1 Several concepts about fabric luster
The national standard explains light, gloss and gloss in this way:
light - electromagnetic radiation capable of inducing the perception of bright colors in the human visual system;
Gloss - the property of surface directional selective reflection, manifested in the appearance of different degrees of bright spots on the surface or the formation of images of objects overlapping on the surface;
Glossiness——Using numbers to indicate the glossiness of the surface of the object.
1.1 Gloss Amount and Gloss Quality
When people look at something, according to their own experience, in addition to looking at its shape and color, they will also look at its reflection under light sources such as light bulbs to evaluate whether its gloss is high or low. Generally, we say that the luster of silk is better than that of rayon. This evaluation of luster is a psychological reaction of human vision to the luster of the object being observed. According to the intensity of fabric luster, fabrics can be divided into strong luster fabrics and weak luster fabrics, and sometimes the intensity of luster is expressed by the amount of luster. Fabrics can be distinguished according to the strength of the fabric luster, which is called the quality of luster. The concept of gloss has a lot to do with psychological factors.
1.2 Gloss of fabric
Color depends on the wavelength of light, and image perception depends on the imaging of light on the retina. At present, it is not completely clear which properties of light affect the size of the gloss, but according to the existing knowledge, the gloss of an object has a great relationship with the reflected light. The optical properties related to gloss include surface reflected light and internal reflected light.
1.2.1 Surface reflected light
Surface reflected light is divided into regular reflected light and diffused light. The surface state of the fabric is quite different, and the proportion of these two parts of light in the reflected light of the entire surface is also very different. The intensity and distribution of surface reflected light have always been the main aspects of fabric gloss research and testing.
1.2.2 Internally reflected light
After the light is refracted into the object, the part of the light reflected by the object and re-enters the original medium is called the internal reflection light. The internal reflection light shows the color of the object due to the selective absorption of the material. From the perspective of distribution, the internal reflection light can also be divided into two parts: directional reflection light and diffuse light. In addition, due to the dispersion phenomenon, the internal reflected light will form a colored halo, which is the chroma of the textile material.
2 Evaluation method of fabric gloss
When evaluating fabric luster, not only its luster is considered, but also its use (type of clothing) should be associated with the commodity attributes (type, raw material, etc.) of the fabric. With these prerequisites, the fabric luster can be evaluated and the fabric style can be integrated consider. The evaluation results are affected by personal characteristics, customs and fashion trends. It can be said that the evaluation of fabric luster is a complicated issue. There are currently two commonly used methods: sensory evaluation and instrumental testing.
2.1 Sensory evaluation method
The sensory evaluation method refers to the use of human vision to evaluate the luster of fabrics. Generally, a certain number of experienced professionals are gathered to evaluate fabrics in a specific environment. The evaluation results are an overall reflection of the visual style of fabrics. When comparing the gloss of different fabrics, the rank method is widely used. It means that several professionals evaluate the fabrics separately, and rank the gloss according to their own judgments, and then evaluate the quality of these fabrics according to the total number of ranks of various fabrics; or by A professional evaluates the luster of several fabrics repeatedly, ranks the pros and cons of each evaluation, and finally calculates the total rank. The sensory evaluation method of fabric luster has the advantages of simplicity and speed, and other methods cannot replace it at present, so this method is mostly used at present. The disadvantage of this method is that it has human factors, and the evaluation results are also related to the proficiency and psychological state of professionals. In addition, subjective assessments can only give an idea of the relative quality of fabric gloss, not quantitative values.
2.2 Instrument test method
Woven fabrics are interwoven with warp and weft yarns, and the surface structure is very complex. The reflected light is distributed in different parts of the space, and the maximum reflection is often not in the direction of regular reflection. Therefore, it is difficult to get accurate results by testing the luster of fabrics only from one or several angles. The variable goniophotometer can measure the distribution of reflected light intensity in space, and make a comprehensive description of the light reflection properties of the object. Therefore, the variable goniophotometry has become one of the important means to study the luster of fabrics.
3 Factors Affecting Fabric Gloss
The entire process from the properties of the fiber itself to the processing of the fiber into the fabric will have varying degrees of influence on the luster of the fabric.
3.1 The luster of the fiber itself
The sheen of the fiber plays a role in the sheen of the fabric. After dyeing, the fabric still shows the luster characteristic of its original fiber. Therefore, the geometry of the fibrils has a great influence on the gloss of the fabric. The following only introduces the reflection of several fibers to light.
3.1.1 Wool fiber
The unique scale structure of wool fiber makes it have partial diffuse reflection characteristics in the longitudinal direction, and the elliptical shape in the transverse direction has the characteristics of total diffuse reflection. When the light hits the surface of the fiber, different scales have similar reflections to the light, which shows that the wool fiber has better luster.
3.1.2 Cotton fiber Cotton fiber is naturally curly in the longitudinal direction, and it will have a certain diffuse reflection of light, while in the transverse direction, because of its waist shape, the reflected light has two situations: inward refraction and outward diffuse reflection. When the light hits the surface of the cotton fiber, the cotton fiber looks shiny and soft due to the effect of diffuse reflection. After the cotton fiber is mercerized, due to the irreversible expansion of the concentrated alkali on the fiber in the longitudinal direction, the fiber becomes a smooth cylindrical shape, which produces regular reflections on light, thereby improving the luster of the fiber.
3.1.3 Polyester fiber
For polyester fibers with circular cross-section, the circular cross-section fibers with uniform fineness have total diffuse reflection in the transverse direction, and total reflection in the longitudinal direction, giving people a shiny and dazzling visual effect. The polyester fiber with special-shaped cross-section makes the fiber luster soft due to the diffuse reflection of light.
3.2 Effect of Yarn on Gloss
Another factor that affects the sheen of the finished fabric is the yarn. Yarn twist, twist direction, surface hairiness, yarn thickness (yarn count), length of fiber spun into yarn, fiber blending ratio in yarn and many other aspects will affect the fabric luster. The following is a brief analysis of the influence of yarn twist, twist direction and surface hairiness on fabric gloss.
3.2.1 Twist of yarn
The twisting of the yarn will make the fibers in the yarn tilt and bend, thereby changing the distribution of reflected light of the fibers, increasing the diffuse reflected light on the surface of the fabric, and weakening its luster.
3.2.2 The twist direction of the yarn
The twist direction of the yarn has two kinds of 'S' twist and 'Z' twist. These two twist directions have different reflections on light, and the twist direction of the yarn should be selected comprehensively. 3.2.3 Hairiness on the yarn surface
During the weaving process of the yarn, there will be many fiber ends exposed from the surface of the yarn, forming hairiness, and the arrangement of these hairiness is irregular, which will enhance the diffuse reflection light, thus weakening the luster of the fabric.
3.3 Effect of fabric structure on gloss
Most of the fabrics used in clothing are woven and knitted. The knitted fabric has a coil structure, and the bending of the fibers increases the diffuse reflection and reduces the luster of the fabric. Therefore, the luster of knitted fabrics is generally weak. The structure of woven fabrics is different, and the gloss is quite different. The main influencing factors are the following two aspects.
3.3.1 Arrangement of fabric warp and weft yarns
The different arrangement of the fabric yarns determines the bending state of the warp and weft yarns in the fabric. The closer the warp or weft yarns are to the surface of the fabric, the greater the degree of bending of the yarns, the stronger the diffuse reflection light, and the weaker the gloss. Under certain lighting conditions, the distribution of reflected light of the two systems of warp and weft yarns is quite different, so the closer the yarn of one system is to the surface of the fabric, the greater the impact on the luster of the fabric.
3.3.2 Fabric warp and weft coverage
Due to the difference in the structure of the fabric, the degree of coverage of the warp and weft yarns on the surface of the fabric varies greatly. Under certain lighting conditions, due to the different proportions of warp and weft yarns on the surface of the fabric, it has a great influence on the distribution of reflected light of the fabric, and then obtain completely different glossy visual effects.
3.4 Effect of fabric finishing on gloss
Fabric finishing has a greater impact on gloss, mainly in two aspects: enhancing or weakening the gloss of fabrics. The following is an analysis of this influencing factor from the collation method.
3.4.1 General finishing
In order to improve the luster of the fabric, the finishing methods usually include singeing, shearing and setting, etc. Through these finishing methods, the hairiness on the surface of the fabric is removed, the fabric becomes smooth and smooth, the diffuse reflection is reduced, and the specular reflection is increased, thereby improving the luster of the fabric. The finishing that weakens the luster of fabrics is mainly through mechanical processing such as sanding, which increases the hairiness of the fabric surface, improves diffuse reflection, and reduces specular reflection to weaken the luster.
3.4.2 Calendering finishing
At present, the textiles produced by new calenders in CHINA mainly have the following three effects: One is to obtain high-gloss fabrics. The fabrics are calendered by chrome-plated heated steel rolls, and high gloss is obtained by means of friction, which is the so-called hot rolled. The second is the fabric with soft hand. After lamination and calendering with soft rolls, the fabric has a soft hand without the dazzling "aurora" phenomenon. The third is to finish the embossed fabric with concave-convex rolls, and then roll with engraved rolls to form concave-convex patterns, which have the effect of three-dimensional relief.
3.4.3 Special finishing There are three special finishing methods related to the optical properties of fabrics:
(1) Metal luster finishing. This method is to spray metal on the surface of the fabric, or process it by coating. Generally, copper or aluminum is sprayed on the surface of the fabric to form a golden or silver luster.
(2) Pearlescent finishing is to apply pearlescent powder to the surface of the fabric by coating to form an effect similar to pearlescent.
(3) Reflective finishing. This finishing method is to treat glass beads and reflective materials on the surface of the fabric with a special coating method. This fabric has a directional reflection function and can be used as a sign material such as warnings, traffic or signs.
3.4.4 Bioenzyme polishing
In recent years, bio-polishing finishing technology has been rapidly applied in the textile industry, and it is mainly used for finishing of cellulose fiber fabrics and garments. Biological enzymes can partially hydrolyze the fiber fluff on the surface of the fabric in a controlled manner, greatly reducing the fluff on the surface of the fabric, thereby improving the surface properties of the fabric. The fabric has a long-lasting finishing effect after biological enzyme treatment, which not only improves the gloss of the fabric, but also improves the anti-pilling performance of the fabric. In addition, the fabric becomes softer and the color becomes more vivid after biological enzyme treatment.
Editor's note: The gloss of fabrics is a relatively complicated issue. This article only describes the influence on gloss from several factors such as fiber properties, yarn structure, fabric organization and finishing, and focuses on sensory evaluation. Generally, the evaluation of the gloss of fabrics should combine the sensory evaluation with the instrumental method. In addition to the variable goniophotometry method mentioned in this article, there are also electron microscope method and FRL-Topometer appearance Tester, etc., which are important means to study the gloss of fabrics. In addition to the factors listed in the article, the factors that affect the gloss of the fabric include the transparency and refractive index of the fiber, the gloss of the external and internal structure of the fiber, and the unevenness of the fiber surface, all of which have an impact on the reflection and scattering of light. The editor hopes to deepen the research on fabric luster and publish more articles reflecting these research results.
