JP2011178207A - In-tank tube for automotive fuel, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an in-tank tube excellent in pressure resistance performance. <P>SOLUTION: The in-tank tube 1 for automotive fuel of a single-layer structure is disposed in a fuel tank 2 and has a structure of absorbing the displacement of a fuel tank 2 and the vibration of a fuel pump 5. The in-tank tube 1 for automotive fuel is formed from a resin material which uses high-density polyethylene (HDPE) of not less than 0.950 in specific gravity as a primary component, and has the following pressure-proof characteristics (X). (X) The in-tank tube immersed in test solution [Fuel C: 85:15 (capacity reference)] at 80°C for 168 hours is filled with silicone oil as a pressurizing medium, both ends of the in-tank tube are covered with a test pipe, pressure-proof test are implemented at a boosting speed of 1.0 MPa/min and at a room temperature. The pressure (burst pressure) when the in-tank tube has burst or the test pipe is pulled out is not less than 2.5 MPa. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is an in-tank tube for automobile fuel (hereinafter, abbreviated as “in-tank tube” as appropriate) provided in a fuel tank and having a bellows structure for absorbing displacement of the fuel tank and vibration of the fuel pump. .) And its manufacturing method.

  In general, a fuel piping system of an automobile has a mechanism for sucking and supplying fuel (gasoline, alcohol-added gasoline (gasohol), etc.) necessary for operating an engine from a fuel tank as needed. At this time, the fuel is sucked up by a pump (referred to as a fuel pump) that is permanently installed in the fuel tank. A hose connected to the fuel pump in the fuel tank is called an in-tank tube, and this hose is also permanently installed in the fuel tank, like the fuel pump. Here, FIG. 1 schematically shows the inside of the fuel tank, wherein 1 is an in-tank tube (1 ′ is a return-side in-tank tube usually provided in the case of a diesel vehicle, 2 is a fuel tank, 3 is a fuel, 4 is a filter, 5 is a fuel pump, 6 is a jet pump, 7 is a polyoxymethylene (POM) housing, and 8 is a spring. It is. That is, the fuel 3 in the fuel tank 2 passes through the filter 4, is sent into the in-tank tube 1 by the fuel pump 5, and is sent as it is to an external fuel circuit such as an engine. The housing 7 holding the in-tank tube 1 and the like is provided with a spring 8 to cope with deformation due to thermal expansion of the fuel tank 2. Further, the in-tank tube 1 also has a bellows structure as shown in the drawing in order to cope with deformation due to expansion of the fuel tank 2 and vibration absorption of the pump. The return side fuel 3 is returned into the housing 7 by the venturi effect of the jet pump 6.

  By the way, although the said in-tank tube 1 is provided in the above-mentioned state, it originates in the use aspect, and the tolerance (sour gasoline resistance) with respect to the sour gasoline produced | generated when the said gasoline 3 is oxidized. In addition to the inner peripheral surface of the hose, the outer peripheral surface of the hose is also required. Therefore, conventionally, the entire hose has been made to meet these demands by forming it with a material excellent in sour gasoline resistance such as polyamide 11 (PA11), polyamide 12 (PA12), etc. ( For example, see Patent Document 1).

JP-A-7-118349

  By the way, the in-tank tube 1 shown in FIG. 1 and the fuel pump 5 are usually connected by a connector 10 as shown in FIG. The press-fitting portion 11 of the connector 10 is connected to the in-tank tube 1 by press-fitting into the end portion of the in-tank tube 1, and the engaging portion 12 of the connector 10 is engaged with the engaged portion of the fuel pump 5. It is connected by. By the way, in recent years, alcohol-added gasoline tends to be used, and there is a shortage of heat in gasoline, and in order to compensate for the fuel shortage, the in-tank tube has a large diameter and tends to increase the flow rate of alcohol-added gasoline. is there. However, due to a decrease in pressure resistance due to an increase in the diameter of the in-tank tube and a pressure of the fuel pump, etc., there are significant problems such as the end of the in-tank tube 1 coming out of the press-fit portion 11 of the connector 10.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an in-tank tube excellent in pressure resistance and a manufacturing method thereof.

In order to achieve the above object, the present invention is an in-tank tube for automobile fuel having a single-layer structure, which is disposed in a fuel tank and has a structure for absorbing displacement of the fuel tank and vibration of the fuel pump. The in-tank tube for automobile fuel is made of a resin material mainly composed of high density polyethylene (HDPE) having a specific gravity of 0.950 or more, and the in-tank tube for automobile fuel having the following pressure resistance (X) is It is set as the summary of 1.
(X) An in-tank tube immersed in a test solution [Fuel C: methanol = 85: 15 (volume basis)] at 80 ° C. for 168 hours is filled with silicon oil as a pressurizing medium, and both ends of the in-tank tube are connected to each other. Sealed with a test pipe, pressure resistance test is performed at a pressure increase rate of 1.0 MPa / min at room temperature, and the pressure (breaking pressure) when the in-tank tube bursts or the test pipe comes out is 2.5 MPa or more. It is.

  The present invention also relates to a method for producing an in-tank tube for an automobile fuel having a single layer structure, which is disposed in a fuel tank and has a structure for absorbing displacement of the fuel tank and vibration of the fuel pump, and has a specific gravity of 0.950. The step of extruding the resin material mainly composed of high density polyethylene (HDPE) into a tube shape, the step of irradiating the tube with an electron beam, and the glass transition temperature (Tg) of the HDPE with respect to the tube irradiated with the electron beam. ) As described above, the second gist is a method for producing an in-tank tube for automobile fuel comprising a step of heat-treating at a temperature lower than the melting point.

  That is, the present inventors have intensively studied to obtain an in-tank tube excellent in pressure resistance. In the course of that research, I recalled using high density polyethylene (HDPE) with a specific gravity of 0.950 or higher as the material for forming the in-tank tube, and crosslinking it with electron beam irradiation. A sufficient crosslinking effect was not obtained. Thus, as a result of further experiments, it was found that when heat treatment was performed after electron beam irradiation, in-tank tubes with sufficient cross-linking and excellent pressure resistance were obtained, and the present invention was achieved. The reason is considered as follows. That is, when electron beam irradiation is performed on high density polyethylene (HDPE) having a specific gravity of 0.950 or more, radicals are generated by the energy of the electron beam, crosslinking proceeds, strength is increased, and heat resistance is also improved. Since this polymer radical has a long lifetime, a large amount of unreacted radicals remain only by the previous electron beam irradiation. For this reason, by heating, in the amorphous part (glass-like part) in which radicals are freely moved, crosslinking is promoted, and the strength and pressure resistance of the entire in-tank tube are increased. However, if heat treatment is performed at a temperature higher than the melting point, cross-linking occurs in the crystal part, and the presence of the resulting cross-linked product disturbs the crystal state of the crystal part and lowers its crystallinity. It will end up.

  As described above, the in-tank tube of the present invention is obtained by performing heat treatment at a predetermined temperature after electron beam irradiation. That is, the in-tank tube of the present invention is made of a resin material mainly composed of high density polyethylene (HDPE) having a specific gravity of 0.950 or more and has a predetermined pressure resistance characteristic (X). However, it is possible to prevent the in-tank tube from coming off from the connector. In addition, in the present invention, since high-density polyethylene (HDPE) crosslinked by electron beam irradiation and heat treatment is used, it is hardly affected by alcohol and has excellent resistance to alcohol-added gasoline (alcohol-resistant gasoline resistance). It is also suitable for bioalcohol fuel, which is expected to become popular in the future. In the present invention, since unreacted radicals are consumed by heat treatment, the decomposition reaction that cleaves the main chain of high-density polyethylene (HDPE) is suppressed, and changes with time are less likely to occur. Therefore, the in-tank tube can be shipped immediately, and a necessary function can be exhibited immediately after the in-tank tube is mounted on the automobile as an automobile part. Furthermore, the in-tank tube of the present invention mainly composed of high-density polyethylene (HDPE) can realize a significant cost reduction as compared with a conventional in-tank tube using a polyamide resin such as PA11.

It is explanatory drawing which showed the mode inside the fuel tank of a motor vehicle typically. It is explanatory drawing of the connector which connects an in-tank tube and a fuel pump.

  Next, embodiments of the present invention will be described in detail. However, the present invention is not limited to this embodiment.

  As shown in FIG. 1, the in-tank tube of the present invention is provided in the fuel tank 2 and has a bellows structure that absorbs the displacement of the fuel tank 2 and the vibration of the fuel pump 5. However, since the in-tank tube of the present invention has a large diameter, the dimensions of each part are changed accordingly. The in-tank tube 1 and the fuel pump 5 are normally connected by a connector 10 as shown in FIG. 2 as described above. The press-fitting portion 11 of the connector 10 is connected to the in-tank tube 1 by press-fitting into the end portion of the in-tank tube 1, and the engaging portion 12 of the connector 10 is engaged with the engaged portion of the fuel pump 5. It is connected by.

  Here, the in-tank tube of the present invention has a large diameter, and is usually set to an inner diameter of 3 to 10 mm, preferably 5 to 8 mm, and a wall thickness of 0.5 to 1.5 mm, preferably 0. .7 to 1.2 mm. In addition, the in-tank tube of this invention can be made smaller than the said aperture, and there exists the same pressure | voltage resistant improvement effect etc.

  The in-tank tube is a single layer structure made of a resin material whose main component is high density polyethylene (HDPE) having a specific gravity of 0.950 or more. Here, the main component means that the high-density polyethylene usually occupies a majority of the resin material, but includes the case where the resin material is made of only high-density polyethylene.

<< High density polyethylene (HDPE) >>
The high density polyethylene (HDPE) has a specific gravity of 0.950 or more, preferably 0.955 or more, particularly preferably 0.969 or more. That is, when a polyethylene resin having a specific gravity of less than 0.950 is used, the flexibility is good to some extent, but the pressure resistance is poor. The specific gravity is a value measured according to JIS K6899-1: 2000.

  As the resin material for forming the in-tank tube, pigments, dyes, lubricants, plasticizers, antioxidants and the like may be blended in addition to the high density polyethylene (HDPE) having a specific gravity of 0.950 or more. These may be used alone or in combination of two or more.

  The in-tank tube of the present invention can be produced, for example, as follows. That is, first, a resin material mainly composed of high density polyethylene (HDPE) having a specific gravity of 0.950 or more is prepared, and this is extruded into a large-diameter tube shape by an extruder or the like, and further, by a corrugator or the like. A bellows structure is formed. Next, the tube having the bellows structure is irradiated with an electron beam by an electron beam irradiation device or the like. Then, it cuts into predetermined length with a cutting machine etc., puts this in a heat treatment furnace, and can perform the target in-tank tube by performing heat processing.

《Electron beam irradiation》
The dose of the electron beam irradiation is preferably in the range of 50 to 250 kGy, particularly preferably in the range of 100 to 250 kGy. That is, if the dose of electron beam irradiation is too small, the crosslinking effect is small, whereas if it is too large, the in-tank tube tends to deteriorate.

"Heat treatment"
The temperature condition of the heat treatment needs to be performed at a temperature not less than the glass transition temperature (Tg) of the high-density polyethylene having a specific gravity of 0.950 or more and less than the melting point, specifically, a range of 80 ° C. or more and less than 130 ° C. Is preferable, and the range of 80 to 120 ° C. is particularly preferable. That is, when heat treatment is performed at a temperature equal to or higher than the melting point of the high-density polyethylene (HDPE), the cross-linking of the crystal part of the high-density polyethylene (HDPE) increases, the crystallinity decreases, and the cross-linking of the crystal part returns to the original structure. This is because the pressure resistance performance is degraded. Conversely, when heat treatment is performed at a temperature lower than the glass transition temperature (Tg), the molecules are frozen, radical recombination hardly occurs, and the effect is hardly exhibited.

  The heat treatment time is preferably 10 to 60 minutes, particularly preferably 20 to 40 minutes. That is, if the heat treatment time is too short, cross-linking does not proceed sufficiently, causing variations. Conversely, if the heat treatment time is too long, the resin may be deteriorated.

  The in-tank tube (inner diameter 3 to 10 mm, wall thickness 0.5 to 1.5 mm) of the present invention thus obtained has the following pressure resistance characteristics (X).

《Pressure resistance (X)》
An in-tank tube immersed in a test solution [Fuel C: methanol = 85: 15 (volume basis)] at 80 ° C. for 168 hours is filled with silicon oil as a pressurizing medium, and both ends of the in-tank tube are pipes for testing. The pressure test was performed at room temperature (23 ° C.) at a pressure increase rate of 1.0 MPa / min, and the pressure (breaking pressure) when the in-tank tube burst or the test pipe was pulled out was 2.5 MPa. It is above, Preferably it is 2.6 MPa or more, Most preferably, it is 2.7 MPa or more. That is, if the pressure (breakdown pressure) is too small, problems such as the in-tank tube coming out of the connector occur.

  Some of the dimensions of the in-tank tube of the present invention have been described earlier, but the details are as follows. The thickness of the in-tank tube (thickness at the straight portions at both ends) is usually 0.5 to 1.5 mm, preferably 0.7 to 1.2 mm. Further, the inner diameter of the straight portion is preferably in the range of 3 to 10 mm, particularly preferably in the range of 5 to 8 mm, and the outer diameter of the straight portion is preferably in the range of 4 to 13 mm, particularly preferably in the range of 6 to 10 mm. It is. Further, the ratio of the valley outer diameter to the mountain outer diameter at the bellows portion in the hose is preferably about valley outer diameter / peak outer diameter = about 7 mm / 10 mm and the pitch length is about 3 mm. .

  Next, examples will be described together with comparative examples. However, the present invention is not limited to these examples.

  First, prior to the examples and comparative examples, the following materials were prepared.

[High-density polyethylene (HDPE)]
<High-density polyethylene A>
Made by Prime Polymer, Hi-Zex 5000SR (specific gravity 0.955)

<High-density polyethylene B>
Made by Prime Polymer, Hi-Zex 5000S (specific gravity 0.950)

<High-density polyethylene C>
Made by Prime Polymer, Hi-Zex 5202B (specific gravity 0.960)

<High-density polyethylene a (for comparative example)>
Made by Prime Polymer, Hi-Zex 5100B (specific gravity 0.944)

[Example 1]
High-density polyethylene A (manufactured by Prime Polymer Co., Ltd., Hi-Zex 5000SR, specific gravity 0.955) is extruded (inner diameter: 6 mm, outer diameter: 8 mm), and vacuum forming corrugator (manufactured by Colma, model 120HS) has a bellows structure (Bellows structure part: 150 mm, trough outer diameter / crest outer diameter = 7 mm / 10 mm, pitch length: 3 mm) (both ends straight part: 10 mm, both ends straight part inner diameter: 6 mm, outer diameter: 8 mm) . Next, this was irradiated with an electron beam (a dose of 100 kGy) and cut into a predetermined length with a cutting machine (length: 180 mm). Next, the cut tube is put into a heat treatment furnace [manufactured by Espec Corp., PV (H) -212] and subjected to heat treatment (80 ° C. × 30 minutes) to produce an in-tank tube (having the above inner diameter and outer diameter). did.

[Examples 2 to 5, Comparative Examples 1 to 5]
An in-tank tube was produced in accordance with Example 1 except that the type of high-density polyethylene, the conditions of electron beam irradiation and heat treatment, and the like were changed as shown in Tables 1 and 2 below.

  Using the in-tank tubes of Examples and Comparative Examples thus obtained, each characteristic was evaluated according to the following criteria. These results are shown in Tables 1 and 2 above.

(Breaking pressure)
<Initial room temperature (23 ℃)>
The in-tank tube is filled with silicon oil as a pressurizing medium, both ends of the in-tank tube are closed with test pipes, and a pressure resistance test is performed at a pressure increase rate of 1.0 MPa / min at room temperature (23 ° C.). The pressure (breaking pressure) when the tank tube bursts or the test pipe was removed was measured. In the evaluation, a sample having a pressure (breaking pressure) of 3.1 MPa or more was evaluated as “◯”, and a sample having a pressure less than 3.1 MPa was evaluated as “X”.

<After immersion at 80 ° C>
The in-tank tube was immersed in the test solution [Fuel C: methanol = 85: 15 (volume basis)] at 80 ° C. for 168 hours, then taken out, and filled with silicon oil as a pressurized medium in the in-tank tube. When both ends of the in-tank tube are plugged with test pipes, a pressure resistance test is performed at a pressure increase rate of 1.0 MPa / min at room temperature (23 ° C.), and the in-tank tube bursts or the test pipe is removed The pressure (breaking pressure) was measured. In the evaluation, those having a pressure (breaking pressure) of 2.5 MPa or more were evaluated as ◯, and those having a pressure less than 2.5 MPa were evaluated as ×.

  From the above results, it is considered that any of the example products can prevent the in-tank tube from coming off from the connector or the like because the breaking pressure after immersion at 80 ° C. is 2.5 MPa or more.

  On the other hand, all of the comparative example products had a breaking pressure after immersion at 80 ° C. of less than 2.5 MPa.

  The in-tank tube for an automobile of the present invention is a single-layer structure having a structure (such as a bellows structure) that absorbs the displacement of the fuel tank, the vibration of the fuel pump, and the like, and is used in a fuel tank of an automobile or the like. It is done.

1 in-tank tube 2 fuel tank 3 fuel 4 filter 5 fuel pump 6 jet pump 7 housing 8 spring

Claims (6)

An in-tank tube for automobile fuel having a single-layer structure provided in the fuel tank and configured to absorb the displacement of the fuel tank and the vibration of the fuel pump, wherein the in-tank tube for automobile fuel has a specific gravity of 0. An in-tank tube for automobile fuel comprising a resin material mainly composed of 950 or more high-density polyethylene (HDPE) and having the following pressure resistance (X).
(X) An in-tank tube immersed in a test solution [Fuel C: methanol = 85: 15 (volume basis)] at 80 ° C. for 168 hours is filled with silicon oil as a pressurizing medium, and both ends of the in-tank tube are connected to each other. Sealed with a test pipe, pressure resistance test is performed at a pressure increase rate of 1.0 MPa / min at room temperature, and the pressure (breaking pressure) when the in-tank tube bursts or the test pipe comes out is 2.5 MPa or more. It is.   The in-tank tube for automobile fuel according to claim 1, wherein the in-tank tube for automobile fuel is a single-layer structure having a bellows structure that has been irradiated and heat-treated with an electron beam.   A method for producing an in-tank tube for automobile fuel having a single-layer structure, which is disposed in a fuel tank and has a structure for absorbing displacement of the fuel tank and vibration of the fuel pump, and comprising a high density polyethylene (specific gravity 0.950 or more) A step of extruding a resin material mainly composed of HDPE) into a tube shape, a step of irradiating the tube with an electron beam, and a glass transition temperature (Tg) of the HDPE above the melting point of the tube irradiated with the electron beam. And a process for heat-treating at a temperature.   The method for producing an in-tank tube for automobile fuel according to claim 3, wherein the in-tank tube for automobile fuel is a single-layer structure having a bellows structure.   The method for producing an in-tank tube for automobile fuel according to claim 3 or 4, wherein the temperature in the heat treatment step is in the range of 80 to 120 ° C.   The method for producing an in-tank tube for automobile fuel according to any one of claims 3 to 5, wherein a dose of the electron beam irradiation in the electron beam irradiation step is in a range of 50 to 250 kGy.

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