① The label is placed on the inner wall of the mold by a robotic arm.

② While the preformed plastic tube is inserted into the mold, vacuum micro-holes on the mold hold the in-mold label in place until the mold is fully closed.

③ Air is blown into the heated plastic preform tube, filling the entire space inside the closed mold.

④ The heated plastic rapidly expands and presses against the inner wall of the mold, blowing into a bottle and securing the label onto the bottle.

⑤ The completed bottle is ejected from the mold. In-mold labels are divided into front labels and back labels according to their placement position — that is, trademarks attached to the front or back of the packaging. Printed labels are stacked in sheet form, with front labels and back labels placed separately in two boxes of the in-mold labeling machine.

In-mold label materials are mainly divided into two categories: paper and plastic film. In the early days of in-mold labels, paper labels coated with a hot-melt adhesive backing layer were placed in the mold to adhere to or fuse with blow-molded bottles. All in-mold label materials must have good flatness so that no malfunctions occur when fed from the blow nozzle of the injection molding machine.

① Paper Type

Ordinary synthetic paper has poor surface smoothness, relatively low strength, and small elastic deformation, making high-end color printing difficult. It is suitable for large-area applications such as buckets. Paper labels are prone to deformation when exposed to water or moisture, reducing their use value. However, they are less affected by static electricity during use, and the loss during bottle blowing and label suction is relatively small. Paper labels and plastic bottles are not the same material, which is not conducive to bottle recycling.

② Film Materials

These are specially made multi-layer co-extruded face materials with smooth surfaces that can be printed using various printing methods. During label processing, problems with registration and die cutting inaccuracy due to deformation do not occur.

Some film materials can be stretched and shrink-deformed. When applied to bottle bodies, they can deform along with the bottle shape, and after being laminated to the bottle surface, label wrinkling does not occur. Film material surfaces do not absorb ink, so labels printed with film materials have bright colors, strong three-dimensional effect, and color effects significantly superior to paper materials. They are suitable for high-end color printing and generally for various refined product applications, mostly being PE, PP, or composites of PE and PP.

After die cutting into labels, a robotic arm picks them up one by one and places them into the mold cavity. Using the temperature of the extruded plastic and the pressure of the inhaled air, the label and plastic bottle are fused into one body. Currently, there are two methods of in-mold labeling: vacuum negative pressure suction method and electrostatic suction method.

The vacuum suction method is a relatively common method. A few vacuum suction micro-holes are added to the existing mold. No dedicated equipment is required, the cost is low, the usage effect is very good, and vacuum marks are not easily noticeable. This technology is currently very mature.

The electrostatic suction method can also achieve in-mold label adsorption. Its advantage is that there is no need to modify existing blow molding equipment. However, currently no such equipment has been seen in China. The electrostatic suction method requires the in-mold labeling technology equipment and the physical properties of the label to have the following characteristics:

① A high-voltage electrostatic generation system must be added to the equipment to uniformly apply sufficient electrostatic charge to the label in a short time, and the label is applied to the inner cavity of the blow mold at zero potential through a robotic arm.

② A static elimination system must be added to the equipment to eliminate residual static electricity after each labeling, avoiding impact on the electrical control system of the in-mold labeling machine and label adhesion caused by static electricity.

③ There are requirements for the label substrate and printing ink.

① Novel and Beautiful Appearance

In-mold labels naturally integrate with the plastic bottle body, with firm embedding. The label changes along with the bottle shape, and no label edges or corners can be seen on the plastic bottle body, making the appearance look very beautiful. Phenomena such as bubbling and wrinkling do not occur, and it can resist bumps, twists, scratches, and contamination during production and transportation, allowing the label to remain intact and beautiful for a long time. In humid environments, in-mold labels do not bulge or become moldy. The feel is smooth, and the advantages are self-evident especially for daily chemical products where the label serves as the main outer packaging.

② Good Printing Performance

In-mold labels have good printing effects and can print design patterns with rich details and delicate images, with strong visual expressiveness. In-mold labels can reflect the exquisite patterns and fine text of self-adhesive labels, while also having the overall effect of direct screen printing — whereas common direct screen-printed labels have difficulty achieving fine graphics and text.

③ Safety and Environmental Protection

In-mold labels have properties such as water resistance, oil resistance, acid and alkali resistance, friction resistance, freezability, and immersibility, with good chemical stability. Precise and accurate labeling not only maintains the label's integrity and aesthetics for a longer time but is also beneficial to environmental protection, unlike heat-shrink labels which are easily damaged.

④ Cost Advantage

If the print run is large, in-mold labels cost less than self-adhesive labels, and also cost less than direct screen printing when there are many printing colors. It eliminates the cost of adding labeling equipment or labeling workers, shortens the production cycle, and improves production efficiency.

⑤ Anti-Counterfeiting Function

The in-mold labeling process and molds are relatively complex, with high manufacturing difficulty and requiring robotic arm operation. Compared to self-adhesive labels, they have stronger anti-counterfeiting properties.

With these characteristics, the in-mold labeling process can meet the needs of precise labeling for high-quality, low-weight containers. Labels are made from the same material as the container (for example, PP labels on PP containers), which is conducive to bottle recycling and beneficial to environmental protection.

Currently, in-mold labels are widely used in packaging of various plastic materials, such as HDPE, PP, PET, and PS. They are mainly applied to one-time molded trademarks of hollow blow-molded bottles:

① Household and Personal Care: Packaging for care products that frequently come into contact with water, such as shampoo, conditioner, body wash, shower gel, and personal care products; packaging for cleaning products that frequently come into contact with water and have decontamination effects, such as dish soap, laundry detergent, washing liquid, kitchen cleaner, and stain remover.

② Lubricants and Chemical Products: Trademarks and instructions for large-capacity blow-molded buckets and injection containers for lubricating oil, refined oil, gear oil, antifreeze, chemical raw materials, pesticides, etc.

③ Food and Beverage Industry: Labels and instructions for plastic buckets, bottles, and boxes that are long-term frozen or come into contact with water, such as dairy products, ice cream, condiments, salad oil, soy sauce, vinegar, coffee, juice, tea beverages, yogurt, etc.

④ Pharmaceutical Industry: Packaging for high-end pharmaceuticals.

Corresponding to the usage scenarios of in-mold labels, traditional labels mainly include 3 types: heat-shrink labels, direct screen-printed labels, and adhesive labels (mainly self-adhesive labels).

① Direct screen-printed labels print patterns and text on container packaging using screen printing. The overall effect is good and the patterns and text have texture, but the quality of direct screen printing is not ideal — it is difficult to reflect exquisite patterns and fine text, and if there are many colors, the price of direct screen printing is relatively expensive. When label colors exceed 4, the cost of direct screen printing is the most expensive among the 3 traditional label printing methods. From the perspective of label material cost, in-mold labels do not require a backing paper, so there is some room for material cost reduction.

② Using heat-shrink film (mainly PVC film) as packaging labels costs much less than self-adhesive labels and direct screen-printed labels, but heat-shrink labels are easily damaged, the overall image is not good, and they are not conducive to environmental protection.

③ Adhesive labels (mainly self-adhesive labels) are exquisitely printed, but the cost is relatively more expensive than heat-shrink film labels.