Masatoshi Iji

Silicone derivatives as new flame retardants for aromatic thermoplastics used in electronic devices

New silicone derivatives that generate no toxic gas during combustion have been developed for use as flame retardants in the aromatic thermoplastics (polycarbonate and its derivatives, acrylonitrile–butadiene–styrene, polystyrene) used in many electronic devices. A special silicone with a branched chain structure, a phenyl-rich mixture of phenyl and methyl groups in the chain and methyl groups at the chain terminals was found to be effective in retarding the combustion of these plastics, and particularly so for polycarbonate (PC) and its derivatives. These silicone derivatives have shown themselves to be a perfect replacement for halogen compounds, which have been claimed to have a potential environmental hazard when the materials are subjected to combustion. Further, adding these silicone derivatives to PC does not adversely affect important other properties, such as strength, moldability and heat resistance; impact strength is in fact better than that of PC containing a bromine compound as a flame retardant.

Recycling of printed wiring boards with mounted electronic parts

A practical technology has been developed for the recycling of printed wiring boards (PWBs) with electronic parts mounted on them. The recycling ratio of useful materials recovered from a test PWB with our method was 65%, as compared to 23% with a previous method of refining useful metals from the PWB as a whole. The electronic parts on the PWBs were effectively removed by combination of heating to above the melting point of solder and applying such external forces as impact, shear and vibration. We have developed an automatic part removal apparatus (practical model) on the basis of tests for the removal of electronic parts and of our measurements of the forces needed for part removal. The apparatus successfully removes through-hole devices (THDs) as well as surface mounted devices (SMDs) from PWBs with almost no damage. Most of the solder is also removed in this process, while that remaining on the resin board surface can effectively be removed later by surface abrading followed by heating/impacting. Tests shows final solder removal to total 96 wt%. After electronic part and solder removal, the resin-boards are pulverized, and the resulting materials are separated into a copper-rich powder and a powder consisting of glass fiber and resin (GR powder). The recovered electronic parts (including gold) are valuable metal resources for refining, while some have the potential to be reused for their original purpose after being checked for reliability. The copper-rich powder (copper content: 82 wt%) is also a valuable metal resource for refining.

Recycling of epoxy resin compounds for moulding electronic components

This study reports the recycling of the cured epoxy resin compounds containing silica filler and additives for moulding electronic components, which is generated as a mould residue in moulding process. The pulverized residue (moulding resin powder) showed good surface reactivity due to the functional groups contained (silanol, hydroxy and epoxy) and reacted with polar resins such as epoxy resin and phenol resin in a similar manner to silica powder. Recycling a low-stress-type moulding resin powder containing silicone elastomer into a standard moulding resin yielded a new moulding resin that has far better thermal impact resistance than that made with the original standard moulding resin. Moreover, the moulding resin powder was found to be suitable as a filler for epoxy resin products such as insulating materials, paints and adhesives to supply them with sufficient insulating, strength and adhesive properties. Use of the powder as a decorating agent for an acrylic-resin-type construction material also produced a marble-like appearance and improved the surface hardness of the material.

Self-extinguishing epoxy molding compound with no flame-retarding additives for electronic components

A self-extinguishing epoxy molding compound that does not have any flame-retarding additives, such as halogen compounds, has been developed for electronic components. This compound enables the overcoming of environmental issues posed by these flame-retarding additives when compounds containing such additives are burned and disposed of. The molding compound contains phenol aralkyl-type epoxy resin and hardener, both of which include a specific multi-aromatic moiety (biphenylene) in novolac resin structure. The compound extinguished itself after ignition because it formed a stable foam layer on the resin surface during the ignition due to the low elasticity at high temperatures and high pyrolysis resistance of the compound after curing. The foam layer effectively retarded the transfer of heat to the inside during the ignition. Adding silica filler to the molding compound resulted in the synergistic effectiveness of the compound for flame resistance because it increased the foam-layer stability during burning. The molding compound showed other excellent characteristics, including moldability, water resistance, and package reliability. In fact, its resistance to soldering heat, humidity, and high-temperature storage was much better than that of current high-quality epoxy molding compounds containing halogen-type flame-retarding additives.

Flame resistant glass-epoxy printed wiring boards with no halogen or phosphorus compounds

A highly flame-resistant glass-epoxy laminate-type printed wiring board (PWB) that does not contain such flame-retarding additives as halogen compounds and phosphorus compounds has been developed to overcome environmental problems caused by these flame-retarding additives. The PWB contains a self-extinguishing epoxy resin compound (phenol aralkyl type) and a limited amount of harmless metal hydroxide (aluminum hydroxide). It has high flame-resistance with no inclusion of halogen or phosphorus compounds and shows other good characteristics, including resistance to solder heating and chemical agents in processing, electronic properties, and moldability, which make it a practical FR-4 board. These good characteristics were obtained by utilizing the epoxy resin compounds superior properties, including its pyrolysis resistant, hydrophobicity and non-polar properties, and by minimizing the amount of metal hydroxide. The board is very safe when burned, disposed of, and reused as a filler after pulverizing.

Recycling system for printed wiring boards with mounted parts

A practical recycling system has been developed for printed wiring boards (PWBs) with electronic parts mounted on them. This system consists of part-removing, solder-removing and resin-board pulverizing/separating processes, and is effective in the recovery of useful materials. The authors have developed a part-removal apparatus which successfully removes through-hole devices as well as surface mounted devices from PWBs with almost no damage to the devices themselves. Most of the solder is removed by the part-removal, and later by surface abrasion followed by heat/impact. After the removal of parts and solder, the resin-boards are pulverized and the resulting powder is then separated into two types: a copper-rich powder and a powder which consists of glass fiber and resin (GR powder). The copper-rich powder is a good copper resource for refining; the GR powder is usable as a filler for polymer products. Recovered parts which contains valuable metal resources (including gold), can be refined out, as is most commonly the case in other recycling systems, but a more economic and ecologically sound approach would be to exploit the potential of parts removed in this system to be reused for their original purposes after being checked for reliability.

Mechanical and other characteristics of cellulose ester bonded with modified cardanol from cashew nut shells and additional aliphatic and aromatic components

Novel cellulose-based bioplastics, mainly using inedible plant resources, were produced by bonding cellulose diacetate (CDA), a modified cardanol, and additional aliphatic and aromatic components. Cardanol is a phenol derivative with a linear unsaturated hydrocarbon side chain (carbon number: 15), derived from cashew nut shells. Esterification of the modified cardanol (3-pentadecylphenoxy acetic acid: PAA) and CDA resulted in a thermoplastic PAA-bonded CDA with high tenacity (long elongation while keeping maximum bending strength), heat resistance, and water resistance. These properties were better than those of a conventional CDA composite consisting of CDA and a conventional plasticizer. By comparing the PAA-bonded CDA with a CDA bonded with stearic acid (SA), which has a linear structure similar to that of PAA’s side chain but has no phenyl part, it was suggested that the linear side chain in PAA has a main role in these prominent properties of the PAA-bonded CDA, while the phenyl part in PAA has pronounced effects on its maximum bending strength and water resistance. Additional bonding of linear alkanoic acids, especially SA as aliphatic components improved the PAA-bonded CDA’s impact strength, and additional bonding of benzoic acid (BA) as an aromatic component further increased its maximum bending strength and elastic modulus. These components improved the thermoplasticity and water resistance of the PAA-bonded CDA while maintaining its high heat resistance relatively well.

Recycling of printed wiring board waste

We have developed a new material recycling process for printed wiring board (PWB) wastes. The main characteristics of the process are pulverizing the PWB wastes under 1 millimeter effectively, and separating copper rich powder from glass fiber and resin powder gravitationally. Copper recovery is up to 97 wt %. The residual glass fiber and resin powder is recyclable as a filler for resin construction materials. With the process, the PWB wastes can be reduced and utilized for valuable resources.<<ETX>>

A pyrolysis-based technology for recovering useful materials from IC package molding resin waste

This paper describes a pyrolysis-based technology for recovering useful materials from molding resin waste, which is the main type of thermosetting plastic waste generated in the fabrication of IC packages. In our pyrolysis of molding resin waste, the main impurities in the recovered silica were carbon (C), antimony (Sb) and phosphoric acid ion (PO/sub 4//sup 3/). The amount of carbon and phosphoric acid ion decreased with increased heating temperature and oxygen concentration. However, the antimony remained constantly between 400 and 1000/spl deg/C because diantimony tetraoxide (Sb/sub 2/O/sub 4/), which is hard to volatilize, was formed by oxidation. Our experimental results suggest that the most effective way to reduce the impurities is to heat at between 1000-1100/spl deg/C and to keep oxygen concentration at about 8 vol%. On the basis of these results, we used a roller kiln type furnace as a prototype practical pyrolysis system for recovering high purity silica. The purity achieved was as follows: C<100 ppm, Sb<1000 ppm, and PO/sub 4//sup 3/<20 ppm, pure enough to be used as inorganic filler for cast insulating materials. The combustion exhaust gas generated by pyrolysis of the molding resin waste was decomposed by a secondary combustion method which was found to decrease organic brominated substances to a sufficiently safe level, and also, to convert the antimony tribromide to diantimony trioxide, which can be collected by a dry recovery process at a high recovery rate and at a useful purity.

Highly Functional Bioplastics (PLA compounds) Used for Electronic Products

We have developed highly functional bioplastics (biomass-based plastics), polylactic acid composites, which improve the environmental friendliness of electronic products. A kenaf-fiber-reinforced polylactic acid has high heat resistance, high impact strength, and good moldability, and its use in PC parts and mobile phone housing has started from September 2004 and May 2006 respectively. A thermoreversibly cross-linked polylactic acid has excellent shape memory and recyclability (i.e., rewritable shape memory), and was used to create freestyle (wearable) mobile products, shape of which users can easily adjust to their own preferences.