Heat Seal and Hot Tack Testing Machine
ASTM F1921
In the packaging industry, ensuring the integrity of heat seals is crucial for maintaining product quality and safety. Heat seal and hot tack testing machines play a vital role in evaluating the strength and reliability of seals formed between thermoplastic materials. These tests are especially important for industries that rely on form-fill-seal (FFS) processes, such as food packaging and medical device packaging. By assessing hot tack strength and heat seal properties, manufacturers can ensure their products meet industry standards and perform reliably under real-world conditions.
What is Heat Seal and Hot Tack Testing?
Heat seal testing involves evaluating the strength and durability of the seals created when two thermoplastic films are joined by heat. A hot tack test, on the other hand, measures the ability of a hot seal to resist separation forces immediately after the sealing process, before the seal has fully cooled. Both tests are crucial in industries where the integrity of a seal is essential to ensure product safety, quality, and shelf life.
For packaging materials, especially those used in vertical form-fill-seal (VFFS) systems, the heat seal and hot tack properties determine the strength of the bond formed between the materials under specific conditions of temperature, time, and pressure. This is particularly important in scenarios where packages are filled with heavy or hot products immediately after sealing.
Instruments for Heat Seal and Hot Tack Testing
To perform accurate heat seal and hot tack testing, specialized equipment like the HTT Hot Tack Tester is used. These instruments are designed to precisely control parameters such as sealing temperature, pressure, and dwell time, allowing manufacturers to replicate real-world conditions. The tests are highly customizable, offering different test speeds and temperature controls to match the materials being tested.
Main Parameter
| Sealing Temp. | Ambient~250℃ |
| Temp Accuracy | ±0.2℃ |
| Dwell Time | 0.1~9999s(Heat Seal ) |
| Dwell Time | 0.1~9999s(Hot Tack ) |
| Sealing Pressure | 0.15MPa~0.7MPa |
| Sealing Jaws | 50mmx10mm Teflon Coated |
| Jaws Heating | Double Heating |
| Load Cell | 200N(Optional:30N50N100N, etc) |
| Accuracy | 0.5 F.S. |
| Resolution | 0.01N |
| Power | 220V, 50 HZ |
Key Features of Heat Seal and Hot Tack Testing Machines
A high-quality heat seal and hot tack testing machine should offer precise control over various parameters to accurately simulate real-world conditions. Key features of these machines include:
Precision Temperature Control: Heat sealers and hot tack testers must maintain consistent sealing temperatures, which can range from ambient temperature up to 250°C. Accurate control is essential for reliable testing results.
Adjustable Dwell Time: The machine should allow for adjustments in dwell time to match the requirements of different materials. Dwell time refers to the amount of time the material is exposed to heat and pressure during sealing.
Load Cells and Force Measurement: The ability to measure force accurately is essential for determining hot tack strength. Load cells with high accuracy (e.g., 0.5 F.S.) ensure precise readings.
User-Friendly Interface: Modern machines are equipped with PLC (Programmable Logic Controller) systems and touch-screen interfaces for easy operation and data analysis.
Compliance with ASTM F1921: It is important that the testing machine meets the requirements of ASTM F1921, ensuring that tests are conducted under standardized conditions.
The Importance of Hot Tack Strength
Hot tack testing measures the strength of the seal immediately after the heat-sealing process, before the material has cooled down. This is critical for packaging lines where sealing and filling occur simultaneously, especially when heavy contents are involved. Without adequate hot tack strength, a package’s seal may fail during the early stages of cooling, leading to spills or compromised product safety.
Hot tack strength is a key factor in vertical form-fill-seal (VFFS) applications. In these systems, sealing occurs quickly, leaving little time for the seal to cool before the package is filled with its contents. The test evaluates the maximum force a sealed layer can withstand while still hot, helping manufacturers assess the seal’s durability in real-world conditions.
Understanding ASTM F1921 and Its Role in Hot Tack Test
ASTM F1921 is the standard test method for measuring the hot tack strength of thermoplastic polymers and blends used in flexible webs. It provides specific guidelines for measuring the force required to separate a heat-sealed area while still in a hot state. This standard is widely used in the packaging industry to ensure the performance and safety of seals in flexible materials.
The ASTM F1921 test method involves sealing two sample strips between heated jaws under controlled temperature, pressure, and dwell time conditions. After the seal is formed, the sealed sample is pulled apart, and the force required for separation is measured. This process helps to determine whether the heat-sealed package will hold under the stress it may encounter during its lifecycle.
This standard outlines two methods for determining the hot tack strength of thermoplastic polymers:
- Method A (Fixed Delay): Measures the hot tack strength at various times after the jaw separation, with a predetermined delay.
- Method B (Variable Delay): Measures the maximum hot tack strength at different delay intervals.
By following ASTM F1921 guidelines, manufacturers can ensure that their packaging materials meet the required strength standards. This ensures that packaging will perform well under real-world conditions, such as during high-speed production and when subjected to varying environmental factors.
Testing Procedures for Hot Tack Test
1. Preparing the Sample
Before beginning the heat seal and hot tack tests, the material samples are cut to the required size. For the hot tack test, the sample strips are typically between 15 mm and 25 mm wide. The material may be conditioned under controlled atmospheric conditions to ensure accuracy.
2. Sealing Process
The sample is placed between two heated jaws, which apply pressure and heat to form the seal. The temperature and pressure parameters used depend on the specific material being tested and the type of packaging being produced. For example, films with thicker layers may require higher temperatures or longer dwell times.
3. Hot Tack Measurement
Once the material has been sealed, it is quickly withdrawn from the jaws. The force required to separate the sealed material is measured. This force is the hot tack strength, and it is assessed at various time intervals, typically in a cooling curve.
- Fixed Delay Method: Measures the force at different time intervals after the seal is made.
- Variable Delay Method: Determines the maximum force exerted during the seal withdrawal.
These tests are crucial for ensuring the seals’ ability to withstand the forces exerted on them during production and storage.
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