Research of Durability of Braille Formed in Paper

Volodymir MAYIK*, Taras DUDOK**, Edmundas KIBIRKŠTIS***, Ingrida VENYTĖ**** *Ukrainian Academy of Printing, Pidholosko 19, 79020 Lvov, Ukraine, E-mail: maik@uad.lviv.ua **Ukrainian Academy of Printing, Pidholosko 19, 79020 Lvov, Ukraine, E-mail: j007@uad.lviv.ua ***Kaunas University of Technology, Studentų 56, 51424 Kaunas, Lithuania, E-mail: edmundas.kibirkstis@ktu.lt ****Kaunas University of Technology, Studentų 56, 51424 Kaunas, Lithuania, E-mail: ingrida.venyte@ktu.lt


Introduction
Certain studies, e.g. a simulation of a Braille image longevity evaluation process by developing a digital control system of the conformity of parameters of Braille symbols with the representation of a model of factors affecting the quality of Braille in their active usage by the blind [1], are known.Furthermore, the influence of a superficial topography and friction on human perception is studied, because there is a presumption that superficial geometric peculiarities play an important role in perception [2], friction coefficients are analysed, analysis or study methods are suggested, wherein different types of surfaces may be correlated with friction and tactile response [3][4][5][6][7].Moreover, there are studies on friction force of a finger with and without artificial sweat, friction coefficients of the humanoid finger on the acrylic, paper surface with/without the artificial sweat [8].It is obvious that aforementioned and many other studies provide a capability to comprehend processes that occur during a human finger movement on a certain material [9], as well as demonstrate how to qualitatively measure, for example, the force of friction.
Another line of research includes modes of material processing for the purpose of obtaining relief images, i. e. Braille, or studying processes that take place in the material, where on a Braille is applied [10,11].
However, the aforementioned studies do not an-swer the following question: how long will the Braille possess properties sufficient for being perceived by people with visual impairment?There is an obvious supposition that, during the friction process of a finger on a paper surface, where on a Braille is applied, (at least) lowering the height of a Braille dot will be evident.Our experiments carried out earlier demonstrate that such an effect is present [12].The aim of the studies is to determine how the Braille applied onto ordinary paper by a Braille embosser will wear, and how the height of a Braille dot will change depending on the load (during storage in pallets, stacking, etc.).
In the present article, studies of the process of the change of height of a Braille dot taking into account factors that imitate not only the reading process but also factors that usually occur during use, storage and shipment of Braille have been expanded.
Table 1 Technical characteristics of coated paper Volume Gloss (Cezex) Grammage, g/m 2 Thickness, µm Density, g/cm 3  Opacity, % Brightness (ISO), % Roughness, µm Gloss, % Coating with a laminating film aimed at two things.The first aim was: during the application of a Braille with a Braille embosser, not infrequently "breaks" occur (Fig. 1).These "breaks" obviously are poorly tactilely perceived, and a laminating film aids in eliminating this issue.Secondly, this operation also contributes to a longer service life, due to the paper not being affected by sweat, dirt, etc.
Apart from the laminating film, a page with Braille was also coated with a layer of acrylic paint (the reverse side) (Fig. 2 For the purpose of the research of the wear of a Braille, an original device was manufactured: a working tool a leather cylinder, 1.5 cm in diameter, that moved on a sample in segments, one line of Braille each.The height of a Braille dot was measured every 500 cycles.The pressure was 1.0 N.
Small loads were left on an element of the script, and its settlement was examined with periodical contactless measurements of its height.The device FAG BRAI³ Braille Dot Checker was employed for the study of the change in height of a Braille dots.

Results and discussion
The dependence of Braille dot diameter from paper grammage and thickness of a laminating film is presented in Figs. 3 and 4. Fig. 3 The dependence of the diameter of the basis of a Braille dot from the paper grammage and the thickness of a laminating film If the paper grammage is higher Braille dot diameter increases (see Fig. 3).Braille dot diameter also depends on the thickness of laminating film.If there is no film, the largest Braille dot diameter is obtained.When the laminating film is of a higher thickness, the Braille dot diameter is lower.4 The dependence of the height of the Braille dot from the paper grammage and thickness of a laminating film Fig. 4 and Table 3 show that in presence of 90 g/m 2 and higher paper grammage and the absence of laminating film, Braille dot is at its maximum height.
Braille dot attrition research disclosed its dependency on attrition cycles.Braille dot height reduction's dependence on the layer of laminating film and acrylic ink has also been researched.The results are delivered in Figs.5-9.As it might be seen from Fig. 5, covering samples with acrylic ink affects their resistance to attrition.In cases without acrylic ink, Braille dot height decreased at greater extend.Respectively, when samples were covered with a layer of acrylic ink, Braille dot height was higher by 30-50 %.
The results presented in Fig. 6 disclose that Braille dot height reduction increased under higher number of wear cycles.This tendency is especially obvious from 2000 cycles; when paper grammage is lower, Braille dot height reduction slows down.Fig. 7 shows that the higher paper grammage, the smaller reduction of Braille dot height.Respectively, the higher paper grammage, the smaller number of cycles is needed to obtain Braille dot height stability.
Using a laminating film of 50 and 75 µm, when the number of attrition cycles is from 2000, Braille dot height reduction does not change (Figs. 8 and 9).It might be noticed that when Braille is made on a paper with grammages 115 g/m 2 , 130 g/m 2 ,150 g/m 2 and covered with different layers of a laminating film, Braille dot height decreased under short-term (up to 30 min) loads of 1.0 N or 0.5 N (Fig. 10-12).When samples are affected longer time period (up to 24 hours) with a load of 0.1 N, Braille dot height changes no more than 0.05 mm and with a load of 0.2 N mm it changes 0.09 mm.Fig. 12 The remaining height (mm) of the Braille dot of the load action time for 150 g/m 2 paper with a laminating coating

Conclusions
Strengthening by a polymer layer after producing a Braille by a Braille embosser has a positive effect on a wear resistance, due to the height after 500 cycles (e.g. for 115 g/m 2 paper) without strengthening being lowered by 58 microns, and with strengthening by 48 microns.It is corresponding 29 and 19 microns for 130 g/m 2 paper.After 2500 cycles, these same numbers are 122 microns without strengthening and 101 microns with strengthening for 115 g/m 2 paper.
On the other hand, one of the conclusions of the analysis is the following: a strengthened structure demonstrates an equivalent drop of height after 3000 cycles, as a non-strengthened one after 2000 cycles, i. e. a positive effect is present.
Unacceptable changes (more than 50 microns) of a Braille dot height for 115 g/m 2 paper with a strengthening polymer layer and laminated films occur even with a shorttime load (less than 30 min) weighting 1.0 N or 10.5 N in all samples without exception.For other samples (with loads weighting 0.1 N and 0.2 N.For laminating films from the whole thickness range), even with a long-term load, a height changes not exceeding 0.09 microns is observed.
Analogous conclusions may be formulated regarding all types of paper (130 g/m 2 , 150 g/m 2 ) and laminating films.

Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9
Fig. 5 The dependence of the lowering of the height of the Braille dot from the number of wear cycles without lamination and with/ without strengthening.Load force -1.0 N

Fig. 10
Fig. 10 The remaining height (mm) of the Braille dot of the load action time for 115 g/m 2 paper with a laminating coating

Table 3
The height of the Braille dot (mm) formed on different paper grammage and strengthening