Printing Paste Composition Testing

Printing paste composition inspection mainly conducts scientific testing and analysis on the colourants, binders, thickener types and rheological properties, auxiliaries, moisture and volatile organic compounds, and limits of heavy metals and hazardous substances, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Composition and content of the colourants (dyes/pigments): The detection of the core colouring components of the printing paste, including the chemical categories of the dyes (such as the reactive dyes, disperse dyes and pigment dyes), the inorganic/organic types of the pigments, the specific colour names and contents. Through the qualitative and quantitative analysis, its colour fastness, brilliance, environmental friendliness and the compatibility with the fibres can be evaluated.

Composition analysis of the binders (film-forming agents): Detects the chemical compositions of the binders, such as the acrylate copolymers, polyurethane and styrene-butadiene latex. The monomer residues, molecular weight distribution and glass transition temperature (Tg) are analysed. These parameters directly affect the softness, elasticity, washing resistance and rubbing fastness of the printing film.

Thickener types and rheological properties: Determines the types of the thickeners, such as the synthetic thickeners (polyacrylic acid type), natural thickeners (sodium alginate) or mineral thickeners (bentonite). Their rheological properties (pseudoplasticity and thixotropy) are detected, to evaluate the printing suitability, outline definition and permeability of the paste.

Qualitative and quantitative analysis of the auxiliaries (crosslinking agents, softeners, etc.): Analyses the various functional auxiliaries added in the printing paste, such as the crosslinking agents (such as the melamine formaldehyde resins), softeners (organosilicon type), defoamers, wetting agents and fixing agents. The effective component contents and the possible hazardous residues (such as the formaldehyde and APEO) are detected.

Moisture and volatile organic compounds (VOCs) content: Determines the moisture content in the paste, as well as the types and total amounts of the volatile organic compounds such as the toluene, xylene and ethyl acetate. This testing is related to the production safety, compliance with the environmental protection regulations (such as GB 38507-2020) and storage stability.

Limits of heavy metals and hazardous substances: In accordance with the ecological textile standards (such as the OEKO-TEX® STANDARD 100 and GB/T 18885), the contents of the heavy metals such as the lead, cadmium, mercury, arsenic and hexavalent chromium, as well as the hazardous chemical substances such as the banned azo dyes, phthalates and short-chain chlorinated paraffins, are detected, ensuring the product safety.

Testing Scope

Pigment printing pastes for the textiles: Mainly for the pastes with the pigments as the colourants and the binders as the film-forming main bodies. The testing emphasis is on the pigment dispersion stability, binder film-forming performance, formaldehyde content and the various colour fastnesses, applicable to the printing of the fabrics such as the cotton and chemical fibres.

Reactive/disperse dye printing pastes: Applicable to the printing pastes of the cellulose fibres such as the cotton and flax (reactive dyes) and the synthetic fibres such as the polyester (disperse dyes). The testing scope includes the dye purity, fixation rate, hydrolysed dye content, urea content, as well as the soaping and rubbing fastness after printing.

Water-based printing pastes: The environmentally friendly pastes with the water as the main dispersion medium. In addition to the routine composition testing, the pH value, microbial content, freeze-thaw stability and whether the restricted substances such as the alkylphenol polyoxyethylene ethers (APEO) are contained need to be emphatically focused on.

Plastisol and foaming pastes: The plastisol usually refers to the pigment pastes with the high solid content and high hiding power; the foaming pastes contain the foaming agents. The testing needs to cover the film thickness, elastic recovery rate, foaming ratio, cell uniformity and aging resistance.

Digital printing pre-treatment pastes (pre-treatment liquids): Used for the sizing treatment before the digital printing of the fabric. The testing items include the effective components of the paste (such as the alginates and synthetic thickeners), hygroscopicity, anti-bleeding performance and the influence on the ink colours.

Special functional printing pastes: Including the fluorescent pastes, reflective pastes, fragrance microcapsule pastes and phase-change temperature-regulating pastes. The testing scope extends to the qualitative and quantitative analysis of the special functional components, function persistence (such as the washing resistance) and safety evaluation.

Testing Methods

High-performance liquid chromatography method (HPLC): Mainly used to separate and quantitatively analyse the organic components in the paste, such as the specific dye monomers, auxiliaries (such as the softeners and crosslinking agents) and preservatives. This method has the high separation efficiency and can carry out the precise qualitative and quantitative analysis of the complex mixtures.

Gas chromatography-mass spectrometry method (GC-MS): Applicable to the detection of the volatile and semi-volatile organic compounds in the paste, such as the solvent residues, monomer residues, plasticizers (phthalates) and some decomposition products of the crosslinking agents. It is the key means for the VOCs and hazardous substance screening.

Fourier transform infrared spectroscopy method (FTIR): Through the analysis of the characteristic absorption of the infrared light by the substances, the rapid qualitative analysis of the polymers (such as the binders and thickeners) in the paste is carried out, identifying their main functional groups and chemical structure categories.

Inductively coupled plasma mass spectrometry method (ICP-MS): Used to precisely determine the trace and ultra-trace heavy metal element contents in the paste (such as the lead, cadmium, mercury and arsenic). This method has the extremely high sensitivity and low detection limits, and can meet the requirements of the strictest ecological standards.

Thermogravimetric-differential scanning calorimetry method (TG-DSC): Through the programmed temperature control, the changes of the mass and heat enthalpy of the paste with the temperature are measured. It can be used to analyse the moisture, volatile matter, polymer decomposition temperature and glass transition temperature in the paste, evaluating its thermal stability.

Laser particle size analysis and viscosity determination: A laser particle size analyser is used to analyse the particle size distribution of the pigments or fillers, which affects the hiding power and colour. A rotational viscometer is used to determine the viscosity of the paste at the different shear rates, to comprehensively characterize its rheological properties and guide the printing process.

Testing Standards

Domestic Standards:

1. GB/T 3920-2024, Textiles — Tests for colour fastness — Colour fastness to rubbing

2. GB 18401-2010, National general safety technical code for textile products

3. GB/T 3921-2008, Textiles — Tests for colour fastness — Colour fastness to soaping

4. GB/T 3922-2013, Textiles — Tests for colour fastness — Colour fastness to perspiration

5. GB/T 2910, Textiles — Quantitative chemical analysis

6. GB/T 7573-2009, Textiles — Determination of pH of the aqueous extract

7. GB 38507-2020, Limits of volatile organic compounds (VOCs) content in printing inks

8. GB/T 18885-2020, Technical specification for ecological textiles

International Standards:

1. ISO 105, Textiles — Tests for colour fastness

2. ISO 13934-1, Textiles — Tensile properties of fabrics — Part 1: Determination of maximum force and elongation at maximum force using the strip method

3. OEKO-TEX® STANDARD 100, General and special conditions for the authorisation to use the OEKO-TEX® STANDARD 100 mark

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

High-performance liquid chromatograph (HPLC): The core components include a high-pressure infusion pump, chromatographic column and detectors (such as the UV/visible light detector and diode array detector). It is used for the high-precision separation and quantification of the organic substances in the paste, and is the essential instrument for the composition analysis.

Gas chromatography-mass spectrometer (GC-MS): Composed of a gas chromatography unit and a mass spectrometry detector. The chromatography unit realizes the component separation, and the mass spectrometry provides the molecular structure information. It is suitable for the qualitative and quantitative analysis of the trace organic pollutants in the complex systems.

Fourier transform infrared spectrometer (FTIR): Composed of a light source, interferometer, detector and computer system. Equipped with the ATR (attenuated total reflectance) accessory, it can directly carry out the non-destructive testing of the paste and paste films, rapidly obtaining the "fingerprint" spectra of the chemical compositions.

Inductively coupled plasma mass spectrometer (ICP-MS): Composed of a sample introduction system, ICP ion source, mass analyser and detector. It can atomize and ionize the sample, realizing the rapid simultaneous analysis of the multiple elements, and is the "gold standard" equipment for the ultra-trace detection of the heavy metals.

Thermal analysis system (simultaneous thermal analyser): Usually integrates the functions of the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) into one instrument. The mass change and heat flow change information of the sample can be synchronously obtained under the same experimental conditions, used to study the thermal behaviour of the paste.

Rheometer and laser particle size analyser: The rheometer (such as the rotational rheometer) characterizes the rheological parameters such as the viscosity and elastic modulus of the paste by measuring the torque and angular velocity. The laser particle size analyser utilizes the light scattering principle to precisely measure the particle size distribution of the particles in the paste.