It’s a big step up—in both volume potential and technology requirements—from molded automotive headlamp covers to window glazing. Polycarbonate has dominated the market for vehicle headlamp covers for 15 years, but until now it never challenged glass in windows. Now, advances in materials, machinery, and tooling do more than overcome previous limitations. PC glazing is being molded into ever-larger parts that save considerable weight and offer styling and design potential—such as distinctive 3D shapes—that glass cannot match.
“The wide choice of styling options possible with PC is testing conventional assumptions of window design,” says Paul Platte, director of automotive industry innovation at Bayer MaterialScience. “This is creating a whole new world for the shape of the vehicle. Molders can incorporate features such as holes in the window, or a sharp corner or smooth corner radiuses, or complex 3D shapes on just one edge of the part. With laminated or tempered glass, features such as these are undesirable, unmoldable, and cost-prohibitive. In polycarbonate they can be done readily.”
Glass auto windows are produced up to 1.5 or even 2 m2. With the latest technology, PC auto glazing can be molded up to 1.4 m2 (around 15 ft2), although some believe sizes up to 2 m2 (21.5 ft2) aren’t far off. Larger auto glazing can deliver weight savings up to 50% versus glass.
Parts integration is another new benefit that PC glazing brings to the table. “We are able to create a roof-module frame and optical panel in one piece, allowing for parts consolidation and weight savings,” says Dr. Gerald Aengenheyster, managing director of Freeglass GmbH in Schwaikheim, Germany, a molder and pioneer in PC auto glazing.
PC auto-glazing is spawning new design concepts such as a side window with the rear-view mirror mounted on it rather than on the door panel, and vehicle roofs that wrap onto the rear of the vehicle. Unlike glass, PC glazing can now have integral ribs or brackets to lock the parts onto the vehicle or support another feature. There has even been some success in molding heating/defrosting elements and radio antennas into a PC window panel with in-mold films that have preprinted circuitry.
Current applications include front and rear quarter windows, fixed side windows, rear-door fixed window sections, small transparent body panels, and panoramic roof (sunroof) systems. These applications are concentrated in Europe at present but the advantages are attracting Tier One automotive suppliers in Asia and the U.S.
Recent developments in scratch-resistant coating systems have significantly broadened the PC glazing market in the U.S. Until last June, PC was limited in the U.S. to non-passenger areas of the vehicle, typically in back cargo areas of SUVs, though there are no such applications yet in the U.S. Regulations are less stringent in Europe and Asia.
In June, The U.S. Dept. of Transportation’s National Highway Traffic Safety Administration (NHTSA) approved the Exatec 900 material and coating system from Exatec LLC, the GE-Bayer joint venture, for all non-windshield glazing, provided that it meets all existing auto glazing specifications for laminated glass. NHTSA determined that no new regulations were necessary—rather, PC glazing can be validated using existing specifications for laminated glass. “It is now possible to use PC in all non-windshield locations globally,” says Exatec CEO Clemens Kaiser.
Manufacturing of PC auto-glazing requires a special set of manufacturing techniques that go beyond the conventional in machinery, molds, materials, and processing methods. Every phase of the process is undergoing intense development.
First, the new auto glazing parts are large—up to 1.4 m2 (around 15 ft2)—and they must to be molded under low-stress conditions for optical quality and for retention of a hard coat. “Residual stresses in the part negatively influence optical quality as well as coating quality,” says Kaiser. “High stress in the part can lead to haze or delamination of the coating. Injection-compression rather than conventional injection molding is the ideal process for making large parts with low stress.”
In fact, the pressures for PC glazing are low even by the standards of normal injection-compression. These parts are molded with injection pressures from 2600 to 2900 psi versus approximately 3050 to 3500 psi for typical injection-compression molding.
Machinery suppliers such as Battenfeld, Engel, and Krauss-Maffei have developed injection-compression processes to meet these low-pressure, low-stress requirements. Because large glazing panels are essentially thin-wall parts and must have parallel surfaces for good optical qualities, molding machines must be able to maintain close parallelism of platens and molds—i.e., within 0.1 mm.
New tooling concepts were developed by European firms such as Summerer to keep the pressure on the material low throughout the molding cycle. Hot-runner designs were also affected by the new molding criteria, and firms such as HRS, Mold-Masters, and Synventive were among the first to respond.
New PC materials had to be developed for good flow, higher optical clarity than conventional materials, and adhesion to a hard coat. Bayer MaterialScience and GE Plastics each developed advanced PC resins expressly for this market. Part thickness averages 4 to 5 mm, and the flow-length to thickness ratio is around 300:1. “So in effect, we are speaking of thin-wall parts,” says Engel’s Markus Kralicek, manager of applications engineering for large machines.
At the same time, post-mold coating technology had to advance in order to deliver high resistance to abrasion, scratching, and uv exposure/ weathering, as well as good light transmission and anti-reflective properties. This led to proprietary “wet-coat” formulations as well as a new wet-coat/plasma-coating technique.
Exatec was created by Bayer and GE in 1998 to develop premium coating technology for this market. Exatec and other suppliers have created silicone hard coating technologies for use with polycarbonate that are applied at temperatures ranging from 302 to 350 F. The coating process takes about one hour. At least one supplier of glass coatings, Schott HiCotec in Germany (U.S. office in Elmsford, N.Y.) is adopting its glass-coating process for plastics.
Multi-component molding is emerging as another requirement for auto glazing, especially the larger parts. “All of the commercial applications are and will be two-component parts,” declares Joachim Berthold, head of process technology at Battenfeld. “A second material is typically used as the frame or border and serves to hide gate marks and any functional elements mounted on or molded into the part while keeping the exterior part shape seamless.” The challenge here is that both materials of the two-component process must be molded at low pressure conditions to minimize stresses. Most of the commercial glazing applications have a transparent center overmolded with a darker, more opaque frame.
Molders are turning to injection-compression machines with rotary center-stack tooling for two-component overmolding of glazing. According to Engel’s Kralicek, “The two-component part is best molded in one press with two injection units. It is easier to handle in a single press rather than in a transfer process using a robot between two separate machines. Molding the completed part in one cycle can mean using the same resin for consistent temperature and uniform shrinkage of material and better part quality.”
Auto glazing also requires some modification of hot-runner and gate designs. “A molder should inject quickly into the mold yet with as little shear as possible, so special gate designs are required,” says Kralicek. All molding of large auto glazing today uses off-center gating to avoid a visible gate mark. Three approaches include film edge gating, in which excess material containing the gate is removed from the part in a secondary operation. There is also the option of direct gating using either a large single gate or sequential valve gating.
The huge potential of PC auto glazing is driving investment in new processing plants by automotive part molders who are collaborating with glass suppliers, moldmakers, and hot-runner firms. Material suppliers are bringing their own technical centers up to speed as well. At present this activity is still concentrated in Europe, where more than a dozen applications are already in commercial production. There are several more projects in the pipeline and numerous concepts under evaluation.
Freeglass is the unquestioned world leader in supplying automotive glazing parts. It was created in 2001 as a 50:50 joint venture of Saint-Gobain Sekurit, a leader in European car glazing, and Schefenacker, the world’s leading maker of exterior mirrors. Freeglass is dedicated to producing large and small auto glazing parts. It uses MX two-platen machines from Krauss-Maffei; a brand-new 2970-ton IMPmore system from Battenfeld; resins from Bayer, GE, and Teijin of Japan; and its own polysiloxane wet-coating technology. Freeglass molded around 1.5 million PC glazing parts in 2005 and expects to hit 5 million by 2008. It has five injection presses from 242 to 4400 tons, all dedicated to automotive glazing.
Another glazing producer is Organikglass in Carate Brianza, Italy, created late last year by Ranger S.p.A., an Italian molder of automotive technical parts. The new company is dedicated to the production of two-component side and rear windows and panoramic roofs.
The plant has as its centerpiece an Engel 1650-ton Duo Combimelt injection-compression machine with Glazemelt technology. The press has two injection units and a horizontal rotary table. It can mold parts up to 1100 x 800 mm. The facility also has a silicone hard-coating line in a Class 100 cleanroom environment. The firm will use GE’s Lexan GLX auto-glazing material. Ranger also produces the molds for Organikglass.
Organikglass just began production last month of a window for a vehicle being sold in Europe this year. The company is working to validate several other components. “Today we can mold a roof up to 0.8 m2,” says Matteo Terragni, Ranger’s R&D manager.
INglass Group, San Polo di Piave, Italy, is the new name of the Incos Group, an Italian moldmaker and owner of HRS hot runners. The new name signifies its new focus on molds for large auto glazing. The new operation benefits from its parent’s tooling expertise in multi-shot tooling as well as hot-runner know-how for two-color PC from Incos’s HRS Div. INglass installed a 2530-ton Engel Duo Combimelt machine with Glazemelt technology, which will be used to develop and test tools it produces for two-component auto-glazing parts. It has other machines from 220 to 1650 tons for mold tryouts. It can produce a two-component part up to 2 m2, says Alessandra Bosco, manager of global business development. She adds that INglass has built the tool for the “largest two-component PC glazing component with a complex shap ever used on a production car.” It’s a tailgate window for the Honda Civic, molded by Freeglass. INglass will show one of its two-component tools for auto-glazing at NPE.
CleverGlass is a new company created to mold PC glazing by automotive molder Cadence (formerly known as Peguform) of Liberec, Czech Republic. CleverGlass expects to produce up to 2 million m2 (21.5 million ft2) per year of PC glazing for side and rear windows and sunroofs after it starts up in 2007. The new facility will use Lexan GLX materials.
Two other auto glazing molders are WebastoAG in Stockdorf, Germany, a sunroof system producer that is just gearing up for glazing production; and the former Dynamit Nobel Kunststoff (DNK) of Weissenburg, Germany, an auto-parts molder recently acquired by Plastal Holding AB of Sweden. DNK/Plastal is molding a rear window for the Mercedes CL.
Hitting the road
North Americans may not realize how many PC auto glazing parts are already on the road in Europe. Freeglass is producing a five-segment, two-component, grey-tinted panel as part of an optional lamella system for Mercedes A and B Class cars. Freeglass is also making a B-pillar finisher that resembles dark-tinted glass for Mercedes’ CLS model, as well as a fixed side window for the DaimlerChrysler Smart coupe, both a fixed door window and front panorama roof panel for the Smart ForFour, and a rear fixed side light for SEAT. This year Freeglass began producing a 1.2-meter-wide tailgate window for the Honda Civic. The first shot of clear PC is overmolded with black PC, reportedly a very challenging application.
Bayer sources note that adhesive technology is vital to applications like PC panorama roofs because the plastic’s thermal expansion is five times that of steel. A suitably elastic adhesive and the location where it is applied are the keys to allowing the plastic to grow and shrink, says key account manager Frank Schiemann.
Panoramic roofs, which are the high-end of the PC glazing market, are expected to emerge this year from German automakers and in Japan in 2007, says Exatec’s Kaiser.
Three machinery suppliers have their equipment and process technology in use or slated for use in PC glazing projects, and a fourth will be unveiling its technology at NPE. Each machinery supplier has a different concept for the coining (injection-compression) process. Variations include coining by moving the machine platens or moving mold sections independent of platen movement.
Engel’s Duo Combimelt Glazemelt model now features improved injection-compression ability that delivers higher optical quality, says Kralicek. “Our compression process can be adapted to the part with either a smaller or larger coining gap. For a “long coining” approach, the tool gap is open at the start of filling and pressure on the melt increases during the coining/compression stage,” he explains. “One can also opt for a “short coining” approach, which starts with a smaller gap at the start of injection. Here the melt is under higher pressure during injection, followed by lower pressure during coining,” says Kralicek. The selection of one process over another is determined by part parameters. Engel’s control for Glazemelt has a 6-millisec response time and ±25-micron resolution to maintain tool parallelism. Engel will show newly developed Glazemelt technology at NPE. Engel’s largest Glazemelt press to date is a 2530-ton Duo Combimelt Glazemelt unit that can mold parts up to 1.8 m2 (19.4 ft2). Glazemelt technology is available on presses up to 4400 tons.
In 2000, Krauss-Maffei came out with its Spinform line, which consisted of its MC-Series two-platen machines with a sliding central rotary platen. The two-platen line has been redesigned and is now called the MX line. The MX Spinform system ranges up to 4400 tons. The clamp has active parallelism control with 5-millisec responsiveness.
In addition to standard injection-compression, Krauss-Maffei employs an “expansion-compression” technique. The process starts with the mold completely closed at the start of injection and then expands the cavity through moving mold sections as the part fills. First, the cavity is filled completely, then the cavity is enlarged under controlled pressure as additional melt is injected. At a predetermined point, the gate is closed and compression force is applied to compensate for the shrinkage of the plastic, like a holding pressure distributed over a large area. This technique requires very careful monitoring and control of clamp stroke. The reported benefit of this measure is that it addresses the phenomenon of jetting that occurs with standard injection-compression molding.
Last year Battenfeld created the Wendi platen, a rotary stack concept that allows for two-component molding in one machine. The system runs with Battenfeld’s HM two-platen series, which features its Vector Force Control module (VFC) for platen parallelism. Battenfeld also teamed up with moldmaker Summerer, which has created new tooling designs for auto glazing (see below).
All of Battenfeld’s current and future auto-glazing applications will use the Wendi platen approach, says Berthold. The company has a 1430-ton Wendi platen unit at its lab in Meinerzhagen, Germany, which will be moved to a new facility near its world headquarters in Kottingbrunn, Austria. The company has also built two 2970-ton Wendi machines with the IMPmore technology, one of which was recently installed at Freeglass.
Husky is developing multi-material glazing applications for its new Quadloc Tandem Index (QTI) machine at its Luxembourg technical center. This two-platen machine has a center stack that rotates 180° on a horizontal axis to permit molding the first and second components simultaneously using conventional tools.
Summerer developed the In-Mold Pressing (IMPmore) process together with Battenfeld. It uses an articulated mold with a tilting top half that pools the melt under low pressure and then squeezes the melt down into the rest of the cavity. A row of retractable hydraulic cylinders extends toward the other mold half to provide counterpressure during initial injection. The cylinders retract to a flush position during the compression stage.
Summerer’s IMPmore tooling can be used with other presses besides Battenfeld—for example, Krauss-Maffei has two projects using this technology. In addition, Summerer has developed “advanced parallel compression molding” for parts up to 1 m2 (10.75 ft2). Also, its Gate Sealing technique uses a special sliding valve for direct gating of the part. “The sliding valve functions similar to a needle valve, but the design eliminates the chance of black specks ending up in the part,” says project leader Gerald Birner.
The problem with a needle, he says, is that imperfect mating between a needle and bushing can create or hold degraded material. Instead, Summerer uses a hydraulically driven bar inside the mold between the injection nozzle and cavity. The “slider bar” has a special S-shaped channel cut into it. When the slider is in the molding position, melt flows into the cavity, entering from the bottom of one side and exiting on the top of the opposite end. A recess in the channel opposite the melt entry point catches cold slugs or specks from the previous shot. When mold filling is complete, the slider moves to an idle position, closing off the cavity, and compression takes place. This allows residual melt in the channel to cool. The slider then moves to an ejection position where the cold slug is pushed out by the ejectors at the same time that the part is ejected from the mold. The system was developed for auto glazing. It is used with the same tilting-tool design as in IMPmore.
MeltSealing is another technology from Summerer for glazing applications. It allows production of flash-free edges with smooth radii, even in combination with in-mold film laminating.
INglass also has developed tooling technology for injection-compression. “The compression step is carried out by the machine. However, the tool itself is actively controlling the cavity pressure and the parallelism between the tool plates,” says Bosco. INglass also developed a sequential direct-gating system with a cascade control to deliver low shear, low stresses, and no witness lines.
Another German moldmaker active in glazing is Hofmann Werkzeugbau GmbH in Lichtenfels. It has built a mold for a Smart car glazing application at Freeglass.
Mold-Masters reduces stresses in auto glazing by using a larger melt channel, says Michael Schiele, marketing manager. For these applications, Mold-Masters uses a modified version of its Dura nozzles in the Hecto size.
Special PC resins are needed to deliver higher clarity and impact strength than standard grades. Bayer and GE Plastics have developed specialized resins for auto glazing. (Freeglass is also using PC from Teijin of Japan.) At least 70% of current applications use Bayer’s PC, according to Volhard Krause, head of the firm’s auto glazing team in Germany. Its Makrolon 2607 was used in one of the earliest glazing parts, a front section of a panorama roof for the Smart car. In 2004, Bayer rolled out its Makrolon AG-2677 grade, which has improved optical purity and a balance of high flow and good impact resistance required for large parts like roof modules.
GE’s new entry is its Lexan GLX grade, which is being used for the first time on a panoramic roof for a prototype minivan. The three-panel roof appears on the ASC TriLite, a modified Toyota Solara designed by specialty-vehicle company ASC. Inc., Southgate, Mich.
Derek Buckmaster, GE’s global market director for body panels and glazing, notes that GE Plastics is conducting R&D on large glazing and bod-panel applications on a Krauss-Maffei MX injection-compression press at its Plastics Global Application Technology center in Bergen op Zoom, Netherlands. In addition, GE’s application development center in Shanghai will also conduct research into glazing and body panels in cooperation with Husky.
Both Bayer and GE are just now coming out with brand-new infrared-blocking grades designed to reduce heat flow through panoramic roofs. Bayer says its IR-absorbing transparent colors can cut IR transmission by up to 50% compared with standard colors.
Coatings are as essential to this application as the base material. The polysiloxane coatings are similar in chemistry to those used to coat headlamp lenses but are upgraded for higher performance.
Exatec’s latest offering is a special wet-coat and plasma hard-coat system that comes in two versions. Its Exatec 900 system is aimed at general glazing applications, while its newest 900VT (Vehicle Top) system, introduced last September, is designed expressly for panoramic roofs, says Kaiser. It offers significant cost savings by applying a hard coating only to the inside of the part instead of both sides.
The 900 series is a system that includes a PC substrate (from Bayer or GE), a water-based adhesion promoter (Exatec SHP 9X), a 10-year proprietary weathering layer (Exatec SHX), a uv-protection layer, and a glass-like plasma-enhanced chemical vapor deposition (PECVD) hard coat. The 900 system passes the Taber abrasion test, keeping haze under 2%, says Kaiser.
Exatec also offers 2D and 3D printing technologies suitable for use with the PC glazing systems, and has developed bonding methods to join the panels to the structure of the vehicle. In 2008 Kaiser expects to see the first vehicle hit the road with Exatec’s new plasma-coating solution.“It will not be a roof,” he adds.
Another coating supplier, Schott HiCotec, originally developed its plasma-impulse chemical vapor deposition (PICVD) technology for glass, but it is now being transferred to plastics. The challenge was to develop a process to apply several different functional coatings that add scratch resistance and reduce reflections and dust pickup in one operation.
Ranger’s Organikglass division has developed a flow-coating line designed to eliminate waste that can plague standard lines. Terragni says this new capability combined with its know-how in producing vehicle panel structures is moving Ranger Group toward supplying complete modular roofing or door systems. He foresees that parts like a rear panel with a windshield wiper could need a harder coating than is provided by Ranger’s current technology. He speculates that a plasma hard coat might be needed.
Coatings may not be enough to allow PC entry into movable side windows. Door panels will require redesign to eliminate metal parts that can cause scratches.
What lies ahead?
Future developments in coating technology could add strength to glazing parts or could contain electro-chromatic elements that let the driver control the amount of light entering the vehicle.
On the other hand, machinery suppliers report there is speculation that coatings might be replaced altogether by a second overmolded thermoplastic resin component such as acrylic (PMMA). “The idea behind this is that using a second component such as PMMA instead of a hard coat would allow a molder to produce completely finished parts right out of the mold,” says Bernd Klotz, application technology leader at Krauss-Maffei. “This approach would eliminate downstream coating and reduce the chance for scrap generation during parts handling. The second component could be applied in a relatively thin layer on the polycarbonate at the same cost as a coating.” However, bonding of the PC and the PMMA under low pressure is an unresolved issue.
Other avenues may include a hard coated PC that is then overmolded with a TPE. FreeGlass says it is using this approach to make a window with a surround. The TPE has a natural adhesion to the PC, so no prior cleaning or priming is needed.