Abstract: The present invention relates to a high-strength porous film or sheet consisting essentially of a high-molecular-weight polyethylene resin having a viscosity-average molecular weight of not less than 300,000, wherein the said film has a thickness of 5 to 50 .mu.m, an air permeability of 200 to 1,000 sec/100 cc, a porosity of 10 to 50% and a pin puncture strength of not less than 600 gf/25 .mu.m, and a process for producing the said film.

Abstract: A process for the extrusion of polyethylene having a broad molecular weight distribution wherein the polyethylene is prepared in pellet form, said extrusion taking place in a pelletizing extruder having one or more zones essentially filled with polyethylene and two or more zones partially filled with polyethylene including(i) introducing the polyethylene into the extruder at a temperature sufficient to melt the polyethylene; (ii) introducing a mixture of an inert gas and oxygen into each partially filled zone wherein the mixture contains about 1 to about 21 percent by volume oxygen based on the volume of the gaseous mixture; (iii) passing the molten polyethylene through each zone at melt temperature; and (iv) extruding the polyethylene into pellets and cooling same.

Abstract: The invention relates to a barrier layer resisting the transmission of oxygen for multi-layer barrier film characterized in that it is made of a transparent copolyamide comprising three components. The first component is hexamethylenediamine and adipic acid. The second component is hexamethylenediamine and azelaic acid, hexamethylenediamine and sebacic acid, and mixtures thereof. The third component is hexamethylene-diamine and isophthalic acid, hexamethylenediamine and terephthalic acid, and mixtures thereof. The total of all components is 100 mol %, and the ratio of the barrier effects in the barrier layer with respect to carbon dioxide and oxygen is at least 3:1.

Abstract: A porous film or sheet including a resin composition mainly of an ultra-high molecular weight polyethylene having a viscosity-average molecular weight of not less than 500,000, and having a thickness of 10 to 100 .mu.m, an air permeability of 20 to 2,000 sec/100 cc, a porosity of 15 to 80%, a pin puncture strength (per 25 .mu.m of film thickness) of not less than 120 g, a thermal-shut down temperature of 90.degree. to 150.degree. C. and a heat puncture temperature of not less than 160.degree. C., and a process for producing the same.

Abstract: A withdrawal device for a plastic tubular film is manufactured in a blowing method by an extruder. To prevent the formation of center wrinkles in the withdrawal of plastic tubular film, at least one deflection cylinder and/or angle bar has a differing diameter across its length.

Abstract: A method is provided to produce a blown film of a vinyl aromatic/conjugated block copolymer, the method including the steps of:providing an elastomeric composition, the composition comprising a block copolymer of vinyl aromatic and a conjugated block copolymer;melting the composition in an extruder;passing the melted composition from the extruder through a die, the die being a circular die comprising a circular outlet and a tapered channel leading to the circular outlet, the circular outlet having an opening width of about 10.sup.-2 inches, the taper being a linear taper of at least a one inch length, the center of the linear taper being angled away from the center of the circular outlet at an angle of at least 10.degree. from a line normal to the circular outlet, and the die having a source of gas pressure inside of the circular outlet; andcooling the extruded composition that has been passed through the die with a cooling gas stream.

Abstract: In a method for forming a cellulose tube suitable for use as a food casing or as cellophane film, in which a solution of nonderivatized cellulose, tertiary amine N-oxide and water is extruded through an air gap of at least five inches, and into a water bath, such that a wet cellulose tube is formed. The wet tube is inflated from about 55% to 140% or more and dried thereby substantially retaining its work-to-rupture characteristics, especially when compared to viscose-derived tubes.

Abstract: Moisture-shrinkable films can be extrusion blown from flour-poly(methyl acrylate) graft copolymers. The films shrink when exposed at room temperature to relative humidities approaching 100%. The films have potential application in shrink-wrapping irregularly shaped articles without application of heat. Easy removal of the films by water washing is another feature suitable for this use. This invention allows the use of unmodified cereal flour in lieu of gelatinized starch as the substrate for graft polymerization. This substitution greatly simplifies the preparation and isolation of the graft copolymers and reduces the expense of the process by lowering raw material costs.

Abstract: Underground pipelines that carry wastewater, water, natural gas, and industrial fluids deteriorate with age. This invention is a process and apparatus for installing a thermoplastic liner in a dry pipeline to accomplish in situ rehabilitation. It involves extruding a tube of thermoplastic liner material within the interior of a dried and preheated pipeline in situ, said tube having an outside diameter smaller than the inside diameter of said pipeline. The tube is next expanded so that the outside diameter of said tube is substantially equal to the inside diameter of said pipeline. The expanded tube is then cooled and hardened in a liner configuration.

Abstract: The relationship between the average degree of roughness of the faces of rough appearance, expressed in microns, and the percentage by weight of units derived from vinyl acetate in the copolymer of which the film consists is greater than 0.019.The film is extruded in the form of an extruded sleeve which is cooled in the die by a circulation of a coolant fluid whose temperature T satisfies the relationship: ##EQU1## in which Tc is the temperature at which the Napierian logarithm of the relationship between the length at break and the initial length of a test specimen of the copolymer has a value of 87% of its value at 180.degree.Tm is the mean temperature of the copolymer as it leaves the diea is equal to 0.24G is given by the relationship .rho..times.Cp.times.V.times.H.sup.2 /.lambda..times.Lin which.rho. is the density of the copolymerCp is the specific heat of the copolymerV is the mean flow velocity of the copolymer through the extrusion dieH is the height of the gap between the core and the extrusion die.

Abstract: A method of manufacturing a monolayer heat-shrinkable, puncture-resistant biaxially oriented film is disclosed. The method includes a double bubble orientation step and extruding a primary tube that includes at least one substantially linear ethylene homopolymer or interpolymer, wherein the substantially linear ethylene homopolymer or interpolymer has an uniform branching distribution, a melt flow ratio I.sub.10 /I.sub.2, .gtoreq.5.63, and a molecular weight distribution, M.sub.w /M.sub.n, defined by the equation M.sub.w /M.sub.n .ltoreq.(I.sub.10 /I.sub.2)-4.63, and is also characterized as having essentially no linear polymer fraction, a single DSC melting peak, a density greater than about 0.85 g/cc, and a favorable gas extrusion critical shear rate at the onset of surface melt fracture.

Abstract: A method for making a film which is useful in the packaging of newly formed blocks of cheese and demonstrates flexibility, extensibility, and improved sealing strength comprises extruding an ethylene vinyl acetate/very low density polyethylene sealing layer. In addition to barrier properties, flexibility and extensibility are, preferably, also provided by coextruding a core layer of ethylene vinyl alcohol copolymer containing at least 32% by weight of ethylene with the sealing layer.

Abstract: Disclosed is a normally solid, high molecular weight, gel-free, amorphous to predominantly crystalline, propylene polymer characterized by high melt strength due to strain hardening which is believed to be caused by free-end long chain branches of the molecular chains forming the polymer.Also disclosed is a process for making the polymer by high energy radiation of a normally solid, high molecular weight, linear, propylene polymer in a reduced active oxygen environment, maintaining the irradiated material in such environment for a specific period of time, and then deactivating free radicals in the material.Further disclosed is the use of the strain hardening polymer in extensional flow operations such as, for example, extrusion coating, film production, and thermoforming.

Abstract: The present invention is directed to melt blown polyolefin film which is produced cheaply by melt blowing polyolefin resins which contain 25 to 60 wt % fillers selected from the fillers including an inorganic carbonate, synthetic carbonates, nepheline syenite, talc, magnesium hydroxide, aluminum trihydrate, diatomaceous earth, mica, natural or synthetic silicas and calcined clays or mixtures thereof, having a particle size less than 150 mesh.A further aspect of the present invention is directed to polyolefin resins, especially polyethylene, which are chemically degradable by the incorporation of the combination of the above group of fillers and a metal carboxylate. The metal carboxylates of the present invention are inclusive of a large number of metals, such as cerium, cobalt, iron, and magnesium.

Abstract: A normally solid, high molecular weight, gel-free, irradiated ethylene polymer is characterized by high melt strength due to strain hardening elongational viscosity, which is believed to be caused by free-end long chain branching of the molecular chains forming the polymer. The polymer is prepared by (1) irradiating a normally solid, high molecular weight ethylene polymer without strain hardening elongational viscosity while in the solid state in an environment in which the active oxygen concentration is less than 15% by volume, maintaining the irradiated material in this environment while in the solid state for a specific period of time, and then deactivating free radicals present in the material.

Abstract: The present invention relates to an apparatus for automatically blowing a bubble in the production of tubular biaxially stretch oriented thermoplastic flexible film by the "bubble" method comprising a high flow fluid conduit having a proximal end for introducing a high flow fluid, and a distal end substantially perpendicular to said proximal end, and having attached to said distal end a bullet mounted proximate to the distal end of the high fluid flow conduit through which the high flow fluid may pass into the tubular thermoplastic film; a cutting device located on said high flow fluid conduit and in line with the bullet, said high flow fluid conduit, bullet, and cutting device disposed downstream from a first and second pair of rolls defining the bubble; and an automatic bubble blowing control system means comprising means for controlling the flow of fluid into the interior of the tape, and means for controlling the speed of a driven set of squeeze rolls located downstream from the high flow fluid conduit.

Abstract: A travelling mold has mold block sections which are driven around an endless track. The mold has a drive system including a first drive component which drives the mold block sections in abutting positions with one another to a second component in the drive system which accelerates and separates the mold block sections and which then decelerates and regroups the mold block sections in their abutting positions before the mold block sections are returned to the first drive component. This separation and regrouping of the mold block sections eliminates the necessity of having a complete chain of abutting mold block sections completely around the mold.

Abstract: There is provided a method for preparing biodegradable films from plant-based raw materials in the form of carbohydrates which method is continuous and carried out in one step. In the process the plant-based raw materials are modified and plastified and the films are prepared without interruption and in one step. The advantages of the invention reside in reduced shear stress of the starch molecules and thus in the improved properties of the films as well as in the cost-efficient, time-, energy- and space-saving manufacture.

Abstract: A method and apparatus for blown film extrusion is described. An annular die receives a molten material and extrudes a film tube. At least one cooling ring is positioned adjacent the annular die for passing an air stream along a particular surface of the film tube. A blower entrains and supplies air to the cooling ring. A flow sensor is positioned in an air flow path intermediate the at least one cooling ring and the blower. It provides a mass air flow signal which is a measure of air mass flow per unit time. An adjustable air flow attribute modifier is placed in communication with the air flow path and operates to selectively modify the air mass flow per time unit. A controller member is in communication with the flow sensor and the adjustable air flow attribute modifier, for receiving the mass air flow signal and for controlling the adjustable air flow attribute modifier to provide a preselected value of air flow in terms of air mass flow per unit time.

Abstract: A sizing tool for extruding plastic tubing is disclosed. The tool includes a peripheral wall having an inner surface that defines the outer dimension of a plastic tubing advancing from an extruder through the tool under influence of an internal pressure exceeding the pressure prevailing in the tool. The tool also includes a lubricating water channel system in the peripheral wall and extending along the tool length and having at least one opening communicating with the inner surface of said peripheral wall. The tool also includes a cooling medium channel system in the peripheral wall and extending along the length. The cooling medium channel system being substantially closed within the peripheral wall and being separate from the lubricating water channel system.

Abstract: This invention relates in general to a method for the formation of films having a controlled molecular orientation prepared from rod-like extended chain aromatic-heterocyclic ordered polymers, and containing a binder in the micro-infrastructure. Such films have high tensile strength, modulus, and environmental resistance characteristics.

Abstract: A pipe liner bag is provided for reliably lining a pipe into which water may penetrate. The pipe liner bag has a double layer structure including an inner layer of a tubular nonwoven fabric made of fine yarn of three deniers or less and an outer layer of a tubular nonwoven fabric made of fat yarn of 3-15 deniers. The tubular nonwoven fabric constituting the inner layer is impregnated with highly viscous and thixotropic hardenable resin mixed with granule fillers of a small diameter, while the tubular nonwoven fabric constituting the outer layer is impregnated with hardenable resin mixed with granule filler of a large diameter. After the pipe liner bag is everted and inserted into a pipe to be repaired by fluid pressure, the hardenable resin impregnated in the pipe liner bag is cured while maintaining the internal pressure thereof constant. When this pipe liner bag is used to repair a pipe from which a branch pipe is branched off, it can be integrated with a branch pipe liner bag.

Abstract: Applications of isotactic polypropylene resin compositions produced from metallocene catalyst wherein the resins yield articles with comparable shear modulus and heat distortion temperature values to those of conventional polypropylene, but in which the fabrication of the article is achieved at temperatures much lower than possible for conventional polypropylene.

Abstract: In a method for forming a cellulose tube suitable for use as a food casing, in which a solution of nonderivatized cellulose, tertiary amine N-oxide and water is extruded through a die gap and the extruded tube downwardly flowed through an air length while being internally cooled, and passed into a water bath, the tube transverse direction tensile strength is substantially increased by drawing the extruded tube through an air length of at least about six inches.

Abstract: The present invention is directed to melt blown polyolefin film which is produced cheaply by melt blowing polyolefin resins which contain 25 to 60 wt% fillers selected from the fillers including an inorganic carbonate, synthetic carbonates, nepheline syenite, talc, magnesium hydroxide, aluminum trihydrate, diatomaceous earth, mica, natural or synthetic silicas and calcined clays or mixtures thereof, having a particle size less than 150 mesh.A further aspect of the present invention is directed to polyolefin resins, especially polyethylene, which are chemically degradable by the incorporation of the combination of the above group of fillers and a metal carboxylate. The metal carboxylates of the present invention are inclusive of a large number of metals, such as cerium, cobalt, iron, and magnesium.

Abstract: The invention concerns apparatus for molding tube (20) utilizing a travelling mold tunnel. The tunnel is made up of mold blocks (16) each comprising parts (13, 15) which are hinged together to be closeable to form the tunnel and openable to release tube from the tunnel. The opened mold blocks (16) from the downstream end of the tunnel are opened and returned to the upstream end without change in their orientation to reform the tunnel about an extrusion nozzle (18) for thermoplastic extrudate.

Abstract: In a blown film extrusion system in which film is extruded as a tube from an annular die and then pulled along a predetermined path, an apparatus is provided for gauging and controlling the circumference of the extruded film tube. At least one transducer, preferably ultrasonic, is mounted adjacent the extruded film tube for transmitting and receiving interrogating pulses along paths normal to the extruded film tube, and for producing a current position signal corresponding to the circumference of the extruded film tube. The current position signal is continuously compared with at least one previous position signal, preferably with a computer program resident in a controller memory. If at least one preselected condition is violated, the current position signal is disregarded in favor of an estimated position signal.

Abstract: Processing, particularly extruding polyolefins having low MI, narrow MWD at extrusion temperatures less than about 200.degree. C. and at shear rates less than about 2000 sec.sup.-1 but immediately above the shear rate corresponding to the end of the slipstick region of the polyolefin produces a new window of processing conditions to produce smooth polymers that do not have sharkskin melt fracture or wavy surfaces.

Abstract: A process for making gelatine films, in particular sheet gelatine, from powdered gelatine includes the following steps: The powdered gelatine with the addition of water is plasticized by the application of shearing forces at an elevated pressure and an elevated temperature, the plasticized mass is pressed in the form of a film through a slotted die, the film is drawn off the slotted die under tension and the taut film is dried.

Abstract: A system for monitoring and controlling the output of extruder apparatus for producing a blown synthetic resin film. An infrared imaging system provides for measuring the temperature of the blown film simultaneously at multiple points on the film between the blowing head and the frost line of the film bubble. The multi-dimensional temperature profile measured by an infrared camera is processed in a computer controller in order to provide control inputs to various components of the extruder apparatus. The extruder apparatus is controlled so as to maintain a desired temperature profile substantially at that which is known to provide a high quality end product.

Abstract: To determine and/or automatically control the degree of orientation of tubular films which have been made in a film-blowing plant including an extruder having a film-blowing head and apparatus for internal cooling and also including flattening and take-off apparatus, the rate of exchange of the air for internal cooling, the speed of the extruder, the temperature of the plastic composition being extruded and/or the take-off velocity are controlled. To ensure that the degree of orientation can be determined and/or automatically controlled in a simple manner and without an occurrence of trouble, that shape of the flaring portion of the bubble which corresponds to the desired degree of orientation is determined and/or adjusted and is recorded as the desired shape of the bubble. The actual shape of the flaring portion of the bubble is detected and compared with and adapted to the desired shape.

Abstract: A method of manufacturing heat-shrinkable, puncture resistant, biaxially stretched thermoplastic films from very low density polyethylene (VLDPE). The film may be entirely VLDPE or it may be multilayer with an oxygen barrier core layer formed of material such as a polyvinylidene chloride copolymer or an ethylene vinyl alcohol copolymer, and two outer layers. One of these outer layers may for example be a blend of ethylene vinyl acetate (EVA) and VLDPE, and the other outer layer may be EVA. The film may be fabricated into bags suitable for packaging food articles such as frozen poultry, primal meat cuts, and processed meat products. The bags have high shrink and improved toughness.

Abstract: A process of having a microporous multiply sheet product which is capable of becoming non-porous at a predetermined elevated transformation temperature is formed by first forming a non-porous, multiply initial sheet product having at least one first ply and at least one second ply, each with its own viscosity profile. The initial sheet product is then stretched and annealed to impart porosity to the sheet product.

Abstract: Apparatus and method for cooling an extruded blown film in which the interior surface of the thin film bubble is contacted with a gas which does not contain water vapor to thereby cool the extruded film. The apparatus and method may employ an enclosed circulation system to provide for the reuse of the gas through cooling with a liquid coolant such as liquid cryogen.

Abstract: An improved blown-film extrusion process with particular application for high modulus thermoplastic resins. A cylinder is mounted above the cooling air ring. The film bubble passes through this cylinder, which has a diameter approximating the final diameter of the bubble. The frost line remains at or slightly higher than the top of the cylinder, leaving a small gap between the top of the cylinder bubble. The improvement enhances bubble cooling and stability and results in wrinkle-free film.

Abstract: A process for substantially eliminating surface melt fracture during extrusion of a thermoplastic polymer such as a molten narrow molecular weight distribution, linear, ethylene copolymer, by incorporating into the thermoplastic polymer a wood rosin or wood rosin derivative.

Abstract: A process and apparatus for controlling the thickness of film made in a blown film machine having a rotating die, wherein a variable speed motor is used to control the haul-off speed of the film from the machine, by subdividing the die rotation into angular segments, measuring the blown film thickness at a point fixed in space and across each of the angular segments, and calculating an average film thickness for an angular segment, and comparing the measured thickness against a preselected desired thickness, and increasing or decreasing the speed of the variable speed motor to change the haul-off speed to bring the measured thickness into agreement with the preselected thickness.

Abstract: A method of creating a score in a pouch formed from a thermoplastic film is described. Ultrasonic energy is used to create the score in a film that is later formed into a pouch. The score can be used to open the pouch by pulling opposite sides of the scored area. The ultrasonic force is applied to the film as a part of a downstream process in a blown film manufacturing line to produce the pouch.

Abstract: Blown or flat-extruded plastic film having systematic plus or minus errors in thickness along the width of the film have a thickness profile measured and the measured profile is fed to a computer which controls the extruded film or tube from which the film is blown so that the foil thickness will be increased between regions of plus-thickness error or decreased in sense between regions of minus-thickness errors, or both alternatingly, so that the resulting coil is cylindrical with significant precision and without the need to move the blowing head or tube flattening device.

Abstract: A process involving mixing an ethylene/vinyl acetate copolymer and an organopolysiloxane at a temperature of at least 160.degree. C. for a sufficient length of time to provide a melt index of 0.05 to 8 grams per 10 minutes.

Abstract: A process for the production of a plastic foil of thermoplastic material as well as for winding this plastic foil into a coil. The produced plastic foil has systematic thickness errors with plus thickness errors and minus thickness errors. The coil is practically free of thickness errors summed during winding. In order to achieve this, the thickness-error profile of the produced plastic foil with its systematic plus thickness errors and/or minus thickness errors is measured prior to the winding of the coil. A number n of layers of the plastic foil produced with the systematic plus thickness errors and/or minus thickness errors is wound up to a coil. After that, approximately a number n of layers of the plastic foil with the inverse thickness-error profile is wound on the coil. This is periodically repeated, n layers of plastic foil with the thickness-error profile alternating with approximately n layers with inverse thickness-error profile, until in the end the adequately cylindrical coil is produced.

Abstract: A process is known for the tool-free reshaping of a tubular hollow body of amorphous, especially vitreous material to a rod by pressure constriction wherein a pressure depression below atmospheric pressure is sustained in the tubular part by continual evacuation during the constriction, while the hollow body is continually fed horizontally, at a given speed of rotation, to a heating zone, and there its viscosity is so lowered that, as a result of the pressure difference between the absolute value of pressure below atmospheric pressure in the hollow body and the external pressure acting on the hollow body, the hollow body becomes constricted to form a rod in the closing zone and the rod is continually pulled from the closing zone at a given rotatory speed; in order by such a process to produce homogeneous, rod-shaped bodies from hollow bodies in a single procedure and at reasonable cost, the outside dimensions and inside dimensions of the hollow body, the viscosity of the vitreous material in the closing zone,

Abstract: A condom having a blow formed tubular main sheath portion, and a method for making the condom. Blow extrusion techniques of fabrication are described, together with the use of various thermoplastic materials of construction, including polyurethanes, polyether block amides, styrene-rubber-styrene block copolymers, ethylene-octene copolymers, and polyesters. The condom is made by blow extruding a tubular film of thermoplastic material to form a main sheath portion, severing the main sheath portion into one or more condom pieces, and sealing one end of each piece.

Abstract: A method of making a coil of a plastic foil forms a flat web by extrusion through a wide slit nozzle or by film blowing and determines the thickness-error profile of the foil wound on a coil. Based upon monitoring the contour of the coil the inverse thickness-error profile is produced by control of the die gap and wound on the coil so that the coil is built-up alternatingly with the original thickness-error profile and the inverse thickness-error profile until completion of winding so that it has a sufficiently cylindrical coil contour.

Abstract: For measuring thickness of films of synthetic thermoplastic which have been solidified but not yet fully cooled after extrusion, a capacitive measuring head is moved into contact with the film and during a measuring cycle is moved over the surface of the film in the area in which the measurement is to be effected. The measuring head is disengaged from the film after each measuring cycle. To ensure that the measurement will not be affected by a temperature rise of the measuring head during a measuring cycle, the measuring head is moved into contact with the film before the measuring cycle begins and the measuring cycle is not initiated until a time has elapsed in which the measuring head has assumed a temperature which remains substantially constant throughout the measuring cycle.

Abstract: A process for producing a transparent film includes forming a melt from a copolyester having structural units represented by the following formulas I and II, respectively: ##STR1## wherein R groups may be the same or different from each other are each selected from the group consisting of--CH.sub.2 CH.sub.2, --CH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 --, --CH--CH.sub.2 --, ##STR2## and the molar fraction ratio of the structural units of formula II to the total structural units of formulas I and II is between 0.02 to 0.020, which a melt of the copolyester is formed into a film, rapidly quenched to solidify the copolyester and impart low crystallinity thereto. The solidified film is aged at a temperature of 60 degree centigrade or below, and then heat-treated at a temperature between the glass transition point (Tg) of the copolyester and no greater than 2.degree. C. below the melting point of the copolyester minus 2.

Abstract: A stretchable, heat shrinkable ethylene-.alpha.-olefin copolymer film which has excellent stretchability as well as shrinkability at a low temperature and is useful as a good packaging material is prepared by melt extruding a composition including at least one ethylene-.alpha.-olefin copolymer as a main component to give a non-stretched film and biaxially stretching the film in a temperature region where an orientation can be induced and at an area stretching ratio of not less than 8 under conditions such that a tensile strength is from 30 to 170 kg/cm.sup.2. The film has an index of refraction N of 1.500 to 1.522, a degree of orientation Wk according to X-ray diffraction method of 0.78 to 0.93 and an area shrinkage of not less than 15% at 90.degree. C.

Abstract: A constraining structure for an open tube apparatus for continuously producing a rotating elongate strip of material is disclosed. The constraining structure controls expansion of an extruded blown film tube to a desired outer diameter range after the tube is formed. The constraining structure includes a casing positionable around the tube, and an annular sleeve in the casing having a generally cylindrical central passageway adapted to receive the tube to permit movement of the tube along its longitudinal axis in a downline direction. The casing and the sleeve walls define a gas chamber with pressurized gas separate from the passageway. The gas layer along the inner surface of the sleeve is at a sufficiently large pressure to constrain the tube to the desired outer diameter while the tube solidifies and to prevent the tube from contacting the sleeve.

Abstract: A method of providing uniform thickness of a synthetic resin film upon molding of the synthetic resin film with a die having a plurality of heating elements arranged adjacent a die lip of the die. The thickness of a film molded by the die is measured by cutting a sample of the molded film in a direction perpendicular to the direction of drawing of the film, and measuring the thickness of the sample in the direction of cutting with a film thickness measuring device. The measured values are then fed to an arithmetic unit. At the arithmetic unit, a corresponding relationship is calculated, based on the measured film thickness values, between a one-sided material portion of the film and the plurality of heating elements, and amounts of heat to be generated by the corresponding heating elements are individually controlled in accordance with the relationship.

Abstract: A foil-blowing apparatus has at least one deformable lip defining the annular orifice from which the thermoplastic tube which is blown to form the coil is extruded. The lip can be provided with an array of effectors which, in response to a thickness-profile measuring unit, can radially deform the lip to correct thickness errors. The lip can be under prestress and the radial deformation is effected by measuring the thickness and superimposing a radial force on the prestress.