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Developments in thermoforming: new technology opens up new applications.

Thermoforming has been used to make plastic products and parts for almost every industry, but that doesn't mean that there isn't room to grow. New technology and an economy driven increasingly driven by costs are taking the process to new applications.

"Thermoforming will continue to grow in applications," says Ken Darby, chair of the SPE European Thermoforming Division. "It is important to increase awareness of the technology and its potential."

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One of the main technologies competing with thermoforming is injection molding, but thermoforming has some strong pluses. A company would likely invest in an injection-molding system only if it knew that the volume needs for a specific product were going to exist for some time. "Thermoforming has advantages in performance and in that it is versatile," Darby says. "It can be economical because it is so flexible."

In terms of market, the U.S. and European markets have traditionally been quite different, but similarities are beginning to appear. "The U.S. market seems to like lower cost. The European market likes higher precision," says Sven Engelmann, managing director of polymer technology at Gerhard Schubert GmbH in Crailsheim, Germany. "However, this is changing because they need to lower cost in Europe as well."

The U.S. and European markets have also differed in terms of scale. "With the market becoming more global, there is more 'coming together' in technologies," Darby says. "The U.S. has a massive market and the scale is bigger, but Europe is beginning to get more interested in that."

Material Trends

In terms of thermoforming packaging materials, the U.S. market has typically used polystyrene, but it is moving to polypropylene, says Reiner Albrecht, the sales director at Illig Germany. The reasons behind this shift are many. Among them he cites polypropylene's raw material price (price in general as well as stability of prices), flexibility (no cracking), transparency, heat resistance (microwave-oven), and ability to be recycled.

Rudi Salmang, the application technology leader at Dow Benelux B.V. in The Netherlands, sees another material trend. "PET was only making some inroads at the end of the millennium, and now it is one of the largest players for the transparent packaging industry."

Sustainability is driving material choices and final product designs. More companies are decreasing the weight of thermoformed products through geometry design and by incorporating foamed cores into the sheets, Salmang says. He adds that bioplastics are becoming more interesting and are showing an increasing demand, but he believes they still have a long way to go.

In addition, there is a lot of interest in recycled materials. "In recycling, there are now stabilizers and additives that let reground substrates be used without loss of performance," Darby says.

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"Manufacturers use as much recycled material as they can because it is cheaper and good for the environment."

Darby points out that modern sheet materials are becoming increasingly complex, with multilayers being formulated for specific applications across all fields. Salmang comments, "Combined materials structures for functionality will still be the leading effort and approach, as the vast industrial experience is in this direction as well."

Microwave heating is a technology to watch. Salmang sees it becoming a true technology to improve the efficiency of the thermoforming process, and this means that materials need to be susceptible to this type of energy. For thermoforming as a whole, he expects the largest innovations to come in the trimming and finishing.

Combined Tools

Gerhard Schubert's Sven Engelmann says that thermoforming is ideal for companies processing many products and many different formats. The company's thermoforming machines are used to manufacture packaging for pharmaceutical vials, printer cartridges, toothbrushes, and foods such as cheese.

The company has a technology that combines ultrasound cutting and sealing into one tool. The ultrasound equipment is tied to the machine instead of to the format set, and the combined tool can be changed in several minutes.

When sound waves at 20,000 kHz heat the film, the vibration creates heat only at the cutting edge, which melts through the polymer as it is cut. The result is smooth edges and in some applications up to 17 times less force required for cutting, compared with conventional systems. Almost any geometry can be cut.

The ultrasound vibration can seal packages in only 200 to 400 milliseconds--much faster than the 1 to 1.5 seconds typically required with heat sealing. This sealing process requires energy for only milliseconds each cycle, whereas heat sealing constantly uses energy to keep the heat plate hot. The tool remains cool, which is important for packaging temperature-sensitive products such as chocolate.

Engelmann says that the company is working on new heating technologies for film and more automation for tool and mold changes.

"There will be more applications for thermoforming as more people realize it is compatible with other plastics manufacturing technologies, is flexible, and cost-effective," Engelmann says.

Quick Labeling

Illig Maschinenbau GmbH & Co. in Heilbronn, Germany, manufactures machinery and tooling for thermoforming; it has a technology that can speed in-mold labeling (IML) of thermoformed cups.

IML involves applying labels during the manufacturing of a container. The plastic label is integrated into the final product. In the past, IML thermoforming used a glue to adhere the label, but Illig's third-generation IML line uses heat instead. "The thermoform process on our third-generation machines is much faster," says Illig's Albrecht.

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The labels are integrated into the normal thermoforming process, with the heated polypropylene (PP) film's surface remaining hot enough for the PP label to combine with the thermoformed cup. "The labels today without the glue layer are the same price as labels used in injection IML," Albrecht says. "And there are several suppliers of these labels."

The company has a client in Austria using the IML line to apply 50- to 70-um-thick labels to yogurt cups. Albrecht points out that there are many advantages to using thermoforming for this type of application. Worldwide, companies want to reduce cup weight, he says, and thermoformed cups are 15% to 20% lighter than injection-molded ones, while remaining sufficiently stiff.

Less material saves material costs and means better environmental sustainability, as does the lower energy requirements for thermoforming (as compared to injection molding).

In addition, unlike injection molding, thermoforming allows integration of barrier layers that can extend the shelf life of food products. For example, a layer might be designed to keep out oxygen or to protect food that is frozen.

Injection molding can typically produce about 10 cycles in a minute (4 to 8 cavities), while Illig's machine has 16-cavity tools and can produce 18 to 20 cycles per minute.

"Injection molding was first on the market, so customers are more familiar with it," Albrecht says. "It is not easy to get into the market." However, the company has sold systems to at least two customers that have switched from injection molding to thermoforming because of the cost savings.

Thermoforming holds advantages for bottle forming as well. Here, blow molding is the primary competing technology. IUig hopes to get into this market with its new bottle thermoformer, Albrecht says. Thermoformed bottles are lighter than blow-molded bottles. For example a blown bottle weighing 6.5 grams can weigh 2 grams less if thermoformed.

The company is working on more automation for its lines and also plans to introduce a system that allows computer control of the whole line from one location rather than from various sites along the line.

Microscale Thermoforming

Thermoforming is being applied on a smaller scale to make film-based biomedical microdevices. These include biochips for cell culture and tissue engineering as well as lab-on-a-chip devices, which have a small footprint and can perform analytics with small amounts of sample.

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However, for these small devices to find more common use, possibly even getting into the doctor's office, requires manufacturing methods that can replicate them and make precise patterned surface modifications on the microscale.

Roman Truckenmiiller from the University of Twente in the Netherlands, Stefan Giselbrecht of Karlsruhe Institute of Technology in Germany, and colleagues from other institutions developed microscale thermoforming techniques mainly for making planar, chip-type devices such as cell culture chips or PCR cartridges but that can also produce tube-like devices such as a pressure-driven microcatheter (Lab Chip, 2008, 8, 1570-79).

"The advantage of using thermoforming for these products is that it can provide parts with much thinner walls compared to all other polymer microreplication processes (microinjection molding, hot embossing, etc.)," say the researchers. Thin walls allow the use of small material quantities in terms of volume and mass, high flexibility, low heat resistance and capacity, high permeability (or low permeability with multilayer barrier films), and low light absorption and background fluorescence. For the microcatheter, thermoforming is easier to scale down than blow molding, they say.

In the researchers' method, called substrate modification and replication by thermoforming (SMART), the material modifications of the unformed film during the pre-process define where later modifications will take place on the spatially formed film. Then the post-process generates the final local modifications. The technique allows highly resolved patterns to be added to hard-to-access side walls and behind undercuts.

Microscale thermoforming is still a technique performed only in the lab, and the researchers say that developments in the technology are focused on new processes such as forming by temporary back-molding, machines for small and medium-scale production, and new tool concepts with low thermal masses or that allow easy or no evacuation of the microcavities.

They anticipate multiscale thermoformed devices in the future. "Such devices will combine functional structures with characteristic dimensions ranging from the micro- or nanoscale to the miniature or macroscale in one single piece." Extending plastic parts by functional substructures adds value and functionality, and using parts molded in one piece rather than assembled from multiple pieces reduce costs for the device, they say.

They also see technologies coming together in the form of microthermoformed devices integrated into devices manufactured by microinjection molding or hot embossing. "In this way, the characteristics of thermoformed, flexible, and adaptable film microdevices could be combined, for example, with the rigidity and shape definition of injection-molded devices."

Software Savings

Computers and software play an increasingly important role in today's thermoforming machines and processes. "Today there is a high degree of sophistication in the machines," says Ken Darby of the SPE European Thermoforming Division. Everything is controlled by computer--the temperature, deloading, part movement, and mold release. "Computer-based programs ensure that every stage of the process can be accurately monitored and controlled, resulting in improved quality and less waste," he adds.

Toolvision is a data-logging system made by Schoberl Messtechnik in Zusmarshausen, Germany. It uses sensors in the tool and machine frame to allow users to watch and document every stage of the thermoforming process. The data can save money and increase quality when it is used, for example, to standardize the process for an individual product or to enhance the availability of the tool. The system can identify problems such as a double product in the cavity because the strain gauge is too high or a hole in the product occurring because the vacuum is losing pressure. It can also let the user know that the process is running properly.

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In addition, the software can track the condition and maintenance history for a tool. This allows the calculation of the cost of maintenance downtime and elimination of any detected weak points.

The software collects data that includes the temperature in various locations, plug position, punch force, forming pressure, and vacuum status. Peter Schoberl, CEO of the company, says that around 30 customers have installed the software.

Another tool for thermoformers is simulation software, which can save time and money by allowing simulation of production before an actual product is made. One such software package is T-SIM (www.t-sim.com). It was developed twelve years ago by Accuform in Jetelova, the Czech Republic, in collaboration with a group of academic researchers, molders, and machine manufacturers. The software has continuously improved since.

"T-SIM lets processors and designers see, with a high degree of accuracy, what the product will look like before a tool is cut," says David Russell, the UK agent for TSIM. "Its 'what-if' capability allows changes to design and processing conditions to optimize the product and minimize the cost."

Technical thermoformers in heavy-gauge and thin-gauge applications, materials suppliers, and endusers all use the software, and univerrsities use as a teaching aid. T-SIM lets users better understand their process by using the measured flow characteristics of the actual material grade being molded to predict thickness distribution based on parameters such as pressure level, speed of tools, and sheet temperature distribution.

"The latest version, just released, can optimize the design of the plug-something molders have wanted for years," Russell says. He adds that it has always been difficult to design the best shape of plug; this is normally accomplished through expensive trial-and-error. The ability to do this automatically with the T-SIM software can save a lot of cost and time and ensure better quality moldings.

The software holds the most benefit for packaging, the largest thermoforming sector. "A saving of even 9% on material and processing costs multiplied by thousands or millions of moldings is a substantial amount of cash," Russell says.

Russell says that T-SIM is more accurate than 'add-on' CAD simulation packages. He adds that T-SIM will continue to be further refined with increases in accuracy and the addition of extra features in response to needs identified by users. Accuform also offers similar simulation software called B-SIM for blow moulding.

"As a long-term believer in thermoforming, and particularly in today's economic circumstances, I see its role in reducing risk as a main opportunity for the future," Russell says. "The process's benefits need to be better communicated to the decision-makers so that they select the process and design for it. But it must offer state-of-the-art technology as already offered by other processes, i.e., simulation to optimize designs and cost off-line."

Sturdy and Shock-Absorbent Packaging

product developers have to examine the capabilities of any manufacturing method they choose, and the thermoforming process can offer advantages and flexibility for product design.

Protective Packaging Systems Ltd. of Stratford upon Avon, UK, a designer of protective packaging, chose thermoforming when designing a new packaging system. The technology allowed the design of an effective and cost-saving product called the Lo-g-pax system. The one-piece wrap replaces the multiple elements often used in packaging such as foam, cardboard, bags, and twist ties.

"Thermoforming allows the engineering of impact-absorption features into the package, resulting in an overall reduction in the number and size of packaging elements as well as the volume of the finished article," says Jeff Pitt, director of the company.

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The packaging has individual cavities to hold all the products, such as a laptop and its associated cords and accessories. The elastic nature of the thermoformed material allows springs on the inside, buffers that protrude outside, and bellows at the end of the unit to act to like an accordion to absorb any impact during transit.

"Today manufacturers are moving away from excessive packaging toward recyclable, lighter, less bulky packaging," Pitt says. Lo-g-pax is reusable, recyclable, and lightweight, making it environmentally friendly. Its one-piece design allows rapid assembly, which improves output and reduces labor costs.

The company used high-density polyethylene because it is readily recyclable, tough and durable, and can absorb impact. But Pitt points out that this material is not the easiest to process. It requires well-engineered thermoforming tools and, preferably, high pressure forming equipment.

The versatile nature of the process means it is easy to change the gauge of material to match the required packaging performance, resulting in cost savings. The company has global patents on the Lo-g-pax system and its other Lo-g packaging designs, and the designs can be tailored to a specific product, ranging from electronic goods to large white goods.
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Comment:Developments in thermoforming: new technology opens up new applications.
Author:Lamontagne, Nancy D.
Publication:Plastics Engineering
Geographic Code:1USA
Date:Apr 1, 2010
Words:2654
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