Foam boards produced using halogen-free blowing agents

Details Foam boards produced using halogen-free blowing agents Foam boards produced using halogen-free blowing agents

1995-11-21

1996-11-19

Foelak, Morton

Stock material or miscellaneous articles

Structurally defined web or sheet

Physical dimension specified

4283055, 4283148, 521 79, 521 81, 521146, B32B 326, B32B 712

Patent

active

055760945

DESCRIPTION:

BRIEF SUMMARY
The invention relates to foam boards produced using halogen-free blowing agents and a process for their production. The invention relates in particular to foam boards having a thickness of at least 20 mm and comprising a thermoplastic matrix based on a styrene polymer and closed cells which are free of halogen-containing gases.
For the production of foam boards based on styrene polymers by extrusion, many blowing agents have been proposed.
For example, EP-A-464 581 discloses a process for producing foam boards having high compressive strength and a cross section of at least 50 cm.sup.2, in which process a mixture of a styrene polymer, from 5 to 16% by weight, based on the styrene polymer, of a blowing agent and, if desired, customary additives is extruded, with the blowing agent used being a mixture comprising range from 56.degree. to 100.degree. C., hydrogen-containing fluorochlorinated or fluorinated hydrocarbon which boils in the range from -30.degree. C. to +30.degree. C.
The foam boards produced by the known processes have the disadvantage that the final values, for example for the dimensional stability on heating, are established relatively slowly.
JP-A-60/145 835 discloses the production of a laminated board having a polystyrene foam layer which has been produced by extrusion using an ether such as dimethyl ether, methyl ethyl ether or methyl vinyl ether as blowing agent. The example describes the production of a 6 mm thick plate using 3.7 parts by weight of dimethyl ether, based on polystyrene, as blowing agent.
It is also known that use of blowing agents which diffuse rapidly from the foam, eg. CO.sub.2, frequently no longer ensure sufficient dimensional stability and compressive strength of foam boards having a board thickness of 20 mm or more, in particular equal to or greater than 50 mm. In addition, use of blowing agents having a high blowing power frequently gives foams having a high proportion of open cells.
Thus, in the process described in EP-A-464 581, the production of high-quality foam boards having a thickness of 20 mm or above is frequently possible only when using fluorochlorinated or fluorinated hydrocarbons as blowing agent. However, the latter are undesirable for environmental reasons.
The German Patent Application P 42 36 579.1 relates to a process for producing polystyrene foam boards using a blowing agent mixture which contains a dialkyl ether. In the examples, the thermoplastic matrix is always a homopolystyrene having a melt flow index of 4.5. The Vicat softening temperature of polystyrene is 101.degree. C.
It is an object of the present invention to provide extruded foam boards based on styrene polymers which are produced using halogen-free blowing agents.
Another object of the invention is to provide a process for producing foam boards of styrene polymers having a minimum thickness of 20 mm, which process leads to foams having closed cells, only a low water absorbency and, apart from good dimensional stability and compressive strength, a high dimensional stability on heating. It is a further object of the invention to provide a process which makes possible the rapid establishment of the final values, particularly for the dimensional stability on heating, in the foam boards produced. The proportion of carbon dioxide in the blowing agent should be able to be very large.
A further object of the invention is the production of foam boards having a thickness of more than 50 mm, preferably from 80 to 200 mm, using blowing agent mixtures comprising ethanol and carbon dioxide and, in particular, carbon dioxide as sole blowing agent.
We have found that these objects are achieved by extruded foam boards having a minimum thickness of 20 mm and a cross section of at least 50 cm.sup.2 produced using halogen-free blowing agents and comprising a thermoplastic matrix based on a styrene polymer, closed cells which are free of halogen-containing gases and, if desired, additives insoluble in the thermoplastic matrix, with the thermoplastic matrix having a Vicat softening temperature VST B 50 (

REFERENCES:
patent: 4636527 (1987-01-01), Suh et al.
patent: 4916166 (1990-04-01), Suh et al.
patent: 5106882 (1992-04-01), Suh et al.
patent: 5269987 (1993-12-01), Reedy

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