Madeline Olsen, Captain

Team 19-3

Christopher Shaw

Philip Huntoon

Anthony Romano

Matthew Thanakit

May 30, 2007

Dr. Christopher Li

443 Lebow

3141 Chestnut Street

Philadelphia, PA19104

Re: Improving the Durability of Compact Discs

Dear Dr. Li:

We have enclosed a copy of our Freshman Design Report entitled, “Improving the Durability of Compact Discs.” The report concludes the solution that most appropriately addresses the issue of compact disc damage is an alteration of the disc’s composition. Enhancing the current polycarbonate layer with silicon dioxide nanoparticulates to create a polycarbonate-silicon dioxide nanocomposite would result in a more scratch-resistant form of this already popular mode of data storage.

Sincerely,

Team 19-3

Madeline Olsen, Captain / Christopher Shaw
Philip Huntoon / Matthew Thanakit
Anthony Romano

ENGR 103

Freshman Engineering Design

Final Project

Design Team No. / 19-3
Submitted to: / Dr. Christopher Li

AND THE

ENGR 103 PROJECT DESIGN FACULTY OF DREXELUNIVERSITY

ENTITLED: / Improving the Durability of Compact Discs

TEAM MEMBERS (include email addresses)

Madeline Olsen
Christopher Shaw
Philip Huntoon
Matthew Thanakit
Anthony Romano

Submitted in partial fulfillment of the requirements for

Freshman Engineering Design, ENGR 103, Design Project

Submitted on 5/30/07

ABSTRACT

The middle layer of a CD is composed of a reflective metallic compound onto which information is stored in the form of microscopic pits and falls. To protect this thin information coating, the layer is sandwiched between an acrylic plastic and a polycarbonate plastic; the polycarbonate layer is on the bottom of the disc and accounts for more than half of the CD’s volume. Though this material is flexible and cheap, it is prone to damage. This results in misread data or loss of information. In order to optimize the performance of this popular method of information storage, we aim to enhance the polycarbonate plastic with silicon dioxide based particulates, making the material much more dense. Altering this material will dramatically reduce the frequency of information damage on CDs resulting in a more reliable product.

EXECUTIVE SUMMARY

Because of the growing amount of documents that members of our society rely on, digital mass storage technology is a field always searching for improvements. Today various methods are used to store this digital information such as USB drives, iPods, and CDs. Though the CD is the least advanced of these methods, it remains most convenient and popular because of its user-friendly design and simplicity. Despite their prominence, CDs are easily damaged. Scratches on the surface can corrupt data resulting in the loss of important documents. Increasing the strength of a CD’s surface would reduce the frequency of scratches, creating a more reliable product. Improving upon such a widely marketed product as the CD can secure its dominance within the industry.

This can be accomplished through the utilization of nanotechnological principles, which is a promising new avenue of material development. Already nanotechnology has been used to decrease the oxygen permeability of packaged foods to increase shelf life. It has also proven effective in increasing the strength and reducing the flammability of certain materials. This demonstrates the mass production capability of the field. Enhancing the plastic composites of CDs with silicon dioxide nanoparticulates can cause a dramatic increase in the properties of the material; this would not only decrease the risk of scratches but also increasing the temperatures the disc could withstand. With this added stability, people can depend more on this method of information storage.

This technology is not limited to audio CDs but can also be applied to higher density information storage such as DVDs, HD-DVDs, and BluRay Discs. As for the future of CDs, these advancements in production exemplify evolution of the technology rather than falling into disuse. Employing this technology will result in a longer product life.

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TABLE OF CONTENTS

ABSTRACT...... i

EXECUTIVE SUMMARY...... ii

TABLE OF CONTENTS...... 1

INTRODUCTION...... 2
Problem Background...... 2

Figure 1-1 Stratification of Materials in a CD...... 2

Figure 1-2 Operating Principles of an Audio CD...... 3

1.2.Survey of Literature...... 4

1.3.Objectives...... 5

1.4.Constraints...... 5

1.5.Criteria...... 6

SOLUTION...... 6
Statement of Work...... 6
Results...... 7

Figure 2-1 Example of a Polymer Matrix...... 8

DISCUSSION...... 9
RECOMMENDATIONS FOR FUTURE WORK...... 11
REFERENCES...... 12
ACKNOWLEDGMENTS...... 14

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Improving the Durability of Compact Discs

INTRODUCTION
Problem Background

Compact discs, more commonly known as CDs, were originally developed for music storage combining a low cost with high quality and easily accessible music (Pohlmann). Due to technological improvements, today CDs are appropriate for a greater variety of data forms such as videos and documents as well as music.

A standard CD is 1.2 mm thick and 120 mm in diameter (“Compact Disc”). It is composed of multiple layers of different materials that each serve a different purpose. A reflective metallic layer, usually composed of aluminum, contains the information on the disc in the form of a series of microscopic pits and lands (“Compact Disc”). If this layer is scratched or marred, that part of the data is permanently lost. In order to prevent this from occurring, the metallic layer is placed below a protective acrylic plastic and above a clear polycarbonate plastic substrate (“Compact Disc”). Because the protection of the metallic layer is essential to the proper function of the disc, the polycarbonate composes approximately half of the CD as seen in Figure 1-1.

Figure 1-1 Stratification of Materials in a CD (Marshall)

The information is read off of a CD using a laser. The light from a semiconductor laser permeates the polycarbonate substrate and reflects off of the aluminum layer pits and falls that are coded along the spiral track of the disc (Pohlmann). When the beam strikes a land, it is reflected back to a photodiode and generates an electric pulse; however in striking a pit, no electrical pulse is generated, for the reflected beam is out of phase (“Compact Disc”). This series of pulses is translated into binary code in the form of a sequence of 1s and 0s based on the length and combination of the electrical pulses (“Compact Disc”). Figure 1-2 displays a diagram of such a hardware system used to decode audio CDs.

Figure 1-2 Operating Principles of an Audio Compact Disc (Pohlmann)

Scratches on the polycarbonate substrate will effect the reflection of the laser and result in misreading of the information; if the scratch is deep enough or large enough, it can result in corruption of the file and loss of the information entirely. Not all scratches will cause fatal damage to the information. Minor scratches are analogous to light scratches on a pair of eyeglasses; because the data is far enough below the surface of the disc, the laser is still able to focus beyond the scratch (Byers). Though CDs have error correction coding for small imperfections, deep, wide, or bunched scratches can cause the laser to misread enough data to create an error, and if the scratch is deep enough to pervade the metal layer, the data cannot be read or repaired (Byers). Polycarbonate is also subject to crazing, which reduces the clarity of the material in exclusive locations (Ranky). With reduced optical clarity, the information storage device is likely to often experience misreads. Oils in fingerprints and vapors in the environment all contribute to crazing (Ranky).

1.2.Survey of Literature

Since its introduction in 1982, the CD has completely redefined prerecorded music; the medium has expanded beyond audio recordings permeating all forms of digital storage including documents and videos (“Compact Disc”). CDs are a very convenient and common source of data storage and are marketed worldwide, but they are prone to error. The first step in understanding the problems they encounter is to comprehend the correct function of a disc. The majority of errors occur as a result of damage to the polycarbonate layer, which composes more than 50% of the total volume of the disc (“Compact Disc”). This layer’s main purpose is to protect the aluminum stratum holding the information. Information is retrieved from this layer as a laser from the hardware system passes through the polycarbonate and reflects off of the thin aluminum coating. It is central to the correct information translation of the disc that the polycarbonate permits the laser to reflect appropriately; however, this material is easily scratched and subject to crazing (Pohlmann). If the optical clarity of the material is reduced or the surface is scratched, the CD will skip, misinterpret, or permanently lose data (Ranky).

We aimed to alter the polycarbonate to a more durable material that displayed much better resistance to the everyday wear of discs. While researching the materials field of engineering we frequently encountered research in the field nanotechnology.

Nanotechnology is a term coined recently in 2004 referring to the manufacturing of materials at an extremely small scale of 100 nanometers or less (Stewart). At a scale this small, particles or thin films of some materials may display enhanced chemical and physical properties compared to those in bulk, and the field holds promise for significant advances in a variety of applications (Stewart). Using its principles, a scratch resistant coating has been developed for some plastics to be used in glasses and helmet visors (Shadler). Nanotechnology has also been utilized in the production of more flame retardant materials and in fuel tank linings to protect against gas leakages (Hay and Shaw). Introducing nanoparticulates, nano-sized particles, into the matrix of the material present, certain properties can be enhanced without sacrificing others (Stewart). In the cases we found, the optical clarity of the glasses and visors was not affected, but the new nanocomposite was harder to damage (Schadler). This displayed that this avenue of nanotechnology could in fact be applicable in solving our problem.

A polycarbonate nanocomposite offered the most promising solution, and we decided to enhance the polycarbonate with silicon dioxide nanoparticulates. We choose this material because it is transparent, stable, strong, and readily available. Since the nanoparticulates will exemplify the same properties as the bulk material, these qualities represented exactly what we wanted (Schadler). To get our desired nanoparticulates of silicon dioxide a method known as the Sol-Gel process can be utilized (Baik). Once we have our nanoparticulates, a common technique for creating composites known as the melt blending process will combine the polycarbonate and silicon dioxide giving us our desired nanocomposite. This can potentially produce a much stronger material that will mirror the properties of the polycarbonate while creating a much stronger surface.

1.3.Objectives

Because of the growing amount of data and documents that members of our society create and continually rely on, digital mass storage technology is a field always searching for improvements. The compact disc is still the most convenient source of data storage, but scratches on its surface can easily result in the loss of important documents. By increasing the durability of CDs and simultaneously reducing the frequency of scratches, one would improve the everyday usage of this method of information storage making this technology more reliable.

By enhancing the polycarbonate protective layer with a less damage prone material, CD errors would occur less often, making the technology more reliable.

1.4.Constraints

In order for information to still be readable by current hardware systems, any alteration must match certain specifications. As the laser beam passes through the protective substrate absorption and scattering loss take place. In order for information to be properly read from the CD, the protective plastic and reflective metal layers must demonstrate at least 70% optical reflection (Wochele). Because information is coded on such a small scale, the substrate material must also be transparent within the range of 320 to 380 nanometers (Wochele). To ensure that the newly manufactured disc can be played in any player, it must adhere to certain geometrical specifications. The CD must be 1.25 mm with a degree of variance of only 0.1 mm (Wochele). One must also ensure these optical and geometrical properties remain unaffected under various climatic conditions likely to be encountered during storage or general usage. Normally, CD properties are tested to ensure they are able to withstand temperatures of 20o to 45o Celsius and remain unchanged in relative humidity conditions up to 90% (Wochele).

1.5.Criteria

In order to be deemed successful, our new CD composition should be compatible with current hardware systems and produce a more scratch resistant surface. Altering the composition should not compromise any of the characteristics of a polycarbonate disc, and the disc should still function as well under similar conditions. Because the completion of this design project will result in a marketable product, consumer opinion must be considered. Because CDs can be easily replaced, the cost increase of our newly composed CDs should not be too significant.

SOLUTION
Statement of Work

In solving this problem, we considered two tracks- repair and prevention. The first approach we considered was a dependable way to correct errors caused by scratches after they have already occurred. Because these methods often left room for error and were inconvenient for consumers, we were motivated to take a more preventative standpoint by changing the material to better resist damage.

Initially we considered entirely replacing the polycarbonate layer with a more durable material. Prospective materials needed to be light permeable and more resistant to abrasion than the current matter. As we searched for potential replacements we frequently happened upon references to nanotechnology (Wochele). Nanotechnology is a field of science where one manipulates matter on a scale of less than 1 μm (Stewart). Nanoparticulates are particles with dimensions smaller than 100 nm. In nanocomposites these small particles (also called fillers) are combined with a host material characterized as a matrix (Stewart).

We found nanopolymers that were being used as scratch-resistant, transparent coatings in cell phones. This material, with a few adjustments, could be tailored specifically to protect CD surfaces, making CD damage a thing of the past (Schadler). Knowing what can be done with this technology, we further researched the field of nanocomposites and polymers.

Although nanocomposites are still a young technology, they are nothing new to the field of materials engineering. Nanocomposites have been used to improve upon more common items than people realize. It has already been used to keep non-refrigerated food fresh for a much longer period of time by reducing oxygen transmission (Hay and Shaw). The automotive industry also made advancements through nanotechnology. Using nanoparticulates, the industry has achieved reductions in fuel transmittal (Hay and Shaw). Haghighat of Triton Systems demonstrated that it is possible to use nanoclays in light transmitting applications (Hay and Shaw). Through the use of nanoclays as fillers, transparency was enhanced and haze reduced. Triton Systems also showed that nanocomposites could be used to enhance both toughness and hardness of a transparent material without jeopardizing the performance or transparency level of the application (Hay and Shaw).

2.2.Results

Specifically we are suggesting the use of a silicon dioxide based nanocomposite. This polymer nanocomposites would consist of filling the spaces in the matrix of a polymer with nanoscale size particles of silicon dioxide. Silicon dioxide, also known as silica, is the filler of choice because it is a translucent crystalline solid and exemplifies the properties we wish to enhance in the polycarbonate (Time Domain). In our newly composed CD, the bulk of the material will remain the already used polycarbonate. The figure below exemplifies a polymer matrix. All the visible black space is what we aim to fill in a precise order with silica molecules.

Figure 2-1. Example of a Polymer matrix (Accelrys)

Silicon dioxide is one of the most abundant compounds on our planet and has been discovered in 35 crystalline shapes (Time Domain). It is bonded by double covalent bonds making it extremely stable. The density of each crystalline shape varies depending on the arrangement of atoms. The densities can range from 2.0 g/cm3 to 2.65 g/cm3 (CERAM Research). This could result in a dramatic increase in strength from the currently existing CD. The quartz crystal is one of the most common forms of SiO2, and is at the higher end of the varying densities. Silicon dioxide has a melting point of up to 1830o Celsius, and such a high melting point can help prevent deformation and warping of the disc in high temperatures (CERAM Research). The bond distance is quite small; at 0.18 nm it is a perfect candidate for being our nanocomposite filler (Time Domain). It is easy to see how this compound could dramatically improve strength and durability. It is no big secret that silicon dioxide can be used for a refractive application, for it has already been used for eyewear lenses, prisms, and numerous other lens applications (CERAM).

Filling the gaps in the matrices of the polymer will result in a dramatic increase in durability and strength. Only about 5% of the polymer nanocomposite’s volume is composed of the nanomaterial or filler molecules (Schadler). This means that dramatic increases in physical and chemical properties of the material can be obtained with only small additions. Comparatively, micrometer sized fillers have been recorded to occupy as high as 60% of the total volume (Schadler). The smaller sized particles allows for more particles to be carefully placed into the desired locations in the matrix resulting in a filler with more surface area.

The most complicated and potentially pricey segment of this design is the acquisition of the nanoparticles themselves. A method called the sol-gel process seems to be the best for producing the desired nanoparticulates of silicon dioxide (Baik). High purity fumed silica has already been used in a sol-gel process to create reinforced scratch resistant glass. In this process the silica is mixed with water at room temperature then cast into a mold and let to form a gel (Baik). Once the gel is ready, through hydrolysis bonds are formed. The gel is dried at approximately 250o Celsius and a pressure of 6,000 KPa (Baik). The use of high purity fumed silica is known to improve properties such as scratch resistance and has a transparency over a wide spectrum from ultraviolet to infrared light (Baik).