Source：Link Testing Instruments Co.,Ltd.
How to test the content resistance of pickled packaging?
The so-called content resistance of pickled packaging refers to whether the barrier properties, flexibility and other properties of the finished pickled vegetable packaging bag have changed compared with the unpacked pickled vegetable packaging bag. Therefore, the content resistance of pickled packaging can be verified by testing the composite fastness of the packaging before and after packaging the pickled vegetables (tested by peel strength test) or the tensile force and elongation at break (tested by tensile strength, elongation and elastic modulus test).
What are the common packaging forms and materials for pickled vegetables?
Why does oil seep out of the surface of the pickled vegetable packaging bag?
Quality problem: The surface of pickled vegetable packaging bags often seeps oil or liquid.
Cause analysis:
(1) Poor grease resistance (or acid and alkali resistance) of packaging materials - When the composite film layers become the adhesive of the packaging bag and the grease resistance (or acid and alkali resistance) of each layer of film are poor, grease or acid and alkali liquids will slowly penetrate through the packaging bag to the packaging surface. For example, the composite strength (tested by peel strength test) and tensile strength and elongation at break (these two indicators are tested by tensile strength, elongation and elastic modulus test) between the layers of film of the packaging bag without pickled vegetables and the packaging bag with pickled vegetables are quite different.
(2) Finished product packaging production process • Poor sealing of heat seals - If the parameters of the heat sealing equipment are not set properly, it is easy to cause poor sealing quality at the heat seals, resulting in poor heat sealing (i.e., the two sides of the heat seals are easy to separate) or excessive heat sealing (i.e., the heat seal strength is too high, and the root of the heat seal is broken), which can easily cause leakage at the heat seals and the appearance of oil seepage on the surface of the packaging bag.
Expert advice:
- Pay attention to the monitoring of packaging thickness, tensile strength, elongation and elastic modulus of the packaging roll film, peel strength of the packaging roll film, tensile strength, elongation and elastic modulus of the finished packaging, peel strength of the finished packaging, heat seal strength of the empty packaging bag, heat seal strength of the finished packaging, and sealing performance (negative pressure method).
- Select packaging materials and composite adhesives with high grease resistance (acid and alkali resistance), appropriately increase the thickness of the packaging bag, and improve its grease resistance (acid and alkali resistance). Typical quality cases:
--Test samples: plastic composite film used for flavored radish packaging (customers reported that after the product was stored for a period of time, oil seepage appeared on the surface of the packaging bag).
--Targeted test items: tensile strength, elongation and elastic modulus of the packaging roll film, tensile strength, elongation and elastic modulus of the finished product packaging.
--Test results: The elongation at break of the packaging roll film in the horizontal and longitudinal directions were 102.21% and 116.65% respectively, and the elongation at break of the finished packaging bag in the horizontal and longitudinal directions were 81.32% and 79.15% respectively. Therefore, the poor oil resistance of the packaging bag is an important reason for the above problems of the product.
Why does pickle packaging leak?
Quality problem: Some pickled vegetables often leak at the heat seal of finished product packaging.
Cause analysis:
(1) Packaging material • Poor heat seal performance - During the packaging process of pickled vegetables, small droplets or particles often stick to the heat seal. If the film material used as the heat seal layer of the packaging bag is not properly selected, the heat seal strength of the heat seal part mixed with fine particles is easy to reduce, the sealing performance deteriorates, and leakage is easy to occur due to external force compression or prolonged storage time. The heat seal strength of the finished packaging bag and the empty packaging bag without filling can be tested separately for comparative verification.
(2) Finished product packaging production process • Poor heat seal sealing - If the parameters of the heat seal equipment are not set properly, it is easy to cause poor sealing quality at the heat seal, resulting in poor heat seal (i.e., the two sides of the heat seal are easy to separate) or excessive heat seal (i.e., the heat seal strength is too large, and the root of the heat seal is broken), which is easy to cause leakage at the heat seal.
Expert advice:
- Pay attention to the daily monitoring of the main properties of packaging, such as heat seal strength (empty packaging bags), heat seal strength (finished packaging bags), and sealing performance (negative pressure method).
- Select packaging materials that still have good heat seal performance after foreign matter is mixed in (that is, when the heat seal is stained with debris, droplets, powder and other particles, it still has good heat seal performance), or appropriately increase the thickness of the heat seal layer material.
- Adjust the heat seal process parameters to avoid fine particles sticking to the heat seal part and ensure that the heat seal part has good heat seal quality.
Typical quality case:
- Test sample: radish strips plastic composite film packaging (customers reported that the product is prone to slow leakage at the heat seal).
- Targeted test items: sealing performance (negative pressure method), heat seal strength of empty packaging bags, and heat seal strength of finished packaging.
——Test results: In the sealing performance (negative pressure method) test, the products without leakage did not leak at -90KPa, and the products with leakage leaked at -31KPa, that is, at the heat seal. The heat seal strength of the empty packaging bag was 50N/15mm, and the heat seal strength of the finished product packaging was uneven, with the heat seal strength of the tightly sealed part being 51N/15mm, and the heat seal strength of the part with poor heat seal quality being only 15N/15mm. Therefore, the poor uniformity of the heat seal strength of the finished product packaging is an important reason for the leakage at the heat seal of the product.
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