Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-10-12
2002-10-29
Codney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C264S045100, C264S101000, C264S239000, C521S155000
Reexamination Certificate
active
06472449
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for the preparation of compressed polyurethane rigid foams and to the use thereof as support materials for vacuum insulation units.
By removing air and other gases as fully as possible from a porous moulded article, the insulation properties thereof can be improved substantially. This effect is utilised in vacuum insulation units. An example thereof is that of vacuum panels which may be used to reduce the energy consumption of refrigerators. In order to produce said panels, a largely open-cell substrate is evacuated and surrounded by a permneation-tight casing. The properties of the substrate are of great importance for the performance characteristics of the vacuum panel. The proportion of open cells must be as high as possible in order to permit rapid and complete gas removal. It must have a high compressive strength so that the vacuum panel may withstand the external air pressure. The cells of the substrate must be as small as possible so that good insulation properties may be obtained even at internal pressures that are industrially easy to achieve.
It is well known to use open-cell polyurethane rigid foams of the kind described, e.g., in U.S. Pat. No. 5,350,777, EP-A-498 628, DE-A-43 03 809, U.S. Pat. Nos. 5,250,579 and 5,312,846, as support material for vacuum insulation units. A disadvantage of said rigid foams is their relatively large cell diameter which necessitates evacuating the moulded article filled therewith to very low pressures, this being associated with a high level of technical complexity.
U.S. Pat. No. 5,844,014 teaches that the insulation properties of evacuated open-cell foams of thermoplastics may be improved by compressing the foam. Polyurethane rigid foams are thermosets, however, so during a standard compression process their structure is destroyed to such an extent that the high compressive strength required for vacuum insulation units is no longer obtained.
SUMMARY OF THE INVENTION
It has now been found that it is possible to prepare fine-cell, open-cell polyurethane rigid foams if the foamed polyurethane foam is compressed shortly before or after the fibre time has ended.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides, therefore, a process for the preparation of fine-cell polyurethane or polyisocyanurate rigid foams wherein
1. an open-cell polyurethane or polyisocyanurate rigid foam is prepared by mixing a suitable polyol formulation with a polyisocyanate, and
2. the polyurethane or polyisocyanurate rigid foam thus obtained is compressed to 5% to 95%, preferably 30% to 70%, particularly preferably 40% to 60% of its starting volume after 80% to 200%, preferably 100% to 150%, particularly preferably 105% to 130% of the fibre time.
In the first step of the process according to the invention, an open-cell polyurethane or polyisocyanurate rigid foam is prepared in a manner known in principle to the skilled person by mixing a polyisocyanate with a suitable polyol component which may also contain blowing agents, catalysts and other auxiliaries, e.g., foam stabilisers, antioxidants etc. According to the invention, the polyurethane or polyisocyanurate rigid foam prior to compression has an average cell diameter of less than 250 &mgr;m, preferably less than 150 &mgr;m and a volume proportion of open cells measured to DIN ISO 4590-92 from 50% to 100%, preferably 80% to 100%.
In order to achieve the functionality required for foaming, polyol formulations according to the invention contain at least one polyol having at least two hydrogen atoms which are reactive towards isocyanates and having a number-average molecular weight from 150 to 12,500 g/mole, preferably 200 to 1500 g/mole. Such polyols may be obtained by polyaddition of alkylene oxides such as, for example, ethylene oxide, propylene oxide, butylene oxide, dodecyl oxide or styrene oxide, preferably propylene oxide or ethylene oxide, to starter compounds such as water or polyhydric alcohols such as sucrose, sorbitol, pentaerythritol, trimethylolpropane, glycerol, propylene glycol, ethylene glycol, diethylene glycol and mixtures of the starter compounds mentioned. Suitable starter compounds also include ammonia or compounds having at least one primary, secondary or tertiary amino group, for example, aliphatic amines such as ethylenediamine, oligomers of ethylenediamine (e.g. diethylenetriamine, triethylenetetramine or pentaethylenehexamine), ethanolamine, diethanolamine, triethanolamine, N-methyl or N-ethyl diethanolamine, 1,3-propylenediamine, 1,3-or 1,4-butylenediamine, 1,2-hexamethylenediamine, 1,3-hexamethylenediamine, 1,4-hexamethylenediamine, 1,5-hexamethylenediamine or 1,6-hexamethylenediamine, aromatic amines such as phenylenediamines, diaminotoluenes (2,3-diaminotoluene, 3,4-diaminotoluene, 2,4-diaminotoluene, 2,5-diaminotoluene, 2,6-diaminotoluene or mixtures of said isomers), 2,2′-diaminodiphenylmethane, 2,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane or mixtures of said isomers. The polyol formulation contains from 0 to 95 parts by weight, preferably from 10 to 40 parts by weight of said component.
Polyol formulations according to the invention may also contain polyester polyols having a number-average molecular weight from 100 to 30,000 g/mole, preferably 150 to 10,000 g/mole, particularly preferably 200 to 600 g/mole which may be prepared from aromatic and/or aliphatic dicarboxylic acids and polyols having at least two hydroxyl groups. Examples of dicarboxylic acids include phthalic acid, fumaric acid, maleic acid, azelaic acid, glutaric acid, adipic acid, suberic acid, terephthalic acid, isophthalic acid, decane dicarboxylic acid, malonic acid, glutaric acid and succinic acid. Individual dicarboxylic acids or any mixtures of different dicarboxylic acids may be used. Instead of free dicarboxylic acids it is also possible to use the corresponding dicarboxylic acid derivatives such as, e.g., dicarboxylic acid mono- or diesters of alcohols having one to four carbon atoms or dicarboxylic acid anhydrides. Examples of the preferred alcohol component for esterification include: ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propane 1,2-diol, propane 1,3-diol, butane 1,4-diol, pentane 1,5-diol, hexane 1,6-diol, decane 1,10-diol, glycerol, trimethylolpropane or mixtures thereof. The polyol formulations according to the invention may also contain polyether esters of the kind obtained, e.g., according to EP-A-250 967 by reaction of phthalic anhydride with diethylene glycol and afterwards with ethylene oxide. The polyol formulation may contain from 0 to 90 parts by weight, preferably 5 to 30 parts by weight of polyester polyol.
The polyol formulations according to the invention also contain at least one catalyst in amounts from 0 to 10 parts by weight, preferably 0.5 to 5 parts by weight. The catalysts customarily used in polyurethane chemistry may be used according to the invention. Examples of such catalysts include: triethylenediamine, N,N-dimethylcyclohexylamine, tetramethylenediamine, 1-methyl-4-dimethylaminoethylpiperazine, triethylamine, tributylamine, dimethylbenzylamine, N,N′,N″-tris-(dimethylaminopropyl)-hexahydrotriazine, diemethylaminopropyl formamide. N,N,N′,N′-tetramethyl-ethylenediamine, N,N,N′,N′-tetramethylbutanediamine, tetramethylhexanediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, dimethylpiperazine, 1,2-dimethylimidazole, 1-azabicyclo[3.3.0]octane, bis-(dimethylaminopropyl)urea, N-methylmorpholine, N-ethylmorpholine, N-cyclohexylmorpholine, 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, triethanolamine, diethanolamine, triisopropanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, dimethylethanolamine, tin-(II)acetate, tin-(II)-octoate, tin-(II)-ethylhexoate, tin-(II)-laurate, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dioctyltin diacetate, tris-(N,N-dimethylaminopropyl)-s-hexahydrotriazine, tetramethylammonium hydroxide, potassium acetate, sodium ac
Dietrich Karl-Werner
Heinemann Torsten
Klän Walter
Bayer Aktiengesellschaft
Codney, Jr. John M.
Gil Joseph C.
Whalen Lyndanne M.
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