Infl uence of the Washing Process and the Perspiration Eff ects on the Qualities of Printed Textile Substrates

Clothes are exposed to diff erent impacts during usages and maintenance. The more frequent impacts on textile materials are the washing processes and the perspiration eff ects. These mentioned eff ects are the causes of specifi c changes of the textile fi bres and on colour reproduction on printed materials. This paper presents research into the impacts of a series of washing and perspiration eff ects on the colour reproduction studied with a spectrophotometric analysis and the water retention capacities of the prints using the screen-printing technique. The research results indicate that with the increase in the number of washes, major changes occurred in the reproduced colours compared to the colours of the samples that did not undergo the process of washing. It was determined that, besides the series of washings, the perspiration effects also had an impact on the reproduced colour changes. The impacts were also affi rmed of printing and a series of washings on water retention on textile materials.


Introduction
Th e main task for the clothing is to protect the body from various environmental impacts and to mitigate the eff ects of various climatic and mechanical infl uences (such as pressure, friction, stretching, etc.). Th e rises in the living standards of individuals have conditioned the major shift in textile and clothing manufacturing because the demands of customers today are higher than they used to be. For today's customers it is insu cient for clothes just to meet only basic functions such as protecting the body and functionality, selective clothing is also expected to meet the aesthetic and fashion requirements so that it can better depict the personal characters and lifestyles of individuals [1]. Increases in the aesthetic values of clothes are o en achieved by printing on these materials. Printing on textile materials can more appropriately be described as an art and a science of desired design transfer onto textile materials' surfaces [2]. Some estimates indicate that more than 27 billion m2 of textile material substrates are printed every year [3]. Also, it is considered that printing on textile materials has an annual growth of 2% [4]. e most important printing technique in textile printing is screen printing [3,5,6] that is characterised by the fact that the print of a larger circulation has signicantly lower costs and higher productivity [7,8]. Factors a ecting the quality of screen printing are closely related to each other [9]. Hal one value reproduction depends on the thread counts and thicknesses of the threads [10], whilst printing form, ink and substrates' characteristics a ect the reproductions of lines and dots [11]. Print quality also depends on process parameters such as the printing speed, squeegee hardness, squeegee pressure and distance of mesh from the substrate. Pan and others have found that the squeegee hardness and printing speed have decisive in uences on print quality [12]. In order to obtain high quality print, it is necessary to choose the appropriate ink [13]. e more common inks applied on textile materials in screen printing are plastisol inks that contain PVC resin dispersed in plasticiser [11]. During the printing they penetrate into textile material and a er drying they create a strong connection with textile material, which makes this product very resistant when exposed to di erent in uences. It is signi cant that they are characterised by very good coverage [14]. A er printing, textile materials are o en exposed to external in uences such as washing heat, abrasion, UV light etc. One of the more in uential factors that textile materials are exposed to is the washing process. It has been proven that the washing process causes certain changes in the physicochemical features [15], as well as changes in the micromechanical properties (air permeability, resistance to cracking, sti ness) [16].In addition it has been noted that the washing process causes a change in colour [17]. e degree of change in the properties of textile materials and the colour depends on: ways of washing, washing temperature, water hardness, washing time. In addition, modern detergents consist of whitening substances and their enzyme activators and also inhibitors of the dye transfer. All of these substances can son In the printing textile industry, achieving the highest colour reproduction quality and also the maintaining of the same a er production, requires standardisation and the introduction of objective methods of quantifying colour. A common way of controlling the print quality consists of the spectrophotometric analysis of colour. e basis of this process is to determine the colour di erences between two prints. Determination of colour di erences is based on the determination of the di erences in the colour space coordinates (ΔL*, Δa*, Δb*) [19,20].
at di erence is expressed as a number (ΔE) and corresponds to the visual di erence between two colours. e gained values can be classi ed into several groups: ∆E between 0 and 1 (generally, di erence cannot be noticed), ΔE between 1 and 2 (small colour di erence, visible to the "trained" eye), ΔE between 2 and 3.5 (medium colour di erence, visible to "untrained" eye), ΔE between 3.5 and 5 (obvious colour di erence), and ΔE above 5 (massive colour di erence). [21]. In addition to the esthetic demands, clothing should ful ll the ergonomic and physiological requirements [22]. Clothing must allow a certain thermal insulation, a high degree of moisture permeability and good ventilation for maintaining optimal thermal regulation of the human body. e result of balanced interaction the system " personair -clothing" is expressed as human comfort when wearing clothes. More than 90% of the body surface is directly in contact with the clothing that is worn practically 24 hours a day, at work and leisure time, and partly in bed. is means that most of the surface of the human body is exposed to "microclimate" that is created between the skin and the clothes [23]. Based on all the above-mentioned parameters, the goal of the research was set and that was to determine how the washing process a ects colour reproduction, and how much resistance reproduced colour has on perspiration as well. In addition to this, the aim was to determine what are the impacts of the material type, printing and washing on changes of material sorption properties, i.e. the water retention capacity of the textile material. In order to obtain more accurate results, there were analyses of a large number of samples that were printed by the screen-printing technique on two types of textile substrates, and subjected to a series of ve washes.

Materials and methods
Research into the e ects of washing and perspiration on colour reproduction and the in uence of the printing and number of washings on the change of water retention capacity was performed on two types of textile materials of approximately the same surface masses but di erent surface structures. Material characterisation was done according to the following parameters: material composition (ISO 1833), mass per unit area (ISO 3801), and number of threads per unit length (ISO 7211-2). e characteristics of the materials are presented in Table 1. A special test image was created for this study using Adobe Illustrator CS 5 so ware.
is test image contained two 150 1 pt 150mm patches with 100% tone values of the processed black colour. Samples were printed by the screen-printing technique, using the 6-colour graphic M&R Sportsman E Series system. Printing speed was 10cm/sec, squeegee hardness -70 Shore Type A, printing pressure 275.8 ϫ 10 3 Pa, and 4mm snap-o distance. It was printed with Sericol Texopaque Classic OP (OP001) Plastisol black ink. Ink xation was done at a temperature of 160°C, exposure time 150 seconds. Whilst preparing a printing form a screen was used with mesh count of 90 threads per cm. A printing form was made conventionally using positive lms. e optimal densities of the transparent areas of the lm were 0.04 and 3.9 on opaque areas. Photosensitive Sericol Dirasol 915 emulsion was used.
Light exposure was done using a metal-halogen UV lamp (1000W) at a 1m distance from the mesh. e exposure time was calculated using a control tape Autotype Exposure Calculator by the Sericol Company and it lasted 3.5 minutes. e printed samples were subjected to a series of washings that consisted of ve washes. e washing bath contained 5g/l of textile soaps, and the ratio of solution to the textile substrate was 50:1. Soaps, containing not more than 5% moisture and complying with the following requirements based upon dry mass: free alkali, calculated as Na 2 CO 3 : 0.3% maximum; free alkali, calculated as NaOH, 0.1% maximum; total fatty matter: 850g/kg minimum; titer of mixed fatty acids, prepared from soap: 30°C maximum; iodine value: 50 maximum. e samples were washed for 30 minutes at 40°C. A er washing, the samples were rinsed twice with distilled water and then rinsed for 10 minutes in cold water. e washed samples were drained and in spread-out state dried at a temperature of 60°C. e persistence of each reproduced colour a er each wash and a er the e ect of perspiration was tested according to ISO 105-C10: 2006 [24]. e persistence of reproduced colour was analysed by measuring the CIE L* a* b* coordinates of the solid tones of black, determining the di erences between the reproduced colours (∆E) a er the printing process and exposing the printed samples to a series of washes. CIE L* a* b* coordinates were determined using a Konica Minolta CM-2600d di use spectrophotometer (Illumination types D65, standard observer angle 10°, measurement geometry d/8°, measurement aperture 8mm). Measuring was repeated ve times for each sample, and as the results used values corresponding to the arithmetic mean of a series of measurements. A test of resistance to perspiration staining was performed according to standard EN ISO 105-E04: 2012, with treatment in alkaline and acidic solutions without L-histidine monochlor -hydrate. A combined sample for testing, size 100 x 40mm, is wetted with alkaline solution (pH 9.5) previously heated to 45°C. e cuvettes were treated for 30 minutes under these conditions, and a er that acetic acid was added to the solution diluted to pH 4.7 and the treatment prolonged for a further 30 minutes. us the processed samples were drained, split on three sides and dried without rinsing. Rating of discolouration was performed with spectrophotometric colour measuring and determination of colour di erences (∆E). Determination of the water retention capacities in the textile materials W ZV was carried out according to DIN 53 814. Acclimatised fabric samples (approximately 1.6g) were cut up into small pieces. Four parallel tests were made for each sample then into each pre-weighted cuvette was placed 0.4g of the sample. Cuvettes with samples were placed in a glass and topped with a previously prepared solution (1g of anionic agents -Leonil FW (Hoechst AG) in 1 litre of distilled water). Air bubbles were expelled from the cuvette with a needle and thus the prepared samples were le to stand for two hours.
erea er the cuvettes were centrifuged for 20 min at 3000rpm; the centrifuge device was a CENTRIC 150A from the Tehtnica manufacturer. A er centrifugation the cuvettes with the samples were weighed and the di erences in weights between the cuvettes with samples a er centrifugation and those cuvettes with 0.4g of dry samples before centrifugation produced a mass of treated samples. Retention water capacity in the fabrics W ZV (%) was calculated according to Equation 1: where: m c -centrifugated sample mass [g], m kl -acclimatised sample mass [g].

Results and discussion
3.1 Spectrophotometric analysis of a sample before and after the washing process Spectrophotometric measurements were used to determine CIE L* a* b* coordinates of colours a er printing and washing treatments. e measured values are shown in Table 2.
When calculating the colour di erence (ΔE), values taken as reference were the values of the printed samples and by comparing with them the colour di erence values were obtained a er a series of washings for each material. Taking into account the results in Table 2, it can be concluded that in both materials, with the increasing number of washings came major changes of reproduced colour compared to the colours of the samples which had not undergone the process of washing. It also notes that the di erences in reproduced colour were greater on material 2 in relation to the colour di erences arising on the material 1. When analysing the results of the measurements of colour di erences for material 1, it could be observed that the colour di erence a er the rst washing treatment couldn't be noticed by the human eye. e colour di erence a er the second and third washing treatments was very small and culd only be noticed by "trained eye". A er the fourth and h washing treatments of material 1, the result was a medium colour di erence and could be noticed by an "untrained eye". At the same time, the colour di erence a er the rst washing treatment of material 2 belonged to a group of very small colour di erences (may be noticed by the "trained eye"). e medium di erence of reproduced colour, i.e. the di erence noticed by the "untrained eye" on material 2 was already there a er the second washing treatment and was held until the h treatment. In the reproduction on material 1 these colour di erences did not occur until the fourth washing treatment. e resulting changes of reproduced colours can be explained by the fact that in the process of washing it happens that some of the paint particles wash away thus reducing the possibility of light absorption and re ection increases, which a ects the experience of colour. Larger deviations of reproduced colour on material 2 can be interpreted by di erent surface structures, and due to less surface roughness of fabric and ink layer during the process of printing was lower than in material 1 (knitwear).

Colour fastness to perspiration
Determination of colour fastness to perspiration was done by measuring the CIE L* a* b* coordinates of reproduced colours and specifying the colour di erences (∆E). e tested samples a er printing and each of the washing treatment were exposed to the e ects of perspiration and the colour di erence calculated. When calculating the colour di erences the (∆E) values taken as reference were those values of the printed samples not subjected to the washing and perspiration e ects, and the colour differences compared to them. e obtained values are presented in Figure 1. When considering the obtained values in Figure 1, they show the e ect of perspiration causes a change in reproduced colour. It can also be noted that increasing the number of washings with the perspiration e ect formed greater changes of the reproduced colours. Also, analysing the value of the colour differences of the printed samples when exposed to a series of washings (Table 2) and the values of the colour di erences of the printed samples exposed to a washing e ect with perspiration ( Figure 1) conrmed that the e ect of perspiration causes additional changes in reproduced colours. Looking at the results for material 1 it was noted that the colour difference between the printed sample and the printed sample exposed to the e ect of perspiration (P-S) was 0.45, which represents a colour di erence that cannot be noticed. e colour di erence a er the rst washing treatment and the e ects of perspiration (W1-S) also belong to this group of colour differences. A er the second washing treatment of the samples with the e ect of perspiration (W2-S) the resulting colour di erence was very small, noticeable only to the "trained eye". e series of three washing treatments with the e ect of perspiration (W3-S) resulted in medium colour di erence that can be noticed by the "untrained eye". By increasing the number of washes with the e ect of perspiration the di erences became obvious colour di erences. At the same time, on the material 2 colour di erence between the printed sample and the printed sample exposed to the e ect of perspiration (P-S) represented a colour di erence that cannot be noticed. Di erences of colour a er the rst, second and third washing treatments with the e ects of perspiration (W1-S, W2-S, and W3-S) were signi cantly greater and belong to the group of medium colour di erences that can be can notice by the "untrained eye". e colour di erence a er the fourth washing treatment and the e ects of perspiration was the obvious colour di erence, and a er the h washing treatment the perspiration e ect caused massive colour di erence. ese results indicate that the e ect of perspiration causes a change of reproduced colours. is is explained by the fact that sweat "breaks" paint particles, and that is why there is the colour di erence between printed colour and printed colour exposed to the e ects of perspiration. Furthermore, with the "digestion" of paint particles, the e ect of perspiration enhances the wash-out of colour during the washing process, and brings greater colour di erences with the combination of the above actions.

Water retention capacities of printed samples before and after the washing process
Determinations of the water retention capacities in textile materials W ZV were carried out by measur-ing the di erences between the masses of the centrifugated samples and masses of the acclimatised samples. e study analysed the water retention capacities of unprinted materials, printed materials and printed materials exposed to a series of washes. e obtained values are presented in Figure 2. e results of the water retention capacities of the analysed materials indicated that the printing reduces the value of this parameter, i.e. the sorption capability of the material. By exposing the samples to washing processes increased their water retention capabilities. It was also noted that the measured value of this parameter was greater for material 1 than for material 2, which can be explained by the in uence of the surface structure and the various constructional characteristics of the materials.
e results of the water retention capacity can be explained by the fact that during the process of printing, ink penetrates into the brous materials, and closes the pores between the bres in the yarn and between the threads of yarn in textile materials. In this way it reduces the di usion of water in the material and the possibility of its absorption, which directly re ects the reduction of water retention capacity. During the washings of the samples parts of the printing inks were washed, which increased the absorption of water in the textile materials and that's how there were greater values of the water retention capacities a er a series of washings.

Conclusion
Textile products are exposed to a variety of impacts during usages and maintenance. Amongst the more common operations that these materials are exposed to are the washing process and the effects of perspiration. is paper showed the e ects of a series of washings and the perspiration e ects on print quality and the water retention capacities of screen printed textile materials. In order to determine the print quality, spectrophotometric analysis of reproduced colours before and a er a series of washings and the e ects of perspiration were made, and also the water retention capacities of unprinted and printed materials before and a er a series of washings. Spectrophotometric analysis of the printed samples before and a er a series of washings showed that with the increasing number of washes major changes of reproduced colour occurred compared to the colours of those samples which had not undergone the process of washing. e cause of this phenomenon was that during the process of washing part of the ink was washed away, thus leading to di erent light re ection from the surface of the material and di erent experiences of printed colour. It was observed that the surface structure or structural characteristics of the textile materials signi cantly affected the colour change. e performed spectrophotometric analysis of the samples con rmed that the e ect of perspiration also caused changes in the reproduced colours. Perspiration a ects the printed material in such a way that it "breaks" ink particles, which cause di erences in reproduced colours before and a er exposure. It was also revealed that perspiration had enhanced the wash-outs of printed ink during the washing processes. Analysis of the water retention capacities of the unprinted materials, printed materials and printed materials exposed to the washing process indicates that the penetrating of printing inks to the bres, reduces the water absorption capacities of the textile materials. e washing of the samples and washing out of the ink particles causes an increase in the number of hydroxyl groups capable of binding with water molecules. is leads to an increase in the water retention capacity, which is a parameter of the sorption characteristics of textile materials.
Summarising the results we can conclude that the washing process and its frequency, as well as the effect of perspiration have a signi cant impact on the print quality of a textile material and the water retention capacity as one of the important parameters for de ning the thermal comfort of textile materials. In addition to these impacts, the materials with their raw material compositions and structural characteristics partially a ect the print quality and the water retention capacities. In order to gain further knowledge testing is planned on how other external in uences a ect the print quality, and examining the in uence of the print on the thermal properties of textile materials as well. Completed research would be related to the prints made by the screen printing technique, so the same research should be obtained and with prints occurred by digital printing technology.