Summary
The basic factors of coating uniformity are several conditions directly related to the coating process: coating substrate, adhesive, coating steel roller/coating roller and laminating machine, etc.
There are many factors influencing the uniformity of coating, including human, machine, material, method and environment, but the basic factors are several conditions directly related to the coating process: coating substrate, adhesive, coating Steel roller / rubber roller and laminating machine, etc.
1) Coated substrate: mainly material, surface characteristics, thickness and uniformity, etc.
2) Adhesive: Mainly its working viscosity, affinity and adhesion to the surface of the substrate, etc.
3) Coating steel roller: It is not only the direct carrier of the adhesive, but also the supporting reference for the coating substrate and the rubber roller, so it is the core of the entire coating mechanism. Its shape and position tolerance, rigidity, dynamic and static balance quality, surface quality, temperature uniformity and thermal deformation conditions all affect the uniformity of coating.
4) Coating rubber roller: Coating roller refers to an important variable of coating quality, and its material (such as rubber layer life), hardness, form and position tolerance, rigidity, dynamic and static balance quality, surface quality, thermal deformation conditions, etc. are also affected To the uniformity of coating.
5) Laminating machine: It is the basic platform for coating. In addition to the precision and sensitivity of the coating steel roller and rubber roller pressing mechanism, it also includes the highest speed of design and the overall stability of the machine.
The influencing factors of coating uniformity in the horizontal and vertical directions are different, so the control measures are correspondingly different. In the specific implementation, it is not only related to the design and manufacturing of the machine, but also related to the operation and process control.
â–ŒHorizontal uniformity of coating and its control
The uniformity of the coating width direction is mainly affected by the following factors:
1) The shape and position tolerance of steel roller and rubber roller.
2) Relative to the contact pressure between the steel pipe and the base material.
3) The adhesive is distributed horizontally, which mainly refers to the viscosity of the adhesive and the corresponding transfer rate. It is mainly determined by the combination of the first two factors and its working viscosity.
The first benchmark for guaranteeing coating accuracy is the shape and position tolerance of the steel roll and its rigidity. During operation, the shape and position tolerance, rigidity, balance accuracy, assembly accuracy and built-in heating and heat preservation system of the steel roll directly affect the state of the adhesive, thereby affecting the transfer rate and coating uniformity. Therefore, the design and selection of high-precision and good wear-resistant steel rollers is a basic task.
The rubber roller, especially the coating rubber roller, is the first influencing factor or variable of the lateral uniformity of the coating. The material, form and position tolerances, rigidity of the rubber roller, the hardness of the rubber layer, the dynamic balance of the rubber roller, the support structure of the rubber roller, the pressure adjustment status, etc. will obviously affect the uniformity of the coating. As a slender shaft, the rigidity of the rubber roller is the most obvious factor. From the perspective of use, the cleanliness of the rubber roller surface is also an important variable in the production process that affects the uniformity of the rubber roller coating. Therefore, the quality and maintenance of rubber rollers need to be carefully controlled.
It can be seen from the above analysis that the wider the substrate or coating width, the more difficult it is to guarantee the uniformity of the coating. When the coating width reaches a certain value, the uniformity of the coating may become the first major challenge to the accuracy of the entire solvent-free laminating machine.
â–ŒThe longitudinal uniformity of coating and its control
The longitudinal uniformity of the coating is the uniformity along the feeding direction of the substrate. It depends on many factors, including:
Substrate type, surface quality and consistency;
The operating speed of the machine, the number and frequency of the machine's speed increase
The viscosity of the adhesive, especially the consistency of viscosity during long-term operation;
The quality of the rubber roller, especially the elasticity, wear resistance and heat resistance of the rubber roller;
The control mechanism and structure of the amount of glue applied by the solvent-free laminating machine;
The structure of the glue system of the compound machine, etc.;
Environmental factors, etc.
Under normal circumstances, when the machine is running at a steady speed, the transfer rate of the adhesive is the same, so the uniformity of the glue is basically the same. But when the machine speeds up or down, the transfer rate of the adhesive will change slightly, sometimes even significantly, which affects the uniformity of coating. Therefore, the machine must be pre-processed in the program designed to reduce the impact of frequent startup or rising and falling speeds on coating uniformity.
The steel roller and the rubber roller will not only produce bending deformation and extrusion deformation, but also will be deformed by heating after continuous operation. These deformations usually affect the pressure condition and contact width of the contact area, which will affect the transfer rate and coating uniformity to a certain extent. Among them, the impact of rubber roller material and hardness on coating uniformity is sometimes very obvious. Therefore, the influence of these deformations must be fully considered in the design of the machine, especially the design and selection of high-quality and durable rubber rollers.
The length of the downtime will also affect the viscosity of the adhesive in the glue tank and on the steel roller of the coating rubber roller, which may also affect the uniformity of the glue. Therefore, we must pay attention to control the downtime to prevent the adhesive viscosity from being too high.
The coating amount control mechanism and structure of the solvent-free laminating machine is a very important but often overlooked factor that affects the uniformity of longitudinal coating. The adjustment and control method of the amount of glue will seriously affect the control accuracy of the amount of glue and its response speed.
For example, modern solvent-free laminating machines generally use a multi-roll transfer coating method to control the amount of glue applied through the speed difference. However, some machines use the adjustment of the metering interval to control the amount of glue applied. The reaction speed of this system is usually very slow, and the coating accuracy and uniformity are very low.
The glue dispensing system of some solvent-free laminating machines cannot continuously or arbitrarily set the glue width, or the glue width and the glue width are inconsistent, so that there is a certain dead corner of glue in the glue tank (area near the glue block) . After a long time of operation, the adhesive concentration or whitening will appear in the area near the rubber block, thereby reducing the transfer rate of the local (edge) adhesive, which directly affects the uniformity of the transfer. The result is that the amount of glue applied locally is lower, usually the edge is lower than the amount of glue in the middle area. This kind of unevenness is very special. The appearance is mainly lateral unevenness, but it is caused by continuous operation, and it will be repeated according to the time of adding glue. Therefore, it is necessary to pay attention to choosing a compound machine with reasonable coating amount control and arbitrarily set glue width.
The influence of environmental factors will be more obvious in long-term continuous production. Changes in relative humidity and temperature will affect the coating conditions of the adhesive to a certain extent.
In short, the overall uniformity of the coating can only be achieved if the horizontal and vertical uniformity are guaranteed. In contrast, the uniformity of the coating width direction is usually affected by the machine itself. However, in long-term or mass production, the uniformity in the length direction will be affected by more factors, and its uniformity is more difficult to control than the width direction.
Of course, from the observation of different time periods in the short-term, mid-term and long-term, the main factors affecting the unevenness of the coating will be different, and corresponding measures must be taken according to different situations.
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