SE522623C2 - Method of manufacturing nozzle plate with miniature nozzles, nozzle plate with miniature nozzles and inkjet type printhead - Google Patents

Abstract

A method of making a nozzle plate structure with miniature nozzles, said nozzles having an accurately defined geometry and an upper and a lower surface, and said nozzle plate structure comprising a stable base plate (14) provided with holes and each hole containing a moulded structure forming the miniature nozzles (22). The method comprising the steps of providing a positive lower half of a mould (10) having protrusions (12) defining the size and shape of the said miniature nozzle, in which the protrusion mate with the holes of the stable base plate, and inserting the stable base plate in the mould, closing the mould with a lid (16) and applying a curable polymer (18) to the mould and exposing the curable resin to curing conditions. A nozzle plate structure (20) made according to the method is also disclosed.

Description

522,623 nozzle plates in durable and mechanically and thermally stable materials such as metal, but the variations in the size of the nozzles will be too large to meet the requirements of, for example, high-resolution printing.

The latest developments in casting techniques have made it possible to cast complex miniature structures in polymers such as ink jet nozzles with very good accuracy and precision. Advanced examples are described in the applicant's own Swedish patent application SE- 0003799-4, and of references therein. Cast nozzle plates can be manufactured with the high accuracy and precision, and at a reasonable cost, required for ink jet printer applications. Compared to the above methods, it has the additional advantage of providing a substantially identical (reverse) copy of the positive mold each time, whereas previous methods produce an original each time, which may be impaired by unpredictable variations. In some applications, especially when large nozzle plates are advantageous, the polymer molded nozzle plates may lack the mechanical stability required. Another area of importance is the low abrasion resistance of polymers, the abrasion caused by contact with the print medium.

U.S. Patent 6,23,8,584 discloses a method of designing ink jet nozzle plates which applies a combination of etching and bonding of silicon substrates. Advanced and mechanically stable plates can be constructed with this method, but a large number of production steps are required to achieve the same functionality as with the cast nozzle constructions. Since this must be done for all manufactured nozzles, it entails a high production cost. Furthermore, only a limited number of materials can be used, for example silicon.

There is a need for nozzles and constructions with nozzle plates with miniature nozzles of high accuracy and precision in combination with high mechanical and thermal stability and durability. Furthermore, the constructions with nozzle plates must be possible to manufacture in a way that ensures that high reproducibility is achieved and at a reasonable cost per unit.

None of the known methods and the holes made according to the known methods meet the requirements in a satisfactory manner. Summary of the Invention Thus, there is a need to produce mechanically and terinically stable nozzle structures which additionally provide well-defined miniature nozzles.

The nozzle constructions must also be possible to manufacture in large quantities at reasonable costs.

The object of the present invention is to provide such a method. The innovative method is defined by requirement l.

Another aspect of the invention is to provide a nozzle structure having the above-mentioned features. Such a construction is defined by claim 15.

An advantage given by the present invention is that it is possible to produce mechanically and thermally stable nozzle plates with miniature nozzles with the dimensions required for high-resolution printing.

Another advantage of the present invention is that the method allows the properties of the nozzle plate to be optimized for the intended application. In particular, the mechanical and thermal properties of the nozzle plate can be checked. The former is used to reduce the sensitivity of the nozzle plate to abrasion. The latter is used to match the tennis expansion of the nozzle plate with the thermal expansion of, for example, other parts of the printhead.

Another advantage of the innovative method is the possibility of manufacturing a large number of substantially identical nozzle plates, which enables a low cost per produced nozzle plate.

Brief Description The invention will be described in detail with reference to the drawings, in which Figure 1d illustrates the casting process according to the invention, Figure 2 ac shows the resulting construction with the nozzle plate according to the invention, and Figures 3 a and b show the construction with the nozzle plate according to two embodiments of the invention . Detailed Description of the Embodiments In the context of the present invention, the term "ink jet printer" is intended to include all printing devices based on the principle that ink is dispensed through a nozzle onto a print medium. Such printing devices are known by many names, such as BubbleJetTM (Trademark of Canon K.K.) and hp deskj etTM (Trademark of the Hewlett Packard Company).

The term "diameter" of a geometric shape should be given a broader interpretation than the strictly mathematical one. In the context of the present invention, it should mean the diameter of the smallest circle that can rewrite the shape in question.

The development of inkjet printers has been outstanding in recent years. Today, printers that provide almost photographic quality are available at reasonable costs. The pursuit of even faster printing, higher resolution, reliability and lower cost continues. A key element in the development is the print head with one or more nozzle plates.

The nozzle plates provide the miniature openings, the nozzles, from which the ink leaves the printhead as a stream of droplets to be received on the print medium, usually paper. The size and shape of the nozzles directly affect quality measures such as resolution and color reproduction. Nozzles with diameters around 15 μm are needed for high-resolution printers. In addition, the variations between different nozzles must be small, preferably less than 0.5 microns. This can be achieved with nozzle plates cast in polymer. Electroplating and laser ablation provide the best nozzles with diameters of 15 i2 μm.

To increase the printing speed, larger nozzle plates are constructed with a large number of nozzles (several nozzles provide the same color). A large number of nozzles provides fewer strokes for the printhead over the paper and thus faster printing. A large nozzle plate tightens the requirements that all nozzles should have substantially the same diameter and that the nozzle plate itself is mechanically and thermally stable. In addition, since the nozzle plate will be subject to abrasion of the print medium, it will need to be resistant to abrasion and abrasion. A measure of a material's resistance to abrasion is its hardness. Table 1 shows the hardness of some materials from which the nozzle plate can be made. From Table 1, it can be concluded that a metal or a metal alloy has suitable properties to provide a large nozzle plate.

Llv 10 15 522 625 Material Hardness [V ickers] Polymer (plain) 25 Brass (plain) 15 0 Steel 3 00 Hardened steel 700 Table 1 The print head will be heated during use. Some ink jet technologies, such as BubbleJetTM, friends ink and shield will be spread to the nozzle plate as well as to other parts of the printhead. Another source of heat production is the friction between parts of the printhead and the print media. If the nozzle plate has a thermal expansion that differs significantly from its housing, ie the printhead, thermally induced voltage will affect the nozzle plate and possibly deform it.

The deformation may be such that the print quality or printer reliability is affected. This problem increases with increasing size of the nozzle plate. To reduce the effects of thermal expansion, low thermal expansion materials should be selected.

In addition, the different materials found in the printhead can be matched with respect to the thermal expansion so that they have the same, or similar, coefficient of thermal expansion.

Table 2 shows the thermal expansion coefficients for some materials that can be found in a printhead. Expansion coefficient [l0'6 KJ] Material PZT ceramic 5 Nilo42 (42% Ni, 58% Fe) 150 Steel 12 Nickel 12 Aluminum 24 Epoxy 45-65 Nylon 6.6 70-100 Table 2 A preferred embodiment of the invention will now be described. Referring to Figure 1. In a first step (Figure 1a), a positive lower half of a mold 10 has been provided.

A mold with suitable dimensions and with the accuracy and precision required can be produced in a process involving lithographic etching of a silicon wafer. The etched silicon structure can then be covered with a metal layer, for example of nickel, by electroplating. Nickel has mechanical properties and surface properties that make it suitable as a molding material, but other materials are possible. The manufacture of molds is known, for example in the manufacture of CDs, and should not be construed as part of the invention. The lower part of the mold 10 is provided with a number of well-defined projections 12, which will define the shape and diameter of the nozzles. Figure 1 shows projections with a simple conical shape with a substantially circular cross-section. Through the use of anisotropic etching and advanced lithographic techniques, such as those described in the Swedish patent application SE0003799-4, more complex geometries are possible.

In a second step (Figure 1b) a stable base plate 14 is inserted into the mold. The insert 14 has holes corresponding to the projections 12 of the lower half of the mold 10. The stable base plate 10 is carefully positioned with guide pins (not shown). The guide pins may, for example, be an integral part of the lower part of the mold 10. The holes in the stable base plate 14 are preferably arranged so that they are larger than the projections 12 and positioned so that no physical contact takes place between the projections 12 and the stable base plate. 14. This is to ensure in a later process step that the injected polymer fills all parts of the mold. The stable base plate 14 may be made of a variety of materials, including metals, polymers, carbon fiber, ceramics, etc. As will be discussed below, the material for the stable base plate is preferably selected to optimize its mechanical properties. As indicated in the figure, the stable base plate 14 is positioned so that its upper surface lies in the planes defined by the upper surface of the projections. This is preferred in many applications, but it is of course also possible to place the stable base plate further down in the mold if a nozzle plate with polymer on all surfaces is desired.

In a third step, shown in Figure 1c, the mold is closed with a lid 16 and the trapped volume is evacuated. A curable polymer 18 has been introduced into the mold. The polymer may, for example, be of the UV light curable type, of the thermally curable type or a combination of both. Preferably, a polymer is selected in which the curing process is initiated by UV light, but where curing also takes place in areas which are not directly exposed to light. It should also be taken into account that the polymer must have good properties in combination with the ink to be used, ie not affected by solvents that are common in ink or water. The polymer is cured inside the mold, preferably with UV light or thermally, or by a combination of both.

After the curing process, the mold is opened and the molded structure with nozzle plate is removed. The resulting construction with the nozzle plate is seen in Figure 2a. The part which consists of polymer and which defines the size and shape of the individual nozzles will be called a cast nozzle 22. The projections have formed channels 24 which extend from the upper to lower surface of the nozzle plate, and which have well-defined openings 26 on the upper surface of the cast the nozzle. If required, the polymer on the lower surface of the stable base plate 14, i.e. on the side of the nozzle plate which does not face the print medium, can be removed mechanically or chemically. Thereby, the thickness of the structure is defined by the stable base plate 14. A thin "skin" of polymer can be formed on the upper surface of the stable base plate 14, caused by lack of contact between the insert and the lid. This "skin" can, if required, also be removed mechanically or chemically. After the optional step of removing excess polymer, the structure with the nozzle plate 28 will have the appearance depicted in Figure 2b and in a top view according to Figure 2c.

The manufactured nozzle plate will to a large extent have its mechanical properties defined by the stable base plate 14, and the nozzle dimensions, precision and accuracy defined by the cast polymer nozzle 22. This can be used to optimize performance for the intended application. The increased mechanical stability achieved by the introduction of the stable base plate also simplifies the operation of the nozzle plate in a further manufacturing process.

The described method according to the invention makes it possible to produce a large number of substantially identical nozzle plates, in contrast to a part of the prior art which gives individually different plates. As described above, the lower part of the mold is preferably manufactured from a silicon wafer. In most cases, there is room for more than one nozzle plate on the surface of the wafer. As much of the surface as possible should preferably be used for casting in nozzle plates, and in most cases a plurality of nozzle plates can be cast simultaneously. In one embodiment of the invention, more than one molded nozzle is provided in each of the holes of the stable base plate. In this way, the openings of the nozzles can be made closer to each other, but at the same time the mechanical stability of the construction diol deteriorates somewhat.

A preferred embodiment which considers the choice of material for the stable base plate 14 is described on the basis of an illustrative example. In an example of an ink jet approach, the printhead actuator is made of PZT ceramics. Referring to Table 2, it is pointed out that the coefficient of thermal expansion for PZT ceramics is 5> <1 0-6 Kil (a low thermal expansion is typical of ceramic materials). A wide range of metal alloys with thermal expansion coefficients in a range from 0 (a nickel alloy with the product name “invar”) up to 50> <l0'6 KJ are commercially available. In this example, an alloy with the product name Nilo42 is selected, which matches the thermal expansion coefficient of the ceramic (see Table 2).

The alloy also provides the stability and abrasion resistance required for a large nozzle plate construction. To form the stable base plate 14, a lithographic etching foil is prepared to create the openings which will accommodate the cast nozzles. The openings in the non-metallic base plate can be made considerably larger than the diameter required by the nozzles, and need not have exactly the same cross-sectional geometry as the cast inlet pieces. Etching process usually produces openings with a diameter of 100: 20 μm. Since the size and tolerance of the openings are not critical, a number of other techniques can be used to produce the metallic base plate, such as electroplating. The nozzle plate resulting from the casting process will in principle have the mechanical and thermal properties of the metal alloy, but the nozzles will have the size and tolerance given by the casting process (usually 15: 2 μm). It should be obvious to the person skilled in the art that the material choices can be varied to a large extent to meet the requirements of different applications.

In a further embodiment of the invention, illustrated in Figure 3 a-b, the construction with the nozzle plate is further optimized to withstand abrasion caused by the print medium.

Since the nozzles are made of relatively soft polymer, with relatively low abrasion resistance, it would be advantageous for some applications if the surface of the molded nozzles were slightly below the surface of the stable base plate 22. Many polymers reduce their volume slightly during the curing process. This can be advantageously utilized in that the polymer, which constitutes the cast nozzle 22, at its outer diameter is fixed to the metal and thus will reduce its volume by reducing its thickness. This results in a depression 30, which is indicated in Figure 3a (the depth of the depression has been exaggerated in the figure for illustrative reasons). If required, a greater distance between the surface of the metallic base plate and the surface of the nozzles can be achieved by arranging by electroplating an additional metal layer 32 on the upper surface of the metallic base plate.

Electroplating can only take place on a conductive surface and therefore the construction of an extra layer can only take place on the surface of the conductive metallic base plate and not on the surface of the insulating cast nozzles. The possibility of electroplating additional layers of metal on the metallic base plate can be used to further adapt the mechanical properties of the nozzle plate structure. The upper surface of the cast nozzles can alternatively be made to be in a plane below the upper surface of the stable base plate by changes in the casting process.

For example, the lid can be provided with projections which fit together with the holes in the stable base plate and thereby form the depressions. Alternatively, sacrificial moldings are defined which define the recesses fixed to the lid or to the upper surface of the stable base plate.

The procedure described above with reference to Figures 1 a-c, gives a construction shown in Figures 2 a-c and which is characterized in that the upper surface consists of two different materials. This can, in addition to the improved mechanical properties, be advantageous for being able to control the size and shape of a drop, for example an ink drop formed around the opening of the nozzle. In an exemplary embodiment of the invention, the insert has a lower wetting ability than the polymer, and consequently the drop can be made to cover only the part of the upper surface which is made of polymer.

The insert 14 does not necessarily need to be inserted by placing a structure in a mold, but can, for example, be molded in another polymer, by using a first lower half of the mold. In a subsequent step, the first lower half of the casting liner is replaced with a second lower half and the rest of the hole structure is cast in another polymer.

Aligning the individual nozzle plates with a feed chip to make, for example, a printhead is a time consuming process because it must be done with great care. The method of the invention uses a silicon wafer to create the positive mold. The feed chip will usually also be based on a silicon wafer and by coordinating the layout of the feed chips and nozzle plates it will be possible in a phase to align an entire batch of nozzle plates with the feed chips.

The method and construction of the nozzle plate according to the invention has been described here with reference to an application in ink jet printer maintenance. Those skilled in the art will appreciate that the invented design and method can be used in many other applications where a liquid is to be dispensed with high precision. Such applications include dosing devices for chemical and biochemical analyzes.

Other applications which will be apparent to those skilled in the art upon reading the specification are intended to fall within the scope of the appended claims.

Claims (1)

A patent for manufacturing a nozzle plate with engineered nozzles, wherein the nozzles have a precisely defined geometry and an upper and a lower surface, and the nozzle plate comprises a stable base plate (14) with an upper and a lower surface, which nozzle plate is provided with at least one hole and each at least one hole contains a molded construction which forms at least one of said nozzles, the method comprising the steps: providing a positive lower half of a mold (10) which is provided with at least one projection (12), which projection defines the size and shape of the engineering nozzle and fits with the hole in the stable base plate; insertion of the stable base plate into the mold; closing the mold with a lid (16); applying a curable polymer (18) to the mold and exposing the curable resin to curing conditions; and removing the nozzle slat 20 from the molds. The method according to claim 1, wherein the insertion step further comprises that the stable base plate is arranged so that it is not in physical contact with the corresponding projection. The method according to claim 1, wherein the insertion step further comprises that the stable base plate is arranged so that its upper surface lies in the plane defined by the upper surface of the projections. A method according to any one of claims 1-3, wherein the stable base plate is a metal or a metal alloy. A method according to any one of claims 1-4, wherein the stable base plate is selected to have a high abrasion resistance. A method according to any one of claims 1-5, wherein the method further comprises a step of removing excess polymer from the upper surface of the stable base plate. A method according to any one of claims 1-6, wherein the method further comprises a step of removing polymer from the lower surface of the nozzle plate so that the thickness of the structure 10 is defined by 10. 11. 14. 16. 522 623 1 ") 4. defined by The method of claim 1, further comprising the steps of: mounting the nine-piece plate in a support structure, and adjusting the thermal expansion coefficient of the stable base plate to the thermal expansion coefficient of the support structure so that their respective thermal expansion coefficients are substantially equal. The method of claim 1, wherein the curing step. The method of claim 1, wherein the polymer is allowed to reduce its volume so as to form a depression (30) on the upper surface of the nozzle.The method of claim 1, wherein the method further comprises a step of adding an additional layer of material (32) to the upper surface of the stable base plate. The method of claim 10, wherein the base plate is provided with an additional metal layer by electroplating. according to any one of claims 1-1 1, in which the lid is provided with projections arranged to fit into the holes of the base plate. . The method according to claim 12, in which the projections are sacrificial elements. The method according to claim 1, in which a plurality of nozzle plates have been manufactured in the same casting step, the method further comprising a step of simultaneously aligning the plurality of nozzle plates towards a corresponding structure. . Nozzle plate with miniature nozzles, comprising a stable base plate (14) which is provided with at least one hole passing through the base plate, characterized in that the miniature nozzles (22) have a precisely defined geometry with at least one channel extending through the miniature nozzles, and that the at least partial nozzles are housed in and fixed in the holes of the base plate. The nozzle plate according to claim 15, wherein the miniature nozzles are cast polyiner nozzles. U! The nozzle plate according to claim 16, wherein the mechanical properties of the nozzle plate are substantially given by the mechanical properties of the stable base plate and the dimensions, precision and accuracy of the nozzle are given by the cast polymer nozzle. The nozzle plate according to claim 17, wherein the material of the stable base plate is a metal or a metal alloy. The nozzle plate according to claim 17, wherein the stable base plate has high resistance to abrasion. The nozzle plate according to claim 17, wherein the stable base plate has a substantially flat upper surface, which upper surface lies in the same plane as the upper surface of the cast nozzles. The nozzle plate according to claim 17, wherein the stable base plate has a substantially flat upper surface, wherein at least a part of the upper surface of the cast plates is sunk below the plane defined by the upper surface of the stable base plate. . The nozzle plate according to claim 18, wherein the upper surface of the stable base plate has been provided with an additional layer (32) of a metal. . Inkjet type printhead comprising nozzle plate according to claim 15.. The ink jet type printhead according to claim 23, further comprising a support structure on which at least one nozzle plate is mounted, the stable expansion coefficient of the stable base plate being substantially equal to the thermal expansion coefficient of the support structure. . The ink jet type printhead according to claim 22, wherein the support structure is made of PZT ceramic and the stable base plate is made of a nickel-iron alloy.