In textile finishing and coating, a few percent error in chemical dosing can mean a >15% drop in strength or >30% loss in repellency, while over-dosing stiffens fabric and wastes cash. Plants are turning to automated dosing and in-line sensors to hold concentration, temperature, and residence time exactly on spec.
The finishing bath — a liquid recipe that imparts repellency, softness, flame resistance, or other functions — decides how a fabric will feel and perform. And it is sensitive. In one peer‑reviewed study, raising a fluorochemical water‑repellency finish from 30 to 60 g/L significantly improved initial repellency; beyond 60 g/L the gain was negligible (www.mdpi.com) (www.mdpi.com). At 60 g/L, though, warp elongation dropped 18% versus untreated and bending rigidity jumped by more than 50% — a stiffer hand with less stretch (www.mdpi.com) (www.mdpi.com).
That’s the knife-edge modern mills operate on. Temperature tweaks alter reaction speed and fiber swelling. A minute less in the bath leaves effects under‑developed; longer times sap throughput or stress fibers. Even pH can flip outcomes: softener baths must stay near neutral; too high makes fabric stiff, too low makes softeners ineffective (www.boquinstrument.com).
Fabric property drivers in finishing
Finished fabric properties hinge on interrelated variables: finish chemistry and dosage (including functional additives, crosslinkers, catalysts), bath composition (pH and auxiliary salts), temperature, and residence time (dwell time: the fabric’s contact/cure duration). Fabric type and construction (fiber blend, weight, porosity) matter, as do mechanical application parameters such as padder pressure, pickup percentage (liquor retained), and fabric tension. A padder is the two‑roll system that applies and squeezes the finish uniformly.
Small deviations shift exhaustion/fixation equilibria and thus final hand, repellency, durability, or strength. In the fluorochemical case, Mehta et al. showed that the 30→60 g/L increase lifted initial repellency markedly, but >60 g/L brought negligible gains (www.mdpi.com) (www.mdpi.com). At the same 60 g/L, the study recorded an 18% drop in warp elongation and a >50% flexural rigidity rise versus untreated (www.mdpi.com) (www.mdpi.com).
Concentration, temperature, and time control
Chemical concentration is unforgiving. Under‑dosing yields weak effects (e.g., low repellency or poor wash durability) and scrap; over‑dosing burns money and harms hand. Mehta et al. identified ~60 g/L as an optimal fluoro‑finish dose for high water/oil repellency; using only 30 g/L left about 50% less repellency after 30 washes (www.mdpi.com). Pushing above 60 g/L did not further improve repellency but sharply increased stiffness and reduced elongation (www.mdpi.com) (www.mdpi.com). The authors conclude: “use of an optimal concentration can result in cost reduction and is environmentally preferable” (www.mdpi.com).
Temperature and time also have tight windows. Too low, and finishes (crosslinkers, silicones, flame retardants) do not react fully; too high, and cellulosics can yellow or tear. Precise temperature control — often within ±1°C — keeps reaction kinetics uniform. Residence time must be fixed: fabric moved too fast under‑treats; too slow drags productivity. In pad‑batch processes, dwell depends on padder spacing and dryer length; even minor flow rate shifts alter effective contact time. In practice, ±1–2% dosing errors translate into measurable quality shifts or extra reprocessing.
Automated dosing architectures
Modern finishing plants use automated dosing systems to hit recipes exactly. Examples include TecnoDos and Lenzing MPS; Thies’ MPS series is marketed as “a complete solution for fully automated supply of a finishing plant with chemicals, dyes and auxiliaries” (www.thiestextilmaschinen.com). Software planning systems compute each chemical amount by recipe, fabric weight, and pickup, then remote pumps dispense to a mix tank or directly to the machine, removing manual weighing errors. State‑of‑the‑art dispensers achieve ±0.01 g accuracy in lab trials (textilelearner.net), and industry reviews note this “prevents uncontrolled weighing errors and minimizes product wastage… ensures consistent solution preparation” (textilelearner.net).
Many mills pair these platforms with accurate chemical dosing hardware such as dosing pumps to maintain setpoints while recipes change. In 4.0‑era dyehouses, proper dosing algorithms yield significant chemical savings and cut water use by matching supply to actual needs (www.escarre.com), and brands such as Inditex and Nike demand such traceable controls for high quality and sustainability (www.escarre.com).
In‑line sensing and feedback control
On‑line sensors close the loop. Common probes measure pH and temperature, feeding PID controllers (proportional-integral-derivative control that corrects deviations). Automated pH monitoring “utilizes advanced sensors” to provide real‑time feedback and remote control (www.boquinstrument.com). A drop in pH during finishing can automatically trigger an alkali pump (or acid bath) to correct it, keeping tight pH windows needed for fixation (www.boquinstrument.com).
Other in‑line tools include conductivity meters (for salt/binder levels), turbidity or optical probes (for liquor concentration), and concentration cells for additives. Advanced lines embed fabric sensors: the Triatex Mayer transfer coater uses β‑ray detectors (a radiation‑based sensor to gauge mass/add‑on) aimed at the fabric to measure actual wet pickup; a feedback loop adjusts coating roll speed to hit target add‑on across the web (www.intechopen.com). In high‑speed pad‑steam machines, camera or laser sensors can check fabric color/lightness in real time, prompting automatic dye or auxiliary dosing — more common in dyeing but applicable to pigmented coatings as well.
Closed‑loop outcomes and compliance
Combined, dosing software and sensors form closed‑loop control: manufacturing execution systems plan and deliver precise chemical volumes, and sensor feedback corrects any drift in real time. Labs at major mills report automated dispensers stabilize bath formulations and cut reworks dramatically. One article puts it plainly: precise robotic dosing “ensures uniform dosing of chemicals, thereby reducing variations in quality” (textilelearner.net). A vendor case study similarly stresses that optimized dosages have “great impact on the quality of the final product” (www.escarre.com).
The financials are tangible: plants report lower scrap rates and chemical costs, with studies mentioning cost reductions of tens of percent simply by avoiding over‑dosing. Tight chemical control also helps meet environmental rules. Indonesia’s 2022 Standar Industri Hijau for textile finishing (Permenperin No.40/2022) explicitly aims to minimize waste chemicals and water use (www.peraturan.my.id).
Bottom line for finishing lines
Precision control of concentration, temperature, and dwell time ensures each yard meets targets for repellency, softening, flame resistance, and strength without wasting chemistry. Data‑driven dosing and sensing — from dosing pumps to pH probes and β‑ray pickup detectors — remove human error, maintain recipe fidelity, and adapt to variation in real time. As documented, even a few percent error in finish dosing can cause a >15% drop in strength or >30% loss in repellency (www.mdpi.com) (www.mdpi.com). Industry case studies consistently find that implementing closed‑loop control “represents a step forward in process optimization and chemical savings” (www.escarre.com).
