Patent Description:
Blow molding ("hot parison" process) apparatuses are one of commonly known apparatuses for producing resin containers. In a "hot parison" process blow molding apparatus, preforms are blow-molded into resin containers as the preforms are intermittently transferred sequentially from one to another of an injection molding unit, a temperature adjusting unit, and a blow molding unit, on a rotating transfer plate. The above blow molding apparatus forms resin containers by utilizing the residual heat contained in injection-molded preforms, which offers advantage over a "cold parison" process in producing a wide variety of resin containers with good appearance.

For the molds used for injection molding, there have been proposed a configuration, for example, in which solid lubricants are embedded in each of sliding surfaces of guide holes used for guiding a mold when the mold is opened and closed, and sliding surfaces of a sliding mold (e.g., Patent Literature <NUM>), and a configuration in which a lubricant-impregnated member is accommodated in a groove formed in a surface that makes contact with a moving mold used for removing the molded piece from a core (e.g., Patent Literature <NUM>).

<CIT> discloses a self-lubricating metallic matrix for injection molding.

<CIT> discloses a locking finger for a unit for moulding containers made of thermoplastic material.

<CIT> discloses a guide column bearing, e.g. for moving platens on an injection molding machine, that includes lubrication with viscous lubricant in addition to a solid lubricant.

<CIT> discloses a mold device, along with an injection molding apparatus and an injection molding method.

<CIT> discloses a self-lubricating sliding body.

<CIT> discloses a mold for plastic molding and an injection molding method.

The mold used in the blow molding apparatus described above is made up of a plurality of mold components, many of which are driven by actuators. These mold components must be positioned precisely relative to the preform when the mold is closed for favorable molding of the preforms or resin containers.

In the above blow molding apparatus, mold components that face each other have inclined surfaces, for example, which slide against one another, to ensure accuracy in positioning the mold components that hold and transfer the preforms and other mold components. In such a case, it is essential to apply a lubricant on the sliding surfaces so as to prevent abnormal wear (galling) of the mold components. Application of lubricant to numerous parts of a blow molding apparatus is a cumbersome task. Absence of lubricant by oversight can significantly increase risk of damage to the mold components.

Accordingly, the present invention was made in view of this problem, and aims at providing a mold that can reduce the workload of lubricant application while preventing galling on surfaces between a mold that holds preforms and another mold.

The present invention in one aspect resides in a mold including a first mold for receiving a neck mold that holds a neck part of a resin preform having a bottom, and for enclosing the preform inside, and a second mold inserted into the neck mold, at least one of a first sliding surface between the neck mold and the first mold and a second sliding surface between the neck mold and the second mold including a solid lubricant embedded therein.

According to one aspect of the present invention, the workload of lubricant application is reduced, and galling on surfaces between a mold that holds preforms and another mold can be prevented.

One embodiment of the present invention is described below with reference to the drawings.

For ease of understanding of the embodiment, description of the structures and elements other than primary features of the present invention will be simplified or omitted. Same elements in the drawings are given the same reference numerals. It should be understood that the drawings are schematics of various elements and not illustrations of actual shapes and dimensions.

<FIG> is a schematic diagram illustrating the configuration of the blow molding apparatus in one embodiment. The blow molding apparatus in this embodiment is a "hot parison" process (herein also referred to as a one-stage process) apparatus in which preforms are not cooled down to room temperature and blow-molded into containers utilizing the residual heat (internal energy) from the injection molding step retained in the preforms.

The blow molding apparatus <NUM> preferably includes four molding stations, specifically, an injection molding unit <NUM>, a temperature adjusting unit <NUM>, a blow molding unit <NUM>, an ejection unit <NUM>, and a transfer mechanism <NUM>. The injection molding unit <NUM>, temperature adjusting unit <NUM>, blow molding unit <NUM>, and ejection unit <NUM> are disposed in positions rotated by a predetermined angle (of, for example, <NUM> degrees) around the transfer mechanism <NUM>.

The transfer mechanism <NUM> includes a rotating plate 26a (not shown in <FIG>) that rotates around an axis perpendicular to the paper plane of <FIG>. On the rotating plate 26a are arranged neck molds <NUM> (not shown in <FIG>) that hold neck parts <NUM> of preforms <NUM> or resin containers (hereinafter simply "container") <NUM>, one or more at every predetermined angle. The transfer mechanism <NUM> rotates the rotating plate 26a and transports preforms <NUM> (or containers <NUM>), held by the neck molds <NUM> at their neck parts <NUM>, sequentially from one to another of the injection molding unit <NUM>, temperature adjusting unit <NUM>, blow molding unit <NUM>, and ejection unit <NUM>. The transfer mechanism <NUM> is also able to move the rotating plate 26a up and down, and to perform operations relating to the closing and opening of the mold (demolding) of the preforms <NUM> in the injection molding unit <NUM>.

The injection molding unit <NUM> includes an injection mold cavity <NUM> and an injection mold core <NUM> as shown in <FIG> and produces preforms <NUM>. As shown in <FIG>, to the injection molding unit <NUM> is connected an injection device <NUM> that melts and supplies resin material that is the raw material of the preforms <NUM>.

The preform <NUM> has an overall cylindrical shape with a bottom, one end open and the other end closed, as shown in <FIG>. A neck part <NUM> is formed at the open end of the preform <NUM>.

The container and preform <NUM> are made of a thermoplastic synthetic resin. The material may be selected as suited in accordance with the specifications of the container. Concrete examples of the material include PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PCTA (polycyclohexylenedimethylene terephthalate), Tritan (registered trademark, copolyester made by Eastman Chemical Company), PP (polypropylene), PE (polyethylene), PC (polycarbonate), PES (polyethersulfone), PPSU (polyphenylsulfone), PS (polystylene), COP/COC (cyclic olefin polymer/copolymer), PMMA (polymethyl methacrylate or acrylic), PLA (polylactic acid), and so on. Additives such as colorant may be added to these resin materials as required.

<FIG> is a diagram illustrating a state before the mold is closed in the injection molding unit <NUM>, and <FIG> is a diagram illustrating a state after the mold has been closed in the injection molding unit <NUM>.

The injection mold cavity <NUM> is the mold that defines the outer contour of the preform <NUM> except the neck part <NUM> and receives the neck mold <NUM> (i.e., the injection mold cavity <NUM> abuts against or engages with the neck mold <NUM>). The inner circumference of the neck mold <NUM> serves as the mold that defines the shape of the neck part <NUM> of the preform <NUM>. The injection mold core <NUM> is the mold that defines the inner contour of the preform <NUM>. The injection mold core <NUM> is inserted into the neck mold <NUM> from above in the drawing, with the neck mold <NUM> being set on the injection mold cavity <NUM> and the molds are closed. The injection mold cavity <NUM> is one example of a first mold, and the injection mold core <NUM> is one example of a second mold.

In the injection molding unit <NUM>, the injection mold cavity <NUM>, injection mold core <NUM>, and the neck mold <NUM> of the transfer mechanism <NUM> are clamped together to form a mold cavity conforming to the shape of the preform. Preforms <NUM> are produced at the injection molding unit <NUM> by injecting resin material from the injection device <NUM> into this mold cavity in the shape of the preform as shown in <FIG>.

Solid lubricants (solid lubricants) <NUM> are embedded in respective first sliding surfaces between the neck mold <NUM> and injection mold cavity <NUM>, and second sliding surfaces between the neck mold <NUM> and injection mold core <NUM>. These solid lubricants embedded in respective sliding surfaces can minimize galling of the mold components in the injection molding unit <NUM>.

For example, as shown in <FIG>, a plurality of solid lubricants <NUM> are embedded at equal intervals in an annular form along the outer circumference of the injection mold core <NUM> in a tapered proximal end part 32a of the injection mold core <NUM> that slides against the inner circumferential surface 27b of the neck mold <NUM>. Similarly, a plurality of solid lubricants <NUM> are embedded at equal intervals in an annular form along the inner circumference of the injection mold cavity <NUM> in a tapered bearing surface 31a of the injection mold cavity <NUM> that receives the neck mold <NUM>.

In each sliding surface, the solid lubricants <NUM> are arranged at intervals also in the axial direction along which the components slide against each other. The number of solid lubricants arranged in the axial direction is suitably set in accordance with the axial length of the sliding surface.

<FIG> is a diagram illustrating the outer appearance of the neck mold <NUM>. <FIG> is a longitudinal cross-sectional view of <FIG> is a lateral cross-sectional view of line IIIc-IIIc in <FIG> is a lateral cross-sectional view of line IIId-IIId in <FIG>.

As shown in <FIG>, a plurality of solid lubricants <NUM> are embedded in the outer circumferential surface 27a of the neck mold <NUM> that faces the bearing surface 31a of the injection mold cavity <NUM>. As shown in <FIG>, the solid lubricants <NUM> embedded in the outer circumferential surface 27a of the neck mold <NUM> are arranged at equal intervals in an annular form along the outer circumference of the neck mold <NUM>. Similarly, a plurality of solid lubricants <NUM> are embedded in the inner circumferential surface 27b of the neck mold <NUM> that faces the proximal end part 32a of the injection mold core <NUM> as shown in <FIG>. As shown in <FIG>, the solid lubricants <NUM> embedded in the inner circumferential surface 27b of the neck mold <NUM> are arranged at equal intervals in an annular form along the inner circumference of the neck mold <NUM>.

The solid lubricant <NUM> described above is made of powder containing, for example, a main ingredient such as carbon material powder, graphite powder, molybdenum sulfide, polytetrafluoroethylene, paraffin, or the like and a binder, and produced by sintering the powder that has been packed and molded into a predetermined shape and demolded. The solid lubricants <NUM> may be anchored to the mold components by press-fitting them into the mold components, or may be fixed using an adhesive.

Solid lubricants <NUM> similar to those in the injection molding unit <NUM> are given the same reference numeral and repetitive descriptions of their configuration will be omitted in the following.

The neck mold <NUM> of the transfer mechanism <NUM> stays closed even after the molds are opened in the injection molding unit <NUM>, and keeps holding the neck part <NUM> and transfers the preform <NUM>. The number of preforms <NUM> that can be molded simultaneously in the injection molding unit <NUM> (i.e., the number of containers <NUM> that can be molded simultaneously in the blow molding apparatus <NUM>) may be suitably set.

The temperature adjusting unit <NUM> adjusts the temperature of the preform <NUM> produced at the injection molding unit <NUM> to temperature suited for final blowing (about <NUM> to <NUM>, for example) by making the temperature of the preform <NUM> uniform or by removing temperature variations. The temperature adjusting unit <NUM> also serves to cool down hot preforms <NUM> after the injection molding.

As shown in <FIG>, the temperature adjusting unit <NUM> includes a cavity <NUM> and a core <NUM>. The cavity <NUM> is one example of a first mold, and the core <NUM> is one example of a second mold.

The cavity <NUM> is a mold having a temperature adjusting space 41a of substantially the same shape as that of the preform <NUM> produced at the injection molding unit <NUM>, i.e., is able to accommodate a preform <NUM> inside. Air outlet holes 41c are formed in a bottom part of the temperature adjusting space 41a of the cavity <NUM> for letting out the air as the preform <NUM> is being inserted.

The core <NUM> is a mold to be inserted into the preform <NUM>, and disposed such as to be moved to and from the neck mold <NUM> holding the preform <NUM> at the temperature adjusting unit <NUM>. In <FIG>, the core <NUM> is retracted and not shown. <FIG> on the other hand shows a state in which the core <NUM> has moved downward in the drawing and is inserted into the neck mold <NUM>.

The cavity <NUM> and the core <NUM> each have a flow passage (not shown) inside for a temperature adjusting medium (cooling medium) to flow through. Therefore the cavity <NUM> and the core <NUM> are maintained at a predetermined temperature by the temperature adjusting medium flowing inside. The preform <NUM> at the temperature adjusting unit <NUM> is adjusted to a predetermined temperature by heat exchange between the cavity <NUM> facing the preform on the outside and the core <NUM> facing the preform on the inside.

Solid lubricants <NUM> are embedded in respective first sliding surfaces between the neck mold <NUM> and the cavity <NUM>, and second sliding surfaces between the neck mold <NUM> and the core <NUM>. These solid lubricants <NUM> embedded in respective sliding surfaces can minimize galling of the mold components in the temperature adjusting unit <NUM>.

For example, as shown in <FIG>, a plurality of solid lubricants <NUM> are embedded at equal intervals in an annular form along the outer circumference of the core <NUM> in a tapered proximal end part 42a of the core <NUM> that slides against the inner circumferential surface 27b of the neck mold <NUM>. Similarly, as shown in <FIG>, a plurality of solid lubricants <NUM> are embedded at equal intervals in an annular form along the inner circumference of the cavity <NUM> in a tapered bearing surface 41b of the cavity <NUM> that receives the neck mold <NUM>. As described in the foregoing, solid lubricants <NUM> are embedded in the outer circumferential surface 27a and inner circumferential surface 27b of the neck mold <NUM> that transfers the preform <NUM>.

Referring back to <FIG>, the blow molding unit <NUM> performs blow molding to the preform <NUM> that is temperature-adjusted at the temperature adjusting unit <NUM>, to produce containers.

The blow molding unit <NUM> includes a blow mold cavity <NUM> that is a pair of split mold halves corresponding to the shape of the container <NUM>, a bottom mold <NUM>, and an air injection member (not shown) that doubles as a stretch rod. <FIG> illustrates a state before the blow mold cavity <NUM> and bottom mold <NUM> are closed, and <FIG> illustrates a state after the blow mold cavity <NUM> and bottom mold <NUM> have been closed.

The blow mold cavity <NUM> is a mold part that defines the shape of the container <NUM> except for the bottom surface. The blow mold cavity <NUM> is split in a parting plane along the up-down direction in <FIG> and configured to be opened and closed in the left-right direction in <FIG>. The blow mold cavity <NUM> is one example of a first mold.

The bottom mold <NUM> is a mold that defines the shape of the bottom surface of the container <NUM> and is disposed below the blow mold cavity <NUM>. A mold cavity that defines the shape of the container <NUM> is formed by the bottom mold <NUM> and the blow mold cavity <NUM> being closed. The bottom mold <NUM> waits below the preform <NUM> where it does not touch the bottom of the preform <NUM> before the blow mold cavity <NUM> is closed, for example, and is driven to move up quickly to a molding position (<FIG>) after the mold is closed.

The air injection member, which is a hollow tubular body for blowing air into the preform, is brought into contact with the neck part of the preform. The air injection member is movable up and down in the drawing and serves to stretch the preform <NUM> along the vertical axis by moving down. The air injection member is one example of a second mold.

Solid lubricants <NUM> are embedded in third sliding surfaces between the blow mold cavity <NUM> and the bottom mold <NUM>. These solid lubricants <NUM> embedded in the sliding surfaces can minimize galling of the mold components of the blow mold cavity <NUM> and bottom mold <NUM>. Although not shown in <FIG>, solid lubricants <NUM> are embedded in respective first sliding surfaces between the blow mold cavity <NUM> and the outer circumferential surface 27a of the neck mold <NUM>, and second sliding surfaces between the inner circumferential surface 27b of the neck mold <NUM> and the air injection member.

For example, as shown in <FIG>, a plurality of solid lubricants <NUM> are embedded at equal intervals in an annular form along the outer circumference of the bottom mold <NUM> in a cylindrical or tapered proximal end part (contact part) 52a of bottom mold <NUM> that slides against the blow mold cavity <NUM>. On the other hand, a plurality of solid lubricants <NUM> are embedded at equal intervals in an annular form along the inner circumference of a cylindrical or tapered opening 51a in the blow mold cavity <NUM> that receives the proximal end part 52a of the bottom mold <NUM> (bearing surface that receives the proximal end part 52a of the bottom mold <NUM>).

The bottom mold <NUM> further includes a forming part 52c that defines the bottom surface shape of the container <NUM>, a cylindrical or tapered middle part 52b that connects the forming part 52c and the proximal end part 52a, and a step 52d that connects the middle part 52b and the proximal end part 52a and defines an uppermost position of the bottom mold <NUM>. The proximal end part 52a has a larger diameter than the middle part 52b. The blow mold cavity <NUM> further includes a second opening 51b that is cylindrical or tapered in a portion that faces or opposes the middle part 52b when the mold is closed. The opening 51a has a larger diameter than the second opening 51b. No solid lubricants <NUM> are embedded in the outer circumferential surface of the middle part 52b and the inner circumferential surface of the second opening 51b and they are configured such that there is a predetermined gap between them, this gap serving as an air vent.

The ejection unit <NUM> is configured to release the neck part <NUM> of the container produced at the blow molding unit <NUM> from the neck mold <NUM> and allow the container to be taken out of the blow molding apparatus <NUM>.

Next, a blow molding method using the blow molding apparatus <NUM> of this embodiment is described.

<FIG> is a flowchart illustrating the steps of the blow molding method.

First, resin material is injected from the injection device <NUM> into the mold cavity formed by the injection mold cavity <NUM>, injection mold core <NUM>, and the neck mold <NUM> of the transfer mechanism <NUM> at the injection molding unit <NUM> to produce a preform <NUM>.

After the molds are opened in the injection molding unit <NUM>, the rotating plate 26a of the transfer mechanism <NUM> rotates a predetermined angle so that the preform <NUM> held by the neck mold <NUM> and containing the residual heat from the injection molding step is transferred to the temperature adjusting unit <NUM>.

Next, at the temperature adjusting unit <NUM>, the temperature of the preform <NUM> is adjusted to be closer to a temperature suitable for final blow molding.

In the temperature adjusting step, first, the preform <NUM> is accommodated inside the temperature adjusting space 41a of the cavity <NUM>. Next, the core <NUM> is inserted into the preform <NUM> held in the cavity <NUM>.

Since the cavity <NUM> and the core <NUM> are configured to conform to the shape of the preform <NUM>, the preform <NUM> remains in a desired shape even during the temperature adjusting step.

The preform <NUM> faces the cavity <NUM> and the core <NUM> during the temperature adjusting step so that the temperature of the preform <NUM> is adjusted such as not to fall below a temperature suitable for blow molding, and also any unevenness in temperature that occurred during the injection molding is reduced.

After that, the rotating plate 26a of the transfer mechanism <NUM> rotates a predetermined angle so that the preform <NUM>, whose temperature has been adjusted, held by the neck mold <NUM>, is transferred to the blow molding unit <NUM>.

Next, blow molding of a container <NUM> is performed at the blow molding unit <NUM>.

First, the blow mold cavity <NUM> is closed to accommodate the preform <NUM> in the mold cavity. In the case where the preform <NUM> is longer than the container <NUM>, the bottom mold <NUM> waits below far enough not to touch the bottom part of the preform <NUM> before the blow mold cavity <NUM> is closed. After the blow mold cavity <NUM> is closed, the bottom mold <NUM> is then quickly lifted to a molding position.

The air injection member (blow mold core) is brought down approximately at the same time as the blow mold cavity <NUM> and bottom mold <NUM> are closed, and brought into contact with the neck part <NUM> of the preform <NUM>. The stretch rod is moved down to press the bottom part of the preform <NUM> from inside, and air is blown into the preform from the air injection member to stretch the preform <NUM> inside the mold cavity in the horizontal axis, while also stretching the preform in the vertical axis as required. The preform <NUM> is thus inflated to make tight contact with the mold cavity formed by the blow mold cavity <NUM> and the bottom mold <NUM> and formed into the desired shape, i.e., blow-molded into the container <NUM>.

After the blow molding has ended, the molds are opened in the blow molding unit <NUM>. This allows the container <NUM> to be moved away from the blow molding unit <NUM>.

Successively, the rotating plate 26a of the transfer mechanism <NUM> rotates a predetermined angle so that the container <NUM> is transferred to the ejection unit <NUM>. At the ejection unit <NUM>, the neck part <NUM> of the container <NUM> is released from the neck mold <NUM>, and the container <NUM> is taken out of the blow molding apparatus <NUM>.

A series of blow molding process steps is thus complete. The rotating plate 26a of the transfer mechanism <NUM> is then rotated a predetermined angle, whereupon the steps S101 to S104 described above are repeated.

The present invention is not limited to the embodiment described above. Various improvements and design changes may be made without departing from the subject matter of the present invention.

In the above embodiment, one example was described in which solid lubricants <NUM> are embedded in both of the two mold components sliding against each other. Instead, the solid lubricants <NUM> may be embedded in only one of the two mold components sliding against each other. Alternatively, the mold for the injection molding, for example, may have solid lubricants <NUM> embedded in one of the first sliding surface between the neck mold <NUM> and the injection mold cavity <NUM> and the second sliding surface between the neck mold <NUM> and the injection mold core <NUM>, and may not have solid lubricants in the other.

A blow molding apparatus <NUM> that uses the mold according to the present invention may be equipped with a plurality of injection molding units upstream of the temperature adjusting unit <NUM> to mold multilayer preforms <NUM> by performing injection molding twice or more, for example (which would be a "hot parison" process blow molding apparatus with <NUM> or <NUM> molding stations). Another alternative is an apparatus configuration without the temperature adjusting unit <NUM> (which would be a "hot parison" process blow molding apparatus with three molding stations, i.e., an injection molding unit <NUM>, a blow molding unit <NUM>, and an ejection unit <NUM>).

The mold according to the embodiment may also be applied to a blow molding apparatus without an injection molding unit. <FIG> is a diagram illustrating a schematic configuration of a two-stage ("cold parison") process blow molding apparatus 20a.

The blow molding apparatus 20a includes a preform supply unit <NUM>, a blow molding unit <NUM>, a heating unit <NUM> (temperature adjusting unit 22a in a broader sense), a transfer mechanism <NUM>, and a container ejection unit <NUM>. The heating unit <NUM> includes a looped heated transfer path, and a heating device (not shown) such as an infrared heater that can heat up the body part of the preform to a temperature suitable for blowing. The transfer mechanism <NUM> includes a first holding member 26a1 disposed in the heating unit <NUM> for holding a preform received from the preform supply unit <NUM> and transports the same, a second holding member 26b1 that receives the preform from the heating unit <NUM> and transports the same to the blow molding unit <NUM>, and a third holding member 26c1 that transports the container from the blow molding unit <NUM> to the container ejection mechanism <NUM>. The mold used in the blow molding unit <NUM> of the blow molding apparatus 20a has the same configuration as that of the embodiment described in the foregoing.

The preform supply unit <NUM> receives preforms (made of PET, for example) that were produced and prepared beforehand in an injection molding apparatus elsewhere, and loads the same onto the first holding member 26a1. The container ejection unit <NUM> includes a container holding part (not shown) disposed adjacent the blow molding unit <NUM> for receiving containers that were produced in the blow molding unit <NUM> and transported thereto by the third holding member 26c1. The heating unit <NUM> heats the preform held on the first holding member 26a1, as the preform is spun and transported inside the heating device.

In this blow molding apparatus 20a, preforms fed by the preform supply unit <NUM> are heated in the heating unit <NUM> up to a temperature suited for blowing (<NUM> to <NUM>, for example), after which the preforms are transferred to the blow molding unit <NUM>. In the blow molding unit <NUM>, the preform is accommodated in a mold made up of a blow mold cavity <NUM> and a bottom mold <NUM>, and blow-molded into a container of a desired shape. After the blow molding, the containers are transferred to the container ejection unit <NUM>.

The mold according to the embodiment may also be applied to an injection molding apparatus without a blow molding unit. <FIG> is a schematic diagram illustrating the configuration of a two-stage injection molding apparatus <NUM>.

The injection molding apparatus <NUM> includes an injection molding unit <NUM>, an ejection unit <NUM>, a cooling unit <NUM> (temperature adjusting unit 22a in a broader sense), and a transfer mechanism <NUM>. The cooling unit <NUM> includes a cooling pot (not shown) that accommodates the preform to cool the body part of the preform from outside, and a cooling rod (not shown) inserted into the hollow body part of the preform to cool the body part from inside. The transfer mechanism <NUM> includes a first holding member 26a1 that transports the preform from the injection molding unit <NUM> to the cooling unit <NUM>, and a second holding member 26b1 that transports the preform from the cooling unit <NUM> to the ejection unit <NUM>. To the injection molding unit <NUM> is connected an injection device <NUM>. The mold used in the injection molding unit <NUM> of the injection molding apparatus <NUM> has the same configuration as that of the embodiment described in the foregoing.

Claim 1:
A mold comprising:
a first mold (<NUM>, <NUM>, <NUM>) for receiving a neck mold (<NUM>) that holds a neck part (<NUM>) of a resin preform (<NUM>) having a bottom, and for enclosing the preform (<NUM>) inside; and
a second mold (<NUM>, <NUM>) inserted into the neck mold (<NUM>),
characterized in that at least one of a first sliding surface between the neck mold (<NUM>) and the first mold (<NUM>, <NUM>, <NUM>) and a second sliding surface between the neck mold (<NUM>) and the second mold (<NUM>, <NUM>) includes a solid lubricant (<NUM>) embedded therein.