machine design, Vol.3(2011) No.4, ISSN 1821-1259 pp. 241 … · · 2017-05-12Each textile material including polyester has specific ... and that is reason why this unit was adopted

machine design, Vol.3(2011) No.4, ISSN 1821-1259 pp. 241-246

*Correspondence Author’s Address: University of Novi Sad, Faculty of Technical Science, Department for Graphic Engineering and Design, Trg Dositeja Obradovića 6, 21000 Novi Sad, Serbia, [email protected]

Original scientific paper

INVESTIGATION OF THERMAL EFFECTS ON TEXTILE MATERIALS PRINTED BY DIGITAL PRINTING

Dragoljub NOVAKOVIĆ1, * - Nemanja KAŠIKOVIĆ2 - Gojko VLADIĆ3

1,2,3 University of Novi Sad, Faculty of Technical Science, Department for Graphic Engineering and Design, Novi Sad, Serbia

Received (14.05.2011); Revised (06.07.2011); Accepted (12.12.2011) Abstract: This paper presents research of thermal influence on the textile material printed by digital ink jet technique. In the theoretical part of the research we offer overview of relevant research related to surface roughness and the color difference on textile materials which were subjected to thermal load. The parameters of surface roughness before printing, after printing and after various thermal effects were analyzed in experimental part. Thermal effect was analyzed in a given period of time, with thermal imaging camera to obtain surface temperature distribution of the observed sample. The differences in color were analyzed also before and after printing and after various thermal loads. As a reference point the field of 100% of cyan, magenta, yellow and black coverage was taken. For determining the color differences a model CIEDE 2000 was used. SEM analyses of the changes were observed on the surface of textile materials before and after printing and after the thermal effects. The analysis confirmed some theoretical assumptions. Key words: polyester, surface roughness, color difference, SEM analysis, thermal effects 1. INTRODUCTION Great number of different textile materials of artificial origin is present today and they can be printed with digital printing technique with good results. One of these materials is polyester, which is made from chemicals found in petroleum. Each textile material including polyester has specific characteristics and they differ from the characteristics of other textile materials. In general, their surface is not absolute flat because it is influenced by the mode of production and processing of materials [1, 2]. The parameters of surface roughness are influenced by the printing process and also in process of exploitation of printed material [3, 4]. After the printing process, the material usually gets treated with heat to achieve better visual effect of the image. Heat affects the color and the textile fibers also. Generally, one should point out that the effect of the same heat input will not cause the same change in different textile materials, because different textile materials have different thermal conductivity which is actually a process where the energy is transmitted from place of greater to place of lower temperatures, as a result of the direct influence on the molecule [5, 6]. Thermal conductivity also depends on the weight of fibers, thickness, porosity and structure. Generally temperature is transmitted through the materials in three ways: conduction, convection and electromagnetic radiation [1, 7, 8]. Consequence of thermal effects is a change in the structure of textile fibers [9], and the fact is that the mere change in the structure of textile materials, resulting in color differences between the prints with different thermal treatment [5]. In order to analyze thermal effects, it is necessary to get the values of temperature of the heating element in the

function. The best solution is a thermo vision camera, which provides the possibility of non-contact measurement based on the infrared (IR) technology with high accuracy [7, 10, 11, 12]. The value of the measured temperature is expressed as a function of five parameters [10, 13, 14]:

Tob =f (εob

,Tatm

,T0,ω,d ),(K) (1)

where: εob - emissivity of surface, Tatm - temperature of the atmosphere, To - temperature of measuring point, ω - relative humidity, d - distance thermo vision IR camera Thermal effect leads to a color difference between the two impression [4, 15, 16], and there is need to be determined it. To determine the color difference, today there are few systems [7] for calculation. They are using different formulas like CMC (l: c) [17], BFD (l: c) [18], CIE94 [19], LCD [20] and the latest CIE∆E2000 [21]. Determination of color differences based on determining the difference in the color space coordinates (∆L*, ∆a*, ∆b*) [22]. Generally, there are opposing opinions, which system for determining of color differences is better. Some researchers believe that CIE∆E2000 is better [21, 23] and in some studies apply [24.25, 16], the formula:

⎟⎟⎠

⎞⎜⎜⎝

⎛ ∆⎟⎟⎠

⎞⎜⎜⎝

⎛ ∆+⎟⎟

⎠

⎞⎜⎜⎝

⎛ ∆+⎟⎟

⎠

⎞⎜⎜⎝

⎛ ∆+⎟⎟

⎠

⎞⎜⎜⎝

⎛ ∆=∆

HHCCT

HHCCLL SkH

SkCR

SkH

SkC

SkLE ''''

222

00(2)

*1

*2

' LLL −=∆ '1

'2

' CCC −=∆ (3)

⎟⎟⎠

⎞⎜⎜⎝

⎛ ∆=∆

2sin2

''2

'1

' hCCH ( ) ( )2*2''iii baC += (4)

2. EXPERIMENTAL

In the experimental part we investigated the influence of three characteristic values of thermal load on the

Dragoljub Novaković, Nemanja Kašiković, Gojko Vladić: Investigation of Thermal Effects on Textile Materials Printed by Digital Printing; Machine Design, Vol.3(2011) No.4, ISSN 1821-1259; pp. 241-246

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impression (155, 187 and 205 ° C). The textile material with 100% polyester was taken as the sample, whose properties are the following: 100% polyester fiber, SRPS F.S3.112, (100% polyester textured filament with a reduced fineness 110 dtex; embroidery fabric: knitting machine with a base (Ketten Stuhl), measuring 36 (number of needles per 1 inch). Test chart 2002 ECI CMYK was printed on the material by digital printing technique using DTG Kiosk Printers (Digital Garment Printers, USA). Printed material was subjected to thermal load by heating element Quick Tech 45 warmed to the desired temperature, in order to obtain uniform steady state in the whole temperature range. The exact value of the thermal effect is determined by the thermo vision camera P65 (FLIR). Parameters of surface roughness were measured before printing, after it and between the thermal treatments, with the reference length of 0.25 mm using a device TR 200 (Portable Testers, USA). By the spectrophotometric measurements of the samples the color difference before and after printing was determined, using a system CIE∆E2000. Analyzed fields were with the following values: C = 100 %, M = 0 %, Y = 0 %, K = 0 %, C = 0 %, M = 100 %, Y = 0 %, K = 0 %, C = 0 %, M = 0 %, Y = 100 %, K = 0 %, C = 0 %, M = 0 %, Y = 0 %, K = 100 %. Measurements were made with standard measurement geometry by illumination D50 and 2 ° standard observer on the unit X-Rite i1, where the measurement results

analyzed in GretagMachbet (Measure Tool).In the later

stages of the experiment, samples tested with SEM microscopy were analyzed before and after printing, and after the thermal effects. Analysis of materials was made by using JEOL 6460 LV electronic microscope, where the changes in particular areas of textile material were observed, as a result of printing and thermal effects. According to the specifications for laboratory measurements samples were classified, marked and prepared, samples were streamed by gold in vacuum for the electrical conductivity. 3. RESULTS AND DISCUSSION

The influence of thermal effects on the printed textile material will definitely affect the change of the surface roughness, the difference in color measuring fields, surface morphology, and at the end on the proof. To test the thermal effect the heating surface was first prepared in order to remove any impurities which might cause errors during the analysis. Printed samples were subjected to thermal effects; the thermo vision camera measured the exact temperature emitted by the heating element. Special attention is given to the elimination of temperature variations. All samples in the experiment were treated with the same thermal action in a time interval of 10 s, and the three thermal effects of the temperatures of 155, 187 and 205 ° C were considered. The thermal measurements showed quite accurate results when the temperature of 155 ° C was chosen, , and the mean value for this predicted temperature was 154.55 ° C, with the

difference in the entire area between the maximum and minimum temperatures by the heating body emitted was 1.5 ° C. Value of deviation in the thermal effects was 1.06. The second level of heat load, predicted the action with a temperature of 187 ° C. Value of deviation in this case was 1.56, while the difference between maximum and minimum temperatures at the surface was 2.2 °C. The largest thermal effect was supposed to be with a temperature of 205 °C, and measurements showed that the heating body emitted an average temperature of 204.9 °C, with a deviation of 1.13 and 1.6 °C difference between maximum and minimum temperatures. Figure 1 shows the results and it is seen that the measurements pointed to a small temperature variations in the whole field of heating, and can say that the temperature was held constant.

Fig.1. Thermal effect on the printed material The surface roughness was measured on the raw material, after printing and after all thermal effects which are exposed samples. Basic parameters for measuring surface roughness are as follows: Ra - arithmetic average of the absolute values of deviations of the profile inside the reference run, Rz - the arithmetic average of the deepest single file roughness measuring several adjacent tracks, Rt - total height profile, Rp - maximum height profile, Rv - deepest valley. Of all the above parameters the parameter Ra was analyzed, which in relation to the Rz gives a better correlation between subjective and measurement results, and that is reason why this unit was adopted as a principal in determining the surface roughness [5]. The results are shown in Figure 2 and it is seen that the change of surface roughness acts as a polynomial function, where the correlation factor was 0.789, which represented the relationship between thermal effects and changes in surface roughness. Spectrophotometric measurements, before and after the thermal effects of heating element results were obtained in color difference (Figure 3). To determine the color difference is taken CIE∆E2000 system. All four of the colors behave in the same pattern. The biggest color difference is at the lowest temperature and lowest at the higher temperature. In all three thermal effects color difference was the smallest in the fields of cyan color, and


243

the biggest in black areas, while the fields of magenta color has a bigger difference than a field of yellow color. Values of ∆E for color cyan amounted to 4.4 in the first case the deviation of 0.18, second 4.19 (deviation 0.37) in the third last event of 3.76 (deviation 0.48). Magenta on the other hand had the following values (sorted from lowest to highest temperatures, the deviation is given in parentheses): 6.09 (2.48), 5.55 (2.42) 4.08 (2.19), while those of yellow amounted 5.39 (2.12), 5.33 (2.33), 3.87 (2.87). Last analyzed color is black, and the results are as follows: 6.35 (1.67) 5.65 (1.31) and 3.83 (1.38).

Fig.2. Thermal effects on changes Ra factor

Fig.3. Mean values for ∆E after thermal effects

Fig.4. Mean values for ∆E after thermal effects (cyan)

If the color differences are presented graphically by the curve, it can be noticed that all the curves behave as a polynomial function, with a correlation coefficient of 1. Based on this formula the color difference could be calculated for other temperatures also. Figure 4. presents the average color differences under the influence of different temperatures for the cyan, while Figure 5 presents magenta.

Fig.5. Mean values for ∆E after thermal effects (magenta) Figure 6, represents the required results for yellow, and Figure 7 for black color.

Fig.6. Mean values for ∆E after thermal effects (yellow)

Fig.7. Mean values for ∆E after thermal effects (black)


244

Fig.8. SEM image of a sample of 100% polyester fibers before printing

Fig.9. SEM image of a sample of 100% polyester fibers after printing

Fig.10. SEM image of a sample of 100% polyester fibers after thermal load with 154,55 °C

Samples were analyzed by the means of SEM analysis before printing, after printing and after thermal load. In Figure 8. pure polyester fiber is shown, while in Figure 9. we can see polyester fibers with ink, and formation of “ink bridges”.

Figure 10 represent fibers after thermal load and it can be seen that there is a merger of several fibers. All textile materials have specific characteristics. Their surface is not absolutely flat, which means that they have a specific surface roughness. During the printing process, there is an increase of surface roughness parameters by the layers of ink, because the application ink partially falls between the fibers and in some places they are connected, while retaining the ink of the surface of the material or fibers, which causes the increase of roughness parameters. Thermal effect causes the colors to be located on the surface and between fibers even more penetrating between them and connecting them more at a time (SEM images 8-10). That basically means that a certain amount of color that was on the fibers decreased, and thus a reduction in roughness parameters of the analyzed samples. The higher the temperature the effect of roughness parameters of the printed surfaces are reduced (Figure 2). The thermal measurements have shown that the whole heating area has a uniform thermal load, which can be seen from Figure 1. By determining the color changes under the influence of heat load, for the four process color, we have documented that all samples showed similar behavior (Figure 3). The biggest color difference for all four was at the lowest temperature of 154.55 °C, while the slightly smaller difference was at the thermal load of 185.9 °C. Thermal load of 204.9 °C gave the lowest values for color differences. Generally, cyan had the lowest values in colors difference and they could be classified as large color differences, while the magenta on the other side in the first two cases had values that belong to the massive differences and in the third case demonstrated the value that belongs to the big difference. Yellow had lower values in colors differences of magenta, but in the first two cases it also had values of massive color differences, and in the third large color differences. Black comes out with the highest values of color differences, although value for third measurement belongs to the group of major differences while the first two are in the group a massive difference. Larger color differences can be noticed with the darker process colors and minor changes were found in lighter process color such as cyan and yellow. 4. CONCLUSION Conclusion of the experiment is that there are changes in the printed textile material subjected to the thermal treathment. Measurement of surface roughness show increscent in those parameters when ink is applied, but parameters are reduced with the thermal treatment, which might indicate that there is a leveling influence of surface by the applied heat. Also, the thermal effect causes the change of the surface structure of textile fibers, where the surface becomes smoother, which causes changes of surface reflectivity, and therefore the subjective sense of


245

color. Thermal treatment is influencing darker colors like magenta and black, although significant changes are noticed also in lighter colors, yellow and cyan. SEM analysis showed that other than binding to the fibers of the textile material ink also connected them. Thermal treatment lead to the additional fiber connecting in tested samples. Research has concluded that all of these influences must be taken in the consideration in order to obtain higher quality prints and higher customer satisfaction. ACKNOWLEDGMENT This work was supported by the Serbian Ministry of Science and Technological Development, Grant No.:35027 "The development of software model for improvement of knowledge and production in graphic arts industry"

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machine design, Vol.3(2011) No.4, ISSN 1821-1259 pp. 241 … · · 2017-05-12Each textile material including polyester has specific ... and that is reason why this unit was adopted