EP1273450A2 - Manufacturing process for inhomogeneous sponge and sponge obtained therefrom - Google Patents

Abstract

A process for producing a sponge comprises locating a porous thermoplastic member (1) between two plates (2,3) in a press unit, then pressing the member (1) at a temperature that produces an inhomogeneous pore density distribution. The member (1) is later cooled and cut into a number of sections. Heat is applied via the plate(s) (2,3) at 100-250 degrees C and pressing lasts 10-90 minutes. The press plates (2,3) have a three dimensional surface structure, especially a corrugated or zig-zag shape.

Description

The invention relates to a method for producing an inhomogeneous sponge, in particular for use as an ink storage, and one made by the process Sponge.

Sponges used as ink storage in inkjet printers or so-called "inkjet systems" are used are known from the prior art. They consist of one large number of open pores (capillaries). These pores are when used with ink filled. The ink is stored in the sponge and is only by using the the wetting of the pore generated capillary force again. In this way it is created negative pressure in the ink system by using a sponge as an ink reservoir, which results from the capillary action of the individual sponge pores. Insist If only sponged from pores of a defined size, the vacuum would be during the ink removal from the sponge, apart from the hydrostatic pressure of the ink column, constant.

In the sponges currently produced, the pore sizes or pore volumes are distributed statistically, i.e. their frequency can be approximated by a Gaussian distribution. Such a Gaussian distribution of the pore size is shown in FIG. Becomes a sponge filled with ink, the pore size distribution plays an important role. Depending on whether the contact angle between the sponge material and the ink is greater or less than 90 ° First fill the large or small pores until the entire sponge has absorbed ink Has. When ink is removed from the sponge, the large ones first Pores are emptied because they generate the smallest capillary force, i.e. at the slightest negative pressure can be emptied. Once all the large pores have been emptied, the ink will gradually become out smaller pores are used, but for which a correspondingly stronger negative pressure is applied must become. This behavior causes the so-called "sponge curve", which is shown in Fig. 2 is shown. As can be seen from this, the vacuum in the first part of the curve increases System because gradually smaller pores have to be emptied. In the middle part of the The ink is taken from the main portion of the pores of a defined similar size. The straight line that is almost present in this area is the result of the decreasing line when ink is removed hydrostatic pressure of the ink column. Always in the back of the curve Smaller capillaries of the sponge are used, which in turn results in a curve noticeable. Eventually the ink end is reached, which is reflected in one expresses a sharp rise.

Please note that emptying a pore is only possible if the pore can be ventilated. This means that the volume of ink removed must be replaced by a corresponding one Air volume can be compensated. This has the consequence that the sponge from the outside is emptied inwards (in this context, the outside means the directly ventilated one Sponge page).

According to the above statements, different pore sizes and therefore capillary forces result a corresponding distribution of the ink in the sponge. The ink wets the Sponge well, then the ink will spread in the sponge so that as small as possible Capillaries are filled, while the large capillaries are only used when one appropriate amount of ink must be stored in the sponge. A corresponding redistribution the ink in the sponge also takes place during ink removal. If the Aeration of the large capillaries mentioned above is possible, the ink becomes the smaller Capillaries. This process is used according to the prior art in order to Transport ink in a desired direction. As a result, an inhomogeneous attempt is made To achieve pore distribution.

According to the prior art, the inhomogeneous pore distribution becomes towards the ink outlet in that the sponge locally through a nozzle protruding into the container space is compressed. This will create the desired capillary hierarchy (smaller pores at the ink outlet) stamped on the homogeneous sponge inside the cartridge. Such a process is known for example from US 6,086,193. Here, the sponge is made by external Forced kept in this partially compressed state. Depending on the elasticity of the As a result, sponge material can have a constant, high pressure on cartridge walls and cartridge cover are exercised. It is also such a compression process not reliably reproducible. Depending on the sponge and container geometry as well the materials involved differ when assembling the sponge Sponge shapes and thus capillary distributions.

Another disadvantage of this method is that it compresses the Sponge can cause wrinkles. This has undesirable small sponge pores inside the sponge, which often cannot be emptied because of penetrating Air this volume of ink is cut off from the ink flow. A disadvantage of this cartridge design is finally the nozzle protruding into the container space. This takes up a part of the container volume and thus reduces the maximum storable Amount of ink and thus user benefit.

The object of the invention is to use a method for producing a sponge specify as ink storage in ink cartridges, with the disadvantages described can be largely avoided.

The object is achieved by a method according to claim 1. According to this Process is a body made of a porous thermoplastic material between at least two plates of a pressing device arranged and compressed under the action of heat and thermoplastic deformed, creating an inhomogeneous and irreversible density distribution is formed, or one or more density gradients. With In other words, the process is carried out so that different areas of the porous body have different pore densities.

After the sponge has cooled, it maintains its inhomogeneous pore density distribution at. Due to the different degrees of compression during the procedure The sponge material creates a sponge with the mean pore volume inside of the sponge body varies. 1, this means the distribution of the pore size can have a positive or negative excess, it can be asymmetrical, flat or steep or it can be two or more peaks. The advantage of this method is in particular in that the different pore volumes within the body also after the Keep cool. The sponge can therefore be cut or shaped in this way be that it can be inserted into a corresponding ink cartridge. Since the Sponge inside the ink cartridge no longer needs to be compressed are cartridge walls and the cartridge cover are not exposed to constant pressure. There is also no need for an inner nozzle to close areas of different pore volumes produce. The entire space inside the cartridge is therefore used for ink storage to disposal.

The inhomogeneous distribution of the pore density or pore sizes or pore volumes becomes achieved according to the process by the different degrees of compression of individual areas of the porous sponge material under the influence of heat, i.e. through thermoplastic deformation of the sponge material.

This can be done, for example, by suitable selection of the sponge material, the process temperature, the compression factor, the geometry of the body and the duration of the compression. Another possibility is that the different parts of the porous body be heated to different degrees. In areas of higher temperature the sponge structure softer than in areas with lower temperatures, and therefore under pressure deformed more thermoplastic, thus reducing the pore volume. By cooling of the sponge becomes this changed pore size distribution within the sponge body "Frozen". With different heating of different areas of the It must be ensured that the temperature of the sponge body is never at any point Melting point of the sponge material used, otherwise the entire pore structure can be destroyed.

A temperature gradient inside the body during the method according to the invention can also be generated in that the shutter speed of the pressing device is relatively short is chosen. That is, the pressing process is ended before a homogeneous sponge body Temperature distribution has set. The choice of the respective shutter speed is also depending on how thick the sponge material is.

The local compression factor, i.e. the compression factor in a certain range of the sponge, plays a role in setting a density gradient within the Body. The compression factor is the ratio of unpressed to pressed Understand volume of the sponge. To create a density gradient inside of the body, the sponge material is compressed more in some places than in others, i.e. the local compression factor varies within the body. For example can also be achieved in that the thickness of the sponge is not uniform is above its footprint. Another option is to put the sponge in the Arrange press device so that it is only partially covered by the press plates and thus a part of the sponge body is compressed and heated. Beyond that it is also possible to make the pressing surface of the plates inconsistent. That the bottom can have elevations and / or depressions. This option is described below be discussed in more detail. These are just a few examples of how a density gradient is to be trained within the body.

The method according to the invention differs from previously used methods of Thermocompression as z. B. in JP 04357046, characterized in that the process is aimed at training a density gradient. While so far thermocompression has been used to achieve pores that are sized not be produced by the foaming process, the known method according to the invention modified so that permanent inhomogeneous sponge structures arise.

The sponge materials known in the prior art can be used as sponge bodies for Ink sponges are used. The porous material of the sponge body can in particular contain one or more of the following: polyurethane polyether; Polyurethane-polyester; Melamine. In addition, the usual for these sponges can be used as required Additives are added. The porosity of these materials is determined by the usual Foaming process generated.

The heat is preferably exerted on the body by at least one of the plates. This means that the plate (s) will be heated before the compression process starts. During the compression process, heat is transferred to the porous body over the side surfaces of the same, which are connected to the plate (s) stand. In this case, the heat penetrates from these side surfaces into the interior of the porous body. This creates a temperature gradient during the pressing process inside the porous body, which results in a density gradient.

However, two plates can also be used, both of which are heated become. In this case, the center of the porous body is least heated, so that the original pore volumes are retained or only slightly reduced (this naturally assumes that the shutter speed of the pressing device is so low is kept that no uniform temperature distribution can occur in the body). The side areas of the porous body that come into contact with the press plates become in contrast, heated more and therefore softer. These parts are therefore becoming stronger compressed, and the pore volumes reduced accordingly. Because preferably in ink cartridges the smallest pore volume of the porous body only at a certain point is provided, namely adjacent to the ink outlet, the sponge body in this case be cut accordingly after it has cooled.

In another embodiment, only one of the plates is heated. In this case the pore volume, starting from the side that the compression process to the heated plate limits to increase steadily through the thickness of the body. Thus, at this embodiment possibly on a subsequent cutting of the porous Body to be dispensed with, since the area of minimal average pore size is only on one side of the porous body.

Depending on the sponge material selected, the plate temperature is between approximately 100 ° C and 250 ° C. As already mentioned, care must be taken that the temperature of the porous The body never reaches the melting temperature of the sponge material.

The compression process takes about 10 to 90 minutes. The cooling of the Body preferably takes place after the end of the compression process.

A value in the range between 1.5 and. Is suitably used as the local compression factor 10 selected. The pore volumes of the original porous material can be based on this Partially reduced by a multiple.

A generally known pressing device is used to carry out the method according to the invention used, between their stamps in the form of two plane-parallel plates The body is introduced from porous material and through which the body is avoided is subjected to pressure by transverse forces.

As already mentioned, it is also possible to heat up only one of the two plates. However, both or all of the plates can also be heated, but to different degrees Temperatures. Also in this case there will be a temperature gradient inside the porous Train your body. The embodiment is particularly advantageous when the existing pore volume of the porous body as a whole, but with different Degree to be reduced.

According to one embodiment, plates can be used in the method according to the invention be, which have a flat surface on their side facing the body. In this case, a density gradient can also be achieved in that the one used Sponge body three-dimensional on its sides facing the plates structured, in particular corrugated or serrated, surface. In other words the body may have a non-uniform thickness over its base area. The thicker ones Areas of the body are then compressed more, i.e. the local compression factor is bigger in these places. Accordingly, the pore volume decreases at these points.

According to a further embodiment, plates are selected which are based on the Body-facing side a three-dimensionally structured, especially wavy or serrated Have surface. In this case, the press plates act like an embossing stamp under the influence of which the local compression factor is varied, since the sponge material in those places where the plates bulge away from the sponge body there is a weaker compression. A similar effect can, for example can also be achieved in that several printing plates are used, each of which exert different pressures.

According to one variant, a sponge body is used in the method according to the invention cuboid body used. This variant is particularly related to structured press plates advantageous.

After the compressed sponge body has cooled, it can, preferably by Cut up, divided into several units. This can also be used for a special Cartridge necessary shape of the sponge can be made.

The sponge produced by the method according to the invention is characterized in that that its average pore volume or its pore distribution within the sponge varied.

According to a particularly preferred embodiment, the sponge formed has one Area of minimal mean pore volume in an edge area of the sponge. That the average pore volume, starting from this edge area, increases towards the inside of the Sponge body towards. This edge area becomes contiguous when the sponge is used arranged on an ink outlet of the cartridge, so that the anisotropy of the Capillary forces run in the desired direction.

The sponge according to the invention can be designed so that its average pore volume decreases continuously from one side to the other. The characteristic sponge curve is significantly smoothed in an advantageous manner compared to FIG.

Fig. 1 eine Verteilung der Porengröße in einem herkömmlichen Tintenschwamm;

Fig. 2 den Unterdruckverlauf bei kontinuierlicher Entnahme von Tinte aus einem Schwamm;

Fig. 3 ein Beispiel des Strömungsverlaufes von Tinte in einer Patrone;

Fig. 4 ein Beispiel eines in eine Patrone eingesetzten Schwammes nach dem Stand der Technik;

Fig. 5a bis 5c den Vorgang einer homogenen Schwammkompression unter Druck- und Wärmeeinwirkung;

Fig. 6a bis 6c eine Ausführungsform des erfindungsgemäßen Verfahrens;

Fig. 7a bis 7c eine zweite Ausführungsform des erfindungsgemäßen Verfahrens;

Fig. 8a und 8b eine dritte Ausführungsform des erfindungsgemäßen Verfahrens und

Fig. 9a bis 9c eine vierte Ausführungsform des erfindungsgemäßen Verfahrens.

The invention is explained below with reference to the accompanying drawings. In this show:

1 shows a distribution of the pore size in a conventional ink sponge;

2 shows the course of negative pressure with continuous removal of ink from a sponge;

3 shows an example of the flow pattern of ink in a cartridge;

4 shows an example of a sponge inserted into a cartridge according to the prior art;

5a to 5c the process of a homogeneous sponge compression under the action of pressure and heat;

6a to 6c an embodiment of the method according to the invention;

7a to 7c a second embodiment of the method according to the invention;

8a and 8b a third embodiment of the method according to the invention and

9a to 9c a fourth embodiment of the method according to the invention.

Figure 1 shows the relative distribution of the pore size or the pore volume, as in a conventional ink sponge. The associated pressure curve Figure 2 shows the removal of ink from such a sponge.

In Figure 3 are the flow conditions of the ink within the ink storage sponge an ink cartridge shown. When the ink is removed through the designated ink removal opening, or the outlet, the removed ink must pass through continuously flowing ink can be replaced from other sponge areas. This ink shift within the sponge, or this afterflow of ink, is characterized by a Sponge with an inhomogeneous pore distribution supports when the pores to the ink outlet are getting finer and finer.

One way to achieve this capillary gradient due to decreasing pore diameter towards the outlet is shown in FIG. Here is the protruding into the cartridge Spigot, additionally supported by ribs on the container lid, the sponge locally compressed at the outlet, reducing the pore volume.

The principle of thermal sponge compression is shown in FIGS. 5a to 5c: A body 1 made of a porous material is here between two plates 2, 3 Press device arranged and under the action of pressure and heat to a fraction compressed to its original volume. After compression, it is replaced by the Plates exerted pressure, the porous body taking its compressed form maintains. The homogeneous reduction of the pore volume compared to the process The initial state, and thus the increase in capillary action, takes place here in particular towards normal to the plates.

According to the invention, this thermocompression process is carried out inhomogeneously, like this is shown in Figures 6a to 6c. In this case, the plates 2, 3 are heated to the supply heat to the porous body 1 during the compression process. The Shutter speed kept so short that there is no uniform temperature over the whole porous body 1 can adjust. As a result, different, different strengths compressed areas within the porous body 1 arise. So are the edge areas 1a more compressed and therefore have a lower average pore volume than that central area 1b. As the sponge cools, this changes the pore size distribution frozen. Splitting such a sponge in the middle, like this in figure 6b, a sponge with an inhomogeneous pore distribution is obtained, in which the Pore size decreases from top to bottom, as shown in Figure 6c. When using a such a sponge in an ink cartridge, the compacted end of the ink outlet is assigned, the ink then flows to the ink outlet without a corresponding Compression of the sponge must take place in the cartridge.

FIGS. 7a to 7c show a further possibility of generating an inhomogeneous pore distribution shown in the sponge body 1. In this case, the top plate 2 is on a heated to a higher temperature than the lower plate 3. During the compression process the sponge structure becomes softer due to the increased heat in the upper area, than is the case in the lower area of the sponge and is therefore more compressed. It this results in a one-dimensional anisotropy of the pore distribution in the sponge.

Figures 8a and 8b represent a third way of carrying out the invention Process there. In this case, no plane-parallel, i.e. H. cuboid, sponge plate used, as is the case in the previous examples, but a sponge plate with three-dimensional surface structure. This sponge plate structured in this way compressed, you get again a plane-parallel plate, but with an inhomogeneous pore distribution. In this case, the inhomogeneous pore distribution results from the fact that the areas 1a larger thickness can be compressed more. By cutting out the individual Sponges from the entire plate create an inhomogeneous sponge for each cartridge defined pore distribution. Examples of cut edges for subdivision into single sponge areas are represented by lines 4. The different pore distribution can Example serve the hydrostatic pressure component when ink is removed to compensate for slanted sponge cartridges. Generally, this example works therefore, by shaping the original sponge during the forming process to be plane-parallel Sponge plate to create a defined inhomogeneous pore distribution.

A last example of a method according to the invention is shown in FIGS. 9a to 9c. To produce a sponge with an inhomogeneous pore distribution, the plates 2, 3 of the pressing device in this case designed as a stamp. This creates Sponge zones 1a, which are characterized by stronger compression than sponge zones 1b are. It can also be used to adapt the sponge to a specified one Ink tank geometry done.

The exemplary embodiments specified above can be combined with one another as desired become. For example, it is possible to compress a structured sponge to use different plate temperatures.

Claims (15)

A process for producing a sponge, which is particularly suitable for use as an ink reservoir, characterized in that a body (1) made of a porous thermoplastic material is arranged between at least two plates (2; 3) of a pressing device and an inhomogeneous one under the influence of pressure and heat Pore density distribution is generated in the body (1), wherein the body (1), after it has cooled, is divided into several units by a cutting process. A method according to claim 1, characterized in that the porous material contains at least one of the following components: polyurethane polyether, polyurethane polyester, melamine. Method according to claim 1, characterized in that the heat is exerted on the body by at least one of the plates (2; 3). A method according to claim 3, characterized in that the temperature of the at least one plate is between about 100 ° C and 250 ° C. Method according to one of claims 1 to 4, characterized in that the duration of the compression process is approximately 10 to 90 minutes. Method according to one of the preceding claims 1 to 5, characterized in that the local compression factor is approximately 1.5 to 10. Method according to one of the preceding claims 1 to 6, characterized in that the body (1) made of porous material is introduced between two plates (2; 3) of the pressing device which are arranged opposite one another. Method according to one of claims 1 to 7, characterized in that the plates (2; 3) of the pressing device are heated to different temperatures. Method according to one of the preceding claims, characterized in that plates (2; 3) are selected for the pressing device which have a flat surface on their side facing the body (1). Method according to one of Claims 1 to 8, characterized in that plates (2; 3) are selected for the pressing device which have a three-dimensionally structured, in particular corrugated or serrated, surface on their side facing the body (1). Method according to one of the preceding claims 1 to 10, characterized in that a cuboid body is used as the body (1). Method according to one of Claims 1 to 10, characterized in that the body (1) used is a body which has a three-dimensionally structured, in particular corrugated or serrated, surface on its sides facing the plates (2; 3). Sponge, in particular for use as an ink reservoir, which according to a Method according to at least one of the preceding claims, wherein the mean pore volume within the sponge varies. Sponge according to claim 13, characterized in that there is a region of minimal mean pore volume adjacent to an edge region of the sponge. Sponge according to one of the preceding claims 13 to 14, characterized in that its average pore volume decreases continuously from one side to the opposite side.

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