Abstract:
A capillary wick running through the reservoir so that at least a portion of the capillary wick along the longitudinal axis is in direct contact with the liquid within the reservoir. This allows liquid in the reservoir to convey to a tip with minimal flow resistance. As such, a sufficient amount of liquid is provided to the tip, even when the writing instrument is used in quick strokes or for a long duration of time. In a writing position, a capillary storage is above the reservoir so that the capillary storage remains substantially dry without the head pressure affecting the capillary storage. The present invention is also directed to providing a porous divider wall between a reservoir that is below the storage, but without a capillary wick. Here, the porous divider wall is used to regulate air flow into the reservoir. Without the capillary wick, the unit costs and the manufacturing costs are substantially reduced.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a fluid dispensing utensil and, more particularly, to a writing instrument having a reservoir between a tip and a capillary storage. 
     2. General Background and State of the Art 
     Writing instruments are commonly used to deliver liquids such as ink, paint, adhesive, shoe polish, lotion, medicine, perfume, makeup, Whiteout® and food. In one type of fluid dispensing utensil, a relatively large volume of fluid is stored in a non-capillary container (or reservoir) where it is allowed to move freely. Pens which incorporate such a container, for example, are referred to as “free ink” pens or markers. U.S. Pat. No. 6,095,707 issued to Kaufmann discloses such a pen. That is, the ink in the reservoir is usually in a liquid state and is free to move about as the writing utensil is moved. One of the nice features of free ink markers is that they are visually appealing to users as the liquid moves around within the container. Moreover, free ink markers tend to last longer than other pens. 
     Liquid in these utensils is transferred from the container to the delivery end (often referred to as a tip or a nib) via a capillary conveying line or referred to as a capillary wick. A slight vacuum (underpressure) relative to the atmosphere is maintained within the container which prevents liquid in the conveying line from escaping from the utensil until the tip is brought into contact with the surface onto which liquid is to be dispensed. At this point, the force of attraction of the surface and the capillary force of the space between the surface and portions of the tip, which are not in direct contact with the surface, will cause the liquid to flow from the tip to the surface. As liquid is dispensed, air enters the container in a controlled manner via an air inlet that is formed in the container and ends within the liquid. The air replaces the liquid so as to maintain the vacuum at a relatively constant level. 
     To deal with the problem of leakage caused by air expansion within the container, a capillary storage is used to absorb the excess liquid. Specifically, when the air within the container is heated, it expands. Alternatively, as the writing instrument is used in a higher elevation, the underpressure within the container will rise and increase the vapor pressure on the liquid. This forces excess liquid to flow through the conveying line via capillarity action. To handle the excess liquid, some ink pens or markers include an overflow chamber having a capillary storage that will absorb the excess ink. Fountain pens, for example, include a capillary storage in the front section of the writing instrument next to the tip. 
     Because the capillary storage is on the front section of the writing instrument or below the reservoir in a writing position, the head pressure of the liquid in the reservoir may keep at least a portion of the capillaries in the capillary storage wet. This means that when there is a rise in temperature or pressure within the reservoir, only the unwetted or dry capillaries in the capillary storage can absorb the excess ink from the reservoir. As such, the capillary storage may need to be oversized to account for the fact that at least some portion of the capillaries will be wetted due to the head pressure in the reservoir. However, a larger capillary storage means that the circumference of the writing instrument, which is housing the capillary storage, needs to be bigger as well. This is one of the reasons why a free ink writing instrument is generally thicker than a ballpoint pen, for example, and therefore not as comfortable for the user to utilize. 
     Still further, the longer the capillary conveying line, the greater flow resistance it has to convey the ink from the reservoir to the tip. This means that if a user writes quickly or for a long duration of time, the conveying line may dry out and therefore not write properly. 
     Still further, most free ink writing instruments are assembled from several pieces including a capillary conveying line capillary storage, a divider separating the reservoir and a storage area, all enclosed in a container. All of the above pieces add cost and manufacturing time to manufacture a writing instrument. To minimize the cost of the writing instrument, there is a need to manufacture a writing instrument with fewer pieces. Moreover, there is a need to keep most if not all of the capillaries in a capillary storage dry so that most, if not all, of the capillaries in a capillary storage may absorb excess ink from the reservoir. Even further, there is a need to minimize the flow resistance in the conveying line so that a sufficient amount of ink is delivered to the tip of the writing instrument under most if not all writing conditions. 
     BRIEF SUMMARY OF THE INVENTION 
     One of the features of the present invention is to provide a writing instrument having a relatively small circumference so that it may be comfortably held in a user&#39;s hand for writing. Another feature of the present invention is to minimize the flow resistance in a conveying line so that a sufficient amount of ink or liquid may be delivered to a tip of the writing instrument. Still another feature is to provide a writing instrument that is easier to manufacture at a lower cost. 
     The present invention accomplishes the above features by providing a reservoir for holding liquid or ink between a capillary storage and a tip. That is, according to one embodiment of the present invention, the capillary storage is above the reservoir so that any head pressure in the reservoir or the column of liquid does not affect the capillary storage. This means that the capillary storage will remain substantially dry so that most, if not all, the capillaries in the capillary storage may absorb the excess ink in the reservoir due to a rise in temperature or pressure within the reservoir. 
     Still another feature of the present invention is to have a conveying line running through the reservoir so that at least a portion of the conveying line along the longitudinal access is in direct contact with the liquid within the reservoir. This means that the liquid in the reservoir may convey to the tip with minimal flow resistance. As such, a sufficient amount of liquid is provided to the tip, even when the writing instrument is used in quick strokes or for a long duration of time. 
     Yet another embodiment of the present invention is to provide a reservoir between the storage and the tip, but without a conveying line. That is, without the conveying line, the unit costs and the manufacturing costs are substantially reduced. In this embodiment, the reservoir is also below the capillary storage, and they are divided by a porous or a capillary divider wall. Here, the porous divider wall is used to regulate air flow into the reservoir. That is, as the temperature or pressure in the reservoir increases, air will displace the liquid in the largest pore in the porous divider wall to equalize the pressure in the reservoir. With regard to the displaced liquid from the largest pore size in the porous divider wall, such liquid may be temporarily stored in the capillary storage that is in direct contact with the porous divider wall. On the other hand, as the temperature or pressure within the reservoir drops, air will flow back into the reservoir through the largest pore size in the porous divider wall. 
     In situations where the tip is facing upward or in an inverted position, the porous divider wall may be fully saturated and, if there is a rise in temperature or pressure within the reservoir, the excess ink from the reservoir may be temporarily stored in the capillary storage. Likewise, as with the previous embodiment, since the capillary storage is above the reservoir in a normal writing position, a smaller capillary storage may be used because, under normal conditions, most if not all the capillaries in the capillary storage will be empty of liquid. This is principally due to the fact that the capillary storage which is above the reservoir is not affected by the head pressure due to the column of liquid in the reservoir. 
    
    
     The above described and many other features and attendant advantages of the present invention will become apparent from a consideration of the following detailed description when considered in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exemplary cross-sectional view of a writing instrument showing a reservoir between a capillary storage and a tip; 
     FIG. 2 is an exemplary distribution of pore sizes or capillarity between a capillary wick, a capillary storage, and a tip; 
     FIG. 3 is an exemplary cross-sectional view of a writing instrument in accordance with another embodiment showing a capillary conveying line partially through a capillary storage; 
     FIG. 4 is an exemplary cross-sectional view of yet another embodiment of the present invention showing a capillary conveying line adjacent a capillary storage; 
     FIG. 5 is an exemplary cross-sectional view of still another embodiment of the present invention showing a tube partially sealing a capillary conveying line within a reservoir; 
     FIG. 6 is an exemplary cross-sectional view of another embodiment of the present invention showing a reservoir between a capillary storage and a nib, but without a capillary conveying line; 
     FIG. 7 is an exemplary distribution of pore sizes or capillarity between a capillary storage, a porous divider wall, and a tip; and 
     FIG. 8 is an exemplary cross-sectional view of yet another embodiment of the present invention showing a capillary storage being adjacent a hole. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention. The section titles and overall organization of the present detailed description are for the purpose of convenience only and are not intended to limit the present invention 
     By way of background, it should be noted that the descriptive term “capillarity” has been used herein to indicate the height up to which a liquid ascends within a pore of a given diameter. The greater the height, the greater the capillarity. In general, small size pores have greater capillarity than the larger size pores. In other words, the term “capillarity” is indicative of the attractive force between a liquid and a pore. Moreover, U.S. Pat. Nos. 6,089,776 and 6,183,155 B1, and U.S. patent application Ser. Nos. 09/591,114 filed Jun. 9, 2000, 09/839,380 filed Apr. 20, 2001, 09/839,842 filed Jun. 20, 2001, and 09/839,843 filed Jun. 20, 2001, are all hereby incorporated by reference into this patent application. 
     FIG. 1 illustrates by example a writing instrument  10  comprising a container  12  having a divider wall  18  defining a first storage area  14  (reservoir) and a second storage area  16 . The first storage area  14  is used to store liquid, and within the second storage area is a capillary storage  20 . The divider wall  18  also has an opening  22  which allows a capillary wick  24  having a proximal portion  26  and a distal portion  28  to extend through the second storage area  16  and the first storage area  14 . That is, the distal portion  28  penetrates through the opening  22  and into the capillary storage  20 . Note that at least a portion, if not all, of the distal portion  28  of the capillary wick  24  is in direct contact with the capillary storage  20 . Also, the proximal portion  26  protrudes through the writing side  30  of a container  12  and may be aligned to be in direct contact with a tip  33 . 
     As further illustrated in FIG. 1, the distal portion  28  of the capillary wick  24  substantially fills the opening  22  in the divider wall  18 . This way, the capillary storage  20  only comes into contact with the liquid in the first storage area  14  via the capillary wick  24 . Moreover, a proximal portion  26  protrudes from the writing side  30  such that it is completely sealed between the capillary wick  24  and the writing side  30 . A seam may be provided, for example, by crimping the capillary wick  24  and the contact area between the capillary wick and the writing side  30 . Alternatively, any other methods known to one skilled in the art may be used to seal the capillary wick  24  from the writing side  30 . 
     FIG. 2 illustrates by way of example a general distribution of pore sizes between the capillary wick  24  and the capillary storage  20 . With regard to the graph in FIG. 2, axis “X” represents a capillarity potential of pores or smaller pore sizes from left to right, and axis “Y” generally represents percentage pores. Moreover, graphs  24  and  20  illustrate exemplary measurable distribution of pore sizes in the capillary storage and capillary wick, respectively. Reference points “SL” refer to a measurable largest pore size in the capillary storage, “SM” refers to a measurable mean flow pore in the capillary storage, and “SS” refers to a measurable smallest pore size in the capillary storage; “CL” refers to a measurable largest pore size in the capillary wick, “CM” refers to a measurable mean flow pore in the capillary wick, and “CS” refers to a measurable smallest pore size in the capillary wick. Note that with the above distribution of pore sizes, there may be an overlap  32  between the smallest pore size in the capillary storage SS and the largest pore size in the capillary wick CL. Moreover, since the liquid  30  is in direct contact with the capillary wick  24  and because the capillarity force in the capillary wick  24  is greater than the capillary storage  20 , the capillary wick  24  will remain wetted. The pore size in the capillary wick and capillary storage may be measured by Porous Materials, Inc., located at 83 Brown Road, Ithaca, N.Y. 24850. 
     Moreover, if there is an overlap region  32  between the capillary wick  24  and the capillary storage  20 , some portion of the capillary storage  20  may be wetted depending on the orientation of the writing instrument  10 . For instance, if the writing instrument is in an inverted position, i.e., the tip  33  is facing up, then liquid in the first storage area  14  is held in place by an “underpressure” (slight vacuum) of the air above the ink, which counteracts the force of gravity or weight of the column of liquid in the first storage area, i.e., the head pressure. With the head pressure above the capillary storage  20  in an inverted position, some portion of the capillary storage  20  may be wet. 
     If the writing instrument  10  is in a writing position, i.e., the tip is facing down, so that the capillary storage  20  is above the first storage area  14 , then the capillary storage  20  is not affected by the head pressure. Accordingly, most if not all of the capillaries in the capillary storage  20  may be substantially empty, i.e., dry. This improves the performance of the capillary storage because most if not all of the capillaries in the capillary storage  20  may absorb the excess liquid from the first storage area  14 . This means that with the present invention, a smaller size capillary storage may be used, which means a container having a smaller circumference may be used as well. Therefore, with the present invention, a free ink writing instrument may be as small as a ballpoint pen to write more comfortably. 
     Moreover, with the above distribution of pore sizes between the capillary wick  24  and the capillary storage  20 , as the underpressure within the first storage area subsides, i.e., increase in absolute pressure in the first storage area  14 , some liquid within the first storage area will convey through the capillary wick  24  and be absorbed by the capillary storage  20 , until the underpressure in the first storage balances out. That is, at least some of the excess liquid will convey through the capillary storage  20  and store temporarily in the capillary storage  20 . On the other hand, once the underpressure within the first storage area rises, i.e., a decrease in absolute pressure within the first storage area, liquid in the capillary wick is drawn back into the first storage area  14 . Note that the underpressure in the first storage area  14  may change for a number of reasons such as a change in the temperature or elevation at which the writing instrument is used. 
     With regard to head pressure or column pressure in the first storage container, the smaller the capillary pore size, the greater resistance it has to the head pressure, and conversely, the larger the capillary pore size, the less resistance it has to the head pressure. That is, if the largest pore size in the tip  33  is too big, then there is a possibility that the liquid in the first storage  14  may leak through that largest pore size. As such, the largest pore size needs to be properly sized or controlled. 
     In general, the head pressure within the first storage  14  may be derived by knowing the height “H” of the liquid above the proximal portion  26 , and also based on the density of the liquid. Based on head pressure, the capillary resistance to pressure, in other words, the resistance in the largest pore size in the tip may be calculated. Capillary resistance to pressure, commonly referred to as “bubble point,” is the pressure required to displace liquid with air in the largest pore, which may be derived from the following equation: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 P = 4 * γ * cosθ 
                 where: 
               
               
                   
                 p is capillary pressure 
               
               
                   
                 γ is the surface tension of the liquid; and 
               
               
                   
                 θ is the contact angle of the liquid and solid, 
               
               
                   
                 that is when the liquid completely wets the 
               
               
                   
                 solid, cos θ  goes to 1. 
               
               
                   
               
             
          
         
       
     
     Moreover, other methods known to one skilled in the art may be used to size the pore sizes in the tip. For example, a variety of tips having different pore sizes may be experimented with until a tip sufficiently restricts the head pressure. Referring back to FIG. 2, graph  33  illustrates the exemplary measurable distribution of pore sizes in tip  33 . Reference point “TL” refers to a measurable largest pore size in the tip, and “TM” refers to a measurable mean flow pore in the tip. Accordingly, TM is smaller than CM, and TL is smaller than CL. That is, the pore sizes in the tip  33  are sized to provide sufficient resistance to head pressure in the first storage area  14  to restrict liquid from leaking through the tip. And, because TL is smaller than CL, air will enter through the distal portion of the capillary wick  28  to relieve the rise in underpressure in the first storage area rather than through the proximal portion  26  due to smaller capillaries blocking passage of air through the tip. As such, to provide air passage, a hole  34  may be provided in the rear side  36  of the container  12  to allow outside air to enter through the hole  34  and then through the largest pore size in the distal portion  28  of the capillary wick  24 . 
     FIG. 3 illustrates by way of example an alternative embodiment to the present invention having a distal portion  28 ′ of a capillary wick  24 ′ that runs partially through a capillary storage  20 ′, unlike the embodiment illustrated in FIG.  1 . Still further, FIG. 4 illustrates by way of example a distal portion  28 ″ of a capillary wick  24 ″ that runs through the opening  22  and is in direct contact with a capillary storage  20 ″ without penetrating it. In other words, air enters through the capillary storages  20 ′ and  20 ″ and then to the distal portions  28 ′ and  28 ″, respectively, to relieve the rise in underpressure. 
     FIG. 5 illustrates by way of example yet another embodiment of the present invention to minimize the head pressure due to the column of liquid in the first storage area  14 . To do so, a sleeve or tube  50  is provided from the writing side  30  to form a lip  52  in the first storage area  14  around the capillary wick  24 . The sleeve  50  seals at least a portion of the capillary wick  24  from the liquid in the first storage area  14 . The sleeve or tube  50  may be a film wrapped around the capillary wick  24 . As such, the head pressure “H” within the first storage area  14  is reduced because the column of liquid now applied to the capillary wick  24  is from the lip  52  rather than from the writing side  30 . With reduced head pressure, smaller capillaries in the tip may not be needed to resist the head pressure like the embodiment discussed above in FIG.  1 . In other words, in this embodiment, the head pressure may be adjusted based on the length of the sleeve  50  so that the largest pore size in the capillary wick can resist the head pressure, yet allow air to enter through the largest pore size to compensate for a rise in underpressure in the first storage area  14 . 
     Accordingly, with the embodiment illustrated in FIG. 5, a tip may not be needed to resist the head pressure and air may pass through the proximal portion  26  of the capillary wick  24 . Still further, a porous divider wall  18 ′ may be provided with the hole  34  on the rear side  36  to allow air to pass through the porous divider wall  18 ′ to compensate for the changes in underpressure within the first storage area, rather than through the largest pore size in the capillary wick  24 . In this regard, U.S. patent application Ser. No. 09/591,114 filed Jun. 9, 2000 is hereby incorporated by reference into this application. 
     FIG. 6 illustrates by way of example still another embodiment of the present invention having a tip  33 ′ (or sometimes referred to as a nib) within a sleeve  50 ′ extending partially into the first storage area  14  without touching the porous divider wall  18 ″. Moreover, the porous divider wall  18 ″ does not have an opening between the first and second storage areas  14 ,  16  so that liquid or air in the first storage area  14  goes through the pores or the capillaries in the divider wall  18 ″. In the second storage area  16 , the capillary storage  20 ″ is in direct contact with the divider wall  18 ″. 
     FIG. 7, generally illustrates the distribution of pore sizes among the tip  33 ′, porous divider wall  18 ″, and capillary storage  20 ″. As in FIG. 2, axis “X” represents a capillarity potential of pores or smaller pore sizes from left to right, and axis “Y” generally represents percentage pores. Accordingly, the measurable largest pore size in the porous divider wall “DL” is greater than the measurable largest pore size in the tip “TL” so that air will pass through the porous divider wall  18 ″ rather than through the tip  33 ′ to compensate for the changes in the underpressure within the first storage area  14 . Moreover, DL is generally smaller than the measurable mean flow pore of the capillary storage “SM” so that the capillary storage  20 ″ substantially remains dry relative to the porous divider wall  18 ″. With regard to the tip  33 ′, the sleeve  50 ′ may be provided to minimize the head pressure within the first storage area  14 , and TL is sized to sufficiently resist the head pressure to restrict the liquid from leaking through TL. 
     With the above embodiment and the distribution of pore sizes as illustrated in FIG. 7, as the underpressure in the first storage subsides, i.e., absolute pressure increases, air above the liquid in the first storage area will pass through the largest pore size in the porous divider wall DL and into the capillary storage  20 ″ and out of the hole  34 . Conversely, as the underpressure rises in the first storage area  14 , air will pass through DL and into the first storage area  14  to compensate for the rise in underpressure. For instance, as the writing instrument is used, liquid or ink will convey through the tip  33 ′ and onto a writing surface, such as paper, causing underpressure to develop in the first storage area  14 . To relieve the underpressure in the first storage  14 , air will pass through DL and into the first storage area  14 . In other words, the porous divider wall  18 ″ is used to regulate the air in and out of the first storage area  14 . 
     When the writing instrument is in a horizontal or inverted position, the porous divider wall  18 ″ may be fully saturated or wet. And if the underpressure subsides in the first storage area, then the capillary storage  20 ″ which is in direct contact with the porous divider wall  18 ″ will absorb the excess liquid from the first storage. Conversely, as the underpressure rises, liquid will convey back into the first storage area. 
     There are a number of advantages to the above embodiment. First, there is no need for a capillary wick, which saves cost. And, second, a smaller capillary storage may be used because the capillary storage remains substantially dry. 
     FIG. 8 illustrates by way of example yet another embodiment of the present invention where the capillary storage  20 ″′ is adjacent hole  34  on the rear side  36 . Such an arrangement prevents any liquid droplets that may be formed within the second storage area  16  from leaking out of the hole  34 . 
     In closing, it is noted that specific illustrative embodiments of the invention have been disclosed hereinabove. However, it is to be understood that the invention is not limited to these specific embodiments. For instance, sleeve  50  may be molded within the first storage area along with the container  12 . The porous divider wall may be a porous plastic to control the size of the pores. Moreover, the tip in FIG. 6 may extend from the writing side  30  without the sleeve within the first storage area. In such a case, the pore sizes in the tip may be smaller than a tip with a sleeve to restrict greater head pressure. With regard to FIGS. 2 and 7, the percentage of pores along the Y axis may vary among the capillary storages, capillary wick, tip, and the porous divider wall. For instance, the percentage of pores in the capillary storage may be less than the capillary pore or the porous divider wall. With regard to liquid, it may be a solvent-based ink or a water based ink or any other ink known to one skilled in the art. With regard to the nib  18 ′, it may be manufactured by Teibow Hanbai Co. Ltd., located at 10-15 Higashi Nihonbashi 3 chome, Chou-Ku, Tokyo 103, Japan. Moreover, the pore sizes in the capillary storage, capillary wick, tip, and porous divider wall may be measured by Porous Material, Inc., 83 Brown Road, Ithaca, N.Y. 14850. 
     With respect to the claims, it is applicant&#39;s intention that the claims not be interpreted in accordance with the sixth paragraph of 35 U.S.C. §112 unless the term “means” is used followed by a functional statement.