Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1991-05-28
1992-04-21
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
264 53, 264DIG5, 521 98, 521146, 521147, 521910, 521131, C08J 914
Patent
active
051068826
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for making dimensionally stable insulating alkenyl aromatic polymer foam extruded in large cross sections employing a blowing agent (or mixture) that is solely 1,1-difluoro-1-chloroethane (or more than 70 percent by weight 1,1-difluoro-1-chloroethane).
One major application for alkenyl aromatic, polymer foams (such as polystyrene) is in the field of thermal insulation. Desirably a styrene polymer foam for thermal insulation has an average cell size of less than 0.5 millimeters and excellent dimensional stability.
One manner in which the thermal insulation value of styrene polymer foams is increased is by the addition of certain fully-halogenated compounds, such as dichlorodifluoromethane, into the styrene polymer foam as a blowing/insulating agent. Such a compound, when contained in the cells of the extruded styrene polymer foam, increases the thermal insulation value.
It is extremely well known that dimensional stability is particularly important when the extruded styrene polymer foam is employed as thermal insulation in construction uses or is laminated to a cementitious layer. For most commercial applications regular rectangular forms are required and while a distorted shape can be cut into a rectangular form, considerable product is lost in cutting and must be discarded as scrap. Another consideration is that if an extruded styrene polymer foam product is not dimensionally stable, then the foamed polystyrene must be maintained in storage for a sufficient length of time until substantially all dimensional instability, such a shrinking, swelling, warping or bulging has stopped.
Still another important consideration is the choice of a blowing/insulating agent. Certain of these agents, particularly fully-halogenated compounds such as dichlorodifluoromethane, when released to the atmosphere upon extrusion of the styrene polymer foam or upon aging of the foam are believed to cause harm to the atmosphere. Thus, it is desirable to reduce or eliminate these fully-halogenated compounds
Canadian Patent No. 1,086,450 refers to this problem and proposes a variety of low permeability, insulating/blowing agents, or mixtures of those agents, having a permeability through an alkenyl aromatic resinous polymer of not greater than 0.017 times the permeability of nitrogen through the body, a thermal conductivity of 0.07.+-.20 percent British Thermal Units-inch per hour per square foot per degree Fahrenheit and having the following formula: difluoromethyl, chlorofluoromethyl, fluoromethyl, or trifluoromethyl radical and R.sub.2 is hydrogen or a chloro, fluoro, methyl or trifluoromethyl radical with the further characterization that the compound contain no more than 3 carbon atoms and if the compound contains as halogen only 2 fluorine atoms, the compound must have 3 carbons.
However, in Table II of the Canadian patent, it can be seen that polystyrene foam prepared from certain blowing agents, particularly 1,1-difluoro-1-chloroethane, have a dimensional stability which is excessive. This is particularly noted in Example 16.
U.S. Pat. No. 3,960,792 teaches how to prepare a dimensionally stable expanded closed cell polystyrene foam body while employing as the fluid foaming agent a volatile material which has a diffusion rate through the polystyrene resin about 0.75 to 6 times the diffusion rate of air through polystyrene resin with the foaming agent being a mixture of at least two compounds having carbon chemically combined therein.
U.S. Pat. No. 4.636.527 teaches how to prepare an expanded closed cell polystyrene foam body while employing as the fluid foaming agent a mixture of carbon dioxide and ethyl chloride. Optionally dichlorodifluoromethane, 1,1-difluoro-1-chloroethane and mixtures thereof may also be included as part of the blowing agent mixture.
There is a need to be able to produce a dimensionally stable extruded polystyrene foam body with a non-fully halogenated insulating/blowing agent.
More particularly there is a need to be able to produce a dimensionally stable extruded polyst
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Severson Jerry L.
Suh Kyung W.
Foelak Morton
The Dow Chemical Company
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