Classifications

• • 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
  • B01J13/20—After-treatment of capsule walls, e.g. hardening
  • B01J13/22—Coating
• • 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
  • B01J13/20—After-treatment of capsule walls, e.g. hardening
  • B01J13/206—Hardening; drying

Definitions

• the present invention relates to the drying and, optionally, to the expansion of thermoplastic microspheres.
• Microspheres are heat expandable thermoplastic polymeric hollow spheres containing a thermally activatable expanding agent. Such materials, the method of their manufacture, and considerable information concerning the properties and uses of microspheres, are all set forth in U.S. Patent 3,615,972, issued to Donald S. More ouse. Other teachings concerning such materials and uses are found in, for example, U.S. 3,864,181; 4,006,273/ and 4,044,176.
• the microspheres are made in an aqueous system by the limited coalescence process under pressure, and the resulting product is a "wet cake" of the unexpanded microsphere beads wetting agents and water.
• the wet cake is typically about 40 to 75 weight percent solids, and because of the wetting agents employed in the formation of the beads, the surface will be wet.
• Many important uses of the microspheres require the removal of the water. It has also become common to expand the beads before use. In unexpanded form, the dry microsphere beads typically have a displacement density of about 1.1 g/cm .
• Dry, expanded microspheres typically have a density by displacement generally of less than 0.06 g/cm ** *, and are highly useful in the production of syntactic foams in a wide variety of polymer matrices. Free-flowing, expanded microspheres have now achieved a commercial recognition and market demand for such uses and others.
• Expansion of microsphere beads is attained in the process of U.S. Patent 4,513,106, where the wet cake is injected into a flow stream of steam, which is subsequently quenched in cool water. This produces pre- expansion of the microspheres, but still wet with water, at low solids content. While solids contents as high as fifteen percent have been occasionally been produced, the typical product is more often about 3 to 5 percent solids. The water limits the applications to which the procedure is applicable.
• a further object is to provide continuously dried and, optionally, expanded microspheres from wet cake. It is also an object of the present invention to provide dried, water free and, optionally, expanded microspheres, by a process which is reasonably inexpensive to capitalize and operate, which can be provided at the site of use of the product at economical levels of utilization, and which can be operated with modest labor and utility costs. It is an object of the present invention to provide free-flowing, optionally expanded, microspheres having unusual and unique properties and characteristics.
• dry microspheres are dried and optionally expanded with an adherent coating of a surface barrier liquid or mixture of such a liquid with a solid by a procedure which results in the attainment of low density, as low as 0.015 to 0.020 g/cm 3 , and with materially reduced proportions of agglomerates in the product, generally less than 1% of the product, and often less than ' 0.1%.
• the procedure of the present invention is based on sequential or concurrent steps of first mixing of dry microspheres and the surface barrier liquid or mixture of such a liquid with a solid and then drying the microspheres to remove water and leaving the surface barrier liquid or mixture of such a liquid with a solid to coat the surface thereof. Subsequent or concurrent expansion of the microsphere is facilitated.
• the discovery of the benefit of employing a surface barrier liquid or mixture of such a liquid with a solid has resulted in excellent properties, particularly the reduction of agglomeration, even at the lowest levels of surface barrier liquid or mixture of such a liquid with a solid, at high product quality. Agglomeration does not occur to any substantial degree in the expansion operation.
• the expanded microsphere product may be a free flowing powder, a compacted powder, or a coherent, flowable mass.
• Figure 1 is a schematic representation of the appearance of a microsphere of the present invention after drying, showing the microsphere with a thin film of barrier liquid or mixture of such a liquid with a solid adhered on the surface thereof.
• Figure 2 is a schematic flow diagram showing th drying operation of the present invention as described i Example I, infra .
• the microsphere density can be less than 0.03, often 0.02 to 0.015 g/cm 3 .
• Low proportions of the surface barrier liquid or mixture of such a liquid with a solid can be employed without agglomerates in the product.
• Process control requirements are simple and equipment requirements are undemanding, permitting operation in inexpensive equipment with simple control requirements while still achieving high levels of product quality, uniformity and productivity.
• the liquid surface barrier coating will facilitate subsequent or concurrent compounding operations, making mixing of the microsphere component into formulations and the achievement of homogeneous dispersion of the microsphere component faster, simpler and more reliable.
• the volumetric considerations which are most often of dominant importance, so that even quite substantial proportions of the surface barrier liquids on a weight basis form a negligible or very minor component on a volumetric basis.
• DINP di-isononyl phthalate
• the volume and weight relationships of the dry, expanded microspheres with varying amounts of DINP show the relationships detailed in TABLE I.
• non-flammable surface barrier liquids or materials which are non-flammable under the conditions of the operating and processing characteristics of the mixture, it has become possible to employ equipment that permits effective subsequent or concurrent expansion at temperatures where the need for an inert atmosphere is eliminated without the introduction of substantial fire and explosion hazards. This represents a quite material reduction in manufacturing expense, and a real gain in system safety.
• the beads produced by the present invention are generally free from dusting, and do not require an inert atmosphere or other processing provisions intended to control dusting related hazards.
• flammable materials may be employed as the surface barrier liquid or mixture of such a liquid with a solid, if adequate safety precautions are employed, although it will generally by preferred to avoid such materials whenever possible.
• Microspheres are generally available in the form of a wet cake, which is typically about 40 percent water, about 60 percent unexpanded microsphere beads, and minor additional amounts of the materials employed in the manufacture of the beads by the process of the Morehouse patent, i.e., "wetting agents.”
• microspheres are those available from Pierce & Stevens Corporation, 710 Ohio Street, P.O. Box 1092 Buffalo, New York 14240-1092, which are predominantly polyvinylidene chloride microspheres with an inclusion of iso-butane as the blowing agent.
• Some of the microspheres presently available contain co- monomers in minor proportions in the bead polymerization.
• the available materials are preferred in the present invention, primarily for their availability and reasonable cost.
• the co-polymers generally have higher T g and expansion temperatures. As the Morehouse patent indicates, microspheres can be made from a rather wide diversity of thermoplastic polymers.
• microspheres are generally limited to polyvinylidene chloride or a random COPOLYMER of vinylidene chloride and acrylonitrile, or a random terpolymer of polyvinylidene chloride, acrylonitrile, and divinyl benzene.
• Microspheres of other materials such as polyacrylonitrile, poly-alkyl methacrylates, polystyrene, or vinyl chloride, are known, but these materials are not widely and generally available.
• the present invention is applicable to any thermoplastic of which microspheres is made, but since the polyvinylidene chloride based materials are those most readily available to the art, the discussion herein will be directed predominantly to those materials.
• blowing agents can be employed in microspheres.
• the commercially available materials are more limited in range, most often being selected from the lower alkanes, particularly propane, butane, pentane, and mixtures thereof, suited to the polyvinylidene chloride polymer.
• the selection of the blowing agent is a function of the particular thermoplastic polymer employed, and in the context of the present discussion, those ordinarily used with the commercially available microspheres are given the greatest attention. Isobutane is most often used with polyvinylidene chloride microspheres.
• the microspheres can be made in a variety of sizes, those readily available in commerce being most often on the order of 2 to 20 microns, particularly 3 to 10 microns. When expanded, these materials will have bead diameters on the order of 10 to 100 micrometers. It is possible to make microspheres in a wider range of sizes, and the present invention is applicable to them as well. It has been demonstrated, for example, that microspheres can be made from as small as about 0.1 micron, up to as large as about 1 millimeter, i diameter, before expansion. Such materials are not generally available. While variations in shape are possible, the available microspheres are characteristically spherical, with the central cavity containing the blowing agent being generally centrally located.
• Dry, unexpanded microspheres typically have a displacement density of just greater than 1 g/cm 3 , typically about 1.1.
• microspheres When such microspheres are expanded, they are typically enlarged in diameter by a factor of 5 to 10 times the diameter of the unexpanded beads, giving rise tc a displacement density, when dry, of 0.1 or less, most often about 0.03 to 0.06, In the present invention is now possible to achieve expanded densities as low as 0.015 tc 0.020 g/cm 3 . While the microspheres are produced in an aqueous suspension, it is common to break and de-water the suspension, and to supply the microspheres in the form of a "wet cake" of about sixty percent solids. This avoids shipping larger than necessary quantities of the aqueous system.
• the solids content of the wet cake is substantially all unexpanded microspheres, but also includes the suspension components, including the wetting agents, so that the remaining water in the wet cake is extremely difficult to remove.
• the drying operation is conveniently based on the use of conventional contact type, indirect heat exchange mixing driers with high speed, high shear capabilities.
• a wide diversity of types of equipment are applicable.
• the requirements are for good temperature control, good mixing of powder and granular materials, and high shear, optionally with operation at reduced pressure provided, and the removal and recovery, preferably with condensation of the evaporated water.
• Active cooling of the microspheres, either in the mixing drier itself, or in ancillary equipment is also optional.
• the surface barrier liquid or mixture of such a liquid with a solid in the present invention is any one of a wide diversity of materials which meet the requirements of the intended function. It is required that the surface barrier liquid or mixture of such a liquid with a solid be a free flowing liquid or mixture of such a liquid with a solid at the temperature and pressure of the drying operation, that it not react chemically with the microspheres, and preferably not with the other constituents of the system, e.g. the wetting agents and related components of the wet cake and, at the temperature of the expansion, that it function to separate the microspheres undergoing expansion so that they do not come into contact and bond to one another.
• the surface barrier liquid or mixture of such a liquid with a solid may be selected from one or more components meeting the following general characteristics:
• the barrier coating material should be a non-solvent for the thermoplastic polymer of the microspheres, and preferably should not swell the polymer of the microspheres.
• the liquid should freely wet the surface of the microspheres.
• the liquid should not polymerize, oxidize, degrade or otherwise react under the conditions of mixing, drying, handling, packaging or storage employed. It may, however, be a material selected to chemically react in or physically alter subsequent formulations into which the liquid-bead composite is compounded.
• the liquid must have a melting point below the temperature of the drying operation, which may be conducted at any convenient temperature where water has a substantial vapor pressure, preferably at least about 100 C, and preferably where bead expansion does not occur, usually at least 20° C below T g of the microsphere polymer. If the surface barrier liquid has a melting point above ambient, it is preferred to cool the coated and dried microspheres below that temperature with mixing at a shear which produces a granular product.
• the liquid should have a boiling point above, and preferably substantially above, the temperature of the drying process and the subsequent or concurrent expansion process.
• the primary function of the surface barrier liquid or mixture of such a liquid with a solid is to prevent the microspheres from coming into direct contact with one another and with the surfaces of the processing equipment during expansion and thus to prevent them adhering.
• the barrier coating material wets the surface of the microspheres, and forms a barrier between the thermoplastic material and any other materials with which it might otherwise come into contact.
• the present invention When the present invention is being conducted for a particular, known end use, it is ordinarily possible to tailor the selection of the surface barrier liquid or mixture of such a liquid with a solid to the requirements of use. It is generally desirable to consider the surface barrier liquid or mixture of such a liquid with a solid as a unit for unit replacement for the same material in the intended use. As those of ordinary skill in the art will readily recognize, the fact that the surface barrier liquid or mixture of such a liquid with a solid will adhere to the surface of the microspheres may be a factor that will require adjustment of proportions, but such requirements will not ordinarily be substantial or critical.
• the composite product has a greatly reduced tendency to become entrained in gas streams or in the environmental atmosphere.
• the tendency to dusting is a material safety hazard, both in terms of exposure to workers and in terms of fire and explosive hazards. Since the microspheres contain an alkane blowing agent in substantial proportions, large quantities of these materials in the atmosphere presents a substantial problem in some circumstances. These difficulties, and the effort and expense of their resolution are minimized or eliminated altogether in the present invention.
• the microspheres are homogeneously dispersed in the liquid in a composite product.
• the dried microspheres will be in a relatively dry, free-flowing granular form in cases where the melting point of the surface barrier liquid is above ambient.
• the composite product When the surface barrier remains liquid at ambient temperatures, the composite product will be a coherent, flowable floc-like mass at relatively high proportions of surface barrier liquid to microspheres. At lower proportions of the surface barrier liquid, the mass will remain relatively coherent, in the form of a number of loosely associated "clumps" which may be somewhat granular or powder-like in character.
• Such "granular floes” permit the handling of the composite like a moist powder or granular material in solids handling and processing equipment, and still afford the compounding advantages of a liquid dispersion; these forms of the composite are accordingly generally preferred for the majority of applications.
• the mass of the dispersion will exhibit a viscosity dependent on the specific liquid employed.
• the flocculation occurs with no agglomeration of the microsphere, which remain in discrete form. If . the microspheres are subsequently or concurrently expanded, all the forgoing characteristics are preserved.
• the surface barrier liquid wets the surface of the microspheres
• the liquid will often be dissolved or dispersed in the system, and the surface of the microspheres will be wet with the final formulation rather than the surface barrier liquid, so that the final formulation has a greater homogeneity.
• syntactic foams for example, compression strength, compression set, impact strength, and some or all tensile properties will be improved.
• adhesive bond strength may be considerably enhanced.
• the selection of the surface barrier liquid, and the optional solid particulate, should be based on the end use intended for the composite, and is preferably a component desirable for inclusion in the intended formulation.
• the liquid is preferably a functional component of the product.
• the liquid material chosen may be, for example, a plasticizer, a surfactant or wetting agent which preferentially wets the surface of the microspheres, an extender or diluent, a solvent for components of the formulation (but not for the microspheres) , a reactive monomer, oligomer, pre-polymer, or low molecular weight polymer, or even a polymer solution or non-aqueous dispersion.
• Other like materials may be employed from among the many common to the compounding of such formulations.
• microsphere products which offer exceptional solvent and temperature resistance, and the like, may be produced.
• polymerizations or cross-linking reactions When such polymerizations or cross-linking reactions are employed, they may be thermally activated or catalyzed, addition or condensation polymerizations or cross-linking reactions may be employed, and the reaction may be conducted in air, inert gas atmosphere, in the presence of a solvent or dispersing medium, or in an interfacial reaction. Interfacial condensation reactions are of particular interest, whether liquid-liquid or vapor-liquid since these types of reactions offer great flexibility in the selection of reactants while still permitting the protection of the microspheres from the effects of constituents which may disrupt the microspheres.
• the surface barrier liquid or mixture of such a liquid with a solid is used in the present invention in an amount sufficient to permit the expansion of the microspheres without sticking to the equipment employed or forming agglomerations of microspheres. While this amount will vary depending on the particular equipment employed, and with the particular processing conditions, the surface barrier liquid or mixture of such a liquid with a solid will most often be in the range of about 5 to 97 weight percent of the mixture of barrier coating material and microspheres, on a dry weight basis. As a general rule, in most circumstances the amount employed should be the least amount that will reliably and consistently achieve the defined function of the barrier coating material. It is generally preferred that the barrier coating material be employed in amounts less than 90 and preferably less than 80 weight percent of the blend.
• An excess of the minimum amount of surface barrier liquid or mixture of such a liquid with a solid required to prevent agglomeration may be employed when desired, but it is generally desirable to avoid proportions substantially greater than the amount which will reliably and completely wet the surface of the microspheres.
• the optional expansion of the microspheres is accomplished by heating with active mixing, optionally at low pressure, in admixture with the surface barrier liquid or mixture of such a liquid with a solid.
• Contact drying processes employing indirect heat exchange are generally the most effective, but in the context of the present invention, must be adapted tc accommodate the particular and unusual conditions of operation, as described infra .
• the expansion operation may be conducted in a plow mixer, such as those available from Littleford Bros., Inc., of Florence, Kentucky. These mixers produce the vigorous mixing required to achieve complete dispersion and intermixing of the microspheres and the surface barrier liquid or mixture of such a liquid with a solid, and provides the heat exchange capacity to effectively remove the water from the mix.
• the mixer may be vented to provide for removal of volatiles, under reduced pressure or vacuum if appropriate.
• the use of active mixing is employed in the mixing and, when employed, in the expansion steps.
• substantial shear was avoided to prevent rupture of the microsphere beads, particularly at higher temperatures employed to soften the surface of the beads to achieve expansion. We have observed that at the lower, very controlled temperatures employed for the operation of the present invention, the beads are not ruptured at quite substantial shear levels.
• agglomerates constitute less than 1%, and often less than 0.1%, of the total product.
• active mixing is ultimately a functional term, signifying a level at least sufficient to eliminate aggregates in the dried product, and less than the level at which significant disruption of the beads occurs. Specific values of the minimum and maxima will be dependent on the specific equipment employed and the particular conditions of its usage and operation.
• the plow mixer is operated at temperatures at which expansion occurs, affording exceptional control over the process.
• the surface barrier liquid or mixture of such a liquid with a solid will form a substantially homogeneous blend with the microsphere beads substantially free of agglomeration.
• the microsphere component can be expanded to a density as low as about 0.015 grams per cubic centimeter.
• the expansion can be carried out in any convenient equipment, in either batch or continuous operations suited to effect heat transfer to the microspheres. Since the adherence of the surface barrier liquid or mixture of such a liquid with a solid is maintained at expansion temperatures, and since the water, was previously removed, only the thermal requirements for expansion need to be considered and controlled. It has been found that the homogeneous blend produced in the mixture can be expanded with low shear mixing to aid in uniform and efficient heat transfer by indirect heat exchange in very simple and inexpensive equipment. High speed, high shear mixing is not required in the expansion operation, so long as the dry beads to be expanded already have reduced agglomerates and have been fully wet and achieved sufficient homogeneity in the blend. While the expansion can be conducted in the plow mixer, it will generally be desirable to expand, continuously if desired, in faster, less expensive equipment. Suitable for such use are the Solidaire® continuous heat transfer units available from Bepex Corporation of Rolling Meadows, Illinois.
• the expansion equipment must provide the energy for the expansion alone. This is not large, and in most circumstances achieving a bead temperature (depending on the specific polymer) at which expansion occurs, as previously defined, there will be little difficulty in attaining the desired degree of expansion. In most circumstances, full expansion is desired, i.e., to a microsphere density of less than 0.03 g/cm 3 , preferably about 0.02 g/cm3 (without the surface barrier liquid or mixture of such a liquid with a solid) .
• thermoplastic polymer It is important not to melt the polymer mass, so that the hollow spherical structure is lost through over expansion. On the other hand, if the temperature is not high enough to soften the polymer and to develop an adequate pressure of the blowing agent, expansion may not occur, or may be insufficient.
• Residence time at the appropriate temperature is also a useful control parameter, since there is a definite duration of the expansion process. Even when adequate temperatures are achieved, if the residence time at temperature is too short, the expansion may be insufficient. If the time is too long, the microspheres themselves may be over-expanded and disrupted, leaving broken spheres and polymer fragments and grit in the product, with attendant losses of production. While heat transfer rates are generally dependent on the specific equipment employed, residence times on the order of 0.5 to 3 minutes are often sufficient.
• the temperatures for expansion are generally near, but not materially above, the glass transition temperature of amorphous materials and the melting temperature of crystalline polymers. These matters are discussed in more detail in the Morehouse patent.
• the degree of expansion can range from substantially none, to the known limits of expansion. This parameter is determined by the temperature, the residence time at temperature, and to a lesser degree, by the pressure in the system.
• Expansion requires that the blowing agent develop a substantial internal pressure (as compared with the external pressure) , and that the polymer become softened enough to flow under the effect of the internal pressure.
• the upper limit of temperature should be about 180° for the co-polymer beads, and preferably no higher than 150° for polyvinylidene chloride. At these higher temperatures, the residence time at temperature should be brief.
• the surface barrier liquid or mixture of such a liquid with a solid wets to the surface and prevents agglomeration, and good mixing operates to maximize the extent of heat transfer to the microspheres at this stage in the process.
• the extent of the mixing is not narrowly critical, so long as the mixing maintains a uniform, substantially homogeneous blend of surface barrier liquid or mixture of such a liquid with a solid and microspheres and relatively even heat transfer is obtained.
• the dried and expanded microspheres it is generally preferred to permit the dried and expanded microspheres to cool before they are collected and packaged or otherwise handled. This minimizes the degree to which handling can disrupt the bead structure while the polymer is in the plastic state. Active cooling may be employed if desired.
• the resulting microspheres with their coating of the surface barrier liquid can be conveniently recovered from the expander, collected and handled by entirely conventional procedures and equipment usually employed in such operations for dealing with powdered or granular materials. When unusually high proportions of the surface barrier liquid are employed, handling equipment usual for such liquids may be employed.
• the result of the process is the production of a unique form of the microspheres.
• the microspheres will have an adherent surface coating of the surface barrier liquid or mixture of such a liquid with a solid.
• the liquid or mixture of such a liquid with a solid will completely coat the surface in a substantially continuous layer.
• the thickness of the coating may be controlled.
• the microspheres of the present invention will often have a low incidence of deformed, non-spherical shapes when compared to the dried and expanded microspheres from the processes of the prior art. It has been found that the level of disrupted microspheres, where the hollow structure with a continuous form is broken, are not frequent, and are as low or even lower than the norms of the prior art processes.
• the microsphere product of the present invention can be expanded to very near the limit of expandability, i.e., to a density of less than about 0.03, often 0.02 or even 0.015 g/cm 3 . Higher densities are also possible. When the barrier coating material is taken into account, the composite density will, of course, be somewhat higher.
• the composite density of the product will be determined by the density of the particular barrier coating material employed, the amount of the barrier coating material included, and the degree of expansion. Those of ordinary skill in the art will be able to readily determine the composite density of the product from the information and guidance provided in the present disclosure.
• the expanded beads of the present invention will have less than one percent, and often less than 0.1 percent agglomerates. In the present invention, this signifies that at least about 99 percent of the product, and preferably at least about 99.9 percent, will pass a 100 mesh screen.
• the very low level of agglomerates is attained up to 80 percent by weight (in excess of 99 percent by volume) .
• Such low proportions of the surface barrier liquid or mixture of such a liquid with a solid may be highly desirable in some applications of the product.
• the present invention is illustrated in the following results, set out in Table II, wherein six formulations of microspheres with four different surface barrier liquids are employed to illustrate the drying, and the optional expansion of the microspheres.
• microsphere wet cake of the indicated type and the surface barrier coating liquid are charged to a high shear mixing vessel provided with a heating jacket and venting to a vacuum source. Mixing was initiated, pressure within the vessel was reduced to about 250 mm Hg., and the temperature was increased over about ten minutes to 110° C, and then held at that temperature for a period of ten minutes. At that time, the temperature was gradually raised over an additional fifteen minutes to a peak temperature indicated in Table II, and held at that temperature for a period of two minutes. The mixing and vacuum were stopped and ambient air vented into the vessel to cool the composite, which was examined and found to have the properties reported in Table II.
• Microsphere Type A is a wet cake of an unexpanded 5 micrometer diameter terpolymer microsphere of vinylidene chloride, acrylonitrile, and divinyl benzene, having a Tg of about 180° C, and an unexpanded density of 1.1, and a fully expanded diameter of 50 micrometers at a density of
• Microsphere Type B is a wet cake of an unexpanded 5 micrometer diameter microsphere of vinylidene chloride having a Tg of about 125° C, and an unexpanded density of
• Liquid Type A is a 120° C melting point microcrystalline wax, solid at room temperature.
• Liquid Type B is dioctyl phthalate.
• Liquid Type C is Dow Corning Silicone fluid DC-200.
• Liquid Type D is a silicone wetting agent PA-57.
• Processing Temp is in degrees F.

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• 1992
  • 1992-05-19 WO PCT/US1992/004156 patent/WO1992020465A1/en not_active Application Discontinuation
  • 1992-05-19 EP EP19920912509 patent/EP0586541A4/en not_active Withdrawn
  • 1992-05-19 CA CA 2109728 patent/CA2109728A1/en not_active Abandoned
  • 1992-05-19 KR KR1019930703590A patent/KR100216886B1/ko not_active IP Right Cessation
  • 1992-05-19 JP JP05500247A patent/JP3140463B2/ja not_active Expired - Lifetime
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