Benzoxazine compound and use thereof

Abstract

The present invention provides: a benzoxazine compound obtained using a polyethylene glycol modified lignin as a raw material; a resin composition containing said benzoxazine compound; and a cured product thereof. Specifically, the present invention provides: a benzoxazine compound which dissolves in an organic solvent and has a meltable lignin skeleton; and a method for producing the same. Also provided are: a resin composition which contains said benzoxazine compound and produces a cured product exhibiting excellent heat-resistance, high strength, and low tensile elastic modulus; and a cured product of the same. The present invention pertains to: a benzoxazine compound including a reaction product of an aldehyde compound, an amine compound, and a novolak-type phenol resin derived from lignin modified by a polyethylene glycol; a resin composition containing said benzoxazine compound; a cured product of said resin composition; a complex (a prepreg or the like) including said resin composition and a base material; a cured product of said complex; and a method for producing said benzoxazine compound.

Description

Benzoxazine compounds and their uses

[0001] The present invention relates to a benzoxazine compound and its use.

[0002] Benzoxazine compounds have been studied for a long time (for example, Patent Document 1), and these compounds are synthesized by reacting a phenol compound, an amine compound, and a formaldehyde compound (see reaction formula (1)). Benzoxazine compounds (monomers) undergo ring-opening polymerization (curing) when heated to produce benzoxazine resins (polymers), and are therefore attracting attention as a new type of phenolic resin that can replace conventional phenolic resins.

[0003] While benzoxazine resins have excellent mechanical properties, their hardness and brittleness limit their applicability. Although they have better heat resistance than epoxy resins and phenolic resins, their heat resistance is not sufficient for applications requiring strict heat resistance, such as power semiconductors and automotive applications.

[0004] Meanwhile, a new benzoxazine compound has been reported that is made from lignin, a plant-derived component (Patent Document 2). In addition to the lignin, a lignin modified with polyethylene glycol (PEG) (Patent Document 3) and a novolac phenolic resin with excellent heat resistance and flexibility that is made from the PEG-modified lignin, phenols, and aldehydes (Patent Document 4) have also been reported.

[0005] Japanese Patent Application Laid-Open No. 49-47378 Japanese Patent Application Laid-Open No. 2013-53205 Japanese Patent Application Laid-Open No. 2017-197517 Japanese Patent Application Laid-Open No. 2021-123716

[0006] An object of the present invention is to provide a benzoxazine compound made from polyethylene glycol (hereinafter, sometimes referred to as "PEG")-modified lignin as a raw material, a resin composition containing the benzoxazine compound, and a cured resin product thereof.

[0007] Specifically, the present invention aims to provide a benzoxazine compound having a lignin skeleton that is soluble or meltable in an organic solvent, a method for producing the same, a resin composition containing the benzoxazine compound that gives a cured product having excellent heat resistance, high strength, and a low tensile modulus, and a cured product thereof.

[0008] The present inventors confirmed that the benzoxazine compound derived from modified lignin described in Patent Document 2 has extremely low solubility and meltability in solvents and resins, making it difficult to apply to applications such as forming prepregs. The present inventors conducted extensive research to solve this problem and found that a benzoxazine compound derived from a novolac phenolic resin derived from PEG-modified lignin has excellent solubility and meltability in solvents and resins. Furthermore, the present inventors discovered that a cured product of a resin composition containing this benzoxazine compound has high heat resistance (high glass transition temperature) and also exhibits high strength (high tensile strength) and elongation (low tensile modulus) compared to cured products of resin compositions containing conventional benzoxazine compounds. Based on this finding, the present inventors conducted further research and completed the present invention.

[0009] That is, the present invention encompasses the following aspects. [1] A benzoxazine compound comprising a reaction product of a novolac phenolic resin derived from lignin modified with polyethylene glycol, an amine compound, and an aldehyde compound. [2] The benzoxazine compound according to [1], wherein the novolac phenolic resin is a novolac phenolic resin obtained by reacting lignin modified with polyethylene glycol, a phenolic resin, and an aldehyde compound. [3] A resin composition containing the benzoxazine compound according to [1] or [2]. [4] A cured product of the resin composition according to [3]. [5] A composite comprising the resin composition according to [3] and a substrate. [6] A prepreg comprising the resin composition according to [3] and a substrate. [7] A cured product of the composite according to [5] or the prepreg according to [6]. [8] A method for producing a benzoxazine compound, comprising: (1) a step of reacting lignin modified with polyethylene glycol, a phenolic resin, and an aldehyde compound to obtain a novolac phenolic resin; and (2) a step of reacting the novolac phenolic resin obtained in (1), an amine compound, and an aldehyde compound to obtain a benzoxazine compound.

[0010] The benzoxazine compound having a lignin skeleton of the present invention has excellent solubility in organic solvents and is meltable. Because the benzoxazine compound is meltable, it can be melt-mixed with other resins. Therefore, it is suitable for use in applications such as prepreg formation and casting processes. The cured product obtained by curing a resin composition containing the benzoxazine compound having a lignin skeleton of the present invention is characterized by excellent heat resistance (high glass transition temperature (Tg)), excellent strength (high tensile strength), and ease of elongation (relatively small tensile modulus). The curing reaction of the benzoxazine compound having a lignin skeleton of the present invention proceeds at a relatively low temperature.

[0011] 1 is an IR spectrum chart of the black solid obtained in Example 1.

[0012] 1. Benzoxazine Compound The benzoxazine compound of the present invention is characterized by containing a reaction product of (1) a novolac phenolic resin derived from lignin modified with polyethylene glycol (PEG), (2) an amine compound, and (3) an aldehyde compound.

[0013] (1) Novolac-type phenolic resin derived from lignin modified with PEG Novolac-type phenolic resin derived from lignin modified with PEG contains a reaction product obtained from lignin modified with PEG (hereinafter also referred to as "PEG-modified lignin"), a phenolic compound, and an aldehyde compound. Typically, it can be produced by reacting PEG-modified lignin, a phenolic compound, and an aldehyde compound under an acid catalyst. Specifically, it can be produced according to or in accordance with Patent Document 4 (JP 2021-123716 A). For example, it is as follows.

[0014] (PEG-Modified Lignin) In the PEG-modified lignin, which is a raw material for the novolac-type phenolic resin derived from the PEG-modified lignin, the polyethylene glycol (PEG) is appropriately selected depending on the physical properties required for the benzoxazine compound of the present invention.

[0015] From the viewpoint of achieving both high tensile strength and low tensile modulus in the benzoxazine compound of the present invention, the number average molecular weight of the polyethylene glycol is, for example, 100 or more, preferably 200 or more, more preferably 300 or more, and even more preferably 400 or more, and for example, 1000 or less, preferably 900 or less, more preferably 800 or less, and even more preferably 600 or less. The number average molecular weight can be determined as a polyethylene glycol-equivalent molecular weight by a known gel permeation chromatography method.

[0016] In PEG-modified lignin, lignin is a polymeric phenolic compound consisting of a basic skeleton such as guaiacyl lignin (G type), syringyl lignin (S type), or p-hydroxyphenyl lignin (H type), and is found in plants as a natural product (natural lignin).

[0017] Known examples of natural lignins extracted industrially include soda lignin, sulfite lignin, and kraft lignin, which are contained in the waste liquid (black liquor) discharged when pulp is produced from plant materials (lignocellulose) as raw materials by the soda process, sulfite process, kraft process, etc.

[0018] Specific examples of lignin include woody plant-derived lignin and herbaceous plant-derived lignin. Examples of woody plant-derived lignin include coniferous lignin contained in conifers (e.g., cedar) and broadleaf lignin contained in broadleaf trees. Woody plant-derived lignin does not contain an H-type basic skeleton. More specifically, among woody plant-derived lignins, coniferous lignin does not contain an S-type basic skeleton and has a G-type basic skeleton. Furthermore, broadleaf lignin has both a G-type basic skeleton and an S-type basic skeleton.

[0019] Examples of herbaceous plant-derived lignins include rice-derived lignins contained in grasses (wheat straw, rice straw, corn, bamboo, etc.). Herbaceous plant-derived lignins have all of the basic skeletons of H-type, G-type, and S-type. These lignins can be used alone or in combination of two or more types.

[0020] From the viewpoint of homogeneity of the PEG-modified lignin, the lignin is preferably a woody plant-derived lignin that does not contain an H-type basic skeleton, more preferably a coniferous lignin that does not contain an S-type basic skeleton and has a G-type basic skeleton, and particularly preferably a coniferous lignin derived from cedar.

[0021] The PEG-modified lignin is not particularly limited, but can be produced, for example, in accordance with the method described in Patent Document 3 (JP 2017-197517 A).

[0022] More specifically, for example, PEG-modified lignin can be obtained by solvolyzing a plant material (lignocellulose), which is the raw material for lignin, with polyethylene glycol.

[0023] The method of solvolysis is not particularly limited, but for example, a plant material that is the raw material for lignin, polyethylene glycol, and an inorganic acid (e.g., hydrochloric acid, sulfuric acid, etc.) as an acid catalyst are mixed and reacted.

[0024] The mixing ratio of polyethylene glycol is, for example, 200 parts by mass or more, preferably 300 parts by mass or more, and for example, 1000 parts by mass or less, preferably 600 parts by mass or less, per 100 parts by mass of the plant material that is the raw material for lignin.

[0025] The mixing ratio of the inorganic acid (100% equivalent) relative to 100 parts by mass of polyethylene glycol is, for example, 0.1 parts by mass or more, preferably 0.2 parts by mass or more, and for example, 2 parts by mass or less, preferably 1 part by mass or less.

[0026] The reaction conditions are as follows: under normal pressure, the reaction temperature is, for example, 120° C. or more, preferably 130° C. or more, and for example, 180° C. or less, preferably 150° C. or less, and the reaction time is, for example, 60 minutes or more, and for example, 240 minutes or less, preferably 120 minutes or less.

[0027] After the reaction is completed, a known alkali (for example, ammonia, sodium hydroxide, etc.) is added in an appropriate ratio to adjust the pH, thereby extracting the PEG-modified lignin into the solution.

[0028] The pH after adjustment is, for example, 8 or more, preferably 10 or more, more preferably 10.5 or more, and for example, 14 or less.

[0029] By such a method, pulp is obtained as a solid component, and PEG-modified lignin is obtained as a solution component (pulp waste liquor).

[0030] Next, in this method, the solid component (pulp) is separated from the reaction product by a known separation method such as filtration, pressing, or centrifugation, and the solution component (pulp waste liquor) is recovered.

[0031] In this method, if necessary, the solid component (pulp) can be washed and the solution (PEG-modified lignin) impregnated into the solid component can be recovered.

[0032] In this method, an inorganic acid (e.g., hydrochloric acid, sulfuric acid, etc.) is then added to adjust the pH to precipitate and deposit the PEG-modified lignin.

[0033] The pH after adjustment is, for example, 1.5 or more, and for example, 5 or less, preferably 3 or less, and more preferably 2 or less.

[0034] This allows precipitation of PEG-modified lignin. The resulting precipitate can be collected by a known method such as filtration, pressing, or centrifugation to obtain the PEG-modified lignin as a solid content.

[0035] (Phenol Compound) The phenol compound used as the raw material for the novolac phenolic resin derived from PEG-modified lignin is phenol or its derivative (phenol-modified product). Examples of such phenol compounds include phenol, bifunctional phenol derivatives such as o-cresol, p-cresol, p-tert-butylphenol, p-phenylphenol, p-cumylphenol, p-nonylphenol, and 2,4- or 2,6-xylenol, trifunctional phenol derivatives such as m-cresol, resorcinol, and 3,5-xylenol, and tetrafunctional phenol derivatives such as bisphenol A and dihydroxydiphenylmethane. Phenol derivatives also include halogenated phenol compounds substituted with halogens such as chlorine and bromine. These phenol compounds can be used alone or in combination. When a phenol derivative (phenol-modified product) is used, the timing of phenol modification is not particularly limited, and it can be performed before, after, or simultaneously with the reaction of the PEG-modified lignin with the phenol compound and the aldehyde compound.

[0036] As the phenol compound, preferably, phenol is used.

[0037] (Aldehyde Compound) Examples of aldehyde compounds that are raw materials for novolac phenolic resins derived from PEG-modified lignin include formaldehyde, paraformaldehyde, acetaldehyde, propionaldehyde, butylaldehyde (n-butylaldehyde, isobutylaldehyde), furfural, glyoxal, benzaldehyde, trioxane, and tetraoxane. Furthermore, a portion of the aldehyde may be substituted with furfuryl alcohol or the like. These aldehyde compounds can be used alone or in combination of two or more.

[0038] The aldehyde compound is preferably formaldehyde or paraformaldehyde. The aldehyde compound can be used, for example, as an aqueous solution. In such a case, the concentration of the aldehyde compound is, for example, 10% by mass or more, preferably 20% by mass or more, and for example, 99% by mass or less, preferably 95% by mass or less.

[0039] In addition to the aldehyde compound, a ketone compound can also be blended. Examples of the ketone compound include acetone, methyl ethyl ketone, diethyl ketone, acetophenone, and diphenyl ketone. These ketone compounds can be used alone or in combination of two or more.

[0040] When a ketone compound is blended, the blending ratio of the ketone compound, based on the solid content, relative to 100 parts by mass of the aldehyde compound is, for example, 0.01 parts by mass or more, preferably 1 part by mass or more, and for example, 200 parts by mass or less, preferably 100 parts by mass or less.

[0041] (Reaction) To react the PEG-modified lignin, phenolic compound, and aldehyde compound (and optionally a ketone compound, the same applies below), the above components (PEG-modified lignin, phenolic compound, aldehyde compound, etc.) are mixed and heated. This reaction can also be carried out in the presence of an acid catalyst.

[0042] In this reaction, the blending ratio of the phenol compound is, for example, 30 parts by mass or more, preferably 50 parts by mass or more, more preferably 100 parts by mass or more, and for example, 1000 parts by mass or less, preferably 500 parts by mass or less, more preferably 350 parts by mass or less, relative to 100 parts by mass of the PEG-modified lignin.

[0043] From the viewpoint of improving heat resistance, the blending ratio of the phenol compound is preferably 200 parts by mass or more, more preferably 250 parts by mass or more, and preferably 1000 parts by mass or less, more preferably 500 parts by mass or less, per 100 parts by mass of the PEG-modified lignin.

[0044] The blending ratio of the aldehyde compound relative to 100 parts by mass of the phenol compound is, for example, 5 parts by mass or more, preferably 10 parts by mass or more, and for example, 35 parts by mass or less, preferably 30 parts by mass or less. The blending ratio of the aldehyde compound relative to 100 parts by mass of the PEG-modified lignin is, for example, 1.5 parts by mass or more, preferably 3 parts by mass or more, and for example, 350 parts by mass or less, preferably 300 parts by mass or less.

[0045] In this reaction, an acid catalyst can be added. The above components can be reacted in the presence of an acid catalyst. Examples of the acid catalyst include organic acids and inorganic acids.

[0046] Examples of organic acids include sulfonic acid compounds such as methanesulfonic acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, cumenesulfonic acid, dinonylnaphthalene monosulfonic acid, and dinonylnaphthalenedisulfonic acid; phosphate esters having an alkyl group having 1 to 18 carbon atoms such as trimethyl phosphate, triethyl phosphate, monobutyl phosphate, dibutyl phosphate, tributyl phosphate, and trioctyl phosphate; and formic acid, acetic acid, and oxalic acid. Examples of inorganic acids include phosphoric acid, hydrochloric acid, sulfuric acid, and nitric acid. These acid catalysts can be used alone or in combination of two or more.

[0047] The acid catalyst is preferably an organic acid, more preferably oxalic acid.

[0048] The mixing ratio of the acid catalyst relative to 100 parts by mass of the phenol compound is, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, and for example, 10 parts by mass or less, preferably 5 parts by mass or less.

[0049] The timing of adding the acid catalyst is not particularly limited, and the acid catalyst may be added in advance to at least one of the PEG-modified lignin, the phenolic compound, and the aldehyde compound, or may be added simultaneously when the PEG-modified lignin, the phenolic compound, and the aldehyde compound are blended, or may be added after the PEG-modified lignin, the phenolic compound, and the aldehyde compound are blended.

[0050] The reaction conditions are as follows: under atmospheric pressure, the reaction temperature is, for example, 50° C. or more, preferably 80° C. or more, and for example, 200° C. or less, preferably 180° C. or less, and the reaction time is, for example, 1 hour or more, preferably 2 hours or more, and for example, 20 hours or less, preferably 15 hours or less.

[0051] As a result, a novolac phenolic resin is obtained as a reaction product of the PEG-modified lignin, the phenolic compound, and the aldehyde compound. More specifically, a novolac phenolic resin is obtained by the reaction of the phenolic compound with the aldehyde compound in the presence of an acid catalyst, and the novolac phenolic resin is then modified with the PEG-modified lignin.

[0052] That is, a novolac type phenolic resin derived from PEG-modified lignin is obtained.

[0053] In the production of a novolac-type phenolic resin derived from PEG-modified lignin, unreacted raw materials (unreacted phenolic compounds, etc.) and acid catalysts can be removed, if necessary, by a known method such as distillation.

[0054] The novolac-type phenolic resin derived from the PEG-modified lignin thus obtained contains a reaction product obtained by reacting lignin modified with polyethylene glycol, a phenolic compound, and an aldehyde compound in the presence of an acid catalyst.

[0055] (2) Amine Compound Examples of the amine compound include primary amines. Specific examples include alkyl or alkenyl monoamines such as methylamine, ethylamine, n-propylamine, n-butylamine, n-dodecylamine, n-nonylamine, cyclopentylamine, cyclohexylamine, and allylamine; and aromatic monoamines such as aniline, p-cyanoaniline, p-bromoaniline, o-toluidine, m-toluidine, p-toluidine, 2,4-xylidine, 2,5-xylidine, 3,4-xylidine, α-naphthylamine, β-naphthylamine, and 3-aminophenylacetylene.

[0056] In addition, benzylamine, 2-aminobenzylamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,10-diaminodecane, 2,7-diaminofluorene, 1,4-diaminocyclohexane, 9,10-diaminophenanthrene, 1,4-diaminopiperazine, p-phenylenediamine, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, 4,4'-diaminobiphenyl, 4,4'-oxydianiline, fluorenetetraamine, tetraaminediphenyl ether, melamine, and the like can also be used. Among these, aniline and methylamine are preferred, and aniline is more preferred. Aniline has a phenyl group in the molecule, and this phenyl group further improves the heat resistance of the molded article.

[0057] (3) Aldehyde Compound The aldehyde compound is not particularly limited. Examples include formaldehyde, paraformaldehyde, acetaldehyde, propionaldehyde, butylaldehyde (n-butylaldehyde, isobutylaldehyde), furfural, glyoxal, benzaldehyde, trioxane, and tetraoxane. In addition, a portion of the aldehyde may be substituted with furfuryl alcohol or the like. These aldehyde compounds can be used alone or in combination of two or more.

[0058] A formaldehyde compound is preferred. Examples of formaldehyde compounds include formalin, which is an aqueous solution of formaldehyde, and its polymers, such as paraformaldehyde and trioxane. The aldehyde compound used may be in any state, such as a solid or liquid. Paraformaldehyde is particularly preferred because it is easy to handle since it is a solid (powder) at room temperature.

[0059] (4) Production Method The benzoxazine compound of the present invention can be produced by reacting components including (1) a novolac phenolic resin derived from PEG-modified lignin, (2) an amine compound, and (3) an aldehyde compound.

[0060] The benzoxazine ring is formed at the phenolic skeleton in the molecule of the novolac phenolic resin derived from PEG-modified lignin. For example, by mixing and reacting the above components, a cyclization reaction proceeds at the phenolic skeleton to form the benzoxazine ring.

[0061] The novolac-type phenolic resin derived from PEG-modified lignin, the amine compound, and the aldehyde compound may be in a molar ratio theoretically required to form a benzoxazine ring. For example, when each component molecule contains one functional group, the novolac-type phenolic resin derived from PEG-modified lignin, the amine compound, and the aldehyde compound are in a molar ratio of 1:1:2.

[0062] The amine compound and the aldehyde compound can be used in appropriate proportions depending on the degree of modification of the novolac phenolic resin derived from PEG-modified lignin. For example, the amine compound is used in an amount of 0.5 to 30 moles, preferably 0.8 to 20 moles, and more preferably 1 to 10 moles, and the aldehyde compound is used in an amount of 1 to 40 moles, preferably 1.2 to 20 moles, and more preferably 1.5 to 15 moles, relative to 1 mole of the phenolic hydroxyl group equivalent of the novolac phenolic resin derived from PEG-modified lignin.

[0063] In this reaction, an acid catalyst can be added. That is, the above components can be reacted in the presence of an acid catalyst. Examples of the acid catalyst include organic acids and inorganic acids.

[0064] Examples of organic acids include sulfonic acid compounds such as methanesulfonic acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, cumenesulfonic acid, dinonylnaphthalene monosulfonic acid, and dinonylnaphthalenedisulfonic acid; phosphate esters having an alkyl group having 1 to 18 carbon atoms such as trimethyl phosphate, triethyl phosphate, monobutyl phosphate, dibutyl phosphate, tributyl phosphate, and trioctyl phosphate; and formic acid, acetic acid, and oxalic acid. Examples of inorganic acids include phosphoric acid, hydrochloric acid, sulfuric acid, and nitric acid. These acid catalysts can be used alone or in combination of two or more.

[0065] The acid catalyst is preferably an organic acid, more preferably oxalic acid.

[0066] The mixing ratio of the acid catalyst relative to 100 parts by mass of the phenol compound is, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, and for example, 10 parts by mass or less, preferably 5 parts by mass or less.

[0067] The reaction temperature is preferably about 50 to 200° C., more preferably about 100 to 150° C. The reaction time is preferably about 5 minutes to 6 hours, more preferably about 20 minutes to 3 hours.

[0068] The benzoxazine compound produced as described above has superior solubility in solvents and meltability compared to benzoxazine compounds based on herbaceous lignin, and also cures faster than conventional benzoxazine compounds, resulting in cured products with superior heat resistance, strength, and flexibility.

[0069] 3. Uses of Benzoxazine Compound The present invention further provides a resin composition containing the benzoxazine compound produced above, a cured product thereof, a composite (prepreg, etc.) containing the resin composition and a substrate, and a cured product of the composite. These are specifically described below.

[0070] The resin composition of the present invention contains the benzoxazine compound and, if necessary, may further contain additives such as toughening agents, catalysts, reinforcing agents, fillers, adhesion promoters, flame retardants, and thixotropic agents. The additives may be used alone or in combination of two or more. The content of the additives may be appropriately set depending on the purpose and application, as long as the excellent effects of the present invention are not impaired.

[0071] The resin composition of the present invention may contain other resins as needed. Examples of other resins include thermosetting resins and thermoplastic resins. Examples of thermosetting resins include epoxy resins, phenolic resins, bismaleimide resins, polyimide resins, silicon resins, melamine resins, urea resins, unsaturated polyester resins, alkyd resins, furan resins, and polyurethane resins. Examples of thermoplastic resins include thermoplastic epoxy resins and thermoplastic polyimide resins.

[0072] The resin composition of the present invention contains a benzoxazine compound as a main component, and may contain other resins (such as thermosetting resins and thermoplastic resins), additives, and the like as secondary components, as required.

[0073] In the present invention, the resin composition containing a benzoxazine compound includes both the benzoxazine compound and a mixture containing the benzoxazine compound and other components (additives, other resins, etc.).

[0074] The content of the benzoxazine compound in the resin composition of the present invention is, for example, 1 to 100 mass%, preferably 1 to 90 mass%, more preferably 3 to 85 mass%, and particularly preferably 5 to 80 mass%.

[0075] The minimum melt viscosity (complex viscosity) of the benzoxazine compound and resin composition of the present invention is preferably 0.1 to 10,000 (Pa s), more preferably 0.1 to 1,000 (Pa s), particularly preferably 1 to 500 (Pa s) at 100 to 160°C, from the viewpoint of being able to knead with other resins.

[0076] In this specification, the minimum melt viscosity (complex viscosity) is specified by the following method: the viscoelasticity is measured using a 25 mm diameter parallel plate rheometer (MCR300, manufactured by Anton Paar Japan) under conditions of a gap of 1 mm, a frequency of 1 Hz, a strain of 0.5%, a heating rate of 2°C / min, and a temperature range of 100°C to 180°C, and the minimum melt viscosity (Pa s) is determined from the obtained viscoelasticity curve.

[0077] When the resin composition of the present invention contains additives and / or other resins, the benzoxazine compound and the additives and / or other resins can be mixed (kneaded) by a known method.

[0078] The kneading method is not particularly limited, and for example, known kneaders such as a single-screw extruder, a multi-screw extruder, a roll kneader, a kneader, a Henschel mixer, or a Banbury mixer can be used. Kneading conditions include a kneading temperature of, for example, 80°C or higher, preferably 90°C or higher, and more preferably 100°C or higher, and 180°C or lower, preferably 170°C or lower, and more preferably 160°C or lower. Furthermore, the kneading time is, for example, 3 minutes or higher, preferably 5 minutes or higher, and for example, 30 minutes or lower, preferably 20 minutes or lower. This provides a resin composition containing the benzoxazine compound and additives and / or other resins.

[0079] The cured product of the resin composition of the present invention can be obtained by curing the resin composition. The curing of the resin composition can be carried out, for example, at 100 to 200°C for 1 minute to 8 hours.

[0080] The glass transition temperature of the resulting cured product is preferably at least 200° C., more preferably at least 215° C., and particularly preferably at least 230° C. In this specification, the glass transition temperature (Tg) is a value measured from the peak temperature of the loss tangent (tanδ) obtained from a dynamic viscoelasticity test.

[0081] The present invention provides a composite comprising the resin composition of the present invention and a substrate. A typical example of the composite is a prepreg comprising the resin composition and a substrate. The prepreg of the present invention is usually a composite in which a substrate is impregnated with the resin composition. The substrate is not particularly limited as long as it can be used to form a prepreg, and examples thereof include paper and reinforcing fibers.

[0082] Examples of paper include linter paper made from cotton and kraft paper made from hardwood.

[0083] Examples of reinforcing fibers include glass fibers, carbon fibers, graphite fibers, aramid fibers, boron fibers, alumina fibers, and silicon carbide fibers. A wide variety of fibers can be used, but are not limited to these. There is no particular limitation or restriction on the form of the reinforcing fibers, and various forms of fibers can be used, including, for example, long fibers (unidirectionally stretched), tows, woven fabrics, mats, knits, braids, and short fibers (cut to lengths of less than 10 mm). Here, long fibers refer to single fibers or fiber bundles that are substantially continuous over at least 10 mm. On the other hand, short fibers are fiber bundles cut to lengths of less than 10 mm. For applications requiring high specific strength and specific modulus, a fiber arrangement in which the reinforcing fiber bundles are aligned in the same direction is suitable.

[0084] The content of the resin composition in the prepreg is usually 30 to 70 mass%, preferably 35 to 65 mass%, and more preferably 40 to 60 mass%. The content of the base material in the prepreg is usually 30 to 70 mass%, preferably 35 to 65 mass%, and more preferably 40 to 60 mass%.

[0085] The prepreg can be produced by a known method, for example, a sheet molding compound method when the substrate is a reinforcing fiber.

[0086] The prepreg can be produced by impregnating a substrate (paper, reinforcing fiber, etc.) with a resin composition. Impregnation methods include wet methods and hot melt methods (dry methods). In this case, the viscosity of the resin composition impregnated into the substrate is preferably within the above range.

[0087] The wet method is a method for preparing a prepreg by immersing a substrate (paper, reinforcing fiber, etc.) in a solution prepared by dissolving a resin composition in an organic solvent (methyl ethyl ketone, tetrahydrofuran, methanol, etc.), and then removing the substrate from the solution, and then evaporating and removing the organic solvent in an oven, etc.

[0088] The hot melt method is a method in which a resin composition that has been fluidized by heating is directly impregnated into a substrate (paper, reinforcing fiber, etc.). Alternatively, to use it as a resin film, the resin composition is coated on release paper or the like, and the film is then placed on one or both sides of a substrate (paper, reinforcing fiber, etc.) arranged in a flat shape, and then heat and pressure are applied to impregnate the substrate with the resin. By using this hot melt method, a prepreg that is substantially free of residual solvent can be obtained.

[0089] For applying heat and pressure under the prepreg lamination molding method, press molding, autoclave molding, bagging molding, wrapping tape method, internal pressure molding, etc. may be used as appropriate.

[0090] Autoclave molding is a process in which prepregs are stacked on a shaped tool plate, then covered with a bagging film, and subsequently cured by applying heat and pressure while air is drawn out of the laminate. It can allow precise control of fiber orientation and can also provide high-quality molded materials with excellent mechanical properties by minimizing void content. The pressure applied during the molding process is typically 0.3-1.0 MPa, while the molding temperature is typically in the range of 90-300°C.

[0091] Because the cured product of the resin composition containing the benzoxazine compound of the present invention has a high Tg, it is advantageous to cure the prepreg at a relatively high temperature (e.g., a temperature of at least 180°C or at least 200°C). For example, the molding temperature may be 200 to 275°C. Alternatively, the prepreg may be molded at a slightly lower temperature (e.g., 90 to 200°C), demolded, and then post-cured at a higher temperature (e.g., 200 to 275°C) after removal from the mold.

[0092] The wrapping tape method is a method in which prepreg is wrapped around a mandrel or some other core to form a tubular fiber-reinforced composite material. This method can be used to manufacture golf shafts, fishing rods, and other rod-shaped products. More specifically, this method involves wrapping prepreg around a mandrel and wrapping a wrapping tape made of a thermoplastic film over the prepreg under tension to secure the prepreg and apply pressure to it. After curing the resin by heating in an oven, the core is removed to obtain a tubular body. The tension used in wrapping the wrapping tape can be 20 to 100 N. The molding temperature can be in the range of 80 to 300°C.

[0093] In the internal pressure molding method, a preform obtained by wrapping a prepreg around a thermoplastic resin tube or some other internal pressure applicator is placed inside a metal mold, and then high-pressure gas is introduced into the internal pressure applicator to apply pressure, and the metal mold is simultaneously heated to mold the prepreg. This method can be used to mold objects with complex shapes, such as golf shafts, bats, and tennis or badminton rackets. The pressure applied during the molding process can be 0.1 to 2.0 MPa. The molding temperature can be in the range of room temperature to 300°C, or 180 to 275°C.

[0094] The cured products of the resin composition of the present invention and the cured products of the composites (prepregs, etc.) of the present invention obtained in this manner are made from the above-mentioned (1) novolac phenolic resin derived from lignin modified with PEG, (2) an amine compound, and (3) a benzoxazine compound containing a reaction product of an aldehyde compound. Therefore, they are characterized by excellent heat resistance (high glass transition temperature (Tg)), excellent strength (high tensile strength), and easy elongation (relatively small tensile modulus). Therefore, they are suitable for a wide range of applications, such as the production of molded products such as electrical parts, automotive parts, building materials, daily necessities, fiber-reinforced composite materials, structural materials, and electrical and electronic materials.

[0095] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited thereto. <Raw Materials> The main raw materials used are as follows. Modified lignin novolac resin 1 (PEG600LN-2; a novolac-type phenolic resin derived from lignin modified with polyethylene glycol, modified lignin content 40%, manufactured by the Forestry and Forest Products Research Institute) (see Example 7 of Patent Document 4). Modified lignin novolac resin 2 (PEG400LN-2; a novolac-type phenolic resin derived from lignin modified with polyethylene glycol, modified lignin content 40%, manufactured by the Forestry and Forest Products Research Institute) (see Example 4 of Patent Document 4). Phenol novolac resin N1 (Phenolite TD2131, mp 80°C, OH equivalent 103, manufactured by DIC Corporation).

[0096] <Evaluation Method> The benzoxazine compounds, prepregs, and cured products obtained as described below were evaluated as follows.

[0097] (1) Softening Point and Minimum Melt Viscosity of Benzoxazine Compounds For the benzoxazine compounds obtained in Examples 1 and 2 and the benzoxazine compound obtained in Comparative Example 3, the endothermic peak temperatures of differential scanning calorimetry (DSC) were measured and defined as the softening points (°C). The results are shown in Table 1. Furthermore, for each benzoxazine compound, the viscoelasticity was measured using a 25 mm diameter parallel plate rheometer (MCR300, manufactured by Anton Paar Japan) under conditions of a gap of 1 mm, a frequency of 1 Hz, a strain of 0.5%, a heating rate of 2°C / min, and a temperature range of 100°C to 180°C, and the minimum melt viscosity (Pa s) was determined from the resulting viscoelastic curve. The results are shown in Table 1.

[0098] (2) Solubility Test of Benzoxazine Compounds The benzoxazine compounds obtained in Examples 1 and 2 and the benzoxazine compound obtained in Comparative Example 3 were evaluated for solubility in various solvents shown in Table 2. Specifically, 5 g of solvent was added to 1 g of each benzoxazine compound, and the benzoxazine compound was dissolved at room temperature (23°C). The resulting mixture was then filtered, and the presence or absence of residual material was visually confirmed. The solubility of each benzoxazine compound in the solvent was evaluated according to the following criteria. The results are shown in Table 2. ○: Completely dissolved (no residual material) △: Partially dissolved (some residual material present) ×: Not dissolved at all

[0099] (3) Evaluation of Curing Behavior of Benzoxazine Compounds The curing behavior of each benzoxazine compound was evaluated by differential scanning calorimetry (DSC) in a nitrogen atmosphere, by heating each benzoxazine compound from room temperature to 300°C at a heating rate of 10°C / min, and measuring the onset temperature and peak temperature of the curing exothermic peak. The results are shown in Table 3.

[0100] (4) Evaluation of Heat Resistance of Cured Products (Measurement of Glass Transition Temperature Tg) The glass transition temperatures (Tg) of the cured products obtained in Examples 3 and 4 and Comparative Examples 4 and 5 were evaluated based on the peak temperatures of the temperature dispersion curves of the loss tangent (tan δ) obtained from dynamic viscoelasticity measurements. Dynamic viscoelasticity measurements were performed using a Rheogel-E4000 manufactured by UBM Corporation at a frequency of 1 Hz, a heating rate of 2°C / min, and in bending mode. The results are shown in Table 3.

[0101] (5) Evaluation of tensile strength and modulus of elasticity of cured products Tensile tests were conducted at room temperature using rectangular test pieces (length 100 mm, width 10 mm, thickness approximately 5 mm) of the cured products obtained in Examples 3 and 4, and the cured products obtained in Comparative Examples 4 and 5, at a test speed of 1 mm / min and a gripping distance of 70 mm, to measure the tensile strength (MPa) and tensile modulus (GPa). The results are shown in Table 3.

[0102] <Synthesis of benzoxazine compound> [Example 1] 15.0 g of modified lignin novolak resin 1 (equivalent weight of phenolic hydroxyl group of resin: 97.5 mmol), 150 g of 4-methyltetrahydropyran, 9.1 g (97.5 mmol) of aniline, and 5.9 g (195 mmol) of paraformaldehyde were charged into a 300 ml three-necked eggplant flask, and the mixture was stirred at 106°C for 3 hours while removing water from the system using a Dean-Stark apparatus. The mixture was then cooled to 80°C, and the insoluble matter was filtered off. The filtrate was then concentrated to obtain 15.1 g of a black solid.

[0103] This black solid １ The H-NMR spectrum data was as follows: １ H-NMR (DMSO-d ６ ) δ / ppm: 6.4-7.2 ppm (benzene ring derived from novolac resin skeleton), 4.5-4.6 ppm (methylene of benzoxazine ring), 5.3 ppm (methylene of benzoxazine ring), 3.5-3.6 ppm (methylene of novolac resin skeleton), 3.5 ppm (methylene of polyethylene glycol). The IR spectrum data of this black solid was as shown in the chart in Figure 1. From this spectrum data, the obtained black solid was identified as a benzoxazine compound. The obtained benzoxazine compound was evaluated for softening point, minimum melt viscosity, and solubility. The results are shown in Tables 1 and 2.

[0104] [Example 2] 15.0 g of modified lignin novolac resin 2 (equivalent weight of phenolic hydroxyl group of resin: 97.5 mmol), 150 g of 4-methyltetrahydropyran, 9.1 g (97.5 mmol) of aniline, and 5.9 g (195 mmol) of paraformaldehyde were charged into a 300 ml three-necked flask, and the mixture was stirred at 106°C for 3 hours while removing water from the system using a Dean-Stark apparatus. The mixture was then cooled to 80°C, and the insoluble matter was filtered off. The filtrate was concentrated to obtain 15.1 g of a black solid. １ The H-NMR spectrum data was as follows: １ H-NMR (DMSO-d ６) δ / ppm: 6.6-7.2 ppm (benzene ring derived from novolac resin skeleton), 4.3-4.6 ppm (methylene of benzoxazine ring), 5.3 ppm (methylene of benzoxazine ring), 3.2-3.7 ppm (methylene of novolac resin skeleton), 3.5 ppm (methylene of polyethylene glycol). From the IR spectrum data of this black solid, the obtained black solid was identified as a benzoxazine compound. The obtained benzoxazine compound was evaluated for softening point, minimum melt viscosity, and solubility. The results are shown in Tables 1 and 2.

[0105] Comparative Example 1 (Fa-type benzoxazine) Benzoxazine Fa manufactured by Shikoku Chemicals Corporation was used.

[0106] Comparative Example 2 (Phenol Novolac Benzoxazine) A 2 L four-neck flask equipped with a reflux condenser, a thermometer, a dropping funnel, and a stirrer was charged with 4 mol of a 37% aqueous formaldehyde solution, and the solution was cooled to below 10°C in an ice bath and stirred, while 2 mol of aniline was slowly added dropwise. Next, 2 mol of phenol novolac resin N1 was added, and the mixture was reacted by stirring for 6 hours under dioxane reflux conditions, followed by drying under reduced pressure to obtain phenol novolac benzoxazine (N1-a).

[0107] Comparative Example 3 (Lignin-Derived Benzoxazine) Herbaceous lignin having an average particle size of approximately 40 μm was obtained from wastewater generated during the pulp manufacturing process using wheat straw as a raw material. The obtained herbaceous lignin, aniline, and paraformaldehyde were then charged into a reaction vessel at a molar ratio of lignin:aniline:paraformaldehyde = 1:10:20. The reaction vessel was then maintained at 100°C for 30 minutes to obtain herbaceous lignin-derived benzoxazine. The obtained herbaceous lignin-derived benzoxazine compound was evaluated for softening point, minimum melt viscosity, and solubility. The results are shown in Tables 1 and 2.

[0108] <Preparation of Prepreg and Cured Product> [Example 3] A 6.4 g weight of A4-sized paper (paper base phenolic resin kraft paper, approximately 0.23 mm thick) was measured. The same weight of the benzoxazine compound obtained in Example 1 was measured and dissolved in 30 ml of tetrahydrofuran. The paper was then completely impregnated with the tetrahydrofuran solution and dried at 50°C for 24 hours to produce a prepreg containing approximately 50% of the benzoxazine compound. The obtained prepreg was sandwiched between hot plates in an oven and heated at 150°C for 4 hours and then at 200°C for 2 hours to obtain a cured product. The obtained cured product was evaluated for heat resistance and mechanical properties. The results are shown in Table 3.

[0109] Example 4 A prepreg containing approximately 50% benzoxazine and a cured product were obtained in the same manner as in Example 3, except that the benzoxazine compound obtained in Example 2 was used. The heat resistance and mechanical properties of the obtained cured product were evaluated. The results are shown in Table 3.

[0110] Comparative Example 4 A prepreg and a cured product were obtained in the same manner as in Example 3, except that the conventional monomer-type benzoxazine compound (Fa-type benzoxazine) of Comparative Example 1 was used instead of the benzoxazine compound obtained in Example 1. The heat resistance and mechanical properties of the obtained cured product were evaluated. The results are shown in Table 3.

[0111] Comparative Example 5 A prepreg and a cured product were obtained in the same manner as in Example 3, except that the conventional phenol novolac benzoxazine compound (N1-a) of Comparative Example 2 was used instead of the benzoxazine compound obtained in Example 1. The heat resistance and mechanical properties of the obtained cured product were evaluated. The results are shown in Table 3.

[0112] Comparative Example 6 An attempt was made to prepare a prepreg in the same manner as in Example 3, except that the benzoxazine compound (non-PEG chain) derived from herbaceous lignin of Comparative Example 3 was used instead of the benzoxazine compound obtained in Example 1. However, the compound was unable to dissolve in tetrahydrofuran and other solvents, and preparation of a prepreg was impossible.

[0113] From Table 1, it was confirmed that the benzoxazine compounds of the present invention obtained in Examples 1 and 2 have softening points, the softening points are low, and the minimum melt viscosity is also small. Therefore, the present benzoxazine compounds are applicable to prepreg formation, casting processes, etc. In contrast, the conventional benzoxazine compound of Comparative Example 3 (corresponding to the lignin-modified benzoxazine compound of Patent Document 2) does not have a softening point. Therefore, it is not applicable to prepreg formation, casting processes, etc.

[0114] As can be seen from Table 2, the benzoxazine compounds of the present invention obtained in Examples 1 and 2 have high solubility in various organic solvents, whereas the benzoxazine compound of Comparative Example 3 was insoluble in any organic solvent.

[0115] From Table 3, it was confirmed that the benzoxazine compounds of the present invention obtained in Examples 1 and 2 had lower DSC peak onset temperatures and DSC peak temperatures than the monomer-type benzoxazine compound of Comparative Example 1 (Fa-type benzoxazine) and the phenol novolac-type benzoxazine compound (N1-a) of Comparative Example 2, and therefore the curing reaction started and completed in the low temperature range.

[0116] From Table 3, it was confirmed that the cured products obtained in Examples 3 and 4 had significantly higher glass transition temperatures and superior heat resistance than the cured products obtained in Comparative Examples 4 and 5.

[0117] From Table 3, it was confirmed that the cured products obtained in Examples 3 and 4 had higher tensile strength and lower tensile modulus than the cured products obtained in Comparative Examples 4 and 5.

[0118] The benzoxazine compound of the present invention has high solubility and meltability in organic solvents. Furthermore, a cured product obtained by curing a resin composition containing the benzoxazine compound of the present invention is characterized by excellent heat resistance (high glass transition temperature (Tg)), excellent strength (high tensile strength), and easy elongation (relatively small tensile modulus). Therefore, it is suitable for use in molded products obtained by forming prepregs, etc.

Claims

1. A benzoxazine compound comprising a reaction product of a novolac-type phenolic resin derived from lignin modified with polyethylene glycol, an amine compound, and an aldehyde compound.

2. The benzoxazine compound according to claim 1, wherein the novolac phenolic resin is obtained by reacting lignin modified with polyethylene glycol, a phenolic resin, and an aldehyde compound.

3. A resin composition containing the benzoxazine compound according to claim 1 or 2.

4. A cured product of the resin composition according to claim 3.

5. A composite comprising the resin composition of claim 3 and a substrate.

6. A prepreg comprising the resin composition of claim 3 and a substrate.

7. A cured product of the composite of claim 5.

8. A method for producing a benzoxazine compound, comprising: (1) a step of reacting lignin modified with polyethylene glycol with a phenolic resin and an aldehyde compound to obtain a novolac phenolic resin; and (2) a step of reacting the novolac phenolic resin obtained in (1) above with an amine compound and an aldehyde compound to obtain a benzoxazine compound.

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