Thermosetting resin manufacturing method

Abstract

To provide a novel method for producing a thermosetting resin with low melt-viscosity and excellent handleability, enabling the production of a benzoxazine cured molded body with excellent balance between breaking stress and elongation as well as flexibility.SOLUTION: A method for producing a thermosetting resin having a benzoxazine ring structure in a main chain includes: a step (I) of reacting a diamine compound and an aldehyde compound in a solvent containing an aromatic non-polar solvent; a step (II) of removing water produced in the step (I) together with alcohol in the solvent; and a step (III) of reacting a reaction product obtained in the step (II) with a bifunctional phenol compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a thermosetting resin. [Background technology]

[0002] A typical method for producing a benzoxazine compound, which is a type of thermosetting resin, is to add three components, i.e., an amine component, a phenol component, and an aldehyde component, to a solvent all at once and react them. For example, Patent Document 1 describes a method for producing a flame-retardant self-curing phenolic resin-based resin, which includes a step of reacting a phenol, an aldehyde, and a primary amine in a solvent to obtain a reaction liquid. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-106466 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional techniques have room for improvement in terms of handling properties based on melt viscosity and the physical properties of the resulting cured benzoxazine molded articles.

[0005] An object of one aspect of the present invention is to provide a novel method for producing a thermosetting resin that can produce a flexible cured benzoxazine molded article with an excellent balance between breaking stress and elongation, and that has a low melt viscosity and excellent handleability. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, one embodiment of the present invention provides a method for producing a thermosetting resin having a benzoxazine ring structure in its main chain, the method comprising the steps of: (I) reacting a diamine compound with an aldehyde compound in a solvent containing an aromatic nonpolar solvent; (II) removing water generated in the step (I) together with alcohol in the solvent; and (III) reacting the reaction product obtained in the step (II) with a bifunctional phenol compound. [Effects of the Invention]

[0007] According to one aspect of the present invention, a novel method for producing a thermosetting resin can be realized, which can produce a cured benzoxazine molded article that has an excellent balance between breaking stress and elongation and flexibility, and which has a low melt viscosity and excellent handleability. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1. Method for producing thermosetting resin A method for producing a thermosetting resin according to one embodiment of the present invention (hereinafter also referred to as the present production method) is a method for producing a thermosetting resin having a benzoxazine ring structure in its main chain, and includes the steps of: step (I) of reacting a diamine compound with an aldehyde compound in a solvent containing an aromatic nonpolar solvent; step (II) of removing water produced in step (I) together with alcohol in the solvent; and step (III) of reacting the reaction product obtained in step (II) with a bifunctional phenol compound.

[0009] As described above, the present inventors have succeeded in producing a thermosetting resin that is easy to handle and a cured molded product that has an excellent balance between breaking stress and elongation and is flexible by removing alcohol and water at the time of reaction of two of the raw components of the thermosetting resin. Surprisingly, this technology for producing a thermosetting resin based on this concept is unprecedented.

[0010] The inventors hypothesize the reason for the improvement in the physical properties of the cured molded body as follows: The alcohol solubilizes the triazine produced by the reaction between the diamine compound and the aldehyde compound, preventing gelation of the thermosetting resin. However, since the alcohol interferes with the reaction at the stage of adding the bifunctional phenol compound, removing the alcohol before reaching this stage improves the physical properties of the cured molded body. In addition, removing water, which is a by-product of the reaction between the diamine compound and the aldehyde compound, also contributes to the improvement in the physical properties of the cured molded body.

[0011] In this specification, "excellent handleability" can be evaluated based on the melt viscosity measurement described in the Examples below. The lower the viscosity of the thermosetting resin, the better the handleability can be evaluated.

[0012] <1-1. Process (I)> This production method includes step (I) of reacting a diamine compound and an aldehyde compound in a solvent containing an aromatic nonpolar solvent. Step (I) can be carried out, for example, by adding the diamine compound and the aldehyde compound to a solvent, stirring, then raising the temperature and stirring under reflux. In step (I), by reacting the two components, the diamine compound and the aldehyde compound, in advance, the viscosity of the thermosetting resin is reduced, improving handleability.

[0013] In step (I), the reaction temperature is, for example, preferably 23°C or higher, more preferably 50°C or higher, and even more preferably 80°C or higher. The upper limit of the reaction temperature may be, for example, 200°C or lower. The reaction time is, for example, preferably 0.1 hour or longer, more preferably 0.2 hour or longer, and even more preferably 0.5 hour or longer. The upper limit of the reaction time may be, for example, 10 hours or shorter. When stirring is performed in step (I), the stirring method may be, for example, but is not limited to, a stirring blade, a magnetic stirrer, or a shaker.

[0014] In step (I), the molar ratio of diamine compound to aldehyde compound is preferably 1:2 to 1:10, more preferably 1:2.5 to 1:6, and even more preferably 1:3 to 1:5. When the molar ratio is within the above range, excellent productivity is achieved.

[0015] Examples of the diamine compound include aromatic diamine compounds, aliphatic diamine compounds, etc. Among these, aromatic diamines are preferred in terms of the physical properties of the resulting resin.

[0016] Examples of the aromatic diamine compound include 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 3-(aminomethyl)benzylamine, 3,3'-sulfonyldianiline, 4,4'-sulfonyldianiline, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-methylenedianiline, 4,4'-methylenedianiline, 1,3-bis(4-aminophenoxy)benzene, and 1,3-bis(3-aminophenoxy) Examples of suitable amines include benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2'-dimethylbiphenyl-4,4'-diamine, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, 9,9-bis(4-aminophenyl)fluorene, and 4,4'-isopropylidenebis[(4-aminophenoxy)benzene].

[0017] The aldehyde compound is not particularly limited, but formaldehyde is preferred. As formaldehyde, paraformaldehyde, which is a polymer, or formalin, which is in the form of an aqueous solution, can be used.

[0018] Examples of the aromatic non-polar solvent include benzene, toluene, xylene, mesitylene, and tetralin toluene.

[0019] In the step (I), the solvent preferably contains an alcohol in advance. Examples of the alcohol include aliphatic alcohols, aromatic alcohols, and alicyclic alcohols, and among these, aliphatic alcohols are preferred.

[0020] Examples of aliphatic alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and tert-butanol. Examples of aromatic alcohols include benzeneethanol (phenethyl alcohol) and methylbenzyl alcohol. Examples of alicyclic alcohols include cyclopentanol, cyclohexanol, and cyclooctanol.

[0021] The mass ratio of the alcohol to the aromatic nonpolar solvent in the solvent may be, for example, 1:5, but is preferably 1:1 to 1:50, more preferably 1:2 to 1:25, and even more preferably 1:3 to 1:10. When the solvent contains an alcohol, it is possible to prevent the formation of a gel-like triazine during the reaction of the diamine compound with the aldehyde compound.

[0022] When the solvent does not contain an alcohol, a step of adding an alcohol to the solvent may be further carried out during the step (I). The amount of alcohol to be added is not particularly limited, but it is preferable to add the alcohol so that the mass ratio of the alcohol to the aromatic nonpolar solvent falls within the above-mentioned preferred range.

[0023] (Step (II)) Step (II) of this production method is a step of removing the water generated in step (I) together with the alcohol contained in the solvent. When the diamine compound and the aldehyde compound react with each other, water is generated as a by-product along with the reaction product triazine. By removing the by-product water, the cured molded product of the thermosetting resin has an excellent balance between breaking stress and elongation and is flexible. Furthermore, as mentioned above, the alcohol contained in the solvent hinders the reaction when the bifunctional phenol compound is added. Therefore, by removing the alcohol together with water before carrying out step (III), the reaction in step (III) can proceed more efficiently.

[0024] In step (II), the method for removing water together with the alcohol contained in the solvent is not particularly limited, but examples thereof include a method using a desiccant or an azeotropic method. From the viewpoint of process cost, it is preferable to remove water from the system by azeotropy. In step (II), the azeotropic method is not particularly limited, but examples thereof include passing a gas such as nitrogen (N) to reduce the partial pressure of the water / alcohol vapor, heating, or reducing the pressure using a vacuum pump.

[0025] (Process (III)) Step (III) is a step of reacting the reaction product obtained in step (II) with a bifunctional phenol compound. The method for carrying out step (III) is not particularly limited, but for example, the bifunctional phenol compound may be added to the reaction product heated to 50 to 200°C, preferably 80 to 150°C, and the mixture may be refluxed and stirred for 0.1 to 20 hours.

[0026] The molar ratio of the diamine (based on the charged amount) used to produce the reaction product obtained in step (II) to the bifunctional phenol compound is preferably 1:0.5 to 1:1.5, more preferably 1:0.7 to 1:1.3, and even more preferably 1:0.9 to 1:1.1.

[0027] Examples of the bifunctional phenol compound include dihydroxydiphenylmethane compounds, dihydroxydiphenylethane compounds, dihydroxydiphenylpropane compounds, dihydroxydiphenylbutane compounds, dihydroxydiphenylcyclohexane compounds, and other dihydroxyphenyl compounds.

[0028] Examples of dihydroxydiphenylmethane compounds include bis(4-hydroxyphenyl)diphenylmethane and bis(4-hydroxyphenyl)methane (commonly known as bisphenol F).

[0029] Examples of dihydroxydiphenylethane compounds include 1,1-bis(4-hydroxyphenyl)-1-phenylethane and 1,1-bis(4-hydroxyphenyl)ethane (commonly known as bisphenol E).

[0030] Examples of dihydroxydiphenylpropane compounds include 2,2-bis(4-hydroxyphenyl)propane (commonly known as bisphenol A or BPA), 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(4-hydroxy-3-isopropylphenyl)propane, and 5,5'-(1-methylethylidene)-bis[1,1'-(bisphenyl)-2-ol]propane.

[0031] Examples of dihydroxydiphenylbutane compounds include 2,2-bis(4-hydroxyphenyl)butane (commonly known as bisphenol B).

[0032] Examples of the dihydroxydiphenylcyclohexane compound include 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and 1,1-bis(4-hydroxyphenyl)cyclohexane.

[0033] Other dihydroxydiphenyl compounds include bis(4-hydroxyphenyl)-2,2-dichloroethylene, bis(4-hydroxyphenyl)sulfone, 1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene, and 1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene.

[0034] In step (III), it is preferable to further add a monofunctional phenol compound, which can cap the ends of the resulting thermosetting resin and improve its stability.

[0035] Examples of the monofunctional phenol compound are not particularly limited, but preferred examples include phenol, o-cresol, m-cresol, p-cresol, p-tert-butylphenol, p-octylphenol, p-cumylphenol, dodecylphenol, o-phenylphenol, p-phenylphenol, 1-naphthol, 2-naphthol, m-methoxyphenol, p-methoxyphenol, m-ethoxyphenol, p-ethoxyphenol, 3,4-dimethylphenol, 3,5-dimethylphenol, etc. Among these, phenol is preferred.

[0036] After step (III) is completed, a purification step of purifying the thermosetting resin may be carried out as needed. The purification step is not particularly limited as long as it is a method usually used for purifying thermosetting resins, and can be carried out, for example, by mixing the dried thermosetting resin with alcohol or the like, filtering the mixture, and then drying it again.

[0037] [2. Thermosetting resin] A thermosetting resin according to one embodiment of the present invention is produced through the steps (I) to (III). The thermosetting resin obtained through the steps (I) to (III) has a benzoxazine ring in the main chain.

[0038] The melt viscosity of the thermosetting resin at a temperature of 150°C is preferably 5000 / Pa·s or less, more preferably 3900 / Pa·s or less, and most preferably 3100 / Pa·s or less. If the melt viscosity of the thermosetting resin at a temperature of 150°C is within the above range, it can be said that the thermosetting resin has excellent handleability. The lower limit of the melt viscosity of the thermosetting resin at a temperature of 150°C is not particularly limited, but it may be 100 / Pa·s or more. The melt viscosity can be measured by the method described in the examples below. The melt viscosity of the thermosetting resin at a temperature of 180°C is preferably 100 to 5000 / Pa·s, more preferably 1000 to 4000 / Pa·s, and most preferably 2100 to 3500 / Pa·s. If the melt viscosity of the thermosetting resin at a temperature of 180°C is within the above range, it can be said that the thermosetting resin has excellent handleability.

[0039] From the viewpoint of improving the mechanical properties of the cured molded article, the thermosetting resin preferably has a number average molecular weight (Mn) of 1,000 to 5,000, more preferably 2,000 to 4,000, and even more preferably 2,600 to 3,500. From the viewpoint of processability, the thermosetting resin preferably has a weight average molecular weight (Mw) of 8,000 or less, more preferably 7,500 or less, and even more preferably 7,000 or less. The lower limit of Mw is not particularly limited, but may be, for example, 4,400 or more. The number average molecular weight and weight average molecular weight can be measured by gel permeation chromatography (GPC) as shown in the examples described later.

[0040] The thermosetting resin may or may not contain a structure other than the benzoxazine ring structure. For example, it may have a structure derived from a monocyclic phenol compound for terminally capping the benzoxazine ring structure. The thermosetting resin may also contain a structure derived from an aliphatic monoamine or a (poly)oxyalkylene monoamine compound.

[0041] The thermosetting resin may be combined with other resins as needed to form a resin composition, in which case the resin composition may contain the thermosetting resin as a main component and other thermosetting resins, thermoplastic resins, and compounding agents as secondary components.

[0042] Other thermosetting resins include, for example, epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, silicon resins, melamine resins, urea resins, allyl resins, phenolic resins, unsaturated polyester resins, bismaleimide resins, alkyd resins, furan resins, polyurethane resins, aniline resins, etc. Thermoplastic resins include, for example, thermoplastic epoxy resins, thermoplastic polyimide resins, etc.

[0043] Examples of compounding agents include flame retardants, nucleating agents, antioxidants, antiaging agents, heat stabilizers, light stabilizers, ultraviolet absorbers, lubricants, flame retardant assistants, antistatic agents, antifogging agents, fillers, softeners, plasticizers, and colorants, as needed. These may be used alone or in combination of two or more. Reactive or non-reactive solvents may also be used.

[0044] [3. Cured molded body] An embodiment of the present invention also includes a cured molded article obtained by curing the above-mentioned thermosetting resin or composition. Since the thermosetting resin is produced through steps (I) to (III), the cured molded article has an excellent balance between elongation and breaking stress, and is excellent in flexibility.

[0045] The size and shape of the cured molded product are not particularly limited, and examples thereof include a film, sheet, plate, block, etc. The uncured molded product and the cured molded product may have other layers (e.g., an adhesive layer) in addition to the layer made of the thermosetting resin or composition described above.

[0046] The tensile modulus of elasticity of the cured molded body is preferably 0.5 GPa or more, more preferably 1.0 GPa or more, and even more preferably 1.5 GPa or more.

[0047] The tensile strength at break of the cured molded body is preferably 55 MPa or more, more preferably 60 MPa or more, and even more preferably 70 MPa or more. There is no particular upper limit to the tensile strength at break of the cured molded body, but it may be, for example, 200 MPa or less. If the tensile strength at break of the cured molded body is in the above range, it can be said to have excellent durability.

[0048] The tensile elongation at break of the cured molded product is preferably 2.7% or more, more preferably 2.9% or more, and even more preferably 3.0% or more. The upper limit of the tensile elongation at break is not particularly limited, but may be, for example, 10% or less. The tensile elongation at break of the cured molded product can be measured by the method described in the Examples below.

[0049] From the viewpoint of heat resistance, the glass transition temperature (Tg) of the cured molded product is preferably 100° C. or higher, more preferably 150° C. or higher, and even more preferably 180° C. or higher. There is no particular upper limit to Tg, but it may be 300° C. or lower, 250° C. or lower, or 200° C. or lower.

[0050] The cured molded product is preferably flexible. Whether the cured molded product has flexibility can be determined by, for example, forming the cured molded product into a sheet and checking whether it breaks when bent by hand, as described in the Examples below.

[0051] The method for molding the cured molded article is not particularly limited, and examples thereof include a method in which the above-mentioned thermosetting resin or composition is dissolved in a solvent and the resulting solution is cast onto a substrate to form the molded article (casting method), and a method in which the above-mentioned thermosetting resin or composition is pressed and molded (pressing method). Examples of solvents used in the casting method include N,N-dimethylformamide (DMF), tetrahydrofuran (THF), chloroform, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N,N-diethylacetamide, N-methylcaprolactam, γ-butyrolactone, cyclohexanone, dimethyl sulfoxide, cyclopentanone, 1,4-dioxane, and 1,3-dioxolane. The pressure used in the pressing method is not particularly limited, and may be, for example, 0.1 to 20 MPa.

[0052] The curing temperature of the cured molded product (the highest temperature when the temperature is gradually increased) is not particularly limited, but is preferably 200 to 300° C., more preferably 210 to 280° C., and even more preferably 220 to 260° C. The curing time of the cured molded product is also not particularly limited, but is preferably 10 minutes to 4 hours, preferably 30 minutes to 3 hours, and even more preferably 45 minutes to 2 hours.

[0053] The cured molded articles can be suitably used for electronic components and electronic devices, as well as for materials therefor, particularly for applications requiring excellent dielectric properties, such as multilayer substrates, laminates, sealants, and adhesives, and can also be used for other applications such as aircraft components, automobile components, and building components.

[0054] The cured molded article may contain reinforcing fibers to improve the mechanical strength of the cured molded article. Examples of reinforcing fibers include inorganic fibers, organic fibers, metal fibers, and hybrid reinforcing fibers that combine these. The reinforcing fibers may be one type or two or more types.

[0055] Examples of inorganic fibers include carbon fibers, graphite fibers, silicon carbide fibers, alumina fibers, tungsten carbide fibers, boron fibers, and glass fibers. Examples of organic fibers include aramid fibers, high-density polyethylene fibers, and other common nylon fibers and polyester fibers. Examples of metal fibers include stainless steel and iron fibers. Examples of metal fibers include carbon-coated metal fibers in which metal fibers are coated with carbon. Among these, carbon fibers are preferred as the reinforcing fibers from the viewpoint of increasing the strength of the cured molded body.

[0056] Generally, the carbon fibers are subjected to a sizing treatment, but they may be used as they are, or, if necessary, fibers containing a small amount of sizing agent may be used, or the sizing agent may be removed by an existing method such as an organic solvent treatment or a heat treatment. Alternatively, the carbon fiber bundles may be opened in advance using air or a roller, and a treatment may be performed to facilitate impregnation of the resin between the single carbon fiber yarns.

[0057] One embodiment of the present invention also includes a prepreg or semipreg obtained by impregnating reinforcing fibers with the above-mentioned thermosetting resin or composition. In this specification, semipreg refers to a composite in which reinforcing fibers are partially impregnated (semi-impregnated) with a thermosetting resin or composition and integrated. Furthermore, a prepreg can be obtained from the semipreg. For example, a prepreg can be obtained by further heating and melting the semipreg to impregnate the reinforcing fibers with the resin. In other words, in this specification, a prepreg can also be said to be a material in which the reinforcing fibers are more highly impregnated with the resin than in a semipreg.

[0058] The semipreg or prepreg may be obtained, for example, by placing the cured molded body on both sides of a sheet (plain woven reinforcing fiber material) in which the reinforcing fibers have been pre-impregnated with resin, and pressing the sheet at a predetermined temperature and pressure.

[0059] The cured molded article can also be used as a carbon fiber composite material. Carbon fiber composite materials are also called carbon fiber reinforced plastics (CFRP). The method for producing the carbon fiber composite material is not particularly limited, but for example, a method using semipreg or prepreg, which is a sheet of carbon fiber impregnated with resin, or a method of impregnating carbon fiber (bundle-like or woven) with liquid resin may be used. The cured molded article described above may be molded into a semipreg or prepreg, and the semipreg or prepreg may be used to produce the carbon fiber composite material.

[0060] Although a carbon fiber composite material is given as an example here, as mentioned above, the reinforcing fibers that can be used are not limited to carbon fibers. That is, one embodiment of the present invention also includes a reinforced fiber composite material obtained by impregnating a reinforcing fiber with the above-mentioned thermosetting resin or composition and curing the thermosetting resin or composition.

[0061] According to the above-described configuration, the physical properties of the cured molded body are improved, thereby improving the durability of articles using the cured molded body, which can contribute to the achievement of Sustainable Development Goals (SDGs) such as Goal 12 "Ensure sustainable consumption and production patterns."

[0062] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0063] [4. Other] An embodiment of the present invention may have the following configuration. <1> A method for producing a thermosetting resin having a benzoxazine ring structure in a main chain, comprising: Step (I) of reacting a diamine compound with an aldehyde compound in a solvent containing an aromatic non-polar solvent; a step (II) of removing the water generated in the step (I) together with the alcohol in the solvent; A method for producing a thermosetting resin, comprising: a step (III) of reacting the reaction product obtained in the step (II) with a bifunctional phenol compound. <2> In the step (I), the solvent contains an alcohol in advance. <1> A method for producing the thermosetting resin described in claim 1. <3> The method further comprises the step of adding an alcohol to the solvent while carrying out the step (I). <1> A method for producing the thermosetting resin described in claim 1. <4> In the step (II), water is removed from the system by azeotropy with alcohol. <1> ~ <3> 10. A method for producing a thermosetting resin according to any one of claims 1 to 9. <5> In the step (III), a monofunctional phenol compound is further added. <1> ~ <4> 10. A method for producing a thermosetting resin according to any one of claims 1 to 9. <6> The diamine compound is an aromatic diamine compound. <1> ~ <5> 10. A method for producing a thermosetting resin according to any one of claims 1 to 9. [Example]

[0064] An embodiment of the present invention will be described below, in which benzoxazine resin corresponds to a thermosetting resin and a cured film corresponds to a cured molded product.

[0065] [Test method] (molecular weight measurement) The molecular weight of the benzoxazine resin was measured using a gel permeation chromatograph (GPC) (Shimadzu Corporation, Prominence UFLC). The eluent was DMF containing 0.01 mol / L lithium chloride, and three TSKgel GMHHR-M columns connected in series were used. The flow rate was 1 mL / min, the injection volume was 20 μL, and the column temperature was 40°C. A UV detector was used for detection, and polystyrene was used as the calibration curve sample.

[0066] (Melt viscosity measurement) Using an ARES G2 (manufactured by TA Instruments), measurements were taken using 25 mm parallel plates at a heating rate of 5°C / min, an angular frequency of 10.0 rad / s (1.6 Hz), and a strain of 0.01%. The minimum melt viscosity measured under these conditions was taken as the "minimum melt viscosity."

[0067] (glass transition temperature (Tg)) The Tg of the cured film was measured using a dynamic viscoelasticity measuring device (DMA, manufactured by TA Instruments, RSA G2, tensile mode) at a frequency of 1 Hz and a heating rate of 5°C / min. The extrapolated glass transition onset temperature (the intersection point between the straight line extrapolated from the baseline before the inflection point to the higher temperature side and the tangent to the inflection point) calculated from the storage modulus (E') of the DMA curve obtained was used as the Tg in this example.

[0068] (Mechanical properties of cured film) A tensile test was performed on the cured film using a tensile testing machine (Shimadzu Corporation, EZ-SX). The test temperature was room temperature, the tensile speed was 5 mm / min, and the test specimen was 40 mm long and 3 mm wide. The tensile modulus, tensile strength, and elongation at break were measured.

[0069] (Hand bending properties of cured film) The hand bending properties of the prepared cured film were evaluated by bending it by hand. The test temperature was room temperature, and the test specimen was 6 cm long and 4 cm wide. The hand bending properties were evaluated according to the following criteria. ○: Not damaged even when bent by hand. ×: Breaks when bent by hand.

[0070] 〔material〕 The materials used to prepare the benzoxazine resin are listed below.

[0071] (Bifunctional phenolic compounds) 2,2-bis(4-hydroxyphenyl)propane (bisphenol A, BisA) (Tokyo Chemical Industry Co., Ltd.) (aromatic diamine compounds) 4,4'-Isopropylidenebis[(4-aminophenoxy)benzene] (BAPP) (manufactured by TCI) (aldehyde compounds) Paraformaldehyde (Merch) (PF)

[0072] [Production Example 1] 25 mL of toluene and 5 mL of ethanol were weighed and mixed in a 200 mL flask as the solvent. Paraformaldehyde (2.45 g) and BAPP (8.12 g) were added to the solvent and stirred at room temperature for 10 minutes. The flask was then placed in an oil bath and heated to 100 °C, followed by reflux stirring. After 1 hour, N2 was introduced to remove the water and alcohol (10 mL) contained in the solvent via azeotropy. After removing the solvent, the oil bath was set to 90 °C. After confirming that the oil bath temperature had reached 90 °C, BisA (4.51 g) was added to the reaction solution. The mixture was refluxed and stirred at 90 °C for 5 hours, after which the reaction was stopped. Measurement of the molecular weight of this reaction solution by GPC revealed a weight-average molecular weight (Mw) of 5454 and a number-average molecular weight (Mn) of 2936, calculated as standard polystyrene. The reaction solution was dried under vacuum at 90 °C for 1 hour to obtain a solid. The resulting solid was powdered, mixed with methanol to a concentration of 5% and stirred for 1 hour. The solid was then filtered to obtain a solid. The resulting solid was dried at 90°C under vacuum for 1 hour to obtain the target benzoxazine resin 1. 1 By H-NMR measurement (heavy solvent: CDCl3), the generation of peaks of benzoxazine rings at 4.5 ppm and 5.3 ppm was observed, confirming the synthesis of benzoxazine resin 1. The melt viscosity of this resin was measured.

[0073] [Production Example 2] 25 mL of toluene was weighed into a 200 mL flask as the solvent. Paraformaldehyde (2.45 g) and BAPP (8.12 g) were added to the solvent and stirred at room temperature for 10 minutes. The flask was then placed in an oil bath and heated to 100 °C, followed by reflux stirring. After 10 minutes, gel formation was confirmed in the reaction solution, and 5 mL of ethanol was added. After 1 hour, the gel was confirmed to have dissolved and a clear solution was obtained. N2 was introduced to remove the water and alcohol (10 mL) contained in the solvent by azeotropy. After removing the solvent, the oil bath was set to 90 °C. After confirming that the oil bath temperature had reached 90 °C, BisA (4.51 g) was added to the reaction solution. The mixture was refluxed at 90 °C and stirred for 5 hours, after which the reaction was stopped. The molecular weight of this reaction solution was measured by GPC, and the weight-average molecular weight (Mw) was 6400 and the number-average molecular weight (Mn) was 3400, calculated as standard polystyrene. The reaction solution was dried under vacuum at 90°C for 1 hour to obtain a solid. The obtained solid was powdered, mixed with methanol to a concentration of 5% and stirred for 1 hour. The solid was then filtered to obtain a solid. The obtained solid was dried under vacuum at 90°C for 1 hour to obtain the target benzoxazine resin 2. 1 By H-NMR measurement (heavy solvent: CDCl3), the generation of peaks of benzoxazine rings at 4.5 ppm and 5.3 ppm was observed, confirming the synthesis of benzoxazine resin 2. The melt viscosity of this resin was measured.

[0074] [Production Example 3] 25 mL of toluene and 5 mL of ethanol were weighed and mixed in a 200 mL flask as the solvent. Paraformaldehyde (2.45 g), BAPP (8.12 g), and BisA (4.51 g) were added to the solvent and stirred at room temperature for 10 minutes. The flask was then placed in an oil bath and heated to 90°C, with reflux stirring. The reaction was stopped after 6 hours. Measurement of the molecular weight of this reaction solution by GPC revealed a weight-average molecular weight (Mw) of 3700 and a number-average molecular weight (Mn) of 2300, calculated in terms of standard polystyrene. The reaction solution was dried under vacuum at 90°C for 1 hour to obtain a solid. The resulting solid was powdered and mixed with methanol to a concentration of 5% and stirred for 1 hour. The solid was then filtered to obtain the target product, benzoxazine resin 3. The resulting solid was dried under vacuum at 90°C for 1 hour to obtain the target product, benzoxazine resin 3. 1 By H-NMR measurement (heavy solvent: CDCl3), the generation of peaks of benzoxazine rings at 4.5 ppm and 5.3 ppm was observed, confirming the synthesis of benzoxazine resin 3. The melt viscosity of this resin was measured.

[0075] [Production Example 4] 25 mL of toluene and 5 mL of ethanol were weighed and mixed in a 200 mL flask as the solvent. Paraformaldehyde (2.45 g), BAPP (8.12 g), and BisA (4.51 g) were added to the solvent and stirred at room temperature for 10 minutes. The flask was then placed in an oil bath and heated to 90°C, with reflux stirring. The reaction was stopped after 30 hours. Measurement of the molecular weight of this reaction solution by GPC revealed a weight-average molecular weight (Mw) of 8700 and a number-average molecular weight (Mn) of 4000, calculated in terms of standard polystyrene. The reaction solution was dried under vacuum at 90°C for 1 hour to obtain a solid. The resulting solid was powdered and mixed with methanol to a concentration of 5% and stirred for 1 hour. The solid was then filtered to obtain the target product, benzoxazine resin 4. The resulting solid was dried under vacuum at 90°C for 1 hour to obtain the target product, benzoxazine resin 4. 1 By H-NMR measurement (heavy solvent: CDCl3), the generation of peaks of benzoxazine rings at 4.5 ppm and 5.3 ppm was observed, confirming the synthesis of benzoxazine resin 4. The melt viscosity of this resin was measured.

[0076] [Production Example 5] 25 mL of toluene and 5 mL of ethanol were weighed and mixed in a 200 mL flask as the solvent. Paraformaldehyde (2.45 g) and BAPP (8.12 g) were added to the solvent and stirred at room temperature for 10 minutes. The flask was then placed in an oil bath and heated to 90°C, followed by reflux and stirring for 1 hour. After stirring, BisA (4.51 g) was added to the reaction solution. The mixture was refluxed and stirred at 90°C for 30 hours, after which the reaction was stopped. Measurement of the molecular weight of this reaction solution by GPC revealed a weight-average molecular weight (Mw) of 9900 and a number-average molecular weight (Mn) of 4500, calculated in terms of standard polystyrene. The reaction solution was dried under vacuum at 90°C for 1 hour to obtain a solid. The resulting solid was powdered and mixed with methanol to a concentration of 5% and stirred for 1 hour. The solid was then filtered to obtain the target product, benzoxazine resin 5. The resulting solid was dried under vacuum at 90°C for 1 hour to obtain the target product, benzoxazine resin 5. 1 By H-NMR measurement (heavy solvent: CDCl3), the generation of peaks of benzoxazine rings at 4.5 ppm and 5.3 ppm was observed, confirming the synthesis of benzoxazine resin 5. The melt viscosity of this resin was measured.

[0077] Example 1 Benzoxazine resin 1 obtained in Production Example 1 was placed in a 125 μm-thick PI film mold (external dimensions: 10 cm × 8 cm, internal dimensions: 6 cm × 4 cm) and pressed together with a Teflon (registered trademark) sheet (release paper) and a stainless steel plate to obtain a cured film. A MINI TEST PRESS-10 (manufactured by Toyo Seiki Seisakusho) was used as the press. The processing conditions for obtaining the cured film were as follows. Processing conditions for the cured film: Pressed at 5 MPa for 5 minutes at 150°C, and then pressed at the same pressure for 1 hour at 240°C to obtain a cured film. The obtained cured film was flexible enough that it could not be broken by slight bending by hand. The glass transition temperature (Tg) and mechanical properties of the obtained cured film were measured.

[0078] Example 2 A cured film was obtained in the same manner as in Example 1, except that benzoxazine resin 2 obtained in Production Example 2 was used. This cured film was flexible enough that it was not broken when lightly bent by hand. The glass transition temperature (Tg) and mechanical properties of this cured film were measured.

[0079] Comparative Example 1 A cured film was obtained in the same manner as in Example 1, except that benzoxazine resin 3 obtained in Production Example 3 was used. This cured film was so brittle that it broke when lightly bent by hand. The glass transition temperature (Tg) and mechanical properties of this cured film were measured.

[0080] Comparative Example 2 A cured film was obtained in the same manner as in Example 1, except that benzoxazine resin 4 obtained in Production Example 4 was used. This cured film was flexible enough that it was not broken when lightly bent by hand. The glass transition temperature (Tg) and mechanical properties of this cured film were measured.

[0081] Comparative Example 3 A cured film was obtained in the same manner as in Example 1, except that benzoxazine resin 5 obtained in Production Example 5 was used. This cured film was flexible enough that it was not broken when lightly bent by hand. The glass transition temperature (Tg) and mechanical properties of this cured film were measured.

[0082] [Evaluation results] The method for producing the thermosetting resin of each production example is shown in Table 1. The physical properties of the thermosetting resin and the cured film are shown in Table 2 below.

[0083] [Table 1]

[0084] [Table 2]

[0085] From Table 2, it can be seen that the resin of Example 1 before curing has a low melt viscosity, and therefore has excellent processability, and the film, which is a cured resin molded product, has an excellent balance between breaking stress and elongation, and is flexible enough not to break even when lightly bent by hand.Furthermore, it can be seen that the resin of Example 2 before curing also has a low melt viscosity, and therefore has excellent processability, and the film, which is a cured resin molded product, has an excellent balance between breaking stress and elongation, and is flexible enough not to break even when lightly bent by hand.

[0086] On the other hand, the film made by curing the resin of Comparative Example 1 had a poor balance between breaking stress and elongation, and was broken even when bent lightly by hand, indicating poor flexibility. Furthermore, the resins before curing in Comparative Examples 2 and 3 had high melt viscosities, which resulted in poor processability, and the films made from the cured resins also had a poor balance between breaking stress and elongation.

[0087] As described above, the resin obtained by the production method in which a diamine compound and an aldehyde compound are reacted in a solvent, water and alcohol are removed, and then the resin is reacted with a phenolic compound has been shown to have excellent processability and excellent physical properties when formed into a cured molded product. This is thought to be because the adoption of this production method makes it possible to suppress undesirable side reactions during production (such as the ring-opening reaction of the benzoxazine ring and the crosslinking reaction (gelation)), thereby making it possible to control the molecular weight of the resin within a desired range and to control the melt viscosity of the resin within a desired range.

[0088] Furthermore, if the water and alcohol are not removed (Comparative Examples 1 to 3) or if the three components are reacted all at once (Comparative Examples 1 and 2), the undesirable side reactions described above may occur during the production of the resin, which may result in a high melt viscosity in the resin before curing, or in a poor balance between the breaking stress and elongation in the cured film, causing it to break even when lightly bent by hand.

[0089] Furthermore, the resins used in the films of Comparative Examples 2 and 3 required approximately 30 hours to produce, whereas the resins used in Examples 1 and 2 could be produced in approximately 6 hours. In addition, the resin used in the film of Comparative Example 1, which was produced in approximately the same time as the resins used in Examples 1 and 2, 6 hours, had inferior physical properties. In other words, it can be said that by adopting the above production method, it is possible to produce cured molded products with excellent physical properties in a shorter time. [Industrial Applicability]

[0090] One aspect of the present invention can be used in fields where thermosetting resins are used.

Claims

1. A method for producing a thermosetting resin having a benzoxazine ring structure in a main chain, comprising: Step (I) of reacting a diamine compound with an aldehyde compound in a solvent containing an aromatic nonpolar solvent; a step (II) of removing the water generated in the step (I) together with the alcohol in the solvent; A method for producing a thermosetting resin, comprising: a step (III) of reacting the reaction product obtained in the step (II) with a bifunctional phenol compound.

2. The method for producing a thermosetting resin according to claim 1 , wherein in step (I), the solvent already contains an alcohol.

3. 2. The method for producing a thermosetting resin according to claim 1, further comprising the step of adding an alcohol to the solvent during the step (I).

4. 4. The method for producing a thermosetting resin according to claim 1, wherein in the step (II), water is removed from the system by azeotropy with an alcohol.

5. The method for producing a thermosetting resin according to any one of claims 1 to 4, wherein a monofunctional phenol compound is further added in the step (III).

6. The method for producing a thermosetting resin according to any one of claims 1 to 5, wherein the diamine compound is an aromatic diamine compound.

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