JP2008174614A - Lubricant composition, and decelerator and electrically driven power steering device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricant composition maintaining effects of reducing the noises in the vehicle interior over a period longer than the conventional one by decreasing contact sound of gear teeth without causing excessive increase of a steering torque of a pinion-type EPS or the like caused by buffering particles and without generating sliding sound even if the composition is used by being packed in a decelerator of the pinion-type EPS, etc., under a high-temperature environment, a high-humidity environment, a low-temperature environment, an environment of continuously receiving high torque, etc.; and to provide the decelerator and an electrically driven power steering device using the lubricant composition. <P>SOLUTION: The lubricant composition contains the buffering particles comprising a polyurethane resin synthesized by reacting a polyol component at least containing a polycaprolactone polyol, and having 250-1,300 number average molecular weight per one active hydrogen group, with an isocyanate, and having a crosslinked structure. The decelerator 17 packed with the lubricant composition, and the electrically driven power steering device having the decelerator incorporated therein are also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lubricant composition, a speed reducer filled with the lubricant composition, and an electric power steering apparatus including the speed reducer.

  A reduction gear is used for an electric power steering device for an automobile. For example, in a column type EPS, the rotation of the electric motor is transmitted from a small gear such as a worm to a large gear such as a worm wheel in the speed reducer to reduce the rotational speed and amplify the output, and then the steering shaft. The steering operation is torque-assisted by applying to the above. Appropriate backlash is required for meshing between the small gear and the large gear.

  However, if the backlash is too large, for example, when the rotation of both gears is reversed, or when the reaction force from the tire is input (referred to as kickback) while traveling on a rough road such as a cobblestone For example, a rattling noise may occur due to backlash, and if this is transmitted as noise in the passenger compartment, the driver is uncomfortable. For this reason, conventionally, so-called layered assembly has been adopted in which a combination of a small gear and a large gear is selected to assemble a reduction gear so that an appropriate backlash is achieved. Therefore, there has been a problem that the productivity of the reduction gear cannot be improved.

  Further, the unevenness of the steering torque caused by the eccentricity of the shaft of the worm wheel could not be eliminated even by layered assembly. Moreover, these problems exist not only in the speed reducer of the electric power steering apparatus but also in a general speed reducer having a small gear and a large gear. Therefore, in order to solve these problems, in Patent Document 1, the worm shaft is arranged to be deflectable toward the worm wheel, and the worm shaft is elastically directed to the worm wheel using a spring or the like. Thus, a reduction gear of an electric power steering apparatus has been proposed that substantially eliminates backlash between the two by biasing the motor. However, the above configuration has a problem that the structure of the speed reducer is complicated and the manufacturing cost is increased.

  Therefore, in Patent Documents 2 and 3, it is proposed to fill a lubricant composition containing buffer material particles made of rubber, soft resin or the like into a region including at least a meshing portion of a small gear and a large gear. It was. When the lubricant composition is used, the cushioning material particles are interposed between the tooth surfaces of both gears so as to buffer the collision between the tooth surfaces. Can be reduced. However, there has been a problem that the steering torque of the electric power steering device increases when the lubricant composition containing the buffer particles is used in a speed reducer in which a worm shaft and a worm wheel are combined.

  Therefore, in Patent Document 4, as a buffer material particle, a polyurethane resin synthesized by reacting a long-chain polyol having a number average molecular weight of 500 or more, a crosslinking agent having three or more active hydrogen groups in one molecule, and isocyanate. It has been proposed to use particles consisting of Specifically, an aromatic polyester polyol obtained by reacting an aromatic carboxylic acid or derivative thereof (acid anhydride, polyester, etc.) and a low molecular weight polyol, and an aliphatic carboxylic acid or derivative thereof (acid anhydride, polyester, etc.). And an aliphatic polyester polyol obtained by reacting a low molecular weight polyol with the above long-chain polyol and reacting with a crosslinking agent and an isocyanate in the form of droplets dispersed in an arbitrary dispersion medium. Then, a polyurethane resin (hereinafter sometimes referred to as “polyester type polyurethane resin”) is synthesized, and buffer particles are produced.

The cushioning material particles made of the polyester type polyurethane resin can be adjusted in elasticity and hardness in an arbitrary range by selecting the type and ratio of each component. Therefore, by filling a lubricant composition containing buffer material particles made of the polyester-type polyurethane resin, adjusted to have appropriate elasticity and hardness, into a region including a meshing portion of a small gear and a large gear, It is possible to reduce the rattling noise more effectively without increasing the steering torque of the electric power steering device or generating a sliding noise, thereby increasing the noise in the passenger compartment. It becomes possible.
JP 2000-43739 A (columns 0007 to 0009, FIG. 1) JP 2003-214529 A (Claim 1, columns 0005 to 0006) JP 2004-162018 (Claim 1, column 0009) Japanese Patent Laying-Open No. 2005-263898 (claim 1, column 0010)

  Recently, it has been required to use a lubricant composition containing buffer particles not only in the column type EPS described above but also in other types of reduction gears of electric power steering devices such as pinion type EPS. It's getting on. The pinion-type EPS transmits the rotation of the electric motor from the small gear to the large gear in the reduction gear, thereby reducing the rotation speed and amplifying the output, and then the pinion shaft of the rack-and-pinion mechanism as the steering mechanism. To assist the torque in the steering operation.

  However, as a result of examination by the inventors, when a lubricant composition containing the buffer material particles made of the polyester type polyurethane resin is filled in a reduction gear of a pinion type EPS or the like, the steering torque by the buffer material particles is increased. Not only may there be a risk that the effect of reducing the noise in the vehicle interior by reducing the rattling noise without excessively raising or generating a sliding sound, but also the cushioning material It has been clarified that there is a case where the durability of the particles is insufficient, and in that case, the effect may be lowered in a relatively short period of time.

  This is because the polyester-type polyurethane resin buffer material particles are used in a pinion-type EPS speed reducer or the like to reduce the rattling noise over a long period of time. Is not enough. That is, in the pinion type EPS or the like, a higher torque is required for driving as compared to the column type EPS, and the kickback described above is directly applied to the speed reducer during traveling. Even if the cushioning material particles made of polyester polyurethane resin having elasticity and hardness suitable for EPS speed reducers are used for pinion type EPS speed reducers as they are, the elasticity is insufficient and the above effects are sufficiently obtained. In addition to lack of hardness, the shock absorber particles interposed between the tooth surfaces of the small gear and the large gear of the reduction gear are crushed in a relatively short time by continuing to receive high torque. The effect may be reduced.

  As another cause, in the pinion type EPS or the like, the speed reducer is mainly installed around the steering gear box near the engine of the automobile and close to the outside environment. The filled lubricant composition can continue to be used in a high temperature environment of approximately 120 ° C. or higher due to heat from the engine, or in a high humidity environment mainly due to moisture from the outside of the vehicle. In other cases, the lubricant composition is often exposed to a low temperature when the automobile is parked outdoors.

  That is, the polyester type polyurethane resin generally has low heat resistance, and as the proportion of the aliphatic polyester polyol as the long-chain polyol increases, the moisture resistance and water resistance tend to decrease. Hydrolysis may occur when used in a high humidity environment. As a result, when the polyester-type polyurethane resin is hydrolyzed and has a low molecular weight, the elasticity of the buffer particles is drastically reduced, and when interposed between the tooth surfaces of the small gear and the large gear of the speed reducer, As a result of being easily crushed or having a low molecular weight, the tackiness increases and a large number of buffer particles aggregate in the lubricant composition. There exists a possibility that the effect which reduces a sound may fall.

  Furthermore, as the proportion of the aromatic polyester polyol as the long-chain polyol increases, the glass transition temperature of the polyester-type polyurethane resin increases, and the temperature at which the buffer particles become brittle and lose elasticity in a low temperature environment tends to increase. Therefore, when a steering operation is performed in a state where the lubricant composition is exposed to a low temperature, the cushioning material particles interposed between the tooth surfaces of the small gear and the large gear are easily crushed. As a result, there is a possibility that the effect of reducing the rattling noise is reduced in a relatively short period of time. Therefore, the lubricant composition including the buffer material particles made of polyester type polyurethane resin described in Patent Document 4 has a sufficient effect of reducing rattling noise particularly when used in a reduction gear of a pinion type EPS. In addition to the possibility of not being obtained, there may be a case where the durability of the buffer particles is insufficient, and in that case, the effect may be reduced in a relatively short period of time.

  The object of the present invention is to fill a pinion-type EPS speed reducer, etc., and use it under a high temperature environment, a high humidity environment, a low temperature environment, or an environment in which high torque continues to be applied. Noise in the passenger compartment can be reduced by reducing the rattling noise without excessively increasing the steering torque of the electric power steering device such as the pinion type EPS or generating the sliding noise due to the buffer material particles. It is an object of the present invention to provide a lubricant composition capable of maintaining the effect of reducing the above for a longer period than before.

  Further, the object of the present invention is to use the lubricant composition of the present invention, particularly for a long period of time, in a high temperature environment, a high humidity environment, or an environment where high torque is continuously applied. However, the present invention is to provide a reduction gear that is low in noise and that does not increase the steering torque when incorporated in an electric power steering device or the like, and an electric power steering device that uses the reduction gear.

The present invention includes at least
(1) a polyol component containing polycaprolactone polyol and having a number average molecular weight of 250 to 1300 per active hydrogen group;
(2) isocyanate and
A lubricant composition comprising buffer particles made of polyurethane resin having a cross-linked structure synthesized by reacting with a lubricant, and a lubricant.

  According to the inventors' investigation, a polyurethane resin having a crosslinked structure synthesized by reacting at least an isocyanate with a polyol component containing polycaprolactone polyol (hereinafter sometimes referred to as “polycaprolactone type polyurethane resin”) is: Since the polycaprolactone polyol is excellent in oil resistance, the polycaprolactone polyol has oil resistance equal to or higher than that of a conventional polyester polyurethane resin, and the polycaprolactone polyol has a function of lowering the glass transition temperature of the polyurethane resin. Therefore, the temperature at which the buffer material particles become brittle and lose elasticity under a low temperature environment can be significantly reduced as compared with the conventional case.

  In addition, the polycaprolactone type polyurethane resin has a number average molecular weight per active hydrogen group of the polyol component in the range of 250 to 1300, so that the molecular crosslinking density is higher than the conventional one. Tend to be. Therefore, the polycaprolactone type polyurethane resin is excellent in heat resistance, moisture resistance, and water resistance as compared with the conventional polyester type polyurethane resin, and the elasticity and strength of the buffer material particles as compared with the conventional one. The durability can be improved significantly.

  Therefore, according to the lubricant composition of the present invention including the buffer particles composed of the polycaprolactone type polyurethane resin, it is particularly filled in a pinion type EPS speed reducer and the like in a higher temperature environment and higher humidity than before. Even when used in an environment, a low temperature environment, or an environment that continues to receive high torque, the shock absorber particles excessively increase the steering torque of the electric power steering device such as the pinion-type EPS or the sliding noise. It is possible to maintain the effect of reducing the rattling noise and reducing the noise in the passenger compartment for a longer period of time without generating the noise. In the present invention, the number average molecular weight of a polyol component such as polycaprolactone polyol is represented by a value obtained from the hydroxyl value of the polyol component and the number of functional groups.

  In the case where the polycaprolactone polyol is a trifunctional polycaprolactone polyol having three active hydrogen groups in one molecule, the cross-linking density of the molecule is further improved, and the above-described characteristics are further improved. Can be improved. As the polyol component, the trifunctional polycaprolactone polyol may be used alone, or two or more kinds of polyols including at least trifunctional polycaprolactone polyol may be used in combination.

For example, as a polyol component,
(i) Two or more kinds of trifunctional polycaprolactone polyols having different number average molecular weights are used in combination so that the number average molecular weight per active hydrogen group is in the range of 250 to 1300,
(ii) A trifunctional polycaprolactone polyol and a bifunctional polycaprolactone polyol having two active hydrogen groups in one molecule have a number average molecular weight per active hydrogen group in the range of 250 to 1,300. Or use together or
(iii) A polyester polyol which is a reaction product of a carboxylic acid or a derivative thereof (an acid anhydride, polyester, etc.) and a polyol and a trifunctional polycaprolactone polyol have a number average molecular weight of 250 per active hydrogen group. ˜1300 and formula (a):

〔式中、Ｐ_Kはポリカプロラクトンポリオールの質量、Ｐ_Eはポリエステルポリオールの質量を示す。〕
で求められる、ポリカプロラクトンポリオールの、両ポリオールの総量中に占める割合Ｒ_P（質量％）が５０質量％を超える範囲内となるように併用する
ことによって、先に説明した種々の特性を維持しながら、ポリカプロラクトン型ポリウレタン樹脂に、併用するポリオール成分に基づく、様々な、新たな特性を付与することができる。

Wherein, P _K is the mass of polycaprolactone polyols, P _E represents the weight of the polyester polyol. ]
By using together such that the ratio R _P (% by mass) of the polycaprolactone polyol in the total amount of both polyols determined in (1) is in the range exceeding 50% by mass, the various characteristics described above are maintained. However, various new properties based on the polyol component used in combination can be imparted to the polycaprolactone type polyurethane resin.

  As the isocyanate, a polyfunctional isocyanate having an isocyanurate skeleton in the molecule and three or more NCO groups in one molecule is preferable. By using the polyfunctional isocyanate, an isocyanurate skeleton is introduced into the molecule of the polycaprolactone-type polyurethane resin, and the cross-linking density of the molecule is further improved to further improve the heat resistance of the polycaprolactone-type polyurethane resin. Can be improved. Moreover, in this invention, the crosslinking agent which has 3 or more of active hydrogen groups in 1 molecule can also be used together, and the crosslinking density of a molecule | numerator can further be improved by this combined use. However, when there are too many crosslinking agents, the crosslinking density of the molecules becomes too high, and the polycaprolactone type polyurethane resin becomes hard and brittle, so the molar ratio of the crosslinking agent to the polyol component is 2.0 times. Within the range of less than.

  When the polycaprolactone polyol is a bifunctional polycaprolactone polyol having two active hydrogen groups in one molecule, the glass transition temperature of the polyurethane resin is further lowered, and the buffer particles become brittle in a low temperature environment. Thus, the temperature at which the elasticity is lost can be further reduced. The isocyanate to be reacted with the bifunctional polycaprolactone polyol is preferably a polyfunctional isocyanate having an isocyanurate skeleton in the molecule and three or more NCO groups in one molecule. By using the polyfunctional isocyanate, an isocyanurate skeleton is introduced into the molecule of the polycaprolactone-type polyurethane resin, and the cross-linking density of the molecule is further improved. Under a low-temperature environment due to the bifunctional polycaprolactone polyol, The heat resistance of the polycaprolactone type polyurethane resin can be further improved while maintaining the effect of reducing the temperature at which the buffer material particles become brittle and lose elasticity.

  Also, a bifunctional polycaprolactone polyol as a polyol component and a bifunctional isocyanate having two NCO groups in one molecule can be combined. In this case, the polycaprolactone type polyurethane resin to be synthesized is crosslinked. In order to introduce a structure, it is preferable to use a crosslinking agent having three or more active hydrogen groups in one molecule. In such a combined system, polycaprolactone type polyurethane is obtained by crosslinking with a crosslinking agent while maintaining the effect of reducing the temperature at which the buffer particles become brittle and lose elasticity under a low temperature environment by the bifunctional polycaprolactone polyol. In addition to improving the heat resistance, moisture resistance and water resistance of the resin, the elasticity and strength of the buffer particles can be improved. However, when the amount of the crosslinking agent is too small, the crosslinking effect cannot be obtained, so that the molar ratio of the crosslinking agent to the polyol component is within a range of 0.5 times or more.

  The buffer material particles are preferably spherical particles made of a polyurethane resin synthesized by reacting at least with an isocyanate in a state where the polyol component is dispersed in the form of droplets in a dispersion medium. When the spherical particles are used, the fluidity of the lubricant composition can be improved, and the increase of the steering torque of the electric power steering device and the generation of sliding noise can be prevented more reliably. Moreover, according to the said manufacturing method, there exists an advantage that the buffer material particle | grains which were spherical and uniform in particle size can be manufactured efficiently.

  The speed reducer of the present invention includes a small gear and a large gear, and the region including the meshing portion of both the gears is filled with the lubricant composition of the present invention. It is preferable in that it is low in noise even if it is used in an environment, a high humidity environment, or an environment where it continues to receive high torque, and there is no risk of increasing its steering torque when incorporated in an electric power steering device or the like. . In addition, the electric power steering apparatus of the present invention transmits the output of the steering assist motor to the steering mechanism via the reduction gear, so that noise in the vehicle compartment can be reduced at low cost. preferable.

  According to the present invention, in particular, a pinion type EPS reduction gear or the like is filled, and even when used in a high temperature environment, a high humidity environment, a low temperature environment, or an environment in which high torque is continuously received, Noise in the passenger compartment can be reduced by reducing the rattling noise without excessively increasing the steering torque of the electric power steering device such as the pinion type EPS or generating the sliding noise due to the buffer material particles. Thus, it is possible to provide a lubricant composition that can keep the effect of reducing the temperature better for a longer period than before.

  Further, according to the present invention, by using the lubricant composition of the present invention, it is continued to be used under a high temperature environment, a high humidity environment, or an environment in which high torque is continuously applied, particularly for a long period of time. However, it is possible to provide a reduction gear that is low in noise and that does not increase the steering torque when incorporated in an electric power steering device or the like, and an electric power steering device that uses the reduction gear.

<Lubricant composition>
The lubricant composition of the present invention includes at least
(1) a polyol component containing polycaprolactone polyol and having a number average molecular weight of 250 to 1300 per active hydrogen group;
(2) isocyanate and
It contains buffer material particles made of polyurethane resin having a crosslinked structure and synthesized by reacting and a lubricant.

  As described above, the lubricant composition of the present invention is filled in a pinion-type EPS speed reducer, etc., in a higher temperature environment, a higher humidity environment, a lower temperature environment, or higher torque than before. Even if it is used in an environment where it continues to be subject to shocks, it does not excessively increase the steering torque of the electric power steering device such as the pinion-type EPS or generate sliding noise due to the buffer material particles. There is a specific effect that the effect of reducing the noise and reducing the noise in the passenger compartment can be maintained satisfactorily.

  Among the polyol components (1), examples of the polycaprolactone polyol include those synthesized by ring-opening polymerization of ε-caprolactone. The polycaprolactone polyol is an active hydrogen as a functional group that is introduced into a molecule based on the number of functional groups that function as a polymerization starting point of a polymerization initiator used in ring-opening polymerization of ε-caprolactone. The number of groups can be adjusted. For example, when a trimethylolpropane having three active hydrogen groups as functional groups in one molecule is used as a polymerization initiator, it has three active hydrogen groups in one molecule by ring-opening polymerization. A trifunctional polycaprolactone polyol can be synthesized.

  In addition, when ethylene glycol or the like having two active hydrogen groups as functional groups in one molecule is used as a polymerization initiator, 2 having two active hydrogen groups in one molecule by ring-opening polymerization. Functional polycaprolactone polyols can be synthesized. The number average molecular weight per active hydrogen group of the polyol component containing the polycaprolactone polyol is limited to 250 to 1300. When the number average molecular weight per active hydrogen group of the polyol component exceeds 1300, the crosslink density of the polycaprolactone type polyurethane resin having a crosslinked structure synthesized by reacting with at least an isocyanate is insufficient. In addition, the heat resistance, moisture resistance, and water resistance of the polycaprolactone type polyurethane resin are improved, and the effect of improving the elasticity and strength of the buffer material particles cannot be obtained. End up.

  Further, when the number average molecular weight is less than 250, the polycaprolactone type polyurethane resin having a crosslinked structure synthesized by reacting at least with an isocyanate has a too high molecular crosslinking density, and the polycaprolactone type polyurethane resin is On the other hand, the durability of the buffer particles is lowered because it is too hard and brittle. The durability of the buffer particles is improved by adjusting the molecular crosslinking density of the polycaprolactone type polyurethane resin to an appropriate range and improving each of the properties of the polycaprolactone type polyurethane resin. In view of the above, the number average molecular weight per active hydrogen group of the polyol component is preferably 300 to 1250, particularly preferably 350 to 1200 even within the above range.

  In order to adjust the number average molecular weight per active hydrogen group of the polyol component so as to be within the above range, a trifunctional polycaprolactone polyol or a bifunctional polycaprolactone polyol is used as the polyol component. When any one of them is used alone, the number average molecular weight of the polycaprolactone polyol may be adjusted. For example, when a trifunctional polycaprolactone polyol is used alone, the number average molecular weight thereof is adjusted to a range of 750 to 3600, so that one per active hydrogen group of the polycaprolactone polyol, and hence the polyol component, is adjusted. The number average molecular weight can be in the range of 250 to 1300.

  In addition, when a bifunctional polycaprolactone polyol is used alone as the polyol component, the active hydrogen of the polycaprolactone polyol, and thus the polyol component, is adjusted by adjusting the number average molecular weight in the range of 500 to 2600. The number average molecular weight per group can be in the range of 250-1300. Further, when two or more polyols including at least polycaprolactone polyol are used in combination as the polyol component, one active hydrogen group determined from the total number average molecular weight of each polyol and the total amount of active hydrogen groups What is necessary is just to adjust the number average molecular weight of each polyol, the number of active hydrogen groups, and the blending ratio of each polyol so that the number average molecular weight per one may become in the said range.

  When two or more kinds of polyols are used in combination, other polyols used in combination are not particularly limited as long as at least one of them is polycaprolactone polyol, but the combination of (i) to (iii) described above is adopted. Is preferred. Among these, when two or more kinds of tri-functional polycaprolactone polyols (i) having different number average molecular weights are used in combination, the number average molecular weight per active hydrogen group is within the above range as each polycaprolactone polyol. An inner one may be used, and at least one of them may have a number average molecular weight outside the above range. In any case, the number average molecular weight and blending ratio of each polycaprolactone polyol should be adjusted so that the number average molecular weight per active hydrogen group is in the range of 250 to 1300 when viewed as the whole polyol component. That's fine.

  When (ii) the trifunctional polycaprolactone polyol and the bifunctional polycaprolactone polyol are used in combination, only one kind may be used alone as the trifunctional polycaprolactone polyol, or the number average molecular weight may be used. Two or more different types may be used in combination. Similarly, as the bifunctional polycaprolactone polyol, only one kind may be used alone, or two or more kinds having different number average molecular weights may be used in combination.

  Other configurations are the same as those in the case (i). That is, as each polycaprolactone polyol, those having a number average molecular weight per active hydrogen group within the above range may be used, and at least one of the polycaprolactone polyols has a number average molecular weight outside the above range. It can also be used. In any case, the number average molecular weight and blending ratio of each polycaprolactone polyol should be adjusted so that the number average molecular weight per active hydrogen group is in the range of 250 to 1300 when viewed as the whole polyol component. That's fine.

  In (iii), the polyester polyol which is a reaction product of a carboxylic acid or a derivative thereof (an acid anhydride, polyester, etc.) and a polyol used in combination with a trifunctional polycaprolactone polyol is the aromatic carboxylic acid described above. Examples thereof include aromatic polyester polyols obtained by reacting an acid or a derivative thereof with a low molecular weight polyol, and aliphatic polyester polyols obtained by reacting an aliphatic carboxylic acid or a derivative thereof with a low molecular weight polyol. As said polyester polyol, only 1 type may be used independently and 2 or more types from which a number average molecular weight and a structure differ may be used together. Moreover, also as a trifunctional polycaprolactone polyol, only 1 type may be used independently and 2 or more types from which a number average molecular weight differs may be used together. By the combined use, an effect of improving the tensile strength of the buffer material particles or improving the heat resistance of the buffer material particles when the polyester polyol is an aromatic polyester polyol can be obtained.

  In the combination system, the formula (a):

〔式中、Ｐ_Kはポリカプロラクトンポリオールの質量、Ｐ_Eはポリエステルポリオールの質量を示す。〕
で求められる、ポリカプロラクトンポリオールの、両ポリオールの総量中に占める割合Ｒ_P（質量％）が５０質量％を超える範囲内である必要がある。割合Ｒ_Pが前記範囲未満では、ポリオール成分として、ポリカプロラクトンポリオールを用いたことによる、先に説明した、ポリウレタン樹脂のガラス転移温度を引き下げて、低温環境下で、緩衝材粒子が脆化して弾性を失う温度を低下させる効果が得られなくなってしまう。

Wherein, P _K is the mass of polycaprolactone polyols, P _E represents the weight of the polyester polyol. ]
It is necessary that the ratio R _P (% by mass) of the polycaprolactone polyol determined in (1) to the total amount of both polyols exceeds 50% by mass. When the ratio R _P is less than the above range, the glass transition temperature of the polyurethane resin described above is lowered by using polycaprolactone polyol as the polyol component, and the buffer particles become brittle and elastic in a low temperature environment. The effect of lowering the temperature will be lost.

The ratio R _P is 60 to 95 even within the above range, considering that the above effects can be exhibited more satisfactorily and that the above-described effects due to the combined use of the polyester polyol are taken into account. It is preferable that it is mass%, especially 70-90 mass%. Other configurations are the same as those in the cases (i) and (ii).
That is, as each polyol, those having a number average molecular weight per active hydrogen group within the above range may be used, and at least one of those having a number average molecular weight outside the above range may be used. You can also. In any case, the number average molecular weight and the blending ratio of each polyol may be adjusted so that the number average molecular weight per active hydrogen group is in the range of 250 to 1300 when viewed as the whole polyol component. .

  As the isocyanate to be reacted with the polyol component, various isocyanates containing two or more NCO groups in the molecule can be used. Examples of the isocyanate include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, and 4,4′-diphenylmethane diisocyanate; aliphatic diisocyanates such as 1,6-hexamethylene diisocineate and 1,12-dodecane diisocyanate; And alicyclic diisocyanates such as cyclohexane-1,4-diisocyanate and isophorone diisocyanate.

  As the isocyanate, an isocyanate group-terminated compound obtained by reacting each isocyanate with an active hydrogen group-containing compound; an isocyanate-modified product obtained by carbodiimidization reaction, isocyanurate reaction, etc .; a condensate of aniline and formaldehyde is phosgene The thing etc. which were made into a thing are also mentioned. In addition, some or all of it was stabilized with an appropriate blocking agent having one active hydrogen in one molecule such as methanol, n-butanol, benzyl alcohol, ε-caprolactam, methyl ethyl ketone oxime, phenol, cresol, etc. Isocyanates can also be used.

  Among them, the isocyanate having an isocyanurate skeleton in the molecule and having three or more NCO groups in the molecule has the effect of improving the heat resistance of the polycaprolactone type polyurethane resin as described above. From the above, the isocyanate is preferably a trimerized isocyanate (NCO group number: 3.5) obtained by trimming 1,6-hexamethylene diisocyanate by an isocyanurate-forming reaction.

  Isocyanate has an NCO group equivalent to the equivalent of the active hydrogen group of the polyol component, or when a cross-linking agent having three or more active hydrogen groups in one molecule is used in combination. The mixing ratio may be set so that the equivalent amount is substantially equal to the total amount of the equivalent of active hydrogen groups of the polyol component and the equivalent of active hydrogen groups of the crosslinking agent. Specifically, it is preferable to set the blending ratio of the isocyanate so that the equivalent of the NCO group is about 0.9 to 1.1 times the equivalent of the active hydrogen group.

  As the crosslinking agent, various compounds having three or more active hydrogen groups in one molecule can be used. Examples of the crosslinking agent include glycerin, sorbitol, trimethylolpropane, trimethylolbutane, trimethylolethane, 1 Polyols such as 1,2,6-hexanetriol and pentaerythritol, and amino alcohols such as triethanolamine, diethanolamine, N, N, N ′, N′-tetra (hydroxypropyl) diamine, etc., particularly active hydrogen groups Are all primary hydroxyl groups, and trimethylolpropane and trimethylolbutane are preferred.

  In the system containing at least trifunctional polycaprolactone polyol as the polyol component, the molar ratio of the crosslinking agent to the polyol component is set within a range of less than 2.0 times. When the molar ratio of the crosslinking agent exceeds the above range, the molecular crosslinking density becomes too high, and the synthesized polycaprolactone type polyurethane resin becomes hard and brittle. In the above system, since a crosslinked structure is formed by the reaction of trifunctional polycaprolactone polyol and isocyanate without adding a crosslinking agent, the lower limit of the molar ratio is 0 times, that is, the crosslinking agent is not used. Although it is included up to the range not added, in the case of adding a crosslinking agent, the molar ratio is preferably in the range of 0.5 to 1.5 times in consideration of effectively exhibiting the effect of addition. .

Further, in a system in which the polyol component is a bifunctional polycaprolactone polyol and the isocyanate is also a bifunctional isocyanate, a crosslinking agent is an essential component for crosslinking the polycaprolactone type polyurethane resin to be synthesized. It mix | blends and the molar ratio with respect to the polyol component of the said crosslinking agent shall be 0.5 times or more.
If the molar ratio of the cross-linking agent is less than the above range, the cross-linking density of the molecule is too low, and the bifunctional polycaprolactone polyol maintains the effect of reducing the temperature at which the buffer particles become brittle and lose elasticity under a low temperature environment. However, the effect of improving the heat resistance, moisture resistance and water resistance of the synthesized polycaprolactone type polyurethane resin and improving the elasticity and strength of the buffer material particles cannot be obtained. In the system, considering that the elasticity and strength of the buffer particles are adjusted to an appropriate range, the molar ratio of the crosslinking agent is 2.5 times or less, particularly 0.8-2. It is preferably within the range of 0 times.

  Various additives may be contained in the buffer particles made of polycaprolactone type polyurethane resin synthesized by reacting the above components, if necessary. Examples of additives include antioxidants for preventing deterioration of polycaprolactone type polyurethane resins, antioxidants, flame retardants, magnetic powders for imparting magnetism to buffer particles, and particles for coloring. And the like.

The average particle diameter D ₁ of the volume fraction of the buffer particles is preferably 50 μm <D ₁ ≦ 300 μm. An average particle diameter D ₁ of the volume fraction less than the range, there is a limit to the effect of reducing small gear and shock buffer to rattle engagement with the gear wheel, the noise in the passenger compartment, significantly May not be reduced. Further, when the average particle diameter D ₁ of the volume fraction exceeds the above range, there is a possibility that the steering torque of the electric power steering apparatus is or, or generates a sliding sound increase. In addition, the average particle diameter of the volume fraction of the buffer particles is preferably 100 μm or more, even within the above range, in consideration of further improving the effect of reducing the rattling noise. In consideration of more reliably preventing an increase in steering torque and generation of sliding noise, it is particularly preferably 200 μm or less even within the above range.

  The buffer particles can be produced by various methods, but the polyol component is dispersed in the dispersion medium according to the dispersion polymerization method in which the polyol component is dispersed in the dispersion medium in the form of droplets and reacted with at least the isocyanate. While maintaining the spherical shape, it is possible to efficiently produce buffer particles having a uniform particle size. As the dispersion medium, any of various non-aqueous organic solvents that do not dissolve at least the polyol component and the polyurethane resin produced by the reaction can be used. Specific examples thereof include n-hexane, isooctane, dodecane, fluid Examples thereof include aliphatic hydrocarbons such as paraffin, and alicyclic hydrocarbons such as cyclohexane. In particular, considering the heating during the reaction, the dispersion medium preferably has a boiling point of 60 ° C. or higher. If necessary, as the dispersion medium, a polar solvent such as toluene, butyl acetate, or methyl ethyl ketone may be used in combination.

  If necessary, a catalyst for promoting urethanization may be added to the reaction system. Examples of the catalyst include di-n-butyltin dilaurate, stannous octoate, tertiary amines (N-methylmorpholine, triethylamine, etc.), lead naphthenate, lead octoate and the like. The amount of the catalyst added is preferably about 0.01 to 1 part by mass with respect to 100 parts by mass as the total of the components that form the polycaprolactone type polyurethane resin such as the polyol component.

  A dispersion stabilizer may be added to the reaction system in order to stably disperse at least the polyol component in the non-aqueous dispersion medium. Any of various dispersion stabilizers (surfactants) can be used as the dispersion stabilizer. As a preferable dispersion stabilizer, for example, 100 parts by mass of a polyester polyol or polycarbonate polyol having an unsaturated bond in the molecule and an ethylenically unsaturated monomer 20 to 20 having a side chain composed of a hydrocarbon group having 6 or more carbon atoms. The compound obtained by making 400 mass parts react is mentioned. The dispersion stabilizer is preferably about 1 to 30 parts by mass with respect to 100 parts by mass as a total of the components that form the polycaprolactone type polyurethane resin such as a polyol component.

  For carrying out the dispersion polymerization method, various conventionally known emulsification apparatuses and the like can be used. The procedure for charging each component can be selected as appropriate, but is preferably performed according to the following procedure. That is, a polyol component and a dispersion medium are charged into a reaction vessel of an apparatus, and a dispersion stabilizer is added and stirred to disperse the polyol component in a spherical shape in the dispersion medium. Added. Then, when the reaction is continued until the production and crosslinking of the polycaprolactone-type polyurethane resin by the reaction between the polyol component and the isocyanate proceeds and the unreacted NCO group disappears, buffer particles are produced. The amount of unreacted NCO groups can be determined by titrating the concentration of terminal NCO groups in the polyurethane resin sampled from the reaction vessel.

  The cross-linking agent can be added at any point of the reaction, but when the production of polycaprolactone-type polyurethane resin by the reaction between the polyol component and the isocyanate proceeds to some extent, the cross-linking agent is added to assist It is preferable to produce a crosslinked structure. The progress of the production of the polycaprolactone type polyurethane resin can be determined by titrating the concentration of the terminal NCO group in the polyurethane resin sampled from the reaction vessel in the same manner as described above.

  In the system in which the polyol component is a bifunctional polycaprolactone polyol and the isocyanate is a bifunctional isocyanate as described above, the catalyst and the isocyanate are dispersed in a spherical state in the dispersion medium. Is added to react the polyol component with the isocyanate to produce a polycaprolactone type polyurethane resin having basically no cross-linked structure. Then, when the chain length of the polycaprolactone type polyurethane resin reaches a predetermined value, a crosslinking agent is added to crosslink the polyurethane resin to produce buffer particles. The chain length of the polyurethane resin can be determined by titrating the terminal NCO group concentration of the polyurethane resin sampled from the reaction vessel.

  In the dispersion polymerization method, in order to adjust the average particle size of the volume fraction of the buffer material particles within the range described above, the stirring conditions (stirring speed, temperature, etc.) are adjusted, or the dispersion stability is increased. The type and amount of the agent may be selected, and the type and amount of the dispersion medium may be selected. Moreover, what is necessary is just to mix an additive in the polyol component used for superposition | polymerization, for example, in order to add the said additive to the buffer material particle manufactured by a dispersion polymerization method.

  The content ratio of the buffer particles in the lubricant composition of the present invention is preferably 5 to 50% by mass, particularly 20 to 40% by mass, based on the total amount of the lubricant composition. If the content ratio is less than the above range, the impact of the meshing between the small gear and the large gear by the buffer material particles is buffered, and the effect of reducing the rattling noise cannot be sufficiently obtained. There is a risk that it cannot be reduced. Further, when the range is exceeded, the steering torque of the electric power steering device may increase, or a sliding noise may be generated, which may increase the noise in the passenger compartment.

The lubricant constituting a lubricant composition with a buffer particles, kinematic viscosity ^{5~200mm 2 / s (40 ℃)} , particularly preferable to use those which are 20~100mm ² / s (40 ℃) . The lubricating oil is preferably a synthetic hydrocarbon oil [for example, poly α olefin oil (PAO)], but synthetic oils such as silicone oil, fluorine oil, ester oil, and ether oil, mineral oil, and the like can also be used. Lubricating oils can be used alone or in combination of two or more. The lubricant composition may be liquid or semi-solid so-called grease.

  The grease preferably has a penetration degree (25 ° C.) of 265 to 475, particularly 355 to 430, with the addition of buffer particles. In order to make the lubricant composition into grease, a thickener may be added. Examples of the thickener include various conventionally known thickeners such as a soap-based thickener, a urea-based thickener, an organic thickener, and an inorganic thickener.

  Among these, soap-type thickeners include aluminum soaps, calcium soaps, lithium soaps, metallic soaps such as sodium soaps, mixed soap-type thickeners such as lithium-calcium soaps and sodium-calcium soaps, aluminum Complex thickeners such as complex, calcium complex, and lithium complex sodium complex are listed, and lithium soap such as lithium stearate is particularly preferable. Examples of the urea thickener include polyurea, and examples of the organic thickener include polytetrafluoroethylene (PTFE) and sodium terephthalate. Further, examples of the inorganic thickener include organic bentonite, graphite, silica gel and the like.

  Liquid or grease lubricant compositions include solid lubricants such as fluororesin (PTFE, etc.), molybdenum disulfide, graphite, polyolefin wax (including amide, etc.), phosphorus-based Sulfur-based extreme pressure additives, antioxidants such as tributylphenol and methylphenol, rust inhibitors, metal deactivators, viscosity index improvers, oiliness agents and the like may be added.

  The lubricant composition of the present invention can be used by filling not only the pinion type EPS described above but also a reduction gear of various types of electric power steering devices such as a column type EPS and a rack type EPS. In addition, for example, by filling various power transmission parts such as a spline joint incorporated in an intermediate shaft that connects between the steering shaft and a steering mechanism such as a rack and pinion mechanism, abnormal noise such as rattling noise is obtained. Can be made to function.

<Reduction gear and electric power steering device>
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, an intermediate shaft 5 connected to the steering shaft 3 via a universal joint 4, A pinion shaft 7 connected to the intermediate shaft 5 via a universal joint 6 and a rack tooth 8a meshing with a pinion tooth 7a provided in the vicinity of the end of the pinion shaft 7 and extending in the lateral direction of the automobile. A rack bar 8 is provided as a rudder shaft, and the pinion shaft 7 and the rack bar 8 constitute a rack and pinion mechanism A as a steering mechanism.

  The rack bar 8 is supported in the housing 9 so as to be capable of linear reciprocation through a plurality of bearings (not shown). Both end portions of the rack bar 8 protrude to both sides of the housing 9, and tie rods 10 are coupled to the respective end portions. Each tie rod 10 is connected to a corresponding wheel 11 via a corresponding knuckle arm (not shown). When the steering member 2 is operated and the steering shaft 3 is rotated, the rotation is converted into a linear motion of the rack bar 8 along the left-right direction of the automobile by the pinion teeth 7a and the rack teeth 8a. Steering is achieved.

  The steering shaft 3 is divided into an input shaft 3a connected to the steering member 2 and an output shaft 3b connected to the pinion shaft 7. These input / output shafts 3a and 3b are on the same axis line via a torsion bar 12. Are connected to each other so as to be relatively rotatable. In the vicinity of the torsion bar 12, there is provided a torque sensor 13 for detecting a steering torque from the relative rotational displacement amount between the input / output shafts 3a and 3b via the torsion bar 12, and the torque detection result of the torque sensor 13 is provided. Is given to an ECU (Electric Control Unit) 14. The ECU 14 drives and controls the steering assist electric motor 16 via the drive circuit 15 based on a torque detection result, a vehicle speed detection result given from a vehicle speed sensor (not shown), and the like. Then, the output rotation of the electric motor 16 is decelerated through a reduction gear 17 as a transmission device and transmitted to the pinion shaft 7 constituting the rack and pinion mechanism A, and the rack bar 8 is transmitted through the pinion shaft 7. It is converted into a linear motion of, and steering is assisted.

The speed reducer 17 is rotationally driven by an electric motor 16 and a worm shaft 18 as a small gear and a worm wheel 19 as a large gear that meshes with the worm shaft 18 and is connected to the pinion shaft 7 so as to be integrally rotatable. And is housed in a housing 9 that houses the rack bar 8.
Referring to FIG. 2, the worm shaft 18 is connected to the rotating shaft 16 a of the electric motor 16 via a spline joint 34, and the first and second rolling bearings 20, 21 held by the housing 9. Are respectively supported rotatably. The inner rings 22 and 23 of the first and second rolling bearings 20 and 21 are fitted in corresponding constricted portions of the worm shaft 18. The outer rings 24 and 25 are respectively held in bearing holding holes 26 and 27 of the housing 9. The housing 9 includes a portion 9 a that is radially opposed to a part of the peripheral surface of the worm shaft 18.

  The outer ring 24 of the first rolling bearing 20 that supports the one end portion 18 a of the worm shaft 18 is positioned in contact with the step portion 28 of the housing 9. On the other hand, the movement of the inner ring 22 toward the other end portion 18 b is restricted by contacting the positioning step portion 29 of the worm shaft 18. Further, the inner ring 23 of the second rolling bearing 21 that supports the vicinity of the other end 18b (joint side end) of the worm shaft 18 is brought into contact with the positioning step portion 30 of the worm shaft 18 to thereby end one end. Movement toward the portion 18a is restricted.

  The outer ring 25 is urged toward the first rolling bearing 20 by a preload adjusting screw member 31. The screw member 31 is screwed into a screw hole 32 formed in the housing 9 to apply a preload to the pair of rolling bearings 20 and 21 and position the worm shaft 18 in the axial direction. Reference numeral 33 denotes a lock nut engaged with the screw member 31 in order to fix the screw member 31 after the preload adjustment.

  The worm wheel 19 includes an annular cored bar 19a coupled to the pinion shaft 7 so as to be integrally rotatable, and a synthetic resin member 19b surrounding the cored bar 19a and having teeth formed on the outer peripheral surface thereof. ing. The cored bar 19a is inserted into the mold when the synthetic resin member 19b is molded with resin, for example. The core metal 19a and the synthetic resin member 19b are combined and integrated by resin molding in the inserted state.

  A region including at least the meshing portion B of the worm shaft 18 and the worm wheel 19 in the housing 9 is filled with the lubricant composition of the present invention described above. That is, the lubricant composition may be filled only in the meshing part B, or may be filled in the entire periphery of the meshing part B and the worm shaft 18 or in the entire housing 9. The present invention is not limited to the embodiment shown in FIGS. For example, as described above, the configuration of the electric power steering device of the present invention can be applied to other types of electric power steering devices other than the pinion type EPS, and the configuration of the speed reducer of the present invention is: Various modifications can be made within the scope of the matters described in the claims of the present invention, such as being applicable to a reduction gear for devices other than the electric power steering device.

<Polyol component>
(Trifunctional polycaprolactone polyol)
As the trifunctional polycaprolactone polyol, ε-caprolactone was synthesized by ring-opening polymerization using trimethylolpropane as a polymerization initiator, the number of active hydrogen groups n _P was 3, and the number average molecular weight M _P , active hydrogen Eight types of polycaprolactone polyols of 3PCL1 to 3PCL8 having a number average molecular weight M _P / n _P per group and a hydroxyl value as shown in Table 1 were prepared.

(Bifunctional polycaprolactone polyol)
As the bifunctional polycaprolactone polyol, ε-caprolactone was synthesized by ring-opening polymerization using ethylene glycol as a polymerization initiator, the number of active hydrogen groups n _P was 2, and the number average molecular weight M _P , active hydrogen groups Two polycaprolactone polyols, 2PCL1 and 2PCL2, having a number average molecular weight M _P / n _P per one and a hydroxyl value as shown in Table 1 were prepared.

(Polyester polyol)
As a polyester polyol which is a reaction product of a carboxylic acid or a derivative thereof and a polyol, polybutylene glycol adipic acid ester as an aliphatic polyester polyol [number of active hydrogen groups n _P : 2, number average molecular weight M _P : 2000, active hydrogen groups Number average molecular weight per unit M _P / n _P : 1000, hydroxyl value: 56.1 mgKOH / g, 2PEP1], and polyhexamethylene glycol isophthalic acid ester [aromatic group number n _P : 2, Number average molecular weight M _P : 1000, number average molecular weight per active hydrogen group M _P / n _P : 500, hydroxyl value: 112.2 mgKOH / g, 2PEP2] were prepared.

〈緩衝材粒子の製造〉
（実施例１）
ポリオール成分としては、前記表１に示した３官能のポリカプロラクトンポリオール３ＰＣＬ３〔活性水素基数ｎ_P：３、数平均分子量Ｍ_P：８００、活性水素基１つあたりの数平均分子量Ｍ_P／ｎ_P：２６６．７、水酸基価：２１０．４ｍｇＫＯＨ／ｇ〕を用いた。窒素置換した１リットルのフラスコ中に、前記ポリカプロラクトンポリオール５７０ｇと、分散媒としてのイソオクタン９９５ｇと、分散安定剤〔日本ポリウレタン工業(株)製のＮ−５７４１〕１０ｇとを仕込んだ。

<Manufacture of buffer particles>
(Example 1)
As the polyol component, the trifunctional polycaprolactone polyol 3PCL3 shown in Table 1 above [number of active hydrogen groups n _P : 3, number average molecular weight M _P : 800, number average molecular weight M _P / n _P per active hydrogen group] : 266.7, hydroxyl value: 210.4 mg KOH / g]. In a 1-liter flask purged with nitrogen, 570 g of the polycaprolactone polyol, 995 g of isooctane as a dispersion medium, and 10 g of a dispersion stabilizer [N-5741 manufactured by Nippon Polyurethane Industry Co., Ltd.] were charged.

Next, stirring was started, and the polycaprolactone polyol was trimerized and modified with hexamethylene diisocyanate in the form of droplets dispersed in isooctane [NCO group number n _C : 3.5. , Number average molecular weight M _C : 695.3, number average molecular weight per NCO group M _C / n _C : 198.7, NCO group content: 21.1%, C-HX] 425 g, -N-butyltin dilaurate [U-600 manufactured by Nippon Polyurethane Industry Co., Ltd.] was added and reacted at 80 to 90 ° C for about 8 hours until the unreacted NCO group disappeared. 2) Mixing and drying 5 g of a silica-based dusting agent (average particle size: 0.1 μm), removing foreign matter having a large particle size using a sieve having a mesh opening of 300 μm, and using a polycaprolactone type polyurethane resin. Were prepared buffer particles 980 g.

  The buffer particles measured using a laser diffraction particle size distribution meter (registered trademark Microtrac manufactured by Nikkiso Co., Ltd.) had an average volume fraction of 150 μm and a particle size distribution of 40 to 300 μm. Moreover, about the said buffer material particle, the glass transition temperature Tg measured using the differential scanning calorimeter (DSC) was -48 degreeC. In addition, the physical properties at a measurement temperature of 25 ° C. of a test piece cut out from a sheet (thickness: about 2 mm) prepared with the same formulation excluding the dispersion medium and the dispersion stabilizer are as follows: Japanese Industrial Standard JIS K6301: 1995 “vulcanized rubber physics The elongation at break EB was 160% and the strength at break TB was 33 MPa as measured according to the measurement method described in “Test Method”.

  Further, after immersing the test piece in warm water at 80 ° C. for 250 hours and 1000 hours, the strength TB at break was measured again to obtain the TB retention (%) with respect to the initial value measured previously. However, it was 92% after immersion for 250 hours and 80% after immersion for 1000 hours. In addition, the sheet | seat which becomes the base of a test piece inject | pours the liquid mixture which mix | blended each component except a dispersion medium and a dispersion stabilizer with the same prescription into the thin plate-shaped mold made from polypropylene, and heats to 90 degreeC. After curing, it was formed by aging at the same temperature.

(Examples 2-5, Comparative Examples 1-3)
As the polyol component, any one of the trifunctional polycaprolactone polyols 3PCL1, 3PCL2, 3PCL4 to 3PCL8 shown in Table 1 was used, and the amount of each component charged was changed to the values shown in Table 2 In the same manner as in Example 1, 980 g of buffer material particles were produced. In addition, a sheet of polycaprolactone type polyurethane resin was prepared with the same formulation except for the dispersion medium and the dispersion stabilizer. And each characteristic demonstrated previously was evaluated about the said buffer material particle | grains and a sheet | seat. The results are shown in Table 2 together with the results of Example 1.

表２より、ポリオール成分として、活性水素基１つあたりの数平均分子量Ｍ_P／ｎ_Pが２５０未満である３官能のポリカプロラクトンポリオール３ＰＣＬ１、３ＰＣＬ２のいずれかを用いて製造された比較例１、２の緩衝材粒子は、共に、試験片の破断時伸びＥＢが小さかったことから、分子の架橋密度が高すぎて、硬く、かつ脆いものとなっており、耐久性が不十分であることが判った。また、ポリオール成分として、活性水素基１つあたりの数平均分子量Ｍ_P／ｎ_Pが１３００を超える３官能のポリカプロラクトンポリオール３ＰＣＬ８を用いて製造された比較例３の緩衝材粒子は、試験片の破断時強度ＴＢの保持率が、温水に浸漬することによって大きく低下したことから、分子の架橋密度が不足して、耐熱性、耐湿性、および耐水性が十分でなく、やはり耐久性が不十分であることが判った。

From Table 2, Comparative Example 1 produced using any one of trifunctional polycaprolactone polyols 3PCL1 and 3PCL2 having a number average molecular weight M _P / n _P per active hydrogen group of less than 250 as a polyol component, In both of the buffer particles, the elongation EB at break of the test piece was small, so that the cross-linking density of the molecule was too high, it was hard and brittle, and the durability was insufficient. understood. Further, as a polyol component, the buffer material particle of Comparative Example 3 produced using trifunctional polycaprolactone polyol 3PCL8 having a number average molecular weight M _P / n _P per active hydrogen group exceeding 1300 is Since the retention rate of strength TB at break was greatly reduced by immersion in warm water, the crosslink density of molecules was insufficient, heat resistance, moisture resistance, and water resistance were not sufficient, and durability was still insufficient It turned out that.

On the other hand, as a polyol component, it was produced using any of trifunctional polycaprolactone polyols 3PCL3 to 3PCL7 having a number average molecular weight M _P / n _P per active hydrogen group in the range of 250 to 1300. In each of the buffer particles of Examples 1 to 5, since the elongation EB at break of the test piece was large and the decrease in the retention rate of the strength TB at break was small, the molecular crosslinking density was within an appropriate range. In addition to being flexible and tough, it was confirmed to be excellent in heat resistance, moisture resistance and water resistance, and excellent in durability. In addition, since all the buffer particles of Examples 1 to 5 had a sufficiently low glass transition temperature, the temperature at which the buffer particles became brittle and lost elasticity under a low temperature environment was greatly increased. It was also confirmed that it can be lowered.

<Preparation of lubricant composition>
The buffer particles produced in Examples 1 to 5 and Comparative Examples 1 to 3 were blended with grease [kinematic viscosity (40 ° C.): 48 mm 2 / s] obtained by adding calcium sulfonate to poly α-olefin oil, and lubricated. A grease as an agent composition was prepared. The content of the buffer particles was 30% by mass of the total amount of grease. Next, the grease is heated in a constant temperature bath at 140 ° C., and the elasticity of the buffer particles separated from the grease after 168 hours, 336 hours, 504 hours, 1008 hours, and 1440 hours from the start of heating. The rate was measured by the following method.

(Measurement of elastic modulus)
As shown in FIG. 3, the buffer material particles 101 produced in each of the examples and comparative examples were placed on a flat quartz base 102, and the tip surface was flattened from above. In the state where the tip end surface of the detection rod 103 made of quartz is in contact with the buffer material particles 101, the buffer material particles 101 are applied with a certain load F by the detection rod 103 in the direction of the base 102. The distance G between the surface of the base 102 and the tip surface of the detection rod 103 when compressed is measured, and from the measurement result, the formula (b):
^{F = (2 1/2 / 3)} · S 3/2 · R 1/2 · E / (1-ν 2) (b)
[In the formula, R is a radius before compression of the buffer material particles 101, S is a radius R of the buffer material particles 101, and the interval G, and the formula (c)
S = 2R-G (c)
Is the amount of compressive deformation of the buffer material particles 101, E is the elastic modulus of the buffer material particles 101, and ν is the Poisson's ratio (= 0.49). ]
Based on the above, the elastic modulus E of the buffer particles 101 was determined.

Then, before adding to the grease, from the initial value E ₀ of the elastic modulus and the measured value E of the buffer particles of each example and comparative example, which were previously measured by the same measurement method, the formula (d):
ΔE (%) = (1−E / E0) × 100 (d)
Thus, the elastic modulus maintenance factor ΔE (%) was obtained. The results are shown in FIG. From the figure, when the buffer material particles of Comparative Example 3 were added to grease and held at a high temperature, the elastic modulus decreased greatly compared to Examples 1 to 5 and Comparative Examples 1 and 2, It was confirmed that the heat resistance was not sufficient.

(Examples 6 to 9, Comparative Examples 4 and 5)
As shown in Table 3, two types of tri-functional polycaprolactone polyols are used in combination as the polyol component, and the number average molecular weight M _P / n _P per active hydrogen group of the polycaprolactone polyol used in combination is charged. By adjusting the amount, the number average molecular weight M _P / n _P per active hydrogen group as a whole of the polyol component is set to the value shown in Table 3, and the charged amount of each component is shown in Table 3. 980 g of buffer material particles were produced in the same manner as in Example 1 except that the values shown in FIG. In addition, a sheet of polycaprolactone type polyurethane resin was prepared with the same formulation except for the dispersion medium and the dispersion stabilizer. And each characteristic demonstrated previously was evaluated about the said buffer material particle | grains and a sheet | seat. The results are shown in Table 3.

表３より、２種の３官能のポリカプロラクトンポリオールを併用したものの、ポリオール成分の全体としての、活性水素基１つあたりの数平均分子量Ｍ_P／ｎ_Pが２５０未満であった比較例４、５の緩衝材粒子は、共に、試験片の破断時伸びＥＢが小さかったことから、分子の架橋密度が高すぎて、硬く、かつ脆いものとなっており、耐久性が不十分であることが判った。

From Table 3, Comparative Example 4 in which the number average molecular weight M _P / n _P per active hydrogen group as a whole of the polyol component was less than 250, although two types of trifunctional polycaprolactone polyols were used in combination. Both of the cushioning material particles 5 had a small elongation EB at break of the test piece, so that the cross-linking density of the molecule was too high, and it was hard and brittle, and the durability was insufficient. understood.

In contrast, two trifunctional polycaprolactone polyols were used in combination, and the number average molecular weight M _P / n _P per active hydrogen group as a whole of the polyol component was in the range of 250 to 1300. The buffer particles in Examples 6 to 9 each had a large elongation EB at break of the test piece and a small decrease in the retention rate of the strength TB at break, so that the molecular crosslinking density was within an appropriate range. In addition, it was confirmed to be flexible and tough, excellent in heat resistance, moisture resistance and water resistance, and excellent in durability. In addition, since all of the buffer material particles of Examples 6 to 9 had a sufficiently low glass transition temperature, the temperature at which the buffer material particles became brittle and lost elasticity under a low temperature environment was greatly increased. It was also confirmed that it can be lowered.

(Examples 10 to 13, Comparative Examples 6 and 7)
As shown in Table 4, as the polyol component, a trifunctional polycaprolactone polyol and a bifunctional polycaprolactone polyol or a bifunctional polyester polyol are used in combination, and the polyol used in combination per active hydrogen group By adjusting the number average molecular weight M _P / n _P and the charged amount, the number average molecular weight M _P / n _P per active hydrogen group as a whole of the polyol component is set to the value shown in Table 4, Further, 980 g of buffer material particles were produced in the same manner as in Example 1 except that the charged amounts of the respective components were set to the values shown in Table 4. In addition, a sheet of polycaprolactone type polyurethane resin was prepared with the same formulation except for the dispersion medium and the dispersion stabilizer. And each characteristic demonstrated previously was evaluated about the said buffer material particle | grains and a sheet | seat. The results are shown in Table 4.

表４より、３官能のポリカプロラクトンポリオールと２官能のポリカプロラクトンポリオールとを併用するとともに、ポリオール成分の全体としての、活性水素基１つあたりの数平均分子量Ｍ_P／ｎ_Pを２５０〜１３００の範囲内とした実施例１０、１１は、いずれも、試験片の破断時伸びＥＢが大きく、かつ、破断時強度ＴＢの保持率の低下が小さかったことから、分子の架橋密度が適度な範囲内にあり、柔軟でかつ強靭である上、耐熱性、耐湿性、および耐水性に優れていて、耐久性に優れていることが確認された。また、前記実施例１０、１１の緩衝材粒子は、いずれも、ガラス転移温度が十分に低い値にあったことから、低温環境下で、緩衝材粒子が脆化して弾性を失う温度を、大幅に低くできることも確認された。

As shown in Table 4, the trifunctional polycaprolactone polyol and the bifunctional polycaprolactone polyol are used in combination, and the number average molecular weight M _P / n _P per active hydrogen group as a whole of the polyol component is 250 to 1300. In Examples 10 and 11 within the range, the elongation EB at break of the test piece was large and the decrease in the retention rate of the strength TB at break was small, so that the molecular crosslinking density was within an appropriate range. In addition to being flexible and tough, it was confirmed to be excellent in heat resistance, moisture resistance and water resistance, and excellent in durability. Moreover, since the buffer material particles of Examples 10 and 11 both had a glass transition temperature at a sufficiently low value, the temperature at which the buffer material particles became brittle and lost elasticity under a low temperature environment was greatly increased. It was also confirmed that it can be lowered.

Further, among the examples and comparative examples in which a trifunctional polycaprolactone polyol and a bifunctional polyester polyol are used in combination, the number average molecular weight M _P / n _P per active hydrogen group as a whole of the polyol component is 250. The buffer particles of Comparative Examples 6 and 7 in which the ratio R _P (% by mass) of the polycaprolactone polyol to the total amount of both polyols was 50% by mass, although both were within the range of ˜1300, Since the retention of strength TB at break was greatly reduced by immersion in warm water, the crosslink density of the molecule was insufficient, heat resistance, moisture resistance, and water resistance were not sufficient, and durability was insufficient. It turns out that there is. Further, since the buffer material particles of Comparative Example 7 have a high glass transition temperature, it was also found that the buffer material particles become brittle and easily lose elasticity under a low temperature environment.

In contrast, the buffer material particles of Examples 12 and 13 in which the ratio R _P (% by mass) of the polycaprolactone polyol in the total amount of both polyols is less than 50% by mass are all the elongation at break of the test piece. Since the EB was large and the decrease in the retention ratio of the strength TB at break was small, the crosslink density of the molecule was within an appropriate range, and it was flexible and tough, as well as heat resistance, moisture resistance, and water resistance. It was confirmed that it was excellent in durability. In addition, since the buffer material particles of Examples 12 and 13 all had a sufficiently low glass transition temperature, the temperature at which the buffer material particles become brittle and lose elasticity in a low temperature environment is greatly increased. It was also confirmed that it can be lowered.

(Examples 14 to 16)
As shown in Table 5, as the isocyanate, trimerized modified isocyanate C-HX and hexamethylene diisocyanate [number of NCO groups n _C : 2, number average molecular weight M _C : 168.2, number average molecular weight M per NCO group _C / n _C : 84.1, NCO group content: 50.0%, HDI] or the HDI alone, and the amount of each component charged is the value shown in Table 5. Except for this, 980 g of buffer material particles were produced in the same manner as in Example 2. In addition, a sheet of polycaprolactone type polyurethane resin was prepared with the same formulation except for the dispersion medium and the dispersion stabilizer. And each characteristic demonstrated previously was evaluated about the said buffer material particle | grains and a sheet | seat. The results are shown in Table 5 together with the results of Example 2.

表５より、実施例１４〜１６の緩衝材粒子は、いずれも、実施例２と同様に、試験片の破断時伸びＥＢが大きく、かつ、破断時強度ＴＢの保持率の低下が小さかったことから、分子の架橋密度が適度な範囲内にあり、柔軟でかつ強靭である上、耐熱性、耐湿性、および耐水性に優れていて、耐久性に優れていることが確認された。また、前記実施例１４〜１６の緩衝材粒子は、いずれも、ガラス転移温度が十分に低い値にあったことから、低温環境下で、緩衝材粒子が脆化して弾性を失う温度を、大幅に低くできることも確認された。

From Table 5, the buffer particles of Examples 14 to 16 all had a large elongation EB at break of the test piece and a small decrease in the retention rate of strength TB at break as in Example 2. From the results, it was confirmed that the cross-linking density of the molecules is within an appropriate range, is flexible and tough, has excellent heat resistance, moisture resistance, and water resistance, and has excellent durability. In addition, since all of the buffer particles of Examples 14 to 16 had a sufficiently low glass transition temperature, the temperature at which the buffer particles became brittle and lost elasticity under a low temperature environment was greatly increased. It was also confirmed that it can be lowered.

(Examples 17 to 19, Comparative Example 8)
Trimethylolpropane as a crosslinking agent having three or more active hydrogen groups in one molecule [number of active hydrogen groups n _L : 3, number average molecular weight M _L : 134.2, number average molecular weight M _L per active hydrogen group / N _L : 44.7, hydroxyl value: 1254.5 mgKOH / g, TMP] is added so that the molar ratio to the polyol component is the value shown in Table 6, and the amount of each component charged is shown in Table 6. 980 g of buffer material particles were produced in the same manner as in Example 2 except that the values shown in FIG. In addition, a sheet of polycaprolactone type polyurethane resin was prepared with the same formulation except for the dispersion medium and the dispersion stabilizer. And each characteristic demonstrated previously was evaluated about the said buffer material particle | grains and a sheet | seat. The results are shown in Table 6 together with the results of Example 2.

表６より、ＴＭＰの、ポリオールに対するモル比を２．０倍とした比較例８の緩衝材粒子は、試験片の破断時伸びＥＢが小さかったことから、分子の架橋密度が高すぎて、硬く、かつ脆いものとなっており、耐久性が不十分であることが判った。

From Table 6, the buffer material particle of Comparative Example 8 in which the molar ratio of TMP to polyol was 2.0 times was low because the elongation EB at break of the test piece was small, and the molecular crosslinking density was too high and hard. In addition, it was found to be brittle and insufficient in durability.

  On the other hand, all of the buffer particles of Examples 17 to 19 having the molar ratio of less than 2.0 times had a large elongation EB at break of the test piece as in Example 2, and at break. Since the decrease in strength TB retention was small, the cross-linking density of the molecules was in an appropriate range, flexible and tough, and excellent in heat resistance, moisture resistance, and water resistance, and durable It was confirmed to be excellent. In addition, since all of the buffer material particles of Examples 17 to 19 had a sufficiently low glass transition temperature, the temperature at which the buffer material particles became brittle and lost elasticity under a low temperature environment was greatly increased. It was also confirmed that it can be lowered.

(Examples 20 and 21)
As shown in Table 7, as a polyol component, a bifunctional polycaprolactone polyol is used alone, and a trimerized modified isocyanate C-HX is used as an isocyanate. Except for the above, 980 g of buffer material particles were produced in the same manner as in Example 1. In addition, a sheet of polycaprolactone type polyurethane resin was prepared with the same formulation except for the dispersion medium and the dispersion stabilizer. And each characteristic demonstrated previously was evaluated about the said buffer material particle | grains and a sheet | seat.

(Comparative Examples 9 and 10)
As shown in Table 7, as a polyol component, a bifunctional polyester polyol is used alone, and a trimerized modified isocyanate C-HX is used as an isocyanate. Except for this, 980 g of buffer material particles were produced in the same manner as in Example 1. In addition, a sheet of polycaprolactone type polyurethane resin was prepared with the same formulation except for the dispersion medium and the dispersion stabilizer. And each characteristic demonstrated previously was evaluated about the said buffer material particle | grains and a sheet | seat.

(Comparative Examples 11 and 12)
In order to reproduce the conventional buffer particles described in Patent Document 4, two types of bifunctional polyester polyols are used in combination as a polyol component, and HDI is used as an isocyanate, and TMP is used as a crosslinking agent. 980 g of buffer material particles were produced in the same manner as in Example 1 except that the charged amounts of the respective components were set to the values shown in Table 7. In addition, a sheet of polycaprolactone type polyurethane resin was prepared with the same formulation except for the dispersion medium and the dispersion stabilizer. And each characteristic demonstrated previously was evaluated about the said buffer material particle | grains and a sheet | seat. The results are shown in Table 7.

表７より、ポリオール成分として、脂肪族ポリエステルポリオール２ＰＥＰ１を単独で使用した比較例９の緩衝材粒子、および特許文献４の従来の緩衝材粒子を再現した比較例１１、１２の緩衝材粒子は、いずれも、試験片の破断時強度ＴＢの保持率が、温水に浸漬することによって大きく低下したことから、分子の架橋密度が不足して、耐熱性、耐湿性、および耐水性が十分でなく、耐久性が不十分であることが判った。また、ポリオール成分として、芳香族ポリエステルポリオール２ＰＥＰ２を単独で使用した比較例１０の緩衝材粒子は、ガラス転移温度が高いことから、低温環境下で、緩衝材粒子が脆化して弾性を失いやすいことが判った。

From Table 7, as the polyol component, the buffer material particles of Comparative Example 9 and the conventional buffer material particles of Patent Document 4 in which the aliphatic polyester polyol 2PEP1 alone was used and the conventional buffer material particles of Patent Document 4 were reproduced. In both cases, the retention rate of the strength TB at break of the test piece was greatly reduced by immersing in warm water, so that the cross-linking density of the molecule was insufficient, and the heat resistance, moisture resistance, and water resistance were not sufficient, It was found that the durability was insufficient. Moreover, since the buffer material particles of Comparative Example 10 using the aromatic polyester polyol 2PEP2 alone as the polyol component have a high glass transition temperature, the buffer material particles tend to become brittle and lose elasticity in a low temperature environment. I understood.

  On the other hand, the bifunctional polycaprolactone polyol was used as the polyol component, and the buffer particles of Examples 20 and 21 using the trimerized modified isocyanate C-HX as the isocyanate were both tested when the test piece was broken. Since the elongation EB was large and the decrease in the retention rate of the strength TB at break was small, the crosslink density of the molecule was within an appropriate range, and it was flexible and tough, and also had heat resistance, moisture resistance, and water resistance. It was confirmed that it was excellent in durability and durability. Moreover, since the buffer material particles of Examples 20 and 21 both had a sufficiently low glass transition temperature, the temperature at which the buffer material particles became brittle and lost elasticity under a low temperature environment was greatly increased. It was also confirmed that it can be lowered.

(Examples 22 and 23, Comparative Example 13)
As shown in Table 8, as the polyol component, a bifunctional polycaprolactone polyol is used alone, and HDI is used as the isocyanate, and TMP as a crosslinking agent is shown in Table 8 in terms of a molar ratio to the polyol component. 980 g of buffer material particles were produced in the same manner as in Example 1 except that the amount of each component was added and the amount of each component charged was changed to the value shown in Table 8. In addition, a sheet of polycaprolactone type polyurethane resin was prepared with the same formulation except for the dispersion medium and the dispersion stabilizer. And each characteristic demonstrated previously was evaluated about the said buffer material particle | grains and a sheet | seat. The results are shown in Table 8.

表８より、ＴＭＰの、ポリオールに対するモル比を０．５倍未満とした比較例１３の緩衝材粒子は、耐熱性が低く、耐久性が不十分であることが判った。
これに対し、前記モル比を０．５倍以上とした実施例２２、２３の緩衝材粒子は、共に、試験片の破断時伸びＥＢが大きく、かつ、破断時強度ＴＢの保持率の低下が小さかったことから、分子の架橋密度が適度な範囲内にあり、柔軟でかつ強靭である上、耐熱性、耐湿性、および耐水性に優れていて、耐久性に優れていることが確認された。また、前記実施例２２、２３の緩衝材粒子は、いずれも、ガラス転移温度が十分に低い値にあったことから、低温環境下で、緩衝材粒子が脆化して弾性を失う温度を、大幅に低くできることも確認された。

From Table 8, it was found that the buffer material particles of Comparative Example 13 in which the molar ratio of TMP to polyol was less than 0.5 times had low heat resistance and insufficient durability.
In contrast, the buffer particles of Examples 22 and 23 in which the molar ratio was 0.5 times or more both had a large elongation EB at break of the test piece and a decrease in the retention rate of the strength TB at break. Since it was small, it was confirmed that the crosslink density of the molecule was within an appropriate range, was flexible and tough, and was excellent in heat resistance, moisture resistance, water resistance, and durability. . In addition, since the buffer material particles of Examples 22 and 23 all had a sufficiently low glass transition temperature, the temperature at which the buffer material particles became brittle and lost elasticity under a low temperature environment was greatly increased. It was also confirmed that it can be lowered.

<Preparation of lubricant composition>
The lubricant particles produced in Examples 22 and 23 and Comparative Example 13 were blended with grease (kinematic viscosity (40 ° C.): 48 mm 2 / s) in which calcium sulfonate was added to poly α-olefin oil, and a lubricant composition. As a product, a grease was prepared. The content of the buffer particles was 30% by mass of the total amount of grease.

  Next, the grease is heated in a constant temperature bath at 140 ° C., and the elasticity of the buffer particles separated from the grease after 168 hours, 336 hours, 504 hours, 1008 hours, and 1440 hours from the start of heating. The modulus was measured by the method described above to determine the elastic modulus retention rate ΔE (%). The results are shown in FIG. From the figure, since the buffer material particles of Comparative Example 13 were added to grease and held at a high temperature, the elastic modulus was greatly reduced as compared with Examples 22 and 23, so that the heat resistance was not sufficient. Was confirmed.

It is a mimetic diagram showing a schematic structure of an electric power steering device of one embodiment of the present invention. It is sectional drawing of the principal part of an electric power steering device. It is sectional drawing explaining the method to measure the elasticity modulus of the buffer material particle of an Example and a comparative example. It is a graph which shows the transition by the test time of the elastic modulus maintenance factor (DELTA) E (%) in the buffer material particle of Examples 1-5 and Comparative Examples 1-3 measured by the method of FIG. It is a graph which shows the transition by the test time of the elastic modulus maintenance factor (DELTA) E (%) in the buffer material particle of Examples 22 and 23 and the comparative example 13 measured by the method of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering device, 16 Electric motor, 17 Reduction gear, 18 Worm shaft (small gear), 19 Worm wheel (large gear), B meshing part

Claims (12)

at least,
(1) a polyol component containing polycaprolactone polyol and having a number average molecular weight of 250 to 1300 per active hydrogen group;
(2) isocyanate and
A lubricant composition comprising buffer particles made of polyurethane resin having a cross-linked structure synthesized by reacting and a lubricant.   The lubricant composition according to claim 1, wherein the polycaprolactone polyol as a raw material of the polyurethane resin is a trifunctional polycaprolactone polyol having three active hydrogen groups in one molecule.   Two or more trifunctional polycaprolactone polyols having different number average molecular weights as the polyol component that is a raw material of the polyurethane resin are used in combination so that the number average molecular weight per active hydrogen group is in the range of 250 to 1300. The lubricant composition according to claim 2.   As a polyol component which is a raw material of the polyurethane resin, a trifunctional polycaprolactone polyol and a bifunctional polycaprolactone polyol having two active hydrogen groups in one molecule have a number average molecular weight of 250 per active hydrogen group. The lubricant composition according to claim 2, which is used in combination so as to be in the range of ˜1300. As a polyol component which is a raw material of a polyurethane resin, a polyester polyol which is a reaction product of a carboxylic acid or a derivative thereof and a polyol, and a trifunctional polycaprolactone polyol have a number average molecular weight per active hydrogen group of 250 to Within the range of 1300 and formula (a):

Wherein, P _K is the mass of polycaprolactone polyols, P _E represents the weight of the polyester polyol. ]
The lubricant composition according to claim 2, which is used in combination so that the ratio R _P (% by mass) of the polycaprolactone polyol determined in (1) to the total amount of both polyols exceeds 50% by mass.   The lubricant composition according to any one of claims 2 to 5, wherein the isocyanate as a raw material of the polyurethane resin is an isocyanate having an isocyanurate skeleton in a molecule and having three or more NCO groups in one molecule. .   The crosslinking agent having three or more active hydrogen groups in one molecule is used in combination, and the molar ratio of the crosslinking agent to the polyol component is within a range of less than 2.0 times. The lubricant composition described in 1.   The polycaprolactone polyol as a raw material of the polyurethane resin is a bifunctional polycaprolactone polyol having two active hydrogen groups in one molecule, and the isocyanate has an isocyanurate skeleton in the molecule, and in one molecule The lubricant composition according to claim 1, which is an isocyanate having 3 or more NCO groups.   The polycaprolactone polyol as a raw material of the polyurethane resin is a bifunctional polycaprolactone polyol having two active hydrogen groups in one molecule, and the isocyanate is an isocyanate having two NCO groups in one molecule. The lubricant composition according to claim 1, wherein a crosslinking agent having three or more active hydrogen groups in one molecule is used in combination, and the molar ratio of the crosslinking agent to the polyol component is within a range of 0.5 times or more. object.   The buffer material particles are spherical particles made of a polyurethane resin synthesized by reacting at least with an isocyanate in a state where the polyol component is dispersed in the form of droplets in a dispersion medium. The lubricant composition described in 1.   A speed reducer comprising a small gear and a large gear, wherein the lubricant composition according to any one of claims 1 to 10 is filled in a region including a meshing portion of the two gears.   An electric power steering apparatus, wherein the output of a steering assist motor is decelerated via the reduction gear according to claim 11 and transmitted to a steering mechanism.

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