The rechargeable battery manufacturer MOLL located in the northern Bavarian town of Bad Staffelstein is a specialist in battery technologies with over 60 years of experience in the field. MOLL has been an original equipment manufacturer for the auto industry for several decades now and supplies vehicle batteries to customers such as Audi, Volkswagen, Porsche, Seat, Liebherr, Lamborghini and Terex Demag, as well as to retailers. The company places particular importance on continuous innovation and has already developed a diverse range of industry-related patents. MOLL batteries are being continuously further developed and adapted to the current trends and requirements of the auto industry.
The demand for permanent traceability
A fundamental requirement on auto suppliers today is the labeling of all supplier parts in order to guarantee permanent and complete traceability. Vehicle batteries prove to be particularly difficult to label in practice. Battery housings are subjected to high temperatures, need to be acid-resistant, and significant material expansion is also likely to occur. The labeling employed therefore needs to be exceptionally durable and meet stringent specifications.
MOLL was faced with the task of applying a continuous serial number in the form of a 2-D datamatrix code onto its battery housings made from black polypropylene. The marking needed to fulfill the necessary durability standards as well as being both machine readable and recognizable with the naked eye.
MOLL tested various marking methods for its battery housings. Both pad and inkjet printing were not able to deliver the required durability. The use of adhesive labels was precluded because they can be damaged or removed. While labeling of the housing by means of laser direct marking provided durability, the readability was not acceptable. Direct marking did not achieve the desired color contrast between the label and the black background.
Laser Color Transfer produces durable and clear labeling
This is where the novel marking system from the stamping foil manufacturer KURZ came into play. The so-called Laser Color Transfer (LCT® 1) method is a patented labeling technology for thermoplastic resins that was jointly developed by KURZ and the pigment manufacturer Merck. LCT® combines the advantages of color printing and laser direct marking. The designs are produced digitally, without the use of printing plates, and are therefore readily interchangeable. This makes LCT® ideally suited for the printing of continuous numbering. At the same time the process offers color contrasts equal to that of color printing, and significantly higher durability than, for example, inkjet printing. In the LCT® process, the ink is released from a transfer color ribbon by means of a laser beam and thereby transferred to the plastic part being decorated. Through the application of heat, the ink and plastic fuse together to form a permanent bond.
Design and laser specialists act as project partners
MOLL commissioned KURZ, in conjunction with DOMINO, a labeling specialist and laser manufacturer, and the design office Will's Ideenschmiede, to incorporate the LCT®-based housing labeling operation into the overall battery production process. Will's Ideenschmiede supervised the overall production line and ensured the trouble-free integration of the labeling operation within the production process.
The company DOMINO supplied a suitable laser for the labeling operation. The intensity of the laser beam, the focal length and the labeling speed needed to be tailored to the transfer technology and the actual processing times within the battery production line. DOMINO, in consultation with KURZ application engineers, determined the required laser settings and the optimum separation distance of the foil.
The labeling unit
The LCT® labeling unit developed by KURZ comprises a motorized foil feeding unit with supply and take-up facilities for the transfer foil rolls. The unit can accommodate foil rolls with a width of up to 100 millimeters and a diameter up to 120 millimeters. As the labeling process requires very good contact between the LCT® foil and the substrate, the unit is equipped with a pneumatically-controlled, movable clamping facility that enables a vacuum to be created between the foil and the substrate being labeled. The unit also includes a laser mount that guarantees a vibration-free suspension and stable positioning of the laser. In addition, the unit has been provided with the necessary fittings and connections for fixing it in place and creating a flange connection to the machine or conveyor bed.
Laser Color Transfer in the production line
The labeling unit was integrated as the first work center in the battery transport and handling system designed by Will. The empty battery case is delivered to the work center by means of a conveyor belt and positioned and fixed in place. The central production controller installed by Will then initiates the labeling operation. First a vacuum is established between the foil and battery case, then the laser is activated to heat the foil and substrate thereby releasing the ink layer from the transfer ribbon to form a permanent bond with the plastic. The carrier foil is then advanced for the next cycle. This operation requires about five seconds. To provide easier access to the markings, the housing is labeled again in a second location. The complete labeling unit is mounted on a transverse sliding carriage that can be displaced to produce the second marking. The two labeling operations, including the carriage displacement, are performed within a cycle time of about twelve seconds. The battery housing is then available for the subsequent processing operations.
The new labeling method is now well established within the serial production facility at MOLL. The battery manufacturer is very pleased with this innovative labeling solution, which not only fulfills the requirements of the vehicle manufacturer but also its own quality requirements.