Faculty of Natural Science and Engineering

University of Ljubljana

Faculty of Natural Science and Engineering

Department of Textiles

Assoc. Prof. Krste Dimitrovski,

Helena Gabrijelčič, B. Sc,

INFLUENCE OF FOUNDATION REFLECTANCE ON COLOUR VALUES OF WOVEN FABRICS

Abstract:

Colour values of woven structure depend on colour of warp and weft threads and constructional parameters. Beside colour, constructional parameters influence also on cover factor of woven fabric. Both size and disposition of spaces between threads, in consequence, influence not only on air and light permeability and fabric's tightness but also on colour of woven fabric's surface.

The aim of the research is to analyse the influence of foundation reflectance and its colour on colour values of woven structure. In this purpose, three groups of woven fabrics were woven on the loom, taking into account three different warp densities and five different weft densities in each group. Colour of warp threads differed from the colour of weft threads, but both were constant in all fabrics. The measurements of colour values of woven structures by three different foundations were carried out with spectrophotometer. The colours of foundation were: white, black and colour of analysed woven fabrics. The constructional parameters of fabrics and threads (thread fineness, density, weave) were used in order to design simulations with CAD system Arahne. Colour values of woven fabrics and simulations were, furthermore, also theoretically calculated. Finally, colour differences between calculated and measured colour values of real woven fabrics and simulations and colour differences between fabrics with different foundations were analysed.

The results numerically present the influence of foundation and its colour no colour values of both real woven fabrics and simulations by changing constructional parameters of woven fabrics. Moreover, colour values of woven structures and simulations can be theoretically predicted, but only if the influence of foundation reflectance with its dimensions and colour values is considered.

Key words: foundation reflectance, colour values, constructional parameters, theoretical calculation of colour values, colour differences

1 INTRODUCTION

In practice standardised methods of measuring colour values of woven fabrics are used. These methods recommend besides the usage of spectrophotometer the elimination of foundation influence on colour effect of woven fabrics, what is achieved with many-layered fabrics during measuring. In this way, the problem of foundation, which rises from practical usage of woven fabrics, is omitted. Rarely any woven structure is so tight that no foundation reflectance passes between warp and weft threads. The aim of this research is to numerically analyse different foundations and their influence on colour effect of woven fabrics.

2 THEORETICAL PART

Woven fabric is a structure of warp and weft threads, which interlace with each other. The density of warp and weft threads, threads fineness and the way in which threads interlace-weave are constructional parameters which influence on mechanical and physical properties of a structure. Moreover, the change of cover factor's value and fabric's tightness are a consequence of a change of constructional parameters (1). The higher density and fineness are the tighter is woven fabrics. Depending on the weave, colour repeat of can be determined on the surface of woven structure. Colour repeat is a sequence of warp and weft interlacing points of different or similar colour and is composed of three colour surfaces: surface of warp and weft threads and space between threads. The dimensions of three surfaces depend on constructional parameters of woven fabrics, as it is presented on Figure 1, where 1 and 2 are warp and weft threads and 3 is a space between threads. Ao and Aw are spaces between warp and weft threads and do and dw are warp's and weft's diameters (2). With the change of warp density, for example, the size of this component remain constant, but the dimensions of both other components, weft thread and space between threads, are changed. As a consequence, the fractions of three components in one colour repeat change their values with the change of constructional parameter. Likewise, the influence of changing weave and fineness on fractions of colour component could be explained (3).

Figure 1: Presentation of woven fabric with the change of warp density.

On the basis of the diameter of the thread, the thread density and the weave the fractions of individual thread and space between threads in the pattern can be calculated. Furthermore, taking into account colour values of warp and weft threads, colour of the surface of woven structure can be theoretically determined (4).

2.1 Foundation and its influence

Foundation is a space between threads in a woven structure. Its shape depends on weave, considering four types of pore: in plain weave, in Basket 4 weave between two warps or between one warp and one weft thread and in Twill 4 weave (5). On the other hand, its size depends on thread density and fineness, so that the higher values of density and fineness are the lower is the size of foundation. Such a parameter that take into account foundation is cover factor, which considers density and fineness of threads and presents the influence of foundation on air and light permeability.

The colour of woven structure depends besides on colour of warp and weft threads, on foundation reflectance, too. Optically we realise that the woven textile seems brighter, when the foundation colour is bright and darker in the case of dark foundation. The past researches have been avoided the numerical evaluation of the influence of foundation on colour of woven structure because of standardised method of colour measuring. This method recommends the use of multilayered woven fabric in order to exclude the influence of foundation. The non-objective evaluation of the colour of foundation that reflects between the threads consequently remains the problem to consider only with the usage of fabric.

3 EXPERIMENTAL PART

In experimental part of the paper the influence of foundation reflectance by different constructional parameters is spectrophotometrically determined. With this purpose, woven fabrics in plain weave are woven on the loom Minifaber with Tis jacquard mechanism. The constructional parameters of warp and weft threads are equal but their colour is different: warp is blue and weft is red, as it is presented in Table 1.

Table 1: Constructional parameters and colour values of warp and weft threads and their simulations.

Thread / Fineness / Diameter / Torsion / Real / Simulation
Warp / 8´2 tex / 0,187 mm / 1040 S / L* = 22,82 / L* = 25,00
a* = 9,67 / a* = 5,95
b* = -34,55 / b* = -22,13
Weft / 8´2 tex / 0,187 mm / 1040 S / L* = 37,63 / L* = 39,11
a* = 47,22 / a* = 37,13
b* = 16,70 / b* = 14,39

Woven structures are prepared in three different warp densities and fifteen different weft densities, five with each warp density as is presented in Table 2.

Table 2: Warp and weft density of woven fabrics.

Weave / Warp density (thr/cm) / Weft density
(thr/cm)
plain / go / gw1 / gw2 / gw3 / gw4 / gw5
40 / 21 / 17 / 13,5 / 11 / 8,5
36 / 22 / 20 / 17 / 14 / 11
31 / 23 / 21 / 19 / 17 / 15

Three groups of fabrics are analysed taking into account colour values of three different foundations: white printing paper (Epson Ink Jet Photo Paper), black plate included in the measuring equipment of DataColour Spectrophotometer SpectraFlash SF 600 Plus-CT and colour values of many-layered fabric, which is above all standardised method. Such a white and black foundations are chosen because they have minimal a* and b* values but very high (white) or very low (black) L* colour value. White: L* =94,61, a* = 3,79, b* = -12,72. Black: L* = 29,63, a* = 0,03, b* = -0,79.

Theoretical predictions of colour values of real fabrics and simulations are calculated according to equations presented in reference (2) and (3).

Colour values of threads and woven structure with different foundations are measured with DataColour Spectrophotometer SpectraFlash SF 600 Plus-CT. Additionally, simulations of woven fabrics are prepared with CAD system Arahne considering the same constructional parameters and colour values of threads as in real woven structures (6). Simulations are printed on Epson Ink Jet Photo Paper with Epson Stylus Photo 870.

Finally, colour values L*, a* and b* of real woven fabrics and their simulations with different foundations are accurately analysed. Colour differences DE*ab between theoretically predicted and measured colour values are calculated and numerical measurements of the influence of foundations reflectance are evaluated (7).

4 RESULTS OF MEASUREMENTS

In Tables from 3 to 5 and Figures from 2 to 4 present measured and calculated colour values of real fabrics -F and their simulations -S are presented with warp density go 40, 36 and 31 threads/cm and different weft densities gw.

Table 3: Measured and calculated colour values L*, a*, b* and colour differences DE*ab between real woven fabrics -F and simulations –S, when white colour is used as a foundation.

go / 40 / 36 / 31
gw / 21 / 17 / 13,5 / 11 / 8,5 / 22 / 20 / 17 / 14 / 11 / 23 / 21 / 19 / 17 / 15
F / measured
L* / 28,1 / 29,1 / 27,9 / 27,6 / 26,9 / 31,0 / 31,5 / 30,8 / 31,2 / 30,6 / 31,7 / 32,1 / 31,6 / 32,3 / 33,3
a* / 17,5 / 16,4 / 14,5 / 13,8 / 12,6 / 19,9 / 18,8 / 17,5 / 15,5 / 14,5 / 22,3 / 20,6 / 19,6 / 19,1 / 17,4
b* / -23,1 / -24,1 / -27,4 / -28,8 / -31,0 / -19,7 / -20,6 / -22,5 / -24,6 / -26,5 / -16,8 / -18,8 / -20,1 / -20,5 / -21,8
calculated
L* / 37,5 / 38,2 / 38,8 / 39,2 / 39,6 / 40,7 / 41,2 / 42,0 / 42,8 / 43,6 / 44,6 / 45,3 / 46,1 / 46,8 / 47,5
a* / 18,0 / 16,1 / 14,5 / 13,3 / 12,2 / 18,8 / 17,8 / 16,3 / 14,8 / 13,3 / 19,7 / 18,6 / 17,5 / 16,4 / 15,4
b* / -18,6 / -20,6 / -22,3 / -23,6 / -24,8 / -16,4 / -17,4 / -18,9 / -20,4 / -21,9 / -13,7 / -14,7 / -15,7 / -16,7 / -17,7
DE*ab / 10,5 / 9,7 / 12,0 / 12,7 / 14,2 / 10,4 / 10,3 / 11,8 / 12,3 / 13,8 / 13,5 / 14,0 / 15,3 / 15,2 / 14,9
S / measured
L* / 29,5 / 29,4 / 29,2 / 29,2 / 29,0 / 30,7 / 30,6 / 30,5 / 30,4 / 30,7 / 33,6 / 34,2 / 34,8 / 35,2 / 35,6
a* / 10,7 / 8,7 / 8,1 / 7,5 / 6,9 / 10,4 / 10,0 / 9,2 / 8,4 / 7,6 / 12,1 / 11,3 / 10,7 / 9,9 / 9,1
b* / -16,9 / -18,9 / -20,7 / -22,0 / -23,1 / -16,3 / -17,4 / -19,2 / -21,0 / -22,4 / -14,5 / -15,9 / -17,1 / -18,3 / -19,5
calculated
L* / 39,2 / 39,8 / 40,4 / 40,8 / 41,2 / 42,3 / 42,8 / 43,6 / 44,3 / 45,1 / 46,0 / 46,8 / 47,5 / 48,2 / 48,9
a* / 13,3 / 11,8 / 10,5 / 9,5 / 8,6 / 14,0 / 13,2 / 12,0 / 10,8 / 9,6 / 14,9 / 14,1 / 13,2 / 12,4 / 11,5
b* / -11,7 / -13,2 / -14,6 / -15,5 / -16,5 / -10,4 / -11,1 / -12,3 / -13,5 / -14,7 / -8,7 / -9,5 / -10,4 / -11,2 / -12,0
DE*ab / 11,3 / 12,3 / 13,0 / 13,5 / 14,0 / 13,5 / 14,1 / 15,0 / 15,9 / 16,5 / 14,0 / 14,4 / 14,5 / 15,1 / 15,4

Figure 2: Measured-m and calculated-c colour values L*, a*, b* of real woven fabrics -F and simulations –S, when white colour is used as a foundation.

Table 4: Measured and calculated colour values L*, a*, b* and colour differences DE*ab between real woven fabrics -F and simulations –S, when black colour is used as a foundation.

go / 40 / 36 / 31
gw / 21 / 17 / 13,5 / 11 / 8,5 / 22 / 20 / 17 / 14 / 11 / 23 / 21 / 19 / 17 / 15
F / measured
L* / 26,8 / 26,4 / 25,5 / 25,4 / 24,5 / 28,6 / 28,0 / 27,0 / 26,4 / 25,7 / 28,9 / 28,8 / 27,9 / 27,9 / 26,9
a* / 17,6 / 16,2 / 14,4 / 13,5 / 12,3 / 19,3 / 18,6 / 17,8 / 16,2 / 14,5 / 21,8 / 20,4 / 19,7 / 19,1 / 17,7
b* / -22,3 / -23,8 / -26,7 / -28,0 / -29,7 / -19,8 / -20,1 / -21,6 / -22,8 / -25,5 / -16,1 / -17,9 / -18,8 / -19,3 / -20,6
calculated
L* / 27,5 / 26,9 / 26,4 / 26,1 / 25,7 / 28,2 / 27,9 / 27,5 / 27,0 / 26,6 / 29,0 / 28,7 / 28,4 / 28,1 / 27,8
a* / 17,4 / 15,5 / 13,8 / 12,6 / 11,3 / 18,0 / 17,0 / 15,4 / 13,9 / 12,3 / 18,8 / 17,7 / 16,5 / 15,4 / 14,2
b* / -16,8 / -18,5 / -20,1 / -21,2 / -22,3 / -14,0 / -14,9 / -16,2 / -17,5 / -18,8 / -10,8 / -11,6 / -12,5 / -13,3 / -14,1
DE*ab / 5,6 / 5,4 / 6,8 / 6,9 / 7,6 / 5,9 / 5,5 / 6,0 / 5,9 / 7,1 / 6,1 / 6,8 / 7,1 / 7,0 / 7,4
S / measured
L* / 27,6 / 27,3 / 27,0 / 26,7 / 26,4 / 28,0 / 27,6 / 27,3 / 27,0 / 26,5 / 28,3 / 27,9 / 27,8 / 27,4 / 27,0
a* / 8,2 / 7,2 / 6,3 / 5,6 / 4,9 / 8,9 / 8,4 / 7,5 / 6,6 / 5,7 / 10,5 / 9,7 / 9,1 / 8,2 / 7,4
b* / -12,4 / -13,5 / -14,4 / -15,6 / -15,7 / -11,2 / -11,7 / -12,3 / -13,4 / -14,0 / -9,1 / -9,8 / -10,2 / -10,8 / -11,2
calculated
L* / 28,7 / 28,1 / 27,6 / 27,2 / 26,8 / 29,2 / 28,8 / 28,4 / 27,9 / 27,4 / 29,7 / 29,4 / 29,0 / 28,7 / 28,3
a* / 12,6 / 11,1 / 9,7 / 8,7 / 7,7 / 13,2 / 12,4 / 11,1 / 9,8 / 8,6 / 13,9 / 13,0 / 12,1 / 11,2 / 10,2
b* / -10,1 / -11,4 / -12,5 / -13,4 / -14,2 / -8,3 / -8,9 / -9,9 / -10,9 / -11,9 / -6,1 / -6,8 / -7,4 / -8,1 / -8,7
DE*ab / 5,2 / 4,5 / 3,9 / 3,8 / 3,2 / 5,3 / 5,0 / 4,5 / 4,1 / 3,6 / 4,8 / 4,7 / 4,3 / 4,2 / 3,9

Figure 3: Measured-m and calculated-c colour values L*, a*, b* of real woven fabrics -F and simulations –S, when black colour is used as a foundation.

Table 5: Measured and calculated colour values L*, a*, b* and colour differences DE*ab between real woven fabrics -F and simulation s –S, when multilayered fabric is used as a foundation.