Self-standing spout bags, as a packaging form that combines portability and display, are widely used in the fields of food, daily chemicals, medicine, etc. Its printing process directly affects the appearance and texture of the product, the efficiency of information transmission and the shaping of the brand image. The following is a systematic analysis of the printing process of self-standing nozzle bags from the dimensions of pre-printing treatment, process types, color management, surface finishing and quality control. ​

I. Pre-printing treatment: Technical preparation of substrate and design

(1) Optimization of substrate surface energy

Self-standing nozzle bags mostly use multi-layer composite films (such as PET/PE, PA/AL/PE). Before printing, corona treatment is required to enhance the surface energy of the base material.

Processing standard: The surface tension of polyolefin type (PE/PP) should reach 38-42mN/m, and that of polyester type (PET/PA) should reach 40-44mN/m to ensure the adhesion of the ink (ISO 2409 standard for the grid method ≥4B grade). ​

Online detection: Real-time detection is carried out through a Dyne pen. If the surface energy is insufficient, the halo needs to be repeated to avoid defects such as ink delamination and mottling. ​

(II) Key Points of Prepress design technology

Structural adaptation design

Considering the visual distortion after the bag is formed, a 2-3mm bleed should be reserved for printing graphics and text to avoid content loss due to bag-making and cutting. ​

The suction nozzle should be placed away from the main visual area and is usually designed at the top 1/3 of the bag to ensure that consumers can still fully view the brand logo after opening it. ​

Color separation and mesh filling technology

The CMYK four-color plus spot color (Pantone) mixing mode is adopted. Key colors (such as brand standard colors) are printed with spot colors, and the color difference △E is ≤1.5 (under D65 light source). ​

The number of lines added should be adjusted according to the roughness of the base material: for smooth PET film, use 175-200lpi; for matte film or woven fabric base, use 133-150lpi to avoid dot expansion causing tonal distortion. ​

Ii. Types and Characteristics of Mainstream Printing Processes

(1) Gravure Printing

Technological advantage

The printing plate has a durability of over a million times, making it suitable for mass production. The ink layer thickness can reach 8-15μm, with high color saturation. It is often used in high-end food packaging (such as coffee and milk powder). ​

Solvent-based inks have a fast drying speed (dried by hot air at 50-80℃), are suitable for composite film printing, and the peel strength after lamination is ≥3N/15mm (GB/T 7707-2008 standard). ​

Limitations

The plate-making cost is high (the cost of a single set of plates is 5,000-20,000 yuan), and organic solvents such as toluene are required. The VOCs emissions need to be controlled below 80mg/m³ (environmental protection standard HJ 371-2018). ​

(2) Flexo Printing

Technological innovation

It adopts digital plate-making technology (CDI laser engraving), with a dot restoration accuracy of 95%, and can print gradient mesh patterns and fine text (font ≥6pt). ​

The proportion of water-based ink exceeds 90%, and the VOCs content is less than 100g/ L. It meets the requirements of the national standard GB 31604.30-2016 for food contact materials and is suitable for children's food packaging. ​

Process parameters

The printing pressure is controlled at 2-5kg/cm², the cell volume of the screen roller is 80-120cm³/m², and the drying temperature is 60-90℃ to ensure the ink is completely cured. ​

Iii. Color Management and Surface Finishing

(1) Color consistency control

Standardized process

Establish the enterprise standard color card (QCS), and use a spectrodensitometer (such as X-Rite 530) to detect the ΔE*ab value of printed matter. The color difference between batches should be ≤1.0, and within the same batch, it should be ≤0.5. ​

Update the ICC color characteristic files regularly to ensure the matching of color data between the design end (Adobe Illustrator) and the printing end (ERP system). ​

(2) Surface finishing process

Lamination process

Light film: Enhances glossiness to over 90GU, suitable for products that require high brightness display (such as candy packaging). ​

Matte film: The glossiness is controlled at 30-50GU, creating a high-end texture, and is often used in the packaging of skin care products. ​

Special process application

Gold/silver hot stamping: Holographic positioning hot stamping technology is adopted, with registration accuracy ≤0.1mm, metal layer thickness 0.02-0.05μm, and adhesion passes the 3M tape peeling test (no metal layer peeling off). ​

Embossing: Create a relief effect around the suction nozzle or at the brand LOGO, with a depth of 0.05-0.1mm, to enhance tactile recognition. ​

Iv. Quality Control and Inspection Standards

(I) Environmental Protection and Safety Inspection

Solvent residue: Detected by gas chromatography, the residue of benzene solvents was ≤0.01mg/m², and the total VOCs was ≤5mg/m² (GB/T 10004-2023 standard). ​

Migration test: Under simulated food contact conditions (4% acetic acid, n-hexane), the migration amount of heavy metals should be ≤1mg/kg, and no fluorescent substances should be detected (GB 9683-1988). ​

V. Trends in Technological Development

(1) Popularization of green printing technology

The substitution rate of water-based ink has reached 65% (data from the China Packaging Federation in 2023), and in the future, it will develop towards low odor and high solid content (≥50%), with a 30% reduction in drying energy consumption. ​

The application of solvent-free lamination process has expanded, eliminating the solvent evaporation stage after printing, reducing the comprehensive energy consumption by 40%, and the lamination strength is ≥5N/15mm. ​

The printing process of self-standing nozzle bags is a technology-intensive link, which requires a precise balance among color reproduction, adhesion and environmental friendliness.