Shaft seal

Abstract

To provide a shaft seal having a substantially U-shaped cross section, which prevents cracks from occurring in a molded body caused by a gate mark even when a high surface pressure (maximum of about 10 MPa) is applied to a substantially U-shaped inside surface.SOLUTION: A shaft seal 1 is an annular shaft seal that seals high-pressure sealed fluid by adhering to an outer peripheral surface of a rotational shaft, and is an injection molded body that is approximately U-shaped in an axially cross-sectional view. The shaft seal has a seal lip part 2 that extends to one axial side and slides against the rotational shaft, a stationary part 3 that is provided on an outer diameter side with respect to the seal lip part 2, and a base end part 4 that connects the seal lip part 2 and the stationary part 3. The shaft seal 1 does not have an injection molding gate mark g on the substantially U-shaped inside surface A, but has a gate mark g on a substantially U-shaped outside surface B.SELECTED DRAWING: Figure 4

Description

Technical Field

[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.

Background Art

[0002] A seal member for preventing leakage of refrigerant and refrigerating machine oil is used in a compressor. For example, in a scroll compressor including a compression mechanism portion that combines a fixed scroll and a movable scroll that makes a turning motion with respect to the fixed scroll, a shaft seal is attached to a rotating shaft that drives the compression mechanism portion.

[0003] Patent Document 1 discloses a shaft seal used for a rotating shaft of a scroll compressor of an in-vehicle air conditioner. The shaft seal has a substantially U-shaped cross section in the axial direction, includes a seal lip portion that extends to one side in the axial direction and slides on the rotating shaft, and an outer lip portion provided on the outer diameter side of the seal lip portion. The shaft seal is a molded body of a thermoplastic elastomer composition mainly composed of a polyester-based elastomer, and is characterized in that the flexural modulus according to ASTM D790 is 200 MPa to 2400 MPa. This shaft seal is manufactured by injection molding.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In injection molding, the gate for injecting molten resin into the cavity forming the molded body and the set position on the molded body of the ejector pin for taking out the molded body from the injection mold are positions that do not cause problems in terms of function and appearance, and are usually known as common techniques to be set at positions where they can be easily ejected without forced ejection during ejection.

[0006] In the annular shaft seal with a substantially U-shaped cross-section in the axial direction described in Patent Document 1, the diameter in the tip direction of the seal lip portion is in a reduced diameter state, and the diameter in the tip direction of the outer lip portion provided on the outer diameter side of the seal lip portion is in an enlarged diameter state. For this reason, in injection molding, in order to avoid forced ejection, it is a setting position in line with common techniques to set the ejector pin on the outer surface of the base end portion connecting the seal lip portion and the outer lip portion, and to set the gate on the inner surface of the base end portion. Also, it has been said that by setting the gate on the inner surface of the base end portion, the gate mark is hidden in terms of appearance, and no functional problems occur by setting the gate on the inner surface of the base end portion.

[0007] However, market requirements for further low leakage and low torque of the shaft seal have increased, and the development of shaft seals made of materials with flexibility, low friction, and wear resistance has been carried out. Flexibility causes a decrease in the strength of the shaft seal, and it is conceivable that gate marks and weld portions further reduce the strength.

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

[0009] By the way, in an injection molded body, a gate mark is formed at the position of the gate during injection molding. Since this gate mark is the fracture surface of the resin or elastomer forming the shaft seal, it is also a portion where the strength in the tensile direction decreases. Therefore, when pressure is applied to the substantially U-shaped inner surface, there is a risk that cracks will occur in the molded body starting from the gate mark.

[0010] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a shaft seal in which, even when a high surface pressure (about 10 MPa at maximum) is applied to the substantially U-shaped inner surface in a shaft seal having a substantially U-shaped cross section, cracks do not occur in the molded body starting from the gate mark.

Means for Solving the Problems

[0011] The shaft seal of the present invention is an annular shaft seal that adheres to the outer peripheral surface of a rotating shaft to seal a sealing fluid. The shaft seal is an injection molded body having a substantially U-shaped cross section in the axial direction, and includes a seal lip portion that extends to one side in the axial direction and slides on the rotating shaft, a fixing portion provided on the outer diameter side of the seal lip portion, and a base end portion that connects the seal lip portion and the fixing portion. The shaft seal is characterized by having no gate mark on the substantially U-shaped inner surface (concave side surface), and having the gate mark on the substantially U-shaped outer surface (anti-concave side surface).

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

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

[0014] In the shaft seal, the circumferential positions of the gate mark and the protruding pin mark do not overlap.

[0015] In the shaft seal, the radial positions of the gate mark and the protruding pin mark do not overlap. 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 protruding pin mark.

[0016] The fixing portion has a lip shape.

[0017] The shaft seal is characterized in that it is a molded body of a thermoplastic elastomer composition mainly composed of a polyester-based elastomer.

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

Advantages of the Invention

[0019] The shaft seal of the present invention includes 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. It has no gate mark on the substantially U-shaped inner surface (concave side surface), and has a gate mark on the substantially U-shaped outer surface (opposite concave side surface). Therefore, even when a high surface pressure is applied to the substantially U-shaped inner surface during the use of the shaft seal, it is possible to prevent cracks from occurring in the molded body starting from the gate mark.

[0020] Since the gate mark is formed on the outer surface of the base end portion of the substantially U-shaped outer surface, 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] Since the ejector pin mark is formed on the inner surface of the base end portion of the substantially U-shaped inner surface, it is difficult to remove the shaft seal from the injection mold by forced ejection, but it is difficult for the removed shaft seal to be deformed.

[0022] Since the circumferential positions of the gate mark and the ejector pin mark of the shaft seal do not overlap, the ejector pin located on the opposite side is not pushed by the injection pressure from the gate. As a result, unevenness does not occur on the inner surface of the shaft seal, and the generation of burrs can be prevented.

[0023] Since the radial positions of the gate mark and the ejector pin mark of the shaft seal do not overlap, the ejector pin located on the opposite side is not pushed by the injection pressure from the gate. As a result, unevenness does not occur on the inner surface of the seal, and the generation of burrs can be prevented.

[0024] Since the fixing part has a lip shape, when the shaft seal is taken out of the injection mold, it is easy to perform forced ejection, so that the taken-out shaft seal is less likely to be deformed.

[0025] Since the shaft seal is mainly composed of a polyester-based elastomer, it has excellent slidability and sealing performance with the shaft, and is also easy to perform forced ejection.

[0026] The shaft seal is used in a scroll compressor including a compression mechanism portion combining a fixed scroll and a movable scroll that rotates with respect to the fixed scroll, and the rotating shaft is a rotating shaft that drives the compression mechanism portion. Therefore, the reliability of the scroll compressor is improved. Further, it is preferable that the scroll compressor is a scroll compressor for an in-vehicle air conditioner.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

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

[0029] The shaft seal 1 receives the sealing fluid on the inner surface (concave side surface) on the side of the gap surrounded by the seal lip portion 2, the fixing portion 3, and the base end portion 4, and seals the space on the outer surface (opposite concave side surface) side, which is the opposite side of the inner surface. As shown in Fig. 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 an inner surface 2a of the seal lip portion 2, an inner surface 3a of the fixing portion 3, and an inner surface 4a of the base end portion 4, and these are connected. Further, the substantially U-shaped outer surface has an outer surface 2b of the seal lip portion 2, an outer surface 3b of the fixing portion 3, and an outer surface 4b of the base end portion 4, and these are connected.

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

[0031] In Fig. 1, the shaft seal 1 is mounted in the annular groove 5b such that the seal lip portion 2 and the fixing portion 3 each extend to the high-pressure side H. In the mounted state, the fixing 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] Note that the fixing portion 3 does not slide in either the axial direction or the circumferential direction with respect to the annular groove 5b and is fixed to the annular groove 5b. Further, the fixing 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 FIG. 1, the shaft seal 1 prevents the fluid on the high-pressure side H from leaking to the low-pressure side L by the fixing portion 3 abutting against the annular groove 5b and the seal lip portion 2 closely contacting the outer peripheral surface of the rotating shaft S. The fluid is oil or a mixture containing oil. Specific examples of the mixture containing oil include a mixture of a refrigerant and oil.

[0034] In order to ensure the sealing performance of the shaft seal 1, it is necessary to make the minimum inner diameter dimension of the shaft seal 1 before installation smaller than the outer diameter dimension of the rotating shaft S. That is, when incorporating the shaft seal 1 into the rotating shaft S, the shaft seal 1 needs to have an interference fit. The minimum inner diameter dimension and the interference fit of the shaft seal 1 are not particularly limited. For example, when the minimum inner diameter dimension of the shaft seal 1 is 10 mm to 50 mm, the interference fit is about 0.1 mm to 3 mm. As will be described later, the shaft seal of the present invention is, for example, a molded body of a thermoplastic elastomer composition and belongs to a predetermined range of flexural modulus, so it is excellent in flexibility and there are no problems during installation even if a certain degree of interference fit is ensured. Also, by ensuring a certain degree of interference fit, even if the seal lip portion 2 wears due to the use of the shaft seal 1, the sealing performance can be maintained.

[0035] The shaft seal 1 will be described in more detail with reference to FIGS. 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 orthogonal to the central axis in a plan view seen from the axial direction is referred to as the radial direction, and the direction of orbiting 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 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 fixing portion 3, and a base end portion 4, and a concave circumferential groove is formed between the seal lip portion 2 and the fixing portion 3. The surface constituting this circumferential groove corresponds to a substantially U-shaped inner surface.

[0037] Fig. 4(a) is a plan view seen from the side where the seal lip portion of the shaft seal extends, Fig. 4(b) is a cross-sectional view taken along the line X-X thereof, and Fig. 4(c) is a rear view. In Fig. 4(a), for the sake of convenience, the protruding pin mark p is indicated by cross-hatching (the same applies to Fig. 6(a) described later).

[0038] As shown in Fig. 4, the shaft seal 1 has no gate mark g on the substantially U-shaped inner surface A and has a gate mark g on the substantially U-shaped outer surface B. More specifically, the gate mark g is formed on the outer surface 4b of the base end portion 4 among the substantially U-shaped outer surfaces B, and further formed on the end surface at the most end side in the axial direction among the outer surfaces 4b of the base end portion 4. This end surface is formed by a plane orthogonal to the axial direction of the shaft seal 1 in Fig. 4(b).

[0039] As shown in Fig. 4, since the gate mark g of the shaft seal 1 is not present on the substantially U-shaped inner surface A, even when the inner surface A receives an operating pressure exceeding, for example, 0.2 MPa, especially when receiving a high-pressure operating pressure (sealing fluid) of 1 MPa to 10 MPa, no tensile force is applied to the gate mark g, which is the fracture surface of the forming material of the shaft seal 1 such as resin or elastomer. Therefore, no crack occurs in the molded body starting from the gate mark g.

[0040] A plurality of (six in Fig. 4) gate marks g are formed and are provided at equal intervals on the circumference concentric with the central axis of the shaft seal 1. In the shaft seal 1, the number of gate marks g is not particularly limited and is, for example, three to seven. In this case, injection molding is performed by a multi-point gate of three to seven points.

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

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

[0043] In FIG. 4, the protruding pin mark p is formed in a circumferential shape (sleeve shape) on the inner surface 4a of the base end portion 4. The radial positions of the gate mark g and the protruding pin mark p are not overlapping positions. In this case, the radial distance from the central axis of the shaft seal 1 to the formation region of the gate mark g and the radial distance from the central axis of the shaft seal 1 to the formation region of the protruding pin mark p are different from each other. The location indicated by the dotted line in FIG. 4(c) corresponds to the protruding pin mark p. Further, in FIG. 4, the gate mark g is formed on the seal outer diameter side rather than the protruding pin mark p.

[0044] Other examples of the shaft seal of the present invention are shown in FIGS. 5 and 6. FIG. 5 is a perspective view of the shaft seal as viewed from the side where the seal lip portion extends. The shaft seal 11 has a seal lip portion 12, a fixing portion 13, and a base end portion 14. In the shaft seal 11, the fixing portion 13 has a lip shape.

[0045] As shown in FIG. 6, the shaft seal 11 does not have a gate mark g of injection molding on the substantially U-shaped inner surface A, but has a gate mark g on the substantially U-shaped outer surface B. More specifically, the gate mark g is formed on the outer surface 14b of the base end portion 14 of the substantially U-shaped outer surface B, and further formed on the end face at the most end side in the axial direction on the outer surface 14b of the base end portion 14. This end face is formed by a plane orthogonal to the axial direction of the shaft seal 11 in FIG. 6(b).

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

[0047] Further, the shaft seal 11 has protruding pin marks p protruding from the substantially U-shaped inner surface A. Specifically, the protruding pin marks p are formed in plural (six in FIG. 6) on the inner surface 14a of the base end portion 14 among the substantially U-shaped inner surfaces A. In FIG. 6, the number of the protruding pin marks p is the same as that of the gate marks g, and the circumferential positions of the gate marks g and the protruding pin marks p of the shaft seal 11 are non-overlapping positions. Preferably, the protruding pin marks p are formed at intermediate positions between adjacent gate marks g on the circumference. In this case, although the radial positions of the gate marks g and the protruding pin marks p overlap, further, the radial positions of the gate marks g and the protruding pin marks p may not overlap.

[0048] Note that the shaft seal of the present invention is not limited to the forms of FIGS. 1 to 6. For example, in FIGS. 1 to 6, the seal lip portion is formed in a straight line shape, but the seal lip portion may be formed in a curved shape. Further, a lip portion other than the seal lip portion and the outer lip portion (for example, a dust lip that slides with the rotating shaft) may be provided on the shaft seal.

[0049] In the compressor of FIG. 1, a compression mechanism portion is provided on the high-pressure side H of the housing 5. The form of the compression mechanism portion may be any mechanism in which fluid is compressed by the rotation of the rotating shaft, and a scroll type, a swash plate type, or the like can be adopted. For example, in the case of the scroll type, the compression mechanism portion is configured by combining a fixed scroll and a movable scroll that rotates 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 substrate 23a and a fixed scroll vane 23b standing upright on the surface thereof, and a movable rotor 24 having a substrate 24a and a movable scroll vane 24b standing upright on the surface thereof. The fixed rotor 23 and the movable rotor 24 are engaged with each other in an eccentric state, and a compression chamber 22 is formed therebetween. The movable rotor 24 is directly or indirectly connected to the above-described rotating shaft. As the movable rotor 24 revolves around the axis of the fixed rotor 23, the compression chamber 22 moves toward the center side of the spiral shape, and the fluid is compressed. The compressed fluid is discharged from the discharge pipe through the discharge port 25 at the center of the movable rotor 24 and flows out into the refrigeration cycle. Then, the fluid (such as refrigerant gas) of the refrigeration cycle is introduced into the compression chamber 22 through an inlet (not shown).

[0051] The shaft seal of the present invention is preferably formed of a molded body of a thermoplastic elastomer composition mainly composed of a polyester-based elastomer. As described above, the shaft seal of the present invention has no gate mark on the substantially U-shaped inner surface and has a gate mark on the substantially U-shaped outer surface. The shaft seal may have a protruding pin mark on the substantially U-shaped inner surface. In such a configuration, it is difficult to remove the shaft seal from the injection mold without force, but by using a polyester-based elastomer as the main component, it is possible to easily remove it without force. The polyester-based elastomer includes a hard segment and a soft segment, and a polyester unit is used for the hard segment, and a polyether unit or a polyester unit is used for the soft segment. The polyester-based elastomer is a polyester-polyether type or polyester-polyester type multi-block copolymer.

[0052] The polyester unit of the hard segment preferably mainly consists of an aromatic polyester unit. The aromatic polyester unit is usually a polyester unit 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 its ester derivative can be used. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid (for example, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid), 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and the like. Examples of the ester derivative of the aromatic dicarboxylic acid include alkyl esters (such as methyl ester, ethyl ester) of the above aromatic dicarboxylic acid, aryl esters, carbonate esters, and the like. The aromatic dicarboxylic acid component may be used alone or in combination of two or more.

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

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

[0056] As the diol component, for example, a diol or its ester derivative can be used. Examples of the diol include aliphatic diols such as ethylene glycol, 1,4-butanediol, 1,6-hexanediol, and alicyclic diols such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol. Examples of the ester derivative of the diol 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 the structural unit containing a naphthalene ring, a polybutylene naphthalate unit is particularly more 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 having a polybutylene naphthalate unit may be formed only of the polybutylene naphthalate unit, or may be formed including other structural units (for example, polybutylene isophthalate unit).

[0058] The polyether unit of the soft segment contains, 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 included alone or in combination of two or more.

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

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

[0061] [Chemical formula]

[0062] When using a hard segment composed of an aromatic polyester containing a naphthalene ring in the molecule, such as the Perprene EN type, the chemical resistance and oil resistance of the polyester-based elastomer can be improved compared to the case where it does not contain a naphthalene ring. Therefore, it is suitable for the shaft seal of the rotating shaft of a compressor used in the presence of a fluid in which a refrigerant and refrigerating machine oil are mixed.

[0063] In the polyester-based elastomer, the ratio of the hard segment to the soft segment in the copolymerization is not particularly limited. However, as the ratio of the hard segment increases, the elastic modulus increases. Therefore, it is adjusted so that the flexural modulus of the thermoplastic resin elastomer composition is in the range of 200 MPa to 2400 MPa. In addition, since it is easy to make the flexural modulus of the molded body within a desired range, it is preferable to use an elastomer having a flexural modulus (ASTM D790) of 150 MPa to 1700 MPa for the polyester-based elastomer.

[0064] For the thermoplastic elastomer composition according to the present invention, with respect to 100% by volume of the thermoplastic elastomer composition, the polyester-based 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.

[0065] In the thermoplastic elastomer composition according to the present invention, with respect to 100% by volume of the thermoplastic elastomer composition, the PTFE resin is preferably contained in an amount of 1% by volume to 40% by volume. The PTFE resin is a solid lubricant, and by blending 1% by volume or more, the coefficient of kinetic friction of the molded body of the thermoplastic elastomer composition can be reduced. On the other hand, when the content of the PTFE resin exceeds 40% by volume, the elongation characteristics of the thermoplastic elastomer composition deteriorate, and there is a risk of cracking when the shaft seal is incorporated into the rotating shaft. More preferably, the content of the PTFE resin is 1% by volume to 10% by volume.

[0066] The thermoplastic elastomer composition according to the present invention may be blended with solid lubricants other than the PTFE resin such as graphite and molybdenum disulfide. Graphite is a solid lubricant and can reduce the coefficient of kinetic friction of the molded body of the thermoplastic elastomer composition. As the graphite, either natural graphite or artificial graphite may be used.

[0067] In addition, to the extent that the effects of the present invention are not inhibited, 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 whisker may be used in the thermoplastic elastomer composition. Colorants such as carbon black and iron oxide can also be blended. These can be blended alone or in combination.

[0068] The shaft seal of the present invention is suitable when formed of a material with high flexibility and softness, but can also be used when formed of a material with low flexibility and hardness. Note that the flexibility can be defined by the flexural modulus.

[0069] As the material for forming the shaft seal of the present invention, it is preferable that the flexural modulus measured in accordance with ASTM D790 is 200 MPa to 2400 MPa. When the flexural modulus is 200 MPa to 2400 MPa, it becomes easy to perform forced ejection without damaging or deforming the seal lip of the shaft seal in the ejection process of the molded body in injection molding. Further, when the flexural modulus is less than 200 MPa, it tends to wear easily and the sealing performance tends to deteriorate. Further, when the flexural modulus exceeds 2400 MPa, the pressing force of the shaft seal against the rotating shaft becomes high and tends 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 form of the shaft seal of the present invention is an injection molded body of a thermoplastic elastomer composition in which a PTFE resin is blended with a polyester-based elastomer, and the polyester-based elastomer is a copolymer of a hard segment containing polybutylene naphthalate units and a soft segment containing aliphatic polyether units. The PTFE resin is contained in an amount of 1 to 10% by volume based on 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 of an in-vehicle air conditioner. The scroll compressor may be either belt drive using engine power or motor drive not using engine power. Further, the shaft seal of the present invention can be used not only for compressors.

Industrial Applicability

[0072] The shaft seal of the present invention has no risk of crack generation from gate marks and does not deform even when forced out of an injection mold, so it can be widely used as a shaft seal for sealing a sealing fluid while slidingly contacting the outer peripheral surface of a rotating shaft. In particular, it is suitable for the shaft seal of a rotating shaft that rotates the compression mechanism portion of a scroll refrigerant compressor of an in-vehicle air conditioner.

Explanation of Symbols

[0073] Single-axis seal Two seal lip parts Fixing part Base end part Housing Single-axis seal Two seal lip parts Fixing part Base end part Compression mechanism part Compression chamber Fixed rotor Rotating rotor Discharge port A substantially U-shaped inner surface B substantially U-shaped outer surface Rotating shaft Gate mark Protruding pin mark

Claims

1. An annular shaft seal that seals a sealing fluid in close contact with the outer peripheral surface of a rotating shaft, wherein the shaft seal is an injection molded body having a substantially U-shaped cross section in the axial direction, includes a seal lip portion that extends to one side in the axial direction and slides on the rotating shaft, a fixing portion provided on the outer diameter side of the seal lip portion, and a base end portion that connects the seal lip portion and the fixing portion, and the shaft seal is characterized in that it does not have a gate mark on the inner surface of the substantially U shape and has the gate mark on the outer surface of the substantially U shape.

2. The shaft seal according to claim 1, wherein the gate mark is formed on the outer surface of the base end portion of the outer surface of the substantially U shape.

3. The shaft seal according to claim 1 or claim 2, wherein the shaft seal has a protruding pin mark on the inner surface of the substantially U shape, and the protruding pin mark is formed on the inner surface of the base end portion of the inner surface of the substantially U shape.

4. The shaft seal according to claim 3, wherein in the shaft seal, the circumferential positions of the gate mark and the protruding pin mark do not overlap.

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

6. The shaft seal according to claim 5, wherein in the shaft seal, the radial position of the gate mark is located on the outer diameter side of the radial position of the protruding pin mark.

7. The shaft seal according to claim 1 or claim 2, wherein the fixing portion has a lip shape.

8. The shaft seal according to claim 1 or claim 2, wherein the shaft seal is a molded body of a thermoplastic elastomer composition mainly composed of a polyester-based elastomer.

9. The shaft seal according to claim 1 or claim 2, wherein the shaft seal is used in a scroll compressor including a compression mechanism combining a fixed scroll and a movable scroll that rotates relative to the fixed scroll, and the rotating shaft is a rotating shaft that drives the compression mechanism.

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