|Publication number||US3623941 A|
|Publication date||Nov 30, 1971|
|Filing date||Dec 22, 1969|
|Priority date||Jun 27, 1966|
|Publication number||US 3623941 A, US 3623941A, US-A-3623941, US3623941 A, US3623941A|
|Inventors||Goodenow Elden Lucerne, O'sullivan James, Seregely Daniel William|
|Original Assignee||Gillette Co|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Non-Patent Citations (1), Referenced by (13), Classifications (10)|
|External Links: USPTO, USPTO Assignment, Espacenet|
 Inventors Elden Lucerne Goodenow Los Angeles; James O'Sulllvan, Culver City; Daniel William Seregely, Los Angeles, all of Calif.  Appl. No. 886,899  Filed Dec. 22, 1969  Patented Nov. 30, 1971  Assignee The Gillette Company Boston, Mass. Original application June 27, 1966, Ser. No. 560,405, now Patent No. 3,558,392. Divkled and this application Dec. 22, 1969, Ser. No. 886,899
 POROUS OBJECTS FOR WRITING INSTRUMENTS 5 Claims, 3 Drawing Figs.
57/140 C, 161/173, 161/181,40l/196  Int. Cl B431: 1/00  Field of Search 161/172, 173,175,176,181;401/196,198,199
 References Cited UNITED STATES PATENTS 2,688,380 9/1954 MacHenry..... ....1 61/Cig. Filter lQigest 3,111,702 11/1963 Berger 401/198X 3,106,501 10/1963 Cobb,.lr. et al....16l/Cig. Filter Digest 3,189,506 6/1965 Cobb,.|r. et al....1 6 1 Cig. Filter Digest 3,400,998 9/1968 Daugherty et a1. "161 170 x 3,442,739 5/1969 Johnson 401/198 nite States Patent OTHER REFERENCES Linton, George E. The Modern Textile Dictionary, Duell, Sloan, and Pearce, New York, 1963. pp. 372, 959. Copies available in Art Unit 164 Primary Examiner-Robert F. Burnett Assislanl Examiner-Linda C, Koeckert Auorne vMiketta, Glenny, Poms 8: Smith ABSTRACT: Directed to an elongated, coherent and self-supporting object of predetermined contour and cross section composed of a large number of longitudinally extending strands of filamentary thermoplastic devoid of added resinous binder between strands, some of said strands being heat-set or lightly sintered together to provide a plurality of longitudinally extending and interconnected channels of virtually capillary size, the pore volume of the object being between 25 percent and 95 percent of the total bulk volume of the object, its bulk density being lower than the density of the filamentary thermoplastic before the strands thereof were heat-set to the predetermined contour and cross section. An elongated object as above stated, particularly adapted for use as a writing in strument tip and ink feeder, containing added resinous binder which discontinuously bonds the heat-set strands and imparts strength and nonbrushing life to the tip while pore volume of such tip is maintained at between 15 percent and 70 percent of the total volume of the tip and effective ink absorption and capillary flow of ink through the tip is maintained to permit fine-line writing for a prolonged time. lnk conveying channels of between 1 and 10 mils in average transverse dimension are preferred.
POROUS OBJECTS FOR WRITING INSTRUMENTS This is a division of copending application Ser. No. 560,405 filed by applicants June 27, 1966, now U.S. Pat. No. 3,558,392 relating to the manufacture of porous tips. This divisional application is particularly directed to porous, elongated and self-supporting objects of novel composition and characteristics capable of being readily made in accordance with the methods described in the above application.
The development of writing instruments which employ porous tips (instead of metallic nibs) is based upon the earlier devices for applying water to gummed surfaces, shoe blacking, etc., and utilized tips made of felt, sponge, etc. These prior devices employed rather soft, easily deformable applicating ends which produced very wide, rather brushlike strokes and therefore could not be used for normal writing of letters, where a relatively thin, uniform line is desired.
Many problems have been encountered in attempting to produce uniform, reproducible tips capable of depositing a written line of suitable delicacy; it was found that the entire structure of the tip had to conform to many standards and limitations such as density, strength, flexibility, ability to feed ink to the tip in a uniform manner irrespective of axial rotational position so as to permit rapid writing, and, at the same time, not accumulate gobs of ink during periods of nonuse, etc. Uniformly distributed channels and pores must be provided for the ink and such channels should be within a suitable range of transverse average width size and area. Furthermore, an acceptable writing tip must write smoothly, with very little, if any, resistance and without squeaking.
An economical, continuous manufacturing process whereby under controlled conditions, the structure, density, flexibility and other requirements can be controlled so that uniform writing tips, of uniform characteristics, may be manufactured in a reproducible manner is shown in copending application Ser. No. 560,405. The materials, conditions and sequence of steps there and hereinafter described permits the manufacture of writing tips in a reproducible manner so that the entire output can either consist of relatively hard, nonflexible fine writing tips or, when it is desired to produce a softer writing tip capable of producing a line of greater width and shading, the operator can be assured that all of the tips will now conform to the predetermined standards of strength, density, flexibility, porosity, feeding characteristics, capillarity, etc., which characterize such tips. It will be readily recognized that the economical manufacture of tremendous numbers of writing tips precludes individual testing of each tip, and therefore the process must be capable of control so as to insure predetermined uniformity.
' Generally stated, the invention utilizes yarns or strands selected from the family of thermoplastic fibers (since natural fibers are not satisfactory), the arrangement of such fibers in substantially parallel longitudinal relation and suitably spaced from each other so as to form a predetermined array (generally cylindrical), heat treating and compacting the cylindrical bundle to form a preliminary structure of desired porosity and size, thus fixing the fibers in such desired position with respect to each other and with the longitudinally extending porosities or channels of a desired size and distribution. The structure thus formed may then be impregnated with a solution of resinous binder in a volatile solvent, followed by evaporation of the solvent and curing of the fixed or resin treated rods so as to produce a continuously moving rod which now can be cut, have its ends shaped and otherwise treated for use as a writing tip, ink feeder, or the like. The materials and conditions which permit continuous, rapid manufacture of reproducible, substantially uniform writing tips will be described in detail hereafter.
The present invention is directed to porous, absorptive, selfsustaining elongated objects composed essentially of filamentary thermoplastic materials having novel characteristics which render such objects particularly effective as writing tips or ink feeders.
Another object of this invention is to define novel products and their characteristics which impart unanticipated effectiveness and long life when such products are used in writing instruments.
These and various other objects and advantages of the present invention will become apparent from the following description; for purposes of illustration and in order to facilitate understanding, reference will be had to the appended drawings wherein:
FIG.. 1 is a diagrammatic representation of the various stages and operations involved in the continuous process;
FIGS. 2 and 3 are enlarged somewhat diagrammatic representations of partial cross sections taken through an exemplary writing tip in the course of its manufacture.
As previously indicated, the body material of the porous writing tips is composed of any one or more synthetic, preferably thermoplastic fibers such as polyvinyl chloride, polyethylene, polyethylene terephthalate, polypropylene, polyacrylonitrile and copolymers with vinyl acetate, cellulose acetate and various polyamides such as nylon 6 and nylon 66. As shown in FIG. 1, the selected yarn supply 1, in the form of a plurality of spools, bobbins or reels 2, 2', etc., is provided. The spools are preferably provided with individually adjustable friction drags so as to control the tension in the strands which are drawn from the reels. Each yarn strand is passed through a perforation in a gathering or arranging plate generally indicated at 4, the perforations or openings therein being smooth walled, closely spaced, may be about /a inch in diameter and provided with conical or flaring inlets so as to facilitate the feeding of the strands therethrough in a predetermined and desired array. The number and arrangement of individual yarns employed will vary with the size of the writing tip and the size and number of longitudinally extending channels desired in the product; from 17 to as high as 60 strands of yarn may be used, depending upon the total denier of the yarn employed and the final diameter or other form of the writing tip being manufactured. For example, in the manufacture of a writing tip which will finally have an outside diameter of about 0.1 inches, 23 strands of crimped yarns each having an uncrimped denier of 1,050, each composed of seventy l5 denier continuous filaments, can be successfully used. The total denier of the entire assembly may vary from between 20,000 and 40,000; a preferred range (for the exemplary sized tip) being between about 21 ,000 and 26,000 denier uncrimped. The filament denier may range from as small as 1.0 d.p.f. to 25 d.p.f., 1.0 to 15 being preferred.
The perforated metal plate gathers and properly arranges and positions the individual strands of yarn in accordance with a predetermined pattern. The procedure insures the desired placement of the individual strands of yarn in the completed writing tip with longitudinally extending channels dispersed between the strands. It is to be understood that all of the strands are constantly under tension (on the order of 2 to 10 grams per strand at the feed end) and are being pulled from the supply reels in zone 1 by means at the far end of the production line hereinafter described. The gathered strands may then pass through a drying zone generally indicated at 6; this drying tube may comprise a tube 7 (having a diameter from 2 to 8 times the diameter of the ultimate product). The tube may be lined with a polytetrafluoro composition capable of presenting a surface of a low coefficient of friction. The tube may be enclosed by an electrically heated housing 8. The temperatures in this zone should not be sufficiently high to produce any softening of the filaments or strands but only sufficieut to dry the strands; when nylon is used temperatures on the order of C. are adequate when the strands are drawn at from about 1% to 2 feet a minute, the length of the treating zone being a factor. Purging of water vapor and other volatile material from the fibrous strands is facilitated by passing nitrogen or other inert gas through the tube in a direction countercurrent to the movement of the fibers.
The now dried bundle of strands is passed through another tunnel which has an internal contour or diameter of the required size and establishes the external contour or diameter of the finished writing tip or applicator. This tunnel provides a heat-setting zone indicated generally as 9, has a flaring inlet and is lined with heat resistant material of low coefficient of friction; it is surrounded by a heating chamber 11. The temperature in this heat-setting zone is very accurately controlled so that the bundle of yarn, while moving under tension, in longitudinally extending relation and in the relative cross-sectional distribution established in the positioning zone 4, is now compressed and subjected to a temperature below the melting point of the yarn but sufficient to cause softening and ad herence of the adjoining strands (or crimped portions thereof) to each other, the time, temperature and tension being insufficient to completely destroy the crimped form of all of the crimped filaments in the bundle. When employing nylon 6 yarn (which has a melting point of about 220 C.), a temperature 3 to 6 lower (say 216 C.) is maintained, it being understood that the temperature may have to be varied in accordance with the speed of travel of the yarn through the heatset zone 9 and the characteristics of the yarn being employed. The heat setting operation appears to produce a random discontinuous and minute incipient fusion which bonds the strands without forming nodules or droplets of solid matter. After the heat setting operation, very little residual crimp is visible and the average fiber direction in the heat-set bundle or rod does not appear to depart more than about 5 from the rod axis. It is highly desirable that the porosity of the tip, as it is discharged from the heat setting zone, be maintained in a high range, for example, at the stage indicated by the section line "-11, between 25 percent and 95 percent of total volume of the bundle should be pores and channels.
The heat-set bundle of yarn now passes through a cooling zone 12 and an enlarged somewhat diagrammatic transverse section taken through the bundle at the plane llll is illustrated in FIG. 2. At this stage of the continuous operation, the bundle is a coherent, self-supporting elongated object of predetermined size, contour and cross section, and the individual strands are in the positions desired with longitudinally extending channels or pores of a desired average dimension and distribution. It will be noted from an examination of FIG. 2 that a certain proportion of the individual strands (particularly crimped filaments thereof) have been caused to sinter together; they are heat-bound to each other, as for example, the fibers 3, 3' and 3", but it will be noticed that longitudinally extending channels or pores, such as 13 and 13', exist and such channels are rather uniformly distributed throughout the cross section of the object. At this stage, the produce may be used in the reservoir of a writing instrument as a storage elementor feeder ofink.
The preset bundle of yarn now passes through an impregnation zone 14. In the diagrammatic representation, this impregnation zone is shown to include a tube 15 with short very gently upwardly inclined end portions, the tube being constantly supplied with a dilute solution of resin in a volatile solvent from a reservoir 16 through a valved supply line leading to the central section of the tunnel. When a plurality of production lines are used, a traylike arrangement takes the place of tube 15. The preset yarn bundle barely deviates by more than its diameter from a rectilinear path in its travel through 14. The entire tunnel may be enclosed by a temperature control bath 17. The exit end of tube 15 includes a rubber orifice which wipes excess resin solution from the treated bundle or rod. Although the density of the packing between individual strands of yarn and the arrangement of the yarn is well controlled by prior steps (and these factors influence the amount of resin solution that will be absorbed and the distribution of the resin among the fibers after the volatile solvent in which the resin is dissolved has evaporated), the impregnating step must be carried out at a temperature below the boiling point of the solvent and below the curing temperature of the resin. The concentration of the resin in the volatile solvent is also of considerably importance in insuring the proper distribution of the resin so that the resin does not accumulate in large clusters or droplets and does not block the passageways or channels in the writing tip; a large number of minute surface bonds between fibers produces the ideal combination of high strength and high porosity. Crimps in the fibers assist in producing a multiplicity of fiber-to-fiber contacts in which the resin is held. The crimps also provide frequent interruptions of excessively large contacts, insure that they remain unfilled with resin and thereby facilitate the retention of channels or passages for ink flow in the finished writing tip.
It has been found that the resin content of the impregnating solution can be in the range of 5 percent to 45 percent by weight (20 percent to 30 percent is preferred); higher concentrations within the range produce a hard tip whereas lower concentrations facilitate the production of a softer tip. A great variety of resins may be employed and those skilled in the art will appreciate that different catalysts, hardeners or curing additives may be employed if setting of the resin requires their presence. Addition polymers such as the epoxies, isocyanates, polyesters, vinyl compounds, acrylics, alkyd resins, silicones and acetals may be employed. For example, Epon 828 (a monomer manufactured by the Shell Chemical Co.) may be used and an aliphatic polyamine can be used as the hardening or curing agent; Epon 1,001, which is a polymer, can also be employed using an acid anhydride as the catalyst. Reference is made here to the copendin g application for other examples of resins and polymers.
The solvents to be employed should be relatively volatile and preferably capable of being removed at temperatures not greatly exceeding C. and at all events below the melting point of the fibers. Solvents compatible with the resin used can be selected from ethers, esters, alcohols, aromatics, chlorinated solvents, ketones or glycol ethers, and may have boiling points as high as C. or as low as 35 C. (diethyl ether).
After the bundle of preset fibers has been impregnated in zone 14, it is then drawn through the drying or solvent removal zone indicated at 18 and then through a heat curing zone generally indicated at 24, although, in some instances, the drying and heat curing steps may be combined in one unit or zone. In the illustrated arrangement, the drying zone may simply consist of an elongated chamber 19 which may be heated in the event the solvent employed requires some heat to facilitate its removal. The solvent vapors may pass into a condenser, generally indicated at 20, for recovery. In some instances, the solvent removal step may be conducted in the open.
The next step is a curing of the preformed, continuously moving rod. As shown in the drawing, curing may take place in an elongated chamber 25 through which hot air is circulated by means of a motor driven fan 26, the air moving over suitable electric heating units generally indicated at 27, 27', etc. Radiant heat may be employed directly within the primary drying chamber through which the preformed object is continuously drawn. As previously indicated, solvent removal and curing may take place concurrently in the same unit, or, in successive sections of a unit. Again, the temperature to which the preformed object is heated will depend upon the resin composition employed. For example, Epon 828-Triethylene Tetramine can be cured at l60190 C. for 15 minutes.
The continuously moving column is then cooled in a zone indicated at 28 and by section line lll-lll. The cooled object then passes through a series of rollers indicated at 30, these rollers constituting the tensioning and advancing means for the entire production line. The rollers are preferably contoured to fit around the object Ming formed, and are yieldingly pressed against the object and driven by suitable speed control mechanisms so that the strands being fed from the supply zone 1 are drawn at a predetermined speed and a suitable tension is applied to all of the strands throughout the production line. The tension on a continuously moving heat treated resin-bonded rod made of 23 strands is on the order of 3 to 5 lbs; the tension on each of the strands being drawn off the supply reels is on the order of 3 to 4 grams. The cooled cylinder, rod or other continuous formed object is then sent to zone 32 where mechanism cuts and preferably simultaneously forms the ends of the cutoff sections so as to produce completed writing tips of a desired length and contour at the shaped end or ends. These writing elements or tips can then be collected in baskets and suitably treated or sent to storage, sent to production for fitting into complete writing instruments, such as pens, etc.
In many instances, it has been found desirable to treat the writing tips discharged from the cutting and forming zone 32. For example, it has been found desirable to treat the writing tips with a wetting agent so as to facilitate the wetting of the tips and the movement of ink through the minute channels or passageways in the tip. Any anionic or nonionic wetting agent, such as for example, sodium dodecyl benzene sulfonate may be effectively used on the writing elements. In order to facilitate the application of such wetting agent to the interior surfaces of a finely porous writing tip, vacuum impregnation may be used, foraminous baskets filled with precut writing tips being immersed in a solution of wetting agent and subjected to subatmospheric pressure which facilitates removal of air and entry of the solution. In the treatment of writing tips made from nylon yarn and epoxy resin, immersion of the preformed tips into a 1 percent aqueous solution of sodium dodecyl benzene sulfonate has been found very effective, particularly if combined with subatmospheric pressure treatment.
It is desirable to assemble such wetting agent treated tips with pen bodies and reservoirs before the tips have completely dried in order to establish good ink flow. Another procedure is to assemble the tip into a pen body, contact the dry tip with an ink reservoir and then apply a few drops of methyl or ethyl alcohol to the tip to facilitate ink feeding to the tip.
FIG. 3 is a partial section of a substantially completed resinbonded writing tip, the section being taken along plane IIIIII in FIG. 1. By comparing FIG. 3 with FIG. 2, it will be noted that substantially the same arrangement and distribution of channels or passageways for the ink exists in FIG. 3 that existed in FIG. 2. It will be noted that the strands are now in bonded clusters of various cross-sectional form. The size or average transverse dimension of the channels has been but slightly decreased (since a minute coating of resin now bonds the various strands and particularly the crimped portions thereof more firmly that the initial heat-set or sintering which took place in zone 9.
The main ink conveying channels now preferably have average or mean transverse dimensions of from lXl mils to 3X6 mils; channels of 1.5 to 3 mils in one transverse direction and between 3 and 6 in another direction are representative of a most desirable capillary channel sizes, and should predominate since 1X1 mil channels are relatively ineffective; some channels may measure 10 mils in one direction. Differently stated, the ink conveying channels are predominantly of between about 4.5 and 18 square mils in cross-sectional area. The total number of channels and pores is lower in FIG. 3 than in FIG. 2, and there has been a reduction in the number of minute spaces between the fibers. The total number of channels (in a preformed rod 0.1 inches in diameter) may vary within wide limits, depending upon the number of strands employed and denier of the filaments, but for writing tip products, the number may be between about 200 and 600, the larger number occurring when filament of say 6 d.p.f. is used and the smaller number when say d.p.f. is employed. The pore volume of the heat set, impregnated and cured objects is between 15 percent and 70 percent of total volume.
One of the characteristics of the products produced in accordance with this invention is that the individual channels are not longitudinally continuous from one end to another of a finished rod and rarely have an uninterrupted length of over about one-half inch. It is to be remembered that preferably the unheated, original yarn is crimped and the crimped filaments often contact and become bonded, thereby tending to block the continuity of a discrete channel but each channel feeds into another short longitudinal channel, this being partly due to the effect of drawing tension, heat and compaction in the heat setting zone, which greatly reduce the original crimp of the filamentary material. This characteristic structure of the product results in added strength and stiffness to the product and provides a multiplicity of interconnected small feeding reservoirs for ink whereby (when the product is used as a writing tip), movement of ink along the finished rod or tip is facilitated, ink is always available for writing purposes, but will not flow at an excessive rate nor flow or gob when subjected to shock. The writing tip will not dry out and be ineffective when a writing instrument has been left uncovered and exposed to air for a day or two; no difficulty is experienced in starting writing at any angle of the tip or writing instrument to the paper.
Cylindrical writing tip stock made by our method (from strands of Nylon 6) will show increase in stiffness (and ability to produce fine-writing points) as the concentration of bonding resin is increased, lower resin concentrations producing softer, broader writing tips. Both types of tips appear to require the presence of channels having cross-sectional areas of the sizes noted above, such channels being readily observable at a magnification of say 45. From about 25 percent to about 40 percent of the total cross-sectional area of writing tips may be constituted of these channels, the rest of the porosity being attributable to finer capillaries, although very dense points may be made with channels constituting 15 percent to 20 percent of total cross-sectional area.
The inherent desirable properties of products made in accordance with the parent application by heat setting (lightly sintering) and thereby preforming the bundle before impregnating with a dilute resin solution were demonstrated by conducting comparative tests using identical strands, resin solution and drawing speeds, although it was necessary to use a higher tension in pulling the unsintered and resin impregnated bundle through a heated forming die than the tension employed in making the product herein claimed.
The two different products are identified in the following table as A and B, A being made by the preferred method (gather and position strands, compress to size and sinter, impregnate with dilute resin, evaporate solvent, heat to cure), whereas B did not involve 'preliminary heat setting, the method consisting in gathering the strands, impregnating with identical resin solution, drawing the impregnated bundle through a heated die to form, and curing. Twenty pens with points of each product were then tested.
Writing tests in an accepted write test machine included determination of lay down (in milligrams per foot), line width and periodic hand writing tests, in accordance with standard procedure. Good writing" represents number of feet written with no defects observed, whereas end of life indicates that defects were observed at the footage indicated, such defects including excessive brush-out, line width deviation, material change in lay down, etc. It is evident that changes in bulk density, total pore volume, the size of the pores and writing life were attributable to the preliminary positioning and heat setting of the yarn.
As previously indicated, the denier of filaments employed exerts an effect upon the number and size of the channels formed. The effect is illustrated in the following table wherein A represents a cylindrical writing tip product made in accordance with this invention from 29 strands 840/136 Nylon 6 having a filament denier of 6 d.p.f., the binder being 28 percent of Epon 828, and B is a similar product made from 23 strands 1050/70 of l d.p.f. filament using 31 percent Epon 828: each 0.1 inches in diameter.
Number of Product Porosity Main Channels Average Size A 39% 550 5.54 x [0" sq. in. B 33% 250 10455 X" sq. in.
Density and porosity of the products obtained may be calculated from the densities of the synthetic fiber and resin employed. The effect of the resin treatment is illustrated by the following example, wherein Nylon 6 having a density of 1.14 grams/cc) was used in the yarn and epoxy resin for the bonding step in the making of relatively rigid writing tips:
Density Porosity Heal set only 0.6l gJcc. BB%46% After resin impregnation 0.75 gr./cc. Mia-40% Deflection Under l0 gram Load k Resin in Samples 22% 0.0l9-0.02l in. 31% 0.0l90.2020 in.
40% (LOIS-0.016 in.
It may be noted at this point that some resins produce surfaces which are more readily wetted by ink than others and for this reason the impregnation step described hereinabove is not illustrated in FIG. 1, but has been mentioned since it provides a means of insuring greater uniformity and reproducibility of writing tips, and can be readily determined by testing with the particular ink composition being used.
it is to be understood that not all of the strands of yarn used in making the porous objects need be of the same denier nor of the same synthetic fiber, since advantage can be taken of different physical characteristics of different fibers. Also, when writing tips are being manufactured, the presence of a virtually nonporous outer skin is often advantageous since such tips are usually ground to a point and only the central or inner portion of the tip need be provided with a multiplicity of longitudinally extending, spaced channels or passageways for ink. The prepositioning in zones 4 and 9 is important in insuring the production of channels of desired size and number located in a desired uniform or homogenous manner.
1. An elongated, coherent and self-supporting writing instrument object of uniform, predetermined contour and cross section adapted to receive fluid ink and feed such ink from one end thereof to the other, composed of a multitude of longitudinally extending strands of yarn of thermoplastic filamentary material, some of the strands being lightly bonded to each other by the action of heat not above the melting point of the filamentary material and in the absence of an added bonding resin, said object having longitudinally extending ink conveying channels between strands, said ink conveying channels being predominantly of between about 4.5 and 18 square mils in cross-sectional area, the bulk density of the object being lower than the density of the unheated filamentar material and the pore volume of the ObjCCt being between 5 percent and percent of the total volume of the object.
2. An object as stated in claim 1 wherein the filamentary material is of between about 1.0 and 25 d.p.f.
3. An absorbent elongated writing tip provided with minute longitudinally extending ink conveying channels adapted to feed ink from one end to the other of such tip during active writing, comprising a multiplicity of strands of yarn of thermoplastic filamentary material, some of the strands being lightly sintered to each other by the action of heat and then discontinuously bonded together by an added synthetic resin, said resin filling some of the smaller interfilament and interstrand spaces without reducing the pore volume of the tip to below the range of between 15 percent and 70 percent of the total volume of the tip, said ink conveying channels being predominantly of between about 4.5 and 18 square mils in cross-sectional area.
4. An absorbent writing tip provided with minute longitudinally extending, open-ended channels adapted to feed ink from a reservoir to the end of such tip during writing, comprising a multiplicity of strands of synthetic yarn, including originally crimped filaments, said yarn strands being lightly and discontinuously sintered together and then bonded by a synthetic resin whereby said strands are held in virtually parallel relation and in predetermined array to provide longitudinally extending channels therebetween, said ink conveying channels being predominantly of between about 4.5 and 18 square mils in cross-sectional area.
5. A writing tip as stated in claim 4 wherein the yarn is composed of synthetics from the group consisting of polyvinyl chlorides, polyamides, polyethylene, polypropylene, acrylonitrile, polyethylene terephthalate and cellulose acetate.
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|U.S. Classification||401/196, 57/246, 401/292, 428/401, 428/369, 57/251|
|International Classification||B43K1/12, B43K1/00|