Patent Application
20070091153
Biocides are routinely added to ink and other marking fluid formulations in order to mitigate growth of bacteria, fungi, mold and other such microbial organisms. However, regulatory or compatibility issues may limit the amount of biocide added to the marking fluid formulation. This may limit the useful shelf life of the marking fluid.
In the following detailed description of the present embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments of the disclosure which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the subject matter of the disclosure, and it is to be understood that other embodiments may be utilized and that process, chemical, electrical or mechanical changes may be made without departing from the scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims and equivalents thereof.
The various embodiments involve incorporation of a biocide, such as a metal ion biocide, into one or more components of the printing system where ink contact may be found. For one embodiment, the metal ion biocide is a silver ion-containing compound including silver ions bonded to a zeolite carrier. As one example, the AgION™ antimicrobial compound available from AgION Technologies, Inc., Wakefield, Mass., USA, is a compound of silver ions bonded to a ceramic support structure. The structure allows the ions to be released at a slow and steady rate. Ambient moisture in the air can cause low-level release sufficient to provide biocidal effects. The ion exchange is increased in high humidity environments, where bacterial growth is often more prevalent. However, the interstices of the carrier limit the release of the silver ions such that long-term efficacy, perhaps years, can be achieved.
An ink formulation was prepared for testing efficacy of the silver-ion biocide. The ink formulation is an amphoteric system which is positively charged at a pH of about 4-5. As tested, the ink formulation had a pH of approximately 4, making it cationic. The ink formulation contained, approximately, 3.5 wt % carbon black dispersion, 8 wt % 1,1,1-tris(hydroxymethyl)propane, 4 wt % glycerol ethoxylate, and 0.4 wt % propylene glycol butyl ether in an aqueous carrier. The biocide was used in the form of pellets containing approximately 20 wt % of the AgION™ antimicrobial compound in high-impact polystyrene (HIPS). Differing levels of the biocidal pellets were added to the ink formulations before inoculating the ink formulation with a microbe cocktail containing Bacillus subtilis, Pseudomonas cepacia, Candidas albicans and Aspergillus niger, and allowed to incubate for up to two weeks. Aliquots were removed from the test solutions at intervals and plated out on to an Agar dish, which was then placed in an oven to help further organism growth. The colonies on the Agar dish were then counted and compared against a control without a biocidal component added. Table 1 represents data obtained from such a testing procedure.
As can be seen from Table 1, significant and rapid reductions in plate counts can be achieved with 16 g of the HIPS pellets with 20 wt % AgION™ compound per 100 g of the tested ink formulation. Although the example of Table 1 corresponds to an acidic marking fluid, i.e., pH<7, marking fluids with pH>=7 may also be used.
Print system components are commonly constructed of resins, plastics, elatomers and the like. Some examples include bonded nylon fiber; bonded polyester fiber; Delrin® synthetic resin; terpolymers of ethylene, propylene, and a non-conjugated diene; PET (polyethylene terephthalate); polyimides; polyurethanes; polypropylenes; polyethylenes; polysulfones; polyesters; Santoprenes thermoplastic elastomer; isoprene; Teflon® fluorine-containing resins; and the like. Slow-release biocides of the type described may be incorporated within such resins, plastics and elastomers at levels sufficient to provide efficacy against microbial growth without materially degrading their structural integrity. Alternatively, such slow-release biocides may be coated onto these materials as well as other materials of construction, such as metals, e.g., stainless steel, ceramics, e.g., aluminum oxide, and the like. By incorporating inorganic biocides into the materials used to form print system components that are likely to contact marking fluid during storage and delivery, or adhering the biocides to such surfaces of the print system components, the inclusion of biocides within the marking fluid formulation may be reduced or eliminated, thus facilitating the development of a wider variety of marking fluid formulations.
One common form of print system component is a replaceable pen for inkjet printers. These pens commonly provide both storage and delivery of the ink to a substrate. Returning to the testing detailed in Table 1, as the surface area of 16 g of the tested HIPS pellets corresponds roughly to an internal surface area of an inkjet pen of dimension 2.5 cm×2.5 cm×4.5 cm, it can be seen that a pen body formed of plastics containing the AgION™ compound can be efficacious at controlling microbial growth in the contained ink. Empirically, for one embodiment, an amount of silver ion in resin for formation of a print system component might be expressed as:
C(Ag)>=0.01*[Mink/Mresin]
where C(Ag) is the wt % of silver in resin used to form the print system component;
Mink=mass of the ink in contact with the print system component; and
Mresin=mass of the resin used to make the print system component.
Note, however, that such an empirical equation is to be used as guidance only. Efficacy may need to be tested in conditions simulating actual use.
The volume within the body 222 is adapted to contain marking fluid 230, e.g., ink. The cut-away portion of the body 222 represented by dashed lines may represent the cross-section of a one-color marking fluid reservoir or an individual chamber of a multi-color marking fluid reservoir, with each chamber having a different marking fluid formulation. Thus, the various embodiments include one-color and multi-color marking fluid reservoirs 220. The body 222 includes a biocide adhered to, or incorporated within, an inner surface 232 configured to be in contact with the marking fluid 230. For one embodiment, the biocide is a metal ion-containing material. For a further embodiment, the biocide is a ceramic zeolite structure having silver ions bonded thereto. For an alternate embodiment, a metal ion-containing support structure is added directly to the marking fluid 230.
In addition to a wall of the body 222 itself, the inner surface 232 may also include structures enclosed within the body 222. For example, back-pressure within a marking fluid reservoir 220 may be controlled using reticulated foam or other filler material of controlled capillary force, or bladders or spring bags may also be used to control flow.
While such integrated pens for storage and delivery of marking fluid are common in the consumer market, storage and delivery need not be combined.
For one embodiment, fluid reservoir 340 is fixedly attached to printer 300. For another embodiment, each of conduits 342 conveys a different fluid, e.g., a different colored ink, from fluid reservoir 340 to fluid-ejection device 324. For another embodiment, a portion of conduits 342 are fluid delivery lines that respectively convey different fluids to fluid-ejection device 324 and another portion of conduits 342 are fluid return lines for conveying fluids that are not ejected by fluid-ejection device 324 back to fluid reservoir 340.
For various embodiments, one or more of the fluid-ejection device 324, conduits 342 and fluid reservoir 342 include a biocide adhered to, or incorporated within, an inner surface configured to be in contact with the marking fluid.
Oftentimes, components for transporting marking fluid in systems such as printer 300 are normally empty and contain marking fluid only intermittently during transport from the reservoir 340 to the fluid-ejection device 324. For example, fluid-ejection device 324 may contain an integral reservoir (not shown) and the conduits 342 may only be in contact with marking fluid when re-filling the integral reservoir of the fluid-ejection device 324 and may be flushed or otherwise emptied of marking fluid upon completion of the re-filling operation. It is noted that the conduits 342 may represent components in addition to mere tubing, such as fittings, filters, check valves and the like. Any or all components of such conduits 342 may include a biocide adhered to, or incorporated within, an inner surface configured to be in intermittent contact with the marking fluid. Including a biocide in such components subject to only intermittent contact with marking fluid may lead to extended efficacy of the biocidal system.
