Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1998-01-06
2001-07-17
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S094000, C521S098000, C521S140000, C521S142000, C521S144000, C521S143000, C521S149000, C521S154000, C522S109000, C522S120000
Reexamination Certificate
active
06262137
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to foamed articles and non-foam flexible materials formed from ethylene-vinyl acetate copolymers and maleic anhydride.
Ethylene-vinyl acetate (EVA) copolymers provide materials that can be processed like other thermoplastics, but which approach a rubbery character in softness and elasticity. EVA copolymers are generally soft materials. However, materials containing EVA copolymers can be difficult to process due to the tackiness of the material.
Generally, polymer materials can be used to produce a variety of articles including foams. Foamed polymeric materials have a variety of uses. For example, natural rubber latex foams provide soft materials for body contact and the application of cosmetics. Polyvinyl chloride (PVC) plastisol foams can have a soft, durable feel that simulates leather to the touch. Open cell foams based on polyurethanes have been made suitable for many applications, such as cushions for packaging, automotive applications, home bedding, filters (e.g., for air conditioners), applicators (e.g., for shoe polish), or sound attenuating panels (e.g., for rooms or speakers).
SUMMARY OF THE INVENTION
In one aspect, the invention features a polymer article including a mixture having a maleic anhydride grafted component and an ethylene-vinyl acetate copolymer. A portion of the mixture is cross-linked (e.g., sufficiently crosslinked to form a flexible polymer article having low tackiness). The mixture can be foamed or non-foamed. In non-foamed articles, the maleic anhydride grafted component can be a polyolefinic polymer.
In another aspect, the invention features a method of making a polymer article. The method includes providing a mixture including an ethylene-vinyl acetate copolymer and maleic anhydride, and cross-linking the mixture sufficiently to form the polymer article. The maleic anhydride is grafted to a portion of the mixture. The mixture can be expanded to form a foamed article. The cross-linking can be peroxide, silane cross-linking, radiation cross-linking, or combinations thereof. The peroxide can be dicumyl peroxide.
The polymer article generally has low tackiness and is flexible. The mixture can include an ethylene-vinyl acetate copolymer, a polyolefinic polymer, or a mixture thereof.
A polymer article having low tackiness has a low degree of self sticking. In other words, a low tackiness material substantially does not stick to itself. Foamed materials having low tack do not block. For example, the materials do not block when surfaces of two foam pieces slide over each other without sticking to each other.
A flexible article bends readily without cracking or permanently deforming. The flexibility of an article can be tested by measuring the compression deflection of the article according to ASTM-3575.
The vinyl acetate content of the ethylene-vinyl acetate copolymer can be between about 9 and about 60 percent, preferably between about 15 and about 50 percent, and more preferably between about 15 and about 35 percent.
The polyolefinic polymer can be grafted with maleic anhydride. In other embodiments, the ethylene-vinyl acetate copolymer can be grafted with maleic anhydride. The method can include grafting maleic anhydride to the polyolefinic polymer, the ethylene-vinyl acetate copolymer, or combinations thereof.
The article can include between about 1 and about 90 weight percent of a maleic anhydride grafted polyolefinic polymer, preferably between about 5 and about 30 weight percent, and more preferably between about 5 and about 15 weight percent. The maleic anhydride content of the grafted polyolefinic polymer can be between about 0.01 and about 10 weight percent, preferably between about 0.5 and about 2.0 weight percent.
In preferred embodiments, the article is a foamed article. The foamed article can be an open cell or closed cell foam. The article can have a foam density between about 1.5 and 50 pounds per cubic foot. When the article is a closed cell foam, the foam can have a 25% compression deflection of less than 3 psi. In other preferred embodiments, the article is non-foamed. The non-foamed article is flexible and has low tackiness. The foamed and non-foamed article can be suitable for use in, for example, wire and cable applications. The article can be a bead or particulated foam.
The article can be expanded to form a foam. Expansion of the mixture can include free expansion or compression molding of the mixture. Expanding can take place before cross-linking, during cross-linking, and/or after cross-linking. Compression molding can include the steps of pressing the polymer mixture using a high tonnage press at a temperature of between 240 and 480° F. (e.g., between 275 and 320° F.) and a pressure of between 50 and 5000 psi (e.g., between 250 and 2500 psi) for between 20 and 90 minutes followed by heating the polymer mixture at a temperature between 300 and 380° F.
The foamed material can be crushed after expansion to form an open cell foamed article. A coating, an adhesive, or a laminated layer can be applied to a surface of then article, or the article can be dipped to form a layer on the surface of the article.
The mixture can include other resins, foaming agents, cross-linking agents, activators (e.g., between 0.1 and 5 weight percent), foaming agents (e.g., between 2 and 50 weight percent), particulate fillers, fibrous fillers, antioxidants, ultraviolet stabilizers, thermal stabilizers, pigments and colorants, cell-growth nucleants such as talc, cell-structure stabilizers such as fatty acids or amides, property-modifiers, processing aids, additives, fire retardants, antistatic components, antimicrobial components, or catalysts to accelerate cross-linking and other reactions.
In another aspect, the invention features a method of manufacturing a foamed polymer article. The method includes providing a mixture including an ethylene-vinyl acetate copolymer and maleic anhydride grafted to a portion of the mixture, cross-linking the mixture sufficiently to form a flexible polymer article having low tackiness, and expanding the mixture to form a foamed polymer article in a vertical oven. The cross-linking can be silane, peroxide, or irradiation cross-linking, or a combination thereof. The foamed polymer article has a thickness between about 0.015 and 5/8 inch and a density between about 1.5 and 40 pounds per cubic foot. The method can include applying an adhesive to a surface of the foamed polymer article. The maleic anhydride can improve bonding to the adhesive.
An open cell foam is a foam where there is an interconnection between cells in the foam. There can be greater than about 10 percent open cells (i.e., between 10 and 50 percent) in an open cell foam article, preferably greater than 40 percent, more preferably greater than 80 percent, and most preferably greater than 90 percent. The amount of open cells in a foam can be increased by crushing the foam. A crushed open cell foam can have between 50 and about 98 percent open cells.
A closed cell foam has a predominance of closed cells. For example, a preferred closed cell foam can have 70% or greater closed cells.
The open cell content of a foam can be determined by measuring the amount of water that is absorbed into the foam when the foam is immersed in water. Another method is a gas-volume method using a pycnometer, such as a Quantachrome Model 1000 pycnometer, which measures the percentage of open cells according to method ASTM D-2858.
A low-density polyethylene, or LDPE, is a polymer of ethylene with a density typically between 0.915 and 0.930 g cm
—3
. LDPE resin densities directly relate to the resulting bulk property stiffness. This can limit the degree of mechanical flexibility in foam structures thereof since the lower limit of secant moduli for LDPE is about 20 ksi. While processability of LDPE is quite good, the physical properties, in particular the tensile strength, low-temperature flexibility and toughness, are less than would be obtained from a linear low density polyethylene (LLDPE), due in part to the substantially non-linear
Bambara John D.
Hurley Robert F.
Kozma Matthew L.
Smith Scott C.
Fish & Richardson P.C.
Foelak Morton
Sentinel Products Corp.
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