Prepreg preparation method and matrix resin raw material composition

Abstract

The present invention provides a prepreg production method comprising: an impregnation step in which a fiber base material is impregnated with a matrix resin raw material composition containing a main agent of a matrix resin, a curing agent, and a solvent; and a drying step for drying the matrix resin raw material composition impregnated into the fiber base material in the impregnation step. The main agent is epoxy resin. The curing agent is a PEG lignin derivative. The solvent is composed of a first solvent composed of glycol ethers and a second solvent composed of ethers.

Description

Technical Field

[0001] This invention relates to a method for preparing a prepreg by impregnating a matrix resin, which uses epoxy resin as the main agent and PEG lignin derivatives extracted from cedar wood using polyethylene glycol (PEG) as the curing agent, into a fiber substrate, as well as a matrix resin raw material composition. Background Technology

[0002] Methods for preparing resin compositions comprising epoxy resin and PEG lignin derivatives are known in the past. For example, in the preparation method of Patent Document 1, modified lignin obtained by chemical modification with polyethylene glycol is liquefied by treating it in a methanol solvent, and after mixing with epoxy resin, the methanol is removed by drying the resulting solid.

[0003] However, the base resin of the prepreg needs to maintain a uniform varnish state in order to fully impregnate the fiber substrate. However, as described in Patent Document 1, when methanol is used as a solvent, it is difficult to fully dissolve lignin, making it difficult to maintain a uniform varnish state during the impregnation process into the fiber substrate.

[0004] Existing technical documents Patent documents Patent document 1: JP2020-203968A. Summary of the Invention

[0005] A prepreg preparation method according to one embodiment of the present invention includes: an impregnation step, in which a matrix resin raw material composition containing a matrix resin main agent, a curing agent, and a solvent is impregnated into a fiber substrate; and a drying step, in which the matrix resin raw material composition impregnated into the fiber substrate in the impregnation step is dried. The main agent is an epoxy resin. The curing agent is a PEG lignin derivative. The solvent includes a first solvent composed of ethylene glycol ethers and a second solvent composed of ethers.

[0006] Another technical solution of the present invention provides a matrix resin raw material composition comprising a main agent, a curing agent, and a solvent. The main agent is an epoxy resin. The curing agent is a PEG lignin derivative. The solvent includes a first solvent composed of ethylene glycol ethers and a second solvent composed of ethers. Attached Figure Description

[0007] The objectives, features, and advantages of the present invention are further illustrated by the following description of embodiments in conjunction with the accompanying drawings.

[0008] Figure 1 This is a flowchart illustrating an example of a prepreg preparation method according to an embodiment of the present invention. Detailed Implementation

[0009] The following is for reference Figure 1 Embodiments of the present invention will be described. The prepreg in the embodiments of the present invention is an intermediate material for fiber-reinforced resin, which is a sheet material in which a matrix resin is impregnated into a fiber substrate such as glass fiber. Fiber-reinforced resin can be prepared by stacking and pressing the prepregs together. The stacked prepregs are bonded to each other with a viscous matrix resin. The stacked prepregs are then pressed at a temperature above the curing temperature of the matrix resin, thereby curing the matrix resin and completing the fiber-reinforced resin.

[0010] Epoxy resin is cited as a representative thermosetting resin used as a matrix resin. PEG lignin derivatives derived from biological sources can be used as curing agents for epoxy resins. However, PEG lignin derivatives are powders at room temperature and are difficult to dissolve. Therefore, in this embodiment, the matrix resin raw material composition is configured such that the PEG lignin derivative is dissolved in a suitable solvent and, by mixing with the epoxy resin, is made into a state suitable for impregnation into a fibrous substrate.

[0011] Figure 1 This is a flowchart illustrating an example of a prepreg preparation method according to an embodiment of the present invention. For example... Figure 1 As shown, in the prepreg preparation method of the embodiment of the present invention, firstly in step S1, 75 parts (e.g., 585 g) of powdered PEG lignin derivative are measured as a curing agent. For example, SD4 manufactured by LignoMateria Corporation can be used as the PEG lignin derivative.

[0012]

[0013] Next, in the first mixing step S2, 50 parts (e.g., 390 g) of liquid ethylene glycol monomethyl ether are metered as the first solvent and added to the powdered PEG lignin derivative metered in step S1. The mixture is then stirred for 2 minutes using a mixer. The PEG lignin derivative has phenolic groups derived from lignin and hydroxyl groups derived from PEG. By selecting a solvent with high compatibility with phenolic groups, the PEG lignin derivative can be fully dissolved through the reaction of the solvent with the phenolic groups, resulting in a uniformly mixed varnish.

[0014] The solubility parameter SP value can be selected relative to the SP value of the hydroxyl group, which is 14.6 [cal / cm]. 3 ] 1 / 2 The SP value, which is closer to that of a phenolic group, is 11.5 [cal / cm]. 3 ] 1 / 2 The solvent is chosen because it has high compatibility with phenolic groups. More specifically, a solubility parameter SP value of 8 [cal / cm³] can be selected. 3 ] 1 / 2Above and 12.5 [cal / cm] 3 ] 1 / 2 The following solvents.

[0015] As such a solvent, an SP value of, for example, 11 [cal / cm] can be selected. 3 ] 1 / 2 Propylene glycol monomethyl ether (CH3OCH2CH(CH3)OH) (boiling point: 120℃), SP value 12.1 [cal / cm] 3 ] 1 / 2 Ethylene glycol monomethyl ether (CH3OCH2CH2OH) (boiling point: 124℃), SP value 8.9 [cal / cm] 3 ] 1 / 2 Ethylene glycol monoethyl ether (C2H5OCH2CH2OH) (boiling point: 136℃), SP value 8.4 [cal / cm] 3 ] 1 / 2 Ethylene glycol tert-butyl ether (CH3C(CH3)2OCH2OH) (boiling point: 152℃), SP value 10.2 [cal / cm] 3 ] 1 / 2 Ethylene glycol monobutyl ether (C4H9OCH2CH2OH) (boiling point: 171℃), SP value 8.4 [cal / cm] 3 ] 1 / 2 3-Methoxy-3-methyl-1-butanol (CH3OC(CH3)2CH2CH2OH) (boiling point: 174℃), SP value 8.2 [cal / cm] 3 ] 1 / 2 Ethylene glycol monopropyl ether (CH3CH2CH2OCH2CH2OH) (boiling point: 150℃), SP value 10.2 [cal / cm] 3 ] 1 / 2 Diethylene glycol monobutyl ether (C4H9O(CH2CH2O)2H) (boiling point: 230℃), SP value 8.4 [cal / cm] 3 ] 1 / 2 Triethylene glycol monobutyl ether (C4H9O(CH2CH2O)3H) (boiling point: 271℃), SP value 8.2 [cal / cm] 3 ] 1 / 2 Dipropylene glycol monomethyl ether (CH3O(C3H6O)2H) (boiling point: 188℃) and other ethylene glycol ethers, with an SP value of 10.2 [cal / cm]. 3 ] 1 / 2 1,3-Dioxolane (C3H6O2) (boiling point: 75℃), SP value 10.3 [cal / cm] 3 ] 1 / 21,4-Dioxane (C4H8O2) (boiling point: 101℃), SP value 9.3 [cal / cm] 3 ] 1 / 2 Ethers such as tetrahydrofuran (THF) (C4H8O) (boiling point: 66℃).

[0016] The solvent needs to evaporate and be removed during the drying process before stamping. The temperature conditions for this drying process are set according to the boiling point of the solvent. The curing temperature of the matrix resin, which is the temperature at which the curing reaction between the epoxy resin (the main component of the matrix resin) and the PEG lignin derivative (the curing agent) begins, is approximately 140°C. To maintain the unreacted state of the matrix resin after the drying process and to maintain the viscosity of the matrix resin, a solvent with a boiling point lower than the curing temperature needs to be selected. More specifically, a solvent with a boiling point below 140°C can be selected.

[0017] For example, propylene glycol monomethyl ether (SP value: 11 [cal / cm]) can be selected. 3 ] 1 / 2 ), Ethylene glycol monomethyl ether (SP value: 12.1 [cal / cm) 3 ] 1 / 2 ), Ethylene glycol monoethyl ether (SP value: 8.9 [cal / cm) 3 ] 1 / 2 ), ethers of the 1,3-dioxolane ring (SP value: 10.2 [cal / cm³] 3 ] 1 / 2 ), 1,4-dioxane (SP value: 10.3 [cal / cm³] 3 ] 1 / 2 THF (SP value: 9.3 [cal / cm)) 3 ] 1 / 2 ) as such a solvent. In particular, among these solvents, a SP value close to that of the phenolic group, 11.5 [cal / cm], was selected. 3 ] 1 / 2 Ethylene glycol ether solvents, such as ethylene glycol monomethyl ether, can be used as the first solvent to fully dissolve PEG lignin derivatives and obtain a uniformly mixed varnish.

[0018] It should be noted that although solvents for PEG lignin derivatives are known, such as N,N-dimethylformamide (DMF) (boiling point: 153℃), dimethyl sulfoxide (DMSO) (boiling point: 189℃), N-methyl-2-pyrrolidone (NMP) (boiling point: 202℃), and N,N-dimethylacetamide (DMAc) (boiling point: 165℃), the boiling points of these solvents are higher than the curing temperature (140℃). Furthermore, for example, DMSO has an SP value of 14.5 [cal / cm³]. 3 ] 1 / 2Compared to the phenolic group, the SP value is 11.5 [cal / cm]. 3 ] 1 / 2 The SP value, which is closer to the hydroxyl group, is 14.6 [cal / cm]. 3 ] 1 / 2 Similarly, methanol, a known solvent for PEG lignin derivatives, has an SP value of 14.5 [cal / cm]. 3 ] 1 / 2 It is also close to the SP value of the hydroxyl group.

[0019] Next, in the second mixing step S3, 50 parts (e.g., 390g) of liquid THF are metered as a second solvent and added to the mixture (varnish) of the curing agent and the first solvent obtained in the first mixing step S2, and stirred for 2 minutes using a mixer. Glycol ethers with high compatibility with phenolic groups and ethers with relatively low boiling points can be selected as the second solvent. More specifically, 1,3-dioxolane (boiling point: 75°C), 1,4-dioxane (boiling point: 101°C), and THF (boiling point: 66°C) with boiling points above 25°C and below 110°C can be selected, especially THF with a low boiling point, for example.

[0020] Thus, by adding a second solvent with a low boiling point to the varnish, which is a mixture of the curing agent and the first solvent, not only can the curing agent be further dissolved, but the first solvent can also be diluted, and the overall boiling point of the solvent mixture can be lowered. When the overall boiling point of the solvent is high, sometimes the solvent cannot completely evaporate due to temperature conditions in the drying process, leaving some solvent residue after the drying process. By lowering the overall boiling point of the solvent, the solvent can be completely evaporated and removed during the drying process.

[0021] Next, in step S4, 100 parts (e.g., 780 g) of liquid epoxy resin are measured as the main agent and added to the mixture (varnish) of the curing agent and solvent (first solvent, second solvent) obtained in the second mixing step S3, and stirred for 2 minutes using a mixer. Sorbitol glycidyl ether, such as DenacolEX-614B manufactured by Nagase ChemteX, can be used as the epoxy resin. In addition, epoxy resins such as limonene diepoxide (e.g., Celloxide 3000 from Daicel Corporation), epoxidized soybean oil (e.g., Adekasizer O-130P from ADEKA Corporation), epoxidized castor oil (e.g., EPOX MK R151 from Plintec Corporation), epoxidized linseed oil (e.g., Adekasizer O-180A from ADEKA Corporation), and epoxidized linseed oil (e.g., Sansosizer E-9000H from Shin Nippon Rikka Corporation) can also be used. Hereinafter, the mixture of curing agent, solvent (first solvent, second solvent), and main agent (varnish) obtained in mixing processes S1 to S4 will sometimes be referred to as the "matrix resin raw material composition".

[0022] Next, in the impregnation step S5, one fiber substrate is impregnated in the varnish obtained in the mixing steps S1 to S4, thereby impregnating the fiber substrate with the varnish. Glass fiber fabrics, such as glass cloth (e.g., 7628WLA209105BZ) manufactured by Nittobo Co., Ltd., can be used as the fiber substrate. In addition to glass fiber fabrics, other materials that can be used as the fiber substrate include glass fiber nonwoven fabric, glass fiber mat, carbon fiber fabric, carbon fiber nonwoven fabric, carbon fiber mat, aramid fiber fabric, aramid fiber nonwoven fabric, aramid fiber mat, plant fiber fabric, plant fiber nonwoven fabric, plant fiber mat, and paper.

[0023] When the solvent consists solely of low-boiling-point ethers (e.g., THF with a boiling point of 66°C), the solvent evaporates and is lost during the impregnation process S5, sometimes leading to an increase in the viscosity of the varnish. When the viscosity of the varnish increases during a stage where impregnation on the fiber substrate is insufficient, the varnish may not be able to continue penetrating the fiber substrate, potentially resulting in unimpregnated areas on the fiber substrate. By using a solvent prepared in appropriate proportions (e.g., in equal amounts) of low-boiling-point ethers (boiling points above 25°C and below 110°C, such as THF with a boiling point of 66°C) and high-boiling-point glycol ethers (boiling points above 120°C and below 140°C, such as ethylene glycol monomethyl ether with a boiling point of 124°C), it is possible to prevent the solvent from evaporating entirely during the impregnation process, thereby maintaining a uniform varnish state throughout the entire impregnation process.

[0024] Next, in step S6, the fiber substrate impregnated with the matrix resin raw material composition (varnish) in the impregnation step S5 is passed through a roller gap set to 0.2 mm, and excess varnish is removed by extrusion.

[0025] Next, in the drying step S7, the matrix resin raw material composition (varnish) that was impregnated into the fiber substrate in the impregnation step S5 and partially removed in step S6 is dried to allow the solvents (first solvent and second solvent) to evaporate and be removed. More specifically, the fiber substrate impregnated with the matrix resin raw material composition is dried in a drying oven at 120°C for 10 minutes. When the solvents contained in the matrix resin raw material composition evaporate and are removed, a prepreg impregnated with the matrix resin composition, which is a mixture of curing agent and main agent, is obtained.

[0026] By using a solvent prepared in appropriate proportions (e.g., equal amounts) of high-boiling-point glycol ethers (e.g., glycol monomethyl ether with a boiling point of 124°C) and low-boiling-point ethers (e.g., THF with a boiling point of 66°C), the solvent can be evaporated and removed in a shorter time (e.g., 10 minutes), even under relatively mild temperature conditions (e.g., 120°C). For example, at around 120°C, which is lower than the curing temperature, drying takes a long time when the solvent is entirely glycol monomethyl ether with a boiling point of 124°C, but by using half the amount of solvent as THF with a boiling point of 66°C, the drying time can be shortened.

[0027] Next, in the lamination process S8, the prepreg obtained in the drying process S7 is laminated (for example, 10 sheets are laminated). The laminated prepregs are bonded to each other using a viscous matrix resin.

[0028] Next, in the stamping process S9, the prepreg laminated in the lamination process S8 is stamped at 160°C and 2MPa for 80 minutes. By stamping at a temperature above the curing temperature of the matrix resin (140°C), the matrix resin is cured, resulting in a fiber-reinforced resin integrally laminated prepreg.

[0029] The embodiments of the present invention can achieve the following effects.

[0030] (1) The prepreg preparation method includes: an impregnation step S5, in which a matrix resin raw material composition comprising a matrix resin main agent, a curing agent, and a solvent is impregnated into a fiber substrate; and a drying step S7, in which the matrix resin raw material composition impregnated into the fiber substrate in the impregnation step S5 is dried. Figure 1 The main component is epoxy resin. The curing agent is a PEG lignin derivative. The solvents include a first solvent composed of ethylene glycol ethers and a second solvent composed of ethers.

[0031] By using glycol ethers and other ethers with high compatibility with phenolic groups as solvents for PEG lignin derivatives, the PEG lignin derivatives can be fully dissolved, resulting in a uniformly mixed varnish. Furthermore, by using glycol ethers with higher boiling points and ethers with lower boiling points, the solvents can evaporate quickly even during the drying process under relatively mild temperature conditions, and a uniform varnish state can be maintained during the impregnation process.

[0032] (2) The boiling point of the first solvent is 120°C or higher and 140°C or lower. The boiling point of the second solvent is 25°C or higher and 110°C or lower. By using a solvent with a boiling point below the curing temperature (140°C) of the base resin, the viscosity of the base resin can be maintained even after the drying process in which the solvent evaporates and is removed. In addition, by using the second solvent with a boiling point below 110°C as part of the solvent, the solvent can be evaporated and removed in a shorter time even in the drying process under relatively mild temperature conditions. Furthermore, by using the first solvent with a boiling point above 120°C as part of the solvent, it is possible to prevent all the solvent from evaporating during the impregnation process, and to maintain a uniform clear varnish state throughout the entire impregnation process.

[0033] (3) The prepreg preparation method also includes mixing steps S1 to S4 of mixing the main agent, curing agent, and solvent to obtain a matrix resin raw material composition. Figure 1 The mixing processes S1 to S4 include a first mixing process S2, which mixes the curing agent and the first solvent, and a second mixing process S3, which mixes the mixture of the curing agent and the first solvent with a second solvent. Figure 1 By first mixing a first solvent composed of ethylene glycol ethers and a second solvent composed of ethers, the first solvent, whose SP value is close to the SP value of phenol (11.5 [cal / cm3]1 / 2) and has relatively high compatibility with phenols, can effectively dissolve PEG lignin derivatives.

[0034] (4) The main agent is at least one of epoxidized soybean oil and sorbitol glycidyl ether. In addition to using a curing agent derived from PEG lignin, the application of bio-resin can be promoted by also using bio-resin in the main agent.

[0035] (5) The first solvent is ethylene glycol monomethyl ether. The second solvent is THF. By using ethylene glycol monomethyl ether, which has particularly high compatibility with phenolic groups, as the first solvent, the PEG lignin derivative can be fully dissolved, resulting in a uniformly mixed varnish. In addition, by using THF, a solvent with high compatibility with phenolic groups, especially with a low boiling point, as the second solvent, the solvent can be evaporated and removed in a shorter time during the drying process under relatively mild temperature conditions.

[0036] It is possible to combine one or more of the above-described embodiments and variations, and to combine the variations with each other.

[0037] Using this invention, a uniform varnish state can be maintained during the impregnation process.

[0038] [Example 1] In Example 1, Figure 1 In the prepreg preparation method, ethylene glycol monomethyl ether is used as the first solvent and THF is used as the second solvent. In this case, it was confirmed that the varnish (matrix resin raw material composition) at the point when the mixing steps S1 to S4 were completed was completely transparent and in a uniformly mixed state where the main agent and curing agent were fully compatible. Furthermore, it was confirmed that the matrix resin composition at the point when the drying step S7 was completed was in a viscous, uniformly mixed state where it permeated the entire fiber matrix and the main agent and curing agent had not reacted. Moreover, when observing the cross-section of the fiber-reinforced resin after the stamping step S9, it was confirmed that there were no internal voids. That is, if solvent remained in the varnish at the point when the drying step S7 was completed, voids would be generated in the matrix resin of the fiber-reinforced resin during the subsequent stamping step S9 due to the hardening of the matrix resin and the evaporation of the residual solvent. Since there were no voids inside the fiber-reinforced resin after the stamping step S9, the solvent was completely evaporated and removed during the drying step S7.

[0039] [Example 2] In Example 2, Figure 1 In the prepreg preparation method, THF is used as the first solvent and ethylene glycol monomethyl ether is used as the second solvent. In this case, at the point when the mixing steps S1 to S4 are completed, a portion of the varnish (matrix resin raw material composition) appears cloudy, but in the impregnation step S5, the varnish (matrix resin raw material composition) impregnates the entire fiber matrix. Furthermore, when observing the cross-section of the fiber-reinforced resin after the stamping step S9, it is confirmed that there are no internal voids, and a fiber-reinforced resin in a suitable state can be prepared.

[0040] [Comparative Example 1] In Comparative Example 1, Figure 1The first mixing step S2 and the second mixing step S3 of the prepreg preparation method are solvent mixing steps, using only THF as the solvent. That is, 100 parts of THF (e.g., 780 g) are metered and added to the PEG lignin derivative metered in step S1, and stirred for 2 minutes using a mixer. In this case, the varnish (matrix resin raw material composition) at the point when the mixing steps up to step S4 are confirmed to be in a state of overall transparency and a uniform mixture in which the main agent and curing agent are fully compatible. However, in the impregnation step S5, before the varnish (matrix resin composition) impregnates the entire fiber matrix, the solvent evaporates and flows away, the viscosity of the varnish increases, and the varnish fails to impregnate the entire fiber matrix.

[0041] [Comparative Example 2] In Comparative Example 2, Figure 1 The first mixing step S2 and the second mixing step S3 of the prepreg preparation method are solvent mixing steps, using only ethylene glycol monomethyl ether as the solvent. Specifically, 100 parts (e.g., 780 g) of ethylene glycol monomethyl ether are metered and added to the PEG lignin derivative metered in step S1, and stirred for 2 minutes using a mixer. In this case, the varnish (base resin raw material composition) at the point in time where the mixing steps up to step S4 are completed is confirmed to be completely transparent and in a uniformly mixed state where the main agent and curing agent are fully compatible. However, when observing the cross-section of the fiber-reinforced resin after the stamping step S9, internal spaces are confirmed, indicating that the solvent was not completely evaporated and remained in the drying step S7.

[0042] [Comparative Example 3] In Comparative Example 3, Figure 1 The first mixing step S2 and the second mixing step S3 of the prepreg preparation method are considered as a solvent mixing step, using only methyl ethyl ketone (MEK) (CH3COC2H5) (SP value: 9.3 [cal / cm³]). 3 ] 1 / 2 (Boiling point: 79℃) is used as a solvent. That is, 100 parts of MEK (e.g., 780g) are measured and added to the PEG lignin derivative measured in step S1, and stirred for 2 minutes using a stirrer. In this case, the PEG lignin derivative cannot be fully dissolved, and a uniformly mixed varnish (base resin raw material composition) is not obtained.

[0043] [Comparative Example 4] In Comparative Example 3, Figure 1The first mixing step S2 and the second mixing step S3 of the prepreg preparation method are solvent mixing steps, using only ethanol (alcohol) (C2H5OH) (boiling point: 78°C) as the solvent. That is, 100 parts (e.g., 780g) of alcohol are metered and added to the PEG lignin derivative metered in step S1, and stirred for 2 minutes using a mixer. Even under these conditions, the PEG lignin derivative cannot be fully dissolved, and a uniformly mixed varnish (matrix resin raw material composition) is not obtained.

[0044] The present invention has been described above in conjunction with preferred embodiments and examples. However, those skilled in the art should understand that various modifications and changes can be made without departing from the scope of the claims.

Claims

1. A method for preparing a prepreg, comprising an impregnation step and a drying step, wherein in the impregnation step, a matrix resin raw material composition comprising a matrix resin main agent, a curing agent, and a solvent is impregnated into a fiber substrate; and in the drying step, the matrix resin raw material composition impregnated into the fiber substrate in the impregnation step is dried. The method for preparing a prepreg is characterized in that… The main agent is epoxy resin. The curing agent is a PEG lignin derivative. The solvent includes a first solvent composed of ethylene glycol ethers and a second solvent composed of ethers.

2. The prepreg preparation method according to claim 1, characterized in that, The boiling point of the first solvent is above 120°C and below 140°C. The second solvent has a boiling point above 25°C and below 110°C.

3. The method for preparing prepreg according to claim 1 or 2, characterized in that, It also includes a mixing process. In the mixing process, the main agent, the curing agent, and the solvent are mixed to obtain the matrix resin raw material composition. The mixing process includes: A first mixing step involving mixing the curing agent and the first solvent; and The second mixing step involves mixing the mixture of the curing agent and the first solvent with the second solvent.

4. The method for preparing prepreg according to claim 1 or 2, characterized in that, The main agent is at least one of epoxidized soybean oil and sorbitol glycidyl ether.

5. The method for preparing prepreg according to claim 1 or 2, characterized in that, The first solvent is ethylene glycol monomethyl ether. The second solvent is tetrahydrofuran.

6. The method for preparing prepreg according to claim 1 or 2, characterized in that, The PEG lignin derivative has phenolic groups derived from lignin and hydroxyl groups derived from PEG, and is in powder form at room temperature.

7. The method for preparing prepreg according to claim 1 or 2, characterized in that, The temperature conditions for the drying process are set according to the boiling point of the solvent.

8. The method for preparing prepreg according to claim 1 or 2, characterized in that, The boiling point of the solvent is lower than the curing temperature at which the curing reaction between the epoxy resin and the PEG lignin derivative begins.

9. A matrix resin raw material composition, comprising a main agent, a curing agent, and a solvent, characterized in that, The main agent is epoxy resin. The curing agent is a PEG lignin derivative. The solvent includes a first solvent composed of ethylene glycol ethers and a second solvent composed of ethers.

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