Barex Resins Thermoforming Barex Resins are clear, rubber modified acrylonitrile copolymers, developed and marketed primarily for their chemical resistance, gas barrier, and high modulus (stiffness). Barex Resin s high rigidity combined with even material distribution and excellent flow characteristics during thermoforming allows superior material utilization and source reduction. The high melt strength of the polymer allows for extremely deep draws to be achieved, while flow characteristics allow for extremely fine mold detail to be achieved. Additionally, a broad thermoforming temperature range allows a wide processing latitude resulting in low scrap rates and fast cycle times. Because of these excellent thermoforming properties, clarity, and low density, Barex Resins are very competitive with the more commonly used thermoforming materials. Some commercial thermoforming applications for which Barex sheet is in common use includes processed meats, pharmaceuticals, portion packs, air freshener containers, cosmetics, candy molds, and more. Thermoforming Although thermoforming is often regarded as a relatively simple process whereby plastic articles can be formed with heat and pressure (vacuum), the mechanisms involved to facilitate flow and deformation are actually extremely complex. The plot of ultimate strain as a function of temperature shown in Figure 1 can be used to determine the temperature for the desired draw ratio and how necessary it is to maintain this temperature during thermoforming. An ideal thermoforming material will have a very rapid increase in ultimate strain and elongation at break with increasing temperature and with little or no decrease at higher temperatures. Since the strain-temperature curve is relatively broad, the thermoforming temperature range to form good parts is also broad and will not be as critical as it would for other thermoplastics. Figure 1: The thermoforming envelopes show the higher draw ratio and a broader forming temperature range for Barex 210 sheet
Visco-Elastic Properties The high melt strength of Barex Resins allows very even and deep draws. With this superior elasticity, uniform material distribution over the entire mold surface is achieved. This allows extremely deep draw ratios depending upon forming temperatures, as illustrated in Figure 2. Figure 2: Maximum draw ratio vs. Draw temperature for Barex sheet In addition, flow characteristics of Barex Resins at forming conditions allow for excellent mold detail reproduction. Compliance is a time dependent form of viscosity and as such can be used to predict mold reproduction fidelity. Figure 3 illustrates the high compliance of Barex Resins. Figure 3: Barex Resin s high compliance shows good flow characteristics and mold reproduction fidelity
The plateau exhibited by Barex Resins, simply demonstrates a region in which temperature variation would not materially affect the amount of detail obtainable in thermoforming. Based on the aforementioned data, the optimum thermoforming temperature range for Barex Resins (from Figure 1 and 3) is 120-165 C (250-330 F). For the manufacturer of deep draw parts, the lower temperature range is recommended since that is the area of highest elongation before break and high melt strength for evenness of flow. On the other hand, if mold fidelity is important, a temperature slightly higher than the plateau on the compliance curve is recommended since that is where higher plastic flow takes place. However, Figure 4, the dimensional stability curve, when combined with Figures 1 and 3, suggests that highest quality parts with the least residual stress are formed in the 145-162 C (295-325 F) range. Figure 4; Dimensional Stability Gauge Selection Barex sheet can usually be down gauged due to its stiff flexural modulus coupled with its ability to draw better than competitive materials. Gauge can be approximated by ratioing the flexural modulus of Barex Resins to the previously used materials. For example, comparing to PVC, this amounts to a 20% allowable gauge reduction of Barex sheet over PVC sheet. The ability of Barex Resins to better maintain gauge during thermoforming can further add to source reduction. Testing must be done to find the optimal gauge that balances economics with product protection.
Molds and Mold Design There are three basic thermoforming techniques to force the hot, flexible sheet against the mold; vacuum, mechanical, and positive pressure are used for packaging. Any of these techniques can be employed to form quality parts from Barex sheet. Molds used in the thermoforming process are of three basic designs: 1. The male mold where all the mold surfaces are raised. 2. The female mold where all the mold surfaces are recessed. 3. Combinations of 1 and 2 where the mold surfaces are either raised or recessed. In general, the male molds allow deeper draws than the female mold since the plastic can be draped (pre-stretched) over it. Male molds are also easier to fabricate and are cheaper to produce than female molds. Male molds are more popular and are more commonly used for blister packaging because they produce a stronger blister package. The top of a blister package is generally subjected to the greatest amount of stress and male molds distribute more material into this critical area, hence giving it more strength. Female molds, on the other hand, provide easier release of the material from the mold, are less damage-prone, and provide the sharpest definition on the exterior package. Barex sheet forms readily on all of these mold types. In designing molds for Barex sheet, the minimum draft angle for female molds should be 1 to 2, while for male molds it should be slightly larger. If the molds are designed without draft angles, release from the mold may prove difficult due to high material stiffness. Although other materials of construction can be used, aluminum is the preferred material since it is easily cast, easily machinable and has a high rate of heat conduction. Normally, mold temperatures should be below the heat distortion temperature of the sheet material. Mold temperatures in the range of 20 C to 60 C (70-140 F) are commonly used when working with Barex sheet. It is dependent upon cycle time, relative humidity, sheet thickness, and temperature. Mold temperature in this range allows for excellent material distribution, good production rates and production of blisters with good dimensional stability. Without mold temperature control, results may vary due to heat variations of the mold. Plug Assist The deep draw shortcoming of the female mold can usually be overcome by the use of the plug assist. Plus assist is commonly used in deep drawn articles, or where the distribution of materials needs to be altered. For Barex sheet, plug temperature, design, and penetration are important variables in achieving optimum quality thermoformed articles. The plug contours for forming Barex sheet should conform closely to that of the mold, with plug dimensions being 10-20% smaller than the mold. This allows the plug to maintain a clearance between itself and the mold cavity when it bottoms to prevent thinning of the materials. The amount of penetration allowed for optimum material distribution is usually 70-80% of the mold cavity depth. This penetration usually provides a good bottom thickness to wall thickness ratio. The plug assist should also have sufficient radii to allow for even material distribution.
Figure 5: Barex Forming Temperature In using complicated molds with grooves, pockets or recesses, the plug should be designed to carry more material into these areas. Plug temperatures for Barex thermoformed articles range from 135 C to 155 C (280 310 F) for the more common draw ratios encountered in blister packaging. For the best results, the plug temperature should be maintained just below the temperature at which the Barex sheet is being thermoformed (Figure 5). The plug should be made out of polished, non-sticking heat transfer material that can withstand these temperatures over a sustained period of time, and yet impart good optical properties to Barex sheet. Temperature below the suggested range can result in chill marks and thin spots in the material. Materials used for plug assist with Barex usually consists of aluminum or syntactic foam for easy temperature control. Mold Shrinkage Shrinkage allowance for Barex sheet will be in the range of 0.002-0.004 cm/cm, depending on forming temperature. If the blister dimensions are critical, the shrinkage allowances for the individual mold and its associated thermoforming conditions (i.e. rate and temperature), as well as mold expansion, must be accounted for. Undercuts Although generally not needed in all packaging, undercuts in molds are handled by using split molds that separate for easy part removal. Alternatively, removable parts which move out of position after the web is formed are also used, but much less frequently. Both methods will allow for the release of the formed article. If undercuts are small (0.13-0.20 mm/.005-.008 in.) Barex parts can be stripped rather easily from the mold without the use of special designs. The mold surface finish is also quite critical because of its relation to the finish of the blister package. In general, however, the finish will take on the surface appearance of the mold. Therefore, a SPE 1 or 2 finish is required for good optics. The blister finish can also be affected by mold design and the thermoforming technique employed. The greatest transparency, critical to blister packaging, is needed at the top and is easily obtained if the hot web does not touch the tip of the mold at all. This can readily be done by several male mold designs and thermoforming techniques such as recessed tops (female mold) and billow assists.
Vacuum Holes Vacuum holes should be kept to the minimum needed to provide quick and uniform air evacuation between the plastic web and the mold. These holes are generally between 0.04 and 0.08 mm (0.0015 and 0.003 in) diameter to avoid any visual marks being left on the thermoformed blister package. The larger holes are generally recommended for thicker gauged materials. Careful placement of these holes and counter-boring them from the backside will reduce the pressure drop during evacuation and decrease cycle time. Further cycle time reduction can be achieved if the part design allows the use of long slots for quick air removal. Secondary Operations Cutting. Blisters formed from Barex sheet can be cut by normal methods, such as matched metal punch dies, rotary shear knives, guillotine cutters and steel rule dies. Whichever method is employed, the cutting surfaces should be hard and well maintained to provide clean cut sheet edges. Denesting. Barex blisters are not as susceptible to blocking during denesting as are most other blister forming materials. Denesting agents such as cornstarch and silicone are not required for Barex blisters. If a blister design necessitates a low draft angle, then reducing the contact area of the blister to a minimum is suggested. Rotating alternate blisters as well as designing non-matching ribs (lugs) along the sides of the blisters will help to eliminate the problem. Decoration. Conventional decorating techniques such as printing (silk screen and offset), hot stamping, adhesion labels, and painting can be successfully used on Barex blisters. No surface pretreatment is required, although the correct solvent system is important for adhesion of silk screen and offset printing inks. The types of inks most commonly used are polyamide and epoxy. A list of commercial suppliers of inks for printing is available upon request. Barex film has been successfully vacuum metallized with aluminum at commercial rates, and excellent adhesion without the use of a basecoat has been achieved. Improved aesthetics and barrier can be realized. Card Stock Coatings. Adhesion of a blister to boardstock is critical for protecting contents. Barex boardstock coatings for this purpose are available in either solvent or aqueous form, from several commercial suppliers. A list of commercial suppliers of coatings is available upon request. Depending upon the property requirements of the blister package, plastic lidding stock may also be employed. Barex sheet and film serve as an excellent lidding stock that provides a very strong seal to Barex blisters. Other plastic lidding stocks can be used as well but often require a heat-seal coating. Sealing Barex blister packages are easily sealed to boardstock coatings by several methods as follows: Resistance Sealing. At normal sealing pressures, a sealing bar dwell time of 1-3 seconds is required to effectively seal Barex blisters through card stock at bar temperatures of 150-190 C (300-375 F).
Impulse Sealing. Barex blisters can be impulse sealed. Sealing is accomplished by bringing the plastic to its welding temperature under pressure with a short, powerful impulse of heat followed by cooling under pressure. Other Techniques. In addition to the various types of heat sealing used for Barex blister packages, dielectric sealing (radio frequency), ultrasonic sealing, Hellerbond technique (induction) and spin welding have also been successfully used. Mechanical sealing of Barex blisters can easily be accomplished by the use of staples, brads, pressure sensitive tapes, hot melts and other suitable mechanical devices. Solvent sealing of Barex blisters to carded stock coatings can also be accomplished using various different types of solvent. Moisture. As with most nitrile polymers, Barex sheet should be thermoformed after extrusion, or stored for later use in a polyethylene bag in an area where moisture absorption would be minimal.
Regulatory Information The product and uses described herein may require global product registrations and notifications for chemical inventory listings, or for use in food contact or medical devices. For further information, send an e-mail to: info@ineosbarex.com. Health and Safety Information The product described herein may require precautions in handling and use because of toxicity, flammability, or other consideration. The available product health and safety information for this material is contained in the Material Safety Data Sheet (MSDS) that may be obtained by calling 1-302-838-3278, or by sending an e-mail to: info@ineosbarex.com. Before using any material, a customer is advised to consult the MSDS for the product under consideration for use. The Material Safety Data Sheet for this product contains shipping descriptions and should be consulted, before transportation, as a reference in determining the proper shipping description. If the material shipped by INEOS is altered or modified, different shipping descriptions may apply and the MSDS of the original material should not be used. For additional information, samples, pricing and availability, please contact: INEOS Barex PO. Box 537 1389 School House Road Delaware City, DE 19706-0537 USA Customer Service: +(1) 302-838-3278 Fax: +(1) 302-838-3222 email: info@ineosbarex.com www.ineosbarex.com For Sales in Europe Velox GmbH Brandstwiete 1 D-20457 Hamburg Germany Tel: +(49) (0) 40 36 96 88-0 Fax: +(49) (0) 40 36 96 88 88 email: info@velox.com www.velox.com Technical information contained herein is furnished without charge or obligation, and is given and accepted at recipient's sole risk. Because conditions of use may vary and are beyond our control, INEOS makes no representation about, and is not responsible or liable for the accuracy or reliability of data, nor for toxicological effects or Industrial Hygiene requirements associated with particular uses of any product described herein. Nothing contained in this document shall be considered a recommendation for any use that may infringe patent rights, or an endorsement of any particular material, equipment, service, or other item not supplied by INEOS. The Properties and Applications listed in this document are not specifications. They are provided as information only and in no way modify, amend, enlarge, or create any specification or warranty, and ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ARE EXCLUDED. The name Barex is a trademark of INEOS USA LLC. June 2006 2006 INEOS USA LLC A division of INEOS USA LLC