A heat sealer is a machine used to seal products, packaging, and other thermoplastic materials using heat. This can be with uniform thermoplastic monolayers or with materials having several layers, at least one being thermoplastic. Heat sealing can join two similar materials together or can join dissimilar materials, one of which has a thermoplastic layer.
Types of heat sealing
- Hot bar sealers- have heated tooling kept at a constant temperature (also known as Direct Contact Thermal Sealing). They use one or more heated bars,Iron, or Dies which contact the material to heat the interface and form a bond. The bars, Irons, and Dies have various configurations and can be covered with a release layer or utilize various slick interposer materials (i.e. Teflon films) to prevent sticking to the hot tooling.
- Continuous heat sealers- (also known as Band type heat sealers) utilize moving belts over heating elements.
- Impulse heat sealers- have heating elements (one or two) of Nichrome placed between a resilient synthetic rubber and a release surface of film or fabric. The heating elements are not continuously heated; heat is generated only when current flows. When the materials are placed in the heat sealer, they are held in place by pressure. An electric current heats the heating element for a specified time to create the required temperature. the Jaws hold the material in place after the heat is stopped, sometimes with cooling water: this allows the material to fuse before stress can be applied.
- Hot melt adhesive can be applied in strips or beads at the point of joining. It can also be applied to one of the surfaces during an earlier manufacturing step and reactivated for bonding.
- Hot wire sealing - involves a heated wire that both cuts the surfaces and joins them with a molten edge bead. This is not usually employed when barrier properties are critical.
- Induction sealing is a non-contact type of sealing used for inner seals in bottle caps.
- Ultrasonic welding uses high-frequency ultrasonic acoustic vibrations to workpieces being held together under pressure to create a weld.
Good seals are a result of time, temperature and pressure for the correct clean material. Several standard test methods are available to measure the strength of heat seals. In addition, package testing is used to determine the ability of completed packages to withstand specified pressure or vacuum. Several methods are available to determine the ability of a sealed package to retain its integrity, barrier characteristics, and sterility.
Heat sealing processes can be controlled by a variety of quality management systems such as HACCP, statistical process control, ISO 9000, etc. Verification and validation protocols are used to ensure that specifications are met and final materials/packages are suited for end-use.
Seal Strength Testing
The efficacy of heat seals is often detailed in governing specifications, contracts, and regulations. Quality management systems sometimes ask for periodic subjective evaluations: For example, some seals can be evaluated by a simple pull to determine the existence of a bond and the mechanism of failure. With some plastic films, observation can be enhanced by using polarized light which highlights the birefringence of the heat seal. Some seals for sensitive products require thorough verification and validation protocols that use quantitative testing. Test methods might include:
Seal Strength per ASTM F88 and F2824
Seal Strength testing, also known as Peel Testing, measures the strength of seals within flexible barrier materials. This measurement can then be used to determine consistency within the seal, as well as evaluation of the opening force of the package system. Seal strength is a quantitative measure for use in process validation, process control and capability. Seal strength is not only relevant to opening force and package integrity, but to measuring the packaging processes’ ability to produce consistent seals.
Burst and Creep per ASTM F1140 and F2054
The burst test is used to determine the packages strength and precession. The burst test is performed by pressurizing the package until it bursts. The results for the burst test include the burst pressure data and a description of where the seal failure occurred. This test method covers the burst test as defined in ASTM F1140.The Creep test determines the packages ability to hold pressure for an extended period. The creep test is performed by setting the pressure at about 80% of the minimum burst pressure of a previous burst test. The time to seal failure or a pre-set time is measured.
Determination of package integrity. The package is submerged in a transparent container filled with a mixture of water and dye. Vacuum is created inside the container and maintained for a specific length of time. When the vacuum is released, any punctured packages will draw in dye revealing the imperfect seal.
- Tensile testing
- Hermetic seal
- Plastic bag
- Shrink wrap
- Plastic welding
- Plastic Sealing/Welding Technologies
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- Trillich, C (2007). "Process Control Improves Heat Seal Quality". Packaging Digest
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- Yuan, C. S.; Hassan (2007). "Effect of bar sealing parameters on OPP/MCPP heat seal strength". Journal of Applied Polymer Science 1 (11): 753–760.
- Morris, B. A (July 2002). "Predicting the Heat Seal Performance of Ionomer Films". J Plastic Film and sheeting 18 (3): 157–167. doi:10.1177/8756087902018003002. Retrieved 19 December 2011.
- Selke, S,. "Plastics Packaging", 2004, ISBN 1-56990-372-7
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- Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6
- Crawford, Lance, "Port Sealing: An Effective Heat Sealing Solution". Plastic Decorating Magazine. January/February 2013 Edition. ISSN 1536-9870. (Topeka, KS: Peterson Publications, Inc.). Section: Assembly: pages 36-39, covers Crawford's article.
- ASTM F88 - Test Method for Seal Strength of Flexible Barrier Materials
- ASTM F2029 - Standard Practice for Making Heat Seals for Determination of Heat Sealability of Flexible Webs Measured by Seal Strength
- ASTM F2824 - Standard Test Method for Mechanical Seal Strength Testing for Round Cups and Bowl Containers with Flexible Peelable Lids
- ASTM F2504 - Standard Practice for Describing System Output of Implantable Middle Ear Hearing Devices
- ASTM D3078 - Standard Test Method for Determination of Leaks in Flexible Packaging by Bubble Emission