Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-12-28
2002-11-05
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...
C521S131000, C521S181000
Reexamination Certificate
active
06476090
ABSTRACT:
TECHNICAL FIELD
This invention relates to a phenolic foam for heat insulation which is excellent in heat insulating performance and mechanical strength and is environment-friendly.
BACKGROUND ART
Phenolic foam is useful as various constuctional materials because of its superiority among resin foams particularly in flame retardance, heat resistance, low fuming properties, dimensional stability, solvent resistance, and fabricability.
Phenolic foam is generally produced by expanding and curing a foamable composition prepared by uniformly mixing a resol resin obtained by polymerization of phenol and formalin in the presence of under an alkaline catalyst, a blowing agent, a surface active agent, a curing catalyst, and other additives.
Blowing agents known for phenolic foam include so-called CFCs such as trichlorotrifluoroethane (CFC-113) and trichloromonofluoromethane (CFC-11), HCFCs such as dichlorotrifluoroethane (HCFC-123) and dichlorofluoroethane (HCFC-141b), HFCs such as 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1-difluoroethane (HFC-152a), and hydrocarbons such as cyclohexane, cyclopentane, and normal pentane (hereinafter referred to as HCs).
Among them CFCs have been used for preference for their advantages that they can be prepared with high safety, the gas they generate has a low thermal conductivity, they exhibit excellent expanding properties in resol resins and easily form fine closed cells on expansion, and the resulting foams have a low thermal conductivity.
However, it recently turned out that CFCs and HCFCs decompose ozone in the stratosphere to cause destruction of the ozonophere. These substances have now been recognized as a world issue as a cause of global environmental destruction, and global restrictions have been imposed on their production and use.
HFCs and HCs which do not destroy the ozonophere have then been attracting attention as a blowing agent. Note is taken particularly of use of HCs as a blowing agent because of their smaller coefficient of global warming than HFCs'.
HFCs and HCs are, however, difficult to apply as a blowing agent to phenolic foam on an industrial scale for such reasons as poor expanding performance. In particular, application of an HC blowing agent has not yet succeeded in obtaining a phenolic foam with satisfactory heat insulating performance on account of the high thermal conductivity of the blowing agent itself.
W097/08230 proposes a process of making a phenolic foam having a low thermal conductivity by use of a hydrocarbon blowing agent, in which a resol resin containing substantially no free formaldehyde is used, stating that a phenolic foam having an initial thermal conductivity of 0.0181 (kcal/m·hr·° C.) was obtained. Although the description states that the phenolic foam shows a small increase in thermal conductivity, the thermal conductivity of the phenolic foam shows a 10% or more increase up to 0.020 (kcal/m·hr·° C.) after 200 days. Further, the phenolic foam has fine holes in the cell walls as demonstrated in Comparative Example 7 of the present invention. The large change of thermal conductivity with time is assumed attributable to gradual displacement of the blowing agent with air through the fine holes of the cell walls.
JP-W-4-503829 (The term “JP-W” used herein means a “published Japanese national stage of international application”) reports that addition of a fluorocarbon to a hydrocarbon blowing agent leads to production of a phenolic foam with satisfactory heat insulating properties, giving Example in which a phenolic foam having a thermal conductivity of 0.0186 W/m·K was obtained by using a pentane blowing agent to which a perfluorocarbon had been added. However, a phenolic foam prepared in accordance with the description of the Example was found to have fine holes in the cell walls as revealed in Comparative Example 8 of the present invention. Addition of a perfluorocarbon, being expensive, creates another problem that the production cost will increase.
As stated above, we have had no phenolic foams which are produced by using a hydrocarbon-containing blowing agent and yet exhibit satisfactory heat insulating performance, excellent mechanical strength, such as compressive strength, and reduced brittleness.
An object of the present invention is to provide a phenolic foam which has a low thermal conductivity despite use of an HC as a blowing agent, undergoes little change in thermal conductivity with time, and has excellent mechanical strength, such as compressive strength, and reduced brittleness.
DISCLOSURE OF THE INVENTION
The present inventors found that a resol resin whose reactivity falls within a specific range provides a phenolic foam having the cellular structure as defined in the present invention when produced under specific conditions of expansion and curing, the above object of the invention can be achieved thereby. The present invention has been completed based on this finding.
The present invention provides:
(1) A phenolic foam having a density of 10 kg/m
3
to 100 kg/m
3
and containing a hydrocarbon, which is characterized by having an average cell diameter in a range of from 5 &mgr;m to 200 &mgr;m, a void area ratio of 5% or less in its cross section, and substantially no holes in the cell walls;
(2) The phenolic foam according to the above (1), which has a closed cell ratio of 80% or more, a thermal conductivity of 0.022 kcal/m·hr·° C. or less, and a brittleness of 30% or less;
(3) The phenolic foam according to the above (1) or (2), wherein the hydrocarbon is a constituent of a blowing agent;
(4) The phenolic foam according to the above (3), wherein the blowing agent comprises 50% by weight or more of the hydrocarbon;
(5) The phenolic foam according to the above (4), wherein the blowing agent contains 0.1 to 100 parts by weight of a fluorohydrocarbon per 100 parts by weight of the hydrocarbon;
(6) The phenolic foam according to any one of the above (1) to (5), wherein the hydrocarbon is at least one compound selected from isobutane, normal butane, cyclobutane, normal pentane, isopentane, cyclopentane, and neopentane;
(7) The phenolic foam according to any one of the above (1) to (6), wherein the hydrocarbon is a mixture of 5 to 95% by weight of a butane selected from isobutane, normal butane and cyclobutane and 5 to 95% by weight of a pentane selected from normal pentane, isopentane, cyclopentane and neopentane;
(8) The phenolic foam according to the above (7), wherein the hydrocarbon is a mixture of 5 to 95% by weight of isobutane and 5 to 95% by weight of normal pentane and/or isopentane;
(9) The phenolic foam according to the above (5), wherein the fluorohydrocarbon is at least one compound selected from 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane and pentafluoroethane;
(10) A process for producing a phenolic foam, comprising mixing a resol resin having a viscosity increase rate constant of 0.005 to 0.5, a water content of 4 to 12% by weight and a viscosity of 1000 to 30000 cps at 40° C., a surface active agent, a hydrocarbon-containing blowing agent, and a curing catalyst in a mixing machine having a temperature of 10 to 70° C. and a pressure of from the vapor pressure of the blowing agent to the blowing agent's vapor pressure plus 5 kg/cm
2
, expanding the mixture, and elevating the temperature stepwise in a subsequent curing reaction stage;
(11) The process for producing a phenolic foam according to the above (10), wherein the hydrocarbon-containing blowing agent comprises 50% by weight or more of a hydrocarbon; and
(12) The process for producing a phenolic foam according to the above (11), wherein the blowing agent contains 0.1 to 100 parts by weight of a fluorohydrocarbon per 100 parts by weight of the hydrocarbon.
REFERENCES:
patent: 4033910 (1977-07-01), Papa
patent: 4369259 (1983-01-01), Tiroux et al.
patent: 4370424 (1983-01-01), Baumann
patent: 5397807 (1995-03-01), Hitchcock et al.
patent: 6013689 (2000-01-01), Rader
patent: 11-140216 (1999-05-01), None
patent: 11-172033 (1999-06-01), None
Arito Yuichi
Takasa Kenji
Asahi Kasei Kabushiki Kaisha
Foelak Morton
Pennie & Edmonds LLP
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