Patent Application
20130135391
1. Field of the Invention
Aspects of the present disclosure are related to printhead assemblies and in particular to adhesive bonding materials used in a composite manner to laminate printhead structures using a two film method.
2. Background of the Invention
Solid ink jet printing machines include printheads that include one or more ink-filled channels communicating at one end with an ink supply chamber or reservoir and having an orifice at the opposite end, commonly referred to as the nozzle. An energy generator, such as a piezo-electric transducer, is located within the channels near the nozzle to produce pressure pulses. Another type system, known as thermal ink jet or bubble jet, produces high velocity droplets by way of a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble.
Ink jet printheads typically require multiple layers of materials as part of their fabrication. Traditional methods use layers of gold plated stainless steel sheet metal with photo chemically etched features which are brazed together to form robust structures. However, with the continued drive to improve cost and performance, use of alternate materials and bonding processes are required. Polymer layers can replace certain sheet metal components, but polymers require adhesives to bond to each other or to metal layers. Compatibility of these adhesives with the various chemistries used in ultraviolet (UV) and UV gel inks can be problematic including the case with the acrylic monomers in the UV curable inks and a baseline acrylic adhesive, such as R1500. When chemistry matching like this occurs, the R1500 adhesive swells, looses bond strength and ultimately delaminates causing color to color mixing along with poor jetting performance. The swelling of R1500 can also cause non-flatness of the nozzle plate to occur, which causes misdirectional jetting along with poor jetting performance.
What is needed is an improved method of adhesive bonding materials used in a composite manner to laminate printhead structures.
In accordance with various embodiments of the present disclosure, a printhead assembly arranged to dispense ultraviolet curable ink or gel ink is disclosed. The printhead can include a plurality of functional plates stacked together; a first adhesive layer arranged between adjacent functional plates to provide bonding between the plates; and a second adhesive layer arranged between adjacent functional plates to provide chemical resistance to the ultraviolet curable ink or the gel ink.
The first adhesive layer can have a thickness of between about 1 mil and 4 mils. The second adhesive layer has a thickness of between about 1 mil and 4 mils.
The first adhesive layer can include a crosslinkable acrylic adhesive or a thermoplastic polyimide. The second adhesive layer can include epoxies or thermoplastic polyimide.
The functional plates can be formed of a metal, ceramic or plastic material.
In accordance with various embodiments of the present disclosure, a method for fabricating a printhead assembly for ultraviolet curable ink or gel ink jet printing machine in which the printhead includes a plurality of functional plates stacked together is disclosed. The method can include applying a first adhesive at a first area between layers of the functional plates to provide bonding strength; applying a second adhesive at a second area between layers of the functional plates to provide chemical resistance to the ultraviolet curable ink or the gel ink; and forming the stack of functional plates with the bonded and chemical resistant functional plates.
In accordance with various embodiments of the present disclosure, a method for adhering two or more components of an ultraviolet curable ink or gel ink inkjet printhead is disclosed. The method can include applying a first adhesive material to a first portion of a outward surface of a first component of the printhead to provide mechanical bonding strength; applying a second adhesive material to second portion of the outward surface of the first component of the printhead to provide chemical resistance to the ultraviolet curable ink or the gel ink; and arranging the first component of the printhead with a second component of the printhead to provide bonding between first component and the second component.
The first adhesive can include a crosslinkable acrylic adhesive or a thermoplastic polyimide. The second adhesive can include a liquid epoxy that is chemically resistant to the ultraviolet curable ink or the gel ink.
The components can include a compliant wall, an external manifold attach, a heater attach and a Boss plate adhesive.
In some aspects, the first adhesive applied at a first area between layers of the functional plates can satisfy all other functional requirements except the chemical resistance and the second adhesive applied at a second area between layers of the functional plates can provide all functional requirements including chemical resistance to the ultraviolet curable ink or the gel ink except low storage modulus.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.
a and 3b show an illustration of percent weight gain and dimensional change data for Resin Design 12300.
Reference will now be made in detail to the present embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
To bond any combination of stainless, aluminum or polyimide layers requires a thin film adhesive, such as R1500, which is a commercially available adhesive from Rogers Corporation. This adhesive, when used at the 0.002″ thickness, also has the ability to take up surface flatness non-uniformities, a necessary requirement at the manifold and heater interfaces.
When printheads using the R1500 baseline adhesive are used with hostile UV curable inks, the acrylate monomers in the ink can attack the acrylics in the adhesives over time. This matching of chemistries causes material swelling, which reduces both the inlet diameter and flow as well as causes material delamination at the material interfaces. This failure mechanism results in weak and missing jets, misdirectional jetting, and color mixing. The chemistry of these inks, in terms of percent weight, is composed mostly of a Di acrylate monomer (50-80%) and a multi functional acrylate co-monomer (5-25%). Initial testing has shown these monomers to be incompatible with the acrylic used in the baseline R1500 adhesive.
Table 2 below lists a set of functional requirements for B-staged adhesives that need to be considered to compatible with UV-type ink.
To reduce the difficulty in finding one adhesive which satisfies all the functional requirements listed in Table 2, a method of meeting these requirements is disclosed that divides the functional requirements into two sets. A first adhesive can be chosen to address compliance performance, or sometimes called elasticity and which is the inverse of hardness or stiffness, by choosing a material having a relatively low modulus. For example, the first adhesive can have a storage modulus between about 100 MPa and 1500 MPa range at about 20° C. and between about 3 MPa and 700 MPa range at about 120° C. A second adhesive can be chosen to address chemical resistance (swelling). Aspects of the present disclosure describe how utilizing two adhesives at any given layer, one for compliance (bonding) strength and one for chemical resistance, can be used for building low cost, high performance printheads. Printheads built in this manner can meet the demands not only for the hostile UV curable ink and gel ink application, but for all market ink chemistries as well. In some aspects, the two adhesives can be an epoxy film or a liquid dispensed adhesive.
To illustrate the difficultly of a good chemically resistant adhesive that satisfies all eleven requirements listed in Table 2, Resin Design's 12300 epoxy thin film chemical compatibilty is shown in
Generally, aspects of the present disclosure are directed an integration of two adhesive materials (a thin B-stage film and a liquid adhesive) at any given layers in the upper jetstack. The baseline adhesive, such as R1500, is chosen to satisfy a first set of requirements in Table 2 with the exception of #5 (chemical resistance) and second adhesive material, such as Resin Design's 12300 or any other chemically compatible liquid epoxy formulation, is chosen to be arranged at a region where chemical compatibility with ink, such as UV curable ink, is required.
In some configurations, the diameter of each ink inlet 505 can be about 1.5 mm. Depending on type of first adhesive and the diameter of the ink inlet 505, each ink inlet 505 may need to be enlarged about an additional 15 mils (1 mil=0.001 inch) on the radius to allow a bead of liquid epoxy to be deposited in a controlled fashion on a surface away from the inlet circumference. By way of a non-limiting example, since deposition needle diameters typically only go down to a minimum of 4 mils, the 2 mils R1500 layer can cause a 8 mil wide final bead width. This results in a total of about 15 mils extra space on the radius. It is also possible to reduce the 4 mils diameter epoxy bead further by adding a solvent (such as methylene chloride) to the liquid epoxy. This is typically done with sheet type coatings where a thin coating on the order of microns can be achieved given an original coating thickness of 25 microns and ½ a day or so of evaporation time. This approach can be implemented at any of the R1500 layers, such as the compliant wall, the external manifold attach, the heater attach and the Boss plate adhesive.
The first or baseline adhesive, such as R1500, can be used over the region where geometry details are small (the openings shown in the R1500 shaded regions enable electrical contact between the flex and PZT components. The remaining region of the standoff layer is made of the Resin Design epoxy resin adhesive which has been tested and shown itself to be chemically compatible with the UV inks. To prevent squeeze out into the ink inlets, the adhesive features can be oversized by roughly 15 mils on the radius. The R1500 stays in contact with the PZT's and not the higher modulus Resin Design Epoxy. To reduce or eliminate cross-talk between PZT, which is a print quality concern, the low modulus R1500 can be maintained in the in the appropriate region, as indicated in the Figure.
a (top view) and
While the invention has been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular function. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” As used herein, the term “one or more of” with respect to a listing of items such as, for example, A and B, means A alone, B alone, or A and B.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
