Heat shrinkable label
Also known as shrink label. At present, the commonly used materials are mainly PVC, PET, OPS, all of which are horizontal high shrinkage labels, which are sleeved in the form of sleeves; other few applications are OPP longitudinal shrink wrap labels, and PLA biodegradable materials. Shrink sleeve label. Commonly used printing processes are gravure printing, flexographic printing, and digital printing.
In the process of product packaging, circulation and use, the label needs to withstand the test of resistance to the content, the test of the label material in the transportation environment, and the test in the process of customer use.
Content influence relationship
When the content is acidic, alkaline, and corrosive to the material, we must consider the risk of liquid leakage during filling and the risk of liquid leakage during customer use, which will damage the label.
Therefore, try to choose a material with better resistance to the content as the base material of the label.
The relationship between transportation and use environment
It is analyzed from two aspects: the restriction and influence of the label transportation environment on the label material before shrinkage and the label performance requirements in the transportation of the finished product after the label shrinkage.
Before shrinking, it is mainly the test of environmental temperature changes on the material. If the storage and transportation environment temperature of the label exceeds 25°C, and there is no constant temperature control, it is easier to cause the natural shrinkage and deformation of the label, which will cause it to be unable to use it normally.
Mutual impact and abrasion during transportation after shrinkage, and pre-heating of containers and labels in final sales test the material.
In addition to heat shrinkage, the heat shrinkable label also has a certain degree of natural shrinkage under normal temperature conditions. The so-called natural shrinkage means that when the material is stored under natural conditions, the material will shrink to a certain extent.
The material of the same material is mainly related to the shrinkage rate under low temperature (60℃～70℃) and the stability of the material itself. The greater the shrinkage rate under low temperature conditions, the more obvious the natural shrinkage.
In terms of material types, OPS has the largest natural shrinkage rate among several heat-shrinkable standard materials, followed by PVC, and PET is the material with the smallest natural shrinkage rate.
When the label needs to be transported for a long distance and time, and the product production cycle span is relatively large, it is also necessary to properly consider the impact of transportation and storage safety. If the selected material type cannot be changed, certain protection must be taken in the high temperature season. Measures for distribution and storage.
Common storage conditions
There are two main recommended storage conditions for commonly used heat shrinkable label materials:
(1) Store at a constant temperature below 25°C, away from heat sources;
(2) Direct sunlight is strictly prohibited.
For transportation, a slightly flexible arrangement can be made according to the long-term transportation distance. For example, if the transportation schedule is within 6 hours, when the maximum temperature is below 35°C, the direct delivery method can be adopted for transportation; the maximum temperature is 30~35. If the temperature is between ℃ and the distance is more than 6 hours and the highest temperature is higher than 35℃, it is recommended to use a thermostatic box truck for delivery.
Special attention should be paid to the temperature management of the constant temperature room and the balance of the ambient temperature in the storage link of the label. From the above comparison chart, it is obvious that OPS is sensitive to ambient temperature. Therefore, it is necessary to pay more attention to the storage conditions of OPS tags in the storage process. Improper placement or insufficient power is likely to cause regional environmental temperature differences. The temperature of the near refrigeration equipment is low, and the temperature of the far away area will be higher, which will also cause obvious natural shrinkage of the label.
In the same way, when the production line takes the labels from the constant temperature warehouse to the production site, you must also pay attention to the control of the amount of on-site spare labels. Generally, it is recommended not to exceed the 4 hours usage. Management, because the temperature of the production site is usually not lower than the temperature of the natural conditions outside. The storage location of the temporary spare label on site should be kept away from some heating equipment (such as: high-power motor, heat shrinkable channel, steam pipe, etc.), and it is strictly forbidden to be exposed to sunlight.
After shrinking and setting, in the transportation and distribution of finished products, the labels will be worn and damaged due to the bumpy impact during transportation. This is also an important factor that must be considered in the label design and selection. The material density and surface strength are different, and their resistance to wear and impact is also very different. Among the three commonly used label materials of PVC, PET, and OPS, the surface strengths of PVC and PET are equivalent, while OPS is significantly weaker. In order to overcome the shortcomings of the weak surface strength of OPS, we can make up for it by coating the surface with anti-scratch varnish and increasing the thickness of the substrate. At the same time, the PET/OPS/PET co-extrusion material that came into being was developed by combining the wear resistance and impact resistance of PET with the good shrinkage performance of OPS.
The special processing method used by the end customer requires label performance. For example, in winter dairy products, coffee beverages and other products that need to be heated, whether the heat-shrinkable label film on the surface can withstand the test of preheating temperature is also an issue that designers cannot ignore. For example, when the PVC material is boiled at a high temperature above 80℃ for about 1 minute, the material will be whitened, that is, the transparent film becomes white and the transparency will be significantly reduced; in addition, the OPS material is likely to occur during the second preheating. Excessive stretching or even hole phenomenon, and PET performs well in terms of high temperature resistance.
Concluding remarks
The application of a small contraction mark affects all processes from materials, contents, containers, equipment to circulation, and is directly related to the requirements of production efficiency, yield, and automation in the actual industrial production process. Because of the matching choice between the label and the other elements, it is difficult to give a universal judgment principle. But this is not completely impossible. According to the scenario of tag application, we can rationalize the idea in this way. First, determine the necessary label conditions (such as maximum shrinkage, material resistance) according to the characteristics of the container, and select the matching sufficient conditions (such as channel equipment, storage and transportation conditions) based on the specific needs of product packaging.