JP3913777B2 - Method and apparatus for coating metal strip and product thereof - Google Patents

Description

The present invention relates to a method and apparatus for applying a polymer coating to a metal strip, in particular an aluminum strip by means of an extruder and an extrusion mold arranged to deposit a thermoplastic resin on opposite or opposite sides of the strip. The present invention relates to a method for coating a thermoplastic resin on both sides of a material. The product of the present invention is a metal strip such as aluminum with thin polymer coatings on both sides and has many applications, especially for packaging applications such as can ends and can bodies It is suitable for doing.
It is well known to coat one or both surfaces of a metal plate or metal strip with a thermoplastic resin to improve corrosion resistance, formability, appearance, or other properties of the material. The coating can be applied by various methods such as roll coating, reverse roll coating, spraying, electrocoating, powder coating and lamination. The coated strip can be used in applications such as can bodies and can ends, foil pouches, lidding stock, appliances, electrical equipment, structures, aerospace vehicles or automotive boards.
U.S. Pat. No. 5,093,208 to Heies et al. Presses a precast-formed thermoplastic polyester film against one or both sides of a metal sheet and forms the film in an amorphous state. A method for forming a laminated metal plate to be attached to a plate is disclosed. The uncoated metal sheet is heated to a temperature higher than the melting point of the polyester thin film, and the polyester thin film is applied with pressure to the metal sheet so as to form a laminated material. Thereafter, the laminate material is heated to a temperature above the melting point of the thin film to improve the bonding of the plastic thin film to the metal plate and is quenched to a temperature below the glass transition temperature of the polyester to form an amorphous polyester. Made. The rapid cooling is performed by passing the laminated material through a water curtain.
European Patent Application No. 0067060, filed in the name of Taiyo Steel Limited, discloses a method of manufacturing a coated metal plate by directly extruding a thermoplastic resin on a heated metal plate. Yes. According to this patent application, the molten resin is applied directly to the metal plate from the extrusion die without forming the resin as an independent thin film. The thickness of the thin film can be less than 50 microns and is preferably reduced to 35-5 microns. This patent application states that the cost of producing the coated sheet metal is reduced because the separate thin film formation step is omitted. Suitable thermoplastic resins used as coatings on metal surfaces include polyolefins, acrylic resins, polyesters, polyamides, polyvinyl chloride, and many other resins listed in the published patent application. It is. The resin can be coated as a single layer or as multiple layers of the same or different resins. This patent application discloses applying resin to only one side of a metal strip.
An improved method for providing a thin polymer coating on both sides of a metal strip suitable for use in applications such as packages is desired. It would be desirable to have a method of intimate adhesion or welding of the polymer to the strip so that the polymer does not delaminate during subsequent strip forming steps or when using products made from the strip.
The present invention provides a method of coating both sides of a metal strip with a thermoplastic resin to form a coated strip suitable for use in packages and other applications.
Accordingly, it is an object of the present invention to provide an improved method of depositing a polyester resin on both sides of a metal strip.
The above and other objects and advantages of the present invention will be more fully understood and appreciated by reference to the following description and the accompanying drawings.
FIG. 1 is a schematic side elevational view of one embodiment of the apparatus of the present invention.
FIG. 2 is a schematic side elevation view of a portion of another embodiment of the present invention.
3 and 4 are schematic side elevation views of yet another embodiment of the present invention.
FIG. 5 is a partial cross-sectional view of the strip of FIG. 4 and the extrusion mold, greatly enlarged to show the application of resin to the strip.
6-14 are schematic side elevational views of yet another embodiment of the present invention.
The drawings attached to this specification show an apparatus that coats both sides of a metal strip as the metal strip moves from the first coil to the second coil. Winded on two coils. With particular reference to FIG. 1, an aluminum alloy strip 10 is unwound from a coil 12, moves around a tensioning roller 14, moves vertically upwards and rolls over a roll 16, then the roll 16 From below to pass through the coating device. When the metal strip 10 moves on the support roll 16, a backup roll 18 can be used to hold the metal strip flat.
As the strip 10 moves downward from the roll 16, the metal strip is first heated by the heater 20 to a temperature close to or above the melting point of the polymer applied to the metal strip. The In the embodiment shown in FIG. 1, the heater is an induction heater, but other heaters or preconditioners, such as flame treatment, infrared, plasma and / or corona discharge, alone or in combination Can also be used. Flame heaters can be used in duplicate (one on each side) or only on one side to improve performance (bonding and heating). Coils 12 that are still hot can be used for previous processes such as rolling or heat treatment, so that the need for heating by the heater 20 is minimized and can even be omitted. Typical temperatures at which the metal strip is heated range from about 121 ° -260 ° C. (250 ° -500 ° F.) prior to being applied with the thermoplastic material, and this temperature is a number of factors. In part, it depends on the specific polymer to be applied to the strip.
In order to apply a thin web of thermoplastic polymer such as polyester resin to both sides of the heated web, two separate extrusion coating devices 21, 31 are provided. The devices 21 and 31 are disposed immediately below the induction heater 20. The extrusion coating devices 21 and 31 each include an extruder that feeds the molten polymer to be extruded through sheet dies 22 and 32, the sheet dies being narrow to form thin extruded webs 24 and 34. It has an exit slot and the extruded web is passed through a three-roll stack. Alternatively, both extruders can be fed through a feed pipe or other manifold with a single extruder.
The first rolls 26, 36 of the devices 21, 31 are thinned and drawn rolls and are held at a temperature that promotes the sticking of the polymeric extrudate to the polished surface of the rolls. Typical temperatures for this range from about 120 ° to 180 ° C (248 ° to 356 ° F), depending on the resin used. The surface speed of the rolls 26, 36 is substantially higher than the speed at which they exit and exit the molds 22, 32, thus stretching the polymer to reduce the thickness. Typical ratios of drawing speed to extrusion speed range from about 5: 1 to 40: 1. The resin from the extruder is typically about 0.127 to 0.635 mm (0.005 to 0.025 inch) thick and stretched to about 0.0076 to 0.038 mm (0.0003). Reduced to a thickness of ~ 0.0015 inches).
The second rolls 28, 38 are cooler than the first roll and are designed to polish and cool the extrudate by rolling contact between the roll and the extrudate. The second rolls 28 and 38 also send the extruded material to a third roll which is an application roll. The third rolls 30, 40 are tensioned using springs, fluid pressure, air pressure, etc., and are elastic (heat resistant) to press the semi-cooled extruded material against the heated metal web or strip 10. It is preferred to have an outer surface (such as a highly functional elastomer), i.e. a roll shell. The third rolls 30, 40 of the two sets of extruders support opposite sides of the strip 10 against each other's pressure or acting force, so that the semi-cooled extrudates 24, 34 become such third The belt 30 can be pressed against the strip under the pressure of the rolls 30 and 40.
The coated metal strip 11 continues to be moved vertically downward through the second heater 42, which may deteriorate the properties desired for the metal strip or its plastic coating. Metal or metal, so as to increase the temperature to the point where the polymer bond to the metal strip is perfect, especially at the interface between the metal strip and the plastic coating, without adversely affecting it. Uniformly heat one of the plastics or both metal and plastic. The desired temperature depends on the particular polymeric material applied as a coating, but is approximately in the range of about 200 ° -260 ° C (392 ° -500 ° F). The second heater 42 is preferably an induction heater well known in the art. Alternatively, the heater 42 can be a convection furnace or an infrared heater.
While leaving the second heater 42 and continuing to move vertically downward, the coated strip 11 is quenched by a water spray 44, water curtain, or other suitable cooling means. This cooling must cool the temperature of the composite structure to a temperature low enough to allow the coated strip to turn around the roller without adversely affecting the coating or metal. In a preferred method of coating a polyester resin on an aluminum alloy can plate such as 3004 alloy, the composite structure is preferably cooled to about 40 ° C. (104 ° F.) or less before contacting the roller 48. In such a preferred embodiment, the cooling is fast enough that the polyester coating solidifies in a substantially amorphous form. The cooling rate to achieve this depends on the polyester. The cooling rate is controlled by adjusting the temperature and volume flow rate of the cooling water for the coated strip.
In the embodiment shown in FIG. 1, the coated strip passes through a bath 46, such as a water bath, before the coating is dried, and rollers 48, 50 disposed on opposite or opposite ends of the bath. Move around. A water bath completes the cooling process.
The coated strip 11 is moved vertically upward from the water bath 46 through the drying device 52 so that residual moisture is removed from the strip before winding. The drying device 52 typically comprises a warm air blower. The composite strip then travels through rollers 54, 56 and 58 to the winding roll 60. Although not shown, this apparatus can include an accumulator to allow roll or coil changes, and can also include means for smoothing the metal strip after it has been coated. The device also preferably includes a trimmer to trim the edge of the coated metal web 11 (not shown), i.e. to remove any polymer protruding beyond the edge of the metal web. Trimmers can be wavelengthd at various locations along the strip travel path, for example, immediately after the polymer resin is applied to the strip, after the spray cooler, or after the dryer. .
The aluminum strip coated according to the present invention can be made by various alloys and tempering depending on the use of the strip. Some typical aluminum alloys suitable for forming can ends and can bodies are tempered to medium hardness, including H-14, H-19 and H-39, among others. AA5042 alloy, AA5182 alloy and AA3004 alloy. The metal strip is typically 0.1778 to 0.356 mm (0.007 to 0.014 inches) thick.
In accordance with the present invention, various thermoplastic polymers such as polyester can be used to coat aluminum strips designed for use in packages such as can bodies or can ends. A preferred polyester resin is a high melt viscosity (HMV) resin of the type previously used to coat furnace treatable metal trays, liquid foil packages and heat sealable foil packages. E. I. A copolymer resin of SELAR®, PT 8307 HMV, available from Du Pontde Nemours Company, is an example of a high performance polyester resin suitable for use in the present invention. Such copolymers can be blended with other thermoplastic polyesters such as bottle grade polyesters having an intrinsic viscosity of about 0.72 or greater. For example, a blend of SELAR®, PT8307 HMV copolymer and T89PET (polyethylene terephthalate) sold by Hoescht-Celanese is used to make products such as the end of beverage cans. In addition, the performance of the aluminum strip coated by the present invention is improved. Other thermoplastic polymers suitable for use in this application include polypropylene, polyethylene, polyamide (nylon), polyimide, polycarbonate, and polyvinyl chloride (PVC), among others.
FIG. 2 shows a portion of an alternative apparatus for implementing the present invention. In this device, the metal strip 70 is not moved vertically downward as in FIG. 1, but instead is coated on both sides as it is preferably moved vertically upward. The metal strip 70 moves around the feed roll 72 and is moved vertically upward from the roll through a preheater 74 such as an induction heating device. The strip is then moved through an optional flame treatment device 76 and between extrusion devices 78, 80 located on opposite sides to cover both sides of the strip. The flame treatment device improves the acceptability of the strip for bonding the resin coating.
The extrusion coating apparatus 78, 80 of FIG. 2 is the same as that of FIG. 1 except that each of the extrusion coating apparatuses 78, 80 includes only two rolls instead of three rolls as in FIG. Is the same. The surface speed of the thinning and drawing rolls 82 and 84 is several times faster than the exit speed of the polymer from the extrusion dies 90 and 92. The rolls 86 and 88 that are cooler than the rolls 82 and 84 receive the extruded material from the rolls 82 and 84 and apply the extruded material to the band material 70.
After the strip 70 is coated on both sides, the strip 70 continues to move vertically upward and enters the heat insulation chamber 94. The heat insulation chamber cools the strip and also has a cooling diverting roll 96 that directs it vertically downward. Contained. The heat insulation chamber 94 is preferably insulated so that accurate temperature control can be performed when the strip moves on the cooling turning roll 96. Roll 96 preferably has an outer diameter of at least about 91 centimeters (3 feet). The large roll diameter minimizes the stress generation of the metal strip due to the bending action. The temperature of the roll 96 and the strip 71 is controlled by the fluid 91 in the annular chamber 93 between the roll outer shell 97 and the inner shell. The annular chamber 93 is preferably not filled with space so as to minimize the influence of inertia (giving viscous damping) and to allow speed control and tracking.
The coated composite strip 71 moves vertically downward from the cooling diversion roll 96 and passes through the post heater. The post heater passes the composite strip about 204 to 260 ° as in the embodiment of FIG. Heat to C (400-500 ° F.) to improve the binding of the polymer, such as polyester resin, to the strip. The heater 98 can be a conventional induction heater, a convection furnace or an infrared heater. The composite strip 71 moves from the heater 98 to the second cooling turning roll 99 through the cooling (not shown), that is, the rapid cooling means, and moves from the second cooling turning roll to the winding roll (not shown). The second cooling turning roll 99 has the same design and dimensions as the roll 96 described above.
FIG. 3 is a schematic view of another embodiment of the present invention in which a clean and room temperature adjusted sheet stock 100 is unwound from an unwinding roll 102 and drawn roll set. Feeded upwards 104, this extended roll set is comprised of a roll 103 and optionally a backup roll 105 located at the top of its processing stack. Although not shown, an accumulator can be included to allow for changes in the coil on the unwind roll 102.
The web 100 is preferably moved vertically downward from the draw roll set 104 and is inclined about 30 ° to 45 ° from the vertical. Such tilt facilitates downstream extrusion coating and processing machine placement. The web 100 passes through a preheater 106 where an induced magnetic field is generated to bond the metal to the metal strip without degrading or otherwise adversely affecting the properties desired for the metal strip. Heat is applied uniformly to a temperature that improves the “green peel” strength downstream of the polymer. As used herein, “raw peel” strength means that the polymer is bonded to the metal strip with a sufficiently strong holding force so that the polymer does not peel from the metal strip in subsequent processing steps. . The desired temperature should be in the range of about 204 ° -260 ° C. (400-500 ° F.) and about 215 ° -246 ° C. (425 ° -475 ° F.) when applying polyester. Is preferred.
The preheated web 100 continues to move in a downwardly inclined direction and is passed through an optional flame surface treatment device 108. The flame treatment device can reduce the surface of the preheated metal to remove oxides and minimize or increase it, thereby increasing the adhesion of the subsequently applied polymer. .
The heated and processed web 100 then enters the first of the two extrusion coating stations. Although not shown, an extruder melt-plasticizes a polyethylene terephthalate (PET) polymer or other thermoplastic resin, which is placed either in the vertical direction or in a vertical to diagonal direction and has a narrow exit slit Supply through sheet mold 110. This slit is set so that a back pressure is generated in the extruder so that the extruded material 112 can be expanded so as to have at least the same width as the width of the strip 100. The slit can vary in width of the strip 100 depending on several factors such as the nature and thickness of the polymer resin, the relative speed and shape of the extruder and the metal strip, the shape of the extruded thin film, among others. It can be made narrower. The extruder 112 is drawn into the roll stack 114 so that its thickness is reduced to the final thickness imparted to the web. The ratio of stretched thickness should be about 10-25: 1, depending on the polymer being extruded.
The two-roll stack 114 is arranged such that a plane passing through the center line of the roll is inclined by about 30 ° from the horizontal. The “inner” or turning roll 116 has an elastic surface made of a temperature resistant elastomer and is preferably cooled internally and / or externally to minimize degradation of the elastomer.
The outer or press roll 118 is polished with chrome-plated steel and is preferably maintained at a temperature of about 150 ° F. or 66 ° C. (for polyester) or less, this temperature being applied to the strip by the polymer. Lower than the “stick” temperature of the molten polymer which gives the line pressure to the polymer when done. This improves the adhesion of the polymer to the metal strip 100 and at the same time improves the appearance of the surface. The surface layer degree of the rolls 116 and 118 is about 10 times the exit speed of the extruded material exiting the extrusion mold 110, whereby the polymer is drawn on the web 100 to about 0.00762 mm to 0.02032 mm (0 .3 to 0.8 mils), preferably about 0.01016 mm (0.4 mils) thick. The two roll stack 114 has a suitable “green peel” strength on the first side of the web 100 to form a coating that prevents the polymer from peeling from the metal in subsequent processing steps.
The single-sided coated web 101 exits the stack 114 and is turned around the elastomer-coated roll 116 by about 60 ° (which is the result of the preferred positioning of the second extrusion station) and directed down the web. It is inclined 30 ° to 45 ° from the vertical (about 60 ° from the state of entering the first stack). The preheated single sided coated web 101 continues to move downward at an angle of 30 ° to 45 ° and is passed through an optional second (possibly larger) flame heater or other type of boost heater 120. In this, the preheated metal surface is treated to remove / minimize the second side oxide to improve the adhesion of the polymer and at the same time any necessary temperature to achieve the optimum bonding state. "Boost" is also performed.
The preheated and preheated web 101 then enters a second of the two extrusion coating stations to cover the web surface opposite that coated at the first coating station. . Extruder performance conditions, placement and processing steps for the second extruder are the same as for the first extruder. The molten extruded material 122 coming out of the extrusion die 124 enters the nip of the two-roll stack 126, and this roll stack has a plane passing through the center line of the rolls 128 and 130 of about 30 ° to 45 ° (first It is inclined 45-60 ° from the center line position of the roll stack 114.
The geometry, arrangement, performance and function of the rolls 128, 130 are the same as those of the first stack 114. The second side of the preheated web 101 is coated with the extrudate 122 to produce a suitable “raw peel” strength as described above with respect to the first side. The double-sided coated web 103 then exits the stack 126 and is turned by about 45 ° -90 ° on the rubber-coated roll, thereby favoring positioning for the inductively coupled heater 132, ie, downwardly from about vertical. 30 ° to 45 ° is obtained.
The double-coated web 103 continues to move downwardly at an incline and passes through a second heater 132, which is preferably an induction heater, to substantially exacerbate the desired metal properties or plastic. Otherwise, the metal / plastic interface is uniformly heated to a temperature at which the polymer bond to the metal strip is perfect without adverse effects. This temperature is preferably about 204 ° to 228 ° C (400 ° to 550 ° F), and in the case of polyester is preferably 215 ° to 246 ° C (425 ° to 475 ° F).
While exiting the induction heater 132 and continuing to move downwardly, the spray nozzle 134 (or other suitable device) cools the composite structure, adversely affecting the end use performance conditions of the composite structure. The temperature is low enough to allow the roller 136 to turn around without being applied. The semi-cooled composite 103 is turned and passed through a horizontal water bath 138 to complete the cooling process.
The drying device 140 is used after the composite 103 exits the water bath 138 so as to remove residual moisture before winding. Smoothing (leveling) is performed in order to remove stress generated by turning around the roller of the metal strip 100, that is, bending. The finished material 103 is then wound up by a winding roller 142. Although not shown, an accumulator can be used to allow roll and coil changes of the winding roller 142.
4 and 5 show another embodiment of the present invention in which the metal strip 150 moves vertically upward during the coating process, and the extrusion dies 152, 154 are used to melt the molten resin. Apply directly to the opposite side of The apparatus of FIG. 4 includes an unwind roller 156 from which the strip 150 moves upward through the preheater 158 and is then moved between the two extrusion dies 152,154. Although not shown, these extrusion dies 152 and 154 are supplied by a normal extruder.
FIG. 5 is a greatly enlarged view showing the extrusion dies 152 and 154 when the extrusion materials 160 and 162 are directly applied to the metal strip 150. The mold opening is positioned close to the strip, so that the force of the extruded material exiting the extrusion mold is applied to the strip. The extrusion mold is placed in the range of about 5-20 mm from the strip, preferably in the range of less than 10 mm from the strip. The metal strip 150 moves at a speed approximately 10 to 20 times faster than the moving speed of the extruded material exiting from the extrusion molds 152 and 154, whereby the extruded material is stretched by stretching the strip acting on the extruded material. It is made to reduce the thickness. The extruded material may be in the range of 0.0127 to 0.0508 mm (0.0005 to 0.002 inches) on each side of the strip.
Extrusion dies 152, 154 are arranged directly opposite each other on opposite sides of the strip 1510 so that the pressure of the extrusion from opposite sides of the strip positions the strip at the center of the extrusion die. Preferably it is made. The molten polymer is abutted against the surface of the metal strip almost immediately after the extrudate exits the extrusion mold, thereby cooling or neck-in before the polymer is applied to the strip. There will be no such thing. This helps to ensure a uniform resin coating on both sides of the strip.
The coated strip 151 is preferably moved from the extrusion dies 152, 154 through the induction type post heater 164, which heats the composite strip to a temperature above the melting point of the polyester resin, The bonding strength of the resin to the material is improved. The composite strip is then rapidly cooled by means not shown and moved to rolls 170 through rolls 166 and 168.
6-14 show an alternative embodiment of the present invention for coating both sides of a metal strip such as aluminum, steel, copper, metal laminates. In each of these examples, means for preheating the metal strip, first and second extrusion coating apparatuses comprising an extrusion die and an application roll, and post heating the strip after coating on both sides Means and means for cooling the strip. These devices also optionally include means for reheating the strip between the first and second coating devices. Both of these devices include one or more extruders for feeding polymer extrudate to the extrusion mold. Each of the first and second extrusion coating devices in this apparatus supports a casting roll that contacts the web of polymer extrudate to press the polymer extrudate against the metal strip, and the metal strip. And a backup roll that presses the metal strip and polymer web together to form a rolling nip for attaching the polymer to the strip surface. The apparatus can optionally include a support roll for one or both of the backup rolls that support and assist in cooling the backup roll.
The preheater, reheat heater and post heater in these devices are various types such as induction type, flame type, infrared type, radiation type, electric type, fossil fuel convection furnace, heating roll, or a combination of these units. Can be taken. The strip can be preheated in the form of a coil and can be preheated in the previous process of the strip to assist or replace the preheater device. A preferred form of heater is a TFX® induction heater, which can be purchased from Davy McKee (Pool) Limited, UK Pool.
The extrusion dies in these devices are about 10.2 to 30.5 cm (4 to 12 inches), preferably 15.2 to 20.3 cm (6 to 8) of the die nip between each pair or roll. Inches) (determined by the dimensions of the extrusion mold and roll). The extruded polymer web preferably contacts the metal strip and the casting roll substantially simultaneously at the roll nip location, or contacts the metal strip slightly prior to the roll nip. Alternatively, the extruded web can contact the casting roll at several degrees of rotation before entering the roll nip. Such contact of the casting roll before the roll nip is such as about 0-25 ° of the roll to minimize cooling of the polymer before the polymer contacts the metal strip at the roll nip position. Do not exceed a few degrees of rotation.
The polymer extruded web is approximately 0.127 to 0.76 mm (0.005 to 0.030 inch) thick and is drawn downward by a metal strip and roll to reduce the web thickness. It is preferred that it be made. The draw ratio is about 1: 1 to 200: 1, preferably about 10: 1 to 40: 1. As used herein, the draw ratio refers to the ratio of the web thickness when extruded to the web thickness when applied to a metal strip. The draw ratio is determined by the difference between the speed of extrusion from the extrusion mold and the speed of the metal strip being coated. For example, a draw ratio of 20: 1 generally means that the strip moves about 20 times faster than the web speed as it exits the extrusion opening. Drawing and thinning polymer extruded webs is well known in the art.
For some devices, it may be desirable to provide ancillary means prior to the set rolls to secure or apply the extruded web to the surface of the metal strip. Fastening aids can include knives, electrostatic devices, and vacuum fastening means, among others. The web can be cast on the metal strip at full width or it can be cast to a wider width than the metal strip and trimmed to remove the excess surplus coating.
For most applications, the casting roll is preferably a hard metal roll having a chrome plating, chromium oxide, aluminum oxide or other hard metal roll surface. Such a roll surface can be polished or woven. The casting roll is preferably cooled to a temperature lower than the sticking temperature of the polymer, that is, a temperature lower than the softening temperature, so that the polymer does not stick to the roll. Backup rolls for most applications include silicone rubber, polyurethane, chlorotrifluoroethylene polymers such as VITON® or KEL-F®, and tetrafluoroethylene fluorocarbon heavy polymers such as TEFLON®. It is preferred to have a resilient outer surface portion made of a coalesced or other heat resistant rigid rubber or elastomeric material, or a combination of those materials. VITON, KEL-F or TEFLON I. Du Pontde Nemours Company trademark. The outer surface of such elastomeric material has a Shore A durometer hardness of about 75-85. In some applications, a hard surface such as a VITON, KEL-F or TEFLON elastomer is used rather than a more elastic material such as natural or synthetic rubber to provide a hard wear surface and appropriate compressibility. It is desirable to have. Both the casting roll and the backup roll must have a relatively smooth surface with an effective value (rms) in the range of about 2-20. In some embodiments, the casting roll can alternatively have a hard, heat resistant synthetic rubber surface as described for the backup roll.
Casting rolls and backup rolls are pressed against the metal strip and polymer web as they are moved through the roll nip, thereby adhering the web to the strip. The Pressing the rollers together means pressing the metal strip against the elastic material on the backup roll and crossing the entire width of the roller nip with the polymer web having no gaps in the contact area. Helps to ensure that it is pressed against. This acting force across the roll nip varies very little due to roll misalignment or changes in strip thickness and roll finish, but there should be no inadequate roll force gaps. Pressing the rolls together compresses the elastomeric material on the backup roll and / or casting roll to form a banded contact area portion in the roll nip along the roll length, which is flat It is believed to allow for a more uniform force distribution of the polymer web against the metal strip to allow for any misalignment of the roll of metal strip out of degree and to provide good coating uniformity and bonding. It is done. Devices for applying and controlling the force between rolls are well known in the art and include pneumatic and hydraulic cylinders, jacks, and screws acting on the rolls. .
The polymer coating provided by the present invention can be any of a variety of resins as described above with respect to FIG. The resin is essentially 100% polymer and preferably contains little or no volatile solution. Homogeneous or dissimilar resins are applied to the opposite sides of the strip, and one or both coatings can contain colorants or other additives. The metal strip is preferably medium to hard tempered aluminum having a thickness of about 0.1778 to 0.3556 mm (0.007 to 0.014 inches) as described above in connection with FIG. However, other metals or laminates such as steel or copper can also be used. The strip is preferably pre-cleaned and is subjected to pre-treatment such as by anodizing or conversion coating (preferably non-chromium), or pre-treatment such as by surface roughening to improve performance and The adhesion of the polymer to the strip can be improved. For example, the aluminum strip can be cleaned and treated with a titanium or zirconium phosphate treatment, a silicate treatment, or a BETZ METCHEM conversion coating. BETZ METCHEM is a registered trademark of Betz Laboratories, Inc. of Horseham, Pennsylvania. The strip can also be pre-coated or finished on one or both sides with an organic coating to improve the bond strength of the polymer to the strip.
In the operation of these devices, the metal strip passes through the device at a speed in the range of about 90-450 m / min (300-1500 ft / min), preferably 180-360 m / min (600-1200 ft / min). Moved. High speed obviously increases productivity and shortens the time the metal is at elevated temperature (residence time). Short residence times are often preferred in order to minimize degradation of metal properties.
Referring to FIG. 6, a coating apparatus is shown which includes a roll 172 on which a metal strip 174 moves and is fed to a preheater 173 such as an induction heater. This preheater passes the strip to about 121 ° -288 ° C. (250 ° -550 ° C. depending on the metal and tempering of the strip, the properties desired for the coated strip, and the polymer applied. It is designed to heat to a temperature in the range of ° F). For aluminum strips that are coated with polyester resin to use the strips that are coated in package applications, a more preferred preheating temperature range is about 204-288 ° C (400-550 ° F). This preheating temperature as well as the post heating temperature should not be so high as to adversely affect the desired properties of the metal strip or its polymer coating.
The preheated strip 174 is then coated on opposite sides by two extrusion dies 176, 178 and two sets of rolls 180, 182 and 184, 186. Although not shown, one of the two extruders feeds the molten polymer resin to extrusion dies 176 and 178. This resin has a temperature of 177 ° to 343 ° C. (350 ° to 650 ° F.) when fed to the extrusion dies 176 and 178, and the extrusion die is an electric resistance means for maintaining the resin at a desired temperature. It is preferable to be heated at. Extrusion molds 176 and 178 have an elongated narrow mold opening, the length of which is approximately equal to the width of strip 174 to be coated, and can be about 10 inches to about 85 inches. . The length of the mold opening is preferably at least as large as or wider than the width of the strip 174 so that the polymer web extruded from the extrusion mold can completely cover the strip. The mold opening is long and narrow to extrude a thin web. The mold opening may be in the range of up to 0.730 mm (0.030 inch), preferably about 0.127 to 0.381 mm (0.005 to 0.015 inch). Extrusion molds are generally conventional molds and can be purchased from a variety of vendors. Extrusion dies 176 and 178 extrude thin webs 188 and 190 which are applied to opposite sides of strip 174 with roll sets 180, 182 and 184 and 186.
In the first roll set, the roll 182 is a casting roll that contacts the polymer web 188 extruded from the extrusion die 176, and the roll 180 is a backup roll that presses and supports the strip 174 against the casting roll. . As noted above, casting roll 182 is preferably a hard metal roll, and backup roll 180 preferably has an elastic outer roll surface or shell, such as an outer layer of silicone rubber. Both rolls 180 and 182 are cooled by a coolant such as water circulated through the interior. The casting roll is cooled to a temperature of less than about 66 ° C. (150 ° F.) to prevent the polymer web from sticking to the roll. The backup roll 180 is cooled from the inside and / or outside to minimize damage to the elastic layer on the roll. The support roll 181 is provided to support the backup roll 180 and assist in cooling it.
As shown, the rolls 180, 182 are arranged in parallel with their axes aligned in a substantially horizontal plane so that the metal strip 174 and polymer web 188 are fed downward into the nip between the rolls, and the roll nip It can come out through the bottom. Before the metal strip 174 moves away from the surface of the backup roll and moves toward the reheat heater 192, the backup roll can wrap around an arc of about 0-120 ° to follow the outer surface. The polymer web 188 on the metal strip 174 is preferably brought into minimal contact with the casting roll 182 in order to minimize sticking or adverse effects on the casting roll 182. Minimizing this contact is particularly applicable to polyester resins, and what is desired for polypropylene resins (see FIG. 14) is to be strongly contacted and cooled strongly by the casting roll. It is. Rolls 180, 182 are about 9.0 to 53.7 kg / cm (50 to 300 pounds / inch), preferably about 21.5 to 32.2 kg / cm (120 to 180 pounds / inch) along the length of the roll nip. ), More preferably, with a force of about 2.69 kg / cm (150 pounds per inch). This force slightly deforms or compresses the outer portion of the elastic and compressible backup roll 180 to ensure that there is no gap in the force due to the roll acting on the metal strip along the entire length of the roll nip. , Providing means for accepting or accepting misalignment of rolls or loss of flatness of the plate. However, this force does not reduce the gauge size of the polymer or strip. As described above, compression of the compressible layer of the backup roll 180 creates a narrow contact area on the can between the rolls 180, 182 and the strip 174 at the roll nip position. Depending on the amount of force pressing the rolls and the elasticity of the support roll 180 among other factors, the typical contact band area is about 1/4 to 1 inch. The width is typically about 1.9 cm (3/4 inch).
After the strip 174 is coated on one side, the strip can optionally be reheated with an induction heater 192 or the like. The strip is dependent on the polymer applied but is in the range of about 120-288 ° C (250 ° -550 ° F), preferably about 204 ° -288 ° C (400 ° -550 ° F for polyester coatings). ) Is reheated. For some applications and some polymers, it is not necessary to reheat the strip before the strip 174 is coated on the opposite side.
A strip 174 from the reheat heater 192 is applied to the second extrusion die 178 and roll set 184, 186 and optionally the second strip surface opposite the surface coated with the first web 188. It is moved toward the cooling roll 187 for the polymer web 190. The distance from the first nip to the second nip is preferably shortened in order to control the heat loss from the metal as the strip moves between the two roll nips. The second extrusion die 178 and the second roll set 184, 186 are the same as the first extrusion die 176 and the roll set 180, 182, but the rolls are arranged oppositely, and the second casting roll is stripped from the first roll. The opposite is that the roll axis is in a different plane and the second extrusion die 178 is oriented differently. In order to pass the metal strip 174 through the second extrusion nip along a substantially straight line, the plane passing through the axis of the rolls 184, 186 moves through the extrusion nip at an angle relative to the vertical. It is substantially perpendicular to the surface of the strip. Therefore, the strip 174 comes into minimal contact with the rolls 184 and 186 except for a narrow band-shaped contact area portion formed by elastic deformation of the outer portion made of the elastic material of the backup roll 186. As discussed above, minimizing the contact of rolls 184 and 186 to the polymer of strip 174 is believed to help improve the quality and performance of some polyester resin final coated products. For other polymers, such as polypropylene, it is preferred that the polymer be rolled and cooled significantly before the coated strip leaves the roll.
As with the first roll set, the second roll set 184, 186 causes the polymer web 190 to be pressed tightly against the strip along the entire width of the roll nip against the metal strip 174 and the polymer web. Must be pressed with sufficient force to guarantee The force between the second set of rolls 184 and 186 is about 9.0 to 53.7 kg / cm (50 to 300 pounds / inch), preferably about 21.5 to 32.2 kg / cm (120 to 180 pounds / inch). Must be in the range of inches).
After the strip 174 is coated on both sides with the polymer webs 188, 190, the fully coated strip passes through the post heater 194 and moves through a device that cools the coated strip. Although not fundamental to the invention, the area of contact of the strip coated by a roll or other machine between the coated rolls 184, 186 when the polymer is cooled and solidified is minimal. It is thought that it is desirable to limit. For example, strip 174 is shown from rolls 184 and 186 through post-heater 194 to at least partially cool the strip to a temperature at least below the melting point of the polymer coating on the strip. It is desirable to be moved through no means. In this way, contact with the polymer on the strip by a roll or the like is avoided before the polymer is solidified, and the coating is unlikely to be adversely affected by the roll or the like.
The post heater 194 is preferably an induction heater, an infrared heater, a convection furnace, or a combination of two or three thereof, which at least bring the resin on the plate to a softening temperature, preferably the melting point of the polymer. Rapid heating to higher temperatures. It is important that such heating should not be heated to a high temperature in order to have a significant adverse effect on the properties of the strip metal or polymer coating on the strip. Heating the polymer to at least the melting point causes the polymer to flow, thereby repairing coating flaws on the strip and / or smoothing uneven spots. desirable.
The strip is post-heated and then rapidly cooled to solidify the coating in a substantially amorphous form. It is desirable to first partially cool the strip with air or other gas, and then quench the partially cooled strip with a water spray or water bath. It is believed that partial cooling of the strip with air minimizes the potential for adverse effects that would have on the polymer as it was melted in water. As used herein, “quenching” means that the strip is about 90-450 m / min (300-1500 ft / min), preferably 180-360 m / min, after the coated strip leaves the post heater. When moving at a speed of (600-1200 feet / min), it means that the polymer coating is cooled. The cooling or quench unit is located within a few feet, such as 5-50 feet, of the post heater so that the polymer coating is preferred after the coated strip exits the post heater. Is solidified in less than about 10 seconds, more preferably in less than about 1 second.
After the strip has been cooled, it can be further trimmed, cut, smoothed, wound up as a coil, made into products such as can ends and can bodies, with or without winding. Can be done.
FIG. 7 shows an alternative similar to the apparatus shown in FIG. 6 except that the upper roll pairs 202, 204 are positioned in a plane perpendicular to the strip 196 passing through the roll nip with their roll axis. The device is shown. Although not shown, cooling rolls may be added to assist in cooling the rolls 202, 208, 212. In this apparatus, the contact of the strip with the backup roll is minimized, heat transfer loss from the strip to the backup roll is reduced, and thermal damage to the elastic outer portion of the backup roll is reduced. This also means that the cooling of the metal strip is reduced, which eliminates the need for auxiliary heating or reheating before the strip is coated on the opposite side. If reheating is desired, the single-sided strip is turned on roll 208 and passed through auxiliary heater 210. This strip is then covered on the opposite side by an extrusion die 216 and rolls 212,214. The fully coated strip is then post-heated and cooled / quenched in the same manner as described above in connection with FIG.
FIG. 8 shows an alternative embodiment of the present invention in which the lower coating station rolls 218, 220 are horizontally positioned with their axes positioned substantially in a horizontal plane, and the strip 222 is a backup. It is similar to the embodiment of FIG. 6 except that it is rotated about 90 ° after the roll 210 and then moves towards a post heater and cooling device not shown. FIG. 8 also shows several strip movement paths after the strip 222 has exited the lower casting station roll nip by dotted lines.
FIG. 9 shows another embodiment of the present invention in which the moving direction of the metal strip 230 is substantially vertical through the pre-heater 231, the first roll set 232, the auxiliary heater 234 and the second roll set 236. The strip coated on both sides from the second roll set is moved through a post heater (not shown) and a cooling device (not shown). If spatially permitted, the post-heater is preferably placed linearly below the two coating rolls, and the strip is cooled to a temperature below the polymer melting point before contacting the turning roll. It is preferred that Cooling to a temperature lower than the melting point of such a polymer is performed by air cooling, and then the strip is turned and passed through a quenching section by a fluid such as a water cooling bath.
FIG. 10 shows another embodiment of the present invention in which the metal strip 240 moves substantially horizontally between the extrusion dies 242 and 244 and the roll set. In this apparatus, the strip 240 is turned around a backup roll 246 that forms a roll nip with the casting roll 248. Extrusion mold 242 extrudes a thin polymer web 250 above the roll nip, and the web is stretched to reduce thickness before being pressed against the strip and applied. Both casting roll 248 and backup roll 246 are cooled in the manner described above.
The strip 240 from the backup roll 246 is optional but moves horizontally through the auxiliary heater 252 and then moves around another backup roll 254 that forms a roll nip with the casting roll 256. Extrusion die 244 extrudes a second web of polymer that is stretched to reduce thickness and is pressed against strip 240 at the nip between rolls 254 and 256. Both rolls 254, 256 are preferably cooled in the same manner as in the first roll set. The double coated strip is then moved through the post heater 260 and then moved through the cooling / quenching device 262 to produce the final product, which is wound up as a coil or further processed. Can do.
FIG. 11 shows that the metal strip 264 is adapted so that the strip travels around the diverting roll 265, moves through the preheater 266, and the polymer webs 268, 270 are applied substantially simultaneously to opposite sides of the strip. Another embodiment of coating is shown. Extrusion molds 272 and 274 of this apparatus extrude polymer webs 268 and 270, which are drawn by casting rolls 276 and 278, fed between roll nips, and pressed against opposite sides of the metal strip. If not both, at least one of the casting rolls 276, 278 has a compressible outer layer, such as TEFLON, VITON, KEL-F and elastomer, to ensure continuous bonding force over the entire length of the roll nip. . The apparatus preferably includes cooling rolls 280, 282 to assist in cooling the casting rolls 276, 278 and to extend the life of the casting roll. The apparatus further includes quenching means such as a post heater 284 and a water spray 284, which are similar to those shown in the previous figures.
A polymer web 298 extruded from an upper extrusion die 296 is moved by a strip, such as an aluminum strip 290, around a turning roll, passing through a pre-heater 294, moving between an upper casting roll 300 and an upper backup roll 302. Another embodiment of the present invention adapted to be coated on the first side is shown in FIG. The casting roll is preferably an abrasive steel roll and the backup roll preferably has a compressible outer layer. An upper cooling roll 303 is preferably included to extend the life of the backup roll 302 compressible material. The strip coated on one side from the roll nip between the rolls 300, 302 is reheated or heated to coat the opposite surface with the second polymer web 312 extruded from the lower extrusion die 310. Move through heater 304 to be assisted. The lower casting roll 308 and the backup roll 306 press and adhere the web 312 to the strip. The lower casting roll 308 is preferably ground steel and the lower backup roll 306 has a compressible outer surface such as TEFLON, VITON or KEL-F and elastomer. The lower cooling roll 314 is optional but included in the same manner as the upper roll set. After applying the second polymer web, the double-sided strip is post-heated to a temperature higher than the melting point (one or more) of the polymer (one or more) by a heater 316 and then by water spray 318. It is rapidly cooled.
FIG. 13 shows yet another embodiment of the present invention in which the metal strip 320 has two opposite faces that are sequentially opposed as they travel through an "S" shaped path through the apparatus. Covered. In this apparatus, the metal strip 320 passes around the turning roll 322, passes through the preheater 324, and passes between the casting roll 330 and the backup roll 332, and the first polymer web 326 from the extrusion mold 328 is stripped. It is made to adhere to one side. A cooling roll 348 is preferably included to extend the life of the backup roll compressible material. In this apparatus, the position of the casting roll 330 and the backup roll 332 is such that the strip 320 partially circulates around the roll for about 45 ° to 90 ° with the rotation of the roll. It depends on the moving direction of the strip relative to the plane passing through the axis of the roll.
After receiving the first coating, the metal strip 320 is preferably diverted by the diverting roll 336 and is moved through the heater 338 to assist in heating the strip temperature, followed by the casting roll 344, The backup roll 346, the cooling roll 348 and the extrusion die 340 provide a coating on the opposite side of the strip, which pushes the polymer web 342 into the roll nip. The position of the rolls 344, 346 relative to the direction of travel of the strip 320 is similar to the upper coating station, and the strip also partially circulates around the roll as it moves through the lower coating station. The strip 320 coated on both sides from the lower coating station can be post-heated to a temperature above the melting point of the polymer (s) and then rapidly cooled to solidify the polymer on the strip. preferable.
FIG. 14 shows yet another embodiment of the present invention, which is a particularly suitable example for applying a polypropylene coating to both sides of an aluminum strip. In this apparatus, the metal strip 352 moves around the turning roll 354 and moves downward through the preheater 356 at an angle of about 30 ° -60 ° with respect to the vertical, and the backup roll 358 and casting / cooling roll 360 are moved. The polymer web 364 from the extrusion die 362 is applied to the band material. In this apparatus, the metal strip 352 partially circulates around the casting / cooling roll 360 so that the polymer on the strip is cooled, so that the polymer, particularly the polypropylene material, is peeled from the roll. It is guaranteed to be held on the strip. A take-off roll 370 can be used to cause the strip 352 to follow the casting / cooling roll 360 as shown. The casting / cooling roll is preferably cooled from the inside and has a relatively large diameter, such as a diameter of about 0.91 to 1.83 m (3 to 6 feet), and a strip and polymer thereon. Can be cooled sufficiently. The take-off roll has a compressible outer layer and is preferably cooled from the inside and / or from the outside.
From the upper coating station, the strip 352 travels around the turning roll 372 and moves through the heater 374 so that a second coating is applied by the lower coating station, which is essentially the upper coating. Same as station. The lower coating station includes an extrusion die 382, a backup roll 376, a casting / cooling roll 378, and a take-off roll 384 to apply a polymer web such as polypropylene to the strip. The strip coated on both sides from the take-out roll 384 is then post-heated and quenched as with other devices described herein.
For some embodiments of the present invention, the coating can be a heteropolymer on opposite sides of the metal strip and can be of different thickness. For example, one side coating can be a blend of high melt viscosity polymer and bottle grade polyester, and the other side coating can be polyester or vinyl resin. One or both side coatings can also contain pigments or colorants.
The coated metal strip according to the present invention requires that the coating be intimately bonded to the metal strip for use in package applications such as those used to make can bodies or can ends. . The use of strips for packing applications also requires that the coated surface be smooth and glossy. The surface should have minimal irregularity and surface stains. It is desirable that the mechanical properties of the metal strip, such as tensile strength, yield strength, elongation, formability, and corrosion resistance, are also maximized. The coating must also be flexible so that it does not crack or peel when the strip is processed into a final product such as a can body, can end or other product. The coating of the package application must also be very thin, such as about 0.0127 mm (0.5 mil) thick, and the thickness should be uniform.
In practicing the present invention, the metal strip passage through the roll set, post-heating device and cooling / quenching device plays a critical role in the quality of the coated strip. In particular, it is desirable to minimize the coating on the strip from contacting the roll before the coating has cooled to at least a temperature below the melting point and possibly to the softening temperature of the coating polymer. In some devices it is desirable to air cool the coated strip to a temperature below the melting point of the polymer after post-heating and before water quenching. This air cooling minimizes as much as possible the negative effects of water on the melt coating during quenching.
Aluminum strips coated according to the present invention have many advantages over strips coated or laminated by prior art methods. One important advantage is that the coating is tightly attached or bonded to both sides of the metal strip, and the strip is stretched or stretched and ironed to the can body, can end, or automotive or airplane decorative trim No peeling or peeling occurs when formed into a product such as This strip can also be manufactured at a lower cost than prior art strips. This is because the present invention can omit the secondary steps of forming, rolling and unrolling the thin film laminated on the strip in the prior art.
Therefore, it can be seen that the present invention provides an improved continuous process for coating a thermoplastic coating on both sides of a metal strip, and an improved strip so formed. While several alternative embodiments for practicing the invention have been described, it is clear that the claims section is intended to cover all embodiments and examples that fall within the spirit of the invention. It is. For example, the coating (s) of the metal strip can be polished while the coating is being brought to a temperature near or above the melting point by a polished kiss roll, and the coated metal The strip is post-heated and passed over a metal strip roll before the coating is cooled. Other alternative processing methods will be apparent in view of the description herein.

Claims (7)

A method of extrusion coating a metal strip to produce a coated metal strip comprising:
Providing a metal strip having a thickness in the range of 0.1778 to 0.356 mm (0.007 to 0.014 inches);
Heating the metal strip to a temperature of at least 121 ° C. (250 ° F.) but not so high as to adversely affect the desired properties of the metal strip;
Passing the first roll set through the metal strip and then passing the second roll set, each roll set including a casting roll and a backup roll, which comprises the metal strip and the heavy roll. Forming a nip for passing the polymer resin between them to join the polymer resin to the metal strip;
The heated metal to form a coating that is at least partially bonded to the metal strip and each has a thickness in the range of 0.0003 to 0.0015 inches. A polymer resin is extruded on one side of the strip and the same polymer resin or a different polymer resin is sequentially extruded on the other side of the heated metal strip, and the extruded polymer resin is 1: 1. 200: a method comprising 1 of the steps you引延to be reduced thickness in stretching ratio,
Cooling the casting roll to a temperature lower than the softening temperature of the polymer resin;
Cooling the backup roll;
Before polymer tree covering fat into a polymer is a post-coating of the resin and the other surface of the to one surface, the method comprising: heating the metal strip,
After the metal strip exits said second roll sets, said a metal strip to a temperature above the melting point of the polymer resin, heated to the desired characteristics not as high as adversely affect the temperature of the metal strip And thereby bonding the resin to the metal strip,
Cooling the coated metal strip to a temperature below 40 ° C. (104 ° F.) to solidify the resin in an amorphous form. The method as claimed in claim 1, by extruding a polymer resin to each of the casting roll, a method of imparting the extruded resin to the metal strip. 2. The method of claim 1 wherein the extruded polymer resin is in the range of 0.00254 to 0.127 mm (0.0001 to 0.005 inches) or 0.00508 to 0.0508 mm (0.005 inch). wherein that引延a thickness in the range of 0002 to .002 inches). The method as claimed in claim 1, the pre-Symbol extruded polymer resins, 10: 1 to 40: 1 or 25: that引延to reduce the thickness at the first stretching ratio Feature method. The method as claimed in claim 1, the pre-Symbol extruded polymer resin, that one thickness than other polymer resins of the extruded polymer resin is引延to reduce A method characterized by . The method as claimed in claim 1, before Symbol metal strip,
(A) an aluminum alloy,
(B) 0.178-0.356 mm (0.007-0.014 inch) thick, consisting of an intermediate to hard tempered aluminum alloy,
(C) is and processed is purified prior to being coated with a polymer web, and / or (d) wherein the processed in conversion coating. The method as claimed in claim 1 or claim 2, B Lumpur,
(A) the metal strip is arranged to move downward through a nip between the first and second roll sets;
(B) The axis of the first roll set is substantially horizontal, and the metal strip moves downward at an angle in a range of 30 ° to 70 ° with respect to the horizontal, so In between the nips and arranged to exit the rolls downward at an angle in the range of 60 ° to 140 ° with respect to the direction of entry of the metal strip into the rolls,
(C) The metal strip is arranged so as to enter the first roll set at an angle of 45 ° with respect to the horizontal direction and to exit the roll of the first roll set at an angle of 45 ° with respect to the horizontal direction. ,
(D) the metal strip is arranged to move in a substantially straight path from the first roll set to the second roll set roll and through the second roll set roll; ,
(E) arranged so that the axis of the roll of the second roll set is positioned in a plane existing at 90 ° with respect to the plane of movement of the metal strip through the second roll set, or ( f) as the metal strip is substantially moved vertically downward through the nip between the first and second roll sets, wherein the disposed.

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