Shaft seal

Abstract

Provided is a shaft seal having a substantially U-shaped cross section, wherein occurrence of cracks in a molded body from a gate mark as a starting point is prevented even when a high surface pressure (about 10 MPa maximum) is applied to a substantially U-shaped inner surface. A shaft seal 1 is an annular shaft seal that is closely attached to an outer peripheral surface of a rotary shaft to seal a high-pressure sealed fluid, the shaft seal 1 being an injection molded body having a substantially U-shaped cross section in an axial direction. The shaft seal 1 comprises: a seal lip part 2 that extends to one side in the axial direction and slides with the rotary shaft; a fixed part 3 provided radially outward of the seal lip part 2; and a base end part 4 connecting the seal lip part 2 and the fixed part 3. The shaft seal 1 does not have a gate mark g of injection molding on a substantially U-shaped inner surface A, and has a gate mark g on a substantially U-shaped outer surface B.

Description

Shaft seal

[0001] The present invention relates to a shaft seal for a rotating shaft, and more particularly to a shaft seal for a rotating shaft in a scroll compressor of an in-vehicle air conditioner.

[0002] Compressors use seals to prevent leakage of refrigerant and refrigeration oil. For example, in scroll compressors that have a compression mechanism that combines a fixed scroll and a movable scroll that orbits relative to the fixed scroll, a shaft seal is attached to the rotating shaft that drives the compression mechanism.

[0003] Patent Document 1 discloses a shaft seal used for the rotating shaft of a scroll compressor in an automotive air conditioner. The shaft seal has a generally U-shaped cross section in the axial direction, and includes a seal lip portion extending axially to one side and sliding against the rotating shaft, and an outer lip portion provided radially outward of the seal lip portion. The shaft seal is molded from a thermoplastic elastomer composition primarily composed of a polyester-based elastomer, and is characterized by a flexural modulus of elasticity of 200 MPa to 2400 MPa according to ASTM D790. The shaft seal is manufactured by injection molding.

[0004] Japanese Patent Application Laid-Open No. 2021-092279

[0005] In injection molding, it is common practice to set the positions on the molded body of the gate that injects molten resin into the cavity that forms the molded body, and the ejector pin that removes the molded body from the injection molding mold, at positions that do not cause functional or appearance problems and that allow easy ejection without forcible removal.

[0006] In the annular shaft seal having a generally U-shaped cross section in the axial direction described in Patent Document 1, the diameter of the seal lip portion toward the tip is reduced, and the diameter of the outer lip portion provided radially outward of the seal lip portion is increased toward the tip. Therefore, in order to avoid forced removal during injection molding, an ejector pin is provided on the outer surface of the base end connecting the seal lip portion and the outer lip portion, and the gate is provided on the inner surface of the base end, which is a setting position consistent with conventional technology. Furthermore, it was believed that providing the gate on the inner surface of the base end would hide gate marks from the outside, and that providing the gate on the inner surface of the base end would not cause any functional problems.

[0007] However, as market demand for even lower leakage and torque in shaft seals increases, shaft seals made from materials that combine flexibility, low friction, and wear resistance are being developed. Flexibility can lead to a decrease in the strength of the shaft seal, which can further weaken the strength of gate marks and welds.

[0008] When a shaft seal with an approximately U-shaped cross section is used, the sealing fluid causes a higher surface pressure on the inner surface of the approximately U-shaped shaft seal than on the outer surface.For example, when used on the main shaft of a scroll compressor, a surface pressure of up to 10 MPa can be applied to the inner surface.

[0009] In injection-molded articles, gate marks are formed at the gate positions during injection molding. These gate marks are the fracture surfaces of the resin or elastomer that forms the shaft seal, and are also areas where strength in the tensile direction is reduced. Therefore, when pressure is applied to the inner surface of the approximately U-shaped part, the gate marks may become the starting point for cracks in the molded article.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a shaft seal having a generally U-shaped cross section that does not cause cracks in the molded body to originate from gate marks, even when a high surface pressure (up to approximately 10 MPa) is applied to the inner surface of the generally U-shape.

[0011] The shaft seal of the present invention is an annular shaft seal that fits tightly against the outer peripheral surface of a rotating shaft to seal against a sealed fluid, and the shaft seal is an injection-molded article that is approximately U-shaped in axial cross section, and is equipped with a seal lip portion that extends to one axial side and slides against the rotating shaft, a fixed portion that is provided on the outer diameter side of the seal lip portion, and a base end portion that connects the seal lip portion and the fixed portion, and is characterized in that the shaft seal does not have any injection molding gate marks on the inner surface (concave side) of the approximately U-shape, but has the gate marks on the outer surface (anti-concave side) of the approximately U-shape.

[0012] The gate mark is formed on the outer surface of the base end of the outer surface of the substantially U-shaped portion.

[0013] The shaft seal has an ejector pin mark on the inner surface of the approximately U-shaped portion, and the ejector pin mark is formed on the inner surface of the base end portion of the inner surface of the approximately U-shaped portion.

[0014] In the shaft seal, the gate mark and the ejector pin mark are not overlapped in circumferential positions.

[0015] In the shaft seal, the radial positions of the gate mark and the ejector pin mark do not overlap, and further, in the shaft seal, the radial position of the gate mark is located on the outer diameter side of the radial position of the ejector pin mark.

[0016] The fixing portion is characterized in that it has a lip shape.

[0017] The shaft seal is characterized in that it is a molded article made of a thermoplastic elastomer composition containing a polyester-based elastomer as a main component.

[0018] The shaft seal is used in a scroll compressor having a compression mechanism that combines a fixed scroll and a movable scroll that orbits relative to the fixed scroll, and the rotating shaft is a rotating shaft that drives the compression mechanism.

[0019] The shaft seal of the present invention comprises a seal lip portion, a fixed portion provided on the outer diameter side of the seal lip portion, and a base end portion connecting the seal lip portion and the fixed portion, and has no gate marks on the inner surface (concave side) of the approximately U-shape but has gate marks on the outer surface (anti-concave side) of the approximately U-shape. Therefore, even if high surface pressure is applied to the inner surface of the approximately U-shape when the shaft seal is in use, it is possible to prevent cracks from occurring in the molded body starting from the gate marks.

[0020] The gate mark is formed on the outer surface of the base end of the approximately U-shaped outer surface, so the gate portion is not subjected to stress such as pressure, and there is no risk of cracks occurring in the molded body starting from the gate mark.

[0021] The ejector pin marks are formed on the inner surface of the base end of the approximately U-shaped inner surface, so although the shaft seal is forcibly removed from the injection molding die, the removed shaft seal is less likely to deform.

[0022] The circumferential positions of the gate marks and ejector pin marks on the shaft seal do not overlap, so the ejector pin located on the opposite side is not pushed by the injection pressure from the gate. As a result, no irregularities are created on the inner surface of the shaft seal, preventing the occurrence of burrs.

[0023] The radial positions of the gate mark and ejector pin mark on the shaft seal do not overlap, so the ejector pin located on the opposite side is not pushed by the injection pressure from the gate. As a result, no irregularities are created on the inner surface of the shaft seal, preventing the occurrence of burrs.

[0024] Since the fixing portion is lip-shaped, the shaft seal can be easily removed by force when it is removed from the injection mold, and deformation of the removed shaft seal is unlikely to occur.

[0025] The shaft seal is primarily made of polyester elastomer, which provides excellent sliding and sealing properties with the shaft, and makes it easy to remove.

[0026] The shaft seal is used in a scroll compressor having a compression mechanism that combines a fixed scroll and a movable scroll that orbits relative to the fixed scroll, and the rotating shaft is the rotating shaft that drives the compression mechanism, thereby improving the reliability of the scroll compressor.Furthermore, it is preferable that the scroll compressor is a scroll compressor for an automotive air conditioner.

[0027] Fig. 5 is a diagram showing an example of a shaft seal of the present invention attached to a rotating shaft. Fig. 6 is a cross-sectional view for explaining an example of a shaft seal of the present invention. Fig. 7 is a perspective view of an example of a shaft seal of the present invention. Fig. 8 is a plan view, a cross-sectional view, and a back view of the shaft seal of Fig. 3. Fig. 9 is a perspective view of another example of a shaft seal of the present invention. Fig. 10 is a plan view, a cross-sectional view, and a back view of the shaft seal of Fig. 5. Fig. 11 is a schematic cross-sectional view showing a compression mechanism part of a scroll compressor.

[0028] A compressor to which the shaft seal of the present invention is applied will be described with reference to Figure 1. Figure 1 shows an axial cross-sectional view of the shaft seal attached to a rotating shaft. As shown in Figure 1, the shaft seal 1 is an injection-molded annular member that is approximately U-shaped in axial cross-section. The shaft seal 1 has a seal lip portion 2 on the seal inner diameter side that extends to one side in the axial direction, and a fixed portion 3 provided on the seal outer diameter side of the seal lip portion 2. The seal lip portion 2 and the fixed portion 3 are connected at a base end 4.

[0029] The shaft seal 1 receives a sealed fluid on its inner surface (concave side) on the side of the gap surrounded by the seal lip portion 2, the fixed portion 3, and the base end portion 4, and seals the space on the outer surface (anti-concave side) opposite the inner surface. As shown in Figure 2, the shaft seal 1 has a substantially U-shaped inner surface A and a substantially U-shaped outer surface B. The substantially U-shaped inner surface A has the inner surface 2a of the seal lip portion 2, the inner surface 3a of the fixed portion 3, and the inner surface 4a of the base end portion 4, which are connected to each other. The substantially U-shaped outer surface B has the outer surface 2b of the seal lip portion 2, the outer surface 3b of the fixed portion 3, and the outer surface 4b of the base end portion 4, which are connected to each other.

[0030] 1 , the housing 5 is provided with an insertion hole 5a through which the rotating shaft S is inserted, and an annular groove 5b is formed around the rotating shaft S by inserting the rotating shaft S into the insertion hole 5a. The shaft seal 1 is fitted in this annular groove 5b, and as the rotating shaft S rotates around the axis O, the seal lip portion 2 slides on the rotating shaft S.

[0031] 1, the shaft seal 1 is mounted in the annular groove 5b so that the seal lip portion 2 and the fixed portion 3 each extend toward the high-pressure side H. In the mounted state, the fixed portion 3 of the shaft seal 1 abuts against the annular groove 5b, and the outer surface 4b of the base end portion 4 on the substantially U-shaped outer surface of the shaft seal 1 abuts against the low-pressure side wall surface 5c of the annular groove 5b.

[0032] The fixed portion 3 does not slide in either the axial or circumferential direction relative to the annular groove 5b, but is fixed to the annular groove 5b. The fixed portion 3 may have a rectangular cross section as shown in Fig. 1, or may have a lip shape (see Fig. 6).

[0033] As shown in Figure 1, the shaft seal 1 has a fixed portion 3 abutting against the annular groove 5b and a seal lip portion 2 tightly contacting the outer circumferential surface of the rotating shaft S, thereby preventing fluid from leaking from the high-pressure side H to the low-pressure side L. The fluid is oil or a mixture containing oil. A specific example of an oil-containing mixture is a mixture of refrigerant and oil.

[0034] To ensure the sealing performance of the shaft seal 1, the minimum inner diameter of the shaft seal 1 before installation must be smaller than the outer diameter of the rotating shaft S. In other words, the shaft seal 1 must have some interference when assembled to the rotating shaft S. The minimum inner diameter and interference of the shaft seal 1 are not particularly limited. For example, when the minimum inner diameter of the shaft seal 1 is 10 mm to 50 mm, the interference is approximately 0.1 mm to 3 mm. As described below, the shaft seal of the present invention is, for example, a molded product of a thermoplastic elastomer composition. Since the flexural modulus of the shaft seal 1 falls within a predetermined range, it has excellent flexibility and does not cause problems during installation even if a certain amount of interference is ensured. Furthermore, by ensuring a certain amount of interference, sealing performance can be maintained even if the seal lip portion 2 wears due to use of the shaft seal 1.

[0035] The shaft seal 1 will be described in more detail with reference to Figures 3 and 4. In the present invention, the direction along the central axis of the shaft seal 1 is referred to as the axial direction, the direction perpendicular to the central axis in a plan view from the axial direction is referred to as the radial direction, and the direction circumferentially around the central axis in the plan view is referred to as the circumferential direction.

[0036] Fig. 3 is a perspective view of the shaft seal as seen from the side where the seal lip portion extends. As shown in Fig. 3, the shaft seal 1 has a seal lip portion 2, a fixed portion 3, and a base end portion 4, and a concave circumferential groove is formed between the seal lip portion 2 and the fixed portion 3. The surface that forms this circumferential groove corresponds to the inner surface of the approximately U-shape.

[0037] Fig. 4(a) is a plan view of the shaft seal from the side where the seal lip portion extends, Fig. 4(b) is a cross-sectional view taken along line X-X, and Fig. 4(c) is a rear view. For convenience, in Fig. 4(a), ejector pin marks p are indicated by cross-hatching (the same applies to Fig. 6(a) described later).

[0038] As shown in Figure 4, the shaft seal 1 does not have an injection molding gate mark g on the generally U-shaped inner surface A, but does have a gate mark g on the generally U-shaped outer surface B. More specifically, the gate mark g is formed on the outer surface 4b of the base end 4 of the generally U-shaped outer surface B, and further on the end surface of the outer surface 4b of the base end 4 that is closest in the axial direction. In Figure 4(b), this end surface is formed as a plane perpendicular to the axial direction of the shaft seal 1.

[0039] 4, the gate mark g of the shaft seal 1 is not located on the approximately U-shaped inner surface A, so even if the inner surface A is subjected to an operating pressure exceeding 0.2 MPa, for example, or even if it is subjected to a high operating pressure (sealed fluid) of 1 MPa to 10 MPa, no tensile force is applied to the gate mark g, which is the fracture surface of the resin or elastomer material that forms the shaft seal 1. As a result, cracks do not occur in the molded body starting from the gate mark g.

[0040] Multiple gate marks g (six in FIG. 4) are formed, and are provided at equal intervals on a circumference concentric with the central axis of the shaft seal 1. The number of gate marks g in the shaft seal 1 is not particularly limited, and may be, for example, three to seven. In this case, the shaft seal 1 is injection molded using three to seven multi-point gates.

[0041] In FIG. 4, the radial position of the gate mark g is located on the outer diameter side of the circumferential groove formed in the shaft seal 1.

[0042] The shaft seal 1 also has an ejector pin mark p on the substantially U-shaped inner surface A. The ejector pin mark p is a mark left by the tip of an ejector pin (ejector pin) on the surface of the molded body. In FIG. 4 , the ejector pin mark p is formed on the inner surface 4a of the base end 4 of the substantially U-shaped inner surface A, and is further formed at the deepest position within the recess on the inner surface 4a of the base end 4. The ejector pin mark p may be formed on a plane perpendicular to the axial direction of the shaft seal 1 on the inner surface 4a of the base end 4.

[0043] In Figure 4, the ejector pin mark p is formed circumferentially (sleeve-shaped) on the inner surface 4a of the base end 4. The gate mark g and the ejector pin mark p are positioned so that they do not overlap in the radial direction. In this case, the radial distance from the central axis of the shaft seal 1 to the area where the gate mark g is formed is different from the radial distance from the central axis of the shaft seal 1 to the area where the ejector pin mark p is formed. The area indicated by the dotted line in Figure 4(c) corresponds to the ejector pin mark p. Furthermore, in Figure 4, the gate mark g is formed closer to the outer diameter of the seal than the ejector pin mark p.

[0044] Another example of the shaft seal of the present invention is shown in Figures 5 and 6. Figure 5 is a perspective view of the shaft seal as seen from the side where the seal lip portion extends. The shaft seal 11 has a seal lip portion 12, a fixed portion 13, and a base end portion 14. In the shaft seal 11, the fixed portion 13 has a lip shape.

[0045] As shown in Figure 6, the shaft seal 11 does not have an injection molding gate mark g on the generally U-shaped inner surface A, but does have a gate mark g on the generally U-shaped outer surface B. More specifically, the gate mark g is formed on the outer surface 14b of the base end 14 of the generally U-shaped outer surface B, and further formed on the end surface of the outer surface 14b of the base end 14 that is closest in the axial direction. In Figure 6(b), this end surface is formed as a plane perpendicular to the axial direction of the shaft seal 11.

[0046] In Figure 6, the radial position of the gate mark g is such that it overlaps with the circumferential groove formed in the shaft seal 11. In addition, multiple gate marks g (six in Figure 6) are formed and are provided at equal intervals on a circumference concentric with the central axis of the shaft seal 1.

[0047] The shaft seal 11 also has ejector pin marks p on the generally U-shaped inner surface A. Specifically, multiple ejector pin marks p (six in FIG. 6 ) are formed on the inner surface 14a of the base end 14 of the generally U-shaped inner surface A. In FIG. 6 , the number of ejector pin marks p is the same as the number of gate marks g, and the gate marks g and ejector pin marks p on the shaft seal 11 are positioned so as not to overlap in the circumferential direction. Preferably, the ejector pin marks p are formed midway between adjacent gate marks g on the circumference. In this case, the gate marks g and ejector pin marks p overlap in the radial direction, but the gate marks g and ejector pin marks p may also not overlap in the radial direction.

[0048] The shaft seal of the present invention is not limited to the configuration shown in Figures 1 to 6. For example, although the seal lip portion is formed in a straight line in Figures 1 to 6, the seal lip portion may also have a curved shape. Furthermore, the shaft seal may be provided with a lip portion other than the seal lip portion and the outer lip portion (for example, a dust lip that slides against the rotating shaft).

[0049] In the compressor of Figure 1, a compression mechanism is provided on the high-pressure side H of the housing 5. The compression mechanism may be of any type, such as a scroll type or a swash plate type, as long as it compresses a fluid by rotation of a rotating shaft. For example, in the case of a scroll type, the compression mechanism is configured by combining a fixed scroll and a movable scroll that orbits relative to the fixed scroll.

[0050] FIG. 7 shows a partial cross-sectional view of a scroll-type compression mechanism. As shown in FIG. 7, the compression mechanism 21 includes a fixed rotor 23 having a base plate 23a and fixed scroll blades 23b standing upright on the base plate 23a, and a movable rotor 24 having a base plate 24a and movable scroll blades 24b standing upright on the base plate 24a. The fixed rotor 23 and the movable rotor 24 are eccentrically meshed with each other, forming a compression chamber 22 therebetween. The movable rotor 24 is directly or indirectly connected to the rotating shaft. As the movable rotor 24 revolves around the axis of the fixed rotor 23, the compression chamber 22 moves toward the center of the spiral shape, compressing the fluid. The compressed fluid is discharged from a discharge pipe through a discharge port 25 at the center of the movable rotor 24 and flows into the refrigeration cycle. A refrigeration cycle fluid (e.g., refrigerant gas) is introduced into the compression chamber 22 through a suction port (not shown).

[0051] The shaft seal of the present invention is preferably a molded article made of a thermoplastic elastomer composition primarily composed of a polyester-based elastomer. As described above, the shaft seal of the present invention has no gate marks from injection molding on the inner surface of the generally U-shaped structure, but has gate marks on the outer surface of the generally U-shaped structure. The shaft seal may have ejector pin marks on the inner surface of the generally U-shaped structure. In such a configuration, the shaft seal must be forcibly removed from the injection mold. However, using a polyester-based elastomer as the primary component facilitates this forcible removal. The polyester-based elastomer contains hard segments and soft segments, with polyester units in the hard segments and polyether or polyester units in the soft segments. The polyester-based elastomer is a polyester-polyether or polyester-polyester multiblock copolymer.

[0052] The polyester units of the hard segments are preferably mainly composed of aromatic polyester units, which are usually polyester units having an aromatic dicarboxylic acid component and a diol component as polymerization components.

[0053] As the aromatic dicarboxylic acid component, for example, an aromatic dicarboxylic acid or an ester derivative thereof can be used. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acids (e.g., naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid), 4,4'-diphenyldicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid. Examples of ester derivatives of aromatic dicarboxylic acids include alkyl esters (methyl esters, ethyl esters, etc.), aryl esters, and carbonate esters of the above aromatic dicarboxylic acids. The aromatic dicarboxylic acid component may be used alone or in combination of two or more.

[0054] In addition to the aromatic dicarboxylic acid components, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid and azelaic acid, and ester derivatives thereof may also be used as other copolymerization components.

[0055] The total amount of aromatic dicarboxylic acid components is preferably 80 mol % or more, more preferably 90 mol % or more, based on the total number of moles of all acid components (100 mol %). Furthermore, it is particularly preferred that the copolymer is composed essentially of aromatic dicarboxylic acid components and does not substantially contain other copolymerization components (acid components other than aromatic dicarboxylic acid components).

[0056] As the diol component, for example, a diol or an ester derivative thereof can be used. Examples of diols include aliphatic diols such as ethylene glycol, 1,4-butanediol, and 1,6-hexanediol, and alicyclic diols such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol. Examples of ester derivatives of diols include acetyl derivatives of the above diols. The diol component may be used alone or in combination of two or more.

[0057] In the hard segment, it is preferable that the aromatic polyester unit contains a naphthalene ring. As a structural unit containing a naphthalene ring, a polybutylene naphthalate unit is particularly preferable. The polybutylene naphthalate unit can be obtained, for example, by using naphthalene-2,6-dicarboxylic acid as the aromatic dicarboxylic acid component and 1,4-butanediol as the diol component. The aromatic polyester unit containing the polybutylene naphthalate unit may be formed solely from the polybutylene naphthalate unit, or may also contain other structural units (for example, a polybutylene isophthalate unit).

[0058] The polyether unit of the soft segment includes, for example, an aliphatic polyether unit. Examples of the aliphatic polyether unit include a poly(ethylene oxide) glycol unit, a poly(propylene oxide) glycol unit, a poly(tetramethylene oxide) glycol unit, a poly(hexamethylene oxide) glycol unit, and a copolymer of ethylene oxide and propylene oxide. These structural units may be contained alone or in combination.

[0059] The polyester unit of the soft segment includes, for example, an aliphatic polyester unit. Examples of the aliphatic polyester unit include a poly(ε-caprolactone) unit, a polyenantholactone unit, a polycaprylolactone unit, a polybutylene adipate unit, and a polyethylene adipate unit. These structural units may be contained alone or in combination of two or more types.

[0060] Suitable commercially available polyester elastomers include, for example, Pelprene EN type (manufactured by Toyobo Co., Ltd.). Pelprene EN type has the chemical structure shown in formula (1) below, with the hard segment shown in formula (2) below and the soft segment shown in formula (3) below. As shown in formula (1) below, the structural units of the hard segment and the structural units of the soft segment are bonded by ester bonds or carbonate bonds. In Pelprene EN type, the hard segment consists only of aromatic polyester units, more specifically, only of polybutylene naphthalate units. Specific grades of Pelprene EN type include EN-1000, EN-2000, EN-3000, EN-5000, and EN-16000. Each grade has a different ratio of hard segments to soft segments and different physical properties (such as flexural modulus).

[0061]

[0062] The use of hard segments made of aromatic polyesters containing naphthalene rings in the molecule, such as Pelprene EN type, improves the chemical resistance and oil resistance of polyester elastomers compared to those that do not contain naphthalene rings, making them suitable for shaft seals for rotating shafts of compressors used in the presence of a mixture of refrigerants and refrigerating machine oils.

[0063] In the polyester-based elastomer, the ratio of hard segments to soft segments in the copolymerization is not particularly limited, but since an increase in the ratio of hard segments increases the modulus of elasticity, the flexural modulus of the thermoplastic resin elastomer composition is adjusted to be in the range of 200 MPa to 2400 MPa. Note that, since it is easier to adjust the flexural modulus of a molded article to the desired range, it is preferable to use an elastomer with a flexural modulus (ASTM D790) of 150 MPa to 1700 MPa as the polyester-based elastomer.

[0064] The polyester elastomer is preferably contained in an amount of 60% by volume or more, more preferably 80% by volume or more, and even more preferably 90% by volume or more, relative to 100% by volume of the thermoplastic elastomer composition according to the present invention.

[0065] The thermoplastic elastomer composition according to the present invention preferably contains 1 to 40% by volume of PTFE resin relative to 100% by volume of the thermoplastic elastomer composition. PTFE resin is a solid lubricant, and adding 1% or more by volume can reduce the coefficient of dynamic friction of a molded product of the thermoplastic elastomer composition. On the other hand, if the PTFE resin content exceeds 40% by volume, the elongation properties of the thermoplastic elastomer composition decrease, and cracks may occur when the shaft seal is assembled into a rotating shaft. More preferably, the PTFE resin content is 1 to 10% by volume.

[0066] The thermoplastic elastomer composition according to the present invention may contain a solid lubricant other than PTFE resin, such as graphite or molybdenum disulfide. Graphite is a solid lubricant that can reduce the dynamic friction coefficient of a molded body of the thermoplastic elastomer composition. Either natural graphite or artificial graphite may be used as the graphite.

[0067] The thermoplastic elastomer composition may contain fibrous reinforcing materials such as carbon fiber, glass fiber, and aramid fiber, spherical fillers such as spherical silica, scaly reinforcing materials such as mica, sliding reinforcing materials such as calcium phosphate and calcium sulfate, and microfiber reinforcing materials such as potassium titanate whiskers, to the extent that the effects of the present invention are not impaired. Colorants such as carbon black and iron oxide may also be added. These may be added alone or in combination.

[0068] The shaft seal of the present invention is suitable for use with a highly flexible, soft material, but can also be used with a less flexible, hard material. Flexibility can be defined by the flexural modulus.

[0069] The material forming the shaft seal of the present invention preferably has a flexural modulus of 200 MPa to 2400 MPa as measured in accordance with ASTM D790. A flexural modulus of 200 MPa to 2400 MPa facilitates the forced removal of the seal lip of the shaft seal during the ejection process of the molded body in injection molding without damaging or deforming it. Furthermore, if the flexural modulus is less than 200 MPa, the material tends to be prone to wear and have poor sealing properties. Furthermore, if the flexural modulus exceeds 2400 MPa, the tension force of the shaft seal on the rotating shaft increases, tending to result in high torque. The flexural modulus of the shaft seal is preferably 200 MPa to 1800 MPa, more preferably 400 MPa to 1800 MPa.

[0070] In consideration of the above, a particularly preferred embodiment of the shaft seal of the present invention is an injection-molded article of a thermoplastic elastomer composition in which a PTFE resin is blended with a polyester-based elastomer, wherein the polyester-based elastomer is a copolymer of a hard segment containing a polybutylene naphthalate unit and a soft segment containing an aliphatic polyether unit, the PTFE resin is contained in an amount of 1 to 10% by volume relative to 100% by volume of the thermoplastic elastomer composition, and the flexural modulus of the shaft seal according to ASTM D790 is 200 MPa to 1800 MPa.

[0071] The shaft seal of the present invention can be used in a scroll compressor for an automotive air conditioner. The scroll compressor may be either belt-driven, using engine power, or motor-driven, not using engine power. The shaft seal of the present invention can also be used in applications other than compressors.

[0072] The shaft seal of the present invention is free from concerns about cracks occurring from gate marks and does not deform even when forcibly removed from an injection molding die, making it suitable for a wide range of applications as a shaft seal that seals in sealed fluid while making sliding contact with the outer circumferential surface of a rotating shaft, and is particularly suitable as a shaft seal for the rotating shaft that rotates the compression mechanism of a scroll-type refrigerant compressor in an automotive air conditioner.

[0073] REFERENCE SIGNS LIST 1 Shaft seal 2 Seal lip portion 3 Fixed portion 4 Base end portion 5 Housing 11 Shaft seal 12 Seal lip portion 13 Fixed portion 14 Base end portion 21 Compression mechanism portion 22 Compression chamber 23 Fixed rotor 24 Movable rotor 25 Discharge port A Approximately U-shaped inner surface B Approximately U-shaped outer surface S Rotating shaft g Gate mark p Ejector pin mark

Claims

1. An annular shaft seal which fits tightly against the outer peripheral surface of a rotating shaft to seal against a sealed fluid, said shaft seal being an injection-molded body which is roughly U-shaped when viewed in axial cross section, and which comprises a seal lip portion which extends to one axial side and slides against the rotating shaft, a fixed portion which is provided on the outer diameter side of the seal lip portion, and a base end portion which connects the seal lip portion and the fixed portion, said shaft seal having no gate mark from injection molding on the inner surface of said roughly U-shaped portion, and having said gate mark on the outer surface of said roughly U-shaped portion.

2. A shaft seal according to claim 1, characterized in that the gate mark is formed on the outer surface of the base end of the outer surface of the approximately U-shaped portion.

3. A shaft seal as described in claim 1, characterized in that the shaft seal has an ejection pin mark on the inner surface of the approximately U-shaped inner surface, the ejection pin mark being formed on the inner surface of the base end of the approximately U-shaped inner surface.

4. A shaft seal according to claim 3, characterized in that the gate mark and the ejector pin mark are not overlapped in circumferential positions in the shaft seal.

5. The shaft seal according to claim 3, characterized in that the radial positions of the gate mark and the ejector pin mark in the shaft seal do not overlap.

6. A shaft seal according to claim 5, characterized in that in said shaft seal, the radial position of said gate mark is located on the outer diameter side of the radial position of said ejector pin mark.

7. The shaft seal according to claim 1, wherein said fixed portion is lip-shaped.

8. The shaft seal according to claim 1, characterized in that the shaft seal is a molded body made of a thermoplastic elastomer composition containing a polyester-based elastomer as a main component.

9. The shaft seal according to claim 1, characterized in that the shaft seal is used in a scroll compressor having a compression mechanism that combines a fixed scroll and a movable scroll that orbits relative to the fixed scroll, and the rotating shaft is a rotating shaft that drives the compression mechanism.

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