1. Heat sealing temperature
The choice of the heat-sealing temperature of the composite film is closely related to the performance and thickness of the composite substrate, the model, speed, and heat-sealing pressure of the bag making machine, which directly affects the strength of the heat-sealing.
The initial sealing temperature of the composite film is determined by the viscous flow temperature Tf (or melting temperature Tm) of the heat sealing material, and the maximum temperature of the heat sealing cannot exceed the decomposition temperature Ta of the heat sealing material. The temperature range between Tf (Tm) and Ta is the heat sealing temperature range of the heat sealing material. It is a key factor affecting the quality control of heat sealing. The wider the heat sealing temperature range, the better the heat sealing performance, and the easier and more stable the quality control.
At the same time, the heat sealing temperature of the composite film cannot be higher than the heat setting temperature of the printing material. Otherwise, it will cause shrinkage and wrinkling of the heat-sealed part, reducing the heat-sealing strength and the impact resistance of the bag. Printing materials have good heat resistance, such as PET, ONY, etc., in production, the heat sealing temperature can be increased for rapid production; printing materials have poor temperature resistance, such as BOPP, try to use a lower heat sealing temperature, but by increasing Pressure, reduce vehicle speed or choose low temperature heat sealing material to ensure heat sealing strength.
The setting of the heat sealing temperature should be within the heat sealing temperature range of the heat sealing material, generally 15℃～30℃ above the viscous flow temperature Tf (or melting temperature Tm) (if within this range, the heat sealing layer cannot be truly sealed We must try to improve the pressure, speed, and mechanical properties. The greater the pressure, the better. If the pressure is too large, it will damage the welding edge and cause root breakage. "Supplementary discussion"). The heat sealing material is melted and extruded, reducing the thickness of the heat sealing, and increasing the thickness and unevenness of the welding edge. Although the apparent heat seal strength is relatively high, it will cause root breakage and greatly reduce the impact resistance of the seal (prone to break the bag, "replenishment") and sealing performance. (This analysis is very reasonable.) The heat-sealing temperature is lower than the softening point of the heat-sealing material, and increasing the pressure and extending the heat-sealing time cannot make the heat-sealing layer truly sealed.
The heat sealing temperature setting of continuous automatic filling equipment is often higher, because it is easily affected by the contamination, extrusion, and cooling speed of the contents during heat sealing.
2. Heat sealing pressure
At the heat-sealing temperature, the heat-sealing material begins to melt, and pressure is applied to the bonding surface to make the corresponding heat-sealing materials contact, permeate and diffuse with each other, and also promote the escape of gas on the surface of the film to make the molecules on the surface of the heat-sealing material The distance between them is reduced, resulting in greater intermolecular force, thereby increasing the strength of the heat seal. (Add heat sealing theory)
The heat sealing pressure is provided by the spring on the bag making machine. For thin and light packaging bags, the heat sealing pressure should be at least 1.96N/cm. The size of the heat sealing pressure is related to the structural properties, thickness, and heat sealing width of the composite film.
The heat-sealing material has a higher activation energy, and the increase in temperature has a greater influence on the decrease of its viscosity. The required heat-sealing pressure is small to prevent the molten material at the heat-sealing part from being extruded and reducing the heat-sealing effect. PE and PP are non-polar heat-sealing materials with very low activation energy and high pressure required, which is beneficial to heat-sealing strength and interface heat-sealability. (How to understand this paragraph, it should be the heat sealing material with higher activation energy and the heat sealing material with lower activation energy in the heat sealing material. PE and PP are commonly used heat sealing materials, and the general type of PE should be referred to here. , PP materials are heat-sealing materials with low activation energy, and heat-sealing materials such as mPE, EVA, EAA, EMAA, Surlyn, etc., are copolymerized, blended and modified, or special catalytic, ionic resins, etc. A heat-sealing material with a higher activation energy. I wonder if this is the right way to understand it?)
The heat-sealing pressure increases as the thickness of the composite film increases. If the heat-sealing pressure is insufficient, the heat-sealed C-layer film will be difficult to heat, and it will be difficult to exhaust the bubbles sandwiched between the welds; if the heat-sealing pressure is too high, the molten material will be squeezed away. Damage the welding edge and cause broken roots. When calculating the heat sealing pressure, the width of the required heat sealing rod (refers to the heat sealing width rather than the entire width of the rod) and the actual surface area (refers to the heat sealing contact area) should be considered. The wider the width of the heat sealing rod, the greater the pressure required. If the width of the heat-sealing rod is too wide, it is easy to entrain bubbles in the heat-sealed part, and it is difficult to heat-seal firmly. Generally, a hollow heat sealing rod is used to strengthen the heat sealing fastness in the last letter. For heat-sealing rods of the same width (heat-sealing width), if the surface is engraved, the actual contact area is greatly reduced, and the pressure per unit area increases accordingly. This is beneficial for heat-sealing bags with larger widths.
3. Heat sealing speed
The heat sealing speed reflects the production efficiency of the bag making machine, and is also an important factor affecting the heat sealing strength and appearance. The faster the heat-sealing speed, the higher the heat-sealing temperature should be to ensure that the heat-sealing strength and heat-sealing state reach the best value; under the same heat-sealing temperature and pressure, the slower the heat-sealing speed will lead to the fusion of the heat-sealing material It will be fuller and stronger, but it will not cause root breaking.
On domestic bag making machines, the length of heat sealing time is mainly determined by the speed of the bag making machine. To increase the heat-sealing time, the bag-making speed must be reduced and the efficiency of manual production must be reduced. If an independent frequency conversion motor is used to control the lifting and feeding of the heat sealing rod, and the heat sealing time is independently adjusted without changing the bag making speed, it will greatly facilitate the operation and quality control of the bag making machine. (Several domestic manufacturers can produce this kind of bag making machine, using three frequency conversion motors and one independently controlling the heat sealing time. The currently purchased Smick 600 bag making machine belongs to this type, not the domestic one mentioned above The bag making machine controls the heat-sealing time and the output is determined by the speed.)
Fourth, the cooling situation
The cooling process is a process of shaping the welds that have just been melted and sealed with a lower temperature under a certain pressure to eliminate stress concentration, reduce the shrinkage of the welds, improve the appearance of the bag, and increase the strength of the heat seal. The cooling water of the bag making machine is generally tap water or circulating water at about 20°C. If the water temperature is too high, the pressure of the cooling rod is not enough, the cooling water circulation is not smooth, the circulation is not enough, etc. will lead to poor cooling, and the strength of the heat seal will be affected.
Five, heat sealing times
In continuous automatic filling equipment and some bag making machines, longitudinal heat sealing generally adopts the welding method of ring-shaped steel strip coated with PTFE, and the transverse heat sealing adopts the hot plate welding method. However, most of the longitudinal and transverse heat sealing of the bag making machine use hot plate welding, the number of longitudinal heat sealing depends on the ratio of the effective length of the heat sealing rod to the bag length, and the number of transverse heat sealing is determined by the number of heat sealing devices on the machine.
Good heat sealing generally requires more than two heat seals. Most of the transverse heat sealing devices are three groups. In order to meet the heat sealing requirements of the wide side, transverse heat sealing devices are often added, and the number of heat sealing is increased to reduce the heat sealing temperature and reduce the shrinkage phenomenon. For packaging bags of longer specifications, multiple feeding technology can be used to reduce the length of each feeding to one-half or one-third of the bag length, thereby increasing the number of heat sealing and improving the heat sealing effect, but it will reduce production Efficiency, so some bag making machines increase the length of the longitudinal sealing rod to increase the number of heat sealing and ensure the quality of heat sealing.
Six, heat sealing rod gap
The gap of the heat-sealing rod refers to the application distance of the predetermined heat-sealing pressure to the heat-sealing surface when the upper heat-sealing rod contacts the bottom plate. With the same film thickness and the same heat sealing speed, the gap between the heat sealing rods is small and the heat sealing time is relatively short, and the heat sealing strength of the product will be reduced. Generally, the gap of the heat-sealing rod is set at 1～1.5mm, which is related to the film thickness, transfer performance, and bag making speed. (If an independent variable frequency motor is used to control the lifting and feeding of the heat sealing rod, and the heat sealing time is independently adjusted, the bag making speed does not matter.)
Seven, tension control
The tension control device is used to keep the film flat, easy to fold, uniform intermittent feeding, and reduce shrinkage and warpage of the heat-sealed part of the bag. The tension of the bag making machine is generally 1～1.5㎏/㎝?. (The role of tension control and the difference between good and bad needs to be added after discussing with Fan Gongliu.)
to sum up
1. The heat-sealing quality of composite flexible packaging bags is mainly to evaluate appearance inspection, heat-sealing strength, compressive strength, impact strength, etc. In the professional standards, there are some deficiencies in terms of heat sealing strength and pressure time. (Where is the lack, it needs to be contacted or supplemented by checking information.)
2. Process factors such as heat-sealing temperature, heat-sealing pressure, heat-sealing speed, cooling system, heat-sealing times, heat-sealing rod gap, tension control, etc. are all important factors that affect heat-sealing strength and appearance.
3. The quality of heat sealing depends on the selection of heat sealing materials and the determination of the production process, but at the same time other factors that affect the strength of heat sealing should be paid attention to: the structure and material of the composite film, the composite strength between layers, printing and layout, layout design (Ink area), heat resistance of ink and adhesive, etc.
This procedure is applicable to the bag-making process. This procedure is divided into five major parts: preparation before starting up, adjustment, sampling and testing, starting up and running, and shutting down and cleaning.
1. Preparation before starting:
1.1 Collar composite film: According to the requirements of the production task list, determine the composite film to be processed, and pick up the composite film in the maturation room or the specified location.

1.2 Precautions for the composite membrane: check the maturation time and composite strength of the composite membrane, and check whether there is a "process transfer order" on the composite membrane according to the serial number of the "process transfer order"