2-Cyanoacrylate and method for producing the same

Abstract

To provide a 2-cyanoacrylate that has improved adhesiveness to difficult-to-adhere material, particularly thermoplastic elastomer (TPE) such as olefinic thermoplastic elastomer (TPO) and cross-link type olefinic thermoplastic elastomer (TPV).SOLUTION: The present inventors have made intensive studies to solve the above problem, and as a result, have found that the above problem can be solved by a production method including (A) a step of contacting 2-cyanoacrylate with a neutral to acidic porous clay, and (B) a step of separating the 2-cyanoacrylate and the porous clay by distillation.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a 2-cyanoacrylate having excellent adhesiveness to a difficult-to-adhere material and a method for producing the same.

Background Art

[0002] 2-Cyanoacrylate (especially a 2-cyanoacrylate adhesive composition containing 2-cyanoacrylate as a main component) is instantaneously polymerized and cured by anionic species such as moisture on the surface of an adherend or in the air in a short time due to its high anionic polymerizability to adhere various materials, and thus is widely used as an instant adhesive in various industrial fields such as electronics, electrics, and automobiles, the leisure field, and ordinary households.

[0003] However, the adhesiveness of 2-cyanoacrylate may be extremely poor depending on the material of the adherend. For example, polyolefins such as polypropylene and polyethylene, crystalline engineering plastics such as polyacetal and polybutylene terephthalate, and ethylene-propylene rubbers (EPM) such as ethylene-propylene-diene copolymer (EPDM) have low polarity, so the amount of moisture and interaction on the surface are small, and the adhesive strength cannot be sufficiently exhibited.

[0004] Therefore, various methods for adhering an adherend showing poor adhesiveness to the above-mentioned 2-cyanoacrylate using 2-cyanoacrylate have been studied. For example, a method of applying a surface treatment agent (so-called primer) in advance to modify the surface of the adherend to improve adhesiveness (for example, Patent Documents 1 and 2) is known.

[0005] In recent years, thermoplastic elastomers (TPE) that can be injection-molded like plastics and have elasticity like rubber have begun to be used as substitutes for rubber. Among them, olefin-based thermoplastic elastomers (TPO) composed of polypropylene and EPM (EPDM), and crosslinked olefin-based thermoplastic elastomers (TPV) composed of crosslinked rubber such as EPM (EPDM) crosslinked with polypropylene are excellent in terms of light weight, weather resistance, and material cost, and are widely used.

[0006] Furthermore, since TPO and TPV are composed of materials that exhibit the aforementioned poor adhesion properties, it is expected that they will exhibit similar poor adhesion properties when bonded using 2-cyanoacrylate. However, when the inventors of this application conducted adhesion tests on these substrates, it was found that the adhesion properties were even lower than those of EPDM, which is known to exhibit particularly poor adhesion properties. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2015-129215 [Patent Document 2] Japanese Patent Publication No. 2015-224277 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention aims to provide a 2-cyanoacrylate with improved adhesion to difficult-to-bond materials, particularly thermoplastic elastomers (TPEs) such as olefin-based thermoplastic elastomers (TPO) and crosslinked olefin-based thermoplastic elastomers (TPV). [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems and have found that the above problems can be solved by a manufacturing method comprising (A) a step of contacting 2-cyanoacrylate with porous clays exhibiting neutral to acidic pH, and (B) a step of separating 2-cyanoacrylate and porous clays by distillation. Specifically, the present invention includes the following inventions.

[0010] [1] (A) A process of contacting 2-cyanoacrylate with porous clays that exhibit neutral to acidic properties. and (B) A process of separating porous clays exhibiting neutral to acidic pH from 2-cyanoacrylate by distillation. A method for producing 2-cyanoacrylate containing (however, step (B) is carried out simultaneously with step (A) or after step (A)).

[0011] [2] The method for producing 2-cyanoacrylate according to [1], wherein the porous clay is at least one selected from the group consisting of activated clay and acidic clay.

[0012] [3] 2-cyanoacrylate obtained by the manufacturing method described in [1] or [2].

[0013] [4] An adhesive composition containing the 2-cyanoacrylate described in [3]. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a 2-cyanoacrylate with excellent adhesion to difficult-to-bond materials, particularly TPO and TPV. Therefore, it can be suitably used as a raw material for 2-cyanoacrylate adhesive compositions used in fields where these difficult-to-bond materials are used (e.g., automotive parts).

[0015] Furthermore, according to the manufacturing method of the present invention, by carrying out step (A) above, it becomes possible to carry out step (B) above at a lower temperature than general distillation conditions, thereby avoiding abnormal polymerization due to heat exposure and further improving the quality of 2-cyanoacrylate. [Modes for carrying out the invention]

[0016] The 2-cyanoacrylate of the present invention can be produced by a manufacturing method (manufacturing method of the present invention) comprising the steps of (A) contacting the 2-cyanoacrylate with porous clays exhibiting neutral to acidic pH, and (B) separating the 2-cyanoacrylate from the porous clays by distillation. Step (B) is performed simultaneously with or after step (A).

[0017] In the present invention, the 2-cyanoacrylate used can be any 2-cyanoacrylate commonly used as a raw material for 2-cyanoacrylate adhesive compositions. Specifically, examples include esters of 2-cyanoacrylic acid such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, octyl, neopentyl, cyclohexyl, ethylhexyl, allyl, methoxyethyl, ethoxyethyl, and methoxypropyl, with methyl, ethyl, n-butyl, methoxyethyl, and ethoxyethyl esters being preferred. In addition, one or more of these 2-cyanoacrylates may be used in combination as needed.

[0018] The 2-cyanoacrylate used in step (A) above may be a commercially available product or one produced by a known manufacturing method. Known manufacturing methods include, for example, a method in which cyanoacetic acid ester and formaldehyde are condensed in an organic solvent in the presence of a basic catalyst, and the resulting condensate is depolymerized in an acidic gas stream under high temperature and reduced pressure conditions in the presence of a polymerization inhibitor and a depolymerization catalyst to obtain 2-cyanoacrylate.

[0019] In the above step (A), examples of the porous clays showing neutral to acidic properties and contacting with 2-cyanoacrylate include montmorillonite, zeolite, silica gel, celite, diatomaceous earth, talc, etc. Examples of montmorillonite include acid clay, activated clay, etc. Acid clay is a neutral to acidic clay mineral mainly composed of montmorillonite, and activated clay is obtained by treating acid clay or bentonite mainly composed of montmorillonite with an acid such as an inorganic acid. Among these porous clays showing neutral to acidic properties, acid clay and activated clay are preferred, and activated clay is more preferred. These porous clays may be used alone or in combination of two or more. On the other hand, there are also porous clays showing basic properties. However, when a porous clay showing basic properties is contacted with 2-cyanoacrylate, it may cause problems such as aggregation and solidification of the porous clay (poor dispersion in 2-cyanoacrylate), polymerization of 2-cyanoacrylate, and deterioration of storage stability, so it is not preferred.

[0020] The liquidity (acidic, neutral or basic) of the porous clay can be determined, for example, by measuring the pH of the porous clay by the method described in the section of the examples to be described later.

[0021] The shape of the porous clay is not particularly limited and can take various shapes such as powdery, granular, bead-like, pellet-like, etc. From the viewpoint of increasing the contact area with 2-cyanoacrylate, it is preferably granular or powdery.

[0022] Examples of activated clay that are commercially available include Galleon Earth V2R (manufactured by Mizusawa Chemical Co., Ltd.), Galleon Earth NV (manufactured by Mizusawa Chemical Co., Ltd.), Galleonite #251 (manufactured by Mizusawa Chemical Co., Ltd.), Galleonite #336 (manufactured by Mizusawa Chemical Co., Ltd.), SA35 (manufactured by Nippon Activated Clay Co., Ltd.), SA1 (manufactured by Nippon Activated Clay Co., Ltd.), R-15 (manufactured by Nippon Activated Clay Co., Ltd.), Nikkanite G-36 (manufactured by Nippon Activated Clay Co., Ltd.), Nikkanite G-153 (manufactured by Nippon Activated Clay Co., Ltd.), Nikkanite G-168 (manufactured by Nippon Activated Clay Co., Ltd.), etc.

[0023] In addition, examples of acid clays available commercially include Mizuka Ace #20 (manufactured by Mizusawa Chemical Co., Ltd.), Mizuka Ace #400 (manufactured by Mizusawa Chemical Co., Ltd.), Galeonite #036 (manufactured by Mizusawa Chemical Co., Ltd.), Galeonite #0612 (manufactured by Mizusawa Chemical Co., Ltd.), Nikkanite S-200 (manufactured by Nippon Activated Clay Co., Ltd.), Nikkanite A-36 (manufactured by Nippon Activated Clay Co., Ltd.), and Nikkanite A-168.

[0024] In step (A), specific methods for contacting 2-cyanoacrylate with porous clays include, for example, adding porous clays to 2-cyanoacrylate (immersion method) or passing 2-cyanoacrylate through a column packed with porous clays. In the immersion method, stirring or shaking may be performed after adding the porous clays to increase the contact efficiency between 2-cyanoacrylate and porous clays. Furthermore, when performing steps (A) and (B) simultaneously, for example, both steps can be performed simultaneously by adding 2-cyanoacrylate and porous clays to a reactor used for distillation and then performing step (B) as described later.

[0025] The amount of porous clay to be brought into contact with 2-cyanoacrylate is, for example, 0.01 to 10 parts by weight, preferably 0.1 to 6 parts by weight, per 100 parts by weight of 2-cyanoacrylate. The temperature at that time is, for example, 0 to 100°C, preferably 10 to 80°C, more preferably 20 to 60°C.

[0026] Furthermore, since 2-cyanoacrylate undergoes polymerization in the presence of moisture in the air, step (A) is usually carried out in the presence of an inert gas such as nitrogen. In addition, the immersion method can be carried out under reduced pressure for degassing and separation of low-boiling components. Typically, this is done while stirring under reduced pressure, preferably 16 kPa or less, more preferably 8 kPa or less, even more preferably 1.3 kPa or less, and particularly preferably 0.67 kPa or less, while adjusting the temperature between 0 and 50°C so that it is below the boiling point of 2-cyanoacrylate.

[0027] After step (A) and before step (B), porous clays may be separated by filtration, decantation, or other means as needed. Specifically, examples include a method of separating the porous clays by allowing the suspension of 2-cyanoacrylate and porous clays to stand and allowing the porous clays to settle (decantation), or a method of filtration using a filter or mesh. However, as a result of the inventors' investigation, although the cause is unclear, as shown in the Examples section below, separation by filtration or decantation alone does not improve the adhesion compared to 2-cyanoacrylate before applying the manufacturing method of the present invention, and storage stability deteriorates, with particularly significant thickening in accelerated tests at high temperatures of 70°C or higher. Therefore, the inventors concluded that step (B) is essential.

[0028] In step (B), the pressure and temperature during distillation can be appropriately selected according to the boiling point of 2-cyanoacrylate, but the pressure is preferably reduced, and more preferably 0.1 to 2 kPa. The temperature is preferably 30 to 150°C, and more preferably 30 to 120°C.

[0029] In process (B), the initial and final distillates are usually cut off, and only the main distillate is recovered. Here, "initial distillate" refers to the fraction containing a large amount of low-boiling components from the start of distillation until a predetermined weight ratio (initial distillate cut-off rate) is reached, "main distillate" refers to the fraction from the time the initial distillate is cut off until the contents of the still reach a predetermined weight ratio (final distillate cut-off rate), and "final distillate" refers to the fraction containing a large amount of high-boiling components and the still residue after the recovery of the main distillate. The initial distillate cut-off rate is, for example, 0.1 to 8% by weight relative to the 2-cyanoacrylate used in process (A). The final distillate cut-off rate is, for example, 0.1 to 20% by weight relative to the 2-cyanoacrylate used in process (A). Furthermore, if processes (A) and (B) are performed simultaneously, or if the porous clays are not separated by filtration, decantation, etc., after process (A) but before process (B), the value obtained by subtracting the weight of the porous clays used in process (A) from the weight of the "post-distillation" shall be used as the reference value for the post-distillation cut-off rate.

[0030] In step (B), if necessary, radical polymerization inhibitors such as hydroquinone and pyrogallol, which are normally used in the distillation of 2-cyanoacrylate, or anionic polymerization inhibitors such as phosphorus pentoxide, sulfur dioxide, methanesulfonic acid, p-toluenesulfonic acid, boron trifluoride diethyl ether, hydrofluoric acid, and trialkylborate may be used.

[0031] The 2-cyanoacrylate obtained in this manner exhibits superior adhesion to difficult-to-bond materials, particularly TPO and TPV, and superior storage stability (especially storage stability measured by accelerated tests at high temperatures of 70°C or higher), compared to known 2-cyanoacrylates.

[0032] Furthermore, it is believed that the 2-cyanoacrylate of the present invention exhibits the above-mentioned effects due to some difference from known 2-cyanoacrylates, such as the removal of trace amounts of impurities normally contained in 2-cyanoacrylates, the addition of trace amounts of substances derived from porous clays, or a change in a part of the structure of 2-cyanoacrylate. However, the number of trace components that could be considered as contributing factors is far too large, and it is impossible to analyze trace components below the detection limit. In fact, although the inventors of this application attempted to find differences between the 2-cyanoacrylate of the present invention and known 2-cyanoacrylates using known analytical methods at the time of filing (e.g., ion chromatography, mass chromatography, etc.), they were unable to find any differences. Therefore, it must be said that "directly identifying the 2-cyanoacrylate of the present invention that can exhibit the above-mentioned effects by its structure or properties" is generally impractical.

[0033] Furthermore, the 2-cyanoacrylate of the present invention may be combined with additives to form a 2-cyanoacrylate adhesive composition. As additives, for example, stabilizers (e.g., anionic polymerization inhibitors such as sulfur dioxide, methanesulfonic acid, p-toluenesulfonic acid, boron trifluoride diethyl ether, hydrofluoric acid, trialkylborate, etc., and radical polymerization inhibitors such as hydroquinone, hydroquinone monomethyl ether, etc.), plasticizers (dimethyl phthalate, diethyl phthalate, dibutyl phthalate, 2-ethylhexyl phthalate, diisodecyl phthalate, etc.), colorants, fragrances, solvents, curing accelerators, strength improvers, aliphatic polycarboxylic acids, etc., which are known additives for 2-cyanoacrylate adhesive compositions, can be appropriately blended within a range that does not impair the adhesive properties of the 2-cyanoacrylate of the present invention. [Examples]

[0034] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. The various tests and evaluations in the examples and comparative examples were carried out as follows. In the examples, the cut rate of the initial distillate, the yield of the main distillate, and the cut rate of the final distillate are the weight ratios of the initial distillate, main distillate, and final distillate to the weight (initial weight) of the raw material 2-cyanoacrylate, respectively.

[0035] <Testing and Evaluation Methods> (1) Exterior Samples were prepared using each adhesive composition according to the method in accordance with JIS K 6861-4, and their appearance was evaluated visually. <Evaluation Criteria> ○: Transparent (no cloudiness, etc.), and colorless. ×: Semi-transparent (may be cloudy, etc.), and / or colored.

[0036] (2) Storage stability The initial viscosity of each adhesive composition and the viscosity after filling 20g of each adhesive composition into a polyethylene bottle, sealing it tightly, and letting it stand for 7 days in a 70°C atmosphere ("viscosity after 7 days at 70°C") were used to determine the viscosity increase ratio. Storage stability was then evaluated based on the following evaluation criteria. Viscosity was measured using a TVE-25H viscometer manufactured by Toki Sangyo Co., Ltd., under the conditions of temperature: 20°C, cone rotor: 1°34'×R24, and rotation speed: 100rpm. The viscosity increase ratio was the ratio of the initial viscosity to the viscosity after 7 days at 70°C ("viscosity after 7 days at 70°C" / "initial viscosity"). <Evaluation Criteria> ○: Thickening ratio ≤ 3.0 times ×: Thickening ratio > 3.0x

[0037] (3) Adhesiveness Test specimens were prepared by bonding each adhesive composition and each adherend at 22°C and 60% RH, and then curing them under pressure at 22°C and 60% RH for 24 hours. To prevent deformation of each adherend during the bonding process, the specimens were sandwiched between two 2×25×50mm PTFE plates. After the predetermined curing time, the PTFE plates were removed to obtain the test specimens. Tensile shear adhesion tests were performed on the prepared test specimens using an Autograph scanner manufactured by Shimadzu Corporation, and the adhesion was evaluated based on the following evaluation criteria. Three types of adherends were used: EPDM test specimens (2×25×50mm) from Standard Test Pieces, Thermoplastic elastomer test specimen <1> (Santoprene 101-73BK, 2×25×50mm) from Yuko Trading Co., Ltd., and Thermoplastic elastomer test specimen <2> (Torexprene QT60MB, 2×25×50mm) from Yuko Trading Co., Ltd. Adherent shape: rectangular 2×25×50mm, Adhesion area (overlap area): 25 x 12.5 mm Initial fixture spacing for the Autograph (precision universal testing machine): 40mm (initial shape of the test piece, with the center of the adhesive part set at the center (20mm)). Deformation speed: 100 mm / min A tensile shear adhesion test was conducted under the specified conditions. The "elongation" used to evaluate adhesion refers to the strain of the test specimen at the time of adhesive failure, and is calculated as follows: "Elongation (%)" = {Jig spacing of the autograph at the time of adhesive failure (mm) - Initial jig spacing (mm)} ÷ Initial jig spacing (mm) × 100. <Evaluation Criteria> ○: For all three types of adherends, the "elongation rate" is 35% or higher. ×: At least one of the three adherends has an elongation rate less than 35%.

[0038] (Example 1) 100 parts by weight of ethyl 2-cyanoacrylate (manufactured by Taoka Chemical India Private Limited) and 5.0 parts by weight of Nikkanite G-36 (granular activated clay, pH 3.6, manufactured by Nippon Activated Clay Co., Ltd.) as porous clays were filled into a nitrogen-purged 1L polyethylene bottle, and the ethyl 2-cyanoacrylate and activated clay were brought into contact with each other for 1 hour at 40°C and 145 rpm using a shaker. Next, the contents were filtered using a polyethylene 150-mesh filter and a polypropylene heat-sealed felt filter (filtration accuracy 1 μm, 3M heat-sealed felt filter bag NB series, manufactured by 3M Japan). Then, 0.002 parts by weight (20 ppm) of boron trifluoride diethyl ether complex was added, and the mixture was transferred to a 1 L three-necked pear-shaped flask. A thermometer, a Claisen-type connecting tube with a stopper and thermometer connected, a Liebig condenser, an adapter with an insertion tube, a three-way adapter, and receiving containers (30 mL pear-shaped flask, 500 mL pear-shaped flask, 50 mL pear-shaped flask) were connected, and distillation was carried out under reduced pressure of 0.6 kPa. After cutting 1.8 parts by weight (initial distillation cut rate: 1.8% by weight) of the fraction obtained at an internal temperature of 30°C to 50°C as the initial distillate, the fraction obtained at an internal temperature of 50°C to 90°C was recovered as the main distillate, yielding 82.8 parts by weight (main distillation yield: 82.8% by weight) of the 2-cyanoacrylate of the present invention. The post-distillation, including the residue in the kettle, was 9.6 parts by weight (post-distillation cut rate: 9.6% by weight). To the obtained 2-cyanoacrylate of the present invention, 3 ppm of HBF4 was added as an anionic polymerization inhibitor and 750 ppm of hydroquinone (HQ) was added as a radical polymerization inhibitor, and the mixture was stirred at a temperature of 10-30°C for 1 hour to prepare an adhesive composition. After preparation, the above-described tests were performed on the obtained 2-cyanoacrylate adhesive composition. The results are shown in Table 1.

[0039] (Examples 2-7, Comparative Examples 1-5) An adhesive composition was prepared using the same procedure as in Example 1, except that the raw materials (2-cyanoacrylate, porous clays, etc.) and manufacturing conditions were changed as shown in Tables 1 and 2, and the tests described above were carried out. The results are shown in Tables 1 and 2.

[0040] In Tables 1 and 2 below, the abbreviations for each additive refer to the compounds listed below. Furthermore, the pH of the porous clays was measured using the following method. <Method for measuring the pH of porous clays> A 5% by weight aqueous suspension was prepared according to the method compliant with JIS K 5101-17-2:2004, and its pH was measured at 25±1℃ using a pH meter manufactured by Horiba, Ltd.

[0041] A-1: Ethyl 2-cyanoacrylate (a fraction obtained by thermal depolymerization of a condensate of ethyl cyanoacetate and formaldehyde under reduced pressure, manufactured by Taoka Chemical India Private Limited) A-2: Ethyl 2-cyanoacrylate obtained in Comparative Example 1 B-1: Nikkanite G-36 (granular activated clay, pH 3.6, manufactured by Nippon Activated Clay Co., Ltd.) B-2: Galeonite #336 (granular activated clay, pH 2.7, manufactured by Mizusawa Chemical Industries Co., Ltd.) B-3: Galleon Earth NV (Powdered activated clay, pH 3.7, manufactured by Mizusawa Chemical Industry Co., Ltd.) B-4: Activated clay (powdered, pH 3.7, manufactured by Fujifilm Wako Chemical Co., Ltd.) B-5: Nikkanite G-168 (granular activated clay, pH 4.1, manufactured by Nippon Activated Clay Co., Ltd.) B-6: Nikkanite A-36 (granular acidic clay, pH 5.6, manufactured by Nippon Activated Clay Co., Ltd.)

[0042] [Table 1]

[0043] [Table 2]

Claims

1. (A) A step of contacting ethyl 2-cyanoacrylate with porous clays that exhibit neutral to acidic properties. and (B) A process of separating porous clays that exhibit neutral to acidic pH from ethyl 2-cyanoacrylate by distillation. A method for producing ethyl 2-cyanoacrylate containing (however, step (B) is carried out simultaneously with step (A) or after step (A). Furthermore, the porous clays are at least one selected from the group consisting of activated clay and acid clay, and in step (B), distillation is carried out at an internal pressure of 0.1 to 2 kPa, a temperature of 30 to 120°C, and with a first distillate cut rate of 0.8 to 5.1% by weight and a second distillate cut rate of 2.6 to 17.9% by weight relative to 100% by weight of ethyl 2-cyanoacrylate subjected to step (A)).

2. Ethyl 2-cyanoacrylate obtained by the manufacturing method described in claim 1.

3. An adhesive composition comprising ethyl 2-cyanoacrylate as described in claim 2.

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