Number

195-EN

Section

General Section

Use

Abstract

Arsenic is used in special glass production to eliminate air bubbles that may lower quality in applications like electronics (TVs, cell phones, computers etc), for example. An alternative technology that maintains glass at high temperature for longer periods allows for bubbles elimination, without the need of arsenic containing additives.

Substituted substances

Reliability of information

Evidence of implementation: there is evidence that the solution was implemented and in use at time of publication

Reason substitution

CMR
skin/respiratory sensitizing
ecotoxicity

Other type of alternative

Technology: thermal desorption of gas bubbles in glass

Hazard Assessment

Substance to be substituted: Arsenic trioxide is a Substance of very high concern and is included on the REACH restriction list, according to Article 73 of Regulation (EG) No. 1907/2006. (REACH Regulation). Alternative substance: Non chemical alternative.

Description of Substitution

Materials for thin- film -transistor liquid- crystal -displays (TFT-LCD) need to be very flat, with a thickness 0.4-0.7 mm and should not contain gas bubbles. ACG group adapted the widely used float method to a technology that allows achieving the qualities mentioned above and does not use arsenic additives. The technological line is presented in figure 1. Ingredients are melted in a high temperature furnace (16000C or higher) and the liquid glass is directed to a refining furnace where gaseous bubbles are removed after which the temperature is lowered, but still kept above melting point. Degassed glass then flows over the surface of the molten tin, forming very flat glass layers that are slowly cooled and finally cut to size.  Fig. 1. Float method for degassed flat glass. Source ASAHI Glass. Advantages: the technology is efficient in degassing glass (not even a single bubble of 0,1 mm diameter, as the producer says) and avoids using arsenic. Disadvantages: fuel consumption is high, though technological improvements managed to lower it.CO2 emissions were lowered in some furnaces by using natural gas instead of heavy oil.

Case/substitution evaluation

The technology described does not eliminate all the hazards related to flat glass production, but it eliminates the use of very hazardous arsenic. By maintaining liquid glass at high temperatures for long hours the technology allows thermal degassing. High temperature decreases glass viscosity and increases gas formation and dynamics, making it easier for bubbles to grow and to migrate towards the free glass surface, where they are eliminated. The float bath is not used for degassing. It is the characteristic of this type of technology – to which it gives the name-and it allows obtaining a flat surface by floating liquid glass over melted metal tin. Exposure to tin aerosols is hazardous and is likely to happen, because of high temperatures and because such systems are run at positive pressure protective atmosphere to avoid tin oxidation. The technology is not free of chemical risks (carcinogen quartz in raw material is another example) but the elimination of the use of arsenic (carcinogen, neurotoxicant, highly volatile/sublimating) is an improvement and it lowers the risk level of the process, of the product and of the wastes.

State of implementation

Full capacity

Date and place of implementation

Japan

Availability ofAlternative

Alternative is available.

Type of information supplier

Producer / distributor

Further information

Asahi Glass to Establish New Production Site for Large-sized TFT LCD GlassSubstrates in Korea, 2004

Glass Substrates for TFTs (AN100)

Date, reviewed

November 26, 2021