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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a continuous process for shaping, polymerizing, and optionally drying porous polymeric foam from water-in-oil high internal phase emulsions (HIPEs).
2. Description of the Prior Art
Water-in-oil emulsions are dispersions of discontinuous or discrete water particles commonly referred to as the "internal" aqueous phase in a continuous or "external" oil phase. Emulsions can contain as much and more than 70 volume percent
internal phase. These are often referred to as high internal phase emulsions. 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 and is described, for example, in Shell Oil Company (Shell) U.S. Pat. Nos. 5,210,104 and 5,200,433; Lever Brothers Company (Lever) U.S. Pat.
Nos. 4,536,521 and 4,788,225; and The Procter & Gamble Company (P&G) U.S. Pat. Nos. 5,147,345; 5,331,015; 5,260,345; 5,268,224 and 5,318,554. 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 one is not already present in the oil phase) and an electrolyte. To form a stable
emulsion, a surfactant is added to the oil phase prior to emulsification. Commonly used emulsion stabilizing surfactants include, for example, nonionic surfactants, such as sorbitan esters (e.g., sorbitan monooleate and sorbitan monolaurate). The
resulting emulsion is then subjected to polymerization conditions which are sufficient to polymerize the monomers in the oil phase to form a porous polymer.
Ideally, one would like to produce polymerized HIPE foam in a continuous manner, thereby making efficient use of equipment space and volume while simplifying the production process. Continuous processes for the production of HIPE have been
documented (see for example U.S. Pat. Nos. 3,565,817; 3,946,994; 4,018,426; 4,844,620; 5,149,720; 5,198,472; 5,250,576; and 5,827,909) however all of these patents fall short of a fully continuous process by not addressing how to continuously shape,
polymerize, and dry the HIPE once prepared.
U.S. Pat. Nos. 3,565,817; 3,946,994; 4,018,426; and 4,844,620 disclose continuous processes for the production of high internal phase emulsions (HIPEs) but do not address shaping, polymerizing or drying the emulsion.
U.S. Pat. Nos. 5,149,720; 5,198,472; and 5,250,576, issued to Des Marais et al., as well as U.S. Pat. No. 5,827,909, issued to Des Marais disclose continuous processes for the production of polymerizable high internal phase emulsions
(HIPEs). These patents teach that the HIPE, once prepared, can be polymerized by placing the HIPE emulsion in a suitable polymerization container and subjecting the emulsion therein to curing conditions. Therefore, the disclosed process, including HIPE
preparation, shaping, polymerization, and drying is limited to a batch or semi-batch process.
A recent attempt to achieve a more complete continuous process is U.S. Pat. No. 5,670,101 ('101 patent), issued to Nazim et al., which discloses a process whereby a polymeric "tube" is filled with HIPE. The HIPE-filled tube is then spooled and
polymerized. The primary disadvantage of the process disclosed in the '101 patent lies in the fact that it is actually a semi batch process rather than a continuous process. In the '101 process, tubes are filled with HIPE and then wrapped on a spool
until the spool is full. The spool is then removed from the line for polymerization while another spool is wrapped. (see, for example, column 7 lines 39 ff.). The invention of U.S. Pat. No. 5,670,101 is more accurately described as a process of
semi-continuously filling a plastic tube with a polymerizable HIPE. Further, the process of the '101 requires one to unwrap the polymerized foam from the spool, remove the bag from the HIPE and either discard the bag or re-implement at the beginning of
the process.
Unfortunately, while the continuous production of HIPEs is known, current technology is limited to batch or semi-batch processes for shaping, polymerizing and drying the HIPE. It would be desirous to have a continuous process for shaping,
polymerizing and drying polymerized HIPE foam so that the whole process of HIPE foam production could be continuous.
In contrast, the invention of the instant application is continuous in nature all the way through the drying of the final HIPE foam. Unlike prior art processes, the instant invention requires no interruption of the process from the making of the
HIPE through the curing and drying process of the HIPE. The process of the instant invention overcomes the disadvantages of the prior art, since it does not require the HIPE to be placed in containers for polymerization and then removed again for drying
and/or use; nor does the process of the instant invention require the HIPE to be place in bags which need to be wrapped, unwrapped and re-implemented or discarded. Rather, the invention of the application uses a continuous HIPE web to move the HIPE
through the process.
SUMMARY OF THE INVENTION
The invention comprises a fully continuous process for shaping and polymerizing a high internal phase emulsion (HIPE). The process begins by providing a high internal phase emulsion (HIPE) comprising a)at least 70 percent by volume of an
external phase comprising one or more polymerizable monomers, b) a surfactant in an amount effective to produce a high internal phase emulsion and c) an internal phase. The HIPE is then deposited onto a lower moving support substrate and is leveled to a
desired thickness above the support substrate. The support then carries the emulsion through a heating zone for a time sufficient to polymerize at least 75% of the monomers in the HIPE. Finally, the polymerized HIPE is run through a drying zone for a
time sufficient to remove greater than 50% of the internal phase from the final product.
The foams produced by the process of the invention can be useful as, for example, absorbent materials, thermally insulating materials, acoustically insulating materials, and filters.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the invention comprising two lower moving support substrates, an upper moving substrate, an oven for the heating zone, a pair of nip rollers and an oven for the drying zone and a mandrel for rolling the final foam.
FIG. 2 is a schematic view of the invention comprising a lower moving support substrate that becomes bound to the foam, a blade to level the HIPE to a desired thickness, a steam tunnel for the heating zone, a shuttle knife to slice the
polymerized HIPE into sections while on a conveyor belt, and an oven for the drying zone.
FIG. 3 is a schematic view of the invention comprising a lower support substrate, a leveling blade, an oven for the heating zone, nip rollers for the drying zone, and a mandrel onto which the dry foam is collected as rollstock.
FIG. 4 is a side view of the invention comprising vertically oriented moving substrates comprising two lower moving support substrates, one of which becomes bound to the foam, and two moving upper substrates, one of which becomes bound to the
foam; an oven for the heating zone; both nip rollers and an oven for the drying zone; and a mandrel onto which the dry foam is collected as rollstock.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
The invention comprises a fully continuous process for shaping and polymerizing a high internal phase emulsion (HIPE) comprising the steps of:
1) providing a high internal phase emulsion (HIPE) comprising:
a) at least 70 percent by volume of an external phase comprising one or more polymerizable monomers,
b) a surfactant in an amount effective to produce a high internal phase emulsion; and
c) an internal phase
2) depositing the emulsion onto a lower moving support substrate;
3) leveling the emulsion to a desired thickness above the support substrate
4) polymerizing the monomers by running the emulsion and the lower moving support substrate through a heating zone for a time sufficient to polymerize at least 75% of the monomers in the HIPE by the end of the heating zone;
5) running the polymerized HIPE through a drying zone for a time sufficient to produce a foam having greater than 50% of the internal phase removed.
Methods for preparing water-in-oil emulsions are known in the art such as, for example, in U.S. Pat. Nos. 4,522,953 and 5,210,104, the disclosures of which are incorporated herein by reference, and these methods can be employed in the practice
of the present invention. Methods for continuous flow HIPE preparation are also well established in the literature. See, for example, U.S. Pat. Nos. 3,565,817; 3,946,994; 4,018,426; 4,844,620; 5,149,720; 5,198,472; 5,250,576; and 5,827,909, the
disclosures of which are incorporated herein by reference. According to these methods, a HIPE is formed by continuously introducing a certain type of monomer-containing oil phase and a certain type of electrolyte-containing water phase into a dynamic
mixing zone at relatively low water to oil phase ratios. Flow rates are then steadily adjusted to increase the water to oil ratio of the streams fed to the dynamic mixing zone while subjecting the dynamic mixing zone contents to shear agitation which is
sufficient to form a HIPE. The contents of the dynamic mixing zone are then fed to and through a static mixing zone.
While production of polymerizable HIPEs, including processes for the continuous production of HIPEs, are known, current technology is limited to batch or semi-batch processes for shaping, polymerizing and drying the HIPE.
In contrast to known processes, the claimed invention is continuous in nature all the way through the drying of the final HIPE foam. Unlike prior art processes, the instant invention requires no interruption of the process from the making of the
HIPE through the steps of curing and drying. Advantageously, the process of the instant invention does not require the HIPE to be placed in containers for polymerization and then removed again for drying and/or use. Further, the claimed process does
not require the HIPE to be secured in wrappings which need to be wrapped, unwrapped and re-implemented or discarded. Rather, the invention of the application uses a continuous HIPE web to move the HIPE through the process.
Polymerizable HIPEs suitable for use in the instant invention can be either water-in-oil or oil-in water, whereby "water" is not limited to an aqueous based phase but more generally the more polar of the two phases. Similarly, "oil" refers to
the least polar of the two phases. The external phase comprises one or more monomers which can be polymerized to form a foam structure. The internal phase may also contain monomers or crosslinkable polymers, for example as described in U.S. Pat. No.
5,250,576.
Preferably, water-in-oil HIPEs are used wherein the water phase makes up at least 75%, more preferably at least 90%, still more preferably at least 95%, most preferably at least about 98% of the emulsion volume.
The oil phase preferably comprises vinyl polymerizable monomers. Vinyl polymerizable monomers which can be employed in the practice of the present invention are any polymerizable monomer having an ethylenic unsaturation that can be prepared as
part of the oil phase of a HIPE. 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.degree. 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.degree. 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.
While the amount of the vinyl polymerizable monomers most advantageously employed depends on a variety of factors, such as the specific monomers, in general, the vinyl polymerizable monomers are used in an amount up to 100 weight percent of the
total oil phase. Preferably, the vinyl polymerizable monomers are used in an amount greater than 10 weight percent, more preferably greater than about 25 weight percent, still more preferably greater than about 50 weight percent, even more preferably in
an amount greater than 75 weight percent, based on the total oil phase.
Additionally, the HIPE may include a cross-linking monomer. Cross-linking monomers which can be employed in the practice of the present invention for preparing the HIPE include any multifunctional unsaturated monomers capable of reacting with
the vinyl monomers. Preferably, though not required, the cross-linking monomer is soluble in the oil phase. Multifunctional unsaturated cross-linking monomers include, for example, divinylbenzene, ethylene glycol dimethacrylate, 3-butylene
dimethacrylate, trimethylolpropane triacrylate and allyl methacrylate. The amount of cross-linking monomers most advantageously employed depends on a variety of factors, such as the specific monomers and the physical properties desired in the final
foam. If used, the cross-linking monomer is typically used in an amount greater than 0, preferably greater than 5, and most preferably greater than about 10 weight percent based on the total oil phase. The cross-linking monomer can be used in an amount
up to and including 100 weight percent.
Radical initiators are preferably employed in the practice of the present invention to increase the rate of polymerization of the HIPE. Initiators that can be used in this invention include water-soluble initiators such as, for example,
potassium or sodium persulfate and various redox systems such as ammonium persulfate together with sodium metabisulfite and oil-soluble initiators, such as, for example, azobisisobutyronitrile (AIBN), benzoyl peroxide, methyl ethyl ketone peroxide and
di-2-ethylhexyl-peroxydicarbonate and lauroyl peroxide. The initiator can be added to the aqueous phase or to the oil phase, depending on whether the initiator is water-soluble or oil-soluble. Combinations of water-soluble and oil-soluble initiators
can also be used. The initiator should be present in an effective amount to polymerize the monomers. Typically, the initiator can be present in an amount of from about 0.005 to about 20 weight percent, preferably from about 0.1 to about 10 weight
percent and most preferably from about 0.1 to about 5 weight percent, based on the total oil phase.
Optionally, the internal aqueous phase can include a water-soluble electrolyte for aiding the surfactant in forming a stable emulsion, controlling porosity of the foam and/or enhancing the hydrophilicity of the resulting polymeric foam material
if left as a residual component of the foam material. Water-soluble electrolytes which can be employed in the practice of the present invention include inorganic salts (monovalent, divalent, trivalent or mixtures thereof), for example, alkali metal
salts, alkaline earth metal salts and heavy metal salts such as halides, sulfates, carbonates, phosphates and mixtures thereof. Such electrolytes include, for example, sodium chloride, sodium sulfate, potassium chloride, potassium sulfate, lithium
chloride, magnesium chloride, calcium chloride, magnesium sulfate, aluminum chloride and mixtures thereof. Mono- or divalent salts with monovalent anions, such as halides, are preferred. While the amount of electrolytes most advantageously employed
depends on a variety of factors, such as the specific compound, the desired porosity of the foam and the surfactant employed, in general, the electrolytes can be employed up to about 10, more preferably up to about 5 and most preferably up to about 1
weight percent, based on the total aqueous mixture.
Polymeric electrolytes, such as sodium polyacrylate, can also be included in the aqueous phase if desired. Often, polymeric electrolytes can be used to increase the aqueous fluid retention in the final foam as described, for example in U.S.
Pat. No. 5,900,437, the disclosure of which is incorporated herein by reference.
The internal aqueous phase can additionally comprise a non-electrolyte hydrophilizing component, such as, for example, glycerin, which can be left in the foam to enhance hydrophilicity as long as the HIPE can still be prepared and polymerized
into a foam.
The HIPE is generally stabilized by the inclusion of a HIPE-stabilizing surfactant. Surfactants which can be employed in the practice of the present invention for preparing water-in-oil high internal phase emulsions include nonionic surfactants,
such as, for example, sorbitan esters, including sorbitan monooleate and sorbitan monolaurate; glycerol esters, such as glycerol monooleate; diglycerol monoleate; PEG 200 dioleate, partial fatty acid esters of polyglycerol; cationic surfactants, such as
ammonium salts; and anionic surfactants, such as certain organic sulfate and sulfonate compounds. Also suitable are nonionic, anionic, and cationic polymerizable surfactants such as those described in U.S. Pat. No. 5,977,194, the disclosure of which
is incorporated herein by reference. Such surfactants include non-ionic and cationic surfactants having polymerizable vinyl groups and surfactants capable of undergoing a graft reaction (graftable surfactants) at the conditions of polymerization.
Preferred are block copolymer surfactants comprising one or more poly(butylene oxide) block and one or more poly(ethylene oxide) block. Also suitable are polymerizable and non-polymerizable poly(butylene oxide/ethylene oxide) sulfate-based surfactants.
The amount of surfactant used must be such that a water-in-oil high internal phase emulsion will form. Generally, the surfactant need be present in an amount greater than 0, preferably greater than about 0.1 percent by weight of the oil phase.
Generally, the surfactant is used in an amount less than about 25, preferably less than 15, more preferably less than about 10, most preferably less than about 5 percent by weight, based on the oil phase.
According to the instant invention, the polymerizable HIPE is deposited from an emulsifier onto the surface of a lower moving support substrate. Deposition can be accomplished any number of ways including, for example, by extruding the HIPE
through a tube that shuttles back and forth across the lower moving support substrate in the plane of the lower moving support substrate but perpendicular to the direction the lower moving support substrate is moving. The primary role of the lower
moving support substrate is to retain continuity of the HIPE as it is transported into the heating zone for polymerization. The lower moving support substrate can be, for example, a Teflon-coated fiberglass webbed conveyor belt. Such a conveyor belt
can run through the whole process of the shaping, polymerizing and drying process or it can be included in only a portion of the process.
Alternatively, the conveyor can be such that it has 3-dimensional structure to which the HIPE is molded so as to define the HIPE into a web having non-planar 3-dimensional shape. For example, the conveyor can have regularly (or irregularly)
placed dimples that become filled with HIPE such that the final foam will have nipples on its surface. Other examples include a conveyor with embossed or depressed patterns or designs including geometric shapes, insignia, and logos. Similarly, the
conveyor can comprise a series of repeating 3-dimensional molds that are filled with HIPE to produce multiple articles that are either connected or not.
Alternatively, the lower moving support substrate can comprise a webbing that is intended to be incorporated onto or into the final foam. For example, the HIPE can be deposited onto a nonwoven material such as a spunbond polypropylene or
polyester or a polypropylene or polyester mesh material. Additional carrier substrates include materials such as cotton, rayon, nylon, or wood pulp. The primary requirement is a porous structure such that water can permeate through the substrate in the
drying operation. An additional substrate could be a perforated film such that the viscous emulsion does not flow through the perforations but water could be removed through the holes during the drying step. This film could be any combination of
polymeric material or metal deposition with laminate with polymeric materials. An additional option would be to use a non-perforated film to encapsulate the emulsion during the polymerization step and perforate the film prior to the continuous web
entering the drying operation.
One skilled in the art can identify many materials that can be employed as moving support layers. It is not intended that the aforementioned materials be an exhaustive list of possible moving support layers. Additionally, one can employ a
combination of moving support layers such that, for example, one support layer becomes bound to the foam while another does not. One can orient the support layers such that the HIPE is deposited partially on a substrate intended to bind to the final
foam and partially deposited on a moving support substrate not intended to be bound to the final foam, resulting in a HIPE foam with a substrate bound onto or into only a portion of the foam. In addition a substrate can be added to the top foam surface
such that the final product is encapsulated between the substrates.
The lower support substrate can have sides preferably as high as the desired thickness of the HIPE foam extending on opposing edges and perpendicular to the lower support substrate between which the HIPE is deposited. The sides can act as a
gasket against which an optional upper moving substrate positioned above the HIPE can be held thereby sealing the HIPE and preventing oil or aqueous vapors from escaping during polymerization. The sides can also be used to define the shape of the HIPE
sheets regardless of whether they are used to seal the HIPE during polymerization. For example, the sides can be sinusoidal in the plane of the web and with one side out of phase with the side on the opposing edge such that the HIPE is deposited into a
continuous sheet of repeating hour-glass shapes. Once polymerized, the sheet can be cut into individual hour-glass pieces for use in, for example, diapers.
After depositing the HIPE onto the lower moving support substrate the HIPE is leveled to the desired thickness above t | | |
