Abstract:
Disclosed is a sheet repositionable that is attracted to a nearby object by electrostatic charges. The sheet requires no pressure sensitive adhesive to stick to the object. The sheet is attracted to the nearby object by electrostatic charges on the sheet. The sheet has a first surface and a second surface. The electrostatic charges may be on the first surface, on the second surface, or on both the first surface and the second surface. The electrostatic charges have both a magnitude and a polarity that can be either positive or negative. The charges on the sheet may be all positive, the charges may be all negative, or the sheet may have regions of positive electrostatic charges and regions of negative electrostatic charges. In each case, the magnitude of the charges is sufficient to attract the sheet to the nearby object. Once the sheet is in contact with the object, electrostatic charges causes the sheet to stick to the object.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND 
       [0003]    Repositionable adhesive note papers, charts and posters are available commercially and provide a substantial volume of business. The adhesive utilized in many of these products is applied to a narrow band along the edge of the repositionable sheets. Information relevant to adhesives used for these products can be found in U.S. Pat. No. 3,691,140 September 1972 to Silver, U.S. Pat. No. 3,857,731 December 1974 to Merrill, and U.S. Pat. No. 5,153,041 June 1992 to Clements et al. that describes a pressure sensitive adhesive comprising inherently tacky, elastomeric copolymer microspheres protruding from a binder. The narrow band of pressure sensitive adhesive must be applied to the edge of each sheet during the manufacturing process. 
         [0004]    The binders for the pressure sensitive adhesive layer are often polymers that are soluble in solvents that are harmful to human health and to the environment. The manufacturing processes that uses these solvents employ safeguard to protect operators and machinery to capture the solvents before they are emitted to the environment. Even with state-of-the-art safeguards and solvent capture technologies, workers continue to be exposed to solvents and solvents continue to be emitted into our environment. 
         [0005]    A common feature of pressure sensitive adhesive layers is that the layer on the note paper, chart or poster must physically touch the surface to stick the sheet to the surface. When the adhesive layer does not touch the surface, the sheet does not stick to the surface. 
         [0006]    Commonly, the adhesive layer on a sheet will become contaminated with dust or paper fibers. Consequently, the sheet loses its ability to stick to surfaces after a few repeated uses. 
         [0007]    For the foregoing reasons, there is a need for a method to attract sheets to nearby objects while eliminating the use of solvents in the manufacturing process and so that the sheets are attracted to the object even when the sheets are simply near the object and do not touch the surface. 
       SUMMARY 
       [0008]    The present invention is directed to a sheet that is attracted to a nearby object. The sheet requires no pressure sensitive adhesive to stick to the object. The sheet is attracted to the nearby object by electrostatic charges on the sheet. Electrostatic charges have both a magnitude and a polarity that can be either positive or negative. As will be describe, the charges on the surface of the sheet may be all positive, the charges may be all negative, or the sheet may have regions of positive electrostatic charges and regions of negative electrostatic charges. In each case, the magnitude is sufficient to attract the sheet to the nearby object. Once the sheet is in contact with the object, electrostatic charges causes the sheet to stick to the object. 
         [0009]    Electrostatic charges may be applied to the surface of the sheet during the manufacturing process using, for example, a corona device as described in U.S. Pat. No. 4,591,713 to Gundlach and Bergen entitled “An Efficient, Self-Limiting Corona Device For Positive Or Negative Charging.” The electrostatic charges must persist to cause the sheet to be attracted to nearby objects later when the sheet is used. Electrostatic charges persists on electrically insulating surfaces, which have high surface electrical resistivities. The electrical resistivities of surfaces may be measured by several different methods. One such method is describe in ASTM D257 Standard Test Method for DC Resistance or Conductance of Insulating Materials. Using this method, we find that the surface electrical resistivity of the sheet must be at least 1.0×10 +13  ohms for the electrostatic charges applied to the surface of the sheet to persist and later cause the sheet to be attracted to a nearby object. 
         [0010]    The electrostatic charges on the sheet may be measured by several different methods. One such method is to place the sheet on a grounded, conducting object such as a flat piece of sheet metal. The electrostatic charges on the exposed surface of the sheet cause the exposed surface to have a surface potential. The surface potential may be measured using a non-contacting electrostatic voltmeter such as Trek Model 370 electrostatic voltmeter. The non-contacting electrostatic voltmeter measures the surface potential in units of volts. Using this method, we find that the magnitude of the surface potential must exceed 100 volts for the sheet to be attracted to nearby objects. 
         [0011]    The electrostatic charges on the sheet need not cover the entire surface of the sheet. In another version of the present invention, the electrostatic charges are confined to a row of charges on a surface of the sheet. 
         [0012]    The sheet has a first surface and a second surface. In yet another version of the present invention, the electrostatic charges on the sheet are confined to a first row of charges on the first surface and a second row of charges on the first surface of the sheet where the charges in the second row have the same polarity as the electrostatic charges in the first row. 
         [0013]    In yet another version of the present invention, the electrostatic charges are confined to a first row of charges on the first surface and a second row of charges on the second surface of the sheet where the charges in the second row have the same polarity as the electrostatic charges in the first row. 
         [0014]    When the electrostatic charges on the sheet have only one polarity, that is, when the charges on the sheet are all positive or the charges on the sheet are all negative, the sheet is attracted to the nearby object when the distance between the sheet and the nearby object is smaller than the width of the sheet. For larger sheets that are, for example, the size of a wall poster, electrostatic attraction when the sheet is relatively far from the nearby object makes the sheet hard to handle and difficult to position onto the nearby object. 
         [0015]    In yet another version of the present invention, the electrostatic attraction to the nearby object occurs only when the sheet is very close to the nearby object making the sheet easier to handle and easier to position onto the surface. In this version of the present invention, the electrostatic charges are confined to a first row of charge on the first surface and a second row of charge also on the first surface. The second row of charges has a polarity opposite to the polarity of the first row of electrostatic charges. The magnitude of the first row of charges together with the magnitude of the second row of charges are sufficient to attract the sheet to a nearby object. 
         [0016]    With two rows of electrostatic charge having opposite polarities, the sheet is attracted to the nearby object when the distance from the sheet to the nearby object is no greater than the distance from the centerline of the first row to the centerline of the second row. For example, when the distance from the centerline of the first row to the centerline of the second row is one inch, a wall poster sized sheet will be attracted to the nearby object when the sheet is no greater than one inch to the object. Having the sheet attracted to the nearby object only when the sheet is close to the nearby object makes the sheet easier to handle and position. 
         [0017]    The electrostatic charges in the first row cause the sheet surface in the row to have a surface potential. Similarly, the electrostatic charges in the second row cause the sheet surface of the second row also to have surface potential. The surface potentials may be measured using a non-contacting electrostatic voltmeter such as Trek Model 370 electrostatic voltmeter. Using this method, we find that the magnitudes of the surface potentials must exceed 100 volts in each row for the sheet to be attracted to the nearby object. 
         [0018]    In yet another version of the present invention, the first surface of the sheet has a first row of electrostatic charges and the second surface of the sheet has a second row of electrostatic charges. The electrostatic charges applied to the sheet in the manufacturing process must persist to cause the sheet to be attracted to a nearby object later when the sheet is used. Consequently, both the first surface and the second surface of the sheet must be electrically insulating. The electrical resistivities of surfaces may be measured by several different methods. One method is describe in ASTM D257 Standard Test Method for DC Resistance or Conductance of Insulating Materials. Using this method, we find that the surface electrical resistivity of the top surface of the sheet and the surface electrical resistivity of the bottom surface of the sheet must be at least 1.0×10 +13  ohms for the electrostatic charges to persist and later cause the sheet to be attracted to a nearby object. 
         [0019]    In yet another version of the present invention, the electrostatic charges are arranged in multiple rows on the first surface of the sheet. The electrostatic charges in each row have the same polarity. 
         [0020]    In yet another version of the present invention, the electrostatic charges are arranged in multiple rows on the first surface of the sheet. The electrostatic charge in each row have alternating polarities. That is, the first row has positive electrostatic charge, the second row has negative electrostatic charges, and the polarities of subsequent rows alternate. 
         [0021]    In yet another version of the present invention, the electrostatic charges on the first surface are arranged in multiple rows and the electrostatic charges on the second surface are also arranged in multiple rows. The polarities of the charges arranged in rows on the first surface all have the same polarity. And, the polarities of the charges arranged in rows on the second surface all have the same polarity that is opposite to the polarity of charges on the top surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawing where: 
           [0023]      FIG. 1  is perspective view showing electrostatic charges arranged in rows on the first surface of the sheet. 
           [0024]      FIG. 2  is a side view showing a sheet attracted to a nearby object by rows of positive electrostatic charges and by rows of negative electrostatic charges. 
           [0025]      FIG. 3  is a side view showing a sheet with rows of positive electrostatic charges and rows of negative electrostatic charges with no attraction to a nearby object that is too far away. 
           [0026]      FIG. 4  is a perspective view showing a mask for depositing rows of positive electrostatic charges on the first surface of the sheet. 
           [0027]      FIG. 5  is a perspective view showing a mask for depositing rows of negative electrostatic charges on the first surface of the sheet. 
           [0028]      FIG. 6  is a side view showing rows of electrostatic charges being measured using a non-contacting electrostatic voltmeter. 
           [0029]      FIG. 7  is a plot of the surface potential measured using a non-contacting electrostatic voltmeter showing rows of electrostatic charges. 
           [0030]      FIG. 8  is a perspective view showing rows of positive electrostatic charges on the first surface and rows of positive electrostatic charges on the second surface of the sheet. 
           [0031]      FIG. 9  is a side view of the sheet attracted to a nearby object by rows of electrostatic charges. 
           [0032]      FIG. 10  is a perspective view showing rows of positive electrostatic charges on the first surface and rows of negative electrostatic charges on the second surface of the sheet. 
           [0033]      FIG. 11  is a side view showing a sheet attracted to the nearby object by rows of positive charges on the first surface and rows of negative charges on the second surface. 
           [0034]      FIG. 12  is a side view showing a sheet with rows of positive charges on the first surface and rows of negative charges on the second surface with no attraction to the nearby object that is too far away. 
           [0035]      FIG. 13  is a perspective view showing positive rows of static charges being applied to a sheet by a conductive brush. 
           [0036]      FIG. 14  is a perspective view showing rows of negative static charges being applied to a sheet by a conductive brush. 
       
    
    
     DESCRIPTION 
       [0037]    In the Summary above, in this Description, in the claims below, and in the accompanying drawings, reference is made to particular features of the invention. It is to be understood that the disclosure of the invention in this specification includes all possible combinations of such particular features. For example, where a particular feature is disclosed in the context of a particular aspect or embodiment of the invention, or a particular claim, that feature can also be used to the extent possible, in combination with and/or in the context of other particular aspects and embodiment of the invention, and in the invention generally. 
         [0038]    The term “comprises” and grammatical equivalents thereof are used herein to mean that other components, ingredients, steps etc. are optionally present. For example, an article “comprising” (or “which comprises”) components A, B, and C can consist of (i.e., contain only) components A, B, and C, or can contain not only components A, B, and C but also one or more other components. 
         [0039]    The term “at least” followed by a number is used herein to denote the start of a range beginning with that number (which may be a range having an upper limit or no upper limit, depending on the variable being defined). For example, “at least 1” means 1 or more than 1. The term “at most” followed by a number is used herein to denote the end of a range ending with that number (which may be a range having 1 or 0 as its lower limit, or a range having no lower limit, depending upon the variable being defined). For example, “at most 4” means 4 or less than 4, and “at most 40%” means 40% or less than 40%. When, in this specification, a range is given as “(a first number) to (a second number)” or “(a first number)-(a second number),” this means a range whose lower limit is the first number and whose upper limit is the second number. For example, 25 to 100 mm means a range whose lower limit is 25 mm and whose upper limit is 100 mm. 
         [0040]      FIG. 1  shows a prospective view of a sheet  101  having width W SHEET    112  and length L SHEET    113 . The sheet comprises a first surface  102  and a second surface  103 . The first surface  102  has rows of positive electrostatic charges  104  and has rows of negative electrostatic charges  106 . The distance between the rows of charge is C  108 . 
         [0041]      FIG. 2  shows a side view of a sheet  201  having length L SHEET    213 . The sheet  201  has a bottom surface  202  and top surface  203 . The top surface  203  has positive static charges arranged in rows  204  and negative static charges arranged in rows  206 . When the distance D  217  from the sheet  201  to the nearby object  220  is at most the distance C  208  from a row of positive electrostatic charges to a row of negative electrostatic charges, electric field lines  222  reach the nearby object  220 . Consequently, the rows of positive electrostatic charges  204  and the rows of negative electrostatic charges  206  attract the sheet  201  to the nearby object  220 . For example, when distance C  208  from a row of positive electrostatic charges to a row of negative electrostatic charges is 1 inch, the rows of positive static  204  and rows of negative static  206  attract the sheet to the nearby object  220  when the distance D  217  is at most 1 inch. 
         [0042]    In use, dust or paper fibers may be on the second surface  203  of the sheet  201 . The dust particles or paper fibers separate the second surface of the sheet  203  from the nearby object  220 . Consequently, in repeated use, the second surface  203  my not touch the nearby object  220 . However, even when the second surface  203  of the sheet  201  does not touch the nearby object  220 , the rows of positive electrostatic charge  204  and the rows of negative electrostatic charge  206  attract the sheet  201  towards the nearby object  220 . 
         [0043]      FIG. 3  shows a side view of a sheet  301  that is not attracted to a nearby object  320 . The sheet  301  has a first surface  302  and a second surface  303 . The first surface  302  has rows of positive charges  304  and rows of negative charges  306 . The distance D  317  between the sheet  301  and the nearby object  320  is greater than the distance C  308  from a row of positive charges  304  to a row of negative charges  306 . The electric field lines  322  do not reach the nearby object  320 . Consequently, the rows of positive charges  304  and the rows of negative charges  306  do not attract the sheet towards the nearby object  320 . 
         [0044]    The separation distance C  308  between rows of positive electrostatic charges  304  and rows of negative electrostatic charges  306  is selected to determine the distance at which the electrostatic charges will attract the sheet  301  towards the nearby object  320 . The rows of positive electrostatic charge  304  and the rows of negative electrostatic charges  306  must provide strong attraction to the nearby object  320  when the distance D  317  from the sheet  301  to the nearby object  320  is small. We find that the distance C  307  must be at least 0.04 inches. 
         [0045]    It is highly desirable for the rows of positive electrostatic charge  304  and rows of negative electrostatic charges  306  to provide no attraction when the distance D  317  from the sheet  301  is at least 6 inches. In use, wall poster size sheets need to be positioned prior to being stuck to a surface. When the sheet  301  is far from the nearby object  320 , that is, when the distance D  317  between the sheet  301  and the nearby object  320  is at least 6 inches, attraction of the sheet  301  to the nearby object  320  is undesirable because this attraction interferes with positioning of the sheet  301  onto the nearby object  320 . 
         [0046]    Consequently, the distance C  308  between rows of positive electrostatic charges  304  and rows of negative electrostatic charges  306  should be at most 6 inches. The useable range for the distance C  308  is 0.04 inches to 6 inches. Preferably, the distance C should be 0.5 inches. 
         [0047]      FIG. 4  is a prospective view showing a method for applying rows of positive electrostatic charges  404  to a sheet  401 . A mask  405  is placed on the first surface  402  of the sheet. Positive electrostatic charges are then applied uniformly from above the sheet  401  towards the first surface  402  of the sheet covered by the mask  405 . Holes  428  in the mask expose the first surface  402  of the sheet  401  allowing positive electrostatic charges to be applied to the first surface  402  in rows  404 . The spacing between the rows of positive electrostatic charges is 2 C  409  that is determined by the spacing between the holes  428  in the mask. 
         [0048]    The positive electrostatic charges may be applied using, for example, a corona charge such as found in U.S. Pat. No. 4,591,713 May 1986 to Gundlach and Bergen entitled “AN EFFICIENT, SELF-LIMITING CORONA DEVICE FOR POSITIVE OR NEGATIVE CHARGING.” After the charges are applied, the mask  405  is removed. Rows of positive static charges remain on the first surface  402  of the sheet  401 . 
         [0049]      FIG. 5  is a prospective view showing a method for applying rows of negative electrostatic charges  506  to a sheet  501 . A mask  507  for making rows of negative electrostatic charges is placed on the top surface  502  of the sheet. Negative electrostatic charges are then applied uniformly from above the sheet  501  towards the upper surface  502  of the sheet covered by the mask  507 . Holes  528  in the mask expose the first surface  502  of the sheet  501  allowing negative electrostatic charges to be applied to the first surface  502  in rows  506 . The spacing between the rows of negative electrostatic charges is 2 C  510  that is determined by the spacing between the holes  528  in the mask. 
         [0050]    The negative electrostatic charges may be applied using, for example, a corona charge such as found in U.S. Pat. No. 4,591,713 May 1986 to Gundlach and Bergen entitled “AN EFFICIENT, SELF-LIMITING CORONA DEVICE FOR POSITIVE OR NEGATIVE CHARGING.” After the charges are applied, the mask is removed. Rows of negative static charges  506  remain on the first surface  502  of the sheet  501 . 
         [0051]      FIG. 6  is a side view showing a method for measuring the rows of positive electrostatic charges  604  and the rows of negative electrostatic charges  606  on the first surface  602  of a sheet  601 . The second surface  603  of the sheet  601  is in contact with a grounded, conducting object  621  such as a piece of sheet metal connected electrically to ground potential. Rows of positive electrostatic charges  604  and rows of negative electrostatic charges  606  on the exposed first surface  602  of the sheet  601  cause the top surface  602  to have a surface potential that is proportional to the charge. The surface potential is measured by the probe  615  of a non-contacting electrostatic voltmeter such as a Trek Inc. Model 370 DC-Stable Electrostatic Voltmeter is positioned above the top surface  602  of the sheet  601  at a distance G ESVM    616  that is 1.5±0.5 mm that is recommended by the vendor. 
         [0052]    The probe  615  of the electrostatic voltmeter is moved by hand from the first end  629  of the sheet  601  down the length L SHEET    613  of the sheet  601  to the second end  630  of the sheet  601 . Then, the probe  615  of the electrostatic voltmeter is moved by hand from the second end  630  of the sheet  601  down the length L SHEET    613  of the sheet  601  back to the first end  629  of the sheet  601 . The voltage V ESVM    614  measured by the non-contacting electrostatic voltmeter is proportional to the positive charges arranged in rows  604  and to the negative charges arranged in rows  606  on the exposed first surface  602  of the sheet  601 . 
         [0053]      FIG. 7  shows a plot of the voltage V ESVM    614  measured on a sheet  601  in  FIG. 6  having 3 rows of positive electrostatic charges  604  and 3 rows of negative electrostatic charges  606 . The horizontal axis of the plot in  FIG. 7  is time measured in seconds beginning at 0 seconds and ending at 20 seconds. The vertical axis of the plot in  FIG. 7  is the surface potential measured in volts beginning at −600 volts and ending at +1000 volts. 
         [0054]    On the plot in  FIG. 7 , for the time from 0 to 2 seconds, the probe  615  in  FIG. 6  was stationary positioned over the first end  629  of sheet  601 . During the period of time from 0 to 2 seconds, the measured surface potential was constant having a value of approximately +90 volts. 
         [0055]    On the plot in  FIG. 7 , for the time from 2 to 8.5 seconds, the probe  615  was moved by hand from the first end  629  to the second end  630  of the sheet  601 . During the period of time from 2 to 8.5 seconds, the measured surface potential V ESVM    614  alternated 3 times from a voltage having a positive polarity and a magnitude exceeding 400 volts to a voltage having a negative polarity and a magnitude exceeding 200 volts. The  3  peaks in the surface potential having a positive polarity and a magnitude exceeding 400 volts correspond to rows of electrostatic charges having a positive polarity. The  3  peaks in the surface potential having a negative polarity and a magnitude exceeding 200 volts correspond to rows of electrostatic charges having a negative polarity. 
         [0056]    On the plot in  FIG. 7 , for the time from 8.5 to 9.0 seconds, the probe  615  in  FIG. 6  was stationary positioned over the second end  630  of sheet  601 . During the period of time from 8.5 to 9.0 seconds, the measured surface potential was constant having a value of approximately −350 volts. 
         [0057]    On the plot in  FIG. 7 , for the time from 9.0 to 16.5 seconds, the probe  615  was moved by hand from the second end  630  back to the first end  629  of the sheet  601  in  FIG. 6 . During the period of time from 9.0 to 16.5 seconds, the measured surface potential V ESVM    614  again alternated 3 times from a voltage having a negative polarity and a magnitude exceeding 200 volts to a voltage having a positive polarity and a magnitude exceeding 400 volts. During the period of time from 9.0 to 16.5 seconds, the shape of the surface potential is a mirror image of the shape of the surface potential measured during the period of time from 2.0 to 8.5 seconds because the probe  615  was moved over the exposed top surface  603  of sheet  601  having the same positive electrostatic charges arranged in rows  604  and the same negative electrostatic charges arranged in row  606 . 
         [0058]    On the plot in  FIG. 7 , for the time from 16.5 to 20.0 seconds, the probe  615  in  FIG. 6  was stationary positioned over the first end  630  of sheet  601 . During the period of time from 16.5 to 20.0 seconds, the measured surface potential was constant having a value of approximately +120 volts. The surface potential measured during the time period from 16.5 to 20.0 seconds is different from the surface potential measured of +90 volts during the time period from 0 to 2 seconds because the probe  615  was moved by hand and it was returned to a slightly different position at a time of 20 seconds than it started at a time of 0 seconds. 
         [0059]      FIG. 8  shows a prospective view of a sheet  801  having width W SHEET    812  and length L SHEET    813 . The sheet comprises a first surface  802  and a second surface  803 . The first surface  802  has rows of positive electrostatic charges  804 . The second surface  803  has rows of positive electrostatic charges  818 . The distance between a row of positive charges on the first surface  804  and a row of positive charges on the second surface  818  is C  808 . 
         [0060]      FIG. 9  shows a side view of a sheet  901  having width W SHEET    913 . The sheet  901  being attracted to a nearby object  920  has a first surface  902  and second surface  903 . The first surface  902  has rows of positive charges  904 . The second surface  903  has rows of positive static charges  918 . When the distance D  917  from the sheet  901  to the nearby object  920  is at most the width of the sheet W SHEET    913 , electric field lines  922  reach the nearby object  920 . Consequently, the rows of electrostatic charges  904  on the first surface  902  and the rows of positive charges  918  on the second surface  902  attract the sheet  901  towards the nearby object  920 . 
         [0061]      FIG. 10  shows a prospective view of a sheet  1001  having width W SHEET    1012  and length L SHEET    1013 . The sheet comprises a first surface  1002  and a second surface  1003 . The first surface  1002  has positive charges arranged in rows  1004 . The second surface  1003  has negative charges arranged in rows  1019 . The distance between the centerlines of rows of positive charges  1004  on the first surface  1002  and the centerlines of rows of negative charges  1018  on the second surface  1003  is C  1008 . 
         [0062]      FIG. 11  shows a side view of a sheet  1101  having Width W SHEET    1112 . The sheet  1101  has a first surface  1102  and a second surface  1103 . The first surface  1103  has positive charges arranged in rows  1104 . The second surface  1103  has negative charges arranged in rows  1119 . The distance between the centerlines of rows of positive charges  1104  and the centerlines of rows of negative charges  1119  is C  1108 . When the distance D  1117  from the sheet  1101  to the nearby object  1120  is at most the distance C  1108 , electric field lines  1122  reach the nearby object  1120 . Consequently, the rows of positive charges  1104  and the rows of negative charges  1119  attract the sheet  1101  to the nearby object  1120 . For example, when distance C  1108  is 1 inch, the sheet  1101  is attracted to the nearby object  1120  when the distance D  1117  is at most 1 inch. 
         [0063]      FIG. 12  shows a side view of a sheet  1201  having Width W SHEET    1212 . The sheet  1201  has a first surface  1202  and second surface  1203 . The first surface  1203  has positive charges arranged in rows  1204 . The second surface  1203  has negative charges arranged in rows  1219 . The distance between the centerlines of rows of positive charges  1204  and the centerlines of rows of negative charges  1219  is C  1208 . When the distance D  1217  from the sheet  1201  to the nearby object  1220  is greater than the distance C  1208 , electric field lines  1222  do not reach the nearby object  1220 . Consequently, the sheet  1201  is not attracted to the nearby object  1220 . For example, when distance C  1208  is 1 inch, the sheet is not attracted to the nearby object  1220  when the distance D  1217  is greater than 1 inch. 
         [0064]      FIG. 13  is a prospective view showing sheet  1301  arranged so that the first surface  1302  is exposed and so that the second surface  1303  is in contact with the metal bench top  1323  that is connected electrically to ground potential. The sheet  1301  is being pulled by hand so that it moves  1325  between a conductive brush  1311  and the metal bench top  1323 . 
         [0065]    U.S. Pat. No. 2,774,921 December 1956 to Walkup entitled “APPARATUS FOR ELECTROSTATICALLY CHARGING INSULATING IMAGE SURFACES FOR ELECTROPHOTOGRAPHY” describes an apparatus for applying electrostatic charges uniformly to an electrically insulating material that is on a conductive backing plate. The bristles of the conductive brush need not touch the surface of the insulating plate that is moving beneath the brush. Satisfactory results may be obtained with the bristles positioned somewhat above and out of contact with the surface. A potential source provides a DC voltage to the conductive brush through a suitable high-resistance electrically conductive material having a resistance in the range 10,000 ohms to 100 megaohms. 
         [0066]    The conductive brush  1311  in  FIG. 13  having a length L BRUSH    1332  is modified by removing some bristles forming regions having a width W GAP    1334  having no bristles and leaving regions having a width W BRISTLE    1333  having full length bristles. The full length bristles of the conductive brush  1311  may touch the exposed top surface  1302  of the sheet  1301 . The bristles need not touch the top surface  1302 . Satisfactory results may be obtained with the bristles positioned somewhat above and out of contact with the surface. 
         [0067]    The power supply  1326  provides a DC voltage V BRUSH    1327  to the conductive brush through a suitable resistor R  1331  having a resistance in the range 10,000 ohms to 100 megaohms. Preferably, resistor R  1331  has a resistance of 1 megaohm. 
         [0068]    When the power supply  1326  provides a positive voltage V BRUSH    1327 , electrostatic charges arranged in rows  1304  are applied to the exposed first surface  1302  of sheet  1301 . The distance 2 C  1309  between the centerlines of rows of positive charges  1304  is the sum of W BRISTLE    1333  and W GAP    1334 . 
         [0069]      FIG. 14  is a prospective view showing sheet  1401  arranged so that the second side  1403  is exposed and so that the first side  1402  is in contact with a metal bench top  1423  that is connected electrically to ground. The sheet  1401  is being pulled by hand so that it moves  1425  between a conductive brush  1411  and the metal bench top  1423 . The exposed second surface  1403  may touch the full length bristles of conductive brush  1411 . The bristles need not touch the bottom surface  1403 . Satisfactory results may be obtained with the bristles positioned somewhat above and out of contact with the surface. 
         [0070]    Power supply  1426  provides DC voltage V BRUSH    1427  to conductive brush  1411  through resistor R  1431  that has a resistance in the range 10,000 ohms to 100 megaohms. Preferably, resistor R  1431  has a resistance of 1 megaohm. 
         [0071]    When voltage V BRUSH    1427  is negative, rows of negative electrostatic charges  1419  are applied to the exposed second surface  1403  of the sheet  1401 . The conductive brush  1411  is physically identical to conductive brush  1311  in  FIG. 13 . However, conductive brush  1411  is shifted horizontally so that the rows of negative electrostatic charges  1419  are offset from the rows of positive electrostatic charge  1304  applied to the first surface  1301  in  FIG. 13 . The resulting pattern of rows of electrostatic charges are shown in  FIG. 12 . 
         [0072]    Using the method shown in  FIG. 13  and in  FIG. 14 , positive electrostatic charges arranged in rows were applied to the first surface of an insulating polypropylene sheet and negative electrostatic charges arranged in rows were applied to the second surface of the polypropylene sheet. The conductive brush had regions with no bristles having a width W GAP  of 0.5 inches. The conductive brush had regions with full length bristles having a width W BRISTLE  of 0.5 inches. The spacing from the tips of full length bristles of the conductive brush to the surface of the insulating sheet, the voltages used to apply the positive and negative electrostatic charges, and the resulting amount of sticking are summarized in Table 1. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Voltage set-points for samples 
               
             
          
           
               
                   
                   
                 Positive 
                 Negative 
                   
               
               
                 Sample 
                 Brush Spacing 
                 Voltage 
                 Voltage 
                 Comments 
               
               
                   
               
             
          
           
               
                 1 
                 0.25 inches 
                 +4.0 KV 
                 −2.8 KV 
                 Low level of sticking 
               
               
                 2 
                 0.25 inches 
                 +5.7 KV 
                 −4.0 KV 
                 Low level of sticking 
               
               
                 3 
                 0.25 inches 
                 +6.0 KV 
                 −4.3 KV 
                 Low level of sticking 
               
               
                 4 
                 Contacting 
                 +3.7 KV 
                 −3.0 KV 
                 Very sticky 
               
               
                 5 
                 Contacting 
                 +3.5 KV 
                 −2.7 KV 
                 Very sticky 
               
               
                 6 
                 Contacting 
                 +3.7 KV 
                 −3.0 KV 
                 Very 
               
               
                 7 
                 Contacting 
                 +3.7 KV 
                 −3.0 KV 
                 Sticky 
               
               
                 8 
                 Contacting 
                 +3.7 KV 
                 −3.0 KV 
               
               
                 9 
                 Contacting 
                 +3.7 KV 
                 −3.0 KV 
               
               
                 10 
                 Contacting 
                 +3.7 KV 
                 −3.0 KV 
               
               
                 11 
                 Contacting 
                 +3.7 KV 
                 −3.0 KV 
               
               
                 12 
                 Contacting 
                 +3.7 KV 
                 −3.0 KV 
               
               
                   
               
             
          
         
       
     
         [0073]    Preferably, the width W GAP  on the conductive brush having no bristles should be 0.5 inches and the width W BRISTLE  on the conductive brush having bristles should be 0.5 inches. Preferably, the full length bristles should touch the surface of the insulating sheet. Preferably, the positive voltage should be +3.7 KV and the negative voltage should be −3.0 KV.