurethane Rigid Foams" by G. Eeckhout and A. Cunningham, Proceedings of Society of Plastics Industry, 1994). The results are given in Table 1.

These results show that foams of the present invention made using tetramethylsilane as co-blowing agent have improved thermal insulation properties initially as well as aged, finer cells and higher compression strengths than foams of the prior art made in the absence of this tetramethylsilane.

Table 1

Claims

1. Process for preparing rigid polyurethane or urethane-modified polyisocyanurate foams comprising the step of reacting an organic polyisocyanate with a polyfunctional isocyanate-reactive component in the presence of an environmentally acceptable blowing agent, characterised in that an alkylsilane is used as a co-blowing agent.

2. Process according to claim 1 wherein the alkylsilane is tetramethylsilane.

3. Process according to claim 1 or 2 wherein the amount of alkylsilane is in the range 0.1 to 10 pbw per 100 pbw of isocyanate-reactive composition.

4. Process according to claim 3 wherein the amount of alkylsilane is in the range 0.5 to 3 pbw per 100 pbw of isocyanate-reactive composition.

5. Process according to any one of the preceding claims wherein the environmentally acceptable blowing agent is selected from the group consisting of hydrofluorocarbons, hydrochlorofluorocarbons and nydrocarbons.

6. Process according to claim 5 wherein the hydrocarbon blowing agent is selected form the group consisting of isobutane, n-pentane, isopentane and/or cyclopentane

7. Process according to claim 6 wherein the hydrocarbon blowing agent is a mixture of isopentane ana cyclopentane.

8. Process according to any one of the preceding claims wherein the isocyanate-reactive composition comprises a polyetner polyol initiated with an aromatic amine.

9 Process according to claim 3 wherein said aromatic amine initiated polyether polyol is present in an amount of at least 20 - by weight based on total isocyanate-reactive components.

l _* . Process according to claim 8 or 9 wnerein the aromatic amine comprises diaminodiphenylmethane and/or higher homologues tnereof or tolylene diamine.

11 Rigid polyurethane or urethane-modified polyisocyanurate foams obtainable by the process as defined in any one of the preceding claims .

12. Isocyanate-reactive composition comprising an alkylsilane.

13. Composition according to claim 12 wherein the alkylsilane is tetramethylsilane.

14. Composition according to claim 12 or 13 wherein the amount of alkylsilane is in the range 0.1 to 10 pbw per 100 pbw of isocyanate- reactive composition.

15. Composition according to any one of claims 12, 13 and 14 wherein the composition further comprises a hydrocarbon blowing agent.

16. Composition according to claim 15 wherein the hydrocarbon blowing agent is selected from the group consisting of isobutane, n-pentane, isopentane, cyclopentane or any mixture thereof.

17. Composition according to any one of claims 12 to 16 wnerem the composition comprises an aromatic amine initiated polyether polyol.

18. Composition according to claim 17 wherein said aromatic amine initiated polyether polyol is present in an amount of at least 20 * by weight.

19. Composition according to claim 17 or 18 wherein the aromatic amine comprises diaminodiphenylmethane or any mgher homologue thereof or tolylene diamine.

! 0 . Polyisocyanate composition comprising an alkyl silane .