US3359128A

US3359128A - Dusting of surfaces

Info

Publication number: US3359128A
Application number: US286672A
Authority: US
Inventors: Loren K Humphrey; Robert A Dunning; Curtis A Layman
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1963-06-10
Filing date: 1963-06-10
Publication date: 1967-12-19
Anticipated expiration: 1984-12-19

Description

1967 K. HUMPHREY ETAL 3,359,128

DUSTING 0F SURFACES Filed June 10, 1965 2 Sheets-Sheet 1 INVENTORS. Loren K. Hum hrey Robert 4. Dunn/n9 iv CUrf/s A. ogmafl Dec. 19, 1967 K. HUMPHREY ETAL 3,359,128

DUSTING 0F SURFACES Filed June 10, 1963 2 Sheets-Sheet 2 INVENTORS.

tare/7 K. Humphrey XWJJ United States Patent 3,359,128 DUSTING 0F SURFACES Loren K. Humphrey, Alma, and Robert A. Dunning and Lurtis A. Layman, Midland, Mich, assignors to The Dow Chemical Qompany, Midland, MiclL, a corporation of Delaware Filed June 10, 1963, Ser. No. 286,672 3 Claims. (Cl. 117--16) This invention relates to a method and apparatus for supplying a uniform coating of a powdered material to the surface of plastic films or other sheets, especially to reduce the electrostatic cling and tendency to block which is characteristic of many such sheets.

It is well known that any type of sheet materials, especially those comprising synthetic plastics, are highly dielectric and that such sheets have a normal tendency to cling to other sheets which are similar. It is also known that this clinging tendency is aggravated by accumulation of an electrostatic charge thereon, as may be encountered during extrusion of the sheet and in such subsequent operations as winding into or out of storage rolls, or in other manipulations wherein the sheet surface is subjected to friction.

It is a conventional and normal practice to apply an anti-sticking agent to the surfaces of many sheet materials to reduce their clinging tendency. Numerous powders or dusts have been proposed and are used for such purposes. The choice in any given instance depends largely on the intended use of the treated sheet. Plastic films intended for use as food wrappers are commonly dusted with starch. Sheets intended for industrial or non-food uses are often dusted with such other agents as talc, mica, various polymer powders and assorted chemicals that have anti-static properties. Such powders have been applied to the surface of the dielectric sheet by such means as sifting or aspirating the powder from a continuously diminishing supply. These methods necessarily result in the deposition of varying doses of the powder per unit area of the sheet surface. Consequently, the extent to which the clinging tendency is overcome has varied according to the amount of powder remaining in the duster at the moment each area is treated.

As is apparent, more uniform and controllable results would be desirable to attain in such dusting operation. Such dusts should be uniformly distributed across the surface of the film.

Many of these devices of the prior art which have been designed to distribute powder uniformly on surfaces have had many shortcomings. For example, most devices are relatively complicated and require a large number of parts of relatively high precision. Many devices apply the dust to a film in a position remote from the mill roll onto which the sheet or web is being wound, thus providing ample opportunity for electrostatic forces, drafts, and the like to cause uneven distribution of the dust on the surface thereof.

It is an object of this invention toprovide an improved method and apparatus for the application of dust to a web.

It is a further object of this invention to provide a simple apparatus for the application of dust to a web.

It is a further object of this invention to provide a method of applying dust to a web as it is wound onto a roll.

It is a still further object of this invention to provide a method and apparatus for applying dust to a web in an economical manner.

These and other advantageous results, purposes and benefits are achieved in accordance with the method of the invention by utilizing a dust source directed toward the surface of a web as it is being wound onto a'roll in such a manner that dust is applied in a gaseous dispersion to the surface of the roll and the web just prior to the contact on maintaining said dust source at about the same distance from the roll during the dusting operation. The apparatus of the invention comprises a rewinding stand, said rewinding stand being provided With means to support a roll of a web, a dusting chamber adapted to deliver a generally planiforrn stream of dust dispersed in a gas, said planiform stream directed generally toward the point of contact of the web with the roll at a location between the roll surface and the surface of the web about to contact the roll and means to maintain the dusting chamber in spaced relationship from said point of contact.

Further features and advantages of the invention will be more apparent from the following description and specification taken in connection with the accompanying drawing wherein:

FIGURE 1 is a schematic partly-in-section side view of a dusting apparatus in accordance with the invention;

FIGURES 2 and 3 are views of the dusting chamber utilized in FIGURE 1, and

FIGURE 4 depicts an alternate manner of positioning the dusting chamber with respect to the roll.

In FIGURE 1 there is delineated a partly-in-section schematic representation of a dusting apparatus generally designated by the reference numeral 10. The apparatus 10 comprises a base member 11 carrying an unwind stand 12 which in turn supports a mill roll 13. Adjacent to the unwind stand 12 is a roll support 15 supported from the base 11 by the pivot 16. The roll support 15 carries a snubber roll 17 remotely positioned from the pivot roll 16 and secured in generally parallel relationship to the mill roll 13. Generally adjacent to the snubber roll 17 is an idler roll 19. Adjacent the idler roll 19 and remote from the snubber roll 17 is a dancer roll 21. Generally adjacent to the dancer roll 21 and remote from the idler roll 19 is a second idler roll 22. Generally adjacent the idler roll 22 is a movable idler roll 24. The movable idler roll 24 is supported by the roll support arms 26 which are pivotally afiixed to the base member 11 by means of the pivot 28. The roll supports 15 and 26 are joined by means of arms 29 which are aflixed to the roll support 15 at the pivot 30 and to the roll support 26 by the pivot 32. A dusting chamber 35 is adjustably afiixed to the roll support 26. The chamber 35 is provided with conduits 36. The conduits 36 are in full communication with a flexible conduit 38 which in turn receives a dust air dispersion from the mixing device 40. The mixing device 40 comprises a trough having a hollow body 42 and an upwardly facing opening 43. The body 42 has a gas inlet 45 which terminates in a nozzle 46. The nozzle 46 is spaced from and is generally coaxial with an outlet 48 to which is secured the conduit 38. A vibratory feeder 50 provides a continuous supply of undispersed dust 51 to the mixing device 40. Positioned generally adjacent to the roll support 26 is a rewind stand 54. The rewind stand 54 carries a roll 55 formed from a web 55a which is Withdrawn from the mill roll 13, passed under roll 17, over roll 19, under roll 21, over roll 22 and under roll 24 and onto the surface of roll 55.

In FIGURES 2 and 3 there is represented a side and end View of the dusting chamber 35. The dusting chamber 35 comprises a body portion 54 partially defining a generally cylindrical space 56. The body 54 also defines a tampering slot-like orifice 57 for the discharge of the dust dispersion. The terminal portions of the cavity 56 are closed by the

end plates

59 and 59a. A plurality of spaced conduits 36 penetrate the body 54 and discharge into the cavity 56 generally along the axis of the conduits 36.

FIGURE 4 depicts an alternate follower arrangement generally designated by the reference numeral 60. This embodiment of the invention comprises a dusting chamber carrier 61 supporting a movable idler roll 62. The carrier 61 also supports a dusting chamber 64 which delivers a generally planiform stream of dust. The carrier 61 is supported by a pair of bell cranks 67 and 68. The bell crank 67 is pivotally attached to the carrier 61 by the pivot 70 while the bell crank 68 is pivotally attached to the carrier 61 by the pivot 71. The bell cranks 67 and 68 are rotatably supported by a frame 69 at the pivot points 73 and 74. The arm of the bell crank 67 opposite the pivot point 70 is pivotally attached to a follower arm 75 and a connecting link 76 by means of the pivot 78. The connecting arm 76 is connected to the bell crank 68 by means of the pivot 79. The follower arm 75 is connected to the pivot 78 of the bell crank 67, passes through a guide 80 which is fixed relative to the pivot points 73 and 74. A follower roll 81 is carried by the end of the follower arm 75 remote from the pivot 78. The follower roll 81 is adapted to engage a mill roll 84 upon which is being wound a web 85. The planiform dust dispersion 65 is directed toward the point of contact between the web 85 and the roll 84.

The apparatus of FIGURE 1 in normal operation feeds the web 55a from the mill roll 13 underneath the follower roll 17 over the idler roll 19 under the dancer roll 21, which serves to maintain constant tension on the web between the mill roll 13 and the mill roll 55. The idler roll 22 serves to guide the web beneath the movable idler 24 and maintain a desired point of contact between the web 55a and the roll 55. As the mill roll 13 is reduced in diameter the mill roll 55 increases in diameter. The follower roll 17 contacts the periphery of mill roll 13 and moves toward its axis of rotation. Thus the roll support causes the connecting arm 29 to move toward the unwind stand 12 thus withdrawing the dusting chamber 35 from the center of rotation of the mill roll 55 as its diameter increases. The dusting chamber 35 provides for a generally circular path of the dust dispersion within the container prior to being ejected from the slot 57. The configuration of the inlet conduits 36 to the chamber 35 effectively prevents dust from being retained within the chamber 35 due to the generally tangential entry of the air. Beneficially a dust mixture may be supplied to the dusting apparatus in accordance with the invention by means of an air conveyer substantially as shown in FIGURE 1. The trough or container 42 is filled with the dust to be dispersed. A gas such as air issuing from the nozzle 46 tends to entrain the surrounding dust and force it into the conduit 48. Effectively the arrangement of the nozzle and the conduit comprises a venturi system and is eminently successful in providing dispersions of finely divided particles in a gas such as a dispersion of finely powdered starch in air. Advantageously a vibratory feeder may be utilized to maintain a convenient level of the undispersed dust in the dispersing unit 40. The embodiment illustrated in FIGURE 1 is eminently suitable for most dusting applications wherein the variation in diameter of a roll being rewound is not greater than about 4:1. That is, the maximum diameter of the roll is about 4 times the diameter of the core from which the film is being rewound or the undusted roll is not reduced to a diameter less than A of its original diameter. As is obvious the displacement of the dusting chamber 35 is not directly in relation to the increase in diameter of the mill roll 55. However, for many dusting operations this arrangement is eminently satisfactory.

When extremely large rolls wound on small cores are utilized, the embodiment of FIGURE 4 is particularly advantageous. In operation of the embodiment of FIG- URE 4 the dusting chamber 64 and the idlerroll 62 are supported on the carrier 61. The carrier 61 in turn is movably supported at the pivot points 70 and 71 by the bell cranks 67 and 68 respectively. As the mill roll 84 increases in diameter the follower roll 81 positioned against the outer undusted surface of the film is forced through the guide rotating the bell crank 67 about its pivot point 73; however, the connecting arm 76 alters the bell crank 68 about its pivot point 74 in a manner similar to the positioning of the bell crank 67. Thus the dusting chamber is positioned relative to the contact point of the web and the roll 84 in a manner which is substantially proportional to the diameter of the mill roll 84.

By way of further illustration, the dusting apparatus has been employed successfully with very satisfactory results for applying starch dusts to normally crystalline vinylidene chloride polymer films varying in thickness from one-half to 3 mils at rates of between 3 to 500 feet per minute. No significant operation difiiculties have been encountered when dry dispersible dusts are employed. However, when dust carrying appreciable quantities of water or when dusts are dispersed with air in which water was entrained, tendencies to plug may be encountered.

Under normal operating conditions, the apparatus runs continuously for extended periods of several months and longer, continuously providing a uniform coating of dust to the surface of the dielectric film and removing and cleaning the dust laden air without contamination of adjacent areas. Tendency to give dust patterns or streaks or non-uniform application, as is plainly evident in the conventional types of apparatus that are usually employed for such operation, is absent for all practical purposes when the apparatus of this invention is used.

The apparatus of the invention has been illustrated and described in its most simple form. It should be understood that more elegant positioning devices may be utilized, for example, the follower roll 81 is readily replaced with an optical sensing device or even an ultrasonic sensing device in order to avoid any contact with the surface of the roll and pushing of the carrier 61 is then readily accomplished by means of suitable servo mechanisms well known to the art. Conveniently a sensing element such as an ultrasonic detector or optical detector in conjunction with a null-balance bridge is suitably used to control the servo mechanism. However, for the majority of applications such elegant instrumentation is not necessary. Extended operation of dusters fabricated substantially as shown in lFIGURES 1-3 of the present application indicate that dispersion of dust is very uniform, control is precise, and changes in the dust coating with changes in humidity of room air are very small and are generally insignificant. Also films having varying electrostatic charges on their surfaces are dusted uniformly. One significant advantage of the present invention is the lack of stray dust and loss of dust to the surrounding atmosphere. As the dust is, blown through the windup net, it appears to be retained by the film rather than losing a majority portion of the dust to the surrounding atmosphere.

As is apparent from the foregoing specification, the apparatus and method of the present invention are susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. For this reason, it is to be fully understood that all of the foregoing is intended to be merely illustrative and is not to be construed or interpreted as being restrictive or otherwise limiting of the present invention, excepting as it is set forth and defined in the hereto appended claims.

What is claimed is:

1. A method of dusting the surface of a web comprising directing a gaseous dispersion of the dust in the form of a generally planiform blast on to the surface of a web as it is being wound onto a roll the planiform blast being directed toward the point of contact of the web surface with the roll and maintaining the supply of said dust at about a constant rate for the entire winding operation.

2. A method of claim 1 wherein a source of dust dis- 2,057,548 10/1936 Wallach et a1. 117--16 persion is maintained at substantially a constant distance 2,163,642 6/1939 Waliaeh 11716 from the point of contact of the web with the roll. 2,936,473 5/1961 Ritzerfeld t a1, 117- 16 3. The method of claim 1 wherein the dust dispersion ,035 5 4 19 4 sheeban 117 1 is a dispersion of dust in air and the web is a therm pl 5 3,163,553 12/1964 Commanday et a1. 7 tic web.

References sited WILLIAM D. MARTIN, Primary Examiner. UNITED STATES PATENTS A. H. ROSENSTEIN, P. F. ATTAQUILE, 1,008,993 11/1911 Seward 242--83 Assistant Examiners.

1,745,644 2/1930 Royle 242-82 10

Claims

1. A METHOD OF DUSING THE SURFACE OF A WEB COMPRISING DIRECTING A GASEOUS DISPERSION OF THE DUST IN THE FORM OF A GENERALLY PLANIFORM BLAST ON TO THE SURFACE OF A WEB AS IT IS BEING WOUND ONTO A ROLL THE PLANIFORM BLAST BEING DIRECTED TOWARD THE POINT OF CONTACT OF THE WEB SURFACE WITH THE ROLL AND MAINTAINING THE SUPPLY OF SAID DUST AT ABOUT A CONSTANT RATE FOR THE ENTIRE WINDING OPERATION.