60/128,669, filed April 9,1999, the entire disclosure of which is hereby incorporated by reference.

Field of the Invention This invention relates to a multilayer construction and method for undersurface marking. More specifically, this invention relates to a multilayer construction and method that provide markings, such as identification information, which are made and occur under one of more layers of the construction.

Background of the Invention Variable imaging techniques place variable images on a film or paper. These images are used for vehicle identification numbers or product numbers that are sequential, etc. Also, tags and other labels may require variable images. Typically, the image is exposed to abrasion or environmental damage. A protective varnish or laminate is placed over the variable image after the image is formed. Laminates may be used but additional processing steps are required for protecting the variable images. These solutions are not practical because not all manufacturing facilities have the equipment or resources to provide these less desirable solutions.

Summary of the Invention This invention relates to a multilayer construction that may have a subsurface variable image. The multilayer construction comprises a clear layer; a metallic layer underlying the clear layer; a polymeric film layer underlying the metallic layer; a pressure sensitive adhesive layer underlying the polymeric film layer; and a release liner releasably adhered to the pressure sensitive adhesive layer. The metallic layer

is absorbent of laser irradiation such that the metallic layer is ablated upon laser irradiation to a variable image, and the dear layer and the polymeric film layer are non-absorbing of such laser irradiation. The multilayer construction optionally contains at least one first mask sheet overlying the clear layer.

The invention also includes the method of providing variable images. The variable image is placed into the construction by ablating portions of the metallic layer with laser radiation to form the images. The ablation may occur during manufacture of the construction or later at the facility using the construction. The present invention may be used in making labels for manufacturing parts, vehicle identification numbers, serial badges, decorative faceplates, and functional circuits.

The present construction and method provides a simple and effective means of providing subsurface variable images.

Brief Description of the Drawings Fig. 1 is a cross sectional view of a construction of the present invention.

Fig. 2 is a cross sectional view of a construction of the present invention.

Fig. 3 is a cross sectional view of a construction of the present invention.

Fig. 4 is a cross sectional view of a construction of the present invention.

Fig. 5 is a cross sectional view of a construction of the present invention.

Fig. 6 is a cross sectional view of a construction of the present invention.

Fig. 7 is a cross sectional view of a construction of the present invention.

Fig. 8 is a cross sectional view of a construction of the present invention.

Detailed Description of Preferred Embodiments As described above, the multilayer construction optionally contains a first mask sheet. The first mask sheet provides protection for the other parts of the multilayer construction during processing an application. This layer is generally removed after the multilayer construction is placed on the substrate. Typically, the first mask layer has a thickness of about 0.5 to about 5 mils, or from about 1 to about 3 mils or most preferably about 2 mils. Examples of mask sheets include polyesters, polyolefins, and vinyl films. The first mask layer may be a thermoplastic polymer film or a removable adhesive. The first mask layer is transparent to the

laser, i. e., it does not have significant absorption in the wavelength range of the laser used to ablate the underlying metallic layer. In one embodiment, the first mask film is coated with a removable acrylic pressure sensitive adhesive. The removable pressure sensitive adhesive may be a solvent oremulsion removable adhesive such as those commercially available from Fasson, division of Avery Dennison Corporation, or a UV adhesive commercially available from Beacon or Polychem.

In another embodiment, the first mask sheet is a polymerfilm. The polyesters useful as the first mask film include polyethylene terephthalates and polyethylene naphthalates. Examples of useful olefins include oriented polypropylene, polypropylene copolymers, etc. Preferably, the polyolefins are biaxially oriented.

Examples of useful polymers include Mylar7 polyesters and Kaladex'polyesters available from DuPont Chemical, biaxially oriented polypropylene available commercially from Mobil.

Underlying the mask sheet is a clear layer. The clear layer is prepared from optically clear thermoplastic polymers such as optically clear polyesters, optically clear polyolefins and optically clear vinyl polymers. The clear layer is transparent to the laser, i. e., it does not have significant absorption in the wavelength range of the laser used to ablate the metallic layer. Specific examples of these clear polymers include polyethylene terephthalate, polyethylene napthalate, biaxially oriented polypropylene, biaxially oriented ethylene propylene copolymer, polyvinylchloride, polyvinylfluoride, polyvinylidene difluoride, and acrylic. The commercially available examples of those polymers are described above, in addition to the acrylic film available under the tradename Koradw. Typically, the clear layer has a thickness of about 0.5 to about 7 mils, preferably from about 1.5 to about 3 mils.

The next layer of the construction is a metallic layer. The metallic layer is prepared by chemical vapor deposition, sputtering coating or printing of a metallic ink. The metallic layer typically consists of titanium, silver, gold, aluminum, copper, and alloys of these metals, and stainless steel. The layer typically has an optical density from about 0.9 to about 4 on the McBeth scale. The layer may be continuous as in the case of chemical vapor deposition and sputtering or may be

either continuous or noncontinuous as in the case of printing with metallic ink.

Examples of such inks include solvent and water based metallic inks, ultraviolet cured metallic inks, aluminum effect pigments such as those commercially available under the trade name METALLURETM, and solvent, mulsion or hot melt rubber metallic adhesives. The printing may be accomplished by any means known to those in the arts, such as gravure, flexographic, letter press, lithographic offset and other printing means.

Underlying the metallic layer is a polymeric film layer. The polymeric film layer may be pigmented or non-pigmented. This layer is, however, transparent to the laser, i. e., it does not have significant absorption in the wavelength range of the laser used to ablate the metallic layer. Examples of useful polymeric films are films made of polyester, polyolefin, and vinyl polymers. Specific examples include polyethylene terephthalate, polyethylene napthalate, biaxially oriented polypropylene, biaxially oriented ethyiene propylene copolymer, polyvinylchloride, polyvinylfluoride, polyvinylidene difluoride and acrylic film such as the acrylic film available under the tradename Koradw. The polymeric film layer provides image sharpness to the metallic layer. If the polymeric film layer is pigmented, a contrast between the non-ablated portions of the metallic layer and the ablated portions can be achieved.

Alternatively, contrast can be achieved by printing pigmented ink onto the underside of the polymeric film layer. Useful inks include solvent based flexographic or screen ink such as those commercially available from Sun Chemical, water based flexographic or screen ink such as those commercially available from Water Ink Technologies, and ultraviolet cured flexographic or screen inks such as those commercially available from Daw Ink or Akzo Nobel.

A pressure sensitive adhesive underlies the polymeric film layer. Examples of useful pressure sensitive adhesives include solvent borne acrylic adhesives such as those commercially available from Avery under the trade designations N28, N48, N27, N47, P76, P29 and P9, and mulsion acrylic adhesives such as those available from Avery under the trade designations N31 and P12, and hot melt rubber adhesives such as those commercially available from Avery under the trade

designations N81, N86, N87, N98 and N92. The pressure sensitive adhesive is then releasably bonded to a release liner. Examples of useful release liners include silicone release coated paper and silicone release coated polyester.

In another embodiment of the present invention, a destructible layer comprising a lacquer or varnish layer is included in the multilayer construction. This layer provides tamper indication when the multilayer construction is applied to a substrate and subsequently removed. An example of such destructible layer material is the varnish commercially available from Avery under the trade name DestruXTM. The destructible layer may be positioned such that it overlies the metallic layer or positioned such that it is coated on the underside of the polymeric film underlying the metallic layer.

In referring to Figure 1, the multilayer construction 10 has a mask sheet 11 attached to clear layer 12. An adhesive layer 11 a underlies and is adhered to sheet 11. Clear layer 12 is adhered to adhesive layer 11 a. Adhesive layer 12a underlies and is adhered to clear layer 12. The metallic layer 13 is adhered to adhesive layer 12a and to polymeric film layer 14. The polymeric film layer 14 overlies pressure sensitive adhesive layer 15, which in turn is releasably bonded to release liner 16.

In referring to Figure 2, the multilayer construction is prepared by printing the metallic layer. The multilayer construction 20 has mask sheet 21. An adhesive layer 21 a underlies and is adhered to sheet 21. Clear layer 22 is adhered to adhesive layer 21 a. Adhesive layer 22a underlies and is adhered to clear layer 22.

A noncontinuous metallic layer 23 with gaps 24 is adhered to adhesive layer 22a and to polymeric film layer 25. The polymeric film layer 25 overlies pressure sensitive adhesive layer 26, which in turn is releasably bonded to release liner 27.

In another embodiment, the mask sheet may be a multilayer carrer sheet and have one or more polymer films associated with the removable adhesive. In Figure 3, multilayer construction 30 has mask sheet composed of polymer layer 31, such as a polyester, attached to removable adhesive 32 to make the mask sheet. The removable adhesive 32 is removably bonded to clear layer 33 which has metallic layer 34 on its opposite side. The metallic layer 34 is bonded to polymeric film layer

35. Pressure sensitive adhesive layer 36 underlies polymeric film layer 35 and is releasably bonded to release liner 37.

In reference to Figure 4, multilayer construction 40 comprises a mask sheet that is composed of polymer film 41 such as a polyester layer, and removable adhesive 42. The mask sheet is attached to clear layer 43 through the removable adhesive 42. Clear layer 43 overlies metallic layer 44, which may be continuous or noncontinuous. The metallic layer 44 is bonded to polymeric film layer 45, which is undercoated with contrast layer 46. Contrast layer 46 is a pigmented ink. Pressure sensitive adhesive layer 47 underlies contrast layer 46 and is releasably bonded to release liner 48.

In another embodiment, as shown in Figure 5, multilayer construction 50 contains a multilayer mask sheet comprised of polyester film 51, which is bonded to adhesive 52, such as a removable acrylic pressure sensitive adhesive, a second polyester layer 53 and removable adhesive 54. The mask sheet is attached to clear layer 55 through removable pressure sensitive adhesive 54. Clear layer 55 is attached to metallic layer 56, which may be continuous or noncontinuous. The metallic layer is then bonded to polymeric film layer 57. Polymeric film layer 57, is then bonded to pressure sensitive adhesive 58, which in turn is releasably bonded to release liner 59.

Referring to Figure 6, in another embodiment, multilayer construction 60 comprises a mask sheet that is composed of polymer film 61 such as a polyester layer, and removable adhesive 62. The mask sheet is attached to clear layer 63 through the removable adhesive 62. Clear layer 63 overlies destructible layer 64, which in turn overlies metallic layer 65, which may be continuous or noncontinuous.

The metallic layer 65 is bonded to polymeric film layer 66. Pressure sensitive adhesive layer 68 underlies polymeric film layer 67 and is releasably bonded to release liner 68.

In reference to Figure 7 which shows another embodiment, multilayer construction 70 comprises a mask sheet that is composed of polymer film 71 such as a polyester layer, and removable adhesive 72. The mask sheet is attached to clear layer 73 through the removable adhesive 72. Clear layer 73 overlies metallic

layer 74, which may be continuous or noncontinuous. The metallic layer 74 is bonded to polymeric film layer 75, which is undercoated with destructible layer 76.

Pressure sensitive adhesive layer 78 underlies destructible layer 76 and is releasably bonded to release liner 79.

In referring to Figure 8, the multilayer construction 80 has a clear film 81 attached to metallic layer 82. Metallic layer 82 is a non-adhesive containing layer.

A clear pressure sensitive adhesive layer 83 is attached to and underlies metallic layer 82. A polymeric film layer 84 is adhered to and underlies pressure sensitive adhesive layer 83. A clear or pigmented layer 85, which would include non-woven materials, is adhered to and underlies adhesive layer 85. The layer 85 overlies pressure sensitive adhesive layer 86, which in turn is releasably bonded to release liner 87.

As discussed above, the present invention also relates to a method of preparing constructions with variable images. The method involves obtaining a multilayer construction having metallic layer and ablating a portion of the metallic layer to form an image with a laser. A useful laser is an Nd: YAG laser light source operating at an optical wavelength of approximately 1.064 micrometers.

The laser light source may be a Nd: YAG laser light source producing a focused beam of laser light at a wavelength of 1.064 microns and is directed through the multilayerconstruction approximately perpendicularto the plane ofthe multilayer construction. The beam will typically have a diameter of between 20 to 300 microns.

The laser light source may be configured to produce a pulsed output laser light beam. Pulsing of the laser light beam is necessary in order to avoid localized heating of the multilayer construction around the region of exposure of the metallic layer. Localized heating of the construction material can lead to visible damage of the material around the exposed areas, which degrades the quality of the patterns recorded in the construction.

The energy in each laser light pulse is adjusted such that as the laser light passes through the clear layer and the metallic layer sufficient energy in the region of incidence of the laser light that the metallic layer in that region is ablated-i. e. vaporized-while the remaining layers of the construction are relatively undamaged

by the laser light. The ablated material, which is trapped between the clear layer and adhesive layer re-condenses as micro-particles, which are too small to be seen with the naked eye. Hence the metallic layer appears transparent in the regions, which have been exposed, to the laser light beam. An area of the construction that has been exposed to the laser beam therefore takes on the color of either the contrast layer (if one is present), or the adhesive layer, or (if the adhesive is transparent) any substrate to which the multilayer construction is applied.

Typical parameters for the output of the laser light source are as follows: output wavelength-1.064 micrometers; pulse duration-between 1 and 10 microseconds; and pulse repetition rate-around 50 kHz. It should be appreciated that these laser parameters are indicative only and may be varied.

The stream of laser light is directed so as to produce a pattern in the metallic layer. Steering of the light beam may be achieved by controlling the orientation of a steering mirror apparatus in the path of the light beam. The scanning speed of the laser beam across the construction is adjusted in coordination with the repetition rate of the laser light pulses such that continuous lines can be recorded in the construction.

A computer may be useful to control the laser. The pattern recorded in the construction is therefore specified by a set of computer instructions. The computer instructions may originate from any of the following: bar code or two dimensional bar code pattern generation software; computer graphics or image files such as ATIFF@ files; and computer text files.

The present method thereby enables the recording of alphanumeric, bar codes, two- dimensional bar codes and other two-dimensional data patterns, graphics and images within the multilayer construction.

An example of the laser useful in producing the variable images of the present invention is described in PCT Publication WO 98/45827 published in the name of Mikoh Corporation Limited. This disclosure is incorporated herein by reference for the disclosure of the laser and the apparatus.

In one embodiment, the inventive method is applied to so-called hot stamping foil. All layers of the hot stamping foil except the metallized layer are substantially transparent or non-absorbing at the wavelength of the laser beam (i. e. at an optical wavelength of around 1.064 micrometers), while the metallized layer is substantially absorbing at this wavelength. Hence the metallised layer is ablated in the regions of exposure to the laser beam, leaving the"size"layer visible in such regions. In one embodiment, the size layer is visibly colore. The above described method of laser marking may be carried out with the hot stamping foil either before or after the foil is applied to a substrate.

In one embodiment, the hot stamping foil will include an additional contrast layer between the metallized layer and size layer in order to provide visible contrast between areas of the metallized layer which have been laser marked and areas which have not been laser marked.

Another variation is in relation to the construction of the label. In one embodiment the clear coat may be transparent at an optical wavelength of 1.064 microns but opaque at visible wavelengths. In this embodiment a pattern such as a bar code or two dimensional bar code can be recorded in the metallic layer but this pattern will not be visible to the naked eye. The recorded pattern may then be read via existing methods but using readers which have a light source with a wavelength at which the top coat is substantially transparent (such as a wavelength of 1.064 microns). In this embodiment the contrast layer (if included) will preferably be reflective at the said reader wavelength.

In one embodiment, the laser light source may be a laser diode light source operating at or near the optical wavelength of 1.064 micrometers.

It should be appreciated that the metallic layer need not be a metallized layer, but could be a layer of any material which is visibly and irreversibly damaged or modified by exposure to the laser beam.

While the invention has been explained in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.