Lightweight rubber and rubber molded article

Abstract

To provide a lightweight rubber in which fibers are uniformly dispersed in the rubber, and which has high strength and rigidity.SOLUTION: A lightweight rubber has a density of 1.0 g / cm3 or less and contains micronized wholly aromatic polyamide fibers having a specific surface area of 30 m2 / g or more and 300 m2 / g or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a lightweight rubber having a low density and a rubber molded body formed therefrom.

Background Art

[0002] Conventionally, in order to improve the mechanical properties of a rubber molded body, it has been studied to compound short fibers such as cellulose fibers, nylon fibers, polyester fibers, and aramid fibers into the rubber to reinforce the rubber molded body. Among these short fibers, short aramid fibers are widely used because they are excellent in mechanical properties, fatigue resistance, heat resistance, and chemical properties.

[0003] However, since the surface of short aramid fibers is relatively inert, the adhesive force with the rubber to be reinforced is low, and the dispersibility when compounded into the rubber is poor. Therefore, the original excellent properties of short aramid fibers cannot be fully exhibited.

[0004] Even when short aramid fibers are compounded into the rubber, the short aramid fibers are not completely uniformly distributed in the molded body. Therefore, wear progresses from the portion where the short aramid fibers do not exist, and sufficient wear resistance cannot be obtained.

[0005] Generally, as a means for improving the adhesive force between the reinforcing short fibers and the rubber, the fiber diameter of the reinforcing short fibers is made thinner, or fibrils are provided on the surface of the reinforcing short fibers to use them as refined short fibers, thereby increasing the contact area between the reinforcing short fibers and the rubber.

[0006] For example, Patent Document 1 discloses a rubber molded body using aramid nanofibers having an average fiber diameter of 500 nm or less. Patent Document 2 discloses a rubber molded body using existing refined cellulose fibers or refined aramid fibers. Patent Document 3 discloses a rubber molded body using cellulose nanofibers.

[0007] By adding such reinforcing fibers, the physical strength and chemical stability of the rubber molded body are improved, but the weight of the rubber or the rubber molded body has not been intensively studied so far. Therefore, an operator using the rubber molded body has to choose either to endure the heavy rubber molded body or to use a resin molded body that is lighter than the rubber molded body but has reduced strength.

[0008] As a method for reducing the weight of the rubber molded body, there is a method of adding a foaming agent and causing foaming inside the rubber molded body to reduce the density. However, in a rubber molded body to which short reinforcing fibers are added, the short reinforcing fibers in the rubber molded body inhibit the formation of uniform foaming, and thus foaming unevenness occurs. This unevenness becomes a defect, and a sufficient reinforcing effect is not exhibited.

[0009] As another method for reducing the weight of the rubber molded body, there is a method of adding a filler having a low specific gravity to the rubber. For example, Patent Document 3 discloses a method of adding porous polyester resin powder as a rubber compounding agent. In this method, the strength of the molded body decreases due to the addition of the filler. Further, when short reinforcing fibers are contained, the filler and the short reinforcing fibers adhere to each other, the dispersibility of the short reinforcing fibers in the rubber decreases, and the performance of the rubber molded body deteriorates.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0011] In the present invention, even in lightweight rubber with low density, uniform dispersion of fibers within the rubber is achieved, thereby providing lightweight rubber with high strength and rigidity.

Means for Solving the Problems

[0012] As a result of intensive studies, the inventor has found that the above problems can be solved by using finely divided wholly aromatic polyamide fibers having a specific specific surface area. That is, the present invention is a lightweight rubber having the following density, and contains finely divided wholly aromatic polyamide fibers having a specific surface area of 30 m 3 / g or more and 300 m 2 / g or less. 2 It is a lightweight rubber characterized by containing finely divided wholly aromatic polyamide fibers.

Advantages of the Invention

[0013] According to the present invention, even in lightweight rubber with low density, uniform dispersion of fibers within the rubber is achieved, thereby enabling the provision of lightweight rubber with high strength and rigidity.

Modes for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in detail.

[0015] 〔Finely Divided Wholly Aromatic Polyamide Fibers〕 The finely divided wholly aromatic polyamide fibers are wholly aromatic polyamide fibers having a specific surface area of 30 m 2 / g or more and 300 m 2 / g or less, preferably 30 m 2 / g or more and 100 m 2 / g or less. If the specific surface area is less than 30 m 2 / g, when a filler with low density is used in combination, the dispersibility of the finely divided wholly aromatic polyamide fibers in the lightweight rubber will be low. Also, when a foaming agent is used in combination, uniform foaming will be inhibited, and sufficient strength and elastic modulus of the molded body cannot be obtained. On the other hand, 300 m 2When it exceeds / g, it becomes difficult to disperse the fibers during the rubber kneading. In addition, the rubber reinforcement performance of the micronized wholly aromatic polyamide fiber itself will decline.

[0016] When the specific surface area is 30 m 2 / g or more and 300 m 2 / g or less, the micronized wholly aromatic polyamide fibers in the rubber are uniformly dispersed, and the original rubber reinforcement performance of the micronized wholly aromatic polyamide fibers is expressed. Also, when the specific surface area is 30 m 2 / g or more and 100 m 2 / g or less, it is difficult to inhibit uniform foaming even when a foaming agent is added. Furthermore, the fiber dispersion during rubber kneading is good, and the reinforcement effect is not impaired, so the balance is good.

[0017] Examples of the micronized wholly aromatic polyamide fibers include aramid nanofibers and aramid fibrils.

[0018] Aramid nanofibers are aramid fibers with a fiber diameter refined to the nanometer level. These aramid nanofibers can be produced by known methods using wholly aromatic polyamide fibers.

[0019] For example, like ACS Nano 2011, 5, 6945. and RSC Adv. 2014, 4, 40377., by treating in a dimethyl sulfoxide solvent containing potassium hydroxide respectively or by subjecting alkali-treated aramid fibers to high-pressure water spray treatment, nano-sized wholly aromatic aramid fibers, that is, aramid nanofibers can be obtained. These aramid nanofibers can also be obtained by the electrospinning method.

[0020] Aramid fibrils can be obtained by fibrillating a dope of wholly aromatic polyamide using a jet spinning nozzle under a gas flow. Since the dope, which is a solution of an aramid polymer, shows a low kinematic viscosity, it can be spun at a temperature below 60°C, preferably at room temperature.

[0021] Aramid fibrils can also be obtained by treating wholly aromatic polyamide fibers under high shear force. Examples of the method of treating under high shear include the method of beating with a stone mill refiner (manufactured by Masuoka Sangyo Co., Ltd., Hyper Mascoloider MKZA-20JA), and the method of beating with a high-pressure homogenizer (manufactured by Koshuichi Co., N-2000 110).

[0022] The micronized wholly aromatic polyamide fibers are preferably contained in an amount of 0.1 to 20 parts by mass, more preferably 0.5 to 20 parts by mass, based on 100 parts by mass of the rubber in the lightweight rubber. When the content is less than 0.1 part by mass, a sufficient reinforcing effect cannot be exhibited, which is not preferable. On the other hand, when it exceeds 20 parts by mass, it becomes difficult to sufficiently disperse the micronized wholly aromatic polyamide fibers during rubber kneading, and a sufficient reinforcing effect cannot be exhibited, which is not preferable.

[0023] 〔Wholly aromatic polyamide fiber〕 Specific examples of the wholly aromatic polyamide fiber used as the raw material for the micronized wholly aromatic polyamide fiber include polyparaphenylene terephthalamide fiber (for example, "Twaron" manufactured by Teijin Aramid B.V.), which is a para-type wholly aromatic polyamide fiber, copolyparaphenylene·3,4'-oxydiphenylene·terephthalamide fiber (for example, "Technora" manufactured by Teijin Limited), which is a copolymer-type aromatic polyamide fiber, and polymetaphenylene isophthalamide fiber (for example, "Conex" manufactured by Teijin Limited), which is a meta-type wholly aromatic polyamide fiber. Among the wholly aromatic polyamide fibers, para-type wholly aromatic polyamide fibers and copolymer-type aromatic polyamide fibers are preferably used because of their high strength and modulus of elasticity.

[0024] 〔Lightweight rubber〕 The lightweight rubber of the present invention has a density of 1.0 g / cm 3 Hereinafter, preferably 0.9 g / cm 3 Hereinafter, more preferably 0.8 g / cm 3 Hereinafter, particularly preferably 0.8 g / cm 3 Hereinafter. When the density is 1.0 g / cm3 By being as follows, it is possible to reduce the weight of a rubber molded body using lightweight rubber, such as a tire or a transmission belt. The lower limit of the density of the lightweight rubber is, for example, 0.1 g / cm 3 , and further, for example, 0.2 g / cm 3 , and particularly, for example, 0.3 g / cm 3 .

[0025] [Rubber] As the rubber for producing lightweight rubber, unvulcanized rubber or uncrosslinked rubber can be used. Specifically, natural rubber (NR) before vulcanization, styrene-butadiene rubber (SBR), nitrile rubber (NBR), polyisoprene rubber (IR), butadiene rubber (BR), butyl rubber (IIR), ethylene-propylene rubber (EPM), chloroprene rubber (CR), acrylic rubber (ACM), silicone rubber (Q), fluororubber (FKM) can be exemplified. A plurality of types of these rubbers may be used.

[0026] [Additive] The lightweight rubber may contain a foaming agent, a resin filler with a low specific gravity, etc. as an additive for weight reduction. When a foaming agent is contained, when the rubber composition obtained by adding and kneading the foaming agent to the rubber is pressurized and heated, a rubber molded body whose weight is reduced by the foaming of the foaming agent can be obtained.

[0027] Examples of the foaming agent include sodium bicarbonate, ammonium carbonate, nitrous acid, ammonium, calcium azide, magnesium carbonate, ferrous oxalate, ammonium persulfate, sodium borohydride, azodicarbonamide, azobisformamide, azobisisobutyronitrile, diazobenzene, N,N'-dinitrosopentamethylenetetramine, N,N'-dimethyl N,N'-dinitroterephthalamide, benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, p,p'-oxybisbenzenesulfonyl hydrazide.

[0028] These foaming agents may be used in combination with a foaming aid. Examples of the foaming aid include carboxylic acids such as oxalic acid and citric acid, zinc compounds such as zinc chloride and zinc acetate, mercury compounds, and lead compounds such as barium stearate and lead acetate.

[0029] As a resin filler with a low specific gravity, a filler made of a thermosetting resin containing a large number of small bubbles can be used. Specifically, as this resin filler, an aqueous solution of a base is dispersed in an oil phase composed of an unsaturated polyester and a polymerizable monomer, and the dispersion is redispersed in an aqueous solution of a suspension stabilizer and crosslinked and cured, and this is dried to obtain a porous polyester resin powder that can be used.

[0030] [Rubber precursor containing micronized wholly aromatic polyamide fiber] The rubber molded article obtained by molding the lightweight rubber of the present invention is a rubber precursor that is an unvulcanized and uncrosslinked rubber containing micronized wholly aromatic polyamide fibers having a specific surface area of 30 m 2 / g or more and 300 m 2 / g or less, and can be produced by first producing a rubber precursor and then vulcanizing and crosslinking this rubber precursor into a desired shape.

[0031] The micronized wholly aromatic polyamide fibers are usually obtained in the form of an aqueous dispersion. When this is dried, it aggregates and becomes difficult to disperse in the rubber. Therefore, the micronized wholly aromatic polyamide fibers and the rubber latex are mixed and dried to a state containing a small amount of moisture to obtain a rubber precursor. Details of this method are described in Patent Easy Document 1.

[0032] Alternatively, an aqueous dispersion of micronized wholly aromatic polyamide fibers and a rubber latex are stirred and mixed, and the mixed solution is sprayed and dried in an atmosphere of a shock wave by pulse combustion to obtain a rubber precursor. In this method, by previously mixing the micronized wholly aromatic polyamide fibers and the rubber latex, rubber adheres to the surface of the micronized wholly aromatic polyamide fibers, and aggregation of the micronized wholly aromatic polyamide fibers can be suppressed.

Examples

[0033] Hereinafter, the present invention will be described in more detail with reference to Examples. The evaluation methods used in the Examples are as follows. Note that "wt%" means "weight %".

[0034] (1) Specific surface area of fibers A sample for measuring the specific surface area was obtained by heating and drying an aqueous dispersion containing the micronized wholly aromatic polyamide fibers in an oven at 120°C. The specific surface area of the obtained sample was measured using a flow-type automatic specific surface area measuring device (manufactured by Shimadzu Corporation, FlowSorbIII).

[0035] (2) Density of vulcanized rubber sheet The vulcanized rubber sheet was cut into a 5 cm × 5 cm rectangle, and the thickness and weight of the obtained rubber sheet were measured. The density was calculated from the volume and weight.

[0036] (3) Fiber dispersibility in vulcanized rubber sheet The cross-section of the vulcanized rubber sheet was cut, and a photograph magnified with an optical microscope (magnification: 300 times) was visually observed to visually determine the dispersion state of the micronized wholly aromatic polyamide fibers according to the following criteria. A No lumps due to poor dispersion are observed at all. B Slight lumps of poor dispersion are confirmed. C Poor dispersion of fibers is seen throughout the rubber sheet.

[0037] (4) Tensile strength of vulcanized rubber sheet For the vulcanized rubber sheet, a sample was cut out in the orientation direction of the fiber material, and a tensile test was carried out by the method using a dumbbell-shaped No. 3 according to JIS K6251, and the stress at break was measured. The higher these stresses are, the better the strength.

[0038] (5) Stress at 10% elongation of vulcanized rubber sheet In the same manner as the evaluation method in (4) above, a tensile test was carried out, and the stress at 10% elongation was measured. The higher these stresses are, the better the elastic modulus.

[0039] [Materials 1 to 5] As materials for producing a vulcanized rubber sheet, Materials 1 to 5 described below were prepared. 〔Material 1〕 <Aramid nanofiber (microfine wholly aromatic polyamide fiber)> 202 g of Twaron (registered trademark) pulp (product number: Type 1094) manufactured by Teijin Aramid Co., Ltd. (including 50 g of solid content weight and 152 g of moisture weight), 64 g of additional water, 25 g of potassium hydroxide, and 1950 g of dimethyl sulfoxide (DMSO) were placed in a 2 L plastic container and mixed at room temperature to form a mixed solution, which was held in a dryer set at 70°C for 3 hours.

[0040] By holding the mixed solution at 70°C for 3 hours, the color of the mixed solution changed from yellow to reddish-brown, and no pulp-like substance was observed in the mixed solution. At this point, the mixed solution was returned to room temperature, and it was visually confirmed that the viscosity had increased compared to immediately after mixing.

[0041] Thereafter, a sufficient amount of water was added to this mixed solution to coagulate the aramid fiber component derived from Twaron pulp, and while removing the mixed solution of DMSO, potassium hydroxide, and water, the addition of water was continuously carried out to obtain an aggregate of the aramid fiber component. This aggregate was passed through a wet pulverizer to obtain an aqueous dispersion of aramid nanofibers. The specific surface area of the obtained aramid nanofibers was as shown in Table 1.

[0042] 〔Material 2〕 <Microfine jet spunfibrid (microfine wholly aromatic polyamide fiber)> According to the following method, a water-containing molded article made of para-type wholly aromatic polyamide fiber was obtained. 2.5 m 3 The polymerization of para-phenyleneterephthalamide (PPTA) was carried out using a 2.5 m Drais reactor. The reactor was thoroughly dried, and 1140 L of NMP / CaCl2 (N-methylpyrrolidone / calcium chloride) containing 2.5 wt% of CaCl2 was added to the reactor. Then, 27.50 kg of para-phenylenediamine (PPD) was added and dissolved at room temperature.

[0043] Thereafter, the PPD solution was cooled to 10°C, and 51.10 kg of terephthalic acid dichloride (TDC) was added. After the addition of TDC, the polymerization reaction was carried out for 45 minutes. Then, the polymer solution was neutralized with calcium oxide / NMP suspension (14.10 kg of CaO in 28 L of NMP). After the addition of the CaO suspension, the polymer solution was further stirred for at least 15 minutes. This neutralization reaction was carried out to remove hydrogen chloride (HCl) generated during the polymerization. A gel-like polymer solution with a para-phenyleneterephthalamide (PPTA) concentration of 4.5 wt% and a relative viscosity of 2.8 (in 0.25 wt% H2SO4) was obtained.

[0044] The above polymer solution was supplied to a spinning pump for feeding a spinning nozzle having 20 circular holes with a diameter of 350 μm (feeding rate 120 L / h). The spinning temperature was the ambient temperature (20°C). PPTA was spun through the nozzle into a low-pressure region. A 6 bar air jet (160 Nm 3 / h) (normal cubic meters per hour) was independently supplied in a direction perpendicular to the polymer flow to the same region where the air expands through the annular channel.

[0045] Thereafter, fibrils were coagulated in the same region (H2O / 30 wt% NMP / 1.3 wt% CaCl2) by supplying a coagulant jet (600 L / h) at an angle with respect to the direction of the polymer flow through the annular channel, and the generated fibrils were collected on a filter and washed.

[0046] Water was added to this fibril to prepare a 1 wt% concentration, thereby obtaining an aqueous dispersion of fibrils. This aqueous dispersion was subjected to three beating treatments using a high-pressure homogenizer (manufactured by Koshuichi Co., Ltd., N-2000 110) with a clearance of 100 μm and a rotation speed set at 1,500 rpm to obtain micronized jet spun fibrids (micronized wholly aromatic polyamide fibers). The specific surface area of the obtained micronized jet spun fibrids (micronized wholly aromatic polyamide fibers) was as shown in Table 1.

[0047] 〔Material 3〕 <Cellulose nanofiber> As an example of a refined fiber material other than aromatic polyamide fibers, cellulose nanofibers "trade name BiNFi-s, product number: FMa-10005" manufactured by Sugino Machine Limited were used. The specific surface area of the cellulose nanofibers was as shown in Table 1.

[0048] [Material 4] <All aromatic polyamide fiber "Tiara"> All aromatic polyamide fibers "trade name Tiara, product number KY-100S" manufactured by Daicel Chemical Industries, Ltd. were used. The specific surface area of the all aromatic polyamide fibers was as shown in Table 1.

[0049] [Material 5] <All aromatic polyamide fiber "Twaron (registered trademark) pulp"> Twaron (registered trademark) pulp (product number: type 1094) manufactured by Teijin Aramid Co., Ltd. was used. The specific surface area of the Twaron (registered trademark) pulp was as shown in Table 1.

[0050] [Table 1]

[0051] [Example 1] First, an unvulcanized rubber compound described in Table 2 was prepared. Next, the aramid nanofibers of Material 1 and natural rubber latex (manufactured by Rejtex Co., Ltd., product number: ULACOL, containing 61 wt% natural rubber) were mixed and diluted with water to obtain a mixture in which the weight ratio of aramid nanofibers to natural rubber was 20:80 and the concentration of the solid content of the combined aramid nanofibers and natural rubber was 5 wt%. By heating and stirring this mixture until the water disappeared, a precursor of refined fibers and rubber was obtained.

[0052] The obtained micronized fiber material and the rubber precursor were compounded into the above unvulcanized rubber compound such that the incorporation amount of aramid nanofibers was 3.5 wt% per total weight of the fiber material, the rubber precursor, and the unvulcanized rubber compound to form a rubber mixture, and this was kneaded at 140 °C for 60 minutes using an MS pressure kneader (manufactured by Moriyama Seisakusho Co., Ltd., DS3-10MHHS) while evaporating the moisture contained in the rubber mixture to obtain a solid rubber composition. Thereafter, the obtained solid rubber composition was allowed to stand overnight and cooled.

[0053]

Table 2

[0054] To the solid rubber composition, sulfur, N-cyclohexyl-2-benzothiazolylsulfenamide as a vulcanization accelerator, and N,N'-dinitrosopentamethylenetetramine powder (manufactured by Eimei Kasei Kogyo Co., Ltd., product number Celular GX) as a foaming agent were each added in an amount of 2 wt% based on the solid rubber composition to obtain an unvulcanized rubber composition.

[0055] The unvulcanized rubber composition was sheeted out to a thickness of about 1 mm using an open roll (manufactured by Kansai Roll Co., Ltd., 9-inch test roll) to obtain a vulcanized rubber composition sheet. One sheet of this vulcanized rubber composition sheet was placed in a mold with a depth of 2 mm and pressed at 150 °C for 30 minutes under the condition of 1 MPa to vulcanize the rubber and foam the foaming agent, thereby creating a 2-mm-thick lightweight rubber sheet. The density of the obtained lightweight rubber sheet, the fiber dispersibility in the rubber, the breaking strength, and the stress at 10% elongation are shown in Table 3.

[0056]

Table 3

[0057] 〔Example 2〕 Using the micronized jet spunbonded fabric of Material 2, a lightweight rubber sheet was obtained in the same manner as in Example 1. The density of the obtained lightweight rubber sheet, the fiber dispersibility in the rubber, the breaking strength, and the stress at 10% elongation are shown in Table 3.

[0058] [Comparative Example 1] A lightweight rubber sheet was obtained in the same manner as in Example 1 without using fibers. The density, fiber dispersibility in the rubber, breaking strength, and stress at 10% elongation of the obtained lightweight rubber sheet are shown in Table 3.

[0059] [Comparative Example 2] A lightweight rubber sheet was obtained in the same manner as in Example 1 using the cellulose nanofibers of Material 3. The density, fiber dispersibility in the rubber, breaking strength, and stress at 10% elongation of the obtained lightweight rubber sheet are shown in Table 3.

[0060] [Comparative Example 3] A lightweight rubber sheet was obtained in the same manner as in Example 1 using the teara of Material 4. The density, fiber dispersibility in the rubber, breaking strength, and stress at 10% elongation of the obtained lightweight rubber sheet are shown in Table 3.

[0061] [Comparative Example 4] A lightweight rubber sheet was obtained in the same manner as in Example 1 using the Twaron (registered trademark) pulp of Material 5. The density, fiber dispersibility in the rubber, breaking strength, and stress at 10% elongation of the obtained lightweight rubber sheet are shown in Table 3.

[0062] As shown in Table 3, the lightweight rubber sheets of Examples 1 and 2 showed high fiber dispersibility in the rubber, breaking strength, and stress at 10% elongation compared to the rubber vulcanized sheets of Comparative Examples 2 to 4. Among Examples 1 and 2, the lightweight rubber sheet of Example 2 in particular showed particularly high breaking strength and stress at 10% elongation.

Industrial Applicability

[0063] The lightweight rubber of the present invention can be used as a rubber molded body for various applications such as tires, power transmission belts, underwater clothing, rubber packings, oil seals, various sealing materials such as waterstops, vehicle buffers, vibration-proof rubbers, and sound-proof rubbers.

Claims

1. A density of 1.0 g / cm ３ The following lightweight rubber, having a specific surface area of 30 m ２ / g or more and 300 m ２ / g or less, and containing a micronized wholly aromatic polyamide fiber. A lightweight rubber characterized by containing the same.

2. The lightweight rubber according to claim 1, wherein the amount of the micronized wholly aromatic polyamide fiber is 0.1 to 20 parts by mass with respect to 100 parts by mass of the rubber in the lightweight rubber.

3. A rubber molded article using the lightweight rubber according to claim 1 or 2.

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