1. The type, thickness and quality of the heat seal layer material have the most direct influence on the heat seal strength.

Commonly used heat sealing materials for composite packaging are CEP, LPPE, CPP, OPP, EVA, hot melt adhesive and other ionic resin co-extruded or blended modified films. The thickness of the heat seal layer material generally floats between 20 and 80 μm. In special cases, there are also 100-200μm, the same heat-sealing material, and the heat-sealing strength increases with the thickness of the heat-sealing. For example, the heat seal strength of the retort pouch is generally required to be 40-50 Newtons, and therefore, the heat seal thickness should be 60-80 μm or more. The temperature involved in the heat sealing bag process is controlled by the temperature meter. In the process of heat-sealing composite bag processing, the precision of the thermometer should be as fine as possible, and the error range and set value should preferably be no more than ±5 °C. The heat sealing temperature has the most direct influence on the heat seal strength. The melting temperature of various materials directly determines the minimum heat sealing temperature of the composite bag.

In the actual production process, due to various effects such as heat sealing pressure, bag making speed and thickness of the composite substrate, the actual heat sealing temperature is often higher than the melting temperature of the heat sealing material. The lower the pressure of the heat sealing, the higher the heat sealing temperature is required, and the faster the machine speed is, the thicker the surface layer material of the composite film is, and the higher the heat sealing temperature is required. If the heat sealing temperature is lower than the softening point of the heat sealing material, the heat sealing layer cannot be completely sealed regardless of the pressure or the heat sealing time. However, if the heat sealing temperature is too high, and the heat sealing material at the welding edge is easily damaged, the melt extrusion produces a "root cutting" phenomenon, which greatly reduces the heat sealing strength of the sealing and the impact resistance of the composite bag. In the actual bag making heat sealing process, the pressure of the heat sealing tool is often adjusted by a rotatable spring. The adjustment process generally consists of two springs, which are divided into left and right sides. If the pressure affects the heat seal strength, the detection method is: take a positively processed composite bag and observe the stitches carefully. If the pressure is uniform, no bubbles will be generated. Phenomenon; another method is to test with a smooth bamboo block with a length of 500px, a width of 75px and a thickness of 5000px. Due to insufficient pressure, low strength and frequent leakage, uniform pressure and temperature are low in strength and stratification. One of the basic phenomena.

2. To achieve the desired heat seal strength, heat sealing pressure is essential.

For light and thin packaging bags, the heat sealing pressure should be at least 2kg/cm2, and correspondingly increase with the increase of the total thickness of the composite film; if the heat sealing pressure is insufficient, it is difficult to achieve true fusion between the two films, resulting in partial heat sealing. It is good or difficult to eliminate the air bubbles trapped in the middle of the weld, resulting in a false weld. However, the heat sealing pressure is not as large as possible, and the weld edge should not be damaged, because at the higher heat sealing temperature, the heat sealing material of the welded edge is in a semi-molten state, and too much pressure is easy to squeeze away part of the heat seal. Material, so that the edge of the weld is formed in a semi-cut state. The weld is brittle and the heat seal strength is reduced. Therefore, the adjustment of pressure is very critical.

3. The heat sealing time is mainly determined by the speed of the bag making machine.

The speed is fast, the heat sealing time is short; the speed is slow, and the heat sealing time is long. Heat sealing time is also a key factor affecting weld seal strength and appearance. Under the same heat sealing temperature and pressure, the heat sealing time is longer, the heat sealing layer is more fully fused, and the bonding is stronger; but the heat sealing time is too long, which is easy to cause the weld seam to wrinkle and deform, affecting the flatness and appearance. If the welded joint after heat sealing is not well cooled, it will not only affect the flatness of the appearance of the welding, but also have a certain influence on the heat sealing strength. The cooling process is to heat the heat by a lower temperature under a certain pressure. The sealed weld is shaped. Therefore, the pressure is insufficient, the cooling and circulation are not smooth, the circulation amount is insufficient, the water temperature is too high, or the cooling is not timely, which causes poor cooling and a decrease in heat sealing strength.

4. The more heat seal times, the higher the heat seal strength, and the number of longitudinal heat seals depends on the ratio of the effective length of the longitudinal weld rod to the length of the bag.

The number of transverse heat seals is determined by the number of sets of machine transverse heat seals. Good heat sealing requires at least two heat seals. For composite films of the same structure and thickness, the higher the peeling degree between the composite layers, the greater the heat seal strength; for products with low composite peel strength, the weld damage is often the first layer peeling of the composite film at the weld, resulting in heat from the inner surface. The sealing layer is independently subjected to the breaking tensile force, and the surface layer material loses the reinforcing effect, so that the heat sealing strength of the welded joint is greatly reduced; if the peeling degree between the composite layers is strong, the peeling of the layer at the welding edge is not caused, and the measured The actual heat seal strength obtained is much better; when the heat seal inner layer is PE or OPP, the heat seal strength is much better than the BOPP of the same thickness.

5. The influence of the contents of the composite bag.

Some products are powdered and are susceptible to contamination during filling. For example, when LDPE is used as the inner layer, the seal is found to be easily broken. This is because the heat sealing property of the LDPE to the inclusions is not very good, and the heat seal strength can be improved by replacing the inner film material or increasing the thickness of the material.

6, the impact of composite additives.

In the process of composite polyethylene film, polyethylene is precipitated after being pressed by hot pressing roller, and a layer of white powder like white powder. This phenomenon is that polyethylene is added with a certain amount of lubricant in the production process. Some low melting waxes are easily deposited on the surface of the film. The most direct hazard of this low-melting wax is that it greatly weakens the composite strength and greatly weakens the heat-sealing strength, especially in the edge-sealing position, resulting in easy opening and separation.

Solution: 1) Re-treat the polyethylene to achieve the desired surface tension; 2) Select a suitable adhesive to enhance its composite fastness; 3) Reduce the curing temperature and try not to precipitate the material, thereby increasing the composite fastness and Heat seal strength.

7. The delamination of the flexible packaging composite bag after heat sealing is related to the printing ink layer and the corona surface.

In the actual production process, in order to achieve the true reproduction of color, it is inevitable that the printing and printing inks are mixed and printed. Theoretically, the printing and surface printing inks are incompatible. If the ink layer of the printing film is mixed with the inner surface, the fastness between the ink layers is not good, and the layering is easy, and the heat sealing seam is also easy. This causes delamination and the heat seal strength is thus deteriorated.

Solution: Try to avoid the mixing of the surface printing ink and the printing ink, thereby improving the heat sealing strength and reducing the stratification phenomenon.