Abstract:
A ball pen ink of transiently erasable type to be dispensed from a pressurized ball pen incorporates an elastommeric polymer, pigment and a mixed solvent system. The mixed solvent system includes a volatile solvent component, a non-volatile solvent component and a non-volatile solvent/plasticizer component in such relative amounts and with relation to the elastomer and pigment combination as achieves a balance between ink viscosity and thixotropy to provide good writing qualities.

Description:
This is a continuation of co-pending application Ser. No. 681,615 filed on Dec. 14, 1984 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to an improved ink composition for ball pens, the ink being of the type whcih produces a mark on a writing surface of initially erasable character by means of an ordinary pencil eraser but which becomes permanent after a period of time of a few hours. Inks of this type are well known as are illustrated, for example, by Daugherty et al. U.S. Pat. No. 3,875,105; Muller et al. U.S. Pat. No. 4,097,290; Muller U.S. Pat. Nos. 4,329,262 and 4,329,264; and Ferguson U.S. Pat. No. 4,390,646. 
     2. Description of the Prior Art 
     The prior art suggests various elastomers in a mixed solvent system together with colorant to form a pressurized pen ink composition. The Ferguson &#39;646 patent suggests the use of block copolymers having butadiene or isoprene midblocks which may replace the use of natural rubber as in the Daugherty et al. &#39;105 patent to eliminate the necessity for milling the rubber. The Muller &#39;264 patent suggests the use of a solvent system containing little or no volatile component. The Muller et al. &#39;290 patent suggests the use of a mixed solvent system emphasizing low boiling and high boiling components. The Muller &#39;262 patent suggests the use of a mixed solvent system comprising a volatile component and an essentially non-volatile component having a low viscosity and the optional additon of non-volatile, high viscosity material. 
     BRIEF SUMMARY OF THE INVENTION 
     To be successful, ink compositions of the type contemplated must possess the requisite rheological properties to enable them to be dispensed from a ball pen with ease of starting and smoothness in writing so as to lay down an intense line or mark which has the initially erasable character noted above. Additionally, such inks must have the requisite viscosity characteristic to flow evenly and smoothly but these inks particularly must possess the requisite thixotropy to prevent oozing when the pen is not in use, especially as they normally are dispensed under positive pressure. Thus, the ink should possess a sufficiently high viscosity within the pen reservoir as resists flow under the pressure feed conditions, but must also be sufficiently thixotropic that when the ink is subjected to the high shearing force produced by the rotating ball, the apparent viscosity is significantly lowered to a value which allows easy starting and a smooth, even flow of the ink onto the writing surface. 
     In order to impart the requisite balance between viscosity and thixotropic properties to the ink composition, it has been discovered that the solvent system in the colorant/elastomer/solvent composition must consisit of a three component mixed solvent system characterized essentially by a highly volatile solvent component, a substantially non-volatile solvent component having a low viscosity of only a few centipoises and a substantially non-volatile solvent/plasticizer component having a high viscosity typically of 50 or more centipoises. It has been discovered that where the components of the mixed solvent system are present in a narrow range of relative amounts and within definite ranges relative to the colorant and elastomer, the requisite balanced combination of viscosity and thixotropy is imparted thereto. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following table represents certain principles of this invention with reference to the six Examples set forth below. In Table 1, the parts are by weight and the ratios given are w/w. The compositions of Example 1 and 4 represent thixotropic inks which have a low shear rate viscosity of about 500,000 cps whereas the compositions of Example 4 and 5 have low shear rate viscosity of about 2.5×10 6  cps. The preferred Examples 2 and 3 have a low shear rate viscosity of about 200,000-250,000 cps. 
     
                       TABLE I______________________________________      Ex. 1           Ex. 2  Ex. 3   Ex. 4                               Ex. 5                                    Ex. 6______________________________________Elastomer    24     20     19    31.8 18   19.6Pigment      18.4   19.13  17.66 16.7 20.2 22Volatile solvent        17     27     25    20.9 35   29.3Non-volatile solvent        19.7   23.15  26.41 17.1 9.7  10.5Non-volatile 16.2   4.67   5.0   10.6 12.8 13.9solvent/plasticizerTotal solvent system        52.9   54.82  56.41 48.6 57.5 53.7Solvent system:        1.25   1.40   1.54  1.0  1.5  1.29elastomer + pigmentElastomer:pigment        1.30   1.05   1.08  1.90 .89  .890Non-volatiles:        2.11   1.03   1.26  1.33 .64  .83volatileNon-volatile solvent:        1.2    4.95   5.28  1.6  1.3  .76solvent/plasticizer______________________________________ 
    
     With respect to the preferred lower viscosity Examples 2 and 3, the weight ratio of elastomeric polymer to pigment is approximately 1; the weight ratio of the non-volatiles to volatile solvent is approximately 1-1.26; and the weight ratio of the solvent system to the elastomeric polymer plus pigment is approximately 1.40-1.54. In addition, it is important that the weight ratio of the non-volatile solvent/plasticizer component is about 5. These values as well as the ranges thereof illustrated in Table 1 result in ink compositions having balanced viscosity and thixotropy essential to good writing qualities when the inks are dispensed from a pressurized ball pen. 
    
    
     EXAMPLE 1 
     
         ______________________________________Elastomeric polymer         Kraton 1107        24Colorant      Alkali Blue (Red Shade)                            2.88         Alkali Blue (Green Shade)                            2.88         Phthalo Blue (Green Shade)                            .64         Victoria Blue      12Volatile solvent         Laquer Diluent #6  17componentNon-volatile solvent         Penreco 2257 oil   19.7component     (viscosity 1.5 cps)Non-volatile solvent/         D-15 mineral oil   9.6plasticizer component         (viscosity 50 cps)         DOP                6.6         (viscosity 58 cps)Lubricants    Oleic acid         1.7         Lauric acid        1.5         Stearic acid       1.5                            100______________________________________ 
    
     In addition to the elastomer/pigment/solvent system described above, lubricant in amount of 4.7 parts by weight is included. The Kraton 1107 is a block copolymer available from Shell Oil Company, Houston, Tex., and is referenced in the Ferguson U.S. Pat. No. 4,390,646 incorporated by reference herein. The Alkali Blue pigments are available from Sherwin-Williams Co., Cleveland, Ohio and the Victoria Blue from E. I. Dupont, Wilmington Del. and are referenced in the Muller &#39;262 patent which is incorporated herein by reference. Laquer Diluent #6 is available from Chem Central Company, Chicago, Ill., is an aliphatic petroleum distillate having a boiling range of 94°-120° C. and is identified in the Muller et al. &#39;290 patent, incorporated by reference, and in the Muller &#39;262 patent. 
     The Penreco 2257 oil and the D-15 mineral oil are identified in the Muller &#39;262 patent, DOP is dioctyl phthalate and the fatty acids are conventional lubricants for ball pen inks. 
     EXAMPLE 2 
     
         ______________________________________Elastomeric polymer           Kraton D-1107                        20Colorant        Blue Pigments                        19.13Volatile solvent           Cyclo hexane 23.2component       Ethyl acetate                        3.8Non-volatile solvent           TX1B         8.0component       (viscosity 2 cps)           Light mineral oil                        15.15           (viscosity 2 cps)Non-volatile solvent/           DOP          4.67plasticizer componentLubricants      Oleic acid   1.0           Lauric acid  1.5           Stearic acid 1.5Other           Polyvis 30-SH                        1.23           Sarcosyl - 0 .82                        100______________________________________ 
    
     KODAFLEX (TX1B) is marketed by Eastman Kodak Company, Kingsport, Tenn. and is identified in the Muller &#39;262 patent. Example 2 is a commercial formulation and, as is usual with the inks of this invention, the pigment is milled into a paste which contains the DOP and some light mineral oil. The Polyvis 30-SH is a low molecular weight polymer which is added to the pigment paste mill for lubrication purposes and the Sarbosyl-0 is oleoyl sarcosine, a wettability agent as identified in the Daugherty et al. &#39;105 patent. 
     EXAMPLE 3 
     
         ______________________________________Polymer         Kraton D-1107                        19.0Colorant        Black Pigments                        17.66Volatile solvent           Cyclo hexane 21.5component       Ethyl acetate                        3.5Non-volatile solvent           TX1B         8.0component       (viscosity 2 cps)           Light mineral oil                        18.41           (viscosity 2 cps)Non-volatile solvent/           DOP          5.0plasticizer componentLubricants      Oleic acid   1.5           Lauric acid  1.5           Stearic acid 1.17Other           Polyvis 30-SH                        1.96           Sarcosyl - 0 .8                        100______________________________________ 
    
     Example 3 is also a commercial ink. Both the inks in Example 2 and 3 have low shear viscosity of 200,000-250,000 cps. 
     EXAMPLE 4 
     
         ______________________________________Elastomeric polymer           Oppanol B-15  22.3           Oppanol B-50  9.5Colorant        Blue Pigments 16.7Volatile solvent           Laquer Diluent #6                         20.9componentNon-volatile solvent           Penreco 2257 oil                         17.1component       (viscosity 1.5 cps)Non-volatile solvent/           D-15 mineral oil                         8.8plasticizer component           Polybutene    1.8Lubricants      Oleic acid    1.1           Lauric acid   .9           Stearic acid  .9                         100______________________________________ 
    
     Oppanol is an elastomeric polyisobutylene polymer available from BASF of Norwalk, Calif. 
     EXAMPLE 5 
     
         ______________________________________Elastomeric polymer           Epcar 346     18.0Colorant        Blue Pigments 20.2Volatile solvent           Laquer Diluent #6                         35.0componentNon-volatile solvent           Penreco 2257 oil                         9.7componentNon-volatile solvent/           D-15 mineral oil                         10.6plasticizer component           Polybutene    2.2Lubricants      Oleic acid    4.3                         100______________________________________ 
    
     Epcar 306 is a copolymer of ethylene and propylene and Epcar 346 is a terpolymer of ethylene, propylene and an unconjugated diene available from B. F. Goodrich. 
     EXAMPLE 6 
     
         ______________________________________Elastomeric polymer           Epcar 306     19.6Colorant        Blue Pigments 22.0Volatile solvent           Laquer Diluent #6                         29.3componentNon-volatile solvent           Penreco 2257 oil                         10.5componentNon-volatile solvent/           D-15 Mineral Oil                         11.5plasticizer component           Polybutene    2.4Lubricants      Oleic acid    4.7                         100______________________________________ 
    
     As will be seen from the above, various elastomeric polymers may be used, their selection depending upon choice of molecular weight within that range of Mooney viscosity to which rubber would be milled to formulate an ink based thereon. Other and different elastomeric polymers may be used such as the Solprenes which are no longer available commercially and thus have not been included herein.