In recent years, due to the features of heat-shrinkable labels such as body-fitting, bright printed patterns, and suitable for mass production, etc., they have been increasingly used by various products, especially PVC labels, which are favored by major beverage manufacturers. However, due to the large differences in shrinking equipment and processes used by manufacturers, which leads to differences in shrinking effects, here is a brief discussion on shaped bottles.
Before talking about the shrinking effect, we first compare several different shrinking processes, see the table below.
project
Water bath
electro-thermal
Steam
Heat distribution in the drying tunnel
Uniform
Uneven
Uniform
Temperature gradient in the drying tunnel
No gradient
No gradient
With gradient
Position of functional heat source in drying tunnel
No location
No location
Have
Can the label be initially positioned
no
no
can
Productivity
low
low
high
Empty bottle shrinkage effect
There are some pits and deformations caused by poor shrinkage, which need to be left to dry.
There are local pits and deformations caused by poor shrinkage, which can easily cause wrinkles on the standard surface.
Since empty bottles can be poured, they cannot be produced, and the method of shrinking after filling must be adopted.
Shrinkage effect after filling
Same as above
Same as above
good
It can be seen from the above table that both the shrinking effect and the production efficiency reflect the superiority of the steam process. At least the following points should be noted for the shrinkage of shaped bottles:
1. Bottle shape with small upper part and big lower part
The bottle type is mostly used in peanut butter, milk, juice and other food industries, such as Shanghai Danone Weishuang Cheese Drink Bottle, Mengniu Large Grain Fruit Bottle, Xuzhou Tianshan Snow Ice Baby Bottle, Beijing Huabang Juice Vinegar Cooling Bottle, etc. When the trademark is shrinking, the best solution is to use the steam process. First shrink the bottom, and make the shrinkage stress reach the maximum value to prevent it from being affected by the upward vector stress generated during the upper shrinkage process, and the mark will move upwards, causing the defect that the lower part of the bottle will not be covered; if The electrothermal process is used, because its heat source does not have position, so it cannot be operated according to the aforementioned method of shrinking the lower part first, that is to say, it is inevitable that more bottles will leak out of the lower part. If you want to improve under this process condition, you can start from improving the curvature of the lower part of the bottle body, and reduce the original gradient surface to form an obvious step to lock the lower part of the label. Improvement from the perspective of the longitudinal shrinkage rate of the label is also an auxiliary method, but it is not as good as the previous improvement method.
2. The upper and lower bottles
The bottle type is mostly used in industries such as cup-type instant noodles and ice cream. For example, ice cream packaging boxes such as Heluxue and Nestle. This type of cup has a smooth surface without protrusions, etc., and generally uses an empty packaging electric heating process for trademark shrinkage. Since the position of the heat source cannot be adjusted, the shrinking process is carried out simultaneously at the upper and lower parts. At this time, the label will move down due to the vector stress generated during the shrinking process. By changing the shape of the local cup (for example, we can add a protruding part on the upper end to fix the upper end of the label), this phenomenon can be fundamentally eliminated, and some manufacturers take the form of applying glue on the upper end of the back of the label. Solution, but not as good as the previous solution.
3. Two big and small bottles
This bottle type is mostly used in milk, beverages and other industries, such as Shanghai Danone high-calcium milk bottle, Mengniu yogurt bottle, Beijing prince milk lactic acid bacteria bottle, etc. This type of bottle generally uses steam process, if it is difficult to control if using electric heating process , It is difficult to avoid the label moving to the middle. When using steam, it is also necessary to follow the order of the next-middle-to shrink. If the surface of the bottle body is smooth without vertical stripes, in order to avoid the accumulation of air in the middle of the label, it is necessary to make a number of ventilation holes on the surface of the label.
4. Two small bottles in the middle
The bottle type is also mostly used in the beverage industry, such as Watsons water bottles. This type of bottle type generally adopts steam technology and shrinks in the order of middle-down-up to ensure the accuracy of the label position.
In addition to the precautions mentioned above in the shrinking process, the following problems in the design of special-shaped bottle labels, product shrinkage standard production, and user acceptance inspection should be paid attention to.
1. For the design of the label of the special-shaped bottle, the deformation of the pattern must be taken into account. We call it the pre-deformation design link, which uses 3DMAX software to perform three-dimensional simulation of the manuscript in the computer. The result is to inversely obtain the printed pattern before shrinking, so that the label pattern design scheme is perfect and reasonable. Since the longitudinal shrinkage rate of the substrate used for printing will be different (generally there is an error of 2% to 3%), the longitudinal position of the pattern of the shrinked label will also be different, resulting in slight deformation and displacement ( Generally about 0.5mm ～ 2mm); For the lateral direction, if the steam process is used, the deformation is small (generally about 0.5mm ～ 1mm), if the electric heating process is used, due to the inherent shortage of uneven heat distribution inside the drying tunnel, It leads to unstable heat during the shrinking of the label. The shrinkage of the horizontal deformation of the pattern caused by the shrinkage of the bottle and the trademark of the same product (the deformation value is generally about 1mm ~ 5mm), there is no regularity, and it is difficult to control.
2. With the change of people's aesthetic views on products, most of the recognized bottle appearances are irregular smooth surfaces, and most of them are made of HDPE. After shrinking, the label will rotate relative to the bottle body. This is because the shrinkage rate of the HDPE bottle itself is different from the shrinkage rate of the label. When heated, the label wraps the bottle body very tightly and cannot rotate, waiting to be cooled to room temperature Later, due to the shrinkage of the bottle itself, the size was reduced, and the label basically did not shrink, so there was a phenomenon of rotation. For general non-frozen food, we can use the method of gluing on the back of the label. For frozen and low-temperature products such as yogurt products, if the glue method is used, micro-wrinkles will occur in frozen and low-temperature environments ,Affect the appearance. How to solve this problem fundamentally needs to be further discussed by professionals.
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