Field of the Invention

This invention relates to the ion deposition printing of multiple layer sheets, such as sheets of labels having pressure sensitive adhesive thereon mounted on backing sheets.

Background of the Invention

Ion deposition printing is well known, and one of many U.S. patents describing ion printing apparatus is U.S. Patent No. 4,494,129, granted January 15, 1985 to Delphax Systems. Ion deposition printers may be purchased from various sources, including from C. Itoh Electronics Company, 2515 McCabe Way, P. O. Box 19628, Irvine, California 92713-9628.

Ion deposition printers provide an excellent printing capability, but have certain shortcomings. In this regard, it is noted that ion deposition printers apply relatively high levels of pressure between the output roller and the electrostatically chargeable drum, as the toner is being ap^ied to the sheet being printed. In the case of sheets of pressure sensitive labels which are fully coated with adhesive, and are mounted on backing sheets, ion deposition printing has the effect of curling up the edges and corners of the sheets, so that the sheets cannot practically be stacked, or used.

Accordingly, a principal object of the present invention is to provide a method for printing sheets of labels or similar materials mounted on backing sheets, by the ion deposition method; and a related object is to provide an improved dual thickness label-adhesive- backing sheet combination which may be used in ion deposition printers, without the curling problem discussed above.

Summary of the Invention

In accordance with the present invention, a method for preparing curl-free printed sheet of labels adhered with pressure sensitive adhesive to backing sheets includes the steps of (1) preparing dual layer sheets of labels and associated backing sheets with a discontinuous pattern of adhesive on the labels with the pattern of adhesive being in the form of closely spaced geometric figures with a narrow space between the 0 geometric figures of adhesive, and (2) printing onto the dual layer label sheets using an ion deposition type electrostatic printer, and (3) applying substantial pressure to the sheets in the course of the printing operation between an output pressure roller and an , c electrostatically chargeable drum employed in applying toner to the sheets.

In accordance with an additional feature of the invention, the geometric figures are preferably arranged so that at least some of the sides of the geometric figures are not parallel to the edges of the

20 labels, so that die cutting of the labels on the backing sheets does not provide edges which are likely to fold up out of the plane of the dual layer sheets. The patterns are preferably in an hexagonal configuration, but other configurations, such as adjacent diamonds,

25 could also be employed. The edges of the sheets may be provided with a narrow adhesive-free area.

In accordance with a further aspect of the invention, the adhesive is preferably a fairly resilient adhesive and not unduly hard, so that the high pressure

30 of the output rollers used in the ion deposition printing process do not damage the label stock, or cause the adhesive pattern to deform the labels stock significantly; but wherein the adhesive is sufficiently resilient to expand or flex under the high pressure of

35 the output rollers of the ion deposition printer,

absorbing the stress, and maintaining the flat configuration of the dual layer sheet, so that high resolution printing takes place. Other objects, features, and advantages of the invention will become - apparent from a consideration of the following detailed description and from the accompanying drawings.

Brief Description of the Drawings

Figure 1 is a perspective view of a dual layer i _Q sheet of printed labels mounted on a backing sheet;

Figure 2 is a top view of one of the labels from the sheet shown in Fig. 1;

Figure 3 is a rear view of the label of Fig. 2 showing the adhesive pattern; -, Figure 4A shows a dual layer sheet in accordance with the invention following printing through an ion deposition printer;

Figure 4B shows a dual layer label sheet having continuous adhesive on the back of the label sheet, which has been curled up as a result of being

20 printed in an ion deposition printer; and

Figure 5 is a schematic cross-sectional view of an ion deposition printer.

Detailed Description

25

Referring more particularly to the drawings, Fig. 1 shows a dual layer sheet 12 including an upper sheet made up of a large number of labels 14 which have been die-cut to be separate from one-another, and which are mounted on a backing sheet 16.

30

Figures 2 and 3 are front and back views, respectively, of one of the labels 14 which has been removed from the backing sheet 16. More specifically, on the front of the label 14 as shown in Fig. 2, is some printing or advertising 18, and a bar code configuration

35 20.

On the back of the label 14, as shown in Fig. 3 is a hexagonal pattern of pressure-sensitive adhesive 22. The adhesive pattern is made up of a series of hexagons 24 which are approximately 7/8 of an inch across from side to side, and which are separated by narrow bands 26 of adhesive-free label stock. The narrow adhesive-free bands are less than 1/16 inch in width, and are preferably in the order of 1/32 inch wide. 0 Around the entire periphery of the dual layer sheet of Fig. 1, is an adhesive-free zone. In this regard, attention is drawn to the label of Fig. 3 in which an adhesive-free narrow border 28 is shown at the right-hand edge of the label. The label of Fig. 3 may, _. _ for example, be drawn from the area designated 30 in Fig. 1, lying in the middle of the left-hand side of the sheet labels, so that the adhesive-free area 28 lies along the left-hand side of the sheet 12 as shown in Fig. 1.

Figure 4A shows a dual layer label sheet 12,

20 of the present invention, and having an adhesive pattern as shown in Fig. 3, in which the label sheet 12, following printing, is entirely level and flat. In Fig. 4B, however, the dual layer label sheet 32 has a continuous layer of adhesive on the back of the labels

25 between the label sheet and the backing sheet, and, following printing in an ion deposition printer, it curls up as indicated, particularly at the corners 34. This curling was found to be so significant that proper stacking of the printed sheet labels was not practical,

30 nor was further mechanical processing of the sheets.

Figure 5 is a diagrammatic showing of an ion deposition printer, of the type shown and described in some detail in U.S. Patent No. 4,494,129, cited hereinabove. More particularly, with reference to Fig.

35 5, the electrostatically chargeable drum 42 is shown

toward the center of Fig. 5, and the ion deposition matrix 44 is shown located immediately above the center of the drum 42. Following the electrostatic charging of selected areas on the drum 42 to form an image, toner from the toner hopper 46 is applied to the outer surface of the drum 42 via the toner applicator 48. The image produced by the application of toner to selected areas previously charged by the ion deposition matrix 44, is applied to the copy paper sheet 50 at point 52 where the pressure roller 54 bears against the drum 42. In the ion deposition process, moderately high levels of pressure, normally greater than 50 pounds per linear inch, and in some cases more than 100 pounds per inch, are present between the pressure roller 54 and the drum 42. It is this relatively high pressure which produces the curled copy paper sheets, as shown in Fig. 4B, when continuous adhesive is employed between the label sheet and the backing sheet. It is believed that the high pressure applied to the adhesive stresses the adhesive, deforming it to some extent, and causes the indicated deformation.

However, by utilizing a moderately resilient adhesive, and the narrow adhesive-free zones as shown at 26 in Fig. 3 of the drawings, the tension or strain produced by the high pressures at the nip area between the pressure roller 54 and the drum 42, may be accommodated, and printing accomplished while still producing flat output label sheets.

Various patterns of geometric areas of adhesive, with adhesive-free bands between the geometric areas, have been tried, and some configurations are superior to others. Thus, the hexagonal configuration shown in Fig. 3 is preferred. In this connection, it may be noted that the die-cut edges 62, 64 and 66 of the label 14 each have some zones along their length where adhesive is present, although in certain other areas

along their length, the edge may be coincident with one of the adhesive-free bands. In some cases where rectangular patterns were tried, the die-cut edge would extend entirely along an adhesive-free zone, and under these conditions, occasionally the label edge would de- laminate and interfere with the smooth feeding of the sheet. In addition, when very fine patterns were employed, particularly when relatively hard and unyielding adhesives were employed, interference with the smooth and even printing of the bar code was encountered, poor printing resolution resulted, with the result that some errors in the reading of the bar code occasionally occurred.

By way of example, one adhesive which was determined to be somewhat harder than desirable is the adhesive aesignated P-32 and available from Avery International Corporation, the assignee of the present invention. Typical adhesives which are more resilient and flexible, and which may preferably be employed in the implementation of the present invention include an adhesive made by Avery International Corporation, the assignee of the present invention, and designated No.P- 39, and an adhesive made by Malcom Nickel elt Company, of Lyndhurst, New Jersey, and designated Adhesive No. 1580. With regard to the coverage of the adhesive, it is desirable that the adhesive have relatively full coverage, and only have relatively narrow breaks in the coverage. In this regard, as mentioned above, the hexagonal pattern of adhesive, as shown in Fig. 3 of the drawings, includes hexagons having a size in which the distance between opposite flat sides is approximately 7/8 of an inch, and wherein the narrow spaces or bands between hexagons is approximately one thirty-second of an inch. It is believed that, as printing takes place, the resilient adhesive is squeezed by the high pressure at the nip between the pressure roller 54 and the drum

42, so that the adhesive advances at least partially into the narrow, normally adhesive-free bands between the hexagons; and printing of patterns, such as the bar code 20, shown in Fig. 2, is uniform and readable. However, in the event that the space between the geometric patterns is larger, for example, greater than 1/16 inch, or in the event that a harder adhesive is employed, the bar code printing is less regular, and occasional errors will occur in the reading of the bar code information in the course of marketing.

Concerning the adhesive pattern, it may be noted that the ratio of adhesive covered areas to adhesive-free areas is substantially greater than 10 to 1. More generally, it is considered that a ratio of more than 5 to 1 is preferred. Adhesive configurations using small circular areas or squares of adhesive were also tested, and they had good curl-free properties, but the printing resolution was not as good as would be desired. The squares used in the test were about 1/4 inch square and were spaced apart by about 1/4 inch. The circular areas were about 1/8 inch in diameter, and were spaced apart by about 1/8 inch.

In conclusion, it is to be understood that the foregoing description and the accompanying drawings relate to one illustrative embodiment of the invention. Various changes and modifications may be made without departing from the spirit and scope of the invention. Thus, the present invention is applicable to other printing methods where high pressures are applied to the multi-layer label sheets. In addition, it is to be understood that different geometric figures, such as diamonds, for example, could be used in place of the hexagonal pattern shown in the drawings. Further, the width of the narrow spaces between the geometric patterns may vary, in accordance with the type of adhesive which is employed, with slightly wider spacing

being employed, when the adhesive is softer and more resilient, and somewhat narrower spacing may be used when the adhesive is less soft and resilient. Accordingly, the present invention is not limited to the apparatus and method precisely as described in detail hereinabove, and as shown in the drawings.