Research On The Effect Of Size Coating On Sized Yarn Performance By Means Of The Image Detection Method

Cotton fabric has the advantages of good skin-friendly and comfortable wearing,and is still the main fabric of clothing and home textile products.In the production process of cotton fabrics,warp yarns need to be sized to improve the loading performance in the weaving process,so as to improve production efficiency and product quality.However,the sizing process requires the consumption of size agent and energy,and the desizing process produces a large amount of waste discharge,which is detrimental to sustainable development and ecology.Therefore,on the premise of meeting the requirements of weaving conditions,low size pick-up and easy desizing was the development trend of warp sizing.The distribution of slurry in sized yarns is in two forms,coating and penetration,the synergistic effect of them directly determines the sizing quality of warp.Among them,the size coating plays a major role in attaching hairiness and effectively resisting weaving friction,which determines the weavability of warp yarns to a large extent.However,limited by the size coating test method,it is difficult to achieve fine control of sizing process.Starch is cheap and environmentally friendly,and PVA has good adhesion and film-forming properties.In this paper,the above two kinds of slurry were used.A slurry coating test device was designed and developed to realize the continuous acquisition of apparent images after the color reaction of starch/PVA and iodine on the yarn surface.According to the color depth difference of yarn apparent image after color reaction,the relevant features were extracted,and the evaluation indexes of size coating were constructed using computer image processing technology.Based on the above evaluation system,the effects of prewetting,plasma and ultraviolet irradiation pretreatment conditions on the sized yarn properties were analyzed from the perspective of size coating.Finally,the influence of sizing process on size coating effect and sized yarn properties was studied,and the relationship between size coating and sized yarn properties was analyzed.Through the optimization and control of sizing process,the sized properties were improved without increasing size pick-up.The specific research contents and conclusions of this paper are as follows:（1）Based on the starch/PVA-iodine color reaction principle,a size coating test device was built by means of computer image processing technology,and the size coating effect test method and evaluation indexes were proposed,which provided the technology support for the full-text.The test device can control the speed of yarn in I₂-KI solution to stabilize the process of color reaction,realize the automatic acquisition and image processing of yarn apparent images,and give the evaluation results of size coating effect.6 yarns can be tested on the device at the same time.The size coating was converted into the color depth of the sized yarn after the color reaction with iodine,which make it possible to quantitatively evaluate the size coating.Aiming at the evaluation of size coating effect,an evaluation system composed of size coating coefficient,size coating strength and size coating unevenness was proposed,which reflected the integrity of the size coating,coating amount and coating uniformity,respectively.Taken sized yarns with different linear density and size pick-up as examples,the effectiveness of the image processing method and the size coating effect indexes was verified.Taken sized yarns with different ratios of starch and PVA as examples,the applicability of this method to different sizing formulations was verified.（2）In order to ensure the stability and efficiency of the size coating effect test,the color reaction parameters,sampling illumination parameters and image analysis sampling parameters in the test system were optimized.Firstly,the effects of I₂-KI solution concentration and yarn immersion time on the results and stability of size coating effect were analyzed by single factor experiment,the above parameters were optimized by response surface analysis with the variation coefficient of size coating coefficient,variation coefficient of size coating strength and variation coefficient of size coating unevenness as response values.After that,the relationship between the concentration of I₂-KI solution and the absorbance was established.Through the test of absorbance,the influence of illumination time,illumination intensity and illumination distance on the stability of I₂-KI solution concentration was studied,and the sampling illumination parameters were determined.According to the statistical calculation of the gray value of the yarn images,the image analysis sampling parameters were determined,including the sample size and the effective statistical area.The experimental results indicated that immersion time of 209.4 s and I₂-KI concentration of 11 mg/L led to the optimal stability of size coating effect,and the model prediction value matched well with the experimental results.I₂-KI solution had no significant change when the illumination time was within 3600 s,the illumination intensity was below80000 lux and the illumination distance was within 10-200 mm.Thus,the test conditions and image processing parameters were determined as:the I₂-KI concentration was 11 mg/L,the yarn immersion time was 210 s,the illumination intensity was 18000 lux,the illumination distance was 50 mm,the sample size of the yarn picture was 200,and the gray value effective statistical area was 5 rows of pixels in the yarn center axis area.（3）The effects of prewetting,plasma and ultraviolet irradiation on the size coating effect and sized yarn properties were studied,and the pretreatment conditions were optimized.Firstly,the effects of prewetting treatment,plasma pretreatment and UV irradiation pretreatment on the modification of the raw yarn was studied from the aspects of surface element composition and wettability.Secondly,by using single yarn sizing machine,the effects of three pretreatment conditions on size coating coefficient,size coating strength and size coating unevenness were studied respectively.Finally,the effects of three pretreatment process parameters on the mechanical properties and hairiness of sized yarn were studied.The results showed that the wettability of the raw yarn was improved after the three pretreatments,which was conducive to the integrity and uniform coating of the slurry on the yarn surface,and also benefited for improving sized yarn performance.The three kinds of pretreated yarns were sized,and it can be found by testing of sized yarn performance that after prewetting treatment,the size coating coefficient was increased by 5.50%,the size coating strength was increased by 14.31%,and the size coating unevenness was decreased by 20.71%.The tensile strength of sized yarn was increased by 6.56%,the abrasion resistance was increased by25.43%,and the hairiness was decreased by 38.71%;After plasma treatment,the size coating coefficient was increased by 21.07%,the size coating strength was increased by 57.27%,and the size coating unevenness was decreased by 52.57%.The tensile strength of sized yarn was increased by 19.82%,the abrasion resistance was increased by 160.24%,and the hairiness was decreased by 85.14%;After UV irradiation treatment,the size coating coefficient was increased by 15.61%,the size coating strength was increased by 30.38%,and the size coating unevenness was decreased by 24.20%.The tensile strength of sized yarn was increased by20.13%,the abrasion resistance was increased by 103.49%,and the hairiness was decreased by 88.32%.（4）The effects of sizing process parameters such as slurry formula,slurry concentration and squeezing pressure on size coating effect and sized yarn performance were studied,and the sized yarn performance was improved by enhancing size coating effect without increasing size pick-up.Taken two proportions of starch/PVA（starch 60%/PVA40%and starch80%/PVA20%）as examples,the sizing experiments were carried out on the sheet yarn sizing machine.Firstly,the effects of slurry concentration and squeezing force on size coating effect and sized yarn properties were studied.Then,the slurry concentration and squeezing force were synergistically changed to obtain the sized yarns with constant size pick-up under different sizing processes.Finally,the influence of the synergistic change of slurry concentration and squeezing force on the size coating effect and sized properties was studied.The single factor experiment results showed that in the range of test samples in this experiment,with the increase of slurry concentration,the size coating coefficient and size coating strength increased,the size coating unevenness decreased,the mechanical properties increased,and the hairiness decreased.With the increase of squeezing force,the size coating coefficient and size coating strength decreased,the size coating unevenness increased,the mechanical properties decreased and the hairiness increased.In the case of the same size pick-up under the synergistic change of slurry concentration and squeezing force,compared with low slurry concentration and squeezing force process,the size coating coefficient and size coating strength of 14.6 tex sized yarn under high slurry concentration and squeezing force process increased by 4.08%and 12.76%,the size coating unevenness decreased by8.20%,the tensile strength and abrasion resistance increased by 2.51%and 4.34%,and the hairiness above 3 mm decreased by 16.93%.The size coating coefficient and size coating strength of 9.7 tex sized yarn under high slurry concentration and squeezing force increased by 4.19%and 7.19%,the size coating unevenness decreased by 10.89%,the tensile strength and abrasion resistance increased by 3.19%and 6.35%,and the hairiness above 3 mm decreased by 6.63%.The results indicated that under the same size pick up,the high slurry concentration and squeezing process was more conducive to improve the size coating effect and sized yarn performance.