Open-cell foam and method of making

Details Open-cell foam and method of making Open-cell foam and method of making

2000-04-20

2001-01-16

Foelak, Morton (Department: 1711)

Plastic and nonmetallic article shaping or treating: processes

Pore forming in situ

By gas forming or expanding

C521S079000, C521S081000, C521S134000, C521S140000, C521S060000

Reexamination Certificate

active

06174471

ABSTRACT:

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
FIELD OF THE INVENTION
The present invention relates to an open-cell foam, and more particularly, to an open-cell foam having a controllable level of open cells, and a method of making such a foam.
The art has recognized that using blends of two thermoplastic resins in the formation of foams may enable one to obtain the advantageous properties of each resin in the resulting foam. For example, foams formed from polystyrene are lightweight and exhibit rigidity and good shape retention, while foams formed from polyolefins have flexibility and good impact absorbing properties. However, blending polyolefin and polystyrene resins has been complicated by the incompatibility of the two resins.
Attempts have been made to solve this incompatibility problem with the use of compatibilizers such as graft or block copolymers which improve adhesion between the two polymer interfaces. However, it has been found that even with the use of a compatibilizer, most polymer blends of polyolefins and polystyrenes are difficult to form into good quality open-cell foams by a conventional extrusion process. Most blended polymer foams formed by extrusion processes result in foams exhibiting poor skins, uneven cell distribution, partial collapse, or weak mechanical strength. This is mainly due to the fact that during the extrusion process, control of the foaming temperature plays a critical role in the formation of a good quality foam, and the foaming temperature range, or “window”, is extremely narrow for the formation of open-cell foams. Thus it would be desirable to be able to provide a wider foaming temperature range to ensure formation of a good quality foam.
Attempts have been made to overcome some of these problems. For example, Park, in U.S. Pat. No. 4,605,682 discloses the production of open-cell foams by an extrusion process, from a blend of polystyrene and polyethylene resins, by lightly crosslinking the resins with a peroxide. However, the addition of a peroxide makes the process more complex as the peroxide is highly reactive. In addition, the resulting foam has a low open cell content and is relatively soft, as polyethylene constitutes the major phase of the blend. It would be advantageous to be able to make a foam in which polystyrene is the major phase so that the resulting foam would have a higher compressive strength, making the foam more suitable for construction applications. It would also be desirable to control the level of open cells so as to achieve the desired foam properties.
U.S. Pat. No. 5,411,687 (D. Imeokparia et al.) describes an extruded open cell alkenyl aromatic polymer foam in which a nucleating agent is used in combination with a foaming temperature from 3 to 15° C. higher than the highest foaming temperature for a corresponding closed-cell foam, resulting in an extruded open cell foam having an open cell content of about 30 to about 80 percent.
U.S. Pat. No. 5,674,916 (C. Scmidt et al.) describes a process for preparing an extruded open cell microcellular alkenyl aromatic polymer foam in which a nucleating agent is used in combination with a blowing agent which has a relatively high intrinsic nucleation potential in an amount small enough to allow formation of an open cell structure and a relatively high foaming temperature. This results in an extruded open cell foam having an open cell content of about 70 percent or more and microcellular cell size of 70 microns or less.
WO/9858991 describes a method of enhancing open cell formation using a blend of alkenyl aromatic polymer and up to about seven weight percent of an ethyleneic copolymer having a Vicat softening point of less than or equal to 85° C. (such as ethylvinyl acetate, EVA).
However, use of incompatible polymeric materials such as LLDPE and EVA as a cell-opening agent at the foaming temperatures used to generate open cells in the foam body, results a deterioration in the surface quality of the foam.
Thus, there is still a need in the art for a good quality open-cell polymer blend foam and to a process for making the foam which provides a wider foaming temperature window improved surface quality and a controllable level of open cells.
SUMMARY OF THE INVENTION
The present invention meets that need by providing an open-cell foam prepared from a blend of an alkenyl aromatic polymer and a substantially random interpolymer and an extrusion process for its preparation, wherein said foam has a controllable level of open-cells and said process for making the foam provides a wider foaming temperature window, resulting in a foam having improved surface quality and a controllable level of open cells.
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 20 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 “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 “open cell foam” is used herein to indicate a foam having at least 20 percent open cells as measured according to ASTM D 2856-A.
The term “optimum foaming temperature” is used herein to indicate a foaming temperature at or above the blends glass transition temperature or melting point and within a range in which the foam does not collapse.
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 copolymerizeable ethylenically unsaturated comonomers (other than ethylene or linear C
3
-C
12
&agr;-olefins) with at least one substantially random interpolymer.
The alkenyl aromatic polymer material may be comprised solely of one or more alkenyl aromatic homopolymers, one or more alkenyl aromatic copolymers, a blend of one or more of each of alkenyl aromatic homopolymers and copolymers, or blends of any of the foregoing with a non-alkenyl aromatic polymer. The alkenyl aromatic polymer material may further include minor proportions of non-alkenyl aromatic polymers. Regardless of composition, 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 homopolymers and copolymers derived from alkenyl aro

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