Conveyance apparatus for ultrathin webs comprising a roller with contoured surface

Abstract: A web conveying roller (18) is provided with circumferentially or spirally extending grooves (42) and lands (44), the lands having convex curvatures (46, 48; 54) to cause a conveyed, ultrathin web (30), at the beginning of a wrap angle (α) onto the roller, to undulate along the width of the roller over the lands and into the grooves while remaining spaced from the convex curvatures of the lands; so that, air entrained between the web and the lands can flow into the grooves.

Description: The invention concerns apparatus for conveying web material such as indeterminate lengths of plastic sheet or paper. More particularly, the invention concerns such apparatus which includes rollers having specially contoured surfaces for conveying at high speeds wide webs of ultrathin or very small thickness, such as less than 0.001 inch (0.0254 mm). Figure 1 illustrates schematically one example of a wide variety of manufacturing apparatus for conveying and treating web materials. A source 10, such as a stock roll, provides a web 12 of indeterminate length. In the familiar manner, the web is conveyed through a process zone 14 to a take-up roller 16 by means of a plurality of right circular cylindrical driver and idler rollers 18, only one being illustrated, which typically have widths greater than the width of the web. Rolls 10 and 16 also may be driven. Some rollers 18 may be driven by means such as a motor 20. The relative positions of the rollers and other conventional web guidance features in the apparatus,. not illustrated, serve as means to guide the web to wrap onto each roller over a wrap angle α, which may be in the range of 10 to 300°. Various surface treatments may be performed on the web in the process zone, such as coating, printing, surface texturing and the like, which often require that there be no slippage between the web and the driver or idler rollers. Slippage or loss of traction between a web and a roller is undesirable since it may cause problems for the web such as weaving movement, electrostatic charging, scratching, creasing and the like. Sufficient frictional force is required between the web and each roller to prevent such slippage, this force commonly being known as roller traction. In EP 590253, another example of an apparatus for conveying a web material is disclosed. According to this reference a guide roller has a polished outer surface with grooves formed on the outer surface of the roller tube. Roller traction can be achieved with smooth-surfaced rollers at low web speeds; however, as web speed increases to as much as 100 feet per minute (30.5 meters per minute), air typically becomes entrained between the web and the roller, as indicated by the arrow in Figure 1. The entrained air causes the web at least partially to lose contact with the roller; so that, slippage can occur. To permit entrained air to escape from between the web and the roller, surface patterns of various types have been provided on roller surfaces, thus permitting adequate traction to be maintained at low and high web speeds. Figure 2 illustrates schematically an axial cross section of one such surface pattern and an engaged web, just at the beginning of wrap angle α. The exterior surface of roller 18 is provided with a plurality of circumferentially extended grooves 24, which may be individual annular grooves or one or more continuous spiral grooves. The grooves are separated by circumferentially extended lands 26 whose outer surfaces are flat or straight when viewed in such an axial section. That is, the lands have a flat profile when viewed in the direction of movement of the web through the apparatus. There may be, for example, 6 to 60 such grooves per inch (2.36 to 23.6 grooves per cm), the axial widths of the grooves and lands being about the same and each groove having a depth in the range of 0.002 to 0.010 inch (0.0508 to 0.254 mm). When a polyethyleneterephthalate web having a thickness t in the range of 0.002 to 0.0075 inch (0.0508 to 0.191 mm) is conveyed using 2.8 inch (71.1 mm) diameter rollers of the type illustrated in Figure 2, the web has sufficient stiffness, beam strength or bending resistance to enable it to engage fully the flat profile surfaces of lands 26 at the beginning of wrap angle α, in the manner illustrated in Figure 2. Thus, any air moving with the web at the beginning of the wrap angle is forced into grooves 24 and good traction is maintained due to the engagement of the web with the lands. Figure 3 illustrates how, for such relatively thick webs, the coefficient of friction between a 0.0025 inch (0.0635 mm) thick, 54 inch (1372 mm) wide web and a grooved, 2.8 inch (71.1 mm) roller changes only slightly over a range of web speeds up to 1,000 feet per minute (305 meters per minute). A somewhat larger drop in coefficient of friction is observed for web tension of 15 pounds or 0.27 pounds per linear inch across the web (6.8 kg or 0.0048 kg per mm), compared to a tension of 25 pounds or 0.45 pounds per linear inch across the web (11.34 kg or 0.008 kg per mm). However, if web 12 is ultrathin, with a thickness of less than 0.001 inch (0.0254 mm), rollers of the type shown in Figure 2 fail to provide adequate traction at web speeds above a few hundred feet per minute. Traction no longer remains essentially constant but rather becomes a function of web thickness and web speed. We have discovered that this degradation in performance of such grooved rollers results from a decrease in the bending resistance of the ultrathin web. For the thicker webs, the bending resistance is sufficient to enable the webs to bridge the grooves and engage the lands of known grooved rollers with minimal radial deformation of the web, as shown in Figure 2. For the ultrathin webs, however, the webs are so flimsy that at the beginning of the wrap angle they bend into the grooves and lift above the lands in the manner illustrated in Figure 4. A similar effect can be observed with webs thicker than 0.001 inch (0.0254 mm), depending on the material of the web and the geometry of the lands and grooves. An ultrathin web 30 thus deforms transversely into a series of relatively high ridges 32 and low valleys 34; so that, web 30 makes contact with the roller essentially only at the edges or corners 36, 38 of each land. As a result, a volume 40 of air can become more or less trapped beneath high ridges 32 since contact of the web with edges 36, 38 prevents or severely impedes flow of air into the grooves. With essentially line contact between the web at the edges 36, 38, traction is reduced drastically, leading to the problems previously mentioned. Figure 5 illustrates how, for a 0.00025 inch (0.0064 mm) thick, 55 inch (1397 mm) wide, polyethyleneterephthalate web running on a 5.6 inch (142.2 mm) grooved roller, the coefficient of friction between the web and the roller drops rapidly over a range of web speeds up to 800 feet per minute (244 meters per minute). A somewhat larger drop in coefficient of friction is observed for web tension of 10 pounds or 0.18 pounds per linear inch across the web (4.5 kg or 0.0032 kg per mm), compared to a tension of 15 pounds or 0.27 pounds per linear inch across the web (6.8 kg or 0.0048 kg per mm) or to a tension of 25 pounds or 0.45 pounds per linear inch across the web (11.34 kg or 0.008 kg per mm). Thus, a need has existed for a roller which can convey ultrathin and other webs, which tend to deform into conventional grooved rollers, with good traction at elevated web speeds. The primary objective of our invention is to provide an improved roller for conveying ultrathin webs at elevated web speeds, without substantial loss of traction or risk of damage to the web. The object of the present invention is achieved through an apparatus according to claim 1. Dependent claims disclose further advantageous embodiment of the invention. This apparatus is particularly suited for conveying ultrathin webs having a width. It comprises a source of a web to be conveyed, such as a stock roll, feeds the web over at least one cylindrical roller having an exterior surface with a length, the length being longer than the width of the web to be conveyed and a portion of the web being wrapped onto the roller over an angle α. Uniquely in accordance with our invention, the roller comprises a plurality of circumferentially extending, axially spaced grooves formed in the exterior surface along the length, each groove having an axial width; and a plurality of lands formed in the exterior surface and extended between the grooves, each land having an axial width and a central surface with a convex circular shaped curvature. The lands may be continuous. For best conveyance of ultrathin webs, the convex circular shaped surface of the lands and the axial widths of the grooves and lands are chosen so that, at about a beginning of the wrap angle α during rotation of the roller, the web undulates along the width of the roller over the lands and into the grooves but is spaced from the convex circular shaped surface of the lands, so that air entrained between the web and the lands can flow into the grooves. Some contact at the apex of the convex circular shaped surface of the lands is acceptable at this location. Typically, a minimum clearance between the web and the exterior surface occurs at the apex of the convex circular shaped surface and the clearance between the web and the convex circular shaped surface increases with axial distance from the minimum clearance. The wrap angle α may be in the range of 10 to 300°. Means may be provided for moving the web at a speed in the range of 300 to 1,000 feet per minute (91.4 to 305 meters per minute). The roller may be an idler roller or a driven roller. The circular shaped surface may have a radius of curvature in the range of 0.020 to 1.2 inch (0.508 to 30.5 mm); the axial width of the grooves may be in the range of 0.020 to 0.105 inch (0.508 to 2.67 mm); and the axial width of the lands may be in the range of 0.020 to 0.105 inch (0.508 to 2.67 mm). The cylindrical roller may have a diameter in the range of 1.5 to 10.0 inch (38.1 to 254 mm). Rather than circumferentially extending grooves and lands as just described, the roller of our invention may include at least one spiral groove formed in the exterior surface along the length, the spiral groove having an axial width; and at least one continuous spiral land formed in the exterior surface and extended between turns of the spiral groove, the spiral land having an axial width and a central surface with a convex circular shaped surface. As in the previous example, the convex circular shaped surface of the spiral land and the axial widths of the spiral groove and spiral land may be chosen so that, at a beginning of the wrap angle α during rotation of the roller, the web undulates along the width of the roller over the turns of the land and into the turns of the groove but is spaced from the convex circular shaped surface of the spiral land, so that air entrained between the web and the spiral land can flow into the spiral groove. The spiral groove and spiral land may be formed by at least one wire wound onto the roller. The apparatus and conveying rollers according to our invention provide various advantages. Ultrathin webs can be conveyed at elevated web speeds with good traction. Web weaving and scratching are minimized due to maintenance of adequate traction. The coefficient of friction between ultrathin webs and rollers of our invention varies only moderately over a wide range of web speeds. The wound wire embodiments of our roller have a high quality surface finish and are simple and economical to manufacture and maintain. Existing apparatus is easily modified for conveying ultrathin webs simply by replacing prior art rollers with those of our invention. The foregoing and other objectives, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings. Figure 1 illustrates schematically a manufacturing apparatus for conveying and treating web materials, of the general type suitable for use of rollers in accordance with our invention. Figure 2 illustrates a fragmentary, sectional view in the direction of web movement, showing the engagement of a relatively thick web with a prior art grooved roller just as the web enters the wrap angle α in the apparatus of Figure 1. Figure 3 illustrates how the measured coefficient of friction varies with web speed for a web and roller pair of the type shown in Figure 2. Figure 4 illustrates a fragmentary, sectional view in the direction of web movement, showing the engagement of an ultrathin web with a prior art grooved roller just as the web enters the wrap angle on the roller. Figure 5 illustrates how the coefficient of friction varies with web speed for a web and roller pair of the type shown in Figure 4. Figure 6 illustrates a fragmentary, sectional view in the direction of web movement, showing the engagement of an ultrathin web with one embodiment of a contoured roller in accordance with our invention just as the web enters the wrap angle on the roller. Figure 7 illustrates a schematic, sectional view in the direction of web movement, showing the engagement of an ultrathin web with a further embodiment of a contoured roller in accordance with our invention just as the web enters the wrap angle on the roller. Figure 8 illustrates a calculated radial displacement of an ultrathin web as a function of axial position along a convex land on a contoured roller in accordance with one embodiment of our invention. 'Figure 9 illustrates a calculated interfacial air pressure between an ultrathin web and a convex land on a contoured roller in accordance with the embodiment of our invention of Figure 8, as a function of axial position along the land. The following is a detailed description of the preferred embodiments of the invention, reference being made to the drawings in which the same reference numerals identify the same elements of structure in each of the several Figures. Figure 6 illustrates a fragmentary, sectional view in the direction of web movement, showing the engagement of ultrathin web 30 with one embodiment of a contoured roller in accordance with our invention, just as the web enters the wrap angle α on roller 18. In accordance with our invention, the flat profile grooves and lands of the prior art rollers are replaced with an undulating, contoured surface somewhat geometrically similar to the shape assumed by an ultrathin web when used with a prior art grooved roller, as shown in Figure 4. Our contoured surface may be provided on right cylindrical or concave rollers; however, we have found that concave rollers are preferable for more flimsy webs. Our recognition of the advantages of such a contoured surface was, in our experience, contrary to the expectations of persons skilled in the web conveying arts. Prior to our invention, the typical expectation of the skilled persons was that a contoured surface such as used in our invention would result in poor traction due to anticipated line contact. We have found, surprisingly, that such contoured surfaces are quite effective when used with ultrathin webs. In accordance with our invention, the exterior surface of roller 18 is provided with a plurality of circumferentially extended grooves 42, which may be individual annular grooves or one or more continuous spiral grooves. The grooves are separated by circumferentially extended lands 44. At least the central portion of the outer surfaces of lands 44 have convex circular shaped curvature when viewed in the illustrated, axial section. That is, lands 44 have an outwardly rounded profile when viewed in the direction of movement of the web through the apparatus. In the illustrated embodiment, which may be formed by diamond turning, for example, grooves 42 may have a generally concave surface with an axial width w 1 in the range of 0.020 to 0.105 inch (0.508 to 2.67 mm). Lands 44 have a generally convex circular shaped central portion on surface 46 with an axial width w 2 in the range of 0.020 to 0.105 inch (0.508 to 2.67 mm). As illustrated, the radius of curvature may be in the range of 0.020 to 1.2 inch (0.508 to 30.5 mm). When grooves 42 and lands 44 are shaped and spaced in this manner, at about the beginning of wrap angle α and upon rotation of roller 18, web 30 will undulate along the width of the roller over the lands and into the grooves while remaining spaced slightly from the surfaces of the lands and grooves. Because web 30 assumes this undulating configuration at about the beginning of the wrap angle, air entrained between the web and the lands can flow readily into the grooves to permit the web to engage the roller further along in the wrap angle. Figure 7 illustrates another embodiment of a roller made in accordance with our invention. In this instance, roller body 18 is wrapped with a circular cross section wire 50 to provide spiral grooves 42 and lands 44. Wire 50 may have a radius of about 0.020 inch (0.508 mm), for example, and be wrapped tightly onto the roller so that successive turns of the wire abut in the manner illustrated. Roller body 18 may be a circular cylinder having a diameter in the range of 1.5 to 10.0 inch (38.1 to 254 mm). When the roller is to be used to convey more flimsy webs, a concave axial profile may be advantageous. A concave profile is suitable whose diameter tapers about 0.2% from its ends to its center. Figure 8 illustrates a calculated radial displacement of an ultrathin web at about the beginning of the wrap angle as a function of axial position along a convex land on a contoured roller in accordance with the embodiment of Figure 7. A web 30 having a thickness of about 0.00025 inch (0.0064 mm) was assumed to be wrapped onto a roller having a diameter of about 2.75 inch (69.85 mm). As shown in the figure, the clearance between the web and the convex land was calculated to be a minimum at the point of maximum radius of the land, corresponding to high point 48 in Figures 6 and 7. On either side of the point of maximum radius, the clearance between the web and the land was calculated to increase, thus indicating that air would be able to escape into the neighboring grooves. Figure 9 illustrates a calculated interfacial air pressure at about the beginning of the wrap angle between web 30 and convex land 44 on a contoured roller in accordance with the embodiment of Figure 7, as a function of axial position along the land. Consistent with Figure 8, this plot indicates that the calculated pressure between the web and the convex land decreases from a maximum at high point 48 to a minimum at the center of the neighboring groove. The convex shape of the curve indicates that the relatively high pressure air at the center of the land can escape readily into the lower pressure area in the grooves. 10...source of web, such as stock roll 12...web of indeterminate length, having width and thickness 14...process zone, such as coating machine 16...take-up roll for web 18...right cylindrical roller, having length longer than width of web 20...motor, optional α...wrap angle of web onto roller 24...conventional circumferentially extended groove or valley, circular or spiral 26...conventional circumferentially extended land, circular or spiral t ...thickness of web 30...ultrathin web at beginning of wrap angle 32...high ridge 34...low valley 36, 38...edges of land 40...volume of trapped air 42...circumferentially extended groove or valley of invention, circular or spiral w 1 .... axial width of groove 42 44...circumferentially extended land of invention, circular or spiral w 2 ...axial width of land 44 46...convex surface of land 44 48...central location of maximum radius or high point of land 44.

Claims: A conveyance apparatus, comprising: a source (10) of web to be conveyed, the web (30) to be conveyed having a width; at least one cylindrical rotatable roller (18) having an exterior surface with a length, the length being longer than the width of the web to be conveyed, a portion of the web to be conveyed being wrapped onto the at least one roller over a wrap zone defined by a wrap angle (α); a plurality of circumferentially extending axially spaced grooves (42) formed on the exterior surface along the length each of the plurality of grooves (42) having an axial width; a plurality of lands (44) formed on the exterior surface (46) and extended between the grooves (42), each of the plurality of lands (44) having an axial width and a central surface, characterized in that the exterior surface (46) has an undulating contour each of the plurality of lands (44) have a convex circular shape upon which the web is to be conveyed having a radius of curvature in the range of.0,508 mm to 30,5 mm, the axial width of each of the plurality of lands being in the range of 0,508 mm to 2,67 mm; the convex circular shapes of the lands (44) and the axial widths of the grooves (42) and lands (44) are chosen so that, at a beginning of the wrap zone during rotation of the at least one roller (18), the web (30) to be conveyed undulates along the width of the roller (18) over the lands (44) and into the grooves but is spaced from the convex circular shapes of the lands, whereby air entrained between the web to be conveyed and the lands can flow into the grooves. Apparatus according to claim 1, wherein the wrap angle (α) is in the range of 10 to 300°. Apparatus according to claim 1, further comprising means for driving said at least one roller (18) to convey the web at a speed in the range of 91,5 m per minute to 305 m per minute. Apparatus according to claim 1, wherein the lands (44) are continuous. Apparatus according to claim 1, wherein the generally cylindrical roller (18) has a diameter in the range of 38,1 mm to 254 mm. The apparatus according to claim 1, wherein said plurality of circumferential extending, axially spaced grooves (42) comprises at least one spiral groove having an axial width, and said plurality of lands (44) comprises at least one spiral land, the spiral land having an axial width and a central convex circular shaped surface. The apparatus according to claim 6 wherein the spiral land (44) is continuous. The apparatus according to claim 6, wherein the convex circular shaped curvature of the spiral land (44) and the axial width of the spiral groove (42) and spiral land (44) are chosen so that, at a beginning of the wrap zone during rotation of the at least one roller (18), the web (30) to be conveyed undulates widthwise along the at least one roller (18) over the turns of the land (44) and into the turns of the groove (42) but is spaced from the convex circular shaped curvature of the spiral land, whereby air entrained between the web (30) to be conveyed and the spiral land (44) can flow into the spiral groove (42).

Inventors: COLE KEVIN A, STEWART ARTHUR MOORE, COLE, KEVIN A., STEWART, ARTHUR MOORE, Cole, Kevin A., c/o Eastman Kodak Company, Stewart, Arthur Moore, c/o Eastman Kodak Company
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1995
Main classification: B65H27
IPC codes: B65H27, F16C13