B. ROTAR et al.: MORPHOLOGICAL AND DIMENSIONAL PROPERTIES OF UNMODIFIED AND MODIFIED BRAILLE DOTS ...
879–887
MORPHOLOGICAL AND DIMENSIONAL PROPERTIES OF
UNMODIFIED AND MODIFIED BRAILLE DOTS PRODUCED
WITH UV INKJET PRINTING
MORFOLO[KE IN DIMENZIJSKE LASTNOSTI NEMODIFICIRANE
IN MODIFICIRANE BRAJICE IZDELANE Z UV KAPLJI^NIM
TISKOM
Bojan Rotar
1
, Ur{ka Stankovi} Elesini
1
, Peter Hajdu
2
, Bla` Leskovar
3
,
Ra{a Urbas
1*
1
Chair of Information and Graphic Arts Technology, Faculty of Natural Sciences and Engineering, University of Ljubljana,
A{ker~eva 12, 1000 Ljubljana, Slovenia
2
Grec d. o. o., Cesta Andreja Bitenca 68, 1000 Ljubljana, Slovenia
3
Department of Materials and Metallurgy, Faculty of Natural Sciences and Engineering, University of Ljubljana,
A{ker~eva 12, 1000 Ljubljana, Slovenia
Prejem rokopisa – received: 2020-01-27; sprejem za objavo – accepted for publication: 2020-09-01
doi:10.17222/mit.2020.016
Texts in braille are longer than texts in Latin, and so some modifications have taken place over the years, most referring to the
contractions of words, with fewer focusing on the possibilities offered by newer printing techniques. In the research, the braille
dot was modified, printed with a UV inkjet technique and analysed. The modified braille dot was composed of the basic (un-
modified) dot with an additional element printed on its top. The research was focused on the surface and structure morphology,
and the dimensional changes of the dots printed with clear, acrylate-based UV ink. According to the SEM images, the surfaces
of the unmodified and modified dots were smooth and regular. The spreading of the clear UV ink was reduced with a pre-printed
layer of black acrylate-based UV ink on the surface of cardboard, which consequently increased the surface tension. The crack-
ing of the clear UV ink was observed to a smaller extent at the base of the dot. The clear UV ink polymerised in a ridge pattern
typical of an amorphous polymer microstructure. The dot dimensions changed compared to the preformulated dimensions. An
obvious shrinkage of dots during curing was determined by measuring the diameter and area; however, an increase in the perim-
eter applied to the uneven dot boundary as a consequence of the slight spreading of the clear UV ink. The height of the basic dot
was reduced for the modified dots due to a slight "collapse" of the layers, probably resulting from a small fraction of uncured
UV ink, a dark substrate etc., as illustrated in the article.
Keywords: UV inkjet printing, curing, braille dot, dimensional changes
Besedila zapisana v brajici so dalj{a kot besedila v latinici, zato se je v zadnjih letih pojavilo nekaj modifikacij, ki so se
ve~inoma nana{ale na kraj{e zapise besed, manj pa jih je bilo osredoto~enih na mo`nosti, ki jih omogo~ajo sodobnej{e tehnike
tiska. V pri~ujo~i raziskavi smo modificirali brajevo piko, natisnjeno z UV kaplji~nim tiskom, in jo analizirali. Modificirana
pika je bila sestavljena iz osnovne (nemodificirane) pike z dotisnjenim dodatnim elementom na njenem vrhu. V raziskavi smo
preu~evali povr{inske in strukturne morfolo{ke lastnosti ter dimenzijske spremembe pik, natisnjenih s prozornim UV ~rnilom na
osnovi akrilata. Iz SEM-posnetkov je bilo ugotovljeno, da je bila povr{ina nemodificiranih in modificiranih pik gladka in
pravilne oblike. Razlivanje prozornega UV ~rnila se je zmanj{alo s predhodnim potiskom plasti ~rnega UV akrilatnega ~rnila na
povr{ino kartona, kar je posledi~no zvi{alo povr{insko napetost. Pokanje prozornega UV ~rnila je bilo opaziti v manj{em obsegu
na tanj{i plasti ob robu pike. Prozorno UV ~rnilo je polimeriziralo v valovitem vzorcu, tipi~nem za mikrostrukturo amorfnih
polimerov. Dimenzije pik so se spremenile v primerjavi z izhodi{~nimi. O~itno skr~enje pik med strjevanjem (polimerizacijo) je
bilo dolo~eno z merjenjem premera in povr{ine. Pove~an obseg pike je posledica neenakomernosti robov pik, nastalih zaradi
rahlega razlivanja prozornega UV ~rnila. Kot je razvidno iz prispevka, se je vi{ina osnovnih pik, v primerjavi z
modificiranimim, zmanj{ala zaradi rahlega sesedanja plasti. Vzrokov za to je lahko ve~, in kot je navedeno v prispevku, smo jih
iskali v mo`nem dele`u nepolimeriziranega UV ~rnila, v ~rni podlagi itd.
Klju~ne besede: UV-kaplji~ni tisk, strjevanje, braillova pika, dimenzijske spremembe
1 INTRODUCTION
According to the International Council on English
Braille (ICEB) and The Rules of Unified English
Braille,
1
braille is defined as a tactile method of reading
and writing for blind people. Digital technology has
made braille more accessible for its users (e.g., with
braille notetakers, transcription software, refreshable
braille displays for computers etc.). However, the Royal
Blind organisation emphasises that reading printed
braille still remains important, as it allows users to learn
spelling, punctuation and gain an understanding of how a
text is formatted on a page. Therefore, printed texts in
braille are still desirable and valuable for the visually im-
paired and blind.
Braille text can be printed with different techniques,
e.g. embossing,
2,3
thermo-vacuum technique (mainly
used to produce tactile diagrams, figures etc.), screen
printing,
4,5
UV inkjet and 3D printing.
5,6
Materiali in tehnologije / Materials and technology 54 (2020) 6, 879–887 879
UDK 67.017:681.625.923:681.625.838 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(6)879(2020)
*Corresponding author's e-mail:
rasa.urbas@ntf.uni-lj.si (Ra{a Urbas)

Compared to other techniques, a lot of attention has
been given to UV inkjet printing in the last decade. It is
used in various fields, such as the coating industry
(anti-static, flame-retardant, dental industry, metal and
textile coatings, etc.), graphics (also for braille printing)
and microelectronics (display switches and drivers, e-pa-
per, smart labels, radio-frequency identification tags
(RFID), sensors etc.).
7–10
UV inkjet printing uses
UV-curable inks, cured in a few seconds or minutes at
room temperature, thus reducing the overall energy con-
sumption, which are applicable to various materials (pa-
per, textile, wood, glass, etc.). Yang et al.
11
noted that dif-
ferent materials also have different requirements. It is
therefore important to adjust the surface tension and vis-
cosity of the ink to improve the printability. Mendes-
Felipe et al.
12
suggested that problems such as the bad
adhesion of ink to the substrate, deformations, cracks or
pores in printed elements or even incompletely cured
materials could be reduced by optimizing the printing
parameters and conditions (temperature, humidity etc.),
surface treatments or modifying the design of printing el-
ements.
Various researchers have been focusing on the prob-
lem of the volume shrinkage of photopolymers (cured
materials). UV ink is composed of a photo-initiator, oli-
gomers (forming the basic structure of the polymer net-
work) or prepolymers, and monomers (acting as a reac-
tive diluent to adjust the system viscosity). When the
photo-initiator is exposed to UV light, it generates free
radicals and initiates UV curing (crosslinking) until all
the oligomers and monomers are crosslinked, forming a
three-dimensional polymer structure. Park et al.
13
high-
lighted that the volume shrinkage in acrylate and
methacrylate systems occurs during the polymerisation.
The weak and long Van der Waals interactions are re-
placed by shorter covalent bonds between carbon atoms
of different monomer units. In another research, Park et
al.
9
concluded that the free volume of three-dimensional
polymer structures is smaller than the free volume of
molecules involved, which means that cured ink has a
smaller volume than ink in the liquid state, which is re-
flected in the shrinkage of the material. K. Koseki et al.
14
stated that the shrinkage of acrylate compounds has a re-
ciprocal correlation with the molecular weight and when
the cured system includes oligomers (mixed system), the
time lag between the polymerisation reaction and the
shrinkage behaviour occurs. Volume shrinkage causes
aesthetic problems (deformation of the cured material
shape) and reduces its adhesion to the surface.
9,14
J. W.
Park et al.
13
emphasised that the shrinkage of the poly-
mer depends on some variables (i.e., photo-initiator con-
tent, UV light intensity, environmental temperature) that
must be controlled during curing.
As already mentioned, UV ink-jet printing is inter
alia used for printing braille, since it is possible to use
various materials for substrates (a well-known example
is the metal buttons with braille inscription in elevators;
they can be embossed but also printed with the UV
ink-jet technique). G. Golob et al.
15
showed that the tech-
nology of UV inkjet printing enables precise printing of
even the smallest elements, which can be printed in one
or more layers. In their research, a horizontal and vertical
line, triangle and square were printed on the top of the
braille dot. The basic braille dots and added elements
were printed using five basic varnish layers. As shown in
the research, blind people recognised and distinguished
some shapes of added elements; however, not all, as
shown in the research by Urbas et al.
16
In the latter re-
search, the added elements in the shape of a small dot
and vertical line printed on a basic braille dot with the
UV inkjet technique were the most recognisable ele-
ments for the blind. The possibility of upgrading dots
opens up new possibilities for modifying braille writing,
as explained in the continuation. In standardised braille,
an additional character is used as an indicator for capital
letters, as shown in Figure 1a. This indicator was, in the
research, avoided by using modified braille dots instead
of classic ones (hereinafter unmodified dots), as shown
in Figure 1b. The term modified braille thus refers to the
use of characters that are composed of base dots with an
B. ROTAR et al.: MORPHOLOGICAL AND DIMENSIONAL PROPERTIES OF UNMODIFIED AND MODIFIED BRAILLE DOTS ...
880 Materiali in tehnologije / Materials and technology 54 (2020) 6, 879–887
Figure 1: Letter R written with a) unmodified and b) modified braille
dots; two columns of three dots represent a braille cell; white dots rep-
resent unoccupied and unprinted places in the braille cell, while black
dots are occupied, printed and tactile; grey dots are added elements
printed on top of the basic dots in modified braille dots.

additional element printed on the top of them (hereinaf-
ter modified dots).
By including modified dots into braille, the number
of braille cells that need to be scanned with fingers can
be reduced and the length of braille texts shortened. In
this paper, a more extensive research of the structure and
dimensions of modified braille dots in comparison to un-
modified dots is presented. For that purpose, a new set of
unmodified and modified braille dots was printed with
the UV inkjet printing technique. The analysis was per-
formed on a printing substrate before and after the
pre-printing with a black UV ink, as well as on unmodi-
fied and modified braille dots printed with a clear UV
ink. The surface and structure morphology were studied
with a stereo microscope and scanning electron micro-
scope. The measurements of dots were performed using
the ImageJ program on captured images.
2 EXPERIMENTAL PART
2.1 Materials
For the purpose of the research, a prepared text was
first translated into braille. The Marburg Medium font
was used as a standard, recommending that the braille
dot diameter be within the range of 1.3–1.6 mm and the
height of up to 0.2 mm. The text translation to braille
was made by a computer program converting the text
with the PharmaBraille SI font. When the text in braille
was ready, appropriate layouts for inkjet printing were
prepared in the Adobe Illustrator program. Each unmodi-
fied braille dot was composed of three layers. The diam-
eter of the braille dot circle in each layer was different,
gradually reducing; thus, for each layer, a separate layout
was prepared. The first printed layer of a dot had the
largest diameter (i.e., 1.586 mm) and the third layer the
smallest. In this way, the rounded shape of the braille dot
was obtained. In the case of modified braille dots, the ba-
sic dot was first printed in three layers (the same as in
unmodified dots), while an additional three layers were
printed to get the smaller added element on the top of the
basic dot. The same as in the basic dot, the first layer of
the added element had the largest diameter (i.e., 0.500
mm), while the other two added layers had their diameter
gradually reduced.
After the layouts were prepared, the text in unmodi-
fied and modified braille was printed with a Roland DG
LEC-330 piezoelectric UV inkjet printer (Roland DG
Corporation, Japan) with a dual UV-LED lamp, with a
printing resolution of 720 dpi × 1440 dpi. The printing
was performed at room temperature (approx. 21 °C) and
65 % relative humidity. With one passage of the sub-
strate through the printing machine, one layer of braille
dots was printed and cured.
The cardboard Kromopak (Koli~evo Karton d. o. o.,
Slovenia), with declared grammage of 275 g/m
2
,w a s
used as the printing substrate. The cardboard was prelim-
inary pre-printed with one layer of acrylate-based black
EUV4-5BK printing ink (Roland DG Corporation, Ja-
pan) (hereinafter black UV ink). Braille dots were finally
printed with acrylate-based clear EUV4-5GL ink
(Roland DG Corporation, Japan) (hereinafter clear UV
ink) onto the cardboard surface pre-printed with black
UV ink. In both inks, 2,4,6-trimethylbenzoyldiphenyl-
phosphine oxide (TPO) was used as the photo-initiator,
which is used especially in thicker coatings. According
to the technical data for the composition of commercial
black and clear ink, it was assumed that the curing was
proceeded as a free-radical chain polymerisation. The
layer of black ink and the first layer of dots were cured
under both lamps, while the other layers of dots were
cured under the light of one lamp. The intensity of light
in both lamps was constant while printing.
2.2 Methods
The properties of the unprinted and pre-printed card-
board were determined with different methods. The
grammage (g/m
2
) was determined by weighing samples
according to the standard SIST EN ISO 536:2012. The
thickness (mm) was measured with a Mitutoyo digital
micrometre (Mitutoyo Corporation, Japan; measuring
range 0–25 mm, with accuracy ±1 μm) according to the
standard EN ISO 534:2012. The roughness (mL/min)
was measured on samples in accordance with the stan-
dard ISO 5636-3:1992. The capillary rise (mm) is a test
of the water-absorbing capacity of a material and was
measured according to the Klemm method (standard ISO
8787:1986). The resistance to bending (N) was measured
according to the standard ISO 2493-2:2011 on a dyna-
mometer INSTRON mod. 5567 (Instron Ltd., USA) and
was recorded as the force needed to bend a sample by
15° at a bending length of 50 mm. The surface tension
(mJ/m
2
) was determined by measuring the contact angles
on a Dynamic Absorption Tester DAT 1100 (Fibro sys-
tem, Sweden) according to the standardised method
TAPPI T558.
The study of shape and dimensions of braille dots
was performed with the use of a Leica S9i stereo micro-
scope (Leica Microsystems Ltd., Germany) and the
Java-based image-processing program ImageJ (NIH,
USA). The images of five unmodified and five modified
braille dots were captured with the program Leica Appli-
cation Suite. The diameter (mm) and perimeter (mm)
were obtained by analysing five captured images of each
sample, while the mean values and standard variations
were calculated separately for each set of measurements.
The surface area (mm
2
) of the dots was calculated from
the diameter.
The surface and structure morphology of the samples
were studied with a scanning electron microscope (SEM)
JSM-6060LV (Jeol, Japan). For the surface observation,
the samples were fixed on a specimen stub and the sam-
ple cross-sections were prepared using a low-speed dia-
mond saw (Buehler, USA). The samples were than
clamped into a special stub for parallel viewing. All the
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Materiali in tehnologije / Materials and technology 54 (2020) 6, 879–887 881

samples were covered with an ultra-thin coating of gold
(with high-vacuum evaporation). From the cross-section
images, the heights (mm; μm) of the different elements
of the braille dots were measured.
3 RESULTS AND DISCUSSION
3.1 Unprinted and pre-printed cardboard properties
As can be seen from Table 1, the unprinted card-
board had a smooth surface, with a low roughness value
and low surface tension due to the calendered coating on
the felt side (Figures 2a and 2b). The pre-printed layer
of black UV ink was applied in the process of braille
printing due to the noticed spreading of clear UV ink
during the printing of the braille dots. The spreading was
also noticed in the research of B. Rotar,
17
offering an ex-
planation that a thin layer of UV black ink reduced the
spreading of clear ink, while the printed dots had better
sharpness. As determined by our measurements, the
layer of black UV ink pre-printed on the surface in-
creased the surface tension, roughness and capillary rise.
The increase of the surface tension reduced the spreading
of the clear UV ink on the surface and the braille dots
had nearly round boundaries. The layer of black UV ink
pre-printed on the cardboard surface, clearly visible in
Figure 2, was approximately 15.7 μm thick. The
grammage of the pre-printed cardboard slightly in-
creased, the resistance to bending increasing in the ma-
chine direction (MD) and slightly decreasing in the cross
direction (CD).
3.2 Surface and structure morphology of unmodified
and modified braille dots
The images of the unmodified and modified braille
dots captured with the SEM are presented in Figure 3.
The edges of each dot were slightly less expressed due to
the moderate spreading of the liquid UV ink before cur-
ing, as shown in Figure 4a. The upper layer of an un-
modified braille dot can be seen as a small circle with a
reduced diameter (Figure 3a). In the cross-section of the
unmodified braille dot (Figure 3b), the layer of cured
black UV ink is visible. The three applied cured layers of
B. ROTAR et al.: MORPHOLOGICAL AND DIMENSIONAL PROPERTIES OF UNMODIFIED AND MODIFIED BRAILLE DOTS ...
882 Materiali in tehnologije / Materials and technology 54 (2020) 6, 879–887
Figure 2: a) Surface of unprinted and pre-printed cardboard with
black UV ink, and b) cross section of cardboard pre-printed with UV
black ink (mag. a) 2500× and b) 1400×)
Table 1: Properties of unprinted and pre-printed cardboard; CV – Coefficient of variation; % Change – change of measured value of unprinted
cardboard against measured value of pre-printed cardboard as percentages
Property Unprinted cardboard Pre-printed cardboard % Change
Thickness (μm)/CV (%) 460.30/1.17 476.00/0.28 3.41
Thickness of UV ink layer (μm) – 15.7 –
Grammage (g/m
2
)/CV (%) 274.24/0.76 274.56/0.99 0.12
Roughness (mL/mm)/CV (%)
Side A (felt side)
Side B (wire side)
40.0/14.4
359.0/8.5
138.0/6.7
393.0/4.9
245.00
4.18
Resistance to bending (N)
CD
MD
0.1110
0.2418
0.1017
0.2685
–8.38
11.04
Capillary rise (mm)/CV (%)
CD
MD
4.72/1.95
3.83/2.15
4.82/2.14
3.99/2.92
2.12
4.18
Surface tension (mJ/m
2
) 34.88 46.84 34.29

clear UV ink in the braille dot were obviously firmly
crosslinked together; thus, no boundary lines represent-
ing the intermediate surfaces of the layers applied on
each other were noticed. In the modified braille dot,
some deviation of the added element from the centre of
the basic dot can be noticed (Figure 3c); however, this
deviation does not disturb the appearance and tactile ex-
perience of the braille dot on the whole. The inner struc-
ture of the modified dot was homogeneous (Figure 3d),
and the same as in the case of the unmodified dot, the
layers of clear UV ink were again firmly crosslinked to-
gether without any intermediate boundaries.
The cracking of the cured clear UV ink (Figure 4b)
only appeared between the basic dot and the thin,
20–50-μm-wide edges, which corresponded to the slight
spreading of the UV ink (Figure 4a). According to
Mendes-Felipe et al.,
12
some irregularities, e.g., cracking,
spreading, could be reduced by optimizing the printing
variables. However, in our research, these irregularities
were insignificant according to the purpose and we
therefore did not focus on a further optimisation of the
parameters.
The surface of the pre-printed cardboard and dots
was mainly smooth (Figure 5a and Figure 2a); however,
by tilting the sample holder during the SEM observa-
tions, the deposited small droplets appeared due to the
inkjet principle of printing. In inkjet printing, regardless
of its technology (e.g., piezoelectric or drop-on-demand),
an image is created from an array of extremely small liq-
uid printing-ink droplets printed on various surfaces, ei-
ther side by side or overlapping. The density of the dis-
tribution of the individual droplets depends on the colour
shade, saturation and image design (content). These
small black and clear UV ink droplets could also be seen
on the surface of the pre printed cardboard and the
printed braille dots (Figure 5b). They were evenly dis-
tributed throughout the surface. Their approximate size,
measured from captured SEM images, was 50 μm.
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Figure 3: Unmodified and modified braille dot: a) and c) top view, b)
and d) cross-section of dots (mag. 40×)
Figure 5: Surface of braille dot: a) smooth, and b) deposited by drop-
lets of clear UV ink (mag. a) 1000×, b) 500×)
Figure 4: a) Spreading and b) cracking of clear UV ink (mag. a) 170×,
b) 220×)

While preparing the cross-sections of braille dots,
some brittle fractures with revealed ridge pattern (wavi-
ness) microstructure appeared (Figure 6).
3.3 Braille dot dimensions
The images of unmodified and modified braille dots
captured with a stereo microscope were analysed with
the ImageJ program (Figure 7). For diameter measure-
ments (Figure 7a), the centre of each dot was first deter-
mined according to the circle that was approximated to
the dot boundary. A set of diameter measurements was
performed by measuring the distance from one side to
the opposite through a marked centre (d in Figure 7a).
The mean values and standard deviations were calculated
from the measurements. The diameter of the elements
added on the modified dots was measured and calculated
in the same way. The centre of the added element did not
always exactly overlap with the centre of the basic dot;
therefore, for more exact measurements, the centres had
to be determined separately (Figure 7b).
The area of the dots was calculated from the mea-
sured diameter. The perimeter was measured using the
ROI (Regions of interest) function in the ImageJ pro-
gram to obtain the real value of the UV ink spreading ex-
tension (Figure 8).
Table 2: Dimensions of unmodified braille dot; mean value ± SD
(standard deviation); d
b2
and h
b2
– diameter and height of printed base
dot; % Change – change of measured dimension compared to
preformulated dimension of braille dot from layout as percentages
Property Mean ± SD % Change
Diameter – d
b2
(mm) 1.390±0.027 –12.33
Area (mm
2
) 1.518 –23.18
Perimeter
ROI
(mm
2
) 6.080±0.057 22.01
Height – h
b
(mm) 0.193±0.008 –
Thickness of one layer
(μm)
64.33 –
The height of the unmodified and modified dots was
obtained with the SEM, while the approximate thickness
of one printed layer was calculated from the height
knowing the number of layers in each dot. The results of
the measurements for the unmodified and modified dots
are presented as mean ± standard deviation (SD) in Ta-
ble 2 and Table 3.
As can be seen from Table 2, the diameter of the
printed unmodified dot (d
b2
) decreased by 12.33 % ( d
b
for unmodified dot in Figure 9) compared to the pre-for-
mulated diameter of the dot (d
b2
, which was 1.586 mm).
The same was observed for the basic dot of the modified
dot (Table 3), where the diameter (d
b2
) was reduced by
11.41 % ( d
b
for modified dot in Figure 9). The de-
crease in area was consequently noticed in both types of
dots. The decrease in diameter and area was a result of
clear UV ink shrinkage during curing, which is as previ-
ously mentioned not an unknown problem arising from
the difference in the volume of ink in the liquid and
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884 Materiali in tehnologije / Materials and technology 54 (2020) 6, 879–887
Figure 6: Surface of braille dot fracture (mag. a) 4000× and b) 5000×)
Figure 7: a) Measuring diameter of unmodified braille dot, and b)
shifted centres of basic dot and added element of modified dot (origi-
nal mag. of captured images 40×)

cured states (the free volume of three-dimensional poly-
mer structures is smaller than the free volume of mole-
cules (monomers and oligomers) involved).
9
The perimeter calculated with the ROI function in-
creased by 22.01 % and 18.32 % for the unmodified dot
and the basic dot of the modified dot, respectively, ac-
cording to pre-formulated dimensions of the braille dot.
In both cases, the increase was a consequence of slight
spreading of the UV ink on the surface before curing.
However, slightly different results were obtained for the
added element in the modified dot according to prefor-
mulated dimensions. The diameter and area increased by
5.51 % and 11.46 %, respectively, although the shrinkage
of the UV ink was in progress during curing. The perim-
eter increased significantly, which implies that the added
element increased in size. The layers of the added ele-
ment were not applied on a flat but on a rounded surface
of the basic dot (Figure 3), which implies that the jetted
drop of liquid UV ink spread slightly down the slope of
the basic dot, resulting in an increased diameter, area and
especially perimeter in the case of the modified dot.
The difference in height ( h in Figure 10) between
the unmodified dot and the basic dot of the modified dot
was21.1%( Table 2 and Table 3), although they were
both printed simultaneously in the same manner, under
the same conditions.
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Table 3: Dimensions of modified braille dot; mean value ± SD (standard deviation); d
b2
and h
b2
– diameter and height of printed base dot; d
e2
and
h
e2
– diameter and height of printed added element; % Change – change of measured dimension compared to preformulated dimension of dot
from layout as percentages
Property
Basic dot Added element (smaller dot)
Mean ± SD % Change Mean ± SD % Change
Diameter – d
b2
/d
e2
(mm) 1.405±0.025 –11.41 0.528±0.047 5.51
Area (mm
2
) 1.550 –21.56 0.218 11.46
Perimeter
ROI
(mm
2
) 5.896±0.017 18.32 2.506±0.025 59.52
Height – h
b
/h
e
(mm) 0.152±0.013 – 0.105±0.007 –
Thickness of one layer (μm) 50.66 – 35.00 –
Figure 9: Diameters of preformulated and printed unmodified and modified dots; d
b1
– diameter of preformulated base dot; d
b2
– diameter of
printed base dot; d
e1
– diameter of preformulated added element; d
e2
– diameter of printed added element
Figure 8: ROI (Regions of interest) of a) unmodified braille dot, b) modified dot, and c) added element (original mag. of captured images 40×)

Apart from shrinkage, which can influence the height
of the dot, a tiny "collapse" of slightly less crosslinked
layers or parts (especially the centre) of the dot could be
possible under the weight of the added element. Decker
18
stated in his research that the ratio between the cure
speed and the cure depth must be taken into consider-
ation during the polymerisation. He also concluded that
an increase in the light intensity leads to a faster poly-
merisation and more extensive cure with a smaller num-
ber of unreacted functional groups. In our study, the cur-
ing of UV ink was performed at the same light intensity.
It is possible that in the first (lower) layers of the dot (es-
pecially in the case of the modified dot) some uncured
UV ink was still present, forming "softer" areas that
could collapse during the printing and reduce the heights
of the unmodified dot. Another explanation relates to the
colour of the substrate, which can influence the curing
speed. Brunner
19
discovered that dark substrates, espe-
cially black, require more energy for curing the UV ink
layer than the bright ones. In our research, the curing of
each layer of dots was conducted under the same condi-
tions and it is thus possible that the layer of the dot,
which was printed directly onto a black coloured surface,
was slightly less crosslinked than the other two layers.
Such a layer is more susceptible to deformation as well
as collapse, consequently resulting in a reduced height of
the basic dot.
4 CONCLUSIONS
UV inkjet printing is a suitable technique for printing
braille. It enables the production of clear and precise
prints, which is an important issue in printing modified
braille dots, as presented in our research. According to
the results, unmodified and modified braille dots printed
with clear acrylate-based UV ink had a smooth tactile
surface and were suitably shaped as preformulated by the
layout. All the printed dots had a ridge-pattern formed
microstructure, which applies to the amorphous polymer.
Although slight spreading and cracking of the clear UV
ink was observed, this should not affect the visual and
tactile experience of the visually impaired and the blind
as it was confirmed by the study
16
in which printed un-
modified and modified braille with a group of blind peo-
ple was performed. According to the results, when pre-
paring layouts for inkjet printing, shrinkage during UV
curing should be considered.
Although the shrinkage was determined with mea-
surements, the dimensions of the printed unmodified and
modified dots were still within the acceptable range ac-
cording to the Marburg Medium Standard, i.e., the diam-
eter of the dot being in the range 1.3–1.6 mm. The Mar-
burg Medium Standard does not specify the braille dot
height, but the height target of 0.20 mm is, e.g., recom-
mended for pharmaceutical packaging. In our research,
the unmodified dot was within the proposed dimensions;
however, the modified dot was higher by almost 30 %
due to the added printed element. The modified dot was
intentionally higher, as it indicated a capital letter.
The dimensional changes of the unmodified and
modified braille dots established by measurements origi-
nate from different causes, such as UV ink spreading, the
shrinkage of printed dots during curing, a small percent-
age of uncured ink, a black surface of the substrate, etc.
Some of the mentioned reasons are assumptions based
on the literature cited; nevertheless, they are a good start-
ing point for further research.
Acknowledgment
The authors acknowledge Grec d. o. o. Grafi~no eko-
lo{ki center, Poclain Hydraulics d. o. o., Tiskarna Novo
mesto, Department of Materials and Metallurgy, Univer-
sity of Ljubljana, and the Pulp and Paper Institute for
technical support.
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