Method for producing resol-type phenolic resin, method for producing phenol resin composition and method for producing resin-coated sand

Abstract

To provide a method for producing a resol-type phenolic resin modified by lignin.SOLUTION: A modified lignin modified by glycols, phenols and aldehydes are reacted in the presence of an alkaline catalyst. By using a modified lignin modified by glycols as lignin, a resol-type phenolic resin by the modified lignin can be produced. At this time, a solid resol-type phenolic resin can be produced by dehydrating and drying a reaction product in a hydrous state.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a lignin-modified resol-type phenolic resin using lignin as one of the raw materials, and also relates to a phenolic resin composition using this phenolic resin and a method for producing resin-coated sand.

Background Art

[0002] Phenolic resins are widely used as one of the thermosetting resins. Phenolic resins are generally produced by reacting phenols such as phenol with aldehydes such as formaldehyde in the presence of various catalysts.

[0003] On the other hand, in recent years, from the perspective of global environmental protection, etc., it has been required to reduce the usage amount of petroleum resources, and using plant-derived materials as an alternative to petroleum resources has been under consideration. Lignin has been attracting attention as one of such plant-derived materials. Although phenolic resins mainly use petroleum resources as raw materials, using plant-derived lignin as one of the raw materials of phenolic resins has been attracting attention.

[0004] Lignin is contained in the waste liquid discharged when producing pulp from plants, and it can be recovered from this waste liquid and used. And by reacting this lignin with phenols and aldehydes under an acid catalyst, a lignin-modified phenolic resin using lignin as one of the raw materials can be obtained (see, for example, Patent Document 1, Patent Document 2, etc.).

[0005] However, lignin has low reactivity, and it is difficult to sufficiently progress the modification by lignin. In some cases, most of the lignin is only contained as a filler in the phenolic resin, and currently, the effect of modifying the phenolic resin by the modifying action of lignin cannot be expected very much.

[0006] Therefore, the use of modified lignin as lignin is being considered. For example, in Patent Document 3, lignin modified (denatured) with polyethylene glycol is used as lignin, and this modified lignin (denatured lignin), phenols, and aldehydes are reacted under an acid catalyst such as oxalic acid to produce a novolak-type phenolic resin modified with lignin.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] As described above, the lignin-modified phenolic resin obtained by reacting lignin, phenols, and aldehydes under an acid catalyst is a novolak-type phenolic resin, but the novolak-type phenolic resin does not have self-curing properties. Therefore, in order to cure the novolak-type phenolic resin, it is necessary to blend a curing agent such as hexamethylenetetramine.

[0009] Although it is necessary to blend a curing agent with the novolak-type phenolic resin in this way, there are problems such as difficulty in obtaining a homogeneous cured product if the curing agent is not uniformly dispersed in the novolak-type phenolic resin. In addition, as the curing agent for curing the novolak-type phenolic resin, hexamethylenetetramine as described above is mainly used, but there are also problems such as environmental pollution by ammonia gas generated by the decomposition of hexamethylenetetramine when mixing and curing hexamethylenetetramine with the novolak-type phenolic resin.

[0010] The present invention has been made in view of the above points, and an object thereof is to provide a method for producing a resol type phenol resin modified with lignin. Another object is to provide a method for producing a phenol resin composition and a resin-coated sand using the thus-produced phenol resin.

Means for Solving the Problems

[0011] The method for producing a resol type phenol resin according to claim 1 of the present invention is characterized in that a modified lignin modified with glycols, phenols, and aldehydes are reacted in the presence of an alkaline catalyst, and the reaction product in a water-containing state is dried.

[0012] When reacting lignin, phenols, and aldehydes to obtain a phenol resin modified with lignin, by using an alkaline catalyst as a reaction catalyst, it is possible to produce a resol type lignin-modified phenol resin that can be cured without the need for a curing agent. Moreover, by using a modified lignin modified with glycols as lignin, lignin can react well with phenols and aldehydes, and a lignin-modified resol type phenol resin modified with lignin efficiently can be obtained.

[0013] Here, the resol type phenol resin is self-curable and can be cured without the need for a curing agent. However, the resol type phenol resin is generally liquid and has very inconvenient handling depending on the application.

[0014] Therefore, the method for producing a resol type phenol resin according to claim 2 of the present invention is characterized in that a modified lignin modified with glycols, phenols, and aldehydes are reacted in the presence of an alkaline catalyst to prepare a reaction product in a water-containing state, and this reaction product in a water-containing state is dried to prepare a solid at normal temperature.

[0015] Since the above reaction is a condensation reaction, a reaction product in a water-containing state can be obtained. By drying the reaction product in a water-containing state, a resol-type phenolic resin that is solid at normal temperature and convenient to handle can be obtained.

[0016] The present invention is also characterized in that a reaction product in a water-containing state is solidified, and after obtaining a water-containing granular material by pulverizing the solidified reaction product into granules, the water-containing granular material is heated and dried.

[0017] By solidifying the reaction product in a water-containing state, it becomes possible to pulverize it into granules, and by heating the pulverized water-containing granular material, it becomes possible to efficiently and uniformly dry it, and a solid resol-type phenolic resin can be obtained without excessive progress of curing by heating.

[0018] The present invention is also characterized in that the water-containing granular material is dried by bringing it into contact with heated air.

[0019] By bringing the water-containing granular material into contact with heated air, the heated air can effectively act on the surface of the particles of the water-containing granular material to efficiently evaporate the moisture, and it becomes possible to dry without the need to heat to a high temperature, and a solid resol-type phenolic resin can be obtained without the risk of excessive progress of curing.

[0020] The present invention is also characterized in that the modified lignin modified by the above glycols is a modified lignin modified by polyethylene glycol.

[0021] By producing a phenolic resin using a modified lignin modified by polyethylene glycol, a resol-type phenolic resin better modified with lignin can be obtained.

[0022] In addition to the modified lignin, lignin that has not been modified with glycols may be reacted in a blending amount of 50% by mass or less of the modified lignin. Even if lignin that has not been modified with glycols is used in combination in this way, a resol-type phenolic resin modified with the modified lignin can be obtained.

[0023] The method for producing a resin-coated sand according to the present invention is characterized in that the phenolic resin obtained by the above method is coated on refractory aggregates.

[0024] According to this invention, when molding a mold by filling a resin-coated sand into a mold and heating it, since the resol-type phenolic resin is modified with modified lignin, a mold having high strength such as bending strength and excellent collapsibility after casting can be obtained.

[0025] The method for producing a phenolic resin composition according to the present invention is characterized in that it is prepared by containing the phenolic resin obtained by the above method.

[0026] According to this invention, when performing molding using a phenolic resin composition as a molding material, since the resol-type phenolic resin is modified with modified lignin, a molded article having a high surface hardness can be obtained.

Effects of the Invention

[0027] According to the present invention, by using modified lignin modified with glycols as lignin and an alkaline catalyst as a reaction catalyst, respectively, lignin can be reacted well with phenols and aldehydes, and a resol-type lignin-modified phenolic resin that can be cured without the need for a curing agent can be obtained.

[0028] Also, by drying the reaction product in a water-containing state, a lignin-modified resol-type phenolic resin that is solid at room temperature and convenient to handle can be obtained.

[0029] Also, when molding a mold using the resin-coated sand produced by the present invention, since the resol-type phenolic resin is modified with modified lignin, a mold with high strength such as flexural strength and excellent collapsibility after casting can be obtained.

[0030] Also, when molding using the phenolic resin composition produced by the present invention as a molding material, since the resol-type phenolic resin is modified with modified lignin, a molded product with high surface hardness can be obtained.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0032] Hereinafter, embodiments of the present invention will be described.

[0033] In the present invention, as the lignin, modified lignin (also referred to as modified lignin) modified (also referred to as modification) with glycols is used. As the glycols used for modification, those obtained by polymerizing glycols such as ethylene glycol, propylene glycol, and diethylene glycol are preferably used, and among them, polyethylene glycol is most preferably used.

[0034] When polyethylene glycol is used as the glycol, its number average molecular weight is 100 or more, preferably 200 or more, more preferably 300 or more, still more preferably 400 or more, and 1000 or less, preferably 900 or less, more preferably 800 or less, still more preferably 600 or less. The number average molecular weight can be determined as the polyethylene glycol equivalent molecular weight by a known gel permeation chromatography method.

[0035] Lignin is a high molecular phenolic compound composed of basic skeletons such as guaiacyl lignin (G type), syringyl lignin (S type), and p-hydroxyphenyl lignin (H type), and is contained in all plants as a natural product (natural lignin). As industrial lignin extracted from plants, for example, soda lignin, sulfite lignin, kraft lignin, etc. contained in the waste liquid (black liquor) discharged when producing pulp from plant materials (lignocellulose) as raw materials by the soda method, sulfite method, kraft method, etc. are known.

[0036] Specific examples of lignin include lignin derived from woody plants and lignin derived from herbaceous plants. Examples of lignin derived from woody plants include coniferous lignin contained in coniferous trees (e.g., cedar, etc.) and broad-leaved lignin contained in broad-leaved trees. Lignin derived from woody plants does not contain the basic skeleton of the H type. More specifically, among lignin derived from woody plants, coniferous lignin does not contain the basic skeleton of the S type and has the basic skeleton of the G type. Also, broad-leaved lignin has the basic skeletons of the G type and the S type.

[0037] Examples of lignin derived from herbaceous plants include rice lignin contained in gramineous plants (rice straw, wheat straw, corn, bamboo, etc.). Lignin derived from herbaceous plants has all the basic skeletons of the H type, G type, and S type. In the present invention, as lignin, the above various types can be used alone, or two or more types can be used in combination.

[0038] In the preparation of modified lignin using the above lignin, although there are no particular restrictions, it can be carried out according to the methods disclosed in JP-A-2017-197517 or the methods disclosed in JP-A-2021-123716.

[0039] For example, by digesting plant material (lignocellulose) serving as a raw material for lignin with glycols such as polyethylene glycol, modified lignin modified with glycols can be obtained.

[0040] Digestion can be carried out by mixing plant material serving as a raw material for lignin, glycols such as polyethylene glycol, and an inorganic acid (for example, hydrochloric acid, sulfuric acid, etc.) as an acid catalyst and reacting them.

[0041] When carrying out digestion using polyethylene glycol, the blending ratio of polyethylene glycol is 200 parts by mass or more, preferably 300 parts by mass or more, and 1000 parts by mass or less, preferably 600 parts by mass or less, based on 100 parts by mass of the plant material serving as a raw material for lignin. Also, the blending ratio of the inorganic acid is 0.1 part by mass or more, preferably 0.2 part by mass or more, and 2 parts by mass or less, preferably 1 part by mass or less, based on 100 parts by mass of polyethylene glycol.

[0042] The reaction conditions for digestion are such that under normal pressure, the reaction temperature is 120°C or higher, preferably 130°C or higher, and 180°C or lower, preferably 150°C or lower. The reaction time is 60 minutes or more and 240 minutes or less, preferably 120 minutes or less.

[0043] After the completion of the digestion reaction, an alkali such as ammonia or sodium hydroxide is added at an appropriate ratio to adjust the pH, and the modified lignin is extracted into a solution. The pH adjustment is carried out so that the pH is 8 or higher, preferably 10 or higher, more preferably 10.5 or higher, and 14 or lower.

[0044] In this way, pulp is obtained as a solid component, and modified lignin modified with polyethylene glycol is obtained in the solution component (pulp waste liquid). Then, the solid component (pulp) is separated from the solution component (pulp waste liquid) by any separation method such as filtration, pressing, and centrifugation, and the solution component (pulp waste liquid) is recovered. After that, an inorganic acid such as hydrochloric acid or sulfuric acid is added to adjust the pH to precipitate and deposit the modified lignin. The pH adjustment is carried out so that the pH is 1.5 or more and 5 or less, preferably 3 or less, more preferably 2 or less.

[0045] As described above, the modified lignin modified with glycols such as polyethylene glycol can be precipitated, and the obtained precipitate can be recovered by any method such as filtration, pressing, and centrifugation to obtain the modified lignin as a solid component. Here, FIG. 1 shows an example of the chemical structural formula of the modified lignin modified with polyethylene glycol as glycols. As can be seen in FIG. 1, lignin is modified by the condensation of glycols such as polyethylene glycol with lignin.

[0046] By subjecting the modified lignin obtained as described above, phenols, and aldehydes to a polycondensation reaction, a phenol resin modified with the modified lignin can be produced.

[0047] As the above-mentioned phenols, in addition to phenol, derivatives of phenol can be used. Examples of phenol derivatives include trifunctional ones such as m-cresol, resorcinol, 3,5-xylenol, tetrafunctional ones such as bisphenol A, bisphenol S, dihydroxydiphenylmethane, and difunctional o- or p-substituted phenols such as o-cresol, p-cresol, p-tert-butylphenol, p-phenylphenol, p-cumylphenol, p-nonylphenol, 2,4- or 2,6-xylenol, etc. Furthermore, halogenated phenols substituted with chlorine or bromine can also be used. As phenols, one kind can be selected and used from these, or multiple kinds can be used in combination.

[0048] Also, as the above-mentioned aldehydes, formalin in the form of an aqueous solution of formaldehyde is optimal, but forms such as paraformaldehyde, acetaldehyde, benzaldehyde, trioxane, and tetraoxane can also be used, and it is also possible to use those in which a part or most of the aldehyde is replaced with furfural or furfuryl alcohol. One kind can be selected and used from these, or multiple kinds can be used in combination.

[0049] When reacting the modified lignin, phenols, and aldehydes as described above, the reaction is carried out in the presence of a catalyst. Here, in the present invention, an alkaline catalyst is used as this reaction catalyst.

[0050] Although there is no particular limitation on the alkaline catalyst, oxides, hydroxides, carbonates of alkali metals such as sodium, potassium, and lithium, oxides, hydroxides, carbonates of alkaline earth metals such as calcium, magnesium, and barium, primary amines, secondary amines, tertiary amines, etc. can be used. Among these, one kind can be used alone, or two or more kinds can be used in combination. Specific examples include sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, calcium hydroxide, magnesium oxide, calcium oxide, hexamethylenetetramine, trimethylamine, triethylamine, triethanolamine, 1,8-diazabicyclo[5,4,0]undecene-7, etc.

[0051] Although the compounding amount of the reaction catalyst is not particularly limited, a range of 5 to 30 parts by mass is preferable with respect to 100 parts by mass of phenols. The lower limit is more preferably 8 parts by mass or more, and the upper limit is more preferably 25 parts by mass or less.

[0052] Also, although the compounding amount of the modified lignin is not particularly limited, a range of 5 to 200 parts by mass is preferable with respect to 100 parts by mass of phenols. The lower limit is more preferably 10 parts by mass or more, and the upper limit is more preferably 180 parts by mass or less.

[0053] Also, although the compounding amount of aldehydes is not particularly limited, a range in which the molar ratio of phenols to aldehydes is 1:0.5 to 1:3.5 is preferable. The lower limit is more preferably 0.8 or more, and the upper limit is more preferably 3.0 or less.

[0054] When reacting modified lignin, phenols, and aldehydes in the presence of the above catalyst, the reaction conditions are not particularly limited. However, under atmospheric pressure, it is preferable to set the reaction temperature in the range of 50 to 110 °C and the reaction time in the range of 1 to 10 hours. The lower limit of the reaction temperature is more preferably 60 °C or higher, and the upper limit is more preferably 105 °C or lower. Also, the lower limit of the reaction time is more preferably 2 hours or longer, and the upper limit is more preferably 8 hours or shorter.

[0055] The lignin-modified phenol resin obtained by reacting modified lignin, phenols, and aldehydes with an alkaline catalyst as described above is a resol-type phenol resin and has self-curing properties. Therefore, it can be easily cured by heating or the like without the need to mix it with a curing agent such as hexamethylenetetramine.

[0056] Furthermore, modified lignin, phenols, and aldehydes undergo a dehydration condensation reaction in a solvent such as water, and the lignin-modified resol-type phenol resin is obtained in a state dispersed in water. Then, by dehydration concentration and filtration, the resol-type phenol resin can be taken out from the reaction solution. The resol-type phenol resin thus obtained is in a water-containing state and is liquid at room temperature (25 °C).

[0057] This liquid resol-type phenol resin can be used as it is or diluted with a solvent such as water. For example, in addition to being used as a component of a paint or a photoresist, it can be used as a varnish for impregnating and curing a substrate to manufacture abrasive materials, printed circuit boards, etc., or further used as a binder for kneading with refractory aggregates to manufacture refractory bricks, etc.

[0058] On the one hand, when the resol-type phenolic resin is in such a liquid state, it is very troublesome to handle in storage, transportation, metering, mixing with other materials, etc. In particular, when the resol-type phenolic resin is a viscous liquid, for example, when preparing resin-coated sand by mixing it with refractory aggregates, it is difficult to uniformly mix the resol-type phenolic resin with the refractory aggregates. Also, when preparing a phenolic resin composition as a molding material or the like by blending and mixing various additives, it is difficult to uniformly mix or knead the resol-type phenolic resin with the refractory aggregates.

[0059] Therefore, in the present invention, the solid resol-type phenolic resin is obtained by drying the reaction product (resol-type phenolic resin) in a water-containing state obtained by reacting as described above to evaporate the water. Here, the solid means being in a solid form at normal temperature (25°C).

[0060] It is also possible to directly dry the reaction product in the water-containing state as it is discharged from the reaction vessel to obtain the solid resol-type phenolic resin. However, since the reaction product in the water-containing state solidifies when cooled, it can be made into granular matter by pulverizing the solidified reaction product. Then, it is desirable to obtain a granular solid resol-type phenolic resin by drying this water-containing granular matter.

[0061] Hereinafter, a method for obtaining a granular solid resol type phenol resin will be described. That is, since the reaction product (resol type phenol resin) dehydrated and concentrated by vacuum distillation or the like contains water as described above, it is a viscous liquid at room temperature and can be easily discharged from the reaction vessel. Since this reaction product in a water-containing state becomes solid by cooling, it can be granulated by pulverizing it (even to a rough pulverization degree), and a water-containing granular material can be obtained. At this time, when cooling the reaction product in a water-containing state so as to freeze the water, it becomes a hard solid state, so that pulverization can be easily performed. The cooling temperature may be a temperature at which the reaction product freezes and becomes solid, such as 0 °C or lower. Also, the particle size of the water-containing granular material is not restricted at all, but is arbitrary, for example, about several millimeters. Then, this pulverized water-containing granular material is brought into contact with warm air at a temperature at which excessive reaction progress of the resol type phenol resin and agglomeration of the granular material do not occur, for example, about 40 to 70 °C, and the water in the water-containing granular material is vaporized and removed, whereby a solid resol type phenol resin at room temperature can be obtained.

[0062] Here, when drying the water-containing granular material as described above, a fluidized bed type drying device as shown in FIG. 2 can be used. The fluidized bed type drying device will be described with reference to FIG. 2. 1 is an inlet through which the water-containing granular material is introduced. 2 is a first drying chamber, and a fluidized bed 3 provided with a large number of holes having a diameter of about 1 mm, for example, is attached to the bottom thereof. 4, 5, 6, and 7 are second, third, fourth, and fifth drying chambers provided in an arbitrary number by being partitioned by a partition plate 8, and a fluidized bed 9 provided with a large number of holes is commonly attached to each of the drying chambers 4, 5, 6, and 7 at the bottom. 10 is an outlet from the final drying chamber 7 and is communicated with a receiver 11. 12 is a blower, which is connected to the first drying chamber 2 and the second to fifth drying chambers 4, 5, 6, and 7 by ducts 14 and 15 via a heater 13 formed of a gas heater, an electric heater, a heat exchanger, or the like. 16 and 17 are dampers. 18 and 19 are exhaust pipes, which are respectively communicated with the first drying chamber 2 and the second to fifth drying chambers 4, 5, 6, and 7 and are connected to an exhaust fan 21 via a cyclone 20.

[0063] In the fluidized bed dryer thus formed, the warm air exiting the heater 13 is introduced from below the fluidized beds 3, 9 into each of the drying chambers 2, 4, 5, 6, 7 by ducts 14, 15 as relatively low-temperature air at about 40 to 70°C, for example. The water-containing granular material introduced into the first drying chamber 2 from the inlet 1 is blown up by the warm air from below, undergoes drying while moving in the fluidized bed, and further moves from the second drying chamber 4 to the fifth drying chamber 7 in sequence by climbing over the partition plate 8 or passing under the partition plate 8. In this way, the granular material is blown up and fluidized on the fluidized beds 3, 9 and undergoes drying, enabling efficient, rapid, and uniform drying, and there is no risk of promoting the reaction of the resin in the granular material. The granular material thus dried is discharged from the outlet 10 to the receiver 11. The warm air introduced into each of the drying chambers 2, 4, 5, 6, 7 is exhausted by an exhaust fan 21 via a cyclone 20 from the exhaust pipes 18, 19, and the fine particles in the exhaust are separated by the cyclone 20 and returned to the drying chamber 2.

[0064] As described above, with the fluidized bed dryer, drying can be performed at a lower temperature, and even a resol type phenolic resin that is likely to gel upon heating can be easily dried and solidified.

[0065] As described above, a resol-type phenolic resin can be produced by reacting the modified lignin with phenols, aldehydes, and an alkaline catalyst. As the lignin, in addition to this modified lignin modified with glycols, lignin not modified with glycols (such lignin is referred to as industrial lignin) may also be used in combination. Industrial lignin refers to lignin other than the above-mentioned modified lignin and is not particularly limited. For example, in the above, an example of obtaining modified lignin by steaming using glycols was described, but lignin obtained by steaming without using glycols can be used as industrial lignin. Examples of industrial lignin include kraft lignin, lignin sulfonic acid, lignin acetate, soda lignin, Klason lignin, enzyme lignin, exploded lignin, ground lignin, lignophenol, ethanol lignin, and the like.

[0066] When using industrial lignin in combination with modified lignin as the lignin, the amount of industrial lignin used is not particularly limited, but it is preferably 50% by mass or less of the modified lignin, that is, 50 parts by mass or less of industrial lignin with respect to 100 parts by mass of the modified lignin. If the amount of industrial lignin used is 50% by mass or less, the denaturing effect of the resol-type phenolic resin by the modified lignin is sufficiently ensured.

[0067] And the above-mentioned lignin-modified resol-type phenolic resin that is solid at room temperature can obtain a phenolic resin composition for various uses by blending various additives and mixing or kneading them. As the additives, fillers such as wood powder, pulp, and fiber, plasticizers, stabilizers, colorants, mold release agents, lubricants, etc. can be blended according to the use. For example, using this phenolic resin composition as a molding material, molded products can be molded by methods such as transfer molding and compression molding, and it can be used in various fields such as electrical parts, automotive parts, building materials, and daily necessities.

[0068] Here, since the resol type phenolic resin is modified with modified lignin, the molded article formed from the phenolic resin composition of the present invention can increase the hardness of the surface of the molded article as seen in the examples described later. Therefore, by adjusting the modification rate of the resol type phenolic resin with modified lignin, it becomes possible to some extent to control the surface hardness of the molded article.

[0069] Also in the present invention, the lignin-modified resol type phenolic resin obtained as described above can be used as a binder when manufacturing a mold in the field of casting. For example, this phenolic resin is mixed with a refractory aggregate such as silica sand, this mixture is filled into a mold heated to a high temperature, and after the phenolic resin is cured by heating with the mold, the mold is removed from the mold, whereby a mold in which the refractory aggregate is bound with a phenolic resin binder and shaped can be obtained. When mixing the phenolic resin with the refractory aggregate, a curing agent and various other additives may be added as necessary.

[0070] Alternatively, by coating the surface of the refractory aggregate with the lignin-modified resol type phenolic resin obtained in the present invention, resin-coated sand (RCS) in which a solid binder layer made of a phenolic resin is formed on the surface of the refractory aggregate can be prepared.

[0071] In order to improve the fluidity of the resin-coated sand, a lubricant may be contained in the binder layer. As the lubricant, aliphatic hydrocarbon-based lubricants such as paraffin wax and carnauba wax, higher aliphatic alcohols, aliphatic amide-based lubricants such as ethylene bisstearic acid amide and stearic acid amide, metal soap-based lubricants, fatty acid ester-based lubricants, composite lubricants, etc. can be used, among which metal soap-based lubricants are preferred. As the metal soap-based lubricant, calcium stearate, barium stearate, zinc stearate, aluminum stearate, magnesium stearate, etc., or a combination of a plurality of these can be used.

[0072] As methods for preparing resin-coated sand by coating the surface of refractory aggregate with a solid binder layer made of phenolic resin, there are a hot coat method, a cold coat method, a semi-hot coat method, a powder solvent method, etc.

[0073] The hot coat method is a method of obtaining granular and free-flowing resin-coated sand by mixing a solid phenolic resin with refractory aggregate heated to 110 to 180°C, melting the solid phenolic resin, etc. by heating with the refractory aggregate, wetting and coating the surface of the refractory aggregate with the melted phenolic resin, and then cooling while maintaining this mixture. Alternatively, it is also possible to obtain resin-coated sand by dissolving or dispersing a phenolic resin, etc. in a solvent such as water, mixing it with refractory aggregate heated to 110 to 180°C, and volatilizing the solvent.

[0074] The cold coat method is a method of obtaining resin-coated sand by dispersing or dissolving a solid phenolic resin in a solvent such as water or methanol to make it liquid, adding this to refractory aggregate and mixing, and volatilizing the solvent.

[0075] The semi-hot coat method is a method of obtaining resin-coated sand by adding and mixing a liquid in which a phenolic resin is dispersed or dissolved in the above solvent to refractory aggregate heated to 50 to 90°C, and volatilizing the solvent.

[0076] The powder solvent method is a method of obtaining resin-coated sand by pulverizing a solid phenolic resin, adding this pulverized material to the particles of refractory aggregate, further adding a solvent such as water or methanol, mixing this, and volatilizing the solvent.

[0077] In any of the above methods, it is possible to obtain granular, free-flowing resin-coated sand in which the surface of the refractory aggregate is coated with a solid coating layer at room temperature (25°C). However, the hot coat method is preferred in terms of workability and other aspects. Also, when mixing a phenolic resin with the refractory aggregate as described above, various additives such as a curing agent, various coupling agents such as a silane coupling agent for making the refractory aggregate and the phenolic resin compatible, and a carbonaceous material such as graphite can be blended as necessary.

[0078] When manufacturing a mold using the resin-coated sand prepared in this way, in the same manner as above, that is, filling the resin-coated sand into a mold heated to a high temperature, curing the resol-type phenolic resin in the binder layer of the refractory aggregate by heating with the mold, and then demolding from the mold, a mold formed by binding the refractory aggregate with a resol-type phenolic resin binder can be obtained.

[0079] Also, since the resin-coated sand is granular, voids through which gas passes are formed between the particles of the resin-coated sand in the state where the mold is filled with the resin-coated sand. Therefore, after filling the mold with the resin-coated sand, the resin-coated sand in the mold can be heated by blowing steam such as superheated steam into the mold.

[0080] That is, an inlet and an outlet are formed in the mold. When steam is blown into the mold through the inlet, the steam passes through the resin-coated sand filled in the mold and is discharged from the outlet. At this time, when the steam contacts the surface of the resin-coated sand, the latent heat is taken away from the steam by the resin-coated sand and the steam condenses. However, since the steam has high latent heat and sensible heat, the temperature of the resin-coated sand rapidly rises to around 100 °C due to this latent heat transferred when the steam condenses. The time for the resin-coated sand to be heated to around 100 °C by the heat transfer of the latent heat of the steam varies depending on the temperature of the steam, the blowing flow rate, the filling amount of the resin-coated sand in the mold, etc., but is usually a short time of about 3 to 30 seconds. In this way, it becomes possible to heat the resin-coated sand in the mold in an extremely short time to cure the resol-type phenolic resin and form a mold in a short heating time.

[0081] Here, since the resol-type phenolic resin is modified with modified lignin, as seen in the examples described later, the mold formed with the resin-coated sand of the present invention has high strength, and moreover, the mold has good collapsibility during casting, making it easy to demold the casting. And by adjusting the modification rate of the resol-type phenolic resin with modified lignin, it becomes possible to control the collapsibility of the mold.

Examples

[0082] Next, the present invention will be specifically described by way of examples.

[0083] (Production Example of Modified Lignin) 230 parts by mass of polyethylene glycol (PEG) with a number average molecular weight of 600 and 0.69 parts by mass of sulfuric acid as an acid catalyst (0.3 parts by mass with respect to 100 parts by mass of PEG) were placed in a reaction vessel and stirred. Next, 46 parts by mass of absolutely dry Japanese cedar sawdust was put into the reaction vessel, the temperature was raised to 140 °C under normal pressure, and the reaction was carried out for 90 minutes while stirring.

[0084] Next, the reaction vessel was cooled, and after confirming that the temperature had reached 40°C or lower, 280 parts by mass of sodium hydroxide (0.2 mol / L) was added and stirred for 30 minutes. Next, the obtained solid component (pulp) was removed by a filter press, and the solution component was recovered.

[0085] Next, sulfuric acid was added to the obtained solution component to adjust the pH to 2.0. Thereby, a suspension of lignin modified with PEG was obtained. Thereafter, this modified lignin was recovered by centrifugation.

[0086] (Example 1) 120 parts by mass of phenol, 50 parts by mass of 92% paraformaldehyde, 21 parts by mass of the modified lignin obtained in the above Production Example, 18 parts by mass of hexamethylenetetramine as a reaction catalyst, and 91 parts by mass of water were charged into a reaction vessel, heated, and raised from room temperature to 70°C over about 40 minutes. Next, the heating was stopped, and the exothermic reaction was allowed to proceed to boiling over about 20 minutes, and the reaction was carried out in this boiling state for about 6 minutes.

[0087] Thereafter, the liquid was removed under reduced pressure at -86.7 kPa until the liquid temperature dropped to 60°C, maintained at 60°C for 20 minutes, and then the internal temperature of the reaction vessel was maintained at 58°C and the liquid was removed under reduced pressure at -86.7 kPa for about 120 minutes.

[0088] The reaction product in the reaction vessel was a viscous liquid, which was poured into a vat and stored in a freezer at -10°C for 2 hours to be frozen. This frozen and stored reaction product was put into a power mill crusher (Showa Chemical Machinery Works Co., Ltd. "P-3 type") and crushed using a screen with an aperture of φ2.5 mm. Further, this crushed product was passed through a fluidized bed dryer (manufactured by Kurimoto Iron Works Co., Ltd.) and dried with hot air at 60°C for 150 minutes to perform freeze-drying. Then, the freeze-dried product was cooled to room temperature to obtain granules with a diameter of about 1 mm.

[0089] This particulate matter is a solid resol-type phenolic resin modified with modified lignin, and the yield was 180 parts by mass. Also, this modified lignin-modified resol-type phenolic resin is such that 180 parts by mass of the resin is modified with 21 parts by mass of modified lignin, and the lignin modification rate is about 10%.

[0090] (Example 2) Into a reaction vessel, 110 parts by mass of phenol, 46 parts by mass of 92% paraformaldehyde, 40 parts by mass of the modified lignin obtained in the above Production Example, 16 parts by mass of hexamethylenetetramine as a reaction catalyst, and 84 parts by mass of water were charged, and the reaction was carried out in the same manner as in Example 1, and the liquid was removed under reduced pressure in the same manner as in Example 1.

[0091] Furthermore, the viscous reaction liquid in the reaction vessel was freeze-dried in the same manner as in Example 1 to obtain 180 parts by mass of particulate solid resol-type phenolic resin modified with modified lignin. The modified lignin modification rate of this modified lignin-modified resol-type phenolic resin is about 20%.

[0092] (Example 3) Into a reaction vessel, 100 parts by mass of phenol, 42 parts by mass of 92% paraformaldehyde, 62 parts by mass of the modified lignin obtained in the above Production Example, 15 parts by mass of hexamethylenetetramine as a reaction catalyst, and 76 parts by mass of water were charged, and it was heated for about 60 minutes until it boiled. Next, the heating was stopped, and the reaction was carried out for about 6 minutes while maintaining the boiling by the exothermic reaction.

[0093] Thereafter, the liquid was removed under reduced pressure in the same manner as in Example 1, and further, the viscous reaction product liquid in the reaction vessel was freeze-dried in the same manner as in Example 1 to obtain 190 parts by mass of particulate solid resol-type phenolic resin modified with modified lignin. The modified lignin modification rate of this modified lignin-modified resol-type phenolic resin is about 30%.

[0094] (Example 4) Into a reaction vessel, 120 parts by mass of phenol, 55 parts by mass of 92% paraformaldehyde, 21 parts by mass of the modified lignin obtained in the above production example, 13 parts by mass of hexamethylenetetramine as a reaction catalyst and 1.1 parts by mass of a 48% sodium hydroxide aqueous solution, and 89 parts by mass of water were charged, heated, and raised to 60°C over about 40 minutes, and reacted at a temperature of 60°C for about 130 minutes. Further, it was heated to boiling over about 20 minutes, and after stopping the heating, it was reacted for about 6 minutes while maintaining boiling by an exothermic reaction.

[0095] Thereafter, pressure-reducing and liquid-removing were carried out in the same manner as in Example 1, and further, the viscous reaction liquid in the reaction vessel was freeze-dried in the same manner as in Example 1 to obtain 190 parts by mass of a granular solid resol-type phenol resin modified with modified lignin. The modified lignin modification rate of this modified lignin-modified resol-type phenol resin is about 10%.

[0096] (Example 5) Into a reaction vessel, 110 parts by mass of phenol, 50 parts by mass of 92% paraformaldehyde, 40 parts by mass of the modified lignin obtained in the above production example, 12 parts by mass of hexamethylenetetramine as a reaction catalyst and 1 part by mass of 48% sodium hydroxide, and 82 parts by mass of water were charged, heated, and raised to 60°C over about 40 minutes, and reacted at a temperature of 60°C for about 100 minutes.

[0097] Thereafter, pressure-reducing and liquid-removing were carried out in the same manner as in Example 1, and further, the viscous reaction liquid in the reaction vessel was freeze-dried in the same manner as in Example 1 to obtain 180 parts by mass of a granular solid resol-type phenol resin modified with modified lignin. The modified lignin modification rate of this modified lignin-modified resol-type phenol resin is about 20%.

[0098] (Example 6) Into a reaction vessel, 90 parts by mass of phenol, 41 parts by mass of 92% paraformaldehyde, 56 parts by mass of the modified lignin obtained in the above production example, 10 parts by mass of hexamethylenetetramine and 0.8 parts by mass of 48% sodium hydroxide as reaction catalysts, and 67 parts by mass of water were charged, heated, and raised to 60°C over about 40 minutes, and reacted at a temperature of 60°C for about 100 minutes. Further, heating was carried out over about 20 minutes to cause boiling, and after stopping the heating, a boiling reaction was carried out for about 6 minutes by an exothermic reaction.

[0099] Thereafter, pressure-reducing dehydration was carried out in the same manner as in Example 1, and further, the viscous reaction liquid in the reaction vessel was freeze-dried in the same manner as in Example 1 to obtain 170 parts by mass of a granular solid resol-type phenol resin modified with modified lignin. The modification rate of this modified lignin-modified resol-type phenol resin is about 30%.

[0100] (Example 7) As the industrial lignin not modified with glycols or the like and used in combination with the modified lignin, lignin (deaikalized) "L0045" manufactured by Tokyo Chemical Industry Co., Ltd. was used. This "L0045" is obtained by treating coniferous and broad-leaved trees with sodium sulfite and subjecting it to desulfonation, oxidation, hydrodistillation, and demethylation treatments.

[0101] Then, 110 parts by mass of phenol, 46 parts by mass of 92% paraformaldehyde, 34 parts by mass of the modified lignin obtained in the above production example, 6 parts by mass of the above industrial lignin, 16 parts by mass of hexamethylenetetramine as a reaction catalyst, and 84 parts by mass of water were charged into a reaction vessel, reacted in the same manner as in Example 1, and pressure-reducing dehydration was carried out in the same manner as in Example 1.

[0102] Furthermore, the viscous reaction liquid in the reaction vessel was freeze-dried in the same manner as in Example 1 to obtain 180 parts by mass of a granular solid resol-type phenol resin modified with modified lignin and industrial lignin. The modification rate by the modified lignin of this lignin-modified resol-type phenol resin is about 17%, and the modification rate by the industrial lignin is about 3%.

[0103] (Example 8) Charge 110 parts by mass of phenol, 46 parts by mass of 92% paraformaldehyde, 46 parts by mass of the modified lignin obtained in the above production example, 26 parts by mass of the above industrial lignin, 16 parts by mass of hexamethylenetetramine as a reaction catalyst, and 84 parts by mass of water into a reaction vessel, react in the same manner as in Example 1, and perform liquid removal under reduced pressure in the same manner as in Example 1.

[0104] Furthermore, the viscous reaction solution in the reaction vessel was freeze-dried in the same manner as in Example 1 to obtain 180 parts by mass of a granular solid resol-type phenol resin modified with modified lignin and industrial lignin. The modification rate of this lignin-modified resol-type phenol resin with modified lignin is about 14%, and the modification rate with industrial lignin is about 6%.

[0105] (Comparative Example 1) Charge 140 parts by mass of phenol, 65 parts by mass of 92% paraformaldehyde, 15 parts by mass of hexamethylenetetramine as a reaction catalyst, and 120 parts by mass of water into a reaction vessel, heat and raise the temperature to 60 °C over about 40 minutes, and react at a temperature of 60 °C for about 120 minutes. Further heat to raise the temperature to 70 °C, and react at this temperature for about 80 minutes.

[0106] After that, maintain the internal temperature of the reaction vessel at 58 °C and perform liquid removal under reduced pressure at -86.7 kPa for about 120 minutes. Furthermore, the viscous reaction solution in the reaction vessel was freeze-dried in the same manner as in Example 1 to obtain 190 parts by mass of a granular solid resol-type phenol resin.

[0107] (Comparative Example 2) Charge 110 parts by mass of phenol, 46 parts by mass of 92% paraformaldehyde, 40 parts by mass of the above industrial lignin, 16 parts by mass of hexamethylenetetramine as a reaction catalyst, and 84 parts by mass of water into a reaction vessel, react in the same manner as in Example 1, and perform liquid removal under reduced pressure in the same manner as in Example 1.

[0108] Furthermore, the viscous reaction solution in the reaction vessel was freeze-dried in the same manner as in Example 1 to obtain 180 parts by mass of a granular solid resol-type phenol resin modified with industrial lignin. The lignin modification rate of this industrial lignin-modified resol-type phenol resin is about 20%.

[0109] (Comparative Example 3) 110 parts by mass of phenol, 50 parts by mass of 92% paraformaldehyde, 40 parts by mass of the above industrial lignin, 12 parts by mass of hexamethylenetetramine as a reaction catalyst, 1 part by mass of a 48% sodium hydroxide aqueous solution, and 82 parts by mass of water were charged into a reaction vessel, heated, and raised to 60°C over about 40 minutes, and reacted at a temperature of 60°C for about 100 minutes.

[0110] Thereafter, dehydration under reduced pressure was carried out in the same manner as in Example 1, and further, the viscous reaction solution in the reaction vessel was freeze-dried in the same manner as in Example 1 to obtain 180 parts by mass of a granular solid resol-type phenol resin modified with industrial lignin. The lignin modification rate of this industrial lignin-modified resol-type phenol resin is about 20%.

[0111] For the resol-type phenol resins obtained in the above Examples 1 to 8 and Comparative Examples 1 to 3, the molecular weight, softening point, and gelation temperature were measured. The results are shown in Table 1.

[0112] The molecular weight was measured using gel permeation chromatography (GPC) (HLC-8400GPC manufactured by Tosoh Corporation), and the number average molecular weight (Mn) and weight average molecular weight (Mw) were determined in terms of polystyrene conversion. The softening point and gelation time were measured in accordance with JIS K 6910, and the gelation time was determined as the gelation time at 150°C. The results are shown in Table 1.

[0113] [Table 1]

[0114] As shown in Table 1, the resol type phenolic resins of each example modified with modified lignin had a lower softening point and a longer gelation time than the resol type phenolic resin of Comparative Example 1 without modification with lignin. By having a lower softening point and a longer gelation time in this way, for example, when preparing resin-coated sand as described later, the filling property of the resin between the aggregates is enhanced (the wettability is enhanced and the contacts between the aggregates are more easily filled with the resin), and the flexural strength is improved. Also, in Comparative Examples 2 and 3 modified with industrial lignin, the softening point and the gelation time did not change much compared to those of Comparative Example 1 without lignin modification, and the effect of modification with industrial lignin was not very expectable. This is presumably due to the low reactivity of industrial lignin and insufficient modification with lignin. On the other hand, as seen in Examples 7 and 8 using industrial lignin in combination with modified lignin, the effect of modification with modified lignin could be sufficiently confirmed even when industrial lignin was used in combination.

[0115] When considering the gelation time here, it is confirmed that the higher the lignin modification rate, the longer the gelation time, and the effect of modification with modified lignin can be improved by increasing the lignin modification rate. Also, when comparing Examples 1 to 3 using only hexamethylenetetramine as a reaction catalyst with Examples 4 to 5 using hexamethylenetetramine and sodium hydroxide in combination, the gelation time is shorter in Examples 4 to 5, and it is confirmed that the gelation time can be adjusted by the type of catalyst and its combination.

[0116] Next, resin-coated sand was produced using the resol-type phenolic resins of Examples 1 to 8 and Comparative Examples 1 to 3 obtained as described above. That is, 10 kg of ACI-G silica sand heated to 140°C was put into a Turbula mixer, 200 g of any one of the resol-type phenolic resins obtained in Examples 1 to 8 and Comparative Examples 1 to 3 was added, and kneaded for 40 seconds. Next, 150 g of water was added and kneaded until the sand grains disintegrated. Further, 10 g of calcium stearate was added as a lubricant, kneaded for 30 minutes, and then discharged from the Turbula mixer to obtain the resin-coated sand of Examples 9 to 16 and Comparative Examples 4 to 6.

[0117] Using the resin-coated sand of Examples 9 to 16 and Comparative Examples 4 to 6, the flexural strength, collapsibility, and rapid heat expansion rate were measured. The measurement results of the flexural strength and collapsibility are shown in Table 2, and the measurement results of the rapid heat expansion rate are shown in Table 3.

[0118] The flexural strength test was conducted as follows. According to JIS-K-6910 (1999), a test piece of 10×10×60 mm was formed by filling a mold with resin-coated sand and firing it under the conditions of 250°C for 60 seconds, and the flexural strength was measured according to the JACT test method (SM-1).

[0119] The collapsibility test was conducted as follows. According to JIS-K-6910 (1999), a test piece (assuming a mold) of 10×10×60 mm was formed by filling a mold with resin-coated sand and firing it under the conditions of 250°C for 60 seconds, and then allowed to cool. This cooled test piece was wrapped with aluminum foil as much as possible while removing air, put into a circulating dryer heated to 450°C, and heated for 30 minutes. Next, it was taken out and allowed to cool, then the aluminum foil was removed, and the residual strength was measured according to the JACT test method (SM-1). From this residual strength, the ease of mold collapse during casting can be evaluated. That is, from the flexural strength (room temperature flexural strength) obtained above and this residual strength, the collapse rate was calculated by the following formula. Collapse rate = (Flexural strength - Residual strength) × 100 / Flexural strength

[0120] The rapid heat expansion rate reproduces the rapid thermal expansibility caused by the rapid heating when pouring the molten metal into the mold during casting. A cylindrical test piece of φ20×50 mm (assuming the mold) is prepared by filling the mold with resin-coated sand and firing it under the conditions of 250 °C × 90 seconds, and the rapid heat expansion rate at the explosion heat temperature of 1000 °C is measured according to the JACT test method (SM-2).

[0121]

Table 2

[0122] Regarding the evaluation of the flexural strength, as shown in Table 2, there is no significant difference between each example of the resol-type phenolic resin modified with modified lignin and Comparative Example 4 of the resol-type phenolic resin not modified with lignin. Rather, each example is higher, and it was confirmed that a resol-type phenolic resin having a flexural strength equal to or higher than that can be obtained by modifying with modified lignin. On the other hand, the flexural strength of Comparative Examples 5 to 6 of the resol-type phenolic resin modified with industrial lignin has decreased. This is considered to be due to the low reactivity of industrial lignin, which inhibits the curing (crosslinking reaction) of the resol-type phenolic resin and insufficient polymerization.

[0123] Regarding the collapsibility, the collapsibility rates of the examples of the resol type phenolic resin modified with modified lignin are higher than those of Comparative Example 4 of the resol type phenolic resin not modified with lignin. It is confirmed that the resin-coated sand using the resol type phenolic resin modified with modified lignin can form a mold excellent in collapsibility. Particularly, in Examples 13 to 14 in which hexamethylenetetramine and NaOH are used in combination as a reaction catalyst, the residual strength is significantly reduced and the collapsibility rate is increased, and the collapsibility of the mold can be further improved. Also, as seen in Examples 9 to 11 and Examples 12 to 14, the collapsibility rate tends to increase as the lignin modification rate increases, and it is confirmed that the collapsibility can be controlled by adjusting the modification rate with modified lignin. Also, in Comparative Examples 5 and 6 of the resol type phenolic resin modified with industrial lignin, the collapsibility rates are rather lower than those of Comparative Example 4. This is considered to be due to the low flexural strength of Comparative Examples 5 and 6.

[0124]

Table 3

[0125] As shown in Table 3, in the initial stage (10 to 60 seconds) of the explosion heat, the expansion rates of the examples are lower than those of Comparative Example 4. From this, it is confirmed that by modifying the resol type phenolic resin with modified lignin, the initial rapid heat expansion during heating at high temperature can be suppressed, and the benning due to core breakage or crack generation of the mold during pouring in casting can be reduced. On the other hand, in Comparative Examples 5 to 6 modified with industrial lignin, the rapid expansion rate in the initial stage (10 to 60 seconds) of the explosion heat is rather high, and the effect of reducing the occurrence of benning during casting cannot be expected.

[0126] Next, using the resol type phenolic resins of Examples 1 to 8 and Comparative Examples 1 to 3 obtained as described above, 20 parts by mass of this resol type phenolic resin was pulverized and mixed with a crash mixer, and further 80 parts by mass of cork powder (product with 200 mesh, manufactured by Nagayagi Kogyo Co., Ltd.) as a filler was blended to prepare the phenolic resin compositions (molding materials) of Examples 17 to 24 and Comparative Examples 7 to 9.

[0127] Then, each of the molding materials of Examples 17 to 24 and Comparative Examples 7 to 9 was filled into a mold at 100 °C, the heating temperature was raised while applying pressure under the condition of a pressure of 9.8 MPa, the heater was stopped at 160 °C while degassing at 110 °C, and after allowing curing to proceed for 10 minutes, molding was performed by a process of cooling to 80 °C, thereby molding a molded product of 100 × 100 × 7 mm.

[0128] Test pieces of 10 × 100 × 5 mm were cut out from the obtained molded products, and using an autograph "AGS-10KNX" manufactured by Shimadzu Corporation, in accordance with JIS K-6911, under the conditions of a span distance of 80 mm and a crosshead speed of 5 mm / min, the flexural strength was measured, and the flexural modulus and flexural strain were also determined. Further, using a Shore hardness tester type D ("GS-702N" manufactured by TECLOCK CORPORATION), the hardness of the above test pieces was measured. The measurement results of the flexural strength, flexural modulus, and flexural strain are shown in Table 4, and the measurement results of the hardness are shown in Table 5, respectively.

[0129]

Table 4

[0130]

Table 5

[0131] As shown in Table 4, there were no significant differences in flexural strength, flexural modulus, or flexural strain among Examples 17 to 24 and Comparative Example 7. It was confirmed that the resol type phenolic resins of each Example modified with modified lignin had properties such as strength equivalent to those of the unmodified resol type phenolic resin.

[0132] On the other hand, as shown in Table 5, all of Examples 17 to 24 had higher hardness than Comparative Example 7, and it was possible to increase the surface hardness of the molded products of the resol type phenolic resin by modifying with modified lignin. As shown in Comparative Examples 8 and 9, the surface hardness of the resol type phenolic resin modified with industrial lignin was not increased, and it was confirmed that the improvement in the hardness of the molded product was an effect due to modification with modified lignin.

Claims

1. A method for producing a resol-type phenolic resin, characterized by reacting a modified lignin modified with glycols, phenols, and aldehydes in the presence of an alkaline catalyst.

2. A method for producing a resol-type phenolic resin, characterized by reacting a modified lignin modified with glycols, phenols, and aldehydes in the presence of an alkaline catalyst to prepare a reaction product in a water-containing state, and drying the reaction product in the water-containing state to prepare a solid at room temperature.

3. The method for producing a resol-type phenolic resin according to claim 2, characterized in that the reaction product in the water-containing state is solidified, the solidified reaction product is pulverized to obtain a water-containing granular material, and then the water-containing granular material is heated and dried.

4. The method for producing a resol-type phenolic resin according to claim 3, characterized in that the water-containing granular material is dried by bringing it into contact with hot air.

5. The method for producing a resol-type phenolic resin according to any one of claims 1 to 4, characterized in that the modified lignin modified with the above glycols is a modified lignin modified with polyethylene glycol.

6. The method for producing a resol-type phenolic resin according to any one of claims 1 to 4, characterized in that, in addition to the above modified lignin, lignin that has not been modified with glycols is reacted in a blending amount of 50% by mass or less of the modified lignin.

7. A method for producing resin-coated sand, characterized by coating a refractory aggregate with the phenolic resin obtained by the method according to any one of claims 1 to 6.

8. A method for producing a phenolic resin composition, characterized by being prepared by containing the phenolic resin obtained by the method according to any one of claims 1 to 6.

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