JP2007045919A - Method of modification of plastic molding and plastic molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of modification to improve the heat resistance of a plastic molding and a plastic molding which has an excellent heat resistance and is favorably used under severe conditions for use. <P>SOLUTION: The modification treatment comprises penetrating an antioxidant into the surface of a cap-shaped holder 14 composed of a glass fiber-reinforced polyamide 66 by immersing it in supercritical carbon dioxide. The modified cap-shaped holder 14 is incorporated in a deep groove ball bearing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for modifying a plastic molded article using a supercritical fluid, and a modified plastic molded article.

Conventionally, the heat resistance of a plastic molded product depends on the heat resistance of the plastic itself. And when antioxidant was added, heat resistance was determined by the grade of suppression of thermal degradation by it.
Japanese Patent Laid-Open No. 5-214243 JP-A-5-311014

However, in the past, by compounding an antioxidant into the raw material of the plastic molded product, the antioxidant is uniformly dispersed throughout the plastic molded product, and this causes the oxidative degradation of the surface layer portion of the plastic molded product that occurs first. No consideration was given to effective suppression.
Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a reforming method for improving the heat resistance of a plastic molded product (particularly the surface layer portion). Another object of the present invention is to provide a plastic molded article having excellent heat resistance.

In order to solve the above problems, the present invention has the following configuration. That is, in the method for modifying a plastic molded article according to the first aspect of the present invention, after the supercritical fluid containing the antioxidant is brought into contact with the plastic molded article, the antioxidant and super Of the critical fluid, only the supercritical fluid is removed from the plastic molded product.
According to a second aspect of the present invention, there is provided a method for reforming a plastic molded article according to the first aspect, wherein the supercritical fluid is supercritical carbon dioxide. .
Furthermore, the plastic molded article according to claim 3 of the present invention is characterized by being modified by the method for modifying a plastic molded article according to claim 1 or claim 2.

  According to the method for modifying a plastic molded product of the present invention, an antioxidant can be infiltrated into the plastic molded product, so that excellent heat resistance can be imparted to the plastic molded product (particularly the surface layer portion). In addition, the plastic molded article of the present invention has excellent heat resistance since the antioxidant penetrates.

  The method for modifying a plastic molded product according to the present embodiment includes an immersion treatment process and an evaporation removal process. The immersion treatment step is a step of immersing the plastic molded article in supercritical carbon dioxide containing an antioxidant, and the antioxidant and carbon dioxide penetrate into the plastic molded article by this process. Specifically, the plastic molded product is placed on a pedestal provided in an apparatus (hereinafter referred to as a processing apparatus) used for reforming the plastic molded product, and an antioxidant is disposed below the pedestal. When the inside of the processing apparatus is brought into a supercritical state, the antioxidant is mixed with supercritical carbon dioxide to fill the processing apparatus, and the penetration of the antioxidant into the plastic molded article proceeds.

Supercritical carbon dioxide is carbon dioxide in a region having a temperature higher than the critical temperature and a pressure higher than the critical pressure. Incidentally, the critical temperature of carbon dioxide is 31 ° C., and the critical pressure is 72.8 atm (7.39 MPa).
The immersion temperature in the immersion treatment step is not less than the critical temperature of carbon dioxide, more preferably not less than the critical temperature of carbon dioxide and less than the glass transition temperature of the plastic constituting the plastic molded product. When the plastic material exceeds the glass transition temperature, the free volume increases until the micro-brown motion of the molecular main chain becomes possible, and the carbon dioxide in the supercritical state becomes more easily penetrated into the plastic. If it does so, it is also considered that the various additives previously added in the plastic will be extracted on the contrary, and as a result, there exists a possibility that a physical property may fall, and it is not preferable.

  However, since the solubility of supercritical carbon dioxide in plastics is higher at higher temperatures, it is easier for the antioxidant to penetrate when the immersion temperature is as high as possible. The immersion temperature is preferably determined with reference to the melting point and glass transition temperature of the plastic material, and is about 150 ° C. at the maximum. If the temperature is higher than this, the plastic and the antioxidant may be deteriorated.

  In addition, the pressure in the immersion treatment step is equal to or higher than the critical pressure of carbon dioxide, and a higher pressure is preferable because the degree of penetration of carbon dioxide into the plastic is improved and the efficiency of reforming is improved. However, since the processing apparatus needs to be able to withstand high pressure, the processing apparatus becomes large and expensive. Accordingly, in consideration of the operability of the processing apparatus, equipment costs, etc., the pressure is suitably in the range of 100 to 300 atmospheres (10.13 to 30.4 MPa).

Furthermore, the immersion time in the immersion treatment process is not particularly limited, and is appropriately set in consideration of the thickness and size of the plastic molded product.
Furthermore, the concentration of the antioxidant in the supercritical carbon dioxide is adjusted so as to be approximately saturated solubility in the supercritical state of carbon dioxide.
In addition, when performing an immersion process, it is preferable to substitute the inside of a processing apparatus with a carbon dioxide. If the immersion treatment is performed with oxygen remaining, the plastic may be oxidized and deteriorated during the treatment.

  Next, the evaporation removal process will be described. After the temperature in the processing apparatus is set to be lower than the glass transition temperature of the plastic constituting the plastic molded product, the pressure in the processing apparatus is slowly lowered to gradually return to atmospheric pressure by gradually discharging carbon dioxide. As a result, only the carbon dioxide of the antioxidant and carbon dioxide that has penetrated into the plastic molded product is evaporated and removed, and the antioxidant is left in the plastic molded product. When not in the supercritical state, the antioxidant separates and accumulates at the bottom of the processing equipment.

When almost all of the carbon dioxide in the processing apparatus has evaporated, the plastic molded product is removed. At this time, if necessary, the antioxidant attached to the surface of the plastic molded article may be removed by washing. Further, carbon dioxide remaining in the plastic molded product may be removed by vacuum drying or the like.
In addition, it is preferable that the temperature in a processing apparatus shall be less than the glass transition temperature of the plastic which comprises a plastic molded product. When the temperature is equal to or higher than the glass transition temperature, foaming is likely to occur when carbon dioxide is removed from the plastic molded article.

  Through the two steps as described above, the antioxidant molecules penetrate into the plastic molded article and are fixed to the free volume between the plastic molecules. As a result, the antioxidant is present at a high concentration in the surface layer portion of the plastic molded product, so that the oxidative deterioration that progresses from the surface toward the inside is effectively suppressed, and the heat resistance of the entire plastic molded product is reduced. Improves. In addition, since the antioxidant is fixed in the free volume that it originally had, the antioxidant hardly oozes out to the outside, and the heat resistance improvement effect lasts for a long time, while at the same time mechanical strength There is almost no risk of causing a drop.

In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment.
For example, in the present embodiment, an example in which supercritical carbon dioxide is used as the supercritical fluid has been described. However, various other types of supercritical fluids can be used in the present invention. For example, nitrogen dioxide, ammonia, ethane, propane, ethylene, methanol, ethanol and the like can be mentioned. However, carbon dioxide is most preferred because it becomes a supercritical fluid under relatively mild conditions, and is non-toxic and non-flammable.

  In addition, as a plastic to which the method for modifying a plastic molded article of the present invention can be suitably applied, the glass transition temperature (Tg) is a critical temperature of a supercritical fluid in order to prevent foaming of the plastic molded article in the evaporation removal process. Higher than that is preferred. Specific examples include polyester resins such as polyethylene terephthalate (Tg 69 ° C.) and polybutylene phthalate (Tg 45 ° C.), and polyamide resins such as polyamide 6 (Tg 53 ° C.) and polyamide 66 (Tg 57 ° C.). Moreover, polystyrene (Tg100 degreeC), a polycarbonate (Tg145 degreeC), etc. are mention | raise | lifted.

  However, even if the glass transition temperature (Tg) is not higher than the critical temperature of the supercritical fluid, the method for modifying a plastic molded product of the present invention may be applicable. Examples of plastics having a glass transition temperature (Tg) below the critical temperature of supercritical carbon dioxide include, for example, polyethylene (Tg-125 ° C), polyoxymethylene (Tg-82 ° C), polypropylene (Tg-8 ° C), poly And methyl acrylate (Tg 10 ° C.).

  These plastics may contain a filler such as glass fiber and various additives such as a heat stabilizer. However, since various additives are expected to be extracted depending on the processing conditions for reforming, care is required for the processing temperature and processing pressure. Various additives may be added in advance to the supercritical fluid together with the antioxidant.

  Furthermore, the kind of antioxidant that can be used in the present invention is not particularly limited, and examples thereof include the following. 2,4-bis [(octylthio) methyl] -o-cresol, triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] (melting point 75-79 ° C.), Pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (melting point 110-125 ° C.), 1,3,5-trimethyl-2,4,6-tris ( 3,5-di-tert-butyl-4-hydroxybenzyl) benzene (melting point 244 ° C.), N, N′-hexamethylenebis (3,5-di-tert-butyl-4-hydroxyhydrocinnamamide) ( And hindered phenol compounds such as a melting point of 156 to 161 ° C.).

  Further, hydroquinone derivatives such as 2,5-di-tert-butylhydroquinone (melting point 170 ° C. or higher), bis [2-methyl-4- {3-n-alkylthiopropionyloxy} -5-tert-butylphenyl] sulfide (The alkyl group has 12 or 14 carbon atoms) such as sulfur compounds and phosphite compounds.

  Furthermore, diphenylamine compounds such as 4,4′-bis (α, α-dimethylbenzyl) diphenylamine (melting point 90 ° C.), 4,4′-dioctyldiphenylamine (melting point 95 ° C. or higher), N, N′-diphenyl- p-phenylenediamine (melting point 130 ° C. or higher), N-isopropyl-N′-phenyl-p-phenylenediamine (melting point 70 ° C. or higher), N, N′-di-2-naphthyl-p-phenylenediamine (melting point 224 ° C. N, N′-bis (1-methylheptyl) -p-phenylenediamine, N, N′-bis (1,4-dimethylpentyl) -p-phenylenediamine, N- (1,3-dimethylbutyl) ) -N′-phenyl-p-phenylenediamine (melting point: 44 ° C. or higher).

  Of these, diphenylamine compounds and p-phenylenediamine compounds are most preferred because of their great antioxidant effect. In consideration of solubility in the supercritical fluid, an antioxidant that is in a liquid state at the immersion temperature is preferable. Therefore, when the supercritical fluid is supercritical carbon dioxide, the melting point is 40 ° C. or higher and 150 ° C. or lower. Antioxidants are preferred.

Next, an example in which the plastic molded product modified as described above is used as a part of a rolling bearing, a linear guide device, an electric power steering device, and a magnetic encoder will be described.
[Usage example 1]
FIG. 1A is a longitudinal sectional view showing the configuration of a deep groove ball bearing, and FIG. 1B is a perspective view of a crown-shaped cage used in this deep groove ball bearing.
This deep groove ball bearing holds an inner ring 11, an outer ring 12, a plurality of balls 13 disposed between the inner ring 11 and the outer ring 12, and a plurality of balls 13 between the inner ring 11 and the outer ring 12. And the shield plates 15 and 15 are provided.
The bearing space surrounded by the inner ring 11, the outer ring 12, and the shield plates 15 and 15 is filled with a grease composition (lubricant) (not shown), and is sealed in the deep groove ball bearing by the shield plate 15. Yes. And the contact surface of the raceway surface of the inner ring | wheel 11 and the outer ring | wheel 12, and the ball | bowl 13 is lubricated with this grease composition.

  Next, the structure of the crown-shaped cage 14 shown in FIG. The crown-shaped cage 14 includes an annular main portion 21 and a plurality of pockets 22 provided on one side of the main portion 21, and the pockets 22 are arranged to face each other with a space therebetween. It is formed from a pair of elastic pieces 23, 23. The mutually opposing surfaces of the pair of elastic pieces 23, 23 constituting each pocket 22 are generally concentric spherical concave surfaces. However, there are also cases where each surface is a cylindrical surface.

Such a crown-shaped cage 14 pushes the ball 13 between the pair of elastic pieces 23, 23 while elastically expanding the interval between the elastic pieces 23, 23, so that the balls 13 are inserted into the pockets 22. Can be held freely.
This crown-shaped cage 14 is composed of polyamide 66 (UBE nylon 2020GU5 manufactured by Ube Industries, Ltd.) reinforced with glass fiber (content is 25% by mass), and includes supercritical carbon dioxide containing an antioxidant. As described above, the antioxidant is permeated into the surface layer portion (the content of the antioxidant in the crown cage 14 after the supercritical carbon dioxide is removed) Is 0.1% by mass). The conditions of the treatment immersed in supercritical carbon dioxide are a temperature of 140 ° C., a pressure of 20 MPa, a treatment time of 1 hour, and the antioxidant used is N, N′-diphenyl-p-phenylenediamine (Ouchi Shinsei Chemical Co., Ltd.) Nocrack DP made by company.

  In such a deep groove ball bearing, the crown-shaped cage 14 is made of a plastic molded product that has been modified as described above, and thus has excellent heat resistance. Therefore, even if a deep groove ball bearing is used under severe conditions such that a high surface pressure is applied to the crown cage 14, the crown cage 14 has excellent performance such as durability and reliability. As a result, the deep groove ball bearing has a long life.

[Usage example 2]
FIG. 2 is a perspective view showing the configuration of the linear guide device.
On a rectangular guide rail 31, a slider 32 having a substantially U-shaped cross section is straddled so as to be relatively movable in the axial direction. The slider 32 is configured by detachably fixing end caps 32B and 32B to both end portions of the slider body 32A in the axial direction.
In addition, rolling element rolling grooves 33A and 33A, which are concave grooves having a substantially arc-shaped cross section, are formed in the axial direction at the ridgeline where the upper surface 31a of the guide rail 31 intersects with both side surfaces 31b and 31b. Yes. Furthermore, rolling element rolling grooves 33B and 33B, which are concave grooves having a substantially semicircular cross section, are formed in the axial direction at intermediate positions between both side surfaces 31b and 31b of the guide rail 31. An escape groove 33a for the retainer 36 that prevents the rolling element 35 from dropping off is formed in the axial direction at the groove bottom of the rolling element rolling groove 33B.

On the other hand, a load rolling element rolling groove 41 having a substantially semicircular cross section facing the rolling element rolling groove 33A of the guide rail 31 is formed in the corner portion inside the sleeves 34, 34 of the main body 32A of the slider 32. In addition, a load rolling element rolling groove 42 having a substantially semicircular cross section facing the rolling element rolling groove 33 </ b> B of the guide rail 31 is formed at the center of the inner side surfaces of the sleeve portions 34, 34.
Then, the rolling element rolling groove 33A of the guide rail 31 and the load rolling element rolling groove 41 of the slider 32 constitute a load rolling element rolling path 43, and the rolling element rolling groove 33B of the guide rail 31 and the slider. A load rolling element rolling path 44 is constituted by the 32 load rolling element rolling grooves 42.

Further, a rolling element return path 45 including a through hole having a circular cross section extending in the axial direction parallel to the load rolling element rolling path 43 is formed in the upper wall thickness of the sleeve section 34 of the slider main body 32A. In the lower wall thickness, a rolling element return path 46 composed of a similar axially extending through hole parallel to the load rolling element rolling path 44 is formed.
The end cap 32B is an injection-molded product made of a plastic material and has a substantially U-shaped cross section. As shown in FIG. 3, a semicircular upper concave portion 51 and a lower concave portion 52 that are inclined obliquely are formed above and below the sleeve portions 34, 34 on the joint surface (back surface) with the slider body 32 </ b> A. A semi-cylindrical concave groove 53 is provided across the center of both semicircular concave portions 51 and 52 while being formed to face each other.

  A semi-cylindrical return guide 55 (see FIG. 4) obtained by injection molding of a plastic material is fitted into the semi-cylindrical concave groove 53. FIG. 5 is a perspective view of the end cap 32B to which the return guide 55 is attached. In the center of the outer diameter surface of the return guide 55, a concave groove 56 having a circular arc cross section serving as the guide surface of the rolling element 35 is formed in a semicircular shape, and the concave portion 57 on the inner diameter side of the return guide 55 is lubricated. A through hole 57 </ b> A that is an agent passage and extends from the concave portion 57 to the concave groove 56 on the outer diameter side is formed as an oil supply hole.

  By incorporating such a return guide 55 into the semi-cylindrical concave groove 53, a semi-doughnut-shaped curved path 58 having a circular cross section is formed on the back surface of the end cap 32B (see FIG. 6). When this end cap 32B is attached to the slider main body 32A, the load rolling element rolling path 44 and the rolling element return path 46 of the slider main body 32A communicate with each other through the curved path 58. And the upper load rolling element rolling path 43 and rolling element return path 45 are similarly communicated.

A large number of rolling elements 35 are slidably loaded in the rolling element infinite circulation path constituted by the above-described load rolling element rolling paths 43 and 44, rolling element return paths 45 and 46, and a curved path 58.
When the slider 32 moves on the guide rail 31, the rolling element 35 moves in the moving direction of the slider 32 at a speed slower than the slider 32 while rolling in the load rolling element rolling paths 43 and 44, and the curved path on one end side. Circulation returns to the load rolling element rolling paths 43 and 44 by making a U-turn at 58 and moving while rolling the rolling element return paths 45 and 46 in the opposite direction, and making a reverse U turn at the curved path 58 on the other end side. repeat.

In the end cap 32B, a rolling body scooping protrusion 59 that protrudes in a semicircular shape is formed at the inner end of the curved path 58 that guides the rolling element 35, and the acute end of the rolling end of the guide rail 31 rolls. The moving body rolling grooves 33A and 33B are arranged close to the groove bottoms. The lower rolling element scooping protrusion 59 is provided with a mounting groove 59a and a mounting hole 59b of the retainer 36.
Further, the lubricant injected from the oil supply nipple 37 on the front side of the end cap 32B passes through the oil supply groove 60 on the back surface of the end cap 32B, passes through the recess 57 on the inner diameter side of the return guide 55, passes through the through hole 57A, and enters the curved path 58. To be sent to. Further, an attachment hole 61a for the retainer 61 is formed below the oil supply groove 60 on the back surface of the end cap 32B.

  Here, the end cap 32B and the return guide 55 are made of polyacetal resin (Duracon M90S manufactured by Polyplastics Co., Ltd.), and the above-described reforming process using supercritical carbon dioxide containing an antioxidant. And the surface layer portion is permeated with an antioxidant (the content of the antioxidant in the end cap 32B and the return guide 55 after removing the supercritical carbon dioxide is 0.12% by mass, respectively) is there). The conditions of the treatment immersed in supercritical carbon dioxide are a temperature of 100 ° C., a pressure of 20 MPa, a treatment time of 1 hour, and the antioxidant used is triethylene glycol-bis [3- (3-tert-butyl-5-methyl). -4-hydroxyphenyl) propionate] (Irganox 245 manufactured by Ciba Specialty Chemicals Co., Ltd.).

  In such a linear guide device, the end cap 32B and the return guide 55 are made of the plastic molded product modified as described above, and thus have excellent heat resistance. Therefore, even if the linear guide device is used under severe use conditions in which a high surface pressure is applied to the end cap 32B and the return guide 55, the end cap 32B and the return guide 55 have performance such as durability and reliability. As a result, the linear guide device has a long life.

[Usage example 3]
FIG. 7 is a diagram showing a configuration of the electric power steering apparatus, and FIG. 8 is a cross-sectional view of a housing portion of the electric power steering apparatus. FIG. 9 is a perspective view showing only the worm wheel gear and the worm gear in the housing.
The worm wheel gear 81 and the worm gear 82 provided in the housing 71 of the electric power steering device 70 have a function of transmitting the rotational driving force of the electric motor 73 generated along with the rotation of the input shaft 72 to the output shaft 74. is doing.

  The worm wheel gear 81 and the worm gear 82 are made of polyamide 66 (UBE nylon 2020GU6 manufactured by Ube Industries Co., Ltd.) reinforced with glass fiber (content is 30% by mass) and contain an antioxidant. The above-described reforming process using carbon dioxide is performed, and the antioxidant penetrates into the surface layer portion (preventing oxidation in the worm wheel gear 81 and the worm gear 82 after the supercritical carbon dioxide is removed) The content of each agent is 0.09% by mass). The conditions of the treatment immersed in supercritical carbon dioxide are a temperature of 140 ° C., a pressure of 20 MPa, a treatment time of 2 hours, and the antioxidant used is N, N′-diphenyl-p-phenylenediamine (Ouchi Shinsei Chemical Co., Ltd.) Nocrack DP made by company.

  In such an electric power steering device 70, since the worm wheel gear 81 and the worm gear 82 are formed of the plastic molded product modified as described above, the worm wheel gear 81 and the worm gear 82 have excellent heat resistance. Yes. Therefore, even if the electric power steering device 70 is used under severe use conditions in which a high surface pressure is applied to the worm wheel gear 81 and the worm gear 82, the durability, reliability, etc. of the worm wheel gear 81 and the worm gear 82 The performance is excellent, and as a result, the electric power steering device 70 has a long life.

[Usage example 4]
FIG. 10 is a cross-sectional view showing a configuration of a hub unit bearing that is supported by an independent suspension and supports non-driving wheels. In the following description, when the hub unit bearing is mounted on a vehicle such as an automobile, the portion facing the width direction outside of the vehicle is referred to as an outer end portion, and the portion facing the width direction center side is the inner end portion. Called. That is, in FIG. 10, the left side is the outer end portion, and the right side is the inner end portion.

  The hub unit bearing includes an outer ring 105 that is a fixed ring, a hub 107 and an inner ring 116 that are rotating together with a mounting flange 112 that fixes a wheel (not shown), and an outer ring 105, a hub 107, and an inner ring 116. And a ball 117 as a plurality of rolling elements disposed in an annular gap formed in the ring so as to be freely rollable in the circumferential direction. A magnetic encoder 126 is attached to the inner ring 116 so that the rotational speed of the wheel can be detected.

  A small diameter step 115 is formed at the inner end of the hub 107, and an inner ring 116 is fitted on the small diameter step 115. The inner ring 116 is fixed to the hub 107 by pressing the inner end portion with a caulking portion 123 formed by caulking and expanding the inner end portion of the hub 107 radially outward. A mounting flange 112 is formed at a portion of the outer end portion of the hub 107 protruding from the outer end portion of the outer ring 105. A wheel can be attached to the mounting flange 112 by studs 108 planted at a predetermined interval in the circumferential direction.

Further, a coupling flange 111 is formed on the outer peripheral surface of the outer ring 105, and the outer ring 105 can be fixed to a knuckle (not shown) constituting the suspension device via the coupling flange 111. A plurality of balls 117 guided by a cage 118 are arranged between the outer ring 105, the hub 107 and the inner ring 116 so as to be able to roll in the circumferential direction.
Further, seal rings 121, 121, which are sealing devices, are provided between the inner peripheral surfaces of both ends of the outer ring 105, the outer peripheral surface of the intermediate part of the hub 107, and the outer peripheral surface of the inner end part of the inner ring 116. These seal rings 121 and 121 are formed between the inner peripheral surface of the outer ring 105 and the outer peripheral surfaces of the hub 107 and the inner ring 116 and block an annular gap provided with balls 117 and 117 from the outer space.

  Each of the seal rings 121 and 121 is formed by reinforcing the elastic members 122 and 122 with cored bars 124 and 124 that are formed of a mild steel plate and have an L-shaped cross section and have an annular shape as a whole. In such seal rings 121 and 121, the respective core bars 124 and 124 are fitted into the both ends of the outer ring 105 by interference fitting, and the tip ends of the seal lips formed by the respective elastic members 122 and 122 are formed. The slinger 125 or the intermediate portion of the hub 107 is slidably contacted with the outer peripheral surface of the inner end 116 of the inner ring 116 over the entire periphery.

  As shown in FIG. 11, the magnetic encoder 126 includes a slinger 125 that is a fixing member, and a magnetic pole forming ring 127 that is a magnet portion integrally joined to the side surface of the slinger 125. As shown in FIG. 12, the magnetic pole forming ring 127 is a multipolar magnet, and N poles and S poles are alternately formed in the circumferential direction. Then, the magnetic sensor 128 is disposed facing the magnetic pole forming ring 127 (see FIG. 10).

  Here, the magnetic encoder 126 will be described in more detail. As the magnetic material of the magnetic pole forming ring 127 of the magnetic encoder 126, a magnetic compound containing magnetic powder such as ferrite and using a thermoplastic resin as a binder can be suitably used. The magnetic pole forming ring 127 is made of 90% by mass of strontium. It is comprised with the resin composition which mixed the ferrite, 10 mass% polyamide 12, and a trace amount additive.

  The magnetic pole forming ring 127 is formed by magnetic field injection molding using a slinger 125 baked with a phenol-based adhesive in a precure state as a core. Due to the heat during injection molding, the phenolic adhesive is completely cured and the magnetic pole forming ring 127 and the slinger 125 are joined. However, if necessary, secondary heating may be performed to cure the phenolic adhesive more completely.

  Such a magnetic pole forming ring 127 is subjected to the above-described modification treatment using supercritical carbon dioxide containing an antioxidant, and the antioxidant penetrates into the surface layer portion thereof (supercritical dioxide dioxide). The content of the antioxidant in the magnet part after removing carbon is 0.01% by mass). The conditions of the treatment immersed in supercritical carbon dioxide are a temperature of 100 ° C., a pressure of 20 MPa, a treatment time of 1 hour, and the antioxidant used is N-isopropyl-N′-phenyl-p-phenylenediamine (Ouchi Shinsei Chemical). NOCLACK 810-NA) manufactured by Kogyo Co., Ltd.

  In such a magnetic encoder 126, the magnetic pole forming ring 127 is formed of a plastic molded product that has been modified as described above, and thus has excellent heat resistance. Therefore, even when the magnetic encoder 126 is used under severe use conditions, the magnetic pole forming ring 127 has excellent performance such as durability and reliability. As a result, the magnetic encoder 126 has a long life.

  Other examples of use of the modified plastic molded products include linear motion plain bearings, radial plain bearings, one-way clutches, needle roller bearings, turbocharger bearings, and wheel support bearings. Examples of plastics suitable for use as a part of a needle roller bearing include polyphenylene sulfide and polyamide 46. An example of a plastic suitable for use as a turbocharger bearing component is thermoplastic polyimide. Furthermore, as a kind of plastic suitable for use as a wheel support bearing component, for example, polyamide 66 containing 10% by mass of glass fiber can be cited.

  Next, the results of evaluating the heat resistance of the modified plastic molded product will be described. Prepared JIS No. 1 tensile test piece composed of polyamide 66 (UBE Nylon 2020GU6 manufactured by Ube Industries, Ltd., with a small amount of copper heat stabilizer added) reinforced with glass fiber (content: 30% by mass) Then, the above-described modification treatment using supercritical carbon dioxide containing an antioxidant was performed (the content of the antioxidant in the test piece after removing the supercritical carbon dioxide was 0.12 mass) %). The conditions of the treatment immersed in supercritical carbon dioxide are a temperature of 140 ° C., a pressure of 20 MPa, a treatment time of 2 hours, and the antioxidant used is N, N′-diphenyl-p-phenylenediamine (Ouchi Shinsei Chemical Co., Ltd.) Nocrack DP made by company.

  The test piece (Example) in which the surface was modified in this way and the antioxidant was fixed to the surface layer part, and the test piece not subjected to the modification treatment (Comparative Example) were left in a high temperature environment of 160 ° C. The change in tensile strength over time was measured. The results are shown in the graph of FIG. In this graph, the heat resistance is shown by the retention rate based on the initial value of the tensile strength. From the graph of FIG. 13, it can be seen that the surface-modified test piece is less prone to thermal degradation and has better heat resistance than the test piece not subjected to the modification treatment.

It is the longitudinal cross-sectional view of the deep groove ball bearing explaining the usage example of the modified plastic molded product, and the perspective view of a holder | retainer. It is a perspective view of the linear guide apparatus explaining another example of use of the modified plastic molded product. It is the figure which abbreviate | omitted the return guide and showed the back surface of the end cap. It is a front view of a return guide. It is a perspective view of an end cap in the state where a return guide is attached. It is a fragmentary sectional view of the end cap vicinity of the linear guide apparatus of FIG. It is a figure of the electric power steering apparatus explaining another example of use of the modified plastic molded product. It is sectional drawing of the housing part of the electric power steering apparatus of FIG. It is a perspective view of a worm wheel gear and a worm gear. It is sectional drawing of the bearing apparatus for wheel support explaining another example of use of the modified plastic molded product. It is a partial expanded sectional view which shows the vicinity part of the sealing device of FIG. It is a conceptual diagram explaining a magnetic encoder. It is a graph which shows the result of having evaluated the heat resistance of the modified plastic molded product.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Inner ring 12 Outer ring 13 Ball 14 Cage 31 Guide rail 32 Slider 32B End cap 35 Rolling element 55 Return guide 70 Electric power steering device 81 Worm wheel gear 82 Worm gear 126 Magnetic encoder 127 Magnetic pole formation ring

Claims (3)

  After the supercritical fluid containing the antioxidant is brought into contact with the plastic molded article, only the supercritical fluid out of the antioxidant and the supercritical fluid permeating the plastic molded article is removed from the plastic molded article. A method for modifying plastic molded products.   The method for reforming a plastic molded article according to claim 1, wherein the supercritical fluid is supercritical carbon dioxide.   A plastic molded article modified by the method for modifying a plastic molded article according to claim 1 or 2.

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