WO2000037547A2 - Microspheres polymeriques expansibles, leurs procede de production et utilisations, et produits fabriques a partir desdits microspheres - Google Patents

Microspheres polymeriques expansibles, leurs procede de production et utilisations, et produits fabriques a partir desdits microspheres Download PDF

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Publication number
WO2000037547A2
WO2000037547A2 PCT/US1999/029358 US9929358W WO0037547A2 WO 2000037547 A2 WO2000037547 A2 WO 2000037547A2 US 9929358 W US9929358 W US 9929358W WO 0037547 A2 WO0037547 A2 WO 0037547A2
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Prior art keywords
polymer
microspheres
microsphere
polymeric
blowing agent
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PCT/US1999/029358
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English (en)
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WO2000037547A3 (fr
Inventor
David S. Soane
Michael R. Houston
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Zms, Llc
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Priority to AU39968/00A priority Critical patent/AU3996800A/en
Publication of WO2000037547A2 publication Critical patent/WO2000037547A2/fr
Publication of WO2000037547A3 publication Critical patent/WO2000037547A3/fr
Priority to US09/877,992 priority patent/US20010044477A1/en
Priority to US10/235,367 priority patent/US6617364B2/en
Priority to US10/235,418 priority patent/US6638984B2/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/02—Making microcapsules or microballoons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/02—Making microcapsules or microballoons
    • B01J13/04—Making microcapsules or microballoons by physical processes, e.g. drying, spraying
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/22—After-treatment of expandable particles; Forming foamed products
    • C08J9/228—Forming foamed products
    • C08J9/232—Forming foamed products by sintering expandable particles
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/32—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof from compositions containing microballoons, e.g. syntactic foams
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/22—Expandable microspheres, e.g. Expancel®

Definitions

  • This invention relates to the field of plastic particles, more specifically to the field of expandable and optionally fusible plastic microspheres, and hollow plastic microballoons, microcellular foam or foamed composite materials produced therefrom.
  • Hollow microspheres otherwise known as microballoons or microbubbles, find prevalent use throughout industry, most commonly as additives or fillers.
  • the primary benefit of hollow microspheres over more conventional fillers e.g., silicates, aluminates, clays, talcs, etc.
  • Hollow microspheres offer a means of introducing controlled, small voids in a closed-cell configuration. This can be difficult to obtain in both viscous and non- viscous fluids, resins, coatings, and cements using conventional foaming agents due to problems associated with the foaming process such as unequal cell growth, time- and temperature-dependent gas diffusion, cell coalescence, etc.
  • hollow microspheres provide a means for uniformly and homogeneously increasing product bulk while simultaneously decreasing the overall density, lowering product cost on a volumetric basis without sacrificing (or while enhancing) performance.
  • hollow microspheres offer many other advantages in a wide variety of products.
  • fluid products such as printing inks and paints benefit from the spherical shape of hollow microspheres, resulting in viscosity reduction, enhanced flow and leveling, faster dispersion time, smoother surface finish, and an overall increased volume load capacity.
  • Higher loading capacities in turn lead to increased hiding power, maximum tint strength, better gloss control, VOC reduction, dimensional stability, improved applicability, and further overall weight or density reduction.
  • thermoplastic resins such as thermoplastic resins, epoxies, sealants, pipe insulation, potting compounds, spackling compounds, underbody coatings, papers, fabrics, dielectric laminates, prosthetic devices, synthetic foams, cultured marble, polymer concretes, and synthetic cements also benefit from hollow microsphere additives.
  • the primary improvement is again weight reduction, but additional improvements may include: increased volume load capacity; reduced product warpage, shrinkage, and/or cracking; abrasion resistance or abradability; corrosion resistance; increased impact strength; smoother surface finishes; improved molding of intricate parts; disruption of directional orientation (in polymer systems); decreased dielectric constant and/or increased capacitance; increased bulk and stiffness in paper and paperboard; improved sensitivities in explosives (greater thermal insulation and shock resistance); easier machinability; water resistance; better sound absorption; and increased compressibility.
  • microspheres are composed of glass or ceramic oxide shell walls, exhibiting a true particle density in the range of 0.1 to 0.4 g/cc.
  • Microspheres such as these must often be washed in a series of treatment baths to reduce alkali content. The microspheres must further be dried from said bath, an operation that is energy inefficient and which leads to clumping unless special drying agents are used.
  • Due to their poor impact strength glass microspheres are subject to rupture under conditions of high shear, which may be experienced during such common operations as pumping, injection molding, extruding, calendering, or milling. Ruptured microspheres no longer possess the benefit of low density, and the nonspherical shape of the resulting fragments negates many of the other beneficial properties to be realized from the incorporation of spherically shaped additives.
  • thick-walled glass or ceramic microspheres have been proposed, e.g. see US Pat. Nos. 3,838,998 (thick-walled glass), 4,349,456 (ceramic), 4,983,550 (strong glass), 5,077,241 (ceramic bubbles), and 5,225,123 (sintered particle-walls).
  • Thick-walled microspheres exhibit a significantly higher density, however, since their internal void volume is greatly sacrificed to increase structural integrity.
  • thick-walled microspheres exhibit a particle density of 0.3 to 0.7 g/cc, diminishing the overall effect of density reduction, and are more costly due to increased material usage.
  • Ceramic microspheres tend to have thicker shell walls as well, exhibiting densities up to 0.7 g/cc, and their production requires significantly more expensive precursor materials.
  • glass or ceramic microspheres possess many disadvantages that inhibit their full commercial exploitation.
  • plastic microspheres have been developed, e.g. see US Pat. Nos. 3,615,972, 3,945,956, 4,049,604, 4,075,134, 4,303,603, and 5,053,436.
  • These hollow microspheres are typically composed of a thermoplastic shell wall material that sometimes encapsulates a solid or liquid core.
  • Farnand and Puddington disclose a process for hollow microsphere production that utilizes a solid core material which sublimes at room temperature by rapid diffusion through the shell wall, leaving behind a liquid shell which is then dried.
  • the materials of construction are chosen such that the polymeric shell walls soften upon heating, and a volatile liquid core expands the shell wall by vaporizing to form a hollow, nominally spherical particle.
  • a volatile liquid core expands the shell wall by vaporizing to form a hollow, nominally spherical particle.
  • thermoplastic polymers are incorporated into such particles, the microsphere shell walls are significantly more fracture-resistant than glass, and are therefore less prone to rupture and breakage during high shear operations.
  • Liquid-filled thermoplastic microcapsules have another advantage over glass or ceramic microspheres in that the expansion of the liquid-filled plastic microcapsules can be triggered after formulation in the end-use product. Glass and ceramic microspheres soften only at extremely high temperatures, making their expansion process incompatible with most end-use products.
  • Liquid-filled, expandable plastic microcapsules on the other hand can be incorporated into products such as resins, coatings, cements, paints or inks in an unexpanded state. These products may then be mixed, pumped, extruded, or otherwise handled and applied in a manner consistent with their use, followed by a heating step which inflates the microcapsules into their hollow, thin-walled, low-density configuration.
  • the expansion caused by the inflating microspheres aides in molding, shaping, or texturing the end-use product. Furthermore, since mixing, extrusion, and molding operations occur while the plastic microcapsules are in an unexpanded (and therefore less fragile) state, the likelihood of rupturing or breaking the particles is greatly diminished. Since the thermoplastic microsphere materials typically have good fracture strength properties and the microballoons are not subjected to high-shear operations after expansion, the microspheres may also be expanded to a greater extent than glass or ceramic microspheres, leading to thin-walled thermoplastic balloons with densities as low as 0.01 g/cc, much lower than hollow glass or ceramic microspheres.
  • Thermoplastic microspheres in the present art are manufactured by an emulsion polymerization process in which a polymerizable monomer and an inert, hydrophobic liquid (blowing agent) are mixed together, then are emulsified in an immiscible aqueous phase to form very small droplets of monomer/ blowing agent. Initiators are then used to trigger polymerization within the droplets among the monomeric precursors. The polymer forms at or migrates to the droplet surface, creating a shell wall that becomes thicker as polymerization proceeds.
  • the blowing agent is chosen to be insoluble in both the polymer and aqueous phase, so it remains inside the droplet, surrounded by the polymeric shell. See, for example, Pat. No. 3,615,972.
  • the thermoplastic, liquid-filled expandable microspheres and/or their method of fabrication have one or more disadvantages or limitations that have hindered their commercialization or restricted their field of use.
  • emulsion polymerization is a difficult process to control from a manufacturing standpoint. Particle sizes, shell-wall thicknesses, blowing agent content, and ultimately the overall expansion amount, all vary with only slight changes in the formulation of the overall emulsion mixture.
  • Such formulations must be tightly controlled with respect to the concentration of monomers, crosslinkers, blowing agents, polymerization catalysts, surfactants and colloids (used to control droplet size and dispersion), colloid promotors, thickening agents, and free-radical scavengers such as oxygen (oxygen generally must be excluded by flushing the system with an inert gas).
  • the current art of microsphere production often uses chemical drying agents such as sodium, calcium, or magnesium chlorides or hydroxides, in addition to moderate temperature evaporative drying, to dry the particles and keep them from clumping.
  • chemical drying agents such as sodium, calcium, or magnesium chlorides or hydroxides
  • These agents typically leave a residue on the surface of the particles that cannot be easily removed prior to their incorporation into an end-use product. This residue can also render the microsphere surfaces inert and unable to bond to or react with the surrounding matrix in the end-use products. It is therefore less than desirable that such drying agents are used in the current art to dry microspheres from the aqueous phase in which they are polymerized.
  • a more advantageous approach would be one that requires no drying from a mother liquor, or at least a drying process which does not require chemical drying agents which may later contaminate end-use products.
  • the specialized polymerization techniques that make up the current art of microcapsule production also limit microcapsule compositions to polymers amenable to emulsion or suspension free-radical polymerizations. That is, the polymer composition is limited to those monomers that are not miscible with water and that polymerize by free-radical addition mechanisms. Unfortunately, many modern engineering thermoplastics can not be polymerized by free-radical addition polymerization techniques.
  • Polymers formed by anionic "living" polymerization techniques, and by poly-condensation reactions, for example, are not amenable to free-radical, emulsion polymerizations.
  • polymers which might be advantageously chosen for use as microsphere shell-wall materials, such as certain engineering thermoplastics may not be incorporated into microballoons using the current art.
  • incorporating reactive entities or sites within the microsphere shell wall is problematic since a reactive environment is necessary to initiate the polymerization of the monomeric precursors.
  • Reactive entities contemplated for incorporation into the microcapsules must not only be restricted to ones that are inert towards the reactive intermediates taking part in the polymerization reaction, but the reactive entities must also be compatible with the monomeric precursors and polymeric shell walls thereby formed, and must also not be appreciably extracted into the surrounding aqueous phase.
  • the emulsion or suspension polymerization processes used in the current art to form expandable microspheres inherently limit the types of additives, reactive or otherwise, that can be incorporated into the final product.
  • Another limitation of the current art is that only liquid-filled, expandable microcapsules are available using the current production techniques.
  • liquid propellants may be desirable since they exert a sufficient vapor pressure to expand the polymeric shell walls, yet recondense into a liquid state after the expanded microballoons have hardened and cooled. In other situations, however, liquid propellants may not be desirable.
  • the main drawback to liquid propellants is their finite permeability in the polymer shell wall. This permeability, combined with the inherent volatility of the liquid blowing agent, leads to evaporation of the propellant when it reaches the surface of the microcapsule. Thus, the loss of propellant through the polymer shell wall changes the microcapsule composition over time, which can ultimately change or degrade the microcapsule performance as it ages.
  • the current expandable microsphere technology typically uses volatile hydrocarbon blowing agents, which, unfortunately, produce very flammable vapors. Since the liquid blowing agent typically accounts for about 10 to 50 weight percent of the expandable microcapsules, it can present a significant fire hazard both during storage and upon expansion. This hazard is especially acute if propellant vapors are allowed to migrate and accumulate inside a closed container. This problem is exacerbated by the tendency of many dust-like materials to accumulate static charge, since such charge build up can provide an ignition source for the accumulated flammable vapors. While the use of halogenated propellants may mitigate the flammability problem, the use of these materials has been greatly curtailed in recent years mostly due to environmentally concerns. Thus, there are certain situations where a nonflammable propellant that also does not leak or diffuse out of the micropsheres would be useful in the production, storage, and/or use of expandable microspheres.
  • thermo-expandable, thermoplastic or thermosettable microspheres are directed to thermo-expandable, thermoplastic or thermosettable microspheres, their method of production, and the hollow, nominally spherical microballoons and/or microcellular foam that result upon heating said thermo-expandable microspheres.
  • the thermo-expandable microspheres of the present invention are characterized by having a polymeric shell surrounding one or more pockets or particles of liquid or solid blowing agent or propellant within the microsphere.
  • the microspheres are free-flowing; that is, they do not agglomerate and are detached from each other. Because they do not agglomerate, the microspheres do not require the use of drying agents that remain with the microspheres after drying, leaving a surface coating or residue.
  • the microspheres of the present invention are drying agent- or residue-free.
  • the microspheres are also fusible or crosslinkable with each other and/or a surrounding matrix.
  • thermo-expandable microsphere or “expandable microsphere” or “expandable microcapsule”, as used herein and in the appended claims, mean a particle which is capable of increasing in size upon heating due to the formation of one or more gaseous voids or bubbles in the interior of the particle to give a microbubble or microballoon.
  • microbubble or “microballoon”, as used herein and in the appended claims, mean a hollow particle defined by having a polymeric shell wall surrounding one or more internal, gaseous voids.
  • fuusible as used herein and in the appended claims, means able to fuse together into a connected foamed or foamable mass.
  • the present invention discloses a unique approach that overcomes the drawbacks of commercially established processes for the production of expandable plastic microspheres. It is unique in that it uses only physical processes and solution thermodynamics to create expandable microspheres. Polymerization is not an intrinsic step in the microsphere formation process of this invention. The process is also unique in that any pre-polymerized material having a suitable solvent may be used to form the microsphere shell walls, irrespective of the polymerization technique used to synthesize the polymer.
  • expandable microspheres may be readily produced which are fusible or crosslinkable with adjacent microspheres or with a matrix material in which the microspheres have been incorporated.
  • the present invention is an extremely economical process suitable for mass production.
  • a polymer, co-polymer, or polymer blend is solvated by an appropriate solvent, and combined with an inert liquid, which serves as a blowing agent or propellant.
  • an inert liquid which serves as a blowing agent or propellant.
  • crosslinkers, catalysts, plasticizers, stabilizers, pigments, and other desirable additives may be added to the mixture.
  • the mixture is then atomized into air, or homogenized in a second immiscible liquid, to produce microscopic dropiets. Either by evaporation or liquid-liquid extraction, the solvent is then removed from the droplets, precipitating the polymer from solution and effectively solidifying the droplets into hard-walled polymeric microspheres containing liquid blowing agent cores and other optional additives.
  • a polymer, co-polymer, or polymer blend is solvated by an appropriate solvent, and is combined with a solid that produces a gas upon heating.
  • crosslinkers, catalysts, plasticizers, stabilizers, pigments, and other desirable additives may be added to the mixture.
  • the mixture is then atomized into air, or homogenized in a second immiscible liquid, to produce microscopic droplets. Either by evaporation or liquid-liquid extraction, the solvent is then removed from the droplets, precipitating the polymer and additives from solution and effectively solidifying the droplets into hard-walled polymeric microspheres surrounding blowing agent cores that are solid at room temperature.
  • the final product is a powder consisting of flowable, dispersible, residue-free, thermoplastic or thermosetting expandable microspheres.
  • the polymer, co- polymer, or polymer blend may be chosen from any existing polymers, provided there exists a suitable solvent capable of dissolving said polymer.
  • the microspheres preferably possess reactive functionalities, either built into the polymer chains or added to the formulation in the form of crosslinking or other reactive groups, that allow the microspheres to fuse to each other or to a surrounding matrix upon expansion into hollow microballoons.
  • this invention makes possible a broad selection of microsphere compositions. It may be used to obtain microspheres made from conventional thermoplastics, thermosets, elastomers, naturally occurring polymers, engineering thermoplastics, or mixtures of these or other polymers.
  • the polymer and propellant may further be chosen to give a wide range of blowing temperatures at which the polymer softens and the microspheres expand to produce microballoons, which may optionally be fused to each other or to a surrounding matrix.
  • the invention further provides a means to manufacture said microspheres without the need for emulsification or suspension polymerization techniques, emulsification agents or additives, or chemical drying agents for drying the particles from the mother liquor.
  • the present invention is directed to the production of expandable microspheres capable of expanding into microballoons, which optionally may fuse with adjacent microballoons or the surrounding matrix.upon the application of heat.
  • These expandable, optionally fusible microspheres are synthesized by using purely physical processes.
  • the present invention is unique in that it uses commercially available, pre-polymerized materials in a physical process governed solely by solution thermodynamics for the economical manufacture of expandable and fusible microspheres.
  • Polymeric microspheres containing liquid blowing agents are produced by first forming a solution consisting of the polymer that is to form the microballoon shell walls and a suitable solvent.
  • the wall-forming polymer may be a thermoplastic, a thermoset, an elastomer, or a mixture of polymers, optionally mixed with cross-linkers (i.e., thermosettable precursors), plasticizers, or other desirable additives.
  • a "suitable solvent” is a solvent capable of dissolving the polymer to form a polymer solution that is homogeneous on a macroscopic scale and is free-flowing.
  • the polymer may be solvated to a concentration between about 0.5 and 90 wt%.
  • the polymer is solvated at as high a concentration as possible where solution atomization or break-up into microdroplets is still achievable, such as by atomization or suspension and agitation in a second immiscible liquid.
  • solution atomization or break-up into microdroplets is still achievable, such as by atomization or suspension and agitation in a second immiscible liquid.
  • an inert liquid blowing agent (or propellant) is also added to the solvated polymer solution.
  • inert it is meant that the blowing agent does not chemically react with either the polymer solvent or the polymer during the normal course of microsphere formation and processing.
  • the blowing agent is selected such that it is miscible with the polymer solvent, but incompatible with the pure polymer, i.e., it does not act as a solvent for the polymer.
  • the blowing agent is also typically selected such that it disperses in the polymer-solvent solution with no phase separation up to its desired concentration.
  • the blowing agent is further chosen such that it produces a vapor pressure sufficient to expand the polymer shell walls at or above the temperature at which the polymer softens.
  • the concentration of blowing agent in the polymer-solvent solution is chosen according to the desired amount of microsphere expansion.
  • the blowing agent concentration must be high enough that the desired amount of expansion is achieved upon vaporizing the blowing agent. However, the blowing agent concentration must be low enough that the polymer is able to form a coherent shell wall around one or more blowing agent pockets within the microcapsule.
  • the polymer shell wall must also be sufficiently thick so as to prevent excessive diffusion and depletion of the propellant from the microcapsule over the desired shelf-life of the microcapsules.
  • the polymer shell wall must further be sufficiently thick so as to withstand, without rupture, the shell wall thinning which accompanies expansion.
  • the concentration of the blowing agent necessary to provide a given amount of expansion will depend on the volume change upon vaporization of the liquid propellant, as well as the resistance to stretching exhibited by the polymer. It is also recognized that some of the polymer solvent may remain entrapped within the dried microsphere along with the propellant itself, which will act to provide additional expansion in conjunction with the liquid blowing agent. Therefore, exact blowing agent concentrations providing a given amount of expansion must to some extent be empirically determined and optimized for each system in order to achieve the best possible performance. Methods for doing so are known in the art and do not require undue experimentation.
  • the blowing agent concentration as given by the ratio of its weight to the weight of polymer added to the solution, is preferably within the range of 1 to 200%. More preferably, the blowing agent to polymer weight ratio shall be between 2 and 100%, and most preferably between 5 and 50%.
  • the solution used to produce expandable, optionally fusible microspheres containing liquid blowing agents in accordance with this invention comprises the following components: a polymer or polymer mixture that is to form the microsphere shell walls, a liquid blowing agent or propellant that creates a vapor pressure sufficient to expand the microsphere shell walls upon heating, optional additives to promote crosslinking or other desirable properties, and a solvent that solvates both the polymer and liquid propellant to form a homogeneous, free-flowing solution.
  • Polymeric microspheres having blowing agent cores that are solid at room temperature are produced by first forming a solution consisting of the polymer that is to form the microballoon shell walls and a suitable solvent.
  • the wall-forming polymer may be a thermoplastic, a thermoset, an elastomer, or a mixture of polymers, optionally mixed with cross-linkers (i.e., thermosettable precursors), plasticizers, or other desirable additives.
  • a "suitable solvent” is a solvent capable of dissolving the polymer to form a polymer solution that is homogeneous on a macroscopic scale and is free-flowing.
  • the polymer may be solvated to a concentration between about 0.5 and 90 wt%.
  • the polymer is solvated at as high a concentration as possible where solution atomization or break-up into microdroplets is still achievable, such as by atomization or suspension and agitation in a second immiscible liquid.
  • an inert solid blowing agent or propellant
  • inert it is meant that the blowing agent does not chemically react with either the polymer solvent or the polymer during the normal course of microsphere formation and processing.
  • the blowing agent may be insoluble in the polymer solvent, in which case it should be in the form of a finely divided powder having a sufficiently small particle size.
  • efficient dispersion of the solid propellant may be aided by first treating the propellant with a surface active agent before mixing with the polymer solution, or by adding surfactants into the total mixture. Ultrasonic agitation can also be used to speed up dispersion.
  • the blowing agent may be soluble in the polymer solvent such that it dissolves in the polymer-solvent solution with no phase separation up to its desired concentration. The blowing agent is further chosen such that it produces a vapor pressure sufficient to expand the poiymer shell walls at or above the temperature at which the polymer softens.
  • the vapor pressure generated upon heating may be caused by the evaporation or sublimation of the propellant (physical blowing agent), or may be generated by a thermally-induced chemical decomposition of the propellant (chemical blowing agent), in which case a sufficient quantity of gas is produced by the decomposition reaction to expand the microcapsule shell walls.
  • concentration of blowing agent in the polymer-solvent solution is chosen according to the desired amount of microsphere expansion.
  • the blowing agent concentration must be high enough that the desired amount of expansion is achieved upon vaporizing or decomposing the blowing agent. However, the blowing agent concentration must be low enough that the polymer is able to form a coherent shell wall around one or more blowing agent pockets within the microcapsule.
  • the polymer shell wall must further be sufficiently thick so as to withstand, without rupture, the shell wall thinning which accompanies expansion. It is recognized that the concentration of the blowing agent necessary to provide a given amount of expansion will depend on the volume of gas produced upon vaporization or decomposition of the propellant, as well as the resistance to stretching exhibited by the polymer. It is also recognized that some of the polymer solvent may remain entrapped within the dried microsphere along with the propellant itself, which will act to provide additional expansion in conjunction with the solid blowing agent. Therefore, the exact blowing agent loading level which provides a given amount of expansion must to some extent be empirically determined and optimized for each system in order to achieve the best possible performance. Methods for doing so are known in the art and do not require undue experimentation.
  • the blowing agent concentration is preferably within the range of 1 to 200%.
  • the solution or mixture used to produce expandable, optionally fusible microspheres in accordance with this invention comprises, in another embodiment, the following components: a polymer or polymer mixture that is to form the microsphere shell walls, a blowing agent or propellant that generates a vapor pressure sufficient to expand the microsphere shell walls upon heating (said blowing agent or propellant being normally a solid at or near ambient pressure and temperature), optional additives to promote crosslinking or other desirable properties, and a solvent that solvates the polymer (and optionally the solid propellant) to form a free-flowing mixture.
  • expandable, optionally fusible microcapsules are manufactured by atomizing or otherwise breaking up the solution or mixture from section A above into microdroplets by any one of several conventional techniques well known in the art.
  • the purpose of this step is to form small, nominally spherical droplets of the solution.
  • the spherical shape is achieved by means of surface tension effects, which cause a deformable fluid to minimize its surface area.
  • breaking up the solution into very fine droplets provides an efficient avenue for the removal of the solvent from the droplet composition by evaporation or extraction. As the solvent is removed from the droplets, phase separation occurs whereby the polymer no longer stays in solution within each individual droplet.
  • the polymer will typically phase separate at the droplet surface first, creating a thin polymer shell surrounding the droplet.
  • the polymer may precipitate within the droplet and migrate to the droplet surface. Further drying occurs as the remaining solvent in the droplet interior diffuses through the polymer shell to the surface and evaporates or is extracted. Diffusion of the solvent through the polymer occurs readily in this case because the solvent is compatible with the polymer, and because the diffusion distance in the microdroplets is short.
  • the blowing agent is a liquid
  • the agent is essentially trapped within the droplet during drying due to its incompatibility with the polymer, which greatly hinders its permeability through the polymer shell wall.
  • the blowing agent is a solid
  • the agent does not leave the droplet to any appreciable degree during drying due to its non-volatility.
  • the solid propellant will precipitate out of solution as the solvent leaves the droplet.
  • the solid particles will be initially coated with the polymer solution and a polymer coating will be left behind as the solvent is dried or extracted.
  • drying or extraction of the polymer solvent leads to the formation of a polymer shell wall.
  • the final product consists of a polymer shell wall surrounding one or more pockets or particles of the solid blowing agent.
  • additives such as crosslinkers, catalysts, plasticizers, pigments, etc., will generally remain within the droplet upon solvent removal since these agents typically have low volatilities.
  • the formation of microdroplets is achieved by atomizing the polymer solution into a drying gas atmosphere where solvent removal proceeds by simple evaporative drying.
  • a particular advantage of this embodiment is that the microsphere is automatically cooled as the solvent evaporates due to the latent heat of vaporization associated with such a phase change.
  • heated gases may be used to facilitate microsphere drying without unduly raising the microsphere temperature and thereby expanding the particles prematurely.
  • Such atomization techniques include, for example, high- pressure atomization, two-fluid atomization, rotary atomization, and ultrasonic atomization. The type of technique used, as well as the operating parameters, will depend on the desired particle size distribution and the composition of the solution being sprayed. Such techniques are well taught in the literature, and ample description can be found in many texts such as, for example, Spray Drying Handbook by K. Masters, herein incorporated by reference.
  • Droplet formation may be alternatively accomplished by introducing the polymer- propellant-solvent solution into a second, immiscible liquid in which the polymer and propellant are immiscible and the polymer solvent is only slightly soluble. With agitation the polymer solution will break up into finely dispersed droplets, forming a suspension of spherical polymer solution droplets distributed within the second liquid.
  • the second liquid shall be chosen such that it is not a solvent for the polymer, and is somewhat incompatible with the polymer solvent such that the overall polymer solution is dispersible as discrete droplets with the second liquid.
  • the second liquid must, however, provide a reasonable solubility for the polymer solvent such that the polymer solvent is extracted from the microdroplets in a manner analogous to evaporative drying. That is, as the microdroplets make contact with and disperse in the second, immiscible liquid, the polymer solvent is extracted from the droplets at their surfaces. Once sufficient solvent has been removed, the polymer will phase separate and form a polymer shell at the droplet surface, as in the case of evaporative drying. Further extraction of the solvent through the polymer shell wall results in microspheres composed of a polymer shell wall surrounding, in one embodiment, the liquid blowing agent. The liquid propellant will not be substantially extracted into the second liquid due to its incompatibility and low permeability in the polymeric shell walls.
  • removal of the solvent results in microspheres composed of a polymer shell wall surrounding one or more pockets or particles of the solid blowing agent.
  • the solid propellant will not be substantially extracted into the second liquid due to its extremely low permeability in the polymeric shell walls.
  • the extent to which additional components remain in the droplets during solvent extraction will depend on the component's diffusivity in the polymer and compatibility with the polymer, the blowing agent, and the second liquid medium, among other things.
  • Additives such as crosslinkers, catalysts, plasticizers, pigments, etc., will generally remain within the droplet upon solvent removal since these agents are typically chosen to be compatible with the polymer or polymer solvent.
  • the microspheres When the microspheres have sufficiently solidified, they may be collected by filtration, centrifugation, sedimentation, flotation, or other separation methods known in the art.
  • This second liquid may be advantageously selected to be water, as many of the known polymer solvents are immiscible and only slightly soluble in water.
  • Other examples include hydrophobic liquids such as fluorocarbons and silicone fluids.
  • Emulsifying agents may also be added to the second liquid or the polymer solution to promote and stabilize the suspension and particle size distribution of polymer solution droplets.
  • Another technique that may be used to produce expandable microcapsules in accordance with this invention is to introduce the polymer-propellant-solvent mixture into a second immiscible liquid, similarly to the case mentioned above.
  • the polymer solution Upon agitating the solution, and perhaps with the aid of an emulsifying agent, the polymer solution will disperse into a suspension of microdroplets within the second liquid.
  • the entire solution may then be spray dried by conventional means using an atomization nozzle or other technique well known in the art, whereby the suspension will be dispersed into fine droplets in a gaseous, drying environment.
  • an atomization nozzle or other technique well known in the art whereby the suspension will be dispersed into fine droplets in a gaseous, drying environment.
  • solvent from the polymer mixture can then evaporate from the droplets instead of being extracted into the second liquid as discussed above.
  • the advantage of this approach is that the energy necessary for microdroplet formation (the interfacial energy corresponding to the increase in interfacial area between the two phases) may be added to the system mechanically, independent of the drying step. That is, the surface energy necessary for droplet formation can be provided separately by agitating the two-phase liquid system (the surface energy necessary for droplet formation can also be reduced by the addition of adequate surfactants).
  • the mixture may then be atomized or spray dried in order to evaporate both the polymer solvent and the second immiscible liquid, effectively drying the droplets in a process independent of the droplet formation step.
  • microspheres are composed of a polymeric shell wall surrounding one or more core pockets of a solid or liquid propellant, and preferably contain reactive functionalities, either built into the polymer chains or added to the formulation in the form of crosslinking or other reactive groups, that allow the microspheres to fuse to each other or to a surrounding matrix upon expansion into hollow microballoons. Prior to expansion, however, these microspheres are free-flowing; that is, they do not agglomerate and are detached from each other. Because they do not agglomerate, drying agents are not necessary and the microspheres are free of chemical drying agents, that is, they are residue-free.
  • microballoons or microcellular foam of the invention are prepared by heating the thermo-expandable microspheres, either by themselves or admixed with a matrix resin or other binder composition. Upon heating, the shell wall material of the microsphere softens and stretches under the expansion force created by the blowing agent, forming a microbubble characterized by one or more gaseous interior voids surrounded by a polymer shell. Having gone through said expansion, the microbubbles are larger than the unexpanded microspheres and have a lower true density.
  • the shell walls of the microballoons join with one another (melt or fuse together) to form a semi-continuous microcellular foam.
  • the microballoon walls harden to give a microcellular foam.
  • Such a foam can be formed that is at least two to three times the original volume of the unexpanded microspheres.
  • This foam consisting of fused microballoons, exhibits voids associated with the microballoon interiors. Additional voids may exist in the extra-cellular regions where the microballoon shells do not merge completely. While the voids associated with the microballoon interiors will be singular and discrete (i.e., generally not connected to each other), the voids attributable to the extracellular regions may be interconnected to the extent that a semi- continuous void structure is formed. Fusing of the walls of the microballoons may occur by simple physical means (in the case of semi-molten surfaces coming into contact), or may occur with the help of crosslinking reactions between the adjacent microballoons.
  • the foam formation and microballoon fusing process will not be hindered by the presence of chemical drying agents or residues on the microballoon surfaces that result from current manufacturing practices.
  • the unexpanded microspheres are a free-flowing powder, they may be blown, sprayed, dusted, or otherwise spread onto curved or flat surfaces, into cavities or molds, into tubes or pipes, or otherwise into difficult-to-reach places. Once in place, the microspheres may be heated to create a microcellular foam which fills in the voids within a given constrained space to give the foam in a desired geometry.
  • the microsphere shell walls may react with the matrix formulation to create a shell wall that is fused with the surrounding matrix.
  • the result is a microcellular, foamed composite material where the voids within the resin are individual microballoons, which have walls that are integrally bonded with the surrounding matrix.
  • Such bonding with the matrix can eliminate delamination between the microballoons and the matrix resin, providing an overall stronger composite material. It may also help prevent crack initiation within the resin, or may help mitigate crack propagation once a crack tip develops.
  • the matrix resin may be thought of as a binder that bonds to or holds together the expanded microballoons to give a foamed composite material.
  • the resulting composite may or may not contain voids outside the microballoons, depending on the nature of the matrix resin and the mixing conditions used.
  • any polymer or polymer mixture for which there is a suitable solvent or solvent mixture, and which softens and is stretchable upon the application of heat, may be formed into an expanding, optionally fusible microsphere using the technology provided by this disclosure.
  • polystyrene ⁇ -methyl, brominated
  • polybutadiene poly(meth)acrylates, poly(meth)acrylic acids, poly(meth)acrylamides, poly(meth)acrylonitrile, polyethylene (propylene or butylene), polyesters, polyolefins, polyvinylidene fluoride or chloride, polyvinyl alcohol, polyvinyl acetate, polyvinyl ether, or blends or copolymers of these or other homopolymers thereof.
  • polystyrene ⁇ -methyl, brominated
  • polybutadiene poly(meth)acrylates, poly(meth)acrylic acids, poly(meth)acrylamides, poly(meth)acrylonitrile, polyethylene (propylene or butylene), polyesters, polyolefins, polyvinylidene fluoride or chloride, polyvinyl alcohol, polyvinyl acetate, polyvinyl ether, or blends or copolymers of these
  • polymers that are not directly polymerizable by free-radical emulsion or suspension polymerization techniques. These polymers are especially significant with respect to the present invention because they are not viable candidates for use in the expandable microsphere production technologies known prior to this invention.
  • Such polymers enabled by the technology disclosed in the present invention are blocky (diblock, triblock, or multiblock), and sometimes alternating or random copolymers, terpolymers, star-polymers, etc., such as styrene-butadiene (SBR), styrene-acrylonitrile, butadiene-acrylonitrile, styrene- maleic anhydride (SMA), ethylene-(meth)acrylic acid, ethylene glycol-terephthalate (PEG/PET), acrylonitrile-butadiene-styrene (ABS), and other copolymers or blends of polymers and/or copolymers thereof.
  • SBR styrene-butadiene
  • SMA styrene-acrylonitrile
  • PEG/PET ethylene glycol-terephthalate
  • ABS acrylonitrile-butadiene-styrene
  • Naturally occurring polymers such as polysaccharides (e.g., celluloses, modified celluloses, starches, chitin, chitosan, etc.), lipids, or proteins or other polypeptides for example, may also be used in accordance with the present invention.
  • This class of polymers is significant in that they are not man-made, but rather are obtained from renewable resources, and are generally not reproducible by synthetic means (emulsion free-radical polymerization or otherwise).
  • Another benefit of naturally occurring polymers is their inherent biocompatibility and biodegradability, properties not often achieved with conventional, free-radical polymerized thermoplastics.
  • Another very important class of polymers which becomes available for use in the production of expandable microspheres by the present invention is the class of polymers known as engineering thermoplastics. These polymers have a special significance in the present application because of their high dimensional stability, good chemical resistance, good impact strength, high strength at elevated temperatures, and other superlative engineering properties, which may be advantageously incorporated into hollow microspheres or microcellular foams for further property enhancement.
  • thermoplastics enabled for use by the present invention include, but are not limited to, polymers such as nylon, polycarbonate, polyamide, polysulfone (polyethersulfone, polyphenylsulfone, polyphenylene ether-sulfone, etc.), polyetherimide, polyketone, polyetherketone, and other engineering thermoplastics thereof.
  • polymers such as nylon, polycarbonate, polyamide, polysulfone (polyethersulfone, polyphenylsulfone, polyphenylene ether-sulfone, etc.), polyetherimide, polyketone, polyetherketone, and other engineering thermoplastics thereof.
  • These polymers cannot be used to form expandable microspheres using conventional technology known in the art because they are not amenable to or producible by emulsion or suspension polymerization techniques.
  • the present invention has an inherent advantage over previously disclosed expandable microsphere technologies because heretofore-unavailable polymers may now be used in an economical and straightforward manner to produce expandable microcapsul
  • Polymers which contain one or more reactive functionalities built into the polymer chains will be particularly beneficial in the practice of this invention because such groups can react with a surrounding matrix or can react with suitable crosslinkers to more effectively fuse together the microballoon walls with any adjacent constituents.
  • reactive groups could be, for example, alcohols, anhydrides, vinyls, amines, caboxylates, sulfhydryls, aldehydes, epoxies, etc.
  • Specific polymer examples include styrene-maleic anhydride co-polymers (maleic anhydride functionalities), hydrolyzed poly vinyl acetates/poly vinyl alcohol (hydroxyl functionalities), polyethylene imines (primary, secondary, and tertiary amine functionalities), and naturally occurring polymers such as the celluloses and proteins (hydroxyl, carboxyl, amine, sulfhydryl, and other functionalities).
  • the reactive functionalities enable the bonding or reaction of the microballoon shell walls to an appropriately chosen surrounding matrix or to each other.
  • two types of microspheres can be manufactured, one possessing one type of functionality (primary or secondary amines, for example) and another possessing a different type of functionality (anhydrides, for example).
  • microspheres may then be mixed with each other by simple mechanical means. When this mixture is heated, the microballoons so produced will fuse and react with adjacent microballoons having the opposite functionality, forming a crosslinked microcellular foam.
  • a particular microsphere composition which may be advantageously exploited by the present invention is one in which the microsphere shell walls are comprised of one or more polymers mixed with one or more reactive components.
  • the reactive components may be of the monomer, crosslinker, reactive oligomer, or oligomeric crosslinker types. Such reactive components may be mono- or multi-functional, having one or more reactive groups per entity.
  • microsphere shell wall materials may be incorporated into the microsphere shell wall material in order to provide crosslinking between the polymer chains, or to form an interpenetrating polymer network (IPN) or semi-interpenetrating polymer network (semi-IPN - produced by the polymerization of the reactive components primarily with themselves) within and across the microballoon walls to adjacent microballoons.
  • IPN interpenetrating polymer network
  • si-IPN - semi-interpenetrating polymer network
  • the reactive components may also be used to provide reaction with and bonding to the surrounding matrix.
  • the crosslinking reaction or IPN or semi-IPN formation may be designed to proceed during or after the heating and expansion of the microspheres.
  • a thermal initiator may be used which activates crosslinking at a temperature about equal to or higher than the microsphere expansion temperature, such that the microsphere shell walls crosslink only during or after expansion.
  • Photo-initiators may also be incorporated, which make the crosslinking reactions mostly independent of the temperature and allow them to proceed only when the microspheres are exposed to a source of polymerizing energy either before or after expansion has taken place.
  • thermosetting polymers have more desirable properties than thermoplastic-type polymers, including increased dimensional stability, high- temperature performance, chemical resistance, and durability.
  • a lightly crosslinked shell wall, IPN, or semi-IPN can also provide improved solvent resistance prior to microsphere expansion when the crosslinking reactions or IPN formation are triggered independently from, just prior to, or concurrently with the microsphere expansion step.
  • di-functional crosslinkers may be employed such as diols, diepoxies, di-isocyanates, di-anhydhdes, aldehydes, acrylates, methacrylates, melamines, etc., such as: ethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, butanediol diglycidyl ether, bisphenol A diglycidyl ether, partially or completely methylated or butylated melamines, epichlorohydrin, glutaraldehyde, and many others.
  • the reactive functional groups may be chosen from acrylate, methacrylate, vinyl ether, vinyl, diene, allyl, epoxy, alcohol, amine, caboxyl, isocyanate, melamine, or others.
  • the reactive components may be used singly or in mixtures. Below are listed acrylate-functional components, but similar structures with other reactive groups could alternatively be used in their place.
  • silicates such as trimethoxy-silane, dimethoxy-silane, triethoxy-silane, trichlorosilane, etc.
  • suitable reactive compounds are commercially available from companies such as Sartomer, Henkel, Radcure, Gelest, Allied Signal, Aldrich, and others.
  • Photo-initiators such as the Irgacure and Darocure series are well-known and commercially available from Ciba Geigy, as is the Escacure series from Sartomer.
  • Thermal initiators such as azobisisobutyronitrile (AIBN) benzoyl peroxide, dicumyl peroxide, t-butyl hydroperoxide, and potassium persulfate are also well-known and are available from common chemical suppliers, as are catalysts which may be desirably incorporated to facilitate the crosslinking, IPN, or semi-IPN reactions.
  • AIBN azobisisobutyronitrile
  • the single requirement with respect to polymer selection in accordance with the current invention is that a suitable solvent or solvent combination must exist for the said polymer or polymer mixture.
  • the solvent must be capable of solvating the polymer to form a nominally homogenous, free-flowing liquid, which in turn must be capable of being atomized or broken up into droplets of the desired size.
  • Solvent selection will depend on the polymer chosen to form the microcapsule shell walls, and may also be influenced by factors such as volatility, flammability, viscosity, toxicity, chemical reactivity, recoverability, cost, and interactions with the blowing agent or other components.
  • Typical solvents which may be used in the practice of this invention include, but are not limited to: acetone, methyl ethyl ketone, ethyl ether, tetrahydrofuran, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methanol, ethanol, iso-propanol, toluene, methylene chloride, chloroform, dichloroethane, trichloroethane, tetrachioroethylene, water, and others.
  • the present invention places no requirements on the solvent selected, although it is recognized that certain solvents will be more preferable than others based on the above- stated criteria. It is also recognized that in some situations it may be advantageous or necessary to use a mixture of two or more solvents instead of a single solvent in order to obtain the desired solvation, evaporation, and/or extraction properties.
  • the solvent may further be chosen such that it produces a less viscous solution or a solution that is more amenable to microdroplet breakup, either by atomization or agitation in a second immiscible liquid.
  • the viscosity of the solution is not a critical property with respect to the present invention, except insofar as the solution viscosity is low enough for the solution to be atomized or broken up into microdroplets.
  • the solvent and polymer concentration shall be chosen so as to provide a dissolved polymer solution with a viscosity less than about 500 centipoise. More preferably, the solution will have a viscosity less than 300 centipoise, and between 0.1 and 100 centipoise most preferably, in order to facilitate atomization or microdroplet formation.
  • a liquid blowing agent When a liquid blowing agent is used, it is typically chosen to be incompatible with the polymer. That is, it does not solvate the polymer to any appreciable degree. This is not an absolute requirement in accordance with the present invention; however, the use of blowing agent-polymer combinations which are incompatible will generally lead to a longer shelf-life for the polymer microspheres since, in this case, the blowing agent will exhibit greatly reduced diffusion through the polymer shell walls.
  • the choice of expanding agent will vary depending on the nature of the polymer chosen to form the microsphere walls, as well as the solvent chosen to solvate the polymer.
  • Solid propellants When solid propellants are to be used, the interactions with the polymer are much less important since the solid propellants will not typically act to solvate the polymer shell wall.
  • One important consideration when selecting a liquid blowing agent or propellant is that it must produce a vapor pressure sufficient to expand the polymer walls once the polymer has softened due to heating. Propellant selection in this regard will thus depend on the softening temperature of the polymer chosen to form the microsphere shell walls as well as the vapor pressure of the liquid propellant at this softening temperature.
  • a solvent that has a boiling point at atmospheric pressure of no more than 10 degrees above the softening temperature (or glass transition temperature, T g ) of the polymer will provide a sufficient vapor pressure to expand said polymer shell walls upon heating the microspheres to the boiling point of the blowing agent.
  • the boiling point of the propellant liquid at atmospheric pressure will be equal to or less than the polymer T g , and even more preferably, the propellant boiling point will be at least 10 degrees lower than the polymer T g .
  • Particularly preferred liquid blowing agents are the small chain hydrocarbons since they are inert towards most polymers, miscible with most solvents, and have boiling points near ambient temperatures.
  • liquid blowing agents that have boiling points below ambient temperatures
  • the process may advantageously be carried out at low temperatures and/or under a pressurized atmosphere.
  • liquid propellants that may be used in conjunction with the polymers and solvents listed above include, but are not limited to, hydrocarbons (n-butane, iso-butane, n- pentane, iso-pentane, trimethyl-2-pentene, hexane, heptane, n-octane, iso-octane, nonane, decane, benzene, toluene, etc.), ethers and ketones (ethyl ether, isopropyl ether, acetone, methyl ethyl ketone, etc.), alcohols (methanol, ethanol, iso-propanol, etc.), halogentated hydrocarbons (methylene chloride, chloroform, carbon tetrachloride, dichloroethane, trich
  • Suitable physical blowing agents include, but are not limited to: neopentyl alcohol, hexamethyl ethane, tertiary-butyl carbazate, tertiary- butyl dimethylsilyl chloride, tertiary-butyl N-allylcarbamate, and tetramethy 1-1 ,3- cyclobutanedione, etc. This list is not meant to be exhaustive as one knowledgeable in the field of chemistry will find many substances that meet the criteria described above. In selecting a suitable physical blowing agent, consideration may be given to toxicity, polymer compatibility, solvent compatibility, melting point, boiling point, vapor pressure, or other issues, depending on the particular polymer-solvent system under consideration.
  • Chemical blowing agents typically solid at ambient pressure and temperature, undergo decomposition or other chemical reactions that produce gaseous vapors as at least one of the reaction by-products. These reactions are most often triggered by heat, but can alternatively be triggered by the presence of a co-reactant. For instance, a chemical blowing agent could be triggered by the presence of water, whereby water is included in the formulation but only becomes available for reaction upon the addition of heat. (Such would be the case for certain hydrated salt compounds mixed with the chemical blowing agent sodium borohydride.)
  • Chemical propellants can be categorized as either organic or inorganic chemical blowing agents. Inorganic chemical blowing agents typically decompose to give off carbon dioxide gas in an endothermic reaction. Organic chemical blowing agents typically decompose to give off nitrogen gas (which has a lower diffusion rate in most polymers) in an exothermic reaction.
  • Examples of chemical blowing agents include, but are not limited to: sodium bicarbonate, potassium hydrogencarbonate, sodium borohydride (decomposes upon the addition of a proton donor such as water), polycarbonic acid, ammonium carbonate, ammonium carbamate, ammonium acetate, ammonium diethyldithiocarbamate, dinitrosopentamethylene-tetraamine, p-toluenesulfonyl hydrazide, 4,4'-oxybis(benzenesulfonyl hydrazide), azodicarbonamide, p-toluenesulfonyl semicarbazide, 5-phenyltetrazole, diazoaminobenzene, etc.
  • chemical blowing agents is that the carbon dioxide or nitrogen gas typically evolved is inert, nonflammable, and nontoxic. Another advantage is that the inorganic blowing agents can themselves be very inert and nontoxic, which makes them easy and safe to work with during production and in the end-use products.
  • Solid blowing agents both physical and chemical (organic and inorganic), avoid the inherent hazards associated with volatile, flammable liquids.
  • Another advantage to be realized by the solid propellants is that the temperature at which microsphere expansion occurs may be altered independent of the polymer used to make the microsphere shell walls. In conventional microspheres, the temperature at which expansion occurs is determined by the softening temperature of the polymer. That is, expansion occurs when the polymer shell walls soften, allowing the vapor pressure of a volatile liquid to stretch the walls outward.
  • the polymer-propellant combination may be chosen so that the expansion temperature is dictated by the decomposition temperature of the solid propellant rather than the softening temperature of the polymer.
  • the softening temperature of the polymer is below the decomposition temperature of the propellant.
  • the polymer may soften, but as long as no gas is generated, no expansion will occur. Only upon heating further, to the decomposition temperature of the propellant, will a vapor pressure sufficient to expand the polymer shell walls be generated.
  • the temperature at which microsphere expansion occurs may be controlled by the selection of the propellant rather than by the softening temperature of the polymer. This feature can provide added flexibility in designing the temperature ramp-up cycle during the molding processes used to produce final products.
  • the greatly decreased volatility of the solid propellants used in accordance with this invention further helps to preserve the shelf-life of the expandable microspheres. Since the solid propellants have virtually no vapor pressure and little propensity to permeate through the polymer shell walls, the long-term shelf-life of unexpanded microspheres is expected to be substantially increased.
  • Chemical blowing agents offer an additional advantage over physical blowing agents (liquid or solid) in that they are capable of generating a higher expansion pressure than their physical blowing agent counterparts. This is because physical blowing agents will always be in a state of reversible equilibrium between the liquid and vapor phases. In contrast, the chemical blowing agents decompose to form inert gases in an essentially irreversible process. Because the decomposition is virtually irreversible and the gases produced are difficult to condense, chemical blowing agents are capable of producing much greater pressures than those generated by even the most volatile physical blowing agents.
  • the solid propellants In order to incorporate the solid propellants into expandable microcapsules, they must be mixed with the polymer-solvent mixture. Whether physical or chemical blowing agents are used, the solid propellant may optionally be dissolved in the polymer-solvent mixture. In the case of soluble systems, the blowing agent is simply dissolved up to its desired composition; the mixture is broken up into microdroplets; and the solvent is dried or extracted from the droplets. When the solid propellant is not soluble in the polymer-solvent mixture, the solid propellant is typically added to the mixture in the form of a finely divided powder. In this case, the size of the propellant particles will be as small as or smaller than the desired microcapsule size.
  • the final microspheres might contain one or only a few solid propellant particles. If the solid propellant particles are significantly smaller than the droplets formed by solution break-up, then the final microspheres will typically contain many solid propellant particles.
  • the former case ordinarily produces an expanded microsphere with one or only a few voids within the interior of the resulting microballoon. The latter case often produces many voids within the interior of the microballoon.
  • Solubility of the propellant in the polymer-solvent mixture, the amount of gas generated, the vapor pressure generated, and the temperature at which vapor generation occurs are all parameters that will influence the selection of an appropriate solid propellant for use in accordance with this invention.
  • the matrix materials with which these microspheres may be incorporated to give a foamed composite material are numerous.
  • Example matrices suitable for microsphere incorporation include paints, inks, epoxies, sealants, insulation, potting compounds, spackling compounds, underbody coatings, papers, fabrics, dielectric laminates, prosthetic devices, synthetic foams, cultured marble, polymer concretes, and synthetic cements.
  • the matrices may be simple one- or two-component mixtures, or may contain any number of additives such as crosslinkers, catalysts, initiators, stabilizers, pigments, fibers, inert fillers, etc.
  • the matrix is an epoxy-based resin mixed with a suitable initiator package.
  • expandable microspheres made from the copolymer styrene-maleic anhydride also containing crosslinkers, catalysts, etc.
  • crosslinking occurs in the bulk of the epoxy matrix, within the microballoon walls, and across or between the microballoon walls and the epoxy matrix.
  • the final product is a fully crosslinked composite system wherein the microballoons are integrally bonded to the surrounding matrix.
  • the matrix is a mixture of pulp fibers and, optionally, a sucrose solution.
  • Expandable microspheres made from a prolamine, a protein derived from corn also known as Zein (containing suitable crosslinkers, catalysts, etc.) are mixed into the fiber-sucrose solution, and the mixture is transferred to a mold, filling about half of the total mold cavity volume.
  • Zein containing suitable crosslinkers, catalysts, etc.
  • the resultant material is a crosslinked, biodegradable, composite foam that is suitable for use as insulation, drink cups, food containers, packaging material, paper or cardboard products, and other traditional foam products.
  • Example 1 Expandable Microspheres Using Atomization and a Homopolymer
  • Polymethacrylonitrile (PMN) polymer was obtained from Scientific Polymer Products, Inc., Ontario, New York , Catalog #310. Approximately 1.5 grams of PMN was solvated in 15 mL of acetone to form a slightly translucent solution. For the blowing agent, 0.9 mL of iso- pentane was dissolved in the polymer solution. This solution was then atomized with a Preval portable sprayer from Precision Valve Corporation, Yonkers, New York, Product # 267, which used its own internal pressure source and a liquid suction feed. The solution was sprayed into a closed box, which was immediately sealed and allowed to sit for several hours. The box was then opened and a fine powder was collected from the bottom of the box. The powder consisted of small, nominally spherical particles ranging in size from about 10 to 80 microns in diameter and which consisted of PMN shells encapsulating a propellant. Upon heating to
  • microspheres typically became more spherical after blowing, and upon cooling, they remained in their expanded state.
  • SMA Polystyrene-co-maleic anhydride
  • Aldrich Chemical Company, Inc. Milwaukee, Wl, Catalog #44,238-0. This product has about a 1.3-to-1 styrene- to-maleic anhydride ratio, and a softening temperature of 154 C.
  • Approximately 2.0 grams of SMA was dissolved in 5 mL of ethyl acetate, and an additional 0.2 mL of iso-octane was dissolved to serve as the blowing agent. After mixing, this solution became clear and free- flowing.
  • the solution was atomized using an external-mix touch-up spray gun from DeVilbiss Industrial Spray Equipment, Inc., Maumee, OH, model EGA-503-395E. This spray gun used suction feed for the liquid stream, and 20 psi nitrogen was used for the atomization.
  • the polymer-blowing agent-solvent solution was atomized into a closed box, which was immediately sealed and allowed to sit for several hours. The box was then opened and a fine white powder was collected from the bottom of the box.
  • the powder consisted of small, nominally spherical particles ranging in size from about 1 to 40 microns in diameter.
  • microballoons Upon heating several of the microspheres to 160°C, most of the particles turned clear and expanded. The amount of expansion varied, but most of the expanded particles appeared to be at least twice their original diameter or greater.
  • the expanded microballoons could be seen to have thin shell walls surrounding an internal void (in some cases, more than one internal void was seen, separated by an internal polymer membrane). As evidence of their decreased densities, the microballoons could be seen to rise in an oil bath upon void formation and expansion.
  • the particles expanded and coalesced to form a foam that occupied several times the original volume of the unexpanded microspheres.
  • the expanded foam could be seen to consist of individual fused microballoons having thin shell walls surrounding an internal void (in some cases, more than one internal void was seen, separated by an internal polymer membrane).
  • Polycarbonate resin was obtained from Bayer Corporation, Pittsburgh, PA, under the tradename Makrolon. Approximate 2 grams of polycarbonate was solvated in 10 mL of chloroform, and 0.7 mL of 2,4,4 trimethyl-1-pentene was dissolved in the mixture to serve as the liquid blowing agent. Upon mixing, these components formed a clear, homogenous, free- flowing liquid. The solution was sprayed into a closed box using the Preval portable spray gun, forming a fine mist within the box. The box was then closed. After a few hours the box was opened and a fine powder was collected which consisted of polycarbonate microcapsules ranging in size from 1 to 50 microns in diameter.
  • microballoons When several of these microspheres were heated to 120°C, the polycarbonate microcapsules softened and expanded. The resulting microballoons could be seen to consist of a clear shell surrounding one or more internal voids (usually just a single void). Many of the expanded microballoons appeared to approximately triple in diameter from their unexpanded state, corresponding to a 10- to 20-fold volume increase and density decrease.
  • the polycarbonate microspheres softened and expanded, forming a foamed material which consisted of the individual microballoons fused together.
  • Example 4 Example 4.
  • Expandable Microspheres Using Atomization and a Copolymer Mixed with a Reactive Component Polystyrene-co-maleic anhydride (SMA) polymer was obtained from Elf-Atochem North America, Philadelphia, PA, Product # SMA3000. This product has about a 3-to-1 styrene-to- maleic anhydride ratio, and a softening temperature of about 110 °C. Approximately 4.0 grams of SMA was dissolved in 10 mL of ethyl acetate, and an additional 0.2 mL of iso-octane was dissolved to serve as the blowing agent.
  • SMA polystyrene-co-maleic anhydride
  • microspheres were collected and placed into a convection oven at 90°C (below the softening temperature of the SMA) for four minutes to cure and crosslink the HDODA. After this curing step, substantially fewer of the particles dissolved in an epoxy-based solvent than microspheres created and treated comparably except without the HDODA component.
  • substantially fewer of the particles dissolved in an epoxy-based solvent than microspheres created and treated comparably except without the HDODA component Upon heating to 120°C on a microscope slide, virtually all of the particles turned clear and expanded to several times their original diameters.
  • the expanded spheres could be seen to have thin shell walls surrounding an internal void (in some cases, more than one internal void was seen, separated by an internal polymer membrane). As evidence of their decreased densities, the particles could be seen to rise in an oil bath upon void formation and expansion.
  • the resin When mixed into an epoxy-based resin and heated to 120 °C in a test tube, the resin rose in height in the test tube (increased in volume), then cured into a hard, foamed composite.
  • the microballoons within the composite were bonded to the epoxy matrix by means of the maleic anhydride groups in the polymer chains.
  • Example 5 Expandable Microspheres Using Atomization and a Copolymer Mixed with Crosslinking Components
  • Polystyrene-co-maleic anhydride (SMA) polymer was obtained from Elf-Atochem North America, Philadelphia, PA, Product # SMA3000. This product has about a 3-to-1 styrene-to- maleic anhydride ratio, and a softening temperature of about 110 °C.
  • SMA polystyrene-co-maleic anhydride
  • This product has about a 3-to-1 styrene-to- maleic anhydride ratio, and a softening temperature of about 110 °C.
  • Approximately 2.0 grams of SMA was dissolved in 5 mL of methyl acetate, and an additional 0.5 mL of iso-octane was dissolved to serve as the blowing agent. Also added were 0.5 grams of a plasticizer (Santicizer S160, Solutia, Inc. St.
  • the expanded microballoons could be seen to have thin shell walls surrounding an internal void (in some cases, more than one internal void was seen, separated by an internal polymer membrane).
  • the foam could be seen to consist of expanded, fused microballoons having thin shell walls surrounding an internal void (in some cases, more than one internal void was seen, separated by an internal polymer membrane). Both the individual microballoons and the foam were also able to withstand higher or more prolonged temperatures without loosing their shape or integrity compared to samples without the crosslinkers, initiator, and catalyst.
  • the unexpanded microspheres were mixed into an epoxy-based resin and heated to 120 °C in a test tube, the resin rose in height in the test tube (increased in volume), then cured into a hard, foamed composite.
  • the microballoons within the composite were bonded to the epoxy matrix by means of the maleic anhydride groups in the polymer chains, and the polymer chains were crosslinked to each other by the reaction of the tetraethylene glycol with the maleic anhydride units.
  • Example 6 Expandable Microspheres Using Liquid-Liquid Extraction and a Homopolymer Poly- ⁇ -methylstyrene (PMS) polymer was obtained from Aldrich Chemical Company, Inc., Milwaukee, Wl, Catalog #19,184-1. Approximately 2 grams of PMS was solvated in 4 mL of tetrahydrofuran along with 0.9 mL of 2-methyl butane as the blowing agent. The mixture formed a clear, homogeneous solution.
  • PMS Poly- ⁇ -methylstyrene
  • microspheres When several of the microspheres were heated to120°C, the spheres expaned to 2 to 3 times their original diameter, forming microballoons in which a polymeric shell wall surrounded one or more internal voids.
  • the microcapsules When heated together to 120°C in a test tube in an oil bath, the microcapsules expanded and merged together to form a foamed material consisting of fused microballoons.
  • Example 7 Expandable Microspheres Using Atomization and a Naturally Occurring Polymer Mixed with a Crosslinking Component
  • a natural protein extracted from corn gluten known as prolamine or zein (Zein) was obtained from Freeman Industries, LLC, Tuckahoe, NY, Product # F4000. This product has a softening temperature of about 105 °C. Approximately 1 gram of Zein was dissolved in 1 gram of isopropyl alcohol, 1 gram of ethyl alcohol, and 0.9 grams of water. About 0.2 grams of glutaric dialdehyde (50% in water, Aldrich product # 34,085-5) and 0.15 grams of ethylene glycol were added to crosslink and plasticize the polymer, respectively.
  • the expanded microballoons could be seen to have thin shell walls surrounding an internal void (in some cases, more than one internal void was seen, separated by an internal polymer membrane). As evidence of their decreased densities, the microballoons could be seen to rise in an oil bath upon void formation and expansion.
  • the resultant article was a biodegradable foam having the shape of the internal mold cavity, comprised of fused microballoons which could be seen to have thin shell walls surrounding an internal void (in some cases, more than one internal void was seen, separated by an internal polymer membrane).
  • the resin When mixed into an epoxy-based resin and heated to 120 °C in a test tube, the resin rose in height in the test tube (increased in volume), then cured into a hard, foamed composite.
  • the microballoons within the composite were bonded to the epoxy matrix by means of the alcohol groups in the polymer chains (to a lesser extent by the other protein residues), and the polymer chains were crosslinked to each other by the reaction of the glutaric dialdehyde. Reaction of the sulfhydryl groups in the polymer chain to form disulfide bonds is also expected to contribute to crosslinking.
  • Example 8 Expandable Microspheres Using Atomization and a Naturally Occurring Polymer Mixed with a Crosslinking Component Approximately 3 grams of Zein was dissolved in 7 grams of methyl alcohol and 5 grams of acetone. About 0.25 grams of a butylated melamine-formaldehyde resin (Cymel 1156, Cytec Industries, West Paterson, NJ), 0.125 grams of an acid catalyst (Cycat 600, Cytec
  • the resultant article was a biodegradable foam having the shape of the internal mold cavity, comprised of fused microballoons which could be seen to have thin shell walls surrounding an internal void (in some cases, more than one internal void was seen, separated by an internal polymer membrane).
  • the resin rose in height in the test tube (increased in volume), then cured into a hard, foamed composite.
  • microballoons within the composite were bonded to the epoxy matrix by means of the alcohol groups in the polymer chains (to a lesser extent by the other protein residues), and the polymer chains were crosslinked to each other by the reaction of the melamine resin. Reaction of the sulfhydryl groups in the polymer chain to form disulfide bonds is also expected to contribute to crosslinking.
  • Example 9 Expandable Microspheres Using Atomization and Polycarbonate Polycarbonate resin was obtained from Bayer Corporation, Pittsburgh, PA, under the tradename Makrolon. Approximate 2 grams of polycarbonate was solvated in 10 mL of chloroform, along with 2.0 grams of a solid blowing agent, 4,4'-oxydibenzenesulfonyl hydrazide (ODBSH, from Aldrich Chemical Company, Inc., Milwaukee, Wl, Catalog #25,046-5) and 1.0 gram of triethanolamine (to lower the ODBSH decomposition temperature). Upon mixing, these components formed a clear, homogenous, free-flowing mixture.
  • ODBSH 4,4'-oxydibenzenesulfonyl hydrazide
  • the polycarbonate microcapsules softened, the solid blowing agent decomposed, and the microspheres expanded.
  • the spheres could be seen to consist of a clear shell surrounding one or more internal voids. Many of the expanded spheres appeared to approximately double in diameter from their unexpanded state, corresponding to an approximately 10-fold volume increase and density decrease.
  • a polyetherimide resin was obtained from GE Plastics, Pittsfield, MA, under the tradename UltemlOOO. Approximately 2.0 grams of the UltemlOOO was dissolved in 10 mL of chloroform along with 1 gram of t-butyl carbazate (TBC, from Aldrich Chemical Company, Inc., Milwaukee, Wl, Catalog #B9,100-5). These components formed a uniform, clear, free-flowing mixture which was subsequently atomized with the Preval sprayer into a closed box. The box was sealed and allowed to sit for several hours, after which a fine powder was collected from the bottom of the box. The powder consisted of UltemlOOO microspheres ranging in size from about 5 to 50 microns.
  • microballoons were heated to 150°C, a plurality of the capsules expanded to 2-3 times their original diameters, corresponding to a 10- to 20-fold increase in particle volume. It was clearly observed that the microballoons consisted of a thin, clear polymeric shell wall, usually surrounding a single internal void.
  • Example 11 Expandable Microspheres Using Liquid-Liquid Extraction and a Homopolymer Polymethacrylonitrile (PMN) polymer was obtained from Scientific Polymer Products, Inc., Ontario, New York, Catalog #310. Approximately 1.0 gram of PMN was solvated in 5 mL of nitromethane to form a slightly translucent solution. For the solid blowing agent, 1.0 gram of p-toluenesulfonyl hydrazide (TSH, from Aldrich Chemical Company, Inc., Milwaukee, Wl, Catalog #13,200-4) was dissolved in the polymer solution. These components formed a translucent, macroscopically homogeneous solution.
  • TSH p-toluenesulfonyl hydrazide
  • the powder consisted of PMN microcapsules ranging in size from 25 to 100 microns. When heated to 120°C, the microcapsules expanded up to 2 to 3 times their original diameter, forming microballoons in which a polymeric shell wall surrounded one or more internal voids.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Dispersion Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Manufacturing Of Micro-Capsules (AREA)
  • Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)

Abstract

La présente invention concerne des microsphères thermoexpansibles, et les microbilles, la mousse microcellulaire ou le matériau composite expansé résultant du chauffage des microsphères. Les microsphères thermoexpansibles de l'invention se caractérisent en ce qu'ils présentent une paroi polymérique entourant une ou plusieurs poches ou particules d'un gonflant ou propulseur à l'intérieur des microsphères. La surface de la paroi polymérique peut comporter des groupes fonctionnels réactifs pouvant donner un microsphère fusible. Lorsque les microsphères sont chauffés, ils s'expansent pour former des microbilles présentant des coquilles polymériques entourant un ou plusieurs vides gazeux internes, et lorsque les microsphères sont expansés pendant qu'ils sont au contact les uns des autres, une mousse microcellulaire peut être formée. La mousse est constituée d'une pluralité de microbilles agrégées par fusion, avec le concours éventuel de groupes fonctionnels présents à la surface des microsphères chauffés et agissant pour réticuler le matériau. Lorsque des microsphères sont mélangés avec une matrice pouvant éventuellement réagir au contact de groupes fonctionnels à la surface des microsphères et que la combinaison résultante est chauffée, les microsphères s'expansent pour donner un matériau composite expansé dans lequel les microbilles peuvent être fusionnées ou réticulées chimiquement à la matrice.
PCT/US1999/029358 1998-12-10 1999-12-10 Microspheres polymeriques expansibles, leurs procede de production et utilisations, et produits fabriques a partir desdits microspheres WO2000037547A2 (fr)

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AU39968/00A AU3996800A (en) 1998-12-10 1999-12-10 Expandable polymeric microspheres, their method of production, and uses and products thereof
US09/877,992 US20010044477A1 (en) 1998-12-10 2001-06-08 Expandable polymeric microspheres, their method of production, and uses and products thereof
US10/235,367 US6617364B2 (en) 1998-12-10 2002-09-05 Method for synthesizing thermo-expandable polymeric microspheres
US10/235,418 US6638984B2 (en) 1998-12-10 2002-09-05 Microcellular foams, their method of production, and uses and products thereof

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US11177898P 1998-12-10 1998-12-10
US60/111,777 1998-12-10
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WO2002044255A1 (fr) * 2000-11-28 2002-06-06 United States Gypsum Company Pate a joints prete a l'emploi legere
US6617364B2 (en) 1998-12-10 2003-09-09 Nano-Tex, Llc Method for synthesizing thermo-expandable polymeric microspheres
WO2006129127A1 (fr) * 2005-05-31 2006-12-07 Malvern Cosmeceutics Limited Compositions comprenant un lipide et un copolymere de styrene et d’acide maleique
US7230036B2 (en) 2001-05-25 2007-06-12 Ip Rights, Llc Foam insulation made with expandable microspheres and methods
EP2204428A1 (fr) * 2007-10-16 2010-07-07 Matsumoto Yushi-Seiyaku CO., LTD. Microsphères thermoexpansibles, leur procédé de fabrication et leurs utilisations
EP2724775A1 (fr) * 2011-06-22 2014-04-30 Consejo Superior De Investigaciones Científicas (CSIC) Procédé d'obtention de micro-, submicro- et nanocapsuiles à partir de protéines de sérum du lait
US20170333351A1 (en) * 2012-04-13 2017-11-23 Trustees Of Tufts College Methods and compositions for preparing a silk microsphere
WO2020099440A1 (fr) 2018-11-13 2020-05-22 Nouryon Chemicals International B.V. Microsphères à base de cellulose thermo-expansibles
WO2020152362A1 (fr) 2019-01-25 2020-07-30 Nouryon Chemicals International B.V. Capsules sphériques à base de dialcool-cellulose
WO2021198492A1 (fr) 2020-04-03 2021-10-07 Nouryon Chemicals International B.V. Microsphères thermiquement expansibles préparées à partir de monomères d'origine biologique
WO2021198487A1 (fr) 2020-04-03 2021-10-07 Nouryon Chemicals International B.V. Microsphères thermiquement expansibles préparées à partir de monomères d'origine biologique
WO2021234010A1 (fr) 2020-05-20 2021-11-25 Nouryon Chemicals International B.V. Microsphères à base de cellulose expansibles thermiquement ayant de faibles températures d'expansion
WO2022174947A1 (fr) 2021-02-22 2022-08-25 Nouryon Chemicals International B.V. Microsphères à base de cellulose thermo-expansibles
CN115233499A (zh) * 2022-07-29 2022-10-25 贵州赤天化纸业股份有限公司 高松厚度的生活用纸及其制备方法
WO2024089208A1 (fr) 2022-10-26 2024-05-02 Nouryon Chemicals International B.V. Post-chauffage de microsphères expansibles à base de cellulose

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Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6617364B2 (en) 1998-12-10 2003-09-09 Nano-Tex, Llc Method for synthesizing thermo-expandable polymeric microspheres
US6638984B2 (en) 1998-12-10 2003-10-28 Nano-Tex, Llc Microcellular foams, their method of production, and uses and products thereof
EP1263853A1 (fr) * 2000-11-28 2002-12-11 United States Gypsum Company Pate a joints prete a l'emploi legere
US6545066B1 (en) 2000-11-28 2003-04-08 United States Gypsum Company Lightweight ready-mix joint compound
EP1263853A4 (fr) * 2000-11-28 2005-08-17 United States Gypsum Co Pate a joints prete a l'emploi legere
KR100777640B1 (ko) * 2000-11-28 2007-11-27 유나이티드 스테이츠 집섬 컴파니 경량 레디-믹스 이음화합물
WO2002044255A1 (fr) * 2000-11-28 2002-06-06 United States Gypsum Company Pate a joints prete a l'emploi legere
US7230036B2 (en) 2001-05-25 2007-06-12 Ip Rights, Llc Foam insulation made with expandable microspheres and methods
US8088482B2 (en) 2001-05-25 2012-01-03 Ip Rights, Llc Expandable microspheres for foam insulation and methods
US8623414B2 (en) 2005-05-31 2014-01-07 Malvren Cosmeceutics Limited Compositions comprising a lipid and copolymer of styrene and maleic acid
WO2006129127A1 (fr) * 2005-05-31 2006-12-07 Malvern Cosmeceutics Limited Compositions comprenant un lipide et un copolymere de styrene et d’acide maleique
EP2204428A4 (fr) * 2007-10-16 2014-04-30 Matsumoto Yushi Seiyaku Kk Microsphères thermoexpansibles, leur procédé de fabrication et leurs utilisations
EP2204428A1 (fr) * 2007-10-16 2010-07-07 Matsumoto Yushi-Seiyaku CO., LTD. Microsphères thermoexpansibles, leur procédé de fabrication et leurs utilisations
EP2724775A1 (fr) * 2011-06-22 2014-04-30 Consejo Superior De Investigaciones Científicas (CSIC) Procédé d'obtention de micro-, submicro- et nanocapsuiles à partir de protéines de sérum du lait
EP2724775A4 (fr) * 2011-06-22 2015-04-08 Consejo Superior Investigacion Procédé d'obtention de micro-, submicro- et nanocapsuiles à partir de protéines de sérum du lait
US11576862B2 (en) * 2012-04-13 2023-02-14 Trustees Of Tufts College Methods and compositions for preparing a silk microsphere
US20170333351A1 (en) * 2012-04-13 2017-11-23 Trustees Of Tufts College Methods and compositions for preparing a silk microsphere
WO2020099440A1 (fr) 2018-11-13 2020-05-22 Nouryon Chemicals International B.V. Microsphères à base de cellulose thermo-expansibles
WO2020152362A1 (fr) 2019-01-25 2020-07-30 Nouryon Chemicals International B.V. Capsules sphériques à base de dialcool-cellulose
WO2021198492A1 (fr) 2020-04-03 2021-10-07 Nouryon Chemicals International B.V. Microsphères thermiquement expansibles préparées à partir de monomères d'origine biologique
WO2021198487A1 (fr) 2020-04-03 2021-10-07 Nouryon Chemicals International B.V. Microsphères thermiquement expansibles préparées à partir de monomères d'origine biologique
WO2021234010A1 (fr) 2020-05-20 2021-11-25 Nouryon Chemicals International B.V. Microsphères à base de cellulose expansibles thermiquement ayant de faibles températures d'expansion
WO2022174947A1 (fr) 2021-02-22 2022-08-25 Nouryon Chemicals International B.V. Microsphères à base de cellulose thermo-expansibles
CN115233499A (zh) * 2022-07-29 2022-10-25 贵州赤天化纸业股份有限公司 高松厚度的生活用纸及其制备方法
WO2024089208A1 (fr) 2022-10-26 2024-05-02 Nouryon Chemicals International B.V. Post-chauffage de microsphères expansibles à base de cellulose

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