HK1020745A - Rigid isocyanurate-modified polyurethane foams - Google Patents

Description

Rigid isocyanurate-modified polyurethane foams

The present invention relates to rigid isocyanurate-modified polyurethane foams and to a process for their preparation.

Rigid isocyanurate-modified polyurethane foams are, in general, prepared by reacting a stoichiometric excess of polyisocyanate with isocyanate-reactive compounds in the presence of blowing agents, surfactants, and catalysts. One use of such foams is as a thermal insulation medium in, for example, buildings.

In general, isocyanurate-modified polyurethane foams exhibit better fire resistance than polyurethane foams due to the presence of isocyanurate groups; however, these foams tend to be extremely brittle, leading to deterioration of other properties such as surface cure and adhesion. In order to obtain good fire-retardant properties, polyester polyols are advantageously used as isocyanate-reactive compounds in the manufacture of isocyanurate-modified polyurethane foams. Generally these polyester polyols are of an aromatic nature and in some cases are used in combination with polyether polyols.

It is therefore an object of the present invention to provide a rigid isocyanurate-modified polyurethane foam having a combination of desirable properties, including suitable reaction characteristics and reduced brittleness.

According to the present invention, rigid isocyanurate-modified polyurethane foams are provided which are formed by reacting an organic polyisocyanate composition with an isocyanate-reactive composition having an isocyanate index of 180 to 380% (preferably 200 to 270%, most preferably 220 to 250%), wherein the isocyanate-reactive composition comprises an aliphatic polyester polyol and an aromatic polyester polyol.

The isocyanurate-modified polyurethane foams of the present invention are less brittle than prior art polyurethane foams made solely from aromatic polyester polyols, resulting in improved physical properties such as surface cure and adhesion.

They are particularly useful in the manufacture of building panels in which the foam is coated onto one or more non-combustible outer skins.

U.S. Pat. No. 5,430, 2551 describes the use of polymer dispersions in the manufacture of rigid polyisocyanurate foams. These polymer dispersions comprise a continuous phase and a dispersed phase; polyester polyols may be used as the continuous phase. The invention is not carried out by using polymer dispersions.

U.S. patent 4859523 describes the use of aromatic polyester polyols along with aliphatic polyester polyols in the manufacture of viscoelastic resins (and thus not rigid polyisocyanurate foams).

French patent 1548298 relates to the use of mixtures of aliphatic and aromatic polyester polyols in the manufacture of thermoplastic polyester-urethanes (and therefore not rigid polyisocyanurate foams).

The term isocyanate index as used herein is meant to denote the molar ratio of NCO-groups to reactive hydrogen atoms present in a foam formulation, other than those derived from any water present, expressed as a percentage.

The polyester polyols used in the present invention advantageously have an average functionality of about 1.8 to 8, preferably about 1.8 to 5 and more preferably about 2 to 2.5. The hydroxyl number is typically in the range of about 15 to 750, preferably about 30 to 550 and more preferably about 200 to 500, mg KOH/g. Preferably the polyester polyol has an acid number between 0.1 and 20 mg KOH/g; the acid number can be as high as 90 mg KOH/g in general.

The polyester polyols of the present invention can be prepared by known procedures from a polycarboxylic acid or acid derivative, such as an anhydride or ester of a polycarboxylic acid, and any polyol component. In the preparation of the polyester polyol, the polybasic acid and/or the polyhydric alcohol component may be used in the form of a mixture of two or more compounds.

The polyols may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic. Low molecular weight aliphatic polyhydric alcohols, such as aliphatic dihydric alcohols having no more than about 20 carbon atoms are highly desirable. The polyols may optionally include substituents that are inert in the reaction, for example, chlorine and bromine substituents, and/or may be unsaturated. Suitable amino alcohols may also be used, such as, for example, monoethanolamine, diethanolamine, triethanolamine, or the like. A preferred polyol component is a diol. The diol may contain heteroatoms (e.g., thiodiglycol) or may be composed entirely of carbon, hydrogen and oxygen. They are advantageously of the formula C_nH_2n(OH)₂Simple diols or polyglycols distinguished by the insertion of ether linkages in the hydrocarbon chain, e.g. by the general formula C_nH_2nO_x(OH)₂And a representative. Examples of suitable polyhydric alcohols include: ethylene glycol, propylene glycol- (1,2) and- (1,3), butylene glycol- (1,4) and- (2,3), hexylene glycol- (1,6), octanediol- (1,8), neopentyl glycol, 1, 4-bishydroxymethylcyclohexane, 2-methyl-1, 3-propanediol, glycerol, trimethylolethane, hexanetriol- (1,2,6), butanetriol- (1,2,4), quinolones, methylglycosides, triethylene glycol, tetraethylene glycol and higher polyethylene glycols, dipropylene glycol and higher polypropylene glycols, diethylene glycol, glycerol, pentaerythritol, trimethylolpropane, sorbitol, mannitol, dibutylene glycol and higher polybutylene glycols.Particularly suitable polyols are alkylene glycols and oxyalkylene glycols, such as ethylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, tetraethylene glycol, tetrapropylene glycol, trimethylene glycol, tetramethylene glycol and 1, 4-cyclohexanedimethanol (1, 4-bis-hydroxymethylcyclohexane).

The polycarboxylic acid component may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic and may optionally be substituted, for example, by halogen atoms, and/or may be unsaturated. Examples of suitable carboxylic acids and derivatives thereof for use in the preparation of polyester polyols include: oxalic acid, malonic acid, adipic acid, glutaric acid, succinic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic anhydride, terephthalic anhydride, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrophthalic anhydride, 1,2,4, 5-benzenetetracarboxylic dianhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, dimethyl terephthalate, bis-ethylene terephthalate, fumaric acid, di-and tri-basic unsaturated fatty acids optionally mixed with monobasic unsaturated fatty acids, such as oleic acid.

While polyester polyols may be prepared from substantially pure reactant materials, more complex ingredients may be used, such as side streams, waste materials, and slag residues from the manufacture of phthalic acid, terephthalic acid, dimethyl terephthalate, polyethylene terephthalate, and the like. These compositions can be converted to polyester polyols by reaction with polyols via conventional transesterification or esterification procedures.

The polyester polyols are produced by simply reacting the polycarboxylic acid or acid derivative with the polyol component in a known manner until the hydroxyl and acid values of the reaction mixture are within the desired ranges. After transesterification or esterification, the reaction product may optionally be reacted with an alkylene oxide.

As used herein, the term "polyester polyol" includes any minor amount of unreacted polyol left after preparation of the polyester polyol and/or unesterified polyol (e.g., diol) added after preparation. The polyester polyol may advantageously include up to about 40 weight percent free diol. Preferably, the free diol content is from 2 to 30, more preferably from 2 to 15 wt.% of the total polyester polyol component.

Among aliphatic polyester polyols, the polyols and polycarboxylic acids used to produce the polyester polyols are aliphatic compounds. However, certain polyols or polycarboxylic acids may be of aromatic nature; the aromatic character of the aliphatic polyester polyol (expressed as weight% of the groups containing at least one aromatic ring per molecule) is less than 50%.

In the aromatic polyester polyol, at least one of the polyhydric alcohol or polycarboxylic acid, preferably an acid, is an aromatic compound and the aromaticity is at least 50%. Polyester polyols whose acid component advantageously comprises at least 30% by weight of phthalic acid (or isomer thereof) residues are particularly useful. Preferably, the aromatic character of the aromatic polyester polyol is between 70 and 90%. Preferred aromatic polyester polyols are crude polyester polyols obtained by transesterification of crude reaction residues or polyester resin residues.

One or more different aromatic and one or more different aliphatic polyester polyols may be used according to the present invention. The weight ratio of aromatic to aliphatic polyester polyols used in the present invention is preferably between 90: 10 and 20: 80, more preferably between 80: 20 and 30: 70, most preferably between 80: 20 and 40: 60.

For the production process of the isocyanurate-modified polyurethane foam of the present invention, the above-mentioned polyester polyol preferably constitutes the total amount of the reactive mixture to be reacted with the polyisocyanate; however, it will be appreciated that these polyols may also be used in admixture with other isocyanate-reactive compounds commonly used in the art: preferably, the isocyanate-reactive composition comprises at least 90% by weight of the polyester polyol described above.

The isocyanate-reactive compounds that may be used in combination with the polyester polyol in the preparation of the isocyanurate-modified polyurethane foams of the present invention include any compounds known in the art for such purposes. Of particular importance for the preparation of rigid foams are polyols and polyol mixtures having an average hydroxyl number of from 300 to 1000 (in particular from 300 to 700) mg KOH/g, and a hydroxyl functionality of from 2 to 8 (in particular from 3 to 8). Suitable polyols have been fully described in the prior art and include the reaction products of alkylene oxides, such as ethylene oxide and/or propylene oxide, with initiators containing from 2 to 8 active hydrogen atoms per molecule. Suitable initiators include: polyhydric alcohols such as glycerin, trimethylolpropane, triethanolamine, pentaerythritol, sorbitol, and sucrose; polyamines such as ethylenediamine, tolylenediamine, diaminodiphenylmethane, and polymethylenepolyphenylenepolyamine; and aminoalcohols, such as ethanolamine and diethanolamine; and mixtures of such initiators. Additional suitable polymeric polyols include hydroxyl-terminated polythioethers, polyamides, polyesteramides, polycarbonates, polyacetals, polyolefins and polysiloxanes.

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 isocyanurate-modified polyurethane foams, and in particular aromatic polyisocyanates such as diphenylmethane diisocyanate in the form of 2,4 ' -, 2 ' -and 4,4 ' -isomers and mixtures thereof, mixtures of diphenylmethane diisocyanate (MDI) with oligomers thereof having an isocyanate functionality greater than 2, known in the art as "crude" or polymeric MDI (polymethylene polyphenylene polyisocyanate), toluene diisocyanate in the form of its 2, 4-and 2, 6-isomers and mixtures thereof, 1, 5-naphthalene diisocyanate and 1, 4-diisocyanato (diisocyanato) benzene. Other organic polyisocyanates which may be mentioned include aliphatic diisocyanates such as isophorone diisocyanate, 1, 6-diisocyanato (diisocyanato) hexane and 4, 4' -diisocyanatodicyclohexylmethane. For use in the process of the present invention, further suitable polyisocyanates are described in European patent A-0320134.

Modified polyisocyanates, such as carbodiimide or uretonimine modified polyisocyanates, may also be used.

Still other useful organic polyisocyanates are isocyanate-terminated prepolymers prepared by reacting an excess of organic polyisocyanate with a minor amount of an active hydrogen-containing compound.

The preferred polyisocyanate for use in the present invention is polymeric MDI.

The amount of the reacted polyisocyanate composition and the polyfunctional isocyanate-reactive composition is such that the molar ratio of isocyanate groups (NCO) to active hydrogen groups (OH) (excluding water) is generally between 180 and 380%, preferably between 200 and 270% and most preferably between 220 and 250%.

The process of the present invention is carried out in the presence of any blowing agent known in the art for the preparation of rigid isocyanurate-modified polyurethane foams. Such blowing agents include water or other carbon dioxide-evolving compounds, or inert low boiling compounds having a boiling point above-70 ℃ at atmospheric pressure.

When water is used as blowing agent, the amount may be selected in a known manner to provide a foam of the desired density, typically in an amount in the range of from 0.05 to 5% by weight, based on the total reaction system.

Suitable inert blowing agents include those well known and described in the art, for example, hydrocarbons, dialkyl ethers, alkyl alkanoates, aliphatic and cycloaliphatic hydroxides, hydrochlorofluorocarbons, chlorofluorocarbons, hydrochlorocarbons, and fluorine-containing ethers.

Examples of preferred blowing agents include isobutane, n-pentane, isopentane, cyclopentane or mixtures thereof, 1, 1-dichloro-2-fluoroethane (HCFC 141b), 1,1, 1-trifluoro-2-fluoroethane (HFC 134a), chlorodifluoromethane (HCFC 22), 1, 1-difluoro-3, 3, 3-trifluoropropane (HFC 245fa), and blends thereof.

Particular mention may be made of the blowing agent mixtures described in WO 96/12758, and incorporated herein by reference, for the production of low density, dimensionally stable rigid foams. These blowing agent mixtures generally comprise at least three and preferably at least four components, of which preferably at least one is a (cyclo) alkane (preferably of 5 or 6 carbon atoms) and/or acetone.

The blowing agent is used in an amount sufficient to provide the foam with the desired bulk density, which is generally in the range of from 15 to 70 kg/m, preferably from 20 to 50 kg/m, most preferably from 25 to 40 kg/m. Typical amounts of blowing agent are in the range of from 2 to 25% by weight, based on the total reaction system.

When a blowing agent has a boiling point at or below ambient temperature, it is maintained under pressure until mixed with the other ingredients. Alternatively, it may be maintained at a temperature below ambient until mixed with the other ingredients.

In addition to the polyisocyanate and polyfunctional isocyanate-reactive composition and blowing agent, the foam-forming reaction mixture will generally include one or more other adjuvants or additives commonly used in formulations for the production of rigid isocyanurate-modified polyurethane foams. Such optional additives include crosslinking agents, e.g., low molecular weight polyols such as triethanolamine, processing aids, viscosity reducers, dispersants, plasticizers, mold release agents, antioxidants, fillers (e.g., carbon black), cell size regulators such as insoluble fluorinated compounds, e.g., as described in U.S. Pat. No. 4981879, U.S. Pat. No. 5034424, U.S. Pat. No. 4972002, European patent 0508649, European patent 0498628, WO 95/18176), catalysts, surfactants such as polydimethylsiloxane-polyoxyalkylene block copolymers, and non-reactive and reactive flame retardants, e.g., halogenated alkyl phosphates such as trichloropropyl phosphate, triethyl phosphate, diethyl ethylphosphonate, and dimethyl methylphosphonate. The use of such additives is well known to those skilled in the art.

Catalysts useful in the present invention include catalysts that promote the formation of isocyanurates. Examples include alkali metals or bases of carboxylic acidsAn earth metal salt. The cation of the organic acid metal salt, which is preferably an alkali metal salt, is advantageously K or Na, more preferably K. Particularly preferred is C₁-C₈Carboxylates, including sodium and potassium salts of formic, acetic, propionic, and 2-ethylhexanoic acids.

Other suitable trimerisation catalysts include triazine compounds such as Polycat 41 (available from Air Products) and quaternary ammonium carboxylates.

Catalyst compositions such as those described in european patent 228230 and british patent 2288182; including combinations with urethane catalysts such as tertiary amines that promote reaction between isocyanate groups and an active hydrogen-containing group.

In operating the process for producing rigid foams according to the invention, which may be produced in the form of foamed plastic blocks (slabstock), fillets (moulding), pocket fillers, sprayed foam, frothed foam or in the form of multi-layer sheets with other materials such as rigid boards, plasterboards, plastics, paper or metal, the known one-pot reaction (one-shot), prepolymer or semi-prepolymer techniques may be used together with the usual mixing methods.

In the manufacture of rigid polyurethane foams, the use of two pre-formulated compositions, commonly referred to as the a-component and the B-component, is a commonly practiced method. Generally, the A-component contains a polyisocyanate compound and the B-component contains a polyol together with a blowing agent, a catalyst and other auxiliaries.

The foams of the present invention are advantageously used to make multi-layer sheets, wherein the foam is supplied on one or both sides in a sheet-covering sheet (sheeting). Multilayer sheets are advantageously manufactured in a continuous manner by depositing a foamable mixture on a facing sheet conveyed along a production line, and preferably positioning another facing sheet over the deposited mixture. Any facing sheet previously used to make building panels may be used, which may have a rigid or flexible nature.

Various aspects of the invention are illustrated by, but not limited to, the following examples, in which the following ingredients are used: DALTOLAC P710: an aliphatic polyester polyol (28% aromatic) available from ICI (Imperial Chemical Industries). STEPANPOL PS 2502A: an aromatic polyester polyol (75% aromatic) available from Stepan company (Stepan). Isoexter 4537: an aliphatic polyester polyol available from billionm Corporation (COIM). DALTOLAC R105: a polyether polyol available from ICI corporation. Isoexter 4565: an aliphatic polyester polyol available from billionm corporation. DALTOLAC P744: an aliphatic polyester polyol available from ICI corporation. Terate 203: an aromatic polyester polyol (89% aromatic) available from Hoechst Celanese corporation. Terate 2541: an aromatic polyester polyol (78% aromatic) available from husky brocade corporation. TCPP: trichloropropyl phosphate, a fire retardant available from Courtalds company. Polycat 43: a catalyst available from air products company. L6900: a silicone surfactant available from OSI corporation. Niax Al: a catalyst available from eisai corporation. Catalyst LB: a catalyst available from ICI corporation. Polycat 8: a catalyst available from air products company. DMEA: a catalyst available from ICI corporation. SUPRASEC 2085: a polymeric MDI available from ICI corporation. SUPRASEC and DALTOLAC are trademarks of ICI corporation. Example 1

Rigid foams were prepared from the ingredients listed in table 1 below. The reaction characteristics are related to the cream time (fresh time), string time (string) and the viscosity breaking time arrangement. The Free rise density (Free rie density) was determined (according to standard DIN 53420). The surface friability of the foams obtained was visually checked and the adhesion of the Facing (Facing adhesion) was measured according to the standard ASTM D162. Peel adhesion (Paper peel adhesion) was assessed qualitatively with 100 grams per square meter of Paper; 1 indicates good (paper breaks), 2 indicates medium stripping requiring some strength, and 3 indicates poor (stripping is easy).

The results are shown in table 1 below.

The results show that the use of aliphatic polyester polyols plus aromatic polyester polyols reduces the brittleness of the foams obtained and improves adhesion. TABLE 1

Foam number		1	2	3	4	5	6	7	8	9
											DALTOLAC P710	Parts by weight						24.8	37.2
STEPANPOL PS2502A	Parts by weight					24.8
											Isoexter 4537	Parts by weight		30	30						30
DALTOLAC R105	Parts by weight	5	5	5	5				10	5
											Isoexter 4565	Parts by weight		7	7	6					7
DALTOLAC P744	Parts by weight				32.8
											Terate 203	Parts by weight					24.8	24.8	12.4
Terate 2541	Parts by weight	95	58	58	32.8				90	60
											TCPP	Parts by weight				5	6	6	6
Polycat 43	Parts by weight	1	1.7	1.7	1.5					2
											L6900	Parts by weight	2	2	2	2	2	2	2	2	2
Niax Al	Parts by weight	0.2	0.3	0.3	0.3				0.3	0.3
											Catalyst LB	Parts by weight	1	1.5	1.5	1.5	2	2	2	1.5	1.5
Polycat 8	Parts by weight				0.5	0.4	0.4	0.4	0.75	1
											DMEA	Parts by weight	1	1.3	1.3

Water (W)	Parts by weight	2	2.5	2.3	2.1	0.4	0.4	0.4	0.5	0.5
											N-pentane	Parts by weight	9	9	9	9	12	12	12
HCFC 141b	Parts by weight								37	39
											SUPRASEC 2085	Parts by weight	230	268	221	192	143.2	143	143	220	235
Index of refraction	％	275	262	212	223	362	356	373	262	262
											Aromatic polyester/Total polyester	％	100	61	61	46	100	50	25	100	62
Milk white time	Second of	10		11	12	13	12	14	13	9
											Time of wire drawing	Second of	45		37	44	37	38	42	29	22
Time to tack free	Second of	55		42			58	64	33	24
											Density of	Kilogram per cubic meter	35	30.2	26.9	27.2		31.6	31.6	33	33
Surface brittleness		Height of	Medium and high grade	Medium and high grade	Stilbene mixture	Height of	Medium and high grade	Is low in	Height of	Is low in
											Paper stripping adhesion		3	2	2	1	3	2	1	3	1
Adhesion of surface layer	Kilopascal	3	40	55	160	5	47	177	8	189

Claims (23)

1. A process for the manufacture of rigid isocyanurate-modified polyurethane foam comprising the step of reacting an organic polyisocyanate composition with an isocyanate-reactive composition having an isocyanate index of 180 to 380% in the presence of a blowing agent, characterized in that the isocyanate-reactive composition comprises an aliphatic polyester polyol and an aromatic polyester polyol.

2. The process according to claim 1, wherein the process is carried out in the absence of a polymer dispersion.

3. The process according to claim 1 or 2, wherein the isocyanate index is between 200 and 270%.

4. A process according to claim 3, wherein the isocyanate index is between 220 and 250%.

5. The method of any preceding claim, wherein the polyester polyol has an average functionality of about 1.8 to 8 and a hydroxyl number of about 15 to 750 mg KOH/gram.

6. The process according to any one of the preceding claims, wherein the polyester polyol is prepared from a polycarboxylic acid or acid derivative and a polyol.

7. The process according to claim 6, wherein the polyol is a diol or a polyglycol distinguished by the insertion of an ether linkage in the hydrocarbon chain.

8. A method according to claim 6 or 7 wherein the polycarboxylic acid or acid derivative is selected from the group consisting of adipic acid, glutaric acid, succinic acid, phthalic acid and derivatives (including isophthalic acid and terephthalic acid) and residues thereof.

9. The process according to claim 6, wherein the polycarboxylic acid used to make the aromatic polyester polyol is of aromatic nature.

10. The method of any of the preceding claims wherein the aromatic character of the aromatic polyester polyol is at least 50 weight percent.

11. The method according to any of the preceding claims, wherein the weight ratio of aromatic to aliphatic polyester polyols is between 80: 20 and 40: 60.

12. The method of any preceding claim wherein the aromatic and aliphatic polyester polyols make up at least 90 weight percent of the total isocyanate-reactive compounds.

13. A process according to any one of the preceding claims wherein the organic polyisocyanate is a polymeric MDI.

14. A method according to any preceding claim, wherein the blowing agent comprises a hydrocarbon.

15. The process according to claim 14, wherein the blowing agent is n-pentane, isobutane, isopentane, cyclopentane or any mixture thereof.

16. The process according to any of the preceding claims, wherein the reaction is carried out in the presence of a trimerisation catalyst.

17. Rigid isocyanurate-modified polyurethane foam obtained by the process according to any of the preceding claims.

18. Use of the foam of claim 17 in the manufacture of a multi-layer sheet.

19. An isocyanate-reactive composition comprising an aromatic polyester polyol and an aliphatic polyester polyol.

20. The isocyanate-reactive composition according to claim 19, wherein the weight ratio of aromatic to aliphatic polyester polyols is between 80: 20 and 40: 60.

21. The isocyanate-reactive composition according to claim 19 or 20 wherein the aromatic and aliphatic polyester polyols make up at least 90% by weight of the total isocyanate-reactive compounds.

22. The isocyanate-reactive composition according to any of claims 19 to 21 further comprising a blowing agent.

23. The isocyanate-reactive composition according to any of claims 19 to 22 further comprising a trimerisation catalyst.