OUTSTANDINGLY DURABLE AND HEAT-RESISTANT POLARISING ELEMENT, POLARISING PLATE AND IMAGE-DISPLAY DEVICE, AND POLARISING-ELEMENT PRODUCTION METHOD

摘要

The present invention relates to an outstandingly durable and more particularly heat-resistant polarising element, polarising plate and image-display device in which the zinc, boron and potassium contents are controlled within a specific range, and to a production method for the polarising element. In one embodiment, the present invention provides a polarising element in which, based on the weight of the polarising element, the value of zinc content (wt.%) x boron content (wt.%)/potassium content (wt.%) is from 0.1 to 4.0, and the boron content is from 1.0 to 5.0 wt.% and the potassium content is from 0.3 to 2.0 wt.%, and provides a polarising plate and an image-display device comprising the same. Further, the invention provides a production method for a polarising element at least comprising the steps of dyeing, crosslinking and washing, in which: in the dyeing step, a poly(vinyl alcohol) based film is immersed for between 150 and 300 seconds in an aqueous dyeing solution having an iodine concentration of from 0.05 to 0.2 wt.%, a potassium iodide concentration of from 0.2 to 1.5 wt.% and a temperature of from 20 to 40°C; in the crosslinking step, the poly(vinyl alcohol) based film is immersed for between 30 and 120 seconds in an aqueous crosslinking solution having a boron concentration of from 0.36 to 0.83 wt.%, a potassium iodide concentration of from 4 to 7 wt.% and a temperature of from 15 to 60°C; at least one type of zinc salt selected from the group comprising zinc chloride, zinc iodide, zinc sulphate, zinc nitrate and zinc acetate is included, at a concentration of from 0.4 to 7.0 wt.% in at least one aqueous solution constituted by either the aqueous dyeing solution or the aqueous crosslinking solution or another zinc-salt aqueous processing solution; and, in the washing step, the poly(vinyl alcohol) based film is immersed for between 10 and 30 seconds in pure water at a temperature of from 25 to 30°C. The polarising element, polarising plate and image-display device of one embodiment of the present invention exhibit outstanding durability and heat-resistance in that they maintain their initial orthogonal transmittance and colour tone, and they maintain their transmittance, degree of polarisation and colour tone even under high-temperature conditions.