Although solvent-free cooking compound has obvious advantages such as environmental protection, energy saving, sanitary safety and cost reduction, and has broad development prospects, at present, domestic high-temperature cooking solvent-free glue and compound technology are not mature enough. , Medium resistance, peel strength and other comprehensive properties can not keep up with solvent-based adhesives, and need to be improved in use adaptability.
Therefore, for solvent-free cooking composite membranes, whether it is from the selection of glue and the determination of the process, it should be carefully tested and verified, and it cannot be put into mass production without a small trial.
Generally speaking, when using high-temperature solvent-free compound process, enterprises should pay attention to the following points from the material aspect:
1. PET
When the corona treatment value is less than 50mN / m, it will affect the peel strength of the composite, so it should be tested before being used on the machine.
2 , AL
If the oil stain is serious, the compound fastness will not be high, especially after cooking at high temperature, the delamination and peeling will occur. Therefore, the aluminum foil should be selected with high surface cleanliness, no oil and dust, and a surface tension of 72mN / m or more. A grade should be checked when it is used on the machine.
3 , BOPA
Due to the amide group in the molecular structure, it maintains extremely high polarity and surface tension, up to 52mN / m. When it is used as an intermediate layer for high-temperature cooking composite membranes, if the wetting tension of its non-corona surface cannot reach 48mN Above / m, the composite fastness of the non-corona surface will not be guaranteed, which will easily lead to the delamination of the composite film. At the same time, because there are a large number of amide-based polar groups in the molecular structure, its surface is easily absorbed. Highly polar water molecules are also likely to cause laxity when they are compounded with a high-temperature resistant two-component polyurethane adhesive.
4. RCPP
For RCPP, first, we must pay attention to its surface wetting tension. Before the machine is compounded, it must be tested roll by roll. If it is above 40mN / m, it can be used with confidence. Pay attention to whether there is precipitation on the surface of the RCPP film. If there is precipitation, it will cause the composite peeling force to drop or even delaminate, and at the same time affect the composite appearance and product hygiene. Unsatisfactory performance affects compound peeling force and high temperature cooking and delamination.
5. Ink
High-temperature-resistant cooking ink must be selected, otherwise the high-temperature-resistant solvent-free composite products will be delaminated due to poor ink during cooking.
There are relatively few manufacturers of solvent-free compound production of cooking products. Although many manufacturers can meet the requirements after testing, the stability and risk of mass production are still to be discussed.
Differentiated by cooking temperature, the current solvent-free cooking process is mainly suitable for 121 ℃ cooking products, 135 ℃ cooking products are still rarely used, mainly because the solvent-free adhesives and solvent-free processes are not very mature, and need glue The adhesive is further improved and perfected. Even for 121 ℃ transparent cooking products, if they are not properly controlled during the production operation, there will be abnormal phenomena such as broken bags and delamination after cooking. In general, we can strengthen the management and control in terms of materials, temperature and humidity, the amount of glue, winding and curing.
1. The material thickness deviation should be small
The solvent-free cooking compound film has a very small amount of glue, only 1/2 ~ 1/3 of the dry compound, that is, about 2g / ㎡, so the thickness deviation of each layer of material is required to be very small, especially the inner layer material RCPP Thickness control. Generally speaking, solvent-free compound cooking products, the inner layer material will be more than 50um, and the amount of glue is only about 1.5 ~ 2.5um thickness. If the thickness deviation of the material is large, it will cause the solvent-free adhesives to flow in the roll film after the composite semi-finished product is wound, which will cause the glue amount of the thin material position to become larger and the material thick position to become smaller. This is because the position of the thick material is larger than the position of the thin material. The internal stress is larger, which will cause the glue to flow from the thick material to the thinner material. .
2. The influence of temperature and humidity on curing
The curing process of the solventless adhesive is actually the reaction process of the NCO group of the solventless main agent and the OH group of the curing agent at a certain temperature and humidity, so the completeness of the reaction of the solventless adhesive is affected by the main agent curing agent The proportion and humidity affect, and the high-temperature cooking product has a larger amount of glue than ordinary products, so the proportion of main agent curing agent and humidity have a greater impact on the curing of the adhesive. Therefore, in actual production, the proportion of the main agent curing agent should be adjusted according to different seasons in different regions.
For example, in the dry season in winter and the rainy season in summer, the humidity in the air is very different. When the same product is produced in these two seasons, the proportion of glue should be slightly adjusted, otherwise the incomplete reaction of the adhesive will occur, which will affect the cooking compound. The effect of membrane products after cooking.
3. Balancing quantity and winding system
As we all know, one drawback of the solvent-free compound process is that after the compound semi-finished product is off the machine, the glue has no initial tack and still has fluidity. Therefore, the solvent-free process requires very high equipment rewinding systems. If the winding system of the machine is not good, the glue will flow out to the end surface after getting off the machine, the winding will be uneven, and the bottom of the roll will be wrinkled.
The solvent-free cooking process determines the gumming amount of the cooking product is 25% to 40% higher than that of the ordinary product due to the subsequent processability of the finished product, so the glue outflow phenomenon is more likely than the ordinary product.
In addition to the solvent-free winding system, the uniformity of the amount of glue in the vertical and horizontal directions is also very important when solvent-free compounding. If the amount of glue is not balanced, although the glue will have a certain fluidity to make up, it can not be completely avoided. The amount of local glue in the finished product is too small, which affects the cooking performance of the finished composite film .
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