|Title of Invention||
A CONTINUOS PROCESS OF FORMING A POLYMERIC FOAM MATERIAL
|Abstract||The present invention is directed to a method for reducing monomer loss during curing of a high internal phase emulsion. The method has the steps of: forming a water-in-oil emulsion, curing the monomer component in the emulsion in a saturated steam environment, and forming a saturated polymeric foam material. The water-in-oil emulsion has an aqueous phase and an oil phase comprising a monomer component.|
|Full Text||FIELD OF THE INVENTION The present invention relates to a continuous process of forming a polymeric foam material. More specifically, the present invention relates to a method for reducing monomer loss during curing of a high internal phase emulsion.
BACKGROUND OF THE INVENTION
The development of microporous foams is the subject of substantial commercial interest. Such foams have found utility in various applications, such as thermal, acoustic, electrical, and mechanical (e.g., for cushioning or packaging) insulators; absorbent materials; filters; membranes; floor mats; toys; carriers for inks, dyes, lubricants, and lotions; and the like. References describing such uses and properties of foams include Oertel, G., "Polyurethane Handbook"; Hanser Publishers: Munich, 1985, and Gibson, L. J.; Ashby, M. F.. "Cellular Solids. Structure and Properties"; Pergamon Press: Oxford, 1988. The term "insulator" refers to any material which reduces the transfer of energy from one location to another. The term "absorbent" refers to materials which imbibe and hold or distribute fluids, usually liquids, an example being a sponge. The term "filter" refers to materials which pass a fluid, either gas or liquid, while retaining impurities within the material by size exclusion, interception, electrostatic attraction, adsorption, etc. Other uses for foams are generally obvious to one skilled in the art.
Open-celled foams prepared from High Internal Phase Emulsions (hereinafter referred to as "HIPE") are particularly useful in a variety of applications including absorbent disposable articles (US Patents 5,331, 015 (DesMarais et al.) issued July 19, 1994, 5,260,345 (DesMarais et al.) issued November 9, 1993, 5,268, 224 (DesMarais et al.) issued December 7, 1993, 5,632,737 (Stone et al.) issued May 27, 1997, 5,387,207 (Dyer et al.) issued February 7, 1995, 5,786,395 (Stone et al.) July 28, 1998, 5,795,921 (Dyer et al.) issued August 18, 1998), insulation (thermal, acoustic, mechanical) (US Patents 5,770,634 (Dyer et al.) issued June 23, 1998, 5,753,359 (Dyer et al.) issued May 19, 1998, and 5,633,291 (Dyer et al.) issued May 27,1997), filtration (Bhumgara, Z. Filtration & Separation 1995, March, 245-251; Walsh et al. J. Aerosol Sci. 1996, 27,5629-5630; published PCT application W/O 97/37745, published on October 16, 1997, in the name of Shell Oil Co.), and various other uses. The HIPE process provides facile control over the density, cell and pore size and distribution, proportion of cell struts to windows, and porosity in these foams.
Economics is an important issue in making HIPE foams commercially attractive.
Especially, it is important to make HIPE efficiently and with cost effective equipment. There are
some attempts to achieve the goal; however there is still a substantial opportunity for substantial
improvement of efficiency during the process for making HIPE. Accordingly, it would be
desirable to develop a method for reducing material loss during the process for making and curing
the HIPE and to use cost effective equipment.
SUMMARY OF THE INVENTION
The present invention relates to a method for reducing monomer loss during curing of
HIPE. The method has the steps of a) forming a water-in-oil emulsion having an aqueous phase
and an oil phase containing a; monomer component; b) curing the monomer component in the
emulsion in a saturated steam environment with a quiescent atmospheric layer above the
emulsion; and c) forming a saturated polymeric foam material. In the present invention, the
monomer loss can be less than 10%, preferably less than 5%, and more preferably less than 3.5%.
Preferably, the saturated steam is in equilibrium with the emulsion's aqueous component
and a small headspace is in equilibrium with the monomer component. As a result, the
evaporation or disruption of the emulsion is prevented. Preferably, the headspace is less than 80
mm, preferably less than 40 mm.
In another embodiment, the method of the present invention has the steps of a) forming a
water-in-oil emulsion; b) curing the emulsion in a saturated steam environment in an oven which
is preferably a serpentine design which can preferably be formed from belts; and c) forming a
saturated polymeric form material. Preferably, the oven can have exit and entrance points which
are covered to minimize steam loss but allow entry of the emulsion and exit of the cured emulsion
The present invention may provide a method for avoiding monomer loss during the curing
process. Also, the present invention may provide a method for using a space of an oven more
efficiently during the curing process.
BfrlEF DESCRIPTION OF THE DRAWINGS
Figure 1 describes an overall view of an oven suitable for forming HIPE foams according to
the present invention.
Figure 2 describes a cutaway view of the oven showing the relationship of belts.
Figure 3 describes a detailed view of a deposition area at the entrance to the oven.
DETAILED DESCRIPTION OF THE INVENTION
The following definitions are offered relative to the current invention.
All percentages, ratios and proportions herein are by weight of the final composition,
unless otherwise specified. But we refer to volume to weight ratio in the body. All
temperatures are hi degrees Celsius (°C) unless otherwise specified.
As used herein, the term "comprising" and its derivatives, as used herein, are intended to
be open ended terms that specify the presence of the stated features, elements, components,
groups, integers, and/or steps, but do not exclude the presence of other, unstated features,
elements, components, groups, integers, and/or steps. This definition also applies to words of
similar meaning, for example, the terms "have", "include", "be provided with" and their
derivatives. It also means that other steps, structures, elements, etc. which do not affect the end
result can be added. This term encompasses the terms "consisting of and "consisting essentially
"Curing" is the process of converting a HIPE to a HIPE foam. Curing involves the
polymerization of monomers into polymers. A further step included in the curing process is
crosslinking. A cured HIPE foam is one which has the physical properties, e.g., mechanical
integrity, to be handled in subsequent processing steps (which may include a post-curing
treatment to confer the final properties desired). Generally, curing is effected via the application
of heat. An indication of the extent of cure is the mechanical strength of the foam, as measured by
yield stress using the method described in the Test Methods section below.
"Polymerization" is the part of the curing process whereby the monomers of the oil phase
are converted to a relatively high molecular weight polymer.
"Crosslinking" is the part of the curing process whereby monomers having more than one
functional group with respect to free radical polymerization are copolymerized into more than one
chain of the growing polymer.
A "batch" process for producing HIPE foam generally involves collecting the HIPE in a
specific container in which the HIPE is cured. "Batch" would include processes wherein multiple
small containers of relatively sophisticated shapes are used to collect the HIPE. Such shaped
vessels can provide for "molded" shapes having three-dimensional features. A "continuous"
process for producing HIPE foam generally involves collecting the HIPE on a moving web or
within a pipe or tube or manifold which may pass through a heating zone and produce a
continuous element of cured HIPE foam of varied shape and cross-section.
The term "equilibrium" is used to describe the atmosphere above the HIPE.
Specifically, the saturated steam is in equilibrium with the emulsion's aqueous component and the
small headspace is in equilibrium with the monomer component. Equilibrium is defined to mean
that there is a reduced driving force for molecules to leave the material and go into the head space.
The fully saturated water vapor phase reduces any water evaporation and helps to prevent
molecules from leaving the material. Equilibrium is not used to mean that the composition,
temperature, and pressure are the same in the material and the headspace.
A. General Foam Materials
1 .Oil Phase Components
The continuous oil phase of the HIPE comprises monomers that are polymerized to form
the solid foam structure and the emulsifier necessary to stabilize the emulsion. In general, the
monomers will include from about 20 to about 97% by weight of at least one substantially waterinsoluble
monofunctional alkyl acrylate or alkyl methacrylate. Exemplary monomers of this type
include C4 -C18alkyl acrylates and C2-C18 methacrylates. Preferred monomers of this type
include 2-ethylhexyl acrylate, n-butyl acrylate, hexyl acrylate, n-octyl acrylate, n-nonyl acrylate,
n-decyl acrylate, isodecyl acrylate, n-tetradecyl acrylate, benzyl acrylate, nonyl phenyl acrylate,
n-hexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, n-nonyl methacrylate, ndecyl
methacrylate, isodecyl methacrylate, n-dodecyl methacrylate, n-tetradecyl methacrylate, and
n-octadecyl methacrylate. As the level of these monomers in the oil phase formulation is
increased, the Tg of the resulting polymeric HIPE foam tends to be reduced. This group of
monomers is referred to as Tg lowering monomers and will generally comprise 20% to about
97%, more preferably 45% to about 70%, by weight of the monomer component.
The oil phase will also comprise from about 2 to about 50% by weight of a substantially
water-insoluble, polyfunctional crosslinking alkyl acrylate or methacrylate. This crosslinking
comonomer, or crosslinker, is added to confer strength and resilience to the resulting HIPE foam.
Exemplary crosslinking monomers of this type comprise monomers containing two or more
activated acrylate and/or methacrylate groups. These generally are the result of condensation
reaction of acrylic acid or methacrylic acid with polyfunctional alcohols. Nonlimiting examples
of this group include 1,6-hexanedioldiacrylate, 1,4-butanedioldimethacrylate, trimethylolpropane
triacrylate, trimethylolpropane trimethacrylate, 1,12-dodecyldimethacrylate, 1,14-
tetradecanedioldimethacrylate, ethylene glycol dimethacrylate, neopentyl triacrylate, glucose
pentaacrylate, sorbitan pentaacrylate, and the like. Such di-, tri-, terra-, and higher acrylates and
methacrylates as provided by suppliers often contain impurities such as incompletely esterified
alcohols that may be inimical to emulsion formation and stability. It can be useful, as detailed
hereinafter, to remove these alcohols at least partially to improve emulsion stability and formation
quality of the resulting HIPE foams.
Any third substantially water-insoluble comonomer may be added to the oil phase in weight
percentages of from about 0% to about 10%, preferably from about 2% to about 8%, to modify
properties in other ways. In certain cases, "toughening" monomers may be desired which impart
toughness to the resulting HIPE. These include monomers such as styrene, vinyl chloride,
isoprene, and chloroprene. Without being bound by theory, it is believed that such monomers
aid in stabilizing the HIPE during curing to provide a more homogeneous and better formed HOPE
foam which results in better toughness, tensile strength, abrasion resistance, etc. Monomers may
also be added to confer flame retardancy as disclosed in U.S. Patent 6,160,028 to Dyer.
Monomers may be added to confer color (e.g., vinyl ferrocene), fluorescent properties, radiation
resistance, opacity to radiation (e.g., lead tetraacrylate), to disperse charge, to reflect incident
infrared light, to absorb radio waves, to form a wettable surface on the HIPE foam struts, or for
any other purpose. In some cases, these additional monomers may slow the overall process of
conversion of HIPE to HIPE foam, the tradeoff being necessary if the desired property is to be
conferred. Thus, it is desired in some cases to minimize the amount of such monomers to keep
the slowing of the rate of conversion to a minimum, or to exclude these types unless needed.
The oil phase will further contain a effective amount of emulsifier necessary for stabilizing
the HIPE. Such emulsifiers are generally well known to those skilled in the art and examples are
The oil phase may also contain an oil soluble initiator such a benzoyl peroxide, di-t-butyl
peroxide, lauroyl peroxide, azoisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-
azobisisobutyronitrile, and other such initiators well known to those skilled in the art. When oil
phase initiators are employed, it can be preferred that their addition to the monomer phase be
immediately before or just during emulsification to reduce the potential for premature
2. Aqueous Phase Components
The discontinuous aqueous internal phase of the HIPE is generally one or more aqueous
solutions containing one or more dissolved components. One essential dissolved component of
the water phase is a water-soluble electrolyte. The dissolved electrolyte minimizes the tendency
of monomers, comonomers, and crosslinkers that are primarily oil soluble to also dissolve in the
water phase. Such electrolyte can include a buffering agent for the control of pH during the
polymerization, including such inorganic counterions as phosphate, borate, and carbonate, and
mixtures thereof, for example.
Another component of the aqueous phase is a water-soluble free-radical initiator or a
"polymerization initiator" as may be known to the art. The initiator can be present at up to about
20 mole percent based on the total moles of polymerizable monomers present in the oil phase.
More preferably, the initiator is present in an amount of from about 0.001 to about 10 mole
percent based on the total moles of polymerizable monomers in the oil phase. Suitable initiators
include ammonium persulfate, sodium persulfate, potassium persulfate, 2,2'-azobis (N,N'-
dimethyleneisobutyramidine) dihydrochloride, and other azo initiators of this type. A delayed
initiator or free radical inhibitor can also be used. The delayed initiators will extend the curing
time but will help to extend the life of the mixing equipment. A suitable delayed initiator is
TEMP (2,2,6,6-53543methyl-l-piperidinyloxy) which can be obtained from Aldrich;
Yet another optional corttponent is a potentiator of the initiator, including salts comprising
the sulfite moiety. A preferred example is sodium hydrosulfite (NaHSO3). Other examples
include inorganic salts of reduced transition metals such as Fe(II) sulfate and the like. Small
amounts of water soluble monomers may also be included. Examples include acrylic acid and
vinyl acetate. The water soluble monomer may aid in making the surface of the HIPE more
Before combining the aqueous phase with the oil phase, it may be desired to degas the
aqueous phase. Examples of processes to degas a component of a HIPE are included in US
5,362,244 to DesMarais et al.
The emulsifier is necessary for forming and stabilizing the HIPE. The emulsifier is
generally included in the oil phase and tends to be relatively hydrophobic in character. (See for
example Williams, J. M., Langmuir 1991, 7, 1370-1377.) For preferred HIPEs that are
polymerized to make polymeric foams, suitable emulsifiers can include sorbitan monoesters of
branched Cie -C24 fatty acids, linear unsaturated Cj6 -C^ fatty acids, and linear saturated C12 -Ci4
fatty acids, such as sorbitan monooleate, sorbitan monomyristate, and sorbitan monoesters derived
from coconut fatty acids. Preferred emulsifiers include sorbitan monolaurate (e.g., SPAN® 20,
preferably greater than about 40%, more preferably greater than about 50%, most preferably
greater than about 70% sorbitan monolaurate), sorbitan monooleate (e.g., SPAN® 80, preferably
greater than about 40%, more preferably greater than about 50%, most preferably greater than
about 70% sorbitan monooleate), diglycerol monooleate (e.g., preferably greater than about 40%,
more preferably greater than about 50%, most preferably greater than about 70% diglycerol
monooleate), diglycerol monoisostearate (e.g., preferably greater than about 40%, more preferably
greater than about 50%, most preferably greater than about 70% diglycerol monoisostearate),
diglycerol monomyristate (e.g., preferably greater than about 40%, more preferably greater than
about 50%, most preferably greater than about 70% sorbitan monomyristate), the cocoyl (e.g.,
lauryl and myristoyl) ethers of diglycerol, and mixtures thereof.
Particularly useful are diglycerol monoesters of branched C)6-C24 fatty acids, linear
unsaturated Cie-C22 fatty acids, or linear saturated C]2-Ci4 fatty acids, such as diglycerol
monooleate (i.e., diglycerol monoesters of C18:l fatty acids), diglycerol monomyristate,
diglycerol monoisostearate, and diglycerol monoesters of coconut fatty acids; diglycerol
monoaliphatic ethers of branched C\& -€24 alcohols (e.g. Guerbet alcohols), linear unsaturated Cie-
€22 alcohols, and linear saturated Cn -Cu alcohols (e.g., coconut fatty alcohols), and mixtures of
these emulsifiers. See US Patent 5,287,207 (Dyer et al.), issued Feb. 7, 1995 which describes
the composition and preparation suitable polyglycerol ester emulsifiers and US Patent 5,500,451,
issued Mar. 19, 1996 to Stephen A. Goldman et al., which describes the composition and
preparation suitable polyglycerol ether emulsifiers. An exemplary emulsifier which functions
very well is diglycerol monooleate (DGMO). Other emulsifiers of this general sort also include
diglycerol monomyristate (DGMM), diglycerol monoisostearate (DGMIS), diglycerol
monopalmitate (DGMP), other diglycerol monoesters of coconut fatty acids, sorbitan monooleate,
sorbitan monomyristate, sorbitan monoesters of coconut fatty acids, sorbitan isostearate, and like
compounds and mixtures thereof. US Patent 5,786,395 (Stone et al.) issued July 28, 1998 offer
further examples of these emulsifiers. Another preferred emulsifier, referred to herein as
PGMIS, is a polyglycerol isostearate.
Another preferred emulsifier is described in copending US Patent 6,207,724, entitled Foam
Materials and High Internal Phase Emulsions Made Using Oxidatively Stable Emulsifiers, filed in
the name of Hird, et al. Such emulsifiers comprise a composition made by reacting a
hydrocarbyl substituted succinic acid or anhydride or a reactive equivalent thereof with either a
polyol (or blend of polyols), a polyamine (or blend of polyamines) an alkanolamine (or blend of
alkanol amines), or a blend of two or more polyols, polyamines and alkanolamines. An
exemplary emulsified which functions very well is polyglycerol succinate. The lack of
substantial carbon-carbon unsaturation renders them substantially oxidatively stable.
Such emulsifiers are advantageously added to the oil phase so that they comprise between
about 1% and about 15% thereof. Obviously, emulsifiers that are particularly able to stabilize
HIPEs at high temperatures are preferred. Diglycerol monooleate (DGMO) is exemplary in this
Coemulsifiers may also be used to provide additional control of cell size, cell size
distribution, and emulsion stability, particularly at higher temperatures (e.g., greater than about
65°C). Exemplary coemulsifiers include phosphatidyl cholines and phosphatidyl cholinecontaining
compositions, aliphatic betaines, long chain C}2-C22 dialiphatic, short chain C\-C^
dialiphatic quaternary ammonium salts, long chain C,\2-^22 dialkoyl(alkenoyl)-2-hydroxyethyl,
short chain C\-C$ dialiphatic quaternary ammonium salts, long chain ^\i-^11 dialiphatic
imidazolinium quaternary ammonium salts, short chain C^-C4 dialiphatic, long chain C \2~^22
monoaliphatic benzyl quaternary ammonium salts, the long chain C\2~C22 dialkoyl(alkenoyl)-2-
aminoethyl, short chain C^-fe^ monoaliphatic, short chain Ci-C^ monohydroxyaliphatic
quaternary ammonium salts. Particularly preferred is ditallow dimethyl ammonium methyl
sulfate (DTDMAMS). Such coemulsifiers and additional examples are described in .greater detail
in US Patent 5,650,222, issued in the name of DesMarais, et al. on July 22,1997.
4. Optional Ingredients
Various optional ingredients may also be included in either the water or oil phase for
various reasons. Examples inplude antioxidants (e.g., hindered phenolics, hindered amine light
stabilizers, UV absorbers), plasticizers (e.g., dioctyl phthalate, dinonyl sebacate), flame retardants
(e.g., halogenated hydrocarbons, phosphates, borates, inorganic salts such as antimony trioxide or
ammonium phosphate or magnesium hydroxide), dyes and pigments, fluorescers, filler particles
(e.g., starch, titanium dioxide, carbon black, or calcium carbonate), fibers, chain transfer agents,
odor absorbers such as activated carbon particulates, dissolved polymers and oliogomers, and
such other agents as are commonly added to polymers for a variety of reasons. Such additives
may be added to confer color, fluorescent properties, radiation resistance, opacity to radiation
(e.g., lead compounds), to disperse charge, to reflect incident infrared light, to absorb radio
waves, to form a wettable surface on the HIPE foam struts, or for any other purpose.
B. Processing Conditions for Obtaining HIPE Foams
Foam preparation typicajly involves the steps of: a) forming a water-in-oil emulsion having
an aqueous phase and an oil phase including a monomer component; b) curing the monomer
component in the emulsion in a saturated steam environment; and c) forming a saturated
polymeric form material. After Step c), it is optional to add the step of squeezing and washing
the cellular polymeric structure to remove the original residual water phase from the polymeric
foam structure and, if necessary, treating the polymeric foam structure with a hydrophilizing
surfactant and/or hydratable salt to deposit any needed hydrophilizing surfactant/hydratable salt,
and thereafter dewatering this polymeric foam structure.
a) Formation a water-in-oil emulsion
The HIPE is formed by combining the water and oil phase components in a ratio between
about 8:1 and 140:1. This is termed the "water-to-oil" or W:O ratio and is significant as it is the
primary determinant of the density of the resulting dried HIPE foam. Preferably, the ratio is
between about 10:1 and about 75:1, more preferably between about 13:1 and about 65:1. An
exemplary W:O ratio is about 45:1. (The ratio is generally expressed as volume of aqueous
phase to weight of organic phase.) As discussed above, the oil phase will typically contain the
requisite monomers, comonomers, crosslinkers, and emulsifiers, as well as optional components.
The water phase will typically contain electrolyte or electrolytes and polymerization initiator or
The HIPE can be formed from the combined oil and water phases by subjecting these
combined phases to shear agitation. Shear agitation is generally applied to the extent and for a
time period necessary to form a stable emulsion. Such a process can be conducted in either
batchwise or continuous fashion and is generally carried out under conditions suitable for forming
an emulsion where the water phase droplets are dispersed to such an extent that the resulting
polymeric foam will have the requisite structural characteristics. Emulsification of the oil and
water phase combination will frequently involve the use of a mixing or agitation device such as an
One preferred method of forming HIPE involves a continuous process that combines and
emulsifies the requisite oil and water phases. In such a process, a liquid stream comprising the
oil phase is formed. Concurrently, a separate liquid stream comprising the water phase is also
formed. The two separate streams are provided to a suitable mixing chamber or zone at a
suitable emulsification pressure and combined therein such that the requisite water to oil phase
weight ratios previously specified are achieved. More than one stream of oil phase and water
phase can also be used.
In the mixing chamber or zone, the combined streams are generally subjected to shear
agitation provided, for example, by an impeller of suitable configuration and dimensions, or by
any other means of imparting shear or turbulent mixing generally known to those skilled in the
art. Examples of such alternative means of providing shear include in-line mixers as are
described in commonly assigned US Patent 6,369,121 Bl (Catalfamo et al), issued April 9, 2002.
Shear will typically be applied to the combined oil/water phase stream at an appropriate rate and
extent. Once formed, the stable liquid HIPE can then be withdrawn or pumped from the mixing
chamber or zone. One preferred method for forming HIPEs using a continuous process is
described in greater detail in US Patent 5,149,720 (DesMarais et al), issued September 22, 1992.
See also commonly assigned US Patent 5,827,909 (DesMarais) issued on October, 27, 1998
which describes an improved continuous process having a recirculation loop for the HIPE. The
process also allows for the formation of two or more different kinds of HIPEs in the same vessel
as disclosed in US Patent 5,817/704 (Shiveley et al.) issued October 6, 1998. In this example,
two or more pairs of oil and water streams may be independently mixed and then blended as
Many different variations of the above described process for forming the emulsion may be
used. A multistage mixing process where the 'water to oil ratio is increased after the initial
emulsion is formed may also be used. An initiator may also be added in separate steps.
b) Curing the rnpnomer component in the oil phase of the water-in-oil emulsion
The process of the present invention has a step of curing the monomer component in the oil
phase of the water-in-oil emulsion using a polymerization reaction to form a saturate polymeric
foam material. The HIPE may be cured in a batch process or in a continuous process. A
measure of the extent of cure of the polymer is the strength of the foam, as measured by the yield
stress. Another measure of the extent of cure of the polymer is the extent to which it swells in a
good solvent such as toluene (being crosslinked, the HIPE foam does not dissolve without being
chemically altered). A suitable curing step is described in US Patent 6,365,642 (Dyer et al.)
issued April 2, 2002.
During the curing, the monomer in the emulsion is reduced because of evaporation. The
evaporation rate is affected by the such factors as the turbulence of the atmosphere above the
emulsion, the monomer content of the atmosphere, the reaction rate of polymerization, and the
temperature of the atmosphere and the temperature of the emulsion. Additionally, loss of water
from the internal phase due to rapid evaporation can cause the emulsion at the surface to break,
creating defects such as an occluded surface, especially harmful if the intended use of the
emulsion is as an absorbent foam.
Thus, there is a need to reduce such a monomer loss and any evaporation of either monomer
or aqueous internal phase. As the monomer loss would occur because of an exposed surface, a
film covering is conventionally utilized. However, these films can also cause surface defects by
interaction with the emulsion, or can be difficult to keep clean if the intent is to use them over and
over for economy, or very expensive is the intent is to only use them once.
The present invention achieved to prevent the monomer loss by performing the curing
process in a saturated steam environment with little movement of the atmosphere above the
emulsion. Preferably, the saturated steam is hi equilibrium with the emulsion. The temperature
of the steam is preferably greater than 90 degrees C, more preferably, greater than 95 degrees C,
further more preferably, greater than 9S7 degrees C. It is also desired that the polymerization
proceed quickly to further reduce any evaporation of the monomer.
Without being bound by theory, it is believed that such a saturated steam can work for (1)
raising the temperature of the emulsion from Step a) and making the curing process end faster and
(2) preventing evaporation of the Water from the aqueous phase, and the quiescent atmosphere
above the emulsion becomes rapidly in equilibrium with the monomer components without much
loss of monomer. As a result, the method of the present invention can reduce the monomer loss
during the curing less to than 10%, preferably, less than 5%,'more preferably, less than 3.5%.
One of the advantages of the present invention is the ability to heat up the emulsion to a
higher temperature where the reaction takes place more quickly without suffering losses from
monomer evaporation. This allows for the use of lower temperatures in mixing and sheet
forming, which reduces the buildup of reacted material in the mixing and sheet forming
equipment. Another way to reduce buildup of reacted material is the use of free radical
inhibitors. These typically suffer from the trade-off of extending both the life of the equipment
and the cure time required. One such free radical inhibitor that helps in the inhibition in the
mixing equipment while not prolonging curing to an unacceptable amount of time was TEMPO
(2,2,6,6-tetremethyl-l-piperidinyloxy) which can be obtained from Aldrich.
The HIPE is formed in a continuous process, as is shown schematically in Figure 1. If the
vessel is closed and adequately pressure resistant, the curing temperature can be increased beyond
100°C as needed. Another preferable oven is described hi US Patent 5,634,281 (Nugent et al.)
issued Jun. 3, 1997. In the present invention, the curing process is preferably performed in an
oven. The oven most preferably has a serpentine design. The serpentine design can have any
number of tiers to meet the material and space requirements. The serpentine design is cost
effective as the oven itself takes up a minimal amount of floor space compared to other oven
The oven can utilize belts to support the HIPE foams during the curing process. The belts
can be configured to a serpentine design or other desired formation. The belts are more cost
efficient as they do not require the tight specifications often found in conveyors commonly used
in the industry. The belts do not require high tension, allow for smaller diameter pulleys, allow
for the stacking and serpentining set-up, and permit quick changes and simple maintenance. The
low speed and supporting equipment such as slider bed technology, bearings, and pulleys all make
this oven design very cost effective. The belts additionally allow for manipulation of the HIPE
surface. For example, if the belt material is incompatible with the foam, the foam structure
collapses leaving a heavily occluded surface which is impermeable. This may be desired for a
foam material having one side impermeable and one side permeable. The steam cured side of
the foam material, which is permeable, can be misted with water, particulates, organic materials,
or any desired substance. The belts may also be coated with a material. Suitable materials
Figure 1 describes an overall view of an oven suitable for forming HIPE foams according to
the present invention. Figure 2 describes a cutaway view of the oven, detailing the first and last
modules (which may be one module if desired) with the broken lines exemplifying that other
modules could be contained within, and showing the relationship of belts. Figure 3 describes a
detailed view of a deposition area.
In Fig. 1, the oven 100 comprises four modules. Each module 101 has a vent 110, a vent
collection 120 and a steam inlqt 130. The vent collection 120 connects vent 110 and module
101. The steam enters at the stfeam inlet 130 and goes through from vent 110.
In Fig. 2, the oven is shown with five belts, 201,202,203,204, and 205. Belt 201, the top
belt, is covered with a close fitting cover 210. At left end of belt 201, where the material enters
the oven 101 at the deposition area 230, a bottom belt seal 220 typically constructed of a nonabrasive
material such as rubber, contacts the belt 201 to prevent steam leakage. Belt 201
terminates at deposition area 230 which is for deposition of the emulsion from the die. Belt 202
starts from tail pulley 240 and ends at drive pulley 250 as other belts do. The right hand module
has further a discharge opening 260 through which the cured emulsion exits and a steam
balancing vent 250 which is powered by a variable speed exhaust fan in order to be able to adjust
the pressure pulling the steam out of the discharge opening 260 in order to keep steam from
naturally rising and exiling from the higher entry. If the entry and exit are on the same level, for
example if there is only one oven belt, then the steam balancing vent may not be needed. At the
bottom of each module 101, there is a steam distribution 270, in which steam is distributed.
In Fig. 3, the deposition area 230 is shown in detail. Deposition area 230 has a pulley seal
310 and belt seals 320. The belt seals are conveniently cut from a non-abrasive material such as
rubber and have approximately the same arc as the belt so as to seal the steam in the oven. The
pulley seal 310 is conveniently constructed of sheet metal and surrounds the support member and
belt so that steam does not escape though the space between the incoming and outgoing belt as it
proceeds to the pulley. The discharge end is comparably equipped with bottom seals and belt
A porous, water-filled, open-celled HERE foam is the product obtained after curing in the
polymerization reaction. Sheets of cured HIPE foam are easier to process during subsequent
treating/washing and dewatering steps, as well as to prepare the HIPE foam for use in the intended
application. Alternatively, the product HIPE foam may be cut, ground or otherwise comminuted
into particles, cubes, rods, spheres, plates, strands, fibers, or other desired shapes. The aqueous
phase remaining with the HIPE is typically removed by compressing the .foam. Residual
moisture can be removed as desired by conventional evaporative drying techniques.
C. Specific Examples:
Example 1) An oil phase is prepared comprising 50.91.% EHA, 31.82% EGDMA, 5.45%EHMA,
2.73% HDDA, 7.27% polyglycerol succinate, and 1.82% DTDMAMS. An aqueous phase is
prepared comprising 3.85% CaC12, pH adjusted to 6.3. The aqueous phase is heated to 72°C and
pumped at a volumetric flow rate of 5.037 1/min through a tube, a 4.76 mm diameter hole drilled
through a 19.05 mm set screw in the top mounting plate of a dynamic mixer. The dynamic mixer
comprises a 7.82 cm diameter shell with a 28.58 mm shaft mounted with 3 rows of 58 3.18mm
pins positioned 120° with respect to each other around the circumference with a center to center
distance between each pin along the shaft of 3.23mm, with another set of 3 rows of 58 3.18mm
pins offset from first set by 60° and offset on the shaft such that they are halfway between the
other set of rows. Thus, the rows, if they were free to bypass one another would have a clearance
of about 0.025 mm The length of the shaft pins is such that the shaft pin to shell gap is 3.05 mm.
The aqueous stream enters the vertically positioned mixer approximately 2 cm above the first row
of pins on the shaft, which rotates at about 800 RPM. Fluids are withdrawn from the bottom of the
mixer, and a portion is directed to a Waukesha Model 030 U2 lobe pump. At the inlet to the pump
the unheated oil phase is injected at a rate of 251.6 grams per minute through a 1.98 mm hole
drilled in a 6.35 mm set screw mounted in a section of tubing that entered the center of a 90°
elbow and directs the stream in a path parallel with the fluid flowing from the mixer through a
1.91 cm diameter section of stainless steel tubing. All mixer parts and tubing and connection are
stainless steel with sanitary fittings. The discharge of the pump, rotating at an RPM to give a flow
of 5.5 1/min, is conveyed back to the top of the mixer, which has a 1.91 cm entry just below the
mounting flange, nearly concentric with the first row of pins on the shaft. In this way fresh
aqueous phase is introduced into a more highly concentrated emulsion. The product of the first
mixer is a HIPE with small droplets of internal phase at an internal phase ratio of about 20:1
The other portion of the material withdrawn from the mixer is directed to a another
dynamic mixer via an entry identical to the one described for the first mixer's recirculation line,
with the same shell as the first The impeller pin diameter is 4.76mm and there are only 2 pins per
row offset by 180°, with 34 rows spaced approximately ll.lmm on center, and a complementary
set of another 34 rows with 2 pins per row offset by 90° from the first row and spaced halfway
between rows.. The second portion of the aqueous phase which is heated to 70° (to approximately
match the temperature of the emulsion leaving the first mixer) and is flowing at 3.962 1/min is
introduced through a 3.97 mm diameter hole drilled through a 19.05 mm set screw in the top
mounting plate of the second dynamic mixer approximately 2cm above the first pin row. The pinshell
gap is 6.35mm and the impeller is rotating at 1000 RPM. The resultant, small droplet
internal phase emulsion has an internal phase ratio of about 35.8:1
The emulsion from the second mixer is directed to the bottom of a third mixer, a vertically
oriented dynamic mixer with a 5.23 cm diameter shell having an impeller pinned along 21.59 cm
of its length. The impeller shaft is 1.91cm in diameter with one row of 4.76mm pins having 21
rows of three pins per row offset from each other by 120°, and with another 21 rows of three
similar pins per row, 60° offset from the first row of pins. The pins are spaced 10.5 mm on
centers, with the rows offset by half that distance. The pin to wall gap is 3.05mm, and the mixer
rotates at about 1800 RPM. The initiator phase comprises 11.4% sodium persulfate in potable city
water, and its flow of 60.3 g/rriin is introduced into the bottom of the mixer through a 1.59 mm
diameter hole drilled in a 6.35rnm tube centered on the mass center of the annulus formed by the
shaft and shell, again directed parallel to the mass flow entering the bottom of this mixer. The
resultant emulsion, now about 36:1 internal phase ratio, is directed to a die similar to that used in
standard extrusions, called a coat-hanger die. The die has an exit gap of 2.6mm and a width of
25cm. The emulsion issuing from the die is collected on a Teflon coated belt moving at 8 m/min
to convey the emulsion through a serpentine curing chamber with 5 levels and 7 sections, each 2.5
meters long. The entry and exit of the oven have powered ventilation to capture escaping steam,
the top belt is about 0.6 m below the top of the chamber, and each section is fitted with a
ventilation port 10 cm in diameter. The ports are piped to dampers that can restrict the flow but
not stop it completely. The exit from the dampers is piped to a central conduit and then to an
exhaust fan nominally rated at 150 cubic meters per minute. Material balance samples lost 25 to
30% of the incoming monomer weight, or about 31 to 38 grams/square meter of product
Example 2) The same emulsion, die and oven were used as in example 1, but the top level of the
oven was fitted with a close fitting cover. The cover is higher in the middle than on the sides in
order to allow any steam condensate to run to the edge rather than drop on the curing web. The
cover is about 5 cm above the belt in the middle and about 4 cm at the edge. Material balance
samples lost 10 to 12% of the incoming monomer weight, or about 13 to 15 grams/square meter
of product produced.
Example 3) The same emulsion, die, and oven with close fitting covers on the top level conveyor
as used in example 2 was modified to eliminate the internal ventilation ports. The material balance
samples lost between 4 and 6% of the incoming monomer weight, or about 5 to 8 grams/square
meter of product produced.
Example 4) The same emulsion, die, and oven as modified in example 3 was further modified to
gasket all areas where steam might leak out of the entry and exit of the oven except in the places
where emulsion enters and cured material exits. Also, the exhaust fan at the entry was eliminated,
and the exhaust fan at the exit was equipped with a variable speed drive. The exit fan speed was
adjusted until no steam was observed to exit from the front of the oven, taking care not to have it
too fast as to pull in cold air from the front of the oven with the incoming emulsion. Without
being limited by theory, the intent of the exhaust fan at the exit of the oven is to overcome the
natural tendency of hot gasses to rise, creating a chimney effect in a curing chamber. Without the
exit fan pulling the rising gas back, air rushes in the exit to displace the steam, and this can be
observed both by the great increase in condensing steam vapor coming out of the entry to the
oven and by the much lower temperature of a thermocouple positioned within the last section of
the oven 1 meter from the exit. The material balance samples from this example are difficult to
evaluate within the noise of the method. Stack measurements using condensing tubes indicate less
than 3.2 grams per square meter of product is lost, or less than about 2% of the incoming
The disclosures of all patents, patent applications (and any patents which issue thereon, as
well as any corresponding published foreign patent applications), and publications mentioned
throughout this description are hereby incorporated by reference herein. It is expressly not
admitted, however, that any of the documents incorporated by reference herein teach or disclose
the present invention.
While various embodiments and/or individual features of the present invention have been
illustrated and described, it would be obvious to those skilled in the art that various other changes
and modifications can be made without departing from the spirit and scope of the invention. As
will be also be apparent to the skilled practitioner, all combinations of the embodiments and
features taught in the foregoing disclosure are possible and can result in preferred executions of
the invention. It is therefore intended to cover in the appended claims all such changes and
modifications that are within the scope of this invention.
1. A continuous process of forming a polymeric foam material comprising the
a. Forming a high internal phase water-in-oil emulsion;
b. Curing the monomer component in the emulsion in a saturated steam
environment in an oven with a quiescent atmospheric layer above the emulsion, said
oven utilizing belts to support the polymeric foam material during the curing process;
c. Forming a saturated polymeric foam material.
2. The method as claimed in Claim 1, wherein the saturated steam is in equilibrium with the emulsion.
3. The method as claimed in Claim 1, wherein a small head space of less than 80mm above the emulsion is present in Step b.
4. The method as claimed in Claim 1, wherein the oven has a serpentine design.
5. The method as claimed in Claim 1, wherein the oven has an exit and entrance
point which are covered.
6. The method according to Claim 4, wherein the serpentine design is formed
from said belts.
|Indian Patent Application Number||5316/DELNP/2006|
|PG Journal Number||31/2010|
|Date of Filing||14-Sep-2006|
|Name of Patentee||THE PROCTER & GAMBLE COMPANY|
|Applicant Address||ONE PROCTER & GAMBLE PLAZA, CINCINNATI, OH 45202 (US)|
|PCT International Classification Number||F26B 17/08|
|PCT International Application Number||PCT/US2005/007346|
|PCT International Filing date||2005-03-02|