Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/88—Thermal treatment of the stream of extruded material, e.g. cooling
  • B29C48/919—Thermal treatment of the stream of extruded material, e.g. cooling using a bath, e.g. extruding into an open bath to coagulate or cool the material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
  • B29C48/07—Flat, e.g. panels
  • B29C48/08—Flat, e.g. panels flexible, e.g. films
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
  • B29C48/09—Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
  • B29C48/10—Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels flexible, e.g. blown foils
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/16—Articles comprising two or more components, e.g. co-extruded layers
  • B29C48/18—Articles comprising two or more components, e.g. co-extruded layers the components being layers
  • B29C48/21—Articles comprising two or more components, e.g. co-extruded layers the components being layers the layers being joined at their surfaces
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/30—Extrusion nozzles or dies
  • B29C48/32—Extrusion nozzles or dies with annular openings, e.g. for forming tubular articles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/30—Extrusion nozzles or dies
  • B29C48/32—Extrusion nozzles or dies with annular openings, e.g. for forming tubular articles
  • B29C48/335—Multiple annular extrusion nozzles in coaxial arrangement, e.g. for making multi-layered tubular articles
  • B29C48/337—Multiple annular extrusion nozzles in coaxial arrangement, e.g. for making multi-layered tubular articles the components merging at a common location
  • B29C48/338—Multiple annular extrusion nozzles in coaxial arrangement, e.g. for making multi-layered tubular articles the components merging at a common location using a die with concentric parts, e.g. rings, cylinders
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
  • B29C48/49—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die using two or more extruders to feed one die or nozzle
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/88—Thermal treatment of the stream of extruded material, e.g. cooling
  • B29C48/91—Heating, e.g. for cross linking
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/001—Combinations of extrusion moulding with other shaping operations
  • B29C48/0018—Combinations of extrusion moulding with other shaping operations combined with shaping by orienting, stretching or shrinking, e.g. film blowing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/001—Combinations of extrusion moulding with other shaping operations
  • B29C48/0019—Combinations of extrusion moulding with other shaping operations combined with shaping by flattening, folding or bending
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/001—Combinations of extrusion moulding with other shaping operations
  • B29C48/0022—Combinations of extrusion moulding with other shaping operations combined with cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/355—Conveyors for extruded articles

Definitions

• Object of the invention is a plant for the production of a multi- layer heat shrinkable polymeric film, based on a twin-bubble co- extrusion technique, said plant differing from those already known as to a new multi-layer extrusion die and as to the modifications to and improvements in the steps of
• multi-layer is used herein to mean also a film (and relevant tubular film) consisting of two or more layers made of the same polymeric material.
• the polymeric material polypropylene or an equivalent polymeric material, added with resins and/or other additives securing the desired mechanical, chemical and physical properties
• the die is hot extruded and leaves the die as a tubular film consisting of one or more superimposed layers, made of the same polymeric material or of two or more different polymeric materials;
• the cold tubular film is fed to an after-heating system (e.g. consisting at least of an IR-ray oven) , where it is heated to a temperature close to softening;
• an after-heating system e.g. consisting at least of an IR-ray oven
• the hot tubular film is stretched in the longitudinal direction and, at the same time, inflated e.g. with compressed air: therefore, the tubular film is simultaneously stretched in two orthogonal directions to obtain an adequate orientation of molecules;
• the stabilized tubular film is cut in the longitudinal direction and the film obtained is wound round reels.
• the tubular film and/or film tearing tendency also increases (which causes a decrease in the production process yield) and/or the film heat shrinking capacity decreases (which results in a lower quality and, consequently, in a lower commercial value of the final product) .
• the more amorphous the polymeric material during the production process the better plant productivity and final product quality: in fact, the more amorphous the polymeric material, the more uniform its softening point and, therefore, the simpler the control of its temperature during the whole production process, which allows the obtainment of a better quality film.
• a markedly amorphous material can be obtained only through an as accurate as possible control of the cooling system enabling a rapid and uniform decrease in the temperature of the extruded tubular film and of the stretched film (and of the single layers thereof) and/or of the after-heating system enabling a uniform rise in the temperature of the tubular film (and of the single layers thereof) to the value required.
• Said control is simpler and more effective if the tubular film and the layers thereof have an extremely precise and uniform thickness throughout the circumference and length of same.
• the die being an object of the present invention allows the production of a multi-layer tubular film whose layers have an extremely precise and uniform thickness.
• Objects of the present invention are, therefore, a new extrusion die as well as the modifications to and improvements on an already known production plant based on the twin-bubble co-extrusion technique.
• Said findings allow a drastic reduction in or, at least, a more accurate control of the degree of crystallization of the polymeric material during the whole production process, by maintaining the polymeric material as amorphous as possible. The efficiency of the production process is thus improved.
• An object of the present invention is a plant for the production of a multi-layer heat shrinkable polymeric film, based on the twin- bubble co-extrusion technique, said plant differing from those already known as to the following operating characteristics:
• the extrusion die multi-layer type, can produce a multi-layer tubular film consisting of a number of particularly homogeneous and uniform layers;
• the thickness adjusting unit is located very close to the extrusion die outlet and the distance between the die and the thickness adjusting unit can be adjusted; - the thickness adjusting unit outer ring is integral with the extruded tubular film cooling system and its rotary motion is uniform;
• the first and the second ovens of the system after-heating the tubular film from the thickness adjusting unit house several probes for the measurement of the tubular film surface temperature and the control of the intensity of the heating elements inside the .
• the stretched tubular film cooling system atomizes water into the aforesaid cold air jets.
• the second oven consists of two superimposed and communicating chambers of different diameter, wherein the distance between the oven wall and the tubular film wall contained therein is substantially the same.
• Fig. 1 is a simplified block diagram of a "twin-bubble" production plant
• Fig. 2 is a schematic view of a " twin-bubble" production plant including an after-heating system as modified according to the present invention
• Fig. 3 is a schematic view of thickness adjusting unit and cooling system (3 , 4) of Fig. 2
• Fig. 4 is a longitudinal sectional view of extrusion die 1 of Fig. l ;
• Fig. 5 is a cross-sectional view - taken along plane AA of Fig. - of extrusion die of Fig. 4.
• AA Fig. - of extrusion die of Fig. 4.
• Fig. 1 illustrates a simplified block diagram of an already known plant for the production of polymeric film, based on the twin-bubble co-extrusion technique.
• the polymeric material is fed to die 1.
• the melted polymer leaves the die as a substantially cylindrical tubular film 2, consisting of one or more superimposed layers of the same polymeric material or of two or more polymeric materials.
• the thickness of tubular film 2 is set by unit 3 and the film is rapidly cooled by the first cooling system 4 (only a sectional view thereof is given in the figure to illustrate unit 3) consisting of an annular chamber containing water (or an equivalent liquid coolant; the liquid coolant referred to hereinafter will exclusively be water) .
• a uniform water film is caused to adhere to the outer surface of tubular film 2 to increase its cooling rate and facilitate its flowing to unit 3.
• Tubular film 2 is flattened by wringing apparatus 5, where the water film is removed, fed to after-heating system 6 (consisting of one or more ovens) where it is heated to a temperature close to softening, stretched in the longitudinal direction and, at the same time. inflated, e.g. with compressed air.
• number 8 represents tubular film 2 being stretched in the longitudinal direction and being inflated.
• stretched tubular film 9 is rapidly cooled by a second cooling system 10 (preferably by cold air jets) and cut in the longitudinal direction by slitter 13, not shown in detail in the figure.
• the film obtained is wound round reels 12 or equivalent means.
• Figure 2 is a schematic view of a "twin-bubble" production plant including after-heating system 6 as modified according to the present invention. Further modifications and improvements, not shown in Fig. 2, will be illustrated hereinafter with the aid of the following figures.
• Figure 2 shows extrusion die 1 and tubular film 2 that, after leaving thickness adjusting unit and cooling system (3, 4), is fed to wringing apparatus 5 where the water film is removed and tubular film 2 is flattened.
• Tubular film 2 is fed through pull rolls or equivalent equipment to after-heating system 6 which, in a plant of known type, consists of two ovens 60, 61.
• Flattened tubular film 2 is heated in oven 60 to be made "softer", then inflated with compressed air (or other fluid at equivalent pressure) blown, as already known, at the basis of swollen area 8 of tubular film 2; the second oven 61 - not shown in detail in the figure - further heats the tubular film leaving oven 60 up to a temperature close to softening, which is the most favourable for the tubular film transversal stretching by compressed air blowing.
• the different rotation speed of at least one pull- rolls couple (not shown in the figure) downstream of oven 60 and of pull-rolls couple 14 of slitter 13 provides longitudinal stretching of swollen tubular film 8.
• Double hot stretching turns out well subject to as uniform and homogeneous as possible thickness of the tubular film (and of the layers forming same), crystalline content, if any, of the tubular film and/or single layers material, heat emission from the ovens heating elements, and temperature distribution along the tubular film wall section. Should one or more of the aforesaid factors fail to be entirely homogeneous, the response of the heated tubular film to the mechanical stresses caused by double stretching would not be uniform, with consequent risks of tubular film tearing and/or worsening of the film characteristics caused by a wrong or incomplete orientation of the film molecules.
• the techniques adopted under the present invention to meet the aforementioned uniformity and homogeneity requirements are illustrated below.
• the die already known was redesigned: the new die 1 - illustrated in figs. 4 and 5 " can produce multi-layer tubular film 2, whose layers have precise and uniform thickness. Furthermore, it allows the type of polymeric material forming each layer of tubular film 2 to be easily modified.
• Unit 3 and cooling system 4 (illustrated in Fig. 3) are located as close as possible to the outlet of die 1: extruded tubular film 2, being hotter hence more ductile, can be adjusted as to thickness with greater precision and lower power absorption and can be more rapidly cooled, thus preventing or at least hindering the crystallization process of the polymeric material (or materials).
• the distance between the outlet of the die 1 and the cooling system 4 is from 10 to 30 cm.
• cooling system 4 (consisting of a water-filled chamber integral with the outer ring of unit 3) is caused to rotate at constant speed around the tubular film itself.
• the inner surface of the outer ring of unit 3 houses at least two superimposed circular slots (35 of Fig. 3) . allowing water to flow from the chamber with formation of a uniform film along the outer surface of tubular film 2. Constant levels in cooling system 4 are maintained by addition of make-up water; this secures a constant pressure of the water flowing from slots 35- "
• the distance between die 1 outlet and thickness adjusting unit and cooling systems 3. 4 can be modified (by known mechanical means) depending on the characteristics of the polymeric material and/or the plant capacity to optimize the operation of same.
• Tubular film 2 is made "softer” in oven 60 and further heated in oven 61 (not shown in Figure 2) to a temperature close to softening, which is most favourable to double hot stretching.
• the tubular film made "softer” in oven 60 has a narrow diameter, which rapidly increases to the final value as soon as the polymeric material of the tubular film reaches the optimal temperature. Therefore, oven 61 was implemented in two contiguous and communicating cylindrical sections 62, 63 having a different diameter, wherein the distance between the oven heating elements and the wall of tubular film 2 is always the same. This favours maximum (or at least uniform) energy absorption by tubular film 2 in every area of oven 61; at the same time, air convective movements inside oven 61 - which might negatively affect the uniform heating of tubular film 2 - are avoided.
• the external temperature of tubular film 2 is measured in significant points by several probes (already known) located inside the ovens (in particular in oven 61) controlling, according to a substantially linear law (individually or groupwise) the heating elements inside ovens 60 and 61 and, in particular, the elements inside oven 61.
• the heating elements are always kept live independently of the oven operating conditions, which secures continuous heating of the tubular film wall by radiation (as well as by conduction).
• heating by radiation and heating by conduction are distributed according to complementary curves (one being concave and one being convex) .
• the resulting curve can be "flattened” and the temperature of the whole tubular film section becomes uniform. It follows that the layers forming the tubular film wall are deformed uniformly by the mechanical stresses caused by double hot stretching.
• the heating elements preferably consist of IR radiation panels, whose emission spectrum shows a peak substantially coinciding with the peak of IR radiations absorption by the polymeric materials forming the wall (or the various wall layers) of tubular film 2.
• the highest efficiency is thus secured, the IR radiations being almost completely absorbed by the tubular film without any overheating of the surrounding air.
• water atomization into air jets from cooling system 10 provides a more rapid cooling of stretched tubular film 8, which increases the plant production rate.
• the mechanical properties of the film thus obtained would be better by 20% in respect of those of a film being cooled exclusively by air jets. Fig.
• FIG. 3 is a schematic representation of cooling system 4 (consisting of a water-filled annular chamber integral with the outer ring 30 of unit 3) which is caused to rotate at constant speed (as already known) around the tubular film itself (not shown in Fig. 3)-
• outer ring 30 bearing chamber l is driven by motor 33 through pinion 32 engaged in crown gear 3 *
• the inner surface of outer ring 30 of unit 3 houses two superimposed circular slots (35 of Fig. 3) connected to chamber 4 through passages 36 to allow water regularly to flow from the chamber for the formation of a uniform film along the outer surface of tubular film 2.
• Fig. 3 does not show body 4l (represented in Fig. 4), substantially cylindrical and preferably water cooled, located inside central hole 3 of outer ring 30. Said body and said outer ring 30 constitute thickness adjusting unit 3- A particularly accurate surface finishing of 4l improves tubular film 2 sliding during cooling and reduces body wear.
• Figs. 4 and 5 are, respectively, a longitudinal sectional view of extrusion die 1 of Fig. 1 and a cross-sectional view, taken along plane AA, of said extrusion die of Fig. 4.
• Die 1 multiple screw type, consists of body 42 housing channels 43, 44, and 45, which connect the feed points of each polymeric material meant to form each layer of tubular film 2 to the corresponding extrusion screws 46, 47, 48; of body 49 including said extrusion screws 46, 47, and 48 and unit 50 forming tubular film 2 by compression of the layers leaving extrusion screws 46, 47, and 48.
• Extrusion die 1 differs from the dies already known in that i) body 42 consists of three superimposed elements 51, 52, and 53 fastened together and to body 49 by several bolts or equivalent removable fasteners. ii) as shown by Fig.
• a film with external layers consisting of the same polymeric material can be easily obtained by lining up the feed points of internal extrusion screw 46 and of external extrusion screw 48, and feeding them simultaneously (e.g. through element 5 of Fig. 4) with the same polymeric material.
• each of extrusion screws 46, 47, and 48 has a section and a gap in respect of the corresponding external spindle which are reduced by 10% to 30% (preferably by 12% to 18%) in respect of those of the extrusion dies already known. It follows that - the volume of extruded polymeric material in the unit of time being the same and the screws inclination being unchanged - the length of said screws increases by 10-15% .
• GHI0LDI 200 190 0.8

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Laminated Bodies (AREA)
• Shaping By String And By Release Of Stress In Plastics And The Like (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)
• Wrappers (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=11366765

Family Applications (1)

Country Status (4)

Cited By (1)

Citations (6)

• 1993
  • 1993-08-02 IT IT93MI001758A patent/IT1264550B1/it active IP Right Grant
• 1994
  • 1994-03-16 TW TW083102391A patent/TW255856B/zh active
  • 1994-04-21 AU AU66464/94A patent/AU6646494A/en not_active Abandoned
  • 1994-04-21 WO PCT/EP1994/001236 patent/WO1995003929A1/en not_active Ceased

Patent Citations (6)

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