Rubber composite, masticated product, kneaded product, crosslinked rubber composition

Abstract

The present invention provides a rubber composite material which shortens the time required for winding around a rotor. The rubber composite material comprises: a plurality of layers containing fibrous cellulose and a rubber component; and voids formed between the plurality of layers, wherein in a binarized image of a microscope image (magnification: 200 times) of a cross section of the rubber composite material including the plurality of layers if a scanning electron microscope is used, if the length of the binarized image in the vertical direction is denoted as v and mutually parallel line segments A1, A2, and A3 passing through the plurality of layers are drawn at positions of 1 / 4v, 1 / 2v, and 3 / 4v, respectively, the number of layers per 1 μm of the line segments A1, A2, and A3 is each at least 0.0100, or if the length of the binarized image in the horizontal direction is denoted as h and line segments B1, B2, and B3 orthogonal to the line segment A1 are drawn at positions of 1 / 4h, 1 / 2h, and 3 / 4h, respectively, the number of layers per 1 μm of the line segments B1, B2, and B3 is each at least 0.0100.

Description

Rubber composites, compounded products, blended products, crosslinked rubber compositions

[0001] This invention relates to rubber composites, compound products, blended products, and crosslinked rubber compositions.

[0002] In recent years, materials made from renewable natural fibers have attracted attention as an alternative to petroleum resources and due to growing environmental awareness. Among natural fibers, fibrous cellulose with a fiber diameter of 10 μm to 50 μm, particularly fibrous cellulose (pulp) derived from wood, has been widely used, mainly in paper products.

[0003] While carbon black has traditionally been used as a reinforcing agent in rubber products, particularly tire rubber products, in recent years there have been instances of fibrous cellulose being incorporated instead of carbon black.

[0004] In manufacturing rubber products from rubber compositions, methods may be employed in which the rubber composition is wound onto a rotating body such as a roll or kneader and kneaded, or mixed together with additive components.

[0005] For example, Patent Document 1 discloses an example of preparing a natural rubber masterbatch by stirring and mixing cellulose xantate and natural rubber latex. Furthermore, it discloses that the obtained masterbatch was kneaded using two rolls heated to 50°C, and then various additives were added and mixed to produce a sheet.

[0006] International Publication No. 2017 / 111103

[0007] When processing rubber compositions on a rotating body, such as during kneading and mixing with two rolls, the rubber composition is usually plasticized by applying shear force until it can wrap around the rotating body. However, because rubber compositions containing fibrous cellulose tend to increase in hardness, the time required for the rubber composition to plasticize and wrap around the rotating body is long, requiring multiple passes between the rolls, etc., and there was room for improvement from the viewpoint of the manufacturing efficiency of rubber products. The object of the present invention is to provide a rubber composite material in which the time required to wrap around a rotating body is shortened.

[0008] As a result of diligent research by the inventors, we have found that the above problems can be solved by giving the rubber composite material a specific layered structure. In other words, the present invention includes the following.

[0009] [1] A rubber composite material having a plurality of layers containing fibrous cellulose and rubber components, and voids formed between the plurality of layers, wherein in a binarized image of a microscope image (magnification 200x) of a cross-section of the rubber composite material including the plurality of layers, when the vertical length of the binarized image is v, and parallel line segments A1, A2, and A3 passing through the plurality of layers are drawn at positions 1 / 4v, 1 / 2v, and 3 / 4v, the number of layers per 1 μm of each of the line segments A1, A2, and A3 is 0.0100 or more, or when the horizontal length of the binarized image is h, and line segments B1, B2, and B3 perpendicular to line segment A1 are drawn at positions 1 / 4h, 1 / 2h, and 3 / 4h, the number of layers per 1 μm of each of the line segments B1, B2, and B3 is 0.0100 or more. [2] The rubber composite material according to [1], wherein the rubber component is natural rubber. [3] The rubber composite material according to [1] or [2], wherein the number average fiber width of the fibrous cellulose is 1000 nm or less. [4] A kneaded product of the rubber composite material according to any one of [1] to [3]. [5] A kneaded product obtained by kneading at least the kneaded product of [4] and a crosslinking agent. [6] A crosslinked rubber composition obtained by crosslinking the kneaded product according to [5]. [7] A method for producing a rubber composite material comprising the following steps (1) and (2): (1) A sheeting step to obtain a rubber sheet from a mixed liquid containing fibrous cellulose and a rubber component. (2) A multi-layering step to obtain a rubber composite material by multi-layering the rubber sheet. [8] A method for producing a kneaded product comprising step (3): (3) A kneading step to knead the rubber composite material produced by the method of [7]. [9] A method for producing a kneaded product comprising step (4). (4) A method for producing a crosslinked rubber composition, comprising a kneading step (5) of kneading a paste produced by at least the method of [8] and a crosslinking agent. (5) A crosslinking step of crosslinking a paste produced by the method of [9]

[0010] According to the present invention, it is possible to provide a rubber composite material in which the time required for wrapping around a rotating body is shortened.

[0011] This is a microscopic image of the cross-section of the dried product according to Example 4 (photograph used as a substitute for drawing). This is a microscopic image of the cross-section of the dried product according to Comparative Example 1 (photograph used as a substitute for drawing).

[0012] The present invention will be described in detail below, but the description of the constituent elements described below is just one example (representative example) of an embodiment of the present invention, and the present invention is not limited to these contents, and can be implemented in various ways within the scope of its gist. In this specification, a numerical range expressed using "~" means a range that includes the numerical values ​​written before and after "~" as the lower limit and upper limit.

[0013] One embodiment of the present invention is a rubber composite material having a plurality of layers containing fibrous cellulose and rubber components, and voids formed between the plurality of layers, wherein in a binarized image of a microscope image (magnification 200x) of a cross-section of the rubber composite material including the plurality of layers, when the vertical length of the binarized image is v, and parallel line segments A1, A2, and A3 passing through the plurality of layers are drawn at positions 1 / 4v, 1 / 2v, and 3 / 4v, the number of layers per 1 μm of each of the line segments A1, A2, and A3 is 0.0100 or more, or when the horizontal length of the binarized image is h, and line segments B1, B2, and B3 perpendicular to line segment A1 are drawn at positions 1 / 4h, 1 / 2h, and 3 / 4h, the number of layers per 1 μm of each of the line segments B1, B2, and B3 is 0.0100 or more.

[0014] In this embodiment, the rubber composite material, when a scanning electron microscope is used to obtain a binarized image of a cross-section of the rubber composite material including the plurality of layers, if the vertical length of the binarized image is v, and parallel line segments A1, A2, and A3 passing through the plurality of layers are drawn at positions 1 / 4v, 1 / 2v, and 3 / 4v, then the number of layers per 1 μm of each line segment A1, A2, and A3 is 0.0100 or more. Alternatively, if the horizontal length of the binarized image is h, and line segments B1, B2, and B3 perpendicular to line segment A1 are drawn at positions 1 / 4h, 1 / 2h, and 3 / 4h, then the number of layers per 1 μm of each line segment B1, B2, and B3 is 0.0100 or more. In a preferred embodiment, the number of layers per 1 μm of each line segment A1, A2, A3, B1, B2, and B3 is 0.0100 or more. Furthermore, it is preferable that the number of layers per 1 μm of line segments A1, A2, and A3 is 0.0150 or more. Also, it is preferable that the number of layers per 1 μm of line segments B1, B2, and B3 is 0.0150 or more. There is no particular upper limit to the number of layers per 1 μm of line segments A1, A2, A3, B1, B2, and B3, but examples include 0.0500 or less and 0.0350 or less. Within this range, the rubber composite material is appropriately multilayered, and the time required for wrapping around the rotating body when processing with a rotating body can be shortened. The number of layers per 1 μm of the line segments can be measured as follows, for example. The number of layers per 1 μm of line segments A1, A2, and A3 is, for example, 0.0100 to 0.0500, and preferably 0.0150 to 0.0350. The number of layers per 1 μm of line segments B1, B2, and B3 is, for example, 0.0100 to 0.0500, preferably 0.0150 to 0.0350.

[0015] (Sample preparation) The rubber composite material is cut to include multiple layers, and a cross-section is created. In this case, it is preferable to create a cross-section that includes as many layers as possible. For example, in the case of rubber composite material dried using a drum dryer, the sheet-like dried material can be bundled in a direction parallel to the rotation axis of the drum dryer, and a cross-section can be created by cutting it in a direction perpendicular to the rotation axis of the drum dryer. A scanning electron microscope (S-3600N, manufactured by Hitachi High-Tech Corporation) is used to acquire a microscopic image of the cross-section (magnification 200x, 470 μm vertical x 630 μm horizontal).

[0016] (Binarization Process) The acquired microscope image is binarized using free software (Fiji ImageJ). Specifically, perform the following steps 1) to 4). 1) Open the image to be analyzed using File > Open. 2) Draw a line segment so that it overlaps the image's scale bar, and set the scale using Analyze > Set Scale. 3) Set the threshold to a lower limit of 10 and an upper limit of 100 using Image > Adjust > Threshold. 4) Perform binarization using Process > Binary > Make Binary to obtain the binarized image.

[0017] (Analysis of the number of layers) When the vertical length of the binarized image is v, three horizontal line segments are drawn at the positions of 1 / 4v, 1 / 2v, and 3 / 4v, and these are designated as line segments A1, A2, and A3 from top to bottom. Also, when the horizontal length of the binarized image is h, three vertical line segments are drawn at the positions of 1 / 4h, 1 / 2h, and 3 / 4h, and these are designated as line segments B1, B2, and B3 from left to right. If the binarized image contains parts other than the rubber composite material (excluding the space between layer regions) or scale bars or other characters (hereinafter collectively referred to as "other parts"), line segments may be drawn so as not to include these other parts. However, the lengths of line segments A1 to A3 should be 80% or more of h. Also, the lengths of line segments B1 to B3 should be 80% or more of v.

[0018] For each line segment, obtain a histogram from Analyze > Plot Profile. Display the raw data in List and save the CSV file using File > Save As. Open the CSV file in Excel. When microscopic images obtained using a scanning electron microscope are binarized, regions where the gray value is usually 0 correspond to layer regions. Therefore, regions where the gray value is 0 for 1 μm or more consecutively are judged to be layer regions. More specifically, check the gray value from one end of the line segment and determine the end of a layer region where the gray value is 0 for 1 μm or more consecutively, and immediately after that, there is a region where the gray value is not 0 for 1 μm or more consecutively. Count the number of layer regions and determine the number of layers traversed by each line segment LR Ｘ (Let X be A1, A2, A3, B1, B2, or B3). Also, let L be the length of each line segment. Ｘ (μm, X is A1, A2, A3, B1, B2, or B3). LR obtained by the above procedure Ｘ and L Ｘ From the value, the number of layers per 1 μm of each line segment (LR Ｘ / L Ｘ ) can be calculated.

[0019] The area of ​​the binarized image is not particularly limited as long as the magnification is 200x. The vertical length v of the binarized image is preferably 350 μm or more and 500 μm or less, more preferably 450 μm or more and 500 μm or less, and particularly preferably 470 μm. The horizontal length h of the binarized image is preferably 500 μm or more and 750 μm or less, more preferably 600 μm or more and 650 μm or less, and particularly preferably 630 μm.

[0020] <Fibrous Cellulose> Fibrous cellulose may be a modified product, and may be fibrous cellulose or a modified product thereof that has been defibrated and beaten. Examples of fibrous cellulose include fine fibrous cellulose. Fine fibrous cellulose is not particularly limited and known types may be used.

[0021] The maximum fiber width of the fine fibrous cellulose is preferably 1000 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, even more preferably 20 nm or less, and particularly preferably 10 nm or less.

[0022] The number-average fiber width of the microfiber cellulose is, for example, 1000 nm or less. Preferably, the number-average fiber width of the microfiber cellulose is, for example, 2 nm to 1000 nm, more preferably 2 nm to 100 nm, even more preferably 2 nm to 50 nm, and particularly preferably 2 nm to 10 nm. The microfiber cellulose is, for example, monofiber cellulose.

[0023] The fiber width of fine fibrous cellulose is measured, for example, using an electron microscope as follows: First, an aqueous suspension of fine fibrous cellulose with a concentration of 0.05% to 0.1% by mass is prepared, and this suspension is cast onto a hydrophilic carbon film-coated grid to prepare a sample for TEM observation. If wide fibers are present, an SEM image of the surface cast on glass may be observed. Next, observation of electron microscope images is performed at a magnification of 1000x, 5000x, 10000x, or 50000x depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification should be adjusted to meet the following conditions.

[0024] (1) Draw a straight line X at any point in the observed image, and 20 or more fibers intersect with this straight line X. (2) Draw a straight line Y perpendicular to the straight line X in the same image, and 20 or more fibers intersect with this straight line Y.

[0025] For observation images that satisfy the above conditions, the width of the fibers intersecting with lines X and Y is visually read. In this way, at least three sets of observation images of surface areas that do not overlap are obtained. Next, for each image, the width of the fibers intersecting with lines X and Y is read. This allows for the reading of at least 20 × 2 × 3 = 120 fiber widths. The largest of these fiber widths is taken as the maximum fiber width. The average of the read fiber widths is then taken as the number-average fiber width of the microfiber cellulose.

[0026] The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably 0.1 μm to 1000 μm, more preferably 0.1 μm to 800 μm, and even more preferably 0.1 μm to 600 μm. By keeping the fiber length within the above range, the destruction of the crystalline region of the fine fibrous cellulose can be suppressed. The fiber length of the fine fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0027] It is preferable that the fine fibrous cellulose has a type I crystalline structure. The presence of a type I crystalline structure in fine fibrous cellulose can be identified in the diffraction profile obtained from a wide-angle X-ray diffraction photograph using graphite-monochromatized CuKα (λ = 1.5418 Å). Specifically, it can be identified by the presence of typical peaks at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°. The proportion of type I crystalline structure in the fine fibrous cellulose is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and analyzing its pattern using conventional methods (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0028] The axial ratio (fiber length / fiber width) of the fine fibrous cellulose is not particularly limited, but is preferably 50 to 10,000, and more preferably 100 to 1,000. Setting the axial ratio above the lower limit makes it easier to form composite materials containing fine fibrous cellulose. Setting the axial ratio below the upper limit is preferable in that it makes handling easier, such as dilution, when handling the fine fibrous cellulose as a dispersion.

[0029] The fine fibrous cellulose in this embodiment, for example, has both crystalline and amorphous regions.

[0030] Examples of modification include oxidation, etherification, esterification, silane coupling, fluorination, and cationization. Esterification refers to the condensation reaction between an oxoacid of an organic or inorganic acid and the hydroxyl group of cellulose. Specifically, it is a reaction that produces carboxylic acid esters, thioesters, phosphate esters, sulfate esters, nitrate esters, carbonate esters, etc.

[0031] For defibration or beating, for example, a wet pulverizer, a high-speed defibrator, a grinder (stone mill type grinder), a high-pressure homogenizer or ultra-high-pressure homogenizer, a high-pressure impact grinder, a ball mill, a bead mill, a disc refiner, a conical refiner, a twin-screw kneader, a vibrating mill, a homomixer at high speed rotation, an ultrasonic disperser, or a beater can be used.

[0032] The concentration of fibrous cellulose is preferably 0.1% by weight or more and 10% by weight or less, more preferably 0.5% by weight or more and 5.0% by weight or less, and particularly preferably 1.0% by weight or more and 2.5% by weight or less.

[0033] <Rubber Components> Examples of rubber components include natural rubber, modified natural rubber, deproteinized natural rubber, and synthetic rubber. Examples of modified natural rubber include epoxidized natural rubber, hydrogenated natural rubber, chlorinated natural rubber, chlorosulfonated natural rubber, and natural rubber grafted with methyl methacrylate or styrene monomer.

[0034] Examples of synthetic rubbers include styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), ethylene propylene rubber (EPDM), butyl rubber (IIR), chlorobutyl rubber (CIIR), acrylic rubber (ACM), silicone rubber (Q), fluororubber (FKM), butadiene rubber (BR), epoxidized butadiene rubber (EBR), epichlorohydrin rubber (CO,CEO), urethane rubber (U), and polysulfide rubber (T). Examples of nitrile rubbers include hydrogenated nitrile rubber (H-NBR), carboxyl group-modified nitrile rubber, silicone-modified nitrile rubber, maleic acid-modified nitrile rubber, hydroxyl group-modified nitrile rubber, and other modified nitrile rubbers, or hydrogenated versions thereof, as well as acrylonitrile-butadiene-isoprene copolymers in which part of the butadiene is replaced with isoprene. Hydrogenated nitrile rubber is sometimes called hydrogenated nitrile rubber or hydrogenated acrylonitrile-butadiene rubber. Hydrogenated nitrile rubber can be obtained by hydrogenating the double bonds contained in nitrile rubber. These rubber components may be used individually or in mixtures of two or more types. Furthermore, these rubber components may be pre-crosslinked raw materials without a crosslinked structure, or they may have a crosslinked structure.

[0035] <Method for Manufacturing Rubber Composites> Rubber composites can be manufactured by a manufacturing method comprising the following steps (1) and (2): (1) A sheeting step in which a rubber sheet is obtained from a mixed liquid containing fibrous cellulose and rubber components. (2) A multi-layering step in which the rubber sheet is multi-layered to obtain a rubber composite.

[0036] The above explanation applies to fibrous cellulose and rubber components.

[0037] The mixed liquid containing fibrous cellulose and a rubber component can be prepared by a known method. For example, a mixed liquid can be obtained by mixing an aqueous dispersion of fibrous cellulose and a rubber latex. The rubber latex is a dispersion of the above rubber component in an aqueous medium. The aqueous medium mainly consists of water, and the content ratio of water in the whole aqueous medium is preferably 50 to 100% by mass, more preferably 80 to 100% by mass, still more preferably 90 to 100% by mass, and even more preferably 95 to 100% by mass. It may contain a known organic solvent or the like as long as the effects of the present invention are not impaired when added to water.

[0038] The mixing can be carried out using a known device such as a homomixer, a homogenizer, a propeller stirrer, etc. The mixing temperature is not limited, but room temperature (20 to 30 °C) is preferred. The mixing time can also be adjusted appropriately.

[0039] The method for obtaining a rubber sheet from the above mixed liquid is not particularly limited. For example, a rubber sheet can be obtained by a heat drying process. In the heat drying process of the mixed liquid, a known heat drying device can be used, such as a hot air drying device, a stirring drying device, a rotary drying device, a disk drying device, a roll type heating device, a plate type heating device, a fluidized bed drying device, a band type drying device, a filtration drying device, a vibration fluidized bed drying device, an air current drying device, a vacuum drying device, an infrared heating device, a far infrared heating device, a microwave heating device, a high frequency drying device, etc.

[0040] The thickness of the rubber sheet is not particularly limited, but is usually 0.001 mm to 0.5 mm, preferably 0.005 mm to 0.25 mm, and more preferably 0.01 mm to 0.1 mm. When the thickness of the rubber sheet is within the above range, the rubber composite material is likely to be multilayered.

[0041] When adding rubber latex to an aqueous dispersion of fibrous cellulose, the lower limit of the solid content of fibrous cellulose with respect to 100 parts by mass of the solid content of the rubber component is preferably 1 part by mass or more, more preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more. Also, the upper limit of the solid content of fibrous cellulose with respect to 100 parts by mass of the solid content of the rubber component is preferably 500 parts by mass or less, more preferably 50 parts by mass or less, and particularly preferably 25 parts by mass or less. That is, the solid content of fibrous cellulose with respect to 100 parts by mass of the solid content of the rubber component may be, for example, 5 to 500 parts by mass, 10 to 50 parts by mass, or 15 to 25 parts by mass.

[0042] The solid content concentration can be calculated by the following formula from the mass of the obtained dried product and the mass of the liquid subjected to drying after drying a measurement target such as a predetermined amount of dispersion liquid in a dryer at 105 °C until it reaches a constant weight. Solid content concentration of the liquid subjected to drying [%] = mass of dried product [g] / mass of liquid subjected to drying [g] × 100

[0043] The method for producing the rubber composite material has a lamination step of laminating the rubber sheets to obtain a rubber composite material. In this step, by adjusting the degree of lamination, the number of layers per 1 μm of the line segment can be made within a predetermined range.

[0044] The lamination step may include a step of bundling the rubber sheets. The rubber sheets to be bundled in this step may be single or multiple. The bundling method is not particularly limited, and known methods such as folding in a pleated shape or winding in a roll shape can be adopted. Also, the lamination step may include a step of stacking a plurality of the rubber sheets. When stacking a plurality of rubber sheets, the stacked rubber sheets may be further bundled. Furthermore, the lamination step may include a step of applying pressure to the bundled rubber sheets or the stacked plurality of rubber sheets. Examples of the method of applying pressure include applying pressure by a press machine or nip rolls. It is preferable to stack 2 or more rubber sheets, more preferably 3 or more rubber sheets, and particularly preferably 6 or more rubber sheets. The larger the number of stacked rubber sheets, the easier it is for the number of layers per 1 μm of each line segment to increase.

[0045] A rubber composite material is obtained through the above multi-layering process. The thickness of the rubber composite material is not particularly limited, but may be between 50 μm and 2000 μm, and preferably between 100 μm and 1000 μm. The smaller the thickness of the rubber composite material, the larger the number of layers per 1 μm of each line segment tends to be.

[0046] The above rubber composite material can be subjected to mashing to obtain a mashed rubber product. That is, another embodiment of the present invention is a mashed rubber product of the above rubber composite material. Yet another embodiment of the present invention is a method for manufacturing a mashed rubber product, comprising (3) a mashing step of mashing the above rubber composite material.

[0047] By performing a rough mixing, the viscosity of the rubber composite material decreases, improving the dispersibility of crosslinking agents and other components that are subsequently added. Rough mixing can be carried out by known methods, but it can also be done using a roll machine such as an open roll or a Banbury mixer. Rough mixing can be performed at low temperatures or high temperatures. The temperature for low-temperature mixing is preferably 15°C to 70°C, more preferably 20°C to 65°C, and even more preferably 25°C to 60°C. The temperature for high-temperature mixing is preferably 80°C to 200°C.

[0048] Compounded rubber can be obtained by compounding the above-mentioned paste with at least a crosslinking agent. That is, another embodiment of the present invention is a compounded rubber obtained by compounding at least the above-mentioned paste and a crosslinking agent. Yet another embodiment of the present invention is a method for producing a compounded rubber, comprising (4) a compounding step of compounding at least the paste produced by the above method and a crosslinking agent.

[0049] Mixing is the process of uniformly dispersing a crosslinking agent and other compounding agents in a masterbatch (in this specification, a composition containing fibrous cellulose and rubber components but not a crosslinking agent). That is, the mixed product may be obtained by mixing the above-mentioned masterbatch, the crosslinking agent, and other compounding agents. Mixing may be carried out in known manner, for example, using a Banbury mixer, kneader, open roll, etc. Examples of crosslinking agents include sulfur and peroxides. Examples of other compounding agents include sulfenamides (such as N-t-butyl-2-benzothiazole sulfenamide), vulcanization accelerators and auxiliary vulcanization accelerators such as zinc oxide and stearic acid, reinforcing agents such as carbon black and silica, silane coupling agents, oils, cured resins, waxes, fillers, softeners, fatty acids, antioxidants, deoxidizing agents, colorants, pH adjusters, and other substances usable in the rubber field. Furthermore, a rubber composition can be obtained by adding rubber components as additional compounding agents along with the crosslinking agent to the masterbatch and mixing, thereby diluting the fibrous cellulose concentration.

[0050] The rubber component used as another compounding agent is preferably solid rubber. Solid rubber can be obtained by solidifying rubber latex by heating and drying or by coagulation with the addition of acid. Heat drying is not particularly limited, but can be carried out in the same manner as the heat drying process described above. Typical acids used for coagulation include sulfuric acid, hydrochloric acid, formic acid, and acetic acid. The temperature for coagulation is preferably 10 to 40°C. During coagulation, it is preferable to adjust the pH of mixture A to 3 to 5, and more preferably to 3 to 4. In addition, a flocculant may be added to control the state of coagulation (size of the coagulated aggregated particles). Cationic polymers can be used as flocculants.

[0051] In addition, as the crosslinking agent, sulfur-based crosslinking agents (e.g., sulfur such as powdered sulfur, sulfurous salt, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur; sulfur-containing compounds such as disulfide amines, polymer polysulfides, sulfur olefin adducts, sulfur chloride, sulfur dichloride; insoluble polymer sulfur, etc.), peroxide-based crosslinking agents (e.g., dicumyl peroxide, dichlorobenzoyl peroxide, benzoyl peroxide, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl-4,4-bis(t-butylperoxy)valerate, di-t-butylperoxy-diisopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane), quinoid-based crosslinking agents (e.g., p-quinone dioxime, p,p'-dibenzoylquinone dioxime), etc. may be used, and among these, sulfur-based crosslinking agents or peroxide-based crosslinking agents are preferred. The amount of crosslinking agent added is not particularly limited, but is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1.0 part by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of rubber component.

[0052] Furthermore, a crosslinking accelerator that promotes crosslinking by the crosslinking agent may be added, and when using a sulfur-based crosslinking agent, it is preferable to add a crosslinking accelerator (vulcanization accelerator). When using a sulfur-based crosslinking agent (vulcanization agent) as the crosslinking agent, it is preferable to use a sulfenamide-based vulcanization accelerator, a guanidine-based vulcanization accelerator, a thiazole-based vulcanization accelerator, a thiram-based vulcanization accelerator, a dithiocarbamate-based vulcanization accelerator, etc., as the crosslinking accelerator (vulcanization accelerator).

[0053] Examples of fillers include carbon black and silica. There are no particular restrictions on the amount of filler added, but it is preferably 10 to 150 parts by mass, and more preferably 20 to 100 parts by mass, per 100 parts by mass of rubber component.

[0054] Examples of softening agents include aromatic oils, paraffin oil, naphthenic oil, vegetable oils other than castor oil, low PCA oils such as MES, TDAE, SRAE, and heavy naphthenic oil. Suitable low PCA oils include various plant-derived oils that can be harvested from vegetables, nuts, and seeds. Examples of plant-derived oils include soybean oil, sunflower oil, safflower oil, corn oil, linseed oil, cottonseed oil, rapeseed oil, cashew oil, sesame oil, camellia oil, jojoba oil, macadamia nut oil, coconut oil, and palm oil. The amount of softening agent added is preferably 1 to 35 parts by mass, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and even more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less, per 100 parts by mass of rubber component.

[0055] Examples of fatty acids include stearic acid, palmitic acid, arachidic acid, oleic acid, linoleic acid, and arachidonic acid. Among these, stearic acid is preferred. There are no particular restrictions on the amount of fatty acid added, but it is preferably 0.1 parts by mass to 5 parts by mass, and more preferably 1 part by mass to 4 parts by mass, per 100 parts by mass of rubber component.

[0056] Examples of anti-aging agents include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), N,N'-diphenyl-p-phenylenediamine (DPPD), and 2-mercaptobenzimidazole (MBI). There are no particular restrictions on the amount of anti-aging agent added, but preferably it is 0.1 parts by mass to 5 parts by mass, more preferably 1 part by mass to 3 parts by mass, per 100 parts by mass of the rubber component. The total content of anti-aging agents is preferably 0.2 parts by mass to 10 parts by mass, more preferably 1 part by mass to 5 parts by mass, per 100 parts by mass of the rubber component.

[0057] There are no particular restrictions on the amount of zinc oxide (zinc oxide) added, but it is preferably 1 to 10 parts by mass, and more preferably 1.5 to 8 parts by mass, per 100 parts by mass of the rubber component.

[0058] A crosslinked rubber composition can be obtained by crosslinking the above-mentioned compound. That is, another embodiment of the present invention is a crosslinked rubber composition obtained by crosslinking the above-mentioned compound. Yet another embodiment of the present invention is a method for producing a crosslinked rubber composition, comprising (5) a crosslinking step of crosslinking the above-mentioned compound.

[0059] After mixing is complete, molding may be performed as needed. Examples of molding equipment include die molding, injection molding, extrusion molding, hollow molding, and foam molding, and should be appropriately selected according to the shape, application, and molding method of the final product. The mixing process and the molding process may be performed separately or continuously.

[0060] Regarding crosslinking, there are no particular restrictions on temperature as long as the conditions for the crosslinking reaction proceed, but generally, a crosslinked rubber composition is obtained by heating the kneaded product to crosslink it (also called vulcanization if sulfur is included). The heating temperature is preferably 140°C or higher, preferably 200°C or lower, and more preferably 180°C or lower. Therefore, the heating temperature is preferably around 140 to 200°C, and more preferably around 140 to 180°C. For crosslinking, vulcanization equipment such as mold vulcanization, can vulcanization, and continuous vulcanization can be used.

[0061] The features of the present invention will be further described in detail below with reference to examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0062] <Comparative Example 1> A 1.0% by mass fine fibrous cellulose dispersion and a 61% by mass aqueous dispersion of natural rubber latex (Hyper HA, manufactured by Nomura Trading Co., Ltd.) were placed in a rotary-rotating agitator (ARE-500, manufactured by Thinky Co., Ltd.) so that the amount of fibrous cellulose solids was 20 parts by mass per 100 parts by mass of rubber solids, and the mixture was stirred at 1000 rpm for 60 minutes. Next, the mixture was poured into a tray and dried in an oven at 40-50°C for about 24 hours to remove moisture, obtaining a 400 μm thick sheet-like dried product.

[0063] <Examples 1-3> Except for adjusting the amount of the mixed liquid poured into the tray, the procedure was the same as in Comparative Example 1 to obtain sheet-like dried materials with thicknesses of 50 μm, 100 μm, and 200 μm. Example 1 was obtained by stacking eight 50 μm thick dried materials. Example 2 was obtained by stacking four 100 μm thick dried materials. Example 3 was obtained by stacking two 200 μm thick dried materials. The thickness of the dried materials was measured using a constant-pressure thickness measuring instrument (TECLOCK CORPORATION, PG-02). Specifically, the dried materials were conditioned at 23°C and 50% relative humidity for 24 hours, and then the thickness was measured at four arbitrary points. The average value was taken as the thickness of each layer of the dried material.

[0064] <Example 4> A 1.0% by mass fine fibrous cellulose dispersion and a 61% by mass aqueous dispersion of natural rubber latex (Hyper HA, manufactured by Nomura Trading Co., Ltd.) were placed in a rotary-rotating agitator (ARE-500, manufactured by Thinky Co., Ltd.) so that the amount of fibrous cellulose solids was 20 parts by mass relative to 100 parts by mass of rubber solids, and the mixture was stirred at 1000 rpm for 60 minutes. Next, the mixture was dried at 150°C for about 10 seconds using a drum dryer (JM-T, manufactured by Johnson Boiler Corporation) to remove moisture. The drum clearance of the drum dryer was 0.2-0.3 mm, the steam pressure was 0.4 MPa, and the drum rotation speed was 2.7 rpm. The sheet formed by the drum dryer was further folded using a nip roll in a direction parallel to the rotation axis of the drum dryer to obtain a dried material in which thin films with a thickness of about 20 μm per layer were folded together, which is Example 4. The thickness of the dried material in Example 4 was measured in the same manner as in Examples 1 to 3.

[0065] The dried materials from Comparative Example 1 and Examples 1-4 were fed into a double-roll mixing machine (Yasuda Seiki Co., Ltd., 191-TH test mixing rolls) and kneaded. Immediately after the start of kneading, each dried material fell off the rolls, but by repeatedly feeding the fallen dried materials into the double-roll mixing machine, each dried material became wrapped around the rolls and stopped falling. The time taken for the materials to wrap around the rolls is shown in Table 1.

[0066] The crosslinked rubber sheet was produced by heating the kneaded dried product at 150 °C for crosslinking. Then, test pieces were produced from the crosslinked rubber sheet in accordance with JIS P 8113:2006, except that the length of the test piece was 80 mm and the distance between chucks was 50 mm. The maximum tensile load of each test piece was measured using a tensile testing machine, Tensilon (manufactured by A&D Company, Limited). The tensile strength (unit: MPa) was calculated by dividing this maximum tensile load by the cross-sectional area of the test piece (thickness of the test piece × width [15 ± 0.1 mm]). When measuring the maximum tensile load, it was conditioned at 23 °C and 50% relative humidity for 24 hours. Also, the thickness of the test piece was measured with a constant pressure thickness measuring instrument (PG-02, manufactured by TECLOCK CORPORATION). Specifically, after conditioning the test piece at 23 °C and 50% relative humidity for 24 hours, the thicknesses at four arbitrary points were measured, and the average value was taken as the thickness of the test piece.

[0067] The dried products of Examples 1 to 4 and Comparative Example 1 were frozen in liquid nitrogen. After 2 minutes, immediately after taking them out of the liquid nitrogen, an impact was applied in a direction perpendicular to the thickness direction of the dried product using a razor, and it was cut. Microscopic images of the cross sections (magnification: 200 times, horizontal 630 μm × vertical 470 μm) were acquired using a scanning electron microscope (S-3600N, manufactured by Hitachi High-Technologies Corporation). Microscopic images of the cross sections of Example 4 and Comparative Example 1 are shown in FIGS. 1 and 2, respectively.

[0068] The microscopic images of the cross sections were binarized by the above method, and line segments A1 to A3 and B1 to B3 were drawn as described above. The number of layers LR Ｘ through which each line segment passed was divided by the length L Ｘ of each line segment to obtain the number of layers LR Ｘ per 1 μm of each line segment, LR Ｘ / L.

[0069] In Examples 1 to 4 where the time until winding around the roll during kneading was short, the number of layers LR Ｘ / L Ｘ per 1 μm of each line segment was all 0.0100 or more. On the other hand, in Comparative Example 1, LR Ｘ / L Ｘ was less than 0.0100 in all except A1.

Claims

1. A rubber composite material having a plurality of layers containing fibrous cellulose and rubber components, and voids formed between the plurality of layers, wherein in a binarized image of a microscope image (magnification 200x) of a cross-section of the rubber composite material including the plurality of layers, when the vertical length of the binarized image is v, and parallel line segments A1, A2, and A3 passing through the plurality of layers are drawn at positions 1 / 4v, 1 / 2v, and 3 / 4v, the number of layers per 1 μm of each of the line segments A1, A2, and A3 is 0.0100 or more, or when the horizontal length of the binarized image is h, and line segments B1, B2, and B3 perpendicular to line segment A1 are drawn at positions 1 / 4h, 1 / 2h, and 3 / 4h, the number of layers per 1 μm of each of the line segments B1, B2, and B3 is 0.0100 or more.

2. The rubber composite material according to claim 1, wherein the rubber component is natural rubber.

3. The rubber composite material according to claim 1 or 2, wherein the number-average fiber width of the fibrous cellulose is 1,000 nm or less.

4. A compound product of the rubber composite material according to claim 1 or 2.

5. A kneaded product obtained by kneading at least the kneaded product of claim 4 and a crosslinking agent.

6. A crosslinked rubber composition obtained by crosslinking the compound product of claim 5.

7. A method for producing a rubber composite material comprising the following steps (1) and (2): (1) A sheeting step of obtaining a rubber sheet from a mixed liquid containing fibrous cellulose and rubber components. (2) A multi-layering step of obtaining a rubber composite material by multi-layering the rubber sheet.

8. A method for manufacturing a compounded product comprising step (3). (3) A compounding step of compounding a rubber composite material manufactured by the method of claim 7.

9. A method for producing a kneaded product comprising step (4). (4) A kneading step of kneading a kneaded product produced by at least the method of claim 8 and a crosslinking agent.

10. A method for producing a crosslinked rubber composition, comprising step (5). (5) A crosslinking step of crosslinking the kneaded product produced by the method of claim 9.

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