Foamable compositions comprising low viscosity thermoplastic mat

Details Foamable compositions comprising low viscosity thermoplastic mat Foamable compositions comprising low viscosity thermoplastic mat

1997-09-16

1999-12-28

Nutter, Nathan M.

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

Synthetic resins

Cellular products or processes of preparing a cellular...

521 60, 521 74, 521 841, 521134, 521142, 521144, 526330, 526331, 526352, 5263522, C08L 2304

Patent

active

060082623

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a foamable composition comprising a low viscosity thermoplastic composition comprising at least one ethylene/.alpha.-olefin. The foamable composition may comprise a single ethylene/.alpha.-olefin or a blend of such. Optionally the foamable composition may further comprise at least one diluent including waxes, plasticizers such as oil, tackifying resin, and mixtures thereof. The present invention also relates to a method of foaming such compositions and articles constructed therefrom. More specifically, the present invention relates to foamable thermoplastic compositions having particular utility as cabinet sealant and as foam layers in disposable articles such as disposable diapers, incontinent devices, medical devices such as bandages and dressings, as well as a variety of other uses.


BACKGROUND OF THE INVENTION

Cabinet sealant is used in the manufacture of appliances such as refrigerators, freezers and refrigerated vending machines. The sealant is foamed over all the holes, gaps, and spaces of the appliance housing, which typically comprises ABS plastic or painted metal, prior to filling the housing with urethane based insulation. The primary purpose of the sealant is to prevent the insulation from leaking out during the filling process. Further, the cabinet sealant must withstand temperatures ranging from about 60.degree. C. (140.degree. F.) to about 82.degree. C. (180.degree. F.) and gas pressures associated with the urethane insulation filling and foaming processes. It is difficult to cover all the holes and gaps in the appliance housing without also unintentionally over-spraying the foam onto the exterior of the appliance at visible locations. Accordingly, it is critical that the cabinet sealant be cleanly strippable from the appliance housing in order to easily remove the over-sprayed foam.
Other methods of sealing the appliance housing prior to filling with insulation include pliable permagum/duragum based mastics, masking tape, and foam/fiberglass pads coated with a pressure sensitive adhesive. Since these alternative methods are slow, costly and labor intensive, the method of sealing the appliance housing with a foamed sealant is far preferred.
Block copolymer based cabinet sealant, particularly S-EB-S based have been used extensively. Other block copolymers such as S-B-S and S-I-S are typically used to a lesser degree, as block copolymers having an unsaturated midblock tend to exhibit poor thermal stability. Such block copolymers are compounded with diluents such as oil and wax.
Amorphous polyalphaolefins (APAO's) are available in low viscosity versions. However, most compositions are not cleanly strippable from ABS plastic or painted metal due at least in part to the pressure sensitive nature of such compositions. To compensate for this disadvantage, formulators have attempted to dilute higher molecular weight APAO's with diluents such as oil and/or wax to lower the viscosity and reduce adhesion. These attempts have been unsuccessful in that the mixture once foamed lacks sufficient cohesive strength to be cleanly strippable. Accordingly, the use of APAO based compositions requires the use of solvent to remove the overspray.
Foams for disposable articles are often required to exhibit somewhat different properties than that of a foamable cabinet sealant. For example, U.S. Pat. Nos. 5,342,858 and 5,389,168 issued to Litchholt et al. are directed to an elastomeric adhesive foam comprising an A-B-A block copolymrer; an aromatic modified hydrocarbon resin; and optionally a processing oil. Columns 1 and 2 of the U.S. Pat. No. 5,342,858 patent discusses in detail the advantages of forming elastomeric foams on-line as well as the shortcomings of the prior art elastomeric adhesive compositions. Exemplified are adhesive compositions comprising 45 wt-% of an S-I-S block copolymer, 40 wt-% tackifying resin, and 15 wt-% oil having viscosities ranging from 11,125 cP to 34,000 cP at 163.degree. C. (325.degree. F.). Although the compositions of Litchho

REFERENCES:
patent: 5342858 (1994-08-01), Litchholt et al.
patent: 5369136 (1994-11-01), Park et al.
patent: 5389168 (1995-02-01), Lichholt et al.
patent: 5407965 (1995-04-01), Park et al.
patent: 5416129 (1995-05-01), Chaudhary et al.

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