Patent Grant
8163819
The disclosure relates to adhesive compositions, and in one particular embodiment, to flexible compounds that can be cured for use as adhesives in micro-fluid ejection devices.
Micro-fluid ejection heads are useful for ejecting a variety of fluids including inks, cooling fluids, pharmaceuticals, lubricants and the like. A widely used micro-fluid ejection head is an inkjet print head used in an ink jet printer. Ink jet printers continue to be improved as the technology for making their micro-fluid ejection heads continues to advance.
In the production of conventional thermal ink jet print cartridges for use in ink jet printers, one or more micro-fluid ejection heads are typically bonded to one or more chip pockets of an ejection device structure. A micro-fluid ejection head typically includes a fluid-receiving opening and fluid supply channels through which fluid travels to a plurality of bubble chambers. Each bubble chamber includes an actuator such as a resistor which, when addressed with an energy pulse, momentarily vaporizes the fluid and forms a bubble which expels a fluid droplet. The micro-fluid ejection head typically comprises an ejector chip and a nozzle plate having a plurality of discharge orifices formed therein.
A container, which may be integral with, detachable from or remotely connected to (such as by tubing) the ejection device structure, serves as a reservoir for the fluid and includes a fluid supply opening that communicates with a fluid-receiving opening of a micro-fluid ejection head for supplying ink to the bubble chambers in the micro-fluid ejection head.
During assembly of the micro-fluid ejection head to the ejection device structure, an adhesive is used to bond the ejection head to the ejection device structure. The adhesive “fixes” the micro-fluid ejection head to the ejection device structure such that its location relative to the ejection device structure is substantially immovable and does not shift during processing or use of the ejection head. The bonding and fixing step is often referred to as a “die attach step.” Further, the adhesive may provide additional functions such as serving as a fluid gasket against leakage of fluid and as corrosion protection for conductive tracing. The latter function for the adhesive is referred to as part of the adhesive's encapsulating function, thereby further defining the adhesive as an “encapsulant” to protect electrical components of or used with the micro-fluid ejection head, such as a flexible circuit (e.g., a TAB circuit) attached to the micro-fluid ejection head.
However, the micro-fluid ejection head and the ejection device structure typically have dissimilar coefficients of thermal expansion. For example, micro-fluid ejection heads may have silicon or ceramic substrates that are bonded to an ejection device structure that may be a polymeric material such as a modified phenylene oxide. Thus, the adhesive must often accommodate both dissimilar expansions and contractions of the micro-fluid ejection head and the ejection device structure, and be resistant to attack by the ejected fluid.
Conventional adhesive materials tend to be non-flexible and brittle after curing due to high temperatures required for curing and relatively high shear modulus of the adhesive materials upon curing. Such properties may cause the adhesive materials to chip or crack. It may also cause the components (e.g., micro-fluid ejection head and/or ejection device structure) to bow, chip, crack, or otherwise separate from one another, or to be less resilient to external forces (e.g., chips may be more prone to crack when dropped). For example, during a conventional thermal curing process, the ejection device structure typically expands before a conventional die bond adhesive material is fully cured. The diebond material thus moves with the expanding device structure, wherein the diebond material cures with the device structure in an expanded state. Upon cooling the device structure, the device structure contracts and, with a rigid, cured diebond material, induces high stress onto the ejection head to cause the aforementioned bowing, chipping, cracking, separating, etc. Among other problems, such events can result in fluid leakage and poor adhesion as well as malfunctioning of the micro-fluid ejection heads, such as misdirected nozzles. Moreover, attempts to make adhesive materials more flexible after curing often lead to adhesive materials that are less resistant to chemical degradation by the fluids being ejected.
Accordingly, a need exists for, amongst other things, a flexible adhesive composition that is curable at relatively low temperatures and that is suitable for use in assembling micro-fluid ejection head components, and particularly, for attaching micro-fluid ejection heads to ejection device structures.
With regard to the foregoing and other object and advantages, various embodiments of the disclosure provide a thermally curable adhesive composition for attaching a micro-fluid ejection head to a device wherein the adhesive has a relatively low shear modulus upon curing. Various exemplary embodiments also provide a micro-fluid ejection head having an ejector chip and a thermally curable adhesive attached thereto, the adhesive having a shear modulus of less than about 10 MPa at 25° C., wherein “MPa” stands for “MegaPascals” (i.e., 1.0×106 Pascals).
Additionally, embodiments provide a micro-fluid ejection device having an ejector chip and a thermally curable adhesive attached thereto, the adhesive having a glass transition temperature of less than about 65° C. Various other embodiments provide a method for attaching a micro-fluid ejection head to a device. One such method includes attaching the head to a device with a thermally curable adhesive with a relatively low shear modulus dispensed between the head and the device, and curing the adhesive composition to provide the micro-fluid ejection device.
Advantages of the exemplary embodiments may include, but are not limited to, a reduction in ejector chip substrate bow, an increase in ejector head durability, increased planarity of the ejector head, and the like. Other advantages might include the provision of adhesives having improved mechanical, adhesive, and ink resistive properties. Reduced stresses may be present in the ejector head substrates due to the presence of improved adhesives according to the disclosed embodiments.
Further features and advantages of the disclosed embodiments may become apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale, wherein like reference numbers indicate like elements through the several views, and wherein:
In general, the disclosure is directed to describing improved compositions, structures, and methods related to thermally curable adhesives used to assemble component parts of micro-fluid ejection devices. More specifically, the improved adhesive compositions discussed herein might be used to, for example, reduce residual stresses that may result from heat-treating micro-fluid ejection heads to cure the adhesives.
In order to more fully disclose various embodiments of the invention, attention is directed to the following description of a representative micro-fluid ejection device incorporating the improved thermally curable adhesive described herein. With reference to
In order to control the ejection of fluid from the nozzles 18, each of the micro-fluid ejection heads 12 is usually electrically connected to a controller in an ejection control device, such as, for example, a printer 21 (
Exemplary connections between a flexible circuit and a micro-fluid ejection head are shown in detail by reference to
As shown in
The adhesive 48 may be a heat curable adhesive such a B-stageable thermal cure resin, including, but not limited to phenolic resins, resorcinol resins, epoxy resins, ethylene-urea resins, furane resins, polyurethane resins and silicone resins. The adhesive 48 may be cured before attaching the substrate 34 to the head portion 14 and, in an exemplary embodiment, the adhesive 48 has a thickness ranging from about 1 to about 25 microns.
After bonding the nozzle plate 20 and substrate 34 together, the substrate/nozzle plate assembly 20/34 may be attached to the head portion 14 in chip pocket 46 using a die bond adhesive 50. In various embodiments of the disclosure, the die bond adhesive 50 used to connect the substrate/nozzle plate assembly 20/34 to the head portion 14 includes one or more adhesive components that make up a composition having a relatively low shear modulus.
“Shear modulus” involves the relation of stress to strain according to Hooke's Law as shown in Equation (1) as follows:
(stress)=μ(strain) (1)
In Equation (1), “μ” represents a quantity often referred to as rigidity. When the relationship illustrated by Equation (1) is applied to a force “F” across a given area “A,” Equation (1) may be more specifically represented by Equation (2) as follows:
F/A=μ(ΔL/L) (2)
In Equation (2) above, the variable “L” represents original length of an object before said object was acted upon by force F. “ΔL” represents the change in length occurring after force “F” has acted upon the object. Therefore, the rigidity (“μ”) of the object is a proportionality constant relating the pressure applied to an object with the ratio between the object change in length with the objects original length.
When Equation (2) and a given rigidity value “μ” are used to determine elastic properties of an object, Equation (3), shown below, is used to derive a shear modulus value from the rigidity “μ” value determined in Equation (2). Equation (3) is shown below as follows:
μ=E/2(L+v) (3)
In Equation (3) above, shear modulus is the proportional relationship between rigidity “μ” and the right hand side of the equation, including the Poisson ratio “v” and Young's modulus “E.”
Applying Hooke's Law and elasticity theory to physical properties of micro-fluid ejection heads, reliable data may be established to correlate the elastic properties of adhesives with the effect of said adhesives on one or more surfaces of a micro-fluid ejection head. Shear modulus values are dependent on temperature, therefore, a given shear modulus value for a given adhesive will be given in pressure units at a specific temperature. Various embodiments of the disclosure include compositions with shear modulus values of less than 10 MPa at 25° C. as determine by a rheometer from TA Instruments of New Castle, Del. under the trade name ARES in a dynamic parallel plate configuration with a frequency of 1.0 rad/sec and a strain of 0.3% after the material is cured. In certain exemplary embodiments, one or more of the claimed compositions have shear modulus values of less than about 1.0 MPa at 25° C.
With reference now to
The example shown in
Chip fragility is believed to increase in severity because the adhesive layer reaches its glass transition temperature (Tg) before the substrate/nozzle plate assembly 20/34 and head portion 14 have finished cooling and contracting relative to one another after the curing of the adhesive layer 58, imparting stress onto the substrate/nozzle plate assembly. Accordingly, in an exemplary embodiment of the invention, an adhesive is used that has glass transition temperature below the temperature to which the head portion 14 is cooled. For example, an adhesive with a glass transition temperature of less than about 65° C., such as one having a glass transition temperature of less than about 50° C. or less than about 25° C. might be used in an exemplary embodiment.
The glass transition temperature of a material with elastic properties is the temperature at which the material transitions to more brittle physical properties or more elastic physical properties, depending on whether the temperature is decreasing or increasing, respectively. After curing, as the adhesive layer 58 cools below its glass transition temperature, the adhesive 58 becomes significantly more brittle than before reaching its glass transition temperature. If the adhesive 58 is stretched or compressed at a temperature below its glass transition temperature, the adhesive may crack or buckle. Therefore, using adhesives with lower glass transition temperatures will decrease the chances of adhesive cracking or buckling. Similarly, considering that shear modulus values directly relate to how brittle an adhesive will be at a given temperature, adhesives having lower shear modulus values are more flexible at lower temperatures, thereby decreasing the likelihood of adhesive cracking or buckling. Adhesive layer cracking may result in a compromised fluid seal, whereby micro-fluid ejection fluid leaks from the substrate/nozzle plate assembly 20/34 might cause undesirable deposits of fluid, and/or corrosion of electrical components.
High curing temperatures may also cause increased fragility. Adhesives having lower shear modulus values and lower glass transition temperatures may be cured with lower temperatures thereby, decreasing the chances for micro-fluid ejection head fragility. Increased fragility of micro-fluid ejection heads increases the chances for micro-fluid ejection products becoming unfit for use due to shattering of micro-fluid ejections heads and other parts of the micro-fluid ejection device.
In contrast to
In an exemplary embodiment, die attach adhesive 50 is a composition including (1) from about 50.0 to about 95.0 percent by weight of at least one cross-linkable resin selected from the group of epoxy resins, siloxane resins, urethane resins, and functionalized olefin resins; (2) from about 0.1 to about 25.0 percent by weight of at least one thermal curative agent selected from the group of imidazoles, amines, peroxides, organic accelerators, and sulfur; and (3) from about 0.0 to about 30.0 percent by weight filler, wherein the composition exhibits a relatively low shear modulus upon curing. In some variations of these exemplary embodiments, the adhesive 50 may include from about 0.0 to about 10.0 percent by weight silane coupling agent. In the embodiments described above, the filler may include from about 0.0 to about 30.0 percent by weight titanium dioxide, and from about 0.0 to about 30.0 percent by weight fumed silica or another filler component such as clay or functionalized clay, silica, talc, carbon black, carbon fibers.
More specific exemplary embodiments of the composition of adhesive 50 are listed in Tables 1 through Table 7 below.
As shown above, composition 1 includes from about 25.0 to about 50.0 percent by weight multi-functional epoxy resin; from about 25.0 to about 50.0 percent by weight aliphatic di-functional epoxy resin; and from about 0.1 to about 15.0 percent by weight phenolic cross-linking agent. The composition also includes from about 0.1 to about 20.0 percent by weight of an imidazole catalyst and from about 0.0 to about 30.0 weight percent fillers. As shown in Table 8, Composition 1 has a relatively low shear modulus value of about 0.225 MPa at 25° C. and a low glass transition temperature of about 10.5° C.
There are a number of epoxy resins, curing agents, and fillers available for application with various embodiments of the invention. In the first composition illustrated in Table 1, an exemplary multi-functional epoxy resin is available from CVC Specialty Chemicals, Inc. under the trade name ERISYS GE-35. An exemplary aliphatic di-functional epoxy resin is available from CVC Specialty Chemicals, Inc. under the trade name EPALLOY 3-23. A suitable phenolic cross-linking agent is available from Sigma Aldrich Company under the trade designation Bisphenol M. A useful curing agent is available from Air Products and Chemicals, Inc. under the trade name CUREZOL C17Z. A suitable epoxy silane coupling agent is available from GE Advanced Materials, Silicones of Wilton, Conn. under the trade name SILQUEST A-187 SILANE. Suitable fillers such as titanium dioxide, and fumed silica are available from a number of different suppliers. For example, titanium dioxide is available from DuPont Titanium Technologies under the trade name TI-PURE R-900 and fumed silica is available from Cabot Corporation of Boston, Mass. under the trade name CAB-O-SILTS-720.
In Table 2, composition 2, includes from about 50.0 to about 95.0 percent by weight diphenyl siloxane resin, from about 0.1 to about 20.0 percent by weight of tetraethylenepentamine, and from about 0.0 to about 10.0 percent by weight epoxy silane. The fillers include from about 0.0 to about 30.0 percent by weight titanium dioxide; and from about 0.0 to about 30.0 percent by weight fumed silica. As shown in Table 8, Composition 2 has a relatively low shear modulus value of about 1.98 MPa at 25° C. and a low glass transition temperature of about −11.2° C.
In accordance with the foregoing composition, a suitable diphenyl siloxane resin is available from Gelest, Inc. of Morrisville, Pa. under the trade name PMS E-15. A useful tetraethylenepentamine curing agent for this composition is available from Air Products or Sigma Aldrich Company under the trade designation TEPA (Tetraethylenepentamine).
Table 3 illustrates yet another exemplary adhesive composition. Composition 3 includes from about 0.0 to about 50.0 percent by weight multi-functional epoxy resin; from about 0.0 to about 50.0 percent by weight epoxy siloxane resin; from about 0.0 to about 90.0 percent by weight carboxyl-terminated butadiene; and from about 0.1 to about 20.0 percent by weight of an amine adduct thermal curative agent. This embodiment also includes from about 0.0 to about 15.0 percent by weight epoxy silane, from about 0.0 to about 30.0 percent by weight titanium dioxide, and from about 0.0 to about 30.0 percent by weight fumed silica. As shown in Table 8, Composition 3 has a substantially low shear modulus value of about 0.175 MPa at 25° C. and a low glass transition temperature of about −6.7° C.
In accordance with the foregoing composition, the epoxy siloxane that may be used is available from Gelest, Inc. is under the trade designation SIB1115.0. The carboxyl-terminated butadiene that may be used is available from Noveon Specialty Chemicals of Cleveland, Ohio under the trade name HYCAR CTB 2000×162. A suitable curing agent in the form of an amine adduct is available from Air Products and Chemicals, Inc. under the trade name ANCAMINE 2337S.
As provided in Table 4, Composition 4 includes from about 0.0 to about 50.0 percent by weight epoxidized butadiene resin; from about 0.0 to about 75.0 percent by weight anhydride functional butadiene; from about 0.1 to about 20.0 percent by weight anhydride cross-linking agent; and from about 0.1 to about 20.0 percent by weight of an azine imidazole thermal curative agent. From about 0.0 to about 15.0 percent by weight epoxy silane; from about 0.0 to about 30.0 percent by weight titanium dioxide; and from about 0.0 to about 30.0 percent by weight fumed silica are also included in the composition. As shown in Table 8, Composition 4 has a considerably lower shear modulus value of about 0.151 MPa at 25° C. and a considerably lower glass transition temperature of about −30° C.
For composition 4, a suitable epoxidized butadiene resin is available from Sartomer Company, Inc. of Exton, Pa. under the trade name POLY BD 600E. A suitable anhydride functional butadiene resin that may be used is available from Sartomer Company, Inc. of Exton, Pa. under the trade name RICON 130MA8. The cross-linking agent that may be used is available from Miller-Stephenson Chemical Company, Inc. under the trade designation Anhydride MHHPA. A suitable curing agent is an azine imidazole that is available from Air Products and Chemicals, Inc. under the trade name CUREZOL® 2MZ Azine.
As provided in Table 5, Composition 5 includes from about 50.0 to about 95.0 percent by weight methacrylated butadiene resin, and from about 0.1 to about 30.0 percent by weight of peroxide catalyst thermal curative agent. A suitable methacrylated butadiene resin is available from Sartomer Company, Inc. of Exton, Pa. under the trade name RICACRYL 3100. The curing agent is suitably a peroxide catalyst available from Sigma Aldrich Company under the trade name LUPEROX LP. As shown in Table 8, Composition 5 has a low shear modulus value of about 0.74 MPa at 25° C. and a considerably lower glass transition temperature of less than −60° C.
As provided in Table 6, Composition 6 includes from about 50.0 to about 95.0 percent by weight flexible epoxy resin, from about 0.0 to about 30 percent by weight bisphenol-M, and from about 0.1 to about 20.0 percent by weight of imidazole catalyst thermal curative agent. A suitable flexible epoxy resin is available from Dainippon Ink and Chemicals, Inc. of Tokyo, Japan under the trade name EPICLON EXA-4850. As shown in Table 8, Composition 6 has a low shear modulus value ranging from about 1.75 to about 4.4 MPa at 25° C. and a glass transition temperature ranging from about 20 to about 31° C.
As provided in Table 7, Composition 7 includes from about 50.0 to about 95.0 percent by weight flexible epoxy resin, from about 0 to about 50 percent by weight bisphenol-F, from about 0.1 to about 20.0 percent by weight of imidazole catalyst thermal curative agent, from about 0.1 to about 20 percent by weight epoxy silane coupling agent, from about 0 to about 20 percent by weight of amine adduct, and from about 0 to about 30 percent by weight fumed silica. As shown in Table 8, Composition 7 has a low shear modulus value ranging from about 3.9 to about 8.7 MPa at 25° C. and a glass transition temperature ranging from about 27 to about 60° C.
A comparison of the shear modulus and glass transition temperature properties of the Compositions 1-7 compared to a conventional die bond adhesive available from Emerson & Cuming of Monroe Township, N.J. under the trade name ECCOBOND 3193-17 are provided in Table 8.
As illustrated in Table 8, the ECCOBOND 3193-17 adhesive has a relatively high shear modulus value of 15.4 MPa at 25° C. as compared to the shear modulus values of the Compositions 1-7 which are all less than 10 MPa at 25° C. Similarly, the ECCOBOND 3193-17 has a relatively high glass transition temperature of 92.3° C. compared to the much lower values of the compositions 1-7 which are all less than 65° C. In other words, ECCOBOND 3193-17 becomes significantly more rigid when it cools to about 92° C., whereas Compositions 1-7 do not become significantly more rigid until cooling to at least about 65° C.
Various embodiments of the invention are also directed to a micro-fluid ejection device including a substrate/nozzle plate assembly and a thermally curable adhesive attached thereto, the adhesive having a shear modulus of less than about 10.0 MPa at 25° C. In one particular embodiment, shown in
It is contemplated, and will be apparent to those skilled in the art from the preceding description and the accompanying drawings that modifications and/or changes may be made to the embodiments of the disclosure. Accordingly, it is expressly intended that the foregoing description and the accompanying drawings are illustrative of exemplary embodiments only, not limiting thereto, and that the true spirit and scope of the present disclosure be determined by reference to the appended claims.
This application is a continuation application of parent application Ser. No. 11/382,876, filed May 11, 2006 (now abandoned), entitled “Adhesive Compositions, Micro-Fluid Ejection Devices, and Methods for Attaching Micro-Fluid Ejection Heads” which claims priority to provisional application Ser. No. 60/743,920, filed Mar. 29, 2006.
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| Number | Date | Country | |
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| Child | 12767857 | US |
