| 摘要 |
<p>Transparent sheet material (monolithic or laminated) based on methyl methacrylate homo- or co-polymer (PMMA) (or with at least one outer layer of PMMA in the case of laminated sheet), in which the material shows an increase of 0.1-1 g/cm<3> in average density from the surface to a depth of at least 50 nm, as determined by X-ray reflectometry. Independent claims are also included for: (1) A method for the production of this material by subjecting PMMA sheet to surface fluorination or oxyfluorination in a reactor with a mixture of fluorine, nitrogen trifluoride or chlorine trifluoride plus a carrier gas such as helium, nitrogen or carbon dioxide, in presence of residual atmospheric oxygen if the case arises, until the required increase in density is obtained; (2) Glazing which is resistant to micro-cracking (crazing) following surface densification, i.e. incorporating the above material, especially external porthole glazing; (3) A method for the production of such glazing by cutting PMMA sheet to shape and subjecting each plate to a drawing process, an (oxy)fluorination process as above being carried out before cutting or before or after drawing; (4) A method for repairing aircraft windows by grinding off the outer layer to a depth of 0.3-0.7 mm and subjecting the new surface to (oxy)fluorination as above; and (5) A method for making PMMA sheet resistant to crazing and/or improving its resistance to sticking, in which the PMMA polymer is selected from copolymers of methyl methacrylate and fluorinated comonomers, polymers of methyl methacrylate treated by immersion in a solution of anhydrous hydrofluoric acid or a fluoride salt (NaF, KF, LiF or CaF2) followed electrolytic fluorination, and polymers of methyl methacrylate treated by method (1).</p> |
