DIGITALLY PRINTED HEAT TRANSFER LABEL

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/197,090, filed October 23, 2008, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

This disclosure is directed generally to heat transfer labels and, more particularly, digitally printed heat transfer labels and methods of making such labels.

BACKGROUND

Digital printing is used widely in the field of printing, particularly for the preparation of prototypes, low quantity print runs, and for the customization of print media. In contrast to many other printing techniques, digital printing does not require the preparation of costly printing plates and therefore allows for rapid transitioning between designs.

Despite its advantages, it is believed that digital printing has not been used to make heat transfer labels. Heat transfer labels are labels that are printed in reverse onto a release carrier and transferred to a container using heat and pressure. The present inventors have discovered that there are unique challenges associated with the use of digital printing technology to print onto substrates with release layers. In particular, the heat associated with the digital printing process can cause premature softening of the release layer, which may result in defects in the print quality of the label and/or the decorated container. Thus, there remains a need for a heat transfer label and assembly suitable for use with digital printing.

SUMMARY

This disclosure is directed generally to a heat transfer label assembly that may be suitable for use with digital printing technology. The heat transfer label assembly includes a plurality of layers or components in a facing, contacting relationship with one another. In one example, the heat transfer label assembly includes a primer layer that comprises one or more materials that work in concert to assist with maintaining the stability of the heat transfer label assembly during the digital printing process. Other features and aspects of the invention will be apparent from the following description and the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which: FIG. IA is a schematic cross-sectional view of an exemplary heat transfer label assembly;

FIG. IB is a schematic perspective view of a decorated container including, for example, the label of FIG. IA; and

FIG. 2 is a schematic cross-sectional view of another exemplary heat transfer label assembly.

DESCRIPTION

Various aspects of the disclosure may be illustrated by referring to the figures, in which the relative widths of the various layers generally indicate the relative area of each layer in the structure. It will be understood that the relative thicknesses of the various layers may be altered or exaggerated for purposes of illustration, and that such thicknesses are not indicative of actual or relative thicknesses of actual structures. Further, although several different exemplary aspects, implementations, and embodiments are provided, numerous interrelationships between, combinations thereof, and modifications of the various inventions, aspects, implementations, and embodiments are contemplated hereby.

FIG. IA depicts a schematic cross-sectional view of an exemplary heat transfer label structure or assembly 100. The assembly 100 generally includes a plurality of layers including a carrier or substrate 102, a release coating or layer 104, a primer or primer layer 106, an ink 108, which may be digitally printed, and an adhesive (or adhesive coating or layer) 110. Each layer 102, 104, 106, 108, 110 is in a substantially facing, contacting relationship with the respective adjacent layer(s). Layers 106, 108, 110, and in some instances, at least a portion of layer 104, generally define a label 112. When the label 112 is joined to a container 114 (FIG. IB), the adhesive 110 generally faces the exterior surface of the container 114.

While one specific structure or assembly 100 is illustrated schematically in FIG. 1, it will be appreciated that each of the layers of the heat transfer label assembly 100 may vary for each packaging application. All layer names are provided for convenience of explanation and not limitation in any manner. Further, layers may be added or omitted as needed. By way of example, the adhesive 110 may be omitted in some embodiments where another means of securing the label 112 is provided. Other modifications are contemplated.

The heat transfer label assembly 100 may be used in the conventional manner using heat and pressure to transfer the ink 108, primer 106, and adhesive coating 110 of the label 112 to a container 114 in the conventional manner. Specifically, according to one exemplary method, the assembly 100 may be brought into intimate contact with the surface of the container 114 with the adhesive 110 facing the container 114. Heat and pressure may be applied to the assembly 100. The heat softens the release coating 104 and allows the primer 106, ink 108, and adhesive 110 to separate from the carrier 102, while the application of pressure transfers the primer 106, ink 108, and adhesive 110 to the container 114. Additionally, at least some of the release coating 104 may transfer to the container 114. Thus, the outermost layer of the transferred label 112 may comprise primer 108 and/or release coating 104. The decorated container may then be subject to a flaming process, during which any release layer 104 material

transferred to the container is re-melted, thereby imparting a glossy finish to the label 112 on the container 114.

A plurality of labels 112 may be indexed along the length of the carrier 102 so that a multitude of containers 114 can be decorated using an automated process. It will be noted that the figures illustrate only one of such labels 112.

Various materials may be used to form each layer of the heat transfer label assembly 100, and each layer may have various basis weights or coat weights, depending on the particular application.

The substrate or carrier 102 generally comprises a base material on which the remaining layers of the assembly are supported. Accordingly, some layers may be described as "overlying" or being "on" other layers. However, it will be appreciated that the assembly 100 may be inverted, such that the carrier 102 overlies the other layers. Accordingly, such terminology is provided merely for convenience of explanation and not limitation in any manner. The carrier 102 may generally comprise a flexible material, for example, paper. The paper may include a clay coating on one or both sides. The paper may have a basis weight of from about 5 to about 75 lbs/ream (i.e., lbs/3000 sq. ft.), for example, about 10 to about 50 lbs/ream, for example, from about 20 to about 30 lbs/ream. However, other ranges and basis weights are contemplated. In other instances, the carrier 102 may comprise other materials, for example, a polymer film. Other suitable carriers may be used.

The release layer 104 generally comprises a substance that softens in response to heat. In one particular example, the release layer comprises a wax or a blend of waxes. Generally, the release layer 104 is formed from a material having a sufficiently low softening point so the transfer of the label 112 (i.e., the separation of the carrier 102 from the label 112) can be initiated at a relatively low temperature ("release temperature" or "transfer temperature"), for example, from about 50 ⁰ C to about 85°C, for example, from about 55°C to about 75°C, for example, from about 60 ⁰ C to about 70 ⁰ C. In one particular example, the release layer 104 comprises a blend of waxes having a softening temperature of about

65°C. However, the softening temperature of the release layer may vary for each application. Accordingly, other suitable materials may be used.

As with the various other layers of the assembly 100, the release layer 104 may be present in any suitable amount needed to achieve the desired printing and/or transfer characteristics. In one example, the release layer 104 may have a basis weight of from about 2 to about 12 lbs/ream (on a dry basis), for example, from about 5 to about 9 lbs/ream. Other ranges and basis weights are contemplated. The release layer 104 may be deposited on or applied to the carrier 102 using any suitable technique, for example, using a Meyer rod or roll coater. Where the carrier 102 is a clay coated paper, the release layer 104 may be applied to the clay coated side of the paper if desired.

The primer 106 generally comprises a substance that prepares the surface of the release layer 104 for receiving ink 108, which may be applied using digital printing or any other suitable technique. The selection of the primer determines the visual quality of the printing, i.e., the ink receptivity, ink adhesion, and rub resistance of the ink.

Where the ink 108 is to be printed using digital printing, the present inventors have found that the temperatures associated with typical digital printing processes (e.g., the blanket temperature, typically about 30-40°C) may exceed the softening temperature of the release layer 104, which may cause the release layer 104 to soften and/or destabilize, thereby potentially causing various defects in the label 112. Such defects may include a reduction in print quality due to the overall destabilization of the printing surface (e.g., the primer 106 on the softened release layer 104), premature separation of the label 112 from the carrier 102, and/or "stringing" of the release layer 104 (and possibly primer 106), particularly along the peripheral edges or boundaries of the transferred label 112. Accordingly, the primer 108 may be selected to assist with stabilizing the release layer 104, for example, by having a chemical affinity for the release layer material 104 (e.g., wax), and/or by providing some degree of thermal insulation to reduce the amount of heat transferred from the blanket to the release layer 104.

It will be appreciated that numerous primers (i.e., primer compositions) may be suitable for stabilizing the release layer 104. In one example, the primer 108 may comprise a polyacrylic acid polymer, for example, a polyacrylic acid copolymer. In one particular example, the polyacrylic acid polymer may comprise an ethylene acrylic acid copolymer. The primer 108 also may include other polymeric components, for example, a polyethylene polymer, or any other suitable polymer. The primer 108 also may include one or more non-polymeric components, for example, silica, wax, and/or talc. Still other components may be included. Thus, in one specific example, the primer 108 may comprise a blend of a polyacrylic acid polymer and optionally, one or more non-polymeric components, for example, silica, wax, and/or talc. In another specific example, the primer 108 may comprise a blend of a polyacrylic acid polymer, a polyethylene polymer, and optionally, one or more non-polymeric components, for example, silica, wax, and/or talc. In still another specific example, the primer 108 may comprise a blend of a polyacrylic acid polymer and a polyethylene polymer. However, numerous other primer compositions are contemplated.

Some examples of materials that may be suitable for use in the primer include DIGIPRIME 4500 primer (formerly referred to as "GPI X5 experimental primer") (Michelman, Inc., Cincinnati, Ohio) and DIGIPRIME 4501 (formerly referred to as "GPI X12 experimental primer") (Michelman, Inc., Cincinnati, Ohio), both of which are believed to comprise at least one polyacrylic acid polymer, for example, a polyacrylic acid copolymer, such as an ethylene acrylic acid copolymer. It is also believed that DIGIPRIME 4500 primer and/or DIGIPRIME 4501 primer may include one or more non-polymeric components, for example, silica, wax, and/or talc. Another material that may be suitable for use in the primer is ADCOTE 50C35 adhesive (Rohm & Hass, Philadelphia, Pennsylvania), which is believed to comprise a polyethylene polymer. While not wishing to be bound by theory, it is believed that the ADCOTE 50C35 adhesive may assist with adhering the ink 108 to the release layer 104.

The amount of each component in the primer may vary for each application, depending on the particular digital printing application. By way example, in various exemplary primers including a polyacrylic acid polymer and a polyethylene polymer, the ratio of the polyacrylic acid polymer to the polyethylene polymer may be from about 1 :1 to about 20:1, for example, from about 2:1 to about 15:1, for example, from about 3:1 to about 12:1, for example, from about 3:1 to about 7:1, for example, from about 4:1 to about 6: 1. In some specific examples, the ratio may be about 4:1, about 4.5:1, about 5:1, about 5.5:1, about 6:1, about 6.5:1, about 7:1, about 7.5:1, about 8:1, about 8.5:1, about 9:1, about 9.5:1, about 10:1, about 10.5:1, about 11 :1, about 11.5:1, about 12:1, or any other suitable ratio.

Likewise, for the specific example of an exemplary primer comprising a blend of DIGIPRIME 4501 primer and ADCOTE 50C35 adhesive, the ratio of DIGIPRIME 4501 primer solids (including the polyacrylic acid polymer) to ADCOTE 50C35 adhesive solids (including the polyethylene polymer) may be from about 1:1 to about 20:1, for example, from about 2:1 to about 15:1, for example, from about 3:1 to about 12:1, for example, from about 3:1 to about 7:1, for example, from about 4:1 to about 6:1. In some specific examples, the ratio of solids may be about 4: 1, about 4.5:1, about 5:1, about 5.5:1, about 6:1, about 6.5:1, about 7:1, about 7.5:1, about 8:1, about 8.5:1, about 9:1, about 9.5:1, about 10:1, about 10.5:1, about 11:1, about 11.5:1, about 12:1, or any other suitable ratio.

As illustrated in the Examples, the present inventors have discovered that a primer including one or more polyacrylic acid polymers and, optionally, one or more non-polymeric components (e.g., example, silica, wax, and/or talc), provides the desired level of printing quality and temperature resistance for digital printing applications. The present inventors have also discovered that the addition of an additional polymeric component, for example, a polyethylene polymer, may enhance the quality of the label even further. However, it will be appreciated that numerous other suitable primers or primer compositions may be used.

The primer 106 may be present in the heat transfer label assembly in any suitable amount. For example, the primer may have a coat weight (dry) of from about 0.25 to about 2 lb/ream, for example, from about 0.5 to about 1 lb/ream. The primer 106 may be deposited on the release layer 104 using any suitable technique, for example, by flexographic or gravure printing. If needed or desired, the release layer 104 on the carrier 102 (e.g., a wax coated paper) may be subject to a corona treatment process to prepare the surface of the release layer 104 for receiving the primer. In one example, the corona treatment may be conducted at about 0.8 kW. However, other treatments are contemplated. After the primer 108 is applied, the partially constructed heat transfer label assembly may be dried.

The adhesive coating 110 generally comprises a material that is capable of adhering the ink to the container 114. Accordingly, the type of adhesive used may vary depending on the type of container being used. For example, when the container is polyethylene, one suitable adhesive may be a polyamide adhesive. Alternatively, when the container is glass, one suitable adhesive may be a polyester adhesive. Numerous other possibilities are contemplated. Additionally, as stated previously, in some embodiments the adhesive 110 may be omitted.

Likewise, the amount of adhesive may vary for each application. The adhesive may generally be applied in an amount of from about 0.5 to about 3 lbs/ream (dry), for example, from about 1 to about 1.5 lb/ream. As shown in FIG. IA, the adhesive coating 110 may extend beyond the peripheral margin of the ink 108 to facilitate adhesion to the container 114. The adhesive may be applied to the ink using any suitable process, for example, by flexographic or gravure printing.

FIG. 2 schematically illustrates an exemplary variation of the heat transfer label structure 100 of FIG. 1. The heat transfer label assembly 200 of FIG. 2 includes features that are similar to the assembly 100 shown in FIG. 1, except for variations noted and variations that will be understood by those of skill in the art. For simplicity, the reference numerals of similar features are preceded in the figures with a "2" instead of a "1". In this example, the carrier (e.g., paper) 202 may be coated with a curable hold-out coating 216, for example, an electron beam crosslinkable polymer. One

such coated paper is commercially available from Coating Excellence, International (Wrightstown, Wisconsin) under the reference name "35# ClS/2# EB Coating".

A release coating 204 may overlie the hold-out coating 216. One example of a release coating that may be suitable is commercially available from Michelman, Inc. (Cincinnati, Ohio) under the trade name ML 162. However, numerous other release coatings are contemplated. The ink 208 then may be applied digitally to the primer 206. The adhesive coating may 210 be omitted in some embodiments, as stated above. The present disclosure may be understood further in view of the following examples, which are not intended to be limiting in any manner.

EXAMPLE l

A heat transfer label assembly was prepared using digital printing. The ink was printed directly onto the wax side of a wax-coated paper. The wax somewhat softened during the printing process, presumably because the softening point of the wax (about 57°C) was slightly lower than the temperature of the ink applied (about 30-40°C). The premature softening of the wax rendered the label unsuitable for further use and evaluation.

EXAMPLE 2

A heat transfer label assembly was prepared using digital printing and a commercially available primer. First, paper having a basis weight of about 30 lb/ream coated with about 6 lb/ream wax (coat weight varied from about 4-9 lb/ream) was coated on the wax side with about 1 lb/ream of DIGIPRIME 4450 primer (Michelman, Inc., Cincinnati, Ohio). The primer was dried at a temperature of about 38°C at a line speed of about 50 ft/min. Next, an HP 4450 digital printer was used to apply a printed design over the primer.

The completed structure then was applied to a polyethylene terephthalate container in the conventional manner under heat and pressure (preheater temp about 90°C, platen temperature about 190°C +/- 25°C). The results were

acceptable and comparable to conventional heat transfer labels (e.g., printed using gravure printing or other conventional printing techniques). However, some "stringing" was observed as the wax-coated paper was separated from the label.

EXAMPLE 3

A heat transfer label assembly was prepared using digital printing and a primer including a polyacrylic acid polymer. Specifically, DIGIPRIME 4500 primer (Michelman, Inc., Cincinnati, Ohio) (previously termed "GPI X5" by Michelman, Inc. as an experimental primer) was applied to a wax-coated paper (same as used in Example 2) in an amount of about 1 to 1.5 lb/ream (dry). As stated previously, it is believed that DIGIPRIME 4500 primer may include at least one polyacrylic acid polymer and possibly one or more non-polymeric additives, for example, silica, wax, and/or talc. It is also believed that DIGIPRIME 4500 primer has a lower tensile strength than the DIGIPRIME 4450 primer. The completed structure then was applied to a polyethylene terephthalate container in the conventional manner under heat and pressure as described in Example 2. The label was successfully applied without stringing. Thus, digital printing was used to prepare a heat transfer label successfully. While not wishing to be bound by theory, it is believed that the primer reduced heat transfer from the digitally applied ink to the wax-coated paper and assisted with reducing the stringing of the label when the remainder of the structure was removed.

EXAMPLE 4

Various primer compositions were used to prepare heat transfer label assemblies and evaluated as described in Example 3. The primer compositions included DIGIPRIME 4501 primer (about 21.5% solids, as provided) (Michelman,

Inc., Cincinnati, Ohio) (previously termed "GPI X12" by Michelman, Inc. as an experimental primer) and, in some examples, ADCOTE 50C35 adhesive (about

34.0% solids, as provided) (Rohm & Hass, Philadelphia, Pennsylvania). The results are set forth in Table 1, in which the solids ratio refers to the ratio of

DIGIPRIME 4501 primer solids to ADCOTE 50C35 adhesive solids, and in which

all values are approximate. It will be noted that although some blocking was observed with Sample 4, it is contemplated that this may be addressed using antiblocking agents or otherwise.

Table 1.

Although certain embodiments of this invention have been described with a certain degree of particularity, those skilled in the art could make numerous alterations without departing from the spirit or scope of this invention. Any directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are used only for identification purposes to aid the reader's understanding of various embodiments, and do not create limitations, particularly as to the position, orientation, or use of the invention unless specifically set forth in the claims. Joinder references (e.g., joined, attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily imply that two elements are connected directly and in fixed relation to each other. It will be recognized by those skilled in the art, that various elements discussed with reference to the various embodiments may be interchanged to create entirely new embodiments coming within the scope of the present

invention. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention. The detailed description set forth herein is not intended nor is to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications, and equivalent arrangements of the present invention.

Accordingly, it will be readily understood by those persons skilled in the art that, in view of the above detailed description of the invention, the present invention is susceptible of broad utility and application. Many adaptations of the present invention other than those herein described, as well as many variations, modifications, and equivalent arrangements will be apparent from or reasonably suggested by the present invention and the above detailed description thereof, without departing from the substance or scope of the present invention. While the present invention is described herein in detail in relation to specific examples or aspects, it is to be understood that this detailed description is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the present invention and to set forth the best mode of practicing the invention known to the inventors at the time the invention was made. The detailed description set forth herein is not intended nor is to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications, and equivalent arrangements of the present invention.