Abstract:
A printing ink for use within multiple ambient temperatures which comprises a mixture of two or more inks having different viscosities at a given temperature. Thus, one or more lower viscosity inks having, for example, a viscosity in the range of about 300 cps to about 900 cps is mixed with one or more higher viscosity inks having, for example, a viscosity range of about 1100 cps to about 1800 cps to provide a multi-viscosity ink mixture useful over a wide temperature range. A print ribbon which carries the multi-viscosity ink mixture and, the combination of an impact printer incorporating said print ribbon are provided. A method for printing with an ink mixture to compensate for varying ambient temperatures includes the steps of mixing together two or more inks each having a different viscosity at the same given temperature to form an ink mixture; and, printing with said ink mixture on a medium to be printed upon.

Description:
[0001]    This application claims the benefit and priority of U.S. Provisional Application Serial No. 60/411,959; filed Sep. 19, 2002; entitled: MULTI-VISCOSITY PRINTER INK; Applicants: Jeng-Dung Jou, Irvine, Calif. 92620, Dennis R. White, Fountain Valley, Calif., and Gordon B. Barrus, San Juan Capistrano, Calif. 
     
    
     
         [0002]    Your Petitioners, Jeng-Dung Jou, a citizen of Taiwan and a resident of Orange County in the State of California whose residence and post office address is: 19 Mount Vernon, Irvine, Calif. 92620; Dennis R. White, a citizen of the United States of America and a resident of Orange County in the State of California whose residence and post office address is: 11561 Azalea Avenue, Fountain Valley, Calif. 92708; and Gordon B. Barrus, a citizen of the United States of America and a resident of Orange County in the State of California whose residence and post office address is: 31516 Paseo Christina, San Juan Capistrano, Calif. 92675, pray that letters patent may be granted to them for the invention of A MULTI-VISCOSITY PRINTER INK as set forth in the following Specification.  
         BACKGROUND OF THE INVENTION  
         [0003]    The background of this invention resides within the field of printer inks and printing systems. In particular, it resides in the field of printer inks which are utilized for various applications such as with printer ribbons or other printing ink applications. More specifically it resides within the field of systems for impact printers and inks which cooperate to provide printing with the aid of a print ribbon.  
         PRIOR ART  
         [0004]    Viscosity for an ink is a measure of the ink&#39;s thickness. Low viscosity printer ink loses shear strength at high temperatures even when disposed on a carrier such as a printer ink ribbon. Within impact printing applications such as those using an ink ribbon, this can result in ink smearing and ink migration. This lowers the print quality.  
           [0005]    On the other hand, the viscosity of an ink that performs well at elevated temperatures becomes excessively high as to its viscosity at lower temperatures. Excessively high ink viscosity exhibits other printing problems. The problems can include poor transfer into and out of the printer ribbon, resistance to pumping through small tubing, and a very slow transfer through foam materials. Such foam materials can be used in an ink reservoir roller to replace ink within the printer ribbon.  
           [0006]    An ideal printer ink should flow easily when the ambient temperature is cold. The ideal ink should also remain thick enough so that it will not excessively migrate when the temperature is hot. Low ambient temperatures require a light (i.e. low viscosity) ink and high temperature requires a heavy (i.e. high viscosity) ink.  
           [0007]    Viscous flow as to ink can be pictured as taking place by the movement of molecules or segments of molecules from one place in a lattice to a vacant hole. The total “hole” concentration can be regarded as a space free of polymer or free volume (Rodriguez, F., Principles of Polymer Systems, 3:177, 1989). Doolittle proposed (Doolittle, A. K., J. Appl. Phys., 22:1471, 1951) that the viscosity should vary with the free volume and free volume is expected to vary with temperature. The diffusion and movement is closely related to the size of a molecule represented by the hydrodynamic volume.  
           [0008]    Low temperatures are favorable to small molecule movement whereas high temperatures are conducive to the movement of either small or large molecules. Thus when inks having small molecules are exposed to high temperatures they move with great freedom. Inks having large molecules can also move freely at high temperatures but not as freely as with small molecules, and not effectively at low temperatures.  
           [0009]    It has been found according to the invention that when both small and large molecules are mixed together, they intermingle so that the smaller molecules are carried along with the larger molecules. This causes a synergistic property wherein the combined fluid acts more like the small molecules at lower temperatures and the large molecules at elevated temperatures.  
           [0010]    This invention establishes that a mixture of two or more inks of different viscosities form multi-viscosity inks wherein the high molecule-weight spread (i.e. high poly-dispersity) performs well at a full temperature range in which print systems such as impact printers are expected to operate. These multi-viscosity inks remain sufficiently viscous at elevated temperatures, while maintaining a lower-than-normal viscosity at lower temperatures.  
         SUMMARY OF THE INVENTION  
         [0011]    In summation, this invention comprises a blended, multi-viscosity (MV) ink mixture for printing applications, yielding a more consistent viscosity throughout the operational temperature range expected of industrial impact printers.  
           [0012]    More particularly, the invention utilizes an ink formulation that incorporates two or more mono-viscous ink components, combined in ratios to produce a united multi-viscosity ink. The lower viscosity inks or components influence the combination by lowering its “apparent viscosity” at lower operating temperatures. The higher viscosity inks or components influence the combination by maintaining sufficient viscosity for printing applications at the higher end of operating temperatures. The net effect is that the “apparent viscosity” remains more nearly constant across the printer&#39;s operating temperature range, than is the case with single or mono-viscosity inks.  
           [0013]    Using multi-viscosity ink mixtures in impact or other printing technologies improves printing results. It helps to reduce or eliminate the propensity for ink smearing on the print media and ink migration into the printing mechanism at high temperatures. It also helps to maintain print density and ink distribution in an ink ribbon at lower temperatures.  
           [0014]    Inks are primarily composed of pigments, vehicles and supplementary additives. Pigments are finely divided solid materials that give inks color and opacity or transparency. The function of the vehicle is to act as a carrier and as a binder to affix the pigment to the printed surface. The nature of the vehicle determines in a large measure the tack and flow characterization including viscosity. Supplementary additives include among others lubricants which act to influence flow characteristics, and dyes which impart ink color.  
           [0015]    A method for printing with an ink mixture to compensate for varying ambient temperatures is also provided which includes mixing together two or more inks each having a different viscosity modulus to form an ink mixture; and, printing with said mixture on a medium to be printed upon.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 shows a graph of viscosity versus temperature on a logarithmic scale for a 50/50 by volume mixture of inks, one ink having a viscosity of 750 cps and one ink having a viscosity of 1600 cps as compared with each single or mono-viscosity ink.  
         [0017]    [0017]FIG. 2 shows a graph of a viscosity comparison of a single viscosity ink of 1050 cps and a 50/50 by volume ink mixture of an ink having a viscosity of 750 cps and an ink having a viscosity of 1600 cps.  
         [0018]    [0018]FIG. 3 shows a graph on a logarithmic scale of viscosity versus temperature for a 50/50 mixture and a 70/30 mixture of an ink having a viscosity of 750 cps and an ink having a viscosity of 1600 cps respectively.  
         [0019]    [0019]FIG. 4 shows on a logarithmic scale two different mixtures of low viscosity inks combined in the same volume proportions with the same high viscosity ink.  
         [0020]    [0020]FIG. 5 shows a perspective view of a fragmented portion of an impact printer having a print ribbon which can use the ink of this invention.  
         [0021]    [0021]FIG. 6 is a fragmented perspective view showing a hammerbank, platen, and the associated portions in the direction of lines  6 - 6  of FIG. 5.  
         [0022]    [0022]FIG. 7 is a sectional view in the direction of lines  7 - 7  of FIG. 6.  
         [0023]    [0023]FIG. 8 is a fragmented perspective elevation view of the hammerbank and print hammer details.  
         [0024]    [0024]FIG. 9 is a sectional view in the direction of lines  9 - 9  of FIG. 6 showing the magnetics and hammers of the impact printer of this invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Looking more specifically at FIG. 5, it can be seen that a printer  10  is shown having spindles or hubs  12  and  14 .  
         [0026]    The hubs  12  and  14  receive respectively spools of print ribbon  16  and  18 . The ribbon in these respective spools moves forwardly and backwardly across the face of a number of hammers on a printer hammerbank facing the print ribbon  20  that is wound around the spools  16  and  18 .  
         [0027]    In order to support paper, a paper support  26  is shown with a splined shaft  24  and knob  28  to advance paper along a tractor.  
         [0028]    Looking specifically at FIG. 6, it can be seen that a hammerbank portion of the impact line printer in the form of a fragmented segment toward the end of the hammerbank is shown. The fragmented portion of the hammerbank is a segment that is cut from an elongated hammerbank having approximately anywhere from forty to one hundred print hammers more or less. The print hammers can be retained and then fired or released against a print ribbon as is well known in the art.  
         [0029]    The hammerbank  50  is such wherein the base or shuttle is generally machined or cut from an elongated metal portion such as an aluminum casting or extrusion. It can be formed in any other suitable manner to provide for an elongated mounting of the hammers on the hammerbank. In this particular case, it can be seen that the hammerbank has a rear channel area  52  which can receive an elongated circuit board or other controlling means such as in U.S. Pat. No. 5,743,665 Entitled a Printer Integrated Driver and Hammerbank dated Apr. 8, 1998 naming Robert P. Ryan and Gordon Barrus as inventors. The hammerbank  50  has an elongated channel or groove  54  which receives a permanent magnet as will be described hereinafter.  
         [0030]    As is customary in line printer hammerbanks, they can comprise a series of hammers  56  connected to and formed on a fret  58 . The fret  58  is secured to the hammerbank by screws, nuts or bolts or any other securement means shown generally as screws  60 .  
         [0031]    As detailed in FIG. 9, the hammers  56  comprise an enlarged portion  66  to which a pin  68  is welded, brazed or otherwise connected thereto. The enlarged portion  66  terminates in a necked down spring portion  70  connected to and formed with the fret  58 . This entire structure and shape of the hammers  56  can be configured in other suitable manners to allow for the dynamics of printing as is understood in the art.  
         [0032]    As seen in FIGS. 8 and 9, each pin  68  has a reduced tip  80 . The reduced tip  80  is the portion that is impacted against the ribbon  20 . This forms a dot matrix printing array, pattern, alpha numeric symbols, Oriental style lettering, a particular pattern, or pictorial representation.  
         [0033]    In order to retain the hammers  56  which are sprung for printing movement away from the hammerbank, a permanent magnetic force is applied through a pair of pole pins, pole pieces, or pole members which provide the magnetic circuit. These terminate in upper and lower pole piece termination sections, hammer contacts, terminals or pins,  84  and  86 . These pole piece terminal portions  84  and  86  are generally provided with a surface  88  therebetween against which a hammer  56  can be retracted and creates an impact or wear surface.  
         [0034]    Looking more particularly at FIG. 9 the terminal points or magnetic contact portions of the pole pieces  84  and  86  are shown with their pole pieces  92  and  94 . The pole pieces  92  and  94  are wound with wire coils  96  and  98 .  
         [0035]    In FIGS. 8 and 9 it is seen that a retention magnet  100  is shown. The magnet  100  allows for the magnet to be placed in the channel  54  against the rearward ends of the pole pieces  92  and  94 . The pole pieces  92  and  94  allow placement of the magnet  100  there against to provide in turn for a magnetic circuit through the pole pieces  94  and  96 .  
         [0036]    The leads and terminals  119  and  121  are utilized to allow for conduction of a driving voltage to the respective coils  96  and  98  around pole pieces  92  and  94 .  
         [0037]    The hammerbank fret  58  terminates in the upwardly projecting hammers  56 . The hammers  56  have the attendant enlarged portions  66  and necked down intermediate portions  70  serving a dominant spring function with the pins  68  having the striking portions or tips  80 .  
         [0038]    The foregoing configuration as to the pole pieces  92  and  94 , and the magnet  100 , are potted.  
         [0039]    Looking more specifically at FIGS. 6 and 7, it can be seen that the operational aspects of the line printer are shown with paper or other media  140  passing there through. The hammerbank  50  has been fragmented to show the attachment of the cover thereon.  
         [0040]    The fret  58  and the attendant hammer  56  has been shown in FIG. 7 in a dotted configuration along with the tip  80  extending therefrom. In FIG. 7, the details are more pronounced in the cross-section. The printer includes a platen  122  with a platen adjustment extension  124  which provides for the rotation of the platen in and out of the operating position.  
         [0041]    Looking more particularly beyond the cover  120  and the respective hammers  56  that are therebehind, it can be seen that the ribbon  20  is shown. The ribbon  20  is the one impacted by the tips  80  of the hammers  56 . The tips  80  extend through the openings  128 .  
         [0042]    Between the ribbon  20  and the paper or media  140  to be printed on is a ribbon mask  130 . This ribbon mask  130  is such wherein it provides for masking of the print from the entire ribbon  20 . This helps to eliminate print ribbon smear and ink being spread in an unwanted manner as the hammer tips  80  pass through the openings  136  of the mask  130 . The paper or media  140  passes over the platen face  142  of the platen  122 . This allows the hammers  56  when released to be impacted against the ribbon  20  and attendantly cause printing on the underlying media or paper  140 .  
         [0043]    The cover  120  incorporates the hammer tip openings  128  in a plural line of openings along the length thereof. This allows for the tips  80  of the hammers  56  to extend therefrom and provide an impact upon the paper or underlying media  140  on the opposite side of the mask  130 .  
         [0044]    As can be appreciated from the foregoing description with regard to a line printer such as that shown in FIGS. 6 through 9, it can be seen that ink when placed on the print ribbon  20  would have a chance for migration if it can readily flow. This is based upon not only gravitational forces but also merely the aspects of movement and impact of the ink ribbon  20 .  
         [0045]    In order to compensate for this, it has often been necessary to disadvantageously use overly viscous or light inks in order to compensate for ambient temperatures. As can be appreciated, if the ambient temperature were not correct, the ink would either be gummy on the ribbon  20  or flow excessively.  
         [0046]    Looking more particularly at FIGS. 7, 8, and  9 , it can be seen that ink from the print ribbon  20  when placed thereon could gravitate and smudge through the openings  136  against the media  140  that is to be printed upon. It becomes particularly apparent when considering the fact that the hammer pins  68  with the hammer tips  80  when striking the ribbon cause greater migrational flow of the ink. Further to this extent, the ink tends to flow more rapidly in high ambient temperatures. Of course, in low ambient temperatures the lighter or less viscous ink on the ribbon  20  would be to an advantage because of the fact that it wouldn&#39;t flow as readily.  
         [0047]    This invention allows for more controlled flow of the ink from the ribbon  20  against the media  140 . It helps to prevent smudging through the openings such as opening  136  or on the mask  130 . The ink mixture of this system functions to substantially diminish many of the problems in the prior art of such impact printers.  
         [0048]    In FIG. 1, based upon a logarithmic scale, the multi-viscosity ink mixture consists of inks of high and low viscosity mixed together. This produces a hybrid ink mixture with synergistic properties. The foregoing example utilized a mixture containing 50% by volume of an ink having a low viscosity of 750 cps and 50% by volume of an ink having a high viscosity of 1600 cps at room temperature. For purposes of this application with respect to the given viscosities, room temperature is defined as 25° C. A 50% mixture by volume was chosen in order to determine whether the resultant viscosity would exhibit a proportional relationship to the constituent viscosities. If so, then the resultant viscosity curve would lie equidistant from the constituent curves.  
         [0049]    From the results, it was found that low temperature is not detrimental to small molecule movement. High temperature is conducive to the movement of either small or large molecules. The resultant effect on viscosity was not proportional to the percentage of the mix. For instance by adding an equal amount of high viscosity ink (for example 50%) to an amount of low viscosity ink (for example 50%), a disproportional effect in a low ambient temperature was found. The resulting “apparent viscosity: exhibits high temperature viscosity only slightly lower than the high viscosity constituent, yet significantly lower viscosity at low temperatures, than the high viscosity constituent.  
         [0050]    [0050]FIG. 2 shows a viscosity comparison between a multi-viscosity ink mixture and a single viscosity ink. The multi-viscosity ink mixtures consists of equal parts by volume of an ink having a viscosity of 750 cps and an ink having a viscosity of 1600 cps. The single or mono-viscosity ink has a viscosity of 1050 cps.  
         [0051]    The graph of FIG. 2 shows that a multi-viscosity ink mixture can improve the flow conditions at cold temperatures and maintain the same properties as single viscosity inks at room temperature and higher temperatures. However, other viscosities may be preferred and can be formulated for use in varying printing temperatures.  
         [0052]    Viscosity studies have been conducted for inks with different pigment loads within the temperature range of 5° to 40° C. A preferred or idealized viscosity range was found to be around 1000 cps at room temperature. If the viscosity is too low at room temperature, it can cause ink smearing and ink migration at hot temperatures (40° C.).  
         [0053]    From the data of FIG. 2, the multi-viscosity (MV) ink mixture can maintain ideal apparent ink viscosity at ambient room to high temperatures in comparison with uni-viscosity inks. This applies to both dye-based ink and pigmented ink.  
         [0054]    In addition as seen in FIG. 2, the “apparent” (or “MV”) ink viscosity is 3000 cps lower than uni-viscosity inks at 5° C. The temperature range (5° C. to 40° C.) within which the experiments were conducted corresponds to standard operational temperatures of many printers. In order to predict viscosity beyond this range, the following equation is helpful: 
         ln(μ)= A−B T   (1) 
         [0055]    The viscosity μ is given in centipoises and the temperature T is expressed in Celsius. The coefficients, A and B in the equation are determined from regressing experimental ink-viscosity data. The equation can be used to anticipate results at temperatures beyond the limits of the experiments. The equation itself is limited in scope. Any viscous liquid, blended or not, will exhibit linear behavior (in logarithmic scale) only within some practical range. The actual limits of linearity will be dependent upon a particular material&#39;s characteristics.  
         [0056]    [0056]FIG. 3 shows the comparison of two different multi-viscosity ink mixtures or combinations. The high viscosity ink has a viscosity of 1600 cps at room temperature. The low viscosity ink has a viscosity of 750 cps at room temperature.  
         [0057]    The ink designated “Viscosity (50/50)”: 50% by volume is a mixture of a Low viscosity ink of 750 cps and 50% by volume of a High viscosity ink of 1600 cps.  
         [0058]    The equation for viscosity (50/50) pertaining thereto is: 
         ln(μ)=8.4−0.0593  T   (2). 
         [0059]    The ink designated “Viscosity (70/30)”: 70% by volume is a mixture of Low viscosity ink of 750 cps and 30% by volume high viscosity ink of 1600 cps.  
         [0060]    The equation of viscosity (70/30) pertaining thereto is: 
         ln(μ)=8.0−0.0563 T   (3). 
         [0061]    From regressing equations, the ink combination (70/30) flattens the slope of the curve 5% and the intercept declines 5% in a logarithmic scale in comparison with a 50/50 by volume mixture.  
         [0062]    [0062]FIG. 4 shows a logarithmic graph of viscosity versus temperature for two different multi-viscosity ink mixtures in a 50% to 50% ratio by volume. One mixture incorporates a low viscosity ink of 550 cps with a high viscosity ink of 1600 cps. The other mixture incorporates a low viscosity ink of 750 cps with a high viscosity ink of 1600 cps. This diagram illustrates that by varying the viscosity values, and mixture percentages, it is possible to tailor a multi-viscosity ink mixture to optimize ink performance for a particular application.  
         [0063]    While the examples shown and described herein illustrate a mixture of two inks of different viscosities it should be understood that the invention is not limited to a mixture of two inks of different viscosities but is intended to include mixtures of two or more inks of different viscosities. For example, three or more inks of different viscosities can be selected based on the particular mono-viscosity of each ink forming the ink mixture so that the ink mixture can be tailored to provide a multi-viscosity ink mixture which would be particularly useful over a given temperature range. The given temperature ranges of more than two monoviscosity inks when mixed can be temperature specific. For example if a printer is to be used in a warehouse, a heated industrial area, and an office interchangeably, the ink can be compounded to accommodate the three or more given ambient temperatures. As a further example, some line printers are now moved from one environment to another, which changes the relationship of the ambient temperature. Using the two or more ink compounds of this invention can cause the ink to be temperature specific and perform in an improved way with respect to each ambient temperature.  
         [0064]    In summation it has been found that an optimum blend of two, three or more inks having different viscosities can be made for use in impact printing applications such as line printing, and within other types of printers. The resulting product is a synergistic multi-viscosity blend that performs well throughout the temperature range anticipated in many applications. Other factors that influence the actual percentages of the different viscosity inks used to optimize the blend include, but need not be limited to the presence or absence of additives and pigments and the type of media to be printed upon.  
         [0065]    Various modifications of the invention are contemplated which will be obvious to those skilled in the art and can be resorted to without departing from the spirit and scope of the invention as defined in the following claims.