WO1999034347A1

WO1999034347A1 - Uv-stable identification sign

Info

Publication number: WO1999034347A1
Application number: PCT/US1997/023793
Authority: WO
Inventors: Gabriele I. Weber
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1997-12-29
Filing date: 1997-12-29
Publication date: 1999-07-08
Anticipated expiration: 2000-06-29
Also published as: AU5716998A

Abstract

An identification sign, e.g., for fixing to the rear of a transparent or translucent substrate, comprises a backing layer; an adhesive layer formed on at least a portion of the backing layer; and indicia on at least a portion of the adhesive layer, the indicia comprising UV-stable ink applied by a pressure-contact transfer process. The sign exhibits surprisingly good UV stability in spite of the lack of a protective film or protective adhesive layer and is especially useful for applications that require low cost plus the ability to rapidly customize the information on the sign immediately prior to use.

Description

UV-STABLE IDENTIFICATION SIGN

Field of the Invention

This invention relates to a self-adhesive article comprising indicia that are stable to ultraviolet (UV) radiation.

Background of the Invention

EP-A-0 358 850 describes an identification sign for fixing to the rear of transparent panes of glass or plastic. The sign has a lower removable protective sheet, a film carrying the identification and carried by the protective sheet, an adhesive layer with UV light resistance arranged on the display side of the film, and a removable protective film externally covering the adhesive layer. A hinged flap is formed in the protective film by predetermined mechanical weaknesses, and the flap carries on its rear side a removable protective film covering the adhesive layer with respect to the film. The identification sign is applied to the rear of a transparent substrate by lifting the flap to expose the film, applying some form of information to the thus exposed film, removing the removable protective film which covers the adhesive layer on the flap, and re-positioning the flap on the identification film. The protective film may then be completely removed and the adhesive layer applied to the inside of a transparent substrate. The information on the film is protected from UN rays by the layer of UN light resistant adhesive. This construction is complex, as it is necessary to selectively cut through the outer protective film as well as the adhesive in order to form the flap.

German Utility Model 1937561 describes a self-adhesive information sign in which recesses are provided in the backing material for the acceptance of pieces of printed material which fit within the recesses. One potential problem with this identification sign is that it can be removed and the pieces of printed material can be replaced. The information sign is therefore not suitable for uses that require some form of security against tampering. In the short time available and under the limited conditions normally experienced at state boundaries or at entrances to motorways, it is difficult to provide pre-printed identification signs or windshield stickers that include a UV absorbing film or adhesive layer to protect the printed information and that are also customized to the vehicle or individual. The prior art signs described above are either too complex or do not provide adequate security. Furthermore, as explained in EP-A-0 358 850, it is generally considered that no handwriting instrument that is readily available, such as a felt-tip pen, can apply written indicia which are UV stable. Some commercially available pens are marked "permanent," but this normally refers to the insolubility of the inks in water. Writeability and UV stability tests are normally carried out on paper or polymer substrates that have been specially adapted for writing applications (e.g., overhead transparency films and writeable tape backings) and are thus not relevant to the performance of inks on adhesive surfaces. Adhesive surfaces are not conventional writing surfaces and are energetically different from those of typical polymer surfaces used for signage or display. It has been discovered that tests done on flat, smooth, adhesive-free polymer or paper surfaces do not correlate well with the same tests done on adhesive surfaces.

Hence, there remains a need for an identification sign that can be easily and quickly marked with suitable indicia (for instance the name of a user or a vehicle license plate number), that can be easily applied to the surface of a substrate, and that will exhibit sufficient UV resistance of its indicia that the sign will remain legible for its intended lifetime (which may be one year or more). Preferably, the identification sign will be reasonably tamper-proof and will have some means for indicating when an attempt has been made to remove it or modify it. The indicia on the identification sign will also preferably not be easily removable or modifiable by commonly available chemicals such as bleaching agents.

Summary of the Invention

The present invention provides an identification sign, e.g., for fixing to the rear of a transparent or translucent substrate, comprising a backing layer; an adhesive layer formed on at least a portion of the backing layer; and indicia on at least a portion of the adhesive layer, the indicia comprising UV-stable ink applied by a pressure-contact transfer process. Preferably, the adhesive layer comprises acrylic adhesive (more preferably, an acrylic pressure-sensitive adhesive (PSA)), and the ink comprises at least one pigment.

The identification sign of the invention exhibits surprisingly good UN stability in spite of the lack of a protective film or protective adhesive layer and in spite of the adhesive nature of the substrate bearing the indicia. The sign is especially useful for applications that require the ability to rapidly customize the sign immediately prior to use, that also require UN stability, and yet require a sign that can be economically produced. It has been discovered that UV-stable indicia can be applied to adhesive surfaces by a pressure-contact ink transfer process, e.g., by writing with a felt- tipped pen or a ball-point pen or by use of a mechanical typewriter. Such a process provides rapidly customizable indicia, e.g., writing with a felt-tip pen allows rapid customizing of an adhesive surface with lines, numbers, characters, letters, etc. Thus, in other aspects, this invention also provides a process and a kit for producing a UV-stable identification sign, the kit comprising a backing layer; an adhesive layer formed on at least a portion of the backing layer; and a hand-held marking instrument adapted for producing UV-stable indicia on the adhesive layer.

Brief Description of the Drawings

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 drawings, wherein:

Fig. 1 is a schematic representation of an identification sign in accordance with a first embodiment of the present invention.

Fig. 2 is a schematic representation of another identification sign in accordance with a second embodiment of the present invention.

Fig. 3 is a schematic cross-sectional representation of an identification sign in accordance with a further embodiment of the present invention. Fig. 4 is a schematic cross-sectional representation of another identification sign in accordance with a further embodiment of the present invention. Fig. 5 is a schematic cross-sectional representation of yet another identification sign in accordance with a further embodiment of the present invention. These figures, which are idealized, are not drawn to scale and are intended to be merely illustrative and nonlimiting.

Detailed Description of the Invention

Fig. 1 is a schematic representation of a first embodiment 1 of the identification sign of the invention. The identification sign 1 comprises a backing layer 2 and an adhesive layer 4 onto which indicia 6 have been applied by pressure- contact transfer of a suitable marking medium. Rapidly customizable pressure- contact transfer processes in accordance with the present invention include writing with ball-point or felt-tip pens or stamps which apply legends or emblems rapidly by exerting mechanical pressure between an inked, suitably profiled surface and an adhesive surface, and mechanical typewriters which apply ink from a ribbon by the mechanically-induced impact of a suitably profiled head against the ribbon which is sandwiched between the head and the adhesive layer 4. Such processes can be carried out without the use of an external power supply and require little maintenance. They are therefore suitable for application of indicia to window stickers at remote locations such as motor- or freeway entrances or state boundaries. Pressure-contact transfer processes in accordance with the present invention do not generally include non-impact printing such as ink-jet or electrostatic printing, which typically involve the use of complex and delicate devices requiring a separate electrical supply, careful maintenance, and special substrates. Fig. 2 is a schematic representation of a second embodiment of the present invention. The identification sign 1 in accordance with the second embodiment includes a backing layer 12, an adhesive layer 14, and a removable protective film 16. Within the removable protective film 16, a movable flap 18 is provided which, when raised, exposes a portion 14a of the underlying adhesive layer 14. Indicia can be applied to the exposed portion 14a by pressure-contact transfer as defined above, and the flap 18 can be replaced, thereby protecting the indicia. When the identification sign is to be applied to the inside of a transparent or translucent substrate such as the windscreen of a car, the protective film 16 is completely removed and then the adhesive layer 14 is applied to the inside of the transparent or translucent substrate. Backings suitable for use in preparing the identification sign of the invention are those which are capable of serving either as a temporary liner or as a permanent carrier for the adhesive layer. Suitable backings include papers, polymers (e.g., polyesters, polyvinyl chloride, polyolefins such as polypropylene or polyethylene, and the like, and blends thereof), and metals, e.g., metal foils. Preferably, the backings are flexible, with polymer film being most preferred. Protective films can be made of the same materials as those listed for use as backings, can be transparent or opaque (preferably, transparent), are also preferably flexible, and, if desired, can be coated or treated so as to release easily from the adhesive layer.

Suitable adhesives for use in preparing the identification sign of the invention are those that will form, e.g., upon drying or curing, a layer that will adhere to the backing (which can be primed) and at least somewhat to the protective film until its removal. Preferred adhesives also exhibit, upon drying or curing to form the adhesive layer, sufficient adhesive and cohesive strength to enable the sheeting to adhere to a substrate surface and to remain adhered until removal is desired. The adhesive strength should also preferably be sufficiently high that attempts to remove and/or transfer the sign to another substrate result in at least partial destruction of the applied indicia or the layered construction itself. In addition, the adhesive layer will preferably be flexible and dimensionally stable (so that the sign will maintain its structural integrity). Preferred adhesives are light-transmissive, so as to form an adhesive layer having a suitable refractive index (preferably, between about 1.4 and about 1.6) that will, e.g., permit viewing of any information printed on an underlying layer or that will enable the retroreflective embodiments of the invention (described below) to provide the desired retroreflection.

Representative examples of suitable adhesives include acrylic adhesives, silicone adhesives, rubber resin adhesives, poly(alpha-olefin) adhesives, and the like, and mixtures thereof. Heat-activatable adhesives (e.g., polyolefins, polyesters, urethanes, and acrylics) can be utilized, but, most preferably, the adhesive is a normally tacky pressure-sensitive adhesive (PSA). PSAs possess a balance of the properties of adhesion, cohesion, stretchiness, and elasticity, and can be utilized to provide preferred embodiments of the signs of the invention that can be easily bonded to the surface of a substrate. Preferably, the adhesive is an acrylic adhesive, more preferably, an acrylic PSA

The third and fourth embodiments of the present invention include a marking instrument such as a felt-tip pen that is suitable for writing on adhesive layer 4 or 14 of the first and second embodiments to provide easily readable and UV stable indicia on the adhesive layer 4, 14. Such indicia may include one or more characters, letters, numbers, legends, or emblems, e.g., the coat of arms of an authorizing organization, the name of an authorized person, or the number plate of a vehicle to which the identification sign is to be applied.

Surprisingly, it has been determined by experiment that suitable marking instruments comprise ink which preferably comprises at least one pigment.

Inorganic or mineral pigments are preferred, such as carbon black for a black color. Organic or polymer-based pigments (e.g., as described in U.S. Patent No. 5,486,550) can also be utilized, but are typically less preferred.

Preferred embodiments of the invention further comprise constructional features that improve security and reduce the possibility of tampering, e.g., in the form of additional components. Preferred embodiments also comprise retroreflective elements, as shown for example in Figures 3 through 5. In Fig. 3, an embodiment of the identification sign of the invention comprises a retroreflective layer 50 which preferably comprises either microparticles or cube corner elements. Preferably the sign includes a holographic layer which is preferably a microstructured layer. The sign also includes an adhesive layer 150 that is protected by protective film 160, which can include the flap 18 of Fig. 2. As shown in Figs. 3 to 5, the sign is provided with adhesive layer 150 for application to, e.g, the inside of a window. A holographic layer 10 is provided which comprises two parts: a structured layer 20 and an optional reflective layer 30. The structured layer can be formed by several methods that are well known in the art, e.g., as described in U. S. Patent No. 4,856,857, the descriptions of which are incorporated herein by reference. It can be made of materials such as polymethyl methacrylate (PMMA), nitrocellulose, and polystyrene. The structured layer 20 can include a microstructured relief pattern of holographic or diffraction grating images in the form of logos or patterns that reflect light. In one embodiment, an embossed microstructured layer can be formed by contacting the material from which the structured layer will be made with a non-deformable embossing plate having a microstructured relief pattern, and applying heat and pressure. Alternatively, the structured layer 20 can be made by any other suitable process such as radiation curing, and can be made of materials such as urethane, epoxy, polyester, and acrylic monomers and oligomers, which are formulated with photoinitiators, cast on a non-deformable tool having a microstructured relief pattern, and radiation cured.

An optional reflective layer 30 is coated on the structured layer 20 either before or after embossing. The reflective layer 30 preferably has a higher refractive index than the structured layer 20. In a preferred embodiment, the reflective layer 30 is substantially transparent and colorless. Illustrative examples of suitable reflective layer materials include but are not limited to bismuth trioxide, zinc sulfide, titanium dioxide, and zirconium oxide, which are described in U.S. Patent No. 4,856,857. Less transparent materials such as thin aluminum or silver or patterned reflectors can also be used. The reflective layer 30 enhances the reflection of light through the structured layer 20 due to the difference in refractive index between the structured and reflective layers, 20, 30. Thus, the structured holographic pattern is more readily visible to the unaided eye once the reflective layer 30 is coated on the structured layer 20, and an adhesive can be directly applied to the structured layer 20 without diminishing the visibility of the structured pattern.

As shown in Fig. 3, retroreflective layer 50, as disclosed in U.S. Patent No. 2,407,680, can comprise an enclosed monolayer of glass microspheres 60, which are coated in a spacing resin 70 comprising, for example polyvinyl butyral or polyester. The spacing resin conforms to the microspheres. A reflector layer 80 underlies spacing resin 70, and can comprise opaque materials such as silver, aluminum, chromium, nickel, or magnesium, or transparent high-index reflector materials such as zinc sulfide, or multilayer reflectors as described in U.S. Patent No. 3,700,305. Thus, light that enters the retroreflective layer 50 is focused by the glass microspheres through the spacing resin and reflected by the reflector layer back through the spacing resin and glass microspheres to an observer. Finally, the sign further comprises backing layer 200, which can optionally bear a heat- activatable or pressure-sensitive adhesive to aid in adhesion to the reflector layer.

As shown in Fig. 4, an optional beadbond layer 90 can also be provided. In this embodiment, glass microspheres have been coated onto the beadbond layer 90, and then spacing resin was coated onto the glass microspheres. The beadbond layer can contain a colored pigment (including black pigment) that gives the retroreflective material a colored appearance in normal light, and the appearance of a different color, such as silver, in retroreflective light. This is described further in U.S. patent No. 2,40,680. The reverse side of the microspheres can be protected by any suitable protective or sealing material 155. Layer 155 can be an additional adhesive layer if the identification sign is to be attached at its rear to, e.g, a non- transparent substrate, in which case backing layer 200 can be a temporary liner and protective film 160 can be removed and, after application of indicia to adhesive layer 150, replaced with a permanent protective film. Fig. 5 illustrates an alternative retroreflective layer 50 comprising a multiplicity of cube-corner elements 100 instead of glass microspheres and resin. The cube-corner elements 100 can be made of materials such as vinyl, polycarbonate, or acrylic for embossed cube-corner elements and urethane, epoxy, polyester, and acrylic oligomers and monomers for radiation cured cube-corner retroreflective elements 100. The cube-corner elements typically have three mutually perpendicular faces with surface areas of approximately 1.9 x 10^'3 mm² to 0.1 mm². Cube-corner retroreflective elements 100 can be embossed by a master mold into a sheeting material under suitable temperature and pressure. The elements can also be created by coating a radiation curable resin onto a master mold, laminating an overlay film under sufficient pressure, and solidifying the resin by radiation curing. Cube-corner retroreflective elements 100 can optionally have a reflective coating 105 as shown in Fig. 5. The reflective coating 105 can be made of the same material as those previously described for microsphere retroreflective material and is typically applied on the back surface of the cube corners. A sealant film or adhesive layer 155 can be applied over the metallized layer 105 while still allowing retroreflection. Also, cube-corner retroreflective elements 100 can be used without a reflective coating.

The holographic layer 10 and the retroreflective layer 50 of the above embodiments can be bonded together by a tie layer 120 as shown in Fig. 3. Suitable materials for such a tie layer include primers or adhesives, either as coatings or as film, such as urethanes, olefins, vinyls, and acrylics. The tie layer 120 can be any appropriate thickness and can be applied either to the holographic layer 10 or to the retroreflective layer 50 or both prior to bonding these layers together.

The tie layer 120 shown in Fig. 3 can be made of a heat-shrink material. In this embodiment, the heat-shrink layer provides protection against tampering by the application of heat, because the application of a sufficient amount of heat causes the heat-shrink layer to deform. The deformed layer causes the identification sign to deform, thus providing an indication of tampering. Polyolefin film is a preferred material for the heat-shrink layer and can also be used as a tie layer and adhesive. An optional patterned coating layer 170 that either increases or decreases adhesion can be provided as shown in Fig. 3 to aid in detecting tampering. The patterned coating layer 170 can be provided at or near the interface of the adhesive layer 150 and the underlying layer or at the interface of the holographic and retroreflective layers. A particularly useful application of the patterned layer 170 is one in which this layer is used adjacent to a layer having readable indicia or an arrangement of one or more holographic emblems. When the sign is delaminated at the patterned coating layer, a portion of the readable indicia or emblem(s) remains bonded to each delaminated portion. Thus an observer can see more easily whether the sticker has been tampered with. An optional indicia pattern 180, as shown in Fig. 4, can be applied in the same locations as the patterned coating layer described above, or in other locations within the construction. The indicia pattern or logos are preferably printed with colored inks, pearlescent inks, or inks visible under ultraviolet light or are imaged using toners or dyes in a pattern. These colored indicia are especially useful when printed at some location above the front surface of the retroreflective layer shown in Fig. 3, which has a colored beadbond. In normal light, the colored (preferably black) beadbond hides the colored indicia and only the hologram is typically visible, because the hologram detracts from the visibility of the colored indicia. However, under retroreflective lighting the colored indicia are brightly visible against the background, which is preferably silver, and the hologram is no longer visible. Wide or narrow angular indicia 190, as shown schematically in Fig. 1, can also be imaged into the microsphere retroreflective layers by, e.g., the laser imaging process generally described in U.S. Patent Nos. 4,688,894 and 4,200,875. Usually, when this process is used to image enclosed microsphere retroreflective materials with opaque reflectors, the indicia are visible in both normal and retroreflective light. This invention also includes using enclosed microsphere retroreflective material with transparent reflectors with which the indicia are not visible in normal light but are visible only under retroreflection. Thus the indicia are hidden until viewed retroreflectively.

Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.

Examples In the following Examples, various felt-tipped pens were used to apply indicia to a variety of adhesive surfaces, writeability was evaluated, and the resulting identification signs were subjected to a variety of tests, as detailed below.

Pens PI Papermate™ M16 pen, available from Gilette Schreibgerate GmbH, Baden- Baden Germany P2 Papermate™ M51 pen, available from Gilette Schreibgerate GmbH, Baden- Baden Germany LI Lumocolor™ F316 pen, available from Staedtler Mars GmbH & Co,

Nuernberg, Germany L2 Lumocolor™ S313 pen, available from Staedtler Mars GmbH & Co,

Nuernberg, Germany L3 Lumocolor™ F318 pen, available from Staedtler Mars GmbH & Co,

Nuernberg, Germany P3 Pancolor™ S303 pen, available from Staedtler Mars GmbH & Co, Nuernberg, Germany

P4 Pancolor™ F (Fineline) 303 pen, available from Staedtler Mars GmbH &

Co, Nuernberg, Germany P5 Pelikan™ 416 pen, available from Pelikan AG, Hannover, Germany El Edding™ 89 pen, available from Edding AG, Ahrensburg, Germany E2 Edding™ 404 pen, available from Edding AG, Ahrensburg, Germany E3 Edding™ 780 pen, available from Edding AG, Ahrensburg, Germany E4 Edding™ 3000 pen, available from Edding AG, Ahrensburg, Germany SSI Schwan Stabilo™ 88/46 pen, available from Schwan-Stabilo

Schwanhausser GmbH & Co., Nurnberg, Germany Bl Berol™ pen supplied by Berol Limited, Norfolk, United Kingdom

B2 BIC™ ballpoint pen supplied by BIC Deutschland GmbH & Co., Ettlingen,

Germany

Adhesives Al Acrylate-based pressure-sensitive adhesive comprising a copolymer of 90 parts by weight isooctyl acrylate and 10 parts by weight acrylic acid, the copolymer having an inherent viscosity in the range 1.7 - 2.0, prepared essentially as described in U.S. Patent No. Re. 24,906 (Ulrich)

A2 Acrylate-based pressure-sensitive adhesive comprising a copolymer of 90 parts by weight isooctyl acrylate and 10 parts by weight acrylic acid, the copolymer having an inherent viscosity in the range 0.7 -0.8, prepared essentially as described in U.S. Patent No. Re. 24,906 (Ulrich)

A3 Acrylate-based, tackified, crosslinked pressure-sensitive adhesive comprising an acrylic copolymer of 93 parts by weight isooctyl acrylate and 7 parts by weight acrylic acid having an inherent viscosity in the range of 1.5 - 1.75 and NTREZ 2019 tackifier (available from Arizona Chemical, Panama City, Florida; a terpene phenol resin), as generally described in U. S. Patent No. 4,418,120

A4 Acrylate-based, tackified, crosslinked pressure-sensitive adhesive comprising an acrylic copolymer of 94 parts by weight isooctyl acrylate and 6 parts by weight acrylic acid having an inherent viscosity of 0.75 - 0.85, tackified with a rosin ester resin, as generally described in U. S. Patent No. 4,418,120

A5 Acrylate-based pressure-sensitive adhesive comprising a copolymer of 95.5 parts by weight isooctyl acrylate and 4.5 parts by weight acrylic acid, as generally described in U.S. Patent No. Re. 24,906, in particular, essentially as in Example 5

A6 Acrylate-based pressure-sensitive adhesive available as Scotch™ 9457 laminating adhesive

A7 Acrylate-based repositionable pressure-sensitive adhesive available as Scotch™ 9449 laminating adhesive

A8 Acrylate-based pressure-sensitive adhesive comprising a copolymer of 96.5 parts by weight isooctyl acrylate and 3.5 parts by weight acrylic acid polymerized in the presence of 15 parts by weight (based on 100 parts by weight of the acrylic copolymer) hydrophobic fumed silica (available as AEROSIL R-972 from Degussa) and 0.13 parts by weight (based on 100 parts by weight of the acrylic copolymer) hexanedioldiacrylate crosslinker, essentially as described in Example 1 of International Patent Publication No. WO 97/44769 (Adhesive A)

A9 Acrylate-based, heat-activated adhesive comprising a terpolymer of 57 parts by weight isooctyl acryate, 35 parts by weight methyl acrylate, and 7 parts by weight acrylic acid, the terpolymer having an inherent viscosity of 1.5, as generally described in U. S. Patent No. 4,248,748

Test Samples Test samples for use with the test methods described below were prepared by applying adhesives to a substrate in the following manner:

Substrate

The substrate onto which adhesives were coated consisted of a multilayer retroreflective article comprising:

1) a backing layer of polyethylene terephthalate of 10 - 200 microns thickness;

2) a retroreflective layer comprising glass microspheres as shown schematically in U.S. Patent Nos. 2, 407, 680 and 3, 801, 183;

3) a 1 micron thick patterned prime coat of polyurethane (layer 170 in Fig. 1); and 4) a holographic layer of about 2.5 microns thickness made of polymethyl methacrylate (PMMA) bearing a hologram (layer 30 in Fig. 1 ).

Adhesive Al was coated as an organic solution onto a siliconized release liner and dried in a forced air oven. The dry thickness of the adhesive layer was 30 microns (ca. 30 g/m²). The adhesive layer was then applied to the substrate by lamination with a hand roller of 6.8 kg weight.

Adhesive A2 was coated as an organic solution onto a siliconized release liner and dried in a forced air oven. The dry thickness of the adhesive layer was 40 microns (ca. 40g/m²). The adhesive layer was then applied to the substrate by lamination with a hand roller of 6.8 kg weight. Adhesive A3 was coated as an organic solution onto a siliconized release liner and dried in a forced air oven. The dry thickness of the adhesive layer was 45 microns (ca. 45 g/m²). The adhesive layer was then applied to the substrate by lamination with a hand roller of 6.8 kg weight.

Adhesive A4 was coated as an organic solution onto a siliconized release liner and dried in a forced air oven. The dry thickness of the adhesive layer was 50 microns (ca. 50 g/m²). The adhesive layer was then applied to the substrate by lamination with a hand roller of 6.8 kg weight.

Adhesive A5 was coated as an organic solution onto a siliconized release liner and dried in a forced air oven. The dry thickness of the adhesive layer was 80 microns. The adhesive layer was then applied to the substrate by lamination with a hand roller of 6.8 kg weight.

Adhesive A6, a commercially available laminating adhesive having a thickness of 25 microns, was applied to the substrate by lamination with a hand roller of 6.8 kg weight.

Adhesive A7 , a commercially available laminating adhesive having a thickness of 10 microns, was transferred to the substrate by lamination with a hand roller of 6.8 kg weight.

Adhesive A8 was prepared in a layer of 150 microns in thickness between two polyester liners as described under A8 in the section "Adhesives". One liner was removed and the exposed adhesive face laminated to the substrate described above by lamination with a hand roller of 6.8 kg weight.

Adhesive A9 was prepared by coating a solution of the non-tacky acrylic terpolymer onto a siliconized release layer and drying in a forced air oven. The final coating weight of adhesive was 31-36 g/m². The dried adhesive layer was laminated to the substrate using a rubber-coated roller having a weight of 6.8 kg.

Test Methods: Writeabilitv (Drag and Wettabilitv.

A variety of pens were used to apply indicia by hand to a variety of adhesive layers as detailed in Table 1. Writing instruments for normal paper and polymer surfaces are known to suffer from a problem sometimes known as "drag" which is related to the degree to which the instrument moves easily over the surface or tends to catch or falter in its movement. Application of liquid ink to an adhesive surface using a writing instrument such as a pen may suffer more severely from drag. The mere presence of some drag (Category B in Table 1) was not considered to exclude a candidate combination of adhesive/pen. Where the drag became so serious that writing became very difficult, the candidate combination of adhesive/pen was judged less preferable (Category C in Table 1). Some combinations were relatively drag free (Category A in Table 1).

Further, the application of ink to a non-absorbent polymeric surface, of which an adhesive surface may be one kind, can result in the ink forming a series of droplets or pools rather than a uniform line. While the ink is still wet, the surface tension of the ink draws the ink in a line towards ever increasing round droplets resulting in thinning of the lines between the droplets. This effect is sometimes called "barbed wire". The effect need not occur immediately but may develop over a period of seconds or minutes until the ink is dry. In extreme cases, the ink flows completely out of the lines after application to the adhesive surface and only a string of droplets of ink remains. The ability of the ink to wet the adhesive surface and therefore the quality of the writing was judged in three grades. In the first grade (Category 1 in Table 1) the ink wetted the surface of the adhesive completely and the writing was of good quality. A second grade ink (Category 2 in Table 1) was acceptable initially, but produced some droplet formation after a period of time. The third grade (Category 3 in Table 1) formed droplets immediately and was unacceptable. It is known from ink jet printing to cure this problem by application of an ink receptor layer to the adhesive surface as explained in WO 95/23698. The effect of an ink receptor layer is to seriously denature the adhesive properties of an adhesive layer. In all the tests carried out with the writing instruments in accordance with the present invention no ink receptor layer was used, neither is an ink receptor layer necessary in accordance with the present invention.

It is preferred if the tip width of the writing instrument is at least 0.6 mm.

Table 1. Writeability

I

Drag

A = relatively drag free, B = some drag, C = substantial drag

Wetting

1 = good wetting, 2 = some eventual droplet formation, 3 = substantial immediate droplet formation

Contact Angle Measurement

Wetting was further investigated by placing a drop of each of a series of inks on the surface of a series of adhesives, as shown in Table 2. The contact angle was measured directly by plotting the tangent line on the contour of the drop at the wetting point using a goniometer-microscope (essentially as described in GIT Fachzeitschrift fur das Laboratorium 24, 642-48 and 734-42 (1980), GIT VERLAG GmbH, Darmstadt). The smaller the contact angle, the better the wetting. The results are given in Table 2. As shown in Table 2, inks having a contact angle of less than about 70 exhibited sufficient wetting of the adhesive surfaces tested to provide preferred writeability.

Table 2. Contact Angle

Accelerated Weathering

Test samples were prepared as described above, and indicia were applied to the surface of each using various pens, as detailed in Table 3. For each group of samples, one sample was maintained under normal room conditions as a control sample. All other samples were protected at the front, i.e., to the adhesive side of each sample was applied a glass panel of 3 mm thickness. The samples were placed in a Xenotest™ 1200 LM accelerated weathering chamber supplied by Hereaus of Germany and subjected to a sequence of UV radiation and moisture in accordance with DIN 53387 (exposure conditions A). The samples were examined at regular intervals and each time compared with the control sample. Any color change, bleaching effect, or poor legibility was noted. The results of the tests are given in Table 3 (where Category 1 represents no change or slight color fading only, Category 2 represents some fading but with the indicia still visible, and Category 3 represents strong fading or a complete lack of visibility of the indicia). The tests were completed after 2000 hours. An adhesive/pen combination should preferably provide legible indicia after at least 500 hours exposure (more preferably 1000 hours, and most preferably 2000 hours for the most severe sunlight environments).

Table 3. Accelerated Weathering

1= no change to slight color fading, 2= some fading but indicia still visible, 3= substantial fading or complete invisibility of indicia

Indelibility (Bleaching/Rubbing)

Different bleaching agents were applied to indicia applied by four different pens to four different adhesives, as detailed in Table 4.

BA1 was a solution said to contain less than 5% sodium hypochlorite sold under the brand name Klorix™ supplied by Colgate-Palmolive GmbH, Hamburg,

Germany.

BA2 was a commercially available stain remover sold under the brand name

Fleckenteufel™ and supplied by Delta Pronatura, Neu-Isenburg, Germany. The solution was believed to contain non-ionic tenzides. BA3 was a solution of 30% hydrogen peroxide.

Each sample was tested in the following way: Indicia were applied to each adhesive surface by writing. Then drops of bleaching agent were placed on the indicia. After 20' min. dwell time at room temperature, the bleaching of the indicia was evaluated. The results are given in Table 4 (where Category 1 represents no bleaching, Category 2 represents slight bleaching and, in some cases, also slight yellowing, and Category 3 represents significant or complete bleaching).

To further test indelibility, the indicia to which bleaching agent had been applied were subjected to physical rubbing. The results of the rubbing tests are given in Table 5 (where Category 1 represents no smearing, Category 2 represents slight smearing, and Category 3 represents substantially complete removal of the indicia).

Table 4. Indelibility: Bleaching

1 = No bleaching,

2 = Slight bleaching,

3 = Writing completely bleached

Table 5. Indelibility: Rubbing

1 = no smearing

2 = slight smearing

3 = substantially complete removal by nibbing

Ink Analysis

Inks from five pens (E3, PI, P4, P5, and L2) were examined analytically. The latter four inks were filtered through a fine 0.1 micron Millex™ filter. Only the ink from PI left a colorless filtrate, indicating that the coloring matter in the ink of PI was solely pigment based. The inks were subjected to thin layer chromatography (TLC) by spotting silica gel plates with inks from PI, P4, P5, and L2 and developing the plates in acetonitrile. The primary colors in the inks from L2 and P4 moved with the solvent front. The ink from L2 left nothing at the origin, indicating that all its coloring matter comprised dyes rather than pigment. The ink from P4 left a red dot at the origin. No movement or separation was observed with the ink from PI, confirming that the coloring matter of this ink was likely to be a pigment that is not soluble in organic solvent. The majority of the coloring matter of the ink from P5 remained at the origin, but a second colored component was observed. This indicated that the inks from P5 and P4 may include both pigments and dyes.

Samples of the inks from L2 and P4 pens were dried and subjected to infrared spectroscopy. The spectra indicated that both samples contained solvent black 29 which is a metallized azo dye of undetermined structure. This test confirmed that the coloring matter of the inks from L2 and P4 most likely comprised organic dyes.

Ink from E3 was examined spectroscopically (infrared, NMR, and Raman). The data was consistent with the ink comprising inorganic pigment along with organic components.

Results: Pens E3, PI, and P5 provided preferred performance on the adhesives tested, with adhesive A8 in combination with pen E3 being most preferred.

Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention.

Claims

What Is Claimed Is:

1. An identification sign comprising (a) a backing layer; (b) an adhesive layer formed on at least a portion of said backing layer; and (c) indicia on at least a portion of said adhesive layer, said indicia comprising UV-stable ink applied by a pressure-contact transfer process.

2. The sign of Claim 1 wherein said adhesive layer comprises acrylic adhesive.

3. The sign of Claim 1 wherein said adhesive layer comprises at least one pressure-sensitive adhesive.

4. The sign of Claim 3 wherein said pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive.

5. The sign of Claim 1 wherein said UV-stable ink comprises at least one pigment.

6. The sign of Claim 5 wherein said pigment is an inorganic or mineral pigment.

7. The sign of Claim 6 wherein said inorganic or mineral pigment is carbon black.

8. The sign of Claim 1 further comprising a protective film applied to said adhesive layer.

9. The sign of Claim 8 wherein said protective film comprises a movable flap and wherein said indicia are located on the portion of said adhesive layer that is below said flap.

10. The sign of Claim 1 further comprising a holographic layer.

11. The sign of Claim 1 further comprising a retroreflective layer.

12. The sign of Claim 1 further comprising a patterned coating layer with differential adhesion.

13. The sign of Claim 1 wherein said pressure-contact transfer process comprises writing by hand with a marking instrument.

14. An identification sign comprising (a) a backing layer; (b) an acrylic pressure-sensitive adhesive layer formed on at least a portion of said backing layer; and (c) indicia that have been hand-applied to at least a portion of said acrylic pressure-sensitive adhesive layer using a marking instrument, said indicia comprising UV-stable ink comprising at least one inorganic or mineral pigment.

15. A kit for producing a UV-stable identification sign comprising (a) an article comprising (i) a backing layer; and (ii) an adhesive layer formed on at least a portion of said backing layer; and (b) a hand-held marking instrument adapted for producing UV-stable indicia on said adhesive layer.

16. The kit of Claim 15 wherein said hand-held marking instrument comprises a UV-stable ink that comprises at least one pigment.

17. The kit of Claim 16 wherein said pigment is an inorganic or mineral pigment.

18. The kit of Claim 17 wherein said inorganic or mineral pigment is carbon black.

19. The kit of Claim 15 wherein said hand-held marking instrument is a felt-tipped pen.

20. A kit for producing a UV-stable identification sign comprising (a) an article comprising (i) a backing layer; and (ii) an acrylic pressure-sensitive adhesive layer formed on at least a portion of said backing layer; and (b) a felt-tipped pen comprising UV-stable ink comprising at least one inorganic or mineral pigment.

21. A process for preparing a UV-stable identification sign comprising the steps of (a) selecting an article comprising (i) a backing layer; and (ii) an adhesive layer formed on at least a portion of said backing layer; and (b) applying UV-stable indicia to at least a portion of said adhesive layer by a pressure-contact transfer process.