Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/16—Writing inks
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/16—Writing inks
  • C09D11/18—Writing inks specially adapted for ball-point writing instruments

Definitions

• This invention is an ink composition which makes erasable marks, especially transparent, colored marks.
• the present invention relates to an erasable marking or writing medium or ink that can be dispensed through a porous tip writing instrument, or by means of various types of roller-ball pens.
• the marks which result from application of the medium can be removed with comparative ease with a non-abrasive eraser, such as a common pencil eraser.
• a person When a person is producing written images, characters or highlight marks with writing instruments, it is not necessarily desirable to obtain a high degree of indelibility.
• a person may want a writing medium which is easily removable from the writing surface by mechanical means, i.e., an erasable writing medium.
• an erasable writing medium To be truly erasable, the writing medium must be capable of being removed from the writing surface to which it has been applied without significant damage, such as abrasion, to the writing surface. Since the most commonly used writing surface is paper, a general discussion of the characteristics and composition of paper is helpful for an understanding of the present invention.
• Paper is essentially a mat of randomly distributed cellulose fibers. Because of the random orientation, the paper surface contains numerous voids which exist between the randomly oriented cellulose fibers. Therefore, for a writing medium to be truly erasable, at least that portion of the writing medium that contains the optically-effective portion (e.g., colorant) of the medium must be prevented from penetrating, to any substantial degree, into those voids. Otherwise, removal of the mark by erasing could not be accomplished without some damage in the form of abrasion to the writing surface. Therefore, a need exists for a writing medium that is not absorbed by the writing surface, namely paper, but which writing medium can be used in porous tip pens.
• the optically-effective portion e.g., colorant
• the writing medium should also resist drying on the tip of the pen, but dry relatively rapidly when applied to a writing surface.
• the ink in order to allow the ink to effectively pass through the porous tip, the ink must have a very low surface tension, low viscosity, and any particles in the ink must be very small. These characteristics, however, will cause the ink to penetrate deeply into the paper.
• the ink composition must be very stable, under a wide range of conditions, in order to have a practical shelf life. Thus, an ink that can flow through a porous tip is probably not erasable, while an ink that can be made erasable will probably not pass through a porous tip and will have a poor shelf life.
• the rubber layer can then be removed by eraser, taking the dye with it.
• the Ferree patent teaches that it achieves its erasability by chemically bonding the specific family of chemically-active (highly-polar) dyes with a chemically-active (highly-polar) carboxylated rubber.
• the Ferree patent teaches away from the use of pigments or other colorants that do not react with the rubber.
• the Ferree patent also teaches away from using a non-reactive rubber such as a non-carboxylated styrene-butadiene rubber.
• the Ferree patent composition has been found to have a problem with sludge formation during formulation. This sludge must be filtered out of the ink, as noted in the patent, before the ink can be used. It appears that the sludge may be a by-product of the reaction between the dye and the rubber.
• the filter requirement creates cost and processing problems in the Ferree composition.
• the formation and isolation of the sludge creates disposal problems. Furthermore, it appears that the sludge formation reaction limits the amount of dye that can be bonded to the rubber and, therefore, unacceptably limits the intensity of color that can be realized using the Ferree concept.
• the preferred embodiments of the present invention avoid using a combination of reactive dyes and rubber.
• the selected colorant e.g., pigment
• selected rubber e.g., non-carboxylated SBR
• the LOFTIN patent application teaches the concept of incorporating a silicone-based release component into a latex having a Mooney value of above 90, to form an ink with a viscosity of 10-30 cps.
• the release component is adapted so that, as the ink is applied to the paper, the release component forms a barrier between the paper and the rubber phase of the latex. The barrier keeps the rubber from infiltrating into the paper and allows the rubber phase to be easily removed (erased) from the paper.
• the presence of the silicone-based release agent has a number of effects which may not be desirable.
• the silicone-based release agent when the silicone-based release agent is present in concentration sufficient to have the effect taught by LOFTIN, the viscosity is forced above 10 cps. This viscosity can be too high for use in felt-tipped markers.
• the release agent can remain in the paper after erasure and interfere with subsequent writing on the same area of the paper.
• the silicone-based release agents are difficult and expensive to mix into and stabilize in the ink. For those reasons and because the "shock-out" effect of the present invention makes the release agent unnecessary, the preferred embodiments of the present invention do not include a release agent, or silicone-based release agent, or any other agent that separates the rubber from the paper.
• the teaching is a broad recitation of the resins available in the selected glass transition temperature range. The teaching does not recognize the "shock out" effect of the present invention nor does it teach the resin systems which results in that effect.
• Another object of this invention is the provision of a marker composition that forms a conventional (opaque) mark or highlight-type (colored, but transparent) mark, which mark is easily and completely erasable using a conventional eraser.
• a further object of the present invention is the provision of a marker composition which is highly stable under normal storage conditions.
• a writing medium or ink that comprises an emulsion having a discontinuous phase that comprises a rubber, a continuous phase of water, and a colorant that associates with the rubber. Careful selection of the rubber and colorant and a proper proportion of the rubber relative to the continuous phase results in an ink composition which forms a colored layer on a writing surface, which layer does not penetrate into the voids of a writing surface, such as stationary paper, and which layer is easily erasable from the writing surface for an indefinite period of time after application.
• composition according to the present invention involves the use of colorant dispersions, specifically dispersions of hydrophobic, oliophilic pigments, dyes, or toners.
• emulsion incorporated into the erasable writing medium compositions allows the writing medium to be easily erasable after application, but to adhere to the paper without chipping or cracking, even when the paper is bent or folded.
• compositions of the present invention may also be incorporated into the compositions of the present invention.
• a plasticizer including a plasticizer, surface tension reducers, and anti-drying agent (antioxidants and humectants)
• anti-drying agent antioxidants and humectants
• the marking composition is designed to exist as a stable emulsion except when deposited on the surface of conventional stationary-type paper.
• Such paper almost universally has a surface treatment which is acidic and contains water-soluble polyvalent cations, especially calcium, magnesium, and aluminum.
• the marking composition of the present invention is designed so that the emulsion, which is normally stable, becomes unstable and the rubber agglomerates, on contact with the paper surface. More specifically, the instability is triggered by the surface treatment components substantially universally present in stationary-type paper.
• the stability is caused by a soap-type surfactant which stabilizes rubber-phase particles in a basic (pH > 7) aqueous medium.
• FIG. 1 is a diagrammatic view of a composition embodying the principles of the present invention as it is applied to a sheet of paper by a marker,
• FIG. 2 is a diagrammatic view of the composition on the paper prior to film formation and escape of the carrier
• FIG. 3 is a diagrammatic view of the composition after escape of the carrier, and after film formation
• FIG. 4 is a diagrammatic view of the film formed in FIG. 3 being removed by an eraser
• FIG. 5. is a graphical representation of the effect of ink system surfactant on ink surface tension.
• the erasable writing medium compositions of the present invention comprise an emulsion containing a pigment and preferably other components as hereinafter described.
• FIGS. 1-4 The typical operation of the present invention is shown diagrammatically in FIGS. 1-4.
• the marking composition denoted generally by the numeral 10 is shown being applied from the porous tip 11 of a porous tipped marker 12 and onto the writing surface 13 of a sheet of paper 14.
• the marking composition would be stored in a storage chamber 20 at the upper end of the tip 11.
• the composition would flow down through the porous tip 11 and would flow from the porous tip 11 when the porous tip 11 is placed in contact with a suitable writing surface 13.
• the marking composition is being applied in the form of a stripe 15, which is shown in FIG. 1 in its as - applied form, that is, as the non-dried emulsion.
• FIG. 2 shows the stripe 15 after it has been applied to the writing surface 13 of the sheet of paper 14, but prior to the escape of the continuous phase 16 from the non-continuous phase 17 which contains the pigment 18.
• the continuous phase 16 very quickly dissolves protons (H+) (acidity) and polyvalent cations (calcium, Ca+ +, magnesium, Mg+ +, and/or aluminum, Al+ + +) from the surface treatment components on the paper. This causes the emulsion to break, and the noncontinuous phase 17 to agglomerate into a film 21. Furthermore, the continuous phase 16 is absorbed into the paper 14.
• protons H+
• polyvalent cations calcium, Ca+ +, magnesium, Mg+ +, and/or aluminum, Al+ + +
• the mechanism for the almost instantaneous destabilization of the emulsion and agglomeration of the pigmented particles into a rubbery, coherent film is believed to involve the surfactant used to stabilize the latex from which the ink is made.
• this surfactant is an amphipathic soap molecule, especially a sodium salt of a carboxylic acid.
• These surfactants function in an emulsion with a pH greater than 9.5.
• the pH of the emulsion drops (becomes more acid) and when polyvalent cations are added to the emulsion, as occurs when the emulsion contacts the prepared surface of the paper, the surfactant becomes ineffective.
• the resulting salts of the carboxylic acids are water-insoluble and the hydrophilic character of the molecule is effectively lost. This effect on the ink deposited on the papers is almost instantaneous and quite remarkable.
• FIG. 3 shows the pigmented rubber film 21 which forms as the continuous phase 16 separates from the non-continuous phase 17 by absorption of the continuous phase 16 into the paper and/or by evaporation of the continuous phase 16.
• the pigmented film does not penetrate into the body of the paper but rather adheres to the outward projections of the surface of the paper. In this way, the pigmented film 21 is attached to the paper under normal circumstances but does not penetrate into the body of the paper to any significant degree.
• FIG. 4 shows the affect of applying a standard pencil eraser 25 on the end of a pencil 26 to the pigmented film 21.
• the shearing effect of the eraser 25 causes the pigmented film to disconnect from the high points of the writing surface and to be stripped off as a relatively unitary mass or a series of unitary masses.
• the pigmented film 21 is reasonably cohesive, it does not smear into the paper and tends to separate from the paper in clean chunks which can be easily removed from the writing surface without leaving any residual shadowing or without any pigment migration into the surface of the paper 13.
• the emulsion is the most important component of the writing medium compositions of the present invention, since it significantly affects characteristics such as flow, stability and erasability.
• the emulsion is a rubber latex. It is diluted, in the final ink, to about 30 % to about 96 % water by weight. While there are numerous types of rubber latexes and, particularly, styrene-butadiene (SBR) latexes, care must be exercised in the selection of a rubber latex in order for the ink compromise to have the desired properties.
• SBR styrene-butadiene
• Tg glass transition temperature
• This parameter provides a convenient indication of the critical room temperature properties of the rubber.
• a glass transition temperature which is too high might indicate a rubber which will be too stiff, brittle and non-tacky for an effective marking film on the paper.
• a glass transition temperature that is too low might indicate a rubber that will be smeared into the paper fiber by the eraser and will be so tacky that blocking will result.
• Tg does not necessarilly define these properties, and that Dalquist Modulus, molecular weight, and viscoelastic flow characteristics will be inportant in optimizing the product.
• the emulsion should possess certain characteristics and parameters which are hereinafter described.
• the preferred emulsion is a non-carboxylated styrene-butadiene latex.
• the styrene-butadiene inks of the present invention should have a room temperature viscosity in the range of from about 1 cps to about 35 cps and preferably from about 5 cps to about 10 cps and most preferably about 7 cps.
• the rubber emulsions used in accordance with the invention when dried on a paper surface, should have a "low adhesion" to the writing surface.
• low adhesion means that the dried emulsion can be removed from the writing surface, such as paper, with a low abrasion eraser, such as a common pencil eraser, without causing more damage than erasure of a pencil mark would cause.
• the emulsion should, after drying (water evaporation and absorption into paper), have greater cohesion than adhesion to the writing surface.
• the emulsion should, when applied to a writing surface, form a cohesive film on the surface, generally within about 20 seconds.
• the characteristics of the emulsion are determined in part by the ratio of the number of styrene units to the number of butadiene units in a copolymer chain.
• the styrene-butadiene ratio should be in the range of from about 20:80 to about 55:45.
• the preferred styrene-butadiene ratio is from about 20:80 to about 45:55, with the preferred ration 24:76. If the styrene-butadiene ratio is much higher than 55:45 the ink composition has a greater tendency to become brittle when dried, this could result in cracking and chipping of the ink that has been applied to a writing surface. Therefore, use of styrene-butadiene ratio greater than 55:45 is not particularly advisable.
• the emulsion In selecting or formulating an emulsion for use in the ink composition of the present invention, it is desirable that the emulsion have a relatively low surface tension as compared to the critical surface tension of the inner surface of the tip, thereby maximizing the ability the composition to penetrate the porous tip of a standard "felt-tipped" marker.
• the inks of the present invention have a surface tension of from about 10 to about 60 dynes/cm as acceptable, when used in conventional acrylic or polyester felt tips. 25 to 35 dynes/cm is preferred and 29.5 is most preferred. It is believed that the amount and type of emulsifier present to stabilize the latex may cause the surface tension of the emulsion to be to high.
• the type and amount of wetting agent should be adjusted to provide for the necessary low surface tension without so supplementing the emulsifier as to negate the emulsion breaking action which is critical to this invention.
• Higher surface tension inks can be used if the surface tension of the felt tip is increased as by plasma treating the inner surface of the tip or heating the tip.
• the emulsion be slightly tacky when dried so that it can easily adhere to, for example, a rubber eraser during the erasing process. If the emulsion is too tacky when dry, the paper sheets may stick together. It is also preferred that the emulsion have "freeze-thaw" stability and not deteriorate over long periods of shelf-life.
• the pH of the ink should generally be in the range of from about 9 to about 14. A pH outside of this range is not particularly desirable, since it may result in a composition that is unstable before use or composition in which the colorant cannot be dispersed.
• This compound is a non-carboxylated, styrene-butadiene latex having a ratio of styrene- butadiene of 24:76, a solids content of about 40.0 percent by weight, a pH of about 11.4, and a surface tension of about 58 dynes/cm.
• the colorants or pigments present in the erasable ink compositions of the present invention are water dispersible pigments which are also oliophilic. These pigments are selected from industry standard products known to be appropriate when selecting pigments which are to be dispersed in water systems.
• pigments are selected from the group of hydrophobic pigments which are capable of dispersion in or in intimate association on the styrene-butadiene phase without significant penetration into a writing surface when the composition is applied to a writing surface, such as paper, for example. It is believed that this effect results because the pigment remains entirely occluded by or in intimate exclusive association with the rubber phase, which is selected so that it does not, itself, penetrate the paper. The pigment apparently does not enter the water phase, which does penetrate the paper.
• Specific pigments which can be used in accordance with the erasable writing medium compositions of the present invention include carbon black and ultra-fine fluorescent pigments and dyes and mixtures thereof.
• the colorant is generally formed into a stable suspension in water prior to being added into the ink composition. Generally, it has been found that colorants that are not stabilized prior to addition will not be stable in the ink.
• the pigment should be dispersed in the emulsion, but, when the pigment-containing emulsion is applied to a writing surface, such as paper, for example, the pigment should not penetrate into the paper sufficiently to form visible images in the paper.
• the pigment should not penetrate from the emulsion into the paper fibers or the voids between the paper fibers, since removal of the writing medium by erasing, without damage or removal of portion of the paper fiber, would then be precluded.
• the pigment will be present in an amount of from about 1% to about 50% by weight of the total writing medium composition.
• the size of the pigment particles is important to the effectiveness of the composition of the present invention.
• the particles preferably have a small diameter and/or chemistry which appears to cause them to so strongly favor the rubber phase and to form a stable ink.
• the particles must be large enough to create the desired optical effect.
• the size of the rubber particles in the emulsion is also important to the present invention. A size ranged about 700 Angstroms (0.07 microns) is preferred. Normally, particles that are this small would penetrate into the body of the paper and defeat erasability. The emulsion breaking effect of this invention is so rapid and dramatic that even these fine particles are forced to coalesce into a continuous coherent, rubbery film before paper penetration can occur.
• the non-continuous rubber phase (which contains, or absorbs, or adsorbs on its surfaces, the pigment) is collapsed and merges into a thin continuous coherent, rubbery layer on and attached to, but not absorbed by, the surface of the paper. This results in a pigmented mark which appears to mark the surface of the paper, while, in fact, only adheres to the surface of the paper.
• the layer is so loosely bound to the paper surface that physical abrasion will strip off the layer and the local pigment in the area of the abrading. This leaves the abraded portion of the paper apparently unmarked.
• an anti-drying agent can be used to prevent the emulsion from drying on, for example, the marker tip when water from the emulsion evaporates, thereby facilitating the smooth flow of marking composition from the marker, especially after long periods of non-use.
• Suitable anti-drying agents include water-soluble organic ketones, esters and alcohols that do not have a significant deterious effect on the composition or its properties and whose boiling-point is relatively high, from about 140" C. to about 300° C.
• anti-drying agents include, for example, 2-octanone, 5-methyl-2-hexanone, cellosolve acetate, glycerol, ethylene glycol, propylene glycol, diethylene glycol and butyl cellosolve (2-butoxyethanol).
• sorbitol or butyl cellosolve is preferred.
• the anti-drying agent prevents drying of the emulsion, it also facilitates the spreading of the rubber and pigment on paper and can cause undesirable penetration of the rubber and pigment into, for example, paper fibers. Therefore, it is important that the concentration of the anti-drying agent be kept to a minimum, and in most cases, the concentration of anti-drying agent should not exceed 15 % by weight of the total erasable writing medium composition.
• the erasable writing medium compositions of the present invention may also optionally (though no preferably) include a plasticizer to increase the "tack" of composition and slow the film forming process to allow long lift-off times.
• a plasticizer to increase the "tack" of composition and slow the film forming process to allow long lift-off times.
• the ink composition is more easily erasable, and has adhesion to the eraaser,if it is very slightly tacky.
• the plasticizer increases the tackiness of the composition and, therefore, provides a composition which is more easily erasable with an ordinary non-abrasive eraser. Any plasticizer which is compatible with the compositions of the present invention may be utilized.
• the prefe ⁇ ed plasticizer is dipropylene glycol dibenzoate which is marketed under the trade name Benzoflex 9-88 by the Velsicol Chemical Corporation of Chattanooga, Tenn.
• Another preferred plasticizer is marketed under the trade pame "Santicizer 8" by the Monsanto Industrial Chemicals Co. of St. Louis, Mo.
• “Santicizer” is a mixture of N-ethyl-ortho-toluene sulfonamides and N-ethyl-para-toluene sulfonamides.
• compositions according to the present invention can be utilized in fiber tip marker, and, preferably, marking devices known as felt-tipped markers.
• a body of porous felt-like material usually of synthetic fabric, is encased in a marker case.
• a broad, flat tip extends from the marker case.
• the body is loaded with the ink of the present invention.
• an elongated band of the emulsion is applied to the surface.
• the non-continuous rubber phase which contains the pigment, merges into a layer of pigmented rubber imposed on and attached on the surface of the paper.
• This layer might be transparent, but colored, for highlighting, or might be opaque and black or, opaque and colored for conventional marking or writing. Whichever the case, the layer can be removed by erasing and this would remove all visible trace of the marking.
• Latex (Pliolite LPF 2108) (40.5) 24.44 60.35
• This formulation was prepared in the same way as Example 1 and resulted in an excellent erasable black mark.
• Colorant characterization The colorant which is currently used in the development of the black ink is LPF 4343 Flexiverse Black from Sun Chemical. It contains a non-ionic surfactant, Joncryl 68 (an alkaline soluble acrylic), a bactericide, and carbon black. Oil soluble dyes were also tried initially with some success but were not as easy to disperse in the system as the pigmented colorants. The stability of the ink system using pigments is good due to the wide availability of water-based pigment dispersions in the market.
• This invention includes dispersions/emulsions of fluorescent colorants (dyes and toners) in water-based systems of this invention.
• this invention includes use of these new small particle size emulsions and dispersions since they are particularly well adapted for use in the highlighter version of the erasable marker.
• a very effective version uses a Dian Co., Ltd. of Japan finished ink as the colorant.
• Resin emulsions The following emulsions have been tried using the Flexiverse 4343 black dispersion from Sun Chemical. The general formula is 10% Flexiverse black pigment dispersion, 50% resin emulsion, 40% water (by volume).
• Goodyear LPF 5356 resin is an agglomerated version of the LPF 2108 resin and therefore has a wider range of particle sizes, most much larger than 700 Angstroms. This is reflected in the cream, higher solids nature of the 5356 compared to the almost translucent 2108 resin.
• the resultant ink is not as stable and settles into layers upon standing for a few days. It nevertheless functions in this invention.
• the present invention includes an important discovery about the effect of the glass transition temperature (Tg) (film-forming temperature) of the rubber on erasability. It was previously believed that the rubber used as an erasable mark should have a glass transition temperature well above room temperature. It was believed that a relatively stiff, non-film-forming material would penetrate the paper less on application, would adhere less to the paper, and would flake off more cleanly during erasure. These ideal effects of high Tg do not, in fact, occur as well as expected.
• Tg glass transition temperature
• the present inventors have discovered that rubbers with sub-room temperature Tg's (e.g. -52 +/- 5 degrees C), surprisingly, work better. This superior behavior is particularly effective when combined with the shock agglomeration concept in which the destabilizable emulsion is instantly broken on contact with the paper.
• the low Tg allows even the tiniest rubber particles to instantly form a coherent, and non-penetrating film on the surface of the paper.
• the highly rubbery film does not adhere unacceptably to the paper.
• the film performs a self-scavenging action during erasure, that is, it appears that any free particles of the film are absorbed from the paper texture by the body of film which forms during erasure. As a result, the entire erased area of the film falls cleanly from the paper as a small number of relatively large coherent masses. This self-scavenging effect results in a clean, shadow-free, erased paper surface.
• Goodyear's LPF 2108 resin and the BASF competitive product Butonal NS 103 are latexes which share the property of ion instability.
• the emulsifier used in the latex is only effective at a pH of 9.5 or greater.
• the surface of most paper is acidic or cationic in nature and the latex is flocculated (the emulsion "breaks") immediately on contact with the surface of the paper.
• flocculated the emulsion "breaks"
• Ashless filter paper is substantially free of acid and polyvalent cations and when the erasable ink formulation was marked on this surface, the ink penetrated all the way through to the other side of the paper and erasability was lost.
• Carboxylated latexes are more ion stable and, consistent with the above theory, they tended to penetrate regular paper to a greater extent than the non-carboxylated latexes such as LPF 2108.
• Humectants We are using Sorbitol (a polyhydric alcohol sold under the name "Sorbitol” by ICI Americas Inc. of Wilmington, Del.) as the humectant in the current system to improve the Cap Off performance of the marker. Cap Off is the measurement of the ability of the unit to withstand drying and still maintain functionality. The names of the humectants that are most effective are listed.
• Surfactants As was mentioned above, an ink system surfactant will be used to lower the surface tension of the ink to the point where the nib can be wet out. Apparently, because of the very small (700 Angstrom) particle size of the LPF 2108 latex, a relatively large amount of surfactant is required to lower the surface tension of the system.
• FC129 a fluorochemical surfactant
• FC129 a potassium salt of a fluorinated alkyl-carboxylate, effective in alkaline systems.
• Viscosity It is generally accepted that a marker ink should have a viscosity of under 5-10 cps.
• Antimicrobials or Preservatives, Bactericides, Fungicides Even though we have not seen any evidence of microbial growth in the Flexiverse based ink formulation, we suggest that some sort of antimicrobial agent will be appropriate.
• Anti-foam Agents Because of the extensive mixing which must be accomplished to formulate this product, a conventional anti-foaming agent may be employed to reduce foaming during manufacture.
• Antioxidant The LPF 2108 which is used in the current formulations is sold by Goodyear without an antioxidant. This emulsion results in an ink which slowly oxidizes with exposure to air and makes the ink mark lose erasability. With the addition of antioxidants, the erasability can be extended indefinitely.
• Another important aspect of this invention is control of the indelibility or erasability time.
• a short time a few days
• a very long time a few years
• Addition of antioxidant causes a functional increase in the length of the time that the mark remains erasable.
• An antioxidant that works well in this system is sold under the commercial designation "Octolite 453" by Textile Rubber and Chemical Company of Dalton, GA.
• the product is 55% solids and is employed up to about 3 percent (by weight) on dry basis, to maintain erasability for at least a few months.
• the product is said to be a 50:50 emulsified blend of two polymeric hindered phenol thioester antioxidants sold under the commercial names "Wing Stay L” and “Wing Stay SN1 " by Goodyear Tire and Rubber Company.
• Ghosting/residue Using a microscope, the residue from a mark was analyzed.
• the residual color or "ghosting" which was visible on some substrates using the Flexiverse 4343 colorant with the LPF 2108 resin emulsion, is resin and colorant which is trapped in small caverns on the surface of the paper.
• the residue does not appear to be unbound colorant.
• the residue is resin/colorant matrix which is able to escape abrasion by the eraser. When a needle is used to remove the residue, there is no underlying stain on the paper.
• the rubber found most effective in this invention is designated LPF 2108 and sold by The Goodyear Tire & Rubber Company, Houston, Texas.
• the product is 40.0% solids. It has a residual styrene percentage of 0.019. It has a pH of 11.4 (highly basic). It has a surface tension, at 40% total solids content, of 58 dynes/cm. It contains 23.4% bound styrene. It has a 0.001 % coagulum. It has 0.008% stability MG. It contains 8.64% soap, which we believe is a potassium oleate.
• a pigment dispersion consisting of solid pigment particles suspended in alkaline aqueous medium containing a first surfactant.
• a latex which is an emulsion of rubber in an alkaline aqueous medium containing a second soap-type surfactant.
• the pigment dispersion and the latex are mixed with a substantial amount of a third surfactant which is sufficiently in excess of the amount needed to stabilize the mixture so that the surface tension of the total mixture is significantly reduced. This forms the ink.
• ordinary writing paper shall mean paper of the type normally used for commercial and domestic writing and typing and which has a surface which is treated or sized in a standard manner, and as a result, the surface releases ions when the surface is wetted.
• ions is used to denote water-soluble charged particles.
• cations is used to denote water-soluble charged particles having at least one positive charge.
• polyvalent cations is used to denote water-soluble charged particles having at least two positive charges.
• the ink mixture is an aqueous emulsion of rubber particles in or on which particles of the colorant are exclusively associated.
• This emulsion is stable as long as the pH is high (basic) and ion content of the mixture is undisturbed, i.e., mono-valent cations (Na+ and K+).
• the water is absorbed into the paper. This causes the ink to form a pigmented film on the surface of the paper. Because the soap-type surfactant is essentially non-functional, the surface tension of the rubber is very high and the rubber has only minimal "wetting" on interaction with the paper surface. This is true even though the glass transition temperature of the preferred rubber is -52 +/- 5 degrees C. and therefore, the film would be expected to be quite flexible. Because the adhesion between the film and the paper is minimal, the pigmented film can be easily removed from the paper by friction.
• roller-ball pens Another application of the erasable ink composition of the present invention would be in a class of writing instruments which will be referred to herein as " roller-ball " pens.
• This class of pens which is very closely related to classic ball-point pens, developed in a manner which makes its useful to consider them a separate class (or perhaps a subclass) of writing instruments from the ball-point pen class of instruments.
• the classic ball-point pen writing instrument had developed into a fairly standard construction in which a tube of approximately two millimeter inner diameter was filled with highly viscous, organic-solvent-based ink, which was exposed to a rotating ball at one end of the tube.
• the non-aqueous inks which are used in this type of instrument were specifically designed to be highly- viscous in order that they did not flow out of the open end of the tube and in order that they did not leak out of the relatively large clearance between the ball and toroidal seat in which the ball was held. This relatively large space between the ball and seat was probably required because of the practical tolerance problems associated with the manufacturing methods.
• the organic inks were also specifically selected to have minimal evaporation from the tube in order that the ink did not dry out prior to use either through the open-back end of the tube or at the ball end. The latter would, of course, clog the ball's action.
• One of the first of the roller-ball class of pens resolved the problems of low viscosity ink by absorbing the ink reservoir in a fibrous, porous filler.
• Porous ink feed rods were provided to lead the ink from the filler to the rotating ball at the end of the pen. These feed rods controlled the rate of flow of the ink and thereby, reduced the potential seriousness of leaking of the ink around the periphery of the ball, and over-flowing and "globbing" of ink at the start and stop of writing.
• the feed rods or nib fails to provide a sufficiently continuous flow of ink to the ball for rapid use.
• the use of the filler to physically stabilize the ink in the reservoir significantly reduced (to about 1/2) the amount of ink available in the writing instrument.
• the use of inks which employ pigments as their colorant, as opposed to soluble dyes can clog the capillary passages in the fibrous reservoir and feed rods further inhibiting and interrupting the rate of flow and the amount of ink that is delivered to the ball.
• the viscosity drops to less than 100 cps.
• the normal high-viscosity reduces the incidents of leakage, while the low-viscosity during and in the vicinity of the writing operation provides the smooth feel of low-viscosity ink.
• the system requires the presence of a high-viscosity filler plug between the back end of the ink reservoir and atmosphere in order to control evaporation and drying of the reservoir ink.
• the erasable ink system of the present invention can be applied effectively to all three classes of the roller-ball technology.
• ball-roller-point pen technology is particularly beneficial in the context of the present water-based erasable ink invention.
• the ball which is used in writing instruments is formed of metal. Because water-based inks do not "wet" the metal surface of the ball as effectively as certain existing organic-based ink formulations, water-based inks frequently had somewhat inferior writing characteristics when used in metal-ball-point pens.
• the use of ceramic balls in the ball-roller-point pen systems provides a superior method for applying water-based inks. The ceramic surface frequently is much more effectively "wetted" by the water-based inks and, therefore, provides a smoother, more uniformed application of the ink.
• the ink of the present invention is essentially the same formulation and behaves in about the same manner as that used in the felt tip marker applications.
• composition of the present invention substantially in the same form as described for felt-tipped markers, can be used in the second class of roller-ball products, namely the fillerless, nib, ball system, and in the third class of roller-ball pens, namely the fillerless, nibless, ball pen, designed for the gelled ink.
• a Class 1 commercially-available roller-ball pen, sold under the trademark "BIC METAL POINT ROLLER FINE POINT” was obtained and disassembled. It included a tube, a filler, a nib, and a ball. The parts were all cleaned of ink, the pen was loaded with test ink, and the pen was reassembled. The test ink had the following composition.
• FC 129 surfactant 1.1 gm.
• Sorbitol/glycerine 3.5 gm.
• Demineralized water 9.82 gm.
• the working Sorbitol/glycerine mixture was two parts by weight Sorbitol and one part by weight glycerine.
• the mixture was prepared using the standard procedure described in earlier examples above.
• the viscosity was about 5.3 cps.
• the surface tension was about 23.7 dynes/cm.
• the resulting product wrote in an acceptable manner and the resulting mark was erasable. After five days, the product would still write and the resulting mark was erasable.
• PILOT PRECISE ROLLER BALL V5" was obtained and disassembled. It included a tube, no filler, a nib, and a ball. The parts were all cleaned of ink, the pen was loaded with test ink, and the pen was reassembled. The test ink had the following composition. Carbon Black KS5725 3.23 gm.
• Sorbitol/glycerine 3.5 gm.
• the mixture was prepared using the standard procedure described in earlier examples above.
• the viscosity was about 5.3 cps.
• the surface tension was about 23.7 dynes/cm.
• the resulting product wrote in an acceptable manner and the resulting mark was erasable. After five days, the product would still write and the resulting mark was erasable.
• a Class 3 commercially-available roller-ball pen, sold under the trademark "SAKURA BALL SIGN” was obtained and disassembled. It included a tube, no filler, no nib, and a ball. The parts were all cleaned of ink, the pen was loaded with test ink, and the pen was reassembled. The test ink had the following composition.
• FC 129 surfactant 1.1 gm.
• Sorbitol/glycerine 3.5 gm.
• Demineralized water 9.82 gm.
• the working Sorbitol/glycerine mixture was two parts by weight Sorbitol and one part by weight glycerine.
• the mixture was prepared using the standard procedure described in earlier examples above.
• the viscosity was about 5.3 cps.
• the surface tension was about 23.7 dynes/cm.
• the resulting product did not write in an acceptable manner. It would "skip" , that is, make a noncontinuous mark, and then stopped writing . The ball appeared clogged.
• a Class 3 commercially-available roller-ball pen, sold under the trademark "SAKURA BALL SIGN” was obtained and disassembled. It included a tube, no filler, no nib, and a ball. The parts were all cleaned of ink, the pen was loaded with test ink, and the pen was reassembled. The ball end was replaced by the ball end from a product sold under the trademark "PARKER VECTOR ROLLER BALL", because the Sakura ball have become clogged in earlier experiments.
• the test ink had the following composition.
• FC 129 surfactant 0.5 gm.
• Sorbitol/glycerine 25 gm.
• the working Sorbitol/glycerine mixture was two parts by weight Sorbitol and one part by weight glycerine.
• the mixture was prepared using the standard procedure described in earlier examples above.
• the viscosity was about 12 cps.
• the surface tension was about 42.5 dynes/cm.
• the resulting product wrote in an excellent manner and the resulting mark was erasable. After five days, the product would still write and the resulting mark was erasable.
• the erasable inks of the present invention possess the Theological properties normally associated with the pseudo plastic or shear-thinning ("jelled") inks described above. In fact, tests thus far indicate that the present inks are Newtonian and perhaps even dilatant.
• the high-viscosity versions of the inks of the present invention work very well in this class of writing instruments. Furthermore, it has been found that the high-viscosity versions of this product have excellent erasability characteristics and as a result, essentially provide a whole new product category of erasable roller-ball writing instruments.
• roller-ball pens can effectively employ a "jelled" ink form of the ink formula recited above with the addition of the shear-thinning, shock-resisting, and water-fast enhancing additives recited in the "jelled ink" patents recited above.
• the effectiveness of the inks of the present invention in the gelled-ink-type class three roller-ball pens appears to be effected by shear instability ( rather than shear-thinning) of the present inks. It has been observed that the shear that occurs at the working end of a felt tipped marker is about 6000 sec -1 . The large ball of a classic ball-point pen creates a shear of about 6000 sec -1 . At this level of shear, the standard formulation of the present ink appears to be non-shear-stable. There is evidence that the emulsion starts to become unstable and break when the marker or pen is used to write.
• the shear-stabilizing additives must stabilize the emulsion against the shear created by the pen in which the ink is to be used, without unduly increasing the ion- instability which is so beneficial to the, operation of the invention.
• the polyhyric alcohols for example Sorbitol and glycerol, when added in concentrations equal to or greater than would typically be required by their role as humectants in the formula of this invention, stabilize the emulsion to the point that the resulting ink can be used without clogging, in the higher shear ball pens.
• This high amount of shear stabilizer also increases the cap-off time, that is, the time that the pen can be left without a cap before the ink on the tip becomes too dry for the pen to be used.
• the concentration of shear stabilizer must be optimized because too much humectant can extend the drying time of the written mark to an unacceptable length and cause "ghosting" that reduces erasability.
• the unit contained ink number X 1265-90-1 from our lab notebook. This ink was composed of the following (wt %):
• This roller-ball ink has more rubber emulsion than our standard marker ink.
• This ink also has more sorbitol/glycerine than our standard marker ink to prevent drying of the roller tip and to lubricate the roller tip.
• roller-ball ink would not penetrate into the fibers of the paper and would have an extended cap-off time. Though not erasable, the new ink would allow roller-ball units to compete with high molecular weight solvent inks which do not require a cap.
• the viscosity of the ink has been found to be one of the critical parameters in optimizing the ink for a particular writing instrument. Because the variation of viscosity can effect other critical parameters, the achievement of a functional ink with optimum viscosity for a given writing instrument is sometimes difficult. It has been found useful to divide writing inks into three ranges; low viscosity (less than 10 cps) for capillary type writing instrument such as felt-tipped markers, high viscosity (greater than 30 cps) for bulk flow type instruments such as ball-point pens and gel-type roller-ball pens, and mid-range viscosity (10-30 cps). By experimentation (set out below) it was established that the "shock out” effect and the resulting superior erasability of the ink, can be achieved in all three viscosity ranges.
• Ink X1265-105-2 has a viscosity of 64 cps and is composed of the following: 60g BASF NS 103 SBr latex
• This ink had excellent writability and excellent erasability when applied from a pen formed of the Bic parts.
• Ink X1265-105-3 (a repeat mixing of ink X1265-90-1), has a viscosity of 26 cps and is composed of the following:
• This ink had excellent writability and excellent erasability in the Bic parts.
• Ink X1625-105-4 has a viscosity of 559 cps, because of the use of higher amounts of tragacanth gum and is composed of the following:
• This ink also had excellent writability and erasability in the Bic parts.
• the upper viscosity limit of the present invention will be determined by the maximum amount of pigment and rubber that can be added to the formulation. Very thick inks will require higher pigment and rubber loadings.
• viscosity ranges are given for erasable, as well as non-erasable, inks. For standard non-erasable ball pens, the viscosity range is 50-150 poise (5,000-150,000 cps). For erasable inks the range is 48-500 poise (4,800-50,000 cps). These erasable inks sometimes use a pressurized cartridge. Effective versions of our erasable inks could be formulated in these higher ranges with the use of various thickeners available in the art.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Wood Science & Technology (AREA)
• Organic Chemistry (AREA)
• Inks, Pencil-Leads, Or Crayons (AREA)
• Pens And Brushes (AREA)

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• 1993
  • 1993-10-20 TW TW082108710A patent/TW294703B/zh active
  • 1993-10-22 MX MX9306589A patent/MX9306589A/es not_active Application Discontinuation
  • 1993-10-25 KR KR1019950701557A patent/KR100326966B1/ko not_active IP Right Cessation
  • 1993-10-25 CA CA002146978A patent/CA2146978C/en not_active Expired - Fee Related
  • 1993-10-25 WO PCT/US1993/010231 patent/WO1994010251A1/en not_active Application Discontinuation
  • 1993-10-25 BR BR9307294A patent/BR9307294A/pt not_active IP Right Cessation
  • 1993-10-25 EP EP94901199A patent/EP0665869A1/en not_active Withdrawn
  • 1993-10-25 JP JP51123794A patent/JP3619251B2/ja not_active Expired - Fee Related
  • 1993-10-25 AU AU55871/94A patent/AU5587194A/en not_active Abandoned

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