Denim kumaşlarda yıkamanın dikiş ve kumaş üzerindeki etkisi

Abstract

Denim kumaşlar üretim aşamasından tüketiciye hazır hale getirilene değin pek çok işleme tabi tutulurlar/özellikle konfeksiyon bölümünde gördükleri dikim ve daha sonraki yıkama prosesleri, mamul bazında önemli etkiler oluşturmaktadır. Dikim ve yıkama sonucu talep edilen renk ve dizaynlar elde edilmekle birlikte bazı olumsuz sonuçlarda ortaya çıkmaktadır. Ürünlerin satış sonrası tüketici tarafından kullanımı esnasında bu sorunlar daha büyük oranlara ulaşabilmektedir. Bu tezin hazırlanmasındaki amaç denim kumaşların gördükleri işlemler sonucu ortaya çıkan olumsuzlukların hangi aşamalardan sonra hangi oranlarda gerçekleştiğini araştırmak ve bunların giderilebilmesi için yapabilecek öneriler varsa ortaya koymaktır. Değişik firmalardan alınan 15 denim kumaş numunesi öncelikle laboratuvar ortamında kondisyone edilmiş ve kumaş yapı özellikleri incelenmiştir. Farklı fiziksel özelliklere sahip bu kumaşlardan standartlara uygun olarak kesilen parçalara atkı ve çözgü yönünde düz dikiş uygulanmış ve Grab testine göre dikiş dayanım mukavemetlerine bakılmıştır. Ayrıca her kumaş tipi için bu dikilmiş parçalardan toplam dört adet numune kesilerek aşındırma cihazında test edilmiş ve böylece kumaş aşınma dayanımları belirlenmiştir. Daha sonra yine standartlara uygun şekilde atkı ve çözgü dikiş numuneleri dikilip bir firmada yıkamaya tabi tutulmuşlardır. Bütün numuneler haşıl sökme, taş yıkama, durulama işlemlerine aynı şartlarda sokulmuşlar ve laboratuvarda aynı yöntemlerle dikiş dayanım mukavemetleri ve kumaş aşınma dayanımları deneyler sonucu belirlenmiştir. Elde edilen deney sonuçları kumaş özellikleri de göz önüne alınarak yorumlanmış, ayrıca daha iyi kaliteye ulaşabilmek için yeni öneriler getirilmeye çalışılmıştır.

Blue jeans, past time's workwear garments, are now the most common casual clothes for both young and old people. In the worlds continually growing comfortable garments market, denim fabrics have a dominant position. Denim fabrics with such a great range of use, pass through quite a few number of processes before they are delivered to the customers. One of the most important stage of denim manufacturing is the preparation of the warp yarns which form the characteristics of the fabrics since they are dyed with indigo dyestuff. Although a number of different methods are used for that purpose, the most common one is the "rope dye" technique. In this method, warp yarns ropes are former by putting 350-400 warp yarns together. Then they are passed through indigo dye bath and are given the demanded colour. During dyeing process, oxidation is occured by means of exposing the ropes to air contact after each dye bath. Both OE and ring yarns can be used as warps and wefts in denim fabrics. After weawing and finishing processes, produced fabrics go to quality control section. The quality control of denim fabrics are carried out in accordance with the standarts which are developed by Levi Strauss&CO. Fabrics will be graded using the "4 Point" system. All defects which are clearly noticeable from three feet and not considered a part of the character of a particular fabric by LS&CO., and supplier shall be scored as defects and demerit points assigned according to severity. In the blue jean production, sewing and washing processes play an important role.The central feature of any manufactory is seam. Assuming that the fabric is sewable and suitable for garments, the achievement, at an economical level, of the various requirements of appearance and performance of sewn seams, both initially and during use, is the result of the selection of the correct combination of five factors during manufacturing: a) the seam type which is a particular configuration of fabrics; b) the stitch type which is a particular configuration of thread in the fabric; VIII c) the sewing machine feeding mechanism which moves the fabric past the needle and enables a succession of stitches to be formed; d) the need which inserts the thread into the fabric; e) the thread which forms the stitch which either holds the fabric together, neatens it or decorates it. Superimposed seam is the commonest construction seam on garments and the one used to illustrate the various methods of depicting seam constructions. The simplest seam type within the class is formed by superimposing the edge of one piece of material on another. A variety of stitch types can be used on this type of seam, both for joining the fabrics and for neatening the edges or for achieving both simultaneously. The stitch types in class 300 (lockstitches) are formed with two or more groups of threads, and have for a general characteristic the interlacing of the two or more groups. Loops of one group are passed through the material and are secured by the thread or threads of a second group. One group is normally referred to as the neddle threads and the other group as bobbin threads. Straight lockstitch, 301, with a single needle thread and a single bobbin thread, is still the commonest stitch used in the clothing industry. Correct and even stitch length is achieved by means of the mechanism that feeds the fabrics past the needle. The way in which fabric is penetrated by the needle during sewing has a direct effect on seam strength and on garment appearance and wearable life. The functions of the sewing machine needle in general are; - to produce a hole in the material for the thread to pass through and to do so without causing any damage to the material; - to carry the needle thread through the material and there form a loop which can be picked up by the hook on the bobbin case in a lockstitch machine or by the looper or other mechanism in other machines; - to pass the needle thread through the loop formed by the looper mechanism on machines other than lockstitch. Needles are available in a wide range of sizes and the choice of size is detrmined by the fabric and thread comination which is to be sewn. Correct size is essential to good sewing performance but as fabrics tend to become finer and, in many cases, more densely constructed, the demand is for neddles and threads which can be used satisfactorily in smaller sizes. If the needle is too small for the thread, the thread will neither pass freely through the eye nor fit properly into the long groove and will suffer from excessive abrasion as a result. This can lead to costly thread breakages in production because the machinist must stop to rethread the needle. IX If the needle is too large for the thread there will be poor control of the loop formation which may cause slipped sticthes. There will also be holes in the fabric which are too big for the stitches and give an unattractive seam appearance. An unnecessarily large neddle also tends to give rise to damaged fabric along the stitch lineand, in closely woven fabrics, pucker along the seam line due to fabric distortion. Needles can become damaged as a result of striking a harsh material over a period of time. Material such as the type of denim used for jeans which is made up in a stiff state and then washed in garment form can require that the needles sewing it are changed every two hours before they become so damaged that they in turn damage the material. If seams are to have satisfactory appearance and performance, a prime contributory factor is the sewing thread used. Correct selection of sewing thread requires consideration of its performance properties during sewing as well as its performance in the completed garment under conditions of wear and cleaning. It also requires consideration of its appearance in the sewn seam, which is both its appearance as sewing thread and the effect it has on the appearance of the materials being sewn, this last factor being also partly connected with thread performance. A sewing thread must be something more than just an ordinary piece of yarn. Denim fabrics are sewn with a different type of thread construction which is known as corespun where a continuous multifilament core is wrapped around with a sheath of spun fibres, two or three of these yarns then being plied together. This is the construction of the threads referred to earlier that can be a mixture of natural and synthetic fibres, the majority of these corespun threads consisting of a polyester core and a cotton cover. The continuous filament core produces high tenacities and excellent loop forming characteristics through the sewing machine needle. The cotton covering gives maximum protection from damage by needle heat in severe sewing operations. Corespun threads must often withstand high temperatures when used as needle threads and thus need a high level of lubricant. The thread strength and loop formation are well maintained in multidirectional sewing and on automatic machines. These threads also have a satisfactory amount of stretch and low shrinkage. When good sewing performance is taken into consideration, sewing thread choice is important as well as sewing needle. A difficulty with the polyester and cotton combination is that the thread must be dyed twice and this adds to cost. Selection of needle and thread sizes for a particular seaming situation is a question of achieving a balance between minimum damage and pucker and seam strength which may require a more substantial needle and thread. For minimum damage and pucker, choosing of small size and fine thread is very important. The length of life of a seam in a garment should be as long as that of the other materials and both should be appropriate to the required end use of the garment. The seam can be considered to have failed in durability terms if either the thread or the fabric in the seam fails at an early stage. An immediate failure of the tread would be regarded as a failure of seam strength or extensibility. Jeans and workwear garments suffer considerable abrasion in wear and seams must be designed to resist this abrasion as effectively as possible. A typical area of a garment where abrasion may be experienced is on the inside leg seams of denim jeans. The traditional strong jeans seams consisting of a lap felled seam with two rows of 401 chainstitch does not always perform well in this position because the stitching suffers considerable abrasion, a heavily built wearer adding to the problem. Superimposed seams sewn with safety stitch are more commonly used, prefarably sewn such that the neddle side of the chainstitch row is worn against the skin with the chain underside protected by the seam allowance. A different problem of seam durability and abrasion can arise with denim fabrics when they are subjected to stonewashing. In this process they are severely abraded to produce a worn and faded look. Careful thread selection is required to prevent damage to seams requiring immeadiate repair or damage which shows later and shortens the life of the garment. Severe damage to the seams can result if the wrong thread selection is made. In the washing department, desizing, stonewashing and rinsing processes are applied to the fabrics in the appropriate conditions to obtain demanded colour and effects. In this study, 15 different denim fabrics were manufactured by various firms are conditioned in the standart conditions and then all of the fabrics are tested in many ways to determine their fabric construction and yarn count values are obtained. For each fabric, test speciments both in warpwise and weftwise are prepared as discribed in the standarts. While sewing the fabrics, with a weight of over 270 g/m2, polyester- cored 60 tex threads are used. Since it is meeting all necessery conditions, the sewing thread labelled by 50, is used in the study. The thread's strength, count and twist values are determined for the first and the last ply. The test speciments which were cut in accordance with the test conditions mentioned in the standarts are sewn by using an industrial type sewing machine. Stitch density was 3,1 ±1/2 stitch/cm and the distance between the stitches and the edge was 16 cm. The flat sewing process is carried out by using Ssa-1 seam type and 301 stitch type is used with a needle of 18 Nm. Following these preparation processes, 5 test speciments in warpwise and weftwise for each fabric are tested by means of the statigraph seam strength tester as described in the standart. After that, from each fabric 4 abrasion speciments are prepared and their abrassion values are obtained by using the Martindale abrassion tester. XI To help the determination of the warp and weft types of the fabrics, warp and weft threads counts and twist values are determined. Samples from the same fabrics which were tested earlier on, are reprepared in the same conditions, washed and the same tests applied again. Their seam strength and abrassion values after washing are obtained. The vital point while determining the seam strength is the necessity of equalizing the fabric density which might increase in case of shrinkage after washing, to the initial fabric density. The test results obtained before and after washing are evaluated. During the evaluation fabric properties are taken into account. In the light of the knowledge obtained, new succestions are made in order to help increasing quality.