Solvent-resistant elastic glue for inkjet print heads

Abstract

The present invention provides an elastic adhesive having good chemical resistance to solvent-based inks, and a method for preparing the elastic adhesive. The elastic adhesive is used as a hydraulic adhesive inside an inkjet printhead, and is capable of tightly bonding a chip to a hydraulic component of a reservoir of a cartridge, and is capable of tightly bonding a plug to a reservoir of the inkjet printhead. Accordingly, an inkjet printhead having the elastic adhesive of the present invention is tolerant to both conventional solvent-based inks and UV-curable inks, and is capable of printing on porous and non-porous surfaces.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal inkjet print heads; and specifically, to an elastic glue, a preparation method of the elastic glue, and a use of the elastic glue for an inkjet print head. Background Art

[0002] For example, in the prior art described in Patent EP 1896262 B1 (see Figure 1 therein), a typical inkjet print head cartridge in the prior art is made of a print head ejection assembly, which is composed of a print head chip bonded to a flexible printed circuit. The print head chip houses electrical and hydraulic components to direct ink to various ejection sites and supply power thereto as needed to produce ink droplets for printing. A nozzle plate is applied to the upper surface of the chip to provide nozzles for inkjet. Then the entire ejection assembly is bonded to a cartridge that contains an ink reservoir closed by a lid. A suitable ink channel is obtained in the cartridge body to allow ink to reach the print head chip and, depending on the print head design, through channels machined into the chip or from the chip edge to a microfluidic circuit. In multiple ink print head cartridges, there are of course multiple ink reservoirs and multiple ink paths leading to the print head, and they are hydraulically isolated from each other to prevent ink mixing. Since the cartridge is assembled from different components and materials, the joint between the components must not only ensure good bonding but also ensure a perfect and durable ink seal in the area in contact with the ink. To bond the chip to the cartridge body, a suitable glue can be dispensed onto a flat surface around the flow path in the cartridge body to ensure a good seal around the lower surface of the channels in the chip. In this way, ink can flow from the reservoir to the chip without any mixing or leakage.

[0003] In addition, the cartridge bodies of multiple ink print heads require special production processes: for example, in three ink cartridges with a parallel nozzle array, casting techniques do not allow a single piece to be obtained in one forming process. As shown in Figure 2 of Patent EP 1896262 B1, the cartridge body has three ink reservoirs separated by walls. Due to the small lateral distance between nozzle arrays of different colors, three separate straight ink paths cannot be made while maintaining the necessary hydraulic characteristics and suitable structural robustness. A possible solution is to use a more complex mold as described, for example, in Patent EP 1896262 B1, where two additional parallel sliding inserts are used to create the required fluid structure inside the cartridge body. Once the casting process is completed, the extraction of the two sliding inserts leaves two windows on the side surface of the cartridge body: these windows must be closed with suitable plugs, which are conveniently bonded to the cartridge. A possible way to bond the plugs is to use a glue material dispensed along a flat concave surface at the window boundary to ensure a tight seal of the opening without allowing ink to leak from the reservoir.

[0004] Thus, a typical printhead cartridge requires a suitable glue to bond the chip to the cartridge body and to bond the plug to the reservoir. Traditionally, the glue used in printheads filled with aqueous ink is a one-component epoxy-based glue such as Ecobond E3200 (Henkel). This one-component epoxy-based glue ensures a strong bond between the silicon chip and the plastic reservoir of the printhead. However, when using solvent-based ink, this one-component epoxy-based glue (extensively tested for inkjet applications) shows severe failure. For example, due to the chemical action of the solvent, the adhesiveness of the glue is weakened, and due to the swelling of the glue under the action of the solvent, the printhead will experience electrical failures during its lifetime. Another critical aspect is the low flexibility of the epoxy-based glue, such that thermal stresses during the manufacturing process and during the storage life of the printhead may damage the brittle silicon chip components.

[0005] Therefore, there is an urgent need in the art to develop a special elastic glue that ensures the required chemical resistance in a solvent environment once cured, while ensuring high flexibility. The elastic glue also needs to include: good adhesiveness to surfaces such as polyolefins, silicon, Kapton, thermoplastic adhesives; dispensability through pneumatic or cochlear deposition systems; appropriate thixotropy; good visibility of the glue through an optical detection system once dispensed; time / temperature curing conditions compatible with other components of the printhead; most preferably a one-component system; a low Young's modulus to reduce the mechanical stress between the bonded components of the device during the manufacturing process and during the lifetime of the article; and / or reduced gas permeability. Summary of the Invention

[0006] To solve the above technical problems, the present invention proposes a new type of elastic glue. The elastic glue has appropriate thixotropy and viscosity, and thus has good dispensability through a pneumatic or cochlear system. Once the new glue is dispensed onto the surface to be bonded, it assumes the desired shape, thereby minimizing the undesired drainage effect during the curing temperature, which will be compatible with the components of the printhead and the production line.

[0007] As a first aspect of the present invention, there is provided a method for preparing an elastic glue from a composition, the elastic glue being used for bonding components inside an inkjet printhead, the composition comprising:

[0008] - a linear, unsaturated hydrocarbon-based polymer, the polymer comprising at least one non-aromatic unsaturated bond in at least one monomer, wherein the linear, unsaturated hydrocarbon-based polymer comprises polyisoprene grafted maleic anhydride and polybutadiene-styrene;

[0009] - more than one sulfur donor molecule; and

[0010] - an organometallic zinc catalyst,

[0011] The method comprises the following steps:

[0012] a) Reacting one or more sulfur donor molecules with an organometallic zinc catalyst to form a sulfurized zinc complex as an active crosslinking initiator;

[0013] b) Catalyzing the vulcanization reaction of one or more linear, unsaturated hydrocarbon polymers with the sulfurized zinc complex to obtain a vulcanized polymer and a thiol;

[0014] c) Crosslinking the polymer chains of the vulcanized polymer obtained in step b) via polysulfide bridges between the units through a curing process.

[0015] As a second aspect of the present invention, there is provided an elastic glue prepared by the method according to the first aspect of the present invention.

[0016] As a third aspect of the present invention, there is provided an inkjet print head comprising an elastic glue prepared by the method according to the first aspect of the present invention.

[0017] As a fourth aspect of the present invention, there is provided the use of an elastic glue prepared by the method according to the first aspect of the present invention for bonding components inside an inkjet print head.

[0018] The elastic glue of the present invention has the following beneficial technical effects. The elastic glue of the present invention allows for the manufacture of solvent-resistant inkjet print heads and can tightly bond the components inside the inkjet print head. For example, it can bond a chip (e.g., a silicon chip) to a hydraulic component of a reservoir (e.g., a plastic polyolefin-based reservoir) of a cartridge body, and bond a plug to the reservoir. Therefore, an inkjet print head including the elastic glue of the present invention is tolerant to both traditional solvent-based inks and UV-curable inks and can print on both porous and non-porous surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Non-limiting and non-exhaustive embodiments of the present invention will be described by way of examples with reference to the following drawings, wherein:

[0020] Figure 1 A schematic diagram of a hot air blower for curing a hydraulic glue for an inkjet print head is shown. DETAILED DESCRIPTION

[0021] To make the above and other features and advantages of the present invention clearer, the present invention will be further described below with reference to the drawings. It should be understood that the specific embodiments of the present invention are illustrative and not restrictive.

[0022] As a first aspect of the present invention, there is provided a method for preparing an elastic glue from a composition for bonding components inside an inkjet print head, the composition comprising:

[0023] - Linear, unsaturated hydrocarbon polymers, said polymers comprising at least one non-aromatic unsaturated bond in at least one monomer, wherein the linear, unsaturated hydrocarbon polymers comprise polyisoprene grafted maleic anhydride and polybutadiene-styrene;

[0024] - More than one sulfur donor molecule; and

[0025] - Organometallic zinc catalyst,

[0026] The method comprises the following steps:

[0027] a) Reacting more than one sulfur donor molecule with the organometallic zinc catalyst to form a sulfurized zinc complex as an active crosslinking initiator;

[0028] b) Catalyzing the vulcanization reaction of more than one linear, unsaturated hydrocarbon polymer with the sulfurized zinc complex to obtain a vulcanized polymer and a thiol;

[0029] c) Crosslinking the polymer chains of the vulcanized polymer obtained in step b) via polysulfide bridges between units through a curing process.

[0030] In a preferred embodiment, more than one linear, unsaturated hydrocarbon polymer further comprises more than one covalently bonded polar group in at least one monomer.

[0031] In a preferred embodiment, the organometallic zinc catalyst is zinc carbamates, zinc guanidines, and / or zinc xanthates. Zinc carbamates can be, for example, zinc ethyl phenyl dithiocarbamate (ZEPC), and / or zinc dibutyl dithiocarbamate (ZDBC).

[0032] In one embodiment, the composition comprises:

[0033] - 15% to 60% of more than one linear, unsaturated hydrocarbon polymer;

[0034] - 3.3% to 10.6% of more than one sulfur donor molecule; and

[0035] - 2.0% to 7.0% of the organometallic zinc catalyst;

[0036] wherein the percentages are calculated based on the total weight of the composition.

[0037] In a preferred embodiment, the composition comprises:

[0038] - 20% to 50% of more than one linear, unsaturated hydrocarbon polymer;

[0039] - 5.0% to 8.5% of more than one sulfur donor molecule; and

[0040] - 3.0% to 6.0% of an organometallic zinc catalyst;

[0041] wherein the percentages are calculated based on the total weight of the composition.

[0042] In a more preferred embodiment, the composition comprises:

[0043] - 35% to 40% of one or more linear, unsaturated hydrocarbon-based polymers;

[0044] - 6.5% to 7.5% of one or more sulfur donor molecules; and

[0045] - 4.0% to 5.0% of an organometallic zinc catalyst;

[0046] wherein the percentages are calculated based on the total weight of the composition.

[0047] Linear, unsaturated hydrocarbon polymer

[0048] As described above, the composition of the present invention comprises one or more linear, unsaturated hydrocarbon-based polymers, said polymers comprising at least one non-aromatic unsaturated bond in at least one monomer. The unsaturated bond is a reaction site (especially allylic hydrogen) during the vulcanization reaction of the linear, unsaturated hydrocarbon-based polymer. During the vulcanization reaction, the allylic hydrogen is replaced by a sulfur atom from the polysulfide chain of the zinc catalyst after vulcanization (substitution reaction).

[0049] In a preferred embodiment, the linear, unsaturated hydrocarbon-based polymer further comprises one or more covalently bonded polar groups in at least one monomer, such as alcohols, ketones, esters, amides, carboxyls, amines, acid anhydrides, for covalent bonding. The presence of one or more covalently bonded polar groups in the polymer chain increases surface interaction and thus improves adhesion.

[0050] In a more preferred embodiment, the polar group is an acid anhydride. For example, the acid anhydride is a functional group that reacts with a hydroxyl group or an amino group or a carboxyl group, which ultimately exists on the surface to be bonded, and undergoes a nucleophilic substitution reaction. Due to the acid anhydride, the new bond formed between the polymer and the surface is a strong covalent bond. Without wishing to be bound by theory, the acid anhydride can also have weaker interactions with other functional groups, such as dipole-dipole or Van der Walls interactions.

[0051] In a preferred embodiment, one or more linear, unsaturated hydrocarbon-based polymers of the present invention further comprise an in-chain aromatic moiety, which improves the final mechanical properties and chemical resistance of the rubber.

[0052] In an exemplary embodiment, one or more linear, unsaturated hydrocarbon polymers include one of the following:

[0053]

[0054] where m + n equals 113, and neither m nor n is equal to zero,

[0055]

[0056] where (x + z) / (x + y + z) equals 20%, and y / (x + y + z) equals 80%, and

[0057]

[0058] where x / (x + y) equals 33%, and y / (x + y) equals 67%.

[0059] In a particular embodiment, the linear, unsaturated hydrocarbon polymer includes polyisoprene grafted maleic anhydride and / or polybutadiene-styrene, which are commercially available from ALDRICH.

[0060] Sulfur donor molecule

[0061] As described above, the compositions of the present invention include one or more sulfur donor molecules. One or more sulfur donor molecules are essential components for sulfur-based vulcanization reactions. They react with an organometallic zinc catalyst (discussed in detail below) to form an active vulcanized zinc complex, which effectively initiates the crosslinking reaction of linear, unsaturated hydrocarbon polymer chains.

[0062] In one embodiment, one or more sulfur donor molecules are selected from elemental sulfur or dispersed sulfur. Elemental sulfur or dispersed sulfur can be dispersed with a suitable polymeric dispersant additive (usually a polymer or wax) to improve the uniformity of dispersion in cases where solubility is not complete.

[0063] In a preferred embodiment, one or more sulfur donor molecules are soluble crystalline sulfur with an average granulometry of no more than 100 mesh. In this way, the resulting elastomer will have good uniformity and good dispensability through a pneumatic or cochlea dispensing system.

[0064] Organometallic zinc catalyst

[0065] The composition of the present invention comprises an organometallic zinc catalyst. The organometallic zinc catalyst is an active compound that first reacts with a sulfur donor molecule to form an active sulfurized zinc complex. The sulfurized zinc complex catalyzes the sulfur substitution reaction of allylic hydrogen of linear, unsaturated hydrocarbon-based polymers during the vulcanization reaction. As a result of the vulcanization reaction, the sulfurized zinc complex decomposes into some by-products such as ZnS and mercaptans, and the polymer chains are effectively crosslinked via the corresponding long polysulfide chains.

[0066] In one embodiment, the organometallic zinc catalyst can be zinc carbamates, zinc guanidines, and / or zinc xanthates. In a preferred embodiment, the organometallic zinc catalyst is zinc carbamates and / or zinc xanthates, which have better performance once introduced into the complete elastomer in terms of the scorch time, reactivity, and curing temperature of the final elastomer.

[0067] Examples of organometallic zinc catalysts suitable for the vulcanization reaction include:

[0068]

[0069] In a particular embodiment, the organometallic zinc catalyst is zinc ethyl phenyl dithiocarbamate (ZEPC) or zinc dibutyl dithiocarbamate (ZDBC), such as those commercially available from Henan Xuannuo Imp&Exp Co.,Ltd, or zinc isopropyl xanthate, such as PROPYL Commercially available from Vanderbilt.

[0070] In one embodiment, the composition of the present invention further comprises:

[0071] - Metal oxides;

[0072] - One or more organic ligands;

[0073] - One or more hydrocarbon-based organic solvents or oils having a boiling point not lower than the curing temperature of the composition; a coupling agent of an organosilane molecule having one or more unsaturated bonds; and / or - an organic or inorganic filler dispersible in the composition.

[0074] In a particular embodiment, the composition comprises:

[0075] - 1.9% to 6.2% of metal oxides;

[0076] - 2.5% to 8.5% of one or more organic ligands;

[0077] - 14% to 45% of one or more hydrocarbon-based organic solvents or oils;

[0078] -2.5% to 9.0% coupling agent; and / or

[0079] -1.5% to 12% organic or inorganic filler;

[0080] wherein the percentages are calculated based on the total weight of the composition.

[0081] In a preferred embodiment, the composition comprises:

[0082] -3.0% to 5.0% metal oxide;

[0083] -4.0% to 7.0% one or more organic ligands;

[0084] -20% to 35% one or more hydrocarbon-based organic solvents or oils;

[0085] -4.0% to 7.5% coupling agent; and / or

[0086] -3.0% to 10.0% organic or inorganic filler;

[0087] wherein the percentages are calculated based on the total weight of the composition.

[0088] In a more preferred embodiment, the composition comprises:

[0089] -4.0% to 4.5% metal oxide;

[0090] -5.0% to 5.5% one or more organic ligands;

[0091] -25% to 30% one or more hydrocarbon-based organic solvents or oils;

[0092] -5.5% to 6.0% coupling agent; and / or

[0093] -5.0% to 8.0% organic or inorganic filler;

[0094] wherein the percentages are calculated based on the total weight of the composition.

[0095] Metal oxide

[0096] As described above, the composition of the present invention further comprises a metal oxide, and preferably the metal oxide is zinc oxide (ZnO). The metal oxide may be in the form of particles. In this way, metal oxide particles such as ZnO particles can be dispersed into the composition and react with the thiols generated from the first vulcanized zinc complex during the vulcanization reaction and form a zinc complex.

[0097] In a preferred embodiment, the zinc complex first complexes and vulcanizes with the organic ligand and then participates in the vulcanization reaction and crosslinking reaction of the polymer.

[0098] Organic ligand

[0099] As described above, the composition of the present invention further comprises more than one organic ligand. The organic ligand is intended to increase the solubility and dispersibility of zinc-containing materials (e.g., organometallic zinc catalysts, zinc sulfide complexes, and zinc oxide) in organic non-polar compositions to avoid over-vulcanization effects due to improper dispersion and / or dissolution. The organic ligand is a molecule capable of forming a coordination complex with the zinc atom of the organometallic zinc catalyst, or with the zinc complex, or with ZnO.

[0100] In a preferred embodiment, the organic ligand is a carboxylic acid and / or an amine having a non-polar molecular moiety. In a more preferred embodiment, the organic ligand is a C18-C30 carboxylic acid, an aliphatic amine, and / or an aromatic amine.

[0101] Examples of more than one organic ligand suitable for the vulcanization reaction of polymers include the following:

[0102]

[0103] Organic solvent or oil

[0104] As described above, the composition of the present invention further comprises more than one hydrocarbon-based organic solvent or oil. The organic solvent or oil is used to dissolve and / or disperse the other components of the present composition and is a hydrocarbon-based solvent such as styrene, diisopropylbenzene (DIPB), mesitylene, xylene, nonane, decane, undecane, dodecane, heptane, octane, toluene, etc. Additionally, the selected organic solvent or oil should have a boiling point not lower than the curing temperature of the composition or the elastomer of the present invention to avoid boiling of the solvent or oil and generation of bubbles during the curing process. For example, suitable organic solvents or oils for curing temperatures equal to or lower than 130 °C include mesitylene, xylene, nonane, decane, undecane, dodecane, etc., and suitable organic solvents or oils for curing temperatures equal to or lower than 80 °C include heptane, octane, toluene, and all of the above hydrocarbon-based solvents.

[0105] Coupling agent

[0106] As described above, the composition of the present invention further comprises a coupling agent. The coupling agent (which is also a bonding promoter) can be a silane molecule, which is soluble in the glue and has reactive functional groups such as hydroxyl, amino and / or carboxyl groups that are ultimately present on the surface to be bonded (silicon and / or plastic). In the presence of such functional groups, the coupling agent or particularly the silane molecule is capable of reacting with both other components of the glue and the surface. In a particular embodiment, the reactive functional group refers to more than one unsaturated bond contained in the coupling agent or silane molecule.

[0107] The coupling agent or particularly the silane molecule can be vulcanized and reacted with the remainder of the glue, thus ensuring a high bonding strength between the elastic glue prepared from the composition and the silicon and / or plastic surface to be bonded.

[0108] Examples of silane molecules suitable for the sulfur-based vulcanization reaction according to the present invention include one or more of the following:

[0109]

[0110] For example, the silane molecule can be Silquest A 171 commercially available from MOMENTIVE.

[0111] Organic or inorganic filler

[0112] As described above, the composition of the present invention further comprises an organic or inorganic filler that can be dispersed in the composition with or without a dispersant. The organic or inorganic filler imparts appropriate viscosity and thixotropy to the glue, and thus imparts good dispensability of the glue on the silicon and / or plastic surface bonded by the pneumatic and cochlear dispensing systems.

[0113] In a preferred embodiment, the organic or inorganic filler has gas and solvent barrier properties and an average particle size of no more than 50 microns.

[0114] Optimal performance of the glue is achieved by using a layered talc filler, which ensures good dispersibility in the polymer matrix and good solvent / gas barrier properties for the final elastomeric material. Therefore, in a more preferred embodiment, the organic or inorganic filler is a layered talc filler (for example, Talc HAR commercially available from IMERYS).

[0115] As is known to those skilled in the art, each component in the above composition has unique properties and contributes to imparting appropriate reactivity and the required final physical, chemical and mechanical properties to the glue.

[0116] The composition for preparing the elastic glue of the present invention can be quickly crosslinked and achieve high adhesion to the silicon and / or plastic surface to be bonded.

[0117] As a second aspect of the present invention, there is provided an elastic adhesive prepared from the composition according to the first aspect of the present invention.

[0118] The prepared elastic adhesive is a one-component adhesive, so there is no need to mix the components before use. The adhesive is used as a hydraulic adhesive inside an inkjet printhead to bond the components of the inkjet printhead. For example, to bond a silicon chip to a plastic polyolefin-based reservoir (hydraulic component) and / or to bond a plastic plug to the reservoir. It can also be used to seal a part of the edge of a flexible circuit to prevent ink from flowing under the flexible circuit, which will cause possible chemical and electrical defects.

[0119] In addition, the elastic adhesive can absorb the stress caused by the manufacturing process, thereby protecting the final product from chip breakage during and after the manufacturing process. The final heating of the printhead during its lifetime causes the bonded materials (such as silicon and plastic reservoir) to expand differently due to their coefficients of thermal expansion; this mismatch causes a bending effect on the chip and thus causes the brittle silicon to break, making the printhead unusable. The elasticity of the adhesive ensures that the stress caused by the manufacturing process or occurring during the storage life is absorbed into the printhead.

[0120] Once vulcanized, the elastic adhesive is also compatible with solvent-based inks. These inks can include alcohols, diols, ethylene glycol ethers, ethers, esters, hydrocarbons, amides, lactones, ketones. The adhesive contains additives studied to impart high adhesion of the polymer to the back of the silicon chip of the printhead and additives capable of binding to plastics of reservoirs that are typically polyolefin-based in order to be compatible with solvent-based inks.

[0121] As a third aspect of the present invention, there is provided a method for preparing an elastic adhesive according to the second aspect of the present invention from the composition according to the first aspect of the present invention, the method comprising the following steps:

[0122] a) Reacting one or more sulfur donor molecules with an organometallic zinc catalyst to form a first vulcanized zinc complex as an active crosslinking initiator;

[0123] b) Catalyzing the vulcanization reaction of one or more linear, unsaturated hydrocarbon-based polymers with the first vulcanized zinc complex to obtain a vulcanized polymer and a thiol;

[0124] c) Crosslinking the polymer chains of the vulcanized polymer obtained in step b) via polysulfide bridges between units by curing, preferably by a thermal curing process.

[0125] As a result, the present elastic adhesive is obtained.

[0126] In one embodiment, the method further comprises step d) of reacting a metal oxide such as zinc oxide with the thiol obtained in step b) to form a zinc complex.

[0127] In another embodiment, a zinc complex is complexed with more than one organic ligand and then sulfided to obtain a second sulfided zinc complex. The second sulfided zinc complex further participates in the vulcanization reaction of the polymer. Thus, in the context of the present invention, adding a metal oxide such as zinc oxide to the rubber aims to maximize the use of by-product sulfides.

[0128] It should be noted that the first sulfided zinc complex and the second sulfided zinc complex herein may be the same or similar in structure.

[0129] In one embodiment, the method further includes step e) of desulfurizing the polysulfide bridge by an organometallic zinc catalyst. Step e) is carried out to reduce the length of the crosslinked polymer and thus increase its Young's modulus.

[0130] In one embodiment, the method further includes step f) of sulfiding a coupling agent having more than one unsaturated bond to participate in step c).

[0131] In a preferred embodiment, steps d), e) and f) are not ordered.

[0132] In a preferred embodiment, step c) of crosslinking the polymer chains of the vulcanized polymer in step b) via the polysulfide bridge between the units by a thermal curing process.

[0133] As a fourth aspect of the present invention, there is provided an inkjet print head including an elastic rubber according to the second aspect of the present invention, or an elastic rubber prepared from the composition according to the first aspect of the present invention, or an elastic rubber prepared by the method according to the third aspect of the present invention.

[0134] As a fifth aspect of the present invention, there is provided the use of the elastic rubber according to the second aspect of the present invention, or the elastic rubber prepared from the composition according to the first aspect of the present invention, or the elastic rubber prepared by the method according to the third aspect of the present invention for binding components inside the inkjet print head.

[0135] For example, the elastic rubber of the present invention can be used as a hydraulic rubber inside the inkjet print head to bond the chip to the reservoir and / or bond the plug to the reservoir. It is also used to seal a part of the edge of the flexible circuit to prevent ink from flowing under the flexible circuit, which will cause possible chemical and electrical defects.

[0136] Glue curing

[0137] As described above, the elastic glue of the present invention is thermosetting. Therefore, in order to thermally cure the elastic glue of the present invention, a curing system is used in this application. The curing systems commonly used in the automated manufacturing and assembly line of inkjet printheads include hot air blowers and / or ovens.

[0138] Hot air blower

[0139] Figure 1 A hot air blower system is shown, which causes the thermal reticulation of the glue by heating the silicon ejector group of the inkjet printhead.

[0140] As Figure 1 shown, heat is rapidly transferred to the glue through the silicon. The hot air blower system allows the manufacturing process to reach a higher curing temperature (compatible with the silicon components of the ejector group) in a relatively short time, which is necessary to fully cure the glue without damaging any other heat-sensitive components of the inkjet printhead. The time and temperature of the hot air blower can be adjusted to protect the plastic reservoir and the components near the printhead from thermal damage due to heat transfer.

[0141] Oven

[0142] When using an oven as the curing system, the entire printhead is placed in a hot oven at a certain temperature for a certain period of time. In this case, the heating is not directional, so all the printhead components will be heated.

[0143] It is important to avoid reaching a temperature higher than the critical temperature, which may be dangerous for at least a part of the printhead. In the oven, more than one printhead can be heated in parallel at a time, so the heating time may be longer than that required by the hot air blower.

[0144] The curing conditions of the glue and the corresponding reactivity should be compatible with the application to protect all other components of the printhead from heat-induced damage. For example, when the maximum curing temperature at which at least a part of the printhead starts to be damaged is 90 °C, once the components of the printhead are combined, it is best to introduce the entire printhead into an oven with a temperature lower than 90 °C; otherwise, a hot air blower can also be selected to be introduced into the production line to locally heat the silicon and / or plastic surface to be combined to a higher temperature (e.g., up to about 130 °C) in a short time (e.g., < 3 minutes) without damaging the final printhead.

[0145] The reticulation degree achieved after the curing process should be high. The enthalpy consumed during the curing process measured by a DSC instrument should be higher than 50% of the total effective enthalpy.

[0146] Example

[0147] In the following examples, the characteristics of the elastic glue according to the present invention were evaluated. Those of ordinary skill in the art will understand that the examples described below are merely exemplary to illustrate the embodiments of the present invention without any limitation.

[0148] Examples E1 - E4 and Comparative Examples C5 - C6

[0149] Table 1 illustrates exemplary glue compositions (by weight) of the present invention (E1 - E4) and comparative examples (C5 - C6).

[0150] Table 1. Exemplary glue compositions of the present invention and comparative examples (by weight).

[0151]

[0152] Preparation method of the elastic glue of the present invention

[0153] Taking formulation E3 as an example, the elastic glue according to the present invention was manufactured by the following method.

[0154] First, the following raw materials were put into a container: 20.6 wt% polyisoprene grafted maleic anhydride, 17.5 wt% polybutadiene - styrene, 29.65 wt% mesitylene, and 5.78 wt% Silquest A171. The raw materials were mixed with a mixer (ARE - 250THINKY, USA) for 9 cycles (10 minutes for each cycle), and stopped for 5 minutes after 3 cycles. After cooling the resulting mixture, 4.12 wt% zinc oxide, 5.48 wt% stearic acid, 7.09 wt% sulfur (mesh 150 μm), and 5.16 wt% Talc HAR were put into the mixture, and then further mixed with a mixer (ARE - 250THINKY, USA) for 3 cycles (10 minutes for each cycle), and stopped for 5 minutes after each single cycle. Finally, 4.62 wt% ZDBC as a zinc catalyst was put into the mixture, and mixed with a mixer (ARE - 250THINKY, USA) for 10 minutes.

[0155] Other elastic glues according to the present invention and those comparative glues were prepared in a similar manner.

[0156] The developed glue was cured for a time equal to or less than 3 minutes at a maximum temperature of 135 °C by using a hot air blower curing system, and / or optionally, cured for a time equal to or less than 3 hours at a maximum curing temperature of 80 °C by using an oven, which ensured the following requirements for the elastic glue of the present invention:

[0157] - Tolerance to stress;

[0158] - High chemical resistance to both water - based ink and solvent - based ink;

[0159] - High crosslink density;

[0160] - High degree of conversion (% carbon-sulfur bond formation or C-H bond disappearance);

[0161] - High adhesiveness to the surface to be bonded (silicon or polyolefin-based plastics);

[0162] - Good flexibility;

[0163] - Good dispensability and scorch time; and

[0164] - Reduced gas permeability.

[0165] The following will give a detailed description of these beneficial properties through experimental tests and / or analysis of the materials.

[0166] Tolerance to stress

[0167] The elastic adhesive of the present invention can absorb the stress caused by the manufacturing process, thereby protecting the final print head from chip breakage during and after the manufacturing process. The final heating of the print head during its lifetime causes the bonded components (such as silicon and plastic reservoirs) to expand differently due to different coefficients of thermal expansion. This mismatch causes a bending effect on the chip and thus causes the brittle silicon to break, rendering the print head unusable. However, the elasticity of the elastic adhesive of the present invention ensures that the stress caused by the manufacturing process or occurring during the storage life is absorbed by the print head.

[0168] Chemical tolerance to solvent-based ink

[0169] Once the print head manufacturing process is completed, one or more inks are loaded into one or more reservoirs. If the print head is a three-color print head, three inks (usually cyan, magenta, yellow) are loaded into three reservoirs. Generally, each reservoir must contain ink.

[0170] When the ink-filled print head is ready, it is placed in its packaging and, for each step of the storage time, placed in an oven set at 45 °C for 1 week, 3 weeks, 5 weeks, and 7 weeks. The samples are removed from the oven and cooled at room temperature for 2 hours. The packaging is opened, and the print head is placed in the printer, and a predetermined printing pattern is executed on the paper; by observing the printing pattern, it can be verified whether any failures occur in the hydraulic adhesive during storage. If some contaminated ink printing is observed in the technical pattern, the chemical resistance of the adhesive is considered insufficient.

[0171] The elastic glue of the present invention is formulated to be compatible with solvent-based inks used in inkjet printheads once vulcanized. These solvent-based inks generally include alcohols, diols, ethylene glycol ethers, ethers, esters, hydrocarbons, amides, lactones, and ketones. The elastic glue of the present invention contains components capable of imparting high adhesiveness of the polymer to the back surface of the silicon chip of the printhead, and components capable of binding to plastics of reservoirs, which are usually polyolefin-based, so as to be compatible with solvent-based inks.

[0172] In the present invention, in order to evaluate the chemical compatibility (or chemical resistance) between the elastic glue of the present invention and common solvent-based inks, solvent-based inks cyan, magenta, and yellow were used. The ink compositions are listed in Table 2.

[0173] Table 2. Compositions of Solvent-Based Inks Cyan, Magenta, and Yellow

[0174]

[0175] Three reservoirs of the printhead were respectively filled with the above-mentioned solvent-based inks and kept at 45 °C for 7 weeks. The chemical compatibility was evaluated by observing the final failure of the bonded components (hydraulic components, plugs, beads) of the printhead after 1, 3, 5, and 7 weeks. The glue of the present invention that was properly cured did not show any separation from the surface and / or related swelling.

[0176] The chemical resistance of the printhead, especially the hydraulic glue, was positively evaluated by observing the printing quality after storing at 45 °C for 1, 3, 5, and 7 weeks. Typically, when an unusual color of the printed pattern on the paper was observed, it highlighted the failure of the glue; this was the result of mixing the ink into the macroscopic hydraulic area of the printhead. Another possible defect was the lack of nozzles during the printing process, which was due to the loss of the sealing performance of the hydraulic system of the printhead.

[0177] Table 3 shows the printing quality of the printheads using the glues of E1 - E4 and C5 - C6 at time 0 and after storing at 45 °C for 1, 3, 5, and 7 weeks.

[0178] Table 3. Printing Quality of Printheads with Different Elastic Glues

[0179]

[0180] The above results in Table 3 show that for E1 - E4, the printing quality of the printhead is good, while for C5, the printing quality of the printhead is poor after 5 and 7 weeks. Therefore, the chemical resistance of the elastic glue of the present invention is good, while the chemical resistance of Comparative Examples C5 and C6 is medium.

[0181] Crosslinking density

[0182] In the present invention, the crosslink density of the elastic glue of the present invention and the comparative example once cured was measured according to this procedure.

[0183] Rubber samples were prepared by casting glue in an aluminum mold having the following three dimensions: 10 mm × 20 mm × 20 mm.

[0184] The samples were cured with appropriate required curing conditions (hot air blower and / or oven), and after cooling and measuring the weight and volume, the samples were placed in isooctane of a known volume at room temperature.

[0185] This organic solvent (isooctane) has a very high affinity for the polymer matrix of the elastic glue, so it causes swelling. After 2 minutes, the samples were taken out of the solvent and the final weight and volume were measured.

[0186] Using the following Flory Rehner equation, the crosslink density of the glue sample was then calculated:

[0187]

[0188] Note: For a tetrafunctional network

[0189] v = crosslink density per unit volume in mol (mol / cm 3 )

[0190] V r = volume fraction of rubber in the equilibrium swollen vulcanized rubber sample

[0191] V s = molar volume of the solvent used at room temperature, in cm 3 / mol (based on molecular weight and density)

[0192] χ = Flory-Huggins polymer-solvent interaction parameter.

[0193] For vulcanized rubber containing fillers, Vr is obtained from the following equation:

[0194]

[0195] V rf = volume fraction of filled rubber in the swollen gel,

[0196] φ = volume fraction of filler in the unswollen filled rubber,

[0197] c = filled rubber interaction parameter.

[0198] Table 4 shows the crosslink density of the elastic glue of the present invention and the comparative example. The crosslink density calculated for the most promising glue reached 10 -3 mol / cm 3Magnitude. For both Comparative Examples C5 and C6, due to the difficulty in preparing the samples, the crosslinking density was not obtained.

[0199] Table 4. Properties of Different Elastic Glues

[0200]

[0201] Degree of conversion

[0202] In the context of the present invention, the degree of conversion of the glue refers to the percentage of carbon-sulfur (C-S) bond formation or C-H bond disappearance. Once cured, the degree of conversion of the glue is measured by FTIR spectroscopy.

[0203] The vulcanization reaction involves a certain number of reaction steps that are difficult to monitor by FTIR. However, using FTIR spectroscopy techniques, it has been observed that a satisfactory detection of the reaction can be obtained by simply observing the appearance or disappearance of C-S and C-H bonds.

[0204] Monitoring the increase in the signal at 1520 cm -1 normalized on the reference peak at -1 1603 cm, it has been observed that the elastic glue of the present invention has an increase in absorbance value of at least 0.4, as listed in Table 4. For Comparative Examples C5 and C6, the increases in absorbance value are 0.14 and 0.30 respectively, which are significantly lower than the values of the present invention (E1-E4).

[0205] Adhesion to the surface to be bonded

[0206] The adhesion of the surface (silicon and polyolefin-based plastics) of the elastic glue was tested by preparing at least 10 printheads, where the elastic glue was under test. The glue was dispensed by an assembly on a manufacturing assembly line of a cochlea or a pneumatic dispensing system and cured under appropriately selected conditions determined by analysis.

[0207] The adhesion of the glue was evaluated using the "scraper test". After glue dispensing and the correct curing time, the chip was observed to determine whether it maintained its position.

[0208] In particular, the "scraper test" was carried out in the following manner:

[0209] - Remove the flexible circuit (or flat part) from the printhead;

[0210] - Place the tip of the scraper at the edge of the chip and perform a leverage pressing with a gentle force;

[0211] - If the force pressing results in the removal of the chip, the test is evaluated as negative, with a grade of "KO"; complete removal of the chip can be observed, with the adhesive on its back; and

[0212] - If force pressing results in the breakage of the chip or makes it difficult to remove the chip, the evaluation test is positive and the grading test is "good" or "very good".

[0213] As listed in Table 4, all the examples and comparative examples of the present invention show acceptable adhesiveness, ranging from a "medium" level to "very good".

[0214] Flexibility

[0215] Generally, the flexibility of a polymeric material, or its glass transition temperature, is indirectly measured by performing a temperature increase at a determined heating rate in a temperature range between room temperature and higher temperatures through DSC technology. If the material is rubbery at room temperature, it will not exhibit any glass transition within the detected temperature range. An adhesive with a glass transition temperature at room temperature inherently has a rich free volume within its macromolecular structure. Therefore, during or after the manufacturing process, vibrations, etc., the thermal expansion of the bonded surfaces is absorbed by the material.

[0216] However, since the glass transition temperatures of the elastic adhesives E1 - E4 according to the present invention are significantly lower than zero degrees Celsius, the precise values obtained with a DSC instrument (which has lower precision at low temperatures below 0°C) have a higher instrumental error. Therefore, in this application, the glass transition temperatures of the elastic adhesives E1 - E4 and C5 and C6 are evaluated by placing the adhesives in a refrigerator at -45°C and pressing them in with the tip of a spatula. It is observed that none of the adhesives are in a glassy state and all the adhesives remain flexible until at least -40°C. It can be seen that the glass transition temperatures of the elastic adhesives E1 - E4 are all not higher than -30°C.

[0217] Gas permeability

[0218] Once dispensed and properly cured, the printing and storage tests performed on the print head did not highlight the air permeability of the elastic adhesives used to bond the components of the print head.

[0219] The presence of air in the microhydraulics of the print head is critical and can lead to nozzle shortages during the service life of the device.

[0220] The above various technical features can be combined arbitrarily. Although not all possible combinations of various technical features are recorded, all combinations of these technical features should be considered to be within the scope recorded in this specification as long as they do not conflict.

[0221] Although the present invention has been described in connection with embodiments, those skilled in the art should understand that the above description and the accompanying drawings are illustrative rather than restrictive, and the present invention is not limited to the disclosed embodiments. Various modifications and variations are possible without departing from the concept of the present invention.

Claims

1. A method for preparing an elastic glue from a composition, the elastic glue being used for bonding components inside an inkjet print head, the composition comprising: A linear, unsaturated hydrocarbon polymer, the polymer comprising at least one non-aromatic unsaturated bond in at least one monomer, wherein the linear, unsaturated hydrocarbon polymer comprises polyisoprene grafted maleic anhydride and polybutadiene-styrene; One or more sulfur donor molecules; and An organometallic zinc catalyst; The method comprises the following steps: a) Reacting one or more sulfur donor molecules with the organometallic zinc catalyst to form a first sulfurized zinc complex as an active crosslinking initiator; b) Catalyzing the vulcanization reaction of one or more linear, unsaturated hydrocarbon polymers with the first sulfurized zinc complex to obtain a vulcanized polymer and a thiol; c) Crosslinking the polymer chains of the vulcanized polymer obtained in step b) via polysulfide bridges between units through a curing process.

2. The method according to claim 1, wherein in step c), the polymer chains of the vulcanized polymer obtained in step b) are crosslinked via polysulfide bridges between units through a thermal curing process.

3. The method according to any one of claims 1-2, wherein the composition comprises: - 15% to 60% of a linear, unsaturated hydrocarbon polymer; - 3.3% to 10.6% of one or more sulfur donor molecules; And - 2.0% to 7.0% of an organometallic zinc catalyst; Wherein the percentages are calculated based on the total weight of the composition.

4. The method according to any one of claims 1-2, wherein the linear, unsaturated hydrocarbon polymer comprises one of the following: Where m + n equals 113, and neither m nor n is equal to zero, Where (x + z) / (x + y + z) equals 20%, and y / (x + y + z) equals 80%, and Where x / (x + y) equals 33%, and y / (x + y) equals 67%.

5. The method according to any one of claims 1-2, wherein the one or more sulfur donor molecules are selected from elemental sulfur or dispersed sulfur.

6. The method according to claim 5, wherein the one or more sulfur donor molecules are soluble crystalline sulfur with an average particle size not greater than 100 mesh.

7. The method according to any one of claims 1-2, wherein the organometallic zinc catalyst is selected from the group comprising:

8. The method according to any one of claims 1-2, wherein the organometallic zinc catalyst is selected from the group comprising zinc ethyl phenyl dithiocarbamate ZEPC, zinc dibutyl dithiocarbamate ZDBC, guanidine zincs, and / or isopropyl xanthate zincs.

9. The method according to any one of claims 1-2, wherein the composition further comprises: - Metal oxides; - One or more organic ligands selected from C18-C30 carboxylic acids, aliphatic amines, or aromatic amines; - One or more hydrocarbon organic solvents or oils with a boiling point not lower than the curing temperature of the composition; - A coupling agent of an organosilane molecule having one or more unsaturated bonds; and / or - An organic or inorganic filler that can be dispersed in the composition, and the organic or inorganic filler further has gas and solvent barrier properties and an average particle size of not more than 50 microns.

10. The method according to claim 9, wherein the metal oxide is zinc oxide.

11. The method according to claim 9, wherein the organic or inorganic filler is a layered talc filler.

12. The method according to claim 9, wherein the composition comprises: - 1.9% to 6.2% of a metal oxide; - 2.5% to 8.5% of one or more organic ligands; - 14% to 45% of one or more hydrocarbon-based organic solvents or oils; - 2.5% to 9.0% of a coupling agent; and / or - 1.5% to 12% of an organic or inorganic filler; wherein the percentages are calculated based on the total weight of the composition.

13. The method according to claim 9, wherein the one or more organic ligands are selected from the group consisting of:

14. The method according to claim 9, wherein the coupling agent is selected from the group consisting of:

15. The method according to claim 9, wherein the method further comprises step d) of reacting the metal oxide with the thiol obtained in step b) to form a zinc complex.

16. The method according to claim 15, wherein the metal oxide is zinc oxide.

17. The method according to claim 15 or 16, wherein the zinc complex is complexed with one or more organic ligands and then sulfided to obtain a second sulfided zinc complex.

18. The method according to any one of claims 1-2, wherein the method further comprises step e) of desulfurizing the polysulfide bridge by an organometallic zinc catalyst.

19. The method according to any one of claims 1-2, wherein the method further comprises step f) of sulfiding a coupling agent having more than one unsaturated bond to participate in step c).

20. An elastic glue prepared by the method according to any one of claims 1-19.

21. An inkjet print head comprising the elastic glue prepared by the method according to any one of claims 1-19.

22. Use of an elastic glue prepared by the method according to any one of claims 1-19 for bonding components inside an inkjet print head.

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