JP5676312B2 - Automotive fuel cap - Google Patents

Description

The present invention relates to an automobile fuel cap for opening and closing a fuel filler port of a fuel tank mounted on an automobile or the like.

The fuel tank for automobiles is provided with a fuel filler port for supplying fuel from a fuel gun at the upper end of a filler tube that rises upward from the tank body, and this fuel filler port is closed with a filler cap so as to be freely opened and closed. In order to prevent the fuel vapor from diffusing into the atmosphere from the gap between the filler tube filler port and the filler cap, the filler cap is provided with a rubber seal member.

As a material of the seal member used for the filler cap, for example, Patent Document 1 describes a material such as vinylidene fluoride / hexafluoropropylene copolymer (FKM) or hydrogenated butadiene acrylonitrile rubber (HNBR). Yes.

By the way, in the field of sealing materials and the like, as a method of reducing the friction coefficient while utilizing the characteristics of rubber, for example, a method of laminating a fluororesin fiber layer on the surface of rubber (see Patent Document 2) is disclosed.

JP 2009-74576 A JP 7-227935 A

However, a sealing member using a material as described in Patent Document 1 has a problem in that a sticking phenomenon occurs due to a reaction at the interface between the sealing member and the fuel filler port when the seal member is in contact with the fuel filler port for a long time. Could occur.

Also, as in Patent Document 2, when a layer made of a fluororesin is laminated on rubber, the layer made of the fluororesin and the rubber are peeled off, or a layer made of the fluororesin is formed on the rubber surface. Therefore, there were cases where flexibility was poor.

An object of this invention is to provide the fuel cap excellent in low sticking property.

The present invention is an automobile fuel cap attached to a fuel filler of an automobile fuel tank, wherein the automobile fuel cap includes a gasket that is pressed against the filler opening to seal the filler opening, and the gasket includes fluorine. The fluororesin is a copolymer comprising a polymer unit based on ethylene and a polymer unit based on tetrafluoroethylene. The fluororubber is a copolymer containing a polymer unit based on vinylidene fluoride, and relates to a fuel cap for automobiles.

In the automobile fuel cap, the ratio of the fluorine resin on the gasket surface is preferably higher than the inside.

The fluororubber is a copolymer comprising polymerized units based on vinylidene fluoride and polymerized units based on at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether. A polymer is preferred.

The composition containing fluororubber and fluororesin preferably has a mass ratio of fluororubber to fluororesin of 60/40 to 97/3.

Since the fuel cap for automobiles of the present invention has the above-described configuration, it has excellent low adhesion.

FIG. 1 is a schematic view showing an example of a form of a fuel cap for automobiles of the present invention. In FIG. 1, the left side of the broken line shows an appearance when the fuel cap is viewed from the side, and the right side of the broken line shows a cross section of the fuel cap. (A) is a perspective view showing the shape of the convex portion having the gasket schematically, (b) cutting the convex portion 31 in the plane including the straight line B ₁ and the line B ₂ perpendicular to the surface of (a) (C) is a cross-sectional view cut along a plane including a straight line C ₁ and a straight line C ₂ having a distance of 0.15 μm from the surface of (a).

The fuel cap for automobiles of the present invention is attached to the fuel filler of an automobile fuel tank. FIG. 1 is a schematic cross-sectional view showing an example of a form of an automobile fuel cap according to the present invention. As a form of the fuel cap for automobiles of the present invention, for example, as shown in FIG. 1, an automobile fuel cap 100 has a cap portion 1 and a screw portion 2, and a filler neck 3 that leads to a fuel tank. The form which attaches to the filler port by screwing the screw thread 2a of the screw part 2 to the filler neck side screw 3b formed in the filler port 3a is mentioned. The cap part 1 may be formed from synthetic resin materials, such as nylon, and may be formed from other materials. Generally, a grip portion for rotating the cap portion 1 is provided on the upper surface of the fuel cap for an automobile. The threaded portion 2 is a cylindrical body in which a thread 2a that is screwed into the filler neck side screw 3b of the filler neck 3 is formed.

Normally, the gasket 4 is provided on the upper outer periphery of the screw portion 2. The gasket is pressed against the sealing surface 3c of the filler neck 3a by sealing the automobile fuel cap 100 into the filler port 3a of the filler neck 3, and seals the fuel port 3a. In general, a rib 2b for preventing the gasket 4 from dropping off is provided on the outer periphery of the upper portion of the screw portion 2.

Although not shown in FIG. 1, a ratchet mechanism is usually provided between the cap portion 1 and the screw portion 2, and one-way rotation of the cap portion 1 is allowed by the action of the ratchet mechanism. At the same time, when the rotation reaches a predetermined torque or more, the vehicle is idled to prevent the vehicle fuel cap 100 from being over-tightened with respect to the fuel filler opening 3a.

The fuel cap for automobiles of the present invention includes a gasket that is pressed against a fuel filler and seals the fuel filler. As shown in FIG. 1, the gasket 4 comes into contact with the filler port 3 a of the filler neck 3 and is pressed against the seal surface 3 c of the filler neck 3, thereby sealing the filler port 3 a.

The gasket is not particularly limited as long as it can seal the fuel filler port as described above. As described above, the gasket is usually provided on the outer periphery of the screw portion of the automobile fuel cap, and is usually annular. In addition, the cross-sectional shape of the gasket may be circular, polygonal (triangular, quadrangular, pentagonal, hexagonal, etc.), or other shapes. For example, as shown in FIG. 1, it may be circular (C-shaped) provided with slits 4a.

The said gasket consists of a composition containing a fluororesin and fluororubber. The composition containing fluororesin and fluororubber is a mixture of fluororesin and fluororubber, for example, fluororubber is dispersed in fluororesin, or fluororesin is dispersed in fluororubber. It can also be said that In this respect, the gasket is clearly distinguished from the one in which a layer made of a fluororesin is laminated on the surface of the fluororubber and the one in which a fluororesin coating film is formed on the surface of the fluororubber. Since the gasket is composed of a composition containing fluororesin and fluororubber, the above-described fluororubber surface is laminated with a fluororesin layer, or a fluororesin coating is formed on the fluororubber surface. No delamination like things.

Moreover, since it consists of a composition containing a fluororesin and fluororubber, it is superior in characteristics such as heat resistance and chemical resistance compared to the case of using a general-purpose rubber such as NBR.

The gasket has a fluororesin deposited on the surface. Since the fluororesin is deposited on the surface, the gasket surface is excellent in low adhesion as compared with the one made of fluororubber. In addition, since fluororesin and fluororubber exist together, the above-mentioned fluororubber surface is laminated with a fluororesin layer, or fluororesin coating is formed on the fluororubber surface. Excellent flexibility compared to Furthermore, since the above-mentioned gasket has a fluororesin deposited on its surface, it is excellent in non-adhesiveness, low friction, water / oil repellency (high contact angle), heat resistance, and chemical resistance.

The ratio of the fluorine resin on the gasket surface is preferably higher than that inside. That is, the fluororesin ratio is preferably higher on the outer side (surface) than on the inner side of the gasket. Since the fluororesin deposited on the surface of the gasket has migrated from the inside to the surface, the ratio of the fluororesin on the gasket surface is usually higher than that inside. It is preferable that the said gasket is obtained by the method containing process (I), process (II), and process (III) mentioned later. The fluororesin ratio can be determined by ESCA analysis or IR analysis described later.

In the gasket, the internal fluororesin preferably does not exhibit a clear particle shape. Such a form can be realized, for example, by sufficiently uniformly kneading the fluororesin and the uncrosslinked fluororubber in the step (I) described later. Usually, when a fluororesin and uncrosslinked fluororubber are kneaded, they are not kneaded at a temperature at which the fluororesin melts. This is because uncrosslinked fluororubber has lower heat resistance than fluororesin.

The gasket is useful as a sealing material for an automobile fuel cap by utilizing its low adhesion, non-adhesiveness, low friction, water / oil repellency (high contact angle).

The gasket is made of a composition containing fluororubber and fluororesin.

The composition containing fluororubber and fluororesin preferably has a mass ratio of fluororubber to fluororesin (fluororubber) / (fluororesin) of 60/40 to 97/3. If the amount of the fluororesin is too small, the effect of reducing the friction coefficient may not be sufficiently obtained. On the other hand, if the amount of the fluororesin is too large, rubber elasticity may be remarkably impaired and flexibility may be lost. From the viewpoint of good flexibility and low friction, (fluororubber) / (fluororesin) is more preferably 65/35 to 95/5, and 70/30 to 90/10. Further preferred.

The fluororubber is made of an amorphous polymer having a fluorine atom bonded to a carbon atom constituting the main chain and having rubber elasticity. The fluororubber may be composed of one kind of polymer or may be composed of two or more kinds of polymers.

The fluororubber is a polymer containing polymerized units [VdF units] based on vinylidene fluoride [VdF].

The fluororubber is preferably a copolymer containing polymer units (excluding VdF units) based on VdF units and fluorine-containing ethylenic monomers. The copolymer containing a VdF unit further comprises a copolymer unit based on a monomer copolymerizable with VdF and a fluorine-containing ethylenic monomer (provided that the copolymer is based on a VdF unit and a fluorine-containing ethylenic monomer). It is also preferable to include a unit.

The fluororubber preferably contains 30 to 85 mol% of VdF units and 70 to 15 mol% of copolymerized units based on a fluorine-containing ethylenic monomer, and 30 to 80 mol% of VdF units and 70 to 20 mol%. More preferably, it contains a copolymer unit based on a mole% of a fluorine-containing ethylenic monomer. The copolymer unit based on the monomer copolymerizable with VdF and the fluorine-containing ethylenic monomer is 0 to 10 mol based on the total amount of the copolymer unit based on the VdF unit and the fluorine-containing ethylenic monomer. % Is preferred.

Examples of the fluorine-containing ethylenic monomer include tetrafluoroethylene [TFE], chlorotrifluoroethylene [CTFE], trifluoroethylene, hexafluoropropylene [HFP], trifluoropropylene, tetrafluoropropylene, pentafluoropropylene, and trifluoro. Examples include fluorine-containing monomers such as lobutene, tetrafluoroisobutene, perfluoro (alkyl vinyl ether) [PAVE], and vinyl fluoride. Among these, at least selected from the group consisting of TFE, HFP, and PAVE One type is preferable.

The PAVE is preferably perfluoro (methyl vinyl ether), perfluoro (ethyl vinyl ether) or perfluoro (propyl vinyl ether), and more preferably perfluoro (methyl vinyl ether). These can be used alone or in any combination.

Examples of the monomer copolymerizable with VdF and the fluorine-containing ethylenic monomer include ethylene, propylene, alkyl vinyl ether and the like.

The fluororubber is composed of VdF / HFP copolymer, VdF / HFP / TFE copolymer, VdF / CTFE copolymer, VdF / CTFE / TFE copolymer, VdF / PFE copolymer, VdF / TFE / PAVE copolymer. It is preferably at least one copolymer selected from the group consisting of a polymer, a VdF / HFP / PAVE copolymer, and a VdF / HFP / TFE / PAVE copolymer, heat resistance, compression set From the viewpoint of processability and cost, at least one copolymer selected from the group consisting of a VdF / HFP copolymer and a VdF / HFP / TFE copolymer is more preferable.

The fluororubber preferably has a Mooney viscosity (ML _{1 + 10} (121 ° C.)) of 5 to 140, more preferably ₁₀ to 120, and preferably 20 to 100 from the viewpoint of good processability. Further preferred.

The fluorine rubber preferably has a number average molecular weight of 20,000 to 1,200,000, more preferably 30,000 to 300,000, and even more preferably 50,000 to 200,000. The number average molecular weight can be measured by GPC using a solvent such as tetrahydrofuran or n-methylpyrrolidone.

A cross-linking system can be selected for the fluororubber depending on the application. Examples of the crosslinking system include a peroxide crosslinking system, a polyol crosslinking system, and a polyamine crosslinking system.

The fluororesin is a copolymer [ETFE] including a polymerized unit [Et unit] based on ethylene and a polymerized unit [TFE unit] based on tetrafluoroethylene.

The content molar ratio of TFE units to Et units is preferably 20:80 to 90:10, more preferably 37:63 to 85:15, and particularly preferably 38:62 to 80:20.

ETFE may contain polymerized units based on monomers copolymerizable with TFE and ethylene. As copolymerizable monomers, CTFE, trifluoroethylene, HFP, trifluoropropylene, tetrafluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, perfluoro (alkyl vinyl ether), vinyl fluoride, 2 , 3,3,4,4,5,5-heptafluoro-1-pentene (CH ₂ ═CFCF ₂ CF ₂ CF ₂ H) and the like, and HFP is preferable. The monomer copolymerizable with TFE and ethylene may be an aliphatic unsaturated carboxylic acid such as itaconic acid or itaconic anhydride.

The polymerization unit based on the monomer copolymerizable with TFE and ethylene is preferably 0.1 to 5 mol%, more preferably 0.2 to 4 mol%, based on all monomer units. preferable.

ETFE preferably has a melting point of 120 to 340 ° C, more preferably 150 to 320 ° C, and still more preferably 170 to 300 ° C.

In the above composition, usual compounding agents blended in the fluororubber as necessary, for example, fillers, processing aids, plasticizers, colorants, stabilizers, adhesion aids, mold release agents, imparting conductivity. Various additives such as an agent, a thermal conductivity imparting agent, a surface non-adhesive agent, a flexibility imparting agent, a heat resistance improving agent, and a flame retardant can be blended, and these additives and blending agents are the effects of the present invention. May be used within a range that does not impair it.

The fluororesin on the gasket surface may form a convex portion or may be a film.

The automobile fuel cap of the present invention preferably has a convex portion on the gasket surface. In this case, the said convex part consists of a fluororesin substantially contained in the said composition. There is no clear interface or the like between the convex portion and the gasket, and the convex portion is configured integrally with the gasket.
Here, the fact that the convex portion is substantially made of a fluororesin contained in the above composition means that the convex portion is substantially fluorine by obtaining a peak ratio derived from the fluororubber and the fluororesin by IR analysis or ESCA analysis. It can show that it consists of resin. Specifically, the ratio of the peak of characteristic absorption derived from fluororubber to the peak of characteristic absorption derived from fluororesin (component-derived peak ratio = (peak intensity derived from fluororubber)) by IR analysis in a region having a convex portion. / (Peak intensity derived from fluororesin)) is measured at each part outside the convex part and the convex part, and the component-derived peak ratio outside the convex part is at least twice the peak ratio derived from the component of the convex part, Preferably it means 3 times or more.

The shape of the convex portion will be described in more detail with reference to the drawings.
FIG. 2A is a perspective view schematically showing the shape of the convex portion of the gasket, and FIG. 2B is a plane including a straight line B ₁ and a straight line B ₂ perpendicular to the surface of FIG. FIG. 6C is a cross-sectional view taken along a plane including the straight line C ₁ and the straight line C ₂ having a distance of 0.15 μm from the surface of FIG.
2 (a) to 2 (c) schematically depict a minute region of the gasket of the present invention.
As shown in FIGS. 2A to 2C, for example, a substantially conical (conical) convex portion 31 may be formed on the surface of the gasket 30.

Here, the height of the convex portion 31 refers to the height of the portion protruding from the gasket surface (see H in FIG. 2B).
Moreover, the diameter of the convex part 31 is the convex part 31 cut | disconnected in parallel with the surface of the gasket by the predetermined height (0.15 micrometer / refer FIG.2 (b) in FIG. 2 (b) in this application) from the gasket surface. Assuming the smallest rectangle inscribed in the closed curve forming the outer edge of the cross section in the cross section of the convex portion 31 (see FIG. 2C) observed on the surface, the sum of the long side L1 and the short side L2 of this rectangle is The value divided by 2 ((L1 + L2) / 2).

As for the shape of the said convex part, it is preferable that average height is 0.5-5 micrometers. When the average height is within this range, the gasket is excellent in low slidability. A more preferable average height is 0.5 to 3 μm. More preferably, it is 0.5-2 micrometers, Most preferably, it is 0.7-2 micrometers.

Moreover, it is preferable that the average diameter of the said convex part is 5-20 micrometers. More preferably, it is 5-15 micrometers, Most preferably, it is 8-15 micrometers. When the average diameter of the convex portions is within this range, the gasket is excellent in low slidability.

Moreover, it is preferable that the ratio of the area | region which has the said convex part on the surface of a gasket is 10% or more. If a convex part is formed in the area | region of at least 10%, the low friction property of a gasket will improve. A more preferable ratio is 15% or more. More preferably, it is 18% or more. On the other hand, the preferable upper limit of the ratio of the area | region which has the said convex part is 80%.
In addition, the ratio of the area | region which has the said convex part means the ratio of the area which a convex part occupies in the cut surface which evaluates the diameter of the said convex part.

In the fuel cap for automobiles of the present invention, it is sufficient that the convex portion is formed at least on the surface of the gasket, may be formed partially, or may be formed on the entire surface. In the fuel cap for automobiles of the present invention, any shape may be used as long as a convex portion is formed at the contact portion that contacts the fuel filler port.

The shape of the convex portion can be confirmed by an atomic force microscope. For example, by observing the gasket surface using an atomic force microscope and analyzing the hardness of the surface from the obtained phase image, it can be confirmed that there is a convex portion substantially made of a fluororesin. Moreover, the average diameter of the convex part in the gasket surface is, for example, 100 average diameters in the measurement visual field, and the average diameter in the measurement visual field is the same for all convex parts in the measurement visual field (150 μm square). It is an average value of values obtained by dividing the sum of the major axis and minor axis of a region formed by cutting on a plane having a height of 0.15 μm by 2.
Moreover, the average height of a convex part is the average height in 100 measurement visual fields, for example, and the measurement visual field height is the height of each convex part about all the convex parts in a measurement visual field (150 micrometers square). It is the value which averaged the value of.
Moreover, the ratio of the area | region which has a convex part is the occupation rate in 100 measurement visual fields, for example, and the occupation rate in a measurement visual field is the height of a convex part about all the convex parts in a measurement visual field (150 micrometers square). This is the ratio of the area of the region cut by a 0.15 μm plane to the area of the measurement visual field (150 μm square).

Atomic force microscope: PM920-006-101 made by VEECO Multi-mode V system cantilever: HMX-10 made by VEECO Probes
Measurement environment: Normal temperature and humidity Measurement field of view: 150μm square measurement mode: harmonics mode

The shape of the convex portion can also be confirmed by a laser microscope. For example, using a laser microscope and analysis software, which will be described later, for all convex portions existing in an arbitrary area (270 μm × 202 μm) on the gasket surface, measure the diameter and height of the bottom cross section of each convex portion, An average diameter and average height can be obtained by averaging. Further, the occupation ratio can be obtained as a ratio of the total sectional area of the convex portions existing in an arbitrary region (270 μm × 202 μm) on the gasket surface to the area of the measurement visual field.
Laser microscope: Keyence Corporation color 3D laser microscope (VK-9700)
Analysis software: manufactured by Mitani Shoji Co., Ltd., WinRooF Ver. 6.4.0
Measurement environment: Normal temperature and humidity Measurement field of view: 270 μm × 202 μm

One of the preferred embodiments of the present invention is that the fluororesin on the gasket surface is in the form of a film. The film-like fluororesin is obtained by depositing the fluororesin contained in the composition. In the gasket, there is no clear interface between the film-like fluororesin formed on the surface and the inside of the gasket, and the film-like fluororesin is integrally formed with the inside of the gasket. The film-like fluororesin may cover the entire surface of the gasket, but it is not necessary to cover the entire surface, and there may be a portion where the fluororubber is exposed on the surface of the gasket.

Next, a method for manufacturing the gasket will be described.

The gasket is
(I) a kneading step of kneading the fluororesin and uncrosslinked fluororubber at a temperature of 5 ° C. lower than the melting point of the fluororesin,
(II) It can be produced by a method including a molding crosslinking step in which the obtained kneaded product is molded and crosslinked, and (III) a heat treatment step in which the obtained crosslinked molded product is heated to a temperature equal to or higher than the melting point of the fluororesin. That is, an automobile fuel cap including a gasket obtained by this manufacturing method is also one aspect of the present invention.

Uncrosslinked fluororubber is a fluororubber before crosslinking.

(I) Kneading Step In the kneading step (I), the uncrosslinked fluororubber and the fluororesin are melt kneaded at a temperature that is 5 ° C. lower than the melting point of the fluororesin, preferably at a temperature that is higher than the melting point of the fluororesin. The upper limit of the heating temperature is less than the lower thermal decomposition temperature of uncrosslinked fluororubber or fluororesin.

Melt kneading of uncrosslinked fluororubber and fluororesin is not performed under conditions that cause crosslinking at that temperature (such as in the presence of a crosslinking agent, crosslinking accelerator, and acid acceptor), but at least 5 ° C lower than the melting point of the fluororesin Any component that does not cause crosslinking at the melt kneading temperature (for example, only a specific crosslinking agent or only a combination of a crosslinking agent and a crosslinking accelerator) may be added and mixed during melt kneading. Examples of conditions that cause crosslinking include a combination of a polyol crosslinking agent, a crosslinking accelerator, and an acid acceptor.

Therefore, in the kneading step (I) in the present invention, uncrosslinked fluororubber and fluororesin are melt-kneaded to prepare a pre-compound (preliminary mixture), and then other additives and compounding agents at a temperature lower than the crosslinking temperature. A two-stage kneading method is preferable in which knead is made into a full compound. Of course, a method of kneading all the components at a temperature lower than the crosslinking temperature of the crosslinking agent may be used.

As said crosslinking agent, well-known crosslinking agents, such as an amine crosslinking agent, a polyol crosslinking agent, and a peroxide crosslinking agent, can be used.

Melt-kneading is performed by kneading with fluororubber using a Banbury mixer, a pressure kneader, an extruder, or the like at a temperature of 5 ° C. or lower than the melting point of the fluororesin, for example, 200 ° C. or higher, usually 230 to 290 ° C. It can be carried out. Among these, it is preferable to use an extruder such as a pressure kneader or a twin screw extruder because a high shear force can be applied.

Further, full compounding in the two-stage kneading method can be performed using an open roll, a Banbury mixer, a pressure kneader, or the like at a temperature lower than the crosslinking temperature, for example, 100 ° C. or lower.

As a treatment similar to the melt kneading, there is a treatment (dynamic crosslinking) in which an uncrosslinked fluororubber is crosslinked in a fluororesin under the melt condition of the fluororesin. Dynamic crosslinking is a method in which uncrosslinked rubber is blended in a matrix of thermoplastic resin, uncrosslinked rubber is crosslinked while kneading, and the crosslinked rubber is dispersed microscopically in the matrix. In melt-kneading, melt-kneading is performed under conditions that do not cause crosslinking (the absence of a component necessary for crosslinking, or a compound that does not cause a crosslinking reaction at that temperature), and the matrix becomes uncrosslinked rubber, which is uncrosslinked rubber. It is essentially different in that it is a mixture in which the fluororesin is uniformly dispersed.

(II) Molding / Crosslinking Step This step is a step for producing a crosslinked molded product having the same shape as the gasket to be produced by molding and crosslinking the kneaded product obtained in the kneading step.

Examples of the molding method include, but are not limited to, an extrusion molding method, a pressure molding method using a mold, an injection molding method, and the like.

As the crosslinking method, a steam crosslinking method, a pressure molding method, a normal method in which a crosslinking reaction is started by heating, a radiation crosslinking method, or the like can be adopted. Among them, a crosslinking reaction by heating is preferable.

The molding and crosslinking methods and conditions may be within the range of known methods and conditions for the molding and crosslinking employed. Further, the molding and the crosslinking may be performed in any order, or may be performed in parallel at the same time.

For example, in a gasket used for a fuel cap for automobiles, molding and crosslinking with a mold or the like are usually performed in parallel.

Specific crosslinking conditions that are not limited may be appropriately determined depending on the type of the crosslinking agent to be used, usually within a temperature range of 150 to 300 ° C. and a crosslinking time of 1 minute to 24 hours. Further, in the heat treatment step described later, from the viewpoint of forming a convex portion made of a fluororesin on the surface of the cross-linked molded product, the molding cross-linking condition is preferably a temperature lower than the melting point of the fluororesin, more preferably the melting point of the fluororesin. The temperature is lower by 5 ° C. or more. Moreover, the minimum of the temperature in bridge | crosslinking conditions is the crosslinking temperature of fluororubber.

In addition, in the crosslinking of uncrosslinked rubber, a post-treatment step called secondary crosslinking may be performed after the first crosslinking treatment (referred to as primary crosslinking), which will be described in the next heat treatment step (III). As described above, the conventional secondary crosslinking step is different from the molding crosslinking step (II) and the heat treatment step (III) of the present invention.

(III) Heat treatment step In this heat treatment step (III), the obtained crosslinked molded product is heated to a temperature equal to or higher than the melting point of the fluororesin. Through the heat treatment step (III), convex portions (mainly made of fluororesin) can be formed on the surface of the elastic member to be manufactured.

The heat treatment step (III) in the present invention is a treatment step carried out to increase the ratio of the fluororesin on the surface of the crosslinked molded product. A temperature below the pyrolysis temperature is employed.

When the heating temperature is lower than the melting point of the fluororesin, the ratio of the fluororesin on the surface of the crosslinked molded product is not sufficiently high. In order to avoid thermal decomposition of fluororubber and fluororesin, the heating temperature must be lower than the thermal decomposition temperature of fluororubber or fluororesin, whichever is lower. A preferable heating temperature is a temperature that is higher by 5 ° C. or more than the melting point of the fluororesin from the viewpoint of easily reducing friction in a short time.

The heating time is closely related to the heating temperature, and it is preferable to perform heating for a relatively long time when the heating temperature is relatively close to the lower limit, and to adopt a relatively short heating time when the heating temperature is relatively close to the upper limit. . As described above, the heating time may be appropriately set in relation to the heating temperature. However, if the heat treatment is performed at a very high temperature, the fluororubber may be thermally deteriorated. Therefore, the heat treatment temperature is practically up to 300 ° C. .

The phenomenon of increasing the ratio of the fluororesin on the gasket surface through the heat treatment step (III) was first found by the present inventors.

In addition, when the gasket manufactured through the steps (I) to (III) has a convex portion, an unnecessary portion of the convex portion may be removed by a polishing process or the like after the step (III). Good.

By the way, the conventional secondary cross-linking completely decomposes the cross-linking agent remaining at the end of the primary cross-linking to complete the cross-linking of the fluororubber, thereby improving the mechanical properties and compression set properties of the cross-linked molded product. This is a process to be performed.

Therefore, the conventional secondary cross-linking conditions that do not assume the coexistence of fluororesin are the factors for setting the cross-linking conditions in the secondary cross-linking even if the cross-linking conditions coincide with the heating conditions of the heat treatment step. The heating condition within the range of the purpose of completing the crosslinking of the uncrosslinked fluororubber (completely decomposing the crosslinking agent) is adopted without considering it as a rubber cross-linked product (rubber The condition for softening or melting the fluororesin is not deduced.

In the molding crosslinking step (II), secondary crosslinking may be performed in order to complete crosslinking of the uncrosslinked fluororubber (to completely decompose the crosslinking agent).

Further, in the heat treatment step (III), the remaining crosslinking agent may be decomposed and the crosslinking of the uncrosslinked fluororubber may be completed, but the crosslinking of the uncrosslinked fluororubber in the heat treatment step (III) is only a secondary effect. Only.

The gasket obtained by the manufacturing method including the kneading step (I), the molding cross-linking step (II), and the heat treatment step (III) is in a state in which the ratio of the fluororesin is increased in the surface region due to the surface migration phenomenon of the fluororesin. It is estimated that

In particular, the kneaded product obtained in the kneading step (I) has a structure in which the uncrosslinked fluororubber forms a continuous phase and the fluororesin forms a dispersed phase, or both the uncrosslinked fluororubber and the fluororesin have a continuous phase. It is presumed that the structure is formed, and by forming such a structure, the crosslinking reaction in the molding crosslinking step (II) can be performed smoothly, and the crosslinked state of the resulting crosslinked product is also The surface becomes uniform and the surface transition phenomenon of the fluororesin in the heat treatment step (III) smoothly occurs, and the surface of the fluororesin ratio is increased.

In addition, since the transition to the surface layer of a fluororesin occurs smoothly, the heat treatment at the melting point of the fluororesin is particularly excellent in the heat treatment step.

The state in which the fluororesin ratio has increased in this surface region can be verified by chemically analyzing the surface of the gasket by ESCA or IR.

For example, although the atomic depth of up to about 10nm from the surface of the molded article can be identified by ESCA analysis after the heat treatment, the peak of binding energy from fluorocarbon rubber _{(P ESCA} 1) and a fluororesin derived from the peak _{(P ESCA} The ratio of 2) (P _ESCA 1 / P _ESCA 2) is smaller than that before the heat treatment, that is, the atomic groups of the fluororesin are increased.

In addition, IR analysis can identify atomic groups having a depth of about 0.5 to 1.2 μm from the surface of the molded product, but after heat treatment, a characteristic absorption peak derived from fluororubber at a depth of 0.5 μm ( P _IR0.5 1) and the fluororesin ratio derived from the peak _{(P IR0.5 2) (P IR0.5} 1 / P IR0.5 2) is smaller relative to prior heat treatment, i.e. fluororesin atoms The group is increasing. Moreover, even if the ratio at the depth of 0.5 μm (P _IR0.5 1 / _PIR0.52 ) and the ratio at the depth of 1.2 μm ( _PIR1.21 / _PIR1.22 ) are compared, The ratio at the depth of 0.5 μm (P _IR0.5 1 / P _IR0.52 ) is smaller, indicating that the fluororesin ratio is increasing in the region closer to the surface.

By the way, when the surface of the fluororubber is modified by application or adhesion of fluororesin, the fluororesin ratio is not inclined. The fluororesin is deposited on the gasket surface of the fuel cap for automobiles of the present invention, and usually has a gradient distribution of the fluororesin ratio. Such a gasket is an unprecedented novel gasket.

And since the ratio of the fluororesin on the surface is high, the characteristics of the fluororesin such as low adhesion, non-adhesiveness, low friction and water / oil repellency are remarkably improved. In addition, the properties of fluororubber can be exhibited on the other side than the surface portion, and as a whole, an excellent gasket can be obtained with a good balance in all of low adhesion, non-adhesiveness, low friction, water / oil repellency, and elastomeric properties. . Furthermore, since there is no clear interface state between the fluororesin and the fluororubber, the surface-rich region of the fluororesin is not dropped and the durability is excellent.

Next, the present invention will be described with reference to examples, but the present invention is not limited to such examples.

Fluoro rubber: A binary fluoro rubber capable of polyol crosslinking (G7401 manufactured by Daikin Industries, Ltd.).
Fluororesin: ETFE (EP-610 manufactured by Daikin Industries, Ltd.)
Filler: Carbon black (MT carbon manufactured by Cancarb: N990)
Acid acceptor: Magnesium oxide (MA150 manufactured by Kyowa Chemical Industry Co., Ltd.)
Crosslinking aid: Calcium hydroxide (CALDIC2000 manufactured by Omi Chemical Co., Ltd.)

Example 1
(I) Kneading step (Precompound preparation)
100 parts by mass of fluororubber and 33 parts by mass of fluororesin are introduced into a pressure type kneader having an internal volume of 3 liters so that the volume filling rate is 85%, and the material (fluororubber and fluororesin) temperature becomes 230 ° C. To prepare a pre-compound. The rotation speed of the rotor was 45 rpm.

(Preparation of full compound)
The obtained pre-compound was wound around an open roll having two 8-inch rolls, 1 part by mass of filler, 3 parts by mass of acid acceptor, and 6 parts by mass of a crosslinking aid were added and kneaded for 20 minutes. Further, the obtained full compound was cooled for 24 hours, and again kneaded at 30 to 80 ° C. for 20 minutes using an open roll equipped with two 8-inch rolls to prepare a full compound.

The cross-linking (vulcanization) characteristics of this full compound were examined. The results are shown in Table 1.

(II) Forming and cross-linking process Full compound is charged into a fuel filler packing mold, pressurized to 10 MPa, vulcanized at 170 ° C. for 10 minutes, and a cross-linked formed product having a cross section of gasket (packing) 4 in FIG. The outer diameter was Φ52.6 mm, the inner diameter was Φ40 mm, and the sectional height was 6.7 mm.

(III) Heat treatment step The obtained cross-linked molded article was put into a heating furnace maintained at 230 ° C. for 24 hours and subjected to heat treatment to obtain a fuel filler packing.

Crosslinking (vulcanization) characteristics were measured at a measurement temperature of 170 ° C. using a JSR Clastometer Type II.

By observing the surface of the fuel filler packing using an atomic force microscope and analyzing the hardness of the surface from the obtained phase image, it was confirmed that there were substantially convex portions made of a fluororesin. In addition, the average diameter of the convex portions on the surface of the fuel filler packing is the average diameter within 100 measurement fields, and the average diameter within the measurement field is defined for all convex portions within the measurement field (150 μm square). This is an average value of values obtained by dividing the sum of the major axis and the minor axis of a region formed by cutting on a plane having a height of 0.15 μm by 2. In addition, the average height of the convex portion is the average height in 100 measurement visual fields, and the height in the measurement visual field is the value of the height of each convex portion for all the convex portions in the measurement visual field (150 μm square). Is an average value.
Further, the occupancy ratio of the convex portion is an occupancy ratio of 100 pieces in the measurement visual field, and the occupancy ratio in the measurement visual field is a height of the convex portion of 0.15 μm for all the convex portions in the measurement visual field (150 μm square). The area of the region formed by cutting along the plane is the ratio of the area of the measurement visual field (150 μm square).

Atomic force microscope: PM920-006-101 made by VEECO Multi-mode V system cantilever: HMX-10 made by VEECO Probes
Measurement environment: Normal temperature and humidity Measurement field of view: 150μm square measurement mode: harmonics mode

Table 1 shows the results of identifying the atomic groups of 0.5 μm depth from the tip of the convex portion on the surface of the fuel filler and 0.5 μm depth from the surface outside the convex portion by IR analysis. Here, the characteristic absorption peak derived from fluororubber is _defined as ( _PIR0.51 ), the characteristic absorption peak derived from fluororesin ( _PIR0.52 ), and the ratio ( _PIR0.51 / _PIR0.5). 2).
Here, the convex portion refers to a portion having a height of 0.15 μm or more.

Next, adhesion of the fuel filler packing was measured by the method described below. The results are shown in Table 1.
As shown in FIG. 1, the fuel filler packing of the present invention is assembled to a commercially available fuel filler cap (Honda vehicle part number: 17670-SJA-013) as shown in FIG. Part No .: 17670-TM8-013), left in a heating furnace at 150 ° C. for 72 hours, and then left at room temperature for 24 hours. After leaving, the fuel filler cap was removed, and the state of rubber sticking to the fuel filler pipe was confirmed.
The fixing state was confirmed visually and with an optical microscope (× 10), and ○: no fixing with an optical microscope, Δ: fixing with an optical microscope, and X: fixing with an eye.

Examples 2-5
Table 1 (24 (Example 2), 48 (Example 3), 96 (Example 4), or 168 hours (Example 5) in a heating furnace maintained at 250 ° C.) The fuel filler packing was obtained in the same manner as in Example 1 except that the change was made as described in the above, and the fixation state was confirmed. The results are shown in Table 1.

Examples 6-8
A fuel filler packing was obtained in the same manner as in Example 2 except that the ratio between the fluororesin and the fluororubber was changed as shown in Table 1, and the adhesion test and the adhesion state were confirmed. The results are shown in Table 1.

Comparative Examples 1 and 2
A fuel filler packing is obtained through a molding and crosslinking process using a binary fluororubber material not mixed with a fluororesin and a material that is mixed with a fluororesin similar to that of Example 1 but not subjected to heat treatment. In the same manner as above, adhesion was confirmed. The results are shown in Table 1.

From the results of Table 1, it can be seen that each example of the automotive fuel cap of the present invention is superior in adhesion test characteristics to each comparative example.

The fuel cap for automobiles of the present invention exhibits excellent performance as a fuel cap for opening and closing a fuel filler port of a fuel tank of an automobile.

1: Cap part 2: Thread part 2a: Thread 2b: Rib 3: Filler neck 3a: Filling port 3b: Filler neck side screw 3c: Seal surface 4, 30: Gasket 4a: Slit 31: Convex part 100: Fuel for automobile cap

Claims (4)

A fuel cap for automobiles attached to a fuel filler of an automobile fuel tank,
The automobile fuel cap includes a gasket that is pressed against a fuel filler and seals the fuel filler;
The gasket is made of a composition containing fluororubber and fluororesin, and the fluororesin is deposited on the surface.
The fluororesin is a copolymer containing polymerized units based on ethylene and polymerized units based on tetrafluoroethylene,
The fluorine rubber, Ri polymer der containing polymerized units based on vinylidene fluoride,
The gasket surface has a convex part,
The automobile fuel cap, wherein an average diameter of the convex portions is 5 to 20 m . The fuel cap for automobiles according to claim 1, wherein the ratio of the fluorine resin on the gasket surface is higher than the inside. Fluoro rubber is
Polymerized units based on vinylidene fluoride;
Polymerized units based on at least one monomer selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, and perfluoro (alkyl vinyl ether);
The fuel cap for automobiles according to claim 1, which is a copolymer containing The automobile fuel cap according to claim 1, 2 or 3, wherein the composition containing fluororubber and fluororesin has a mass ratio of fluororubber to fluororesin of 60/40 to 97/3.

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