Process control of wuxi Dingmao machine bag making machine

Current location：Home > Newsnews

First, heat sealing temperature

The choice of heat sealing temperature of composite film is closely related to the performance and thickness of composite substrate, the type, speed and heat sealing pressure of bag-making machine, which directly affects the level of heat sealing strength.

The sealing temperature of composite film is determined by the viscous temperature Tf (or melting temperature Tm) of the heat sealing material, and the high temperature of heat sealing can not 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 the key factor affecting the quality control of heat sealing. The wider the temperature range of heat sealing, the better the performance of heat sealing, the easier and more stable the quality control.

At the same time, the heat sealing temperature of the composite film can not be higher than the heat setting temperature of the printing material. Otherwise, it will cause shrinkage and wrinkling of the heat sealing part, reducing the heat sealing strength and the impact resistance of the bag. Good heat resistance of printing materials, such as PET, ONY, etc., can increase the heat sealing temperature in production to rapid production; Printing materials with poor temperature resistance, such as BOPP, try to use a lower heat sealing temperature, and by increasing pressure, reduce the speed or choose low temperature heat sealing materials to ensure the heat sealing strength.

Heat sealing temperature setting should be in heat sealing temperature range of heat sealing material, generally in the viscous flow temperature Tf (or melting temperature Tm) on 15 ℃ ~ 30 ℃ (if within the scope of this, cannot make heat sealing layer sealing, must be from the pressure up to try to improve, speed, mechanical properties, the greater the pressure is not the better, too big welding edge will damage, increased problem. "Supplementary discussion"), the heat sealing material in the heat sealing part is easy to be fused out due to the high heat sealing temperature, which reduces the heat sealing thickness and increases the thickness and non-uniformity of welding edge. Although the apparent heat sealing strength is high, it will cause root breakage phenomenon, greatly reducing the impact resistance of sealing (easy to produce the problem of broken bag, "supplement"), sealing performance. (This analysis makes a lot of sense.) Heat sealing temperature is lower than the softening point of heat sealing material, increasing pressure and prolonging heat sealing time can not seal the heat sealing layer.

The heat sealing temperature of continuous automatic filling equipment is often set at a higher temperature, because during heat sealing, it is easy to be affected by the pollution of the contents, extrusion and cooling speed.

Two, heat seal pressure

At the heat sealing temperature, the heat sealing material begins to melt, and pressure is applied on the bonding surface to make the corresponding heat sealing material contact with each other, penetrate and diffuse, and also promote the gas on the surface of the film to escape, so that the distance between molecules on the surface of the heat sealing material is reduced, resulting in greater intermolecular force, thus improving the heat sealing strength. (Add heat seal theory)

The heat sealing pressure is provided by a spring on the bag-making machine. For lightweight packaging bags, the heat sealing pressure is at least 1. Larger than 96N/ cm ². The size of heat sealing pressure is related to the structure, thickness and heat sealing width of the composite film.

The heat sealing material has high activation energy, and the temperature rise has a great influence on the decrease of its viscosity. The heat sealing pressure required is small, so as to avoid the molten material in the heat sealing part being extruded and reduce the heat sealing effect. PE and PP are non-polar heat sealing materials with very small activation energy and high pressure, which are favorable for heat sealing strength and interface heat sealing property. (how to understand this time, should be heat sealing materials of heat sealing material has high activation energy and low activation energy of heat sealing materials, PE, PP is a common heat sealing materials, referred to in here should be a common type of PE, PP material, belongs to the activation energy of smaller heat sealing materials, with copolymerization, blending modification, or special heat sealing materials, such as catalytic, ionic resin Such as mPE, EVA, EAA, EMAA, Surlyn, etc., are heat sealing materials with high activation energy pickaxe. I wonder if this understanding is correct.

The heat sealing pressure increases with the increase of the thickness of the composite film. If the heat sealing pressure is insufficient, it is difficult to heat seal the propylene film and exhaust the bubbles sandwiched in the middle of the weld. The heat sealing pressure is too high, will squeeze out the molten material, damage the welding edge, cause root breakage. When calculating the heat sealing pressure, consider the required width of the heat sealing rod (the width of the heat sealing rod rather than the entire width of the rod) and the actual surface area (the area of the heat sealing contact). The wider the heat sealing rod width, the greater the pressure required. The width of the heat sealing rod is too wide, easy to entrap bubbles in the heat sealing part, it is difficult to heat sealing firmly. Hollow heat sealing rod is generally used to strengthen the heat sealing fastness. For heat sealing rod with the same width (heat sealing width), if the surface is engraved, the actual contact area is greatly reduced and the pressure per unit area is correspondingly higher. This is beneficial to heat seal wide packaging bags.

Three, heat sealing speed

Heat sealing speed reflects the production efficiency of bag making machine, and is also an important factor affecting heat sealing strength and appearance. The higher the heat sealing speed, the higher the heat sealing temperature to ensure the heat sealing strength and state; Under the same heat sealing temperature and pressure, the slower the heat sealing velocity is, the fusion of the heat sealing material will be more sufficient and stronger, but the phenomenon of root breakage can not be caused.

In domestic bag making machine, the length of heat sealing time is mainly determined by the speed of bag making machine. Increase the heat sealing time, must reduce the bag-making speed, reduce the hand production efficiency. If an independent variable frequency motor is used to control the lifting and feeding of the heat sealing rod, and adjust the heat sealing time independently without changing the bag-making speed, the operation and quality control of the bag-making machine will be greatly convenient. (Several domestic manufacturers can produce this kind of bag-making machine, using three frequency conversion motors, one independent control of heat sealing time. At present, the smic 600 bag making machine purchased belongs to this kind, not the above mentioned domestic bag making machine controlled heat sealing time production is determined by speed.)

Four, cooling conditions

Cooling process is under a certain pressure, with a lower temperature to just melt sealing weld shape, eliminate stress concentration, reduce the contraction of the weld, improve the appearance of the bag flatness, improve the heat sealing strength of the process. The cooling water of bag-making machine is generally tap water or circulating water of about 20℃. If the water temperature is too high, the pressure of the cooling rod is not enough, the circulation of cooling water is not smooth, and the circulation amount is not enough, it will lead to poor cooling, and the heat sealing strength will be affected.

Five, the number of heat sealing

In continuous automatic filling equipment and some bag-making machines, longitudinal heat sealing generally adopts the ring steel belt welding method coated with POLYtetrafluoroethylene, and transverse heat sealing adopts hot plate welding method. However, most of the longitudinal and transverse heat sealing of bag making machine adopts hot plate welding method. The number of longitudinal heat sealing depends on the effective length of heat sealing rod and the ratio of bag length, and the number of transverse heat sealing is determined by the number of heat sealing device group of the machine. Good heat sealing generally requires heat sealing in more than two times. Transverse heat sealing devices are mostly composed of three groups. In order to meet the requirements of wide edge heat sealing, transverse heat sealing devices are often added to increase the number of heat sealing to reduce the heat sealing temperature and reduce the necking phenomenon. For longer specifications of the packaging bag, can use multiple feeding technology, so that each feeding length is reduced to half or one-third of the bag length, so as to increase the number of heat sealing, improve the heat sealing effect, but will reduce the production efficiency, so some bag making machine to increase the length of longitudinal sealing rod, to increase the number of heat sealing, to ensure the quality of heat sealing.

Six, heat sealing bar clearance

The heat sealing bar gap refers to the applied distance of the predetermined heat sealing pressure to the heat sealing surface when the upper heat sealing bar contacts the bottom plate. When the film thickness is the same and the heat sealing speed is the same, the heat sealing rod gap is small and the heat sealing time is relatively small, and the heat sealing strength of the product will be reduced. Generally, the gap of heat sealing rod is set at 1 ~ 1.5mm, which is related to film thickness, transfer performance and bag-making speed. (If an independent variable frequency motor is used to control the lifting and feeding of the hot sealing rod and adjust the heat sealing time independently, the bag-making speed should not matter.)

7. Tension control

Tension control device is used to keep the film smooth, easy to fold, intermittent feeding uniform, reduce the shrinkage and warping of the bag heat sealing part. The tension of bag-making machine is generally in 1 ~ 1.5㎏/㎝². (The effect of tension control and the difference between good and bad is to be added after discussion with the normal flow.)

conclusion

1, the heat sealing quality of composite soft packaging bags is mainly evaluated by appearance inspection, heat sealing strength, compressive strength, impact strength, etc. In professional standards, the provisions of heat seal strength and pressure time are lacking. (The deficiency is in what place, need to contact or check information supplement.)

2, heat sealing temperature, heat sealing pressure, heat sealing speed, cooling system, heat sealing times, heat sealing bar clearance, tension control and other technological factors are important factors affecting the strength and appearance of heat sealing.

3, the quality of heat sealing depends on the selection of heat sealing materials and the determination of production process, but also pay attention to other factors affecting the heat sealing strength: the structure and material of composite film, the composite strength between layers, printing typesetting, layout design (ink area), heat resistance of ink and adhesive, etc..