JP2003065998A - Bush, lead wire unit and oxygen sensor for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molding of bush being used for securing a lead wire and having high heat resistance causing no thermal deterioration, corrosion, cracking, or the like, even after long term use under pressure at high temperature in which excellent caulking properties compressible with a low load are exhibited without damaging the sealing performance, and a load required for compression can be selected appropriately. SOLUTION: The bush does not deteriorate thermally when it is placed under conditions of 25% compression rate conforming to JIS K 6262 at 300 deg.C for 1000 hours and/or does not crack when it is placed under conditions of 25% compression rate conforming to ASTMD 1414 (1994) clause 10 at 300 deg.C for 70 hours.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bush that can be compressed under a low load, has excellent caulking properties, retains sealing properties even at high temperatures for a long time, and has excellent high temperature durability. TECHNICAL FIELD The present invention relates to a bush suitably used for an oxygen sensor.

[0002]

2. Description of the Related Art An oxygen sensor (O ₂ sensor) for detecting oxygen concentration is used, for example, for detecting oxygen concentration in exhaust gas from an internal combustion engine of an automobile. Although the oxygen sensor for automobiles is usually protected by a metal cylinder, it is attached to a hot exhaust pipe, etc., and contains a large amount of oxidizing substances, so the inside of the sensor is exposed to a hot exhaust gas flow, so heat resistance, chemical resistance, etc. Need to be excellent.

[0003] The oxygen sensor for automobiles is often mounted downstream of a catalyst for purifying exhaust gas, or when it is necessary to detect catalyst deterioration, and is often mounted under the floor of a vehicle body.
In this case, the oxygen sensor for automobiles is subject to external impacts such as vibration impacts from the engine and road surface, stone splashes, water splashes, etc., so it may also have mechanical shock resistance, thermal shock resistance, waterproofness, etc. Required.

[0004] The oxygen sensor for automobiles is usually cylindrical, and the electric output of the oxygen concentration detecting element inside the cylinder is taken out to the outside, or the atmosphere serving as the oxygen concentration reference is introduced into the oxygen concentration detecting element. It contains several lead wires.

The lead wire is arranged so as to pass through a sealing material called a bush in order to fix the lead wire at a portion taken out from the oxygen sensor for an automobile without contacting each other. The taken-out portion is also required to have properties such as heat resistance, impact resistance, and waterproofness.

Therefore, the bush is required to have these properties in addition to the sealing properties such as waterproofness and airtightness as a sealing material. Therefore, as the bush, a material having both elasticity and heat resistance has been conventionally used, and a heat resistant rubber such as silicone rubber or fluororubber has been selected according to the operating temperature and the like.

[0007] In recent years, with higher performance of engines and equipment, awareness of environmental protection, etc., more precise sensor control is required, and an oxygen sensor for automobiles is mounted for early activation of the sensor. The position is moving to the upstream side of the exhaust gas flow. Therefore, bushes are required to have higher heat resistance.

[0008] However, the heat resistant rubber which has been conventionally used cannot sufficiently exhibit such a high degree of heat resistance, and continuous use at a high temperature causes thermal deterioration and corrosion, resulting in a seal. The problem was that sex was lost.

The bush usually has a basic shape of a cylinder having a height as required, and when used, a lead wire is passed through several through-holes extending in the height direction which are provided in advance. After that, crimping is performed by applying pressure in the radial direction.
In this specification, the radial direction means a direction from the side surface of the cylinder toward the center of a circle which is a horizontal cross section of the cylinder.

Since the bush is compressed to a certain extent by crimping, the lead wire can be securely fixed, and a sealing property can be obtained, it is desirable that the bush has elasticity. Although conventional heat-resistant rubber has elasticity, when stress strain remains due to caulking, it may cause cracks, and there is also a problem that cracks are likely to occur particularly when used at high temperatures.

In order to solve the problem of heat resistance of heat resistant rubber, polytetrafluoroethylene [PTFE] and tetrafluoroethylene / hexafluoropropylene copolymer have higher heat resistance and have been widely used in a high temperature range. It has been considered to use a fluororesin such as a combination [FEP].

However, at present, as the fluororesin, for example, a molded article formed by general compression molding such as resin powder obtained by polymerization is placed in a mold, pressurized, preformed and then fired is used. However, since such a molded product has no elasticity, it has poor caulking property and sealing property, and there is a problem that it is difficult to use as a bush.

[0013]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is a bush used for fixing a lead wire, which is deteriorated by heat even when used for a long time under high temperature and pressure.
It has a high degree of heat resistance that does not cause corrosion, cracks, etc., does not impair the sealability, has excellent caulking properties that enable compression at low loads, and the load required for compression can be appropriately selected. It is to provide a molded product that can be formed.

[0014]

The present invention is based on JIS K
According to 6262, no thermal deterioration occurs when the compression ratio is 25% at 300 ° C. for 1000 hours, and / or ASTM D 1414 (1994).
7 at 300 ° C under the condition of compression rate of 25% according to paragraph 10.
The bush is characterized in that it does not crack when left for 0 hours. The bush preferably has a specific gravity of 0.4 to 1.8. The bush is preferably made of unmodified polytetrafluoroethylene or modified polytetrafluoroethylene. The bush is preferably used for an oxygen sensor for automobiles.

The present invention is also a bush made of unmodified polytetrafluoroethylene or modified polytetrafluoroethylene, which has a specific gravity of 0.4 to 1.8. The present invention will be described in detail below.

The present invention relates to bushes. In the present specification, the bush means an article having a through hole for allowing the conductor to pass therethrough and insulating and supporting the conductor.
The bush is a bushing.
Sometimes referred to as g). The conductor is not particularly limited, and examples thereof include various lead wires such as a heater lead wire and a sensor lead wire.

As the bush of the present invention, a general bush has a circular bottom surface and a cylindrical shape having a height as required as a basic shape, and a through hole extending in a height direction for inserting a conductor. Several holes are preliminarily drilled. The bush may have a single cylindrical diameter or may have a portion having a large diameter and a portion having a small diameter, depending on the application.

The size of the bush of the present invention depends on the size and structure of the oxygen sensor used and the like, but normally the diameter is 5 to 15 mm and the height (length) is 5 to 20 mm.

The bush of the present invention is JIS K 626.
100 at 300 ° C under the condition of 25% compression rate
It is characterized in that it does not cause thermal deterioration even after 0 hour. Thermal degradation is generally manifested as a phenomenon of weight loss, possibly accompanied by a melt.

In the present specification, the above-mentioned heat deterioration does not occur, and the above-mentioned bush is used as a test object according to JIS K 62.
According to No. 62, when the test was conducted in the radial direction so that the compressibility was 25%, and the sample was kept at 300 ° C. for 1000 hours (hereinafter, referred to as “heat resistance under compression test”), It means that the reduction rate of the weight (G2) of the bush after the heat resistance test under compression is 0.5% or less with respect to the weight (G1) of the bush before the property test. The weight (G1) is a measured value at room temperature, and the weight (G2) is a measured value after returning to room temperature after performing the heat resistance test under compression. In the present specification, the above reduction rate is referred to as a weight reduction rate. The weight reduction rate is a value calculated by the following formula.

[0021]

[Equation 1]

If the weight reduction rate exceeds 0.5%, the durability for long-term use at high temperature tends to be poor. Weight reduction is a factor that causes performance deterioration. If the weight reduction rate is small, it can be used for a long period of time, leading to a reduction in the frequency of replacement of the bush or parts having the bush. Therefore, the weight reduction rate is 0.5%
If it is below, there is no problem in use, but 0.1% or less is preferable from the viewpoint of ensuring long-term use and reduction in replacement frequency.

The bushings of the present invention are ASTM D 14
It does not cause cracks when left at 300 ° C. for 70 hours under the condition of a compression rate of 25% according to paragraph 14 (1994) 10. Above ASTM D 1414
(1994) According to paragraph 10, the bush is
The sample is used as it is without being cut or the like, and is pressed in a radial direction using a predetermined pressurizing device so that the compression rate is 25%, and is kept under the above heating conditions. In the present specification, not to cause the crack, after being placed under the heating conditions, the test object is returned to room temperature, and, in a state of being taken out from the pressure device, the test object is cut in a radial direction. This means that cracks cannot be visually confirmed on the cross section obtained. When visually inspecting for the presence or absence of cracks, the test object is crushed by a method such as applying pressure in a specific direction using a finger, a hand, an instrument, etc.,
Deformation such as bending may be added.

When the above-mentioned bush does not cause the above-mentioned cracks, it retains the sealing property during long-term use at high temperature, can prevent damage, and can have sufficient durability for use. The bush, which causes the cracks, is also affected by the presence or absence of the above-mentioned thermal deterioration, but it can be said that mainly the compressive stress remains.
Use durability is insufficient.

The bush of the present invention has a specific gravity of 0.4-1.
It is preferably 8. Within the above range, the load required for compression / deformation such as caulking can be reduced, and the caulking property is excellent, so that the bush has less residual stress strain and does not generate cracks. It is possible to obtain a product having excellent durability.

In the present specification, the load required for the compression / deformation may be referred to as a deformation load. In the present specification, the caulking property means a property capable of caulking. In the case of the bush, the caulking property is sometimes referred to as workability.

If the specific gravity is less than 0.4, the mechanical strength may be poor, and industrial production may not be easy. When it exceeds 1.8, a large deformation load is required, a large amount of residual stress strain occurs, and durability may be poor.
It is more preferably 0.7 to 1.5, and even more preferably 0.7 to 1.2.

In the present specification, the specific gravity means JIS.
K 7112 (1999) 5.1A method (underwater replacement method)
It is a value obtained by a specific gravity measuring method in accordance with. In the specific gravity measuring method, when the test object has a lower density than the immersion liquid used, it is determined by the same method as the specific gravity measuring method, in the specific gravity measuring method,
A weight made of lead or other high-density material is attached to a metal wire, and when the test object is immersed, the weight is measured so that the weight is below the liquid level of the immersion liquid.

The deformation load can be controlled by producing the bush by appropriately adjusting the specific gravity within the above range, if desired. Therefore, the bush can increase the deformation load by relatively increasing the specific gravity within the range, and can reduce the deformation load by decreasing the specific gravity within the range. The range of design choices can be expanded according to the application and caulking conditions.

The bush of the present invention is preferably made of fluororesin. Since the bush is made of a fluororesin, it can have a high degree of heat resistance.

The above-mentioned fluororesin is not particularly limited, but unmodified PTFE and / or modified PTFE is preferable, and modified PTFE is preferable because it is excellent in heat resistance and a bush having a specific gravity within the above range can be easily obtained. More preferable.

In the present specification, the modified PTFE means tetrafluoroethylene [TF] as a monomer component.
E] and a small amount of other comonomer, and means a copolymer obtained by copolymerization. In the present specification, the unmodified PTFE means a homopolymer of TFE obtained by polymerizing without containing the other copolymer as a monomer component.

The above-mentioned other copolymers are not particularly limited as long as they can be copolymerized with TFE.
Perfluoro (alkyl ethylene) such as hexafluoropropene [HFP]; chlorotrifluoroethylene [CTFE]; trifluoroethylene; perfluorovinyl ether and the like.

The above-mentioned perfluorovinyl ether is not particularly limited and is, for example, perfluoro represented by the following general formula (I) CF ₂ ═CF—ORf (I) (wherein Rf represents a perfluoro group). An unsaturated compound etc. are mentioned. In the present specification, perfluoro means that all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The perfluoro may have ether oxygen.

Examples of the perfluorovinyl ether include perfluoro (alkyl vinyl ether) [PFVE] in which Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms in the general formula (I).

When the carbon number of the perfluoroalkyl group in the PFVE is within the above range, the bush of the present invention having the specific gravity within the above range can be easily obtained. It is preferably 1 to 5.

Examples of the perfluoroalkyl group in the above PFVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group and a perfluorohexyl group. A perfluoropropyl group is preferable from the viewpoint of easily obtaining a specific gravity within the range and the cost.

As the perfluorovinyl ether, Rf has a carbon number of 4 in the general formula (I).
~ 9 perfluoro (alkoxyalkyl) group, the following formula

[0039]

[Chemical 1]

(Wherein, m is 0 or an integer of 1 to 4), or an organic group represented by the following formula:

[0041]

[Chemical 2]

(In the formula, n represents an integer of 1 to 4) and examples thereof include perfluoro (alkoxyalkyl vinyl ether) and perfluoro (alkoxy vinyl ether).

The proportion (% by weight) of the above-mentioned other comonomer in the whole monomer components depends on the kind, but is preferably a small amount that does not impart melt fluidity to the obtained copolymer. . For example, when the above-mentioned perfluorovinyl ether is used as the above-mentioned other comonomer, it is usually 2
It is preferably at most wt%, more preferably 0.01 to 1 wt%.

The above unmodified PTFE and the above modified PTFE
For example, two or more kinds having different average molecular weights, copolymer compositions and the like may be used, or one kind may be used.

The above unmodified PTFE and the above modified PTFE
The method for producing is not particularly limited, and can be obtained, for example, by a usual suspension polymerization method. Unmodified PTFE mentioned above
The modified PTFE depends on the method for producing the bush described later, but in order to easily obtain the specific gravity within the range described above, the raw material in the method for producing the bush is preferably prepared as a solid such as powder.

The above-mentioned unmodified PTFE powder and the above-mentioned modified P
As the TFE powder, for example, a powder having a desired average particle diameter suitable for the above-mentioned bush production method can be obtained by appropriately pulverizing it by a conventionally known method or the like and classifying it as necessary.

Examples of the bush manufacturing method for manufacturing the bush of the present invention include the following methods. In addition, in the following production methods (1) to (4), "PTFE" means the above-mentioned unmodified PTFE.
And modified PTFE mentioned above, and can be applied to any of them by appropriately adjusting the production conditions and the like.

Production Method (1) Firing obtained by firing an unfired PTFE powder at a temperature above the melting point of PTFE (327 ° C.), preferably 327 ° C. to 400 ° C., then pulverizing and classifying if necessary. Done PT
There is a method of molding a PTFE porous body by filling a mold with FE powder, taking out a preform obtained by pressurizing the mold, and firing it again at a temperature equal to or higher than the melting point of PTFE.

The unsintered PTFE powder preferably has an average particle size of less than 230 μm, more preferably 80 μm or less. The lower limit of the average particle diameter is determined by the pulverizing device and the pulverizing technique, but usually 1 μm is preferable,
40 μm is more preferable.

The calcined PTFE powder preferably has an average particle size of 8 to 250 μm. When the average particle diameter is within the above range, the specific gravity within the above range can be easily obtained. More preferably, it is 50 to 100 μm. The baked PTFE powder may be referred to as a gelled powder.

The pressure applied in the manufacturing method (1) is 0.
It is preferable to carry out at 001 to 800 kg / cm ² . When the pressure is within the above range, the baked PTFE powder is hardened and hardened, so that the powder particles are not completely crushed and not evenly bound, and a place where the powder particles are in contact with each other. Or only the place where the powder particles are close to each other is bound by the thermal expansion force, so that a porous preform is obtained, and by re-baking it as described above. A PTFE porous body can be obtained.
More preferably, it is 100 to 500 kg / cm ² .

The production method (1) is preferably used when the specific gravity of the bush is set to 1 to 1.8. In addition,
The manufacturing method similar to the above manufacturing method (1) is described in JP-B-4-2.
It is described in Japanese Patent No. 3658.

Manufacturing method (2) After filling the mold with the baked PTFE powder used in the manufacturing method (1), the mold is filled with the above-mentioned P without pressing.
By heating to a temperature above the melting point of TFE, the above-mentioned baked PTFE powders are partially bound to each other to form PTFE.
A method of forming a porous body can be mentioned.

The baked P in the manufacturing method (2)
The mechanism for binding the TFE powders to each other is the same as that described in the manufacturing method (1). The manufacturing method (2) is preferably used when the specific gravity of the bush is 0.4 to 1. A manufacturing method similar to the above manufacturing method (2) is described in Japanese Patent Laid-Open No. 7-149941.

Production Method (3) The PTFE powder obtained by the suspension polymerization method and the decomposition temperature PT
A preform is prepared by using a mixture with a pore-forming agent powder having a melting point lower than that of the FE resin, and the preform is heat-treated at a temperature not lower than the decomposition temperature of the pore-forming agent and not higher than the melting point of the PTFE resin. A method for producing a PTFE porous body is characterized in that after the pore-forming agent is decomposed and removed, it is fired at a temperature equal to or higher than the melting point of PTFE.

The pore-forming agent in the above production method (3) is preferably an organic foaming agent and / or an inorganic foaming agent,
More preferably, it is at least one selected from ammonium hydrogen carbonate, ammonium carbonate, and ammonium nitrite.

The particle size of the pore-forming agent in the above production method (3) is preferably 1 to 500 μm,
The particle diameter of the FE powder is preferably 1 to 900 μm. A manufacturing method similar to the above manufacturing method (3) is described in JP-A No. 11-124458.

Manufacturing Method (4) A method for manufacturing a PTFE foam is described in which PTFE is irradiated with ionizing radiation at a dose rate of 0.5 to 100 kGy / s in the absence of oxygen at a temperature above the crystal melting point. To be

In the above production method (4), PTFE is crosslinked by irradiation with radiation under the above conditions, and at this time, decomposition products such as PTFE monomers and oligomers produced by thermal decomposition at high temperature and radiolysis are When irradiated in a vacuum, bubbles remain in the PTFE and are cooled by P
A TFE foam is obtained. Nitrogen, argon,
When irradiation is performed in an inert gas such as helium, a PTFE foam is obtained by degassing at a high temperature after irradiation and then cooling.

The irradiation temperature is preferably around 340 to 350 ° C. The dose rate is preferably 0.5 to 50 kGy. Examples of the ionizing radiation include γ-rays, electron beams, X-rays, neutron rays, and high-energy ions, and electron beams are preferable. A manufacturing method similar to the manufacturing method (4) is described in JP-A-7-118424.

Manufacturing method (5) A fluoropolymer-containing product which has already been processed is heated to a foamable state and then pressurized with supercritical CO ₂ to perform depressurization while the resulting product is in the foamable state. The method for producing a foam is characterized in that the foaming is performed with CO ₂ and then cooled.

The heating in the above production method (5) is carried out at a temperature not higher than the melting point of the resin, for example not higher than the melting point.
It is carried out at a temperature of 0 ° C. or lower, for example, 310 to 350 ° C. for PTFE, 220 to 250 ° C. for FEP (melting point 260 ° C.), and 280 to 325 ° C. for PFA (melting point 310 ° C.).

As the manufacturing method (5), for example, T
FE and perfluoro (propyl vinyl ether) [P
The unsintered molded product molded from the modified PTFE granular resin (melting point 340 ° C.) which is a copolymer of PVE] is heated at 325 ° C. for 4 hours, during which CO ₂ pressure is applied to 1000 psi.
From an initial pressure of (6.9 MPa) to 4200 psi (29
(MPa) and then cooled to 250 ° C. over 25 minutes, and then CO ₂ is discharged from the pressure vessel to obtain a foam having a void content of 33%. A manufacturing method similar to the above manufacturing method (5) is described in JP-A-10-130419.

As the bush manufacturing method, the manufacturing method (1) and the manufacturing method (2) are preferable. According to the manufacturing method (1) and the manufacturing method (2), the specific gravity of the bush can be adjusted mainly by adjusting the filling degree of the fired PTFE powder into the mold. The production method (2) is more preferable because of the ease of adjusting the specific gravity of the bush and reducing the specific gravity.

As described below, the bush is usually
Although the conductor is inserted into the through hole and caulking is performed, the bush of the present invention includes not only the bush before the caulking but also the bush after the caulking. .

The bush is mainly used in the lead wire unit. A lead wire unit having the above bush is also one aspect of the present invention. In the present specification, the lead wire unit means the bush and the lead wire inserted through the bush as the conductor.

The lead wire may be a lead wire coated with a coating material. The coating material is not particularly limited, but a material having heat resistance, abrasion resistance and the like is preferable, and examples thereof include a material obtained by knitting glass fiber and impregnated with silicon resin, and a fluororesin. When the above coating is performed, the conductor wire is protected and
The adhesion with the bush can be improved.

The lead wire is not particularly limited and is appropriately selected depending on the application, and examples thereof include various lead wires for sensors, heaters, etc. as described above. The length, diameter, etc. of the lead wire are not particularly limited and are determined according to the application. The number of the lead wires per one lead wire unit is not particularly limited and may be, for example, 2 to 10 or the like depending on the application, and is usually 4 when used in an automobile oxygen sensor, for example.

The lead wire unit is not particularly limited, but an example is shown in the perspective view of FIG. In FIG.
A through hole 2 is formed in the bush 1 in the length direction thereof, and a lead wire 3 is inserted into the through hole 2. A part 1a of the bush 1 is compressed, and the bush 1 and the lead wire 3 are in close contact with each other. In addition,
As another example of the lead wire unit, there may be mentioned one that performs the compression not only on the part 1a of the bush 1 but also on the entire bush 1.

The method of manufacturing the lead wire unit is not particularly limited and may be, for example, a conventionally known method. For example, after the lead wire is passed through a through hole previously drilled in the bush, , A method of applying pressure in the radial direction and caulking, and the like.

The caulking is usually 5 to 15 kg / cm.
The pressure of ² is applied so that the volume of the bush is compressed to 85 to 95% before being caulked. The crimping may be performed at a temperature of 300 to 370 ° C., for example.
By caulking under heating in this way, the adhesion between the lead wire and the bush is improved, especially when the lead wire is covered with the coating.

When the crimping is used for an automobile oxygen sensor, for example, in the process of manufacturing the automobile oxygen sensor, pressure is generally applied in the radial direction from the outside of the metal cylinder which is the outer wall of the automobile oxygen sensor. By doing.

The lead wire unit of the present invention includes not only the lead wire unit after the above crimping but also the one before the above crimping.

The application of the lead wire unit is not particularly limited, and examples thereof include those requiring insulation and protection of the lead wire, sealability, and heat resistance. For example, as an electric wiring member, an oxygen sensor, Various sensors such as temperature sensors, air-fuel ratio sensors, brake wear detectors, gas meters, etc .; heaters, washing machines, flash light emitting devices for cameras, fluorescent lamps and other electronic devices and electrical products; pressure switches, motor operated valves, electrodes, etc. Various electronic parts, electric parts, etc. are mentioned, but they are preferably used for oxygen sensors.

In the present specification, the oxygen sensor means a sensor having the lead wire unit and the oxygen concentration detecting element. As the oxygen sensor, since the lead wire unit can sufficiently withstand use under severe conditions such as high heat, compression and water exposure, an oxygen sensor for automobiles for detecting oxygen concentration in exhaust gas of automobiles Is preferred.

An oxygen sensor for automobiles having the above-mentioned lead wire unit is also one aspect of the present invention.

The automobile oxygen sensor of the present invention may have a metal cylinder as an outer wall in order to protect the whole. The metal cylinder is not particularly limited. The metal cylinder is usually partially crimped from the outside according to the shape of the built-in object, the shape of the place where it is mounted, etc., has unevenness due to the difference in diameter, and has a step.

The oxygen sensor for automobiles of the present invention is usually
It has an elongated tubular shape as described above, and one end of the tubular shape is attached to an exhaust pipe or the like for use. The oxygen sensor for an automobile has the lead wire unit on the side of the portion to be attached to the exhaust pipe and the like of the tubular type, and has the oxygen concentration detection element on the opposite side. At least one end of the lead wire is connected to the oxygen concentration detection element.

The oxygen sensor for automobiles of the present invention is not particularly limited, but one example is shown in the schematic view of FIG. In FIG. 2, the automobile oxygen sensor 11 has an oxygen concentration detection element 12, and an inner surface electrode 13 on the inner surface side and an outer surface electrode 14 on the outer surface side of the oxygen concentration detection element 12,
A lead wire 15 and a lead wire 16 for extracting a signal to the outside are connected.

A heater 19 is inserted in the internal space of the oxygen concentration detecting element 12 for heating the oxygen concentration detecting element 12, and the lead wire 17 and the lead wire 18 are connected to the electrode 110 of the heater 19. Has been done.

An element cover 111 is attached to the tip of the oxygen concentration detecting element 12, and a metal cylinder 112 is attached by caulking to the remaining portion of the vehicle oxygen sensor 11. Inside the metal cylinder 112, the bush 113 of the present invention is arranged in the through hole through the lead wires 15 to 18, and a separator 114 made of ceramic or the like is arranged immediately below the bush 113 inside the metal cylinder 112. ing.

The method for producing the oxygen sensor for automobiles of the present invention is not particularly limited, and examples thereof include conventionally known methods. For example, the lead wire unit of the oxygen sensor for automobiles, the oxygen concentration detecting element, etc. There is a method of arranging the above-mentioned constituents inside the metal cylinder and caulking from the outside of the metal cylinder under the conditions as described above in the method for manufacturing the lead wire unit.

The bush of the present invention does not cause thermal deterioration even when the pressurization / heating under the specific conditions is performed for a long time as described above. Under such harsh conditions, conventional bushes usually crack and then
Although it had undergone thermal degradation, the bushing of the present invention did not crack or corrode. The mechanism by which the bush of the present invention exerts such an advantageous effect is not clear, but it is considered as follows.

The bush of the present invention is different from the conventional compression molded product produced by firing the preformed product obtained by filling the mold with the fluororesin powder and then pressurizing the bush as in the conventional case. As described above, the porous body has a low specific gravity and has a structure in which pores are continuous. Therefore, since the bush of the present invention has a low elastic modulus, it is considered to have the following excellent effects.

(1) After inserting the conductor into the bush, compression can be performed by pressurization, and the caulking property is excellent. (2) Since it has elasticity, it can be brought into close contact with a conductor, an external metal cylinder, etc. by compression to exert sealing property, and is excellent in waterproof property and airtightness. (3) Since the load required for compressive deformation (deformation load) is lower than that of the conventional bush, a desired compression rate can be realized with a low load and the energy of the load can be reduced. (4) Since the amount of residual stress strain due to compression is small, cracks and thermal deterioration do not occur even when heated and pressed for a long time, and it has high heat resistance and can maintain the sealing property. (5) By appropriately selecting the specific gravity within the above range,
The deformation load can be changed, the range of manufacturing conditions can be selected, and the applications can be expanded.

Therefore, the bush of the present invention can be suitably used for the lead wire unit. The lead wire unit having the bush of the present invention can be suitably used for an oxygen sensor for automobiles.

[0087]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Example 1 (Production of low specific gravity porous molded article) Modified PTFE (product number: M
-112, manufactured by Daikin Industries, Ltd.) at 360 ° C., and then pulverized by a jet mill to obtain an average particle diameter of about 84 μm.
A gelled powder of m was obtained. This gelled powder was filled in a mold having a diameter of 5 mm, baked at 370 ° C. for 60 minutes, heated, and then put into water for rapid cooling. A low specific gravity porous molded product having a specific gravity of 1.0291 and a diameter of 4.7 mm was obtained.

(Evaluation) The obtained low specific gravity porous molded article (diameter 4.7 mm, length 30 mm) was evaluated as follows. The results are shown in Table 1.

1. According to JIS K 6262, thermal compression was performed in the radial direction so that the compression rate would be 25%, and at 300 ° C. for 500 hours and 10 hours.
After performing a heat resistance test by placing each heating condition of 00 hours and 325 ° C. for 500 hours and 1000 hours,
After the test, the molded product returned to room temperature was visually evaluated according to the following criteria. ○ No thermal deterioration could be confirmed. △ There was thermal deterioration. × Melted.

2. Crack According to ASTM D 1414 (1994) paragraph 10, compressed in the radial direction so that the compressibility becomes 25%, and 300 ° C.
After performing a heat resistance test by heating for 70 hours at room temperature, return to room temperature, and after the test, take out the molded product and cut the molded product in the radial direction to visually check for cracks on the fracture surface. Was evaluated according to. ○ No cracks occurred. × A crack was generated.

Comparative Example 1 Instead of the low specific gravity porous molded article, heat resistant rubber (trade name: k
Example 1 except that an O-ring (AS568-214) made by Alrez 4079, DuPont) was used.
It evaluated similarly to.

[0092]

[Table 1]

From Table 1, it can be seen that the heat-resistant rubber used in Comparative Example 1 causes thermal deterioration and melt and cracks when left at a high temperature for a long time, whereas the low specific gravity porous molding used in Example 1 It was found that the product did not undergo thermal deterioration or cracks under any of the above heating conditions.

Example 2 The gelled powder of modified PTFE obtained in Example 1 (average particle size of about 84 μm) was filled in a mold of about 23 mm in diameter, and 370
After baking at 60 ° C for 60 minutes, the mold was put into water to perform rapid cooling, diameter 22 mm, length 32 m.
JIS for low specific gravity molded products with m and specific gravity of 1.0463
The compression properties were investigated according to K 7181. The results are shown in Fig. 1.

Comparative Example 2 Modified PTFE (product number: M-112, manufactured by Daikin Industries, Ltd.)
The powder of 50 mmf / 350 mmf /
It was compressed at cm ² to obtain a preform. Then, the preform is placed in an electric furnace, heated to 360 ° C. at a heating rate of 50 ° C./hour and held at 360 ° C. for 6 hours, and then cooled to room temperature at a cooling rate of 50 ° C./hour to obtain a diameter of 50 mm. Length 5
A molded product having a diameter of 10 mm, a length of 20 mm, and a specific gravity of 2.1517, which was obtained by cutting, was examined for compression characteristics according to JIS K 7181.

From FIG. 1, in comparison with Comparative Example 2 using a molded product having a specific gravity of more than 1.8, in Example 2 using a low specific gravity porous molded product, the load required to obtain a specific compressibility was obtained. Was found to be low.

[0097]

EFFECTS OF THE INVENTION Since the bush of the present invention has the above-mentioned structure, it has a high degree of heat resistance that does not cause thermal deterioration, cracks, etc. even under a high temperature and pressure for a long period of time, and does not impair the sealing property. At the same time, it has an excellent caulking property that enables compression with a low load, and the load required for compression can be appropriately selected.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a lead wire unit of the present invention.

FIG. 2 is a partial cross-sectional schematic view showing an example of an automobile oxygen sensor of the present invention.

FIG. 3 is a graph showing compression characteristics in Example 2 and Comparative Example 2.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Michio Asano             Daiichi Nishiichitsuya 1-1, Settsu City, Osaka Prefecture             Yodogawa Manufacturing Co., Ltd. (72) Inventor Kazuo Ishiwari             Daiichi Nishiichitsuya 1-1, Settsu City, Osaka Prefecture             Yodogawa Manufacturing Co., Ltd. F term (reference) 2G004 BB01 BC03 BC07 BF18 BG05                       BH02 BH11 BH20 BJ02 BM04                       BM07 BM10

Claims (7)

[Claims] 1. No deterioration by heat is caused when the material is left at 300 ° C. for 1000 hours under a condition of a compression rate of 25% according to JIS K 6262, and / or ASTM.
D 1414 (1994) Section 10 compression rate 2
A bush that does not crack when left at 300 ° C. for 70 hours under 5% conditions. 2. The bush according to claim 1, which has a specific gravity of 0.4 to 1.8. 3. The bush according to claim 1, which is made of unmodified polytetrafluoroethylene or modified polytetrafluoroethylene. 4. The bush according to claim 1, 2 or 3, which is used for an oxygen sensor for an automobile. 5. A bush made of unmodified polytetrafluoroethylene or modified polytetrafluoroethylene, having a specific gravity of 0.4 to 1.8. 6. A lead wire unit comprising the bush according to claim 1, 2, 3, 4 or 5. 7. An oxygen sensor for an automobile, comprising the bush according to claim 1, 2, 3, 4 or 5.