GOOD VIBRATIONS. Paul B. Foreman, National Adhesives, Bridgewater, NJ. Abstract

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1 GOOD VIBRATIONS Paul B. Foreman, National Adhesives, Bridgewater, NJ Abstract The ability of pressure sensitive adhesives (PSAs) to absorb and dissipate energy has led to their widespread use in vibration damping applications. This paper will discuss measurement of damping, the sources of noise and vibration and the requirements for outgassing in computer disk drives, and the methods by which PSA damping properties can be modified for a particular application. Introduction Vibration in structures and mechanical devices is always present to a greater or lesser degree. While often inconsequential, there are times when control is necessary to avoid structural fatigue or mechanical malfunction or, perhaps, to abate acoustic noise. Because excessive vibration can result in sometimes catastrophic failures, engineers conduct detailed analyses to determine whether vibration control is needed and, if so, to select the appropriate remedies. The mass and stiffness of the structure or device are two of the primary determinants of vibrational behavior. An increase in either one will reduce the amplitude of vibration, but these options are not always practical or cost effective. In this situation vibration control is achieved by materials selection. When a material is deformed by a transient shock or a cyclic vibration the energy may be stored elastically (i.e. it is recoverable upon removal of the applied force) or dissipated as heat. The mechanisms for dissipation are varied and complex but all are associated with reorganization of the internal material structure. These material responses are often nonlinear. In the study of vibration damping it is convenient to subject the sample to a uniaxial force, either in extension or more usually in shear, which varies sinusoidally with time. Tests are normally performed with a very small deformation (strain) such that the measured modulus is independent of the strain. This is known as the linear viscoelastic regime. The energy dissipated per unit volume per cycle is the specific damping energy D. Typical metals used as structural elements have very small values of D. Certain alloys, for example Mn-Cu, exhibit higher damping and are used mainly in applications such as naval ship propellers. Highest levels of damping are achieved with many polymeric materials. Among these, pressure sensitive adhesives, being highly viscoelastic in nature, play an important role in vibration damping. One such application for PSAs which has received considerable attention is their use in hard disk drive (HDD) data storage devices. Figure illustrates how a PSA layer sandwiched within a laminated structure is subjected to shear when the structure is deformed as a result of noise or vibration. This results in dissipation of some of the energy and attenuation of the amplitude of vibration as depicted in Figure 2. 4

2 Constraining metal layers Vibration induced deformation generates shear strain in the PSA Pressure sensitive adhesive Figure Shear deformation of a PSA in a constrained layer construction (crosssectional view). Undamped beam Displacement versus time Beam with damping layer Figure 2 Effect of a damping layer on the response to an impulse excitation. Requirements for hard disk drives (a) Vibration and noise control Vibration in hard disk drives arises from several sources and is transmitted to the other components which in turn resonate to produce noise. These primary sources include the spindle motor ball bearings, shaft and sleeve and the voice coil motor which controls the actuator arm (see Figure 3). While ball bearing spindle motors still account for a significant market share, the HDD industry is transitioning to fluid dynamic bearings. These reduce non-repeatable runout (off-axis rotation), the largest contributor to track 42

3 mis-registration, thus permitting higher areal density of data storage, improved reliability and reduced acoustic noise []. Interaction between the rotating disk and the air within the enclosure is an additional source of low frequency noise and air-induced vibration of the head gimbals assembly. Voice coil motor damper Actuator arm damper Suspension damper Spindle shaft damper Figure 3 Typical PSA noise and vibration damping components in a hard disk drive. Additional components not shown include PSA dampers for the flexible cable (connects to a preamplifier), the base and cover plate as well as screw holes. Mechanical vibration is detrimental to drive performance and is exacerbated by the trend to higher rotational speeds and lower flying height in order to improve read/write performance. Vibration transmitted to the actuator arm on which the suspension and head are attached increases the seek time. Of particular concern for seek time reduction is damping of the so-called sway mode of vibration in which the head moves radially over the desired data track in a plane parallel to the rotating disk. PSA laminates are used to provide vibration damping of the voice coil motor, the actuator arm and suspension, the spindle as well as the flexible cable which connects to the printed circuit board, the cover plate, base and screw holes (Figure 3). Acoustic noise is an increasingly important consideration as hard disk drives find use in home electronics as well as office environments. Noise is transmitted via the disk enclosure, particularly by the cover plate which is normally a thin metal sheet. This can be attenuated by replacing the sheet with a metal bilayer separated by a damping polymer, by attachment of constrained layer PSA dampers in contact with the inner surface at areas of highest vibrational amplitude, or by placement of a pressure sensitive label on the exterior of the cover. To be most effective the label backing material should contribute to the structural stiffness and preferably should completely cover the whole plate [2]. 43

4 (b) Contamination Disk drive performance can be degraded by outgassing and subsequent condensation of monomers, solvents, volatile additives and impurities from damping polymers within the drive enclosure. Increased storage capacity has required reductions in head flying height and disk surface roughness thus increasing sensitivity to the detrimental effects of contamination. Tribological methods have been used to study the effects of model vapor phase compounds on the head/disk interface. For example, Jesh and Segar [3], using organo-acids, an organo-sulfur compound, a phthalate plasticizer and an amine, measured the effects on short duration stiction, fly stiction and head smearing. Fly stiction results from extended flying in the data zone during which organic vapors are believed to condense on the head, followed by an extended park in the landing zone where the accumulated liquid is thought to wick onto the disk and flood the interface. The various compounds exhibited different failure modes not readily predictable from their physical properties but all failures appeared to result from corrosion. Most relevant for acrylic PSAs was the observation that acrylic acid monomer vapor aggressively degraded head/disk interface performance leading to increased stiction, fly stiction and formation of smears on the head. Each drive manufacturer sets their own specifications for adhesive outgassing, usually expressed in nanograms per square centimeter of coating, limiting the allowable levels of specific chemicals or classes of chemical as well as the total emission of organic compounds. The International Disk Drive Equipment and Materials Association (IDEMA) publishes standardized test methods for microcontamination arising from ionic compounds, particulates and organics. IDEMA Document M3-98 includes a catalog of contaminants known to cause component or drive failure. Outgassing may be determined by static headspace GC/MS (standard M8-98) or preferably by dynamic headspace analysis (M-99). Meeting the specifications requires a collaborative approach between the adhesive manufacturer and the coater. In the case of solvent borne acrylics this means paying close attention to reducing residual monomers at the end of polymerization and optimizing solvent blends and drying conditions. (c) Adhesion Good adhesion is necessary to ensure energy coupling between the PSA layer and the constraining substrates. However, in contrast to typical PSA tape and label applications, measures of peel and shear resistance, while not unimportant, are very much secondary to the modulus and damping properties when assessing PSA suitability for vibration control in disk drives. (d) Heat resistance PSAs use in disk drives are typically called upon to operate up to about 65 C. The trend, however, is to higher operating temperatures. This is especially true in some consumer electronics applications, for example in a digital video recorder which, in order to eliminate a source of noise, may not use a cooling fan. There are commercially available grades of adhesive capable of providing good damping at temperatures up to 05 C (while giving up some low temperature service range). These adhesives have low tack, however, and require heat and pressure to form a bond. They are not, therefore, typical 44

5 PSAs. The challenge for adhesive manufacturers is to raise the service temperature while avoiding the need to laminate with heat. Progress has been made in striking an optimal balance for heat resistance but the fundamental limitations of PSA technology remain. Materials selection Solvent borne acrylics are the most important class of PSAs for hard disk drive applications. This is because they provide the necessary damping properties as well as clean films, free of extractable ions or potentially corrosive adjuvants. In addition, the inherent resistance of an acrylic polymer to long term thermal and oxidative degradation is an important attribute for components requiring high reliability. Standard PSA film thicknesses for HDDs are 50 and 00 microns depending upon the amount of energy dissipation required for a specific part. Thus coating line speeds tend to be considerably slower than is customary for run-of-the-mill PSA tape manufacture. It is natural then, to look at hot melts for improved productivity. Typical rubber-resin hot melt PSAs are formulated from SIS or SBS block copolymers, tackifying resin and a processing oil. The technology provides the formulator with simple yet highly versatile means to modify the viscoelastic properties of the adhesive. To reduce outgassing the processing oil must be eliminated and a liquid or low softening point tackifier substituted, but it has proved difficult to meet the industry outgassing specifications following this approach. A more promising approach may be to use UV crosslinkable acrylic hot melt PSAs. These incorporate polymerizable photoinitiators which are non-extractable and crosslink upon exposure to UV light by abstraction of a hydrogen atom from the polymer. This type of photoinitiator avoids the creation of a new molecule which can outgas [4]. It should be noted that this type of PSA is manufactured via a conventional polymerization in organic solvent which is removed by the adhesive manufacturer using heat and vacuum. The task of meeting the disk drive manufacturers specifications is therefore a challenge which devolves upon the adhesive supplier rather than the adhesive coater. Viscoelastic behavior It is customary to describe viscoelastic behavior in terms of the temperature dependence of the modulus, E* when the material is in tension or G* in the case of shear deformation. E* and G* are complex numbers, each with real (E, G) and (mathematically) imaginary components (E", G") representing the elastic storage and loss moduli respectively. We need to define a loss factor, #, (not to be confused with a viscosity) which is expressed as the ratio of the loss modulus to the elastic modulus: # = G"/G = tan $ where $ is the phase angle difference between the strain of an applied harmonic excitation and the resulting stress. 45

6 Figure 4 Stress response of a viscoelastic material to an applied cyclic strain with frequency % (rad/s). strain stress time #t phase lag time t = /" Figure 5 shows the behavior of a self-curing solution acrylic PSA which is typical of an amorphous, lightly crosslinked polymer. This type of representation will be familiar to most practitioners of PSA technology but a short phenomenological description is in order as introduction to the later discussion. At low temperatures (below -50 C in the example) the polymer is glassy and has insufficient thermal energy for the chain segments to overcome potential barriers to rotational and translational motion. Here very little damping is possible, as indicated by the loss factor which is less then 0.. As the temperature increases, the amplitude of molecular vibrational motion is sufficient to overcome these barriers and short range segmental motions begin. Above this glass transition the modulus drops dramatically until reaching a rubber-like, slowly varying plateau region where segmental motions occur rapidly but long range translational motions of complete molecules remain restricted by the presence of crosslinks. The maximum dissipation of energy (high loss factor) can be seen to occur in the transitional region between the glassy and rubber-like states. In this example, at sufficiently high temperature, above about 40 C, the chelated metal crosslinks, which have some ionic character, begin to break permitting the onset of viscous flow and a further, more gradual decrease in modulus and return to increasing loss factor G" ( ) [Pa] G' ( ) [Pa] tan() ( ) [ ] Temp [ C] Figure 5 Temperature dependence of G", G# and # (= tan $) for an acrylic PSA (%=0 rad/s)

7 Time-temperature superposition From the foregoing discussion one sees that the material response to an excitation depends not only upon the temperature but also upon whether the time scale is sufficiently long to permit stress relaxation to occur. The data in Figure 5 was obtained by applying a sinusoidal shear force with a cycle time of 0.63 seconds. Instead of studying temperature dependence using a fixed time period, it is more informative when studying damping behavior to follow the time dependent response to excitation at a series of fixed temperatures. A number of instruments are available to make such measurements, but the range of accessible time intervals by any one technique is not sufficient to cover the whole range of viscoelastic behavior. For example, at low oscillation frequency data is gathered very slowly while mechanical considerations may limit high frequency measurements. However, experimentalists have found that it is possible to shift the individual plotted curves horizontally with respect to any chosen curve (designated as the reference temperature) in order to construct a master curve. (An additional small vertical shift is used to account for changing temperature and density [5].) This is the principle of time-temperature correspondence which states that a measured response at higher temperature yields an identical result to one made over longer times. Conversely one made at lower temperature is equivalent to a measurement made over shorter time scales. Applying this principle it is then possible to cover the full range of polymer relaxations using experimentally accessible time scales. The construction and interpretation of modulus versus frequency master curves is very familiar to polymer scientists and discussed in standard texts such as Ferry [5]. The construction of a master curve is shown in Figure Unshifted data Master curve Shear storage modulus, G' (MPa) C -25C -5C -5C 5C 5C 25C 35C 45C 55C 65C 75C 85C 95C 05C Selected reference temperature Shift factor $ % Temperature C Shear storage modulus, G' (MPa) Time (s) Time (seconds) Figure 6 Master curve for an industry standard acrylic PSA used in hard disk drives. One sees that the reduced variable time scale covers almost 8 decades from 2 picoseconds to 3.5 days which is far beyond the range of direct measurements. We are interested in knowing the time constants for attenuation of a shock or vibration and so 47

8 there are some advantages in working, as in the above example, in the time domain. However, the mathematical analysis of damping is simplified by working in the frequency domain (i.e. the inverse of time) which on a log plot is simply the mirror image of Figure 6 and is the more familiar form of a master curve. The loss factor has been omitted from Figure 6 for clarity but it must also form a smooth overlaid curve using the same set of shift factors in order for the reduced variable method to be correctly applied. Damping nomograms While a conventional master curve is useful it suffers from the limitation that a new curve must be constructed for each desired reference temperature. A major advance in presenting the data in a user friendly format was due to Jones who devised a nomogram to include both frequency and temperature dependent data on a single plot [6]. This depends upon the observation that the reduced frequency f R, i.e. the product of the frequency f multiplied by the temperature shift factor & T is a linear equation when expressed in logarithmic form: log f R = log f + log & T This enables one to superimpose on the master curve a series of lines using the value of & T corresponding to each temperature. These isotherms are sometimes referred to as Jones temperature lines. The master curve in Figure 6 has been replotted as a nomogram in Figure 7: Shear Storage Modulus (MPa) and Loss Factor $=.4 G = Temperature ( C) Method: torsional rheometer Ref. temp. 25 C T=40 C Reduced frequency (f$ ) T f=20hz Figure 7 Damping nomogram for an industry standard acrylic PSA used in hard disk drives. To find the properties at any given vibrational frequency and temperature using the nomogram (e.g. 20Hz at 40 C) draw a line from the right hand frequency axis to the Frequency (Hz) 48

9 desired isotherm. Then draw a vertical line from their intersection and read off the values for the storage modulus and loss factor on the left hand axis. Shift factor relationships In order to create temperature lines at convenient intervals for graphical display it is usually necessary to interpolate between experimentally obtained values of & T (shown inset in Figure 6) which means that a function must be fitted. Several functional forms have been proposed for this purpose and there is no consensus on which is the best. It should be noted that the choice of function has no impact on the shape of the modulus and loss factor curves or their relationship to one another. However, to the extent that the chosen shift factor function does not fit the experimental data perfectly, the spacing of the temperature lines is affected and extrapolation beyond the experimental temperature range (caution required) is strongly affected. When log & T plotted against /T ( K - ) is linear the data follows an Arrhenius form which is often preferred by engineers and has the advantage of generating simple analytical expressions for G and #. In practice there is usually some deviation from linearity. A better fit can then be obtained using the Williams-Landel-Ferry (WLF) equation which is well known to polymer scientists. Alternative forms are discussed by Jones [7] and in ISO standard 02 [8]. The Wicket Plot The modulus and loss factor plots are sometimes independently fitted to empirical equations for use in modeling structural responses to vibration. This approach, while practically useful, is based on a conceptual error [9] since they are interrelated and both are contained in the complex modulus which has a unique value at any given temperature and frequency. An essential check on the consistency of the shifted data is to plot log # versus log G: Loss factor Wicket plot - data sorted by temperature 0 0. Systematic error at 45 C Storage modulus -35 C Loss factor Wicket plot - data sorted by frequency 0 0. Systematic error at 400 rad/s Storage modulus 0.0 rad/s Figure 8 Consistency check on data procedure using Wicket plots of log # versus log G. 49

10 The plot should be continuous and, in the case of a thermorheologically simple material, form an inverted U-shaped curve. Data points resulting from a systematic error can be distinguished from random noise and corrected or removed from the data analysis (see Figure 8). Jones has noted that the available literature, both commercial and academic, often contains unreliable data through a failure to apply this test [7]. Measurement of damping When practicable it is preferred to make measurements in the range of frequencies and temperatures for which damping is required rather than to rely upon time-temperature superposition. Measurements in the low to mid acoustic range can be made with one of several vibrating beam arrangements, clamped at one end, as depicted in Figure 9. Soft materials such as PSAs use the sandwich beam construction. PSA metal Oberst beam (damped one side) Modified Oberst beam (damped both sides) Sandwich beam Figure 9 Vibrating cantilever beam test method configurations (cross-sectional view). The test methods are specified in ASTM E756 [0]. Sufficient time (at least 30 minutes [7]) for thermal and mechanical equilibration must be allowed at each increment in temperature to avoid erroneous data. PSA developers are more likely to have a torsional shear rheometer at their disposal. However, the typical commercial rheometer is restricted to maximum operational frequencies of 00 or perhaps 500 rad/second, i.e. 6 or 80 Hz. For these instruments superposition is necessary to access the frequencies of interest in sound damping. Comparison of damping measurement test methods End user engineers are familiar and comfortable with the cantilever beam test method. When presented with data generated using a rheometer the question naturally arises as to whether the results can be trusted. On the plus side these instruments are capable of generating highly reproducible data with significantly less noise than the vibrating beam method. A graphical comparison of test results is complicated by the fact that unless the two sets of data employ identical shift factors they cannot be plotted on the same nomogram. Fortunately, the Wicket plot is independent of the frequencies and temperatures used to collect the data. In the following Figure (0) the adhesive data of Figure 7, measured using a torsional shear rheometer (RDA III from Rheometrics, Inc.) is 50

11 compared with published industry data for the same adhesive measured with a cantilevered sandwich beam. 0 Rheometer Sandwich beam Loss factor Shear storage modulus (kpsi) Figure 0 Comparison of rheometer and cantilevered beam test data for an industry standard adhesive. The agreement, while not perfect, is very good and well within the experimental uncertainty of the vibrating beam method. Back-calculating the shift factors from the published data and mapping readings of G and # at 000Hz onto Figure 7 using the rheometer derived shift values allows one to compare methods on the same nomogram: Shear Storage Modulus, G' (kpsi) and Loss Factor, & Figure Modulus loss factor Sandwich beam: Modulus loss factor Temperature ( F) Ref. temp. 3 F Rheometer: spacer line Reduced frequency (f$ ) T Test method comparison: rheometer versus ASTM E756 (vibrating cantilever beam) Frequency (Hz) 5

12 Examination of Figure shows excellent agreement, permitting one to conclude that when data is obtained and analyzed with care, a rheometer generated nomogram can yield reliable information about the loss factor in the acoustic frequency range. It is worth repeating that caution must be exercised in using the nomogram in regions of extrapolated data. To avoid this temptation Jones has proposed a direct nomogram [] based on the Wicket plot. Loss factor 0 0. "=.5 00 C Temperature 50 C 0 C G =.2 MPa Shear storage modulus (MPa) Figure 2 Direct nomogram for an industry standard acrylic PSA. The example shows values of modulus and loss factor for a frequency of 0Hz at 20 C. This presentation of data makes clear the G and # interrelationship and has the additional advantage of eliminating the reduced frequency axis which can be a source of confusion but does not eliminate the need to apply the reduced variable method in order to create the nomogram. Of course, it is possible to display isotherms which extrapolate into regions of frequency not directly measured, as demonstrated in the ISO standard [8] but to do so subverts the intent of this data format. The desire to extrapolate may explain why this form of nomogram has not gained wider acceptance. Tools to change damping properties The adhesive developer has several tools available to tailor the damping properties to the needs of a particular application. Since peak damping occurs in the transitional region between the glassy and rubber-like states it is necessary to move the glass transition temperature (T g ) up or down to optimize damping at a new temperature (or frequency). For an acrylic random copolymer T g is controlled by the choice of monomers and can be varied from about -70 C to about 0 C, as measured by DSC. The practical range, however, is somewhat narrower in order to balance the requirements for sufficient cohesive strength and tack. As a simple example, Figure 3 shows the effect on T g of combining 2-ethylhexyl acrylate with methyl methacrylate in different ratios. Cyclic frequency (Hz) 52

13 50 00 MMA = Methyl Methacrylate 2-EHA = 2-Ethyl Hexyl Acrylate T g ( C) % MMA 0 % 2-EHA Monomer Ratios Figure 3 The relationship of glass transition temperature to monomer composition. The following Figure shows how the temperature/frequency dependence of loss factor can be varied for a series of acrylic PSAs by control of composition Loss Factor Temperature C A B C D E Figure 4 Temperature dependence of loss factor for a series of acrylic PSAs measured at a frequency of 0 rad/s (.6 Hz). Often a broad spectrum of noise needs to be damped. The breadth of polymer damping can be influenced by the introduction of polar functional monomers and specialty monomers capable of hydrogen bonding and polar interactions. Note that adhesives C and D exhibit maximum energy dissipation at similar temperatures but adhesive C has a significantly broader range of damping, making it suitable for hard disk drive applications; this is achieved by use of proprietary specialty monomers. Adhesives A and B perform with high dissipation at lower temperatures whereas adhesive E, intended for higher temperature use, pushes the limits of room temperature tack. Formulation can also be used to create large changes in viscoelastic properties. Addition of tackifier raises the T g and increases the loss as shown in Figure 5. One problem with this approach is that low molecular weight components contribute to outgassing which may preclude it from disk drive applications. 53

14 Tackified 0 G' ( ) [Pa] tan() ( ) [ ] Temp [ C] Figure 5 Effect on storage modulus, G", and loss factor, # (= tan $), of tackifier addition to an acrylic PSA (%=0 rad/s). Another valuable tool is to make use of different polymer architectures. Introduction of a block structure can create microphase separated domains, each with characteristic damping properties, thus broadening the overall material response. For acrylic adhesives this is conveniently achieved through the use of macromers which allow the introduction of macromolecular side chains at random intervals along the main acrylic backbone. Two macromers which have been used commercially are methacrylate terminated polystyrene and poly(ethylene-butylene). These impart domains with T g of 00 C and -6 C respectively offering considerable latitude to adjust properties. Figure 6 shows the effect of poly(eb) macromer on the viscoelastic properties of an acrylic where two distinct components are visible in the loss factor Acrylic phase G" ( ) [Pa] G' ( ) [Pa] Rubber phase tan() ( ) [ ] Temp [ C] Figure 6 Dynamic mechanical analysis of a saturated rubber grafted acrylic PSA (%=0 rad/s). This hybrid acrylic-rubber technology has also proved useful as a means of formulating an otherwise incompatible acrylic with synthetic hydrocarbon tackifiers [2]. These

15 compounded adhesives have outstanding tack and adhesion to difficult to bond substrates. When suitably compounded, their very broad damping characteristics make them excellent candidates for vibration and sound control, bearing in mind that any low molecular weight components need to be evaluated for their potential to outgas. Summary Pressure sensitive adhesives are ideally suited to meet the requirements for noise and vibration damping in many applications and offer versatile chemistry and polymer architecture with which to tailor the energy dissipation to specific ranges of frequency and temperature. In particular, solution acrylic PSAs have been developed to meet the current and emerging requirements for high energy dissipation and low outgassing necessary for use on critical components in hard disk drives. It was further shown that a dynamic mechanical analyzer of the torsional shear type found in most PSA development laboratories can, with careful attention to detail in sample preparation, data acquisition and analysis, provide reliable data on damping at acoustic frequencies. References. Blount, W.C., Fluid dynamic bearing spindle motors: Their future in hard disk drives, White Paper published by Hitachi Global Storage Technologies (2007). 2. Sugihara, Y. and Yoshida, J., Vibration control evaluation technology gives birth to vibration damping labels, Nitto Denko Technical Report no. 82, vol. 39, no., p 79-84, July Jesh, M.S. and Segar, P.R., The effects of vapor phase chemicals on head/disk interface tribology, Tribology Transactions, 42(2), (999). 4. Roan, G.A., New radiation curable acrylic PSAs, Pressure Sensitive Tape Council TECH 30 Technical Seminar, p 69-83, Orlando FL, May Ferry, J.D., Viscoelastic properties of polymers, Wiley, 3 rd ed. (980). 6. Jones, D.I.G., A reduced-temperature nomogram for characterization of damping polymer material, Shock and Vibration Bulletin, 48(2), 3-22 (978). 7. Jones, D.I.G., Handbook of viscoelastic vibration damping, Wiley (200). 8. International Organization for Standardization, ref. ISO 02:99(E), Damping materials Graphical presentation of the complex modulus. 9. Rogers, L., Operators and fractional derivatives of viscoelastic constitutive equations, J. Rheology, 27(4), (983). 0. American Society for Testing Materials, Test Method E756-98, Standard test method for measuring vibration-damping properties of materials.. Jones, D.I.G., A new method for representing damping material properties, ASME Vibrations Conference Proceedings, p 43-49, Boston MA, Sep Foreman, P., Eaton, P. and Shah, S., Rubber-acrylic hybrid pressure sensitive adhesives, Pressure Sensitive Tape Council Technical Seminar TECH XXIV, Orlando FL, May

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