CMS for Vat and Discharge Printing: What Should You Test Before Production Approval?

Carboxymethyl starch (CMS) can be evaluated as a thickener in selected vat and discharge printing systems, but production approval should never be based on stock-paste viscosity alone. These routes can expose the thickener to strong alkali, reducing agents, electrolytes, heat, steaming and intensive washing. A CMS grade must therefore maintain useful paste rheology before printing, pass the screen consistently, resist unacceptable viscosity collapse during the realistic holding period, allow the vat or discharge chemistry to develop correctly, and wash away without leaving excessive residue. This guide explains how textile mills should separate vat and discharge trials and what to test before bulk production approval.

Why Vat and Discharge Printing Need a Special CMS Qualification

Vat and discharge printing are chemically more demanding than a simple neutral thickener-in-water test.

Depending on the route, the printing paste may contain:

• Strong alkali
• Reducing agents
• Electrolytes
• Agents hydratants
• Oxidation or post-treatment chemicals
• Dyes or pigments for colored discharge

These ingredients can change CMS viscosity, hydration state and rheology.

At the same time, the thickener must not prevent the color chemistry from working.

Research on two-phase vat dye printing has shown that thickeners undergo several transformations during spreading, drying and coagulation, so both wet-paste rheology and dried-thickener behavior matter. See research on thickeners in vat dye textile printing.

FSX Chemical therefore places vat and discharge applications in a separate specialty route where alkali/reducing-agent compatibility, paste holding, pattern development and post-treatment must be confirmed before production use.

Review the FSX Chemical CMS product range for the current H5 specialty route.

Vat Printing and Discharge Printing Are Not the Same Test

Impression sur cuve

Vat dyes are normally applied in a form that must be converted into a soluble reduced state under alkaline conditions and then returned to the insoluble colored form through oxidation.

A simplified process may include:

Printing → Drying → Reduction / Alkaline Development → Steaming → Oxidation → Rinsing / Soaping → Drying

The exact sequence depends on whether the mill uses a one-phase, two-phase or other vat-printing route.

Impression par décharge

Discharge printing starts with a dyed ground. A discharge paste is printed only where the mill wants to remove or modify the ground color.

A simplified process may be:

Ground-Dyed Fabric → Discharge Printing → Drying → Steaming / Heat Development → Washing → Finished White or Colored Discharge

The chemical package depends on the ground dye, fabric and whether the target is white discharge or colored discharge.

Therefore:

Passing a vat-printing trial does not automatically approve the same CMS grade for discharge printing.

What Role Does CMS Play in These Systems?

CMS is a modified starch thickener. In selected vat or discharge printing systems it may be used to:

• Build paste viscosity
• Control paste transfer through the screen
• Limit uncontrolled lateral spreading
• Hold reactive chemicals in the printed pattern
• Support uniform application before steaming or development

The required grade should be process-specific.

A CMS designed for disperse printing should not automatically be moved into vat or discharge printing because the chemical environment can be completely different.

FSX Chemical currently positions its H5 flake starch route for evaluation in vat dye, discharge and selected burn-out/devoré applications, with the final result confirmed under the customer’s complete formula and fabric conditions.

The Main Chemical Stresses: Alkali, Reducing Agents and Electrolytes

The thickener may experience several stresses at the same time.

Alkali

Strong alkaline conditions can change CMS chain ionization, swelling and viscosity.

Reducing Agents

Vat and discharge systems may use different reducing agents according to dye chemistry and process design.

The thickener must remain sufficiently stable for the intended holding period while still allowing the reducing chemistry to function.

Electrolytes

Alkali salts, reducing-agent salts and other auxiliaries increase ionic strength.

Because CMS is an anionic modified starch, this can change:

• Viscosité apparente
• Paste body
• Flow under shear
• Stabilité de la prise

Do not evaluate these variables independently only. After one-factor screening, test the full chemical package.

What to Test in a Vat Printing Paste

For vat printing, the CMS qualification should include:

• Stock-paste preparation
• Viscosity after the full vat-printing formula is prepared
• Alkali tolerance
• Reducing-agent compatibility where present in the selected route
• Stabilité de la prise
• Screen transfer
• Pattern sharpness
• Drying behavior
• Steaming/development
• Oxidation
• Soaping/wash-off
• Final color strength and shade

In two-phase vat printing, the printed thickener layer can affect the later penetration and action of reducing and alkaline development chemicals.

This is one reason the dried CMS film should be evaluated together with wet-paste rheology rather than judged from viscosity alone.

What to Test in a Discharge Printing Paste

For discharge printing, the thickener must hold the discharge chemicals precisely where the effect is required.

Evaluate:

• Compatibility with the selected discharge agent
• Compatibility with alkali or acid components in that discharge system
• Paste stability during the realistic color-kitchen holding time
• Screen running
• Discharge edge sharpness
• Degree of ground-color removal
• Colored-discharge shade where relevant
• Post-steam washing
• Residual odor or chemical residue where relevant
• Fabric strength and hand

Historic discharge-printing processes have used modified starches and cellulose-based thickeners in reducing/alkaline pastes, which supports the general principle that the thickener must tolerate the chemical package. See an example of a discharge print paste using modified starch/cellulose thickening systems.

However, historic recipe levels should not be copied as modern production specifications. The actual discharge chemistry must be supplied by the mill or dye/auxiliary supplier.

Why Stock Viscosity Is Not Enough

A CMS TDS may list viscosity at a defined concentration and temperature.

That value is useful for incoming QC.

But the vat or discharge paste can contain much higher ionic and chemical loading than the standard water test.

The meaningful sequence is:

CMS Stock Paste → Add Full Chemical Package → Measure Again → Hold → Measure Again → Print

Record:

• CMS concentration
• Qualité de l'eau
• Température
• Viscometer
• Spindle/rotor
• RPM
• Temps de lecture
• Durée de maintien

Same stock viscosity does not mean the same chemical resistance.

Paste Holding Stability Before Printing

Vat and discharge pastes can change while waiting before printing.

Possible changes include:

• Viscosity loss
• Viscosity increase
• Gel formation
• Phase separation
• Foaming
• Loss of discharge/reducing activity

A useful holding test uses realistic time points:

• Immediately after formula preparation
• After the normal waiting period
• Near the end of the planned production window

At each point, record both paste properties and printing effect.

A paste can retain viscosity while the discharge chemistry loses activity, so viscosity stability alone is not enough.

Screen Running and Pattern Definition

CMS must provide enough structure at rest while still flowing under printing shear.

Evaluate:

• Flat vs. rotary screen behavior
• Passage à l'écran
• Squeegee pressure
• Mousse
• Screen drying
• Pattern filling
• Edge definition
• Pénétration

If the paste is too weak, discharge chemicals or vat dye can spread beyond the intended pattern.

If it is too resistant to flow, screen transfer may become incomplete.

Therefore:

Higher viscosity is not automatically better pattern control.

Drying, Steaming and Process Temperature

After printing, the paste usually enters a thermal stage.

The exact process depends on the printing route.

Temperature can change:

• Moisture retention
• Chemical mobility
• Reducing-agent activity
• Alkali transport
• Thickener-film structure

Do not publish or copy one universal steaming temperature or time for all vat/discharge systems.

Use the actual dye and auxiliary supplier process, then check whether CMS remains compatible with that thermal window.

Vat Dye Reduction, Development and Oxidation

The vat route depends on controlled reduction and later oxidation.

CMS should not interfere with the transfer of reducing/alkaline chemicals or create a dried film that prevents effective development.

After printing and development, evaluate:

• Color strength
• Shade
• Planéité
• Définition des traits fins
• Pénétration
• Oxidation completeness
• Soaping cleanliness

Research on vat printing shows that modified starch, alginate and other thickeners can behave differently through drying and chemical development, so the dried thickener morphology is part of the process, not just a passive carrier.

Discharge Effect: What Should Be Measured?

A discharge trial should quantify more than “it looks white.”

Useful observations include:

• Ground-color removal
• Residual ground shade
• Netteté des contours
• Haloing
• Fabric penetration
• Colored-discharge shade where used
• Uniformity across large areas

Compare the same ground-dyed fabric and the same discharge chemistry when evaluating two CMS candidates.

If the CMS grade changes and the discharge depth changes, investigate both:

• Chemical compatibility
• Paste deposit / penetration

A stronger discharge effect is not useful if the pattern edge becomes unacceptable or the fabric is damaged.

Wash-Off, Soaping and Residue Removal

Vat and discharge printing normally require substantial post-treatment.

The thickener should wash away sufficiently after the chemical process.

Evaluate:

• Residual paste
• Surface harshness
• Background staining
• Color redeposition
• Résistance au frottement
• Fabric hand

A CMS grade that gives excellent screen behavior but requires excessive washing can increase:

• Water use
• Energy
• Processing time
• Total cost

Final approval should therefore be made after the full washing sequence.

Fabric and Ground-Dye Variables

Vat printing is used mainly on suitable cellulosic materials, while discharge printing can involve several fabric and ground-color systems.

Important variables include:

• Cotton vs. viscose
• Woven vs. knitted structure
• Fabric weight
• Absorbency
• Ground-dye class
• Ground-dye depth
• Finishing history

Not every ground dye is equally dischargeable.

If a discharge test is weak, do not blame CMS before confirming that the ground dye and discharge agent are chemically compatible.

Water Quality and Formula Variation

CMS behavior can change with water hardness, conductivity and dissolved multivalent ions.

Vat/discharge formulas already contain significant ionic loading, so plant water can become an additional variable.

If laboratory results do not match production, compare:

• Reference water
• Plant water
• Hardness
• Conductivity
• pH

Also confirm that production follows the same chemical addition order as the laboratory.

How to Run a CMS Chemical-Resistance Test

Step 1: Prepare a Standard CMS Stock Paste

Use controlled concentration, water, mixing and hydration.

Step 2: Record Baseline Viscosity

Use one defined method.

Step 3: Add the Production Chemical Package

Use the actual alkali, reducing agent and other key auxiliaries at the real trial concentration.

Step 4: Measure Immediately

Record viscosity, pH, appearance and any gel or separation.

Step 5: Hold for Realistic Time Points

Repeat viscosity and appearance checks.

Step 6: Compare Chemical Activity

For discharge, print a small controlled test. For vat, proceed through the actual development route.

Step 7: Compare Against the Current Thickener

A reference product helps distinguish “acceptable process behavior” from a theoretical viscosity target.

How to Run a Controlled Printing Trial

Use one fabric lot and keep the dye/chemical system constant.

Print a diagnostic pattern containing:

• Rides fines
• Petit texte
• Solid blocks
• Half-tone or gradient areas where relevant
• Large discharge areas

Then use identical:

• Séchage
• Steaming/development
• Oxidation where relevant
• Lavage
• Soaping

Evaluate:

• Pattern definition
• Vat color yield or discharge depth
• Shade
• Pénétration
• Fastness
• Residue
• Hand

Production Approval Checklist

Before bulk approval, verify:

• Large-batch CMS hydration
• Full formula viscosity
• Holding-time stability
• Screen running over realistic production length
• Left-center-right pattern consistency
• Thermal process repeatability
• Vat development or discharge depth
• Post-treatment cleanliness
• Fabric strength and hand
• Repeat-batch CMS consistency

Retain the final approved:

• CMS batch
• Printing formula version
• Fabric lot
• Ground-dye information for discharge
• Machine settings
• Steaming/development record
• Finished fabric reference

This creates a practical production standard rather than relying on memory.

Troubleshooting Table

Problème constaté	First Variables to Check	Do Not Assume
Viscosity collapses after alkali/reducer addition	CMS grade, chemical concentration, ionic load, addition order	Stock viscosity predicts chemical resistance
Paste viscosity is stable but discharge is weak	Discharge agent activity, ground dye, steaming, penetration	CMS is automatically the cause
Discharge is strong but edges spread	Paste rheology, deposit, screen settings	More discharge agent is the solution
Vat shade is weak after development	Reduction, alkali, steaming, thickener-film effect	More dye alone will solve it
Paste works fresh but fails after waiting	Holding stability, reducer life, pH, temperature	Viscosity is the only aging variable
Residue remains after washing	CMS dosage, post-treatment, film formation, process temperature	Good printing automatically means good wash-off
Les résultats des tests en laboratoire sont satisfaisants, mais la production échoue	Batch scale, water, machine shear, steam uniformity, chemical addition	The laboratory sample proves production approval

Coût total d'utilisation

A vat/discharge thickener should not be selected from price per kilogram alone.

Compare:

• CMS dosage
• Paste preparation time
• Chemical stability
• Screen interruptions
• Discharge/vat effect
• Steam/development efficiency
• Washing and soaping load
• Rework
• Rejected fabric

A useful framework is:

Total Cost in Use = CMS Cost + Chemical/Preparation Cost + Machine Efficiency + Steaming/Post-Treatment + Rework + Quality Loss

A grade with higher powder cost may still be commercially better if it uses a lower dosage and maintains stability through the full production window.

What Information Should You Send to a CMS Supplier?

For vat or discharge CMS matching, send:

• Printing route: vat or discharge
• Fabric composition and construction
• Ground-dye class and shade depth for discharge
• Current thickener sample/TDS
• Current thickener dosage
• Target viscosity and full test method
• Alkali type and dosage
• Reducing/discharge agent type and dosage
• Complete or simplified formula
• Paste holding time
• Flat or rotary screen
• Drying and steaming/development conditions
• Oxidation/soaping/washing route
• Current stability, pattern, discharge, color or residue problem

FSX Chemical can use this information through Échantillons et correspondances to determine whether the H5 flake-starch route or another process-matched thickener should enter a controlled trial.

How Should CMS Be Approved for Vat and Discharge Printing?

A practical qualification chain is:

CMS Stock Paste → Full Chemical Formula → Holding Stability → Screen Printing → Drying → Vat/Discharge Development → Washing/Soaping → Finished Fabric → Production Repeatability

The key principles are:

1. Vat and discharge printing require separate qualification.
2. Stock-paste viscosity does not prove alkali or reducing-agent tolerance.
3. Paste holding stability and chemical activity must both be monitored.
4. Screen performance must be judged together with pattern development.
5. Final approval should be made after steaming/development and full washing.
6. The complete formula, fabric and process—not the CMS name alone—determine suitability.

Foire aux questions

1. Can CMS be used for vat dye printing?

Selected CMS grades can be evaluated for vat printing when they maintain useful rheology under the actual alkaline/reducing process and do not interfere with development, oxidation and wash-off.

2. Can CMS be used for discharge printing?

Selected CMS or modified-starch grades can be evaluated for discharge printing, but compatibility with the actual discharge agent, ground dye, fabric and steaming process must be confirmed.

3. Is the same CMS grade suitable for both vat and discharge printing?

Not automatically. The chemical systems and quality targets differ, so each route should be approved separately.

4. What is the most important CMS test for vat printing?

There is no single test. Evaluate full-formula viscosity, holding stability, screen running, vat development, oxidation, wash-off and final color.

5. What is the most important CMS test for discharge printing?

Evaluate chemical compatibility, holding stability, screen definition, degree of discharge, edge sharpness and final washing result.

6. Does high CMS viscosity mean good alkali resistance?

No. Stock viscosity and chemical resistance are different properties. Test the full alkaline formula.

7. Can a CMS paste remain viscous but still fail in discharge printing?

Yes. The discharge agent may lose activity or fail to penetrate/develop correctly even if viscosity remains stable.

8. Why does discharge paste lose viscosity after preparation?

Possible causes include electrolyte loading, pH, reducing-agent chemistry, addition order, temperature or unsuitable CMS grade.

9. Why is the discharge effect good but the pattern edge poor?

The chemistry may be active while paste rheology or screen-transfer conditions allow excessive spreading.

10. Should production approval be based on a laboratory viscosity target?

No. The CMS should be approved through the complete vat/discharge process and finished-fabric result.

11. Is H5 automatically suitable for every vat/discharge mill?

No. H5 is an FSX starting route for evaluation, but final suitability depends on the customer’s fabric, chemicals, machine and post-treatment.

12. What should I send FSX Chemical for vat/discharge matching?

Send the current thickener, formula, fabric, ground dye where relevant, alkali/reducing agent, viscosity method, screen route, steaming/development and washing conditions.

Evaluate CMS for Vat and Discharge Printing with FSX Chemical

If your current vat or discharge thickener loses viscosity after chemical addition, runs poorly through the screen, gives weak discharge, reduces vat color development or leaves difficult residue, FSX Chemical can help structure a controlled comparison.

For a useful technical review, send:

• Your current thickener sample, TDS or COA
• Vat or discharge printing route
• Fabric composition and construction
• Ground dye and shade depth for discharge
• Current thickener dosage
• Viscosity and complete test method
• Alkali and reducing/discharge agents
• Complete or simplified printing formula
• Paste holding time
• Flat/rotary screen information
• Drying and steaming/development conditions
• Oxidation and washing/soaping route
• Current viscosity, pattern, discharge, color or residue target

Commencez par Échantillons et correspondances for a controlled comparison.

Critique FSX Chemical Carboxymethyl Starch (CMS) for the current H5 specialty-printing route.

You can also Demander un devis directement auprès du fabricant after the suitable process route is confirmed or Contacter FSX Chemical for technical discussion📧 E-mail: Service@fsxchemical.com

For vat and discharge printing, production approval should answer two separate questions: does the CMS keep the paste printable under aggressive chemistry, and does the complete chemical process still deliver the required color or discharge effect after steaming and washing?