Water-repellent resin and liquid ejecting head using the same

Abstract

To provide a resin composition that maintains satisfactory water repellency during the long-term use, and a liquid ejecting head that includes the resin composition in a water-repellent layer.SOLUTION: A resin composition comprises a silicone resin, an epoxy resin, and an acrylic resin, wherein the acrylic resin is constituted by an acrylic monomer having an oxygen equivalent of 100 or more. The resin composition can be prepared through the reaction of a mixture containing a silicone monomer, an epoxy monomer, and an acrylic monomer having an oxygen equivalent of 100 or more with a cationic polymerization initiator.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-repellent resin and a liquid ejection head using the same as a water-repellent layer. [Background technology]

[0002] In a droplet ejection device such as an inkjet printer, droplets of ink or the like are ejected from an ejection port of a droplet ejection member (called a liquid ejection head, or simply an ejection head). An electromechanical transducer such as a piezoelectric element is used as an energy generating element for ejection. Other examples of energy generating elements include those that emit electromagnetic waves such as a laser to generate heat, and eject ink droplets using the heat generated by the element, and those that heat liquid using an electrothermal transducer having a heating resistor. In the ejection head, water-repellent treatment is applied around the ejection port to prevent ejection failure or non-ejection due to residual ink on the ejection port surface. Examples of materials that exhibit water-repellent properties include fluorine-based resins and silicone resins. Silicone resins do not exhibit water-repellent properties unless the siloxane chain is relatively long, but the longer the silicone chain, the lower the compatibility with other materials and the more difficult it is to mix uniformly. For the water-repellent treatment of the ejection head, silicone resins are mixed with reactive materials, catalysts, and photosensitizers to prepare a water-repellent agent, but only a relatively small amount can be mixed to obtain a compatible and uniform water-repellent agent. Meanwhile, Patent Document 1 discloses a resin composition containing a resin (A) having a polysiloxane unit, an active energy ray curable compound (B), and a liquid medium (C). The resin (A) contains a structural unit having a hydrophilic epoxy group, and is repelled by the hydrophobic polysiloxane unit due to hydrophilic-hydrophobic interaction, so that the resin (A) tends to float on the outermost surface of the coating film after application. Therefore, even if a small amount of silicone-based resin is added, the contamination resistance and weather resistance are further improved.

[0003] Generally, when epoxy monomers and acrylic monomers are cured with a cationic polymerization initiator, the epoxy monomer reacts by cationic polymerization, while the acrylic monomer reacts by radicals generated in the reaction system. In addition, as the epoxy monomer and acrylic monomer react individually, they form an interpenetrating polymer network (IPN) structure. This allows the acrylic resin to compensate for the physical properties that lack toughness of epoxy resin. Generally, the radical polymerization of acrylic resin is inhibited by the oxygen in the air, but since it can be maintained by mixing it with epoxy resin, it is less susceptible to curing inhibition. In addition, since the acrylic monomer also has sites where the reaction proceeds independently, the anti-blocking properties of the acrylic monomer improve the slipperiness of the ejection head against wiping, and wear on the water-repellent layer formed on the ejection head can be suppressed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-206636 A Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, silicone-based water-repellent resins have low compatibility and cannot be mixed in large amounts to be mixed uniformly with other resins, so a small amount is mixed and then segregated on the surface side of the layer to form a coating film so that only the surface area exhibits water repellency. In liquid ejection heads, wiping is performed to prevent ink droplets and ink from sticking, so with long-term use, the surface of the water-repellent layer wears away due to wiping and it no longer repels ink. Furthermore, when a silicone monomer for imparting water repellency is polymerized together with an epoxy monomer and an acrylic monomer for imparting abrasion resistance, the compatibility is low to begin with, and only a small amount can be added. SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to obtain a resin composition that can maintain good water repellency even after long-term use, and to obtain a liquid ejection head using this resin composition as a water-repellent layer. [Means for solving the problem]

[0006] The present inventors have discovered that when polymerizing an epoxy monomer, an acrylic monomer, and a silicone monomer for imparting water repellency, the above-mentioned problems can be solved by using an acrylic monomer with a low oxygen content in order to increase compatibility and increase the amount of silicone monomer added. That is, one aspect of the present invention relates to a resin composition containing a silicone resin, an epoxy resin, and an acrylic resin, wherein the oxygen equivalent of an acrylic monomer constituting the acrylic resin is 100 or more. Another aspect of the present invention relates to a water-repellent layer made of the above resin composition. A further aspect of the present invention relates to a liquid ejection head having the above-mentioned water-repellent layer at least around the ejection ports. Effect of the Invention

[0007] It is possible to obtain a resin composition that can maintain good water repellency even after long-term use, and a liquid ejection head having a water-repellent layer made of said composition. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic perspective view of a liquid ejection head according to an embodiment of the present invention. [Diagram 2] 2 is a schematic cross-sectional view showing the configuration of the liquid ejection head as viewed from the cross-sectional direction of the XX' portion in FIG. 1. [Diagram 3] 5A to 5C are cross-sectional process diagrams illustrating a manufacturing method of a liquid ejection head according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The resin composition according to one embodiment of the present invention will be described below. The resin composition is obtained by polymerizing a silicone monomer, which is a water-repellent substance having a siloxane skeleton, with an epoxy monomer and an acrylic monomer, and contains a silicone resin, an epoxy resin, and an acrylic resin.

[0010] Patterning performance is required to form a water-repellent film avoiding the discharge port of a liquid discharge head, so a photocationic polymerization initiator is preferably used as a polymerization initiator when polymerizing a monomer. Specific examples of photocationic polymerization initiators include the following: aromatic onium salts [see J.POLYMERSCI: Symposium No. 56 383-395 (1976)], Irgacure (registered trademark) 261 marketed by BASF Japan, SP-150 (trade name), SP-170 (trade name), and SP-172 (trade name) marketed by ADEKA. Other examples include Triazine A, Triazine PMS, Triazine PP, and Triazine B marketed by DKSH Japan, and PHOTO INITIATOR 2074 (trade name) marketed by Solvay Japan. In addition, in areas where an improvement in crosslink density or patterning is not required, a thermal cationic polymerization initiator can be used alone or in combination.

[0011] Specific examples of the thermal cationic polymerization initiator include San-Aid SI-60L (trade name), San-Aid SI-80L (trade name), and San-Aid SI-100L (trade name) marketed by Sanshin Chemical Industry Co., Ltd. In addition, CP-66 (trade name) and CP-77 (trade name) marketed by ADEKA Corporation, and a combination of an aromatic onium salt and a reducing agent (see JP-A-54-102394, J. POLYMERSCI: Polymer Chemical Edition Vol. 1121, 97-109 (1983)) can be mentioned.

[0012] The epoxy monomer is not particularly limited, but may be an alicyclic epoxy monomer having high activity against cations. Examples of the alicyclic epoxy monomer include polyglycidyl ether of polyhydric alcohol having at least one aliphatic ring, or cyclohexene, and a dicyclopentadiene skeleton obtained by epoxidizing a cyclopentene ring-containing compound with an oxidizing agent. Examples of the epoxy monomer include a cyclohexene oxide structure-containing compound and a cyclopentene oxide structure-containing compound obtained by epoxidizing a vinylcyclohexane structure-containing compound with an oxidizing agent. Examples of the epoxy monomer include a vinylcyclohexane oxide structure-containing compound obtained by epoxidizing a vinylcyclohexane structure-containing compound with an oxidizing agent. Examples of the commercially available products include EHPE-3150 (trade name, manufactured by Daicel Chemical Industries, Ltd.) and Celloxide 2021 (trade name, manufactured by Daicel Chemical Industries, Ltd.). From the viewpoint of reactivity, polyfunctional epoxy resins such as biphenyl type, bisphenol A novolac type, bisphenol F novolac type, and phenol novolac type are also preferably used. Among them, a dicyclopentadiene type epoxy resin is preferably used because it also has compatibility. Other aliphatic types may also be used if necessary.

[0013] Acrylic resin forms an interpenetrating polymer network structure with epoxy resin, and the raw material acrylic monomer plays a role in compatibilizing silicone monomer and epoxy monomer, which will be described later. Therefore, in order to increase compatibility with silicone monomer, it is preferable that the acrylic monomer has no oxygen atoms other than the acrylic part, and in order to increase compatibility with epoxy monomer, it is preferable that the hydrocarbon chain has an appropriate length. Specifically, one with an oxygen equivalent of 100 or more is used. By making the oxygen equivalent 100 or more, compatibility with the silicone monomer is improved, the amount of silicone monomer that can be added can be increased, and segregation of the silicone resin on the surface layer of the resin composition can be prevented. Here, the "oxygen equivalent" is the value obtained by dividing the molecular weight of the acrylic monomer by the number of oxygen atoms contained in the monomer molecule. For example, the molecular weight of acrylic acid is 72.06, and since it has two oxygen atoms, the oxygen equivalent is 36.03 (approximately 36). Specific examples of acrylic monomers having an oxygen equivalent of 100 or more include the following (the number in parentheses indicates the oxygen equivalent): isobornyl acrylate (104), isodecyl acrylate (106), lauryl acrylate (120), stearyl acrylate (162), isostearyl acrylate (162), dicyclopentanyl acrylate (103), etc. In particular, at least one selected from the group consisting of isobornyl acrylate and dicyclopentanyl acrylate is preferred.

[0014] Examples of silicone monomers for achieving water repellency include monomers having a siloxane structure as shown in the following general formula (1). That is, by having an alkyl group at one end, compatibility with epoxy monomers and acrylic monomers is improved. By providing a reactive unit at the other end, the silicone resin after polymerization can be uniformly dispersed in the resin composition. Here, when the siloxane structure has about 10 repeating units, sufficient water repellency is exhibited, and when the repeating units has about 80 units, compatibility with the composition is not impaired.

[0015] [ka] (wherein R1 is an alkyl group having 3 to 5 carbon atoms, R2 is an alkylene group having 1 to 5 carbon atoms, R3 is at least one functional group represented by the following formulas (2) to (5), and n is an integer of 10 to 76.

[0016] [ka]

[0017] In addition, various additives can be used in the resin composition of the present invention. For example, silane coupling agents can be used as adhesion improvers and compatibilizers. Specific examples of silane coupling agents that can be used preferably include SILQUEST (registered trademark) A-186 and A-187 (manufactured by Momentive Performance Materials Japan, Inc.). The resin composition of the present invention can be used as a water-repellent resin. The resin composition can be produced by adding a cationic polymerization initiator to a mixture containing a silicone monomer, an epoxy monomer, and an acrylic monomer having an oxygen equivalent of 100 or more, and then carrying out photopolymerization and thermal polymerization.

[0018] <Liquid ejection head> Fig. 1 is a schematic perspective view of a liquid ejection head according to an embodiment of the present invention, Fig. 2 is a schematic cross-sectional view showing the configuration of the liquid ejection head as viewed from the cross-sectional direction along the line XX' in Fig. 1. As shown in FIG. 1 and FIG. 2, this recording head includes a nozzle plate 4 having an ejection port 7 on a head substrate 1 (also simply referred to as a substrate) having liquid ejection energy generating elements 2 that generate energy for ejecting ink. In addition, a bubbling chamber 8 that communicates with the ejection port 7 is provided facing the substrate surface on which the liquid ejection energy generating elements are formed, and an ink supply port 9 that supplies ink to the bubbling chamber 8. The ink supply port 9 penetrates the substrate 1 and supplies ink from the surface opposite to the surface on which the nozzle plate 4 is formed. As shown in FIG. 2, a water-repellent layer 5 is provided on the outer surface of the nozzle plate 4, and by reducing the wettability of the area around the ejection port to the liquid, the size, ejection direction, ejection speed, etc. of the droplets can be stabilized, and high-quality printing can be performed.

[0019] <Method of Manufacturing Liquid Ejection Head> Next, the manufacturing process of the liquid ejection head of the present invention will be described in order of steps with reference to FIG. First, as shown in FIG. 3(a), a substrate 1 on which a plurality of liquid discharge energy generating elements 2 are formed is prepared. The substrate 1 is preferably a silicon single crystal substrate on which a driving circuit and wiring connecting the driving circuit and the liquid discharge energy generating elements can be easily fabricated. The liquid discharge energy generating elements 2 can be a heater type that generates heat by passing electricity through a resistor, or any other element that can convert electricity into bubbling energy. In addition, in order to suppress corrosion of the liquid discharge energy generating elements 2 by the discharge liquid and to improve electrical insulation, a protective film (not shown) such as SiO, SiN, or tantalum can be provided on the substrate 1. In this case, a protective layer may be formed over the entire surface of the substrate 1. In FIG. 2 and other figures, the liquid discharge energy generating elements 2 are shown as if they are embedded in the substrate 1 because the substrate 1 includes such a protective layer. Next, a removable mold 3 is formed in the area that will become the liquid flow path and the bubble-forming chamber on the side of the substrate 1 where the liquid discharge energy generating elements 2 are formed. The mold material is selected in consideration of the surrounding materials, and is selected from organic resin materials and metal materials. If it is an organic resin material, a positive photosensitive resin can be used. 3(b), a layer 4' that will become the nozzle plate material 4 is formed so as to cover the substrate 1 and the mold material 3. Either an organic material or an inorganic material can be used for this layer. In this embodiment, it is preferable to use a negative photosensitive resin because it can be patterned together with the water-repellent layer, and the photosensitive resin layer 4' is formed to a desired thickness. Next, as shown in FIG. 3(c), a coating solution of the resin composition according to the present invention is applied by spin coating or slit coating so as to cover the photosensitive resin layer 4', and then dried, or a dry film is formed and laminated by transfer or the like to form a water-repellent layer precursor 5'.

[0020] Next, the photosensitive resin layer 4' and the water-repellent layer precursor 5' are pattern-exposed to light through a mask 6. Ultraviolet light can be used as the exposure light, and exposure at a single wavelength using, for example, i-line (365 nm) can be used. In the irradiated area, the nozzle plate material 4 and the water-repellent layer 5 are formed by acid generated from the photocationic polymerization initiator present in the photosensitive resin layer 4' and the water-repellent layer precursor 5' (Fig. 3(d)). Finally, the uncured portion and the mold material 3 are removed to form the discharge port 7 and the bubbling chamber 8 (Fig. 3(e)). EXAMPLES

[0021] Next, the present invention will be described with reference to examples and comparative examples. Unless otherwise specified, "parts" refers to mass units.

[0022] <Production of Resin Composition> The method for producing the resin composition is to add a cationic polymerization initiator to a mixture containing a silicone monomer, an epoxy monomer, and an acrylic acid monomer with an oxygen equivalent of 100 or more. That is, the epoxy monomer, the acrylic monomer, and the silicone monomer are each weighed, and then dissolved and mixed. The mixture was mixed using a mixer (EME V-mini300) at 1600 rpm revolution and 800 rpm rotation under vacuum for 10 minutes to obtain a monomer composition.

[0023] After visually checking the compatibility of the monomer composition, SP-172 (ADEKA) was added as a cationic polymerization initiator, and the monomer composition was placed on a fluororesin (trademark Teflon) sheet and exposed to a high-pressure mercury lamp at 60 mw for 33 seconds. The cured state was confirmed, and thermal curing was performed at 100°C for 3 hours to obtain a resin composition. The composition of each component used here is shown in Tables 1 and 2. The silicone monomers used were those in which R1 was CH3(CH2)3-, R2 was -(CH2)3-, and R3 was a hydroxy group (formula 2) or a dihydroxy group (formula 3) in the general formula (1).The ...

[0024] <Measurement of physical properties of resin composition> The resin composition was peeled off from the fluororesin sheet, and the contact angle between the cured surface and the reverse surface (fluororesin sheet surface) was measured, as well as the static friction coefficient of the cured surface (using a portable friction meter Type: 37i manufactured by Shinto Scientific Co., Ltd.). The measurement results are shown in Tables 1 and 2.

[0025] [Table 1]

[0026] R-45EPT Nagase Chemtec Corporation HP7200L DIC Jer152 Mitsubishi Chemical Corporation EHPE-3150 Daicel Chemical Industries, Ltd. EP400V Kaneka FA-513AS manufactured by Resonac IBXA Osaka Organic Chemical Co., Ltd.

[0027] [Table 2]

[0028] [Table 3]

[0029] In the above Examples 1 to 10, the silicone monomer and the epoxy monomer can be uniformly mixed and cationic polymerization can be carried out by using an acrylic monomer with an oxygen equivalent of 100 or more, whereby the silicone resin can be incorporated into the interpenetrating polymer network (IPN) of the epoxy resin and the acrylic resin. These configurations allow the resin composition to incorporate 10% by mass or more of water-repellent silicone resin, which can be distributed throughout the resin composition without segregation. This allows the silicone resin to be contained not only on the surface but also in the layer and on the back surface, allowing water repellency to be maintained for a long period of time even after wiping. In Comparative Example 15 described later, it is understood that a large amount of silicone resin cannot be mixed in. As a result, water repellency is only exhibited on the surface.

[0030] In terms of the static friction coefficient, the present invention has a low coefficient of 0.18 to 0.41, whereas Comparative Example 15 has a coefficient of 0.8, which is about three times higher. This is because the present invention uses an acrylic monomer with an oxygen equivalent of 100 or more, which allows the cationic curable silicone resin to be uniformly dispersed in the resin composition. Furthermore, the anti-blocking performance, which is a characteristic of the acrylic resin, allows the material to exhibit good slip properties.

[0031] Example 5 shows the case where dicyclopentadiene epoxy resin and dihydroxy type silicone resin are used, which is cured to the inside at the time of UV irradiation, making it a highly reactive combination. Furthermore, the static wear coefficient, which is an index of the anti-blocking performance characteristic of acrylic resin, is the lowest value.

[0032] The compatibility and reactivity of each acrylic monomer with the silicone monomer are confirmed in Comparative Examples 1 to 4. In Comparative Example 1, the acrylic monomer has a low oxygen equivalent, and is not compatible with the silicone monomer due to its high polarity. In Comparative Example 2, when the oxygen equivalent is 5600, the mixture is slightly cloudy and compatible. This is thought to be because the molecular weight of the acrylic monomer is too high and it is in a polymer state. Comparative Examples 3 to 5, in which the oxygen equivalent is around 100, show good compatibility.

[0033] Therefore, if the oxygen equivalent is 100 or more, acrylic monomers and oligomers will mix well. Even if the acrylic is close to a polymer, it can be mixed and cured. There is no particular upper limit to the oxygen equivalent, but it can be 6000 or less, for example.

[0034] In Comparative Examples 4 to 6, the compatibility with the acrylic monomer was confirmed depending on the molecular weight of the silicone monomer. It was found that the silicone monomer was compatible up to a molecular weight of 5,000, but was not compatible at a molecular weight of 10,000. It is clear that in Comparative Examples 1 and 6, the silicone monomer and the acrylic monomer are not compatible with each other, and the reaction does not proceed.

[0035] In Comparative Examples 2 to 5 and 7, the silicone monomer and the acrylic monomer are compatible and react with each other, but the reactivity of the silicone monomer is low. Furthermore, because it is a radical polymerization reaction, it is susceptible to oxygen inhibition, and therefore stickiness remains. The compatibility of the epoxy monomer and the silicone monomer is confirmed in Comparative Examples 8 to 15. Since the epoxy monomer is often highly viscous or solid, an alicyclic silane coupling agent that is highly reactive to the cationic polymerization initiator is added in all the examples except Comparative Example 8. In Comparative Examples 8 to 14, all of the materials were incompatible and formed a gel.

[0036] In Comparative Example 15, the silicone monomer was small, so the solution was slightly cloudy, but curing was possible. The contact angle between the cured surface and the back surface was 85 / 60, which suggests that the cationic curable silicone resin was segregated on the cured surface. The static friction coefficient μ against fine paper was 0.8.

[0037] <Comparative Test> A blade resistance test was carried out for Example 7 and Comparative Example 15, in which the contact angles of the cured surfaces were comparable.

[0038] Each resin was spin-coated onto a silicon wafer to a thickness of 10 μm, exposed to light at 60 mW for 33 seconds, and then heat-cured at 100° C. for 3 hours. Next, a rubber blade made of HNBR, with a rubber hardness of 70 and a thickness of 1 mm was pressed in and wiped in a dry state at a speed of 80 mm / s for 1 mm. Observations were made under a microscope every 50 wipes.

[0039] In Comparative Example 15, wear was observed on the surface after 50 wipes, whereas in Example 9, no change was observed even after 1,500 wipes. This confirmed that a resin composition with good water repellency even when used for a long period of time can be obtained by carrying out cationic polymerization using an acrylic monomer with an oxygen equivalent of 100 or more, which has good compatibility with both the epoxy monomer and the silicone monomer. In addition, by using an acrylic monomer with an oxygen equivalent of 100 or more, a cationic curable silicone resin can be incorporated into the interpenetrating polymer network structure of the epoxy resin and the acrylic resin. This provides high reactivity and high wiping resistance, and since the cationically curable silicone resin is incorporated throughout the composition, good water repellency is maintained.

[0040] The present invention includes the following configurations. [Configuration 1] A resin composition comprising a cationically curable silicone resin, an epoxy resin, and an acrylic resin, wherein the oxygen equivalent of the acrylic monomer constituting the acrylic resin is 100 or more. [Configuration 2] The resin composition according to Configuration 1, wherein the cationically curable silicone monomer constituting the cationically curable silicone resin is a siloxane monomer represented by the following general formula (1):

[0041] [ka] (wherein R1 is an alkyl group having 3 to 5 carbon atoms, R2 is an alkylene group having 1 to 5 carbon atoms, R3 is at least one functional group represented by the following formulas (2) to (5), and n is an integer of 10 to 76.

[0042] [ka]

[0043] [Configuration 3] The resin composition according to configuration 1 or 2, wherein the silicone resin is 10% by mass or more of the resin composition. [Configuration 4] The resin composition according to any one of configurations 1 to 3, wherein the acrylic monomer having an oxygen equivalent of 100 or more is at least one selected from the group consisting of isobornyl acrylate and dicyclopentanyl acrylate. [Configuration 5] The resin composition according to any one of Configurations 1 to 4, wherein the epoxy monomer constituting the epoxy resin has a dicyclopentadiene skeleton. [Configuration 6] A water-repellent resin comprising the resin composition according to any one of Configurations 1 to 5. [Configuration 7] A liquid ejection head having the resin composition according to any one of Configurations 1 to 5 patterned on at least the surface around an ejection port. The present invention also includes the following methods. [Method 1] A method for producing the resin composition according to any one of the above items 1 to 5, comprising reacting a mixture containing a silicone monomer, an epoxy monomer, and an acrylic monomer having an oxygen equivalent of 100 or more using a cationic polymerization initiator. [Explanation of symbols]

[0044] 1 Board 2 Energy generating element 4 Nozzle plate material 5. Water-repellent layer 7 Outlet

Claims

1. A resin composition comprising a cationically curable silicone resin, an epoxy resin, and an acrylic resin, wherein the oxygen equivalent of an acrylic monomer constituting the acrylic resin is 100 or more.

2. 2. The resin composition according to claim 1, wherein the cationically curable silicone resin comprises a cationically curable silicone monomer which is a siloxane monomer represented by the following general formula (1): 【Chemistry 1】 (R in the formula １ is an alkyl group having 3 to 5 carbon atoms, R ２ is an alkylene group having 1 to 5 carbon atoms, R ３ represents at least one functional group represented by the following formulas (2) to (5), and n represents an integer of 10 to 76. 【Chemistry 2】

3. The resin composition according to claim 1 , wherein the silicone resin is present in an amount of 10% by mass or more of the resin composition.

4. 2. The resin composition according to claim 1, wherein the acrylic monomer having an oxygen equivalent of 100 or more is at least one selected from the group consisting of isobornyl acrylate and dicyclopentanyl acrylate.

5. 2. The resin composition according to claim 1, wherein an epoxy monomer constituting the epoxy resin has a dicyclopentadiene skeleton.

6. A water-repellent resin comprising the resin composition according to any one of claims 1 to 5.

7. A liquid ejection head having the resin composition according to any one of claims 1 to 5 patterned on at least a surface around an ejection port.

8. The method for producing the resin composition according to any one of claims 1 to 5, wherein a mixture containing a silicone monomer, an epoxy monomer, and an acrylic monomer having an oxygen equivalent of 100 or more is reacted using a cationic polymerization initiator.

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