Patent Application
20060024487
The present invention relates in general to creation of stencils and in particular to creating stencils by imaging microencapsulated material to weaken the borders around the desired stencil characters.
Stencils are useful for making personal items with an individual's name or other identifying information. A problem with making stencils is that they must be either assembled from precut stencil letters and numbers, or the desired message must be cut into the sheet of material to be used for the stencils by a knife or blade. Yet another alternative is stenciling one letter at a time, which is tedious. Both processes are time-consuming and labor intensive. This is especially true for consumers who wish to stencil information on personal items and may only use the stencil one time for one item. An additional problem is that there is no present method for easily creating stencils to make multicolored images.
Photohardenable imaging systems employing microencapsulated radiation sensitive compositions are the subject of U.S. Pat. Nos. 4,399,209; 4,416,966; and 4,440,846. These imaging systems are characterized in that an imaging sheet including a layer of microcapsules containing a photohardenable composition in the internal phase is image-wise exposed to actinic radiation. In the most typical embodiments, the photohardenable composition is a photopolymerizable composition including a polytthylenically unsaturated compound and a photoinitiator and is encapsulated with a color former. Exposure to actinic radiation hardens the internal phase of the microcapsules. Following exposure, the imaging sheet is subjected to a uniform rupturing force by passing the sheet through the nip between a pair of pressure rollers.
Briefly, according to the present invention an apparatus for creating stencils uses microencapsulated material and a printhead for image-wise exposing of the microencapsulated material in a pattern which leaves unexposed an outline of stencil characters. A roller ruptures unexposed microcapsules and a chemical in the ruptured microcapsules weakens material outlining the stencil characters.
A printhead, which exposes microcapsules to form images in materials, is adapted for making stencils cheaply and efficiently. In one embodiment of the invention, the letter or numeral to be cut into the stencil is imaged on the microencapsulated material. The microcapsules in the exposed area contain chemicals that weaken the sheet material in the exposed area. The weakened area is then removed to form a stencil.
In another embodiment, a computer is used to form words, numbers, bar codes, or combinations of all of these, and transmit the image pattern to a printhead. The image pattern may be transmitted by computer cable, the Internet, or other electronic means. The printhead forms the image in the microencapsulated material. The exposed material is passed through a set of rollers which ruptures the unexposed microcapsules. Chemicals contained within the unexposed microcapsules weaken the support material so that the characters generated by the computer may be removed from the sheet, thus inexpensively and quickly creating stencils. The stencils could be adapted for home use, ordered from a web site by transmitting the information to be used to create stencils, or ordered at a kiosk.
In the preferred embodiment, the imaged area may be weakened only along the borders of the area to be removed, rather than weakening the entire area of the stencil character. In another embodiment, a series of stencils is formed for each color in a composite image to create a color image stencil. In this embodiment, the computer parses the image into a series of images based on colors present in the image, and generates a series of sub-images, which are then used to generate stencils for each color.
A self-contained imaging assembly comprises a composition comprising photohardenable microcapsules and a degradable polymer material disposed between a first transparent support and a second support, which may be opaque or transparent to form a sealed assembly. The assembly is image-wise exposed to actinic radiation and subjected to an uniform rupturing force to provide stencil character in the composition.
The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below.
The present invention will be directed in particular to elements forming part of, or in cooperation more directly with an apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
In the self-contained imaging system 10 of the present invention, shown in
In the imaging system of the invention, the previously mentioned first support 11 is transparent and the second support 20 may be transparent or opaque. Sometimes herein the first support may be referred to as the “front” support and the second support may be referred to as the “back” support.
In order to insure that the self-contained imaging system 10 is effectively sealed between the supports, a subbing layer (not shown) may be provided between one of the supports and the imaging layer 12 and an adhesive 18 is provided between the other support and the imaging layer. For optical clarity, the subbing layer will typically be located between the first support and the imaging layer. However, which support receives the subbing layer and which support receives the adhesive is a function of which support is coated with the wet imaging layer composition and which support is assembled with the coated and dried imaging layer. The support which is coated with the imaging layer composition (which is typically the front support) will be provided with the subbing layer and the support which is assembled will receive the adhesive. In accordance with the preferred embodiment of the invention, the subbing layer is formed from a compound having chemical moieties such as hydroxy groups which will react with and bind to the microcapsules 14.
One of the most difficult technical hurdles in providing the sealed self-contained assembly of the invention arises from the use of an imaging layer 12 containing both the microcapsules 14 and the material 16 containing a degradable polymer. This format is desirable because the image, in this case the stencil pattern, is formed in direct contact with the front transparent support through which the image is viewed. If the amount of the photoinitiator in the microcapsules is reduced to reduce undesirable background degradation, the film speed of the system is often reduced to such a level that the microcapsules cannot be fully cured without excessively long exposures. In accordance with a particular embodiment of the invention it has been found that an imaging layer containing microcapsules in admixture with the degradable polymer can be provided if the microcapsules contain a disulfide coinitiator as described in U.S. Pat. No. 5,230,982 which is incorporated herein by reference.
Another problem encountered in blending microcapsules 14 and material 16 in a single layer is that the two materials may not be compatible and may agglomerate. If there is an interaction between the degradable polymer and the microcapsules which results in agglomeration, the imaging layer can not be coated with the uniformity and continuity required in a photographic product. The difficulty here is that the microcapsules are prepared from emulsions which incorporate certain system modifiers or emulsifiers and the degradable polymers are also frequently obtained as emulsions which incorporate emulsifiers. If the two emulsifier systems are not compatible with each other, agglomeration results and high photographic quality cannot be obtained. In particular, the applicants have found that it is preferred to encapsulate photohardenable compositions containing acrylates in melamine formaldehyde microcapsules prepared using pectin as the system modifier.
As illustrated in
Imaging layer 12 typically contains about 80 to 20% (dry weight) microcapsules and 0 to 20% of a binder. The layer is typically applied in a dry coat weight of about 8 to 20 g/cm.sup.2. An example of such a coating formulation is illustrated below.
In the self-contained photohardenable imaging assembly as shown in
Adhesive materials useful in the adhesive layer 18 in the present invention can be selected from the general class of “modified acrylics” which have good adhesion, and which may be formulated with improved “tack” by addition of tackifying resins or other chemical additives. A useful adhesive must be designed for high initial adhesion and for adhesion to plastic substrates like polyester. It must have the ability to flow quickly for laminating to porous material (the imaging layer) and yet have inertness to the imaging layer. High strength adhesives specifically found useful in this invention are the film label stock adhesives of the 3M Company; preferred are 3M's #300 and #310 adhesive formulas which have shown good “inertness” to the imaging layer and its stability, and are useful when applied in the amount of about 0.5 to 2.0 g/m.sup.2.
Useful photohardenable compositions, photoinitiators, chromogenic materials, carrier oils and encapsulation techniques for the layer of microcapsules 14 are disclosed in U.S. Pat. Nos. 4,440,846 and 5,230,982 which are herein incorporated by reference. Preferred photohardenable compositions are described in U.S. Pat. No. 4,772,541, which is incorporated herein by reference. The aforesaid photohardenable compositions are non-silver systems. Also useful in the present invention is a silver-based photohardenable microencapsulated system such as that described in U.S. Pat. Nos. 4,912,011; 5,091,280 and 5,118,590 and other patents assigned to Fuji Photo Film Co.
In accordance with one embodiment of the invention, a system is provided in which the microcapsules are sensitive to red, green, and blue light respectively. The photohardenable composition in at least one and preferably all three sets of microcapsules is sensitized by a cationic dye-borate anion complex, e.g., a cyanine dye/borate complex as described in U.S. Pat. No. 4,772,541. Yellow, red and green sensitive cyanine borate initiators are examples. Such a material is useful in making contact prints or projected prints of color stencils. They are also useful in electronic imaging using lasers, light emitting diodes, liquid crystal displays or pencil light sources of appropriate wavelengths.
In accordance with a preferred embodiment of the invention, the photohardenable compositions used in the microcapsules contain a dye borate photoinitiator and a disulfide coinitiator. Examples of useful disulfides are described in U.S. Pat. No. 5,230,982 and are compounds of the formula (I)
wherein X is selected from the group consisting of S and O except in a specific case in which the disulfide is derived from one or more tetrazolyl groups; n represents 0 or 1; A represents the residue of a ring containing the N, C and X atoms, the ring containing five or six members and, in addition, the ring members may be fused to an aromatic ring; and R.sup.5 is an aromatic radical selected from the group consisting of (i) phenyl, (ii) benzothiazolyl, (iii) benzoxazolyl, (iv) tetrazolyl, (v) pyridinyl, (vi) pyrimidinyl, (vii) thiazolyl, (viii) oxazolyl, (ix) quinazolinyl, and (x) thiadiazolyl, each of which may have a substituent on one or more C or N atoms of the ring. Two of the most preferred disulfides are mercaptobenzothiazo-2-yl disulfide and 6-ethoxymercaptobenzothiazol-2-yl disulfide. By using these disulfides as described in the referenced patent, the amount of the photoinitiators used in the microcapsules can be reduced to levels such that the background coloration or residual stain is less than 0.3 and preferably less than 0.25 density units. At these low levels, the low density image area coloration of the imaging layer does not detract unacceptably from the quality of the image.
The photohardenable compositions of the present invention can be encapsulated in various wall formers using techniques known in the area of carbonless paper including coacervation, interfacial polymerization, polymerization of one or more monomers in an oil, as well as various melting, dispersing, and cooling methods. To achieve maximum sensitivities, it is important that an encapsulation technique be used which provides high quality capsules which are responsive to changes in the internal phase viscosity in terms of their ability to rupture. Because the borate tends to be acid sensitive, encapsulation procedures conducted at higher pH (e.g., greater than about 6) are preferred. Melamine-formaldehyde capsules are particularly useful. It is desirable in the present invention to provide a polyurea pre-wall in the preparation of the microcapsules. U.S. Pat. No. 4,962,010 discloses a particularly preferred encapsulation useful in the present invention in which the microcapsules are formed in the presence of pectin and sulfonated polystyrene as system modifiers. A capsule size should be selected which minimizes light attenuation. The mean diameter of the capsules used in this invention typically ranges from approximately 1 to 25 microns. As a general rule, image resolution improves as the capsule size decreases. Technically, however, the capsules can range in size from one or more microns up to the point where they become visible to the human eye.
Images are formed in the present invention in the same manner as described in U.S. Pat. No. 4,440,846. By image-wise exposing this unit to actinic radiation, the microcapsules are differentially hardened in the exposed areas. The exposed unit is subjected to pressure to rupture the microcapsules.
The imaging sheet, in the form of a continuous web 19, is typically supplied from a supply roll 48 and transported by feed rollers 40 powered by a motor (not shown) along a longitudinal path in the direction of the arrow to the exposure head 32. The second pair of rollers 56 may or may not be powered by a motor. It is conceivable that the second pair of rollers 56 are powered by a motor and the first set of rollers 40 act as non-powered guide rollers.
As the web 19 passes between the beam-forming aperture plate 42 and support plate 52, a driving system causes the exposure head 32, to oscillate laterally on a carriage rail 44 across the web 19 to form a latent image thereon. After exposure, the web 19 is transported, in one aspect of the invention, the exposed web 19 is passed between the pressure applicator head 34, sometimes referred to as a “roller,” and the support plate 52 to develop the exposed web 19. After the exposed web 19 is developed, the web may be cut transversely using a cutting means (not shown) to provide an individual sheet containing the desired image or stencil. In another aspect of the invention, the exposure head 32 and the pressure applicator head 34 not only oscillate laterally across the imaging media but also traverse through the imaging media in the machine direction longitudinally in a stepwise manner.
The pressure applicator head 34 comprises at least one point contact element 58 and, preferably, a plurality of such point contact elements. The pressure applicator head 34 oscillates laterally across the exposed web 19 so that the point contact elements 58 provide a plurality of overlapping lateral paths across the exposed web 19. The pressure exerted on the exposed web 19 by the point contact elements 58 as they traverse the exposed web 19 causes the unexposed microcapsules to rupture thereby allowing the image-forming material to contact the degradable polymer material and develop the exposed web 19 to form an image thereon. Movement of the advancing web 19 in the machine direction may be continuous or in a stepwise manner and is synchronized with the lateral oscillation of the combined scanning exposure and pressure applicator apparatus 30; or the web 19 may be stationary as indicated above, in which case the exposure head 32 and the pressure applicator head 34 not only oscillate laterally across the imaging media but also traverse the media in the machine direction in a stepwise manner to expose and develop the imaging media. The invention may also be practiced with single sheets rather than a continuous web.
The drive system which causes the exposure head 32 and the pressure applicator head 34 to oscillate across the imaging media may be any device which influences the exposure head 32 and the pressure applicator head 34 to oscillate. Typically, the drive system comprises but is not limited to a continuous motor, a step motor, programmed motors, and the like. The motor which causes the exposure head and the pressure applicator head, or the imaging media, to move in the machine direction may be the same motor which oscillates the exposure head and pressure applicator head laterally or a different motor may be used.
To effect complete diffusion and to activate the chemical contained in the capsules, a post heating step may be desirable. In this case a very simple heated roller may be employed. Other methods include thermal radiation, a thermal head such as is used in thermal dye transfer printers. Any method for heating can be used which is broad area and controllable.
The chemical in the capsule is a material which can cause degradation of the polymer. An acid can be used if it is compatible with the capsule making process. In the event that the method of making the capsules is acid sensitive then an acid precursor is used. This is the preferred embodiment in that the acid precursor is not an acid until it has been heated. Upon heating the acid precursor generates a strong acid which causes the degradation of the degradable polymer.
An acid precursor which can be used in the present invention is discussed below. Specific examples of such acid precursors include the diazonium salts described in S. I. Schlesinger; “Photopolymerization of Epoxides” Society of Photographic Scientists and Engineers, Volume 18, No. 4, July/August 1974, pages 287-393; and T. S. Bal et al.; “Photopolymerization of 1,2-epoxypropane and 1,2-epoxybutane by arenediazonium salts: evidence for anion dependence of the extent of polymerization” Polymer, Volume 21, April 1980, pages 423-428. Other examples are cited in U.S. Pat. No. 5,658,708.
One material which may be used for the degradable polymer is Polyacetal resin, which is sold under the trade name of Duracon. It is also called polyoxymethylene resin or POM resin, and has the chemical structure as shown below.
—(CH2O)n—
This resin is highly crystalline, tough, and resistant to various chemicals, therefore it is used as a typical engineering plastic in various applications. Although polyacetal resin is highly crystalline, tough, chemically resistant, and superior in friction and wear properties, it is decomposed or degraded under extremely high temperature or in the environment containing acidic components. Furthermore, this decomposition reaction continues successively, once it is started. It is sometimes called unzipping reaction, since it seems as if a zipper were unzipped one tooth by one tooth. Another example of a suitable degradable polymer is polyphthalaldehyde.
In one embodiment of the invention, microcapsules containing an acidic solution are mixed with a degradable polymer. The microcapsules and the degradable polymer are sandwiched between a first and second layer using an adhesive to form a self-contained imaging sheet. The microcapsules are selectively hardened to form an image of a word, number, image, or any combination of these or other characters, which collectively form a “stencil.” The self-contained imaging sheet is passed under a roller or a similar device, which ruptures microcapsules which have not been hardened. The rupture microcapsules release the acid which reacts with the degradable polymer causing the degradable polymer to weaken. In the example shown in
Another embodiment uses an acid precursor exactly as in the previous example, followed by passage through a heated roller generating acid where the acid precursor is liberated from the capsules.
In another embodiment of the invention, shown in
In yet another embodiment of the invention, shown in
Although the present invention may be practiced at home using an inkjet printer with a specialized cartridge containing an acidic material or acid precursor in combination with a sheet of material comprised of a degradable polymer, the process may be difficult for many home users. In a similar matter, the first embodiment using an LED printhead and sheets containing microencapsulated materials, may be difficult for the average home user to use, especially when applications requiring producing stencils may be utilized in frequency. The invention, therefore, is adaptable for use by transmitting the desired image to a remote location for printing stencils. In the embodiment shown in
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.
