Patent Application
20080087379
The present invention can be further described with reference to the following drawings, wherein:
These figures are idealized, are not drawn to scale, and are intended merely for illustrative purposes.
Turning to the construction of the repositionable adhesive backed photographs and photo media, each of the various components will be discussed in detail including the imageable substrate and the attachment mechanism.
The imageable substrate that can be used in the present invention can be single or multilayer in construction and contains one major surface that is capable of being imaged, either digitally imaged or imaged via the conventional silver halide wet chemical process. The imageable substrate can be paper based or polymer based. Paper based imageable substrates have a basis weight in the range of about 125 to 210 gram/square meter (g/m2). As described above with reference to the figures, the imageable substrate can be first laminated to the attachment mechanism and then digitally imaged. Alternatively, the imageable substrate is first imaged, and then laminated to the attachment system. In the latter approach, one suitable substrate is the silver halide photo paper that has been processed through the wet chemical process to yield a photograph.
A silver halide photo paper typically contains a cellulose fiber paper support that has a polyolefin resin extrusion laminated on at least one major surface of the paper and more commonly on both major surfaces. A common polyolefin material used in the industry is polyethylene. The coated paper then goes through a series of processing steps where various chemicals are coated to a first major surface of the paper resulting in an image receptive side, to form the photosensitive silver halide chemistry. U.S. Pat. No. 6,045,965 (Cournoyer et al.) describes the various coatings and chemistries used to produce photosensitive silver halide paper. Manufacturers such as Eastman Kodak Company and Fuji Photo Film Company are well known suppliers silver halide photo paper. A second major surface of the paper (opposing the first major surface) is the backside. On the backside, over the polyolefin coating, there may be additional coatings that modify the surface properties of the polyolefin (such as, e.g., its coefficient of friction or its electrical resistivity).
Suitable thermally activating adhesive that can be used in the present invention includes polyamides, polyolefin homopolymers (such as, e.g., polyethylene and polypropylene), derivates thereof, and copolymers thereof. Examples of polyolefin copolymers include ethylene-acrylic acid copolymers, polypropylene acrylic acid and polyethylene acrylic acid copolymers, polyethylene vinyl acetate copolymers, and blends of polyethylene and ethylene vinyl acetate. Homopolymers of ethylene vinyl acetate can also be used. Useful commercially available thermally activating adhesives include Primacor™ 3330 from Dow Chemcial, Polybond 1001 from BP Performance Polymers, Santoprene™ (dynamically vulcanized polyolefins) from Monsanto Chemical Company. The thermally activating adhesive adheres to thermoplastic and thermoset substrates. When exposed to heat and in a molten form, the thermally activating adhesive achieves a high degree of compatible interfacial mixing with a thermoplastic substrate. With a thermoset substrate, the molten thermally activating adhesive wets out the substrate surface resulting in a high strength bond between the two when cooled. The thermally activating adhesive may also contain fillers such as pigments, cross linking agents, viscosity agents, dispersants, antioxidants, plasticizers, and extrusion aids.
As stated above, photographic prints exposed to high or low humidity conditions will expand and contract. In order for the attachment mechanism to accommodate the expansion and contraction the photograph experiences, the attachment mechanism needs to be to sufficiently elastic. It should be noted that the concept of elasticity and stiffness are related. A highly elastic material will have a low stiffness and vice versa.
The inventors have discovered that the carrier film of the attachment mechanism can be chosen to accommodate the expansion and contraction of the photograph. The carrier film should be able to stretch and contract, i.e., should be sufficiently elastic, without applying sufficient lateral force to the photograph to cause substantial curling. Curling is substantial if it causes debonding or lifting of the repositionable adhesive from the display surface of more than about 3 mm after conditioned for seven days at about 23° C. and 20% relative humidity. Curl can be measured by the height of the highest region, typically a corner, of the photograph when laid on a flat surface.
The elastic properties, and thus the stiffness, of the carrier film are determined by the combination of its thickness and its Young's modulus. Suitable carrier films have a Young's modulus of about 0.5 giga-Pascal (GPa) or less. In one embodiment, the carrier film has a Young's modulus of about 0.1 GPa or less. In contrast, the printed literature and text books list a Young's modulus of 2.5 to 7 GPa for bond paper, such as paper used in photo copying machines. The present invention is inoperable when bond paper is used as the carrier film of the attachment mechanism. The thickness of the carrier film is less than about 200 micrometer and preferably less than about 100 micrometer.
The combination of the carrier film's thickness and its Young's modulus should be such that the stiffness of the carrier film is less than about 50,000 Newton per meter in its cross-web direction, as measured according to ASTM 882-02, Standard Test Method for Tensile Properties of Thin Plastic Sheeting. In another embodiment, the carrier film has a stiffness of less than about 20,000 Newton per meter in its cross-web direction, as measured according to ASTM 882-02. In brief summary, the test involves cutting a cross-web sample strip from a web of carrier film. The strip measures about 25 mm wide and 305 mm long. The initial separation distance of the jaws is about 254 mm. The ends of the strip are inserted into the jaws of an Instron Model 4464 stress-strain machine. The Instron machine pulls the strip apart (i.e., the jaw distance widens from its initial separation distance) at a rate of about 25.4 mm per minute. A graph of the load (in Newtons) versus the extension (in meters) of the sample strip is then plotted to generate a curve. A change in strain (Δ Strain) between two points on a linear portion of the curve is calculated as the change in separation of the jaw distance divided by the initial jaw separation distance. The change in load (Δ Load) between the same two points on the linear portion of the curve is recorded. The stiffness of the sample can then be calculated according to the following equation: Stiffness=(Δ Load÷W)÷(Δ Strain), where W represents the width of the sample over which the load is applied.
Suitable carrier films include tissue paper, natural polymer film, synthetic polymer film, woven fabric, and non-woven fabric. It should be noted that the stiffness of the carrier films can differ in the down web and cross web directions. Dimensional changes of a photograph, however, at high and low relative humidity conditions tend to be greater in the cross web direction than the down web direction. Thus, it is the cross web stiffness of the carrier film that is measured.
Suitable repositionable PSA that can be used in the present invention includes microsphere adhesives. An exemplary microsphere adhesive includes polyacrylic derivatives. The repositionable adhesive can be solvent based, water based, or can be a solventless, hot melt adhesive. Suitable repositionable adhesives includes those disclosed in the following U.S. Pat. No. 3,691,140 (Silver); U.S. Pat. No. 3,857,731 (Merrill et al.); U.S. Pat. No. 4,166,152 (Baker et al.); U.S. Pat. No. 4,495,318 (Howard); U.S. Pat. No. 5,045,569 (Delgado); U.S. Pat. No. 5,073,457 (Blackwell); U.S. Pat. No. 5,571,617 (Cooprider et al.), U.S. Pat. No. 5,663,241 (Takamatsu et al.); U.S. Pat. No. 5,714,327 (Cooprider et al.); US RE 37563 (Cooprider et al.); U.S. Pat. No. 5,756,625 (Crandall et al.); U.S. Pat. No. 5,824,748 (Kesti et al.); and U.S. Pat. No. 5,877,252 (Tsujimoto et al.).
The liner covers and protects the repositionable adhesive and the substrate until it is imaged and ready for display. The liner can be any paper or plastic sheet that bonds to the repositionable adhesive securely during storage and while passing through the feed mechanism of a printer. The liner releases cleanly and easily from the repositionable adhesive after the photo media has been imaged. The liner may be treated with a release coating to achieve the desired release performance. The release coating would be disposed on the first surface of the liner such that it would be disposed on the repositionable adhesive. Suitable coatings include are those that based on straight chain alkane derivatives, polydialkyl siloxane derivatives, or fluorocarbon derivatives. One exemplary release coating is described in U.S. Pat. No. 5,032,460 (Kantner et al.). The release coating will be applied on the liner, typically the entire surface area of the liner, to reach a dry coating weight of from 0.05 to 0.1 g/ft2 (0.54 to 1.1 g/m2). Suitable silicone-based release liners are commercially available from Loparex, Inc., Willowbrook, Ill.
The repositionable adhesive backed photographs and photo media of the present invention can be further characterized by two adhesion tests: (1) adhesion to polyester (specifically polyethylene terephthalate), and (2) static angle test (SAT). Both are described below in detail.
The adhesion to polyester test is performed by laminating a 1.25 inch (32 mm) strip of plain polyester, product designation OR16 film from 3M Company, St. Paul, Minn., over the previously coated and dried sample of repositionable adhesive. The polyester is laminated to the adhesive by using a 2 kg rubber coated roller rolling at a rate of 12 inch/min (25.4 mm/min). Using a stress/strain gauge, such as one available from Instron Corp., the polyester film is pulled away from the adhesive at a 90° angle at a peel rate of 12 inch/min (305 mm/min). The peel force is recorded in grams/inch.
The SAT measures the ability of the photo media with its repositionable pressure sensitive adhesive to remain adhered on a standard test panel while being subjected to removal pressure at a specified peel angle under a constant load. The static angle test is one quantitative procedure for measuring detachment resistance of the photo media.
In performing static angle test, six photo media samples can be prepared using the following exemplary process. The samples are all the same size, 33 mm wide by 76 mm long. Each sample of photo media includes an adhesive stripe that is 18 mm wide by 33 mm long, where the long dimension of each adhesive stripe is positioned along the short dimension of, and at the top of, each photo media sample.
The test panel is a steel panel with a painted surface. Each sample is applied to the painted steel panel with the long dimension of the adhesive stripe horizontally oriented and located at the top of the photo media sample. Then, the sample is pressure adhered to the painted steel surface by two passes of an application roller with an application pressure of 1.5 pounds per square inch (77.6 mm of mercury).
The mounted sample is placed in a holder frame that is vertically oriented approximately perpendicular to a ground surface. The painted steel panel is held at a 30° downward angle relative to the vertically oriented frame. A 100 gram load is applied to the lower end of the photo media sample, proximate to the lower end of the holder frame. A timer is started upon application of the 100 gram load to measure how long the sample remains attached to the painted steel surface before the photo media sample detaches from the steel panel. The SAT usually runs to failure, i.e., until the sample actually detaches form the steel panel. The time to detachment is usually measured in seconds as the average of six results.
The repositionable photo media and repositionable photograph has an adhesion to polyester value of 300 gram/inch (11.8 gram/mm) or less, preferably less than 200 gram/inch (7.9 gram/mm), and more preferably less than 160 gram/inch (6.3 gram/inch), and a SAT value of 600 seconds or greater, preferably 1800 seconds or greater. The lower the adhesion to polyester value, the easier it will be to remove the photo media from the substrate to which it has been attached. The higher the SAT value, the more likely the photo media will remain adhered to the intended substrate once it has been applied.
The stiffness of various carrier films was measured according to ASTM 882-02. The results are tabulated in Table 1. All the samples had a width of 0.025 meters except for Comparative Example A, wherein a narrower sample width of 0.005 m was used to keep the load measurements for all examples on the same scale.
The carrier film of Example 1 was a semi-crepe white tissue paper having a basis weight of about 13 grams per square meter having an average caliper of 38 micrometers and a Gurley porosity 22 by TAPPI test method 460. The paper was supplied from Burrows Paper Corporation, Little Falls, N.Y. and with an Internet website address of www.burrowspaper.com.
The carrier film of Example 2 was a Grade 85, 22 pound towel tissue paper supplied from SCA Tissues North America (Svenska Cellulosa Aktiebolaget, translating to Swedish Cellulose Incorporated), Neenah, Wis. and with an Internet website address of www.scatissue.com.
The carrier film of Example 3 was a spunbound polypropylene non-woven fabric having a basis weight of 34 grams per square meter. The non-woven fabric was supplied from Polymer Group, Inc., Charlotte, N.C. and with an Internet website of www.polymergroupinc.com.
The carrier film of Example 4 was a spunbond, meltblown, spunbond composite polypropylene non-woven fabric having a basis weight of 22 grams per square meter. The non-woven fabric was supplied from First Quality Nonwovens, Inc., Great Neck, N.Y. and with an Internet website address of www.fqnonwovens.com.
The carrier film of Comparative Example A was bond paper having a basis weight of 80 grams per square meter and an average thickness of 100 micrometer. The bond paper was supplied from Boise Cascade, LLC, Boise, Id. and with an Internet website address of www.bc.com.
As the data in Table 1 shows, carrier films of Examples 1 to 4, all had a stiffness value of less than 50,000 Newton per meter. Comparative Example A, however, had a stiffness value well in excess of 50,000 Newton per meter and thus would be too stiff (i.e., not elastic enough) to function as a carrier film in the attachment mechanism. In fact, a photograph having the attachment mechanism incorporating the carrier film of Comparative Example A curled through an angle of about 100 degrees after being conditioned in a low humidity, i.e., at 20% relative humidity, at 23° C. for four weeks.
Although specific embodiments of the present invention have been shown and described, it is understood that these embodiments are merely illustrative of the many possible specific arrangements that can be devised in application of the principles of the invention. Numerous and varied other arrangements can be devised in accordance with these principles by those of ordinary skill in the art without departing from the spirit and scope of the invention. Thus, the scope of the present invention should not be limited to the structures described in this application, but only by the structures described by the language of the claims and the equivalents of those structures.
This application claims priority to U.S. Provisional application 60/829024 filed on Oct. 11, 2006. This application is also related to application 63603US002, entitled Adhesive Composite, application 63604US002, entitled Photographic Print with Adhesive Composite, and application 63605US002, entitled Method of Making a Photographic Print with Adhesive Composite, all applications being filed on even date herewith.
| Number | Date | Country | |
|---|---|---|---|
| 60829024 | Oct 2006 | US |
