Background of the Invention Printers and plotters for applying ink and other printing fluids are well known. Such devices typically include a supply of printing fluid and a printing mechanism. In a typical printer or plotter, printing fluid is routed to the printing mechanism using tubing to supply the required printing fluid to the printing mechanism.

In one particular type of printer, i.e., an inkjet printer, an ink supply is connected to a print head to supply ink to the print head. It is preferred that the ink supply be under slightly negative pressure at the print head to avoid weeping and leakage of ink which can reduce the quality of printing and, potentially, also cause clogging of the print head.

One of the problems associated with inkjet ink supplies is the limited ink capacity of such systems. This problem is particularly acute in larger printers, especially for ink jet printers that are at least 90 cm wide, and plotters which use ink at a much faster rate than office or letter size inkjet printers.

Large reservoir ink delivery systems commercially available employ tubing for each color approximately 2-3 meters long between each reservoir and each printhead.

Summarv of the Invention Conventional tubing for large reservoir ink delivery systems generally use poly(vinyl chloride) tubing.

One aspect of the invention has found that poly(vinyl chloride) is quite permeable to water and a significant factor in controlling the concentration and viscosity of the ink within the tubing. More significantly, the present invention has found that the concentration and viscosity of ink within the high water permeability tubing increases if the ink is left to sit in the tubing for long periods of time, such as a week between printing jobs.

Another aspect of the invention has found that poly(vinyl chloride) has poor chemical resistance with another ingredient of water-based ink jet inks, diethylene glycol. Moreover, plasticizers in poly(vinyl chloride) tubing can interact with ink jet inks.

Each of these deficiencies in conventional tubing can result in instability in the ink jet ink, poor jet-ability, and clogging of ink in the tubing. Poor printing results. Printers can malfunction or, at a minimum, require increased maintenance.

The present invention provides polymeric tubing for an ink delivery system that has low water permeability and good chemical resistance to ink jet inks.

One feature of the present invention is reduced evaporative volume loss of ink jet inks within tubing of the ink delivery system, resulting in more consistent concentration and viscosity for the ink being delivered to a print mechanism.

Another feature of the present invention is better compatibility of ink and the tubing through which the ink either flows during use or rests between printing jobs.

An advantage of the present invention is better ink jet ink printing.

Another advantage of the present invention is reduced maintenance of tubing and the ink delivery system.

Another advantage of the present invention is the ability to retain ink within tubing between the ink reservoir and the ink print head without fear of clogging of ink within the tubing.

The present invention provides a system for delivering printing fluid from a reservoir to a printing mechanism, comprising a fluid line of low water permeability polymeric tubing between the reservoir and the printing mechanism.

The present invention also provides an ink jet ink fluid line comprising polymeric tubing having an ink-contacting surface of poly(ethylene) or poly(tetrafluoroethylene).

Embodiments of the invention are described using a drawing.

Brief Description of the Drawing Fig. 1 is a schematic diagram of an ink delivery system having tubing of the present invention.

Embodiments of the Invention The present invention provides tubing connecting a printing fluid supply and an outlet for the printing fluid. Typically, the outlet will comprise some print mechanism, such as an inkjet print head, spray jet print head, toner drum, etc.

The discussion below will focus on large reservoir ink jet delivery systems, but it should be understood that the present invention is applicable to any printing system in which the printing is accomplished using a liquid printing material that is transported via tubing to the printing mechanism as a fluid for printing onto a medium.

Furthermore, although ink is described for use with the inkjet printing systems below, it will be understood that any liquid printing material could be used in conjunction with the present invention. Examples of liquid printing materials include, but are not limited to, water-based pigmented inks and water-based dye inks.

Referring now to Fig. 1, an illustrative embodiment of one schematic inkjet delivery system 10 according to the present invention is depicted including an inkjet printer or plotter 11 and corresponding print head 12, fluid line 14 and ink supply reservoir 20. The reservoir 20 is preferably open to ambient pressure through an opening such as 26. Opening 26 also preferably allows for refilling of the reservoir 20 as ink 22 is consumed during printing. Fluid line 14 is provided to supply ink 22 from reservoir 20 to the print head 12.

While only one reservoir 20 and one print head 12 and one fluid line 14 are shown in Fig. 1, it is to be understood that any number of sets of reservoir/fluid line/print head can be employed according to printing requirements. For monochromatic printing, typically black, one set can be used. For polychromatic printing, typically four colors (cyan, magenta, yellow and black) are used, each requiring its own set of reservoir, fluid line, and print head. For more elaborate printing, special or "spot" colors can be employed, such as a specific color demanded for printing of marketing brands that have a specific recognizable color, such as the particular color of red employed in the 3M brand used by Minnesota Mining and Manufacturing Company.

Inks that particularly benefit from the present invention can be any commercially available pigmented or dye ink jet ink, including those available as 3MTM Durable Pigment Inks from Minnesota Mining and Manufacturing Company of St. Paul, Minnesota.

Nonlimiting examples of commercially available large reservoir ink delivery systems include a Big InkTM delivery system from LaserMaster Corporation of Eden Prairie, Minnesota and Bulk InkTM delivery system from Colossal Graphics Inc. of Palo Alto, California. Further, a 3MTM Ink Delivery System from Minnesota Mining and Manufacturing Company of St. Paul, Minnesota being offered for sale

can use tubing of the present invention. Other ink delivery systems are disclosed in U.S. Pat. No. 5,367,328; U.S. Pat. No. 5,369,429; U.S. Pat. No. 4,831,389; and PCT Publication WO97/1 0106.

Fluid line 14 can be constructed from tubing that has an inside diameter ranging from about 0.1 to about 0.3 cm and typically has a length of about 2-3 meters from each reservoir 20 and each print head 12. The inside diameter of fluid line 14 is a factor for the rate of evaporative volume loss, all other parameters being constant. For example, if the same composition of tubing having the same wall thickness has different inside diameters, the surface area of the tubing that can absorb water increases with increasing inside diameter. However, the volume of ink within tubing of greater inside diameter is also greater. Therefore, based on a change in surface area (circumference multiplied by length) of absorption and volume (circular area multiplied by length), it has been calculated that a doubling of the radius of the inside diameter would halve the percent evaporative volume loss rate. Based on commercially available polymeric tubing useful for the present invention and this calculation of tubing surface area to ink volume, fluid line 14 preferably has an inside diameter ranging from about 0.20 to about 0.3 cm.

Fluid line 14 can be made from any low water permeability polymeric tubing. Low water permeability in the polymeric tubing for fluid line 14 reduces evaporative volume loss of pigmented ink jet inks to less than about 0.7 percent of initial volume per day and desirably less than about 0.6 or even 0.5 percent of initial volume per day. Preferably, the evaporative volume loss is less than about 0.3 percent of initial volume per day.

Nonlimiting examples of such polymeric tubing include poly(ethylene); poly(ethylene)-lined polymeric tubing; poly(tetrafluoroethylene); and poly(tetrafluoroethylene)-lined polymeric tubing. Commercially available polymeric tubing that can be lined with poly(ethylene) or poly(tetrafluoroethylene) includes poly(vinyl chloride) tubing that provides good flexibility for use as a fluid line 14.

Use of tubing of the present invention not only reduces evaporative volume loss of water from ink jet ink within fluid line 14 but also minimizes the possibility of separation of ink components caused by leaching of plasticizers from polymeric tubing containing poly(vinyl chloride).

Further features and advantages of tubing of the present invention are described in the following examples.

Examples 1-3 and Comparative Examples A-C Evaporative Volume Loss Test: The rate of initial volume loss of ink was determined by filling a variety of polymeric tubing, each 30.48 cm long, about half full with water-based ink and sealing both ends closed. Measurements were made over several days while the sealed tubing resided in room temperature, pressure, and humidity conditions, i.e., dry humidity conditions of winter in Minnesota (approximately 25% R.H.)). The length of the ink column in each polymeric tube was measured compared with the initial length to determine the average percentage evaporative volume loss per day.

Table 1 shows the compositions of polymeric tubing, the inside diameter of the tubing, and the average percentage evaporative volume loss per day for Examples 1-3 and Comparative Examples A-C.

Table 1 Example Tubing Composition Inside Evaporative Diameter Volume Loss Rate (cm) (Percent per Day) A Poly(vinyl chloride)* (PVC) 0.239 0.72 1 Poly(ethylene)-lined PVC1 0.239 0.31 2 Poly(ethylene)2 0.216 0.12 3 Poly(tetrafluoroethylene)3 0.172 0.28 B PVC 4 0.160 1.33 C PVC 4 0.239 0.97 Commercially available tubing trom LaserMaster Corporation believed to be PVC.

Commercially available from Natvar Company of Clayton, N.C.

2 Commercially available as polyflow brand tubing from Imperial Eastman Chemicals and distributed by Duncan Company of Minneapolis, Minnesota, among others.

3 Commercially available as VoltrexTM TeflonTM tubing from SPC Technologies and distributed by New ark Electronics of Minneapolis, Minnesota, among others.

4 Commercially available as TygonTM brand tubing from Norton Company of Akron, Ohio and, distributed by Cole-Parmer Company of Chicago, Illinois.

Use of a fluid line 14 that has tubing with an ink-contacting surface of poly(ethylene) or a poly(tetrafluoroethylene) unexpectedly reduces evaporative volume loss rate. The use of any of the compositions of Examples 1-3 is preferred over the use of conventional tubing compositions of Comparative Examples A-C.

Further, a comparison between Comparative Examples B and C shows that an

increase in inside diameter of about 50% (0.160 to 0.239) reduces evaporative volume loss by about 27% (1.33 to 0.97). The difference between the theoretical direct inverse relationship and the actual results for Comparative Examples B and C can be attributed to effects of water vapor within the unfilled portion of the sealed tubing, among other things.

There can be different portions of fluid line 14 that require different levels of flexibility due to movement of the print head 12 across the printer. For this reason, those portions of fluid line 14 requiring more flexibility can use poly(ethylene)-lined poly(vinyl chloride) tubing and those portions of fluid line 14 requiring less flexibility can use poly(ethylene) tubing. Suitable fittings can be used to connect different portions of fluid line 14.

The invention is not limited to the above embodiments. The claims follow.