How to test the hot tack property of plastic package for ...

The packages for liquid food products are usually sealed by heating in the meanwhile of filling process i.e. when the sealing sides of the package are still uncooled, the liquid food products have been filled into the package, which may apply impact force on the sealing sides.

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We call the heat seal strength when the sealing side uncooled hot tack. If the hot tack of sealing sides is insufficient, they may break in filling process of liquid food products or in transportation and storage process of finished products. As a result, the package may leak or break because of external pressure or compression. Therefore, it is necessary to ensure that the packaging materials used for liquid food products can produce sufficient hot tack during heating process of sealing sides. According to the test results, the manufacturers can select proper materials and suitable sealing parameters in production to meet the requirements for hot tack.

This article provides a simplified test method of the hot tack property of packaging materials for liquid food for your reference. The testing instrument used for determination of hot tack property is Labthink&#;s i-Thermotek Heat Seal & Hot Tack Tester.

In the tests, the two ends of the specimen are clamped in left sample grips and right sample grips (with load cell) respectively. Then pull the specimen to the hot tack test area. After the hot tack test, the driving mechanism will pull the left and right sample grips in opposite directions and the load cell can detect the electric signal and then the hot tack strength, peel strength and tensile strength can be analyzed or calculated.

The tests shall be performed according to the following procedures.

(1)  Cut specimens along the machine direction of the sample materials. The length and width of the specimen shall be 25mm and 15mm, respectively.

(2)  Set sealing temperature, sealing pressure and dwell time. Select hot tact test and test method.

(3)  When sealing temperature is reached, please clamp the specimen in left and right sample grips. Pull the handle and place the specimen between the two sealing jaws. Then step on the pedal switch to seal the specimen and release the handle at the same time.

(4)  When the dwell time is reached, the sealing process is finished. The left and right sample grips will move and separate the sealed specimen apart to measure the hot tack property.

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(5)  The test results will be displayed automatically.

For more details about i-Thermotek Heat Seal & Hot Tack Tester, please visit en.labthink.com

Hot Seal Strength (Hot Tack) of Thermoplastics ASTM F method B data for optimizing heat seals in film and flexible packaging materials.

Scope:
Hot tack measures the strength of heat seals formed between thermoplastic surfaces of flexible webs, immediately after the seal has been made and before it cools to room temperature. This property is important since this situation frequently occurs on vertical form-fill-seal packaging. In this process, the contents are dropped into the bag immediately after the horizontal seal bars have opened. Since the content can be heavy, the hot seal must be able to withstand high loads, thus requiring a high hottack force.

Procedure:
The film sample is fixed in the upper specimen grip which is connected to a load cell and the lower specimen grip which is connected to a peeling actuator. The film sample is inserted between the sealing bars by means of a specimen insertion mechanism. A seal is made under defined conditions of temperature, contact time and pressure. At the end of the sealing time, and after a preset delay time, the peeling actuator moves down with a preset speed and peels the hot seal totally apart. The maximum force required to peel or break the seal is the hottack force.

Specimen size:
A rectangular specimen is used. The specimen width may be either 25 mm, 15 mm or 1.00 inch. Specimen length must be adequate for the testing machine (range of 30 to 35 cm; 12 to 14 in).

Data:
Threshold sealing temperature; this is the minimum temperature at which the required hot tack strength is reached.

Seal strength, which is the maximum peak force.

The hot tack temperature range, this is the temperature range in which the required hottack strength is obtained.

Failure Mode (Equivalent to ASTM F88)

**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. Standards can be obtained from appropriate standards authorities.