Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1992-12-18
1994-08-02
Seidleck, James J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525240, 525 86, 525 95, 525 98, 525241, C08L 2510, C08L 2302, C08L 2308
Patent
active
053346572
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a thermoplastic resin composition having high resistance to attack by chemicals such as halogenated hydrocarbons and especially hydrochlorofluorocarbons (HCFC's) and good sheet thermoforming characteristics. More particularly, the present invention relates to such a composition and to thermoformed objects therefrom, such as refrigerator or freezer liners. In a further embodiment the present invention relates to structures comprising such thermoformed articles having adhered to one surface thereof a polyurethane foam, especially such a foam prepared by the use of hydrochlorofluorocarbon blowing agents.
It is previously known in the art to prepare thermoformable sheets from thermoplastic resins such as impact modified polystyrene (HIPS) and impact modified styrene acrylonitrile (ABS) resins. Such thermoformable resins have found wide use in the preparation of numerous objects such as containers, toys, and appliance components. In particular, refrigerator or freezer liners are often thermoformed from such a sheet material. In the manufacture of a typical refrigerator or freezer such a liner is placed into an outer jacket formed of metal or similar material that forms the outer cabinet or door of the refrigerator or freezer, and the space between the outer jacket and the liner is filled with a thermosetting foam, usually polyurethane foam. Typically polyurethane foams are prepared by blending a polyurethane forming mixture comprising a polyhydroxyl compound and a polyisocyanate compound with a suitable blowing agent and allowing the viscous liquid mixture to expand due to the effects of the blowing agent while the reaction to form the polyurethane takes place. By injecting the polyurethane forming mixture in the free space between the refrigerator or freezer liner and the outer jacket, and allowing the mixture to foam in place, a unitary structure is formed that greatly aids in the rigidity of the resulting refrigerator or freezer. Varying degrees of adhesion between the polyurethane foam and the liner may be obtained during the foaming process.
A number of chemicals are suitably employed as blowing agents, especially halogenated hydrocarbons, many of which are aggressive solvents for vinyl aromatic polymers. Recently, hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC) blowing agents have been employed in a number of applications due to the reduced environmental degradation believed to result from releasing such blowing agents to the environment. However, HCFC and HFC blowing agents (also referred to as soft blowing agents), particularly HCFC 123 (CCl.sub.2 HCF.sub.3), HCFC 141 -b (CCl.sub.2 HCH.sub.2 F), HCFC 22 (CHCIF.sub.2), HFC 134a (CF.sub.3 CH.sub.2 F), and HFC 152a (CH.sub.3 CHF.sub.2), have been found to be highly aggressive solvents with respect to many thermoplastic resins, particularly styrene containing resins, typically employed in thermoforming compositions. Due to this increased solubility, greater chemical attack of the thermoplastic resin can result if HCFC blowing agents come in contact with the surface of such thermoformable resin during the manufacturing process or while in use. This can lead to blistering and/or cracking of the thermoplastic resin due to the chemical attack at the point of contact with the thermoformed sheet.
Attempts to overcome such aggressive attack by compounds on typical thermoformable sheet materials have included use of an intervening barrier layer which may be coextruded or heat laminated to the thermoformable sheet material. Disadvantageously such film layer adds expense to the resulting thermoformable structure and often is cut or abraided during the manufacturing process thereby losing its barrier properties. Other solutions, such as coatings, similarly have not proven acceptable. Special resins which have improved resistance to the effects of HCFC's have also been attempted, but often such resins possess poor thermoformability, inadequate strength, inability to include reground scrap material from the manufacturing proce
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Bonekamp Jeffrey E.
Donald Robert J.
Swartzmiller Steven B.
Clark W. R. H.
Deline Douglas N.
Guffey James B.
Seidleck James J.
The Dow Chemical Company
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