Reimageable paper
An imaging layer and imaging medium technology, applied in the field of documents, can solve the problems of black and white images with low image contrast, short duration, unable to provide application life time, etc., and achieve the effect of wide application and high image contrast.
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Embodiment 1
[0082] Compound 2 spiropyran photochromic materials containing carboxylic acid functional groups were synthesized according to the following reaction scheme:
[0083]
[0084] Compound 2
[0085] The overall yield of synthesis was 82%. This compound was recrystallized from absolute ethanol to provide a powder compound. The compound is pure, as determined by 1 Confirmed by H-NMR.
Embodiment 2
[0087] 50 mg of compound 2 of Example 1 was dissolved in a solution of polystyrene in THF (2.5 ml) as solvent. A sheet of paper was coated with this solution by using a blade. Allow the disc to dry to remove solvent.
[0088] The coated paper is irradiated with UV light with a wavelength of 365nm for one minute to obtain a colored state. The color starts out as a very dark purple, but fades to a dark gray within a few minutes. Immediately after exposure to UV light, the colored state consists of precipitated material (black) and purple. The purple color is attributed to a small amount of merocyanine still dispersed in the polymer base (compound MC-2, colored state of spiropyran compound SP-2). The purple color faded within hours, as expected when the merocyanine remained dispersed in the polymer matrix and did not precipitate or phase separate out as a stable dark solid.
Embodiment 3
[0092] Another instant document sheet was prepared in the same manner as in Example 2, except that the substrate was replaced by a PET plastic sheet. In this example, the coating solution of Example 2 was applied on one side to a plastic (PET) sheet. The coated paper was imaged as in Example 2. slices have the same long-live image features. However, a disadvantage of coated PET flakes relative to coated paper is that coated PET flakes can be erased faster since it can be heated at higher temperatures when compared to the paper backed version.
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