# US 6,723,761 B1 · Microcellular foaming > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,723,761 B1 - Document ID: US6723761B1 - Status: Granted - Kind: B1 - Application number: 08/601,785 - Filed: 1996-02-15 - Granted: 2004-04-20 - Earliest claimed: 1996-02-15 - Assignees: Bose Corporation - Inventors: David E. Thomas; Jian Xing Li - Web page: https://patentgrep.com/patent/US6723761B1 ## CPC - B29C 44/352: {Means for giving the foam different characteristics in different directions} - B29C 44/04: consisting of at least two parts of chemically or physically different materials, e.g. having different densities - B29C 44/3446: {Feeding the blowing agent} - B29C 44/3453: {Feeding the blowing agent to solid plastic material} - B29C 44/348: {by regulating the temperature and/or the pressure, e.g. suppression of foaming until the pressure is rapidly decreased} - C08J 9/122: {Hydrogen, oxygen, CO2, nitrogen or noble gases} - H04R 7/00: Diaphragms for electromechanical transducers (in general F16J3/00); Cones (for musical instruments G10 ){(cones, diaphragms or the like, for emitting or receiving sound in general G10K13/00; Mounting thereof)} - B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00) - C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29) - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) ## Abstract A method for forming microcellular foams that causes the material to expand uniaxially during the foaming process, and a method for forming objects from the foam. Liquid crystal polymers or polymers having a planar crystalline structure are saturated with a fluid, normally a gas such as carbon dioxide. The ambient conditions are changed such that the fluid is in a supersaturated state, and the material is brought to near its glass transition temperature to induce the formation of nonspherical elongated gas-filled cells. A process for making objects, such as transducer diaphragms, from microcellular foams includes the step of forming the objects prior to the foaming process. ## Claims ### Claim 1 A method of producing a foamed polymeric material, comprising saturating a portion of unfoamed polymeric material having a thickness dimension transverse to opposed surfaces with a fluid; and expanding said unfoamed polymeric material in only said thickness dimension to form said foamed polymeric material with interplanar gas-filled cells in said material having a dimension in a direction parallel to said opposed surfaces treater than a dimension in a direction parallel to said thickness dimension. ### Claim 2 (depends on 1) The method as claimed in claim 1, wherein the only said material has a planar crystalline structure and wherein expanding said unfoamed polymeric material causes the formation of said interplanar gas-filled cells in said materials. ### Claim 3 (depends on 1) The method as claimed in claim 1, wherein the unfoamed polymeric material is polyethylene naphthalate. ### Claim 4 (depends on 2) The method as claimed in claim 2, wherein the gas filled cells have a substantially nonspherical shape. ### Claim 5 (depends on 4) The method as claimed in claim 4 wherein each of the gas-filled cells has at least one dimension in a direction parallel to said opposed surfaces that is significantly larger than at least one other dimension in a direction parallel to said thickness dimension. ### Claim 6 (depends on 5) The method as claimed in claim 5 wherein the at least one dimension is approximately 50 microns and the at least one other dimension is approximately 20 microns. ### Claim 7 (depends on 5) The method as claimed in claim 5 wherein the at least one dimension is more than two times the at least one other dimension. ### Claim 8 (depends on 1) The method as claimed in claim 1, wherein said saturating a portion is with a fluid in a supercritical state. ### Claim 9 A method for forming a foamed polymeric object, comprising preforming the object from an unfoamed polymeric material having a planar crystalline structure; saturating the preformed object with a fluid in an atmosphere at a predetermined ambient pressure; and reducing the ambient pressure to a pressure at which the preformed object is supersaturated with the fluid. ### Claim 10 (depends on 9) The method as claimed in claim 9, further comprising forming gas filled cells in said object each having at least one dimension that is significantly larger than at least one other dimension. ### Claim 11 (depends on 10) The method as claimed in claim 10, wherein the material comprises polyethylene naphthalate. ### Claim 12 (depends on 10) The method as claimed in claim 10, wherein the object comprises a transducer diaphragm. ### Claim 13 (depends on 9) The method as claimed in claim 9, wherein said saturating the preformed object is with the fluid in a supercritical state. ### Claim 14 (depends on 9) The method as claimed in claim 9, wherein the object has a thickness dimension transverse to opposed surfaces and further comprising expanding in said object only thickness dimension. ### Claim 15 A foamed polymeric material, having a thickness dimension transverse to opposed surfaces comprising gas-filled cells each having one dimension in a direction that is parallel to said opposed surfaces that is larger than a second dimension in a direction parallel to said thickness dimension. ### Claim 16 (depends on 15) The material as claimed in claim 15, wherein the gas filled cells are formed by a process that comprises: saturating an unfoamed polymeric material with a gas; heating the unfoamed material to approximately its glass transition temperature; and reducing the ambient pressure to a pressure at which the unfoamed material is in an atmosphere having an ambient pressure supersaturated with the gas. ### Claim 17 (depends on 16) The material as claimed in claim 16, wherein the unfoamed polymeric material is polyethylene naphthalate. ### Claim 18 (depends on 15) The material as claimed in claim 15, wherein the one dimension is approximately 50 microns. ### Claim 19 (depends on 15) The material as claimed in claim 15, wherein the second dimension is approximately 20 microns. ### Claim 20 (depends on 15) The material as claimed in claim 15, wherein the one first dimension is more than twice the second dimension. ### Claim 21 A foamed polymeric object, formed by: shaping the object from an unfoamed polymeric material having a planar crystalline structure; saturating the shaped object with a fluid in an atmosphere having an ambient pressure; and reducing the ambient pressure to a pressure at which the shaped object is supersaturated with the fluid. ### Claim 22 (depends on 21) The object as claimed in claim 21, wherein reducing the ambient pressure step causes the shaped object to locally delaminate. ### Claim 23 (depends on 22) The object as claimed in claim 22, wherein the polymeric material comprises polyethylene naphthalate. ### Claim 24 (depends on 21) The object as claimed in claim 21, wherein the object comprises a transducer diaphragm. ### Claim 25 A diaphragm comprising, a foamed polymeric material having a thickness transverse to opposed surfaces having gas-filled voids between the opposed surfaces, the voids having a first dimension of less than 30 microns measured in the direction of said thickness and a second dimension greater than said first dimension in a direction parallel to said opposed surfaces. ### Claim 26 (depends on 25) A loudspeaker diaphragm as claimed in claim 25, wherein the polymeric material has a planar crystalline structure in a preformed state. ### Claim 27 (depends on 26) A loudspeaker diaphragm as claimed in claim 26, wherein the voids are interplanar between said opposed surfaces. ### Claim 28 (depends on 26) A loudspeaker diaphragm as claimed in claim 26, wherein the polymeric material comprises polyethylene naphthalate. ### Claim 29 (depends on 25) A loudspeaker diaphragm as claimed in claim 25, wherein the diaphragm is self-skinned. ### Claim 30 (depends on 25) A loudspeaker diaphragm as claimed in claim 25, wherein said second dimension is significantly larger than the first dimension. ### Claim 31 (depends on 30) A diaphragm as claimed in claim 30, wherein the second dimension is more than two times the first dimension. ### Claim 32 (depends on 30) A diaphragm as claimed in claim 30 wherein the second dimension is approximately 50 microns.