Patent Application
20130127950
The present invention relates to a coating for providing a wetting gradient to an orifice surface, to a method for applying said coating and to an ink jet printer comprising an orifice plate provided with said coating.
In a known print head, the print head comprises an orifice surface, the orifice surface having arranged thereon at least one orifice. Ink is ejected from the print head through said orifice. When printing, ink may be spilled on the orifice surface of the print head. Ink present on the orifice surface close to an orifice may have a negative influence on the performance of a print head during jetting of the ink. Therefore, it is important to prevent presence of ink on the orifice surface close to an orifice.
EP 2 072 261 describes an orifice surface, having applied thereon a wetting gradient around an orifice, i.e. having a wettability changing with a distance from the orifice. The wettability of a surface is correlated to the contact angle between a surface and a droplet present on that surface. The more wettable the surface is, the smaller is the contact angle. The smaller the contact angle, the more spreading of the droplet of fluid over the surface. On a wetting gradient, as disclosed in EP 2 072 261 and as used herein, the wettability of the surface gradually changes as a function of the position on the surface. As a consequence, the contact angle between the surface and a droplet on that surface changes as a function of the position on the surface. The droplet tends to move from a part of the surface having lower wettability towards a part of the surface having higher wettability. Hence, a wetting gradient generates a driving force for a droplet to move on the surface towards a part having lower wettability.
In EP 2 072 261, the wetting gradient is created on an orifice surface by providing the orifice surface with a patterned anti-wetting coating, wherein the pattern is more dense close to an orifice and becomes less dense with increasing distance from the orifice. As a consequence, a wetting gradient is provided on macroscopic scale, by providing a pattern on a microscopic scale. Hence, this wetting gradient prevents the presence of ink close to an orifice. However, since the wetting gradient according to EP is provided by providing a pattern on a microscopic scale, and not, by a process providing a random distribution of the coating forming the wetting gradient, the wetting gradient created according to EP 2 072 261 does not provide a wetting gradient on a microscopic scale. Moreover, it is difficult and consequently expensive to accurately apply such a patterned coating around a nozzle.
It is an object of the invention to provide a wetting gradient on an orifice surface, wherein the wetting gradient is provided both on a macroscopic and a microscopic scale. It is a further object of the invention to provide a method for applying a wetting gradient on an orifice surface in an efficient, cost-efficient and accurate way.
The object of the invention is achieved in a coating for providing a wetting gradient to an orifice surface around an orifice, the coating providing anti-wetting properties to the orifice surface, the coating having a local coverage, the local coverage being highest close to the orifice, the local coverage decreasing gradually with decreasing distance from the orifice, wherein the coating is distributed randomly.
A print head, used in an ink jet printer, comprises an orifice surface, the orifice surface having arranged therein at least one orifice. Marking material, for example ink, is ejected through the orifice onto an image-receiving member. Marking material may be spilled on the orifice surface. Marking material present on the orifice surface may interact with marking material that is ejected through the orifice, thereby influencing the jetting performance of the print head. To prevent the jetting performance being influenced by marking material present on the orifice surface, the marking material should be removed from the vicinity of the orifice. It is known to remove marking material from the vicinity of an orifice by applying a wetting gradient around the orifice. As above mentioned, it is desirable to control a wetting property of the ink and the orifice surface such that a wetting gradient is provided, e.g. around the orifice.
In the present invention, a coating is formed on an orifice surface upon bonding of a compound for forming the coating to the orifice surface. The amount of coating that is locally bond to the orifice surface per unit area is the local coverage of the coating. The coverage of coating decreases gradually with increasing distance from the orifice. This is in contrast to, for example, a coating provided on a surface, wherein the coating is provided as a pattern around the orifice, the coating having a homogeneous coverage throughout the pattern. Outside of the pattern, there is no coating. Although in the latter example, the coverage of coating decreases with increasing distance from the orifice—close to the orifice the coating has a homogeneous, non-zero coverage, outside of the pattern the coverage is zero—the coverage in that example does not decrease gradually. The advantage of the gradual decrease in coverage is that a driving force for a droplet of marking material to move, said driving force being provided by the continuous wetting gradient provided by the coating according to the present invention, is present throughout the coated surface and not only on a border of a coated and a non-coated area of a surface. In the coating according to the present invention, the coating is distributed to the surface randomly.
From EP 2 072 261, a coating is known that has a coverage of coating that gradually decreases with increasing distance from the orifice. However, that coating is a patterned coating. The coating providing the wetting gradient according to EP 2 072 261 is applied by applying a pre-determined pattern of a first compound to the orifice surface. A second compound is subsequently bond to the first compound applied on the orifice surface, thereby forming a coating on the orifice surface. The pattern is consequently provided as a pattern. The pattern is a pre-determined pattern. To apply this pattern, the first compound has to be applied on predetermined positions on the orifice surface. Bonding of the second compound to the first compound provides a coating on the orifice surface. The predetermined pattern yields a wetting gradient on a macroscopic scale. However, on a microscopic scale, the patterns consist of islands having a homogeneous, non-zero coverage of coating. These islands having a homogeneous coverage of coating are alternated by regions having no coating at all. Consequently, the coating providing the wetting gradient according to EP 2 072 261 does not provide the wetting gradient on a microscopic scale.
The coating according to the present invention, on the other hand, is applied to the orifice surface in a random fashion. The orifice surface may be regarded as a surface, comprising a certain number of places to which a compound for forming the coating may bond. A place to which a compound for forming the coating may bond, may be for example an atom or a group of atoms, to which the compound may bond. For example, if the orifice surface is a silicon surface, the place, to which the compound may bond may be a silicon hydroxide group. If the orifice surface is a layer of gold atoms, the place to which a compound, for example a thiol compound, may bond is a gold atom. If a compound is bond to every place to which a compound may bond, the maximum coverage of the surface is reached and a monolayer is formed. However, it is also possible to bond a compound to only a certain percentage of the places to which a compound may bond. In the coating according to the present invention, the percentage of places to which a compound has bond, decreases with increasing distance from the orifice. However, the specific places to which a compound bonds and to which no compound bonds are divided randomly. As a consequence, in the coating according to the present invention, there are no regions having a homogeneous coverage of coating alternated by regions having a zero coverage of coating. Instead, there is a random distribution of the coating on the orifice surface. Therefore, a gradient is not only provided on a macroscopic scale, but also on a microscopic scale.
Because the coating is randomly distributed, the coating may be e.g. applied to the orifice surface in a process, wherein the coating is statistically distributed on the orifice surface.
In an aspect of the invention, a method for applying a wetting gradient on an orifice surface is provided, the method comprising the steps of:
In the present invention, a wetting gradient is applied on an orifice surface in a two-step procedure. In order to form a coating on the orifice surface, a compound for forming the coating on the orifice surface may be required. In the first step of the procedure in accordance with the present invention, a compound for forming the coating on the orifice surface is provided.
In the second step of the procedure the compound is locally bond to the orifice surface, thereby forming a coating for providing a wetting gradient to the orifice surface. The amount of compound that locally bonds to the orifice surface is locally controlled such that the local coverage is highest close to the orifice, and the local coverage decreases gradually with decreasing distance from the orifice and such that the coating is distributed randomly. Provided that the compound is selected to provide wetting or anti-wetting property to the marking material to be used, a wetting gradient may be provided in accordance with the present invention.
In an embodiment, in step a), the orifice surface is arranged to be in contact with a medium comprising the compound for forming a coating on the orifice surface; and in step b), the orifice surface is locally irradiated through the medium with electromagnetic radiation, thereby locally supplying energy to the orifice surface and the compound to enable the orifice surface and the compound to locally bond to form the coating on the orifice surface, wherein in step b) the method further comprises;
In the first step, the orifice surface is arranged to be in contact with the medium comprising the compound for forming the coating on the surface. To form the coating on the orifice surface, the compound for forming the coating may need to be in contact with the orifice surface. The medium may be, for example, a liquid solution comprising the compound, wherein a suitable solvent is used to dissolve the compound. Alternatively, the medium may be a gas, wherein the compound for forming the coating is present in the gas phase. In any case, the medium should allow suitable contact with the orifice surface and allow transfer of the molecules of the compound towards the orifice surface.
In the second step, the orifice surface is locally irradiated through the medium with electromagnetic radiation, thereby locally supplying energy to the orifice surface and the compound to enable the orifice surface and the compound to locally bond to form the coating on the orifice surface. In order to locally form a coating on the orifice surface, the orifice surface and the compound for forming a coating have to bond. Energy is needed to form the bond. Therefore, energy has to be supplied to the orifice surface and the compound for forming the coating such that a bond between the orifice surface and the compound is formed locally and the orifice surface is locally provided with the coating. The energy is provided by irradiating with electromagnetic radiation, for example visible light, UV-light or IR radiation. The orifice surface is irradiated through the medium comprising the compound. As a consequence, energy is supplied to both the orifice surface and the compound, thereby providing the energy necessary for bonding the compound and the orifice surface. The medium may be selected suitably, such that not all energy is absorbed by the medium.
Zuilhof at al., Langmuir 2009, 25(19), 11592-11597 describes the formation of alkene-derived monolayers on silica surfaces. A silica surface is irradiated with light to react the silica with alkenes, that are present in the vicinity of the silica surface. Zuilhof at al. also describes the use of a mask to create patterns of monolayers on a silica surface. On the parts of the orifice surface that are covered by the mask no monolayer is formed, whereas a monolayer is formed on parts of the orifice surface that are not covered by the mask. However, even if the monolayer of alkenes would be a monolayer of anti-wetting material, then the monolayer would still not provide a wetting gradient.
In the second step, a suitable amount of energy is supplied to the orifice surface and the compound such that locally a higher coverage of coating is obtained on the orifice surface by locally supplying a larger amount of energy. Energy is provided to form the bond between the orifice surface and the compound for forming the coating. By controlling an amount of energy, the quantity of compound that bonds to the orifice surface may be controlled. If a larger amount of energy is supplied, a larger quantity of compound may bond to the orifice surface, providing a higher coverage of the coating on the orifice surface. If a smaller amount of energy is supplied, a smaller quantity of compound may bond to the orifice surface, providing a lower coverage of the coating to the orifice surface. Hence, by locally supplying a larger amount of energy, locally a higher coverage of coating may be obtained. Provided that the compound is selected to provide wetting or anti-wetting property to the marking material to be used, a wetting gradient according to the present invention may be provided.
The amount of energy supplied to the orifice surface by irradiation may be controlled by controlling the wave length of the electromagnetic radiation. The energy of a photon of electromagnetic radiation is related to the wavelength of the radiation:
wherein E is the energy of the photon, h (Planck's constant) and c (speed of light) are constants and wherein λ is the wavelength of the electromagnetic radiation. Therefore, the amount of energy supplied may be controlled by supplying electromagnetic radiation of a suitable wavelength. For example, UV radiation has a higher energy than visible light, and visible light has a higher energy than IR radiation. Of course, any wavelength used in the method should at least be suited to bond the compound and the surface to a certain extend. Since not each and every wavelength may be absorbed by the compound and/or surface, the wavelengths should be selected corresponding to the materials used.
In an embodiment, an amount of energy is supplied close to the orifice and a smaller amount of energy is supplied at a larger distance from the orifice. The smaller the amount of energy supplied to the orifice surface, the less compound bonds to the orifice surface and the lower is the coverage of the coating applied to the orifice surface. Therefore, in this embodiment, the coverage of the coating is highest close to the orifice. If the coating is an anti-wetting coating and the coating is applied to the orifice surface, the orifice surface close to an orifice has a low wettability. At a larger distance from the orifice, the orifice surface is provided with a lower coverage of the coating. In case of an anti-wetting coating, the orifice surface further away from the orifice has a higher wettability. Consequently, a fluid present on the orifice surface, for example a droplet of marking material, experiences a wetting gradient and flows away from the orifice.
In an embodiment, the source of electromagnetic radiation produces a beam of electromagnetic radiation, said beam having a non-uniform intensity profile, wherein the beam is directed to an orifice and wherein the radiation is most intense at a position of the orifice. A source of electromagnetic radiation may generate a beam of radiation. The beam may have a non-uniform intensity profile, wherein more radiation is emitted in one direction and less radiation is emitted in another direction. If a beam of electromagnetic radiation having a non-uniform intensity profile is used to irradiate the orifice surface and the compound for forming the coating, the amount of energy supplied may differ for various parts of the orifice surface. If the highest intensity is directed to the orifice, the radiation is most intense at a position of the orifice and it may decrease with increasing distance from the orifice. As a consequence, a wetting gradient may be provided around an orifice by radiating an orifice surface with a beam of electromagnetic radiation, the beam being directed to the orifice.
Alternatively, the wetting gradient may be provided by radiating an orifice surface with a plurality of beams of electromagnetic radiation, wherein the beams of electromagnetic radiation show interference, such as constructive interference, providing an non-uniform intensity profile of the energy supplied to the orifice surface.
In an embodiment, the beam is a laser beam and a lens is placed between the source of the laser beam and the orifice surface to diverge the beam and to provide a larger amount of energy close to an orifice and a smaller amount of energy away from the orifice. A leaser beam is a beam that is usually non-divergent; radiation is emitted in one direction only. Hence, by irradiating using a laser beam, energy is supplied to one specific point on the orifice surface only. However, if a lens is placed in between the source of the laser and the orifice surface, the laser beam passes the lens and the beam may be diverged, such that not only one specific point, but a larger area of the orifice surface is irradiated. The amount of energy supplied may differ for each point in the area, such that locally, for example, close to an orifice, a larger amount of energy is supplied. Locally supplying a larger amount of energy to the orifice surface may result in the formation of a coating on the orifice surface, locally having a higher coverage.
In an embodiment, a mask is used to expose an area of the orifice surface to radiation. A mask may be placed between the source of electromagnetic radiation and the orifice surface. The mask may be in contact with the orifice surface or may not be in contact with the orifice surface. The mask may expose an area of the orifice surface to be irradiated and prevent another area from irradiation. When irradiation of an area of the orifice surface is prevented, no energy may be supplied to the orifice surface and no bond may be formed between the orifice surface and the compound. As a consequence, no coating is applied on the area of the orifice surface, that is covered by a mask. However, a mask may not only be used to create an orifice surface that is divided into predetermined sections, the sections either being provided with the coating or not being provided with the coating. Instead, a mask may also be used to provide an orifice surface that is locally provided with a higher coverage of coating and that is locally provided with a lower coverage of coating, such that a wetting gradient may be provided on the orifice surface. Additionally, the orifice surface may locally not be provided with any coating. The formation of a wetting gradient on the orifice surface by using a mask will be explained in more detail with reference to the below mentioned embodiments.
In a further embodiment, the amount of energy supplied to the orifice surface is controlled by using at least a first and a second mask, wherein the first mask is used to expose a first area of the orifice surface to radiation and wherein the second mask is used to expose a second area of the orifice surface to irradiation and wherein the amount of energy supplied to the first area of the orifice surface differs from the energy supplied to the second area of the orifice surface. A plurality of masks may be used to provide the orifice surface with wetting gradient. A first mask is used to expose a first area of the orifice surface to irradiation. As a consequence, a first coverage of coating is applied to the first area of the orifice surface. Now, the first area of the orifice surface is provided with the coating, whereas the other parts are not provided with the coating. However, no wetting gradient is provided yet on the orifice surface. To convert the area provided with the coating into an area with a wetting gradient, at least a second mask is employed in this embodiment. By using a second mask for exposing a second area of the orifice surface to irradiation and irradiating the surface, after a first coverage of coating has been applied to the first area of the orifice surface, a second coverage of coating is applied to the second area of the surface. The second area at least partially overlaps with the first area. The second area may be smaller than the first area. In that case, the part of the first area that does not overlap with the second area is only provided with a first coverage of coating. The part of the first area that overlaps with the second area of the orifice surface is provided with a second coverage of coating, the second coverage being higher than the first coverage. Provided that the coating is selected to provide either wetting or anti-wetting property to the marking material, a wetting gradient may thus be provided. The difference in coverage of coating of the different areas of the orifice surface provides a difference in wettability for the different areas of the orifice surface. Thus, a driving force may be generated for a droplet of marking material to move from one area of the orifice surface to another area of the orifice surface. Alternatively, the second area may be larger than the first area. In that case, the first area is provided with a larger coverage of coating than the part of the second area that does not overlap with the first area. Also in this case, a wetting gradient may be provided on the orifice surface. Optionally, a third, fourth, fifth, etc. mask may be used to expose a corresponding third, fourth, fifth, etc area of the orifice surface to irradiation and to apply a third, fourth, fifth, etc coverage of coating to the third, fourth, fifth, etc area of the orifice surface, wherein the respective areas of the orifice surface at least partially overlap. The more masks are used, the smoother the wetting gradient that is obtained. Moreover, the smaller the difference in size and position between two areas of the orifice surface, the smoother is the wetting gradient. The different areas (first, second, etc) may be positioned concentrically around an orifice.
In a further embodiment, the amount of energy supplied to the orifice surface by irradiation is controlled by means of optical transmission properties of the mask. A mask, used to expose an area of the orifice surface to irradiation may absorb or reflect all radiation, such that no radiation is supplied to the orifice surface covered by the mask. Alternatively, the mask may have optical transmission properties, such that a predetermined part of the radiation is able to pass through the mask and is thus supplied to the orifice surface. The amount of energy supplied to the orifice surface may be controlled by using a mask having optical transmission properties that enable the formation of a wetting gradient. For example, a semi-transparent mask may be used. By locally varying the optical properties of the semi-transparent mask, the amount of energy that is locally supplied to the orifice surface may be controlled. Alternatively, a mask may be used that is partially non-transparent and partially semi-transparent.
In a further embodiment, at least two of the mask, the orifice surface and the source of electromagnetic radiation move relative to one another. In this embodiment, a mask is used to expose an area of the orifice surface to irradiation. By moving at least two of the mask, the orifice surface and the source of electromagnetic radiation relative to one another, a local exposure time, i.e. a period during which each location is exposed to radiation, may be controlled. As a consequence, each location receives a predetermined amount of energy determined by the exposure time and hence, a local coverage of coating corresponds to the local exposure time.
In a particular embodiment, the amount of energy supplied to the orifice surface by irradiation is controlled by moving at least one of the mask, the orifice surface and the source of electromagnetic radiation with varying velocity. By moving at least one of the mask, the orifice surface and the source of electromagnetic radiation, at least two of the mask, the orifice surface and the source of electromagnetic radiation move relative to one another. As a consequence, the local exposure time may be controlled and may be different for different parts of the orifice surface. For example, by moving with predetermined, different velocities, the local exposure time for a first part of the orifice surface may be a longer period of time than the exposure time for a second part of the orifice surface. This results in a larger amount of energy being supplied to the first part of the orifice surface than to the second part of the orifice surface. As a consequence, a higher coverage of coating is applied to the first part of the orifice surface than to the second part of the orifice surface and a wetting gradient may be provided.
In a further embodiment, the amount of energy supplied to the orifice surface is controlled by using at least a first and a second mask, wherein the first mask is used to expose a first area of the orifice surface to radiation and wherein the second mask is used to expose a second area of the orifice surface to irradiation and wherein the two masks are moved in opposite direction. The part of the surface that is not exposed to radiation by the mask is prevented from radiation. However, in case two masks are used, a part of the surface is only exposed to radiation if it is not prevented from radiation, neither by the first mask nor by the second mask. For example, if the first area of the surface is not prevented from radiation by the first mask, but is prevented from radiation by the second mask, then the first area is not exposed to radiation. Alternatively, if the second area of the surface is not prevented from radiation by the second mask, but is prevented from radiation by the first mask, then the second area is not exposed to radiation. Since the two masks are moved, the area exposed to radiation and the area prevented from radiation change with time. At a certain moment in time, the first and second area start overlapping, i.e.: at that moment, a part of the orifice surface is not prevented from radiation by either of the first and the second mask and the area is exposed to radiation. At that moment, a relatively small part of the surface is irradiated. Upon further movement of the mask, the area that is irradiated becomes larger and consequently, a larger area is irradiated. When the masks are moved even further, the area of the surface exposed to radiation decreases again and a smaller part of the surface is exposed to radiation. As a consequence, the part of the surface that is irradiated when the first and the second area start overlapping and the area that is irradiated when the first and the second area nearly stop overlapping, are irradiated for a longer time than the area that is exposed only when the exposed area has reached a maximum size. Depending on the size of the first and the second area and on the relative speed of the first and the second mask, the part of the surface that is irradiated when the first and the second area start overlapping and the area that is irradiated when the first and the second area nearly stop overlapping, may overlap. Thus, locally, the surface is irradiated for a longer period of time and therefore, locally, a higher coverage of coating may be applied on the surface. Preferably, the part of the surface that is irradiated longest, may be the position of the orifice on the orifice surface. In that case, a part of the surface close to the orifice is irradiated longer and a higher coverage of coating is applied to the part of the surface close to the orifice. In summary, by using two masks that are moved in opposite directions, locally, the orifice surface may be irradiated for a longer time and a larger amount of energy may be supplied to the orifice surface. As a consequence, locally a higher coverage of the coating may be obtained.
In an embodiment, the coating applied in accordance with the steps a) and b) is a first coating, the method further comprising applying a second coating at a part of the orifice surface not coated with the first coating, and wherein one of the first and second coating is a wetting coating and the other one of the first and second coating is an anti-wetting coating. After applying the first coating to the orifice surface in accordance with the present invention, not the entire orifice surface may be coated with the first coating. The first coating may be either a wetting or an anti-wetting coating. After the first coating has been applied, a second coating may be applied. The second coating may be either a wetting or an anti-wetting coating. By applying a second coating, the wetting gradient may be further improved. For example, in case the first coating is an anti-wetting coating and the coverage of the coating depends on the distance from the orifice, being highest close to the orifice, a wetting gradient is obtained and fluid tends to move away from the orifice. By applying a wetting coating on the parts of the orifice surface, not yet provided with a coating, fluid tends to move from the anti-wetting coating to the wetting coating and fluid is removed even further away from the orifice.
In a further embodiment, the second coating is applied by chemical vapor deposition. Chemical vapor deposition (CVD) is an efficient way to provide an area of the orifice surface, that is not provided with a first coating, with a second coating. The second coating has properties that differ from the properties of the first coating.
In an alternative embodiment, the orifice surface comprises at least one orifice, the orifice surface being in fluid communication with a reservoir through the orifice, wherein in step a)
In the first step, a compound for forming a coating is provided in the reservoir. The reservoir is in fluid communication with the orifice surface through the orifice. The compound may be dissolved in a suitable medium. The medium may be, for example, a solvent. In any case, the solvent should be inert towards the compound for forming the coating and towards the orifice surface. Suitable media are for example alkenes, such as octane, decane, but also different alkenes may be used as the medium. Alternatively, also other solvents may be applied, provided that they are inert towards the compound for forming the coating. However, it may not be necessary to dissolve the compound in a medium; instead, neat compound may be provided in the reservoir. The reservoir is at least partially filled with the medium comprising the compound for forming the coating, or with the neat compound for forming the coating because the compound is needed to form the coating on the orifice surface. The reservoir may be filled to such extend, that also the orifice is at least partially filled with the compound and/or medium. The reservoir and the orifice are in fluid communication and hence, at a certain point when filling the reservoir, the orifice will be partially filled, too. In any case, the orifice surface should not be provided with the medium comprising the compound or with the neat compound, because in that case, the compound will bond to the orifice surface forming a homogeneous coverage of compound on the part of the orifice surface that is provided with the medium and hence, no gradient will be obtained.
In the second step the compound for forming the coating is evaporated. The medium, comprising the compound for forming the coating may be evaporated as well, but this is not necessary. The compound, upon evaporation, diffuses through the orifice. After diffusing through the orifice, the compound for forming the coating diffuses away from the orifice and thereby creates a gradient of concentration in the vapour phase, whereby the concentration of the compound is highest close to the orifice. The compound for forming the coating and the material of the orifice surface are suitably selected, such that the orifice surface and the compound for forming the coating bond spontaneously (without the need of additional energy) under the conditions applied for conducting the method in accordance with the present invention.
In the second step, the coating is formed on the orifice surface upon bonding of the compound for forming the coating to the orifice surface. The more compound for forming the coating bonds to the orifice surface, the higher is the coverage of the coating obtained. Because there is a gradient in concentration in the vapour phase of the compound for forming the coating and the concentration is highest close to the orifice, more compound bonds to the orifice surface at a position close to the orifice than to the orifice surface at a position further away from the orifice. Hence, the gradient in concentration in the vapour phase is transferred to the orifice surface and a higher coverage of coating is obtained close to the orifice, whereas a lower coverage of coating is obtained further away from the orifice. Provided that the compound is selected to provide wetting or anti-wetting property to the marking material to be used, a wetting gradient according to with the present invention may be provided. Please note that there is an upper limit to the coverage and supplying more compound by evaporating the compound does not lead to an even higher coverage. Therefore, the evaporation of the compound is suitably controlled, for example by controlling the temperature and pressure or by selecting a suitable compound for forming the coating. Moreover, by controlling parameters such as temperature, pressure and period of time during which the compound is evaporated, and by selecting a suitable compound for forming the coating, control is provided over the formation of the coating providing the wetting gradient to the orifice surface in accordance with the present invention. Moreover, by suitably controlling the environment in which the compound is evaporated, the occurrence of circumstances which may hamper the bonding of the compound for forming the coating to the orifice surface may be prevented. For example, the presence of contaminants, which may bond either to the orifice surface or to the compound, thereby preventing the bonding of the compound for forming the coating to the orifice surface may be prevented. This may be done, for example, by selecting a suitable medium or by selecting a suitable gas composition for forming the atmosphere surrounding the orifice surface and the reservoir.
In an embodiment, in step b)
an airflow is generated in a direction substantially parallel to the orifice surface to control the direction and the shape of the coating applied on the orifice surface around the orifice. After evaporation of the compound and diffusion of the compound through the orifice, the compound diffuses away from the orifice and bonds to the orifice surface. In this way, the gradient in concentration of the compound in the vapour phase is transferred to the orifice surface, creating a wetting gradient on the orifice surface. Absent any driving force, the compound will diffuse away from the orifice equally in all directions. Consequently, a wetting gradient will be obtained that is symmetrical with respect to the orifice. As a result, a droplet of fluid will experience an equal driving force to flow away from the orifice, irrespective of on which side of the orifice the droplet is located. However, in some cases, it may be preferred to have a wetting gradient that is stronger in one direction, than in another direction. For example, if the orifice surface of a print head in a printing device is placed in a vertical position, gravity provides an additional driving force for a droplet of fluid to move. To compensate for this additional driving force, the wetting gradient around the orifice may be adapted by adapting the shape of the coating applied on the orifice surface to provide a gradient that is stronger on one side of the orifice than on another side of the orifice. This object may be achieved by generating an airflow substantially parallel to the orifice of the surface in step b) of the method. Compound present in the vapour phase experiences a driving force to move in the direction of the airflow. The combination of the diffusion process and the airflow, which together provide the driving forces for the compound to move in the vapour phase results in the formation of a wetting gradient, wherein the distance between the orifice and the edge of the gradient is smaller in a direction downstream with respect to the airflow than in a direction upstream with respect to the airflow. Thus, the gradient will be stronger in one direction than in another direction. It will be clear to the person skilled in the art that the airflow may alternatively be a flow of inert gas. In any case, the composition of the gas phase should not hamper the bonding of the compound to the orifice surface.
In an embodiment, in step a), a layer of porous material is placed on the orifice surface to control the diffusion of the compound. The diffusion of the compound in the vapour phase will be different, respective of whether the compound diffuses through a gas or diffuses through a porous material. In a porous material, there are small channels and cavities within the material. The compound for forming the coating, once it has entered into the channel or the cavity of the porous material, diffuses through these channels and cavities. Hence, the porous material influences the diffusion process. As a result, the distance over which the compound diffuses in the vapour phase may be suitably controlled by placing a layer of porous material on the orifice surface, thereby controlling the area over which the wetting gradient extends on the orifice surface. Not only the channels within a layer of material may influence the diffusion process, also the surface conditions, in particular the roughness of the surface of said layer, may influence the diffusion.
In an embodiment, in step b), the pressure in the reservoir is reduced to improve evaporation of the compound for forming the coating. Generally, the volatility of a compound increases with decreasing pressure. Hence, by lowering the pressure in the reservoir, the compound for forming the coating will evaporate quicker and consequently, the orifice surface can be provided with a coating in a shorter period of time.
In an embodiment, in step b), the temperature of the compound for forming the coating is controlled to improve control over the evaporation of the compound for forming the coating. The higher the temperature, the higher is the rate of evaporation of the compound. Consequently, more compound evaporates and more compound may bond to the orifice surface for forming the coating. Alternatively, the compound may be cooled. Upon cooling of the compound, evaporation of the compound will be slower. In case the evaporation is slower, it may be easier to suitably control the evaporation of the compound and the subsequent formation of the coating on the orifice surface.
In an embodiment, the orifice surface and the reservoir for containing the compound are placed in a closed environment. It is important to control the relevant parameters, such as temperature, pressure, presence of water vapour, etc., in the environment of the reservoir and the orifice surface to thereby control the evaporation of the compound and the formation of the wetting gradient on the orifice surface. By placing the orifice surface and the reservoir for containing the compound in a closed environment, the environment may be suitably controlled. Thus, parameters such as pressure and temperature may be suitably controlled. Also presence of water may be prevented and/or the presence of gasses, such as oxygen may be prevented by placing the orifice surface and the reservoir in a closed environment. For example, oxygen and/or water may react with the orifice surface or the compound for forming the coating, thereby preventing the orifice surface and the compound to bond. If the orifice surface and the compound do not bond, no coating is provided on the orifice surface and hence, no wetting gradient is generated. By placing the orifice surface and the reservoir in a closed environment, the environment may be controlled, thereby providing better control over the formation of the wetting gradient on the orifice surface.
In an embodiment, the reservoir is formed by at least a second surface and the method further comprises
The orifice surface, comprising at least one orifice, is arranged at a second end of the orifice. At a first end of the orifice the reservoir is arranged. The reservoir may be for example the ink channel of a print head. Alternatively, the reservoir may be formed by a vessel and by an orifice plate, the orifice plate being positioned on top of the vessel and the vessel being adapted to contain the medium comprising the compound. In any case, the reservoir comprises a second surface. The second surface may be for example a surface of the orifice plate or may be a surface inside the ink channel of a print head. When the compound is evaporated the compound starts diffusing towards the orifice. Before it reaches the orifice, the compound may come into contact with the second surface and bond to the second surface, thereby forming a coating on the second surface. Also when the second surface is exposed to the medium comprising the compound or to the neat compound, the compound may bond to the second surface. It may be preferred to remove the coating from the second surface after providing the orifice surface with a wetting gradient. For example, if the coating provides the second surface with anti-wetting properties, the anti-wetting properties of the second surface may negatively influence the jetting performance of the orifices.
In a particular embodiment, the coating is removed from the second surface by etching. The coating may be efficiently removed from the second surface by etching, for example using an etching solution or a plasma. The wetting gradient should not be removed and therefore, it is preferred to protect the wetting gradient on the orifice surface from being etched, for example by using a protective layer, which may be removed after etching. The protective layer may be a layer of tape, for example PVC tape. Optionally, the second surface may be selectively exposed to etching. In the latter case, protecting the wetting gradient may not be necessary.
In a particular embodiment, the coating is removed from the second surface using a laser beam. A laser beam is a suitable means to remove the coating from the second surface. To prevent the wetting gradient from being removed by the laser beam, the laser beam may be suitably directed to not irradiate the orifice surface provided with the wetting gradient. In an alternative embodiment, an intense light beam may be used instead of a laser beam.
In an embodiment, the compound for forming the coating comprises a Si—Cl bond. A Si—Cl bond generally is a reactive bond. Hence, the compound for forming the coating comprising a reactive Si—Cl bond may bond spontaneously to the orifice surface by chemically reacting with the surface, thereby providing the orifice surface with a coating.
In a particular embodiment, the compound for forming the coating is a trichlorosilane compound.
In an embodiment, orifice surface consists of a material, the material being selected from the group of silicon, silica, Ni or metal-coated Ni. An orifice surface, which may be part of for example, an orifice plate or a print head often comprises Ni or a metal-coated Ni, such as Ni coated with a gold layer. Alternatively, the orifice surface may comprise silicon. Silicon comprises Si—OH bonds. These bonds are reactive, for example towards Si—Cl bonds. Thus, by suitable selecting the compound for forming the coating and the material of which the orifice surface consists, for example a silicon orifice surface and a compound comprising a Si—Cl bond, the compound may bond to the orifice surface spontaneously, thereby providing the orifice surface with a coating.
In an embodiment, the coating applied in accordance with the steps a) and b) is a first coating, the method further comprising applying a second coating at a part of the orifice surface not coated with the first coating, and wherein one of the first and second coating is a wetting coating and the other one of the first and second coating is an anti-wetting coating. After applying the first coating to the orifice surface in accordance with the present invention, not the entire orifice surface may be coated with the first coating. The first coating may be either a wetting or an anti-wetting coating. After the first coating has been applied, a second coating may be applied. The second coating may be either a wetting or an anti-wetting coating. By applying a second coating, the wetting gradient may be further improved. For example, in case the first coating is an anti-wetting coating and the coverage of the coating depends on the distance from the orifice, being highest close to the orifice, a wetting gradient is obtained and fluid tends to move away from the orifice. By applying a wetting coating on the parts of the orifice surface, not yet provided with a coating, fluid tends to move from the anti-wetting coating to the wetting coating and fluid is removed even further away from the orifice.
In an embodiment, the second coating is applied by chemical vapor deposition. Chemical vapor deposition (CVD) is an efficient way to provide an area of the orifice surface, that is not provided with a first coating, with a second coating. The second coating has properties that differ from the properties of the first coating.
In an aspect of the invention, the present invention further comprises an ink jet printing device, the ink jet printing device comprising a print head provided with an orifice surface, the orifice surface having arranged therein an orifice and the orifice surface having a wetting gradient around the orifice, wherein the wetting gradient has been applied to the orifice surface by a method in accordance with the present invention.
In an aspect, the present invention further comprises a print head provided with an orifice surface, the orifice surface having arranged therein an orifice and the orifice surface having a wetting gradient around the orifice, wherein the wetting gradient has been applied to the orifice surface by a method in accordance with the present invention.
These and further features and advantages of the present invention are further explained hereinafter with reference to the accompanying drawings showing non-limiting embodiments and wherein:
In the drawings like reference numbers refer to like elements.
The image-receiving member 2 may be a medium in web or in sheet form and may be composed of e.g. paper, cardboard, label stock, coated paper, plastic or textile. Alternatively, the image-receiving member 2 may also be an intermediate member, endless or not. Examples of endless members, which may be moved cyclically, are a belt or a drum. The image-receiving member 2 is moved in the sub scanning direction A by the platen 1 along four print heads 4a-4d provided with a fluid marking material.
A scanning print carriage 5 carries the four print heads 4a-4d and may be moved in reciprocation in the main scanning direction B parallel to the platen 1, such as to enable scanning of the image-receiving member 2 in the main scanning direction B. Only four print heads 4a-4d are depicted for demonstrating the invention. In practice an arbitrary number of print heads may be employed. In any case, at least one print head 4a-4d per color of marking material is placed on the scanning print carriage 5. For example, for a black-and-white printer, at least one print head 4a-4d, usually containing black marking material is present. Alternatively, a black-and-white printer may comprise a white marking material, which is to be applied on a black image-receiving member 2. For a full-color printer, containing multiple colors, at least one print head 4a-4d for each of the colors, usually black, cyan, magenta and yellow is present. Often, in a full-color printer, black marking material is used more frequently in comparison to differently colored marking material. Therefore, more print heads 4a-4d containing black marking material may be provided on the scanning print carriage 5 compared to print heads 4a-4d containing marking material in any of the other colors. Alternatively, the print head 4a-4d containing black marking material may be larger than any of the print heads 4a-4d, containing a differently colored marking material.
The carriage 5 is guided by guiding means 6,7. These guiding means 6,7 may be rods as depicted in
Each print head 4a-4d comprises an orifice surface having at least one orifice 8, in fluid communication with a pressure chamber containing fluid marking material provided in the print head 4a-4d. On the orifice surface, a number of orifices 8 is arranged in a single linear array parallel to the sub scanning direction A. Eight orifices 8 per print head 4a-4d are depicted in
Upon ejection of the marking material, some marking material may be spilled and stay on the orifice surface of the print head 4a-4d. The ink present on the orifice surface, may negatively influence the ejection of droplets and the placement of these droplets on the image-receiving member 2. Therefore, it may be advantageous to remove excess of ink from the orifice surface. The excess of ink may be removed for example by wiping with a wiper and/or by application of a suitable anti-wetting property of the surface, e.g. provided by a coating.
The carriage 5 and the print heads 4a-4d as well as the platen 1 are driven by driving means 10, which are schematically shown.
Images are printed on a image-receiving member, for example paper, supplied by a roll 28, 30. The roll 28 is supported on the roll support R1, while the roll 30 is supported on the roll support R2. Alternatively, cut sheet image-receiving members may be used instead of rolls 28, 30 of image-receiving member. Printed sheets of the image-receiving member, cut off from the roll 28, 30, are deposited in the delivery tray 32.
Each one of the marking materials for use in the printing assembly are stored in four containers 20 arranged in fluid connection with the respective print heads for supplying marking material to said print heads.
The local user interface unit 24 is integrated to the print engine and may comprise a display unit and a control panel. Alternatively, the control panel may be integrated in the display unit, for example in the form of a touch-screen control panel. The local user interface unit 24 is connected to a control unit 34 placed inside the printing apparatus 36. The control unit 34, for example a computer, comprises a processor adapted to issue commands to the print engine, for example for controlling the print process. The image forming apparatus 36 may optionally be connected to a network N. The connection to the network N is diagrammatically shown in the form of a cable 22, but nevertheless, the connection could be wireless. The image forming apparatus 36 may receive printing jobs via the network. Further, optionally, the controller of the printer may be provided with a USB port, so printing jobs may be send to the printer via this USB port.
By using an anti-wetting coating as the coating, a wetting gradient is generated, wherein the high coverage area 45 surrounding the orifice 8 is anti-wetting. The wettability of the orifice surface 43 increases with increasing distance from the orifice 8 and in this way a wetting gradient is obtained.
Please note that, although a cross-section of the orifice plate 42 is shown, a print head does not necessarily comprise the orifice plate 42. Alternatively, print head may not comprise the orifice plate 42, for example in case the print head is formed out of one piece, but the print head still comprises an orifice surface 43. It will be clear to the person skilled in the art that the present invention is also applicable to print heads that comprise such an orifice surface 43, but do not comprise the orifice plate 42.
The part of the orifice surface 43 that is closest to the orifice 8, is supplied with the largest amount of energy. Therefore, more compound 41 for forming the coating bonds to the orifice surface 43 at a position close to the orifice 8 and a higher coverage of coating is obtained at a position close to the orifice 8. If the coating has either wetting properties or anti-wetting properties, a decrease of the coverage of the coating with increasing distance from the orifice 8 results in the generation of a wetting gradient around the orifice 8. Application of an anti-wetting coating around the orifice 8 generates such a wetting gradient, that a driving force for marking material to flow away from the orifice 8 is provided. On the other hand, application of a wetting coating around the orifice 8 generates such a wetting gradient, that a driving force for marking material to flow towards the orifice 8 is provided.
A lens 60 is placed between the source 44 of the laser beam and the orifice surface 43. The lens 60 diverges the laser beam. The divergent laser beam irradiates a part of the orifice surface 43. The laser beam may be diverged by the lens in such a way, that a higher radiation intensity is provided on a part of the orifice surface 43 close to the orifice 8 and a lower intensity is directed to a part of the orifice surface 43 further away from the orifice 8. This results in more energy being supplied to the part of the orifice surface 43 close to the orifice 8 and consequently, a higher coverage of coating is obtained on the part of the orifice surface 43 close to the orifice 8, as explained above. In an embodiment, the laser may have a transversal intensity profile, e.g. a Gaussian intensity profile. This means that the laser beam is most intense in the center of the beam. By aligning a laser beam to the center of the orifice 8, more energy is supplied to the part of the orifice surface 43 close to the orifice 8 and consequently, a higher coverage of coating is obtained on the orifice surface 43 close to the orifice 8. The laser beam having a transversal intensity profile may be used in combination with the lens 60 or may be used without the lens 60.
By placing the mask 45, only a part of the orifice surface 43 is exposed. The part of the orifice surface 43 covered by the mask 45 is not exposed to radiation, since radiation does not penetrate the mask 45. Since only a part of the orifice surface 43 is expose to radiation, energy is only supplied to an area of the orifice surface 43. Consequently, only locally a coating is formed on the orifice surface 43 by bonding of the compound 41 to the orifice surface 43. By suitably selecting the mask 45, a suitable area of the orifice surface 43 is exposed to radiation and a coating is formed on the suitable area of the orifice surface 43.
The first area, the second area and the third area of the surface 43 partially overlap. Since the second area partially overlaps the first area of the orifice surface 43, both a first and a second amount of energy are supplied to the area of the orifice surface 43, where the first and the second area overlap. Consequently, to this area of the orifice surface 43, where the first and the second area overlap, a first and a second coverage of coating are applied and the coverage of the coating is higher there than on an area of the orifice surface 43 where only a first coverage of coating is applied. Because the third area partially overlaps with the second area, a part of the orifice surface 43 is provided with a second and a third coverage of coating, or the third area may partially overlap with the first area, etc.
The first, second and third time interval may comprise the same amount of time or alternatively, the amounts of time may differ. The difference in coverage of coating obtained on the orifice surface 43 may be influenced by the time interval during which energy is supplied to the orifice surface 43. In an embodiment, the difference between the first, second and third coverage of coating may be controlled by controlling the time intervals, at which energy is supplied to a first, second and third area of the surface. By controlling the difference in coverage between the respective areas, the strength of the wetting gradient, may be controlled.
In an embodiment, the difference in coverage of the respective areas of the surface may be controlled by applying radiation of a suitable wavelength to each one of the first, second and third area.
The application of a gradient, using three different levels of coverage is described here. Of course, it will be clear to the person skilled in the art, that any number of masks may be used to obtain a wetting gradient on a surface. The more masks are used, the smoother is the gradient obtained.
The mask 45 has an opening 53. A beam 61 of radiation, supplied by the source 44 of radiation is not impeded by the mask 45 in case the beam 61 travels through the opening 53 of the mask 45 and thus, energy may be supplied to the orifice surface 43 and to the compound 41 to bond and to thereby form a coating. In case the beam 61 emitted by the source of radiation 44 does not travel through the opening 53 of the mask 45, but reaches the mask 45, then no energy is supplied by the beam 61 to the orifice surface 43, but the energy is prevented to be supplied to the orifice surface 43 by the mask 45. Due to the relative movement, the position of the opening 53 of the mask 45, with respect to the orifice surface 43 and the source 44 of radiation changes with time. At a certain moment, energy may be supplied to a first part of the orifice surface 43, whereas at another moment, energy may be supplied to a second part of the orifice surface 43. Hence, the part of the orifice surface 43 that is supplied with energy by irradiation may be controlled and as a consequence, the part of the orifice surface 43 on which a coating is applied also changes with time. In
In an alternative embodiment, a wetting gradient may also be applied to the orifice surface 43 by moving the source 44 of radiation and the orifice plate with respect to one another with varying velocity, without the use of the mask 45. By moving the source 44 of radiation and/or the orifice plate, such that an area of the orifice surface 43 close to the orifice 8 is irradiated longer than an area of the orifice surface away from the orifice 8. Consequently, locally a higher coverage op the coating may be applied on the orifice surface 43, without the use of the mask 45.
In
The area of the orifice surface 43 close to the orifice 8 is prevented from irradiation for a shorter period of time than an area of the orifice surface 43 further away from the orifice. This is because above the orifice, the two masks 45a, 45b cross one another. A relative amount of energy E (vertical axis) locally supplied to the orifice surface 43 is schematically shown in
By applying a second coating having properties different from the properties of the first coating, the wetting properties of the surface 43 may be further improved. Please note that the wetting properties of the coated surface 43 should be judged compared to the wetting properties of an uncoated surface 43. Moreover, the wettability also depends on the nature of the fluid that may be present on the surface 43. For example, when applying a wetting coating, the wettability of the surface 43 provided with the wetting coating should be higher than the wettability of the uncoated surface 43. Thus, if the wettability of the uncoated surface 43 is high, the wettability of the coated surface 43 should be even higher, in order to obtain a wetting coating. As explained above, applying the first coating around the orifice 8, wherein the coverage of the coating decreases with increasing distance from the orifice 8 generates a driving force for a droplet of marking material to flow. In case the first coating is wetting, the orifice surface 43 may be more wetting close to the orifice 8 and marking material may flow towards the orifice 8 and in case the first coating is anti-wetting, the orifice surface 43 may be least wetting close to the orifice 8 and marking material may flow away from the orifice 8. As mentioned above, the second coating may have different properties compared to the first coating. Applying a second coating on the orifice surface 43 may generate an additional driving force. For example, applying an anti-wetting coating around an area where an wetting gradient is provided by application of an anti-wetting coating does not provide an additional driving force for the marking material to flow further away from the orifice 8. If the first coating is anti-wetting, then the second coating may be a wetting coating. By application of a wetting gradient on the basis of the first coating, marking material may flow away from the orifice 8. By applying a second coating, which may be wetting, an additional driving force may be created for the marking material to move ever further away from the orifice 8.
Alternatively, an area near the virtual border of the wetting gradient may be provided with a low coverage of the first coating. Locally, the orifice surface 43 may be able to bond more compound for forming a coating. Therefore, the second coating may be applied to an area of the orifice surface 43 within the virtual borders 47 of the wetting gradient, such that an area directly surrounding the orifice 8 is provided with a first coating, the area outside the virtual border 47 is provided with a second coating and an area in between the virtual border 47 and the area directly surrounding the orifice 8 is provided with both a first and a second coating, wherein relative more first coating is present closer to the orifice 8 and relatively more second coating is present close to the virtual border 47.
Two embodiments of a orifice surface 43, provided with a first and a second coating have been described. However, a wetting gradient can be generated in alternative ways as well. For example, the gradient of coverage of the coating around the orifice 8 may be varied; the coverage may increase or may decrease with increasing distance from the orifice 8. The virtual border 47, which confines the area, of the orifice surface 43, on which the first coating is applied, may be close to the orifice 8 or may be further removed from the orifice 8. The second coating may be applied only on a part of the surface outside of the virtual border 47, or a part of the orifice surface within the virtual border 47, having a low coverage of the first coating, may also be provided with a coverage of the second coating. The above cited parameters may be varied independently.
The parameters should be suitably controlled during the evaporation process and before. Parameters, like temperature, pressure, concentration of the compound 41 in the medium 40, rate of evaporation of the compound 41, the geometry of the orifice 8 and the nature of the compound 41 for forming the coating, but also other parameters, may influence the generation of the wetting gradient. Please note that there is an upper limit to the coverage and supplying more compound by evaporating the compound 41 from the medium 40 than required to provide such a maximum coverage does not lead to an even higher coverage. Therefore, it is, important to expose the orifice surface 43 to the compound 41 for a predetermined period of time. Once the maximum coverage has been reached on a part of the orifice surface 43 close around the orifice 8 and the orifice surface 43 is still exposed to the evaporated compound 41, also further away from the orifice 8 the maximum coverage of coating may be reached. In that case, the initially formed gradient around the orifice 41 is converted into a layer of coating, having a continuous coverage of coating throughout the surface 43 and no gradient is provided anymore. Therefore, the amount of time, during which the orifice surface 43 is exposed to the evaporated compound 41 for forming the coating should be suitably controlled. As stated above, the compound 41 for forming the coating may not only diffuse through the orifice 8, it may also diffuse throughout the reservoir, formed by the vessel 65 and the orifice plate 42. Therefore, also surfaces of the vessel 65 and orifice plate 42 may be in contact with the compound 41, either in the medium 40 or in the vapor phase. Depending on the material, of which the surfaces of the vessel 65 and the orifice plate 42 consist and on the conditions in the reservoir, the compound 41 for forming the coating may bond to the surfaces of the vessel 65 and the orifice plate 42, providing these surfaces with a coating.
Furthermore, heating means 64 are provided in the reservoir to heat the medium 40 comprising the compound 41. Generally, the rate of evaporation is higher at a higher temperature. Thus, by heating the medium 40 and thereby heating the compound 41, the wetting gradient may be applied to the orifice surface 43 in a shorter period of time. The heating means 64 may be provided or may not be provided, depending on the conditions applied and on the properties, such as boiling point, of the medium 40 and the compound 41. Alternatively, cooling means may be provided to suitably control the temperature of the compound 41.
In a particular embodiment, a reservoir contained neat tridecafluoro-1,1,2,2,-tetrahydro-octyl-trichlorosilane as the compound for forming the coating. The reservoir as well as the orifice plate were placed in a nitrogen atmosphere, at a pressure of 0.5 mbar and at room temperature. On top of the orifice plate, a layer of single side polished (SSP) silicon was positioned, the polished side of the silicon layer pointing away from the orifice surface. The compound was evaporated and diffused through the orifice and the SSP silicon layer, during 30 seconds forming a wetting gradient around the orifice.
An alternative method to prevent the presence of an unwanted coating on the second surface 72, is to apply a protective coating on the second surface 72, different from the coating forming the wetting gradient, before the wetting gradient 70 is applied to the orifice surface 43 by evaporation. The protective coating applied to the second surface 72 may be e.g. a wetting coating. A wetting coating may allow the inside of the print head from being wetted by the marking material, which is beneficial for the jetting performance of the print head. The protective coating may be applied selectively to the second surface. Alternatively, the protective coating may be applied to the second surface 72 and to the orifice surface 43 and later be selectively removed from the orifice surface 43.
In step a), when providing the medium 40 comprising the compound 41 for forming the coating, the compound preferably should leave the protective coating intact. In step b), by evaporating the compound 41 through the orifice 8, a wetting gradient may be provided to the orifice surface 43 and no compound 41 will bond to the second surface anymore 72, thereby preventing the jetting performance of the print head 4a to be negatively influenced. Optionally, the protective coating may be selectively removed from the second surface after application of the coating providing the wetting gradient on the orifice surface.
Please note that, as stated above, the time during which compound 41 for forming the coating is evaporated and may bond to the orifice surface 43, should be suitably controlled. During the process of applying the wetting gradient, presence of components that may hamper the formation of the wetting gradient should be prevented. However, allowing these components to enter the system after the orifice surface 43 has been exposed to the evaporated compound 41 for a predetermined period of time may be a suitable method for efficiently stopping the formation of the wetting gradient and the amount of compound 41, locally bond to the orifice surface 43 may be suitably controlled. For example, when the compound 41 for forming the coating is a trichlorosilane compound and the orifice surface 43 consists of silicon, allowing water or water vapour to enter the system may be a suitable way of quenching the compound 41 for forming the coating, such that the formation of the wetting gradient stops.
The compound 41 for forming the coating may not only be selected for the reactivity towards the material of the orifice surface, it may also be suitable selected for providing the desired wetting or anti-wetting properties to the surface upon formation of the coating. For example, compound containing a —(CF2)nCF3 chain are generally suitable compounds for providing anti-wetting properties to the orifice surface 43. Please note that the wetting properties of the coated surface 43 should be judged compared to the wetting properties of an uncoated surface 43. Moreover, the wettability also depends on the nature of the fluid that may be present on the surface 43. For example, when applying a wetting coating, the wettability of the surface 43 provided with the wetting coating should be higher than the wettability of the uncoated surface 43. Thus, if the wettability of the uncoated surface 43 is high, the wettability of the coated surface 43 should be even higher, in order to obtain a wetting coating.
The compound 41 is evaporated and diffuses throughout the reservoir—in case the reservoir is only partially filled with the medium 40- and diffuses through the orifice 8. The orifice surface 43 is covered with the layer of porous material 78. Therefore, the evaporated compound 41 cannot contact the orifice surface 43, because the orifice surface 43 is covered with the layer of porous material 78.
The compound may diffuse within the pores of the porous material 78. Also within the porous material, a gradient in concentration forms, because of the diffusion process. Thus, the further away from the orifice 8, the less compound 41a, 41b, 41c is present within a pore of the porous material 78. Therefore, less compound 41a, 41b, 41c may diffuse out of the layer of porous material 78 at a position further away from the orifice 8 and a coating having a lower coverage is provided on a part of the orifice surface 43 further away from the orifice 8. However, compared to the formation of a wetting gradient according to any of the embodiments of the present invention not using porous material, there is a difference in the size of the area of the orifice surface 43 that is provided with the coating. This is caused by the presence of the pores 81, 82 within the porous material 78. Because of this pores, the evaporated compound 41a, 41b, 41c has to travel a different path to arrive at the orifice surface compared to the situation, wherein the compound 41a, 41b, 41c diffuses through the gas phase.
Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually and appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination and any combination of such claims are herewith disclosed. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language).
| Number | Date | Country | Kind |
|---|---|---|---|
| 10170738.8 | Jul 2010 | EP | regional |
| 10185814.0 | Oct 2010 | EP | regional |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2011/062059 | Jul 2011 | US |
| Child | 13739062 | US |
