In-mold Label Printing Process

Polishing of in-mold labels

Through polishing, the surface of the label is effectively protected, and surface gloss, stiffness, slip resistance, and friction resistance are improved. However, during the drying process of the varnish, the internal stress changes, and the volume of the varnish decreases; the shrinkage of the varnish changes, so that the back tension of the varnish-coated label is inconsistent, and bending is likely to occur. In order to reduce labeling failures, when vacuum-adsorbing in-mold labels are used, an antistatic agent should be added to the coating oil to adjust the smoothness of the varnish. However, if electrostatic adsorption is used, antistatic agents should not be added.

In-mold labels for hot stamping

The in-mold label shall be gilded after printing, and UV varnish shall be used to avoid the appearance of waste products. The factors that affect bronzing are mainly bronzing temperature, pressure and speed. Based on the characteristics of the in-mold label material and the adaptability of the aluminum foil, the bronzing temperature and pressure are determined according to the size of the bronzing plate and the bronzing speed.
There are three types of hot stamping methods for in-mold labels: flat-press flat hot stamping, round-press hot stamping, round-press hot stamping.

1. Flat Pressing Hot Stamping: Hot stamping pressure, good text line effect, not suitable for large areas in the field; due to the high temperature of bronzing, easily lead to thermal deformation of the film material, suitable for small area pattern bronzing.
2. Round press hot stamping: The hot stamping press is in line contact with the printing material. The material is heated to a small area and is suitable for a large area. The material is deformed after hot stamping, and the fine pattern is clear. It is the ideal way for the label stamping process in the mold.
3. Round press cold bronzing: It is a new process, suitable for all kinds of patterns, bronzing effect is slightly inferior to hot stamping. Due to the need to install a dedicated device, the application is not yet universal, and cold foil is currently used primarily on flexo. To obtain better visual effects, it is recommended to use the process of printing after the first cold stamping to cover the cold-edged edge burrs with a thicker ink layer.

In-mold label die cutting

The die cutting of in-mold labels is divided into two types: flat pressing and round pressing.
1. Web circular die cutting: usually die-cut in-line, that is, printing and die-cutting are completed at once, or after die-cutting can be completed on a round die-cutting die-cutting machine before printing.
2. Web flat die-cutting: Usually done on a dedicated in-mold label die-cutting machine and automatically discharged.
3. Sheet-fed circular die-cutting: It is completed on special equipment. The equipment is divided into two types: automatic feeding and manual feeding.
4. Sheet-fed flat die-cutting: the same as the traditional die-cutting process, several pieces of material are die-cut together, and manually discharged.

The die-cutting of in-mold labels is divided into a web material die-cutting, an offline die-cutting of a web material, and an offline die-cutting of a single-sheet material according to the material profile. Since die-cutting is the last processing step in the in-mold label, the electrostatic removal in this process is very important. If the removal is not ideal, the stacking will be uneven, resulting in inaccurate labeling and double-sheeting problems.

1. Offline die-cutting of in-mold labels can use CNC automatic die-cutting machines and semi-automatic die-cutting machines

(1) Attention should be paid when using CNC automatic punching machine
A. For the semi-finished products with different needle positions, the starting and ending positions of the labels and the die cutting distance should be promptly corrected.
B. The number of semi-finished products can not be too much, and the same semi-finished product can not produce too much relative slip when die-cutting, so as to avoid the size, asymmetry of the finished product.
C. The bottom protective rubber should use elastic and flexible materials to protect the die cutter.

(2) Pay attention when using semi-automatic die cutting machine

A. The pressure of the whole page remains the same.
B. Constantly determine if the positioning block is slipping.
C. Avoid punching the entire stack of labels when punching.

2. In-mold label machine die cutting

In-mold label manufacturers are prone to disorderly marking when they are used in online die-cutting with flexographic printing presses. This is caused by static electricity and poor label transfer. Attention should be paid to checking inverted labels and back labels when finished products are collected and disposed.

Removal of static electricity from in-mold labels

The static electricity of the in-mold label is a natural phenomenon that can be artificially or artificially eliminated. Because of its good insulation, the static electricity generated by friction during the printing process is difficult to eliminate by self-conduction. It is easy to generate static electricity, which makes the robot prone to double-sheet phenomenon when labeling. The reason for this is static electricity, so in-mold labels must completely eliminate static electricity before they are applied.

1. The main influence of static electricity on in-mold labels

(1) Adsorption of dust from the air causes dirt, pinholes, and burrs on the printed matter that affect the appearance of the label.
(2) Adsorption of in-mold labels with static electricity is easy, which can easily result in difficulties in printing and die-cutting and double labeling.

2. Elimination of static electricity in the mold

(1) Improve the environment: The ideal ambient temperature is 22oC ± 2oC, humidity greater than 50%, and 70-80% is the most ideal.
(2) Mechanical contact: Ground the various printing machines and processing machines to eliminate static electricity automatically.
(3) Conductive copper wire is installed in the printing, die-cutting, cutting, etc., and the copper wire is grounded separately to eliminate static electricity.
(4) Install the electric static elimination device at different stations to eliminate static electricity by ion discharge.