SURFACE RESTRUCTURING PROCESS AND IMAGED MEDIA PRODUCED THEREFROM

Abstract: A method for increasing reflective optical density on a surface of an imaged substrate without adding pigments or dyes to the image is disclosed. The method provides a restructuring of the surface without adversely affecting the image. Restructuring is achieved by applying heat, pressure, or a combination of both to the surface of the imaged substrate. Once the restructuring step has been applied, the imaged substrate exhibits a higher gloss measurement and higher reflective optical density measurements than the same imaged substrate prior to the restructuring step. The restructuring step may also be used to apply topographical features to the imaged surface.

Description: Surface Restructuring Process and Imaged Media Produced Therefrom Field ofthe Invention This invention relates to a process of restructuring a surface of an imaged substrate and the imaged media produced therefrom. Background ofthe Invention Graphic images can be created on films, paper, and other media by a variety of well-known techniques including, but not limited to electrostatic imaging and, inkjet imaging. Such images, however, typically exhibit a rough or low gloss finish. One example of imaged media having a generally low gloss finish is the subject of U.S. Pat. No. 5,114,520 (Wang et al.). Typically, both the imaged media and the ink or pigment used to create the graphic image comprise thermoplastic materials. Because the graphic image is easily damaged after formation, additional layers are often provided over the image in order to provide desired surface characteristics. Clear polymeric films are often used as supplemental layers to provide decorative effects (e.g., a high gloss finish), abrasion resistance, and/or ultraviolet light protection. Unfortunately, the use of an additional layer increases the cost ofthe imaged media. In applications in which the purpose ofthe additional layer is primarily for decorative effect, such additional costs can render the use of a supplemental layer in connection with an imaged medium uneconomical in a competitive business environment. Summary ofthe Invention The present invention provides a method of restructuring a surface of an imaged medium without adversely affecting the image. More particularly, the invention relates to a method for restructuring a surface of an imaged substrate, including the steps of providing a substrate having an image on at least one surface, the image provided by at least one thermoplastic, providing a restructuring agent such as a substantially planar structure having an image contacting surface, contacting the imaged surface ofthe substrate with the image contacting surface of the restructuring agent under conditions of elevated temperature, pressure or a combination of temperature and pressure, and separating the restructuring agent from the imaged surface. As used herein, the term "restructuring" is intended to mean any process involving embossing, smoothing, texturing, patterning, impressing, engraving, or otherwise altering the surface of an imaged medium, typically, although not exclusively by the application of pressure, heat, or a combination thereof. In one aspect ofthe invention, is a method of changing the reflective optical density of an image on a surface of an imaged substrate without adding compositions to the image, is achieved by restructuring the surface to render it smoother. The method is intended to be carried out in a manner that does not adversely affect the image. Another aspect ofthe invention relates to a method for improving adhesion of a clear film to a surface of a substrate, bearing an image comprising the step of restructuring the surface ofthe substrate without adversely affecting the image. One feature ofthe present invention is that the method of restructuring the surface ofthe imaged substrate provides an altered surface according to a desired decorative effect. Another feature ofthe invention is that the imaged media can have an increased reflective optical density or a decreased reflective optical density depending on the desired decorative effect. The reflective optical density preferably is increased with a restructuring ofthe surface ofthe imaged media by smoothing the surface on which the image resides. The smoothing decreases surface aberrations that may reduce reflection ofthe image by incident light. Another feature ofthe invention is that the decorative effect can be controlled by a pattern on the surface of a restructuring agent used in the restructuring process. Another feature ofthe invention is that the decorative effect can also provide an improved surface that provides a higher gloss finish for the imaged media. Another feature ofthe invention is the ability to control optical properties ofthe surface ofthe imaged media by improving reflective density values. This results from a lessening of surface variations which can improve the regularity of light reflected from the surface. One advantage ofthe present invention is that of an added surface characteristic can be provided to the imaged medium without providing an additional material layer. This advantage provides an added benefit to the final imaged product without added materials cost. Another advantage is the ability to integrate the embossing process into a conventional electronic graphics system such as that disclosed in U.S. Pat. No. 5,114,520 (Wang et al.). Other features and advantages ofthe invention will become apparent as embodiments ofthe invention are described with reference to the following drawings. Brief Description ofthe Drawings Fig. 1 is a scanning electron micrograph showing the surface of a substrate prior to imaging and restructuring. Fig. 2 is a scanning electron micrograph showing the surface of an imaged substrate after imaging, but prior to restructuring. Fig. 3 is a scanning electron micrograph showing the surface of an imaged substrate after both imaging and restructuring. Embodiments ofthe Invention The restructuring process ofthe present invention may be applied to any of a variety of commercially available graphic imaging systems, techniques and materials. For example, one such graphic imaging systems is the Scotchprint™ Electronic Graphic System commercially available from 3M Company of St. Paul, MN. Likewise, the inventive restructuring method may be applied to a wide variety of methods of printing graphic images on media including, but not limited to electrostatic imaging, inkjet imaging, screenprinting, and the like. Nonlimiting examples of media used in the printing of graphics on media include paper; polymeric films (e.g., vinyl or polyester); and the like. Nonlimiting examples of inks used to print images on media include toners commercially available from a variety of suppliers including Scotchprint™ toners from 3M Company, American Inkjet Printing Fluid commercially available from American Ink Jet Corporation of Billerica, MA. Restructuring equipment In one embodiment, the restructuring equipment useful in the method ofthe present invention includes a roll laminator or another device that can provide pressure heat or a combination thereof. The restructuring equipment further includes a restructuring agent, preferably in the form of a plate, roll, sheet or three-dimensional master that has a restructuring effect (e.g., a smoothing effect in one aspect, or a texture, contour, or pattern in another aspect) that is used to generate the desired decorative effect on the imaged media by restructuring the surface ofthe imaged substrate. In one embodiment, the restructuring agent is a polymeric film sheet or web. If the restructured surface is to be smoothed, the film may be a smooth, high tensile strength film. The film may be provided with a silicone or other surface-energy reducing medium which allows the restructuring agent to be immediately removed from the restructured surface and reused. In a further embodiment, the roll laminator and restructuring agent can be combined to provide the desired decorative effect by providing the characteristics ofthe restructuring agent directly on at least one roll ofthe roll laminator. Non-limiting examples of commercially available roll laminators include the Pro-Tech Orca III brand laminator commercially available from Pro-Tech Engineering, Inc. of Madison, WI or a 3M™ Model 9540 laminator commercially available from 3M Company. Non-limiting examples of restructuring agents include polymeric sheeting such as Mylar brand film from Du Pont or Melinex brand film from ICI Americas. Such restructuring agents may be used to smooth the surface of imaged media. When a raised relief is desired, nonlimiting examples of restructuring agents include textured or patterned sheeting, either as a separate restructuring agent, or incorporated directly onto a laminator roll. Restructuring Method As stated above, the restructuring method uses a roll laminator and restructuring agent during the preparation of imaged media. After the image is provided on the media according to conventional techniques, the restructuring method can be carried out. This may be either prior or subsequent to completion of the final imaged graphic product. The restructuring agent is selected to provide desired smoothing or embossing effect on the imaged substrate by placing it in contact with the surface of the imaged substrate in an environment of elevated heat, pressure or both. In one embodiment, an optional protective cover sheet can be placed between the restructuring agent and the roll laminator to protect the laminator rolls. In use, the combination of imaged substrate, restructuring agent, and optional cover sheet is fed through the roll laminator. Once through the nip ofthe roll laminator, the cover sheet, if present, is removed, and then the restructuring agent is removed. The restructured surface ofthe imaged substrate may then be processed further in any conventional manner (such as described in U.S. Pat. No. 5,114,520) for packaging, storage, and later usage. The restructuring process can use a web speed of from about 0.1 to about 120 inches per second approx. (0.25 to 300 cm/sec), depending to the ability ofthe restructuring agent to restructure the imaged substrate under acceptable processing conditions, preferably from about 0.5 to about 3 inches per second (approx. 1.3 to 7.5 cm/sec) to assure even restructuring, and most preferably from about 1 to about 2 inches per second (approx. 2.5 to 5.1 cm/sec). The restructuring process can use a nip pressure in the roll laminator ranging from about 30 lbs/in 2 to about 70 lbs/in 2 (2.07xl0 5 to 4.82xl0 5 N/m 2 ) to provide sufficient pressure for the restructuring agent to cause the change in the surface ofthe imaged substrate. In one embodiment, the nip pressure is preferably maintained, from about 40 lbs/in 2 to about 60 lbs/in 2 (2.76xl0 5 to 4.13xl0 5 N/m 2 ) to assure an even restructuring ofthe imaged substrate, and most preferably is maintained about 60 lbs/in 2 (4.13xl0 5 N/m 2 ). The restructuring process can also use the application of heat, either alone or in combination with pressure application, during the restructuring. In particular, the restructuring agent or the roll laminator drums need to be heated, either prior to or while in contact with, the surface to be restructured. The temperature ofthe restructuring agent can range from about 30 to about 200 °C depending on the polymeric composition ofthe imaged substrate, the composition ofthe toners or inks used to create the image, and the composition ofthe restructuring agent. In one embodiment, the temperature ofthe restructuring agent is preferably maintained between about 50°C and about 175°C to more effectively smooth the roughened surface of a low gloss surface. Most preferably, the temperature is maintained between about 65°C and about 150°C. The characteristics of restructuring agent can vary greatly according to the desired surface effect on the final imaged substrate. The nature ofthe restructuring effect as an embossing effect can be geometrical, fractal, symbolic, or ornamental depending on the pattern appearing on the embossing agent. Non-limiting examples of patterns include diamond shapes, hammer tones, spirals, and other decorative effects. The nature ofthe restructuring effect as a smoothing effect can create a high gloss appearance due to a change in reflective optical density by smoothing roughness ofthe surface on which the image resides. When creating a high gloss surface, a smooth polymeric sheet can be used as the restructuring agent, and this can be applied to the imaged surface under conditions of elevated pressure and temperature to smooth the imaged surface and increase its reflective optical density. The resulting surface is generally free of any raised pattern or other topographical features. The interposition ofthe restructuring process in the production of the imaged media does not consume additional raw materials or add additional layers to the final imaged media. Furthermore, the restructuring agent may be reused repeatedly to reduce waste and material expense, while assuring reproducibility ofthe desired effect on large quantities ofthe media. Usefulness ofthe Invention Use ofthe restructuring method ofthe present invention can provide graphic image media having gloss measurements ranging from about 1 to about 200 according to the test described below under Gloss Measurement. Figs. 1-3 show a direct comparison ofthe same vinyl substrate before imaging (Fig. 1), after imaging (Fig. 2), and after the use ofthe inventive restructuring method (Fig. 3). The imaged substrate shown in Fig. 2 has a gloss measurement of about 10-15. After using the restructuring method, the imaged substrate shown in Fig. 3 has a gloss measurement of about 92-120. Use ofthe restructuring method ofthe present invention can provide an imaged medium having an improved reflective optical densities as well. For example, in the samples shown in FIGS. 2 and 3, reflective optical density measurements for black, yellow, cyan and magenta regions show increased optical density in the restructured samples. Specifically, the unrestructured black sample had a measured optical density of 1.43 and a restructured optical density of 1.79. This represents an improvement of approximately 25 %. The unrestructured yellow sample had a measured optical density of 0.94 and a restructured optical density of 1.05. This represents an improvement of approximately 12 %. The unrestructured cyan sample had a measured optical density of 1.43 and a restructured optical density of 1.85. This represents an improvement of approximately 29 %. The unrestructured magenta sample had a measured optical density of 1.39 and a restructured optical density of 1.63. This represents an improvement of approximately 17 %. At present, it is not known exactly how the restructuring method of the present invention provides improved gloss and reflective optical density measurements. While not being limited to a particular theory, it is believed that surface aberrations are restructured by application of heat, pressure, or a combination thereof into a surface that is more capable of reflecting incident light, all without the image being distorted during the restructuring process. While embodiments ofthe invention have been identified, the following examples provide further demonstration ofthe features and advantages ofthe present invention. Examples Materials and Equipment: Transfer Materials 8601 media— Scotchprint™ transfer material commercially available from 3 M Company of St. Paul, MN (hereinafter "3M") 8603 media— Scotchprint™ transfer material commercially available from 3M Substrates 8610 media— Scotchprint™ Electronic Imaging paper commercially available from 3M 8612 media— Scotchprint™ Electronic Imaging Exterior Poster paper commercially available from 3M 8620 media— Scotchprint™ vinyl receptor film commercially available from 3M 8640 media— Scotchprint™ vinyl receptor film commercially available from 3M 8641 media— Scotchprint™ vinyl receptor film commercially available from 3M Clear Films (used in Comparative Examples) 8910 media— Scotchprint™ film commercially available from 3M 8930 media— Scotchprint™ film commercially available from 3M Restructuring Agent Polyester— Mylar™ film commercially available from E.I. du Pont de Nemours & Co., Wilmington, DE (hereafter "Dupont") Laminator 9540 laminator— Scotchprint™ Laminator commercially available from 3M Printer 9512 printer— Scotchprint™ electrostatic printer commercially available from 3M Measuring Devices Glossmeter— Hunterlab glossmeter D48-7 commercially available from Hunter Associates Laboratory Inc. Densitometer— X-Rite 418 densitometer commercially available from X-Rite, Inc., Grandville, Michigan. Experimental and Test Descriptions: Density measurements: In the following tables, "K" means black; "Y" means yellow; "C" means cyan, and "M" means magenta. Measurements were made using the X-Rite 418 densitometer described above Gloss measurements: Measurements were made using the Hunterlab D48-7 glossmeter using Specular Glass Standard (D33G-4656) instrument #2. Tape test: 3M Scotch™ brand 610 tape is applied to the sample. A 3M squeegee is used to apply to the tape with 3 strokes. The tape is pulled off in a single motion, slowly at an angle of 180°. For each ofthe Examples described herein, the 9512 printer was used with toners commercially available from 3M to generate an image on the transfer material. Then the image was transferred to the substrate at standard transfer conditions of 205 °F, 60 psi, and 1.5 inches/sec (96 °C, 4.13xl0 5 N/m 2 , and 3.81 cm sec) Next, a 2x9 inch (5.1x22.9 cm) sample ofthe graphic imaged substrate with restructuring agent and optional cover sheet thereon were run through the laminator under a variety of conditions shown in the following tables. Once through the laminator, the optional cover sheet and the embossing agent were removed from the graphic image substrate. Gloss measurements and density measurements were performed as described above. The results of such tests are presented in Table 1 below which shows the construction of the transfer material, substrate, and clear film (if used), to form the Examples and Comparative Examples. None ofthe data presented in Table 1 reflects samples that have been subjected to the inventive restructuring process. Rather, the Table is intended to establish a baseline by which gloss and optical density of restructured samples can be compared. TABLE 1 Transfer Substrate Clear Gloss Black Yellow Cyan Magenta — 8610 none 2-5 1.46 0.98 1.37 1.37 8601 * 8620 none 10-15 1.43 0.94 1.43 1.39 8601 8640 none 10-15 — 0.98 1.40 1.37 8603 8620 none 17-25 1.49 0.90 1.31 1.30 8603 8640 none 15-20 1.53 0.93 1.42 1.37 8603 8641 none 15-20 1.47 0.88 1.31 1.27 — 8610 8910 83-85 1.99 1.13 1.76 1.66 8601 8620 8910 87-88 1.76 1.03 1.65 1.56 8601 8640 8910 86-88 1.75 1.00 1.59 1.48 8603 8620 8910 84-86 1.65 0.95 1.39 1.38 8603 8640 8910 86-88 1.59 0.96 1.44 1.42 8603 8641 8910 80-82 1.70 0.94 1.51 1.43 — 8610 8930 118-120 1.88 1.15 1.73 1.64 8601 8620 8930 116-120 1.70 1.06 1.61 1.55 8601 8640 8930 118-120 1.58 1.00 1.60 1.48 8603 8620 8930 115-118 1.60 0.98 1.45 1.38 8603 8640 8930 115-118 1.63 0.97 1.47 1.40 8603 8641 8930 — 1.63 0.95 1.45 1.40 The sample referenced in this row is that shown in FIG. 2 As can be seen from Table 1, samples having a layer of 8910 or 8930 clear film exhibit generally higher gloss and optical density values than samples lacking such films. In Table 2, a variety of film structures are compared. In these examples, the samples are provided with a layer of 8910 film, a layer of 8930 film, or restructured. Samples lacking the additional film or restructuring are included as controls. TABLE 2 Transfer Substrate Clear Gloss Black Yellow Cyan Magenta 8601 8620 8930 111-121 1.65 1.02 1.56 1.50 8601 8620 8910 83-85 1.70 1.03 1.66 1.58 8601 8620 None 12-16 1.39 0.94 1.40 1.33 860 l f 8620 R 92-120 1.79 1.05 1.85 1.63 8603 8620 None 20-22 1.50 0.89 1.33 1.29 8603 8620 R 80-86 1.66 0.95 1.45 1.40 8603 8620 8930 117-118 1.62 0.97 1.45 1.38 8603 8620 8910 83-87 1.65 0.94 1.46 1.41 8603 8641 None 17-18 1.55 0/89 1.37 1.31 8603 8641 R 76-79 1.71 0.94 1.47 1.30 8603 8641 8930 115-118 1.70 0.93 1.51 1.40 8603 8641 8910 86-87 1.73 0.93 1.49 1.40 τ The sample referenced in this row is that shown in FIG. 3 In each case, the value "R" in the clear column, indicates that the sample was subject to the inventive restructuring process. Restructuring was carried out using a 3M SCOTCHPRINT™ 9540™ Laminator using cylinders having a diameter of between 4 and 6 inches (10.2-15.2 cm). The laminator was run at a temperature of approximately 205 °F, a speed of approximately 1.5 inches/second, and a pressure set point of approximately 60 psi. The results from Table 2 show that the use ofthe restructuring agent in the midst of a commercially available process to produce imaged graphics substantially improves the gloss finish and the reflective optical densities ofthe image without harming the image and without introducing additional layers or coatings. The resulting image on the restructured surface appears more vivid with same amount of toners in the image. Qualitative tape tests were carried out on numerous restructured and non-restructured samples. In each case, removal ofthe tape caused significant surface alteration and damage (i.e., pigment removal) on the non-restructured samples, and little, if any, detectable alteration or damage to the restructures samples. As such, the tape tests demonstrate that surface durability of printed substrates can be substantially improved by the restructuring method ofthe present invention. The scanning electron micrographs of Figs. 1, 2, and 3 show an imaging substrate surface prior to imaging and restructuring, after imaging and prior to restructuring, and after imaging and after restructuring, respectively. The restructuring shown in Fig. 3 does provide significant smoothing, although some debris 10 (resulting in the depression seen in the center of Fig. 3) can affect the consistency of restructuring. Equivalents Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope ofthe invention intended to be limited only by the claims set forth herein as follows.

Claims: CLAIMS What is claimed is: 1. A method for restructuring a surface of an imaged substrate, comprising: a) providing a substrate having an image on at least one surface thereof, the image provided by at least one thermoplastic material; b) providing a restructuring agent comprising a substantially planar structure having an image contacting surface; c) contacting the surface ofthe substrate with the image contacting surface ofthe restructuring agent under conditions of elevated temperature, pressure or a combination thereof and restructuring the surface ofthe substrate without adversely affecting the image on the surface; and d) separating the restructuring agent from the restructured surface. 2. The method of Claim 1, wherein the restructuring agent comprises a polymeric material in a film, sheet, roll, or continuous web. 3. The method of Claims 1 or 2, wherein, prior to the contacting step, the image contacting surface ofthe restructuring agent is smoother than the imaged surface. 4. The method of Claims 1 or 2, wherein the image contacting surface ofthe restructuring agent has a surface adapted to impart a texture to the imaged surface. 5. An imaged substrate having a restructured surface made by the process of any of Claims 1-4.

Inventors: PEDERSON JEFFREY C, PEDERSON, JEFFREY, C.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1996
Main classification: B41M7
IPC codes: B41F23, B41M7, B44C1