Shielded direct thermal label and methods

A label comprises a facestock adapted to be adhered or attached to an object. A direct thermal coating is on the facestock, the direct thermal coating configured to selectively darken by heat activation when direct thermal printed. A cured ultraviolet coating is on the direct thermal coating, the cured ultraviolet coating having photoinitiators with substantial activation at an exposure limited to radiation at a 315 nm-450 nm wavelength range, and configured to allow direct thermal printing of the direct thermal coating therethrough. The ultraviolet coating is cured without heat activating the direct thermal coating.

TECHNICAL FIELD

The present application relates to direct thermal printing and labels.

BACKGROUND OF THE ART

Direct thermal printing involves the heating of selected areas or zones of a coating on a substrate in order to heat activate a dye by reaction with a matrix. According toFIGS. 1A-1Bof the prior art, a typical direct thermal label10is shown as having a facestock11, an adhesive12covering an undersurface of the facestock11, an adhesive release layer13, and a support liner14, in one possible embodiment. The facestock11and adhesive12are united together and upon removal of the facestock11from the support liner14, the adhesive12remains bonded to it. The removal of the facestock11from the support liner14may be facilitated by the adhesive release layer13. The label10has a direct thermal coating15, with dye and matrix. The print head A is controlled to heat the desired areas of the direct thermal and cause the reaction between dye and matrix, to blacken the areas. The blackened areas define the printing on the label10.

Direct thermal printing is known to be cost effective, notably by not requiring a toner, a printer-applied ink or an inked ribbon in a printer, and thus printed by the relatively inexpensive printers used in direct thermal printing. However, areas printed with direct thermal may tend to fade over time, and may lack the capacity of resisting to liquids such as solvents and chemicals. It is known to apply an ultraviolet (UV) varnish over labels, but conventional wide-spectrum UV curing will heat the direct-thermal material and cause blackening and renders the use of the UV varnish impractical in some instances.

SUMMARY

It is an aim of the present disclosure to provide a label with UV coating that addresses issues related to the prior art.

It is a further aim of the present disclosure to provide a method for printing and protecting a direct thermal label with a LED UV coating.

Therefore, in accordance with the present disclosure, a label comprising: a facestock adapted to be adhered to an object; a direct thermal coating on the facestock, the direct thermal coating configured to selectively darken by heat activation when direct thermal printed; and a cured ultraviolet coating on the direct thermal coating, the cured ultraviolet coating having photoinitiators with substantial activation at an exposure limited to radiation at a 315 nm-450 nm wavelength range, and configured to allow direct thermal printing of the direct thermal coating therethrough, wherein the ultraviolet coating is cured without heat activating the direct thermal coating.

Further in accordance with the present disclosure, there is provided a label comprising: a facestock adapted to be adhered to an object; a direct thermal coating on the facestock, the direct thermal coating configured to selectively darken by heat activation when direct thermal printed; a cured ultraviolet coating on the direct thermal coating, the cured ultraviolet coating having photoinitiators activated to at least 75% with exposure limited to a 315 nm-450 nm wavelength range, and configured to allow direct thermal printing of the direct thermal coating therethrough, wherein the ultraviolet coating is cured without heat activating the direct thermal coating.

Further in accordance with the present disclosure, there is provided a method for fabricating a direct thermal label comprising: applying an ultraviolet coating on a direct thermal coating on a facestock; substantially curing the ultraviolet coating by exposure to ultraviolet light-emitting diodes producing light in a wavelength range of 315 nm-450 nm; and while substantially curing the ultraviolet coating, maintaining the direct thermal coating below a threshold temperature above which the direct thermal coating is activated.

Still further in accordance with the present disclosure, there is provided a method for using a direct thermal label comprising: obtaining a label with a direct thermal coating shielded by a cured ultraviolet coating; heat activating selected zones of the direct thermal coating through the ultraviolet coating to darken the selected zones; and adhering the label with the selected zones darkened to an object.

DETAILED DESCRIPTION

Referring to the drawings and more particularly toFIGS. 2A-2C, a direct thermal label with LED UV coating in accordance with the present disclosure is generally shown at20. The label20may have a facestock21, an adhesive22covering an undersurface of the facestock21, an adhesive release layer23, and/or a support liner24, in one possible embodiment. For example, the label20may be without the adhesive release layer23, and/or with the support liner24having a low adherence surface in contact with the adhesive22. The facestock21and adhesive22may be pulled out of engagement with the support liner24, for instance as assisted by the adhesive release layer23if present. The facestock21may then be adhered to an object by way of the adhesive22. The facestock21may be made of any appropriate materials, such as paper or fiber-based materials, polymers, synthetic films, thermoplastic films such as polyolefins, polypropylenes, biaxially oriented polypropylene (BOPP), polyesters, polyvinyl, polyethylene, polystyrene and similar polymer based materials, etc. According to an embodiment, the facestock21has a thickness between 0.5 mil-10 mil, although it may also be thinner or thicker. The label material may include an ink layer over the facestock21and/or over direct thermal coating25. In another embodiment, the facestock21and/or direct thermal coating25may comprise an additional layer of a topcoat. The facestock21of the material might be opaque or transparent, or have different degrees of opacity and transparency. Yet in another embodiment, the facestock21may be void of adhesive22and support liner24, for the facestock21to be used as a non-adhesive material in a roll, sheet, tag or a fanfold format. The facestock21may be a static cling film on a support liner without an adhesive. The label20with such a facestock21may be attached to surfaces through static.

FIGS. 4A-4Dshows different embodiments of the direct thermal label20, for example when in a roll40. When in a roll40, the direct thermal label20is in an elongated strip that is wound on itself. Accordingly, inFIG. 4Athere are shown two passes of the direct thermal label20on itself, but it is understood that there may be numerous other passes of the direct thermal label20on itself. InFIG. 4A, the direct thermal label20is as inFIG. 3A, with adhesive release layer23and support liner24. InFIG. 4B, the adhesive release layer23and support liner24on the bottom of the adhesive layer22are absent. In such an embodiment, as the label20with direct thermal coating25is without a support liner24, an adhesive release layer41may be laid on top of the LED UV coating30. The adhesive release layer41is present to facilitate the release of the label20from itself, with the adhesive22from a top pass detaching from the adhesive release layer41from an under pass. The adhesive release layer41is selected so as not to interfere with the direct thermal printing. The adhesive release layer41may be a transparent coating comprising silicone or wax that can facilitate the release of the adhesive22while not interfering with the LED UV coating functions. The adhesive release layer41may be added after the LED UV layer is applied and cured. InFIG. 4C, the adhesive release layer23and support liner24on the bottom of the adhesive layer22are also absent, as the LED UV coating30described hereinafter serves as an adhesive release layer. In such an embodiment, the LED UV coating30may incorporate silicone or other compounds and additives facilitating a release of the adhesive22from the LED UV coating. In another configuration, shown inFIG. 4D, the adhesive layer22, the adhesive release layer23and support liner24are absent. The facestock21of a top pass lays on the LED UV coating30of a lower pass, without adhesion therebetween.

Stated differently, other embodiments for the label20include a label and/or uncut label material without the adhesive release layer23, a support liner24shared by numerous facestocks21and adhesive22, or the label20without the support liner24. The label20may have any appropriate shape, including round, square, rectangular, to name but a few of the possibilities. Moreover, a plurality of the labels20may be interconnected in a sheet, roll, etc., for example with tear-off perforations or cuts.

The label20has a direct thermal coating25, with dye and matrix. For example, the direct thermal coating25includes a thermochromic ink and/or a thermochromic ink activation substance. The direct thermal coating25is heat sensitive as it reacts to heat to darken. Zones or surfaces are selectively heated to darken, these zones contrasting with the color of the facestock21and constituting the printing on the label20. According to an embodiment, a thermochromic ink of the coating25is a leuco dye. These dyes have a colorless leuco form when crystalline in a pH neutral environment, and become colored when exposed to an acid. Examples of acids suitable for thermochromic materials are phenols, e.g., Bisphenol A (BPA) and Bisphenol S (BPS). Other suitable acidic substances can be used as developers for leuco dyes (sulfonyl ureas, zinc salts of substituted salicylic acids, etc.). To optimize the colorization temperature and to facilitate mixing, sensitizers can optionally be added to the direct thermal coating25, such as 1,2-bis-(3-methylphenoxy)ethane or 2-benzyloxynapthalene. These ethers are solvents for leuco dyes and developers, and facilitate color formation at a specific temperature. To stabilize the color formed by the leuco dye, developer and sensitizer, a stabilizer might be added to the direct thermal coating25prior to application on the label20. As a non-limitative example, stabilizers may be phenols that inhibit recrystallization of the dye and developer, thereby stabilizing the printed image. The above described technology is presented as an example, and not all constituents thereof are required to be present in the direct thermal coating25in order to achieve a thermal printing. For example, the direct thermal coating25might be activated without a sensitizer or stabilizer or both. Different types of thermochromic inks and developers can be used.

A LED UV coating30covers the direct thermal coating25. As an example, the LED UV coating30may be a benzophenone-free transparent coating that forms a protective shield to protect the printing on the label20from solvents and chemicals. The LED UV coating30has photoinitiators. The photoinitiators are molecules that create reactive species when exposed to radiation. In the present disclosure, the LED UV coating30is selected to have photoinitiators with substantial activation in the wavelength range of around 365 nm to 450 nm. In another embodiment, or in the same embodiment, some other photoinitiators of the LED UV coating30can be activated in a wavelength range of 315-405 nm as well, within the ambit of the present disclosure. Accordingly, the LED UV coating30has the property of being curable with light-emitting diode (LED) generated waves due to the relatively short wavelength range. As a consequence, the LED UV coating30is curable while limiting the temperature of the surface of the substrate supporting the LED UV coating30, for example to around 55° C. The substantial activation may be of at least 75%, and up to 90-95% of photoinitiators. Therefore, the curing is done without heat activating the direct thermal coating25. As shown inFIG. 2C, the label20therefore has a LED UV coating30prior to being thermally printed. Basic constituents of a LED UV coating30are oligomers, prepolymers, monomers and photoinitiators for curing. A more efficient cure is possible with a formulation designed specifically for LED curing using a photoinitiator with more concentrated absorption in the UV-A range.

As a non-limitative example, the UV LED coating30described above was tested and its curing was attempted with ordinary mercury based UV curing system, in comparison to LED curing. In particular testing conditions, the mercury based curing showed a lower level of resistance to alcohol, around 1-2 minutes, compared to 60 minutes of resistance when a similar coating30was cured with a LED UV diode source. The mercury based UV light source creates a wider range of UV light and the specific wavelength necessary for activating the photoinitiators within the spectrum can only partially cure the LED UV coating30. As a result, a significant portion of the LED UV coating30may not be properly cured with a mercury based UV curing system, resulting in less resistance to chemicals. Therefore, tests may indicate that the chemical resistance of the LED UV coating30may be dependent on the percentage of photoinitiator (PI) activations and as a result to the percentage of curing taking place during the UV radiation of the LED UV coating30. The activation of the photoinitiators depends on a few factors, such as the moving speed of the label20or the material of the label20prior to die-cutting through the press, the distance of the light from the label20, and how much exposure the UV LED coating30gets during the curing process. Under optimal conditions approximately 95% of the photoinitiators get activated in LED diode generated radiation resulting a strong protection of the ink underneath the UV LED coating30.

Referring toFIG. 3A, the label20is shown in its ready-for-printing condition, i.e., with the cured LED UV coating30thereon. InFIG. 3A, the label20is blank meaning there has been no heat activation of the direct thermal coating25. The facestock21and the direct thermal coating25are thus shielded by the LED UV coating30. When print head A is applied to the label20, it may heat the selected zones of the direct thermal coating25through the LED UV coating30. The heat may be for example conducted through the LED UV coating30to the selected zones of the direct thermal coating25. The LED UV coating30does not lose its shielding properties in spite of the heating with the direct thermal printer A.

Therefore, in accordance with an embodiment, the label20has a facestock21adapted to be adhered to an object. The object may be any type of object, such as objects used in laboratories, including vials, tubes, blood collection tubes such as Vacutainers, sample collection tubes, microscope slides, tissue processing cassettes, plates, cell culture plates, microtiter plates, microarray plates, other types of plates, petri dishes, bottles, flasks, freezer boxes, cryogenic boxes, cryogenic straws, goblets other type of laboratory plastic containers, laboratory glassware and metal objects such as freezer racks, liquid nitrogen racks, canisters, etc. Furthermore, other objects, containers and surfaces in other industries are covered by the present disclosure. A direct thermal coating25is on the facestock21. The direct thermal coating25is configured to locally darken by heat activation when direct thermal printed. A cured ultraviolet coating30is on the direct thermal coating25. The cured ultraviolet coating30has photoinitiators activated to at least 75% with exposure to a 365 nm-450 nm wavelength range, such as light produced by UV LEDs. The cured ultraviolet coating is configured to allow direct thermal printing of the direct thermal coating therethrough. The ultraviolet coating30is cured without creating heat sufficient to heat activating the direct thermal coating25.

In accordance with another embodiment, a method is defined fabricating a direct thermal label20. The ultraviolet coating30is applied on the direct thermal coating25on the facestock21. The ultraviolet coating30is substantially cured by exposure to ultraviolet light-emitting diodes producing light in a wavelength range of 365 nm-450 nm. While substantially curing the ultraviolet coating, the direct thermal coating25is maintained below a threshold temperature above which the direct thermal coating25is activated.

In accordance with another embodiment, a method for using a direct thermal label is provided. The label20is obtained with the direct thermal coating25shielded by the cured ultraviolet coating30. Selected zones of the direct thermal coating25are heat activated through the ultraviolet coating30to darken the selected zones. The label20is adhered with the selected zones darkened to an object.