Safety glasses were designed as a necessity to protect workers' eyes as an answer to occupational health and safety. evolution of different labor rights, but also they adapted to the different technologies, that have been available in each epoch.
Initially, the technologies focused on achieving faster, more accessible and easier to produce manufacturing, and different companies had a stellar participation.
It was in 1947 that the CR39 ( diallyl) was discovered diglycol carbonate ) a resin that promised great results and in fact evolved the optical industry, as it had a very low refractive index of only 1.498, and acceptable resistance and its main advantages are offering a lower density (1.32 g/cm3). and greater resistance
In 1992, Industrias de Óptica SA (INDO) introduced to the market a material with a refractive index of 1.523 which it called Superfin (Artus et al., 2008) and which belongs to the same chemical family as CR-39, but half Its composition contains an aromatic polyester oligomer and a significant combination of sodium and calcium that, in addition to increasing its refractive index, also modifies its mechanical properties, including resistance.
and it was precisely with the introduction of different companies and very different degrees of resistance that a reference standard was created that could establish a minimum of quality with very concise tests for the evaluation of different impact and penetration tests.
And so in parallel, starting in 1996, tests began with anti-scratch treatments that were created by immersing the lenses in silicon dioxide lacquers (SiO2) in order to manufacture thinner and more resistant lenses, but it turned out to be an ideal material to protect from the scratches.
It was later found in tests that applying these treatments absorbed very little or almost no UV light up to 99.9% less UV and UBA light rays,
It was in 1997 with different manufacturers on the market that the following reference standards were established for the manufacture of lenses. The Z80.1 standard for lenses for optical correction use and Z87.1 for lenses for industrial use from the American national Standards Institute (ANSI, 1997, 2003). Of course it was necessary to include certain standards for manufacturers to carry out their tests.
Simultaneously, workers and employers found that under certain processes the lenses fogged, it was not until the revision of ANSI Z87.1+ that the need to include tests for anti-fog lenses was included in it.
I already explained then that the incorporation of technology to prevent humidity or water from suddenly condensing on the lenses has been an evolution, preventing the worker's vision for a certain time.
The treatments applied to them and the change in the production process have caused the lens to become Hydrophobic, that is, it rejects the molecular tension of water, preventing it from adhering to the lens.
But in the same way, the most recent treatment called Hidroshield, a patented Uvex technology that prevents water from condensing or fogging up to 90 times, incorporates a Hydrophilic effect inside, that is, it quickly condenses the water, allowing it to instead If they condense, they become slightly large droplets that quickly descend down the lens and in combination with the first, it prevents water from fogging up the lens under any circumstances.
It is worth mentioning that these anti-fog treatments on lenses are permanent, and do not require maintenance or additional chemicals of any kind.
Among the most used tests to measure the resistance of lenses to impacts is the so-called Drop Ball Test, which was approved since 1971 (OLA, 1998) and consists (Stephens, 1995) of dropping a steel ball. of 0.56 oz (15.8757 g) and 5/8 in (1.5875 cm) in diameter at a height of 50 in (127 cm) and a speed of 5 m/s. which makes this test consistent with that applied by ANSI Z87.1 for a basic resistance test.
During the beginning of the first quality standards, tests were carried out on different groups to which treatments such as Anti-reflective, Anti-fog, Anti-scratch were applied, the results were conclusive.
The last two do not affect the quality of the lens. It should not be forgotten that when anti-reflection is applied, in addition to measuring the resistance of the material in which the lens is made, stress tests such as ASTM D794 (dry heat), ASTM D543 are also used. (chemical solvents), ASTM D4329 (UV light exposure) and DIN 58196 (boiling salt water), to verify the strength and hardness of the material. That is, an anti-reflective treatment if it affects the hardness of the lens,
Lenses without any type of treatment have a better response and greater resistance to impacts, and can present damage with shots at speeds of 63.97 + 5.46 m/s.
In lenses with anti-scratch and anti-fog treatment The speeds in these studies were 50 to 62 m/s, generated by a 6.35 mm diameter steel pellet, fired by a pneumatic gun.
Lenses with anti-reflective treatments only tolerated speeds between 29.58 and 46.19 m/s. They presented low resistance.
After analyzing the different studies, it can be stated that the anti-reflective treatment directly influences the decrease in impact resistance offered by any material used in the manufacture of ophthalmic lenses. Regardless of its central thickness, these studies also found that polycarbonate is more resistant to impacts than CR39, up to 16 times more resistant. but it can also be affected by the anti-reflection treatment regardless of its thickness.
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