Retort Process - Selection of Inks for Liquid Milk and Milk Beverage Soft Packaging

### Milk and Beverage Film Ink Requirements

The ink requirements for milk and beverage packaging films vary based on the sterilization process, filling method, and storage conditions. Below are the key considerations for different types of milk and beverage films:

#### 1. **Ink for Basil Milk Film**

- **Processing Method**: Pasteurized milk, cooled to 4°C, and non-aseptically filled.

- **Storage Conditions**: Requires refrigeration (2–10°C) with a shelf life of less than 7 days.

- **Ink Requirements**:

- Good hygiene and cold water resistance.

- Glossy, smooth ink layer with wear resistance.

- Alcohol-soluble polyamide or polyester surface inks are recommended.

- Must pass a cold water resistance test: printed film soaked in water for 12 hours to check adhesion and rubbing resistance.

#### 2. **Ink for UHT Sterilized Milk Film**

- **Processing Method**: UHT sterilized at 125°C for 1–3 seconds, aseptically filled, and stored at room temperature.

- **Packaging**: Paper-aluminum-plastic composite or black-and-white co-extruded LDPE film.

- **Ink Requirements**:

- Resistance to hydrogen peroxide oxidation (used for pre-sterilization).

- Glossy, smooth ink layer with wear resistance.

- Low friction coefficient and non-stick properties for high-speed aseptic filling.

- Test for hydrogen peroxide resistance by exposing printed film to 35% hydrogen peroxide at 50°C for 30–60 seconds.

#### 3. **Ink for Pasteurized Non-Aseptic Hot-Fill Milk (Beverage) Film**

- **Processing Method**: Pasteurized and hot-filled, naturally cooled without refrigeration.

- **Storage Conditions**: Heat-sealed bags stored at ambient temperature.

- **Ink Requirements**:

- Heat-blocking resistance to withstand 70–90°C for extended periods during cooling.

- Abrasion resistance and a glossy, smooth ink layer.

- Forced cooling may require cold-water-resistant inks.

- Abrasion resistance can be tested manually by rubbing with boiling water or instrumentally.

#### 4. **Ink for Steamed Soymilk Films**

- **Processing Method**: Soymilk steamed at 121–125°C for 30 minutes, followed by intermittent retort sterilization.

- **Packaging**: Heat-resistant co-extruded PE film.

- **Ink Requirements**:

- High scratch and retort resistance due to sharp edges of stacked bags during sterilization.

- Two-component reactive, high-temperature-resistant polyurethane surface printing ink is recommended.

- Test by steaming printed film in a retort sterilizer for 30 minutes to check for discoloration or sticking.

### **General Considerations for Milk Film Ink**

- **Hygiene and Safety**: Low residual solvent content, anti-migration properties, and minimal heavy metal content in pigments.

- **Performance Testing**: Manufacturers often simulate customer usage conditions to ensure ink performance consistency.

- **Market Trends**: Milk films are a growing category in flexible packaging, offering cost-effective alternatives to high-cost composite materials.

By tailoring ink properties to specific processing and packaging needs, manufacturers can ensure high-quality, hygienic, and cost-effective solutions for liquid dairy and beverage products.