Abstract:
A free ink roller ball pen for dispensing low viscosity inks containing pigments that are prone to sedimentation. The instrument contains an ink reservoir chamber, a nib chamber provided with a roller ball socket assembly, a pressure equalization overflow chamber for the low viscosity ink, and a special agitation system for the ink reservoir and nib chamber. The agitation system comprises a weight, with a cross section smaller than the interior of the nib chamber, connected to a wire having a diameter smaller than the back inner diameter of the ball socket assembly. The length of the weight and its confinement are selected to provide for a predetermined stroke, on shaking the pen, that sweeps out the internal space of the nib and also the back of the roller ball assembly, to re-disperse any pigment that has precipitated.

Description:
FIELD OF THE INVENTION 
   The invention relates to pens for applying pigmented ink, and more particularly to a novel and improved roller ball-type pen suitable for the application of low viscosity, highly pigmented inks. 
   BACKGROUND OF THE INVENTION 
   There is a significant demand for the use of inks with exotic and unusual colors, in order to achieve special effects on a variety of writing surfaces. Such special effects often require the incorporation of large and/or dense pigment particles in the writing inks. The use of such pigments, however, creates problems with respect to precipitation of the pigment out of the low viscosity ink carrier, especially after periods of nonuse of the writing instrument. 
   One of the known devices for applying pigmented inks is the use of squeeze tube cartridge, which is filled with a high viscosity ink. The ink is sufficiently viscous to minimize precipitation of the pigment particles. These instruments are difficult to use, however, and offer little control over the width, and even the precise location, of the intended line. The high viscosity of the ink medium is also disadvantageous in that its penetration into the writing surface is very limited, so that the desired optical effects are not fully achieved. In addition, the resulting heavy lines of high viscosity ink take an excessive amount of time to dry and are subject to smudging. An example of a pen employing a squeezable cartridge tube is the Aoki U.S. Pat. No. 5,688,061, which employs a main body that is flexible, so that the ink can be extruded by squeezing with the fingers. Even so, the pen is provided with a spring-based agitating system to stir the ink and promote dispersion of the pigment. 
   Conventional ballpoint pens utilize a roller ball in connection with a relatively high viscosity ink which can hold pigment materials in suspension. The ballpoint pen relies upon pressure of the atmosphere to maintain the high viscosity ink in contact with the dispensing ball. When the ball is rotated, a shearing action of the ball surface against the ink body reduces the viscosity of the ink contacting the ball sufficiently to allow the ink to be transferred by the ball from the back of the ball socket to the intended writing surface. The relatively high viscosity of the ink, however, limits its penetration into the paper. Smudging is also a problem with the higher viscosity inks of ballpoint pens. Even with some ballpoint pens, it may be desirable to provide an agitating arrangement to redisperse any coagulated pigment. An example of such is the Nishitani U.S. Pat. No. 6,536,969. 
   So-called gel pens utilize somewhat lower viscosity ink than the standard ballpoint pens, and thus are an improvement over such ballpoint pens. However, the ink utilized in gel pens is still of relatively high viscosity, so as not to leak from the reservoir or the tip of the pen. The “gel” ink is applied in a manner similar to the ballpoint pen, by the rotating ball subjecting the ink to a shear force to reduce its viscosity as it is being transferred by the ball from the ink supply to the writing surface. While the gel pen is a marginal improvement over the ballpoint pen, it suffers some of the same disadvantages of limited penetration of the ink into the writing surface and some degree of smudging of the applied ink. 
   Free ink roller ball pens, utilizing low viscosity inks, are in general well known and have been manufactured and sold for many years. Representative such roller ball pens, as made for example by Chartpak, Inc., and also by Pentel, Pilot and Mitsubishi, provide a chamber for low viscosity, liquid ink communicating with a roller ball tip assembly. The ink reservoir has a confined air space above the ink, and the reservoir is maintained in communication with the atmosphere through a pressure equalization chamber, typically a single path or multiple path labyrinthine passageway, such as an injection molded lamella of wetable plastic. This allows air to enter the reservoir as the ink is consumed, and also provides for expansion and contraction of the reservoir air in response to variations in the temperature and/or ambient pressure. 
   Conventional free ink roller ball pens typically utilize a stainless or tungsten carbide roller balls, manufactured to very tight tolerances and closely received in suitable sockets. Typically, a fibrous feed rod extends up into the ink reservoir, providing a capillary system to maintain the ink supply at the back of the roller socket. It is well known that conventional free ink roller ball pens are unsuitable for use in connection with inks containing pigment that is inherently unstable in the low viscosity ink vehicle. The specialty pigments, desired to achieve effects such as metallic appearance, pearlization, pastel colors, luminescence, thermo-chromic effects and the like, tend to be too large and/or too dense to be retained in suspension in the low viscosity inks over any significant time period, as when the pen is stored between uses. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a new and improved roller ball pen, utilizing a low viscosity, free flowing ink medium. The new pen is constructed to enable the use of such low viscosity, free flowing inks carrying pigments that are inherently unstable in the fluid medium and may settle out during periods of nonuse of the pen. A novel agitator arrangement is provided, which can be activated when the pen is to be used, such that any precipitated pigment is redispersed throughout the ink supply, and the flow passages to the roller ball are cleared of sedimented pigment particles. 
   In a preferred embodiment of the invention, the agitator arrangement includes a reciprocating weight element which is movably confined within the nib structure of the pen, for limiting axial motion. The weight element carries a forwardly projecting wire at its front end, which projects into the roller ball socket assembly. When the pen is shaken in an axial direction, the weight and the wire mounted thereon reciprocate through a limited axial travel in a manner to effectively agitate and redisperse any pigment that has sedimented from the low viscosity ink vehicle. 
   In one alternative form of the invention, the wire element carried by the reciprocating weight is arranged such that, in its forwardmost position, the end of the wire is extremely close to or in contact with the roller ball at the end of the ball socket assembly. The arrangement is such that, as the wire and weight reciprocate within the nib structure, the wire positively displaces any sedimented pigment that is behind the roller ball, redispersing the pigment and enabling a free flow of low viscosity ink through the capillary passages leading to the roller ball, for application to a writing surface. The weight itself, reciprocating within a confined internal space in the nib structure, serves to sweep the internal space of the nib and to agitate and redisperse pigment within that area such that, with a few shakes of the pen, sedimented ink is effectively redispersed and the pen is fully reactivated for normal writing to apply the pigmented ink. 
   In another alternative form of the invention, a wire, carried at the front of a reciprocating weight, is permitted to travel up to, but not enter, the final capillary passage to the back of the roller ball. The arrangement is such that, with a vigorous shaking of the pen, a shockwave is created within the final capillary passage leading to the roller ball, to disturb and redisperse any sedimented pigment present therein. This action takes place in conjunction with the action of the reciprocating weight within a confined passage of the nib structure, to effectively agitate the ink supply throughout the nib structure and thoroughly redisperse the pigments therein. 
   In any of its forms, the pen of the invention may advantageously include one or more free weights, such as metal spheres, within the main ink reservoir, so that the ink supply within the reservoir itself is agitated when a user shakes the pen in the manner contemplated. 
   For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments of the invention, and to the accompanying drawings. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevational view, partly in section, showing features of one preferred embodiment of the invention. 
       FIG. 2  is an enlarged cross sectional view of a nib structure and reciprocating weight arrangement incorporated in the pen of  FIG. 1 . 
       FIG. 3  is an end elevational view of the nib structure of  FIG. 2 . 
       FIG. 4  is a cross sectional view as taken generally on line  4 — 4  of  FIG. 2 . 
       FIG. 5  is an enlarged cross sectional view of a ball socket assembly incorporated in the pen of  FIG. 1 , illustrating a portion of a reciprocating wire element that extends, in its forwardmost position, into contact or near contact with the back of a roller ball. 
       FIG. 6  is a cross sectional view as taken generally on line  6 — 6  of  FIG. 5 , with the roller ball removed from the socket assembly. 
       FIG. 7  is a side elevational view of the nib structure of  FIG. 2 , illustrating a form of capillary passage formed in the nib structure to enable communication between the ink reservoir and the atmosphere, to accommodate expansion and contraction of the ink and air in the ink reservoir, in response to temperature and pressure variations. 
       FIG. 8  is an enlarged, fragmentary cross sectional view showing a nib structure and an alternative form of agitating element associated therewith. 
       FIG. 9  is an enlarged, fragmentary cross sectional view of the ball socket assembly incorporated with the nib structure of  FIG. 8 . 
       FIG. 10  is a fragmentary cross section of a further alternative form of the invention, utilizing a lamella-type nib structure. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring now to the drawings, the reference numeral  20  designates generally a roller ball pen according to the invention, for use particularly in applying pigmented inks to a writing surface. The pen includes an elongated pen body  21 , typically of molded plastic construction, which is closed at one end  22  and formed at the opposite end with a first cavity  23 , for the reception of a nib structure to be described, and a second cavity  24  forming a reservoir for an ink supply and a confined air space above the ink. In the illustrated form of the invention, the reservoir cavity  24  is formed by the walls of the pen body. However, it is contemplated that the ink supply may be contained in a replaceable cartridge (not shown) which is removably received within the cavity  24 . The use of such removable cartridges is well known in the art and does not form part of this invention. 
   The forward cavity  23  of the pen body is of a size to snugly receive the generally cylindrically shaped body portion  25  of a nib structure  26  ( FIG. 2 ). The nib structure  26  is slightly tapered to seat tightly within the cavity  23  and serves as a closure for the ink reservoir cavity  24 . The nib structure  26  is configured to form an upper cylindrical cavity  27  and a lower cylindrical cavity  28 , providing ink flow communication from the reservoir cavity  24  to the lower end extremity  29  of the nib structure. 
   A roller ball tip assembly  30 , comprising a socket  31  and roller ball  32  ( FIG. 5 ) is tightly received within the lower cylindrical cavity  28  of the nib structure and provides the mechanism by which ink is transferred from the cavity  28  on to a writing surface (not shown). The tip assembly  30  is a product which is available commercially from such sources as Premec SA, Lugano, Switzerland. These tip assemblies are designed to function exclusively with low viscosity liquid inks. A typical such tip structure may include a roller ball  32  seated in a close-fitting socket  33 . The socket engages the roller ball over a diametral region thereof, such that the ball is retained in a generally fixed location, but is able to roll in any direction. The ball  32  typically may be formed of materials such as tungsten carbide, ceramic, or synthetic sapphire, for example, which is fitted to very tight tolerances in the socket  33 . The diameter of the roller ball  32  may be varied as appropriate to achieve line width in a range of about 0.008 inch to about 0.080. A typical roller ball diameter is about 0.040 inch. 
   The upper portion of the tip assembly  30  comprises a narrow ink-receiving recess  34  of relatively small diameter (e.g., 0.045 inch) which connects at its lower extremity with a narrow capillary flow passage  35  leading to the back of the roller ball  32 . The capillary flow passage  35  communicates a short distance above the roller ball  32  with a plurality of ink distributing passages  36  that allow the ink to flow to various portions of the surface of the roller ball as the latter rotates against a writing surface. The structure of the roller ball tip assembly as thus described is previously known and is not by itself part of the present invention. 
   Pursuant to one aspect of the invention, the upper chamber  27  of the nib structure  26  receives an elongated weight element  38 , which is closely received within the cavity  27  and is somewhat shorter than the overall length of the cavity  27 . In the form of the invention illustrated in  FIGS. 1–7 , the weight  38  comprises upper and lower end caps  39 ,  40 , preferably formed of plastic material, and a central portion  41  formed of a heavy material, preferably stainless steel or the like. The weight of the components  39 – 41  is such that the weight  38  as a whole is negatively buoyant in the low viscosity ink fluid (i.e. has a greater density than the displaced fluid). 
   A shoulder  42 , formed where the larger upper cavity  27  joins with the smaller diameter lower cavity  28 , is positioned to engage the front face of the lower end cap  40  and thus to serve as a limit stop for downward/forward movement of the weight within the cavity  27 . An upper stop member  43  is inserted into the upper end of the cavity  27  and includes radially disposed web elements  44  which serve to engage the upper end cap  39  of the weight element, and thus function as an upper limit stop to movements of the weight  38  within the cavity  27 . Open spaces  45  between the radial webs  44  enable a free flow of ink into and from the cavity  27 . 
   Pursuant to another aspect of the invention, a long, slender agitating wire  46  is anchored at one end in the front end cap  40  of the reciprocating weight element  38  and extends downward/forward to the lower end of the roller ball tip  30 . In this first illustrated form of the invention, the agitating wire  46 , in its forwardmost limit position, as determined by engagement of the front end cap  40  with the shoulder  42 , is positioned such that the forwardmost tip  47  of the wire is extremely close to the back surface of the roller ball  32 , and preferably is in light, touching contact therewith. The wire  46  has a diameter which is somewhat less than the diameter of the capillary flow passage  35  leading to the back of the roller ball. For example, in a preferred embodiment of the invention, the agitating wire  46  may have a diameter of approximately 0.010 inch, while the diameter of the capillary flow passage  35  may be around 0.020 inch. Accordingly, when the wire  46  is positioned within the capillary flow passage  35 , there is sufficient clearance space available to accommodate the flow of ink from the internal recess  34  of the tip assembly through the capillary flow passage  35  and the distribution passages  36  to the back surface of the roller ball  32 . 
   In the embodiment of  FIGS. 1–7 , the reciprocating weight  38  is dimensioned to have a length somewhat less than the effective length of the cavity  27 , between the shoulder  42  and the stop element  43  at the opposite end. In a preferred embodiment of the invention, the effective length of the weight element  38  is around 0.015 inch shorter than the effective length of the cavity  27 , and preferably 0.015 inch to 0.030 inch shorter. Accordingly, when the assembled pen unit is shaken in an axial direction by the user, the weight  38  can reciprocate through a short stroke of the above-indicated dimensions within the cavity  27 . As will be understood, when the weight element reciprocates to its upper/rearward position, with the end cap  38  abutting the stop element  43 , the wire  46  is completely withdrawn from the capillary flow passage  35 . When the weight element reciprocates in the opposite direction, the wire element  46  enters the capillary passage and extends into contact with or immediately proximity of the back surface of the roller ball  32 . When the wire  46  enters and passes through the capillary flow passage  35 , it not only stirs up and agitates the liquid therein, but will physically displace any sedimented pigment in the capillary passage and clear out the passage for a proper flow of ink to the back of the roller ball. 
   The axial reciprocating movements of the weight element  38  within the cavity  27  tend to scour the chamber and agitate the ink contained therein, in order to disperse pigments carried by the ink and to redisperse and distribute any pigments that may have settled out. The agitation of the ink supply by the main body of the weight element also thoroughly agitates ink contained in the lower chamber portion  28 , as a result of the scouring action of the weight in the cavity  27 . 
   In the form of the invention illustrated in  FIGS. 1–7 , the end caps  39 ,  40  of the weight element  38  advantageously have a clearance space with the internal walls of the cavity  27  of about 0.010 inch to about 0.100 inch, and preferably in the range of 0.010 inch to 0.030 inch. In the illustrated embodiments, the end caps  39 ,  40  and the cavity  27  are of cylindrical configuration. However, the cross sectional configuration of the weight element and of the cavity  27  may be formed with ridges and channels, if desired, to further promote fluid flow and pigment redispersion when the weight element is reciprocated. In practice, only a few shakes of the pen are sufficient to thoroughly agitate the ink supply and disperse its contained pigments. 
   Preferably and advantageously, the ink reservoir cavity  24 , provided in the pen body  20  above the nib structure, is provided with one or more agitating elements  48 , preferably in the form of small (e.g., ⅛th – 3/16th inch diameter) stainless steel balls, which are freely movable within the cavity  24 . When the shaking action is imparted to the weight element  38 , to clear the chambers and passages of the nib structure, the agitator elements  48  move randomly about the cavity  24  and thoroughly agitate and stir the ink supply retained therein. Addtionally, when the pen is shaken, the agitating elements  48  will impact the upper end of the nib structure and serve in some measure to contribute to the agitation and pigment dispersion of the ink contained within the nib structure. 
   The roller ball pen of the invention is intended specifically for use with free bodies of low viscosity inks, which are far superior to gel inks and ballpoint pen inks for use in connection with pigmentation. In particular, the inks contemplated for use in the pen of the invention may range from around 3 to around 20 centipoise in viscosity, and preferably in the range of 3 to around 8 centipoise. These low viscosity inks are particularly desirable for decorative work with pigments, because the liquid vehicle for the pigment is quickly and substantially absorbed by the paper or other writing surface, so that the pigmentation is more visible and therefore more effective. When gels and higher viscosity inks are utilized, the ink vehicle does not absorb well into the writing surface and to some degree remains on top of the pigment particles reducing their optical effectiveness. The unabsorbed ink also remains a smudging problem, for at least a period of time. Some of the desired pigments are in the form of large particles which easily precipitate for that reason. Others (for example, titanium dioxide) are very dense and will tend to precipitate out of the low viscosity ink regardless of particle size. The highly effective agitating system of the present invention, however, makes it possible to effectively utilize the desired pigments in a low viscosity vehicle, such that the optical effects of the pigments can be optimally realized. 
   In the roller pen of the invention, provision is made for equalization of pressure between the ink reservoir cavity  24  and the atmosphere, so that as the low viscosity ink is consumed, it can be replaced in the reservoir by air, and also so that accommodation can be made for changes in pressure and/or temperature that may cause expansion or contraction of the air and ink in the reservoir. The provision for such equalization, which in itself is well known, involves the provision of a labyrinthine capillary system in the nib structure which accommodates the flow of air into the ink reservoir as needed to replace consumed ink, and also provides for the temporary storage of some of the ink, for pressure equalization. 
   As shown in  FIG. 7 , the nib structure  26  is provided externally with a spiral capillary pathway  50  which is closed on the outside by a cylindrical wall  51  forming the lower end of the pen body. At its lower end, the spiral pathway terminates in an axially directed passage  52 , which is open to the atmosphere at the lower end of the pen. At its upper end, the spiral pathway  50  communicates with a radial passage  53  extending inwardly, and communicating with an upper portion of the nib cavity  27 . The arrangement is such that ink can flow into and out of the spiral capillary pathway  50  as necessary to respond to pressure/temperature changes within the pen, and air can enter the pen as necessary to replace ink as it is consumed from the reservoir. The spiral capillary pathway  50 , in itself well known, is an advantageous form of capillary system to utilize in connection with pigmented inks. 
   In a second preferred embodiment of the invention, shown in  FIGS. 8 and 9 , an agitating wire  60  is employed, which is considerably larger in diameter than the wire  46  of the embodiment of  FIGS. 1–7 . Thus, whereas the wire  46  ( FIG. 2 ) may be about 0.010 inch diameter, small enough to easily enter and pass through the capillary flow passage  35  in the tip assembly  30 , the wire  60 , shown in  FIGS. 8 and 9 , may have a diameter on the order of 0.031 inch, somewhat larger than the capillary flow passage  35   a  in the writing tip assembly  30   a.    
   The nib structure  61  shown in  FIG. 8  is similar to that shown in  FIG. 2  and comprises a molded plastic element provided with an upper cavity  62  communicating directly with a lower cavity  63  of somewhat smaller diameter, in which the tip assembly  30   a  is inserted and mounted. A reciprocating agitator weight  64 , comprising plastic front and rear caps  65 ,  66  and a metal center portion  67 , is arranged for a reciprocating movement of defined and limited stroke within the upper cavity  62 . A stop element  68  at the upper end of the cavity  62  serves as an upper limit for the agitator weight  64 , and a shoulder  69 , formed at the juncture of the upper and lower cavities  62 ,  63 , serves as a lower limit stop for the weight. The wire  60  is anchored in and projects forwardly from the front end cap  65  of the weight, as shown in  FIG. 8 . 
   In the illustration of  FIG. 9 , the wire  60  is shown in its forwardmost position, in which the forward tip  70  of the agitating wire  60  is spaced a short distance (e.g., less than 0.010 inch) away from the entrance to the capillary flow passage  35   a . The forwardmost position of the wire  60  is determined by engagement of the front surface  71  of the agitator front portion  65  with the shoulder  69 . Preferably, the front end cap  65  is formed with opposed flat tapered surfaces  72 ,  73  on opposite sides of the front surface  71  such that, when the front surface is abutted against the shoulder  69 , there is clearance space to accommodate ink flow between the cavities  62 ,  63 . Sufficient clearance is also provided between the wire tip  70  and the capillary flow passage  35   a  to accommodate the flow of ink from the internal recess  34   a  of the tip assembly  30   a  into the capillary flow passage  35   a  when the agitator weight  64  is in its forwardmost position. 
   In the embodiment of  FIGS. 8 and 9 , when the agitator weight  64  is reciprocated, the motion of the wire  60  within the recess  34   a  displaces ink within that recess and also creates a shockwave directed into the capillary flow passage  35   a  to agitate and disperse any sedimentation within that passage. Additionally, the agitator weight  64  is of a size and shape to provide a small clearance space with the side walls of the cavity  62  of about 0.010 inch to about 0.100 inch, and preferably in the range of 0.010 inch to 0.030 inch. The component elements  65 – 67  of the weight  64  have an overall length which is slightly shorter (e.g., 0.015 inch to 0.030 inch) than the length of the cavity  62  as defined by the stop element  68  and the shoulder  69 . Thus, when the pen body is vigorously shaken, the weight  64  reciprocates through a defined distance, impacting the nib at both ends of its stroke, to thoroughly agitate the ink supply and redisperse any precipitated pigment. 
   The nib structure  75  shown in  FIG. 10  optionally incorporates an equalization system different from that of the nib structure of  FIG. 7 , in that the capillary system provided for pressure equalization is not in the form of a continuous spiral but rather in the form of a series of closely spaced annular capillary spaces  76  separated by thin annular lamellae  77 . The individual annular spaces  76  are connected by an axial capillary slot (not shown). This form of nib structure is well known, and is shown in more detail in, for example, U.S. Pat. No. 6,464,420. The structure of  FIG. 10  can utilize an agitator arrangement  64   a  of either of the types heretofore described, or of other configuration suitable to provide a sweeping action within the nib cavities and redispersal of the ink pigments when the pen is shaken. 
   In any of the various forms of the invention, it will be understood that the ink supply may take the form of a separable ink cartridge arranged to be inserted into the pen body above nib structure and arranged to communicate with the nib structure when the pen is assembled by the user. Such cartridge arrangements are well known in the art. In the present instance, it may be advantageous to provide the cartridges with agitating elements such as the balls  48  ( FIG. 1 ) to facilitate agitation of the ink supply in the cartridge. 
   The pen of the present invention represents a significant advance in the art, in that it provides an effective and practical instrument for the delivery of highly pigmented inks using a roller ball pen and a low viscosity ink medium. While pigmented inks are widely used, it is customary to utilize such inks in other than roller ball pens. With standard ballpoint pens and gel pens, for example, pigmented inks can be effectively employed because of the high viscosity of the ink vehicle effectively maintains the pigments in suspension. However, because of the relatively high viscosity of such inks, the ink from these pens is not easily absorbed in the writing paper. The higher viscosity inks tend to largely remain on the surface, partially obscuring the pigments and also creating a potential for smudging. Utilizing the roller ball pen, with low viscosity inks according to the present invention, enables the low viscosity inks to be readily absorbed into the writing paper such that the pigment particles are more visible and optically more effective for their intended purposes. The use of a roller ball instrument with low viscosity inks also enables the writer to have optimum control over the form and width of the line. 
   The combination of elements incorporated in the pens of the invention enable the user, in a few shakes of the pen, to redisperse any settled pigments, and also to clear the capillary passages leading to the back of the roller ball. This makes it quite feasible to utilize pigments of large particle size and/or density in conjunction with low viscosity inks, for superior optical results. 
   It should be understood, of course, that the specific forms of the invention herein illustrated and described are intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claims.