EP0516538A1 - Writing implement with fluid comprising a microporous buffer reservoir - Google Patents

Abstract

The writing implement (1) comprises a reservoir (8) for the liquid ink in the free state, a transfer tip (12), the rear end (12a) of which emerges into the reservoir (8) and the front end (12b) of which forms the writing head. It comprises a buffer reservoir (13) capable of absorbing the ink excess, which is a compact unit made from a hydrophobic material having open pores and is fitted loosely around the tip. This porous material is especially obtained by heat-melting a mixture of microspheres of at least two thermoplastics of different grades, for example made from polypropylene having a diameter of the order of 140 micrometers, having a void content of the order of 40% after heat-melting. The buffer reservoir (13) preferably has a capillarity which varies over its height, the zone close to the reservoir (8) having a greater capillary effect. <IMAGE>

Description

The present invention relates to a writing article with liquid ink, that is to say in which the ink is in the free state, not being trapped: in a fibrous reservoir. This writing article comprises a reservoir for the ink and a point ensuring by capillary action the transfer of the ink from the reservoir to the writing head proper, the writing head possibly consisting of the end of said tip. It relates more particularly to a writing article of the aforementioned type equipped with a buffer tank, intended to absorb and restore the excess ink in the event of variation in the conditions of use.

There are two categories of liquid ink and transfer point writing items. In articles of the first category, the reservoir which contains the ink is isolated from the ambient air and does not contain air; a flexible piston moves in the reservoir as ink is consumed and seals

In articles of the second category, the reservoir which contains the ink is not isolated from the ambient air. In this case, a variation in the conditions of use, in particular the increase in the pressure of the air contained in the tank due to heating of the air results in an abnormal inflow of ink in the transfer point and can cause stains or drips when the item is uncapped. To avoid this phenomenon, provision has been made to equip this type of article with a buffer tank such as that which is the subject of document EP D380696. The function of such a buffer or temporary reservoir is to absorb the excess ink coming from the reservoir before it reaches the writing head, that is to say from the front end of the point serving to write, and then, once normal conditions have been restored, to restore the ink it contains to the point.

The buffer tank of document EP D380696 is a molded part, comprising comb-shaped radial slots and longitudinal slots connecting the radial slots and the central hollowed out part in contact with the transfer point.

To obtain good results, it is necessary that the radial slots have a very small and very regular thickness, that they are in large number and that in addition the buffer tank has grooves intended for the passage of air.

The realization of such a tank is not simple and is of a high cost, especially since the corresponding mold can only be suitable for one standard article.

We had already proposed in document CH.A. 422 575 a writing article, in liquid ink, provided with a flow-regulating device which was constituted by a capacity in which was placed a spongy mass with open cells preferably in a material which does not absorb ink, this ability to communicate with the channels which bring ink to the scripting organ, for example with a wick serving as a writing tip.

The article presented in this document CH.A. 422.575 which dates from 1966 has not been industrialized to date. According to the applicant, the preferred embodiment described therein has several drawbacks.

First, the capacity in which the spongy mass is placed is in the front part of the article; there is therefore an intermediate chamber between this capacity and the tank, which is in communication with the ambient air through a lateral orifice. The applicant has noted that in the event of a pressure variation resulting in an excess of ink in the tip, this excess may appear in the area of the tip close to the reservoir. In the case of an article conforming to document CH.A. 422 575, excess ink can flow into the intermediate chamber and through the side port.

Then, the wick is fitted into a wick guide, provided over a part of its length with a so-called capillary tip. The spongy mass is arranged, in the capacity, around the drill guide. Thus there is strictly speaking no contact between the wick and the spongy mass. It therefore requires a very large excess of ink in the wick so that it leaves through the capillary slit and is absorbed by the spongy mass. This This arrangement can cause malfunctions and drips by the wick itself, before the flow regulator plays its role.

Finally, it is essential that the article is equipped with a covering cap, that is to say a cap which is long enough to close the lateral orifice, in order to avoid drying of the wick at the level of the intermediate chamber, in the event of non-use.

The aim which the applicant has set himself is to propose an article for writing in liquid ink, of the second category, but which overcomes the aforementioned drawbacks of the two aforementioned known articles.

This object is perfectly achieved by the article of the invention. It is a writing article with liquid ink which is composed of a body whose rear part constitutes the reservoir for the ink, of a transfer point whose rear end opens into the reservoir and of which the front end, forming a writing tip, opens out of the body through a central orifice and a buffer tank which is able to absorb and restore the excess ink coming from the tip by capillarity in the event of variation of the pressure prevailing in the reservoir and which is in a hydrophobic material with open pores.

Typically the buffer tank is in the form of at least one compact block adjusted loosely around the tip, and there are free spaces for air circulation between the tip and the wall of the central orifice and on the other hand between the internal wall of the body and the buffer tank.

In the event of a pressure variation in the reservoir, the excess ink which flows into the tip is captured by capillarity in the pores of the hydrophobic material and therefore penetrates into the buffer reservoir. The air circulation for the restoration of the pressure, is done thanks to the free spaces between the tank and the body of the article and between the point and the wall of its central outlet. When normal pressure conditions are restored, the ink that is consumed by the tip preferably comes from the pores of the hydrophobic material, which gradually empty. The desired technical effect is achieved thanks to the material itself and its porosity, the open pores fulfilling the role of radial and longitudinal slots in the buffer tank of document EP 0380696. The production of this tank, by molding or by machining from 'a block of said material is very simple.

It is important that the hydrophobic material is adjusted loosely around the tip. Over-tightening would crush and seal the pores and / or capillaries of the tip and prevent ink from rising by capillary action from the tip to the buffer tank.

The compact block shape, fitted around the tip, allows intimate contact of the hydrophobic material with open pores, over the entire periphery of the tip.

Preferably, the porous hydrophobic material constituting the reservoir is based on microspheres and is obtained by thermofusion of a mixture of microspheres of at least two thermoplastic materials of different grades.

It is for example a material based on polypropylene, produced with microspheres having a diameter of the order of 140 micrometers, and comprising of the order of 40% vacuum, after thermomolding the microspheres together.

According to a first advantageous embodiment, the body and the buffer tank both have a circular transverse section, the outside diameter of the buffer tank being less than at least one millimeter than the inside diameter of the body. Air circulation can thus take place in the annular zone surrounding the buffer tank.

According to a second advantageous embodiment, the buffer tank has, in cross section, the shape of a regular polygon whose vertices are in close proximity to the internal wall of the body and whose sides delimit free spaces with said internal wall. This particular arrangement allows the circulation of air in the free spaces thus delimited between the internal wall of the body and the different faces of the buffer tank; on the other hand it allows centering and holding the buffer tank inside the body, the longitudinal edges of the regular polygon resting on the inside wall of the body.

According to a particular version, the buffer tank consists of modular blocks stacked, joined or having a determined spacing between them. This makes it possible to standardize the manufacture of modular blocks and to use the same components regardless of the size of the article.

For example, the buffer tank consists of a stack of washers, at least some of which have an annular shoulder so as to create recesses around the tip and between the washers. These recesses contribute to better air circulation around the tip.

The annular shoulders are for example located towards the peripheral part of the washer.

Preferably, the capillarity of the buffer tank is differentiated in the longitudinal direction taken in the direction of the tip, being more capillary near the tank than near the central outlet orifice of the tip.

This makes it possible to obtain an immediate absorption of the excess ink, as close as possible to its appearance in the wick and to optimize the ink retention capacity of the reservoir.

This differentiated capillarity can be achieved either using a stack of modular blocks, or using a monobloc reservoir.

In the case of stacking, each block will have a given capillarity, different from that of one of the other blocks, and the stacking is carried out by placing the blocks in decreasing order of capillarity starting from the reservoir.

In the case of the monobloc reservoir, the differentiated capillarity is obtained for example, in the case of microspheres linked by thermofusion, by a differentiated heat treatment, according to the desired capillarity, or also by a choice of microspheres of different sizes being smaller in the area with greater capillarity.

Other characteristics and advantages of the invention will appear more clearly on reading the description which will be given of an exemplary embodiment of a writing article in liquid ink and with a buffer tank, illustrated by the appended drawing in which:

Figure 1 is a schematic view in longitudinal section of the article.

FIG. 2 is a diagrammatic view in cross section along the line AA in FIG. 1.

Figure 3 is a schematic sectional view of a buffer tank consisting of a stack of washers.

Figure 4 is a schematic cross-sectional view of an article with a buffer tank of circular section.

Figure 5 is a partial schematic sectional view of a buffer tank fitted on the outer wall of the ink tank.

The writing article 1 consists firstly of a substantially cylindrical hollow body 2, the bottom 3 of which is closed, the front part 4 of which is terminated by a cone 5 comprising a central orifice 6, and the rear part 7 acts as a reservoir 8 for liquid ink 9. Said reservoir 8 is closed by an internal partition 10 which has a central orifice 11.

Article 1 consists secondly of a cylindrical transfer point 12, made of a material capable of ensuring the transfer of the ink by capillary action, in particular made of felt made of compacted acrylic or polyester fibers. This tip 12 is positioned along the longitudinal axis of symmetry of the body 2. Its rear end 12 a is force-fitted slightly into the central orifice 11 of the partition 10 so that the tightness of the reservoir 8 is ensured, but without crushing of this end 12 a so that there can be circulation of ink and air by the tip 12. Its front end 12 b , bevelled in a warhead or other configuration and forming a head d 'writing, is centered in the central hole 6 of the conical part 5 of the body 2.

Article 1 is made up, thirdly, of the buffer tank 13 which surrounds the transfer point 12 in the internal part of the body 2 between the tank 8 and the cone 5.

The buffer tank 13 is a hydrophobic material, with open pores, of very high porosity. In the example illustrated in Figure 2, it has the shape of a rectangular parallelepiped of square cross section. It has a cylindrical central recess 14, shaped to accommodate the transfer point 12, in an adjusted manner but without clamping, that is to say without crushing the capillaries of the felt constituting the point 12 or the pores on the surface of the recess central 14 of the buffer tank 13.

The longitudinal edges 14 of the buffer tank 13 are substantially supported on the inner cylindrical wall 15 of the body 2. They delimit four free spaces 16 between said wall 15 and the flat faces 17 of the buffer tank 13.

In the example illustrated in Figure 4, it has a cylindrical outer shape, with the same central recess. Its outside diameter d is less than the inside diameter D of the body by at least one millimeter, leaving sufficient annular space for air circulation.

The hydrophobic, open-pore material constituting the buffer reservoir 13 is obtained by thermofusion of a mixture of microspheres or microbeads of two types of polypropylene of different grades, that is to say of polypropylene having different melting temperatures. After a homogeneous mixing of the microspheres in a suitable mold, they are brought to a given temperature which is higher than the melting temperature of polypropylene of the first type and lower than the melting temperature of polypropylene of the second type. In this way the polypropylene constituting the microspheres of the first bottom type, which on the one hand creates the microcavities corresponding to the open pores and on the other hand ensures the cohesion of all the polypropylene microspheres of the second type.

In a specific embodiment, these were microspheres having a diameter of 140 micrometers. After thermofusion the open pore material obtained had a void percentage of the order of 40%.

The operation of the writing article is as follows. In normal use, the ink 9 which is contained in the tank 8 and which is in contact with the rear end 12a of the tip 12 is absorbed and migrates by capillary action in the tip 12 to its front end 12 b . The ink consumed by the writing head is replaced progressively with ink coming from the reservoir 8. A pressure balance is established between the air contained in the reservoir 8 and the air prevailing in the rest of the body 2.

In the event of a disturbance due in particular to an increase in pressure in the reservoir 8, for example due to heating of the article 1, there is an excess of ink 9 which flows from the reservoir 8 into the tip 12.

In the absence of a buffer reservoir 13, this excess ink would migrate to the writing head 12 b and cause an abnormal supply of the article 1, liable to form spots or drips on the writing medium. .

Thanks to the presence of the buffer tank 13, this excess ink does not reach the writing head 12b ; by capillary action, the excess ink diffuses into the open pores of the microporous material in contact with the capillaries of the tip 12, until the pressure balance is restored. Thus the microporous material acts well as a complementary reservoir for the ink.

When use of the article 1, the ink that is consumed by the writing head 12 b preferentially from the buffer tank 13. The buffer tank 13 gradually empty the ink contained in the outermost pores from the tip 12 diffusing by capillary action to said tip 12.

After use, the article 1 is closed using the cap 26 (FIG. 1), the configuration of which is designed to secure it on the cone 5 and to cover the end 12 b of the point 12 without contact.

We understand that the principle of operation of the buffer tank 13 is based on the thermodynamic balance of the constituents of article 1. For this balance to be reached quickly, it is necessary to have good air circulation between the outside and inside the article. For this purpose the central orifice 6 of the cone 5 terminal of the body 2 may delimit free spaces around the front end 12 b of the point, allowing this air circulation. This can be obtained by lugs 18 distributed over the periphery of the internal wall of the neck 19 extending the cone 5, and serving to maintain the tip 12.

In a second example illustrated by FIG. 3, the reservoir 13 is made up of stacked modules 20, each module being in accordance with the invention in a hydrophobic material with open pores, of high porosity.

The realization in stacked modules makes it possible to use identical modules for articles of different sizes, by varying the number of modules of the stack.

In the present case, each module 20 has the shape of a washer, pierced with a central orifice 21 for the insertion of the point and provided on one of the faces 23 with an annular shoulder 22, extending the external part of the washer 20.

As is clearly shown in FIG. 3, the stacking is carried out by superimposing the washers, so that the face 23, comprising a shoulder 22, of a given washer applies to the flat face 24 of the adjacent washer. This arrangement forms in the buffer tank 13 a set of internal recesses 25 around the tip 12, which promotes the circulation of air.

According to a preferred embodiment, illustrated in FIG. 5, the buffer tank has a differentiated capillarity in the longitudinal direction, this direction being taken in the direction of the tip. More precisely, the capillarity of the buffer tank 13 in its upper part 13 a , that is to say that which is close to the ink tank 8, is greater than that of the lower part 13 b of the tank 13 c ' that is to say that which is close to the central outlet orifice 6. This differentiated capillarity makes it possible to capture the excess ink produced in the event of a pressure variation as soon as this excess is created, namely close to the reservoir d 'ink. Thus the buffer tank 13 begins to fill in its upper part 13 a and then gradually towards the lower part 13 b . It is therefore possible to obtain a progressive and complete filling of the buffer tank 13.

This differentiated capillarity can be obtained in several ways. One can, during the constitution of the compact block constituting the buffer tank 13, using microspheres of different grades, have in the mold microspheres of different sizes over the height of the mold. The microspheres present in the lower part 13 b of the block will have a larger diameter than the microspheres present in the upper part 13 a . The applicant has in fact noticed that the capillarity is greater the smaller the microspheres.

It is also possible to obtain a differentiated capillarity by varying the thermofusion conditions. The applicant has in fact noticed that during the production of the compact block using the microspheres, it was possible to vary the temperature slightly while obtaining the bonding of the microspheres and the partial melting sought. In a specific embodiment, for a block having microspheres of a determined diameter, it was noted that the capillarity was all the greater as the thermofusion was carried out at a low temperature. Thus to obtain the differentiated capillarity, it was sufficient to apply to the mold a temperature which was, in the zone corresponding to the upper part 13 a of the buffer tank 13, lower than that applied in the zone corresponding to the low part 13 b of the buffer tank 13.

This effect of differentiated capillarity over the height of the buffer tank can be obtained by using several stacked modular blocks, each having a determined capillarity. For this, it suffices, during stacking, to arrange the modular blocks, around the tip 12, in decreasing order of capillarity, from the modular block closest to the rear end 12 a of the tip.

A better positioning of the buffer tank inside the body 2 can be obtained by fitting the upper part 13 a of the tank onto a tubular shoulder 26 of the internal partition 10, surrounding the central orifice 11 through which the tip passes. 12. This tubular shoulder 26 has a determined height H and the buffer tank 13 is hollowed out in its upper part 13 a at a height h less than H , so that when the buffer tank 13 is adjusted around the tip 12 said tank can be fitted onto the tubular shoulder 26 at the height h . The presence of the tubular shoulder 26 makes it possible to obtain a blocking in position of the buffer tank 13, at a predetermined distance e which is equal to the difference in the heights H and h , so that the buffer tank is not in contact with the inner wall 10 closing off the reservoir 10.

The invention is not limited to the embodiments which have been described by way of non-exhaustive examples.

In particular, the microporous hydrophobic material, with high porosity, can be based on a material other than polypropylene, for example polyethylene marketed under one of the trademarks HOSTALEN or GUR from the company HOECHST, or polytetrafluoroethylene. It can be a material having the same structure or an equivalent structure, obtained by other means than the thermofusion of microspheres of two materials of different grades.

It can also be a material obtained by thermofusion of microspheres of more than two materials of different grades.

The shape of the buffer tank is not limited to the two cases described above, in which it was square and cylindrical. It is possible to choose any shape which is on the one hand adapted to the geometrical configuration of the interior volume of the body of the article and on the other hand which allows the circulation of air as has been explained.

Claims (12)

Writing article with liquid ink which is composed of a body (2) whose rear part constitutes the reservoir (8) for the ink (9), of a transfer point (12) whose rear end ( 12 a ) opens into the tank (8) and the front end (12 b ) of which forms a writing tip, opens out of the body (2) through a central orifice (6) and a buffer tank (13) which is capable of absorbing and restoring the excess ink coming from the tip (12) by capillary action in the event of variation of the pressure prevailing in the reservoir, and which is made of a hydrophobic material with open pores, characterized in that the buffer tank (13) is in the form of at least one compact block adjusted loosely around the tip (12), and in that there are free spaces for air circulation between the tip on the one hand (12) and the wall of the central orifice (6) and on the other hand between the internal wall of the body (2) and the buffer tank (13). Writing article according to claim 1 characterized in that the porous hydrophobic material constituting the buffer tank (13) is based on microspheres and is obtained by thermofusion of a mixture of microspheres of at least two thermoplastic materials of different grades. Writing article according to Claim 2, characterized in that the hydrophobic micro-porous material, constituting the buffer tank (13) is produced from polypropylene microspheres having a diameter of the order of 140 micrometers and comprising of the order of 40% vacuum after thermofusion. Writing article according to Claims 1 to 2, characterized in that the body (2) and the buffer tank (13) both have a circular cross-section, the outside diameter ( d ) of the buffer tank (13) being less than at least one millimeter to the inside diameter ( D ) of the body (2). Writing article according to one of Claims 1 to 3, characterized in that the buffer tank (13) has, in cross section, the shape of a regular polygon whose vertices (14) are in the immediate vicinity of the internal wall (15) of the body (2) and whose sides (17) delimit free spaces (16) with said internal wall (15). Writing article according to one of claims 1 to 3 characterized in that the buffer tank (13) consists of modular blocks (20) stacked. Writing article according to Claim 6, characterized in that each module is a washer (20), provided on one of its faces (23) with an annular shoulder (22), so that the buffer tank (13) has recesses (25) around the point (12) inserted in the central orifice (21) of the stacked washers (20). Writing article according to one of Claims 1 to 3, characterized in that the capillarity of the buffer tank is differentiated in the longitudinal direction taken in the direction of the tip, being more capillary near the tank than near the central orifice of exit of the point. Writing article according to claims 6 and 8 characterized in that each modular block has a given capillarity, different from that of one of the other blocks, and in that the stacking is carried out by placing on the tip (12) the blocks in decreasing order of capillarity from the tank. Writing article according to claims 2 and 8 characterized in that, being a monobloc tank, the differentiated capillarity is obtained by a differentiated heat treatment over the height of the tank. Writing article according to claims 2 and 8 characterized in that, being a one-piece reservoir, the differentiated capillarity is obtained by a choice of microspheres of different sizes being smaller in the zone with greater capillarity. Writing article according to claim 1 characterized in that the internal partition (10) closing the ink tank (8) comprises a tubular shoulder (26) of author H given, surrounding the central orifice (11) through which passes the tip (12) and in that the buffer tank (13) is hollowed out in its upper part (13 a ) over a height h less than H , so as to obtain the fitting of the buffer tank (13) on the tubular shoulder (26).

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