Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1999-08-31
2002-03-12
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S314800, C428S314400, C428S220000, C428S338000, C521S081000, C521S079000, C521S134000, C521S139000
Reexamination Certificate
active
06355341
ABSTRACT:
FIELD OF THE INVENTION
This invention describes a method for enlarging cell sizes of alkenyl aromatic foams by blending polymers which comprise; (A) alkenyl aromatic polymers, and (B) vinyl or vinylidene aromatic and/or sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene substantially random interpolymers. Suitable alkenyl aromatic polymers include alkenyl aromatic homopolymers and copolymers of alkenyl aromatic compounds and copolymerizable ethylenically unsaturated comonomers. The alkenyl aromatic polymer material comprises greater than 50 and preferably greater than 70 weight percent alkenyl aromatic monomeric units. Most preferably, the alkenyl aromatic polymer material is comprised entirely of alkenyl aromatic monomeric units. Suitable alkenyl aromatic polymers include those derived from alkenyl aromatic compounds such as styrene, alpha-methylstyrene, etc. A preferred alkenyl aromatic polymer is polystyrene. Examples of copolymerizable compounds include acrylic acid, methacrylic acid, acrylonitrile, etc. The substantially random interpolymers comprise polymer units derived from ethylene and/or one or more &agr;-olefin monomers with specific amounts of one or more vinyl or vinylidene aromatic monomers and/or sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers. A preferred substantially random interpolymer is an ethylene/styrene interpolymer. Incorporation of the substantially random interpolymer in the blend with the alkenyl aromatic polymer allows the formation of foams having enlarged cell sizes when blowing agents of reduced or zero ozone-depletion potential (which have low solubility and relatively high nucleation potential) are employed.
BACKGROUND OF THE INVENTION
Due to present environmental concerns over the use of ozone-depleting blowing agents, it is desirable to make alkenyl aromatic polymer foams with blowing agents having reduced or zero ozone-depletion potential. Such blowing agents include inorganic blowing agents such as nitrogen, sulfur hexafluoride (SF
6
), and argon; organic blowing agents such as carbon dioxide and hydrofluorocarbons such as 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,3,3-pentafluoropropane, difluoromethane (HFC-32), 1,1-difluoroethane (HFC-152a), pentafluoroethane (HFC-125), fluoroethane (HFC-161) and 1,1,1-trifluoroethane (HFC-143a) and hydrocarbons such as methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane and neopentane; and chemical blowing agents which include azodicarbonamide, azodiisobutyro-nitrile, benzenesulfonylhydrazide, 4,4-oxybenzene sulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, barium azodicarboxylate, N,N′-dimethyl-N,N′-dinitrosoterephthalamide, trihydrazino triazine and mixtures of citric acid and sodium bicarbonate such as the various products sold under the name Hydrocerol™ (a product and trademark of Boehringer Ingelheim). All of these blowing agents may be used as single components or any mixture in combination thereof, or in mixtures with other co-blowing agents.
A problem with using the above non ozone-depleting blowing agents is their tendency to form foams of relatively small cell size and cross-section. Such blowing agents typically result in foams having small cell sizes due to their relatively high nucleation potential. Small cell size is especially a problem when particular infrared attenuating agents are employed such as carbon black, graphite, and titanium dioxide.
It would be desirable to be able to employ the non-ozone depleting blowing agents in making alkenyl aromatic polymer foams with or without infrared attenuating agents yet be able to enlarge the cell size of the foam. Enlarging the cell size of the foams would enable greater thicknesses and larger cross-sectional areas to be obtained, as well as afford a reduction in foam density in some cases. Lower foam densities would be desirable for both extruded and expanded alkenyl aromatic polymer foams. Greater foam thicknesses and cross-sections would enable a broader range of products to be manufactured, and reducing density would allow foams to be manufactured more economically. It is also desirable for the foams to exhibit acceptable physical properties.
Prior art attempts to make a foam having enlarged cell size include the integration of a wax in a foam forming gel prior to extrusion of the gel through a die to form a foam. Such use of a wax is seen in U.S. Pat. No. 4,229,396, which is incorporated herein by reference. The use of a wax may however, present processing problems and cause thermal stability variations or diminution in physical properties in product foams. The wax may also cause inconsistency in extrusion temperatures. Additional prior art attempts to make a foam having enlarged cell size include the incorporation of a non-waxy compound in a foam forming gel prior to extrusion of the gel through a die to form a foam. Such use of a non-waxy compound is seen in U.S. Pat. No. 5,489,407, which is incorporated herein by reference. Large cell size alkenyl aromatic polymer foams have been prepared using glycerol monoesters of C
8
-C
24
fatty acids as cell size enlarging agents as disclosed in U.S. Pat. No. 5,776,389, the entire contents of which are incorporated herein by reference. However the concentration of such agents in a foam that can be used is limited, as high levels depress the glass transition temperature of the polymer and can result in degradation of physical properties such as creep under load (at 80° C.).
Thus it would be desirable to identify cell size enlarging compounds which can be used in conjunction with non-ozone depleting blowing agents and do not have an adverse effect on the physical or mechanical properties of the foam.
BRIEF SUMMARY OF THE INVENTION
The present invention pertains to improved closed cell alkenyl aromatic polymer foams having enlarged cell size, comprising;
(A) from about 80 to about 99.7 percent by weight (based on the combined weight of Components A and B) of one or more alkenyl aromatic polymers, and wherein at least one of said alkenyl aromatic polymers has a molecular weight (M
w
) of from about 100,000 to about 500,000; and
(B) from about 0.3 to about 20 percent by weight (based on the combined weight of Components A and B) of one or more substantially random interpolymers having an I
2
of about 0.01 to about 1000 g/10 min, and an M
w
/M
n
of about 1.5 to about 20; comprising;
(1) from about 8 to about 65 mol % of polymer units derived from;
(a) at least one vinyl or vinylidene aromatic monomer, or
(b) at least one hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer, or
(c) a combination of at least one aromatic vinyl or vinylidene monomer and at least one hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer, and
(2) from about 35 to about 92 mol % of polymer units derived from at least one of ethylene and/or a C
3-20
&agr;-olefin; and
(3) from 0 to about 20 mol % of polymer units derived from one or more of ethylenically unsaturated polymerizable monomers other than those derived from (1) and (2); and
(C) optionally, one or more nucleating agents and
(D) optionally, one or more other additives; and
(E) one or more blowing agents having zero ozone depletion potential and, optionally one or more co-blowing agents, present in a total amount of from about 0.2 to about 5.0 g moles per kg (based on the combined weight of Components A and B); wherein
the cell size of said foam is enlarged about 5 percent or more relative to a
corresponding foam without the substantially random interpolymer.
This combination allows the manufacture of low density alkenyl aromatic polymer foams of enlarged cell size and relatively thick cross-section, when blowing agents of relatively high nucleation potential are employed. When these blowing agents are used with alkenyl aromatic polymer in the absence of the substantially random interpolymers, small cell foams result. In addition, we have unexpectedly found that cell size can be enlarged by using substantiall
Barry Russell P.
Chaudhary Bharat I.
Hood Lawrence S.
Park Chung P.
Copenheaver Blaine
The Dow Chemical Company
Vo Hai
LandOfFree
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