Study on Optical Properties of Silk-Like Fabrics by Ikuko Maekawa
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Study on Optical Properties of Silk-like Fabrics By Ikuko Maekawa*,Toshihiro Gunji* and TsuneyoTsuboi**, Members, TMSJ *OtsumaWomen's University , Sanban-cho12, Chiyoda-ku,Tokyo, 102 **AichiInstitute of Technology, Yatsugasa-machi,Toyota-shi, Aichi Pref., 470-03 Basedon Journal of theTextile Machinery Society of Japan, Transactions, Vol. 35, No. 8, T117-T125(1982-8) Abstract Testswere carried out with a gonio-photometer toinvestigate optical properties ofsilk-like synthetic fiberfabrics. To compare silk-like fabrics with natural silk fabrics, habutai and crepe de chine of silk- likesynthetic fibers as wellas thoseof naturalsilk fibers were used as samples.The following results wereobtained : 1. Thedifference in optical properties of silk-likeand natural silk fabrics can be distinguished by comparingtheir reflected light distribution curves and quantity of reflectionobtained by revolving specimens. 2. Littledifferences have essentialy been found between silk-like and natural silk fabrics. However a detailedobservation has revealed that a silk-likefabric has little amount of diffusedreflected light and thespecular reflected light of a silk-likefabric tends to gather. This causes the visual sensory differences in luster. 3. Sensory tests were carried out of a differencein luster of a silk-likeand a naturalsilk fabric. The crepede chine of a silk-likesynthetic fibers can be distinguished from that of natural silk fibers by the differenceof degree of creping. By contrast, a habutai of silk-like synthetic fibers can not completely be distinguishfrom that of naturalsilk fibers. In otherwords, a habutai of polyesterfibers is much similar invisual luster to that of natural silk fibers. 1. Introduction density, and weaving processes. There have been many reports~l-57 published on the sub- 2) Increase of intra-fiber spaces by sodium hydroxide re- duction of polyster fabrics. ject of silk-like synthetic fibers. Efforts to improve the tex- ture and the dyeability of marketed silk-like fibers and fab- 3) Production of soft texture by the use of finishing oil. rics have focused on the following: Through the use of the above techniques, it has now be- A. Fibers come possible to produce all syntheric fabrics with silk-like 1) Alteration of polymer structure. gloss and texture. 2) High Young's modulus by altering spinning, drawing, The authors have hitherto investigated~s-13) the light and heat-setting processes. reflection and the transparency characteristics of both single 3) Alteration of fiber surface properties. and multifilament fibers, and the relationship between luster 4) Good luster by making the fiber cross-section irregular. and goniophotometric curves of fabrics. In the present re- 5) Soft touch by the use of fine-denier multifilament fibers. search, the optical properties of marketed silk-like synthetic B. Yarns fiber fabrics produced by the techniques mentioned above 1) Application of silk-like twists to yarns by texturing. were investigated using both a usual goniophotometer and a 2) Moderate intra-fiber spaces by blending fibers with special goniophotometer to which an integrating sphere high and low shrinkage factors. was attached for measuring reflectivity and transparency. Results obtained were compared with those obtained on 3) Twisting of fibers having different denier, dyeability, similar real silk fabrics. and physical characteristics. Research is also being carried on into both the number and the direction of yarn twists, 2. Samples and Experimental Method with the aim of altering the characteristic synthetic fiber texture, and of producing silk-like finish. 2.1 Samples C. Fabrics The following fabrics of almost identical specification were I) Production of silk-like finish by modifying weave, yarn used : marketed polyester (hereafter PET) plain-weave habu- 18 Journal of The Textile Maclhine,~' Society of Japan Table 1 Fabric Samples Fig. 1 Surface of fabrics (habutai) (No. 1) Vol. 30 (No. 1) (1984) 19 Fig. 1 Surface of fabrics (crepe de chine) (No. 2) Fig, I Cross-section of fabrics (habutai) (No. 3) tai and crepe de chine, and real silk plain-weave habutai habutai sample, Fig. 1(a), clearly shows that the aligned flat and crepe de chine (see Table 1). Surface and cross-section surfaces of uniformly-thick tri-lobal cross-section fibers micrographs of samples were made with a scanning electron give rise to smooth fabric surface. Moreover, it can be seen microscope, and shown in Fig. 1, in which (a) is PET plain- from Fig. 1(a") that the uniform tri-lobal fibers of the PET weave habutai; (b) silk plain-weave habutai; (c) PET crepe plain-weave habutai interlock together neatly, producing de chine; (d) silk crepe de chine. Micrographs of samples (a) compactness. In contrast, the silk plain-weave habutai sam- to (d) taken at an inclination of 60° are shown in Figs. (a')- ple shows thickness variation and natural twisting of individ- (d'). ual fibers, and fibers separate each other resulting from In plain-weave habutai fabrics there is not twisting in sericin reduction. either warp or filling yarns. Especially, the PET plain-weave In the crepe de chine fabrics, the combination of virtually 20 Journal of ' The Textile Machinery Society of Japan Fig. 2 Cross-section of yarns untwisted warp yarns and strongly twisted filling yarns 2.2 Experimental Method gives rise to surface undulation. In the PET crepe de chine, A. Goniophotometric Curve Measurement it can be seen that the flat surfaces of tri-lobal fibers are Figure 3 shows a schematic diagram of the goniophotome- aligned on the yarn surface in the same way as in the PET ter (Murakami Color Research Laboratory Model CP-1R) plain-weave habutai. Because of the strong twist applied to used in the experiment. filling yarns, there would appear little essential difference be- As shown in Fig. 4, the apparatus was set to give incident tween PET and silk yarns. In the PET crepe de chine, how- angles of 45° and 60°, and could be continuously adjusted to ever, strongly-twisted and heat-set filling yarns gives rise to give reflected angles of from -35° to 90°, and from -50° to a comparatively smooth surface with no crimping. In con- 90°. Variations in reflected light values were recorded, and trast, the silk crepe de chine shows both more irregularity of goniophotometric curves were derived. Furthermore, taking single-fiber arrangement arising from variation in silk denier into consideration the surface properties of the samples, the and natural twist, and wider intra-fiber spaces resulting from diameter of the incident beam was set at 10 mm. de-gumming. Fig. 2(a) shows a cross-section of polyester B. Angle Measurement of Sample Rotation and Varia- fibers used in the present experiment. It can be seen that the tions in Reflected Light fiber cross-sections exhibit a regular tri-lobal form. Using the method developed by R. Jeffries,115Jboth inci- Fig. 3 Schematic diagram of goniophotometer. 21 Vol. 30 (No. 1) (1984) Fig. 6 Method to measure reflectivity by integrating sphere. Fig, 4 Optical diagram to measure the goniophotometric reflec- tion curve. Fig. 5 Measurement of sample rotation. Fig. 7 Method to measure reflectivity by integrating sphere. dent and reflected light angles were set at 60° (45°), and the ured. From this, diffuse reflectivity values at vertical inci- samples were rotated from 0° to 360°, as shown in Fig. 5. dence were derived. Continuous goniophotometric measurements were made of b. Measurement of Total and Diffuse Reflectivity at 45~ the relationship between the angle of sample rotation and Incidence. reflected light values. As shown in Fig. 7, sample holders were inclined at 45°, C. Measurement of Reflectivity and Transparency Using and standard white plates attached to Sample Holders an Integrating Sphere. No. 2 and No. 3. After adjustment to give a value of 100, the Hitherto, two methods have been used in the measurement sample was attached to Sample Holder No. 2 in such a way of luster: the two-dimensional method's and the three- as to bring filling yarns of the fabric parallel to the incident dimensional method.t17~ To investigate three-dimensional light flux. Total reflectivity at 45° incidence was measured. reflectivity, the authors constructed an integrating sphere Next, the standard white plate was removed from Sample attached to a goniophotometer. Measurements were made Holder No. 3, and in its place was affixed a trap of fully of reflectivity at vertical incidence, of both diffuse and total black color (to absorb specular reflected light). Total diffuse reflectivity at 45° incidence, and of overall transparency val- reflected light values at 45° incidence were measured. ues. The internal diameter of the integrating sphere was 120 c. Measurement of Overall Transparency mmz5, and a silicon photocell (SP-R20) manufactured by After removing Sample Holder No. 1 in Fig. 6, standard Kodenshi Industrial Research Laboratories was used as the white plates were attached to Sample Holders No. 2 and light receptor. Measurement accuracy was + 1 %, and the area No. 3, and their values set at 100. The sample was affixed to illuminated has a maximum diameter of 20 mm. Further- Sample Holder No. 1, and the value obtained was taken as more, the ratio of the internal surface area of the integrating the overall transparency. sphere to that of the aperture was 144:1. The flux aperture 3. Experimental Results and Observations was adjusted to the diameter of 10 mm. a. Measurement of Diffuse Reflectivity at Vertical Inci- 3.1 Measurement of Reflected Light Distribution dence. If fibers, including both PET and silk, are considered to be In Fig. 6, after removing Sample Holder No. 1 of the in- dielectric substances, then reflectivity can be determined by tegrating sphere, standard white plates were attached to using Fresnel's Coefficient : Sample Holders No. 2 and No. 3. Sample Holder No. 3 was R _ 21 tan2(Bit -O) + sln2(Oi -dt) adjusted to receive a vertical light flux, and the reflected an2(Bi+Bt) sln2(ei+et) light value set at 100.