1.Factorscausinghead-to-tailcolordifference
(1)Dyedirectness
Sincedyeshaveacertaindegreeofdirectnesstocellulosefibers,theconcentrationofthedyeliquorsqueezedoutduringpaddingmustbelowerthanthatoftheinitialdyeliquor.Concentration,thehigherthedirectness,themoretheconcentrationwilldecrease;themoretimesthedyeliquorisrepeatedlypadded,themoretheconcentrationwilldecrease.
Inthisway,theconcentrationofthedyeliquorinthepaddingtankwillcontinuetodecrease,lowerthantheconcentrationofthenewlyprepareddyeliquorinthestoragetank,andonlyafterrunningforacertainperiodoftime,theconcentrationofthedyeliquorinthepaddingtankwillbecomeconstant.Changesintheconcentrationofthedyesolutioninthepaddingtankwillcausethecolorofthedyedfabrictobedarkeratfirstandlighterattheend,resultinginheadandtailcolordifference.Thedegreeofhead-to-tailcolordifferencemainlydependsonthedirectnessofthedye.Thehigherthedirectness,themoreseriousthecolordifference.Thereisalsotheoppositesituation,thatis,theconcentrationofthepadbathdyeliquorisconstantlyincreasing,especiallywhenthedyesareinsufficientlydissolvedoraggregatedinlargequantities,theiradsorptioncapacitybythefiberswillbelowerthanthatofwater.Atthistime,thedyeconcentrationinthedyeingtankdoesnotdecrease,butincreases.Atthistime,thecolordifferencebetweentheheadandthetailisfirstlighterandthendarker.Butinmostcases,thecolordifferencebetweentheheadandtailisdarkerfirstandthenlighter.
(2)Otherfactors
Inadditiontothefiber’sadsorptionofdyes(thatis,thedirectnessofdyes),otherfactorsthataffecttheheadFactorsoftailcolordifferencealsoincludefiberproperties,dyebathtemperature,othercomponentsinthedyebath(suchaselectrolyteconcentration),andequipment.
Infact,whenthedyescontainedinthepaddingtankarecommercialized,additivessuchaselectrolytesaregenerallyadded;iftheone-phasepaddyeingmethodisused,thepaddingtankalsocontainsanalkaliagent;inordertoreducedryingWhenthedyemigrates,ananti-migrationagentwillbeadded.
Therefore,afterdyeingforaperiodoftime,theconcentrationofothersubstancesinthedyetankwillalsochange,whichwillaffectthedirectnessofthedyeandthetimeittakesfortheconcentrationtoreachequilibrium,therebyaffectingthedyeuptakerateandcolorfixationrate.,orproducehead-to-tailchromaticaberration.However,thereislittleresearchontheconcentrationchangesandbalanceissuesofthesesubstancesinthedyeingtank,sotheydeserveattention.Forexample,neutralelectrolytesindyeshavelittledirecteffectoncellulosefibers.Asthepaddyeingrunningtimeincreases,theelectrolyteconcentrationinthepadbathwillgraduallyincrease,reducingthesolubilityofthedye,increasingdyeaggregation,andofcoursestrengtheningtheDye-promotingeffect.Asforanti-migrationagents,mostofthemarepolymercompounds.Whentheconcentrationinthedyeingtankincreases,especiallyafterformingagelwithmetalions,colorspotswillappearandsticktotherollersandguiderollers,makingdyeingdifficultorcausingColordifference.
Inaddition,somedyeswillbehydrolyzedinthedyeingtank.Especiallywhendyeingbytheone-phasemethod,thealkaliagentanddyesareinthesamebath.Colordifference.Therefore,therearemanyreasonsforthehead-to-tailcolordifferencecausedbypaddyeing.Themostimportantoneisthechangeindyeliquorconcentrationcausedbythedirectnatureofthedyeitself.
It should be pointed out that the above analysis is only for the one-time pad dyeing process, that is, the one-phase dyeing process. If it is a two-phase dyeing process, after padding the dye solution, the color-fixing alkali solution must be padded, that is, a second padding must be performed. The second padding will also cause head-to-tail color difference problems. First, the dye that is not fixed on the fabric will desorb during the second padding. The desorption rate varies with the type and amount of dye. In order to reduce the color difference caused by this desorption, an appropriate amount of dye is usually added to the fixing solution to balance the desorption of unfixed dye on the fabric and prevent the head and tail color difference caused by the second dyeing. However, this desorption and second dyeing are also affected by many factors. Therefore, the amount of dye added depends on the directness, reactivity and color depth of the dye. Currently, it can only be judged based on experience.
In addition, the concentration of alkali agents and salts in the fixative solution will also change as the driving time increases. Their directness to fibers is also different from water. Some will become thinner, such as alkali agents; some will become thicker, such as neutral salts. These also have an impact on the head and tail color difference, but not as much as the directness of dyes. The effect of the fixative liquid on color difference will be further introduced in the two-phase process.
2. Specific measures to reduce head-to-tail color difference
In short, although the padding process of the pad-dyeing process is very short, it is a continuous process. The uniform distribution of dye on the fabric (i.e. the levelness of the pad-dyed product) has a great influence.
At present, there are mainly the following measures to reduce the head-to-tail color difference:
(1) Reasonable selection of dyes
To choose directness Lower dye is appropriate, which can reduce color difference and shorten the time for the dye in the dye tank to reach equilibrium concentration.
(2) Reduce the volume of the pad dyeing tank
The volume of the pad dyeing tank is small, and the time for the dye concentration in the dyeing tank to reach equilibrium is short. If tankless dyeing is achieved, that is, all the pad dyeing liquid is directly and evenly distributed Applied to the fabric, it can fundamentally eliminate the head and tail color difference.
(3) Appropriately increase the vehicle speed
On the basis of ensuring level dyeing and through-dying, increasing the vehicle speed can shorten the immersion time of the fabric in the dye liquor and reduce the damage caused by directness. Head and tail chromatic aberration. However, increasing the speed of the vehicle will reduce the amount of liquid carried by the fabric. Therefore, the dye concentration should be adjusted.to balance.
(4) Properly dilute the dye solution at the initial start-up
For different dyes and dye concentrations, the dilution ratios are different.
(5) Increase the dye concentration of the supply solution
Some processes can use the method of continuously increasing the concentration of the dye solution in the dye tank after padding the fabric (the dye solution is diluted) to stabilize the dyeing process. liquid concentration level. The increased amount of dye also depends on the dye, vehicle speed, and dye tank volume.
The above measures can be adopted separately or in combination. The above measures to solve the head and tail chromatic aberration are done through manual operation. Although they have certain effects, they cannot be stably controlled.
In order to solve this problem, dye manufacturers continue to improve their products and screen out dyes with moderate directness and reactivity to reduce head-to-tail color difference. Therefore, recommended products can be selected according to different pad dyeing processes.
In addition, dyeing machinery manufacturers are also improving their equipment to reduce head-to-tail color difference by controlling the liquid squeeze rate online. This automatic control processing method is the direction of future development, which can greatly reduce labor burden and improve the processing quality of pad dyeing.
</p
