The different components of both paper and BOPP film determine different changes in the composite process and new natural conditions after compounding. After observing, analyzing, and comparing a longer period of time, a larger range, and more varieties, we found that the curled paper-plastic composite products have one thing in common, namely, "short film length." After the affixed film was completely peeled from the paper, the transverse dimension of the film was always smaller than the same dimension of the paper.
(a) Several factors related to the degree of curling of paper-plastic composite products 1. Paper quantification Low paper curl ratio is higher than that of high-quantity paper.
2. The loose, rough paper texture of paper quality is more serious than that of dense, smooth paper.
3. The tensile deformation of the film is more serious than the stretching deformation of the film.
4. Temperatures Before April and after the end of October each year, the difference between the production workshop and the large air temperature increased, and curling accidents appeared.
5. Humidity Rain, snow, fog and other weather with high humidity are important conditions for inducing curling of paper-plastic composite products.
6. The production process, ie, the glue compounding process, can cause product curling more easily than the precoating film dry compounding process.
(2) Causes of curling of paper-plastic composite products Different heat-pressing working conditions produce different stresses BOPP biaxially oriented films used in paper-plastic composite production are at temperatures higher than the softening point of PP (polypropylene) resins. With mechanical vertical and horizontal biaxial stretching to a certain width (4000-4000mm), a certain thickness (28-15μm), and then cooling set.
The BOPP film is improved in heat resistance and weather resistance by extending the orientation, and the life is prolonged. When the BOPP film is cooled and set, the orientation of the molecular segment is frozen, the expansion coefficient in the stretching direction becomes smaller (including thermal expansion and wet expansion), and the thermal shrinkage rate increases.
When the BOPP film is reheated by the heating roller of the laminating machine, the frozen molecular segments produce a tendency to recover the unstretched size, ie, the film undergoes thermal contraction both in the vertical and horizontal directions. National standards stipulate that the shrinkage of BOPP film in the longitudinal and transverse directions is not more than 4%.
The shrinkage characteristics of BOPP film when it is heated by composites determine that it must produce shrinkage internal stress.
BOPP film in the composite heat shrinkage time, but also have to withstand the hot rolling machine roll rolling and stretching traction pulling mechanism of the two longitudinal forces. These types of forces act on the BOPP film at the same time, increasing its transverse shrinkage and the shrinking tension after it is released from the thermocompression mechanism at room temperature.
The paper in the paper-plastic composite is a net-like fabric made of natural fiber free and filler. The combination of fiber and fiber is always water-based and almost always reversible. Under the bridge of water, loose plant fibers are combined through a series of actions, dehydrated and baked to make paper. When the moisture of the paper increases to a certain value, it will be loosened and become pieces and pulp.
The moisture content of the paper is generally 5-7%, which is equivalent to the equilibrium moisture when the relative temperature is 50-60%. When the relative humidity of the surrounding environment changes, the paper has the function of absorbing moisture or dehumidifying, so as to achieve a new balance between its own moisture and the content of water vapor in the ambient air.
Paper is a hygroscopic material that absorbs moisture from the air. The rate of moisture absorption depends on the amount of water vapor in the air and the temperature of the air. It can also transmit moisture to the air and lose moisture. The rate of water loss depends on the moisture content of the paper and its temperature.
In the paper-plastic composite production process, there are two interrelated movements when the paper and BOPP film pass through the hot lamination mechanism. The first is the thermal movement. The heat of the heating roller is continuously conducted to the pressure rubber roller, the BOPP film, and the adhesive coated on the film and the paper compounded therewith. Followed by fluid movement. The movement of the fluid includes two aspects: one is the leveling of the adhesive and two-way infiltration between the film, the paper and the ink micropores, and the second is the evaporation of moisture contained in the paper under the hot extrusion of the heating roller. Thermal motion and fluid motion are interrelated, the former is the basis of the latter, and the latter is the dynamic response of the former. As a result, most of the adsorbed water and free water present in the pores and cell cavities of the paper are removed, the fibers are dried and shrunk, and the paper size becomes small.
The hot-pressing working conditions of the paper-plastic composites cause the BOPP film to produce shrinking tension. Paper pushes moisture to produce shrinkage stress. The heat shrinkage of the film is mainly manifested in the transverse direction, and the drying shrinkage of the paper is mainly manifested in the opposite lateral direction. Although the reaction of these two different solid-phase substances to heat shows shrinkage, there is a vectorial difference in directionality and size, and the shrinkage tension of the film is greater than the shrinkage stress of the paper.
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Triple C International (ShenZhen) Co.,Ltd. was established in 2018. It`s a professional foreign trade company engaged in import and export trade, and carries out business operations such as international trade, cooperative production and intermediary trade. The company mainly provides high-quality OEM-product and ODM-product services for customs in Japan, Southeast Asia, Europe and Unite States, and has a professional technical team that provides hundreds of OEM-product services for dozens of customers, and has dozens of excellent suppliers. The company mainly provides sewing products, plastic products, paper products, wooden products, household products and other OEM services, including handbags, gift boxes, Storage Boxes, stationery boxes, kid toys, Paper Boxes, school supplies, office supplies and other products import and export business.
