This part of YY/T 0681 covers the measurement of the strength of seals in flexible barrier materials.
The test may be conducted on seals between a flexible material and rigid material.
Seals tested in accordance with this test method may be from any source, laboratory or commercial.
This test method may measure the force required to separate the tested seal. It can also identify the mode of specimen failure.
Note: Annexes C and D respectively show the precision and bias of the test method specified in this standard, and relevant information determined.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 2918 Plastics - Standard atmospheres for conditioning and testing
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11607-12) and the following apply.
3.1
average seal strength
average force per unit width of seal required to separate progressively a flexible material from a rigid material or another flexible material, under the conditions of the test
Note: The average force normally is calculated by the testing machine from the digitized plot of force versus grip travel. The plot starts from zero force after clack has been removed from the test strip. The initial ramp-up from zero to the force level required to peel the seal is not indicative of seal strength, and data from that part of the curve should not be included in the calculation of average strength, nor should the return to zero following complete failure of the specimen. The amount of data actually discarded on each end of the measured seal-profile curve must be the same for all tests within any set of comparisons of average seal strength (see 6.1 and 9.8.1).
3.2
flexible
indicates a material with flexural strength and thickness permitting a turn back at an approximate 180 degree angle
3.3
maximum seal strength
maximum force per unit width of seal required to separate progressively a flexible material from a rigid material or another flexible material, under the conditions of the test
4 Significance and use
4.1 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. Seal strength at some minimum level is a necessary package requirement, and at times it is desirable to limit the strength of the seal to facilitate opening.
The maximum seal force is important information, but for some applications, average force to open the seal may be useful, and in those cases also should be reported.
4.2 When a seal fails adhesively (peel seal) the value of the bond strength measured is reported. A cohesive failure of the bond, delamination, or failure elsewhere in the test strip indicates that the substrate, not the seal interface, would be the limiting factor in the strength of a package. In those cases seal strength may be reported as “no less than” the strength measured.
4.3 A portion of the force measured when testing materials may be a bending component and not seal strength alone. A number of fixtures and schemes have been devised to hold samples at various angles to the pull direction to control this bending force. Because the effect of each of these on test results is varied, consistent use of one technique throughout a test series is recommended. Examples of fixtures and schemes are illustrated in Figure 1.
