JPH0788905B2 - Cover boots - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cover boot that is hermetically sealed to protect equipment such as constant velocity joints and suspensions.
More specifically, the present invention relates to a cover boot having a bellows shape, a part of which has high kinetic characteristics and which does not swell and deteriorate due to hydraulic oil and has excellent durability.

2. Description of the Related Art Conventionally, chloroprene rubber has been widely used as this type of cover boot, but there are problems with weather resistance and durability as a drawback of rubber itself, and currently, it is mainly used for constant velocity joint cover boots for vehicles. Ester-based elastomers are being used as the material. The cover boots made of ester elastomers not only have excellent weather resistance and durability, but also have extremely low temperature dependence of hardness.
In particular, it has the feature of maintaining a stable material in a high temperature atmosphere exceeding 80 ° C.

Problems to be Solved by the Invention However, since the cover boot made of an ester elastomer has a high hardness itself in terms of physical properties, it should be inserted when both ends of the cover boot are fixedly inserted into a constant velocity joint or suspension equipment. It has a drawback that it is difficult to assemble and workability is extremely deteriorated. Further, since the constant velocity joints and suspensions described above are provided with working oil such as grease in order to improve operability, working oil adheres to the inner surface of the cover boot, and further, the working oil of the cover boot is It is common to fill and seal the inside with hydraulic oil to enhance the operability to a high degree.However, when the above-mentioned ester-based elastomer adheres to the hydraulic oil, it absorbs the hydraulic oil and swells, causing the physical properties to drop extremely. Therefore, various measures were required because the strength and performance of the cover boot deteriorated and the deterioration of grease rapidly progressed, which adversely affected the performance of the main body of equipment such as constant velocity joints. .

The present invention has been invented in view of the problems of the conventional ones, and an object thereof is to use a hydraulic oil even if it is used as a cover boot of a machine having an improved operability by interposing a hydraulic oil. Swelling does not cause deterioration.

It is a relatively flexible cover boot that is easy to insert when both ends of the cover boot are inserted and fixed to the equipment such as a constant velocity joint or suspension, and no special consideration is given to the boot shape and tightening band. That is necessary.

It has high weather resistance and can withstand long-term use.

It is highly durable and will not be punctured by the impact of small stones.

Means for Solving Problems The present invention has the following technical means for achieving the object. That is, in a cover boot made of an elastic body and partially having a bellows shape, the base material layer is formed of an ester elastomer, and a coating layer made of a urethane elastomer is provided on the inner surface of the base material layer. It is a thing.

As described above, since the base material layer is formed of the ester-based elastomer and the coating layer made of the urethane-based elastomer is provided on the inner surface of the material layer, as a cover boot for a device having an operability improved by interposing hydraulic oil. Even when used, not only can the working oil be separated from the ester elastomer by the urethane elastomer on the inner surface to prevent the swelling deterioration of the ester elastomer due to the working oil, but the urethane elastomer coating also makes the cover boot flexible. Therefore, when it is inserted and fixed in the above-mentioned equipment, the insertion is easy and the workability is improved, and special consideration is not given to the boot shape and the tightening band.

The ester-based elastomer of the present invention is a multi-block copolymer having a soft segment composed mostly of an aliphatic polyether or an aliphatic polyether ester and a hard segment composed of a high melting point crystalline aromatic polyester and the like. It is a united one. In principle, various types of ester elastomers can be obtained by changing the types and proportions of dibasic acids, glycols and polyesters or polyethers.

Further, the urethane-based elastomer of the present invention is obtained by polyadding various polyether or polyester diols and glycols with diisocyanate, and in this case, triol, diamine or triamine is also used in combination. For example, it is referred to as a polyester-based polyurethane, a polyether-based holliene, or the like. The diisocyanate includes 4,4′-diphenylmethane diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, isophorone diisocyanate, etc., and the glycols include ethylene glycol and 1,4-butylene. Glycol, 1,4 hexanediol,
Examples of the polyester diol include polyethylene adipate, poly 1,
4-butylene adipate, poly-1,6 hexane adipate,
Examples thereof include polycaprolactone and polycarbonate, and examples of the polyether diol include polyoxytetramethene glycol.

The cover boots of the present invention are for protecting constant velocity joints and suspensions for vehicles such as automobiles and agricultural vehicles,
In particular, it is used as a sealing material for constant velocity joints of automobiles. This constant velocity joint is generally used in the drive system of automobiles, but in recent years, especially with the spread of front engine-front drive system (FF type) automobiles, the drive of the front drive shaft of this FF type automobile has been promoted. It has many markets for joints of parts.

The cover boot according to the present invention is formed by hollow molding, which is a multilayer tubular parison or a multilayer sheet having a laminated structure in which a urethane elastomer is arranged on the inner surface of a plasticized ester elastomer. It is coextruded and then molded into a three-dimensional shape by positive pressure or negative pressure. Here, as the laminating means, a multi-layer blow molding method by coextrusion is used, but particularly, the total wall thickness composition ratio of the ester elastomer layer and the urethane elastomer layer is 97: 3 to 35:65, preferably In the range of 85:15 to 55:45, the object of the present invention can be effectively achieved. If the urethane elastomer content is less than 3%, the oil resistance will be poor, and if it exceeds 65%, the hardness will be high and the assembly workability will be poor. The cover boot according to the present invention has an extremely high interlayer adhesive strength,
Appropriate adhesive layers may be interposed between the layers, or various blend layers may be interposed to add various functions such as strength or to reuse burrs.

Furthermore, the cover boot of the present invention has a Shore D hardness of 35 to 5.
0, and more preferably a Shore D hardness of 38 to 50. If the Shore D hardness is less than 35, the expansion at high temperature becomes large, and if the Shore D hardness exceeds 50, a large force is required to insert the constant velocity joint into the tool, resulting in poor assembling workability.

Example A cover boot for a constant velocity joint for an automobile according to an example of the present invention is shown in FIG. In the figure, 1 and 2 are a first rotating shaft and a second rotating shaft, respectively. 3 is a cover boot having a bellows portion 4 at the center and fixing portions 5 and 6 at both ends thereof. The fixing portion 5 is fixed to the first rotating shaft 1, and the fixing portion 6 is fixed to the second rotating shaft 2. The outer diameter A of the fixed portion 5 is 75 mm,
The outer diameter B of the fixed portion 6 is 24 mm, and the maximum peak portion of the bellows portion 4 is
83mm, minimum peak 60mm, maximum valley 59mm, minimum valley 46
mm. The cover boot 3 has an average thickness of 1.2 mm, and is composed of a base material layer 7 and an inner surface layer 8 as shown in FIG. 2. The material and the thickness thereof are shown in Table 1.

However, TPE-1: Hytrel HTG5612J [made by DuPont] TPE-2: Perprene P55B-07 [made by Toyobo] TPE-3: Hytrel HTG4275J [made by DuPont] TPE-4: Perprene S2001 [made by Toyobo] TPU-1: Elastran E385 [made by Japan Elastollan] TPU-2: Elastollan E585 [made by Japan Elastollan] Shore D hardness (ASTMD224 of the above Examples and Comparative Examples)
0), tensile strength (ASTM638), elongation (ASTMD638), tear strength (ASTMD624), and tensile modulus (ASTMD638) are shown in Table 2.

According to the above Examples 1 to 8 as shown in Table 2,
Since various strengths are higher than those of single-layer chloroprene rubber, it will not break or puncture even when used under adverse conditions. In particular, since the tear strength is as high as 100 kg / cm or more, it is possible to prevent the occurrence of cracks against the arrival and collision of small stones. In addition, looking at the hardness and the tensile elastic modulus, it can be seen that Examples 1 to 8 have rubber elasticity as compared with Comparative Example 2, and the insertability of the device body is good.
Therefore, the following assembling test was conducted on Examples 2 and 3 and Comparative Examples 1 and 2 to observe the insertability. The results are shown in Table 3.

Assembleability test method At room temperature, place a tubular jig with the same diameter as the rotary shaft of the constant velocity joint on the compression load measuring device, and insert the large diameter side of the fixed part of the cover boot from above to insert the tubular jig. The maximum insertion force required to reach the prescribed fixed position of is measured. This was taken as the maximum insertion force.

Next, the cover boot fixed to the tubular jig is pulled to remove the cover boot from the tubular jig. The tensile force at this time is measured with a push-pull cage. This was taken as the maximum removal force.

As can be seen from Table 3, the maximum insertion force and the maximum removal force are in a proportional relationship with the tensile elastic modulus and hardness, and the higher the tensile elastic modulus and hardness, the more force is required for insertion and removal. According to the above, it can be seen that insertion and removal can be performed with a force of half or less as compared with Comparative Example 2 of the ester elastomer single layer. Considering workability, it is preferable to set the Shore D hardness to 50 or less.

Furthermore, a high-temperature high-speed rotation test of the cover boot is performed,
The results are shown in Table 4.

Here, the high-temperature high-speed rotation test means that the cover boot is fixed to the constant-velocity joint as shown in FIG. 1, the atmosphere is kept at 80 ° C., the constant-velocity joint is rotated at 2000 rpm, and the cover boot at that time is rotated. The amount of expansion of is measured as a change in the bellows in the radial direction.

It can be seen from Table 4 that the amount of expansion at high temperature is proportional to the hardness of the cover boot. From Examples 4 and 5, when the Shore D hardness of the cover boot is 38 or less, the expansion amount is
You can see that it exceeds 10 mm.

Next, the oil resistance to hydraulic oil was examined. This is shown in JIS K6301 where the cover boot is heated to 120 ℃.
It was dipped in No. rubber swelling oil for a certain period of time, and the weight change ratio of the cover boot was measured. The results are shown in Table 5.

As shown in Table 5, Comparative Example 1 and Comparative Example 2 rapidly increased to 3
It was found that swelling with No. swelling oil caused a rapid change in volume, and with this, the physical properties decreased. This swelling can be prevented rapidly as going from Example 1 to Example 4, and can be prevented by making the urethane elastomer at least 3% of the total wall thickness. More preferably, the weight change due to swelling can be suppressed within 10% by making the urethane elastomer at least 15% of the total thickness.

Effects of the Invention The present invention has the following effects.

That is, the base material layer is formed of an ester-based elastomer having high hardness and poor elasticity but excellent in wear resistance and deformation resistance, and the inner surface of the base material layer has a property almost opposite to that of grease and the like. By providing a coating layer made of a urethane-based elastomer having excellent oil resistance, even if it is used as a cover boot of a device having an improved operability by interposing hydraulic oil, it does not swell and deteriorate due to the hydraulic oil.

It is a relatively flexible cover boot that is easy to insert when inserting and fixing both ends of the cover boot into a constant velocity joint or suspension equipment, and special consideration is also given to the cover boot shape and tightening band. Unnecessary.

It has high weather resistance and can withstand long-term use.

It is highly durable and will not be punctured by the collision of small stones.

[Brief description of drawings]

FIG. 1 is a sectional view illustrating a state in which a cover boot for a constant velocity joint according to an embodiment of the present invention is incorporated in the constant velocity joint, FIG.
The figure is a partial sectional view of the cover boot. 3 ... Cover boots, 4 ... Bellows part 7 ... Base material layer, 8 ... Inner surface layer

Claims (1)

[Claims] 1. In a cover boot made of an elastic material and partially having a bellows shape, a base material layer is formed of an ester elastomer, and a coating layer made of a urethane elastomer is provided on an inner surface of the base material layer. Cover boots characterized by that.