Waste of material is a critical aspect when it comes to printing. It is a problem related both with the the setup phase of a print job or with the production process itself, and its consequences on the costs incurred by a manufacturer can be relevant. Fortunately, we have the means to enable you to reduce this waste.
The setup phase can lead to a substantial amount of material waste due to the various adjustments to be made (e.g. color registration, repeat length) in order to obtain final products of the desired quality, while in the case of problems in the production process, like an incorrect tensioning of the material, the result will be a non-compliant reel in relation to the customer’s standards, with consequences on both costs and, potentially, on business relationships.
With this in mind, the reduction of waste made possible by today’s printing technology is vital to a company’s continued success and reputation. Here are four solutions to address this problem.
1. Process automation
The number of activities involved in the machine set up and quality control phases, as well as their different level of complexity, are determining factors for the performance of a machine. The automation implemented to support the actual speed of both the process and the print job change of a flexographic printing machine, other than being a significant advantage compared to many other printing methods, has a major impact on the reduction of material waste.
Automation in printing is currently available in different levels according to the technologies developed by each manufacturer, and now covers almost all processes involved. Just to give an example, the work preparation, in case of a total print job change performed by one operator for a 4-color type printing machine can take about 18 minutes when automation is implemented, against 168 minutes required with manual operations.
The ability to integrate the printing machine with other systems like the lamination machine or the slitter rewinder is invaluable to achieving a substantial waste reduction.
Suppose we need to print a LDPE or a breathable material and then bond it with spunbond material in the lamination line. The substrate coming off the printing machine will be wound onto a reel where the material may have a different tensioning between the internal layers, closest to the reel core, and the external ones. This has repercussions on the repeat length, that must remain within a certain tolerance range to be compliant with the converter’s requirements.
When the reel is transported to the the unwinder of the lamination line, the processings and tensioning utilized in the lamination process can have an impact on the printed material structure with a consequent further variation of the repeat length. In conclusion, at the end of the production line we would obtain printed and laminated reels with a repeat length outside the tolerance requested by the customer.
The solution, that is integrating the printing machine with the lamination line, will allow you to eliminate the need of wounding the printed product before the lamination process, thus avoiding the aforementioned problem with the tension in the reel, and to laminate the material right after the printing, obtaining a better management of the repeat length in relation to the desired tolerances directly on the finished product.
If, on the other hand, we need to print spunbond material that will have to be subsequently slit, such as in the case of reels intended to be converted into femcare products, the integration of the slitter-rewinder with the printing machine is the best choice to make.
By doing so, the material will move seamlessly from the flexographic printer to the inline rewinder; the elimination of a phase of the process with the consequent formation of an intermediate reel and greater control over the tensioning of the product during the entire process will give life to a final product without problems related to the repeat length, ready for the converting process.
3. Tension control
It should be clear at this point that the tensioning of the substrate in every phase of the processing is a critical aspect to take into consideration, given its significant impact on the repeat length.
Let's take the case of an in-line slitting winder integrated with a flexographic printer again. The tension control traditionally occurs at six different points during the printing process:
- In-feed nip roll
- Printing unit
- Out-feed nip roll (positioned after the drying hood of the printing machine)
- Winder pulling unit
If at any of these points a different tension than that which has been set is detected, in excess or in defect, the flexographic printer will automatically make corrections in the tension at the in-feed nip roll level in order to achieve a constant repeat length.
With today’s automation technology we are able to detect the slightest change in tension thanks to the use of sensors located along the printing line. This allows the operator, or better still the software in a fully automatic way if automation processes are implemented, to immediately make the necessary adjustments to ensure the ideal substrate tensioning at all times.
4. Repeat length control
Controlling the repeat length is a critical aspect of the printing process when it comes to reducing material waste. This is typically done by setting registration marks which acts as a guide to ensure the image size and dimensions remain constant throughout the entire print job. The main factors that influence repeat length are:
- Tension of the material during the printing process
- Drying temperature
- Machine stability
- Tension of the material during rewinding
The drying temperature is extremely important to achieve an excellent final result. The volume and temperature of the air in the drying hoods, along with the tensioning of the substrate, must be set correctly in relation to the inks utilized in order to not cause structural damage to the substrate itself or a change in the repeat length.
When it comes to the structural stability of the machinery, it is important to understand that this is the result of a balance between all the various interdependent parts, both electronic and mechanical, that make up the machine as a whole.That is why it is necessary to combine, for example, a sufficiently robust structure with fewer joints and bolts to minimize vibrations (e.g. machine shoulders manufactured in thick mono-blocks etc...), an appropriate sizing of the motors used in relation to the various needs, an excellent mechanical rigidity of the support system of the plate holder cylinder and many other elements to achieve the best result possible without wasting product.
Lastly, it goes without saying that the rewinding of the printed material must be done with the same tensioning used in the printing process, as to not vary the repeat length obtained during processing.
In conclusion, the issue of waste reduction in the printing process is one that must be dealt with in order to reduce costs, increase the production efficiency and effectiveness and deliver a superior quality product.
If you want to find out more about waste reduction and printing automation, check out our eBook "How to Optimize the Flexo Printing Process for the Hygiene Products"!