Polystyrene resin foam and process for producing the foam body

Details Polystyrene resin foam and process for producing the foam body Polystyrene resin foam and process for producing the foam body

1997-08-22

2000-05-16

Foelak, Morton

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

521139, C08J 914

Patent

active

060638230

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a process for preparing a polystyrene-based resin foam body.


BACKGROUND ART

A widely used process for preparing polystyrene-based resin foam bodies is one by which a volatile blowing agent is added to a molten resin and the mixture is kneaded under high temperature and pressure and then, after temperature adjustment, extruded through a low temperature, low pressure zone to foam the mixture and obtain an extruded foam body.
As such extruded foam bodies of polystyrene-based resins are light-weight and have excellent insulating properties as well as being relatively economical, they have found wide use as insulating materials for buildings.
Conventional production of such polystyrene-based resin foam bodies has involved the use of saturated chlorofluorocarbons (hereunder, CFCs) such as dichlorodifluoromethane (F-12), dichlorotetrafluoroethane (F-114) and trichlorofluoromethane (F-11). This is because the incombustibility and low thermal conductivity of these special freons are extremely useful for extruded foam insulating materials which must have excellent insulating properties.
However, since these special freons are very stable chemically, after they escape from the foam body they diffuse into the atmosphere and rise to the stratosphere without being degraded and result in destruction of the ozone layer, for which reason restrictions on their production and use are presently being promoted on a worldwide scale.
In place of the above-mentioned freons there have also been used hydrochlorofluorocarbons (hereunder, HCFCS) such as 1-chloro-1,1-difluoroethane (F-142b), monochlorodifluoromethane (F-22) and 1-chloro-1,2,2,2-tetrafluoroethane (F-124). Since these HCFCs have a hydrogen atom in the molecule, the lifetime of the molecule is shorter than the above-mentioned special freons and as a result they are less destructive to the ozone layer.
Nevertheless, the ozone destruction parameter (ODP) is not completely reduced to zero by including a hydrogen atom in the molecule, and thus restrictions will almost certainly be placed on their use as with special freons. Therefore, it has become an important and urgent issue to develop a blowing agent with an ODP of zero and low thermal conductivity, to replace HCFCs.
When aliphatic hydrocarbon-based blowing agents such as propane or butane have-been used in place of HCFCs, it has been impossible to obtain foam bodies with the same low thermal conductivity achieved by using the aforementioned special freons (especially F-12) or HCFCS. Furthermore, the flammability of these blowing agents has led to combustion of the resultant foam bodies, leaving a problem from the viewpoint of safety.
Here, the present inventors have made efforts to obtain extruded foam bodies with excellent insulating properties using as blowing agents hydrofluorocarbons (hereunder, HFCs), i.e. fluorocarbons with at least one hydrogen atom and containing no chlorine, which have an ozone destruction parameter of zero and excellent thermal conductivity. These contain no chlorine atoms in the molecule and thus are not ozone-destructive. Furthermore since they contain at least one hydrogen atom in the molecule, they have a short lifetime in the atmosphere and are thus considered to contribute very little to the greenhouse effect.
Despite the above-mentioned advantages of these HFCs, however, their low compatibility with polystyrene-based resins means that when large amounts of HFCs are added for more satisfactory insulating properties, under conventional production conditions, gas is released inside the die from the molten resin during the extrusion foaming which causes occurrence of foaming prior to leaving the die and thus leaves the resin torn, making it impossible to obtain aesthetically pleasing foam bodies which are uniform and have a high expansion ratio. Methods of further raising the pressure of the system in order to increase the solubility of HFCs in polystyrene have been considered. However, even when the system pressure is raised, many nuclei

REFERENCES:
patent: 5086080 (1992-02-01), Anfuso
patent: 5091256 (1992-02-01), Bopp et al.
patent: 5189072 (1993-02-01), Rhoads et al.
patent: 5641549 (1997-06-01), Johnston et al.
patent: 5898039 (1999-04-01), Smith et al.

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