Field of the Invention

This invention relates to label assemblies for improved non-jamming operation in all types of laser printers, and further relates to a method for making and printing on such label assemblies.

Background of the Invention

Sheets of labels are normally double thickness sheets which include a continuous backing sheet, often coated with a very thin release layer of silicone or the like, and an overlying label facestock sheet coated with a pressure-sensitive adhesive, so that the adhesive is between the backing and facestock sheets. The label facestock is often printed using laser printers. The most widely used laser printers are made by Hewlett-Packard and include the earlier-generation HP LaserJet 1, 2 and 3 models and the newer HP LaserJet 4 model. The HP LaserJet 4 printer was designed to have a smaller "footprint," i.e., take up less space on a desktop. Therefore, paper paths therein are more tortuous than in the earlier models as the twists and turns are more pronounced. Therefore, when label sheets are fed through the printers, there is a tendency for the label sheet to jam therein, particularly the HP LaserJet 4. There is also a tendency for some of the pressure- sensitive adhesive from the label sheets to build up on critical points and components in the printer, causing undesired jamming and misprinting. A user would then have to open the printer up and clean the accumulated pressure- sensitive adhesive off the components with a solvent. This procedure is bothersome and unproductive.

It has been determined that certain types of label sheets which are relatively stiff actually remove or "scrub" the pressure-sensitive adhesive from the

components. But these label sheets have also been relatively smooth and jam in the earlier models of Hewlett-Packard printers.

Therefore, there is an unfulfilled need in the prior art for a label assembly which is sufficiently stiff and which may be used in all types of laser printers, avoiding and even ameliorating the problems outlined above.

Summary of the Invention In accordance with a broad aspect of the present invention, label assemblies are made fairly stiff and with a relatively high coefficient of friction.

By making the label assemblies fairly stiff, they tend to pass through HP LaserJet 4 printers without depositing pressure-sensitive adhesive, and even pick up previous deposits of adhesive and clean up the machines.

With increased stiffness, however, using relatively smooth label assemblies, it has been determined that the labels do not feed readily through certain laser printers, such as the HP LaserJet models 1, 2 and 3. To overcome this problem and to provide a general purpose laser- printable label assembly, the coefficient of friction of the label assembly has been increased; and this may be accomplished by making the stiffer labels out of paper in the cross grain direction.

One object of the present invention is to provide a label assembly which does not jam in printers. It has been determined that label assemblies with a Taber stiffness in the neighborhood of 2.5 to 5.5 are able to pick up or "scrub" accumulated pressure-sensitive adhesive from printer components such as rollers, guide ribs, output guides, and paper sensors. In addition, a label assembly possessing such Taber stiffness preferably should also possess a coefficient of friction of at least 0.180 so that the label assembly is able to travel through the earlier-generation printers.

Furthermore, in order to achieve greater coefficients of friction, label assemblies of the present invention are cut from roll stock in the cross direction; that is, the longitudinal axis of the label assembly (defined as the axis parallel to the paper path of a printer) is parallel to the cross direction of the roll stock. As the physical properties of papers differ with respect to direction, the coefficient of friction of paper is greater in the cross direction than in the machine direction, such that the label assembly with the longitudinal axis in the cross direction has a greater coefficient of friction and is thus preferred, although high coefficients of friction may also be obtained with the longitudinal axis aligned with the machine direction of the papers. A further object of the present invention is to provide a label assembly which does not leak or deposit pressure-sensitive adhesive onto components of printers while being printed. It has been found that one of the primary reasons printing stock jams in printers is because of the build up of pressure-sensitive adhesive, particularly where the label sheets are experiencing a sharp turn or bend, for example at the rollers of the printers. Therefore, the label assembly according to a further preferred embodiment has the pressure-sensitive adhesive reduced at the leading edge and the trailing edge thereof, thereby reducing to a significant extent the amount of pressure-sensitive adhesive that leaks or is deposited within the printer. Furthermore, by cutting the label assembly from roll stock in the cross direction such that the leading edge and the trailing edge thereof are defined as the outside edges of the roll stock, the amount of pressure-sensitive adhesive to leak or ooze out of the side of the roll prior to cutting the label assemblies from the roll stock is reduced. Moreover, the processing of the label assemblies with reduced adhesive at the outside edges and longitudinally with respect to the roll

stock is more readily achieved than if the variations in adhesive thickness were accomplished in some type of alternating method across the width thereof in order to achieve the desired reduction at the leading and trailing edges of the label sheets.

Further objects of the present invention entail methods for preparing the label assemblies from roll stock. In order to yield a label assembly with the desired Taber stiffness and the corresponding desired coefficient of friction, the novel method provides steps for preparing and cutting the roll stock in such a way so as to achieve the desired physical properties of the label assemblies. More specifically, such a method includes the steps of forming roll stock out of facestock material releasably adhered to backing material by means of pressure-sensitive adhesive. The roll stock has with respect to a transverse axis thereof (which is in the cross direction) a Taber stiffness between about 2.5 and about 5.5 and a coefficient of friction of at least approximately 0.180. The roll stock is then cut into label assemblies such that longitudinal axes thereof (as defined as parallel to a paper path in a printer) are parallel to the transverse axis of the roll stock.

Another inventive method of the present invention defines the steps required for printing on label assemblies so that the label assemblies do not jam in various printers. This method is similar to the method outlined above but with an additional step of loading the label assemblies onto the multipurpose tray of a printer in a backing-to-face orientation. This orientation is defined as the backing sheet of the top label assembly abutting the facestock sheet of the second label assembly and so on. It has been found that this orientation yields the most preferred coefficients of friction, thereby reducing the chance of jamming and subsequent down-time to the greatest extent.

Other objects, features, and advantages of the invention will become apparent from a consideration of the following detailed description and the accompanying drawings.

Brief Description of the Drawings

FIG. 1 is a top plan view of an enhanced label assembly illustrating the principles of the present invention; FIG. 2 is a cross-sectional view of the label assembly taken along section 2-2 of FIG. 1;

FIG. 3 is a schematic cross-sectional view of a Hewlett-Packard LaserJet 4 laser printer, particularly showing paper paths therein; FIG. 4 is a perspective view of a roll of label assemblies illustrating the principles of the present invention;

FIG. 5A and 5B are graphs of coefficients of friction in the cross direction of four label assembly samples with respect to face-to-backing and backing-to-face orientations, respectively;

FIGS. 6A and 6B are graphs of coefficients of friction in the machine direction of four label assembly samples with respect to face-to-backing and backing-to- face orientation, respectively;

FIG. 7 is a top view of a label assembly according to another preferred embodiment, showing microperforations which divide the label assembly into subsheets; and

FIG. 8 is a cross-sectional view of the label assembly taken along section 8-8 of FIG. 7.

Detailed Description of the Preferred Embodiments

Referring to the drawings, particularly to FIGS. 1 and 2, an enhanced label assembly 10 for laser or other printers is shown in a preferred embodiment. The label assembly 10 generally comprises a facestock sheet 12 and

a backing sheet 14. Typically, the facestock sheet 12 is coated with pressure-sensitive adhesive 16, and the backing sheet 14 is coated with a release coating such as a silicone-based product. The pressure-sensitive adhesive 16 may also be applied directly to the release coating with the facestock sheet 12 subsequently applied thereto; In either case, the facestock sheet 12 is releasably mounted to the backing sheet 14. The facestock sheet 12 generally has one or more labels 18 die cut therein on which information may be printed.

Further referencing FIG. 3, a schematic cross- sectional view of a typical laser printer in use today, specifically a Hewlett-Packard LaserJet 4 laser printer, is shown. The printer employs a number of rollers 20 to propel paper, label sheets, or other printing stock therethrough. Paper Paths A and B illustrate paths which printing stock follow depending upon whether the printing stock is loaded into a multipurpose tray 22 or a paper cassette 24, respectively. As Paths A and B illustrate, the printing stock must travel a relatively tortuous path through the printer, a path consisting of a number of turns through the rollers 20. As the HP LaserJet 4 printer was designed to have a smaller "footprint" than earlier models (to take up less space on the desktop) . Therefore, the paper paths on the HP LaserJet 4 printer are more tortuous than previously, consisting of severe and pronounced turns around the rollers 20.

A drawback of printers of this type is that printing stock occasionally jams in the rollers 20. More specifically, pressure-sensitive adhesive of label sheets occasionally leaks or oozes out of the label sheets and becomes deposited on the rollers 20 and other components of the printer, such as guide ribs, output guides and paper sensors. The pressure-sensitive adhesive accumulates over time, thereby causing label sheets to jam and/or lowering the printing quality on labels. A user

must then clean the components with a solvent in order to restore normal operation and printing.

It has been found that by increasing the coefficient of friction of label sheets with respect to longitudinal axes thereof, i.e., axes parallel to paper paths in printers, particularly of the facestock sheet, label sheets are able to travel the tortuous paths found in many types of laser printers, even earlier generation models. It has been further found that label sheets with greater Taber stiffness with respect to the longitudinal axes thereof remove pressure-sensitive adhesive that may have accumulated on the rollers 20 or other components.

Incidentally, in order to avoid the rollers 20 needed to propel label sheets out of the paper cassette 24 along Path B, most users today feed label sheets into printers from the multipurpose tray 22; therefore, the multipurpose tray 22 is the preferred loading means.

Turning to another aspect of the label feeding analysis, by convention, the phrases "face to backing" and "backing to face" indicate the orientation of the printing stock while being loaded into the multipurpose tray 22 or the paper cassette 24. For label sheets being loaded into the multipurpose tray 22, backing to face is the orientation with the facestock sheet up and the backing sheet down such that the backing sheet abuts the facestock of the next lower label sheet. These designations will be discussed below, in connection with the analysis of the coefficient of friction of the label sheets.

With reference to FIG. 4, the label assemblies 10 are cut from roll stock as shown. By definition, the term "machine direction" (with the grain) refers to the direction in which paper-making machines form paper, such as the facestock sheet 12 and the backing sheet 14, as shown by reference arrow B. Conversely, the term "across machine direction" or "cross direction" (across the grain) is perpendicular to the machine direction, as shown by

reference arrow A. Furthermore, physical properties, e.g., Taber stiffness and coefficient of friction, of paper may be quite different in the machine direction and in the cross direction. Now, with reference to FIGS. 5A and 5B and FIGS. 6A and 6B, tests according to the "Standard Test Method for Coefficient of Static and Kinetic Friction of Uncoated Writing and Printing Paper by Use of the Horizontal Plane Method," as set forth by the America-- Society for Testing and Materials designation D4917, show coefficients of friction for different label sheets in the cross direction (FIGS. 5A and B) and the machine direction (FIGS. 6A and B) . As can be seen, coefficients of friction of the four samples are generally greater in the cross direction, as shown in FIGS. 5A and 5B, than in the machine direction, as shown in FIGS. 6A and 6B (but with certain exceptions) . Furthermore, coefficients of friction are generally greater in the backing-to-face orientation than in the face-to-backing orientation. Therefore, the coefficients of friction are greatest when the label assemblies are cut with the longitudinal axes thereof in the cross direction and loaded into printers in the backing-to-face orientation (with the facestock up) , particularly for Sample B and Sample C. Specifically, referring to FIGS. 6A and 6B, a label sheet according to the prior art is represented by Samples D-2 and D-4. This prior label sheet is cut from roll stock with the longitudinal axis thereof in the machine direction, has coefficients of friction in the different orientations which are lower than the other samples, and has a Taber stiffness of approximately 5.0. [Taber stiffness was determined according to the "Standard Test Method for Resistance to Bending of Paper and Paperboard (Taber-Type Tester)," ASTM designation D5342-93.] Although the Taber stiffness is relatively high, the coefficients of friction are significantly low so that

Samples D-3 and D-4 have the tendency to jam in printers, particularly in early generation laser printers.

Specifically referring to FIGS. 5A and 5B, Samples A- 1 and A-2 also represent label sheets according to prior art. Sample A is cut from roll stock with the longitudinal axis thereof in the cross direction, thereby yielding a greater coefficient of friction than if cut in the machine direction (cf., Samples A-3 and A-4 of FIGS. 6A and 6B) . But Samples A-l and A-2 have Taber stiffness of approximately 2.0. Therefore, although Samples A-l and A-2 do not readily jam in printers, there is not a preferable "scrubbing" of possibly accumulated adhesive within the printer.

Therefore, it is preferable for the label assembly 10 to have a Taber stiffness sufficiently great so as to "scrub" adhesive off components of the printer but not so great so as to cause the label assembly 10 to jam in the printer. Furthermore, it is preferable for the label assembly 10 to have a coefficient of friction sufficiently great so as to allow the label assembly 10 with an increased Taber stiffness to travel through all generations of printers without jamming, but not so great so that more than one label assembly is loaded into a printer from the multipurpose tray 22 or the paper cassette 24 by the rollers 20.

A label assembly according to a preferred embodiment of the present invention is represented by Sample B in FIG. 5B. The Taber stiffness of Sample B is generally in the range of 2.5 to 5.5 and is specifically approximately 3.20. It has been found that this Taber stiffness value is sufficiently great so that the label assembly 10 removes pressure-sensitive adhesive that has accumulated on components of printers. Furthermore, in order for the label assembly 10 to have Taber stiffness of the above magnitude and not to jam in printers, the coefficient of friction of the label assembly 10 should be at least about

0.180 and preferably about 0.214 to about 0.238.

A specific assembly of the label assembly 10 with these values is to have the facestock sheet 12 made from stock according to "Hammermill 50-pound accent opaque," and the backing sheet 14 made from stock according to "Rhinelander 2.5-mil EL, RHI Liner 20, No. 122-4212." It is preferable that the label assembly 10 be substantially rectangular, e.g., 8^ inches by 11 inches, Al size, legal size, etc., with the greater dimension in the longitudinal direction. The thickness of this label assembly is approximately 6.1 mils in that the thickness of the facestock sheet is approximately 3.6 mils and the thickness of the backing sheet is approximately 2.4 mils.

Likewise, a label assembly according to another preferred embodiment of the present invention is represented by Sample C in FIG. 5B. The Taber stiffness of Sample C is generally in the range of about 2.5 to about 5.5 and is specifically approximately 3.85. In order for the label assembly 10 with this Taber stiffness to possess the same desirable non-jamming characteristic as described above, the coefficient of friction of the label assembly 10 should be at least about 0.180 and preferably about 0.237 to about 0.289.

A specific assembly of the label assembly 10 with these values is to have the facestock sheet 12 made from stock according to "Georgia-Pacific 50-pound white Barracuda Label stock," and the backing sheet 14 made from stock according to "Rhinelander 2.5-mil EL, RHI Liner 20, No. 122-4212." Like above, it is also preferable for this label assembly to be rectangular. The overall thickness is approximately 6.3 mils in that the thickness of the facestock sheet is approximately 3.7 mils and the thickness of the backing sheet is approximately 2.5 mils.

Particularly referencing FIG. 2, the label assembly 10 is further distinguished from the prior art in that the pressure-sensitive adhesive 16 is reduced in thickness or

concentration at or near leading and trailing edges of the label assembly 10 as shown by reference A. The pressure- sensitive adhesive 16 is typically applied to the facestock sheet 12 uniformly at a concentration of approximately 17 grams per square meter, which corresponds to a thickness of approximately 0.68 mil. According to the present invention, this concentration is reduced at or near the leading and trailing edges of the sheet assembly 10 by at least eight percent and preferably by approximately 12%, or to a concentration of about 15 grams per square meter, which corresponds to a thickness of approximately 0.60 mil. Preferably, the pressure- sensitive adhesive 16 is reduced within approximately one- quarter inch of the leading and trailing edges. The reduction of pressure-sensitive adhesive 16 at the leading and trailing edges reduces or eliminates the leakage of the pressure-sensitive adhesive 16 onto components of printers, thereby further preventing jamming and misprinting. Furthermore, as the leading and the trailing edges represent the outside edges or transverse ends of the roll stock, less pressure-sensitive adhesive 16 is present on the transverse ends of the roll stock, thereby reducing waste and mess.

With reference to FIGS. 7 and 8, the label assembly 25 according to another preferred embodiment of the present invention may further be cut with icroperforations 26, thereby dividing the label assembly 25 into subsheets 28. The microperforations 26 are sized such that when torn through, the resultant edges of the subsheets 29 are substantially smooth. The label assembly 25 as shown in FIGS. 7 and 8 has been generally disclosed in U.S. Patent Application Serial No. 08/063,213, filed on May 17, 1993, and entitled "Divisible Laser Label Sheet." This species of label assembly provides a user the choice of printing the entire label assembly 25 or only one of the subsheets 28, thereby reducing the number of unused

labels and being more economical and less wasteful.

The present invention further provides a method for the preparation of the enhanced label assemblies. The method includes the steps of forming roll stock of facestock material and backing material with pressure- sensitive adhesive therebetween. It is preferable that the roll stock has a Taber stiffness between about 2.5 and about 4.5 and a coefficient of friction of at least approximately 0.180 in the cross direction, i.e., along the transverse axis. The roll stock is then cut along the transverse axis, thereby forming the label assemblies such that the longitudinal axes thereof are parallel with the cross direction. Furthermore, the pressure-sensitive adhesive 16 may be readily reduced in concentration as the leading edge and the trailing edge of the label assemblies are defined as the outside edges of the roll stock or in the longitudinal direction.

The present invention provides another method for printing label assemblies, particularly printing without the label assembly jamming in a printer. In addition, to the steps outlined about, this printing method further provides the step of loading the label assemblies onto the multipurpose tray of a printer in the backing-to-face orientation. As outlined above, this orientation as the backing sheet 14 of one label assembly abutting the facestock sheet 12 of a next lower label assembly. As the analysis of coefficients of friction indicated, this orientation is the most preferred in reducing the chance of jamming to the greatest extent. Accordingly, the present invention is not limited by the specific embodiments shown in the drawings and described in the detailed description, but is to be broadly interpreted commensurate with the scope of the appended claims.