Abstract: A carbonaceous fiber having a carbon content of from 70 to 90%, a high tensile strength and a high modulus of elasticity, which is produced by a method which comprises preoxidizing an acrylic fiber in an oxidizing atmosphere at a temperature of from 10.degree. to 60.degree. C. below the decomposition point of said fiber, to prepare a preoxidized fiber having a degree of orientation of not less than 78% at an angle of X-ray diffraction (2.theta.) of 25.degree. and a specific gravity of from 1.30 to 1.40, pyrolyzing the preoxidized fiber in an inert gas atmosphere by passing the fiber firstly through a lower temperature zone having a temperature of not higher than 750.degree. C. and then through a higher temperature zone having a temperature of from 750.degree. to 950.degree. C., during the pyrolysis controlling the tension of the fiber so that the change of the fiber length during pyrolyzing is from +16% to -8.8% based on the length of the preoxidized fiber.

Abstract: A pitch having optical anisotropy for use in production of carbon fibers, wherein the pitch is prepared using a compound represented by the formula (I) as a raw starting material and subjecting the compound to thermal modification and then removing light fractions ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.6, R.sub.7, R.sub.8, R.sub.9 and R.sub.10 each represents a hydrogen atom or a methyl group or an ethyl group; R.sub.5 represents a hydrogen atom or a methyl group; the total number of carbon atoms of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 is from 2 to 4 and the total number of carbon atoms of R.sub.6, R.sub.7, R.sub.8 and R.sub.9 is from 2 to 4; and m is at least 3. The pitch is substantially homogeneous in quality, has a low softening point and has excellent molecular orientation.

Abstract: Cupola-shaped plastic pieces with a flat, unwarped rim can be produced from an equally large blank without trimming of the rim, by heating an optionally preheated plastic sheet by radiant heat. The radiant heat acts only on the area surrounded by the rim area until the area exposed to the radiant heat has reached a temperature just below the softening temperature of the plastic. Up to this point, the rim is left without tension, or at most a low clamping pressure is applied which allows a thermal movement of the rim. Then, but before the beginning of the forming, the clamping pressure is increased so that the rim is held tight. The radiation activity continues until the area exposed to the radiant heat has exceeded the softening temperature, the radiation activity is then stopped, and the area heated to the forming temperature is formed.

Abstract: The rate of preoxidation-stabilization of polyacrylonitrile carbon fiber precursors is substantially increased by applying an aqueous solution of an accelerator compound containing a C.dbd.N group such as guanidine carbonate to the fiber, suitably by immersing the fiber in a bath of the solution.

Abstract: Novel carbon-carbon laminate composite materials capable of significantly increased strengths in at least one predetermined direction of load are disclosed. The composites can comprise plies of resin impregnated woven carbon or graphite cloth material in combination with resin impregnated carbon or graphite filament unidirectional tape or can be fabricated from the unidirectional tape alone. Generally the unidirectional reinforcement of the tape plies provides higher strengths and moduli in specific directions which can be controlled during lay up of parts. The processes for obtaining the beneficial increase strength of unidirectional tape ply materials while avoiding fabrication problems resulting therefrom are also disclosed.

Abstract: Oxidative stabilization of pitch fiber is accelerated in an oxidizing atmosphere wherein the oxidizing gas is at a pressure of at least about two atmospheres.

Abstract: A plastics composite of fibres in a thermoformable matrix is formed by contacting the composite with a sheet of metal and deforming the metal plastically. The thermoformable matrix may be thermoplastic or thermosetting and the metal may be superplastic. The matrix may be deformed between the sheet and another sheet or between the sheet and a mould. Thin bodies of complex shape may be formed.

Abstract: In the process for producing pitch carbon fibers by melt-spinning a carbonaceous pitch, and infusiblizing the resulting pitch fibers followed by carbonization and, additionally as needed, graphitization, the pitch fibers are subjected to infusiblization treatment following application of a dimethyl polysiloxane having a viscosity at 25.degree. C. in the range between 0.5 and 500 cSt and removing said dimethyl polysiloxane by washing prior to the carbonization.

Abstract: A novel polycyanogen (MW at least 500) is made by electrochemical polymerization of cyanogen in solution. Fiber and pyrolyzed forms of this polymer and methods of making same are also described.

Abstract: A diaphragm or membrane for use in electrolysis cells resistant to chemical action thereof is disclosed. In the preferred and illustrated embodiment, a fluoropolymer binder cooperative with a random mix of carbon fibers up to about 13 mm long and up to about 0.01 mm in diameter forms such diaphragm or membrane. The carbon fibers are preferably pliable, nonbrittle, resilient, electrically nonconductive, impervious to chemical attack, and are annealed up to a specified temperature.

Abstract: An ultrahigh strength carbon fiber having a surface layer having a crystalline completeness which is substantially the same as or higher than that of the central region of the fiber, and a functional group amount ratio (O.sub.ls /C.sub.ls) of 0.1 to 0.4 as detected in the fiber surface by X-ray photoelectron spectroscopy, the surface layer preferably having an ultrathin outermost layer having a lower crystalline completeness than the central region of the fiber.

Abstract: A tubular article with a closed end is formed from a thermoformable polymer material, e.g. a high molecular weight saturated linear polyester such as polyethylene terephthalate, by forcing a punch (21) through the plane of a pre-heated and clamped sheet (13) of the polymer, centrally within an annular die (10) so as to draw the sheet into tubular form without exerting compressive stresses on the sheet between the punch and die, the punch being maintained at a temperature below the glass transition temperature of the polymer, e.g. by passing cooling fluid through internal passages (16), and being moved at a speed of at least 1/2 meter per second to effect the drawing. The punch head (21) may be convex or concave to produce a shaped closed end on the article, e.g. for making a pressure-resistant container, and the punch may co-operate with a shaped movable anvil (201) at the end or at an intermediate point in its stroke.

Abstract: This invention concerns a process for producing a molded thermoplastic resin by interposing during molding a thermoplastic resin different from the thermoplastic resin to be molded as a skin layer between the die surface and the thermoplastic resin to be molded. A lubricant is provided to lubricate the interface between the die surface and the skin layer. After molding, the skin layer with lubricant is removed.

Abstract: A pitch-based carbon or graphite fiber having a leafy lamella arrangement in at least 30% of the fiber cross-sectional area and having a tensile strength of at least 300 kg/mm.sup.2. The fiber is prepared by melt-spinning an optically anisotropic pitch having an optically anisotropic phase content of at least 50% through a spinneret in which at least one central line distance in a spinning hole simultaneously satisfies the following requirements I and II,Ln<10 I1.5.ltoreq.Ln/Wn.ltoreq.20 IIwherein Ln stands for central line distances in mm in the spinning hole and Wn stands for wetted perimeter widths in mm in the spinning hole, and infusibilizing and carbonizing the formed pitch fiber.

Abstract: In a method of making a fluted core radome from resin impregnated glass cloth, an outer skin, a fluted core, an inner skin, an edge band and a drain cap are individually fabricated from plies of resin impregnated glass cloth which are laid up on a mold and then subjected to pressure using a vacuum bag and to resin curing heat using an autoclave. The fluted core is formed on a mold having recesses in the surface thereof by placing silicone rubber mandrels within the recesses and on top of the plies of glass cloth, the mandrels tending to expand in response to the application of heat thereto and at the same time tending to contract in response to the application of pressure thereto so that an equilibrium is reached which provides a tight fit of the glass plies over the mold and a relatively even flow of resin within the glass cloth.

Abstract: Decorative panels having the appearance of tongue-in-groove construction and the method of making such panels. The panels are made from a composite structure including a base member and a decorative surface veneer on such member. A portion of the base member is removed. The removed portion includes a segment to a first depth less than the total depth of the base member measured from the surface of the base member opposite the veneer, and spaced segments to a total depth of the base member. This leaves an intermediate part of the base member connected to the veneer between the removed spaced segments. The sides of the base member opposite the removed portion are urged toward one another; and the intermediate part is substantially simultaneously urged toward the surface of the base member opposite the veneer. The intermediate part is then secured to such sides of the base member to complete the panel.

Abstract: Provided is a process for producing pitch carbon fibers by subjecting pitch fibers obtained by melt-spinning a carbonaceous pitch to infusibilization treatment and then to carbonization treatment or both carbonization treatment and subsequent graphitization treatment, characterized in that a dimethyl polysiloxane having a viscosity at 25.degree. C. in the range of 12,000 to 1,000,000 cSt is applied to the fibers after the infusibilization treatment, and the infusibilized fibers with the dimethyl polysiloxane thus applied thereto are then subjected to the carbonization treatment or both the carbonization treatment and the subsequent graphitization treatment.

Abstract: High tensile carbon fibers are provided with a high yield process in which, after oxidation of a precursor, the fibers are first precarbonized in an inert atmosphere to to about 600.degree. C. while imparting 5-10% stretch. In precarbonizing, the fibers are initially heated in a sweeping manner with substantial volumes of hot inert gas which is extracted along with products of decomposition before the fibers are cooled to a low, non-reactive exit temperature. The arrangement minimizes redeposition of tars on the fibers and stretches the fibers in a range in which substantial off-gassing occurs. Thereafter the fibers are finally carbonized at a higher temperature with a different tension being applied, to provide a more reliable less sensitive process that enables oxidation to be effected more rapidly.

Abstract: A process for producing a carbon fiber having a tenacity of 450 kg/mm.sup.2 or more, preferably 500 kg/mm.sup.2 or more, and a modulus of elasticity of 25 ton/mm.sup.2 or more which comprises subjecting a polyacrylonitrile-type fiber to a flame-resisting treatment in a flame-resisting treatment furnace provided with a plural number of driving rolls in an oxidizing atmosphere at 200.degree. to 400.degree. C. under application of multistep elongation, during said treatment the respective percentage of elongation in said multistep elongation being set respectively at a value which is equal to or within .+-.3% of the value of the percentage of elongation En indicating an inflection point Pn obtainable from the load and the percentage of elongation determined in advance by experimental measurements, and then subjecting the treated fiber to carbonization.

Abstract: The ear plug (40) includes an elongate body with a rounded tip portion and of an elastic material enveloped by a deep-drawn sheath (41) of thin flexible plastics film material. Rearwardly the plug preferably has a neck portion from which the sheath projects in the form of a stiffer collar or flange. Production of the ear plug includes deep-drawing a thermoplastic film or foil into a sheath with desired thickness distribution, and filling the sheath with elastic material (53). Filling may take place simultaneously with deep-drawing, the body of elastic material constituting a die for deep-drawing in a forming hole (45), or after the deep-drawing. In the latter case, an elastic die body is used to advantage, the shape of which generally corresponds to that of the finished plug, for deep-drawing in a forming hole suited to the die body.

Abstract: A method for spinning filament yarns of high strength, high modulus carbon fibers is provided by way of a melt-spinning process in which a heated inert gas or a non-oxidative gas such as hydrocarbons of small C-numbers is injected steadily onto the surfaces of spinning nozzles to stabilize and ease the melt-spinning.

Abstract: Improved process for producing a carbon fiber having high tensile strength and high modulus involves oxidation of acrylonitrile fiber which has been treated with selected ammonium salts, from the group of ammonium sulfamate, ammonium bromide and ammonium iodide.

Abstract: There is disclosed a method for making high strength carbon fibers which comprises carbonizing acrylic fibers applied with an aqueous dispersion of a silicone compound represented by the following general formula [I] dispersed with an emulsifier represented by the following general formula [II], the total amount of the silicone compound and the emulsifier being 0.01 to 10.0% by weight (owf) and the weight ratio of the emulsifier to the silicone compound being 0.05 to 0.4: ##STR1## (where the symbols are as defined hereinbefore).

Abstract: An ultrahigh strength carbon fiber having a surface layer having a crystalline completeness which is substantially the same as or higher than that of the central region of the fiber, and a functional group amount ratio (O.sub.ls /C.sub.ls) of 0.1 to 0.4 as detected in the fiber surface by X-ray photoelectron spectroscopy, the surface layer preferably having an ultrathin outermost layer having a lower crystalline completeness than the central region of the fiber.

Abstract: A method of forming a preform having crystallized thermoplastic material from a blank of orientable thermoplastic material, such as polyethylene terephthalate, which comprises laterally displacing first and second regions of a blank, preferably tubular, of orientable thermoplastic material to form an intermediate region between the displaced regions having outer surfaces facing in opposite directions. Pressure is applied to the outer surfaces of the intermediate region to relatively displace these outer surfaces longitudinally of the blank while concurrently reducing the thickness of one of the first and second regions to the value of the thickness that the material would obtain if freely stretched to flow to achieve crystallization of the material in the aforesaid one region. The material in the one region, during the reduction of thickness thereof flowing from the orientable material thereof to a transition zone to form the one region which is reduced in thickness and is elongated in length.

Abstract: The invention provides carbon fibers having mechanical properties equival to or even better than those of the polyacrylonitrile-based carbon fibers from a bituminous material, e.g. coal tar pitch, as the starting material. The starting pitch is first partially hydrogenated in tetrahydroquinoline under specific conditions followed by a heat treatment to give a pitch composition suitable for spinning which can be characterized by several parameters including the proportions of the carbons and hydrogens having different chemical shifts in the NMR analysis. The pitch composition for spinning is then subjected to spinning under specific conditions including the temperature condition for controlling the viscosity behavior of the molten pitch composition determined by use of the Andrade's equation and the pitch filament is then infusibilized in an oxidative atmosphere and carbonized in an inert atmosphere into carbon fibers having a tensile strength of at least 200 kg/mm.sup.

Abstract: The instant invention involves a process for use in preparing tapes or rovings, which are formed from a thermoplastic material used to impregnate longitudinally extended bundles of carbon fibers. The process involves the steps of (a) gas spreading a tow of carbon fibers; (b) feeding the spread tow into a crosshead die; (c) impregnating the tow in the die with a thermoplastic polymer; (d) withdrawing the impregnated tow from the die; and (e) gas cooling the impregnated tow with a jet of air.The crosshead die useful in the instant invention includes a horizontally extended, carbon fiber bundle inlet channel, means for providing melted polymer under pressure to the die, means for dividing the polymeric material flowing into the die into an upper flow channel and a lower flow channel disposed above and below the moving carbon fiber bundle, means for applying the thermoplastic material from both the upper and lower channels to the fiber bundle, and means for withdrawing the resulting tape from the die.

Abstract: A process for producing a carbon fiber from pitch material, which comprises melt spinning pitch material through spinning nozzles to form precursory pitch fibers and oiling the precursory pitch fibers, followed by infusible treatment and carbonization and optionally by graphitization, characterized in that an oiling agent composed essentially of a silicone oil is applied to the precursory pitch fibers prior to or during the oiling operation.

Abstract: Provided is a starting pitch for producing carbon fiber by heat-treating the starting pitch to obtain a precursor pitch, melt-spinning the precursor pitch, then rendering the resultant pitch fiber infusible, followed by carbonization, and further followed by graphitization if required, the starting pitch comprising a mixture of (a) 100 parts by weight of a pitch and (b) 5 to 500 parts by weight of a methanol-insoluble and benzene-soluble component contained in a heavy oil obtained in a fluid catalytic cracking of petroleum, the heavy oil having a boiling range not lower than 200.degree. C.

Abstract: A door having an improved design is provided, which improved design consisting of a door frame made of a rigid material, a first skin mounted on this frame and forming a first face of the door, and a second skin also mounted on the frame and forming a second face of the door. One of the first and second skins comprises a portion thereof which constitutes at least in part the peripheral edge of the door. In this design, at least one of the first and second skins is made of moldable material and is shaped by vacuum forming to provide the corresponding face of the door with decorative patterns, which decorative patterns as well as the door frame being designed so that the shaped skin can be mounted on the frame. Any empty space between the two skins of the door may be filled with a convenient material, thereby increasing the rigidity of the door.

Abstract: A composite, single material, one-piece turbomachinery rotor constructed of fibers bonded in a matrix is disclosed together with a method of manufacture thereof.

Abstract: This invention provides a process for the production of poly(p-phenylene) which involves subjecting a liquid reaction medium containing 4,4'-dihalobiphenyl and alkali metal, e.g. lithium coupling reactants to activation with ultrasonic energy.

Abstract: Active carbon fibers derived from acrylic fibers and having a BET specific surface area (SA) of 800 to 2,000 m.sup.2 /g, a pore volume (Vp) to (SA) ratio, i.e., (Vp)/(SA), of from 5.times.10.sup.-4 to 14.5.times.10.sup.-4, and a methylene blue adsorption rate constant of not less than 5.times.10.sup.-1 sec.sup.-1, and a filter adsorption unit for water purification using said active carbon fibers; the unit is useful to remove compounds having a wide range of molecular weights from an aqueous liquid.

Abstract: A spinnerette for mesophase pitch includes a spinnerette body with a plurality of mesophase pitch fiber forming channels through it. Each bore includes a capillary bore section at the outlet side of the spinnerette body, a wider diameter counter bore at the inlet side and an entrance between the wider bore and capillary bore sections with the entrance wall defining a relatively flat angle for increasing the proportion of tangential cross-section pitch fibers, as compared with radial cross-section fibers.

Abstract: The oxidation of carbon fibers from pitch is carried out directly by winding the spun fibers on to a spinning spool or bobbin, said spool comprising an open ended, porous, non-expanding or collapsible spool. The spun carbon fibers are wound on such a spinning spool so as to leave open areas between fiber bundles. A mixture of an inert gas such as air or nitrogen containing a minor amount of oxygen is used as the oxidizing gas. Oxidation is carried out in a closed zone, e.g. an oven, for a period of time of at least 4 hours at a temperature that is initially below the glass transistion temperature of the carbon fibers and is slowly increased over the oxidation time to a maximum of about 340.degree. C. The gaseous oxidation atmosphere is continuously recycled and passed through the spool to ensure that the fibers are essentially completely oxidized.

Abstract: Provided is a process for producing a pitch-based graphite fiber, which process comprises treating a pitch fiber in an oxidative gas atmosphere to render it infusible, said pitch fiber being obtained by melt-spinning a carbonaceous pitch, then heat-treating the infusibilized fiber at 400.degree.-750.degree. C. in an inert gas atmosphere to obtain a precarbonized fiber substantially containing oxygen, then raising the temperature to 2,000.degree.-3,000.degree. C. at a rate of 500.degree. C. or higher per minute in an inert gas atmosphere and heat-treating the precarbonized fiber at the raised temperature of 2,000.degree.-3,000.degree. C. in said inert gas atmosphere.

Abstract: A sheet of embroidered lace material or the like is temporarily attached to a relatively heat and stretch resistant fabric and subjected to a heat molding process to form a cup in the lace material. The design in the edge of the lace material to which the heat and stretch fabric is attached is held against deformation by the fabric so that the cup is formed with minimum deformation of the design. Thereafter the cup is cut into shape.

Abstract: A process of preparing carbon fibers in a floating state by reacting a mixed gas consisted of a gas of organic metal compound or compounds, a carrier gas and desirably a gas of carbon compound or compounds at the elevated temperature of 600.degree. to 1300.degree. C. is disclosed, in which the fine carbon fibers having a diameter of 0.05 to 2 .mu.m, a length of 2 to 3000 .mu.m and an aspect ratio of 2 to 30,000 as well as a high degree of preferred orientation of carbon layers may be produced in a high yield and a high productivity.

Abstract: A process for producing binderless, single phase bulk carbon or graphite articles having a fibrillar microstructure comprising the steps of assembling a plurality of polymer fibers into a preselected pattern, subjecting them to a temperature and pressure sufficient to cause heat distortion flow and concomitant self-bonding of contiguous fibers and pyrolyzing the fibers in a nonoxidizing atmosphere.

Abstract: Herein disclosed is a process of manufacturing drawn tubing, in which steps of applying a lubricant to the surface of a bottomed blank fitted on a mandrel, pushing out the mandrel to draw the blank through a die, and pulling in the drawn blank together with the mandrel out of the die are repeated in the recited order. The drawn blank is turned a predetermined angle, e.g., 180 degrees on the axis thereof during each of the repeating steps i.e., during or after the pulling step. As a result, the lubricant can be applied to another portion of the blank surface at a second or subsequent applying step so that the working conditions which might otherwise become different to cause the drawn blank to have a locally irregular or offset thickness can be made uniform in the circumferential direction of the blank.

Abstract: A method of producing a container of polyethylene terephthalate or similar thermoplastic material from a tubular blank of amorphous material. A mechanical forming element moves a transitional zone between amorphous (thicker) material and thinner oriented material stretched to flow during simultaneous elongation of the blank in the direction of movement of the transitional zone. The stretched and oriented material is heated to a temperature higher than the temperature of the material immediately before stretching. As a result, the internal stresses produced in the material during earlier stretching are relieved. Heating causes the length of the material in the direction of stretching also to be reduced. Each subsequent forming stage for shaping the container takes place at a temperature lower than the temperature at the immediately preceding forming stage.

Abstract: An apparatus and method for producing articles by stretch-forming or pressure-forming of thermoplastics in the solid crystalline phase which permits forming from a billet of given thickness articles of greater wall thickness than would be formed by stretch-forming or pressure-forming the clamped billets.

Abstract: A laminate, including an aluminum foil layer and a polyester layer, has the aluminum foil layer wrinkled or contracted into a large number of wrinkles. These can be straightened out when the plastic material is stretched, without any breaking of the aluminum foil layer.

Abstract: Apparatus and method for forming curved needlepoint canvases from initially flat perforated sheet by applying pressure to a first side of the sheet, thus driving and deforming it into an aperture in a die, and by supporting the opposite side of the sheet during deformation with a pressure pad which includes a recess into which the deformed sheet is driven.

Abstract: Thermoforming machines with a heating station and a downstream mold station have carrier clamp frames for gripping the edges of sheets of plastic at a load station and indexing them successively to a heating station and a mold station. The carrier frame members to which the plastic may be releasably clamped carry their own remotely operated clamps and are themselves expandable and contractible to a condition in which, prior to molding, they control the sag in the sheet formed during heating of the sheets to differential pressure forming temperature. The plastic sheet can be molded to only a portion of a product which functions as a mold member.

Abstract: A process for the preparation of carbon fibers, including the steps of:subjecting a raw material oil to thermal cracking conditions at a temperature of between 400.degree. to 500.degree. C. while removing cracked, light hydrocarbon components to obtain a pitch product containing at least 5 weight % of mesophase and not more than 10 weight % of light hydrocarbon components with a boiling point at 60 mmHg (absolute) of 300.degree. C. or less and having a softening point of between 140.degree. and 220.degree. C., the raw material oil having a boiling point of at least 500.degree. C. and containing at least 30 weight % of a residual oil which has a boiling point of at least 500.degree. C. and a metal content of at least 200 weight ppm and which is derived from a napthene base and/or intermediate base petroleum crude;removing the mesophase having a particle size of more than 10 .mu.

Abstract: A process for producing carbon fiber is disclosed, which comprises a preoxidation step for heating precursor fibers in an oxidizing atmosphere and converting them into partially oxidized fibers, an oxidizing step for heating the partially oxidized fibers in an oxidizing atmosphere and converting them into oxidized fibers, and a carbonization step for heating the oxidized fibers in an inert atmosphere and converting them into carbonized fibers, in which in the preoxidation step the precursor fibers are heated at a temperature of about 200.degree. to 250.degree. C. and in which a portion or the whole of the exhaust gas from the oxidation step is supplied into the preoxidation step as the oxidation atmosphere gas and the exhaust gas from the preoxidation step is subjected to a burning treatment.

Abstract: A method of forming a soft, deformable tip at the distal end of an elongated, flexible catheter made from a thermoplastic or elastomeric material in which the tip portion is first heated to soften the plastic and, subsequently, a specially prepared forming tool is inserted into the lumen of the catheter at the distal end and advanced to the point where an annular protuberance of a predetermined outside diameter is forced into the lumen so as to stretch and shape the plastic to conform to the forming tool. The distal end is then cooled and the forming tool removed, leaving a soft, collapsible segment integrally formed at the distal end of the catheter.

Abstract: A method for producing carbon fibers in a vertical carbonizing furnace and an apparatus for producing carbon fibers using such a method are disclosed. The furnace includes a heating chamber for carbonizing fibers, the furnace including,(i) a fiber inlet at the upper end of the chamber(ii) an air tight sealed fiber outlet at the lower end of the furnace,(iii) an inert gas inlet provided on the wall of the chamber and above the fiber outlet,(iv) at least one inert gas injection portion, formed on the wall of the chamber, each capable of forming a curtain of inert gas across the heating chamber, each injection portion being provided between the gas inlet and the fiber inlet,(v) at least one outlet each being provided below each inert gas injection portion, and(vi) a heating member capable of controlling the temperature in the heating chamber in such a manner that the temperature gradually increases from the upper end toward a lower end of the heating chamber.

Abstract: A preoxidized fiber suitable for producing carbon fiber, comprising preoxidizing an acrylic fiber having thereon an ammonium salt of a fatty ester represented by formula [A] and [B] ##STR1## wherein R.sub.1 is an aliphatic hydrocarbon group having from 11 to 17 carbon atoms; R.sub.2 and R.sub.3 can each be hydrogen, a lower alkyl group, a hydroxyethyl group, or an hydroxyisopropyl group; and X.crclbar. is an anion.The preoxidized fiber produced from the acrylic fiber has very little coalescence, and therefore high-strength carbon fiber can be obtained from this preoxidized fiber.