JP7785261B2 - Friction material - Google Patents

Description

The present invention relates to a friction material.

Friction materials are used, for example, in vehicle braking components. Braking components include, for example, brake components and clutch components. Friction materials include, for example, a fibrous base material, a filler, a lubricant, and a binder that binds these together.

More specifically, the following friction material has been proposed. This friction material includes a binder, a fibrous base material, a filler, and a solid lubricant. The binder includes a novolac phenolic resin and a curing agent. The novolac phenolic resin includes a reaction product of phenol, acetic acid-modified lignin, and paraformaldehyde. The fibrous base material includes aramid fibers and copper fibers. The filler includes acrylonitrile butadiene rubber, cashew dust, and barium sulfate. The solid lubricant includes graphite. This friction material has excellent friction characteristics (see, for example, Patent Document 1 (Example 1)).

International Publication No. 2018/190171

In addition to friction characteristics, friction materials are required to suppress abnormal noise (squeal) caused by friction.

The present invention is a friction material with excellent friction characteristics and noise suppression.

The present invention [1] relates to a friction material containing a binder, wherein the binder contains a reaction product of lignin modified with polyethylene glycol, a phenol, and an aldehyde.

The present invention [2] includes the friction material described in [1] above, in which the lignin is softwood lignin.

The present invention [3] includes the friction material described in [1] or [2] above, in which the number-average molecular weight of the polyethylene glycol is 400 or more.

In the friction material of the present invention, the binder contains a reaction product of lignin modified with polyethylene glycol, a phenol, and an aldehyde. As a result, the friction material has excellent friction characteristics and can also suppress noise (squeal) caused by friction.

The friction material of the present invention contains a binder (binding agent).

The binder (binding agent) contains a reaction product of lignin modified with polyethylene glycol (PEG) (hereinafter sometimes referred to as PEG-modified lignin), phenols, and aldehydes.

In PEG-modified lignin, polyethylene glycol (PEG) modifies the lignin, improving the friction characteristics of the friction material and also suppressing noise.

The number-average molecular weight of polyethylene glycol is, for example, 100 or more, preferably 200 or more, more preferably 300 or more, even more preferably 400 or more, and particularly preferably 500 or more. The number-average molecular weight of polyethylene glycol is, for example, 1000 or less, preferably 900 or less, more preferably 800 or less, and even more preferably 600 or less. A number-average molecular weight within the above range results in a friction material that combines excellent friction characteristics and noise suppression, and also ensures excellent productivity of the friction material. The number-average molecular weight can be determined as the polyethylene glycol equivalent molecular weight using the known gel permeation chromatography method.

In PEG-modified lignin, lignin is a high molecular weight phenolic compound. Lignin is a natural product (natural lignin) found in all plants. Examples of the basic structure of lignin include guaiacyl lignin (G-type), syringyl lignin (S-type), and p-hydroxyphenyl lignin (H-type).

Lignin is industrially extracted from plant materials. Examples of plant materials include lignocellulose. Examples of lignin include soda lignin, sulfite lignin, and kraft lignin. Methods for extracting lignin include the soda process, sulfite process, steam explosion method, solvolysis method, and kraft process.

More specifically, lignin includes lignin derived from woody plants and lignin derived from herbaceous plants.

Examples of woody plant-derived lignin include coniferous lignin contained in conifers (e.g., cedar) and hardwood lignin contained in hardwoods. 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. Hardwood lignin has both a G-type basic skeleton and an S-type basic skeleton.

Examples of lignin derived from herbaceous plants include rice lignin, which is found in grasses. Examples of grasses include wheat straw, rice straw, corn, and bamboo. Lignin derived from herbaceous plants has 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. As the lignin, woody plant-derived lignin that does not contain an H-type basic skeleton is preferred, and coniferous lignin that does not contain an S-type basic skeleton and has a G-type basic skeleton is more preferred, with coniferous lignin derived from Japanese cedar being particularly preferred. PEG-modified lignin obtained from coniferous lignin derived from Japanese cedar has excellent homogeneity.

PEG-modified lignin is produced, for example, according to the method described in JP 2017-197517 A.

In this method, for example, plant material (lignocellulose), the raw material for lignin, is digested using polyethylene glycol.

The cooking method is not particularly limited, but for example, plant material that serves as the raw material for lignin, polyethylene glycol, and an inorganic acid (e.g., hydrochloric acid, sulfuric acid, etc.) serving as an acid catalyst are mixed and reacted.

The blending ratio of polyethylene glycol is, for example, 200 parts by mass or more, preferably 300 parts by mass or more, per 100 parts by mass of the plant material that serves as the lignin raw material. The blending ratio of polyethylene glycol is, for example, 1,000 parts by mass or less, preferably 600 parts by mass or less, per 100 parts by mass of the plant material that serves as the lignin raw material.

The blending ratio of the inorganic acid (100% equivalent) is, for example, 0.1 parts by mass or more, preferably 0.2 parts by mass or more, per 100 parts by mass of polyethylene glycol. The blending ratio of the inorganic acid (100% equivalent) is, for example, 2 parts by mass or less, preferably 1 part by mass or less, per 100 parts by mass of polyethylene glycol.

Reaction conditions include atmospheric pressure. The reaction temperature is, for example, 120°C or higher, preferably 130°C or higher. The reaction temperature is, for example, 180°C or lower, preferably 150°C or lower. The reaction time is, for example, 60 minutes or longer. The reaction time is, for example, 240 minutes or shorter, preferably 120 minutes or shorter.

After the reaction is complete, an alkali is added to the reaction solution in an appropriate ratio to adjust the pH. Examples of alkali include ammonia and sodium hydroxide. This extracts the PEG-modified lignin into the solution. The adjusted pH is, for example, 8 or higher, preferably 10 or higher, and more preferably 10.5 or higher, and is, for example, 14 or lower.

This method yields pulp as a solid component and PEG-modified lignin as a solution component.

Next, in this method, the solid component (pulp) is separated from the reaction product using known separation methods such as filtration, pressing, and centrifugation, and the solution component is recovered.

In addition, with 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.

Then, in this method, an inorganic acid (e.g., hydrochloric acid, sulfuric acid, etc.) is added to adjust the pH, causing the PEG-modified lignin to precipitate and precipitate.

The pH after adjustment is, for example, 1.5 or higher, and, for example, 5 or lower, preferably 3 or lower, and more preferably 2 or lower.

This allows PEG-modified lignin to precipitate. The resulting precipitate can then be collected by known methods, such as filtration, pressing, or centrifugation, to obtain PEG-modified lignin as a solid.

Phenols include phenol and phenol derivatives (modified phenols). Examples of phenols include phenol, difunctional phenol derivatives, trifunctional phenol derivatives, and tetrafunctional phenol derivatives. Examples of difunctional phenol derivatives include o-cresol, p-cresol, p-ter-butylphenol, p-phenylphenol, p-cumylphenol, p-nonylphenol, 2,4-xylenol, and 2,6-xylenol. Examples of trifunctional phenol derivatives include m-cresol, resorcinol, and 3,5-xylenol. Examples of tetrafunctional phenol derivatives include bisphenol A and dihydroxydiphenylmethane. Phenol derivatives also include halogenated phenols. Halogenated phenols are halides of phenol or phenol derivatives. Examples of halogens include chlorine and bromine. These phenols can be used alone or in combination. There are no particular restrictions on the timing of phenol derivatization (modification) in phenol derivatives. For example, the derivatization of phenol may be carried out before, after, or simultaneously with the reaction of the phenol with the aldehyde. Phenol is a preferred example of the phenol.

Examples of aldehydes include formaldehyde, paraformaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, furfural, glyoxal, benzaldehyde, trioxane, and tetraoxane. Furthermore, a portion of the aldehyde may be substituted with furfuryl alcohol or the like. These aldehydes can be used alone or in combination of two or more. Preferred aldehydes include formaldehyde and paraformaldehyde.

Aldehydes can also be used, for example, as an aqueous solution. In such cases, the concentration of the aldehydes 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.

Ketones can also be blended together with aldehydes. Examples of ketones include acetone, methyl ethyl ketone, diethyl ketone, acetophenone, and diphenyl ketone. These ketones can be used alone or in combination of two or more. When ketones are blended, the blending ratio of the ketones, based on the solid content, 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, per 100 parts by mass of aldehydes.

To react the PEG-modified lignin with the phenols and aldehydes (and optionally ketones (hereinafter the same)), the above components (PEG-modified lignin, phenols, and aldehydes) are mixed and heated.

In this reaction, the blending ratio of the phenols is, for example, 30 parts by mass or more, preferably 50 parts by mass or more, and more preferably 100 parts by mass or more, per 100 parts by mass of the PEG-modified lignin. Furthermore, the blending ratio of the phenols is, for example, 1,000 parts by mass or less, preferably 500 parts by mass or less, and more preferably 350 parts by mass or less, per 100 parts by mass of the PEG-modified lignin. In other words, the blending ratio of the PEG-modified lignin is, for example, 10 parts by mass or more, preferably 20 parts by mass or more, and more preferably 30 parts by mass or more, per 100 parts by mass of the phenols. Furthermore, the blending ratio of the PEG-modified lignin is, for example, 300 parts by mass or less, preferably 200 parts by mass or less, and more preferably 100 parts by mass or less, per 100 parts by mass of the phenols.

The blending ratio of the aldehydes is, for example, 5 parts by mass or more, preferably 10 parts by mass or more, per 100 parts by mass of the phenols. The blending ratio of the aldehydes is, for example, 35 parts by mass or less, preferably 30 parts by mass or less, per 100 parts by mass of the phenols.

The blending ratio of the aldehydes is, for example, 1.5 parts by mass or more, preferably 3 parts by mass or more, per 100 parts by mass of the PEG-modified lignin. The blending ratio of the aldehydes is, for example, 350 parts by mass or less, preferably 300 parts by mass or less, per 100 parts by mass of the PEG-modified lignin.

When the blending ratio of each component is within the above range, a friction material with excellent physical properties can be obtained.

In addition, an acid catalyst is added to this reaction. That is, the above components react in the presence of an acid catalyst.

Examples of acid catalysts include organic acids and inorganic acids. Examples of organic acids include carboxylic acid compounds, sulfonic acid compounds, and phosphoric acid compounds. Examples of carboxylic acid compounds include formic acid, acetic acid, and oxalic acid. Examples of sulfonic acid compounds include methanesulfonic acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, cumenesulfonic acid, dinonylnaphthalene monosulfonic acid, and dinonylnaphthalenedisulfonic acid. Examples of phosphoric acid compounds include phosphate esters. More specifically, examples of phosphate esters include phosphate esters having an alkyl group containing 1 to 18 carbon atoms. Examples of phosphoric acid compounds include trimethyl phosphate, triethyl phosphate, monobutyl phosphate, dibutyl phosphate, tributyl phosphate, and trioctyl phosphate. Examples of inorganic acids include phosphoric acid, hydrochloric acid, sulfuric acid, and nitric acid. These acid catalysts can be used alone or in combination. Preferred acid catalysts are organic acids, more preferably carboxylic acid compounds, and even more preferably oxalic acid.

The proportion of the acid catalyst 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, per 100 parts by mass of phenols.

The timing of adding the acid catalyst is not particularly limited. For example, the acid catalyst may be added in advance to at least one of the PEG-modified lignin, phenols, and aldehydes. Alternatively, the acid catalyst may be added simultaneously with the blending of the PEG-modified lignin, phenols, and aldehydes. Furthermore, the acid catalyst may be added after the blending of the PEG-modified lignin, phenols, and aldehydes.

Reaction conditions include atmospheric pressure. The reaction temperature is, for example, 50°C or higher, preferably 80°C or higher. The reaction temperature is, for example, 200°C or lower, preferably 180°C or lower. The reaction time is, for example, 1 hour or longer, preferably 2 hours or longer. The reaction time is, for example, 20 hours or shorter, preferably 15 hours or shorter.

This results in a binder (binding agent) as a resin composition containing the reaction product of PEG-modified lignin, phenols, and aldehydes.

The reaction product of PEG-modified lignin, phenols, and aldehydes is a novolac-type phenolic resin modified with PEG-modified lignin. More specifically, the reaction of phenols with aldehydes in the presence of an acid catalyst produces a novolac-type phenolic resin, which is then modified with PEG-modified lignin. In other words, the above reaction produces a resin composition (binder) containing a novolac-type phenolic resin modified with PEG-modified lignin.

The binder (binding agent) obtained in this way produces a friction material with excellent friction properties and the ability to suppress noise.

In addition, in the reaction between PEG-modified lignin, phenols, and aldehydes, the above components can be mixed together and reacted as described above, or the above components can be mixed sequentially and reacted. More specifically, for example, PEG-modified lignin can be reacted with phenols first, and then the resulting reaction product can be reacted with aldehydes.

Specifically, in the sequential reaction, PEG-modified lignin is first reacted with phenols to prepare a PEG-modified lignin-phenol composition containing the reaction product of the PEG-modified lignin and phenols, and then the PEG-modified lignin-phenol composition is reacted with aldehydes.

In the reaction between PEG-modified lignin and phenols, the phenols are blended in an excess amount relative to the PEG-modified lignin. Specifically, the blending ratio of the phenols is, for example, 30 parts by mass or more, preferably 50 parts by mass or more, and more preferably 100 parts by mass or more, per 100 parts by mass of the PEG-modified lignin. Furthermore, the blending ratio of the phenols is, for example, 1,000 parts by mass or less, preferably 500 parts by mass or less, and more preferably 350 parts by mass or less, per 100 parts by mass of the PEG-modified lignin. In other words, the blending ratio of the PEG-modified lignin is, for example, 10 parts by mass or more, preferably 20 parts by mass or more, and more preferably 30 parts by mass or more, per 100 parts by mass of the phenols. Furthermore, the blending ratio of the PEG-modified lignin is, for example, 300 parts by mass or less, preferably 200 parts by mass or less, and more preferably 100 parts by mass or less, per 100 parts by mass of the phenols.

The acid catalyst described above is also added to this reaction. The amount of the acid catalyst added is, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, per 100 parts by mass of the phenols. The amount of the acid catalyst added is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, per 100 parts by mass of the phenols.

The timing of adding the acid catalyst is not particularly limited. For example, the acid catalyst may be added in advance to at least one of the PEG-modified lignin and the phenols. Alternatively, the acid catalyst may be added simultaneously with the blending of the PEG-modified lignin and the phenols. Alternatively, the acid catalyst may be added after the blending of the PEG-modified lignin and the phenols.

Reaction conditions include atmospheric pressure. The reaction temperature is, for example, 60°C or higher, preferably 80°C or higher. The reaction temperature is, for example, 250°C or lower, preferably 200°C or lower. The reaction time is, for example, 0.5 hours or longer, preferably 1 hour or longer. The reaction time is, for example, 10 hours or shorter, preferably 5 hours or shorter.

This reaction causes the PEG-modified lignin to be modified with phenols. Specifically, the aliphatic hydroxyl groups in the PEG-modified lignin molecules are replaced with phenols.

In the above reaction, excess phenols remain as unreacted components. Therefore, the PEG-modified lignin-phenol composition obtained by the above reaction contains the reaction product of PEG-modified lignin and phenols (PEG-modified lignin modified with phenols) and free phenols.

Next, in this method, the PEG-modified lignin-phenol composition obtained above (i.e., containing PEG-modified lignin modified with phenols and free phenols) is reacted with aldehydes.

In this reaction, the blending ratio of the aldehydes 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, per 100 parts by mass of the phenols (phenols used as raw materials in the above reaction).

If necessary, the above-mentioned acid catalyst can be added in an appropriate proportion to this reaction.

Reaction conditions include atmospheric pressure. The reaction temperature is, for example, 50°C or higher, preferably 80°C or higher. The reaction temperature is, for example, 200°C or lower, preferably 180°C or lower. The reaction time is, for example, 1 hour or longer, preferably 2 hours or longer. The reaction time is, for example, 20 hours or shorter, preferably 15 hours or shorter.

As a result, the PEG-modified lignin-phenol composition reacts with aldehydes to produce a novolac phenolic resin modified with PEG-modified lignin (PEG-modified lignin-modified novolac phenolic resin). Furthermore, a binder is obtained as a resin composition containing this PEG-modified lignin-modified novolac phenolic resin.

In addition, when producing PEG-modified lignin-modified novolac phenolic resin, unreacted raw materials (such as unreacted phenols) and acid catalysts can be removed, if necessary, by known methods such as distillation.

The binder (binding agent) obtained in this way produces a friction material with excellent friction properties and the ability to suppress noise.

The binder may also contain a phenolic resin curing agent as needed. The binder preferably contains a novolac phenolic resin and a phenolic resin curing agent, and more preferably consists of a novolac phenolic resin and a phenolic resin curing agent.

The phenolic resin curing agent is not particularly limited, and known curing agents can be used. Examples of phenolic resin curing agents include hexamethylenetetramine, methylolmelamine, and methylolurea. These phenolic resin curing agents can be used alone or in combination of two or more. The blending ratio of the phenolic resin curing agent can be appropriately set depending on the purpose and application, as long as it does not impair the excellent effects of the present invention.

The binder may further contain additives. Examples of additives include known additives added to binders. Examples of additives include colorants, plasticizers, stabilizers, and release agents. Examples of release agents include metal soaps, more specifically zinc stearate. These additives can be used alone or in combination of two or more types. There are no particular restrictions on the timing of adding the additives, and they can be set appropriately depending on the purpose and application. The blending ratio of the additives can be set appropriately depending on the purpose and application, as long as it does not impair the excellent effects of the present invention.

The friction material may also contain other binders as needed. These other binders are binders other than the resin composition described above (a resin composition containing a novolac-type phenolic resin modified with PEG-modified lignin). Examples of other binders include known thermosetting resins. Examples of thermosetting resins include melamine resins, epoxy resins, and polyimide resins. These can be used alone or in combination of two or more types.

When other binders are blended, the blending ratio is set appropriately within a range that does not impair the effects of the present invention. The friction material preferably does not contain other binders. In other words, the friction material preferably contains only the above-mentioned resin composition as a binder.

The friction material preferably also contains a fibrous base material. Examples of fibrous base materials include organic fibers and inorganic fibers.

Examples of organic fibers include polyamide fibers and acrylic fibers. Examples of polyamide fibers include aramid fibers. Examples of acrylic fibers include flame-retardant acrylic fibers. These can be used alone or in combination of two or more types. Preferred organic fibers include polyamide fibers, and more preferred organic fibers include aramid fibers.

Examples of inorganic fibers include metal fibers, ceramic fibers, glass fibers, and carbon fibers. Examples of metal fibers include copper fibers and brass fibers. Examples of ceramic fibers include potassium titanate fibers, Al ₂ O ₃ —SiO ₂ ceramic fibers, and biosoluble ceramic fibers. These can be used alone or in combination of two or more types. Preferred inorganic fibers include metal fibers, and more preferably copper fibers.

The fiber substrate can be used alone or in combination of two or more types. Preferred fiber substrates include organic fibers and inorganic fibers, and more preferably, a combination of organic fibers and inorganic fibers.

The size of the fiber substrate is set appropriately depending on the purpose and application. For example, the length (fiber length) of the fiber substrate is not particularly limited, but is, for example, 100 μm or more and 2500 μm or less. The diameter of the fiber substrate is also not particularly limited, but is, for example, 3 μm or more and 600 μm or less.

The friction material preferably also contains a friction modifier. Examples of friction modifiers include fillers, solid lubricants, and abrasives.

Fillers include, for example, organic fillers and inorganic fillers.

Examples of organic fillers include wood flour, pulp, rubber powder, cashew particles (cashew dust), and melamine dust. In the rubber powder, examples of rubber include acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), and butadiene rubber (BR). These can be used alone or in combination of two or more types. Preferred organic fillers include rubber powder and cashew particles.

Examples of inorganic fillers include calcium carbonate, barium sulfate, calcium hydroxide, iron sulfide, copper sulfide, silicon oxide, metal powder, and minerals. In the case of metal powder, examples of metals include copper, aluminum, bronze, and zinc. Examples of minerals include vermiculite. These can be used alone or in combination. A preferred inorganic filler is barium sulfate.

Fillers can be used alone or in combination of two or more types. Preferred fillers include organic fillers and inorganic fillers, and more preferably, a combination of organic fillers and inorganic fillers.

Examples of solid lubricants include known solid lubricants. More specifically, examples of solid lubricants include graphite and molybdenum disulfide. These can be used alone or in combination of two or more types. Graphite is a preferred solid lubricant.

Abrasives include known abrasives. More specific examples of abrasives include alumina, magnesia, and zirconia. These can be used alone or in combination of two or more types.

These friction modifiers can be used alone or in combination of two or more types. Friction modifiers are selected appropriately depending on the required physical properties. Preferred friction modifiers include fillers and solid lubricants, and more preferably, a combination of fillers and solid lubricants is used.

The size of the friction modifier is set appropriately depending on the purpose and application. For example, the average particle diameter of the friction modifier is, for example, 1 μm or more, preferably 5 μm or more. The average particle diameter of the friction modifier is, for example, 500 μm or less, preferably 250 μm or less.

When producing friction materials, for example, the above-mentioned binder, fibrous base material, and friction modifier are first blended and kneaded to produce a molding material (composition) for the friction material.

In the friction material molding material, the total amount of the fibrous base material and friction modifier per 100 parts by mass of the binder is, for example, 250 parts by mass or more, preferably 400 parts by mass or more. Furthermore, the total amount of the fibrous base material and friction modifier per 100 parts by mass of the binder is, for example, 950 parts by mass or less, preferably 900 parts by mass or less.

Furthermore, the amount of binder is, for example, 2 parts by mass or more, preferably 5 parts by mass or more, per 100 parts by mass of the total amount of binder, fibrous base material, and friction modifier. Furthermore, the amount of binder is, for example, 40 parts by mass or less, preferably 30 parts by mass or less, per 100 parts by mass of the total amount of binder, fibrous base material, and friction modifier.

Furthermore, the amount of the fibrous base material is, for example, 1 part by mass or more, preferably 5 parts by mass or more, per 100 parts by mass of the total of the binder, fibrous base material, and friction modifier. Furthermore, the amount of the fibrous base material is, for example, 65 parts by mass or less, preferably 30 parts by mass or less, per 100 parts by mass of the total of the binder, fibrous base material, and friction modifier.

Furthermore, the amount of friction modifier is, for example, 40 parts by mass or more, preferably 50 parts by mass or more, per 100 parts by mass of the total of the binder, fibrous base material, and friction modifier. Furthermore, the amount of friction modifier is, for example, 95 parts by mass or less, preferably 85 parts by mass or less, per 100 parts by mass of the total of the binder, fibrous base material, and friction modifier.

Furthermore, when the friction modifier contains an abrasive, the amount of the abrasive is, for example, 1 part by mass or more, preferably 2 parts by mass or more, per 100 parts by mass of the binder, fibrous base material, and friction modifier combined. The amount of the abrasive is, for example, 30 parts by mass or less, preferably 25 parts by mass or less, per 100 parts by mass of the binder, fibrous base material, and friction modifier combined.

Furthermore, when the friction modifier contains a filler, the amount of filler is, for example, 30 parts by mass or more, preferably 35 parts by mass or more, per 100 parts by mass of the binder, fibrous base material, and friction modifier combined. Furthermore, the amount of filler is, for example, 90 parts by mass or less, preferably 85 parts by mass or less, per 100 parts by mass of the binder, fibrous base material, and friction modifier combined.

Furthermore, when the friction modifier contains a solid lubricant, the amount of the solid lubricant is, for example, 1 part by mass or more, preferably 3 parts by mass or more, per 100 parts by mass of the binder, fibrous base material, and friction modifier combined. Furthermore, the amount of the solid lubricant is, for example, 30 parts by mass or less, preferably 25 parts by mass or less, per 100 parts by mass of the binder, fibrous base material, and friction modifier combined.

The kneading method is not particularly limited, and a known kneading machine can be used. Examples of kneading machines include single-screw extruders, multi-screw extruders, roll kneaders, kneaders, Henschel mixers, and Banbury mixers.

The kneading temperature is, for example, 80°C or higher, preferably 90°C or higher, and more preferably 100°C or higher. The kneading temperature is, for example, 180°C or lower, preferably 170°C or lower, and more preferably 160°C or lower. The kneading time is, for example, 3 minutes or longer, preferably 5 minutes or longer. The kneading time is, for example, 30 minutes or shorter, and preferably 20 minutes or shorter.

This type of molding material for friction materials contains the above-mentioned novolac phenolic resin as a binder. Therefore, by using this type of molding material for friction materials, a friction material with excellent friction characteristics and the ability to suppress abnormal noise can be obtained.

Next, in this method, the above-mentioned friction material molding material is molded using a known method. This results in a friction material.

Known molding methods can be used. Specific examples of molding methods include transfer molding and compression molding. There are no particular restrictions on molding conditions, and they can be set appropriately depending on the purpose and application.

For example, the temperature condition is, for example, 140°C or higher, preferably 150°C or higher. The temperature condition is, for example, 200°C or lower, preferably 180°C or lower. The pressure condition is, for example, 20 MPa or higher, preferably 30 MPa or higher. The pressure condition is, for example, 100 MPa or lower, preferably 80 MPa or lower. The processing time is, for example, 2 minutes or longer, preferably 10 minutes or longer. The processing time is, for example, 60 minutes or shorter, preferably 30 minutes or shorter.

By molding the friction material molding material in this way, the friction material is obtained.

The friction material may also be treated by known methods, if necessary. Examples of such treatments include degreasing and primer treatment. The molded friction material may also be after-cured (thermosetting) by known methods.

The processing conditions for after-curing are not particularly limited, but normal pressure is used. The temperature is, for example, 10 to 100°C higher than the temperature during molding. The temperature is, for example, 150°C or higher, preferably 160°C or higher. The temperature is, for example, 300°C or lower, preferably 200°C or lower. The processing time is, for example, 1 hour or longer, preferably 2 hours or longer. The processing time is, for example, 10 hours or shorter, preferably 8 hours or shorter. After-curing can improve frictional properties and heat resistance.

The friction material contains a reaction product of lignin modified with polyethylene glycol, phenols, and aldehydes (novolac-type phenolic resin modified with PEG-modified lignin). Therefore, the friction material has excellent friction characteristics and can also suppress noise (squeak) caused by friction.

More specifically, friction characteristics can usually be improved by improving the mechanical strength of the friction material. However, improving the mechanical strength of the friction material reduces the flexibility of the friction material, making it more susceptible to vibration due to friction and generating abnormal noise (squeak). In other words, improving friction characteristics and suppressing abnormal noise are mutually exclusive.

In contrast, the binder in the above-mentioned friction material contains a reaction product of lignin modified with polyethylene glycol, phenols, and aldehydes (novolac-type phenolic resin modified with PEG-modified lignin). This improves the mechanical strength of the friction material while maintaining its flexibility.

As a result, the friction characteristics of the friction material are improved, vibration of the friction material is suppressed, and the occurrence of abnormal noise (squealing) is reduced.

For this reason, friction materials are suitable for use in, for example, vehicle braking components. Examples of vehicles include automobiles, motorcycles, and trains. Examples of braking components include brake pads and clutch components. Friction materials are particularly suitable for use as brake pads for automobiles.

When the friction material is used as a brake pad for an automobile, the brake component and the above-mentioned friction material molding material may be molded integrally. An example of a brake component is a known pressure plate.

More specifically, for example, the above-mentioned friction material molding material is first preformed. If necessary, the preformed friction material molding material is degreased and primed. Next, the friction material molding material and the brake component are bonded together with an adhesive. After that, the friction material molding material and the brake component are thermoformed together. At the same time, the friction material molding material and the brake component are fixed together.

The processing conditions for thermoforming are not particularly limited and are set appropriately depending on the purpose and application. For example, the temperature condition is, for example, 140°C or higher and 170°C or lower. The pressure condition is, for example, 30 MPa or higher and 80 MPa or lower. The heat treatment time is, for example, 2 minutes or higher and 10 minutes or lower.

The thermoformed friction material may be after-cured and finished using known methods, if necessary. The after-curing conditions are not particularly limited. For example, the temperature conditions are 150°C or higher and 300°C or lower under normal pressure. The processing time is, for example, 1 hour or higher and 4 hours or lower.

Because the brake pads are made using the above-mentioned friction material, they have excellent friction characteristics and can also suppress abnormal noise (squeal) caused by friction.

Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to the following examples. Furthermore, unless otherwise specified in the following description, "parts" and "%" are based on mass. Note that specific numerical values for blending ratios (content ratios), physical properties, parameters, etc. used in the following description can be substituted with the corresponding upper limit values (numeric values defined as "equal to or less than") or lower limit values (numeric values defined as "equal to or greater than" or "exceeding") of the blending ratios (content ratios), physical properties, parameters, etc. described in the "Description of the Invention" above.

<Synthesis of lignins>
Production Example 1 (Mn200-PEG-modified lignin)
Lignin modified with polyethylene glycol having a number average molecular weight of 200 (hereinafter referred to as Mn200-PEG-modified lignin) was produced by the following method.

Specifically, 230 parts by weight of commercially available polyethylene glycol (PEG200) with a number-average molecular weight of 200 and 0.69 parts by weight of sulfuric acid as an acid catalyst (0.3 parts by weight per 100 parts by weight of PEG200) were placed in a reaction vessel and stirred.

Next, 46 parts by mass of bone-dry cedar wood flour was added to the reaction vessel, the temperature was raised to 140°C under normal pressure, and the mixture was allowed to react for 90 minutes while stirring.

The reaction vessel was then cooled, and after confirming that the temperature had dropped to 40°C or below, 280 parts by mass of sodium hydroxide (0.2 mol/L) was added and stirred for 30 minutes.

The resulting solid component (pulp) was then removed using a filter press, and the solution component was recovered.

Next, sulfuric acid was added to the resulting solution components to adjust the pH to 2.0. This resulted in a suspension of Mn200-PEG-modified lignin.

The Mn200-PEG-modified lignin was then recovered by centrifugation.

Production Example 2 (Mn400-PEG-modified lignin)
An Mn400-PEG-modified lignin was obtained in the same manner as in Production Example 1, except that polyethylene glycol having a number average molecular weight of 400 (hereinafter, Mn400-PEG) was used instead of polyethylene glycol having a number average molecular weight of 200.

Production Example 3 (Mn600-PEG-modified lignin)
An Mn600-PEG-modified lignin was obtained in the same manner as in Production Example 1, except that polyethylene glycol having a number average molecular weight of 600 (hereinafter, Mn600-PEG) was used instead of polyethylene glycol having a number average molecular weight of 200.

Production Example 4 (Acetic Acid Modified Lignin)
100 parts by weight of corn stover was mixed with 1,000 parts by weight of 95% acetic acid and 3 parts by weight of sulfuric acid and reacted under reflux for 4 hours. After the reaction, the mixture was filtered to remove the pulp and recover the pulp waste liquid. Next, the acetic acid in the pulp waste liquid was removed using a rotary evaporator, and the liquid was concentrated to 1/10 of its original volume. After that, 10 times the amount (by weight) of water was added to the concentrated liquid, and the mixture was filtered to obtain acetic acid-modified lignin as a solid.

<Synthesis of novolac phenolic resin>
Synthesis Example 1 (PEG200 Lignin-Novolac Resin)
493.5 g of phenol was placed in a flask and heated to about 50° C. to liquefy the phenol, after which 150 g of Mn200-PEG modified lignin was added.

Next, 7.62 g of oxalic acid (acid catalyst) and 117.3 g of paraformaldehyde were added, and the mixture was reacted at 95°C for 2.5 hours. The temperature was then raised to 110°C at 0.5°C/min, and the mixture was reacted at 110°C for 1.5 hours. The temperature was then raised to 120°C at 0.5°C/min, and the mixture was reacted at 120°C for 2 hours.

After the reaction, 2,300 g of water was added, and the mixture was stirred vigorously and then allowed to stand. The water was then removed by decantation to remove the oxalic acid and phenol. Furthermore, the mixture was subjected to vacuum distillation at 120°C and 0.08 MPa while adding water as needed to remove residual phenol. Vacuum distillation was repeated until the residual phenol rate was reduced to 1% or less.

This resulted in a novolac-type phenolic resin modified with Mn200-PEG-modified lignin (PEG200 lignin-novolac resin).

Synthesis Example 2 (PEG400 Lignin-Novolac Resin)
Instead of the Mn200-PEG-modified lignin, 150 g of Mn400-PEG-modified lignin was used. The remaining operations were the same as in Synthesis Example 1. As a result, a novolac-type phenolic resin modified with Mn400-PEG-modified lignin (PEG400 lignin-novolac resin) was obtained.

Synthesis Example 3 (PEG600 Lignin-Novolac Resin)
Instead of the Mn200-PEG-modified lignin, 150 g of Mn600-PEG-modified lignin was used. The remaining operations were the same as in Synthesis Example 1. As a result, a novolac-type phenolic resin modified with Mn600-PEG-modified lignin (PEG600 lignin-novolac resin) was obtained.

Synthesis Example 4 (Lignin acetate-novolac resin)
Instead of the Mn200-PEG-modified lignin, 150 g of acetic acid lignin was used. The remaining operations were the same as in Synthesis Example 1. As a result, a novolac-type phenolic resin modified with acetic acid lignin (acetic acid lignin-novolac resin) was obtained.

Synthesis Example 5 (Unmodified Novolak Resin)
846 g of phenol, 13.02 g of oxalic acid (acid catalyst), and 172.5 g of paraformaldehyde were placed in a flask and reacted at 95° C. for 2.5 hours. The temperature was then increased to 110° C. at a rate of 0.5° C./min and the reaction was continued at 110° C. for 1.5 hours. The temperature was then increased to 120° C. at a rate of 0.5° C./min and the reaction was continued at 120° C. for 2 hours.

After the reaction, 3030 g of water was added, and the mixture was stirred vigorously and then allowed to stand. The water was then removed by decantation to remove the oxalic acid and phenol. Furthermore, the mixture was subjected to vacuum distillation at 120°C and 0.08 MPa while adding water as needed to remove residual phenol. Vacuum distillation was repeated until the residual phenol rate was reduced to 1% or less.

This resulted in a novolac phenolic resin that was not modified with lignin (unmodified novolac resin).

<<Production of friction materials>>
Reference example 1
The following components were blended in order and kneaded with two heated rolls at 100° C. for 5 minutes to obtain a resin composition.
100 parts by mass (450 g) of PEG 200 lignin-novolac resin of Synthesis Example 1
Hexamethylenetetramine (hardening agent, manufactured by Lignite) 12 parts by mass (54 g)
Zinc stearate (mold release agent, manufactured by Wako Pure Chemical Industries, Ltd.) 1 part by mass (4.5 g)

Next, the following components were mixed in a mixer to obtain a molding material for friction material.
20 parts of the above resin composition (binder) 5 parts by weight of aramid fiber (Kevlar® Pulp 1F538 manufactured by Toray DuPont) 5 parts by weight of copper fiber (CCW-208 manufactured by Nippon Steel Wool) 5 parts by weight of acrylonitrile butadiene rubber (NBR) manufactured by JSR PN30A) 5 parts by weight of cashew particles (FF-1500 manufactured by Tohoku Kako) 10 parts by weight of barium sulfate (Sakai Chemical Industry Co., Ltd. elutriated barium sulfate BA) 45 parts by weight of graphite (SGP-100 manufactured by SEC Carbon) 10 parts by weight

The resulting friction material was then compression molded at 170°C for 15 minutes to obtain a 100mmφ disc-shaped test piece. The resulting test piece was then heat-cured (after-cured) at 180°C for 4 hours. This produced a friction material.

Examples 2 and 3 and Comparative Examples 1 and 2
A friction material was obtained in the same manner as in Example 1, except that the formulation was changed as shown in Table 1.

<<Evaluation>>
The friction materials obtained in the Reference Example, Examples and Comparative Examples were evaluated by the following methods.

(1) Friction coefficient (friction characteristics)
The friction coefficient of the friction material was determined by the following method. That is, the friction coefficient (static friction coefficient and dynamic friction coefficient) was determined using HEIDON-14 in accordance with ASTM D1894. The various conditions for determining the friction coefficient and the dimensions of the test specimen used are shown below.
Test piece: 100 mm diameter, approximately 3 mm thick disc test piece Mating material: 19 mm diameter cylinder Mating material: S45C
Test speed: 100 mm/min

(2) Maximum elongation (mechanical property)
The maximum elongation of the friction material was determined by the following method. That is, a three-point bending test was performed in accordance with JIS K6911 (1995) at a crosshead speed of 3 mm/min and a span of 100 mm, and the maximum elongation was measured. The maximum elongation is the strain (maximum elongation) when the friction material is bent until it breaks, and was calculated using the following formula.

Maximum point elongation (ε) = [6T/L ² ] x ΔL
(T: thickness of sample, L: distance between supporting points, ΔL: amount of bending deflection)

(3) tanδ (flexibility)
The tan δ of the friction material at 200°C was determined by the following method. Specifically, solid dynamic viscoelasticity was measured using Rheogel-E4000 (manufactured by UBM Corporation) (frequency 1 Hz, temperature rise rate 2°C/min). The measurement mode was bending, and the measurement temperature range was room temperature (20°C) to 300°C. The tan δ value at 200°C was then determined from the tan δ curve. Note that tan δ is an index of flexibility. It was determined that the larger the tan δ value, the higher the flexibility, and the more capable of suppressing vibration and abnormal noise.

Claims (2)

A friction material containing a binder,
The binder is
Lignin modified with polyethylene glycol;
Phenols and
Contains reaction products with aldehydes ,
The friction material is characterized in that the number average molecular weight of the polyethylene glycol is 400 or more . The friction material according to claim 1, wherein the lignin is softwood lignin.