Novel catechol compound and adhesive resin composition containing the same

Abstract

To provide a hot-melt adhesive which enables prevention of VOC emission into the environment during use by avoiding use of organic solvent, and which permits adhesion at a relatively low temperature, thereby reducing energy consumption and being suitable for an adherend having low heat resistance.SOLUTION: There is provided a catechol compound represented by the following general formula (1), a polymer having the catechol compound as a constituent component, and a hot-melt adhesive containing the polymer. (In formula (1), R1 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, p and q each independently represent an integer of 1 to 6, and n represents an integer of 1 to 6.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel catechol compound and a polymer containing the compound as a constituent component. The polymer can be imparted with fluidity at relatively low temperatures and has adhesive properties to plastics such as polyolefins and polyesters, making it suitable for use in hot-melt adhesives. [Background technology]

[0002] Hot melt adhesives are adhesives that bond adherends by heating a composition containing a thermoplastic resin to its melting temperature, discharging it onto the surface of the adherend, and then cooling it to its solidification temperature. The hot melt adhesive process is known as a low-environmental-impact process that does not use water, organic solvents, etc., and is used to bond films, nonwoven fabrics, packaging materials, building materials, etc.

[0003] Hot melt adhesives are commonly made from thermoplastic resins whose main components are polyester, polyurethane, polyolefin, rubber, etc., and generally require a melting temperature of 100°C or higher to achieve adhesion. In recent years, with the need to reduce energy costs and CO2 emissions, lowering the melting temperature is desirable to reduce the environmental impact.

[0004] Adherends to which hot melt adhesive processes can be applied include various materials such as resins, metals, rubber, wood, etc. Focusing on materials used for packaging materials, medical devices, biomaterials, biological tissues, etc., commonly used plastic materials such as polyolefins, polyesters, and polyamides have relatively low heat resistance and relatively few highly reactive functional groups exposed on the surface, resulting in poor adhesive properties and making it difficult to apply hot melt adhesive processes to them.

[0005] To solve the above problems, surface treatment methods such as plasma treatment of the adherend surface to oxidize the surface, etching, and formation of a primer layer are known. However, these surface treatments are complicated and difficult to apply to components with precision structures that are difficult to surface treat. Therefore, a simple bonding method that does not require pretreatment such as surface oxidation for hot melt adhesives is desired.

[0006] Recently, adhesives invented from a biomimetic perspective have attracted attention. For example, a catechol-containing adhesive mimicking the adhesive protein of mussels has been developed. Mussel adhesive proteins are composed of polyphenols with a catechol group, the basic structure of L-3,4-dihydroxyphenylalanine. Its biomimetic counterpart, dopamine and its compounds, are materials with a simplified chemical structure of the adhesive protein. Polydopamine, formed from dopamine, can adhere to a variety of substrates, including metals and ceramics, as well as fluororesins and polyolefins, which are difficult to bond using conventional adhesive methods (Non-Patent Document 1). This example demonstrates that a composition containing catechol groups exhibits adhesion to a variety of substrates simply by dip-coating in solution, without the need for physical oxidation treatments such as plasma treatment.

[0007] As an example of the above-mentioned catechol group-containing adhesive, Patent Document 1 discloses a compound in which a catechol group is introduced into polysilsesquioxane, and discloses that a composition in which this compound is dissolved in an organic solvent has good adhesive properties for bonding aluminum plates and glass plates.

[0008] Patent Document 2 discloses a hydrolyzable alkoxysilane containing a catechol group and a composition containing the same and a solvent, and discloses that the composition is used as a surface modifier for glass fibers to improve adhesion to epoxy resins.

[0009] Patent Document 3 discloses an adhesive composition containing an acrylic resin containing a catechol group and a solvent, and describes good adhesive properties to metals, glass, and resins. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent Publication No. 2021-176953 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-182977 [Patent Document 3] Japanese Patent Application Publication No. 2022-135398 [Non-patent literature]

[0011] [Non-Patent Document 1] Science,2007,318,426. Summary of the Invention [Problem to be solved by the invention]

[0012] As mentioned above, adhesives containing catechol groups are known to exhibit good adhesion to metals, glass, poorly bondable resins, and plastics. However, because they are primarily used as solutions, their use inevitably involves the emission of volatile organic compounds (VOCs), posing a problem in terms of environmental impact. If adhesives containing catechol groups could be used as hot-melt adhesives, it would be possible to avoid VOC emissions. Furthermore, if the melting temperature of hot-melt adhesives could be lowered, the energy consumed during bonding could be reduced, thereby reducing the environmental impact. Furthermore, they could potentially be used to bond materials with low heat resistance, such as polyethylene.

[0013] The present invention was made in response to these problems of the prior art. Specifically, the object of the present invention is to provide a hot melt adhesive that does not use organic solvents and thereby avoids the emission of VOCs into the environment during use, and that can bond at relatively low temperatures, thereby consuming less energy and being applicable to adherends with low heat resistance. [Means for solving the problem]

[0014] As a result of extensive research, the present inventors have found that the above problems can be solved by the following means, and have arrived at the present invention.

[0015] That is, the present invention comprises the following configurations. Item 1. A catechol compound represented by the following general formula (1): (R in formula (1) 1 represents hydrogen or an alkyl group having 1 to 6 carbon atoms, p and q in formula (1) each independently represent an integer of 1 to 6, and n in the formula represents an integer of 1 to 6. [ka] Item 2. In the general formula (1), R 1 Item 3. The compound according to item 1, wherein: is hydrogen or an alkyl group having 1 to 2 carbon atoms; and n in the formula is 1. Item 3. A polymer having the catechol compound according to item 1 or 2 as a constituent component. Item 4. A polymer having, as a constituent, a reaction product of a compound having two or more reactive groups in the molecule capable of reacting with an aliphatic hydroxyl group to form a bond with the catechol compound according to Item 1 or 2. Item 5. The polymer according to Item 4, wherein the reactive group capable of reacting with an aliphatic hydroxyl group to form a bond is an alkoxysilane group. Item 6. The polymer according to any one of Items 3 to 5, which has a melting temperature of 30°C or higher and 100°C or lower. Item 7. A hot melt adhesive containing the polymer according to any one of items 3 to 6. [Effects of the Invention]

[0016] The hot melt adhesive of the present invention does not use organic solvents, thereby avoiding the emission of VOCs into the environment during use, and is capable of bonding at relatively low temperatures, thereby consuming less energy and being applicable to adherends with low heat resistance. Furthermore, the hot melt adhesive of the present invention exhibits high adhesion due to the presence of catechol groups, and therefore exhibits excellent adhesion not only to adherends with large surface irregularities, such as fabrics, but also to adherends with smooth surfaces, such as films and sheets. Furthermore, the hot melt adhesive of the present invention exhibits excellent adhesion to a variety of materials due to the presence of catechol groups, and therefore exhibits excellent adhesion even to adherends made of plastics, such as polyolefins, polyesters, and polyamides, which have relatively few highly reactive functional groups exposed on their surfaces. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is an example showing the results of 1H-NMR measurement of the catechol compound of the present invention. [Figure 2] 1 is an example showing the results of 1H-NMR measurement of a polymer (1:1) of MPA-DPE and ODTMS of the present invention. [Figure 3] 1 is an example showing the results of IR measurement of a polymer (1:1) of MPA-DPE and ODTMS of the present invention. [Figure 4] 1 is an example showing the results of DSC measurement of a polymer (1:1) of MPA-DPE and ODTMS of the present invention. [Figure 5] 1 is an example showing the measurement results of the tensile strength of the polymer of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The adhesive resin composition containing a catechol compound of the present invention is a compound having a catechol group represented by formula (1) or a reaction product using the compound as a raw material, or a composition containing them.

[0019] [ka]

[0020] R in formula (1) 1 is preferably hydrogen or an alkyl group having 1 to 6 carbon atoms, and more preferably hydrogen or an alkyl group having 1 to 2 carbon atoms. p and q in formula (1) are each preferably an integer of 1 to 6, and more preferably 1. n in formula (1) is preferably an integer of 1 to 6, and more preferably 1.

[0021] The catechol compound of formula (1) can be obtained, for example, by a substitution reaction between a diol compound represented by formula (2) below and a catechol compound. In the formula, M of the diol compound represents a cation species such as hydrogen, an alkali metal, an alkaline earth metal, or a quaternary ammonium. In the formula, X of the catechol compound represents a halogen atom such as iodine, bromine, or chlorine, or a leaving group such as a tosylate or mesylate group.

[0022] [ka]

[0023] Various catechol compound derivatives can be obtained from the catechol compound of the present invention through addition reactions, condensation reactions, substitution reactions, etc., starting from the aliphatic hydroxyl groups. Furthermore, since the catechol compound of the present invention has two aliphatic hydroxyl groups in its molecule, a polymer can be produced by reacting it with a compound having two or more reactive groups in the molecule that react with the aliphatic hydroxyl groups to form a bond. Examples of reactive groups that react with the aliphatic hydroxyl groups to form a bond include alkenyl groups, alkynyl groups, isocyanate groups, haloalkyl groups, carbonate ester groups, halosilyl groups, and alkoxysilyl groups. Specific examples of reactants that react with the aliphatic hydroxyl groups include unsaturated compounds such as alkenes and alkynes, isocyanate compounds, halides, carbonyl compounds, and silane compounds. Silane compounds are particularly preferred from the perspective of imparting adhesive properties when used as a hot-melt adhesive. When producing a polymer, it is essential to use a compound with two or more reactive groups, and it is preferable to mainly use compounds with two, three, or four reactive groups. Here, "mainly" refers to a compound with a higher molar ratio. It is possible to use a compound with one reactive group in combination. It is also possible to use a compound with five reactive groups in combination.

[0024] In the present invention, a suitable example of the silane compound is a compound represented by formula (3). The compound represented by formula (3) may be a compound that is commercially available or used as a general silane coupling agent. From the viewpoint of imparting adhesiveness to polyolefin, polymethyl methacrylate, polystyrene, polyvinyl chloride, etc., R 2 is preferably an alkyl group composed of hydrogen or a hydrocarbon, and more preferably an alkyl group having 8 to 18 carbon atoms.

[0025] [ka]

[0026] -SiOR in formula (2) 3The group preferably has reactivity with alcohols, and in that case, R 3 is, for example, preferably hydrogen or a linear or branched alkyl group having 1 to 6 carbon atoms, and more preferably hydrogen, a methyl group, or an ethyl group.

[0027] The polymer containing the catechol compound of the present invention can be obtained as a hyperbranched polymer represented by the following formula (4) by, for example, reacting the catechol compound represented by the above formula (1) with the compound represented by the above formula (3). The hyperbranched polymer is a polymer with a high degree of branching, and its physical properties, such as melting temperature and viscosity, are suitable for use as a hot-melt adhesive.

[0028] [ka]

[0029] The polymer of the formula (4) can be obtained by reacting the catechol compound with the silane compound in an organic solvent, and the reaction can be carried out in the presence of a catalyst.

[0030] The molar ratio of the silane compound to the catechol compound of formula (4) is preferably in the range of 0.5 to 5.0, more preferably 1.0 to 3.0. By setting the molar ratio of the silane compound to the catechol compound within the above range, excellent adhesion to the adherend can be achieved, and the strength of the bond itself can be ensured.

[0031] The organic solvent used in the reaction of the catechol compound represented by formula (1) with the compound represented by formula (3) is preferably a solvent in which the raw materials or the product are soluble during the reaction. Examples of such solvents include tetrahydrofuran (THF), ethyl acetate, butyl acetate, dimethylformamide (DMF), dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO). From the viewpoint of the solubility of the product, ethyl acetate and butyl acetate are more preferred.

[0032] In the present invention, the catalyst may be any catalyst that promotes a condensation reaction, and examples thereof include p-toluenesulfonic acid, methanesulfonic acid, hydrochloric acid, sulfuric acid, etc. The amount of the catalyst is preferably 0.01 to 0.1 mol % based on the raw materials.

[0033] In the present invention, the molecular weight of the polymer obtained by the formula (4) is preferably in the range of 1,000 to 10,000, more preferably 2,000 to 6,000, in terms of polystyrene, as measured by gel permeation chromatography (GPC).

[0034] In the present invention, the polymer obtained by the formula (4) preferably exhibits a melting temperature of 30 to 100°C, more preferably 31 to 80°C, even more preferably 32 to 60°C, even more preferably 33 to 50°C, and particularly preferably 34 to 45°C, in thermal property measurement by differential scanning calorimetry (DSC). A melting temperature of less than 100°C is preferred in terms of energy cost and application to materials with low heat resistance. A melting temperature of more than 30°C is expected to provide sufficient adhesive strength, assuming use under room temperature conditions. Furthermore, it is preferable that the resin composition exhibits a crystallization peak drop of 100°C or less in DSC.

[0035] The resin composition containing the catechol compound of the present invention has thermoplastic properties and can be used as a thermoplastic resin. Examples include hot-melt adhesives, 3D printing materials, and recyclable resin materials used as raw materials for various molded products. Examples of applications include food packaging, sanitary products, medical devices, and building materials. Taking advantage of the excellent adhesive properties due to the inclusion of catechol groups, a good example is the use of hot-melt adhesives.

[0036] The resin composition containing the catechol compound of the present invention may be used as an adhesive or a primer. In a molten state and / or in a solution state, it may be treated by a method such as dip coating, spraying, immersion, or printing. Functional additives such as crosslinkers, additives, and curing agents may also be added. Hot-melt adhesives are a preferred form of use because they do not use organic solvents, reducing the environmental impact.

[0037] The adherend may be made of any material that can be bonded, and examples thereof include plastics, ceramics, metals, rubber, biological tissue, etc. Examples of poorly adhesive plastics include general-purpose plastics such as polyvinyl chloride, polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polyvinyl alcohol, engineering plastics such as polyamide, polycarbonate, polyacetal, polyvinylidene fluoride, polyethersulfone, and polyamideimide, and thermosetting resins such as phenolic resins, epoxy resins, silicone resins, and polyurethane, and these can also be used as adherends. [Example]

[0038] The present invention will be specifically explained below by showing examples, but the present invention is not limited to these examples.

[0039] (Example 1) Synthesis of dimethylolpropionic acid 1-(3,4-dihydroxyphenyl)ethanoyl ester (MPA-DPE) Dimethylolpropionic acid (bis-MPA) (11.0 g, 82.1 mmol) and acetonitrile (60 mL) were placed in a flask, and 2-chloro-1-(3,4-dihydroxyphenyl)ethanone (CDPE) (13.9 g, 74.6 mmol) and triethylamine (8.3 g, 82.1 mmol) were added. The mixture was stirred at 80°C for 24 hours. After the reaction, the reaction mixture was cooled to room temperature, diluted with ethyl acetate (50 mL), and water (50 mL) was added. The organic and aqueous layers were separated, and the aqueous layer was extracted five times with ethyl acetate (50 mL). The organic layer was washed twice with water (50 mL) and saturated brine (50 mL), dehydrated over magnesium sulfate, and concentrated to dryness. The resulting product was washed with a small amount of ethyl acetate and dried in vacuo at 60°C for 1 day. 11 g of MPA-DPE was obtained as a pale yellow solid in a yield of 52%. The resulting product was 1 The compound was identified by measuring the 1 H-NMR spectrum (BRUKER, MR400). 1 The H-NMR spectrum is shown in Figure 1. 1 H-NMR(DMSO-d6):δ10.0-9.58 (s, 2H), 7.38-7.31 (m, 2H), 6.85 (d, 1H), 5.33 (s, 2H), 4.64 (s, 2H), 3.59-3.43 (m, 4H), 1.17 (s, 3H)

[0040] [ka]

[0041] (Example 2) Synthesis of MPA-DPE and ODTMS polymer (1:1) The above MPA-DPE (580 mg, 2.04 mmol) and octadecyltrimethoxysilane (ODTMS) (764 mg, 2.04 mmol) were added to a flask at a molar ratio of 1:1. Ethyl acetate (25 mL) and p-toluenesulfonic acid hydrate (40 mg, 0.204 mmol) were then added, and the mixture was heated and stirred at 80°C for 24 hours. The resulting reaction solution was cooled to room temperature and diluted with ethyl acetate (30 mL). The organic layer was washed with water (30 mL) and saturated brine (30 mL), dehydrated over magnesium sulfate, and concentrated to dryness. The resulting solid was washed with isopropanol (10 mL), filtered with suction, and vacuum dried at 50°C for 24 hours. The yield was 1.2 g. 1 The H-NMR spectrum (THF-d8) is shown in Figure 2. The IR spectrum was measured as an absorption spectrum by applying a THF solution of the product to a high-density polyethylene (HDPE) substrate, drying it, and then using the attenuated total reflectance method (ATR, JASCO FT-IR-6100). The IR spectrum is shown in Figure 3. The NMR and IR spectra confirm that the product has a polysiloxane structure corresponding to the molar ratio of the amounts of each raw material charged. Furthermore, gel permeation chromatography (GPC) measurements showed that the weight-average molecular weight (Mw) in terms of polystyrene was 5896, and the Mw / Mn was 1.638.

[0042] [ka]

[0043] (Example 3) Synthesis of polymer of MPA-DPE and ODTMS (1:2) The same procedure as in Example 2 was repeated except that the molar ratio of MPA-DPE and ODTMS was 1:2.

[0044] (Example 4) Synthesis of polymer of MPA-DPE and ODTMS (1:3) The same procedure as in Example 2 was repeated except that the molar ratio of MPA-DPE and ODTMS was 1:3.

[0045] (Example 5) Synthesis of MPA-DPE and HDTMS polymer (1:1) The same procedure as in Example 2 was repeated, except that hexadecyltrimethoxysilane (HDTMS) was used instead of ODTMS.

[0046] (Example 6) Synthesis of MPA-DPE and DDTMS polymer (1:1) The same procedure as in Example 2 was repeated except that dodecyltrimethoxysilane (DDTMS) was used instead of ODTMS.

[0047] (Comparative Example 1) Synthesis of polymer of MPA-M and ODTMS (1:1) As a comparative example, a polymer without catechol groups (methyl ester groups) was produced. Dimethylolpropionic acid (2.5 g, 18.6 mmol) and methanol (19 mL) were placed in a flask, and Amberlyst 15H form (0.9 g) was added. The mixture was stirred under reflux for 24 hours. After the reaction, the mixture was cooled to room temperature, filtered, and the filtrate was concentrated to dryness. The dried product was extracted with chloroform (15 mL), and the extract was filtered, concentrated to dryness, and dried in vacuo at 50°C for 1 day. 2.0 g of the methyl ester (MPA-M) was obtained as a colorless oil in a yield of 71%. Next, the above MPA-M (302 mg, 2.04 mmol) and octadecyltrimethoxysilane ODTMS (764 mg, 2.04 mmol) were added to the flask at a molar ratio of 1:1. Ethyl acetate (25 mL) and p-toluenesulfonic acid hydrate (40 mg, 0.204 mmol) were then added, and the mixture was heated and stirred at 80°C for 24 hours. The resulting reaction solution was cooled to room temperature and diluted with ethyl acetate (30 mL). The organic layer was washed with water (30 mL) and saturated brine (30 mL), dehydrated over magnesium sulfate, and concentrated to dryness. The resulting solid was washed with isopropanol and collected by suction filtration. It was then vacuum dried at 50°C for 24 hours.

[0048] [ka]

[0049] (Test Example 1) DSC Measurement The thermal properties of the resulting polymers were measured using a differential scanning calorimeter (DSC, TA Instruments, DSC2500). Using the DSC, the polymers were heated from -80 to 100°C at a rate of 10°C / min, cooled from 100 to -80°C at a rate of 10°C / min, and then heated back up to 100°C. The endothermic and exothermic peaks were measured. The onset temperature of the endothermic peak during the second heating process was designated the melting temperature (Tm), and the onset temperature of the exothermic peak during the cooling process was designated the crystallization temperature (Tc). The onset temperatures of the endothermic and exothermic peaks were defined as the intersections (onset temperatures) of the tangents at the inflection points of the endothermic and exothermic peaks of the observed heat flow curves with the extensions of the baseline. The results are shown in Table 1. In Examples 1 to 6 and Comparative Example 1, Tm and Tc were observed within the temperature range of room temperature to 100°C, confirming the polymers' thermoplasticity below 100°C. As an example, the DSC chart of Example 2 is shown in Figure 4.

[0050] (Test Example 2) TGA Measurement The polymer obtained above was subjected to thermogravimetry (TGA). The temperature was raised from room temperature to 500°C at a rate of 10°C / min, and the temperature at which a 5% weight loss occurred was defined as the decomposition temperature Td5. The results are shown in Table 1.

[0051] [Table 1]

[0052] (Test Example 3) Hot melt adhesiveness test Adhesion tests were conducted on the hot-melt adhesive. A substrate was cut to a size of 1.5 cm x 6 cm, and 5 mg of the polymer obtained above, in powder form, was placed on the tip (1.5 cm x 1.5 cm) of the substrate and placed in a thermostatic chamber set at 80°C. After the polymer melted, another test piece cut to the same size was attached to the substrate, secured with clothespins, and cooled to room temperature. Tensilon universal testing machine (A&A, RTG-1310) was used to measure the tensile adhesive strength of the resulting test piece with an initial chuck distance of 35 mm. The temperature during measurement was 23°C, humidity was 50% RH, and the pulling speed was 10 mm / min. The tensile adhesive strength was calculated from the resulting strain-stress curve. The tensile adhesive strength was calculated as the average of three measurements. The substrates used were PET film (Toyobo PET film, thickness 158 μm) and HDPE sheet (AS ONE Resin Sheet, polyethylene sheet PEN-05002). The results of the tensile strength are shown in Table 1 and Figure 5. As is clear from Table 1, the results of the adhesion tests conducted on PET film and HDPE sheet showed that the polymers having catechol groups in Examples 2 to 6 exhibited higher adhesion than the methyl ester form without catechol groups (Comparative Example 1). An attempt was made to prepare a test piece using the PET film in Comparative Example 1, but it peeled off easily, so it was excluded from the adhesion test. [Industrial Applicability]

[0053] The novel catechol compound of the present invention can be used as a raw material for polymers. Polymers using the novel catechol compound of the present invention as a raw material have thermoplasticity at relatively low temperatures and exhibit adhesive properties even to resins that are difficult to bond with general adhesives and have relatively low heat resistance, so they can be used as a main component constituting hot-melt adhesives.

Claims

1. A catechol compound represented by the following general formula (1): １ represents hydrogen or an alkyl group having 1 to 6 carbon atoms, p and q in formula (1) each independently represent an integer of 1 to 6, and n in the formula represents an integer of 1 to 6. 【Chemical 1】

2. In the general formula (1), R １ 2. The compound according to claim 1, wherein n is 1 and n is hydrogen or an alkyl group having 1 to 2 carbon atoms.

3. A polymer having the catechol compound according to claim 1 as a constituent component.

4. 2. A polymer comprising, as a constituent, a reaction product of a compound having two or more reactive groups in the molecule capable of reacting with an aliphatic hydroxyl group to form a bond with the catechol compound of claim 1.

5. 5. The polymer according to claim 4, wherein the reactive group capable of reacting with an aliphatic hydroxyl group to form a bond is an alkoxysilane group.

6. The polymer according to any one of claims 3 to 5, having a melting temperature of 30°C or higher and 100°C or lower.

7. A hot melt adhesive containing the polymer according to any one of claims 3 to 5.

8. A hot melt adhesive containing the polymer according to claim 6.

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