Metallized and Magnetic Polymers E-Book

Johannes Karl Fink

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 286

Veröffentlichungsjahr: 2016

Beschreibung

This book focuses on the chemistry of metallized and magnetic polymers, as well as the special applications of these materials. After an introductory section on the general aspects of the field, the types and uses of these polymers are detailed, followed by an overview of the testing methods. The book is divided equally into two parts - metallized polymers and magnetic polymers - and both parts follow the same structure: * All methods of fabrication * Properties and methods of measurement including standard test methods and interface properties * Fields of applications * Environmental issues including recycling and biodegradable polymers

Leseprobe

Contents

Cover

Half Title page

Title page

Copyright page

Preface

Acknowledgements

Part I: Metallized Polymers

Chapter 1: General Aspects

1.1 History

References

Chapter 2: Methods of Fabrication

2.1 Methods for Metallizing

2.2 Welding

2.3 Molding

2.4 Special Aspects

2.5 Special Uses

References

Chapter 3: Properties and Methods of Measurement

3.1 Standard Test Methods

3.2 Interface Properties

3.3 Combustion of Metallized Polymers

3.4 Fluorine Diffusion in Metallized Polymers

References

Chapter 4: Fields of Application

4.1 Shielding Electromagnetic Interference

4.2 Microwave Components

4.3 Conductive Fibers

4.4 Intermetallic Layers

4.5 Metallized Polymer Mirror

4.6 In-Mold Metallized Polymer Articles

4.7 Camera Housing

4.8 Metallized Polymer Film Capacitors

4.9 Micro-fuel Cell

4.10 Printed Circuit Boards

4.11 Electrostatic Miniature Valve

4.12 Antennas

4.13 Gas Transmission

4.14 Micromechanical Sensor and Actuator Devices

4.15 Medical Uses

References

Chapter 5: Environmental Issues

5.1 Recycling

5.2 Metallized Plastic Packages

5.3 Biodegradable Metallized Polymers

References

Part II: Magnetic Polymers

Chapter 6: General Aspects

6.1 History

6.2 Basic Issues of Magnetism

6.3 Types of Magnetic Organic Polymers

References

Chapter 7: Methods of Fabrication

7.1 Preparation of Magnetic Polymer Particles

7.2 Special Types

References

Chapter 8: Properties and Methods of Measurement

8.1 Standard Test Methods

8.2 Phase Diagram of Magnetic Polymers

8.3 Adsorption Mechanism of Amino-Functionalized Magnetic Polymers

8.4 Cyano-Bridged Coordination Polymers

8.5 Spin-Glass Behavior in Some Schiff-Base Co-containing Magnetic Polymers

8.6 Neutron Scattering from Magnetic Polymers

8.7 Shape-Memory Effect

References

Chapter 9: Fields of Application

9.1 Improvement of Drilling Performance

9.2 Electronic Uses

9.3 Biotechnology

9.4 Medical Uses

References

Chapter 10: Environmental Issues

10.1 Analysis Methods

10.2 Magnetic Polymers in Water Treatment

References

Index

Acronyms

Chemicals

General Index

Metallized and Magnetic Polymers

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Publishers at Scrivener Martin Scrivener ([email protected]) Phillip Carmical ([email protected])

Copyright © 2016 by Scrivener Publishing LLC. All rights reserved.

Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Salem, Massachusetts. Published simultaneously in Canada.

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Library of Congress Cataloging-in-Publication Data:

ISBN 978-1-119-24232-1

Preface

This book focuses on the chemistry of metallized and magnetic polymers, as well as special applications of these materials.

After an introductory section on the general aspects of the field, the types and uses of these polymers are summarized, followed by an overview of some testing methods.

The text focuses on the literature of the past decade. Beyond education, this book may serve the needs of industry engineers and specialists who have only a passing knowledge of these issues, but need to know more.

How to Use this Book

Utmost care has been taken to present reliable data. Because of the vast variety of material presented here, however, the text cannot be complete in all aspects, and it is recommended that the reader study the original literature for more complete information.

The reader should be aware that mostly US patents have been cited where available, but not the corresponding equivalent patents of other countries. In particular, in this field of science, most of the original patents are of Japanese origin.

For this reason, the author cannot assume responsibility for the completeness, validity or consequences of the use of the material presented here. Every attempt has been made to identify trademarks; however, there were some that the author was unable to locate.

Index

There are three indices: an index of acronyms, an index of chemicals, and a general index. In the index of chemicals, compounds that occur extensively, e.g., acetone, are not included at every occurrence, but rather when they appear in an important context. When a compound is found in a figure, the entry is marked in boldface letters in the chemical index.

Acknowledgements

I am indebted to our university librarians, Dr. Christian Hasenhüttl, Dr. Johann Delanoy, Franz Jurek, Margit Keshmiri, Dolores Knabl, Friedrich Scheer, Christian Slamenik, Renate Tschabuschnig, and Elisabeth Groß for their support in literature acquisition. In addition, many thanks to the head of my department, Professor Wolfgang Kern, for his interest and permission to prepare this text.

I also want to express my gratitude to all the scientists who have carefully published their results concerning the topics dealt with herein. This book could not have been otherwise compiled.

Last, but not least, I want to thank the publisher, Martin Scrivener, for his abiding interest and help in the preparation of the text. In addition, my thanks go to Jean Markovic, who made the final copyedit with utmost care.

Johannes Fink Leoben, 2nd February 2016

PART I

METALLIZED POLYMERS

Chapter 1

General Aspects

There are monographs on the issues of metallized polymers (1). The topic of metallization of polymers has been reviewed (2).

Metallized plastic components have the same high-quality look and feel as chromium-plated metal parts and are less costly to produce (3). For these reasons, these materials are used in auto manufacturing for radiator grills or mirror caps, as well as for electronic appliances and bathroom fittings.

With a high-quality metallic coating, plastic components take on a luxurious chrome look. thus, they are popularly used in design elements for cars, electrical appliances, kitchens and bathrooms. In vehicles, radiator grills, mirror caps, door handles and trim are some items with such a finish. Push buttons and covers for hi-fi equipment, cell phones and coffee machines, as well as shower heads, are further examples of products coated with this method (3).

Plastic parts can be coated with metal, a process called metallization, for both aesthetic and mechanical purposes (4). Visually, a metal-coated piece of plastic features increased gloss and reflectivity. Other properties, such as abrasion resistance and electric conductivity, which are not innate characteristics of plastic, are often obtained through metallization. Metallized plastic components are used in similar applications as metal-plated parts, but tend to be lower in weight and have higher corrosion resistance, although not in all cases. In addition, electrical conductivity can be controlled in metallized plastic components, and they are inexpensive to manufacture. To metallize a piece of plastic, several common methods are used (4):

1. Vacuum metallization,

2. Arc spraying,

3. Flame spraying, and

4. Plating.

It is also possible to metallize a transfer film, and use alternative methods to apply the film to the surface of the substrate (4).

1.1 History

The history of fabrication of metallized polymers has been summarized (5, 6). The first commercial plating of polymers was done in 1905 (7). Also during World War II a fair amount of production took place. The large-scale production started in the mid-1950s (8). An electrical condenser with coated paper was described in 1910 (9).

This was refined some 50 years ago (10). The first metal spraying experiments were done around 1896. However, the zinc arc spray and flame-spray methods were commercialized only after 1910 (5). Sputtering was basically observed in the 1850s by the electric discharges of gases. Metal spraying experiments have already been done in 1896. Practical zinc arc spraying and flame spraying were commercialized after 1910.

1.1.1 Capacitors

Before the introduction of plastic films, capacitors had been fabricated by sandwiching a strip of impregnated paper between strips of metal, and rolling the composite into a cylinder (11).

The manufacture of these types started in 1876. These capacitors were used from the early 20th century onwards (12). With the development of plastic materials, the capacitor industry started to replace paper with thin polymer films. One very early development in film capacitors was described in 1947 (13). The introduction of plastics in plastic film capacitors follows the historic order summarized in Table 1.1.

Table 1.1 Historic order of plastics as capacitors (14).

Polymer

Abbreviation

Introduced in

Poly(styrene)

PS

1949

Poly(ester)

PET

1951

Cellulose acetate

CA

1951

Poly(carbonate)

PC

1953

Poly(tetrafluoroethylene)

PTFE

1954

Poly(parylene)

1954

Poly(propylene)

PP

1954

Poly(ethylene)

PE

1958

Poly(phenylene sulfide)

PPS

1967

An early special type of plastic film capacitors were made from cellulose acetate films. The polar insulating dielectric cellulose acetate was a synthetic resin that could be made for metallized capacitors in paint film thickness down to about 3 µm. A liquid layer of cellulose acetate was first applied to a paper carrier, then covered with a wax, dried and then metallized. During the winding of the capacitor body, the paper was removed from the metallized film. The remaining thin cellulose acetate layer showed a dielectric breakdown of 63 V. This was sufficient for many general purpose uses. Further, the small thickness of the dielectric material decreased the overall dimensions of these capacitors in comparison to other film capacitors at this time.

References

1. K.L. Mittal, ed., Metallized Plastics: Fundamentals and Applications, Marcel Dekker, New York, 1998.

2. W.J. Miller, “Metallizing,” in J.I. Kroschwitz, ed., Encyclopedia of Polymer Science and Engineering, Vol. 9, pp. 580–622. Wiley-Interscience, New York, 2nd edition, 1987.

3. Oerlikon, Revolutionary new process for metallizing plastic components, electronic: http://www.oerlikon.com/en/company/company-overview/surface-solutions-segment/success-stories/epd/, 2015.

4. Thomasnet, How to metalize plastic, electronic: http://www.thomasnet.com/articles/custom-manufacturing-fabricating/how-to-metalize-plastic, 2015.

5. G.A. Krulik, J.A. Thornton, and W.J. Miller, “Metallizing,” in K. Matyjaszewski, ed., Encyclopedia of Polymer Science and Technology. Wiley-Blackwell, online edition, July 2011.

6. W.J. Miller, “Metallizing,” in A. Seidel, ed., Processing and Finishing of Polymeric Materials, pp. 947–948. Wiley, Hoboken, N.J, 2011.

7. H. Narcus, Transactions of the Electrochemical Society, Vol. 88, p. 371, 1945.

8. C. Saywer, Printed circuit techniques, Technical Report 192, National Bureau of Standards, Washington (DC), 1948.

9. W.W. Dean, Electrical condenser, US Patent 965 992, assigned to Dean Electric Co., August 2, 1910.

10. C.W. Mckee, R.W. Mckee, and C.M. Rich, Capacitor with metallic embedded plastic electrodes, US Patent 3 185 907, assigned to Welding Service Inc., May 25, 1965.

11. Wikipedia, Film capacitor — Wikipedia, the free encyclopedia, 2015. [Online; accessed 3-October-2015].

12. J. Ho, T.R. Jow, and S. Boggs, IEEE Electrical Insulation Magazine, Vol. 1, p. 20, 2010.

13. J.T. Sharples and G.L. Woolnough, Improvements in electrical energy regulators for electric cookers, ovens, hot-plates and the like, GB Patent 587 953, assigned to Vickers Electrical Co. Ltd., May 5, 1947.

14. H. Loth, Filmkondensatoren: Bauarten, Technologien und Anwendungen, Verlag Moderne Industrie, Landsberg/Lech, 1990.

Chapter 2

Methods of Fabrication

2.1 Methods for Metallizing

Common methods for metallizing a polymer film surface are lamination of a metal sheet or foil, wet metal plating, vacuum deposition, sputtering or electrically conductive paint coating (1).

2.1.1 Laminating

In the method for laminating a metal sheet or foil, it is common to use an adhesive, whereby it is difficult to obtain an inexpensive product having a well-balanced property such as adhesive strength between the film and the metal sheet or foil, and it is technically difficult to obtain a smooth well-finished surface (1).

2.1.2 Wet Plating

The wet metal plating is conducted in such a manner that catalysts for metal plating are applied to the portions where a metal layer is to be formed, or the portions where no metal layer is to be formed are covered with metal plating resist, prior to the formation of a metal layer (1). However, it is not easy to roughen the surface of the polymer base sheet to such an extent that adequate adhesion strength can thereby be ensured between the metal layer and the polymer base sheet. Accordingly, the polymer capable of providing adequate practical peeling strength, is rather limited. Further, the selective application of the catalysts for wet metal plating or the precise application of the plating resist, involves technical difficulties. Besides, the process steps are rather complicated, the metal layer-forming speed is rather slow, and there is a problem of how to dispose of the waste plating solution. Thus, the wet metal plating method is costly.

2.1.3 Fluid Electrolytic Deposition

A method for metallizing polymers has been described that is generating anionic sites on the structures, contacting these with a metal cation then reducing the metal cation to metal at the anionic sites or treating the metal cations to form a semiconductor. The metallized polymers are useful as electrical conductors or semiconductors. The process runs as (2, 3):

1. The polymer substrate is treated with a solution of a strong base to generate surface anionic sites.

2. These treated structures are then contacted with a solution of the desired metal cation, which is adhered to it via ion exchange.

3. The metal cation is then treated with a compound that forms a semiconductor to yield a semiconductor imbibed polymer or is reduced to the metal state by interaction with the polymer structure to obtain a metal imbibed polymer.

4. If the polymer structure does not have sufficient reduction potential, the cation can be reduced by the interaction with a solution of a strong reducing agent.

5. Optionally, then a second metal can be deposited via electroless plating or electrodeposition to obtain a metal-coated polymer.

Suitable polymers are poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), poly(p-benzamide), poly(4,4′-biphenylene isophthalamide), poly(benzimidizole), poly(chloro-p-phenylene isophthalamide) and the corresponding copolymers.

Preferred bases are CH2SOCH−3, potassium tert-butoxide, and the polyanions of the polymers described above either used alone or in the presence of alcohols, amines or nitrates. A preferred mixture of bases is potassium tert-butoxide and lithium nitrate.

The preferred solvent to use is dimethyl sulfoxide (DMSO). The combination of base and solvent should cause a swelling of the polymers, as this permits an improved contact with the reagents.

The operating at temperatures depend on the particular solvent that is used, and typically vary between the melting and boiling points of the solvents. For example, when the solvent is DMSO, basically, the temperature range is 17–190°C. However, the preferred temperature range is room temperature to about 60°C. Metals which can be used for the metallization of the polymer substrate are summarized in Table 2.1.

Table 2.1 Metals for metallization (2).

Normal use

Semiconductive use

Copper

Copper

Silver

Gold

Cadmium

Cadmium

Zinc

Zinc

Platinum

Iron

Iron

Cobalt

Cobalt

Chromium

Tin

Tin

Lead

Lead

Rhodium

Ruthenium

Nickel

Nickel

Germanium

Gallium

Aluminum

Typically, the concentration of the metal cations is about 0.2 mol l−1. Any metal or metal complex can be used that has appropriate solubility in the solvent of choice (2, 3). Examples for the preparation have been disclosed (2):

Preparation 2–1: Silver-imbibed poly(p-phenylene terephthalamide) yarn was prepared as follows. Six-inch lengths of poly(p-phenylene terephthalamide) yarn were washed with water, followed by acetone and methylenechloride and then oven dried. Sections of yarn were dipped for 5 min into a solution of 0.5 mol l−1 potassium tert-butoxide in DMSO. This generated an orange gel on the surface of the fibers. The yarn was then placed into a solution of 0.5 moll−1 silver trifluoroacetate in DMSO for two minutes. This caused the orange gel to become black. The yarn was next placed in a solution of 0.5 mol l−1 sodium borohydride in DMSO for two minutes. This caused no further color change, but gas evolution took place from the fiber surface. Finally, the yarn was washed with water, followed by acetone, and then hexane. The yarn sample was then air dried. A second section of poly(p-phenylene terephthalamide) yarn was similarly treated only with residence times of 2 min in the potassium tert-butoxide solution, 1 min in the silver trifluoroacetate solution, and 2 min in the sodium borohydride solution. Conductivity measurements showed that both of these samples were electrical conductors.

Nickel sulfide semiconductor imbibed poly(p-phenylene terephthalamide) films were prepared as follows (2):

Preparation 2–2: A solution of 0.10 g of nickel chloride hydrate in 2 ml of DMSO was added to a solution of 74.9 g of a 1.33% poly(p-phenylene terephthalamide) polyanion solution as the potassium salt. A gel immediately formed, but vigorous stirring restored a viscous solution with some small gel particles. The resulting solution was used to cast a film which was quenched with water to restore the neutral poly(p-phenylene terephthalamide) polymer. Treatment of the film with an aqueous solution of sodium sulfide gave a poly(p-phenylene terephthalamide) film containing nickel sulfide particles.

2.1.4 Plating-out Method

The preparation of metallized films using the plating-out method has been demonstrated (4). Various metal powders with lower reduction potential were dispersed in a poly(vinyl alcohol) (PVA) aqueous solution, dried to form a film, then treated with metal salt solutions having metal ions in the metal salt with higher reduction potential.

Metallized PVA films exhibited a low surface resistivity around 100–101 Ohm cm−2 when using the plating-out method. The surfaces of these films were shown to be metallized by means of X-ray analysis.

2.1.5 Retroplating-out Method

A method to prepare polymer metallized films was found by using polymer metal chelate films treated with wetted metal plates or metal powders (5). The polymer metal chelate films can be prepared by metal salts mixed with the polymers containing a functional group, such as PVA, poly(amide) (PA), poly(acrylamide), and poly(urethane) (PU). This method is addressed as the retroplating-out method.

Polymer metallized films exhibit a low surface resistivity around 0.1 Ohm cm−2. The surfaces of these films were shown to be metallized by means of X-ray analysis. The conduction mechanism was verified reasonably well by using a scanning electron microscope and UV-visible absorption data (5).

2.1.6 Electroless Plating

Since most plastic surfaces are not electrically conductive, the traditional electroplating methods are not quite suitable for providing a metallic coating (6). However, electroless plating is one feasible method for the plating of polymeric materials.

The development of chemical etchants resulted in a controlled microporous surface of the polymeric material and greatly improved electroless plating baths, leading to metal depositions which adhere well to the polymeric surface and which may serve as a conductive preplating for subsequent electroplating.

Electroless plating processes are labor intensive, complicated and hence expensive. For example, a typical electroless plating procedure involves the steps of etching the polymeric material with strongly oxidizing solutions of chromic acid in order to physically roughen the polymeric surface and chemically modifying it to give it a hydrophilic nature; neutralizing it with a mildly acidic or basic reducing agent for removing the detrimental hexavalent chromium; sensitizing it with stannous chloride and palladium chloride for nucleation of palladium, accelerating it with acidic or basic solutions for removing excess tin and exposing palladium nuclei and electroless depositing metals such as nickel and copper on it from a plating bath (6).

2.1.7 Vacuum Deposition

The vacuum deposition method is a good metallizing method (1). However, the adhesive strength of the metal layer with the base film is rather weak, and surface pretreatment of the base film will be required.

In order to form a metal layer only at a predetermined portion, other portions must be covered. A vacuum system or an inert atmosphere is employed and, accordingly, a difficult high technique will be required for a continuous process and the apparatus will be expensive.

Besides, since a vacuum system is employed, an apparatus capable of producing a film having a wide width will be expensive, and a high level of technical skill will be required. Decorative applications account for ca. 80% of metallizing (7).

Metals used in industrial vacuum coating applications are summarized in Table 2.2. Polymers used in industrial metallizing are summarized in Table 2.3.

Table 2.2 Metals used for vacuum coating (7).

Metal

Melting point/[°C]

Uses

Aluminum

660

Decorative finish

Cadmium

321

Aircraft parts

Chromium

1900

Mirror surface on glass

Copper

1083

Electronic circuits

Gold

1083

Electronic circuits

Table 2.3 Polymers used for metallizing (7).

Polymer

Uses

Cellulosics

Costume jewelry, toys, appliances

Acrylics

Lenses, light diffusers

ABS

Auto interiors, housewares

Poly(styrene)

Appliances, knobs, cosmetic containers

Poly(carbonate)

Automotive applications

poly(ethylene)

Housewares, toys, enclosures

2.1.8 Sputtering

Sputtering is a material transportation phenomenon caused by energetic ions striking a cathode, causing the material making up the cathode to be transferred to a different surface through a momentum transfer mechanism (8). In the performance of a sputtering technique, the substrate to be coated is placed adjacent to a cathode made of the substance which will form the coating. The cathode is subject to a high negative voltage and is placed in an inert gas atmosphere at low pressure.

Under the influence of the high voltage potential difference, atmospheric ions are accelerated against the surface of the cathode wherein the momentum of the ions is transferred to atoms on the surface of the cathode, ejecting the atoms from the surface of the cathode and causing them to contact and adhere to the adjacent substrate. Such sputtering process parameters which affect the sputtering rate include (8):

1. Mass and energy of the impinging ions,

2. Gas temperature,

3. Electrode spacing,

4. Material and crystallographic orientation of the cathode,

5. Cathode surface, and

6. Cathode shape and shielding.

The inert gases useful for such sputtering techniques include helium, neon, argon, krypton, xenon and nitrogen. Preferably, a chromium metal or chromium alloy is sputtered to a layer having a thickness of 2–100 Å (8).

It has been stated that the sputtering method has disadvantages such as it is difficult to form a thick metal layer and the production rate is slow (1).

2.1.9 Paint Coating

The electrically conductive paint coating is a simple metallizing method. However, the metal layer thereby formed tends to be peeled off as time passes, and it is therefore difficult to form a thin uniform metal layer on a base film (1). The method of applying a metal sheet or foil on a polymer film surface, followed by removing the metal layer except for the predetermined pattern, is widely used for the production of printed circuit boards.

Electrochemical impedance spectroscopy (EIS) was used to evaluate a high resistance paint coating immersed in a 10% sodium chloride solution. The coating resistance and coating capacitance were extracted from Bode and Nyquist plots during a period of 90 d of immersion (9).

A protective paint coating has been described (10). The composition contains a polymeric binder with both hydrophobic and hydrophilic moieties, i.e., an acrylic-graft terpolymer with glycidyl acrylate and an epoxy resin. The preparation of a glycidyl acrylate copolymer runs as (10):

Preparation 2–3: Into a 3 l round bottom flask fitted with a nitrogen inlet, water cooled condenser, temperature probe, and mechanical stirrer was charged 748.6 g of 2-butoxyethanol. The flask was heated to 115°C under nitrogen sparge. A monomer mixture of 1632.0 g of 2-ethylhexyl acrylate, 68.0 g glycidyl methacrylate, 21.8 g dibenzoyl peroxide (78% in water), and 65.0 g of 2-butoxyethanol was added to solvent in 2.5 hours. The mixture was held at 115°C for 30 min, and then 4.3 g of tert-butyl perbenzoate were added. The reaction was continued for 1 h and then the mixture was allowed to cool. The product obtained was a viscous clear resin solution of 68.2% nonvolatile and 0.38% oxirane.

In addition, several other examples of preparation have been detailed (10).

2.1.10 Pressure-Sensitive Conductive Rubber

Conventional pressure-sensitive conductive rubber-like polymer films are usually prepared by blending and dispersing into a rubber-like base material, a conductive powder as a conductive material, for instance, a carbon powder such as carbon black or graphite powder, or a metal powder such as gold, silver, nickel, stainless steel or copper stabilized with a noble metal (1).

It is common that the conductive powder is mechanically dispersed into the rubber-like polymer by means of a ball mill, a roll mill, a Bumbury mixer or a screw extruder. However, the degree of dispersion is largely dependent on the dispersing method and the dispersing conditions. Accordingly, it has been difficult to obtain pressure-sensitively conductive rubber-like polymer films which are capable of providing predetermined characteristics consistently. Further, the selection of the conductive powder is also important. Even when the same kind of the conductive powder is used, the pressure-sensitive conductivity or the durability for repeated use, varies to a large extent depending upon the shape, particle size or particle size distribution of the conductive powder.

With the conventional pressure-sensitively conductive rubber-like polymer film, it is intended to utilize the change of electric resistance caused by a strain exerted on the film. However, it used to be difficult to optionally control the electric resistance to change in proportion to the strain. Nevertheless, pressure-sensitively conductive rubber-like polymer film is preferably used for various switches, such as switches for automatic doors, mat switches of electromotive sewing machines, etc., in view of the merits of it containing no mechanical driving parts and thus being free from an electric noise, and it thereby making it possible to substantially reduce the size and the weight. Accordingly, such pressure-sensitively conductive film is expected to find a wider range of applications.

On the other hand, a metal-containing polymer is usually intended for the utilization of the nature of the metal, i.e., the characteristics of the metal against electricity, magnetism, heat, light, sound, chemicals or radiation. Particularly, a polymer in which fine metal particles are uniformly dispersed, is of great interest. As a method for producing a polymer containing a metal, it is known to mix a polymer with metal powder. However, there is a limitation to the size of the metal particles which can be mixed and dispersed with the polymer. For instance, it is practically difficult to uniformly disperse metal particles having a size of not greater than 10 m, in a polymer, and a shaped article thereby obtained tends to be inferior in its mechanical strength.

When metal particles are to be dispersed into the polymer in a high concentration the metal particles are likely to contact one another and, accordingly, the amount of the metal particles to be incorporated is limited to a certain level.

A process for precipitating a metal in a resin by using the pyrolytic characteristics of metal hydrides has been described. However, the metal hydrides have a low pyrolytic temperature and are susceptible to moisture. Thus, such a process is not practical.

2.1.11 Grafting of Polyelectrolytes

Polyelectrolytes could be grafted onto hydrocarbon surfaces by a dry-process and chemical-free approach using hydrogen projectiles with high kinetic energy but properly controlled to selectively cleave the C–H bonds. Then, electroless plating was carried out after loading Pd moieties by ion exchange (11). This procedure resulted in high quality metallized polymer films with excellent conductivity and mechanical stability.

2.1.12 Selective Deposition of Metal onto Plastic Substrates

A method of selectively plating a plastic article uses a first polymer resin portion and a second polymer resin portion. The first polymer resin portion is not rendered plateable by sulfonation and the second polymer resin portion is rendered plateable by sulfonation. The method uses the steps of (12):

1. Sulfonating the plastic article, wherein the second polymer resin portion is rendered plateable by sulfonation,

2. Activating the sulfonated plastic article to accept electroless plating thereon, and

3. Plating the sulfonated and activated article in an electroless plating bath.

The plastic article is thereby selectively plated such that the first polymer resin portion does not have plating thereon and the second polymer resin portion is electrolessly plated (12).

2.2 Welding

2.2.1 Ultrasonic Welding of Metallized Plastic

Ultrasonic welding allows accurate and precise application of energy to selectively melt or weld the desired portions of a plastic assembly (13). An ultrasonic assembly is suitable for most thermoplastic materials, and is widely used to weld thermoplastic parts in the automotive, packaging, electronic, and consumer industries. In practice, high-frequency mechanical vibrations are transmitted by the ultrasonic welding machine to mating plastic parts. At the joint or interface of the two parts, a combination of applied force and surface or intermolecular friction increases the temperature until the melting point of the thermoplastic is reached. The ultrasonic energy is then removed and a molecular bond or weld is produced between the two plastic parts.

An ultrasonic welding system typically contains a high-frequency power supply, usually 20–40 kHz. The high-frequency energy is directed into a horn, which is a bar or a metal section, typically of titanium, aluminum, or hardened steel, dimensioned to be resident at the applied frequency. The horn contacts the workpiece and transmits the mechanical vibrations into it. A fixture or nest supports and aligns the two parts to be welded. It is generally made of aluminum or steel, and is sometimes lined with cast urethane or another material that is resilient.

Also, a metallized plastic assembly can be effectively created by joining two metal-coated plastic parts using ultrasonic welding. An effective weld, equivalent to that obtained with unplated plastic, can be obtained on plastic parts that are completely plated with metal in the weld joint areas (13).

2.3 Molding

2.3.1 Molded Products

Metallized plastic molded products can be made from a plastic and multiple coating layers (14). These layers are a base coat layer, a dry metallic film layer, an inter coat layer and a top coat layer.

As the base coating material, either UV curing coating materials or thermosetting coating materials may be used. They can be selected depending on the particular dry type metal film-forming method used, the type of metal to be coated, and the suitability of the coating. UV curing coating materials are preferred because of various factors such as the inter coating materials and top coating materials used.

The starting materials for the resin used as the inter coat layer are acrylamides. The most preferred special comonomer is N-octylacrylamide. This is copolymerized with acrylic acid esters (14).

The top coating material for the top coat layer is an UV curing type coating material. This composition contains 40–90% of a urethane modified polyvinyl compound or epoxy modified polyvinyl compound and 10–60% of a polyvinyl compound which is lower in viscosity than the modified polyvinyl compounds (14). Suitable polyvinyl compounds are summarized in Table 2.4 and in Figure 2.1.

Figure 2.1 Monomers for polyvinyl compounds.

Table 2.4 Monomers for polyvinyl compounds (14).

Monomer

Ethylene glycol di(meth)acrylate

Diethylene glycol di(meth)acrylate

Triethylene glycol di(meth)acrylate

Neopentyl glycol di(meth)acrylate

1,6-Hexanediol di(meth)acrylate

Trimethylolpropane tri(meth)acrylate

Pentaerythritol tri(meth)acrylate

Pentaerythritol tetra(meth)acrylate

Bisphenol A dioxypropyl ether di(meth)acrylate

These compounds preferably can reduce the viscosity of the epoxy or urethane modified polyvinyl compounds when they are mixed together. When curing the inter coating material and top coating material by irradiation with UV rays, it is preferred to add to the coating materials a photopolymerization initiator. Examples of photopolymerization initiators are collected in Table 2.5. Also, some are shown in Figure 2.2.

Figure 2.2 Photopolymerization initiators.

Table 2.5 Photopolymerization initiators (14).

Initiator

Initiator

Benzophenone

4,4′-Bis(di-methylamino)benzophenone

Benzoin

Benzoin methyl ether

Benzoin-

n

-butyl ether

Benzoin isobutyl ether

Acetophenone

2,2-Diethoxyacetophenone

Propiophenone

Methyl phenylglyoxylate

Ethylphenylglyoxylate

9,10-Phenanthraquinone

Preferably, the photopolymerization initiator is added in an amount of 0.1–10 phr into the coating material. The top coating material may also contain polymeric or silicone coating surface improvers, flow improvers, various dyes and pigments, which are also commonly added to conventional coating materials (14).

2.3.2 Metallized Plastic Molding

A metallized plastic molding has been developed that contains a primer on the plastic substrate, on which a metallic film is deposited. Unsaturated compounds which are used for forming a primer layer are summarized in Table 2.6.

Table 2.6 Unsaturated compounds for primer (15).

Compound

Poly(ethylene glycol) diacrylate

Poly(ethylene glycol) sebacate diacrylate

Bisphenol A dioxyethyl ether diacrylate

1,6-Hexanediol diacrylate

Neopentyl glycol diacrylate

Trimethylolpropane triacrylate

Trimethylolpropane tri(meth)acrylate

Pentaerythritol tetracrylate

Lauryl acrylate

The primer is cured by a photopolymerization reaction. For this reason a photoinitiator is added. Suitable examples of the photopolymerization initiators are shown in Table 2.7.

Table 2.7 Photopolymerization initiators for primer (15).

Compound

Compound

Benzophenone

Propiophenone

Benzoin

Benzoin methyl ether

Benzoin isobutyl ether

Methylphenyl glyoxime

Ethylphenyl glyoxime

Phenanthraquinone

Photopolymerization initiators are shown in Figure 2.3. The coated substrates were treated using dry type metallic film-forming methods (15).

Figure 2.3 Photopolymerization initiators.

2.4 Special Aspects

2.4.1 Metallized Polymer Granules

Polymer granules which have a metal layer have been developed (16). These can be prepared by currentless chemical metallization or by combined currentless chemical and galvanic metallization.

Organic synthetic and natural polymers are generally electrical insulators. Their specific resistance is between 1010 and 1018Ohm cm.

If certain polymers having a main chain with a polyconjugated structure are treated with strong oxidizing or reducing agents, their specific resistance drops from about 109 to about 101Ohm cm (17).

However, such conjugated polymers cannot be processed by such customary methods in plastics technology, such as injection molding, extruding or laminating, and they are insoluble in conventional organic and inorganic solvents.

Another way of providing polymers with antistatic properties is to add charge transfer complexes, which are based, for example, on tetrathiofulvalene or tetracyanoquinodimethane. The incorporation of these complexes into polymer matrices is very involved, and therefore of no interest to the plastics processing industry save in very special cases.

It is also known to apply antistatic agents to the surface of a prepared plastic component or to incorporate antistatic agents during the preparation directly into the polymer matrices, examples of antistatic agents being fatty alcohols and quaternary ammonium salts.

In the first case only a temporary antistatic effect is obtained, while in the second case the incorporation of antistatic agents has an adverse effect on the original physical and chemical properties of the polymer material.

It is also known that polymer surfaces can be provided by chemical or physical means with an electrically conductive metal surface (18).

However, these metal layers have an undesirably high specific electrical conductivity. Another disadvantage is that this process is only possible in the case of certain polymers.