Packaging bag inspection items and reference standards, practical

As an important component of goods, packaging plays a crucial role in protecting product quality after leaving the factory. The packaging bags encountered in daily life are diverse, including clothing packaging bags, food packaging bags, cosmetic packaging bags, hardware packaging bags, gift packaging bags, and a series of various plastic packaging bags. How exactly should packaging bags, which occupy an important part of the product, be inspected, and are there any reference standards?

Today, Shunxingyuan Packaging, a professional flexible packaging manufacturer, will share the packaging bag inspection items and reference standards.

I. Basic Inspection Items

The main purpose of appearance inspection is to identify visual defects in samples. It generally adopts manual sensory identification, so the evaluation of product appearance quality has a certain subjectivity. In this process, the author suggests paying attention to the following points.

Certain conditions must be established for the evaluation of appearance quality. For example, factors such as environmental conditions, evaluation methods, and evaluators' eyesight, touch, practical experience, and technical level should be as consistent as possible when evaluating the appearance quality of flexible packaging.

The appearance quality is mostly evaluated by the sensory inspection of testers, so the evaluation terms for appearance quality must be clearly defined. For example, terms such as "must" or "must not", "should" or "should not", "can be used" or "not allowed to be used", "allowed" or "not allowed" should be clearly specified to reduce the subjectivity of the evaluation.

GB/T 10004-2008 stipulates visual inspection under natural light and measurement with measuring tools with an accuracy of no less than 0.5mm, mainly checking whether the sample surface has wrinkles, bubbles, scratches, perforations, adhesion, foreign matter, delamination, dirt, etc.

2. Print Quality Inspection

The printed patterns on packaging are crucial for product promotion and display effects. Laboratories use testing equipment such as densitometers and spectrophotometers to objectively evaluate the printing quality of flexible packaging. When necessary, standard samples can be established as physical references for printing quality, providing clear evaluation criteria for inspection personnel.

Regarding the standards for printing quality, gravure printed products should be inspected according to the provisions of GB/T7707-2008 "Gravure Decorative Prints", flexographic printed products should be inspected according to the provisions of GB/T 17497-2012 "Flexographic Decorative Prints", commodity barcode printing should be inspected according to the provisions of GB/T 18348-2008 "Commodity Barcodes - Inspection of Barcode Symbol Print Quality", and other one-dimensional barcodes should be inspected according to the provisions of GB/T 14258-2003 "Information Technology - Automatic Identification and Data Capture Techniques - Barcode Symbol Print Quality Inspection".

The printing performance of plastic films can be preliminarily judged by measuring their surface tension. A higher surface tension value indicates better printing performance (generally, if the film surface tension is greater than 38mN/m, its printing performance is sufficient to meet usage requirements).

3. Dimensional Deviation Inspection

The main dimensions of flexible packaging are thickness, length, and width. Among these, thickness is the basic guarantee for all performance aspects of flexible packaging and is one of the important factors affecting its mechanical and barrier properties, as well as a key consideration when controlling product quality and cost. The factors causing dimensional deviations in finished flexible packaging are numerous and complex, including external environmental temperature and humidity, equipment conditions, and process factors, as well as internal molecular crystallization, orientation, and internal stress changes within the film. Therefore, when selecting materials, the homogeneity of film materials should be considered, and the influence of film material shrinkage on the dimensional accuracy of finished flexible packaging should be emphasized. In printing and post-press processing, special attention should be paid to the sensitivity of film materials to environmental temperature and humidity.

The length and width deviations of flexible packaging should be inspected according to the provisions of GB/T 6673-2001 "Determination of Length and Width of Plastic Films and Sheets", and thickness deviations should be inspected according to the provisions of GB/T 6672-2001 "Determination of Thickness of Plastic Films and Sheets - Mechanical Method". The heat seal width and the distance between the seal and the bag edge of flexible packaging should be measured using measuring tools with an accuracy of no less than 0.5mm.

II. Physical and Chemical Performance Inspection

Flexible packaging produced from pure resin films has excellent hygiene and can be directly used for food packaging without causing any harm to consumers. However, to improve the physical and mechanical properties, chemical stability, and processing performance of the film, a certain amount of additives such as plasticizers, stabilizers, antioxidants, fillers, colorants, lubricants, and foaming agents are often added to the resin during the film blowing process. Furthermore, large quantities of organic solvents, such as toluene, xylene, ethyl acetate, methyl ethyl ketone, butyl acetate, ethanol, and isopropanol, are used in the printing, laminating, and coating processes during flexible packaging production. These solvents will, to varying degrees, remain in the packaging material, and when the residual solvent content exceeds the safe value, it will cause harm to human health or the environment. Therefore, in addition to meeting the basic requirements for food packaging, conducting the following physical and chemical performance inspections on flexible packaging is particularly important.

1. Migratory Substances Inspection

Based on the analytical methods for the hygienic performance of plastic films, migratory substances in samples are tested by simulating different environments. The specific experimental procedure is: immerse multiple sets of samples separately in ethanol aqueous solution, acetic acid aqueous solution, n-hexane, and water at certain proportions and temperatures for a specified period to obtain immersion liquids. These test solutions simulate liquid environments that food flexible packaging may contact, such as alcoholic beverages, acidic substances, oils, and water. Finally, the hygienic performance of the flexible packaging is evaluated by testing the dissolved substances, potassium permanganate consumption, heavy metal content, etc., in the immersion liquids.

2. Sensory Indicator Inspection

There are two methods for sensory indicator inspection of flexible packaging film. A relatively simple and intuitive method is: open the packaging box containing the flexible packaging film and immediately check for any peculiar smell. A more objective method is: take a piece of film measuring 10cm×10cm, cut it into strips, place it in an Erlenmeyer flask, add 150ml of distilled water, seal the flask with a stopper, place it in an oven or water bath at 60℃ for 30min, then remove it, open the stopper, smell the vapor, and determine if there is any peculiar smell.

3. Residual Solvent Content Inspection

Residual solvents refer to volatile organic compounds used in the production process of flexible packaging but not completely removed during the process. Using a gas chromatograph to detect solvent residue not only helps flexible packaging enterprises gain a comprehensive understanding of the safety of various additives and solvents used in printing and lamination (whether they contain components that do not meet requirements or if the content of certain components exceeds standards), but also effectively solves the problem of odor in some packaging materials caused by residual solvents (which can be detected using sensory indicator methods), thereby better controlling the hygienic safety of flexible packaging.

The amount of solvent residue in flexible packaging composite films is related to factors such as the type and water content of the solvents used, the properties of the film substrate, the properties of the adhesive, the printing area of the ink, drying temperature, air volume, and production speed. Currently, highly toxic organic solvents (such as benzenes) pose significant harm to the human body. Therefore, printing inks and coatings are currently transitioning towards benzene-free, water-based, and solvent-free formulations, while most adhesives have shifted from fat-soluble (using lipid solvents) to alcohol-soluble, water-soluble, and solvent-free.

III. Food Packaging Bag Testing Items

Key indicators for food packaging testing and control mainly include: barrier properties, physical and mechanical properties, hygiene performance, thickness, solvent residue, retort resistance, sealing performance, cap torque, headspace gas analysis, printing quality, and seam performance.

1. Barrier Properties of Food Packaging Materials

The main reasons for food spoilage are the growth and reproduction of microorganisms. Oxygen and water vapor in the environment can permeate packaging materials and affect food quality. Therefore, the oxygen and water vapor transmission rates of packaging materials are directly and closely related to their shelf life. Another main reason for food spoilage is the oxidative deterioration of fats and other components. Thus, food packaging is required to have excellent barrier properties.

Oxygen transmission testing standards include: ASTM D3985, ASTM F2622, ASTM F1927, ASTM F1307, ISO 15105-2, GB/T 19789.

Water vapor transmission testing standards include: ISO 15106-3, DIN 53122-2, GB/T 21529.

2. Physical and Mechanical Properties of Food Packaging Materials

1. Tensile Strength and Elongation at Break Performance

The most basic function of food packaging is to serve as a container for food, which requires its materials to have a certain strength to prevent accidental breakage. The tensile strength and elongation at break of packaging materials are fundamental performance requirements. We can use a universal testing machine to perform a constant-speed tensile test to obtain tensile strength and elongation at break.

Common testing standards include GB/T 13022.

2. Thickness

The thickness and width of packaging materials must meet certain requirements. A precision thickness gauge can be used to measure the thickness of films or sheets within a certain standard pressure range.

Testing standards include ASTM D374, ISO 534, GB/T 6672.

3. Heat Sealing Performance

Heat sealing performance directly affects the overall physical properties of food packaging. Selecting appropriate heat sealing parameters (temperature, pressure, time) to heat seal packaging materials achieves the best heat seal strength. The heat sealing effect can be tested for heat seal strength on the seal using a universal testing machine.

Testing standards include ASTM F2029, QB/T 2358.

4. Coefficient of Friction

The coefficient of friction is a physical quantity used to characterize the resistance generated when flexible plastic packaging materials come into contact with themselves or other objects, such as packaging machinery, and move relative to each other during use. Both excessively high or low coefficients of friction in packaging materials can adversely affect the production process. For example, if the coefficient of friction is too high, the packaging material feels sticky, requiring greater pulling force to rotate the roll for bag making, which not only increases energy consumption and reduces production efficiency but may even cause the packaging material to stretch and deform, affecting its barrier properties, impact resistance, and puncture resistance. Conversely, if the coefficient of friction is too low, it can lead to problems such as slipping, deviation, unstable stacking, and edge misalignment during material use. Therefore, controlling the coefficient of friction of flexible plastic packaging rolls within an appropriate range is crucial for improving their usability.

Common testing standards include GB/T 10006.

5. Tear Resistance

Tear strength tests primarily measure the energy required for tear propagation. The main measurement methods include the trouser tear method and the Elmendorf tear method, with the Elmendorf tear method for constant radius specimens being preferred. For consumers, the tear resistance of a material is a key indicator of whether the packaging is easy to open.

Common testing standards include ASTM D1922, ISO 6383/2.

6. Printing Surface Roughness

Finished packaging products typically have clear patterns and logos. However, we may find blurred printing on some materials (especially paper or paper-laminated packaging). Some blurring is related to ink quality and color registration processes, but a significant portion is related to the roughness of the printing surface. Since the ink layer in general printing is only a few tens of micrometers thick, if the printing surface roughness is too high, the ink layer will embed deeply into the material, leading to uneven ink layer thickness on the surface, which causes blurring and whitening. We should perform roughness tests on printing surfaces, measuring surface roughness by simulating printing machine conditions, and examining the impact of material smoothness on printability from a microscopic perspective. Based on the roughness results, the ink layer thickness can be adjusted by 2 to 2.5 times.

Common testing standards include ISO 8791/4, TAPPI T555.

7. Ink Abrasion Resistance

Food packaging uses a large amount of ink during the printing process. Sometimes, when handling food packaging, we encounter situations where ink stains hands or ink detaches, which severely affects consumer purchasing desire. This necessitates testing ink abrasion resistance, using standard loads to rub two materials against each other at a set speed to check the fastness of the printing ink. Depending on actual usage conditions, types include dry rub, wet rub, wet transfer, wet smear, and heat rub.

3. Seal Integrity and Modified Atmosphere Packaging of Food Packaging Materials

Seal performance refers to the reliability of package sealing. This test ensures the integrity of the entire product package seal, preventing leakage, contamination, and deterioration due to poor product seal performance. There are two testing methods: positive pressure and negative pressure.

More and more packaging is using modified atmosphere packaging to increase shelf life. For example, milk powder, coffee, potato chips, and cheese often use nitrogen and carbon dioxide packaging. To test the actual inflation effect, a headspace analyzer is needed to analyze the actual gas composition inside the package.

Relevant instruments: oxygen permeability tester, moisture permeability tester, heat sealer, thickness gauge, peel strength tester, universal testing machine, coefficient of friction tester, tear strength tester, peel tester, printing surface roughness tester, leak detector, sealing tester, headspace analyzer.