Wiper blade rubber

Abstract

A wiper blade rubber (10) includes a contact sliding part (121) that makes contact with and slides on the surface of another member. The surface layer of the contact sliding part (121) is formed of a graphite coat layer (121b). The thickness of the graphite coat layer (121b) is 3-7 µm, and the arithmetic average height of the surface of the graphite coat layer (121b) is 1.5 µm or less.

Description

wiper blade rubber

[0001] The present invention relates to a wiper blade rubber.

[0002] As a wiper blade rubber for an automobile, one in which the lip portion, which is the portion that comes into contact with the windshield and slides, is coated with a graphite coating layer is known. For example, Patent Document 1 discloses a wiper blade rubber in which the lip portion is coated with a graphite coating layer that uses a polyurethane resin as a binder.

[0003] Patent No. 3821634

[0004] The present invention provides a wiper blade rubber including a contact sliding part that contacts and slides on the surface of another member, wherein the surface layer of the contact sliding part is made of a graphite coating layer, the thickness of the graphite coating layer is 3 μm or more and 7 μm or less, and the arithmetic mean height of the surface of the graphite coating layer is 1.5 μm or less.

[0005] 1 is a perspective view of a piece of wiper blade rubber according to an embodiment; FIG. 2 is a first explanatory diagram of a method for manufacturing wiper blade rubber according to an embodiment; FIG. 3 is a second explanatory diagram of a method for manufacturing wiper blade rubber according to an embodiment; and FIG. 4 is a third explanatory diagram of a method for manufacturing wiper blade rubber according to an embodiment.

[0006] The embodiments will be described in detail below.

[0007] FIG. 1 shows a wiper blade rubber 10 according to an embodiment. The wiper blade rubber 10 is a generally flat, elongated rubber component having an attachment / holding portion 11 on one side in the width direction, a lip portion 12 on the other side in the width direction, and a neck portion 13 connecting the attachment / holding portion 11 and the lip portion 12. The thin portion of the lip portion 12 on the side opposite the neck portion 13 constitutes a contact-sliding portion 121. The contact-sliding portion 121 has a main body portion 121a in the center in the thickness direction and graphite coating layers 121b covering both sides of the main body portion 121a. Therefore, the surface layers of both sides of the contact-sliding portion 121 are constituted by the graphite coating layers 121b.

[0008] The wiper blade rubber 10 of this embodiment has an attachment and holding portion 11 attached to a vertebra of a wiper drive unit provided, for example, on the underside of the windshield of an automobile, and when the wiper drive unit is driven, the lip portion 12 tilts with the neck portion 13 as a fulcrum, and the contact sliding portion 121 comes into contact with and slides against the surface of the windshield, which is another component, to wipe away rain, etc.

[0009] In the wiper blade rubber 10 according to the embodiment, the portions excluding the graphite coating layer 121b, i.e., the attachment / holding portion 11, the portions of the lip portion 12 other than the graphite coating layer 121b, and the neck portion 13, are integrally formed from a cross-linked rubber composition containing a rubber component and a rubber compounding agent.

[0010] Examples of the rubber component of the crosslinked rubber composition include natural rubber (NR), chloroprene rubber (CR), ethylene propylene diene rubber (EPDM), and styrene butadiene rubber (SBR). Examples of CR include sulfur-modified, mercaptan-modified, and xanthogen-modified types. The rubber component preferably contains one or more of these, and from the viewpoint of obtaining excellent wiping properties and durability, a blend rubber containing NR and CR is more preferred.

[0011] When the rubber component contains NR, the Mooney viscosity of the NR is preferably 50 ML / s or less from the viewpoint of suppressing hardening in a low-temperature atmosphere.１＋４ (100℃) or more 80ML １＋４ (100°C) or less, more preferably 55ML １＋４ (100℃) or more 65ML １＋４ (100°C) or less. The Mooney viscosity is measured in accordance with JIS K6300-1:2013 (the same applies hereinafter).

[0012] When the rubber component contains CR, the CR is preferably a mercaptan-modified type from the viewpoint of obtaining excellent wiping ability and durability. From the same viewpoint as above, the Mooney viscosity of the CR is preferably 40 ML １＋４ (100℃) or more 60ML １＋４ (100°C) or less, more preferably 45ML １＋４ (100℃) or more 53ML １＋４ (100°C) or less.

[0013] When the rubber component is a blend rubber containing NR and CR, the NR content is preferably greater than the CR content from the viewpoint of obtaining excellent wiping ability and durability. From the same viewpoint as above, the mass ratio of the NR content to the CR content (NR / CR) is preferably greater than 50 / 50 and not more than 70 / 30, more preferably 55 / 45 or more and not more than 65 / 35.

[0014] Examples of rubber compounding agents for the crosslinked rubber composition include carbon black, vulcanization accelerators, processing aids, vulcanization accelerators, and antioxidants.

[0015] Carbon black may be, for example, SRF (Semi Reinforcing Furnace, ASTM number N700 series, nitrogen adsorption specific surface area 27 m ２ / g), GPF (General Purpose Furnace, ASTM number N600 series, nitrogen adsorption specific surface area is 27 m ２ / g). The carbon black preferably contains SRF and / or GPF, and more preferably contains SRF from the viewpoint of obtaining excellent wiping properties and durability. The nitrogen adsorption specific surface area of ​​these carbon blacks is measured in accordance with JIS K6217-2:2017.

[0016] The nitrogen adsorption specific surface area of ​​the carbon black is preferably 20 m from the viewpoint of obtaining excellent wiping properties and durability. ２ / g or more 40m ２ / g or less, more preferably 25m ２ / g or more 30m ２ / g or less. From the same viewpoints as above, the arithmetic mean particle diameter of carbon black is preferably 50 nm or more, more preferably 65 nm or more, and preferably 100 nm or less, more preferably 70 nm or less. This arithmetic mean particle diameter is determined by observing carbon black with an electron microscope. Carbon black forms an aggregate structure in which fine particles are connected together. The particle diameter here is the primary particle diameter measured by regarding the fine particle portion as a single particle (primary particle) and approximating its diameter to a perfect circle. This primary particle diameter is measured by taking an electron microscope image of carbon black and approximating it to a perfect circle. The arithmetic mean particle diameter dn is the average of the primary particle diameters and is determined by dn = (Σnidi) / (Σni).

[0017] From the viewpoint of obtaining excellent wiping ability and durability, the content of carbon black in the crosslinked rubber composition is preferably 20 parts by mass or more and 30 parts by mass or less, more preferably 22 parts by mass or more and 29 parts by mass or less, and even more preferably 24 parts by mass or more and 28 parts by mass or less, per 100 parts by mass of the rubber component. Note that the content in the crosslinked rubber composition in the present application means the amount blended into the uncrosslinked rubber composition before crosslinking of the crosslinked rubber composition.

[0018] Examples of the vulcanization accelerator aid include metal oxides such as zinc oxide (zinc white) and magnesium oxide, metal carbonates, fatty acids, and derivatives thereof. The vulcanization accelerator aid preferably contains one or more of these, and from the viewpoint of obtaining excellent wiping ability and durability, it is more preferable to contain a metal oxide, even more preferable to contain zinc oxide and / or magnesium oxide, and even more preferable to contain both zinc oxide and magnesium oxide. Note that when the rubber component contains CR and the vulcanization accelerator aid contains a metal oxide, the metal oxide also acts as a crosslinking agent for the CR.

[0019] From the viewpoint of obtaining excellent wiping ability and durability, the content of the vulcanization acceleration aid in the crosslinked rubber composition is preferably 5 parts by mass or more and 10 parts by mass or less, more preferably 6 parts by mass or more and 8 parts by mass or less, per 100 parts by mass of the rubber component. When the vulcanization acceleration aid contains both zinc oxide and magnesium oxide, the content of zinc oxide is preferably greater than the content of magnesium oxide, from the same viewpoint as above. The mass ratio of the content of zinc oxide to the content of magnesium oxide is preferably 1.5 to 3.5, more preferably 2 to 3, from the same viewpoint as above.

[0020] Examples of processing aids include stearic acid, polyethylene wax, and metal salts of fatty acids. The processing aid preferably contains one or more of these, and from the viewpoint of obtaining excellent wiping ability and durability, it is more preferable that the processing aid contains stearic acid. From the same viewpoint as above, the content of the processing aid in the crosslinked rubber composition is preferably 0.5 parts by mass or more and 1.5 parts by mass or less per 100 parts by mass of the rubber component.

[0021] Examples of the vulcanization accelerator include sulfenamide-based vulcanization accelerators, thiourea-based vulcanization accelerators, aldehyde-ammonia-based vulcanization accelerators, aldehyde-amine-based vulcanization accelerators, guanidine-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiuram-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, etc. The vulcanization accelerator preferably contains one or more of these, and from the viewpoint of obtaining excellent wiping ability and durability, it is more preferable to contain a sulfenamide-based vulcanization accelerator and / or a thiourea-based vulcanization accelerator, and it is even more preferable to contain both a sulfenamide-based vulcanization accelerator and a thiourea-based vulcanization accelerator.

[0022] The content of the vulcanization accelerator in the crosslinked rubber composition is preferably 2 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the rubber component, from the viewpoint of obtaining excellent wiping properties and durability.

[0023] Examples of the antioxidant include p-phenylenediamine-based antioxidants, diphenylamine-based antioxidants, amine-ketone-based antioxidants, monophenol-based antioxidants, bisphenol-based antioxidants, polyphenol-based antioxidants, benzimidazole-based antioxidants, dithiocarbamate-based antioxidants, phosphorous-based antioxidants, organic thioacid-based antioxidants, etc. The antioxidant may contain one or more of these.

[0024] The content of the antioxidant in the crosslinked rubber composition is preferably 2 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the rubber component, from the viewpoint of obtaining excellent wiping properties and durability.

[0025] From the viewpoint of obtaining excellent wiping properties and durability, the crosslinked rubber composition is preferably crosslinked using sulfur as a crosslinking agent. In this case, from the same viewpoint as above, the amount of sulfur blended into the uncrosslinked rubber composition is preferably 1 part by mass or more and 4 parts by mass or less per 100 parts by mass of the rubber component. Note that the crosslinked rubber composition may be crosslinked using an organic peroxide as a crosslinking agent.

[0026] At least the portion of the crosslinked rubber composition that is to be coated with graphite coating layer 121b is preferably subjected to a chlorination treatment on the surface, from the viewpoint of enhancing adhesion to graphite coating layer 121b.

[0027] The graphite coating layer 121b is composed of a thin film layer in which graphite is bound via a binder.

[0028] Examples of graphite include natural graphite and artificial graphite. Examples of natural graphite include flake graphite, block graphite, and clay graphite. The graphite preferably contains one or more of these, and more preferably contains flake graphite from the viewpoint of obtaining excellent wiping properties and durability. The particle diameter of the graphite is, for example, 2 μm or more and 8 μm or less.

[0029] Examples of binders include thermosetting resins, thermoplastic resins, and photocurable resins. Examples of thermosetting resins include thermosetting polyurethane resins, silicone resins, epoxy resins, phenolic resins, urea resins, and melamine resins. Examples of thermoplastic resins include polyethylene resins, polypropylene resins, polyamide resins, polyester resins, and thermoplastic polyurethane resins. Examples of photocurable resins include epoxy compounds and urethane compounds to which acrylic acid is added. From the viewpoint of obtaining excellent wiping properties and durability, the binder is more preferably a thermosetting resin, and even more preferably a thermosetting polyurethane resin.

[0030] The mass ratio of the graphite content to the binder content in graphite coating layer 121b is preferably 0.5 or more and less than 1.5, more preferably 0.75 or more and 1.25 or less, from the viewpoint of obtaining excellent wiping properties and durability.

[0031] The thickness t of the graphite coating layer 121b is 3 μm or more and 7 μm or less, but from the viewpoint of obtaining excellent wiping ability and durability, it is preferably 3.5 μm or more and 6.5 μm or less, and more preferably 4 μm or more and 6 μm or less. The thickness t of the graphite coating layer 121b is determined from an enlarged image (e.g., 1000x magnification) of a cross section of the contact-sliding part 121 in the thickness direction using a digital microscope (e.g., VHX-7000 manufactured by KEYENCE Corporation). Specifically, a reference position is set on the main body part 121a in the thickness direction of the contact-sliding part 121, and the distance from the reference position to the interface between the main body part 121a and the graphite coating layer 121b is measured at multiple points (e.g., four points) and averaged. The distance from the reference position to the surface of the graphite coating layer 121b is also measured at multiple points (e.g., ten points) and averaged. The difference between the former and the latter is defined as the thickness t of the graphite coating layer 121b.

[0032] The arithmetic mean height Sa of the surface of graphite coating layer 121b is 1.5 μm or less, but from the viewpoint of obtaining excellent wiping ability and durability, it is preferably 0.3 μm or more and 1.2 μm or less, and more preferably 0.3 μm or more and 1.1 μm or less. This arithmetic mean height Sa is measured from a magnified image of the surface (for example, 1000 times magnification) using a digital microscope (for example, VHX-7000 manufactured by KEYENCE) based on ISO 25178.

[0033] The ratio (t / Sa) of the thickness t of graphite coating layer 121b to the arithmetic mean surface height Sa is preferably 3.5 or more and 6 or less, more preferably 4.5 or more and 5.5 or less, from the viewpoint of obtaining excellent wiping performance and durability.

[0034] According to the wiper blade rubber 10 of the embodiment having the above-described configuration, the thickness t of the graphite coating layer 121b constituting the surface layer of the contact sliding portion 121 is 3 μm or more and 7 μm or less, and the arithmetic mean height Sa of the surface is 1.5 μm or less, thereby achieving excellent wiping performance and durability.

[0035] Next, a method for manufacturing the wiper blade rubber 10 according to the embodiment will be described.

[0036] First, an uncrosslinked rubber composition is prepared by compounding and kneading a rubber compounding agent containing carbon black and a crosslinking agent with a rubber component, and this uncrosslinked rubber composition is molded and crosslinked to produce a tandem molded body 20 as shown in Figure 2A. This tandem molded body 20 has a shape in which a pair of parts of the wiper blade rubber 10 excluding the graphite coating layer 121b are butted together and bonded together with their main bodies 121a facing each other. Examples of molding methods for the tandem molded body 20 include press molding, extrusion molding, injection molding, and transfer molding.

[0037] 2B, a coating agent is applied to both surfaces of the pair of joined main bodies 121a of tandem compact 20 and then solidified to form graphite coating layer 121b. When chlorination treatment is performed, it is preferable to perform the chlorination treatment on tandem compact 20 before the coating agent is applied.

[0038] The coating agent contains solids including graphite and a binder before solidification, and an organic solvent for dissolving or dispersing the solids. The solids concentration of the coating agent is, for example, 3% by mass or more and 30% by mass or less. Examples of organic solvents include aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, alcohol solvents, ketone solvents, and ester solvents. Examples of aromatic hydrocarbon solvents include benzene, toluene, and xylene. Examples of aliphatic hydrocarbon solvents include n-hexane, isohexane, cyclohexane, n-octane, isooctane, decane, and dodecane. Examples of alcohol solvents include methanol, ethanol, and isopropanol. Examples of ketone solvents include methyl ethyl ketone and methyl isobutyl ketone. Examples of ester solvents include ethyl acetate and isobutyl acetate. It is preferable that the organic solvent contains one or more of these.

[0039] The coating of the coating agent is preferably performed by spray coating using a spray nozzle from the viewpoint of controlling the thickness t of the graphite coating layer 121b and the arithmetic mean height Sa of the surface. The thickness t of the graphite coating layer 121b can be controlled by the amount of coating agent sprayed. The arithmetic mean height Sa of the surface of the graphite coating layer 121b can be controlled by the back pressure, nozzle opening, atomization pressure of the spray nozzle, and the relative movement speed between the spray nozzle and the tandem compact 20, which is the workpiece. Specifically, the arithmetic mean height Sa of the surface of the graphite coating layer 121b can be increased by increasing at least one of the back pressure, nozzle opening, and atomization pressure of the spray nozzle and / or decreasing the relative movement speed between the spray nozzle and the tandem compact 20, which is the workpiece. Conversely, to reduce the arithmetic mean height Sa of the surface of the graphite coating layer 121b, at least one of the back pressure, nozzle opening and atomization pressure of the spray nozzle can be reduced, and / or the relative movement speed between the spray nozzle and the workpiece, i.e., the tandem molded body 20, can be increased.

[0040] Then, as shown in FIG. 2C, the tandem molded body 20 having the graphite coating layer 121b formed thereon is cut in the center, thereby producing a pair of wiper blade rubbers 10.

[0041] In the above embodiment, the graphite coating layer 121b is provided on each of both surfaces of the contact sliding portion 121 of the lip portion 12, but this is not particularly limited to this, and the graphite coating layer 121b may also be provided on other portions.

[0042] (Wiper Blade Rubber) Wiper blade rubbers having the same configuration as the above embodiment were produced as the following Examples 1 to 4 and Comparative Examples 1 to 6. The configurations of each are also shown in Tables 1 and 2.

[0043] Example 1 NR (Mooney viscosity: 60 ml １＋４ (100°C)) and CR (mercaptan modified type, Mooney viscosity: 45-53ML １＋４A blend rubber obtained by mixing NR and CR in a mass ratio of 60 / 40 (100°C) was used as the rubber component, and SRF (nitrogen adsorption specific surface area: 27 m) was used for 100 parts by mass of this rubber component. ２ An uncrosslinked rubber composition was prepared by blending and kneading 26 parts by mass of 100% propylene glycol stearate (0.1% wt. / g, arithmetic mean particle size: 66 nm) and 26 parts by mass of other additives with types and amounts thereof as shown in Table 1. This uncrosslinked rubber composition was press-molded and crosslinked to prepare a tandem molded article, which was then subjected to a chlorination treatment.

[0044] A coating agent was prepared containing 8 mass% of flake graphite, a polyether-based urethane prepolymer for forming a binder, 8 mass% of a mixture of a blocked isocyanate chain extender and a curing agent, and 50 mass% of methyl ethyl ketone and 10 mass% of xylene as organic solvents.

[0045] A graphite coating layer was formed by spraying a coating agent onto the contact sliding portions on both sides of the tandem compact using a spray nozzle and then hardening the coating agent. The thickness t of the graphite coating layer and the arithmetic mean surface height Sa were controlled by combining the settings of the coating conditions, namely, the back pressure of the spray nozzle, the nozzle opening, the atomization pressure, and the relative movement speed between the spray nozzle and the tandem compact.

[0046] A pair of wiper blade rubbers was produced by cutting the tandem molded article having the graphite coating layer formed thereon in the center. This wiper blade rubber was designated Example 1. The wiper blade rubber of Example 1 had a graphite coating layer thickness t of 3.5 μm and an arithmetic mean height Sa of the graphite coating layer surface of 0.71 μm. The graphite coating layer thickness t and the arithmetic mean height Sa of the surface were measured using a digital microscope (VHX-7000, manufactured by KEYENCE Corporation) with a magnification of 1000 times, in the same manner as in the above embodiment (the same applies hereinafter).

[0047] Example 2 A wiper blade rubber was produced in the same manner as in Example 1, except that the coating conditions were set so that the thickness t of the graphite coating layer was 5.1 μm and the arithmetic mean height Sa of the surface was 1.02 μm.

[0048] Example 3 A wiper blade rubber was produced in the same manner as in Example 1, except that the coating conditions were set so that the thickness t of the graphite coating layer was 6.7 μm and the arithmetic mean height Sa of the surface was 1.2 μm.

[0049] Example 4 A wiper blade rubber was produced in the same manner as in Example 1, except that the coating conditions were set so that the thickness t of the graphite coating layer was 4.9 μm and the arithmetic mean height Sa of the surface was 1.32 μm.

[0050] Comparative Example 1 A wiper blade rubber was prepared in the same manner as in Example 1, except that the coating conditions were set so that the thickness t of the graphite coating layer was 2.7 μm and the arithmetic mean height Sa of the surface was 0.58 μm.

[0051] Comparative Example 2 A wiper blade rubber was prepared in the same manner as in Example 1, except that the coating conditions were set so that the thickness t of the graphite coating layer was 6.1 μm and the arithmetic mean height Sa of the surface was 1.53 μm.

[0052] Comparative Example 3 A wiper blade rubber was produced in the same manner as in Example 1, except that the coating conditions were set so that the thickness t of the graphite coating layer was 1.9 μm and the arithmetic mean height Sa of the surface was 0.35 μm.

[0053] Comparative Example 4 A wiper blade rubber was produced in the same manner as in Example 1, except that the coating conditions were set so that the thickness t of the graphite coating layer was 7.2 μm and the arithmetic mean height Sa of the surface was 1.68 μm.

[0054] Comparative Example 5 A wiper blade rubber was produced in the same manner as in Example 1, except that the coating conditions were set so that the thickness t of the graphite coating layer was 7.8 μm and the arithmetic mean height Sa of the surface was 1.35 μm.

[0055] Comparative Example 6 A wiper blade rubber was produced in the same manner as in Example 1, except that the coating conditions were set so that the thickness t of the graphite coating layer was 2.9 μm and the arithmetic mean height Sa of the surface was 1.51 μm.

[0056]

[0057]

[0058] (Test and Evaluation Methods and Results) The following test and evaluation were carried out on the wiper blade rubbers of Examples 1 to 4 and Comparative Examples 1 to 6. The test results are shown in Table 2.

[0059] <Initial Wiping Performance> For each of the wiper blade rubbers of Examples 1 to 4 and Comparative Examples 1 to 6, the number of water droplets remaining unwiped in the M zone was classified into hairline, heavy line, and wide line and recorded as the initial wiping performance in each of the up-wiping (OPEN) and down-wiping (CLOSE) states based on JIS D5710:1998.

[0060] <Coefficient of Friction> Test specimens measuring 100 mm in length were cut from each of the wiper blade rubbers of Examples 1 to 4 and Comparative Examples 1 to 6. The mounting and holding portion of the test specimen was attached to an elongated fixture equipped with a load cell. The fixture with the attached test specimen was positioned on a rotatable glass disk with a diameter of 400 mm, extending radially and with the tip of the lip of the test specimen abutting against it. A normal load of 1.67 N was applied to the fixture to press the lip of the test specimen against the glass disk. Water was sprayed onto the glass disk to wet it, and the glass disk was rotated so that the speed at the center of the test specimen accelerated from 0.025 m / s to 2.0 m / s over 20 seconds. During this time, the friction force acting on the test specimen detected by the load cell was logged. The maximum static friction force when the test specimen began to slide on the glass disk was determined, and this was divided by the normal load (normal force) of 1.67 N to calculate the static friction coefficient. The frictional force at a speed of 2.0 m / s was calculated and divided by the normal load (normal force) of 1.67 N to calculate the coefficient of dynamic friction. The ratio of the static friction coefficient to the dynamic friction coefficient was then calculated. If this ratio is close to 1, the vehicle can start from a stationary state and smoothly transition to a sliding state.

[0061] <Abrasion Resistance Durability Test> Each of the wiper blade rubbers of Examples 1 to 4 and Comparative Examples 1 to 6 was mounted on an actual vehicle so that the wiper arm pressure was 16.7 N / m. A test was conducted in which 800 ml / min of water was sprayed onto the windshield to wet it, and the wiper drive motor was driven to wipe the water off the windshield with the wiper blade rubber. The speed was set so that the number of times the wiper blade rubber slid against the windshield was 45±2 times per minute, and the test was continued until the number of times it slid 300,000 times.

[0062] After the test, the sliding contact portion of the wiper blade rubber was observed from the side at a magnification of 200 times using a digital microscope (VHX-7000, manufactured by KEYENCE Corporation). The distance from the tip line of the sliding contact portion to the tip line of the graphite coating layer was measured. This distance corresponds to the amount of wear caused by the sliding contact portion of the wiper blade rubber repeatedly sliding against the windshield.

[0063] The present invention is useful in the technical field of wiper blade rubber.

[0064] REFERENCE SIGNS LIST 10 wiper blade rubber 11 attachment holding portion 12 lip portion 121 contact sliding portion 121a main body portion 121b graphite coating layer 13 neck portion 20 tandem molded body

Claims

1. A wiper blade rubber including a contact sliding part that contacts and slides on the surface of another member, wherein the surface layer of the contact sliding part is made of a graphite coating layer, the thickness of the graphite coating layer is 3 μm or more and 7 μm or less, and the arithmetic mean height of the surface of the graphite coating layer is 1.5 μm or less.

2. A wiper blade rubber according to claim 1, wherein the ratio of the thickness of the graphite coating layer to the arithmetic mean height of the surface is 3.5 or more and 6 or less.

3. A wiper blade rubber according to claim 1 or 2, wherein the graphite coating layer is composed of a thin film layer in which graphite is bonded via a binder.

4. The wiper blade rubber according to claim 3, wherein the binder is a thermosetting resin.

5. A wiper blade rubber according to any one of claims 1 to 4, wherein the portion excluding the graphite coating layer is formed of a crosslinked rubber composition.

Images