Coating implements with material supply – Including floating follower in reservoir – Fluid follower
Reexamination Certificate
2001-05-09
2002-09-03
Walczak, David J. (Department: 3751)
Coating implements with material supply
Including floating follower in reservoir
Fluid follower
C401S141000
Reexamination Certificate
active
06443647
ABSTRACT:
The invention relates to an ink follower piston for a ball-point pen and also to a method of manufacturing such a piston.
This type of piston comprises a gell element, optionally containing a solid element, and intended more particularly for use in combination with an ink of viscosity lying in the range 10 mPa.s to 30,000 mPa.s (or presenting thixotropic properties), the ink being placed in a reservoir fitted at one of its ends with a writing point.
Inks suitable for ball-point pens comprise three main groups, namely:
aqueous inks that are liquid and of low viscosity, which are used in writing implements where flow rate regulation is provided by means of a system of baffles or a fiber reservoir;
high viscosity inks in a solvent, used in tubular reservoirs that feed the tip directly; the flow rate in such pens being adjusted by modifying the viscosity of the ink; and
aqueous inks of medium viscosity, used in tubular reservoirs that feed the tip directly.
In the third group, it is necessary to ensure that the ink does not flow out of the rear end of the reservoir cartridge by placing a follower piston on top of the column of ink. The piston is insoluble in the ink and is generally constituted by a plug of grease, thereby also serving to limit evaporation of any volatile solvents contained in the ink (water in particular), and to some extent serving to regulate the flow rate of the ball-point pen. Furthermore, when the pen is in use, the piston follows the column of ink along the tube, which is why it is referred to as a “follower”, thus avoiding any residual ink deposits on the walls of the reservoir.
In the state of the art, various chemical compositions are mentioned for use as a follower piston and are formulated on the basis of one of or more low-volatility organic solvents, in particular polybutene, together with a thickening agent of the di- or tribenzylidene sorbitol type (JP 6220418) for forming grease that corresponds to a reversible semisolid state obtained by setting up physical internal bonds (such as hydrogen bonds and/or vanderWaals' bonds). In order to guarantee proper behavior in the tube, regardless of the conditions under which the pens are stored, these compositions generally have a high viscosity. In addition, while the pen is in use, these greases tend to adhere to the walls of the tube, thereby spoiling the appearance of the reservoir. Furthermore, such adhesion gives rise to a loss of material from, or to deformation of, the piston, thus causing the system to misfunction and running the risk of ink leaking out from the rear of the tube, and also the risk of the volatile solvents contained in the ink evaporating. Furthermore, in the event of an impact, the high viscosity of such follower pistons can lead to the column of ink becoming separated from the piston, giving rise to gaps in writing or indeed to a permanent stoppage.
In order to limit the negative effects due to the viscosity of the follower piston, various techniques have been investigated. These include incorporating an additive in the above-mentioned greases, which additive is of the poly(siloxane) modified polyether type (U.S. Pat. No. 5,348,989), or polar compounds (WO 98/04421) that are intended to improve sliding along the tube, and to guarantee better contact between the ink and the follower, in particular in the event of an impact.
Another solution, as envisaged in U.S. Pat. No. 4,671,691, consists in formulating viscoelastic grease compositions based on mineral oil, polybutene, and onium-treated organophilic clays. Such compositions which have high viscosity at rest can become substantially fluid under the effect of stress (normal flow in a tube or fast displacement of the follower piston in the event of an impact) so as to follow the ink better.
Nevertheless, the viscosities of such greases, even after shear, remain relatively high, thereby making them difficult to transfer, in particular when filling cartridges.
Furthermore, such greases made of a mixture of mineral oil and polybutene, are subject to large variations in viscosity as a function of temperature, such that a pen stored under conditions that vary significantly and that can sometimes be severe (tropical climates, back window of a car, ) can lead to the grease plug becoming liquid and can thus lead to the ink flowing out through the rear end.
Replacing the mixture of mineral oil+polybutene with silicone oils thickened by aluminum silicate, e.g. as in EP 0 792 759, always forms a grease whose viscosity is nevertheless not so sensitive to variations in temperature.
However, certain technical problems remain. Thus, it remains difficult to introduce such compositions of viscosity that is still high into cartridges, particularly when the tube diameter is small. In addition, the flexibility of all previously proposed solutions remains limited in that their properties must be matched to the characteristics of the intended pen, thus requiring the follower piston to be completely reformulated for each pen, and that is a lengthy effort.
Furthermore, those greases form pistons having excessive capacity for deformation which tends to disturb writing quality. In addition, those greases are opaque which makes the piston visible in a translucent or transparent tube or reservoir, and that is not satisfactory from the appearance point of view.
Finally, when the follower piston also has a solid element (as in FR 2 709 444), then the solid element is necessarily made with closed pores since the viscosity of the greases is too great for them to be able to penetrate into open pores. Such a configuration causes the solid element to float, thus making it particularly unstable.
Follower pistons developed in the context of the present invention are intended to solve the technical problems inherent in using conventional follower pistons.
SUMMARY OF THE INVENTION
According to the invention, this object is achieved by means of a first embodiment of a follower piston for a ball-point pen comprising, in particular, an element in the form of a stable gel of hardness measured by cone penetration lying in the range 100×10
−1
millimeters (mm) to 400×10
−1
mm.
DETAILED DESCRIPTION
In a particular variant, the gel element is made from a reaction medium containing at least one liquid component selected from silicone polymers, polyurethanes, polyesters, and epoxy resins.
Preferably, the reaction medium contains a first liquid component and a second liquid component of the same chemical nature and suitable for participating in a condensation or addition chemical reaction, and in particular in hydrosilylation.
In a particular embodiment, the first liquid component is constituted by at least one silicon polymer provided with at least two unsaturated ethylene functions.
In another embodiment, the second liquid component is constituted by at least one silicon polymer provided with at least two Si—H functions.
According to an advantageous characteristic, the molar ratio in the reaction medium of the unsaturated ethylene functions of the first component and of the Si—H functions of the second component lies in the range 1:5 to 5:1, and preferably in the range 1:3 to 3:1.
In another variant, the follower piston also includes a platinum-based hydrosilylation agent at a concentration such that the platinum content lies in the range 0.1 parts per million (ppm) to 1000 ppm.
According to an advantageous characteristic, the unsaturated ethylene functions are located at opposite ends of the chain of the silicone polymer of the first component.
According to another characteristic, said silicone polymer with an Si—H function of the second component is a copolymer of dimethylsiloxane and of methylhydro-siloxane.
In yet another variant, the piston further comprises a diluant agent constituted by at least one inert silicone polymer such as trimethylsiloxy-terminated poly(dimethylsiloxane).
In a specific variant, the piston further comprises at least one lubricating agent selected from white mineral oils and isoparaffin oils and/or fatty materials s
Bocquenet Frédéric
Duez Jose
Lerch Jean-Philippe
Antonelli Terry Stout & Kraus LLP
Societe BIC
Walczak David J.
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