GB2352782A - Flexible resin boot for a constant-velocity universal joint - Google Patents

Abstract

A flexible resin boot having a large port and a small port at the opposite ends that are connected with each other via a bellows therebetween is integrally molded from a molding material that comprises 100 parts by weight of a thermoplastic elastomer resin and from 0.5 to 5 parts by weight of mineral oil added thereto. Applied to a constant velocity joint in an automobile, the flexible resin boot makes no noise in early stages even when continuously rotated while being bent at a wide angle. In that condition, in addition, the noise-preventing effect of the boot lasts long, and the boot ensures improved sealability and durability.

Description

2352782 FLEXIBLE RESIN BOOT AND METHOD FOR PRODUCING IT The present

invention relates to a bellows-shaped flexible resin boot to be used, for example, in constant velocity joints for automobiles, and to a method for producing it.

A flexible resin boot of the type has a large port at one end to be fitted to the housing of a constant velocity joint of an automobile, and a small port at the other to be fitted to the axle thereof, and has a tapered bellows between the two ports. Applied to a constant velocity joint, it prevents grease from leaking out of the joint and prevents dust from entering the joint.

For forming such flexible boots, heretofore, chloroprene rubber has been used generally. However, flexible boots formed from chloroprene rubber are much expanded and deformed by the rotational centrifugal force, especially when they are rotated at high speed. In case where they are kept expanded and deformed under the condition for a long period of time, or where they undergo repeated expansion and contraction, they will be soon mechanically degraded and broken. Accordingly, the problem with such flexible boots is that their life is short.

Recently, thermoplastic elastomer resins such as 1 thermoplastic polyester elastomer resins and the like having high elasticity havecome to beused for forming flexibleboots. The materials have the advantages of good heat resistance, good flexure resistance and high strength. However, flexible boots made from such high-elasticity thermoplastic elastomer resins are still problematic. Specifically, when the flexible boot is applied to a constant velocity joint in an automobile and when rotated therein while being bent at a wide angle, the mountains of its bellows are much rubbed against each other to make a noise and they are often worn away. In particular, in case where water adheres to the outer surf ace of the flexible boot, the noise is serious.

To solve the noise problem, proposed is adding silicone oil or fatty acid amide to thermoplastic polyester elastomer resins for flexible boots. For example, Japanese Patent Laid-Open No. 177971/1997 discloses a technique of adding a fatty acid amide to the resins for forming flexible boots.

When applied to the constant velocity joint in an automobile and when continuously rotated therein while being bent at a wide angle, the f lexible resin boot of Japanese Patent Laid-Open No. 177971/1997 in which a fatty acid amide is added to a thermoplastic polyester elastomer resin makes no noise in early stages, but its noise-preventing ef f ect could not last long. In fact, in the driving test of the flexible resin bootmounted constant velocity joint in an automobile, it has 2 been found that the boot soon makes a noise after a certain period of time. To enhance and prolong the ef f ect of the boot for noise prevention, the amount of the fatty acid amide to be added to the resin maybe taken into consideration. However, increasing the amount of the f atty acid amide added to the resin results in the increase in the powdery fatty acid amide deposited on the surface of the flexible boot, and the acid amide deposit easily peels off. As a result, adding such an increased amount of the fatty acid amide is ineffective for actually enhancing and prolonging the effect of the boot for noise prevention. In addition, since the amount of the acid amide deposit increases, the frictional factor of the flexible boot lowers, and, as a result, the large port or the small port of the boot will slip more easily around the housing of the constant velocity joint to which the boot has been fitted or around the axle of an automobile, whereby the boot will be dislocated to cause grease leakage from the joint. In fact, we, the present inventors have experienced grease leakage from the joint that worsens the ability of the boot to seal the joint.

The object of the present invention is to solve the problems as above, and to provide a flexible resin boot having the advantages of long- lasting noise prevention, sealability and durability.

The flexible resin boot of the invention is formed from 3 a base resin material of a thermoplastic elastomer resin and has a large port and a small port at the opposite ends that are connected with each other via a bellows therebetween, and it is characterized in that mineral oil or vegetable oil is added to the thermoplastic elastomer resin.

When applied to a constant velocity joint in an automobile and even when continuously rotated therein while being bent at a wide angle, the flexible resin boot of the invention having the constitution as above makes no noise in early stages, and, in addition, its noise-preventing effect lasts long. Another advantage of the resin boot is that it ensures good sealability and durability. The reason is because the mineral oil and the vegetable oil to be added to the thermoplastic elastomer resin for the boot of the invention are both liquid. Therefore, even when the oil serving as a noise-preventing agent deposits on the surface of the boot, the liquid deposit is in the form of an oily film tightly adhering to the surface of the boot. It is believed that, the oily film thus tightly adhering to the surface of the boot does not easily peel off, being different from the powdery solid of a fatty acid amide deposit in the related art technology as above.

In the flexible resin boot of the invention, it is desirable that at most 5 parts by weight of mineral oil or vegetable oil is added to 100 parts by weight of the 4 thermoplastic elastomer resin. In case where too much mineral oil or vegetable oil of over 5 parts by weight, relative to 100 parts by weight of the thermoplastic elastomer resin, is added to the resin, the valleys of the bellows of the boot will be damaged to have through-cracks in early stages even though the time of noise prevention could be prolonged. In that case, the boot could not ensure good durability indispensable to it. More preferably, the amount of mineral oil or vegetable oil to be added thereto is at most 3 parts by weight relative to 100 parts by weight of the thermoplastic elastomer resin. In the more preferred case, the period of time after which the boot will be cracked can be prolonged more than in the case where the amount of the oil added is at most 5 parts by weight, and therefore the durability of the boot could be much more improved.

Preferably, the mineral oil for use herein comprises, as the essential ingredient, a paraffinic oil, including 100 % paraffinic oil.

In this case, it is desirable that the paraf f inic oil has a numberaverage molecular weight of from 200 to 2000, more preferably from 500 to 1000.

It is also desirable that the paraffinic oil has a weight-average molecular weight of from 200 to 2000, more preferably from 500 to 1400.

Also preferably, the paraffinic oil has a Z-average molecular weight of from 200 to 3000, more preferably from 500 to 2000.

Still preferably, the kinematic viscosity of the paraffinic oil, when measured with a B-type viscometer at an ambient temperature of 250C, falls between 100 and 1000 mm'/S, more preferably between 100 and 500 MM2/S.

The thermoplastic elastomer resin for use herein is preferably a thermoplastic polyester elastomer resin. Especially preferably, the thermoplastic polyester elastomer resin is represented by the following formula (1):

(C OC)COO(C H 2)40]a[CO C 0 0{(C H 2)401c]b one method for producing the flexible resin boot of the invention of which the large port and the small port at the opposite ends are connected with each other via a bellows therebetween, from a base resin material of a thermoplastic polyester elastomer resin comprises adding mineral oil or vegetable oil to hot pellets of a thermoplastic polyester elastomer resin and mixing and stirring them, thereafter further kneading the resulting mixture and extruding it through an extruder to prepare a molding material, and f inally molding the molding material into the flexible resin boot.

According to the method, mineral oil or vegetable oil 6 is added to hot pellets of a thermoplastic polyester elastomer resin, and they are mixed and stirred. Theref ore, in the method, the surf aces of the hot pellets are softened and are well wetted with the mineral oil or the vegetable oil added thereto, and the mineral oil or the vegetable oil can uniformly adhere to the surfaces of the pellets. Accordingly, when the mixture comprising the thermoplastic polyester elastomer resin pellets and the mineral oil or the vegetable oil is kneaded and extruded out through an extruder in the next step, obtained is a molding material that comprises the mineral oil or the vegetable oil uniformly dispersed in the thermoplastic polyester elastomer resin. The advantage of the flexible boot formed from the molding material is that its noise- preventing effect lasts long.

In the method, if desired, a solid additive may be added to and mixed with the mixture of the pellets and the mineral oil or the vegetable oil by stirring them, and the resulting mixture is then f urther kneaded and extruded to give the molding material.

If desired, after the pellets and the solid additive have been heated, they may be mixed by stirring them, and thereafter mineral oil or vegetable oil may be added to and mixed with the resulting mixture by further stirring them.

Also if desired, after mineral oil or vegetable oil has been heated, it may be mixed with the pellets by stirring them.

7 Also if desired, after the pellets, mineral oil or vegetable oil, and the solid additive have been all heated, they may be stirred and mixed to prepare their mixture.

In the method for producing the flexible resin boot of the invention, the temperature at which the resin pellets and other components are heated is preferably not lower than 600C, and more preferably falls between 70 and 1000C. If the heating temperature is lower than 60'C, the viscosity of the mineral oil or vegetable oil added to the resin pellets will be high and the oil could not be uniformly dispersed in the resin. on the other hand, the heating temperature higher than 1000C is uneconomical. This is because, when the thermoplastic polyester elastomer resin pellets are stirred in a mixer or the like to generate frictional heat by which they are heated, the heating time will be too long, and the productivity will be low.

Fig. 1 is a cross-sectional view of a flexible resin boot of one embodiment of the invention.

Fig. 2 is a partly cut cross-sectional view of the flexible resin boot of Fig. 1 built in an automobile.

Figs. 3A to 3 C are graphs s howing the depos ition pro f ile of the noise-preventing agent on the flexible resin boots produced in Example 23 and Comparative Example 17. The graph of Fig. 3A indicates the data of a test where the boots were 8 left as they were with no specific treatment applied thereto; that of Fig. 3B indicates the data of a test where the boots were wiped at intervals of 14 days; and that of Fig. 3C indicates the data of a test where the boots were wiped at intervals of 7 days.

Fig. 1 is a cross-sectional view of a flexible resin boot 1 of one embodiment of the invention. Integrally molded through injection molding or press blow molding, the flexible resin boot 1 has a large port 2 at one end and a small port 3 at the other end, in which the large port 2 and the small port 3 are connected with each other via a tapered bellows 4 therebetween.

The thus-molded flexible -resin boot 1 is built into an automobile, for example, as in Fig. 2. Briefly, as illustrated, two boots 1 are built into an automobile in such a manner that the large port 2 of one boot 1 is engaged over the outer case 8 of the inboard joint (universal joint) 7 that turnably and displacably interlocks the driving shaft 6 to the rear axle 5 while the large port 2 of the other boot 1 is engaged over the outer case 10 of the outboard joint 9, and the two ports 2 are fastened and clamped by the fastening clamps 12. The small ports 3 of the two boots 1 are engaged over the rear axle 5, and are fastened and clamped by the fastening clamps 12. In that manner, the two boots 1 cover the joints 7 and 9, while 9 forming grease-sealing spaces 11, 11 inside each bellows 4. The molding material for the flexible resin boot 1 comprises, as a base resin, a thermoplastic elastomer resin, and mineral oil or vegetable oil added thereto. Regarding the blend ratio of the constituent components, the amount of the mineral oil or the vegetable oil may be at most 5 parts by weight, but preferably at most 3 parts by weight, more preferably from 0. 5 to 3 parts by weight, relative to 100 parts by weight of the thermoplastic elastomer resin. Too much mineral oil or vegetable oil of over 5 parts by weight, if added to the resin, will form through-cracks in the valleys of the bellows 4 in early stages. If so, the durability of the boot 1 will be poor.

The thermoplastic elastomer resin (TPE) for use in the invention may be any of. polyester-based ones (TPEE), polyolefin-based ones (TPO), polyurethane-based ones (TPU) and others having good grease resistance, flexure fatigue resistance and flexibility; but preferred are polyesterbased ones (TPEE). For the thermoplastic polyester elastomer resins, f avorably used are PELPRENE@ (f rom Toyo Boseki), HYTREL@ (f rom TorayDuPont), etc.

Preferably, the thermoplastic polyester elastomer resins for use herein are represented by formula (1) mentioned. above. These are composed of a hard segment of a polyester of the following formula (2) and a soft segment of a polyether of the following formula (3):

[C OOCOO (C H 2) 4 0] a... (2) C 0 OC 00(C H2) 4 0 1 c] b ..(3) wherein a, b and c each indicate an integer of I or more.

The mineral oil to be added to the thermoplastic elastomer resin includes paraffinic oil, naphthenic oil, and aromatic oil. The vegetable oil to be added thereto includes rapeseed oil, linseed oil, soybean oil, castor oil, etc. of these, mineral oil that comprises, as the essential ingredient, paraffinic oil is preferred for use in the invention, as ensuring good durability of flexible boots. More preferred is mineral oil of paraffinic oil only, not containing any of naphthenic oil and aromatic oil and not. containing any impurities of olefins, or that is, paraffinic oil having a purity of about 100 %. For paraffinic oil of that type, favorably used is BJ Oil@ (from Kyodo Yushi).

Adding mineral oil of the type that comprises, as the essential ingredient, paraffinic oil to the thermoplastic polyester elastomer resin of formula (1) brings about the following benef its, as the two are well miscible with each other in good balance. The paraf f inic oil deposits little by little on the surface of the thermoplastic elastomer resin, and it 11 can exhibits its noise-preventing ef f ect for a long period of time. In addition, the mineral oil has no negative influence on the physical properties of the thermoplastic elastomer resin, and the boots f ormed f rom the resin well satisfy the durability standards in the art.

Preferred ranges of the mean molecular weight, including number-average molecular weight, weight-average molecular weight and Z-average molecular weight, of paraffinic oil usable herein as mineral oil are mentioned below. The molecular weight is measured through gel permeation chromatography (GPC) with SYSTEM-21 (from Shodex), in which monodispersed polystyrene is used as the standard substance and the molecular weight of the oil sample measured is derived from the differential refractive index (RI) thereof in terms of polystyrene.

Preferably, the number-average molecular weight of paraf f inic oil f or use in the invention f alls between 200 and 2000, more preferably between 500 and 1000. Flexible boots 1 formed from a thermoplastic elastomer resin that contains paraffinic oil having a number-average molecular weight of larger than 2000 will soon make a noise in early stages. Flexible boots 1 formed from a thermoplastic elastomer resin that contains paraf f inic oil having a number-average molecular weight of smaller than 200 could not prevent a noise for a long period of time, though they do not make a noise in early stages.

12 Accordingly, it is desirable that the number-average molecular weight of paraf f inic oil f or use herein f alls within the def ined range.

Also preferably, the weight-average molecular weight of paraffinic oil for use in the invention falls between 200 and 2000, more preferably between 500 and 1400. Flexibleboots 1 formed from a thermoplastic elastomer resin that contains paraffinic oil having a weight-average molecular weight of larger than 2000 will soon make a noise in early stages. Flexible boots 1 formed from a thermoplastic elastomer resin that contains paraffinic oil having a weight-average molecular weight of smaller than 200 could not prevent a noise for a long period of time, though they do not make a noise in early stages. Accordingly, it is desirable that the weight-average molecular weight of paraf f inic oil f or use herein falls within the defined range.

Also preferably, the Z-average molecular weight of paraf f inic oil for use in the invention falls between 200 and 3000, more preferably between 500 and 2000. Flexible boots 1 formed from a thermoplastic elastomer resin that contains paraffinic oil having a Z-average molecular weight of larger than 3000 will soon make a noise in early stages. Flexible boots 1 formed from a thermoplastic elastomer resin that contains paraffinic oil having a weight-average molecular weight of smaller than 200 could not prevent a noise for a long 13 period of time, though they do not make a noise in early stages. Accordingly, it is desirable that the Z-average molecular weight of paraf f inic oil f or use herein falls within the def ined range.

Al so pref erably, the kinemat ic vis cos ity o f para f f inic oil for use in the invention falls between 100 and 1000 mm'/S, more preferably between 100 and 500 mm'/S. The kinematic viscosity is measured with a Btype viscometer at an ambient temperature of 250C (according to JIS K7117).

Paraffinic oil having a kinematic viscosity of larger than 1000 MM2/S could hardly deposit on the surf aces of f lexible boots, and its noisepreventing ability will be poor. Paraffinic oil having a kinematic viscosity of smaller than 100 mm2/S will deposit too rapidly on the surfaces of flexible boots, and its noise-preventing effect could not last long. Accordingly, it is desirable that the kinematic viscosity of paraf f inic oil f or use herein f alls within the def ined range.

In adding a liquid additive such as mineral oil or vegetable oil to a thermoplastic elastomer resin and kneading them, the problem is how to uniformly disperse the liquid additive in the resin. To the base resin of a thermoplastic elastomer, generally added are solid additives such as antioxidant, pigment, etc. In case where a liquid additive such as mineral oil or vegetable oil is added to an elastomer resin af ter solid additives have been added thereto and stirred, 14 the solid additives and the liquid additive will clump and could not be uniformly dispersed in the resin.

Another problem is that the viscosity of the liquid additive such as mineral oil or vegetable oil increases in a low-temperature atmosphere in the winter season or the like, and the liquid additive will more readily clump together with solid additives in a resin. Even when the resin mixture in that condition is kneaded and extruded out through a doublescrew extruder, it is often impossible to obtain a resin material containing solid and liquid additives uniformly dispersed therein.

We, the present inventors have f ound that, when hot pellets of a thermoplastic polyester elastomer resin are mixed and stirred with mineral oil or vegetable oil added thereto, then the mineral oil or the vegetable oil can uniformly adhere onto the surfaces of the resin pellets. In addition, we have further found that, when the resin mixture in that condition is stirred with any other solid additives such as antioxidant, pigment, etc., then the solid additives and the liquid additive such as mineral oil or vegetable oil can uniformly adhere onto the surfaces of the resin pellets.

If desired, after thermoplastic polyester elastomer. resin pellets and mineral oil or vegetable oil are all heated, mixed and stirred, solid additives such as antioxidant, pigment, etc. may be added thereto, and further mixed and stirred. Also if desired, after thermoplastic polyester elastomer resin pellets and solid additives such as antioxidant, pigment, etc. are all heated, mixed and stirred, mineral oil or vegetable oil may be added thereto, and further mixed and stirred. Still if desired, thermoplastic polyester elastomer resin pellets, mineral oil or vegetable oil, and other solid additives such as antioxidant, pigment, etc. may be all heated, and then mixed and stirred.

In case where the mixture having been prepared by mixing and stirring thermoplastic polyester elastomer resin pellets, a liquid additive such as mineral oil or vegetable oil, and solid additives such as antioxidant, pigment, etc., and therefore comprising them is kneaded and extruded out through a double-screw extruder, obtained is a boot-f orming material in which the liquid additive and the solid additives are uniformly dispersed in the thermoplastic polyester elastomer resin. The material can be formed into flexible boots having the advantage of lon-lasting noise prevention.

Preferably, the temperature at which the resin pellets and other components are heated is not lower than 60'C, and more preferably falls between 70 and 1000C. If the heating temperature is lower than 60'C, the viscosity of the mineral oil or vegetable oil added to the resin pellets will be high and the oil could not be uniformly dispersed in the resin. On the other hand, the heating temperature higher than 100'C is 16 uneconomical. This is because, when the base resin pellets of thermoplastic polyester elastomer are stirred in a mixer or the like to generate f rictional heat by which they are heated, for example, according to the heating method mentioned below, the heating time will be too long, and the productivity will be low.

For heating thermoplastic polyester elastomer resin pellets, employable is a method of stirring the pellets in a mixer or the like to generate frictional heat by which they are heated, or a method of using an ordinary hot-air drier.

In the stirring method, generally used is a mixer or a tumbler. For kneading and extruding the resin mixture to give a boot-forming material, usable is any ordinary single-screw extruder, but preferred is a doublescrew extruder. In the boot-forming material obtained through a doublescrew extruder, the liquid additive and the solid additive can be uniformly dispersed in the base resin.

EXAMPLES

The invention is described in more detail with reference to the following Examples, which, however, are not intended to restrict the scope of the invention.

Examples 1 to 5:

To a base material of a thermoplastic polyester elastomer of formula (1) (PELPRENE P46D@ from Toyo Boseki), added was mineral paraffinic oil (Bi OilS from Kyodo Yushi, 17 having a number-average molecular weight of 682, a weightaverage molecular weight of 834, and a Z-average molecular weight of 1057). Using an injection molding machine, the resulting mixture was molded into flexible resin boots. The blend ratio of mineral oil was varied within a range of from 0.5 to 5.0 parts by weight to 100 parts by weight of the thermoplastic polyester elastomer resin, as in Table 1 below. Comparative Examples 1 to 6:

The same thermoplastic polyester elastomer resin as in Examples 1 to 5 was used as the base material. In Comparative Example 1, however, no mineral oil was added to the resin, and the resin was molded into flexible resin boots in the same manner as inExamples 1 to 5, using an injection molding machine. In Comparative Example 2, 7 parts by weight of the same mineral oil as in Examples 1 to 5 was added to 100 parts of the thermoplastic elastomer resin, and the mixture was molded into flexible resin boots in the same manner as above. In Comparative Examples'3 to 6, a low-melting-point fatty acid amide A (oleyloleamide) and a high-meltingpoint fatty acid amide B (ethylenebisstearamide) were added to 100 parts by weight of the thermoplastic elastomer resin, the blend ratio of the acid amides being indicated in Table 1, and the mixture was molded into flexible resin boots in the same manner as above.

The flexible resin boots of Examples 1 to 5 and 18 Comparative Examples 1 to 6, having been molded in the manner as above, were built into constant velocity joints, and tested for their capability of noise prevention, sealability and durability. The test results are given in Table 1 - The test methods employed herein are mentioned below.

(1) Noise Prevention:

A boot to be tested is built into a constant velocity joint, and rotated at low speed. Being thus rotated, the boot is checked as to whether or not it makes a noise in early stages. Boots that rotate noiselessly in the test are good (0); and those that rotate noisily therein are not good (x). Rotating the boot is continued, and the time at which the rotating boot has become noisy is read. Boots having become noisy before the target time of noise prevention, 25 minutes, are not good (x); and those still noiselessly rotating even after that target time of noise prevention are good (0). Regarding the condition for the noise test, the ambient atmosphere is at room temperature (RT); the maximum angle to the constant velocity joint (the angle a in Fig. 1) is 49'; and the number of revolution is 150 rpm. The surface of the flexible boot being tested is kept wetted with water all t he time during the test.

(2) Sealability:

A boot to be tested is built into a constant velocity joint and continuously rotated for a predetermined period of time. After having thus tested, the boot is checked as to whether or not its large port 2 or small port 3 airtightly fastened by the fastening clamp 12 is loosened from the outer cases 8, 10 or from the outer surface of the rear axle 5, and is thereby dislocated f rom the predetermined original position, or as to whether or not grease is leaked out of the boot. Boots that suffer from any of dislocation and grease leakage in the test are not good (x); and those not suf f ering from any of them are good (0). Concretely, a flexible boot to be tested is built into a constant velocity joint, and continuously rotated for 6 weeks at an ambient temperature of 300C and at a maximum angle to the constant velocity joint of 470. The number of revolution is 100 rpm. Immediately after the test, the boot is checked for its condition.

(3) Durability:

A boot to be tested is built into a constant velocity joint, and continuously rotated in a high-temperature atmosphere at 1000C until it is cracked to have through-cracks in the valleys of its' bellows. During the test, the maximum angle to the constant velocity joint is 430, and the number of revolution is 500 rpm. The time at which the boot being tested is cracked is read. Boots cracked before the target time of durability, 3 0 hours, are not good (x); and those not cracked even after that target time of durability are good (0).

As in Table 1, the boots of Examples 1 to 5, to which was added from 0.5 to 5 parts by weight of mineral paraffinic oil, are all good with respect to their noise-preventing capability, sealability and durability.

The boot of Comparative Example 1, to which was added no mineral oil, made a noise in early stages. The boot of Comparative Example 2, to which was added 7 parts by weight of mineral paraffinic oil, has good noisepreventing capability and sealability. However, it cracked in relatively early stages in the valleys 'of its bellows. This means that the durability of the boot of Comparative Example 2 is poor.

The boots of Comparative Examples 3 and 4, to which was added a lubricant of fatty acid amides (A/B) in a blend ratio of 0.7/0.06 parts by weight or1.5/0-15 parts by weight, have good sealability and durability, and make no noise in early stages. However, their noise-preventing effect did not last long, and their noise-preventing capability is unsatisf actory. The boot of Comparative Example 5, to which was added a lubricant of f atty acid amides (A/B) in a blend ratio of 1.8/0.15 parts by weight, makes no noise in early stages. However, its noise-preventing effect did not last long, and its sealability and durability are both poor. The boot of Comparative Example 6, to which was added a lubricant of fatty acid amides (A/B) in a blend ratio of 1.5/0.2 parts by weight, makes no noise in early stages and its noise-preventing effect lasted relatively long. It has good noise-preventing capability, but its sealability and durability are both poor.

21 Table 1 - Example Comparative Example 1 2 3 4 5 2 3 1 4 1 5 6 _T Additive Mineral Oil Mineral Oil Fatty Acid Amides (A/B) Amount Added (wt.pts.) 0.5 1 2 3 5 0 7 0.7/ 1.5/ 1.8/ 1.5/ 0.06 0.15 0.15 0.2 Noise noise in early stages 0 0 0 0 0 X 0 0 0 0 0 Preven tion duration of noise >60 >60 >60 >60 >60 0 >60 15 18 23 28 prevention (min) for the target time of 0 0 0 0 0 X 0 0 noise prevention, 25 X X X minutes Sealability 0 0 0 0 0 0 0 0 0 X X Durabi- time before formation 35 33 33 33 31 32 27 33 33 28 27 lity of through-cracks (hr) f or the target time of 0 0 0 0 0 0 0 0 durability, 30 hours X X X I 22 Examples 6 to 10:

The same thermoplastic polyester elastomer resin as in Examples 1 to 5 was used as the base material. To this was added mineral paraffinic oil (BJ Oil@ from Kyodo Yushi) having a number-average molecular weight of 200 (Example 6), 500 (Example 7), 750 (Example 8), 1000 (Example 9), or 2000 (Example 10), as in Table 2 below. Using an injection molding machine, the resulting mixture was molded into flexible resin boots. In these Examples 6 to 10, the blend ratio of the paraffinic oil was 1.5 parts by weight to 100 parts by weight of the thermoplastic polyester elastomer resin.

Comparative Example 7 to 9:

Flexible resin boots were produced in the same manner as in Examples 6 to 10, except that paraffinic oil (BJ Oil(& from Kyodo Yushi) having a number-average molecular weight of 100 (Comparative Example 7), 2250 (Comparative Example 8) or 2500 (Comparative Example 9) was used as in Table 2.

The flexible 'resin boots of Examples 6 to 10 and Comparative Examples 7 to 9, having been molded in the manner as above, were built into constant velocity joints, and tested for their capability of noise prevention. The test method is as follows: A boot to be tested is built into a constant velocity joint, and rotated at low speed. Being thus rotated, the boot is checked as to whether or not it makes a noise in early stages. Rotating the boot is continued, and the time 23 at which the rotating boot has become noisy is read. The target time of noise prevention is 25 minutes. In the test, the ambient atmosphere is at room temperature (RT); the maximum angle to the constant velocity joint (the angle a in Fig. 1) is 49'; and the number of revolution is 150 rpm. The surface of the flexible boot being tested is kept wetted with water all the time during the test. The test results are given in Table 2.

The boot of Comparative Example 7, to which was added paraf f inic oil having a small number-average molecular weight, made no noise in early stages - With it, however, the duration of noise prevention is only 10 minutes and is relatively short. This means that the noise-preventing capability of the boot is not satisfactory. The boots of Comparative Examples 8 and 9, to which was added paraffinic oil having an extremely large number-average molecular weight, were not good, since the paraffinic oil added thereto hardly deposit on their surfaces. Therefore, the boots -made a noise in early stages. As opposed to these, the boots of Examples 6 and 10 ensured long duration of noise prevention for 25 minutes. Their data reached the target. The boots of Examples 7, 8 and 9 produced better results, having ensured longer duration of noise prevention for longer than 60 minutes.

24 Table 2

Example Comparative Example 6 7 8 9 10 7 8 9 Paraffinic oil, number- 200 500 750 1000 2000 100 2250 2500 average molecular weight - 1 1 ITime before noise (min) 25 >60 >60 >60 25 10 1 Examples 11 to 15:

The same thermoplastic polyester elastomer resin as in Examples 1 to 5 was used as the base material - To this was added mineral paraffinic oil (BJ Oil@ from Kyodo Yushi) having a weight-average molecular weight of 200 (Example 11), 500 (Example 12), 950 (Example 13), 1400 (Example 14), or 2000 (Example 15), as in Table 3 below. Using an injection molding machine, the resulting mixture was molded into flexible resin boots. In these Examples 11 to 15, the blend ratio of the paraf f inic oil was 1. 5 parts by weight to 10 0 parts by weight of the thermoplastic polyester elastomer resin.

Comparative Example 10 to 12:

Flexible resin boots were produced in the same manner as in Examples 11 to 15, except that paraffinic oil (BJ Oil(b from Kyodo Yushi) having a weight-average molecular weight of 100 (Comparative Example 10), 2250 (Comparative Example 11) or 2500 (Comparative Example 12) was used as in Table 3.

The flexible 'resin boots of Examples 11 to 15 and Comparative Examples 10 to 12, having been molded in the manner as above, were built into constant velocity joints, and tested for their capability of noise prevention. The test method is the same as in Examples 6 to 10 and Comparative Examples 7 to 9. The test results are given in Table 3.

The boot of Comparative Example 10, to which was added paraf f inic oil having a small weight-average molecular weight, 26 made no noise in early stages. With it, however, the duration of noise prevention is only 10 minutes and is relatively short. This means that the noise-preventing capability of the boot is not satisfactory. The boots of Comparative Examples 11 and 12, to which was added paraf f inic oil having an extremely large weight-average molecular weight, made a noise in early stages. As opposed to these, the boots of Examples 11 and 15 ensured long duration of noise prevention for 25 minutes. Their data reached the target. The boots of Examples 12, 13 and 14 produced better results, having ensured longer duration of noise prevention for longer than 60 minutes.

27 Table. 3

Example Comparative Example 11 12 13 14 15 10 11 12 Paraffinic oil, weight- 200 500 950 1400 2000 100 2250 2500 average molecular weight Time before noise (min) 25 >60 >60 >60 25 10 1 1 1 28 Examples 16 to 20:

The same thermoplastic polyester elastomer resin as in Examples 1 to 5 was used as the base material. To this was added mineral paraffinic oil (BJ Oil@ from Kyodo Yushi) having a Z-average molecular weight of 200 (Example 16), 500 (Example 17), 1300 (Example 18), 2000 (Example 19), or 3000 (Example 20), as in Table 4 below. Using an injection molding machine, the resulting mixture was molded into flexible resin boots. In these Examples 16 to 20, the blend ratio of the paraffinic oil was 1.5 parts by weight to 100 parts by weight of the thermoplastic polyester elastomer resin.

Comparative Example 13 to 15:

Flexible resin boots were produced in the same manner as in Examples 16 to 20, except that paraffinic oil (BJ Oil& from Kyodo Yushi) having a Zaverage molecular weight of 100 (Comparative Example 13), 3500 (Comparative Example 14) or 4000 (Comparative Example 15) was used as in Table 4.

The flexible 'resin boots of Examples 16 to 20 and Comparative Examples 13 to 15, having been molded in the manner as above, were built into constant velocity joints, and tested for their capability of noise prevention. The test method is the same as in Examples 6 to 10 and Comparative Examples 7 to 9. The test results are given in Table 4.

The boot of Comparative Example 13, to which was added paraffinic oil having a small Z-average molecular weight, made 29 no noise in early stages. With it, however, the duration of noise prevention is only 10 minutes and is relatively short. This means that the noise-preventing capability of the boot is not satisfactory. The boots of Comparative Examples 14 and 15, to which was added paraffinic oil having an extremely large Z-average molecular weight, made a noise in early stages - As opposed to these, the boots of Examples 16 and 20 ensured long duration of noise prevention for 25 minutes. Their data reached the target. The boots of Examples 17, 18 and 19 produced better results, having ensured longer duration of noise prevention for longer than 60 minutes.

Table 4

Example Comparative Example 16 17 19 20 13 14 15 Paraffinic Oil, Z-average 200 500 1300 2000 3000 100 3500 4000 molecular weight Time before noise (min) 25 >60 >60 >60 25 10 1 1 1 31 Examples 21 and 22:

A thermoplastic polyester elastomer resin of formula (1) (PELPRENE9 from Toyo Boseki) was used as the material for flexible resin boots. The resin has a hardness of 46D, and it is a material for constant velocity joints. Pellets of the thermoplastic polyester elastomer resin were heated at 600C (Example 21) or 800C (Example 22), to which was added 1.5 parts by weight of paraf f inic oil (Bi Oil@ f rom Kyodo Yushi), relative to 100 parts by weight of the resin. These were stirred in a mixer, and other solid additives, 1.0 part by weight of antioxidant (NOCRAC 8 10 -NA8 f rom Ouchi Shinko) and 1. 0 part by weight of pigment (carbon black, SEAST GSO having a mean particle size of 43 nm) were added thereto, and further stirred. The resulting mixture was kneaded and extruded out through a double-screw extruder (Toshiba's double-screw extruder, TEM100) to prepare a molding material. The molding material was molded into flexible boots. To heat them, the pellets were stirred in Kawata's Super Mixer SMC- 30ON at 100 rpm. In the extruder, the screw revolution was 100 rpm, and the cylinder temperature was 2400C.

Comparative Example 16:

From the same thermoplastic polyester elastomer resin pellets and the same additives as in Examples 21 and 22, a molding material was prepared in the same manner as above. The molding material was molded into flexible boots. In 32 Comparative Example 16, however, the pellets were not heated, and the paraffinic oil was added thereto at room temperature (23-C).

The flexible resin boots of Examples 21 and 22 and Comparative Example 16, having been molded in the manner as above, were tested for their capability of noise prevention in the same test method as in Examples 6 to 10 and Comparative Examples 7 to 9. The test results are given in Table 5.

As in Table 5, the boots of Example 21 (for which the pellets were at 60'C) and Example 22 (for which the pellets were at 800C) ensured duration of noise prevention for longer than 25 minutes, and these reached the target. However, the duration of noise prevention with the boot of Comparati-ve Example 16 was 15 minutes and was short. This is because the dispersibility of the liquid additive and the solid additives in the resin in Comparative Example 16 was relatively poor. Table 5 Example Comparative Example

21 22 16 Liquid Additive paraffinic oil paraffinic oil paraffinic oil 1.5 wt.pts. 1.5 wt.pts. 1.5 wt.pts.

Solid Additives pigment Pigment pigment 1.0 Wt.pt. 1.0 Wt.pt. 1.0 Wt.pt.

antioxidant Antioxidant antioxidant 1.0 Wt.pt. 1.0 Wt.pt. 1.0 Wt.pt.

Temperature of 60 so 23 Pellets (OC) Time before Noise >60 min >60 min 15 min Example 23:

The same thermoplastic polyester elastomer resin as in 33 Examples I to 5 was used as the base material. To this was added the same mineral paraf f inic oil as in Example 1 to 5. The blend ratio of the oil was 1. 5 parts by weight to 100 parts by weight of the resin. Using an injection molding machine, the resulting mixture was molded into flexible resin boots. Comparative Example 17:

The same thermoplastic polyester elastomer resin as in Example 23 was used as the base material. In this, no para f f inic oil was added to the resin, but 0. 3 parts by weight of oleyloleamide and 0.08 parts by weight of ethyl enebis s t earamide, relative to 100 parts by weight of the resin, were added thereto. The resulting mixture was molded into flexible resin boots in the same manner as above.

The flexible boots of Example 23 and Comparative Example 17, having been molded in the manner as above, were tested for the deposition profile of the noise-preventing agent, oil or fatty acid amide. Concretely, the molded flexible boots were left at room temperature in three different manners: (A) The boots were left as they were with no specific treatment applied thereto; (B) the boots were wiped at intervals of 14 days; and (C) the boots were wiped at intervals of 7 days. While being lef t in those manners, the boots were checked f or the deposition amount of oil or fatty acid amide on their surfaces. Tomeasure the amount of the deposit, the inner and outer surfaces of each boot were wiped with soft cloth, and the cloth was weighed 34 before and after the surfaces were wiped. The weight change indicates the amount of the deposit.

In the test (A) where the boots were lef t as they were with no specific treatment applied thereto, the amount of the deposit was measured on days 1, 3, 4, 7, 14, 28, 42 and 56 after the boots were molded. In the test (B) where the boots were wiped at intervals of 14 days, the deposit on the surfaces of each boot was wiped away at intervals of 14 days and the amount of the deposit was measured on predetermined days after the boots were molded. In the test (C) where the boots were wiped at intervals of 7 days, the deposit on the surfaces of each boot was wiped away at intervals of 7 days and the amount of the deposit was measured on predetermined days after the boots were molded.

The data are plotted in Figs. 3A to 3C. As in these, the amount of the noise-preventing agent deposited on the surfaces of the boots of Example 23 is larger than that of Comparative Example 16. Even in the tests where the surfaces of the boots were wiped at regular intervals, the amount of the noise-preventing agent deposited on the surfaces of the boots of Example 23 is still larger than that of Comparative Example 16, even though it gradually decreases after repeated wiping operations. Immediately after the surfaces of the boots of Example 23 were wiped, the amount of the deposit soon reached the lowermost level (13 mg) for noise prevention.

However, after the surfaces of the boots of Comparative Example 16 were wiped, the noise-preventing agent could deposit only a little on the surfaces and its amount could not soon reach the lowermost level (7 mg) for noise prevention.

36

Claims (23)

CLAIMS:

1. A flexible resin boot formed from a base resin material of a thermoplastic elastomer resin and having a large port and a small port at the opposite ends that are connected with each other via a bellows therebetween, wherein mineral oil or vegetable oil is added to the thermoplastic elastomer res in.

2. The flexible resin boot as claimed in claim 1, wherein at most 5 parts by weight of mineral oil or vegetable oil is added to 100 parts by weight of the thermoplastic elastomer resin.

3. The flexible resin boot as claimed in claim 1, wherein at most 3 parts by weight of mineral oil or vegetable oil is added to 100 parts by weight of the thermoplastic elastomer resin.

4. A flexible resin boot formed from a base resin material of a thermoplastic elastomer resin and having a large port and a small port'at the opposite ends that are connected with each other via a bellows therebetween, wherein mineral oil that comprises, as the essential ingredient, paraffinic oil is added to the thermoplastic elastomer resin.

5. The flexible resin boot as claimed in claim 4, wherein the paraffinic oil has a number-average molecular weight of from 200 to 2000.

6. The flexible resin boot as claimed in claim 4, 37 wherein the paraffinic oil has a number-average molecular weight of from 500 to 1000.

7. The flexible resin boot as claimed in claim 4, wherein the paraffinic oil has a weight-average molecular weight of from 200 to 2000.

8. The flexible resin boot as claimed in claim 4, wherein the paraffinic oil has a weight-average molecular weight of from 500 to 1400.

9. The flexible resin boot as claimed in claim 4, wherein the paraffinic oil has a Z-average molecular weight of from 200 to 3000.

10. The flexible resin boot as claimed in claim 4, wherein the paraffinic oil has a Z-average molecular weight of from 500 to 2000.

11. The flexible resin boot as claimed in claim 4, wherein the paraffinic oil has a kinematic viscosity of from 100 to 1000 MM2/S, measured with a B-type viscometer at an ambient temperature 'of 250C.

12. The flexible resin boot as claimed in claim 4, wherein the paraffinic oil has a kinematic viscosity of from 100 to 500 MM2/S, measured with a Btype viscometer at an ambient temperature of 250C.

13. The flexible resin boot as claimed in any one of claims 1 to 12, wherein the thermoplastic elastomer resin is a thermoplastic polyester elastomer resin.

38

14. The flexible resin boot as claimed in claim 13, wherein the thermoplastic polyester elastomer resin is represented by a formula (1):

[COC)COO(CH'2)40]a[COOCOO(CH2)401c]b

15. A method for producing a flexible resin boot having a large port and a small port at the opposite ends that are connected with each other via a bellows therebetween, from a base resin material of a thermoplastic polyester elastomer resin, which comprises adding mineral oil or vegetable oil to hot pellets of a thermoplastic polyester elastomer resin and mixing and stirring them, thereafter further kneading the resulting mixture and extruding it through an extruder to prepare a molding material, and finally molding the molding material into the flexible resin boot.

16. The method for producing a flexible resin boot as claimed in claim 15, wherein a solid additive is added to and mixed with the mixture of the pellets and the mineral oil or the vegetable oil by stirring them, and the resulting mixture is then further kneaded and extruded to give the molding material.

17. The method for producing a flexible resin boot as claimed in claim 15, wherein the pellets and the solid additive 39 are heated and then mixed by stirring them, and thereafter mineral oil or vegetable oil is added to and mixed with the resulting mixture by further stirring them.

18. The method for producing a flexible resin boot as claimed in any one of claims 15 to 17, wherein mineral oil or vegetable oil is, after having been heated, added to and mixed with the pellets by stirring them.

19. The method for producing a flexible resin boot as claimed in claim 15, wherein the pellets, the mineral oil or vegetable oil, and a solid additive are all heated, and then mixed together by stirring them to prepare the mixture.

2 0. The method for producing a flexible resin boot as claimed in claim 15, wherein the heating temperature is not lower than 600C.

21. The method for producing a flexible resin boot as claimed in claim 15, wherein the heating temperature falls between 70 and 1000C.

22. A flexible resin boot produced by a method as claimed in any one of claims 15 to 21.

23. A flexible resin boot as claimed in claim 1, substantially as hereinbefore described with reference to and as shown in Figs. 1 and 2 of the accompanying drawings.