Converting companies are companies that specialize in combining raw materials such as polyesters, adhesives, silicone, tapes, foams, plastics, felts, rubbers, liners and metals, as well as other materials, to create new products. Some of the top converters in the industry are Sealed Air Corporation, Bemis Co. and Sigma Plastics Group.
Materials such as paper, plastic film, foil and cloth often are produced in long, continuous sheets that are rolled up for more-convenient handling and transportation. These rolls of material vary significantly in size and weight — ranging from 2 to 200 in. wide and weighing as much as several tons. The converting industry takes these continuous rolls of thin, flat materials — known as webs — threads them though processing machines (such as printing presses, laminating, coating and slitting machines) and converts or changes the web of material into an intermediate form or final product. For example, a converter’s equipment might take a web of plastic film, cut it into lengths, and fuse their edges, thus converting it into plastic bags. This activity is known as web processing.
Typical converting processes are coating, laminating and printing. Coating technologies can include hot melt coating, gravure coating, curtain coating and slot-die coating. The most common printing techniques are flexo printing and rotogravure (gravure) printing. Both print processes are suited to high speed roll to roll processing.
Many converting companies will process large diameter, wide rolls of material as this increases the converting efficiency by minimising changes. On completion of the converting process the rolls may be cut into smaller rolls on a slitting machine. These rolls are then a convenient size for handling on packaging and other machines. Alternatively, the rolls may be sheeted-cut into sheets — as happens in newspaper and book printing. Further processes such as collation may occur after sheeting.
Web alignment is an important part of a converting operation as a moving web of material has a tendency to track off course and wander out of alignment during the converting processes. To avoid these problems, engineers have developed a variety of automatic web-guiding systems that assure production accuracy and reduce waste. Web-guiding systems typically are positioned just before a critical stage on a converting machine (for example, just before a print station on a printing press).
Each type of web guiding system uses a sensor to monitor the web position for lateral tracking, and each has an actuator to shift the running web mechanically back on course whenever the sensor detects movement away from the set path. Actuators may be pneumatic or hydraulic cylinders, or some kind of electromechanical device. Because the web may be fragile — particularly at its edge — non-contact sensors are used. These sensors may be pneumatic, photoelectric, ultrasonic, or infrared. The system’s controls must put the output signals from the sensors in to a form that can drive the actuator. Many controls today are electronic, typically using an amplifier to convert signals from the sensor, then commanding a special servo motor incorporating a lead or ball screw for guiding actuation. The latest web guiding systems have touch screen controls to simplify the set up procedure. Some web guiding systems have been designed specifically for the converting industry.
Many converters specialize in
- Adhesive coating to make labels and adhesive tape;
- Silicone coating to make a release liner;
- Die-cutting materials into finished parts or labels;
- Printing services;
- Roll slitting of wide webs into narrow webs or coils;
- Laminating services; and
Some converting companies now incorporate electronics in their finished products. For example, converters producing RFID stock labels must incorporate RFID chips and antenna inlays. The electronic components make up the RFID tag. The tag stores the information about the items that has been tagged. These converters therefore sometimes incorporate volume electronics manufacturing practices including controlling static electricity, electronic manufacturing test and similar processes. Solving some of the issues of inclusion of materials sensitive to external influences has led to more tech companies embracing roll-based manufacturing processes, with particular success in the lithium ion and solar cell manufacturing sectors.