Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By gas forming or expanding
Reexamination Certificate
1998-12-04
2001-05-15
Foelak, Morton (Department: 1711)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By gas forming or expanding
C264S054000, C264SDIG005, C521S079000, C521S081000, C521S134000, C521S139000, C521S059000, C521S060000
Reexamination Certificate
active
06231795
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
FIELD OF THE INVENTION
This invention describes a method for making soft and flexible foams by expanding blends of polymers comprising (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. A preferred alkenyl aromatic polymer is polystyrene.
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 results in an increase in the softness and flexibility of the resulting foam.
BACKGROUND OF THE INVENTION
Crosslinked olefinic foams are typically made from ethylenic polymers such as low density polyethylene, ethylene vinylacetate copolymer, homogeneous ethylene and/or &agr;-olefin homopolymers or interpolymers comprising ethylene and/or C
3
-C
20
&agr;-olefins including the substantially linear ethylene/&agr;-olefin interpolymers. These include the polyolefin plastomers, such as those marketed by The Dow Chemical Company under the AFFINITY™ tradename and polyethylene elastomers, such as those marketed under the ENGAGE™ tradename by Du Pont Dow Elastomers PLC.
Crosslinking is achieved by conventional means such as peroxides, silane and/or radiation. Some of the advantages of crosslinked foam over noncrosslinked foams are smaller cell sizes (typically less than about 1 mm), smooth skin and thermoformability. However, there are several disadvantages of crosslinked foams, such as: (1) the chemical blowing agents used (for example, azodicarbonamide) are expensive; (2) crosslinked foams expanded with nitrogen are made in energy intensive equipment at high pressures (typically about 10,000 to 30,000 psi); (3) the processes used to make the foams are typically batch processes which are expensive to operate; and (4) the foams cannot be recycled. On the other hand, non-crosslinked olefinic foams are made in continuous processes at relatively high production rates using less expensive physical blowing agents (such as isobutane) and the foams can be recycled (which is environmentally desirable), but these foams are difficult to thermoform.
It is desirable to make soft and flexible non-crosslinked foams with small cell sizes and good aesthetics that could be used as alternatives to crosslinked foams without the disadvantages listed above. We have surprisingly found that non-crosslinked foams made from blends of alkenyl aromatic polymers and specific types and amounts of substantially random interpolymers are soft and flexible with small cell sizes. Furthermore, the foams are thermoformable and can be recycled.
SUMMARY OF THE INVENTION
The present invention pertains to soft and flexible foams having an Asker C hardness of less than about 65 (and processes for their preparation), comprising;
(A) from about 30 to about 70 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 30 to about 70 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 0.1 to about 50 g/10 min, and an M
w
/M
n
of about 1.5 to about 20; comprising
(1) from about 8 to about 45 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 55 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 present in a total amount of from about 0.4 to about 5.0 gram-moles per kilogram (based on the combined weight of Components A and B).
This combination allows the manufacture of soft and flexible low density foams when 30 to 70 wt % of substantially random interpolymers of about 8 to about 45 mol % styrene are blended with alkenyl aromatic polymers. When similar foams are made from blends containing less than 30 wt % of the substantially random interpolymer, the resulting foams are not as soft and flexible as traditional crosslinked olefinic foams. Also when foams are made from blends containing more than 70 wt % of the substantially random interpolymer, the foams collapse at the temperatures required to avoid solidification of the alkenyl aromatic polymer fraction.
Definitions
All references herein to elements or metals belonging to a certain Group refer to the Periodic Table of the Elements published and copyrighted by CRC Press, Inc., 1989. Also any reference to the Group or Groups shall be to the Group or Groups as reflected in this Periodic Table of the Elements using the IUPAC system for numbering groups.
Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.
The term “hydrocarbyl” as employed herein means any aliphatic, cycloaliphatic, aromatic, aryl substituted aliphatic, aryl substituted cycloaliphatic, aliphatic substituted aromatic, or aliphatic substituted cycloaliphatic groups.
The term “hydrocarbyloxy” means a hydrocarbyl group having an oxygen linkage between it and the carbon atom to which it is attached.
The term “copolymer” as employed herein means a polymer wherein at least two different monomers are polymerized to form the copolymer.
The term “interpolymer” is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer. This includes copolymers, terpolymers, etc.
The term “soft foam” is used herein to indicate a foam having an Asker C hardness of less than about 65, preferably less than about 60, more preferably less than about 55 at a foam density of about 95 kg/m
3
or less.
The term “small cell size” is used herein to indicate a foam having a cell size of less than about 1.8 mm.
DETAILED DESCRIPTION OF THE INVENTION
The invention especially covers foams comprising blends of one or more alkenyl aromatic homopolymers, or copolymers of alkenyl aromatic monomers, and/or copolymers of alkenyl aromatic monomers with one or more
Barry Russell P.
Chaudhary Bharat I.
Hood Lawrence S.
Foelak Morton
The Dow Chemical Company
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