JP7630498B2 - Magnetic recording tape having an elastic substrate - Google Patents

Description

The present invention relates to magnetic recording media, and more particularly to various configurations of substrates for magnetic recording tape media.

In a magnetic storage system, a magnetic transducer reads data from and writes data to a magnetic recording medium. Data is written to the magnetic recording medium by moving a magnetic recording transducer to a location on the medium where the data is to be stored. The magnetic recording transducer then generates a magnetic field that encodes and writes the data to the magnetic medium. Data is read from the medium by similarly positioning a magnetic read transducer and then sensing the magnetic field of the magnetic medium. To ensure that data can be read from and written to desired locations on the medium, read and write operations can be independently synchronized with the movement of the medium.

A continuing key goal of the data storage industry is to increase the density of data stored on the media. For tape storage systems, this goal has led to increasing the track and linear bit density on the recording tape, and decreasing the thickness of the magnetic tape media. However, the development of higher performance tape drive systems with smaller footprints has created a variety of challenges, ranging from designing tape head assemblies for use in such systems to dealing with dimensional instability of the tape.

One challenge that arises with increasing track and data density, and which is increasingly limiting formats, is the dimensional stability of the tape, especially in the lateral direction. Lateral contraction and expansion of the tape are well-known phenomena that arise from numerous effects, including water absorption, thermal expansion and contraction, etc. As the tape width changes, many undesirable consequences can result, including overwriting previously written data tracks when performing shingled writing, and the inability to read from data tracks that are no longer aligned with the reader (this is especially prevalent for tracks near the outer edges of the reader array).

More permanent changes in the lateral dimensions of the media may also occur, such as long-term media creep (also known in the art as "aging"). Long-term media creep tends to occur over time as the tape is wound around the hub of a tape cartridge. Long-term media creep is particularly problematic when dealing with tape dimensional stability issues, since the two ends of the tape exhibit different modes of creep. The inner wrap of the tape located closest to the cartridge hub tends to expand laterally over time due to compressive stresses imposed on the inner wrap by the wrap of tape wound around it. The wrap located closer to the outer diameter of the spool of tape is under less compressive stress, but experiences greater tensile stress, which tends to cause the tape to shrink laterally; i.e., the tape becomes narrower over time. Thus, both ends of the tape tend to exhibit opposing lateral dimensional changes.

Variations in tape dimensions can cause problems. They increase the likelihood of overwriting a single track while writing; overwritten data is often irrecoverable. Similarly, if the tape width changes after the desired data has been written, the reader may no longer be positioned over the track that is to be read, which can increase read errors.

The substrate is typically the thickest layer in a magnetic recording tape and therefore tends to have the greatest effect on the lateral stability of the tape. In other words, the substrate tends to dominate the overall laminate tape structure with respect to dimensional changes.

Current magnetic recording tape substrate materials, such as polyethylene naphthalate (PEN) and aramid, have a variety of problems, such as poor tape dimensional stability (TDS), sensitivity to humidity, poor creep recovery or other shortcomings, or a combination thereof, that render them inadequate to meet the demand for magnetic recording tapes having higher data densities than are currently available on the market.

Current substrates are reaching the limits of possible modifications to improve the substrate's sensitivity to water and temperature and solve the problems mentioned above.

Therefore, there is a need in this technical field to solve the above problems.

Viewed from a first aspect, the present invention provides a magnetic recording tape, the magnetic recording tape comprising a substrate including polyether ether ketone (PEEK), an underlayer on the substrate, and a recording layer on the underlayer.

Viewed from an additional aspect, the present invention provides a tape cartridge comprising a housing and a magnetic recording tape at least partially contained within the housing, the magnetic recording tape comprising a substrate comprising polyetheretherketone (PEEK), an underlayer on the substrate, and a recording layer on the underlayer.

In an additional aspect, the present invention provides a method of manufacturing a magnetic recording tape, the method comprising bonding an underlayer to a substrate, the substrate comprising polyetheretherketone (PEEK).

In an additional aspect, the present invention provides a method of manufacturing a magnetic recording tape, the method comprising bonding an underlayer to a substrate comprising polyetheretherketone (PEEK) by radiation-induced grafting, and bonding a recording layer to the underlayer.

A magnetic recording tape according to one approach includes a substrate comprising polyetheretherketone (PEEK). An underlayer is disposed over the substrate. A recording layer is disposed over the underlayer.

Magnetic recording tapes with PEEK substrates have excellent elasticity for normal tape operation and exhibit stable creep and recovery for normal storage and operating temperatures of about 0°C to about 60°C. Shrinkage of the PEEK substrate is expected to be less than 1% over a temperature range of 100°C, including the operating range noted above. Such advantages are achieved in preferred approaches where the chain length of the PEEK is greater than about 20, and more preferably where the chain length of the PEEK is about 50 to about 100.

Magnetic recording tape with a PEEK substrate also has low sensitivity to temperature and humidity throughout its operating range. PEEK is generally hydrophobic, which makes it stable to water. Water absorption is expected to be much less than 1% at 50% relative humidity, which is much lower than aramid, which tends to have a water absorption of about 10% at 50% relative humidity.

Magnetic recording tapes with PEEK substrates have stable mechanical properties. For example, both the tensile storage (E') modulus and the tensile loss (E"") modulus, measured using dynamic mechanical analysis techniques such as Dynamic Mechanical Thermal Analysis (DMTA) for typical operating and storage environments of the tape media, are lower than conventional media substrates. In one aspect, the tensile storage (E') modulus of the substrate, measured by dynamic mechanical thermal analysis, is in the range of about 4 GPa to about 20 GPa.

An additional advantage of PEEK is that the PEEK raw material can be melted without degradation, allowing it to be processed into thin films at temperatures near its melting point without losing its desirable properties.

In one embodiment, the underlayer is grafted to the substrate. This grafting results in a stronger bond between the layers than traditional bonding techniques. This is advantageous in terms of robustness and resistance to stress.

Each of the above is important for maintaining dimensional stability both during use and long-term storage.

A tape cartridge according to one embodiment includes a housing and a magnetic recording tape at least partially contained within the housing. The magnetic recording tape has the structure described above.

Other aspects and approaches of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate the principles of the invention.

The invention will now be described, by way of example only, with reference to preferred embodiments illustrated in the following figures:

1 is a schematic diagram of a simplified tape drive system. 1 is a schematic diagram of a tape cartridge according to one aspect of the present invention. FIG. 1 is a side view of a flat-lapped, bi-directional, two-module magnetic tape head in accordance with one aspect of the present invention. FIG. 2B is a view of the tape bearing surface taken from line 2B of FIG. 2A. FIG. 2C is a detail view taken from circle 2C of FIG. 2B. FIG. 1 illustrates a tape layout according to one approach. FIG. 2 illustrates a hybrid servo pattern written in a dedicated area of a tape medium according to one technique. FIG. 1 is a detailed view of a portion of a TBS pattern according to one technique. FIG. 13 is a partial top view showing the effects of tape expansion and contraction. FIG. 13 is a partial top view showing the effects of tape expansion and contraction. FIG. 13 is a partial top view showing the effects of tape expansion and contraction. 1A to 1C are partial cross-sectional views of the basic structure of magnetic recording media according to various techniques. 1 is a graph comparing dynamic mechanical thermal analysis (DMTA) results for tensile storage modulus (E') in gigapascals (GPa) over a temperature range for an example of the present tape substrate with an 8 micron thick PEEK film. 8 is a graph showing the data of FIG. 7 for a temperature range of 0° C. to 60° C. 1A-1D illustrate exemplary PEEK in various ways. 1A-1D illustrate exemplary PEEK in various ways. 1A-1D illustrate exemplary PEEK in various ways. 1A-1D illustrate exemplary PEEK in various ways.

The following description is provided to illustrate the general principles of the present invention and is not intended to limit the inventive ideas described herein. Also, specific features described herein can be used in combination with other features described, in each of the various possible combinations and permutations.

Unless otherwise defined herein, all terms are to be given their broadest possible interpretation, including the meaning implied by this specification, as well as the meaning understood by a person of ordinary skill in the art and/or defined in dictionaries, academic treatises, etc.

It should also be noted that, unless expressly stated otherwise, when used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents.

The following description discloses various configurations of substrates that are particularly useful in magnetic recording tape media, as well as methods of forming the substrates and magnetic recording tape media.

In one general approach, a magnetic recording tape includes a substrate comprising polyetheretherketone (PEEK). An underlayer is disposed over the substrate. A recording layer is disposed over the underlayer.

In another general approach, a tape cartridge includes a housing and a magnetic recording tape at least partially contained within the housing. The magnetic recording tape has the structure described above.

Exemplary Operating Environment Figure 1A illustrates a simplified tape drive 100 of a tape-based data storage system that may be used in connection with the present invention. Although one particular embodiment of a tape drive is illustrated in Figure 1A, it should be noted that the techniques described herein may be implemented in connection with any type of tape drive system.

As shown, a tape supply cartridge 120 and a take-up reel 121 are provided to support tape 122. One or more of these reels may form part of a removable cartridge and do not have to be part of tape drive 100. A tape drive such as the tape drive shown in FIG. 1A may further include a drive motor for driving tape supply cartridge 120 and take-up reel 121 to move tape 122 over any type of tape head 126. Such a head may include an array of readers or an array of writers, or both.

A guide 125 guides the tape 122 across a tape head 126. Such tape head 126 is coupled to a controller 128 via a cable 130. The controller 128 may be or may include a processor and/or any logic for controlling any subsystem of the drive 100. For example, the controller 128 typically controls head functions such as servo following, data writing, data reading, etc. The controller 128 may include at least one servo channel and at least one data channel, each of which includes data flow processing logic configured to process and/or store information written to and/or read from the tape 122. The controller 128 may operate under logic known in the art and disclosed herein, and thus may be considered a processor for any of the descriptions of tape drives in various ways contained herein. The controller 128 may be coupled to any type of known memory 136 that may store instructions executable by the controller 128. Additionally, the controller 128 may be configured to perform or control some or all of the methods presented herein, or may be programmable to perform or control them, or both. Thus, the controller 128 may be considered to be configured to perform various operations by, and combinations of, programmed logic in one or more chips, modules, or blocks, or combinations thereof; software, firmware, or other instructions available to one or more processors, or combinations thereof; and the like.

The cable 130 may include read/write circuitry for transmitting data to be recorded on the tape 122 to the tape head 126 and for receiving data from the tape 122 read by the tape head 126. An actuator 132 controls the position of the tape head 126 relative to the tape 122.

Additionally, an interface 134 may be provided for communication between the tape drive 100 and a host (internal or external) to send and receive data, and to control the operation of the tape drive 100 and communicate the status of the tape drive 100 to the host, all of which will be understood by those skilled in the art.

FIG. 1B illustrates an exemplary tape cartridge 150, which in various approaches can include any of the configurations of magnetic recording media described herein in the form of a tape. Such a tape cartridge 150 can be used with a system such as the system illustrated in FIG. 1A. As shown, the tape cartridge 150 includes a housing 152, a tape 122 within the housing 152, and an optional non-volatile memory 156 coupled to the housing 152. In some approaches, the non-volatile memory 156 can be embedded inside the housing 152, as illustrated in FIG. 1B. In more approaches, the non-volatile memory 156 can be attached to the inside or outside of the housing 152 without modifying the housing 152. For example, the non-volatile memory can be embedded in an adhesive label 154. In one preferred approach, the non-volatile memory 156 may be solid-state memory (e.g., flash memory), a read-only memory (ROM) device, or the like, embedded inside or outside the tape cartridge 150, or coupled to the inside or outside of the tape cartridge 150. This non-volatile memory may be accessed by the tape drive and tape operating software (driver software), or another device, or a combination of these.

2A, by way of example, illustrates a side view of a flat-wrap bi-directional two-module magnetic tape head 200 that may be implemented in conjunction with the present invention. As shown, the head includes a pair of bases 202, each with a module 204, fixed at a small angle α relative to one another. The bases may be "U-beams" bonded together with an adhesive. Each module 204 includes a substrate 204A and a closure 204B having a thin film portion, commonly referred to as a "gap," in which a reader and/or writer 206 is formed. In use, to read and write data on the tape 208 using the reader and writer, the tape 208 is moved over the modules 204 along a media (tape) support surface 209 as shown. The wrap angle θ of the tape 208 at the edge that rests on and exits the flat media support surface 209 is typically between about 0.1 degrees and about 3 degrees.

The substrate 204A is typically constructed of a wear-resistant material such as ceramic. The closure 204B can be made of the same ceramic as the substrate 204A or the same type of ceramic as the substrate 204A.

The readers and writers can be arranged in a piggyback or merged configuration. An exemplary piggyback configuration has a (magnetically inductive) writer transducer on top of (or underneath) a (magnetically shielded) reader transducer (such as a magnetoresistive reader), with the writer pole and reader shield generally being separate. An exemplary merged configuration has one writer pole and one reader shield in the same physical layer (hence the "merged" term). The readers and writers can also be arranged in an interleaved configuration. Alternatively, each array of channels can be only readers or only writers. Any of these arrays can include one or more servo track readers for reading servo data on the media.

Figure 2B shows the tape support surface 209 of one of the modules 204 taken from line 2B of Figure 2A. A typical tape 208 is shown in dashed lines. The module 204 is preferably long enough to support the tape as the head steps between the data bands.

In this example, the tape 208 includes 4 to 32 data bands, e.g., 16 data bands and 17 servo tracks 210 as shown in FIG. 2B on a 1/2 inch wide tape 208. The data bands are defined between the servo tracks 210. Each data band can include several data tracks, e.g., 1024 data tracks (not shown). During a read/write operation, the reader and/or writer 206 is positioned at a specific track location within a data band. An outer reader, sometimes called a servo reader, reads the servo tracks 210. These servo signals are then used to keep the reader and/or writer 206 aligned with a particular set of tracks during a read/write operation.

2C shows multiple readers and/or writers 206 formed in gaps 218 on module 204 in circle 2C of FIG. 2B. As shown, the array of readers and writers 206 includes, for example, 16 writers 214, 16 readers 216, and two servo readers 212, although the number of elements may vary. Exemplary approaches include 8, 16, 32, 40, and 64 active readers and/or writers 206 per array, or an interleaved design having an odd number of readers or writers, such as 17, 25, 33, etc. One exemplary approach includes 32 readers per array or 32 writers per array, or both, although the actual number of transducer elements may be greater than 32, for example, 33, 34, etc. This allows the tape to move slower, thereby reducing speed-induced tracking and mechanical difficulties, or to perform fewer "wraps" of the tape to fill or read the tape, or both. The readers and writers can be arranged in a piggyback configuration as shown in FIG. 2C, but the readers 216 and writers 214 can also be arranged in an interleaved configuration. Alternatively, each array of readers and/or writers 206 can be readers only or writers only, and the array can include one or more servo readers 212. It will be noted when considering FIGS. 2A and 2B-2C together that each module 204 can include a complementary set of readers and/or writers 206 for bidirectional reading and writing, read-while-writing capabilities, backward compatibility, etc.

Timing-Based Servo Write and read elements magnetize magnetic regions in a recording layer of a magnetic recording tape to form bits of magnetic segments that appear as rectangular sections that display increased or decreased magnetic signals when detected by a magnetically sensitive detector, such as a magnetic force microscopic (MFM) detector.

In order to place the data on separate tracks, real-time position information is required regarding the location of existing written information on the tape to prevent accidental erasure of previously written information. When data is first written to a blank, formatted tape, the position of the first data band must be carefully controlled and recorded to allow subsequent data bands to be accurately positioned so as not to overwrite or corrupt previously written data.

Modern high density tape formats use a highly accurate servo pattern known to those skilled in the art as a timing-based servo. A description of an exemplary timing-based servo scheme is provided below.

The track following servo includes transitions recorded in two or more azimuthal orientations across the width of the servo track. Signal timing derived by reading at any point across the width of a written pattern created on the tape media in a controlled and precise factory formatting operation is used to calculate the position of the magnetic recording head in real time. The pattern is read by a servo reader having a width that is small compared to the width of the servo track. The combination of a wide servo pattern and a narrow servo reader provides excellent position sensing linearity and dynamic range.

Position sensing with a timing-based servo system is achieved by deriving the ratio of two servo pattern spacings and is therefore insensitive to tape speed during readback of the recorded signal. Detection of the center of the servo pattern during tape motion provides a precise reference point for each data band. The difference between the centers of the two servo readers used in each read or write motion of the tape across the recording head is a measure of the spacing between the two servo bands on the tape that was previously recorded during factory formatting. The servo readers are fixed within the head structure but move on the very small nanometer scale due to stress and environmental factors. Thus, the actual positions of the spacing between the servo bands written on the tape move relative to each other, resulting in a change in the actual spacing between data bands that pre-exist or are written on top of existing data tracks.

Briefly referring to FIG. 3, an exemplary tape layout according to one approach is shown. As shown, the tape 300 has a tape layout that implements five servo bands, namely servo band 0 through servo band 4, and four data bands, namely data band 0 through data band 3, as defined in the LTO (LTO is a trademark of HP. IBM Corp. Quantum) format and the IBM® Enterprise format. IBM is a trademark of International Business Machines Corporation, registered in many jurisdictions worldwide. The height H of each servo band is measured in a cross-track direction 304 that is generally perpendicular to the length L of the tape 300. According to one example, the height H of each servo band may be approximately 186 microns according to the LTO format. Additionally, the pitch β between the servo bands shown may be approximately 2859 microns, also according to the LTO format.

Also shown is an exemplary tape head 302 having two modules and disposed over a portion of the tape 300 according to one approach. Read and/or write transducers can be disposed in any of the modules of the tape head 302 according to any of the approaches described herein, and the read and/or write transducers can be used to read data from and/or write data to the data bands. Additionally, according to any of the approaches described herein, the tape head 302 can include servo readers that can be used to read servo patterns in the servo bands. It should also be noted that the dimensions of the various components included in FIG. 3 are provided by way of example only, and are in no way intended to limit the invention.

Some tape drives may be configured to operate at low tape speeds or nanometer head position settings, or both. These tape drives may use barium ferrite (BaFe) tape media, four or eight data bands, 32 or 64 data channel operation, servo formats that allow very slow operation, support large bandwidth actuator operation, and improve parameter estimation to minimize the standard deviation of the position error signal (PES), thereby enabling track density scaling for tape cartridge capacities of 100 TB or more.

However, according to some approaches, magnetic tape can be further augmented with additional features that provide additional functionality. Accordingly, instead of the standard TBS servo pattern as shown in FIG. 3, for example, an HD servo pattern can be implemented. This HD servo pattern can be used to improve track following performance.

In yet another approach, a standard TBS servo pattern (e.g., as shown in FIG. 3) may be implemented in combination with one or more HD servo patterns (see, e.g., FIG. 4A below). One embodiment includes a hybrid servo pattern scheme in which the standard TBS pattern is maintained and additional HD patterns are provided in a dedicated area of the tape media, preferably an area that is not currently in use. In some approaches, this type of pattern may be implemented by increasing the number of data channels from 16 to 32 and reducing the width of the TBS pattern from 186 microns to 93 microns.

Figure 4A shows a hybrid servo pattern 410 including a standard TBS pattern 402 written in a servo band of a tape medium 408 and an HD pattern 404 written in an HD band (e.g., a dedicated area). Each HD pattern 404 further includes several HD tracks, each having a respective periodic waveform. In some approaches, important features of the original TBS pattern 402 are maintained, such as a servo frame structure consisting of four servo bursts containing several servo stripes. These servo bursts are written with alternating azimuth angles of the servo stripes of adjacent servo bursts. Other parameters of the conventional servo pattern, such as the height and other geometric dimensions of the servo pattern and the number of servo stripes per burst, can be changed as desired.

The HD pattern 404 may include periodic waveforms of various frequencies written in alternating fashion along the longitudinal axis of the tape in the length direction L. The standard TBS pattern 402 may be used to provide initial identification of the servo band (e.g., by providing a servo band ID); initial positioning of the head 406 to the appropriate servo position; initial acquisition of servo channel parameters such as tape speed, head lateral position, head-tape skew, and longitudinal position (LPOS); and the like. Additionally, the HD pattern 404 may enable more accurate and more frequent estimation of the servo channel parameters, thereby achieving improved head positioning over a much wider tape speed range, and support for larger bandwidth head operation. This may enable track density scaling for very large cartridge capacities, and may further improve data rate scaling with host computer requirements by supporting a wider speed range.

Referring again to FIG. 4A, which shows a tape layout 400 with a hybrid servo pattern 410 according to one approach, in the hybrid servo pattern 410, an HD pattern 404 is written in the space next to a standard TBS pattern 402. According to this approach, because the TBS pattern 402 is used, no quadrature sequence is included. This is the opposite of products that implement servo functions in hard disk drives.

Briefly referring now to FIG. 4B, a detailed partial view of a TBS pattern 402 (e.g., a TBS frame) is shown according to one exemplary approach. As shown, a plurality of servo stripes 412 form a servo burst 414, and corresponding pairs of the servo bursts 414 form a servo subframe. Thus, the illustrated TBS frame has four servo bursts 414 and two servo subframes. In this approach, the servo bursts 414 in the left servo subframe each have five servo stripes 412, and the servo bursts 414 in the right servo subframe each have four servo stripes 412. The servo stripes 412 in a given servo burst 414 are oriented such that the azimuth gradients of the servo stripes 412, represented by the angle α, are the same. Additionally, corresponding pairs of servo bursts 414 have opposite azimuth gradients, thereby forming a chevron-type pattern. The height H and width t of the servo stripes 412 may vary depending on the servo writer used to write the TBS pattern 402. According to one exemplary approach, which is in no way intended to limit the invention, the height H may be approximately 186 μm, the angle α may be approximately 6°, and the width t may be approximately 2.1 μm. Additionally, the spacing S between each servo stripe 412 and/or the distance d between servo bursts 414 having the same azimuthal gradient may vary depending on the desired approach. According to one exemplary approach, which is in no way intended to limit the invention, the spacing S may be approximately 5 μm and the distance d is approximately 100 μm. As described above, transitions through a pattern such as that shown in FIG. 4B allow an estimate of the lateral position of the head to be determined by evaluating the relative timing of pulses generated by a servo reader reading the servo stripes 412 of the servo bursts 414 as they pass over the servo reader.

Tape Dimensional Stability Issues Figures 5A-5C illustrate the effects of lateral tape expansion and contraction on transducer array position relative to the tape, and are not intended to limit the invention in any way. Figure 5A illustrates a transducer array 500 relative to a tape 502, which has a nominal width. As shown, the transducers 504 are conveniently aligned with the data tracks 506 on the tape 502. However, Figure 5B illustrates the effect of lateral tape contraction. As shown, the tape contraction causes the data tracks to shrink, resulting in the outermost transducers 505 being positioned along the outer edge of the outer data tracks. Additionally, Figure 5C illustrates the effect of lateral tape expansion. In this illustration, the tape expansion causes the data tracks to move farther apart, resulting in the outermost transducers 505 being positioned along the inner edge of the outer data tracks. If the lateral contraction of the tape were greater than that shown in Figure 5B, or if the lateral expansion of the tape were greater than that shown in Figure 5C, the outermost transducers 505 would straddle adjacent tracks, causing adjacent tracks to be overwritten during a write operation, or the wrong track to be read back during a read back operation, or both. Additionally, tape skew and lateral shift effects can exacerbate such problems, especially for tapes having a single data track.

Thus, lateral expansion and contraction of tape is an ongoing challenge in tape development and currently remains a limiting factor in further increasing data density on tape.

Fabrication of Magnetic Recording Media and Layers Thereof FIG. 6 shows a partial cross-sectional view of a basic structure of a magnetic recording medium 600 according to the various approaches described herein. This view is not drawn to scale. Optionally, this magnetic recording medium 600 can be implemented with features of other approaches described herein, such as those described with respect to other figures. However, it should be understood that such magnetic recording medium 600 and other magnetic recording media presented herein can be used in various applications or permutations or combinations thereof that may or may not be expressly stated in the exemplary approaches described herein. Furthermore, the magnetic recording medium 600 presented herein can be used in any desired environment. The various permutations of the magnetic recording medium 600 disclosed herein have been developed to improve the stability and performance of tape storage media across the environments required for use and storage.

Unless otherwise stated herein, the various layers of the magnetic recording medium 600 may have conventional structures, designs, or functions, or combinations thereof. In various approaches, new and novel layers may be used in conjunction with conventional layers. In additional approaches, multiple new and novel layers may be used in conjunction with other conventional layers.

Unless otherwise stated herein, the various layers of the magnetic recording medium 600 may be formed using conventional methods, particularly when each layer has a conventional structure.

The magnetic recording medium 600 is preferably a magnetic recording tape, but in other embodiments, the magnetic recording medium 600 is a different type of deformable medium.

As shown in FIG. 6, there are typically four basic layers in the magnetic recording medium 600. An optional backcoat 602 is disposed along one side (the bottom side in FIG. 6) of a substrate 604. An underlayer 606 is disposed along the other side (the top side in FIG. 6) of the substrate 604. A recording layer 608 is disposed on the underlayer 606. In various approaches, there may be additional layers of conventional construction in the magnetic recording medium 600.

Backcoat The backcoat 602 may or may not be present in the magnetic recording medium 600. The backcoat 602 may be made of known materials and may be selected as a material that can be grafted to the substrate 604 by radiation induced grafting. The backcoat 602 is preferably constructed from a material that provides one or more of the following advantages: ease of separation of the tape wound on the backcoat from another section on the spool, improved tribology, dissipation of static electricity, etc. The preferred thickness of the backcoat 602 is less than about 0.3 microns, preferably less than about 0.2 microns.

Substrate The substrate 604 has a new and novel structure as disclosed herein. The substrate 604 is formed of polyetheretherketone (PEEK). As used herein, PEEK more broadly refers to a class of materials collectively known in the art as PEEK materials, including various types of polyaryletherketones (PAEKs), polyetheretherketones, and other similar materials.

Magnetic recording tape with PEEK substrate 604 has stable mechanical properties. For example, both the tensile storage (E') modulus and the tensile loss (E"") modulus, measured using dynamic mechanical analysis techniques such as dynamic mechanical thermal analysis (DMTA), for the normal operating and storage environment of the tape media are lower than conventional media substrates. In general, the normal operating and storage environment of the tape media ranges from about 0°C to about 60°C and a relative humidity of about 5% to about 80%.

Magnetic recording tape with a PEEK substrate 604 also has low sensitivity to temperature and humidity throughout its operating range. PEEK is generally hydrophobic, which makes it stable to water. Water absorption is expected to be much less than 1% at 50% relative humidity, which is much lower than aramid, which tends to have a water absorption of about 10% at 50% relative humidity.

The magnetic recording tape having the PEEK substrate 604 further has excellent elasticity for normal tape operation and exhibits stable creep and recovery for normal storage and operating temperatures of about 0° C. to about 60° C. The shrinkage of the PEEK substrate is expected to be less than 1% over a temperature range of 100° C., including the operating range mentioned above.

An additional advantage of PEEK is that the PEEK raw material can be melted without degradation, allowing it to be processed into thin films at temperatures near its melting point without losing its desirable properties.

Each of the above is important for maintaining dimensional stability both during use and long-term storage.

PEEK has never been considered a suitable material for use in magnetic recording tape because of its focus on use in capacitors and other applications. It has also never been one of the materials used for other applications by tape media substrate manufacturers. Furthermore, conventional wisdom in attempting to improve the dimensional stability of tape media to address tape width variations and therefore data track placement stability has been to seek to increase the transverse direction (TD) stiffness or modulus of the substrate. However, in the process, conventional substrate compositions must be adjusted to achieve an increase in the substrate TD modulus. Thus, the inventive findings disclosed herein regarding the use of PEEK as a substrate material go in the opposite direction to conventional wisdom.

Figure 7 is a graph 700 comparing DMTA results for example current tape substrates for tensile storage modulus (E') in GPa over a temperature range with an 8 micron thick PEEK film from Shin Etsu, Ltd. (DMTA @ 10 Hz). The current tape substrates used in this experiment are TORAY Spaltan™, a blend of polyethylene terephthalate (PET) with chopped modified aramid (Micron), TORAY Micron™, a modified aramid, and TD Tensilized PEN from TEIJEN Ltd.

Graph 800 in FIG. 8 further extends this comparison across the temperature range (0° C. to 60° C.) where tapes are typically used and stored. Only two substrates, Toray Spaltan™ and the PEEK film sample, show a stable mechanical response across this temperature. Toray Spaltan™ was found to show good lateral dimensional stability (TDS), an increasingly important attribute of tapes to enable higher track densities. However, Toray Spaltan™ suffers from sensitivity to humidity and poor creep recovery. The PEEK substrate, in accordance with the various approaches disclosed herein, addresses and resolves these issues.

The tensile storage modulus E' of the PEEK substrate according to various embodiments is preferably in the range of about 4 GPa to about 20 GPa, more preferably in the range of about 5 GPa to about 15 GPa, and ideally in the range of about 5.5 GPa to about 12 GPa, preferably near the upper end of this range. The tensile storage modulus E' can be controlled to some extent by controlling the molecular weight of the PEEK, and potentially improved by increased crystalline chain orientation of higher molecular weight PEEK materials, which are not currently available but will become available in light of the teachings presented herein, and potentially once the need for them is established for future tape media.

For the substrate material, in various approaches, a PEEK material having an aromatic polyaryletherketone chemical structure and a chain length n of at least n=20 is preferred. The chain length is preferably n=40 or greater, such as n=50 to 100. The chain length should not be so long that the PEEK becomes unworkable or brittle.

A variety of aromatic polyaryletherketones can be used in a variety of ways within the scope of the present invention. Some exemplary PEEK materials are described below. The descriptions are provided by way of example only to illustrate some of the various types of PEEK that can be used in many aspects of the present invention, and are not intended to be limiting.

Referring again to FIG. 6, the substrate 604 may be the thickest layer in the magnetic recording tape. The use of PEEK allows for a thinner substrate than conventional substrates currently in use, thereby allowing more tape to be wound into a conventional tape cartridge. In some approaches, the substrate has a thickness of about 2.5 microns or more, measured in a direction perpendicular to the plane of the tape, such as a thickness in the range of about 3 microns to about 8 microns, and preferably in the range of about 3 microns to about 4.5 microns, although the substrate can be thicker or slightly thinner than the upper and lower limits of these ranges.

Exemplary PEEK Material FIG. 9 illustrates an exemplary PEEK 900 according to various approaches described herein. Optionally, this PEEK 900 can be implemented with features of other approaches described herein, such as those described with respect to other figures. However, it should be understood that such PEEK 900 and other PEEKs presented herein can be used in a variety of applications or permutations or combinations thereof that may or may not be expressly stated in the exemplary approaches described herein. Furthermore, the PEEK 900 presented herein can be used in any desired environment. The various permutations of PEEK 900 disclosed herein enhance the stability and performance of tape storage media throughout the required environments of use and storage.

Figure 10 shows another exemplary PEEK 1000 according to various approaches described herein. Optionally, this PEEK 1000 can be implemented with features of other approaches described herein, such as those described with respect to other figures. However, it should be understood that such PEEK 1000 and other PEEKs presented herein can be used in a variety of applications or permutations or combinations thereof that may or may not be expressly stated in the exemplary approaches described herein. Furthermore, the PEEK 1000 presented herein can be used in any desired environment. The various permutations of PEEK 1000 disclosed herein improve the stability and performance of tape storage media throughout the required environments of use and storage.

Known manufacturing techniques can be used to produce PEEK feedstock that can be used to form substrates. Some techniques use a step growth condensation polymerization reaction.

Figure 11 shows another exemplary PEEK 1100 according to various approaches described herein. Optionally, this PEEK 1100 can be implemented with features of other approaches described herein, such as those described with respect to other figures. However, it should be understood that such PEEK 1100 and other PEEKs presented herein can be used in a variety of applications or permutations or combinations thereof that may or may not be expressly stated in the exemplary approaches described herein. Furthermore, the PEEK 1100 presented herein can be used in any desired environment. The various permutations of PEEK 1100 disclosed herein improve the stability and performance of tape storage media throughout the required environments of use and storage.

12 illustrates another exemplary PEEK 1200 and its exemplary formation route according to various approaches described herein. Optionally, this PEEK 1200 can be implemented with features of other approaches described herein, such as those described with respect to other figures. However, it should be understood that such PEEK 1200 and other PEEKs presented herein can be used in various applications or permutations or combinations thereof that may or may not be expressly stated in the exemplary approaches described herein. Furthermore, the PEEK 1200 presented herein can be used in any desired environment. The various permutations of PEEK 1200 disclosed herein improve the stability and performance of tape storage media throughout the required environments of use and storage.

As mentioned above, a step-growth condensation polymerization reaction can be used to manufacture PEEK 1200. An exemplary step-growth condensation polymerization reaction process shown in Figure 12 involves reacting a diphenyl ether such as diphenyl oxide with terephthalic acid chloride (TPC) in the presence of a metal chloride such as _AlCl3 or _FeCl3 , liberating HCL as a by-product. This reaction is usually carried out in a melt or aromatic hydrocarbon solvent at high temperature so that HCL is released as a gas, leading to a very efficient chain growth reaction.

The end groups of the PEEK 1200 can be similar to those shown in Figure 9 or other figures.

In some approaches, PEEK raw material can be purchased commercially from a manufacturer or supplier of PEEK raw material. In a preferred approach, a manufacturer can manufacture suitable PEEK material having desired properties, such as chain length, at the request of a magnetic recording tape manufacturer following the guidelines set forth herein. PEEK is typically sold in pellet form, and the pellets can be processed as described below to form a substrate for magnetic recording tape. In other approaches, PEEK substrate sheets can be manufactured, purchased, or both manufactured and purchased for use in the tape manufacturing process.

KETASPIRE(R) PEEK material is available from Solvay (Solvay Specialty Polymers USA, LLC, 4500 McGinnis Ferry Road, Alpharetta. GA30005-3914 USA).

PEEK material is also available from Victrex (Victrex USA, Inc., 300 Conshohocken State Road Suite 120, West Conshohocken, PA, 19428 USA).

Currently produced PEEK films are not well suited for use as a tape substrate. However, by using the teachings presented herein, one skilled in the art can produce suitable PEEK films having the appropriate thickness, molecular weight, extrudability and molecular orientation for use as a tape substrate.

PEEK is particularly advantageous for tape applications because it has a very low hygroscopic coefficient of expansion and is insoluble in organic solvents. Thus, PEEK substrates are not susceptible to water-induced dimensional changes. However, PEEK can be melted and formed into films. PEEK does not degrade at the high temperatures used during manufacturing, for example, in melt extrusion. In contrast, aramids used in conventional tape products are modified to be soluble. This is because aramids degrade during melting and cannot be melt extruded into films. To make aramids soluble in very hot polar organic solvents, the aramid chains must be modified to increase solubility. This results in increased water absorption and reduced overall dimensional stability at normal use and storage temperatures of the tape medium.

To form the substrate, according to one approach, PEEK feedstock is extruded by melt extrusion and oriented to align the crystalline regions of the resulting substrate so that they are generally aligned with one another. The melt extrusion process involves heating the PEEK feedstock to a temperature at which it can be extruded by a melt extrusion apparatus to form a film of a desired thickness. The melt extrusion apparatus and process can be of known design for PEEK materials used in other industries and generally include a die (e.g., nozzle, rollers, etc.) through which the PEEK is extruded and a mechanism for pulling the extruded PEEK. An exemplary substrate manufacturing line may use melt extrusion and a process called tenting, which uses grippers on rails and chain frames that grip the edges of the extruded sheet and pull the sheet laterally and longitudinally through a heated furnace to achieve very controlled MD and TD orientation or tensilization.

As will be understood by those skilled in the art after learning this description, the temperature used during melt extrusion should be below the degradation temperature of the PEEK feedstock, which varies from material to material and is usually significantly higher than the melting temperature as determined by conventional thermal analysis techniques such as differential scanning calorimetry (DSC) or thermogravimetric analysis (TGA). Typically, PEEK polymers are very stable up to temperatures well above their softening or true melting point. Depending on the molecular structure and chain length of the PEEK polymer, softening occurs at temperatures well above 150°C. For some PEEK polymers, degradation in air can occur when heated to temperatures above 300°C, but 300°C is considered to be well above the effective processing temperature actually used in forming films suitable for magnetic tape substrates. In general, the processing temperatures used in film manufacturing processes are optimized around the specific properties of the polymer feed to the initial extrusion die head to allow good flow and orientation of the initial sheet as it is picked up by the gripper. The grippers then pull the films simultaneously across and across the web to achieve the desired orientation or tensilization of the final cooled film.

Conventional conditions that align the crystalline domains of conventional substrate films can be used with PEEK in a manner that would be understood by one of ordinary skill in the art in the knowledge of this disclosure. For example, as molten PEEK is drawn during melt extrusion, the molecular chains tend to align in the direction of flow and toward the minimum free volume. Orienting the film to align the crystalline domains would enable the production of films with higher modulus and nearly perfect elastic creep recovery without sensitivity to water, which is expected to provide the control of TDS that current tension compensation schemes require.

The resulting PEEK sheet can be stored for further processing at a later time, or additional layers can be added to the PEEK sheet. In one embodiment, the PEEK sheet is wound onto a spool. In another embodiment, one or more additional layers are added to the PEEK sheet.

The PEEK sheet with or without the additional layer can then be cut to the width required for further processing, or to meet the final product specifications, or both. For example, a wide PEEK sheet can be cut into strips of a width suitable for use in conventional coating equipment to add the additional layer to the sheet.

Underlayer According to various approaches, any underlayer 606 known in the art can be used with the PEEK substrate 604. The underlayer 606 can be made of any known material, and is preferably made of a material that can be grafted to the substrate 604 by radiation-induced grafting.

Recording Layer Any recording layer 60 known in the art can be used with the PEEK substrate 604 according to various approaches.

Exemplary Tape Manufacturing Techniques As discussed in more detail below, to manufacture magnetic recording tape, one or more additional layers, such as an underlayer or a backcoat, or both, are bonded to the PEEK substrate.

Current magnetic recording tape manufacturing techniques rely on solvent interactions to adhere the layers together or require surface treatments such as plasma cleaning prior to coating. A significant drawback of this surface modification is that the modified substrate is susceptible to water-induced dimensional changes.

One or more additional layers may also be added to the PEEK film to improve adhesion of the coating or to provide a controlled roughness for improved handling, as is currently used in tape substrates. Modification of PEEK films to improve adhesion of coatings, perhaps used to manufacture future magnetic recording tape products, may require modification of the PEEK film surface by co-extruding another film material onto one surface, or by oxidizing one surface using plasma treatment, as is currently done with existing tape substrates. In the case of radiation cured coatings, particularly those for very thin coatings anticipated in future tape designs, sufficient activation of the locations on the PEEK film may be achieved with UV light to solve adhesion problems and eliminate the need for additional surface treatments. Modification of the monomers used to build PEEK specifically optimized for use as a substrate for magnetic media may completely solve any adhesion problems and introduce functional groups into the PEEK film that are activated upon exposure to UV light and can react with functional groups of the coating to further improve the performance of the film for application to magnetic tape media.

In a preferred approach, one or more additional layers, such as an underlayer or a backcoat, or both, are bonded to the PEEK substrate by radiation-induced grafting, e.g., photoinduced curing (e.g., crosslinking), of these layers to the substrate. For example, an underlayer can be extruded next to the PEEK substrate, laminated onto the PEEK substrate, and grafted to the PEEK substrate in real time by exposure to ultraviolet (UV) light and/or other radiation. The aromatic compounds in PEEK tend to be photoactive and therefore tend to lend themselves to the desired radiation-induced curing. Additionally, as will be appreciated by those of skill in the art upon reading this description, the PEEK feedstock and/or adjacent layers can be manufactured to have the desired chemical structure that allows for radiation-induced grafting. In some approaches, no adhesive is present between the underlayer and the substrate.

It should be noted that the degree of cure is not necessary; a few chemical bonds per 100 monomer units are sufficient for good adhesion, as the chemical bonds are much stronger than the weaker bonding techniques used in conventional tape media. The preferred embodiment of chemical bonding is also advantageous in terms of robustness and resistance to stress, since chemical bonds must be broken to separate the layers.

Generally, UV light will not penetrate plastics that are more than 1 micron thick. However, the underlayer used in the preferred technique is less than 1 micron thick, thus allowing UV curing to occur.

Various advantages of magnetic recording tapes having the novel PEEK substrate compared to current magnetic recording tape media include, but are not limited to, one or more of higher dimensional stability, greater tear resistance, and greater resistance to the effects of aging (creep).

It will be apparent from the above description that various features of the above systems and/or methods can be combined in various ways to produce multiple combinations.

It is also understood that the techniques of the present invention can be provided in the form of a service that is deployed for customers.

The ideas of the present invention disclosed herein are presented as examples to illustrate the myriad features thereof in a number of illustrative scenarios, embodiments or implementations, or combinations thereof. It should be understood that the ideas generally disclosed should be considered as modules and can be implemented in any combination, permutation or composition thereof. In addition, any changes, modifications or equivalents of the features, functions and ideas disclosed herein that would be understood by a person skilled in the art upon reading the description herein should also be considered within the scope of the present disclosure.

The description of various embodiments of the present invention is provided for illustrative purposes and is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations that do not depart from the scope of the described embodiments will be apparent to those skilled in the art. The terms used in this specification have been selected to best explain the principles of the embodiments, practical applications, or technical improvements not found in the art on the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims (19)

A magnetic recording tape comprising:
A substrate including polyetheretherketone (PEEK);
an underlayer over the substrate;
a recording layer on the lower layer, wherein the chain length of the PEEK is greater than 20 ;
Magnetic recording tape. A magnetic recording tape comprising:
A substrate including polyetheretherketone (PEEK);
an underlayer over the substrate;
a recording layer on the underlayer, wherein the tensile storage modulus of the substrate is between 4 GPa and 50 GPa as measured by dynamic thermomechanical analysis.
20 GPa range,
Magnetic recording tape. 2. The magnetic recording tape of claim 1, wherein the PEEK has a chain length of 50 to 100 . 4. The magnetic recording tape of claim 1, wherein the substrate has a tensile storage modulus in the range of 5.5 GPa to 12 GPa as measured by dynamic thermomechanical analysis. The magnetic recording tape of any one of claims 1 to 4, wherein the crystalline domains of the substrate are generally aligned with one another. 6. The magnetic recording tape of claim 1, wherein the substrate has a thickness in the range of 2.5 to 8 microns. 7. The magnetic recording tape of claim 1, wherein the substrate has a thickness in the range of 3 to 4.5 microns. The magnetic recording tape of any one of claims 1 to 7, wherein the underlayer is grafted to the substrate. The magnetic recording tape of any one of claims 1 to 8, wherein no adhesive is present between the underlayer and the substrate. 1. A tape cartridge comprising:
Housing and
a magnetic recording tape at least partially contained within said housing, said magnetic recording tape being the magnetic recording tape of any one of claims 1 to 9.
Tape cartridge. 1. A method for manufacturing a magnetic recording tape, the method comprising bonding an underlayer to a substrate, the substrate comprising polyetheretherketone (PEEK), the PEEK having a chain length greater than 20 . 1. A method for manufacturing a magnetic recording tape, the method comprising bonding an underlayer to a substrate, the substrate comprising polyetheretherketone (PEEK), the substrate having a tensile storage modulus in the range of 4 GPa to 20 GPa as measured by dynamic thermomechanical analysis. The method of claim 11 , wherein the PEEK has a chain length of 50 to 100 . 14. The method of any of claims 11 to 13, wherein the substrate has a tensile storage modulus in the range of 5.5 GPa to 12 GPa as measured by dynamic thermomechanical analysis. The method of any of claims 11 to 14, wherein the crystalline regions of the substrate are generally aligned with one another. 16. The method of any of claims 11 to 15, wherein the thickness of the substrate is in the range of 2.5 microns to 8 microns. 17. The method of any of claims 11 to 16, wherein the thickness of the substrate is in the range of 3 microns to 4.5 microns. The method of any one of claims 11 to 17, wherein no adhesive is present between the underlayer and the substrate. 1. A method for manufacturing a magnetic recording tape, the method comprising: bonding an underlayer to a substrate comprising polyetheretherketone (PEEK) by radiation-induced grafting; and bonding a recording layer to the underlayer.

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