Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-02-09
2002-01-01
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C510S415000, C516S010000, C521S115000, C521S174000
Reexamination Certificate
active
06335378
ABSTRACT:
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 in the process.
Rigid polyurethane and urethane-modified polyisocyanurate foams are in general prepared by reacting the appropriate polyisocyanate and isocyanate-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 of ozone in the atmosphere has led to an urgent need to develop reaction systems in which chlorofluorocarbon blowing agents are replaced by alternative materials which are environmentally acceptable and which also produce foams having the necessary properties for the many applications in which they are used.
Initially, the most promising alternatives appeared to be hydrogen-containing chlorofluorocarbons (HCFC's). U.S. Pat. No. 4,076,644, for example, discloses the use of 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1,1-dichloro-1-fluoroethane (HCFC-141b) as blowing agents for the production of polyurethane foams. However, HCFC's also have some ozone-depletion potential. There is therefore mounting pressure to find substitutes for the HCFC's as well as the CFC's.
Alternative blowing agents which are currently considered promising because they contain no ozone-depleting chlorine are partially fluorinated hydrocarbons (HFC's) and hydrocarbons (HC's). One of the most viable HFC candidate is 1,1,1,3,3-pentafluoropropane (HFC-245fa) as described in U.S. Pat. No. 5,496,866 and EP 381989. In respect of HC's especially five-carbon member hydrocarbons are considered such as isopentane and n-pentane, as described in WO 90/12841.
Currently a lot cf attention is paid to blowing agent mixtures, which could, apart from a possible reduction in cost, also provide additional benefits such as foam density reduction and thermal conductivity. U.S. Pat. No. 5,562,857 describes the use of mixtures containing from 50 to 70 mole % of HFC-245fa and from 30 to 50 mole % isopentane as blowing agent for rigid polyurethane foams.
It is an object of the present invention to provide a novel blowing agent mixture containing no chlorine and therefore of zero ozone depletion potential yielding foams having good thermal insulation and physical properties.
This object is met by using in the process of making rigid polyurethane or urethane-modified polyisocyanurate foams from polyisocyanates and isocyanate-reactive components a mixture containing from 1 to 50 mole. HFC-245fa and from 50 to 99 mole % isopentane and/or n-pentane.
Preferably the mole ratio HFC 245fa/iso- and/or n-pentane is between 10/90 and 40/60.
Preferably on the hydrocarbon side only isopentane or n-pentane is used and most preferably only isopentane. But also mixtures of isopentane and n-pentane can be used; in these mixtures the mole ratio isopentane
-pentane is preferably between 80/20 and 20/80.
Suitable isocyanate-reactive compounds to be used 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. Of particular importance for the preparation of rigid foams are polyols and polyol 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 8, especially from 3 to 8. Suitable polyols have been 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, trlethanolamlne, pentaerythritcl, 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, polyamides, polyesteramides, polycarbonates, polyacetals, polyolefins and polysiloxanes.
The present blowing agent mixture is especially suitable for use in isocyanate-reactive compositions containing polyether polyols, especially those derived from aliphatic or aromatic amine containing initiators, especially aromatic ones such as TDA and DADPM. A preferred isocyanate-reactive composition contains from 10 to 75 wt % (based on total isocyanate-reactive components) of aromatic amine initiated polyether polyols.
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 diisocyanate in the form of its 2,4′-, 2,2′- and 4,4′-isomers and mixtures thereof, the mixtures of diphenylmethane diisocyanates (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 diisocyanate in the form of its 2,4- and 2,6-isomers and mixtures thereof, 1,5-naphthalene diisocyanate and 1,4-diisocyanatobenzene. Other organic polyisocyanates which may be mentioned include the aliphatic diisocyanates such as isophorone diisocyanate, 1,6-diisocyanatohexane and 4,4′-diisocyanatodicyclohexylmethane.
The quantities of the polyisocyanate compositions and the polyfunctional 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.
Other physical blowing agents known for the production of rigid polyurethane foam can be used in small quantities (up to 30 wt % of the total physical blowing agent mixture) together with the blowing agent mixture of the present invention. Examples of these include dialkyl ethers, cycloalkylene ethers and ketones, (per)fluorinated ethers, chlorofluorocarbons, perfluorinated hydrocarbons, hydrochloroflucrocarbons, other hydrofliuorocarbons and other hydrocarbons. For example a mixture of HFC-245fa, isopentane and cyclopentane can be used.
Analogously to the present invention mixtures of HFC-245fa and other hydrocarbons (preferably linear alkanes) containing from 3 to 7 carbon atoms (such as cyclopentane, isobutane and n-hexane) can be used as blowing agent for rigid polyurethane foams.
Generally water or other carbon dioxide-evolving compounds are used together with the physical blowing agents. Where water is used as chemical coblowing 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
Foelak Morton
Imperial Chemical Industries PLC
Pillsbury & Winthrop LLP
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