Patent Application
20120092434
This disclosure relates to the use of powders to create images on food products, moving webs or sheets, and other objects.
It sometimes is desirable to mark an object, web or sheet with an image. Although packaging may include various information, marking directly on the product or object may provide additional product identification, ornamentation, advertising or marketing. For materials in web form that are often used for packaging or made into products where it is desirable to include various information, marking directly on the web material may provide additional product identification, ornamentation, advertising or marketing. Sheets of material are used to convey information, and it is desirable to mark directly on such sheets.
Several techniques are known for coating or marking various types of substrates. Electrostatic processes represent one group of such techniques. For example, in the reprographics industry, two primary powder-based processes and a liquid-based process are sometimes used for creating images. Such processes may use either monocomponent or dual component development systems. In the dry dual component system, for example, a carrier powder and an imaging powder, also known as a toner, are used. The carrier typically is reused in the system; whereas the imaging powder may be depleted depending on the quantity of material used to create the image and is replenished from a reservoir or other source.
A particular type of such processes includes laser printer techniques in which an image is transferred to a relatively flat surface. Current processes are complex, using up to seven process steps. Furthermore, these processes cannot be used to directly mark heat-sensitive substrates or nonplanar surfaces, and these processes are wasteful of the marking powder.
In one aspect of the invention, a method of directly marking an object, web or sheet with a powder comprises moving the object, web or sheet to first, second and third stations. The method includes establishing an electric field between the object, web or sheet and the first station and transferring or applying electrostatically charged powder to a surface of the object, web or sheet at the first station by means of the electric field. The powder is imagewise fused or sintered on the surface of the object, web or sheet at the second station. Unfused or unsintered portions of the powder are removed from the surface of the object, web or sheet at the third station.
The techniques may be used for creating a monochromatic mark or a multichromatic mark on the surface of the object, web or sheet. In the event that a multichromatic mark is to be created, the object, web or sheet may be moved to multiple groups of stations, each of which includes a powder transfer station, an imaging station, and a powder removal station. Other stations may be present as well.
The position of the object, web or sheet with respect to the various stations is controlled by the provision of a holder or transport system that securely holds the object, web or sheet until imaging is completed. Various features may be present in some implementations. For example, in a particular implementation an object may be held by a holder using a mechanical fastener, tool or a vacuum as it is moved to each station. The holder may include a contact portion adapted to be in electrical contact with the object, and a conductive shield disposed about the object and electrically isolated from the object. The conductive shield is adapted to be biased with a voltage of a first polarity, the contact portion is adapted to bias the object with a voltage of an opposite polarity, and the powder transfer station is adapted to bias the powder with a voltage of the first polarity. The conductive shield may be disposed relative to the object and the bias voltage applied to the shield so as to limit areas of the object to which the powder is transferred at the powder transfer station. For example, the conductive shield may be disposed relative to the object and electrically biased so that the resulting electric field prevents the powder from being transferred to a back or sides of the object.
In another implementation where a mechanical holding system is not preferred, the contact portion of the holder may comprise, for example, a conductive elastomer bellows. The holder may include a tube to which a vacuum is applied to hold the object securely in place with respect to the conductive elastomer bellows.
In another implementation, a web or sheet of material is securely held and moved serially to the powder transfer station, the imaging station and the powder removal station. An electric field is set up between the web or sheet and the powder transfer station so that the web or sheet is coated with powder. The electric field may be created by arranging a biased roll or plate in close contact with the web or sheet and on the side opposite from the powder transfer station. Charged powder is transferred to the surface of the web or sheet at the powder transfer station. The imaging station is then used to fuse the image in this powder layer on the web or sheet, and finally, the powder removal station is used to remove the powder that has not been imaged, leaving a final image on the web or sheet.
In another implementation, the object, web or sheet is not sufficiently conductive or is too thick for an electrical bias to be used to create the electric field between the object, web or sheet and the powder transfer station. In this implementation, an electrostatic charge may be induced on the surface of the object, web or sheet using a corona or biased roll prior to moving to the powder transfer station.
The powder transfer station may include a means for continually bringing electrostatically charged powder into close proximity to the surface of the object, web or sheet so that the powder may be influenced by the electric field to move to the surface of the object, web or sheet. The electric field may be completed by electrically biasing all or part of the powder transfer station with respect to the object, web or sheet.
The station may also include a means for replenishing powder and for electrostatically charging replenished powder. Powder charging may be by means of, but not limited to, corona means, or triboelectric means such as surface area contact. The powder transfer station may bring the powder into proximity to the surface of the object, web or sheet by means of, but not limited to, mechanical, gravitational, fluid, magnetic, electrostatic, or air or gas pressure systems.
The imaging station may include a laser or diode to provide local fusing or sintering of the powder on the object, web or sheet and may be adapted to scan, modulate and focus a beam from the laser or diode across the surface of the object, web or sheet in an imagewise fashion. The object, web or sheet may be stationary or moving during the creation of the image. In an implementation where the object, web or sheet is moving during the creation of the image, a means for synchronizing the laser's or diode's action with the speed and/or position of the object, web or sheet is provided.
The powder removal station may use electrostatic, mechanical, fluid, positively pressurized gas, or vacuum or a combination of these means to remove the excess powder from the surface of the object, web or sheet after imaging has been completed.
In a particular implementation, the powder removal station has a pair of rolls adapted to rotate in opposite directions from one another. The rolls may comprise fur brushes so that surfaces of nonplanar objects can be physically contacted by the powder removal system. The brushes may include, for example, synthetic conductive fibers. The rolls may be biased with a voltage having a polarity opposite that of the object, web or sheet to remove unfused or unsintered portions of the powder from the surface of the object, web or sheet.
In an alternative implementation, the rolls may be biased and a powder on the rolls may be brought into contact with, or near, the surface of the object, web or sheet to remove unfused or unsintered portions of the powder from the surface of the object, web or sheet. In this implementation, the polarity of the powder on the rolls may be opposite to the polarity of the powder on the surface of the object, web, or sheet.
Unfused or unsintered portions of the powder from the powder removal station may be recirculated for reuse at the powder transfer station.
Various advantages may be present in some implementations. These advantages include, but are not limited to, the ability to create color and monochrome images on nonplanar surfaces and to control the location of such images, to create images on heat-sensitive surfaces that cannot otherwise accept powder-based melted images, and to create an imaging system that is very simple and uses a significantly reduced number of process steps to make a powder-based melted image, thereby lowering the cost and complexity of the imaging system and process. Other advantages include the ability to reuse powder that has first been applied to the surface of the object, web or sheet, thereby reducing the materials costs for a powder imaging system. Examples of applications may include, but are not limited to, creating an image with powder on the surface of confectionary items such as sugar-shelled candies, and upon toys such as miniature automobiles, and on plastic film such as disposable diaper coverings, and upon sheet metal such as control panels.
Other features and advantages may be readily apparent from the following description, the accompanying drawings and the claims.
As shown in
At the first station 31, powder is transferred electrostatically to the surface of the candy or other object 22 as it is securely held by the holder 21. The object 22 preferably is held such that an electric field is established between the object surface to be coated and the source of powder at the first station. This can be achieved, for example, by biasing the powder transfer station with a voltage of a first polarity, and biasing the object with a voltage of an opposite polarity. The outer shell 23, e.g., conductive shield, of the holder 21 for the object should be isolated electrically from the object and electrically biased with respect to the object so that it does not become coated with powder.
A conductive shield 23 is disposed about the object 22 and is electrically isolated from the object 22. The conductive shield 23 may be disposed relative to the object 22 to limit areas of the object 22 to which the powder is to be transferred. For example, the conductive shield may be positioned to prevent the powder from being transferred to a back or sides of the object. To control the coated area and to prevent the shield 23 from becoming coated with the powder, the shield is biased with a voltage of a first polarity, and the object 22 is biased with a voltage of the opposite polarity.
Imaging powders may include a thermoplastic or thermosetting polymer and may also include a functional agent. Functional agents may be a colorant, flavorant, bioactive, metal, ceramic, photo-responsive, or otherwise active material. The polymer may provide a medium for containment of the functional agent, for developing a triboelectric charge, or for melting the toner on the surface of an object. Polymers with low glass transition temperatures may be desirable for use when imaging on foods to avoid melting the food product during the fusing process. In an implementation with some high temperature functional materials, the powders may not melt but may be sintered together and to the substrate surface in order to form the image.
In addition to the polymer and functional agent, the powder optionally may include one or more of a charge control additive, a wax additive, a plasticizer, a filler or diluent, or a surface additive.
A charge control additive may enhance the magnitude and rate of triboelectric charging and can help ensure stable electrostatic charging over an extended time. A wax additive may help improve the fusing or melt flow behavior of the powder and dispersion characteristics of components in the toner. A plasticizer may significantly lower the glass transition temperature (Tg) of the thermoplastic polymer, making it more pliable and easier to work with. Adding a filler or diluent to the composition of the powder can enable reduction of the overall cost and may enhance capacity. It also can be used as a deglossing agent or to influence powder flow properties.
Imaging powders in the mean particle size range from a few microns to about one hundred microns may be used in this process. In a preferred embodiment, powders having a mean particle size in the range of five microns to forty microns may be used.
Imaging powders of any color may be used in this process. For many applications, a CO2 laser can be used in the imaging station to fuse any color powder. For some applications, it may be desirable to use a laser diode or fiber laser, particularly where cost, size and speed are an issue. Some color powders such as clear, yellow, magenta, some cyans, blue and red will not absorb the wavelength of the light from laser diodes or fiber lasers. In that instance it may be desirable to incorporate infrared absorbing materials in the powder.
An example of an imaging powder using functional agents for a specific purpose is provided for imaging on food products. For food products, it is desirable for the powder to consist essentially of food-grade components. The powder may include, for example, a thermoplastic polymer and colorant, as well as one or more of a charge control additive, a wax additive, a plasticizer, a filler or diluent, or a surface additive. Particular examples of food-grade powders are described in a PCT Patent Application filed on May 10, 2007 and entitled “FOOD-GRADE TONER” (Attorney Docket No. 21175-003WO1). The disclosure of that application is incorporated herein by reference.
The imaging powder may be combined mechanically with a magnetically active powder (i.e., a carrier) to form a developer mix. In this process, the carrier serves to charge the imaging powder triboelectrically, and the smaller imaging powder particles adhere to the larger carrier particles. This then enables the carrier to be used to transport the imaging powder to the surface of the object, web or sheet by electrostatic and magnetic forces. The imaging powder and carrier should be blended so as to optimize the electrostatic and other properties for the particular imaging powder application and imaging system.
In the illustrated implementation, an object 22 held securely by the holder 21 is positioned or moved past at a fixed distance from the roll 33 and may or may not contact the developer mix on the surface of the roll. As the transported developer mix comes opposite the object 22, it begins to react to the electric field between the shell and the object. The electric field is set to be stronger than the remaining electrostatic forces holding the imaging powder particles to the surface of the carrier particles. This results in some of the imaging powder being transferred to the surface of the object 22 where it is held electrostatically. Alternatively, the electric field may be an alternating field with a constant bias, the result of which is to provide forces that separate the imaging powder from the carrier and also cause a net attraction of the imaging powder to the object 22 where it is held electrostatically.
In this implementation, the amount of powder coating on the object may be controlled by the magnitude of the electric field between the object and the outer shell of the magnetic roll 33, the relative speed of the object and the shell or the time during which they are in opposition, the duration of the applied field, and the triboelectric charge on the powder. In this process, the imaging powder is held electrostatically on the surface of the object, web or sheet and will not fall off provided that the imaging powder is electrostatically insulative. The object, web or sheet can be processed without any additional requirement to tack or secure the powder on the surface.
Alternative powder transfer stations using technology and designs used in the reprographic industry also can be used to coat the object, web or sheet. Alternative powder transfer stations may include other roll developer systems such as magnetic brush developers of different configuration, fur brush developers, and single component roll developers using contact triboelectric charging means to charge the powder. Developers that do not employ a roll as the primary powder transport can also be used. These developers may include cascade developers, other gravity fed developers, fluidized bed developers and powder cloud developers. In each implementation, it is required that charged powder be brought into close proximity to the object, web or sheet to be coated and that an electric field be established so that the powder is induced to move to the surface of the object.
In some cases, parts of the surface of the object, web or sheet may be coated selectively with the powder. For example, it may be preferable to coat only one side of the object. In some cases, a screen with one or more openings may be placed near the object, web or sheet so that the screen selectively blocks the powder from being applied to portions of the object, web or sheet. In other cases, the shield or screen may be segmented and each segment biased differently to cause the desired effect.
After the powder is applied to the object 22, the object is moved, while still securely held by the holder 21, to the imaging station 13, where the object is subjected to a source of energy to obtain localized fusing or sintering of the powder on the object surface according to a predetermined pattern or image. This may be accomplished, for example, by laser imaging in which light emitted from a laser melts or sinters the powder so that the powder particles fuse or sinter together and adhere to particular areas on the surface of the object. Thus, the laser power density should be sufficient to melt the powder or raise its temperature so that the particles fuse or sinter together and adhere to the surface of the object. The desired image pattern may be supplied to the laser writing head in a bitmap form using, for example, software executed by a standard personal computer or other industrial controller. The image pattern may be produced by applying modulation and deflection to the laser beam, and by focusing the laser beam into a small spot on the surface of the object, web or sheet where the powder is located.
Various imaging systems may be used. In one implementation, a relatively low power laser diode or diode array can be used. In another implementation, a fiber laser can be used. As shown in
Laser diodes and fiber lasers having the desired power levels may be limited to particular wavelengths (e.g., red or infrared) which makes them suitable for use with black or some cyan powders, but not with certain other colors. Alternatively, uncolored materials that are sensitive to these wavelengths may be incorporated in the powders so that the energy is readily absorbed and fusing or sintering can take place. In these instances, the visible color of the powder may be one that does not absorb the wavelength of the laser.
In another implementation, the imaging station 13 may include a CO2 gas laser package 12. The gas laser package may include a gas laser, power supplies, modulator, focusing optics and galvanometer deflection system in a single casing. The advantage of such a package is that it produces light at a wavelength that can be absorbed by a wide range of clear or color powders, and it has a higher power (e.g., 30 Watts) to enable higher speeds to be met. Even higher speeds may be obtained using a deflection system that makes uses of a reflective polygon driven by a high speed motor. In this case, an external beam modulator may be employed with the CO2 laser. Other laser imaging systems may be used.
In some applications, the object, web or sheet may be securely held and continuously transported past the imaging station during the imaging process. In these applications, the speed and/or position of the object, web or sheet may be sensed and provided to the laser control system to synchronize the laser's action and correctly form the image.
The unfused or unsintered powder remaining on the surface of the object 22 is undisturbed. In some cases, after the imaging has been completed, there may be no easily visible appearance change in the powder on the surface of the object.
After the imaging has been completed, the object 22 is moved, while still securely held by the holder 21, to the powder removal station 41 where the unfused or unsintered powder (if any) is removed from the surface of the object, thus leaving the fused or sintered image on the surface.
The unfused or unsintered portions of the powder may be removed from the object using electrostatic forces. For example, according to a particular implementation, the powder removal station 41 has a pair of rolls 42 adapted to rotate in opposite directions from one another (see
The unfused or unsintered powder that is removed at the powder removal station 41 may be recycled for subsequent use. The powder may be removed from the oppositely rotating rolls by bringing each of the brushes into contact with a metal roll 43 that is oppositely biased to the bias on the brush. Once the powder is transferred to the metal roll, it can be removed, for example, by means of a simple elastomeric scraper or metal blade 44. The powder then can be reused at the powder transfer station 31.
In an alternative implementation, the powder removal station 41 includes one or a pair of magnetic rolls adapted to rotate in opposite directions from one another. In this system, materials similar to those used in the powder transfer process are used to remove excess powder. A magnetically active powder (i.e., a carrier) on the roll or rolls is brought into contact with, or near, the surface of the object 22. The electric field is reversed so that unfused or unsintered powder on the surface of the object is attracted to the magnetic roll and is picked up by the carrier powder and carried away from the object surface as the magnetic rolls rotate. The powder then may be separated from the powder-carrier mixture on the magnetic rolls by providing another electric field to transfer the powder to another set of rolls. As noted above, the powder then can be recirculated for use at the powder transfer station 41.
In another implementation, the unfused or unsintered powder may be removed by the application of pressurized air or another gas.
In another implementation, the unfused or unsintered powder may be removed by the application of vacuum or suction.
In many applications, the powder will be sufficiently fused or sintered on the surface of the object 22, web or sheet at the imaging station 13 such that there will be little likelihood of the fused or sintered powder not adhering well to the surface. Nevertheless, in some applications, it may be desirable to move the object, web or sheet to a fourth station to provide post-imaging flash or radiant fusing of the powder on the surface of the object, web or sheet. Such flash or radiant fusing stations are well known and have been used in the reprographics industry.
In the implementation described above, the object 22 is biased electrically so that the powder can be transferred to the object electrostatically. The holder 21 provides the bias through the conductive contact portion 25. Such techniques may be used for electrostatically conductive objects. For electrostatically nonconductive objects, webs or sheets, a charging station may be provided to induce a charge on the surface of the object, web or sheet. In that case, a ground plane should be placed behind the object, web or sheet. For objects, the contact portion 25 or 27 of the holder 21 can serve that purpose. For webs and sheets, a conductive member 15, for example, a roll, plate or shoe, in contact with the far side of the web or sheet opposite the powder transfer station 31 can serve that purpose. The charging station may be implemented, for example, by a biased roll in contact with the object, web or sheet, or a corona device spaced at a distance from the object, web or sheet.
The images formed on the surface of objects, webs or sheets may include one or more alphanumeric symbols, graphic symbols, or other types of images. The image created by the powder may be monochromatic or multichromatic. In the case of a multichromatic image, the process for applying and fusing the powder on the object, as well as removing unfused or unsintered powder from the object, may be repeated using two or more powders having different colors. In some cases, a first powder may be applied and fused over part or all of the surface of the object, web or sheet and can serve as a coating. A second powder having a different color then may be applied and fused on the surface of the object, web or sheet to form the image.
To facilitate the creation of a multichromatic image on the surface of the object, web or sheet, the apparatus may include two or more sets of the stations 31, 13, and 41 arranged serially (see
The apparatus described above may be used to create images on objects having nonplanar or irregular as well as planar surfaces.
Other implementations are within the scope of the claims.
| Number | Date | Country | |
|---|---|---|---|
| 60800069 | May 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12300232 | May 2009 | US |
| Child | 13336595 | US |
