JP2009120986A - Fiber aggregate and friction material using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fibrillated fiber suitable for improving mechanical strength in the thickness direction of wet friction material. <P>SOLUTION: The fibrillated fiber aggregate has fibrils that are composed of an organic high-molecular polymer and has a fibril diameter of 1 μm or less. The fibrillated fiber aggregate satisfies the following requirements of (a) among fibers constituting the fiber aggregate, the content of crimped fibers has one or more pairs of crimped ridges and valleys in main fibers represented by the following formula: the crimped fiber content =N<SB>c</SB>/N<SB>0.5</SB>×100 is 20% or more (wherein N<SB>c</SB>is the number of crimped fibers having one or more pairs of crimped ridges and valleys in the main stem fibers; N<SB>0.5</SB>is the number of total fibers having a fiber length of 0.5 mm or more), and (b) a specific surface area of fiber aggregate is 3-20 m<SP>2</SP>/g. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fibrillated fiber assembly including fibers having fibrils of 1 μm or less used for applications such as high-performance paper, and a wet friction material using the same.

  Conventionally, fibrillated aramid fiber has high strength and high heat resistance, so it can be used as a substitute for asbestos such as dry friction materials such as brake pads and brake linings, wet friction materials such as clutch facings of automatic transmissions, and reinforcing fibers for sealing materials such as gaskets. Widely used as a material. Particularly in wet friction material applications, as disclosed in, for example, Japanese Patent Publication No. 58-47345 (Patent Document 1) and Japanese Patent Application Laid-Open No. 11-201206 (Patent Document 2), a fibrous material and a friction modifier, A paper-like base material is obtained by making various inorganic fillers such as a solid lubricant, impregnated with a binder resin such as a phenol resin, and heated and cured.

  Although aramid fiber itself is a fiber material with excellent mechanical strength such as tensile strength, paper-like materials made of fibrillated aramid fibers generally do not have chemical bonds and form a fiber network by entanglement of fine fibrils. Therefore, the mechanical strength of the paper-like material greatly depends on the strength of entanglement.

  On the other hand, due to the recent increase in the output of automobile engines and downsizing of transmissions, demands on the mechanical strength, particularly shear strength, of wet friction materials have become strict. A wet friction material is made by impregnating a paper binder obtained by making a base fiber such as pulp or aramid fiber and a filler such as a friction modifier or a body filler with a resin binder made of a thermosetting resin and heating it. It is formed by curing and is not only lightweight and inexpensive, but also has a high oil absorbability due to its porous nature and high elasticity, and it is also relatively excellent in heat resistance, wear resistance, etc. This paper friction material is widely used because of its features. However, since the fibers are deposited in a two-dimensional plane like a papermaking method to form a sheet, although the network in the plane direction is strong, the paper thickness direction is relatively weak, and when a large shear force is applied, it is between paper fibers. Peeling occurred and its mechanical strength was not sufficient.

  In addition, in the wet friction material, a high friction coefficient is obtained by applying a high pressure while being immersed in oil, and a large amount of heat is generated by friction. In the wet friction material, this heat is cooled using oil as a medium, and a friction material having a high porosity as the friction material and high oil permeability is desired. However, when the porosity is increased, the mechanical strength is further reduced, resulting in a dilemma.

  In contrast, in Japanese Patent Laid-Open No. 2003-147335 (Patent Document 3), acrylic chopped fibers having curls are added to achieve porosity, but there is little entanglement between acrylic fibers and shear in the thickness direction. There was a problem that it was not sufficient with respect to stress, and acrylic fibers were softened and melted by frictional heat and could not maintain their form.

Japanese Examined Patent Publication No. 58-47345 Japanese Patent Laid-Open No. 11-201206 JP 2003-147335 A

  To provide a fibrillated fiber assembly suitable for improving the mechanical strength in the thickness direction of a wet friction material.

  As a result of intensive studies, the inventor gives fibrils by refining or the like to fibers made of a specific organic polymer, so that the main fibers have one or more crimped mountain valleys (including crimped fibrillated fibers). (It may be abbreviated in some cases).

Furthermore, when the inventor used the fibrillated fiber assembly containing the crimped fibrillated fiber as a raw fiber of the wet friction material, a wet friction material having high mechanical strength and good oil permeability was obtained. I found out that That is, according to the present invention,
A fibrillated fiber assembly that includes the fibrillated fibers having a fibril of 1 μm or less made of an organic high molecular polymer satisfies the following requirements.
a) The content rate represented by the following formula of the crimped fiber having at least one crimped mountain valley in the main fiber among the fibers constituting the fiber assembly is 20% or more.
Crimp-containing fiber content = N _c / N _0.5 × 100
here,
_Nc : Number of crimped crimped fibers having one or more crimped mountain valleys in the main fiber N0.5; Total number of fibers of _0.5 mm or more
b) The specific surface area of the fiber assembly is 3 to ²⁰ m ² / g.

In a fiber assembly including a fibrillated fiber made of an organic polymer having high heat resistance and having a fibril of 1 μm or less, a fibrillated fiber having a crimped mountain valley as shown in FIGS. By making a fibrillated fiber aggregate containing a specific amount, not only fine fibrils but also thick main fibers contribute greatly to inter-fiber entanglement, so it becomes useful for wet friction materials with excellent mechanical strength. . Further, the fibrillated fiber aggregate is high in wet papermaking paper obtained by papermaking method, etc., and maintains a large porosity, so that the liquid permeability of oil is good.
Therefore, by including the fibrillated fiber assembly of the present invention, a wet friction material having both mechanical strength and porosity can be obtained.

  The fibrillated fiber assembly referred to in the present invention is a fiber assembly including a fibrillated fiber having a fibril diameter of 1 μm or less made of an organic polymer (preferably an aromatic polyamide resin), and is partially fibrillated. If the specific surface area is in a specific range, a fibrillated fiber assembly is obtained.

  As the organic polymer in the present invention, a liquid crystalline polymer having a high degree of molecular orientation is preferable, and aromatic polyamide, aromatic polyester, and polybenzazole can be particularly preferably used. These liquid crystalline polymers are suitable in terms of mechanical strength, heat resistance, and ease of fibrillation. Those obtained by fiberizing these organic polymer polymers by a known method can be used.

  As aromatic polyamide fiber, poly-p-phenylene terephthalamide, poly-p-benzamide, poly-p-amide hydrazide, poly-p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide is spun into fiber. Although what can be illustrated can be illustrated, it is not limited to these.

  The aromatic polyester is synthesized by combining monomers such as aromatic diol, aromatic dicarboxylic acid, and aromatic hydroxycarboxylic acid, and changing the composition ratio. For example, a copolymer of p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid can be mentioned, but it is not limited to this. The aromatic polyester fiber is a fiber obtained by spinning such a polymer.

  In addition, polybenzazole fibers can be obtained by spinning a random, sequential or block copolymer with polybenzazoles containing poly-p-phenylenebenzobisoxazole (PBO) homopolymer and substantially more than 85% PBO component. It is made into fiber.

  The fibrillated fiber as used in the present invention generally means that fine fibers having a size of 1 μm or less are formed on the surface of the main fiber by dispersing a short fiber in water and treating with a known refiner, beater, mill, high-pressure homogenizer, grinding device, or the like. Although it refers to a large number of fibers, it is not limited to the above method as long as fluff is formed on the fiber surface.

The crimped fiber as used in the present invention is a fiber having one or more pairs of peaks and valleys in the main fiber, and the main fiber has two or more bending points as shown in FIG. 1 or an inflection point as shown in FIG. Means one or more. The ratio of the number Nc of the crimped crimped fibers represented by the following formula to the total number of fibers N _{0.5 having a} fiber length of 0.5 mm or more = the content is preferably 20% or more, and 25% or more. Is more preferable, and more preferably 30% or more.
Crimp-containing fiber content = N _c / N _0.5 × 100
_Nc : Number of crimped crimped fibers having one or more crimped mountain valleys in the main fiber N0.5; Total number of fibers of _0.5 mm or more

  If this ratio is less than 20%, the contribution to the inter-fiber entanglement of the main fiber is small when it is used as the raw material for the wet friction material, and not only sufficient mechanical strength is not obtained, but also the porosity is insufficient. It becomes.

Further, the specific surface area of the fibrillated fiber assembly referred to in the present invention is one of the indexes indicating the degree of fibrillation of the fibrillated fiber, and can be measured by a known specific surface area measuring device such as a BET method by adsorption of nitrogen gas. The degree of fibrillation is preferably 3 to 20 m ² / g, more preferably 8 to 15 m ² / g, in terms of specific surface area. When the specific surface area is less than 3 m ² / g, the inorganic filler is less likely to get entangled with the fiber when the papermaking method is used together with the inorganic filler and the like, resulting in poor yield.

The average curl degree C of the fibers constituting the fibrillated fiber aggregate as referred to in the present invention is calculated by the following formula, and this value is preferably 20% or more, and more preferably 25% or more.
Average curl degree C = C _0.5 / N _0.5
C _0.5 ; Sum of the following C of fibers of _0.5 mm or more N _0.5 ; Total number of fibers of _0.5 mm or more C = (l−d) / l × 100
l: Total fiber length of fiber (length without curl) (mm)
d: Distance between both ends of the fiber (mm)
C: Fiber curl degree

  When the average degree of curl of the fibers constituting the fibrillated fiber assembly is less than 20%, the contribution to the inter-fiber entanglement of the main fiber is small when the wet friction material is used, and sufficient mechanical strength is obtained. Not only is it not possible, but also the porosity is insufficient.

  The length weighted average fiber length of the fibers constituting the fibrillated fiber assembly in the present invention is preferably 0.5 to 6 mm, and more preferably 0.8 to 3 mm. When the weighted average fiber length is less than 0.5 mm, the fiber reinforcing effect is low, and when it exceeds 6 mm, the fiber dispersion in the paper making process deteriorates, which is not preferable.

As a method for producing a fibrillated fiber assembly having an average curl degree and a crimped fiber content as described above,
1) Give fibrils to fibers that have been crimped in advance. For example, short fibers cut after being crimped by a known indentation crimping method, knitted and woven, heat-set and crimped are shortened. There is a method in which a product is fibrillated by shearing with a disc refiner or the like.
2) Give crimps to fibrillated fibers For example, in a refinery process, the shear force is further increased to cause crimps on short fibers.
However, the production method is not limited as long as a certain amount of peaks and valleys can be imparted to the main fiber.

Next, a wet friction material using the fibrillated fiber will be described.
The wet friction material of the present invention can be prepared in the following steps. First, a fibrillated fiber aggregate and an inorganic filler are mixed with a dispersion medium such as water using a known disintegrator to form a slurry, and then formed into a sheet using a known paper making apparatus to prepare a paper-like material. . When producing this paper-like material, the composition ratio of the fibrous material and the inorganic filler in the paper-like material is preferably 20 to 80% by weight for the fibrillated fiber aggregate and 20 to 80% by weight for the inorganic filler. The obtained paper substrate can be impregnated with a binder resin such as a phenol resin, and pressurized and cured by hot pressing to obtain a wet friction material.

  In this invention, it is also possible to mix | blend and use another pulp component in the said fibrillated fiber assembly. Cellulose fibers such as linter pulp and wood pulp, organic fibers such as meta-aramid fibers, acrylic fibers, polyimide fibers, polyamide fibers, glass fibers, rock wool, potassium titanate fibers, silica fibers, alumina fibers, metal fibers, etc. Inorganic fibers can be used in combination as a fibrous material. As a fibrillated fiber aggregate, it is used in an appropriate amount within a range where the mechanical strength and heat resistance are not impaired.

The inorganic filler that can be used in the present invention is added for the purpose of friction adjustment and solid lubrication, for example, barium sulfate, calcium carbonate, magnesium carbonate, silicon carbide, titanium carbide, alumina, silica, cashew dust, diatomaceous earth, graphite, talc, An appropriate amount of kaolin, magnesium oxide, or the like can be used in an appropriate amount simultaneously.
Next, although an example of the manufacturing method of this invention is shown, it is not limited to this.

  The present invention will be specifically described below based on examples. The present invention is not limited to these.

<Method for measuring physical properties of fiber constituting fibrillated fiber assembly>
Measurement of average degree of curl of fiber, measurement of length-weighted average fiber length, and count of main fiber peak-valley (inflection point or inflection point) were measured using a commercially available pulp fiber length measuring device (Pulp Expert Fiber Analyzer, manufactured by Metso Automation). ) Using the following procedure.

1) The fiber is weighed in an absolute dry weight of 1.5 g and disaggregated with 1.5 L of water using a known disintegrator.
2) Add 4 sample tube disaggregation slurries of Pull Expert Fiber Analyzer in 50cc increments and start measurement.

The Pull Expert Fiber Analyzer is equipped with a microscope and a CCD camera. The fiber image is taken while stirring the fiber slurry, and the average curl and length are obtained by image analysis based on about 400 images per level. Calculate the weighted average fiber length. Counting the number of crimped fibrillated fibers N _c and the total number N _0.5 of _0.5 mm or more, randomly selected 4 images out of 400 images taken with Pull Expert Fiber Analyzer, and the fiber length The test was carried out on a fiber of 0.5 mm or more. An example of the image is shown in FIG.
The specific surface area of the fibrillated fibers was measured using a commercially available specific surface area measuring device (manufactured by Shimadzu Corporation, Flowsorb III 2310).

<Creation of fiber assembly>
[Example 1]
After creating an aqueous dispersion with a solid content concentration of 0.2 wt% using para-type aramid staple fiber (Teijin Techno Products, Twaron 1072 cut length = 50 mm crimp number 8.4 pcs / inch), an existing disc refiner ( Using Kumaya Riki; KRK High Concentration Disc Refiner), treatment was performed under the treatment conditions of clearance = 0.02 mm and number of passes = 7 to prepare crimped fibrillated fibers. Table 1 shows the physical properties of the resulting crimped fibrillated fiber assembly.

[Example 2]
In Example 1, crimped fibrillated fibers were prepared in the same manner except that the number of passes of the disc refiner was 10. Table 1 shows the physical properties of the resulting crimped fibrillated fiber assembly.

[Example 3]
In Example 1, crimped fibrillated fibers were prepared in the same manner except that the number of passes of the disc refiner was 15. Table 1 shows the physical properties of the resulting crimped fibrillated fiber assembly.

[Example 4]
Para-aramid long fiber filaments (Teijin Techno Products, Twaron 1000) were knitted in a knitted sheet, then heat-set at 250 ° C for 10 minutes, and the knitted fabric was knitted to form para-aramid long fiber filaments. Shrinkage was given. Thereafter, this long fiber filament was cut into a cut length of 10 mm using a guillotine cutter, and subjected to a disc refiner treatment in the same manner as in Example 1 to produce a crimped fibrillated fiber. Table 1 shows the physical properties of the resulting crimped fibrillated fiber assembly.

[Comparative Example 1]
Para-aramid long fiber filaments were cut to a cut length of 50 mm using a guillotine cutter to produce short fibers without crimps, and subjected to a disc refiner treatment in the same manner as in Example 1 to produce fibrillated fibers. Table 1 shows the physical properties of the resulting fibrillated fiber assembly.

[Comparative Example 2]
In Comparative Example 1, fibrillated fibers were prepared in the same manner except that the number of passes of the disc refiner was 10. Table 1 shows the physical properties of the resulting fibrillated fiber assembly.

[Comparative Example 3]
In Comparative Example 1, fibrillated fibers were prepared in the same manner except that the number of passes of the disc refiner was set to 15. Table 1 shows the physical properties of the resulting crimped fibrillated fiber assembly.

[Comparative Example 4]
Para-type aramid filament filament (Teijin Techno Products, Twaron 1000) was cut to a cut length of 10 mm using a guillotine cutter, and subjected to a disc refiner treatment in the same manner as in Example 1 to prepare a fibrillated fiber. Table 1 shows the physical properties of the resulting fibrillated fiber assembly.

[Comparative Example 5]
The para-aramid fiber staple fiber used in Example 1 was cut into 2 mm with a known guillotine cutter, and a short fiber having crimps such as a disc refiner that was not fibrillated was prepared. The physical properties of the obtained short fiber aggregate are shown in Table 1.

[Comparative Example 6]
The crimped fibrillated fiber assembly prepared in Example 1 and the short fiber assembly prepared in Comparative Example 5 were mixed at a weight ratio of 2: 1 to prepare a fiber assembly. Table 1 shows the physical properties of the obtained fiber assembly.

<Create friction material>
[Example 5]
50 parts by weight of the fibrillated fiber of Example 1 and 50 parts by weight of diatomaceous earth (trade name “Radiolite # 200” manufactured by Showa Chemical Industry Co., Ltd.) are added to 2 L of water, and this is added using a JIS standard disintegrator. The slurry was disaggregated at 3000 rpm for 3 minutes to obtain a slurry. Further, this slurry was made with a TAPPI square paper machine, press dehydrated, and then dried with a dryer at 120 ° C. for 2 hours to obtain a paper-like material having a basis weight of 250 g / m ² .

Next, the obtained paper-like product was immersed in a phenol resin methanol solution having a concentration of 16% by weight by diluting a liquid phenol resin (product number PR-53123, manufactured by Sumitomo Bakelite Co., Ltd.) with methanol, and the phenol resin. And then dried at room temperature for 24 hours to obtain a prepreg. Further, this prepreg was pressed with a pressing machine at a surface pressure of 60 kg / cm ² at 180 ° C. for 5 minutes and further cured in an oven at 180 ° C. for 2 hours, whereby fibrillated fiber / inorganic filler / binder resin = 38. A friction material sample having a composition of 0.5 / 38.5 / 23.0 (weight ratio) was obtained.

[Example 6]
In Example 5, a friction material sample was prepared in the same manner except that the fibrillated fiber assembly of Example 2 was used instead of the fibrillated fiber assembly of Example 1.

[Example 7]
A friction material sample was prepared in the same manner as in Example 5 except that the fibrillated fiber fiber assembly of Example 3 was used instead of the fibrillated fiber fiber assembly of Example 1.

[Example 8]
A friction material sample was prepared in the same manner as in Example 5 except that the fibrillated fiber fiber assembly of Example 4 was used instead of the fibrillated fiber fiber assembly of Example 1.

[Comparative Example 7]
A friction material sample was prepared in the same manner as in Example 5 except that the fibrillated fiber fiber assembly of Comparative Example 1 was used instead of the fibrillated fiber fiber assembly of Example 1.

[Comparative Example 8]
A friction material sample was prepared in the same manner as in Example 5 except that the fibrillated fiber fiber assembly of Comparative Example 2 was used instead of the fibrillated fiber fiber assembly of Example 1.

[Comparative Example 9]
A friction material sample was prepared in the same manner as in Example 5 except that the fibrillated fiber fiber assembly of Comparative Example 3 was used instead of the fibrillated fiber fiber assembly of Example 1.

[Comparative Example 10]
A friction material sample was prepared in the same manner as in Example 5 except that the fibrillated fiber fiber assembly of Comparative Example 4 was used instead of the fibrillated fiber fiber assembly of Example 1.

[Comparative Example 11]
In Example 5, a similar method was used except that instead of the fibrillated fiber fiber assembly of Example 1, the para-aramid fiber staple fiber of Comparative Example 5 was cut to 2 mm and without fibrillation treatment. A friction material sample was prepared.

[Comparative Example 12]
In Example 5, a friction material sample was prepared in the same manner except that the short fiber aggregate of Comparative Example 6 was used instead of the fibrillated fiber fiber aggregate of Example 1.

<Evaluation of physical properties of friction material>
Friction material peel resistance was evaluated by using a commercially available friction wear tester (Orientec Co., Ltd., EFM-III-EN / F) with a tripod ring indenter (hard chrome plated bearing steel, outer diameter 25.4 mm, inner diameter 20 mm) was attached, and the legs were rotated while being pressed against the friction material sample, and the number of rotations until the friction material sample surface peeled was counted. The test conditions at this time were a load of 6 kgf and normal temperature oil at 100 rpm. FIG. 4 shows the state of the test method.

The oil permeability was evaluated by dropping about 0.1 cc of Automatic Transmission Fluid (ATF) onto the friction material sample surface with a dropper, and measuring the number of seconds until ATF penetrated the back surface of the dropping surface.
Table 2 shows the peel resistance and oil permeability evaluation results. In addition, a numerical value is an average value of what was evaluated with N number = 5.

  The fibrillated fibers of Examples 1 to 4 were subjected to a fibrillation treatment on fibers that had been crimped in advance, thereby comparing with Comparative Examples 1 to 4 (using short fibers having fibrils but not crimped). The ratio of fibers having peaks and valleys in the main fiber became large. Comparative Example 5 deviates from the present invention that has crimps but is not fibrillated, and Comparative Example 6 is a mixture of crimped fibrillated fibers and crimped fibers without fibrils, and is contained as an aggregate. The content of crimped fibrillated fibers is outside the scope of the present invention.

  Moreover, when friction material Examples 5-8 were created using these and the peeling resistance by the shear force was evaluated, peeling resistance and oil-liquid permeability improved compared with Comparative Examples 5-11. This is presumably because the fibrillated fibers have one or more crimped troughs in the main fiber to form a three-dimensional network and strengthen the entanglement between the fibers in the friction material. In addition, regarding the oil permeability, it is considered that the friction material can be reduced in density by having one or more crimped troughs of the main fiber, and the number of through pores through which oil permeates has increased. In Comparative Example 10, it is considered that the fibrillation is not progressing, the specific surface area is small and the average curl degree is also small, so that the entanglement between the fibers is insufficient. In Comparative Example 11, it is considered that the content of those containing crimped fibrillated fibers is small and the entanglement effect is not obtained, and the wear resistance and oil permeability are lowered.

  According to the present invention, a paper-like material having high entanglement strength between fibers can be obtained even at a low density, a friction material for an automatic transmission such as an automobile or the like that requires a large shear force and a low density, and a lock-up. Effective for improving durability of friction materials for clutches and friction materials for synchronizer rings for manual transmissions.

Schematic diagram of fibrillated fibers with Yamatani crimps (Shariya is sharp). Schematic diagram of fibrillated fibers with Yamatani crimp (smooth Yamatani). An example of an image taken by a Pull Expert Fiber Analyzer (an example of a fibrillated fiber having a crimped mountain valley). Peel resistance test method.

Claims (6)

A fibrillated fiber assembly comprising a fibrillated fiber having a fibril of 1 μm or less made of an organic polymer, wherein the fibrillated fiber assembly satisfies the following requirements.
a) The content rate represented by the following formula of the crimped fiber having at least one crimped mountain valley in the main fiber among the fibers constituting the fiber assembly is 20% or more.
Crimp-containing fiber content = N _c / N _0.5 × 100
here,
_Nc : Number of crimped crimped fibers having one or more crimped mountain valleys in the main fiber N0.5; Total number of fibers of _0.5 mm or more
b) The specific surface area of the fiber assembly is 3 to ²⁰ m ² / g. The fibrillated fiber assembly according to claim 1, wherein an average curl degree C represented by the following formula of the fibers constituting the fiber assembly is 20% or more.
Average curl degree C = C _0.5 / N _0.5
C _0.5 ; Sum of the following C of fibers of _0.5 mm or more N _0.5 ; Total number of fibers of _0.5 mm or more C = (l−d) / l × 100
l: Total fiber length of fiber (length without curl) (mm)
d: Distance between both ends of the fiber (mm)
C: Fiber curl degree   The fiber assembly according to claim 1, wherein the organic polymer is an organic polymer having a carbonization or melting temperature of 300 ° C. or higher.   The fiber assembly according to any one of claims 1 to 3, wherein the organic polymer is an aromatic polyamide.   The fiber assembly according to any one of claims 1 to 4, wherein a length-weighted average fiber length of fibers constituting the fiber assembly is 0.5 to 6 mm.   A wet friction material comprising 1 to 50% by weight of the fiber assembly according to any one of claims 1 to 5.