Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-08-25
2001-10-16
Cooney, Jr., John M. (Department: 1711)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06303834
ABSTRACT:
BACKGROUND OF THE INVENTION
Water-in-oil emulsions are dispersions of discontinuous or discrete aqueous particles commonly referred to as the “internal” aqueous phase in a continuous or “external” oil phase. Emulsions can contain as much as and more than 70 volume percent internal phase. These are often referred to as high internal phase emulsions (HIPEs). The volume fraction of the internal aqueous phase in such emulsions can be as high as 90 percent and frequently is as high as 95 percent with some HIPEs being reported as high as 98 percent aqueous phase.
The use of high internal phase emulsions (HIPEs) in forming porous polymeric materials is well known. See for example: U.S. Pat. Nos. 5,210,104; 5,200,433; 4,536,521; 4,788,225; 5,147,345; 5,331,015; 5,260,345; 5,268,224 and 5,318,554. HIPE polymerization has gained increasing interest as open-celled polymeric foams having the capacity to absorb relatively high amounts of water and other liquids can be produced. In the described HIPEs, the external oil phase typically comprises a vinyl polymerizable monomer, such as 2-ethylhexyl acrylate and styrene, and a cross-linking monomer such as divinylbenzene. The internal aqueous phase typically comprises water, a radical initiator (if not in the oil phase) and an electrolyte. To form a stable emulsion, a HIPE surfactant is added to the oil phase prior to emulsification. Commonly used HIPE stabilizing surfactants include nonionic surfactants such as sorbitan esters (for example, sorbitan monooleate and sorbitan monolaurate). Other known HIPE stabilizing surfactants include certain polyglycerol aliphatic esters such as those described in U.S. Pat. No. 5,500,451 and 5,817,704, the entire contents of which are incorporated herein by reference.
In order to effectively stabilize HIPEs, the aforementioned surfactants must be used in relatively high concentrations (typically above 5 weight percent of the oil phase). When used at lower concentrations (e.g., less than 5 weight percent based on the weight of the oil phase, or about 0.06 weight percent based on the weight of the entire emulsion), these surfactants do not effectively stabilize a HIPE through polymerization to an open-celled foam. See J. M. Williams, D. A. Robleski,
Langmuir
, 4, (1988) 656-662.
Not only does the use of a surfactant add significantly to the cost of HIPE materials, in many applications residual surfactant must be removed from the final product, thus further adding to the cost of producing HIPE materials. For example, as described in U.S. Pat. No. 4,788,225, the surfactant may be an extractable residue which can be removed through post-polymerization rinses. If not removed, the surfactant residue may create a problem when it comes in contact with sensitive human skin.
Therefore, it is desirable to prepare open-celled polymerized HIPE foams with as little extractable surfactant as possible. One way to reduce the amount of extractable surfactant is to use a polymerizable surfactant, as described in U.S. Pat. No. 5,977,194 the contents of which are incorporated herein by reference. Another way is to include a long hydrophobic component which is sufficient to mechanically bind the surfactant into the foam during polymerization.
It would be desirable to provide surfactants which can effectively stabilize HIPEs and form open-celled HIPE materials at relatively low concentrations (e.g., below about 2 weight percent based upon the total weight of the oil phase of the emulsion) and/or which produce HIPE materials with relatively small amounts of extractable surfactants.
SUMMARY OF THE INVENTION
The present invention is a HIPE having at least 70 volume percent of an internal aqueous phase and less than 30 volume percent of an external oil phase wherein the oil phase comprises a polymerizable monomer and a HIPE stabilizing surfactant. Preferably the polymerized HIPE material has a relatively small amount of extractable surfactant (e.g., less than about 5 weight percent and preferably less than about 2 weight percent based upon the weight of the polymer). In one embodiment, the oil phase of the subject HIPE includes less than about 2 weight percent of a highly efficient oil soluble surfactant effective to stabilize the emulsion. In yet another embodiment the invention includes a class of oil soluble, polyoxyalkyl-containing surfactants. Processes for making the subject HIPEs with such surfactants, porous polymeric HIPE materials (e.g., open celled foams) and absorbent articles (e.g., acoustical modulating articles, thermal insulating articles, garments and garment components such as diapers, and/or a filtering article), made from such HIPEs and methods for making such polymeric materials are also part of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The HIPEs of the present invention are useful in preparing low density polymeric foam materials. Highly hydrophilic foam materials made according to the present invention have a particularly useful application in the manufacture of diapers or other articles which absorb or retain aqueous body fluids.
The high internal phase emulsion (HIPE) of the present invention is a water-in-oil emulsion having greater than about 70 volume percent, more preferably greater than about 90 volume percent and, most preferably greater than about 95 volume percent of an internal aqueous phase and less than about 30 volume percent, more preferably, less than about 10 volume percent and, most preferably, less than about 5 volume percent of an external oil phase. HIPEs of as much as 98 volume percent or more of internal aqueous phase can be made by the present invention. The external oil phase comprises one or more vinyl polymerizable monomers and a cross-linking monomer. The internal aqueous phase comprises water. Typically, a water-soluble radical initiator is added in the aqueous phase. If an oil-soluble initiator is employed, it is added in the oil phase. Additionally, the HIPE comprises a HIPE stabilizing surfactant.
Vinyl polymerizable monomers which can be employed in the practice of the present invention are any polymerizable monomer having an ethylenic unsaturation. In general, the HIPEs are advantageously prepared from either or both (i) at least one monomer that tends to impart glass-like properties (glassy monomers) to the resulting porous polymeric material and (ii) at least one monomer that tends to impart rubber-like properties (rubbery monomers) to the resulting porous polymeric materials.
The glassy monomers are, for the purposes of the present invention, defined as monomeric materials which would produce homopolymers having a glass transition temperature above about 40° C. Preferred glassy monomers include methacrylate-based monomers, such as, for example, methyl methacrylate, and styrene-based monomers, such as, for example, various monovinylidene aromatics such as styrene, o-methylstyrene, chloromethylstyrene, vinylethylbenzene and vinyl toluene. More preferred glassy monomers include styrene, o-methylstyrene, and chloromethylstyrene. The most preferred glassy monomer is styrene.
The rubbery monomers are, for the purposes of the present invention, defined as monomeric materials which would produce homopolymers having a glass transition temperature of about 40° C. or lower. Preferred rubbery monomers include alkyl esters of ethylenically unsaturated acids (“acrylate esters” or “methacrylate esters”), such as 2-ethylhexyl acrylate, butyl acrylate, hexyl acrylate, butyl methacrylate, lauryl methacrylate, isodecyl methacrylate and mixtures thereof; vinyl aliphatic and alicyclic hydrocarbons such as butadiene; isoprene; and combinations of these comonomers. More preferred rubbery monomers include butyl acrylate, 2-ethylhexyl acrylate, butadiene, isoprene and combinations of these comonomers. The most preferred rubbery monomer is 2-ethylhexyl acrylate.
Preferably, the HIPE emulsion includes at least one glassy monomer and at least one rubbery monomer. Without being bound by theory, it is believed that the rubbery monomer provides the foams with flexibility and is used in a
Green Daniel Patrick
Mork Steven W.
Rose Gene D.
Black Edward W.
Cooney Jr. John M.
The Dow Chemical Company
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