JP3071859U - Hot melt inkjet print head - Google Patents

Abstract

An object of the present invention is to provide an improved anti-wetting coating for a hot melt ink jet print head. SOLUTION: The nozzle face (1) adapted to print with hot melt ink and provided with an anti-wetting coating (22).
4) The ink jet print head according to 4), wherein the anti-wetting coating contains silicone and / or polysilane as a main component, has a wetting angle of at least 40 °, and is exposed to the hot melt ink for 100 days. 5
Printheads exhibiting a reduction in wetting angle of less than 10%.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to an ink jet print head and a printing apparatus using the print head.

[0002]

[Prior art]

 Ink jet printing devices generally use a liquid ink, that is, a water-based or solvent-based ink that is in a liquid state at room temperature, and a so-called hot-melt ink that has a melting point above room temperature of, for example, 100 ° C. or higher. Are classified as those that use In either device, the printhead typically has a flat nozzle surface with a plurality of orifices through which ink droplets are fired at a constant frequency or on demand to the print media. Have. The print head further includes compression means for generating ink droplets by rapidly increasing the pressure of the ink liquid contained in the nozzle passage corresponding to each nozzle orifice. In the case of a hot melt type device, the printhead further includes heating means for maintaining the temperature of the ink above its melting point during operation of the printhead.

In the technical field, it is generally known that if the periphery of a nozzle orifice on a nozzle surface is wet with ink, the directional stability of ink droplets ejected from the nozzle orifice deteriorates. Such wetting of the nozzle surface also has a problem that dust is attracted to the ink on the nozzle surface and is drawn into the ink passage, thereby causing clogging of the nozzle orifice. A well-known solution to these problems, at least for water-based inking devices, is to provide a hydrophobic coating on the nozzle face of the printhead. For a given ink liquid, the coating material should have a small adhesive force compared to the liquid's condensing force (surface tension). In other words, the wetting angle, ie, the contact angle between the coating and the ink liquid, must be relatively large, and should preferably be on the order of 70 ° or more. As a result, the ink liquid is "repelled" by the coating on the nozzle face, eliminating unwanted wetting of the nozzle face.

[0004] For liquid ink based devices, a number of suitable anti-wetting coating materials are known, especially for water-based inks. For example, U.S. Pat. No. 4,296,421 proposes polyurethane, epoxide resin, and phenolic resin, and in particular, mentions silicone resin as a suitable material for anti-wetting coating of an ink jet print head.

However, coating materials that are effective for aqueous inks are not always suitable for solvent-based inks, especially hot melt inks. Compared to aqueous inks, hot melt inks have a much lower surface tension. For this reason, the coating material must also have a low surface tension, ie a large wetting angle. Given the high temperatures at which hot melt inks are used, it is further required that the coating material does not swell or degrade in high temperature organic solvents. Also, since hot melt inks are generally used in print heads where the ink is compressed by a piezoelectric actuator (ceramic), the cure temperature of the coating resin must be low to prevent depolarization of the piezoelectric material.

[0006] It is known that ordinary organic materials have low chemical resistance to organic solvents such as hot melt inks. For example, many silicone-based elastomers and resins generally swell when exposed to hot hot melt inks, and in effect deteriorate. Of the commonly used low surface tension coating materials, only fluorinated polymers typically have resistance to organic solvents.

[0007] For these reasons, fluorinated resins have been proposed as wet-proof coatings for print heads adapted to print with hot melt inks. For example, EP-A-0 359 365 discloses a print head according to the preamble of claim 1, wherein the nozzle face is provided with a wetting-preventive coating of polytetrafluoroethylene (PTFE) or a similar material. doing.

[0008]

However, the fluorinated resin coating material has some disadvantages. Fluorinated coatings must be cured at relatively high temperatures, ie, above 250 ° C. Such high temperatures tend to cause depolarization of the piezoelectric actuator and are therefore unacceptable in the printhead manufacturing process.

[0009] Furthermore, fluorinated polymers are generally difficult to adhere to substrates. Before the fluorinated resin can be applied, the substrate must be properly primed for adequate performance of the coating. This complicates the manufacturing process and increases costs. Fluorinated polymers also require the use of special solvents in the coating process, which also increases costs.

It is generally known that the scratch strength of fluorinated polymer coatings is low. For this reason, there is a high risk of damage to the coating during the print head cleaning process.

Although fluorinated resins initially have a relatively large wetting angle, it has been found that the wetting angle decreases over time, probably due to swelling and / or dissolution of the coating. This effect is not preferable in obtaining a constant jetting behavior of the print head.

It is an object of the present invention to provide an improved anti-wetting coating for a hot melt inkjet print head.

[0013]

[Means for Solving the Problems]

 According to the invention, the above object is achieved by the features indicated in the independent claims. Useful further details of the invention are specified in the dependent claims.

Certain silanes and silicones, such as organopolysiloxanes, have been found to have excellent properties when used as anti-wetting coatings on hot melt inks. In particular, these materials exhibit surprisingly good ink repelling behavior for most commonly used hot melt inks. Although the wetting angle of the silicone resin is not as large as the initial wetting angle of the fluorinated polymer, a silicone-based coating is suitable as a wetting prevention coating. In particular, the wetting angles of these coatings are almost constant over time and show much less long-term degradation than fluorinated coatings. This is very advantageous in ensuring reliable performance of the print head with high reliability. The coating used in the present invention has also been found to have sufficient chemical stability to the ink and sufficient temperature stability in the expected temperature range of about 100-150 ° C. Furthermore, these coatings have the advantage that they can be applied directly to the substrate, i.e. the nozzle face of the printhead, using readily applicable coating techniques such as spray coating or plasma coating. It is not necessary to use a primer. Therefore, the print head according to the present invention can be manufactured with high quality at a relatively low cost. Yet another advantage over fluorinated coatings is that the coatings are harder and therefore more resistant to scratching and abrasion.

It is important that the anti-wetting coating is deposited only on the nozzle face of the print head and not on the inner wall of the nozzle orifice to prevent adverse effects on droplet formation. In one embodiment of the manufacturing method according to the invention, this requirement is satisfied by plugging the nozzle orifice with solidified ink before the coating step. The solidified ink plug and the coating material deposited on its surface are automatically removed when the printhead is heated to operating temperature and used for the first time. In another embodiment, during the spray coating step, the nozzle orifice is held open by a flow of air directed through the nozzle in a direction opposite to the spray direction.

[0016]

[Embodiment of the invention]

 Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, the print head 10 includes a substrate 12 having a nozzle surface 14. A plurality of nozzle orifices 16 are formed on the nozzle surface 14. FIG. 1 shows a longitudinal cross section of one nozzle orifice 16. A jet of molten hot melt ink is ejected from the nozzle orifice 16 to form ink droplets 20.

As is generally known in the art, printhead 10 includes a heating means and a piezoelectric actuator (both not shown). During operation, the heating means serves to keep the printhead above the melting point of the hot melt ink and keep the ink in a liquid state. The piezoelectric actuators are located upstream of each nozzle orifice 16 and are energized by a corresponding droplet request signal. As a result, the pressure of the ink liquid increases, and the ink is ejected through the nozzle orifice 16.

The nozzle surface 14 is formed by a wetting prevention coating 22 for preventing the nozzle surface, especially the area around each nozzle orifice 16 from being wetted by the liquid ink.

The substrate 12 is made of a metal such as brass (for example, 35% Zn / 65% Cu) or aluminum, or a ceramic material. The anti-wetting coating 22 is formed by a layer directly deposited on the substrate, and is mainly composed of a silicone resin and / or silane having a large wetting angle for hot melt ink. Therefore, it is stable even when exposed to hot melt ink. Therefore, wetting of the nozzle surface 14 by the ink is prevented with high reliability over a long period of use of the print head. As a result, the jet 18 is jetted at a right angle from the nozzle face 14 without being deflected by the residual liquid that wets the nozzle face or the suction force between the meniscus of the liquid jet and the surface of the nozzle face, and the ink jet is ejected. The droplet 20 can be attached to the print medium with high positional accuracy. The thickness of the wetting protection layer is between 10 nm and 10 μm, preferably between 30 nm and 3 μm. It is important that the wetting prevention coating 22 is provided only on the nozzle surface 14 and not on the inner wall of the nozzle orifice 16.

FIG. 2 shows a first embodiment of a method for manufacturing the print head 10 according to the present invention. A plurality of parallel grooves 24 are provided on the lower surface of the substrate 12. Each groove 24 defines an ink passage that is inclined toward the nozzle orifice 16 in the nozzle surface 14. Groove 24 and nozzle orifice 16 are closed by bottom plate 26. The bottom plate 26 may be made of the same material (brass) as the substrate 12, and is firmly fixed to the substrate. The print head 10 is heated to a temperature higher than the melting point of the hot melt ink, and the ink is supplied to each groove 24. Then, as the ink solidifies in the groove 24, each nozzle orifice 16 is closed with a plug of solid ink.

The coating solvent is prepared by dissolving 2.5% by weight of MK-dimethyl-silicone resin (supplied by Wacker Chemie GnbH, Germany) in a mixture of tetrahydrofuran and n-propanol. A ratio of tetrahydrofuran to n-propanol between 1: 1 and 10: 1, preferably 5: 1, is suitable for obtaining a smooth coated surface. 1% (ratio to silicone resin) of tin octoate may be added to the solution as a catalyst. The ink is heated to a temperature slightly above its melting point.

Next, the coating solution is sprayed onto the nozzle face 14 by a conventional spray coating method. As shown in FIG. 2, the print head 10 is held at a slight angle to the axis of the flux of the sprayed coating solution, so that the coating solution is deposited on the nozzle surface 14 and the top surface of the substrate. A small amount is also deposited. The ink stopper 28 prevents the coating solution from penetrating the nozzle orifice 16.

The coating is cured at a temperature of 80 ° C. for 24 hours and the print head 10 is ready for use. The ink plug 28 is automatically removed when the printhead is heated to operating temperature and used for the first time.

In a second embodiment, poly-methyl-methoxysiloxane (silicone resin MSE-100 supplied by Wacker Chemie GmbH, Germany) is used to prepare the coating solution. About 1 g of MSE-100 is dissolved in 100 ml of a tetrahydrofuran / xylene mixture (4: 1). About 5% by weight of polybutyl titanate is added as a catalyst. A coating layer having a thickness of about 2 μm is obtained by the spray coating method. In this case, the nozzle can be kept open by the air flow supplied to the ink passage so as to flow out of the nozzle orifice in a direction opposite to the spray direction.

In yet another embodiment, the anti-wetting coating 22 is formed by a plasma coating method. In this case, the coating material, preferably a silane compound or a mixture of various silane compounds, is vaporized and a high-frequency electric field acts on the vapor in the vicinity of the substrate to be coated. This induces a polymerization reaction in the gas phase, and as a result, atoms, ions, and radicals present in the gas plasma react with the surface of the substrate to form a desired coating layer. In this case, the thickness of the coating layer is preferably only 0.3 μm.

Of course, the anti-wetting coating according to the invention may be applied to other methods, such as dip coating.

Particularly preferred coating compositions are: (a) MK-dimethyl-silicone resin (coating solution prepared as described above) (b) Silicone resin MSE-100 (coating solution prepared as described above) (c) Silicone resin 50E (supplied by Wecker chemie GmbH, Germany) (d) 3-Aminopropyl-polyethoxysilane (a suitable coating solution is obtained by dissolving 4% by weight of this compound in toluene) (e) Silicone resin to which 10% (based on the amount of silicone resin) of n-2 aminoethyl-3-aminopropyltrimethoxysilane has been added. These coating compositions are preferably of the three commonly used types: Used for hot melt inks. I. n-Methyl-p-toluenesulfonamide II. Bisurethane (reaction product of methylethylene glycol and hexamethylene-diisocyanate) III. 1,2-Hexadecanediol FIG. 3 shows the second embodiment of the present invention described above. The measurement result of the wetting angle about the wetting prevention coating which has the silicone resin MSE-100 as a main component concerning an example is shown. Wetting angles were measured not only for fresh coatings, but also when the coatings were exposed to each of the three hot melt inks described above for 90 days. For comparison, the wetting angle of a conventional fluorinated coating (DuPont AF2400) described in EP-A-0 359 365 was also measured under the same conditions. It can be seen that the wetting angle of the coating according to the invention is kept almost constant, whereas the conventional coating shows a significant decrease in the wetting angle after several days of exposure.

Similar results have been obtained for coatings based on MK dimethyl silicone resin or silicone resin 50E. The silicone resin 50E has a relatively large and substantially constant contact angle of around 30 ° in hexacandiol.

While specific embodiments of the present invention have been described, those skilled in the art will be able to modify these examples in various ways without departing from the scope of the present invention, which is limited by the claims. .

[Brief description of the drawings]

FIG. 1 is a sectional view of a nozzle portion of a print head according to the present invention.

FIG. 2 is a diagram showing a method of manufacturing the print head shown in FIG.

FIG. 3 is a diagram showing the change over time of the wetting angle of various types of hot melt inks with the wetting prevention coating according to the present invention and the wetting prevention coating according to the comparative example.

[Explanation of symbols]

 Reference Signs List 10 print head 14 nozzle surface 16 nozzle orifice 22 anti-wetting film

Claims (10)

[Utility model registration claims] 1. A nozzle face (1) adapted to print with hot melt ink and provided with a wetting prevention coating (22).
4) The ink jet print head according to 4), wherein the anti-wetting coating contains silicone and / or polysilane as a main component, has a wetting angle of at least 40 °, and has a wet angle of 5 per 100 days exposed to the hot melt ink.
%, Wherein the print head exhibits a reduction in the wetting angle of not more than%. 2. The print head according to claim 1, wherein the anti-wetting coating contains an organic polysiloxane as a main component. 3. The anti-wetting coating comprises a poly-
3. The print head according to claim 2, comprising methyl-methoxysiloxane. 4. The print head according to claim 1, wherein the anti-wetting coating contains dimethyl-silicone resin as a main component. 5. The print head according to claim 1, wherein the anti-wetting coating contains n-2-aminoethyl-3-aminopropyltrimethoxysilane. 6. The leak-proof coating according to claim 1, which comprises 3-aminopropyl-triethoxysilane as a main component.
The print head as described. 7. The method according to claim 1, wherein the anti-wetting coating is formed by spray coating, and the gas flow is passed through the nozzle orifice in a direction opposite to a spray direction. The print head as described. 8. The anti-wetting coating (22) is formed by plasma coating using a gas phase silane compound.
Or the print head according to 6. 9. A method for clogging the nozzle orifice (16) of the print head (10) with ink (28), forming the anti-wetting coating (22) on the nozzle surface (14) of the print head. A printhead according to any of the preceding claims, formed by removing ink (28) from the nozzle orifice (16). 10. A hot melt comprising a print head according to claim 1 and n-methyl-p-toluenesulfonamide, 1,2-hexadecanediol or bisurethane as a main component. A printing device comprising: an ink;